The advent of microfabricated ion traps for the quantum information community has allowed research groups to build traps that incorporate an unprecedented number of trapping zones. However, as device complexity has grown, the number of digital-to-analog converter (DAC) channels needed to control these devices has grown as well, with some of the largest trap assemblies now requiring nearly one hundred DAC channels. Providing electrical connections for these channels into a vacuum chamber can be bulky and difficult to scale beyond the current numbers of trap electrodes. This paper reports on the development and testing of an in-vacuum DAC system that uses only 9 vacuum feedthrough connections to control a 78-electrode microfabricated ion trap. The system is characterized by trapping single and multiple 40 Ca + ions. The measured axial mode stability, ion heating rates, and transport fidelities for a trapped ion are comparable to systems with external (air-side) commercial DACs.
Several factors are converging to enable atomic clocks to be manufactured with very small dimensions and run at low operating power. MOEMS technology, high-speed vcsels, microelectronics, wafer-scale packaging, and the all-optical CPT method of exciting atomic transitions are key ingredients in the quest to make precision time-keeping devices with chip-scale dimensions. In this paper we report on the design and process that enable an atomic clock to be made with a total volume of 1.7 cm^3, a total power budget of 57 mWatts, and an Allan Deviation at 1 hour of 5E-12.
As gas turbine (GT) temperatures have increased, thermal barrier coatings (TBCs) have become a critically important element in hot section component durability. Ceramic TBCs permit significantly increased gas temperatures, reduced cooling requirements, and improve engine fuel efficiency and reliability. TBCs are in use throughout the GT hot section with turbine blades, vanes, and combustion hardware, now being designed with TBCs or upgraded with TBCs during component refurbishment (Miller, 1987, “Current Status of Thermal Barrier Coatings,” Surf. Coat. Technol., 30(1), pp. 1–11; Clarke et al., 2012, “Thermal-Barrier Coatings for More Efficient Gas-Turbine Engines,” MRS Bull., 37(10), pp. 891–898). While the industry standard 6–9 wt. % yttria stabilized zirconia (7YSZ) has been the preferred ceramic composition for the past 30+ yr, efforts have been underway to develop improved TBCs (Stecura, 1986, “Optimization of the Ni–Cr–Al–Y/ZrO2–Y2O3 Thermal Barrier System,” Adv. Ceram. Mater., 1(1), pp. 68–76; Stecura, 1986, “Optimization of the Ni–Cr–Al–Y/ZrO2–Y2O3 Thermal Barrier System,” NASA Technical Memorandum No. 86905). The principal development goals have been to lower thermal conductivity, increase the sintering resistance, and have a more stable crystalline phase structure allowing to use above 1200 °C (2192 °F) (Levi, 2004, “Emerging Materials and Processes for Thermal Barrier Systems,” Curr. Opin. Solid State Mater. Sci., 8(1), pp. 77–91; Clarke, 2003, “Materials Selection Guidelines for Low Thermal Conductivity Thermal Barrier Coatings,” Surf. Coat. Technol., 163–164, pp. 67–74). National Aeronautics and Space Administration (NASA) has developed a series of advanced low conductivity, phase stable and sinter resistant TBC coatings utilizing multiple rare earth dopant oxides (Zhu and Miller, 2004, “Low Conductivity and Sintering-Resistant Thermal Barrier Coatings,” U.S. Patent No. 6,812,176 B1). One of the coating systems NASA developed is based on Ytterbia, Gadolinia, and Yttria additions to ZrO2 (YbGd-YSZ). This advanced low conductivity (low k) TBC is designed specifically for combustion hardware applications. In addition to lower thermal conductivity than 7YSZ, it has demonstrated thermal stability and sintering resistance to 1650 °C (3000 °F). The Electric Power Research Institute (EPRI) and cincinnati thermal spray (CTS) have teamed together in a joint program to commercialize the YbGd-YSZ TBC coating system for GT combustion hardware. The program consists of validation of coating properties, establishment of production coating specifications, and demonstration of coating performance through component engine testing of the YbGd-YSZ TBC coating system. Among the critical to quality coating characteristics that have been established are (a) coating microstructure, (b) TBC tensile bond strength, (c) erosion resistance, (d) thermal conductivity and sintering resistance, and (e) thermal cycle performance. This paper will discuss the coating property validation results comparing the YbGd-YSZ TBC to baseline production combustor coatings and the status of coating commercialization efforts currently underway.
A chronometric mental rotation paradigm was applied to examine manipulation of visual imagery in early adolescence in relation to age, sex, mental rotation ability (measured psychometrically), and socioeconomic background. Fifth- and seventh-grade boys and girls from middle and lower socioeconomic backgrounds viewed tachistiscopically letters of the alphabet presented at 0 degrees, 60 degrees, 120 degrees, and 180 degrees of rotation and were asked to judge whether the letter was forward or backward. In one condition, children were given no information about the test letter, and in the other, advance visual information about its identity and orientation was provided. With age, children became more skillful at rotating and were more likely to show evidence of using the advance information as a visual image. There were no sex differences. Socioeconomic differences were more pronounced in the fifth than the seventh grade. Children showing high mental rotation ability were more likely than low-ability children to show evidence of rotating visual stimuli on the chronometric measure. The findings are discussed in terms of adolescent cognitive development.
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