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

Deflection microwave amplifier with field‐emitter arrays

A new class of microwave and millimeter‐wave amplifiers, based on the deflection of collimated microscopic electron beams with high‐current density and low voltage from field‐emitter arrays, was analyzed. The deflection concept may be applied in two ways; as microelectronic amplifiers or as bunched beam cathodes to power conventional amplifier configurations such as klystrodes and traveling wave tubes. We found that the frequency fT, at which the short‐circuit current gain attains unit magnitude, depends only on the electron beam energy, current density, and emittance, and is independent of beamwidth and total current. The results indicate that field‐emitter arrays have the potential of making wideband deflection amplifiers at frequencies up to tens of GHz. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69885/2/APPLAB-65-22-2881-1.pd

Tropical cyclone asymmetric eyewall evolution and intensification in a two-layer model

Radar and satellite imagery of numerous intensifying tropical cyclones (TCs) depict an appearance of a polygonal eyewall structure where deep convection is often located near the polygonal vertices. A recent observational study of Hurricane Michael's (2018) polygonal eyewall evolution suggests that the vorticity asymmetries are coupled with the reflectivity asymmetries during rapid intensification. Conceptual theory of a polygonal eyewall structure has been linked to vortex Rossby waves (VRWs) and the breakdown of an enhanced potential vorticity (PV) ring, but how the asymmetries affect TC intensification remains unclear. Non-divergent barotropic models have previously been employed to study polygonal eyewall dynamics, but this approach has limitations due to the importance of diabatic heating to PV generation and the intensification process. Results from prior studies motivate us to explore the nature of the relationship between asymmetric vorticity and vertical velocity in the free atmosphere and the boundary layer and their compound impacts on the TC intensification process. Here we use a simple two-layer model framework with a shallow-water model on top of a slab boundary layer (SBL) model to simulate a frictional boundary layer underneath the free atmosphere. Results from simulating a wavenumber 2 elliptical asymmetry suggest the VRW in the free atmosphere can organize the updrafts in the SBL, which is consistent with radar observations of enhanced reflectivity at the polygonal vertices. Free atmospheric divergence in the shallow-water layer does not explain the coupling between vorticity and reflectivity. The coupling can be explained to first order by the one-way boundary layer response to the pressure gradient associated with the free atmospheric vorticity asymmetries, consistent with prior studies. Further simulations that allow two-way interaction between the layers show that the organization of the updrafts out of the SBL plays a critical role in the growth of a PV ring and intensification of the mean vortex. In this framework, diabatic heating in the shallow-water layer parameterized by a mass sink driven by the free atmosphere–SBL interaction leads to rapid intensification of the vortex, thinning of the PV ring, and eventual barotropic instability and PV mixing. The simplified modeling framework with two-way interactions captures many of the essential dynamics of rapid intensification in the presence of evolving asymmetries, similar to those seen in the observations from Hurricane Michael (2018), which provides new insight into the complex interactions between dynamics and convection during hurricane intensification.</p

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&ndash;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 (&plusmn;8.67), and the average vitamin D level was 30.92 ng/mL (&plusmn;12.46). In univariate analysis, Vitamin D deficiency (levels &lt; 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 &lt; 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&ndash;control study, aging, geriatric

BRST Quantization of the Proca Model based on the BFT and the BFV Formalism

The BRST quantization of the Abelian Proca model is performed using the Batalin-Fradkin-Tyutin and the Batalin-Fradkin-Vilkovisky formalism. First, the BFT Hamiltonian method is applied in order to systematically convert a second class constraint system of the model into an effectively first class one by introducing new fields. In finding the involutive Hamiltonian we adopt a new approach which is more simpler than the usual one. We also show that in our model the Dirac brackets of the phase space variables in the original second class constraint system are exactly the same as the Poisson brackets of the corresponding modified fields in the extended phase space due to the linear character of the constraints comparing the Dirac or Faddeev-Jackiw formalisms. Then, according to the BFV formalism we obtain that the desired resulting Lagrangian preserving BRST symmetry in the standard local gauge fixing procedure naturally includes the St\"uckelberg scalar related to the explicit gauge symmetry breaking effect due to the presence of the mass term. We also analyze the nonstandard nonlocal gauge fixing procedure.Comment: 29 pages, plain Latex, To be published in Int. J. Mod. Phys.

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