Robust Estimation for Linear Panel Data Models

In different fields of applications including, but not limited to, behavioral, environmental, medical sciences and econometrics, the use of panel data regression models has become increasingly popular as a general framework for making meaningful statistical inferences. However, when the ordinary least squares (OLS) method is used to estimate the model parameters, presence of outliers may significantly alter the adequacy of such models by producing biased and inefficient estimates. In this work we propose a new, weighted likelihood based robust estimation procedure for linear panel data models with fixed and random effects. The finite sample performances of the proposed estimators have been illustrated through an extensive simulation study as well as with an application to blood pressure data set. Our thorough study demonstrates that the proposed estimators show significantly better performances over the traditional methods in the presence of outliers and produce competitive results to the OLS based estimates when no outliers are present in the data set

Mutational analysis of fructose-1,6-bisphosphate aldolase of Neisseria meningitidis serogroup B

Fructose-1,6-bisphosphate aldolase (FBA) is a classical cytoplasmic glycolytic enzyme which, despite lacking a predicted signal peptide, has been demonstrated to be expressed and transported to the surface of numerous Gram-positive bacteria and shown to interact with host molecules and perform non-glycolytic biological functions. Genome-based studies have also demonstrated that the glycolytic pathway appears to be non-functional in the meningococcus due to absence of phosphofructokinase, one of the important enzymes in this pathway. This study aimed to investigate whether the FBA, a so-called housekeeping enzyme, is required for maximal in vitro growth of N. meningitidis. An FBA knock-out mutant was created in N. meningitidis using an inverse polymerase chain reaction (PCR) and allelic exchange methodology. Phenotypic analysis of FBA-deficient mutant strains such as growth profiling experiments showed that the FBA-deficient mutant grew at the same rate (in broth culture and on solid media) as the wild-type strain, suggesting that FBA is not required for optimal growth of N. meningitidis under the in vitro conditions tested. No differences in either colony or bacterial cell morphology (using light microscopy) were observed. In summary, despite being a central enzyme in the glycolytic cycle, FBA is not required for in vitro growth of N. meningitidis.Key words: Neisseria meningitidis, aldolase, mutagenesis, growth kinetics, glycolytic cycle

Observations of total RONO2 over the boreal forest: NO x sinks and HNO3 sources

In contrast with the textbook view of remote chemistry where HNO 3 formation is the primary sink of nitrogen oxides, recent theoretical analyses show that formation of RONO2 (ΣANs) from isoprene and other terpene precursors is the primary net chemical loss of nitrogen oxides over the remote continents where the concentration of nitrogen oxides is low. This then increases the prominence of questions concerning the chemical lifetime and ultimate fate of ΣANs. We present observations of nitrogen oxides and organic molecules collected over the Canadian boreal forest during the summer which show that ΣANs account for ∼20% of total oxidized nitrogen and that their instantaneous production rate is larger than that of HNO3. This confirms the primary role of reactions producing ΣANs as a control over the lifetime of NOx (NOx =NO+NO2) in remote, continental environments. However, HNO 3 is generally present in larger concentrations than ΣANs indicating that the atmospheric lifetime of ΣANs is shorter than the HNO3 lifetime. We in-vestigate a range of proposed loss mechanisms that would explain the inferred lifetime of ΣANs finding that in combination with deposition, two processes are consistent with the observations: (1) rapid ozonolysis of isoprene nitrates where at least ∼40% of the ozonolysis producs t ts release NOx from the carbon backbone and/or (2) hydrolysis of particulate organic nitrates with HNO3 as a product. Implications of these ideas for our understanding of NOx and NOy budget in remote and rural locations are discussed. © Author(s) 2013

The role of glyceraldehyde 3-phosphate dehydrogenase (GapA-1) in Neisseria meningitidis adherence to human cells

BackgroundGlyceraldehyde 3-phosphate dehydrogenases (GAPDHs) are cytoplasmic glycolytic enzymes, which although lacking identifiable secretion signals, have also been found localized to the surface of several bacteria (and some eukaryotic organisms); where in some cases they have been shown to contribute to the colonization and invasion of host tissues. Neisseria meningitidis is an obligate human nasopharyngeal commensal which can cause life-threatening infections including septicaemia and meningitis. N. meningitidis has two genes, gapA-1 and gapA-2, encoding GAPDH enzymes. GapA-1 has previously been shown to be up-regulated on bacterial contact with host epithelial cells and is accessible to antibodies on the surface of capsule-permeabilized meningococcal cells. The aims of this study were: 1) to determine whether GapA-1 was expressed across different strains of N. meningitidis; 2) to determine whether GapA-1 surface accessibility to antibodies was dependant on the presence of capsule; 3) to determine whether GapA-1 can influence the interaction of meningococci and host cells, particularly in the key stages of adhesion and invasion.ResultsIn this study, expression of GapA-1 was shown to be well conserved across diverse isolates of Neisseria species. Flow cytometry confirmed that GapA-1 could be detected on the cell surface, but only in a siaD-knockout (capsule-deficient) background, suggesting that GapA-1 is inaccessible to antibody in in vitro-grown encapsulated meningococci. The role of GapA-1 in meningococcal pathogenesis was addressed by mutational analysis and functional complementation. Loss of GapA-1 did not affect the growth of the bacterium in vitro. However, a GapA-1 deficient mutant showed a significant reduction in adhesion to human epithelial and endothelial cells compared to the wild-type and complemented mutant. A similar reduction in adhesion levels was also apparent between a siaD-deficient meningococcal strain and an isogenic siaD gapA-1 double mutant.ConclusionsOur data demonstrates that meningococcal GapA-1 is a constitutively-expressed, highly-conserved surface-exposed protein which is antibody-accessible only in the absence of capsule. Mutation of GapA-1 does not affect the in vitro growth rate of N. meningitidis, but significantly affects the ability of the organism to adhere to human epithelial and endothelial cells in a capsule-independent process suggesting a role in the pathogenesis of meningococcal infection

Climate change promotes parasitism in a coral symbiosis.

Coastal oceans are increasingly eutrophic, warm and acidic through the addition of anthropogenic nitrogen and carbon, respectively. Among the most sensitive taxa to these changes are scleractinian corals, which engineer the most biodiverse ecosystems on Earth. Corals' sensitivity is a consequence of their evolutionary investment in symbiosis with the dinoflagellate alga, Symbiodinium. Together, the coral holobiont has dominated oligotrophic tropical marine habitats. However, warming destabilizes this association and reduces coral fitness. It has been theorized that, when reefs become warm and eutrophic, mutualistic Symbiodinium sequester more resources for their own growth, thus parasitizing their hosts of nutrition. Here, we tested the hypothesis that sub-bleaching temperature and excess nitrogen promotes symbiont parasitism by measuring respiration (costs) and the assimilation and translocation of both carbon (energy) and nitrogen (growth; both benefits) within Orbicella faveolata hosting one of two Symbiodinium phylotypes using a dual stable isotope tracer incubation at ambient (26 °C) and sub-bleaching (31 °C) temperatures under elevated nitrate. Warming to 31 °C reduced holobiont net primary productivity (NPP) by 60% due to increased respiration which decreased host %carbon by 15% with no apparent cost to the symbiont. Concurrently, Symbiodinium carbon and nitrogen assimilation increased by 14 and 32%, respectively while increasing their mitotic index by 15%, whereas hosts did not gain a proportional increase in translocated photosynthates. We conclude that the disparity in benefits and costs to both partners is evidence of symbiont parasitism in the coral symbiosis and has major implications for the resilience of coral reefs under threat of global change

Impact of discontinuity in health insurance on resource utilization

<p>Abstract</p> <p>Background</p> <p>This study sought to describe the incidence of transitions into and out of Medicaid, characterize the populations that transition and determine if health insurance instability is associated with changes in healthcare utilization.</p> <p>Methods</p> <p>2000-2004 Medical Expenditure Panel Survey (MEPS) was used to identify adults enrolled in Medicaid at any time during the survey period (n = 6,247). We estimate both static and dynamic panel data models to examine the effect of health insurance instability on health care resource utilization.</p> <p>Results</p> <p>We find that, after controlling for observed factors like employment and health status, and after specifying a dynamic model that attempts to capture time-dependent unobserved effects, individuals who have multiple transitions into and out of Medicaid have higher emergency room utilization, more office visits, more hospitalizations, and refill their prescriptions less often.</p> <p>Conclusions</p> <p>Individuals with more than one transition in health insurance status over the study period were likely to have higher health care utilization than individuals with one or fewer transitions. If these effects are causal, in addition to individual benefits, there are potentially large benefits for Medicaid programs from reducing avoidable insurance instability. These results suggest the importance of including provisions to facilitate continuous enrollment in public programs as the United States pursues health reform.</p

