1,521 research outputs found
Vertical Tracer Mixing in Hot Jupiter Atmospheres
Aerosols appear to be ubiquitous in close-in gas giant atmospheres, and
disequilibrium chemistry likely impacts the emergent spectra of these planets.
Lofted aerosols and disequilibrium chemistry are caused by vigorous vertical
transport in these heavily irradiated atmospheres. Here we numerically and
analytically investigate how vertical transport should change over the
parameter space of spin-synchronized gas giants. In order to understand how
tracer transport depends on planetary parameters, we develop an analytic theory
to predict vertical velocities and mixing rates () and compare
the results to our numerical experiments. We find that both our theory and
numerical simulations predict that, if the vertical mixing rate is described by
an eddy diffusivity, then this eddy diffusivity should increase
with increasing equilibrium temperature, decreasing frictional drag strength,
and increasing chemical loss timescales. We find that the transition in our
numerical simulations between circulation dominated by a superrotating jet and
that with solely day-to-night flow causes a marked change in the vertical
velocity structure and tracer distribution. The mixing ratio of passive tracers
is greatest for intermediate drag strengths that corresponds to this transition
between a superrotating jet with columnar vertical velocity structure and
day-to-night flow with upwelling on the dayside and downwelling on the
nightside. Lastly, we present analytic solutions for as a
function of planetary effective temperature, chemical loss timescales, and
other parameters, for use as input to one-dimensional chemistry models of
spin-synchronized gas giant atmospheres.Comment: 25 pages, 12 figures, Accepted at Ap
Photon-assisted shot noise in graphene in the Terahertz range
When subjected to electromagnetic radiation, the fluctuation of the
electronic current across a quantum conductor increases. This additional noise,
called photon-assisted shot noise, arises from the generation and subsequent
partition of electron-hole pairs in the conductor. The physics of
photon-assisted shot noise has been thoroughly investigated at microwave
frequencies up to 20 GHz, and its robustness suggests that it could be extended
to the Terahertz (THz) range. Here, we present measurements of the quantum shot
noise generated in a graphene nanoribbon subjected to a THz radiation. Our
results show signatures of photon-assisted shot noise, further demonstrating
that hallmark time-dependant quantum transport phenomena can be transposed to
the THz range.Comment: includes supplemental materia
Coupling of Josephson flux-flow oscillators to an external RC load
We investigate by numerical simulations the behavior of the power dissipated
in a resistive load capacitively coupled to a Josephson flux flow oscillator
and compare the results to those obtained for a d.c. coupled purely resistive
load. Assuming realistic values for the parameters R and C, both in the high-
and in the low-Tc case the power is large enough to allow the operation of such
a device in applications.Comment: uuencoded, gzipped tar archive containing 11 pages of REVTeX text + 4
PostScript figures. To appear in Supercond. Sci. Techno
High prevalence of Sarcocystis calchasi in racing pigeon flocks in Germany
The apicomplexan parasite Sarcocystis calchasi (Coccidia: Eimeriorina: Sarcocystidae) is the causative agent of Pigeon Protozoal Encephalitis (PPE) and infects birds of the orders Columbiformes, Piciformes and Psittaciformes. Accipiter hawks (Aves: Accipitriformes) are the definitive hosts of this parasite. Infections of S. calchasi have been detected in Germany, the United States and Japan. However, the prevalence of the parasite in racing pigeon flocks has not yet been determined. Here, the first cross-sectional prevalence study to investigate S. calchasi in pigeon racing flocks was accomplished including 245 pigeon flocks across Germany. A total of 1,225 muscle biopsies, were taken between 2012 and 2016 and examined by semi-nested PCR for S. calchasi DNA targeting the ITS gene. Additionally, a questionnaire on construction of the aviary as well as management and health status of the flock was conducted. In 27.8% (95% C.I. = 22.3–33.8%) of the flocks, S. calchasi DNA was detected in at least one pigeon. Positive flocks were located in 15 out of 16 federal states. A significant increase of infected racing pigeons was seen in spring. Half-covered or open aviary constructions showed a trend of increase of the prevalence rate, while anti-coccidian treatment and acidified drinking water had no effects. The high prevalence and the geographical distribution of S. calchasi suggest a long-standing occurrence of the parasite in the German racing pigeon population. For pigeons presented with neurological signs or other symptoms possibly related to PPE, S. calchasi should be considered as a potential cause throughout Germany
