217 research outputs found
The ac magnetic response of mesoscopic type II superconductors
The response of mesoscopic superconductors to an ac magnetic field is
numerically investigated on the basis of the time-dependent Ginzburg-Landau
equations (TDGL). We study the dependence with frequency and dc
magnetic field of the linear ac susceptibility
in square samples with dimensions of the order of the London penetration depth.
At the behavior of as a function of agrees very well
with the two fluid model, and the imaginary part of the ac susceptibility,
, shows a dissipative a maximum at the frequency
. In the presence of a magnetic field a
second dissipation maximum appears at a frequency . The most
interesting behavior of mesoscopic superconductors can be observed in the
curves obtained at a fixed frequency. At a fixed number of
vortices, continuously increases with increasing . We
observe that the dissipation reaches a maximum for magnetic fields right below
the vortex penetration fields. Then, after each vortex penetration event, there
is a sudden suppression of the ac losses, showing discontinuities in
at several values of . We show that these
discontinuities are typical of the mesoscopic scale and disappear in
macroscopic samples, which have a continuos behavior of . We
argue that these discontinuities in are due to the effect of
{\it nascent vortices} which cause a large variation of the amplitude of the
order parameter near the surface before the entrance of vortices.Comment: 12 pages, 9 figures, RevTex
Reflections on migration, community, and place
This paper explores different conceptualisations of migration, community, and place as an introduction to a themed issue of this journal concerned with the contextualisation of migrantsâ experiences across a range of nested scales. The purpose of this collection of papers is to draw out the spatial variability, contradictions, and ambiguities in migrant experiences and to explore conceptual frameworks for understanding the connections between migration, community, and place. The papers focus on local places of social encounter, particularly at the neighbourhood and city scale, but they also draw attention to the value of comparative research to tease out structural differences in opportunities, social context, and policy that underpin commonalities and differences in experience between localities
Performance of the CMS Cathode Strip Chambers with Cosmic Rays
The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device
in the CMS endcaps. Their performance has been evaluated using data taken
during a cosmic ray run in fall 2008. Measured noise levels are low, with the
number of noisy channels well below 1%. Coordinate resolution was measured for
all types of chambers, and fall in the range 47 microns to 243 microns. The
efficiencies for local charged track triggers, for hit and for segments
reconstruction were measured, and are above 99%. The timing resolution per
layer is approximately 5 ns
Performance and Operation of the CMS Electromagnetic Calorimeter
The operation and general performance of the CMS electromagnetic calorimeter
using cosmic-ray muons are described. These muons were recorded after the
closure of the CMS detector in late 2008. The calorimeter is made of lead
tungstate crystals and the overall status of the 75848 channels corresponding
to the barrel and endcap detectors is reported. The stability of crucial
operational parameters, such as high voltage, temperature and electronic noise,
is summarised and the performance of the light monitoring system is presented
Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley
TOI-732 is an M dwarf hosting two transiting planets that are located on the
two opposite sides of the radius valley. By doubling the number of available
space-based observations and increasing the number of radial velocity (RV)
measurements, we aim at refining the parameters of TOI-732 b and c. We also use
the results to study the slope of the radius valley and the density valley for
a well-characterised sample of M-dwarf exoplanets. We performed a global MCMC
analysis by jointly modelling ground-based light curves and CHEOPS and TESS
observations, along with RV time series both taken from the literature and
obtained with the MAROON-X spectrograph. The slopes of the M-dwarf valleys were
quantified via a Support Vector Machine (SVM) procedure. TOI-732 b is an
ultrashort-period planet ( d) with a radius
and a mass
(mean density g cm), while the
outer planet at d has ,
, and thus
g cm. Also taking into account our interior structure calculations,
TOI-732 b is a super-Earth and TOI-732 c is a mini-Neptune. Following the SVM
approach, we quantified
,
which is flatter than for Sun-like stars. In line with former analyses, we note
that the radius valley for M-dwarf planets is more densely populated, and we
further quantify the slope of the density valley as
.
Compared to FGK stars, the weaker dependence of the position of the radius
valley on the orbital period might indicate that the formation shapes the
radius valley around M dwarfs more strongly than the evolution mechanisms.Comment: 28 pages (17 in the main text), 18 figures (9 in the main text), 11
tables (7 in the main text). Accepted for publication in A&
A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
Planets with radii between that of the Earth and Neptune (hereafter referred
to as sub-Neptunes) are found in close-in orbits around more than half of all
Sun-like stars. Yet, their composition, formation, and evolution remain poorly
understood. The study of multi-planetary systems offers an opportunity to
investigate the outcomes of planet formation and evolution while controlling
for initial conditions and environment. Those in resonance (with their orbital
periods related by a ratio of small integers) are particularly valuable because
they imply a system architecture practically unchanged since its birth. Here,
we present the observations of six transiting planets around the bright nearby
star HD 110067. We find that the planets follow a chain of resonant orbits. A
dynamical study of the innermost planet triplet allowed the prediction and
later confirmation of the orbits of the rest of the planets in the system. The
six planets are found to be sub-Neptunes with radii ranging from 1.94 to 2.85
Re. Three of the planets have measured masses, yielding low bulk densities that
suggest the presence of large hydrogen-dominated atmospheres.Comment: Published in Nature on November 30, 2023. Supplementary Information
can be found in the online version of the paper in the journa
A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
Funding: A.C.Ca. and T.G.Wi. acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. O.Ba. acknowledges that has received funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (Grant agreement No. 865624). M.La. acknowledges funding from a UKRI Future Leader Fellowship, grant number MR/S035214/1. A.Br. was supported by the SNSA. Contributions at the Mullard Space Science Laboratory by E.M.Br. were supported by STFC through the consolidated grant ST/W001136/1. A.Br. was supported by the SNSA. Contributions at the Mullard Space Science Laboratory by E.M.Br. were supported by STFC through the consolidated grant ST/W001136/1. Ch.He. acknowledges support from the European Union H2020-MSCA-ITN-2019 under Grant Agreement no. 860470 (CHAMELEON).Planets with radii between that of the Earth and Neptune (hereafter referred to as 'sub-Neptunes') are found in close-in orbits around more than half of all Sun-like stars . However, their composition, formation and evolution remain poorly understood . The study of multiplanetary systems offers an opportunity to investigate the outcomes of planet formation and evolution while controlling for initial conditions and environment. Those in resonance (with their orbital periods related by a ratio of small integers) are particularly valuable because they imply a system architecture practically unchanged since its birth. Here we present the observations of six transiting planets around the bright nearby star HDâ110067. We find that the planets follow a chain of resonant orbits. A dynamical study of the innermost planet triplet allowed the prediction and later confirmation of the orbits of the rest of the planets in the system. The six planets are found to be sub-Neptunes with radii ranging from 1.94R to 2.85R . Three of the planets have measured masses, yielding low bulk densities that suggest the presence of large hydrogen-dominated atmospheres.PostprintPeer reviewe
The PLATO 2.0 mission
PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence) providing a wide field-of-view (2232 deg 2) and a large photometric magnitude range (4-16 mag). It focusses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmosphere. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA's Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science
Calibration of the CMS Drift Tube Chambers and Measurement of the Drift Velocity with Cosmic Rays
Peer reviewe
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