277 research outputs found
Shear thickening in densely packed suspensions of spheres and rods confined to few layers
We investigate confined shear thickening suspensions for which the sample
thickness is comparable to the particle dimensions. Rheometry measurements are
presented for densely packed suspensions of spheres and rods with aspect ratios
6 and 9. By varying the suspension thickness in the direction of the shear
gradient at constant shear rate, we find pronounced oscillations in the stress.
These oscillations become stronger as the gap size is decreased, and the stress
is minimized when the sample thickness becomes commensurate with an integer
number of particle layers. Despite this confinement-induced effect, viscosity
curves show shear thickening that retains bulk behavior down to samples as thin
as two particle diameters for spheres, below which the suspension is jammed.
Rods exhibit similar behavior commensurate with the particle width, but they
show additional effects when the thickness is reduced below about a particle
length as they are forced to align; the stress increases for decreasing gap
size at fixed shear rate while the shear thickening regime gradually
transitions to a Newtonian scaling regime. This weakening of shear thickening
as an ordered configuration is approached contrasts with the strengthening of
shear thickening when the packing fraction is increased in the disordered bulk
limit, despite the fact that both types of confinement eventually lead to
jamming.Comment: 21 pages, 14 figures. submitted to the Journal of Rheolog
A Proof-of-Concept Pilot Test of a Behavioral Intervention to Improve Adherence to Dietary Recommendations for Cancer Prevention
OBJECTIVES: Prevention programs that can help adults improve the quality of their diets to reduce cancer risk are needed. This Phase IIa study prospectively tested a mHealth intervention designed to improve adherence to dietary quality guidelines for cancer prevention.
METHODS: All participants (N = 62) received nutrition education and a self-regulation skills curriculum, with a primary target of changing grocery shopping behavior. Using a randomized, factorial design, the study varied whether each of the following 4 components were added to the 20-week intervention: (1) location-triggered app messaging, delivered when individuals arrived at grocery stores, (2) reflections on benefits of change, delivered with extra coaching time and tailored app messages, (3) coach monitoring, in which food purchases were digitally monitored by a coach, and (4) involvement of a household member in the intervention.
RESULTS: Benchmarks were successfully met for recruitment, retention, and treatment acceptability. Across conditions, there were significant reductions in highly processed food intake (
CONCLUSION: This study showed feasibility, acceptability, and preliminary signals of efficacy of a remotely delivered intervention to facilitate adherence to dietary guidelines for cancer prevention and that coach monitoring and household support may be especially effective strategies. A fully powered clinical trial is warranted to test an optimized version of the intervention that includes nutrition education, self-regulation skills training, coach monitoring, and household member involvement.
TRIAL REGISTRATION: ClinicalTrials.gov NCT04947150
Shear thickening and jamming in densely packed suspensions of different particle shapes
We investigated the effects of particle shape on shear thickening in densely
packed suspensions. Rods of different aspect ratios and non-convex hooked rods
were fabricated. Viscosity curves and normal stresses were measured using a
rheometer for a wide range of packing fractions for each shape. Suspensions of
each shape exhibit qualitatively similar Discontinuous Shear Thickening. The
logarithmic slope of the stress/shear-rate relation increases dramatically with
packing fraction and diverges at a critical packing fraction phi_c which
depends on particle shape. The packing fraction dependence of the viscosity
curves for different convex shapes can be collapsed when the packing fraction
is normalized by phi_c. Intriguingly, viscosity curves for non-convex particles
do not collapse on the same set as convex particles, showing strong shear
thickening over a wider range of packing fraction. The value of phi_c is found
to coincide with the onset of a yield stress at the jamming transition,
suggesting the jamming transition also controls shear thickening. The yield
stress is found to correspond with trapped air in the suspensions, and the
scale of the stress can be attributed to interfacial tension forces which
dramatically increase above phi_c due to the geometric constraints of jamming.
The relationship between shear and normal stresses is found to be linear in
both the shear thickening and jammed regimes, indicating that the shear
stresses come from friction. In the limit of zero shear rate, normal stresses
pull the rheometer plates together due to the surface tension of the liquid
below phi_c, but push the rheometer plates apart due to jamming above phi_c.Comment: 13 pages, 13 figures. published in Physical Review
Piano Studio Recital, March 19, 2019
Brooke Ward, from the studio of Professor Raydo
Beth Baker, from the studio of Professor Forman
Robert Stahl, from the studio of Professor Raydo
Joel Sanford, from the studio of Professor Toomey
Nicole Dorobanov, from the studio of Professor Kasparo
Generality of shear thickening in suspensions
Suspensions are of wide interest and form the basis for many smart fluids.
