Nonparametric autocovariance estimation from censored time series by Gaussian imputation

One of the most frequently used methods to model the autocovariance function of a second-order stationary time series is to use the parametric framework of autoregressive and moving average models developed by Box and Jenkins. However, such parametric models, though very flexible, may not always be adequate to model autocovariance functions with sharp changes. Furthermore, if the data do not follow the parametric model and are censored at a certain value, the estimation results may not be reliable. We develop a Gaussian imputation method to estimate an autocovariance structure via nonparametric estimation of the autocovariance function in order to address both censoring and incorrect model specification. We demonstrate the effectiveness of the technique in terms of bias and efficiency with simulations under various rates of censoring and underlying models. We describe its application to a time series of silicon concentrations in the Arctic.

Ultrastructural organisation and functional aspects of the olfactory epithelium of Wallago attu (Bleeker)

The topological architecture and functions of different cells of the olfactory epithelium in Wallago attu (Bleeker) have been systematically studied using a scanning electron microscope. The elongated olfactory rosette of the fish consists of 62 to 64 primary lamellae in each left and right rosette. Each lamella is provided with apical sensory epithelium and basal non-sensory epithelium. Topological analysis reveals that sensory epithelium contains receptor cells, ciliated supporting cells, labyrinth cells, and goblet cells. The non-sensory epithelium is made up of patches of ciliated supporting cells, epidermal or stratified epithelial cells with concentrically arranged microridges, and scattered goblet cells. Different cells on the olfactory epithelium support the view that the olfactory signalling is important to the survival of this fish in an aquatic environment.

Coordination polymers with pyridine-2,4,6-tricarboxylic acid and alkaline-earth/lanthanide/transition metals: synthesis and X-ray structures

Pyridine-2,4,6-tricarboxylic acid (ptcH(3)) reacts with Cd(II), Mn(II), Ni(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts forming different products depending on the reaction conditions. In the presence of pyridine at room temperature the acetate, chloride or nitrate salt of Cd(II) breaks the ligand to form an open framework structure with the empirical formula, {[Cd(Ox)(H(2)O)(2)]H(2)O}(n) (Ox = oxalate), 1. In the absence of pyridine, no crystalline compound could be isolated at room temperature (RT). However, under hydrothermal conditions and in the absence of pyridine, a discrete tetrameric complex with the formula, {[Cd(2)(cda)(2)(H(2)O)(4)](H(2)O)(3)}(2) (cdaH(2) = 4-hydroxypyridine-2,6-dicarboxylic acid), 2, is formed where the carboxylate group at the 4-position of the ligand is reduced to a hydroxyl group. When Ni(II), Mn(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts are used in place of Cd(II), no crystalline product could be isolated at RT. But under hydrothermal conditions, coordination polymers ({[Ni(1.5)(ptc)(pip)(0.5)(H(2)O)(4)].H(2)O}(n), (pip = piperazine), 3; {Mn(1.5)(ptc).2H(2)O}(n), 4; {Mg(3)(ptc)(2).8H(2)O}(n), 5; {[Mg(ptc)(H(2)O)(2)].1/2[Mg(H(2)O)(6)].H(2)O}(n), 6; {Ca(1.5)(ptc).2H(2)O}(n), 7; {Sr(1.5)(ptc).5H(2)O}(n), 8; {[Ba(ptc)(H(2)O)][Ba(ptcH(2))H(2)O]}(n), 9; {[Dy(ptc).3H(2)O].H(2)O}(n), 10) are formed. The structures exhibit different dimensionality depending on the nature of the metal ions. In 1 a discrete acyclic water hexamer is also identified. All the compounds are characterized in the solid state by X-ray crystallography, IR and elemental analysis.

Performance of Information Criteria for Spatial Models

Model choice is one of the most crucial aspect in any statistical data analysis. It is well known that most models are just an approximation to the true data generating process but among such model approximations it is our goal to select the "best" one. Researchers typically consider a finite number of plausible models in statistical applications and the related statistical inference depends on the chosen model. Hence model comparison is required to identify the "best" model among several such candidate models. This article considers the problem of model selection for spatial data. The issue of model selection for spatial models has been addressed in the literature by the use of traditional information criteria based methods, even though such criteria have been developed based on the assumption of independent observations. We evaluate the performance of some of the popular model selection critera via Monte Carlo simulation experiments using small to moderate samples. In particular, we compare the performance of some of the most popular information criteria such as Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), and Corrected AIC (AICc) in selecting the true model. The ability of these criteria to select the correct model is evaluated under several scenarios. This comparison is made using various spatial covariance models ranging from stationary isotropic to nonstationary models.

