1,205 research outputs found
Aerodynamic interference effects on tilting proprotor aircraft
The Green's function method was used to study tilting proprotor aircraft aerodynamics with particular application to the problem of the mutual interference of the wing-fuselage-tail-rotor wake configuration. While the formulation is valid for fully unsteady rotor aerodynamics, attention was directed to steady state aerodynamics, which was achieved by replacing the rotor with the actuator disk approximation. The use of an actuator disk analysis introduced a mathematical singularity into the formulation; this problem was studied and resolved. The pressure distribution, lift, and pitching moment were obtained for an XV-15 wing-fuselage-tail rotor configuration at various flight conditions. For the flight configurations explored, the effects of the rotor wake interference on the XV-15 tilt rotor aircraft yielded a reduction in the total lift and an increase in the nose-down pitching moment. This method provides an analytical capability that is simple to apply and can be used to investigate fuselage-tail rotor wake interference as well as to explore other rotor design problem areas
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Formation and transport of oxidized reactive nitrogen, ozone, and secondary organic aerosol in Tokyo
Measurements of the major reactive nitrogen species (NOy)i (NOx, peroxyacyl nitrates, HNO3, and particulate nitrate (NO3-), total reactive nitrogen (NOy), volatile organic compounds, OH and HO2, and organic aerosol were made near the urban center of Tokyo in different seasons of 2003-2004 to study the processes involving oxidized forms of reactive nitrogen and O3. Generally, NOx constituted the dominant fraction of NOy throughout the seasons. The NOx/NOy and HNO3/NOy ratios were lowest and highest, respectively, in summer, owing to the seasonally high OH concentration. The fraction of NOy that remained in the atmosphere after emission (RNOy) decreased with the decrease in the NOx/NOy ratio in summer and fall. It is likely that the median seasonal-diurnal variations Of Ox = O3 + NO2 were controlled by those of the background O3 levels, photochemical O3 formation, and vertical transport. Ox showed large increases during midday under stagnant conditions in mid-August 2004. Their in situ production rates calculated by a box model were too slow to explain the observed increases. The high Ox was likely due to the accumulation of Ox from previous days in the upper part of the boundary layer (BL) followed by transport down to near the surface by mixing after sunrise. Considering the tight correlation between Ox and secondary organic aerosol (SOA), it is likely that SOA also accumulated during the course of sea-land breeze circulation in the BL. Copyright 2008 by the American Geophysical Union
A magnetic internal mechanism for precise orientation of the camera in wireless endoluminal applications
Background and study aims: The use of magnetic
fields to control operative devices has been recently
described in endoluminal and transluminal
surgical applications. The exponential decrease of
magnetic field strength with distance has major
implications for precision of the remote control.
We aimed to assess the feasibility and functionality
of a novel wireless miniaturized mechanism,
based on magnetic forces, for precise orientation
of the camera.
Materials and methods: A remotely controllable
endoscopic capsule was developed as proof of
concept. Two intracapsular moveable permanent
magnets allow fine positioning, and an externally
applied magnetic field permits gross movement
and stabilization. Performance was assessed in ex
vivo and in vivo bench tests, using porcine upper
and lower gastrointestinal tracts.
Results: Fine control of capsule navigation and
rotation was achieved in all tests with an external
magnet held steadily about 15 cm from the capsule.
The camera could be rotated in steps of 1.8°.
This was confirmed by ex vivo tests; the mechanism
could adjust the capsule view at 40 different
locations in a gastrointestinal tract phantom
model. Full 360° viewing was possible in the gastric
cavity, while the maximal steering in the colonwas
45° in total. In vivo, a similar performance
was verified, where the mechanism was successfully
operated every 5 cm for 40 cm in the colon,
visually sweeping from side to side of the lumen;
360° views were obtained in the gastric fundus
and body, while antrally the luminal walls prevented
full rotation.
Conclusions: We report the feasibility and effectiveness
of the combined use of external static
magnetic fields and internal actuation to move
small permanent intracapsular magnets to
achieve wirelessly controllable and precise camera
steering. The concept is applicable to capsule
endoscopy as to other instrumentation for laparoscopic,
endoluminal, or transluminal procedures
Simultaneous Excitation of Spins and Pseudospins in the Bilayer Quantum Hall State
The tilting angular dependence of the energy gap was measured in the bilayer
quantum Hall state at the Landau level filling by changing the density
imbalance between the two layers. The observed gap behavior shows a continuous
transformation from the bilayer balanced density state to the monolayer state.
Even a sample with 33 K tunneling gap shows the same activation energy anomaly
reported by Murphy {\it et al.}. We discuss a possible relation between our
experimental results and the quantum Hall ferromagnet of spins and pseudospins.Comment: 4 pages, 4 figure
Value of staging squamous cell carcinoma of the anal margin and canal using the sentinel lymph node procedure: an update of the series and a review of the literature.
