30,077 research outputs found
Improvement of dielectric loss of doped Ba0.5Sr0.5TiO3 thin films for tunable microwave devices
Al2O3-Ba0.5Sr0.5TiO3 (Al2O3-BST) thin films, with different Al2O3 contents,
were deposited on (100) LaAlO3 substrate by pulsed laser deposition (PLD)
technique. The Al2O3-BST films was demosnstrated to be a suitable systems to
fabricate ferroelectric thin films with low dielectric loss and higher figure
of merit for tunable microwave devices. Pure BST thin films were also
fabricated for comparison purpose. The films' structure and morphology were
analyzed by X-ray diffractiopn and scanning electron microscopy, respectively;
nad showed that the surface roughness for the Al2O3-BST films increased with
the Al2O3 content. Apart from that, the broadening in the intensity peak in XRD
result indicating the grain size of the Al2O3-BST films reduced with the
increasing of Al2O3 dopant. We measured the dielctric properties of Al2O3-BST
films with a home-made non-destructive dual resonator method at frequency ~ 7.7
GHZ. The effect of doped Al2O3 into BST thin films significantly reduced the
dielectric constant, dielectric loss and tunability compare to pure BST thin
film. Our result shows the figure of merit (K), used to compare the films with
varied dielectric properties, increased with the Al2O3 content. Therefore
Al2O3-BST films show the potential to be exploited in tunable microwave
devices.Comment: 8 pages, 4 figures, 1 table. Accepted & tentatively for Feb 15 2004
issue, Journal of Applied Physic
Decorrelation Times of Photospheric Fields and Flows
We use autocorrelation to investigate evolution in flow fields inferred by
applying Fourier Local Correlation Tracking (FLCT) to a sequence of
high-resolution (0.3 \arcsec), high-cadence ( min) line-of-sight
magnetograms of NOAA active region (AR) 10930 recorded by the Narrowband Filter
Imager (NFI) of the Solar Optical Telescope (SOT) aboard the {\em Hinode}
satellite over 12--13 December 2006. To baseline the timescales of flow
evolution, we also autocorrelated the magnetograms, at several spatial
binnings, to characterize the lifetimes of active region magnetic structures
versus spatial scale. Autocorrelation of flow maps can be used to optimize
tracking parameters, to understand tracking algorithms' susceptibility to
noise, and to estimate flow lifetimes. Tracking parameters varied include: time
interval between magnetogram pairs tracked, spatial binning applied
to the magnetograms, and windowing parameter used in FLCT. Flow
structures vary over a range of spatial and temporal scales (including
unresolved scales), so tracked flows represent a local average of the flow over
a particular range of space and time. We define flow lifetime to be the flow
decorrelation time, . For , tracking results represent
the average velocity over one or more flow lifetimes. We analyze lifetimes of
flow components, divergences, and curls as functions of magnetic field strength
and spatial scale. We find a significant trend of increasing lifetimes of flow
components, divergences, and curls with field strength, consistent with Lorentz
forces partially governing flows in the active photosphere, as well as strong
trends of increasing flow lifetime and decreasing magnitudes with increases in
both spatial scale and .Comment: 48 pages, 20 figures, submitted to the Astrophysical Journal;
full-resolution images in manuscript (8MB) at
http://solarmuri.ssl.berkeley.edu/~welsch/public/manuscripts/flow_lifetimes_v2.pd
Adaptive and coupled continuum-molecular mechanics simulations of amorphous materials
A method to reduce the degrees freedom in molecular mechanics simulation is presented. Although the approach is formulated for amorphous materials in mind, it is equally applicable to crystalline materials. The method can be selectively applied to regions where molecular displacements are expected to be small while simultaneously using classical molecular mechanics (MM) for regions undergoing large deformation. The accuracy and computational efficiency of the approach is demonstrated through the simulation of a polymer-like substrate being indented by a rigid hemispherical indentor. The region directly below the indentor is modelled by classical molecular mechanics while the region further away has the degrees of freedom (DOFs) reduced by about 50 times. The results of automatically reverting regions of reduced DOFs back to classical MM also demonstrate the capability of performing adaptive simulations
Clinical features of nipah virus encephalitis among pig farmers in Malaysia
Background: Between September 1998 and June 1999, there was an outbreak of severe viral encephalitis due to Nipah virus, a newly discovered paramyxovirus, in Malaysia. Methods: We studied the clinical features of the patients with Nipah virus encephalitis who were admitted to a medical center in Kuala Lumpur. The case definition was based on epidemiologic, clinical, cerebrospinal fluid, and neuroimaging findings. Results: Ninety-four patients with Nipah virus infection were seen from February to June 1999 (mean age, 37 years; ratio of male patients to female patients, 4.5 to 1). Ninety-three percent had had direct contact with pigs, usually in the two weeks before the onset of illness, suggesting that there was direct viral transmission from pigs to humans and a short incubation period. The main presenting features were fever, headache, dizziness, and vomiting. Fifty-two patients (55 percent) had a reduced level of consciousness and prominent brain-stem dysfunction. Distinctive clinical signs included segmental myoclonus, areflexia and hypotonia, hypertension, and tachycardia and thus suggest the involvement of the brain stem and the upper cervical spinal cord. The initial cerebrospinal fluid findings were abnormal in 75 percent of patients. Antibodies against Hendra virus were detected in serum or cerebrospinal fluid in 76 percent of 83 patients tested. Thirty patients (32 percent) died after rapid deterioration in their condition. An abnormal doll's-eye reflex and tachycardia were factors associated with a poor prognosis. Death was probably due to severe brain-stem involvement. Neurologic relapse occurred after initially mild disease in three patients. Fifty patients (53 percent) recovered fully, and 14 (15 percent) had persistent neurologic deficits. Conclusions: Nipah virus causes a severe, rapidly progressive encephalitis with a high mortality rate and features that suggest involvement of the brain stem. The infection is associated with recent contact with pigs. (N Engl J Med 2000;342:1229-35.) (C) 2000, Massachusetts Medical Society. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down
