39,562 research outputs found
The MST radar technique: Requirements for operational weather forecasting
There is a feeling that the accuracy of mesoscale forecasts for spatial scales of less than 1000 km and time scales of less than 12 hours can be improved significantly if resources are applied to the problem in an intensive effort over the next decade. Since the most dangerous and damaging types of weather occur at these scales, there are major advantages to be gained if such a program is successful. The interest in improving short term forecasting is evident. The technology at the present time is sufficiently developed, both in terms of new observing systems and the computing power to handle the observations, to warrant an intensive effort to improve stormscale forecasting. An assessment of the extent to which the so-called MST radar technique fulfills the requirements for an operational mesoscale observing network is reviewed and the extent to which improvements in various types of forecasting could be expected if such a network is put into operation are delineated
The MST radar technique: A tool for investigations of turbulence spectra
The feasibility of the MST radar as a tool for investigating turbulence spectra is discussed. Power spectral measurements using radar data are discussed. The characteristics of stratospheric turbulence are described. A model of the mesoscale turbulent process is developed
Representation Growth of Linear Groups
Let be a group and the number of its -dimensional
irreducible complex representations. We define and study the associated
representation zeta function \calz_\Gamma(s) = \suml^\infty_{n=1}
r_n(\Gamma)n^{-s}. When is an arithmetic group satisfying the
congruence subgroup property then \calz_\Gamma(s) has an ``Euler
factorization". The "factor at infinity" is sometimes called the "Witten zeta
function" counting the rational representations of an algebraic group. For
these we determine precisely the abscissa of convergence. The local factor at a
finite place counts the finite representations of suitable open subgroups
of the associated simple group over the associated local field . Here we
show a surprising dichotomy: if is compact (i.e. anisotropic over
) the abscissa of convergence goes to 0 when goes to infinity, but
for isotropic groups it is bounded away from 0. As a consequence, there is an
unconditional positive lower bound for the abscissa for arbitrary finitely
generated linear groups. We end with some observations and conjectures
regarding the global abscissa
Modal Interface Automata
De Alfaro and Henzinger's Interface Automata (IA) and Nyman et al.'s recent
combination IOMTS of IA and Larsen's Modal Transition Systems (MTS) are
established frameworks for specifying interfaces of system components. However,
neither IA nor IOMTS consider conjunction that is needed in practice when a
component shall satisfy multiple interfaces, while Larsen's MTS-conjunction is
not closed and Bene\v{s} et al.'s conjunction on disjunctive MTS does not treat
internal transitions. In addition, IOMTS-parallel composition exhibits a
compositionality defect. This article defines conjunction (and also
disjunction) on IA and disjunctive MTS and proves the operators to be
'correct', i.e., the greatest lower bounds (least upper bounds) wrt. IA- and
resp. MTS-refinement. As its main contribution, a novel interface theory called
Modal Interface Automata (MIA) is introduced: MIA is a rich subset of IOMTS
featuring explicit output-must-transitions while input-transitions are always
allowed implicitly, is equipped with compositional parallel, conjunction and
disjunction operators, and allows a simpler embedding of IA than Nyman's. Thus,
it fixes the shortcomings of related work, without restricting designers to
deterministic interfaces as Raclet et al.'s modal interface theory does.Comment: 28 page
Applications of MST radars: Meteorological applications
Applications of mesosphere stratosphere troposphere radar to mesoscale meteorology are discussed. The applications include using the radar either as a research tool to improve our understanding of certain dynamical systems or as part of a network used to provide input data for weather forecasting. The workhorse of the operational observing network is the radiosonde balloon which provides measurements of pressure, temperature, humidity, and winds up to heights of 16 to 20 km. Horizontal and vertical measurement capabilities, reflectivity data, derivable quantities and parameters, and special operational requirements are surveyed
A comparison of thunderstorm reflectivities measured at the VHF and UHF
Observations of thunderstorms made with two radars operating at different wavelengths of 70 cm and 5.67 m are compared. The first set of observations was made with the UHF radar at the Arecibo Observatory in Puerto Rico, and the second set was made with the Max-Planck-Institut fur Aeronomie VHF radar in the Harz Mountains in West Germany. Both sets of observations show large echo strengths in the convective region above the -10 C isothem. At UHF, there appears to be a contribution from both the precipitation echoes and the normal echoes due to scatter from turbulent variations in the refractive index
CDM, Feedback and the Hubble Sequence
We have performed TreeSPH simulations of galaxy formation in a standard LCDM
cosmology, including effects of star formation, energetic stellar feedback
processes and a meta-galactic UV field, and obtain a mix of disk, lenticular
and elliptical galaxies. The disk galaxies are deficient in angular momentum by
only about a factor of two compared to observed disk galaxies. The stellar
disks have approximately exponential surface density profiles, and those of the
bulges range from exponential to r^{1/4}, as observed. The bulge-to-disk ratios
of the disk galaxies are consistent with observations and likewise are their
integrated B-V colours, which have been calculated using stellar population
synthesis techniques. Furthermore, we can match the observed I-band
Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk
galaxies, (M/L_I), is about 0.8. The ellipticals and lenticulars have
approximately r^{1/4} stellar surface density profiles, are dominated by
non-disklike kinematics and flattened due to non-isotropic stellar velocity
distributions, again consistent with observations.Comment: 6 pages, incl. 4 figs. To appear in the proceedings of the
EuroConference "The Evolution of Galaxies: II - Basic Building Blocks", Ile
de La Reunion (France), 16-21 October 2001 (Slightly updated version). A much
more comprehensive paper about this work with links to pictures of some of
the galaxies can be found at http://babbage.sissa.it/abs/astro-ph/020436
Pulse-height defect due to electron interaction in dead layers of Ge/Li/ gamma-ray detectors
Study shows the pulse-height degradation of gamma ray spectra in germanium/lithium detectors to be due to electron interaction in the dead layers that exist in all semiconductor detectors. A pulse shape discrimination technique identifies and eliminates these defective pulses
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