286 research outputs found
Unravelling the effects of calcium substitution in BaGd2CoO5 Haldane gap 1D material and its thermoelectric performance
Ecobenign and high-temperature-stable oxides are considered a promising alternative to traditional Bi2Te3-, Bi2Se3-, and PbTe-based thermoelectric materials. The quest for high-performing thermoelectric oxides is still open and, among other challenges, includes the screening of various materials systems for potentially promising electrical and thermal transport properties. In this work, a new family of acceptor-substituted Haldane gap 1D BaGd2CoO5 dense ceramic materials was characterized in this respect. The substitution of this material with calcium results in a general improvement of the electrical performance, contributed by an interplay between the charge carrier concentration and their mobility. Nevertheless, a relatively low electrical conductivity was measured, reaching ∼5 S/cm at 1175 K, resulting in a maximum power factor of ∼25 μW/(K × m2) at 1173 K for BaGd1.80Ca0.20CoO5. On the other hand, the unique anisotropic 1D structure of the prepared materials promotes efficient phonon scattering, leading to low thermal conductivities, rarely observed in oxide electroceramics. While the BaGd2–xCaxCoO5 materials show attractive Seebeck coefficient values in the range 210–440 μV/K, the resulting dimensionless figure of merit is still relatively low, reaching ∼0.02 at 1173 K. The substituted BaGd2–xCaxCoO5 ceramics show comparable thermoelectric performance in both inert and air atmospheres. These features highlight the potential relevance of this structure type for thermoelectric applications, with future emphasis placed on methods to improve conductivity.publishe
Energy consumption and capacity utilization of galvanizing furnaces
An explicit equation leading to a method for improving furnace efficiency is presented. This equation is dimensionless and can be applied to furnaces of any size and fuel type for the purposes of comparison. The implications for current furnace design are discussed. Currently the technique most commonly used to reduce energy consumption in galvanizing furnaces is to increase burner turndown. This is shown by the analysis presented here actually to worsen the thermal efficiency of the furnace, particularly at low levels of capacity utilization. Galvanizing furnaces are different to many furnaces used within industry, as a quantity of material (in this case zinc) is kept molten within the furnace at all times, even outside production periods. The dimensionless analysis can, however, be applied to furnaces with the same operational function as a galvanizing furnace, such as some furnaces utilized within the glass industry. © IMechE 2004
Towards the Event Horizon - High Resolution VLBI Imaging of Nuclei of Active Galaxies
We report on new developments in VLBI, with emphasis on experiments performed
at the highest frequencies possible to date (so called mm-VLBI). We have
observed the nucleus of M 87 (Virgo A) with global VLBI at 3 mm. We show a new
image of the inner-most jet region with an angular resolution of approx. 300 x
60 micro-arcseconds. In terms of Schwarzschild radii, this leads to an upper
limit of the jet base of approx. 100 x 20 Schwarzschild radii. We also report
on two VLBI pilot-experiments, which demonstrate the technical feasibility of
global VLBI at 150 and 230 GHz (2 mm and 1.3 mm). The experiments lead to upper
limits to the size of the unresolved AGN-cores in the 25 - 30 micro-arcsecond
range. The participation of new and near-future mm-telescopes (like APEX,
CARMA, SMA, LMT, ALMA, etc.) in global mm-VLBI will provide the necessary
sensitivity for the imaging of black holes and their immediate environment.Comment: To appear in the conference proceedings "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", held in Berlin,
Germany, May 17 - 21, 2004, ESO Astrophysical Symposia Series, in press.
Paper contains 2 pages, 1 figur
High-energy scissors mode
All the orbital M1 excitations, at both low and high energies, obtained from
a rotationally invariant QRPA, represent the fragmented scissors mode. The
high-energy M1 strength is almost purely orbital and resides in the region of
the isovector giant quadrupole resonance. In heavy deformed nuclei the
high-energy scissors mode is strongly fragmented between 17 and 25 MeV (with
uncertainties arising from the poor knowledge of the isovector potential). The
coherent scissors motion is hindered by the fragmentation and for single transitions in this region. The cross
sections for excitations above 17 MeV are one order of magnitude larger for E2
than for M1 excitations even at backward angles.Comment: 20 pages in RevTEX, 5 figures (uuencoded,put with 'figures') accepted
for publication in Phys.Rev.
