2,726 research outputs found
Anomalous Diffusion In Microrheology: A Comparative Study
We present a comparative study on two theoretical descriptions of
microrheological experiments. Using a generalized Langevin equation (GLE), we
analyze the origin of the power-law behavior of the main properties of a
viscoelastic medium. Then, we discuss the equivalence of the GLE with a
generalized Fokker-Planck equation (GFPE), and how more general GFPE's can be
derived from a thermo-kinetic formalism. These complementary theories lead to a
justification for the physical nature of the Hurst exponent of fractional
kinetics. Theory is compared with experiments.Comment: 7 pages, 3 figure
Conductivity of a graphene strip: width and gate-voltage dependencies
We study the conductivity of a graphene strip taking into account
electrostatically-induced charge accumulation on its edges. Using a local
dependency of the conductivity on the carrier concentration we find that the
electrostatic size effect in doped graphene strip of the width of 0.5 - 3 m can result in a significant (about 40%) enhancement of the effective
conductivity in comparison to the infinitely wide samples. This effect should
be taken into account both in the device simulation as well as for verification
of scattering mechanisms in graphene.Comment: 3 pages, 4 figure
Folding of the triangular lattice in a discrete three-dimensional space: Crumpling transitions in the negative-bending-rigidity regime
Folding of the triangular lattice in a discrete three-dimensional space is
studied numerically. Such ``discrete folding'' was introduced by Bowick and
co-workers as a simplified version of the polymerized membrane in thermal
equilibrium. According to their cluster-variation method (CVM) analysis, there
appear various types of phases as the bending rigidity K changes in the range
-infty < K < infty. In this paper, we investigate the K<0 regime, for which the
CVM analysis with the single-hexagon-cluster approximation predicts two types
of (crumpling) transitions of both continuous and discontinuous characters. We
diagonalized the transfer matrix for the strip widths up to L=26 with the aid
of the density-matrix renormalization group. Thereby, we found that
discontinuous transitions occur successively at K=-0.76(1) and -0.32(1).
Actually, these transitions are accompanied with distinct hysteresis effects.
On the contrary, the latent-heat releases are suppressed considerably as
Q=0.03(2) and 0.04(2) for respective transitions. These results indicate that
the singularity of crumpling transition can turn into a weak-first-order type
by appreciating the fluctuations beyond a meanfield level
Fluctuation effects in the theory of microphase separation of diblock copolymers in the presence of an electric field
We generalize the Fredrickson-Helfand theory of the microphase separation in
symmetric diblock copolymer melts by taking into account the influence of a
time-independent homogeneous electric field on the composition fluctuations
within the self-consistent Hartree approximation. We predict that electric
fields suppress composition fluctuations, and consequently weaken the
first-order transition. In the presence of an electric field the critical
temperature of the order-disorder transition is shifted towards its mean-field
value. The collective structure factor in the disordered phase becomes
anisotropic in the presence of the electric field. Fluctuational modulations of
the order parameter along the field direction are strongest suppressed. The
latter is in accordance with the parallel orientation of the lamellae in the
ordered state.Comment: 16 page
Unitary representations of nilpotent super Lie groups
We show that irreducible unitary representations of nilpotent super Lie
groups can be obtained by induction from a distinguished class of sub super Lie
groups. These sub super Lie groups are natural analogues of polarizing
subgroups that appear in classical Kirillov theory. We obtain a concrete
geometric parametrization of irreducible unitary representations by nonnegative
definite coadjoint orbits. As an application, we prove an analytic
generalization of the Stone-von Neumann theorem for Heisenberg-Clifford super
Lie groups
Points of Low Height on Elliptic Curves and Surfaces, I: Elliptic surfaces over P^1 with small d
For each of n=1,2,3 we find the minimal height h^(P) of a nontorsion point P
of an elliptic curve E over C(T) of discriminant degree d=12n (equivalently, of
arithmetic genus n), and exhibit all (E,P) attaining this minimum. The minimal
h^(P) was known to equal 1/30 for n=1 (Oguiso-Shioda) and 11/420 for n=2
(Nishiyama), but the formulas for the general (E,P) were not known, nor was the
fact that these are also the minima for an elliptic curve of discriminant
degree 12n over a function field of any genus. For n=3 both the minimal height
(23/840) and the explicit curves are new. These (E,P) also have the property
that that mP is an integral point (a point of naive height zero) for each
m=1,2,...,M, where M=6,8,9 for n=1,2,3; this, too, is maximal in each of the
three cases.Comment: 15 pages; some lines in the TeX source are commented out with "%" to
meet the 15-page limit for ANTS proceeding
A third cluster of red supergiants in the vicinity of the massive cluster RSGC3
Recent studies have shown that the area around the massive, obscured cluster
RSGC3 may harbour several clusters of red supergiants. In this paper, we
analyse a clump of photometrically selected red supergiant candidates 20' south
of RSGC3 in order to confirm the existence of another of these clusters. Using
medium-resolution infrared spectroscopy around 2.27 microns, we derived
spectral types and velocities along the line of sight for the selected
candidates, confirming their nature and possible association. We find a compact
clump of eight red supergiants and four other candidates at some distance, all
of them spectroscopically confirmed red supergiants. The majority of these
objects must form an open cluster, which we name Alicante 10. Because of the
high reddening and strong field contamination, the cluster sequence is not
clearly seen in 2MASS or GPS-UKIDSS. From the observed sources, we derive
E(J-Ks)=2.6 and d~6 kpc. Although the cluster is smaller than RSGC3, it has an
initial mass in excess of 10000 solar masses, and it seems to be part of the
RSGC3 complex. With the new members this association already has 35
spectroscopically confirmed red supergiants, confirming its place as one of the
most active sites of recent stellar formation in the Galaxy.Comment: Accepted for publication on A&
Electronic structure of the muonium center as a shallow donor in ZnO
The electronic structure and the location of muonium centers (Mu) in
single-crystalline ZnO were determined for the first time. Two species of Mu
centers with extremely small hyperfine parameters have been observed below 40
K. Both Mu centers have an axial-symmetric hyperfine structure along with a
[0001] axis, indicating that they are located at the AB_{O,//} and BC_{//}
sites. It is inferred from their small ionization energy (~6 meV and 50 meV)
and hyperfine parameters (~10^{-4} times the vacuum value) that these centers
behave as shallow donors, strongly suggesting that hydrogen is one of the
primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR
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