Ashish Sharma

Dynamically mapping tasks with priorities and multiple deadlines in a heterogeneous environment

In a distributed heterogeneous computing system, the resources have different capabilities and tasks have different requirements. To maximize the performance of the system, it is essential to assign the resources to tasks (match) and order the execution of tasks on each resource (schedule) to exploit the heterogeneity of the resources and tasks. Dynamic mapping (defined as matching and scheduling) is performed when the arrival of tasks is not known a priori. In the heterogeneous environment considered in this study, tasks arrive randomly, tasks are independent (i.e., no inter-task communication), and tasks have priorities and multiple soft deadlines. The value of a task is calculated based on the priority of the task and the completion time of the task with respect to its deadlines. The goal of a dynamic mapping heuristic in this research is to maximize the value accrued of completed tasks in a given interval of time. This research proposes, evaluates, and compares eight dynamic mapping heuristics. Two static mapping schemes (all arrival information of tasks are known) are designed also for comparison. The performance of the best heuristics is 84% of a calculated upper bound for the scenarios considered.

Optical and RF electrical characteristics of atmospheric pressure open-air hollow slot microplasmas and application to bacterial inactivation

We report electrical properties of radio frequency (RF)-driven hollow slot microplasmas operating in open air but with uniform luminous discharges at RF current densities of the order of A cm −2 . We employ interelectrode separations of 100–600 µm to achieve this open-air operation but because the linear slot dimension of our electrode designs are of extended length, we can achieve, for example, open-air slot shaped plasmas 30 cm in length. This creates a linear plasma source for wide area plasma driven surface treatment applications. RF voltages at frequencies of 4–60 MHz are applied to an interior electrode to both ignite and sustain the plasma between electrodes. The outer slotted electrode is grounded. Illustrative absolute emission of optical spectra from this source is presented in the region from 100 to 400 nm as well as total oxygen radical fluxes from the source. We present both RF breakdown and sustaining voltage measurements as well as impedance values measured for the microplasmas, which use flowing rare gas in the interelectrode region exiting into open air. The requirement for rare gas flow is necessary to get uniform plasmas of dimensions over 30 cm, but is a practical disadvantage. In one mode of operation we create an out-flowing afterglow plasma plume, which extends 1–3 mm from the grounded open slot allowing for treatment of work pieces placed millimetres away from the grounded electrode. This afterglow configuration also allows for lower gas temperatures impinging on substrates, than the use of active plasmas. Work pieces are not required to be part of any electrical circuit, bringing additional practical advantages. We present a crude lumped parameter equivalent circuit model to analyse the effects of changing RF sheaths with frequency of excitation and applied RF current to better understand the relative roles of sheath and bulk plasma behaviour observed in electrical characteristics. Estimates of the bulk plasma densities are also provided. Finally, we present results of afterglow plasma based bacteria inactivation studies (Escherichia coli, Bacillus atrophaeus and B. atrophaeus spores) in which we employ the flowing afterglow plume from a hollow slot microplasma device rather than the active plasma itself, which is fully contained between electrodes. (Some figures in this article are in colour only in the electronic version)

Dynamic mapping in a heterogeneous environment with tasks having priorities and multiple deadlines

In a distributed heterogeneous computing system, the resources have different capabilities and tasks have different requirements. To maximize the performance of the system, it is essential to assign resources to tasks (match) and order the execution of tasks on each resource (schedule in a manner that exploits the heterogeneity of the resources and tasks. The mapping (defined as matching and scheduling) of tasks onto machines with varied computational capabilities has been shown, in general, to be an NP-complete problem. Therefore, heuristic techniques to find a near-optimal solution to this mapping problem are required. Dynamic mapping is performed when the arrival of tasks is not known a priori. In the heterogeneous environment considered in this study, tasks arrive randomly, tasks are independent (i.e., no communication among tasks), and tasks have priorities and multiple deadlines. This research proposes, evaluates, and compares eight dynamic heuristics. The performance of the best heuristics is 83% of an upper bound.

Differential gene expression in Escherichia coli following exposure to nonthermal atmospheric pressure plasma

Aim:u2002 Nonthermal atmospheric‐pressure plasmas offer significant advantages as an emerging disinfection approach. However the mechanisms of inactivation, and thus the means of optimizing them, are still poorly understood. The objective of this study, therefore, was to explore differential gene expression on a genome‐wide scale in Escherichia coli following exposure to a nonthermal atmospheric‐pressure argon plasma plume using high‐density oligonucleotide microarrays.

