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Search Results: 1 - 10 of 311113 matches for " Andres J. Ruiz-Vargas "
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Many disjoint edges in topological graphs
Andres J. Ruiz-Vargas
Mathematics , 2014,
Abstract: A monotone cylindrical graph is a topological graph drawn on an open cylinder with an infinite vertical axis satisfying the condition that every vertical line intersects every edge at most once. It is called simple if any pair of its edges have at most one point in common: an endpoint or a point at which they properly cross. We say that two edges are disjoint if they do not intersect. We show that every simple complete monotone cylindrical graph on $n$ vertices contains $\Omega(n^{1-\epsilon})$ pairwise disjoint edges for any $\epsilon>0$. As a consequence, we show that every simple complete topological graph (drawn in the plane) with $n$ vertices contains $\Omega(n^{\frac 12-\epsilon})$ pairwise disjoint edges for any $\epsilon>0$. This improves the previous lower bound of $\Omega(n^\frac 13)$ by Suk which was reproved by Fulek and Ruiz-Vargas. We remark that our proof implies a polynomial time algorithm for finding this set of pairwise disjoint edges.
Disjoint edges in topological graphs and the tangled-thrackle conjecture
Andres J. Ruiz-Vargas,Andrew Suk,Csaba D. Tóth
Computer Science , 2014,
Abstract: It is shown that for a constant $t\in \mathbb{N}$, every simple topological graph on $n$ vertices has $O(n)$ edges if it has no two sets of $t$ edges such that every edge in one set is disjoint from all edges of the other set (i.e., the complement of the intersection graph of the edges is $K_{t,t}$-free). As an application, we settle the \emph{tangled-thrackle} conjecture formulated by Pach, Radoi\v{c}i\'c, and T\'oth: Every $n$-vertex graph drawn in the plane such that every pair of edges have precisely one point in common, where this point is either a common endpoint, a crossing, or a point of tangency, has at most $O(n)$ edges.
Imaging Grains and Grain Boundaries in Single-Layer Graphene: An Atomic Patchwork Quilt
Pinshane Y. Huang,Carlos S. Ruiz-Vargas,Arend M. van der Zande,William S. Whitney,Shivank Garg,Jonathan S. Alden,Caleb J. Hustedt,Ye Zhu,Jiwoong Park,Paul L. McEuen,David A. Muller
Physics , 2010, DOI: 10.1038/nature09718
Abstract: The properties of polycrystalline materials are often dominated by the size of their grains and by the atomic structure of their grain boundaries. These effects should be especially pronounced in 2D materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, a hexagonal two-dimensional crystal of carbon atoms; Single-atom-thick graphene sheets can now be produced by chemical vapor deposition on up to meter scales, making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic, magnetic, chemical, and mechanical properties which strongly depend on their atomic arrangement. Yet, because of the five-order-of-magnitude size difference between grains and the atoms at grain boundaries, few experiments have fully explored the graphene grain structure. Here, we use a combination of old and new transmission electron microscope techniques to bridge these length scales. Using atomic-resolution imaging, we determine the location and identity of every atom at a grain boundary and find that different grains stitch together predominantly via pentagon-heptagon pairs. We then use diffraction-filtered imaging to rapidly map the location, orientation, and shape of several hundred grains and boundaries, where only a handful have been previously reported. The resulting images reveal an unexpectedly small and intricate patchwork of grains connected by tilt boundaries. By correlating grain imaging with scanned probe measurements, we show that these grain boundaries dramatically weaken the mechanical strength of graphene membranes, but do not measurably alter their electrical properties. These techniques open a new window for studies on the structure, properties, and control of grains and grain boundaries in graphene and other 2D materials.
Ultrafast Relaxation Dynamics of Hot Optical Phonons in Graphene
Haining Wang,Jared H. Strait,Paul A. George,Shriram Shivaraman,Virgil B. Shields,Mvs Chandrashekhar,Jeonghyun Hwang,Carlos S. Ruiz-Vargas,Farhan Rana,Michael G. Spencer,Jiwoong Park
Physics , 2009, DOI: 10.1063/1.3291615
Abstract: Using ultrafast optical pump-probe spectroscopy, we study the relaxation dynamics of hot optical phonons in few-layer and multi-layer graphene films grown by epitaxy on silicon carbide substrates and by chemical vapor deposition on nickel substrates. In the first few hundred femtoseconds after photoexcitation, the hot carriers lose most of their energy to the generation of hot optical phonons which then present the main bottleneck to subsequent carrier cooling. Optical phonon cooling on short time scales is found to be independent of the graphene growth technique, the number of layers, and the type of the substrate. We find average phonon lifetimes in the 2.5-2.55 ps range. We model the relaxation dynamics of the coupled carrier-phonon system with rate equations and find a good agreement between the experimental data and the theory. The extracted optical phonon lifetimes agree very well with the theory based on anharmonic phonon interactions.
