Reflection-type vapor cell for micro atomic clocks using local anodic bonding of 45° mirrors.

This Letter reports the design, fabrication, and evaluation of reflection-type planar vapor cells for chip-scale atomic clocks. The cell with 2-8 mm cavity length contains two 45° Bragg reflector mirrors assembled using a local anodic bonding. Coherent population trapping resonance of Rb atoms is observed, realizing an atomic clock operation. Allan deviations at an averaging time of 1 s are ${2.2} \times {{1}}{{{0}}^{- 10}}$ and ${9.5} \times {{1}}{{{0}}^{- 11}}$ for 2 mm long and 6 mm long vapor cells, respectively. These results show that planar vapor cells compatible with a system-in-package are feasible without degradation of clock stabilities compared to conventional vertically stacked cells.

Highly piezoelectric MgZr co-doped aluminum nitride-based vibrational energy harvesters.

The first MgZr co-doped AlN-based vibrational energy harvester (VEH) is presented. (MgZr)AlN, which is a new class of doped AlN, provides high piezoelectricity and cost advantage. Using 13%-(MgZr)-doped AlN for micromachined VEHs, maximum output power of 1.3 µW was achieved with a Q-factor of 400 when resonant frequency, vibration acceleration, load resistance were 792 Hz, 8 m/s(2), and 1.1 MΩ, respectively. Normalized power density was 8.1 kW·g(-2)·m(-3). This was one of the highest values among the currently available piezoelectric VEHs.

Concurrent life-course trajectories of employment and marijuana-use: exploring interdependence of longitudinal outcomes.

This study analyzes data on 7661 individuals who participated in the 1979 National Longitudinal Survey of Youth (NLSY79) to estimate trajectories of employment and marijuana-use over a 17-year period. Bivariate random intercept and slope modeling is applied to examine concurrently the cross-correlation between the two concurrent longitudinal trajectories from age 23 to 39. Parameter estimates indicate baseline level (at age 23) of employment to be negatively correlated with marijuana, suggesting marijuana-use is associated with lower workforce productivity at age 23. The longitudinal employment slope is positively correlated with employment intercept for both males and females, indicating that survey participants with higher levels of employment at age 23 are more likely to have a positive impact on employment trajectory over time. For males, however, the employment slope is also significantly correlated with marijuana intercept (r=-0.07), indicating marijuana-use in early adulthood may uniquely lower workforce productivity over age.

A thin-film bulk acoustic resonator and filter with optimal edge shapes for mass production.

The manufacturing conditions of a thin-film bulk acoustic resonator (FBAR) filter were investigated to obtain a high Q factor which is stable for mass production. The FBAR consist of patterned electrodes and piezoelectric films. In this study, the influence of edge shape of the films on the anti-resonance characteristics was investigated using a numerical method. Optimized shape was applied to a 2.5-GHz band resonator and filter. As a result, significant improvement of the Q factor and the insertion loss was confirmed.

Use of fluorine-doped silicon oxide for temperature compensation of radio frequency surface acoustic wave devices.

This paper investigates acoustic properties, including the temperature coefficient of elasticity (TCE), of fluorine-doped silicon oxide (SiOF) films and proposes the application of the films to the temperature compensation of RF SAW devices. From Fourier transform infrared spectroscopy (FT-IR), SiOF films were expected to possess good TCE properties. We fabricated a series of SAW devices using the SiOF-overlay/Cu-grating/LiNbO(3)-substrate structure, and evaluated their performance. The experiments showed that the temperature coefficient of frequency (TCF) increases with the fluorine content r, as we expected from the FT-IR measurement. This means that the Si-O-Si atomic structure measurable by the FT-IR governs the TCE behavior of SiO(2)-based films even when the dopant is added. In comparison with pure SiO(2) with the film thickness h of 0.3 wavelengths (λ), TCF was improved by 7.7 ppm/°C without deterioration of the effective electromechanical coupling factor K2 when r = 3.8 atomic % and h = 0.28λ. Fluorine inclusion did not obviously influence the resonators' Q factors when r < 8.8 atomic %.

Correlation between temperature coefficient of elasticity and fourier transform infrared spectra of silicon dioxide films for surface acoustic wave devices.

We investigated the correlation between the temperature coefficient of elasticity (TCE) and Fourier transform infrared (FT-IR) absorption spectra of SiO(2) for SAW devices. The measurement indicated that the TCE is strongly correlated with peak frequencies; that is, with the fractional change of the Si-O-Si bond angle with temperature.

Employment Trajectories: Exploring Gender Differences and Impacts of Drug Use.

This study investigated the impact of drug use on employment over 20 years among men and women, utilizing data on 7,661 participants in the National Longitudinal Survey of Youth. Growth mixture modeling was applied, and five distinct employment trajectory groups were identified for both men and women. The identified patterns were largely similar for men and women except that a U-shape employment trajectory was uniquely identified for women. Early-initiation drug users, users of "hard" drugs, and frequent drug users were more likely to demonstrate consistently low levels of employment, and the negative relationship between drug use and employment was more apparent among men than women. Also, positive associations between employment and marriage became more salient for men over time, as did negative associations between employment and childrearing among women. Processes are dynamic and complex, suggesting that throughout the life course, protective factors that reduce the risk of employment problems emerge and change, as do critical periods for maximizing the impact of drug prevention and intervention efforts.

Influences of a Covariate on Growth Mixture Modeling.

This study investigated the influence of including a covariate and/or a distal outcome on growth mixture modeling (GMM). GMM was used to examine patterns of days of heroin use over 16 years among 471 heroin users and the relationship of those patterns to mortality (distal outcome). Comparisons were made among four types of models: without a covariate and a distal outcome (two-stage approach), with a distal outcome, with a covariate, and with a covariate and a distal outcome in conjunction with three different covariates. The two-stage approach and models with the inclusion of a distal outcome resulted in different conclusions when testing the impact of latent trajectory membership on the distal outcome. Differences in membership classifications between unconditional and conditional models were mainly determined by two factors: (1) the associations of the trajectories with the covariate and the distal outcome, and (2) the distribution of the covariate in the study sample.