10,570 research outputs found
Methodology for evaluating the safety level of current accepted design solutions for limiting fire spread between buildings
External fire spread between buildings is internationally considered as a major concern for buildings in dense urban environments. While design guidelines differ between countries, the fundamental methods currently used for limiting the risk of fire spread between buildings are generally limited to specifying the minimum required separation distance for a given unprotected façade area, or conversely, limiting the maximum allowable unprotected façade area for a given separation distance. The safety level associated with the current design guidelines is however unknown, making the implementation of innovative, safer and more cost-effective design solutions difficult. In order to assess the safety target implicitly incorporated in currently accepted design solutions, a methodology is developed for evaluating the annual probability of reaching unacceptable radiation intensities at the opposite façade. As a case study, the methodology is applied to a design which is in agreement with the current UK requirements specified in BR 187. This case study exposes inconsistencies in the current design guidelines, indicating the need for developing explicit safety targets
Phonon Properties of Knbo3 and Ktao3 from First-Principles Calculations
The frequencies of transverse-optical phonons in KNbO and
KTaO are calculated in the frozen-phonon scheme making use of the
full-potential linearized muffin-tin orbital method. The calculated frequencies
in the cubic phase of KNbO and in the tetragonal ferroelectric phase are in
good agreement with experimental data. For KTaO, the effect of lattice
volume was found to be substantial on the frequency of the soft mode, but
rather small on the relative displacement patterns of atoms in all three modes
of the symmetry. The TO frequencies in KTaO are found to be of the
order of, but somehow higher than, the corresponding frequencies in cubic
KNbO.Comment: 8 pages + 1 LaTeX figure, Revtex 3.0, SISSA-CM-94-00
New distinguished classes of spectral spaces: a survey
In the present survey paper, we present several new classes of Hochster's
spectral spaces "occurring in nature", actually in multiplicative ideal theory,
and not linked to or realized in an explicit way by prime spectra of rings. The
general setting is the space of the semistar operations (of finite type),
endowed with a Zariski-like topology, which turns out to be a natural
topological extension of the space of the overrings of an integral domain,
endowed with a topology introduced by Zariski. One of the key tool is a recent
characterization of spectral spaces, based on the ultrafilter topology, given
in a paper by C. Finocchiaro in Comm. Algebra 2014. Several applications are
also discussed
Some closure operations in Zariski-Riemann spaces of valuation domains: a survey
In this survey we present several results concerning various topologies that
were introduced in recent years on spaces of valuation domains
Thermodynamic Scaling of the Viscosity of Van Der Waals, H-Bonded, and Ionic Liquids
Viscosities and their temperature, T, and volume, V, dependences are reported
for 7 molecular liquids and polymers. In combination with literature viscosity
data for 5 other liquids, we show that the superpositioning of relaxation times
for various glass-forming materials when expressed as a function of TV^g, where
the exponent g is a material constant, can be extended to the viscosity. The
latter is usually measured to higher temperatures than the corresponding
relaxation times, demonstrating the validity of the thermodynamic scaling
throughout the supercooled and higher T regimes. The value of g for a given
liquid principally reflects the magnitude of the intermolecular forces (e.g.,
steepness of the repulsive potential); thus, we find decreasing g in going from
van der Waals fluids to ionic liquids. For strongly H-bonded materials, such as
low molecular weight polypropylene glycol and water, the superpositioning
fails, due to the non-trivial change of chemical structure (degree of
H-bonding) with thermodynamic conditions.Comment: 16 pages 7 figure
Twist1 Is a TNF-Inducible Inhibitor of Clock Mediated Activation of Period Genes.
BACKGROUND: Activation of the immune system affects the circadian clock. Tumor necrosis factor (TNF) and Interleukin (IL)-1β inhibit the expression of clock genes including Period (Per) genes and the PAR-bZip clock-controlled gene D-site albumin promoter-binding protein (Dbp). These effects are due to cytokine-induced interference of E-box mediated transcription of clock genes. In the present study we have assessed the two E-box binding transcriptional regulators Twist1 and Twist2 for their role in cytokine induced inhibition of clock genes.
METHODS: The expression of the clock genes Per1, Per2, Per3 and of Dbp was assessed in NIH-3T3 mouse fibroblasts and the mouse hippocampal neuronal cell line HT22. Cells were treated for 4h with TNF and IL-1β. The functional role of Twist1 and Twist2 was assessed by siRNAs against the Twist genes and by overexpression of TWIST proteins. In luciferase (luc) assays NIH-3T3 cells were transfected with reporter gene constructs, which contain a 3xPer1 E-box or a Dbp E-box. Quantitative chromatin immunoprecipitation (ChIP) was performed using antibodies to TWIST1 and CLOCK, and the E-box consensus sequences of Dbp (CATGTG) and Per1 E-box (CACGTG).
