Kinetics of the BrO + HO2 reaction over the temperature range T = 246-314 K.

The kinetics of the reaction between gas phase BrO and HO2 radicals, BrO + HO2 → HOBr + O2 (1), have been studied over the atmospherically relevant temperature range T = 246-314 K and at ambient pressure, p = 760 ± 20 Torr, using laser flash photolysis coupled with ultraviolet absorption spectroscopy. The reaction was initiated by the generation of bromine monoxide radicals following laser photolytic generation of Br atoms from Br2/Cl2 containing mixtures and their reaction with ozone. Subsequently, the addition of methanol vapour to the reaction mixture, in the presence of excess oxygen, afforded the efficient simultaneous post-photolysis formation of HO2 radicals using well-defined chemistry. The decay of BrO radicals, in the presence and absence of HO2, was interrogated to determine the rate coefficients for the BrO + BrO and the BrO + HO2 reactions. A detailed sensitivity analysis was performed to ensure that the BrO + HO2 reaction was unequivocally monitored. The rate coefficient for reaction (1) is described by the Arrhenius expression: where statistical errors are 1σ. The negative temperature dependence of this reaction is in general accord with those reported by previous studies of this reaction. However, the present work reports greater absolute values for k1 than those of several previous studies. An assessment of previous laboratory studies of k1 is presented. This work confirms that reaction (1) plays a significant role in HOBr formation throughout the atmosphere following both anthropogenic, biogenic and volcanic emissions of brominated species. Reaction (1) therefore contributes to an efficient ozone depleting process in the atmosphere, and further confirms the significance of interactions between two different families of reactive atmospheric trace species.

Generalized Hypermobility, Knee Hyperextension, and Outcomes After Anterior Cruciate Ligament Reconstruction: Prospective, Case-Control Study With Mean 6 Years Follow-up.

PURPOSE: To determine whether generalized hypermobility and contralateral knee hyperextension affect failure rates and patient-related outcomes after anterior cruciate ligament reconstruction (ACLR). METHODS: A total of 226 consecutive patients presenting with acute ACL tears were prospectively evaluated for generalized hypermobility by a modified Beighton criteria. Minimum 2-year follow-up was achieved for 183 knees (81%). Patients underwent ACLR with either bone-patellar-tendon (BPTB) autograft (n = 46), quadrupled hamstring (HT) autograft (n = 85), or allograft tissue (n = 52). KT-1000 measurements, International Knee Documentation Committee (IKDC), Cincinnati, and Lysholm scores were obtained. RESULTS: Forty-one of 183 consecutive patients were categorized as hypermobile. At mean 6 years' follow-up (range 2-12.5 years), IKDC (P = .003), Cincinnati (P = .001), and Lysholm scores (P < .001) were significantly better in the Non-Hypermobile group for patients with an intact graft. The failure rate was higher in the Hypermobile group (10 knees, 24.4% failure rate) compared with the Nonhypermobile group (11 knees, 7.7% failure rate) (P = .006). The overall ACL injury rate (ACL graft injury, excessive graft laxity, plus contralateral ACL tear) was higher in the Hypermobile group (34.1%) compared with the Nonhypermobile group (12.0%) (P = .002). Heel height >5 cm (P = .009) and fifth metacarpophalangeal (MCP) extension >90° (P = .006) were independently predictive of failure for the entire study population. CONCLUSIONS: Graft failure rates were higher and inferior subjective outcomes were observed after ACLR in patients with generalized hypermobility. Heel height and fifth MCP hyperextension were most predictive of ACL injury/reinjury and poorer outcome scores. Nearly one-third of hypermobile patients sustained a contralateral ACL tear, ipsilateral graft failure, or had excessive graft laxity. LEVEL OF EVIDENCE: Level III, case control study.

Radiographic Hip Anatomy Correlates With Range of Motion and Symptoms in National Hockey League Players.

