630 research outputs found
A METHOD OF MOTION ANALYSIS FOR SELF-PROPELLED AQUATIC CRAFTS
Cimematography/videography has been the method of choice for the evaluation of self-propelled aquatic craft kinematics. However, direct measurements of acceleration of this type of craft has proved to be difficult. At Dalhousie the use of acceleration data in combination with video data has facilitated the analysis of rowing and canoeing kinematics. The aim of this study is to describe the method of motion analysis currently used at Dalhousie's Sport Science Lab. Description includes a custom software program developed to divide acceleration data into individual cycles and a cubic spline to normalize the data. In addition, impulse data was calculated integrating by acceleration data using Simpson's Rule as well as the Trapezoidal Rule. A multiple low pass 2nd order Butterworth digital filter has been used successfully to smooth the acceleration data. Video data has been used to confirm that the software correctly detects these variables
AN ANALYSIS OF SELECTED KINEMATIC VARIABLES IN SCULL ROWING USING MACON AND HATCHET OARS
The Hatchet oar is now used extensively in competitive rowing because it is believed to enhance performance. There has been little research to verify this. To determine possible differences between the scull kinematics using the Hatchet and Macon oar, a 24 year old male, lightweight rower, raced 2000 m on two separate days. An 8 mm video camera and a g.analyst accelerometer collected the data. A custom software program, divided the acceleration data into individual strokes and a cubic spline standardized the stroke length. Video data confirmed that the software correctly detected stroke cycles. The acceleration data was integrated using Simpson's Rule as well as the Trapezoidal Rule. First order derivatives where determined using first and second order finite differences and impulse. Velocity data was smoothed using a multiple low pass 2nd order Butterworth digital filter. Twelve discrete measures of percentage stroke length and the value at local vertices, as well as three measures of impulse where examined using one way ANOVAs. Most of the discrete measures examined were statistically significant (
Searches for Stable Strangelets in Ordinary Matter: Overview and a Recent Example
Our knowledge on the possible existence in nature of stable exotic particles
depends solely upon experimental observation. Guided by this general principle
and motivated by theoretical hypotheses on the existence of stable particles of
strange quark matter, a variety of experimental searches have been performed.
We provide an introduction to the theoretical hypotheses, an overview of the
past searches, and a more detailed description of a recent search for
helium-like strangelets in the Earth's atmosphere using a sensitive laser
spectroscopy method
An integrated approach to modelling the fluid-structure interaction of a collapsible tube
The well known collapsible tube experiment was conducted to obtain flow, pressure and materials property data for steady state conditions. These were then used as the boundary conditions for a fully coupled fluid-structure interaction (FSI) model using a propriety computer code, LS-DYNA. The shape profiles for the tube were also recorded. In order to obtain similar collapse modes to the experiment, it was necessary to model the tube flat, and then inflate it into a circular profile, leaving residual stresses in the walls. The profile shape then agreed well with the experimental ones. Two departures from the physical properties were required to reduce computer time to an acceptable level. One of these was the lowering of the speed of sound by two orders of magnitude which, due to the low velocities involved, still left the mach number below 0.2. The other was to increase the thickness of the tube to prevent the numerical collapse of elements. A compensation for this was made by lowering the Young's modulus for the tube material. Overall the results are qualitatively good. They give an indication of the power of the current FSI algorithms and the need to combine experiment and computer models in order to maximise the information that can be extracted both in terms of quantity and quality
High Pressure Thermoelasticity of Body-centered Cubic Tantalum
We have investigated the thermoelasticity of body-centered cubic (bcc)
tantalum from first principles by using the linearized augmented plane wave
(LAPW) and mixed--basis pseudopotential methods for pressures up to 400 GPa and
temperatures up to 10000 K. Electronic excitation contributions to the free
energy were included from the band structures, and phonon contributions were
included using the particle-in-a-cell (PIC) model. The computed elastic
constants agree well with available ultrasonic and diamond anvil cell data at
low pressures, and shock data at high pressures. The shear modulus and
the anisotropy change behavior with increasing pressure around 150 GPa because
of an electronic topological transition. We find that the main contribution of
temperature to the elastic constants is from the thermal expansivity. The PIC
model in conjunction with fast self-consistent techniques is shown to be a
tractable approach to studying thermoelasticity.Comment: To be appear in Physical Review
Ab-initio calculation of the binding energy with the Hybrid Multideterminant scheme
We perform an ab-initio calculation for the binding energy of using
the CD-Bonn 2000 NN potential renormalized with the Lee-Suzuki method. The
many-body approach to the problem is the Hybrid Multideterminant method. The
results indicate a binding energy of about , within a few hundreds KeV
uncertainty. The center of mass diagnostics are also discussed.Comment: 18 pages with 3 figures. More calculations added, to be published in
EPJ
The nuclear energy density functional formalism
The present document focuses on the theoretical foundations of the nuclear
energy density functional (EDF) method. As such, it does not aim at reviewing
the status of the field, at covering all possible ramifications of the approach
or at presenting recent achievements and applications. The objective is to
provide a modern account of the nuclear EDF formalism that is at variance with
traditional presentations that rely, at one point or another, on a {\it
Hamiltonian-based} picture. The latter is not general enough to encompass what
the nuclear EDF method represents as of today. Specifically, the traditional
Hamiltonian-based picture does not allow one to grasp the difficulties
associated with the fact that currently available parametrizations of the
energy kernel at play in the method do not derive from a genuine
Hamilton operator, would the latter be effective. The method is formulated from
the outset through the most general multi-reference, i.e. beyond mean-field,
implementation such that the single-reference, i.e. "mean-field", derives as a
particular case. As such, a key point of the presentation provided here is to
demonstrate that the multi-reference EDF method can indeed be formulated in a
{\it mathematically} meaningful fashion even if does {\it not} derive
from a genuine Hamilton operator. In particular, the restoration of symmetries
can be entirely formulated without making {\it any} reference to a projected
state, i.e. within a genuine EDF framework. However, and as is illustrated in
the present document, a mathematically meaningful formulation does not
guarantee that the formalism is sound from a {\it physical} standpoint. The
price at which the latter can be enforced as well in the future is eventually
alluded to.Comment: 64 pages, 8 figures, submitted to Euroschool Lecture Notes in Physics
Vol.IV, Christoph Scheidenberger and Marek Pfutzner editor
Cross Section Measurements of Charged Pion Photoproduction in Hydrogen and Deuterium from 1.1 to 5.5 GeV
The differential cross section for the gamma +n --> pi- + p and the gamma + p
--> pi+ n processes were measured at Jefferson Lab. The photon energies ranged
from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4
GeV. The pion center-of-mass angles varied from 50 degree to 110 degree. The
pi- and pi+ photoproduction data both exhibit a global scaling behavior at high
energies and high transverse momenta, consistent with the constituent counting
rule prediction and the existing pi+ data. The data suggest possible
substructure of the scaling behavior, which might be oscillations around the
scaling value. The data show an enhancement in the scaled cross section at
center-of-mass energy near 2.2 GeV. The differential cross section ratios at
high energies and high transverse momenta can be described by calculations
based on one-hard-gluon-exchange diagrams.Comment: 18 pages, 19 figure
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