Descripción: We present an approach based on integer programming formulations of the graph coloring problem. Our goal is to develop models that remove some symmetrical solutions obtained by color permutations. We study the problem from a polyhedral point of view and determine some families of facets of the 0/1-polytope associated with one of these integer programming formulations. The theoretical results described here are used to design an efficient Cutting Plane algorithm. © 2007 Elsevier B.V. All rights reserved.

Descripción: Plasma temperature and radial density profiles of the plasma species in a high energy density cutting arc have been obtained by using a quantitative schlieren technique. A Z-type two-mirror schlieren system was used in this research. Due to its great sensibility such technique allows measuring plasma composition and temperature from the arc axis to the surrounding medium by processing the gray-level contrast values of digital schlieren images recorded at the observation plane for a given position of a transverse knife located at the exit focal plane of the system. The technique has provided a good visualization of the plasma flow emerging from the nozzle and its interactions with the surrounding medium and the anode. The obtained temperature values are in good agreement with those values previously obtained by the authors on the same torch using Langmuir probes. © 2010 American Institute of Physics.

Descripción: The crystal structure of the title compound, C12H8-N2O6S, has been determined by single-crystal X-ray diffraction. The compound crystallizes in the noncentrosymmetric P21 space group. The substituted aromatic ring has a slightly deformed boat conformation. The ο-NO2 and p-NO2 groups are twisted out of the plane of the phenyl ring. The unsubstituted aromatic ring is planar and the dihedral angle between the mean plane of the rings is 71.1 (2)○. Short C - H⋯O intermolecular contacts stabilize the three-dimensional structure.

Descripción: Using a quasiclassical approach, we demonstrate that the formation of the low-energy structure in above-threshold ionization spectra by intense, midinfrared laser pulses originates from a two-dimensional focusing of the strong-field dynamics in the energy-angular-momentum plane. We show that the low-energy structure is very sensitive to the carrier-envelope phase of the laser field. © Owned by the authors, published by EDP Sciences, 2013.

Descripción: In the title compound, C13H11N3O4, the substituted aromatic ring has a slightly deformed chair conformation and the unsubstituted ring a deformed boat conformation. The dihedral angle between the mean planes of the rings is 62.9 (1)°. The o-nitro group is twisted out of the plane of the phenyl ring. Short C - H⋯O intermolecular contacts stabilize the three-dimensional structure.

Descripción: A Newtonian equation in the plane is considered. There is a central force (attractive or repulsive) and an external force λh(t), periodic in time. The periodic second primitive of h(t) defines a planar curve and the number of periodic solutions of the differential equation is linked to the number of loops of this curve, at least when the parameter λ is large. © 2011 Springer Basel AG.

Descripción: In this work we present an anamorphic zoom system, based on liquid crystal displays, which allows changing the magnification and distortion of an image very quickly, without mechanical parts and keeping the output plane stationary. The anamorphic lenses that make up the optical processor are obtained by displaying a combination of convergent-divergent cylindrical lenses, with arbitrary orientations, onto the spatial light modulators. In order to illustrate the capabilities of the system, some experimental results are shown.

Descripción: We report experimental results on the magnetic and transport properties of Ag/Co 90Fe 10 multilayers with variable Ag and Co 90Fe 10 thicknesses. The magnetism samples was characterized by magnetization measurements and ferromagnetic resonance spectroscopy. These measurements show that the magnetic layers are in general composed by single-domain particles and that the shape and the size of the magnetic clusters can be changed by using an applied magnetic field (H dep) on deposition. The resistivity of these multilayered systems is described by a mixed model that includes current-in-plane and current perpendicular plane transport contributions. The transport model proposed to explain the experimental results emphasizes the role played by the magnetic entities on the scattering processes and strongly depends on the silver layer thickness. An electrical percolative transition is observed for samples grown at H dep>H* dep while the magnetic properties of these samples still show a granularlike behavior. © 2004 American Institute of Physics.

