Physical Sciences and Mathematics | Open Access Articles

Spectrum Sensing With Energy Detection In Multiple Alternating Time Slots, Călin Vlădeanu, Alexandru Marţian, Dimitrie C. Popescu

Electrical & Computer Engineering Faculty Publications

Energy detection (ED) represents a low complexity approach used by secondary users (SU) to sense spectrum occupancy by primary users (PU) in cognitive radio (CR) systems. In this paper, we present a new algorithm that senses the spectrum occupancy by performing ED in K consecutive sensing time slots starting from the current slot and continuing by alternating before and after the current slot. We consider a PU traffic model specified in terms of an average duty cycle value, and derive analytical expressions for the false alarm probability (FAP) and correct detection probability (CDP) for any value of K . Our …

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Runtime Power Allocation Based On Multi-Gpu Utilization In Gamess, Masha Sosonkina, Vaibhav Sundriyal, Jorge Luis Galvez Vallejo

Electrical & Computer Engineering Faculty Publications

To improve the power consumption of parallel applications at the runtime, modern processors provide frequency scaling and power limiting capabilities. In this work, a runtime strategy is proposed to maximize performance under a given power budget by distributing the available power according to the relative GPU utilization. Time series forecasting methods were used to develop workload prediction models that provide accurate prediction of GPU utilization during application execution. Experiments were performed on a multi-GPU computing platform DGX-1 equipped with eight NVIDIA V100 GPUs used for quantum chemistry calculations in the GAMESS package. For a limited power budget, the proposed strategy …

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Grand Challenges In Low Temperature Plasmas, Xinpei Lu, Peter J. Bruggeman, Stephan Reuter, George Naidis, Annemie Bogaerts, Mounir Laroussi, Michael Keidar, Eric Robert, Jean-Michel Pouvesle, Dawei Liu, Kostya (Ken) Ostrikov

Electrical & Computer Engineering Faculty Publications

Low temperature plasmas (LTPs) enable to create a highly reactive environment at near ambient temperatures due to the energetic electrons with typical kinetic energies in the range of 1 to 10 eV (1 eV = 11600K), which are being used in applications ranging from plasma etching of electronic chips and additive manufacturing to plasma-assisted combustion. LTPs are at the core of many advanced technologies. Without LTPs, many of the conveniences of modern society would simply not exist. New applications of LTPs are continuously being proposed. Researchers are facing many grand challenges before these new applications can be translated to practice. …

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Transient Behavior Of Drift And Ionization In Atmospheric Pressure Nitrogen Discharge, S. K. Dhali

Electrical & Computer Engineering Faculty Publications

The fluid models are frequently used to describe a non-thermal plasma such as a streamer discharge. The required electron transport data and rate coefficients for the fluid model are parametrized using the local field approximation (LFA) in first order models and the local-mean-energy approximation (LMEA) in second order models. We performed Monte Carlo simulations in Nitrogen gas with step changes in the E/N (reduced electric field) to study the behavior of the transport properties in the transient phase. During the transient phase of the simulation, we extract the instantaneous electron mean energy, which is different from the steady state mean …

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High Voltage Design And Evaluation Of Wien Filters For The Cebaf 200 Kev Injector Upgrade, Gabriel Palacios-Serrano, Helmut Baumgart, C. Hernández-García, P. Adderley, J. Benesch, D. Bullard, J. Grames, A. Hofler, D. Machie, M. Poelker, M. Stutzman, R. Suleiman

Electrical & Computer Engineering Faculty Publications

High-energy nuclear physics experiments at the Jefferson Lab Continuous Electron Beam Accelerator Facility (CEBAF) require highly spin-polarization electron beams, produced from strained super-lattice GaAs photocathodes, activated to negative electron affinity in a photogun operating at 130 kV dc. A pair of Wien filter spin rotators in the injector defines the orientation of the electron beam polarization at the end station target. An upgrade of the CEBAF injector to better support the upcoming MOLLER experiment requires increasing the electron beam energy to 200 keV, to reduce unwanted helicity correlated intensity and position systematics and provide precise control of the polarization orientation. …

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Assessment Of Cu(In, Ga)Se₂ Solar Cells Degradation Due To Water Ingress Effect On The Cds Buffer Layer, Deewakar Poudel, Benjamin Belfore, Shankar Karki, Grace Rajan, Sina Soltanmohammad, Angus Rockett, Sylvain Marsillac

