Glassy behavior in neural network models of associative memory

Neural network models of associative memory exhibit a large number of spurious attractors of the network dynamics which are not correlated with any memory state. These spurious attractors, analogous to "glassy" local minima of the energy or free energy of a system of particles, degrade the performance of the network by trapping trajectories starting from states that are not close to one of the memory states. Different methods for reducing the adverse effects of spurious attractors are examined with emphasis on the role of synaptic asymmetry. (C) 2002 Elsevier Science B.V. All rights reserved.

Study of thickness dependence on electrical properties of (Pb,La)TiO3 thin films for memory applications

Lead-lanthanum-titanate (Pb0.72La0.28)TiO3 (PLT) is one of the interesting materials for DRAM applications due to its room temperature paraelectric nature and its higher dielectric permittivity. PLT thin films of different thickness ranging from 0.54- 0.9 mum were deposited on Pt coated Si substrates by excimer laser ablation technique. We have measured the voltage (field) dependence, the thickness dependence, temperature dependence of dc leakage currents and analysis is done on these PLT thin films. Current- voltage characteristics were measured at different temperatures for different thick films and the thickness dependence of leakage current has been explained by considering space charge limited conduction mechanism. The charge transport phenomena were studied in detail for films of different thicknesses for dynamic random access memory applications.

Unsteady mhd flow and heat transfer on a rotating disk in an ambient fluid

An unsteady flow and heat transfer of a viscous incompressible electrically conducting fluid over a rotating infinite disk in an otherwise ambient fluid are studied. The unsteadiness in the flow field is caused by the angular velocity of the disk which varies with time. The magnetic field is applied normal to the disk surface. The new self-similar solution of the Navier-Stokes and energy equations is obtained numerically. The solution obtained here is not only the solution of the Navier-Stokes equations, but also of the boundary layer equations. Also, for a simple scaling factor, it represents the solution of the flow and heat transfer in the forward stagnation-point region of a rotating sphere or over a rotating cone. The asymptotic behaviour of the solution for a large magnetic field or for a large independent variable is also examined. The surface shear stresses in the radial and tangential directions and the surface heat transfer increase as the acceleration parameter increases. Also the surface shear stress in the radial direction and the surface heat transfer decrease with increasing magnetic field, but the surface shear stress in the tangential direction increases. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Asymmetric Warps in Disk Galaxies: Dependence on Dark Matter Halo

Recent observations have shown that most of the warps in the disk galaxies are asymmetric. However there exists no generic mechanism to generate these asymmetries in warps. We have shown that a rich variety of possible asymmetries in the z-distribution of the spiral galaxies can naturally arise due to a dynamical wave interference between the first two bending modes i.e. bowl-shaped mode(m=0) and S-shaped warping mode(m = 1) in the galactic disk embedded in a dark matter halo. We show that the asymmetric warps are more pronounced when the dark matter content within the optical disk is lower as in early-type galaxies.

Composition tunable memory and threshold switching in Al20As xTe80− x semiconducting glasses

I-V studies indicate a composition dependent switching behavior (Memory or Threshold) in bulk Al20AsxTe80−x glasses, which is determined by the coordination and composition of aluminum. Investigations on temperature and thickness dependence of switching and structural studies on switched samples suggest thermal and electronic mechanisms of switching for the memory and threshold samples, respectively. The present results also show that these samples have a wider composition range of threshold behavior with lower threshold voltages compared to other threshold samples.

Design and Implementation of a Flexible and Memory Efficient Operating System for Sensor Nodes

Sensor network nodes exhibit characteristics of both embedded systems and general-purpose systems.A sensor network operating system is a kind of embedded operating system, but unlike a typical embedded operating system, sensor network operatin g system may not be real time, and is constrained by memory and energy constraints. Most sensor network operating systems are based on event-driven approach. Event-driven approach is efficient in terms of time and space.Also this approach does not require a separate stack for each execution context. But using this model, it is difficult to implement long running tasks, like cryptographic operations. A thread based computation requires a separate stack for each execution context, and is less efficient in terms of time and space. In this paper, we propose a thread based execution model that uses only a fixed number of stacks. In this execution model, the number of stacks at each priority level are fixed. It minimizes the stack requirement for multi-threading environment and at the same time provides ease of programming. We give an implementation of this model in Contiki OS by separating thread implementation from protothread implementation completely. We have tested our OS by implementing a clock synchronization protocol using it.

