12,102 research outputs found
Open Cluster Characterization via Cross-Correlation with Spectral Library
We present a characterization method based on spectral cross-correlation to
obtain the physical parameters of the controversial stellar aggregate
ESO442-SC04. The data used was obtained with GMOS at Gemini-South telescope
including 17 stars in the central region of the ob ject and 6 standard-stars.
FXCOR was used in an iterative process to obtain self-consistent radial
velocities for the standard-stars and averaged radial velocities for the
science spectra. Spectral types, effective temperature, suface gravity and
metallicities parameters were determined using FXCOR to correlate cluster
spectra with ELODIE spectral library and selecting the best correlation matches
using the Tonry and Davis Ratio (TDR). Analysis of the results suggests that
the stars in ESO442-SC04 are not bound and therefore they do not constitute a
physical system.Comment: 4-page paper from IAU symposium 266. Contains 3 eps figures and IAU
document class file 'iau.cls
Casimir Force for Absorbing Media in an Open Quantum System Framework: Scalar Model
In this article we compute the Casimir force between two finite-width mirrors
at finite temperature, working in a simplified model in 1+1 dimensions. The
mirrors, considered as dissipative media, are modeled by a continuous set of
harmonic oscillators which in turn are coupled to an external environment at
thermal equilibrium. The calculation of the Casimir force is performed in the
framework of the theory of quantum open systems. It is shown that the Casimir
interaction has two different contributions: the usual radiation pressure from
vacuum, which is obtained for ideal mirrors without dissipation or losses, and
a Langevin force associated with the noise induced by the interaction between
dielectric atoms in the slabs and the thermal bath. Both contributions to the
Casimir force are needed in order to reproduce the analogous of Lifshitz
formula in 1+1 dimensions. We also discuss the relation between the
electromagnetic properties of the mirrors and the spectral density of the
environmentComment: Minor changes, version to appear in Phys. Rev.
Integrable deformations of oscillator chains from quantum algebras
A family of completely integrable nonlinear deformations of systems of N
harmonic oscillators are constructed from the non-standard quantum deformation
of the sl(2,R) algebra. Explicit expressions for all the associated integrals
of motion are given, and the long-range nature of the interactions introduced
by the deformation is shown to be linked to the underlying coalgebra structure.
Separability and superintegrability properties of such systems are analysed,
and their connection with classical angular momentum chains is used to
construct a non-standard integrable deformation of the XXX hyperbolic Gaudin
system.Comment: 15 pages, LaTe
Segregation of an intruder in a heated granular dense gas
A recent segregation criterion [V. Garz\'o, Phys. Rev. E \textbf{78},
020301(R) (2008)] based on the thermal diffusion factor of an
intruder in a heated granular gas described by the inelastic Enskog equation is
revisited. The sign of provides a criterion for the transition
between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE).
The present theory incorporates two extra ingredients not accounted for by the
previous theoretical attempt. First, the theory is based upon the second Sonine
approximation to the transport coefficients of the mass flux of intruder.
Second, the dependence of the temperature ratio (intruder temperature over that
of the host granular gas) on the solid volume fraction is taken into account in
the first and second Sonine approximations. In order to check the accuracy of
the Sonine approximation considered, the Enskog equation is also numerically
solved by means of the direct simulation Monte Carlo (DSMC) method to get the
kinetic diffusion coefficient . The comparison between theory and
simulation shows that the second Sonine approximation to yields an
improvement over the first Sonine approximation when the intruder is lighter
than the gas particles in the range of large inelasticity. With respect to the
form of the phase diagrams for the BNE/RBNE transition, the kinetic theory
results for the factor indicate that while the form of these diagrams
depends sensitively on the order of the Sonine approximation considered when
gravity is absent, no significant differences between both Sonine solutions
appear in the opposite limit (gravity dominates the thermal gradient). In the
former case (no gravity), the first Sonine approximation overestimates both the
RBNE region and the influence of dissipation on thermal diffusion segregation.Comment: 9 figures; to be published in Phys. Rev.
A fluorophore attached to nicotinic acetylcholine receptor beta M2 detects productive binding of agonist to the alpha delta site
To study conformational transitions at the muscle nicotinic acetylcholine (ACh) receptor (nAChR), a rhodamine fluorophore was tethered to a Cys side chain introduced at the beta-19' position in the M2 region of the nAChR expressed in Xenopus oocytes. This procedure led to only minor changes in receptor function. During agonist application, fluorescence increased by (Delta-F/F) approximate to 10%, and the emission peak shifted to lower wavelengths, indicating a more hydrophobic environment for the fluorophore. The dose-response relations for Delta-F agreed well with those for epibatidine-induced currents, but were shifted approximate to 100-fold to the left of those for ACh-induced currents. Because (i) epibatidine binds more tightly to the alpha-gamma-binding site than to the alpha-delta site and (ii) ACh binds with reverse-site selectivity, these data suggest that Delta-F monitors an event linked to binding specifically at the alpha-delta-subunit interface. In experiments with flash-applied agonists, the earliest detectable Delta-F occurs within milliseconds, i.e., during activation. At low [ACh] (less than or equal to 10 muM), a phase of Delta-F occurs with the same time constant as desensitization, presumably monitoring an increased population of agonist-bound receptors. However, recovery from Delta-F is complete before the slowest phase of recovery from desensitization (time constant approximate to 250 s), showing that one or more desensitized states have fluorescence like that of the resting channel. That conformational transitions at the alpha-delta-binding site are not tightly coupled to channel activation suggests that sequential rather than fully concerted transitions occur during receptor gating. Thus, time-resolved fluorescence changes provide a powerful probe of nAChR conformational changes
Eficiência agronômica de tecnologias de tratamento da ureia na cultura do algodão.
