1,169 research outputs found
Elastic Wave Transmission at an Abrupt Junction in a Thin Plate, with Application to Heat Transport and Vibrations in Mesoscopic Systems
The transmission coefficient for vibrational waves crossing an abrupt
junction between two thin elastic plates of different widths is calculated.
These calculations are relevant to ballistic phonon thermal transport at low
temperatures in mesoscopic systems and the Q for vibrations in mesoscopic
oscillators. Complete results are calculated in a simple scalar model of the
elastic waves, and results for long wavelength modes are calculated using the
full elasticity theory calculation. We suggest that thin plate elasticty theory
provide a useful and tractable approximation to the full three dimensional
geometry.Comment: 35 pages, including 12 figure
Effects of burn status and conditioning on colonization of wood by stream macroinvertebrates
The combination of changing climate and anthropogenic activities is increasing the
probability of fire around the world. When fires occur in riparian zones, associated tree mortality can add wood to streams directly, or wood may fall onto the forest floor and remain there for some time before moving into stream channels. Because wood provides critical structure for aquatic macroinvertebrates, our objectives were to assess the effects of wood burn status, conditioning, and their interaction on (1) aquatic taxa community composition; (2) taxa and functional diversities; and (3) trait affinities. We conducted a field experiment
using pieces of freshly-cut wood for which we first manipulated the burn status (burned,
unburned). We then manipulated conditioning status by placing pieces directly into streams (no conditioning), leaving other pieces in streams for a year (water conditioning), or on the forest floor for a year before submergence (soil conditioning). Analyses included distance based redundancy analysis and linear mixed-effects modeling. Our results demonstrated that changes in wood quality resulting from fire may not alter per se the structure of
macroinvertebrate communities. Conditioning status, however, had significant effects on
taxonomic composition, taxa and functional diversities, and trait affinities of wood
invertebrate communities. The terrestrial legacy of soil conditioning was clearly important in structuring macroinvertebrate assemblages. Furthermore, taxonomic and functional patterns of stream macroinvertebrate colonization were not substantially different between burned and
unburned wood, even after a year of incubation in the stream or on the forest floor. This is an
important finding for the research topic on how wildfire structures aquatic communities. This information can function as a guide for post-fire stream and riparian management operations taking ecosystem function into account
Efeitos de sistemas de condução e porta-enxerto sobre a produção e qualidade da uva Cheninc Blanc no Vale do São Francisco: 4. ciclo de produção.
Este trabalho teve como objetivo avaliar os efeitos de sistemas de condução e do porta-enxerto sobre os componentes de produção e qualidade da uva Cheninc Blanc durante o 4. ciclo de produção no Vale do São Francisco
On the low-temperature lattice thermal transport in nanowires
We propose a theory of low temperature thermal transport in nano-wires in the
regime where a competition between phonon and flexural modes governs the
relaxation processes. Starting with the standard kinetic equations for two
different types of quasiparticles we derive a general expression for the
coefficient of thermal conductivity. The underlying physics of thermal
conductance is completely determined by the corresponding relaxation times,
which can be calculated directly for any dispersion of quasiparticles depending
on the size of a system. We show that if the considered relaxation mechanism is
dominant, then at small wire diameters the temperature dependence of thermal
conductivity experiences a crossover from to -dependence.
Quantitative analysis shows reasonable agreement with resent experimental
results.Comment: 12 pages, 3 eps figure
Control of Dephasing and Phonon Emission in Coupled Quantum Dots
We predict that phonon subband quantization can be detected in the non-linear
electron current through double quantum dot qubits embedded into nano-size
semiconductor slabs, acting as phonon cavities. For particular values of the
dot level splitting , piezo-electric or deformation potential
scattering is either drastically reduced as compared to the bulk case, or
strongly enhanced due to phonon van Hove singularities. By tuning via
gate voltages, one can either control dephasing, or strongly increase emission
into phonon modes with characteristic angular distributions.Comment: 4 pages, 3 figures, accepted for publication as Rapid Comm. in Phys.
Rev.
Giant Thermoelectric Effect from Transmission Supernodes
We predict an enormous order-dependent quantum enhancement of thermoelectric
effects in the vicinity of a higher-order `supernode' in the transmission
spectrum of a nanoscale junction. Single-molecule junctions based on
3,3'-biphenyl and polyphenyl ether (PPE) are investigated in detail. The
nonequilibrium thermodynamic efficiency and power output of a thermoelectric
heat engine based on a 1,3-benzene junction are calculated using many-body
theory, and compared to the predictions of the figure-of-merit ZT.Comment: 5 pages, 6 figure
Self-Consistent Relativistic Calculation of Nucleon Mean Free Path
We present a fully self-consistent and relativistic calculation of the
nucleon mean free path in nuclear matter and finite nuclei. Starting from the
Bonn potential, the Dirac-Brueckner-Hartree-Fock results for nuclear matter are
parametrized in terms of an effective - Lagrangian suitable for
the relativistic density-dependent Hartree-Fock (RDHF) approximation. The
nucleon mean free path in nuclear matter is derived from this effective
Lagrangian taking diagrams up to fourth-order into account. For the nucleon
mean free path in finite nuclei, we make use of the density determined by the
RDHF calculation in the local density approximation. Our microscopic results
are in good agreement with the empirical data and predictions by Dirac
phenomenology.Comment: 16 pages RevTex and 6 figures (paper, available upon request from
[email protected]) UI-NTH-931
Fungos associados e fitopatogênicos a espécies florestais nativas e exóticas na Amazônia.
Os ambientes amazônicos possuem grande diversidade de fungos fitopatogênicos e associados a manchas foliares em espécies florestais, entretanto são pouco estudados. A importância do levantamento de doenças no viveiro é fundamental para o sucesso na obtenção de mudas sadias, visto que as condições de alta umidade e densidade de plantas, temperatura, substrato e tecido vegetal tenro presentes neste ambiente favorecem o estabelecimento e desenvolvimento de doenças em níveis epidêmicos. Assim a identificação de novos registros e a descoberta de novas espécies de fungos fitopatogênicos contribuem para a ciência da sistemática e filogenia, assim como possibilita a tomada de decisão quanto ao melhor manejo das doenças com menor impacto arnbiental e econômico. Por outro lado, tem-se como limitações a ausência de esporulação desses fungos in vitro, o pequeno numero de micologistas, e a não identificação da espécie hospedeira
Quantum transport using the Ford-Kac-Mazur formalism
The Ford-Kac-Mazur formalism is used to study quantum transport in (1)
electronic and (2) harmonic oscillator systems connected to general reservoirs.
It is shown that for non-interacting systems the method is easy to implement
and is used to obtain many exact results on electrical and thermal transport in
one-dimensional disordered wires. Some of these have earlier been obtained
using nonequilibrium Green function methods. We examine the role that
reservoirs and contacts can have on determining the transport properties of a
wire and find several interesting effects.Comment: 10 pages, 4 figure
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