1,298 research outputs found
Lattice-point enumerators of ellipsoids
Minkowski's second theorem on successive minima asserts that the volume of a
0-symmetric convex body K over the covolume of a lattice \Lambda can be bounded
above by a quantity involving all the successive minima of K with respect to
\Lambda. We will prove here that the number of lattice points inside K can also
accept an upper bound of roughly the same size, in the special case where K is
an ellipsoid. Whether this is also true for all K unconditionally is an open
problem, but there is reasonable hope that the inductive approach used for
ellipsoids could be extended to all cases.Comment: 9 page
Three-dimensional scapular morphology is associated with rotator cuff tears and alters the abduction moment arm of the supraspinatus.
BACKGROUND: Numerous studies have reported an association between rotator cuff injury and two-dimensional measures of scapular morphology. However, the mechanical underpinnings explaining how these shape features affect glenohumeral joint function and lead to injury are poorly understood. We hypothesized that three-dimensional features of scapular morphology differentiate asymptomatic shoulders from those with rotator cuff tears, and that these features would alter the mechanical advantage of the supraspinatus.
METHODS: Twenty-four individuals with supraspinatus tears and twenty-seven age-matched controls were recruited. A statistical shape analysis identified scapular features distinguishing symptomatic patients from asymptomatic controls. We examined the effect of injury-associated morphology on mechanics by developing a morphable model driven by six degree-of-freedom biplanar videoradiography data. We used the model to simulate abduction for a range of shapes and computed the supraspinatus moment arm.
FINDINGS: Rotator cuff injury was associated with a cranial orientation of the glenoid and scapular spine (P = .011, d = 0.75) and/or decreased subacromial space (P = .001, d = 0.94). The shape analysis also identified previously undocumented features associated with superior inclination and subacromial narrowing. In our computational model, warping the scapula from a cranial to a lateral orientation increased the supraspinatus moment arm at 20° of abduction and decreased the moment arm at 160° of abduction.
INTERPRETATIONS: Three-dimensional analysis of scapular morphology indicates a stronger relationship between morphology and cuff tears than two-dimensional measures. Insight into how morphological features affect rotator cuff mechanics may improve patient-specific strategies for prevention and treatment of cuff tears
Audio vs. Video: Does Viewing Support Learning? A Comparision of an Audio-Visual with an Auditory Virtual Lecture
HĂ€ufig wird behauptet, dass audiovisuelle Informationen gegenĂŒber auditiven lernwirksamer sind. Dies wird meist mit der kognitiv-anregenden Funktion begrĂŒndet, die der audiovisuellen Darstellung zugeschrieben wird. Bisherige empirische Arbeiten konnten das auch tendenziell bestĂ€tigen; allerdings beziehen sich diese Befunde ĂŒberwiegend auf das video- oder fernsehgestĂŒtzte Lernen, bei dem den Lernenden keine zusĂ€tzlichen textbasierten Informationen zur VerfĂŒgung stehen. FĂŒr den Bereich der virtuellen Vorlesung wurde noch nicht untersucht, ob sich eine audiovisuelle PrĂ€sentation des Vortragenden gegenĂŒber einer rein auditiven PrĂ€sentation positiv auf den Lernerfolg auswirkt. In einer empirischen Studie mit 61 Versuchspersonen wurde daher Lernenden ein Ausschnitt aus einer Online-Vorlesung in zwei Variationen prĂ€sentiert. WĂ€hrend die eine Gruppe eine Lerneinheit bearbeitete, in der sie neben textbasierten Informationen eine Videosequenz (Aufnahme des Dozenten) prĂ€sentiert bekam, bearbeitete die zweite Gruppe die gleiche Lerneinheit; hier war jedoch nur die Stimme des Dozenten hörbar. In einem direkt anschlieĂenden Wissens- und spĂ€teren Behaltenstest zeigten sich keine signifikanten Leistungsunterschiede zwischen den beiden Gruppen. Jedoch berichtete die Mehrheit der Versuchspersonen, dass sie die Videovariante fĂŒr affektiv-unterstĂŒtzender hĂ€lt als die Tonvariante. (ZPID
Beta-decay branching ratios of 62Ga
Beta-decay branching ratios of 62Ga have been measured at the IGISOL facility
of the Accelerator Laboratory of the University of Jyvaskyla. 62Ga is one of
the heavier Tz = 0, 0+ -> 0+ beta-emitting nuclides used to determine the
vector coupling constant of the weak interaction and the Vud quark-mixing
matrix element. For part of the experimental studies presented here, the
JYFLTRAP facility has been employed to prepare isotopically pure beams of 62Ga.
