2,555 research outputs found
The Baryonic Tully-Fisher Relation
We explore the Tully-Fisher relation over five decades in stellar mass in
galaxies with circular velocities ranging over 30 < Vc < 300 km/s. We find a
clear break in the optical Tully-Fisher relation: field galaxies with Vc < 90
km/s fall below the relation defined by brighter galaxies. These faint galaxies
are however very gas rich; adding in the gas mass and plotting baryonic disk
mass Md = M* + Mg in place of luminosity restores a single linear relation. The
Tully-Fisher relation thus appears fundamentally to be a relation between
rotation velocity and total baryonic mass of the form Md = A Vc^4.Comment: 10 pages including 1 color figure. Accepted for publication in ApJ
Letter
Dissecting the luminosity function of the Coma cluster of galaxies using CFHT wide field images
[Abridged] We determined the luminosity function (LF) of the Coma cluster
galaxies selected by luminosity, and the LF bi-variate in central brightness.
The Coma cluster and control fields were imaged using the CFH12K (42x28 arcmin)
and UH8K (28x28 arcmin) wide-field cameras at the CFHT. Selected HST images
were used for testing. Quantities were derived from measurements in at least
two colors, which have the following features: (1) Galaxies as faint as three
times the luminosity of the brightest globular clusters are in the completeness
region of our data. (2) We have a complete census (in the explored region) of
low surface brightness galaxies with central surface brightness galaxies almost
as low as the faintest so far cataloged ones. (3) The explored area is among
the largest ever sampled with CCDs at comparable depth for any cluster of
galaxies. (4) The error budget includes all sources of errors known to date.
Using HST images we also discovered that blends of globular clusters, not
resolved in individual components due to seeing, look like dwarf galaxies when
observed from the ground and are numerous and bright. The derived Coma LF is
relatively steep (alpha=-1.4) over the 11 magnitudes sampled, but the slope and
shape depend on color. A large population of faint low surface brightness
galaxies was discovered, representing the largest contributor (in number) to
the LF at faint magnitudes. We found a clear progression for a faintening of
the LF from high surface brightness galaxies (mu~20 mag/arcsec2) to galaxies of
very faint central brightnesses (mu~24.5 mag/arcsec2), and some evidence for a
steepening. Compact galaxies, usually classified as stars and therefore not
included in the LF, are found to be a minor population in Coma.Comment: ApJ, in pres
The Infrared Luminosity Function of Galaxies in the Coma Cluster
An infrared survey of the central 650 arcmin of the Coma cluster is used
to determine the band luminosity function for the cluster. Redshifts are
available for all galaxies in the survey with , and for this sample
we obtain a good fit to a Schechter function with and
. These luminosity function parameters are similar to those
measured for field galaxies in the infrared, which is surprising considering
the very different environmental densities and, presumably, merger histories
for field galaxies. For fainter galaxies, we use two independent techniques to
correct for field galaxy contamination in the cluster population: the
color-magnitude relation and an estimate for the level of background and
foreground contamination from the literature. Using either method we find a
steep upturn for galaxies with , with slope .Comment: 15 pages, 2 figures Accepted by ApJ Letter
Efeito da densidade do solo na incidência de Fusarium spp.
O objetivo deste trabalho foi avaliar o efeito da densidade do solo resultante de dois sistemas de manejo e seis rotações de culturas na população de Fusarium spp
A technological approach to the morphofunctional classification of seedlings of 50 Brazilian forest species.
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Avaliação da composição botânica da dieta consumida por bovinos em pastagens de quicuio-da-amazônia (Brachiaria humidicola) estabelecida em área originalmente de vegetação secundária.
