Shift and asymmetry of the saturated absorption resonance in the field of counterpropagating elliptically polarized waves

The saturated absorption resonance in an atomic gas in the field of counterpropagating light waves with an arbitrary elliptical polarization is investigated. A conclusion about the peculiarities of the resonance shape is drawn from a general analysis of the symmetry of the problem. In particular, a new effect has been found: the polarization parameters of the light waves can lead to an asymmetry and shift of the resonance. These conclusions are corroborated by an approximate analytical solution for the F _g = 1 → F _e = 2 transition and by numerical calculations. Apart from their fundamental importance, the results obtained can have important applications in metrology (frequency and time standards).     

Status of the endcap BGO calorimeter of the CMD-3 detector

The electromagnetic endcap BGO calorimeter of the CMD-3 detector is ready for experiments at the new e ⁺ e ^? collider VEPP-2000. Light readout is performed by silicon photodiodes. A thermalcontrol system that is able to maintain the calorimeter temperature at a level of 12 ±1°C was designed and manufactured. All blocks of the endcap calorimeter are assembled, tested, and prepared for installing at the detector.     

Glass transition of Langmuir-Blodgett polymer films

The dielectric dispersion of vinylidene fluoride-trifluoroethylene copolymer P(VDF/TrFE) (70/30) films obtained by the Langmuir-Blodgett technique was investigated in the low-temperature range from 20 to −100°C. The thickness of the explored films was 40 nm. A glass-transition range from −25 to −40°C was detected; this indicates the presence of an amorphous phase in the LB films.     

Invariants and Chebyshev polynomials

On different compact sets from ? ⁿ , new multidimensional analogs of algebraic polynomials least deviating from zero (Chebyshev polynomials) are constructed. A brief review of the analogs constructed earlier is given. Estimates of values of the best approximation obtained by using extremal signatures, lattices, and finite groups are presented.     

A versatile scaffold for site-specific modification of cyclic tetrapeptides

A novel scaffold that can be used to prepare conformationally homogeneous cyclic tetrapeptides equipped with a β-amino acid residue is disclosed. It is shown that regioselective structural modification can be accomplished using thiols and azide nucleophiles, commonly associated with rich downstream chemistry. The method should find application in efforts to constrain privileged tripeptide sequences in rigid molecular scaffolds.     

Boroalkyl group migration provides a versatile entry into α-aminoboronic acid derivatives

A reaction exemplifying migration of boron-substituted carbon is described. We show that α-boroalkyl groups of transient boroalkyl acyl azide intermediates readily migrate from carbon to nitrogen. This process allows access to a new class of stable molecules, α-boryl isocyanates, from α-borylcarboxylic acid precursors. The methodology facilitates synthesis of a wide range of α-aminoboronic acid derivatives, including α,α-disubstituted analogues.     

Vacuum-evaporated ferroelectric films and heterostructures of vinylidene fluoride/trifluoroethylene copolymer

The potential of the vacuum method for preparing ferroelectric films and photonic heterostructures from organic materials is studied. Vacuum-evaporated films of fluoropolymers and heterostructures on their basis are obtained and their ferroelectric and spectral properties are studied. In particular, homogeneous films of the well-known piezoelectric polymer polyvinylidene fluoride and ferroelectric material vinylidene fluoride/trifluoroethylene copolymer (P(VDF/TFE)) are produced. Experimental studies of vacuum-evaporated P(VDF/TFE) films confirmed their ferroelectric properties. The heterostructures composed of alternating layers of P(VDF/TFE) copolymer molecules and azodye molecules are fabricated by vacuum evaporation. Owing to the controlled layer thickness and a significant difference in the refractive indices of the P(VDF/TFE) copolymer and azodyes, these heterostructures exhibit properties of photonic crystals. This finding is confirmed by the occurrence of a photonic band in the absorption spectra of the heterostructures.     

Thioester-isocyanides: versatile reagents for the synthesis of cycle-tail peptides

A novel class of reagents, thioester isocyanides, have been prepared and applied in the synthesis of peptide macrocycles. The isocyanide part of the molecule is deployed in a multicomponent macrocyclization step. This step is followed by chemoselective peptide ligation at the thioester part of the macrocycle. Our method can now be used for rapid assembly and evaluation of cycle-tail peptides.     

Morphology and structure study of dispersed nickel-molybdenum powders produced by different methods

Ni-Mo powders produced by ultrasonic spray pyrolysis and chemical deposition are comparing in this study. Specimens were investigated by low-temperature nitrogen adsorption, x-ray diffraction, x-ray fluorescence, scanning and transmission electron microscopy methods. It was shown that the composition of the two-phase material, produced by ultrasonic spray pyrolysis method, is easy to control. Powders have spherical shape and high specific surface area.     

Role of reversible dimerization in reactions of amphoteric aziridine aldehydes

Unprotected aziridine aldehydes belong to the amphoteric class of molecules by virtue of their dual nucleophilicity/electrophilicity. The dimeric nature of these molecules, brought together by a weak and reversible aminal "connection", was found to be an important element of reactivity control. We present evidence that reversible dimer dissociation is instrumental in aziridine aldehyde transformations. We anticipate further developments that will unveil other synthetic consequences of remote control of selectivity through forging reversible covalent interactions.