Accurate simple closed-form approximations to Rayleigh sum distributions and densities

Sums of Rayleigh random variables occur extensively in wireless communications. A closed-form expression does not exist for the sum distribution and consequently, it is often evaluated numerically or approximated. A widely used small argument approximation for the density is shown to be inaccurate for medium and large values of the argument. Highly accurate, simple closed-form expressions for the sum distributions and densities are presented. These approximations are valid for a wide range of argument values and number of summands.     

The Project Involvement Index,psychological distress,and psychological well-being: Comparing workers from projectized and non-projectized organizations

It is important to understand the extent to which project involvement affects mental health. As projects and project management expand beyond traditional fields, it is also important to compare project involvement and mental health across settings that vary in terms of management structure. This study is the first to validate a Project Involvement Index (PII) useful in various settings to understand how workload relates to mental health defined as high psychological well-being and low psychological distress. Our results demonstrate that the PII is parsimonious measure showing reliability, predictive validity, and discriminant validity. Furthermore, results show that people involved in projects from a non-projectized organization show less mental health than those from a projectized organization.     

Photodegradation of RDX in aqueous solution: a mechanistic probe for biodegradation with Rhodococcus sp

Recently we demonstrated that Rhodococcus sp. strain DN22 degraded hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) (1) aerobically via initial denitration followed by ring cleavage. Using UL 14C-[RDX] and ring labeled 15N-[RDX] approximately 30% of the energetic chemical mineralized (one C atom) and 64% converted to a dead end product that was tentatively identified as 4-nitro-2,4-diaza-butanal (OHCHNCH2NHNO2). To have further insight into the role of initial denitration on RDX decomposition, we photolyzed the energetic chemical at 350 nm and pH 5.5 and monitored the reaction using a combination of analytical techniques. GC/ MS-PCI showed a product with a [M+H] at 176 Da matching a molecular formula of C3H5N5O4 that was tentatively identified as the initially denitrated RDX product pentahydro-3,5-dinitro-1,3,5-triazacyclohex-1-ene (II). LC/MS (ES-) showed that the removal of RDX was accompanied by the formation of two other key products, each showing the same [M-H] at 192 Da matching a molecular formula of C3H7N5O5. The two products were tentatively identified as the carbinol (III) of the enamine (II) and its ring cleavage product O2NNHCH2NNO2CH2NHCHO (IV). Interestingly, the removal of III and IV was accompanied by the formation and accumulation of OHCHNCH2NHNO2 that we detected with strain DN22. At the end of the experiment, which lasted 16 h, we detected the following products HCHO, HCOOH, NH2CHO, N2O, NO2-, and NO3-. Most were also detected during RDX incubation with strain DN22. Finally, we were unable to detect any of RDX nitroso products during both photolysis and incubation with the aerobic bacteria, emphasizing that initial denitration in both cases was responsible for ring cleavage and subsequent decomposition in water.     

An infinite series for the computation of the complementaryprobability distribution function of a sum of independent randomvariables and its application to the sum of Rayleigh random variables

The properties of the series are studied for both bounded and unbounded random variables. The technique is used to find efficient series for computation of the distributions of sums of uniform random variables and sums of Rayleigh random variables. A useful closed-form expression for the characteristic function of a Rayleigh random variable is presented, and an efficient method for computing a confluent hypergeometric function is given. An infinite series for the probability density function of a sum of independent random variables is also derived. The inversion of characteristic functions, a trapezoidal rule for numerical integration, and the sampling theorem in the frequency domain are related to, and interpreted in terms of, the results     

Multi-component T1 relaxation and magnetisation transfer in peripheral nerve

Corneas of diabetic patients have abnormal healing and epithelial adhesion, which may be due to alterations of the corneal extracellular matrix (ECM) and basement membrane (BM). To identify such alterations, various ECM and BM components and integrin receptors were studied by immunofluorescence on sections of normal and diabetic human corneas. Age-matched corneas from 15 normal subjects, 10 diabetics without diabetic retinopathy (DR), and 12 diabetics with DR were used. In DR corneas, the composition of the central epithelial BM was markedly altered, compared to normal or non-DR diabetic corneas. In most cases the staining for entactin/nidogen and for chains of laminin-1 (alpha1beta1gamma1) and laminin-10 (alpha5beta1gamma1 was very weak, discontinuous, or absent over large areas. Other BM components displayed less frequent changes. The staining for alpha3beta1 (VLA-3) laminin binding integrin was also weak and discontinuous in DR corneal epithelium. Components of stromal ECM remained unchanged even in DR corneas. Therefore, distinct changes were identified in the composition of the epithelial BM in DR corneas. They may be due to increased degradation or decreased synthesis of BM components and related integrins. These alterations may directly contribute to the epithelial adhesion and wound healing abnormalities found in diabetic corneas.     

