7,914 research outputs found
Amortised resource analysis with separation logic
Type-based amortised resource analysis following Hofmann and Jostāwhere resources are associated with individual elements of data structures and doled out to the programmer under a linear typing disciplineāhave been successful in providing concrete resource bounds for functional programs, with good support for inference. In this work we translate the idea of amortised resource analysis to imperative languages by embedding a logic of resources, based on Bunched Implications, within Separation Logic. The Separation Logic component allows us to assert the presence and shape of mutable data structures on the heap, while the resource component allows us to state the resources associated with each member of the structure. We present the logic on a small imperative language with procedures and mutable heap, based on Java bytecode. We have formalised the logic within the Coq proof assistant and extracted a certified verification condition generator. We demonstrate the logic on some examples, including proving termination of in-place list reversal on lists with cyclic tails
Landscape phage, phage display, stripped phage, biosensors, detection, affinity reagent, nanotechnology, Salmonella typhimurium, Bacillus anthracis
Filamentous phage, such as fd used in this study, are thread-shaped bacterial
viruses. Their outer coat is a tube formed by thousands equal copies of the
major coat protein pVIII. We constructed libraries of random peptides fused to
all pVIII domains and selected phages that act as probes specific for a panel
of test antigens and biological threat agents. Because the viral carrier is
infective, phage borne bio-selective probes can be cloned individually and
propagated indefinitely without needs of their chemical synthesis or
reconstructing. We demonstrated the feasibility of using landscape phages and
their stripped fusion proteins as new bioselective materials that combine
unique characteristics of affinity reagents and self assembling membrane
proteins. Biorecognition layers fabricated from phage-derived probes bind
biological agents and generate detectable signals. The performance of
phage-derived materials as biorecognition films was illustrated by detection of
streptavidin-coated beads, Bacillus anthracis spores and Salmonella typhimurium
cells. With further refinement, the phage-derived analytical platforms for
detecting and monitoring of numerous threat agents may be developed, since the
biodetector films may be obtained from landscape phages selected against any
bacteria, virus or toxin. As elements of field-use detectors, they are superior
to antibodies, since they are inexpensive, highly specific and strong binders,
resistant to high temperatures and environmental stresses.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Doppler cooling of gallium atoms: 2. Simulation in complex multilevel systems
This paper derives a general procedure for the numerical solution of the
Lindblad equations that govern the coherences arising from multicoloured light
interacting with a multilevel system. A systematic approach to finding the
conservative and dissipative terms is derived and applied to the laser cooling
of gallium. An improved numerical method is developed to solve the
time-dependent master equation and results are presented for transient cooling
processes. The method is significantly more robust, efficient and accurate than
the standard method and can be applied to a broad range of atomic and molecular
systems. Radiation pressure forces and the formation of dynamic dark-states are
studied in the gallium isotope 66Ga.Comment: 15 pages, 8 figure
Trapping effects on inflation
We develop a Lagrangian approach based on the influence functional method so
as to derive self-consistently the Langevin equation for the inflaton field in
the presence of trapping points along the inflaton trajectory. The Langevin
equation exhibits the backreaction and the fluctuation-dissipation relation of
the trapping. The fluctuation is induced by a multiplicative colored noise that
can be identified as the the particle number density fluctuations and the
dissipation is a new effect that may play a role in the trapping with a strong
coupling. In the weak coupling regime, we calculate the power spectrum of the
noise-driven inflaton fluctuations for a single trapping point and studied its
variation with the trapping location. We also consider a case with closely
spaced trapping points and find that the resulting power spectrum is blue.Comment: 13 pages, 2 figure
Tree growth and management in Ugandan agroforestry systems: effects of root pruning on tree growth and crop yield
Tree root pruning is a potential tool for managing below-ground competition when trees and crops are grown together in agroforestry systems. This study investigates its effects on growth and root distribution of Alnus acuminata (HB & K), Casuarina equisetifolia (L), Grevillea robusta (A. Cunn. ex R. Br), Maesopsis eminii (Engl.), and Markhamia lutea (Benth.) K. Schum. and on yield of adjacent crops in sub-humid Uganda. The trees were 3 years old at the commencement of the study, and most species were competing strongly with crops. Tree roots were pruned 41 months after planting by cutting and back-filling a trench to a depth of 0.3 m, at a distance of 0.3 m from the trees, on one side of the tree row. The trench was re-opened and roots re-cut at 50 and 62 months after planting. Effects on tree growth and root distribution were assessed over a 3 year period, and crop yield after the third root pruning at 62 months is reported here. Overall, root pruning had only a slight effect on tree growth: height growth was unaffected and diameter growth was reduced by only 4 %. A substantial amount of root re-growth was observed by 11 months after pruning. Tree species varied in the number and distribution of their roots, and Casuarina and Markhamia had considerably more roots per unit of trunk volume than the other tree species, especially in the surface soil layers. Casuarina and Maesopsis were the most competitive tree species with crops and Grevillea and Markhamia the least. Crop yield data provides strong evidence of the redistribution of root activity following root pruning, so that competition increased on the unpruned side of tree rows. Thus, one-sided root pruning will only be of use to farmers in a few circumstances.
