Análise de um modelo matemático de localização na reorganização de uma rede logística estabelecida

A crescente competição entre cadeias de suprimento geradas pela globalização da economia e pela inovação tecnológica gerou a necessidade de redes logísticas cada vez mais complexas. Desta forma, o planejamento de redes logísticas tornou-se cada vez mais importante e a localização de instalações um assunto estratégico em busca da vantagem competitiva. O presente estudo insere-se em uma corrente de pesquisa sobre a teoria da localização de instalações e tem como objetivo analisar uma rede logística estabelecida definindo a quantidade e a localização de um ou mais Centros de Distribuição que minimize os custos totais associados à cadeia como um todo, sem comprometimento do nível de serviço. Para tal, um modelo de programação não-linear é proposto para a resolução de um problema real de uma empresa do setor petrolífero. É, ainda, proposto um método de análise para problemas de localização de instalações, onde são listadas as principais etapas a serem seguidas. Por fim, será apresentada uma análise de sensibilidade no intuito de se obterem insights gerenciais, onde serão gerados e otimizados diferentes cenários. Os resultados obtidos com a implementação computacional do modelo por meio do software AIMMS se mostraram adequados para a resolução do problema proposto, estando as conclusões obtidas em concordância com a literatura especializada

The effects of interface morphology on Schottky barrier heights: a case study on Al/GaAs(001)

The problem of Fermi-level pinning at semiconductor-metal contacts is readdressed starting from first-principles calculations for Al/GaAs. We give quantitative evidence that the Schottky barrier height is very little affected by any structural distortions on the metal side---including elongations of the metal-semiconductor bond (i.e. interface strain)---whereas it strongly depends on the interface structure on the semiconductor side. A rationale for these findings is given in terms of the interface dipole generated by the ionic effective charges.Comment: 5 pages, latex file, 2 postscript figures automatically include

Molecular Coancestry and Classical Genetic Distances Depict Different Patterns of Relationship Among Sheep Breeds from Southern Italy

Several molecular-based parameters, such as similarity indexes, can be adopted to optimize the management of genetic diversity in conservation programmes. From simulated data, Oliehoek et al. (2006) showed that molecular coancestry (Toro et al., 2002) is, among the possible relatedness estimators, the one that performs better in structured populations, such as populations in need of conservation usually are. Several studies have, therefore, proposed the use of molecular coancestry coefficients as a measure of genetic variability and as a useful tool for conservation of endangered breeds (Ciampolini et al., 2007; Glowatzki-Mullis et al., 2009). Here we report the results obtained evaluating within- and between-breed molecular coancestry (Toro et al., 2002), together with other classical genetic parameters, for two insular sheep breeds (Sarda from Sardinia and Comisana from Sicily), recently spread almost all over Italy, and for five local rare sheep breeds from Southern Italy

The band structure of BeTe - a combined experimental and theoretical study

Using angle-resolved synchrotron-radiation photoemission spectroscopy we have determined the dispersion of the valence bands of BeTe(100) along $\Gamma X$, i.e. the [100] direction. The measurements are analyzed with the aid of a first-principles calculation of the BeTe bulk band structure as well as of the photoemission peaks as given by the momentum conserving bulk transitions. Taking the calculated unoccupied bands as final states of the photoemission process, we obtain an excellent agreement between experimental and calculated spectra and a clear interpretation of almost all measured bands. In contrast, the free electron approximation for the final states fails to describe the BeTe bulk band structure along $\Gamma X$ properly.Comment: 21 pages plus 4 figure

