Spatiotemporal variation in postlarval recruitment of the Caribbean spiny lobster in the central Bahamas: lunar and seasonal periodicity, spatial coherence, and wind forcing

A large-scale recruitment study of the Caribbean spiny lobster Panulirus argus in the central Bahamas identified (1) strong spatial coherence in settlement to inshore nursery habitats, (2) temporal variability due in part to stochastic wind forcing, and (3) lunar and seasonal periodicity in settlement. First, we quantified lunar variation in settlement on standardized artificial substrates to determine whether or not intra- and inter-annual variability in recruitment could be adequately described by measuring influx of postlarvae during the first quarter of each new moon, as suggested by previous studies. Next, we compared settlement data obtained from artificial surface substrates to concentrations of postlarvae in the water column and benthic settlement. Long-term (6 yr) spatiotemporal variation in postlarval settlement was then quantified at 8 sites spanning a longitudinal and onshore distance of 43 km and 11 km, respectively. Lastly, we examined the relationship between postlarval settlement and environmental variables with time-series analyses. The key findings were that: (1) significant lunar (first quarter of lunar phase) and seasonal (fall peak) periodicities in settlement were consistent across sites; (2) postlarval settlement varied more across sites (similar to 600 %) than between years at a single site (similar to 50%), and inter-site differences were consistent across time (i.e, some sites always had higher settlement than others); (3) settlement was correlated with along-shore winds blowing towards the southeast, but not with cross-shelf winds or water temperature; (4) floating, \u27Witham-type\u27 artificial settlement substrates yielded an accurate index of postlarval concentration and flux past a given point: and (5) floating substrates were a relatively poor indicator of benthic settlement, though the relationship between surface and benthic settlement may depend upon benthic habitat availability and postlarval supply. These results indicate that artificial settlement substrates provide a reliable index of postlarval supply to inshore nursery habitats, and that a combination of stochastic and deterministic forces influence recruitment over various scales of time and space

Comparison of techniques for handling missing covariate data within prognostic modelling studies: a simulation study

Background: There is no consensus on the most appropriate approach to handle missing covariate data within prognostic modelling studies. Therefore a simulation study was performed to assess the effects of different missing data techniques on the performance of a prognostic model. Methods: Datasets were generated to resemble the skewed distributions seen in a motivating breast cancer example. Multivariate missing data were imposed on four covariates using four different mechanisms; missing completely at random (MCAR), missing at random (MAR), missing not at random (MNAR) and a combination of all three mechanisms. Five amounts of incomplete cases from 5% to 75% were considered. Complete case analysis (CC), single imputation (SI) and five multiple imputation (MI) techniques available within the R statistical software were investigated: a) data augmentation (DA) approach assuming a multivariate normal distribution, b) DA assuming a general location model, c) regression switching imputation, d) regression switching with predictive mean matching (MICE-PMM) and e) flexible additive imputation models. A Cox proportional hazards model was fitted and appropriate estimates for the regression coefficients and model performance measures were obtained. Results: Performing a CC analysis produced unbiased regression estimates, but inflated standard errors, which affected the significance of the covariates in the model with 25% or more missingness. Using SI, underestimated the variability; resulting in poor coverage even with 10% missingness. Of the MI approaches, applying MICE-PMM produced, in general, the least biased estimates and better coverage for the incomplete covariates and better model performance for all mechanisms. However, this MI approach still produced biased regression coefficient estimates for the incomplete skewed continuous covariates when 50% or more cases had missing data imposed with a MCAR, MAR or combined mechanism. When the missingness depended on the incomplete covariates, i.e. MNAR, estimates were biased with more than 10% incomplete cases for all MI approaches. Conclusion: The results from this simulation study suggest that performing MICE-PMM may be the preferred MI approach provided that less than 50% of the cases have missing data and the missing data are not MNAR

Combining estimates of interest in prognostic modelling studies after multiple imputation: current practice and guidelines

Background: Multiple imputation (MI) provides an effective approach to handle missing covariate data within prognostic modelling studies, as it can properly account for the missing data uncertainty. The multiply imputed datasets are each analysed using standard prognostic modelling techniques to obtain the estimates of interest. The estimates from each imputed dataset are then combined into one overall estimate and variance, incorporating both the within and between imputation variability. Rubin's rules for combining these multiply imputed estimates are based on asymptotic theory. The resulting combined estimates may be more accurate if the posterior distribution of the population parameter of interest is better approximated by the normal distribution. However, the normality assumption may not be appropriate for all the parameters of interest when analysing prognostic modelling studies, such as predicted survival probabilities and model performance measures. Methods: Guidelines for combining the estimates of interest when analysing prognostic modelling studies are provided. A literature review is performed to identify current practice for combining such estimates in prognostic modelling studies. Results: Methods for combining all reported estimates after MI were not well reported in the current literature. Rubin's rules without applying any transformations were the standard approach used, when any method was stated. Conclusion: The proposed simple guidelines for combining estimates after MI may lead to a wider and more appropriate use of MI in future prognostic modelling studies

