8,552 research outputs found
Designing, engineering, and testing wood structures
The objective of this paper is to introduce basic structural engineering concepts in a clear, simple manner while actively involving students. This project emphasizes the fact that a good design uses materials efficiently. The test structure in this experiment can easily be built and has various design options. Even when the structure is loaded to collapsing, only one or two pieces usually break, leaving the remaining pieces intact and reusable
In Synch but Not in Step: Circadian Clock Circuits Regulating Plasticity in Daily Rhythms
The suprachiasmatic nucleus (SCN) is a network of neural oscillators that program daily rhythms in mammalian behavior and physiology. Over the last decade much has been learned about how SCN clock neurons coordinate together in time and space to form a cohesive population. Despite this insight, much remains unknown about how SCN neurons communicate with one another to produce emergent properties of the network. Here we review the current understanding of communication among SCN clock cells and highlight a collection of formal assays where changes in SCN interactions provide for plasticity in the waveform of circadian rhythms in behavior. Future studies that pair analytical behavioral assays with modern neuroscience techniques have the potential to provide deeper insight into SCN circuit mechanisms
Recent Results on the Decay of Metastable Phases
We review some aspects of current knowledge regarding the decay of metastable
phases in many-particle systems. In particular we emphasize recent theoretical
and computational developments and numerical results regarding homogeneous
nucleation and growth in kinetic Ising and lattice-gas models. An introductory
discussion of the droplet theory of homogeneous nucleation is followed by a
discussion of Monte Carlo and transfer-matrix methods commonly used for
numerical study of metastable decay, including some new algorithms. Next we
discuss specific classes of systems. These include a brief discussion of recent
progress for fluids, and more exhaustive considerations of ferromagnetic Ising
models ({\it i.e.}, attractive lattice-gas models) with weak long-range
interactions and with short-range interactions. Whereas weak-long-range-force
(WLRF) models have infinitely long-lived metastable phases in the
infinite-range limit, metastable phases in short-range-force (SRF) models
eventually decay, albeit extremely slowly. Recent results on the finite-size
scaling of metastable lifetimes in SRF models are reviewed, and it is pointed
out that such effects may be experimentally observable.Comment: 34 pages, LaTex, 8 ps figs. on request, preprint FSU-SCRI-94-6
Patient-specific CFD simulation of intraventricular haemodynamics based on 3D ultrasound imaging
Background: The goal of this paper is to present a computational fluid dynamic (CFD) model with moving boundaries to study the intraventricular flows in a patient-specific framework. Starting from the segmentation of real-time transesophageal echocardiographic images, a CFD model including the complete left ventricle and the moving 3D mitral valve was realized. Their motion, known as a function of time from the segmented ultrasound images, was imposed as a boundary condition in an Arbitrary Lagrangian-Eulerian framework.
Results: The model allowed for a realistic description of the displacement of the structures of interest and for an effective analysis of the intraventricular flows throughout the cardiac cycle. The model provides detailed intraventricular flow features, and highlights the importance of the 3D valve apparatus for the vortex dynamics and apical flow.
Conclusions: The proposed method could describe the haemodynamics of the left ventricle during the cardiac cycle. The methodology might therefore be of particular importance in patient treatment planning to assess the impact of mitral valve treatment on intraventricular flow dynamics
Compact Toroidal Ion Trap Design and Optimization
We present the design of a new type of compact toroidal, or "halo", ion trap.
Such traps may be useful for mass spectrometry, studying small Coulomb cluster
rings, quantum information applications, or other quantum simulations where a
ring topology is of interest. We present results from a Monte Carlo
optimization of the trap design parameters using finite-element analysis
simulations that minimizes higher-order anharmonic terms in the trapping
pseudopotential, while maintaining complete control over ion placement at the
pseudopotential node in 3D using static bias fields. These simulations are
based on a practical electrode design using readily-available parts, yet can be
easily scaled to any size trap with similar electrode spacings. We also derive
the conditions for a crystal phase transition for two ions in the compact halo
trap, the first non-trivial phase transition for Coulomb crystals in this
geometry.Comment: 8 pages, 9 figure
Strain-Modified RKKY Interaction in Carbon Nanotubes
For low-dimensional metallic structures, such as nanotubes, the exchange
coupling between localized magnetic dopants is predicted to decay slowly with
separation. The long-range character of this interaction plays a significant
role in determining the magnetic order of the system. It has previously been
shown that the interaction range depends on the conformation of the magnetic
dopants in both graphene and nanotubes. Here we examine the RKKY interaction in
carbon nanotubes in the presence of uniaxial strain for a range of different
impurity configurations. We show that strain is capable of amplifying or
attenuating the RKKY interaction, significantly increasing certain interaction
ranges, and acting as a switch: effectively turning on or off the interaction.
We argue that uniaxial strain can be employed to significantly manipulate
magnetic interactions in carbon nanotubes, allowing an interplay between
mechanical and magnetic properties in future spintronic devices. We also
examine the dimensional relationship between graphene and nanotubes with
regards to the decay rate of the RKKY interaction.Comment: 7 pages, 6 figures, submitte
Development and evaluation of lessons for class and group situations in grade I. Volume I.
Thesis (Ed.M.)--Boston University
For volume II, please see: http://hdl.handle.net/2144/1415
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