A Concise Total Synthesis of (--)-Maoecrystal Z

The first total synthesis of (--)-maoecrystal Z is described. The key steps of the synthesis include a diastereoselective Ti^(III)-mediated reductive epoxide coupling reaction and a diastereoselective Sm^(II)-mediated reductive cascade cyclization reaction. These transformations enabled the preparation of (--)-maoecrystal Z in only 12 steps from (--)-γ-cyclogeraniol

Superfluid-insulator transition of the Josephson junction array model with commensurate frustration

We have studied the rationally frustrated Josephson-junction array model in the square lattice through Monte Carlo simulations of $(2+1)$D XY-model. For frustration $f=1/4$, the model at zero temperature shows a continuous superfluid-insulator transition. From the measurement of the correlation function and the superfluid stiffness, we obtain the dynamical critical exponent $z=1.0$ and the correlation length critical exponent $\nu=0.4 \pm 0.05$. While the dynamical critical exponent is the same as that for cases $f=0$, 1/2, and 1/3, the correlation length critical exponent is surprisingly quite different. When $f=1/5$, we have the nature of a first-order transition.Comment: RevTex 4, to appear in PR

Analysis of magnetic energy stored in superconducting coils with and without ferromagnetic inserts

Inductance and energy of superconducting coils are calculated by (1) a long solenoid approximation, (2) a finite element model, and (3) working formulas and tables. The results of the finite element model compare favorably with that of the working formulas. The long solenoid approximation overpredicts the energy and the inductance compared to the other two methods. The difference decreases with increasing length to diameter ratio

Association between vitamin D and pressure ulcers in older ambulatory adults: results of a matched case–control study

Usha R Kalava1, Stephen S Cha2, Paul Y Takahashi1,31Department of Internal Medicine, Division of Primary Care Internal Medicine, 2Department of Biostatistics, 3Kogod Center of Aging, Mayo Clinic, Rochester, MN, USABackground: Pressure ulcers are common among older adults, but knowledge about nutritional risk factors is still developing. Vitamin D deficiency is common in the elderly population and is required for normal skin proliferation. The role of vitamin D in pressure ulceration and wound healing is not known. The purpose of this case–control study was to determine the association between vitamin D levels and pressure ulceration in an older community-dwelling cohort.Methods: All cases and controls were community-dwelling elderly older than 60 years in a primary care panel in Olmsted County, MN. Pressure ulcer cases were defined clinically. The controls were age-matched and gender-matched to controls without pressure ulceration. The main exposure variable was 25-hydroxyvitamin D levels in both groups. The other exposure variable was the Charlson Comorbidity Index used to measure medical comorbidity. The analysis included univariate and conditional logistic regression for 25-hydroxyvitamin D levels.Results: The average (standard deviation) age of the study participants with a pressure ulcer was 80.46 years (±8.67), and the average vitamin D level was 30.92 ng/mL (±12.46). In univariate analysis, Vitamin D deficiency (levels < 25 ng/mL) was associated with pressure ulcers (odds ratio: 1.871, P = 0.0154). Comorbidities of the subjects calculated using the Charlson Comorbidity Index were also associated with pressure ulcers (odds ratio: 1.136, P < 0.001). In the final conditional logistical regression model, the association of Vitamin D and pressure ulcers became nonsignificant after adjustment for comorbid illness.Conclusion: Medical comorbidities increased the risk of pressure ulceration. Vitamin D deficiency was not an independent risk factor for pressure ulceration, and may be a marker of comorbid illness.Keywords: pressure ulcer, vitamin D, case–control study, aging, geriatric

