793 research outputs found
Comparison of thermal performance of different wall structures
Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.This study deals with comparison of thermal performance of six different wall structures for a south-facing wall. Numerical model based on an implicit finite difference method under steady periodic conditions is used to determine of heat transmission loads of multilayer walls. For this purpose, the outside surface of the wall is exposed to periodic solar radiation and outdoor environmental temperature. The inside surface is exposed to room air maintained at constant indoor design temperature. Building walls made of brick, concrete and ytong are performed for uninsulated and insulated wall structures. The investigation is carried out for July 21 and January 21 chosen to represent typical summer and winter conditions in Ä°zmir, Turkey. Expanded polystyrene (EPS) as insulation material is selected. It is seen that the maximum temperature swings in both summer and winter occur for the wall made with concrete while minimum temperature swings occur for ytong wall. Besides, insulated wall significantly reduces peak load and load fluctuations at inside surface, compared with uninsulated wall. Results show that time lag of ytong wall without insulation is obtained as 12.95 h while time lags of brick and concrete walls with 10 cm EPS insulation are obtained as 8.35 h and 7.47 h, respectively. Results also show that peak load of ytong wall without insulation is equal peak load when brick and concrete walls are insulated with EPS at 4.25 cm and 4.75 cm thicknesses, respectively.dc201
The millisecond pulsar mass distribution: Evidence for bimodality and constraints on the maximum neutron star mass
The mass function of neutron stars (NSs) contains information about the late
evolution of massive stars, the supernova explosion mechanism, and the
equation-of-state of cold, nuclear matter beyond the nuclear saturation
density. A number of recent NS mass measurements in binary millisecond pulsar
(MSP) systems increase the fraction of massive NSs (with M)
to of the observed population. In light of these results, we
employ a Bayesian framework to revisit the MSP mass distribution. We find that
a single Gaussian model does not sufficiently describe the observed population.
We test alternative empirical models and infer that the MSP mass distribution
is strongly asymmetric. The diversity in spin and orbital properties of
high-mass NSs suggests that this is most likely not a result of the recycling
process, but rather reflects differences in the NS birth masses. The asymmetry
is best accounted for by a bimodal distribution with a low mass component
centred at M and dispersed by
M, and a high-mass component with a mean of
and a dispersion of
M. We also establish a lower limit of M
at 98% C.L. for the maximum NS mass, from the absence of a high-mass truncation
in the observed masses. Using our inferred model, we find that the measurement
of 350 MSP masses, expected after the conclusion of pulsar surveys with the
Square-Kilometre Array, can result in a precise localization of a maximum mass
up to 2.15 M, with a 5% accuracy. Finally, we identify possible
massive NSs within the known pulsar population and discuss birth masses of
MSPs.Comment: submitted to ApJ; 21 pages in aastex6 two-column format, 12 figures,
5 tables. Comments are welcom
Effects of wall orientation and thermal insulation on time lag and decrement factor
Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.In this study, effect of wall orientation on time lag and decrement factor is investigated numerically using an implicit finite difference method under steady periodic conditions. The investigation is carried out for three different insulation materials in the climatic conditions of Istanbul, Turkey. For this purpose, the outside surface of the wall is exposed to periodic solar radiation and outdoor environmental temperature. The inside surface is exposed to room air maintained at constant indoor design temperature. The insulation is placed at outside of wall. It is seen that as expected, as the insulation thickness increases, decrement factor decreases while time lag increases. Results show that wall orientation has a great effect on time lag while it has a small effect on decrement factor. It is seen that maximum time lag and minimum decrement factor are obtained in an east oriented wall.dc201
Photon Propagation Around Compact Objects and the Inferred Properties of Thermally Emitting Neutron Stars
Anomalous X-ray pulsars, compact non-pulsing X-ray sources in supernova
remnants, and X-ray bursters are three distinct types of sources for which
there are viable models that attribute their X-ray emission to thermal emission
from the surface of a neutron star. Inferring the surface area of the emitting
regions in such systems is crucial in assessing the viability of different
models and in providing bounds on the radii of neutron stars. We show that the
inferred areas of the emitting regions may be over- or under-estimated by a
factor of <=2, because of the geometry of the system and general relativistic
light deflection, combined with the effects of phase averaging. Such effects
make the determination of neutron-star radii uncertain, especially when
compared to the ~5% level required for constraining the equation of state of
neutron-star matter. We also note that, for a given spectral shape, the
inferred source luminosities and pulse fractions are anticorrelated because
they depend on the same properties of the emitting regions, namely their sizes
and orientations, i.e., brighter sources have on average weaker pulsation
amplitudes than fainter sources. We argue that this property can be used as a
diagnostic tool in distinguishing between different spectral models. As an
example, we show that the high inferred pulse fraction and brightness of the
pulsar RXS J1708-40 are inconsistent with isotropic thermal emission from a
neutron-star surface. Finally, we discuss the implication of our results for
surveys in the soft X-rays for young, cooling neutron stars in supernova
remnants and show that the absence of detectable pulsations from the compact
source at the center of Cas A (at a level of >=30%) is not a strong argument
againts its identification with a spinning neutron star.Comment: 6 pages, 6 figures, to appear in the Astrophysical Journal; minor
change
Phase diagram of neutron-rich nuclear matter and its impact on astrophysics
Dense matter as it can be found in core-collapse supernovae and neutron stars
is expected to exhibit different phase transitions which impact the matter
