Space Geometry of Rotating Platforms: An Operational Approach

We study the space geometry of a rotating disk both from a theoretical and operational approach; in particular we give a precise definition of the space of the disk, which is not clearly defined in the literature. To this end we define an extended 3-space, which we call relative space: it is recognized as the only space having an actual physical meaning from an operational point of view, and it is identified as the physical space of the rotating platform. Then, the geometry of the space of the disk turns out to be non Euclidean, according to the early Einstein's intuition; in particular the Born metric is recovered, in a clear and self consistent context. Furthermore, the relativistic kinematics reveals to be self consistent, and able to solve the Ehrenfest's paradox without any need of dynamical considerations or ad hoc assumptions.     

矢量衍射理论在光盘中的应用

衍射计算是设计光盘光学系统的基础。只读光盘信息符（ 坑点） 尺寸可以和波长相比拟或在更小时标量衍射理论不再适用。本文将光盘信息符抽象成二维光栅,应用耦合波理论导出了当用平面波检测光盘时衍射波场的计算公式,得到了衍射强度 坑深曲线,并提出了临界坑深的概念。分析表明,临界坑深随着信息符横向尺寸的变小而变小,这将导致衍射波光强变化的减小,从而限制了光盘的存储密度。本文还分析了检测平面波的偏振态对衍射波强度的影响     

Flow of a single magnetic vortex in a submicron-size superconducting Al disk controlled by radio-frequency currents

We report the first observation of a single-vortex flow in a mesoscopic superconductor. A flow of a single vortex is successfully controlled by an rf current superimposed on a dc current, evidence of which is provided by voltage steps in current-voltage (I-V) characteristics. Irrespective of the number of vortices confined to the disk, we unambiguously observe that when a single vortex inside the disk is driven out of the disk, another vortex enters the disk similarly to two balls colliding in billiards: only one vortex passes through the Al disk at the same time in mesoscopic systems.     

高密度光盘径向倾斜对DPD循轨误差信号影响分析

根据高密度光盘参数 ,计算了聚焦光斑在光盘表面扫描过程中每个位置的光瞳光强分布 ,得到DPD(Differ entialPhaseDetection)循轨误差信号。考虑盘片的径向倾斜 ,在光瞳光强分布方程中引入盘片的径向倾斜角度参数 ,计算了高密度盘片产生径向倾斜时DPD循轨误差信号的变化 ,进而分析了盘片的径向倾斜引入的循轨伺服误差及其对循轨伺服的负面影响。结果表明 ,高密度盘片产生 0 .5°的径向倾斜相当于引入了 0 .0 12 μm的循轨误差     

振荡吸积盘的光变研究

理论研究指出随机振荡吸积盘可能引起活动天体的光变,然而观测数据分析表明光变中除了含有随机噪声外还存在混沌因素.将混沌因素引入到随机振荡吸积盘中,构成"混沌+随机"振荡吸积盘模型.通过分析扰动的相图,直观再现了混沌吸引子的状态.研究结果表明:在随机因素占主导时,光变混乱无序;随机因素与混沌因素相当时,光变上下起伏类似于心电图;混沌因素占主导时,光变具有一定有序性.模拟光变曲线的关联维与观测数据的关联维一致,表明模拟光变曲线与观测结果之间存在内在联系.     

Ultrafast nanomagnetic toggle switching of vortex cores

We present an ultrafast route for a controlled, toggle switching of magnetic vortex cores with ultrashort unipolar magnetic field pulses. The switching process is found to be largely insensitive to extrinsic parameters, like sample size and shape, and it is faster than any field-driven magnetization reversal process previously known from micromagnetic theory. Micromagnetic simulations demonstrate that the vortex core reversal is mediated by a rapid sequence of vortex-antivortex pair creation and annihilation subprocesses. Specific combinations of field-pulse strength and duration are required to obtain a controlled vortex core reversal. The operational range of this reversal mechanism is summarized in a switching diagram for a 200 nm Permalloy disk.     

Interface solution for writing-induced nano-deformation of slider body

Writing-induced nano-deformation of slider body becomes a big concern when the mechanical spacing between the head and disk is continuously reduced to achieve higher magnetic recording areal density. Reduced head–disk spacing increases the risk of head/disk contact and causes the thermal instability in head–disk interface (HDI). This paper reports authors’ efforts towards exploration of interface solutions for writing-induced instability in ultra-low head–disk spacing magnetic system. Multi-shallow step structure with optimized rail position is analyzed and a new femto slider with such structure is explored. The results of numerical simulation indicate that the multi-shallow step structure is an effective approach in reducing the flying height change caused by the writing-induced nano-deformation of the slider body.     

