533 research outputs found
3PAC: Enforcing Access Policies for Web Services
Web services fail to deliver on the promise of ubiquitous deployment and seamless interoperability due to the lack of a uniform, standards-based approach to all aspects of security. In particular, the enforcement of access policies in a service oriented architecture is not addressed adequately. We present a novel approach to the distribution and enforcement of credentials-based access policies for Web services (3PAC) which scales well and can be implemented in existing deployments
Fixed-Node Monte Carlo Calculations for the 1d Kondo Lattice Model
The effectiveness of the recently developed Fixed-Node Quantum Monte Carlo
method for lattice fermions, developed by van Leeuwen and co-workers, is tested
by applying it to the 1D Kondo lattice, an example of a one-dimensional model
with a sign problem. The principles of this method and its implementation for
the Kondo Lattice Model are discussed in detail. We compare the fixed-node
upper bound for the ground state energy at half filling with
exact-diagonalization results from the literature, and determine several spin
correlation functions. Our `best estimates' for the ground state correlation
functions do not depend sensitively on the input trial wave function of the
fixed-node projection, and are reasonably close to the exact values. We also
calculate the spin gap of the model with the Fixed-Node Monte Carlo method. For
this it is necessary to use a many-Slater-determinant trial state. The
lowest-energy spin excitation is a running spin soliton with wave number pi, in
agreement with earlier calculations.Comment: 19 pages, revtex, contribution to Festschrift for Hans van Leeuwe
Mid-frequency aperture arrays: the future of radio astronomy
Aperture array (AA) technology is at the forefront of new developments and
discoveries in radio astronomy. Currently LOFAR is successfully demonstrating
the capabilities of dense and sparse AA's at low frequencies. For the
mid-frequencies, from 450 to 1450MHz, AA's still have to prove their scientific
value with respect to the existing dish technology. Their large field-of-view
and high flexibility puts them in an excellent position to do so. The Aperture
Array Verification Program is dedicated to demonstrate the feasibility of AA's
for science in general and SKA in particular. For the mid-frequency range this
has lead to the development of EMBRACE, which has already demonstrated the
enormous flexibility of AA systems by observing HI and a pulsar simultaneously.
It also serves as a testbed to demonstrate the technological reliability and
stability of AA's. The next step will put AA technology at a level where it can
be used for cutting-edge science. In this paper we discuss the developments to
move AA technology from an engineering activity to a fully science capable
instrument. We present current results from EMBRACE, ongoing tests of the
system, and plans for EMMA, the next step in mid-frequency AA technology.Comment: 8 pages, 7 figures, proceedings of Resolving The Sky - Radio
Astronomy: Past, Present and Future (RTS2012), April 17-20, 2012, Manchester,
U
Proof for an upper bound in fixed-node Monte Carlo for lattice fermions
We justify a recently proposed prescription for performing Green Function
Monte Carlo calculations on systems of lattice fermions, by which one is able
to avoid the sign problem. We generalize the prescription such that it can also
be used for problems with hopping terms of different signs. We prove that the
effective Hamiltonian, used in this method, leads to an upper bound for the
ground-state energy of the real Hamiltonian, and we illustrate the
effectiveness of the method on small systems.Comment: 14 pages in revtex v3.0, no figure
Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources
We have measured mid-infrared radiation from an orientation-unbiased sample
of 3CRR galaxies and quasars at redshifts 0.4 < z < 1.2 with the IRS and MIPS
instruments on the Spitzer Space Telescope. Powerful emission (L_24micron >
10^22.4 W/Hz/sr) was detected from all but one of the sources. We fit the
Spitzer data as well as other measurements from the literature with synchrotron
and dust components. The IRS data provide powerful constraints on the fits. At
15 microns, quasars are typically four times brighter than radio galaxies with
the same isotropic radio power. Based on our fits, half of this difference can
be attributed to the presence of non-thermal emission in the quasars but not
the radio galaxies. The other half is consistent with dust absorption in the
radio galaxies but not the quasars. Fitted optical depths are anti-correlated
with core dominance, from which we infer an equatorial distribution of dust
around the central engine. The median optical depth at 9.7 microns for objects
with core-dominance factor R > 10^-2 is approximately 0.4; for objects with R <
10^-2, it is 1.1. We have thus addressed a long-standing question in the
unification of FR II quasars and galaxies: quasars are more luminous in the
mid-infrared than galaxies because of a combination of Doppler-boosted
synchrotron emission in quasars and extinction in galaxies, both
orientation-dependent effects.Comment: 42 pages, 14 figures plus two landscape tables. Accepted for
publication in Ap
Hook plate fixation of acute displaced lateral clavicle fractures: mid-term results and a brief literature overview
