17,057 research outputs found
Stabilized jellium model and structural relaxation effects on the fragmentation energies of ionized silver clusters
Using the stabilized jellium model in two schemes of `relaxed' and `rigid',
we have calculated the dissociation energies and the fission barrier heights
for the binary fragmentations of singly-ionized and doubly-ionized Ag clusters.
In the calculations, we have assumed spherical geometries for the clusters.
Comparison of the fragmentation energies in the two schemes show differences
which are significant in some cases. This result reveals the advantages of the
relaxed SJM over the rigid SJM in dynamical processes such as fragmentation.
Comparing the relaxed SJM results and axperimental data on fragmentation
energies, it is possible to predict the sizes of the clusters just before their
fragmentations.Comment: 9 pages, 12 JPG figure
The slimming effect of advection on black-hole accretion flows
At super-Eddington rates accretion flows onto black holes have been described
as slim (aspect ratio ) or thick (H/R >1) discs, also known as
tori or (Polish) doughnuts. The relation between the two descriptions has never
been established, but it was commonly believed that at sufficiently high
accretion rates slim discs inflate, becoming thick. We wish to establish under
what conditions slim accretion flows become thick. We use analytical equations,
numerical 1+1 schemes, and numerical radiative MHD codes to describe and
compare various accretion flow models at very high accretion rates.We find that
the dominant effect of advection at high accretion rates precludes slim discs
becoming thick. At super-Eddington rates accretion flows around black holes can
always be considered slim rather than thick.Comment: 8 pages, 5 figures. Astronomy & Astrophysics, in pres
Macroscopic Distinguishability Between Quantum States Defining Different Phases of Matter: Fidelity and the Uhlmann Geometric Phase
We study the fidelity approach to quantum phase transitions (QPTs) and apply
it to general thermal phase transitions (PTs). We analyze two particular cases:
the Stoner-Hubbard itinerant electron model of magnetism and the BCS theory of
superconductivity. In both cases we show that the sudden drop of the mixed
state fidelity marks the line of the phase transition. We conduct a detailed
analysis of the general case of systems given by mutually commuting
Hamiltonians, where the non-analyticity of the fidelity is directly related to
the non-analyticity of the relevant response functions (susceptibility and heat
capacity), for the case of symmetry-breaking transitions. Further, on the case
of BCS theory of superconductivity, given by mutually non-commuting
Hamiltonians, we analyze the structure of the system's eigenvectors in the
vicinity of the line of the phase transition showing that their sudden change
is quantified by the emergence of a generically non-trivial Uhlmann mixed state
geometric phase.Comment: 18 pages, 8 figures. Version to be publishe
Point-contact spectroscopy on URuSi
Tunnel and point contact experiments have been made in a URuSi single
crystal along the c-axis. The experiments were performed changing temperature
and contact size in a low temperature scanning tunneling microscope. A
resonance develops at the Fermi level at K. This resonance splits
and becomes asymmetric when the 17.5 K phase transition is crossed. These
results are consistent with the existence of Kondo like bound states of the
U ionic configurations and the conduction electrons. Below the
transition, these configurations are split by the development of quadrupolar
ordering. The peak separation can be interpreted as a direct measurement of the
order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also
reported, with a comparative study of the behavior of both materials.Comment: 4 pages (Latex) + 2 postscript figure
Using the Sound Card as a Timer
Experiments in mechanics can often be timed by the sounds they produce. In
such cases, digital audio recordings provide a simple way of measuring time
intervals with an accuracy comparable to that of photogate timers. We
illustrate this with an experiment in the physics of sports: to measure the
speed of a hard-kicked soccer ball.Comment: 3 pages, 4 figures, Late
Duration of Low Wage Employment: A Study Based on a Survival Model
This paper includes a survival analysis which attempts to explain the duration, as in the number of years a worker remains in a low wage situation. Explanatory variables take into account the characteristics of the employee, such as education, age, tenure with the company, gender and nationality, and the characteristics of the job and the company such as industry affiliation, number of employees, age of the company and location.low wage, survival, Portugal
Avaliação econÎmica de um sistema agroflorestal para conexão de fragmentos da mata atlùntica .
