677 research outputs found
Soldiers of the Spirit
This fireside address was given at the BYU Law School on March 12, 1995
In Search of Atticus Finch
This satellite fireside address was given to the J. Reuben Clark Law Society at the Conference Center in Salt Lake City on February 10, 2006
Soldiers of the Spirit
This fireside address was given at the BYU Law School on March 12, 1995
Determining selection across heterogeneous landscapes: a perturbation-based method and its application to modeling evolution in space
Spatial structure can decisively influence the way evolutionary processes unfold. Several methods have thus far been used to study evolution in spatial systems, including population genetics, quantitative genetics, momentclosure approximations, and individual-based models. Here we extend the study of spatial evolutionary dynamics to eco-evolutionary models based on reaction-diffusion equations and adaptive dynamics. Specifically, we derive expressions for the strength of directional and stabilizing/disruptive selection that apply in both continuous space and to metacommunities with symmetrical dispersal between patches. For directional selection on a quantitative trait, this yields a way to integrate local directional selection across space and determine whether the trait value will increase or decrease. The robustness of this prediction is validated against quantitative genetics. For stabilizing/disruptive selection, we show that spatial heterogeneity always contributes to disruptive selection and hence always promotes evolutionary branching. The expression for directional selection is numerically very effi- cient, and hence lends itself to simulation studies of evolutionary community assembly. We illustrate the application and utility of the expressions for this purpose with two examples of the evolution of resource utilization. Finally, we outline the domain of applicability of reaction-diffusion equations as a modeling framework and discuss their limitations
Breastfeeding, asthma, and allergy : a tale of two cities
BACKGROUND: The effect of breastfeeding duration on subsequent asthma and allergy remains the subject of much controversy.
OBJECTIVE: To investigate whether differences in study design or disease-related exposure modification were the cause of the differences in study findings.
METHOD: The data from two cohorts, the Childhood Asthma Prevention Study (CAPS) from Australia and the Barn Allergi Miljo Stockholm cohort from Sweden, which had reported different findings on the association between breastfeeding and asthma, were combined. For this analysis, the definitions for breastfeeding, asthma, and allergy were harmonized. Subjects were included if they had at least one parent with wheeze or asthma and had a gestational age of more than 36 wks (combined n = 882). The risk of disease-related exposure modification was assessed using survival analysis.
RESULTS: Breastfeeding reduced the risk of asthma at 4/5 and 8 yrs of age in children with a family history of asthma. The effect was stronger in the Swedish cohort. Breastfeeding had no effect on the prevalence of sensitization to inhaled allergens in this cohort with a family history of asthma but was a risk factor for sensitization to cow's milk, peanuts, and eggs in the CAPS cohort at 4/5 yrs and in the combined cohort at 8 yrs. There was no evidence to support the existence of disease-related exposure modification in either cohort.
CONCLUSION: These findings point to the importance of harmonization of features of study design, including subject selection criteria and variable definitions, in resolving epidemiological controversies such as those surrounding the impact of breastfeeding on asthma and allergic sensitization.National Health and Medical Research Council of AustraliaStockholm County CouncilHjärt- och LungfondenThe Swedish Asthma and Allergy AssociationVetenskapsrådetThe Centre for Allergy research Karolinska InstitutetManuscrip
Development and operation of a pixel segmented liquid-filled linear array for radiotherapy quality assurance
A liquid isooctane (CH) filled ionization linear array for
radiotherapy quality assurance has been designed, built and tested. The
detector consists of 128 pixels, each of them with an area of 1.7 mm
1.7 mm and a gap of 0.5 mm. The small pixel size makes the detector ideal for
high gradient beam profiles like those present in Intensity Modulated Radiation
Therapy (IMRT) and radiosurgery. As read-out electronics we use the X-Ray Data
Acquisition System (XDAS) with the Xchip developed by the CCLRC.
Studies concerning the collection efficiency dependence on the polarization
voltage and on the dose rate have been made in order to optimize the device
operation.
In the first tests we have studied dose rate and energy dependences, and
signal reproducibility. Dose rate dependence was found lower than 2.5 % up to 5
Gy min, and energy dependence lower than 2.1 % up to 20 cm depth in
solid water. Output factors and penumbras for several rectangular fields have
been measured with the linear array and were compared with the results obtained
with a 0.125 cm air ionization chamber and radiographic film,
respectively. Finally, we have acquired profiles for an IMRT field and for a
virtual wedge. These profiles have also been compared with radiographic film
measurements. All the comparisons show a good correspondence. Signal
reproducibility was within a 2% during the test period (around three months).
