18,902 research outputs found
Microscopic phase separation in the overdoped region of high-Tc cuprate superconductors
We propose a phenomenological model for high- superconductors (HTSC)
assuming: (1) a microscopic phase separation between superconducting and
normal-metal areas in the overdoped region; and (2) existence of a homogeneous
superconducting phase only below the pseudo-gap line, which shows a
sharp reduction towards at a mildly overdoped critical
concentration . This model explains anomalous doping and temperature
dependences of (superconducting carrier density / effective mass)
observed in several overdoped HTSC systems. We point out an analogy to
superfluid He/He films, and discuss an energetic origin of
microscopic phase separation.Comment: 5 pages, 4 figure
Fibred Fibration Categories
We introduce fibred type-theoretic fibration categories which are fibred
categories between categorical models of Martin-L\"{o}f type theory. Fibred
type-theoretic fibration categories give a categorical description of logical
predicates for identity types. As an application, we show a relational
parametricity result for homotopy type theory. As a corollary, it follows that
every closed term of type of polymorphic endofunctions on a loop space is
homotopic to some iterated concatenation of a loop
A General Framework for the Semantics of Type Theory
We propose an abstract notion of a type theory to unify the semantics of
various type theories including Martin-L\"{o}f type theory, two-level type
theory and cubical type theory. We establish basic results in the semantics of
type theory: every type theory has a bi-initial model; every model of a type
theory has its internal language; the category of theories over a type theory
is bi-equivalent to a full sub-2-category of the 2-category of models of the
type theory
What can we learn from comparison between cuprates and He films ? : phase separation and fluctuating superfluidity
In the underdoped, overdoped, Zn-doped or stripe-forming regions of
high- cuprate superconductors (HTSC), the superfluid density
at shows universal correlations with . Similar
strong correlations exist between 2-dimensional superfluid density and
superfluid transition temperature in thin films of He in non-porous or
porous media, and He/He film adsorbed on porous media. Based on
analogy between HTSC and He film systems, we propose a model for cuprates
where: (1) the overdoped region is characterized by a phase separation similar
to He/He; and (2) pair (boson) formation and fluctuating
superconductivity occur at separate temperatures above in the
underdoped region.Comment: 8 pages, 5 figures. Invited paper presented at the third
international conference on stripes and high-Tc superconductivity
(STRIPE-2000), Sept. 25-30th, 2000, Rome, Italy. To be published in the
International Journal of Modern Physics
Jump-type Hunt processes generated by lower bounded semi-Dirichlet forms
Let be a locally compact separable metric space and be a positive
Radon measure on it. Given a nonnegative function defined on
off the diagonal whose anti-symmetric part is assumed to be less singular than
the symmetric part, we construct an associated regular lower bounded
semi-Dirichlet form on producing a Hunt process on
whose jump behaviours are governed by . For an arbitrary open subset
, we also construct a Hunt process on in an analogous
manner. When is relatively compact, we show that is censored in
the sense that it admits no killing inside and killed only when the path
approaches to the boundary. When is a -dimensional Euclidean space and
is the Lebesgue measure, a typical example of is the stable-like
process that will be also identified with the solution of a martingale problem
up to an -polar set of starting points. Approachability to the boundary
in finite time of its censored process on a bounded open
subset will be examined in terms of the polarity of for the
symmetric stable processes with indices that bound the variable exponent
.Comment: Published in at http://dx.doi.org/10.1214/10-AOP633 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Period Analysis using the Least Absolute Shrinkage and Selection Operator (Lasso)
We introduced least absolute shrinkage and selection operator (lasso) in
obtaining periodic signals in unevenly spaced time-series data. A very simple
formulation with a combination of a large set of sine and cosine functions has
been shown to yield a very robust estimate, and the peaks in the resultant
power spectra were very sharp. We studied the response of lasso to low
signal-to-noise data, asymmetric signals and very closely separated multiple
signals. When the length of the observation is sufficiently long, all of them
were not serious obstacles to lasso. We analyzed the 100-year visual
observations of delta Cep, and obtained a very accurate period of 5.366326(16)
d. The error in period estimation was several times smaller than in Phase
Dispersion Minimization. We also modeled the historical data of R Sct, and
obtained a reasonable fit to the data. The model, however, lost its predictive
ability after the end of the interval used for modeling, which is probably a
result of chaotic nature of the pulsations of this star. We also provide a
sample R code for making this analysis.Comment: 9 pages, 13 figures, accepted for publication in PAS
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