The branching ratio obtained, BR= 99.893(24)%, for the super-allowed branch is
in agreement with previous measurements and allows to determine the ft value
and the universal Ft value for the super-allowed beta decay of 62Ga
Cavity Heating Experiments Supporting Shuttle Columbia Accident Investigation
The two-color thermographic phosphor method has been used to map the local heating augmentation of scaled idealized cavities at conditions simulating the windward surface of the Shuttle Orbiter Columbia during flight STS-107. Two experiments initiated in support of the Columbia Accident Investigation were conducted in the Langley 20-Inch Mach 6 Tunnel. Generally, the first test series evaluated open (length-to-depth less than 10) rectangular cavity geometries proposed as possible damage scenarios resulting from foam and ice impact during launch at several discrete locations on the vehicle windward surface, though some closed (length-to-depth greater than 13) geometries were briefly examined. The second test series was designed to parametrically evaluate heating augmentation in closed rectangular cavities. The tests were conducted under laminar cavity entry conditions over a range of local boundary layer edge-flow parameters typical of re-entry. Cavity design parameters were developed using laminar computational predictions, while the experimental boundary layer state conditions were inferred from the heating measurements. An analysis of the aeroheating caused by cavities allowed exclusion of non-breeching damage from the possible loss scenarios being considered during the investigation
The current state of hospital-based emergency medicine in Germany
Germany has a long tradition of having physicians, often anesthesiologists with additional training in emergency medicine, deliver prehospital emergency care. Hospital-based emergency medicine in Germany also differs significantly from the Anglo-American model, and until recently having separate emergency rooms for different departments was the norm. In the past decade, many hospitals have created âcentralized emergency departmentsâ [Zentrale Notaufnahme (ZNAs)]. There is ongoing debate about the training and certification of physicians working in the ZNAs and whether Germany will adopt a specialty board certification for emergency medicine
Impact of the assimilation of ozone from the Tropospheric Emission Spectrometer on surface ozone across North America
We examine the impact of assimilating ozone observations from the Tropospheric Emission Spectrometer (TES) on North American surface ozone abundances in the GEOS-Chem model in August 2006. The assimilation reduces the negative bias in the modeled free tropospheric ozone, which enhances the ozone flux into the boundary layer. Surface ozone abundances increased by as much as 9 ppb in western North America and by less than 2 ppb in the southeast, resulting in a total background source of ozone of 20-40 ppb. The enhanced ozone in the model reduced the model bias with respect to surface ozone observations in the western USA, but exacerbated it in the east. This increase in the bias in the boundary layer in the east, despite the agreement between the assimilation and ozonesonde measurements in the free troposphere, suggests errors in the ozone sources or sinks or in boundary layer mixing in the model. © 2009
Q-value of the superallowed beta decay of Ga-62
Masses of the radioactive isotopes 62Ga, 62Zn and 62Cu have been measured at
the JYFLTRAP facility with a relative precision of better than 18 ppb. A Q_EC
value of (9181.07 +- 0.54) keV for the superallowed decay of 62Ga is obtained
from the measured cyclotron frequency ratios of 62Ga-62Zn, 62Ga-62Ni and
62Zn-62Ni ions. The resulting Ft-value supports the validity of the conserved
vector current hypothesis (CVC). The mass excess values measured were (-51986.5
+-1.0) keV for 62Ga, (-61167.9 +- 0.9) keV for 62Zn and (-62787.2 +- 0.9) keV
for 62Cu.Comment: 12 pages, 3 figures, 2 tables, submitted to Phys. Lett. B. v2: added
acknowledgement
- âŠ