SPIDER: Probing the Early Universe with a Suborbital Polarimeter

We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a divergence-free polarization pattern ("B-modes") in the Cosmic Microwave Background (CMB). In the inflationary scenario, the amplitude of this signal is proportional to that of the primordial scalar perturbations through the tensor-to-scalar ratio r. We show that the expected level of systematic error in the SPIDER instrument is significantly below the amplitude of an interesting cosmological signal with r=0.03. We present a scanning strategy that enables us to minimize uncertainty in the reconstruction of the Stokes parameters used to characterize the CMB, while accessing a relatively wide range of angular scales. Evaluating the amplitude of the polarized Galactic emission in the SPIDER field, we conclude that the polarized emission from interstellar dust is as bright or brighter than the cosmological signal at all SPIDER frequencies (90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the "Southern Hole." We show that two ~20-day flights of the SPIDER instrument can constrain the amplitude of the B-mode signal to r<0.03 (99% CL) even when foreground contamination is taken into account. In the absence of foregrounds, the same limit can be reached after one 20-day flight.Comment: 29 pages, 8 figures, 4 tables; v2: matches published version, flight schedule updated, two typos fixed in Table 2, references and minor clarifications added, results unchange

Characterization of organotypic keratinocyte cultures on de-epithelialized bovine tongue mucosa

Organotypic cultures have been used to study epithelial cell behavior for many years. The aim of this study was to develop an organotypic culture method that better mimics the three-dimensional morphology of interdigitating rete ridges and connective tissue papillae and that also conserves the basement membrane zone (BMZ). Bovine tongue mucosa connective tissue, separated from epithelium after 1M NaCl incubation, was used as o rganotypic culture substratum for different human keratinocyte cell lines. Organotypic cultures were characterized by electron and immunofluorescence microscopy for expression of integrin subunits and extracellular matrix components. While spontaneously immortalized mucosal keratinocytes produced highly irregular stratified organotypic cultures, the normal human epidermal keratinocytes (NHEK) demonstrated culture morphology that resembled in vivo epidermis. However, in this model, the histomorphology, expression of differentiation markers involucrin, keratin 10 and 14, and integrins varied significantly between the cell lines. Some cultures appeared to have an extended survival since they were maintained up to 40 days without histological signs of degeneration. The ultrastructure of the BMZ including hemidesmosomes was similar to the normal dermo-epidermal junction. Extracellular matrix molecules, including tenascin, laminin-1 and -5, were expressed in the cultures demonstrating their secretion solely by keratinocytes. Distribution and expression of integrins in NHEK cultures was similar to that seen in vivo skin with the exception of additional expression of a5ß1 and avß6 integrins. Organotypic NHEK cultures show similarities to normal stratified epithelium and are potentially useful for multiple applications for studies on epithelial cell behavior in vitro

Night conditions affect morning incubation behaviour differently across a latitudinal gradient

Intermittently incubating birds alternate between sessions of egg warming and recesses for foraging during the day, but stay on the nest continuously at night. Hence, energy costs of nocturnal incubation (which increase during longer and colder nights) cannot be replenished until the next day. Night conditions might therefore be expected to affect morning incubation behaviour the day after. We tested this prediction by exploring latitudinal and seasonal trends in characteristics of the first recess in Eastern Bluebirds Sialia sialis over a 1400‐km latitudinal gradient in the continental USA. The time from civil dawn to leaving the nest (latency) increased with latitude early in the breeding season but decreased with latitude late in the season. Birds breeding at higher latitudes also took longer first recesses throughout the season, which led to a larger drop in nest temperature. At the local scale, birds rose earlier after longer nights if the night was also cold, but night length did not predict latency following warm nights. The first recess was longer if the night was warmer, probably because birds could replenish reserves at lower risk of low egg temperature. Our study shows that characteristics of the night led to behavioural changes in features of early morning incubation that were evident at both continental and local scales. These responses also affected nest temperature. Hence, night conditions carry over to incubation behaviour the following morning, which in turn may impose thermal constraints on embryonic development

Balance measures for determining optimal caliper width in propensity score matching: A simulation study

