"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:eb98389a-10c5-4e3c-b199-a1de87e81618","http://resolver.tudelft.nl/uuid:eb98389a-10c5-4e3c-b199-a1de87e81618","Autogenous deformation-induced stress evolution in cementitious materials considering viscoelastic properties: A review of experiments and models","Liang, M. (TU Delft Materials and Environment); Xie, J. (TU Delft Materials and Environment); He, S. (TU Delft Materials and Environment); Chen, Y. (TU Delft Materials and Environment); Schlangen, E. (TU Delft Materials and Environment); Šavija, B. (TU Delft Materials and Environment)","","2024","Early-age cracking risk induced by autogenous deformation is high for cementitious materials of low water-binder ratios. The autogenous deformation, viscoelastic properties, and stress evolution are three important factors for understanding and quantifying the early-age cracking risk. This paper systematically reviewed the experimental and modelling techniques of the three factors. It is found that the Temperature Stress Testing Machine is a unified experimental method for all these three factors, with a strain-controlled mode for stress evolution, hourly-repeated loading scheme for viscoelastic properties, and free condition for autogenous deformation. Such unified method provides basis for developing various models. By coupling a hydration model for volume fractions of hydrates, a homogenization model for upscaling of viscoelastic properties, and capillary pressure theory for self-desiccation shrinkage, a unified model directly mapping the mix design to the early-age stress can be constructed, which can help optimize the mix design to reduce the early-age cracking risk.","Autogenous deformation; Cementitious materials; Creep; Early-age cracking; Elastic modulus; Relaxation; Stress evolution","en","review","","","","","","","","","","","Materials and Environment","","",""
"uuid:188ee1cc-65bd-4eee-aebc-da4cdd25bf80","http://resolver.tudelft.nl/uuid:188ee1cc-65bd-4eee-aebc-da4cdd25bf80","Rheology control of limestone calcined clay cement pastes by modifying the content of fine-grained metakaolin","Chen, Y. (TU Delft Materials and Environment); Zhang, Y. (TU Delft Materials and Environment); He, S. (TU Delft Materials and Environment); Liang, M. (TU Delft Materials and Environment); Zhang, Yamei (Southeast University); Schlangen, E. (TU Delft Materials and Environment); Copuroglu, Oguzhan (TU Delft Materials and Environment)","","2023","Limestone-calcined clay-cement (LC3), as one of the most promising sustainable cements, has been under development over the past decade. However, many uncertainties remain regarding its rheological behaviors, such as the metakaolin content of calcined clay. This study aims to investigate the effect of increasing the content of fine-grained metakaolin in calcined clay on the rheology of LC3 pastes. Rheological behaviors and early-age hydration of studied mixtures were characterized using flow curve, constant shear rate, small amplitude oscillatory shear and isothermal calorimetry tests. Results show that increasing the content of fine-grained metakaolin decreased flowability but promoted structural build-up and early-age hydration. These phenomena can be attributed to the decrease of mean interparticle distance caused by the increased amount of fine-grained metakaolin, which may enhance colloidal interactions, C-S-H nucleation and direct contact between particles. Overall, modifying the fine-grained metakaolin content is a feasible approach to control the rheology of LC3 pastes.","limestone-calcined clay-cement; metakaolin; rheology; storage modulus; structural build-up; yield stress","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:c77297dd-8cad-4769-b779-7cbaa21b2554","http://resolver.tudelft.nl/uuid:c77297dd-8cad-4769-b779-7cbaa21b2554","Can superabsorbent polymers be used as rheology modifiers for cementitious materials in the context of 3D concrete printing?","Chen, Y. (TU Delft Materials and Environment); Liang, M. (TU Delft Materials and Environment); Zhang, Y. (TU Delft Materials and Environment); Li, Z. (TU Delft Materials and Environment); Šavija, B. (TU Delft Materials and Environment); Schlangen, E. (TU Delft Materials and Environment); Copuroglu, Oguzhan (TU Delft Materials and Environment)","","2023","Autogenous shrinkage may be a critical issue concerning the use of limestone-calcined clay-cement (LC3) in high-performance concrete and 3D printable cementitious materials, which have relatively low water to binder (W/B) ratio. Adding an internal curing agent, i.e., superabsorbent polymer (SAP), could be a viable solution in this context. However, employing SAP (without adding additional water) may also influence the fresh properties of LC3 composites by increasing yield stress and viscosity, which may be beneficial for 3D printability. Therefore, this study attempts to use SAP as a rheology modifying admixture with the aim of investigating the impact of SAP on flow behavior, structural build-up, hydration kinetics, compressive strength, and autogenous shrinkage of LC3 pastes with a fixed W/B (0.3). In addition, hydroxypropyl methylcellulose (a typical rheology/viscosity modifier in 3D printable cementitious materials) was also employed in two mixtures to compare their effects. Results show that adding SAP increases the dynamic yield stress and the apparent viscosity, as well as structural build-up and hydration, but decreases the compressive strength at 3, 7 and 28 days. Furthermore, using SAP (especially 0.2 wt% SAP) not only promotes the early-age expansion but also effectively mitigates the autogenous shrinkage of LC3 pastes for up to 7 days. Overall, the obtained results indicated that SAP could act as a promising rheology modifier for the development of 3D printable cementitious materials.","Autogenous shrinkage; Hydration kinetics; Limestone-calcined clay-cement; Rheology modifier; Structural build-up; Superabsorbent polymer","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:f125de15-4935-41ca-a586-27439a4a1b25","http://resolver.tudelft.nl/uuid:f125de15-4935-41ca-a586-27439a4a1b25","Secure Remote Cloud File Sharing With Attribute-Based Access Control and Performance Optimization","Chen, E. (University of Science and Technology Beijing); Zhu, Yan (University of Science and Technology Beijing); Liang, K. (TU Delft Cyber Security); Yin, Hongjian (University of Science and Technology Beijing)","","2023","The increasing popularity of remote Cloud File Sharing (CFS) has become a major concern for privacy breach of sensitive data. Aiming at this concern, we present a new resource sharing framework by integrating enterprise-side Attribute-Based Access Control/eXtensible Access Control Markup Language (ABAC/XACML) model, client-side Ciphertext-Policy Attribute-Based Encryption (CP-ABE) scheme, and cloud-side CFS service. Moreover, the framework workflow is provided to support the encrypted-file writing and reading algorithms in accordance with ABAC/XACML-based access policy and attribute credentials. However, an actual problem of realizing this framework is that policy matrix, derived from access policy, seriously affects the performance of existing CP-ABE from Lattice (CP-ABE-L) schemes. To end it, we present an optimal generation algorithm of Small Policy Matrix (SPM), which only consists of small elements, and generates an all-one reconstruction vector. Based on such a matrix, the improved CP-ABE-L scheme is proposed to reduce the cumulative errors to the minimum and prevent the enlargement of error bounds. Furthermore, we give the optimal estimation of system parameters to implement a valid Error Proportion Allocation (EPA). Our experimental results indicate that our scheme has short size of parameters and enjoys efficient computation and storage overloads. Thus, our new framework with optimization methods is conducive to enhancing the security and efficiency of remote work on CFS.","ABAC/XACML; attribute-based encryption; cloud file sharing; Security; small policy matrix","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-09-30","","","Cyber Security","","",""
"uuid:1e04f0ca-d362-40b8-a2d8-78d23d7bb650","http://resolver.tudelft.nl/uuid:1e04f0ca-d362-40b8-a2d8-78d23d7bb650","Reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material and precursor for alkali-activated materials","Chen, B. (TU Delft Materials and Environment); Zuo, Yibing (Huazhong University of Science and Technology); Zhang, Shizhe (TU Delft Materials and Environment; Mineralz); Miranda de Lima Junior, L.C. (TU Delft Materials and Environment); Liang, X. (TU Delft Materials and Environment); Chen, Y. (TU Delft DC systems, Energy conversion & Storage); van Zijl, Marc Brito (Mineralz); Ye, G. (TU Delft Materials and Environment; Universiteit Gent)","","2023","This work evaluated the reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material (SCM) and precursor for alkali-activated materials (AAM). The chemical composition of the amorphous phase in MSWI bottom ash was found to be in the same range as that of Class F coal fly ash. The reactivity of MSWI bottom ash as SCM and AAM precursor was tested to be much lower than that of blast furnace slag, but similar to that of Class F coal fly ash. The method of thermodynamic modeling was found useful in providing references for the mix design of MSWI bottom ash-based AAM. Grinding MSWI bottom ash into powder for the application of SCM and AAM precursor increased its leaching potential. Based on the findings of this study, recommendations were provided on how to use MSWI bottom ash to prepare blended cement pastes and AAM.","Alkali-activated materials; Leaching; MSWI bottom ash; Reactivity; Supplementary cementitious material","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:f543ecd2-402e-49c3-9ad2-a9e3cae64d4e","http://resolver.tudelft.nl/uuid:f543ecd2-402e-49c3-9ad2-a9e3cae64d4e","Does early age creep influence buildability of 3D printed concrete? Insights from numerical simulations","Chang, Z. (TU Delft Materials and Environment); Liang, M. (TU Delft Materials and Environment); Chen, Y. (TU Delft Materials and Environment); Schlangen, E. (TU Delft Materials and Environment); Šavija, B. (TU Delft Materials and Environment)","","2023","Cementitious materials may exhibit significant creep at very early age. This is potentially important for concrete 3D printing, where the material is progressively loaded even before it sets. However, does creep actually affect the buildability of 3D printed concrete? Herein, the influence of early-age creep on the buildability of 3D printed concrete is studied numerically. Creep is considered using the “local-force method”, which was developed in our previous work. This 3D printing model be used to quantify the influence of early-age creep on typical failure modes, i.e., structural instability due to buckling and plastic collapse resulting from material yielding. The green strength and early-age creep experiments are conducted to characterize early-age visco-elastic-plastic behaviors. The model is then validated with the comparison to printing experiment about buildability quantification and failure mode prediction. Parametric analyses are subsequently performed to quantify the influence of early-age creep on various printing geometries in which different failure modes are dominant. The numerical results highlight the significance of initial printing time and material mix design for predicting the buildability of 3D printing of concrete. Finally, a discussion on how creep affects structural buildability is given from the perspective of localized damage and element strain.","Buildability quantification; Early-age creep; Lattice model; Local force method","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:4db85814-789b-4bea-8d22-37245045117e","http://resolver.tudelft.nl/uuid:4db85814-789b-4bea-8d22-37245045117e","Degradation of alkali-activated slag subjected to water immersion","Liu, C. (TU Delft Materials and Environment); Liang, X. (TU Delft Materials and Environment); Chen, Y. (TU Delft DC systems, Energy conversion & Storage; South China University of Technology); Li, Z. (TU Delft Materials and Environment; University of Sheffield); Ye, G. (TU Delft Materials and Environment)","","2023","In this study, the impacts of tap water immersion on the pore solution, phase assemblages, gel chemistry and structure, and pore structure of alkali-activated slag (AAS) pastes were studied. AAS degrades under such condition and the potential mechanisms can be concluded as lower reaction rates, gel decomposition and carbonation. The leaching of Na+ and OH− at early stages hinders the reaction of slag, which leads to a slower formation of reaction products. Long-term leaching can result in gel decomposition after 90 d. Coarsened gel pores and capillary pores are both identified in water-immersed samples. Additionally, the leached Ca2+ can react with the dissolved CO2 in tap water to form calcium carbonate. A calcium carbonate layer is observed surrounding the paste while the inner matrix is free of carbonation. The insights provided by this paper contribute to understanding the behaviors and durability of AAS in underwater conditions.","Alkali-activated slag; Carbonation; Curing; Leaching; Water immersion","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-11-30","","","Materials and Environment","","",""
"uuid:0ad54f12-b996-4e9c-b2aa-e5645bd73348","http://resolver.tudelft.nl/uuid:0ad54f12-b996-4e9c-b2aa-e5645bd73348","Distribution of porosity surrounding a microfiber in cement paste","He, S. (TU Delft Materials and Environment); Chen, Y. (TU Delft Materials and Environment); Liang, M. (TU Delft Materials and Environment); Yang, En-Hua (Nanyang Technological University); Schlangen, E. (TU Delft Materials and Environment)","","2023","This study investigates the microstructural changes of cement paste due to the inclusion of polymeric microfiber at different water-to-cement (w/c) ratios. A procedure to quantify the porosity of epoxy impregnated interfacial transition zone (ITZ) is also presented. Results show that the microstructures of the ITZ beneath and above a microfiber, with respect to the gravity direction, are largely different. Though the ITZ at both sides of the fiber are more porous than the bulk matrix, the porosity of the lower ITZ (i.e., the ITZ beneath a fiber) is significantly higher than the upper side (i.e., the ITZ above a fiber). This difference can be attributed to the combined effects of fiber on the initial packing of surrounding cement grains and on the settlement of the fresh mixture. The porosity gradients of the upper ITZs are found to be nearly identical for all the tested w/c ratios, while the porosity gradients of the lower ITZs become steeper when the w/c is higher. The lower side is also found to be the preferred location for the precipitation of calcium hydroxide crystals. Results of energy-dispersive X-ray spectroscopy (EDS) and nano-indentation analyses confirm that the chemical and mechanical properties of the ITZ are also asymmetric.","Characterization (B); Fiber reinforcement (E); Interfacial transition zone (B); Microstructure (B); Nanoindentation","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:51aea123-9bad-4e6f-83db-83ebd2b716ee","http://resolver.tudelft.nl/uuid:51aea123-9bad-4e6f-83db-83ebd2b716ee","Experimental and numerical study on the mitigation of autogenous shrinkage of cementitious material","Lu, T. (TU Delft Materials and Environment; Southwest Petroleum University); Liang, X. (TU Delft Materials and Environment); Liu, C. (TU Delft Materials and Environment); Chen, Y. (TU Delft Materials and Environment; South China University of Technology); Li, Z. (University of Sheffield)","","2023","This study experimentally investigated the effects of surfactants and water-repelling agents on the hydration process, relative humidity, and mechanical properties of Portland cement pastes. Based on the measurement results, the degree of hydration, degree of saturation, capillary tension of autogenous shrinkage, and magnitude of autogenous shrinkage were simulated using a numerical model. In the numerical model, the elastic and creep components of autogenous shrinkage were calculated separately, and the creep component was simulated based on the solidification theory. The simulation results indicated that adding admixtures led to lower degrees of hydration and saturation. The capillary tension of the pure Portland cement was larger than that of the other mixtures. This can be attributed to several factors, including the smaller surface tension of mixtures with surfactants, larger contact angle of mixtures with water-repelling agents, and a lower degree of hydration of mixtures with both admixtures. Analyses of the simulated and measured results for different mixtures also show that creep plays an indispensable role in autogenous shrinkage. Adding a surfactant and a water-repelling agent can effectively mitigate autogenous shrinkage. However, when an excessive amount of water-repelling agent was added, its influence on