1,065 research outputs found
Deconfinement at finite chemical potential
In a confining, renormalisable, Dyson-Schwinger equation model of two-flavour
QCD we explore the chemical-potential dependence of the dressed-quark
propagator, which provides a means of determining the behaviour of the chiral
and deconfinement order parameters, and low-energy pion observables. We find
coincident, first order deconfinement and chiral symmetry restoration
transitions at \mu_c = 375 MeV. f_\pi is insensitive to \mu until \mu \approx
\mu_0 = 0.7 mu_c when it begins to increase rapidly. m_\pi is weakly dependent
on \mu, decreasing slowly with \mu and reaching a minimum 6% less than its
\mu=0 value at \mu=\mu_0. In a two-flavour free-quark gas at \mu=\mu_c the
baryon number density would be approximately 3 \rho_0, where \rho_0=0.16
fm^{-3}; while in such a gas at \mu_0 the density is \rho_0.Comment: 11 pages, 3 figures, epsfig.sty, elsart.st
In situ synchrotron x-ray study of ultrasound cavitation and its effect on solidification microstructures
Considerable progress has been made in studying the mechanism and effectiveness of using ultrasound waves to manipulate the solidification microstructures of metallic alloys. However, uncertainties remain in both the underlying physics of how microstructures evolve under ultrasonic waves, and the best technological approach to control the final microstructures and properties. We used the ultrafast synchrotron X-ray phase contrast imaging facility housed at the Advanced Photon Source, Argonne National Laboratory, US to study in situ the highly transient and dynamic interactions between the liquid metal and ultrasonic waves/bubbles. The dynamics of ultrasonic bubbles in liquid metal and their interactions with the solidifying phases in a transparent alloy were captured in situ. The experiments were complemented by the simulations of the acoustic pressure field, the pulsing of the bubbles, and the associated forces acting onto the solidifying dendrites. The study provides more quantitative understanding on how ultrasonic waves/bubbles influence the growth of dendritic grains and promote the grain multiplication effect for grain refinement
The transfer of fibres in the carding machine
The problem of understanding the transfer of fibres between carding-machine surfaces is addressed by considering the movement of a single fibre in an airflow. The structure of the aerodynamic flow field predicts how and when fibres migrate between the different process surfaces. In the case of a revolving-flats carding machine the theory predicts a “strong” aerodynamic mechanism between taker-in and cylinder and a “weak” mechanism between cylinder and removal cylinder resulting in effective transfer in the first case and a more limited transfer in the second
Persistence in q-state Potts model: A Mean-Field approach
We study the Persistence properties of the T=0 coarsening dynamics of one
dimensional -state Potts model using a modified mean-field approximation
(MMFA). In this approximation, the spatial correlations between the interfaces
separating spins with different Potts states is ignored, but the correct time
dependence of the mean density of persistent spins is imposed. For this
model, it is known that follows a power-law decay with time, where is the -dependent persistence exponent. We
study the spatial structure of the persistent region within the MMFA. We show
that the persistent site pair correlation function has the scaling
form for all values of the persistence
exponent . The scaling function has the limiting behaviour () and (). We then show within the
Independent Interval Approximation (IIA) that the distribution of
separation between two consecutive persistent spins at time has the
asymptotic scaling form where the
dynamical exponent has the form =max(). The behaviour of
the scaling function for large and small values of the arguments is found
analytically. We find that for small separations where =max(), while for large
separations , decays exponentially with . The
unusual dynamical scaling form and the behaviour of the scaling function is
supported by numerical simulations.Comment: 11 pages in RevTeX, 10 figures, submitted to Phys. Rev.
