32,584 research outputs found
Comparative Enumeration Gene Expression
This paper is about differential gene expression measured by transcript counting methods such as SAGE or MPSS. It introduces two significance tests for detection of differential expressed tags: frequentist and Bayesian. Under the frequentist view, it is proposed a test that computes the critical level as a function of each tag total frequency. Under the Bayesian view the Full Bayesian Significance Test is used considering the logistic normal distribution. The two proposed significance levels, the frequentist and the Bayesian, are compared for a data set with four libraries. The linking function between them is a Beta distribution function with mean 0.39 and standard deviation 0.30
Electron impact promoted fragmentation of alkyl-N-(1-Phenylethyl)-carbamates of primary, secondary and tertiary alcohols
Mass spectra of alkyl carbamates derived from primary, secondary, and teriary alcohols by use of deuterium labeling and high resolution mass spectroscop
Sinorhizobium Meliloti, A Bacterium Lacking The Autoinducer-2 (AI-2) Synthase, Responds To AI-2 Supplied By Other Bacteria
Many bacterial species respond to the quorum-sensing signal autoinducer-2 (AI-2) by regulating different niche-specific genes. Here, we show that Sinorhizobium meliloti, a plant symbiont lacking the gene for the AI-2 synthase, while not capable of producing AI-2 can nonetheless respond to AI-2 produced by other species. We demonstrate that S. meliloti has a periplasmic binding protein that binds AI-2. The crystal structure of this protein (here named SmlsrB) with its ligand reveals that it binds (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF), the identical AI-2 isomer recognized by LsrB of Salmonella typhimurium. The gene encoding SmlsrB is in an operon with orthologues of the lsr genes required for AI-2 internalization in enteric bacteria. Accordingly, S. meliloti internalizes exogenous AI-2, and mutants in this operon are defective in AI-2 internalization. S. meliloti does not gain a metabolic benefit from internalizing AI-2, suggesting that AI-2 functions as a signal in S. meliloti. Furthermore, S. meliloti can completely eliminate the AI-2 secreted by Erwinia carotovora, a plant pathogen shown to use AI-2 to regulate virulence. Our findings suggest that S. meliloti is capable of \u27eavesdropping\u27 on the AI-2 signalling of other species and interfering with AI-2-regulated behaviours such as virulence
Chemical abundances and kinematics of barium stars
In this paper we present an homogeneous analysis of photospheric abundances
based on high-resolution spectroscopy of a sample of 182 barium stars and
candidates. We determined atmospheric parameters, spectroscopic distances,
stellar masses, ages, luminosities and scale height, radial velocities,
abundances of the Na, Al, -elements, iron-peak elements, and s-process
elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium
model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found
that the metallicities, the temperatures and the surface gravities for barium
stars can not be represented by a single gaussian distribution. The abundances
of -elements and iron peak elements are similar to those of field giants
with the same metallicity. Sodium presents some degree of enrichment in more
evolved stars that could be attributed to the NeNa cycle. As expected, the
barium stars show overabundance of the elements created by the s-process. By
measuring the mean heavy-element abundance pattern as given by the ratio
[s/Fe], we found that the barium stars present several degrees of enrichment.
