62 research outputs found
The effects of seasonal and latitudinal earth infrared radiance variations on ERBS attitude control
Analysis performed in the Flight Dynamics Facility by the Earth Radiation Budget Satellite (ERBS) Attitude Determination Support team illustrates the pitch attitude control motion and roll attitude errors induced by Earth infrared (IR) horizon radiance variations. IR scanner and inertial reference unit (IRU) pitch and roll flight data spanning 4 years of the ERBS mission are analyzed to illustrate the changes in the magnitude of the errors on time scales of the orbital period, months, and seasons. The analysis represents a unique opportunity to compare prelaunch estimates of radiance-induced attitude errors with flight measurements. As a consequence of this work the following additional information is obtained: an assessment of an average model of these errors and its standard deviation, a measurement to determine and verify previously proposed corrections to the current Earth IR radiance data base, and the possibility of a mean motion model derived from flight data in place of IRU data for ERBS fine attitude determination
THE INFLUENCE OF PASSIVE HIP EXTENSION ON RUNNING BIOMECHANICS
J. Stoewer1, E. Foch2, M.B Pohl1
1University of Puget Sound, Tacoma, WA; 2Central Washington University, Ellensburg, WA
Restricted passive range of motion (PROM) of hip extension has been anecdotally linked with low back pain. A potential mechanism for this may be that restrictions in passive hip extension prevents the hip from fully extending during running. As a consequence, the pelvis may undergo anterior tilt to allow the thigh to extend, thus, resulting in greater loading of the lumbar spine. However, it is currently unclear whether restricted passive hip extension has any bearing on hip and pelvis biomechanics during running. PURPOSE: To determine whether runners who differ in passive hip extension also demonstrate differences in hip extension and anterior pelvic tilt during running. METHODS: Participants included 9 healthy runners (3 males, 6 females) between the ages of 18-28. Passive hip extension was measured using the Thomas Test. Kinematic data during running was collected using a 3D motion capture system. Subjects were split into three groups (tight, normal, & flexible) using tertiles based on their Thomas Test score. Both hip extension and anterior pelvic tilt during running were then compared between groups using Cohenâs effect sizes (ES). RESULTS: The tight group exhibited the least amount of hip extension during running with a large effect size (ES=0.84) when compared to the flexible group (Table 1). The tight group exhibited the greatest amount of anterior pelvic tilt with large effect sizes when compared to both the normal (ES=0.80) and flexible (ES=2.34) groups. CONCLUSION: Limited passive hip extension was linked with alterations in running biomechanics including reduced hip extension and greater anterior pelvic tilt. These kinematic alterations could potentially place greater loading the lumbar spine
Biomechanics associated with tibial stress fracture in runners: A systematic review and meta-analysis
Background Tibial stress fracture (TSF) is an overuse running injury with a long recovery period. While many running studies refer to biomechanical risk factors for TSF, only a few have compared biomechanics in runners with TSF to controls. The aim of this systematic review and meta-analysis was to evaluate biomechanics in runners with TSF compared to controls. Methods Electronic databases PubMed, Web of Science, SPORTDiscus, Scopus, Cochrane, and CINAHL were searched. Risk of bias was assessed and meta-analysis conducted for variables reported in 3 or more studies. Results The search retrieved 359 unique records, but only the 14 that compared runners with TSF to controls were included in the review. Most studies were retrospective, 2 were prospective, and most had a small sample size (5â30 per group). Many variables were not significantly different between groups. Meta-analysis of peak impact, active, and braking ground reaction forces found no significant differences between groups. Individual studies found larger tibial peak anterior tensile stress, peak posterior compressive stress, peak axial acceleration, peak rearfoot eversion and hip adduction in the TSF group. Conclusion Meta-analysis indicated that discrete ground reaction force variables were not statistically significantly different in runners with TSF compared to controls. In individual included studies, many biomechanical variables were not statistically significantly different between groups. However, many were reported by only a single study, and sample sizes were small. We encourage additional studies with larger sample sizes of runners with TSF and controls and adequate statistical power to confirm or refute these findings
Boltzmann equation and hydrodynamic fluctuations
We apply the method of invariant manifolds to derive equations of generalized
hydrodynamics from the linearized Boltzmann equation and determine exact
transport coefficients, obeying Green-Kubo formulas. Numerical calculations are
performed in the special case of Maxwell molecules. We investigate, through the
comparison with experimental data and former approaches, the spectrum of
density fluctuations and address the regime of finite Knudsen numbers and
finite frequencies hydrodynamics.Comment: This is a more detailed version of a related paper: I.V. Karlin, M.
Colangeli, M. Kroger, PRL 100 (2008) 214503, arXiv:0801.2932. It contains
comparison between predictions and experiment, in particular. 11 pages, 6
figures, 2 table
Kinetic Theory of a Dilute Gas System under Steady Heat Conduction
The velocity distribution function of the steady-state Boltzmann equation for
hard-core molecules in the presence of a temperature gradient has been obtained
explicitly to second order in density and the temperature gradient. Some
thermodynamical quantities are calculated from the velocity distribution
function for hard-core molecules and compared with those for Maxwell molecules
and the steady-state Bhatnagar-Gross-Krook(BGK) equation. We have found
qualitative differences between hard-core molecules and Maxwell molecules in
the thermodynamical quantities, and also confirmed that the steady-state BGK
equation belongs to the same universality class as Maxwell molecules.Comment: 36 pages, 4 figures, 5 table
Nearly Perfect Fluidity: From Cold Atomic Gases to Hot Quark Gluon Plasmas
Shear viscosity is a measure of the amount of dissipation in a simple fluid.
