A neutron dosemeter for nuclear criticality accidents

A neutron dosemeter which offers instant read-out has been developed for nuclear criticality accidents. The system is based on gels containing emulsions of superheated dichlorodifluoromethane droplets, which vaporise into bubbles upon neutron irradiation. The expansion of these bubbles displaces an equivalent volume of gel into a graduated pipette, providing an immediate measure of the dose. Instant read-out is achieved using an array of transmissive optical sensors which consist of coupled LED emitters and phototransistor receivers. When the gel displaced in the pipette crosses the sensing region of the photomicrosensors, it generates a signal collected on a computer through a dedicated acquisition board. The performance of the device was tested during the 2002 International Accident Dosimetry Intercomparison in Valduc, France. The dosemeter was able to follow the initial dose gradient of a simulated accident, providing accurate values of neutron kerma; however, the emulsion was rapidly depleted of all its drops. A model of the depletion effects was developed and it indicates that an adequate dynamic range of the dose response can be achieved by using emulsions of smaller droplets.     

Comparison of finite element and lumped parameter methods for oceanic cables

The purpose of this work is to examine the basic foundations, similarities and fundamental differences between the finite element methods (FEM) and the lumped parameter methods (LPM) of analysis for oceanic cables under hydrodynamic load conditions. The continuum method (CM) is presented as a ‘ground truth’ prior to presenting each aspect of the approximate method derivations.     

Dynamic stability of periodic solutions of large scale nonlinear systems

A method suitable for the stability analysis of periodic solutions of large nonlinear systems is presented. The stability behaviour is inferred from a Galerkin approximation of the associated Poincaré map. The practical value of the method is shown by applying it to the nonlinear finite element model of a large scale wind energy convertor.     

Electronic neutron personal dosimetry with superheated drop detectors

The prototype of an electronic personal neutron dosemeter based on superheated drop detectors is presented. This battery operated device comprises a neutron sensor, bubble-counting electronics and a temperature controller ensuring an optimal dose equivalent response. The neutron sensor is a 12 ml detector vial containing an emulsion of about 50,000 halocarbon-12 droplets of 100 microns diameter. The temperature controller is a low-power, solid-state device stabilising the emulsion at 31.5 degrees C by means of an etched foil heater. The microprocessor controlled counting electronics relies on a double piezo-electric transducer configuration to record bubble formation acoustically via a comparative pulse-shape analysis of ambient noise and detector signals. The performance of the dosemeter was analysed in terms of the requirements presently developed for neutron personal dosemeters. The detection threshold is about 1 microSv, while the personal dose equivalent response to neutrons in the thermal to 62 MeV range falls within a factor 1.6 of 13 bubbles per microSv.     

Pervasive Personal Computing in an Internet Suspend/Resume System

The Internet suspend/resume model of mobile computing cuts the tight binding between PC state and PC hardware. By layering a virtual machine on distributed storage, ISR lets the VM encapsulate execution and user customization state; distributed storage then transports that state across space and time. This article explores the implications of ISR for an infrastructure-based approach to mobile computing. It reports on experiences with three versions of ISR and describes work in progress toward the OpenISR version     

TARA: Topology-Aware Resource Adaptation to Alleviate Congestion in Sensor Networks

Network congestion can be alleviated either by reducing demand (traffic control) or by increasing capacity (resource control). Unlike in traditional wired or other wireless counterparts, sensor network deployments provide elastic resource availability for satisfying the fidelity level required by applications. In many cases, using traffic control can violate fidelity requirements. Hence, we propose the use of resource control: increasing capacity by enabling more nodes to become active during periods of congestion. However, a naive approach to increase resources without a careful consideration of the type of congestion, traffic pattern, and network topology make the situation worse. In this paper, we present TARA, a topology-aware resource adaptation strategy to alleviate congestion. The core of TARA is our capacity analysis model, which can be used to estimate capacity of various topologies. Detailed performance results show that TARA can achieve data delivery rate and energy consumption that is close to an ideal offline resource control algorithm.     

Stopping power of Mylar for heavy ions up to copper

The stopping powers of Mylar for several heavy ions covering Z=11 to 29 in the energy range 0.3 to 2.3 MeV/n have been measured using the elastic recoil detection technique and twin detector system. The technique provided a unique method to generate a variety of variable energy ion species utilizing a fixed energy 140 MeV Ag¹³⁺ primary beam from the Pelletron accelerator facility at Nuclear Science Center, New Delhi, India. Most of these measurements are new. The experimentally measured stopping power values have been compared with those calculated using LSS theory, Ziegler et al. formulation and Northcliffe and Schilling tabulations. Merits and demerits of these formulations are highlighted. Stopping power calculations using the Hubert et al. formulation have been extended successfully beyond its recommended range of validity, i.e. 2.5–500 MeV/n down to energies as low as 0.5 MeV/n.     

Above ground standing biomass and carbon storage in village bamboos in North East India

Bamboo forms an important component in the traditional landscape of North East India. For biomass estimation of village bamboos of Barak Valley, North East India, allometric relationships were developed by harvest method describing leaf, branch and culm biomass with DBH as an independent variable using a log linear model. The culm density of the stand was 8950 culms ha⁻¹ during 2005 of which 67% of growing stock was represented by Bambusa cacharensis, 17.88% by Bambusa vulgaris and 15.12% by Bambusa balcooa. Above ground stand biomass was 121.51 t ha⁻¹ of which 86% was contributed by culm component followed by branch (10%) and leaf (4%). With respect to species, B. cacharensis made up to 46% of total stand biomass followed by B. vulgaris (28%) and B. balcooa (26%). Carbon storage in the above ground biomass was 61.05 t ha⁻¹. Allocation of C was more in culm components (53.05 t ha⁻¹) than in branch (5.81 t ha⁻¹) and leaf (2.19 t ha⁻¹). Carbon storage in the litter floor mass was 2.40 t ha⁻¹, of which leaf litter made up the highest amount (1.37 t ha⁻¹) followed by sheath (0.86 t ha⁻¹) and branch (0.17 t ha⁻¹). Carbon stock in the soil up to 30 cm depth was 57.3 t ha⁻¹. Gross C stock in the plantation was estimated to be 120.75 t ha⁻¹. Carbon storage estimated in the bamboo stand of present study offers insights into the opportunity of village bamboos in the rural landscape for carbon storage through carbon sequestration. Management and utilization of village bamboos as a potential source of carbon sink by smallholder farmers are discussed in the context of their livelihood security and the Millennium Development Goals of the United Nations.