RESULTS: We report here that siRNA against Twist1 protects NIH-3T3 cells and HT22 cells from down-regulation of Period and Dbp by TNF and IL-1β. Overexpression of Twist1, but not of Twist2, mimics the effect of the cytokines. TNF down-regulates the activation of Per1-3xE-box-luc, the effect being prevented by siRNA against Twist1. Overexpression of Twist1, but not of Twist2, inhibits Per1-3xE-box-luc or Dbp-E-Box-luc activity. ChIP experiments show TWIST1 induction by TNF to compete with CLOCK binding to the E-box of Period genes and Dbp.
CONCLUSION: Twist1 plays a pivotal role in the TNF mediated suppression of E-box dependent transactivation of Period genes and Dbp. Thereby Twist1 may provide a link between the immune system and the circadian timing system
Autoencoder Based Optimization for Electromagnetics Problems
In this work a novel approach is presented for topology optimization of electromagnetic devices. In particular a surrogate model based on Deep Neural Networks with encoder-decoder architecture is introduced. A first autoencoder learns to represent the input images that describe the topology, i.e., geometry and materials. The novel idea is to use the low dimensional latent space (i.e., the output space of the encoder) as the search space of the optimization algorithm, instead of using the higher dimensional space represented by the input images. A second neural network learns the relationship between the encoder outputs and the objective function (i.e., an electromagnetic quantity that is crucial for the design of the device) which is calculated by means of a numerical analysis. The calculation time for the optimization is greatly improved by reducing the dimensionality of the search space, and by introducing the surrogate model, whereas the quality of the result is slightly affected
The red and blue galaxy populations in the GOODS field: evidence for an excess of red dwarfs
We study the evolution of the galaxy population up to z\sim3 as a function of
its colour properties. In particular, luminosity functions and luminosity
densities have been derived as a function of redshift for the blue/late and
red/early populations. We use data from the GOODS-MUSIC catalogue which have
typical magnitude limits z<26 and Ks<23.5 for most of the sample. About 8% of
the galaxies have spectroscopic redshifts; the remaining have well calibrated
photometric redshifts derived from the extremely wide multi-wavelength coverage
in 14 bands (from the U band to the Spitzer 8 \mu m band). We have derived a
catalogue of galaxies complete in rest-frame B-band, which has been divided in
two subsamples according to their rest-frame U-V colour (or derived specific
star formation rate, SSFR) properties. We confirm a bimodality in the U-V
colour and SSFR of the galaxy sample up to z\sim 3. This bimodality is used to
compute the LFs of the blue/late and red/early subsamples. The LFs of the
blue/late and total samples are well represented by steep Schechter functions
evolving in luminosity with increasing redshifts. The volume density of the LFs
of the red/early populations decreases with increasing redshift. The shape of
the red/early LFs shows an excess of faint red dwarfs with respect to the
extrapolation of a flat Schechter function and can be represented by the sum of
two Schechter functions. Our model for galaxy formation in the hierarchical
clustering scenario, which also includes external feedback due to a diffuse UV
background, shows a general broad agreement with the LFs of both populations,
the larger discrepancies being present at the faint end for the red population.
Hints on the nature of the red dwarf population are given on the basis of their
stellar mass and spatial distributions.Comment: accepted for publication in A&A. Uses aa.cls, 13 pages, 11 figure
UV slope of z3 bright () Lyman-break galaxies in the COSMOS field
We analyse a unique sample of 517 bright () LBGs at redshift
z3 in order to characterise the distribution of their UV slopes
and infer their dust extinction under standard assumptions. We exploited
multi-band observations over 750 arcmin of the COSMOS field that were
acquired with three different ground-based facilities: the Large Binocular
Camera (LBC) on the Large Binocular Telescope (LBT), the Suprime-Cam on the
SUBARU telescope, and the VIRCAM on the VISTA telescope (ULTRAVISTA DR2). Our
multi-band photometric catalogue is based on a new method that is designed to
maximise the signal-to-noise ratio in the estimate of accurate galaxy colours
from images with different point spread functions (PSF). We adopted an improved
selection criterion based on deep Y-band data to isolate a sample of galaxies
at to minimise selection biases. We measured the UV slopes ()
of the objects in our sample and then recovered the intrinsic probability
density function of values (PDF()), taking into account the
effect of observational uncertainties through detailed simulations. The
galaxies in our sample are characterised by mildly red UV slopes with
throughout the enitre luminosity range that is probed by
our data (). The resulting dust-corrected
star formation rate density (SFRD) is , corresponding to a contribution of about 25% to the
total SFRD at z3 under standard assumptions. Ultra-bright LBGs at match the known trends, with UV slopes being redder at decreasing redshifts,
and brighter galaxies being more highly dust extinct and more frequently
star-forming than fainter galaxies. [abridged]Comment: Matched to journal version. 11 pages, 13 figures, Astronomy &
Astrophysics in pres
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