Electrical & Computer Engineering Faculty Publications

The effect of water ingress on the surface of the buffer layer of a Cu(In, Ga)Se2 (CIGS) solar cell was studied. Such degradation can occur either during the fabrication process, if it involves a chemical bath as is often the case for CdS, or while the modules are in the field and encapsulants degrade. To simulate the impact of this moisture ingress, devices with a structure sodalime glass/Mo/CIGS/CdS were immersed in deionized water. The thin films were then analyzed both pre and post water soaking. Dynamic secondary ion mass spectroscopy (SIMS) was performed on completed devices to analyze impurity diffusion …

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Distributed Strategy For Power Re-Allocation In High Performance Applications, Vaibhav Sundriyal, Masha Sosonkina

Electrical & Computer Engineering Faculty Publications

To improve the power consumption of parallel applications at the runtime, modern processors provide frequency scaling and power limiting capabilities. In this work, a runtime strategy is proposed to distribute a given power allocation among the cluster nodes assigned to the application while balancing their performance change. The strategy operates in a timeslice-based manner to estimate the current application performance and power usage per node followed by power redistribution across the nodes. Experiments, performed on four nodes (112 cores) of a modern computing platform interconnected with Infiniband showed that even a significant power budget reduction of 20% may result in …

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Temporary Bonding With Polydimethylglutarimide Based Lift Off Resist As A Layer Transfer Platform, T. Matsumae, A. D. Koehler, J. D. Greenlee, T. J. Anderson, H. Baumgart, G. G. Jernigan, K. D. Hobart, F. J. Kub

Electrical & Computer Engineering Faculty Publications

Bonding of lift off resist (LOR) was performed to realize temporary wafer bonding without residue. Bonding process conditions such as spin speed, pre-bake temperature, and bonding temperature were optimized to obtain a large bonded area with high bond strength. Under optimized process conditions, a bonded area covering over 98% of the wafer surface, with a room temperature bond strength of nearly 5 J/m² is achieved. During razor blade testing, fracture often occurs at the Si wafer. Moreover, debonding using an N-Methyl-2-pyrrolidone (NMP)-based solvent left the wafer surface extremely small amount of residue. Thus, the optimized bonding processed developed in …

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In Situ And Ex Situ Studies Of Molybdenum Thin Films Deposited By Rf And Dc Magnetron Sputtering As A Back Contact For Cigs Solar Cells, K. P. Aryal, H. Khatri, R. W. Collins, S. Marsillac

Electrical & Computer Engineering Faculty Publications

Molybdenum thin films were deposited by rf and dc magnetron sputtering and their properties analyzed with regards to their potential application as a back contact for CIGS solar cells. It is shown that both types of films tend to transition from tensile to compressive strain when the deposition pressure increases, while the conductivity and the grain size decreas. The nucleation of the films characterized by in situ and real time spectroscopic ellipsometry shows that both films follow a Volmer-Weber growth, with a higher surface roughness and lower deposition rate for the rf deposited films. The electronic relaxation time was then …

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Coupled Photonic Crystal Micro-Cavities With Ultra-Low Threshold Power For Stiumulated Raman Scattering, Qiang Liu, Zhengbiao Ouyang, Sacharia Albin

Electrical & Computer Engineering Faculty Publications

We propose coupled cavities to realize a strong enhancement of the Raman scattering. Five sub cavities are embedded in the photonic crystals. Simulations through finite-difference time-domain (FDTD) method demonstrate that one cavity, which is used to propagate the pump beam at the optical-communication wavelength, has a Q factor as high as 1.254 × 10⁸ and modal volume as small as 0.03μm³ (0.3192(λ/n)³). These parameters result in ultra-small threshold lasing power ~17.7nW and 2.58nW for Stokes and anti-Stokes respectively. The cavities are designed to support the required Stokes and anti-Stokes modal spacing in silicon. The proposed structure …

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Cuin1-Xalxse2 Thin Films And Solar Cells, P. D. Paulson, M. W. Haimbodi, S. Marsillac, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications

CuIn[sub 1-x]Al[sub x]Se[sub 2] thin films are investigated for their application as the absorber layer material for high efficiency solar cells. Single-phase CuIn[sub 1-x]Al[sub x]Se[sub 2] films were deposited by four source elemental evaporation with a composition range of 0≤x≤0.6. All these films demonstrate a normalized subband gap transmission >85% with 2 µm film thickness. Band gaps obtained from spectroscopic ellipsometry show an increase with the Al content in the CuIn[sub 1-x]Al[sub x]Se[sub 2] film with a bowing parameter of 0.62. The structural properties investigated using x-ray diffraction measurements show a decrease in lattice spacing as the Al content increases. …