BACKGROUND: Hip disorders in athletes have been increasingly recognized. PURPOSE: To characterize radiographic hip anatomy for National Hockey League (NHL) players and correlate it with hip range of motion and hip symptoms and/or surgery. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Fifty-nine professional hockey players (118 hips) with 1 NHL organization (mean age, 24.2 years; range, 18-36) prospectively underwent history and physician examination by 2 independent orthopaedic surgeons. Current or previous groin and/or hip pain or surgery was noted. Anteroposterior (AP) pelvis and bilateral Dunn lateral radiographs were obtained for all players with assessment of hip morphology by 2 blinded independent orthopaedic surgeons. RESULTS: Good to very good reliability of radiographic assessments was noted (intraclass correlation coefficients = 0.749-0.958). Sixty-four percent of athletes had a positive crossover sign, while 86% and 60% had a positive posterior wall sign and a prominent ischial spine sign, respectively. Twenty-one percent of hips demonstrated dysplastic acetabular features (lateral center edge angle <25°). Eighty-five percent and 89% of hips demonstrated cam-type morphology based on alpha angle (>50° Dunn lateral) and head-neck offset, respectively. Good to very good reliability was noted for ROM assessments (intraclass correlation coefficient >0.69). Mean hip flexion was 107.4º ± 6.7º, and mean hip internal rotation was 26.1º ± 6.6º. Thirty-one percent of hips had a history of hip-related pain and/or surgery. Higher AP, Dunn lateral, and maximal alpha angles correlated with decreased hip internal rotation ( P = .004). Greater AP alpha angle correlated with decreased hip extension/abduction ( P = .025), and greater Dunn lateral and maximal alpha angle correlated with decreased hip flexion/abduction ( P = .001). A positive posterior wall sign correlated with increased straight hip abduction, while other radiographic acetabular parameters were not predictive of range of motion. Only decreased hip external rotation and total arc of motion correlated with an increased risk for current or prior hip symptoms or surgery ( P < .001). CONCLUSION: Hip anatomy in NHL players is characterized by highly prevalent cam-type morphology (>85%) and acetabular retroversion (>60%). In addition, acetabular dysplasia (21%) was relatively common. Greater cam-type morphology correlated with decreased hip range of motion, and a positive crossover sign correlated with increased hip abduction. Decreased hip external rotation and total arc of motion were predictive of hip-related pain and/or surgery.

Kinetics of the ClO + CH3O2 reaction over the temperature range T = 250-298 K.

The kinetics of the potentially atmospherically important ClO + CH3O2 reaction (1) have been studied over the range T = 250-298 K at p = 760 Torr using laser flash photolysis radical generation, coupled with time resolved ultraviolet absorption spectroscopy, employing broad spectral monitoring using a charge coupled device detector array. ClO radicals were monitored unequivocally using this technique, and introduction of CH3O2 precursors ensured known initial methylperoxy radical concentrations. ClO temporal profiles were thereafter analysed to extract kinetic parameters for reaction (1). A detailed sensitivity analysis was also performed to examine any potential systematic variability in k1 as a function of kinetic or physical uncertainties. The kinetic data recorded in this work show good agreement with the most recent previous study of this reaction, reported by Leather et al. The current work reports an Arrhenius parameterisation for k1, given by: . This work therefore concurs with that of Leather et al. implying that the title reaction is potentially less significant in the atmosphere than inferred from preceding studies. However, reaction (1) is evidently a non-terminating radical reaction, whose effects upon atmospheric composition therefore need to be ascertained through atmospheric model studies.

Kinetics of the ClO + HO2 reaction over the temperature range T = 210-298 K.

The rate coefficient for the atmospherically important radical reaction: which leads to ozone depletion, has been studied over the temperature range T = 210-298 K and at ambient pressure p = 760 ± 20 Torr. The reaction was studied using laser flash photolysis radical generation coupled with broadband charge coupled device absorption spectroscopy employing a two-dimensional charge-coupled-device (CCD) detection system. ClO radicals were generated following the photolysis of Cl2 and Cl2O gas mixtures diluted in nitrogen and oxygen. ClO radicals were monitored using broadband fingerprinting of their characteristic vibronic (A(2)Π â† X(2)Π) spectral structure, representing a definitive monitoring of this radical. Addition of hydroperoxy radical precursors to the gas mixture (methanol and oxygen) subsequently led to a competition for photolytically generated Cl atoms and a simultaneous prompt formation of both ClO and HO2 radicals. Detailed analysis and modelling of the radical production routes provided a degree of constraint into numerical integration simulations which were then used to interrogate and fit to ClO temporal profiles to extract the rate coefficient k1. The ambient temperature (T = 298 K) rate coefficient reported is k1 = (8.5 ± 1.5) × 10(-12) cm(3) molecule(-1) s(-1). The rate coefficient, k1, is described by the Arrhenius expression:where errors are 1σ statistical only. This significant rate coefficient is greater than previously reported, with a stronger negative temperature dependence than previously observed. Consequently this suggests that the contribution of to ozone loss, in particular at mid-latitudes might be currently underestimated in models. This work reports atmospheric pressure kinetic parameters for this reaction which are greater than those reported from low pressure studies, perhaps supporting ClO and HO2 association as predicted by previous theoretical studies of this process and highlighting the need for further pressure dependent experimental studies of the title reaction, which has been demonstrated here to be effective as an ozone loss process over a wide temperature range.

