Computational study of the influence of some systematic factors on the fuel temperature in a very high temperature gas-cooled reactor with prismatic fuel assemblies

The influence of the main systematic factors of overheating (such as nonuniformity of power density and cold leaks of coolant) on the fuel temperatures in a very high temperature gas-cooled reactor NGNP (Next Generation Nuclear Plant) with prismatic fuel blocks is studied. The results of computations show a high sensitivity of the fuel temperatures to systematic factors of overheating. This circumstance indicates the necessity of high-precision three-dimensional modeling of the gas dynamics and heat transfer in the core when designing this type of reactor.     

Analysis of Ar line spectra from indirectly-driven implosion experiments on SGII facility

This paper reports on the indirectly-driven implosion experiments on SGII laser facility in which Ar emission spectrum from Ar-doped D-filled plastic capsule is recorded with the crystal spectrometer. Spectral features of Ar Heβ line and its associated satellites are analysed to extract the electron temperature and density of the implosion core. Non local thermal equilibrium (NLTE) collisional-radiative atomic kinetics and Strark broadening line shape are included in the present calculation. By comparing the calculated spectrum with the measured one, the core electron temperature and density are inferred to be 700 eV and 2.5×10²³ cm^-3 respectively. With these inferred values of electron temperature and density, neutron yield can be estimated to agree with the measured value in magnitude despite of the very simple model used for the estimation.     

About impedance spectra and dynamics of charge carriers in neat poly(ethylene oxide) structures

Impedance spectra of linear and cross-linked poly(ethylene oxide) (PEO) are analyzed in a wide range of temperature. Dielectric responses differ at low and high temperature due to tendency of PEO to crystallization below melting temperature. Extent of crystallization depends on cross-linking density. The network in PEO with high cross-linking density is rigid and morphology transition shifts to very low temperature. Debye-like relaxation appears at low temperature similar as in ionic liquids. Onset of polarization relaxation shifts to higher temperature with increasing mesh size that is coupling of electric and structural relaxation appears. This is also nicely reflected by scaled conductivity. It demonstrates that the structure in cross-linked systems is a superposition of chemical and physical networks. They relax separately at low temperature and frequency under condition of sufficient rigidity.     

In situ X-Ray study of thermal expansion and phase transition of iron at multimegabar pressure

The density of varepsilon-iron has been calculated at pressures and temperatures up to 300 GPa and 1300 K, respectively. We observe varepsilon to beta phase transition at pressures between 135 and 300 GPa and temperature above 1350 K; the pattern can be interpreted in terms of double hexagonal close-packed structure. The density calculated at high pressure and temperature (330-360 GPa and 5000-7000 K) closely matches with preliminary reference Earth model density, thereby imposing constraint on the composition of the Earth's inner core.     

Ferromagnetism of Electron Gas

We here investigate the density and temperature dependence of polarization using the relativistic formalism for the electron–electron interaction within the Fermi liquid model. The variational method has been used: the free energy has been minimized with respect to the effective mass and the polarization parameter. Then we obtained the equation of state and magnetic susceptibility of the system. The exact results for polarization and magnetic susceptibility have been obtained at zero temperature. It has been shown that for a given temperature (density) there is a critical density (temperature) at which the ferromagnetic phase can appear in an electron gas. The results are in agreement with previous work. Our results show that at nonzero temperatures and in very low and very high densities the ferromagnetism phase cannot exist.     

The amount and location of amorphous component in polyethylene single crystals

Polyethylene single crystals from dilute solutions usually have a density ρ which is less than that of the ideal crystal lattice (ρ_c = 1.000 g/cm³). This density defect can be formally assigned to an “amorphous” component (1-α) = (ρ_c-ρ)/(ρ_c-ρa) and may be caused by vacancies in the crystal lattice and/or by the surface disorder connected with chain folds. The two-phase concept of single crystal structure assumes a very nearly ideal lattice core and two amorphous layers on the fold-containing surfaces. It is supported by density and heat content data of annealed samples, by small-angle X-ray scattering, by wide-line NMR investigations, and by the results of fuming nitric acid treatment.

The maximum thickness of the amorphous surface layer as a function of temperature may be estimated from the free energy requirement of such a layer. With regular chain folds one has a high concentration of gauche conformations yielding a high surface energy. The need for such a concentration disappears in the amorphous layer with loose loops. This gain in energy may be spent for surface melting. Still more important is the gain in entropy caused by the random distribution of loop lengths.     

Simulations of the effects of density and temperature profile on SMBI penetration depth based on the HL-2A tokamak configuration

Using the trans-neut module of the BOUT++ code, we study how the fueling penetration depth of supersonic molecular beam injection(SMBI) is affected by plasma density and temperature profiles. The plasma densities and temperatures in L-mode are initialized to be a set of linear profiles with different core plasma densities and temperatures. The plasma profiles are relaxed to a set of steady states with different core plasma densities or temperatures. For a fixed gradient, the steady profiles are characterized by the core plasma density and temperature. The SMBI is investigated based on the final steady profiles with different core plasma densities or temperatures. The simulated results suggest that the SMB injection will be blocked by dense core plasma and high-temperature plasma. Once the core plasma density is set to be N_(i0)= 1.4N_0(N_0= 1 × 10~(19)m~(-3)) it produces a deeper penetration depth. When N_(i0) is increased from 1.4N_0 to 3.9N_0 at intervals of 0.8N_0, keeping a constant core temperature of T_(e0)= 725 eV at the radial position of ψ = 0.65, the penetration depth gradually decreases. Meanwhile, when the density is fixed at N_(i0)= 1.4N_0 and the core plasma temperature T_(e0) is set to 365 eV,the penetration depth increases. The penetration depth decreases as T_(e0) is increased from 365 eV to 2759 eV. Sufficiently large N_(i0) or T_(e0) causes most of the injected molecules to stay in the scrape-off-layer(SOL) region, lowering the fueling efficiency.     

SAXS investigation on aggregation phenomena in supercritical CO2

Synchrotron Small-Angle X-Ray scattering (SAXS) measurements on aggregate formation of a Polyvinyl acetate- b-Perfluoro octyl acrylate (PVAc- b-PFOA) block copolymer in supercritical CO(2) are here reported. Experiments were carried out for a series of different thermodynamic conditions, changing the solvent density by profiling both the pressure at constant temperature and the temperature at constant pressure. This block copolymer and in general fluorocarbon-hydrocarbon di-blocks form aggregates depending on the value of CO(2) density. A sharp transition between monomers dissolved as random coils and micelles characterized by a solvophilic shell and a solvophobic core occurs when the CO(2) density reaches a critical value. Results of critical micellization density (CMD) derived from pressure and temperature ramps experiment along with the comparison with previous SANS results are here reported to give additional experimental support to the solvent density-driven aggregation process.     

YBCO线圈在低温下的温度仿真分析

近几年,高温超导线材的制造技术已日趋成熟。作为第二代高温超导带材的代表,YBCO在低温下具有的优点使其在超导磁体领域的应用越来越突出。但是在高温超导磁体的运行中会因为受到扰动而失超。为了探讨这个问题,模拟了一个磁体在低温下(20K左右)有加热点扰动时的稳定性情况,即对YBCO线圈在低温下的工作情况进行了模拟仿真。文中根据实验设计的YBCO单饼线圈参数,利用热传导方程和基本电路方程,采用有限元计算方法,模拟出线圈内部的温度分布。分析仿真结果可以为后续实验设计提供参考。     

Novel Bilayer Structures for Short Wavelength High Density Magneto-Optical Data Storage

We report a novel bi-layer thin film structure for high density magneto-optical (MO) data storage, which combines the advantages of blue wavelength and magnetically induced superresolution (MSR) recording. A double-layer system of exchange-coupled light rare-earth (LRE) element doped NdGdFeCo and traditional TbFeCo is used as the recording medium. The experimental results demonstrate that this NdGdFeCo/TbFeCo double layer has large Kerr rotation under blue wavelength. Centre aperture detection (CAD) MSR effect with temperature rising is also observed. Theoretical calculation is also carried out to verify the experimental results. These results collectively suggest that the new bilayer structure is very promising in next generation high density MO data storage.     

Electric properties of chemically deposited lithium doped cadmium sulphide films

Electrical properties of chemically deposited CdS and lithium doped CdS films have been investigated by using techniques of Photo-thermoelectric and Photo-Hall effects. Dark electron densities are independent of temperature between 100 and 330°K because of shallow donors and quasi-intrinsic behaviour is apparent above 330°K. Electron density and mobility in these films have been measured as a function of temperature under strong photoexcitation. The electron mobility is found to be thermally activated with energies 0.2 and 0.22 eV for CdS:Li and CdS films respectively. The Hall mobility and electron density in these films have also been measured as a function of temperature under strong photoexcitation and found that both the free carrier density and mobility are reduced by the adsorption of oxygen, former by larger factor than the latter. The resulting very high electron density and very low electron mobility in the temperature region studied also indicate that most of the photoconductivity in chemically deposited films is caused by an increase in electron density due to photoexcitation.     

Thermo-physical properties of body-centered cubic iron-magnesium alloys under extreme conditions

Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron-magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi-Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C^′). Magnesium alloying significantly increases C^′ of Fe, and bcc Fe-Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in detail. We show that the thermo-physical properties of a bcc Fe-Mg alloy with 5% Mg agree well with those of the Earth’s inner core as provided by seismic observations.     

Nonmonotonic flux flow in inhomogeneous superconductors above the percolation threshold

Flux flow resistivity above critical temperature is analyzed based on the increased evidences that high temperature superconductors are intrinsically inhomogeneous, and local nonpercolating superconducting domains persist high above the critical temperature. It was found that above a certain field, the resistivity originated in the flow of flux motion starts to decrease with increasing field, due to the predominance of the suppression of the superconducting droplets over the increase of vortex core density.     

