13,481 research outputs found
Study of blade aspect ratio on a compressor front stage aerodynamic and mechanical design report
A single stage compressor was designed with the intent of demonstrating that, for a tip speed and hub-tip ratio typical of an advanced core compressor front stage, the use of low aspect ratio can permit high levels of blade loading to be achieved at an acceptable level of efficiency. The design pressure ratio is 1.8 at an adiabatic efficiency of 88.5 percent. Both rotor and stator have multiple-circular-arc airfoil sections. Variable IGV and stator vanes permit low speed matching adjustments. The design incorporates an inlet duct representative of an engine transition duct between fan and high pressure compressor
Admission Diagnosis of Cerebral Malaria in Adults in an Endemic Area of Tanzania:Implications and Clinical Description
Cerebralmalariais commonly diagnosed in adults in endemic areas in Africa, both in hospitals and in the community. This presents a paradox inconsistent with the epidemiological understanding that the development of immunity during childhood confers protection against severe disease in adult life. To establish the contribution of Plasmodium falciparum infection in adults admitted with neurological dysfunction in an endemic area, to assess the implications of an admission clinical diagnosis of ‘cerebral malaria’ on the treatment and clinical outcome, and to describe the clinical features of patients with malaria parasitaemia. Prospective observational study. We studied adult patients admitted with neurological dysfunction to Muhimbili National Hospital, Dar-es-Salaam, Tanzania from October 2000 to July 2001. A full blood count was done and serum creatinine, blood glucose and P. falciparum parasite load were measured. Of 199 patients (median age 34.5 years), 38% were diagnosed as ‘cerebral malaria’ on admission, but only 7.5% had detectable parasitaemia, giving a positive predictive value of 13.3%. Only 1% fulfilled the WHO criteria for cerebral malaria. The prevalence of parasitaemia (7.5%) was less than that observed in a group of asymptomatic controls (9.3%), but distribution of parasite densities was higher in the patients. Mortality was higher in patients with no parasitaemia (22.3%) than in those with parasitaemia (13%). Cerebral malaria was grossly overdiagnosed, resulting in unnecessary treatment and insufficient investigation of other possible diagnoses, which could lead to higher mortality. Extension of this misperception to the assessment of cause of death in community surveys may lead to an overestimation of the impact of malaria in adults.\u
Charge-transfer Cross Sections For Negative Ions On Atomic And Molecular Targets
Charge-transfer cross sections for H- on O, O2, and NO2; O- on H, O, H2, O2, and NO2; and C- on H and O have been measured over an energy range of 0.5 to 4 keV using a modulated crossed-beam apparatus. The experimental cross sections are compared with theories of resonant and non-resonant charge transfer based on a two-state approximation. For the reactions H-+O O-+H, the cross sections are found to be consistent with detailed balancing. The effect of electron detachment on charge-transfer cross sections is discussed. © 1969 The American Physical Society
Interstellar Carbon in Translucent Sightlines
We report interstellar C II column densities or upper limits determined from
weak absorption of the 2325.4029 A intersystem transition observed in six
translucent sightlines with STIS. The sightlines sample a wide range of
interstellar characteristics including total-to-selective extinction, R_{V} =
2.6 - 5.1; average hydrogen density along the sightline, = 3 - 14
cm^{-3}; and fraction of H in molecular form, 0 - 40%. Four of the sightlines,
those toward HD 37021, HD 37061, HD 147888 and HD 207198, have interstellar
gas-phase abundances that are consistent with the diffuse sightline ratio of
161 +/- 17 carbon atoms in the gas per million hydrogen nuclei. We note that
while it has a gas-phase carbon abundance that is consistent with the other
sightlines, a large fraction of the C II toward HD 37061 is in an excited
state. The sightline toward HD 152590 has a measured interstellar gas-phase
carbon abundance that is well above the diffuse sightline average; the column
density of C in this sightline may be overestimated due to noise structure in
the data. Toward HD 27778 we find a 3 sigma abundance upper limit of <108 C
atoms in the gas per million H, a substantially enhanced depletion of C as
compared to the diffuse sightline value. The interstellar characteristics
toward HD 27778 are otherwise not extreme among the sample except for an
unusually large abundance of CO molecules in the gas.Comment: Accepted for publication in the Astrophysical Journa
