Fe77Cr7B16非晶晶化过程的正电子寿命谱研究

用正电子湮没技术研究了Ｆｅ７７Ｃｒ７Ｂ１６非晶晶化过程。根据平衡寿命τ、寿命τ１τ２及其强度Ⅰ１、Ⅱ２随退火温度的变化，讨论了Ｆｅ７７Ｃｒ７ｂ１６非晶的热稳定性和晶化发生后样品微结构对居里温度Ｔｃ的作用。     

纳米ZrO2的电子顺磁共振特性及其表面效应

用ＢＥＴ（氮吸附法），ＴＥ几ＸＲＤ技术测定了纳米ＺｒＯ２粉的比表面积、粒径、晶粒尺寸以及相结构随煅烧温度的变化、纳米ＺｒＯ２粉具有Ｆｓ－ｃｅｎｔｅｒ和Ｚｒ＾３＋两种电子自旋共振（ＥＳＲ）信号，Ｚｒ＾３＋是一个与体相相关的信号，而Ｆｓ－ｃｅｎｔｅｒ信号强度减弱，而Ｚｒ＾３＋信号强度增强，变化的临界尺寸为１６ｍ＾２．ｇ＾－１，当比表面积小于１６ｍ＾２．ｇ＾－１时，Ｆｓ－ｃｅｎｔｅｒ信号消失，而Ｚｒ＾３     

有环绕声效果的超低音电路

通常,便携式或小型分箱式收录机以及一般组合音响其输出功率有限,在聆听环境中也并非常可将音量开得很大。一些比较高档的唱机或激光唱机虽然其低频重放频率可低达30Hz直至20Hz,但一般小型音响重视这些频段信息十分困难:小音量时频带窄,低频成份显著缺乏,声音出不来,必须增大音量才能使音色丰满厚实,突出有力,这是由于人耳本身生理特性所决定的。人耳听觉对声音的强弱变化的主观感觉(即响度)与声压、频率均有密切关系,这种关系即人耳等响度曲线效应,简言之,人耳对3～4kHz的感觉最灵敏,当频率在这频段向两边延伸时,听觉逐渐迟钝。响度水平…     

复合钙钛矿Pb（Fe1／2Nb1／2）O3的弛豫特性

制备了纯钙钛矿相Ｐｂ（Ｆｅ１／２Ｎｂ１／２）Ｏ３（ＰＦＮ）陶瓷，研究其介电性能表明，ＰＦＮ陶瓷无论退火与否都存在弥散性相变（ＤＰＴ）现象，未退火试样εｍａｘ对应的温度Ｔｍ不随测量频率变化，退火试样的Ｔｍ随频率变化，即表现出Ｔｍ频率色散现象，结合ＸＲＤ分析，指出ＰＦＮ应属弛豫铁电体。     

动态光散射法研究海藻酸钠凝胶化行为

用动态光散技术跟踪了海藻酸钠水溶液在０．１ｍｏｌ／ＬＣａＯｌ２水溶液中透析凝胶化的过程。表现出随反应进行，平均衰减速率（线宽）Γ明显减慢及以１ｇβ＾１／２ｇ（１）（τ）对τ作图表明体系运动模式复杂的特点，这里ｇ＾（１）（τ）和τ分别是归一化电场时间相关函数及延迟时间。最后还以平均等征松驰时间＾－τｃ（≡Γ＾－１）对透析时间ｔ作图，定量描述了该凝胶化反应的动力学过程。     

快速富立叶变换在爆破分析中的应用

美国矿务局开发成功一种计算机软件，应用快速富立叶变换方法（ＦＦＴ）估算双数据。这种软件可用来估算：１）地面振动时间变化数据的频率成分；（２）起爆器起爆时间的分散对地面振动频率谱的影响；３）照片来估算岩石爆堆的破碎分布。在完成１）、２）两项工作中使用的是一维软件，使用了Ｍｏｎｔｅ Ｃａｒｌｏ方法来模拟起爆器的分散。计算结果表示成计算机制的三维彩色轮廓图。为了采用照片数字图象技术，确定破碎块的大小分布     