A cultura do algodão utiliza grande quantidade de fertilizantes nitrogenadas no processo produtivo. O objetivo deste trabalho foi avaliar tecnologias de tratamento da ureia para aumento da sua eficiência, no algodão. Avaliou-se o efeito de cinco fertilizantes nitrogenados em três doses, sob delineamento fatorial, além de um tratamento controle sem adubação nitrogenada, em duas safras no Mato Grosso, no rendimento de algodão em caroço, no número de maças, no peso de capulhos, na altura final e população de plantas. As doses de N avaliadas foram 0, 60, 90 e 120 kg ha-1, correspondentes à 0, 50, 75 e 100% da dose recomendada, respectivamente. Os parâmetros avaliados foram alterados positivamente pelas doses, mas não pelas tecnologias de tratamento da ureia, em ambas as safras. As tecnologias de tratamento para aumento da eficiência da ureia não permitem reduzir a dose de N recomendada, mas aumenta a eficiência agronômica na dose recomendada, em comparação com a ureia comum
Non-standard quantum so(3,2) and its contractions
A full (triangular) quantum deformation of so(3,2) is presented by
considering this algebra as the conformal algebra of the 2+1 dimensional
Minkowskian spacetime. Non-relativistic contractions are analysed and used to
obtain quantum Hopf structures for the conformal algebras of the 2+1 Galilean
and Carroll spacetimes. Relations between the latter and the null-plane quantum
Poincar\'e algebra are studied.Comment: 9 pages, LaTe
Hyperfine magnetic field in ferromagnetic graphite
Information on atomic-scale features is required for a better understanding
of the mechanisms leading to magnetism in non-metallic, carbon-based materials.
This work reports a direct evaluation of the hyperfine magnetic field produced
at 13C nuclei in ferromagnetic graphite by nuclear magnetic resonance (NMR).
The experimental investigation was made possible by the results of
first-principles calculations carried out in model systems, including graphene
sheets with atomic vacancies and graphite nanoribbons with edge sites partially
passivated by oxygen. A similar range of maximum hyperfine magnetic field
values (18-21T) was found for all systems, setting the frequency span to be
investigated in the NMR experiments; accordingly, a significant 13C NMR signal
was detected close to this range without any external applied magnetic field in
ferromagnetic graphite
Building Bridges with Boats: Preserving Community History through Intra- and Inter-Institutional Collaboration
This chapter discusses Launching through the Surf: The Dory Fleet of Pacific City, a project which documents the historical and contemporary role of dory fishers in the life of the coastal village of Pacific City, Oregon, U.S. Linfield College’s Department of Theatre and Communication Arts, its Jereld R. Nicholson Library, the Pacific City Arts Association, the Pacific City Dorymen\u27s Association, and the Linfield Center for the Northwest joined forces to engage in a collaborative college and community venture to preserve this important facet of Oregon’s history. Using ethnography as a theoretical grounding and oral history as a method, the project utilized artifacts from the dory fleet to augment interview data, and faculty/student teams created a searchable digital archive available via open access. The chapter draws on the authors’ experiences to identify a philosophy of strategic collaboration. Topics include project development and management, assessment, and the role of serendipity. In an era of value-added services where libraries need to continue to prove their worth, partnering with internal and external entities to create content is one way for academic libraries to remain relevant to agencies that do not have direct connections to higher education. This project not only developed a positive “town and gown” relationship with a regional community, it also benefited partner organizations as they sought to fulfill their missions. The project also serves as a potential model for intra- and inter-agency collaboration for all types of libraries
Influence functional in two dimensional dilaton gravity
We evaluate the influence functional for two dimensional models of dilaton
gravity. This functional is exactly computed when the conformal invariance is
preserved, and it can be written as the difference between the Liouville
actions on each closed-time-path branch plus a boundary term. From the
influence action we derive the covariant form of the semiclassical field
equations. We also study the quantum to classical transition in cosmological
backgrounds. In the conformal case we show that the semiclassical approximation
is not valid because there is no imaginary part in the influence action.
Finally we show that the inclusion of the dilaton loop in the influence
functional breaks conformal invariance and ensures the validity of the
semiclassical approximation.Comment: 25 pages, RevTex, no figures. Minor changes has been added. To appear
in Physical Review
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