composition and equation of state, with important consequences on the dynamics
of core-collapse supernova explosion and on the structure of neutron stars. In
this paper we will address the specific phenomenology of two of such
transitions, namely the crust-core solid-liquid transition at sub-saturation
density, and the possible strange transition at super-saturation density in the
presence of hyperonic degrees of freedom. Concerning the neutron star
crust-core phase transition at zero and finite temperature, it will be shown
that, as a consequence of the presence of long-range Coulomb interactions, the
equivalence of statistical ensembles is violated and a clusterized phase is
expected which is not accessible in the grand-canonical ensemble. A specific
quasi-particle model will be introduced to illustrate this anomalous
thermodynamics and some quantitative results relevant for the supernova
dynamics will be shown. The opening of hyperonic degrees of freedom at higher
densities corresponding to the neutron stars core modifies the equation of
state. The general characteristics and order of phase transitions in this
regime will be analyzed in the framework of a self-consistent mean-field
approach.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Stability window and mass-radius relation for magnetized strange quark stars
The stability of magnetized strange quark matter (MSQM) is investigated
within the phenomenological MIT bag model, taking into account the variation of
the relevant input parameters, namely, the strange quark mass, baryon density,
magnetic field and bag parameter. We obtain that the energy per baryon
decreases as the magnetic field increases, and its minimum value at vanishing
pressure is lower than the value found for SQM. This implies that MSQM is more
stable than non-magnetized SQM. Furthermore, the stability window of MSQM is
found to be wider than the corresponding one of SQM. The mass-radius relation
for magnetized strange quark stars is also derived in this framework.Comment: 12 pages, 6 figures, 3 table
Replication and exploratory analysis of 24 candidate risk polymorphisms for neural tube defects.
BackgroundNeural tube defects (NTDs), which are among the most common congenital malformations, are influenced by environmental and genetic factors. Low maternal folate is the strongest known contributing factor, making variants in genes in the folate metabolic pathway attractive candidates for NTD risk. Multiple studies have identified nominally significant allelic associations with NTDs. We tested whether associations detected in a large Irish cohort could be replicated in an independent population.MethodsReplication tests of 24 nominally significant NTD associations were performed in racially/ethnically matched populations. Family-based tests of fifteen nominally significant single nucleotide polymorphisms (SNPs) were repeated in a cohort of NTD trios (530 cases and their parents) from the United Kingdom, and case-control tests of nine nominally significant SNPs were repeated in a cohort (190 cases, 941 controls) from New York State (NYS). Secondary hypotheses involved evaluating the latter set of nine SNPs for NTD association using alternate case-control models and NTD groupings in white, African American and Hispanic cohorts from NYS.ResultsOf the 24 SNPs tested for replication, ADA rs452159 and MTR rs10925260 were significantly associated with isolated NTDs. Of the secondary tests performed, ARID1A rs11247593 was associated with NTDs in whites, and ALDH1A2 rs7169289 was associated with isolated NTDs in African Americans.ConclusionsWe report a number of associations between SNP genotypes and neural tube defects. These associations were nominally significant before correction for multiple hypothesis testing. These corrections are highly conservative for association studies of untested hypotheses, and may be too conservative for replication studies. We therefore believe the true effect of these four nominally significant SNPs on NTD risk will be more definitively determined by further study in other populations, and eventual meta-analysis
A Bioinformatics Approach for Determining Sample Identity from Different Lanes of High-Throughput Sequencing Data
The ability to generate whole genome data is rapidly becoming commoditized. For example, a mammalian sized genome (âŒ3Gb) can now be sequenced using approximately ten lanes on an Illumina HiSeq 2000. Since lanes from different runs are often combined, verifying that each lane in a genome's build is from the same sample is an important quality control. We sought to address this issue in a post hoc bioinformatic manner, instead of using upstream sample or âbarcodeâ modifications. We rely on the inherent small differences between any two individuals to show that genotype concordance rates can be effectively used to test if any two lanes of HiSeq 2000 data are from the same sample. As proof of principle, we use recent data from three different human samples generated on this platform. We show that the distributions of concordance rates are non-overlapping when comparing lanes from the same sample versus lanes from different samples. Our method proves to be robust even when different numbers of reads are analyzed. Finally, we provide a straightforward method for determining the gender of any given sample. Our results suggest that examining the concordance of detected genotypes from lanes purported to be from the same sample is a relatively simple approach for confirming that combined lanes of data are of the same identity and quality
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The antibacterial activity and release of quaternary ammonium compounds in an orthodontic primer
The aim of this study was to evaluate the impact of 10 wt% benzalkonium chloride (TB-BAC) or 10 wt% cetylpyridinium chloride (TB-CPC) on the antimicrobial properties of the orthodontic adhesive primer, Transbond XTâą (TB). Antimicrobial activity was assessed using a zone of inhibition diffusion test and the release of the antimicrobial compounds was monitored by high performance liquid chromatography (HPLC). Shear bond strength (SBS) was tested using bovine enamel. Control, TB, specimens failed to demonstrate intrinsic antibacterial activity at 1, 7 and 14 days; whereas, TB-BAC and TB-CPC showed antibacterial effects at all times. HPLC analysis indicated no significant differences in the release behaviour of TB-BAC and TB-CPC (t-test, p > 0.05), except for the 7-day release which was higher for TB-BAC (p 0.05)
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