Descripción: The fundamental space ζ is defined as the set of entire analytic functions [test functions φ(z)], which are rapidly decreasing on the real axis. The variable z corresponds to the complex energy plane. The conjugate or dual space ζ′ is the set of continuous linear functionals (distributions) on ζ. Among those distributions are the propagators, determined by the poles implied by the equations of motion and the contour of integration implied by the boundary conditions. All propagators can be represented as linear combinations of elementary (one pole) functionals. The algebra of convolution products is also determined. The Fourier transformed space ζ̃ contains test functions φ̃(x). These functions are extra-rapidly decreasing, so that the exponentially increasing solutions of higher-order equations are distributions on ζ̃. © 1994 American Institute of Physics.

Descripción: A Three-Dimensional Finite Volume Arbitrary Lagrangian-Eulerian simulation code was developed to study different plasma physics problems in 3D+t. The code is based on a complex multi-component species program with transport and radiation terms written and applied to plasma and fusion physics problems. Three different examples are shown: double-base chemical propellant combustion, ignition and propagation of a thermonuclear detonation wave, and, the development of the Kelvin-Helmholtz (KH) instability in local plane slab models of the magnetopause, showing the response of a background equilibrium to the excitation by finite amplitude perturbations generated upstream. © 2006 American Institute of Physics.

Descripción: A method is developed to solve Laplace's equation with Dirichlet's or Neumann's conditions in plane, single-connected regions bounded by arbitrary single curves. It is based on the existence of a conformal transformation that reduces the original problem to another whose solution is known. The main advantage of the method is that it does not require the knowledge of the transformation itself, so it is applicable even when no transformation is available. The solution and its higher-order derivatives are expressed in terms of explicit quadratures easy to evaluate numerically or even analytically. © 1990 American Institute of Physics.

Descripción: We present an overview of the validity of the Proximity Force Approximation (PFA) in the calculation of Casimir forces between perfect conductors for different geometries, with particular emphasis for the configuration of a cylinder in front of a plane. In all cases we compare the exact numerical results with those of PFA, and with asymptotic expansions that include the next to leading order corrections. We also discuss the similarities and differences between the results for Casimir and electrostatic forces. © 2009 IOP Publishing Ltd.

Descripción: In this paper we study the problem of estimating the generalized Hausdorff dimension of Furstenberg sets in the plane. For α ∈ (0, 1], a set F in the plane is said to be an α-Furstenberg set if for each direction e there is a line segment ℓe in the direction of e for which dimH (ℓe ∩ F) ≥ α. It is well known that dimH (F) ≥ max {2 α, α + frac(1, 2)}, and it is also known that these sets can have zero measure at their critical dimension. By looking at general Hausdorff measures Hh defined for doubling functions, that need not be power laws, we obtain finer estimates for the size of the more general h-Furstenberg sets. Further, this approach allow us to sharpen the known bounds on the dimension of classical Furstenberg sets. The main difficulty we had to overcome, was that if Hh (F) = 0, there always exists g ≺ h such that Hg (F) = 0 (here ≺ refers to the natural ordering on general Hausdorff dimension functions). Hence, in order to estimate the measure of general Furstenberg sets, we have to consider dimension functions that are a true step down from the critical one. We provide rather precise estimates on the size of this step and by doing so, we can include a family of zero dimensional Furstenberg sets associated to dimension functions that grow faster than any power function at zero. With some additional growth conditions on these zero dimensional functions, we extend the known inequalities to include the endpoint α = 0. © 2009 Elsevier Inc. All rights reserved.

Descripción: The Traveling Deliveryman Problem is a generalization of the Minimum Cost Hamiltonian Path Problem where the starting vertex of the path, i.e. a depot vertex, is fixed in advance and the cost associated with a Hamiltonian path equals the sum of the costs for the layers of paths (along the Hamiltonian path) going from the depot vertex to each of the remaining vertices. In this paper, we propose a new Integer Programming formulation for the problem and computationally evaluate the strength of its Linear Programming relaxation. Computational results are also presented for a cutting plane algorithm that uses a number of valid inequalities associated with the proposed formulation. Some of these inequalities are shown to be facet defining for the convex hull of feasible solutions to that formulation. These inequalities proved very effective when used to reinforce Linear Programming relaxation bounds, at the nodes of a Branch and Bound enumeration tree. © 2008 Elsevier B.V. All rights reserved.

