The Experts below are selected from a list of 38052 Experts worldwide ranked by ideXlab platform
Mihaly Bartok - One of the best experts on this subject based on the ideXlab platform.
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modifier substrate interactions of various types in the orito reaction reversal of the enantioselection in the hydrogenation of ketopantolactone on pt modified by β isocinchonine and o phenylcinchonidine
Catalysis Communications, 2013Co-Authors: Gyorgy Szőllősi, Katalin Balazsik, Mihaly Bartok, Imre Bucsi, Tibor BartokAbstract:Abstract The enantioselective hydrogenation of ketopantolactone (KPL) on Pt–alumina catalyst modified by β-isocinchonine (β-ICN) and O -phenylcinchonidine (PhOCD) in toluene, acetic acid and their mixtures under otherwise identical experimental conditions was studied. Reversal of the enantioselection was obtained dependent on the concentration of acetic acid (ee max = 17% ( S ) on Pt–PhOCD and 50% ( R ) on Pt–β-ICN, respectively). The possible role in enantioselection of adducts forming in the reaction mixture and the stability of PhOCD under the conditions of the hydrogenation was investigated by ESI-MS. The results of the Nonlinear Phenomenon measurements on β-ICN + PhOCD mixtures suggest that the intermediate surface complexes β-ICN–KPL and PhOCD–KPL responsible for the opposite enantioselection include different types of interactions and the enantioselection is directed by the competition between these interactions.
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new data on the orito reaction effect of substrate structure on Nonlinear Phenomenon
Catalysis Letters, 2008Co-Authors: Katalin Balazsik, Szabolcs Cserenyi, Gyorgy Szollősi, Ferenc Fulop, Mihaly BartokAbstract:The Nonlinear Phenomenon (NLP) was studied for the first time in the enantioselective hydrogenation of ethyl pyruvate (EP) and ketopantolactone (KPL) under identical conditions, on Pt catalyst modified by quinine and cinchonine, and for comparison with cinchonidine-cinchonine pair. The data obtained using the three methods allowed recognition of a new observation, namely that the NLP depends not only on the chiral modifier but also on the substrate to be hydrogenated. This observation can presumably be interpreted on the basis of differences in the structure of the substrate-modifier complexes formed and in the adsorption-desorption processes of the complexes, thus the NLP is not solely dependent on the adsorption of cinchona alkaloids, as suggested by earlier experimental data.
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new data of Nonlinear Phenomenon in the heterogeneous enantioselective hydrogenation of activated ketones
Catalysis Letters, 2008Co-Authors: Katalin Balazsik, Gyorgy Szollősi, Mihaly BartokAbstract:Results on Nonlinear Phenomenon (NLP) in the liquid phase hydrogenation of methyl benzoylformate (MBF) and pyruvaldehyde dimethyl acetal (PA) on chiral Pt-cinchona catalyst are reported for the first time (enantiomeric excess 90–95%). The new data support the conclusions of the NLP studies on ethyl pyruvate (EP) and ketopantolactone (KPL). Namely, the order of the adsorption strengths of the parent cinchona alkaloids are: CD > CN > QN ~ QD and the results of the NLP measurements indirectly verify the so-called 1:1 model of enantioselection. The new data, however, call attention to a new, substrate and modifier dependent Phenomenon, which necessitates further experiments for a better understanding of the mechanism of the Orito reaction.
Karl Sigfrid Yngvesson - One of the best experts on this subject based on the ideXlab platform.
