292 research outputs found
Agreement between Observed Rainfall Trends and Climate Change Simulations in the Southwest of Europe
Planar millimeter wave radar frontend for automotive applications
A fully integrated planar sensor for 77 GHz automotive applications is presented. The frontend consists of a transceiver multichip module and an electronically steerable microstrip patch array. The antenna feed network is based on a modified Rotman-lens and connected to the array in a multilayer approach offering higher integration. Furthermore, the frontend comprises a phase lock loop to allow proper frequency-modulated continuous wave (FMCW) radar operation. The latest experimental results verify the functionality of this advanced frontend design featuring automatic cruise control, precrash sensing and cut-in detection. These promising radar measurements give reason to a detailed theoretical investigation of system performance. Employing commercially available MMIC various circuit topologies are compared based on signal-tonoise considerations. Different scenarios for both sequential and parallel lobing hint to more advanced sensor designs and better performance. These improvements strongly depend on the availability of suitable MMIC and reliable packaging technologies. Within our present approach possible future MMIC developments are already considered and, thus, can be easily adapted by the flexible frontend design. Es wird ein integrierter planarer Sensor für 77 GHz Radaranwendungen vorgestellt. Das Frontend besteht aus einem Sende- und Empfangs-Multi-Chip-Modul und einer elektronisch schwenkbaren Antenne. Das Speisenetzwerk der Antenne basiert auf einer modifizierten Rotman- Linse. Für eine kompakte Bauweise sind Antenne und Speisenetzwerk mehrlagig integriert. Weiterhin umfasst das Frontend eine Phasenregelschleife für eine präzise Steuerung des frequenzmodulierten Dauerstrichradars. Die aktuellen Messergebnisse bestätigen die Funktionalit¨at dieses neuartigen Frontend-Designs, das automatische Geschwindigkeitsregelung, Kollisionswarnung sowie Nahbereichsüberwachung ermöglicht. Die Qualität der Messergebnisse hat weiterführende theoretische Untersuchungen über die potenzielle Systemleistungsfähigkeit motiviert. Unter Berücksichtigung von kommerziell erhältlichenMMICs werden verschiedene Schaltungstopologien auf der Grundlage des Signal-Rausch-Verhältnisses verglichen. Sowohl für sequenzielle als auch für parallele Ansteuerung der Antennenkeulen wird eine deutliche Leistungssteigerung ermittelt. Diese Verbesserungen hängen maßgeblich von der Verfügbarkeit geeigneter MMICs und einer zuverlässigen Aufbau- und Verbindungstechnik ab. Das vorliegende Frontend-Konzept kann auf Grund seiner Flexibilität leicht an derlei zukünftige Entwicklungen angepasst werden
Small and large polarons in nickelates, manganites, and cuprates
By comparing the optical conductivities of La_{1.67}Sr_{0.33}NiO_{4} (LSNO),
Sr_{1.5}La_{0.5}MnO_4 (SLMO), Nd_2CuO_{4-y} (NCO), and
Nd_{1.96}Ce_{0.04}CuO_{4} (NCCO), we have identified a peculiar behavior of
polarons in this cuprate family. While in LSNO and SLMO small polarons localize
into ordered structures below a transition temperature, in those cuprates the
polarons appear to be large, and at low T their binding energy decreases. This
reflects into an increase of the polaron radius, which may trigger coherent
transport.Comment: File latex, 15 p. incl. 4 Figs. epsf, to appear on the Journal of
Superconductivity - Proc. "Stripes 1996" - Roma Dec 199
Theory for Electron-Doped Cuprate Superconductors: d-wave symmetry order parameter
Using as a model the Hubbard Hamiltonian we determine various basic
properties of electron-doped cuprate superconductors like
and for a
spin-fluctuation-induced pairing mechanism. Most importantly we find a narrow
range of superconductivity and like for hole-doped cuprates -
symmetry for the superconducting order parameter. The superconducting
transition temperatures for various electron doping concentrations
are calculated to be much smaller than for hole-doped cuprates due to the
different Fermi surface and a flat band well below the Fermi level. Lattice
disorder may sensitively distort the symmetry via
electron-phonon interaction
Charge Ordering and Phase Competition in the Layered Perovskite Lasr2mn2o7
Charge-lattice fluctuations are observed in the layered perovskite manganite
LaSr2Mn2O7 by Raman spectroscopy as high as 340 K and with decreasing
temperature they become static and form a charge ordered (CO) phase below
TCO=210 K. In the static regime, superlattice reflections are observed through
neutron and x-ray diffraction with a propagation vector (h+1/4,k-1/4,l).
