Theory of the temporal response of a simple multiquantum-wellavalanche photodiode

Numerical and analytically based calculations of the impulse response function of a simple GaAs-AlGaAs multiquantum-well avalanche photodiode are presented. The numerical approach involves the direct simulation of the electron and hole transport in the device. An iterative approach is used in that the parent electron distribution is first simulated yielding the velocity profile as a function of position, transmit-time distribution of the parent and daughter electrons, and the daughter-hole distribution. The daughter-hole distribution is subsequently simulated using the time of birth and spatial location of each secondary hole as initial conditions. The calculation continues iteratively in this fashion yielding a picture of the time evolution of the impulse response function. Both analytical and simulation results are presented for single-carrier -initiated single-carrier-multiplication (SCISCM) devices. The similarities and differences in the outcomes of the two approaches are instructive, Simulation results are presented only for devices in which secondary hole-initiated ionization occurs     

A new Walrasian mechanism design for optimal pricing and resource allocation in heterogeneous wireless access networks

In this paper, we address joint spectrum allocation and pricing problem in heterogeneous wireless access networks. In contrast to traditional static spectrum allocation approach, we model the spectrum as a market commodity, dynamically arbitrated by a regulatory agent with the aim of maximizing the social welfare. This is of particular importance with the dominance of wireless technologies in access networks and the sharp increase in the number of overlapping wireless technologies and networks. We designed a novel Walrasian mechanism called economic resource allocation and pricing based on a three-stage game model capable of considering multiple networks and clients with individual attributes and preferences. In the first stage, competition among networks for spectrum allocation is handled where the regulatory evaluates the social welfare and takes corrective action. In the bottom two stages, the complex interactions between clients and networks result in bitrate allocations and service pricings. The equilibrium condition is analyzed using the Walrasian market model which is argued to be the Nash equilibrium of the proposed game. The system behavior is analyzed through extensive simulations. The results confirm the effectiveness of the proposed mechanisms in moving the system towards maximal social welfare.

     

In situ and on-line monitoring of CO in an industrial glass furnace by mid-infrared difference-frequency generation laser spectroscopy

A compact mid-infrared (MIR) laser spectrometer based on difference-frequency generation (DFG) is applied as a portable and sensitive gas sensor for industrial process control and pollutant monitoring. We demonstrate the performance of such a MIR DFG gas sensor by recording the absorption spectra of the carbon monoxide (CO) P(28) absorption line in the atmosphere of a gas-fired glass melting furnace. For a gas temperature of approximately 1100 degrees C, the CO concentration in the recuperator channel is measured to be 400 parts per million.     

P-type non-isolated boost DC-DC converter with high voltage gain and extensibility for DC microgrid applications

In this paper, the concept of converter design, using the least number of elements and achieving high voltage gain at the low duty cycle, is proposed for the microgrids. One of the important issues in the microgrids is boosting the low voltage output of sources to the utility voltage level. Therefore, the step-up DC-DC converters are widely used in these systems to attain the utility voltage. The benchmarking of the converters mainly in terms of the voltage gain, efficiency, the number of active and passive components, stresses on semiconductors, and simplicity is considered. In this paper, a new extendable non-isolated boost DC-DC converter is presented. Comparing the conventional boost converter, the basic structure of the proposed converter has a high voltage gain and reduced stress on the switch. To increase the voltage gain, the basic structure of the proposed converter can be easily extended. The modulation technique employed is high-frequency pulse-width modulation (PWM). The detailed analysis of the proposed converter in continuous current mode (CCM) and discontinuous current mode (DCM) is presented. The relations between currents and voltages and the voltage gain in CCM and DCM are obtained. Experimental results are carried out to verify theoretical concepts by using the hardware prototype.     

