7,231 research outputs found
An electrothermally actuated micro valve
Microminiature slide action valve requires power only during actuation and can be used as an on-off or single inlet to alternately selected outlets
Pneumatic system for controlling and actuating pneumatic cyclic devices
Pneumatic system for cyclic control of fluid flow in pneumatic devic
Koalas use a novel vocal organ to produce unusually low-pitched mating calls
SummaryDuring the breeding season, male koalas produce ‘bellow’ vocalisations that are characterised by a continuous series of inhalation and exhalation sections, and an extremely low fundamental frequency (the main acoustic correlate of perceived pitch) [1]. Remarkably, the fundamental frequency (F0) of bellow inhalation sections averages 27.1 Hz (range: 9.8–61.5 Hz [1]), which is 20 times lower than would be expected for an animal weighing 8 kg [2] and more typical of an animal the size of an elephant (Supplemental figure S1A). Here, we demonstrate that koalas use a novel vocal organ to produce their unusually low-pitched mating calls
Spool valve cycles at controlled frequency
Spool valve accurately controls the cycle of a pneumatically-actuated system over long periods. Regulation of pressure from the external source, positioning of the adjusting plugs, and magnet selection, together afford wide variation in cyclic timing and speed of closure in either direction
Mineral Trioxide Aggregate Material Use in Endodontic Treatment: A Review of the Literature
Objective
The purpose of this paper was to review the composition, properties, biocompatibility, and the clinical results involving the use of mineral trioxide aggregate (MTA) materials in endodontic treatment. Methods
Electronic search of scientific papers from January 1990 to August 2006 was accomplished using PubMed and Scopus search engines (search terms: MTA, GMTA, WMTA, mineral AND trioxide AND aggregate). Results
Selected exclusion criteria resulted in 156 citations from the scientific, peer-reviewed dental literature. MTA materials are derived from a Portland cement parent compound and have been demonstrated to be biocompatible endodontic repair materials, with its biocompatible nature strongly suggested by its ability to form hydroxyappatite when exposed to physiologic solutions. With some exceptions, MTA materials provide better microleakage protection than traditional endodontic repair materials using dye, fluid filtration, and bacterial penetration leakage models. In both animal and human studies, MTA materials have been shown to have excellent potential as pulp-capping and pulpotomy medicaments but studies with long-term follow-up are limited. Preliminary studies suggested a favorable MTA material use as apical and furcation restorative materials as well as medicaments for apexogenesis and apexification treatments; however, long-term clinical studies are needed in these areas. Conclusion
MTA materials have been shown to have a biocompatible nature and have excellent potential in endodontic use. MTA materials are a refined Portland cement material and the substitution of Portland cement for MTA products is presently discouraged. Existing human studies involving MTA materials are very promising, however, insufficient randomized, double-blind clinical studies of sufficient duration exist involving MTA for all of its clinical indications. Further clinical studies are needed in these areas
The Kinematic Composition of MgII Absorbers
The study of galaxy evolution using quasar absorption lines requires an
understanding of what components of galaxies and their surroundings are
contributing to the absorption in various transitions. This paper considers the
kinematic composition of the class of 0.4 < z < 1.0 MgII absorbers,
particularly addressing the question of what fraction of this absorption is
produced in halos and what fraction arises from galaxy disks. We design models
with various fractional contributions from radial infall of halo material and
from a rotating thick disk component. We generate synthetic spectra from lines
of sight through model galaxies and compare the resulting ensembles of MgII
profiles with the 0.4 < z < 1.0 sample observed with HIRES/Keck. We apply a
battery of statistical tests and find that pure disk and pure halo models can
be ruled out, but that various models with rotating disk and infall/halo
contributions can produce an ensemble that is nearly consistent with the data.
A discrepancy in all models that we considered requires the existence of a
kinematic component intermediate between halo and thick disk. The variety of
MgII profiles can be explained by the gas in disks and halos of galaxies not
very much different than galaxies in the local Universe.
In any one case there is considerable ambiguity in diagnosing the kinematic
composition of an absorber from the low ionization high resolution spectra
alone. Future data will allow galaxy morphologies, impact parameters, and
orientations, FeII/MgII of clouds, and the distribution of high ionization gas
to be incorporated into the kinematic analysis. Combining all these data will
permit a more accurate diagnosis of the physical conditions along the line of
sight through the absorbing galaxy.Comment: 34 pages including 14 postscript figures; Accepted by the
Astrophysical Journal; URL http://www.astro.psu.edu/users/cwc/pubs.htm
Les besoins alimentaires de l’Afrique et la réponse du Canada : Les limites de l’aide alimentaire au développement
In recent years there has been an important shift in the pattern of Canadian food aid distribution towards a greater concentration on Africa. Recent projections call for increased transfers of food aid to Africa in the foreseeable future. Given the growing concern about the long-term contribution that food aid might make to increasing food sufficiency in Africa, this paper examines the concept of « developmental » food aid and its implications for Canadian food aid policy. First, the article discusses some of the problems that arise out of the provision of increased volumes of non-emergency food aid to Africa. Then, it examines the recent evolution of Canadian food aid policy with particular attention to some of the difficulties involved in implementing a strategy of providing « developmental » food aid to Africa on a long-term basis. The issues of policy dialogue, recipient selection, donor co-ordination, and food aid dependence are discussed respectively
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