Oesophageal peristaltic transition zone defects: real but few and far between

This study analysed the association between oesophageal transition zone (TZ) defects [characterized by a delay and/or spatial gap between the terminus of the proximal oesophageal (striated muscle) contraction and the initiation of the distal oesophageal (smooth muscle) contraction] and dysphagia in a large patient cohort. Four hundred consecutive patients (178 with dysphagia) and 75 controls were studied with 36-channel high-resolution manometry (HRM). The resultant pressure topography plots were first analysed for impaired oesophagogastric junction (OGJ) relaxation, distal segment contractile abnormalities, and proximal contractile abnormalities using normal values from the 75 controls. If these aspects of oesophageal motility were deemed normal, the TZ was characterized by length and duration between the proximal and distal contractions using a 20 mmHg isobaric contour to establish the segment boundaries. Patients were then classified according to whether or not they exhibited TZ defects (spatial separation or delay) and the occurrence of unexplained dysphagia. Of the 400 patients, 267 were suitable for TZ analysis and of these 55 had a spatial or temporal TZ measurement exceeding the 95th percentile of the controls (2 cm, 1 s). Exactly 34.6% of the patients (n = 19) with spatial and/or temporal TZ defects had unexplained dysphagia, which was significantly more than seen with normal TZ dimensions (19.8%). Although far less common than distal peristaltic or OGJ abnormailites, TZ defects may be related to dysphagia in a minority of patients (<4% in this series) and should be considered a distinct oesophageal motility disorder.

SPATIO-TEMPORAL MODELING OF AGRICULTURAL YIELD DATA WITH AN APPLICATION TO PRICING CROP INSURANCE CONTRACTS

This article presents a statistical model of agricultural yield data based on a set of hierarchical Bayesian models that allows joint modeling of temporal and spatial autocorrelation. This method captures a comprehensive range of the various uncertainties involved in predicting crop insurance premium rates as opposed to the more traditional ad hoc, two-stage methods that are typically based on independent estimation and prediction. A panel data set of county-average yield data was analyzed for 290 counties in the State of Paraná (Brazil) for the period of 1990 through 2002. Posterior predictive criteria are used to evaluate different model specifications. This article provides substantial improvements in the statistical and actuarial methods often applied to the calculation of insurance premium rates. These improvements are especially relevant to situations where data are limited.

An autoregressive point source model for spatial processes

We suggest a parametric modeling approach for nonstationary spatial processes driven by point sources. Baseline near-stationarity, which may be reasonable in the absence of a point source, is modeled using a conditional autoregressive (CAR) Markov random field. Variability due to the point source is captured by our proposed autoregressive point source (ARPS) model. Inference proceeds according to the Bayesian hierarchical paradigm, and is implemented using Markov chain Monte Carlo (MCMC) methods. The parametric approach allows a formal test of effectiveness of the point source. Application is made to a real dataset on electric potential measurements in a field containing a metal pole and the finding is that our approach captures the pole's impact on small-scale variability of the electric potential process.

Physiology of the oesophageal transition zone in the presence of chronic bolus retention: studies using concurrent high resolution manometry and digital fluoroscopy

