The (In)Stability of Planetary Systems

We present results of numerical simulations which examine the dynamical stability of known planetary systems, a star with two or more planets. First we vary the initial conditions of each system based on observational data. We then determine regions of phase space which produce stable planetary configurations. For each system we perform 1000 ~1 million year integrations. We examine upsilon And, HD83443, GJ876, HD82943, 47UMa, HD168443, and the solar system (SS). We find that the resonant systems, 2 planets in a first order mean motion resonance, (HD82943 and GJ876) have very narrow zones of stability. The interacting systems, not in first order resonance, but able to perturb each other (upsilon And, 47UMa, and SS) have broad regions of stability. The separated systems, 2 planets beyond 10:1 resonance, (we only examine HD83443 and HD168443) are fully stable. Furthermore we find that the best fits to the interacting and resonant systems place them very close to unstable regions. The boundary in phase space between stability and instability depends strongly on the eccentricities, and (if applicable) the proximity of the system to perfect resonance. In addition to million year integrations, we also examined stability on ~100 million year timescales. For each system we ran ~10 long term simulations, and find that the Keplerian fits to these systems all contain configurations which may be regular on this timescale.Comment: 37 pages, 49 figures, 13 tables, submitted to Ap

Illustrating potential efficiency gains from using cost-effectiveness evidence to reallocate Medicare expenditures

This article is available open access through the publisher’s website at the linke below. Copyright @ 2013, International Society for Pharmacoeconomics and Outcomes Research (ISPOR).This article has been made available through the Brunel Open Access Publishing Fund.Objectives - The Centers for Medicare & Medicaid Services does not explicitly use cost-effectiveness information in national coverage determinations. The objective of this study was to illustrate potential efficiency gains from reallocating Medicare expenditures by using cost-effectiveness information, and the consequences for health gains among Medicare beneficiaries. Methods - We included national coverage determinations from 1999 through 2007. Estimates of cost-effectiveness were identified through a literature review. For coverage decisions with an associated cost-effectiveness estimate, we estimated utilization and size of the “unserved” eligible population by using a Medicare claims database (2007) and diagnostic and reimbursement codes. Technology costs originated from the cost-effectiveness literature or were estimated by using reimbursement codes. We illustrated potential aggregate health gains from increasing utilization of dominant interventions (i.e., cost saving and health increasing) and from reallocating expenditures by decreasing investment in cost-ineffective interventions and increasing investment in relatively cost-effective interventions. Results - Complete information was available for 36 interventions. Increasing investment in dominant interventions alone led to an increase of 270,000 quality-adjusted life-years (QALYs) and savings of $12.9 billion. Reallocation of a broader array of interventions yielded an additional 1.8 million QALYs, approximately 0.17 QALYs per affected Medicare beneficiary. Compared with the distribution of resources prior to reallocation, following reallocation a greater proportion was directed to oncology, diagnostic imaging/tests, and the most prevalent diseases. A smaller proportion of resources went to cardiology, treatments (including drugs, surgeries, and medical devices, as opposed to nontreatments such as preventive services), and the least prevalent diseases. Conclusions - Using cost-effectiveness information has the potential to increase the aggregate health of Medicare beneficiaries while maintaining existing spending levels.The Commonwealth Fun

Psoas major cross-sectional area: A potential marker of cardiorespiratory fitness

Background and Aim: Cardiorespiratory fitness is an important marker for overall health that significantly correlates with obesity-associated morbidities and mortality. Maximal oxygen uptake (VO2max) recorded during an incremental exercise test is the gold standard assessment for aerobic fitness. However, its cost, chronic illness, and frailty often preclude its application. The cross-sectional area (CSA) of the abdominal psoas major muscle is a predictor of sarcopenia and surgery outcomes and represents a promising biomarker for cardiorespiratory health. Therefore, in the present study, we have planned to assess the relationship between psoas major CSA, anthropometry, and body composition in a UK-based cohort of 210 men and women. Methods: Body mass (kg), height (cm), waist circumference (cm), VO2max, and blood pressure were measured in each participant. The CSA of psoas major, rectus abdominus, and another abdominal muscle of the core muscle group were assessed. Results: Following adjustment for height, psoas major CSA was found to be a significant predictor of percentage body fat (P = 0.02) in men, and body mass index (BMI) in both men (P = 0.015) and women (P = 0.004). We found psoas major CSA correlated more strongly with VO2max (r = 0.74, P < 0.01) than any other study outcome, including age and BMI. Conclusion: Psoas major muscle CSA represents an accurate, reproducible, and time-efficient surrogate for cardiorespiratory fitness and body composition

