排序方式: 共有68条查询结果,搜索用时 15 毫秒
1.
Ghandi K Addison-Jones B Brodovitch JC McCollum BM McKenzie I Percival PW 《Journal of the American Chemical Society》2003,125(32):9594-9595
Muoniated free radicals have been detected in muon-irradiated aqueous solutions of acetone at high temperatures and pressures. At temperatures below 250 degrees C, the radical product is consistent with muonium addition to the keto form of acetone. However, at higher temperatures, a different radical was detected, which is attributed to muonium addition to the enol form. Muon hyperfine coupling constants have been determined for both radicals over a wide range of temperatures, significantly extending the range of conditions under which these radicals and the keto-enol equilibrium have been studied. 相似文献
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Mahyar Nasabi Khashayar Khoshmanesh Francisco J. Tovar‐Lopez Kourosh Kalantar‐zadeh Arnan Mitchell 《Electrophoresis》2013,34(22-23):3150-3154
This paper demonstrates the utilization of 3D semispherical shaped microelectrodes for dielectrophoretic manipulation of yeast cells. The semispherical microelectrodes are capable of producing strong electric field gradients, and in turn dielectrophoretic forces across a large area of channel cross‐section. The semispherical shape of microelectrodes avoids the formation of undesired sharp electric fields along the structure and also minimizes the disturbance of the streamlines of nearby passing fluid. The advantage of semispherical microelectrodes over the planar microelectrodes is demonstrated in a series of numerical simulations and proof‐of‐concept experiments aimed toward immobilization of viable yeast cells. 相似文献
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The spin Hamiltonian parameters of Mn2+ have been measured above and below the transition point (180°C) of the lead phosphate. They show that Mn2+ substitutes a PbI ion. Between 175 and 180°C the principal axis OX of the fine tensor is parallel to the wave vector of the soft mode which condensates at the transition point. An exaltation of the linewidth is observed. The linewidth remains constant within 5°C of Tc; in this temperature range, the “static regime” is achieved, and the correlation time of the fluctuations is less than 10?8 sec. 相似文献
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Random dynamics of the Morris-Lecar neural model 总被引:1,自引:0,他引:1
Determining the response characteristics of neurons to fluctuating noise-like inputs similar to realistic stimuli is essential for understanding neuronal coding. This study addresses this issue by providing a random dynamical system analysis of the Morris-Lecar neural model driven by a white Gaussian noise current. Depending on parameter selections, the deterministic Morris-Lecar model can be considered as a canonical prototype for widely encountered classes of neuronal membranes, referred to as class I and class II membranes. In both the transitions from excitable to oscillating regimes are associated with different bifurcation scenarios. This work examines how random perturbations affect these two bifurcation scenarios. It is first numerically shown that the Morris-Lecar model driven by white Gaussian noise current tends to have a unique stationary distribution in the phase space. Numerical evaluations also reveal quantitative and qualitative changes in this distribution in the vicinity of the bifurcations of the deterministic system. However, these changes notwithstanding, our numerical simulations show that the Lyapunov exponents of the system remain negative in these parameter regions, indicating that no dynamical stochastic bifurcations take place. Moreover, our numerical simulations confirm that, regardless of the asymptotic dynamics of the deterministic system, the random Morris-Lecar model stabilizes at a unique stationary stochastic process. In terms of random dynamical system theory, our analysis shows that additive noise destroys the above-mentioned bifurcation sequences that characterize class I and class II regimes in the Morris-Lecar model. The interpretation of this result in terms of neuronal coding is that, despite the differences in the deterministic dynamics of class I and class II membranes, their responses to noise-like stimuli present a reliable feature. 相似文献
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J. S. Yu S. Slivken A. Evans M. Razeghi 《Applied Physics A: Materials Science & Processing》2008,93(2):405-408
