2,536 research outputs found
Noncontacting devices to indicate deflection and vibration of turbopump internal rotating parts
Published report discusses feasibility of ultrasonic techniques; neutron techniques; X-radiography; optical devices; gamma ray devices; and conventional displacement sensors. Use of signal transmitters in place of slip rings indicated possible improvement and will be subject of futher study
The formation of ultra-compact dwarf galaxies and nucleated dwarf galaxies
Ultra compact dwarf galaxies (UCDs) have similar properties as massive
globular clusters or the nuclei of nucleated galaxies. Recent observations
suggesting a high dark matter content and a steep spatial distribution within
groups and clusters provide new clues as to their origins. We perform
high-resolution N-body / smoothed particle hydrodynamics simulations designed
to elucidate two possible formation mechanisms for these systems: the merging
of globular clusters in the centre of a dark matter halo, or the massively
stripped remnant of a nucleated galaxy. Both models produce density profiles as
well as the half light radii that can fit the observational constraints.
However, we show that the first scenario results to UCDs that are underluminous
and contain no dark matter. This is because the sinking process ejects most of
the dark matter particles from the halo centre. Stripped nuclei give a more
promising explanation, especially if the nuclei form via the sinking of gas,
funneled down inner galactic bars, since this process enhances the central dark
matter content. Even when the entire disk is tidally stripped away, the nucleus
stays intact and can remain dark matter dominated even after severe stripping.
Total galaxy disruption beyond the nuclei only occurs on certain orbits and
depends on the amount of dissipation during nuclei formation. By comparing the
total disruption of CDM subhaloes in a cluster potential we demonstrate that
this model also leads to the observed spatial distribution of UCDs which can be
tested in more detail with larger data sets.Comment: 8 pages, 8 figures, final version accepted for publication in MNRA
Envelope Structure of Starless Core L694-2 Derived from a Near-Infrared Extinction Map
We present a near-infrared extinction study of the dark globule L694-2, a
starless core that shows strong evidence for inward motions in molecular line
profiles. The J,H, and K band data were taken using the European Southern
Observatory New Technology Telescope. The best fit simple spherical power law
model has index p=2.6 +/- 0.2, over the 0.036--0.1 pc range in radius sampled
in extinction. This power law slope is steeper than the value of p=2 for a
singular isothermal sphere, the initial condition of the inside-out model for
protostellar collapse. Including an additional extinction component along the
line of sight further steepens the inferred profile. Fitting a Bonnor-Ebert
sphere results in a super-critical value of the dimensionless radius xi_max=25
+/- 3. The unstable configuration of material may be related to the observed
inward motions. The Bonnor-Ebert model matches the shape of the observed
profile, but significantly underestimates the amount of extinction (by a factor
of ~4). This discrepancy in normalization has also been found for the nearby
protostellar core B335 (Harvey et al. 2001). A cylindrical density model with
scale height H=0.0164+/- 0.002 pc viewed at a small inclination to the cylinder
axis provides an equally good radial profile as a power law model, and
reproduces the asymmetry of the core remarkably well. In addition, this model
provides a basis for understanding the discrepancy in the normalization of the
Bonnor-Ebert model, namely that L694-2 has prolate structure, with the full
extent (mass) of the core being missed by assuming symmetry between the
profiles in the plane of the sky and along the line-of-sight. If the core is
sufficiently magnetized then fragmentation may be avoided, and later evolution
might produce a protostar similar to B335.Comment: 38 pages, 7 figures, accepted to Astrophysical Journa
Cs-Induced Surface State on GaAs(110)
Cesium adsorption on GaAs(110) has been studied by angle-resolved photoemission spectroscopy at room temperature in the submonolayer-coverage regime. We report the observation of a Cs-induced surface state in the vicinity of the surface-Brillouin-zone edge. The possible origin of the state is discussed in relation to recent structural observations. The onset of the Cs-induced surface state can be correlated with the appearance of a second Cs 5p core-level emission feature at ∼0.2 monolayer Cs coverage
Surface and Bulk Structural Properties of Single Crystalline Sr3Ru2O7
We report temperature and thermal-cycling dependence of surface and bulk
structures of double-layered perovskite Sr3Ru2O7 single crystals. The surface
and bulk structures were investigated using low-energy electron diffraction
(LEED) and single-crystal X-ray diffraction (XRD) techniques, respectively.
