16,003 research outputs found
The Relativity Concept Inventory: development, analysis and results
We report on a concept inventory for special relativity: the development
process, data analysis methods, and results from an introductory relativity
class. The Relativity Concept Inventory tests understanding of kinematic
relativistic concepts. An unusual feature is confidence testing for each
question. This can provide additional information; for example high confidence
correlated with incorrect answers suggests a misconception. A novel aspect of
our data analysis is the use of Monte Carlo simulations to determine the
significance of correlations. This approach is particularly useful for small
sample sizes, such as ours. Our results include a gender bias that was not
present in other assessment, similar to that reported for the Force Concept
Inventory
The Born and Markov approximations for atom lasers
We discuss the use of the Born and Markov approximations in describing the
dynamics of an atom laser. In particular, we investigate the applicability of
the quantum optical Born-Markov master equation for describing output coupling.
We derive conditions based on the atomic reservoir, and atom dispersion
relations for when the Born-Markov approximations are valid and discuss
parameter regimes where these approximations fail in our atom laser model.
Differences between the standard optical laser model and the atom laser are due
to a combination of factors, including the parameter regimes in which a typical
atom laser would operate, the different reservoir state which is appropriate
for atoms, and the different dispersion relations between atoms and photons. We
present results based on an exact method in the regimes in which the
Born-Markov approximation fails. The exact solutions in some experimentally
relavent parameter regimes give non-exponential loss of atoms from a cavity.Comment: 10 pages, 3 figures. (2 new figues). Exact solutions have been
included in section II. Sections IV and V have been expanded. A new section
discussing the effects of gravity has been include
Overview of office of space transportation systems future planning
The Space Transportation Systems' key milestones as well as the future planning of the Office of Space Transportation Systems are summarized. A brief description and identification of candidate new starts with target development initiation and first flight dates are included
The optimal design of standard gearsets
A design procedure for sizing standard involute spur gearsets is presented. The procedure is applied to find the optimal design for two examples - an external gear mesh with a ratio of 5:1 and an internal gear mesh with a ratio of 5:1. In the procedure, the gear mesh is designed to minimize the center distance for a given gear ratio, pressure angle, pinion torque, and allowable tooth strengths. From the methodology presented, a design space may be formulated for either external gear contact or for internal contact. The design space includes kinematics considerations of involute interference, tip fouling, and contact ratio. Also included are design constraints based on bending fatigue in the pinion fillet and Hertzian contact pressure in the full load region and at the gear tip where scoring is possible. This design space is two dimensional, giving the gear mesh center distance as a function of diametral pitch and the number of pinion teeth. The constraint equations were identified for kinematic interference, fillet bending fatigue, pitting fatigue, and scoring pressure, which define the optimal design space for a given gear design. The locus of equal size optimum designs was identified as the straight line through the origin which has the least slope in the design region
The fermion bag approach to lattice field theories
We propose a new approach to the fermion sign problem in systems where there
is a coupling such that when it is infinite the fermions are paired into
bosons and there is no fermion permutation sign to worry about. We argue that
as becomes finite fermions are liberated but are naturally confined to
regions which we refer to as {\em fermion bags}. The fermion sign problem is
then confined to these bags and may be solved using the determinantal trick. In
the parameter regime where the fermion bags are small and their typical size
does not grow with the system size, construction of Monte Carlo methods that
are far more efficient than conventional algorithms should be possible. In the
region where the fermion bags grow with system size, the fermion bag approach
continues to provide an alternative approach to the problem but may lose its
main advantage in terms of efficiency. The fermion bag approach also provides
new insights and solutions to sign problems. A natural solution to the "silver
blaze problem" also emerges. Using the three dimensional massless lattice
Thirring model as an example we introduce the fermion bag approach and
demonstrate some of these features. We compute the critical exponents at the
quantum phase transition and find and .Comment: 31 pages, 9 figures, 5 table
Life and reliability models for helicopter transmissions
Computer models of life and reliability are presented for planetary gear trains with a fixed ring gear, input applied to the sun gear, and output taken from the planet arm. For this transmission the input and output shafts are co-axial and the input and output torques are assumed to be coaxial with these shafts. Thrust and side loading are neglected. The reliability model is based on the Weibull distributions of the individual reliabilities of the in transmission components. The system model is also a Weibull distribution. The load versus life model for the system is a power relationship as the models for the individual components. The load-life exponent and basic dynamic capacity are developed as functions of the components capacities. The models are used to compare three and four planet, 150 kW (200 hp), 5:1 reduction transmissions with 1500 rpm input speed to illustrate their use
Heavy Quark Fragmentation to Baryons Containing Two Heavy Quarks
We discuss the fragmentation of a heavy quark to a baryon containing two
heavy quarks of mass . In this limit the heavy quarks
first combine perturbatively into a compact diquark with a radius small
compared to , which interacts with the light hadronic
degrees of freedom exactly as does a heavy antiquark. The subsequent evolution
of this diquark to a baryon is identical to the fragmentation of a
heavy antiquark to a meson. We apply this analysis to the production of baryons
of the form , , and .Comment: 9 pages, 1 figure included, uses harvmac.tex and epsf.tex, UCSD/PTH
93-11, CALT-68-1868, SLAC-PUB-622
The optimal design of involute gear teeth with unequal addenda
The design of a gear mesh is treated with the objective of minimizing the gear size for a given gear ratio, pinion torque, pressure angle, and allowable tooth lengths. Tooth strengths considered include scoring, pitting fatigue, and bending fatigue. Kinematic involute interference is avoided. The design variation on standard spur gear teeth called the long and short addendum system, is considered. In this system the mesh center distance and pressure angle are maintained as is the ability to manufacture the teeth with standard tooling. However, the pinion and gear tooth proportions are altered in order to obtain fewer teeth numbers for the same ratio as standard gears without kinematic involute interference. The effect of this nonstandard gearing geometry with on tooth strengths and gear mesh size are studied. For a 2:1 gearing ratio, the optimal nonstandard gear design is compared with the optimal standard gear design
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