Scheduling and Codeword Length Optimization in Time Varying Wireless Networks

In this paper, a downlink scenario in which a single-antenna base station communicates with K single antenna users, over a time-correlated fading channel, is considered. It is assumed that channel state information is perfectly known at each receiver, while the statistical characteristics of the fading process and the fading gain at the beginning of each frame are known to the transmitter. By evaluating the random coding error exponent of the time-correlated fading channel, it is shown that there is an optimal codeword length which maximizes the throughput. The throughput of the conventional scheduling that transmits to the user with the maximum signal to noise ratio is examined using both fixed length codewords and variable length codewords. Although optimizing the codeword length improves the performance, it is shown that using the conventional scheduling, the gap between the achievable throughput and the maximum possible throughput of the system tends to infinity as K goes to infinity. A simple scheduling that considers both the signal to noise ratio and the channel time variation is proposed. It is shown that by using this scheduling, the gap between the achievable throughput and the maximum throughput of the system approaches zero

Theoretical study of equilibrium and nonequilibrium exciton dynamics in disordered semiconductors

We develop a temperature-dependent theory for singlet exciton hopping transport in disordered semiconductors. It draws on the transport level concept within a Förster transfer model and bridges the gap in describing the transition from equilibrium to nonequilibrium time-dependent spectral diffusion.We test the validity range of the developed model using kinetic Monte Carlo simulations and find agreement over a broad range of temperatures. It reproduces the scaling of the diffusion length and spectral shift with the dimensionless disorder parameter and describes in a unified manner the transition from equilibrium to nonequilibrium transport regime. We find that the diffusion length in the nonequilibrium regime does not scale with the the third power of the Förster radius. The developed theory provides a powerful tool for interpreting time-resolved and steady state spectroscopy experiments in a variety of disordered materials, including organic semiconductors and colloidal quantum dots.This project has received funding from the Universidad Carlos III de Madrid, the European Union’s Seventh Frame- work Programme for research, technological development, and demonstration under Grant Agreement No. 600371, el Ministerio de Economía, Industria y Competitividad (COFUND2014-51509), el Ministerio de Educación, cultura y Deporte (CEI-15-17), and Banco Santander

Insight into Photon Recycling in Perovskite Semiconductors from the Concept of Photon Diffusion

Photon recycling has been proven to be an important process in metal halide perovskite thin films. We propose a model of photon recycling based on the photon diffusion concept that can interpret experimental observations on the photoluminescence and transient spectroscopy in perovskite layers. Our model shows how the photon recycling can enhance the apparent photocarrier lifetime and thereby slow down the photoluminescence decay dynamics. We also discuss the interplay between photon recycling and the photocarriers diffusive transport and demonstrate that at high carrier concentrations, photon recycling dominates the diffusion, conveying the carriers inside the absorbing layer over long distances. We also provide a quantitative determination of a diffusion length that is considerably expanded by the photon recycling process. The effect of the photon recycling process on the Auger recombination rate is also addressed here. The results provide insights for both interpreting the experimental observations and also designing experimental schemes

Naltrexone Removal from Aqueous Media by Multi-Walled Carbon Nanotubes

Background: Extensive researches with different techniques are being carried out for removal of pharmaceuticals from aqueous media. The aim of this study was to use multi-walled carbon nanotubes (MWCNTs) to remove naltrexone as a pollutant of the aquatic environment and to investigate the mechanism of absorption and factors affecting it. Methods: In this experimental study, different amounts of MWCNTs were added to different concentrations (200 to 400 mg/L) of naltrexone and adsorption at various conditions including temperature, pH, and time of adsorption was studied. Adsorption on multi-walled carbon nanotubes was adopted on isotherm model equations to estimate the adsorption mechanism. Results: Optimum conditions to remove 90% of naltrexone from 20 ml of its 400mg/ml solution were at adsorbent amount of 0.1g and time of 20 to 30 minutes. Temperature and pH had no effect on adsorption in the examined ranges. The drug can be absorbed as one layer and according to the Langmuir isotherm, on carbon nanotubes. Conclusion: Naltrexone removal by MWCNTs, due to higher surface area and therefore more efficient adsorption properties, is more efficient than by activated carbon and requires no specific conditions in regard to pH, temperature, and concentration. Substances with similar structures, like morphine, compete with naltrexone on adsorption

The effect of P and K availability in soil on nutrient concentrations, uptake, and distribution in corn plants throughout the growing season

