13,919 research outputs found
Skyrme models and nuclear matter equation of state
We investigate the role of pressure in a class of generalised Skyrme models. We introduce pressure as the trace of the spatial part of the energy-momentum tensor and show that it obeys the usual thermodynamical relation. Then, we compute analytically the mean-field equation of state in the high and medium pressure regimes by applying topological bounds on compact domains. The equation of state is further investigated numerically for the charge one skyrmions. We identify which term in a generalised Skyrme model is responsible for which part in the equation of state. Further, we compare our findings with the corresponding results in the Walecka model
Categories of First-Order Quantifiers
One well known problem regarding quantifiers, in particular the 1storder
quantifiers, is connected with their syntactic categories and denotations.
The unsatisfactory efforts to establish the syntactic and ontological categories
of quantifiers in formalized first-order languages can be solved by means of the
so called principle of categorial compatibility formulated by Roman Suszko,
referring to some innovative ideas of Gottlob Frege and visible in syntactic
and semantic compatibility of language expressions. In the paper the principle
is introduced for categorial languages generated by the Ajdukiewicz’s classical
categorial grammar. The 1st-order quantifiers are typically ambiguous. Every
1st-order quantifier of the type k \u3e 0 is treated as a two-argument functorfunction
defined on the variable standing at this quantifier and its scope (the
sentential function with exactly k free variables, including the variable bound
by this quantifier); a binary function defined on denotations of its two arguments
is its denotation. Denotations of sentential functions, and hence also
quantifiers, are defined separately in Fregean and in situational semantics.
They belong to the ontological categories that correspond to the syntactic
categories of these sentential functions and the considered quantifiers. The
main result of the paper is a solution of the problem of categories of the
1st-order quantifiers based on the principle of categorial compatibility
Development of an 400 L Integrated Refrigeration and Storage Cryostat for LNG/LCH4 Research
Research engineers from the Cryogenics Test Laboratory at NASA Kennedy Space Center in Florida have developed a 400 liter Integrated Refrigeration and Storage (IRAS) cryostat to explore advanced techniques for storage, conditioning, and transfer of liquefied natural gas and/or pure methane. A vertical-cylindrical configuration, the vacuum-jacketed apparatus houses a G-M cryocooler to control the state of the fluid, and sample tubes with corresponding temperature sensors fixed at various elevations to allow for sampling of the liquid. Two additional ports were also included for future instrumentation and/or mechanical feed-throughs. A primary goal of this test apparatus will be to study the effect of IRAS on the behavior of LNG during storage; most notably weathering and stratification of the bulk liquid over time. Additionally, in-situ liquefaction of natural gas can be performed, along with zero boil-off control, liquid densification, and slush production
Rydberg transition frequencies from the Local Density Approximation
A method is given that extracts accurate Rydberg excitations from LDA density
functional calculations, despite the short-ranged potential. For the case of He
and Ne, the asymptotic quantum defects predicted by LDA are in less than 5%
error, yielding transition frequency errors of less than 0.1eV.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let
ASME Section VIII Recertification of a 33,000 Gallon Vacuum-jacketed LH2 Storage Vessel for Densified Hydrogen Testing at NASA Kennedy Space Center
The Ground Operations Demonstration Unit for Liquid Hydrogen (GODU-LH2) has been developed at NASA Kennedy Space Center in Florida. GODU-LH2 has three main objectives: zero-loss storage and transfer, liquefaction, and densification of liquid hydrogen. A cryogenic refrigerator has been integrated into an existing, previously certified, 33,000 gallon vacuum-jacketed storage vessel built by Minnesota Valley Engineering in 1991 for the Titan program. The dewar has an inner diameter of 9.5 and a length of 71.5; original design temperature and pressure ranges are -423 F to 100 F and 0 to 95 psig respectively. During densification operations the liquid temperature will be decreased below the normal boiling point by the refrigerator, and consequently the pressure inside the inner vessel will be sub-atmospheric. These new operational conditions rendered the original certification invalid, so an effort was undertaken to recertify the tank to the new pressure and temperature requirements (-12.7 to 95 psig and -433 F to 100 F respectively) per ASME Boiler and Pressure Vessel Code, Section VIII, Division 1. This paper will discuss the unique design, analysis and implementation issues encountered during the vessel recertification process
Symmetry Classes in Graphene Quantum Dots: Universal Spectral Statistics, Weak Localization, and Conductance Fluctuations
We study the symmetry classes of graphene quantum dots, both open and closed,
through the conductance and energy level statistics. For abrupt termination of
the lattice, these properties are well described by the standard orthogonal and
unitary ensembles. However, for smooth mass confinement, special time-reversal
symmetries associated with the sublattice and valley degrees of freedom are
critical: they lead to block diagonal Hamiltonians and scattering matrices with
blocks belonging to the unitary symmetry class even at zero magnetic field.
While the effect of this structure is clearly seen in the conductance of open
dots, it is suppressed in the spectral statistics of closed dots, because the
intervalley scattering time is shorter than the time required to resolve a
level spacing in the closed systems but longer than the escape time of the open
systems.Comment: 4 pages, 4 figures, RevTex, submitted to Phys. Rev. Let
Time-dependent Density Functional calculation of e-H scattering
Phase shifts for single-channel elastic electron-atom scattering are derived
from time-dependent density functional theory. The H ion is placed in a
spherical box, its discrete spectrum found, and phase shifts deduced.
Exact-exchange yields an excellent approximation to the ground-state Kohn-Sham
potential, while the adiabatic local density approximation yields good singlet
and triplet phase shifts.Comment: 5 pages, 4 figures, 1 tabl
The Case for an Accelerating Universe from Supernovae
The unexpected faintness of high-redshift Type Ia supernovae (SNe Ia), as
measured by two teams, has been interpreted as evidence that the expansion of
the Universe is accelerating. We review the current challenges to this
interpretation and seek to answer whether the cosmological implications are
compelling. We discuss future observations of SNe Ia which could offer
extraordinary evidence to test acceleration.Comment: To appear as an Invited Review for PASP 20 pages, 13 figure
Glassy transition and metastability in four-spin Ising model
Using Monte Carlo simulations we show that the three-dimensional Ising model
with four-spin (plaquette) interactions has some characteristic glassy
features. The model dynamically generates diverging energy barriers, which give
rise to slow dynamics at low temperature. Moreover, in a certain temperature
range the model possesses a metastable (supercooled liquid) phase, which is
presumably supported by certain entropy barriers. Although extremely strong,
metastability in our model is only a finite-size effect and sufficiently large
droplets of stable phase divert evolution of the system toward the stable
phase. Thus, the glassy transitions in this model is a dynamic transition,
preceded by a pronounced peak in the specific heat.Comment: extensively revised, with further simulations of metastability
properties, response to referees tactfully remove
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