Phase formation in ion‐irradiated and annealed Ni‐rich Ni‐Al thin films

Phase formation was studied in ion‐irradiated multilayer and coevaporated Ni‐20 at. % Al films supported by Cu, Mo, and Ni transmission electron microscopy (TEM) grids. Irradiation with either 700‐keV Xe or 1.7‐MeV Xe, to doses sufficient to homogenize the multilayers (≥7.5×1015 cm−2), resulted in the formation of metastable supersaturated γ and HCP phases in both film types. Post‐irradiation annealing of multilayers at 450 °C for 1 h transformed the metastable phases to a two‐phase γ+γ′ microstructure. In the absence of Cu, the formation of γ′ appeared to proceed by a traditional diffusional growth mechanism, resulting in small (<50 Å) γ′ precipitates in γ matrix grains. The presence of Cu caused the formation of a dual‐phase γ+γ′ structure (i.e., distinct, equal‐sized grains of γ and γ′) during post‐irradiation annealing. It is suggested that copper affected the nucleation of γ′ precipitates and increased the kinetics of growth resulting in the dual‐phase morphology. Strong irradiation‐induced textures were observed in the multilayers that were less pronounced in the coevaporated films. The texture in the multilayers was attributed to the presence of a slight as‐evaporated texture combined with the enhanced atomic mobility due to the heat‐of‐mixing released during irradiation. The irradiation‐induced texture appeared to be necessary for the formation of the dual‐phase structure since it likely provided high‐diffusivity paths for Cu to diffuse into the film from the TEM grid.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70874/2/JAPIAU-69-4-2021-1.pd

The heat‐of‐mixing effect on ion‐induced grain growth

Irradiation experiments were conducted on multilayer (ML) and coevaporated (CO) thin films in order to examine the role that the heat‐of‐mixing (ΔHmix) has in ion‐induced grain growth. Room‐temperature irradiations using 1.7‐MeV Xe ions were performed in the High Voltage Electron Microscope at Argonne National Laboratory. The ML films (Pt‐Ti, Pt‐V, Pt‐Ni, Au‐Co, and Ni‐Al) spanned a large range of calculated ΔHmix values. Comparison of grain growth rates between ML and CO films of a given alloy confirmed a heat‐of‐mixing effect. With the exception of the Pt‐V system, differences in grain growth rates between ML and CO films varied according to the sign of the calculated ΔHmix of the system. Substantial variations in growth rates among CO alloy films experiencing similar displacement damage demonstrated that a purely collisional approach is inadequate for describing ion‐induced grain growth. Therefore consideration must also be given to material‐specific properties, such as cohesive energy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70305/2/JAPIAU-70-3-1252-1.pd

Ion-induced grain growth in multilayer and coevaporated metal alloy thin films

Irradiation experiments were conducted on multilayer (ML) and coevaporated (CO) thin films in order to examine the role that the heat-of-mixing ([Delta]Hmix) has in ion-induced grain growth. Room-temperature irradiations using 1.7 MeV Xe were performed in the High Voltage Electron Microscope at Argonne National Laboratory. The alloys studied (Pt-Ti, Pt-V, Pt-Ni, Au-Co and Ni-Al) spanned a large range of [Delta]Hmix values. Comparison of grain growth rates between ML and CO films of a given alloy confirmed a heat of mixing effect. Differences in grain growth rates between ML and CO films scaled according to the sign and magnitude of [Delta]Hmix of the system (with the exception of the Pt-V system). Substantial variations in growth rates among CO alloy films experiencing similar irradiation damage demonstrated that a purely collisional approach is inadequate for describing ion-induced grain growth and consideration must also be given to material-specific properties. Results from CO alloy films were consistent with a thermal spike model of ion-induced grain growth. The grain boundary mobility was observed to be proportional to the thermal spike-related parameter, F2D/[Delta]H3coh, where FD is the energy deposited in nuclear interactions and [Delta]Hcoh is the cohesive energy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29259/1/0000316.pd

Grain growth and phase morphology in ion beam mixed, two phase Ni---Al and Ni---Cr---Al alloys

Multilayers of Ni---21Al and Ni---20Cr---10Al were subjected to ion beam mixing using 350 keV Ni+ ions and/or thermal annealing at 440[deg]C to study the development of grain growth and phase morphology. Two film thicknesses of Ni---21 Al (60 and 120 nm) were investigated. Both thermal annealing and irradiation resulted in grain growth in the Ni---21Al samples. Grain size increased by a factor of 7 after irradiation and only 3-4 after annealing. Annealing produced a two phase [gamma] + [gamma]' structure and nonuniform grain sizes while the irradiation produced a supersaturated solid solution with more uniform grain size. Annealing subsequent to irradiation produced a structure consisting of [gamma] + [gamma]' and an HCP phase. There was no difference in grain growth behavior as a function of film thickness. The Ni---Cr---Al film exhibited no grain growth during annealing and only a factor of 6 increase during irradiation. Irradiation alone or post-irradiation annealing produced nearly identical structures of [gamma] and the HCP phase. The [gamma]' phase was never observed in the Ni---Cr---Al film. All irradiated samples showed a more uniform grain size compared to that following annealing. Considerable texture was observed in all irradiated samples in which the gamma grains in the film were aligned with the Ni grains in the substrate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28023/1/0000459.pd

