265 research outputs found
Stuffed Rare Earth Pyrochlore Solid Solutions
Synthesis and crystal structures are described for the compounds
Ln2(Ti2-xLnx)O7-x/2, where Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu, and x ranges from 0
to 0.67. Rietveld refinements on X-ray powder diffraction data indicate that in
Tb and Dy titanate pyrochlores, extra Ln3+ cations mix mainly on the Ti4+ site
with little disorder on the original Ln3+ site. For the smaller rare earths
(Ho-Lu), stuffing additional lanthanide ions results in a pyrochlore to defect
fluorite transition, where the Ln3+ and Ti4+ ions become completely randomized
at the maximum (x=0.67). In all of these Ln-Ti-O pyrochlores, the addition of
magnetic Ln3+ in place of nonmagnetic Ti4+ adds edge sharing tetrahedral spin
interactions to a normally corner sharing tetrahedral network of spins. The
increase in spin connectivity in this family of solid solutions represents a
new avenue for investigating geometrical magnetic frustration in the rare earth
titanate pyrochlores.Comment: 25 pages, 7 figures, submitted to J. Solid State Che
Using health surveillance systems data to assess the impact of AIDS and antiretroviral treatment on adult morbidity and mortality in Botswana
Introduction: Botswana's AIDS response included free antiretroviral treatment (ART) since 2002, achieving 80% coverage of persons with CD450% and >30% through 2011, while continuing to increase in older women. Conclusions: Adult mortality in Botswana fell markedly as ART coverage increased. HIV prevalence declines may reflect ART-associated reductions in sexual transmission. Triangulation of surveillance system data offers a reasonable approach to evaluate impact of HIV/AIDS interventions, complementing cohort approaches that monitor individual-level health outcomes
Spallation reactions. A successful interplay between modeling and applications
The spallation reactions are a type of nuclear reaction which occur in space
by interaction of the cosmic rays with interstellar bodies. The first
spallation reactions induced with an accelerator took place in 1947 at the
Berkeley cyclotron (University of California) with 200 MeV deuterons and 400
MeV alpha beams. They highlighted the multiple emission of neutrons and charged
particles and the production of a large number of residual nuclei far different
from the target nuclei. The same year R. Serber describes the reaction in two
steps: a first and fast one with high-energy particle emission leading to an
excited remnant nucleus, and a second one, much slower, the de-excitation of
the remnant. In 2010 IAEA organized a worskhop to present the results of the
most widely used spallation codes within a benchmark of spallation models. If
one of the goals was to understand the deficiencies, if any, in each code, one
remarkable outcome points out the overall high-quality level of some models and
so the great improvements achieved since Serber. Particle transport codes can
then rely on such spallation models to treat the reactions between a light
particle and an atomic nucleus with energies spanning from few tens of MeV up
to some GeV. An overview of the spallation reactions modeling is presented in
order to point out the incomparable contribution of models based on basic
physics to numerous applications where such reactions occur. Validations or
benchmarks, which are necessary steps in the improvement process, are also
addressed, as well as the potential future domains of development. Spallation
reactions modeling is a representative case of continuous studies aiming at
understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie
Using the past to constrain the future: how the palaeorecord can improve estimates of global warming
Climate sensitivity is defined as the change in global mean equilibrium
temperature after a doubling of atmospheric CO2 concentration and provides a
simple measure of global warming. An early estimate of climate sensitivity,
1.5-4.5{\deg}C, has changed little subsequently, including the latest
assessment by the Intergovernmental Panel on Climate Change.
The persistence of such large uncertainties in this simple measure casts
doubt on our understanding of the mechanisms of climate change and our ability
to predict the response of the climate system to future perturbations. This has
motivated continued attempts to constrain the range with climate data, alone or
in conjunction with models. The majority of studies use data from the
instrumental period (post-1850) but recent work has made use of information
about the large climate changes experienced in the geological past.
In this review, we first outline approaches that estimate climate sensitivity
using instrumental climate observations and then summarise attempts to use the
record of climate change on geological timescales. We examine the limitations
of these studies and suggest ways in which the power of the palaeoclimate
record could be better used to reduce uncertainties in our predictions of
climate sensitivity.Comment: The final, definitive version of this paper has been published in
Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All
rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso
Asteroid Confusions with Extremely Large Telescopes
Asteroids can be considered as sources of contamination of point sources and
also sources of confusion noise, depending whether their presence is detected
in the image or their flux is under the detection limit. We estimate that at
low ecliptic latitudes, ~10,000--20,000 asteroids/sq. degree will be detected
with an E-ELT like telescope, while by the end of Spitzer and Herschel
missions, infrared space observatories will provide ~100,000 serendipitous
asteroid detections. The detection and identification of asteroids is therefore
an important step in survey astronomy.Comment: 8 pages, 4 figures, accepted by Earth, Moon and Planets, ELT
Conference (Elba, 2009 Sept.) S
A Systematic Evaluation of Cost-Saving Dosing Regimens for Therapeutic Antibodies and Antibody-Drug Conjugates for the Treatment of Lung Cancer
Background: Expensive novel anticancer drugs put a serious strain on healthcare budgets, and the associated drug expenses limit access to life-saving treatments worldwide. Objective: We aimed to develop alternative dosing regimens to reduce drug expenses. Methods: We developed alternative dosing regimens for the following monoclonal antibodies used for the treatment of lung cancer: amivantamab, atezolizumab, bevacizumab, durvalumab, ipilimumab, nivolumab, pembrolizumab, and ramucirumab; and for the antibody-drug conjugate trastuzumab deruxtecan. The alternative dosing regimens were developed by means of modeling and simulation based on the population pharmacokinetic models developed by the license holders. They were based on weight bands and the administration of complete vials to limit drug wastage. The resulting dosing regimens were developed to comply with criteria used by regulatory authorities for in silico dose development. Results: We found that alternative dosing regimens could result in cost savings that range from 11 to 28%, and lead to equivalent pharmacokinetic exposure with no relevant increases in variability in exposure. Conclusions: Dosing regimens based on weight bands and the use of complete vials to reduce drug wastage result in less expenses while maintaining equivalent exposure. The level of evidence of our proposal is the same as accepted by regulatory authorities for the approval of alternative dosing regimens of other monoclonal antibodies in oncology. The proposed alternative dosing regimens can, therefore, be directly implemented in clinical practice.</p
The pK0\Sigma+ final state in proton-proton collisions
This paper reports results from a study of the reaction pp->pK0\Sigma+ at
beam momenta of p_{beam} = 2950, 3059, and 3200 MeV/c (excess energies of
\epsilon= 126, 161, and 206 MeV). Total cross sections were determined for all
energies; a set of differential cross sections (Dalitz plots; invariant mass
spectra of all two-body subsystems; angular distributions of all final state
particles; distributions in helicity and Jackson frames) are presented for
\epsilon= 161 MeV. The total cross sections are proportional to the volume of
available three-body phase-space indicating that the transition matrix element
does not change significantly in this range of excess energies. It is concluded
from the differential data that the reaction proceeds dominantly via the
N(1710)P_{11} and/or N(1720)P_{13} resonance(s); N(1650)S_{11} and
\Delta(1600)P_{33} could also contribute.Comment: 15 pages, 10 figure
- …