Optimization of spin-valve parameters for magnetic bead trapping and manipulation

Magneto-optic Kerr effect (MOKE) and magnetoresistance (MR) measurements were used to measure the switching characteristics of spin-valve (SV) arrays currently being developed to trap and release superparamagnetic beads within a fluid medium. The effect of SV size on switching observed by MOKE showed that a 1 μm×8 μm SV element was found to have optimal switching characteristics. MR measurements on a single 1 μm×8 μm SV switched with either an external applied magnetic field or a local magnetic field generated by an integrated write wire (current density ranging from 10⁶ to 10⁷ A/cm²) confirmed the MOKE findings. The 1 μm×8 μm SV low field switching was observed to be +8 and −2 mT with two stable states at zero field; the high field switching was observed to be −18 mT. The low switching fields and the large magnetic moment of the SV trap along with our observation of minimal magnetostatic effects for dense arrays are necessary design characteristics for high-force, “switchable-magnet,” microfluidic bead trap applications.     

Research on the propagation properties of hollow laser beams with three-dimensional trap optical distribution

A new kind of hollow beams - hollow laser beams with three-dimension trap optical distribution - was put forward. With the help of the Collins formula in paraxial optical system, the analytical equation of propagation and transformation of the hollow laser beams was deduced. According to the analytical equation, the propagation properties of the kind of hollow beams that transform in free space were simulated. In the experiment, we obtained the hollow laser beams by means of the combinational optical system of reflecting positive-axis and negative-axis pyramids. The intensity of the vertical loop in different distances was tested, which shows that the analytical equation of propagation and transformation is in agreement with the result.     

Degradation and recovery properties of AlGaN/GaN high-electron mobility transistors under direct current reverse step voltage stress

Direct current (DC) reverse step voltage stress is applied on the gate of AlGaN/GaN high-electron mobility transistor (HEMT). Experiments show that parameters degenerate under stress. Large-signal parasitic source/drain resistance (R_S/R_D) and gate-source forward I-V characteristics are recoverable after breakdown of the device under test (DUT). Electrons trapped by both the AlGaN barrier trap and the surface state under stress lead to this phenomenon, and surface state recovery is the major reason for the recovery of device parameters.     

Effect of pearlitic morphology with varying fineness on the cavitation erosion behavior of eutectoid rail steel

The present work discusses the effect of the pearlitic morphology with varying fineness on the cavitation erosion behavior of eutectoid rail steel. Cavitation erosion of three different types of the pearlitic steels (furnace-cooled, air-cooled, and forced-air-cooled) consisting of coarse, fine, and very fine microstructures were tested in 3.5% NaCl solution and compared with that of the as-received pearlitic rail steel. The variation in the mean depth of erosion (MDE) and mean depth erosion rate (MDER) with erosion time was analyzed. Furthermore, the cavitation erosion resistance of the as-received, the air-cooled, and the forced-air-cooled was found to be 1.03, 1.51, and 2.14 times better than the furnace-cooled pearlitic steel, respectively. It was concluded that the cavitation erosion resistance of the pearlitic steel increased with the increase in the fineness of the microstructure.     

Variational Quantum Chemistry Programs in JaqalPaq

We present example quantum chemistry programs written with JaqalPaq, a python meta-programming language used to code in Jaqal (Just Another Quantum Assembly Language). These JaqalPaq algorithms are intended to be run on the Quantum Scientific Computing Open User Testbed (QSCOUT) platform at Sandia National Laboratories. Our exemplars use the variational quantum eigensolver (VQE) quantum algorithm to compute the ground state energies of the H2, HeH+, and LiH molecules. Since the exemplars focus on how to program in JaqalPaq, the calculations of the second-quantized Hamiltonians are performed with the PySCF python package, and the mappings of the fermions to qubits are obtained from the OpenFermion python package. Using the emulator functionality of JaqalPaq, we emulate how these exemplars would be executed on an error-free QSCOUT platform and compare the emulated computation of the bond-dissociation curves for these molecules with their exact forms within the relevant basis.     

