A travelling wave model to interpret a wound healing migration assay for human peritoneal mesothelial cells

The critical determinants of the speed of an invading cell front are not well known. We performed a "wound-healing" experiment that quantifies the migration of human peritoneal mesothelial cells over components of the extracellular matrix. Results were interpreted in terms of Fisher's equation, which includes terms for the modeling of random cell motility (diffusion) and proliferation. The model predicts that, after a short transient, the invading cell front will move as a traveling wave at constant speed. This is consistent with the experimental findings. Using the model, a relationship between the rate of cell proliferation and the diffusion coefficient was obtained. We used the model to deduce the cell diffusion coefficients under control conditions and in the presence of collagen IV and compared these with other published data. The model may be useful in analyzing the invasive capacity of cancer cells as well in predicting the efficacy of growth factors in tissue reconstruction, including the development of monolayer sheets of cells in skin engineering or the repair of injured corneas using grafts of cultured cells

Single-String Integration Test Measurements of the NEXT Ion Engine Plume

Measurements were made of a 40 cm ion-thruster plume as part of the single-string-integration-test (SSIT) activity of Phase I of the NASA's Evolutionary Xenon Thruster (NEXT) project. The NEXT ion engine incorporates design improvements that extend NSTAR power levels and efficiencies. During SSIT, an engineering model (EM2) 40 cm engine was operated using an advanced xenon propellant system in combination with either a GRC power console or advanced power processing unit. Integral goals of the single-string phase were to characterize engine performance over the full input power range and to detail thruster operation within the specification of the NEXT throttle table. Plume diagnostics measurements of relative Xe(+) and Xe(++) currents were made using near-field and far-field ExB probes. Planar geometry faraday probes were used to obtain beam current density profiles. This paper reports on the characterization of the EM2 plume over a range of SSIT operating conditions, first with the advanced propellant management system teamed with the GRC power console and then with the power-processing unit

Quantum Critical Behavior of Disordered Superfluids

The quantum critical behavior of an interacting, non-relativistic Bose theory with quenched disorder randomly distributed in space is investigated. The renormalization group is carried out in a double $\epsilon$ expansion, where one $\epsilon$ is the deviation of the effective space-time dimensionality from 4, while the other denotes the number of time dimensions. The disordered theory, which displays localization in the superfluid state, is shown to possess an infrared stable fixed point.Comment: REVTEX, 5 page

Photoelectric Tachometer for Precise Centrifuge Speed Determination

Certain chemical and physical investigations such as the mechanical analysis of soils by centrifugation require that the speed of rotation of the centrifuge be precisely determined. For a cost of approximately $40.00, when used with instrumentation normally available in research laboratories, the system outlined provides a vivid, unambiguous indication of the speed of rotation, the accuracy of which is limited only by the frequency standard used

A Photoelectric Seed Counter

Small scale yield studies, germination tests, controlled plantings, and packaging often require the counting of large numbers of seeds. The system described in this paper uses a photosensitive detector and a vacuum pickup to count individual seeds and gives a direct digital readout. The count rate is limited only by how quickly the seeds can be fed through the counting tube without clogging it or having them touch each other. This greatly speeds seed counting, eliminates operator error, and reduces operator fatigue. With the addition of a relatively simple predetermining circuit, a fixed number of seeds may be counted and a control function can be exercised. This capability is immediately applicable to packaging or repetitious batching of seeds. Zero error for any given number of seeds is attainable if the seeds are fed through the count tube carefully because of the completely digital nature of the circuit

A Two-Channel Electrical Counter

Many studies require that the magnitude of 2 variables be determined simultaneously. Usually this is done by an operator using 2 hand-operated mechanical reciprocating counters. The operator records one variable on one counter and the second on the other. Our specific problem was to determine pollinator densities in field plots. The operators counted a fixed number of flowers and recorded the number of pollinators on these flowers. A number of problems arise from the use of these devices. The reciprocating counters are hard to use, resulting in manual fatigue, and are infamous for missing counts, particularly when they become worn. The operator must have both hands full all the time he is making the count. If the operator must do something else with his hands, he must store the counters where they will not become lost or interchanged

Microscopic Oscillations in the Quantum Nucleation of Vortices Subject to Periodic Pinning Potential in a Thin Superconductor

We present a theory for the decay of a supercurrent through nucleation of vortex-antivortex pairs in a two-dimensional superconductor in the presence of dissipation and of a periodic pinning potential. Through a powerful quantum electrodynamics formulation of the problem we show that the nucleation rate develops oscillations in its current-density dependence which are connected to the pinning periodicity. A remnant of the dissipation-driven localization transition is present, and an estimate of the nucleation rate suggests that these effects might be observable in real thin superconductors.Comment: REVTeX file, 4 pages in two-column mode, 1 Postscript figure, to appear in Phys.Rev.B (Rapid Communications

Team based learning and nurse education: a systematic review

YesSummary of: Alberti S, Motta P, Ferri P, Bonetti L. The effectiveness of team-based learning in nursing education: A systematic review. Nurse Educ Today. 2021 Feb;97:104721. doi: 10.1016/j.nedt.2020.104721. Epub 2020 Dec 11