Equation of state of fully ionized electron-ion plasmas

Thermodynamic quantities of Coulomb plasmas consisting of point-like ions immersed in a compressible, polarizable electron background are calculated for ion charges Z=1 to 26 and for a wide domain of plasma parameters ranging from the Debye-Hueckel limit to the crystallization point and from the region of nondegenerate to fully degenerate nonrelativistic or relativistic electrons. The calculations are based on the linear-response theory for the electron-ion interaction, including the local-field corrections in the electronic dielectric function. The thermodynamic quantities are calculated in the framework of the N-body hypernetted-chain equations and fitted by analytic expressions. We present also accurate analytic approximations for the free energy of the ideal electron gas at arbitrary degeneracy and relativity and for the excess free energy of the one-component plasma of ions (OCP) derived from Monte Carlo simulations. The extension to multi-ionic mixtures is discussed within the framework of the linear mixing rule. These formulae provide a completely analytic, accurate description of the thermodynamic quantities of fully ionized electron-ion Coulomb plasmas, a useful tool for various applications from liquid state theory to dense stellar matter.Comment: 13 pages, 2 tables, 7 figures, REVTeX using epsf.sty. To be published in Phys. Rev. E, vol. 58 (1998

BAs and boride III-V alloys

Boron arsenide, the typically-ignored member of the III-V arsenide series BAs-AlAs-GaAs-InAs is found to resemble silicon electronically: its Gamma conduction band minimum is p-like (Gamma_15), not s-like (Gamma_1c), it has an X_1c-like indirect band gap, and its bond charge is distributed almost equally on the two atoms in the unit cell, exhibiting nearly perfect covalency. The reasons for these are tracked down to the anomalously low atomic p orbital energy in the boron and to the unusually strong s-s repulsion in BAs relative to most other III-V compounds. We find unexpected valence band offsets of BAs with respect to GaAs and AlAs. The valence band maximum (VBM) of BAs is significantly higher than that of AlAs, despite the much smaller bond length of BAs, and the VBM of GaAs is only slightly higher than in BAs. These effects result from the unusually strong mixing of the cation and anion states at the VBM. For the BAs-GaAs alloys, we find (i) a relatively small (~3.5 eV) and composition-independent band gap bowing. This means that while addition of small amounts of nitrogen to GaAs lowers the gap, addition of small amounts of boron to GaAs raises the gap (ii) boron ``semi-localized'' states in the conduction band (similar to those in GaN-GaAs alloys), and (iii) bulk mixing enthalpies which are smaller than in GaN-GaAs alloys. The unique features of boride III-V alloys offer new opportunities in band gap engineering.Comment: 18 pages, 14 figures, 6 tables, 61 references. Accepted for publication in Phys. Rev. B. Scheduled to appear Oct. 15 200

Thermal Density Functional Theory in Context

This chapter introduces thermal density functional theory, starting from the ground-state theory and assuming a background in quantum mechanics and statistical mechanics. We review the foundations of density functional theory (DFT) by illustrating some of its key reformulations. The basics of DFT for thermal ensembles are explained in this context, as are tools useful for analysis and development of approximations. We close by discussing some key ideas relating thermal DFT and the ground state. This review emphasizes thermal DFT's strengths as a consistent and general framework.Comment: Submitted to Spring Verlag as chapter in "Computational Challenges in Warm Dense Matter", F. Graziani et al. ed

Linear and Second-order Optical Response of the III-V Mono-layer Superlattices

We report the first fully self-consistent calculations of the nonlinear optical properties of superlattices. The materials investigated are mono-layer superlattices with GaP grown on the the top of InP, AlP and GaAs (110) substrates. We use the full-potential linearized augmented plane wave method within the generalized gradient approximation to obtain the frequency dependent dielectric tensor and the second-harmonic-generation susceptibility. The effect of lattice relaxations on the linear optical properties are studied. Our calculations show that the major anisotropy in the optical properties is the result of strain in GaP. This anisotropy is maximum for the superlattice with maximum lattice mismatch between the constituent materials. In order to differentiate the superlattice features from the bulk-like transitions an improvement over the existing effective medium model is proposed. The superlattice features are found to be more pronounced for the second-order than the linear optical response indicating the need for full supercell calculations in determining the correct second-order response.Comment: 9 pages, 4 figures, submitted to Phy. Rev.

