4,435 research outputs found
Measurement of Shear Modulus Profile Using a Continuous Surface Wave Measurement System
For most ground response analyses, the shear modulus is an important parameter to be determined and it has to be measured over a large strain range, so as to characterise the soil behavior under various loading conditions. Laboratory measurement of shear modulus covers a limited strain range depending on the test method. The main difficulty lies in the determination of the shear modulus at very small strains. In this respect, geophysical methods are more attractive. One of these test methods, which uses a continuous surface wave, is used to obtain the shear modulus profile at two sites in Singapore. The Continuous Surface Wave System (CSWS) is a nonintrusive field geophysical test consisting of a vibrator source and several receiver geophones connected to a computer system. The computer collects and analyses the field data, and provides a shear modulus profile at the test site. Conclusions from the field tests support published literature that such field seismic tests are capable of measuring the low-strain shear modulus well. The interpretation of field test data in the absence of specific stratigraphic information can pose some difficulties. An important part in interpreting continuous surface wave measurement data is in the selection of a suitable inversion tool so as to derive the correct shear modulus profile for the site under consideration. A finite element approach (using LS DYNA) is investigated for inversion of field test data. Data obtained from S-wave cross-hole survey are also compared with field tests data obtained using CSWS
Measurement of Resonant Frequency and Quality Factor of Microwave Resonators: Comparison of Methods
Precise microwave measurements of sample conductivity, dielectric, and
magnetic properties are routinely performed with cavity perturbation
measurements. These methods require the accurate determination of quality
factor and resonant frequency of microwave resonators. Seven different methods
to determine the resonant frequency and quality factor from complex
transmission coefficient data are discussed and compared to find which is most
accurate and precise when tested using identical data. We find that the
nonlinear least-squares fit to the phase vs. frequency is the most accurate and
precise when the signal-to-noise ratio is greater than 65. For noisier data,
the nonlinear least squares fit to a Lorentzian curve is more accurate and
precise. The results are general and can be applied to the analysis of many
kinds of resonant phenomena.Comment: 29 pages, 11 figure
BOSS-LDG: A Novel Computational Framework that Brings Together Blue Waters, Open Science Grid, Shifter and the LIGO Data Grid to Accelerate Gravitational Wave Discovery
We present a novel computational framework that connects Blue Waters, the
NSF-supported, leadership-class supercomputer operated by NCSA, to the Laser
Interferometer Gravitational-Wave Observatory (LIGO) Data Grid via Open Science
Grid technology. To enable this computational infrastructure, we configured,
for the first time, a LIGO Data Grid Tier-1 Center that can submit
heterogeneous LIGO workflows using Open Science Grid facilities. In order to
enable a seamless connection between the LIGO Data Grid and Blue Waters via
Open Science Grid, we utilize Shifter to containerize LIGO's workflow software.
This work represents the first time Open Science Grid, Shifter, and Blue Waters
are unified to tackle a scientific problem and, in particular, it is the first
time a framework of this nature is used in the context of large scale
gravitational wave data analysis. This new framework has been used in the last
several weeks of LIGO's second discovery campaign to run the most
computationally demanding gravitational wave search workflows on Blue Waters,
and accelerate discovery in the emergent field of gravitational wave
astrophysics. We discuss the implications of this novel framework for a wider
ecosystem of Higher Performance Computing users.Comment: 10 pages, 10 figures. Accepted as a Full Research Paper to the 13th
IEEE International Conference on eScienc
Topographic Changes in SARS Coronavirus–infected Cells at Late Stages of Infection
Scanning electron and atomic force microscopy was used for the first time to view the maturation of SARS-CoV at the cell surface
A UK-based pilot study of current surgical practice and implant preferences in lumbar fusion surgery
Lumbar fusion surgery is an established procedure for the treatment of low back pain.
Despite the wide set of alternative fusion techniques and existing devices, uniform
guidelines are not available yet and common surgical trends are scarcely investigated.
The purpose of this UK-based study was to provide a descriptive portrait of current
surgeons' practice and implant preferences in lumbar fusion surgery.
A UK-based in-person survey was designed for this study and submitted to a group of
consultant spinal surgeons (n=32). 15 queries were addressed based on different
aspects of surgeons' practice: lumbar fusion techniques, implant preferences, and
bone grafting procedures. Answers were analysed by means of descriptive statistics.
