250 research outputs found
Satellite Test of the Equivalence Principle (STEP)
This grant provided support for the STEP (Satellite Test of the Equivalence Principle) program between October 1991 and September 1993. STEP, previously supported by NASA under Grant NAG8-837 'A Satellite Test of the Equivalence Principle,' was selected by the European Space Agency for a Phase A study as a candidate for ESA's next medium size mission (M2). STEP was conceived as a joint NASA/ESA mission with equal participation by both agencies. ESA's contribution to the program would be the spacecraft; NASA would provide the launcher and half of the instrument, while the other half of the instrument would be provided by various European agencies. STEP was in competition with three other programs, INTEGRAL, PRISMA, and MARSNET. The final selection of a single mission for M2 took place in April 1993. STEP was not selected for M2 but made a very close second. The program is continuing in modified form
The Stanford equivalence principle program
The Stanford Equivalence Principle Program (Worden, Jr. 1983) is intended to test the uniqueness of free fall to the ultimate possible accuracy. The program is being conducted in two phases: first, a ground-based version of the experiment, which should have a sensitivity to differences in rate of fall of one part in 10(exp 12); followed by an orbital experiment with a sensitivity of one part in 10(exp 17) or better. The ground-based experiment, although a sensitive equivalence principle test in its own right, is being used for technology development for the orbital experiment. A secondary goal of the experiment is a search for exotic forces. The instrument is very well suited for this search, which would be conducted mostly with the ground-based apparatus. The short range predicted for these forces means that forces originating in the Earth would not be detectable in orbit. But detection of Yukawa-type exotic forces from a nearby large satellite (such as Space Station) is feasible, and gives a very sensitive and controllable test for little more effort than the orbiting equivalence principle test itself
Towards risk-informed PBSHM: Populations as hierarchical systems
The prospect of informed and optimal decision-making regarding the operation
and maintenance (O&M) of structures provides impetus to the development of
structural health monitoring (SHM) systems. A probabilistic risk-based
framework for decision-making has already been proposed. However, in order to
learn the statistical models necessary for decision-making, measured data from
the structure of interest are required. Unfortunately, these data are seldom
available across the range of environmental and operational conditions
necessary to ensure good generalisation of the model.
Recently, technologies have been developed that overcome this challenge, by
extending SHM to populations of structures, such that valuable knowledge may be
transferred between instances of structures that are sufficiently similar. This
new approach is termed population-based structural heath monitoring (PBSHM).
The current paper presents a formal representation of populations of
structures, such that risk-based decision processes may be specified within
them. The population-based representation is an extension to the hierarchical
representation of a structure used within the probabilistic risk-based decision
framework to define fault trees. The result is a series, consisting of systems
of systems ranging from the individual component level up to an inventory of
heterogeneous populations. The current paper considers an inventory of wind
farms as a motivating example and highlights the inferences and decisions that
can be made within the hierarchical representation.Comment: Submitted to IMAC-XLI conference (2023), Austin, Texas, US
A decision framework for selecting information-transfer strategies in population-based SHM
Decision-support for the operation and maintenance of structures provides
significant motivation for the development and implementation of structural
health monitoring (SHM) systems. Unfortunately, the limited availability of
labelled training data hinders the development of the statistical models on
which these decision-support systems rely. Population-based SHM seeks to
mitigate the impact of data scarcity by using transfer learning techniques to
share information between individual structures within a population. The
current paper proposes a decision framework for selecting transfer strategies
based upon a novel concept -- the expected value of information transfer --
such that negative transfer is avoided. By avoiding negative transfer, and by
optimising information transfer strategies using the transfer-decision
framework, one can reduce the costs associated with operating and maintaining
structures, and improve safety.Comment: 12 pages, 2 figures. Author accepted manuscript in Proceedings of the
14th International Workshop on Structural Health Monitoring, Stanford
University, California, USA. 202
The genome of Clostridium difficile 5.3
Background Clostridium difficile is the leading cause of infectious diarrhea in humans and responsible for large outbreaks of enteritis in neonatal pigs in both North America and Europe. Disease caused by C. difficile typically occurs during antibiotic therapy and its emergence over the past 40 years is linked with the widespread use of broad-spectrum antibiotics in both human and veterinary medicine. Results We sequenced the genome of Clostridium difficile 5.3 using the Illumina Nextera XT and MiSeq technologies. Assembly of the sequence data reconstructed a 4,009,318 bp genome in 27 scaffolds with an N50 of 786 kbp. The genome has extensive similarity to other sequenced C. difficile genomes, but also has several genes that are potentially related to virulence and pathogenicity that are not present in the reference C. difficile strain. Conclusion Genome sequencing of human and animal isolates is needed to understand the molecular events driving the emergence of C. difficile as a gastrointestinal pathogen of humans and food animals and to better define its zoonotic potential