Outage probabilities of diversity cellular systems with cochannelinterference in Nakagami fading

Analytical, closed-form expressions for cellular outage probabilities in generalized Nakagami fading are derived for three practical diversity combining schemes. The outage is defined as the probability that the signal-to-interference power ratio (SIR) is less than a power protection ratio. The analysis considers L-branch equal gain (EG), selection (SC), and switched (SW) diversity combining schemes. The analyses are not limited to a single interferer, but rather assume the presence of multiple independent cochannel interferers. Previous results have used some approximations to study the performance of the EG combiner. A precise method is used to analyze the performance of an L-branch EG combiner. Selection diversity combining using the total power algorithm, the desired power algorithm, and the signal-to-interference power algorithm is analyzed. The effects of diversity on the reuse factor and on the spectrum efficiency of cellular mobile radio systems are considered in detail. The results for the Rayleigh fading channel are obtained and presented as a special case of the generalized Nakagami fading model     

Approximate SER of H-S/MRC in Nakagami fading with arbitrary branch power correlation

An accurate approximation to the average symbol-error rate of hybrid selection/maximal-ratio combining (H-S/MRC) in correlated Nakagami-m fading with positive integer values of m is obtained by using a Green's matrix approximation. This approach is valid for different M-ary linear modulation schemes. We illustrate our methodology using M-ary phase-shift keying as an example.     

Optimal maximal ratio combining with correlated diversity branches

It is proved that a maximal ratio combiner operating on correlated branches and weighting the branch signals as though they were independent is optimal. It is also proved that performance measures of maximal ratio combining operating with correlated Rayleigh or Ricean fading input branches are identical to performance measures of an equivalent diversity system operating with independent and, in general, unbalanced inputs     

Influence of built environment on pedestrian's crossing decision

The objective of this experimental study is to identify the differentiation made by pedestrians, in their crossing decision, between various urban environments, notably in terms of perception of walking pleasantness and safety. This experiment further aims to identify the environmental features that pedestrians take into account and the inferences they develop and use to explain their road crossing decision. Sets of photographs presenting five different environments (city center, inner suburbs, public housing in the outskirts, commercial zone in the outskirts and countryside) were presented to 77 participants divided up into three age groups (pre-adolescents, young and middle adults). Their decision to cross or not, their perception of pleasantness and safety, and the elements they take into account to make a decision were collected for each environment presented. The quantitative results show the pedestrians’ perceptions of the pleasantness and safety of public spaces, in terms of walking, largely vary with urban environments. Moreover, the crossing decision significantly varies according to the environment. Pedestrians were significantly more inclined to take the decision to cross in city center than in the other sites presented. The qualitative analysis of the interviews shows that the presence and function of the buildings, the quality of the sidewalks and the marked parking spaces are key factors to explain their crossing decision, by enabling them to infer the density of pedestrians and traffic and the vehicle speed.     

Pathogen-produce pair attribution risk ranking tool to prioritize fresh produce commodity and pathogen combinations for further evaluation (P3ARRT)

Foodborne disease outbreaks and cases associated with fresh produce have increased over the past decade. In developing approaches to prevent or reduce illnesses from consumption of contaminated produce, new tools are needed to identify and prioritize appropriate efforts. The purpose of this study was to develop a semi-quantitative risk ranking tool (Pathogen-Produce Pair Attribution Risk Ranking Tool, or P³ARRT) to rank the relative public health impact of pathogen-produce commodity combinations, based on explicit data-driven criteria. To identify candidate pathogen-commodity pairs, a database was created that included all published reports of fresh produce-associated outbreaks in the United States. A total risk score was calculated for each pathogen-commodity pair as the summation of nine criteria scores multiplied by the respective criteria weighting. A total of 53 pathogen-produce commodity pairs were included in the risk ranking, and based on scenario and sensitivity analyses, enterohemorrhagic E. coli in leafy greens consistently ranked first, followed by Salmonella spp. in tomatoes, and Salmonella spp. in leafy greens. The P³ARRT model provides a systematic, transparent, and customizable tool with which to prioritize produce pathogen-commodity pairs for further, more rigorous risk assessment modeling and evaluation efforts. The tool is available to the public at www.FoodRisk.org.