Electrical resistivity of the pseudo-binary system Ce(Fe1-xAlx)2

The Laves phase pseudo-binary system Ce(Fe_1-xAl_x)₂ for x≤0.20 has been studied by means of electrical resistivity measurements from 1.5 to 300 K. It is shown that with Al addition, the long range magnetic order of CeFe₂ is destroyed and that a spin glass phase brings in a minimum in the total resistivity with T_min proportional to x. The freezing temperatures T_f are always smaller than T_min and there appears a negative coefficient of the T^3/2 dependence below T_f. The minimum in d?/dT is well correlated with T_f.     

Thermal softening of curvature elasticity in membranes

Recently, there have been three determinations of the reduction of curvature elasticity due to thermal fluctuations. The results obtained by Helfrich, Peliti and Leibler, and Förster are κ_R=κ-(T/4π)I log(q_max/q_min), with I=1, 3, and 2 respectively. We discuss the differences between the calculations and show that, despite a careless handling of the path integration measure, Peliti and Leibler's result is correct. Förster's paper, on the other hand, has the correct measure but the wrong algebra. As a further result, the gaussian curvature constant is shown to change with temperature as [ovbar|κ]_R=[ovbar|κ]+(T/4π) × 4log(q_max/q_min).     

Higher-order amplitude squeezing of photons propagating through a semiconductor

Kth power photon amplitude squeezing is studied when the coherent photon propagates through a semiconductor containing the exciton. If the exciton is prepared initially in a coherent state, the photon may become Kth power amplitude squeezed. It is shown that, in the short-time limit, the photon squeezing in the P direction does not appear at all while that in the X direction is possible for all the amplitude powers K. In the latter case, the amount of squeezing is larger for higher power K. The dependences on all the system parameters as well as on the output light detection moment are investigated in detail.     

Temperature dependence of the rho-meson mass and width

It is shown, to leading order in the virial expansion, that unitarity of the ππ scattering amplitude implies that if the ρ-meson widthΓ _ρ(T) increases with temperature, then the ρ-meson massM _ρ(T) must also increase. The temperature dependence ofM _ρ(T) is explicitly obtained from a simple, but physically motivated, parametrization of theI=J=1 ππ scattering amplitude.     

Squeezing and sub-Poissonian effects up-to fourth order in fifth harmonic generation

The concept of squeezing of the electromagnetic field is investigated in fundamental mode in fifth harmonic generation with the approximation |gt|²?1, where g is coupling constant and t, the interaction time between waves during the process. It has been found that squeezing occurs in amplitude, amplitude-squared, amplitude-cubed and fourth-order amplitude states of the field for selective phase values of field amplitude of fundamental mode. The dependence of squeezing on the photon number has also been investigated and found to be sub-Poissonian in nature. The signal to noise ratio has been studied in different order. It is found that the signal to noise ratio is higher in lower order.     

Anomalous pulse angle dependence of the single and double quantum echoes in a photoinduced spin-correlated coupled radical pair

In this work the response of a spin-correlated coupled radical pair to the sequence flash-t-P _ζ-τ-P _2ζ-T is investigated. For the theoretical analysis, the density operator formalism is used. Analytical expressions are derived for the electron spin single (SQ ESE) and double-quantum echoes (DQ ESE) as a function of pulse flip angle and singlet-triplet mixing angle. To illustrate the theoretical results, computer simulations are presented. In the limit of weak coupling, the “out-of-phase” SQ ESE is shown to be of a pure two-spin order having the maximal amplitude for the flip angle of 65.9°. The echo following the Hahn sequence vanishes in the same limit. This confirms the theoretical result already presented in the literature. However, the more general analysis shows that outside the weak coupling approximation the Hahn echo is of purely one-spin order, whereas the echo following the flash-t-P _ζ-τ-P _2ζ-t sequence has its maximal amplitude for the flip angle of 75° and the singlet-triplet mixing angle of 27°. The “in-phase” single- and double-quantum echoes are shown to vanish due to averaging out, within the electron spin resonance spectrometer deadtime, of contributions modulated with the sum and difference of the zero-quantum beat frequency and the frequency due to the spin-spin interaction within the pair. The calculated out-of-phase DQ ESE signal is inverted with respect to the out-of-phase SQ ESE and has only the half of its amplitude. The DQ ESE vanishes for the Hahn sequence. The echo has maximal amplitude in the weak-coupling limit for the flip angle of 65.9°. In contradiction to the analytical result previously published, the out-of-phase DQ ESE does not vanish for long τ and large zero-quantum-beat frequency.     

Contribution of tilt boundaries to the total energy spectrum of grain boundaries in polycrystals

By measuring temperatures T _w for the transition from the incomplete to complete wetting of grain boundaries in poly- and bicrystals, the width of the spectrum of tilt grain boundaries and their contribution to the total energy spectrum of grain boundaries in polycrystals have been experimentally estimated. It has been shown that the tilt grain boundaries correspond to a rather narrow (only 5–10%) portion in the total energy spectrum of grain boundaries in polycrystals. In metals with a low stacking fault energy (copper, tin, zinc), the tilt grain boundaries belong to 10–20% of the grain boundaries with the highest transition temperatures T _w (hence, with low energies). In a metal with a high stacking fault energy (aluminum), the values of T _w for the tilt grain boundaries lie nearly in the middle between the minimum (T _w,min) and maximum (T _w,max) transition temperatures from the incomplete to complete wetting of grain boundaries. This means that grain boundaries with the structure corresponding to a lower energy than that of the symmetric twin boundaries (or stacking faults) can exist in aluminum.     

