1,801 research outputs found
Long-lived anomalous thermal diffusion induced by elastic cell membranes on nearby particles
The physical approach of a small particle (virus, medical drug) to the cell
membrane represents the crucial first step before active internalization and is
governed by thermal diffusion. Using a fully analytical theory we show that the
stretching and bending of the elastic membrane by the approaching particle
induces a memory in the system which leads to anomalous diffusion, even though
the particle is immersed in a purely Newtonian liquid. For typical cell
membranes the transient subdiffusive regime extends beyond 10 ms and can
enhance residence times and possibly binding rates up to 50\%. Our analytical
predictions are validated by numerical simulations.Comment: 13 pages and 5 figures. The Supporting Information is included.
Manuscript accepted for publication in Phys. Rev.
Particle mobility between two planar elastic membranes: Brownian motion and membrane deformation
We study the motion of a solid particle immersed in a Newtonian fluid and
confined between two parallel elastic membranes possessing shear and bending
rigidity. The hydrodynamic mobility depends on the frequency of the particle
motion due to the elastic energy stored in the membrane. Unlike the
single-membrane case, a coupling between shearing and bending exists. The
commonly used approximation of superposing two single-membrane contributions is
found to give reasonable results only for motions in the parallel, but not in
the perpendicular direction. We also compute analytically the membrane
deformation resulting from the motion of the particle, showing that the
presence of the second membrane reduces deformation. Using the
fluctuation-dissipation theorem we compute the Brownian motion of the particle,
finding a long-lasting subdiffusive regime at intermediate time scales. We
finally assess the accuracy of the employed point-particle approximation via
boundary-integral simulations for a truly extended particle. They are found to
be in excellent agreement with the analytical predictions.Comment: 14 pages, 8 figures and 96 references. Revised version resubmitted to
Phys. Fluid
Numerical-experimental observation of shape bistability of red blood cells flowing in a microchannel
Red blood cells flowing through capillaries assume a wide variety of
different shapes owing to their high deformability. Predicting the realized
shapes is a complex field as they are determined by the intricate interplay
between the flow conditions and the membrane mechanics. In this work we
construct the shape phase diagram of a single red blood cell with a
physiological viscosity ratio flowing in a microchannel. We use both
experimental in-vitro measurements as well as 3D numerical simulations to
complement the respective other one. Numerically, we have easy control over the
initial starting configuration and natural access to the full 3D shape. With
this information we obtain the phase diagram as a function of initial position,
starting shape and cell velocity. Experimentally, we measure the occurrence
frequency of the different shapes as a function of the cell velocity to
construct the experimental diagram which is in good agreement with the
numerical observations. Two different major shapes are found, namely croissants
and slippers. Notably, both shapes show coexistence at low (<1 mm/s) and high
velocities (>3 mm/s) while in-between only croissants are stable. This
pronounced bistability indicates that RBC shapes are not only determined by
system parameters such as flow velocity or channel size, but also strongly
depend on the initial conditions.Comment: 13 pages, 9 figures (main text). 13 pages, 31 figures (SI
Training high performance skills using above real-time training
The Above Real-Time Training (ARTT) concept is a unique approach to training high performance skills. ARTT refers to a training paradigm that places the operator in a simulated environment that functions at faster than normal time. Such a training paradigm represents a departure from the intuitive, but not often supported, feeling that the best practice is determined by the training environment with the highest fidelity. This approach is hypothesized to provide greater 'transfer value' per simulation trial, by incorporating training techniques and instructional features into the simulator. These techniques allow individuals to acquire these critical skills faster and with greater retention. ARTT also allows an individual trained in 'fast time' to operate at what appears to be a more confident state, when the same task is performed in a real-time environment. Two related experiments are discussed. The findings appear to be consistent with previous findings that show positive effects of task variation during training. Moreover, ARTT has merit in improving or maintaining transfer with sharp reductions in training time. There are indications that the effectiveness of ARTT varies as a function of task content and possibly task difficulty. Other implications for ARTT are discussed along with future research directions
Development of the Steppin\u27 Up for Success Program
School transitions can be challenging for students, especially when students enter junior high school. Junior high school students experience significant developmental growth in the areas of autonomy, relationships, acceptance, cognitive skills, as well as physical differences associated with hormonal changes. When a student transitions into junior high school, evidence indicates possible declines in motivation, school interest, and academic achievement. Personal relationships, self-worth, and coping skills are essential for a successful transition between schools. Adolescents engage in the occupations of education, leisure, social participation, and activities of daily living. Occupational therapy is perfectly positioned as a support service within the school to assist elementary school students transition successfully into junior high school through a universal approach to support positive mental health. This capstone project details the results of a needs assessment conducted with administrators, teachers, parents, and seventh-grade students at the junior high school. Based on the needs assessment, Steppin’ Up forSuccess: A Transition Program for Sixth-Graders was developed and created to assist sixth graders transition successfully from elementary to junior high school
3D tomography of cells in micro-channels
We combine confocal imaging, microfluidics and image analysis to record
3D-images of cells in flow. This enables us to recover the full 3D
representation of several hundred living cells per minute. Whereas 3D confocal
imaging has thus far been limited to steady specimen, we overcome this
restriction and present a method to access the 3D shape of moving objects. The
key of our principle is a tilted arrangement of the micro-channel with respect
to the focal plane of the microscope. This forces cells to traverse the focal
plane in an inclined manner. As a consequence, individual layers of passing
cells are recorded which can then be assembled to obtain the volumetric
representation. The full 3D information allows for a detailed comparisons with
theoretical and numerical predictions unfeasible with e.g.\ 2D imaging. Our
technique is exemplified by studying flowing red blood cells in a micro-channel
reflecting the conditions prevailing in the microvasculature. We observe two
very different types of shapes: `croissants' and `slippers'. Additionally, we
perform 3D numerical simulations of our experiment to confirm the observations.
Since 3D confocal imaging of cells in flow has not yet been realized, we see
high potential in the field of flow cytometry where cell classification thus
far mostly relies on 1D scattering and fluorescence signals
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Water Pressures and Social Oppression: Social and Political Impacts of Smart Water Meter Technology in Cape Town, South Africa
This paper analyzes the social and political consequences of the implementation of “smart” water meters in Cape Town, South Africa. As policymakers around the world implement new solutions to ever-growing concerns about depleting water resources, technologies and ideas are exported to other parts of the world before experts understand how these concepts will function in different environments. It is imperative to assess the implications of technological solutions to ensure they are implemented sustainably. This paper employs a qualitative approach synthesizing findings from government documents, personal conversations, and traditional and social media to evaluate the societal impacts of smart water meters in Cape Town over the course of the city’s 2017-2018 water crisis. The methodological framework created for this study can be used in future contexts to anticipate how urban areas will respond to smart water technology. This paper concludes with policy recommendations including a historical assessment of water-related grievances, government engagement with business and civil society leaders, and the potential for a cap-and-trade-like system for water rights
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