For most suspensions, the viscosity decreases with increasing shear rate, i.e.
they shear thin. Few are reported to do the opposite, i.e. shear thicken,
despite the longstanding expectation that shear thickening is a generic type of
suspension behavior. Here we resolve this apparent contradiction. We
demonstrate that shear thickening can be masked by a yield stress and can be
recovered when the yield stress is decreased below a threshold. We show the
generality of this argument and quantify the threshold in rheology experiments
where we control yield stresses arising from a variety of sources, such as
attractions from particle surface interactions, induced dipoles from applied
electric and magnetic fields, as well as confinement of hard particles at high
packing fractions. These findings open up possibilities for the design of smart
suspensions that combine shear thickening with electro- or magnetorheological
response.Comment: 11 pages, 9 figures, accepted for publication in Nature Material
Piano Studio Recital, February 19, 2019
Elizabeth Baker, from the studio of Professor Forman
Halsey Lawrence, from the studio of Professor Forman
Joel Sanford, from the studio of Professor Toomey
Brooke Ward, from the studio of Professor Raydo
Robert Stahl, from the studio of Professor Raydo
Nicole Dorobanov, from the studio of Professor Kasparo
Lactation and neonatal nutrition: defining and refining the critical questions.
This paper resulted from a conference entitled "Lactation and Milk: Defining and refining the critical questions" held at the University of Colorado School of Medicine from January 18-20, 2012. The mission of the conference was to identify unresolved questions and set future goals for research into human milk composition, mammary development and lactation. We first outline the unanswered questions regarding the composition of human milk (Section I) and the mechanisms by which milk components affect neonatal development, growth and health and recommend models for future research. Emerging questions about how milk components affect cognitive development and behavioral phenotype of the offspring are presented in Section II. In Section III we outline the important unanswered questions about regulation of mammary gland development, the heritability of defects, the effects of maternal nutrition, disease, metabolic status, and therapeutic drugs upon the subsequent lactation. Questions surrounding breastfeeding practice are also highlighted. In Section IV we describe the specific nutritional challenges faced by three different populations, namely preterm infants, infants born to obese mothers who may or may not have gestational diabetes, and infants born to undernourished mothers. The recognition that multidisciplinary training is critical to advancing the field led us to formulate specific training recommendations in Section V. Our recommendations for research emphasis are summarized in Section VI. In sum, we present a roadmap for multidisciplinary research into all aspects of human lactation, milk and its role in infant nutrition for the next decade and beyond
Piano Studio Recital, April 23, 2019
Robert Stahl, from the studio of Professor Raydo
Lawrence Halsey, from the studio of Professor Forman
Jerry Davis, from the studio of Professor Lutsyshyn
Joel Sanford, from the studio of Professor Toomey
Jashkal Germelus, from the studio of Professor Lutsyshyn
Andrei S Johnson, from the studio of Professor Lutsyshyn
Nicole Dorobanov, from the studio of Professor Kasparo
RELICS: A Very Large () Cluster Lens -- RXC J0032.1+1808
Extensive surveys with the \textit{Hubble Space Telescope} (HST) over the
past decade, targeting some of the most massive clusters in the sky, have
uncovered dozens of galaxy-cluster strong lenses. The massive cluster
strong-lens scale is typically \theta_{E}\sim10\arcsec to \sim30-35\arcsec,
with only a handful of clusters known with Einstein radii
\theta_{E}\sim40\arcsec or above (for , nominally). Here we
report another very large cluster lens, RXC J0032.1+1808 (), the
second richest cluster in the redMapper cluster catalog and the 85th most
massive cluster in the Planck Sunyaev-Zel'dovich catalog. With our
Light-Traces-Mass and fully parametric (dPIEeNFW) approaches, we construct
strong lensing models based on 18 multiple images of 5 background galaxies
newly identified in the \textit{Hubble} data mainly from the
\textit{Reionization Lensing Cluster Survey} (RELICS), in addition to a known
sextuply imaged system in this cluster. Furthermore, we compare these models to
Lenstool and GLAFIC models that were produced independently as part of the
RELICS program. All models reveal a large effective Einstein radius of
\theta_{E}\simeq40\arcsec (), owing to the obvious
concentration of substructures near the cluster center. Although RXC
J0032.1+1808 has a very large critical area and high lensing strength, only
three magnified high-redshift candidates are found within the field targeted by
RELICS. Nevertheless, we expect many more high-redshift candidates will be seen
in wider and deeper observations with \textit{Hubble} or \emph{JWST}. Finally,
the comparison between several algorithms demonstrates that the total error
budget is largely dominated by systematic uncertainties.Comment: 23 pages, accepted for publication in Ap
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