311 research outputs found
Necroplanetology : simulating the tidal disruption of differentiated planetary material orbiting WD 1145+017
The WD 1145+017 system shows irregular transit features that are consistent with the tidal disruption of differentiated asteroids with bulk densities and bulk masses . We use the open-source N-body code REBOUND to simulate this disruption with different internal structures: varying the core volume fraction, mantle/core density ratio, and the presence/absence of a thin low-density crust. We allow the rubble pile to partially disrupt and capture lightcurves at a specific point during the disruption at cadences comparable to those from ground-based photometry. As a proof-of-concept we show that varying these structural parameters have observationally distinguishable effects on the transit lightcurve as the asteroid is disrupted and compare the simulation-generated lightcurves to data from Gary et al. With the caveat that our simulations do not model the sublimation in detail or account for its effects on orbital evolution, we find that a low core fraction and low mantle/core density ratio asteroid is most consistent with the stable transit feature present for multiple weeks circa 2016 April (referred to as G6121 in Gary et al. and A1 in Hallakoun et al.). Connecting tidal disruption simulations to photometry suggests characteristics for the interior structure and composition of an exoplanetary body, information that is only possible because we are observing the death of the planetary system in action. All-sky survey missions such as TESS and LSST will be able to detect other systems like WD 1145+017, creating a sample of subjects for a new subfield of planetary science: necroplanetology
Generalized Gravity and a Ghost
We show that generalized gravity theories involving the curvature invariants
of the Ricci tensor and the Riemann tensor as well as the Ricci scalar are
equivalent to multi- scalar-tensor gravities with four derivatives terms. By
expanding the action around a vacuum spacetime, the action is reduced to that
of the Einstein gravity with four derivative terms, and consequently there
appears a massive spin-2 ghost in such generalized gravity theories in addition
to a massive spin-0 field.Comment: 8 pages, a reference adde
Rofecoxib and cardiovascular adverse events in adjuvant treatment of colorectal cancer
Background
Selective cyclooxygenase inhibitors may retard the progression of cancer, but they
have enhanced thrombotic potential. We report on cardiovascular adverse events in
patients receiving rofecoxib to reduce rates of recurrence of colorectal cancer.
Methods
All serious adverse events that were cardiovascular thrombotic events were reviewed
in 2434 patients with stage II or III colorectal cancer participating in a randomized,
placebo-controlled trial of rofecoxib, 25 mg daily, started after potentially curative
tumor resection and chemotherapy or radiotherapy as indicated. The trial was terminated
prematurely owing to worldwide withdrawal of rofecoxib. To examine possible
persistent risks, we examined cardiovascular thrombotic events reported up to 24
months after the trial was closed.
Results
The median duration of active treatment was 7.4 months. The 1167 patients receiving
rofecoxib and the 1160 patients receiving placebo were well matched, with a median
follow-up period of 33.0 months (interquartile range, 27.6 to 40.1) and 33.4 months
(27.7 to 40.4), respectively. Of the 23 confirmed cardiovascular thrombotic events,
16 occurred in the rofecoxib group during or within 14 days after the treatment
period, with an estimated relative risk of 2.66 (from the Cox proportional-hazards
model; 95% confidence interval [CI], 1.03 to 6.86; P = 0.04). Analysis of the Antiplatelet
Trialists’ Collaboration end point (the combined incidence of death from
cardiovascular, hemorrhagic, and unknown causes; of nonfatal myocardial infarction;
and of nonfatal ischemic and hemorrhagic stroke) gave an unadjusted relative
risk of 1.60 (95% CI, 0.57 to 4.51; P = 0.37). Fourteen more cardiovascular thrombotic
events, six in the rofecoxib group, were reported within the 2 years after trial
closure, with an overall unadjusted relative risk of 1.50 (95% CI, 0.76 to 2.94;
P = 0.24). Four patients in the rofecoxib group and two in the placebo group died
from thrombotic causes during or within 14 days after the treatment period, and
during the follow-up period, one patient in the rofecoxib group and five patients in
the placebo group died from cardiovascular causes.
