981 research outputs found
Dynamics of a Monolayer of Microspheres on an Elastic Substrate
We present a model for wave propagation in a monolayer of spheres on an
elastic substrate. The model, which considers sagittally polarized waves,
includes: horizontal, vertical, and rotational degrees of freedom; normal and
shear coupling between the spheres and substrate, as well as between adjacent
spheres; and the effects of wave propagation in the elastic substrate. For a
monolayer of interacting spheres, we find three contact resonances, whose
frequencies are given by simple closed-form expressions. For a monolayer of
isolated spheres, only two resonances are present. The contact resonances
couple to surface acoustic waves in the substrate, leading to mode
hybridization and "avoided crossing" phenomena. We present dispersion curves
for a monolayer of silica microspheres on a silica substrate, assuming
adhesive, Hertzian interactions, and compare calculations using an effective
medium approximation to a discrete model of a monolayer on a rigid substrate.
While the effective medium model does not account for discrete lattice effects
at short wavelengths, we find that it is well suited for describing the
interaction between the monolayer and substrate in the long wavelength limit.
We suggest that a complete picture of the dynamics of a discrete monolayer
adhered to an elastic substrate can be found using a combination of the results
presented for the discrete and effective medium descriptions. This model is
potentially scalable for use with both micro- and macroscale systems, and
offers the prospect of experimentally extracting contact stiffnesses from
measurements of acoustic dispersion
Longitudinal Eigenvibration of Multilayer Colloidal Crystals and the Effect of Nanoscale Contact Bridges
Longitudinal contact-based vibrations of colloidal crystals with a controlled
layer thickness are studied. These crystals consist of 390 nm diameter
polystyrene spheres arranged into close packed, ordered lattices with a
thickness of one to twelve layers. Using laser ultrasonics, eigenmodes of the
crystals that have out-of-plane motion are excited. The particle-substrate and
effective interlayer contact stiffnesses in the colloidal crystals are
extracted using a discrete, coupled oscillator model. Extracted stiffnesses are
correlated with scanning electron microscope images of the contacts and atomic
force microscope characterization of the substrate surface topography after
removal of the spheres. Solid bridges of nanometric thickness are found to
drastically alter the stiffness of the contacts, and their presence is found to
be dependent on the self-assembly process. Measurements of the eigenmode
quality factors suggest that energy leakage into the substrate plays a role for
low frequency modes but is overcome by disorder- or material-induced losses at
higher frequencies. These findings help further the understanding of the
contact mechanics, and the effects of disorder in three-dimensional micro- and
nano-particulate systems, and open new avenues to engineer new types of micro-
and nanostructured materials with wave tailoring functionalities via control of
the adhesive contact properties
Changes in dietary patterns and body composition within 12 months of liver transplantation
Background: Cardiometabolic risk factors are increasing in liver transplant recipients (LTR). Influencing dietary factors have not been assessed. The aim of this observational study was to assess changes in weight, metabolic function, dietary intake and eating behaviours in the first year after orthotopic liver transplantation (OLT). Methods: Consecutive recruitment of 17 patients (14 males) awaiting OLT at a single tertiary hospital. Dietary intake, food behaviours and anthropometry were recorded at baseline, and 6 and 12 months posttransplant. Results: By 12 months, patients had gained on average 7.3% of body weight. The prevalence of overweight or obesity increased from baseline 53% to 77% (P=0.001). By 6 months, 65% (n=11/17) of patients had altered glucose metabolism. Dietary intake was consistent with a Western-style dietary pattern with high saturated fat. Over half of the patients (69%, n=11/16) reported low to no depressive feelings and rated their self-esteem as good (53%, n=9/16). The Power of Food Scale increased between pre and post-transplant, indicating a stronger appetitive drive. Conclusions: Weight gain occurs early post-transplant, with significant metabolic dysfunction present within 6 months, however is not associated with significant psychological distress. Early dietary intervention designed to limit weight gain and target cardiometabolic health is recommended for this unique patient population
‘Back to Life’—Using knowledge exchange processes to enhance lifestyle interventions for liver transplant recipients: A qualitative study
Interventions to prevent excessive weight gain after liver transplant are needed. The purpose of the present study was to enhance a specialist post-transplant well-being program through knowledge exchange with end-users.The study used an interactive process of knowledge exchange between researchers, clinicians and health system users. Data were collected as focus groups or telephone interviews and underwent applied thematic analysis.There were 28 participants (age 24-68 years; 64% male). The results identified experiences that may influence decisions around health behaviours during the course of transplant recovery. Three over-arching themes were identified that impact on liver transplant recipients post-transplant health behaviours. These include (i) Finding a coping mechanism which highlighted the need to acknowledge the significant emotional burden of transplant prior to addressing long-term physical wellness; (ii) Back to Life encompassing the desire to return to employment and prioritise family, while co-ordinating the burden of ongoing medical monitoring and self-management and (iii) Tailored, Personalised Care with a preference for health care delivery by transplant specialists via a range of flexible eHealth modalities.This person-centred process of knowledge exchange incorporated experiences of recipients into service design and identified life priorities most likely to influence health behaviours post-transplant. Patient co-creation of services has the potential to improve the integration of knowledge into health systems and future directions will require evaluation of effectiveness and sustainability of patient-centred multidisciplinary service development
Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves
Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks.National Science Foundation (U.S.) (Grant CMMI-1333858)United States. Army Research Office (Grant W911NF-15-1-0030)University of Washington. Royalty Research FoundationNational Science Foundation (U.S.) (Grant CHE-1111557
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