4,824 research outputs found
The evolution of the number density of compact galaxies
We compare the number density of compact (small size) massive galaxies at low
and high redshift using our Padova Millennium Galaxy and Group Catalogue
(PM2GC) at z=0.03-0.11 and the CANDELS results from Barro et al. (2013) at
z=1-2. The number density of local compact galaxies with luminosity weighted
(LW) ages compatible with being already passive at high redshift is compared
with the density of compact passive galaxies observed at high-z. Our results
place an upper limit of a factor ~2 to the evolution of the number density and
are inconsistent with a significant size evolution for most of the compact
galaxies observed at high-z. The evolution may be instead significant (up to a
factor 5) for the most extreme, ultracompact galaxies. Considering all compact
galaxies, regardless of LW age and star formation activity, a minority of local
compact galaxies (<=1/3) might have formed at z<1. Finally, we show that the
secular decrease of the galaxy stellar mass due to simple stellar evolution may
in some cases be a non-negligible factor in the context of the evolution of the
mass-size relation, and we caution that passive evolution in mass should be
taken into account when comparing samples at different redshifts.Comment: ApJ in pres
Agricultores familiares e adoção de SAF em Medicilândia, Pará.
Sistemas agroflorestais (SAF) são alternativas à s práticas agrÃcolas convencionais e de uso do solo ainda pouco utilizados por agricultores familiares do território da Transamazônica, no Sudoeste do Pará. No entanto, o municÃpio de Medicilândia diferencia-se dos demais daquela região por possuir um dos principais polos cacaueiros do paÃs. Por ser uma cultura de sub-bosque, consequentemente tolerante a sombreamento, o cacaueiro se torna propÃcio à implantação em SAF. Objetivando entender os fatores contribuem e/ou limitam a utilização dos SAF naquele municÃpio, foram aplicados questionários a 73 famÃlias agricultoras. Os principais fatores que determinavam a adoção de SAF pelos agricultores são de caráter econômico e produtivo, sendo o sombreamento, a existência de mercado e a fertilidade dos solos os fatores que se destacam para essa adoção. Em oposição, a principal limitação refere-se à insuficiência e baixa qualidade dos serviços de assistência técnica, afetando, diretamente, a produção dos sistemas uma vez que a gestão de SAF poderá reduzir, consideravelmente, a produtividade da lavoura.Editores técnicos: Roberto Porro, Milton Kanashiro, Maria do Socorro Gonçalves Ferreira, Leila Sobral Sampaio e Gladys Ferreira de Sousa
Quench Propagation and Heating in the Superconducting 600 A Auxiliary Busbars of the LHC
In the Large Hadron Collider (LHC) at CERN 22 km of flexible superconducting cable, the auxiliary busbar cable, will conduct currents of up to 600 A to a large number of corrector magnets distributed throughout the accelerator. A prototype cable with 42 active conductors underwent several experiments to measure the hot spot temperature and the quench propagation velocity as a function of the current. The former was evaluated for various energy extraction scenarios as they are foreseen for the LHC corrector circuits. The experimental results and the heat flow simulations show that the quench behavior in this busbar prototype is strongly influenced by the heat flow through the insulation material (polyimide) into the helium bath, leading to stable configurations above the critical temperature Tc for currents between 250 A and 500 A. Special attention was paid to the study of discontinuities in the wires, like feed-throughs, where the wire is not immersed in liquid helium, and joints, where the wire cross-section is increased. The experiments and simulations led to a thorough understanding of the quench process in the wires of the prototype cable, which resulted in guidelines for the design, the use and the installation of the cable in the LHC
Bright submillimeter galaxies do trace galaxy protoclusters
There is controversy whether dusty starbursts selected at submillimeter
wavelengths can trace galaxy overdensities. We perform the first systematic
search for protoclusters around a homogeneously selected sample of 12
spectroscopically confirmed submillimeter galaxies (SMGs) at in
the GOODS-N field. We applied the Poisson Probability Method (PPM) to search
for Mpc scale overdensities around these SMGs using three photometric redshift
catalogs. We detect galaxy overdensities for 11 out of the 12 SMGs
(\%), distributed over eight protoclusters. We confirm three
previously discovered protoclusters, and we detect five new ones around the
SMGs SMMJ123634 (), ID.19 (), SMMJ123607 (),
SMMJ123606 (), and GN10 (). A wavelet-based analysis shows
that the SMGs live in protocluster cores with a complex morphology (compact,
filamentary, or clumpy) and an average size of Mpc. By comparing
the PPM results obtained using independently the three redshift catalogs, we
possibly witness a transitioning phase at for the galaxy
populations. While protoclusters appear to be populated by dusty
galaxies, those at highest redshifts are detected as overdensities of
Lyman emitters or Lyman break galaxies. We also find a good correlation
between the molecular (H) gas mass of the SMG and the overdensity
significance. To explain the overall phenomenology, we suggest that galaxy
interactions in dense environments likely triggered the starburst and gas-rich
phase of the SMGs. Altogether, we support the scenario that SMGs are excellent
tracers of distant protoclusters. Those presented in this work are excellent
targets for the {\it James Webb Space Telescope.} Surveys with forthcoming
facilities (e.g., {\it Euclid}, LSST) can be tuned to detect even larger
samples of distant protoclusters.Comment: 22 pages, Astronomy & Astrophysics in press. HTML files of Figure 3
are available at https://obswww.unige.ch/~castigna/Figure3_html
Low Levels of p53 Protein and Chromatin Silencing of p53 Target Genes Repress Apoptosis in Drosophila Endocycling Cells
