Pentacene-based organic thin-film transistors

Organic thin-film transistors using the fused-ring polycyclic aromatic hydrocarbon pentacene as the active electronic material have shown mobility as large as 0.7 cm²/V-s and on/off current ratio larger than 10⁸; both values are comparable to hydrogenated amorphous silicon devices. On the other hand, these and most other organic TFT's have an undesirably large subthreshold slope. We show here that the large subthreshold slope typically observed is not an intrinsic property of the organic semiconducting material and that devices with subthreshold slope similar to amorphous silicon devices are possible     

Thermal management of power electronics modules packaged by a stacked-plate technique

The research presented in this paper is part of a multidisciplinary research program of the Center for Power Electronics Systems at Virginia Tech. The program supported by the Office of Naval Research focuses on the development of innovative technologies for packaging power electronics building blocks. The primary objective of this research is to improve package performance and reliability through thermal management, i.e., reducing device temperatures for a given power level. The task of thermal management involves considering trade-offs in the electrical design, package layout and geometry, materials selection and processing, manufacturing feasibility, and production cost. Based on the electrical design of a simple building block, samples of packaged modules, rated at 600 V and 3.3 kW, were fabricated using a stacked-plate technique, termed metal posts interconnected parallel plate structure (MPIPPS). The MPIPPS technique allows the power devices to be interconnected between two direct-bond copper substrates via the use of metal posts. Thermal modeling results on the MPIPPS packaged modules indicate that the new packaging technique offers a superior thermal management means for packaging power electronics modules.     

Towards a Sustainable Green Design for Next-Generation Networks

Recently distributed real-time database systems are intended to manage large volumes of dispersed data. To develop distributed real-time data processing, a reality and stay competitive well defined protocols and algorithms must be required to access and manipulate the data. An admission control policy is a major task to access real-time data which has become a challenging task due to random arrival of user requests and transaction timing constraints. This paper proposes an optimal admission control policy based on deep reinforcement algorithm and memetic algorithm which can efficiently handle the load balancing problem without affecting the Quality of Service (QoS) parameters. A Markov decision process (MDP) is formulated for admission control problem, which provides an optimized solution for dynamic resource sharing. The possible solutions for MDP problem are obtained by using reinforcement learning and linear programming with an average reward. The deep reinforcement learning algorithm reformulates the arrived requests from different users and admits only the needed request, which improves the number of sessions of the system. Then we frame the load balancing problem as a dynamic and stochastic assignment problem and obtain optimal control policies using memetic algorithm. Therefore proposed admission control problem is changed to memetic logic in such a way that session corresponds to individual elements of the initial chromosome. The performance of proposed optimal admission control policy is compared with other approaches through simulation and it depicts that the proposed system outperforms the other techniques in terms of throughput, execution time and miss ratio which leads to better QoS.

     

History of the “Detector Materials Engineering” Crystal Growth Process for Bulk Hg1−x Cd x Te

This paper reviews the history and technology of a bulk Hg_1?x Cd _x Te crystal growth process that was developed in the early 1980s at Honeywell Electro-Optics Division (presently BAE Systems, Electronic Solutions). The crystal growth process name, DME, was an acronym for the department name: Detector Materials Engineering. This was an accelerated crucible rotation technique (ACRT) vertical traveling heater method growth process. Crystal growth occurred in the pseudobinary Hg_1?x Cd _x Te system. ACRT mixing allowed the lower-density, higher-x-value Hg_1?x Cd _x Te growth nutrient in the upper region of the ampoule to replenish the depleted melt and allowed the growth of constant-x-value, higher-density Hg_1?x Cd _x Te. The material grown by this research and production growth process yielded single crystals that had improved purity, compositional uniformity, precipitate density, and reproducibility in comparison with solid-state recrystallization and other bulk Hg_1?x Cd _x Te growth techniques. Radial and longitudinal nonuniformities in x-value for Hg_1?x Cd _x Te were reduced to <0.0008/cm. The net electrically active background impurities did not exceed 1 × 10¹⁴ cm^?3. Electron mobilities in excess of 1.5 × 10⁶ cm²/V-s were observed at 77 K. Structural defects of less than 10⁴ cm^?2 were measured. Te precipitates were not observed. As a result of these material improvements, long-wavelength infrared (LWIR) photoconductive devices fabricated from DME material had highly desired performance characteristics.     

