50,525 research outputs found
Fractional vortices in the XY model with bonds
We define a new set of excitations in the XY model which we call ``fractional
vortices''. In the frustrated XY model containing bonds, we make the
ansatz that the ground state configurations can be characterized by pairs of
oppositely charged fractional vortices. For a chain of bonds, the ground
state energy and the phase configurations calculated on the basis of this
ansatz agree well with the results from direct numerical simulations. Finally,
we discuss the possible connection of these results to some recent experiments
by Kirtley {\it et al} [Phys. Rev. B {\bf 51}, R12057 (1995)] on high-T
superconductors where fractional flux trapping was observed along certain grain
boundaries.Comment: 13 pages, 14 figures included (.eps). No essential differences to
previous version, however more compact forma
Open market operations during 1996.
During 1996, the Trading Desk at the Federal Reserve Bank of New York managed reserve conditions with the objective of maintaining the federal funds rate around the level desired by the Federal Open Market Committee (FOMC). As was the case last year, the need for permanent reserve additions was relatively modest as demand for currency grew moderately and reserve requirements declined because of the continued spread of sweep programs at commercial banks. The decrease in operating balances of depository institutions at Reserve Banks had an impact on bank reserve management strategies and the Desk's choice of operations. The Desk paid close attention to the daily pattern of reserve demands and, by tailoring its operations accordingly, maintained funds trading close to the FOMC's desired rate.Open market operations ; Monetary policy ; Federal Open Market Committee ; Federal funds market (United States)
Comparison tests and experimental compliance calibration of the proposed standard round compact plane strain fracture toughness specimen
Standard round specimen fracture test results compared satisfactorily with results from standard rectangular compact specimens machined from the same material. The location of the loading pin holes was found to provide adequate strength in the load bearing region for plane strain fracture toughness testing. Excellent agreement was found between the stress intensity coefficient values obtained from compliance measurements and the analytic solution proposed for inclusion in the standard test method. Load displacement measurements were made using long armed displacement gages and hollow loading cylinders. Gage points registered on the loading hole surfaces through small holes in the walls of the loading cylinders
Load-displacement measurement and work determination in three-point bend tests of notched or precracked specimens
Suggestions for testing of notched or cracked three-point bend specimens are presented which: (1) correct displacement measurement errors resulting from misalignment between the load applicator and specimen; (2) account for coincidental strains not associated with the work of crack extension; (3) simplify record analysis and processing; and (4) extend displacement gage range without sacrifice of sensitivity or accuracy. These testing details are particularly applicable to procedures in which the crack extension force is determined from the work done on the specimen
C-shaped specimen plane strain fracture toughness tests
Test equipment, procedures, and data obtained in the evaluation of C-shaped specimens are presented. Observations reported on include: specimen preparation and dimensional measurement; modifications to the standard ASTM E 399 displacement gage, which permit punch mark gage point engagement; and a measurement device for determining the interior and exterior radii of ring segments. Load displacement ratios were determined experimentally which agreed with analytically determined coefficients for three different gage lengths on the inner surfaces of radially-cracked ring segments
Quantum Effects and Broken Symmetries in Frustrated Antiferromagnets
We investigate the interplay between frustration and zero-point quantum
fluctuations in the ground state of the triangular and Heisenberg
antiferromagnets, using finite-size spin-wave theory, exact diagonalization,
and quantum Monte Carlo methods. In the triangular Heisenberg antiferromagnet,
by performing a systematic size-scaling analysis, we have obtained strong
evidences for a gapless spectrum and a finite value of the thermodynamic order
parameter, thus confirming the existence of long-range N\'eel order.The good
agreement between the finite-size spin-wave results and the exact and quantum
Monte Carlo data also supports the reliability of the spin-wave expansion to
describe both the ground state and the low-energy spin excitations of the
triangular Heisenberg antiferromagnet. In the Heisenberg model, our
results indicate the opening of a finite gap in the thermodynamic excitation
spectrum at , marking the melting of the antiferromagnetic
N\'eel order and the onset of a non-magnetic ground state. In order to
characterize the nature of the latter quantum-disordered phase we have computed
the susceptibilities for the most important crystal symmetry breaking
operators. In the ordered phase the effectiveness of the spin-wave theory in
reproducing the low-energy excitation spectrum suggests that the uniform spin
susceptibility of the model is very close to the linear spin-wave prediction.Comment: Review article, 44 pages, 18 figures. See also PRL 87, 097201 (2001
Integration of Technology in Math and Science Education – A Model for Teaching Elementary and Middle School Pre-Service Teachers
This paper describes the development and implementation of a course, Integration of Technology in Math and Science Education, to introduce elementary and middle school pre-service teachers to real technology skills that they can use in their future classrooms. Activities allowed the students to learn technology skills while using the Internet to enrich their content skills and share information with their fellow students. The course was designed to allow students to master a variety of technology skills, and see how these skills can be used appropriately in their future classrooms, while also increasing their comfort level to use the technology and reduce their resistance and anxiety to use it later in their real-time classrooms. During the class hands-on activities, the students became fluent at using the Internet for enrichment and communication, and at developing strategies for using their new skills to present SOL-relevant lesson plans. Students enter this course with very little in the way of educational technology skills, but leave with a teaching toolbox filled with new skills
On the speed of pulled fronts with a cutoff
We study the effect of a small cutoff on the velocity of a pulled
front in one dimension by means of a variational principle. We obtain a lower
bound on the speed dependent on the cutoff, and for which the two leading order
terms correspond to the Brunet Derrida expression. To do so we cast a known
variational principle for the speed of propagation of fronts in new variables
which makes it more suitable for applications.Comment: 12 pages no figure
You get what you (don’t) pay for: The impact of volunteer labour and candidate spending at the 2010 British general election
The published version of this article is fully available from the publisher at the link below.Repeated evidence in Britain demonstrates the positive electoral payoffs from constituency campaigning. However, the impact of such campaigning varies depending upon the electoral context and the effectiveness of campaign management. Debate also exists in respect of the relative impact of traditional versus more modern campaign techniques, as well as between campaign techniques that incur cost and those that are carried out voluntarily. Such debates are of interest not only to academics and political parties, but also to regulators when considering whether to restrict campaign spending in the interests of electoral parity. This article uses candidate spending data and responses to an extensive survey of election agents at the British General Election of 2010 to assess the impact of both campaign expenditure and free, voluntary labour on electoral performance. It suggests that both have some independent impact, but that impact varies by party. The implications of these results are highly significant in both academic and regulatory terms—campaign expenditure can affect electoral outcomes but these effects are offset to some extent by voluntary efforts
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