Minimum concave cost multicommodity network design

The minimum concave cost multicommodity network design problem (MCMNDP) arises in many application areas, such as transportation planning, energy distribution systems and especially in the design of both packet and circuit switching backbone networks. Exact concave cost optimization algorithms have been developed but they are applicable only if the network size is small. Therefore, MCMNDP is usually solved using non-exact iterative methods. In this paper, such heuristic techniques proposed within the context of circuit switching and packet switching network design are evaluated in detail. Following a comprehensive literature survey, Yaged’s linearization, Minoux’s greedy and Minoux’s accelerated greedy methods have been selected for the circuit switching network design case for further investigation. Minoux’s greedy methods are found to create routes that include cycles causing degradation in the quality of the solution; therefore, we propose a simple but effective modification scheme as a cycle elimination strategy. Similarly, but within the context of packet switching network design, Gerla and Kleinrock’s concave branch elimination, Gersht’s greedy, and Stacey’s concave link elimination methods have been selected for further investigation. All of these methods consider aggregate flows on each link, simultaneously re-routing more than one commodity in one step. In this paper, we propose an alternative disaggregate approach, where only one commodity is handled at a time. Our final proposal is the adaptation of the algorithms proposed for circuit switching network design to the packet switching case. Then an extensive comparative computational study is performed for a number of networks and cost structures to help establish the best method with respect to time and solution quality. Our computational results have shown that the performances of the MCMNDP algorithms heavily depend on the network type and the cost structure. The results have also revealed that our proposed modification to Minoux greedy to eliminate cycles leads to considerable improvements and our proposed disaggregate approach gives the best result in some networks with certain cost structures.     

A numerical study on low and higher-order potential based BEM for 2D inviscid flows

A formal error analysis of the order of approximation of a potential based boundary element method (BEM) for two-dimensional flows is performed in order to derive consistent approximations for the potential integrals. Two higher-order approaches satisfying consistency requirements to attain second and third order convergence in the potential are selected for numerical implementation. From the formal local expansions of the potential integrals the influence coefficients are derived and evaluated analytically. In order to assess the methods accuracy, the low and higher-order methods are applied to two-dimensional steady flows around analytical foils. A numerical error analysis is done and a comparison between their theoretical and numerical asymptotic order of accuracy performed. The first author acknowledges the financial support granted by Fundação para a Ciência e a Tecnologia, Ph.D. grant PRAXISXXI/BD/2226/99. This work was done under the project PRAXIS/2/2.1/MAR/1723/95.     

Hyperfractionation in the reirradiation of head and neck cancers. Result of a pilot study

Surgical resection of primary lesions and single metastasis can be curative, but surgery, used as the only therapeutic option, is not unanimously accepted in patients with multiple metastasis and, apart from other considerations, there are no established clinical criteria to allow us to predict which patients will benefit from a metastectomy. This study evaluates four patients with advanced RCC. Three had multiple pulmonary metastasis at the time of diagnosis and one presented retroperitoneal mass at 36 months of follow-up. All patients were nephrectomized and received adjuvant immunotherapy with an association of IL-2 and 2b alpha-IFN subcutaneously, obtaining partial response of the disease after two treatment courses. Later, the patients underwent debulking surgery. Two patients are still alive and have no evidence of disease progression at 28 months and 8 months of follow-up. This data and that contrasted with other authors, suggests that surgical management would be a reasonable option in patients who have partially responded to immunotherapy, even though the selection of both candidates and surgical strategy should be considered on an individual basis.     

Determination of tocopherols and phytosterols in sunflower seeds by NIR spectrometry

The objective of this work was to develop a near‐infrared reflectance spectrometry (NIRS) calibration estimating the tocopherol and phytosterol contents in sunflower seeds. Approximately 1000 samples of grinded sunflower kernels were scanned by NIRS at 2‐nm intervals from 400 to 2500 nm. For each sample, standard measurements of tocopherol and phytosterol contents were performed. The total tocopherol content was obtained by high‐performance liquid chromatography coupled with a fluorescence detector, while the total phytosterol content was assessed by gas chromatography. For tocopherol, the calibration data set ranged from 175 to 1005 mg/kg oil (mean value around 510 ± 140 mg/kg oil), whereas for the phytosterol content, the calibration data set ranged from 180 to 470 mg/100 g oil (mean value of 320 ± 50 mg/100 g oil). The NIRS calibration showed a relatively good correlation (R² = 0.64) between predicted by NIRS and real values for the total tocopherol content but a poor correlation for the total phytosterol content (R² = 0.27). These results indicate that NIRS could be useful to classify samples with high and low tocopherol content. In contrast, the estimation of phytosterol contents by NIRS needs further investigation. Moreover, in this study, calibration was obtained by a modified partial least‐squares method; the use of other mathematical treatments can be suitable, particularly for total phytosterol content estimation.     

