950 research outputs found
A static cost analysis for a higher-order language
We develop a static complexity analysis for a higher-order functional
language with structural list recursion. The complexity of an expression is a
pair consisting of a cost and a potential. The former is defined to be the size
of the expression's evaluation derivation in a standard big-step operational
semantics. The latter is a measure of the "future" cost of using the value of
that expression. A translation function tr maps target expressions to
complexities. Our main result is the following Soundness Theorem: If t is a
term in the target language, then the cost component of tr(t) is an upper bound
on the cost of evaluating t. The proof of the Soundness Theorem is formalized
in Coq, providing certified upper bounds on the cost of any expression in the
target language.Comment: Final versio
Liquid Crystal-Solid Interface Structure at the Antiferroelectric-Ferroelectric Phase Transition
Total Internal Reflection (TIR) is used to probe the molecular organization
at the surface of a tilted chiral smectic liquid crystal at temperatures in the
vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are
interpreted using an exact analytical solution of a real model for
ferroelectric order at the surface. In the mixture T3, ferroelectric surface
order is expelled with the bulk ferroelectric-antiferroelectric transition. The
conditions for ferroelectric order at the surface of an antiferroelectric bulk
are presented
SDW and FISDW transition of (TMTSF)ClO at high magnetic fields
The magnetic field dependence of the SDW transition in (TMTSF)ClO for
various anion cooling rates has been measured, with the field up to 27T
parallel to the lowest conductivity direction . For quenched
(TMTSF)ClO, the SDW transition temperature increases
from 4.5K in zero field up to 8.4K at 27T. A quadratic behavior is observed
below 18T, followed by a saturation behavior. These results are consistent with
the prediction of the mean-field theory. From these behaviors,
is estimated as =13.5K for the perfect nesting case. This
indicates that the SDW phase in quenched (TMTSF)ClO, where is less than 6K, is strongly suppressed by the two-dimensionality of
the system. In the intermediate cooled state in which the SDW phase does not
appear in zero field, the transition temperature for the field-induced SDW
shows a quadratic behavior above 12T and there is no saturation behavior even
at 27T, in contrast to the FISDW phase in the relaxed state. This behavior can
probably be attributed to the difference of the dimerized gap due to anion
ordering.Comment: 4pages,5figures(EPS), accepted for publication in PR
Spin-density-wave transition of (TMTSF)PF at high magnetic fields
The transverse magnetoresistance of the Bechgaard salt (TMTSF)PF has
been measured for various pressures, with the field up to 24 T parallel to the
lowest conductivity direction c. A quadratic behavior is observed in
the magnetic field dependence of the spin-density-wave (SDW) transition
temperature . With increasing pressure,
decreases and the coefficient of the quadratic term increases. These results
are consistent with the prediction of the mean-field theory based on the
nesting of the quasi one-dimensional Fermi surface. Using a mean field theory,
for the perfect nesting case is estimated as about 16 K. This
means that even at ambient pressure where is 12 K, the SDW
phase of (TMTSF)PF is substantially suppressed by the
two-dimensionality of the system.Comment: 11pages,6figures(EPS), accepted for publication in PR
Військовополонені Першої світової війни в Кременчуцькому гарнізоні
У статті досліджено правове становище та умови перебування військовополонених Першої світової війни на території Кременчуцького гарнізону в другій половині 1916 року. На основі архівних даних визначено кількісний склад полонених, його розподіл за національною, соціальною та конфесійною ознаками. Досліджено динаміку чисельності, побутові умови та використання праці військовополонених.В статье исследовано правовое положение и условия пребывания военнопленных Первой мировой войны на территории Кременчугского гарнизона во второй половине 1916 года. На основе архивных данных определен количественный состав пленных, его распределение по национальной, социальной и конфессиональной принадлежности. Исследована динамика численности, бытовые условия и использования труда военнопленных.In article the legal status and conditions of stay of prisoners of war of the First World War in territory of the Kremenchug garrison in second half of 1916 is investigated. On the basis of contemporary records the quantitative structure captured, its distribution on a national, social and confessional accessory is defi ned. Dynamics of number, conditions of life and uses of work of prisoners of war is investigated
Field-induced confinement in (TMTSF)2ClO4 under accurately aligned magnetic fields
We present transport measurements along the least conducting c direction of
the organic superconductor (TMTSF)2ClO4, performed under an accurately aligned
magnetic field in the low temperature regime. The experimental results reveal a
two-dimensional confinement of the carriers in the (a,b) planes which is
governed by the magnetic field component along the b' direction. This 2-D
confinement is accompanied by a metal-insulator transition for the c axis
resistivity. These data are supported by a quantum mechanical calculation of
the transverse transport taking into account in self consistent treatment the
effect of the field on the interplane Green function and on the intraplane
scattering time
Determination of the Fermi Velocity by Angle-dependent Periodic Orbit Resonance Measurements in the Organic Conductor alpha-(BEDT-TTF)2KHg(SCN)4
We report detailed angle-dependent studies of the microwave (f=50 to 90 GHz)
interlayer magneto-electrodynamics of a single crystal sample of the organic
charge-density-wave (CDW) conductor alpha-(BEDT-TTF)2KHg(SCN)4. Recently
developed instrumentation enables both magnetic field (B) sweeps for a fixed
sample orientation and, for the first time, angle sweeps at fixed f/B. We
observe series' of resonant absorptions which we attribute to periodic orbit
resonances (POR) - a phenomenon closely related to cyclotron resonance. The
angle dependence of the POR indicate that they are associated with the low
temperature quasi-one-dimensional (Q1D) Fermi surface (FS) of the title
compound; indeed, all of the resonance peaks collapse beautifully onto a single
set of f/B versus angle curves, generated using a semiclassical
magneto-transport theory for a single Q1D FS. We show that Q1D POR measurements
provide one of the most direct methods for determining the Fermi velocity,
without any detailed assumptions concerning the bandstructure; our analysis
yields an average value of v_F=6.5x10^4 m/s. Quantitative analysis of the POR
harmonic content indicates that the Q1D FS is strongly corrugated. This is
consistent with the assumption that the low-temperature FS derives from a
reconstruction of the high temperature quasi-two-dimensional FS, caused by the
CDW instability. Detailed analysis of the angle dependence of the POR yields
parameters associated with the CDW superstructure which are consistent with
published results. Finally, we address the issue as to whether or not the
interlayer electrodynamics are coherent in the title compound.Comment: 28 pages, including 6 figures. Submitted to PR
HST Observations of SGR 0526-66: New Constraints on Accretion and Magnetar Models
Soft Gamma-ray Repeaters (SGRs) are among the most enigmatic sources known
today. Exhibiting huge X- and Gamma-ray bursts and flares, as well as soft
quiescent X-ray emission, their energy source remains a mystery. Just as
mysterious are the Anomalous X-ray pulsars (AXPs), which share many of the same
characteristics. Thanks to recent Chandra observations, SGR 0526-66, the first
SGR, now appears to be a transition object bridging the two classes, and
therefore observations of it have implications for both SGRs and AXPs. The two
most popular current models for their persistent emission are accretion of a
fossil disk or decay of an enormous (~10^15 G) magnetic field in a magnetar. We
show how deep optical observations of SGR 0526-66, the only SGR with small
enough optical extinction for meaningful observations, show no evidence of an
optical counterpart. These observation place strong new constraints on both
accretion disk and magnetar models, and suggest that the spectral energy
distribution may peak in the hard-UV. Almost all accretion disks are excluded
by the optical data, and a magnetar would require a ~10^15-10^16 G field.Comment: 23 pages, 5 figures. Accepted by Ap
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