The Compelling Case for Indentation as a Functional Exploratory and Characterization Tool

The utility of indentation testing for characterizing a wide range of mechanical properties of brittle materials is highlighted in light of recent articles questioning its validity, specifically in relation to the measurement of toughness. Contrary to assertion by some critics, indentation fracture theory is fundamentally founded in Griffith–Irwin fracture mechanics, based on model crack systems evolving within inhomogeneous but well-documented elastic and elastic–plastic contact stress fields. Notwithstanding some numerical uncertainty in associated stress intensity factor relations, the technique remains an unrivalled quick, convenient and economical means for comparative, site-specific toughness evaluation. Most importantly, indentation patterns are unique fingerprints of mechanical behavior and thereby afford a powerful functional tool for exploring the richness of material diversity. At the same time, it is cautioned that unconditional usage without due attention to the conformation of the indentation patterns can lead to overstated toughness values. Limitations of an alternative, more engineering approach to fracture evaluation, that of propagating a pre-crack through a 'standard' machined specimen, are also outlined. Misconceptions in the critical literature concerning the fundamental nature of crack equilibrium and stability within contact and other inhomogeneous stress fields are discussed.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1111/jace.1372

One-stage laparoscopic-assisted resection of gastrojejunocolic fistula after gastrojejunostomy for duodenal ulcer: a case report

<p>Abstract</p> <p>Introduction</p> <p>Gastrojejunocolic fistula is a rare condition after gastrojejunostomy. It was thought to be a late complication related to stomal ulcers as a result of inadequate gastrectomy or incomplete vagotomy. We report a case of gastrojejunocolic fistula after gastrojejunostomy for peptic ulcer treated with one-stage laparoscopic resection.</p> <p>Case presentation</p> <p>A 41-year-old Japanese man complained of diarrhea for 10 months, as well as severe weight loss and weakness. After admission, we immediately started intravenous hyperalimentation. On performing colonoscopy and barium swallow, gastrojejunocolic fistula was observed close to the gastrojejunostomy site leading to the transverse colon. After our patient's nutritional status had improved, one-stage surgical intervention was performed laparoscopically. After the operation, our patient recovered uneventfully and his body weight increased by 5 kg within three months.</p> <p>Conclusions</p> <p>Modern management of gastrojejunocolic fistula is a one-stage resection because of the possibility of early recovery from malnutrition using parenteral nutritional methods. Today, laparoscopic one-stage en bloc resection may be feasible for patients with gastrojejunocolic fistula due to the development of laparoscopic instruments and procedures. We describe the first case of gastrojejunocolic fistula treated laparoscopically by one-stage resection and review the literature.</p

Stable Heterogeneity for the Production of Diffusible Factors in Cell Populations

The production of diffusible molecules that promote survival and growth is common in bacterial and eukaryotic cell populations, and can be considered a form of cooperation between cells. While evolutionary game theory shows that producers and non-producers can coexist in well-mixed populations, there is no consensus on the possibility of a stable polymorphism in spatially structured populations where the effect of the diffusible molecule extends beyond one-step neighbours. I study the dynamics of biological public goods using an evolutionary game on a lattice, taking into account two assumptions that have not been considered simultaneously in existing models: that the benefit of the diffusible molecule is a non-linear function of its concentration, and that the molecule diffuses according to a decreasing gradient. Stable coexistence of producers and non-producers is observed when the benefit of the molecule is a sigmoid function of its concentration, while strictly diminishing returns lead to coexistence only for very specific parameters and linear benefits never lead to coexistence. The shape of the diffusion gradient is largely irrelevant and can be approximated by a step function. Since the effect of a biological molecule is generally a sigmoid function of its concentration (as described by the Hill equation), linear benefits or strictly diminishing returns are not an appropriate approximations for the study of biological public goods. A stable polymorphism of producers and non-producers is in line with the predictions of evolutionary game theory and likely to be common in cell populations

Comparison of methods for handling missing data on immunohistochemical markers in survival analysis of breast cancer

