Temporal characteristics of few-cycle pulse on- and non-resonance propagating in a ladder-type atomic medium

Time evolution characteristic of few-cycle pulse propagating in a ladder-type atomic medium is investigated. It is shown that, time evolution of few-cycle pulse has significant difference in the both cases on- and non-resonance. In the non-resonant case, if the pulse central frequency is twice as large as medium atomic transition frequency, the pulse form (including carry-envelope phase, pulse duration, oscillation amplitude and frequency) remains unchanging or remains unchanging basically (only carry-envelope phase has some variation) in the propagation process, which means that self-induced transparency (SIT) or approximate transparency phenomenon appears. However, in the resonant case, the pulse form changes obviously in the propagation process. In addition, there is evident difference in the propagating velocity for on- and non-resonance when the pulse area is smaller.     

一阶速度-应力Biot双相各向同性介质弹性波

提出一种等价的一阶双曲型速度一应力Biot双相各向同性介质弹性波波动方程,以实现双相介质混合波场中纯快慢纵波和纯横波波场分离的问题.应用散度和旋度理论证明双相介质等价方程波场分离的可行性,采用高阶交错网格有限差分法构建高精度正演算子,推导其PML吸收边界条件和稳定性条件,并对均匀双相介质和层状非均匀双相介质模型进行数值...     

热管冰蓄冷结构设计

从技术角度研究和探讨了热管做为冰蓄冷装置的适用性;对各种热管用金属管材与工质的特性进行了科学比较;从而最终确定了适宜冰蓄冷工作的热管管材、热管工质及其基本尺寸;为热管冰蓄冷装置的深入研究及推广应用,提供了强有力的理论依据。     

胶体铁磁流体的光子特性研究

这篇综述回顾了我们今年来在铁磁流体方面的一些研究工作。铁磁流体是一种纳米磁颗粒或亚铁磁颗粒悬浮在基液（如：水或煤油）中形成的悬浮液。铁磁流体之所以受到广泛关注,是因为它们在许多方面都有着潜在应用,例如在机械工程和生物医学等领域。再次综述中,我们首先介绍了铁磁流体的场感应各向异性结构,然后,介绍了几种铁磁流体基软物质材料的光学性质,即：光学负折射、磁控光子待隙和非线性光学响应。我们采用的研究方法主要是分子动力学模拟,有效煤质近似和有限元模拟.     

离散可激发介质中早期后去极化对螺旋波影响的数值研究

通过考虑某些不应态也可以被激发,在离散可激发介质Greenberg-Hasting模型中引入早期后去极化行为,研究了早期后去极化对螺旋波的影响.数值结果表明:在适当选择参数下,早期后去极化对螺旋波有很大影响,这些影响包括使螺旋波漫游、漂移和破碎,导致螺旋波波纹被扭曲和波臂粗细交替变化,以及导致螺旋波的周期在两个值之间交替变化,产生从稳定螺旋波到呼吸螺旋波和反螺旋波的相变等.当不应态的激发阈值很高时,早期后去极化对螺旋波没有影响.对发生上述现象作了简要的讨论. 关键词： 离散可激发介质 螺旋波 早期后去极化     

亚波长金属线栅的设计、制备及偏振成像实验研究

针对红外偏振成像系统,运用等效介质理论,在氟化钙基底上设计了周期为200 nm,深度为100 nm的金属铝栅.模拟计算结果表明,设计的金属铝栅在中红外(3—5 μm)和远红外(8—12 μm)双波段范围内,以及±20°的视场范围内能够提供大于35dB的消光比.利用电子束曝光、反应离子束刻蚀、等离子去胶等工艺完成了金属铝栅的制作.将金属铝栅放在中波红外热像仪前,得到了目标轮廓清晰的偏振图像. 关键词： 亚波长衍射光栅 偏振成像 等效介质理论     

水平层状介质中电磁场并矢Green函数的一种快速新算法

本文利用提取直射波并结合自适应数字滤波等技术提出一种计算水平层状介质中电磁场并矢Green函数的快速算法. 首先将谱域Green函数中表征均匀介质作用的直射波提取出来并对其积分进行解析计算,这种处理降低了谱域Green函数的奇异性,可在很大程度上缩短其积分收敛区间. 然后在将谱域Green函数剩余部分对应积分转化为三个快速下降积分的基础上,引入一种自适应数字滤波算法对其进行快速求解. 最后通过具体算例验证了本文所述算法的有效性. 关键词： 并矢Green函数 快速算法 水平层状介质     

多孔介质内交变流动与换热的格子Boltzmann研究

针对制约脉冲管制冷机效率提高的蓄冷器内交变流动与换热问题,本文使用格子Boltzmann方法计算并分析了多孔介质内交变流动与换热特性。结果表明,交变流动压力波振幅对速度与压力和温度间的相位差的影响很小;通道界面处速度与压力的相位差在某一孔隙率下有一极小值;多孔介质内最大阻力系数与雷诺数的关系可以为设计蓄冷器时填料结构的...     

半透明介质相变中的辐射变物性问题

半透明介质相变传热在许多工程领域引起关注,其实质是变物性条件下伴随相变的辐射-导热瞬态耦合传热问题,其难点在于相变过程中的辐射变物性问题,尤其是折射率的时空演变问题.本文首次研究相变过程中的变折射率问题.假设相变介质存在固相-糊状-液相区,固/糊界面、液/糊界面假定为半透明漫反射.采用多层辐射传递模型模拟相变介质内的辐...     

A case of Budd-Chiari syndrome: Gd-EOB-DTPA-enhanced MR findings

Budd-Chiari syndrome (BCS) is a rare disorder caused by the obstruction of hepatic venous outflow, leading to sinusoidal congestion, ischemic injury to liver cells and portal hypertension. Long-term survival largely depends on whether hepatocellular carcinoma occurs. A recently available liver-specific contrast medium, gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid (Gd-EOB-DTPA), reportedly has high diagnostic capability for detection of malignant liver tumors. However, there has been no report of the sue of Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) for BCS. We present a case of chronic BCS who underwent both gadopentetate dimeglumine (Gd-DTPA) and Gd-EOB-DTPA-enhanced MRI. Hepatic congestion and edema were seen as slightly hypointense areas on Gd-EOB-DTPA-enhanced hepatobiliary-phase images, although these areas were observed as slightly hyperintense on previously obtained Gd-DTPA-enhanced delayed-phase image. Reduced uptake of Gd-EOB-DTPA by hepatocytes in the region of congestion or edema may account for this difference, which should be recognized in image interpretations.