Light scattering as a Poisson process and first-passage probability

A particle entering a scattering and absorbing medium executes a random walk through a sequence of scattering events. The particle ultimately either achieves first-passage, leaving the medium, or it is absorbed. The KubelkaMunk model describes a flux of such particles moving perpendicular to the surface of a plane-parallel medium with a scattering rate and an absorption rate. The particle path alternates between the positive direction into the medium and the negative direction back towards the surface. Backscattering events from the positive to the negative direction occur at local maxima or peaks, while backscattering from the negative to the positive direction occur at local minima or valleys. The probability of a particle avoiding absorption as it follows its path decreases exponentially with the path-length λ. The reflectance of a semiinfinite slab is therefore the Laplace transform of the distribution of path-length that ends with a first-passage out of the medium. In the case of a constant scattering rate the random walk is a Poisson process. We verify our results with two iterative calculations, one using the properties of iterated convolution with a symmetric kernel and the other via direct calculation with an exponential steplength distribution. We present a novel demonstration, based on fluctuation theory of sums of random variables, that the first-passage probability as a function of the number of peaks n in the alternating path is a step-length distribution-free combinatoric expression involving Catalan numbers. Counting paths with backscattering on the real half-line results in the same Catalan number coefficients as Dyck paths on the whole numbers. Including a separate forward-scattering Poisson process results in a combinatoric expression related to counting Motzkin paths. We therefore connect walks on the real line to discrete path combinatorics

Pathways of rural development in Madagascar

This paper is based on community-level data from 188 villages in rural Madagascar. The survey that was conducted in 1997 made extensive use of long-term recall questions ascertaining changes during the past 10 years in rice yields, wages, population, soil fertility, and other pertinent variables of rural development. We find that—on average for all villages—the yields of irrigated rice, the major food crop, and real agricultural wages declined, while the communities expanded their upland area by nearly a quarter and experienced deteriorating fertility of their upland soils. These patterns are consistent with the wide-held belief that rural areas in Madagascar have witnessed increased poverty, economic stagnation, and a continued degradation of the natural resources. Yet, the five agroecological regions in our sample exhibit quite different patterns of rural development, and at least one of them has experienced increases in yields and wages. From a policy perspective, it is important to better understand the driving forces of such diverse rural change. The overall decline in rural wages over the past 10 years is expected to have contributed to increased poverty, food insecurity and malnutrition in rural areas, as rural wage laborers traditionally belong to the poorest of the poor in Madagascar. In this paper, we present an econometric analysis of the determinants of and interdependencies between the three components of sustainable development: economic growth, environmental sustainability, and poverty alleviation.Crop yields. ,Econometric models. ,Poverty alleviation. ,Rural development projects ,

Pathways of rural development in Madagascar

This paper is based on community-level data from 188 villages in rural Madagascar. The survey that was conducted in 1997 made extensive use of long-term recall questions ascertaining changes during the past 10 years in rice yields, wages, population, soil fertility, and other pertinent variables of rural development. We find that—on average for all villages—the yields of irrigated rice, the major food crop, and real agricultural wages declined, while the communities expanded their upland area by nearly a quarter and experienced deteriorating fertility of their upland soils. These patterns are consistent with the wide-held belief that rural areas in Madagascar have witnessed increased poverty, economic stagnation, and a continued degradation of the natural resources. Yet, the five agroecological regions in our sample exhibit quite different patterns of rural development, and at least one of them has experienced increases in yields and wages. From a policy perspective, it is important to better understand the driving forces of such diverse rural change. The overall decline in rural wages over the past 10 years is expected to have contributed to increased poverty, food insecurity and malnutrition in rural areas, as rural wage laborers traditionally belong to the poorest of the poor in Madagascar. In this paper, we present an econometric analysis of the determinants of and interdependencies between the three components of sustainable development: economic growth, environmental sustainability, and poverty alleviation.Crop yields. ,Econometric models. ,Poverty alleviation. ,Rural development projects ,

233: Symmetric dimethylarginine serum level as a new marker of left ventricular ejection fraction in patients with acute myocardial infarction

Asymmetric dimethylarginine (ADMA) is a by-product of protein methylation implicated in the prognosis after acute myocardial infarction (MI) and heart failure through Nitric Oxide Synthase (NOS) inhibition. We aimed to investigate whether SDMA - the endogenous symmetrical stereoisomer of ADMA - that has insignificant inhibitory effects on NOS might be a marker of left ventricular function in acute MI.MethodsBlood samples from 468 consecutive patients hospitalized <24 hours after acute MI were taken on admission. Serum levels of ADMA and SDMA were determined using high-performance liquid chromatography. Left ventricular ejection fraction (LVEF) was assessed by echocardiography at 2±1 d after admission.ResultsAmong the study population, mean age was 66±14 y, most were male (77%), hypertensive (54%), with prior CAD (20%) or diabetes (20%). On admission, half had ST segment elevation MI (STEMI) (55%), and ¼ suffered from heart failure, as assessed by killip>1 (23%). Mean LVEF was 52±13%. Mean ADMA and SDMA levels were at 0.81±0.42 and 0.61±0.44, respectively. Spearman analysis showed that LVEF was correlated negatively with SDMA (r=-0.135, p=0.006), but neither with ADMA (r=-0.001, p=0.99). SDMA was strongly associated with age (r=+0.354, p<0.001), creatinine clearance (r=-0.416, p<0.001), CRP (r=+0.134, p=0.004) and homocysteine (r=+0.413, p<0.001). By univariate linear regression analysis, age, homocysteine, hypertension, diabetes, prior CAD, admission heart rate, creatinine clearance, anterior wall location, STEMI, CK peak, and acute statin treatment, in addition to SDMA, were significantly associated with LVEF (p<0.05). Backward multivariate analysis including these covariates showed that SDMA remains an independent predictor of LVEF (B=-3.422; SE=1.687, p=0.043), beyond classical determinants of LVEF including age, homocysteine and renal function.ConclusionOur large prospective study showed for the first time that SDMA, but ADMA, may be linked to left ventricular function in patients with acute MI, and suggests that such dimethylarginines may probably exert biological activity by other pathways than NOS activity inhibition and beyond renal function

