Evidence for the absence of gluon orbital angular momentum in the nucleon

The Sivers mechanism for the single-spin asymmetry in unpolarized lepton scattering from a transversely polarized nucleon is driven by the orbital angular momentum carried by its quark and gluon constituents, combined with QCD final-state interactions. Both quark and gluon mechanisms can generate such a single-spin asymmetry, though only the quark mechanism can explain the small single-spin asymmetry measured by the COMPASS Collaboration on the deuteron, suggesting the gluon mechanism is small relative to the quark mechanism. We detail empirical studies through which the gluon and quark orbital angular momentum contributions, quark-flavor by quark-flavor, can be elucidated.     

Nonresonance mechanisms of biological effects of coherent and incoherent light

Two mechanisms of the nonresonance action of light on biological systems are considered. The first of them is caused by gradient effects arising upon interaction of a biological system with spatially inhomogeneous radiation. The second mechanism is determined by light-induced dipole-dipole interactions between biological particles. The first mechanism is characteristic of coherent radiation. A speckle structure arising upon interaction of coherent light with a biological system gives rise to gradient forces, which depend on the intensity of the incident light and the properties of an object. It is shown that the action of the gradient forces on microparticles causes a selective increase in the kinetic energy of the particles. Due to random pulsations of speckles in living tissue, this effect is equivalent to an increase in the “partial” temperature of the particles, which depends on their size and properties. The second mechanism manifests itself both upon coherent and upon incoherent irradiation of a biological object. This mechanism is determined by interactions between oscillating dipole moments of neighboring particles (cells, organelles, biomolecules) induced by incident radiation. The second mechanism is shown to be observed for linearly polarized radiation only. For each mechanism, the forces acting on biological particles are calculated.     

A comparison of the dominant Auger transitions in p-type (Hg,Cd)Te

We predict that the Auger hole-hole collision process involving a transition from the light hole band to the heavy hole band is an important recombination mechanism in non-degenerate p-type (Hg,Cd)Te. This is based on a comparison of the calculated lifetime for this mechanism with that due to the electron-electron collision mechanism discussed by Beattie and Landsberg which involves only the heavy hole valence band. We have estimated the ratio of the intrinsic lifetimes of these two mechanisms by approximating the integrals appearing in the lifetime expressions. We have determined the range of composition, temperature and doping density over which the Auger lifetime in p-type (Hg,Cd)Te is controlled by the light hole mechanism.     

表面低配位原子对声子的散射机制

由于纳米结构具有极高的表体比,声子-表面散射机制对声子的热输运性质起到关键作用.提出了表面低配位原子对声子的散射机制,并且结合量子微扰理论与键序理论推导出该机制的散射率.由于散射率正比于材料的表体比,这种散射机制对声子输运的重要性随着纳米结构尺寸的减小而增大.散射率正比于声子频率的4次方,所以这种散射机制对高频声子的作用远远强于对低频声子的作用.基于声子玻尔兹曼输运方程,计算了硅纳米薄膜和硅纳米线的热导率,发现本文模型比传统的声子-边界散射模型更接近实验值.此发现不仅有助于理解声子-表面散射的物理机制,也有助于应用声子表面工程调控纳米结构的热输运性质.     

Nonlinear interactions that could explain distortion product interference response areas

Suppression and/or enhancement of third- and fifth-order distortion products by a third tone that can have a frequency more than an octave above and a level more than 40 dB below the primary tones have recently been measured by Martin et al. [Hear. Res. 136, 105-123 (1999)]. Contours of iso-suppression and iso-enhancement that are plotted as a function of third-tone frequency and level are called interference response areas. After ruling out order aliasing, two possible mechanisms for this effect have been developed, a harmonic mechanism and a catalyst mechanism. The harmonic mechanism produces distortion products by mixing a harmonic of one of the primary tones with the other primary tone. The catalyst mechanism produces distortion products by mixing one or more intermediate distortion products that are produced by the third tone with one or more of the input tones. The harmonic mechanism does not need a third tone and the catalyst mechanism does. Because the basilar membrane frequency response is predicted to affect each of these mechanisms differently, it is concluded that the catalyst mechanism will be dominant in the high-frequency regions of the cochlea and the harmonic mechanism will have significant strength in the low-frequency regions of the cochlea. The mechanisms are dependent on the existence of both even- and odd-order distortion, and significant even- and odd-order distortion have been measured in the experimental animals. Furthermore, the nonlinear part of the cochlear mechanical response must be well into saturation when input tones are 50 or more dB SPL.     

