Superfluid-helium converter for accumulation and extraction of ultracold neutrons

We report the first successful extraction of accumulated ultracold neutrons (UCN) from a converter of superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. Windowless UCN extraction is performed in vertical direction through a mechanical cold valve. This prototype of a versatile UCN source is comprised of a novel cryostat designed to keep the source portable and to allow for rapid cooldown. We measured time constants for UCN storage and extraction into a detector at room temperature, with the converter held at various temperatures between 0.7 and 1.3 K. The UCN production rate inferred from the count rate of extracted UCN is close to the theoretical expectation.     

Wall-crossing invariants: from quantum mechanics to knots

Journal of Experimental and Theoretical Physics - We offer a pedestrian-level review of the wall-crossing invariants. The story begins from the scattering theory in quantum mechanics where the...     

Dimephosphone analogs: II. Dialkyl(diaryl)-(2-methyl-4-oxopent-2-yl)phosphine oxide oximes: Synthesis,structure, and generation of iminoxyl radicals

Dialkyl(diaryl)-(2-methyl-4-oxopent-2-yl)phosphine oxide oximes have been synthesized for the first time. According to the X-ray diffraction data, these compounds in crystal exist as a single E isomer. Their structure in solution and the E/Z isomer ratio were determined by ¹H and ¹³C NMR spectroscopy.     

Cyanide Complexes Based on {Mo6I8}4+ and {W6I8}4+ Cluster Cores

Compounds based on new cyanide cluster anions [{Mo₆I₈}(CN)₆]^2–, trans-[{Mo₆I₈}(CN)₄(MeO)₂]^2– and trans-[{W₆I₈}(CN)₂(MeO)₄]²⁻ were synthesized using mechanochemical or solvothermal synthesis. The crystal and electronic structures as well as spectroscopic properties of the anions were investigated. It was found that the new compounds exhibit red luminescence upon excitation by UV light in the solid state and solutions, as other cluster complexes based on {Mo₆I₈}⁴⁺ and {W₆I₈}⁴⁺ cores do. The compounds can be recrystallized from aqueous methanol solutions; besides this, it was shown using NMR and UV-Vis spectroscopy that anions did not undergo hydrolysis in the solutions for a long time. These facts indicate that hydrolytic stabilization of {Mo₆I₈} and {W₆I₈} cluster cores can be achieved by coordination of cyanide ligands.     

Metal-organic frameworks based on [Re6Se8(CN)6]4− cluster anions,Yb3+ cations,and thiophene-2,5-dicarboxylate linkers

Russian Chemical Bulletin - The reaction of [Re6Se8(CN)6]4? cluster anions with Ln3+ cations in the presence of thiophene-2,5-dicarboxylate anions in an aqueous solution was studied. Two new...     

Developing methods for observing processes induced by femtosecond laser pulses with high spatiotemporal resolution

A combination of femtosecond laser techniques and nanomicroscopy creates promising new possibilities for studying both matter and a whole number of ultrafast physical processes. The results obtained at the Institute for Spectroscopy as a result of developing a new area of femtosecond nanomicroscopy are presented.     

Parametric excitation of shear waves in soft solids

One of the possible mechanisms that may underlie ultrasound-induced damage of soft solids is discussed. The model of three-wave interaction in a solid is used to consider shear wave generation by a longitudinal sound wave in a solid with a small shear modulus. Numerical estimates are obtained for the excitation threshold of the shear wave in biological tissues. Since the wavelength of ultrasound-generated shear waves is small, the shear stresses may be sufficient to destroy the structure of biological tissue. Results of model experiments are presented.