1,182 research outputs found
Intermittent search strategies
This review examines intermittent target search strategies, which combine
phases of slow motion, allowing the searcher to detect the target, and phases
of fast motion during which targets cannot be detected. We first show that
intermittent search strategies are actually widely observed at various scales.
At the macroscopic scale, this is for example the case of animals looking for
food ; at the microscopic scale, intermittent transport patterns are involved
in reaction pathway of DNA binding proteins as well as in intracellular
transport. Second, we introduce generic stochastic models, which show that
intermittent strategies are efficient strategies, which enable to minimize the
search time. This suggests that the intrinsic efficiency of intermittent search
strategies could justify their frequent observation in nature. Last, beyond
these modeling aspects, we propose that intermittent strategies could be used
also in a broader context to design and accelerate search processes.Comment: 72 pages, review articl
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Development and calibration of an on-line aerosol monitor for PHEBUS test FPT1
An on-line aerosol monitor (OLAM2) has been developed and tested for PHEBUS test FPT1. OLAM2 utilizes new detachable fiber optic cables and sapphire light pipes for light transmission between the OLAM and the electronics. This light transmission system was tested and found to provide better signal-to-noise performance than was achieved with the continuous fibers used for test FPT0. An additional advantage of the detachable fiber/light pipe system is ease of installation. Aerosol testing (OLAM calibration) was performed in order to verify adequate signal-to-noise performance of the new fiber optic system over the specified operating conditions and to check the quantitative light attenuation measurements against theoretical predictions. Results of the testing indicated that light extinction measurements obtained during Phebus tests could be used to estimate aerosol volume concentrations, if diamond window fouling can be avoided. OLAM2 was also subjected to a proof pressure test and a long-term thermal stability test. These tests verified the mechanical and thermal integrity of the OLAM within design specifications. Long-term output signal stability was also verified with the system maintained at design temperature and half-design pressure
High tibial osteotomy in Sweden, 1998â2007: A population-based study of the use and rate of revision to knee arthroplasty
To access publisher's full text version of this article. Please click on the hyperlink in Additional Links field.Most studies on high tibial osteotomies (HTOs) have been hospital-based and have included a limited number of patients. We evaluated the use and outcome-expressed as rate of revision to knee arthroplasty-of HTO performed in Sweden with 9 million inhabitants, 1998-2007. 3, 161 HTO procedures on patients 30 years or older (69% men) who were operated on for knee osteoarthritis in Sweden, 1998-2007, were identified through the inpatient and outpatient care registers of the Swedish National Board of Health and Welfare. Pertinent data were verified through surgical records. Conversions of HTO to knee arthroplasty before 2010 were identified through the Swedish Knee Arthroplasty Register (SKAR). The 10-year survival was determined using revision to an arthroplasty as the endpoint. The number of HTOs decreased by one third between 1998 and 2007, from 388 operations a year to 257 a year. Most of the HTOs were performed with open wedge osteotomy using external fixation. The cumulative revision rate at 10 years was 30% (95% CI: 28-32). The risk of revision increased with increasing age and was higher in women than in men (RR = 1.3, CI: 1.1-1.5). If being without an artificial joint implant is considered to be beneficial, then HTO is an excellent alternative to knee arthroplasty in younger and/or physically active patients suffering from knee osteoarthritis.Swedish Research Council
Swedish Rheumatism Association
King Gustaf V 80-year Birthday Fund
Faculty of Medicine, Lund University
Region Skan
Variable Scintillation Arcs of Millisecond Pulsars observed with the Large European Array for Pulsars
We present the first large sample of scintillation arcs in millisecond
pulsars, analysing 12 sources observed with the Large European Array for
Pulsars (LEAP), and the Effelsberg 100\,m telescope. We estimate the delays
from multipath propagation, measuring significant correlated changes in
scattering timescales over a 10-year timespan. Many sources show compact
concentrations of power in the secondary spectrum, which in PSRs J06130200
and J16003053 can be tracked between observations, and are consistent with
compact scattering at fixed angular positions. Other sources such as PSRs
J16431224 and J0621+1002 show diffuse, asymmetric arcs which are likely
related to phase-gradients across the scattering screen. PSR B1937+21 shows at
least three distinct screens which dominate at different times and evidence of
varying screen axes or multi-screen interactions. We model annual and orbital
arc curvature variations in PSR J06130200, providing a measurement of the
longitude of ascending node, resolving the sense of the orbital inclination,
where our best fit model is of a screen with variable axis of anisotropy over
time, corresponding to changes in the scattering of the source. Unmodeled
variations of the screen's axis of anisotropy are likely to be a limiting
factor in determining orbital parameters with scintillation, requiring careful
consideration of variable screen properties, or independent VLBI measurements.
Long-term scintillation studies such as this serve as a complementary tool to
pulsar timing, to measure a source of correlated noise for pulsar timing
arrays, solve pulsar orbits, and to understand the astrophysical origin of
scattering screens.Comment: Submitted to MNRAS, first revision. 18 pages, 16 figure
Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV
A search for new physics is presented based on an event signature of at least
three jets accompanied by large missing transverse momentum, using a data
sample corresponding to an integrated luminosity of 36 inverse picobarns
collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector
at the LHC. No excess of events is observed above the expected standard model
backgrounds, which are all estimated from the data. Exclusion limits are
presented for the constrained minimal supersymmetric extension of the standard
model. Cross section limits are also presented using simplified models with new
particles decaying to an undetected particle and one or two jets
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Search for anomalous t t-bar production in the highly-boosted all-hadronic final state
A search is presented for a massive particle, generically referred to as a
Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are
sufficiently massive to produce highly Lorentz-boosted top quarks, which yield
collimated decay products that are partially or fully merged into single jets.
The analysis uses new methods to analyze jet substructure, providing
suppression of the non-top multijet backgrounds. The analysis is based on a
data sample of proton-proton collisions at a center-of-mass energy of 7 TeV,
corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits
in the range of 1 pb are set on the product of the production cross section and
branching fraction for a topcolor Z' modeled for several widths, as well as for
a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any
enhancement in t t-bar production beyond expectations of the standard model for
t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version
includes a minor typo correction that will be submitted as an erratu
Combined search for the quarks of a sequential fourth generation
Results are presented from a search for a fourth generation of quarks
produced singly or in pairs in a data set corresponding to an integrated
luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in
2011. A novel strategy has been developed for a combined search for quarks of
the up and down type in decay channels with at least one isolated muon or
electron. Limits on the mass of the fourth-generation quarks and the relevant
Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a
simple extension of the standard model with a sequential fourth generation of
fermions. The existence of mass-degenerate fourth-generation quarks with masses
below 685 GeV is excluded at 95% confidence level for minimal off-diagonal
mixing between the third- and the fourth-generation quarks. With a mass
difference of 25 GeV between the quark masses, the obtained limit on the masses
of the fourth-generation quarks shifts by about +/- 20 GeV. These results
significantly reduce the allowed parameter space for a fourth generation of
fermions.Comment: Replaced with published version. Added journal reference and DO
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