Market structure and the value of overselling under stochastic demands

In the operations management literature, traditional revenue management focused on pricing and capacity allocation strategies in a two-period model with stochastic demand. Inspired by travel and lodging industries, we examine a two-period model in which each seller may also adopt the overselling strategy to customers whose valuations are differentiated by timing of arrivals. Widely seen as a popular hedge against consumers’ skipping reservations, we extend the stylized approaches of Biyalogorsky, Carmon, Fruchter, and Gerstner (1999) and Lim (2009) to understand the value of overselling under various market structures. We find that contrary to existing literature, the impact of period-two pricing competition from overselling spills over to period-one such that overselling may not always be a (weakly) dominant strategy once unlimited early demand ceases to hold in a duopoly regime. We provide some numerical studies on the existence of multiple equilibria at the capacity allocation level which actually lead to different selling strategies at the equilibrium despite identical market conditions and firm characteristics

Dual panel multiplex PCR assay for rapid detection of medically important fungi and resistant species of candida and aspergillus

Invasive fungal infections (IFIs) have risen dramatically in recent years among high risk immunocompromised patients. Rapid detection of fungal pathogens is crucial to timely and accurate antifungal therapy. Two multiplex polymerase chain reaction (PCR) assays were developed to detect major fungal species that cause invasive infections and identify resistant species. Genus specific primers for Candida, Aspergillus, Fusarium and species specific primers for Candida glabrata, Candida krusei and Aspergillus terreus which are known to be clinically resistant species, were designed from the internal transcribed spacer (ITS) regions of ribosomal ribonucleic acid (rRNA) gene complex. Both assays were performed simultaneously to promote rapid detection of fungal isolates based on distinct amplicon sizes. Inclusion of the universal fungal primers ITS 1 and ITS 4 in the genus specific assay produced a second amplicon for each isolate which served to confirm the detection of a fungal target. The limit of detection for the genus specific assay was 1 nanogram (ng) deoxyribonucleic acid (DNA) for Aspergillus fumigatus and Candida albicans, 0.1 ng DNA for Fusarium solani, while the species-specific assay detected 0.1 ng DNA of A. terreus and 10 picogram (pg) DNA of C. krusei and C. glabrata. The multiplex PCR assays, apart from universal detection of any fungal target, are able to detect clinically important fungi and differentiate resistant species rapidly and accurately, which can contribute to timely implementation of effective antifungal regime

Dual panel multiplex PCR assay for rapid detection of medically important fungi and resistant species of Candida and Aspergillus

Invasive fungal infections (IFIs) have risen dramatically in recent years among high risk immunocompromised patients. Rapid detection of fungal pathogens is crucial to timely and accurate antifungal therapy. Two multiplex polymerase chain reaction (PCR) assays were developed to detect major fungal species that cause invasive infections and identify resistant species. Genus specific primers for Candida, Aspergillus, Fusarium and species specific primers for Candida glabrata, Candida krusei and Aspergillus terreus which are known to be clinically resistant species, were designed from the internal transcribed spacer (ITS) regions of ribosomal ribonucleic acid (rRNA) gene complex. Both assays were performed simultaneously to promote rapid detection of fungal isolates based on distinct amplicon sizes. Inclusion of the universal fungal primers ITS 1 and ITS 4 in the genus specific assay produced a second amplicon for each isolate which served to confirm the detection of a fungal target. The limit of detection for the genus specific assay was 1 nanogram (ng) deoxyribonucleic acid (DNA) for Aspergillus fumigatus and Candida albicans, 0.1 ng DNA for Fusarium solani, while the species-specific assay detected 0.1 ng DNA of A. terreus and 10 picogram (pg) DNA of C. krusei and C. glabrata. The multiplex PCR assays, apart from universal detection of any fungal target, are able to detect clinically important fungi and differentiate resistant species rapidly and accurately, which can contribute to timely implementation of effective antifungal regime

A digital library for geography examination resources

We describe a Web-based application developed above a digital library of geographical resources for Singapore students preparing to take a national examination in geography. The application provides an interactive, non-sequential approach to learning that supplements textbooks.Published versio

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Non-invasive diagnostic tests for Helicobacter pylori infection

