Considerable increase in the thermomagnetic stability of multifilament superconductors internally doped by large-heat-capacity substances

It is demonstrated that the thermomagnetic stability of composite superconductors can be considerably increased by introducing into them a small quantity of a material with an extremely high specific heat at low temperatures. Measurements show that the criterion of “adiabatic” stability for a (Nb₃Sn + 7 vol. % PrB₆) wire is 70% higher than for a reference Nb₃Sn wire (at 4.2 K, the specific heat of the doped sample is seven times higher than that of the reference sample). For a (NbTi + 5vol. % Gd₂O₂S) sample, the specific heat of which at 4.2 K is nine times higher than that of a reference NbTi wire, this increase in stability is as small as 10% (because the characteristic thermal time in the transverse direction is much longer than the time of the magnetic flux jump development).     

Ultrafast band-gap shift induced by a strain pulse in semiconductor heterostructures

The conventional piezospectroscopic effect is extended to picosecond time scales by using ultrashort strain pulses injected into semiconductor heterostructures. The strain pulses with durations of approximately 10 ps are generated in a metal transducer film by intense femtosecond laser pulses. They propagate coherently in the GaAs/(Al,Ga)As heterostructure over a distance of 100 microm and shift the band gaps by several meV as detected optically for quantum well exciton resonances by pump-probe techniques and time-resolved photoluminescence.     

Fine tuning the anion binding properties of 2,6-diamidopyridine dipyrromethane hybrid macrocycles

The synthesis, characterization, and anion-binding properties of a series of 2,6-diamidopyridine dipyrromethane hybrid macrocycles is presented. As part of this work, a new method for effecting the oxidation of dipyrromethane-based macrocycles in organic solvents has been developed. The macrocyclic frameworks presented here stand out because of their ease of synthesis and tunable anion-binding properties. Evidence for anion binding was obtained from UV-vis spectroscopic titrations carried out in acetonitrile. The results clearly indicate that by changing the flexibility, cavity size, and directionality of anion-binding moieties in the macrocyclic framework the anion selectivity may be changed dramatically. These results are in accord with density functional theory molecular modeling calculations performed on one member of the series.     

Salicylic aldehyde and 2-<Emphasis Type="Italic">N</Emphasis>-tosylaminobenzaldehyde tetrazolyl hydrazones and their complexes

Tetrazolyl hydrazones of salicylic aldehyde and 2-N-tosylaminobenzaldehyde as well as zinc(II) and copper(II) complexes on their base have been prepared. Quantum-chemical simulation of tautomerism of the hydrazones in vacuum and in the solutions has been performed. IR and NMR spectroscopy and magnetochemistry studies have revealed that the complexes are mononuclear; however, weak intermolecular exchange interaction of the antiferromagnetic type has been detected in the copper(II) complexes.     

EPR spectral study of copper(II) chelates with hetarylhydrazones of glyoxylic acid

Structure of copper(II) chelates based on glyoxylic hetarylhydrazones containing benzazole (quinoxaline and phthalazine) fragments have been studied by EPR spectroscopy. Spectral parameters in polycrystalline state and dimethylformamide solutions have been determined. Spectral parameters of benzimidazole derivative are typical for square planar structure of the chelate node, while phthalazine derivative displays formation of polymeric structures due to reduction of copper(II) atom.     

In Vitro Pharmacological Screening of Essential Oils from Baccharis parvidentata and Lippia origanoides Growing in Brazil

In this study, the in vitro antimicrobial, antiparasitic, antiproliferative and cytotoxic activities of essential oil from Baccharis parvidentata Malag. (EO-Bp) and Lippia origanoides Kunth (EO-Lo) were explored. The relevant effects were observed against the parasitic protozoans Plasmodium falciparum, Trypanosoma cruzi, Trypanosoma brucei and Leishmania amazonensis (ranging 0.6 to 39.7 µg/mL) and malignant MCF-7, MCF-7/HT, 22Rv1, and A431 cell lines (ranging 6.1 to 31.5 µg/mL). In parallel, EO-Bp showed better selective indexes in comparison with EO-Lo against peritoneal macrophages from BALB/c mice and MRC-5 cell line. In conclusion, EO-Lo is known to show a wide range of health benefits that could be added as another potential use of this oil with the current study. In the case of EO-Bp, the wide spectrum of its activities against protozoal parasites and malignant cells, as well as its selectivity in comparison with non-malignant cells, could suggest an interesting candidate for further tests as a new therapeutic alternative.     

Optical and photocurrent spectroscopy with picosecond strain pulses

This paper gives an overview of optical experiments using picosecond strain pulses. The strain pulses, which propagate with the sound velocity, are incident on a semiconductor nanostructure and induce an ultrafast shift of the exciton resonance energy by an amount, that exceeds the spectral width of the corresponding optical transition. When the duration of the high-amplitude strain pulse is long enough compared with the coherence time of the optical resonance, modulation of the resonance takes place adiabatically and exciton energy can be accurately defined at each momentary position. If the coherence time exceeds the characteristic time of the strain pulse, a non-adiabatic regime is realized and the exciton cannot be related to an optical transition with a specific photon energy. In more detail, we describe the recent experiments on the gating of photocurrent in a tunneling p-i-n device and the generation of THz polariton sidebands in an optical microcavity strongly coupled to the excitons in an embedded quantum well. These two experiments represent, respectively, examples of adiabatic and non-adiabatic behaivior of excitons in the presence of the high-amplitude picosecond strain pulse.     

Features of synthesis and structure of ethyl (2<Emphasis Type="Italic">Z</Emphasis>)-3-hydroxy-(2,3,4,5-tetrafluorophenyl)-propyl-2-enoate

The structure of key intermediates in the synthesis of fluoroquinolone antibiotics: diethyl (2,3,4,5-tetrafluorobenzoyl)malonate and ethyl (2Z)-3-hydroxy-(2,3,4,5-tetrafluorophenyl)prop-2-enoate was for first time studied using X-ray diffraction (XRD) and ¹H, ¹⁹F NMR spectroscopy. In solution both the esters were shown to exist as a mixture of enol and ketone tautomeric forms with predominance of the latter. According to the XRD analysis, ethyl (2Z)-3-hydroxy-(2,3,4,5-tetrafluorophenyl)prop-2-enoate in the solid state exists entirely in the enol form.     

DViN—Stationary setup for identification of explosives

A stationary system for the identification of hidden explosives was developed and constructed at the Joint Institute for Nuclear Research (JINR). The results of the examination of the system, as well as the operation principle of the system and design of the main elements are presented. The text was submitted by the authors in English.     

Interaction of excited Cr3+ ions in laser crystals

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 56, No. 1, pp. 77–80, January, 1992.