共查询到20条相似文献,搜索用时 21 毫秒
1.
一定浓度的Pd掺杂能够有效地提高Ni Ti合金的相变温度,并且降低热滞.为了解其作用机理,采用第一性原理计算方法,对不同Pd掺杂浓度下Ni Ti合金(Ni24-n Pd n Ti24,n=2,3,4,5,6,9,12;掺杂浓度分别为4.2 at.%,6.3 at.%,8.4 at.%,10.4 at.%,12.5 at.%,18.8 at.%,25 at.%)的相稳定性和结构特性进行计算讨论.马氏体相变温度可以通过奥氏体与马氏体两相能量差值进行分析,且能量差越大相变温度越高;相变过程中两相晶格常数之比越接近于1则热滞越接近于0.计算结果表明:当掺杂浓度小于10.4 at.%时,B19′是最稳定的马氏体相,体心四方(BCT)结构与B19′相的能量差随掺杂浓度的增加略有下降;当掺杂浓度大于等于10.4 at.%时,B19相是最稳定的马氏体相,BCT与B19的能量差随着掺杂浓度增加显著升高.这意味着在掺杂浓度大于等于10.4 at.%时相变温度随掺杂浓度的增加而显著增加.用几何模型分析了马氏体相变的热滞,结果表明掺杂浓度为10.4 at.%时B2到B19相的相变过程热滞最小,与实验结果一致. 相似文献
2.
为了研究二极管爆炸电子发射初始阶段阴极表面复杂的物理现象及规律, 建立了由场致电子发射阴极构成的一维平板真空二极管物理模型,通过自行编程数值求解泊松方程, 考虑了发射出的电子对阴极表面电场的非线性影响,自洽模拟得到了阴极表面电场随时间的变化情况. 模拟结果表明,爆炸电子发射初期,阴极表面电场随时间的增加而呈现出不断振荡的规律, 且振荡幅度越来越小,最终到达一个稳态的值,二极管两极板之间的外加电场越大, 阴极表面稳态电场的绝对值越大;电场增强系数越大,阴极表面稳态电场的绝对值越大. 在整个时间演变过程中,阴极表面的实际电场强度决定着阴极发射的电流密度大小, 反过来阴极发射的电流密度又会影响到阴极表面的电场. 相似文献
3.
Summary A thermodynamic calculation of the Fe−Cr−Ni phase diagram suggests that the composition 30 at.%Cr-5 at.%Ni is expected to
be found inside the spinodal line, whereas 16 at.%Cr-5 at.%Ni is expected outside at 723 K. These two alloys have been thermally
aged for time periods up to 40 minutes at 723K. A significant broadening of the magnetic-hyperfine-field distribution indicates
that Fe-30 at.%Cr-5 at.%Ni undergoes typical spinodal decomposition in agreement with the calculation. Spinodal decomposition
is distinguished from nucleation-growth by a detailed analysis of the magnetic-hyperfine-field distribution.
Paper presented at ICAME-95, Rimini, 10–16 September 1995 相似文献
4.
5.
A comparative study of myo-inositol quantification using LCmodel at 1.5 T and 3.0 T with 3 D 1H proton spectroscopic imaging of the human brain 总被引:2,自引:0,他引:2
Myo-inositol is a strongly coupled system and resonates at four chemical shift positions. At 1.5 T, only the singlet component at 3.57 ppm is detected. However, at 3 T this resonance is resolved into its components at 3.55 ppm and 3.61 ppm. Due to the increased spectral resolution and signal-to-noise ratio, it is anticipated that the quantification of myo-inositol should improve at 3 T. Using data from normal controls and the LCmodel quantification procedure, we found that the quantification precision, reproducibility and detection sensitivity of myo-inositol is significantly better at 3 T relative to 1.5 T. 相似文献
6.
7.
8.
研究了人肝的癌变及热凝固导致其对710,730,750,770,790,810,830,850,870和890 nm的钛宝石激光的吸收和散射特性的变化,实验采用双积分球测量系统以及反向倍增法获取肝组织的吸收和散射特性参数.结果表明:人肝的癌变导致其吸收系数发生了显著的减小,其变化的最大值在850 nm,其值为86.12%,而变化的最小值在750 nm,其值为82.65%.正常人肝组织热凝固导致其吸收系数明显变化,其吸收系数的变化的最大值在710 nm,其值为79.55%,而变化的最小值在790 nm,其值为0.72%.人肝癌组织热凝固导致其吸收系数显著地增大,其变化的最大值在810 nm,其值为78.69%,而变化的最小值在710nm,其值为38.16%.人肝的癌变导致了肝组织的散射系数发生了显著的增大,其变化的最大值在710 nm,其值为158.37%,而变化的最小值在890 nm,其值为136.03%.正常人肝组织热凝固导致其散射系数显著地增大,其变化的最大值在890 nm,其值为632.92%,而变化的最小值在710 nm,其值为587.40%.人肝癌组织热凝固导致其散射系数显著地增大,其变化的最大值在810 nm,其值为384.25%,而变化的最小值在710 nm,其值为330.86%.肝组织的吸收和散射特性的变化也随着激光波长的变化而变化. 相似文献
9.
