3,412 research outputs found
Relationship between resistivity and specific heat in a canonical non-magnetic heavy fermion alloy system: UPt_5-xAu_x
UPt_(5-x)Au_x alloys form in a single crystal structure, cubic AuBe_5-type,
over a wide range of concentrations from x = 0 to at least x = 2.5. All
investigated alloys, with an exception for x = 2.5, were non-magnetic. Their
electronic specific heat coefficient varies from about 60 (x = 2) to
about 700 mJ/mol K^2 (x = 1). The electrical resistivity for all alloys has a
Fermi-liquid-like temperature variation, \rho = \rho_o + AT^2, in the limit of
T -> 0 K. The coefficient A is strongly enhanced in the heavy-fermion regime in
comparison with normal and transition metals. It changes from about 0.01 (x =
0) to over 2 micro-ohm cm/K^2 (x = 1). A/\gamma^2, which has been postulated to
have a universal value for heavy-fermions, varies from about 10^-6 (x = 0, 0.5)
to 10^-5 micro-ohm cm (mol K/mJ)^2 (x > 1.1), thus from a value typical of
transition metals to that found for some other heavy-fermion metals. This ratio
is unaffected, or only weakly affected, by chemical or crystallographic
disorder. It correlates with the paramagnetic Curie-Weiss temperature of the
high temperature magnetic susceptibility.Comment: 5 pages, 5 eps figures, RevTe
Caracterização e análise estatÃstica de experimentos de agrossilvicultura.
São apresentados métodos de análise estatÃstica de experimentos de Agrossilvicultura, isto é, associação entre plantios ou povoamentos florestais com espécies anuais ou perenes. Aspectos de competição entre culturas agrÃcolas e árvores são considerados, como também os tipos de sistemas agroflorestais e possibilidades de sua aplicação no Brasil. Os métodos foram ilustrados com exemplos numéricos e suas vantagens e desvantagens discutidas
Variable-Speed Induction Motor Drives for Aircraft Environmental Control Compressors
New, more-efficient designs for aircraft jet engines are not capable of supplying the large quantities of bleed air necessary to provide pressurization and air conditioning for the environmental control systems (ECS) of the next generation of large passenger aircraft. System analysis and engineering have determined that electrically-driven ECS can help to maintain the improved fuel efficiencies; and electronic controllers and induction motors are now being developed in a NASA/NPD SBIR Program to drive both types of ECS compressors. Previous variable-speed induction motor/controller system developments and publications have primarily focused on field-oriented control, with large transient reserve power, for maximum acceleration and optimum response in actuator and robotics systems. The application area addressed herein is characterized by slowly-changing inputs and outputs, small reserve power capability for acceleration, and optimization for maximum efficiency. This paper therefore focuses on the differences between this case and the optimum response case, and shows the development of this new motor/controller approach. It starts with the creation of a new set of controller requirements. In response to those requirements, new control algorithms are being developed and implemented in an embedded computer, which is integrated into the motor controller closed loop. Buffered logic outputs are used to drive the power switches in a resonant-technology, power processor/motor-controller, at switching/resonant frequencies high enough to support efficient high-frequency induction motor operation at speeds up to 50,000-RP
Inhibition of growth factor mediated Akt phosphorylation in vascular smooth muscle cells by resveratrol: the contribution of SH2 domain containing phosphatase 2 and reactive oxygen species
Calcium-sensitive modulation of Ig capping: evidence supporting a cytoplasmic control of ligand-receptor complexes.
Resonance production by neutrinos: I. J=3/2 Resonances
The article contains general formulas for the production of J=3/2 resonances
by neutrinos and antineutrinos. It specializes to the P_{33}(1232) resonance
whose form factors are determined by theory and experiment and then are
compared with experimental results at low and high energies. It is shown that
the minimum in the low Q^2 region is a consequence of a combined effect from
the vanishing of the vector form factors, the muon mass and Pauli blocking.
Several improvements for the future investigations are suggested.Comment: 10 pages, LaTeX, misprints corrected, 1 reference adde
Quantitative Comparison of Sinc-Approximating Kernels for Medical Image Interpolation
Abstract. Interpolation is required in many medical image processing operations. From sampling theory, it follows that the ideal interpolation kernel is the sinc function, which is of infinite extent. In the attempt to obtain practical and computationally efficient image processing al-gorithms, many sinc-approximating interpolation kernels have been de-vised. In this paper we present the results of a quantitative comparison of 84 different sinc-approximating kernels, with spatial extents ranging from 2 to 10 grid points in each dimension. The evaluation involves the application of geometrical transformations to medical images from dif-ferent modalities (CT, MR, and PET), using the different kernels. The results show very clearly that, of all kernels with a spatial extent of 2 grid points, the linear interpolation kernel performs best. Of all kernels with an extent of 4 grid points, the cubic convolution kernel is the best (28 %- 75 % reduction of the errors as compared to linear interpolation). Even better results (44 %- 95 % reduction) are obtained with kernels of larger extent, notably the Welch, Cosine, Lanczos, and Kaiser windowed sinc kernels. In general, the truncated sinc kernel is one of the worst performing kernels.
Spin states of zigzag-edged Mobius graphene nanoribbons from first principles
Mobius graphene nanoribbons have only one edge topologically. How the
magnetic structures, previously associated with the two edges of zigzag-edged
flat nanoribbons or cyclic nanorings, would change for their Mobius
counterparts is an intriguing question. Using spin-polarized density functional
theory, we shed light on this question. We examine spin states of zigzag-edged
Mobius graphene nanoribbons (ZMGNRs) with different widths and lengths. We find
a triplet ground state for a Mobius cyclacene, while the corresponding
two-edged cyclacene has an open-shell singlet ground state. For wider ZMGNRs,
the total magnetization of the ground state is found to increase with the
ribbon length. For example, a quintet ground state is found for a ZMGNR. Local
magnetic moments on the edge carbon atoms form domains of majority and minor
spins along the edge. Spins at the domain boundaries are found to be
frustrated. Our findings show that the Mobius topology (i.e., only one edge)
causes ZMGNRs to favor one spin over the other, leading to a ground state with
non-zero total magnetization.Comment: 17 pages, 4 figure
Spectrotemporal Processing in Spectral Tuning Modules of Cat Primary Auditory Cortex
Spectral integration properties show topographical order in cat primary auditory cortex (AI). Along the iso-frequency domain, regions with predominantly narrowly tuned (NT) neurons are segregated from regions with more broadly tuned (BT) neurons, forming distinct processing modules. Despite their prominent spatial segregation, spectrotemporal processing has not been compared for these regions. We identified these NT and BT regions with broad-band ripple stimuli and characterized processing differences between them using both spectrotemporal receptive fields (STRFs) and nonlinear stimulus/firing rate transformations. The durations of STRF excitatory and inhibitory subfields were shorter and the best temporal modulation frequencies were higher for BT neurons than for NT neurons. For NT neurons, the bandwidth of excitatory and inhibitory subfields was matched, whereas for BT neurons it was not. Phase locking and feature selectivity were higher for NT neurons. Properties of the nonlinearities showed only slight differences across the bandwidth modules. These results indicate fundamental differences in spectrotemporal preferences - and thus distinct physiological functions - for neurons in BT and NT spectral integration modules. However, some global processing aspects, such as spectrotemporal interactions and nonlinear input/output behavior, appear to be similar for both neuronal subgroups. The findings suggest that spectral integration modules in AI differ in what specific stimulus aspects are processed, but they are similar in the manner in which stimulus information is processed
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