Kinetic studies of the BrO + ClO cross-reaction over the range T = 246-314 K.

The kinetics of the atmospherically important gas phase radical reaction between BrO and ClO have been studied over the temperature range T = 246-314 K by means of laser flash photolysis coupled with UV absorption spectroscopy. Charge-coupled-device (CCD) detection allowed simultaneous monitoring of both free radicals and the OClO product using 'differential' spectroscopy, which minimised interference from underlying UV absorbing species. In this way, the total rate coefficient for BrO + ClO → products (1) was measured, along with that for the OClO producing channel of this process BrO + ClO → OClO + Br (1c). These reaction rate coefficients are described by the Arrhenius expressions: k1/cm(3) molecule(-1) s(-1) = (2.5 ± 2.2) × 10(-12) exp[(630 ± 240)/T] and k(1c)/cm(3) molecule(-1) s(-1) = (4.6 ± 3.0) × 10(-12) exp[(280 ± 180)/T], where errors are 2σ, statistical only. An extensive sensitivity analysis was performed to quantify the potential additional systematic uncertainties in this work arising from uncertainties in secondary chemistry, absorption cross-sections and precursor concentrations. This analysis identified the reactions of initial and secondarily generated bromine atoms (specifically Br + O3 and Br + Cl2O) as particularly important, along with the reversible combination of ClO with OClO forming Cl2O3. Potential uncertainty in this latter process was used to define the lowest temperature of the present study. Results from this work indicate larger absolute values for k1 and k(1c) than those reported in previous studies, but a weaker negative temperature dependence for k(1c) than previously observed, resulting in a branching ratio for with a positive temperature dependence, in disagreement with previous studies. is the principal source of OClO in the polar stratosphere and is commonly used in atmospheric models as an indicator of stratospheric bromine chemistry. Thus these measurements might lead to a reinterpretation of modelled stratospheric OClO, which has also been suggested by previous comparisons of observations with atmospheric model studies.

Development and validation of a musculoskeletal physical examination decision-making test for medical students.

OBJECTIVE: Despite a renewed emphasis among educators, musculoskeletal education is still lacking in medical school and residency training programs. We created a musculoskeletal multiple-choice physical examination decision-making test to assess competency and physical examination knowledge of our trainees. DESIGN: We developed a 20-question test in musculoskeletal physical examination decision-making test with content that most medical students and orthopedic residents should know. All questions were reviewed by ratings of US orthopedic chairmen. It was administered to postgraduate year 2 to 5 orthopedic residents and 2 groups of medical students: 1 group immediately after their 3-week musculoskeletal course and the other 1 year after the musculoskeletal course completion. We hypothesized that residents would score highest, medical students 1 year post-musculoskeletal training lowest, and students immediately post-musculoskeletal training midrange. We administered an established cognitive knowledge test to compare student knowledge base as we expected the scores to correlate. SETTING: Academic medical center in the Midwestern United States. PARTICIPANTS: Orthopedic residents, chairmen, and medical students. RESULTS: Fifty-four orthopedic chairmen (54 of 110 or 49%) responded to our survey, rating a mean overall question importance of 7.12 (0 = Not Important; 5 = Important; 10 = Very Important). Mean physical examination decision-making scores were 89% for residents, 77% for immediate post-musculoskeletal trained medical students, and 59% 1 year post-musculoskeletal trained medical students (F = 42.07, p<0.001). The physical examination decision-making test was found to be internally consistent (Kuder-Richardson Formula 20 = 0.69). The musculoskeletal cognitive knowledge test was 78% for immediate post-musculoskeletal trained students and 71% for the 1 year post-musculoskeletal trained students. The student physical examination and cognitive knowledge scores were correlated (r = 0.54, p<0.001), but were not significantly different for either class. CONCLUSIONS: The physical examination decision-making test was found to be internally consistent in exposing the deficiencies of musculoskeletal education skills of our medical students and differentiated between ability levels in musculoskeletal physical examination decision-making (residents vs recently instructed musculoskeletal students vs 1 year post-musculoskeletal instruction).

