766 research outputs found
Wave reflection, transmission and spectral changes at permeable low-crested structures
Physical model tests were carried out in order to improve the understanding about the hydrodynamic processes that take place around a LCS when it is under wave attack. In particular, the wave transmission and reflection coefficients as well as the spectrum transformation were analysed for both emerged and submerged structures.
The results of the experiments indicated that there is a clear inverse proportionality between the transmission (Kt)
and reflection (Kr) coefficients and the wave steepness sop. This trend is much more noticeable for emerged than for submerged structures. A comparison with some widely employed formulae was also made; in most of the cases these expressions underpredicted Kt and overpredicted Kr. Moreover, the spectral changes in the waves transmitted through the structure were analyzed, showing a shift of energy to higher frequency bands greater than that observed in previous works. It was also noted that the higher the sop, the more likely it is for the transmitted energy to be retained in the lower frequency bands.Postprint (published version
Modelling of Optical Detection of Spin-Polarized Carrier Injection into Light-Emitting Devices
We investigate the emission of multimodal polarized light from Light Emitting
Devices due to spin-aligned carriers injection. The results are derived through
operator Langevin equations, which include thermal and carrier-injection
fluctuations, as well as non-radiative recombination and electronic g-factor
temperature dependence. We study the dynamics of the optoelectronic processes
and show how the temperature-dependent g-factor and magnetic field affect the
polarization degree of the emitted light. In addition, at high temperatures,
thermal fluctuation reduces the efficiency of the optoelectronic detection
method for measuring spin-polarization degree of carrier injection into
non-magnetic semicondutors.Comment: 15 pages, 7 figures, replaced by revised version. To appear in Phys.
Rev.
Cosmic microwave background anisotropies in multi-connected flat spaces
This article investigates the signature of the seventeen multi-connected flat
spaces in cosmic microwave background (CMB) maps. For each such space it
recalls a fundamental domain and a set of generating matrices, and then goes on
to find an orthonormal basis for the set of eigenmodes of the Laplace operator
on that space. The basis eigenmodes are expressed as linear combinations of
eigenmodes of the simply connected Euclidean space. A preceding work, which
provides a general method for implementing multi-connected topologies in
standard CMB codes, is then applied to simulate CMB maps and angular power
spectra for each space. Unlike in the 3-torus, the results in most
multi-connected flat spaces depend on the location of the observer. This effect
is discussed in detail. In particular, it is shown that the correlated circles
on a CMB map are generically not back-to-back, so that negative search of
back-to-back circles in the WMAP data does not exclude a vast majority of flat
or nearly flat topologies.Comment: 33 pages, 19 figures, 1 table. Submitted to PR
Soil biochemistry and microbial activity in vineyards under conventional and organic management at Northeast Brazil.
The São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that orgThe São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that organic fertilization can improve soil quality, we compared the effects of conventional and organic soil management on microbial activity and mycorrhization of seedless grape crops. We measured glomerospores number, most probable number (MPN) of propagules, richness of arbuscular mycorrhizal fungi (AMF) species, AMF root colonization, EE-BRSP production, carbon microbial biomass (C-MB), microbial respiration, fluorescein diacetate hydrolytic activity (FDA) and metabolic coefficient (qCO2). The organic management led to an increase in all variables with the exception of EE-BRSP and qCO2. Mycorrhizal colonization increased from 4.7% in conventional crops to 15.9% in organic crops. Spore number ranged from 4.1 to 12.4 per 50 g-1 soil in both management systems. The most probable number of AMF propagules increased from 79 cm-3 soil in the conventional system to 110 cm-3 soil in the organic system. Microbial carbon, CO2 emission, and FDA activity were increased by 100 to 200% in the organic crop. Thirteen species of AMF were identified, the majority in the organic cultivation system. Acaulospora excavata, Entrophospora infrequens, Glomus sp.3 and Scutellospora sp. were found only in the organically managed crop. S. gregaria was found only in the conventional crop. Organically managed vineyards increased mycorrhization and general soil microbial activity
Chemical composition of essential oil extracted from leaves of Campomanesia adamantium subjected to different hydrodistillation times
Gelatin-based microspheres crosslinked with glutaraldehyde and rutin oriented to cosmetics
Avaliação fitossociológica da comunidade infestante em áreas de transição para o café orgânico.
Objetivou-se com este trabalho verificar os efeitos dos insumos orgânicos e convencionais na dinâmica de plantas daninhas da lavoura durante o primeiro e o segundo ano de transição agroecológica. Para isso, montou-se um experimento em um cafezal de seis anos, onde iniciou-se a transição para o sistema de cultivo orgânico. A espécie mais importante no primeiro ano da transição, na maioria das áreas avaliadas, foi Ageratum conyzoides; no segundo ano ocorreu considerável mudança na relação de dominância entre as espécies, destacando-se Leunurus sibiricus na maior parte das áreas estudadas. Ocorreu também aumento do número de espécies presentes na maioria das áreas de um ano para o outro. No segundo ano de transição observou-se decréscimo na diversidade de espécies em relação ao primeiro ano. Dessa forma, pode-se concluir que nos dois anos de avaliação verificaram-se mudanças no número, na diversidade e na relação de importância entre as espécies de um ano para o outro
Contaminação por Salmonella spp. em uma cadeia de produção de ovos de uma integração de postura comercial
Single Spin Asymmetry in Polarized Proton-Proton Elastic Scattering at GeV
We report a high precision measurement of the transverse single spin
asymmetry at the center of mass energy GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The was measured
in the four-momentum transfer squared range \GeVcSq, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
and its -dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this , we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure
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