Crystallographic analysis of the CO state demonstrates that the degree of
charge and orbital ordering in this manganite is weaker than the charge
ordering in three dimensional perovskite manganites. A TN=170K a type-A
antiferromagnetism (AF) develops and competes with the charge ordering, that
eventually melts below T*=100K. High resolution diffraction measurements
suggest that that CO- and AF-states do not coincide within the same region in
the material but rather co-exist as separate phases. The transition to type-A
antiferromagnetism at lower temperatures is characterized by the competition
between these two phases.Comment: 9 pages, 6 figure
Infrared optical properties of Pr2CuO4
The ab-plane reflectance of a Pr2CuO4 single crystal has been measured over a
wide frequency range at a variety of temperatures, and the optical properties
determined from a Kramers-Kronig analysis. Above ~ 250 K, the low frequency
conductivity increases quickly with temperature; the resistivity follows the
form e^(E_a/k_BT), where E_a ~ 0.17 eV is much less than the inferred optical
gap of ~ 1.2 eV. Transport measurements show that at low temperature the
resistivity deviates from activated behavior and follows the form
e^[(T_0/T)^1/4], indicating that the dc transport in this material is due to
variable-range hopping between localized states in the gap. The four
infrared-active Eu modes dominate the infrared optical properties. Below ~ 200
K, a striking new feature appears near the low-frequency Eu mode, and there is
additional new fine structure at high frequency. A normal coordinate analysis
has been performed and the detailed nature of the zone-center vibrations
determined. Only the low-frequency Eu mode has a significant Pr-Cu interaction.
Several possible mechanisms related to the antiferromagnetism in this material
are proposed to explain the sudden appearance of this and other new spectral
features at low temperature.Comment: 11 pages, 7 embedded EPS figures, REVTeX
Resonant two-magnon Raman scattering in parent compounds of high-T superconductors.
We propose a theory of two-magnon Raman scattering from the insulating parent
compounds of high-T superconductors, which contains information not only on
magnetism, but also on the electronic properties in these materials. We use
spin density wave formalism for the Hubbard model, and study diagrammatically
the profile of the two-magnon scattering and its intensity dependence on the
incoming photon frequency both for and in the
resonant regime, in which the energy of the incident photon is close to the gap
between conduction and valence bands. In the nonresonant case, we identify the
diagrams which contribute to the conventional Loudon-Fleury Hamiltonian. In the
resonant regime, where most of the experiments have been done, we find that the
dominant contribution to Raman intensity comes from a different diagram, one
which allows for a simultaneous vanishing of all three of its denominators
(i.e., a triple resonance). We study this diagram in detail and show that the
triple resonance, combined with the spin-density-wave dispersion relation for
the carriers, explains the unusual features found in the two-magnon profile and
in the two-magnon peak intensity dependence on the incoming photon frequency.
