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Masulli, Marco (author), Liu, Z. (author), Guo, Feng Zhi (author), Li, Xue (author), Sudhölter, Ernst J. R. (author), Kumar, N. (author)Chemical loss such as surfactants and alkalis by adsorption to reservoir rock surface is an important issue in enhanced oil recovery (EOR). Here, we investigated the adsorption behaviors of anionic surfactants and alkalis on silica for the first time as a function of temperature using quartz crystal microbalance with dissipation (QCM-D). The...journal article 2022
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Nama Ashok kumar, N. (author)Maharashtra, the second largest state in India in terms of population and area, is a fast-developing economy and meeting its electricity demand is crucial for its economic growth. Currently, power production is causing severe environmental and security issues mainly because of the reliance on coal plants in the state. In order to meet SDG 7 ...master thesis 2020
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Liu, Z. (author), Hedayati, Pegah (author), Sudhölter, Ernst J. R. (author), Haaring, Robert (author), Shaik, A.R. (author), Kumar, N. (author)Adsorption behavior of surfactants to rock surfaces is an important issue in oil recovery, especially in the process of surfactant flooding. The surfactant loss through adsorption to rock surfaces makes such process economically less feasible. Here, we investigated the adsorption behavior of anionic surfactants (alcohol alkoxy sulfate, AAS)...journal article 2020
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Liu, Z. (author), Ghatkesar, M.K. (author), Sudhölter, Ernst J. R. (author), Singh, Binder (author), Kumar, N. (author)Surfactants have the ability to mobilize residual oil trapped in pore spaces of matrix rocks by lowering the oil-water interfacial tension, resulting in a higher oil recovery. However, the loss of surfactants by adsorption onto the rock surface has become a major concern that reduces the efficiency of the surfactant flooding process. In this...journal article 2019
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Haaring, Robert (author), Kumar, N. (author), Bosma, D. (author), Poltorak, L. (author), Sudhölter, Ernst J. R. (author)The ability to study the adsorption behavior of surfactant species is of interest in the field of enhanced oil recovery (EOR), especially pertaining to alkaline surfactant flooding. In this work, a calcite model mineral surface was obtained by electrochemically assisted deposition. This was achieved via the nitrate and/or oxygen...journal article 2019
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Kumar, N. (author)A comprehensive understanding of the stability of shear flows is a fundamental problem in fluid mechanics and it has been a subject of both theoretical and practical interest in engineering research. A key aspect of these dynamic flows is the behaviour exhibited by the instabilities as it evolves from initial small perturbations of an...master thesis 2016
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- Petrik, P. (author), Fodor, B. (author), Agocs, E. (author), Kozma, P. (author), Nador, J. (author), Kumar, N. (author), Endres, J. (author), Juhasz, G. (author), Major, C. (author), Pereira, S.F. (author), Lohner, T. (author), Urbach, H.P. (author), Bodermann, B. (author), Fried, M. (author) conference paper 2015
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Kumar, N. (author), Abdi, F.F. (author), Trzesniewski, B. (author), Smith, W.A. (author), Planken, P.C.M. (author), Adam, A.J.L. (author)We demonstrate emission of terahertz pulses from a BiVO4/Au thin film interface, illuminated with femtosecond laser pulses. Based on the experimental observations, we propose that the most likely cause of the THz emission is the Photo-Dember effect caused by the standing wave intensity distribution formed at the BiVO4/Au interfaces.journal article 2015
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Kumar, N. (author)Terahertz radiation is electromagnetic waves with frequencies from 0.1-10 THz. THz radiation can pass through cardboard, paper, plastics, ceramics and many other materials. Hence, it can be used for non-destructive imaging. Another important application of THz radiation is spectroscopy. Many organic molecules absorb light at THz frequencies and...doctoral thesis 2015
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Kumar, N. (author)The electronics which makes our lives easier like mobiles, computers, digital cameras contain chips with very small semiconductor components like transistors. When transistors can be made even smaller, the chip can accommodate a larger number of components, which gives more processing capacity, resulting in a faster device with an increased...doctoral thesis 2014
