对“不良导体导热系数测量”实验中冷却速率求法之我见

张祖寿同志在1990年第2期(《物理实验》发表的《对“不良导体导热系数的测量”实验的研究》中,提出了计算自然冷却速率的一种新方法。文中根据牛顿冷却定律推导出计算冷却速率的理论公式 dT/dτ=1/τ′(T-T_0)1n(T′-T_0)/(T_c-T_0) (1) 式中T_0为环境温度,T_c为开始计时的温度,T′为任一时刻τ′时的温度。只要测得T_c和T′即可由(1)式计算出dT/dτ|_(r=r2)·笔者对此方法持有异见。     

CoGa自旋玻璃的冻结温度与频率的依赖关系

本文报告了β~′相Co_xGa_(1-x)(0.52≤x≤0.56)自旋玻璃的低场交流磁化率的温度关系曲线(温度范围为1.8一40K,频率范围为15—1000或5000Hz);以及直流低场磁化强度的温度关系曲线。实验结果拟会Fulcher定律:τ=τ_0exp[E_a/K(T_f—T_(f_a)],本文对实验结果给出了一个唯象的解释,认为在自旋团玻璃系统中,局域磁矩在T_(f_0)时的取向冻结是平衡的相变过程,但在T≥T_(f_0)的一个小范围内,冻结过程呈现弛豫特性。     

质子辐照对纯铝薄膜微观结构的影响

利用透射电子显微镜(TEM)详细分析了不同剂量的质子辐照纯铝薄膜样品的微观结构, 质子的能量E=160 keV.实验表明,质子辐照能够在Al薄膜中诱发空位位错圈,在实验范围内,位错密度随辐照剂量的增加而增加;质子辐照在1×10¹¹—4×10¹¹/mm²范围内随辐照剂量的增加,位错圈数量密度以及位错圈尺寸都随之增加.在较高剂量6×10¹¹/mm²辐照下,位错圈数量密度减小,但其尺寸显著 关键词： 质子辐照 空位簇缺陷 位错圈 微观结构     

荧光光纤光栅传感特性的实验研究

在载氢掺铒光纤上写入Bragg光纤光栅,得到新型光子学器件-荧光光纤光栅.分别对其Bragg波长（λB）及荧光寿命（τ）的温度（T）及应变（ε）响应特性进行了实验研究,并且给出了λB和τ分别关于（T,ε）的拟合方程.实验结果表明：荧光光纤光栅的λB对T和ε的响应具备一般Bragg光纤光栅的优良特性,测得温度灵敏度为11.1pm /℃,应变灵敏度为1.19pm/με;而且τ对T和ε的响应也具有良好的线性关系,温度灵敏度为0.59 μs/℃,应变灵敏度为6.16 ns/με.实验结论为解决温度应力交叉敏感、实现温度应力的同时监测提供一条新颖的途径.     

有限温度下位错环的脱体现象

在FCC单晶铜中构造了滑移面为（111）,伯格矢量为b=［112］/6的圆形不完全位错环．采用分子动力学方法模拟了该位错环在0—350 K温度区间内的自收缩过程．模拟结果发现：零温度下,位错不能跨越Peierls-Nabarro势垒运动,迁移速度为0;50　K温度下,螺型和刃型位错具有基本相同的迁移速度;随温度增加,刃型位错具有较大迁移速度;温度较高时,位错核宽度进一步增加;小位错环周围的局部应力,引起4个脱体位错环;脱体位错环在原位错的应力作用下逐渐生长,原位错消失后,在自相 关键词： 单晶铜 位错环 分子动力学 位错源     

激光靶等离子体受激Raman散射

用我们研制的一维半电磁粒子模拟程序数值模拟了神光12^#激光器(λ_L=1.053μm,τ=850ps,I_L=3×10¹⁴—3×10¹⁵W/cm²打靶的受激Raman散射。得到了散射光波、静电(Langmuir)波线性增长和非线性饱和的细致图象、热电子和超热电子分布函数随时间的发展以及超热电子的温度和份额。通过对散射光谱的分析得到晕区电子温度约为1.4—2.5keV,还得到靶等离 关键词：     

抑制HMQC实验中与碳-12相连质子的信号

建议了一个新的HMQC实验的脉冲序列,其准备期和混合期分别为90°_x(¹H)-τ/2-180°^x(¹H,¹³C)-τ/2-90°_x(¹H,¹³C)和90°_x(¹³C)-τ/2-180°_x(¹H,¹³C)-τ/2-,以及τ=(2J_CH)^-1(J_CH为C-H偶合常数).在这个新的HMQC实验中,与碳-12相连质子的信号被有效地抑制,其抑制的机理与脉冲的相位循环无关.从而,它可以用于有效地抑制HMQC谱的噪音.特别是,在没有脉冲梯度场装置时,该方法显得非常实用     