A cryogenic liquid-mirror telescope on the moon to study the early universe
We have studied the feasibility and scientific potential of zenith observing
liquid mirror telescopes having 20 to 100 m diameters located on the moon. They
would carry out deep infrared surveys to study the distant universe and follow
up discoveries made with the 6 m James Webb Space Telescope (JWST), with more
detailed images and spectroscopic studies. They could detect objects 100 times
fainter than JWST, observing the first, high-red shift stars in the early
universe and their assembly into galaxies. We explored the scientific
opportunities, key technologies and optimum location of such telescopes. We
have demonstrated critical technologies. For example, the primary mirror would
necessitate a high-reflectivity liquid that does not evaporate in the lunar
vacuum and remains liquid at less than 100K: We have made a crucial
demonstration by successfully coating an ionic liquid that has negligible vapor
pressure. We also successfully experimented with a liquid mirror spinning on a
superconducting bearing, as will be needed for the cryogenic, vacuum
environment of the telescope. We have investigated issues related to lunar
locations, concluding that locations within a few km of a pole are ideal for
deep sky cover and long integration times. We have located ridges and crater
rims within 0.5 degrees of the North Pole that are illuminated for at least
some sun angles during lunar winter, providing power and temperature control.
We also have identified potential problems, like lunar dust. Issues raised by
our preliminary study demand additional in-depth analyses. These issues must be
fully examined as part of a scientific debate we hope to start with the present
article.Comment: 35 pages, 11 figures. To appear in Astrophysical Journal June 20 200
Report on Archaeological Investigations Conducted at the St. Mary's Site (18AP45), 107 Duke of Gloucester Street, Annapolis, Maryland, 1987-1990
In celebration of the 250th anniversary of the birth of Charles Carroll of Carrollton, Archaeology in Annapolis was invited to excavate the Carroll House and garden on 107 Duke of Gloucester Street in Annapolis, Maryland. The site, named the St. Mary's Site (18AP45) for the Catholic church on the property, is currently owned by the Redemptorists, a Roman Catholic congregation of priests and brothers who have occupied the site since 1852. Prior to the Redemptorists' tenure, the site was owned by the Carroll family from 1701-1852 and is perhaps best known as the home of Charles Carroll of Carrollton (1737-1832), signer of the Declaration of Independence. Excavations at the site were conducted during four consecutive summer seasons from 1987-1990. The investigation focused on three research questions. The first line of inquiry were questions surrounding the dating, architectural configuration, and artifact deposits of the "frame house," a structure adjoining the west wall of the brick Carroll House via a "passage" and later a three story addition. The frame house was partially demolished in the mid-nineteenth century but the construction was thought to pre-date the brick portion of the house. The second research question was spurred by documentary research which indicated that the property might have been the location of Proctor's Tavern, a late 17th-century tavern which served as the meeting place of the Maryland Provincial Assembly. Archaeological testing hoped to determine its location and, if found, investigate Annapolis' early Euro-American occupation. The third research question focused on the landscape of the site as it was shaped by its occupants over the past three hundred years. The research questions included investigating the stratigraphy, geometry, and architectural and planting features of Charles Carroll of Carrollton's terraced garden built during the 1770s, and investigating the changes to the landscape made by the Redemptorists in the nineteenth and twentieth centuries. While no structural evidence associated with Proctor’s Tavern was uncovered during limited
excavations along Spa Creek, the historic shore of Spa Creek was identified, buried beneath deep
fill deposits laid down during construction of the Carroll Garden. Features and deposits associated
with this period likely remain intact in a waterlogged environment along the southeastern sea wall at
the St. Mary’s Site. Evidence of extensive earth moving by Carroll is present in the garden and was
identified during excavation and coring. This strongly suggests that the garden landscape visible at
the St. Mary’s Site is the intact Carroll Garden, which survives beneath contemporary and late nineteenth
century strata. The extant surviving garden should be considered highly sensitive to
ground-disturbing activities, and is also highly significant considering demonstrable associations
with the Carroll family. Other garden-related features were also discovered, including planting
holes, and a brick pavilion or parapet located along Spa Creek to the south of the site. The Duke of
Gloucester Street wall was shown to be associated with the Carroll occupation of the site. Finally,
intensive archaeological research was directed at the vicinity of a frame house constructed and
occupied by the Carrolls to the east of the existing brick house, which was replaced by the
Redemptorists in the nineteenth century with a greenhouse. These superimposed buildings were
documented in detail and remain highly significant features at the St. Mary’s Site
- …