the mitigation of autogenous shrinkage was insignificant.","Autogenous shrinkage; Cement paste; Simulation; Surfactant; Water-repelling agent","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:4434dcaa-0121-4c96-976f-3f9f44e0708c","http://resolver.tudelft.nl/uuid:4434dcaa-0121-4c96-976f-3f9f44e0708c","Improving structural build-up of limestone-calcined clay-cement pastes by using inorganic additives","Chen, Y. (TU Delft Materials and Environment); Zhang, Y. (TU Delft Materials and Environment); He, S. (TU Delft Materials and Environment); Liang, X. (TU Delft Materials and Environment); Schlangen, E. (TU Delft Materials and Environment); Copuroglu, Oguzhan (TU Delft Materials and Environment)","","2023","In 3D concrete printing, fast structuration is a prerequisite for ideal buildability. This paper aims to study the impact of inorganic additives, i.e., CaCl2 and gypsum, on structural build-up and very early-age hydration of limestone-calcined clay-cement (LC3) pastes within the first 70–80 min. Results show that, increasing the dosage of CaCl2 or gypsum can accelerate storage modulus G' and static yield stress evolution with time, as well as increase chemically bound water (H) content and total specific surface area (SSAtotal). Furthermore, good correlations were found between G' and H content, as well as static yield stress and the ratio of free water content to SSAtotal. The acceleration by CaCl2 can be attributed to stimulating C3S and C3A hydration and promoting crystal formation, i.e., ettringite, portlandite, and Friedel's salt. Additionally, the increase in gypsum percentage led to a large amount of unreacted gypsum in the system, resulting in an increase in SSAtotal.","3D concrete printing; CaCl; Gypsum; Limestone-calcined clay-cement; Rheology; Structural build-up; Very early-age hydration","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:479160cf-358f-40a2-a925-e5ad08fd9851","http://resolver.tudelft.nl/uuid:479160cf-358f-40a2-a925-e5ad08fd9851","Microstructural evolutions and impact toughness in simulated welding heat affected zones for a high-strength carbide-free bainitic rail steel","Bai, Wei (Southwest Jiaotong University; State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization); Xu, X. (TU Delft Novel Aerospace Materials; Southwest Jiaotong University); Liu, Yaolan (Southwest Jiaotong University); Liang, Yunxiao (Southwest Jiaotong University); Shen, Yijie (Southwest Jiaotong University); Han, Zhenyu (State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization); Sheng, Zhendong (State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization); Chen, Rong (State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization); Zhu, Minhao (Southwest Jiaotong University)","","2023","Systematic experimental investigations were conducted to study the microstructures and impact toughness of each heat affected zone (HAZ) formed during rail flash-butt welding. A high-strength carbide-free bainitic rail steel was subjected to different thermal simulation cycles to separately reproduce each HAZ subzone by tailoring the peak temperature (PT) with respect to 700, 850, 920, 1000 and 1350 °C, and hence to generate the corresponding microstructures by using Gleeble-3500 simulator. Results show that the HAZ subzones exhibit complicated microstructures depending on the PTs, and with increasing PT the dominant bainitic microstructure type evolves from polygonal bainitic ferrite (700 °C) to a mixture of fine bainitic ferrite and granular bainite (850–1000 °C), and finally to coarse bainitic ferrite and granular bainite (1350 °C). Impact tests demonstrate that the impact toughness initially increases significantly as the PT reaches 920 °C (i.e., fine-grained HAZ), beyond which the impact toughness starts to decrease. The fine-grained HAZ displays optimal impact toughness in HAZs, yet which is lower than the base metal. Moreover, the morphology and distribution of martensite-austenite (M-A) constituents is strongly dependent on the welding PT, and the high fraction blocky and coarse slender M-A constituents is considered to be detrimental for the impact toughness.","Bainitic rail steel; Impact toughness; Microstructural evolutions; Peak temperature; Welding thermal simulation","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-12-25","","","Novel Aerospace Materials","","",""
"uuid:b67f7842-5981-4b9e-b995-26b5722ef492","http://resolver.tudelft.nl/uuid:b67f7842-5981-4b9e-b995-26b5722ef492","On the chemo-mechanical evolution process of high-volume slag cement paste","Liang, M. (TU Delft Materials and Environment); Zhang, Y. (TU Delft Materials and Environment); He, S. (TU Delft Materials and Environment); Chen, Y. (TU Delft Materials and Environment); Schlangen, E. (TU Delft Materials and Environment); Šavija, B. (TU Delft Materials and Environment)","","2023","This study investigated the evolution process of high-volume slag cement (HVSC) paste from a chemo-mechanical standpoint. HVSC specimens with a 70 w.t. % slag replacement rate were studied at various ages. Evolution of phase assemblage, microstructure development, and micromechanical properties were analyzed using TGA/XRD/MIP/SEM-EDS and nano-/micro-indentation techniques. A two-scale micromechanical model was built to predict the effective elastic modulus based on the nanoindentation results. Key findings include: 1) Between 7 and 28 days, the formation of calcium silicate hydrate (C-S-H) gel phase improves the effective elastic modulus by filling capillary pores; 2) From 28 to 90 days, the phase assemblage and microstructure remain stable, with a transition from low-density to high-density C-S-H; 3) Between 90 days and 2 years, slag rims produced by slag grains result in increased elastic modulus; 4) The two-scale micromechanical model, combined with nanoindentation data, accurately predicts the effective modulus of HVSC composites, although the unhydrated slag grains-hydrated cement matrix interface may cause an overestimation at an early age. With longer curing time, this interface disappears owing to the continuous hydration of large slag particles and therefore a good match is found between the modelling and experimental results.","Chemo-mechanical properties; Evolution; High volume slag replacement; Low-carbon cement","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:fd506670-bdfa-4e21-b81f-573966c7c456","http://resolver.tudelft.nl/uuid:fd506670-bdfa-4e21-b81f-573966c7c456","ROSE: Robust Searchable Encryption with Forward and Backward Security","Xu, Peng (Huazhong University of Science and Technology); Susilo, Willy (University of Wollongong); Wang, Wei (Huazhong University of Science and Technology); Chen, Tianyang (Huazhong University of Science and Technology); Wu, Qianhong (Beihang University); Liang, K. (TU Delft Cyber Security); Jin, Hai (Huazhong University of Science and Technology)","","2022","Dynamic searchable symmetric encryption (DSSE) has been widely recognized as a promising technique to delegate update and search queries over an outsourced database to an untrusted server while guaranteeing the privacy of data. Many efforts on DSSE have been devoted to obtaining a good tradeoff between security and performance. However, it appears that all existing DSSE works miss studying on what will happen if the DSSE client issues irrational update queries carelessly, such as duplicate update queries and delete queries to remove non-existent entries (that have been considered by many popular database system in the setting of plaintext). In this scenario, we find that (1) most prior works lose their claimed correctness or security, and (2) no single approach can achieve correctness, forward and backward security, and practical performance at the same time. To address this problem, we study for the first time the notion of robustness of DSSE. Generally, we say that a DSSE scheme is robust if it can keep the same correctness and security even in the case of misoperations. Then, we introduce a new cryptographic primitive named key-updatable pseudo-random function and apply this primitive to constructing ROSE, a robust DSSE scheme with forward and backward security. Finally, we demonstrate the efficiency of ROSE and give the experimental comparisons.","Searchable Symmetric Encryption; Forward and Backward Security; Robustness; Key-Updatable PseudoRandom Function","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Cyber Security","","",""
