883 research outputs found
Enhanced tunability of magnetron sputtered Ba[sub 0.5]Sr[sub 0.5]TiO[sub 3] thin films on c-plane sapphire substrates
Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1 to 20 GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200 kV/cm and total device Q of more than 15 (up to 20 GHz) were achieved following postdeposition annealing at 900°C
Design and Fabrication of Three-Dimensional Scaffolds for Tissue Engineering of Human Heart Valves
We developed a new fabrication technique for 3-dimensional scaffolds for tissue engineering of human heart valve tissue. A human aortic homograft was scanned with an X-ray computer tomograph. The data derived from the X-ray computed tomogram were processed by a computer-aided design program to reconstruct a human heart valve 3-dimensionally. Based on this stereolithographic model, a silicone valve model resembling a human aortic valve was generated. By taking advantage of the thermoplastic properties of polyglycolic acid as scaffold material, we molded a 3-dimensional scaffold for tissue engineering of human heart valves. The valve scaffold showed a deviation of only +/- 3-4% in height, length and inner diameter compared with the homograft. The newly developed technique allows fabricating custom-made, patient-specific polymeric cardiovascular scaffolds for tissue engineering without requiring any suture materials. Copyright (c) 2008 S. Karger AG, Base
A Possible Cepheid-Like Luminosity Estimator for the Long Gamma-Ray Bursts
We present a possible Cepheid-like luminosity estimator for the long
gamma-ray bursts based on the variability of their light curves. To construct
the luminosity estimator, we use CGRO/BATSE data for 13 bursts, Wind/KONUS data
for 5 bursts, Ulysses/GRB data for 1 burst, and NEAR/XGRS data for 1 burst.
Spectroscopic redshifts, peak fluxes, and high resolution light curves are
available for 11 of these bursts; partial information is available for the
remaining 9 bursts. We find that the isotropic-equivalent luminosities L of
these bursts positively correlate with a rigorously-constructed measure V of
the variability of their light curves. We fit a model to these data that
accommodates both intrinsic scatter (statistical variance) and extrinsic
scatter (sample variance). If one excludes GRB 980425 from the fit on the
grounds that its association with SN 1998bw at a redshift of z = 0.0085 is not
secure, the luminosity estimator spans approx. 2.5 orders of magnitude in L,
and the slope of the correlation between L and V is positive with a probability
of 1 - 1.4 x 10^-4 (3.8 sigma). Although GRB 980425 is excluded from this fit,
its L and V values are consistent with the fitted model, which suggests that
GRB 980425 may well be associated with SN 1998bw, and that GRB 980425 and the
cosmological bursts may share a common physical origin. If one includes GRB
980425 in the fit, the luminosity estimator spans approx. 6.3 orders of
magnitude in L, and the slope of the correlation is positive with a probability
of 1 - 9.3 x 10^-7 (4.9 sigma). Independently of whether or not GRB 980425
should be included in the fit, its light curve is unique in that it is much
less variable than the other approx. 17 light curves in our sample for which
the signal-to-noise is reasonably good.Comment: Accepted to The Astrophysical Journal, 31 pages, 13 figures, LaTe
Orbital and physical parameters of eclipsing binaries from the ASAS catalogue -- III. Two new low-mass systems with rapidly evolving spots
We present the results of our spectroscopic and photometric analysis of two
newly discovered low-mass detached eclipsing binaries found in the All-Sky
Automated Survey (ASAS) catalogue: ASAS J093814-0104.4 and ASAS J212954-5620.1.
Using the GIRAFFE instrument on the 1.9-m Radcliffe telescope at SAAO and the
UCLES spectrograph on the 3.9-m Anglo-Australian Telescope, we obtained
high-resolution spectra of both objects and derived their radial velocities
(RVs) at various orbital phases. The RVs of both objects were measured with the
TODCOR technique using synthetic template spectra as references. We also
obtained V and I band photometry using the 1.0-m Elizabeth telescope at SAAO
and the 0.4-m PROMPT instruments located at the CTIO. The orbital and physical
parameters of the systems were derived with PHOEBE and JKTEBOP codes. We
compared our results with several sets of widely-used isochrones. Our
multi-epoch photometric observations demonstrate that both objects show
significant out-of-eclipse modulations, which vary in time. We believe that
this effect is caused by stellar spots, which evolve on time scales of tens of
days. For this reason, we constructed our models on the basis of photometric
observations spanning short time scales (less than a month). Our modeling
indicates that (1) ASAS-09 is a main sequence active system with nearly-twin
components with masses of M1 = 0.771(33) Msun, M2 = 0.768(21) Msun and radii of
R1 = 0.772(12) Rsun and R2 = 0.769(13) Rsun. (2) ASAS-21 is a main sequence
active binary with component masses of M1 = 0.833(17) Msun, M2 = 0.703(13) Msun
and radii of R1 = 0.845(12) Rsun and R2 = 0.718(17) Rsun. Both systems confirm
the characteristic of active low-mass stars, for which the observed radii are
larger and the temperatures lower than predicted by evolutionary models. Other