Kinetic studies on the temperature dependence of the BrO + BrO reaction using laser flash photolysis.

The BrO self-reaction, BrO + BrO → products (1), has been studied using laser flash photolysis coupled with UV absorption spectroscopy over the temperature range T = 266.5-321.6 K, under atmospheric pressure. BrO radicals were generated via laser photolysis of Br(2) in the presence of excess ozone. Both BrO and O(3) were monitored via UV absorption spectroscopy using charge-coupled device (CCD) detection. Simultaneous fitting to both temporal concentration traces allowed determination of the rate constant of the two channels of , BrO + BrO → 2Br + O(2) (1a); BrO + BrO → Br(2) + O(2) (1b), hence the calculation of the overall rate of and the branching ratio, α: k(1a)/cm(3) molecule(-1) s(-1) = (1.92 ± 1.54) × 10(-12) exp[(126 ± 214)/T], k(1b)/cm(3) molecule(-1) s(-1) = (3.4 ± 0.8) × 10(-13) exp[(181 ± 70)/T], k(1)/cm(3) molecule(-1) s(-1) = (2.3 ± 1.5) × 10(-12) exp(134 ± 185 /T) and α = k(1a)/k(1) = (0.84 ± 0.09) exp[(-7 ± 32)/T]. Errors are 1σ, statistical only. Results from this work show a weaker temperature dependence of the branching ratio for channel (1a) than that found in previous work, leading to values of α at temperatures typical of the Polar Boundary Layer higher than those reported by previous studies. This implies a shift of the partitioning between the two channels of the BrO self-reaction towards the bromine atom and hence directly ozone-depleting channel (1a).

Kinetic and thermochemical studies of the ClO + ClO + M <=> Cl(2)O(2) + M reaction.

Recent work by von Hobe et al. [Atmos. Chem. Phys., 2007, 7, 3055] has highlighted significant inconsistencies between laboratory results, theoretical calculations and field observations concerning the ClO dimer ozone destruction cycle. This work investigates the temperature dependence of the equilibrium constant of one of the key reactions in this cycle, ClO + ClO + M <=> Cl(2)O(2) + M (1, -1), by means of laser flash photolysis and time-resolved UV absorption spectroscopy. ClO radicals were generated via laser flash photolysis of Cl(2)/Cl(2)O mixtures in synthetic air. Radicals were monitored via UV absorption spectroscopy: the use of a charge coupled device (CCD) detector allowed time resolution over a broad range of wavelengths giving unequivocal concentrations of radicals. The equilibrium constant K(eq) was determined as the ratio of the rate constants of the forward and reverse over the temperature range T = 256.55-312.65 K. Second Law and Third Law thermodynamic methods were employed to determine the standard enthalpy and entropy changes of , Δ(r)H° and Δ(r)S°, from the measured equilibrium constants. The values obtained from Second Law analysis were Δ(r)H° = - 80.7 ± 2.2 kJ mol(-1) and Δ(r)S° = -168.1 ± 7.8 J K(-1) mol(-1). Third Law analysis gave Δ(r)H° = -74.65 ± 0.4 kJ mol(-1) and Δ(r)S° = -148.0 ± 0.4 J K(-1) mol(-1). These values are in good agreement with previous work by Nickolaisen et al. [J. Phys. Chem., 1994, 98, 155] but greater in (negative) magnitude than current JPL-NASA recommendations [Sander et al., Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies, JPL Publication 06-2, NASA Jet Propulsion Laboratory, Pasadena, 2006 (interim update to this reference, 2009)]. The discrepancy between the Second and Third Law analyses also agrees with Nickolaisen et al., possibly indicating an aspect of the ClO recombination reaction not yet fully elucidated. The atmospheric implications of the results and their impact on the current understanding on polar ozone depletion are briefly discussed.

Kinetics of the gas phase HO2 self-reaction: effects of temperature, pressure, water and methanol vapours.