"uuid:a87385e4-99fa-461d-97df-05b74bfa8a1a","http://resolver.tudelft.nl/uuid:a87385e4-99fa-461d-97df-05b74bfa8a1a","DEFEAT: Deep Hidden Feature Backdoor Attacks by Imperceptible Perturbation and Latent Representation Constraints","Zhao, Zhendong (University of Chinese Academy of Sciences; Chinese Academy of Sciences); Chen, Xiaojun (University of Chinese Academy of Sciences; Chinese Academy of Sciences); Xuan, Yuexin (University of Chinese Academy of Sciences; Chinese Academy of Sciences); Dong, Ye (University of Chinese Academy of Sciences; Chinese Academy of Sciences); Wang, Dakui (University of Chinese Academy of Sciences; Chinese Academy of Sciences); Liang, K. (TU Delft Cyber Security)","","2022","Backdoor attack is a type of serious security threat to deep learning models. An adversary can provide users with a model trained on poisoned data to manipulate prediction behavior in test stage using a backdoor. The backdoored models behave normally on clean images, yet can be activated and output incorrect prediction if the input is stamped with a specific trigger pattern. Most existing backdoor attacks focus on manually defining imperceptible triggers in input space without considering the abnormality of triggers' latent representations in the poisoned model. These attacks are susceptible to backdoor detection algorithms and even visual inspection. In this paper, We propose a novel and stealthy backdoor attack - DEFEAT. It poisons the clean data using adaptive imperceptible perturbation and restricts latent representation during training process to strengthen our attack's stealthiness and resistance to defense algorithms. We conduct extensive experiments on multiple image classifiers using real-world datasets to demonstrate that our attack can 1) hold against the state-of-the-art defenses, 2) deceive the victim model with high attack success without jeopardizing model utility, and 3) provide practical stealthiness on image data.","","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Cyber Security","","",""
"uuid:78246300-891e-480b-9cb1-f6b74caae0d9","http://resolver.tudelft.nl/uuid:78246300-891e-480b-9cb1-f6b74caae0d9","A Reconfigurable Cold-Startup SSHI Rectifier with 4X Lower Input Amplitude Requirement for Piezoelectric Energy Harvesting","Yue, X. (TU Delft Electronic Instrumentation); Zou, Yiwei (Student TU Delft); Chen, Zhelun (Student TU Delft); Liang, Junrui (ShanghaiTech University); Du, S. (TU Delft Electronic Instrumentation)","","2022","Synchronized switch harvesting on inductor (SSHI) is an efficient active rectifier to extract energy generated from piezoelectric transducer in piezoelectric energy harvesting system. Unlike passive rectifiers, SSHI rectifiers require a power supply to drive synchronized switches. Unfortunately, there is no stable supply when the system starts from the cold state. Most designs let the system work as a passive full bridge rectifier (FBR) to charge power capacitor until a supply is available. However, a FBR requires high open-circuit voltage (VOC) and the FBR’s output voltage cannot go over VOC. This prevents the system from starting the SSHI rectifier if VOC is low. This paper proposes a new transducer reconfiguration design to lower the required VOC by 4 $\times$ to start up the SSHI system from the cold state. The proposed system is designed in a 0.18$-\mu$m BCD process and post-layout simulations show that the successful cold-startup under low VOC voltage.","Power supplies; Simulation; Rectifiers; Bridge circuits; Switches; Threshold voltage; Power capacitors; Cold-startup; energy harvesting; full bridge rectifier; open-circuit voltage; piezoelectric transducer; SSHI rectifier","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Electronic Instrumentation","","",""
"uuid:60df9a09-c590-499b-a752-6d0c4de4cc94","http://resolver.tudelft.nl/uuid:60df9a09-c590-499b-a752-6d0c4de4cc94","A PV-assisted 10-mV Startup Boost Converter for Thermoelectric Energy Harvesting","Liang, Yansong (Student TU Delft); Wang, Ruizhi (Student TU Delft); Chen, Zhongsheng (Hunan University of Science and Technology); Du, S. (TU Delft Electronic Instrumentation)","","2022","This paper presents a boost converter for thermo-electric energy harvesting with photovoltaic (PV)-assisted startup. The converter employs a new two-phase startup architecture and the PV cell is used in the first phase to provide an initial high voltage for startup. This high voltage drives the boost converter to charge a startup capacitor, which powers the main control block to continue self-startup in phase 2. The proposed system is designed and simulated in a $0.18\mu{\mathrm{m}}$ BCD process. The simulations show successful cold-start from 10 mV thermoelectric voltage. In addition, maximum power point tracking and zero current switching techniques are adopted in the system to achieve 91% peak efficiency. The proposed system can finish the cold-start within 250 ms.","thermoelectric energy harvesting; startup; boost converter","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Electronic Instrumentation","","",""
"uuid:0817df44-5800-4f89-ad86-8b1a9b72b419","http://resolver.tudelft.nl/uuid:0817df44-5800-4f89-ad86-8b1a9b72b419","A Series of Ternary Metal Chloride Superionic Conductors for High-Performance All-Solid-State Lithium Batteries","Liang, Jianwen (University of Western Ontario); van der Maas, E.L. (TU Delft RST/Storage of Electrochemical Energy); Luo, Jing (University of Western Ontario); Li, Xiaona (University of Western Ontario); Chen, Ning (TU Delft Photovoltaic Materials and Devices; Canadian Ligth Source, Saskatoon); Adair, Keegan R. (University of Western Ontario); Li, Weihan (University of Western Ontario); Li, Junjie (University of Western Ontario); Hu, Yongfeng; Liu, Jue (Oak Ridge National Laboratory); Zhang, Li; Zhao, W. (TU Delft RST/Storage of Electrochemical Energy); Parnell, S.R. (TU Delft RID/TS/Instrumenten groep); Ganapathy, S. (TU Delft RID/TS/Instrumenten groep); Wagemaker, M. (TU Delft RST/Storage of Electrochemical Energy)","","2022","Understanding the relationship between structure, ionic conductivity, and synthesis is the key to the development of superionic conductors. Here, a series of Li3-3xM1+xCl6 (−0.14 < x ≤ 0.5, M = Tb, Dy, Ho, Y, Er, Tm) solid electrolytes with orthorhombic and trigonal structures are reported. The orthorhombic phase of Li–M–Cl shows an approximately one order of magnitude increase in ionic conductivities when compared to their trigonal phase. Using the Li–Ho–Cl components as an example, their structures, phase transition, ionic conductivity, and electrochemical stability are studied. Molecular dynamics simulations reveal the facile diffusion in the z-direction in the orthorhombic structure, rationalizing the improved ionic conductivities. All-solid-state batteries of NMC811/Li2.73Ho1.09Cl6/In demonstrate excellent electrochemical performance at both 25 and −10 °C. As relevant to the vast number of isostructural halide electrolytes, the present structure control strategy guides the design of halide superionic conductors.","all-solid-state Li batteries; energy storage; halides; solid-state electrolytes; superionic conductors","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","RST/Storage of Electrochemical Energy","","",""
"uuid:402bd8b6-3b0d-4d05-b0a2-24abae01efa1","http://resolver.tudelft.nl/uuid:402bd8b6-3b0d-4d05-b0a2-24abae01efa1","Predicting early-age stress evolution in restrained concrete by thermo-chemo-mechanical model and active ensemble learning","Liang, M. (TU Delft Materials and Environment); Chang, Z. (TU Delft Materials and Environment); He, S. (TU Delft Materials and Environment); Chen, Y. (TU Delft Materials and Environment); Gan, Y. (TU Delft Materials and Environment); Schlangen, E. (TU Delft Materials and Environment); Šavija, B. (TU Delft Materials and Environment)","","2022","Early-age stress (EAS) is an important index for evaluating the early-age cracking risk of concrete. This paper encompasses a thermo-chemo-mechanical (TCM) model and active ensemble learning (AEL) for predicting the EAS evolution. The TCM model provides the data for the AEL model. First, based on Fourier's law, Arrhenius’ equation, and rate-type creep law, a TCM model is built to simulate the heat transfer, cement hydration, and viscoelasticity, which together determine the EAS evolution. Then, a material model composed of an eXtreme Gradient Boosting model and adjusted Model Code 2010 is built to allow for parametric study and database construction. Finally, an AEL framework is built, which incorporates principal component analysis (PCA), Gaussian process, and light gradient boosting machine (LGBM). This study resulted in the following findings: (1) The dimensionality of the 672-by-1 EAS vector can be effectively reduced by PCA, and the first principal component (PC) is a global index representing the magnitude of the EAS; (2) the mechanical field of the TCM model is validated by testing data. Correlation analysis on the first PC quantifies the influence of various input parameters of the TCM model, which is in accordance with common understandings of the EAS evolution process. (3) The AEL and one-shot ensemble learning (OSEL) both achieve high prediction performance in the testing set, whose R2 reaches 0.961 and 0.948, respectively. Thanks to the uncertainty-based query procedure, comparing with OSEL, AEL shows advantages in prediction performance over the whole training history. (4) AEL can significantly reduce the number of samples required for training, which can be a major improvement in efficiency considering the computational cost of the TCM model.","","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:5c3e052f-9f99-4052-8e77-e01b42b4f1a7","http://resolver.tudelft.nl/uuid:5c3e052f-9f99-4052-8e77-e01b42b4f1a7","Mapping the knowledge domain of soft computing applications for emergency evacuation studies: A scientometric analysis and critical review","Liang, Benbu (TU Delft System Engineering; TU Delft Multi Actor Systems; Wuhan University of Technology); van der Wal, C.N. (TU Delft Multi Actor Systems; TU Delft System Engineering); Xie, Kefan (Wuhan University of Technology); Chen, Y. (TU Delft Materials and Environment; Wuhan University of Technology); Brazier, F.M. (TU Delft Multi Actor Systems; TU Delft System Engineering); Dulebenets, Maxim A. (Florida State University); Liu, Zimei (Huazhong Agricultural University)","","2022","Emergency evacuation is viewed as a common strategy adopted during the disaster preparedness stage of evacuation to ensure the safety of potentially affected populations. In emergency evacuation studies, soft computing approaches and methodologies have been widely used to support effective decision-making, providing robust and low-cost solutions. To understand the current status and trends of research on soft computing applications for emergency evacuation studies, 778 related studies published in the core database of Web of Science from 2000 to 2020 were considered in this study. A scientometric analysis and a comprehensive review were performed using a scientific mapping of the knowledge domain. This paper presents a set of analyses with the following primary objectives: (1) to explore and visualize the bibliometric characteristics and contents of the academic field concerned with the soft computing approaches for emergency evacuation; and (2) to review and analyze the knowledge, hotspots, and future outlooks related to soft computing approaches for emergency evacuation. The results provide some important insights regarding the existing soft computing methods that have been used in the emergency evacuation field over the past 20 years. Based on the conducted review, this paper proposes that future studies should concentrate on exploring the potential of innovative soft computing approaches for crowd modelling and enabling more accurate evacuation simulation and optimization.","Disaster management; Emergency evacuation; Knowledge domain; Scientometric analysis; Soft computing","en","review","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-04-15","","Multi Actor Systems","System Engineering","","",""
"uuid:4e3b1ad1-9099-4c69-ad42-fdd8e3552b7b","http://resolver.tudelft.nl/uuid:4e3b1ad1-9099-4c69-ad42-fdd8e3552b7b","3-D Instance Segmentation of MVS Buildings","Chen, Jiazhou (Zhejiang University of Technology); Xu, Yanghui (Zhejiang University of Technology); Lu, Shufang (Zhejiang University of Technology); Liang, Ronghua (Zhejiang University of Technology); Nan, L. (TU Delft Urban Data Science)","","2022","We present a novel 3-D instance segmentation framework for multiview stereo (MVS) buildings in urban scenes. Unlike existing works focusing on semantic segmentation of urban scenes, the emphasis of this work lies in detecting and segmenting 3-D building instances even if they are attached and embedded in a large and imprecise 3-D surface model. Multiview red green blue (RGB) images are first enhanced to RGB height (RGBH) images by adding a heightmap and are segmented to obtain all roof instances using a fine-tuned 2-D instance segmentation neural network. Instance masks from different multiview images are then clustered into global masks. Our mask clustering accounts for spatial occlusion and overlapping, which can eliminate segmentation ambiguities among multiview images. Based on these global masks, 3-D roof instances are segmented out by mask back-projections and extended to the entire building instances through a Markov random field optimization. A new dataset that contains instance-level annotation for both 3-D urban scenes (roofs and buildings) and drone images (roofs) is provided. To the best of our knowledge, it is the first outdoor dataset dedicated to 3-D instance segmentation with much more annotations of attached 3-D buildings than existing datasets.1 Quantitative evaluations and ablation studies have shown the effectiveness of all major steps and the advantages of our multiview framework over the orthophoto-based method.","3-D urban scene; dataset; instance segmentation; multiview clustering","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2022-12-16","","","Urban Data Science","","",""
"uuid:b051a5b8-e734-48b4-afc7-fbc9184396d0","http://resolver.tudelft.nl/uuid:b051a5b8-e734-48b4-afc7-fbc9184396d0","DEKS: A Secure Cloud-Based Searchable Service Can Make Attackers Pay","Zheng, Yubo (Huazhong University of Science and Technology); Xu, Peng (Huazhong University of Science and Technology); Wang, Wei (Huazhong University of Science and Technology); Chen, Tianyang (Huazhong University of Science and Technology); Susilo, Willy (University of Wollongong); Liang, K. (TU Delft Cyber Security); Jin, Hai (Huazhong University of Science and Technology)","Atluri, Vijayalakshmi (editor); Di Pietro, Roberto (editor); Jensen, Christian D. (editor); Meng, Weizhi (editor)","2022","Many practical secure systems have been designed to prevent real-world attacks via maximizing the attacking cost so as to reduce attack intentions. Inspired by this philosophy, we propose a new concept named delay encryption with keyword search (DEKS) to resist the notorious keyword guessing attack (KGA), in the context of secure cloud-based searchable services. Avoiding the use of complex (and unreasonable) assumptions, as compared to existing works, DEKS optionally leverages a catalyst that enables one (e.g., a valid data user) to easily execute encryption; without the catalyst, any unauthenticated system insiders and outsiders take severe time consumption on encryption. By this, DEKS can overwhelm a KGA attacker in the encryption stage before it obtains any advantage. We leverage the repeated squaring function, which is the core building block of our design, to construct the first DEKS instance. The experimental results show that DEKS is practical in thwarting KGA for both small and large-scale datasets. For example, in the Wikipedia, a KGA attacker averagely takes 7.23 years to break DEKS when the delay parameter T= 2 24. The parameter T can be flexibly adjusted based on practical needs, and theoretically, its upper bound is infinite.","Delay encryption with keyword search; Keyword guessing attack; Privacy; Security","en","conference paper","Springer","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Cyber Security","","",""
"uuid:f2603e8f-895b-4a15-95c4-4c9ed5e1e3c5","http://resolver.tudelft.nl/uuid:f2603e8f-895b-4a15-95c4-4c9ed5e1e3c5","No-Directional and Backward-Leak Uni-Directional Updatable Encryption Are Equivalent","Chen, H. (TU Delft Cyber Security); Fu, S. (TU Delft Cyber Security); Liang, K. (TU Delft Cyber Security)","Atluri, Vijayalakshmi (editor); Di Pietro, Roberto (editor); Jensen, Christian D. (editor); Meng, Weizhi (editor)","2022","Updatable encryption (UE) enables the cloud server to update the previously sourced encrypted data to a new key with only an update token received from the client. Two interesting works have been proposed to clarify the relationships among various UE security notions. Jiang (ASIACRYPT 2020) proved the equivalence of every security notion in the bi-directional and uni-directional key update settings and further, the security notion in the no-directional key update setting is strictly stronger than the above two. In contrast, Nishimaki (PKC 2022) proposed a new definition of uni-directional key update that is called the backward-leak uni-directional key update, and showed the equivalence relation by Jiang does not hold in this setting. We present a detailed comparison of every security notion in the four key update settings and prove that the security in the backward-leak uni-directional key update setting is actually equivalent to that in the no-directional key update setting. Our result reduces the hard problem of constructing no-directional key update UE schemes to the construction of those with backward-leak uni-directional key updates.","Key update; Security notion; Updatable encryption","en","conference paper","Springer","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Cyber Security","","",""