Precision determination of absolute neutron flux
A technique for establishing the total neutron rate of a highly-collimated
monochromatic cold neutron beam was demonstrated using a method of an
alpha-gamma counter. The method involves only the counting of measured rates
and is independent of neutron cross sections, decay chain branching ratios, and
neutron beam energy. For the measurement, a target of 10B-enriched boron
carbide totally absorbed the neutrons in a monochromatic beam, and the rate of
absorbed neutrons was determined by counting 478keV gamma rays from neutron
capture on 10B with calibrated high-purity germanium detectors. A second
measurement based on Bragg diffraction from a perfect silicon crystal was
performed to determine the mean de Broglie wavelength of the beam to a
precision of 0.024 %. With these measurements, the detection efficiency of a
neutron monitor based on neutron absorption on 6Li was determined to an overall
uncertainty of 0.058 %. We discuss the principle of the alpha-gamma method and
present details of how the measurement was performed including the systematic
effects. We also describe how this method may be used for applications in
neutron dosimetry and metrology, fundamental neutron physics, and neutron cross
section measurements.Comment: 44 page
FUSE Measurements of Far Ultraviolet Extinction. I. Galactic Sight Lines
We present extinction curves that include data down to far ultraviolet
wavelengths (FUV; 1050 - 1200 A) for nine Galactic sight lines. The FUV
extinction was measured using data from the Far Ultraviolet Spectroscopic
Explorer. The sight lines were chosen for their unusual extinction properties
in the infrared through the ultraviolet; that they probe a wide range of dust
environments is evidenced by the large spread in their measured ratios of
total-to-selective extinction, R_V = 2.43 - 3.81. We find that extrapolation of
the Fitzpatrick & Massa relationship from the ultraviolet appears to be a good
predictor of the FUV extinction behavior. We find that predictions of the FUV
extinction based upon the Cardelli, Clayton & Mathis (CCM) dependence on R_V
give mixed results. For the seven extinction curves well represented by CCM in
the infrared through ultraviolet, the FUV extinction is well predicted in three
sight lines, over-predicted in two sight lines, and under-predicted in 2 sight
lines. A Maximum Entropy Method analysis using a simple three component grain
model shows that seven of the nine sight lines in the study require a larger
fraction of grain materials to be in dust when FUV extinction is included in
the models. Most of the added grain material is in the form of small (radii <
200 A) grains.Comment: Accepted for publication in the Astrophysical Journal. 31 pages with
7 figure
Adaptive latitudinal variation in Common Blackbird Turdus merula nest characteristics
Nest construction is taxonomically widespread, yet our understanding of adaptive
intraspecific variation in nest design remains poor. Nest characteristics are
expected to vary adaptively in response to predictable variation in spring temperatures
over large spatial scales, yet such variation in nest design remains largely
overlooked, particularly amongst open-cup-nesting birds. Here, we systematically
examined the effects of latitudinal variation in spring temperatures and precipitation
on the morphology, volume, composition, and insulatory properties of
open-cup-nesting Common Blackbirds’ Turdus merula nests to test the hypothesis
that birds living in cooler environments at more northerly latitudes would build
better insulated nests than conspecifics living in warmer environments at more
southerly latitudes. As spring temperatures increased with decreasing latitude, the
external diameter of nests decreased. However, as nest wall thickness also
decreased, there was no variation in the diameter of the internal nest cups. Only
the mass of dry grasses within nests decreased with warmer temperatures at lower
latitudes. The insulatory properties of nests declined with warmer temperatures at
lower latitudes and nests containing greater amounts of dry grasses had higher insulatory
properties. The insulatory properties of nests decreased with warmer temperatures
at lower latitudes, via changes in morphology (wall thickness) and
composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude,
and none of the nest characteristics varied with spring precipitation. This suggests
that Common Blackbirds nesting at higher latitudes were building nests with
thicker walls in order to counteract the cooler temperatures. We have provided evidence
that the nest construction behavior of open-cup-nesting birds systematically
varies in response to large-scale spatial variation in spring temperatures
- …