10.
以浅海声传播模型为基础,通过计算机仿真观察到以下物理现象:浅海中海底水平线列阵的匹配场定位性能优于其他深度水平线列阵.利用简正波建模方法揭示了这一现象的物理机理.按照简正波理论,各号模式的形状是海水深度的函数.通过比较不同深度上各号模式幅度的变化,发现海底模式幅值接近零的模式号数明显小于其他深度.这说明海底水平线列阵可以对更多号模式进行采样,进而获得更多的目标声源信息,取得更好的匹配场定位效果.
关键词:
水平线列阵
匹配场定位
基阵深度 相似文献
11.
原位漫反射红外光谱研究SAPO-34分子筛的吸附性能 总被引:4,自引:1,他引:3
采用漫反射红外光谱原位考察了298-773K范围H2O,NH3和NO在SAPO-34分子筛上的吸附行为结果表明,SAPO-34对水的吸附是可逆的,对NH3和NO的吸附则是不可逆的。吸附水在623K完全脱附,脱水后的分子筛在3625-3600cm^-1出现表征桥式羟基(Si-OH-Al)的特征峰。发现SAPO-34对NH3和NO均有良好的吸附-催化活性。吸附NH3后,桥式羟基消失,位于3135,3032和1399cm^-1处在423K时出现三个吸收峰,在673K达最大,且峰高分别是SAPO-34骨架峰高的3.9,1.7和6.7倍;吸附NO后,在室温下位于1364cm^-1也观测到一强而尖锐的峰,其强度与骨架峰强度相当。对这些峰进行归属表明,吸附NH3和NO后产生了新的物种NO3^-。 相似文献
12.
13.
通过计算给出了在LHC能区非对心核 核碰撞中由椭圆流ν2 表示的高横动量直接光子的方位角不对称性。该高横动量光子是由喷注与热密介质相互作用而辐射出来的。光子椭圆流与强子椭圆流ν2 相差π/2的相位, 是直接光子椭圆流中负值的来源。同时, 计算表明LHC能区直接光子ν2随粒子横动量pT的变化趋势与RHIC上的实验结果一致, 但LHC能区较RHIC能区有更低的直接光子流ν2 值, 且ν2 值由负到正对应的转换pT值更高。这表明在LHC能区喷注淬火效应更为明显, 表面发射的直接光子对光子椭圆流的贡献份额增强。The azimuthal anisotropy of high pT direct photons is investigated by using the coefficient of elliptic flow ν2 in non-central nucleus-nucleus collision at LHC energies. These photons come from radiation induced by the interaction between jet and hot/dense medium. The azimuthal anisotropy of high pT direct photons is investigated by using the coefficient of elliptic flow ν2 in non-central nucleus-nucleus collision at LHC energies. These photons come There is π/2 difference between direct photons and hadrons for the azimuthal elliptic flow ν2. Such photons are the main source of the negative part of ν2 for direct photons. The dependence of the direct photon ν2 on the transverse momentum pT at LHC energy is found to be consistent with the experimental results at RHIC energy. Furthermore, we find that the value of the direct photon ν2 at LHC energy is smaller than that at RHIC energy. The value of the transverse momentum at which the direct photon ν2 changes from negative value to positive at LHC is higher than that at RHIC. It’sfound the enhanced jet quenching effect and enhanced contribution for the elliptic flow ν2 of the direct photons emitted from surface at LHC energy. 相似文献
14.
利用低频光通信波段真空压缩态光场可实现基于光纤的量子精密测量.本文利用简并光学参量振荡器实验制备出1550 nm低频真空压缩态光场.在分析频段10—500 kHz范围内压缩态光场的压缩度均达3 dB.用实验制备的1550 nm真空压缩态光场填补光纤马赫-曾德尔干涉仪的真空通道,实现了量子增强型光纤马赫-曾德尔干涉仪,完成了突破标准量子极限的相位调制频率为500 kHz的低频信号测量.与光纤马赫-曾德尔干涉仪相比,测量信噪比提高了2 dB. 相似文献
15.
