1,118 research outputs found
Some boundary effects in quantum field theory
We have constructed a quantum field theory in a finite box, with periodic
boundary conditions, using the hypothesis that particles living in a finite box
are created and/or annihilated by the creation and/or annihilation operators,
respectively, of a quantum harmonic oscillator on a circle. An expression for
the effective coupling constant is obtained showing explicitly its dependence
on the dimension of the box.Comment: 12 pages, Late
Generalized quantum field theory: perturbative computation and perspectives
We analyze some consequences of two possible interpretations of the action of
the ladder operators emerging from generalized Heisenberg algebras in the
framework of the second quantized formalism. Within the first interpretation we
construct a quantum field theory that creates at any space-time point particles
described by a q-deformed Heisenberg algebra and we compute the propagator and
a specific first order scattering process. Concerning the second one, we draw
attention to the possibility of constructing this theory where each state of a
generalized Heisenberg algebra is interpreted as a particle with different
mass.Comment: 19 page
Effect of phonon scattering by surface roughness on the universal thermal conductance
The effect of phonon scattering by surface roughness on the thermal
conductance in mesoscopic systems at low temperatures is calculated using full
elasticity theory. The low frequency behavior of the scattering shows novel
power law dependences arising from the unusual properties of the elastic modes.
This leads to new predictions for the low temperature depression of the thermal
conductance below the ideal universal value. Comparison with the data of Schwab
et al. [Nature 404, 974 (2000)] suggests that surface roughness on a scale of
the width of the thermal pathway is important in the experiment.Comment: 6 pages, 3 figure
Uso de agentes de biocontrole sobre a brusone das panículas do arroz em campo.
O objetivo foi avaliar a redução da severidade da brusone nas panículas do arroz com uso de rizobactérias Burkholderia pyrrocinia e Pseudomonas fluorensces e quatro isolados do fungo Trichoderma asperellum
Low-temperature heat transfer in nanowires
The new regime of low-temperature heat transfer in suspended nanowires is
predicted. It takes place when (i) only ``acoustic'' phonon modes of the wire
are thermally populated and (ii) phonons are subject to the effective elastic
scattering. Qualitatively, the main peculiarities of heat transfer originate
due to appearance of the flexural modes with high density of states in the wire
phonon spectrum. They give rise to the temperature dependence of the
wire thermal conductance. The experimental situations where the new regime is
likely to be detected are discussed.Comment: RevTex file, 1 PS figur
Quantum chaos in nanoelectromechanical systems
We present a theoretical study of the electron-phonon coupling in suspended
nanoelectromechanical systems (NEMS) and investigate the resulting quantum
chaotic behavior. The phonons are associated with the vibrational modes of a
suspended rectangular dielectric plate, with free or clamped boundary
conditions, whereas the electrons are confined to a large quantum dot (QD) on
the plate's surface. The deformation potential and piezoelectric interactions
are considered. By performing standard energy-level statistics we demonstrate
that the spectral fluctuations exhibit the same distributions as those of the
Gaussian Orthogonal Ensemble (GOE) or the Gaussian Unitary Ensemble (GUE),
therefore evidencing the emergence of quantum chaos. That is verified for a
large range of material and geometry parameters. In particular, the GUE
statistics occurs only in the case of a circular QD. It represents an anomalous
phenomenon, previously reported for just a small number of systems, since the
problem is time-reversal invariant. The obtained results are explained through
a detailed analysis of the Hamiltonian matrix structure.Comment: 14 pages, two column
Pemetrexed na segunda linha de tratamento do carcinoma do pulmão de não pequenas células – A experiência portuguesa
AbstractUntil 2004, docetaxel in monotherapy was the standard for second-line treatment of non-small cell lung cancer (NSCLC). Pemetrexed (P) has shown similar activity in this setting with a better adverse event profile. In Portugal, it was introduced in October of 2004.We have carried out a retrospective analysis of patients (pts) who received P for second-line NSCLC in Portugal from October 2004 to December 2006. Data were collected from the records of pts with locally advanced or metastatic NSCLC and failed first-line chemotherapy enrolled in centers participating in the Portuguese Lung Cancer Study Group (GECP). Objective response (OR; complete [CR] or partial [PR] response) was evaluated using RECIST and safety was assessed using serious or non-serious adverse events (SAEs/AEs).By December 2006, 19 GECP centers had enrolled 244 pts who had received P for ≥1cycle, and were considered evaluable for both objective response and safety. Demography: male/female, 175/69; median age, 57.0years (range 20-81); smoking status, y/ex/n, 116/57/71; adenocarcinoma / squamous-cell carcinoma/other histology, 141/72/31; mean time to progression (TTP) 8.07months. Disease control in 209 evaluable pts was observed in 116 (55.5%): 2 CR, 45 PR and 69 SD; mean TTP 4.70months. The majority of AEs were grade 3 anemia (15 pts) and neutropenia (18 pts). The mean overall survival was 17.27months.Our retrospective analysis has observed a similar disease control rate with P in 2nd line (55.5%), and TTP (4.7months) in our current unselected population to that published in the literature. P is an option for second-line NSCLC with a good tolerability.Rev Port Pneumol 2008; XIV (Sup.2): S9-S2
Vine performance and physicochemical characteristics of berries of new wine grape cultivars in the São Francisco Valley.
This study aimed to evaluate the performance and characteristics of the grapes as subsidies to the recommendation of new wine grape cultivars for the São Francisco Valley
Survey for Emission-Line Galaxies: Universidad Complutense de Madrid List 3
A new low-dispersion objective-prism search for low-redshift (z<0.045)
emission-line galaxies (ELG) has been carried out by the Universidad
Complutense de Madrid with the Schmidt Telescope at the Calar-Alto Observatory.
This is a continuation of the UCM Survey, which was performed by visual
selection of candidates in photographic plates via the presence of the
Halpha+[NII]6584 blend in emission. In this new list we have applied an
automatic procedure, fully developed by us, for selecting and analyzing the ELG
candidates on the digitized images obtained with the MAMA machine. The analyzed
region of the sky covers 189 square degrees in nine fields near R.A.=14h & 17h,
Dec=25 deg. The final sample contains 113 candidates. Special effort has been
made to obtain a large amount of information directly from our uncalibrated
plates by using several external calibrations. The parameters obtained for the
ELG candidates allow for the study of the statistical properties for the
sample.Comment: 13 pages, 18 PostScript figures, 6 JPEG figures, Table 2 corrected.
Accepted for publication in Astrophysical Journal Supplements, also available
at http://www.ucm.es/info/Astrof/opera/LIST3_ApJS99
Anomalous quantum chaotic behavior in nanoelectromechanical structures
It is predicted that for sufficiently strong electron-phonon coupling an
anomalous quantum chaotic behavior develops in certain types of suspended
electro-mechanical nanostructures, here comprised by a thin cylindrical quantum
dot (billiard) on a suspended rectangular dielectric plate. The deformation
potential and piezoelectric interactions are considered. As a result of the
electron-phonon coupling between the two systems the spectral statistics of the
electro-mechanic eigenenergies exhibit an anomalous behavior. If the center of
the quantum dot is located at one of the symmetry axes of the rectangular
plate, the energy level distributions correspond to the Gaussian Orthogonal
Ensemble (GOE), otherwise they belong to the Gaussian Unitary Ensemble (GUE),
even though the system is time-reversal invariant.Comment: 4 pages, pdf forma
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