359 research outputs found
Common mechanism of thermodynamic and mechanical origin for ageing and crystallisation of glasses
The glassy state is known to undergo slow structural relaxation, where the
system progressively explores lower free-energy minima which are either
amorphous (ageing) or crystalline (devitrification). Recently, there is growing
interest in the unusual intermittent collective displacements of a large number
of particles known as "avalanches". However, their structural origin and
dynamics are yet to be fully addressed. Here, we study hard-sphere glasses
which either crystallise or age depending on the degree of size polydispersity,
and show that a small number of particles are thermodynamically driven to
rearrange in regions of low density and bond orientational order. This causes a
transient loss of mechanical equilibrium which facilitates a large cascade of
motion. Combined with previously identified phenomenology, we have a complete
kinetic pathway for structural change which is common to both ageing and
crystallisation. Furthermore, this suggests that transient force balance is
what distinguishes glasses from supercooled liquids.Comment: 13 pages, 13 figure
Study of Black Holes with the ATLAS detector at the LHC
We evaluate the potential of the ATLAS detector for discovering black holes
produced at the LHC, as predicted in models with large extra dimensions where
quantum gravity is at the TeV scale. We assume that black holes decay by
Hawking evaporation to all Standard Model particles democratically. We comment
on the possibility to estimate the Planck scale.Comment: 27 page
Ferromagnetism induced in anisotropic stacked kagome-lattice antiferromagnet CsCuCeF
The magnetic properties of CsCuCeF were investigated through
magnetization and specific heat measurements. CsCuCeF is
composed of a buckled kagome lattice of Cu, which is stacked along the b
axis. The exchange network in the buckled kagome lattice is strongly
anisotropic. Consequently, CsCuCeF can be divided into two
subsystems: alternating Heisenberg chains with strong antiferromagnetic
exchange interactions and dangling spins. The dangling spins couple with one
another via effective exchange interactions, which are mediated by chain spins.
The dangling spins are further divided into two subsystems, DS1 and DS2. The
dangling spins in DS1 undergo three-dimensional ferromagnetic ordering at 3.14
K, while those in DS2 remain paramagnetic down to 0.35 K. The effective
interaction between the DS1 spins is approximately expressed by the
ferromagnetic model with the direction parallel to the
crystallographic c axis. A magnetic phase diagram for was
obtained and was analyzed within the framework of the molecular field
approximation. With increasing magnetic field, the dangling spins are polarized
and the magnetization curve exhibits a wide plateau at one-third of the
saturation magnetization.Comment: 10 pages, 12 figure
From ultra-fast growth to avalanche growth in devitrifying glasses
During devitrification, pre-existing crystallites grow by adding particles to
their surface via a process which is either thermally activated (diffusive
mode), or happens without kinetic barriers (fast crystal growth mode). It is
yet unclear what factors determine the crystal growth mode, and how to predict
it. With simulations of repulsive hard-sphere glasses, we show for the first
time that the same system at the same volume fraction and temperature can
devitrify via both modes depending on the preparation protocol of the glass. We
prepare two types of glass, a conventional glass (CG) via fast quenching and a
uniform glass (UG) via density homogenization. Firstly, we bring either glass
into contact with a crystal (X) and find the inherent structure (CGX/UGX).
During energy minimization, the crystal front grows deep into the CG interface,
while the growth is minimal for UG. When thermal noise is added, this behavior
is reflected in different crystallization dynamics. CGX exhibits a density drop
at the crystal growth front, leading to enhanced dynamics at the interface and
a fast growth mode. This mechanism may explain the faster crystal growth
observed below the glass transition experimentally. In contrast, UGX grows via
intermittent avalanche-like dynamics localized at the interface, a combination
of localized mechanical defects and the exceptional mechanical stability
imposed by the UG glass phase.Comment: 23 pages, 8 figure
Towards glasses with permanent stability
Unlike crystals, glasses age or devitrify over time, reflecting their
non-equilibrium nature. This lack of stability is a serious issue in many
industrial applications. Here, we show by numerical simulations that the
devitrification of quasi-hard-sphere glasses is prevented by suppressing volume
fraction inhomogeneities. A monodisperse glass known to devitrify with
`avalanche'-like intermittent dynamics is subjected to small iterative
adjustments to particle sizes to make the local volume fractions spatially
uniform. We find that this entirely prevents structural relaxation and
devitrification over aging time scales, even in the presence of crystallites.
There is a dramatic homogenization in the number of load-bearing nearest
neighbors each particle has, indicating that ultra-stable glasses may be formed
via `mechanical homogenization'. Our finding provides a physical principle for
glass stabilization and opens a novel route to the formation of mechanically
stabilized glasses.Comment: 6 pages, 4 figures, 1 ancillary video file, 1 supplementary PD
Design, Synthesis, and Biological Applications of Boron-Containing Polyamine and Sugar Derivatives
Boron (B), an element that is present in ultratrace amounts in animal cells and tissues, is expected to be useful in many scientific fields. We have found the hydrolysis of C–B bond in phenylboronic acid-pendant cyclen (cyclen = 1,4,7,10-tetraazacyclododecane) and the full decomposition of ortho-carborane attached with cyclen and ethylenediamines in aqueous solution at neutral pH upon complexation with intracellular metals. The change in the chemical shift of the 11B signals in 11B-NMR spectra of these boron-containing metal chelators can be applied to the magnetic resonance imaging (MRI) of metal ions in solutions and in living cells
Does the number of rescuers affect the survival rate from out-of-hospital cardiac arrests? Two or more rescuers are not always better than one
Review: An increased number of rescuers may improve the survival rate from out-of-hospital cardiac arrests (OHCAs). The majority of OHCAs occur at home and are handled by family members. Materials and methods: Data from 5078 OHCAs that were witnessed by citizens and unwitnessed by citizens or emergency medical technicians from January 2004 to March 2010 were prospectively collected. The number of rescuers was identified in 4338 OHCAs and was classified into two (single rescuer (N = 2468) and multiple rescuers (N = 1870)) or three (single rescuer, two rescuers (N = 887) and three or more rescuers (N = 983)) groups. The backgrounds, characteristics and outcomes of OHCAs were compared between the two groups and among the three groups. Results: When all OHCAs were collectively analysed, an increased number of rescuers was associated with better outcomes (one-year survival and one-year survival with favourable neurological outcomes were 3.1% and 1.9% for single rescuers, 4.1% and 2.0% for two rescuers, and 6.0% and 4.6% for three or more rescuers, respectively (p = 0.0006 and p < 0.0001)). A multiple logistic regression analysis showed that the presence of multiple rescuers is an independent factor that is associated with one-year survival (odds ratio (95% confidence interval): 1.539 (1.088-2.183)). When only OHCAs that occurred at home were analysed (N = 2902), the OHCAs that were handled by multiple rescuers were associated with higher incidences of bystander CPR but were not associated with better outcomes. Conclusions: In summary, an increased number of rescuers improves the outcomes of OHCAs. However, this beneficial effect is absent in OHCAs that occur at home. © 2012 Elsevier Ireland Ltd. All rights reserved
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