16,171 research outputs found
Evidence of a glass transition in a 10-state non-mean-field Potts glass
Potts glasses are prototype models that have been used to understand the
structural glass transition. However, in finite space dimensions a glass
transition remains to be detected in the 10-state Potts glass. Using a
one-dimensional model with long-range power-law interactions we present
evidence that a glass transition below the upper critical dimension can exist
for short-range systems at low enough temperatures. Gaining insights into the
structural glass transition for short-range systems using spin models is thus
potentially possible, yet difficult.Comment: 4 pages, 1 table, 2 figure
Lattice Boltzmann simulations of a viscoelastic shear-thinning fluid
We present a hybrid lattice Boltzmann algorithm for the simulation of flow
glass-forming fluids, characterized by slow structural relaxation, at the level
of the Navier-Stokes equation. The fluid is described in terms of a nonlinear
integral constitutive equation, relating the stress tensor locally to the
history of flow. As an application, we present results for an integral
nonlinear Maxwell model that combines the effects of (linear) viscoelasticity
and (nonlinear) shear thinning. We discuss the transient dynamics of
velocities, shear stresses, and normal stress differences in planar
pressure-driven channel flow, after switching on (startup) and off (cessation)
of the driving pressure. This transient dynamics depends nontrivially on the
channel width due to an interplay between hydrodynamic momentum diffusion and
slow structural relaxation
Thermal and hydrodynamic effects in the ordering of lamellar fluids
Phase separation in a complex fluid with lamellar order has been studied in
the case of cold thermal fronts propagating diffusively from external walls.
The velocity hydrodynamic modes are taken into account by coupling the
convection-diffusion equation for the order parameter to a generalised
Navier-Stokes equation. The dynamical equations are simulated by implementing a
hybrid method based on a lattice Boltzmann algorithm coupled to finite
difference schemes. Simulations show that the ordering process occurs with
morphologies depending on the speed of the thermal fronts or, equivalently, on
the value of the thermal conductivity {\xi}. At large value of {\xi}, as in
instantaneous quenching, the system is frozen in entangled configurations at
high viscosity while consists of grains with well ordered lamellae at low
viscosity. By decreasing the value of {\xi}, a regime with very ordered
lamellae parallel to the thermal fronts is found. At very low values of {\xi}
the preferred orientation is perpendicular to the walls in d = 2, while
perpendicular order is lost moving far from the walls in d = 3.Comment: 8 pages, 3 figures. Accepted for publication in Phil. Trans. of Royal
Soc, Ser
Supercell studies of the Fermi surface changes in the electron-doped superconductor LaFeAsOF
We study the changes in the Fermi surface with electron doping in the
LaFeAsOF superconductors with density-functional supercell
calculations using the linearized augmented planewave (LAPW) method. The
supercell calculations with explicit F substitution are compared with those
obtained from the virtual crystal approximation (VCA) and from a simple rigid
band shift. We find significant differences between the supercell results and
those obtained from the rigid-band shift with electron doping, although quite
remarkably the supercell results are in good agreement with the virtual crystal
approximation (VCA) where the nuclear charges of the O atoms are slightly
increased to mimic the addition of the extra electrons. With electron doping,
the two cylindrical hole pockets along shrink in size, and the third
hole pocket around disappears for an electron doping concentration in
excess of about 7-8%, while the two elliptical electron cylinders along
expand in size. The spin-orbit coupling does not affect the Fermi surface much
except to somewhat reduce the size of the third hole pocket in the undoped
case. We find that with the addition of the electrons the antiferromagnetic
state becomes energetically less stable as compared to the nonmagnetic state,
indicating that the electron doping may provide an extra degree of stability to
the formation of the superconducting ground state.Comment: 7 pages, 8 figure
Duality in Shearing Rheology Near the Athermal Jamming Transition
We consider the rheology of soft-core frictionless disks in two dimensions in
the neighborhood of the athermal jamming transition. From numerical simulations
