1,917 research outputs found
Methane hydrate formation in partially water-saturated Ottawa sand
This paper is not subject to U.S. copyright. The definitive version was published in American Mineralogist 89 (2004): 1202-1207.Bulk properties of gas hydrate-bearing sediment strongly depend on whether hydrate forms primarily
in the pore fluid, becomes a load-bearing member of the sediment matrix, or cements sediment
grains. Our compressional wave speed measurements through partially water-saturated, methane
hydrate-bearing Ottawa sands suggest hydrate surrounds and cements sediment grains. The three
Ottawa sand packs tested in the Gas Hydrate And Sediment Test Laboratory Instrument (GHASTLI)
contain 38(1)% porosity, initially with distilled water saturating 58, 31, and 16% of that pore space,
respectively. From the volume of methane gas produced during hydrate dissociation, we calculated
the hydrate concentration in the pore space to be 70, 37, and 20% respectively. Based on these hydrate
concentrations and our measured compressional wave speeds, we used a rock physics model to differentiate
between potential pore-space hydrate distributions. Model results suggest methane hydrate
cements unconsolidated sediment when forming in systems containing an abundant gas phase.This work was supported by the U.S. Geological Surveyʼs Coastal and Marine
Geology and Eastern Region Gas Hydrate Programs, in addition to DOE contract
DE-AI21-92MC29214
Reduced-Complexity Transmit/Receive-Diversity Systems
We consider wireless systems with transmit and receive diversity. For reduction of complexity, we propose to use hybrid selection/maximal ratio transmission at one link end, choosing L out of N antennas. We analyze the performance of such systems, giving analytical bounds and comparing them to computer simulations. Outage probability, symbol error probability, and capacity are shown. We demonstrate that in typical cases, a small number of used antennas L is sufficient to achieve considerable performance gains. We also analyze the infuence of the number of base station antennas, of fading correlation and channel estimation errors. The simulation results confirm that the proposed scheme is effective in a variety of environments
Novel designs for Penning ion traps
We present a number of alternative designs for Penning ion traps suitable for
quantum information processing (QIP) applications with atomic ions. The first
trap design is a simple array of long straight wires which allows easy optical
access. A prototype of this trap has been built to trap Ca+ and a simple
electronic detection scheme has been employed to demonstrate the operation of
the trap. Another trap design consists of a conducting plate with a hole in it
situated above a continuous conducting plane. The final trap design is based on
an array of pad electrodes. Although this trap design lacks the open geometry
of the traps described above, the pad design may prove useful in a hybrid
scheme in which information processing and qubit storage take place in
different types of trap. The behaviour of the pad traps is simulated
numerically and techniques for moving ions rapidly between traps are discussed.
Future experiments with these various designs are discussed. All of the designs
lend themselves to the construction of multiple trap arrays, as required for
scalable ion trap QIP.Comment: 11 pages, 10 figure
Characterization of Hybrid Ferroelectric/HTS Thin Films for Tunable Microwave Components
Since the discovery of High-Temperature-Superconductors (HTS) in 1986, a diversity of HTS-based microwave components has been demonstrated. Because of their low conductor losses, HTS-based components are very attractive for integration into microwave circuits for space communication systems. Recent advancements have made deposition of ferroelectric thin films onto HTS thin films possible. Due to the sensitivity of the ferroelectric's dielectric constant (epsilon(sub r)) to an externally applied electric field (E), ferroelectric/superconducting structures could be used in the fabrication of low loss, tunable microwave components. In this paper, we report on our study of Ba(0.5)Sr(0.5)TiO3/YBa2Cu3O(7-delta) and Ba(0.08)Sr(0.92)TiO3/YBa2Cu3O(7-delta) ferroelectric/superconducting thin films on lanthanum aluminate (LaAlO3) substrates. For the (Ba:Sr, 0.50:0.50) epitaxial sample, a epsilon(sub r) of 425 and a loss tangent (tan delta) of 0.040 were measured at 298 K, 1.0 MHz, and zero applied E. For the same sample, a epsilon(sub r) of 360 and tan delta of 0.036 were obtained at 77 K, 1.0 MHz, and zero applied E. Variations in epsilon(sub r) from 180 to 360 were observed over an applied E range of 0V/cm less than or equal to E less than or equal to 5.62 x 10(exp 4) V/cm with little change in tan delta. However, the range of epsilon(sub r) variation for the polycrystalline (Ba:Sr, 0.08:0.92) sample over 0V/cm less than or equal to E less than or equal to 4.00 x 10(exp 4) V/cm was only 3.6 percent while tan delta increased markedly. These results indicate that a lack of epitaxy between the ferroelectric and superconducting layers decreases tuning and increases microwave losses
Photo-disintegration cross section measurements on W, Re and Os: Implications for the Re-Os cosmochronology
Cross sections of the W, Re, Os() reactions
were measured using quasi-monochromatic photon beams from laser Compton
scattering (LCS) with average energies from 7.3 to 10.9 MeV. The results are
compared with the predictions of Hauser-Feshbach statistical calculations using
four different sets of input parameters. In addition, the inverse neutron
capture cross sections were evaluated by constraining the model parameters,
especially the strength function, on the basis of the experimental data.
The present experiment helps to further constrain the correction factor
for the neutron capture on the 9.75 keV state in Os.
Implications of to the Re-Os cosmochronology are discussed with a
focus on the uncertainty in the estimate of the age of the Galaxy.Comment: 11 page
The geometry of the close environment of SV Psc as probed by VLTI/MIDI
Context. SV Psc is an asymptotic giant branch (AGB) star surrounded by an
oxygen-rich dust envelope. The mm-CO line profile of the object's outflow shows
a clear double-component structure. Because of the high angular resolution,
mid-IR interferometry may give strong constraints on the origin of this
composite profile.
Aims. The aim of this work is to investigate the morphology of the
environment around SV Psc using high-angular resolution interferometry
observations in the mid-IR with the Very Large Telescope MID-infrared
Interferometric instrument (VLTI/MIDI).
Methods. Interferometric data in the N-band taken at different baseline
lengths (ranging from 32-64 m) and position angles (73- 142{\deg}) allow a
study of the morphology of the circumstellar environment close to the star. The
data are interpreted on the basis of 2-dimensional, chromatic geometrical
models using the fitting software tool GEM-FIND developed for this purpose.
Results. The results favor two scenarios: (i) the presence of a highly
inclined, optically thin, dusty disk surrounding the central star; (ii) the
presence of an unresolved binary companion at a separation of 13.7 AU and a
position angle of 121.8{\deg} NE. The derived orbital period of the binary is
38.1 yr. This detection is in good agreement with hydrodynamic simulations
showing that a close companion could be responsible for the entrainment of the
gas and dust into a circumbinary structure.Comment: 10 pages, 12 figure
Pseudoangiomatous stromal hyperplasia: an unsuspected cause of anisomasty
Breast asymmetry can be congenital or developmental, however a tumorous growth may be the cause of this condition after puberty. A 19-year-old female presented with a slowly developing breast asymmetry pre-operatively diagnosed as Pseudoangiomatous Stromal Hyperplasia (PASH). The patient underwent tumour excision with breast gland remodelling. Postoperative course was uneventful
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