4,634 research outputs found
Film holder for curved vacuum platen
Vacuum apparatus for holding photographic film of various widths against cylindrically curved patens is discussed. Construction details and method of operation are explained. Illustration of equipment is provided
Rydberg states of hydrogen-like ions in braneworld
It has been argued that precise measurements of optical transition
frequencies between Rydberg states of hydrogen-like ions could be used to
obtain an improved value of the Rydberg constant and even to test Quantum
Electrodynamics (QED) theory more accurately, by avoiding the uncertainties
about the proton radius. Motivated by this perspective, we investigate the
influence of the gravitational interaction on the energy levels of
Hydrogen-like ions in Rydberg states within the context of the braneworld
models. As it is known, in this scenario, the gravitational interaction is
amplified in short distances. We show that, for Rydberg states, the main
contribution for the gravitational potential energy does not come from the rest
energy concentrated on the nucleus but from the energy of the electromagnetic
field created by its electrical charge, which is spread in space. The reason is
connected to the fact that, when the ion is in a Rydberg state with high
angular momentum, the gravitational potential energy is not computable in
zero-width brane approximation due to the gravitational influence of the
electrovacuum in which the lepton is moving. Considering a thick brane
scenario, we calculate the gravitational potential energy associated to the
nucleus charge in terms of the confinement parameter of the electric field in
the brane. We show that the gravitational effects on the energy levels of a
Rydberg state can be amplified by the extra dimensions even when the
compactification scale of the hidden dimensions is shorter than the Bohr
radius
Lorentz-violating dimension-five operator contribution to the black body radiation
We investigate the thermodynamics of a photon gas in an effective field
theory model that describes Lorentz violations through dimension-five operators
and Horava-Lifshitz theory. We explore the electrodynamics of the model which
includes higher order derivatives in the Lagrangian that can modify the
dispersion relation for the propagation of the photons. We shall focus on the
deformed black body radiation spectrum and modified Stefan-Boltzmann law to
address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL
Exact Effective action for (1+1)-dimensional fermions in an Abelian background at finite temperature and chemical potential
In this paper we study the effects of a nonzero chemical potential in the
effective action for massless fermions in (1+1) dimensions in an abelian gauge
field background at finite temperature. We calculate the n-point function and
show that the structure of the amplitudes corresponds to a generalization of
the structure noted earlier in a calculation without a chemical potential (the
associated integrals carry the dependence on the chemical potential). Our
calculation shows that the chiral anomaly is unaffected by the presence of a
chemical potential at finite temperature. However, unlike the earlier
calculation (in the absence of a chemical potential) odd point functions do not
vanish. We trace this to the fact that in the presence of a chemical potential
the generalized charge conjugation symmetry of the theory allows for such
amplitudes. In fact, we find that all the even point functions are even
functions of the chemical potential while the odd point functions are odd
functions of it which is consistent with this generalized charge conjugation
symmetry. We show that the origin of the structure of the amplitudes is best
seen from a formulation of the theory in terms of left and right handed
spinors. The calculations are also much simpler in this formulation and it
clarifies many other aspects of the theory
Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way
This paper presents a homogeneous study of abundances in a sample of 79
northern galactic planetary nebulae whose morphological classes have been
uniformly determined. Ionic abundances and plasma diagnostics were derived from
selected optical line strengths in the literature, and elemental abundances
were estimated with the Ionization Correction Factor developed by Kingsbourgh &
Barlow (1994). We compare the elemental abundances to the final yields obtained
from stellar evolution models of low-and intermediate-mass stars, and we
confirm that most Bipolar planetary nebulae have high nitrogen and helium
abundance, and are the likely progeny of stars with main-sequence mass larger
than 3 solar masses. We derive =0.27, and discuss the implication of such
a high ratio in connection with the solar neon abundance. We determine the
galactic gradients of oxygen and neon, and found Delta log (O/H)/Delta R=-0.01
dex/kpc$ and Delta log (Ne/H)/Delta R=-0.01 dex/kpc. These flat PN gradients do
not reconcile with galactic metallicity gradients flattening with time.Comment: The Astrophysical Journal, in pres
Using satellite imagery for studying the dynamics of the Rio de la Plata turbidity front
Both remote sensing and numerical modeling studies heavily rely on field data for calibration and validation, but they are seldom used to validate each other. In this work we used the turbidity front detected from satellite imagery to evaluate the performance of a numerical hydro-sedimentological model of the Rio de la Plata.
