2,713 research outputs found
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
Pectinolytic activity of Aspergillus section Nigri strains
Pectinases are a heterogeneous group of related enzymes that hydrolyze pectic substances
present mostly in plants. Pectinases are produced by plants, fungi, yeasts
and bacteria. Filamentous fungi are good producers of pectinolytic enzymes (e.g.,
exopolygalacturonase (exo-PG) and endopolygalacturonase (endo-PG) and Aspergillus
niger is the most commonly used fungal species for industrial production of pectinolytic
enzymes. The application of pectinolytic enzymes plays an important role
in food technology. In juice production, these enzymes have been used to improve
the yield, decrease the viscosity, clarify the juices and make them more stable. In
this context, the concept of using filamentous fungi and row and cheaper materials
for pectinase production is an important parameter in technological development.
In the present study a microplate method was developed for a rapid screening of
Aspergillus strains. Fifty-tree strains of Aspergillus section Nigri obtained from
the University of Recife Mycology (URM) culture collection and 8 of the Micoteca
da Universidade do Minho (MUM) culture collection were used. Orange peel was
the unique carbon source in the composition of the culture medium. The samples
were incubated at 25 ÂșC for 120 h. After 24, 48, 72, 96 and 120 h the exo-PG and
endo-PG were assessed using absorbance colorimetric and decrease in viscosity
methods, respectively. The utilization of orange peel allowed the detection of exo-PG
and endo-PG activity for all strains studied. The maximum exo-PG and endo-PG
activity was obtained by strain URM5162 to the values 4.37 U and 2.13 U, respectively.
This method and substrate may be useful to reduce the time for selecting
promising strains and in reducing the enzyme production costs. The strain is now
being used in a bioreactor and the enzymes and their mechanisms are also under
further investigation
Verification and validation in CFD for a free-surface gas-liquid flow in channels
This work deals with experimental and numerical studies of a 3-D transient free-surface two-phase flow in a bench-scale channel flow. The aim was to determine how well the homogeneous model can predict the fluid dynamics behavior and to validate the model. The model was validated with experimental data acquired for two hydrodynamic situations. The mathematical model was based on the mass conservation equations for liquid and gas phases and on the momentum conservation equation for the mixture, assuming interpenetrating, continuum and homogeneous hypotheses. Turbulence has been considered for the mixture through the standard k-ε model. The numerical methods were the finite volume method with pressure-velocity coupling and a numerical grid on a generalized Cartesian coordinate system. Good qualitative and quantitative agreements were found for both cases, making the prediction of the fluid dynamics behavior quite robust.32332
Potential benefits of the 19-nor-clerodane trans-dehydrocrotonin on the central nervous system
This study examined the effect of trans-dehydrocrotonin (DCTN), a 19-nor-clerodane diterpene isolated from Croton cajucara Benth (Euphorbiaceae), as analgesic and its effect on the central nervous system (CNS) of rodents using different animal models. The DCTN intraperitoneally exhibited mild analgesic activity on hot-plate test, but exhibited strong antinociceptive activity against acetic acid-induced abdominal writhing and the ED50 was calculated to be 44.88 mg/kg. At higher doses (100 mg/kg) it exhibited mild CNS depressant activities in laboratory animals. Moreover, it has negligible antidepressant activity. After taking consideration of the drug interaction, the DCTN can be used as a potent analgesic agent in case of peripheral algesia, without affecting the CNS. Neste estudo avaliou-se o efeito analgésico do diterpeno 19-nor-clerodano trans-desidrocrotonina (DCTN) isolado de Croton cajucara Benth (Euphorbiaceae), bem como seu efeito no sistema nervoso central utilizando-se diferentes tipos de modelos de animais roedores. A administração intraperitoneal deste diterpeno, no teste da placa quente, revelou sua atividade analgésica moderada. No entanto, no teste de contraçÔes abdominais desencadeadas por åcido acético, a DCTN apresentou forte atividade antinociceptiva com DE50 de 44,88 mg/kg. Doses elevadas de DCTN (100 mg/kg) apresentaram moderada atividade depressiva do sistema nervoso central (SNC), não tendo sido evidenciado ação antidepressiva. Após algumas consideraçÔes da ação de DCTN em algesia periférica, concluiu-se que esta substùncia pode ser utilizada como um potente agente analgésico, sem afetar o SNC
