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271.
Revisiting parametric multi-terminal problems: Maximum flows, minimum cuts and cut-tree computations
Given an undirected network, the multi-terminal network flows analysis consists in determining the all pairs maximum flow values. In this paper, we consider an undirected network in which some edge capacities are allowed to vary and we analyze the impact of such variations on the all pairs maximum flow values. We first provide an efficient algorithm for the single parametric capacity case, and then propose a generalization to the case of multiple parametric capacities. Moreover, we provide a study on Gomory–Hu cut-tree relationships. 相似文献
272.
J. R. Correia S. Cabral-Fonseca F. A. Branco J. G. Ferreira M. I. Eusébio M. P. Rodrigues 《Mechanics of Composite Materials》2006,42(4):325-338
Results of an experimental research into the physical, chemical, mechanical, and aesthetical changes suffered by pultruded
glass-fiber-reinforced polyester profiles during their testing for accelerated aging under the action of moisture, temperature,
and ultraviolet (UV) radiation are presented. The profiles were submitted to the influence of four different exposure environments:
(i) in an immersion chamber, (ii) in a condensation chamber, (iii) in a QUV accelerated weathering apparatus, and (iv) in
a xenon-arc accelerated weathering apparatus. The results obtained were analyzed regarding the changes in their weight, sorption
ability, tensile and flexural strength characteristics, color, and gloss; the chemical changes were investigated by means
of Fourier-transform infrared spectroscopy. Considerable chromatic changes were observed, especially owing to the UV radiation.
Although some reduction in the mechanical properties was observed, particularly in the immersion and condensation chambers,
the durability tests proved a generally good behavior of this material under the aggressive conditions considered.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 463–474, July–August, 2006. 相似文献
273.
274.
275.
I RochaE.C Ferreira 《Analytica chimica acta》2002,462(2):293-304
A two-channel flow injection analysis (FIA) system was developed for the simultaneous on-line monitoring of acetate and glucose during high cell density fed-batch fermentations of recombinant Escherichia coli. Acetate measurement was performed with a modified and optimised version of an existing method, based on acetate diffusion through a gas-diffusion chamber into a stream containing an acid-base indicator. The subsequent decrease in the absorbance was detected with an incorporated photometer. After method optimisation, it was possible to achieve linearity until 10 g/kg with no dilution step and with a detection level of 0.05 g/kg. Although some interferences were found, the performance of the method proved to be sufficiently reliable for on-line control purposes Commercially packed glucose oxidase (GOD) was used for the amperometric measurement of glucose. The method was linear up to 5 g/kg and it was possible to detect concentrations lower than 0.06 g/kg. For these measurements, no significant interferences were detected when the results were compared with other reference methods. The application of a simultaneous parallel configuration of the methods to a high cell density fed-batch E. coli fermentation was tested and reliable results were obtained within a 3 min delay. This information was made available to a supervisory computer running a developed LabVIEW™ programme via an Ethernet network, allowing the immediate implementation of control actions, improving the process performance. 相似文献
276.
Miroslaw Pluta Marius Murariu Amália Da Silva Ferreira Michael Alexandre Andrzej Galeski Philippe Dubois 《Journal of Polymer Science.Polymer Physics》2007,45(19):2770-2780
Starting from calcium sulfate (gypsum) as fermentation by‐product of lactic acid production process, high performance composites have been produced by melt‐blending polylactide (PLA, L/D isomer ratio of 96:4) and β‐anhydrite II (AII) filler, that is, calcium sulfate hemihydrate previously dehydrated at 500 °C. Characterized by attractive mechanical and thermal properties due to good filler dispersion throughout the polyester matrix, these composites are interesting for potential use as biodegradable rigid packaging. Physical characterization of selected composites filled with 20 and 40 wt % AII has been performed and compared to processed unfilled PLA with similar amorphous structure. State of dispersion of the filler particles and interphase characteristic features have been investigated using light microscopy (LM) and scanning electron microscopy (SEM). Addition of AII did not decrease PLA thermal stability as revealed by thermogravimetry analyses (TGA) and allowed reaching a slight increase of PLA crystallizability during melt crystallization and upon heating from the glassy, amorphous state (DSC). It was found by thermomechanical measurements (DMTA) that the AII filler increased pronouncedly storage modulus (E′) of the composites in comparison with PLA in a broad temperature range. The X‐ray investigations showed stable/unchanged crystallographic structure of AII during processing with molten PLA and in the composite system. The notable thermal and mechanical properties of PLA–AII composites are accounted for by the good filler dispersion throughout the polyester matrix confirmed by morphological studies, system stability, and favorable interactions between components. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2770–2780, 2007 相似文献
277.
M.G. Ferreira da Silva 《Journal of Non》2006,352(8):807-820
Glasses in the Al2O3-SiO2 and Nd2O3-Al2O3-SiO2 systems were prepared by the sol-gel method. The gel-glass evolution was studied using near-infrared (NIR) and ultraviolet-visible (UV-VIS) spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The results obtained indicate a relationship between the sample compositions, the treatment temperature and the Al coordination. In the samples of the Nd2O3-Al2O3-SiO2 system the densification of the structure, when the treatment temperature increases, leads to the segregation of neodymium oxide particles. 相似文献
278.
G. Cassabois A. L. C. Triques R. Ferreira C. Delalande Ph. Roussignol F. Bogani 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We have studied the coherent dynamics of a semiconductor microcavity by means of interferometric correlation measurements with subpicosecond time resolution in a backscattering geometry. Evidence is brought of the resolution of a homogeneous polariton line in an inhomogeneously broadened exciton system. Surprisingly, photon-like polaritons exhibit an inhomogeneous dephasing. Moreover, we observe an unexpected stationary coherence up to 8 ps for the lower polariton branch close to resonance. All these experimental results are well reproduced within the framework of a linear dispersion theory assuming a coherent superposition of the reflectivity and resonant Rayleigh scattering signals with a well-defined relative phase. 相似文献
279.
Here we present a system of coupled phase oscillators with nearest neighbors coupling, which we study for different boundary
conditions. We concentrate at the transition to the total synchronization. We are able to develop exact solutions for the
value of the coupling parameter when the system becomes completely synchronized, for the case of periodic boundary conditions
as well as for a chain with fixed ends. We compare the results with those calculated numerically.
相似文献
280.
The properties of the low-energy nuclear spectrum are greatly affected by pairing correlations. We study these effects in the nucleus 210Pb which has two particles moving outside closed shells. The configuration-mixed wave functions describe the motion of particles which are on the average closer together than they would be if the particles were confined to particular orbitals. Since the energy associated with pairing correlations is much smaller than the Fermi energy the width of the associated probability distribution is determined by the wavelength of single particles moving close to the Fermi surface. Despite the fact that the amplitudes associated with high-lying configurations are small, their net effect is important, typically changing the collectivity of the states by a factor of about two. The results of the microscopic calculations compare well with a semiclassical pairing transition density calculated on the basis of the Thomas-Fermi approximation. 相似文献