73 research outputs found
Forced Stratified Turbulence: Successive Transitions with Reynolds Number
Numerical simulations are made for forced turbulence at a sequence of
increasing values of Reynolds number, R, keeping fixed a strongly stable,
volume-mean density stratification. At smaller values of R, the turbulent
velocity is mainly horizontal, and the momentum balance is approximately
cyclostrophic and hydrostatic. This is a regime dominated by so-called pancake
vortices, with only a weak excitation of internal gravity waves and large
values of the local Richardson number, Ri, everywhere. At higher values of R
there are successive transitions to (a) overturning motions with local
reversals in the density stratification and small or negative values of Ri; (b)
growth of a horizontally uniform vertical shear flow component; and (c) growth
of a large-scale vertical flow component. Throughout these transitions, pancake
vortices continue to dominate the large-scale part of the turbulence, and the
gravity wave component remains weak except at small scales.Comment: 8 pages, 5 figures (submitted to Phys. Rev. E
Static overscreening and nonlinear response in the Hubbard Model
We investigate the static charge response for the Hubbard model. Using the
Slave-Boson method in the saddle-point approximation we calculate the charge
susceptibility. We find that RPA works quite well close to half-filling,
breaking, of course, down close to the Mott transition. Away from half filling
RPA is much less reliable: Already for very small values of the Hubbard
interaction U, the linear response becomes much more efficient than RPA,
eventually leading to overscreening already beyond quite moderate values of U.
To understand this behavior we give a simple argument, which implies that the
response to an external perturbation at large U should actually be strongly
non-linear. This prediction is confirmed by the results of exact
diagonalization.Comment: 10 pages, 7 figures, RevTe
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Locally advanced pancreatic cancer: Work-up, staging, and local intervention strategies
Locally advanced pancreatic cancer (LAPC) has several definitions but essentially is a nonmetastasized pancreatic cancer, in which upfront resection is considered not beneficial due to extensive vascular involvement and consequent high chance of a nonradical resection. The introduction of FOLFIRINOX chemotherapy and gemcitabine-nab-paclitaxel (gem-nab) has had major implications for the management and outcome of patients with LAPC. After 4–6 months induction chemotherapy, the majority of patients have stable disease or even tumor-regression. Of these, 12 to 35% are successfully downstaged to resectable disease. Several studies have reported a 30–35 months overall survival after resection; although it currently remains unclear if this is a result of the resection or the good response to chemotherapy. Following chemotherapy, selection of patients for resection is difficult, as contrast-enhanced computed-tomography (CT) scan is unreliable in differentiating between viable tumor and fibrosis. In case a resection is not considered possible but stable disease is observed, local ablative techniques are being studied, such as irreversible electroporation, radiofrequency ablation, and stereotactic body radiation therapy. Pragmatic, multicenter, randomized studies will ultimately have to confirm the exact role of both surgical exploration and ablation in these patients. Since evidence-based guidelines for the management of LAPC are lacking, this review proposes a standardized approach for the treatment of LAPC based on the best available evidence
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