1,953 research outputs found
Paper 99: design guidelines versus practices for the Upper Seascheldt, the inland waterway connection between Antwerp and Ghent
Design guidelines for inland waterways are so far a national matter. PIANC InCom Working Group 141 "Design Guidelines for Inland Waterways" is nevertheless working on a report with a summary of existing guidelines and a methodology for the concept and detailed design of canals and rivers. For tidal rivers the design is a difficult process and an example is given through the accessibility of the Upper-Seascheldt for CEMT class IV and Va inland vessels between the port of Antwerp and the locks in Merelbeke. A combined evaluation based on concept design guidelines for canals, practices measured during a full-scale voyage and detailed design using ship handling simulators is discussed and illustrated
Lattice Glass Models
Motivated by the concept of geometrical frustration, we introduce a class of
statistical mechanics lattice models for the glass transition. Monte Carlo
simulations in three dimensions show that they display a dynamical glass
transition which is very similar to that observed in other off-lattice systems
and which does not depend on a specific dynamical rule. Whereas their analytic
solution within the Bethe approximation shows that they do have a discontinuous
glass transition compatible with the numerical observations.Comment: 4 pages, 2 figures; minor change
Indirect Detection of a Light Higgsino Motivated by Collider Data
Kane and Wells recently argued that collider data point to a Higgsino-like
lightest supersymmetric partner which would explain the dark matter in our
Galactic halo. They discuss direct detection of such dark-matter particles in
laboratory detectors. Here, we argue that such a particle, if it is indeed the
dark matter, might alternatively be accessible in experiments which search for
energetic neutrinos from dark-matter annihilation in the Sun. We provide
accurate analytic estimates for the rates which take into account all relevant
physical effects. Currently, the predicted signal falls roughly one to three
orders of magnitude below experimental bounds, depending on the mass and
coupling of the particle; however, detectors such as MACRO, super-Kamiokande,
and AMANDA will continue to take data and should be able to rule out or confirm
an interesting portion of the possible mass range for such a dark-matter
particle within the next five years.Comment: 10 pages, RevTe
Thermodynamics of glasses: a first principle computation
We propose a first principle computation of the thermodynamics of simple
fragile glasses starting from the two body interatomic potential.
A replica formulation translates this problem into that of a gas of
interacting molecules, each molecule being built of atoms, and having a
gyration radius (related to the cage size) which vanishes at zero temperature.
We use a small cage expansion, valid at low temperatures, which allows to
compute the cage size, the specific heat (which follows the Dulong and Petit
law), and the configurational entropy.Comment: Latex, 13 pages, 4 figure
Statistical Physics of Structural Glasses
This paper gives an introduction and brief overview of some of our recent
work on the equilibrium thermodynamics of glasses. We have focused onto first
principle computations in simple fragile glasses, starting from the two body
interatomic potential. A replica formulation translates this problem into that
of a gas of interacting molecules, each molecule being built of atoms, and
having a gyration radius (related to the cage size) which vanishes at zero
temperature. We use a small cage expansion, valid at low temperatures, which
allows to compute the cage size, the specific heat (which follows the Dulong
and Petit law), and the configurational entropy. The no-replica interpretation
of the computations is also briefly described. The results, particularly those
concerning the Kauzmann tempaerature and the configurational entropy, are
compared to recent numerical simulations.Comment: 21 pages, 6 figures, to appear in the proceedings of the Trieste
workshop on "Unifying Concepts in Glass Physics
Modular and predictable assembly of porous organic molecular crystals
Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for 'one-pot' chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules
Unit-Level Variations in Healthcare Professionals' Availability for Preterm Neonates <29 Weeks' Gestation: An International Survey
INTRODUCTION The availability of and variability in healthcare professionals in neonatal units in different countries has not been well characterized. Our objective was to identify variations in the healthcare professionals for preterm neonates in 10 national or regional neonatal networks participating in the International Network for Evaluating Outcomes (iNeo) of neonates.
METHOD Online, pre-piloted questionnaires about the availability of healthcare professionals were sent to the directors of 390 tertiary neonatal units in 10 international networks: Australia/New Zealand, Canada, Finland, Illinois, Israel, Japan, Spain, Sweden, Switzerland, and Tuscany.
RESULTS Overall, 325 of 390 units (83%) responded. About half of the units (48%; 156/325) cared for 11-30 neonates/day and had team-based (43%; 138/325) care models. Neonatologists were present 24 h a day in 59% of the units (191/325), junior doctors in 60% (194/325), and nurse practitioners in 36% (116/325). A nurse-to-patient ratio of 1:1 for infants who are unstable and require complex care was used in 52% of the units (170/325), whereas a ratio of 1:1 or 1:2 for neonates requiring multisystem support was available in 59% (192/325) of the units. Availability of a respiratory therapist (15%, 49/325), pharmacist (40%, 130/325), dietitian (34%, 112/325), social worker (81%, 263/325), lactation consultant (45%, 146/325), parent buddy (6%, 19/325), or parents' resource personnel (11%, 34/325) were widely variable between units.
CONCLUSIONS We identified variability in the availability and organization of the healthcare professionals between and within countries for the care of extremely preterm neonates. Further research is needed to associate healthcare workers' availability and outcomes
First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data
We report results of a deep all-sky search for periodic gravitational waves from isolated neutron stars in data from the first Advanced LIGO observing run. This search investigates the low frequency range of Advanced LIGO data, between 20 and 100 Hz, much of which was not explored in initial LIGO. The search was made possible by the computing power provided by the volunteers of the Einstein@Home project. We find no significant signal candidate and set the most stringent upper limits to date on the amplitude of gravitational wave signals from the target population, corresponding to a sensitivity depth of 48.7 [1/Hz]. At the frequency of best strain sensitivity, near 100 Hz, we set 90% confidence upper limits of 1.8Ă—10-25. At the low end of our frequency range, 20 Hz, we achieve upper limits of 3.9Ă—10-24. At 55 Hz we can exclude sources with ellipticities greater than 10-5 within 100 pc of Earth with fiducial value of the principal moment of inertia of 1038 kg m2
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