BACKGROUND: Helicobacter pylori (H pylori) infection has been implicated in a number of malignancies and non-malignant conditions including peptic ulcers, non-ulcer dyspepsia, recurrent peptic ulcer bleeding, unexplained iron deficiency anaemia, idiopathic thrombocytopaenia purpura, and colorectal adenomas. The confirmatory diagnosis of H pylori is by endoscopic biopsy, followed by histopathological examination using haemotoxylin and eosin (H & E) stain or special stains such as Giemsa stain and Warthin-Starry stain. Special stains are more accurate than H & E stain. There is significant uncertainty about the diagnostic accuracy of non-invasive tests for diagnosis of H pylori. OBJECTIVES: To compare the diagnostic accuracy of urea breath test, serology, and stool antigen test, used alone or in combination, for diagnosis of H pylori infection in symptomatic and asymptomatic people, so that eradication therapy for H pylori can be started. SEARCH METHODS: We searched MEDLINE, Embase, the Science Citation Index and the National Institute for Health Research Health Technology Assessment Database on 4 March 2016. We screened references in the included studies to identify additional studies. We also conducted citation searches of relevant studies, most recently on 4 December 2016. We did not restrict studies by language or publication status, or whether data were collected prospectively or retrospectively. SELECTION CRITERIA: We included diagnostic accuracy studies that evaluated at least one of the index tests (urea breath test using isotopes such as13C or14C, serology and stool antigen test) against the reference standard (histopathological examination using H & E stain, special stains or immunohistochemical stain) in people suspected of having H pylori infection. DATA COLLECTION AND ANALYSIS: Two review authors independently screened the references to identify relevant studies and independently extracted data. We assessed the methodological quality of studies using the QUADAS-2 tool. We performed meta-analysis by using the hierarchical summary receiver operating characteristic (HSROC) model to estimate and compare SROC curves. Where appropriate, we used bivariate or univariate logistic regression models to estimate summary sensitivities and specificities. MAIN RESULTS: We included 101 studies involving 11,003 participants, of which 5839 participants (53.1%) had H pylori infection. The prevalence of H pylori infection in the studies ranged from 15.2% to 94.7%, with a median prevalence of 53.7% (interquartile range 42.0% to 66.5%). Most of the studies (57%) included participants with dyspepsia and 53 studies excluded participants who recently had proton pump inhibitors or antibiotics.There was at least an unclear risk of bias or unclear applicability concern for each study.Of the 101 studies, 15 compared the accuracy of two index tests and two studies compared the accuracy of three index tests. Thirty-four studies (4242 participants) evaluated serology; 29 studies (2988 participants) evaluated stool antigen test; 34 studies (3139 participants) evaluated urea breath test-13C; 21 studies (1810 participants) evaluated urea breath test-14C; and two studies (127 participants) evaluated urea breath test but did not report the isotope used. The thresholds used to define test positivity and the staining techniques used for histopathological examination (reference standard) varied between studies. Due to sparse data for each threshold reported, it was not possible to identify the best threshold for each test.Using data from 99 studies in an indirect test comparison, there was statistical evidence of a difference in diagnostic accuracy between urea breath test-13C, urea breath test-14C, serology and stool antigen test (P = 0.024). The diagnostic odds ratios for urea breath test-13C, urea breath test-14C, serology, and stool antigen test were 153 (95% confidence interval (CI) 73.7 to 316), 105 (95% CI 74.0 to 150), 47.4 (95% CI 25.5 to 88.1) and 45.1 (95% CI 24.2 to 84.1). The sensitivity (95% CI) estimated at a fixed specificity of 0.90 (median from studies across the four tests), was 0.94 (95% CI 0.89 to 0.97) for urea breath test-13C, 0.92 (95% CI 0.89 to 0.94) for urea breath test-14C, 0.84 (95% CI 0.74 to 0.91) for serology, and 0.83 (95% CI 0.73 to 0.90) for stool antigen test. This implies that on average, given a specificity of 0.90 and prevalence of 53.7% (median specificity and prevalence in the studies), out of 1000 people tested for H pylori infection, there will be 46 false positives (people without H pylori infection who will be diagnosed as having H pylori infection). In this hypothetical cohort, urea breath test-13C, urea breath test-14C, serology, and stool antigen test will give 30 (95% CI 15 to 58), 42 (95% CI 30 to 58), 86 (95% CI 50 to 140), and 89 (95% CI 52 to 146) false negatives respectively (people with H pylori infection for whom the diagnosis of H pylori will be missed).Direct comparisons were based on few head-to-head studies. The ratios of diagnostic odds ratios (DORs) were 0.68 (95% CI 0.12 to 3.70; P = 0.56) for urea breath test-13C versus serology (seven studies), and 0.88 (95% CI 0.14 to 5.56; P = 0.84) for urea breath test-13C versus stool antigen test (seven studies). The 95% CIs of these estimates overlap with those of the ratios of DORs from the indirect comparison. Data were limited or unavailable for meta-analysis of other direct comparisons. AUTHORS' CONCLUSIONS: In people without a history of gastrectomy and those who have not recently had antibiotics or proton ,pump inhibitors, urea breath tests had high diagnostic accuracy while serology and stool antigen tests were less accurate for diagnosis of Helicobacter pylori infection.This is based on an indirect test comparison (with potential for bias due to confounding), as evidence from direct comparisons was limited or unavailable. The thresholds used for these tests were highly variable and we were unable to identify specific thresholds that might be useful in clinical practice.We need further comparative studies of high methodological quality to obtain more reliable evidence of relative accuracy between the tests. Such studies should be conducted prospectively in a representative spectrum of participants and clearly reported to ensure low risk of bias. Most importantly, studies should prespecify and clearly report thresholds used, and should avoid inappropriate exclusions

Gang affiliation, aggression, and violent offending in a sample of youth offenders

Gang affiliation, aggression, and violent offending were examined in case files of 390 youth offenders aged between 16 and 18 years. Results indicated that youth offenders who were gang members and those who were not gang members but exposed to friends in gangs had a significantly higher likelihood of violent offending compared with a reference group of youth offenders who had neither gang affiliation nor friends in gangs. Additionally, youth offenders who had friends in gangs but were themselves not gang members had a lower likelihood of violent offending than youth offenders who were gang members. Finally, results showed that a history of aggressive behavior was significantly associated with violent offending. Implications such as the need to address the influence of delinquent peers and need to address the management of anger and aggression in youths will be discussed. Also, findings point towards the need for prevention and early intervention work