The diet-derived short chain fatty acid propionate improves beta-cell function in humans and stimulates insulin secretion from human islets in vitro

Aims: Diet-derived short chain fatty acids (SCFAs) improve glucose homeostasis in vivo, but the role of individual SCFAs and their mechanisms of action have not been defined. This study evaluated the effects of increasing colonic delivery of the SCFA propionate on β-cell function in humans and the direct effects of propionate on isolated human islets in vitro. Materials and Methods: For 24 weeks human subjects ingested an inulin-propionate ester that delivers propionate to the colon. Acute insulin, GLP-1 and non-esterified fatty acid (NEFA) levels were quantified pre- and post-supplementation in response to a mixed meal test. Expression of the SCFA receptor FFAR2 in human islets was determined by western blotting and immunohistochemistry. Dynamic insulin secretion from perifused human islets was quantified by radioimmunoassay and islet apoptosis was determined by quantification of caspase 3/7 activities. Results: Colonic propionate delivery in vivo was associated with improved β-cell function with increased insulin secretion that was independent of changes in GLP-1 levels. Human islet β-cells expressed FFAR2 and propionate potentiated dynamic glucose-stimulated insulin secretion in vitro, an effect that was dependent on signalling via protein kinase C. Propionate also protected human islets from apoptosis induced by the NEFA sodium palmitate and inflammatory cytokines. Conclusions: Our results indicate that propionate has beneficial effects on β-cell function in vivo, and in vitro analyses demonstrated that it has direct effects to potentiate glucose-stimulated insulin release and maintain β-cell mass through inhibition of apoptosis. These observations support ingestion of propiogenic dietary fibres to maintain healthy glucose homeostasis

Socioeconomic disadvantage but not remoteness affects short-term survival in prostate cancer: A population-based study using competing risks

© 2016 John Wiley & Sons Australia, Ltd Aim: We examined how sociodemographic, clinical and area-level factors are related to short-term prostate cancer mortality versus mortality from other causes, a crucial distinction for this disease that disproportionately affects men older than 60 years. Methods: We applied competing risk survival models to administrative data from the Queensland Cancer Registry (Australia) for men diagnosed with prostate cancer between January 2005 and July 2007, including stratification by Gleason score. Results: The men (n = 7393) in the study cohort had a median follow-up of 5 years 3 months. After adjustment, remoteness and area-level disadvantage were not significantly associated with prostate cancer mortality. However, area-level disadvantage had a significant negative relationship with hazard of death from a cause other than prostate cancer within 7 years; compared with those living in the most advantaged areas, the likelihood of mortality was higher for those in the most disadvantaged (subhazard ratio [SHR] = 1.39; 95% CI, 1.01–1.90; P = 0.041), disadvantaged (SHR = 1.51; 95% CI, 1.14–2.00; P = 0.004), middle (SHR = 1.34; 95% CI, 1.02–1.75; P = 0.034) and advantaged areas (SHR = 1.44; 95% CI, 1.09–1.89; P = 0.009). Those with Gleason score of 7 and higher had a lower hazard of prostate cancer mortality if they were living with a partner, whereas those with lower Gleason scores and living a partner had lower hazards of other-cause mortality. Conclusions: Understanding why men living in more disadvantaged areas have higher risk of non-prostate cancer mortality should be a priority