Large polarization squeezing in non-degenerate parametric amplification of coherent radiation

Polarization squeezing is shown to occur in non-degenerate parametric amplification of coherent light and the degree of squeezing at interaction time T can be as large as 1 ? e^-2T. This gives 86.4% polarization squeezing for T = 1 and 98.2% for T = 2. One simple case when this occurs is on taking initially plane polarized light having equal amplitudes in the two modes that finally has equal intensities of two circular polarizations. This suggest the experimental settings of parameters to achieve this extent of polarization squeezing in coherent light.     

Sudden Vanishing of Atomic Dipole-Squeezing in a Kerr Nonlinear Blackbody

The dynamics of atomic dipole momentum and atomic dipole-squeezing effect are investigated inside a Kerr nonlinear blackbody. It is found that in a Kerr nonlinear blackbody, the atomic dipole momentum and its squeezing effect are heavily dependent on the Kerr nonlinear coefficient. It is also found that below a transition temperature T _c , the dipole momentum and its squeezing effect in a Kerr nonlinear blackbody can vanish much faster with time than those in a normal blackbody. Above T _c , the Kerr nonlinear blackbody becomes a normal blackbody, and the dynamics of the atomic dipole momentum and its squeezing effect behaves as those in normal blackbody radiation. The physical origin of the sudden-vanishing phenomenon in a Kerr nonlinear blackbody is also discussed.     

Amplitude of photostructural changes in chalcogenide vitreous semiconductors

It is shown that a position of an optical absorption edge (OAE) of amorphous AsSe and As₂S₃ films irradiated by light up to saturation is independent on T_exp the temperature at which the sample is exposed, and the amplitude of a reversible photoinduced shift of OAE ΔE is determined by its thermal shift ΔE as it is heated from T_exp up to the glass-transition temperature T_g. So, in order to obtain maximum photoinduced changes we need to use materials with maximum thermal variations of the forbidden zone width, and to tend to a greater difference between T_g and T_exp. The obtained results are well explained within the scope of the local heating model.     

Fe基非晶态合金的低温电阻研究

本文报道Fe_100-xB_x,Fe_87-xSi_xB₁₃,(Fe_1-xCo_x)₇₈Si_9.5B_12.5,(Fe_1-xM_x)_80-84B_16-20(M=Zr,V,Nb,Ta,Cr,Mo,W,Mn)非晶态合金的 关键词：     

Energy gap of a charge density wave in NbSe3 induced by a high magnetic field above the Peierls transition temperature

The effect of a magnetic field on the energy gap of the charge density wave (CDW) in NbSe₃ near the temperature T _p2 of the lower Peierls transition has been investigated using interlayer tunneling spectroscopy. It has been shown that the magnetic field increases the energy gap and can even induce it at temperatures higher than T _p2 by 15–20 K. As the field strength increases, the peak amplitude of the gap singularity of the tunneling spectrum first increases, reaches its maximum at 20–30 T, and then decreases. The increase in the gap peak amplitude is attributed to the field-induced improvement of the condition of the CDW nesting, while the decrease in the amplitude in high fields, to the breakdown of the ground state caused by its Zeeman splitting.     

Spectral shifts and spectral switches of spatially and spectrally partially coherent pulsed beams in Young’s interference experiment

Taking the Gaussian Schell-model pulsed (GSMP) beam as a typical example of spatially and spectrally partially coherent pulsed beams, an analytical expression for the far-field spectrum of diffracted GSMP beams in Young’s interference experiment is derived, and used to study the spectral shifts and spectral switches of GSMP beams in the far field. Numerical calculation results are given to illustrate the dependence of spectral shifts and spectral switches on the obscuration ratio ε, temporal coherent length T_c, spatial correlation parameter β and diffraction angle α. It is shown that the critical angle α_c of the first- and second-order spectral switches moves away from the z axis with increasing T_c, but α_c of the third-order spectral switch moves towards the z axis with increasing T_c. The spectral transition height Δ decreases and spectral minimum S_min increases as T_c increases. α_c decreases, Δ increases and S_min decreases as β increases. The potential application of spectral switches of spatially and spectrally partially coherent pulsed beams in information encoding and transmission is proposed.     

Saturation of sodium fluorescence in a flame irradiated with a pulsed tunable dye laser

Theoretical and experimental saturation curves and associated saturation parameters for the Na-D doublet in an H₂-O₂-Ar flame at 1 atm (T=1700 K) are compared. These parameters are found to agree within the experimental error of 25%. An explanation based on the spatial and temporal distribution of the laser intensity is given for the deviating saturation curves reported by various authors. The shape of the fluorescence pulse is shown to depend on the O₂ concentration in the flame. A lower limit for the rate constant of the doublet mixing transition is estimated from the ratio of the saturated fluorescence intensities of the Na-D components and found to be 3x10⁸s^-1. Conclusions are drawn which restrict the use of saturated atomic fluorescence intensities as a measure for the total atomic number density in the flame.     