A simple method is proposed to dispose the quantum effect and anharmonic effect at the same time. Considering the quantum effect is remarkable only at low temperature, and tends to zero at high temperature, the potential energy of an atom is expanded harmonically to consider the quantum effect of solids within the harmonic oscillator framework. The anharmonic effect is remarkable only at high temperature, and tends to zero at low temperature, it was disposed by using a classical approximation. The universal formalism is applied to the generalized Lennard-Jones solid. The comparison shows that the results with and without anharmonic effect are in agreement with each other at some low temperature, to which the Einstein model is applicable. The results without anharmonic effect become divergent at slightly higher temperatures; however, the results including anharmonic effect are in good agreement with the experimental data of solid xenon. The method proposed in this paper can be extended to other potentials to develop practical molecular thermodynamic equations of state for solids. 相似文献
16.
The focusing performance with a horizontal time- reversal array at different depths in shallow water 下载免费PDF全文
The performance of time-reversal focusing with a horizontal line array at different depths is investigated by normal mode modeling and computer simulation.It is observed that the focusing performance of a bottom-mounted horizontal time-reversal array is much better than that of a horizontal time-reversal array at other depths in shallow water.The normal mode modeling is used to explain this result.The absolute values of the modes at different depths are compared.It is shown that the number of modes whose absolute values close to zero is smaller at the bottom than that at other depths.It means that the horizontal time-reversal array deployed at the bottom can sample more modes,obtain more information of the probe source and achieve better focusing performance.The numerical simulations of time-reversal focusing performance under various conditions,such as different sound speed profiles,and different bottom parameters,lead to similar results. 相似文献
17.
拉曼-光荧光光谱热壁外延生长GaAs/Si薄膜晶体质量研究 总被引:3,自引:2,他引:1
本文研究了用热壁外延(HWE)技术在Si衬底上,不同工艺条件生长的GaAs薄膜的拉曼(Raman)和光荧光(PL)光谱。研究表明,在室温下,GaAs晶膜的拉曼光谱的265cm^-1模声子(TO)峰和290cm^-1纵声子(LO)峰的峰值和面积之比随晶膜质量的变化而逐渐变大,FWHM变窄且峰值频移变小,而PL光谱出现在900nm光谱的FWHM较窄,这表明所测得的薄膜为单晶晶膜,在另外一些工艺条件下生长的GaAs薄膜拉曼光谱峰形好,但测不出PL光谱,所生的膜不是单晶,同时对同一晶膜也可判断出其均匀程度,因此我们可以通过拉曼光谱和荧光光谱相结合评定外延膜晶体质量。 相似文献
18.
A theoretical investigation of the use of normal incidence ultrasonic reflection measurements for the detection and characterization of thin layers embedded between two much thicker media has been carried out. It has been shown that the form of the relationship between the normal incidence longitudinal reflection coefficient and frequency is defined by the reflection coefficients at zero frequency and at half the resonance frequency of the layer. The reflection coefficient at zero frequency is solely a function of the impedances of the media on either side of the layer, while that at half the resonance frequency of the layer is a function of the impedances of all three media. In general, the sensitivity of the reflection coefficient to the presence of the layer increases as the product of frequency and layer thickness increases, the maximum sensitivity being at half the resonance frequency of the layer. Unfortunately, with thin layers, it is generally not practical to test at this frequency. However, the reflection coefficient curve can, in principle, be reconstructed from data measured at lower frequencies and the sensitivity of the reflection coefficient at lower frequencies to the characteristics of the layer can be predicted from the sensitivity at half the resonance frequency. The sensitivity is also critically dependent on the relative impedances of the three media and is generally greatest when the half spaces on either side of the layer have the same impedance. With favourable impedances, it is possible to detect layers whose thickness is a small fraction of the wavelength of the ultrasonic waves employed. However, with other combinations of impedances, the detection of much thicker layers is not possible. 相似文献
19.
The Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) states, characterized by Cooper pairs condensed at finite-momentum are, at the same time, exotic and elusive. It is partially due to the fact that the FFLO states allow superconductivity to survive even in strong magnetic fields at the mean-field level. The effects of induced interactions at zero temperature are calculated in both clean and dirty cases, and it is found that the critical field at which the quantum phase transition to an FFLO state occurs at the mean-field level is strongly suppressed in imbalanced Fermi gases. This strongly shrinks the phase space region where the FFLO state is unstable and more exotic ground state is to be found. In the presence of high level impurities, this shrinkage may destroy the FFLO state completely. 相似文献