6,745 research outputs found
Moisture and dynamical interactions maintaining decoupled Arctic mixed-phase stratocumulus in the presence of a humidity inversion
Observations suggest that processes maintaining subtropical and Arctic stratocumulus differ, due to the different environments in which they occur. For example, specific humidity inversions (specific humidity increasing with height) are frequently observed to occur near cloud top coincident with temperature inversions in the Arctic, while they do not occur in the subtropics. In this study we use nested LES simulations of decoupled Arctic Mixed-Phase Stratocumulus (AMPS) clouds observed during the DOE Atmospheric Radiation Measurement Program's Indirect and SemiDirect Aerosol Campaign (ISDAC) to analyze budgets of water components, potential temperature, and turbulent kinetic energy. These analyses quantify the processes that maintain decoupled AMPS, including the role of humidity inversions. Key structural features include a shallow upper entrainment zone at cloud top that is located within the temperature and humidity inversions, a mixed layer driven by cloud-top cooling that extends from the base of the upper entrainment zone to below cloud base, and a lower entrainment zone at the base of the mixed layer. The surface layer below the lower entrainment zone is decoupled from the cloud mixed-layer system. Budget results show that cloud liquid water is maintained in the upper entrainment zone near cloud top (within a temperature and humidity inversion) due to a down gradient transport of water vapor by turbulent fluxes into the cloud layer from above and direct condensation forced by radiative cooling. Liquid water is generated in the updraft portions of the mixed-layer eddies below cloud top by buoyant destabilization. These processes cause at least 20% of the cloud liquid water to extend into the inversion. The redistribution of water vapor from the top of the humidity inversion to its base maintains the cloud layer, while the mixed layer-entrainment zone system is continually losing total water. In this decoupled system, the humidity inversion is the only source of water vapor for the cloud system, since water vapor from the surface layer is not efficiently transported into the mixed layer. Sedimentation of ice is the dominant sink of moisture from the mixed layer
Thermal infrared observations of near-Earth asteroid 2002 NY40
We obtained N-band observations of the Apollo asteroid 2002 NY40 during its
close Earth fly-by in August 2002 with TIMMI2 at the ESO 3.6 m telescope. The
photometric measurement allowed us to derive a radiometric diameter of
0.28+/-0.03 km and an albedo of 0.34+/-0.06 through the near-Earth asteroid
thermal model (NEATM) and a thermophysical model (TPM). The values are in
agreement with results from radar data, visual and near-IR observations. In
this first comparison between these two model approaches we found that the
empirical NEATM beaming parameter =1.0 corresponds to a thermal inertia
values of about 100 for a typical range of
surface roughness, assuming an equator-on viewing angle. Our TPM analysis
indicated that the surface of 2002 NY40 consists of rocky material with a thin
or no dust regolith. The asteroid very likely has a prograde sense of rotation
with a cold terminator at the time of our observations. Although both model
approaches can fit the thermal spectra taken at phase angles of 22
and 59, we did not find a consistent model solution that describes
all pieces of photometric and spectroscopic data. In addition to the 2002 NY40
analysis, we discuss the possibilities to distinguish between different models
with only very few photometric and/or spectroscopic measurements spread over a
range of phase angles.Comment: 6 pages, 4 figures, A&A accepte
The VIPERS Multi-Lambda Survey. II. Diving with massive galaxies in 22 square degrees since z = 1.5
We investigate the evolution of the galaxy stellar mass function (SMF) and
stellar mass density from redshift z=0.2 to z=1.5 of a <22-selected
sample with highly reliable photometric redshifts and over an unprecedentedly
large area. Our study is based on NIR observations carried out with WIRCam at
CFHT over the footprint of the VIPERS spectroscopic survey and benefits from
the high quality optical photometry from the CFHTLS and UV observations with
the GALEX satellite. The accuracy of our photometric redshifts is <
0.03 and 0.05 for the bright (22.5) samples,
respectively. The SMF is measured with ~760,000 galaxies down to =22 and
over an effective area of ~22.4 deg, the latter of which drastically
reduces the statistical uncertainties (i.e. Poissonian error & cosmic
variance). We point out the importance of a careful control of the photometric
calibration, whose impact becomes quickly dominant when statistical
uncertainties are reduced, which will be a major issue for future generation of
cosmological surveys with, e.g. EUCLID or LSST. By exploring the rest-frame
(NUV-r) vs (r-) color-color diagram separating star-forming and quiescent
galaxies, (1) we find that the density of very massive log() >
11.5 galaxies is largely dominated by quiescent galaxies and increases by a
factor 2 from z~1 to z~0.2, which allows for additional mass assembly via dry
mergers, (2) we confirm a scenario where star formation activity is impeded
above a stellar mass log() = 10.640.01, a value that
is found to be very stable at 0.2 < z < 1.5, (3) we discuss the existence of a
main quenching channel that is followed by massive star-forming galaxies, and
finally (4) we characterise another quenching mechanism required to explain the
clear excess of low-mass quiescent galaxies observed at low redshift.Comment: 22 pages, 20 figures. Accepted for publication in A&A. Version to be
publishe
Discovery of a New Nearby Star
We report the discovery of a nearby star with a very large proper motion of
5.06 +/- 0.03 arcsec/yr. The star is called SO025300.5+165258 and referred to
herein as HPMS (high proper motion star). The discovery came as a result of a
