Non-Hermitian Ising model at finite temperature

As a very simple model, the Ising model plays an important role in statistical physics. In the paper,with the help of quantum Liouvillian statistical theory, we study the one-dimensional nonHermitian Ising model at finite temperature and give its analytical solutions. We find that the nonHermitian Ising model shows quite different properties from those of its Hermitian counterpart. For example, the ‘pseudo-phase transition’ is explored between the ‘topological’ phase and the ‘nontopological’ pha...     

Čerenkov radiation at finite temperature

A power formula for erenkov radiation at finite temperature is derived in the framework of the generalized finite-temperature Cutkosky rules. Spins 1/2 and 0 are considered.     

Do semiclassical zero temperature black holes exist?

The semiclassical Einstein equations are solved to first order in epsilon = Planck's over 2pi/M2 for the case of a Reissner-Nordstr?m black hole perturbed by the vacuum stress energy of quantized free fields. Massless and massive fields of spin 0, 1/2, and 1 are considered. We show that in all physically realistic cases, macroscopic zero temperature black hole solutions do not exist. Any static zero temperature semiclassical black hole solutions must then be microscopic and isolated in the space of solutions; they do not join smoothly onto the classical extreme Reissner-Nordstr?m solution as epsilon-->0.     

QCD at finite temperature—a variational approach

We develop here a nonperturbative framework to study quantum chromodynamics (QCD) at finite temperatures using the thermofield dynamics (TFD) method of Umezawa. The methodology considered here is selfconsistent and variational. There is a dynamical generation of a magnetic gluon mass. This eliminates the infrared problems associated with perturbative QCD calculations at finite temperatures. We obtain here the thermodynamical quantities like free energy density, pressure and entropy density. We also calculate the temperature dependence of SVZ parameter . The condensate vanishes at the critical temperature in accordance with recent hot sum rule calculations. The present method gives an insight to the vacuum structure in QCD at zero temperature as well as at finite temperatures in a coordinated manner.     

Néel temperature of quasi-low-dimensional Heisenberg antiferromagnets

The Néel temperature T(N) of quasi-one- and quasi-two-dimensional antiferromagnetic Heisenberg models on a cubic lattice is calculated by Monte Carlo simulations as a function of interchain (interlayer) to intrachain (intralayer) coupling J(')/J down to J(')/J approximately = 10(-3). We find that T(N) obeys a modified random-phase approximationlike relation for small J(')/J with an effective universal renormalized coordination number, independent of the size of the spin. Empirical formulas describing T(N) for a wide range of J(') and useful for the analysis of experimental measurements are presented.     

Recursive method for opacity expansion at finite temperature

Using a reaction operator approach, we derive the multiple-scattering induced gluon number distribution function to all orders in powers of opacity at finite temperature. The detailed balance effect is analyzed by taking into account both gluon emission and absorption in a thermal medium. We also calculate virtual corrections and show that the infrared divergence cancels out in the gluon distribution function at finite temperature.     

Diode-pumped Tm:LuAG laser at room temperature

The lasing characteristics of Tm:LuAG at room temperature are reported.The maximum output power at 2.023-μm wavelength is 4.91 W and the slope efficiency is 25.39%.The mode matching between pump mode and laser mode is optimized by changing the pump beam waist radius and its location.Different output couplers are used to realize the optimal laser output.The relationship between operation temperature and output power is also discussed.     

Optical fiber temperature sensor based on wavelength-dependent detection

Semiconductor fiber temperature sensors have been used widely in many fields, but most of them pick up temperature by measuring the optical intensity of certain fixed narrow-band in absorption spectrum. Furthermore,they are sensitive to the loss of optical intensity and the fluctuation of light source power. The novel temperature measurement system proposed in this paper is based on the semiconductor absorption theory and the spectral analysis of method.To measure temperature,the sensor model detects not the certain narrow-band spectrum but the most spectra of the optical absorption edge.Therefore the measurement accuracy and the stability can be improved greatly.Experimental results are in agreement with theoretical analysis results perfectly.     

Average temperature and multiplicities ofe + e − annihilation

Hadron temperatures ofe ⁺ e ^?→h \(\bar h\) from PEP experiments at 29 GeV are estimated using theP _⊥ distribution; rather small fluctuations are found for temperatures of π,K,..., Ξ with respect to the average \(\bar T = 196 \pm 7\) MeV. A semi-empirical formula including quark content ofh is proposed to account for multiplicities of π,K, ..., Δ in terms of a unique temperature \(\bar T\) . The formula is further extended to charmed particlesD, F, J/Ψ andΛ _c without free parameters. The property \(\bar T\) ~E _cm ^1/4 holds for other experiments of DESY andCESR.     