Background: When estimating the effects of exposure in observational data, propensity score (PS) methods can be used to control for confounding. When PS matching is used, often a pre-specified caliper width is applied. A crucial part of this matching approach is assessment of how close the co-variate distributions are in the two treatment groups, i.e. balance. The choice of the caliper may influence the balance of covariates between treatment groups and, therefore, the bias and precision of the PS adjusted effect estimate. Although several balance measures have been described as tools for PS model selection, their role in choosing optimal caliper widths is not well studied. Objectives: To explore the usefulness of balance measures in selecting the optimal caliper width for propensity score matching. Methods: We conducted Monte Carlo simulations to assess the usefulness of balance measures (standardized difference) to select optimal caliper width and PS models that yielded the least biased estimates. In different simulations with binary covariates, exposure and outcome status, different sample sizes (n = 500, 1,000, 3,000) and strength of exposure-outcome association (OR = 1, 2) were considered. Caliper widths were varied between 0.05 and 0.6 (steps of 0.05) of the standard deviation of the PS. The balance of covariates between PS matched groups was assessed using the standardized difference (SDif) for each PS model-caliper width combination. PS model with the lowest value of SDif (i.e. most optimal balance) was selected and treatment effects were estimated using conditional logistic regression. Results: The PS models selected using various caliper widths were closely related and these models often included interaction and squared terms. When using balance measures to select a certain PS model, the choice for a certain PS model seems to have much more impact on bias and precision of exposure effects than the caliper width used. Conclusions: Balance measures are useful tools for selecting the optimal PS model and the PS model selected has more impact on bias and precision than the caliper width that is used in PS matching

Balance measures for determining optimal caliper width in propensity score matching: A simulation study

Background: When estimating the effects of exposure in observational data, propensity score (PS) methods can be used to control for confounding. When PS matching is used, often a pre-specified caliper width is applied. A crucial part of this matching approach is assessment of how close the co-variate distributions are in the two treatment groups, i.e. balance. The choice of the caliper may influence the balance of covariates between treatment groups and, therefore, the bias and precision of the PS adjusted effect estimate. Although several balance measures have been described as tools for PS model selection, their role in choosing optimal caliper widths is not well studied. Objectives: To explore the usefulness of balance measures in selecting the optimal caliper width for propensity score matching. Methods: We conducted Monte Carlo simulations to assess the usefulness of balance measures (standardized difference) to select optimal caliper width and PS models that yielded the least biased estimates. In different simulations with binary covariates, exposure and outcome status, different sample sizes (n = 500, 1,000, 3,000) and strength of exposure-outcome association (OR = 1, 2) were considered. Caliper widths were varied between 0.05 and 0.6 (steps of 0.05) of the standard deviation of the PS. The balance of covariates between PS matched groups was assessed using the standardized difference (SDif) for each PS model-caliper width combination. PS model with the lowest value of SDif (i.e. most optimal balance) was selected and treatment effects were estimated using conditional logistic regression. Results: The PS models selected using various caliper widths were closely related and these models often included interaction and squared terms. When using balance measures to select a certain PS model, the choice for a certain PS model seems to have much more impact on bias and precision of exposure effects than the caliper width used. Conclusions: Balance measures are useful tools for selecting the optimal PS model and the PS model selected has more impact on bias and precision than the caliper width that is used in PS matching

Assessment of balance in propensity score analysis in the medical literature: A systematic review

Background: Assessing balance on co-variate distributions between treatment groups with a given propensity score (PS) is a crucial step in PS analysis. Several methodological papers comparing different balance measures have been published in the last decade. However, the current practice on measuring and reporting of balance in PS analysis is not well documented. Objectives: To investigate the current practice of PS analysis with emphasis on assessment of balance of confounders. Methods: A PubMed search was performed to identify studies using propensity score methods published December 2011-May 2012. We extracted information on the applied PS method, whether and how balance on confounders was checked, if PS matching was applied (including the algorithm), and information on the initial sample size of the number of matched pairs. Results: In total, 261 studies that employed PS methods were found. Balance of confounders between treatment groups was checked and reported in 149 (57.1%) of the articles. p-Values from hypothesis testing was the most commonly used statistical tool to report balance (110 studies, 73.8%). The standardized difference and graphical displays of balance were used in 42 (28.2%) and nine (6%) articles, respectively. The most commonly used approach to control for confounding using PS was matching on the PS (67%), followed by co-variate adjustment for the PS (22.2%), PS stratification (14.6%) and inverse probability weighting (7.3%). Balance was most often checked in articles using PS matching and inverse probability weighting: 68.6% and 73.6% respectively. Conclusions: When using PS methods, assessment of balance on confounders between treatment groups is not often conducted or reported. Appropriate methods such as standardized difference should be used to quantify and report balance