112,544 research outputs found
Column size effects of DER fluids
The static yield stress of dielectric electrorheological(DER) fluids of
infinite column state and chain state are calculated from the first principle
method. The results indicate that the column surface contributions to ER
effects is very small and both states will give correct results to the real DER
fluids.Comment: 7 pages, 3 figure
Coincidences of Dark Energy with Dark Matter -- Clues for a Simple Alternative?
A rare coincidence of scales in standard particle physics is needed to
explain why or the negative pressure of cosmological dark energy (DE)
coincides with the positive pressure of random motion of dark matter (DM)
in bright galaxies. Recently Zlosnik et al. (2007) propose to modify the
Einsteinian curvature by adding a non-linear pressure from a medium flowing
with a four-velocity vector field . We propose to check whether a smooth
extension of GR with a simple kinetic Lagrangian of can be constructed,
and whether the pressure can bend space-time sufficiently to replace the roles
of a DE, Cold DM and heavy neutrinos in explaining anomalous
accelerations at all scales. As a specific proof of concept we find a
Vector-for- model (-model) and its variants. With
essentially {\it no free parameters}, these appear broadly consistent with the
solar system, gravitational potentials in dwarf spiral galaxies and the bullet
cluster of galaxies, early universe with inflation, structure formation and
BBN, and late acceleration with a 1:3 ratio of DM:DE.Comment: to appear in ApJ Letters, 4 page
How Well Do We Know the Beta-Decay of 16N and Oxygen Formation in Helium Burning
We review the status of the 12C(a,g)16O reaction rate, of importance for
stellar processes in a progenitor star prior to a super-nova collapse. Several
attempts to constrain the p-wave S-factor of the 12C(a,g)16O reaction at Helium
burning temperatures (200 MK) using the beta-delayed alpha-particle emission of
16N have been made, and it is claimed that this S-factor is known, as quoted by
the TRIUMF collaboration. In contrast reanalyses (by G.M. hale) of all thus far
available data (including the 16N data) does not rule out a small S-factor
solution. Furthermore, we improved our previous Yale-UConn study of the beta-
delayed alpha-particle emission of \n16 by improving our statistical sample (by
more than a factor of 5), improving the energy resolution of the experiment (by
20%), and in understanding our line shape, deduced from measured quantities.
Our newly measured spectrum of the beta-delayed alpha-particle emission of 16N
is not consistent with the TRIUMF('94) data, but is consistent with the
Seattle('95) data, as well as the earlier (unaltered !) data of Mainz('71). The
implication of this discrepancies for the extracted astrophysical p-wave
s-factor is briefly discussed.Comment: 6 pages, 4 figures, Invited Talk, Physics With Radioactive Beams,
Puri, India, Jan. 12-17, 1998, Work Supported by USDOE Grant No.
DE-FG02-94ER4087
Intrinsic electron-doping in nominal "non-doped" superconducting (La,Y)CuO thin films grown by dc magnetron sputtering
The superconducting nominal "non-doped" (LYCO) thin
films are successfully prepared by dc magnetron-sputtering and in situ
post-annealing in vacuum. The best more than 13K is achieved in the
optimal LYCO films with highly pure c-axis oriented T'-type structure. In the
normal state, the quasi-quadratic temperature dependence of resistivity, the
negative Hall coefficient and effect of oxygen content in the films are quite
similar to the typical Ce-doped T'-214 cuprates, suggesting that T'-LYCO shows
the electron-doping nature like known n-type cuprates, and is not a band
superconductor as proposed previously. The charge carriers are considered to be
induced by oxygen deficiency.Comment: 5 pages, 7 figure
Dynamics of self-organized driven particles with competing range interaction
Non-equilibrium self-organized patterns formed by particles interacting
through competing range interaction are driven over a substrate by an external
force. We show that, with increasing driving force, the pre-existed static
patterns evolve into dynamic patterns either via disordered phase or depinned
patterns, or via the formation of non-equilibrium stripes. Strikingly, the
stripes are formed either in the direction of the driving force or in the
transverse direction, depending on the pinning strength. The revealed dynamical
patterns are summarized in a dynamical phase diagram.Comment: 8 pages, 11 figure
The necessity of dark matter in MOND within galactic scales
To further test MOdified Newtonian Dynamics (MOND) on galactic scales --
originally proposed to explain the rotation curves of disk galaxies without
dark matter -- we study a sample of six strong gravitational lensing early-type
galaxies from the CASTLES database. To determine whether dark matter is present
in these galaxies, we compare the total mass (from lensing) with the stellar
mass content (from a comparison of photometry and stellar population
synthesis). We find that strong gravitational lensing on galactic scales
requires a significant amount of dark matter, even within MOND. On such scales
a 2 eV neutrino cannot explain this excess matter -- in contrast with recent
claims to explain the lensing data of the bullet cluster. The presence of dark
matter is detected in regions with a higher acceleration than the
characteristic MONDian scale of m/s. This is a serious
challenge to MOND unless the proper treatment of lensing is qualitatively
different (possibly to be developed within a consistent theory such as TeVeS).Comment: 5 pages, 3 figures, 1 table Amended version to match publication in
Phys. Rev. let
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