The Internet Addiction Test in a Young Adult U.S. Population

Internet use has increased rapidly over the past 20 years, accompanied by a growing number of individuals whose Internet use has adverse effects on their lives. Yet no study to date has administered the Young\u27s Internet Addiction Test (IAT) in the United States, nor has the reliability been assessed in a U.S. population. Thus, we aimed to: (a) assess the reliability of the instrument and (b) examine sociodemographic characteristics associated with the Internet addiction score. Participants included young adults 21–28 years of age, the third generation of a 50-year longitudinal cohort, the New England Family Study. The mean weighted kappa across all 20 items of the instrument was 0.45 and the median was 0.46. To examine correlates of the addiction score, we examined age, gender, race/ethnicity, education, partnership status, employment, social support, and depression diagnosis. In the fully adjusted model, those with social support had −3.96 (95% CI: −6.52 to −1.41) lower Internet addiction scores on average compared to those without social support. Also, those with a depression diagnosis had 3.28 (95% confidence interval [CI]: 1.03–5.84) higher Internet addiction scores on average compared to those without a depression diagnosis. Study findings suggest that Young\u27s IAT had good reliability in a U.S. young adult population. Therefore, this measure can be a useful tool to measure Internet addiction in young adult populations in the United States. Future studies should examine the potential benefits of social support and depression treatment in Internet addiction among young adults in the United States

High Performance Electrocatalysts Based on Pt Nanoarchitecture for Fuel Cell Applications

Fuel cells, converting chemical energy from fuels into electricity directly without the need for combustion, are promising energy conversion devices for their potential applications as environmentally friendly, energy efficient power sources. However, to take fuel cell technology forward towards commercialization, we need to achieve further improvements in electrocatalyst technology, which can play an extremely important role in essentially determining cost-effectiveness, performance, and durability. In particular, platinum- (Pt-) based electrocatalyst approaches have been extensively investigated and actively pursued to meet those demands as an ideal fuel cell catalyst due to their most outstanding activity for both cathode oxygen reduction reactions and anode fuel oxidation reactions. In this review, we will address important issues and recent progress in the development of Pt-based catalysts, their synthesis, and characterization. We will also review snapshots of research that are focused on essential dynamics aspects of electrocatalytic reactions, such as the shape effects on the catalytic activity of Pt-based nanostructures, the relationships between structural morphology of Pt-based nanostructures and electrochemical reactions on both cathode and anode electrodes, and the effects of composition and electronic structure of Pt-based catalysts on electrochemical reaction properties of fuel cells.</jats:p

KMT-2016-BLG-2052L: Microlensing Binary Composed of M Dwarfs Revealed from a Very Long Time-scale Event

We present the analysis of a binary microlensing event KMT-2016-BLG-2052, for which the lensing-induced brightening of the source star lasted for 2 seasons. We determine the lens mass from the combined measurements of the microlens parallax \pie and angular Einstein radius \thetae. The measured mass indicates that the lens is a binary composed of M dwarfs with masses of $M_1\sim 0.34~M_\odot$ and $M_2\sim 0.17~M_\odot$. The measured relative lens-source proper motion of $\mu\sim 3.9~{\rm mas}~{\rm yr}^{-1}$ is smaller than $\sim 5~{\rm mas}~{\rm yr}^{-1}$ of typical Galactic lensing events, while the estimated angular Einstein radius of \thetae\sim 1.2~{\rm mas} is substantially greater than the typical value of $\sim 0.5~{\rm mas}$. Therefore, it turns out that the long time scale of the event is caused by the combination of the slow $\mu$ and large \thetae rather than the heavy mass of the lens. From the simulation of Galactic lensing events with very long time scales ($t_{\rm E}\gtrsim 100$ days), we find that the probabilities that long time-scale events are produced by lenses with masses $\geq 1.0~M_\odot$ and $\geq 3.0~M_\odot$ are $\sim 19\%$ and 2.6\%, respectively, indicating that events produced by heavy lenses comprise a minor fraction of long time-scale events. The results indicate that it is essential to determine lens masses by measuring both \pie and \thetae in order to firmly identify heavy stellar remnants such as neutron stars and black holes.Comment: 9 pages, 11 figure