20,048 research outputs found
Apparatus for making curved reflectors Patent
Forming mold for polishing and machining curved solar magnesium reflector with reinforcing rib
Process sequence produces strong, lightweight reflectors of excellent quality
Large compound curved surfaces for collecting and concentrating radiation are fabricated by the use of several common machining and forming processes. Lightweight sectors are assembled into large reflectors. With this concept of fabrication, integrally stiffened reflective sectors up to 25 square feet in area have been produced
Method and apparatus for making curved reflectors Patent
Fabrication of curved reflector segments for solar mirro
Export of honeybee prepromelittin in Escherichia coli depends on the membrane potential but does not depend on proteins secA and secY
Honeybee prepromelittin (70 amino acid residues), the precursor of an eukaryotic secretory protein, and a hybrid protein between prepromelittin and mouse dihydrofolate reductase (257 amino acid residues) were expressed in Escherichia coli and characterized with respect to their requirements for transport across the plasma membrane. Both precursor proteins are posttranslationally processed and exported into the periplasm, and they both depend on the membrane potential for this to occur. With respect to dependence on components of the export machinery, however, the two precursor proteins show striking differences: the small precursor protein prepromelittin does not require the function of proteins secA and secY; the large precursor protein prepromelittin-dihydrofolate reductase, on the other hand, depends on both components. The implications of these observations with respect to the mechanisms of protein export in E. coli and of protein import into the endoplasmic reticulum are discussed
Stellar laboratories: new Ge V and Ge VI oscillator strengths and their validation in the hot white dwarf RE 0503-289
State-of-the-art spectral analysis of hot stars by means of non-LTE
model-atmosphere techniques has arrived at a high level of sophistication. The
analysis of high-resolution and high-S/N spectra, however, is strongly
restricted by the lack of reliable atomic data for highly ionized species from
intermediate-mass metals to trans-iron elements. Especially data for the latter
has only been sparsely calculated. Many of their lines are identified in
spectra of extremely hot, hydrogen-deficient post-AGB stars. A reliable
determination of their abundances establishes crucial constraints for AGB
nucleosynthesis simulations and, thus, for stellar evolutionary theory.
In a previous analysis of the UV spectrum of RE 0503-289, spectral lines of
highly ionized Ga, Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe were identified.
Individual abundance determinations are hampered by the lack of reliable
oscillator strengths. Most of these identified lines stem from Ge V. In
addition, we identified Ge VI lines for the first time. We calculated Ge V and
Ge VI oscillator strengths to consider their radiative and collisional
bound-bound transitions in detail in our non-LTE stellar-atmosphere models for
the analysis of the Ge IV - VI spectrum exhibited in high-resolution and
high-S/N UV spectra of RE 0503-289. We identify four Ge IV, 37 Ge V, and seven
Ge VI lines. Most of these are identified for the first time in any star. We
reproduce almost all Ge IV, Ge VI, and Ge VI lines in the observed spectrum of
RE 0503-289 (Teff = 70 kK, log g = 7.5) at log Ge = -3.8 +/- 0.3 (mass
fraction, about 650 times solar).
Reliable measurements and calculations of atomic data are a prerequisite for
stellar-atmosphere modeling. Our oscillator-strength calculations have allowed,
for the first time, Ge V and Ge VI lines to be successfully reproduced in a
white dwarf's spectrum and to determine its photospheric Ge abundance.Comment: 54 pages, 8 figure
Observation of Scalar Aharonov-Bohm Effect with Longitudinally Polarized Neutrons
We have carried out a neutron interferometry experiment using longitudinally polarized neutrons to observe the scalar Aharonov-Bohm effect. The neutrons inside the interferometer are polarized parallel to an applied pulsed magnetic field B(t). The pulsed B field is spatially uniform so it exerts no force on the neutrons. Its direction also precludes the presence of any classical torque to change the neutron polarization
Scalar Aharonov-Bohm effect with longitudinally polarized neutrons
In the scalar Aharonov-Bohm effect, a charged particle (electron) interacts with the scalar electrostatic potential U in the field-free (i.e., force-free) region inside an electrostatic cylinder (Faraday cage). Using a perfect single-crystal neutron interferometer we have performed a “dual” scalar Aharonov-Bohm experiment by subjecting polarized thermal neutrons to a pulsed magnetic field. The pulsed magnetic field was spatially uniform, precluding any force on the neutrons. Aligning the direction of the pulsed magnetic field to the neutron magnetic moment also rules out any classical torque acting to change the neutron polarization. The observed phase shift is purely quantum mechanical in origin. A detailed description of the experiment, performed at the University of Missouri Research Reactor, and its interpretation is given in this paper
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