Resonant terahertz generation from InN thin films

Highly efficient conversion from ultrafast optical pulses to their terahertz (THz) counterparts has been achieved with InN thin films. An average THz output power as high as 0.931 microW has been obtained for an average pump power of 1 W, corresponding to a normalized conversion efficiency of 190% mm(-2). Based on our measured dependences of the THz output power on pump polarization, incident angle, pump power, and InN film thickness, resonance-enhanced optical rectification is one of the most plausible mechanisms for the THz generation in the InN films.     

Formyl MIDA Boronate: C1 Building Block Enables Straightforward Access to α-Functionalized Organoboron Derivatives

Formyl MIDA boronate has been known to be an elusive type of acylboronate that has not been obtained to date. In this work, an approach to the one-pot preparation and chemical transformations of formyl MIDA boronate were developed to provide new types of α-functionalized organoboron compounds. Among them are acylboronate reagents which present boron-substituted analogues of ynones and β-dicarbonyl compounds. The developed synthetic procedures, utilizing formyl MIDA boronate, are tolerant to diverse functional groups, making this reagent an advantageous C₁ building block for extending the scope of organoboron chemistry.     

Existence of a solution to the inhomogeneous equation with the one-dimensional Schr?dinger operator in the space of quickly decreasing functions

We prove the theorem of existence of a solution to the inhomogeneous equation with the one-dimensional Schr?dinger operator in the space of quickly decreasing functions arising in the theory of asymptotic solutions to singularly perturbed partial differential equations.     

Persistence of travelling waves in a generalized Fisher equation

Travelling waves of the Fisher equation with arbitrary power of nonlinearity are studied in the presence of long-range diffusion. Using analogy between travelling waves and heteroclinic solutions of corresponding ODEs, we employ the geometric singular perturbation theory to prove the persistence of these waves when the influence of long-range effects is small. When the long-range diffusion coefficient becomes larger, the behaviour of travelling waves can only be studied numerically. In this case we find that starting with some values, solutions of the model lose monotonicity and become oscillatory.     

Composite Zn(II) Ferrocyanide/Polyethylenimine Cryogels for Point-of-Use Selective Removal of Cs-137 Radionuclides

The feasibility of several approaches to the fabrication of monolith composite cryogels containing transition-metal ferrocyanides for Cs⁺ ion uptake has been evaluated. Although in the series of investigated metal ion precursors (Cu(II), Zn(II), Ni(II), and Co(II)), in situ formation of the sorption active phase in polyethyleneimine (PEI) cryogel was feasible only in the case of Zn(II) ferrocyanide, this approach has shown significant advantages over the immobilization of ex situ synthesized ferrocyanide nanoparticles. Nanoparticles of the mixed ferrocyanide Zn_1.85K_0.33[Fe(CN)₆] formed in situ had an average size of 516 ± 146 nm and were homogeneously distributed in the monolith located at the polymer surface rather than embedded in the matrix. The Young modulus of the PEI cryogel increased after modification from 25 to 57 kPa, but composites maintained high permeability to the flow. Sorption of Cs⁺ ions has been investigated at superficial velocity up to 8 m/h. Steep breakthrough profiles and uptake efficiency of >99.5% until breakthrough point confirmed that a supermacroporous structure of the monolith composite assured good mass transfer, so that intraparticle diffusion was not the limiting stage of sorption kinetics. Application of the rate-constant distribution model (RCD model) to analyze the breakthrough curves of Cs⁺ sorption allowed the identification of two types of sorption sites with a difference in sorption rate constants of ~1 log unit. Most likely, sorption on “fast” sorption sites was governed by ion exchange between Cs⁺ ions in solution and K⁺ ions in the ferrocyanide lattice. Cs-137 radionuclide removal was investigated using the monolith composite columns of various geometries at superficial velocity up to the 6.6 m/h; specific gamma activity was reduced from 265 kBq/L to the background level, showing high potential of these materials for POU application.     

A new strategy for asymmetric synthesis of aminophosphonic acid derivatives: the first enantioselective catalytic reduction of C-phosphorylated imines

The first highly enantioselective catalytic reduction of 1-imino-2,2,2-trifluoroethylphosphonates and the synthesis of enantiomerically enriched biorelevant phosphonotrifluoroalanine is reported.     

Error estimate of the modified point-mass trajectory model of an artillery shell

The article deals with the motion of an axially symmetric spinning artillery shell in the gravity field under the action of the system of aerodynamic forces and moments adopted in ballistics. As the starting point, the system of differential equations of motion of the shell is taken, which is obtained from the original “accurate” system by its linearization in the variables describing the angular motion of the symmetry axis and by additional linearization in the angle between the velocity vector of the center of mass and the vertical plane (l-system). This article examines the system of differential equations of the translational motion and axial rotation of the shell which describes its modified point-mass trajectory model as applied to l-system (m-system). By small parameter methods, an estimate is obtained for the difference of the solution of l-system with given initial data and the solution of m-system with the same initial data for the variables of translational motion and axial rotation. This analytical evaluation is built in such a way that it corresponds with certain numerical estimates for components of the translational motion and axial rotation. It is observed that, under accepted assumptions, m-system and l-system determine the translational motion of the shell with the same order of the error as compared to the original “accurate” nonlinear system of equations of motion of the shell. But m-system does not contain rapidly oscillating variables describing the angular motion of the symmetry axis, and so its numerical integration requires tens of times less computational resources than the numerical integration of l-system. Numerical simulation data are represented.     

Temperature dependence of a macrobending edge filter based on a high-bend loss fiber

The temperature dependence of a macrobending bare-fiber-based edge filter is investigated both theoretically and experimentally. The fiber used is a high-bend loss fiber, type 1060XP. The experimental results show a good agreement with the proposed theoretical model over a temperature range from 0 degrees C to 80 degrees C. It is shown that the strong temperature dependence of a high-bend loss fiber has a significant influence on the performance of a fiber edge filter used in a wavelength measurement application. However, it is also concluded that such a temperature-dependent performance can be beneficially utilized in a fiber temperature sensing application.     

O-(α-Phenylethyl)hydroxylamine as a ‘chiral ammonia equivalent’: synthesis and resolution of 5-oxopyrrolidine- and 6-oxopiperidine-3-carboxylic acids

An approach to the synthesis and resolution of five- and six-membered lactams (i.e., 5-oxopyrrolidine- and 6-oxopiperidine-3-carboxylic acids) is described. The method relies on the one-pot Michael reaction—cyclization of itaconic acid or diethyl homoitaconate and enantiopure O-(α-phenylethyl)hydroxylamine as a ‘chiral ammonia equivalent’. It is shown that this chiral auxiliary can be used for the separation of diastereomeric lactam products and then easily removed by catalytic hydrogenolysis.