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分析了二维各向同性均匀随机介质中柱面波的传播特性及局域化现象.用随机泛函理论,在频域内将随机介电起伏展开成柱坐标系下的Wiener积分式,将波场表示为内外行柱面波的线性和,求解二维Helmholtz波动方程,得到随机介电起伏对柱面波幅度与相位调制的解析表达.由柱面波能量的空间分布验证了波的局域化现象,并求解局域化长度.二维随机介质中平面波按柱面波展开的波转换方程与非随机介质中的情形有相似的表达,但具有随机介电起伏对幅度和相位的调制,并给出数值模拟结果. 相似文献
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对激光束投射在具有一维随机道痕(起伏量小于或约等于波长,相当于八级以上光洁度)的工件表面上的情况,导出散射光强分布与起伏大峰高度之间的关系,后者可用作光洁度定标尺度。采用的是较简明的统计模型,对其中涉及的变型的“无规则行走”问题的概率推算,采用一种近似简化而得到简明的公式。给出了计算结果并讨论了简便的测量装置。
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《物理学报》2017,(1)
对于1 k Hz以上声波,海面起伏会对浅海声传播产生显著影响,现有的噪声预报模型在建模过程中基本没有考虑海面起伏的影响.针对这一问题,本文基于传输理论建立了随机起伏界面下噪声场垂直相关性和指向性模型,仿真分析了海面起伏对噪声强度、垂直相关性与指向性的影响.结果表明,对于表面噪声,海面随机起伏使声波能量从中间阶简正波向低阶和高阶简正波转移,而对噪声强度起主要贡献的一般是中间阶简正波,所以海面起伏使得噪声强度减弱;简正波之间能量的耦合导致垂直平面上不同掠射角方向上到达的声波响应发生变化,经由海面反射大掠射角到达的声波响应以及中小角度到达的声波响应变弱,而经由海底反射大掠射角到达的声波响应变强;海面随机起伏还会扰动各阶简正波相位,使不同阶简正波互相关性变弱,致使噪声场的空间相关性也变弱. 相似文献
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一、最佳推力喷管型线计算原理 考虑理想二维定常无旋等熵流动.喷管内流场是轴对称的,选用柱面坐标系,图一中ABTE表示喷管型面与子午面的交线.喷管喉部收敛段AB是曲率半径为R_1的圆弧壁面,喉部下游初始扩张段BT是曲率半径为R_2的圆弧壁面.我们选择一个喷管型线 相似文献
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粗糙热传导表面下激光介质温度场的计算分析 总被引:1,自引:1,他引:0
提出了一种计算温度场的面热源自适应调整算法,该方法通过在研究对象的封闭边界上引入虚拟面热源来求解稳态热传导方程的边值问题。建立了导热联结的具有粗糙表面介质的接触模型,在此基础上建立了随机分布的表面散热边界条件,并用面热源自适应调整算法计算了激光介质的温度场。结果表明,由于实际激光介质散热表面不能完全紧密接触,其温度场呈现一定程度的随机起伏,越靠近边界,随机起伏越明显,介质中心区域随机起伏则不明显;有效热接触面积越小,这种随机起伏越强烈。计算表明热接触面积占50%时,比接触面积占75%时温度场的随机性更明显。 相似文献
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假设粗糙表面为具有正态概率分布的平稳随机过程,研究了平面波在不平表面上的散射,求得了平面波在随机起伏表面上的统计平均反射系数,指出与随机表面空间相关的联系。引出“等效反射面”概念,求得了具有起伏表面的分层介质中点声源发射情况下波场的一般表达式,从而建议了对多种实际水文条件下起伏水面所致声音传播的附加衰减问题的解决,并给出表面声道中各级简正波的附加衰减系数。 相似文献
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本文提出了予测稠苯芳杂环及其烷基链上质子化学位移的计算方法。
将稠苯芳杂环化合物用凯库勒式表示,计算式为为需考虑的苯环内的乙烯基效应。σmi,ci为各苯环的环流效应。σ1,Hc为各芳杂环的屏蔽效应,对杂环上质子它就是该单独芳杂环上相应质子的δ值,对苯环上质子要将它分解为各结构因素的效应,即:σ1,He=(1/2)d-1δx=y(或σz)+σc-c·σm,H.
