The Coulomb Gas at low temperature and low density

We study the quantum Coulomb Gas ofN particles with HamiltonianH at low temperature and negative values of the chemical potential. If is sufficiently negative the Coulomb gas is approximately a perfect rare gas of charged particles, as expected. The interesting fact is that for higher (but still negative) values of the gas changes to a rare gas of some atom or molecule (which is most likely neutral). The type of molecule is determined by the ground state of the HamiltonianH —N with center of mass motion removed.Dedicated to Roland DobrushinWork partially supported by U.S. National Science Foundation grant DMS 8600748 (J.C.), PHY 85-15288-(A03) (E.L.) and DMS-8601978 and DMS-8806731 (H.-T.Y.)     

Acoustic properties of glasses at low temperatures and low frequencies

We generalize the low temperature expressions for the variation of the sound velocity and sound absorption in glasses due to structural defects for the case of arbitrary frequencies. In case ωτ₂ ? 1 our expressions reduce to well known results.     

L波段低温低噪声滤波放大组件设计研究

仿真和设计了一种以超导滤波器和低温低噪声放大器为核心的滤波放大组件,在77K温度下,该组件带外抑制大于100d B,在工作频段内,噪声系数优于0.44d B,增益为29.9±0.4d B,输入回波损耗优于-13.8d B,满足设计指标要求。     

低温低压氢等离子体的光谱分析

采用螺旋波激发氢等离子体,测得氢的Balmer线系前三条谱线的强度.利用二谱线法求电子温度Te,并由Hβ的Stark展宽得到电子密度Ne,简要分析了Te、Ne以及强度与各种参数之间的关系.     

低温材料及低温钻杆的研发现状

随着目前深井和超深井的发展,以及北方、西北地区高寒地带油气井的开发,越来越多的钻杆要求具有抵抗低温或者超低温度的性能需要.低温钻杆成为目前极有发展前景的石油工业技术之一.文中在综述低温材料研究现状的基础上,阐述了低温材料钻杆的工艺现状及其发展趋势.     

Optical fibers with low nonlinearity and low polarization-mode dispersion for terabit communications

Refractive-index nonlinearities have negligible effect on the performance of short-haul fiber-optic communication links utilizing electronic repeaters. However, in long links, nonlinearities can cause severe signal degradations. To mitigate nonlinear effects, a new generation of fibers, referred to as large effective-area fibers, have been introduced in recent years. This paper reviews the latest research and development work on these fibers conducted by several research groups around the world. Attention is focused on a class of large effective-area fibers that are based on a depressed-core multiple-cladding design. Another important issue in long-haul and high capacity fiber optic systems is the polarization-mode dispersion (PMD) which has been recognized as a serious limiting factor. In this paper, an improved fiber design is proposed which, in addition to providing large effective-area and low bending loss, eliminates PMD due to elliptical deformation in the single-mode wavelength region. Furthermore, this design is allowed to provide a small chromatic dispersion about few ps/nmkm, in order to overcome four-wave mixing effects.     

g_1 at low x and low Q^2 with Polarized ep colliders

Measurements of at low x and low are expected to provide a sensitive probe of the transition from Regge to perturbative QCD dynamics, offering a new testing ground for models of small x physics. We discuss the potential of polarized ep colliders (Polarized HERA and eRHIC) to investigate this physics – varying between 0.01 and 1 GeV– and to constrain the high-energy part of the Drell-Hearn-Gerasimov sum-rule for polarized photoproduction. Received: 28 August 2000 / Revised version: 9 November 2000 / Published online: 21 December 2000     

Design and analysis of a wideband photonic crystal waveguide with low group-velocity and low dispersion

The slow light propagation in a line waveguide in the two-dimensional triangular photonic crystal has been numerically studied, based on which a wideband photonic crystal waveguide with low group-velocity and low dispersion is proposed. The numerical simulation analysis shows that it is possible to maximize the group index and minimize the group-velocity dispersion in wide bandwidth by increasing the radius of the basic air hole and changing the position of the first two rows of air holes in photonic crysta...     

常温常压下BiMnO_3纳米粉末的制备与物性分析

钙钛矿型BiMnO3是同时具有铁磁性和铁电性的多铁性材料,在传感器,信息存储等方面具有潜在的应用前景.但是它的制备条件非常苛刻,需要高温、高压、密封等,这极大地限制了它的应用与发展.本文采用共沉淀法,以MnCl2·4H2O,Bi2O3,NaOH,HNO3和聚乙二醇为材料,在100℃的水溶液中成功地制备出了BiMnO3材料,此方法大大降低了制备的温度和压强,从而节约了能源,降低了成本.同时利用X射线衍射仪(XRD),透射电子显微镜(TEM),振动样品磁强计(VSM)等对其结构、相貌及磁性等进行了检测,并讨论了制备条件及煅烧温度对BiMnO3物性的影响.     

采用发射光谱和朗缪尔探针诊断低温低压氢等离子体

 使用发射光谱诊断法和Langmuir探针诊断法,测量了螺旋波激发等离子体化学气相沉积装置中产生的氢等离子体的发射光谱和电流-电压曲线。运用日冕模型和Druyvestey方法,对不同放电参数条件下激发态氢原子密度﹑等离子体密度及电子能量分布的变化规律进行了研究。结果表明：激发态氢原子密度随射频功率增大而增大,随工作气压的增大先增大,后缓慢下降。等离子体密度随射频功率增大线性增大,随工作气压的增加也是先增大,出现峰值后缓慢下降。电子平均能量随射频功率的变化是先增大,后达到平衡;随着工作气压的增大逐渐减小。两种诊断方法得到的结果基本相符。在低温低压等离子诊断中,两种诊断方法结合使用,可以得到更准确和更多的等离子体信息。     

低温低噪声放大器测试平台的结构设计

本文介绍了低温低噪声放大器的应用情况,以及确保它正常工作所需的结构设计方面的一些问题。     

A model for FL and R = FL/FT at low x and low Q2

A model for the longitudinal structure function F_L at low x and low Q² is presented, which includes the kinematical constraint F_L ～ Q⁴ as Q² → 0. It is based on the photon-gluon fusion mechanism suitably extrapolated to the region of low Q². The contribution of quarks having limited transverse momentum is treated phenomenologically assuming that it is described by the soft pomeron exchange mechanism. The ratio R = F_L/(F₂ ? F_L), with the F₂ appropriately extrapolated to the region of low Q², is also discussed.     

A kinetics and dynamics study on the auto-ignition of dimethyl ether at low temperatures and low pressures

Though the combustion chemistry of dimethyl ether (DME) has been widely investigated over the past decades, there remains a dearth of ignition data that examines the low-temperature, low-pressure chemistry of DME. In this study, DME/‘air’ mixtures at various equivalence ratios from lean (0.5) to extremely rich (5.0) were ignited behind reflected shock waves at a fixed pressure (3.0 atm) over the temperature range 625–1200 K. The ignition behavior is different from that at high-pressures, with a repeatable ignition delay time fall-off feature observed experimentally in the temperature transition zone from the negative temperature coefficient (NTC) regime to the high-temperature regime. This could not be reproduced using available kinetic mechanisms as conventionally homogeneous ignition simulations. The fall-off behavior shows strong equivalence ratio dependence and disappears completely at an equivalence ratio of 5.0. A local ignition kernel postulate was implemented numerically to quantifiably examine the inhomogeneous premature ignition. At low temperature, no pre-ignition occurs in the mixture. A conspicuous discrepancy was observed between the measurements and constrained UV simulations at temperatures beyond the NTC regime. A third O₂ addition reaction sub-set was incorporated into AramcoMech 3.0, together with related species thermochemistry calculated using the G3/G4/CBS-APNO compound method, to explore the low-temperature deviation. The new reaction class does not influence the model predictions in IDTs, but the updated thermochemistry does. Sensitivity analyses indicate that the decomposition of hydroperoxy-methylformate plays a critical role in improving the low-temperature oxidation mechanism of DME but unfortunately, the thermal rate coefficient has never been previously investigated. Further experimental and theoretical endeavors are required to attain holistic quantitative chemical kinetics based on our understanding of the low-temperature chemistry of DME.     

Synthesis of corundum structure ITO nanocrystals by hydrothermal process at low pressure and low temperature

The corundum structures of In₂O₃:Sn (ITO) nanoparticles were synthesized by hydrothermal processing of InCl₃ and SnCl₄·5H₂O precursor at low temperature of 250 °C and 40 bar pressure for 3 h. The precursor was precipitated in a white gel of InOOH. After drying at 150 °C in air, it was crystallized in orthorhombic structure. InOOH powder was transformed into dark-gray rhombohedral In₂O₃ by sintering at 420 °C in forming gas for 1 h. The samples were characterized by means of XRD, SEM, and TEM. The particle size of the resulted ITO powder was about 32 nm.     

Soft and hard Pomeron in the structure function of the proton at low x and low Q^2

We study inclusive electroproduction on the proton at low x and low using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model, in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, , proposed by López and Ynduráin. This extension allows to consider both the case and the region of higher on the basis of the same parametrization. A good simultaneous fit to the data on and on the cross section of real photoproduction is obtained for . With four parameters we achieve a for 222 data points. In addition, we use our model of the inclusive interaction to compute the longitudinal structure function . Received: 6 December 1998 / Revised version: 19 April 1999 / Published online: 18 June 1999     

Finite size scaling and low mass glueballs

We propose finite lattice effects as a probe of the glueball mass spectrum, and give an analysis of the recent SU(2) Monte Carlo data of Brower, Nauenberg and Schalk in terms of a gas of free glueballs. For L⁴ lattices with L = 4, 5, 6 fits are made to ξ(m = 1/aξ) which indicate a rather large effective number of degrees of freedom (i.e. statistical degeneracy where a spin J counts as 2J + 1) from 5 to 15 states. As the degeneracy is increased, the central glueball mass increases from $\text{m = (1.3±0.2)}\text{κ}$ at degeneracy 5 to about $\text{m = (1.9±0.2)}\text{κ}$ at degeneracy 15, relative to the SU(2) string tension $\text{κ}$.     

Physics and Astrophysics with low background scintillators

The development and use of low background scintillators offers powerful tools for the investigation of rare phenomena in Physics and Astrophysics. Here main activities and results obtained by means of the DAMA low background set-ups are summarized.Some future perspectives are also mentioned.