A 33 year constancy of the X-ray coronae of AR Lac and eclipse diagnosis of scale height

Extensive X-ray and extreme ultraviolet (EUV) photometric observations of the eclipsing RS CVn system AR Lac were obtained over the years 1997 to 2013 with the Chandra X-ray Observatory Extreme Ultraviolet Explorer. During primary eclipse, HRC count rates decrease by ~40%. A similar minimum is seen during one primary eclipse observed by EUVE but not in others owing to intrinsic source variability. Little evidence for secondary eclipses is present in either the X-ray or EUV data, reminiscent of earlier X-ray and EUV observations. Primary eclipses allow us to estimate the extent of a spherically symmetric corona on the primary G star of about 1.3Rsun, or 0.86Rstar, and indicate the G star is likely brighter than the K component by a factor of 2-5. Brightness changes not attributable to eclipses appear to be dominated by stochastic variability and are generally non-repeating. X-ray and EUV light curves cannot therefore be reliably used to reconstruct the spatial distribution of emission assuming only eclipses and rotational modulation are at work. Moderate flaring is observed, where count rates increase by up to a factor of three above quiescence. Combined with older ASCA, Einstein, EXOSAT, ROSAT and Beppo-SAX observations, the data show that the level of quiescent coronal emission at X-ray wavelengths has remained remarkably constant over 33 years, with no sign of variation due to magnetic cycles. Variations in base level X-ray emission seen by Chandra over 13 years are only ~10%, while variations back to pioneering Einstein observations in 1980 amount to a maximum of 45% and more typically about 15%.Comment: To appear in the Astrophysical Journa

Unprecedented evidence for high viral abundance and lytic activity in coral reef waters of the South Pacific Ocean

Despite nutrient-depleted conditions, coral reef waters harbor abundant and diverse microbes; as major agents of microbial mortality, viruses are likely to influence microbial processes in these ecosystems. However, little is known about marine viruses in these rapidly changing ecosystems. Here we examined spatial and short-term temporal variability in marine viral abundance (VA) and viral lytic activity across various reef habitats surrounding Moorea Island (French Polynesia) in the South Pacific. Water samples were collected along four regional cross-reef transects and during a time-series in Opunohu Bay. Results revealed high VA (range: 5.6 x 10(6)-3.6 x 10(7) viruses ml(-1)) and lytic viral production (range: 1.5 x 10(9)-9.2 x 10(10) viruses l(-1) d(-1)). Flow cytometry revealed that viral assemblages were composed of three subsets that each displayed distinct spatiotemporal relationships with nutrient concentrations and autotrophic and heterotrophic microbial abundances. The results highlight dynamic shifts in viral community structure and imply that each of these three subsets is ecologically important and likely to infect distinct microbial hosts in reef waters. Based on viral-reduction approach, we estimate that lytic viruses were responsible for the removal of ca. 24-367% of bacterial standing stock d(-1) and the release of ca. 1.0- 62 mu g of organic carbon l(-1) d(-1) in reef waters. Overall, this work demonstrates the highly dynamic distribution of viruses and their critical roles in controlling microbial mortality and nutrient cycling in coral reef water ecosystems

Nutrient supply from fishes facilitates macroalgae and suppresses corals in a Caribbean coral reef ecosystem

On coral reefs, fishes can facilitate coral growth via nutrient excretion; however, as coral abundance declines, these nutrients may help facilitate increases in macroalgae. By combining surveys of reef communities with bioenergetics modeling, we showed that fish excretion supplied 25 times more nitrogen to forereefs in the Florida Keys, USA, than all other biotic and abiotic sources combined. One apparent result was a positive relationship between fish excretion and macroalgal cover on these reefs. Herbivore biomass also showed a negative relationship with macroalgal cover, suggesting strong interactions of top-down and bottom-up forcing. Nutrient supply by fishes also showed a negative correlation with juvenile coral density, likely mediated by competition between macroalgae and corals, suggesting that fish excretion may hinder coral recovery following large-scale coral loss. Thus, the impact of nutrient supply by fishes may be context-dependent and reinforce either coral-dominant or coral-depauperate reef communities depending on initial community states

Macroborer Presence on Corals Increases with Nutrient Input and Promotes Parrotfish Bioerosion

Bioerosion by reef-dwelling organisms influences net carbonate budgets on reefs worldwide. External bioeroders, such as parrotfish and sea urchins, and internal bioeroders, including sponges and lithophagid bivalves, are major contributors to bioerosion on reefs. Despite their importance, few studies have examined how environmental (e.g., nutrients) or biological drivers (e.g., the actions of other bioeroders) may influence bioeroder dynamics on reefs. For example, internal bioeroders could promote external bioerosion by weakening the coral skeletal matrix. Our study investigated: ( 1) whether nutrient supply influences the dynamics between internal and external bioeroders and ( 2) how the presence of a boring bivalve, Lithophaga spp., influences parrotfish bioerosion on massive Porites corals. We hypothesized that nutrient supply would be positively correlated with Lithophaga densities on massive Porites colonies, and that as bivalve density increased, the frequency and intensity of parrotfish bioerosion would increase. To test these hypotheses, we analyzed six time points over a 10-yr period from a time series of benthic images and nitrogen content of a dominant macroalga from the fringing reefs around Moorea, French Polynesia. We found Lithophaga densities were positively correlated with nitrogen availability. Further, massive Porites that are more infested with Lithophaga had both a higher probability of being bitten by parrotfish and a higher density of bite scars from parrotfishes. Our findings indicate that increasing nutrient availability may strengthen the relationship between internal and external bioeroders, suggesting that colonies at more eutrophic sites may experience higher bioerosion rates

Modeled vs. Actual Performance of the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS)

The NASA Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) has been completed as an Engineering Demonstration Unit (EDU) and has recently finished thermal vacuum testing and calibration. The GIFTS EDU was designed to demonstrate new and emerging sensor and data processing technologies with the goal of making revolutionary improvements in meteorological observational capability and forecasting accuracy. The GIFTS EDU includes a cooled (150 K), imaging FTS designed to provide the radiometric accuracy and atmospheric sounding precision required to meet the next generation GOES sounder requirements. This paper discusses a GIFTS sensor response model and its validation during thermal vacuum testing and calibration. The GIFTS sensor response model presented here is a component-based simulation written in IDL with the model component characteristics updated as actual hardware has become available. We discuss our calibration approach, calibration hardware used, and preliminary system performance, including NESR, spectral radiance responsivity, and instrument line shape. A comparison of the model predictions and hardware performance provides useful insight into the fidelity of the design approach

Overfishing and nutrient pollution interact with temperature to disrupt coral reefs down to microbial scales

Losses of corals worldwide emphasize the need to understand what drives reef decline. Stressors such as overfishing and nutrient pollution may reduce resilience of coral reefs by increasing coral?algal competition and reducing coral recruitment, growth and survivorship. Such effects may themselves develop via several mechanisms, including disruption of coral microbiomes. Here we report the results of a 3-year field experiment simulating overfishing and nutrient pollution. These stressors increase turf and macroalgal cover, destabilizing microbiomes, elevating putative pathogen loads, increasing disease more than twofold and increasing mortality up to eightfold. Above-average temperatures exacerbate these effects, further disrupting microbiomes of unhealthy corals and concentrating 80% of mortality in the warmest seasons. Surprisingly, nutrients also increase bacterial opportunism and mortality in corals bitten by parrotfish, turning normal trophic interactions deadly for corals. Thus, overfishing and nutrient pollution impact reefs down to microbial scales, killing corals by sensitizing them to predation, above-average temperatures and bacterial opportunism

The Impact of Venous Thromboembolism on Risk of Death or Hemorrhage in Older Cancer Patients

