162 research outputs found
Soil cohesion as affected by freezing, water content, time and tillage
This study was developed to determine whether there are substantial
annual changes in soil cohesion and to identify major factors
causing those changes. Aggregate stability was measured throughout
the year on soils in Utah and Idaho using wet sieving techniques.
Stability generally increased during spring and summer months.
Major decreases of cohesion, found when minimum daily air temperatures
fell to or below 0 °C during winter and early spring months,
were attributed to pressures and associated shearing forces caused
by freezing at high water contents. Equivalent disruption occurred
when confined soils were frozen in controlled laboratory studies.
Disruption also increased as water content at the time of freezing
increased for all soils studied. Disruption of soil by rototilling and
compaction significantly decreased soil cohesion
Mechanisms by which surge irrigation reduces furrow infiltration rates in a silty loam soil
SURGE irrigation, the intermittent supply of water to
furrows or borders, generally reduces infiltration
rates. However, the degree of infiltration reduction is
variable and difficult to predict. Mechanisms by which
surge irrigation reduces infiltration rates include (a)
consolidation of the furrow perimeter due to increased
soil water tension during flow interruptions, (b) filling of
cracks which develop during flow interruptions with bed
load during the following surge, (c) forced settlement of
suspended sediment on the furrow perimeter when the
water supply is interrupted, and (d) greater sediment
detachment and movement caused by more rapid
advance of the surged stream front
Dynamics of intervention adoption, implementation, and maintenance inside organizations: The case of an obesity prevention initiative
Overall impact of public health prevention interventions relies not only on the average efficacy of an intervention, but also on the successful adoption, implementation, and maintenance (AIM) of that intervention. In this study, we aim to understand the dynamics that regulate AIM of organizational level intervention programs. We focus on two well-documented obesity prevention interventions, implemented in food carry-outs and stores in low-income urban areas of Baltimore, Maryland, which aimed to improve dietary behaviour for adults by providing access to healthier foods and point-of-purchase promotions. Building on data from field observations, in-depth interviews, and data discussed in previous publications, as well as the strategy and organizational behaviour literature, we developed a system dynamics model of the key processes of AIM. With simulation analysis, we show several reinforcing mechanisms that span stakeholder motivation, communications, and implementation quality and costs can turn small changes in the process of AIM into big difference in the overall impact of the intervention. Specifically, small changes in the allocation of resources to communication with stakeholders of intervention could have a nonlinear long-term impact if those additional resources can turn stakeholders into allies of the intervention, reducing the erosion rates and enhancing sustainability. We present how the dynamics surrounding communication, motivation, and erosion can create significant heterogeneity in the overall impact of otherwise similar interventions. Therefore, careful monitoring of how those dynamics unfold, and timely adjustments to keep the intervention on track are critical for successful implementation and maintenance
Tau Polarization Asymmetry in
Rare decays provide an opportunity to probe for new physics beyond the
Standard Model. In this paper, we propose to measure the tau polarization in
the inclusive decay and discuss how it can be used, in
conjunction with other observables, to completely determine the parameters of
the flavor-changing low-energy effective Hamiltonian. Both the Standard Model
and several new physics scenarios are examined. This process has a large enough
branching fraction, , such that sufficient
statistics will be provided by the B-Factories currently under construction.Comment: 11 pages, LaTex file with psfig. Figures included via uufiles.