High-temperature, high-power, and continuous-wave (CW) operation of quantum-cascade lasers with 35 active/injector stages
at λ∼8.85 μm above room temperature is achieved without using a buried heterostructure. At this long wavelength, the use of a
wider ridge waveguide in an epilayer-down bonding scheme leads to a superior performance of the laser. For a high-reflectivity-coated
21 μm×3 mm laser, the output power of 237 mW and the threshold current density of 1.44 kA/cm2 at 298 K under CW mode are obtained with a maximum wall-plug efficiency of 1.7%. Further improvements were observed by using
a 4-mm-long cavity. The device exhibits 294 mW of output power at 298 K and it operates at a high temperature, even up to
358 K (85°C). The full widths at half-maximum of the laser beam in CW operation for the parallel and the perpendicular far-field
patterns are 25°and 63°, respectively. 相似文献
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Mehdi Janbazi Yavar T. Azar Farhood Ziaie Khashayar Ghandi Chérif F. Matta Muhammad Shadman Lakmehsari 《International journal of quantum chemistry》2020,120(12):e26211
Alanine is used as a transfer standard dosimeter for gamma ray and electron beam calibration. An important factor affecting its dosimetric response is humidity which can lead to errors in absorbed dose calculations. Ab initio molecular dynamics calculations were performed to determine the environmental effects on the electron paramagnetic resonance (EPR) parameters of L-α-alanine radicals in acidic and alkaline solutions. A new result, not dissimilar to the closed-shell amino acid molecule alanine, is that the non-zwitterionic form of the alanine radical is the stable form in the gas phase while the zwitterionic neutral alanine radical is not a stable structure in the gas phase. Geometric and EPR parameters of radicals in both gas and solution phases are found to be dependent on hydrogen bonding of water molecules with the polar groups and on dynamic solvation. Calculations on the optimized free radicals in the gas phase revealed that for the neutral radical, hydrogen bonding to water molecules drives a decrease in the magnitudes of g-tensor components g xx and g yy without affecting neither g zz component nor the hyperfine coupling constants (HFCCs). The transfer from the gas to solution phase of the alanine radical anion is accompanied with an increase in the spin density on the carboxylic group's oxygen atoms. However, for the neutral radical, this transfer from gas to solution phase is accompanied with the decrease in the spin density on oxygen atoms. Calculated isotropic HFCCs and g-tensor of all radicals are in good agreement with experiment in both acidic and alkaline solutions. 相似文献
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Chrimes AF Kayani AA Khoshmanesh K Stoddart PR Mulvaney P Mitchell A Kalantar-Zadeh K 《Lab on a chip》2011,11(5):921-928
A microfluidic dielectrophoresis platform consisting of curved microelectrodes was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a quartz substrate, which has insignificant Raman response, and integrated with a microfluidic channel that was imprinted in poly-dimethylsiloxane (PDMS). We will show that this novel integrated system can be efficiently used for the determination of suspended particle types and the direct mapping of their spatial concentrations. We will also illustrate the system's unique advantages over conventional optical systems. Nanoparticles of tungsten trioxide (WO(3)) and polystyrene were used in the investigations, as they are Raman active and can be homogeneously suspended in water. 相似文献
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R. Rahbi D. Mathiot J. Chevallier C. Grattepain M. Razeghi 《Physica B: Condensed Matter》1991,170(1-4):135-140
Experimental hydrogen diffusion profiles are reported in undoped and zinc doped GaAs. Hydrogen was introduced by exposure to a hydrogen plasma. The hydrogen profiles are fit using a diffusion model which assumes that hydrogen has a donor level in the band gap and diffuses as H+ and H0 in the material. It is also assumed that H+ can be trapped by ionized acceptors to form neutral complexes. Good simulations are obtained in p-type GaAs for various doping levels. We find that neutral hydrogen is present with high concentration in the diffusion process and the hydrogen molecule formation is absent. The hydrogen donor level, the diffusivities of H+ and H0, the associated activation energies and the dissociation energy of the acceptor-hydrogen pairs are determined. 相似文献