耳声阻抗的数值校测及其与频率的关系

本工作用耳声阻抗测定探头，在接口的长短和直径不同的条件下对等效声顺校正腔进行了实测和比较。当频率低于５００赫时阻抗探头电输出与声顺等效容积间的变化是单调函数关系，８００赫以上则呈“Ｖ”形。接口长短在０—５毫米和直径在１一２毫米范围内变化时，低频的校正误差最大可达０．４毫升，高频的误差更大。校正腔接口的长短和直径都以选用２毫米较为适宜。此外还对国内外五种不同的校正腔进行了比较。     

FeS2薄膜的制备和性能

研究了不同热硫化条件下用纯Ｆｅ膜反应形成的ＦｅＳ２多晶薄膜成分、结晶形态和电阻率的变化规律，结果表明，在４００℃等温２０～３０ｈ时，生成的ＦｅＳ２比较充分，薄膜中的Ｆｅ、Ｓ含量接近ＦｅＳ２计量成分，随硫化温度升高，ＦｅＳ２晶粒明显增大，电阻率显著上升，当在４００℃硫化充分形成ＦｅＳ２晶粒后，继续延长等温时间对组织形态无明显影响。     

磁流变液的流变学性质研究

用球形羧基铁颗粒、硅油和油酸制备了磁流变液（ＭＲＦ），该ＭＲＦ不加外磁场是就呈现非牛顿性，ＭＦＲ的剪切应力τ随剪切率γ的变化关系为一曲线，其表观粒度ηａｐ随剪切速度的增大而减小，在外磁场作用作用，ＭＲＦ的ηａｐ迅速增大两个数量级，ＭＲＦ呈现一定的屈服应力τｙ＝９４．７Ｐａ，当τ〉τｙ后，ＭＲＦ的流变特性满足Ｂｉｎｇｈａｍ模型。     

CSF－1R激酶突变子的构建及其突变体在真核细胞的表达

通过ＰＣＲ二步法，构建了ｍＣＳＦ－１Ｒ激酶负性突变子，以及野生型和突变型ＣＳＦ－１Ｒ的送病毒表达载体ｐＣＥＮ／ＭＰＳＶ。进行了１２５Ｉ－ＣＳＦ－１受体结合分析：检测了激酶负性突变子，删除了ＣＳＦ－１ＲＣ－末端氨基酸９２５以后部分的突变体（ＣＴＲＵＮＣ９２５）和删除了激酶插入区的突变体（△ＫＩ）在３２Ｄ髓细胞表达。表达水平可达１～２×１０４受体／细胞。初步测定了通过ＣＳＦ－１Ｒ所介导的促细胞分裂效应。     

The role of dopants in tailoring the microwave properties of Ba6-xR8+2/3x Ti18O54 R = (La–Gd) Ceramics

Microwave dielectric ceramics with a high dielectric constant need to satisfy very high technical demands. They should possess extremely low losses to achieve high Q-values (Quality factor) a small temperature coefficient of resonant frequency (τf), and a relative permittivity (εr) higher than 80. Industrial applications require very stringent electrical and dimensional tolerances, typically ± 0.5–1.0 ppm K-1 for a specified τf and ± 0.25% for a specified εr. To meet such requirements ceramics based on BaO–R2O3 – TiO2 (R = La–Gd) are used. The investigation of this type of ceramic was stimulated by the observation that ceramics based on compositions in the TiO2-rich region of the system exhibit highly temperature stable electrical properties. Especially interesting are compositions within the solid solubility region with the general formula Ba6-xR8+2/3x Ti18O54. As the ionic radius of the rare earth decreases the extent of the solid solubility region becomes narrower, i.e., 0<x<3 for La and x = 0.5 for Gd. Further improvements in the dielectric microwave properties can be achieved by combining different rare earth oxides, and by partial replacement of Ba2+ with other alkaline earth atoms such as Ca2+ and Sr2+. Typically such ceramics meet the requirements for Q and εr; however, τf must be additionally adjusted by the use of dopants. Most commonly bismuth and lead oxides or titanates are used. In the present contribution the role of different dopants and their influence on the resulting microwave dielectric properties of Ba6-xR8+2/3x Ti18O54 based ceramics are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Viscous oscillations in a circular cylinder with an elastic cover on the free surface