of bidisperse, overdamped, particles, we argue that the divergence of the
viscosity below jamming is characteristic of the hard-core limit, independent
of the particular soft-core interaction. We develop a mapping from soft-core to
hard-core particles that recovers all the critical behavior found in earlier
scaling analyses. Using this mapping we derive a duality relation that gives
the exponent of the non-linear Herschel-Bulkley rheology above jamming in terms
of the exponent of the diverging viscosity below jamming.Comment: 5 pages, 4 figures. Manuscript revisions: new title, additional text
concerning connections to experiment, revised Fig. 4, other minor changes and
clarifications in text. Conclusions remain essentially unchanged. Accepted
for publication in Phys. Rev. Let
High temperature measuring device
Ultrasonic pulse technique for measuring average gas temperature in nuclear rocket engine - sound propagation and environmental studie
Massive stars and globular cluster formation
We first present chemodynamical simulations to investigate how stellar winds
of massive stars influence early dynamical and chemical evolution of forming
globular clusters (GCs). In our numerical models, GCs form in
turbulent,high-density giant molecular clouds (GMCs), which are embedded in a
massive dark matter halo at high redshifts. We show how high-density, compact
stellar systems are formed from GMCs influenced both by physical processes
associated with star formation and by tidal fields of their host halos. We also
show that chemical pollution of GC-forming GMCs by stellar winds from massive
stars can result in star-to-star abundance inhomogeneities among light elements
(e.g., C, N, and O) of stars in GCs. The present model with a canonical initial
mass function (IMF) also shows a C-N anticorrelation that stars with smaller
[C/Fe] have larger [N/Fe] in a GC. Although these results imply that
``self-pollution'' of GC-forming GMCs by stellar winds from massive stars can
cause abundance inhomogeneities of GCs, the present models with different
parameters and canonical IMFs can not show N-rich stars with [N/Fe] ~ 0.8
observed in some GCs (e.g., NGC 6752). We discuss this apparent failure in the
context of massive star formation preceding low-mass one within GC-forming GMCs
(``bimodal star formation scenario''). We also show that although almost all
stars (~97%) show normal He abundances (Y) of ~0.24 some stars later formed in
GMCs can have Y as high as ~0.3 in some models. The number fraction of He-rich
stars with Y >0.26 is however found to be small (~10^-3) for most models.Comment: 10 pages, 8 figures, accepted by Ap
Prospects for observing ultra-compact binaries with space-based gravitational wave interferometers and optical telescopes
Space-based gravitational wave interferometers are sensitive to the galactic
population of ultra-compact binaries. An important subset of the ultra-compact
binary population are those stars that can be individually resolved by both
gravitational wave interferometers and electromagnetic telescopes. The aim of
this paper is to quantify the multi-messenger potential of space-based
interferometers with arm-lengths between 1 and 5 Gm. The Fisher Information
Matrix is used to estimate the number of binaries from a model of the Milky Way
which are localized on the sky by the gravitational wave detector to within 1
and 10 square degrees and bright enough to be detected by a magnitude limited
survey. We find, depending on the choice of GW detector characteristics,
limiting magnitude, and observing strategy, that up to several hundred
gravitational wave sources could be detected in electromagnetic follow-up
observations.Comment: 6 pages, 3 figures Updated to include new results. Submitted to MNRA
Wind tunnel investigation of an all flush orifice air data system for a large subsonic aircraft
The results of a wind tunnel investigation on an all flush orifice air data system for use on a KC-135A aircraft are presented. The investigation was performed to determine the applicability of fixed all flush orifice air data systems that use only aircraft surfaces for orifices on the nose of the model (in a configuration similar to that of the shuttle entry air data system) provided the measurements required for the determination of stagnation pressure, angle of attack, and angle of sideslip. For the measurement of static pressure, additional flush orifices in positions on the sides of the fuselage corresponding to those in a standard pitot-static system were required. An acceptable but less accurate system, consisting of orifices only on the nose of the model, is defined and discussed
- …