Laser-driven micro-explosive bonding of aluminium films to copper and silicon

Laser explosive microfabrication was used to bond micrometre-thick aluminium films to both copper and silicon substrates. Bonding was observed in both systems for laser intensities greater than about 1 × 10 9 W cm −2 and resulted in contiguous, uniform films when performed in a rough vacuum of 25 to 70 millitorr. At intensities greater than 9 × 109 W cm-2 the transferred films were generally black in colour due to oxidation in the aluminium-on-copper shots and due to substrate vaporization in the aluminium-on-silicon shots. SEM examination of the bond interfaces indicated mixing of film and substrate through wave formation and possibly through liquid-phase mixing due to thermal conduction of the laser pulse. Tape adhesion testing of the laser-bonded films showed a significant increase in adhesion over vapour-deposited films in both Al-Cu and Al-Si. Vapour-deposited films were easily removed in their entirety by a single tape pull while metallic portions of the laser-bonded films resisted removal by the tape in all but two tests. The enhanced adhesion evident in the laser-bonded films was a result of intermixing observed at the film-substrate interface.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44689/1/10853_2005_Article_BF01115786.pd

Assessing the validity and reliability and determining cut-points of the Actiwatch 2 in measuring physical activity

Objective: The Actiwatch 2 (AW2) is a wrist-worn accelerometer typically used to measure sleep. Although it can measure physical activity, there is limited evidence supporting its validity. We assessed the validity and reliability of the AW2 to measure sedentary behavior and physical activity (light, moderate, vigorous intensities), and reported their respective count cut-points. Approach: Twenty-eight males and 22 females completed a task battery comprising three sedentary tasks and six randomized physical activity tasks at varying intensities, whilst wearing the AW2, a reference accelerometry device (Actigraph GT3X) and a cardiopulmonary gas analyzer on two separate occasions. Validity was assessed using correlations (AW2 counts versus GT3X counts and metabolic equivalent (MET) values), reliability using Bland–Altman analyses, and cut-points were determined using receiver operating characteristic (ROC) area under the curve (AUC) analyses. Main results: AW2 counts were positively correlated with GT3X counts (rho = 0.902, p < 0.001) and METs (rho = 0.900, p < 0.001). AW2-derived counts were comparable across independent assessment periods. Sedentary (AUC = 0.99, cut-point: 256 cpm) and vigorous activity (AUC = 0.95, cut-point: 720 cpm) were strongly characterized, and moderate activity (AUC = 0.66, cut-point: 418 cpm) was weakly characterized. Significance: The use of the AW2 in physical activity monitoring looks promising for sedentary behavior, moderate and vigorous activity, however, further validation is needed

An Accounting of the Dust-Obscured Star Formation and Accretion Histories Over the Last ~11~Billion Years

(Abridged) We report on an accounting of the star formation and accretion driven energetics of 24um detected sources in GOODS North. For sources having infrared (IR; 8-1000um) luminosities >3x10^12 L_sun when derived by fitting local SEDs to 24um photometry alone, we find these IR luminosity estimates to be a factor of ~4 times larger than those estimated when the SED fitting includes additional 16 and 70um data (and in some cases mid-infrared spectroscopy and 850um data). This discrepancy arises from the fact that high luminosity sources at z>>0 appear to have far- to mid-infrared ratios, as well as aromatic feature equivalent widths, typical of lower luminosity galaxies in the local Universe. Using our improved estimates for IR luminosity and AGN contributions, we investigate the evolution of the IR luminosity density versus redshift arising from star formation and AGN processes alone. We find that, within the uncertainties, the total star formation driven IR luminosity density is constant between 1.15 < z < 2.35, although our results suggest a slightly larger value at z>2. AGN appear to account for <18% of the total IR luminosity density integrated between 0< z < 2.35, contributing <25% at each epoch. LIRG appear to dominate the star formation rate (SFR) density along with normal star-forming galaxies (L_IR < 10^11 L_sun) between 0.6 < z < 1.15. Once beyond z >2, the contribution from ultraluminous infrared galaxies ULIRGs becomes comparable with that of LIRGs. Using our improved IR luminosity estimates, we find existing calibrations for UV extinction corrections based on measurements of the UV spectral slope typically overcorrect UV luminosities by a factor of ~2, on average, for our sample of 24um-selected sources; accordingly we have derived a new UV extinction correction more appropriate for our sample.Comment: Accepted for publication in Ap

