9,276 research outputs found
Anisotropic Relaxation Functions and Strength of Oriented Solids Technical Report No. 106
Anisotropic relaxation functions and strength of oriented solid
Progressor: Social navigation support through open social student modeling
The increased volumes of online learning content have produced two problems: how to help students to find the most appropriate resources and how to engage them in using these resources. Personalized and social learning have been suggested as potential ways to address these problems. Our work presented in this paper combines the ideas of personalized and social learning in the context of educational hypermedia. We introduce Progressor, an innovative Web-based tool based on the concepts of social navigation and open student modeling that helps students to find the most relevant resources in a large collection of parameterized self-assessment questions on Java programming. We have evaluated Progressor in a semester-long classroom study, the results of which are presented in this paper. The study confirmed the impact of personalized social navigation support provided by the system in the target context. The interface encouraged students to explore more topics attempting more questions and achieving higher success rates in answering them. A deeper analysis of the social navigation support mechanism revealed that the top students successfully led the way to discovering most relevant resources by creating clear pathways for weaker students. © 2013 Taylor and Francis Group, LLC
Theoretical Consideration of the Influence of Reforming Processes on the Fracture Strength of Solids Technical Report No. 105
Reformation processes effect on stress time-to- fracture behavior of solid
On Internal Fracture of Solids
Initiation and propagation of internal fracture in solid
Generation of helical gears with new surfaces, topology by application of CNC machines
Analysis of helical involute gears by tooth contact analysis shows that such gears are very sensitive to angular misalignment that leads to edge contact and the potential for high vibration. A new topology of tooth surfaces of helical gears that enables a favorable bearing contact and a reduced level of vibration is described. Methods for grinding of the helical gears with the new topology are proposed. A TCA (tooth contact analysis) program for simulation of meshing and contact of helical gears with the new topology has been developed. Numerical examples that illustrate the proposed ideas are discussed
The Antimicrobial Effect of Silver Ion Impregnation into Endodontic Sealer against Streptococcus mutans.
Pulpal and periradicular diseases are primarily caused by bacterial invasion of the root canal system as a result of caries progression. The presence of residual bacteria at the time of root canal completion (obturation) is associated with significantly higher rate of treatment failure. Re-infection of obturated root canals can be potentially prevented by enhancing the antibacterial activities of root canal obturation materials. We evaluated, in an in vitro model, the antimicrobial efficacy of silver ions added to a common endodontic sealer. For that purpose we performed growth inhibition studies and bacterial viability tests. We measured the zone of inhibition, optical density and performed confocal laser scanning microscopy. Our results show that the silver ions enhance the antimicrobial activity of the root canal sealer against Streptococcus mutans. This study approach may hold promise for studying other biologically based therapies and therefore increasing the success rate of routine orthograde root canal treatment
The Gaseous Extent of Galaxies and the Origin of \lya Absorption Systems. III. Hubble Space Telescope Imaging of \lya-Absorbing Galaxies at z < 1
We present initial results of a program to obtain and analyze HST WFPC2
images of galaxies identified in an imaging and spectroscopic survey of faint
galaxies in fields of HST spectroscopic target QSOs. We measure properties of
87 galaxies, of which 33 are associated with corresponding \lya absorption
systems and 24 do not produce corresponding \lya absorption lines to within
sensitive upper limits. Considering only galaxy and absorber pairs that are
likely to be physically associated and excluding galaxy and absorber pairs
within 3000 \kms of the background QSOs leaves 26 galaxy and absorber pairs and
seven galaxies that do not produce corresponding \lya absorption lines to
within sensitive upper limits. Redshifts of the galaxy and absorber pairs range
from 0.0750 to 0.8912 with a median of 0.3718, and impact parameter separations
of the galaxy and absorber pairs range from 12.4 to kpc with a
median of kpc. The primary result of the analysis is that the
amount of gas encountered along the line of sight depends on the galaxy impact
parameter and B-band luminosity but does not depend strongly on the galaxy
average surface brightness, disk-to-bulge ratio, or redshift. This result
confirms and improves upon the anti-correlation between \lya absorption
equivalent width and galaxy impact parameter found previously by Lanzetta et
al. (1995). There is no evidence that galaxy interactions play an important
role in distributing tenuous gas around galaxies in most cases. Galaxies might
account for all \lya absorption systems with \AA, but this depends on
the unknown luminosity function and gaseous cross sections of low-luminosity
galaxies as well as on the uncertainties of the observed number density of \lya
absorption systems.Comment: Minor changes. Figure 1 stays intact and is available at
ftp://ftp.ess.sunysb.edu/pub/lanzetta/wfpc
The Origin of \lya Absorption Systems at ---Implications from the Hubble Deep Field
The Hubble Deep Field images have provided us with a unique chance to relate
statistical properties of high-redshift galaxies to statistical properties of
\lya absorption systems. Combining an {\em empirical} measure of the galaxy
surface density versus redshift with an {\em empirical} measure of the gaseous
extent of galaxies, we predict the number density of \lya absorption systems
that originate in extended gaseous envelopes of galaxies versus redshift. We
show that at least 50% and as much as 100% of observed \lya absorption systems
of W\apg0.32 \AA can be explained by extended gaseous envelops of galaxies.
Therefore, we conclude that known galaxies of known gaseous extent must produce
a significant fraction and perhaps all of \lya absorption systems over a large
redshift range.Comment: 12 pages, 3 figures, accepted for publication in the Astrophysical
Journal, April 10, 2000 issu
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Protease signaling regulates apical cell extrusion, cell contacts, and proliferation in epithelia.
Mechanisms that sense and regulate epithelial morphogenesis, integrity, and homeostasis are incompletely understood. Protease-activated receptor 2 (Par2), the Par2-activating membrane-tethered protease matriptase, and its inhibitor, hepatocyte activator inhibitor 1 (Hai1), are coexpressed in most epithelia and may make up a local signaling system that regulates epithelial behavior. We explored the role of Par2b in matriptase-dependent skin abnormalities in Hai1a-deficient zebrafish embryos. We show an unexpected role for Par2b in regulation of epithelial apical cell extrusion, roles in regulating proliferation that were opposite in distinct but adjacent epithelial monolayers, and roles in regulating cell-cell junctions, mobility, survival, and expression of genes involved in tissue remodeling and inflammation. The epidermal growth factor receptor Erbb2 and matrix metalloproteinases, the latter induced by Par2b, may contribute to some matriptase- and Par2b-dependent phenotypes and be permissive for others. Our results suggest that local protease-activated receptor signaling can coordinate cell behaviors known to contribute to epithelial morphogenesis and homeostasis
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