Characterization of light contact in head disk interface with dynamic flying height control

This paper presents an investigation of the light contact in a head disk interface with dynamic flying height control. The touchdown test is conducted for a dynamic flying height control slider and the response is recorded using AE sensor. The bouncing instability and light contacts are observed during thermal actuated touching down process of the slider. The physics-based simulation is conducted to correlate with the experiments, so as to characterize bouncing instability and the factors affecting bouncing instability. The enhanced spectrogram and HHT approaches are used to extract and characterize the non-stationary characteristics of the weak signal of slider response under light contact. It is found that the light contacts are constituted by a series of intermittent transient impact responses with frequency identical to slider??s pitch mode.     

Lubricant bonding, chemical structure, and additive effects on tribological performances at head–disk interfaces

 The lubricant film for head/disk application consists of bonded fraction and unbonded (mobile) fraction. It is well known that the mobile fraction of the lubricant film can replenish the surface sites where the lubricant film was depleted, thus, the surface wear is postponed or alleviated. With a continuous decrease in the head disk spacing, however, too much mobile fraction of lubricant may cause head slider lubricant pick-up, and deteriorate the interface. Two perfluoropolyether (PFPE) lubricants of Z-tetraol and Z-DOL are discussed in this paper. Lubricant Z-tetraol is characteristic of stronger bonding to a carbon overcoat, lower vapor pressure, and higher thermal stability but less mobility than Z-DOL. It is found that, for CSS (contact-start-stop) durability, the interfaces with Z-tetraol show no worse in performance than those with Z-DOL, and less head slider lubricant pick-up on those with Z-tetraol. Based on the above-mentioned, it is possible that the interfaces relying more on the lubricant bonding strength and chemical structure stability are more beneficial to tribological performances than those relying more on the lubricant replenishment. The effects of lubricant additive X1P mixed to Z-tetraol, and Z-DOL, respectively are also studied on tribological performances. Stiction, CSS durability, and head slider lubricant pick-up are discussed among lubricants Z-tetraol, Z-DOL, Z-tetraol/X1P and Z-DOL/X1P. Statistical t-test, F-test, and Weibull analyses are applied to CSS data to differentiate CSS durability performances. Additive X1P is found to enhance CSS durability for both lubricants. Lubricant Z-tetraol/X1P is recommended for the best tribological performances, followed by Z-DOL/X1P, Z-tetraol, and Z-DOL. Received: 7 August 2001/Accepted: 11 December 2001 Authors would like to thank Vidya K. Gubbi, Youmin Liu, and Gunter P. Barth at Seagate, Fremont, CA, for media supplies, lubricant properties, and head slider lubricant pick-up measurements. Authors also thank Gunter P. Bath, Frank Chang, Roger Y. Shih, Hamid R. Saman, Caroline Tjengdrawira and Sam Liang at Seagate for fruitful discussions.     

Interactions between nano-spacing flying head sliders and ultra-thin liquid lubricant films with non-uniform distribution in hard disk drives

This paper describes the effect of ultra-thin liquid lubricant films on air bearing dynamics and flyability of less than 10 nm spacing flying head sliders in hard disk drives. In particular, the effect of non-uniform lubricant film distributions on head/disk interface dynamics are studied. The disks with lubricant on one half of disk surface thicker than the other half were used in this study. The dynamics of sliders is monitored using acoustic emission (AE) and the interactions between the slider and disk are investigated experimentally. The disks were also examined with a scanning micro-ellipsometer before and after each test. Complicated slider responses were observed and clarified. In addition, it was found that the periodic lubricant film thickness modulations or non-uniformity caused by the slider-disk contact interactions could be observed. It is suggested that this lubricant film thickness non-uniformity will be one of the technical issues in order to achieve ultra-low head/disk contact interface of less than 10 nm.     

Static and dynamic flying characteristics of a slider on bit-patterned media (dynamic responses based on frequency domain analysis)

Recording media with grooves, such as discrete track media (DTM) and bit-patterned media (BPM), are considered to be promising media for achieving ultrahigh recording densities. It is thus important to analyze the static and dynamic characteristics of flying head sliders on DTM and BPM using the molecular gas film lubrication equation and the van der Waals (vdW) equation. In this study, we consider BPM with rectangular bits. We express the disk recess as a Fourier series and determine the quasi-static and time-dependent components. We also develop a perturbation method for small groove depths for calculating static slider attitudes and dynamic responses in the frequency domain. The numerical results predict that the grooves will significantly reduce the quasi-static flying height h ₀. They also predict that for a small groove depth h _groove, flying height decrease Δh ₀ almost agree with the value of uniform disk recess obtained by a Fourier series expansion, which also agrees with empirical results. Dynamic slider characteristics obtained by the frequency domain analysis is useful for sliders suffering from excitations of several tens of kHz such as sliders flying at transition between data zone and servo zone, although the dynamic spacing fluctuation by realistic BPM media is negligible.     