皮肤组织容积脉搏波400~1000 nm光谱特性仿真研究

根据皮肤组织解剖结构特性建立了六层层状模型,并给出了皮肤组织各层的特性参数;考虑了氧合血红蛋白和还原血红蛋白的吸收特性,依据皮肤组织各层的水、血、脂肪、血氧饱和度含量以及血管大小给出了皮肤组织各层的光谱吸收系数;对不同波长散射系数做了适当简化,给出了皮肤组织各层的光谱散射系数。利用蒙特卡罗方法仿真血管组织在收缩与舒张两种状态下, 400~1 000 nm波长光在皮肤组织多层模型中的传输过程,并通过统计大量光子的分布特性,获得了皮肤组织光谱反射系数,并利用模拟所得的两种状态下的反射系数计算得到了光谱容积脉搏波幅度。仿真结果表明,当入射光强一定时,绿光的容积脉搏波幅度优于红光和蓝光。通过计算不同波长光沿皮肤组织深度方向光能流率衰减为1/e时对应的皮肤组织深度,获得了皮肤组织光谱穿透深度。结果显示,血管舒张状态下蓝光和绿光的穿透深度较小,蓝光大部分只能达到表皮层,绿光能到达微循环层,红光可直达真皮层。考虑到光在皮肤组织中传播包含了一个从收缩到舒张的动态过程,基于此,根据穿透深度定义了脉搏波信号产生深度,利用血管舒张与收缩两种不同状态下的穿透深度计算得到了光谱产生深度。结果表明,不同波长光产生深度大于其穿透深度,蓝光产生深度较浅,且其受到的血液吸收调制较小,因而其获得的脉搏信号易受噪声干扰;红光的容积脉搏波产生深度较大,但是相比于绿光其受血液吸收调制较小,且绿光产生深度足够达到真皮血管层,因而红光容积脉搏波的幅度小于绿光。上述仿真结果明确了皮肤组织部分光谱特性,为皮肤组织多光谱容积脉搏波的精确获取及其他相关研究提供了一定的理论基础。     

Vortex penetration depth of κ-(ET)2Cu[N(CN)2]Br

The magnetic field dependence of the in-plane penetration depth λ_|(H) for single crystal κ-(ET)₂Cu[N(CN)₂]Br has been measured at 3, 9.6, and 36 MHz. Over a limited range, λ_| scales with a characteristic field H^*(T) that coincides with a shoulder in the λ_| vs. H curves. Above that field, λ_| increases sharply toward a second inflection point at H^**(T) that coincides with is close to the irreversibility line measured by magnetization. For fields larger than H^** the penetration depth diverges, suggesting that the vortex lattice has melted. The field dependence at one frequency agrees qualitatively with a model of pinned vortices at low fields giving way to flux flow at higher fields. However, the observed frequency dependence deviates significantly from the predictions of this model, suggesting that collective effects play a major role. Our technique also yields a new measurement for the interplane penetration depth λ 300 μm, implying an anisotropy λ/λ_| > 200.     

对称面形光栅TE模的衍射特性

本文采用耦合波方法计算了对称面形光栅的衍射效率,分析了光栅截面面形为正弦、三角形、矩形、梯形光栅衍射效率与光栅周期、沟槽深度的关系,计算了光栅的峰值衍射效率。理论计算表明:合理地选择光栅周期、沟槽深度,对称面形光栅都可以达到很高衍射效率,接近100%;光栅的峰值衍射效率基本出现在Bragg衍射且光栅的周期等于衍射波长时。     

亮度优化立体视频视觉舒适度评价

结合立体视频帧左右视图的灰度图,采用鲁棒性算法与软剪刀算法相结合的"画笔"方案来提取立体视频帧的前景区域,合成视差图并提取水平视差,计算深度视差;根据主观评价结果建立视差深度-视觉舒适度模型,再结合亮度对视觉舒适度的评价模型进行优化,使模型的评分更接近人类视觉系统的评分;结合人类主观评价实验的结果,用逆向代入法求出模型的系数确定模型,最终实现基于人类视觉系统特性的对立体视频视觉舒适度的评价。实验结果表明:通过视觉舒适度模型计算得到的结果与人类主观评价结果之间的误差率不超过5%,其中大部分视频误差率不超过1%。说明评价模型更符合人类主观感知结果的立体视频视觉舒适度,模型评分更接近人类视觉系统特性的主观实验评分,这为立体视频舒适度的评价提供了参考。     

激光尾流场的2.5维粒子模拟

 用2D3V PIC粒子模拟方法分析了超短脉冲超强激光在稀薄等离子体中激发尾流场的产生过程及电子在尾流场中的加速过程。“前向Raman散射”使得激光脉冲沿传播方向拉长，脉冲的尾部变陡，它导致静电场的相速度和饱和时超热电子的最大动能明显减小，也使得激发尾流场的最佳脉冲宽度变小。