Reassessing the role of urodynamics after cerebrovascular accident. Males versus females

Adult, male Syrian hamsters received daily subcutaneous melatonin (25 microg) injections or vehicle injections at 08:00 or 17:00 hr for 11 weeks. Body weights were measured weekly throughout the experiment and testes weights, spleen weights, and serum was collected at the end of the experiment. The spleens were sectioned and immunocytochemically analyzed for immunoglobulin G and serum levels of interferon-gamma, interleukin-2, and interleukin-4 were determined in heterologous mouse assays. Melatonin injections at 17:00 hr, but not at 08:00 hr, increased body weights, decreased testes weights and serum testosterone levels, and had no effect on immunoglobulin G content in the spleen. Likewise, melatonin injections at 17:00 hr, but not at 08:00 hr, increased serum interferon-gamma levels, had no effect on interleukin-2 levels, and appeared to increase interleukin-4 levels. Since melatonin injections at 08:00 hr were ineffective in altering immune measurements and correlations between reproductive measures and immune measures were high, the most parsimonious explanation for these results is that melatonin injections at 17:00 hr depressed reproductive hormone levels and these depressed levels altered immune measures.     

Game theoretic spectrum allocation for competing wireless access technologies to maximize the social welfare

Wireless Networks - Due to its scarce nature, the limited frequency spectrum must be effectively allocated to competing wireless access technologies. A promising approach is to consider frequency...     

Centralized vs. distributed algorithms for resilient 5G access networks

Photonic Network Communications - Cloud radio access networks (C-RANs), relying on network function virtualization and software-defined networking (SDN), require a proper placement of baseband...     

A popularity-based query scheme in P2P networks using adaptive gossip sampling

As P2P networks, such as many forms of social networking have been rapidly growing, numerous efforts have been made to improve the efficiency of the search operation especially in terms of response time and hit ratio. To this end, popularity-based schemes have recently attracted attention aimed at increasing search efficiency using content popularity ranking; however, these methods suffer from high cost and overhead, or inappropriate level of accuracy in specifying the popularity. In this paper, we propose an adaptive sampling scheme to make a tradeoff between cost and accuracy. This scheme relies on exchanging File Index Table (FIT) between peers in a local neighborhood using a Gossip Exchange Method (GEM). The proposed Hybrid Adaptive Search According to Gossip Exchange Method (HAS-A-GEM) is based on smart unstructured peer to peer overlays. We apply a hybrid overlay that efficiently combines topology-aware and interest-based links instead of random or DHT invoked connections. An analytical model as well as a simulation framework is developed to illustrate the performance of this scheme. The effectiveness of the proposed scheme is demonstrated under various conditions. Simulation results reveal that HAS-A-GEM performs well for large-scale networks, exploiting local content popularity when each local area contains enough number of peers.     

Dedicated and shared solutions for reliable function splitting in 5G X-haul

Photonic Network Communications - Functional splitting, referred as X-haul, is introduced in the 5G networks to support flexibility and meet service requirements. Each split option has a different...     

On the performance and fairness of dynamic channel allocation in wireless mesh networks

Channel assignment in multichannel multiradio wireless mesh networks is a powerful resource management tool to exploit available multiple channels. Channels can be allocated either statically on the basis of long‐term steady state behavior of traffic or dynamically according to actual traffic demands. It is a common belief that dynamic schemes provide better performance; however, these two broad classes of channel allocation schemes have not been compared in detail. In this paper, we quantify the achievable performance gain and fairness improvement through an optimal dynamic channel allocation scheme. We develop optimal algorithms for a dynamic and three static schemes using mixed integer linear programming and compare them in the context of QoS provisioning, where network performance is measured in terms of acceptance rate of QoS sensitive traffic demands. Our extensive simulations show that static schemes should optimize channel allocation for long‐term traffic pattern and maintain max–min fairness to achieve acceptable performances. Although the dynamic and max–min fair static schemes accomplish the same fairness, the dynamic channel allocation outperforms the static scheme about 10% in most cases. In heavily overloaded regimes, especially when network resources are scarce, both have comparable performances, and the max–min fair scheme is preferred because it incurs less overhead. Copyright © 2011 John Wiley & Sons, Ltd.