Effects of disk surface roughness on static flying characteristics of air bearing slider by using a combined method of Reynolds equation and rough disk surface

Reynolds equation was modified with adding the surface roughness parameters to analyze the effects of disk surface roughness on the static flying characteristic of an air bearing slider. However, the modification demands the complicated mathematical expressions and related knowledge of physics and mathematics. In this paper, a combined method of Reynolds equation without introducing the roughness parameters and rough disk surface is proposed to investigate the effects of disk surface roughness on the static flying characteristics of an air bearing slider, it is different from those models of modified Reynolds equation introducing the disk surface roughness used by many researchers. More importantly, this method avoids the complicated numerical calculation resulted from the mathematical expressions including the Peklenik parameter \(\gamma\) and roughness R_a. By using an Ω air bearing slider, we investigated the effects of disk surface roughness on the static flying characteristics of this slider, the results show that the Peklenik parameter \(\gamma\) and roughness R_a have a significant influence on the pressure distribution, the load carrying capacity and the location of the pressure centre.     

An event-based model for continuous media data on heterogeneous disk servers

Over the last few years, there has been intense work on the problem of retrieval of continuous media (CM) data from disk. However, no single unified framework exists within which such retrieval problems can be studied. In this paper, we first propose a formal model for CM data retrieval from heterogeneous disk servers. This model can be used to characterize CM data retrieval problems independently of how data is laid out on disk, and what objectives (e.g., minimize client delay, maximize buffer utilization, etc.) the system manager is interested in. We then show how using this formal model, we can neatly define what it means to optimally handle events that occur in movie-on-demand (MOD) systems. Examples of such events include new clients entering the system, old clients leaving the system, continuing clients doing pause, rewind and fast-forward operations. Multiple events may occur simultaneously and we show how such events trigger state transitions in the system. We then develop an algorithm called the QuickSOL algorithm that handles events occurring in MOD systems. This algorithm works in two phases: in the first phase, it quickly finds a way of handling as many of the events occurring at time t as possible. In the second phase, it optimizes the solution found in the first phase. The advantage is that the algorithm can be interrupted anytime after the first phase is completed. We report on experiments showing that QuickSOL works well in practice.     

A graphical editor and process visualization system for man-machine interfaces of dynamic systems

The process visualization system of a manmachine interface is presented. It allows human operator(s) to interact with a dynamic technical system, here a thermal power plant. Also, a graphical editor for designing dynamic pictures of the process visualization system is explained. Both new systems have a common architecture and are based on the computer graphics standard PHIGS-2D with extensions for handling non-graphical and graphical information. The hierarchical information structures are manipulated with lists and pointers in a dynamic visual database. The two menu-driven interfaces for designers and for operators are described with their multi-window display layouts. The software of both systems is highly portable to different hardware and to other application domains.     

A novel method based on realistic head model for EEG denoising

It is necessary to remove the noise in EEG before further EEG analysis and processing. For EEG is deeply masked in the noise background, it is very difficult to denoise EEG effectively. Proposed in this paper is a novel realistic head model based sparse decomposition algorithm to denoise EEG, which is an iterative procedure combining the subject's physiology of EEG generation into the denoising procedure. In this algorithm, the lead field overcomplete dictionary is numerically calculated according to the realistic head model firstly, and then the instantaneous EEG spatial potential is decomposed into one sparse combination of atoms in the lead field matrix by matching pursuit, and the sparse combination of atoms is to be regarded as the denoised EEG signal. The realistic head based sparse decomposition was tested by the simulated noisy potential and a real EEG recording collected in an oddball stimulus experiment, the results consistently confirmed the new method removed the uncorrelated noise in EEG effectively.     

Psychologically inspired anticipation and dynamic response for impacts to the head and upper body

We present a psychology-inspired approach for generating a character' s anticipation of and response to an impending head or upper body impact. Protective anticipatory movement is built upon several actions that have been identified in the psychology literature as response mechanisms in monkeys and in humans. These actions are parameterized by a model of the approaching object (the threat) and are defined as procedural rules. We present a hybrid forward and inverse kinematic blending technique to guide the character to the pose that results from these rules while maintaining properties of a balanced posture as well as characteristics of the behavior just prior to the interaction. In our case, these characteristics are determined by a motion capture sequence. We combine our anticipation model with a physically-based dynamic response to produce animations where a character anticipates an impact before collision and reacts to the contact, physically, after the collision. We present a variety of examples including threats that vary in approach direction, size and speed.     

Some effects of menu characteristics and user personality on performance with menu-driven interfaces

User performance with menu-based systems was studied. Three experiments concerning the effects of menu structure, menu breadth, menu system depth, several support facilities and user personality characteristics on user performance, measured in terms of search time and accuracy, are reported. The main findings are that performance is affected by menu structure, the depth of the menu system, the presence of escape facilities, the structure of the alternatives within the menu, some methods of informative support and certain personality characteristics. Some expensive support facilities are found to have no effect. The results are discussed in relation to problems of menu interface design.     

