Collisional Stripping and Disruption of Super-Earths

The final stage of planet formation is dominated by collisions between planetary embryos. The dynamics of this stage determine the orbital configuration and the mass and composition of planets in the system. In the solar system, late giant impacts have been proposed for Mercury, Earth, Mars, and Pluto. In the case of Mercury, this giant impact may have significantly altered the bulk composition of the planet. Here we present the results of smoothed particle hydrodynamics simulations of high-velocity (up to ~5 v_esc) collisions between 1 and 10 M_Earth planets of initially terrestrial composition to investigate the end stages of formation of extrasolar super-Earths. As found in previous simulations of collisions between smaller bodies, when collision energies exceed simple merging, giant impacts are divided into two regimes: (1) disruption and (2) hit-and-run (a grazing inelastic collision and projectile escape). Disruption occurs when the impact parameter is near zero, when the projectile mass is small compared to the target, or at extremely high velocities. In the disruption regime, we derive the criteria for catastrophic disruption (when half the total colliding mass is lost), the transition energy between accretion and erosion, and a scaling law for the change in bulk composition (iron-to-silicate ratio) resulting from collisional stripping of a mantle.Comment: 10 pages, 1 table, 4 figures. Accepted for publication in ApJ Letter

Optimising Residential Water Heating System Performance to Minimise Water-energy Penalties

The energy consumption associated with domestic hot water supply services correspond to a significant portion of the total energy consumption of the urban water cycle. The objective of this study is to analyse the performance of domestic water heaters in the three largest cities of Australia (i.e. Sydney, Melbourne and Brisbane). The performance of systems was investigated undertaking a multi-parametric analysis, in which energy efficiency indicators (i.e. energy intensity and power peaks) were combined with level of service indicators (i.e. compliance rate with minimum temperature thresholds for end use points and hot water tanks). The operation of water heaters was modelled using the software EnergyPlus. Results demonstrate the need for a more holistic approach for the design and assessment of domestic water heaters taking into account not only the technology type to heat water, but also site specific aspects

Sesquinary Catastrophe For Close-In Moons with Dynamically Excited Orbits

We identify a new mechanism that can lead to the destruction of small, close-in planetary satellites. If a small moon close to the planet has a sizable eccentricity and inclination, its ejecta that escape to planetocentric orbit would often re-impact with much higher velocity due to the satellite's and the fragment's orbits precessing out of alignment. If the impacts of returning ejecta result in net erosion, a runaway process can occur which may end in disruption of the satellite, and we term this process ``sesquinary catastrophe''. We expect the moon to re-accrete, but on an orbit with significantly lower eccentricity and inclination. We find that the large majority of small close-in moons in the Solar System, have orbits that are immune to sesquinary catastrophe. The exceptions include a number of resonant moonlets of Saturn for which resonances may affect the velocities of re-impact of their own debris. Additionally, we find that Neptune's moon Naiad (and to a lesser degree, Jupiter's Thebe) must have substantial internal strength, in line with prior estimates based on Roche limit stability. We also find that sesquinary instability puts important constraints on the plausible past orbits of Phobos and Deimos or their progenitors.Comment: Accepted for Ap

The Formation of the Collisional Family around the Dwarf Planet Haumea

Haumea, a rapidly rotating elongated dwarf planet (~ 1500 km in diameter), has two satellites and is associated with a "family" of several smaller Kuiper Belt objects (KBOs) in similar orbits. All members of the Haumea system share a water ice spectral feature that is distinct from all other KBOs. The relative velocities between the Haumea family members are too small to have formed by catastrophic disruption of a large precursor body, which is the process that formed families around much smaller asteroids in the Main Belt. Here we show that all of the unusual characteristics of the Haumea system are explained by a novel type of giant collision: a graze-and-merge impact between two comparably sized bodies. The grazing encounter imparted the high angular momentum that spun off fragments from the icy crust of the elongated merged body. The fragments became satellites and family members. Giant collision outcomes are extremely sensitive to the impact parameters. Compared to the Main Belt, the largest bodies in the Kuiper Belt are more massive and experience slower velocity collisions; hence, outcomes of giant collisions are dramatically different between the inner and outer solar system. The dwarf planets in the Kuiper Belt record an unexpectedly large number of giant collisions, requiring a special dynamical event at the end of solar system formation.Comment: Accepted for publication in ApJ, 12 pages, 4 figures, 2 tables

