992 research outputs found
Radiation-reaction-induced evolution of circular orbits of particles around Kerr Black Holes
It is demonstrated that, in the adiabatic approximation, non-Equatorial
circular orbits of particles in the Kerr metric (i.e. orbits of constant
Boyer-Lindquist radius) remain circular under the influence of gravitational
radiation reaction. A brief discussion is given of conditions for breakdown of
adiabaticity and of whether slightly non-circular orbits are stable against the
growth of eccentricity.Comment: 23 pages. Revtex 3.0. Inquiries to [email protected]
The Ori-Soen time machine
Ori and Soen have proposed a spacetime which has closed causal curves on the
boundary of a region of normal causality, all within a region where the weak
energy condition (positive energy density) is satisfied. I analyze the causal
structure of this spacetime in some simplified models, show that the Cauchy
horizon is compactly generated, and argue that any attempt to build such a
spacetime with normal matter might lead to singular behavior where the
causality violation would otherwise take place.Comment: 5 pages, RevTeX, 7 figures with epsf, miscellaneous clarifications in
v2, minor updates to correspond to version to appear in PR
Cauchy horizon singularity without mass inflation
A perturbed Reissner-Nordstr\"om-de Sitter solution is used to emphasize the
nature of the singularity along the Cauchy horizon of a charged spherically
symmetric black hole. For these solutions, conditions may prevail under which
the mass function is bounded and yet the curvature scalar
diverges.Comment: typeset in RevTex, 13 page
Experimental Investigation of Gully Formation Under Low Pressure and Low Temperature Conditions
International audienceIntroduction: A large morphological diversity of gullies is observed on Earth and on Mars. Debris flow – a non-newtonian flow comprising a sediment-water mix – is a common process attributed to gully formation on both planets [1, 2]. Many variables can influence the morphology of debris flows (grainsizes, discharge , slope, soil moisture, etc) and their respective influences are difficult to disentangle in the field. Furthermore effects specific to the martian environment have not yet been explored in detail. Some preliminary laboratory simulations have already been performed that isolate some of these variables. Cold room experiments [3] were already perfomed to test the effect of a melted surface layer on the formation of linear gullies over sand dunes. Low pressure experiments [4] were performed to test the effect of the atmospheric pressure on erosional capacity and runout distance of the flows. Our aim is to develop a new set of experiments both under Martian atmospheric pressure and terrestrial atmospheric pressure in order to reproduce the variability of the observed morphologies under well constrained experimental conditions
Disentangling the Origin and Heating Mechanism of Supernova Dust: Late-Time Spitzer Spectroscopy of the Type IIn SN 2005ip
This paper presents late-time near-infrared and {\it Spitzer} mid-infrared
photometric and spectroscopic observations of warm dust in the Type IIn SN
2005ip in NGC 2906. The spectra show evidence for two dust components with
different temperatures. Spanning the peak of the thermal emission, these
observations provide strong constraints on the dust mass, temperature, and
luminosity, which serve as critical diagnostics for disentangling the origin
and heating mechanism of each component. The results suggest the warmer dust
has a mass of \msolar, originates from newly formed
dust in the ejecta, or possibly the cool, dense shell, and is continuously
heated by the circumstellar interaction. By contrast, the cooler component
likely originates from a circumstellar shock echo that forms from the heating
of a large, pre-existing dust shell ~\msolar~by the late-time
circumstellar interaction. The progenitor wind velocity derived from the blue
edge of the He 1 1.083 \micron~P Cygni profile indicates a progenitor eruption
likely formed this dust shell 100 years prior to the supernova explosion,
which is consistent with a Luminous Blue Variable (LBV) progenitor star.Comment: 12 pages, 10 figures, Accepted to Ap
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Methylation age acceleration does not predict mortality in schizophrenia.