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High-Efficiency Solar Cells Based On Cu(Inal)Se[Sub 2] Thin Films, S. Marsillac, P. D. Paulson, M. W. Haimbodi, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications

A Cu(InAl)Se₂solar cell with 16.9% efficiency is demonstrated using a Cu(InAl)Se₂thin film deposited by four-source elemental evaporation and a device structure of glass/Mo/Cu(InAl)Se₂/CdS/ZnO/indium tin oxide/(Ni/Algrid)/MgF₂. A key to high efficiency is improved adhesion between the Cu(InAl)Se₂ and the Mo back contact layer, provided by a 5-nm-thick Ga interlayer, which enabled the Cu(InAl)Se₂ to be deposited at a 530 °C substrate temperature. Film and device properties are compared to Cu(InGa)Se₂ with the same band gap of 1.16 eV. The solar cells have similar behavior, with performance limited by recombination through …

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Full-Text Articles in Physical Sciences and Mathematics

Spectrum Sensing With Energy Detection In Multiple Alternating Time Slots, Călin Vlădeanu, Alexandru Marţian, Dimitrie C. Popescu

Electrical & Computer Engineering Faculty Publications

Runtime Power Allocation Based On Multi-Gpu Utilization In Gamess, Masha Sosonkina, Vaibhav Sundriyal, Jorge Luis Galvez Vallejo

Electrical & Computer Engineering Faculty Publications

Grand Challenges In Low Temperature Plasmas, Xinpei Lu, Peter J. Bruggeman, Stephan Reuter, George Naidis, Annemie Bogaerts, Mounir Laroussi, Michael Keidar, Eric Robert, Jean-Michel Pouvesle, Dawei Liu, Kostya (Ken) Ostrikov

Electrical & Computer Engineering Faculty Publications

Transient Behavior Of Drift And Ionization In Atmospheric Pressure Nitrogen Discharge, S. K. Dhali

Electrical & Computer Engineering Faculty Publications

High Voltage Design And Evaluation Of Wien Filters For The Cebaf 200 Kev Injector Upgrade, Gabriel Palacios-Serrano, Helmut Baumgart, C. Hernández-García, P. Adderley, J. Benesch, D. Bullard, J. Grames, A. Hofler, D. Machie, M. Poelker, M. Stutzman, R. Suleiman

Electrical & Computer Engineering Faculty Publications

Assessment Of Cu(In, Ga)Se₂ Solar Cells Degradation Due To Water Ingress Effect On The Cds Buffer Layer, Deewakar Poudel, Benjamin Belfore, Shankar Karki, Grace Rajan, Sina Soltanmohammad, Angus Rockett, Sylvain Marsillac

Electrical & Computer Engineering Faculty Publications

Distributed Strategy For Power Re-Allocation In High Performance Applications, Vaibhav Sundriyal, Masha Sosonkina

Electrical & Computer Engineering Faculty Publications

Temporary Bonding With Polydimethylglutarimide Based Lift Off Resist As A Layer Transfer Platform, T. Matsumae, A. D. Koehler, J. D. Greenlee, T. J. Anderson, H. Baumgart, G. G. Jernigan, K. D. Hobart, F. J. Kub

Electrical & Computer Engineering Faculty Publications

In Situ And Ex Situ Studies Of Molybdenum Thin Films Deposited By Rf And Dc Magnetron Sputtering As A Back Contact For Cigs Solar Cells, K. P. Aryal, H. Khatri, R. W. Collins, S. Marsillac

Electrical & Computer Engineering Faculty Publications

Coupled Photonic Crystal Micro-Cavities With Ultra-Low Threshold Power For Stiumulated Raman Scattering, Qiang Liu, Zhengbiao Ouyang, Sacharia Albin

Electrical & Computer Engineering Faculty Publications

Cuin1-Xalxse2 Thin Films And Solar Cells, P. D. Paulson, M. W. Haimbodi, S. Marsillac, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications

High-Efficiency Solar Cells Based On Cu(Inal)Se[Sub 2] Thin Films, S. Marsillac, P. D. Paulson, M. W. Haimbodi, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications