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We present an investigation into the influence of upstream shear on the viscous flow around a steady two-dimensional (2-D) symmetric airfoil at zero angle of attack, and the corresponding loads. In this computational study, we consider the NACA 0012 airfoil at a chord Reynolds number
in an approach flow with uniform positive shear with non-dimensional shear rate varying in the range 0.0–1.0. Results show that the lift force is negative, in the opposite direction to the prediction from Tsien’s inviscid theory for lift generation in the presence of positive shear. A hypothesis is presented to explain the observed sign of the lift force on the basis of the asymmetry in boundary layer development on the upper and lower surfaces of the airfoil, which creates an effective airfoil shape with negative camber. The resulting scaling of the viscous effect with shear rate and Reynolds number is provided. The location of the leading edge stagnation point moves increasingly farther back along the airfoil’s upper surface with increased shear rate, a behaviour consistent with a negatively cambered airfoil. Furthermore, the symmetry in the location of the boundary layer separation point on the airfoil’s upper and lower surfaces in uniform flow is broken under the imposed shear, and the wake vortical structures exhibit more asymmetry with increasing shear rate.
A star cannot have a solar-like corona if the available mechanical energy flux in the chromosphere is either too large or decreases outward more rapidly than the pressure. This result might be relevant for hybrid stars and cool giants.
Extending our previous studies of the dynamics of solar granulation (Nesis et al., 1997) we investigated the relationship between granular flow and the emergence of turbulence in the deep photosphere. Our main goal is to explore if such a relationship exists, and if so, to define it quantitatively. To this end we take advantage of the excellent signal approximation property of wavelets. The material for the present work is a series of spectrograms of high spatial resolution covering a time span of 12 min. They were taken at the center of the solar disk with the German Vacuum Tower Telescope in Izaña (Tenerife, Spain) in 1994, and include several absorption lines of different strengths; for more details see Nesis et al. (1997). The spectrograms were digitized and processed with wavelet techniques and regression analysis, in order to investigate the granular convective flow, the associated turbulence, and their mutual connection.
The retreat of Wurtenkees, a glacier of about 1 km2 in the European East Alps, is described by measurement of frontal change, interpretation of maps and a computed mass-balance series. Since 1850, Wurtenkees has been one of the most strongly retreating glaciers in this region. Mass balance has been measured since 1982. Measured values of the accumulation area ratio and the equilibrium-line altitude as well as a degree-days model are used for the description of the activity conditions of the glacier. Under present climatic conditions Wurtenkees would need a lowering of the mean air temperature during the summer season of 1–1.5° C to return to a balanced mass budget. With predicted global warming, the glacier is likely to disappear early in the 21st century.
Combining atmospheric Δ14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare Δ14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric Δ14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for Δ14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal.
The Sun’s activity has been evolving in the ascending phase of Solar Cycle 23 since 1996. Similarly, the research on solar activity is also in the ascending phase of a new active period. Numerous new results have been obtained from a large amount of space and ground observations covering a wide spectral range. In particular, observations with YOHKOH, SOHO, and TRACE have revealed a multitude of phenomena and processes in the solar atmosphere which provide us a new picture of the Sun.
This article is an executive summary of a report from the Centers for Disease Control and Prevention Ventilator-Associated Pneumonia Surveillance Definition Working Group, entitled “Developing a new, national approach to surveillance for ventilator-associated events” and published in Critical Care Medicine. The full report provides a comprehensive description of the Working Group process and outcome.
In September 2011, the Centers for Disease Control and Prevention (CDC) convened a Ventilator-Associated Pneumonia (VAP) Surveillance Definition Working Group to organize a formal process for leaders and experts of key stakeholder organizations to discuss the challenges of VAP surveillance definitions and to propose new approaches to VAP surveillance in adult patients (Table 1).
We previously documented that cigarette smoking is a risk factor for
subsequent alcohol and drug misuse and dependence in adolescent girls
with attention-deficit hyperactivity disorder (ADHD).
To revisit this hypothesis with a large longitudinal sample of both
genders followed up for 10 years into young adulthood.
We used data from two identically designed, longitudinal, case–control
family studies of boys and girls with and without ADHD ascertained from
psychiatric and paediatric sources. We studied 165 individuals with ADHD
and 374 controls followed up longitudinally and masked for 10 years. We
assessed ADHD, smoking and substance use status using structured
diagnostic interviews. We tested the association between cigarette
smoking and subsequent substance use outcomes using Cox proportional
hazard regression models.
Youth with ADHD who smoked cigarettes (n = 27) were
significantly more likely to subsequently develop drug misuse and
dependence compared with youth with ADHD who did not smoke
(n = 138, P<0.05).
These results confirm that cigarette smoking increases the risk for
subsequent drug and alcohol use disorders among individuals with ADHD.
These findings have important public health implications, and underscore
the already pressing need to prevent smoking in children with ADHD.
As part of the HST/ACS Coma Cluster Treasury Survey, we have undertaken a Keck/LRIS spectroscopic campaign to determine membership for faint dwarf galaxies. In the process, we discovered a population of Ultra Compact Dwarf galaxies (UCDs) in the core region of the Coma Cluster. At the distance of Coma, UCDs are expected to have angular sizes 0.01 < Re < 0.2 arcsec. With ACS imaging, we can resolve all but the smallest ones with careful fitting. Candidate UCDs were chosen based on magnitude, color, and degree of resolution. We spectroscopically confirm 27 objects as bona fide UCD members of the Coma Cluster, a 60% success rate for objects targeted with MR < −12. We attribute the high success rate in part to the high resolution of HST data and to an apparent large population of UCDs in Coma. We find that the UCDs tend to be strongly clustered around giant galaxies, at least in the core region of the cluster, and have a distribution and colors that are similar to globular clusters. These findings suggest that UCDs are not independent galaxies, but rather have a star cluster origin.
Cell-substratum adhesion is important in wound healing , embryogenic development , tissue architecture , and metastasis . Integrins constitute a major class of heterodimeric cell-surface glycoproteins involved in receptor-mediated adhesion to the extracellular matrix (ECM). Focal contacts are regions of the cell-substratum adhesion in which clusters of integrin receptors connect the cytoskeleton to extracellular matrix molecules such as fibronectin. Focal contacts strengthen cell-substrate adhesion, and are sites of biochemical activity. Since cell adhesion strength in part depends on the cell's ability to cluster receptors and cytoskeleton into focal contacts, the integrity of the focal contact, and hence a cell's adhesive strength, will depend both on integrin-cytoskeletal binding as well as integrin-ligand binding.
Using a centrifugation assay, we have quantified cell-substratum adhesion strength of mouse 3T3 cells transfected with the avian β1 integrin receptor (wild type), including various deletion mutants of its cytoplasmic domain, to surfaces containing varying concentrations of CSAT, a monoclonal antibody against the extracellular domain of the avian β1 subunit. For all the transfectants, adhesion strength decreases with decreasing CSAT concentration and increasing centrifugal strength. Different truncations of the cytoplasmic domain lead to different levels of adhesion. There is no simple correlation between the length of the cytoplasmic domain and the strength of adhesion.
Strength and fracture toughness of (100) oriented GaAs wafers are analyzed by fracture and indentation testing. Using finite element method (FEM) critical fracture stresses are calculated from the fracture loads of wafers tested under biaxial bending, whereas atomic force (AFM), scanning electron microscopy (SEM) and acoustic C-scan microscopy of deformation and cracking patterns around micro- and nano-indentations provided information on yielding, crack initiation and crack growth resistance. Through fracture mechanical evaluation of these results critical defect sizes are derived, which are tolerable without strength degradation. It is shown, that a fracture strength of at least 800MPa can be achieved by careful fabrication even of 6' wafers. This figure is much higher then the prescribed minimum strength level estimated to avoid premature failures during wafer handling and processing routes.
The initial stages of iron silicide growth on Si(111) were investigated using LEED, AES and STM experiments together with DFT calculations. In 1:1 stoichiometry, a cubic FeSi develops showing a (1×1) surface periodicity which is stable up to 300°C. The epitaxial strain energy stabilizes this bulk-unstable B2 (CsCl-type) phase for up to 250 Å thickness. The surface is Si terminated, the interface coordination of the so-called B8 type. After annealing at ≈ 600°C, a (2×2)-FeSi2 phase of higher Si content is observed which possesses cubic crystal structure. It is stable below 10 monolayers (ML) initial Fe coverage and grows in an island-like morphology. In the initial growth stage, however, a c(8×4) phase forms that completely covers the surface at 1.5 ML Fe content and appears as potential template for further growth of homogeneous films. The interpretation of atomically resolved STM images suggests that the film contains three Si and two Fe layers in B2 structure with vacancies on Fe positions. The vacancy arrangement seems to be responsible for the c(8×4) periodicity displayed by the Si adatoms in T4-position.
The role of substrate ion bombardment on the structural and H bonding properties of hydrogenated amorphous germanium (a-Ge:H) films was studied by infrared (ir) spectroscopy. A Kaufman type ion source was used to produce an Ar1 beam directed towards a Ge target for a- Ge:H ion beam sputtering deposition in a H2-containing vacuum chamber. A low energy (100 eV) H2++Ar+ beam obtained from an additional ion source was allowed to impinge directly on the substrate during film growth at various beam currents.
It was found that substrate bombardment by 100 eV ions favors the formation of voids, as deduced from the increasing contribution of the surface-like Ge-H stretching mode to the ir spectrum with increasing ion current. The void density was reduced below the ir detection limit by totally removing the ion beam on the substrate while keeping all other parameters fixed. For this condition, we observe no or very small surface-like contributions to the ir spectra, irrespective of substrate temperature (25-260°C) or growth rate used. A narrowing of the infrared Ge-H stretching mode peak is observed with increasing deposition temperature, indicating a concomitant tendency towards a more ordered structure.