Large Eddy Simulation of the water flow around a cylindrical pier mounted in a flat and fixed bed

In the present work, a numerical model based upon the Large Eddy Simulation approach has been set up for predicting the three-dimensional flow around a cylindrical pier, mounted on a flat and fixed bed, a generic case that is relevant for the study of flow and scour around bridge piers. This turbulent flow configuration was studied experimentally by Nogueira et al. (2008) with Particle Image Velocimetry (PIV). The main goal of this paper is a first validation of the numerical model, based upon the available data. The numerical tool is capable to qualitatively reproduce the characteristic flow features around the pier, like e.g. the horseshoe vortex system and the vortex shedding in the wake. The predicted extent of the initial scour hole, based upon the bed shear stress magnitudes, agrees well with the observations at the onset of the souring process during the lab experiments. Further quantitative validation of the numerical model will benefit from additional measurement efforts in the experiments

Medium-modified evolution of multiparticle production in jets in heavy-ion collisions

The energy evolution of medium-modified average multiplicities and multiplicity fluctuations in quark and gluon jets produced in heavy-ion collisions is investigated from a toy QCD-inspired model. In this model, we use modified splitting functions accounting for medium-enhanced radiation of gluons by a fast parton which propagates through the quark gluon plasma. The leading contribution of the standard production of soft hadrons is found to be enhanced by the factor $\sqrt{N_s}$ while next-to-leading order (NLO) corrections are suppressed by $1/\sqrt{N_s}$, where the nuclear parameter $N_s>1$ accounts for the induced-soft gluons in the hot medium. The role of next-to-next-to-leading order corrections (NNLO) is studied and the large amount of medium-induced soft gluons is found to drastically affect the convergence of the perturbative series. Our results for such global observables are cross-checked and compared with their limits in the vacuum and a new method for solving the second multiplicity correlator evolution equations is proposed.Comment: 21 pages and 8 figures, typo corrections, references adde

Atomistic simulations of self-trapped exciton formation in silicon nanostructures: The transition from quantum dots to nanowires

Using an approximate time-dependent density functional theory method, we calculate the absorption and luminescence spectra for hydrogen passivated silicon nanoscale structures with large aspect ratio. The effect of electron confinement in axial and radial directions is systematically investigated. Excited state relaxation leads to significant Stokes shifts for short nanorods with lengths less than 2 nm, but has little effect on the luminescence intensity. The formation of self-trapped excitons is likewise observed for short nanostructures only; longer wires exhibit fully delocalized excitons with neglible geometrical distortion at the excited state minimum.Comment: 10 pages, 4 figure

The Intrinsic Origin of Spin Echoes in Dipolar Solids Generated by Strong Pi Pulses

In spectroscopy, it is conventional to treat pulses much stronger than the linewidth as delta-functions. In NMR, this assumption leads to the prediction that pi pulses do not refocus the dipolar coupling. However, NMR spin echo measurements in dipolar solids defy these conventional expectations when more than one pi pulse is used. Observed effects include a long tail in the CPMG echo train for short delays between pi pulses, an even-odd asymmetry in the echo amplitudes for long delays, an unusual fingerprint pattern for intermediate delays, and a strong sensitivity to pi-pulse phase. Experiments that set limits on possible extrinsic causes for the phenomena are reported. We find that the action of the system's internal Hamiltonian during any real pulse is sufficient to cause the effects. Exact numerical calculations, combined with average Hamiltonian theory, identify novel terms that are sensitive to parameters such as pulse phase, dipolar coupling, and system size. Visualization of the entire density matrix shows a unique flow of quantum coherence from non-observable to observable channels when applying repeated pi pulses.Comment: 24 pages, 27 figures. Revised from helpful referee comments. Added new Table IV, new paragraphs on pages 3 and 1

Nitrogênio mineral e fluxos de N2O em sistemas integrados no Cerrado.

O N2O, dentre os gases de efeito estufa, é o que possui maior importância para o setor agropecuário devido às suas emissões estarem relacionadas com a dinâmica e disponibilidade de nitrogênio (N) do solo nos agroecossistemas. O objetivo desse trabalho foi avaliar as taxas de nitrogênio mineral em solo e os fluxos de N2O sob Integração Lavoura-Pecuária (ILP), Integração Lavoura-Pecuária-Floresta (ILPF), Cerradão e Sistema Agroflorestal (SAF), relacionando-os com precipitação pluviométrica, temperatura e umidade do solo. As coletas de N2O e de solo para o SAF foram realizadas em dois períodos, entre 19/03/2014 a 07/04/2014 e de 22/07/2014 à 24/07/2014 e para os outros sistemas integrados coletou-se no mesmo período do ano de 2013, em Planaltina, DF, correspondente à transição chuva-seca e da estação seca respectivamente. Os fluxos de N2O para os sistemas integrados tiveram uma grande variação, e o Cerradão e o SAF apresentaram menores valores de fluxos de N2O. Os teores de N-NH4+ foram maiores no SAF e Cerradão. O solo sob ILP e ILPF apresentam maiores teores de N-NO3-, consequentemente, fluxos de N2O