Field experiments were conducted in 1981 and 1982 to study the effects of low, moderate and high levels of P and K availability in the soil on growth and nutrient uptake by corn plants. In both seasons, 157 kg of N ha(\u27-1) was applied to all experimental plots prior to planting. Corn grain yields were 4940 and 8600 kg ha(\u27-1) in 1981 and 3920 and 6260 kg ha(\u27-1) in 1982 at the low and high fertility levels, respectively. The corn plants were sampled throughout the growing season, separated into different plant parts, and chemically analyzed;The concentrations of P and K in the plants increased and the concentrations of Zn and Mg (except in the stalks and grain) decreased as the levels of P and K availability in the soil increased. The concentrations of other elements--N, S, Ca, Cu, Mn, Fe, Na, and Al--in the plants did not vary consistently among fertility levels except for slight decreases of N and S in the grain and a slight increase of Ca in the stalks as the PK fertility level increased;Changes in nutrient concentrations during the season varied for different elements, for different plant parts and positions on the plants, and at different levels of P and K availability in the soil;Nutrient contents in the plants increased as fertility level increased. After silking, most of the nutrient accumulation was in upper ear shoots;Soil fertility differences did not markedly influence the amounts of nutrients in the grain at early stages of grain development, but later as the grain developed, the amounts of nutrients in the seeds increased as the fertility level increased

Investigation of Emulsion Bitumen Adhesion to Aggregates in Chipseal at Various Temperatures for Low-Cost Pavement Management

Preventive maintenance is recommended by economic models in pavement management. One of the issues that the Chipseal mix is currently dealing with is the degree of separation of the material from the mixture's surface due to a lack of proper adhesion between the emulsion(green) bitumen, and the aggregate. Have and cause an accident. In this study, it was attempted to reduce material separation by increasing the percentage of bitumen in the mixture as well as the percentage of sand as a filler. The results of this study showed that with increasing the percentage of emulsion bitumen in the chipseal mixture and with it increases the percentage of filler in the mixture, the separation rate of aggregates to less than 10% in the temperature range of -15 to +45 ° C, and a Created a more cohesive mixture

Using stone column as a suitable liquefaction remediation in Persian Gulf coast.

This research investigates behavior of gravel drain piles under high-level earthquake loading beneath the structures foundation. To achieve this purpose one of the waste water septic tank project in north of Persian Gulf in Hormoz Island was selected as a case study to find suitability of gravel drain pile system to reduce excess pore water pressure. According to high susceptibility of local soil layers liquefaction and its short distance of waste water tank to the sea, the mentioned project becomes one of the most important issues regarding geo-enviro nmentally hazards impact after tank structural collapsing. The drain piles were used to control excess pore water pressures beneath the foundation of mentioned project. Furthermore, different static and cyclic triaxial tests, Standard Penetration Test (SPT), the hydraulic conductivity and density tests were conducted to enhance the proper understanding of the dynamic behavior of soil layer under the foundation. According to the numerical modeling results, using these drain piles has focal effects on the excess pore water pressure rate and creates a liquefaction zone during the time of earthquake loading

Consistent formulation of the crossover from density to velocity dependent recombination in organic solar cells

Carrier recombination is a central process in bulk heterojunction organic solar cells. Based on the competition of hopping rates that either implies escape in a broad density of states or recombination across the interface, we formulate a general theory of recombination flux that distinguishes reaction or transport limited recombination according to charge density. The Langevin picture is valid only in the low charge density limit, and a crossover to the reaction controlled regime occurs at higher densities. We present results from impedance spectroscopy of poly(3-hexylthiophene):methanofullerene solar cell that exhibit this crossoverThe work was supported by Generalitat Valenciana (Project No. ISIC/2012/008)

Studies on Trade-off Between Throughput and Reliability in Wireless Systems

In the first part of the thesis, we study the trade-off between the transmission reliability and data rate in high signal-to-noise ratio regime in ad-hoc wireless networks. Bandwidth allocation plays a significant role in this trade-off, since dividing bandwidth reduces the number of users on each band and consequently decreases the interference level, however it also decreases the data rate. Noting that the interference power is substantially influenced by the network density, this trade-off introduces a measure for appropriate bandwidth allocation among users considering the network density. The diversity-multiplexing trade-off is derived for a one-dimensional regular ad-hoc network. In the second part of the thesis, we study the performance of point-to-point and broadcast systems with partial channel state information at the transmitter in a time-varying environment. First, the capacity of time-varying channels with periodic feedback at the transmitter is evaluated. It is assumed that the channel state information is perfectly known at the receiver and is fed back to the transmitter at the regular time-intervals. The system capacity is investigated in two cases: i) finite state Markov channel, and ii) additive white Gaussian noise channel with time-correlated fading. In a multiuser scenario, we consider a downlink system in which a single-antenna base station communicates with single antenna users, over a time-correlated fading channel. It is assumed that channel state information is perfectly known at each receiver, while the rate of channel variations and the fading gain at the beginning of each frame are known to the transmitter. The asymptotic throughput of the scheduling that transmits to the user with the maximum signal to noise ratio is examined applying variable code rate and/or variable codeword length signaling. It is shown that by selecting a fixed codeword length for all users, the order of the maximum possible throughput (corresponding to quasi-static fading) is achieved