The effects of an elastic membrane on the viscous oscillations of liquid filling a circular cylindrical container are studied by using the natural viscous complex eigenfunctions of the problem. The free surface of the liquid is assumed to be fully covered by the membrane. By projecting the governing equations onto an appropriate basis, a nonlinear eigenvalue problem for the complex frequencies is obtained. This is then solved to obtain the modal frequencies as a function of the Reynolds number Re, the tension parameter τ, the mass parameter ζ and the liquid depth h. The zero velocity conditions on both the side and bottom walls are satisfied unlike in earlier studies where either only the sidewall or only the bottom wall conditions were met. Results are presented for the four lowest non-axisymmetric modes as a function of Re, h, τ and ζ. The elastic cover increases the slosh frequencies but only in comparison with an uncovered free surface with a contact line that is free to move; the frequencies are lower when compared with those of a free surface with pinned contact line. There are ranges of Re, h, τ and ζ for which the oscillations are overdamped and the sloshing is aperiodic. Though the frequencies and damping rates decrease for an increasing mass of the elastic cover, there exist ranges of Re, h and τ for which the heavier cover produces higher slosh frequencies.     

Low-frequency fluctuations with 1/<Emphasis Type="Italic">f</Emphasis><Superscript>α</Superscript> power spectrum in transient modes of water boiling on a wire heater

The investigation of transient modes of water boiling on a wire heater reveals the presence of random vibrations with the frequency dependence of power spectra of S ∼ f ^−α, where the exponent α has values in the range 0.8 ≤ α < 2. Large-scale low-frequency fluctuations exhibiting the property of scale invariance, the duration of which is distributed by the power law P ∼ τ^−β, are present in experimental realizations of random processes describing thermal fluctuations. The properties of such fluctuation processes are described using two nonlinear stochastic differential equations which describe the interaction between different phase transitions. Relations of dynamic scaling are determined between the critical exponents which define the frequency dependence of the power spectra of fluctuations α and of the distribution function of the amplitudes of extreme low-frequency fluctuations β. It is demonstrated that the critical exponents are related by the relation α + β = 2 both in the experiments and in the theoretical model of interacting phase transitions. The power spectra of fluctuations are determined in the experiments with greater simplicity and accuracy than the distribution function of extreme amplitudes. In the cases where only the spectral dependence of power spectra of fluctuations is known, the correlations between the exponents enable one to obtain information about the distribution of large-scale surges and estimate dangerous amplitudes.     

Acoustic Modes and Momentum Relaxation in 2D Atomic Hydrogen on Helium Surface

Seeking for manifestations of superfluidity in 2D spin-aligned atomic hydrogen (H↓) adsorbed on the surface of liquid helium at T∼0.1 K we consider possible acoustic modes in this 2D Bose gas depending on frequency and on characteristic times of energy and momentum transfer. At high frequencies, the analogues of ordinary and second sound are realized in 2D H↓. At low frequencies, the 2D analogue of the fourth sound is realized: the normal component of hydrogen and ripplons are immobile and only the superfluid component of hydrogen participates the oscillations. We also estimate the rate of momentum relaxation between superfluid hydrogen and ripplons, τ _HR⁻¹ ∝ T ^13/3. The most promising for observing the superfluidity in 2DH↓ is the fourth sound, which could be excited, e.g., by ESR.     

Evolution of homogeneous turbulence in a density-stratified medium. 1. Analysis in far field

The equations presented in [1] for the evolution of homogeneous turbulence in a density-stratified medium are investigated analytically. The problem involves the small parameter ε = Fr². Applying variants of the small-parameter method, it is possible to calculate the frequency of internal waves and a number of asymptotic regimes in the development of turbulent velocity and scalar fields over time. The so-called far field of evolution, i.e., the field of large values of τ (τ ≫ 1, is considered, in which the differential order of the initial system of equations is lowered. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 30–39, January–February, 1997.     