Distinct contraction waves (CWs) exist above and below the transition zone (TZ) between the striated and smooth muscle oesophagus. We hypothesize that bolus transport is impaired in patients with abnormal spatio-temporal coordination and/or contractile pressure in the TZ. Concurrent high resolution manometry and digital fluoroscopy were performed in healthy subjects and patients with reflux oesophagitis; a condition associated with ineffective oesophageal contractility and clearance. A detailed analysis of space-time variations in bolus movement, intra-bolus and intra-luminal pressure was performed on 17 normal studies and nine studies in oesophagitis patients with impaired bolus transit using an interactive computer based system. Compared with normal controls, oesophagitis patients had greater spatial separation between the upper and lower CW tails [median 5.2 cm (range 4.4-5.6) vs 3.1 cm (2.2-3.7)], the average relative pressure within the TZ region (TZ strength) was lower [30.8 mmHg (28.3-36.5) vs 45.8 mmHg (36.1-55.7), P < 0.001], and the risk of bolus retention was higher (90%vs 12%; P < 0.01). The presence of bolus retention was associated with a wider spatial separation of the upper and lower CWs (>3 cm, the upper limit of normal; P < 0.002), independent of the presence of oesophagitis. We conclude that bolus retention in the TZ is associated with excessively wide spatial separation between the upper and lower CWs and lower TZ muscle squeeze. These findings provide a physio-mechanical basis for the occurrence of bolus retention at the level of the aortic arch, and may underlie impaired clearance with reflux oesophagitis.

Gross morphological changes of placentas associated with intrauterine growth restriction of fetuses: a case control study

The present study aimed to throw light to any gross morphological changes of placenta that might contribute to the development of idiopathic IUGR. Gross examination of placentas from full-term uncomplicated pregnancies delivering singleton live IUGR babies, and live normal-weight babies (controls) were performed; then the results were compared. Fifty full-term freshly delivered placentas were collected both from normal deliveries and C.S. Twenty-eight (28) placentas were associated with IUGR and twenty-two (22) were from controls. The positions of insertion of the umbilical cords, placental weights, volumes and diameters were noted. These gross examinations revealed that the control placentas were bigger in diameters, had usual positions of insertion of umbilical cords, mean placental weight was 416.77 gm and mean placental volume was 343.86 ml. In cases of IUGR placentas, there were some abnormal positions of insertion of umbilical cords in 11% placentas (marginal in 7.14% and velamentous in 3.57%), and placental weight and volume was significantly lower (p value<0.001). The placentas associated with IUGR were smaller in diameters than those of control group of placentas. The mean placental co-efficient of IUGR group in the present study was 0.156 (range 0.11-0.22) and that of the control group was 0.138 (range 0.12-0.18). The greater placental co-efficient in IUGR indicates that although both placentas and babies in IUGR had less weight, placental sizes were not relatively less. In fact, these placentas were functional, and even tried to compensate the abnormal morphology. Therefore, though IUGR fetuses were more frequently associated with morphologically abnormal placentas, it could not be conclusively decided whether this abnormal gross morphology actually contributed to the intrauterine growth restriction.

A Reparametrization Approach for Dynamic Space-Time Models

Researchers in diverse areas such as environmental and health sciences are increasingly working with data collected across space and time. The space-time processes that are generally used in practice are often complicated in the sense that the auto-dependence structure across space and time is non-trivial, often non-separable and non-stationary in space and time. Moreover, the dimension of such data sets across both space and time can be very large leading to computational difficulties due to numerical instabilities. Hence, space-time modeling is a challenging task and in particular parameter estimation based on complex models can be problematic due to the curse of dimensionality. We propose a novel reparametrization approach to fit dynamic space-time models which allows the use of a very general form for the spatial covariance function. Our modeling contribution is to present an unconstrained reparametrization method for a covariance function within dynamic space-time models. A major benefit of the proposed unconstrained reparametrization method is that we are able to implement the modeling of a very high dimensional covariance matrix that automatically maintains the positive definiteness constraint. We demonstrate the applicability of our proposed reparametrized dynamic space-time models for a large data set of total nitrate concentrations.

Molecular characterization and sequence variability of betasatellites associated with leaf curl disease of kenaf (hibiscus cannabinus L.) from different geographical locations of India

Leaf curl disease of kenaf (Hibiscus cannabinus L.) in India has been found to be associated with begomoviruses and betasatellites. Here, we report the molecular characterization and phylogenetic relationship of the nine isolates of betasatellites obtained from three geographical locations in India. The betasatellites coming from northern and eastern region of India shared 84.3% nucleotide sequence identity and formed two sub-clusters within the main cluster containing different isolates of Cotton leaf curl Multan betasatellite (CLCuMB) isolated in Indian subcontinent. Betasatellites coming from the southern part of India were identified as the isolates of Tomato leaf curl Joydebpur betasatellite and shared 45.2 and 44.9% sequences identity with their counterparts coming from the eastern and northern India, respectively. The present study represents the first report about the association of the leaf curl disease of kenaf with the betasatellites infecting both malvaceous and non-malvaceous crops in India.