Este trabalho teve por objetivo realizar uma avaliação econĂŽmica de um corredor agroflorestal implantado em fevereiro de 2005 na Fazendinha AgroecolĂłgica do km 47, SeropĂ©dica â RJ. Foram plantadas espĂ©cies de ciclo curto, como o aipim, banana, cana e abacaxi e 25 espĂ©cies florestais. As culturas agrĂcolas anuais foram avaliadas utilizando-se os critĂ©rios financeiros de avaliação de projetos: Valor Presente LĂquido (VPL) e RazĂŁo BenefĂcio/Custo (RB/C). O custo total acumulado apĂłs trĂȘs anos de implantação chegou a R 6.000,00/ha, foi suficiente para pagar cerca de 38% desses custos. O cultivo da mandioca foi o mais rentĂĄvel, sendo responsĂĄvel por 65% da receita gerada. As culturas de aipim e cana apresentaram VPL positivo de R 144,33, respectivamente, indicando que a produção foi suficiente para pagar os custos de implantação e gerar excedentes. O abacaxi apresentou VPL negativo de R 6,80 de retorno. Para a cultura da cana, chegou-se a relação B/C de 1,27. Para o abacaxi a relação foi de 0,22. A relação benefĂcio/custo total do sistema foi de 0,35. Embora o rendimento gerado durante os dois primeiros anos tenha sido significativo, este ainda nĂŁo foi suficiente para pagar todos os custos de implantação, sendo recomendada a introdução de novas culturas de ciclo curto ou frutĂferas para incrementar a geração de renda ano a ano.bitstream/item/42957/1/BOP-60.pd
Mathematical modeling of handmade recycled paper drying kinetics and sorption isotherms
The objective of this work is to analyze and compare the natural and forced convective drying of handmade recycled paper. Drying of recycled cellulose pulp was carried out under laboratory environment conditions and in a convective dryer with forced air circulation and controlled conditions of air temperature and velocity. The tests were conducted following a two-factor central composed factorial design of experiments, with six runs at the central point. The drying results were analyzed and fitted to mathematical models of Fick, Henderson and Pabis (Fick s modified equation), Page and He (considering the nonlinear Fick effect). The model of Page represented best the experimental data and the one of Henderson and Pabis resulted in an adequate fit for the paper drying kinetics. Sorption isotherms were determined for the dried paper and the models of GAB (Guggenheim-Anderson-de Boer) and GDW (Generalised D Arcy and Watt) resulted in excellent fits of the experimental data. The water sorption mechanism was suggested by the analysis of the calculated parameters of the GDW model.299312Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP
A Comprehensive View of a Strongly Lensed Planck-Associated Submillimeter Galaxy
We present high-resolution maps of stars, dust, and molecular gas in a strongly lensed submillimeter galaxy (SMG) at z = 3.259. HATLAS J114637.9â001132 is selected from the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) as a strong lens candidate mainly based on its unusually high 500 ÎŒm flux density (~300 mJy). It is the only high-redshift Planck detection in the 130 deg^2 H-ATLAS Phase-I area. Keck Adaptive Optics images reveal a quadruply imaged galaxy in the K band while the Submillimeter Array and the Jansky Very Large Array show doubly imaged 880 ÎŒm and CO(1â0) sources, indicating differentiated distributions of the various components in the galaxy. In the source plane, the stars reside in three major kpc-scale clumps extended over ~1.6 kpc, the dust in a compact (~1 kpc) region ~3 kpc north of the stars, and the cold molecular gas in an extended (~7 kpc) disk ~5 kpc northeast of the stars. The emissions from the stars, dust, and gas are magnified by ~17, ~8, and ~7 times, respectively, by four lensing galaxies at z ~ 1. Intrinsically, the lensed galaxy is a warm (T_(dust) ~ 40-65 K), hyper-luminous (L_(IR) ~ 1.7 Ă 10^(13) L_â; star formation rate (SFR) ~2000 M_â yr^(â1)), gas-rich (M_(gas)/M_(baryon) ~ 70%), young (M_(stellar)/SFR ~ 20 Myr), and short-lived (M_(gas)/SFR ~ 40 Myr) starburst. With physical properties similar to unlensed z > 2 SMGs, HATLAS J114637.9â001132 offers a detailed view of a typical SMG through a powerful cosmic microscope
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