Control of the Cross Section Geometry of Extruded Dental Porcelain Slurries for Rapid Prototyping Applications

This study investigates the dependence of the cross section geometry of extruded dental porcelain slurries on the rheological property of the slurry and the extrusion conditions. It is found that a pseudoplastic slurry is a basic requirement for obtaining extruded lines with rectangular cross sections. The cross section geometry of the extrudate is also strongly affected by extrusion parameters including the extrusion nozzle height, nozzle moving speed, and extrusion rate. Proper combinations of these extrusion parameters are necessary in order to obtain extrudates with near rectangular cross sections. The results obtained have been explained in terms of the interactions among the rheological properties of the slurry, the shear rate imposed on the slurry during extrusion, the wettability of the slurry on the substrate, and the forced flow of the slurry during extrusion.The authors gratefully acknowledge financial support provided by the National Science Foundation under Grant Nos: DMI-9908249 and DMI-0218169.Mechanical Engineerin

Molecular antimicrobial resistance surveillance for neisseria gonorrhoeae, Northern Territory, Australia

Neisseria gonorrhoeae antimicrobial resistance (AMR) is a globally recognized health threat; new strategies are needed to enhance AMR surveillance. The Northern Territory of Australia is unique in that 2 different first-line therapies, based primarily on geographic location, are used for gonorrhea treatment. We tested 1,629 N. gonorrhoeae nucleic acid amplification test–positive clinical samples, collected from regions where ceftriaxone plus azithromycin or amoxicillin plus azithromycin are recommended first-line treatments, by using 8 N. gonorrhoeae AMR PCR assays. We compared results with those from routine culture-based surveillance data. PCR data confirmed an absence of ceftriaxone resistance and a low level of azithromycin resistance (0.2%), and that penicillin resistance was \u3c5% in amoxicillin plus azithromycin regions. Rates of ciprofloxacin resistance and penicillinase-producing N. gonorrhoeae were lower when molecular methods were used. Molecular methods to detect N. gonorrhoeae AMR can increase the evidence base for treatment guidelines, particularly in settings where culture-based surveillance is limited

An Elliptic Yangian-Invariant, `Leading Singularity'

We derive closed formulae for the first examples of non-algebraic, elliptic `leading singularities' in planar, maximally supersymmetric Yang-Mills theory and show that they are Yangian-invariant.Comment: 4+2 pages; 2 figures. Ancillary files include computer-usable formula

Giant impacts in the Saturnian System: a possible origin of diversity in the inner mid-sized satellites

It is widely accepted that Titan and the mid-sized regular satellites around Saturn were formed in the circum-Saturn disk. Thus, if these mid-sized satellites were simply accreted by collisions of similar ice-rock satellitesimals in the disk, the observed wide diversity in density (i.e., the rock fraction) of the Saturnian mid-sized satellites is enigmatic. A recent circumplanetary disk model suggests satellite growth in an actively supplied circumplanetary disk, in which Titan-sized satellites migrate inward by interaction with the gas and are eventually lost to the gas planet. Here we report numerical simulations of giant impacts between Titan-sized migrating satellites and smaller satellites in the inner region of the Saturnian disk. Our results suggest that in a giant impact with impact velocity > 1.4 times the escape velocity and impact angle of ~45 degree, a smaller satellite is destroyed, forming multiple mid-sized satellites with a very wide diversity in satellite density (the rock fraction = 0-92 wt%). Our results of the relationship between the mass and rock fraction of the satellites resulting from giant impacts reproduce the observations of the Saturnian mid-sized satellites. Giant impacts also lead to internal melting of the formed mid-sized satellites, which would initiate strong tidal dissipation and geological activity, such as those observed on Enceladus today and Tethys in the past. Our findings also imply that giant impacts might have affected the fundamental physical property of the Saturnian mid-sized satellites as well as those of the terrestrial planets in the solar system and beyond.Comment: 18 pages, 3 figures, Planetary and Space Science, in pres

Collisional Stripping and Disruption of Super-Earths

The final stage of planet formation is dominated by collisions between planetary embryos. The dynamics of this stage determine the orbital configuration and the mass and composition of planets in the system. In the solar system, late giant impacts have been proposed for Mercury, Earth, Mars, and Pluto. In the case of Mercury, this giant impact may have significantly altered the bulk composition of the planet. Here we present the results of smoothed particle hydrodynamics simulations of high-velocity (up to ~5 v_esc) collisions between 1 and 10 M_Earth planets of initially terrestrial composition to investigate the end stages of formation of extrasolar super-Earths. As found in previous simulations of collisions between smaller bodies, when collision energies exceed simple merging, giant impacts are divided into two regimes: (1) disruption and (2) hit-and-run (a grazing inelastic collision and projectile escape). Disruption occurs when the impact parameter is near zero, when the projectile mass is small compared to the target, or at extremely high velocities. In the disruption regime, we derive the criteria for catastrophic disruption (when half the total colliding mass is lost), the transition energy between accretion and erosion, and a scaling law for the change in bulk composition (iron-to-silicate ratio) resulting from collisional stripping of a mantle.Comment: 10 pages, 1 table, 4 figures. Accepted for publication in ApJ Letter