α-Fe纯I型裂纹扩展中位错形成过程的三维分子动力学模拟

通过分子动力学方法模拟了三维 α-Fe I型裂纹的单向拉伸实验中的裂纹扩展过程。研究了在不同温度下裂纹扩展时位错的形成过程和断裂机理。计算结果表明,裂纹扩展过程是位错不断发射的过程。 裂纹尖端附近先形成无位错区和层错,当裂纹处应力增加到KI=0.566 MPam1/2时,裂纹尖端附近的某一层原子会逐渐分叉形成两层原子,分层后的原子层继续分离形成位错;当应力KI 达到0.669MPam1/2时第一个位错发射。随着温度的升高,临界应力强度因子逐渐降低,同时位错发射也相应地加快。     

α-Fe纯I型裂纹扩展中位错形成过程的三维分子动力学模拟

通过分子动力学方法模拟了三维 α-Fe I型裂纹的单向拉伸实验中的裂纹扩展过程。研究了在不同温度下裂纹扩展时位错的形成过程和断裂机理。计算结果表明,裂纹扩展过程是位错不断发射的过程。 裂纹尖端附近先形成无位错区和层错,当裂纹处应力增加到KI=0.566 MPam1/2时,裂纹尖端附近的某一层原子会逐渐分叉形成两层原子,分层后的原子层继续分离形成位错;当应力KI 达到0.669MPam1/2时第一个位错发射。随着温度的升高,临界应力强度因子逐渐降低,同时位错发射也相应地加快。     

光学相关论题 空间光学

V242.2 2006043784材料热膨胀系数对太阳电池板应力的影响=Effect ofthermal property on stress distribution in solar panel[刊中]/王晓燕(哈尔滨工业大学.黑龙江,哈尔滨(150001))耿洪滨…∥航天器环境工程.—2006 ,23(1) .—34-38—108—利用解析法研究了材料热膨胀系数对温度场中太阳电池板最大应力的影响。分析结果表明,聚酰亚胺及其相邻的硅橡胶中存在最大拉压力及切应力,选用较低热膨胀系数的聚酰亚胺薄膜可以显著降低结构最大应力值。图参20(严寒)V447 200604378航天光学遥感器信噪比的人工神经网络评价=Assessment of signal-to…     

铝-镁合金的高温变形机构

用变温变速的拉伸试验,研究了Al-3％Mg和Al-6％Mg合金的高温变形行为,求得各温度下的激活能、激活体积和频率因子等。证明在250—400℃温度范围内,铝-镁合金变形机构可能是带割阶的螺位错作非保守性运动,变形方程为ε=Nι_jb²zAνexp{-(△H_s-ι_jb²τ)/(kT)}。然后计算得到两种合金在不同温度下的割阶间距ι_j,运动位错密度ρ=Nι_j,割阶密度N以及位错速度等数值。     

Dislocation dynamics in pulse-loaded NaCl crystals

The mean path l of freshly introduced dislocations in NaCl crystals under the effect of triangular loading pulses τ(t) is shown to depend only on the pulse amplitude τ_m and be insensitive to the rate of stress growth. The replacement of triangular pulses with trapezoidal ones with a constant-load plateau (τ=const) extension of up to 60 min only insignificantly changes the l(τ_m) dependence. The data obtained are interpreted on the basis of the concept of quasi-static relaxation in a nonequilibrium system of dislocations subject to a combined effect of time-dependent applied stresses τ(t), coordinate-dependent internal stresses τ_i(x), and “dry friction” τ_p due to the pinning of dislocations by point defects. In such a model, the l(τ_m) dependence should saturate at τ_m<2τ_p; this is in fact observed in the range of 0.2τ_m<τ_m<0.3τ_y (here, τ_y is the yield stress), which gives an estimate for the pinning stress τ_p≈0.1τ_y. Based on the model suggested, a series of experimentally confirmed predictions were obtained, e.g., a recipe of “switching-off” of anomalies. Thus, a preliminary treatment of the samples by a series of stress pulses or holding in a magnetic field, which transforms the system of fresh dislocations into a more equilibrium state, sharply decreases the density of mobile dislocations quasi-statically responding to a pulsed load. It is shown that the discussed anomalies of dislocation mobility should be observed only in sufficiently pure crystals, where , and should be absent in contaminated crystals, where τ_p ～ τ_y.     

X-ray and magnetic-field-enhanced change in physical characteristics of silicon crystals

The effect of low-energy (W = 8 keV) low-dose ((0.3?C7.3) × 10² Gy) radiation and a dc magnetic field (B = 0.17 T) on structural, micromechanical, and microplastic characteristics of silicon crystals has been studied. The features in the dynamic behavior of dislocations in silicon crystals, which manifest themselves upon only X-ray exposure and combined (X-ray and magnetic) exposure, have been revealed.     

