ANNIHILATION OF VERTICAL-BLOCH-LINE CHAINS IN THE WALLS OF THE SECOND KIND OF DUMBBELL DOMAINS SUBJECTED TO AN IN-PLANE FIELD

An experiment was statistically performed on the annihilation of vertical-Bloch-line (VBL) chains in the walls of the second kind of dumbbell domains (ⅡDs) subjected to an in-plane field H_ip. It was again confirmed that there is a critical in-plane field H′_ip, above which all VBL chains of hard domains in garnet bubble films, including ⅡDa, disappear. Just like ordinary hard bubbles (OHBs), it was also found that there exists a critical range of H_ip, from (H_ip)_ID to H′_ip, for ⅡD softening. Over this range, with the increase of H_ip, more and more ⅡDs are softened, accompanied by the successive appearance of the first kind of dumbbell domains, OHBs and soft bubbles. In addition, for the five samples tested, the ratio, H′_ip/(H_ip)_ID, is obviously greater than 2^1/2.     

直流偏场和面内场联合作用下第二类哑铃畴的自发收缩

实验研究了第二类哑铃畴在直流偏场和面内场联合作用下的自发收缩现象，发现第二类哑铃畴的自发收缩不仅与面内场的大小有关，而且还与第二类哑铃畴在面内场中所处方向有关.采用照相法形象地揭示出：当第二类哑铃畴与面内场垂直时最容易发生自发收缩；当第二类哑铃畴与面内场平行时最难发生自发收缩.实验还证明了第二类哑铃畴在自发收缩过程中存在垂直布洛赫线的丢失现象.     

ANNIHILATION OF VERTICAL-BLOCH-LINE CHAINS IN THE WALLS OF THE SECOND KIND OF DUMBBELL DOMAINS SUBJECTED TO JOINT STATIC BIAS FIELD AND IN-PLANE FIELD

Experiments were statistically carried out on the behavior of vertical-Bloch-line(VBL) chains in the walls of the second kind of dumbbell domains (IIDs) is garnet bubble films subjected to joint action of static bias field H_b and in-plane field H_ip. The curves of the four critical in-plane fields, (H_ip)_IID-ID (H_ip)_IID-OHB (H_ip)_IID-SB and H'_ip vs H_b were measured and explained. In particular, in terms of two series of IID photos, a new experimental manifestation of the unknown "number effect" of VBL chains was found.     

RADIAL CONTRACTION OF THE FIRST KIND OF DUMBBELL DOMAINS SUBJECTED TO A STATIC BIAS FIELD

On the basis of the "exercise" experiment and the phenomenon of "self-shrink", the behavior of "less-stable" IDs (first kind of dumbbell domains) in radial contraction under an "exercise" bias field, (H_b)_e, was statistically investigated in detail. It was found that the histograms of their stripe-to-bubble transition field, H_sb after exercise, become narrower and shift towards the side of lower H_sb with the increase of (H_b)_e. It illustrates how the less-stable IDs lose part of their vertical Bloch lines under different (H_b)_e. In addition, it was also found that the curve of the upper boundary of these histograms, (H_sb)_max vs. (H_b)_e, consists of two segments of straight lines. This discontinuity was proved to be due to self shrink, and the crosspoint of these two lines is just the lower limit of the self-shrink region. Furthermore, a series of photographs were taken to show the effect of radial contraction on less-stable IDs intuitively.     

面内场和静态偏磁场作用下条畴和泡畴的稳定性

实验研究面内场H_in和静态偏磁场H_b作用下,(111)面磁泡膜内条畴的消失过程。保持H_b恒定,增加H_in,测量条畴消失场H_s^*和泡畴消失场H_k^*与面内场方向β的变化关系。计及立方磁晶各向异性的影响,建立H_in和H_b共同存在时的条畴稳定性理论。定性解释了实验的主要特点。导出黑、白条畴同时消失时的角度 β_n=1/3(2nπ±arc cos│3/(2^1/2)(M_sH_b)/K₁│)(n=0,±1,±2,…)与实验基本符合。 关键词：     

立方磁晶各向异性对面内磁场中条畴和磁泡稳定性的影响

在八个(111)面磁泡膜上,观察了施加面内(in-plane)磁场后在不同晶轴方向上条状畴的消失过程,测量了条畴消失场H_s^*和磁畴消失场H_k^*与面内磁场的方向的关系。本文计及立方磁晶各向异性,完善了面内磁场中条畴的稳定性理论。用该理论定性地解释了实验结果的主要特点。导出了H_s^*与立方各向异性及面内场方向的两种近似的理论关系,它们分别适用于面内场方向靠近和不十分靠近〈110〉晶轴的情形。它们和实验结果是大致符合的。在〈110〉晶轴上,理论关系具有下列简单的形式:H_k^*<110>=H_s^*<110>=H_k{1+(k₁/2K_u)-[al/h(4πM_s/H_k)²]^2/3},此式与实验结果符合得相当好。 关键词：     

