9,047 research outputs found
One Thing After Another: Why the Passage of Time Is Not an Illusion
Does time seem to pass, even though it doesn’t, really? Many philosophers think the answer is ‘Yes’—at least when ‘time’s passing’ is understood in a particular way. They take time’s passing to be a process by which each time in turn acquires a special status, such as the status of being the only time that exists, or being the only time that is present. This chapter suggests that, on the contrary, all we perceive is temporal succession, one thing after another, a notion to which modern physics is not inhospitable. The contents of perception are best described in terms of ‘before’ and ‘after’, rather than ‘past’, ‘present, and ‘future’
Positive Measure Spectrum for Schroedinger Operators with Periodic Magnetic Fields
We study Schroedinger operators with periodic magnetic field in Euclidean
2-space, in the case of irrational magnetic flux. Positive measure Cantor
spectrum is generically expected in the presence of an electric potential. We
show that, even without electric potential, the spectrum has positive measure
if the magnetic field is a perturbation of a constant one.Comment: 17 page
Strain bursts in plastically deforming Molybdenum micro- and nanopillars
Plastic deformation of micron and sub-micron scale specimens is characterized
by intermittent sequences of large strain bursts (dislocation avalanches) which
are separated by regions of near-elastic loading. In the present investigation
we perform a statistical characterization of strain bursts observed in
stress-controlled compressive deformation of monocrystalline Molybdenum
micropillars. We characterize the bursts in terms of the associated elongation
increments and peak deformation rates, and demonstrate that these quantities
follow power-law distributions that do not depend on specimen orientation or
stress rate. We also investigate the statistics of stress increments in between
the bursts, which are found to be Weibull distributed and exhibit a
characteristic size effect. We discuss our findings in view of observations of
deformation bursts in other materials, such as face-centered cubic and
hexagonal metals.Comment: 14 pages, 8 figures, submitted to Phil Ma
Influence of peptidylarginine deiminase type 4 genotype and shared epitope on clinical characteristics and autoantibody profile of rheumatoid arthritis.
Background: Recent evidence suggests that distinction
of subsets of rheumatoid arthritis (RA) depending on anticyclic
citrullinated peptide antibody (anti-CCP) status may
be helpful in distinguishing distinct aetiopathologies and in
predicting the course of disease. HLA-DRB1 shared
epitope (SE) and peptidylarginine deiminase type 4
(PADI4) genotype, both of which have been implicated in
anti-CCP generation, are assumed to be associated with
RA.
Objectives: To elucidate whether PADI4 affects the
clinical characteristics of RA, and whether it would
modulate the effect of anti-CCPs on clinical course. The
combined effect of SE and PADI4 on autoantibody profile
was also analysed.
Methods: 373 patients with RA were studied. SE,
padi4_94C.T, rheumatoid factor, anti-CCPs and antinuclear
antibodies (ANAs) were determined. Disease
severity was characterised by cumulative therapy
intensity classified into ordinal categories (CTI-1 to CTI-3)
and by Steinbrocker score.
Results: CTI was significantly associated with disease
duration, erosive disease, disease activity score (DAS) 28
and anti-CCPs. The association of anti-CCPs with CTI was
considerably influenced by padi4_94C.T genotype (C/C:
ORadj=0.93, padj=0.92; C/T: ORadj=2.92,
padj=0.093; T/T: ORadj=15.3, padj=0.002). Carriage of
padi4_94T exhibited a significant trend towards higher
Steinbrocker scores in univariate and multivariate
analyses. An association of padi4_94C.T with ANAs
was observed, with noteworthy differences depending on
SE status (SE2: ORadj=6.20, padj,0.04; SE+:
ORadj=0.36, padj=0.02) and significant heterogeneity
between the two SE strata (p=0.006).
Conclusions: PADI4 genotype in combination with anti-
CCPs and SE modulates clinical and serological characteristics
of RA
On the Second Law of thermodynamics and the piston problem
The piston problem is investigated in the case where the length of the
cylinder is infinite (on both sides) and the ratio is a very small
parameter, where is the mass of one particle of the gaz and is the mass
of the piston. Introducing initial conditions such that the stochastic motion
of the piston remains in the average at the origin (no drift), it is shown that
the time evolution of the fluids, analytically derived from Liouville equation,
agrees with the Second Law of thermodynamics.
We thus have a non equilibrium microscopical model whose evolution can be
explicitly shown to obey the two laws of thermodynamics.Comment: 29 pages, 9 figures submitted to Journal of Statistical Physics
(2003
Research and development of the dry tape battery concept Quarterly report no. 2, 9 Sep. - 8 Dec. 1965
Magnesium-aluminum chloride, hydrogen chloride- trichlorotriazinetrione system for dry tape batterie
General duality for abelian-group-valued statistical-mechanics models
We introduce a general class of statistical-mechanics models, taking values
in an abelian group, which includes examples of both spin and gauge models,
both ordered and disordered. The model is described by a set of ``variables''
and a set of ``interactions''. A Gibbs factor is associated to each variable
and to each interaction. We introduce a duality transformation for systems in
this class. The duality exchanges the abelian group with its dual, the Gibbs
factors with their Fourier transforms, and the interactions with the variables.
High (low) couplings in the interaction terms are mapped into low (high)
couplings in the one-body terms. The idea is that our class of systems extends
the one for which the classical procedure 'a la Kramers and Wannier holds, up
to include randomness into the pattern of interaction. We introduce and study
some physical examples: a random Gaussian Model, a random Potts-like model, and
a random variant of discrete scalar QED. We shortly describe the consequence of
duality for each example.Comment: 26 pages, 2 Postscript figure
A complete devil's staircase in the Falicov-Kimball model
We consider the neutral, one-dimensional Falicov-Kimball model at zero
temperature in the limit of a large electron--ion attractive potential, U. By
calculating the general n-ion interaction terms to leading order in 1/U we
argue that the ground-state of the model exhibits the behavior of a complete
devil's staircase.Comment: 6 pages, RevTeX, 3 Postscript figure
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