木材微结构对其传热特性影响的实验研究

对落叶松和红松的试样进行了剖面结构的扫描电镜观察,图片显示在木材内部有非常明显而规则的多孔结构。通过实验测量了不同含水率的木材试样在20-200℃范围内的导热系数,并根据其多孔结构的特点对木材的传热特性进行了理论分析。结果表明,木材微结构的不同对其传热特性有显著影响,木材多孔部分在整个传热过程中起重要作用。木材的传热特性随着其多孔部分的孔隙分布和孔隙大小的不同而变化,在相同含水率的情况下,孔隙率高而孔隙小的木材传热能力较弱。     

含棉冰材料在低应变率下的抗压性能

航空飞行器在飞行过程中不可避免地受到冰雹冲击的威胁,严重危害航空器的飞行安全。目前,天然冰材料的冲击特性尚不明确,为此,依据ASTM F320-21标准《航空与航天透明外壳冰撞测试》,研究了不同应变率下天然冰材料的力学性能。天然冰相对于人工冰雹具有密度低、强度高的特点,结合冰雹制备标准,制备了含棉纤维质量分数为0、3%、6%、12%的冰柱试样。利用万能试验机对冰试样进行应变率分别为10^-4、10^-3、10^-2 s^-1的压缩实验,分析了棉纤维质量分数与应变率对冰试样压缩力学性能的影响,以及破坏形式与临界应变能密度的关系。结果表明：透明冰在应变率约为10^-3 s^-1时由韧性向脆性转化,且添加棉纤维有助于提高冰的压缩屈服强度,在压缩过程中表现出“裂而不碎”的现象;在准静态压缩下,两种冰模型破坏时转化为裂纹表面能所需的能量均比转化为塑性能所需的能量更少。     

碳水混合物冲击压缩特性的理论研究

 采用固-液双相混合模型和分子流体的微扰变分统计理论,分别计算了石墨-水体系（ρ₀=1.233 g/cm³）和金刚石-水体系（ρ₀=1.238 g/cm³）的冲击压缩特性。结果表明：（1）在不发生石墨→金刚石相变和化学反应的低压区域（p<20 GPa）,这两种混合体系的冲击压缩曲线的差别并不明显;（2）在发生石墨→金刚石相变的高压区域（p>20 GPa）,这两种混合体系的冲击压缩曲线显著不同,且石墨-水体系更易压缩;（3）在45～60 GPa强冲击压力范围内,冲击波诱发的化学反应也不会显著影响这两种体系冲击压缩曲线的走势。上述结论与文献（高压物理学报,1999,13(2):87-92）发表的实验结果相矛盾。进一步分析了引起理论与实验结果不一致的可能原因,并对文献中的实验结果及其理论分析结论提出质疑。     

自动校准的多相状态方程建模方法及其在锡中的应用

状态方程与描述能量、动量、质量守恒的偏微分方程一起，构成了可求解材料动态压缩行为的完备流体力学方程组。动态压缩下，相变会导致材料内能、密度、强度等物理性质的不连续变化，需要构建多相状态方程模型才能精确描述这些变化。通过多相状态方程模型的自动组装，采用计算机智能优化算法自动校准状态方程模型参数，发展了自动化的多相状态方程建模程序AEOS(automated equation of state)。利用AEOS，构建了锡的3套状态方程模型，3套模型的计算结果与相关实验结果基本一致，验证了AEOS程序的适用性。将构建的状态方程模型应用于一维流体力学模拟，发现锡冲击到17 GPa再等熵卸载到常压的压力-温度路径会经过β相-体心四方相-液相三相点，并且可以很好地解释在15.4 GPa的冲击压力下锡的微喷颗粒呈现固-液混合态的实验现象。AEOS的良好表现证明其在大型数字化科研平台以及高通量材料物性计算中将具有广泛的应用前景。     

40GPa压力范围内铜和铝的准等熵压缩线

 基于自行研制的磁驱动准等熵压缩加载实验装置CQ-1.5,利用全光纤位移干涉仪（Doppler Pins System, DPS）、激光速度干涉计（Velocity Interferometer System for Any Reflectors, VISAR）两种测试手段,以及反积分数据处理方法,实验测量了40 GPa压力范围内T1铜、LY12硬铝和L1纯铝3种材料的准等熵压缩线,将实验准等熵压缩线与基于Grüneisen状态方程的理论等熵压缩线和冲击Hugoniot线进行了比较。结果表明,在该压力范围内,实验准等熵压缩线与理论等熵压缩线相一致,两者偏差小于3%;实验准等熵压缩线靠近冲击Hugoniot线,位于其下方,与国外文献发表的结果相同,进一步表明,实验测量结果正确可靠。     

