Power Allocation Based on SEP Minimization in Two-Hop Decode-and-Forward Relay Networks

The problem of optimal power allocation among the relays in a two-hop decode-and-forward cooperative relay network with independent Rayleigh fading channels is considered. It is assumed that only the relays that decode the source message correctly contribute in data transmission. Moreover, only the knowledge of statistical channel state information is available. A new simple closed-form expression for the average symbol error probability is derived. Based on this expression, a new power allocation method that minimizes the average symbol error probability and takes into account the constraints on the total average power of all the relay nodes and maximum instant power of each relay node is developed. The corresponding optimization problem is shown to be a convex problem that can be solved using interior point methods. However, an approximate closed-form solution is obtained and shown to be practically more appealing due to significant complexity reduction. The accuracy of the approximation is discussed. Moreover, the so obtained closed-form solution gives additional insights into the optimal power allocation problem. Simulation results confirm the improved performance of the proposed power allocation scheme as compared to other schemes.Comment: 27 pages, 5 figures, submitted to the IEEE Trans. Signal Processing in Feb. 201

On the indefinite Helmholtz equation: complex stretched absorbing boundary layers, iterative analysis, and preconditioning

This paper studies and analyzes a preconditioned Krylov solver for Helmholtz problems that are formulated with absorbing boundary layers based on complex coordinate stretching. The preconditioner problem is a Helmholtz problem where not only the coordinates in the absorbing layer have an imaginary part, but also the coordinates in the interior region. This results into a preconditioner problem that is invertible with a multigrid cycle. We give a numerical analysis based on the eigenvalues and evaluate the performance with several numerical experiments. The method is an alternative to the complex shifted Laplacian and it gives a comparable performance for the studied model problems

Molecular Infectious Disease Epidemiology: Survival Analysis and Algorithms Linking Phylogenies to Transmission Trees

Recent work has attempted to use whole-genome sequence data from pathogens to reconstruct the transmission trees linking infectors and infectees in outbreaks. However, transmission trees from one outbreak do not generalize to future outbreaks. Reconstruction of transmission trees is most useful to public health if it leads to generalizable scientific insights about disease transmission. In a survival analysis framework, estimation of transmission parameters is based on sums or averages over the possible transmission trees. A phylogeny can increase the precision of these estimates by providing partial information about who infected whom. The leaves of the phylogeny represent sampled pathogens, which have known hosts. The interior nodes represent common ancestors of sampled pathogens, which have unknown hosts. Starting from assumptions about disease biology and epidemiologic study design, we prove that there is a one-to-one correspondence between the possible assignments of interior node hosts and the transmission trees simultaneously consistent with the phylogeny and the epidemiologic data on person, place, and time. We develop algorithms to enumerate these transmission trees and show these can be used to calculate likelihoods that incorporate both epidemiologic data and a phylogeny. A simulation study confirms that this leads to more efficient estimates of hazard ratios for infectiousness and baseline hazards of infectious contact, and we use these methods to analyze data from a foot-and-mouth disease virus outbreak in the United Kingdom in 2001. These results demonstrate the importance of data on individuals who escape infection, which is often overlooked. The combination of survival analysis and algorithms linking phylogenies to transmission trees is a rigorous but flexible statistical foundation for molecular infectious disease epidemiology.Comment: 28 pages, 11 figures, 3 table

Anthropometrics without numbers!