GEOINFORMATION DENSITY:: A criterion on ANH Block Negotiation
Vargas J.,Carlos A.; Zamora R.,Armando; Pardo,Andres;
Earth Sciences Research Journal , 2007,
Abstract: based on the general information included within the anh exploration and production information service, the information distribution densities of the colombian territory were determined. these densities are referred in seismic length per square kilometer and amounts in magnetic-gravimetric and geochemical information data or drill-hole length per sq. km. a probabilistic distribution was assessed along the density distribution and cost distribution for each variable. the variables, as information layers, were cross-referenced in order to define relative weights that assess information with respect to the presence or absence of information in the treated area. this procedure could be regarded as a methodological support proposal for area negotiation of the oil industry. a better approach to the quandary should include: new input of data into the system, a division of the territory in smaller areas adjusting to complex geometries, and considering the particular market conditions for each basin. nevertheless, it is apparent that the obtained results favor the consolidation of a conceptual framework that at medium term will allow a conscious approach towards block negotiation between the petroleum industry and the anh.
GEOINFORMATION DENSITY: A criterion on ANH Block Negotiation
Vargas J. Carlos A.,Zamora R Armando,Pardo Andres
Earth Sciences Research Journal , 2007,
Abstract: Based on the general information included within the ANH Exploration and Production Information Service, the information distribution densities of the Colombian territory were determined. These densities are referred in seismic length per square kilometer and amounts in magnetic-gravimetric and geochemical information data or drill-hole length per sq. km. A probabilistic distribution was assessed along the density distribution and cost distribution for each variable. The variables, as information layers, were cross-referenced in order to define relative weights that assess information with respect to the presence or absence of information in the treated area. This procedure could be regarded as a methodological support proposal for area negotiation of the oil industry. A better approach to the quandary should include: new input of data into the system, a division of the territory in smaller areas adjusting to complex geometries, and considering the particular market conditions for each basin. Nevertheless, it is apparent that the obtained results favor the consolidation of a conceptual framework that at medium term will allow a conscious approach towards block negotiation between the petroleum industry and the ANH.
Chiral Symmetry Restoration and Scalar-Pseudoscalar partners in QCD
Nicola, A. Gomez;de Elvira, J. Ruiz;Andres, R. Torres
High Energy Physics - Phenomenology , 2013,
Abstract: We present a consistent description of Scalar-Pseudoscalar partner degeneration at the QCD chiral transition in terms of the dominant low-energy physical states for the light quark sector. First, we obtain within model-independent one-loop Chiral Perturbation Theory (ChPT) that the QCD pseudoscalar susceptibility is proportional to the quark condensate. We also show that this chiral-restoring behaviour is compatible with recent lattice results for screening masses and gives rise to degeneration between the scalar and pseudoscalar susceptibilities ($\chi_S$,$\chi_P$) around the transition point, consistently with an O(4)-like current restoration pattern. This scenario is clearly confirmed by lattice data when we compare $\chi_S(T)$ with the quark condensate, expected to scale as $\chi_P(T)$. In addition, we show that saturating $\chi_S$ with the $\sigma/f_0(500)$ broad resonance observed in pion scattering and including its finite temperature dependence, account for the peak structure of $\chi_S(T)$ in lattice data and the associated critical temperature. This is carried out within a unitarized ChPT scheme which generates the resonant state dynamically and is also consistent with partner degeneration.
Experimentos clínicos aleatorizados, o cómo evaluar las intervenciones
Ruiz Morales,álvaro J; Vargas Abello,Lina María;
Revista Colombiana de Psiquiatría , 2007,
Abstract: introduction: randomized clinical trials are used to evaluate interventions (drugs, therapies or surgical techniques), since they control for many possible sources of bias. development: clinical trials must have a control group, assignation to treatment groups must be at random and it is ideal to blind the study subject, the researcher and the analyst for the evaluation. both the experimental and the control interventions must be selected with solid bases, and there should be a genuine uncertainty about their effectiveness and safety. outcome variables should be hard and objective, and if soft variables are used, they must be transformed using predefined methods to make them as objective as possible. if it is not possible to mask the subject or the intervention, double dummy methods should be employed or hard outcomes used.