Constructing dynamic model for thermal flow forecasting based on experimental data

We consider an identification algorithm for a dynamic object. The algorithm allows for choosing any rows from the block of the transformed empirical input-output data. Moreover, the algorithm enables passing to a parameter space and involving a priori information on the domain of parameter existence to improve accuracy. These features serve to construct a model of the dynamic object with a smaller forecasting error. The algorithm is applied for mathematical modeling of a fuel assembly in a nuclear reactor based on experimental heat transfer data.     

基于动态有理函数的功放模型及预失真应用

针对现代无线通信系统中射频功率放大器的非线性与记忆效应,提出一种新的低复杂度的动态有理函数模型,该模型简化了有理函数模型,通过两个多项式的比进行建模,但分子是包络记忆多项式的形式,分母由无记忆多项式构成.通过模型仿真和预失真应用系统验证,结果表明:与记忆多项式模型相比,动态有理函数模型所需的系数要少30.6％,模型精度却与其相近,邻信道功率比(ACPR)改善约20 dB,而与有理函数模型相比,所需系数要少21.9％,模型精度改善2.4 dB,ACPR改善约15 dB.由此证明了该模型在复杂度和精确度上的优越性,对功放预失真的研究具有重要的参考价值.     

一种动态非线性模型传感器的辨识和补偿方法

针对利用Wiener模型表达的具有动态非线性的传感器进行系统辨识和性能补偿。将系统分解为动态非线性环节和静态线性环节,利用函数链人工神经网络和遗传算法分别进行系统辨识,通过静态非线性补偿将系统简化为线性系统,再进行动态性能补偿。利用LabVIEW设计虚拟仪器,经过仿真表明该方法是有效的。     

基于策略的可控服务发现与动态路由模型

如何改进现有服务发现模型使之适应动态可变的服务运行环境并选择最符合用户需求的Web服务正在引起研究领域关注.提出了一种基于策略的可控服务发现与动态路由模型(P-WSDRM).该模型支持抽象服务、服务实例和服务发现者的属性定义,支持携带属性描述信息的服务发布与发现,引入了策略判定机制,支持服务发现者基于已定义的策略进行服务发现和实例路由.目前已经于Linux平台和目录服务实现了该模型的一个原型系统.     

A study on the reference electrode standardization technique for a realistic head model

One oldest technical problem in EEG practice is the effect of an active reference on EEG recording, and it is especially important for identifying the temporal information of EEG recordings. To solve this problem, a reference electrode standardization technique (REST) has been proposed for a concentric three-sphere head model. REST, based on an equivalent distributed source model, reconstructs the potential with a reference at infinity from the potential with a scalp point reference or with the average reference. In this paper, investigated was the REST for a realistic head model. The results of simulation studies show that the potential reconstruction for the realistic head model is more sensitive to noise than that for the concentric three-sphere head model, so a regularized inverse by truncated singular value decomposition was introduced. The results confirm that REST is still an efficient method even for a realistic head model especially for the most important superficial cortex region.     

A dynamic conditional random field model for foreground and shadow segmentation

This paper proposes a dynamic conditional random field (DCRF) model for foreground object and moving shadow segmentation in indoor video scenes. Given an image sequence, temporal dependencies of consecutive segmentation fields and spatial dependencies within each segmentation field are unified by a dynamic probabilistic framework based on the conditional random field (CRF). An efficient approximate filtering algorithm is derived for the DCRF model to recursively estimate the segmentation field from the history of observed images. The foreground and shadow segmentation method integrates both intensity and gradient features. Moreover, models of background, shadow, and gradient information are updated adaptively for nonstationary background processes. Experimental results show that the proposed approach can accurately detect moving objects and their cast shadows even in monocular grayscale video sequences.     

基于进程防火墙与虚拟盘的非法信息流过滤方法

提出一种在虚拟磁盘中对文件映像前后的访问进程进行监控并对非法信息流进行过滤的方法。该方法在关键字或特征信息提取过程中安装各种钩子并对接入主机进行审计,用来提高系统服务器的包转发速率与非法信息的捕捉能力。其目的是阻止病毒或木马程序对文件破坏或数据包劫持,保证信息接入的可控性和安全性。实验测试表明,系统降低了包转发时延,提高了包转发速率和非法信息的识别能力。     

A generic complete dynamic logic for reasoning about purity and effects

For a number of programming languages, among them Eiffel, C, Java, and Ruby, Hoare-style logics and dynamic logics have been developed. In these logics, pre- and postconditions are typically formulated using potentially effectful programs. In order to ensure that these pre- and postconditions behave like logical formulae (that is, enjoy some kind of referential transparency), a notion of purity is needed. Here, we introduce a generic framework for reasoning about purity and effects. Effects are modelled abstractly and axiomatically, using Moggi’s idea of encapsulation of effects as monads. We introduce a dynamic logic (from which, as usual, a Hoare logic can be derived) whose logical formulae are pure programs in a strong sense. We formulate a set of proof rules for this logic, and prove it to be complete with respect to a categorical semantics. Using dynamic logic, we then develop a relaxed notion of purity which allows for observationally neutral effects such writing on newly allocated memory.