2,365 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 Journal of the Center for Interdisciplinary Teaching and Learning
IMPACT: The Journal of the Center for Interdisciplinary Teaching & Learning is a peer-reviewed, biannual online journal that publishes scholarly and creative non-fiction essays about the theory, practice and assessment of interdisciplinary education. Impact is produced by the Center for Interdisciplinary Teaching & Learning at the College of General Studies, Boston University (www.bu.edu/cgs/citl).How do our students learn what it means to be a human being, with all the attendant responsibilities and joys? How do we learn to teach in a truly interdisciplinary manner? These are some of the questions that preoccupy this issue’s contributors
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
Masters of Fate or Victims of Circumstances? Connecting Communication Centers with Locus of Control
Longstanding research correlates locus of control (LOC)— the sense of self-empowerment (internal orientation) versus feeling influenced by events others control (external orientation)—with self-motivation, persistence, high academic achievement, and workplace success. In study 1, undergraduate peer tutors (n = 31) at a midsize, doctoral-granting, minority-serving university completed a variant of the teacher locus of control (TLOC) survey, which measures the degree of internal/external LOC orientation in educational settings. In study 2,communication center supervisors (n = 12) and undergraduate peer tutors (n = 13) from 14 institutions nationwide completed a qualitative survey describing how they approach consultations with student clientele.The studies found: (1) Supervisors exhibited slightly higher external LOC than peer tutors, indicating a keener sense of restrictions on their personal agency and deferring more to specific procedures as solutions to challenging situations. (2) Small but statistically significant correlations were found between a tutor’s self-identified race and LOC orientation. White tutors more readily attributed levels of achievement to the nature of the student (external LOC); non-white tutors treated achievement levels more as products of the consultation techniques (internal LOC). (3) Qualitative data show that communication center personnel must balance the tensions between different LOC orientations, perhaps by ranging across the continuum from highly internal to highly external
The Tools and Technologies of Transdisciplinary Climate Change Research and Community Empowerment in Barbuda
Focusing on the smaller sister-island of Barbuda, part of the Caribbean nation of Antigua and Barbuda, a group of collaborating anthropologists, archaeologists, biologists, education specialists, geographers, and environmental scientists are studying long-term human ecodynamics, the relationship amongst people, place, and the environment from the beginning of the peopling of a place through modern day. Our transdisciplinary approach brings together various field methods, tools and technologies from each field and crosses the boundaries of conventional science. This approach furthers our knowledge of climate change and facilitates practical and sustainable solutions for vulnerable populations
Rescaling Relations between Two- and Three-dimensional Local Porosity Distributions for Natural and Artificial Porous Media
Local porosity distributions for a three-dimensional porous medium and local
porosity distributions for a two-dimensional plane-section through the medium
are generally different. However, for homogeneous and isotropic media having
finite correlation-lengths, a good degree of correspondence between the two
sets of local porosity distributions can be obtained by rescaling lengths, and
the mapping associating corresponding distributions can be found from
two-dimensional observations alone. The agreement between associated
distributions is good as long as the linear extent of the measurement cells
involved is somewhat larger than the correlation length, and it improves as the
linear extent increases. A simple application of the central limit theorem
shows that there must be a correspondence in the limit of very large
measurement cells, because the distributions from both sets approach normal
distributions. A normal distribution has two independent parameters: the mean
and the variance. If the sample is large enough, LPDs from both sets will have
the same mean. Therefore corresponding distributions are found by matching
variances of two- and three-dimensional local porosity distributions. The
variance can be independently determined from correlation functions. Equating
variances leads to a scaling relation for lengths in this limit. Three
particular systems are examined in order to show that this scaling behavior
persists at smaller length-scales.Comment: 15 PostScript figures, LaTeX, To be published in Physica
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
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