Effects of anharmonic strain on phase stability of epitaxial films and superlattices: applications to noble metals

Epitaxial strain energies of epitaxial films and bulk superlattices are studied via first-principles total energy calculations using the local-density approximation. Anharmonic effects due to large lattice mismatch, beyond the reach of the harmonic elasticity theory, are found to be very important in Cu/Au (lattice mismatch 12%), Cu/Ag (12%) and Ni/Au (15%). We find that is the elastically soft direction for biaxial expansion of Cu and Ni, but it is for large biaxial compression of Cu, Ag, and Au. The stability of superlattices is discussed in terms of the coherency strain and interfacial energies. We find that in phase-separating systems such as Cu-Ag the superlattice formation energies decrease with superlattice period, and the interfacial energy is positive. Superlattices are formed easiest on (001) and hardest on (111) substrates. For ordering systems, such as Cu-Au and Ag-Au, the formation energy of superlattices increases with period, and interfacial energies are negative. These superlattices are formed easiest on (001) or (110) and hardest on (111) substrates. For Ni-Au we find a hybrid behavior: superlattices along and like in phase-separating systems, while for they behave like in ordering systems. Finally, recent experimental results on epitaxial stabilization of disordered Ni-Au and Cu-Ag alloys, immiscible in the bulk form, are explained in terms of destabilization of the phase separated state due to lattice mismatch between the substrate and constituents.Comment: RevTeX galley format, 16 pages, includes 9 EPS figures, to appear in Physical Review

Methylation-associated down-regulation of RASSF1A and up-regulation of RASSF1C in pancreatic endocrine tumors

<p>Abstract</p> <p>Background</p> <p><it>RASSF1A </it>gene silencing by DNA methylation has been suggested as a major event in pancreatic endocrine tumor (PET) but <it>RASSF1A </it>expression has never been studied. The <it>RASSF1 </it>locus contains two CpG islands (<it>A </it>and <it>C</it>) and generates seven transcripts (<it>RASSF1A</it>-<it>RASSF1G</it>) by differential promoter usage and alternative splicing.</p> <p>Methods</p> <p>We studied 20 primary PETs, their matched normal pancreas and three PET cell lines for the (i) methylation status of the <it>RASSF1 </it>CpG islands using methylation-specific PCR and pyrosequencing and (ii) expression of <it>RASSF1 </it>isoforms by quantitative RT-PCR in 13 cases. CpG island A methylation was evaluated by methylation-specific PCR (MSP) and by quantitative methylation-specific PCR (qMSP); pyrosequencing was applied to quantify the methylation of 51 CpGs also encompassing those explored by MSP and qMSP approaches.</p> <p>Results</p> <p>MSP detected methylation in 16/20 (80%) PETs and 13/20 (65%) normal pancreas. At qMSP, 11/20 PETs (55%) and 9/20 (45%) normals were methylated in at least 20% of <it>RASSF1A </it>alleles.</p> <p>Pyrosequencing showed variable distribution and levels of methylation within and among samples, with PETs having average methylation higher than normals in 15/20 (75%) cases (<it>P </it>= 0.01). The evaluation of mRNA expression of <it>RASSF1 </it>variants showed that: i) <it>RASSF1A </it>was always expressed in PET and normal tissues, but it was, on average, expressed 6.8 times less in PET (<it>P </it>= 0.003); ii) <it>RASSF1A </it>methylation inversely correlated with its expression; iii) <it>RASSF1 </it>isoforms were rarely found, except for <it>RASSF1B </it>that was always expressed and <it>RASSF1C </it>whose expression was 11.4 times higher in PET than in normal tissue (<it>P </it>= 0.001). A correlation between <it>RASSF1A </it>expression and gene methylation was found in two of the three PET cell lines, which also showed a significant increase in <it>RASSF1A </it>expression upon demethylating treatment.</p> <p>Conclusions</p> <p><it>RASSF1A </it>gene methylation in PET is higher than normal pancreas in no more than 75% of cases and as such it cannot be considered a marker for this neoplasm. <it>RASSF1A </it>is always expressed in PET and normal pancreas and its levels are inversely correlated with gene methylation. Isoform <it>RASSF1C </it>is overexpressed in PET and the recent demonstration of its involvement in the regulation of the Wnt pathway points to a potential pathogenetic role in tumor development.</p