5,895 research outputs found
Two new charismatic Pristimantis species (Anura: Craugastoridae) from the tepuis of “The Lost World” (Pantepui region, South America)
Two new colourful species of direct-developing frogs of the genus Pristimantis are described from the summit of two isolated tepuis (sandstone table mountains) in the Eastern Pantepui District of the Guiana Shield highlands. Pristimantis jamescameroni sp. nov. is described from the summit of Aprada-tepui from 2557-2571 m elevation, and P. imthurni sp. nov. is described from the summit of Ptaritepui at 2471 m elevation. Both species share the absence of a differentiated tympanic membrane and external tympanic annulus (but presence of tiny pharyngeal ostia), the presence of nuptial pads in males, and the presence of lateral fringes on fingers and toes, a combination of characters that immediately distinguishes them from all other known Pantepui congeners. The two new species are morphologically similar to each other and are phylogenetically closely related, but they can be distinguished based on colour pattern and morphological characters such as head proportions, dorsal skin texture, and condition of the supratympanic fold. The IUCN conservation status of the new species is considered as Endangered (EN) owing to their apparent very restricted ranges. The number of described Pristimantis species occurring exclusively on tepui (and faunistically related granitic mountains) summits and upper slopes now reaches eleven
The influence of forward-scattered light in transmission measurements of (exo)planetary atmospheres
[Abridged] The transmission of light through a planetary atmosphere can be
studied as a function of altitude and wavelength using stellar or solar
occultations, giving often unique constraints on the atmospheric composition.
For exoplanets, a transit yields a limb-integrated, wavelength-dependent
transmission spectrum of an atmosphere. When scattering haze and/or cloud
particles are present in the planetary atmosphere, the amount of transmitted
flux not only depends on the total optical thickness of the slant light path
that is probed, but also on the amount of forward-scattering by the scattering
particles. Here, we present results of calculations with a three-dimensional
Monte Carlo code that simulates the transmitted flux during occultations or
transits. For isotropically scattering particles, like gas molecules, the
transmitted flux appears to be well-described by the total atmospheric optical
thickness. Strongly forward-scattering particles, however, such as commonly
found in atmospheres of Solar System planets, can increase the transmitted flux
significantly. For exoplanets, such added flux can decrease the apparent radius
of the planet by several scale heights, which is comparable to predicted and
measured features in exoplanet transit spectra. We performed detailed
calculations for Titan's atmosphere between 2.0 and 2.8 micron and show that
haze and gas abundances will be underestimated by about 8% if
forward-scattering is ignored in the retrievals. At shorter wavelengths, errors
in the gas and haze abundances and in the spectral slope of the haze particles
can be several tens of percent, also for other Solar System planetary
atmospheres. We also find that the contribution of forward-scattering can be
fairly well described by modelling the atmosphere as a plane-parallel slab.Comment: Icarus, accepted for publicatio
A Quantum Rosetta Stone for Interferometry
Heisenberg-limited measurement protocols can be used to gain an increase in
measurement precision over classical protocols. Such measurements can be
implemented using, e.g., optical Mach-Zehnder interferometers and Ramsey
spectroscopes. We address the formal equivalence between the Mach-Zehnder
interferometer, the Ramsey spectroscope, and the discrete Fourier transform.
Based on this equivalence we introduce the ``quantum Rosetta stone'', and we
describe a projective-measurement scheme for generating the desired
correlations between the interferometric input states in order to achieve
Heisenberg-limited sensitivity. The Rosetta stone then tells us the same method
should work in atom spectroscopy.Comment: 8 pages, 4 figure
Information gap for classical and quantum communication in a Schwarzschild spacetime
Communication between a free-falling observer and an observer hovering above
the Schwarzschild horizon of a black hole suffers from Unruh-Hawking noise,
which degrades communication channels. Ignoring time dilation, which affects
all channels equally, we show that for bosonic communication using single and
dual rail encoding the classical channel capacity reaches a finite value and
the quantum coherent information tends to zero. We conclude that classical
correlations still exist at infinite acceleration, whereas the quantum
coherence is fully removed.Comment: 5 pages, 4 figure
Analytical model for flux saturation in sediment transport
The transport of sediment by a fluid along the surface is responsible for
dune formation, dust entrainment and for a rich diversity of patterns on the
bottom of oceans, rivers, and planetary surfaces. Most previous models of
sediment transport have focused on the equilibrium (or saturated) particle
flux. However, the morphodynamics of sediment landscapes emerging due to
surface transport of sediment is controlled by situations out-of-equilibrium.
