1,989 research outputs found
Elastic Convection in Vibrated Viscoplastic Fluids
We observe a new type of behavior in a shear thinning yield stress fluid:
freestanding convection rolls driven by vertical oscillation. The convection
occurs without the constraint of container boundaries yet the diameter of the
rolls is spontaneously selected for a wide range of parameters. The transition
to the convecting state occurs without hysteresis when the amplitude of the
plate acceleration exceeds a critical value. We find that a non-dimensional
stress, the stress due to the inertia of the fluid normalized by the yield
stress, governs the onset of the convective motion.Comment: 4 pages, 6 figure
Benefits of a marketing cooperative in transition agriculture: Mórakert purchasing and service co-operative
The paper analyses the potential benefits of marketing cooperatives in Hungary, employing a transaction cost economics framework. We found that the purchased quantity, the existence of contracts, flexibility and trust are the most important factors farmers consider when selling their products via a cooperative. The most striking result is that diversification has positive influences on the share of cooperatives in farmers’ sale. Furthermore, farmers with larger bargaining power have less willingness to sell their product to the cooperative. Surprisingly, asset specificity has rather negative effects on the share of cooperatives in members’ sales
The [4+2]‐Cycloaddition of α‐Nitrosoalkenes with Thiochalcones as a Prototype of Periselective Hetero‐Diels–Alder Reactions—Experimental and Computational Studies
The [4+2]‐cycloadditions of α‐nitrosoalkenes with thiochalcones occur with high selectivity at the thioketone moiety of the dienophile providing styryl‐substituted 4H‐1,5,2‐oxathiazines in moderate to good yields. Of the eight conceivable hetero‐Diels–Alder adducts only this isomer was observed, thus a prototype of a highly periselective and regioselective cycloaddition has been identified. Analysis of crude product mixtures revealed that the α‐nitrosoalkene also adds competitively to the thioketone moiety of the thiochalcone dimer affording bis‐heterocyclic [4+2]‐cycloadducts. The experiments are supported by high‐level DFT calculations that were also extended to related hetero‐Diels–Alder reactions of other nitroso compounds and thioketones. These calculations reveal that the title cycloadditions are kinetically controlled processes confirming the role of thioketones as superdienophiles. The computational study was also applied to the experimentally studied thiochalcone dimerization, and showed that the 1,2‐dithiin and 2H‐thiopyran isomers are in equilibrium with the monomer. Again, the DFT calculations indicate kinetic control of this process
The Inertio-Elastic Planar Entry Flow of Low-Viscosity Elastic Fluids in Micro-fabricated Geometries
The non-Newtonian flow of dilute aqueous polyethylene oxide (PEO) solutions through
microfabricated planar abrupt contraction-expansions is investigated. The contraction
geometries are fabricated from a high-resolution chrome mask and cross-linked PDMS
gels using the tools of soft-lithography. The small length scales and high deformation
rates in the contraction throat lead to significant extensional flow effects even with dilute polymer solutions having time constants on the order of milliseconds. The dimensionless
extra pressure drop across the contraction increases by more than 200% and is
accompanied by significant upstream vortex growth. Streak photography and videomicroscopy
using epifluorescent particles shows that the flow ultimately becomes
unstable and three-dimensional. The moderate Reynolds numbers (0.03 ⤠Re ⤠44)
associated with these high Deborah number (0 ⤠De ⤠600) microfluidic flows results in
the exploration of new regions of the Re-De parameter space in which the effects of both
elasticity and inertia can be observed. Understanding such interactions will be
increasingly important in microfluidic applications involving complex fluids and can best
be interpreted in terms of the elasticity number, El = De/Re, which is independent of the
flow kinematics and depends only on the fluid rheology and the characteristic size of the
device.NS
Local Entropy Characterization of Correlated Random Microstructures
A rigorous connection is established between the local porosity entropy
introduced by Boger et al. (Physica A 187, 55 (1992)) and the configurational
entropy of Andraud et al. (Physica A 207, 208 (1994)). These entropies were
introduced as morphological descriptors derived from local volume fluctuations
in arbitrary correlated microstructures occuring in porous media, composites or
other heterogeneous systems. It is found that the entropy lengths at which the
entropies assume an extremum become identical for high enough resolution of the
underlying configurations. Several examples of porous and heterogeneous media
are given which demonstrate the usefulness and importance of this morphological
local entropy concept.Comment: 15 pages. please contact [email protected] and have a look
at http://www.ica1.uni-stuttgart.de/ . To appear in Physica
Urinary eicosanoid metabolites in HIV-infected women with central obesity switching to raltegravir: an analysis from the women, integrase, and fat accumulation trial.