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Konijnenberg, A.P. (author), Wei, L. (author), Kumar, N. (author), Couto Correa Pinto Filho, L. (author), Cisotto, L. (author), Pereira, S.F. (author), Urbach, H.P. (author)In several optical systems, a specific Point Spread Function (PSF) needs to be generated. This can be achieved by shaping the complex field at the pupil. The Extended Nijboer-Zernike (ENZ) theory relates complex Zernike modes on the pupil directly to functions in the focal region. In this paper, we introduce a method to engineer a PSF using the...journal article 2014
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Ramakrishnan, G. (author), Ramanandan, G.K.P. (author), Adam, A.J.L. (author), Xu, M. (author), Kumar, N. (author), Hendrikx, R.W.A. (author), Planken, P.C.M. (author)We report on the surprisingly strong, broadband emission of coherent terahertz pulses from ultrathin layers of semiconductors such as amorphous silicon, germanium and polycrystalline cuprous oxide deposited on gold, upon illumination with femtosecond laser pulses. The strength of the emission is surprising because the materials are considered to...journal article 2013
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El Gawhary, O. (author), Wiegmann, A. (author), Kumar, N. (author), Pereira, S.F. (author), Urbach, H.P. (author)Through-focus phase retrieval methods aim to retrieve the phase of an optical field from its intensity distribution measured at different planes in the focal region. By using the concept of spatial correlation for propagating fields, for both the complex amplitude and the intensity of a field, we can infer which planes are suitable to retrieve...journal article 2013
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- Roy, S. (author), Kumar, N. (author), Pereira, S.F. (author), Urbach, Paul (author) journal article 2013
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Pereira, S.F. (author), Wiegman, A. (author), Kumar, N. (author), Da Costa Assafrao, A. (author), Polo, A. (author), Wei, L. (author), Van Haver, S. (author)Measurement techniques to determine the aberration of an optical system, by obtaining through-focus intensity images that are produced when the object is a point source at infinity, are shown. The analysis of the aberrations is made using the extended version of the Nijboer-Zernike diffraction theory. This theory provides a semi analytical...conference paper 2012
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Kajikawa, K. (author), Nagai, Y. (author), Uchiho, Y. (author), Ramakrishnan, G. (author), Kumar, N. (author), Ramanandan, G.K.P. (author), Planken, P.C.M. (author)Electromagnetic wave emission based on optical rectification at terahertz (THz) wavelengths was observed from surface-immobilized gold nanospheres (SIGNs) above a gold surface. Although the excitation wavelength is off-resonant with the localized surface plasmons, the THz emission field was observed to be approximately 4.8 times greater than...journal article 2012
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Kumar, N. (author), Strikwerda, A.C. (author), Fan, K. (author), Zhang, X. (author), Averitt, R.D. (author), Planken, P.C.M. (author), Adam, A.J.L. (author)We report on direct measurements of the magnetic near-field of metamaterial split ring resonators at terahertz frequencies using a magnetic field sensitive material. Specifically, planar split ring resonators are fabricated on a single magneto-optically active terbium gallium garnet crystal. Normally incident terahertz radiation couples to the...journal article 2012
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Ramakrishnan, G. (author), Kumar, N. (author), Planken, P.C.M. (author), Tanaka, D. (author), Kajikawa, K. (author)Emission of terahertz radiation is observed when surface plasmons are excited on a thin film of gold, in the Kretschmann geometry. When a hemicyanine-terminated alkanethiol self-assembled monolayer of thickness 1.2 nm is deposited on the gold film, stronger terahertz emission is observed. Our experimental results confirm that enhanced terahertz...journal article 2012
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El Gawhary, O. (author), Kumar, N. (author), Pereira, S.F. (author), Coene, W.M.J. (author), Urbach, H.P. (author)Scatterometry is a well established technique currently utilized in research, as well as in industrial applications, to retrieve the properties of a given scatterer (the target) by looking at how the light coming from a certain source is diffracted in the far field. Currently the light source is often a discharge lamp that, after wavelength...journal article 2011