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.

Design and Characterization of Stabilized Derivatives of Human CD4D12 and CD4D1

CD4 is present on the surface of T-lymphocytes and is the primary cellular receptor for HIV-1. CD4 consists of a cytoplasmic tail, one transmembrane region, and four extracellular domains, D1-D4. A construct consisting of the first two domains of CD4 (CD4D12) is folded and binds gp120 with similar affinity as soluble 4-domain CD4 (sCD4). However, the first domain alone (CD4D1) was previously shown to be largely unfolded and had 3-fold weaker affinity for gp120 when compared to sCD4 [Sharma, D.; et al. (2005) Biochemistry 44, 16192-16202]. We now report the design and characterization of three single-site mutants of CD4D12 (G6A, L51I, and V86L) and one multisite mutant of CD4D1 (G6A/L511/L5K/F98T). G6A, L51I, and V86L are cavity-filling mutations while L5K and F98T are surface mutations which were introduced to minimize the aggregation of CD4D1 upon removal of the second domain. Two mutations, G6A and V86L in CD4D12 increased the stability and yield of the protein relative to the wild-type protein. The mutant CD4D1 (CD4D1a) with the 4 mutations was folded and more stable compared to the original CD4D1, but both bound gp120 with comparable affinity. In in vitro neutralization assays, both CD4D1a and G6A-CD4D12 were able to neutralize diverse HIV-1 viruses with similar IC(50)s as 4-domain CD4. These stabilized derivatives of human CD4 can be useful starting points for the design of other more complex viral entry inhibitors.

A new family of soft transition converters: Design and dynamic model

The soft switching converters evolved through the resonant load, resonant switch, resonant transition and active clamp converters to eliminate switching losses in power converters. This paper briefly presents the operating principle of the new family of soft transition converters; the methodology of design of these converters is presented through an example. In the proposed family of converters, the switching transitions of both the main switch and auxiliary switch are lossless. When these converters are analysed in terms of the pole current and throw voltage, the defining equations of all converters belonging to this family become identical.Such a description allows one to define simple circuit oriented model for these converters. These circuit models help in evaluating the steady state and dynamic model of these converters. The standard dynamic performance functions of the converters are readily obtainable from this model. This paper presents these dynamic models and verifies the same through measurements on a prototype converter.

Design and Optimization of Broadband Micromachined Antenna

Performance improvement of a micromachined patch antenna operating at 30 GHz with a capacitively coupled feed arrangement is presented here. Such antennas are useful for monolithic integration with active components. Specifically, micromachining can be employed to achieve a low dielectric constant region under the patch which causes (i) the suppression of surface waves and hence the increase in radiation efficiency and (ii) increase in the bandwidth. The performance of such a patch antenna can be significantly improved by selecting a coupled feed arrangement. We have optimized the dimensions and location of the capacitive feeding strip to get the maximum improvement in bandwidth. Since this is a totally planar arrangement, and does not involve any stacked structures, this antenna is easy to fabricate using standard microfabrication techniques. The antenna element thus designed has a -10 dB bandwidth of 1600 MHz

Design and developement of a pulsed power system for a Vircator based HPM source

Pulse Forming Line (PFL) based high voltage pulsed power systems are well suited for low impedance High Power Microwave (HPM) sources such as a virtual cathode oscillator (VIRCATOR) operating in nanosecond regimes. The system under development consists of a primary voltage source that charges the capacitor bank of a Marx pulser over a long time duration. The Marx pulser output is then conditioned by a PFL to match the requirement of the HPM diode load. This article describes the design and construction of an oil insulated pulse forming line for a REB (Relativistic Electron Beam) diode used in a VIRCATOR for the generation of high power microwaves. Design of a 250 kV/10 kA/60 ns PFL, including the PSPICE simulation for various load conditions are described.