Spin-glass-like behaviour in the ternary U3Fe4+xAl12−x uranium–iron aluminide

The U₃Fe_4+xAl_12?x (0 < x < 0.5) intermetallic was prepared by arc melting, followed by annealing at 850 °C. This compound crystallizes in the hexagonal Gd₃Ru₄Al₁₂-type structure (e.g. P6₃/mmc), with room temperature parameters a = 8.7516(3) Å and c = 9.2653(4) Å for x = 0. The structure is characterized by planar layers of M3Al4 (M = Gd, U), containing M atoms in a triangular arrangement and forming a distorted Kagomé net. Magnetic measurements revealed a spin-glass-type behaviour with a freezing temperature, T_f = 7.9 K. The magnitude of the frequency shift of the freezing temperature is ≈0.03 and a Vogel–Fulcher law is followed with values typical for a spin-glass. ⁵⁷Fe Mössbauer data show that there is no freezing of the iron magnetic moments directions below T_f, indicating that the origin of the spin-glass-like behaviour is related to topological frustration of the uranium moments.     

Hybrid coating on steel: ZnNi electrodeposition and surface modification with organothiols and diazonium salts

Sacrificial electrodeposited ZnNi is currently studied for replacing chromate conversion coatings (CCC) in anticorrosion applications. The present-day performances of ZnNi are still away from those of CCCs and the additional organic layers such as polymers and paints are still permeable and cannot prevent the corrosive species to reach the metal. Suitable adhesion primers could improve the situation by minimizing the access of the corrosive species to the polymer/metal interface.As a contribution to this interface problem, the present work provides a comparison of the protective properties of two structurally related molecules (4-nitrothiophenol and 4-nitrobenzenediazonium) grafted on a ZnNi coating electrodeposited on steel. Films of 4-nitrophenyl have been prepared according to the self-assembly process while films of 4-nitrobenzene have been obtained by electrochemical grafting, n-dodecanethiol being used as model system.The adsorption of these molecules as well as the resulting organic film is characterized by X-ray photoelectron spectroscopy (XPS) and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The protective properties of the organic films against corrosion are investigated by linear sweep voltammetry (LSV), cyclic voltammetry (CV) and scanning vibrating electrode technique (SVET).     

Photocatalytic degradation of two volatile fatty acids in monocomponent and multicomponent systems: Comparison between batch and annular photoreactors

This study investigates the influence of the inlet concentrations on the degradation rates of a binary mixture of volatile fatty acids (propionic and butyric acids). TiO₂-coated non-woven fibre textile was used as the photocatalyst in a batch reactor and in an annular reactor at laminar flow regime. The humidity level, temperature, UV intensity and flow rate were kept constant. First, the adsorption isotherms were determined and these showed that the propionic acid is less adsorbed than the butyric acid onto the catalyst. Conversely to the adsorption, the photodegradation of pure propionic acid is better than the degradation of pure butyric acid. Photodegradation is greatly inhibited when the two acids are mixed in comparison to the pure compounds. The propionic acid is more affected. This inhibition is attributed to the competitive adsorption of the two species on the active sites of the catalyst. A model which takes into account the competitive adsorption is proposed in order to determine the outlet concentrations of the compounds knowing the inlet concentrations in the annular reactor.     

Effects of Additives on the Activity and Enantioselectivity of Candida rugosa Lipase in a Biphasic Medium

The effects of Li⁺, Na⁺, K⁺, Mg²⁺ and Zn²⁺ ions on the activity and enantioselectivity of Candida rugosa lipase (CRL) were investigated in a biphasic medium composed of phosphate buffer solution (containing a metal ion within a 50–500 mM concentration range) and isooctane. The hydrolytic activities of CRL towards p‐nitrophenyl acetate were measured after incubation of the enzyme in the presence of metal ions for 24 h, and they were compared to that obtained after incubation in the absence of any metal ion. The CRL activity was stimulated by the chloride salts of Li⁺, K⁺ and Mg²⁺ for all concentrations considered and the highest enhancement was achieved by Li⁺ with a 1.24–1.75 fold increase observed. The effects of metal ions on the enantioselectivity of CRL were investigated by performing the hydrolysis of racemic Naproxen methyl ester in the same biphasic medium containing Li⁺, Na⁺, K⁺, Mg²⁺ and Zn²⁺ ions. The addition of metal ions increased the hydrolysis rate by ca. 1.31–1.45 fold relative to the control, whereas the enantiomeric excess of product increased slightly in the presence of the metal ions. The effect of Triton X‐100 on the activity and enantioselectivity of the CRL was also investigated by employing 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 mM concentrations of it in phosphate buffer solution of the biphasic medium. High concentrations of Triton X‐100 stimulated the enzyme activity up to 1.66 fold after 24 h incubation. Triton X‐100 increased the hydrolysis rate almost independently of the concentration.     

Sur la transformation de pseudo-Wigner-Ville discrète en temps et en fréquence

The pseudo-Wigner-Ville distribution(PWVD) was proposed in the context of digital evaluation of the Wigner-Ville distribution (WVD). It plays a particularly important role in practice. The utilization efficiency of the time-frequency analysis method is in fact directly related to the appropriate use of this notion. To this end, the perfect knowledge of thePWVD’ behaviour in the discrete case is of fondamental importance. In this paper, we investigate, in a precise and systematic way, thePWVD discrete both in time and in frequency, and show the resultant consequence on its numerical computation and digital implementation.