Versatile and stereoselective syntheses of orthogonally protected beta-methylcysteine and beta-methyllanthionine

[reaction: see text] Lantibiotics are a class of lanthionine (and/or beta-methyllanthionine)-containing peptides with antibioitic activity against Gram-positive bacteria. As part of our research effort directed toward the synthesis and mechanistic study of the lantibiotic peptide mersacidin (1), we report stereoselective syntheses of orthogonally protected beta-methylcysteine (beta-MeCys) and beta-methyllanthionine (beta-MeLan), two key nonnatural amino acid components of the mersacidin architecture.     

Electron Capture Probabilities in105Ag

TheK-electron capture probabilities for the 1/2^? → 3/2^? and 1/2^? → 1/2⁺ transitions in the decay of¹⁰⁵Ag were measured for the first time using the sum coincidence method. The experimental P_K values were estimated to be 0.824 ± 0.042 and 0.851 ±0.046 for the allowed and first-forbidden beta transitions, respectively in agreement with the theory. The P_L experimental values to these two levels were also computed using the experimental P_L/P_K values reported by earlier authors. These results are also found to be consistent with the theoretical P_L values.     

On the decomposition of the Feynman propagator

The Feynman propagator, in momentum representation, is a four-dimensional transform over space and time variables. If the space and time integrations are performed separately, the propagator can be decomposed into two parts, one corresponding to positive and the other to negative energy intermediate state. By the use of this decomposed propagator, the relative contributions of the positive and negative energy intermediate states to the matrix element can be estimated. For example in Compton scattering it leads to the apparently paradoxical result that in the “nonrelativistic approximation” it is only the negative energy intermediate state that contributes to the matrix element.     

Dependence of shell mix on feedthrough in direct drive inertial confinement fusion

The mixing of cold, high-density shell plasma with the low-density, hot spot plasma by the Rayleigh-Taylor instability in inertial confinement fusion is experimentally shown to correlate with the calculated perturbation feedthrough from the ablation surface to the inner shell surface. A fourfold decrease in the density of shell material in the mix region of direct drive implosions of gas filled spherical plastic shells having predicted convergence ratios approximately 15 was observed when laser imprint levels were reduced and the initial shell was thicker, corresponding to a reduction in the feedthrough rms level by a factor of 6. Shell mix is also shown to limit the spherical compression of the implosion.     

Effects of fuel-shell mix upon direct-drive,spherical implosions on OMEGA

Fuel-shell mix and implosion performance are studied for many capsule types in direct-drive experiments at OMEGA. The amount of mixing and the size of the mix region are inferred from charged-particle spectrometry data and confirmed with an experimentally constrained model. Measured yields and convergence ratios CR fall short of one-dimensional predictions, especially for low capsule fill pressures. CR is approximately 11 for pressures from 3 to 15 atm, in contrast to predictions of approximately 25 for 3 atm and approximately 12 for 15 atm. The performance shortfalls are likely to be caused by fuel-shell mix.     

Spatiotemporal binary interaction and designer quasi-particle condensates

We introduce a new integrable model to investigate the dynamics of two component quasi-particle condensates with spatiotemporal interaction strengths. We derive the associated Lax pair of the coupled Gross-Pitaevskii （GP） equation and construct matter wave solitons, We show that the spatiotemporal binary interaction strengths not only facilitate the stabilization of the condensates, but also enables one to fabricate condensates with desirable densities, geometries, and properties, leading to the so-called ＂designer quasi-particle condensates＂.     

Synthesis Strategies for Ultrastable Zeolite GIS Polymorphs as Sorbents for Selective Separations

Designing zeolites with tunable physicochemical properties can substantially impact their performance in commercial applications, such as adsorption, separations, catalysis, and drug delivery. Zeolite synthesis typically requires an organic structure‐directing agent to produce crystals with specific pore topology. Attempts to remove organics from syntheses to achieve commercially viable methods of preparing zeolites often lead to the formation of impurities. Herein, we present organic‐free syntheses of two polymorphs of the small‐pore zeolite P (GIS), P1 and P2. Using a combination of adsorption measurements and density functional theory calculations, we show that GIS polymorphs are selective adsorbents for H₂O relative to other light gases (e.g., H₂, N₂, CO₂). Our findings refute prior theoretical studies postulating that GIS‐type zeolites are excellent materials for CO₂ separation/sequestration. We also show that P2 is significantly more thermally stable than P1, which broadens the operating conditions for GIS‐type zeolites in commercial applications and opens new avenues for exploring their potential use in processes such as catalysis.     

Other incarnations of the Gross-Pitaevskii dark soliton

We show that the dark soliton of the Gross-Pitaevskii equation (GPE) that describes the Bose-Einstein condensate (BEC) density of a system of weakly repulsive bosons, also describes that of a system of strongly repulsive hard core bosons at half filling. As a consequence of this, the GPE soliton gets related to the magnetic soliton in an easy-plane ferromagnet, where it describes the square of the in-plane magnetization of the system. These relationships are shown to be useful in understanding various characteristics of solitons in these distinct many-body systems.