Synthesis,structure, ion mobility,phase transitions,and ion transport in rubidium ammonium hexafluorozirconates

Rubidium ammonium hexafluorozirconates Rb_2?x (NH₄)_x ZrF₆ (1.5 < x < 2.0) have been synthesized, and their structure, ion mobility (180–480 K), and electrophysical properties have been studied by X-ray crystallography, ¹H and ¹⁹F NMR, DTA, and impedance methods. Compounds with x > 1.5 are isostructural with (NH₄)₂ZrF₆. Rubidium cations are isomorphously substituted for the ammonium cations. The high-temperature modifications of the compounds, which form upon the phase transitions at 413–418 K, are characterized by translational diffusion of ions in the fluoride and ammonium sublattices. The ¹⁹F NMR spectra are characterized by uniaxial ¹⁹F magnetic shift anisotropy. The electrophysical properties of this series of compounds are studied in the temperature range 300–480 K.     

19F and203,205Tl NMR and structural transformations in chain ammonium and thallium hexafluorozirconates and hexafluorohafnates

Unusual structural transformations were observed in ammonium and thallium hexafluorozirconates and hexafluorohafnates at 300–420 K using high-resolution NMR for solids. It was established that at 300–350 K the initial chain structure of these compounds of orthorhombic symmetry undergoes a transition to disordered state, and at higher temperatures it is transformed into an ordered uniaxial structure which is similar to that of trigonal Cs₂ZrF₆ and Cs₂HfF₆.     

The first general synthesis of 3-iodo-4-R-furazans

The first general synthetic route has been developed for the convenient preparation of iodofurazans. The approach was accomplished by one-pot diazotization-iodation reaction of appropriate aminofurazans. A combination of sodium nitrite and iodine in organic solvent under anhydrous conditions as the reaction conditions allowed to solve problem in iodofurazans preparation. The investigation of the substituent's influence on NMR data of the iodofurazans has been carried out. The X-ray crystal structure of the 3-amino-4-iodofurazan 1d is reported. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:199–207, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20007     

Numerical Simulation of Measurements during the Reactor Physical Startup at Unit 3 of Rostov NPP

The results of numerical calculations and measurements of some reactor parameters during the physical startup tests at unit 3 of Rostov NPP are presented. The following parameters are considered: the critical boron acid concentration and the currents from ionization chambers (IC) during the scram system efficiency evaluation. The scram system efficiency was determined using the inverse point kinetics equation with the measured and simulated IC currents. The results of steady-state calculations of relative power distribution and efficiency of the scram system and separate groups of control rods of the control and protection system are also presented. The calculations are performed using several codes, including precision ones.     

Half-cycle pulses in the mid-infrared from a two-color laser-induced filament

Four-wave mixing (FWM) of femtosecond near-infrared laser pulses and its second harmonic in the filamentation regime is shown to give rise to ultrashort field waveforms in the mid-infrared with pulse widths as short as a half of the field cycle and produce ultrabroadband supercontinuum spectra stretching from the mid-IR to the terahertz region. Generation of 7-fs pulses centered at 4.35 μm is demonstrated by a two-color filamentation experiment, where the 25-fs, 800-nm fundamental-wavelength output of a Ti: Sapphire laser is mixed with its second harmonic. The spectral and temporal properties of the mid-IR waveforms, as well as their emission pattern, are consistent with the FWM scenario of frequency conversion generalized to include the Kerr effect and ionization-induced refractive-index modulation.     

Spin current in an electron waveguide tunnel-coupled to a topological insulator

We show that electron tunneling from edge states in a two-dimensional topological insulator into a parallel electron waveguide leads to the appearance of spin-polarized current in the waveguide. The spin polarization P can be very close to unity and the electron current passing through the tunnel contact splits in the waveguide into two branches flowing from the contact. The polarization essentially depends on the electron scattering by the contact and the electron-electron interaction in the one-dimensional edge states. The electron-electron interaction is treated within the Luttinger liquid model. The main effect of the interaction stems from the renormalization of the electron velocity, due to which the polarization increases with the interaction strength. Electron scattering by the contact leads to a decrease in P. A specific effect occurs when the bottom of the subbands in the waveguide crosses the Dirac point of the spectrum of edge states when changing the voltage or chemical potential. This leads to changing the direction of the spin current.     

Spatiotemporal dynamics of bumblebees foraging under predation risk

We analyze 3D flight paths of bumblebees searching for nectar in a laboratory experiment with and without predation risk from artificial spiders. For the flight velocities we find mixed probability distributions reflecting the access to the food sources while the threat posed by the spiders shows up only in the velocity correlations. The bumblebees thus adjust their flight patterns spatially to the environment and temporally to predation risk. Key information on response to environmental changes is contained in temporal correlation functions, as we explain by a simple emergent model.     

Carboxylato-bis-dibenzoylmethanates of europium(III): Luminescence and magnetic properties

The luminescent and magnetic properties of europium(III) carboxylates, determined from the structure of Stark and Zeeman sublevels, are studied. It is found that the values of the λ_lum energy gap between the ground state ⁷ F ₀ and ⁷ F ₁ term in the luminescence spectra and λ_magn obtained from magnetochemical measurements correlate well.     

2,2‐Bis(methoxy‐NNO‐azoxy)ethyl Derivatives of 4,8‐Dihydro‐bis‐furazano[3,4‐b:3′4′‐e]pyrazine: The Synthesis and X‐ray Investigation

The first synthesis of 4,8‐dihydro‐bis‐furazano[3,4‐b:3′4′‐e]pyrazine bearing 2,2‐bis(methoxy‐NNO‐azoxy)ethyl groups has been developed. These compounds are obtained by aza‐Michael reaction of 1,1‐bis(methoxy‐NNO‐azoxy)ethene or its equivalents, such as 2,2‐bis(methoxy‐NNO‐azoxy)ethanol derivatives, with 4,8‐dihydro‐bis‐furazano[3,4‐b:3′4′‐e]pyrazine.