Does the Bravo pH capsule affect esophageal motor function?

The aim of this study was to determine whether attachment of the Bravo pH monitoring capsule alters esophageal motility. Twenty normal subjects were studied with 36-channel high-resolution manometry before and after Bravo capsule placement. Subjects performed 10 5-mL water-swallows in both upright and supine positions and two 5-mL barium-swallows under fluoroscopy synchronized with manometry recordings. There was no significant change in basal esophagogastric junction (EGJ) pressure, EGJ relaxation pressure or peristaltic function before and after Bravo placement in either position. However, a 2-cm focus of augmented peristalsis was found corresponding to the position of the Bravo capsule. Ten subjects were aware of the capsule (7 had a mild foreign body sensation, 1 had mild discomfort, and 2 had chest pain altering daily activity or diet) while nine subjects were unaware of the capsule. Subjects who were aware of the capsule's presence exhibited a greater augmentation of peristalsis than those who were not (P < 0.05). Neither EGJ function nor peristaltic performance were significantly altered by the presence of a Bravo capsule. However, capsule presence was associated with a locus of augmented peristalsis and this phenomenon was most evident in subjects who perceived the presence of the Bravo capsule.

Larvivorous fish against malaria vectors: a new outlook

The use of larvivorous fish in malaria control is not new but a half-forgotten strategy. It has been shown to be effective and sustainable in many circumstances. A strategic action plan targeting relevant sibling species of the vectors as well as application of global positioning system technology to facilitate rapid re-checking of sites for the continuing presence of fish are important new features of this strategy.

Retroperitoneal Castleman's disease mimicking soft tissue tumour

Castleman's disease is a type of non-neoplastic lymphoproliferative disease having lymph nodal hyperplasia. It has two distinct microscopic types: hyaline-vascular type and plasma cell type. Clinically, it may present either as a solitary mass, most commonly in the mediastinum, or as a multicentric form whose features are generalized lymph-adenopathy, splenomegaly and involvement of other organs like the lungs and kidneys. Here we report a case of isolated retroperitoneal Castleman's disease, which presented as a lump in the iliac fossa in a young female. A clinico-radio-logical diagnosis of retroperitoneal soft tissue tumour was made and the patient underwent complete surgical excision. The exact diagnosis was only obtained at histopathology and there is no evidence of recurrence at six months follow-up.

A new monopartite begomovirus isolated from Hibiscus cannabinus L. in India

Yellow vein mosaic disease of mesta is whitefly-transmitted and found in endemic form in different parts of India, causing great economic losses. Full-length DNA-A of a begomovirus infecting mesta was cloned and sequenced. The genome was homologous to the DNA-A of monopartite begomoviruses originating from the Old World, with six conserved open reading frames. The complete nucleotide sequence of the DNA-A molecule of the present isolate was 2728 nucleotides in length, having the highest sequence identity (83.5%) with an Indian begomovirus causing cotton leaf curl disease. It thus belongs to a novel geminivirus species, and the name Mesta yellow vein mosaic virus is proposed.

Peripheral blood lymphocyte subpopulations in patients with cervical cancer

OBJECTIVE

Impairment of cell-mediated immunity in carcinoma of the cervix (CA CX) and cervical intraepithelial neoplasia (CIN) are reported. Contradictory reports exist on lymphocyte subpopulations associated with this disease. The present study aims to quantitatively analyze peripheral blood lymphocytes subsets in patients with CA CX and CIN.

METHOD

Systemic T lymphocyte subsets, CD19+, CD16+ and CD56+ cells in 58 CA CX and 10 CIN patients were studied. The lymphocyte phenotypes were quantified by monoclonal antibodies (anti-CD4, CD8, CD16, CD19 and CD56).

RESULT

Significant decrease in CD4+ cell population was observed in CA CX and CIN patients as compared to controls (P< or =0.05). CD4+/CD8+ ratio was observed to be less in CIN patients (P< or =0.001). Other lymphocyte subpopulations appeared to be comparable between the groups.

CONCLUSION

Results indicate immunological abnormalities in invasive CA CX and CIN patients. Study on a larger patient population may provide a biomarker for early detection of this disease.