(Anthropometrics without Numbers! An Investigation of Designers' Use and Preference of People Data By Nickpour F and Dong H) There is still missing knowledge to encourage and support designers in adoption and implementation of inclusive design. Some of this missing knowledge comes in the form of anthropometric data which provides accessible information on users' capabilities and limitations. Support and resources for designers on this type of data seems to be limited and exclusive. This study focuses on evaluating the existing use of anthropometric data by professional designers, aiming to explore means of presenting such data more effectively. Ten UK-based design consultancies were interviewed and completed questionnaires collecting information on designer’s current use of anthropometric data, their suggestions on presentation of that data and their preferences on data tools. It is concluded that the use of anthropometric data sources by designers is very limited and minimal; experienced designers tend to rely mainly on experimental methods such as physical prototyping and engagement with people. The results provide insights into designers' existing approaches to data collection and use. This study highlights the need for development of a highly visual, simple and intuitive data tool based on the interviewed designers’ preferences and suggestions. This has to be done by carefully adopting the designers’ existing approaches to data collection and use and by adapting existing data into that

Four-Dimensional Neuronal Signaling by Nitric Oxide: A Computational Analysis

Nitric oxide (NO) is now recognized as a transmitter of neurons that express the neuronal isoform of the enzyme nitric oxide synthase. NO, however, violates some of the key tenets of chemical transmission, which is classically regarded as occurring at points of close apposition between neurons. It is the ability of NO to diffuse isotropically in aqueous and lipid environments that has suggested a radically different form of signaling in which the transmitter acts four-dimensionally in space and time, affecting volumes of the brain containing many neurons and synapses. Although ¿volume signaling¿ clearly challenges simple connectionist models of neural processing, crucial to its understanding are the spatial and temporal dynamics of the spread of NO within the brain. Existing models of NO diffusion, however, have serious shortcomings because they represent solutions for ¿point-sources,¿ which have no physical dimensions. Methods for overcoming these difficulties are presented here, and results are described that show how NO spreads from realistic neural architectures with both simple symmetrical and irregular shapes. By highlighting the important influence of the geometry of NO sources, our results provide insights into the four-dimensional spread of a diffusing messenger. We show for example that reservoirs of NO that accumulate in volumes of the nervous system where NO is not synthesized contribute significantly to the temporal and spatial dynamics of NO spread

Periodic Slab LAPW Computations for Ferroelectric BaTiO3_3

Linearized augmented plane wave (LAPW) calculations are performed for periodic (001) and (111) slabs of BaTiO$_3$ to understand the effects of surfaces on ferroelectric BaTiO$_3$. The (111) slab is found to be much less stable than the (001) slab. The average surface energies are respectively 3700 erg/cm$^2$ and 1600 erg/cm$^2$. The depolarization field is sufficiently large in the ideal unrelaxated slab to completely inhibit the ferroelectric instability. No mid-gap surface states are evident, but there are surface states in the upper gap in the unrelaxed slab and at the top of the valence band. The dangling surface Ti bonds self-heal making the Ti-O surface very reactive and an excellent epitaxial substrate. The charge density on atoms only one unit cell away from the surface are almost identical to the bulk. Keywords: ferroelectric, surface, slab, electronic structure, depolarization, BaTiO$_3$, thin filmComment: LaTeX (RevTex),10 pages, 3 PS figures ( fig. 1 and fig. 3 are color), 1 table, J. Phys. Chem. Solids, Proceedings of Third Williamsburg Workshop on Fundamental Experiments in Ferroeletrics, T. Egami, edito

Re-imaging the Environment

This paper represents a study of selected visualisation and investigative methods that facilitate the exploration and expression of human emotions and perceptions within real world environments during the design development stages of a project, repositioning exploration and visualisation in spatial design education. It puts forward an outline for an iterative enquiry around human experiences in order to assess the value of alternative cognitive tools for spatial design students in higher education. Established tools such as orthographic drawings, axonometric projections or scale models equip spatial designers with the consistency they need to investigate and represent physical attributes of space but don't always constitute the best methods to explore the perceived environment, even though it is a key contributing factor to the way we experience our surroundings. It is therefore in the interest of design educators to investigate complementary interpretations that enable students to consciously explore less tangible aspects of design such as emotions and multi-sensorial modalities. Projects developed using tools and techniques ranging from digital 2D and 3D image making, photography, film, animation and performance provide an insight into the possibilities offered by exisiting visual technologies as dynamic study devices of human experiences and contribute to the generation of alternative processes in spatial design education