536,709 research outputs found
The vertical cloud structure of the West African monsoon: a 4 year climatology using CloudSat and CALIPSO
The West African summer monsoon (WAM) is an important driver of the global climate and locally provides most of the annual rainfall. A solid climatological knowledge of the complex vertical cloud structure is invaluable to forecasters and modelers to improve the understanding of the WAM. In this paper, 4 years of data from the CloudSat profiling radar and CALIPSO are used to create a composite zonal mean vertical cloud and precipitation structure for the WAM. For the first time, the near-coincident vertical radar and lidar profiles allow for the identification of individual cloud types from optically thin cirrus and shallow cumulus to congestus and deep convection. A clear diurnal signal in zonal mean cloud structure is observed for the WAM, with deep convective activity enhanced at night producing extensive anvil and cirrus, while daytime observations show more shallow cloud and congestus. A layer of altocumulus is frequently observed over the Sahara at night and day, extending southward to the coastline, and the majority of this cloud is shown to contain supercooled liquid in the top. The occurrence of deep convective systems and congestus in relation to the position of the African easterly jet is studied, but only the daytime cumulonimbus distribution indicates some influence of the jet position
Nuclear shadowing in Glauber-Gribov theory with Q2-evolution
We consider deep inelastic scattering off nuclei in the Regge limit within
the Glauber-Gribov model. Using unitarized parton distribution functions for
the proton, we find sizeable shadowing effects on the nuclear total and
longitudinal structure functions, and , in the low-x limit.
Extending a fan-diagram analysis for the large-mass region of coherent
diffraction off nuclei to high Q2, we also find significant shadowing effects
in this kinematical regime. Finally, we discuss shortcomings of our approach
and possible extensions of the model to other kinematical regimes.Comment: 16 pages, 9 figure
A numerical analysis of transient planetary waves and the vertical structure in a meso-strato-troposphere model, part 1.4A
The structure of unstable planetary waves is computed by a quasi-geostrophic model extending from the surface up to 80 km by means of eigenvalue-eigenfunction techniques in spherical coordinates. Three kinds of unstable modes of distinct phase speeds and vertical structures are identified in the winter climate state: (1) the deep Green mode with its maximum amplitude in the stratosphere; (2) the deep Charney mode with its maximum amplitude in the troposphere: and (3) the shallow Charney mode which is largely confined to the troposphere. Both the Green mode and the deep Charney mode are characterized by very slow phase speeds. They are mainly supported by upward wave energy fluxes, but the local baroclinic energy conversion within the stratosphere also contributes in supporting these deep modes. The mesosphere and the troposphere are dynamically independent in the summer season decoupled by the deep stratospheric easterly. The summer mesosphere supports the easterly unstable waves 1-4. Waves 3 and 4 are identified with the observed mesospheric 2-day wave and 1.7-day wave, respectively
Numerical investigation of novel microwave applicators based on zero-order mode resonance for hyperthermia treatment of cancer
This paper characterizes three novel microwave applicators based on zero-order mode resonators for use in hyperthermia treatment of cancer. The radiation patterns are studied with numerical simulations in muscle tissue-equivalent model at 434 MHz. The relative performance of the applicators is compared in terms of reflection coefficient, current distribution, power deposition (SAR) pattern, effective field size in 2D and 3D tissue volumes, and penetration depth. One particular configuration generated the most uniform SAR pattern, with 25% SAR covering 84 % of the treatment volume extending to 1 cm depth under the aperture, while remaining above 58% coverage as deep as 3 cm under the aperture. Recommendations are made to further optimize this structure
Mapping the Universe: The 2010 Russell Lecture
Redshift surveys are a powerful tool of modern cosmology. We discuss two
aspects of their power to map the distribution of mass and light in the
universe: (1) measuring the mass distribution extending into the infall regions
of rich clusters and (2) applying deep redshift surveys to the selection of
clusters of galaxies and to the identification of very large structures (Great
Walls). We preview the HectoMAP project, a redshift survey with median redshift
z = 0.34 covering 50 square degrees to r= 21. We emphasize the importance and
power of spectroscopy for exploring and understanding the nature and evolution
of structure in the universe.Comment: 19 pages, 5 figures (2 videos available in the on-line journal
article
The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
The Three-Loop Splitting Functions in QCD: The Helicity-Dependent Case
We present the next-to-next-to-leading order (NNLO) contributions to the main
splitting functions for the evolution of longitudinally polarized parton
densities of hadrons in perturbative QCD. The quark-quark and gluon-quark
splitting functions have been obtained by extending our previous all Mellin-N
calculations to the structure function g_1 in electromagnetic deep-inelastic
scattering (DIS). Their quark-gluon and gluon-gluon counterparts have been
derived using third-order fixed-N calculations of structure functions in
graviton-exchange DIS, relations to the unpolarized case and mathematical tools
for systems of Diophantine equations. The NNLO corrections to the splitting
functions are small outside the region of small momentum fractions x where they
exhibit a large double-logarithmic enhancement, yet the corrections to the
evolution of the parton densities can be unproblematic down to at least x about
10^{-4}.Comment: 52 pages, Latex, 10 figures. FORM and Fortran files of the main
results available with the sourc
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