4,797 research outputs found
Lorentz-violating dimension-five operator contribution to the black body radiation
We investigate the thermodynamics of a photon gas in an effective field
theory model that describes Lorentz violations through dimension-five operators
and Horava-Lifshitz theory. We explore the electrodynamics of the model which
includes higher order derivatives in the Lagrangian that can modify the
dispersion relation for the propagation of the photons. We shall focus on the
deformed black body radiation spectrum and modified Stefan-Boltzmann law to
address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL
Exact Effective action for (1+1)-dimensional fermions in an Abelian background at finite temperature and chemical potential
In this paper we study the effects of a nonzero chemical potential in the
effective action for massless fermions in (1+1) dimensions in an abelian gauge
field background at finite temperature. We calculate the n-point function and
show that the structure of the amplitudes corresponds to a generalization of
the structure noted earlier in a calculation without a chemical potential (the
associated integrals carry the dependence on the chemical potential). Our
calculation shows that the chiral anomaly is unaffected by the presence of a
chemical potential at finite temperature. However, unlike the earlier
calculation (in the absence of a chemical potential) odd point functions do not
vanish. We trace this to the fact that in the presence of a chemical potential
the generalized charge conjugation symmetry of the theory allows for such
amplitudes. In fact, we find that all the even point functions are even
functions of the chemical potential while the odd point functions are odd
functions of it which is consistent with this generalized charge conjugation
symmetry. We show that the origin of the structure of the amplitudes is best
seen from a formulation of the theory in terms of left and right handed
spinors. The calculations are also much simpler in this formulation and it
clarifies many other aspects of the theory
MODELING AND OPTMIZATION POWER REQUIREMENTS OF ACTIVE ACOUSTIC LOUVRES
The development of new technologies for ventilated facades is within the context of energy efficiency of buildings , including the compatibility of the dichotomy between natural ventilation and soundproofing in tropical countries . Given this perspective, this work proposes the application of techniques for active noise control in acoustic louvers . One limitation of the spread of technical active noise control in buildings is the energy inherent in the technique. Thus, the proposed system is based on the reduction of structural vibrations of the shutter blades by using piezoelectric actuators . The acoustic transmission loss and energy requirements for active shutters are investigated from numerical modeling . The results suggest their technical feasibility with superior soundproofing to 30 dB and power consumption less than 35 W. Thus , the active noise control using piezoelectric actuators is presented as a promising technology , aligning soundproofing with low energy consumption Type the text of the abstract here, Times New Roman, 9, lower case letters, justified paragraphs, 1.0 line spacing. The abstract should state the objectives, methodology and main conclusions in 200 to 300 words. No not divide into paragraphs
Carrier relaxation in GaAs v-groove quantum wires and the effects of localization
Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove
quantum wires (QWRs) with a large subband separation (46 meV). Signatures of
inhibited carrier relaxation mechanisms are seen in temperature-dependent
photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we
observe strong emission from the first excited state of the QWR below ~50 K.
This is attributed to reduced inter-subband relaxation via phonon scattering
between localized states. Theoretical calculations and experimental results
indicate that the pinch-off regions, which provide additional two-dimensional
confinement for the QWR structure, have a blocking effect on relaxation
mechanisms for certain structures within the v-groove. Time-resolved PL
measurements show that efficient carrier relaxation from excited QWR states
into the ground state, occurs only at temperatures > 30 K. Values for the low
temperature radiative lifetimes of the ground- and first excited-state excitons
have been obtained (340 ps and 160 ps respectively), and their corresponding
localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct
corrupt figure
Longitudinal photocurrent spectroscopy of a single GaAs/AlGaAs v-groove quantum wire
Modulation-doped GaAs v-groove quantum wires (QWRs) have been fabricated with
novel electrical contacts made to two-dimensional electron-gas (2DEG)
reservoirs. Here, we present longitudinal photocurrent (photoconductivity/PC)
spectroscopy measurements of a single QWR. We clearly observe conductance in
the ground-state one-dimensional subbands; in addition, a highly
temperature-dependent response is seen from other structures within the
v-groove. The latter phenomenon is attributed to the effects of structural
topography and localization on carrier relaxation. The results of
power-dependent PC measurements suggest that the QWR behaves as a series of
weakly interacting localized states, at low temperatures
Comparison of growth and lipid accumulation at three different growth regimes with Desmodesmus sp.
The production of third generation biofuel and use of microalgae as feedstock have recently gained increased attention in the research area in search of more sustainable processes. These microorganisms have characteristics that offer great potential to produce either feedstock to other process or even final use products. They have fast growth rates and accumulation of intracellular metabolites, including lipids. There are three basic types of cultures in which microalgae can develop: autotrophic, heterotrophic and mixotrophic. The objective of this work was to study the growth of the microalgae Desmodesmus sp. in these three types of cultivations in order to establish the most effective farming strain for lipids production. It was observed that the strain had higher yields of biomass and lipids in the mixotrophic cultivation with glucose (10 g L−1) as the carbon source, obtaining 54.5 × 106 cells mL−1 with a growth rate of 0.28 (days−1) and 25.1% of lipids in a 6 day cultivation time9421427COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informação2014/10064-9; 2015/19935-
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