3,629 research outputs found
The grand canonical ABC model: a reflection asymmetric mean field Potts model
We investigate the phase diagram of a three-component system of particles on
a one-dimensional filled lattice, or equivalently of a one-dimensional
three-state Potts model, with reflection asymmetric mean field interactions.
The three types of particles are designated as , , and . The system is
described by a grand canonical ensemble with temperature and chemical
potentials , , and . We find that for
the system undergoes a phase transition from a
uniform density to a continuum of phases at a critical temperature . For other values of the chemical potentials the system
has a unique equilibrium state. As is the case for the canonical ensemble for
this model, the grand canonical ensemble is the stationary measure
satisfying detailed balance for a natural dynamics. We note that , where is the critical temperature for a similar transition in
the canonical ensemble at fixed equal densities .Comment: 24 pages, 3 figure
Research Notes : Australia : Designation of a core collection of perennial Glycine
Over the last decade, a large germplasm collection of the 12 currently recognized perennial species of Glycine has been assembled. This collection, now numbering more than 1400 accessions, is held in Canberra, Australia, and is recognized by the International Board of Plant Genetic Resources as the world base collection for perennial Glycine. The 12 species include five that have been described recently
The recent development of steels with carbide-free acicular microstructures containing retained austenite
After a lengthy period of improvement in carbon steel ferrite/pearlite microstructures by microalloying andcontrolled processing, some attention has focused back more recently upon acicular forms of microstructure.In particular, an interesting advance in this area has been the development, primarily by alloying with Si, ofso-called ‘carbide-free’ bainitic steels, where carbon-stabilized retained austenite is substituted for cementite.Transformation induced plasticity (TRIP) sheet steel with enhanced properties, principally targeted forautomotive use, and future potential ‘nanobainite’ steel, are two noteworthy examples. Even more recently, thisconcept of developing steel microstructures containing carbon-enriched retained austenite has been extendedfurther by introducing novel heat treatment procedures to replace bainite with martensite. This nonequilibrium‘quenching and partitioning’ process route, as it is known, offers possibilities of immediateadvantage: enhanced strength from a martensitic structure protected from the more damaging effects ofcarbon, along with the promise of new properties from the retained austenite phase which could potentiallycontain a very high controlled concentration of carbon
Effect of trunk exercise upon lumbar IVD height and vertebral compliance when performed supine with 1 g at the CoM compared to upright in 1 g
Background: Spinal unloading in microgravity is associated with stature increments, back pain, intervertebral disc (IVD) swelling and impaired spinal kinematics. The aim of this study was to determine the effect of lateral stabilization, trunk rotation and isometric abdominal exercise upon lumbar IVD height, and both passive and active vertebral compliance when performed supine on a short-arm human centrifuge (SAHC)-a candidate microgravity countermeasure-with 1 g at the CoM, compared to that generated with equivalent upright exercise in 1 g.
Methods: 12 (8 male) healthy subjects (33.8 ± 7 years, 178.4 ± 8.2 cm, 72.1 ± 9.6 kg) gave written informed consent. Subjects performed three sets of upper body trunk exercises either when standing upright (UPRIGHT), or when being spun on the SAHC. Lumbar IVD height and vertebral compliance (active and passive) were evaluated prior to SAHC (PRE SAHC) and following the first SAHC (POST SPIN 1) and second Spin (POST SPIN 2), in addition to before (PRE UPRIGHT), and after upright trunk exercises (POST UPRIGHT).
Results: No significant effect upon IVD height (L2-S1) when performed UPRIGHT or on the SAHC was observed. Trunk muscle exercise induced significant (p < 0.05) reduction of active thoracic vertebral compliance when performed on the SAHC, but not UPRIGHT. However, no effect was observed in the cervical, lumbar or across the entire vertebral column. On passive or active vertebral compliance.
Conclusion: This study, the first of its kind demonstrates that trunk exercise were feasible and tolerable. Whilst trunk muscle exercise appears to have minor effect upon IVD height, it may be a candidate approach to mitigate-particularly active-vertebral stability on Earth, and in μg via concurrent SAHC. However, significant variability suggests larger studies including optimization of trunk exercise and SAHC prescription with MRI are warranted.
Trial registration: North Rhine ethical committee (Number: 6000223393) and registered on 29/09/2020 in the German Clinical Trials Register (DRKS00021750).