LiTaO3晶体高压结构相变的理论研究

利用基于密度泛函理论的平面波赝势结合局域密度近似的从头算方法,计算了LiTaO3晶体在0~200 GPa压力范围内的冷压曲线(P-V/V0)和零温焓,以研究它的高压结构相变.参照同构体LiNbO3的高压相结构,对LiTaO3的菱形相(R3c对称群,室温大气压结构)和正交相(Pbnm对称群)进行计算.结果表明,菱形相压缩线与低压冲击实验数据和静压结果符合较好,而正交相压缩线与扣除热压贡献的高压冲击实验数据相符;正交相更难压缩且各轴向的压缩率不同,对应的常态密度比菱形相高约24%.理论预测的相变起始压力约为23 GPa.由此可见LiTaO3的冲击高压相具有正交对称性,与LiNbO3的室温高压相类似.     

碳水混合物相互作用势及混合法则的实验研究和理论探索

 利用二级轻气炮加载技术研究了碳水混合物的冲击压缩特性。研究发现：冲击压力p低于19.0 GPa时,石墨与水混合物冲击压缩特性明显不同于金刚石与水混合物的冲击压缩特性;p大于23 GPa后,它们的特性十分接近;当p为52.9 GPa时,石墨与水混合物表现出反常的冲击压缩特性,压力增加而体积出现膨胀,这与高压下碳与水发生化学反应产生气体相关。还对碳水混合物的相互作用势及混合法则的选取进行了讨论。     

冻融对重塑黏土导热系数影响的试验研究

在工程建设中,导热系数作为温度场的重要参数一直是岩土工程领域的研究热点。为研究冻融作用对土体导热系数的影响规律,室内制作不同含水率和不同干密度的饱和与非饱和试样在低温环境模拟试验箱中进行封闭系统和开敞系统冻融循环,并提出实验室修正系数α和冻结指数相似比C_I对冻融过程温控模式进行优化。结果表明:未冻融试样,导热系数随含水率和干密度的增加而线性增加;封闭系统中,冻融后导热系数减小,且含水率对导热系数的影响大于干密度和冻融循环次数.通过对导热系数的偏相关分析发现,其偏相关系数分别为:0.998,0.994,-0.980.冻融次数与导热系数关系呈负相关,饱和试样中导热系数随冻融循环次数增大而降低.在考虑冻融作用时引入冻融项λ_f对Chung和Horton模型进行修正,修正后模型在预测饱和试样导热系数时与真实值相差较少,模型拟合度R~2为0.88.开敞系统中,冻融作用可改变试样的饱和状态,使非饱和土达到饱和,并且随着冻融次数的增加,试样导热系数先急剧增大后缓慢减小。     

海底表层沉积物声速的环境因素影响特性

应用声速通用模型开展理论分析,结合温度-压力可控实验测量分析,研究地声反演、海底原位声学测量和采样样品声学测量3种主要的海底表层沉积物声学特性测量方法中,存在的环境因素影响机制和特性.理论计算与实验测量研究具有一致性,揭示温度和静水压力对海底表层沉积物的压缩波声速的影响机制主要是通过影响孔隙海水的密度、黏度、体积弹性模...     

不同含水率下岩石材料的能量与损伤演化特征

为研究含水率对硬岩材料的力学性质和能量损伤的影响规律，对不同含水状态的砂岩开展了单轴压缩试验。结果表明：砂岩试样的峰值应力、弹性模量和脆性指数随着含水率的增大而减小，峰值应变随着含水率的增大而增大；在干燥状态下，砂岩试样在破坏之前未发生明显的塑性变形，表现出显著的脆性破坏，而在饱水状态下，砂岩试样在峰前阶段出现显著的塑性变形，破坏前出现屈服平台；砂岩试样的含水率越大，吸能能力越强，能量吸收率越小，但是能量耗散越显著；砂岩试样的含水率越小，破坏时其损伤变量越大，在干燥状态下砂岩试样的破坏具有较强的冲击倾向性。研究结果可为深部地下工程围岩的稳定性控制提供理论参考。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.