33,118 research outputs found
Calorimetry for ILC Experiments: CALICE Collaboration R&D
The CALICE Collaboration is carrying out research and development into
calorimetry for a detector at the International Linear Collider (ILC). CALICE
is investigating a range of technologies for both electromagnetic and hadronic
calorimetry. An overview of the prototypes and selected test-beam results are
presented.Comment: To appear in the proceedings of the ICHEP08 conferenc
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Participatory action research in the development and delivery of self-harm awareness sessions in prison: involving service users in staff development
Discovery of secular variations in the atmospheric abundances of magnetic Ap stars
The stars of the middle main sequence have relatively quiescent outer layers,
and unusual chemical abundance patterns may develop in their atmospheres. The
presence of chemical peculiarities reveal the action of such subsurface
phenomena as gravitational settling and radiatively driven levitation of trace
elements, and their competition with mixing processes such as turbulent
diffusion.
We want to establish whether abundance peculiarities change as stars evolve
on the main sequence, and provide observational constraints to diffusion
theory.
We have performed spectral analysis of 15 magnetic Bp stars that are members
of open clusters (and thus have well-known ages), with masses between about 3
and 4 M_sun. For each star, we measured the abundances of He, O, Mg, Si, Ti,
Cr, Fe, Pr and Nd.
We have discovered the systematic time evolution of trace elements through
the main-sequence lifetime of magnetic chemically peculiar stars as their
atmospheres cool and evolve toward lower gravity. During the main sequence
lifetime, we observe clear and systematic variations in the atmospheric
abundances of He, Ti, Cr, Fe, Pr and Nd. For all these elements, except He, the
atmospheric abundances decrease with age. The abundances of Fe-peak elements
converge toward solar values, while the rare-earth elements converge toward
values at least 100 times more abundant than in the Sun. Helium is always
underabundant compared to the Sun, evolving from about 1% up to 10% of the
solar He abundance. We have attempted to interpret the observed abundance
variations in the context of radiatively driven diffusion theory, which appears
to provide a framework to understand some, but not all, of the observed
anomalous abundance levels and variations.Comment: 13 pages, 5 figures, 5 tables, accepted for publication in A&
Oscillating chiral currents in nanotubes: a route to nanoscale magnetic test tubes
With a view to optimising the design of carbon-nanotube (CNT) windmills and
to maximising the internal magnetic field generated by chiral currents, we
present analytical results for the group velocity components of an electron
flux through chiral carbon nanotubes. Chiral currents are shown to exhibit a
rich behaviour and can even change sign and oscillate as the energy of the
electrons is increased. We find that the transverse velocity and associated
angular momentum of electrons is a maximum for non-metallic CNTs with a chiral
angle of 18. Such CNTs are therefore the optimal choice for CNT windmills
and also generate the largest internal magnetic field for a given longitudinal
current. For a longitudinal current of order amps, this field can be
of order Teslas, which is sufficient to produce interesting spintronic
effects and a significant contribution to the self inductance.Comment: 4 pages, 1 figur
On number fields with nontrivial subfields
What is the probability for a number field of composite degree to have a
nontrivial subfield? As the reader might expect the answer heavily depends on
the interpretation of probability. We show that if the fields are enumerated by
the smallest height of their generators the probability is zero, at least if
. This is in contrast to what one expects when the fields are enumerated
by the discriminant. The main result of this article is an estimate for the
number of algebraic numbers of degree and bounded height which generate
a field that contains an unspecified subfield of degree . If
we get the correct asymptotics as the height tends to
infinity
High temperature static strain gage alloy development program
The literature, applicable theory and finally an experimental program were used to identify new candidate alloy systems for use as the electrical resistance elements in static strain gages up to 1250K. The program goals were 50 hours of use in the environment of a test stand gas turbine engine with measurement accuracies equal to or better than 10 percent of full scale for strains up to + or - 2000 microstrain. As part of this effort, a computerized electrical resistance measurement system was constructed for use at temperatures between 300K and 1250K and heating and cooling rates of 250K/min and 10K/min. The two best alloys were an iron-chromium-aluminum alloy and a palladium base alloy. Although significant progress was made, it was concluded that a considerable additional effort would be needed to fully optimize and evaluate these candidate systems
Open and Closed Loop Stability of Hingeless Rotor Helicopter Air and Ground Resonance
The air and ground resonance instabilities of hingeless rotor helicopters are examined on a relatively broad parametric basis including the effects of blade tuning, virtual hinge locations, and blade hysteresis damping, as well as size and scale effects in the gross weight range from 5,000 to 48,000 pounds. A special case of a 72,000 pound helicopter air resonance instability is also included. The study shows that nominal to moderate and readily achieved levels of blade inertial hysteresis damping in conjunction with a variety of tuning and/or feedback conditions are highly effective in dealing with these instabilities. Tip weights and reductions in pre-coning angles are also shown to be effective means for improving the air resonance instability
Analysis and application of digital spectral warping in analog and mixed-signal testing
Spectral warping is a digital signal processing transform which shifts the frequencies contained within a signal along the frequency axis. The Fourier transform coefficients of a warped signal correspond to frequency-domain 'samples' of the original signal which are unevenly spaced along the frequency axis. This property allows the technique to be efficiently used for DSP-based analog and mixed-signal testing. The analysis and application of spectral warping for test signal generation, response analysis, filter design, frequency response evaluation, etc. are discussed in this paper along with examples of the software and hardware implementation
Climate change at the ecosystem scale: a 50-year record in New Hampshire
Observing the full range of climate change impacts at the local scale is difficult. Predicted rates of change are often small relative to interannual variability, and few locations have sufficiently comprehensive long-term records of environmental variables to enable researchers to observe the fine-scale patterns that may be important to understanding the influence of climate change on biological systems at the taxon, community, and ecosystem levels. We examined a 50-year meteorological and hydrological record from the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, an intensively monitored Long-Term Ecological Research site. Of the examined climate metrics, trends in temperature were the most significant (ranging from 0.7 to 1.3 °C increase over 40–50 year records at 4 temperature stations), while analysis of precipitation and hydrologic data yielded mixed results. Regional records show generally similar trends over the same time period, though longer-term (70–102 year) trends are less dramatic. Taken together, the results from HBEF and the regional records indicate that the climate has warmed detectably over 50 years, with important consequences for hydrological processes. Understanding effects on ecosystems will require a diversity of metrics and concurrent ecological observations at a range of sites, as well as a recognition that ecosystems have existed in a directionally changing climate for decades, and are not necessarily in equilibrium with the current climate
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