Terril Hurst

Disk drive pivot nonlinearity modeling. II. Time domain

For pt. I see ibid. p.2600-3. This paper describes studies done at HP Labs on the actuator pivot bearing nonlinearity of a small disk drive. It presents several models and discusses a time-domain approach, comparing simulated and lab measured torque versus displacement hysteresis curves. Using the measured and simulated time and frequency responses as a guide, the designer can iteratively improve the model of the system and verify the correctness of the measurements.

The PES Pareto method: uncovering the strata of position error signals in disk drives

Describes a method of breaking down the position error signal (PES) of a magnetic disk drive to its contributing components. Once these components are identified, they can be ranked in terms of their overall effect on PES and thus the most critical ones can be worked on first. This method is based on three things: an understanding of how Bodes integral theorem ties into noise measurements, a measurement methodology that allows for the isolation of individual noise sources, and a system model that allows these sources to be recombined to form the drives position error signal. We have found this method to be dramatically useful in identifying the key contributors to PES noise.

Decomposition of baseline noise sources in hard disk position error signals using the PES Pareto method

This paper uses the position error signal (PES) Pareto method and measurement techniques for isolating noise sources to decompose the PES of a Lynx II hard disk drive manufactured by Hewlett-Packard. This accomplishes three things: it demonstrates the utility of the PES Pareto method in a practical example, it allows us to discover which noise sources are insignificant to PES, and it identifies which noise sources are significant to PES. In this particular hard disk drive, it is discovered that the two most significant sources of baseline noise at the disks position error signal are the turbulent wind flow generated by the spinning disks (windage) and the noise involved in the actual readback of the Position Error Signal (position sensing noise).

Data-Centric Routing in Sensor Networks using Biased Walk

We present spiral, a data-centric routing algorithm for short-term communication in unstructured sensor networks. Conventional data-centric routing algorithms are based on flooding or random walk. Flooding returns the shortest route but has a high search cost; random walk has a lower search cost but returns a sub-optimal route. Spiral offers a compromise between these two extremes - it has a lower search cost than flooding and returns better routes than random walk. Spiral is a biased walk that visits nodes near the source before more distant nodes. This results in a spiral-like search path that is not only more likely to find a closer copy of the desired data than random walk, but is also able to compute a shorter route because the network around the source is more thoroughly explored. Our experiments show that in a 500-node network with an average degree of 20 and two copies of every data object, for a short-term communication of 40 packets the total communication cost by spiral is only 72% of that by flooding, 81% of ERS, 74% of random walk, and 73% of DFS

Efficient and robust query processing for mobile wireless sensor networks

We present CNFS, an algorithm for efficient and robust query processing for mobile wireless sensor networks. CNFS is a walk-based algorithm that is biased to visit nodes close to the source first. This bias is accomplished by collecting topology information about the network as the search progresses. This information is also used to compute the shortest return path for the query result and to tolerate changes in the network topology caused by node mobility that could otherwise cause the query to fail. As a result, CNFS requires fewer messages to process a query than flooding-based algorithms, while tolerating node mobility better than random walk-based algorithms. Our experiments show that in medium-density networks (average node degree 8.3) CNFS requires about 38% fewer messages than the other algorithms studied, while experiencing significantly fewer query failures than random walk-based algorithms in both sparse and dense networks. CNFSs success rate is comparable to flooding-based algorithms in dense networks and slightly worse in sparse networks.

WSN01-4: Efficient and Robust Query Processing for Mobile Wireless Sensor Networks

We present CNFS, an algorithm for efficient and robust query processing for mobile wireless sensor networks. CNFS is a walk-based algorithm that is biased to visit nodes close to the source first. This bias is accomplished by collecting topology information about the network as the search progresses. This information is also used to tolerate changes in the network topology caused by node mobility that could otherwise cause the query to fail. As a result, CNFS requires fewer messages to process a query than flooding-based algorithms, while tolerating node mobility better than random walk-based algorithms. Our experiments show that in medium-density networks (average node degree 8.3) CNFS requires about 37% fewer messages than the other algorithms studied, while experiencing significantly fewer query failures than random walk-based algorithms in both sparse and dense networks. CNFSs success rate is comparable to flooding-based algorithms in dense networks and slightly worse in sparse networks.