Institutional logics and interorganizational learning in technological arenas: Evidence from standard-setting organizations in the mobile handset industry

© 2015, INFORMS. Conceptualizing standard-setting organizations (SSOs) as technological arenas within which firms from different countries interact and learn, we offer insights into the interplay between firms' institutional logics and their interorganizational learning outcomes. We suggest that firms' interorganizational learning is embedded in their macrolevel country contexts, characterized by more corporatist versus less corporatist (pluralist) institutional logics. Whereas corporatism spurs coordinated approaches, pluralism engenders competitive interactions that affect the extent to which firms span organizational and technological boundaries and learn from each other. We test our theory using longitudinal analysis of 181 dyads involving 26 firms participating in 17 SSOs in the global mobile handset industry. We find that interorganizational learning, as measured by patent citations, involving corporatist firm dyads significantly increases when the dominant logic within the arena is also corporatist. By making cooperative schemas more accessible, a dominant corporatist logic also enhances interorganizational learning across technologically distant dyads. When a pluralist logic dominates the arena, corporatist dyads learn less because firms in the dyad activate a contradictory logic that decouples them from their natural processes for interorganizational learning. These findings highlight the implications of institutional logics for interorganizational learning outcomes and provide insights into how firms attend to institutional contradictions in arenas that provide opportunities for interorganizational learning

Water Quality and Herbivory Interactively Drive Coral-Reef Recovery Patterns in American Samoa

BACKGROUND: Compared with a wealth of information regarding coral-reef recovery patterns following major disturbances, less insight exists to explain the cause(s) of spatial variation in the recovery process. METHODOLOGY/PRINCIPAL FINDINGS: This study quantifies the influence of herbivory and water quality upon coral reef assemblages through space and time in Tutuila, American Samoa, a Pacific high island. Widespread declines in dominant corals (Acropora and Montipora) resulted from cyclone Heta at the end of 2003, shortly after the study began. Four sites that initially had similar coral reef assemblages but differential temporal dynamics four years following the disturbance event were classified by standardized measures of 'recovery status', defined by rates of change in ecological measures that are known to be sensitive to localized stressors. Status was best predicted, interactively, by water quality and herbivory. Expanding upon temporal trends, this study examined if similar dependencies existed through space; building multiple regression models to identify linkages between similar status measures and local stressors for 17 localities around Tutuila. The results highlighted consistent, interactive interdependencies for coral reef assemblages residing upon two unique geological reef types. Finally, the predictive regression models produced at the island scale were graphically interpreted with respect to hypothesized site-specific recovery thresholds. CONCLUSIONS/SIGNIFICANCE: Cumulatively, our study purports that moving away from describing relatively well-known patterns behind recovery, and focusing upon understanding causes, improves our foundation to predict future ecological dynamics, and thus improves coral reef management

Sacrificing their Careers for their Families? An Analysis of the Family Pay Penalty in Europe

This paper examines the extent of and the mechanisms behind the penalty to motherhood in six European countries. Each country provides different levels of support for maternal employment allowing us to determine institutional effects on labour market outcome. While mothers tend to earn less than non-mothers, the penalty to motherhood is considerably lower in countries with policy support for working mothers. The paper establishes the United Kingdom and West Germany to have the least policy support for working mothers as well as the largest penalties to motherhood

Connectivity and systemic resilience of the Great Barrier Reef

Australia’s iconic Great Barrier Reef (GBR) continues to suffer from repeated impacts of cyclones, coral bleaching, and outbreaks of the coral-eating crown-of-thorns starfish (COTS), losing much of its coral cover in the process. This raises the question of the ecosystem’s systemic resilience and its ability to rebound after large-scale population loss. Here, we reveal that around 100 reefs of the GBR, or around 3%, have the ideal properties to facilitate recovery of disturbed areas, thereby imparting a level of systemic resilience and aiding its continued recovery. These reefs (1) are highly connected by ocean currents to the wider reef network, (2) have a relatively low risk of exposure to disturbances so that they are likely to provide replenishment when other reefs are depleted, and (3) have an ability to promote recovery of desirable species but are unlikely to either experience or spread COTS outbreaks. The great replenishment potential of these ‘robust source reefs’, which may supply 47% of the ecosystem in a single dispersal event, emerges from the interaction between oceanographic conditions and geographic location, a process that is likely to be repeated in other reef systems. Such natural resilience of reef systems will become increasingly important as the frequency of disturbances accelerates under climate change