302 research outputs found
Compressive strength, microstructure and hydration products of hybrid alkaline cements
Ordinary Portland cement (OPC) is the dominant binder in the construction industry with a global
production that currently reaches a total of 3 Gt per year. As a consequence, the cement industry’s
contribution to the total worldwide CO2
emissions is of about 7% of the total emissions. Publications
on the field of alkali-activated binders (also termed geopolymers), state that this new material is,
potentially, likely to become an alternative to Portland cement. However, recent LCA studies show
that the environmental performance of alkali-activated binders depends, to great extent, of their
composition. Also, researchers report that these binders can be produced in a more eco-efficient
manner if the use of sodium silicate is avoided. This is due to the fact that the referred component
is associated to a high carbon footprint. Besides, most alkali-activated cements suffer from severe
efflorescence, a reaction originated by the fact that the alkaline and/or soluble silicates that are added
during processing cannot be totally consumed. This paper presents experimental results on hybrid
alkaline cements. The compressive strength results and the efflorescence observations show that some
of the new mixes already exhibit a promising performance
The Evolution of the Intracluster Medium Metallicity in Sunyaev-Zel'dovich-Selected Galaxy Clusters at 0 < z < 1.5
We present the results of an X-ray spectral analysis of 153 galaxy clusters
observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These
clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected
sample of galaxy clusters discovered in the 2500 square degree South Pole
Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure
time of 9.1 Ms, these data yield the strongest constraints to date on the
evolution of the metal content of the intracluster medium (ICM). We find no
evidence for strong evolution in the global (r<R500) ICM metallicity (dZ/dz =
-0.06 +/- 0.04 Zsun), with a mean value at z=0.6 of = 0.23 +/- 0.01 Zsun
and a scatter of 0.08 +/- 0.01 Zsun. These results imply that >60% of the
metals in the ICM were already in place at z=1 (at 95% confidence), consistent
with the picture of an early (z>1) enrichment. We find, in agreement with
previous works, a significantly higher mean value for the metallicity in the
centers of cool core clusters versus non-cool core clusters. We find weak
evidence for evolution in the central metallicity of cool core clusters (dZ/dz
= -0.21 +/- 0.11 Zsun), which is sufficient to account for this enhanced
central metallicity over the past ~10 Gyr. We find no evidence for metallicity
evolution outside of the core (dZ/dz = -0.03 +/- 0.06 Zsun), and no significant
difference in the core-excised metallicity between cool core and non-cool core
clusters. This suggests that strong radio-mode AGN feedback does not
significantly alter the distribution of metals at r>0.15R500. Given the
limitations of current-generation X-ray telescopes in constraining the ICM
metallicity at z>1, significant improvements on this work will likely require
next-generation X-ray missions.Comment: 11 pages, 8 figures, 2 tables. Submitted to ApJ. Comments welcome
Reconstruction of metabolic networks from high-throughput metabolite profiling data: in silico analysis of red blood cell metabolism
We investigate the ability of algorithms developed for reverse engineering of
transcriptional regulatory networks to reconstruct metabolic networks from
high-throughput metabolite profiling data. For this, we generate synthetic
metabolic profiles for benchmarking purposes based on a well-established model
for red blood cell metabolism. A variety of data sets is generated, accounting
for different properties of real metabolic networks, such as experimental
noise, metabolite correlations, and temporal dynamics. These data sets are made
available online. We apply ARACNE, a mainstream transcriptional networks
reverse engineering algorithm, to these data sets and observe performance
comparable to that obtained in the transcriptional domain, for which the
algorithm was originally designed.Comment: 14 pages, 3 figures. Presented at the DIMACS Workshop on Dialogue on
Reverse Engineering Assessment and Methods (DREAM), Sep 200
Extended radio emission in the galaxy cluster MS 0735.6+7421 detected with the Karl G. Jansky Very Large Array
MS 0735.6+7421 () is a massive cool core galaxy cluster hosting
one of the most powerful active galactic nuclei (AGN) outbursts known. The
radio jets of the AGN have carved out an unusually large pair of X-ray
cavities, each reaching a diameter of kpc. This makes MS 0735.6+7421 a
unique case to investigate active galactic nuclei feedback processes, as well
as other cluster astrophysics at radio wavelengths. We present new
low-radio-frequency observations of MS 0735.6+7421 taken with the Karl G.
Jansky Very Large Array (VLA): 5 hours of P-band ( MHz) and 5 hours of
L-band ( GHz) observations, both in C configuration. Our VLA P-band
( MHz) observations reveal the presence of a new diffuse radio
component reaching a scale of kpc in the direction of the jets and
of kpc in the direction perpendicular to the jets. This component
is centered on the cluster core and has a radio power scaled at GHz of
WHz. Its properties are
consistent with those expected from a radio mini-halo as seen in other massive
cool core clusters, although it may also be associated with radio plasma that
has diffused out of the X-ray cavities. Observations at higher spatial
resolution are needed to fully characterize the properties and nature of this
component. We also suggest that if radio mini-halos originate from jetted
activity, we may be witnessing the early stages of this process.Comment: 11 pages, 7 figures, submitted to MNRA
Star-Forming Brightest Cluster Galaxies at 0.25 < z < 1.25: A Transitioning Fuel Supply
We present a multi-wavelength study of 90 brightest cluster galaxies (BCGs)
in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by
the South Pole Telescope, utilizing data from various ground- and space-based
facilities. We infer the star formation rate (SFR) for the BCG in each cluster,
based on the UV and IR continuum luminosity, as well as the [O II] emission
line luminosity in cases where spectroscopy is available, finding 7 systems
with SFR > 100 Msun/yr. We find that the BCG SFR exceeds 10 Msun/yr in 31 of 90
(34%) cases at 0.25 < z < 1.25, compared to ~1-5% at z ~ 0 from the literature.