Simulation-Based Embedded Agile Development

Developers of embedded systems are driven to constantly improve product quality, reduce cost, and rapidly deliver reliable working code. The embedded software domain applies constraints which can hinder agile methodologies commonly used to achieve such benefits. Simulation-based software development is one proven method that addresses these constraints. When tailored to work in conjunction with agile principles, simulation centric development facilitates meeting product goals. In this article, the authors discuss techniques for leveraging software-in-simulation (SiS) in conjunction with agile methodologies, and illustrate how combining agile with SiS contributes to gaining more benefit from agile practices and facilitates better software development.

Designed Simulation Experiments, Part 1: Roots, Myths, and Limitations of Conventional DOE

This paper illustrates specific challenges encountered in attempting to follow standardized principles and methods, established during the earlier eras of design of experiments (DOE), when the task is the design and analysis of simulation experiments (DASE). These problems are accentuated when DASE is used to develop and improve software-centric systems, such as guided missiles, which manifest a new level of dynamic complexity. An analysis of the current issues paves the way for successful DASE, and a companion paper (Part 2) describes how DOE is being modified and expanded to increase likelihood success in this emerging era. I. Introduction NGINEERED systems and the methods for developing them are as diverse as the imagination of mankind. Robust interaction has always existed between those who are passionate about “making a better mousetrap” (product) and those who are committed to finding a better way (process) to make a better mousetrap. This paper and its companion paper (Part 2) describe lessons learned over several decades of this product/process interaction in the use of design of experiments (DOE). DOE usage is examined when the source of experimental samples is a complex simulation, not an industrial process or an instrumented, “real-world” device under test. Several key issues arise and must be addressed in order for DOE to be used successfully with simulation, especially when the system being simulated includes embedded software, which fundamentally affects hardware functions, leading to a combinatoric explosion in the number system behavioral modes. As developers and users of performance simulations, the authors draw from experience gained during the creation and analysis of guided missile systems. Each of these systems includes real-time software that controls hardware, operating across a vast space of conditions and behavioral modes. Such complex systems call for collaborative engineering methods that are both disciplined and yet able to accommodate rapid rates of change during system design and development. The paper uses specific examples from the authors’ experience, emphasizing the challenges imposed by software-centric systems and simulations. These fast-evolving, multi-mode systems are a far cry from the original agricultural crops where DOE’s roots were established; they defy application of anything approaching an “ANSI-standard” DOE. Two premises are assumed at the outset: (a) that an organized, disciplined approach to engineering generally—and especially for simulating software-centric systems—is preferable to an approach lacking structure and discipline, and that (b) contrary to portrayal by some skeptics, DOE is not intended to be a cookie-cutter recipe that stifles creativity or obviates the need for intense involvement of domain experts. Both points are well-established generally. The devil emerges in the details of implementing DOE for simulation. After a brief review of the histories of DOE and simulation, the paper illustrates several of these troublesome details. A. The Dynamic Complexity of Simulation. Fully testing all combinations of system modes and environments is highly impractical. As a result of the Department of Defense policy of Simulation Based Acquisition, the fundamental requirement for a missile performance simulation is to verify performance in lieu of conducting expensive flight tests. 1 Usage of the simulation for this final assessment occurs late in the development cycle, with a mature simulation that adequately represents the final system. However,

Temperature-dependence of optical constants in phase-change media

The reflectivity of the phase-change media of optical recording changes slightly upon the application of a weak laser pulse (i.e., a pulse of insufficient power to write/erase a mark), returning to its initial value at the end of the pulse. This behavior is shown to be due to the temperature-dependence of the optical constants of the phase-change layer.

Analysis of RBQ: a new cooperative web caching mechanism that adapts to link congestion

A new Web proxy cooperation model is introduced and analyzed that preserves advantages of cooperative caching in the presence of proxy link capacity variations. The Restricted Broadcast Query (RBQ) cooperation model uses a score table containing dynamic information that describes proxy connectivity. This information is used to re-distribute load among proxies, thereby compensating for changes in link capacities. An analytic model was developed to evaluate network congestion effects on alternative Web proxy cooperation mechanisms (CMs). The model was applied to a system of identical, fully connected proxies, in order to compare the performance of two common CMs (Broadcasting and URL-hashing) with that of RBQ.