In kinetic theory shear viscosity is related to the rate of momentum transport
by quasi-particles, and the uncertainty relation suggests that the ratio of
shear viscosity eta to entropy density s in units of hbar/k_B is bounded by a
constant. Here, hbar is Planck's constant and k_B is Boltzmann's constant. A
specific bound has been proposed on the basis of string theory where, for a
large class of theories, one can show that eta/s is greater or equal to hbar/(4
pi k_B). We will refer to a fluid that saturates the string theory bound as a
perfect fluid. In this review we summarize theoretical and experimental
information on the properties of the three main classes of quantum fluids that
are known to have values of eta/s that are smaller than hbar/k_B. These fluids
are strongly coupled Bose fluids, in particular liquid helium, strongly
correlated ultracold Fermi gases, and the quark gluon plasma. We discuss the
main theoretical approaches to transport properties of these fluids: kinetic
theory, numerical simulations based on linear response theory, and holographic
dualities. We also summarize the experimental situation, in particular with
regard to the observation of hydrodynamic behavior in ultracold Fermi gases and
the quark gluon plasma.Comment: 76 pages, 11 figures, review article, extensive revision
Influence of Previous Iliotibial Band Syndrome on Coordination Patterns and Coordination Variability in Female Runners
It is unknown if female runners who have sustained multiple iliotibial band syndrome occurrences run differently compared with runners who developed the injury once or controls. Therefore, the purpose of this study was to determine if differences existed in coordination patterns and coordination variability among female runners with recurrent iliotibial band syndrome, 1 iliotibial band syndrome occurrence, and controls. Overground running trials were collected for 36 female runners (nâ=â18 controls). Lower extremity coordination patterns were examined during running via a vector coding analysis. Coordination variability was calculated via the ellipse area method. Separate 1-way (group) KruskalâWallis tests were performed to compare each coordination pattern and coordination variability. Lower extremity coordination between frontal plane hipâtransverse plane hip, frontal plane pelvisâfrontal plane thigh, and frontal plane thighâtransverse plane shank was similar among groups and so may not be related to the risk of iliotibial band syndrome. Runners with 1 iliotibial band syndrome occurrence demonstrated greater coordination variability for 2 of 3 couplings compared with both controls and runners with recurrent iliotibial band syndrome. Thus, the number of previous injury episodes may influence coordination variability in female runners with a history of iliotibial band syndrome
Relationship between iliotibial band syndrome and hip neuromechanics in women runners
Background Atypical frontal plane hip kinematics are associated with iliotibial band syndrome in women runners. Gluteus medius is the primary muscle controlling the hip adduction angle during the loading response of stance. It is unclear if differences exist in gluteus medius activity magnitude and activity duration between runners with previous iliotibial band syndrome and controls. Furthermore, hip neuromechanics may change after a prolonged run. Research Question Do differences exist in the hip adduction angle and gluteus medius activity between women with previous iliotibial band syndrome and controls at the beginning and end of a 30-minute moderate paced treadmill run? Methods Thirty women participated (n = 15 controls). Lower extremity kinematics and gluteus medius activity were recorded at the start and end of a 30-minute treadmill run at participantsâ self-selected pace. Hip kinematics and gluteus medius activity were analyzed via separate two-way (group x time) mixed-model analysis of variance with time as the repeated measure. Results Hip neuromechanics were similar at the start and end of a 30-minute treadmill run in women with previous iliotibial band syndrome and controls. However, hip adduction excursion was less in women with previous iliotibial band syndrome compared to controls. Average gluteus medius activity magnitude and activity duration were not significantly different between groups. Significance These findings support the growing body of literature that smaller hip adduction motion is related to previous iliotibial band syndrome in women. Regardless of injury history, gluteus medius activity was similar between groups during the loading phase of stance
Structure and thermal behaviour of (SPY-5-12)-(2-aminoethanol-n)(2-aminoethanol-N,O)-bis(theophyllinato)copper(ii)dihydrate: a model for DNA-metal interactions
The title compound (1) is obtained by mixing aqueous 2-aminoethanol
solutions of theophylline and copper(II) salt. According to the single
crystal data the CU2+ ion is pentacoordinated and located in a slightly
distorted square pyramidal configuration. Four short Cu-N bonds to two
N(7) of the theophyllinate anions and to two nitrogen atoms of a
monodentate and a bidentate 2-aminoethanol ligands are almost in the
plane, while a longer Cu-O bond to oxygen of the bidentate
2-aminoethanol in the apex at distance 2.350(8) Angstrom A. When heated
in air or in an inert atmosphere, 1 undergoes a five-step decomposition
process studied by TG, DSC and evolved gas detection (EGD). The solid
intermediates of the thermal decomposition were detected by FTIR and
powder X-ray diffraction. First the water molecules then the mono-and
bidentate 2-aminoethanol ligands are released in the order of their
binding energy, showing a strong structure-stability correlation.
Afterwards chemical degradation of theophyllinato ligands occurs and is
accompanied in air by an intense oxidation process resulting in CuO
formation. (C) 1997 Elsevier Science Ltd
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