The predictive power of depression screening procedures for veterans with coronary artery disease

Depression leads to a worse outcome for patients with coronary artery disease (CAD). Thus, accurately identifying depression in CAD patients is imperative. In many veterans affairs (VA) hospitals, patients are screened for depression once a year using the patient health questionnaire (PHQ-9). Although the PHQ-9 is generally considered a specific and sensitive measure of depression, there is reason to believe that these screening procedures may miss a large number of cases of depression within CAD patients and cardiology patients more generally. The goal of this study was to provide data as to the predictive power of this depression screening procedure by (a) comparing the prevalence rate of depression identified by the PHQ-9 to known prevalence rates and (b) examining whether patients identified as “depressed” also had conditions that consistently co-occur with depression (eg, post-traumatic stress disorder [PTSD], other medical issues). Participants were 813 consecutive patients who received an angiogram in the cardiac catheterization laboratory at a large VA Medical Center. Prevalence of depression was 6.9% in the overall sample and less than 6% when the sample was restricted to CAD patients with significant stenosis. Depression was significantly associated with PTSD, smoking, and alcohol problems. However, depression was not associated with other medical problems such as diabetes, renal failure, peripheral vascular disease, or anemia. In conclusion, the low prevalence rate of depression and lack of associations with comorbid medical problems may suggest that the VA’s depression screening procedures have low sensitivity for identifying depression in CAD patients. It is recommended that clinicians treating CAD regularly screen for depression and do not rely on archival depression screens

Incident pulmonary hypertension in 13488 cases investigated with repeat echocardiography : A clinical cohort study

Background We addressed the paucity of data describing the characteristics and natural history of incident pulmonary hypertension. Methods Adults (n=13 448) undergoing routine echocardiography without initial evidence of pulmonary hypertension (estimated right ventricular systolic pressure, eRVSP <30.0 mmHg) or left heart disease were studied. Incident pulmonary hypertension (eRVSP ≥30.0 mmHg) was detected on repeat echocardiogram a median of 4.1 years apart. Mortality was examined according to increasing eRVSP levels (30.0–39.9, 40.0–49.9 and ≥50.0 mmHg) indicative of mild-to-severe pulmonary hypertension. Results A total of 6169 men (45.9%, aged 61.4±16.7 years) and 7279 women (60.8±16.9 years) without evidence of pulmonary hypertension were identified (first echocardiogram). Subsequently, 5412 (40.2%) developed evidence of pulmonary hypertension, comprising 4125 (30.7%), 928 (6.9%) and 359 (2.7%) cases with an eRVSP of 30.0–39.9 mmHg, 40.0–49.9 mmHg and ≥50.0 mmHg, respectively (incidence 94.0 and 90.9 cases per 1000 men and women, respectively, per year). Median (interquartile range) eRVSP increased by +0.0 (−2.27 to +2.67) mmHg and +30.68 (+26.03 to +37.31) mmHg among those with eRVSP <30.0 mmHg versus ≥50.0 mmHg. During a median 8.1 years of follow-up, 2776 (20.6%) died from all causes. Compared to those with eRVSP <30.0 mmHg, the adjusted risk of all-cause mortality was 1.30-fold higher in 30.0–39.9 mmHg, 1.82-fold higher in 40.0–49.9 mmHg and 2.11-fold higher in ≥50.0 mmHg groups (all p<0.001). Conclusions New-onset pulmonary hypertension, as indicated by elevated eRVSP, is a common finding among older patients without left heart disease followed-up with echocardiography. This phenomenon is associated with an increased morality risk even among those with mildly elevated eRVSP

