2,709 research outputs found
Non-integrability of density perturbations in the FRW universe
We investigate the evolution equation of linear density perturbations in the
Friedmann-Robertson-Walker universe with matter, radiation and the cosmological
constant. The concept of solvability by quadratures is defined and used to
prove that there are no "closed form" solutions except for the known Chernin,
Heath, Meszaros and simple degenerate ones. The analysis is performed applying
Kovacic's algorithm. The possibility of the existence of other, more general
solutions involving special functions is also investigated.Comment: 13 pages. The latest version with added references, and a relevant
new paragraph in section I
Prognostic value and importance of surgery combined with postoperative radiotherapy for oral and oropharyngeal cancer
Student-computer interface on an intelligent tutoring system for Japanese language instruction, The
Includes bibliographical references.This work describes the human-computer interaction of an intelligent tutoring system designed to mediate some of the difficulties of acquiring proficiency in reading technical Japanese material.This material is based upon work supported by the National Science Foundation under Grant No. INT8818039
Kinetic limitations on the use of redundancy in robotic manipulators
Includes bibliographical references (page 210).The kinematic specification of motion for redundant manipulators has relied primarily on a formulation that decomposes joint velocity solutions into a pseudoinverse component and a homogeneous solution component. While such a formulation is conceptually appealing, since it treats the redundant degrees of freedom as independent from those required to maintain a desired end effector trajectory, it has been shown to be physically inaccurate when applied to the kinetic behavior of redundant manipulators. In this work, the kinetic behavior of the homogeneous solution component is analyzed in order to specify realistic limitations on the use of redundancy. It is shown that the equations that govern these limitations are related to the conditions for guaranteeing stability of the local torque minimization formulation
The Effectiveness of Mainstreaming Special Needs Students with Regular Students in a High School Classroom Setting
The goals of this study were to answer the following questions: 1. Are special needs students as successful in a regular classroom setting as other students are? 2. Do special needs students work and learn as well as other students in a regular classroom setting? 3. Do special needs students respond to the various teaching methods as well as other students? 4. Do special needs students respond to media and training aids as well as other students? 5. Is mainstreaming special needs students in a regular classroom setting successful overall or should other improvements be made
Computationally efficient ray tracing of parametric surfaces
Includes bibliographical references (page 9).Abstract also in Japanese.Algorithms for ray tracing parametric surfaces are in general too computationally expensive to be widely applicable. The algorithm presented here combines well-known graphics procedures with a modified Newton iteration to provide a computationally efficient means of including parametric surfaces in a ray traced image. By allowing only planar surfaces to be reflective and/or refractive the resulting high degree of ray coherence is utilized to make the algorithm incremental and results in an order of magnitude improvement in computation speed over existing algorithms
CCD BV survey of 42 open clusters
We present results of a photometric survey whose aim was to derive structural
and astrophysical parameters for 42 open clusters. While our sample is
definitively not representative of the total open cluster sample in the Galaxy,
it does cover a wide range of cluster parameters and is uniform enough to allow
for simple statistical considerations. BV wide-field CCD photometry was
obtained for open clusters for which photometric, structural, and dynamical
evolution parameters were determined. The limiting and core radii were
determined by analyzing radial density profiles. The ages, reddenings, and
distances were obtained from the solar metallicity isochrone fitting. The mass
function was used to study the dynamical state of the systems, mass segregation
effect and to estimate the total mass and number of cluster members. This study
reports on the first determination of basic parameters for 11 out of 42
observed open clusters. The angular sizes for the majority of the observed
clusters appear to be several times larger than the catalogue data indicate.
The core and limiting cluster radii are correlated and the latter parameter is
3.2 times larger on average. The limiting radius increases with the cluster's
mass, and both the limiting and core radii decrease in the course of dynamical
evolution. For dynamically not advanced clusters, the mass function slope is
similar to the universal IMF slope. For more evolved systems, the effect of
evaporation of low-mass members is clearly visible. The initial mass
segregation is present in all the observed young clusters, whereas the
dynamical mass segregation appears in clusters older than about log(age)=8.
Low-mass stars are deficient in the cores of clusters older than log(age)=8.5
and not younger than one relaxation time.Comment: 13 pages, 8 figure
- …