The environmental impact of lightweight HCPV modules: efficient design and effective deployment

We present a life cycle analysis of a lightweight design of high concentration photovoltaic module. The materials and processes used in construction are considered to assess the total environmental impact of the module construction in terms of the cumulative energy demand and embodied greenhouse gas emissions, which were found to be 355.3 MJ and 27.9 kgCO_2eq respectively. We consider six potential deployment locations and the system energy payback times are calculated to be 0.22–0.33 years whilst the greenhouse gas payback times are 0.29–0.88 years. The emission intensities over the lifetimes of the systems are found to be 6.5–9.8 g CO_2eq/kWh, lower than those of other HCPV, PV and CSP technologies in similar locations. Copyright © 2016 John Wiley & Sons, Ltd.     

Efficiency Roll‐Off in Blue Emitting Phosphorescent Organic Light Emitting Diodes with Carbazole Host Materials

The efficiency roll‐off in blue phosphorescent organic light emitting diodes (OLEDs) using different carbazole compounds as the host is systematically studied. While there is no significant difference in device efficiency, OLEDs using ter‐carbazole as the host show a reduction in efficiency roll‐off at high luminance. Data from transient photoluminescence and electroluminescence measurements show that the lower triplet–triplet annihilation (TTA) and triplet–polaron quenching (TPQ) rates in devices with the ter‐carbazole host compared with other carbazole hosts are the reasons for this reduced efficiency roll‐off. It is also found that the host materials with low glass transition temperatures are more susceptible to the efficiency roll‐off problem.     

Magnetically Driven Silver‐Coated Nanocoils for Efficient Bacterial Contact Killing

The increasing threat of multidrug‐resistant bacterial strains against conventional antibiotic therapies represents a significant worldwide health risk and intensifies the need for novel antibacterial treatments. In this work, an effective strategy to target and kill bacteria using silver‐coated magnetic nanocoils is reported. The coil palladium (Pd) nanostructures are obtained by electrodeposition and selective dealloying, and subsequently coated with nickel (Ni) and silver (Ag) for magnetic manipulation and antibacterial properties, respectively. The efficiency of the nanocoils is tested in the treatment of Gram‐negative Escherichia coli (E. coli) and Gram‐positive methicillin‐resistant Staphylococcus aureus (S. aureus), both of which represent the leading multidrug‐resistant bacterial pathogens. The nanocoils show highly effective bacterial killing activity at low concentrations and in relatively short durations of treatment time. Three different investigation techniques, LIVE/DEAD assay, colony‐forming unit counting, and scanning electron microscope, reveal that the antibacterial activity is a result of bacterial membrane damage caused by direct contact with the nanocoil. The low cytotoxicity toward fibroblast cells along with the capability of precise magnetic locomotion makes the proposed nanocoil an ideal candidate to combat multidrug‐resistant bacteria in the field of biomedical and environmental applications.     

Using simulations of reduced precision arithmetic to design a neuro-microprocessor

This article describes some of our recent work in the development of computer architectures for efficient execution of artificial neural network algorithms. Our earlier system, the Ring Array Processor (RAP), was a multiprocessor based on commercial DSPs with a low-latency ring interconnection scheme. We have used the RAP to simulate variable precision arithmetic to guide us in the design of arithmetic units for high performance neurocomputers to be implemented with custom VLSI. The RAP system played a critical role in this study, enabling us to experiment with much larger networks than would otherwise be possible. Our study shows that back-propagation training algorithms only require moderate precision. Specifically, 16b weight values and 8b output values are sufficient to achieve training and classification results comparable to 32b floating point. Although these results were gathered for frame classification in continuous speech, we expect that they will extend to many other connectionist calculations. We have used these results as part of the design of a programmable single chip microprocessor, SPERT. The reduced precision arithmetic permits the use of multiple arithmetic units per processor. Also, reduced precision operands make more efficient use of valuable processor-memory bandwidth. For our moderate-precision fixed-point arithmetic applications, SPERT represents more than an order of magnitude reduction in cost over systems with equivalent performance that use commercial DSP chips.     

Optoelectronic charge coupled device (OECCD) using InP MIScapacitor array

An optoelectronic charge coupled device (OECCD) which is directly compatible with an incident optical signal is proposed. The nonlinear partial differential equation consisting of optical generation and recombination is solved in one dimension using the Crank-Nicolson finite-difference scheme. The charge transfer inefficiency is the main parameter considered for the calculation