830 research outputs found

    Survey of Coherent Approximately 1 Hz Waves in Mercury's Inner Magnetosphere from MESSENGER Observations

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    We summarize observations by the MESSENGER spacecraft of highly coherent waves at frequencies between 0.4 and 5 Hz in Mercury's inner magnetosphere. This survey covers the time period from 24 March to 25 September 2011, or 2.1 Mercury years. These waves typically exhibit banded harmonic structure that drifts in frequency as the spacecraft traverses the magnetic equator. The waves are seen at all magnetic local times, but their observed rate of occurrence is much less on the dayside, at least in part the result of MESSENGER's orbit. On the nightside, on average, wave power is maximum near the equator and decreases with increasing magnetic latitude, consistent with an equatorial source. When the spacecraft traverses the plasma sheet during its equatorial crossings, wave power is a factor of 2 larger than for equatorial crossings that do not cross the plasma sheet. The waves are highly transverse at large magnetic latitudes but are more compressional near the equator. However, at the equator the transverse component of these waves increases relative to the compressional component as the degree of polarization decreases. Also, there is a substantial minority of events that are transverse at all magnetic latitudes, including the equator. A few of these latter events could be interpreted as ion cyclotron waves. In general, the waves tend to be strongly linear and characterized by values of the ellipticity less than 0.3 and wave-normal angles peaked near 90 deg. Their maxima in wave power at the equator coupled with their narrow-band character suggests that these waves might be generated locally in loss cone plasma characterized by high values of the ratio beta of plasma pressure to magnetic pressure. Presumably both electromagnetic ion cyclotron waves and electromagnetic ion Bernstein waves can be generated by ion loss cone distributions. If proton beta decreases with increasing magnetic latitude along a field line, then electromagnetic ion Bernstein waves are predicted to transition from compressional to transverse, a pattern consistent with our observations. We hypothesize that these local instabilities can lead to enhanced ion precipitation and directly feed field-line resonances

    Craters Hosting Radar-Bright Deposits in Mercury's North Polar Region: Areas of Persistent Shadow Determined from MESSENGER Images

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    Radar-bright features near Mercury's poles were discovered in Earth-based radar images and proposed to be water ice present in permanently shadowed areas. Images from MESSENGER's one-year primary orbital mission provide the first nearly complete view of Mercury’s north polar region, as well as multiple images of the surface under a range of illumination conditions. We find that radar-bright features near Mercury's north pole are associated with locations persistently shadowed in MESSENGER images. Within 10 degrees of the pole, almost all craters larger than 10 km in diameter host radar-bright deposits. There are several craters located near Mercury's north pole with sufficiently large diameters to enable long-lived water ice to be thermally stable at the surface within regions of permanent shadow. Craters located farther south also host radar-bright deposits and show a preference for cold-pole longitudes; thermal models suggest that a thin insulating layer is required to cover these deposits if the radar-bright material consists predominantly of longlived water ice. Many small (less than 10 km diameter) and low-latitude (extending southward to 66 degrees N) craters host radar-bright material, and water ice may not be thermally stable in these craters for ~1 Gy, even beneath an insulating layer. The correlation of radar-bright features with persistently shadowed areas is consistent with the deposits being composed of water ice, and future thermal modeling of small and low-latitude craters has the potential to further constrain the nature, source, and timing of emplacement of the radar-bright material

    Molecular Gas in the z=1.2 Ultraluminous Merger GOODS J123634.53+621241.3

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    We report the detection of CO(2-1) emission from the z=1.2 ultraluminous infrared galaxy (ULIRG) GOODS J123634.53+621241.3 (also known as the sub-millimeter galaxy GN26). These observations represent the first discovery of high-redshift CO emission using the new Combined Array for Research in Millimeter-Wave Astronomy (CARMA). Of all high-redshift (z>1) galaxies within the GOODS-North field, this source has the largest far-infrared (FIR) flux observed in the Spitzer 70um and 160um bands. The CO redshift confirms the optical identification of the source, and the bright CO(2-1) line suggests the presence of a large molecular gas reservoir of about 7x10^10 M(sun). The infrared-to-CO luminosity ratio of L(IR)/L'(CO) = 80+/-30 L(sun) (K Km/s pc^2)^-1 is slightly smaller than the average ratio found in local ULIRGs and high-redshift sub-millimeter galaxies. The short star-formation time scale of about 70 Myr is consistent with a starburst associated with the merger event and is much shorter than the time scales for spiral galaxies and estimates made for high-redshift galaxies selected on the basis of their B-z and z-K colors.Comment: Accepted for publication in ApJ Letter

    Associations between atrial cardiopathy and cerebral amyloid: The ARIC-PET study

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    Background Atrial fibrillation (AF) is a risk factor for cognitive decline, possibly from silent brain infarction. Left atrial changes in structure or function (atrial cardiopathy) can lead to AF but may impact cognition independently. It is unknown if AF or atrial cardiopathy also acts on Alzheimer disease-specific mechanisms, such as deposition of β-amyloid. Methods and Results A total of 316 dementia-free participants from the ARIC (Atherosclerosis Risk in Communities) study underwent florbetapir positron emission tomography, electrocardiography, and 2-dimensional echocardiography. Atrial cardiopathy was defined as ≥1: (1) left atrial volume index \u3e34 mL/

    Risk related to pre–diabetes mellitus and diabetes mellitus in heart failure with reduced ejection fraction: insights from prospective comparison of ARNI with ACEI to determine impact on global mortality and morbidity in heart failure trial