32 consultant spinal surgeons completed the survey. There was clear consistency on
the relevance of a patient-centred management (82.3%), along with a considerable
variability of practice on the preferred fusion approach. Fixation surgery was found to
be largely adopted (96.0%) and favoured over stand-alone cages. With regards to the
materials, titanium cages were the most used (54.3%). The geometry of the implants
influenced the choice of lumbar cages (81.3%). Specifically, parallel-shape cages were
mostly avoided (89.2%) and hyperlordotic cages were preferred at the lower lumbar
levels. However, there was no design for lumbar cages which was consistently
favoured. Autograft bone graft surgeries were the most common (60.0%). Amongst the
synthetic options, hydroxyapatite-based bone graft substitutes (76.7%) in injectable
paste form (80.8%) were preferred.
Current lumbar fusion practice is variable and patient-oriented. Factors such as design
and materials are crucial in the choice of the interbody fusion implant. Findings from
this study highlight the need for large-scale investigative surveys and clinical studies
aimed to set specific guidelines for certain pathologies or patient categories
Consistency equations in Randall-Sundrum cosmology: a test for braneworld inflation
In the context of an inflationary Randall-Sundrum Type II braneworld (RS2) we
calculate spectral indices and amplitudes of cosmological scalar and tensor
perturbations, up to second order in slow-roll parameters. Under very simple
assumptions, extrapolating next-order formulae from first-order calculations in
the case of a de Sitter brane, we see that the degeneracy between standard and
braneworld lowest-order consistency equations is broken, thus giving different
signatures of early-universe inflationary expansion. Using the latest results
from WMAP for estimates of cosmological observables, it is shown that future
data and missions can in principle discriminate between standard and braneworld
scenarios.Comment: 13 pages; v3: supersedes the published version, corrected misprint
GEO 600 and the GEO-HF upgrade program: successes and challenges
The German-British laser-interferometric gravitational wave detector GEO 600
is in its 14th year of operation since its first lock in 2001. After GEO 600
participated in science runs with other first-generation detectors, a program
known as GEO-HF began in 2009. The goal was to improve the detector sensitivity
at high frequencies, around 1 kHz and above, with technologically advanced yet
minimally invasive upgrades. Simultaneously, the detector would record science
quality data in between commissioning activities. As of early 2014, all of the
planned upgrades have been carried out and sensitivity improvements of up to a
factor of four at the high-frequency end of the observation band have been
achieved. Besides science data collection, an experimental program is ongoing
with the goal to further improve the sensitivity and evaluate future detector
technologies. We summarize the results of the GEO-HF program to date and
discuss its successes and challenges
ACBAR: The Arcminute Cosmology Bolometer Array Receiver
We describe the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a
multifrequency millimeter-wave receiver designed for observations of the Cosmic
Microwave Background (CMB) and the Sunyaev-Zel'dovich effect in clusters of
galaxies. The ACBAR focal plane consists of a 16-pixel, background-limited, 240
mK bolometer array that can be configured to observe simultaneously at 150,
220, 280, and 350 GHz. With 4-5' FWHM Gaussian beam sizes and a 3 degree
azimuth chop, ACBAR is sensitive to a wide range of angular scales. ACBAR was
installed on the 2 m Viper telescope at the South Pole in January 2001. We
describe the design of the instrument and its performance during the 2001 and
2002 observing seasons.Comment: 59 pages, 16 figures -- updated to reflect version published in ApJ
Cost-benefit analysis for commissioning decisions in GEO600
Gravitational wave interferometers are complex instruments, requiring years
of commissioning to achieve the required sensitivities for the detection of
gravitational waves, of order 10^-21 in dimensionless detector strain, in the
tens of Hz to several kHz frequency band. Investigations carried out by the
GEO600 detector characterisation group have shown that detector
characterisation techniques are useful when planning for commissioning work. At
the time of writing, GEO600 is the only large scale laser interferometer
currently in operation running with a high duty factor, 70%, limited chiefly by
the time spent commissioning the detector. The number of observable
gravitational wave sources scales as the product of the volume of space to
which the detector is sensitive and the observation time, so the goal of
commissioning is to improve the detector sensitivity with the least possible
detector down time. We demonstrate a method for increasing the number of
sources observable by such a detector, by assessing the severity of
non-astrophysical noise contaminations to efficiently guide commissioning. This
method will be particularly useful in the early stages and during the initial
science runs of the aLIGO and adVirgo detectors, as they are brought up to
design performance.Comment: 17 pages, 17 figures, 2 table
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