11,098 research outputs found
The stability of Killing-Cauchy horizons in colliding plane wave space-times
It is confirmed rigorously that the Killing-Cauchy horizons, which sometimes
occur in space-times representing the collision and subsequent interaction of
plane gravitational waves in a Minkowski background, are unstable with respect
to bounded perturbations of the initial waves, at least for the case in which
the initial waves have constant aligned polarizations.Comment: 8 pages. To appear in Gen. Rel. Gra
Determination of confusion noise for far-infrared measurements
We present a detailed assessment of the far-infrared confusion noise imposed
on measurements with the ISOPHOT far-infrared detectors and cameras aboard the
ISO satellite. We provide confusion noise values for all measurement
configurations and observing modes of ISOPHOT in the 90<=lambda<=200um
wavelength range. Based on these results we also give estimates for cirrus
confusion noise levels at the resolution limits of current and future
instruments of infrared space telescopes: Spitzer/MIPS, ASTRO-F/FIS and
Herschel/PACS.Comment: A&A accepted; FITS files and appendices are available at:
http://www.konkoly.hu/staff/pkisscs/confnoise
Dirichlet Boundary Value Problems of the Ernst Equation
We demonstrate how the solution to an exterior Dirichlet boundary value
problem of the axisymmetric, stationary Einstein equations can be found in
terms of generalized solutions of the Backlund type. The proof that this
generalization procedure is valid is given, which also proves conjectures about
earlier representations of the gravitational field corresponding to rotating
disks of dust in terms of Backlund type solutions.Comment: 22 pages, to appear in Phys. Rev. D, Correction of a misprint in
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Techniques for the study of singularities with applications to resolution of 2-dimensional schemes
We give an overview of invariants of algebraic singularities over perfect
fields. We then show how they lead to a synthetic proof of embedded resolution
of singularities of 2-dimensional schemes.Comment: 26 pages; minor changes have been adde
Boosting Serotonin Increases Information Gathering by Reducing Subjective Cognitive Costs
Serotonin is implicated in the valuation of aversive costs, such as delay or physical effort. However, its role in governing sensitivity to cognitive effort, for example, deliberation costs during information gathering, is unclear. We show that treatment with a serotonergic antidepressant in healthy human individuals of either sex enhances a willingness to gather information when trying to maximize reward. Using computational modeling, we show this arises from a diminished sensitivity to subjective deliberation costs during the sampling process. This result is consistent with the notion that serotonin alleviates sensitivity to aversive costs in a domain-general fashion, with implications for its potential contribution to a positive impact on motivational deficits in psychiatric disorders.SIGNIFICANCE STATEMENT Gathering information about the world is essential for successfully navigating it. However, sampling information is costly, and we need to balance between gathering too little and too much information. The neurocomputational mechanisms underlying this arbitration between a putative gain, such as reward, and the associated costs, such as allocation of cognitive resources, remain unclear. In this study, we show that week-long daily treatment with a serotonergic antidepressant enhances a willingness to gather information when trying to maximize reward. Computational modeling indicates this arises from a reduced perception of aversive costs, rendering information gathering less cognitively effortful. This finding points to a candidate mechanism by which serotonergic treatment might help alleviate motivational deficits in a range of mental illnesses
Determination of the cosmic far-infrared background level with the ISOPHOT instrument
The cosmic infrared background (CIRB) consists mainly of the integrated light
of distant galaxies. In the far-infrared the current estimates of its surface
brightness are based on the measurements of the COBE satellite. Independent
confirmation of these results is still needed from other instruments. In this
paper we derive estimates of the far-infrared CIRB using measurements made with
the ISOPHOT instrument aboard the ISO satellite. The results are used to seek
further confirmation of the CIRB levels that have been derived by various
groups using the COBE data. We study three regions of very low cirrus emission.
The surface brightness observed with the ISOPHOT instrument at 90, 150, and 180
um is correlated with hydrogen 21 cm line data from the Effelsberg radio
telescope. Extrapolation to zero hydrogen column density gives an estimate for
the sum of extragalactic signal plus zodiacal light. The zodiacal light is
subtracted using ISOPHOT data at shorter wavelengths. Thus, the resulting
estimate of the far-infrared CIRB is based on ISO measurements alone. In the
range 150 to 180 um, we obtain a CIRB value of 1.08+-0.32+-0.30 MJy/sr quoting
statistical and systematic errors separately. In the 90 um band, we obtain a
2-sigma upper limit of 2.3 MJy/sr. The estimates derived from ISOPHOT
far-infrared maps are consistent with the earlier COBE results.Comment: Accepted for publication in A&A, 17 page
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