ANNIHILATION OF VERTICAL-BLOCH-LINE CHAINS IN THE WALLS OF ORDINARY HARD BUBBLES SUBJECTED TO JOINT STATIC BIAS FIELD AND IN-PLANE FIELD

For the ordinary hard bubbles(OHBs) of garnet bubble films, the annihilation of the vertical-Bloch line (VBL) chains in their walls subjected to joint static bias field H_b and in plane field H_ip was experimentally studied. The curves of two critical in-plane fields, H⁽¹⁾_ip and H′_ip, vs H_b were measured. By means of the so-called "head-cut" and "tail-cut" experiments designed in this work, it was verified that for the OHBs subjected to H_ip, their VBL chains with different lengths lose VBLs and become shorter simultaneously. It was also verified that the critical in-plane fields H⁽¹⁾_ipand H′_ip correspond to the break down of the shortest and longest VBL chains of OHBs, respectively.     

DYNAMIC STABILITY OF SKEW PLATES SUBJECTED TO AERODYNAMIC AND RANDOM IN-PLANE FORCES

This paper presents an investigation into the dynamic stability of skew plates acted upon simultaneously by an aerodynamic force in the chordwise direction and a random in-plane force in the spanwise direction. Due to this random in-plane force, the plate may become unstable before the aerodynamic force reaches its critical value. In this work, the finite element formulation is applied to obtain the discretized system equations. The system equations are then partially uncoupled and reduced in size by the modal truncation method. Finally, the unsmoothed and the smoothed versions of the stochastic averaging are used to calculate the system response, and the second-moment stability criterion is utilized to determine the stability boundary of the system. Numerical results show that the stability boundary obtained by the smoothed stochastic averaging is less conservative than that obtained by the unsmoothed version, and the former is the tangent of the latter at zero spectral density of the random in-plane force.     

INFLUENCE OF IN-PLANE FIELD ON THE STABILITY OF VERTICAL BLOCH LINE CHAINS IN HARD DOMAINS OF GARNET BUBBLE FILMS

The stability of vertical Bloch line (VBL) chains was statistically studied for all three types of bard domains in garnet bubble films subjected to an in-plane field H_ip. With a set of integrate data taken from seven bubble samples and with two typical figures of a sample, four main features of the behavior of VBL chains subjected to H_ip were summarized.     

磁场下量子点的电子态

原子和核结构的少体理论方法改进后用以研究磁场下包含三个电子的二维量子点的电子性质。我们首先解析地证明了对应于三电子系统基态的幻数角动量的存在起源于量子力学对称性的要求。基于少体理论方法的计算确认了上述理论分析的正确性,计算同时显示出磁场强度和约束势对三电子系统基态的影响。 关键词：     

不同温度下ZnS的高场输运特性

研究了ZnS中的电子声子相互作用.以此为基础,利用Monte Carlo方法研究了ZnS中电子在不同温度下的高场输运特性.电子加速的瞬态时间基本不随温度变化.电子的动能分布函数随温度升高向低能方向移动,即平均动能降低.电子在各能谷间的分布随温度升高而向低能谷移动.电子的漂移速度则随温度升高而降低.给出了这些物理量随温度变化的具体规律. 关键词：     

TUNNEL MAGNETORESISTANCE IN THE FERROMAGNETIC TUNNEL JUNCTION WITH FERROMAGNETIC LAYERS OF FINITE THICKNESS SUBJECTED TO AN ELECTRIC FIELD

Based on the two-band model, we investigate the tunnel magnetoresistance(TMR) in ferromagnet/insulator (semiconductor)/ferromagnet(FM/I(S)/FM) tunnel junction covered on both sides by nonmagnetic metal layers subjected to an electric field. Our results show that TMR oscillates with the thickness of ferromagnetic layers owing to the quantum-size effect and can reach very large value under suitable conditions, which may in general not be reached in FM/I(S)/FM with infinitely thick ferromagnetic layer. Although the electric field causes the change of the oscillation period, phase and amplitude of the TMR, a large TMR is still obtained in some situations with the electric field. Furthermore, the electric field does not change the feature that TMR varies monotonously with the change of magnetization angle of the middle ferromagnetic layer.     

