一种新型的低温恒温器

本文描述了一种适用于1K到300K的低温物理实验装置。它既可以作为液氦恒温器使用,又可以作为氦连续流动恒温器使用。如果用液氮作冷源,则可以获得77K到300K的温度。     

用于光学实验的稳态汽泡式低温恒温器

本文报道一台用于光学实验的稳态汽泡式低温恒温器的结构和性能。该恒温器的工作温度是4—300K。     

低温领域中低温恒温器的研究进展

在低温领域中，低温恒温器是最常用的一种测量样品在低温下性能的实验装置，样品常常需要在低温恒温的情况下，进行各种电学，光学，磁热性能等基础实验.文章深入解析并探究了低温恒温器的概念、组成、分类和结构，描述了低温恒温器的进展状况，并提出了未来恒温器发展的趋势。     

一种简便而稳定的用于光学和电学实验的恒温器

为研究物质在低温下的光学性质,我们在G.H.Lesch等人[1]设计的低温光学实验用恒温器的基础上作了改进,设计了一具光学和电学实验用低温恒温器(图 1).既保持了[1]中恒温器的结构简单的优点,又提高了恒温精度,还使样品能在光路中作适当调节. 样品架由整块黄铜做成(图2).它具有较大的热容和较好的导热性,当样品需要加电压时,可在样品架与样品(例如晶体)间用厚0.06mm的聚四氟乙烯薄膜作电的绝缘,又能保持较好的热接触,以保证样品加热均匀. 引出口的外管是黄铜管.所有导线引出之前,在一个类似于绕线轴的黄铜轮上绕一圈,此黄铜轮与黄铜外管大面…     

低温恒温器简介

在低温领域中,经常需要对低温恒温条件下样品的各种低温性能,如热物理性质、机械性能、光学物理性能、磁热性能及超导性能等进行测试。这就需要提供一种实验装置来维持样品的低温恒温条件。而低温恒温器是一种能够提供低温恒温条件并与外界热绝缘的低温装置,它应用广泛,是进行低温实验的必要设备。主要介绍了低温恒温器的概念、应用、分类、结构及其设计。     

用于原位中子散射水合物测量装置

能源与环境问题的日益突出,为可燃冰的研究提供了动力。可燃冰的形成机理、储存及利用,都与其结构性质紧密相关。为了研究可燃冰结构,需要加工一套可以维持可燃冰低温高压环境的低温恒温器。通过恒温器设计及压腔设计,实现了低温高压的耦合,最低温50 K,最高压力20 MPa。经过在通用粉末衍射谱仪(GPPD)测试,成功观察到了可燃冰的衍射峰。测试结果显示,所研制的高压低温恒温器运行稳定可靠,温度梯度较小,控温精度高,可以满足可燃冰中子散射实验需求。     

高精度可控低温恒温器的研制与应用

1引言随着低温技术的发展，迫切需要高精度可控低温恒温装置，以便在低温恒温条件下，对样品的各种低温性能进行测试．本文介绍一种可控低温恒温器，其工作渴度范围约为一130℃－0℃，该仪器结构紧凑，实验人员可自己动手制作，且控温精度高，恒温器内温度稳定性很好，适用于各种材料样品的低温测试．2低温恒温器简介仪器装置如图1所示，用黄铜制成的圆筒（样品室），高scm，外径2．6cm，壁厚3mm，底厚5cm．圆筒的底部连接一根长约12cm直径6mm的导热铜杆，铜杆插入铜套管，套管固定在泡沫塑料块上．导热铜杆上部套着一个小加热器，可以采用…     

4.2—300K热电偶分度用恒温器

本文介绍一种供分度热电偶用的低温恒温器.实验得出:从室温到20K,恒温器的恒温精度可达±0.005K,从20K到4.2K,恒温器的恒温精度可达±0.01K.     

AMS-02超导磁体300K-80K受控冷却系统的工艺流程设计

300K-80K受控冷却系统是AMS-02探测器的低温地面支持设备(CGSE)系统中的重要子系统,其主要作用是实现AMS-02磁体从常温(约300K)到接近液氮温度(约80K)的冷却。对该系统进行了工艺流程设计,在恒温器内设置多个调节阀和温度、压力、流量检测元件,通过自动调节手段控制经该系统冷却后前往磁体的氦气的温度和流量。同时介绍了该系统的组成及低温恒温器、HX1、HX2和HX3的结构和特点。     

一个供穆斯堡尔谱仪用的低温恒温器

研制了一个供穆斯堡尔谱仪用的低温恒温器,利用一个安装在尾管内的活塞改变样品架和致冷剂之间的热阻,可使样品架恒温于78—300K范围内的任意温度上。注入3.2升液氮后,可连续工作80小时以上。     

铜团簇(n=55)结构及能量随温度演变的Monte Carlo 模拟研究

采用Monte Carlo方法及Embeded-Atom Method作用势，以55个铜原子体系为对象，研究了高 温铜团簇的结构及能量.首先计算温度为200?K时Cu₅₅的能量及结构，其结果 与土耳 其Süleyman ?zcelik 等人的研究小组的研究结果符合很好，说明此方法是可靠的.然后， 从12000?K开始逐渐降温，间隔1000?K，每个温度点MCS为10⁶，在达到平衡时 得到体系的结构及能量.结果表明：在10000?K以上时，体系只有少数原子结合在一起成核，成核数很少，且很不稳定，单原子数较多；在10000?K到6000?K温度段，随着温度的降低，体系 结构由单原子双原子数较多渐变到有较多原子结合在一起，形成一个大的成核中心，剩余单 原子、双原子逐渐与成核中心集结；在温度5000?K达到平衡时，体系原子已经完全结合在 一起，没有单个原子存在，体系能量为-11206?eV，在进一步降温的过程中，体系结构由 5000?K时的不对称、不规则渐变到600?K时的规则、对称的双二十面体结构，能量为-168 50?eV；在可视化的显示下，得到一幅十分清晰的关于体系随温度降低的结构演变图. 关键词： 铜团簇 结构及能量 Monte Carlo 模拟 高温     

Test of a method for sampling the internal degrees of freedom of a flexible solute molecule based on adiabatic decoupling and temperature or force scaling

Simulation of the folding equilibrium of a polypeptide in solution is a computational challenge. Standard molecular dynamics (MD) simulations of such systems cover hundreds of nanoseconds, which is barely sufficient to obtain converged ensemble averages for properties that depend both on folded and unfolded peptide conformations. If one is not interested in dynamical properties of the solute, techniques to enhance the conformational sampling can be used to obtain the equilibrium properties more efficiently. Here the effect on particular equilibrium properties at 298?K of adiabatically decoupling the motion a β-hepta-peptide from the motion of the solvent and subsequently up-scaling its temperature or down-scaling the forces acting on it is investigated. The ensemble averages and rate of convergence are compared to those for standard MD simulations at two different temperatures and a simulation in which the temperature of the solute is increased to 340?K while keeping the solvent at 298?K. Adiabatic decoupling with a solute mass scaling factor s _m ?=?100 and a temperature scaling factor of s _T ?=?1.1 seems to slightly increase the convergence of several properties such as enthalpy of folding, NMR NOE atom–atom distances and ³J-couplings compared to a standard MD simulation at 298?K. Convergence is still slower than that observed at 340?K. The system with a temperature of 340?K for the solute and 298?K for the solvent without scaling of the mass converges fastest. Using a force scaling factor s _V ?=?0.909 perturbs the system too much and leads to a destabilization of the folded structure. The sampling efficiency and possible distortive effects on the configurational distribution of the solute degrees of freedom due to adiabatic decoupling and temperature or force scaling are also analysed for a simpler model, a dichloroethane molecule in water. It appears that an up-scaling of the mass of the solute reduces the sampling more than the subsequent up-scaling of the temperature or down-scaling of the force enhances it. This means that adiabatic decoupling the solute degrees of freedom from the solvent ones followed by an up-scaling of temperature of down-scaling of the forces does not lead to significantly enhanced sampling of the folding equilibrium.     

Boron-doped diamond as a new heating element for internal-resistive heated diamond-anvil cell

We have developed an internal-resistive heated diamond-anvil cell (IHDAC) with a new resistance heater – boron-doped diamond (BDD) – along with an optimized design of the cell assembly, including a composite gasket. Our proposed technique is capable of heating a silicate/oxide material with (1) long-term stability (>1?h at 2500?K) and (2) uniform radial temperature distribution (±35?K at 2500?K across a 40-µm area), which are clear advantages over the conventional laser-heated and internal-heated DACs. In addition, the achieved temperature in this study was greater than 3500?K, which mostly covers the possible geotherm of the entire lower mantle. In situ X-ray diffraction (XRD) measurement and ex situ chemical analyses confirmed that weak XRD intensity from the BDD heater and chemical inertness (no boron diffusion into silicate samples). This newly developed IHDAC with a BDD heater can be used to determine the phase diagrams of mantle materials with high precision and be used in lower-mantle petrology.     

Investigation on phase transitions of 1-decylammonium hydrochloride as the potential thermal energy storage material

1-Decylammonium hydrochloride was synthesized by the method of liquid phase synthesis. Chemical analysis, elemental analysis, and X-ray single crystal diffraction techniques were applied to characterize its composition and structure. Low-temperature heat capacities of the compounds were measured with a precision automated adiabatic calorimeter over the temperature range from 78 to 380?K. Three solid–solid phase transitions have been observed at the peak temperatures of 307.52?±?0.13, 325.02?±?0.19, and 327.26?±?0.07?K. The molar enthalpies and entropies of three phase transitions were determined based on the analysis of heat capacity curves. Experimental molar heat capacities were fitted to two polynomial equations of the heat capacities as a function of temperature by least square method. Smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15?K were calculated and tabulated at intervals of 5?K based on the fitted polynomials.     

BSO晶体的高温拉曼光谱与高温结构特征

阐述了BSO晶体在常温下的结构特征,通过测量晶体在常温下的拉曼光谱,对晶格主要振动模式进行了指认,测量晶体升温至熔化过程中不同温度下的拉曼光谱,分析研究了其微观结构在升温过程中的变化以及在高温状态下的结构特征。     

Heating of samples induced by fast magic-angle spinning

Intense sample heating through high-speed magic-angle spinning (MAS; up to 58 K temperature difference) is demonstrated. The role of probehead and spinner design, as well as that of the temperature of the bearing air on the heating of a rotating sample, is examined. MAS-induced heating can affect the accurate determination of the isotropic value of the chemical shift as well as the principal values, asymmetry and anisotropy parameters of the chemical shift tensor. In some cases, a very large temperature gradient (12 K) within the fast rotating sample was found, which may limit the resolution of high-speed 1H MAS nuclear magnetic resonance (NMR) spectra.     

Investigation of atomic anti-site disorder and ferrimagnetic order in the half-metallic Heusler alloy Mn(2)V Ga

The band structure calculation for the compound Mn(2)VGa carried out using the plane wave self-consistent field package with generalized gradient approximation shows that the compound is nearly half-metallic at the equilibrium lattice parameter. However, theoretical investigations have shown that a certain percentage of atomic anti-site disorder can destroy the half-metallic nature of the sample. Hence it is important to quantify the site disorder in these systems. We have deduced the percentage of atomic anti-site disorder from the refinement of the higher angle room temperature (300?K) neutron diffraction (ND) pattern and it was observed to be roughly 8% in our sample. The field variation of resistance recorded at different temperatures shows a positive slope at low temperatures and a negative slope at higher temperatures, indicating the half-metallic character at low temperatures. The ab?initio calculations predict a ferrimagnetic ground state for this system. The analysis of the magnetic structure from ND data measured at 6?K yields magnetic moment values of 1.28?μ(B) and -0.7?μ(B) for Mn and V, respectively, confirming the ferrimagnetic ordering.     

Pressure and temperature dependence of the structure of liquid Sn up to 5.3 GPa and 1373 K

Pressure and temperature dependence of the structure of liquid Sn has been measured up to 5.3?GPa and 1373?K using multi-angle energy-dispersive X-ray diffraction in Paris–Edinburgh cell. Under nearly isobar condition at ～1?GPa, liquid Sn displays a normal behavior with gradual structural changes with temperature up to 1373?K. Under isothermal compressions at 850 and 1373?K, however, the structure factors of liquid Sn both show a turn-over at ～3?GPa in the height of the first diffraction peak. According to the hard sphere cluster model, the structure of liquid Sn may be viewed as two different types of clusters. Below ～3?GPa, it is shown that the packing fraction of the dominant cluster (occupying ～0.94 fraction) changes with compression, while above ～3?GPa, the packing fractions and the hard sphere diameters of both clusters start to influence the structure, causing significant changes with increasing pressure. Our results suggest that the compression behavior of liquid Sn changes from localized densification only in one cluster below ～3?GPa to homogeneous structural changes in both clusters above ～3?GPa.     

A classical molecular dynamics study of a Diels Alder cycloaddition in supercritical water

Molecular dynamics simulations were performed to investigate the Diels Alder cycloaddition of cyclopentadiene and methyl vinyl ketone in high pressure, high temperature water. It was found that the reaction was favoured by high temperatures at 1000?atm due to increasing entropy. Similarly, at 400?atm, the entropy caused both the equilibrium and rate constant to increase to a peak at 698?K before rapidly falling once more with increasing temperature. At a constant temperature of either 598?K or 898?K, increasing pressure resulted in a lowering of the equilibrium constant. This effect was significantly more pronounced for 898?K, caused by less favourable solvation of the products and an increasing amount of work required for reaction.     

Thermal analysis of GaN-based laser diode mini-array

Thermal characteristics of multiple laser stripes integrated into one chip is investigated theoretically in this paper. The temperature pattern of the laser diode mini-array packaged in a TO-can is analyzed and optimized to achieve a uniform temperature distribution among the laser stripes and along the cavity direction. The temperature among the laser stripes varies by more than 5 K if the stripes are equally arranged, and can be reduced to less than 0.4 K if proper arrangement is designed. For conventional submount structure, the temperature variation along the cavity direction is as high as 7 K, while for an optimized trapezoid submount structure, the temperature varies only within 0.5 K.