2,142 research outputs found
Experimental verification of reciprocity relations in quantum thermoelectric transport
Symmetry relations are manifestations of fundamental principles and
constitute cornerstones of modern physics. An example are the Onsager relations
between coefficients connecting thermodynamic fluxes and forces, central to
transport theory and experiments. Initially formulated for classical systems,
these reciprocity relations are also fulfilled in quantum conductors.
Surprisingly, novel relations have been predicted specifically for
thermoelectric transport. However, whereas these thermoelectric reciprocity
relations have to date not been verified, they have been predicted to be
sensitive to inelastic scattering, always present at finite temperature. The
question whether the relations exist in practice is important for
thermoelectricity: whereas their existence may simplify the theory of complex
thermoelectric materials, their absence has been shown to enable, in principle,
higher thermoelectric energy conversion efficiency for a given material
quality. Here we experimentally verify the thermoelectric reciprocity relations
in a four-terminal mesoscopic device where each terminal can be electrically
and thermally biased, individually. The linear response thermoelectric
coefficients are found to be symmetric under simultaneous reversal of magnetic
field and exchange of injection and emission contacts. Intriguingly, we also
observe the breakdown of the reciprocity relations as a function of increasing
thermal bias. Our measurements thus clearly establish the existence of the
thermoelectric reciprocity relations, as well as the possibility to control
their breakdown with the potential to enhance thermoelectric performanceComment: 7 pages, 5 figure
Restricted three-body problem in effective-field-theory models of gravity
One of the outstanding problems of classical celestial mechanics was the
restricted 3-body prob- lem, in which a planetoid of small mass is subject to
the Newtonian attraction of two celestial bodies of large mass, as it occurs,
for example, in the sun-earth-moon system. On the other hand, over the last
decades, a systematic investigation of quantum corrections to the Newtonian
potential has been carried out in the literature on quantum gravity. The
present paper studies the effect of these tiny quantum corrections on the
evaluation of equilibrium points. It is shown that, despite the extreme
smallness of the corrections, there exists no choice of sign of these
corrections for which all qualitative features of the restricted 3-body problem
in Newtonian theory remain unaffected. Moreover, first-order stability of
equilibrium points is characterized by solving a pair of algebraic equations of
fifth degree, where some coefficients depend on the Planck length. The
coordinates of stable equilibrium points are slightly changed with respect to
Newtonian theory, because the planetoid is no longer at equal distance from the
two bodies of large mass. The effect is conceptually interesting but too small
to be observed, at least for the restricted 3-body problems available in the
solar system.Comment: 20 pages, latex, 8 figure
Re-embedding a 1-Plane Graph into a Straight-line Drawing in Linear Time
Thomassen characterized some 1-plane embedding as the forbidden configuration
such that a given 1-plane embedding of a graph is drawable in straight-lines if
and only if it does not contain the configuration [C. Thomassen, Rectilinear
drawings of graphs, J. Graph Theory, 10(3), 335-341, 1988].
In this paper, we characterize some 1-plane embedding as the forbidden
configuration such that a given 1-plane embedding of a graph can be re-embedded
into a straight-line drawable 1-plane embedding of the same graph if and only
if it does not contain the configuration. Re-embedding of a 1-plane embedding
preserves the same set of pairs of crossing edges.
We give a linear-time algorithm for finding a straight-line drawable 1-plane
re-embedding or the forbidden configuration.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016). This is an extended
abstract. For a full version of this paper, see Hong S-H, Nagamochi H.:
Re-embedding a 1-Plane Graph into a Straight-line Drawing in Linear Time,
Technical Report TR 2016-002, Department of Applied Mathematics and Physics,
Kyoto University (2016
Simulation of 3d Ising spin glass model using three replicas: study of Binder cumulants
We have carried out numerical simulations of the three-dimensional Ising spin
glass model with first neighbour Gaussian couplings using three replicas for
each sample of couplings. We have paid special attention to the measure of two
types of Binder cumulant that can be constructed from the three possible
overlaps between the replicas. We obtain new information about the possible
phase transition and perform an initial analysis of the ultrametricity issue.Comment: 14 pages and 7 figures, available at
http://chimera.roma1.infn.it/index_papers_complex.htm
Earth-Moon Lagrangian points as a testbed for general relativity and effective field theories of gravity
We first analyse the restricted four-body problem consisting of the Earth, the Moon and the Sun as the primaries and a spacecraft as the planetoid. This scheme allows us to take into account the solar perturbation in the description of the motion of a spacecraft in the vicinity of the stable Earth-Moon libration points L4 and L5 both in the classical regime and in the context of effective field theories of gravity. A vehicle initially placed at L4 or L5 will not remain near the respective points. In particular, in the classical case the vehicle moves on a trajectory about the libration points for at least 700 days before escaping away. We show that this is true also if the modified long-distance Newtonian potential of effective gravity is employed. We also evaluate the impulse required to cancel out the perturbing force due to the Sun in order to force the spacecraft to stay precisely at L4 or L5. It turns out that this value is slightly modified with respect to the corresponding Newtonian one. In the second part of the paper, we first evaluate the location of all Lagrangian points in the Earth-Moon system within the framework of general relativity. For the points L4 and L5, the corrections of coordinates