冲击加载下材料破坏准则的规范场理论

 本文给出了规范场理论中的Bessel-Hagen散度不变性的广义E. Noether对称定理。应用此定理及缺陷的规范场理论，研究了材料在强动外载作用下的动力学性质，给出了破坏准则的一般公式，此公式定量地反映了缺陷和外载对材料破坏的影响。作为一个例子，研究了强冲击波作用下材料的破坏情况，使一般公式具体化了，而且定量地反映了冲击波的速度、压力和缺陷对材料破坏的影响。     

不同冲角下弯曲扩压叶栅出口流场的实验研究

本文在不同冲角下对直叶片、正倾斜叶片、正弯曲叶片和Ｓ型叶片组成的四种平面扩压时栅的出口流场进行了详细的实验研究。通过与常规直叶栅的对比，分析了正倾斜叶栅降低根区二次流损失的原因，阐述了正弯曲叶栅在正冲角下改善叶栅两端区流动状况，降低能量损失的机理和Ｓ型叶栅降低根区损失、总损失系数对冲角变化不敏感的原因。结果表明，扩压叶栅中采用正弯曲叶片在一定条件下是可行的。     

求解非均匀介质中电场反问题的一个新方法

以由R³中多层介质电场的部分数据出发,确定R³中某一区域的形状为例,抽象为最优控制问题,证明了该问题的解的存在性。给出了有限元方法和图论相结合的新算法,根据这个算法,进行多种数值实验,得到了L²下各种计算结果。     

THE DOUBLE COUPLING OF THE ASHTEKAR GRAVITATIONAL FIELD TO THE DIRAC SPINORAL FIELDS

By introducing the double spacetime manifold, the double gamma matrices and Dirac spinors, the action of the Dirac spinoral fields is doubled. Furthermore, the double coupling of the Dirac fields to the Ashtekar gravitational fields is studied.     

VIBRATION AND STABILITY OF ROTATING POLAR ORTHOTROPIC ANNULAR DISKS SUBJECTED TO A STATIONARY CONCENTRATED TRANSVERSE LOAD

In the present paper, natural frequencies and stability of a spinning polar orthotropic disk subjected to a stationary concentrated transverse load are investigated. The analysis of the free vibration of a spinning disk is performed first to find natural frequencies and corresponding vibration modes. The resulting eigenfunctions obtained from the free vibration are used as deflection functions of the forced vibration of a disk where the load is modelled as a mass-spring-dashpot system fixed in space. By using the Galerkin approximation method, eigenvalues of the whole system are determined. Results show that disks with higher values of modulus ratios or the Poisson ratios have higher natural frequencies, and the stability of the whole system can be improved by raising the value of the modulus ratio or lowering that of the Poisson ratio.     

MYOELECTRIC RESPONSE OF BACK MUSCLES TO VERTICAL RANDOM WHOLE-BODY VIBRATION WITH DIFFERENT MAGNITUDES AT DIFFERENT POSTURES

Back muscle forces contribute essentially to the whole-body vibration-induced spinal load. The electromyogram (EMG) can help to estimate these forces during whole-body vibration (WBV). Thirty-eight subjects were exposed to identical random low-frequency WBV (0·7, 1·0 and 1·4 m/s^-2 r.m.s. weighted acceleration) at a relaxed, erect and bent forward postures. The acceleration of the seat and the force between the seat and the buttocks were measured. Six EMGs were derived from the right side of the m. trapezius pars descendens, m. ileocostalis lumborum pars thoracis, m. ileocostalis lumborum pars lumborum; m. longissimus thoracis pars thoracis, m. longissimus thoracis pars lumborum, and lumbar multifidus muscle. All data were filtered for anti-aliasing and sampled with 1000 Hz. Artefacts caused by the ECG in the EMG were identified and eliminated in the time domain using wavelets. The individually rectified and normalized EMGs were averaged across subjects. The EMGs without WBV exhibited characteristic patterns for the three postures examined. The coherence and transfer functions indicated characteristic myoelectric responses to random WBV with several effects of posture and WBV magnitude. A comprehensive set of transfer functions from the seat acceleration or the mean normalized input force to the mean processed EMG was presented.The results can be used for the development of more sophisticated models with a separate control of various back muscle groups. However, the EMG-force relationship under dynamic conditions needs to be examined in more detail before the results can be implemented. Since different reflex mechanisms depending on the frequency of WBV are linked with different types of active muscle fibres, various time delays between the EMG and muscle force may be necessary.