Search results for "EXPRESSIONS"
showing 10 items of 74 documents
Intraband and interband spin-orbit torques in noncentrosymmetric ferromagnets
2015
Intraband and interband contributions to the current-driven spin-orbit torque in magnetic materials lacking inversion symmetry are theoretically studied using Kubo formula. In addition to the current-driven field-like torque ${\bf T}_{\rm FL}= \tau_{\rm FL}{\bf m}\times{\bf u}_{\rm so}$ (${\bf u}_{\rm so}$ being a unit vector determined by the symmetry of the spin-orbit coupling), we explore the intrinsic contribution arising from impurity-independent interband transitions and producing an anti-damping-like torque of the form ${\bf T}_{\rm DL}= \tau_{\rm DL}{\bf m}\times({\bf u}_{\rm so}\times{\bf m})$. Analytical expressions are obtained in the model case of a magnetic Rashba two-dimension…
Frenkel-Kontorova model with anharmonic interactions
1986
It is shown that consideration of more realistic interatomic potentials (with limited tensile strength) within the framework of the Frenkel-Kontorova model may lead to a breakdown of the soliton picture in systems with competing periodicities. Closed analytical expressions for the form of a single soliton in an anharmonic chain reveal discontinuities which indicate a disintegration of the entire system beyond some critical values of the misfit, and/or of the height of the periodic substrate potential. The length of anharmonic solitons depends essentially on both the sign and the magnitude of the misfit. The influence of misfit on the pinning-unpinning transition is also investigated.
Approximate triangle amplitude for three-body charge exchange processes.
1996
The single-rescattering contribution to the amplitude pertaining to three-body charge exchange reactions (triangle amplitude) contains the off-shell Coulomb {ital T}-matrix {ital T}{sup {ital C}} describing the intermediate-state Coulomb scattering of charged subsystems. For ease of computation, the latter is usually replaced by the potential {ital V}{sup {ital C}} which, however, is unsatisfactory in many cases. An alternative approximation, obtained by {open_quote}{open_quote}renormalizing{close_quote}{close_quote} the {open_quote}{open_quote}triangle{close_quote}{close_quote} contribution with {ital V}{sup {ital C}} instead of {ital T}{sup {ital C}} by a simple analytic expression, is sh…
Estimation of the Repeatedly-Projected Reduced Density Matrix under Decoherence
2007
Decoherence is believed to deteriorate the ability of a purification scheme that is based on the idea of driving a system to a pure state by repeatedly measuring another system in interaction with the former and hinder for a pure state to be extracted asymptotically. Nevertheless, we find a way out of this difficulty by deriving an analytic expression of the reduced density matrix for a two-qubit system immersed in a bath. It is shown that we can still extract a pure state if the environment brings about only dephasing effects. In addition, for a dissipative environment, there is a possibility of obtaining a dominant pure state when we perform a finite number of measurements.
Risken–Nummedal–Graham–Haken instability in class-B lasers
1999
We determine analytical expressions for the Risken-Nummedal-Graham-Haken multimode laser instability outside the uniform field limit in the case of very fast polarization decay (class-B laser). A new condition for the observability of that instability, concerning the value of the cavity mirrors reflectivity, is predicted.
Symmetries and similarities for spin orientation parameters in at SM thresholds
2011
Abstract We consider the spin orientation of the final Z bosons for the processes in the Standard Model. We demonstrate that at the threshold energies of these processes the analytical expressions for the Z boson polarization vectors and alignment tensors coincide ( e + e − → Z H , Z γ ) or are very similar ( e + e − → Z Z ). In addition, we present interesting symmetry properties for the spin orientation parameters.
Time evolution of a pair of distinguishable interacting spins subjected to controllable and noisy magnetic fields
2017
The quantum dynamics of a $\hat{\mathbf{J}}^2=(\hat{\mathbf{j}}_1+\hat{\mathbf{j}}_2)^2$-conserving Hamiltonian model describing two coupled spins $\hat{\mathbf{j}}_1$ and $\hat{\mathbf{j}}_2$ under controllable and fluctuating time-dependent magnetic fields is investigated. Each eigenspace of $\hat{\mathbf{J}}^2$ is dynamically invariant and the Hamiltonian of the total system restricted to any one of such $(j_1+j_2)-|j_1-j_2|+1$ eigenspaces, possesses the SU(2) structure of the Hamiltonian of a single fictitious spin acted upon by the total magnetic field. We show that such a reducibility holds regardless of the time dependence of the externally applied field as well as of the statistical…
Stable control of pulse speed in parametric three-wave solitons.
2006
International audience; We analyze the control of the propagation speed of three wave packets interacting in a medium with quadratic nonlinearity and dispersion. We find analytical expressions for mutually trapped pulses with a common velocity in the form of a three-parameter family of solutions of the three-wave resonant interaction. The stability of these novel parametric solitons is simply related to the value of their common group velocity.
H-function representations for stretched exponential relaxation and non-Debye susceptibilities in glassy systems.
2001
Analytical expressions in the time and frequency domains are derived for non-Debye relaxation processes. The complex frequency-dependent susceptibility function for the stretched exponential relaxation function is given for general values of the stretching exponent in terms of H-functions. The relaxation functions corresponding to the complex frequency-dependent Cole-Cole, Cole-Davidson, and Havriliak-Negami susceptibilities are given in the time domain in terms of H-functions. It is found that a commonly used correspondence between the stretching exponent of Kohlrausch functions and the stretching parameters of Havriliak-Negami susceptibilities are not generally valid.
Suggestioni favolistiche, espressioni sentenziose e tonalità moraleggianti nel «Pamphilus»
2022
Le commedie elegiache latine del XII e XIII secolo sono spesso caratterizzate da echi e suggestioni di origine favolistica, nonché da forti componenti di stampo moralistico, esemplare, proverbiale. In tal dire-zione, una delle più significative è senz’altro il «Pamphilus», composto all’inizio del XII secolo e ampiamente debitore, quanto alla trama, alle tematiche e ai personaggi, nei confronti del «De nuntio sagaci». In questo saggio, attraverso un’approfondita lettura della commedia, si insiste sulle suggestioni favolistiche, sulle espressioni proverbiali e sulle tonalità moraleggianti che largamente la innervano, fino a costituirne un elemento assolutamente indispensabile, già, d’altra pa…