Single-crystal XRD data is in good agreement with previous reports for the bulk
structure with RuO6 octahedral rotation, which increases with decreasing
temperature (~ 6.7(6)degrees at 300 K and ~ 8.1(2) degrees at 90 K). LEED
results reveal that the octahedra at the surface are much more distorted with a
higher rotation angle (~ 12 degrees between 300 and 80 K) and a slight tilt
((4.5\pm2.5) degrees at 300 K and (2.5\pm1.7) degrees at 80 K). While XRD data
confirms temperature dependence of the unit cell height/width ratio (i.e.
lattice parameter c divided by the average of parameters a and b) found in a
prior neutron powder diffraction investigation, both bulk and surface
structures display little change with thermal cycles between 300 and 80 K.Comment: 25 pages, 5 figures, 5 tables, to appear in Physical Review
Surface Structural Analysis of the Layered Perovskite Ca1.9Sr0.1RuO4 by Low Energy Electron Diffraction I-V
– The atomic structure at surface of the layered perovskite Ca1.9Sr0.1RuO4 has been studied by Low Energy Electron Diffraction (LEED) I-V. The perovskite Ca1.9Sr0.1RuO4 of single crystal was cleaved in ultra high vacuum chamber (the pressure in the chamber was about 1x10-10 Torr). The experiments were conducted at room temperature (T=300 K). The sharp LEED pattern was observed which indicates that the surface of Ca1.9Sr0.1RuO4 is flat and it is a well ordered crystal. LEED I-V data, nine equivalent beams of the layered perovskite Ca1.9Sr0.1RuO4 were recorded at room temperature. LEED I-V calculation was performed to fit experimental data to obtain the surface atomic structure. The LEED I-V analysis reveals that in the surface of the layered perovskite Ca1.9Sr0.1RuO4 the RuO6 octahedra are rotated (in-plane rotation) alternating clockwise and counterclockwise. The in-plane rotation at the surface is 11 degree which is smaller than that in the bulk (13 degree). The Ru – O(1) bond-length at the surface is found to be 1.936 Å which is about the same as in the bulk (1.939 Å). The Ru – O(2) bond length at the surface is 1.863 Å which is much shorter than that in the bulk (2.040 Å). The volume of octahedral Ru-O6 at the surface is reduced by 9% with respect to the bulk. This finding shows that the atomic structure at surface of the layered perovskite Ca1.9Sr0.1RuO4is significantly different than that in the bulk. These lattice distortions strongly influence its electronic properties
Hydrogen adsorption on Pd(133) surface
In this study used is an approach based on measurements of the total energy
distribution (TED) of field emitted electrons in order to examine the
properties of Pd (133) from the aspect of both hydrogen adsorption and surface
hydrides formation. The most favourable sites offered to a hydrogen atom to be
adsorbed have been indicated and an attempt to describe the peaks of the
enhancement factor R spectrum to the specific adsorption sites has also been
made.Comment: to be submitted to the Centr. Eur. J. Phy
Evidence for Strong Itinerant Spin Fluctuations in the Normal State of CeFeAsO(0.89)F(0.11) Iron-Oxypnictides
The electronic structure in the normal state of CeFeAsO0.89F0.11 oxypnictide
superconductors has been investigated with x-ray absorption and photoemission
spectroscopy. All the data exhibit signatures of Fe d-electron itinerancy.
Exchange multiplets appearing in the Fe 3s core level indicate the presence of
itinerant spin fluctuations. These findings suggest that the underlying physics
and the origin of superconductivity in these materials are likely to be quite
different from those of the cuprate high-temperature superconductors. These
materials provide opportunities for elucidating the role of magnetic
fluctuations in high-temperature superconductivity.Comment: Shorter version. Accepted in Phys. Rev. Let
Molecular Cloning of Mannose-6-Phosphate Reductase and Its Developmental Expression in Celery
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