8,727 research outputs found
The Cosmic Microwave Background and the Ionization History of the Universe
Details of how the primordial plasma recombined and how the universe later
reionized are currently somewhat uncertain. This uncertainty can restrict the
accuracy of cosmological parameter measurements from the Cosmic Microwave
Background (CMB). More positively, future CMB data can be used to constrain the
ionization history using observations. We first discuss how current
uncertainties in the recombination history impact parameter constraints, and
show how suitable parameterizations can be used to obtain unbiased parameter
estimates from future data. Some parameters can be constrained robustly,
however there is clear motivation to model recombination more accurately with
quantified errors. We then discuss constraints on the ionization fraction
binned in redshift during reionization. Perfect CMB polarization data could in
principle distinguish different histories that have the same optical depth. We
discuss how well the Planck satellite may be able to constrain the ionization
history, and show the currently very weak constraints from WMAP three-year
data.Comment: Changes to match MNRAS accepted versio
Surface sticking probabilities for sputtered atoms of Nb-93 and Rh-103
The capture coefficient probabilities for sputtered atoms of Nb-93 and Rh-103 incident on Al2O3 surfaces were measured using the backscattering of MeV heavy ions. In the circumstance where the collecting surface is thickly covered, the sticking probabilities integrated over the energy distribution of sputtered atoms are 0.97 plus or minus 0.01 for Nb-93 and 0.95 plus or minus 0.01 for Rh-103 respectively. In the limit of negligible areal coverage of the collector, the accuracy is less; in this case the sticking probabilities are 0.97 + 0.03 or -0.08 and 0.95 + 0.05 or -0.08
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A learning object success story
This paper outlines an approach to designing a course entirely in learning objects. It provides a theoretical basis for the design and then presents evaluation data from a master’s level course using this design. It also describes several re-uses of the learning objects on other courses and in different contexts. Each learning object is conceived as a whole learning experience, thus avoiding many of the problems associated with assembling components of disparate kinds
Magnetic properties of PrCu at high pressure
We report a study of the low-temperature high-pressure phase diagram of the
intermetallic compound PrCu, by means of molecular-field calculations and
Cu nuclear-quadrupole-resonance (NQR) measurements under pressure.
The pressure-induced magnetically-ordered phase can be accounted for by
considering the influence of the crystal electric field on the electron
orbitals of the Pr ions and by introducing a pressure-dependent exchange
interaction between the corresponding local magnetic moments. Our experimental
data suggest that the order in the induced antiferromagnetic phase is
incommensurate. The role of magnetic fluctuations both at high and low
pressures is also discussed.Comment: 7 pages, 6 figures, submitted to Eur. Phys. J.
Imaging Diagnosis – The Computed Tomographic Appearance of a Giant Cell Tumor affecting the mandible in a pygmy goat
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OER Evidence Report 2013-2014
The Open Educational Resources Research Hub (OER Research Hub) provides a focus for research, designed to give answers to the overall question ‘What is the impact of OER on learning and teaching practices?’ and identify the particular influence of openness. We do this by working in collaboration with projects across four education sectors (K12, college, higher education and informal) extending a network of research with shared
methods and shared results.
The project combines:
– Targeted research collaboration with high profile OER projects
– A programme of international fellowship
– Global networking and expertise in OER implementation and evaluation
– A hub for research data and excellence in practice
This report is an interim review of evidence recorded against the key hypotheses that focus the research of the
OER Research Hub project
Changes in movement symmetry over the stages of the shoeing process in military working horses
Meteorological factors in Earth-satellite propagation
Using the COMSTAR D/4 28.56 GHz beacon as a source, a differential gain experiment was performed by connecting a 5-meter paraboloidal antenna and a 0.6-meter paraboloidal antenna alternately to the same receiver. Substantial differential gain changes were observed during some, but not all, rain events. A site-diversity experiment was implemented which consists of two 28.56 GHz radiometers separated by 9 km. The look-angle corresponds to that of the D/4 beacon, and data were obtained with one radiometer during several weeks of concurrent beacon operation to verify the system calibration. A theoretical study of the effect of scattering from a nonuniform rain distribution along the path is under way to aid in interpreting the results of this experiment. An improved empirical site diversity-gain model was derived from data in the literature relating to 34 diversity experiments. Work on the experiment control and data acquisition system is continuing with a view toward future experiments
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