Lengthened version. Includes new calculation of Monte Carlo fit to Wilson
coefficient
Country-specific effects of neonicotinoid pesticides on honey bees and wild bees
Neonicotinoid seed dressings have caused concern world-wide. We use large field experiments to assess the effects of neonicotinoid-treated crops on three bee species across three countries (Hungary, Germany, and the United Kingdom). Winter-sown oilseed rape was grown commercially with either seed coatings containing neonicotinoids (clothianidin or thiamethoxam) or no seed treatment (control). For honey bees, we found both negative (Hungary and United Kingdom) and positive (Germany) effects during crop flowering. In Hungary, negative effects on honey bees (associated with clothianidin) persisted over winter and resulted in smaller colonies in the following spring (24% declines). In wild bees (Bombus terrestris and Osmia bicornis), reproduction was negatively correlated with neonicotinoid residues. These findings point to neonicotinoids causing a reduced capacity of bee species to establish new populations in the year following exposure
Inflation: flow, fixed points and observables to arbitrary order in slow roll
I generalize the inflationary flow equations of Hoffman and Turner to
arbitrary order in slow roll. This makes it possible to study the predictions
of slow roll inflation in the full observable parameter space of tensor/scalar
ratio , spectral index , and running . It also becomes
possible to identify exact fixed points in the parameter flow. I numerically
evaluate the flow equations to fifth order in slow roll for a set of randomly
chosen initial conditions and find that the models cluster strongly in the
observable parameter space, indicating a ``generic'' set of predictions for
slow roll inflation. I comment briefly on the the interesting proposed
correspondence between flow in inflationary parameter space and renormalization
group flow in a boundary conformal field theory.Comment: 16 pages, 7 figures. LaTeX. V4: Fixed important error in numerical
constant in the second-order slow roll expressions for the observables r, n,
and dn/dlog(k). See footnote after Eq. (48). New figures, minor changes to
conclusions. Supersedes version published in Phys. Rev.
On the spin distributions of CDM haloes
We used merger trees realizations, predicted by the extended Press-Schechter
theory, in order to study the growth of angular momentum of dark matter haloes.
Our results showed that: 1) The spin parameter resulting from the
above method, is an increasing function of the present day mass of the halo.
The mean value of varies from 0.0343 to 0.0484 for haloes with
present day masses in the range of to
. 2)The distribution of is close to
a log-normal, but, as it is already found in the results of N-body simulations,
the match is not satisfactory at the tails of the distribution. A new
analytical formula that approximates the results much more satisfactorily is
presented. 3) The distribution of the values of depends only weakly
on the redshift. 4) The spin parameter of an halo depends on the number of
recent major mergers. Specifically the spin parameter is an increasing function
of this number.Comment: 10 pages, 8 figure
How to make complexity look simple? Conveying ecosystems restoration complexity for socio-economic research and public engagement
Ecosystems degradation represents one of the major global challenges at the present time, threating peopleâs livelihoods and well-being worldwide. Ecosystem restoration therefore seems no longer an option, but an imperative. Restoration challenges are such that a dialogue has begun on the need to re-shape restoration as a science. A critical aspect of that reshaping process is the acceptance that restoration science and practice needs to be coupled with socio-economic research and public engagement. This inescapably means conveying complex ecosystemâs information in a way that is accessible to the wider public. In this paper we take up this challenge with the ultimate aim of contributing to making a step change in scienceâs contribution to ecosystems restoration practice. Using peatlands as a paradigmatically complex ecosystem, we put in place a transdisciplinary process to articulate a description of the processes and outcomes of restoration that can be understood widely by the public. We provide evidence of the usefulness of the process and tools in addressing four key challenges relevant to restoration of any complex ecosystem: (1) how to represent restoration outcomes; (2) how to establish a restoration reference; (3) how to cope with varying restoration time-lags and (4) how to define spatial units for restoration. This evidence includes the way the process resulted in the creation of materials that are now being used by restoration practitioners for communication with the public and in other research contexts. Our main contribution is of an epistemological nature: while ecosystem services-based approaches have enhanced the integration of academic disciplines and non-specialist knowledge, this has so far only followed one direction (from the biophysical underpinning to the description of ecosystem services and their appreciation by the public). We propose that it is the mix of approaches and epistemological directions (including from the public to the biophysical parameters) what will make a definitive contribution to restoration practice
On the origin and evolution of the material in 67P/Churyumov-Gerasimenko
International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects
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