15,521 research outputs found
Developmental testing of a programmable multizone furnace
A multizone furnace was evaluated for its potential utilization for process experimentation on board the Space Shuttle. A temperature gradient can be created through the use of a series of connected temperature zones and can be translated by the coordinated sequencing of zone temperatures. The Bridgman-Stockbarger thermal configuration for directional solidification was implemented so that neither the sample nor furnace was translated. The thermal behavior of the furnace was measured and characterized. Limitations due to both thermal and electronic (computer) factors are identified. The results indicate that the multizone design is limited to low temperature gradients because of the indirect furnace-to-sample thermal coupling needed to blend the discrete thermal zones. The multizone furnace design inherently consumes more power than a similar (two temperature) conventional Bridgman type directional solidification furnace because every zone must be capable of the high cooling rates needed to produce the maximum desired temperature drop. Typical achievable static temperature gradients for the furnace tested were between 6 and 75 C/in. The maximum gradient velocity was approximately 10 in./hr. Several aspects of the tested system could be improved, but the dependence of the multizone design on high heat loss will limit Space Shuttle applications in the form tested unless additional power is available. The multizone furnace offers great flexibility but requires a high level of operator understanding for full advantage to be obtained
Thermomagnetic analysis of meteorites. 3: C3 and C4 chondrites
Thermomagnetic analysis on all of the C3 and C4 chondrites, conducted under conditions of controlled oxygen fugacity, indicates the presence of a thermally unstable component in at least 5 of the C3 chondrites which upon heating results in magnetite production. This unstable component is most likely troilite (FeS). The presence of the unstable substance may affect the estimation of paleointensities in meteorites which contain it. Our results indicate that Grosnaja, Ornans, Kainsaz, Felix, and Warrenton are likely to be less complicated for paleointensity determinations than the other C3 chondrites. Both C4 chondrites should lead to reliable results
Thermomagnetic analysis of meterorites. 4: Ureilites
Samples of all available ureilites have been analyzed thermomagnetically. For three of the six (Dyalpur, Goalpara and Havero) evidence was found for only low-nickel metallic-iron as the magnetic component and the (saturation magnetization vs, temperature) curves were reversible. In the Novo Urei ureilite, magnetite in addition to low-nickel metallic-iron was indicated and again the Js-T curve was reversible. For the two badly weathered ureilites, Dingo Pup Donga and North Haig, indication was also found that both initial magnetite and low-nickel metallic-iron were present. However, the Js-T curves were somewhat irreversible and the final saturation magnetization was 20% and 50% greater than initially for North Haig and Dingo Pup Donga, respectively. This behavior is interpreted to be the result of magnetite production from a secondary iron oxide during the experiment
Thermomagnetic analysis of meteorites, 2: C2 chondrites
Samples of all eighteen of the known C2 chondrites were analyzed thermomagnetically. For eleven of these, initial Fe3O4 content is low(generally 1%) and the J sub s-T curves are irreversible. The heating curves show variable and erratic behavior, whereas the cooling curves appear to be that of Fe3O4. The saturation moment after cooling is greater (up to 10 times larger) than it is initially. This behavior is interpreted to be the result of the production of magnetite from a thermally unstable phase--apparently FeS. Four of the remaining 7 C2 chondrites contain Fe3O4 as the only significant magnetic phase: initial magnetite contents range from 4 to 13 percent. The remaining three C2 chondrites contain iron or nickel-iron in addition to Fe3O4. These seven C2 chondrites show little evidence of the breakdown of a thermally unstable phase
On the classification of certain fusion categories
We advance the classification of fusion categories in two directions.
Firstly, we completely classify integral fusion categories -- and consequently,
semi-simple Hopf algebras -- of dimension , where and are
distinct primes. This case is especially interesting because it is the simplest
class of dimensions where not all integral fusion categories are
group-theoretical. Secondly, we classify a certain family of \ZZ/3\ZZ-graded
fusion categories, which are generalizations of the \ZZ/2\ZZ-graded
Tambara-Yamagami categories. Our proofs are based on the recently developed
theory of extensions of fusion categories
Suprathermal electron isotropy in high-beta solar wind and its role in heat flux dropouts
[1] Time variations in plasma beta and a parameter which measures isotropy in suprathermal electron pitch angle distributions show a remarkably close correspondence throughout the solar wind. The finding implies that high-beta plasma, with its multiple magnetic holes and sharp field and plasma gradients, is conducive to electron pitch-angle scattering, which reduces heat flux from the Sun without field-line disconnection. Thus the finding impacts our understanding of signatures we use to determine magnetic topology in the heliosphere
Dark cloud cores and gravitational decoupling from turbulent flows
We test the hypothesis that the starless cores may be gravitationally bound
clouds supported largely by thermal pressure by comparing observed molecular
line spectra to theoretical spectra produced by a simulation that includes
hydrodynamics, radiative cooling, variable molecular abundance, and radiative
transfer in a simple one-dimensional model. The results suggest that the
starless cores can be divided into two categories: stable starless cores that
are in approximate equilibrium and will not evolve to form protostars, and
unstable pre-stellar cores that are proceeding toward gravitational collapse
and the formation of protostars. The starless cores might be formed from the
interstellar medium as objects at the lower end of the inertial cascade of
interstellar turbulence. Additionally, we identify a thermal instability in the
starless cores. Under par ticular conditions of density and mass, a core may be
unstable to expansion if the density is just above the critical density for the
collisional coupling of the gas and dust so that as the core expands the
gas-dust coupling that cools the gas is reduced and the gas warms, further
driving the expansion.Comment: Submitted to Ap
NEW AND UPDATED RECORDS FOR AMPHIBIANS AND REPTILES IN MINNESOTA, USA
Following the publication of the revised edition of “Amphibians and Reptiles in Minnesota” by Moriarty and Hall (2014), we accessioned several new or updated records at the Bell Museum of Natural History (JFBM). Records include digital photographs (accession number preceded by “P”) and audio recordings (accession number preceded by “AUD”). In addition, a subset of these observations were accessioned in www.HerpMapper.org. HerpMapper accession numbers are preceded by “HM” and can be viewed online. Benjamin Lowe verified species determinations. Latitude and longitude coordinates are based on datum WGS 84
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