Reference Measurements of the Longitudinal Impedance in the CERN SPS
First reference measurements of the longitudinal impedance were made with beam in the SPS machine in 1999 to quantify the results of the impedance reduction programme, completed in 2001. The 2001 data showed that the low-frequency inductive impedance had been reduced by a factor 2.5 and that bunch lengthening due to the microwave instability was absent up to the ultimate LHC bunch intensity. Measurements of the quadrupole frequency shift with intensity in the following years suggest a significant increase in impedance (which nevertheless remains below the 1999 level) due to the installation of eight extraction kickers for beam transfer to the LHC. The experimental results are compared with expectations based on the known longitudinal impedance of the SPS
Quantum Hall Effect on the Hofstadter Butterfly
Motivated by recent experimental attempts to detect the Hofstadter butterfly,
we numerically calculate the Hall conductivity in a modulated two-dimensional
electron system with disorder in the quantum Hall regime. We identify the
critical energies where the states are extended for each of butterfly subbands,
and obtain the trajectory as a function of the disorder. Remarkably, we find
that when the modulation becomes anisotropic, the critical energy branches
accompanying a change of the Hall conductivity.Comment: 4 pages, 6 figure
Studying patterns of use of transport modes through data mining - Application to U.S. national household travel survey data set
Data collection activities related to travel require large amounts of financial and human resources to be conducted successfully. When available resources are scarce, the information hidden in these data sets needs to be exploited, both to increase their added value and to gain support among decision makers not to discontinue such efforts. This study assessed the use of a data mining technique, association analysis, to understand better the patterns of mode use from the 2009 U.S. National Household Travel Survey. Only variables related to self-reported levels of use of the different transportation means are considered, along with those useful to the socioeconomic characterization of the respondents. Association rules potentially showed a substitution effect between cars and public transportation, in economic terms but such an effect was not observed between public transportation and nonmotorized modes (e.g., bicycling and walking). This effect was a policy-relevant finding, because transit marketing should be targeted to car drivers rather than to bikers or walkers for real improvement in the environmental performance of any transportation system. Given the competitive advantage of private modes extensively discussed in the literature, modal diversion from car to transit is seldom observed in practice. However, after such a factor was controlled, the results suggest that modal diversion should mainly occur from cars to transit rather than from nonmotorized modes to transi
Nanoscale broadband transmission lines for spin qubit control
The intense interest in spin-based quantum information processing has caused
an increasing overlap between two traditionally distinct disciplines, such as
magnetic resonance and nanotechnology. In this work we discuss rigourous design
guidelines to integrate microwave circuits with charge-sensitive
nanostructures, and describe how to simulate such structures accurately and
efficiently. We present a new design for an on-chip, broadband, nanoscale
microwave line that optimizes the magnetic field driving a spin qubit, while
minimizing the disturbance on a nearby charge sensor. This new structure was
successfully employed in a single-spin qubit experiment, and shows that the
simulations accurately predict the magnetic field values even at frequencies as
high as 30 GHz.Comment: 18 pages, 8 figures, 1 table, pdflate
The Mass-Radius Relationship for Very Low Mass Stars: Four New Discoveries from the HATSouth Survey
We report the discovery of four transiting F-M binary systems with companions
between 0.1-0.2 Msun in mass by the HATSouth survey. These systems have been
characterised via a global analysis of the HATSouth discovery data, combined
with high-resolution radial velocities and accurate transit photometry
observations. We determined the masses and radii of the component stars using a
combination of two methods: isochrone fitting of spectroscopic primary star
parameters, and equating spectroscopic primary star rotation velocity with
spin-orbit synchronisation. These new very low mass companions are HATS550-016B
(0.110 -0.006/+0.005 Msun, 0.147 -0.004/+0.003 Rsun), HATS551-019B (0.17
-0.01/+0.01 Msun, 0.18 -0.01/+0.01 Rsun), HATS551-021B (0.132 -0.005/+0.014
Msun, 0.154 -0.008/+0.006 Rsun), HATS553-001B (0.20 -0.02/+0.01 Msun, 0.22
-0.01/+0.01 Rsun). We examine our sample in the context of the radius anomaly
for fully-convective low mass stars. Combining our sample with the 13 other
well-studied very low mass stars, we find a tentative 5% systematic deviation
between the measured radii and theoretical isochrone models.Comment: 17 pages, 8 figures, accepted for publication in MNRA
- …