search of the SkyMorph database, a sensitive and persistent survey that is well
suited for finding stars with high proper motions. There are currently only 7
known stars with proper motions > 5 arcsec/yr. We have determined a preliminary
value for the parallax of 0.43 +/- 0.13 arcsec. If this value holds our new
star ranks behind only the Alpha Centauri system (including Proxima Centauri)
and Barnard's star in the list of our nearest stellar neighbors. The spectrum
and measured tangential velocity indicate that HPMS is a main-sequence star
with spectral type M6.5. However, if our distance measurement is correct, the
HPMS is underluminous by 1.2 +/- 0.7 mag.Comment: 5 pages, 3 figures. Submitted to ApJ Letter
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Construction of a deep shaft for Crossrail
An 8·2 m diameter, 37·5 m deep shaft has been successfully constructed from within the basement of a new development, Moorhouse, near Moorgate in the City of London. Programme constraints led to the shaft being constructed after completion of the foundations, basements and most of the superstructure for the development. At its closest point the shaft is less than 2 m from the large-diameter piles that support Moorhouse, and the presence of these foundations placed tight constraints on acceptable ground movements associated with construction of the shaft. The depth of the shaft is such that it penetrates through stiff London Clay and is founded at the bottom of the Lambeth Group. The paper describes the contingency measures to deal with potentially difficult ground conditions, including the water-bearing layers of the Lambeth Group. The construction processes included a complex temporary works dewatering system around the shaft, with the option to carry out additional dewatering from within the shaft during excavation. Provision was also made for radial grouting to ârestressâ the ground, to prevent long-term settlement of the Moorhouse piles, should the need arise. The success of the project was due, in no small part, to the detailed planning and consideration of contingency measures to deal with perceived risk
On nonsupersymmetric \BC^4/\BZ_N, tachyons, terminal singularities and flips
We investigate nonsupersymmetric \BC^4/\BZ_N orbifold singularities using
their description in terms of the string worldsheet conformal field theory and
its close relation with the toric geometry description of these singularities
and their possible resolutions. Analytic and numerical study strongly suggest
the absence of nonsupersymmetric Type II terminal singularities (i.e. with no
marginal or relevant blowup modes) so that there are always moduli or closed
string tachyons that give rise to resolutions of these singularities, although
supersymmetric and Type 0 terminal singularities do exist. Using gauged linear
sigma models, we analyze the phase structure of these singularities, which
often involves 4-dimensional flip transitions, occurring between resolution
endpoints of distinct topology. We then discuss 4-dim analogs of unstable
conifold-like singularities that exhibit flips, in particular their Type II GSO
projection and the phase structure. We also briefly discuss aspects of
M2-branes stacked at such singularities and nonsupersymmetric AdS_4\times
S^7/\BZ_N backgrounds.Comment: Latex, 43pgs incl. appendices, 2 eps figs, v2. minor clarifications
added, to appear in JHE
The VIPERS Multi-Lambda Survey. I. UV and NIR Observations, multi-color catalogues and photometric redshifts
We present observations collected in the CFHTLS-VIPERS region in the
ultraviolet (UV) with the GALEX satellite (far and near UV channels) and the
near infrared with the CFHT/WIRCam camera (-band) over an area of 22 and
27 deg, respectively. The depth of the photometry was optimized to measure
the physical properties (e.g., SFR, stellar masses) of all the galaxies in the
VIPERS spectroscopic survey. The large volume explored by VIPERS will enable a
unique investigation of the relationship between the galaxy properties and
their environment (density field and cosmic web) at high redshift (0.5 < z <
1.2). In this paper, we present the observations, the data reductions and the
build-up of the multi-color catalogues. The CFHTLS-T0007 (gri-{\chi}^2) images
are used as reference to detect and measure the -band photometry, while
the T0007 u-selected sources are used as priors to perform the GALEX photometry
based on a dedicated software (EMphot). Our final sample reaches ~25
(at 5{\sigma}) and ~22 (at 3{\sigma}). The large spectroscopic sample
(~51,000 spectroscopic redshifts) allows us to highlight the robustness of our
star/galaxy separation, and the reliability of our photometric redshifts with a
typical accuracy 0.04 and a catastrophic failure rate {\eta} <
2% down to i~23. We present various tests on the band completeness and
photometric redshift accuracy by comparing with existing, overlapping deep
photometric catalogues. Finally, we discuss the BzK sample of passive and
active galaxies at high redshift and the evolution of galaxy morphology in the
(NUV-r) vs (r-K_s) diagram at low redshift (z < 0.25) thanks to the high image
quality of the CFHTLS. The images, catalogues and photometric redshifts for 1.5
million sources (down to 25 or 22) are released and
available at this URL: http://cesam.lam.fr/vipers-mls/Comment: 14 pages, 16 figures. Accepted for publication in A&A. Version to be
publishe
Instanton operators in five-dimensional gauge theories
This article is distributed under the terms of the Creative Commons
Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in
any medium, provided the original author(s) and source are creditedN.L. is supported in part by STFC grant ST/J002798/1. C.P. is a Royal Society Research Fellow.N.L. is supported in part by STFC grant ST/J002798/1. C.P. is a Royal Society Research Fellow.N.L. is supported in part by STFC grant ST/J002798/1. OPen Aceess funded by SCOAP
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