Key words: Alnus acuminata, Casuarina equisetifolia, Grevillea robusta, Maesopsis eminii, Markhamia lutea, root distribution, root functio
Higher-order splitting algorithms for solving the nonlinear Schr\"odinger equation and their instabilities
Since the kinetic and the potential energy term of the real time nonlinear
Schr\"odinger equation can each be solved exactly, the entire equation can be
solved to any order via splitting algorithms. We verified the fourth-order
convergence of some well known algorithms by solving the Gross-Pitaevskii
equation numerically. All such splitting algorithms suffer from a latent
numerical instability even when the total energy is very well conserved. A
detail error analysis reveals that the noise, or elementary excitations of the
nonlinear Schr\"odinger, obeys the Bogoliubov spectrum and the instability is
due to the exponential growth of high wave number noises caused by the
splitting process. For a continuum wave function, this instability is
unavoidable no matter how small the time step. For a discrete wave function,
the instability can be avoided only for \dt k_{max}^2{<\atop\sim}2 \pi, where
.Comment: 10 pages, 8 figures, submitted to Phys. Rev.
High-Contrast Interference in a Thermal Cloud of Atoms
The coherence properties of a gas of bosonic atoms above the BEC transition
temperature were studied. Bragg diffraction was used to create two spatially
separated wave packets, which interfere during expansion. Given sufficient
expansion time, high fringe contrast could be observed in a cloud of arbitrary
temperature. Fringe visibility greater than 90% was observed, which decreased
with increasing temperature, in agreement with a simple model. When the sample
was "filtered" in momentum space using long, velocity-selective Bragg pulses,
the contrast was significantly enhanced in contrast to predictions
Quantum Statistical Calculations and Symplectic Corrector Algorithms
The quantum partition function at finite temperature requires computing the
trace of the imaginary time propagator. For numerical and Monte Carlo
calculations, the propagator is usually split into its kinetic and potential
parts. A higher order splitting will result in a higher order convergent
algorithm. At imaginary time, the kinetic energy propagator is usually the
diffusion Greens function. Since diffusion cannot be simulated backward in
time, the splitting must maintain the positivity of all intermediate time
steps. However, since the trace is invariant under similarity transformations
of the propagator, one can use this freedom to "correct" the split propagator
to higher order. This use of similarity transforms classically give rises to
symplectic corrector algorithms. The split propagator is the symplectic kernel
and the similarity transformation is the corrector. This work proves a
generalization of the Sheng-Suzuki theorem: no positive time step propagators
with only kinetic and potential operators can be corrected beyond second order.
Second order forward propagators can have fourth order traces only with the
inclusion of an additional commutator. We give detailed derivations of four
forward correctable second order propagators and their minimal correctors.Comment: 9 pages, no figure, corrected typos, mostly missing right bracket
Forward Symplectic Integrators and the Long Time Phase Error in Periodic Motions
We show that when time-reversible symplectic algorithms are used to solve
periodic motions, the energy error after one period is generally two orders
higher than that of the algorithm. By use of correctable algorithms, we show
that the phase error can also be eliminated two orders higher than that of the
integrator. The use of fourth order forward time step integrators can result in
sixth order accuracy for the phase error and eighth accuracy in the periodic
energy. We study the 1-D harmonic oscillator and the 2-D Kepler problem in
great details, and compare the effectiveness of some recent fourth order
algorithms.Comment: Submitted to Phys. Rev. E, 29 Page
On the construction of high-order force gradient algorithms for integration of motion in classical and quantum systems
A consequent approach is proposed to construct symplectic force-gradient
algorithms of arbitrarily high orders in the time step for precise integration
of motion in classical and quantum mechanics simulations. Within this approach
the basic algorithms are first derived up to the eighth order by direct
decompositions of exponential propagators and further collected using an
advanced composition scheme to obtain the algorithms of higher orders. Contrary
to the scheme by Chin and Kidwell [Phys. Rev. E 62, 8746 (2000)], where
high-order algorithms are introduced by standard iterations of a force-gradient
integrator of order four, the present method allows to reduce the total number
of expensive force and its gradient evaluations to a minimum. At the same time,
the precision of the integration increases significantly, especially with
increasing the order of the generated schemes. The algorithms are tested in
molecular dynamics and celestial mechanics simulations. It is shown, in
particular, that the efficiency of the new fourth-order-based algorithms is
better approximately in factors 5 to 1000 for orders 4 to 12, respectively. The
results corresponding to sixth- and eighth-order-based composition schemes are
also presented up to the sixteenth order. For orders 14 and 16, such highly
precise schemes, at considerably smaller computational costs, allow to reduce
unphysical deviations in the total energy up in 100 000 times with respect to
those of the standard fourth-order-based iteration approach.Comment: 23 pages, 2 figures; submitted to Phys. Rev.
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