A possible quark mechanism for the saturation of nuclear matter

A nuclear matter saturation mechanism based on the quark structure of the nucleon is proposed. Nuclear matter is described by nucleons and mesons but the meson field modifies the internal quark motion and this induces a saturation mechanism. Its possible relevance for nuclear physics is studied in a schematic model where it is the only active mechanism. Though caricatural, this model provides a rather satisfactory interpretation of the nuclear matter properties.     

Brane world generated dynamically from string type IIB matrices

We have recently proposed a dynamical mechanism that may realize a flat four-dimensional space-time as a brane in type IIB superstring theory. A crucial role is played by the phase of the chiral fermion integral associated with the IKKT (Ishibashi-Kawai-Kitazawa-Tsuchiya) matrix theory, which is conjectured to be a nonperturbative definition of type IIB superstring theory. We demonstrate our mechanism by studying a simplified model, in which we find that a lower-dimensional brane indeed appears dynamically. We also comment on some implications of our mechanism on model building of the brane world.     

Diamagnetic and Paramagnetic Effects in Free-Electron Lasers

The effect of high-current relativistic electron beams (REB's) on the undulator field amplitude in free-electron lasers (FEL's) is investigated. Two mechanisms of excitation of periodic magnetostatic self-fields by REB are considered: 1) a static mechanism that is realized at stationary motion of REB in the undulator field; and 2) a dynamic mechanism that is realized at signal wave amplification. The static mechanism in the absence of an axial magnetic field leads to a decrease of the total undulator field amplitude (a diamagnetic effect). The dynamic mechanism for low-density beams leads to an increase of the total undulator field amplitude (a paramagnetic effect), with a subsequent increase of electron efficiency. For high-density beams, the effect of the phase shift of the total undulator field is most essential, due to which the growth of the signal wave amplitude is limited by nonlinear mismatch of synchronism.     

Segmented band mechanism for itinerant ferromagnetism

We introduce a novel mechanism for itinerant ferromagnetism, which is based on a simple two-band model, and, by using numerical and analytical methods, we show that the periodic Anderson model contains this mechanism. We propose that the mechanism, which does not assume an intra-atomic Hund's coupling, is present in both the iron group and some f electron compounds.     

Mechanism of oil production stimulation by low-intensity seismic fields

Experimental studies of the energy balance of oil production stimulation by a low-intensity seismic field are carried out. It is shown that the changes in the properties of a productive oil pool occur at the expense of internal energy activated by the external action. A multistage mechanism of the seismic action is proposed. The mechanism is based on the effect of weak vibrations on the plastic deformation of the productive oil pool disturbed from the thermodynamic equilibrium state by the exploitation process. The proposed mechanism represents the set of the observed phenomena as the manifestation of a system of interrelated physical processes of different nature.     

Microscopic origin of magnetoelectric coupling in noncollinear multiferroics

An universal microscopic mechanism to understand the interplay between the electric and magnetic degrees of freedom in noncollinear multiferroics is developed. In a system with a strong spin-orbit coupling, we show that there is a pure electric mechanism that the ferroelectricity is generated by noncollinear magnetism through an electric current cancellation process, which saves the pure electric energy. This mechanism provides a simple estimation and sets a physical limitation of the value of ferroelectricity in noncollinear multiferroic materials.     

Stabilizing transient nanopatterns in heterogeneous catalysis: A comprehensive explanation of the phenomenon

A pattern-formation mechanism driven by attractive forces—previously studied in the context of lateral interactions between adsorbates—is reassessed through a simplified model. In its original version, such a mechanism needed an additional chemical reaction to stabilize the pattern. Recently, that goal has been achieved by means of a particular multiplicative noise. However, many details of the mechanism have remained obscure. In order to clarify them, we resorted to a simplified model that reproduces qualitatively the results of the studies carried out on the complete model. Our analysis reveals that such a mechanism may largely transcend the context in which it was found.     