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conversion gain and noise of niobium superconducting hot electron mixers
IEEE Transactions on Microwave Theory and Techniques, 1995Co-Authors: Henrik Ekstrom, E Kollberg, Boris S. Karasik, Karl Sigfrid YngvessonAbstract:A study has been done of microwave mixing at 20 GHz using the Nonlinear (power dependent) resistance of thin niobium strips in the resistive state. Our experiments give evidence that electron-heating is the main cause of the Nonlinear Phenomenon. Also a detailed phenomenological theory for the determination of conversion properties is presented. This theory is capable of predicting the frequency-conversion loss rather accurately for arbitrary bias by examining the I-V characteristic, Knowing the electron temperature relaxation time, and using parameters derived from the I-V-characteristic also allows us to predict the -3-dB IF bandwidth. Experimental results are in excellent agreement with the theoretical predictions. The requirements on the mode of operation and on the film parameters for minimizing the conversion loss (and even achieving conversion gain) are discussed in some detail. Our measurements demonstrate an intrinsic conversion loss as low as 1 dB. The maximum IF frequency defined for 3-dB drop in conversion gain, is about 80 MHz. Noise measurements indicate a device output noise temperature of about 50 K and SSB mixer noise temperature below 250 K. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies. >
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conversion gain and noise of niobium superconducting hot electron mixers
IEEE Transactions on Microwave Theory and Techniques, 1995Co-Authors: Henrik Ekstrom, E Kollberg, Boris S. Karasik, Karl Sigfrid YngvessonAbstract:A study has been done of microwave mixing at 20 GHz using the Nonlinear (power dependent) resistance of thin niobium strips in the resistive state. Our experiments give evidence that electron-heating is the main cause of the Nonlinear Phenomenon. Also a detailed phenomenological theory for the determination of conversion properties is presented. This theory is capable of predicting the frequency-conversion loss rather accurately for arbitrary bias by examining the I-V characteristic, Knowing the electron temperature relaxation time, and using parameters derived from the I-V-characteristic also allows us to predict the -3-dB IF bandwidth. Experimental results are in excellent agreement with the theoretical predictions. The requirements on the mode of operation and on the film parameters for minimizing the conversion loss (and even achieving conversion gain) are discussed in some detail. Our measurements demonstrate an intrinsic conversion loss as low as 1 dB. The maximum IF frequency defined for 3-dB drop in conversion gain, is about 80 MHz. Noise measurements indicate a device output noise temperature of about 50 K and SSB mixer noise temperature below 250 K. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies. >
Franz X Kartner - One of the best experts on this subject based on the ideXlab platform.
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supercontinuum generation in silicon bragg grating waveguide
Applied Physics Letters, 2021Co-Authors: Neetesh Singh, Manan Raval, E P Ippen, Michael R Watts, Franz X KartnerAbstract:Supercontinuum generation is an extensively studied and arguably the most important and all-encompassing Nonlinear Phenomenon. Yet, we do not have a good control over all the signals generated in this process. Usually, a large part of an octave spanning spectrum has an orders of magnitude weaker signal than the peak to be useful for any application. In this work, we show strong signal generation within a supercontinuum generated in a complementary metal-oxide-semiconductor compatible silicon Bragg grating waveguide. We show up to 23 dB of signal enhancement over a 10 nm full-width-at-half-maximum bandwidth at the Bragg resonance in the telecom window. Additionally, the grating is made by depositing charge carriers periodically, thus avoiding any dimensional change in the waveguide, and it can allow other functionalities offered by the induced electric field, such as second harmonic generation and free carrier sweeping. We believe this work opens up an avenue for research in Nonlinear integrated photonics and signal enhancement in the supercontinuum by the Bragg effect (whether created through grating formation with dimensional variation in insulators and/or periodic charge carrier doping in semiconductors).
Govind P Agrawal - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear fiber optics its history and recent progress invited
Journal of The Optical Society of America B-optical Physics, 2011Co-Authors: Govind P AgrawalAbstract:This review begins with an historical introduction to the field of Nonlinear fiber optics and then focuses on the propagation of short optical pulses inside optical fibers. The underlying Nonlinear Schrodinger equation is used to discuss the Nonlinear Phenomenon of self-phase modulation that leads to the formation of solitons in the presence of anomalous dispersion. Recent work on supercontinuum generation is reviewed with emphasis on the important Nonlinear processes, such as the fission of higher-order solitons and intrapulse Raman scattering. Applications of fiber-based supercontinuum sources are also discussed in diverse areas ranging from biomedical imaging to frequency metrology. The last part describes applications resulting from Nonlinear phenomena, such as cross-phase modulation, stimulated Raman scattering, and four-wave mixing.