The device has proved its capability to verify on-line therapy beams with
good spatial resolution and signal to noise ratio.Comment: 16 pages, 12 figures Submitted to Phys. Med. Bio
Source control options for reducing emission of priority pollutants from urban areas.
The overall aim of the ScorePP project is to develop comprehensive and appropriate source
control strategies that authorities, cities, water utilities and the chemical industry can employ
to reduce emissions of priority pollutants (PPs) from urban areas into the receiving water
environment. Focus is on the 33 priority and priority hazardous substances and substance
groups identified in the European Water Framework Directive. However, this list may be
expanded to include emerging pollutants or reduced if appropriate model compounds can be
identified. The initial work focuses on 67 substances, including substances identified in the
proposed European environmental quality standard (EQS) directive as well as the defined
example compounds and several organometallic derivatives. Information on inherent
properties, environmental presence and fate, and legislative issues is made available in open
database format, and a data management system combining chemical identification (CAS#),
NACE economic activity classifications and NOSE-P emission source classifications has been
developed as a basis for spatial characterisation of PP sources using GIS. Further work will
focus on dynamic urban scale source-flux models, identifying emission patterns and
optimising monitoring programmes in case studies and multi-criteria comparison of source
control versus end-of-pipe mitigation options in relation to their economic, social and
environmental impacts
Mossbauer spectroscopy study of the "mysterious" magnetic transition in lambda-(BETS)2FeCl4
The compound lambda-(BETS)2FeCl4 provides an effective demonstration of the
interaction of pi-conduction electron and d-electron localized moment systems
in molecular crystalline materials where antiferromagnetic insulating and
magnetic field induced superconducting states can be realized. The
metal-insulator transition has been thought to be cooperative, involving both
the itinerant pi- electron and localized d-electron spins where
antiferromagnetic order appears in both systems simultaneously. However, recent
specific heat data has indicated otherwise [Akiba et al., J. Phys. Soc. Japan
78,033601(2009)]: although the pi-electron system orders antiferromagnetically
and produces a metal-insulator transition, a "mysterious" paramagnetic
d-electron state remains. We report 57Fe Mossbauer measurements that support
the paramagnetic model, provided the d-electron spins remain in a fast
relaxation state below the transition. From the measured hyperfine fields, we
also determine the temperature dependence of the pi-d electron exchange field.Comment: 10 pages, 3 figures, 1 tabl
Strontium as a tracer of weathering processes in a silicate catchment polluted by acid atmospheric inputs, Strengbach, France
This paper determines the weathering and atmospheric contributions of Ca in surface water from a small spruce forested silicate catchment (N–E France) receiving acid atmospheric inputs. The bedrock is a granite with K-feldspar and albite as dominant phases. The calcium content in plagioclase is low and the Ca/Na ratio in surface water is high, reflecting other sources of calcium from those expected from the weathering of major mineral phases. The biotite content is low. Only traces of apatite were detected while no calcite was found in spite of a major hydrothermal event having affected the granite. The strontium isotopic ratio 87Sr/86Sr and Sr content was used as a tracer of weathering and was determined in minerals and bulk bedrock, open field precipitation, throughfall, soil solution, spring and stream water. The Sr isotopic ratio of the reacting weathering end-member was predicted by simulating the alteration of the granite minerals by incorporating strontium into the water–rock interaction kinetic code KINDIS. In the early stages of water–rock interaction, K-feldspar and biotite strongly influence the isotopic composition of the weathering solution whereas, the Na-rich plagioclase appears to be the main long-term reactive weathering end-member. Approximately 50% of dissolved Sr in streamwater are atmospherically derived. The 87Sr/86Sr ratios of exchangeable Sr in the fine fraction at 1-m depth from a soil profile indicate that the amount of exchangeable Sr seems essentially controlled by atmospheric inputs. The exception is the deep saprolite where weathering processes could supply the Sr (and Ca). Na-Plagioclase weathering obviously control the chemistry and the isotopic composition of surface waters. The weathering of trace mineral plays a secondary role, the exception is for apatite when plagioclase is absent. Our hydrochemical, mineralogical and isotopic investigations show that a major part of the strong Ca losses detected in catchment hydrochemical budgets that result from the neutralization of acid precipitation has an atmospheric origin. Consequently, in the long term, in such areas, the availability of such an exchangeable base cation might be strongly limited and surface waters consequently acidified
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