Xuewen Lu

Anthocyanin content and profile within and among blueberry species

Anthocyanins in ripe fruit of four Vaccinium species and genotypes within these species were compared, revealing substantial inter- and intra-species variability among these commercial and non-commercial blueberries. The highest total anthocyanin content occurred in the bilberry (V. myrtillus L.). Commercial lowbush blueberry clonal mixtures and wild velvet leaf blueberries (V. myrtilloides L.) had about 43% of the anthocyanin content of bilberries (fresh weight basis). Three commercial highbush cultivars (V. corymbosum L.) had about 30% of the bilberry level, while wild genotypes of highbush blueberries had almost 60% of the bilberry level. Acetylation of anthocyanins occurred widely among all species, except bilberries. Although the proportions of the five blueberry anthocyanidins varied substantially among the commercial blueberries, these differences probably do not contribute substantially to differences in their relative antioxidant capacity. Key words: Vaccinium, bilberry, acetylation, cluster anal...

Assessment of leptomeningeal collaterals using dynamic CT angiography in patients with acute ischemic stroke

Whole-brain dynamic time-resolved computed tomography angiography (CTA) is a technique developed on the new 320-detector row CT scanner capable of generating time-resolved cerebral angiograms from skull base to vertex. Unlike a conventional cerebral angiogram, this technique visualizes pial arterial filling in all vascular territories, thereby providing additional hemodynamic information. Ours was a retrospective study of consecutive patients with ischemic stroke and M1 middle cerebral artery +/– intracranial internal carotid artery occlusions presenting to our center from June 2010 and undergoing dynamic time-resolved CTA and perfusion CT within 6 hours of symptom onset. Leptomeningeal collateral status was assessed by determining relative prominence of pial arteries in the ischemic region, rate and extent of retrograde flow, and various topographical patterns of pial arterial filling. Twenty-five patients were included in the study. We demonstrate the existence of the following novel properties of leptomeningeal collaterals in humans: (a) posterior (posterior cerebral artery (PCA)–MCA) dominant collateralization, (b) intra-territorial ‘within MCA region’ leptomeningeal collaterals, and (c) significant variability in size, extent, and retrograde filling time in pial arteries. We also describe a simple and reliable collateral grading template that, for the first time on dynamic CTA, incorporates back-filling time as well as size and extent of collateral filling.

Modified censored moment estimation for the two-parameter Birnbaum-Saunders distribution

The maximum likelihood estimators (MLEs) and the moment estimators of a two-parameter Birnbaum-Saunders (BISA) distribution are studied by various authors when data are either complete or subject to Type-I or Type-II censoring. But there is not much research on parameter estimation for the BISA distribution under random censoring. A simple method of modified censored moment estimation is proposed to estimate parameters of the BISA distribution under random censoring. Bias-reduced versions of these estimators are constructed as well. Asymptotic theory for the estimators is established. The performance of these estimators is compared with that of the MLEs through Monte Carlo simulations for small, moderate, and large proportions of censoring and different sample sizes. An analysis of real data is used to illustrate the proposed method.

Role of the biosurfactant viscosin in broccoli head rot caused by a pectolytic strain of Pseudomonas fluorescens

The lipopeptidic biosurfactant viscosin was examined as a pathogenicity factor of a pectolytic strain of Pseudomonas fluorescens that causes broccoli head rot. The critical micellar concentration (CMC) of viscosin was 4 𝛍g/mL in a 2 mM phosphate buffer (pH 7.0), and the surface tension was reduced from 71 mN/m to 25 mN/m. When broccoli florets were immersed in viscosin solutions of increasing concentration, the tissues became wetted at 10 𝛍g/mL and electrolytes were induced to leak at a concentration between 10 and 25 𝛍g/mL. Erythrocytes were lysed at concentrations of 10 𝛍g/mL and above. Since membrane effects occurred above the CMC, it appears that viscosin does not act as a membrane toxin, but rather as a nonspecific detergent. A viscosin deficient mutant, induced by Tn5 mutagenesis, caused decay of wounded florets only, but the decay failed to spread to adjacent nonwounded florets as had occurred with a wild strain. When the mutant strain (1 x 107 cfu/mL) was incubated with viscosin (25 𝛍g/mL), it was...

