Reaction Times Altered by Anterior Cruciate Ligament Tear

The anterior cruciate ligament (ACL) tear is associated with declined performance upon return to sport, with high rates of reinjury. Despite ACL reconstruction, ACL tears induce neuroplasticity, increasing reliance on vision and preparation time in movement. This increased reliance on vision and time could lead to motor control strategy deficits under sport-specific tasks. PURPOSE: To determine if ACL injury results in slower muscle onsets in a reactive stepping task and if this is affected by preparation. METHODS: Reactive balance was assessed in ACL (N=6) and healthy control (CON; N=12) participants using a lean and release device to initiate a temporally unpredictable perturbation to prompt reactions by taking a right or left step dictated via leg blocks. 75% of the time, a predetermined right or left step was taken more often (i.e., frequent step; FS) to create unpredictability. The FS leg was counterbalanced midway through testing. Prior to a perturbation, participants viewed the leg blocks move (proactive; P), or were given 400ms of vision prior to release (reactive; R). Muscle onsets were measured by electromyography sensors. Two separate two-way ANOVAs with Bonferroni post-hoc analyses (p ≤ 0.05) assessed differences in muscle onset between each leg (dominant, nondominant), across groups (CON, ACL), and by preparation time (P, R). RESULTS: The FS reaction was consistently faster (p \u3c 0.05). The ANOVA results had main effects for legs (p \u3c 0.05), and groups (p \u3c 0.05). When the infrequent step was taken, significance was evident, but Bonferroni post-hoc analyses showed significance only in the CON group, where dominant legs (104 ± 55 ms) were faster than nondominant legs (171 ± 50 ms; p \u3c .0001), but not in the ACLR group between uninjured legs (78 ± 36 ms), and injured legs (113 ± 39 ms) (p = 0.2277). There was no significance when comparing preparation time between groups. CONCLUSION: Regardless of condition, the FS was consistently faster, but the ACLR group showed a decreased ability to slow muscle onset when asked to stop action in the FS to initiate the infrequent step. Yet, there is no significant difference between groups regardless of the preparation time given. Such results suggest an impaired motor control strategy after ACL injury, but muscle onset may not be a sensitive enough measure to definitively conclude

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating (FBG) reflectors and distributed feedback via Rayleigh scattering in a ∼22 km long optical fiber. Twenty two lasing lines with spacing of ∼100 GHz (close to ITU grid) in C-band are generated at Watts power level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution which is almost independent on power. The current set up showing the capability of generating Raman gain of about 100-nm wide giving the possibility of multiwavelength generation at different bands

A New Class of Exact Hairy Black Hole Solutions

We present a new class of black hole solutions with minimally coupled scalar field in the presence of a negative cosmological constant. We consider a one-parameter family of self-interaction potentials parametrized by a dimensionless parameter $g$. When $g=0$, we recover the conformally invariant solution of the Martinez-Troncoso-Zanelli (MTZ) black hole. A non-vanishing $g$ signals the departure from conformal invariance. All solutions are perturbatively stable for negative black hole mass and they may develop instabilities for positive mass. Thermodynamically, there is a critical temperature at vanishing black hole mass, where a higher-order phase transition occurs, as in the case of the MTZ black hole. Additionally, we obtain a branch of hairy solutions which undergo a first-order phase transition at a second critical temperature which depends on $g$ and it is higher than the MTZ critical temperature. As $g\to 0$, this second critical temperature diverges.Comment: 18 pages, 6 figures, minor changes, references added, published versio

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters