626 research outputs found
Slowing Down and Scattering of Ions in Solids
The interaction of particle beams with solids yields three parts, i.e. reflected particles, penetrating particles and trapped particles. At very low energies particle reflection is dominant, at very high energies penetration is the most important effect. Trapped particles are the result of energy loss processes, which on the other hand cause radiation damage in the solid. In the energy range discussed here, i.e. above energies where quantum effects, diffraction etc. are important and below energies where nuclear reactions, relativistic effects etc. may occur, the particle trajectories are classical. The energy loss process can be treated separately as nuclear and electronic stopping power. The collisions of the projectiles with target atoms are hence binary collisions involving a properly chosen screened Coulomb-potential. In single crystals the structural properties enable channeling, which is a very useful tool in sol id state analysis. The electronic stopping includes contributions from single collision processes and collective excitations. Both effects can be described by a dielectric response function. The range of applications covers analytical methods, means to modify solid state properties and also the production of thin films
SPUTTER DEPTH PROFILING OF OPTICAL WAVEGUIDES USING SECONDARY ION MASS SPECTROMETRY
The technique of sputter depth profiling by means of secondary ion mass spectrometry
of samples with high resistivity is reviewed. As examples we discuss optical waveguides made
in lithium niobate by titanium indiffusion and implantation and also yttrium iron garnet
waveguides grown by liquid phase epitaxy on gadolinium gallium garnet. Depth profiling of
these waveguide structures has been performed and the necessary precautions to prevent
charging by the primary ion beam are discussed. In some cases, coating with a metallic layer
is adequate, but a more universal method is charge neutralization by an additional electron
beam
A low-rank solution method for Riccati equations with indefinite quadratic terms
Algebraic Riccati equations with indefinite quadratic terms play an important
role in applications related to robust controller design. While there are many
established approaches to solve these in case of small-scale dense
coefficients, there is no approach available to compute solutions in the
large-scale sparse setting. In this paper, we develop an iterative method to
compute low-rank approximations of stabilizing solutions of large-scale sparse
continuous-time algebraic Riccati equations with indefinite quadratic terms. We
test the developed approach for dense examples in comparison to other
established matrix equation solvers, and investigate the applicability and
performance in large-scale sparse examples.Comment: 19 pages, 2 figures, 5 table
Weight-Related Behavior among Adolescents: The Role of Peer Effects
To investigate whether social interactions in friendship networks influence the following weight-related behaviors of adolescents: exercising regularly, playing an active sport, hours of TV/Video viewing, sleeping six or fewer hours, eating breakfast on weekdays, frequency of eating at fast food restaurants, eating five servings of fruits/vegetables daily, and consuming calorie-dense snacks.Data from a nationally representative sample of adolescents are used to examine the association between peer and individual weight-related behaviors. Evidence from multivariate regression analysis controlling for an extensive list of individual- and family-level factors as well as school-level unobserved heterogeneity is obtained.We find a significant positive association between individuals' and friends' behaviors in terms of sports, exercise and fast food consumption. The estimated associations are robust to controls for individual- and family-level factors, unobserved heterogeneity at the school level and our attempts to account for non-random peer selection.The social transmission of weight-related behaviors is a viable explanation for the spread of obesity in friendship networks documented in recent research. Traditional weight reduction interventions may be fruitfully complemented with strategies that focus on harnessing peer support to modify behaviors
Have We Finally Achieved Actuarial Fairness of Social Security Retirement Benefits and Will It Last?
Working Paper: WP 2014-307This paper develops a framework to analyze the actuarial adjustments faced by American workers who claim Social Security benefits before or after their Full Retirement Age (FRA). We derive the conditions under which these adjustments are “actuarially fair” (or “neutral”) and develop measures to characterize the deviation from the fair form. Fair adjustment schedules are increasing at an increasing rate in take-up age and become flatter as longevity rises. We document that the actuarial fit has improved across generations. Our baseline 3% discount rate scenario estimates that the current schedule deviates from its fair form by less than 1% for average-mortality beneficiaries, compared to 5.1% and 4.0% for male and female beneficiaries in 1980, respectively. The improvement is largely due to the increases in the Delayed Retirement Credit. For men, gains in life expectancy combined with the increase in the FRA also contributed to the improved fit. We predict that the designated increase in the FRA to age 67 will have little effect on the actuarial fit. We investigate schedules reflecting (further) increases in the retirement ages, as recommended by the President’s 2010 Fiscal Commission, and propose alternatives. We also discuss results from the analysis of the adjustments to spousal and widow(er) benefits.Social Security Administrationhttp://deepblue.lib.umich.edu/bitstream/2027.42/109395/1/wp307.pdfDescription of wp307.pdf : Working pape
Disability Crossover: Is There a Hispanic Immigrant Health Advantage that Reverses from Working to Old Age?
