An application of the algorithm of the cyclic coordinate descent in multidimensional optimization problems with constrained speed

In this paper we present an application of the algorithm of the cyclic coordinate descent in multidimensional variational problems with constrained speed, the physical motivation of the problem being the optimization of hydrothermal systems. The proof of the convergence of the succession generated by the algorithm was based on the use of an appropriate adaptation of Zangwill’s global theorem of convergence. We have also included an algorithm for the formal construction of the descending succession (the solution of an optimum control problem), the approximation of which we carried out using an adaptation of the Euler method in conjunction with a procedure inspired by the shooting method.     

Stochastic comparisons of multivariate mixture models

In this paper we consider sufficient conditions in order to stochastically compare random vectors of multivariate mixture models. In particular we consider stochastic and convex orders, the likelihood ratio order, and the hazard rate and mean residual life dynamic orders. Applications to proportional hazard models and mixture models in risk theory are also given.     

<Emphasis Type="Italic">X</Emphasis>-coordinates of Pell equations as sums of two tribonacci numbers

In this paper, we find all positive squarefree integers d such that the Pell equation \(X^2 - dY^2 = \pm 1\) has at least two positive integer solutions (X, Y) and \((X^{\prime },Y^{\prime })\) such that both X and \(X^{\prime }\) are sums of two Tribonacci numbers.     

An approximate global solution of Einstein’s equations for a differentially rotating compact body

We obtain an approximate global stationary and axisymmetric solution of Einstein’s equations which can be thought of as a simple star model: a self-gravitating perfect fluid ball with a differential rotation motion pattern. Using the post-Minkowskian formalism (weak-field approximation) and considering rotation as a perturbation (slow-rotation approximation), we find approximate interior and exterior (asymptotically flat) solutions to this problem in harmonic coordinates. Interior and exterior solutions are matched, in the sense described by Lichnerowicz, on the surface of zero pressure, to obtain a global solution. The resulting metric depends on four arbitrary constants: mass density; rotational velocity at \(r=0\); a parameter that accounts for the change in rotational velocity through the star; and the star radius in the non-rotation limit. The mass, angular momentum, quadrupole moment and other constants of the exterior metric are determined in terms of these four parameters.     

Weak hydrogen-, halogen- and stacking ππ bonding in crystalline 5-chloro-1-indanone. An analysis by using X-ray diffraction, vibrational spectroscopy and theoretical methods

Intermolecular forces of C–HO, C–Hπ, COCl and ππ types are present in the stable triclinic crystal structure of 5-chloro-1-indanone. They are analysed from a geometrical point of view supported in some extent by the analysis of the vibrational spectrum of the titled compound. Moreover, the molecular structure of the isolated species is calculated by using ab initio as well as density functional theory (DFT) methods together an assortment of basis sets. In order to obtain some information about the influence of intermolecular forces on the molecular structure, the calculated geometries of a free molecule were compared with the experimental solid phase geometry determined by X-ray crystallography.An analysis and assignment of the vibrational spectrum of the 5-chloro-1-indanone is accomplished by using IR and Raman experimental data along with Pulay et al.’s scaled quantum mechanical force field (SQM) methodology starting from the theoretical B3LYP/6-31G(d) and BLYP/6-31G(d) force fields under C_s symmetry.     

Determination of foscarnet (trisodium phosphonoformate) in pharmaceutical preparations by high-performance liquid chromatography with ultraviolet detection

An isocratic high-performance liquid chromatographic method with UV detection has been developed and validated for the quantitative determination of foscarnet in isoosmotic sodium chloride aqueous solution. The mobile phase consisted of mixture of methanol:water (30:70 v/v), containing 1 mm tetrahexylammonium hydrogen sulphate at pH 5.80. The analyte was separated on a reversed-phase C(18) column packed with 4 microm spherical particles of octadecylsilane. Hydrochlorothiazide was used as internal standard. UV detection at 232 nm allowed a quantification limit of 50 microg/mL. The assay was linear from 50 to 4000 microg/mL. The coefficient of variation was < or =2.52% for intra-assay precision and < or =3.49% for inter-assay precision. The deviation from the nominal value ranged from -0.57 to 0.47% for the same-day accuracy and from -0.75 to 3.06% for day-to-day accuracy.     