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    Background—The prevalence of pre–diabetes mellitus and its consequences in patients with heart failure and reduced ejection fraction are not known. We investigated these in the Prospective Comparison of ARNI With ACEI to Determine Impact on Global Mortality and Morbidity in Heart Failure (PARADIGM-HF) trial. Methods and Results—We examined clinical outcomes in 8399 patients with heart failure and reduced ejection fraction according to history of diabetes mellitus and glycemic status (baseline hemoglobin A1c [HbA1c]: <6.0% [<42 mmol/mol], 6.0%–6.4% [42–47 mmol/mol; pre–diabetes mellitus], and ≥6.5% [≥48 mmol/mol; diabetes mellitus]), in Cox regression models adjusted for known predictors of poor outcome. Patients with a history of diabetes mellitus (n=2907 [35%]) had a higher risk of the primary composite outcome of heart failure hospitalization or cardiovascular mortality compared with those without a history of diabetes mellitus: adjusted hazard ratio, 1.38; 95% confidence interval, 1.25 to 1.52;P<0.001. HbA1c measurement showed that an additional 1106 (13% of total) patients had undiagnosed diabetes mellitus and 2103 (25%) had pre–diabetes mellitus. The hazard ratio for patients with undiagnosed diabetes mellitus (HbA1c, >6.5%) and known diabetes mellitus compared with those with HbA1c<6.0% was 1.39 (1.17–1.64); P<0.001 and 1.64 (1.43–1.87); P<0.001, respectively. Patients with pre–diabetes mellitus were also at higher risk (hazard ratio, 1.27 [1.10–1.47];P<0.001) compared with those with HbA1c<6.0%. The benefit of LCZ696 (sacubitril/valsartan) compared with enalapril was consistent across the range of HbA1c in the trial. Conclusions—In patients with heart failure and reduced ejection fraction, dysglycemia is common and pre–diabetes mellitus is associated with a higher risk of adverse cardiovascular outcomes (compared with patients with no diabetes mellitus and HbA1c <6.0%). LCZ696 was beneficial compared with enalapril, irrespective of glycemic status

    Cost-effectiveness of dapagliflozin for patients with heart failure across the spectrum of ejection fraction:A pooled analysis of DAPA-HF and DELIVER data

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    Aim: To assess the cost-effectiveness of dapagliflozin in addition to usual care, compared with usual care alone, in a large population of patients with heart failure (HF), spanning the full range of left ventricular ejection fraction (LVEF). Methods and results: Patient-level data were pooled from HF trials (DAPA-HF, DELIVER) to generate a population including HF with reduced, mildly reduced and preserved LVEF, to increase statistical power and enable exploration of interactions among LVEF, renal function and N-terminal pro-B-type natriuretic peptide levels, as they are relevant determinants of health status in this population. Survival and HF recurrent event risk equations were derived and applied to a lifetime horizon Markov model with health states defined by Kansas City Cardiomyopathy Questionnaire total symptom score quartiles; costs and utilities were in the UK setting. The base case incremental cost-effectiveness ratio (ICER) was £6470 per quality-adjusted life year (QALY) gained, well below the UK willingness-to-pay (WTP) threshold of £20 000/QALY gained. In interaction sensitivity analyses, the highest ICER was observed for elderly patients with preserved LVEF (£16 624/QALY gained), and ranged to a region of dominance (increased QALYs, decreased costs) for patients with poorer renal function and reduced/mildly reduced LVEF. Results across the patient characteristic interaction plane were mostly between £5000 and £10 000/QALY gained. Conclusions: Dapagliflozin plus usual care, versus usual care alone, yielded results well below the WTP threshold for the UK across a heterogeneous population of patients with HF including the full spectrum of LVEF, and is likely a cost-effective intervention.</p

    Cost-effectiveness of dapagliflozin for patients with heart failure across the spectrum of ejection fraction:A pooled analysis of DAPA-HF and DELIVER data

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    Aim: To assess the cost-effectiveness of dapagliflozin in addition to usual care, compared with usual care alone, in a large population of patients with heart failure (HF), spanning the full range of left ventricular ejection fraction (LVEF). Methods and results: Patient-level data were pooled from HF trials (DAPA-HF, DELIVER) to generate a population including HF with reduced, mildly reduced and preserved LVEF, to increase statistical power and enable exploration of interactions among LVEF, renal function and N-terminal pro-B-type natriuretic peptide levels, as they are relevant determinants of health status in this population. Survival and HF recurrent event risk equations were derived and applied to a lifetime horizon Markov model with health states defined by Kansas City Cardiomyopathy Questionnaire total symptom score quartiles; costs and utilities were in the UK setting. The base case incremental cost-effectiveness ratio (ICER) was £6470 per quality-adjusted life year (QALY) gained, well below the UK willingness-to-pay (WTP) threshold of £20 000/QALY gained. In interaction sensitivity analyses, the highest ICER was observed for elderly patients with preserved LVEF (£16 624/QALY gained), and ranged to a region of dominance (increased QALYs, decreased costs) for patients with poorer renal function and reduced/mildly reduced LVEF. Results across the patient characteristic interaction plane were mostly between £5000 and £10 000/QALY gained. Conclusions: Dapagliflozin plus usual care, versus usual care alone, yielded results well below the WTP threshold for the UK across a heterogeneous population of patients with HF including the full spectrum of LVEF, and is likely a cost-effective intervention.</p
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