BACKGROUND Hispanic immigrants have been found to be more likely to have a disability than US-born populations. Studies have primarily focused on populations aged 60 and older; little is known about immigrant disability at younger ages.
OBJECTIVE Taking a broader perspective, we investigate whether Hispanic immigrants have lower disability rates in midlife; if so, at what ages this health advantage reverses; and the correlates of this pattern.
METHODS Using American Community Survey 2010–2014 data, we estimate age-specific disability prevalence rates by gender, nativity, education, and migration age from age 40 to 80. We also present estimates by six types of disability.
RESULTS Compared to non-Hispanic whites, disability prevalence among foreign-born Mexican women is lower until age 53 (men: 61) and greater after 59 (66). Similar patterns hold for other foreign-born Hispanics. Crossovers are observed in rates of ambulatory, cognitive, independent living, and self-care disability. Evidence of a steeper age– disability gradient among less-educated immigrants is found. Minimal differences are noted by migration age, challenging an acculturation explanation for the crossover.
CONTRIBUTION The paper contributes to a better understanding of immigrant–native disability patterns in the United States. It is the first to systematically document a Hispanic immigrant health advantage in disability that reverses from working to old age. Hispanic immigrants (particularly foreign-born Mexican women), may face steeper risk trajectories, consistent with their greater concentration in low-skill manual occupations. We call for increased scholarly attention to this phenomenon
Electronic structure of the muonium center as a shallow donor in ZnO
The electronic structure and the location of muonium centers (Mu) in
single-crystalline ZnO were determined for the first time. Two species of Mu
centers with extremely small hyperfine parameters have been observed below 40
K. Both Mu centers have an axial-symmetric hyperfine structure along with a
[0001] axis, indicating that they are located at the AB_{O,//} and BC_{//}
sites. It is inferred from their small ionization energy (~6 meV and 50 meV)
and hyperfine parameters (~10^{-4} times the vacuum value) that these centers
behave as shallow donors, strongly suggesting that hydrogen is one of the
primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR
Comparative Analysis of LASIK Flap Diameter and its Centration Using Two Different Femtosecond Lasers
The aim of this study was to compare the diameter, accuracy, variability, and centration with respect to the limbus of corneal flaps created by two femtosecond lasers, the VisuMax, and Wavelight FS200, for laser in situ keratomileusis (LASIK) and how these flaps affect visual outcomes. This is a retrospective chart review of flap morphology created during LASIK Surgery. Overall, 168 eyes underwent flap creation using the WaveLight FS200 laser, and on 189 eyes, the VisuMax laser was used. Of these total number, flap morphology was analyzed in a random sample of 158 eyes; 80 with the Visumax laser and 78 with the WaveLight FS200 laser. Intraoperative photos of the flaps taken by the Wavelight Allegretto EX500 were analyzed. Flap diameters and centration were measured using Adobe Acrobat Pro. All patients had visual acuity measurements including uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent refraction (SE) and refractive astigmatism recorded three months postoperatively. Greater than 90% of patients in both groups achieved a UDVA of 20/20 postoperatively. The mean difference between targeted and achieved flap diameter was 0.50 +/- 0.15 mm in the VisuMax group and 0.35 +/- 0.15 millimeters (mm) in the FS200 group (P<0.01). The flap diameters of the VisuMax group were more precise with a variance of 0.024 mm compared to a variance of 0.038 mm in the FS200 group (P<0.05). VisuMax flaps were more nasally displaced (log(NA/TA) = -0.21 +/- 0.10 mm) compared to the FS200 flaps (log(NA/TA) = 0.03 +/- 0.10 mm), (P< 0.01). We concluded that both the VisuMax and FS200 created flaps larger than the preoperative targeted diameter. VisuMax created corneal flaps that had a greater degree of deviation from the targeted diameter when compared to flaps from the FS200. However, there was less variance in the VisuMax flap diameter. In addition, VisuMax flaps were more nasally displaced. There were no statistically significant differences in visual outcomes when comparing the two femtosecond lasers
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