香港の衛星都市
textabstractThe Drosophila protein Sex-lethal (Sxl) contains two RNP consensus-type RNA-binding domains (RBDs) separated by a short linker sequence. Both domains are essential for high-affinity binding tO the single-stranded polypyrimidine tract (PPT) within the regulated 3' splice site of the transformer (tra) pre- mRNA. In this paper, the effect of RNA binding to a protein fragment containing both RBDs from Sxl (Sxl-RBD1+2) has been characterized by heteronuclear NMR. Newly complete (85-90%) backbone resonance assignments have been obtained for unbound and RNA-bound states of Sxl-RBD1+2. A comparison of amide 1H and 15N chemical shifts between free and bound states has highlighted residues which respond to RNA binding. The β-sheets in both RBDs (RBD1 and RBD2) form an RNA interaction surface, as has been observed in other RBDs. A significant number of residues display different behavior when comparing RBD1 and RBD2. This argues for a model in which RBD1 and RBD2 of Sxl have different or nonanalogous points of interaction with the tra PPT. R142 (in RBD2) exhibits the largest chemical shift change upon RNA binding. The role of R142 in RNA binding was tested by measuring the K(d) of a mutant of Sxl-RBD1+2 in which R142 was replaced by alanine. This mutant lost the ability to bind RNA, showing a correlation with the chemical shift difference data. The RNA-binding affinities of two other mutants, F146A and T138I, were also shown to correlate with the NMR observations
Muon-Spin Rotation Spectra in the Mixed Phase of High-T_c Superconductors : Thermal Fluctuations and Disorder Effects
We study muon-spin rotation (muSR) spectra in the mixed phase of highly
anisotropic layered superconductors, specifically Bi_2+xSr_2-xCaCu_2O_8+delta
(BSCCO), by modeling the fluid and solid phases of pancake vortices using
liquid-state and density functional methods. The role of thermal fluctuations
in causing motional narrowing of muSR lineshapes is quantified in terms of a
first-principles theory of the flux-lattice melting transition. The effects of
random point pinning are investigated using a replica treatment of liquid state
correlations and a replicated density functional theory. Our results indicate
that motional narrowing in the pure system, although substantial, cannot
account for the remarkably small linewidths obtained experimentally at
relatively high fields and low temperatures. We find that satisfactory
agreement with the muSR data for BSCCO in this regime can be obtained through
the ansatz that this ``phase'' is characterized by frozen short-range
positional correlations reflecting the structure of the liquid just above the
melting transition. This proposal is consistent with recent suggestions of a
``pinned liquid'' or ``glassy'' state of pancake vortices in the presence of
pinning disorder. Our results for the high-temperature liquid phase indicate
that measurable linewidths may be obtained in this phase as a consequence of
density inhomogeneities induced by the pinning disorder. The results presented
here comprise a unified, first-principles theoretical treatment of muSR spectra
in highly anisotropic layered superconductors in terms of a controlled set of
approximations.Comment: 50 pages Latex file, including 10 postscript figure
Search for Heavy Neutrino in K->mu nu_h(nu_h-> nu gamma) Decay at ISTRA+ Setup
Heavy neutrino nu_h with m_h < 300MeV/c^2 can be effectively searched for in
kaon decays. We put upper limits on mixing matrix element |U_mu_h}|^2 for
radiatively decaying nu_h from K->mu nu_h (nu_h -> nu gamma) decay chain in the
following parameter region: 30MeV/c^2 < m_h < 80MeV/c^2; 10^{-11}sec < tau_h <
10^{-9}sec. For the whole region |U_{mu h}|^2 < 5 x 10^{-5} for Majorana type
of nu_h and | U_{\mu h}|^2 < 8 x 10^{-5} for the Dirac case.Comment: Published in Phys. Lett.
High speed synchrotron X-ray imaging studies of the ultrasound shockwave and enhanced flow during metal solidification processes
The highly dynamic behaviour of ultrasonic bubble implosion in liquid metal, the multiphase liquid metal flow containing bubbles and particles, and the interaction between ultrasonic waves and semisolid phases during solidification of metal were studied in situ using the complementary ultrafast and high speed synchrotron X-ray imaging facilities housed respectively at the Advanced Photon Source, Argonne National Laboratory, US, and Diamond Light Source, UK. Real-time ultrafast X-ray imaging of 135,780 frames per second (fps) revealed that ultrasonic bubble implosion in a liquid Bi-8 wt. %Zn alloy can occur in a single wave period (30 kHz), and the effective region affected by the shockwave at implosion was 3.5 times the original bubble diameter. Furthermore, ultrasound bubbles in liquid metal move faster than the primary particles, and the velocity of bubbles is 70 ~ 100% higher than that of the primary particles present in the same locations close to the sonotrode. Ultrasound waves can very effectively create a strong swirling flow in a semisolid melt in less than one second. The energetic flow can detach solid particles from the liquid-solid interface and redistribute them back into the bulk liquid very effectively
Model for the hydration of non-polar compounds and polymers
We introduce an exactly solvable statistical-mechanical model of the
hydration of non-polar compounds, based on grouping water molecules in clusters
where hydrogen bonds and isotropic interactions occur; interactions between
clusters are neglected. Analytical results show that an effective strengthening
of hydrogen bonds in the presence of the solute, together with a geometric
reorganization of water molecules, are enough to yield hydrophobic behavior. We
extend our model to describe a non-polar homopolymer in aqueous solution,
obtaining a clear evidence of both ``cold'' and ``warm'' swelling transitions.
This suggests that our model could be relevant to describe some features of
protein folding.Comment: REVTeX, 6 pages, 3 figure
Flame front propagation V: Stability Analysis of Flame Fronts: Dynamical Systems Approach in the Complex Plane
We consider flame front propagation in channel geometries. The steady state
solution in this problem is space dependent, and therefore the linear stability
analysis is described by a partial integro-differential equation with a space
dependent coefficient. Accordingly it involves complicated eigenfunctions. We
show that the analysis can be performed to required detail using a finite order
dynamical system in terms of the dynamics of singularities in the complex
plane, yielding detailed understanding of the physics of the eigenfunctions and
eigenvalues.Comment: 17 pages 7 figure
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