Terrestrial Planet Formation in Disks with Varying Surface Density Profiles

The ``minimum-mass solar nebula'' (MMSN) model estimates the surface density distribution of the protoplanetary disk by assuming the planets to have formed in situ. However, significant radial migration of the giant planets likely occurred in the Solar system, implying a distortion in the values derived by the MMSN method. The true density profiles of protoplanetary disks is therefore uncertain. Here we present results of simulations of late-stage terrestrial accretion, each starting from a disk of planetary embryos. We assume a power-law surface density profile that varies with heliocentric distance r as r^-alpha, and vary alpha between 1/2 and 5/2 (alpha = 3/2 for the MMSN model). We find that for steeper profiles (higher values of alpha), the terrestrial planets (i) are more numerous, (ii) form more quickly, (iii) form closer to the star, (iv) are more massive, (v) have higher iron contents, and (vi) have lower water contents. However, the possibility of forming potentially habitable planets does not appear to vary strongly with alpha.Comment: 10 pages, 5 figures in emulateapj style. tp appear in Oct 20, 2005, issue of Ap

2-Aminoacetophenone as a potential breath biomarker for Pseudomonas aeruginosa in the cystic fibrosis lung

<p>Abstract</p> <p>Background</p> <p><it>Pseudomonas aeruginosa </it>infections are associated with progressive life threatening decline of lung function in cystic fibrosis sufferers. Growth of <it>Ps. aeruginosa </it>releases a "grape-like" odour that has been identified as the microbial volatile organic compound 2-aminoacetophenone (2-AA).</p> <p>Methods</p> <p>We investigated 2-AA for its specificity to <it>Ps. aeruginosa </it>and its suitability as a potential breath biomarker of colonisation or infection by Solid Phase Micro Extraction and Gas Chromatography-Mass Spectrometry (GC/MS).</p> <p>Results</p> <p>Cultures of 20 clinical strains of <it>Ps. aeruginosa </it>but not other respiratory pathogens had high concentrations of 2-AA in the head space of <it>in vitro </it>cultures when analysed by GC/MS. 2-AA was stable for 6 hours in deactivated glass sampling bulbs but was not stable in Tedlar^®bags. Optimisation of GC/MS allowed detection levels of 2-AA to low pico mol/mol range in breath. The 2-AA was detected in a significantly higher proportion of subjects colonised with <it>Ps. aeruginosa </it>15/16 (93.7%) than both the healthy controls 5/17 (29%) (p < 0.0002) and CF patients not colonised with <it>Ps. aeruginosa </it>4/13(30.7%) (p < 0.001). The sensitivity and specificity of the 2-AA breath test compared to isolation of <it>Ps. aeruginosa </it>in sputum and/or BALF was 93.8% (95% CI, 67-99) and 69.2% (95% CI, 38-89) respectively. The peak integration values for 2-AA analysis in the breath samples were significantly higher in <it>Ps. aeruginosa </it>colonised subjects (median 242, range 0-1243) than the healthy controls (median 0, range 0-161; p < 0.001) and CF subjects not colonised with <it>Ps. aeruginosa </it>(median 0, range 0-287; p < 0.003)</p> <p>Conclusions</p> <p>Our results report 2-AA as a promising breath biomarker for the detection of <it>Ps. aeruginosa </it>infections in the cystic fibrosis lung.</p

Overcoming status quo bias in the human brain

Humans often accept the status quo when faced with conflicting choice alternatives. However, it is unknown how neural pathways connecting cognition with action modulate this status quo acceptance. Here we developed a visual detection task in which subjects tended to favor the default when making difficult, but not easy, decisions. This bias was suboptimal in that more errors were made when the default was accepted. A selective increase in subthalamic nucleus (STN) activity was found when the status quo was rejected in the face of heightened decision difficulty. Analysis of effective connectivity showed that inferior frontal cortex, a region more active for difficult decisions, exerted an enhanced modulatory influence on the STN during switches away from the status quo. These data suggest that the neural circuits required to initiate controlled, nondefault actions are similar to those previously shown to mediate outright response suppression. We conclude that specific prefrontal-basal ganglia dynamics are involved in rejecting the default, a mechanism that may be important in a range of difficult choice scenarios