Descripción: Herein we present a detailed analysis of the optical response of artificial opal films realized employing a near-field scanning optical microscope in collection and transmission modes. Near-field patterns measured at the rear surface when a plane wave impinges on the front face are presented with the finding that optical intensity maps present a clear correlation with the periodic arrangement of the outer surface. Calculations based on the vector Korringa-Kohn-Rostoker method reproduce the different profiles experimentally observed as well as the response to the polarization of the incident field. These observations constitute the first experimental confirmation of the collective lattice resonances that give rise to the optical response of these three dimensional periodic structures in the high-energy range. © 2011 American Institute of Physics.

Descripción: Imaging of samples by different microscopy techniques has produced a relevant impact in the development of new diagnosis techniques in biology, medicine and material science. In many biological, applications, where the sample changes or moves during the observation, a moving spot to track an identified sample is required. We introduce here an optical system that can perform, this tracking without mechanical components. The system, is based on the use of a high resolution liquid crystal on silicon (LCoS) device working as a mostly phase wave front modulator. The additional advantage of this system is performing the motion of the spot at video rate. In general, these devices produce coupled phase and amplitude modulation responses as a function of the applied voltage. This coupling effect deteriorates the response of those ideal optical elements designed as phase only or amplitude only functions. By means of an elliptical polarization light we can reduce the amplitude modulation and improve the phase modulation. We have experimentally found a configuration where the amplitude is almost constant while the phase reaches a high modulation. For this configuration we show how the spot can be moved through, focus plane by means of linear phases, or displaced out of this plane by using a quadratic phase. © 2008 American Institute of Physics.

Descripción: In order to increase the understanding of the interactions which define the planar conformation of the methoxy group with respect to the aryl ring in methyl aryl ethers and the effect these interactions have on the methoxy NMR parameters, 17O and 13C spectra were measured and ab initio optimized geometries were calculated for three different conformations of the methoxy group in 2-methoxy-5-X-pyridines (X = H, NO2, and NH2). 17O and 13C chemical shifts were also calculated using the LORG approach. It was found that, contrary to what has been commonly assumed, the oxygen and the carbon of the methoxy group are deshielded when the electronic resonance interaction is increased. Therefore, the large 13C deshielding effect observed for a conformation with an out-of-plane methoxy group in aryl methyl ethers and related compounds has to be attributed to the inhibition of the attractive van der Waals forces between the methyl moiety and the aromatic ortho-cis carbon atom. © 1993 American Chemical Society.

Descripción: Group of microstructures present in the Ordovician Yerba Loca and Los Sombreros Formations (cropping out in the vicinity of Road 150, between cuesta del Viento and Los Túneles), are described and interpreted. Cleavage, joints and fractures, shear zones, planar and sigmoid (en echelon) veins and kink bands are most common among them. Folded and domino faulted quartz veins, resulting from pressure solution contraction during formation of axial plane cleavage, are an outstanding feature and allowed calculation of contraction associated to cleavage development. The assemblage of minor structures shows coherency with the major structures hosting them and evidences a systematic displacement and stacking of rock masses from west to east. They also show the important participation of pressure solution and re-crystallization processes during deformation, along with progressive deformation due to rotation of local structures in the regional stress field.

Descripción: We calculate the exact Casimir interaction energy between two perfectly conducting, very long, eccentric cylindrical shells using a mode summation technique. Several limiting cases of the exact formula for the Casimir energy corresponding to this configuration are studied both analytically and numerically. These include concentric cylinders, cylinder-plane and eccentric cylinders, for small and large separations between the surfaces. For small separations we recover the proximity approximation, while for large separations we find a weak logarithmic decay of the Casimir interaction energy, typical of cylindrical geometries. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.