Effect of external fields on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe<Subscript>2</Subscript>

The effect of external fields (dc electric field, light illumination) on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe₂ is studied using the measured dielectric constant. The results obtained are discussed. It is shown for the first time that the effect of external fields on the anomaly related to the memory effect in TlGaSe₂ can be reduced to the following universal empirical rule: when a sample is held for many hours at a constant temperature T ₀ in the temperature range of the incommensurate phase in a dc electric field, the deflection amplitude in the low-temperature part of the anomaly in the temperature dependence of the relative change in the dielectric constant Δ?/? increases (the deflection in the high-temperature part of the Δ?/? anomaly disappears) as compared to this segment in the dependence obtained during isothermal annealing of this sample at the same temperature without an electric field. The crystal remembers its thermal history at a temperature that is several kelvins higher than T ₀. Light illumination increases the deflection amplitude in the high-temperature part of the Δ?/?(T) anomaly and shifts the temperature at which the crystal remembers its thermal history toward lower temperatures with respect to T ₀.     

Study on the spatial distribution of the liquid temperature near a cavitation bubble wall

A simple new model of the spatial distribution of the liquid temperature near a cavitation bubble wall (T_li) is employed to numerically calculate T_li. The result shows that T_li is almost same with the ambient liquid temperature (T₀) during the bubble oscillations except at strong collapse. At strong collapse, T_li can increase to about 1510 K, the same order of magnitude with that of the maximum temperature inside the bubble, which means that the chemical reactions occur not only in gas-phase inside the collapsing bubble but also in liquid-phase just outside the collapsing bubble. Four factors (ultrasonic vibration amplitude, ultrasonic frequency, the surface tension and the viscosity) are considered to study their effects for the thin liquid layer. The results show that for the thin layer, the thickness and the temperature increase as the ultrasonic vibration amplitude rise; conversely, the thickness and the temperature decrease with the increase of the ultrasonic frequency, the surface tension or the viscosity.     

Anomalous paramagnetic behavior in the paramagnetic phase of La2/3−xYxCa1/3MnO3 studied through EPR and its relation to colossal magnetoresistance

Electron paramagnetic resonance on La_2/3−xY_xCa_1/3MnO₃ in the paramagnetic (PM) regime is presented for 0≤x≤0.133. The resonance linewidth (ΔH_pp) decreases with cooling, reaches the minimum at T_min, and then anomalously increases with further cooling toward T_c. Our analysis on ΔH_pp(T) below T_min shows that the anomalous PM behavior below T_min is due to the appearance of a ferromagnetic (FM) phase within the PM matrix caused by the applied magnetic fields. The correlation between the anomalous PM and the colossal magnetoresistance is discussed. We argue that both are caused by the phase segregation in which the compound is phase-separated into a mixture of FM and PM regions.     

On two-dimensional finite amplitude electro-convection in a dielectric liquid induced by a strong unipolar injection

The hydrodynamic stability of a dielectric liquid subjected to strong unipolar injection is numerically investigated. We determined the linear criterion T_c (T being the electric Rayleigh number) and finite amplitude one T_f over a wide range of the mobility parameter M. A noticeable discrepancy is shown for T_f between our numerical prediction and the value predicted by stability analysis, which is due to the velocity field used in stability analysis. Recent studies revealed a transition of the flow structure from one cell to two with an increase in T. We demonstrate that this transition results in a new subcritical bifurcation.     

Analysis of the active region of overheating temperature in green LEDs based on Group III nitrides

For the first time, the overheating temperature ΔT _p-n of the active region in green light-emitting diodes based on Group III nitrides has been determined as a function of the forward current amplitude I. It has been shown that in contrast to light-emitting diodes, in which the current-voltage characteristics are adequately described by known theories of rectification in p-n junctions and ΔT _p-n ∝ I, in the structures under study, the dependence ΔT _p-n (I) in the current range of 2×10^?3?3×10^?2 A is quadratic in current. At higher currents, the variation of ΔT _p-n with I in the green light-emitting diodes based on Group III nitrides becomes linear, which is the same as in the light-emitting diodes based on known infrared and red III-V structures.     

Statistical properties of a two-photon cavity mode in the presence of degenerate parametric amplifier

A Hamiltonian model that includes two-photon interaction with a two-level atom and a degenerate parametric amplifier is considered. By invoking a canonical transformation an exact solution of the wave function in the Schrödinger picture is obtained. The result presented in this context is employed to discuss the purity, the entropy squeezing, and the variance squeezing, in addition to the normal squeezing. It has been shown that the existence of the second harmonic generation leads to reduction in the squeezing amount for all quadrature variances and we found that as the value of the coupling parameter λ₂ increases the squeezing phenomenon gets more apparent. Further we have also considered the Q-function as an example of the quasi-probability distribution.