Dielectric response of KCN crystal at ultra low frequencies

The dielectric response of pure KCN crystals (ε′, ε″ and tg σ) has been measured as a function of temperature in the frequency range 10⁻² Hz to 10⁴ Hz. In the antiferroelectric phase the width of the loss peak are found practically independent of temperature (1.4 decades) and close to a Debye behavior; the relaxation time of the CN⁻ dipoles is characterized by an Arrhenius behavior τ = τ₀ exp (U/KT) with τ₀ = 7.26 × 10⁻¹⁵s and U = 0, 147 eV confirming a classical temperature activated reorientation of the dipoles.     

Twinning in boron-ion-irradiated bismuth single crystals subjected to mutually orthogonal electric and magnetic fields

The effect of electric pulses (duration 10⁻⁵ s and current density up to 60 A/mm²) and an external magnetic field (0.2 T) on the behavior of wedgelike twin ensembles in boron-irradiated bismuth single crystals was studied. The irradiation energy and dose were, respectively, 25 keV and 10¹⁷ ion/cm². When the crystals were exposed to the magnetic field, both irradiation and pulse application enhanced the mobility of twinning dislocations. An equilibrium condition for twinning dislocations in the irradiated material simultaneously subjected to the electric and magnetic fields was derived.     

The role of dislocations in radiation strenghtening of alkali halide crystals

The dependence of activation volume and dislocation start stress in sodium and calcium chloride crystals on-radiation dosage (in the range 10⁴–10⁹rad) is studied. It is established that these functions indicate that the hardening of crystals subjected to radiation is of a dislocation nature. Analysis of data from the literature leads to the conclusion that in the medium and high radiation dose region planar precipitates and surrounding dislocations formed by halogen molecules are responsible for hardening.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 99–103, June, 1976.     

Models of the cores of dislocations in metals and disclinations in liquid crystals

The development of dislocation core models in metals with non-close-packed crystalline structure is reviewed. The paper starts with the Peierls-Nabarro model generalized to the case of non-planar cores to describe dislocation splitting in bcc metals. Atomistic studies of dislocations cores in bcc metals and intermetallic compounds with L1₂ and B2 structures are then discussed and the principal features of non-planar cores emphasized. Finally, an analogy between dislocations in solid and disclination in liquid crystals is presented and similarities and differences in the treatment of core structures of these defects in solid and liquid crystals discussed.Dedicated to Dr. Frantiek Kroupa in honour of his 70^th birthday.This work was supported by the U.S.-Czech S & T Program under contract No. 94048, by the National Science Foundation-International Programs, INT-93-07418 and by the Grant Agency of the Czech Republic under contract No 106/93/0513.     

Temperature characteristics of the mechanical properties and of the dislocation structure of molybdenum-rhenium alloys

The temperature characteristics of the yield strength and of the dislocation structure of supersaturated molybdenum-rhenium alloys were studied over the 77–673°K temperature range. A lesser dependence of σ_0.1 on the temperature was found to result from twinning. The mobility of screw dislocations was found to become much lower due to alloying with rhenium. An analysis of the peculiarities in the dislocation structure of the alloys under consideration here (plane pileup, screw dipoles, singularities of interaction between glissile dislocations) has led to the conclusion that the lower mobility of screw dislocations is a consequence of the lower energy of the packing defect in molybdenum alloyed with rhenium. The lattice resistance to a movement of screw dislocations (τ_p) at room temperature has been estimated from the distance between dislocations in screw dipoles and found to be τ_p≥16 kgf/mm².     

Spectroscopy of defects in irradiated alpo 4 and GaPO 4 crystals

The time-resolved luminescence spectra in energy region of 2.0-6.0 v eV, as well as the excitation spectra (4-35 v eV), reflectivity and the decay kinetics were studied at T =10 v K and 295 v K using selective vacuum ultraviolet excitation in nominally pure crystals as well as crystals with intrinsic defects and radiation defects induced by fast electrons.     

Kinetics of accumulation of vacancy complexes in dislocated silicon under 60Co γ-ray irradiation

Abstract

Radiation defect accumulation in ⁶⁰Co γ-ray-irradiated n-type Si single crystals (ρ=150ωcm) with various densities of dislocations (N_D = 1 × 10⁴ to 1 × 10⁷ cm ^?2) introduced at plastic deformation was studied. The temperature dependences of the Hall coefficient were measured. The probabilities of interaction of vacancies with oxygen, phosphorus atoms, and dislocation line elements were determined. It has been established that with the increase of N_D they can increase at the expense of complication of dislocation structure, decrease during formation of impurity atmosphere near dislocations and compensation of deformation fields, and they do not change if complex formation of vacancies with impurities occurs far from dislocations. Kinetics of A- and E-centre accumulation in the crystals containing dislocations with different impurity atmosphere was described.