Experimentos clínicos aleatorizados, o cómo evaluar las intervenciones Randomized Clinical Trials in the Evaluation of Interventions
álvaro J Ruiz Morales,Lina María Vargas Abello
Revista Colombiana de Psiquiatría , 2007,
Abstract: Introducción: Para la evaluación de una intervención (medicamento, terapia, técnica quirúrgica) se utilizan los experimentos clínicos aleatorizados, estudios que controlan de manera automática muchas fuentes de sesgos. Desarrollo: Deben tener siempre un grupo control; la asignación a los grupos de tratamiento debe hacerse mediante el azar, e idealmente, para la evaluación, debe cegarse al sujeto de estudio, al evaluador y a quien hace el análisis. Tanto la intervención experimental como la de control deben haber sido seleccionados con bases sólidas, y debe haber una incertidumbre genuina en relación con su efectividad y seguridad. Debe procurarse que las variables de medición del desenlace sean sólidas y objetivas (duras) o variables blandas que hayan sido obtenidas o transformadas mediante métodos ya definidos. Si no es posible cegar al sujeto o cegar la intervención, puede recurrirse a utilizar el método de doble simulación o a variables de desenlace duras. Introduction: Randomized Clinical Trials are used to evaluate interventions (drugs, therapies or surgical techniques), since they control for many possible sources of bias. Development: Clinical Trials must have a control group, assignation to treatment groups must be at random and it is ideal to blind the study subject, the researcher and the analyst for the evaluation. Both the experimental and the control interventions must be selected with solid bases, and there should be a genuine uncertainty about their effectiveness and safety. Outcome variables should be hard and objective, and if soft variables are used, they must be transformed using predefined methods to make them as objective as possible. If it is not possible to mask the subject or the intervention, double dummy methods should be employed or hard outcomes used.
Effectiveness of Compounded Bioidentical Hormone Replacement Therapy: An Observational Cohort Study
Andres D Ruiz, Kelly R Daniels, Jamie C Barner, John J Carson, Christopher R Frei
BMC Women's Health , 2011, DOI: 10.1186/1472-6874-11-27
Abstract: This was an observational cohort study of women between the ages of 18-89 who received a compounded BHRT product from January 1, 2003 to April 30, 2010 in six community pharmacies. Data included patient demographics, comorbidities, therapeutic outcomes, and hormone therapies. Women self-rated menopausal symptoms as absent, mild, moderate, or severe. Descriptive statistics were used to characterize the patient population, BHRT use, and adverse events. Patient symptom severity was compared at baseline and 3 to 6 months follow-up using the Wilcoxon signed-rank test.Women (n = 296) receiving BHRT at Oakdell Pharmacy had a mean (standard deviation) age of 52 (9) years. The most common BHRT dosage forms utilized were topical (71%) and oral (43%). Compounded BHRT regimens were generally initiated at low doses regardless of route. Women experienced a 25% decrease in emotional lability (p < 0.01), a 25% decrease in irritability (p < 0.01), and a 22% reduction in anxiety (p = 0.01) within 3 to 6 months. These women also experienced a 14% reduction in night sweats (p = 0.09) and a 6% reduction in hot flashes (p = 0.50).This study demonstrates that compounded BHRT improves mood symptoms. Larger studies are needed to examine the impact on vasomotor symptoms, myocardial infarction and breast cancer.Bioidentical Hormone Replacement Therapy (BHRT) describes supplementation of hormones that are molecularly identical to those hormones produced in the human body. Unlike manufactured Conventional Hormone Therapy (CHT), such as conjugated estrogens (CE) and medroxyprogesterone acetate (MPA), BHRT hormones do not contain extra structural moieties which may alter hormone receptor binding and function in the human body.The Professional Compounding Centers of America (PCCA) estimates that 1 in 4 compounded products in the United States are a form of Hormone Replacement Therapy (HRT) [1]. Compounded BHRT is a form of personalized medicine whereby the dose, regimen, and dosage forms are custo
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