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The structure and its optimization of 2.45GHz high power microwave ceramic window are introduced in this paper. The structure optimization includes optimization of structure dimensions and coolant flowing rate. The microwave properties are sufficient when the thickness of ceramic disk is 4.4mm and the length of cylindrical waveguide is 52.3mm. The maximum thermal stress on the ceramic disk is far less than the limitation that ceramic disk could sustainable stress when the coolant flowing rate is 0.4t×h^-1 . Optimized ceramic window did not appear crack problem after several runs of experiments.     

In situ FH analysis at disk drive level

Drive-level FH evaluation is important in terms of FH control, FH adjustment and disk drive robustness inside operating hard disk drives. Characterization of FH requires simple methodology, easy implementation in addition to the general requirement to in situ FH analysis. This paper reports authors’ effort in proposing a new FH error function to evaluate harmonic ratio FH methods; and based on the error function, a new FH measurement method named multi-frequency method, which calculates FH by reading back multi-frequency pattern, is proposed to minimize FH measurement error by optimizing pattern frequencies. Such technology is also applied at disk drive level to investigate FH variation when a hard disk drive is operating under variable environmental conditions.     

碟型量子阱微腔激光器的低阈值激射

利用反应离子刻蚀(RIE)和湿法腐蚀方法在InGaAs/InGaAsP多量子阱材料上研制出直径为8μm、4.5μm和2μm的碟型半导体微腔激光器。其中2μm直径的微碟在液氮温度下其光泵浦激射阈值仅为3μW左右。对高光功率密度下泵浦时出现的多模激射、跳模和激射光谱强度饱和现象进行了研究。并对微碟激光器的激射光谱线宽特性进行了初步的分析。     

Dynamic stability of rotating flexible disk perturbed by the reciprocating angular movement of suspension-slider system

To simulate the dynamic process of a magnetic head reading/writing data in a hard disk drive, a rotating flexible thin disk perturbed by the reciprocating angular movement of a suspension-slider system is modelled, where the suspension-slider system is considered as a mass-damping-spring loading system. A system dynamic model is formulated as a parametrically excited system, and its dynamic stability is studied by Hill’s method involving harmonic balance. The reciprocating angular movement of the suspension-slider system causes system parametric instability at some angular movement frequencies. The large-amplitude angular movement is especially dangerous, and angular movement frequency must be reduced when the slider works at large radii of the disk. The parametric instability can be avoided or suppressed by operating at: low-frequency and small-amplitude reciprocating angular movement, small mass, large natural frequency and damping of the suspension-slider system, and low-speed rotation of the disk.     

光束整形系统异形元件的研制

为了实现非球柱面镜的高精度加工,解决这一领域面临的难题,对非球柱面镜的加工和检测方法进行了深入的研究。采用古典与现代制造技术相结合的方法,研制了用于光束整形的异形元件,该异形元件是由非球柱面镜和柱面镜组成。针对非球柱面镜面型难以控制的问题,给出了独特的抛光模设计。结果表明：经过轮廓仪检测面型精度为0.848 7 μm,达到了图纸精度,满足了光学元件的使用要求。     

高分辨率航拍图像实时记录方法

针对某型高分辨率航空摄像机输出数据流达到每秒200兆字节,常规方法难于实现图像数据实时记录的问题,提出一种自启动多通道混合同步直写SCSI硬盘的方法.通过新设计的状态控制器,优化了SCSI硬盘的记录时序,使多个并行记录通道能根据数据缓存器和硬盘的状态自动产生独立的直写脉冲,以混合同步的方式将数据高速记录到硬盘上.实验结果表明:该方法可使图像数据持续记录速率达到每秒200兆字节,储存容量可达280吉字节,且结构简单、实用.     

527nm激光辐照盘靶背向散射能量测量

在星光Ⅱ激光装置上,测量了脉宽1ns、能量40-110J的527nm激光在不同条件下辐照Au盘靶、Al盘靶的背向散射能量。结果表明:激光辐照Au盘靶时．在聚焦条件下背向散射能量约占打靶激光能量的7．8％;在束匀滑条件下背向散射能量份额下降到6.2％左右,证明了束匀滑可有效抑制背向散射。对比Au盘靶、Al盘靶背反能量与打靶激光能量关系曲线,可以看出背向散射能量与打靶激光能量基本上成线性关系。 Au and Al disk target were irradiated with -1 ns, 40-110 J, 527 nm laser at Xingguang-Ⅱ facility. The backscattered lights by laser-produced plasma were studied experimentally. The results are in troduced in this paper. Backscattered light energy is 7.8% of laser energy when laser is focused on Au disk target; when laser beam is smoothed, it is 6.2%. The comparison shows that laser smoothing can restrain backscattered light efficiency. The experimental results :also show that there is a linear relation between backscattered light energy and the laser energy.     