parameters agree within errors with the models of main sequence stars.Comment: 15 pages, 7 figures, 7 tables, to appear in A&
Fe-binding organic ligands in coastal and frontal regions of the western Antarctic Peninsula
Organic ligands are a key factor determining the
availability of dissolved iron (DFe) in the high-nutrient low-chlorophyll
(HNLC) areas of the Southern Ocean. In this study, organic speciation of Fe
is investigated along a natural gradient of the western Antarctic Peninsula,
from an ice-covered shelf to the open ocean. An electrochemical approach,
competitive ligand exchange – adsorptive cathodic stripping voltammetry
(CLE-AdCSV), was applied. Our results indicated that organic ligands in the
surface water on the shelf are associated with ice-algal exudates, possibly
combined with melting of sea ice. Organic ligands in the deeper shelf water
are supplied via the resuspension of slope or shelf sediments. Further offshore,
organic ligands are most likely related to the development of phytoplankton
blooms in open ocean waters. On the shelf, total ligand concentrations
([Lt]) were between 1.2 and 6.4 nM eq. Fe. The organic
ligands offshore ranged between 1.0 and 3.0 nM eq. Fe. The southern boundary
of the Antarctic Circumpolar Current (SB ACC) separated the organic ligands
on the shelf from bloom-associated ligands offshore. Overall, organic ligand
concentrations always exceeded DFe concentrations (excess ligand
concentration, [L′] = 0.8–5.0 nM eq. Fe). The [L′] made up to 80 % of
[Lt], suggesting that any additional Fe input can be stabilized in the
dissolved form via organic complexation. The denser modified Circumpolar
Deep Water (mCDW) on the shelf showed the highest complexation capacity of
Fe (αFe'L; the product of [L′] and conditional binding
strength of ligands, KFe'Lcond). Since Fe is also supplied by shelf
sediments and glacial discharge, the high complexation capacity over
the shelf can keep Fe dissolved and available for local primary productivity
later in the season upon sea-ice melting.</p
PROMPT Observations of the Early-Time Optical Afterglow of GRB 060607A
PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes)
observed the early-time optical afterglow of GRB 060607A and obtained a densely
sampled multiwavelength light curve that begins only tens of seconds after the
GRB. Located at Cerro Tololo Inter-American Observatory in Chile, PROMPT is
designed to observe the afterglows of gamma-ray bursts using multiple automated
0.4-m telescopes that image simultaneously in many filters when the afterglow
is bright and may be highly variable. The data span the interval from 44
seconds after the GRB trigger to 3.3 hours in the Bgri filters. We observe an
initial peak in the light curve at approximately three minutes, followed by
rebrightenings peaking around 40 minutes and again at 66 minutes. Although our
data overlap with the early Swift gamma-ray and x-ray light curves, we do not
see a correlation between the optical and high-energy flares. We do not find
evidence for spectral evolution throughout the observations. We model the
variations in the light curves and find that the most likely cause of the
rebrightening episodes is a refreshment of the forward shock preceded by a
rapidly fading reverse shock component, although other explanations are
plausible.Comment: 23 pages, 3 figures, accepted to Ap
Southern ocean warming, sea level and hydrological change during the Paleocene-Eocene thermal maximum
A brief (~150 kyr) period of widespread global average surface warming marks the transition between the Paleocene and Eocene epochs, ~56 million years ago. This so-called "Paleocene-Eocene thermal maximum" (PETM) is associated with the massive injection of <sup>13</sup>C-depleted carbon, reflected in a negative carbon isotope excursion (CIE). Biotic responses include a global abundance peak (acme) of the subtropical dinoflagellate <i>Apectodinium</i>. Here we identify the PETM in a marine sedimentary sequence deposited on the East Tasman Plateau at Ocean Drilling Program (ODP) Site 1172 and show, based on the organic paleothermometer TEX<sub>86</sub>, that southwest Pacific sea surface temperatures increased from ~26 °C to ~33°C during the PETM. Such temperatures before, during and after the PETM are >10 °C warmer than predicted by paleoclimate model simulations for this latitude. In part, this discrepancy may be explained by potential seasonal biases in the TEX<sub>86</sub> proxy in polar oceans. Additionally, the data suggest that not only Arctic, but also Antarctic temperatures may be underestimated in simulations of ancient greenhouse climates by current generation fully coupled climate models. An early influx of abundant <i>Apectodinium</i> confirms that environmental change preceded the CIE on a global scale. Organic dinoflagellate cyst assemblages suggest a local decrease in the amount of river run off reaching the core site during the PETM, possibly in concert with eustatic rise. Moreover, the assemblages suggest changes in seasonality of the regional hydrological system and storm activity. Finally, significant variation in dinoflagellate cyst assemblages during the PETM indicates that southwest Pacific climates varied significantly over time scales of 10<sup>3</sup> – 10<sup>4</sup> years during this event, a finding comparable to similar studies of PETM successions from the New Jersey Shelf
- …