1,208 research outputs found
Apparent wave function collapse caused by scattering
Some experimental implications of the recent progress on wave function
collapse are calculated. Exact results are derived for the center-of-mass wave
function collapse caused by random scatterings and applied to a range of
specific examples. The results show that recently proposed experiments to
measure the GRW effect are likely to fail, since the effect of naturally
occurring scatterings is of the same form as the GRW effect but generally much
stronger. The same goes for attempts to measure the collapse caused by quantum
gravity as suggested by Hawking and others. The results also indicate that
macroscopic systems tend to be found in states with (Delta-x)(Delta-p) =
hbar/sqrt(2), but microscopic systems in highly tiltedly squeezed states with
(Delta-x)(Delta-p) >> hbar.Comment: Final published version. 20 pages, Plain TeX, no figures. Online at
http://astro.berkeley.edu/~max/collapse.html (faster from the US), from
http://www.mpa-garching.mpg.de/~max/collapse.html (faster from Europe) or
from [email protected]
HAT-P-16b: A 4 Mj Planet Transiting A Bright Star On An Eccentric Orbit
We report the discovery of HAT-P-16b, a transiting extrasolar planet orbiting
the V = 10.8 mag F8 dwarf GSC 2792-01700, with a period P = 2.775960 +-
0.000003 d, transit epoch Tc = 2455027.59293 +- 0.00031 (BJD), and transit
duration 0.1276 +- 0.0013 d. The host star has a mass of 1.22 +- 0.04 Msun,
radius of 1.24 +- 0.05 Rsun, effective temperature 6158 +-80 K, and metallicity
[Fe/H] = +0.17 +- 0.08. The planetary companion has a mass of 4.193 +- 0.094
MJ, and radius of 1.289 +- 0.066 RJ yielding a mean density of 2.42 +- 0.35
g/cm3. Comparing these observed characteristics with recent theoretical models,
we find that HAT-P-16b is consistent with a 1 Gyr H/He-dominated gas giant
planet. HAT-P-16b resides in a sparsely populated region of the mass{radius
diagram and has a non-zero eccentricity of e = 0.036 with a significance of 10
sigma.Comment: Submitted to Ap
Scalar Field Quantum Inequalities in Static Spacetimes
We discuss quantum inequalities for minimally coupled scalar fields in static
spacetimes. These are inequalities which place limits on the magnitude and
duration of negative energy densities. We derive a general expression for the
quantum inequality for a static observer in terms of a Euclidean two-point
function. In a short sampling time limit, the quantum inequality can be written
as the flat space form plus subdominant correction terms dependent upon the
geometric properties of the spacetime. This supports the use of flat space
quantum inequalities to constrain negative energy effects in curved spacetime.
Using the exact Euclidean two-point function method, we develop the quantum
inequalities for perfectly reflecting planar mirrors in flat spacetime. We then
look at the quantum inequalities in static de~Sitter spacetime, Rindler
spacetime and two- and four-dimensional black holes. In the case of a
four-dimensional Schwarzschild black hole, explicit forms of the inequality are
found for static observers near the horizon and at large distances. It is show
that there is a quantum averaged weak energy condition (QAWEC), which states
that the energy density averaged over the entire worldline of a static observer
is bounded below by the vacuum energy of the spacetime. In particular, for an
observer at a fixed radial distance away from a black hole, the QAWEC says that
the averaged energy density can never be less than the Boulware vacuum energy
density.Comment: 27 pages, 2 Encapsulated Postscript figures, uses epsf.tex, typeset
in RevTe
Star formation triggered by HII regions in our Galaxy: First results for N49 from the Herschel infrared survey of the Galactic plane
It has been shown that by means of different physical mechanisms the
expansion of HII regions can trigger the formation of new stars of all masses.
This process may be important to the formation of massive stars but has never
been quantified in the Galaxy. We use Herschel-PACS and -SPIRE images from the
Herschel Infrared survey of the Galactic plane, Hi-GAL, to perform this study.
We combine the Spitzer-GLIMPSE and -MIPSGAL, radio-continuum and sub-millimeter
surveys such as ATLASGAL with Hi-GAL to study Young Stellar Objects (YSOs)
observed towards Galactic HII regions. We select a representative HII region,
N49, located in the field centered on l=30 degr observed as part of the Hi-GAL
Science Demonstration Phase, to demonstrate the importance Hi-GAL will have to
this field of research. Hi-GAL PACS and SPIRE images reveal a new population of
embedded young stars, coincident with bright ATLASGAL condensations. The Hi-GAL
images also allow us, for the first time, to constrain the physical properties
of the newly formed stars by means of fits to their spectral energy
distribution. Massive young stellar objects are observed at the borders of the
N49 region and represent second generation massive stars whose formation has
been triggered by the expansion of the ionized region. Hi-GAL enables us to
detect a population of young stars at different evolutionary stages, cold
condensations only being detected in the SPIRE wavelength range. The far IR
coverage of Hi-GAL strongly constrains the physical properties of the YSOs. The
large and unbiased spatial coverage of this survey offers us a unique
opportunity to lead, for the first time, a global study of star formation
triggered by HII regions in our Galaxy.Comment: 4 pages, 2 figures, accepted by A&A (Special issue on Herschel first
results
The Intrinsic Antiviral Defense to Incoming HSV-1 Genomes Includes Specific DNA Repair Proteins and Is Counteracted by the Viral Protein ICP0
Cellular restriction factors responding to herpesvirus infection include the ND10 components PML, Sp100 and hDaxx. During the initial stages of HSV-1 infection, novel sub-nuclear structures containing these ND10 proteins form in association with incoming viral genomes. We report that several cellular DNA damage response proteins also relocate to sites associated with incoming viral genomes where they contribute to the cellular front line defense. We show that recruitment of DNA repair proteins to these sites is independent of ND10 components, and instead is coordinated by the cellular ubiquitin ligases RNF8 and RNF168. The viral protein ICP0 targets RNF8 and RNF168 for degradation, thereby preventing the deposition of repressive ubiquitin marks and counteracting this repair protein recruitment. This study highlights important parallels between recognition of cellular DNA damage and recognition of viral genomes, and adds RNF8 and RNF168 to the list of factors contributing to the intrinsic antiviral defense against herpesvirus infection
Theories of Reference: What Was the Question?
