9,962 research outputs found
Oscillation Phenomena in the disk around the massive black hole Sagittarius A*
We report the detection of radio QPOs with structure changes using the Very
Long Baseline Array (VLBA) at 43 GHz. We found conspicuous patterned changes of
the structure with P = 16.8 +- 1.4, 22.2 +- 1.4, 31.2 +- 1.5, 56.4 +- 6 min,
very roughly in a 3:4:6:10 ratio. The first two periods show a rotating one-arm
structure, while the P = 31.4 min shows a rotating 3-arm structure, as if
viewed edge-on. At the central 50 microasec the P = 56.4 min period shows a
double amplitude variation of those in its surroundings. Spatial distributions
of the oscillation periods suggest that the disk of SgrA* is roughly edge-on,
rotating around an axis with PA = -10 degree. Presumably, the observed VLBI
images of SgrA* at 43 GHz retain several features of the black hole accretion
disk of SgrA* in spite of being obscured and broadened by scattering of
surrounding plasma.Comment: 24 pages, 20 figures, revised version submitted to MN main journal
(2010, Jan., 12th
Minimizing the linewidth of the Flux-Flow Oscillator
For the first time the linewidth of Flux-Flow Oscillator has been calculated
by direct computer simulation of the sine-Gordon equation with noise. Nearly
perfect agreement of the numerical results with the formula derived in [Phys.
Rev. B, {\bf 65}, 054504 (2002)] has been achieved. It has been demonstrated
that for homogeneous bias current distribution the linewidth actually does not
depend on the junction length for practically interesting parameters range.
Depending on the length of the unbiased tail, the power may be maximized and
the linewidth may be minimized in a broad range of bias currents. The linewidth
can be decreased further by 1.5 times by proper load matching.Comment: 4 pages, 6 figure
Applications of Graphical Condensation for Enumerating Matchings and Tilings
A technique called graphical condensation is used to prove various
combinatorial identities among numbers of (perfect) matchings of planar
bipartite graphs and tilings of regions. Graphical condensation involves
superimposing matchings of a graph onto matchings of a smaller subgraph, and
then re-partitioning the united matching (actually a multigraph) into matchings
of two other subgraphs, in one of two possible ways. This technique can be used
to enumerate perfect matchings of a wide variety of bipartite planar graphs.
Applications include domino tilings of Aztec diamonds and rectangles, diabolo
tilings of fortresses, plane partitions, and transpose complement plane
partitions.Comment: 25 pages; 21 figures Corrected typos; Updated references; Some text
revised, but content essentially the sam
Picosecond Laser Ablation of Polyhydroxyalkanoates (PHAs): Comparative Study of Neat and Blended Material Response
Polyhydroxyalkanoates (PHAs) have emerged as a promising biodegradable and biocompatible material for scaffold manufacturing in the tissue engineering field and food packaging. Surface modification is usually required to improve cell biocompatibility and/or reduce bacteria proliferation. Picosecond laser ablation was applied for surface micro structuring of short- and medium-chain length-PHAs and its blend. The response of each material as a function of laser energy and wavelength was analyzed. Picosecond pulsed laser modified the surface topography without affecting the material properties. UV wavelength irradiation showed halved ablation thresholds compared to visible (VIS) wavelength, revealing a greater photochemical nature of the ablation process at ultraviolet (UV) wavelength. Nevertheless, the ablation rate and, therefore, ablation efficiency did not show a clear dependence on beam wavelength. The different mechanical behavior of the considered PHAs did not lead to different ablation thresholds on each polymer at a constant wavelength, suggesting the interplay of the material mechanical parameters to equalize ablation thresholds. Blended-PHA showed a significant reduction in the ablation threshold under VIS irradiation respect to the neat PHAs. Picosecond ablation was proved to be a convenient technique for micro structuring of PHAs to generate surface microfeatures appropriate to influence cell behavior and improve the biocompatibility of scaffolds in tissue engineerin
The effect of "pre-formed" hadron potentials on the dynamics of heavy ion collisions and the HBT puzzle
The nuclear stopping, the elliptic flow, and the HBT interferometry are
calculated by the UrQMD transport model, in which potentials for "pre-formed"
particles (string fragments) from color fluxtube fragmentation as well as for
confined particles are considered. This description provides stronger pressure
at the early stage and describes these observables better than the default
cascade mode (where the "pre-formed" particles from string fragmentation are
treated to be free-streaming). It should be stressed that the inclusion of
potential interactions pushes down the calculated HBT radius and pulls up
the so that the HBT time-related puzzle disappears throughout the
energies from AGS, SPS, to RHIC.Comment: 6 pages, 4 figures. Accepted for publication in Phys. Lett.
Particle states of Lattice QCD
We determine the degeneracy factor and the average particle mass of particles
that produce the Lattice QCD pressure and specific entropy at zero baryon
chemical potential. The number of states of the gluons and the quarks are found
to converge above 230 MeV to almost constant values, close to the number of
states of an ideal Quark-Gluon Phase, while their assigned masses retain high
values. The number of states and the average mass of a system containing quarks
in interaction with gluons are found to decrease steeply with increase of
temperature between and 160 MeV, a region contained within the
region of the chiral transition. The minimum value of the number of states
within this temperature interval indicates that the states are of hadronic
nature.Comment: 21 pages, 18 figure
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