The Rio de la Plata is a micro-tidal estuary located between Argentina and Uruguay in South America. It is approximately 280 km long and its width increases from 20 km at the inner part to 220 km at its mouth. Due to its large extension, satellite images are one of the few tools able to provide a synoptic view of the estuary. The estuary receives an annual mean flow of 22.000 m³/s from the Parana and Uruguay rivers, and 160x106 tons/yr of sediment, which are mostly cohesive sediments coming from the upper Parana River basin.
The following data was available for studying the response of the system to the main forcings: daily discharges of the main tributaries from 2001 to 2017 (the mean discharge for the 2014-2017 period was 24250 m³/s); wind data every six hours from the European Centre for Medium-Range Weather Forecasts (ECMWF); CTD salinity measurements at two sites along the northern coast of the Rio de la Plata (just in front of Montevideo and approximately 40 km to the W).
We used images from the MODIS-Aqua satellite mission from 2014 to 2017. The images have a spatial resolution of approximately 1 km and a daily time step, and we used the red channel reflectance (wavelength of 645 nm) to detect the turbidity front location. The turbid river water in the inner and intermediate regions of the estuary has high reflectance, while the clear seawater in the outer zone and continental shelf has negligible reflectance. This allowed us to implement an image-based, autonomous algorithm, defining the turbidity front as a reflectance level that ‘best’ separates the two reflectance regions.
We analyzed the distribution of the front location over the 2014-2017 period, and found that the front location along the Uruguayan coast is more often located to the E of Montevideo, approximately 60% of the time, being the maximum eastward distance 143 km. On the other hand, we observed that the front could recede up to 70 km to the W of Montevideo. The turbidity front location along the Uruguayan coast presented statistically significant linear correlation with the Parana and Uruguay river discharges, with larger discharges being associated with positions further to the E. Regarding the wind, we observed as a general trend that positions to the W are associated with relatively weaker winds from all directions, while positions to the E show a larger scatter and are more frequently associated with stronger winds. We also observed a general trend in the data indicating that the front location along the north coast was particularly affected by winds coming from the SW and ENE directions
Metodologia para projeto de sistemas de água de resfriamento
Orientador: Roger Josef ZempDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: Sistemas de água de resfriamento são o método mais comum de rejeição de calor na indústria. Sistemas convencionais de água de resfriamento recirculante possuem uma rede de trocadores de calor em uma configuração paralela, demandando grande quantidade de circulação de água e torres de resfriamento. Embora a reutilização de água de resfriamento reduza a quantidade de água que é necessária no sistema e aumente o desempenho e capacidade da torre de resfriamento, a queda de pressão na rede de trocadores de calor pode aumentar devido ao seu arranjo em série-paralelo. Este estudo introduz uma metodologia para projetar diferentes sistemas de água de resfriamento e para analisar os impactos da reutilização de água sobre a queda de pressão na rede de trocadores de calor e sobre a torre de resfriamento. A partir de um modelo de super-estrutura, utiliza-se um algoritmo combinatorial com o auxílio da ferramenta de otimização Solver do Microsoft Excel para resolver um problema não-linear (NLP) de cada estrutura de rede de trocadores de calor. A queda de pressão em redes de trocadores de calor é avaliada por uma metodologia baseada na Teoria dos Grafos e utiliza os algoritmos de ordenação por topologia e de caminho crítico. Utiliza-se o método de Merkel para modelar a altura de uma torre de resfriamento e poder avaliar o volume necessário de uma torre de resfriamento para cada rede de trocadores de calor. Um estudo de caso é utilizado para ilustrar cada passo a medida que a metodologia é desenvolvida, buscando prover fundamentos para um estágio conceitual durante o projeto de um sistema de água de resfriamentoAbstract: Cooling water systems are the most common method of waste heat disposal in industry. Conventional recirculating cooling water systems have a heat exchanger network in a parallel arrangement, demanding not only substantial cooling water flow, but also large cooling towers. Although cooling water reuse reduces the amount of water that is recirculated in the system, thereby increasing the cooling tower capacity and performance, the pressure drop in the heat exchanger network may significantly increase due to series-parallel arrangements. This study introduces a methodology to design different cooling water systems and to analyse the cooling water reuse impacts on the heat exchanger network pressure drop and on the cooling tower size. From a superstructure model, a combinatorial algorithm in conjunction with the optimisation tool Solver in Microsoft Excel is used to solve a non-linear problem for each heat exchanger network structure. Pressure drop in heat exchanger networks is evaluated by a methodology that is based on Graph Theory and that uses topological sorting and critical path algorithms. Merkel's method is used to model the cooling tower height and to assess the required cooling tower volume for each heat exchanger network. A case study is used to illustrate each step as the methodology is developed, aiming to provide a basis for a conceptual stage during the cooling water system designMestradoEngenharia QuímicaMestre em Engenharia Químic
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