Microstructural Enhancement of Dental Composite and Ceramic Materials by Plasma Etching

Radio frequency plasma etching of a selected number of dental materials , including glass filled polymeric composites, alumina reinforced ceramic, glass ionomer, and zinc oxide eugenol enhanced microstructural detail for scanning electron microscopy analyses. All four plasmas, argon , oxygen, carbon tetrafluoride (CF4), and CF4 + 4% 0 2 , proved effective, but the latter was the most effective. The etching of all materials , except the ceramic, was accomplished by the selective removal of a polymeric component. For the glass filled composites , this involved removal of the Bis-GMA matrix resin, leaving the filler particles in relief. For a microfilled composite, excellent delineation of the microfine particles contained within the prepolymerized polymer blocks was obtained , while for a hybrid composite, delineation of a bimodal particle distribution was revealed. For glass ionomer material , plasma etching enhanced the delineation between the silica gel lined unreacted glass particles and the polyacrylate matrix, as well as clearly defining regions in the matrix that were totally polysalt in nature. For a resin filled zinc oxide eugenol material, plasma etching removed the resin, leaving behind a porous material made-up of zinc oxide particles held together in a matrix partly composed of crystallites

Microstructural Effects Regarding Fracture of Clinically Retrieved Dental Sonic and Hand Scalers

The fracture surfaces of sonic and hand scaler instruments fractured under clinical and laboratory conditions were compared to their etched sections, and analyzed for evidence revealing the process that led to their failure. Scanning electron microscopy and energy-dispersive spectroscopy indicated the quality of the martensitic stainless steel comprising the sonic scalers, all from one manufacturer, was inferior to the steel comprising the hand scalers from another manufacturer. The sonic scalers contained stringer inclusions aligned longitudinally and consisting of calcium, aluminum, silicon, and other elements up to 50 µm in length. The sonic scalers displayed brittle fracture while the hand scalers displayed mainly ductile fracture. Microcracks occurred between stringer inclusions. Microhardness for sonic scalers, although slightly higher and significantly different from hand scalers, proved ineffective for detecting a structure-property relationship. Microscopy, however, proved very useful for this purpose and also well-suited for analyzing the stress state occurring on the instruments at the time of failure. All sonic scalers were stressed by being bent inwards, while a hand scaler was pulled and torqued by twisting. Retained coarse grinding grooves also affected fracture. Recommendations are made for hand instrument standards to include checks on steel quality for inclusions of the stringer type

Does Care Lead to Share? Evidence from a Randomized Field Experiment on Call for Sharing

Information sharing through online WOM has become increasingly important for businesses. Despite the popularity of online referral programs, little is known about how firms can optimally design call for sharing to encourage referrals, as well as the motives underlying those referrals. In collaboration with a large US based online platform, we conduct a randomized field experiment involving 100,000 customers to identify the causal effect of three types of call for sharing (egoistic, equitable and altruistic). Our experiment shows that ‘altruistic’ call for sharing leads to the highest likelihood of sharing and best sharing outcomes. In addition, the analysis results provide direct managerial implications to firms on the optimal design of call for sharing campaigns (how, to whom and when to initial call for sharing). Finally, we discuss the key differences and complementarity between call for sharing and call for purchase, and offer guidance on firm\u27s integrated marketing communication strategy

Surface Analysis of Tarnished Dental Alloys

Six crown and bridge alloys ranging in nobility between 25-63 wt % (18-45 at %) were analyzed by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and secondary ion mass spectroscopy (SIMS), as well as by L*a*b* colorimetry before and after in vitro tarnishing in artificial saliva with and without additions of 0.00016, 0.016, and 1.6 % Na2S with a rotating wheel apparatus. All alloys except the lowest of 18 at % changed colors to about the same degree after 72 h of tarnishing. All alloys decreased in L*, while increased in both a* and b*, thus appearing darker and with increased redness and yellowness. This was due to localized darkening and to other products. For all alloys except one, saliva without sulfide promoted color changes more severe than for saliva with 0.016% Na2S. For the most part, analysis by EDS was unable to detect differences between the tarnished films and the as-polished surfaces. SIMS analysis, however, showed changes in the substrate ion (Cu, Ag, Pd, and In) peak intensities. In most cases the intensities decreased and with the decrease greater with the sulfide-free saliva than with sulfide-containing. This indicated that sulfide promoted insoluble deposition of products. Changes in the Ag, Pd, and In peak intensities followed much the same pattern as with Cu. The as-polished surfaces, even though carefully prepared, showed much contamination in the form of organics, namely C, CH, N, NH, 0, CHN, CN, as well as from Na, K, Ca, Si, S, Cl, and others. Most tarnished surfaces showed large increases in Na, K, and Ca, and with the sulfide-free saliva being more severe in this regard. The mass spectrum also showed peaks with atomic mass units in the ranqe 55-58 related to only some of the tarnished surfaces