Keywords: Artificial gravity; Countermeasures; Exercise; IVD; Spine; Stiffnes
Numerical study of a non-equilibrium interface model
We have carried out extensive computer simulations of one-dimensional models
related to the low noise (solid-on-solid) non-equilibrium interface of a two
dimensional anchored Toom model with unbiased and biased noise. For the
unbiased case the computed fluctuations of the interface in this limit provide
new numerical evidence for the logarithmic correction to the subnormal L^(1/2)
variance which was predicted by the dynamic renormalization group calculations
on the modified Edwards-Wilkinson equation. In the biased case the simulations
are in close quantitative agreement with the predictions of the Collective
Variable Approximation (CVA), which gives the same L^(2/3) behavior of the
variance as the KPZ equation.Comment: 15 pages revtex, 4 Postscript Figure
Measuring helical FCG voltage with an electric field antenna
A method of measuring the voltage produced by a helical explosive flux compression generator using a remote electric field antenna is described in detail. The diagnostic has been successfully implemented on several experiments. Measured data from the diagnostic compare favorably with voltages predicted using the code CAGEN, validating our predictive modeling tools. The measured data is important to understanding generator performance, and is measured with a low-risk, minimally intrusive approach
What About High-Moisture Corn for Hogs?
High-moisture corn is a satisfactory feedstuff for growing-finishing hogs, according to the results of a series of tests at Iowa State. But high-moisture corn calls for special storage and handling to maintain quality
Spontaneous symmetry breaking: exact results for a biased random walk model of an exclusion process
It has been recently suggested that a totally asymmetric exclusion process
with two species on an open chain could exhibit spontaneous symmetry breaking
in some range of the parameters defining its dynamics. The symmetry breaking is
manifested by the existence of a phase in which the densities of the two
species are not equal. In order to provide a more rigorous basis to these
observations we consider the limit of the process when the rate at which
particles leave the system goes to zero. In this limit the process reduces to a
biased random walk in the positive quarter plane, with specific boundary
conditions. The stationary probability measure of the position of the walker in
the plane is shown to be concentrated around two symmetrically located points,
one on each axis, corresponding to the fact that the system is typically in one
of the two states of broken symmetry in the exclusion process. We compute the
average time for the walker to traverse the quarter plane from one axis to the
other, which corresponds to the average time separating two flips between
states of broken symmetry in the exclusion process. This time is shown to
diverge exponentially with the size of the chain.Comment: 42 page
Phase diagram of the ABC model with nonconserving processes
The three species ABC model of driven particles on a ring is generalized to
include vacancies and particle-nonconserving processes. The model exhibits
phase separation at high densities. For equal average densities of the three
species, it is shown that although the dynamics is {\it local}, it obeys
detailed balance with respect to a Hamiltonian with {\it long-range
interactions}, yielding a nonadditive free energy. The phase diagrams of the
conserving and nonconserving models, corresponding to the canonical and
grand-canonical ensembles, respectively, are calculated in the thermodynamic
limit. Both models exhibit a transition from a homogeneous to a phase-separated
state, although the phase diagrams are shown to differ from each other. This
conforms with the expected inequivalence of ensembles in equilibrium systems
with long-range interactions. These results are based on a stability analysis
of the homogeneous phase and exact solution of the hydrodynamic equations of
the models. They are supported by Monte-Carlo simulations. This study may serve
as a useful starting point for analyzing the phase diagram for unequal
densities, where detailed balance is not satisfied and thus a Hamiltonian
cannot be defined.Comment: 32 page, 7 figures. The paper was presented at Statphys24, held in
Cairns, Australia, July 201
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Low-profile high-voltage compact gas switch
This paper discusses the development and testing of a low-profile, high-voltage, spark-gap switch designed to be closely coupled with other components into an integrated high-energy pulsed-power source. The switch is designed to operate at 100 kV using SF6 gas pressurized to less than 0.7 MPa. The volume of the switch cavity region is less than 1.5 cm3, and the field stress along the gas-dielectric interface is as high as 130 kV/cm. The dielectric switch body has a low profile that is only I -cm tall at its greatest extent and nominally 2-mm thick over most of its area. This design achieves a very low inductance of less than 5 nH, but results in field stresses exceeding 500 kV/cm in the dielectric material. Field modeling was done to determine the appropriate shape for the highly stressed insulator and electrodes, and special manufacturing techniques were employed to mitigate the usual mechanisms that induce breakdown and failure in solid dielectrics. Static breakdown tests verified that the switch operates satisfactorily at 100 kV levels. The unit has been characterized with different shaped electrodes having nominal gap spacings of 2.0, 2.5, and 3.0 mm. The relationship between self-break voltage and operating pressure agrees well with published data on gas properties, accounting for the field enhancements of the electrode shapes being used. Capacitor discharge tests in a low inductance test fixture exhibited peak currents up to 25 kA with characteristic frequencies of the ringdown circuit ranging from 10 to 20 MHz. The ringdown waveforms and scaling of measured parameters agree well with circuit modeling of the switch and test fixture. Repetitive operation has been demonstrated at moderate rep-rates up to 15 Hz, limited by the power supply being used. Preliminary tests to evaluate lifetime of the compact switch assembly have been encouraging. In one case, after more than 7,000 high-current ringdown tests with approximately 30 C of total charge transferred, the switch continued to operate satisfactorily with no apparent tracking or deterioration of the insulator
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