磁头/磁盘滑动接触下磁盘温度及热退磁临界条件的研究

采用二维轴对称有限元模型计算磁头/磁盘滑动接触下,铝质磁盘的稳态温度和热应力场以及热退磁临界条件.结果表明:磁盘温度在极短时间内升至摩擦稳态值,然后缓慢线性升高到最终稳态值;经过充分热传导和热交换后磁盘的温度梯度较小,此时磁层内的热应力集中分布于磁盘固定端边缘附近;磁盘的稳态温度和热应力均随速度增大而增大,且载荷越大其值增大越快;热应力小于1.2 GPa时所对应的速度和载荷为安全工况;温升大于373 K时所对应的工况将导致磁盘退磁.     

Study of diode-pumped Yb:YAG disk lasers at low temperature

A Yb:YAG disk laser with V-shaped stable resonator and active-mirror configuration,end-pumped by a 940-nm InGaAs laser diode array,is demonstrated.Performances and optimization of the disk laser at low temperature over a range of 130-200 K are investigated theoretically and experimentally.Laser output energy of 1.46 J/pulse operating at 10-Hz repetition rate is obtained with the optimum output coupler transmission of 30%,and the corresponding optical-to-optical efficiency is 48.7%.     

磁头/磁盘间润滑剂转移机理及影响因素

硬盘存储密度的增加促使磁头的飞行高度不断降低.降低磁头飞行高度所导致的润滑剂在磁头与磁盘之间的转移已成为影响磁头飞行稳定性的一个重要因素.本文采用改进后的粗粒珠簧模型,应用分子动力学模拟方法,对磁头/磁盘之间润滑剂转移的机理进行研究.分析了磁盘表面润滑膜厚度、润滑剂种类以及磁头表面局部温度差对磁头/磁盘之间润滑剂转移量的影响.研究结果表明:转移到磁头上的润滑剂的体积随磁盘表面润滑膜厚度的增加而急剧增加;增加单个分子中羟基的数量,可以显著减少转移到磁头上的润滑剂的体积;磁头表面的局部高温可增加转移到磁头上的润滑剂的体积,且增加单个分子中羟基的数量可显著改善局部温度差对磁头/磁盘之间润滑剂转移的影响.     

Numerical investigations of asymmetric flow of a micropolar fluid between two porous disks

Numerical solution is presented for the two- dimensional flow of a micropolar fluid between two porous coaxial disks of different permeability for a range of Reynolds number Re （-300≤ Re 〈 0） and permeability parameter A （1.0≤A ≤2.0）. The main flow is superimposed by the injection at the surfaces of the two disks. Von Karman＇s similarity transformations are used to reduce the governing equations of motion to a set of non-linear coupled ordinary differential equations （ODEs） in dimensionless form. An algorithm based on the finite difference method is employed to solve these ODEs and Richardson＇s extrapolation is used to obtain higher order accuracy. The results indicate that the parameters Re and A have a strong influence on the velocity and microrotation profiles, shear stresses at the disks and the position of the viscous/shear layer. The micropolar material constants cl, c2, c3 have profound effect on microrotation as compared to their effect on streamwise and axial velocity profiles. The results of micropolar fluids are compared with the results for Newtonian fluids.     

Annulus and Disk Complex Is Contractible and Quasi-convex

The annulus and disk complex is defined and researched. Especially, we prove that this complex is contractible and quasi-convex in the curve complex.     

The mechanism of stiffness increase phenomenon of a rubbing disk

The phase characteristic of a disk rubbing with a ring supported elastically is investigated and used to explain the mechanism of stiffness increase phenomenon. As long as the rubbing is maintained, the averaged phase difference between the disk and the rotating mass on the disk is defi- nitely less than π/2. When the rubbing finishes, the phase difference quickly approaches to 7r. This behavior is inde- pendent of the physics parameters of the rubbing system. The theoretical results are qualitatively verified with experiments.     

A note on a quadratic rational map with two Siegel disks

Suppose f（z） is a quadratic rational map with two Siegel disks. If the rotation numbers of the Siegel disks are both of bounded type, the Hausdorff dimension of the Julia set satisfies Dim （J（f））〈2.     

Compression of the self-Q-switching in semiconductor disk lasers with single-layer graphene saturable absorbers

We demonstrate the first use of single layer graphene for compressing self-Q-switching pulses in semiconductor disk lasers. The gain region of the semiconductor disk laser used InGaAs quantum wells with a central wavelength of 1030 nm. Due to self saturable absorption of the quantum wells, the disk laser emitted at the self-Q-switching state with a pulse width of 13 μs. By introducing the single layer graphene as a saturable absorber into the V-shaped laser cavity, the pulse width of the self-pulse was compressed to 2 μs with a lower pump power of 300 mW. As the pump power was increased, multiple pulses with the pulse width of 1.8 μs appeared. The compression factor was about 7.2.     

热辅助磁盘探针存储的研究

描述了一种热辅助磁盘存储技术，该技术可应用于未来的高密度磁盘存储.记录介质是一种CoNi/Pt多层膜，它可用作垂直模式的磁记录介质.使用扫描隧道显微镜(STM)产生的隧道电流作为热源对磁膜进行局部加热.隧道电流随着加在STM针尖与磁膜之间的脉冲电压幅值的增大而增大.实验结果显示了圆形记录点在磁膜上生成，记录点尺寸与电压值相关，阈值电压为4V左右.当电压高于阈值时，记录点尺寸随着电压的增大而增大,平均尺寸为170nm；当电压低于阈值时，未发现记录点.一个简单的模型解释了以上实验现象. 关键词： 扫描隧道显微镜 热辅助磁盘存储技术 高密度磁盘存储