Competing electric and magnetic excitations in backward electron scattering from heavy deformed nuclei
Important contributions to the cross sections of
low-lying orbital excitations are found in heavy deformed nuclei, arising
from the small energy separation between the two excitations with and 1, respectively. They are studied microscopically in QRPA using
DWBA. The accompanying response is negligible at small momentum transfer
but contributes substantially to the cross sections measured at for fm ( MeV)
and leads to a very good agreement with experiment. The electric response is of
longitudinal type for but becomes almost purely
transverse for larger backward angles. The transverse response
remains comparable with the response for fm
( MeV) and even dominant for MeV. This happens even at
large backward angles , where the dominance is
limited to the lower region.Comment: RevTeX, 19 pages, 8 figures included Accepted for publication in Phys
Rev
Dissociating Variability and Effort as Determinants of Coordination
When coordinating movements, the nervous system often has to decide how to distribute work across a number of redundant effectors. Here, we show that humans solve this problem by trying to minimize both the variability of motor output and the effort involved. In previous studies that investigated the temporal shape of movements, these two selective pressures, despite having very different theoretical implications, could not be distinguished; because noise in the motor system increases with the motor commands, minimization of effort or variability leads to very similar predictions. When multiple effectors with different noise and effort characteristics have to be combined, however, these two cost terms can be dissociated. Here, we measure the importance of variability and effort in coordination by studying how humans share force production between two fingers. To capture variability, we identified the coefficient of variation of the index and little fingers. For effort, we used the sum of squared forces and the sum of squared forces normalized by the maximum strength of each effector. These terms were then used to predict the optimal force distribution for a task in which participants had to produce a target total force of 4–16 N, by pressing onto two isometric transducers using different combinations of fingers. By comparing the predicted distribution across fingers to the actual distribution chosen by participants, we were able to estimate the relative importance of variability and effort of 1∶7, with the unnormalized effort being most important. Our results indicate that the nervous system uses multi-effector redundancy to minimize both the variability of the produced output and effort, although effort costs clearly outweighed variability costs
2mm Wavelength VLBI of SiO Masers and AGN
In April 2002 an array of antennas operating at 129GHz successfully detected
VLBI fringes on both continuum AGN and SiO maser sources. The 129GHz fringes on
maser sources represent the highest frequency spectral line VLBI detections to
date. The AGN 3C279 was detected on long baselines at both 129GHz (and at
147GHz, see Krichbaum et al in these proceedings) yielding fringe spacings of
50-56 micro arc seconds, an angular resolution record. The array consisted of
the University of Arizona Kittpeak 12m antenna, the Heinrich Hertz 10m
Telescope (HHT), and the IRAM 30m dish on Pico Veleta.
At 129GHz, a number of evolved stars and several young stellar objects
exhibit strong SiO maser emission in the v=1 J=3-2 transition. Preliminary
cross power spectra of SiO masers around the red hypergiant VYCMa on the
HHT-KittPeak baseline ~190km are consistent with multiple spatially separate
maser spots associated with the star. Future observations will include
continuum observations of the radio source at the Galactic Center, SgrA*, and
higher frequency maser lines including HCN and methanol.Comment: 4 pages, 3 figures, appears in: Proceedings of the 6th European VLBI
Network Symposium held on June 25th-28th in Bonn, Germany. Edited by: E. Ros,
R.W. Porcas, A.P. Lobanov, and J.A. Zensus. New version includes all editors
in paper heade
Determination of rosmarinic acid in Cordia verbenacea by liquid chromatography : applicability in seasonal study
Neste estudo, uma técnica de cromatografia lÃquida de alta resolução em fase reversa (CLAE-FR) para a determinação de ácido rosmarÃnico em Cordia verbenacea foi desenvolvida e validada. A análise de regressão foi avaliada, com observação de uma boa linearidade (r = 0,9997). Os valores obtidos para a precisão e exatidão estão de acordo com as diretrizes do ICH e com a legislação brasileira. Os valores de repetibilidade e precisão intermediária foram 2,79% e 4,76%, respectivamente. Os limites de detecção e de quantificação de ácido rosmarÃnico foram de 1,92 µg/mL e 5,81 µg/mL, respectivamente. Os resultados mostraram que o método desenvolvido é uma técnica por CLAE-FR de confiança para a determinação de ácido rosmarÃnico em tintura de C. verbenacea. Além disso, essa metodologia foi aplicada em estudo sazonal, que revela uma correlação positiva relativamente forte entre o perÃodo de chuvas e o teor de ácido rosmarÃnico.In this study, a reverse phase-high performance liquid chromatography (RP-HPLC) technique for determination of rosmarinic acid in the Cordia verbenacea was developed and validated. A regression analysis was performed, with the observation of good linearity (r =0.999949). The values obtained for precision and accuracy determination are in agreement with ICH guidelines and the Brazilian legislation. The values of repeatability and intermediate precision were 2.79% and 4.76%, respectively. The detection and the quantitation limits of the rosmarinic acid were 1.92 µg/mL and 5.81 µg/mL, respectively. The results demonstrated that the developed method is a reliable RP-HPLC technique for the determination of rosmarinic acid in C. verbenacea tincture. In addition, this methodology was applied at a seasonal study indicating relatively strong positive correlation between the rain period and the rosmarinic acid content
Towards the Event Horizon - The Vicinity of AGN at Micro-Arcsecond Resolution
We summarize the present status of VLBI experiments at 3 mm (86 GHz), 2 mm
(129-150 GHz) and 1.3 mm (215-230 GHz). We present and discuss a new 3 mm VLBI
map of M87 (Virgo A), which has a spatial resolution of only approx. 20
Schwarzschild radii. We discuss recent VLBI results for SgrA* and argue in
favor of new observations within an extended European mm-VLBI network, in order
to search for variability. We discuss the possibilities to image the `event
horizon' of a super-massive black hole at wavelengths < 2mm, and conclude that
the addition of large and sensitive millimetre telescopes such as CARMA, the
SMA, the LMT and ALMA will be crucial for this.Comment: 4 pages, 2 figures, Proceedings of the 7th European VLBI Network
Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R.
Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicent
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