基于光纤粗锥型马赫-曾德尔干涉仪的高灵敏度温度传感器的研制

光纤传感是现代光纤技术的重要应用之一。制作了一种基于两个单模光纤粗锥串接的全光纤型马赫-曾德尔高温高灵敏温度传感器。纤芯中传输的光通过第一个光纤锥耦合, 一部分进入纤芯传输,另一部分进入包层形成包层模,纤芯模和包层模具有不同的有效折射率,经过干涉臂的传输产生了光程差。纤芯和包层传输的光再经过第二个光纤锥耦合,形成干涉进入输出光纤传输。对不同长度的传感器进行实验研究,得出传感臂长度与干涉周期之间的关系。研究了传感器温度响应特性,给出了温度响应灵敏度。实验结果表明,在30～400 ℃温度范围内,长度为35 mm的传感器可以得到较高的温度响应灵敏度,其响应灵敏度为0.115 nm·℃-1。利用傅里叶变换对传感器透射谱进行了分析,可以确定在长度为35 mm的传感器中仅有基模LP₀₁和高阶模LP₀₈两种模式,透射谱就是由这两种模式干涉形成的。该传感器体积小、精度高、抗电磁干扰,具有易于制作、对比度大、质轻、灵敏度高、耐高温等优点。可用于高温气体温度测量及油气井测井等领域的高灵敏度温度传感测量。     

Formation of a high T(c) electron-hole liquid in diamond

We report on the observation of electron-hole ( e-h) liquid (EHL) in diamond by time-resolved luminescence measurements under an intense femtosecond photoexcitation above the band gap. The EHL luminescence band is observed below the e-h plasma band, showing a finite rise time of several tens of picoseconds. The rise time, which corresponds to the nucleation and the growth of the e-h droplets, plummets on approaching the EHL critical temperature. Time-resolved spectral shape analysis reveals a very high carrier density of 1x10(20) cm(-3) and very high critical temperature of T(c) = 165 K of EHL.     

Study on a low loss, low voltage, polarization-independent EO modulator based LPG

In this paper, a new type of high-speed EO modulator is presented. It is a multi-cladding structure with LPG written in the core, and polymer with high EO coefficient is fabricated as the outer layer. A special material with ultra-negative temperature coefficient is used for the temperature compensation. This modulator is polarization independent, it can be coupled with the optical fiber very easily and can work steadily with low voltage, high speed, is temperature insensitive, and its cost is low. To our knowledge, this is the first time a modulator has been designed with such a simple and effective structure.     

Multispectral imaging of continuum emission for determination of temperature and density profiles inside implosion plasmas

In inertial confinement fusion experiments, implosion of a cryogenic hydrogen isotope-filled capsule produces a plasma with a high-temperature, low-density core (the hot spot) surrounded by a low-temperature, high-density main fuel layer. Experimental measurements of temperature and density profiles in the hot spot are critical for implosion diagnosis. In this paper, we propose a simple technique for measuring core temperature and density profiles in cryogenic implosion plasmas. This technique uses absolutely calibrated continuum emission spectroscopy coupled with two-dimensional imaging to allow temperature and density profiles to be measured directly. We develop the technique analytically, and validate it using synthetic data and hydrodynamics simulation results. We find that the technique should be sufficiently accurate to measure central temperatures and densities to better than 20%. The technique may also find application to the diagnosis of other types of plasmas.     

基于Michelson干涉仪的高灵敏度光纤高温探针传感器

提出了一种简单的高灵敏度的光纤高温探针传感器, 该传感器由一小段多模光纤和一端镀有银膜的单模光纤熔接而成. 由于单模光纤和多模光纤的纤芯直径不同, 当光波从多模光纤传输至多模光纤和单模光纤的熔接端面时, 一部分纤芯光耦合进包层, 因为单模光纤纤芯的折射率和包层的折射率不同, 不同模式的光经过银膜反射后在多模光纤内重新耦合进单模光纤, 最终形成干涉.随着外界温度的升高, 干涉谱峰值会向长波方向漂移. 实验结果证明这种传感器在470 ℃–600 ℃范围内具有很好的稳定性, 线性度达99.7%, 灵敏度为120 pm/℃, 可作为远距离反射型探针温度传感器, 在石油探测和油气田开发等领域有着广泛的应用前景. 关键词： 光纤传感 温度测量 Michelson干涉     

Accelerating multi-echo T2 weighted MR imaging: analysis prior group-sparse optimization

High pressure measurements in most scientific fields rely on metal vessels given the superior tensile strength of metals. We introduce high pressure magnetic resonance imaging (MRI) measurements with metallic vessels. The developed MRI compatible metallic pressure vessel concept is very general in application. Macroscopic physical systems are now amenable to spatially resolved nuclear magnetic resonance (NMR) study at variable pressure and temperature. Metallic pressure vessels not only provide inherently high tensile strengths and efficient temperature control, they also permit optimization of the MRI RF probe sensitivity. An MRI compatible pressure vessel is demonstrated with a rock core holder fabricated using non-magnetic stainless steel. Water flooding through a porous rock under pressure is shown as an example of its applications. High pressure NMR spectroscopy plays an indispensable role in several science fields. This work will open new vistas of study for high pressure material science MRI and MR.