In particular, our theory predicts a maximum of the two-magnon peak intensity
right at the upper edge of the features in the optical data, which has been one
of the key experimental puzzles.Comment: Revtex, 12 postscript figures (uuencoded
QTL detection for milk production traits in goats using a longitudinal model
Summary Eight paternal half-sib families were used to identify chromosomal regions associated with variation in the lactation curves of dairy goats. DNA samples from 162 animals were amplified by PCR for 37 microsatellite markers, from Capra hircus autosomes CHI3, CHI6, CHI14 and CHI20. Milk samples were collected during 6 years, and there were 897 records for milk yield (MY) and 814 for fat (FP) and protein percentage (PP). The analysis was conducted in two stages. First, a random regression model with several fixed effects was fitted to describe the lactation function, using a scale (α) plus four shape parameters: β and γ, both associated with a decrease in the slope of the curve, and δ and φ that are related to the increase in slope. Predictions of α, β, γ, δ and φ were regressed using an interval mapping model, and F-tests were used to test for quantitative trait loci (QTL) effects. Significant (p < 0.05) QTLs were found for: (i) MY: CHI6 at 70-80 cM for all parameters; CHI14 at 14 cM for δ and φ; (ii) FP: CHI14, at 63 cM was associated with β; CHI20, at 72 cM, showed association with α; (iii) PP: chromosomal regions associated with β were found at 59 cM in CHI3 and at 55 cM in CHI20 with α and γ. Analyses using more families and more animals will be useful to confirm or to reject these findings. © 2008 Blackwell Verlag, Berlin.Fil: Roldán, D.L.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; ArgentinaFil: Rabasa, Alicia Elvira. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Saldaño, S.. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; ArgentinaFil: Holgado, F.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Tucuman-santiago del Estero. Campo Experimental Regional Leales; ArgentinaFil: Poli, M. A.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; ArgentinaFil: Cantet, Rodolfo Juan Carlos. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal; Argentin
Systematics of two-component superconductivity in from microwave measurements of high quality single crystals
Systematic microwave surface impedance measurements of YBCO single crystals
grown in crucibles reveal new properties that are not directly seen
in similar measurements of other YBCO samples. Two key observations obtained
from complex conductivity are: a new normal conductivity peak at around 80K and
additional pairing below 65K. High pressure oxygenation of one of the crystals
still yields the same results ruling out any effect of macroscopic segregation
of O-deficient regions. A single complex order parameter cannot describe these
data, and the results suggest at least two superconducting components.
Comparisons with model calculations done for various decoupled two-component
scenarios (i.e. s+d, d+d) are presented. Systematics of three single crystals
show that the 80K quasiparticle peak is correlated with the normal state
inelastic scattering rate. Close to Tc, the data follow a mean-field behavior.
Overall, our results strongly suggest the presence of multiple pairing
temperature and energy scales in .Comment: 14 pages, 2-column, Revtex, 5 embedded postscript figures, uses
graphicx. Postscript version also available at
http://sagar.physics.neu.edu/preprints.htm
Compilation of a panel of informative single nucleotide polymorphisms for bovine identification in the Northern Irish cattle population
<p>Abstract</p> <p>Background</p> <p>Animal identification is pivotal in governmental agricultural policy, enabling the management of subsidy payments, movement of livestock, test scheduling and control of disease. Advances in bovine genomics have made it possible to utilise inherent genetic variability to uniquely identify individual animals by DNA profiling, much as has been achieved with humans over the past 20 years. A DNA profiling test based on bi-allelic single nucleotide polymorphism (SNP) markers would offer considerable advantages over current short tandem repeat (STR) based industry standard tests, in that it would be easier to analyse and interpret. In this study, a panel of 51 genome-wide SNPs were genotyped across panels of semen DNA from 6 common breeds for the purposes of ascertaining allelic frequency. For SNPs on the same chromosome, the extent of linkage disequilbrium was determined from genotype data by Expectation Maximization (EM) algorithm. Minimum probabilities of unique identification were determined for each breed panel. The usefulness of this SNP panel was ascertained by comparison to the current bovine STR Stockmarks II assay. A statistically representative random sampling of bovine animals from across Northern Ireland was assembled for the purposes of determining the population allele frequency for these STR loci and subsequently, the minimal probability of unique identification they conferred in sampled bovine animals from Northern Ireland.</p> <p>Results</p> <p>6 SNPs exhibiting a minor allele frequency of less than 0.2 in more than 3 of the breed panels were excluded. 2 Further SNPs were found to reside in coding areas of the cattle genome and were excluded from the final panel. The remaining 43 SNPs exhibited genotype frequencies which were in Hardy Weinberg Equilibrium. SNPs on the same chromosome were observed to have no significant linkage disequilibrium/allelic association. Minimal probabilities of uniquely identifying individual animals from each of the breeds were obtained and were observed to be superior to those conferred by the industry standard STR assay.</p> <p>Conclusions</p> <p>The 43 SNPs characterised herein may constitute a starting point for the development of a SNP based DNA identification test for European cattle.</p
- …