Diode-pumped high-efficiency Tm:YLF laser at room temperature

High-efficiency continuous-wave (CW) Tm:YLF laser by the dual-end-pumping configuration is presented. Under the total input pump power of 24.0 W,the highest output power reaches 9.8 W in the wavelength range of 1910-1926 nm by use of 10% output coupling,corresponding to optical conversion efficiency of 40.9% and slope efficiency of 51.4%.The free-running laser spectrum of Tm:YLF is measured.     

Finite temperature Casimir effect in Kaluza–Klein spacetime

In this article, we consider the finite temperature Casimir effect in Kaluza–Klein spacetime due the vacuum fluctuation of massless scalar field with Dirichlet boundary conditions. We consider the general case where the extra dimensions (internal space) can be any compact connected manifold or orbifold without boundaries. Using piston analysis, we show that the Casimir force is always attractive at any temperature, regardless of the geometry of the internal space. Moreover, the magnitude of the Casimir force increases as the size of the internal space increases and it reduces to the Casimir force in (3+1)$(3+1)$-dimensional Minkowski spacetime when the size of the internal space shrinks to zero. In the other extreme where the internal space is large, the Casimir force can increase beyond all bound. Asymptotic behaviors of the Casimir force in the low and high temperature regimes are derived and it is observed that the magnitude of the Casimir force grows linearly with temperature in the high temperature regime.     

Measurement of thermal expansion coefficient of nonuniform temperature specimen

A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite material at high temperature.The measuring principle and components of the apparatus are described in detail.The calculation method is derived from the temperature dependence of the therinal expansion coefficient.The apparatus mainly consists of a high temperature environmental chamber,a power circuit of heating,two high-speed pyrometers,and a laser scanning system.A long solid specimen is resistively heated to a steady high-temperature state by a steady electrical current.The temperature profile of the specimen surface is not uniform because of the thermal conduction and radiation.The temperature profile and the total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring system,respectively.The thermal expansion coefficient in a wide temperature range(1000-3800 K)of the specimen can therefore be obtained.The perfect consistency between the present and previous results justifies the validity of this technique.     

Hydrogen dominant metallic alloys: high temperature superconductors?

The arguments suggesting that metallic hydrogen, either as a monatomic or paired metal, should be a candidate for high temperature superconductivity are shown to apply with comparable weight to alloys of metallic hydrogen where hydrogen is a dominant constituent, for example, in the dense group IVa hydrides. The attainment of metallic states should be well within current capabilities of diamond anvil cells, but at pressures considerably lower than may be necessary for hydrogen.     

In-situ measurement of the surface temperature during holographic recording

Photo-induced processes in organic materials mostly occur on molecular levels.Excited molecules may split to form radicals,starting a polymerization process with diffusing monomers.The azo-dyes perform an optically induced cis-trans isomerization.During pattern formation like a holographic grating,the local temperature increase,especially in thin films,is up to date a subject of estimation from absorption and dissipation data.However,the exact knowledge of the surface temperature would help a lot in understanding the resulting refractive index and thickness patterns during holographic exposure.In this paper,in-situ pyrometer measurements are presented.As examples,different photosensitive materials, varying from a photopolymer to polycrystalline azo dyes,are used in order to outline the magnitude of this effect and demonstrate the feasibility of this technique.     

Infrared OPO temperature tuning based on periodically-poled lithium niobate

An optical parametric oscillator (OPO) based on periodically-poled lithium niobate (PPLN) and pumped by 1064.2-nm laser is demonstrated, which can be conveniently tuned by the means of changing its operating temperature. The parameters of the set-up and experimental results are introduced in this paper. We adjusted the operating temperature from 80 to 250 ℃, the output wavelength shifted from 1485.4 to 1540.7 nm. The average of the shifts is 0.33 nm/℃.     

Active temperature compensation design of sensor with fiber gratings

A technique for compensation of temperature effects in fiber grating sensors is reported. For strain sensors and other sensors related to strain such as electromagnetic sensors, a novel structure is designed, which uses two fiber Bragg gratings (FBGs) as strain differential sensor and has temperature effects cancelled. Using this technique, the stress sensitivity has been amplified and gets up to 0.226 nm/N, the total variation in wavelength difference within the range of 3-45 °C is 0.03 nm, 1/14 of the uncompensated FBG. The structure can be used in the temperature-insensitive static strain measurement and minor-vibration measurement.