Polynomial spline estimation of partially linear single-index proportional hazards regression models

The Cox proportional hazards (PH) model usually assumes linearity of the covariates on the log hazard function, which may be violated because linearity cannot always be guaranteed. We propose a partially linear single-index proportional hazards regression model, which can model both linear and nonlinear covariate effects on the log hazard in the proportional hazards model. We adopt a polynomial spline smoothing technique to model the structured nonparametric single-index component for the nonlinear covariate effects. This method can reduce the dimensionality of the covariates being modeled, while, at the same time, can provide efficient estimates of the covariate effects. A two-step iterative algorithm to estimate the nonparametric component and the covariate effects is used for facilitating implementation. Asymptotic properties of the estimators are derived. Monte Carlo simulation studies are presented to compare the new method with the standard Cox linear PH model and some other comparable models. A case study with clinical trial data is presented for illustration.

Multivariate local polynomial regression for estimating average derivatives

In this paper we suggest to use the sample average of the derivative estimators from a local polynomial fitting to estimate the average derivatives of an unknown multivariate function. Using the techniques of Masry (1996a,b), we derive the asymptotic normal distribution of the proposed average derivative estimator. Monte Carlo experiments show that the proposed estimator compares well with the existing estimators.

Estimation of the Birnbaum-Saunders regression model with current status data

Estimation for the Birnbaum-Saunders (BS) regression model has been discussed by various authors when data are either complete or subject to Type-I or random censoring. But, this problem has not been considered for the case of interval censoring. In this article, we discuss the estimation of a regression model with current status data when the failure times follow the BS distribution. We estimate the parameters by the method of maximum likelihood, and derive the asymptotic distribution of these estimators. The performance of these estimators is then assessed through Monte Carlo simulations for different sample sizes under two types of monitoring. Finally, an analysis of real data is used to illustrate the proposed method.

Factors affecting flower infection and disease severity of lowbush blueberry by Botrytis cinerea

Infection of lowbush blueberry (Vaccinium angustifolium Ait. and V. myrtilloides Michx.) flowers by Botrytis cinerea Pers.:Fr. and subsequent disease was determined for differing stages of flower bud development, temperature, and duration of postinoculation wet periods. Conidium germination of B. cinerea at 20°C was poor on immature flower buds when the corolla was beginning to protrude from the calyx (floral stage F4) and when the corolla was half developed (F5), but better when flowers were at the pink bud prebloom stage (F6) or fully open (F7). Infection incidence followed a similar trend; there was none on the F4 flowers, slightly more on F5 flowers, and an increase to over 45 and 98% on F6 and F7 flowers, respectively. Immature green berries were resistant to infection, but nonpollinated ovaries from which corollas had abscised were susceptible to infection. At 4, 8, 12, 16, and 20°C, low levels of infection occurred on F7 flowers after 24, 13, 10, 8, or 6 h of postinoculation wetness, respectively. The infection incidence increased progressively with temperature and wetness duration. Lesions spread from the corolla to the peduncle of flower clusters over a 96-h wet period at 16, 20, and 24°C, but the disease failed to spread beyond the corolla at 4, 8, and 12°C. When flower clusters were inoculated with 105 or 106 conidia/mL at 20°C and incubated over a 96-h wet period, lesions spread from the corolla to the peduncle, but when the inoculum concentration was 103 or 104 conidia/mL, they did not extend beyond the corolla. These results could help to reduce fungicide applications when disease management programs are based on monitored weather conditions.

Estimation of parameters for a Birnbaum–Saunders regression model with censored data

Little work has been published on the analysis of censored data for the Birnbaum–Saunders distribution (BISA). In this article, we implement the EM algorithm to fit a regression model with censored data when the failure times follow the BISA. Three approaches to implement the E-Step of the EM algorithm are considered. In two of these implementations, the M-Step is attained by an iterative least-squares procedure. The algorithm is exemplified with a single explanatory variable in the model.

Empirical likelihood for heteroscedastic partially linear models

We make empirical-likelihood-based inference for the parameters in heteroscedastic partially linear models. Unlike the existing empirical likelihood procedures for heteroscedastic partially linear models, the proposed empirical likelihood is constructed using components of a semiparametric efficient score. We show that it retains the double robustness feature of the semiparametric efficient estimator for the parameters and shares the desirable properties of the empirical likelihood for linear models. Compared with the normal approximation method and the existing empirical likelihood methods, the empirical likelihood method based on the semiparametric efficient score is more attractive not only theoretically but empirically. Simulation studies demonstrate that the proposed empirical likelihood provides smaller confidence regions than that based on semiparametric inefficient estimating equations subject to the same coverage probabilities. Hence, the proposed empirical likelihood is preferred to the normal approximation method as well as the empirical likelihood method based on semiparametric inefficient estimating equations, and it should be useful in practice.