Sex-Specific Heterosis in Line Crosses of Mice Selectively Bred for High Locomotor Activity
When populations with similar histories of directional selection are crossed, their offspring may differ in mean phenotype as compared with the average for the parental populations, often exhibiting enhancement of the mean phenotype (termed heterosis or hybrid vigor). We tested for heterosis in a cross of two replicate lines of mice selectively bred for high voluntary wheel running for 53 generations. Mice were paired to produce four sets of F1 offspring: two purebred High Runner (HR) lines and the hybrid reciprocal crosses. The purebred HR showed statistically significant, sex-dependent differences in body mass, wheel revolutions, running duration, mean running speed, and (controlling for body mass) organ masses (heart ventricles, liver, spleen, triceps surae muscle). Hybrid males ran significantly more revolutions than the purebred males, mainly via increased running speeds, but hybrid females ran intermediate distances, durations, and speeds, as compared with the purebred females. In both sexes, ventricles were relatively smaller in hybrids as compared with purebred HR. Overall, our results demonstrate differential and sex-specific responses to selection in the two HR lines tested, implying divergent genetic architectures underlying high voluntary exercise
Errors in kinematic distances and our image of the Milky Way Galaxy
Errors in the kinematic distances, under the assumption of circular gas
orbits, were estimated by performing synthetic observations of a model disk
galaxy. It was found that the error is < 0.5 kpc for most of the disk when the
measured rotation curve was used, but larger if the real rotation curve is
applied. In both cases, the error is significantly larger at the positions of
the spiral arms. The error structure is such that, when kinematic distances are
used to develope a picture of the large scale density distribution, the most
significant features of the numerical model are significantly distorted or
absent, while spurious structure appears. By considering the full velocity
field in the calculation of the kinematic distances, most of the original
density structures can be recovered.Comment: Accepted for publication in A
Use of technology radiation as a method of reducing the microorganism and conservation postharvest of caja during storage
The caja fruit (Spondias spp.) are among the species considered exotic presents excellent view of economic exploitation to the Northeast of Brazil. However, contamination by microorganisms is a major factor in postharvest losses of fruits and other cultivated in Brazilian territory. Use of ionizing radiation aiming to reduce the use of pesticide products in pest control and microorganisms phytopathological and maintaining the quality of agricultural products has been studied by several researchers of postharvest fruit. This technology meets the requirements of food safety imposed by the various organs of public health. In order to evaluate the action of ionizing radiation on agents phytopathological and the effects on the quality of postharvest of caja fruits when stored under temperature of shelf, the experiment was conducted with application of doses 1.0 and 2.0 kGy, dose zero as fruit control, and storage under temperature of 23°C for twelve days. Control fruit had higher contamination by microorganisms phytopathological throughout the storage period. Analysis of total soluble solids, total titratable acidity, hydrogen potential, soluble solids/titratable acidity ratio, ascorbic acid and color of the flesh have suffered minor variations between the different doses studied.Keywords: Conservation; caja fruit; gamma radiation; postharvest storage; microorganism spoilage
Simultaneous Optical Model Analyses of Elastic Scattering, Breakup, and Fusion Cross Section Data for the He + Bi System at Near-Coulomb-Barrier Energies
Based on an approach recently proposed by us, simultaneous
-analyses are performed for elastic scattering, direct reaction (DR)
and fusion cross sections data for the He+Bi system at
near-Coulomb-barrier energies to determine the parameters of the polarization
potential consisting of DR and fusion parts. We show that the data are well
reproduced by the resultant potential, which also satisfies the proper
dispersion relation. A discussion is given of the nature of the threshold
anomaly seen in the potential
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