At z > 1, this fraction increases to 92(+6)(-31)%, implying a steady decrease
in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific star
formation rate in BCGs is declining more slowly with time than for field or
cluster galaxies, most likely due to the replenishing fuel from the cooling ICM
in relaxed, cool core clusters. At z > 0.6, the correlation between cluster
central entropy and BCG star formation - which is well established at z ~ 0 -
is not present. Instead, we find that the most star-forming BCGs at high-z are
found in the cores of dynamically unrelaxed clusters. We investigate the
rest-frame near-UV morphology of a subsample of the most star-forming BCGs
using data from the Hubble Space Telescope, finding complex, highly asymmetric
UV morphologies on scales as large as ~50-60 kpc. The high fraction of
star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times
suggests that the dominant mode of fueling star formation in BCGs may have
recently transitioned from galaxy-galaxy interactions to ICM cooling.Comment: 20 pages, 10 figures. Submitted for publication in ApJ. Comments
welcom
Revealing the velocity structure of the filamentary nebula in NGC 1275 in its entirety
We have produced for the first time a detailed velocity map of the giant filamentary nebula surrounding NGC 1275, the Perseus cluster’s brightest galaxy, and revealed a previously unknown rich velocity structure across the entire nebula. These new observations were obtained with the optical imaging Fourier transform spectrometer SITELLE at CFHT. With its wide field of view ( ∼11 arcmin × 11 arcmin), SITELLE is the only integral field unit spectroscopy instrument able to cover the 80 kpc  ×  55 kpc ( 3.8 arcmin × 2.6 arcmin) large nebula in NGC 1275. Our analysis of these observations shows a smooth radial gradient of the [N II]λ6583/H α line ratio, suggesting a change in the ionization mechanism and source across the nebula. The velocity map shows no visible general trend or rotation, indicating that filaments are not falling uniformly onto the galaxy, nor being uniformly pulled out from it. Comparison between the physical properties of the filaments and Hitomi measurements of the X-ray gas dynamics in Perseus is also explored
A Multi-Wavelength Mass Analysis of RCS2 J232727.6-020437, a ~3x10M Galaxy Cluster at z=0.7
We present an initial study of the mass and evolutionary state of a massive
and distant cluster, RCS2 J232727.6-020437. This cluster, at z=0.6986, is the
richest cluster discovered in the RCS2 project. The mass measurements presented
in this paper are derived from all possible mass proxies: X-ray measurements,
weak-lensing shear, strong lensing, Sunyaev Zel'dovich effect decrement, the
velocity distribution of cluster member galaxies, and galaxy richness. While
each of these observables probe the mass of the cluster at a different radius,
they all indicate that RCS2 J232727.6-020437 is among the most massive clusters
at this redshift, with an estimated mass of M_200 ~3 x10^15 h^-1 Msun. In this
paper, we demonstrate that the various observables are all reasonably
consistent with each other to within their uncertainties. RCS2 J232727.6-020437
appears to be well relaxed -- with circular and concentric X-ray isophotes,
with a cool core, and no indication of significant substructure in extensive
galaxy velocity data.Comment: 19 pages, 15 figures, submitted to ApJ on March 5, 2015; in press.
Manuscript revised following the referee revie
Current Estimates for HIV-1 Production Imply Rapid Viral Clearance in Lymphoid Tissues
It has recently been estimated that a single HIV-1 infected cell produces between and more than viral particles over its life span. Since body-wide estimates of the ratio of free virus to productively infected cells are smaller than and much smaller than , individual virions must be cleared rapidly. This seems difficult to reconcile with the fact that most of the total body virus is trapped on follicular dendritic cells where it can survive for many months. It has also been difficult to reconcile the vast difference in the rates at which the virus is cleared from the blood in rhesus macaques and in chronically infected patients. Here we attempt to reconcile these seemingly contradictory observations by considering the virion clearance rate in various organs and the virion exchange rates between them. The main results are that the per capita clearance rate of free virus in lymphoid tissue should be fast, the virion exchange rate between lymphoid tissue and the blood should be slow, and the comparatively slow previous estimates for the virion clearance rate from the blood correspond to the rate of virion efflux from the blood to other organs where the virus is ultimately cleared
Lumpability Abstractions of Rule-based Systems
The induction of a signaling pathway is characterized by transient complex
formation and mutual posttranslational modification of proteins. To faithfully
capture this combinatorial process in a mathematical model is an important
challenge in systems biology. Exploiting the limited context on which most
binding and modification events are conditioned, attempts have been made to
reduce the combinatorial complexity by quotienting the reachable set of
molecular species, into species aggregates while preserving the deterministic
semantics of the thermodynamic limit. Recently we proposed a quotienting that
also preserves the stochastic semantics and that is complete in the sense that
the semantics of individual species can be recovered from the aggregate
semantics. In this paper we prove that this quotienting yields a sufficient
condition for weak lumpability and that it gives rise to a backward Markov
bisimulation between the original and aggregated transition system. We
illustrate the framework on a case study of the EGF/insulin receptor crosstalk.Comment: In Proceedings MeCBIC 2010, arXiv:1011.005
- …