We also obtained the [hs/ls] ratio by measuring the photospheric abundances of
the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and
the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our
kinematical analysis showed that 90% of the barium stars belong to the thin
disk population. Based on their luminosities, none of the barium stars are
luminous enough to be an AGB star, nor to become self-enriched in the s-process
elements. Finally, we determined that the barium stars also follow an
age-metallicity relation.Comment: 30 pages, 26 figures, 18 tables, accepted for publication in MNRA
A cross-continental study on children's drawings of football players: implications for understanding key issues and controversies in human figure drawings
Professionals examine various aspects of girls’ and boys’ drawings as a way of understanding their intelligence, personality and emotional state. However, the extent to which such measures could be universally generalised or attributed to a specific cultural norm is still a debatable issue. In the present study five key features of children’s drawings namely: the size (height) of the drawings, profile or full face, figure in action or static, shaded or non-shaded and the nature of additional details were examined from a cross-cultural perspective, and by providing a topic (football) for which children’s drawing of a human figure could provide opportunities for the latter indices to manifest and flourish. Children from three countries; England, Iran and Brazil, representing three continents took part in this study. The participants were asked to draw a football player from their own country and from the other participating countries. The results showed that Brazilian children differ from Iranian and English children by drawing significantly smaller figures and putting more football action in the drawings. Shading of the figure drawn was more prevalent amongst English children. Such findings have implications for the interpretation of key aspects of children's drawings in educational, clinical and therapeutic settings and from a universal vs. culturally-specific viewpoint
A time of flight method to measure the speed of sound using a stereo sound card
We present an inexpensive apparatus for measuring the speed of sound, with a
time of flight method, using a computer with a stereo sound board. Students
measure the speed of sound by timing the delay between the arrivals of a pulse
to two microphones placed at different distances from the source. It can serve
as a very effective demonstration, providing a quick measurement of the speed
of sound in air; we have used it with great success in Open Days in our
Department. It can also be used for a full fledged laboratory determination of
the speed of sound in air.Comment: Accepted for publication in The Physics Teache
Coherent states, constraint classes, and area operators in the new spin-foam models
Recently, two new spin-foam models have appeared in the literature, both
motivated by a desire to modify the Barrett-Crane model in such a way that the
imposition of certain second class constraints, called cross-simplicity
constraints, are weakened. We refer to these two models as the FKLS model, and
the flipped model. Both of these models are based on a reformulation of the
cross-simplicity constraints. This paper has two main parts. First, we clarify
the structure of the reformulated cross-simplicity constraints and the nature
of their quantum imposition in the new models. In particular we show that in
the FKLS model, quantum cross-simplicity implies no restriction on states. The
deeper reason for this is that, with the symplectic structure relevant for
FKLS, the reformulated cross-simplicity constraints, in a certain relevant
sense, are now \emph{first class}, and this causes the coherent state method of
imposing the constraints, key in the FKLS model, to fail to give any
restriction on states. Nevertheless, the cross-simplicity can still be seen as
implemented via suppression of intertwiner degrees of freedom in the dynamical
propagation. In the second part of the paper, we investigate area spectra in
the models. The results of these two investigations will highlight how, in the
flipped model, the Hilbert space of states, as well as the spectra of area
operators exactly match those of loop quantum gravity, whereas in the FKLS (and
Barrett-Crane) models, the boundary Hilbert spaces and area spectra are
different.Comment: 21 pages; statements about gamma limits made more precise, and minor
phrasing change
Flexão composta : análise comparativa REBAP vs. EC2
No contexto actual nacional, o dimensionamento de estruturas de betĂŁo armado tem sido maioritariamente efectuado em conformidade com a norma nacional, o Regulamento de Estruturas de BetĂŁo Armado e PrĂ© Esforçado (REBAP). Com a aprovação, no passado recente, do EurocĂłdigo 2 (EC2) a nĂvel europeu, antevĂŞ-se que em breve lhe seja atribuĂdo o estatuto de norma nacional, atravĂ©s da publicação de um texto idĂŞntico. Em termos gerais o EC2, quando comparado com o REBAP, apresenta diferenças consideráveis na forma e no conteĂşdo que se repercutem no dimensionamento das estruturas de betĂŁo armado. Perante este cenário torna se imperioso efectuar estudos comparativos entre as duas normas aos mais diferentes nĂveis.
O caso particular do dimensionamento Ă flexĂŁo ao nĂvel da secção transversal em elementos estruturais lineares, que tem por base a hipĂłtese de Navier Bernoulli (secções planas antes e apĂłs a deformação), recorre a leis tensões extensões de cálculo dos materiais intervenientes: o betĂŁo e o aço. As propostas do REBAP e do EC2 para definir estas leis sĂŁo ligeiramente diferentes. Em trabalhos anteriores demonstrou se que as diferenças obtidas no dimensionamento de secções rectangulares Ă flexĂŁo simples adoptando as duas regulamentações (REBAP e EC2) sĂŁo marginais.
No presente trabalho pretende se avaliar a mesma diferença, mas desta feita para o caso em que o elemento estrutural se encontra sujeito a flexĂŁo composta. Deste modo, o objectivo Ă© o de analisar a influĂŞncia das diferenças que existem entre o REBAP e o EC2 ao nĂvel dos diagramas tensões extensões de cálculo para os materiais betĂŁo e aço, no dimensionamento de secções rectangulares Ă flexĂŁo composta. No presente trabalho descreve se o estudo comparativo efectuado, assim como as principais conclusões obtidas
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