Numerical prediction of oblique detonation wave structures using detailed and reduced reaction mechanisms

Modelling of the structure and the limiting flow turning angles of an oblique detonation wave, established by a two-dimensional wedge, requires the implementation of detailed chemical kinetic models involving a large number of chemical species. In this paper, a method of reducing the computational effort involved in simulating such high-speed reacting flows by implementing a systematically reduced reaction mechanism is presented. For a hydrogen - air mixture, starting with an elementary mechanism having eight species in 12 reactions, three alternate four-step reduced reaction mechanisms are developed by introducing the steady-state approximation for the reaction intermediates HO2, O and OH, respectively. Additional reduction of the computational effort is achieved by introducing simplifications to the thermochemical data evaluations. The influence of the numerical grid used in predicting the induction process behind the shock is also investigated. Comparisons of the induction zone predicted by two-dimensional oblique detonation wave calculations with that of a static reactor model (with initial conditions of the gas mixture specified by those behind the nonreactive oblique shock wave) are also presented. The reasonably good agreement between the three four-step reduced mechanism predictions and the starting mechanism predictions indicates that further reduction to a two-step mechanism is feasible for the physical flow time scales (corresponding to inflow Mach numbers of 8 - 10) considered here, and needs to be pursued in the future.     

柔性铰链微位移机构在可调谐F-P滤波器中的应用研究

分析了由于反射镜倾斜导致的可调谐F-P(Fabry-Perot)滤波器失谐。设计了一种柔性铰链式微位移机构,由压电陶瓷驱动,采用平行四连杆机构进行传动导向。采用该机构驱动F-P腔镜扫描克服了直接使用压电陶瓷带来的腔镜倾斜问题。该机构已应用于可调谐F-P滤波器中,输出信号多周期峰值幅度均匀,重复性好。     

Walking the path from B4- to B1-type structures in GaN

Molecular dynamics simulations are performed on the wurtzite-type structure (B4) to the rocksalt-type structure (B1) pressure-induced phase transition in GaN. From this, a nucleation and growth mechanism through a tetragonal metastable configuration is found. An intermediate of h-MgO type structure suggested from static calculations is ruled out. However, the pathway through the tetragonal intermediate may be altered by defect incorporation. While the overall transformation mechanism is preserved for both vacancies and Ga substitution by indium, already a 5% aluminum substitution establishes a transition route which avoids the tetragonal structure. Changes in the transformation mechanism and the resulting stabilization of the previously metastable high-pressure modification is elaborated by tracing the interplay of phase nucleation and growth and defect incorporation.     

Radiation-thermal mechanism of initiation of PETN in the region of absorption of a nanosecond-duration electron beam

A radiation-thermal mechanism of initiation of a PETN sample by a nanosecond-duration electron beam is examined. It is assumed that the energy of the electron beam is spent not only on heating the sample, but also on generating active species. The initiation of PETN was simulated using three-step kinetic mechanism. Calculations have shown that taking into account the formation of active species in the mechanism of PETN initiation significantly lowers the initiation energy threshold.     

The effect of deformation and quenching temperature on the mechanism of decomposition in steel EI702

It is shown that the mechanism of decomposition in steel EI702 is determined by the quenching temperature and the degree of prior deformation. On aging after quenching from low temperatures or after heavy deformation, the principal mechanism of decomposition, in which the '-phase is formed, is discontinuous precipitation. However, on aging after quenching from high temperatures, the principal mechanism is continuous decomposition. It is found that discontinuous decomposition in steel E1702 is a very desirable process, since by accelerating aging it greatly increases the strength characteristics. The nature of the effect of the quenching temperature on the mechanism of decomposition in steel E1702 is discussed.     

Scaling behavior of grain-rotation-induced grain growth

Recent investigations of grain growth in nanocrystalline materials have revealed a new growth mechanism: grain-rotation-induced grain coalescence. Based on a simple model employing a stochastic theory and using computer simulations, here we investigate the coarsening of a polycrystalline microstructure due solely to the grain-rotation coalescence mechanism. Our study demonstrates that this mechanism exhibits power-law growth with a universal scaling exponent. The value of this universal growth exponent is shown to depend on the assumed mechanism by which the grain rotations are accommodated.