<p>Abstract</p> <p>Background</p> <p>The clavicle hook plate achieves like most other operative techniques, a high percentage of union and a low percentage of complications however concerns about long term complications still exist, particularly the involvement of the acromioclavicular joint.</p> <p>Methods</p> <p>To evaluate the results and long term effects in use of this plate we performed a retrospective analysis with a mean follow up of 65 months (5.4 years) of 28 consecutive patients with acute displaced lateral clavicle fractures, treated with the clavicle hook plate.</p> <p>Results</p> <p>Short term functional results in all patients were good to excellent. All but one patient had a united fracture (96%). Nine patients (32%) developed impingement symptoms and in 7 patients (25%) subacromial osteolysis was found. These findings resolved after plate removal. Twenty-four patients were re-evaluated at a mean follow-up period of 5.4 years. The Constant-Murley score was 97 and the DASH score was 3.5. Four patients (14%) developed acromioclavicular joint arthrosis of which one was symptomatic. Three patients (11%) had extra articular ossifications of which one was symptomatic. There was no relation between the impingement symptoms, subacromial osteolysis and development of acromioclavicular joint arthrosis or extra articular ossifications.</p> <p>Conclusions</p> <p>The clavicle hook plate is a good primary treatment option for the acute displaced lateral clavicle fracture with few complications. At mid term the results are excellent and no long term complications can be addressed to the use of the plate.</p
Polarization and kinematics in Cygnus A
From optical spectropolarimetry of Cygnus A we conclude that the scattering
medium in the ionization cones in Cygnus A is moving outward at a speed of
170+-34 km/s, and that the required momentum can be supplied by the radiation
pressure of an average quasar. Such a process could produce a structure
resembling the observed ionization cones, which are thought to result from
shadowing by a circumnuclear dust torus. We detect a polarized red wing in the
[O III] emission lines arising from the central kiloparsec of Cygnus A. This
wing is consistent with line emission created close to the boundary of the
broad-line region.Comment: 5 pages, accepted for publication in MNRAS letter
Compliance of general practitioners with a guideline-based decision support system for ordering blood tests
BACKGROUND: Guidelines are viewed as a mechanism for disseminating a
rapidly increasing body of knowledge. We determined the compliance of
Dutch general practitioners with the recommendations for blood test
ordering as defined in the guidelines of the Dutch College of General
Practitioners. METHODS: We performed an audit of guideline compliance over
a 12-month period (March 1996 through February 1997). In an observational
study, a guideline-based decision support system for blood test ordering,
BloodLink, was integrated with the electronic patient records of 31
general practitioners practicing in 23 practices (16 solo). BloodLink
followed the guidelines of the Dutch College of General Practitioners. We
determined compliance by comparing the recommendations for test ordering
with the test(s) actually ordered. Compliance was expressed as the
percentage of order forms that followed the recommendations for test
ordering. RESULTS: Of 12 668 orders generated, 9091 (71%) used the
decision-support software rather than the paper order forms. Twelve
indications accounted for >80% of the 7346 order forms that selected a
testing indication in BloodLink. The most frequently used indication for
test ordering was "vague complaints" (2209 order forms; 30.1%). Of the
7346 order forms, 39% were compliant. The most frequent type of
noncompliance was the addition of tests. Six of the 12 tests most
frequently added to the order forms were supported by revisions of
guidelines that occurred within 3 years after the intervention period.
CONCLUSIONS: In general practice, noncompliance with guidelines is
predominantly caused by adding tests. We conclude that noncompliance with
a guideline seems to be partly caused by practitioners applying new
medical insight before it is incorporated in a revision of that guideline
Evaluation of semiautomated internal carotid artery stenosis quantification from 3-dimensional contrast-enhanced magnetic resonance angiograms
Rationale and Objectives: The performance of a semiautomatic technique for internal carotid artery (ICA) stenosis quantification of the internal carotid artery in contrast-enhanced magnetic resonance angiography was evaluated. Materials and Methods: The degree of stenosis of 52 ICAs was quantified by measuring the cross-sectional area along the center lumen line. This was performed both by 3 independent observers and the semiautomated method. The degree of stenosis was defined as the amount of cross-sectional lumen reduction. Results: Agreement between the method and observers was good (weighted-kappa, kappa(w) = 0.89). Reproducibility of measurements of the semiautomated technique was better (kappa(w) = 0.97) than that of the observers (kappa(w) = 0.76), and the evaluated technique was considerably less time-consuming. Conclusions: Because the user interaction is limited, this technique can be used to replace an expert observer in 3-dimensional stenosis quantification of the ICA at CE-MRA in clinical practice
SKA studies of nearby galaxies : star-formation, accretion processes and molecular gas across all environments
Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike LicenceThe SKA will be a transformational instrument in the study of our local Universe. In particular, by virtue of its high sensitivity (both to point sources and diffuse low surface brightness emission), angular resolution and the frequency ranges covered, the SKA will undertake a very wide range of astrophysical research in the field of nearby galaxies. By surveying vast numbers of nearby galaxies of all types with Jy sensitivity and sub-arcsecond angular resolutions at radio wavelengths, the SKA will provide the cornerstone of our understanding of star-formation and accretion activity in the local Universe. In this chapter we outline the key continuum and molecular line science areas where the SKA, both during phase-1 and when it becomes the full SKA, will have a significant scientific impact.Peer reviewedFinal Published versio
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