6,291 research outputs found
Four-colour photometry of eclipsing binaries. XLI uvby light curves for AD Bootis, HW Canis Majoris, SW Canis Majoris, V636 Centauri, VZ Hydrae, and WZ Ophiuchi
CONTEXT: Accurate mass, radius, and abundance determinations from binaries
provide important information on stellar evolution, fundamental to central
fields in modern astrophysics and cosmology.
AIMS: Within the long-term Copenhagen Binary Project, we aim to obtain
high-quality light curves and standard photometry for double-lined detached
eclipsing binaries with late A, F, and G type main-sequence components, needed
for the determination of accurate absolute dimensions and abundances, and for
detailed comparisons with results from recent stellar evolutionary models.
METHODS: Between March 1985 and July 2007, we carried out photometric
observations of AD Boo, HW CMA, SW CMa, V636 Cen, VZ Hya, and WZ Oph at the
Str"omgren Automatic Telescope at ESO, La Silla.
RESULTS: We obtained complete uvby light curves, ephemerides, and standard
uvby\beta indices for all six systems.For V636 Cen and HW CMa, we present the
first modern light curves, whereas for AD Boo, SW CMa, VZ Hya, and WZ Oph, they
are both more accurate and more complete than earlier data. Due to a high
orbital eccentricity (e = 0.50), combined with a low orbital inclination (i =
84.7), only one eclipse, close to periastron, occurs for HW CMa. For the two
other eccentric systems, V636 Cen (e = 0.134) and SW CMa (e = 0.316), apsidal
motion has been detected with periods of 5270 +/- 335 and 14900 +/- 3600 years,
respectively.Comment: Only change is: Bottom lines (hopefully) not truncated anymore.
Accepted for publication in Astonomy & Astrophysic
A critical analysis of Popper's experiment
An experiment which could decide against the Copenhagen interpretation of
quantum mechanics has been proposed by K. Popper and, subsequently, it has been
criticized by M.J. Collett and R. Loudon. Here we show that both the above
mentioned arguments are not correct because they are based on a misuse of basic
quantum rules.Comment: 12 pages, 3 figures, RevTex; to be published on PR
Causality re-established
Causality never gained the status of a "law" or "principle" in physics. Some
recent literature even popularized the false idea that causality is a notion
that should be banned from theory. Such misconception relies on an alleged
universality of reversibility of laws of physics, based either on determinism
of classical theory, or on the multiverse interpretation of quantum theory, in
both cases motivated by mere interpretational requirements for realism of the
theory. Here, I will show that a properly defined unambiguous notion of
causality is a theorem of quantum theory, which is also a falsifiable
proposition of the theory. Such causality notion appeared in the literature
within the framework of operational probabilistic theories. It is a genuinely
theoretical notion, corresponding to establish a definite partial order among
events, in the same way as we do by using the future causal cone on Minkowski
space. The causality notion is logically completely independent of the
misidentified concept of "determinism", and, being a consequence of quantum
theory, is ubiquitous in physics. In addition, as classical theory can be
regarded as a restriction of quantum theory, causality holds also in the
classical case, although the determinism of the theory trivializes it. I then
conclude arguing that causality naturally establishes an arrow of time. This
implies that the scenario of the "Block Universe" and the connected "Past
Hypothesis" are incompatible with causality, and thus with quantum theory: they
both are doomed to remain mere interpretations and, as such, not falsifiable,
similar to the hypothesis of "super-determinism". This article is part of a
discussion meeting issue "Foundations of quantum mechanics and their impact on
contemporary society".Comment: Presented at the Royal Society of London, on 11/12/ 2017, at the
conference "Foundations of quantum mechanics and their impact on contemporary
society". To appear on Philosophical Transactions of the Royal Society
Equivariant intersection cohomology of the circle actions
In this paper, we prove that the orbit space B and the Euler class of an
action of the circle S^1 on X determine both the equivariant intersection
cohomology of the pseudomanifold X and its localization. We also construct a
spectral sequence converging to the equivariant intersection cohomology of X
whose third term is described in terms of the intersection cohomology of B.Comment: Final version as accepted in RACSAM. The final publication is
available at springerlink.com; Revista de la Real Academia de Ciencias
Exactas, Fisicas y Naturales. Serie A. Matematicas, 201
A perspective on the landscape problem
I discuss the historical roots of the landscape problem and propose criteria
for its successful resolution. This provides a perspective to evaluate the
possibility to solve it in several of the speculative cosmological scenarios
under study including eternal inflation, cosmological natural selection and
cyclic cosmologies.Comment: Invited contribution for a special issue of Foundations of Physics
titled: Forty Years Of String Theory: Reflecting On the Foundations. 31
pages, no figure
Sensory Cells of the Fish Ear: A Hairy Enigma
Analysis of the structure of the ears in teleost fishes has led to the tentative suggestion that otolithic endorgans may function differently, in different species. Recently, evidence has demonstrated different 'types' of sensory hair cells can be found in the ears of teleost fishes, and individual hair cell types are found in discrete regions of individual sensory, epithelia. The presence of multiple hair cell types in fishes provides strong support to the hypothesis of regional differences in the responses of individual otolithic sensory epithelia. The finding of hair cell types in fishes that closely resemble those found in amniote vestibular endorgans also suggests that hair cell heterogeneity arose earlier in the evolution of the vertebrate ear than previously thought
The Science of Phylogenetic Systematics: Explanation, Prediction, and Test
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73926/1/j.1096-0031.1999.tb00279.x.pd
Quantum erasure within the Optical Stern-Gerlach Model
In the optical Stern-Gerlach effect the two branches in which the incoming
atomic packet splits up can display interference pattern outside the cavity
when a field measurement is made which erases the which-way information on the
quantum paths the system can follow. On the contrary, the mere possibility to
acquire this information causes a decoherence effect which cancels out the
interference pattern. A phase space analysis is also carried out to investigate
on the negativity of the Wigner function and on the connection between its
covariance matrix and the distinguishability of the quantum paths.Comment: 7 pages, 3 figure
Audition in sciaenid fishes with different swim bladder-inner ear configurations
We investigated how morphological differences in the auditory periphery of teleost fishes may relate to hearing capabilities. Two species of western Atlantic sciaenids were examined: weakfish (Cynoscion regalis, Block and Schneider) and spot (Leiostomus xanthurus, Lacepede). These species differ in the anatomical relationship between the swim bladder and the inner ear. In weakfish, the swim bladder has a pair of anterior horns that terminate close to the ear, while there are no extensions of the swim bladder in spot. Thus, the swim bladder in spot terminates at a greater distance from the ear when compared to weakfish. With the use of the auditory brainstem response technique, Cynoscion regalis were found to detect frequencies up to 2000 Hz, while Leiostomus xanthurus detected up to 700 Hz. There were, however, no significant interspecific differences in auditory sensitivity for stimuli between 200 and 700 Hz. These data support the hypothesis that the swim bladder can potentially expand the frequency range of detection
Third-order superintegrable systems separable in parabolic coordinates
In this paper, we investigate superintegrable systems which separate in
parabolic coordinates and admit a third-order integral of motion. We give the
corresponding determining equations and show that all such systems are
multi-separable and so admit two second-order integrals. The third-order
integral is their Lie or Poisson commutator. We discuss how this situation is
different from the Cartesian and polar cases where new potentials were
discovered which are not multi-separable and which are expressed in terms of
Painlev\'e transcendents or elliptic functions
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