Apoptotic cell death is an important response to genotoxic stress that prevents oncogenesis. It is known that tissues can differ in their apoptotic response, but molecular mechanisms are little understood. Here, we show that Drosophila polyploid endocycling cells (G/S cycle) repress the apoptotic response to DNA damage through at least two mechanisms. First, the expression of all the Drosophila p53 protein isoforms is strongly repressed at a post-transcriptional step. Second, p53-regulated pro-apoptotic genes are epigenetically silenced in endocycling cells, preventing activation of a paused RNA Pol II by p53-dependent or p53-independent pathways. Over-expression of the p53A isoform did not activate this paused RNA Pol II complex in endocycling cells, but over-expression of the p53B isoform with a longer transactivation domain did, suggesting that dampened p53B protein levels are crucial for apoptotic repression. We also find that the p53A protein isoform is ubiquitinated and degraded by the proteasome in endocycling cells. In mitotic cycling cells, p53A was the only isoform expressed to detectable levels, and its mRNA and protein levels increased after irradiation, but there was no evidence for an increase in protein stability. However, our data suggest that p53A protein stability is regulated in unirradiated cells, which likely ensures that apoptosis does not occur in the absence of stress. Without irradiation, both p53A protein and a paused RNA pol II were pre-bound to the promoters of pro-apoptotic genes, preparing mitotic cycling cells for a rapid apoptotic response to genotoxic stress. Together, our results define molecular mechanisms by which different cells in development modulate their apoptotic response, with broader significance for the survival of normal and cancer polyploid cells in mammals
Quench Propagation in the Superconducting 6 kA Flexible Busbars of the LHC
Flexible superconducting cables with currents up to 6 kA will be used to power magnets individually in the insertion regions of the LHC. In case of a quench, the currents in these circuits will decay very fast (with time constants of about 200 ms) such that relatively small copper cross sections are sufficient for these busbars. Quench propagation experiments on a prototype cable and corresponding simulations led to a detailed understanding of the quench behavior of these busbars and to recommendations for the design and application of the cable. Simulations of the quench process in a multi-strand conductor led to a detailed understanding of the way current crosses from superconducting to pure copper strands and how this affects the quench propagation velocity. At nominal current (6 kA), the quench propagation velocities are high (10 m/s) and the hot spot temperature increases rapidly. In this situation, timely quench detection and energy extraction (current reduction) are vital to prevent damage of circuit components
Fast and efficient critical state modelling of field-cooled bulk high-temperature superconductors using a backward computation method
Abstract: A backward computation method has been developed to accelerate modelling of the critical state magnetization current in a staggered-array bulk high-temperature superconducting (HTS) undulator. The key concept is as follows: (i) a large magnetization current is first generated on the surface of the HTS bulks after rapid field-cooling (FC) magnetization; (ii) the magnetization current then relaxes inwards step-by-step obeying the critical state model; (iii) after tens of backward iterations the magnetization current reaches a steady state. The simulation results show excellent agreement with the H -formulation method for both the electromagnetic and electromagnetic-mechanical coupled analyses, but with significantly faster computation speed. The simulation results using the backward computation method are further validated by the recent experimental results of a five-period Gd–Ba–Cu–O (GdBCO) bulk undulator. Solving the finite element analysis (FEA) model with 1.8 million degrees of freedom (DOFs), the backward computation method takes less than 1.4 h, an order of magnitude or higher faster than other state-of-the-art numerical methods. Finally, the models are used to investigate the influence of the mechanical stress on the distribution of the critical state magnetization current and the undulator field along the central axis
Application of a prioritisation scheme for seismic intervention in schools buildings in Italy
A risk management framework has recently been developed to assign priorities for the rehabilitation of school buildings in Italy, and to give timescales within which retrofit or demolition must take place. Since it is not practical to carry out a detailed assessment of the 60,000 Italian state and public schools, the framework is a multiple-level procedure which aims to identify the highest-risk buildings based on filters of increasing detail, and reduces the size of the building inventory at each step. The first risk ranking is based on a strength deficit, which measures the difference between the current design forces defined for the building site and an estimation of the level of seismic resistance which was required at the time of design. The second ranking is based on lateral strength calculations that are already available for a large portion of the Italian masonry building stock, and that are obtained from a survey form that is familiar to Italian engineers. Finally, a simplified displacement-based methodology is used to give a more accurate assessment of seismic risk based on a limited amount of geometrical and material data. The final assessment leads to a capacity ratio and a risk rating, which are used within a transparent procedure to assign priorities for seismic intervention, and timescales within which detailed assessment leading to retrofit or demolition must take place. The first step of the methodology has been applied herein to the school building stock within two Regions in Italy and preliminary results are presented
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