Lidia Rejtö

Resolving environmental drivers of microbial community structure in Antarctic soils

Abstract Antarctic soils are extremely cold, dry, and oligotrophic, yet harbour surprisingly high bacterial diversity. The severity of environmental conditions has constrained the development of multi-trophic communities, and species richness and distribution is thought to be driven primarily by abiotic factors. Sites in northern and southern Victoria Land were sampled for bacterial community structure and soil physicochemical properties in conjunction with the US and New Zealand Latitudinal Gradient Project. Bacterial community structure was determined using a high-resolution molecular fingerprinting method for 80 soil samples from Taylor Valley and Cape Hallett sites which are separated by five degrees of latitude and have distinct soil chemistry. Taylor Valley is part of the McMurdo Dry Valleys, while Cape Hallett is the site of a penguin rookery and contains ornithogenic soils. The influence of soil moisture, pH, conductivity, ammonia, nitrate, total nitrogen and organic carbon on community structure was revealed using Spearman rank correlation, Mantel test, and principal components analysis. High spatial variability was detected in bacterial communities and community structure was correlated with soil moisture and pH. Both unique and shared bacterial community members were detected at Taylor Valley and Cape Hallett despite the considerable distance between the sites.

Remarks on projection pursuit regression and density estimation

The paper deals with a generalization of the projection pursuit regression algorithm (see P.Huber [4]) in Hilbert space. Theorem 2.1 states the strong convergence of the generalized algorithm. This result then applied to certain spaces in order to define a new density estimator and to obtain results on density approximation and estimation

Spinal Accessory Nerve Monitoring in Selective and Modified Neck Dissection

Objectives: To determine whether a threshold increase in current is required to stimulate the spinal accessory nerve (SAN), comparing current on initial identification of the SAN and after completion of the dissection and before closure for selective neck dissection (SND), zones 1, 2, and 3, and modified radical neck dissection (MRND), zones 1, 2, 3, 4, and 5, and compare clinical outcome measures for “shoulder syndrome” for SND and MRND.

Hormonal regulation of IGFBP-2 proteolysis is attenuated with progression to androgen insensitivity in the LNCaP progression model.

The identification of molecular determinants involved in the promotion of metastasis and development of androgen insensitive prostate cancer (AI‐PCa) is necessary to discriminate aggressive from indolent disease and to identify therapeutic targets for advanced disease. Overexpression of one particular member of the insulin like growth factor (IGF) axis, IGFBP‐2, is implicated in the development of AI‐PCa and other cancers. Using the LNCaP human PCa progression model, we show that the AI and metastatic prostate cancer cell line C4‐2B4 expresses greater amounts of secreted IGFBP‐2 than the androgen sensitive (AS), non‐metastatic LNCaP progenitor cell line. Further, the ability of androgens to decrease extracellular IGFBP‐2 levels is attenuated in the AI and metastatic C4‐2 cell line. The ability of androgen to negatively regulate extracellular IGFBP‐2 levels was blocked by Casodex in a dose‐dependent manner. The mechanism underlying the androgen‐induced downregulation of secreted IGFBP‐2 appears to involve extracellular proteolysis, resulting in the production of IGFBP‐2 fragments lacking the ability to bind IGF‐I and IGF‐II. As C4‐2 cells have an attenuated ability to proteolyze IGFBP‐2 in response to androgen and C4‐2B4 cells express greater amounts of IGFBP‐2, our data implies that the diminished regulation of IGFBP‐2 and loss of associated proteolytic fragments play a role in the increased metastatic behavior of these cells in vivo. Furthermore, our results suggest that either increased levels of intact IGFBP‐2 or decreased levels of IGFBP‐2 proteolytic fragments could serve as a biomarker to monitor for progression to AI‐PCa. J. Cell. Physiol. 213: 261–268, 2007.

Tympanomastoid suture and digastric muscle in cadaver and live parotidectomy.

Objectives/Hypothesis: To prove that the tympanomastoid suture (TMS) is a significantly closer and less variable anatomic landmark to the facial nerve than the posterior‐superior margin of the posterior belly of the digastric muscle (PBD) in parotid surgery.

A new methodology for aggregating tables: Summarizing journal quality data

Abstract Often successive studies are conducted to rank items across time or across different raters. For instance, different consumers may be asked to rank products, or banks may be ranked at different points of time based on their lending practices. In such cases, a simple model would suggest arriving at a summary set of rankings by averaging across the sets. However, when the rank of an item is missing in some of the sets, a simple mean can produce a biased result. This is because the absence of an item in a particular set may be important information that is being ignored. MacMillan conducted a series of studies to identify a forum for publishing business policy research, the most recent of which appeared in this journal. The design of the study involved two stages of selection: first, the journals were to be voted into a set, and second, they were to be ranked by a panel of scholars. This procedure resulted in some of the journals not appearing in every study. Thus, taking a simple average across the studies would result in misleading information, because the absence of a journal in a particular study is information that is important (because the panel chose not to vote it into consideration) but lost in averaging. One of the objectives of the MacMillan studies was to provide scholars with information about the importance of the journal as a publication outlet. Thus, it is important to be able to arrive at a summary set of rankings to provide cumulative information. To achieve this, a left-censored model was developed. Assuming that the ranks follow a normal distribution, with unknown mean and the same variance, maximum likelihood estimates of the means were calculated.. The summary set of ranks were then calculated using these estimates. The summary ranks were compared with those arrived at from an independent estimate of journal quality and found to have validity. Our model helps enhance the value of the MacMillan studies by providing cumulative information on the journals and facilitating their comparison with other studies. We see the applicability of the model in other areas too. Known by the generic term of league tables, such sets of data are generated in marketing research, educational studies, etc. Thus, the model is an important contribution to the tool kit of empirical research.

Testing Goodness of Fit of Random Graph Models

Random graphs are matrices with independent 0–1 elements with probabilities determined by a small number of parameters. One of the oldest models is the Rasch model where the odds are ratios of positive numbers scaling the rows and columns. Later Persi Diaconis with his coworkers rediscovered the model for symmetric matrices and called the model beta. Here we give goodness-of-fit tests for the model and extend the model to a version of the block model introduced by Holland, Laskey and Leinhard.

Relative deficiency op kernel type estimators of quantiles based on right censored data

The problem of estimating the smooth quantile function Q(·) at a fixed point p, 0 < p < 1, is treated under a nonparametric smoothness condition on Q. The asymptotic relative deficiency of product-limit quantile with respect to kernel type estimators of the quantile is evaluated. The comparision is based on the mean square errors of the estimators. It is shown that the relative deficiency tends to infinity as the sample size n tends to infinity.

The Effect of Holidays on Hotel Daily Revenue

The holiday effect phenomenon has been studied in industry sectors such as securities, retail, and so on. Literature is devoid of a purposeful study specific to the hospitality industry that evaluates the economic impact of holidays on the hotel industry. The purpose of this study was to examine the impact of holidays on hotel daily revenue. Using daily occupancy data of the U.S. lodging industry between January 2000 and February 2004, the study found a significant holiday effect prevalent in the hotel industry. Findings indicate that individual effects of holidays on hotel daily revenue differ significantly from one to another. In addition, some holidays have differential impacts depending on the day of the week on which they fall. Findings can be used to develop more targeted strategies by the lodging industry as a whole.

Generalized Projection Pursuit Regression and Density Approximation

The paper deals with a generalization of the projection pursuit regression algorithm (see P.Huber [3]) in Hilbert space. The strong convergence of the generalized algorithm is first proved and this result then applied to certain spaces in order to define a new density estimator and to obtain results on density approximation.