Associations Between Self-Reported Sleep Duration and Mortality in Employed Individuals:Systematic Review and Meta-Analysis

Objective: Sleeping less or more than the 7-8 h has been associated with mortality in the general population, which encompasses diversity in employment status, age and community settings. Since sleep patterns of employed individuals may differ to those of their unemployed counterparts, the nature of their sleep-mortality relationship may vary. We therefore investigated the association between self-reported sleep duration and all-cause mortality (ACM) or cardiovascular disease mortality (CVDM) in employed individuals. Data sources: Based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses, searches between January 1990 and May 2020 were conducted in PubMed, Web of Science and Scopus. Inclusion/exclusion criteria: Included were prospective cohort studies of 18–64-year-old disease-free employed persons with sleep duration measured at baseline, and cause of death recorded prospectively as the outcome. Gray literature, case-control or intervention design studies were excluded. Data Extraction: Characteristics of the studies, participants, and study outcomes were extracted. The quality and risk of bias were assessed using the Newcastle-Ottawa Scale. Data synthesis: The pooled relative risks (RR) with 95% confidence intervals (CI) were obtained with a random-effects model and results presented as forest plots. Heterogeneity and sensitivity analysis were assessed. Results: Shorter sleep duration (less than or equal to 6 h) was associated with a higher risk for (ACM) (RR: 1.16, 95% CI: 1.11 -1.22) and CVDM (RR: 1.26, 95% CI: 1.12 -1.41) compared to 7-8 h of sleep, with no significant heterogeneity. The association between longer sleep (greater than or equal to 8 h) and ACM (RR: 1.18, 95% CI:1.12 -1.23, P < 0.001) needs to be interpreted cautiously owing to high heterogeneity (I2 ¼ 86.0%, P < 0.001). Conclusion: Interventions and education programs targeting sleep health in the workplace may be warranted, based on our findings that employed individuals who report shorter sleep appear to have a higher risk for ACM and CVDM

Measuring specialty indecision among career-decided students

Increasing numbers of career-decided students in professional and graduate schools have difficulty choosing a specialty. To begin to examine this problem, a measure of specialty indecision was devised by changing the Career Decision Scale items to deal with specialty indecision rather than career indecision. The scale was then administered to 567 medical students along with measures of vocational development and exploratory behavior. Initial evaluation of the psychometric properties of the Specialty Indecision Scale indicate that it is internally consistent, relates more to specialty choice than to career choice, and inversely relates to both vocational development and exploratory behavior. A factor analysis of the scale items extracted four factors that reflect cognitive, conative, criterion, and implementation restraints on the decision-making process. The Specialty Indecision Scale seems to be useful for diagnostic and research purposes in the study and treatment of specialty indecision.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25480/1/0000020.pd

A backward evolution model for infrared surveys: the role of AGN- and Color-L_TIR distributions

Empirical "backward" galaxy evolution models for infrared bright galaxies are constrained using multi-band infrared surveys. We developed a new Monte-Carlo algorithm for this task, implementing luminosity dependent distribution functions for the galaxies' infrared spectral energy distributions (SEDs) and for the AGN contribution, allowing for evolution of these quantities. The adopted SEDs take into account the contributions of both starbursts and AGN to the infrared emission, for the first time in a coherent treatment rather than invoking separate AGN and star-forming populations. In the first part of the paper we consider the quantification of the AGN contribution for local universe galaxies, as a function of total infrared luminosity. It is made using a large sample of LIRGs and ULIRGs for which mid-infrared spectra are available in the Spitzer archive. In the second part we present the model. Our best-fit model adopts very strong luminosity evolution, $L=L_0(1+z)^{3.4}$, up to $z=2.3$, and density evolution, $\rho=\rho_0(1+z)^2$, up to $z=1$, for the population of infrared galaxies. At higher $z$, the evolution rates drop as $(1+z)^{-1}$ and $(1+z)^{-1.5}$ respectively. To reproduce mid-infrared to submillimeter number counts and redshift distributions, it is necessary to introduce both an evolution in the AGN contribution and an evolution in the luminosity-temperature relation. Our models are in plausible agreement with current photometry-based estimates of the typical AGN contribution as a function of mid-infrared flux, and well placed to be compared to upcoming Spitzer spectroscopic results. As an example of future applications, we use our best-fitting model to make predictions for surveys with Herschel.Comment: Model available at: (http://www.physics.ubc.ca/~valiante/model) ApJ accepte