Schizophrenia (SCZ) is associated with high mortality. DNA methylation levels vary over the life course, and pre-selected combinations of methylation array probes can be used to estimate "methylation age" (mAge). mAge correlates highly with chronological age but when it differs, termed mAge acceleration, it has been previously associated with all-cause mortality. We tested the association between mAge acceleration and mortality in SCZ and controls. We selected 190 SCZ cases and 190 controls from the Sweden Schizophrenia Study. Cases were identified from the Swedish Hospital Discharge Register with ≥5 specialist treatment contacts and ≥5 antipsychotic prescriptions. Controls had no psychotic disorder or antipsychotics. Subjects were selected if they had died or survived during follow-up (2:1 oversampling). Extracted DNA was assayed on the Illumina MethylationEPIC array. mAge was regressed on age at sampling to obtain mAge acceleration. Using Cox proportional hazards regression, the association between mAge acceleration and mortality was tested. After quality control, the following were available: n = 126 SCZ died, 63 SCZ alive, 127 controls died, 62 controls alive. In the primary analyses, we did not find a significant association between mAge acceleration and SCZ mortality (adjusted p > 0.005). Sensitivity analyses excluding SCZ cases with pre-existing cancer demonstrated a significant association between the Hannum mAge acceleration and mortality (hazard ratio = 1.13, 95% confidence interval = 1.04-1.22, p = 0.005). Per our pre-specified criteria, we did not confirm our primary hypothesis that mAge acceleration would predict subsequent mortality in people with SCZ, but we cannot rule out smaller effects or effects in patient subsets
Ordinary Economic Voting Behavior in the Extraordinary Election of Adolf Hitler
The enormous Nazi voting literature rarely builds on modern statistical or economic research. By adding these approaches, we find that the most widely accepted existing theories of this era cannot distinguish the Weimar elections from almost any others in any country. Via a retrospective voting account, we show that voters most hurt by the depression, and most likely to oppose the government, fall into separate groups with divergent interests. This explains why some turned to the Nazis and others turned away. The consequences of Hitler's election were extraordinary, but the voting behavior that led to it was no
Late-Time Circumstellar Interaction in a Spitzer Selected Sample of Type IIn Supernovae
Type IIn supernovae (SNe IIn) are a rare (< 10%) subclass of core-collapse
SNe that exhibit relatively narrow emission lines from a dense, pre-existing
circumstellar medium (CSM). In 2009, a warm Spitzer survey observed 30 SNe IIn
discovered in 2003 - 2008 and detected 10 SNe at distances out to 175 Mpc with
unreported late-time infrared emission, in some cases more than 5 years
post-discovery. For this single epoch of data, the warm-dust parameters suggest
the presence of a radiative heating source consisting of optical/X-ray emission
continuously generated by ongoing CSM interaction. Here we present
multi-wavelength follow-up observations of this sample of 10 SNe IIn and the
well-studied Type IIn SN 2010jl. A recent epoch of Spitzer observations reveals
ongoing mid-infrared emission from nine of the SNe in this sample. We also
detect three of the SNe in archival WISE data, in addition to SNe 1987A,
2004dj, and 2008iy. For at least five of the SNe in the sample, optical and/or
X-ray emission confirms the presence of radiative emission from ongoing CSM
interaction. The two Spitzer nondetections are consistent with the forward
shock overrunning and destroying the dust shell, a result that places upper
limits on the dust-shell size. The optical and infrared observations confirm
the radiative heating model and constrain a number of model parameters,
including progenitor mass-loss characteristics. All of the SNe in this sample
experienced an outburst on the order of tens to hundreds of years prior to the
SN explosion followed by periods of less intense mass loss. Although all
evidence points to massive progenitors, the variation in the data highlights
the diversity in SN IIn progenitor evolution. While these observations do not
identify a particular progenitor system, they demonstrate that future,
coordinated, multi-wavelength campaigns can constrain theoretical mass-loss
models.Comment: 10 pages, 6 figures, accepted to AJ (with comments
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