Bacterial Inactivation Using an RF-Powered Atmospheric Pressure Plasma

Cells of Escherichia coli were exposed to a downstream plasma afterglow plume emitted from a slotted plasma device operating in open air at atmospheric pressure. Various feed-gas mixtures were capacitively excited, as they flowed into open air past radio frequency-powered electrodes. To estimate the underlying inactivation pathways, various experimental conditions were tested by incorporating ultraviolet filters, varying parameters such as electrical power and frequency, feed-gas composition and flow rates, and the distance of the samples from the electrode. Experimental results demonstrated a colony-forming unit reduction of well over five logs with less than 2 s of exposure per unit area. These results offer a promising means of wide-area inactivation of harmful microbes in a practical environment, where the sample is neither a part of the electrical circuit nor placed in an enclosure. The device is electrically grounded and could be held like a wand applicator

Bacterial deactivation in open-air by the afterglow plume emitted from a grounded hollow slot electrode

Summary form only given. Atmospheric pressure glow discharges provide a low temperature sterilization alternative that can deactivate bacteria, reduce harmful gas emissions and operate with high rates at reduced temperature. Our research focuses on operation in open-air that potentially makes the process inexpensive and operational in more practical conditions, than a sealed chamber. We employ a grounded hollow slot in this work, whose dimensions are: 7.62 cm long, 0.02 cm wide and 0.2 cm deep. Recessed behind the grounded slot is a powered electrode employing 13.56 MHz electrical drive. A mixture of argon and oxygen gases flows from the powered electrode through the grounded slots at a flow rate of 32 liters per minute creating a plasma afterglow plume, which extends 1-8 mm past the open slot and is 7 cm long. The afterglow plume is line shaped and is visible in open-air operation. The potential of the open-air slot reactor to deactivate bacterial growth in a practical environment with a device that is hand held are demonstrated experimentally.

Engine-exhaust abatement using atmospheric pressure plasma

Summary form only given. Vehicular and industrial emissions are a leading cause of air pollution and various countries are imposing stricter standards on both the quality and quantity of permissible emissions. We have created a novel radial plasma reactor at Colorado State University that can potentially be used for treating engine-exhaust. The device is powered by a 60 MHz RF power supply and operates in the non-thermal temperature range. The device uses a feed-gas mixture of ammonia and an inert gas (helium). The engine-exhaust (~250degC) passes through the plasma reactor where powerful plasma species convert harmful nitric oxides (NOx) into relatively harmless products. Also the plasma can potentially reduce unburned hydrocarbons and particulate matter that is routinely present in engine-exhaust. Initial experiments have shown a promising reduction in the levels of NOx from engine-exhaust after plasma treatment. These developments lead us to believe that this reactor with a few refinements can be part of an effective exhaust abatement strategy

Open-Air Bacterial Inactivation using a RF Powered Hollow-Slot Plasma Device

Summary form only given. The use of atmospheric pressure plasma sources for biomedical applications is primarily because of the capability to employ devices for bacterial inactivation at close to room temperature without the use of dangerous chemicals. This improves both the ease of bacterial inactivation and is important for treatment of heat-sensitive materials. Plasma based inactivation is much faster and cleaner compared to some of the conventional technologies like autoclaving and ethylene oxide treatment that are normally used for sterilization. Our research is focused on the impact on bacteria, of a wide area afterglow plume emitted from a hollow-slot electrode configuration that operates in open air and is RF powered. We employ a grounded hollow slot as the interface to the work piece so that the device may be hand held. In the work reported herein the device dimensions are; 7.62 cm long, 0.02 cm wide and 0.2 cm deep, but note 30 cm long versions are operable as well. Recessed behind the grounded slot is a powered electrode employing 60 MHz electrical drive. A mixture of argon and oxygen gases flows from the powered electrode through the grounded slots creating a plasma afterglow plume, which extends 1-8 mm past the open slot and is 7 cm long. The afterglow plume is line shaped and is visible in open-air operation. Use of rare gases is considered a disadvantage for some portable applications. We also report operation in pure air but indicate the limitations we uncovered. Using Escherichia coli as the test bacteria, we have witnessed promising results with a colony forming unit (CFU) reduction of seven logs, which meets commercial sterilization requirements of six logs removal. Moreover, this was accomplished with only 2 seconds total exposure time. The experiments to date demonstrate the potential of the open-air hollow-slot applicator to inactivate bacterial growth in a wide area environment with a device that could be hand held