4,650 research outputs found
A method to correct differential nonlinearities in subranging analog-to-digital converters used for digital gamma-ray spectroscopy
The influence on -ray spectra of differential nonlinearities (DNL) in
subranging, pipelined analog-to-digital converts (ADCs) used for digital
-ray spectroscopy was investigated. The influence of the DNL error on
the -ray spectra, depending on the input count-rate and the dynamic
range has been investigated systematically. It turned out, that the DNL becomes
more significant in -ray spectra with larger dynamic range of the
spectroscopy system. An event-by-event offline correction algorithm was
developed and tested extensively. This correction algorithm works especially
well for high dynamic ranges
Magnetic Phase Diagrams of Manganites-like Local-Moment Systems with Jahn-Teller distortions
We use an extended two-band Kondo lattice model (KLM) to investigate the
occurrence of different (anti-)ferromagnetic phases or phase separation
depending on several model parameters. With regard to CMR-materials like the
manganites we have added a Jahn-Teller term, direct antiferromagnetic coupling
and Coulomb interaction to the KLM. The electronic properties are
self-consistently calculated in an interpolating self-energy approach with no
restriction to classical spins and going beyond mean-field treatments. Further
on we do not have to limit the Hund's coupling to low or infinite values.
Zero-temperature phase diagrams are presented for large parameter intervals.
There are strong influences of the type of Coulomb interaction (intraband,
interband) and of the important parameters (Hund's coupling, direct
antiferromagnetic exchange, Jahn-Teller distortion), especially at intermediate
couplings.Comment: 11 pages, 9 figures. Accepted for publication in Phys. Rev.
Questioning the existence of a unique ground state structure for Si clusters
Density functional and quantum Monte Carlo calculations challenge the
existence of a unique ground state structure for certain Si clusters. For Si
clusters with more than a dozen atoms the lowest ten isomers are close in
energy and for some clusters entropic effects can change the energetic ordering
of the configurations. Isotope pure configurations with rotational symmetry and
symmetric configurations containing one additional isotope are disfavored by
these effects. Comparisons with experiment are thus difficult since a mixture
of configurations is to be expected at thermal equilibrium
Collisions of rigidly rotating disks of dust in General Relativity
We discuss inelastic collisions of two rotating disks by using the
conservation laws for baryonic mass and angular momentum. In particular, we
formulate conditions for the formation of a new disk after the collision and
calculate the total energy loss to obtain upper limits for the emitted
gravitational energy.Comment: 30 pages, 9 figure
Importance of high-angular-momentum channels in pseudopotentials for quantum Monte Carlo
Quantum Monte Carlo methods provide in principle a highly accurate treatment of the many-body problem of calculating the ground and excited states of condensed systems. In practice, however, uncontrolled errors, such as those arising from the fixed-node and pseudopotential approximations can be problematic. We show that the accuracy of some quantum Monte Carlo calculations is limited by the properties of currently available pseudopotentials. The use of pseudopotentials involves several approximations, and we will focus on one that is relatively simple to correct during the pseudopotential design phase. It is necessary to include angular-momentum channels in the pseudopotential for excited angular-momentum states and to choose the local channel appropriately to obtain accurate results. Variational and diffusion Monte Carlo calculations for Zn, O, and Si atoms and ions demonstrate these issues. Adding higher-angular-momentum channels into the pseudopotential description reduces such errors without a significant increase in computational cost
First phylogenetic analyses of galaxy evolution
The Hubble tuning fork diagram, based on morphology, has always been the
preferred scheme for classification of galaxies and is still the only one
originally built from historical/evolutionary relationships. At the opposite,
biologists have long taken into account the parenthood links of living entities
for classification purposes. Assuming branching evolution of galaxies as a
"descent with modification", we show that the concepts and tools of
phylogenetic systematics widely used in biology can be heuristically transposed
to the case of galaxies. This approach that we call "astrocladistics" has been
first applied to Dwarf Galaxies of the Local Group and provides the first
evolutionary galaxy tree. The cladogram is sufficiently solid to support the
existence of a hierarchical organization in the diversity of galaxies, making
it possible to track ancestral types of galaxies. We also find that morphology
is a summary of more fundamental properties. Astrocladistics applied to
cosmology simulated galaxies can, unsurprisingly, reconstruct the correct
"genealogy". It reveals evolutionary lineages, divergences from common
ancestors, character evolution behaviours and shows how mergers organize galaxy
diversity. Application to real normal galaxies is in progress. Astrocladistics
opens a new way to analyse galaxy evolution and a path towards a new
systematics of galaxies
Clock and Trigger Synchronization between Several Chassis of Digital Data Acquisition Modules
In applications with segmented high purity Ge detectors or other detector
arrays with tens or hundreds of channels, where the high development cost and
limited flexibility of application specific integrated circuits outweigh their
benefits of low power and small size, the readout electronics typically consist
of multi-channel data acquisition modules in a common chassis for power, clock
and trigger distribution, and data readout. As arrays become larger and reach
several hundred channels, the readout electronics have to be divided over
several chassis, but still must maintain precise synchronization of clocks and
trigger signals across all channels. This division becomes necessary not only
because of limits given by the instrumentation standards on module size and
chassis slot numbers, but also because data readout times increase when more
modules share the same data bus and because power requirements approach the
limits of readily available power supplies. In this paper, we present a method
for distributing clocks and triggers between 4 PXI chassis containing DGF
Pixie-16 modules with up to 226 acquisition channels per chassis in a data
acquisition system intended to instrument the over 600 channels of the SeGA
detector array at the National Superconducting Cyclotron Laboratory. Our
solution is designed to achieve synchronous acquisition of detector waveforms
from all channels with a jitter of less then 1 ns, and can be extended to a
larger number of chassis if desired.Comment: CAARI 200
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