Differential effects of two-pore channel protein 1 and 2 silencing in MDA-MB-468 breast cancer cells

Two-pore channel proteins, TPC1 and TPC2, are calcium permeable ion channels found localized to the membranes of endolysosomal calcium stores. There is increasing interest in the role of TPC-mediated intracellular signaling in various pathologies; however their role in breast cancer has not been extensively evaluated. TPC1 and TPC2 mRNA was present in all non-tumorigenic and tumorigenic breast cell lines assessed. Silencing of TPC2 but not TPC1 attenuated epidermal growth factor-induced vimentin expression in MDA-MB-468 breast cancer cells. This effect was not due to a general inhibition of epithelial to mesenchymal transition (EMT) as TPC2 silencing had no effect on epidermal growth factor (EGF)-induced changes on E-cadherin expression. TPC1 and TPC2 were also shown to differentially regulate cyclopiazonic acid (CPA)-mediated changes in cytosolic free Ca. These findings indicate potential differential regulation of signaling processes by TPC1 and TPC2 in breast cancer cells

Comparison of aggregate and individual participant data approaches to meta-analysis of randomised trials : An observational study

BACKGROUND: It remains unclear when standard systematic reviews and meta-analyses that rely on published aggregate data (AD) can provide robust clinical conclusions. We aimed to compare the results from a large cohort of systematic reviews and meta-analyses based on individual participant data (IPD) with meta-analyses of published AD, to establish when the latter are most likely to be reliable and when the IPD approach might be required. METHODS AND FINDINGS: We used 18 cancer systematic reviews that included IPD meta-analyses: all of those completed and published by the Meta-analysis Group of the MRC Clinical Trials Unit from 1991 to 2010. We extracted or estimated hazard ratios (HRs) and standard errors (SEs) for survival from trial reports and compared these with IPD equivalents at both the trial and meta-analysis level. We also extracted or estimated the number of events. We used paired t tests to assess whether HRs and SEs from published AD differed on average from those from IPD. We assessed agreement, and whether this was associated with trial or meta-analysis characteristics, using the approach of Bland and Altman. The 18 systematic reviews comprised 238 unique trials or trial comparisons, including 37,082 participants. A HR and SE could be generated for 127 trials, representing 53% of the trials and approximately 79% of eligible participants. On average, trial HRs derived from published AD were slightly more in favour of the research interventions than those from IPD (HRAD to HRIPD ratio = 0.95, p = 0.007), but the limits of agreement show that for individual trials, the HRs could deviate substantially. These limits narrowed with an increasing number of participants (p < 0.001) or a greater number (p < 0.001) or proportion (p < 0.001) of events in the AD. On average, meta-analysis HRs from published AD slightly tended to favour the research interventions whether based on fixed-effect (HRAD to HRIPD ratio = 0.97, p = 0.088) or random-effects (HRAD to HRIPD ratio = 0.96, p = 0.044) models, but the limits of agreement show that for individual meta-analyses, agreement was much more variable. These limits tended to narrow with an increasing number (p = 0.077) or proportion of events (p = 0.11) in the AD. However, even when the information size of the AD was large, individual meta-analysis HRs could still differ from their IPD equivalents by a relative 10% in favour of the research intervention to 5% in favour of control. We utilised the results to construct a decision tree for assessing whether an AD meta-analysis includes sufficient information, and when estimates of effects are most likely to be reliable. A lack of power at the meta-analysis level may have prevented us identifying additional factors associated with the reliability of AD meta-analyses, and we cannot be sure that our results are generalisable to all outcomes and effect measures. CONCLUSIONS: In this study we found that HRs from published AD were most likely to agree with those from IPD when the information size was large. Based on these findings, we provide guidance for determining systematically when standard AD meta-analysis will likely generate robust clinical conclusions, and when the IPD approach will add considerable value