Gauge symmetry and W-algebra in higher derivative systems

The problem of gauge symmetry in higher derivative Lagrangian systems is discussed from a Hamiltonian point of view. The number of independent gauge parameters is shown to be in general {\it{less}} than the number of independent primary first class constraints, thereby distinguishing it from conventional first order systems. Different models have been considered as illustrative examples. In particular we show a direct connection between the gauge symmetry and the W-algebra for the rigid relativistic particle.Comment: 1+22 pages, 1 figure, LaTeX, v2; title changed, considerably expanded version with new results, to appear in JHE

¿Adelantan el diagnóstico de la diabetes tipo 2 los nuevos criterios de la Asociación Americana de Diabetes?

ObjetivoAnalizar el intervalo temporal entre la primera hiperglucemia basal ocasional (HBO) y el diagnóstico de diabetes mellitus tipo 2 (DM2) al aplicar los criterios de la OMS y de la Asociación Americana de Diabetes (ADA).DiseñoEstudio observacional, retrospectivo. Ámbito del estudio. Centro de atención primaria urbano.SujetosUn total de 104 pacientes con DM2, diagnosticados entre 1991 y 1995, con antecedentes de HBO.Mediciones o intervencionesEdad, género y otros factores de riesgo, fechas de la primera HBO (glucemia basal 3 110 mg/dl), del diagnóstico según criterios OMS (2 glucemias basales 3 140 mg/dl o 3 200 mg/dl a las 2 horas de la sobrecarga oral de glucosa [SOG]) y aplicando criterios ADA (2 glucemias basales 3 126 mg/dl) y los intervalos en meses entre ellas.ResultadosDe los 222 pacientes diagnosticados, 104 (47%) presentaban antecedentes de HBO. La edad en el momento del diagnóstico fue 60,8 años (DE, 10,1), siendo un 53% mujeres. En 51 casos (49%) se realizó SOG. La mediana (rango) del intervalo entre la primera HBO y el diagnóstico fue de 16 meses (0–101) en los que se realizó la SOG y de 45 (1–104) en los que no se practicó (p = 0,003). En estos últimos, los criterios ADA lo redujeron a 31 meses (0–97) (p < 0,001) y en 27 de ellos que no cumplían ambos criterios a la vez el intervalo fue de sólo 10 meses (0–93) (p < 0,001). Conclusiones. La no realización de la SOG comporta un retraso en el diagnóstico que puede ser contrarrestado con la aplicación de los criterios de la ADA.ObjectiveTo analyze the period of time between the first occasional fasting hyperglycaemia (OFH) and the diagnosis of type 2 diabetes mellitus (DM2), using the World Health Organization (WHO) criteria or the American Diabetes Association (ADA) criteria.DesignRetrospective, observational study.SettingUrban primary care centre.Subjects104 patients with DM2 diagnosed between 1991 and 1995 who had a previous OFH.MeasurementsAge, gender and other risk factors, dates of the first OFH (fasting plasma glucose 3 110 mg/dl), the diagnosis according to WHO criteria (2 fasting plasma glucose 3 140 mg/dl or 3 200 mg/dl two hours after the oral glucose test tolerance (OGTT)) or with the ADA criteria (2 fasting plasma glucose 3 126 mg/dl), and the intervals in months between them.ResultsOf the 222 diagnosed patients, 104 (47%) had previous OFH. Age at diagnosis was 60.8 (SD 10.1) and 53% were women. OGTT was performed in 51 cases (49%). The median (range) of the interval between the first OFH and diagnosis was 16 months (0–101) for those who were undertaken an OGTT, and 45 months (1–104) for those who were not (p = 0.003). In these last ones, ADA criteria reduced the interval to 31 months (0–97) (p < 0.001). In 27 of these patients who did not satisfy both criteria at the same time, ADA criteria reduced the interval to 10 months (0–93) (p < 0.001).ConclusionsNot performing the OGTT means a delay in diagnosis which can be countered by applying the ADA criteria

Phase-field approach to heterogeneous nucleation

We consider the problem of heterogeneous nucleation and growth. The system is described by a phase field model in which the temperature is included through thermal noise. We show that this phase field approach is suitable to describe homogeneous as well as heterogeneous nucleation starting from several general hypotheses. Thus we can investigate the influence of grain boundaries, localized impurities, or any general kind of imperfections in a systematic way. We also put forward the applicability of our model to study other physical situations such as island formation, amorphous crystallization, or recrystallization.Comment: 8 pages including 7 figures. Accepted for publication in Physical Review

Montagem do sistema para dosimetria de nêutrons com detectores de bolhas

São descritos a montagem e o procedimento desenvolvido para a aquisição e analise de imagens obtidas com os novos detectores de bolha BDS, para dosimetria de nêutrons ou nas medições de fluência e distribuição de energia de nêutrons de uma instalação nuclear