The new theory of reference has won popularity. However, a number of noted philosophers have also attempted to reply to the critical arguments of Kripke and others, and aimed to vindicate the description theory of reference. Such responses are often based on ingenious novel kinds of descriptions, such as rigidified descriptions, causal descriptions, and metalinguistic descriptions. This prolonged debate raises the doubt whether different parties really have any shared understanding of what the central question of the philosophical theory of reference is: what is the main question to which descriptivism and the causal-historical theory have presented competing answers. One aim of the paper is to clarify this issue. The most influential objections to the new theory of reference are critically reviewed. Special attention is also paid to certain important later advances in the new theory of reference, due to Devitt and others
Transit timing variation in exoplanet WASP-3b
Photometric follow-ups of transiting exoplanets may lead to discoveries of
additional, less massive bodies in extrasolar systems. This is possible by
detecting and then analysing variations in transit timing of transiting
exoplanets. We present photometric observations gathered in 2009 and 2010 for
exoplanet WASP-3b during the dedicated transit-timing-variation campaign. The
observed transit timing cannot be explained by a constant period but by a
periodic variation in the observations minus calculations diagram. Simplified
models assuming the existence of a perturbing planet in the system and
reproducing the observed variations of timing residuals were identified by
three-body simulations. We found that the configuration with the hypothetical
second planet of the mass of about 15 Earth masses, located close to the outer
2:1 mean motion resonance is the most likely scenario reproducing observed
transit timing. We emphasize, however, that more observations are required to
constrain better the parameters of the hypothetical second planet in WASP-3
system. For final interpretation not only transit timing but also photometric
observations of the transit of the predicted second planet and the high
precision radial-velocity data are needed.Comment: MNRAS accepte
The importance of quantum decoherence in brain processes
Based on a calculation of neural decoherence rates, we argue that that the
degrees of freedom of the human brain that relate to cognitive processes should
be thought of as a classical rather than quantum system, i.e., that there is
nothing fundamentally wrong with the current classical approach to neural
network simulations. We find that the decoherence timescales ~10^{-13}-10^{-20}
seconds are typically much shorter than the relevant dynamical timescales
(~0.001-0.1 seconds), both for regular neuron firing and for kink-like
polarization excitations in microtubules. This conclusion disagrees with
suggestions by Penrose and others that the brain acts as a quantum computer,
and that quantum coherence is related to consciousness in a fundamental way.Comment: Minor changes to match accepted PRE version. 15 pages with 5 figs
included. Color figures and links at
http://www.physics.upenn.edu/~max/brain.html or from [email protected].
Physical Review E, in pres
Real Potential
There\u27s a student in my philosophy class who has real potential. I might express this thought in any of the following ways: She is potentially a philosopher ; She is a potential philosopher ; She has the potential to be a philosopher. The first way uses a cognate of potential as an adverb to modify is. The second ways uses potential as an adjective to modify philosopher. However, the third way uses potential as a noun to refer to something that the student has. What kind of thing is this potential? One worry about even asking this question is that this nominalization of the adjective potential suggests a metaphysical picture that is an artifact of language. This is even more strongly suggested by the less ambiguous nominalization potentiality. Once we have the term potentiality, we have a new kind of entity to countenance, and questions about its nature arise. One might argue, just because we use the word potentiality, we should not think that it refers to a thing that someone can have.
There is something disingenuous about such an argument. It proceeds as if the adverbial and adjectival uses of potential are unproblematic, and questions only arise with the nominalization. But it is not obvious what it means to potentially be something, or what it means to be a potential something. To say that someone is potentially a philosopher is to talk about a way of being that falls short of actuality. And a potential philosopher is not a kind of philosopher at all. So what is it? Each of the three above formulations is a modal claim. If there is anything philosophical puzzling about a potentiality claim, it is not going to go away by translating it into an equivalent modal claim.
In this chapter I defend the existence of potentialities against anti-realist arguments, and make a proposal as to their nature. The proposal, in short, is that potentialities are properties, specifically dispositions, though more needs to be said about properties and dispositions. I will do this in Part I. In Part II, I will address two lines of argument against potentialities: that they are reducible, and that they are causally inert
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