"uuid:37c3f1fc-fbfe-418b-a1fe-4ecfc62862da","http://resolver.tudelft.nl/uuid:37c3f1fc-fbfe-418b-a1fe-4ecfc62862da","VAL: Volume and Access Pattern Leakage-Abuse Attack with Leaked Documents","Lambregts, Steven (Student TU Delft); Chen, H. (TU Delft Cyber Security); Ning, Jianting (Singapore Management University; Fujian Normal University); Liang, K. (TU Delft Cyber Security)","Atluri, Vijayalakshmi (editor); Di Pietro, Roberto (editor); Jensen, Christian D. (editor); Meng, Weizhi (editor)","2022","Searchable Encryption schemes provide secure search over encrypted databases while allowing admitted information leakages. Generally, the leakages can be categorized into access and volume pattern. In most existing SE schemes, these leakages are caused by practical designs but are considered an acceptable price to achieve high search efficiency. Recent attacks have shown that such leakages could be easily exploited to retrieve the underlying keywords for search queries. Under the umbrella of attacking SE, we design a new Volume and Access Pattern Leakage-Abuse Attack (VAL-Attack) that improves the matching technique of LEAP (CCS ’21) and exploits both the access and volume patterns. Our proposed attack only leverages leaked documents and the keywords present in those documents as auxiliary knowledge and can effectively retrieve document and keyword matches from leaked data. Furthermore, the recovery performs without false positives. We further compare VAL-Attack with two recent well-defined attacks on several real-world datasets to highlight the effectiveness of our attack and present the performance under popular countermeasures.","Access pattern; Attack; Leakage; Searchable encryption; Volume pattern","en","conference paper","Springer","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Cyber Security","","",""
"uuid:9d96e6e9-0203-46d1-9edd-1c8c4304571e","http://resolver.tudelft.nl/uuid:9d96e6e9-0203-46d1-9edd-1c8c4304571e","Your Smart Contracts Are Not Secure: Investigating Arbitrageurs and Oracle Manipulators in Ethereum","Tjiam, Kevin (Student TU Delft); Wang, R. (TU Delft Cyber Security); Chen, H. (TU Delft Cyber Security); Liang, K. (TU Delft Cyber Security)","","2021","Smart contracts on Ethereum enable billions of dollars to be transacted in a decentralized, transparent and trustless environment. However, adversaries lie await in the Dark Forest, waiting to exploit any and all smart contract vulnerabilities in order to extract profits from unsuspecting victims in this new financial system. As the blockchain space moves at a breakneck pace, exploits on smart contract vulnerabilities rapidly evolve, and existing research quickly becomes obsolete. It is imperative that smart contract developers stay up to date on the current most damaging vulnerabilities and countermeasures to ensure the security of users' funds, and to collectively ensure the future of Ethereum as a financial settlement layer. This research work focuses on two smart contract vulnerabilities: transaction-ordering dependency and oracle manipulation. Combined, these two vulnerabilities have been exploited to extract hundreds of millions of dollars from smart contracts in the past year (2020-2021). For each of them, this paper presents: (1) a literary survey from recent (as of 2021) formal and informal sources; (2) a reproducible experiment as code demonstrating the vulnerability and, where applicable, countermeasures to mitigate the vulnerability; and (3) analysis and discussion on proposed countermeasures. To conclude, strengths, weaknesses and trade-offs of these countermeasures are summarised, inspiring directions for future research.","arbitrageurs; ethereum; oracle manipulator; security; smart contract; vulnerability","en","conference paper","Association for Computing Machinery (ACM)","","","","","","","","","","Cyber Security","","",""
"uuid:468a6445-cdc5-4616-94f4-1082193674d2","http://resolver.tudelft.nl/uuid:468a6445-cdc5-4616-94f4-1082193674d2","Super Tough and Spontaneous Water-Assisted Autonomous Self-Healing Elastomer for Underwater Wearable Electronics","He, Cyuan Lun (National Taipei University of Technology); Liang, Fang Cheng (National Taipei University of Technology); Veeramuthu, Loganathan (National Taipei University of Technology); Cho, Chia Jung (National Taipei University of Technology); Benas, Jean Sebastien (National Taipei University of Technology); Tzeng, Yung Ru (National Taipei University of Technology); Tseng, Yen Lin (National Taipei University of Technology); Chen, Wei Cheng (National Taipei University of Technology); Rwei, A.Y. (TU Delft ChemE/Product and Process Engineering); Kuo, Chi Ching (National Taipei University of Technology)","","2021","Self-healing soft electronic material composition is crucial to sustain the device long-term durability. The fabrication of self-healing soft electronics exposed to high moisture environment is a significant challenge that has yet to be fully achieved. This paper presents the novel concept of a water-assisted room-temperature autonomous self-healing mechanism based on synergistically dynamic covalent Schiff-based imine bonds with hydrogen bonds. The supramolecular water-assisted self-healing polymer (WASHP) films possess rapid self-healing kinetic behavior and high stretchability due to a reversible dissociation–association process. In comparison with the pristine room-temperature self-healing polymer, the WASHP demonstrates favorable mechanical performance at room temperature and a short self-healing time of 1 h; furthermore, it achieves a tensile strain of 9050%, self-healing efficiency of 95%, and toughness of 144.2 MJ m−3. As a proof of concept, a versatile WASHP-based light-emitting touch-responsive device (WASHP-LETD) and perovskite quantum dot (PeQD)-based white LED backlight are designed. The WASHP-LETD has favorable mechanical deformation performance under pressure, bending, and strain, whereas the WASHP-PeQDs exhibit outstanding long-term stability even over a period exceeding one year in a boiling water environment. This paper provides a mechanically robust approach for producing eco-friendly, economical, and waterproof e-skin device components.","flexible wearable devices; light-emitting diodes; perovskite quantum dots; underwater electronics; water-insensitive self-healing elastomers","en","journal article","","","","","","","","","","","ChemE/Product and Process Engineering","","",""
"uuid:0f2594b3-a70a-41e8-9003-2d010ef980d6","http://resolver.tudelft.nl/uuid:0f2594b3-a70a-41e8-9003-2d010ef980d6","Effect of metakaolin on the autogenous shrinkage of alkali-activated slag-fly ash paste","Li, Z. (TU Delft Materials and Environment); Liang, X. (TU Delft Materials and Environment); Chen, Y. (TU Delft Materials and Environment; South China University of Technology); Ye, G. (TU Delft Materials and Environment; Universiteit Gent)","","2021","The high autogenous shrinkage of alkali-activated materials made from slag and fly ash is recognised as a major drawback with regard to the use as construction materials. In this study, metakaolin was introduced into the alkali-activated slag-fly ash (AASF) paste to mitigate the autogenous shrinkage. The shrinkage mitigation mechanism of metakaolin was explained by studying the influences of metakaolin on the microstructure, shrinkage related properties, and mechanical properties of AASF paste. It was found that adding metakaolin could significantly reduce the chemical and autogenous shrinkage of AASF paste. This shrinkage mitigation is accompanied by a decrease in the alkalinity of AASF paste pore solution, a reduced drop in internal relative humidity, and an increase in porosity of AASF paste. Moreover, the incorporation of metakaolin does not change the type of the reaction products, but greatly delays the formation of the reaction products of AASF paste. The addition of metakaolin, above 5% of the binder, results in lower 28-day compressive and flexural strength of AASF paste.","Alkali-activated materials; Fly ash; Metakaolin; Shrinkage; Slag","en","journal article","","","","","","","","","","","Materials and Environment","","",""
