1,709 research outputs found
Deployment mechanisms on Pioneer Venus probes
Deployment mechanisms were developed to position scientific instruments during probe descent into the Venus atmosphere. Each mechanism includes a provision for pyrotechnic release of the enclosure door, negator springs for positive deployment torque, and an active damper using a shunted dc motor. The deployment time requirement is under 2 seconds, and the deployment shock must be less than 100 g's. The mechanism is completely dry lubricated and constructed mainly of titanium for high strength and high temperature stability. The mechanism was qualified for descent decelerations up to 565 g's and for instrument alignment up to 940 F. The mechanism requirements, the hardware design details, the analytical simulations, and the qualification testing are described
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Lateral shearing interferometry for high-NA EUV wavefront metrology
We present a lateral shearing interferometer suitable for high-NA EUV wavefront metrology. In this interferometer, a geometric model is used to accurately characterize and predict systematic errors that come from performing interferometry at high NA. This interferometer is compatible with various optical geometries, including systems where the image plane is tilted with respect to the optical axis, as in the Berkeley MET5. Simulation results show that the systematic errors in tilted geometries can be reduced by aligning the shearing interferometer grating and detector parallel to the image plane. Subsequent residual errors can be removed by linear fitting
Modal test of the Viking orbiter
A modal test of the Orbiter Development Test Modal (ODTM) has been conducted to verify, or update, the mathematical model used for load analysis. The approach used to assure the quality and validity of the experimental data is defined, the modal test is described, and test results are presented and compared with analysis results. Good correlation between the analyses and the test data assures an acceptable model for incorporation into the mathematical model of the launch system
Peierls instability, periodic Bose-Einstein condensates and density waves in quasi-one-dimensional boson-fermion mixtures of atomic gases
We study the quasi-one-dimensional (Q1D) spin-polarized bose-fermi mixture of
atomic gases at zero temperature. Bosonic excitation spectra are calculated in
random phase approximation on the ground state with the uniform BEC, and the
Peierls instabilities are shown to appear in bosonic collective excitation
modes with wave-number by the coupling between the Bogoliubov-phonon
mode of bosonic atoms and the fermion particle-hole excitations. The
ground-state properties are calculated in the variational method, and,
corresponding to the Peierls instability, the state with a periodic BEC and
fermionic density waves with the period are shown to have a lower
energy than the uniform one. We also briefly discuss the Q1D system confined in
a harmonic oscillator (HO) potential and derive the Peierls instability
condition for it.Comment: 9 pages, 3figure
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Upgrade to the SHARP EUV mask microscope
The Sharp High-NA Actinic Reticle review Project (SHARP) is a synchrotron-based, extreme ultraviolet (EUV) microscope dedicated to photomask research. A potential upgrade to the SHARP microscope is presented. The upgrade includes changing the light path in the instrument from its current off-Axis configuration to an on-Axis configuration. This change allows for an increased working distance of 2.5 mm or more. A central obscuration, added to the zoneplate aperture, blocks stray light from reaching the central part of the image, thus improving the image contrast. The imaging performance of the two configurations is evaluated by means of ray tracing
Density wave instability in a 2D dipolar Fermi gas
We consider a uniform dipolar Fermi gas in two-dimensions (2D) where the
dipole moments of fermions are aligned by an orientable external field. We
obtain the ground state of the gas in Hartree-Fock approximation and
investigate RPA stability against density fluctuations of finite momentum. It
is shown that the density wave instability takes place in a broad region where
the system is stable against collapse. We also find that the critical
temperature can be a significant fraction of Fermi temperature for a realistic
system of polar molecules.Comment: 10 figure
Two Sizes of Superconducting Gaps on an Under-doped Bi2.1Sr1.9Ca2Cu3O10+δ with TC ∼ 101K by Tunneling Spectroscopy
AbstractWe measured tunneling conductances on an under-doped trilayer cuprate Bi2.1Sr1.9Ca2Cu3O10+≏ (Bi2223) with TC ∼ 101K by a point contact method, which has three CuO2 planes in a unit cell. The tunneling conductances on Bi2223 exhibited two sizes of gaps originated from outer and inner CuO2 plane (OP and IP). The estimated size of superconducting gap from OP ΔOP is 34 ± 6 meV, and the ΔIP from IP is 51 ± 5 meV, respectively. We also observed tunneling conductances which simultaneously displayed two superconducting peaks of OP and IP. Moreover, we propose the model of two superconductor-insulator-normal metal junctions which exhibit two sizes gaps of OP and IP
Random-phase approximation study of collective excitations in the Bose-Fermi mixed condensate of alkali-metal gases
We perform Random Phase Approximation (RPA) study of collective excitations
in the bose-fermi mixed degenerate gas of Alkali-metal atoms at T=0. The
calculation is done by diagonalization in a model space composed of
particle-hole type excitations from the ground state, the latter being obtained
from the coupled Gross-Pitaevskii and Thomas-Fermi equations. We investigate
strength distributions for different combinations of bose and fermi multipole
() operators with . Transition densities and dynamical structure
factors are calculated for collective excitations. Comparison with the sum rule
prediction for the collective frequency is given. Time dependent behavior of
the system after an external impulse is studied.Comment: 28 pages, 13 figures, submitted to Phys. Rev.
Control sideband generation for dual-recycled laser interferometric gravitational wave detectors
We present a discussion of the problems associated with generation of multiple control sidebands for length sensing and control of dual-recycled, cavity-enhanced Michelson interferometers and the motivation behind more complicated sideband generation methods. We focus on the Mach–Zehnder interferometer as a topological solution to the problem and present results from tests carried out at the Caltech 40 m prototype gravitational wave detector. The consequences for sensing and control for advanced interferometry are discussed, as are the implications for future interferometers such as Advanced LIGO
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