21,647 research outputs found
Matter Wave Scattering from Ultracold Atoms in an Optical Lattice
We study matter wave scattering from an ultracold, many body atomic system
trapped in an optical lattice. We determine the angular cross section that a
matter wave probe sees and show that it is strongly affected by the many body
phase, superfluid or Mott insulator, of the target lattice. We determine these
cross sections analytically in the first Born approximation, and we examine the
variation at intermediate points in the phase transition by numerically
diagonalizing the Bose Hubbard Hamiltonian for a small lattice. We show that
matter wave scattering offers a convenient method for non-destructively probing
the quantum many body phase transition of atoms in an optical lattice.Comment: 4 pages, 2 figure
Modulated amplitude waves with nonzero phases in Bose-Einstein condensates
In this paper we give a frame for application of the averaging method to
Bose-Einstein condensates (BECs) and obtain an abstract result upon the
dynamics of BECs. Using aver- aging method, we determine the location where the
modulated amplitude waves (periodic or quasi-periodic) exist and we also study
the stability and instability of modulated amplitude waves (periodic or
quasi-periodic). Compared with the previous work, modulated amplitude waves
studied in this paper have nontrivial phases and this makes the problem become
more diffcult, since it involves some singularities.Comment: 17 pages, 2 figure
A Modelling Approach for Evaluating Agri-Environmental Policies at Sector Level
This paper presents a new approach to evaluate the cost effectiveness of agri-environmental policies at sector level. Policy uptake, cumulative environmental effects and public expenditure are identified as the main determinants of cost-effectiveness. On the basis of the sector-consistent, comparative-static, farm group model FARMIS, the determinants of policy cost-effectiveness at sector level are addressed. Firstly, intensity levels for the FARMIS activities are defined in order to model uptake of agri-environmental policies with FARMIS, secondly, life-cycle assessment data is attached to these intensity levels to determine environmental effects of the policies and thirdly, public expenditure is calculated under consideration of transaction costs. This paper concludes delineating the strengths and limitations of the approach
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Transient [3,3] Cope rearrangement of 3,3-dicyano-1,5-dienes: computational analysis and 2-step synthesis of arylcycloheptanes.
A simple and modular route to arylcycloheptene scaffolds is reported. The two-step route from Knoevenagel adducts and allylic electrophiles is made possible through the design of a Cope rearrangement that utilizes a "traceless" activating group to promote an otherwise thermodynamically unfavorable transformation. Experimentally, the [3,3] rearrangement occurrs transiently at room temperature with a computed barrier of 19.5 kcal mol-1, which ultimately allows for three-component bis-allylation. Ring-closing metathesis delivers the arylcycloheptane and removes the activating group. This report describes the design and optimization of the methodology, scope and mechanistic studies, and computational analysis
A preliminary study of a propeller powered by gas jets issuing from the blade tips
Computations are made of the performance of a propeller designed to develop 56 thrust horsepower at 100 miles per hour. The fuel consumption of the jet-operated propeller would be considerably higher than that of a reciprocating engine and a propeller. The lighter weight of the jet-operated propeller will result in a lighter weight of engine plus fuel for short-range flights. A theoretical analysis is made of a propeller powered by gas jets issuing from the blade tips. In the propeller considered, the air is drawn through the hub and passes through the hollow propeller blades to the tips, where propellers heat the air and expel it through the nozzles in the blade tips. The reaction of the tips rotates the propeller. For long range flights, the weight of the jet-operated propeller with its fuel would be greater than the weight of a reciprocating engine with its propeller and fuel
A Bulk-Parallel Priority Queue in External Memory with STXXL
We propose the design and an implementation of a bulk-parallel external
memory priority queue to take advantage of both shared-memory parallelism and
high external memory transfer speeds to parallel disks. To achieve higher
performance by decoupling item insertions and extractions, we offer two
parallelization interfaces: one using "bulk" sequences, the other by defining
"limit" items. In the design, we discuss how to parallelize insertions using
multiple heaps, and how to calculate a dynamic prediction sequence to prefetch
blocks and apply parallel multiway merge for extraction. Our experimental
results show that in the selected benchmarks the priority queue reaches 75% of
the full parallel I/O bandwidth of rotational disks and and 65% of SSDs, or the
speed of sorting in external memory when bounded by computation.Comment: extended version of SEA'15 conference pape
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