Background:Tissue micro-arrays (TMAs) are increasingly used to generate data of the molecular phenotype of tumours in clinical epidemiology studies, such as studies of disease prognosis. However, TMA data are particularly prone to missingness. A variety of methods to deal with missing data are available. However, the validity of the various approaches is dependent on the structure of the missing data and there are few empirical studies dealing with missing data from molecular pathology. The purpose of this study was to investigate the results of four commonly used approaches to handling missing data from a large, multi-centre study of the molecular pathological determinants of prognosis in breast cancer.Patients and Methods:We pooled data from over 11 000 cases of invasive breast cancer from five studies that collected information on seven prognostic indicators together with survival time data. We compared the results of a multi-variate Cox regression using four approaches to handling missing data-complete case analysis (CCA), mean substitution (MS) and multiple imputation without inclusion of the outcome (MI) and multiple imputation with inclusion of the outcome (MI). We also performed an analysis in which missing data were simulated under different assumptions and the results of the four methods were compared.Results:Over half the cases had missing data on at least one of the seven variables and 11 percent had missing data on 4 or more. The multi-variate hazard ratio estimates based on multiple imputation models were very similar to those derived after using MS, with similar standard errors. Hazard ratio estimates based on the CCA were only slightly different, but the estimates were less precise as the standard errors were large. However, in data simulated to be missing completely at random (MCAR) or missing at random (MAR), estimates for MI were least biased and most accurate, whereas estimates for CCA were most biased and least accurate.Conclusion:In this study, empirical results from analyses using CCA, MS, MI and MI were similar, although results from CCA were less precise. The results from simulations suggest that in general MI is likely to be the best. Given the ease of implementing MI in standard statistical software, the results of MI and CCA should be compared in any multi-variate analysis where missing data are a problem. © 2011 Cancer Research UK. All rights reserved

Safety of selective internal radiation therapy (SIRT) with yttrium-90 microspheres combined with systemic anticancer agents: expert consensus

Selective internal radiation therapy (SIRT) with microspheres labelled with the β-emitter yttrium-90 (Y-90) enables targeted delivery of radiation to hepatic tumors. SIRT is primarily used to treat inoperable primary or metastatic liver tumors. Eligible patients have usually been exposed to a variety of systemic anticancer therapies, including cytotoxic agents, targeted biologics, immunotherapy and peptide receptor radionuclide therapy (PRRT). All these treatments have potential interactions with SIRT; however, robust evidence on the safety of these potential combinations is lacking. This paper provides current clinical experiences and expert consensus guidelines for the use of SIRT in combination with the anticancer treatment agents likely to be encountered in clinical practice. It was agreed by the expert panel that precautions need to be taken with certain drugs, but that, in general, systemic therapies do not necessarily have to be stopped to perform SIRT. The authors recommend stopping vascular endothelial growth factor inhibitors 4-6 weeks before SIRT, and restart after the patient has recovered from the procedure. It may also be prudent to stop potent radiosensitizers such as gemcitabine therapy 4 weeks before SIRT, and restart treatment at least 2‒4 weeks later. Data from phase III studies combining SIRT with fluorouracil (5FU) or folinic acid/5FU/oxaliplatin (FOLFOX) suggest that hematological toxicity is more common from the combination than it is from chemotherapy without SIRT. There is no evidence to suggest that chemotherapy increases SIRT-specific gastro-intestinal or liver toxicities

Evaluation of the Interfacial Sliding Stress of Ceramic Matrix Composites Under Tensile Loading

The fundamental strain mechanisms of Ceramic Matrix Composites are the matrix microcracking that induces a loss of stiffness and the fiber-matrix debonding that leads to interfacial frictional sliding [1]. The interfacial sliding stress is thus a key parameter in the global behavior. The use of an experimental device coupling an ultrasonic immersion tank to a tensile machine and an extensometer allows to detect the anisotropy of the damage mechanisms of a material as well as to perform a strain partition under load because it makes it possible to identify the elastic tensor variation. The inelastic strain identified this way comes from the transverse cracks opening due to both the fiber/matrix elasticity mismatch and relative sliding at the interface. It is then possible to assess the value of the interfacial sliding stress with a micromechanical model derived from the analytical expressions of the elastic properties of a fibrous composite containing cracks and a shear-lag analysis. This can be done because the experimental variation of the compliances gives access to the constitutive law of the transverse crack densities and allows to estimate the debonding length.</p

Gastrojejunocolic fistula after gastrojejunostomy: a case series

<p>Abstract</p> <p>Introduction</p> <p>Gastrojejunocolic (GJC) fistulae represent a significant post-surgical cause of morbidity and mortality. GJC fistulae represent rare post-surgical complications, and most are associated with gastric surgery. In the past, this complication has been under-recognized because a fistula may form years after surgery.</p> <p>Case presentation</p> <p>We describe two cases of gastrojejunocolic fistula in men aged 67 and 60 who both initially presented with watery diarrhea and weight loss. Upper GI studies with small bowel follow-through or barium contrast enema studies allowed a conclusive diagnosis to be made. Both patients underwent one-stage en bloc resection, and their postoperative course was uneventful.</p> <p>Conclusion</p> <p>With surgery, this condition is entirely correctable. Pre-operative nutritional status should be evaluated in patients undergoing corrective surgery, and total parenteral nutrition plays a major role in the provision of bowel rest to allow recovery in malnourished patients.</p