Micro stepping of Shape Memory Alloy based Poly Phase motor

In literature we find broadly two types of shape memory alloy based motors namely limited rotation motor and unlimited rotation motor. The unlimited rotation type SMA based motor reported in literature uses SMA springs for actuation. An attempt has been made in this paper to develop an unlimited rotation type balanced poly phase motor based on SMA wire in series with a spring in each phase. By isolating SMA actuation and spring action we are able achieve a constant force by the SMA wire through out its range of operation. The Poly phase motor can be used in stepping mode for generating incremental motion and servo mode for generating continuous motion. A method of achieving servo motion by micro stepping is presented. Micro stepping consists of controlling single-phase temperature with a position feedback. The motor has been modeled with a new approach to the SMA wire Hysterysis model. Motor is simulated for different responses and the results are compared with the experimental data.

Java Memory Model aware Software validation

The Java Memory Model (JMM) provides a semantics of Java multithreading for any implementation platform. The JMM is defined in a declarative fashion with an allowed program execution being defined in terms of existence of "commit sequences" (roughly, the order in which actions in the execution are committed). In this work, we develop OpMM, an operational under-approximation of the JMM. The immediate motivation of this work lies in integrating a formal specification of the JMM with software model checkers. We show how our operational memory model description can be integrated into a Java Path Finder (JPF) style model checker for Java programs.

Origin of Disk Lopsidedness in Spiral Galaxies

In our work we have used the atomic hydrogen [HΙ] gas distribution in the HΙ 21-cm line emission to study the dark matter halo perturbations. For tHΙs analysis, the 2-D HΙ surface density and velocity maps (arcHΙval) of the galaxies in the Eridanus group (obtained using the GMRT) and in the Ursa Major group (obtained from WSRT) were used. In addition a few HΙckson Compact Groups of galaxies were also studied using the GMRT. The HΙ maps of these galaxies were Fourier analysed to estimate the asymmetry in the distribution and motion of gas. The average asymmetry parameter in the 1.5 to 2.5 K′-band scale lengths was found to be ~ 0.27 for the Eridanus group of galaxies wHΙle it was ~ 0.14 for the Ursa Major group of galaxies. The asymmetries in the distribution of HΙ as a function of Hubble type of galaxies were also studied and was found to be directly correlated with the compactness of the groups. In addition, the trend in the asymmetry as a function of the Hubble type of galaxies was opposite to that seen in the field galaxies, i.e., in the group galaxies, the early type galaxies showed more asymmetry than late type. These two aspects indicated that tidal interactions between the galaxies in a group environment to be the major cause of asymmetries. The observed asymmetry parameters were consistent with recent numerical simulations of asymmetries of gas disk caused by fly-by interactions. We have also estimated the perturbation of dark matter halo using the asymmetry parameter obtained from the Fourier series analysis of the surface density maps.

Memory Architecture Exploration Framework for Cache Based Embedded SoC

Today's feature-rich multimedia products require embedded system solution with complex System-on-Chip (SoC) to meet market expectations of high performance at a low cost and lower energy consumption. The memory architecture of the embedded system strongly influences critical system design objectives like area, power and performance. Hence the embedded system designer performs a complete memory architecture exploration to custom design a memory architecture for a given set of applications. Further, the designer would be interested in multiple optimal design points to address various market segments. However, tight time-to-market constraints enforces short design cycle time. In this paper we address the multi-level multi-objective memory architecture exploration problem through a combination of exhaustive-search based memory exploration at the outer level and a two step based integrated data layout for SPRAM-Cache based architectures at the inner level. We present a two step integrated approach for data layout for SPRAM-Cache based hybrid architectures with the first step as data-partitioning that partitions data between SPRAM and Cache, and the second step is the cache conscious data layout. We formulate the cache-conscious data layout as a graph partitioning problem and show that our approach gives up to 34% improvement over an existing approach and also optimizes the off-chip memory address space. We experimented our approach with 3 embedded multimedia applications and our approach explores several hundred memory configurations for each application, yielding several optimal design points in a few hours of computation on a standard desktop.

Shape memory alloy based motor

Design and characterization of a new shape memory alloy wire based Poly Phase Motor has been reported in this paper. The motor can be used either in stepping mode or in servo mode of operation. Each phase of the motor consists of an SMA wire with a spring in series. The principle of operation of the poly phase motor is presented. The motor resembles a stepper motor in its functioning though the actuation principles are different and hence has been characterized similar to a stepper motor. The motor can be actuated in either direction with different phase sequencing methods, which are presented in this work. The motor is modelled and simulated and the results of simulations and experiments are presented. The experimental model of the motor is of dimension 150mm square, 20mm thick and uses SMA wire of 0·4mm diameter and 125mm of length in each phase.

Bit Steering In The Minimization Of Control Memory In Microprogrammed Digital-Computers

This correspondence presents an algorithm for microprogram control memory width minimization with the bit steering technique. The necessary and sufficient conditions to detect the steerability of two mutually exclusive sets of microcommands are established. The algorithm encodes the microcommands of the sets with a bit steering common part and also extends the theory to multiple (more than two) sets of microcommands.