"uuid:11523521-351a-44e6-802a-34e4c40ccd22","http://resolver.tudelft.nl/uuid:11523521-351a-44e6-802a-34e4c40ccd22","Fluidization dynamics of cohesive Geldart B particles. Part I: X-ray tomography analysis","Ma, Jiliang (Southeast University); van Ommen, J.R. (TU Delft ChemE/Product and Process Engineering); Liu, Daoyin (Southeast University); Mudde, R.F. (TU Delft ImPhys/Imaging Physics; TU Delft Executive board); Chen, Xiaoping (Southeast University); Wagner, E.C. (TU Delft ChemE/Afdelingsbureau); Liang, Cai (Southeast University)","","2019","Due to the presence of inter-particle cohesive force, cohesive particles reveal totally different fluidization behaviors as compared to the non-cohesive system. This paper studies the fluidization dynamics of Geldart B particles with varying thermal-induced cohesive forces. Multi-source X-ray tomography was applied to reconstruct 3D temporal images of bubbles, based on which, various bubble properties were extracted. The results show that increasing cohesive force will decrease bubble number while increase bubble size, implying that the presence of cohesive force facilitates bubble coalescence. By examining the bubble size distribution, cohesive force is found to have no effect on the number of median bubbles but greatly influence small and large bubbles. When the cohesive force is strong, the bubbles grow to a considerable size similar with bed dimension, giving rise to slugging near bed surface. With the action of inter-particle cohesive force, particle slug gradually grows by capturing other freely fluidizing particles, finally inducing “whole-bed” slugging. The particle slug may rupture in the rising process, and the bed turns back to normal fluidization. In comparison to normal bubbles, the gas slug has much larger size but far smaller frequency. The rise velocity of gas slug is also very low due to the particle-wall friction and gas-solid momentum dissipation. Therefore, the averaged values of bubble properties dramatically changed as bed temperature exceeds 35 °C. When the temperature attains 45 °C, the cohesive force is so strong that the fluidization completely fails in terms of stable whole-bed slugging.","Bubble; Cohesive particle; Fluidization; Slugging; X-ray tomography","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2019-05-12","","ImPhys/Imaging Physics","ChemE/Product and Process Engineering","","",""
"uuid:aa175f43-0430-4105-8cf2-92705c026842","http://resolver.tudelft.nl/uuid:aa175f43-0430-4105-8cf2-92705c026842","Fluidization dynamics of cohesive Geldart B particles. Part II: Pressure fluctuation analysis","Ma, Jiliang (Southeast University); van Ommen, J.R. (TU Delft ChemE/Product and Process Engineering); Liu, Daoyin (Southeast University); Mudde, R.F. (TU Delft Executive board); Chen, Xiaoping (Southeast University); Pan, Suyang (Southeast University); Liang, Cai (Southeast University)","","2019","The increase of inter-particle cohesive force greatly changes the fluidization dynamics, finally leading to the partial or complete failure of fluidization. However, few studies concern such transition process. This paper investigates the fluidization dynamics of Geldart B particles with a wide-range of cohesive force by analyzing the in-bed pressure fluctuation signals. Combining the bubble information reported in Part I, the local and global fluidization dynamics under different cohesive forces were discussed. The results show that bulk bubble dynamics is weaken with the presence of inter-particle cohesive force. As the force increases, fluidization changes from multi-bubbling regime to single-bubble regime and the factor governing the pressure fluctuation changes from bubble formation to bubble eruption. When the cohesive force is strong, slugging appears near the bed surface, then gradually extends toward the bottom bed by capturing freely fluidizing particles, and finally develops into the whole-bed slugging. At this time, regular fluidization turns into an alternative process between whole-bed slugging and regular status, corresponding to two distinct peaks in power spectral density of pressure signals at 0.1 Hz and 1 Hz respectively. The size of gas slug decreases with the elevation of measurement height. Basically, any operations that promote bubble growth will also facilitate the appearance of whole-bed slugging under strong cohesive force. Reducing the static bed height is a preferable approach to weaken, or even avoid the defluidization of whole-bed slugging, without changing other operational parameters.","Cohesive particle; Defluidization; Fluidization; Pressure fluctuation; Slugging","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2019-08-26","","Executive board","ChemE/Product and Process Engineering","","",""
"uuid:f4626852-1102-4080-a61a-003cc92677dc","http://resolver.tudelft.nl/uuid:f4626852-1102-4080-a61a-003cc92677dc","Effects of Thermal Reflowing Stress on Mechanical Properties of Novel SMT-SREKs","Cai, Miao (Guilin University of Electronic Technology); Liang, Yonghu (Guilin Xuyan Electromechanical Technology, Co., Ltd., Guilin); Yun, Minghui (Guilin University of Electronic Technology); Chen, Xuan-You (Guilin University of Electronic Technology); Yan, Haidong (Guilin University of Electronic Technology); Yu, Zhaozhe (Guilin University of Electronic Technology); Yang, Daoguo (Guilin University of Electronic Technology); Zhang, Kouchi (TU Delft Electronic Components, Technology and Materials; Guilin University of Electronic Technology)","","2019","A novel silicone rubber elastic key (SREK) is proposed in this paper for surface mounting technology (SMT) applications. Effects of thermal reflowing stress on the mechanical properties of SMT-SREKs are investigated. The manufactured SMT-SREKs, which underwent various reflowing conditions in advance, are subjected to pressing force and fatigue pressing tests. Fatigue lifetime projection model and its predicted error are then assessed systematically. The thermal degradation of silicone rubber materials is illustrated through the dynamic mechanical analysis and the Fourier transform infrared spectroscopy experiments. The mechanical finite element modeling is also conducted to simulate the pressing process. The results show that the pressing force and tactility of the SMT-SREKs are strongly affected by the reflowing condition, which contributes to the degradation of the silicone rubber materials. During the fatigue pressing test, the change rate of tactility increases with the reflowing peak temperature ( T-{p} ) and is accelerated by the repeated reflowing process. Moreover, a linear model can precisely project the tactility before the fatigue pressing number of 2.0E+6 times, and the impact rate of T-{p} on tactility with the increasing fatigue pressing number can be predicted effectively by using a logarithm model.","degradation; fatigue lifetime; mechanical property; modeling; Silicone rubber elastic key (SREK); surface mounting technology (SMT)","en","journal article","","","","","","","","","","","Electronic Components, Technology and Materials","","",""