Chronic inflammation is a hallmark of HIV infection. Eicosanoids reflect inflammation, oxidant stress, and vascular health and vary by sex and metabolic parameters. Raltegravir (RAL) is an HIV-1 integrase inhibitor that may have limited metabolic effects. We assessed urinary F2-isoprostanes (F2-IsoPs), prostaglandin E2 (PGE-M), prostacyclin (PGI-M), and thromboxane B2 (TxB2) in HIV-infected women switching to RAL-containing antiretroviral therapy (ART). Thirty-seven women (RAL = 17; PI/NNRTI = 20) with a median age of 43 years and BMI 32 kg/m(2) completed week 24. TxB2 increased in the RAL versus PI/NNRTI arm (+0.09 versus -0.02; P = 0.06). Baseline PGI-M was lower in the RAL arm (P = 0.005); no other between-arm cross-sectional differences were observed. In the PI/NNRTI arm, 24-week visceral adipose tissue change correlated with PGI-M (rho = 0.45; P = 0.04) and TxB2 (rho = 0.44; P = 0.005) changes, with a trend seen for PGE-M (rho = 0.41; P = 0.07). In an adjusted model, age ≥ 50 years (N = 8) was associated with increased PGE-M (P = 0.04). In this randomized trial, a switch to RAL did not significantly affect urinary eicosanoids over 24 weeks. In women continuing PI/NNRTI, increased visceral adipose tissue correlated with increased PGI-M and PGE-M. Older age (≥ 50) was associated with increased PGE-M. Relationships between aging, adiposity, ART, and eicosanoids during HIV-infection require further study
A protocol for co-creating research project lay summaries with stakeholders:Guideline development for Canada's AGE-WELL Network
Background
Funding bodies increasingly require researchers to write lay summaries to communicate projects’ real-world relevance to the public in an accessible way. However, research proposals and findings are generally not easily readable or understandable by non-specialist readers. Many researchers find writing lay summaries difficult because they typically write for fellow subject specialists or academics rather than the general public or a non-specialist audience. The primary objective of our project is to develop guidelines for researchers in Canada’s AGE-WELL Network of Centres of Excellence, and ultimately various other disciplines, sectors, and institutions, to co-create lay summaries of research projects with stakeholders. To begin, we produced a protocol for co-creating a lay summary based on workshops we organized and facilitated for an AGE-WELL researcher. This paper presents the lay summary co-creation protocol that AGE-WELL researchers will be invited to use.
Methods
Eligible participants in this project will be 24 AgeTech project researchers who are funded by the AGE-WELL network in its Core Research Program 2020. If they agree to participate in this project, we will invite them to use our protocol to co-produce a lay summary of their respective projects with stakeholders. The protocol comprises six steps: Investigate principles of writing a good lay summary, identify the target readership, identify stakeholders to collaborate with, recruit the identified stakeholders to work on a lay summary, prepare for workshop sessions, and execute the sessions. To help participants through the process, we will provide them with a guide to developing an accessible, readable research lay summary, help them make decisions, and host, and facilitate if needed, their lay summary co-creation workshops.
Discussion
Public-facing research outputs, including lay summaries, are increasingly important knowledge translation strategies to promote the impact of research on real-world issues. To produce lay summaries that include information that will interest a non-specialist readership and that are written in accessible language, stakeholder engagement is key. Furthermore, both researchers and stakeholders benefit by participating in the co-creation process. We hope the protocol helps researchers collaborate with stakeholders effectively to co-produce lay summaries that meet the needs of both the public and project funders
Chemical sensitivity to the ratio of the cosmic-ray ionization rates of He and H2 in dense clouds
Aim: To determine whether or not gas-phase chemical models with homogeneous
and time-independent physical conditions explain the many observed molecular
abundances in astrophysical sources, it is crucial to estimate the
uncertainties in the calculated abundances and compare them with the observed
abundances and their uncertainties. Non linear amplification of the error and
bifurcation may limit the applicability of chemical models. Here we study such
effects on dense cloud chemistry. Method: Using a previously studied approach
to uncertainties based on the representation of rate coefficient errors as log
normal distributions, we attempted to apply our approach using as input a
variety of different elemental abundances from those studied previously. In
this approach, all rate coefficients are varied randomly within their log
normal (Gaussian) distribution, and the time-dependent chemistry calculated
anew many times so as to obtain good statistics for the uncertainties in the
calculated abundances. Results: Starting with so-called ``high-metal''
elemental abundances, we found bimodal rather than Gaussian like distributions
for the abundances of many species and traced these strange distributions to an
extreme sensitivity of the system to changes in the ratio of the cosmic ray
ionization rate zeta\_He for He and that for molecular hydrogen zeta\_H2. The
sensitivity can be so extreme as to cause a region of bistability, which was
subsequently found to be more extensive for another choice of elemental
abundances. To the best of our knowledge, the bistable solutions found in this
way are the same as found previously by other authors, but it is best to think
of the ratio zeta\_He/zeta\_H2 as a control parameter perpendicular to the
''standard'' control parameter zeta/n\_H.Comment: Accepted for publicatio
- …