Wormhole geometries supported by a nonminimal curvature-matter coupling
Wormhole geometries in curvature-matter coupled modified gravity are
explored, by considering an explicit nonminimal coupling between an arbitrary
function of the scalar curvature, R, and the Lagrangian density of matter. It
is the effective stress-energy tensor containing the coupling between matter
and the higher order curvature derivatives that is responsible for the null
energy condition violation, and consequently for supporting the respective
wormhole geometries. The general restrictions imposed by the null energy
condition violation are presented in the presence of a nonminimal R-matter
coupling. Furthermore, obtaining exact solutions to the gravitational field
equations is extremely difficult due to the nonlinearity of the equations,
although the problem is mathematically well-defined. Thus, we outline several
approaches for finding wormhole solutions, and deduce an exact solution by
considering a linear R nonmiminal curvature-matter coupling and by considering
an explicit monotonically decreasing function for the energy density. Although
it is difficult to find exact solutions of matter threading the wormhole
satisfying the energy conditions at the throat, an exact solution is found
where the nonminimal coupling does indeed minimize the violation of the null
energy condition of normal matter at the throat.Comment: 8 pages, 3 figures. V2: 9 pages, error and typos corrected;
discussion and references added; to appear in PR
Undergraduate medical textbooks do not provide adequate information on intravenous fluid therapy: a systematic survey and suggestions for improvement
<b>Background</b><p></p>
Inappropriate prescribing of intravenous (IV) fluid, particularly 0.9% sodium chloride, causes post-operative complications. Fluid prescription is often left to junior medical staff and is frequently poorly managed. One reason for poor intravenous fluid prescribing practices could be inadequate coverage of this topic in the textbooks that are used.<p></p>
<b>Methods</b><p></p>
We formulated a comprehensive set of topics, related to important common clinical situations involving IV fluid therapy, (routine fluid replacement, fluid loss, fluids overload) to assess the adequacy of textbooks in common use. We assessed 29 medical textbooks widely available to students in the UK, scoring the presence of information provided by each book on each of the topics. The scores indicated how fully the topics were considered: not at all, partly, and adequately. No attempt was made to judge the quality of the information, because there is no consensus on these topics.<p></p>
<b>Results</b><p></p>
The maximum score that a book could achieve was 52. Three of the topics we chose were not considered by any of the books. Discounting these topics as “too esoteric”, the maximum possible score became 46. One textbook gained a score of 45, but the general score was poor (median 11, quartiles 4, 21). In particular, coverage of routine postoperative management was inadequate.<p></p>
<b>Conclusions</b><p></p>
Textbooks for undergraduates cover the topic of intravenous therapy badly, which may partly explain the poor knowledge and performance of junior doctors in this important field. Systematic revision of current textbooks might improve knowledge and practice by junior doctors. Careful definition of the remit and content of textbooks should be applied more widely to ensure quality and “fitness for purpose”, and avoid omission of vital knowledge
Valor nutritivo de silagens de capim elefante (Pennisetum purpureum Schum.) com adição de diferentes níveis dos subprodutos do processamento de acerola (Malpighia glabra L.) e de goiaba (Psidium guajava L.).
Dois experimentos foram conduzidos no Núcleo de Pesquisa em Forragicultura da Universidade Federal do Ceará, localizado na cidade de Fortaleza . CE. Objetivou-se avaliar o valor nutritivo de silagens de capim elefante com diferentes níveis de adição (0, 5, 10, 15 e 20%) dos subprodutos desidratados da acerola (Malpighia glabra) e da goiaba (Psidium guajava) em delineamento inteiramente casualizado com 4 repetições. Após 40 dias da ensilagem, os silos (tubos de PVC de 100 mm de diâmetro por 340 mm de comprimento) foram abertos e coletadas amostras para determinação dos teores de Matéria Seca (MS), Proteína Bruta (PB), Fibra em Detergente Neutro (FDN), Fibra em Detergente Ácido (FDA), Hemicelulose (HC) e valores de pH das silagens. No nível de adição de 15% de subproduto da acerola e subproduto da goiaba as silagens alcançaram a faixa ideal de MS (30 . 35%) indicada para a ocorrência de um bom processo fermentativo. O nível mínimo de 7% de PB não foi alcançado em nenhum nível de adição de subproduto da goiaba às silagens. Já com a adição de 6,32% de subproduto da acerola este nível foi alcançado. Os teores de FDN não variaram com adição de ambos os subprodutos. No que diz respeito aos teores de FDA, apenas a adição do subproduto da acerola às silagens proporcionou elevações significativas desta variável. Em todos os níveis de adição dos subprodutos, as silagens se mantiveram dentro da faixa ideal de pH considerada para silagens bem conservadas (3,8 . 4,2)
Traversable wormholes coupled to nonlinear electrodynamics
In this work we explore the possible existence of static, spherically
symmetric and stationary, axisymmetric traversable wormholes coupled to
nonlinear electrodynamics. Considering static and spherically symmetric (2+1)
and (3+1)-dimensional wormhole spacetimes, we verify the presence of an event
horizon and the non-violation of the null energy condition at the throat. For
the former spacetime, the principle of finiteness is imposed, in order to
obtain regular physical fields at the throat. Next, we analyze the
(2+1)-dimensional stationary and axisymmetric wormhole, and also verify the
presence of an event horizon, rendering the geometry non-traversable.
Relatively to the (3+1)-dimensional stationary and axisymmetric wormhole
geometry, we find that the field equations impose specific conditions that are
incompatible with the properties of wormholes. Thus, we prove the non-existence
of the general class of traversable wormhole solutions, outlined above, within
the context of nonlinear electrodynamics.Comment: 9 pages, Revtex4. V2: major change in title; considerable additions
in the Introduction and in the rotating solution, no physics changes;
correction of a reference, one reference added; now 10 pages. This version to
appear in Classical and Quantum Gravit
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