11,798 research outputs found
The Direct Detectability of Giant Exoplanets in the Optical
Motivated by the possibility that a coronagraph will be put on WFIRST/AFTA,
we explore the direct detectability of extrasolar giant planets (EGPs) in the
optical. We quantify a planet's detectability by the fraction of its orbit for
which it is in an observable configuration (). Using a suite of
Monte Carlo experiments, we study the dependence of upon the
inner working angle (IWA) and minimum achievable contrast () of
the direct-imaging observatory; the planet's phase function, geometric albedo,
single-scattering albedo, radius, and distance from Earth; and the semi-major
axis distribution of EGPs. We calculate phase functions for a given geometric
or single-scattering albedo, assuming various scattering mechanisms. We find
that the Lambertian phase function can predict significantly larger
's with respect to the more realistic Rayleigh phase function.
For observations made with WFIRST/AFTA's baseline capabilities
(, ), Jupiter-like planets
orbiting stars within 10, 30, and 50 parsecs of Earth have volume-averaged
observability fractions of 12%, 3%, and 0.5%, respectively. At 10
parsecs, such observations yield for low- to
modest-eccentricity planets with semi-major axes in the range
AU. If , this range extends to AU. We find
that, in all but the most optimistic configurations, the probability for
detection in a blind search is low (). However, with orbital
parameter constraints from long-term radial-velocity campaigns and Gaia
astrometry, the tools we develop in this work can be used to determine both the
most promising systems to target and when to observe them.Comment: 16 pages, 16 figures. Accepted for publication in Ap
Introduction to the Special Issue on Liminal Hotspots
This article introduces a special issue of Theory and Psychology on liminal hotspots. A liminal hotspot is an occasion during which people feel they are caught suspended in the circumstances of a transition that has become permanent. The liminal experiences of ambiguity and uncertainty that are typically at play in transitional circumstances acquire an enduring quality that can be described as a “hotspot”. Liminal hotspots are characterized by dynamics of paradox, paralysis, and polarization, but they also intensify the potential for pattern shift. The origins of the concept are described followed by an overview of the contributions to this special issue
Critical Endpoint and Inverse Magnetic Catalysis for Finite Temperature and Density Quark Matter in a Magnetic Background
In this article we study chiral symmetry breaking for quark matter in a
magnetic background, , at finite temperature and quark chemical
potential, , making use of the Ginzburg-Landau effective action formalism.
As a microscopic model to compute the effective action we use the renormalized
quark-meson model. Our main goal is to study the evolution of the critical
endpoint, , as a function of the magnetic field strength, and
investigate on the realization of inverse magnetic catalysis at finite chemical
potential. We find that the phase transition at zero chemical potential is
always of the second order; for small and intermediate values of ,
moves towards small , while for larger it moves
towards moderately larger values of . Our results are in agreement with
the inverse magnetic catalysis scenario at finite chemical potential and not
too large values of the magnetic field, while at larger direct magnetic
catalysis sets in.Comment: 6 pages, 2 figure
On the notion of linguistic influence in syntax: Evidence from medieval Italo-Romance texts
This paper tackles the topic of Latin influence on Italo-Romance syntax by addressing the question how to combine the analysis of structural data with socio-historical reflections. It views the genre and discourse tradition of a given medieval text as governing the extent to which Latin is used as a model in this text. The paper proposes a methodology which incorporates consideration of the historical, cultural, and sociolinguistic context of language change, focusing on evidence from the development of present participles in Italo-Romance. The main conclusion is that, rather than talking about the general influence of Latin syntax on Italian, we should be examining the influence of particular Latin models on the syntax of different texts written in Italo-Romance varieties in a given historical period
On the Path Integral Representation for Spin Systems
We propose a classical constrained Hamiltonian theory for the spin. After the
Dirac treatment we show that due to the existence of second class constraints
the Dirac brackets of the proposed theory represent the commutation relations
for the spin. We show that the corresponding partition function, obtained via
the Fadeev-Senjanovic procedure, coincides with the one obtained using coherent
states. We also evaluate this partition function for the case of a single spin
in a magnetic field.Comment: To be published in J.Phys. A: Math. and Gen. Latex file, 12 page
Large isotope effect on in cuprates despite of a small electron-phonon coupling
We calculate the isotope coefficients and for the
superconducting critical temperature and the pseudogap temperature
in a mean-field treatment of the t-J model including phonons. The
pseudogap phase is identified with the -charge-density wave (-CDW) phase
in this model. Using the small electron-phonon coupling constant obtained previously in LDA calculations in YBaCuO,
is negative but negligible small whereas increases
from about 0.03 at optimal doping to values around 1 at small dopings in
agreement with the general trend observed in many cuprates. Using a simple
phase fluctuation model where the -CDW has only short-range correlations it
is shown that the large increase of at low dopings is rather universal
and does not depend on the existence of sharp peaks in the density of states in
the pseudogap state or on specific values of the phonon cutoff. It rather is
caused by the large depletion of spectral weight at low frequencies by the
-CDW and thus should also occur in other realizations of the pseudogap.Comment: 8 pages, 5 figures, to be publ. in PR
Effect of resonance decays on hadron elliptic flows
The influence of resonance decays on the elliptic flows of stable hadrons is
studied in the quark coalescence model. Although difference between the
elliptic flow of pions from resonance decays, except the rho meson, and that of
directly produced pions is appreciable, those for other stable hadrons are
small. Since there are more pions from the decays of rho mesons than from other
resonances, including resonance decays can only account partially the deviation
of final pion elliptic flow from the observed scaling of hadron elliptic flows,
i.e., the hadron elliptic flow per quark is the same at same transverse
momentum per quark. The remaining deviation can be explained by including the
effect due to the quark momentum distribution inside hadrons.Comment: 13 pages and 5 figures, version pubblished in PRC, updated references
and figure
- …