In particular, it is controlled by the saturation length characterizing the
distance it takes for the particle flux to reach a new equilibrium after a
change in flow conditions. The saturation of mass density of particles
entrained into transport and the relaxation of particle and fluid velocities
constitute the main relevant relaxation mechanisms leading to saturation of the
sediment flux. Here we present a theoretical model for sediment transport
which, for the first time, accounts for both these relaxation mechanisms and
for the different types of sediment entrainment prevailing under different
environmental conditions. Our analytical treatment allows us to derive a closed
expression for the saturation length of sediment flux, which is general and can
thus be applied under different physical conditions
Super-resolving multi-photon interferences with independent light sources
We propose to use multi-photon interferences from statistically independent
light sources in combination with linear optical detection techniques to
enhance the resolution in imaging. Experimental results with up to five
independent thermal light sources confirm this approach to improve the spatial
resolution. Since no involved quantum state preparation or detection is
required the experiment can be considered an extension of the Hanbury Brown and
Twiss experiment for spatial intensity correlations of order N>2
Carbon monoxide and water vapor in the atmosphere of the non-transiting exoplanet HD 179949 b
(Abridged) In recent years, ground-based high-resolution spectroscopy has
become a powerful tool for investigating exoplanet atmospheres. It allows the
robust identification of molecular species, and it can be applied to both
transiting and non-transiting planets. Radial-velocity measurements of the star
HD 179949 indicate the presence of a giant planet companion in a close-in
orbit. Here we present the analysis of spectra of the system at 2.3 micron,
obtained at a resolution of R~100,000, during three nights of observations with
CRIRES at the VLT. We targeted the system while the exoplanet was near superior
conjunction, aiming to detect the planet's thermal spectrum and the radial
component of its orbital velocity. We detect molecular absorption from carbon
monoxide and water vapor with a combined S/N of 6.3, at a projected planet
orbital velocity of K_P = (142.8 +- 3.4) km/s, which translates into a planet
mass of M_P = (0.98 +- 0.04) Jupiter masses, and an orbital inclination of i =
(67.7 +- 4.3) degrees, using the known stellar radial velocity and stellar
mass. The detection of absorption features rather than emission means that,
despite being highly irradiated, HD 179949 b does not have an atmospheric
temperature inversion in the probed range of pressures and temperatures. Since
the host star is active (R_HK > -4.9), this is in line with the hypothesis that
stellar activity damps the onset of thermal inversion layers owing to UV flux
photo-dissociating high-altitude, optical absorbers. Finally, our analysis
favors an oxygen-rich atmosphere for HD 179949 b, although a carbon-rich planet
cannot be statistically ruled out based on these data alone.Comment: 10 pages, 9 figures. Accepted for publication in Astronomy and
Astrophysic
The physics of wind-blown sand and dust
The transport of sand and dust by wind is a potent erosional force, creates
sand dunes and ripples, and loads the atmosphere with suspended dust aerosols.
This article presents an extensive review of the physics of wind-blown sand and
dust on Earth and Mars. Specifically, we review the physics of aeolian
saltation, the formation and development of sand dunes and ripples, the physics
of dust aerosol emission, the weather phenomena that trigger dust storms, and
the lifting of dust by dust devils and other small-scale vortices. We also
discuss the physics of wind-blown sand and dune formation on Venus and Titan.Comment: 72 journal pagers, 49 figure
The apparent roughness of a sand surface blown by wind from an analytical model of saltation
We present an analytical model of aeolian sand transport. The model
quantifies the momentum transfer from the wind to the transported sand by
providing expressions for the thickness of the saltation layer and the apparent
surface roughness. These expressions are derived from basic physical principles
and a small number of assumptions. The model further predicts the sand
transport rate (mass flux) and the impact threshold (the smallest value of the
wind shear velocity at which saltation can be sustained). We show that, in
contrast to previous studies, the present model's predictions are in very good
agreement with a range of experiments, as well as with numerical simulations of
aeolian saltation. Because of its physical basis, we anticipate that our model
will find application in studies of aeolian sand transport on both Earth and
Mars
The GROUSE project III: Ks-band observations of the thermal emission from WASP-33b
In recent years, day-side emission from about a dozen hot Jupiters has been
detected through ground-based secondary eclipse observations in the
near-infrared. These near-infrared observations are vital for determining the
energy budgets of hot Jupiters, since they probe the planet's spectral energy
distribution near its peak. The aim of this work is to measure the Ks-band
secondary eclipse depth of WASP-33b, the first planet discovered to transit an
A-type star. This planet receives the highest level of irradiation of all
transiting planets discovered to date. Furthermore, its host-star shows
pulsations and is classified as a low-amplitude delta-Scuti. As part of our
GROUnd-based Secondary Eclipse (GROUSE) project we have obtained observations
of two separate secondary eclipses of WASP-33b in the Ks-band using the LIRIS
instrument on the William Herschel Telescope (WHT). The telescope was
significantly defocused to avoid saturation of the detector for this bright
star (K~7.5). To increase the stability and the cadence of the observations,
they were performed in staring mode. We collected a total of 5100 and 6900
frames for the first and the second night respectively, both with an average
cadence of 3.3 seconds. On the second night the eclipse is detected at the
12-sigma level, with a measured eclipse depth of 0.244+0.027-0.020 %. This
eclipse depth corresponds to a brightness temperature of 3270+115-160 K. The
measured brightness temperature on the second night is consistent with the
expected equilibrium temperature for a planet with a very low albedo and a
rapid re-radiation of the absorbed stellar light. For the other night the short
out-of-eclipse baseline prevents good corrections for the stellar pulsations
and systematic effects, which makes this dataset unreliable for eclipse depth
measurements. This demonstrates the need of getting a sufficient out-of-eclipse
baseline.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
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