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101.
This paper examines the behavior of the minimum mean-squared error (MMSE) receiver in frequency-nonselective-fading channels. It is noted that the MMSE receiver will often lose phase lock on the desired signal when the desired signal dips into a deep fade. A modification to the MMSE receiver is presented which is demonstrated to function quite nicely in flat-fading channels. Analytical results for the modified MMSE receiver are presented and found to agree very well with simulation results. These analytical results are then compared to the theoretical performance of the conventional (i.e., correlator) receiver in terms of both bit-error rate (BER) and capacity. As expected, the modified MMSE receiver was found to offer a substantial improvement in both BER and capacity. Finally, a simple empirically derived formula is given which will give a good approximation to the BER of the modified MMSE receiver in a Rayleigh-fading environment. This formula can also be used to determine the number of users a given system can support. It is noted that as Eb/N0 grows, it is quite feasible to approach 100% channel utilization with the MMSE receiver, whereas a conventional receiver is typically limited to a utilization of 10%-20% 相似文献
102.
Werner S. Weiglhofer Afonso M. Barbosa Antnio L. Topa 《AEUE-International Journal of Electronics and Communications》2001,55(4):209-210
An introduction to this special issue devoted to Bianisotropics 2000 – 8th International Conference on Electromagnetics of Complex Media, is provided. 相似文献
103.
Antnio L. Topa Carlos R. Paiva Afonso M. Barbosa 《AEUE-International Journal of Electronics and Communications》2001,55(4):281-291
We analyse the reflection, transmission and radiation characteristics of a step discontinuity in a grounded chiral slab and we show that the step radiation can be enhanced due to the effect of the chirality. The analysis is performed using a mode matching technique. The fields are expressed in terms of the discrete modes and the continuous spectrum using two subsets of hybrid radiation modes: incident transverse electric (ITE) and incident transverse magnetic (ITM) modes. The scattering matrix of the step is determined by minimizing the boundary residual error in the sense of the least squares. The influence of chirality on the characterization of the step is demonstrated and we show that control of the radiation pattern is achieved, including angle and width of the radiation beam. 相似文献
104.
Marcus V.C. AlvesJader R. Barbosa Jr. Alvaro T. PrataFernando A. Ribas Jr. 《International Journal of Refrigeration》2011,34(1):74-83
This work presents a mathematical analysis of an oil supply system for reciprocating compressors. The system is based on a single screw pump attached to the bottom end of the vertical rotating shaft immersed in the oil sump. The fluid flow in the pump was modeled with a semi-analytical approach based on the solution for the laminar fully developed oil flow in a screw extruder via the Generalized Integral Transform Technique. The screw pump model is coupled with that for the flow in the shaft region so as to provide an estimate of the oil flow rate and of the so-called ‘climbing-time’, i.e., the amount of time needed for a fluid particle to travel from the oil sump to the top of the shaft. The calculation method was verified against experimental data and Computational Fluid Dynamics modeling results. 相似文献
105.
Sergio Neves Monteiro Felipe Perissé Duarte Lopes Anderson Paula Barbosa Alice Barreto Bevitori Isabela Leão Amaral Da Silva Lucas Lopes Da Costa 《Metallurgical and Materials Transactions A》2011,42(10):2963-2974
Recent investigations on the tensile properties of natural cellulose-based fibers revealed an increasing potential as engineering
materials. This is particularly the case of very thin fibers of some species such as sisal, ramie, and curaua. However, several
other commonly used fibers such as flax, jute, hemp, coir, cotton, and bamboo as well as less known bagasse, piassava, sponge
gourde, and buriti display tensile properties that could qualify them as engineering materials. An overview of the strength
limits attained by these fibers is presented. Based on a tensile strength vs density chart, it is shown that natural fibers stand out as a relevant class of engineering materials. 相似文献
106.
José Lucena Barbosa Júnior Maurício Cordeiro Mancini Miriam Dupas Hubinger 《International Journal of Food Science & Technology》2013,48(12):2463-2473
A simple mathematical model to predict dehydration and impregnation process during osmotic dehydration of orange‐fleshed honeydew in sucrose and corn syrup solutions was proposed. Results showed low dispersion and a good fitting capability for WL and SG kinetics. Diffusivity values for WL ranged from 0.96 × 10?10 to 2.22 × 10?10 and 1.04 × 10?10 to 3.10 × 10?10 m2 s?1 in corn syrup and sucrose solutions, respectively. For SG, the obtained range was 0.72 × 10?10 to 2.35 × 10?10 and 0.71 × 10?10 to 2.46 × 10?10 m2 s?1 in corn syrup and sucrose solutions, respectively. The half‐life of dehydration rates (t1/2) was from 30.9 to 71.2 min and from 19.4 to 57.5 min in corn syrup and sucrose solutions, respectively. Diffusivities values obtained according to the proposed model were close to the ones observed from diffusive model; t1/2 was a promising criterion for the process time definition. 相似文献
107.
Exact corotational shell for finite strains and fracture 总被引:2,自引:2,他引:0
The corotational method for frame-invariant elements is generalized to obtain a consistent large-strain shell element incorporating
thickness extensibility. The resulting element allows arbitrary in-plane deformations and is distinct from the traditional
corotational methods (either quadrature-based or element-based) in the sense that the corotational frame is exact. The polar
decomposition operation is performed in two parts, greatly simplifying the linearization calculations. Expressions for the
strain-degrees-of-freedom matrices are given for the first time. The symbolic calculations are performed with a well-known
algebraic system with a code generation package. Classical linear benchmarks are shown with excellent results. Applications
with hyperelasticity and finite strain plasticity are presented, with asymptotically quadratic convergence and very good benchmark
results. An example of finite strain plasticity with fracture is solved successfully, showing remarkable robustness without
the need of enrichment techniques. 相似文献
108.
Rodrigo R. Oliveira Felipe C. Noguez Cristiano A. Costa Jorge L. Barbosa Mario P. Prado 《Expert systems with applications》2013,40(6):2023-2031
Logistics represent the biggest cost for transportation companies. Companies are investing in monitoring and tracking systems aiming at improving services, reducing costs and ensuring the safety in cargos transports. This article presents an intelligent model to obtain the position of vehicles, using off-the-shelf mobile devices named SWTRACK. The proposal allows distributors companies to track loads and to have real-time information about their whereabouts during a travel. SWTRACK presents an automatic travel management to initialize and finish travels without user interaction. Furthermore, it provides a mechanism to monitor detours in planned routes and to send alarms notification through mobile devices. To build that mechanism, we studied the Geofence concept and existing techniques to prepare two solutions based on continuous monitoring. Those solutions were compared and discussed. We also conducted a model evaluation using off-the-shelf mobile devices. Moreover, we provide an impact analysis regarding GPS precision and battery power consumption. In the end, we show that the proposed model generates a reliable system for tracking vehicles. 相似文献
109.
110.
José Bacelar Almeida Manuel Barbosa Jorge Sousa Pinto Bárbara Vieira 《Innovations in Systems and Software Engineering》2010,6(3):203-218
We apply state-of-the art deductive verification tools to check security-relevant properties of cryptographic software, including
safety, absence of error propagation, and correctness with respect to reference implementations. We also develop techniques
to help us in our task, focusing on methods oriented towards increased levels of automation, in scenarios where there are
clear obvious limits to such automation. These techniques allow us to integrate automatic proof tools with an interactive
proof assistant, where the latter is used off-line to prove once-and-for-all fundamental lemmas about properties of programs.
The techniques developed have independent interest for practical deductive verification in general. 相似文献