8,236 research outputs found
A preliminary design study of a microparticle accelerator final report, 30 jan. - 13 apr. 1964
Design study for 2MV microparticle accelerato
Mechanical and microstructural investigations of tungsten and doped tungsten materials produced via powder injection molding
The physical properties of tungsten such as the high melting point of 3420°C, the high strength and thermal conductivity, the low thermal expansion and low erosion rate make this material attractive as a plasma facing material. However, the manufacturing of such tungsten parts by mechanical machining such as milling and turning is extremely costly and time intensive because this material is very hard and brittle. Powder Injection Molding (PIM) as special process allows the mass production of components, the joining of different materials without brazing and the creation of composite and prototype materials, and is an ideal tool for scientific investigations. This contribution describes the characterization and analyses of prototype materials produced via PIM. The investigation of the pure tungsten and oxide or carbide doped tungsten materials comprises the microstructure examination, element allocation, texture analyses, and mechanical testing via four-point bend (4-PB). Furthermore, the different materials were characterized by high heat flux (HHF) tests applying transient thermal loads at different base temperatures to address thermal shock and thermal fatigue performance. Additionally, HHF investigations provide information about the thermo-mechanical behavior to extreme steady state thermal loading and measurements of the thermal conductivity as well as oxidation tests were done. Post mortem analyses are performed quantifying and qualifying the occurring damage with respect to reference tungsten grades by metallographic and microscopical means
Parallax of PSR J1744-1134 and the Local Interstellar Medium
We present the annual trigonometric parallax of PSR J1744-1134 derived from
an analysis of pulse times of arrival. The measured parallax, pi = 2.8+/-0.3
mas ranks among the most precisely determined distances to any pulsar. The
parallax distance of 357+/-39 pc is over twice that derived from the dispersion
measure using the Taylor & Cordes model for the Galactic electron distribution.
The mean electron density in the path to the pulsar, n_e = (0.0088 +/- 0.0009)
cm^{-3}, is the lowest for any disk pulsar. We have compared the n_e for PSR
J1744-1134 with those for another 11 nearby pulsars with independent distance
estimates. We conclude that there is a striking asymmetry in the distribution
of electrons in the local interstellar medium. The electron column densities
for pulsars in the third Galactic quadrant are found to be systematically
higher than for those in the first. The former correlate with the position of
the well known local HI cavity in quadrant three. The excess electrons within
the cavity may be in the form of HII clouds marking a region of interaction
between the local hot bubble and a nearby superbubble.Comment: revised version accepted for publication in ApJ Letters; reanalysis
of uncertainty in parallax measure and changes to fig
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A new microtelesensor chip for meteorology
A new technology exploiting commercial, micro-sensors developed for atomic force microscopy offers breakthrough capability in high accuracy wireless sensors for meteorological measurements. Historically sensors used in air-borne and buoy-based platforms required compromises in performance to achieve the low-weight and low power requirements of the mobile platforms. Recent innovations in microelectromechanical systems (MEMS) provided opportunities to reduce size, weight, and power requirements but each sensor required a specially fabricated device with inherent calibration, repeatability, and traceability problems. This new approach allows identical sensors to be fabricated on the same semiconductor substrate as the conditioning electronics and the telemetry components. Exploiting semiconductor fabrication technology offers the potential to reduce fabrication costs to a few dollars per component. Sensing humidity, temperature and pressure have been demonstrated with plans for meteorological deployment scheduled for later in 1997. Cost, reliability, size, power consumption, and accuracy are key factors in the deployment of advanced meteorological sensor arrays. ORNL is actively integrating the sensing technologies, electronic processing, and telemetry that build a family of sensors with multiple-input capabilities. One of the key elements in ORNL`s sensor technology is coated microcantilever arrays, which form a powerful universal platform for multiple physical and chemical measurements. Telemetry is also being developed to add robust spread-spectrum data transmission capabilities to the necessary signal processing electronics. In collaboration with the NOAA Atmospheric Turbulence and Diffusion Lab, a chip-level temperature/humidity module with onboard telemetry is slated for demonstration later in 1997. Future additions would include sensors for atmospheric pressure, wind velocity, turbulence measurement, and radiometry
Trapped-Ion Quantum Simulator: Experimental Application to Nonlinear Interferometers
We show how an experimentally realized set of operations on a single trapped
ion is sufficient to simulate a wide class of Hamiltonians of a spin-1/2
particle in an external potential. This system is also able to simulate other
physical dynamics. As a demonstration, we simulate the action of an -th
order nonlinear optical beamsplitter. Two of these beamsplitters can be used to
construct an interferometer sensitive to phase shifts in one of the
interferometer beam paths. The sensitivity in determining these phase shifts
increases linearly with , and the simulation demonstrates that the use of
nonlinear beamsplitters (=2,3) enhances this sensitivity compared to the
standard quantum limit imposed by a linear beamsplitter (=1)
A test of general relativity from the three-dimensional orbital geometry of a binary pulsar
Binary pulsars provide an excellent system for testing general relativity
because of their intrinsic rotational stability and the precision with which
radio observations can be used to determine their orbital dynamics.
