Selective Laser Sintering of Alumina-Boron Oxide Composites

The selection of an optimum composite system for selective laser sintering (SLS) is based on materials properties such as the melting point and the wettability between the components in the composite powder. The alumina-boron oxide composite system is attractive for SLS because the presence of the low melting component B203 (melting point 4500 C) can enhance sintering. A better wetting of solid alumina powder by molten boron oxide can also aid densification process. The alumina-boron oxide conlposite system has been investigated by SLS and selective laser reactive sintering (SLRS). The role of boron oxide content as a binder, laser power density, and secondary heat treatment on the microstructure and mechanical properties is discussed.Mechanical Engineerin

Asymptotically hyperbolic manifolds with small mass

For asymptotically hyperbolic manifolds of dimension $n$ with scalar curvature at least equal to $-n(n-1)$ the conjectured positive mass theorem states that the mass is non-negative, and vanishes only if the manifold is isometric to hyperbolic space. In this paper we study asymptotically hyperbolic manifolds which are also conformally hyperbolic outside a ball of fixed radius, and for which the positive mass theorem holds. For such manifolds we show that the conformal factor tends to one as the mass tends to zero

SEGA mode locking

Korte pulsen licht worden al sinds lange tijd gebruikt voor een heel scala aan toepassingen, voornamelijk in de fotonica. Zo kun je bijvoorbeeld denken aan materiaalbewerking, datacommunicatie via glasvezel, wetenschappelijk onderzoek, microscopie, eigenlijk teveel om op te noemen. De techniek om korte lichtpulsen te maken, met behulp van een laser, heet “mode locking”. Er is echter een groot probleem bij de standaard methode voor mode locking. De combinatie van een hoge repetitie frequentie (lees: een hoog aantal pulsen per seconde) en een hoog gemiddeld lichtvermogen (in de orde grootte van enkele tientallen Watts) is onmogelijk. Maar omdat fysici er niet van houden als iets “onmogelijk” is, hebben wij een methode ontwikkeld die de combinatie hoge repetitie frequentie en hoog lichtvermogen wel degelijk mogelijk gaat maken. Deze methode noemen wij Separate Gain mode locking, of afgekort SEGA mode locking

Calcium sensitivity and the Frank-Starling mechanism of the heart are increased in titin N2B region deficient mice

Previous work suggests that titin-based passive tension is a factor in the Frank-Starling mechanism of the heart, by increasing length-dependent activation (LDA) through an increase in calcium sensitivity at long sarcomere length. We tested this hypothesis in a mouse model (N2B KO model) in which titin-based passive tension is elevated as a result of the excision of the N2B element, one of cardiac titin's spring elements. LDA was assessed by measuring the active tension-pCa (-log[Ca2+]) relationship at sarcomere length (SLs) of 1.95, 2.10 and 2.30mum in WT and N2B KO skinned myocardium. LDA was positively correlated with titin-based passive tension, due to an increase in calcium sensitivity at the longer SLs in the KO. For example, at pCa 6.0 the KO:WT tension ratio was 1.28+/-0.07 and 1.42+/-0.04 at SLs of 2.1 and 2.3mum, respectively. There was no difference in protein expression or phosphorylation of sarcomeric proteins. We also measured the calcium sensitivity after PKA treating the skinned muscle and found that titin-based passive tension was also now correlated with LDA, with a slope that was significantly increased compared to no PKA treatment. Finally, we performed isolated heart experiments and measured the Frank-Starling relation (slope of developed wall stress-LV volume relation) as well as diastolic stiffness (slope of diastolic wall stress - volume relation). The FSM was more pronounced in the N2B KO hearts and the slope of the FSM correlated with diastolic stiffness. These findings support that titin-based passive tension triggers an increase in calcium sensitivity at long sarcomere length, thereby playing an important role in the Frank-Starling mechanism of the heart

Distributed Collaborative Learning Communities Enabled by Information Communication Technology

How and why can Information Communication Technology (ICT) contribute to enhancing learning in distributed Collaborative Learning Communities (CLCs)? Drawing from relevant theories concerned with phenomenon of ICT enabled distributed collaborative learning, this book identifies gaps in the current knowledge. Many questions can be asked about the role of technology in distributed CLCs. How technology is enabling collaborative learning in learning communities is an important one. What are the issues and problems in the context of technology enabled collaborative learning, is another. The articulation of CLC characteristics stem from the Communities of Practice and Communities and Technologies movements that have taken root in twenty-first century Information Society dialog. The theoretical lens provides a framework to study this phenomenon empirically in a case study setting. The research methodology explains the choice and justification for the single case study of the Fielding Graduate University. Fielding offers a unique example of both the phenomenon and context of technology enabled distributed graduate education. The study findings can begin to be generalized to CLCs with similar characteristics to the Fielding Graduate University. Because of the need for intense collaboration, distributed collaborative learning can be facilitated by the use of rich media. Where people use media rich technologies their distributed collaborative learning results seem to be better than their colleagues that did not use ICT. Therefore, media rich ICTs with collaborative features may improve the level of learning and performance in collaborative distributed learning environments

Detection and isolation of chikungunya virus from field collected Aedes albopictus skuse in selected sites, Peninsular Malaysia

Chikungunya fever, an Aedes borne viral disease, is becoming a serious public health concern today since the first reported outbreak in Port Klang in 1998/99. Recently, more outbreaks were reported in Malaysia. Entomological investigations were conducted in Chikungunya virus cases localities in Peninsular Malaysia which cover Johor, Negeri Sembilan, Melaka, Perak, Pahang and Selangor state in order to identify the vector responsible for transmitting the Chikungunya virus. The adult mosquitoes were collected using modified aspirator and sweep net methods, whereas water holding containers were inspected for larvae. Reverse transcriptase polymerase chain reaction (RT-PCR) were used as the detection of the virus. Positive samples were inoculated on the cell to isolate the virus. The most common species collected at the localities was Aedes albopictus followed by Culex quinquefasciatus, Aedes aegypti and Armigeres sp. Five pools (n=78) of female, adult Aedes albopictus collected from Tangkak, Johor were positive for the Chikungunya virus as detected by reverse transcription-polymerase chain reaction. Three isolates were obtained and grouped with Central/East African genotype. The presence of Chikungunya virus in wild Aedes albopictus indicated that this mosquito is the most likely vector responsible for the transmission of virus to humans in Johor during the outbreak

Near-equality of the Penrose Inequality for rotationally symmetric Riemannian manifolds

This article is the sequel to our previous paper [LS] dealing with the near-equality case of the Positive Mass Theorem. We study the near-equality case of the Penrose Inequality for the class of complete asymptotically flat rotationally symmetric Riemannian manifolds with nonnegative scalar curvature whose boundaries are outermost minimal hypersurfaces. Specifically, we prove that if the Penrose Inequality is sufficiently close to being an equality on one of these manifolds, then it must be close to a Schwarzschild space with an appended cylinder, in the sense of Lipschitz Distance. Since the Lipschitz Distance bounds the Intrinsic Flat Distance on compact sets, we also obtain a result for Intrinsic Flat Distance, which is a more appropriate distance for more general near-equality results, as discussed in [LS]Comment: 19 pages, 2 figure

Color Stability of Restorative Resins Under Accelerated Aging

The color stability of seven commercial composite resins, an unfilled resin, and three glazes was studied under conditions of accelerated aging by reflection spectrophotometry and visually with Munsell color tabs. After aging for 900 hours, most of the resins had lower values of luminous reflectance and excitation purity and higher values of dominant wavelength and contrast ratio compared to values at baseline.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66937/2/10.1177_00220345780570111101.pd