Effect of dopants on the low temperature microwave dielectric properties of Ba(Zn1/3Ta2/3)O3 ceramics

Ba(Zn_1/3Ta_2/3)O₃ has been prepared with different dopants that gave best microwave dielectric properties at room temperature. Effects of different dopants on the low temperature microwave dielectric properties of BZT were investigated. With decrease in temperature, loss tangent was found to decrease marginally and then increase at temperatures lower than 100 K. Increase in loss factor at lower temperatures were found to be less for dopants with smaller ionic radii. Dielectric constant was found to be almost independent of temperature. Temperature coefficient of resonant frequency slowly decreased from a positive value to negative value when temperature was lowered. Temperature at which τ_f becomes zero was found to vary for different dopants. There is a temperature stable region for tanδ, ɛ_r and τ_f which varies for different dopants.     

Composites and solid solutions of Pr–Y titanium tantalate microwave ceramics

Pr _x Y_1−x TiTaO₆ solid solutions were prepared through the solid state ceramic route. The materials were sintered in the range 1,525–1,600 °C. The structure of the system was analyzed by X-ray diffraction methods. The scanning electron microscopic images show the co-existence of two phases in the composite. The dielectric constant (ε_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q _u) are measured in the microwave frequency region using cavity resonator method. The dielectric constant (ε_r) varies from 17.6 to 39.6 and temperature coefficient of resonant frequency (τ_f) from −52.2 to +55.9 ppm/°C. These variations are in accordance with the structural variation. Very low temperature coefficient of resonant frequency and high quality factor were obtained for x = 0.2, 0.23 and 0.24 and are useful materials for practical applications.     

Is the Two Dimensional Organic Conductor, τ-(EDO-S,S-DMEDT-TTF)2(AuCl2)1+y Clean or Dirty?

The transport properties of organic τ-type conductors seem to be very clean as well as very dirty depending on what we observe. To clarify this problem, we studied temperature and magnetic field dependence of resistivity, ρ(T, B), in τ-(EDO-S,S-DMEDT-TTF)₂(AuCl₂)_1+y. The properties that favor “probably dirty” are: i) stepwise ρ_a(T) increase below 20 K, which is suppressed by magnetic field, and ii) contrasted difference in ρ(T) as well as magnetization M(T) between field cooled (FC) and zero field cooled (ZFC). On the other hand, Shubnikov de Haas oscillations with very low Dingle temperature (T_D = 1.5 K) are typical of clean system. Based on these observations, we conclude this system changes from “dirty” to “clean” system by increase of magnetic field.     

Is the two dimensional organic conductor, τ-(EDO-S,S-DMEDT-TTF)2(AuCl2)1+y clean or dirty?

The transport properties of organic τ-type conductors seem to be very clean as well as very dirty depending on what we observe. To clarify this problem, we studied temperature and magnetic field dependence of resistivity, ρ(T, B), in τ-(EDO-S,S-DMEDT-TTF)₂(AuCl₂)_1+y. The properties that favor “probably dirty” are: i) stepwise ρ_a(T) increase below 20 K, which is suppressed by magnetic field, and ii) contrasted difference in ρ(T) as well as magnetization M(T) between field cooled (FC) and zero field cooled (ZFC). On the other hand, Shubnikov de Haas oscillations with very low Dingle temperature (T_D=1.5 K) are typical of clean system. Based on these observations, we conclude this system changes from “dirty” to “clean” system by increase of magnetic field.     

Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C,B, and rare earth elements

MnAl alloys are attractive candidates to potentially replace rare earth hard magnets because of their superior mechanical strength, reasonable magnetic properties, and low cost. In this study, the phase transitions and magnetic properties of melt spun Mn₅₅Al₄₅ based alloys doped with C, B, and rare earth (RE) elements were investigated. As-spun Mn–Al, Mn–Al–C, and Mn–Al–C–RE ribbons possessed a hexagonal ε crystal structure. Phase transformations between the ε and the L1₀ (τ) phase are of interest. The ε → τ transformation occurred at ~500 °C and the reversed τ → ε transformation was observed at ~800 °C. Moderate carbon addition promoted the formation of the desired hard magnetic L1₀ τ-phase and improved the hard magnetic properties. The Curie temperature T _C of the τ phase is very sensitive to the C concentration. Dy or Pr doping in MnAlC alloy had no significant effect on T _C. Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially J_S. Doping B could not enhance the magnetic properties of MnAl alloy since B is not able to stabilize either the ε phase or the L1₀ hard magnetic τ phase.