Chikungunya outbreak in a rural area of Western Cameroon in 2006: A retrospective serological and entomological survey

<p>Abstract</p> <p>Background</p> <p>Although arboviral infections including Chikungunya virus (CHIKV) are common in sub-Saharan Africa, data on their circulation and prevalence are poorly documented. In 2006, more than 400 cases of dengue-like fever were reported in Kumbo (Northwest Region of Cameroon). The aim of this study was to identify the aetiology of this fever and to define its extent in the area.</p> <p>Methods</p> <p>We conducted a cross-sectional seroprevalence survey one year after clinical investigations to define the extent of the infection. An entomological survey consisted of the collection and identification of mosquito immature stages in water containers in or around human dwellings.</p> <p>Results</p> <p>A total of 105 sera were obtained from volunteers and tested for CHIKV, O'Nyong-nyong virus (ONNV) and Dengue virus (DENV) specific IgM and IgG antibodies by enzyme-linked immunosorbent assays (ELISA). CHIKV infection was defined as the presence of IgM antibodies to CHIKV. There was serological evidence for recent Chikungunya infection, as 54 subjects (51.4%) had detectable IgM anti-CHIKV in their sera. Amongst these, 52 showed both anti-CHIKV IgM and IgG, and 2 (1.9%) had IgM anti-CHIKV in the absence of IgG. Isolated anti-CHIKV IgG positives were detected in 41 (39%) cases. No anti-ONNV and anti-DENV IgM antibodies were found amongst the sample tested. Out of 305 larvae collected in the different breeding sites, 87 developed to the adult stage; 56 (64.4%) were <it>Aedes africanus </it>and the remaining <it>Culex </it>spp.</p> <p>Conclusions</p> <p>These findings suggest that the outbreak of febrile illness reported in three villages of Western Cameroon was due to CHIKV. The issue of a possible persistence of anti-CHIKV IgM antibodies is discussed. <it>Ae. africanus </it>which was found to be relatively abundant among the raffia palm bushes probably plays a role in the transmission of CHIKV along the chain of sylvatic/domestic mosquito species in this rural area. Particular attention should therefore be given to arbovirus infections in the Central African sub-region where these infections are becoming an emerging public health threat.</p

A single bat species in Cameroon harbors multiple highly divergent papillomaviruses in stool identified by metagenomics analysis

AbstractA number of PVs have been described in bats but to the best of our knowledge not from feces. Using a previously described NetoVIR protocol, Eidolon helvum pooled fecal samples (Eh) were treated and sequenced by Illumina next generation sequencing technology. Two complete genomes of novel PVs (EhPV2 and EhPV3) and 3 partial sequences (BATPV61, BATPV890a and BATPV890b) were obtained and analysis showed that the EhPV2 and EhPV3 major capsid proteins cluster with and share 60–64% nucleotide identity with that of Rousettus aegyptiacus PV1, thus representing new species of PVs within the genus Psipapillomavirus. The other PVs clustered in different branches of our phylogenetic tree and may potentially represent novel species and/or genera. This points to the vast diversity of PVs in bats and in Eidolon helvum bats in particular, therefore adding support to the current concept that PV evolution is more complex than merely strict PV-host co-evolution

Identification of an enterovirus recombinant with a torovirus-like gene insertion during a diarrhea outbreak in fattening pigs

Diarrhea outbreaks in pig farms have raised major concerns in Europe and USA, as they can lead to dramatic pig losses. During a suspected outbreak in Belgium of porcine epidemic diarrhea virus (PEDV), we performed viral metagenomics to assess other potential viral pathogens. Although PEDV was detected, its low abundance indicated that other viruses were involved in the outbreak. Interestingly, a porcine bocavirus and several enteroviruses were most abundant in the sample. We also observed the presence of a porcine enterovirus genome with a gene insertion, resembling a C28 peptidase gene found in toroviruses, which was confirmed using re-sequencing, bioinformatics, and proteomics approaches. Moreover, the predicted cleavage sites for the insertion suggest that this gene was being expressed as a single protein, rather than a fused protein. Recombination in enteroviruses has been reported as a major mechanism to generate genetic diversity, but gene insertions across viral families are rather uncommon. Although such inter-family recombinations are rare, our finding suggests that these events may significantly contribute to viral evolution