Measurements of the rate of orbital decay of two pulsars have been shown to be
consistent with the emission of gravitational waves as predicted by general
relativity, providing the most convincing evidence for the self-consistency of
the theory to date. However, independent verification of the orbital geometry
in these systems was not possible. Such verification may be obtained by
determining the orientation of a binary pulsar system using only classical
geometric constraints, permitting an independent prediction of general
relativistic effects. Here we report high-precision timing of the nearby binary
millisecond pulsar PSR J0437-4715, which establish the three-dimensional
structure of its orbit. We see the expected retardation of the pulse signal
arising from the curvature of space-time in the vicinity of the companion
object (the `Shapiro delay'), and we determine the mass of the pulsar and its
white dwarf companion. Such mass determinations contribute to our understanding
of the origin and evolution of neutron stars.Comment: 5 pages, 2 figure
Harnessing Single Cell Sorting to Identify Cell Division Genes and Regulators in Bacteria
Cell division is an essential cellular process that requires an array of known and unknown proteins for its spatial and temporal regulation. Here we develop a novel, high-throughput screening method for the identification of bacterial cell division genes and regulators. The method combines the over-expression of a shotgun genomic expression library to perturb the cell division process with high-throughput flow cytometry sorting to screen many thousands of clones. Using this approach, we recovered clones with a filamentous morphology for the model bacterium, Escherichia coli. Genetic analysis revealed that our screen identified both known cell division genes, and genes that have not previously been identified to be involved in cell division. This novel screening strategy is applicable to a wide range of organisms, including pathogenic bacteria, where cell division genes and regulators are attractive drug targets for antibiotic development. © 2013 Burke et al
Recruitment of ethnic minority patients to a cardiac rehabilitation trial: The Birmingham Rehabilitation Uptake Maximisation (BRUM) study [ISRCTN72884263]
Background: Concerns have been raised about low participation rates of people from minority ethnic groups
in clinical trials. However, the evidence is unclear as many studies do not report the ethnicity of participants and
there is insufficient information about the reasons for ineligibility by ethnic group. Where there are data, there
remains the key question as to whether ethnic minorities more likely to be ineligible (e.g. due to language) or
decline to participate. We have addressed these questions in relation to the Birmingham Rehabilitation Uptake
Maximisation (BRUM) study, a randomized controlled trial (RCT) comparing a home-based with a hospital-based
cardiac rehabilitation programme in a multi-ethnic population in the UK.
Methods: Analysis of the ethnicity, age and sex of presenting and recruited subjects for a trial of cardiac
rehabilitation in the West-Midlands, UK.
Participants: 1997 patients presenting post-myocardial infarction, percutaneous transluminal coronary angioplasty
or coronary artery bypass graft surgery.
Data collected: exclusion rates, reasons for exclusion and reasons for declining to participate in the trial by ethnic
group.
Results: Significantly more patients of South Asian ethnicity were excluded (52% of 'South Asian' v 36% 'White
European' and 36% 'Other', p < 0.001). This difference in eligibility was primarily due to exclusion on the basis of
language (i.e. the inability to speak English or Punjabi). Of those eligible, similar proportions were recruited from
the different ethnic groups (white, South Asian and other). There was a marked difference in eligibility between
people of Indian, Pakistani or Bangladeshi origin
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