"uuid:65a5f5d2-a864-49b0-b9b2-190f8f7b545e","http://resolver.tudelft.nl/uuid:65a5f5d2-a864-49b0-b9b2-190f8f7b545e","A numerical Bayesian-calibrated characterization method for multiscale prepreg preforming simulations with tension-shear coupling","Zhang, Weizhao (Northwestern University); Bostanabad, Ramin (Northwestern University); Liang, Biao (Northwestern University); Su, Xuming (Ford Motor Company); Zeng, Danielle (Ford Motor Company); Bessa, M.A. (TU Delft (OLD) MSE-5); Wang, Yanchao (Tongji University); Chen, Wei (Northwestern University); Cao, Jian (Northwestern University)","","2019","Carbon fiber reinforced plastics (CFRPs) are attracting growing attention in industry because of their enhanced properties. Preforming of thermoset carbon fiber prepregs is one of the most common production techniques of CFRPs. To simulate preforming, several computational methods have been developed. Most of these methods, however, obtain the material properties directly from experiments such as uniaxial tension and bias-extension where the coupling effect between tension and shear is not considered. Neglecting this coupling effect deteriorates the prediction accuracy of simulations. To address this issue, we develop a Bayesian model calibration and material characterization approach in a multiscale finite element preforming simulation framework that utilizes mesoscopic representative volume element (RVE) to account for the tension-shear coupling. A new geometric modeling technique is first proposed to generate the RVE corresponding to the close-packed uncured prepreg. This RVE model is then calibrated with a modular Bayesian approach to estimate the yarn properties, test its potential biases against the experiments, and fit a stress emulator. The predictive capability of this multiscale approach is further demonstrated by employing the stress emulator in the macroscale preforming simulation which shows that this approach can provide accurate predictions.","Bayesian calibration; Gaussian processes; Multiscale simulations; Preforming; Prepreg","en","journal article","","","","","","Accepted Author Manuscript","","2019-11-22","","","(OLD) MSE-5","","",""
"uuid:3e9873dd-a6d6-49d6-8fc5-57c0ab99acae","http://resolver.tudelft.nl/uuid:3e9873dd-a6d6-49d6-8fc5-57c0ab99acae","Current and future trends in topology optimization for additive manufacturing","Liu, Jikai (University of Pittsburgh); Gaynor, Andrew T. (U.S. Army Research Laboratory); Chen, Shikui (State University of New York); Kang, Zhan (Dalian University of Technology); Suresh, Krishnan (University of Wisconsin-Madison); Takezawa, Akihiro (Hiroshima University); Li, Lei (University of Notre Dame); Kato, Junji (Tohoku University); Tang, Jinyuan (Central South University); Wang, C.C. (TU Delft Materials and Manufacturing); Cheng, Lin (University of Pittsburgh); Liang, Xuan (University of Pittsburgh); To, Albert. C. (University of Pittsburgh)","","2018","Manufacturing-oriented topology optimization has been extensively studied the past two decades, in particular for the conventional manufacturing methods, for example, machining and injection molding or casting. Both design and manufacturing engineers have benefited from these efforts because of the close-to-optimal and friendly-to-manufacture design solutions. Recently, additive manufacturing (AM) has received significant attention from both academia and industry. AM is characterized by producing geometrically complex components layer-by-layer, and greatly reduces the geometric complexity restrictions imposed on topology optimization by conventional manufacturing. In other words, AM can make near-full use of the freeform structural evolution of topology optimization. Even so, new rules and restrictions emerge due to the diverse and intricate AM processes, which should be carefully addressed when developing the AM-specific topology optimization algorithms. Therefore, the motivation of this perspective paper is to summarize the state-of-art topology optimization methods for a variety of AM topics. At the same time, this paper also expresses the authors’ perspectives on the challenges and opportunities in these topics. The hope is to inspire both researchers and engineers to meet these challenges with innovative solutions.","Additive manufacturing; Lattice infill; Material feature; Multi-material; Post-treatment; Support structure; Topology optimization; Uncertainty","en","journal article","","","","","","Accepted author manuscript","","2019-06-30","","","Materials and Manufacturing","","",""
"uuid:dcf0d64c-e4f2-4e93-9a5a-939a4270776e","http://resolver.tudelft.nl/uuid:dcf0d64c-e4f2-4e93-9a5a-939a4270776e","Color Shift Modeling of Light-Emitting Diode Lamps in Step-Loaded Stress Testing","Cai, Miao (Guilin University of Electronic Technology); Yang, Daoguo (Guilin University of Electronic Technology); Huang, J. (TU Delft Electronic Components, Technology and Materials); Zhang, Maofen (Guilin University of Electronic Technology); Chen, Xianping (Chongqing University); Liang, Caihang (Guilin University of Electronic Technology); Koh, S.W. (TU Delft Electronic Components, Technology and Materials); Zhang, Kouchi (TU Delft Electronic Components, Technology and Materials; Chinese Academy of Sciences)","","2017","The color coordinate shift of light-emitting diode (LED) lamps is investigated by running three stress-loaded testing methods, namely step-up stress accelerated degradation testing, step-down stress accelerated degradation testing, and constant stress accelerated degradation testing. A power model is proposed as the statistical model of the color shift (CS) process of LED products. Consequently, a CS mechanism constant is obtained for detecting the consistency of CS mechanisms among various stress-loaded conditions. A statistical procedure with the proposed power model is then derived for the CS paths of LED lamps in step-loaded stress testing. Two types of commercial LED lamps with different capabilities of heat dissipation (CHDs) are investigated. Results show that the color coordinates of lamps are easily modified in various stress-loaded conditions, and different CHDs of lamps may play a crucial role in the various CS processes. Furthermore, the proposed statistic power model is adequate for the CS process of LED lamps. The consistency of CS mechanisms in step-loaded stress testing can also be detected effectively by applying the proposed statistic procedure with the power model. Moreover, the constant assumption in the model is useful for judging the consistency of CS mechanisms under various stress-loaded conditions.","color shift (CS); degradation mechanism; Light-emitting diodes (LEDs); reliability modeling","en","journal article","","","","","","","","","","","Electronic Components, Technology and Materials","","",""
"uuid:af452dbd-92fa-4136-ac0a-9ad1c20bdbf9","http://resolver.tudelft.nl/uuid:af452dbd-92fa-4136-ac0a-9ad1c20bdbf9","First-principles study of the effect of functional groups on polyaniline backbone","Chen, X.P.; Jiang, J.K.; Liang, Q.H.; Yang, N.; Ye, H.Y.; Cai, M.; Shen, L.; Yang, D.G.; Ren, T.L.","","2015","We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone. Analyses of the obtained energy barriers, reaction energies and minimum energy paths indicate that the chemical reactivity of the polyaniline derivatives is significantly enhanced by protonic acid doping of the substituted materials. Further study of the density of states at the Fermi level, band gap, HOMO and LUMO shows that both the unprotonated and protonated states of these polyanilines are altered to different degrees depending on the functional group. We also note that changes in both the chemical and electronic properties are very sensitive to the polarity and size of the functional group. It is worth noting that these changes do not substantially alter the inherent chemical and electronic properties of polyaniline. Our results demonstrate that introducing different functional groups on a polymer backbone is an effective approach to obtain tailored conductive polymers with desirable properties while retaining their intrinsic properties, such as conductivity.","","en","journal article","Nature Publishing Group","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Microelectronics","","","",""
"uuid:858534fe-7e68-49a3-8d67-a47a955ec82d","http://resolver.tudelft.nl/uuid:858534fe-7e68-49a3-8d67-a47a955ec82d","Luminescence of Ce3+ at two different sites in ?-Sr2P2O7 under vacuum ultraviolet-UV and x-ray excitation","Hou, D.; Han, B.; Chen, W.; Liang, H.; Su, Q.; Dorenbos, P.; Huang, Y.; Gao, Z.; Tao, Y.","","2010","A series of Ce3+ doped ?-Sr2?2xCexNaxP2O7 phosphor compounds has been prepared using a high-temperature solid-state reaction technique. The luminescence properties under vacuum ultraviolet-UV and x-ray excitation were studied. Luminescence spectra reveal three UV-emitting peaks at about 310, 330, and 350 nm from which we conclude that Ce3+ occupies two distinct sites in ?-Sr2P2O7. The influences of the doping concentration, the temperature, and the excitation wavelength on the luminescence of Ce3+ at the Ce(I) and Ce(II) sites together with the decay characteristics are discussed. The light yield under x-ray excitation is found to be around 10?000 photons/MeV.","cerium; cerium compounds; doping profiles; luminescence; phosphors; sodium compounds; strontium compounds; ultraviolet radiation effects; X-ray effects","en","journal article","American Institute of Physics","","","","","","","","Applied Sciences","RRR/Radiation, Radionuclides and Reactors","","","",""