The kinetics of the gas phase HO2 self-reaction have been studied using flash photolysis of Cl2/CH3OH/O2/N2 mixtures coupled with time-resolved broadband UV absorption spectroscopy. The HO2 self-reaction rate coefficient (HO2 + HO2 --> H2O2 + O2 (R1)) has been determined as a function of temperature (236 < T < 309 K, at 760 Torr) and pressure (100 < p < 760 Torr, at 296 K). In addition, the effects of water vapour ((0-6.0) x 10(17) molecules cm(-3), 254 < T < 309 K at 760 Torr, 400 < p < 760 Torr at 296 K) and methanol vapour ((0.06-4.7) x 10(17) molecules cm(-3), 254 < T < 309 K, at 760 Torr) on the rate coefficient have been characterised. The observed rate coefficient, k1, was found to exhibit a negative temperature dependence with both pressure dependent and pressure independent components, in agreement with previous studies. Furthermore, the rate coefficient k1 was found to be enhanced in the presence of elevated H2O or CH3OH concentrations, as reported previously. This study reports the most extensive characterisation of the rate coefficient k1 as a function of T, p, [H2O] and [CH3OH]. The present results indicate that k1 is higher at low temperatures, and that enhancement of k1 by H2O is greater, than has been reported previously. The pressure dependence of k1 at ambient temperature is in good agreement with previous studies. The rate enhancement by CH3OH reported here is in good agreement with previous studies at ambient temperatures but is smaller at low temperatures than the most recent previous investigation suggests. The rate coefficient k1 is adequately parameterised by: k1(760 Torr) = {(1.8 +/- 0.8) x 10(-14) exp((1500 +/- 120)/T/K)} x {1 + (2.0 +/- 4.9) x 10(-25) [H2O] exp((4670 +/- 690)/T/K)} x (1 + (0.56 +/- 1.00) x 10(-21) [CH3OH] exp((2550 +/- 500)/T/K)} cm(-3) molecule(-1) s(-1), where [H2O] and [CH3OH] are in molecules cm(-3). Errors are 1 sigma, and statistical only. The atmospheric implications of these results are briefly discussed.

Kinetic studies of the ClO + ClO association reaction as a function of temperature and pressure.

The kinetics of the association reaction of ClO radicals: ClO + ClO + M --> Cl2O2+ M (1), have been investigated as a function of temperature T between 206.0-298.0 K and pressure p between 25-760 Torr using flash photolysis with time-resolved UV absorption spectroscopy. ClO radicals were generated following the photolysis of Br2/Cl2O mixtures in nitrogen diluent gas. Charge coupled device (CCD) detection of time resolved absorptions was used to monitor ClO radicals over a broad wavelength window covering the ClO (A 2Pi<-- X 2Pi) vibronic absorption bands. The high pass filtered ClO absorption cross sections were calibrated as a function of temperature between T = 206.0-320 K, and exhibit a negative temperature dependence. The ClO association kinetics were found to be more rapid than those reported in previous studies, with limiting low and high pressure rate coefficients, in nitrogen bath gas, k0 = (2.78 +/- 0.82) x 10(-32) x (T/300)(-3.99 +/- 0.94) molecule(-2) cm6 s(-1) and k(infinity) = (3.37 +/- 1.67) x 10(-12) x (T/300)(-1.49 +/- 1.81) molecule(-1) cm3 s(-1), respectively, (obtained with the broadening factor F(c) fixed at 0.6). Errors are 2sigma. The pressure dependent ClO association rate coefficients (falloff curves) exhibited some discrepancies at low pressures, with higher than expected rate coefficients on the basis of extrapolation from high pressures (p > 100 Torr). Reanalysis of data excluding kinetic data recorded below p = 100 Torr gave k0 = (2.79 +/- 0.85) x 10(-32) x (T/300)(-3.78 +/- 0.98) molecule(-2) cm6 s(-1) and k(infinity) = (3.44 +/- 1.83)x 10(-12) x (T/300)(-1.73 +/- 1.91) molecule(-1) cm3 s(-1). Potential sources of the low pressure discrepancies are discussed. The expression for k(0) in air bath gas is k0 = (2.62 +/- 0.80) x 10(-32) x (T/300)(-3.78 +/- 0.98) molecule(-2) cm6 s(-1). These results support upward revision of the ClO association rate coefficient recommended for use in stratospheric models, and the stratospheric implications of the results reported here are briefly discussed.