BACKGROUND: Inguinal metastases in patients affected by anal cancer are an independent prognostic factor for local failure and overall mortality. Since 2001, sentinel lymph node biopsy was applied in these patients. This original study reports an update of personal and previous published series, which were compared with Literature to value the incidence of inguinal metastases T-stage related and the overall incidence of false negative inguinal metastases at sentinel node. METHODS: In all, 63 patients diagnosed with anal cancer submitted to inguinal sentinel node. Furthermore a research in the Pub Med database was performed to find papers regarding this technique. RESULTS: In our series, detection rate was 98.4%. Inguinal metastases were evidentiated in 13 patients (20.6%). Our median follow-up was 35 months. In our series, no false negative nodes were observed. CONCLUSION: Sentinel node technique in the detection of inguinal metastases in patients affected by anal cancer should be considered as a standard of care. It is indicated for all T stages in order to select patients to be submitted to inguinal radiotherapy, avoiding related morbidity in negative ones. An overall 3.7% rate of false negative must be considered acceptable
The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a
multipurpose high-contrast imaging platform designed for the discovery and
detailed characterization of exoplanetary systems and serves as a testbed for
high-contrast imaging technologies for ELTs. It is a multi-band instrument
which makes use of light from 600 to 2500nm allowing for coronagraphic direct
exoplanet imaging of the inner 3 lambda/D from the stellar host. Wavefront
sensing and control are key to the operation of SCExAO. A partial correction of
low-order modes is provided by Subaru's facility adaptive optics system with
the final correction, including high-order modes, implemented downstream by a
combination of a visible pyramid wavefront sensor and a 2000-element deformable
mirror. The well corrected NIR (y-K bands) wavefronts can then be injected into
any of the available coronagraphs, including but not limited to the phase
induced amplitude apodization and the vector vortex coronagraphs, both of which
offer an inner working angle as low as 1 lambda/D. Non-common path, low-order
aberrations are sensed with a coronagraphic low-order wavefront sensor in the
infrared (IR). Low noise, high frame rate, NIR detectors allow for active
speckle nulling and coherent differential imaging, while the HAWAII 2RG
detector in the HiCIAO imager and/or the CHARIS integral field spectrograph
(from mid 2016) can take deeper exposures and/or perform angular, spectral and
polarimetric differential imaging. Science in the visible is provided by two
interferometric modules: VAMPIRES and FIRST, which enable sub-diffraction
limited imaging in the visible region with polarimetric and spectroscopic
capabilities respectively. We describe the instrument in detail and present
preliminary results both on-sky and in the laboratory.Comment: Accepted for publication, 20 pages, 10 figure
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Impacts of biomass burning in Southeast Asia on ozone and reactive nitrogen over the western Pacific in spring
Aircraft measurements of ozone (O3) and its precursors (reactive nitrogen, CO, nonmethane hydrocarbons) were made over the western Pacific during the Transport and Chemical Evolution Over the Pacific (TRACE-P) campaign, which was conducted during February-April 2001. Biomass burning activity was high over Southeast Asia (SEA) during this period (dry season), and convective activity over SEA frequently transported air from the boundary layer to the free troposphere, followed by eastward transport to the sampling region over the western Pacific south of 30°N. This data set allows for systematic investigations of the chemical and physical processes in the outflow from SEA. Methyl chloride (CH3Cl) and CO are chosen as primary and secondary tracers, respectively, to gauge the degree of the impact of emissions of trace species from biomass burning. Biomass burning is found to be a major source of reactive nitrogen (NO x, PAN, HNO3, and nitrate) and O3 in this region from correlations of these species with the tracers. Changes in the abundance of reactive nitrogen during upward transport are quantified from the altitude change of the slopes of the correlations of these species with CO. NOx decreased with altitude due to its oxidation to HNO3. On the other hand, PAN was conserved during transport from the lower to the middle troposphere, consistent with its low water solubility and chemical stability at low temperatures. Large losses of HNO3 and nitrate, which are highly water soluble, occurred in the free troposphere, most likely due to wet removal by precipitation. This has been shown to be the major pathway of NOy loss in the middle troposphere. Increases in the mixing ratios of O3 and its precursors due to biomass burning in SEA are estimated using the tracers. Enhancements of CO and total reactive nitrogen (NOy), which are directly emitted from biomass burning, were largest at 2-4 km. At this altitude the increases in NOy and O3 were 810 parts per trillion by volume (pptv) and 26 parts per billion by volume (ppbv) above their background values of 240 pptv and 31 ppbv, respectively. The slope of the O3-CO correlation in biomass burning plumes was similar to those observed in fire plumes in northern Australia, Africa, and Canada. The O3 production efficiency (OPE) derived from the O3-CO slope and NOx/CO emission ratio (ER) is shown to be positively correlated with the C2H4 /NOx ER, indicating that the C2H4/NO x ER is a critical parameter in determining the OPE. Comparison of the net O3 flux across the western Pacific region and total O3 production due to biomass burning in SEA suggests that about 70% of O3 produced was transported to the western Pacific. Copyright 2004 by the American Geophysical Union
Mild electrical stimulation with heat shock guides differentiation of embryonic stem cells into Pdx1-expressing cells within the definitive endoderm
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