Tracking fin whale calls offshore the Galicia Margin, North East Atlantic Ocean

Data recorded during a temporary deployment of ocean bottom seismometers (OBSs) are used in this study to monitor the presence of fin whales around the array. In the summer of 2003, ten OBSs were placed 250 km from the NW coast of Iberia in the Galicia Margin, NE Atlantic Ocean for a period of one month. The recorded data set provided a large variety of signals, including fin whale vocalizations identified by their specific acoustic signature. The use of a dense array of seafloor receivers allowed investigation into the locations and tracks of the signal-generating whales using a seismological hypocentral location code. Individual pulses of different sequences have been chosen to study such tracks. Problems related to the correct identification of pulses, discrimination between direct and multiple arrivals, and the presence of more than one individual have been considered prior to location. Fin calls were concentrated in the last two weeks of the deployment and the locations were spread around the area covered by the array. These results illustrate that, besides its classical seismological aim, deployment of semipermanent seafloor seismic arrays can also provide valuable data for marine mammal behavior studies.     

X-ray photoelectron spectroscopy study of pyrolytically coated graphite platforms submitted to simulated electrothermal atomic absorption spectrometry conditions

The present work is part of an ongoing project aiming to a better understanding of the mechanisms of atomization on graphite furnace platforms used for electrothermal atomic absorption spectrometry (ETAAS). It reports the study of unused pyrolytic graphite coated platforms of commercial origin, as well as platforms thermally or thermo-chemically treated under simulated ETAAS analysis conditions. X-ray photoelectron spectroscopy (XPS) was employed to study the elements present at the surfaces of the platforms. New, unused platforms showed the presence of molybdenum, of unknown origin, in concentrations up to 1 at.%. Species in two different oxidations states (Mo⁶⁺ and Mo²⁺) were detected by analyzing the Mo 3d spectral region with high resolution XPS. The analysis of the C 1s region demonstrated the presence of several signals, one of these at 283.3 eV related to the presence of Mo carbide. The O 1s region showed also various peaks, including a signal that can be attributed to the presence of MoO₃. Some carbon and oxygen signals were consistent with the presence of CO and C-O- (probably C-OH) groups on the platforms surfaces. Upon thermal treatment up to 2900 °C, the intensity of the Mo signal decreased, but peaks due to Mo oxides (Mo⁶⁺ and Mo⁵⁺) and carbide (Mo²⁺) were still apparent. Thermo-chemical treatment with 3 vol.% HCl solutions and heating up to 2900 °C resulted in further diminution of the Mo signal, with complete disappearance of Mo carbide species. Depth profiling of unused platforms by Ar⁺ ion etching at increasing time periods demonstrated that, upon removal of several layers of carbonaceous material, the Mo signal disappears suggesting that this contamination is present only at the surface of the pyrolytic graphite platform.     

Effects of poly(vinyl alcohol) additions on the structure of silica xerogels

Poly(vinyl alcohol)/silica hybrid xerogels were prepared from sonohydrolysis of tetraethoxysilane (TEOS) and additions of water-solution of poly(vinyl alcohol) (PVA). The samples were studied by small-angle X-ray scattering (SAXS), nitrogen adsorption, and differential scanning calorimetry (DSC). On drying at room temperature the resulting xerogels exhibit a fairly bimodal porous structure composed by small mesopores and micropores. The pore size distribution of the mesopores was found to follow approximately a power-law with the pore size. The micropore structure was associated to an evolution at a high resolution level of the mass fractal structure of the original wet gels. The role of the PVA addition on the pore structure of the xerogels is to diminish the specific surface area and the pore volume without to change substantially the pore mean size.     

The hybrid flow shop scheduling problem

The scheduling of flow shops with multiple parallel machines per stage, usually referred to as the hybrid flow shop (HFS), is a complex combinatorial problem encountered in many real world applications. Given its importance and complexity, the HFS problem has been intensively studied. This paper presents a literature review on exact, heuristic and metaheuristic methods that have been proposed for its solution. The paper briefly discusses and reviews several variants of the HFS problem, each in turn considering different assumptions, constraints and objective functions. Research opportunities in HFS are also discussed.