Conclusions
Rofecoxib therapy was associated with an increased frequency of adverse cardiovascular
events among patients with a median study treatment of 7.4 months’ duration.
(Current Controlled Trials number, ISRCTN98278138.
Thermodynamics Analysis of Refinery Sludge Gasification in Adiabatic Updraft Gasifier
Limited information is available about the thermodynamic evaluation for biomass gasification process using updraft gasifier. Therefore, to minimize errors, the gasification of dry refinery sludge (DRS) is carried out in adiabatic system at atmospheric pressure under ambient air conditions. The objectives of this paper are to investigate the physical and chemical energy and exergy of product gas at different equivalent ratios (ER). It will also be used to determine whether the cold gas, exergy, and energy efficiencies of gases may be maximized by using secondary air injected to gasification zone under various ratios (0, 0.5, 1, and 1.5) at optimum ER of 0.195. From the results obtained, it is indicated that the chemical energy and exergy of producer gas are magnified by 5 and 10 times higher than their corresponding physical values, respectively. The cold gas, energy, and exergy efficiencies of DRS gasification are in the ranges of 22.9–55.5%, 43.7–72.4%, and 42.5–50.4%, respectively. Initially, all 3 efficiencies increase until they reach a maximum at the optimum ER of 0.195; thereafter, they decline with further increase in ER values. The injection of secondary air to gasification zone is also found to increase the cold gas, energy, and exergy efficiencies. A ratio of secondary air to primary air of 0.5 is found to be the optimum ratio for all 3 efficiencies to reach the maximum values
The conformal frame freedom in theories of gravitation
It has frequently been claimed in the literature that the classical physical
predictions of scalar tensor theories of gravity depend on the conformal frame
in which the theory is formulated. We argue that this claim is false, and that
all classical physical predictions are conformal-frame invariants. We also
respond to criticisms by Vollick [gr-qc/0312041], in which this issue arises,
of our recent analysis of the Palatini form of 1/R gravity.Comment: 9 pages, no figures, revtex; final published versio
understanding the roles of cytokines and neutrophil activity and neutrophil apoptosis in the protective versus deleterious inflammatory response in pneumonia
SummaryInflammation is a double-edged sword in the outcome of pneumonia. On the one hand, an effective and timely inflammatory response is required to eliminate the invading respiratory pathogen. On the other, a toxic and prolonged inflammatory response may result in lung injury and poor outcomes, even in those receiving advanced medical care. This review focuses on recent understanding of the dynamics of the cytokine response, neutrophil activity, and responsiveness to cytokines and neutrophil lifespan as major elements of lung inflammation resulting in favorable or poor outcomes in lung infection primarily due to pneumococcus and influenza virus. Although some progress has been made in our understanding of the molecular mechanisms of the pneumonia inflammation axis composed of cytokines modulating neutrophil activation and neutrophil apoptosis, important questions remain to be answered. The degree of neutrophil activation, generation of reactive oxygen species, and the release of granule antimicrobial peptides play a key role in microbial pathogen clearance; however, prolonged neutrophil activation may contribute to lung injury and poor outcomes in pneumonia. Molecular markers of the mechanisms regulating neutrophil survival and apoptosis may help in the identification of novel therapeutic targets to modulate inflammation by inducing timely neutrophil apoptosis. A major task is to identify the mechanisms of dysregulation in inflammation leading to toxic responses, thereby targeting a biomarker and enabling timely therapies to modulate inflammation
corrections to the cosmological dynamics of inflation in the Palatini formulation
We investigate the corrections to the inflationary cosmological dynamics due
to a term in the Palatini formulation which may arise as quantum
corrections to the effective Lagrangian in early universe. We found that the
standard Friedmann equation will not be changed when the scalar field is in the
potential energy dominated era. However, in the kinetic energy dominated era,
the standard Friedmann equation will be modified and in the case of closed and
flat universe, the Modified Friedmann equation will automatically require that
the initial kinetic energy density of the scalar field must be in sub-Planckian
scale.Comment: 11 pages, no figures. Accepted by Class.Quant.Grav.v2:References
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