2,312 research outputs found
Black-Hole Uncertainty Entails an Intrinsic Time Arrow. a Note on the Hawking-Penrose Controversy
Any theory that states that the basic laws of physics are time-symmetric must
be strictly deterministic. Only determinism enables time reversal of entropy
increase. A contradiction therefore arises between two statements of Hawking. A
simulation of a system under time reversal shows how an intrinsic time arrow
re-emerges, destroying the time reversal, when even slight failure of
determinism occurs.Comment: 9 pages, 4 figure
Consciousness makes a difference: A reluctant dualistâs confession
This paperâs outline is as follows. In sections 1-3 I give an exposi-tion of the Mind-Body Problem, with emphasis on what I believe to be the heart of the problem, namely, the Percepts-Qualia Nonidentity and its incompatibility with the Physical Closure Paradigm. In 4 I present the âQualia Inaction Postulateâ underlying all non-interactionist theo-ries that seek to resolve the above problem. Against this convenient postulate I propose in section 5 the âBafflement ArÂŹgument,â which is this paper's main thesis. Sections 6-11 critically disÂŹcuss attempts to dismiss the Bafflement Argument by the âBafÂŹflement=MisÂŹperception Equation.â Section 12 offers a refutation of all such attempts in the form of a concise âAsymmetry Proof.â Section 13 points out the bearing of the Bafflement Argument on the evolutionary role of consciousness while section 14 acknowledges the price that has to be paid for it in terms of basic physical principles. Section 15 summarizes the paper, pointing out the inescapability of interactionist dualism
Rotating Disks and Non-Kinematic Double Peaks
Double-peaked line profiles are commonly considered a hallmark of rotating
disks, with the distance between the peaks a measure of the rotation velocity.
However, double-peaks can arise also from radiative transfer effects in
optically thick non-rotating sources. Utilizing exact solutions of the line
transfer problem we present a detailed study of line emission from
geometrically thin Keplerian disks. We derive the conditions for emergence of
kinematic double peaks in optically thin and thick disks, and find that it is
generally impossible to disentangle the effects of kinematics and line opacity
in observed double-peaked profiles. Unless supplemented by additional
information, a double-peaked profile alone is not a reliable indicator of a
rotating disk. In certain circumstances, triple and quadruple profiles might be
better indicators of rotation in optically thick disks.Comment: MNRAS, to be publishe
Comments on (Non-)Chiral Gauge Theories and Type IIB Branes
We use type IIB brane configurations which were recently suggested by Hanany
and Zaffaroni to study four dimensional N=1 supersymmetric gauge theories. We
calculate the one loop beta function and realize Seiberg's duality using a
particular configuration. We also comment on the anomaly cancelation condition
in the case of chiral theories and the beta function in the case of chiral and
SO/Sp theories.Comment: 11 pages, Latex. 5 figures. Several changes in text and a reference
was added. Accepted to Phys.Lett.
Disk Outflows and High-Luminosity True Type 2 AGN
The absence of intrinsic broad line emission has been reported in a number of
active galactic nuclei (AGN), including some with high Eddington ratios. Such
"true type 2 AGN" are inherent to the disk-wind scenario for the broad line
region: Broad line emission requires a minimal column density, implying a
minimal outflow rate and thus a minimal accretion rate. Here we perform a
detailed analysis of the consequences of mass conservation in the process of
accretion through a central disk. The resulting constraints on luminosity are
consistent with all the cases where claimed detections of true type 2 AGN pass
stringent criteria, and predict that intrinsic broad line emission can
disappear at luminosities as high as about 4x erg s and any
Eddington ratio, though more detections can be expected at Eddington ratios
below about 1%. Our results are applicable to every disk outflow model,
whatever its details and whether clumpy or smooth, irrespective of the wind
structure and its underlying dynamics. While other factors, such as changes in
spectral energy distribution or covering factor, can affect the intensities of
broad emission lines, within this scenario they can only produce true type 2
AGN of higher luminosity then those prescribed by mass conservation.Comment: To appear in MNRAS. The L and M columns were inadvertently switched
in the original version (Thank you Giovanni Miniutti for catching). Corrected
in this versio
Dust Emission from IRC+10216
Infrared emission from the dust shell around IRC+10216 is analysed in detail,
employing a self-consistent model for radiatively driven winds around late-type
stars that couples the equations of motion and radiative transfer in the dust.
The resulting model provides agreement with the wealth of available data,
including the spectral energy distribution in the range 0.5--1000 \mic, and
visibility and array observations. Previous conclusions about two dust shells,
derived from modelling the data with a few single-temperature components of
different radii, are not supported by our results. The extended, continuous
temperature and density distributions derived from our model obviate the need
for such discrete shells. The IR properties vary with the stellar phase,
reflecting changes in both the dust condensation radius and the overall
optical depth -- as the luminosity increases from minimum to maximum,
increases while decreases. We find that the angular size of the
dust condensation zone varies from 0.3 arcsec at minimum light to 0.5 arcsec at
maximum. The shortage of flux at short wavelengths encountered in previous
studies is resolved by employing a grain size distribution that includes grains
larger than \about\ 0.1 \mic, required also for the visibility fits. This
distribution is in agreement with the one recently proposed by Jura in a study
that probed the outer regions of the envelope. Since our constraints on the
size distribution mostly reflect the envelope's inner regions, the agreement of
these independent studies is evidence against significant changes in grain
sizes through effects like sputtering or grain growth after the initial
formation at the dust condensation zone.Comment: LaTeX with 3 figures, requires MNRAS mn.sty; figures and/or complete
PS or PS.Z preprint (7 pages) available by anonymous ftp at
ftp://asta.pa.uky.edu/ivezic/irc10216/irc10216.ps (or fig1.ps, fig2.ps,
fig3.ps
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