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analytical study of optical bistability in silicon waveguide resonators
Optics Express, 2009Co-Authors: Ivan D Rukhlenko, Malin Premaratne, Govind P AgrawalAbstract:We present a theoretical model that describes accurately the Nonlinear Phenomenon of optical bistability in silicon-waveguide resonators but remains amenable to analytical results. Using this model, we derive a transcendental equation governing the intensity of a continuous wave transmitted through a Fabry-Perot resonator formed using a silicon-on-insulator waveguide. This equation reveals a dual role of free carriers in the formation of optical bistability in silicon. First, it shows that free-carrier absorption results in a saturation of the transmitted intensity. Second, the free-carrier dispersion and the thermo-optic effect may introduce phase shifts far exceeding those resulting from the Kerr effect alone, thus enabling one to achieve optical bistability in ultrashort resonators that are only a few micrometers long. Bistability can occur even when waveguide facets are not coated because natural reflectivity of the silicon-air interface can provide sufficient feedback. We find that it is possible to control the input-output characteristics of silicon-based resonators by changing the free-carrier lifetime using a reverse-biased p-n junction. We show theoretically that such a technique is suitable for realization of electronically assisted optical switching at a fixed input power and it may lead to silicon-based, nanometer-size, optical memories.
Henrik Ekstrom - One of the best experts on this subject based on the ideXlab platform.
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conversion gain and noise of niobium superconducting hot electron mixers
IEEE Transactions on Microwave Theory and Techniques, 1995Co-Authors: Henrik Ekstrom, E Kollberg, Boris S. Karasik, Karl Sigfrid YngvessonAbstract:A study has been done of microwave mixing at 20 GHz using the Nonlinear (power dependent) resistance of thin niobium strips in the resistive state. Our experiments give evidence that electron-heating is the main cause of the Nonlinear Phenomenon. Also a detailed phenomenological theory for the determination of conversion properties is presented. This theory is capable of predicting the frequency-conversion loss rather accurately for arbitrary bias by examining the I-V characteristic, Knowing the electron temperature relaxation time, and using parameters derived from the I-V-characteristic also allows us to predict the -3-dB IF bandwidth. Experimental results are in excellent agreement with the theoretical predictions. The requirements on the mode of operation and on the film parameters for minimizing the conversion loss (and even achieving conversion gain) are discussed in some detail. Our measurements demonstrate an intrinsic conversion loss as low as 1 dB. The maximum IF frequency defined for 3-dB drop in conversion gain, is about 80 MHz. Noise measurements indicate a device output noise temperature of about 50 K and SSB mixer noise temperature below 250 K. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies. >
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conversion gain and noise of niobium superconducting hot electron mixers
IEEE Transactions on Microwave Theory and Techniques, 1995Co-Authors: Henrik Ekstrom, E Kollberg, Boris S. Karasik, Karl Sigfrid YngvessonAbstract:A study has been done of microwave mixing at 20 GHz using the Nonlinear (power dependent) resistance of thin niobium strips in the resistive state. Our experiments give evidence that electron-heating is the main cause of the Nonlinear Phenomenon. Also a detailed phenomenological theory for the determination of conversion properties is presented. This theory is capable of predicting the frequency-conversion loss rather accurately for arbitrary bias by examining the I-V characteristic, Knowing the electron temperature relaxation time, and using parameters derived from the I-V-characteristic also allows us to predict the -3-dB IF bandwidth. Experimental results are in excellent agreement with the theoretical predictions. The requirements on the mode of operation and on the film parameters for minimizing the conversion loss (and even achieving conversion gain) are discussed in some detail. Our measurements demonstrate an intrinsic conversion loss as low as 1 dB. The maximum IF frequency defined for 3-dB drop in conversion gain, is about 80 MHz. Noise measurements indicate a device output noise temperature of about 50 K and SSB mixer noise temperature below 250 K. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies. >