Further Development of the Sextupole and Decapole Spool Corrector Magnets for the LHC

In the Large Hadron Collider (LHC) the main dipoles will be equipped with sextupole (MCS) and decapole (MCD) spool correctors to meet the very high demands of field quality required for the satisfactory operation of the machine. Each decapole corrector will in addition have an octupole insert (MCO) and the assembly of the two is designated MCDO. These correctors are needed in relatively large quantities, i.e. 2464 MCS Sextupoles and 1232 MCDO Decapole-Octupole assemblies. Half the number of the required spool correctors will be made in India through a collaboration between CERN and CAT (Centre for Advanced Technology, Indore, India), the other half will be built by European industry. The paper describes final choices concerning design, materials, production techniques, and testing so as to assure economic magnet manufacture but while maintaining a homogenous magnetic quality that results in a robust product

The face mask – its role in prevention of COVID-19

The novel coronavirus disease (COVID-19) is causing huge morbidity and mortality throughout the world. Wearing face masks is an important strategy for its prevention, along with hand washing, using alcohol-based sanitizer and physical distancing. In the absence of AGPs (Aerosol Generating Procedures), health workers providing direct care to COVID-19 patients should wear a medical mask. In settings where AGPs are performed (e.g. COVID-19 intensive and semi-intensive care units), health workers should wear respirator masks (N95 or FFP2 or FFP3 standard). Respirators can be reused up to five times assuming there is no soiling and minimal to no viral contamination of the mask. Cloth face masks are advised in public settings. It is crucial to wear, remove and dispose of masks appropriately for maximum protection. With disposable masks becoming an impending threat to nature, reusable LEAF masks with long lasting filters offer a promising solution to protect our environment

Experience with the Fabrication and Testing of the Sextupole Superconducting Corrector Magnets for the LHC

The LHC main dipoles will be equipped with sextupole corrector magnets with a field strength of 1700 x2 (T,m) and a magnetic length of 110 mm to correct sextupole field errors. Within the LHC magnet programme CERN has developed in collaboration with CAT a cosine-q type of design where much emphasis has been put on the cost reduction. The magnet features a two-layer racetrack coil, without end spacers, wound from a rectangular NbTi-wire. The two layers are wound simultaneously turning in opposite directions. The yoke is made of a scissor-type of lamination, which allows bringing the iron close to the coil for field enhancement. In this paper we review the manufacturing experiences with the first 12 prototypes built at CERN and CAT. The results of the training at 4.2 K and 1.9 K are presented along with the magnetic field quality measured at room temperature and at 1.9 K

A heuristic approach for the allocation of resources in large-scale computing infrastructures

An increasing number of enterprise applications are intensive in their consumption of IT, but are infrequently used. Consequently, organizations either host an oversized IT infrastructure or they are incapable of realizing the benefits of new applications. A solution to the challenge is provided by the large-scale computing infrastructures of Clouds and Grids which allow resources to be shared. A major challenge is the development of mechanisms that allow efficient sharing of IT resources. Market mechanisms are promising, but there is a lack of research in scalable market mechanisms. We extend the Multi-Attribute Combinatorial Exchange mechanism with greedy heuristics to address the scalability challenge. The evaluation shows a trade-off between efficiency and scalability. There is no statistical evidence for an influence on the incentive properties of the market mechanism. This is an encouraging result as theory predicts heuristics to ruin the mechanism’s incentive properties. Copyright © 2015 John Wiley & Sons, Ltd

Electronic depiction of magnetic origin in undoped and Fe doped TiO2-d epitaxial thin films

We have investigated the electronic and magnetic properties of the pulsed laser deposited epitaxial thin films of undoped and Fe doped (4 at. %) anatase TiO2-d by photoemission, magnetization measurements, and ab-initio band structure calculations. These films show room temperature magnetic ordering. It is observed that Fe ions hybridize with the oxygen vacancy induced Ti3+ defect states. Our study reveals the formation of local magnetic moment at Ti and Fe sites to be responsible for magnetic ordering. A finite density of states at the Fermi level in both undoped and Fe doped films is also observed, suggesting their degenerate semiconducting nature. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3640212]991