The Experts below are selected from a list of 24720 Experts worldwide ranked by ideXlab platform
C L Yeh - One of the best experts on this subject based on the ideXlab platform.
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an experimental study on ti5si3 formation by combustion synthesis in self Propagating Mode
Journal of Alloys and Compounds, 2005Co-Authors: C L Yeh, C C HsuAbstract:Abstract The production of titanium silicide, Ti5Si3, from elemental powder compacts was conducted by self-Propagating high-temperature synthesis (SHS) in this study. Effects of sample green density and initial sample temperature on the combustion characteristics, as well as on the composition of final products were studied. The combustion process was preceded by the fast propagation of a self-sustained combustion front, followed by vigorous bulk combustion. The phase transformation was found to continue during the cooling of the burned sample, leading to an afterburning stage featuring the emergence of a luminous glow on the luster-lacking compact. The propagation velocity of combustion front was increased by increasing the sample green density or by preheating the sample prior to ignition. For the samples preheated at 200 °C, a significant increase by about twofold in the flame-front velocity was observed in comparison to those without any preheating. This is due to the fact that the combustion temperature not only is higher than the lowest eutectic temperature of the Ti–Si mixture at 1330 °C, but also exceeds the melting point of Si (1410 °C). The dissolution of solid reactants into the molten liquid and the precipitation of products from the oversaturated solution were adopted to describe the formation of titanium silicides. According to the XRD analysis, the dominant composition in combustion products was identified as the Ti5Si3 phase. The presence of an intermediate phase of Ti5Si4 in the final products was the consequence of the insufficient reaction time caused by the rapid propagation of combustion wave and the fast cooling rate on the burned sample. Based upon the measured data of this study, the activation energy with a value of 205.2 kJ/mol was deduced for the synthesis of Ti5Si3 by SHS.
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preparation of coal intermetallic compound by combustion synthesis in self Propagating Mode
Journal of Alloys and Compounds, 2005Co-Authors: C L Yeh, C C YehAbstract:The production of cobalt aluminide (CoAl) from elemental powder compacts was conducted by self-Propagating high-temperature synthesis (SHS) in this study. Effects of the initial sample density, particle size of the reactants, and initial sample temperature on the combustion characteristics, as well as on the composition and morphology of final products were studied. Unlike most of the intermetallic reactions, the combustion on the CoAl powder compact is self-sustained upon initiation even without any preheating prior to ignition, implying that the reactions are highly exothermic. The combustion process was preceded by the fast propagation of the flame-front, followed by vigorous bulk combustion. The flame-front propagation velocity and combustion temperature were found to increase with increasing sample green density. The use of fine particles of Al (10 μm) also increased the flame-front velocity. In addition, the combustion products synthesized from the samples using fine Al particles were slightly shrunk or retained the original shape. However, when the coarse particles of Al (350 mesh) were used the sample exhibited a volume expansion after combustion, resulting in an increase in the sample porosity. According to the XRD analysis, combustion products obtained in this study were all made up of a single-phase composition of CoAl without the presence of any secondary phases or unreacted constituent elements. Based upon the measured data of this study, the activation energy with a value of 121.7 kJ/mol was deduced for the synthesis of CoAl by SHS.
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combustion synthesis of ni3al intermetallic compound in self Propagating Mode
Journal of Alloys and Compounds, 2004Co-Authors: C L Yeh, W Y SungAbstract:Abstract The production of Ni 3 Al intermetallic compound from elemental powder compacts was conducted by self-Propagating high-temperature synthesis (SHS) in this study. Effects of initial sample density, preheating temperature, and particle size of the reactants on the combustion characteristics, as well as on the composition and morphology of final products were studied. Experimental observation indicated that the combustion process was preceded by the propagation of the flame-front, followed by prolonged bulk combustion. It was found that the flame-front propagation velocity was significantly higher for the sample using fine particles of Ni (3–7 μm) when compared to that with coarse Ni particles (−325 mesh). The use of small particles of Ni (3–7 μm) and Al (10 μm) resulted in the formation of dense single-phase products made up of Ni 3 Al from preheated sample compacts with a green density equal to 65% theoretical maximum density (TMD). However, highly porous products composed of Ni 3 Al, NiAl, and unreacted Ni were produced from 60% TMD samples using large particles of Ni (−325 mesh) at a low preheating temperature of 200 °C. Even with the use of coarse Ni powders, a complete reaction yielding the single-phase product Ni 3 Al was achieved by increasing the preheating temperature and the sample green density. The increase of preheating temperature and initial sample density also led to an increase in the product density up to above 90% relative to the density of the Ni 3 Al compound. Based upon the measured data obtained in this study, the activation energy of about 92–98 kJ/mol was deduced for the combustion synthesis of Ni 3 Al.
