The Gamma constant-stress accelerated degradation model is a natural model for monotonous degradation processes. However, unit heterogeneity often exists in practice, necessitating a more realistic model. This study develops a Gamma process with random effects to accurately capture accelerated degradation data for reliability analysis, encompassing both point and interval estimation. First, the Expectation-Maximization (EM) algorithm is developed to obtain point estimates of the proposed model. Since these estimates are sensitive to initial values, potentially impacting the outcomes, an improved EM algorithm is proposed, which iteratively refines the estimation quality by executing two different M-steps, thereby enhancing overall estimation accuracy. Secondly, given the complexity of the model and the constraint of small sample sizes and limited stress levels, a three-step interval estimation method is devised. This method segregates the parameters into three distinct parts and addresses them individually using the generalized pivotal quantity method, which simplifies the parameter interval estimation process and enhances the estimation accuracy. Finally, simulation studies and a real example of O-rings are presented to demonstrate the effectiveness of the proposed method.

The dry-mixed rubberized epoxy asphalt mixture (DREAM) has demonstrated superior mechanical properties. The addition of crumb rubber (CR) improves the damping performance and toughness characteristics of DREAM while offering significant potential for recycling waste materials. However, cracking remains a critical issue for DREAM, necessitating further experimental investigations into its crack resistance performance, especially regarding the sensitivity of evaluation indicators. In this study, semi-circular bending tests were conducted on DREAM with varying CR content under three loading rates and two test temperatures. P-values were utilized to evaluate the sensitivity of nine indicators. Results suggest that not all fracture performance indicators exhibit significant differences due to the varying toughness resulting from the CR content in DREAM. Normalized parameters, such as the pre- and total cracking resistance index (CRI^pre,CRI), tensile stiffness index (TSI), and tensile strength (TS) demonstrate superior performance in distinguishing the effects of CR content and test temperature. Meanwhile, TSI, CRI, and CRI^pre can only significantly distinguish the effects of loading rate in DREAM with high CR content. Moreover, the addition of CR reduces the load-bearing capacity and stiffness of DREAM while increasing its flexibility and crack propagation resistance. Among the effective indicators, TSI is more sensitive to changes in loading rate and test temperature compared to CRI^pre and CRI. This study aims to enhance the understanding of the crack resistance performance and indicator adaptability of DREAM via macro-mechanical experiments and provides guidance for its future applications.

Asphalt overlays have been widely employed in airport runway maintenance in recent years due to their ability to minimize traffic disruption. However, they continue to face the challenge of reflective cracks originating from the expansion joints of the underlying cement concrete runway. To better understand the cracking behavior of asphalt overlays under the combined temperature variations and aircraft loads, this study developed a finite element (FE) model. with the model incorporate two types of landing methods and typical temperature conditions. Simulation results indicate that critical loading positions are located at the edges of original cement concrete slabs, where shear stress is identified as the primary driver of crack evolution, with the peak stress coinciding with the arrival of aircraft load. Furthermore, findings suggest that the use of asphalt overlays significantly reduces the stress intensity in crack-prone areas, particularly under rough landing conditions. Reflective cracks predominantly manifest as type II shear cracks, While aircraft loading and initial crack length exert a relatively limited impact on crack propagation compared to temperature effects, the horizontal location of the initial crack substantially influences both the direction and speed of crack propagation. To mitigate crack propagation, increasing the linear shrinkage coefficient of the overlay material and the thickness of the asphalt overlay are effective strategies for enhancing the cracking resistance of airport runways with asphalt overlays. The methodologies and findings of this study provide valuable insights for engineering practices involving similar structural configurations and materials.

Rubberized asphalt mixture effectively reduces vibrations in railway track due to the elasticity of crumb rubber (CR) and the viscoelasticity of asphalt binder. This study aims to design a rubberized epoxy asphalt mixture using the modified volumetric mix-design method named the multi-point supported skeleton for asphalt mixtures (V-S method). The feasibility and vibration attenuation of the precast epoxy asphalt track was evaluated through a 3D FEM simulation at a 350 km/h speed. By combining the V-S method with the equivalent volume replacement principle between CR and coarse aggregate, four types of rubberized epoxy asphalt mixtures were proposed using the dry method. Indoor test results confirm that these mixtures meet the required specifications. The FEM results demonstrate that the designed epoxy asphalt track meets the design criteria and the components of the EA-4CR track structure demonstrate superior vibration reduction performance among the cases with the same increment in CR content.

NGC 4395 is a dwarf galaxy at a distance of about 4.3 Mpc (scale: ∼0.021 pc mas-1). It hosts an intermediate-mass black hole (IMBH) with a mass between ∼104 and ∼105 solar masses. The early radio observations of NGC 4395 with the very long baseline interferometry (VLBI) network, High Sensitivity Array (HSA), at 1.4 GHz in 2005 showed that its nucleus has a sub-mJy outflow-like feature (E) extending over 15 mas. To probe the possibility of the feature E as a continuous jet with a base physically coupled with the accretion disc, we performed deep VLBI observations with the European VLBI Network (EVN) at 5 GHz, and analysed the archival data obtained with the HSA at 1.4 GHz in 2008, NSF's Karl G. Jansky Very Large Array (VLA) at 12-18 GHz and the Atacama Large Millimetre/submillimetre Array (ALMA) at 237 GHz. The feature E displays more diffuse structure in the HSA image of 2008 and has no compact substructure detected in the EVN image. Together with the optically thin steep spectrum and the extremely large angular offset (about 220 mas) from the accurate optical Gaia position, we explain the feature E as nuclear shocks likely formed by the IMBH's episodic ejection or wide-angle outflow. The VLA and ALMA observations find a sub-mJy pc-scale diffuse feature, possibly tracing a thermal free-free emission region near the IMBH. There is no detection of a jet base at the IMBH position in the VLBI maps. The non-detections give an extremely low luminosity of ≤4.7 × 1033 erg s-1 at 5 GHz and indicate no evidence of a disc-jet coupling on sub-pc scales.

In the time domain, the radio sky in particular along the Galactic plane direction may vary significantly because of various energetic activities associated with stars, stellar, and supermassive black holes. Multi-epoch Very Large Array surveys of the Galactic plane at 5.0 GHz enabled the finding of a catalogue of 39 variable radio sources in the flux density range 1-70 mJy. To probe their radio structures and spectra, we observed 17 sources with the very-long-baseline interferometric (VLBI) imaging technique and collected additional multifrequency data from the literature. We detected all of the sources at 5 GHz with the Westerbork Synthesis Radio Telescope, but only G23.6644-0.0372 with the European VLBI Network (EVN). Together with its decadal variability and multifrequency radio spectrum, we interpret it as an extragalactic peaked-spectrum source with a size of ≲10 pc. The remaining sources were resolved out by the long baselines of the EVN because of either strong scatter broadening at the Galactic latitude < 1° or intrinsically very extended structures on centi-arcsec scales. According to their spectral and structural properties, we find that the sample has a diverse nature. We notice two young H ii regions and spot a radio star and a candidate planetary nebula. The rest of the sources are very likely associated with radio active galactic nuclei (AGNs). Two of them also display arcsec-scale faint jet activity. The sample study indicates that AGNs are common place even among variable radio sources in the Galactic plane.