240 research outputs found
On the global hydration kinetics of tricalcium silicate cement
We reconsider a number of measurements for the overall hydration kinetics of
tricalcium silicate pastes having an initial water to cement weight ratio close
to 0.5. We find that the time dependent ratio of hydrated and unhydrated silica
mole numbers can be well characterized by two power-laws in time, . For early times we find an `accelerated' hydration
() and for later times a `deaccelerated' behavior (). The crossover time is estimated as . We
interpret these results in terms of a global second order rate equation
indicating that (a) hydrates catalyse the hydration process for , (b)
they inhibit further hydration for and (c) the value of the
associated second order rate constant is of magnitude 6x10^{-7} - 7x10^{-6}
liter mol^{-1} s^{-1}. We argue, by considering the hydration process actually
being furnished as a diffusion limited precipitation that the exponents and directly indicate a preferentially `plate' like hydrate
microstructure. This is essentially in agreement with experimental observations
of cellular hydrate microstructures for this class of materials.Comment: RevTeX macros, 6 pages, 4 postscript figure
Suppression of core polarization in halo nuclei
We present a microscopic study of halo nuclei, starting from the Paris and
Bonn potentials and employing a two-frequency shell model approach. It is found
that the core-polarization effect is dramatically suppressed in such nuclei.
Consequently the effective interaction for halo nucleons is almost entirely
given by the bare G-matrix alone, which presently can be evaluated with a high
degree of accuracy. The experimental pairing energies between the two halo
neutrons in He and Li nuclei are satisfactorily reproduced by our
calculation. It is suggested that the fundamental nucleon-nucleon interaction
can be probed in a clearer and more direct way in halo nuclei than in ordinary
nuclei.Comment: 11 pages, RevTex, 2 postscript figures; major revisions, matches
version to appear in Phys. Rev. Letter
The political process of constructing a sustainable London Olympics sports development legacy
This study attempts to develop a research agenda for understanding the process of constructing a sustainable Olympic sports development legacy. The research uses a social constructivist perspective to examine the link between the 2012 London Olympic Games and sustainable sports development. The first part of the paper provides justification for the study of sport policy processes using a constructivist lens. This is followed by a section which critically unpacks sustainable sports development drawing on Mosse’s (1998) ideas of process-oriented research and Searle’s conceptualisation of the construction of social reality. Searle’s (1995) concepts of the assignment of function, collective intentionality, collective rules, and human capacity to cope with the environment are considered in relation to the events and discourses emerging from the legacy vision(s) associated with the 2012 London Olympic Games. The paper concludes by proposing a framework for engaging in process oriented research and highlights key elements, research questions, and methodological issues. The proposed constructivist approach can be used to inform policy, practice, and research on sustainable Olympic sports development legacy
Good Gig, Bad Gig: Autonomy and Algorithmic Control in the Global Gig Economy
This article evaluates the job quality of work in the remote gig economy. Such work consists of the remote provision of a wide variety of digital services mediated by online labour platforms. Focusing on workers in Southeast Asia and Sub-Saharan Africa, the article draws on semi-structured interviews in six countries (N = 107) and a cross-regional survey (N = 679) to detail the manner in which remote gig work is shaped by platform-based algorithmic control. Despite varying country contexts and types of work, we show that algorithmic control is central to the operation of online labour platforms. Algorithmic management techniques tend to offer workers high levels of flexibility, autonomy, task variety and complexity. However, these mechanisms of control can also result in low pay, social isolation, working unsocial and irregular hours, overwork, sleep deprivation and exhaustion
The Hubble Constant
I review the current state of determinations of the Hubble constant, which
gives the length scale of the Universe by relating the expansion velocity of
objects to their distance. There are two broad categories of measurements. The
first uses individual astrophysical objects which have some property that
allows their intrinsic luminosity or size to be determined, or allows the
determination of their distance by geometric means. The second category
comprises the use of all-sky cosmic microwave background, or correlations
between large samples of galaxies, to determine information about the geometry
of the Universe and hence the Hubble constant, typically in a combination with
other cosmological parameters. Many, but not all, object-based measurements
give values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc.
This is in mild discrepancy with CMB-based measurements, in particular those
from the Planck satellite, which give values of 67-68km/s/Mpc and typical
errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that
accuracy rather than precision is the remaining problem in a good determination
of the Hubble constant. Whether a discrepancy exists, and whether new physics
is needed to resolve it, depends on details of the systematics of the
object-based methods, and also on the assumptions about other cosmological
parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by
Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
Second extracellular loop of human glucagon-like peptide-1 receptor (GLP-1R) has a critical role in GLP-1 peptide binding and receptor activation
The glucagon-like peptide-1 receptor (GLP-1R) is a therapeutically important family B G protein-coupled receptor (GPCR) that is pleiotropically coupled to multiple signaling effectors and, with actions including regulation of insulin biosynthesis and secretion, is one of the key targets in the management of type II diabetes mellitus. However, there is limited understanding of the role of the receptor core in orthosteric ligand binding and biological activity. To assess involvement of the extracellular loop (ECL) 2 in ligand-receptor interactions and receptor activation, we performed alanine scanning mutagenesis of loop residues and assessed the impact on receptor expression and GLP-1(1-36)-NH 2 or GLP-1(7-36)-NH2 binding and activation of three physiologically relevant signaling pathways as follows: cAMP formation, intracellular Ca 2+ (Ca 2+ i) mobilization, and phosphorylation of extracellular signal-regulated kinases 1 and 2 (pERK1/2). Although antagonist peptide binding was unaltered, almost all mutations affected GLP-1 peptide agonist binding and/or coupling efficacy, indicating an important role in receptor activation. However, mutation of several residues displayed distinct pathway responses with respect to wild type receptor, including Arg-299 and Tyr-305, where mutation significantly enhanced both GLP-1(1-36)-NH2- and GLP-1(7-36)- NH 2-mediated signaling bias for pERK1/2. In addition, mutation of Cys-296, Trp-297, Asn-300, Asn-302, and Leu-307 significantly increased GLP-1(7-36)-NH 2-mediated signaling bias toward pERK1/2. Of all mutants studied, only mutation of Trp-306 to alanine abolished all biological activity. These data suggest a critical role of ECL2 of the GLP-1R in the activation transition(s) of the receptor and the importance of this region in the determination of both GLP-1 peptide- and pathway-specific effects
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