Studies on Slurry Extrusion for Dental Restoration

This study investigates dental restoration via dental powder delivery by slurry extrusion, followed by laser densification of these extruded slurries. The entire process is fully controlled by a computer. The shape of the extrudate before laser densification depends strongly on the formulation of slurries. Slurries prepared in a stable pH range can disperse high volume of solids, but have low viscosities and spread uncontrollably when extruded. In contrast, slurries first prepared in a stable pH range and subsequently adjusted to an unstable pH range have exhibited pseudoplastic behavior. Such slurries have a low extrusion pressure to avoid phase separation, and at the same time their yield points are high enough to maintain the shape of extrudates.The authors gratefully acknowledge financial support provided by the National Science Foundation under Grant No: DMI-9908249.Mechanical Engineerin

Future Arctic temperature change resulting from a range of aerosol emissions scenarios

The Arctic temperature response to emissions of aerosols—specifically black carbon (BC), organic carbon (OC), and sulfate—depends on both the sector and the region where these emissions originate. Thus, the net Arctic temperature response to global aerosol emissions reductions will depend strongly on the blend of emissions sources being targeted. We use recently published equilibrium Arctic temperature response factors for BC, OC, and sulfate to estimate the range of present‐day and future Arctic temperature changes from seven different aerosol emissions scenarios. Globally, Arctic temperature changes calculated from all of these emissions scenarios indicate that present‐day emissions from the domestic and transportation sectors generate the majority of present‐day Arctic warming from BC. However, in all of these scenarios, this warming is more than offset by cooling resulting from SO2 emissions from the energy sector. Thus, long‐term climate mitigation strategies that are focused on reducing carbon dioxide (CO2) emissions from the energy sector could generate short‐term, aerosol‐induced Arctic warming. A properly phased approach that targets BC‐rich emissions from the transportation sector as well as the domestic sectors in key regions—while simultaneously working toward longer‐term goals of CO2 mitigation—could potentially avoid some amount of short‐term Arctic warming.Key PointsReductions in anthropogenic black carbon emissions alone could slow Arctic warming by mid‐centuryArctic cooling from reduced BC is more than offset by warming from reduced SO2 across all of the RCP mitigation scenariosDomestic and transport emissions from Asia hold the greatest potential for reducing Arctic warming from anthropogenic aerosolsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133610/1/eft2124_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133610/2/eft2124.pd

Neural Entrainment is Associated with Subjective Groove and Complexity for Performed but not Mechanical Musical Rhythms

Both movement and neural activity in humans can be entrained by the regularities of an external stimulus, such as the beat of musical rhythms. Neural entrainment to auditory rhythms supports temporal perception, and is enhanced by selective attention and by hierarchical temporal structure imposed on rhythms. However, it is not known how neural entrainment to rhythms is related to the subjective experience of groove (the desire to move along with music or rhythm), the perception of a regular beat, the perception of complexity, and the experience of pleasure. In two experiments, we used musical rhythms (from Steve Reich’s Clapping Music) to investigate whether rhythms that are performed by humans (with naturally variable timing) and rhythms that are mechanical (with precise timing), elicit differences in 1) neural entrainment, as measured by inter-trial phase coherence, and 2) subjective ratings of the complexity, preference, groove, and beat strength of rhythms. We also combined results from the two experiments to investigate relationships between neural entrainment and subjective perception of musical rhythms. We found that mechanical rhythms elicited a greater degree of neural entrainment than performed rhythms, likely due to the greater temporal precision in the stimulus, and the two types only elicited different ratings for some individual rhythms. Neural entrainment to performed rhythms, but not to mechanical ones, correlated with subjective desire to move and subjective complexity. These data therefore suggest multiple interacting influences on neural entrainment to rhythms, from low-level stimulus properties to high-level cognition and perception

Evaluation of Microstructure and Properties for Multi-Materials Laser Densification of Dental Restoration 159

Traditional dental restorations are produced by the porcelain-fused-to-metal (PFM) process, in which a dental restoration is cast from a metallic alloy and then covered with dental porcelains by several firing processes, which is both labor intensive and expensive. In this paper, the feasibility of dental restorations is investigated using a multi-materials laser densification (MMLD) process. To evaluate the effectiveness of the MMLD process, nickel powders and commercial dental porcelain powders are laser densified using YAG and CO2 lasers respectively. Effects of processing parameters, e.g. laser scanning rate and target temperature, are evaluated and the microstructure of processed nickel and porcelain materials are characterized for the optimization of laser densification. Results indicate that densities of laser processed nickel and dental porcelain are strongly dependent of processing parameters. Fully dense layers are achievable with proper processing conditions.Mechanical Engineerin