Encheliophis chardewalli: A new species of carapidae (Ophidiiformes) from French Polynesia, with a redescription of Encheliophis vermicularis
A specimen of Encheliophis was found in the coelomic cavity of a sea cucumber in Moorea (French Polynesia). The skeletal morphology (skull, girdles, vertebrae) reveal it to be a new species, described herein as Encheliophis chardewalli. It is separable from all described species of Encheliophis (except Encheliophis vermicularis) by the lack of pectoral fins and from E. vermicularis by the larger and fewer teeth on the lower jaw (14 vs more than 20 in E. vermicularis) and by seven branchiostegal rays (vs six in E. vermicularis).Peer reviewe
A high sensitivity ultra-low temperature RF conductance and noise measurement setup
We report on the realization of a high sensitivity RF noise measurement
scheme to study small current fluctuations of mesoscopic systems at milliKelvin
temperatures. The setup relies on the combination of an interferometric ampli-
fication scheme and a quarter-wave impedance transformer, allowing the mea-
surement of noise power spectral densities with GHz bandwith up to five orders
of magnitude below the amplifier noise floor. We simultaneously measure the
high frequency conductance of the sample by derivating a portion of the signal
to a microwave homodyne detection. We describe the principle of the setup, as
well as its implementation and calibration. Finally, we show that our setup
allows to fully characterize a subnanosecond on-demand single electron source.
More generally, its sensitivity and bandwith make it suitable for applications
manipulating single charges at GHz frequencies.Comment: The following article has been submitted to Review of Scientific
Instrument
Hearing and morphological specializations of the mojarra (<i>Eucinostomus argenteus</i>)
The air-filled swimbladder acts as an acoustic amplifier for some fish by converting sound pressure into particle motion, which is transmitted to the inner ear. Here, we describe in detail the specialized connection between the swimbladder and ear in the mojarra, as well as a modified cone on the anal fin in which the posterior end of the swimbladder sits. Hearing tests show the mojarra has better hearing sensitivity than other species of fish without a connection. However, mojarras do not seem to use this adaptation for communication. Furthermore, the inclined position of the swimbladder may help the fish to catch their prey more easily, as the swimbladder will be horizontal when they are picking up benthic prey
Strong back-action of a linear circuit on a single electronic quantum channel
What are the quantum laws of electricity in mesoscopic circuits? This very
fundamental question has also direct implications for the quantum engineering
of nanoelectronic devices. Indeed, when a quantum coherent conductor is
inserted into a circuit, its transport properties are modified. In particular,
its conductance is reduced because of the circuit back-action. This phenomenon,
called environmental Coulomb blockade, results from the granularity of charge
transfers across the coherent conductor. Although extensively studied for a
tunnel junction in a linear circuit, it is only fully understood for arbitrary
short coherent conductors in the limit of small circuit impedances and small
conductance reduction. Here, we investigate experimentally the strong
back-action regime, with a conductance reduction of up to 90%. This is achieved
by embedding a single quantum channel of tunable transmission in an adjustable
on-chip circuit of impedance comparable to the resistance quantum
at microwave frequencies. The experiment reveals important deviations from
calculations performed in the weak back-action framework, and matches with
recent theoretical results. From these measurements, we propose a generalized
expression for the conductance of an arbitrary quantum channel embedded in a
linear circuit.Comment: 11 pages including supplementary information, to be published in
Nature Physic
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