3,336 research outputs found
Full-Scale Investigation of Aerodynamic Characteristics of a Typical Single-Sotor Helicopter in Forward Flight
As part of the general helicopter research program being undertaken by the National Advisory Committee for Aeronautics to provide designers with fundamental rotor information, the forward-flight performance characteristics of a typical single-rotor helicopter, which is equipped with main and tail rotors, have been investigated in the Langley full-scale tunnel. The test conditions included operation of tip-speed ratios from 0.10 to 0.27 and at thrust coefficients from 0.0030 to 0.0060. Results obtained with production rotor were compared with those for an alternate set of blades having closer rib spacing and a smoother and more accurately contoured surface in order to evaluate the performance gains that are available by the use of rotor blades having an improved surface condition. The wind tunnel results are shown to be in fair agreement with the results of both flight tests and theoretical predictions
Static-Thrust Tests of Six Rotor-Blade Designs on a Helicopter in the Langley Full-Scale Tunnel
No abstract availabl
X-ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her
(Abridged) We report on ASCA and BeppoSAX observations of the X-ray source 4U
1700+24 and on (quasi-)simultaneous spectroscopy of its optical counterpart,
V934 Her, from the Loiano 1.5-meter telescope. Archival ROSAT and RXTE data as
well as the RXTE ASM light curve of 4U 1700+24 are also analyzed along with a
1985 EXOSAT pointing. The optical spectra are typical of a M2 III star; a
revised distance to the object of ~400 pc is inferred. While these spectra do
not show either any change between the two epochs or any peculiar feature, the
X-ray spectra reveal a complex and long-term variable shape, with a clear soft
excess. The X-ray spectral properties of the source are best described by a
thermal Comptonization spectrum plus a soft energy(<1 keV) excess, which can be
modeled with a blackbody emission with kT_BB ~ 1 keV; the latter component is
not detected at the lowest source flux levels. The ratio between the two
components varies substantially with the source flux. The X-ray emission from
the object appears to become harder as its luminosity increases, and the RXTE
data acquired during an outburst occurred during Fall 1997 display a hard tail
detected up to 100 keV. Apart from erratic shot-noise variability on timescales
of tens to thousands of seconds, no significant pulsations or QPOs are found
from the timing analysis of the X-ray light curves. With the new distance
determination, the 2-10 keV X-ray luminosity range spanned in the considered
observations lies between ~2x10^32 and ~1x10^34 erg/s. All this allows us to
suggest a scenario consisting of a wide binary system in which a neutron star
accretes matter from the wind of an M giant.Comment: 14 pages, 5 figures, to be published on Astronomy & Astrophysics,
Main Journa
The extreme physical properties of the CoRoT-7b super-Earth
International audience► Here, we discuss the extreme physical properties possible for the first characterized rocky super-Earth, CoRoT-7b ( = 1.58 , = 5.7 ). ► We make the working hypothesis that the planet is rocky with no volatiles in its atmosphere, and derive the physical properties that result. ► The dayside is very hot (2500 K at the sub-stellar point) while the nightside is very cold (∼ 50 K). The sub-stellar point is as hot as the tungsten filament of an incandescent bulb, resulting in the melting and distillation of silicate rocks and the formation of a lava ocean. ► These possible features of CoRoT-7b should be common to many small and hot planets, including Kepler-10b. They define a new class of objects that we propose to name ''Lava-ocean planets''
The Relation Between the Surface Brightness and the Diameter for Galactic Supernova Remnants
In this work, we have constructed a relation between the surface brightness
() and diameter (D) of Galactic C- and S-type supernova remnants
(SNRs). In order to calibrate the -D dependence, we have carefully
examined some intrinsic (e.g. explosion energy) and extrinsic (e.g. density of
the ambient medium) properties of the remnants and, taking into account also
the distance values given in the literature, we have adopted distances for some
of the SNRs which have relatively more reliable distance values. These
calibrator SNRs are all C- and S-type SNRs, i.e. F-type SNRs (and S-type SNR
Cas A which has an exceptionally high surface brightness) are excluded. The
Sigma-D relation has 2 slopes with a turning point at D=36.5 pc: (at 1
GHz)=8.4 D
WmHzster (for
WmHzster and D36.5 pc) and (at 1
GHz)=2.7 10 D
WmHzster (for
WmHzster and D36.5 pc). We discussed the theoretical
basis for the -D dependence and particularly the reasons for the change
in slope of the relation were stated. Added to this, we have shown the
dependence between the radio luminosity and the diameter which seems to have a
slope close to zero up to about D=36.5 pc. We have also adopted distance and
diameter values for all of the observed Galactic SNRs by examining all the
available distance values presented in the literature together with the
distances found from our -D relation.Comment: 45 pages, 2 figures, accepted for publication in Astronomical and
Astrophysical Transaction
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HCV induces transforming growth factor β1 through activation of endoplasmic reticulum stress and the unfolded protein response
HCV replication disrupts normal endoplasmic reticulum (ER) function and activates a signaling network called the unfolded protein response (UPR). UPR is directed by three ER transmembrane proteins including ATF6, IRE1, and PERK. HCV increases TGF-β1 and oxidative stress, which play important roles in liver fibrogenesis. HCV has been shown to induce TGF-β1 through the generation of reactive oxygen species (ROS) and p38 MAPK, JNK, ERK1/2, and NFκB-dependent pathways. However, the relationship between HCV-induced ER stress and UPR activation with TGF-β1 production has not been fully characterized. In this study, we found that ROS and JNK inhibitors block HCV up-regulation of ER stress and UPR activation. ROS, JNK and IRE1 inhibitors blocked HCV-activated NFκB and TGF-β1 expression. ROS, ER stress, NFκB, and TGF-β1 signaling were blocked by JNK specific siRNA. Knockdown IRE1 inhibited JFH1-activated NFκB and TGF-β1 activity. Knockdown of JNK and IRE1 blunted JFH1 HCV up-regulation of NFκB and TGF-β1 activation. We conclude that HCV activates NFκB and TGF-β1 through ROS production and induction of JNK and the IRE1 pathway. HCV infection induces ER stress and the UPR in a JNK-dependent manner. ER stress and UPR activation partially contribute to HCV-induced NF-κB activation and enhancement of TGF-β1
A TALEN Genome-Editing System for Generating Human Stem Cell-Based Disease Models
SummaryTranscription activator-like effector nucleases (TALENs) are a new class of engineered nucleases that are easier to design to cleave at desired sites in a genome than previous types of nucleases. We report here the use of TALENs to rapidly and efficiently generate mutant alleles of 15 genes in cultured somatic cells or human pluripotent stem cells, the latter for which we differentiated both the targeted lines and isogenic control lines into various metabolic cell types. We demonstrate cell-autonomous phenotypes directly linked to disease—dyslipidemia, insulin resistance, hypoglycemia, lipodystrophy, motor-neuron death, and hepatitis C infection. We found little evidence of TALEN off-target effects, but each clonal line nevertheless harbors a significant number of unique mutations. Given the speed and ease with which we were able to derive and characterize these cell lines, we anticipate TALEN-mediated genome editing of human cells becoming a mainstay for the investigation of human biology and disease
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