BACKGROUND: Among older cancer patients, there is uncertainty about the degree to which venous thromboembolism (VTE) and its treatment increase the risk of death or major hemorrhage. OBJECTIVE: To determine the prevalence of VTE in a cohort of older cancer patients, as well as the degree to which VTE increased the risk of death or major hemorrhage. METHODS: We conducted a retrospective cohort study of linked Surveillance, Epidemiology, and End Results cancer registry and Medicare administrative claims data. Patients with any of ten invasive cancers diagnosed during 1995 through 1999 were included; the independent variable was VTE diagnosed concomitantly with cancer diagnosis. Outcomes included major hemorrhage during the first year after cancer diagnosis and all-cause mortality; RESULTS: Overall, about 1% of patients who were diagnosed with cancer also had a VTE diagnosed concomitantly. After adjusting for sociodemographic factors and cancer stage and grade, concomitant VTE was associated with a relative increase in the risk of death for 8 of the 10 cancer types; the increase in risk tended to range 20–40% across most cancer types. Approximately 16.8% (95% confidence interval [CI] 14.9–18.8%) of patients with a concomitant VTE and 7.9% (95% CI 7.7–8.0%) of patients without a VTE experienced a major hemorrhage during the year after cancer diagnosis (P value <.001). The excess risk of hemorrhage associated with VTE varied substantially across cancer types, ranging from no significant excess (kidney and uterine cancer) to 11.5% (lymphoma). CONCLUSION: Concomitant VTE is not only a marker and potential mediator of increased risk of death among older cancer patients, but patients with a VTE have a marked increased risk of major hemorrhage

Impact of safety-related dose reductions or discontinuations on sustained virologic response in HCV-infected patients: Results from the GUARD-C Cohort

BACKGROUND: Despite the introduction of direct-acting antiviral agents for chronic hepatitis C virus (HCV) infection, peginterferon alfa/ribavirin remains relevant in many resource-constrained settings. The non-randomized GUARD-C cohort investigated baseline predictors of safety-related dose reductions or discontinuations (sr-RD) and their impact on sustained virologic response (SVR) in patients receiving peginterferon alfa/ribavirin in routine practice. METHODS: A total of 3181 HCV-mono-infected treatment-naive patients were assigned to 24 or 48 weeks of peginterferon alfa/ribavirin by their physician. Patients were categorized by time-to-first sr-RD (Week 4/12). Detailed analyses of the impact of sr-RD on SVR24 (HCV RNA <50 IU/mL) were conducted in 951 Caucasian, noncirrhotic genotype (G)1 patients assigned to peginterferon alfa-2a/ribavirin for 48 weeks. The probability of SVR24 was identified by a baseline scoring system (range: 0-9 points) on which scores of 5 to 9 and <5 represent high and low probability of SVR24, respectively. RESULTS: SVR24 rates were 46.1% (754/1634), 77.1% (279/362), 68.0% (514/756), and 51.3% (203/396), respectively, in G1, 2, 3, and 4 patients. Overall, 16.9% and 21.8% patients experienced 651 sr-RD for peginterferon alfa and ribavirin, respectively. Among Caucasian noncirrhotic G1 patients: female sex, lower body mass index, pre-existing cardiovascular/pulmonary disease, and low hematological indices were prognostic factors of sr-RD; SVR24 was lower in patients with 651 vs. no sr-RD by Week 4 (37.9% vs. 54.4%; P = 0.0046) and Week 12 (41.7% vs. 55.3%; P = 0.0016); sr-RD by Week 4/12 significantly reduced SVR24 in patients with scores <5 but not 655. CONCLUSIONS: In conclusion, sr-RD to peginterferon alfa-2a/ribavirin significantly impacts on SVR24 rates in treatment-naive G1 noncirrhotic Caucasian patients. Baseline characteristics can help select patients with a high probability of SVR24 and a low probability of sr-RD with peginterferon alfa-2a/ribavirin