G Badenes - One of the best experts on this subject based on the ideXlab platform.
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temperature insensitive photonic crystal fiber interferometer for absolute strain sensing
Applied Physics Letters, 2007Co-Authors: Joel Villatoro, V Finazzi, Vladimir P Minkovich, Valerio Pruneri, G BadenesAbstract:The authors report a highly sensitive (∼2.8pm∕μe) wavelength-encoded strain sensor made from a piece of photonic crystal fiber (PCF) spliced to standard fibers. The authors intentionally collapse the PCF air holes over a short region to enlarge the Propagating Mode of the lead-in fiber which allows the coupling of only two Modes in the PCF. The transmission spectrum of the interferometer is stable and sinusoidal over a broad wavelength range. The sensor exhibits linear response to strain over a large measurement range, its temperature sensitivity is very low, and for its interrogation a battery-operated light emitting diode and a miniature spectrometer are sufficient.
Morteza S Mohseni - One of the best experts on this subject based on the ideXlab platform.
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current induced multi Mode Propagating spin waves in a spin transfer torque nano contact with strong perpendicular magnetic anisotropy
Journal of Magnetism and Magnetic Materials, 2018Co-Authors: M Hamdi, H F Yazdi, T Bracher, Morteza S MohseniAbstract:Abstract Current induced spin wave excitations in spin transfer torque nano-contacts are known as a promising way to generate exchange-dominated spin waves at the nano-scale. It has been shown that when these systems are magnetized in the film plane, broken spatial symmetry of the field around the nano-contact induced by the Oersted field opens the possibility for spin wave Mode co-existence including a non-linear self-localized spin-wave bullet and a Propagating Mode. By means of micromagnetic simulations, here we show that in systems with strong perpendicular magnetic anisotropy (PMA) in the free layer, two Propagating spin wave Modes with different frequency and spatial distribution can be excited simultaneously. Our results indicate that in-plane magnetized spin transfer nano-contacts in PMA materials do not host a solitonic self-localized spin-wave bullet, which is different from previous studies for systems with in plane magnetic anisotropy. This feature renders them interesting for nano-scale magnonic waveguides and crystals since magnon transport can be configured by tuning the applied current.
Valerio Scarani - One of the best experts on this subject based on the ideXlab platform.
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efficient excitation of a two level atom by a single photon in a Propagating Mode
Physical Review A, 2011Co-Authors: Yimin Wang, Jiři Minař, Lana Sheridan, Valerio ScaraniAbstract:State mapping between atoms and photons, and photon-photon interactions play an important role in scalable quantum information processing. We consider the interaction of a two-level atom with a quantized Propagating pulse in free space and study the probability P{sub e}(t) of finding the atom in the excited state at any time t. This probability is expected to depend on (i) the quantum state of the pulse field and (ii) the overlap between the pulse and the dipole pattern of the atomic spontaneous emission. We show that the second effect is captured by a single parameter {Lambda}(set-membership sign)[0,8{pi}/3], obtained by weighting the dipole pattern with the numerical aperture. Then, P{sub e}(t) can be obtained by solving time-dependent Heisenberg-Langevin equations. We provide detailed solutions for both single-photon Fock state and coherent states and for various temporal shapes of the pulses.
M Sumetsky - One of the best experts on this subject based on the ideXlab platform.
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how thin can a microfiber be and still guide light
Optics Letters, 2006Co-Authors: M SumetskyAbstract:For the adiabatically deformed optical fiber the interMode transmission amplitudes and loss vanish exponentially with the characteristic length of the fiber's nonuniformity. For this reason smoothly deformed optical fiber tapers can have very small losses. However, losses dramatically increase with a thinning of the microfiber down to a diameter much smaller than the radiation wavelength. The theory of nonadiabatic interMode transitions is briefly discussed and, by using this theory, the problem of the smallest diameter of a microfiber that can transmit evanescent radiation is studied. It is shown that even for an extremely high uniformity of microfiber the ability of light transmission does not leave much space for microfiber thinning: the Propagating Mode vanishes at a threshold value of the microfiber's diameter, that is smaller than the radiation wavelength by only an order of magnitude.