Magnetic-field effects on exciton–polaron in a CdSe quantum disk

We study theoretically the interaction between excitons and longitudinal optical (LO) phonons in a cylindrical disk-like semiconductor quantum dot under an applied magnetic field. Due to the intensity of the interaction in the strong coupling regime, a composite quasi-particle called exciton–polaron is formed. We focus on the effect of the disk size and an external magnetic field on the exciton–phonon interaction energy and the exciton–polaron modes. The numerical computation for a CdSe quantum disk have shown that the exciton–phonon interaction energy is very significant and is even dominant when the disk height is small, which leads to a large Rabi splitting between the exciton–polaron modes. We investigate also the effect of the temperature on the integrated photoluminescence (PL) intensity, and show that at relatively high temperature the LO phonons have a noticeable effect on it. This physical parameter also shows a great dependence on quantum disk size and on magnetic field.     

Regimes of terminal motion of sliding spinning disks

Analysis of the frictional motion of a uniform circular disk of radius sliding and spinning on a horizontal table reported by Farkas et al. [Phys. Rev. Lett. 90, 248302 2003] shows that the disk always stops sliding and spinning at the same instant with a terminal speed ratio epsilon = v/Romega = 0.653. We show that different terminal behaviors can be found when one considers the motion of a two-tier disk with lower section thickness H(1) and radius R(1), and upper section thickness H(2) and radius H(3). The terminal motion may be analyzed in terms of the normalized radius of gyration k. It is found that while translation and rotation cease simultaneously, their terminal ratio epsilon(0) either vanishes when k > sq.root(2/3), is a nonzero constant when k < 1/2 < k < sq.rt (2/3), or diverges when k < 1/2. Experiments performed with plastic disks sliding on a nylon fabric stretched over a horizontal plate qualitatively corroborate the three different types of terminal motion.     

Stability of general relativistic static thick disks: the isotropic Schwarzschild thick disk

We study the stability of general relativistic static thick disks. As an application we consider the thick disk generated by applying the “displace, cut, fill and reflect” method, usually known as the image method, to the Schwarzschild metric in isotropic coordinates. The isotropic Schwarzschild thick disk obtained from this method is the simplest model to describe, in the context of General Relativity, real thick galaxies. Stability under a general first order perturbation of the disk energy momentum tensor is investigated. The first order perturbation, when applied to the conservation equations, leads to a set of differential equations that have fewer equations than unknowns. In this article we search for perturbations in which the perturbation of the four velocity in a certain direction leads to a pressure perturbation in the same direction. We found that, in general, the isotropic Schwarzschild thick disk is stable under these kinds of perturbations.     

厚圆盘弯曲振动研究

当厚跨比大于五分之一时,研究板弯曲振动中的剪切应力及由此引起的剪切、扭转变形等就不能忽略,经典的薄板理论将失效.从声学应用的角度,基于Mindlin板理论,本文推导了厚圆盘弯曲振动径向位移和横向位移的解析表达式,并得到了自由、简支、固定边界条件下的频率方程.解析方法计算得到的前几阶振型对应的频率与有限元方法计算的结果基本相符,与实验测试结果基本一致.本文的结果对厚圆盘弯曲振动辐射器的设计提供了理论参考. 关键词： 厚圆盘 弯曲振动 频率方程     

Handedness of magnetic-dipolar modes in ferrite disks

For magnetic-dipolar modes in a ferrite, components of the magnetic flux density in a helical coordinate system are dependent on both an orientation of a gyration vector and a sign of a pitch. It gives four types of helical harmonics for magnetostatic-potential wave functions in a ferrite disk. Because of the reflection symmetry breaking, coupling between certain types of helical harmonics takes place in the reflection points. The reflection feature leads to exhibition of two types of resonances: the “right” and “left” resonances. These resonances become coupled for a ferrite disk placed in a homogeneous tangential RF magnetic field. One also observes such resonance coupling for a ferrite disk with a symmetrically oriented linear surface electrode, when this ferrite particle is placed in a homogeneous tangential RF electric field. In a cylindrical coordinate system handedness of magnetic-dipolar modes in a ferrite disk is described by spinor wave functions.     

A 2D equivalent circuit of piezoelectric ceramic ring for transducer design

In this paper a 2D equivalent circuit of longitudinally polarized piezoelectric ceramic rings is established, which is obtained as an approximated analytical solution of 3D constitutive equations in the hypothesis of axial symmetry when the shearing stress and torsion are ignored. The mechanical part of the equivalent circuit can be divided into two branches; one branch characterizes the longitudinal extensional vibration, the other represents the radial vibration. The two branches, which are coupled to an electrical port by two transformers separately, mechanically couple to each other by some mechanical impedance at the same time. Similar circuit is also presented when piezoelectric disk is concerned. Based on this model it is able to compute all the relations between the input applied voltage and the output forces and velocities on every external surface analytically. Compared with the 1D equivalent circuits, the 2D equivalent circuit gives a more comprehensive predicts of the thickness and radial modes with sufficient accuracy when the ring or disk is thin. When the ring or disk is so thick that the 1D theory is not validated, an effective predict of the coupled vibration can also be presented. Comparisons with the experimental results show this model is rather accuracy in frequency calculation.