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The aim of this study was to evaluate the effects of replacing antibiotics with increasing doses of chitosan (CHI) on nutrient intake and digestibility, corn grain excretion, ruminal fermentation, nitrogen metabolism, and feeding behavior in finishing steers fed forage-free diets. Five ruminally cannulated crossbred steers were assigned to a 5 x 5 Latin square experimental design and given the following diets: C0= basal diet with no additives, ANT= basal diet with inclusion of virginiamycin 30 mg/kg DM, C375= basal diet with inclusion of chitosan 375 mg/kg DM, C750= basal diet with inclusion of chitosan 750 mg/kg DM, and C1500= basal diet with inclusion of chitosan 1500 mg/kg DM. Supplementation with CHI did not affect ruminal pH and ammonia nitrogen (N-NH3) concentration. Chitosan quadratically affected corn grain excretion and molar proportion of ruminal butyrate, with greater values for C750. Animals fed C375 showed greater dry matter intake and neutral detergent fiber intake; and greater digestibility of DM, starch, and NDF. Animals fed C750 and C1500 diets presented greater absorbed N compared to ANT. Animals fed ANT, C750, and C1500 spent more time eating and chewing than animals fed CON. More specifically, the dose of 375 mg/kg DM of diet was very promising for steers fed free-forage diet due to its ability to improve nutrient digestibility, with only slight changes in N metabolism. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous machines (PMSMs) drives are attractive and have been used in several applications, because of their noteworthy advantages. In some applications, the continuous operation is necessary, and then the PMSM drive outage is unacceptable or may cause great losses. Thus, several studies have been accomplished in order to detect incipient faults in PMSMs. In this context, the electrical signature analysis (ESA) technique is highlighted, because of the feasibility and non-invasive features. ESA allows the fault detection by only analyzing the electrical machine quantities. This paper proposes a study of ESA for PMSM condition monitoring. The review of some fault patterns is presented as well as the development of a scale model laboratory to simulate faults in a real PMSM in operation. The PMSM is used to drive a fluid pumping system, and different types of fluids are tested, being different load conditions from the PMSM point of view. The presented results are promising, encouraging ESA based methodologies for PMSM fault detection.

Sem resumo

A standard plane-wave expansion technique is used to investigate the evolution of the photonic band structure of a two-dimensional honeycomb lattice composed by cylindrical shell rods with dielectric permittivities [variant_greek_epsilon]1 and [variant_greek_epsilon]2, and embedded in a background with permittivity [variant_greek_epsilon]3. We have considered the effect of dispersive dielectric responses as well as the influence of an externally applied magnetic field aiming to obtain efficient tunable bandgaps. Present results suggest that a combination of a doped semiconductor constituent with an anisotropic geometry, which breaks symmetry and unfolds degeneracies, provides an efficient realization of photonic systems with tunable bandgaps. [ABSTRACT FROM AUTHOR]

The effects of the Dresselhaus spin splitting on the Landé g factor associated with conduction electrons in GaAs–(Ga,Al)As quantum wells are studied by using the nonparabolic Ogg–McCombe effective Hamiltonian. The g factor and cyclotron effective mass are calculated as functions of applied magnetic fields (along both the growth and in-plane directions) and GaAs well widths of the heterostructure. Present calculations indicate that in GaAs–(Ga,Al)As heterostructures, the inclusion of the Dresselhaus term leads to very small corrections in the effective Landé factor. Taking into account the effects of nonparabolic and anisotropic terms in the Hamiltonian is fundamental in obtaining quantitative agreement with experimental measurements. Moreover, the present results suggest that previous theoretical work on the Dresselhaus spin-splitting effects on the effective Landé factor should be viewed with caution if nonparabolic and anisotropic effects are not taken into account. [ABSTRACT FROM AUTHOR]

We have performed a theoretical study of the cyclotron effective mass and electron effective Landé g∥ factor in semiconductor GaAs–Ga1-xAlxAs quantum wells under an applied magnetic field parallel to the growth direction of the quantum well. The theoretical approach is within the nonparabolic and effective-mass approximation and via an Ogg-McCombe effective Hamiltonian [Proc. Phys. Soc. London 89, 431 (1969); Phys. Rev. 181, 1206 (1969)] for the electron in the conduction band of the GaAs–Ga1-xAlxAs heterostructure, which allows a unified treatment of both the cyclotron mass and g∥ factor. Calculations are performed for different widths of the GaAs–Ga1-xAlxAs quantum wells and as functions of the applied magnetic field, with results in very good agreement with reported experimental measurements of the electron cyclotron effective mass and g∥ factor. [ABSTRACT FROM AUTHOR]

Light shifts induced in the electronic and shallow on-center donor states in spherical semiconductor quantum dots, including magnetic field effects, are theoretically investigated. The interaction of light with the spherical GaAs-(Ga, Al)As quantum dot is treated within a dressed-band approach in which the Kane band structure scheme is used to model the GaAs bulk semiconductor whereas the dressing by the laser field is treated through the renormalization of the GaAs energy gap and conduction/valence effective masses. This nonperturbative approach is valid far from resonances and has been successfully adopted for other confined semiconductor heterostructures. The discrete nature of the electronic and impurity states, characteristic of quantum dot systems, and the possibility of adding extra confining effects by laser and applied magnetic fields opens up a promising route of applicability and/or manipulation of quantum-dot states in recent quantum-computer proposals. [ABSTRACT FROM AUTHOR]

We present a theoretical study, within the effective-mass approximation, of the magnetoabsorption spectra of intraexcitonic terahertz transitions of light-hole and heavy-hole confined magnetoexcitons in GaAs-(Ga,Al)As quantum wells. The semiconductor quantum wells are studied under magnetic fields applied in the growth direction of the semiconductor heterostructure. The various magnetoexciton states are obtained in the effective-mass approximation by an expansion of the exciton-envelope wave functions in terms of products of hole and electron quantum-well states with appropriate Gaussian functions for the various excitonic states. Intramagnetoexciton transitions are theoretically studied by exciting the allowed excitonic transitions with σ[sup +] (or σ[sup -]) far-infrared radiation circularly polarized in the plane of the GaAs-(Ga,Al)As quantum well. Theoretical results are obtained for the intramagnetoexciton transition energies and magneto-absorption spectra associated with excitations from 1s-like to 2p ±, and 3p ± -like magnetoexciton states, and found in overall agreement with optically detected resonance measurements. [ABSTRACT FROM AUTHOR]

The acceptor-related photoluminescence of a GaAs-(Ga,A1)As superlattice, under the influence of a magnetic field applied parallel to the interfaces, is theoretically studied following a variational procedure within the effective-mass approximation. Electron and hole magnetic Landau levels and envelope wave functions were obtained by an expansion in terms of sine functions, whereas for the impurity levels the envelope functions were taken as products of sine and hydrogenic-like variational functions. Impurity binding energies and wave functions are obtained for acceptors at a general position in the superlattice and for different in-plane magnetic fields. Theoretical results corresponding to transitions from the conduction subband to states of acceptors (miniband-to-acceptor e – A[sup 0] transitions) at the edge and center positions of the GaAs quantum well compare well with available experimental data by Skromme et al. [tor transitions for different temperatures and values of the superlattice period. [ABSTRACT FROM AUTHOR]

Deals with a study which examined infrared-absorption spectra associated to transitions from donor states to conduction subbands in gallium arsenide-(Ga,Al)As quantum wells. Theoretical assumptions; Experimental results; Conclusion.

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