are of order a few millimeters and describe a tiny departure from the equilateral triangle. After that, we set up a scheme where the theory which is quantum corrected has as its classical counterpart the Einstein theory, instead of the Newtonian one. In other words, we deal with a theory involving quantum corrections to Einstein gravity, rather than to Newtonian gravity. By virtue of the effective-gravity correction to the long-distance form of the potential among two point masses, all terms involving the ratio between the gravitational radius of the primary and its separation from the planetoid get modified. Within this framework, for the Lagrangian points of stable equilibrium, we find quantum corrections of order two millimeters, whereas for Lagrangian points of unstable equilibrium we find quantum corrections below a millimeter. In the latter case, for the point L1, general relativity corrects Newtonian theory by 7.61 meters, comparable, as an order of magnitude, with the lunar geodesic precession of about 3 meters per orbit. The latter is a cumulative effect accurately measured at the centimeter level through the lunar laser ranging positioning technique. Thus, it is possible to study a new laser ranging test of general relativity to measure the 7.61-meter correction to the L1 Lagrangian point, an observable never used before in the Sun-Earth-Moon system. Performing such an experiment requires controlling the propulsion to precisely reach L1, an instrumental accuracy comparable to the measurement of the lunar geodesic precession, understanding systematic effects resulting from thermal radiation and multi-body gravitational perturbations. This will then be the basis to consider a second-generation experiment to study deviations of effective field theories of gravity from general relativity in the Sun-Earth-Moon system
Nimesulide reduces interleukin-1β-induced cyclooxygenase-2 gene expression in human synovial fibroblasts
AbstractObjective To characterize the effects of nimesulide (NIM) on basal and induced cyclo-oxygenase-2 (COX-2) gene expression in human synovial fibroblasts (HSF) and to define the intracellular mechanisms that mediate the changes in COX-2 expression and synthesis in response to the drug.Design HSF were incubated with NIM and NS-398 (0, 0.03, 0.3, 3μg/ml) in the absence or presence of the COX-2 inducers interleukin-1β (IL-1β) or endotoxin (LPS). Treated cells were analysed for COX-2 mRNA and protein by Northern and Western blotting analysis, respectively. Putative transcriptional, post-transcriptional, and signaling effects of NIM on basal and induced-COX-2 expression were investigated by human COX-2 promoter studies, calcium studies, reactive oxygen species (ROS) evaluations, electrophoretic mobility shift analysis (EMSA) and half-life studies of COX-2 mRNA.Results NIM inhibited IL-1β-induced COX-2 expression and protein at sub and therapeutic concentrations (0.03–0.3μg/ml) while the non-specific NSAID, naproxen, did not. Both drugs suppressed PGE2 release by about 95%. NIM had no effect on (1) IL-1β-induced increases in NF-κB or c/EBP signaling, or (2) human COX-2 promoter activity. Stability of induced COX-2 mRNA was unaffected by NIM treatments. Pre-treatment of cells with O2radical scavengers (e.g. PDTC) or with Ca++channel blockers (e.g. verapamil) had a modest effect on IL-1β-induced COX-2 expression. NIM blocked ionomycin+thapsigargin and H2O2-induced increases in COX-2 protein synthesis.Conclusion NIM inhibits cytokine-induced COX-2 expression and protein at sub and therapeutic concentrations. At least part of this activity may be the result of NIM inhibition of calcium and/or free radical generation induced by cytokines
Bar 1-Visibility Drawings of 1-Planar Graphs
A bar 1-visibility drawing of a graph is a drawing of where each
vertex is drawn as a horizontal line segment called a bar, each edge is drawn
as a vertical line segment where the vertical line segment representing an edge
must connect the horizontal line segments representing the end vertices and a
vertical line segment corresponding to an edge intersects at most one bar which
is not an end point of the edge. A graph is bar 1-visible if has a bar
1-visibility drawing. A graph is 1-planar if has a drawing in a
2-dimensional plane such that an edge crosses at most one other edge. In this
paper we give linear-time algorithms to find bar 1-visibility drawings of
diagonal grid graphs and maximal outer 1-planar graphs. We also show that
recursive quadrangle 1-planar graphs and pseudo double wheel 1-planar graphs
are bar 1-visible graphs.Comment: 15 pages, 9 figure
The Effect of Planarization on Width
We study the effects of planarization (the construction of a planar diagram
from a non-planar graph by replacing each crossing by a new vertex) on
graph width parameters. We show that for treewidth, pathwidth, branchwidth,
clique-width, and tree-depth there exists a family of -vertex graphs with
bounded parameter value, all of whose planarizations have parameter value
. However, for bandwidth, cutwidth, and carving width, every graph
with bounded parameter value has a planarization of linear size whose parameter
value remains bounded. The same is true for the treewidth, pathwidth, and
branchwidth of graphs of bounded degree.Comment: 15 pages, 6 figures. To appear at the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
Low T Dynamical Properties of Spin Glasses Smoothly Extrapolate to T=0
We compare ground state properties of 3D Ising Spin Glasses with Gaussian
couplings with results from off-equilibrium numerical simulations at non zero
(but low) temperatures. We find that the non-zero temperature properties of the
system smoothly connect to the T=0 behavior, confirming the point of view that
results established at T=0 typically also give relevant information about the
physics of the system.Comment: 14 pages and 4 ps figure
Numerical Evidence for Spontaneously Broken Replica Symmetry in 3D Spin Glasses
By numerical simulations of the Ising spin glass we find evidence that
spontaneous replica symmetry breaking theory and not the droplet model
describes with good accuracy the equilibrium behavior of the system.Comment: PHYSREV format, 2 .ps figures added with figure command in uufiles
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