σx-y与σz为杂原子或其基团的屏蔽效应,σc=c为存在于芳杂环中的乙烯基的效应,σm,Hc为芳杂环的环流效应,d为对不同质子所考虑的键数。有取代基时需考虑取代基的效应。计算环上烷基质子的公式为:δ=σp,CH3+ασc,CH3+βσt,CH3+σl,G
σl,G为稠苯芳杂环基的某级效应。 相似文献
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Shuji Hasegawa Yasuyoshi Nagai Toshio Oonishi Nobuhiko Kobayashi Takashi Miyake Shuuichi Murakami 《Phase Transitions》2013,86(2-4):87-114
Structural phase transitions between various kinds of superlattice structures formed on a Si(111) surface have been investigated by spot analysis of reflection high-energy electron diffraction (RHEED). Reversible transitions induced by temperature changes and irreversible ones induced by metal depositions were observed. Detailed discussions on the dynamics of the phase transitions are made by quantitative analyses of integrated spot intensity and profile. For a phase transition of 7′7 1′1 structures on a clean Si(111) surface, a hysteresis with temperature difference of 5°C. between in heating and cooling processes was found in the spot intensity change, indicating a first-order transition. Hysteresis was hardly recognized, on the other hand, for transitions of Au-induced superstructures (5×2-Au or ×-Au) 1×1-Au. The spot profiles were found to be broadened during the transition of Si(111)-×-Au 1×1-Au, which was a signature of a continuous transition, while the profiles remained unchanged during the transitions of the 7×7 1×1 and 5×2-Au 1×1-Au phases. Structural conversions induced by In adsorption on the Si(111) surface kept at constant temperatures were also analyzed. The conversions at room temperature were totally dependent on the initial substrate surface structures; the 7×7 surface did not show any structural conversion with In adsorption, while the ×-In surface successively converted to a 2×2 and a × phase with coverage increase. The structural transitions at elevated temperatures were sensitively dependent on the temperatures. Sequences of transitions among the 7×7, 4×1, ×, 1×, and ×4 were quantitatively revealed as changes in RHEED spot intensity. 相似文献
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研究了Er1.0P5O14铒非晶玻璃的红外量子剪裁现象. 从吸收谱和激发光谱的计算比较中肯定了Er1.0P5O14非晶 玻璃的1537.0 nm红外荧光为多光子量子剪裁荧光. 从Er1.0P5O14非晶玻璃的可见和红外荧光发射光谱中发现激发2H11/2, 4G11/2和4G9/2能级所导致的4I13/2→4I15/2量子剪裁红外荧光很强;基于自发辐射速率、无辐射弛豫速率和能量传递速率等参数的计算,对其量子剪裁机理进行了分析.发现起源于基态的强下转换能量传递{2H11/2→4I9/2,4I15/2→4I13/2},{4G11/2→4I13/2, 4I15/2→2H11/2},{4G9/2→4F7/2,4I15/2→4I13/2}和{4G9/2→4I13/2, 4I15/2→2H11/2}是导致Er1.0P5O14非晶玻璃具有强的三光子和四光子量子剪裁红外荧光的原因.研究结果对改善太阳能电池效率有一定意义. 相似文献
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Helga Baum 《Journal of Geometry and Physics》1987,4(4):503-522
Let
(P) be the moduli space of irreducible connections of a G-principal bundle P over a closed Riemannian spin manifold M. Let DA be the Dirac operator of M coupled to a connection A of P and f a smooth function on M. We consider a smooth variation A(u) of A with tangent vector ω and denote Tω:=
(DA(u)−f) (u=0. The coefficients of the asymptotic expansion of trace (Tω · e-t(DA−f)2) near t=0 define 1-forms a(k)f, K=0, 1, 2, … on
(P). In this paper we calculate aa(0)f, a(1)f, a(2)f and study some of their properties. For instance using the 1-form a(2)f for suitable functions f we obtain a foliation of codimension 5 of the space of G-instantons of S4. 相似文献
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An attempt is made to synthesize Nd2Co14C compound by mechanical alloying Nd16Co76B8−xCx (0x8) alloys and subsequent annealing. Phase formation and magnetic properties of Nd2Fe14B-type Nd16Co76B8−xCx alloys and their hydrides are investigated. The Nd2Co14(B,C) phase with Nd2Fe14B-type structure is formed for Nd16Co76B8−xCx (0x7) alloys, while NdCo7Cδ phase with TbCu7-type structure is observed in Nd16Co76C8 alloy. The lattice parameter c of the Nd2Co14(B,C) phase decreases with increasing the carbon content. A limit volume of the unit cell to form the Nd2Fe14B-type structure is estimated to be 0.870 nm3. The spin-reorientation temperature TSR increases with increasing the carbon content, due to an enhancement of magnetocrystalline anisotropy caused by carbon substitution for boron. After hydrogenation, the lattice expansion is observed for Nd16Co76B8−xCx (0x7) alloys. The spin-reorientation temperature of Nd16Co76B8−xCxHy (0x7) is much lower than that of the host alloys. Some structural and magnetic properties of hypothetic Nd2Co14C and Nd2Co14CHy compounds are estimated by extrapolation. 相似文献