27,349 research outputs found
A New Challenge: Testing the Video Course
This paper offers some preliminary thoughts on the testing ofvideo courses, including a review of the literature and an examinationof the research on the subject. The unique characteristics ofvideo courses suggest that different language learning outcomes maybe expected, which means that creating appropriate tests is thereforea new challenge for language teachers. The paper lists subtesttypes, and gives an example of a test used by the authors. Based onthis experience, a number of guidelines are offered regarding thecreation of appropriate tests, and a direction for future research inthe area is suggested
The Mod-2 Cohomology Ring of the Third Conway Group is Cohen-Macaulay
By explicit machine computation we obtain the mod-2 cohomology ring of the
third Conway group Co_3. It is Cohen-Macaulay, has dimension 4, and is detected
on the maximal elementary abelian 2-subgroups.Comment: 12 pages; writing style now more concis
Education School Challenges: The Increasing Demands on K-8 Teachers
The educational needs of future K-8 teachers in the areas of mathematics and science are greater as a result of the increased (and, I would add, appropriate) student expectations in the area of mathematics and science as enunciated in the SOL and the specific content areas as described in the new licensure requirements. The sophistication and understanding of science and mathematics that is needed at both the elementary school and middle school levels is indeed substantial. However, proficiency in science and mathematics is only one portion of the total needs of new teachers. How are we all, from the Colleges of Arts and Sciences and the Colleges of Education, going to best provide the educational needs within the very restrictive total time that we have available
Hydraulic calipers
Hydraulic calipers determine area of annular openings in irregular or concealed passages. With modifications the device could be adapted to investigations of cross-sectional changes in heat flow passages, ducts, conduits, and heat exchanger elements
Electrical gas heater with large flow range capability
Auxiliary heat transfer device in form to tightly-wound helical tube was incorporated into conventional heater design to provide hydrogen heater with turn-down ratio greater than 100. Device greatly increases low flow rate capacity of heater by providing maximum heat-transfer area for low mass flows
Effects of dynamical evolution on the distribution of substructures
We develop a semi-analytical model that determines the evolution of the mass,
position and internal structure of dark matter substructures orbiting in dark
matter haloes. We apply this model to the case of the Milky Way. We focus in
particular on the effects of mass loss, dynamical friction and
substructure--substructure interactions, the last of which has previously been
ignored in analytic models of substructure evolution. Our semi-analytical
treatment reproduces both the spatial distribution of substructures and their
mass function as obtained from the most recent N-body cosmological calculations
of Gao et al. (2004). We find that, if mass loss is taken into account, the
present distribution of substructures is practically insensitive to dynamical
friction and scatterings from other substructures.
Implementing these phenomena leads to a slight increase (~5%) in the number
of substructures at r<0.35 r_vir, whereas their effects on the mass function
are negligible. We find that mass loss processes lead to the disruption of
substructures before dynamical friction and gravitational scattering can
significantly alter their orbits. Our results suggest that the present
substructure distribution at r>0.35 r_vir reflects the orbital properties at
infall and is, therefore, purely determined by the dark matter environment
around the host halo and has not been altered by dynamical evolution.Comment: Submitted to MNRAS. 13 pages, 9 figure
The formation of galaxy disks in a hierarchical universe
The formation of galactic discs and the efficiency of star formation within
them are issues central to our understanding of galaxy formation. We have
developed a detailed and versatile model of disc formation which combines the
strengths of previous studies of isolated discs with those of hierarchical
galaxy formation models. Disc structure is inferred from the distribution of
angular momentum in hot halo gas and the hierarchical build-up of dark matter,
leading to theoretically generated systems where the evolution of surface
density, rotation, velocity dispersion, stability and metallicity is predicted
for annular regions of width 20-100 pc. The model will be used to establish
whether the accepted theory of large-scale structure formation in the universe
is consistent with observed trends in the properties of disc galaxies.
This first paper explicitly examines the importance of embedding such
calculations within a merging hierarchy of dark matter haloes, finding that
this leads to dramatically different formation histories compared to models in
which discs grow in isolation. Different models of star formation are explored,
and are found to have only a secondary influence on the properties of the
resulting galaxy discs, the main governing factor being the infalling gas
supply from the hot halo.Comment: 13 pages, 9 figures, accepted by MNRA
Graphite ionization vacuum gauge
Triode gauge with electron source, electron collector, and positive ion collector made from either graphite or carbon material extends low-pressure ranges of existing gauges by changing only materials used in construction. Advantages of graphite gauge stem from physical properties of graphite (or carbon)
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