Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6

We report on high-field magnetization, specific-heat and electron spin resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes below TN = 4.38 K is described in the frame of the meanfield theory, confirming a collinear magnetic structure with an easy-plane anisotropy. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the inter/intra-plane exchange-interaction ratio, J'/J = 1/16. It is argued that despite the onset of 3D long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and non-monotonic field dependence of the Neel temperature) are strongly affected by two-dimensional spin correlations.Comment: 5 pages, 7 figure

Electron Spin Resonance in a Spin-1/2 Heisenberg Strong-rung Ladder

Cu(C$_8$H$_6$N$_2$)Cl$_2$, a strong-rung spin-1/2 Heisenberg ladder compound, is probed by means of electron spin resonance (ESR) spectroscopy in the field-induced gapless phase above $H_{c1}$. The temperature dependence of the ESR linewidth is analyzed in the quantum field theory framework, suggesting that the anisotropy of magnetic interactions plays a crucial role, determining the peculiar low-temperature ESR linewidth behavior. In particular, it is argued that the uniform Dzyaloshinskii-Moriya interaction (which is allowed on the bonds along the ladder legs) can be the source of this behavior in Cu(C$_8$H$_6$N$_2$)Cl$_2$

High-field spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8

Magnetic excitations in the isostructural spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8 are probed by means of high-field electron spin resonance at sub-terahertz frequencies. Three types of magnetic modes were observed. One mode is gapless and corresponds to transitions within excited states, while two other sets of modes are gapped and correspond to transitions from the ground to the first excited states. The selection rules of the gapped modes are analyzed in terms of a dynamical Dzyaloshinskii-Moriya interaction, suggesting the presence of phonon-assisted effects in the low-temperature spin dynamics of Sr3Cr2O8 and Ba3Cr2O8Comment: 6 pages, 4 figures, all comments are welcome and appreciate

Evaluation of hepatotoxic properties of pyrimidine derivatives

The aim of the study was to evaluate the hepatotoxic properties of new pyrimidine derivatives 3-[2-(1-naphthyl)-2- oxoethyl]-6-bromoquinazoline-4(3H)-oh (VMA–13–06), 3-(2-tert-butyl-2-oxoethyl)quinazoline-4(3H)-one (VMA-13- 11) and 3-(2-isopropyloxy-2-oxoethyl)quinazoline-4(3H)-oh (VMA-13-12). Material and methods. The study was carried out on male rats, which were divided into four groups: control receiving an intragastrically distilled water and experimental groups of animals receiving intragastrically suspended in distilled water pyrimidine compounds VMA- 13-06, VMA-13-11 and VMA-13-12 at doses of 1/10 of the molecular weight (39, 24 and 24 mg/kg respectively) for 60 days. In order to assess possible toxic damage to the liver, blood biochemical parameters were evaluated: alanine aminotransferase, aspartate aminotransferase, gamma-glutamyltransferase, alkaline phosphatase activity, total protein, albumin, total and free bilirubin content. Results. There were no statistically significant changes in total protein, albumin, total and free bilirubin after administration of VMA–13–06 and VMA–13–11 in comparison with the control group. The VMA–13–12 compound contributed to an increase in total and free bilirubin content by 43 % (p < 0.01) and 90 % (p < 0.01), while the increase in the concentration of total protein and albumin did not have any statistical significance. The analysis of enzyme parameters also indicates the absence of hepatocyte damage with the introduction of VMA- 13-06 and VMA-13-11: alanine aminotransferase, aspartate aminotransferase, gamma-glutamyltransferase, alkaline phosphatase activity did not change. VMA–13–12 administration led to an increase in enzyme activity in comparison with the control: alanine aminotransferase – by 59 % (p < 0.01), aspartate aminotransferase – by 28 % (p < 0.05), gamma- glutamyltransferase – by 46 % (p < 0.01), alkaline phosphatase – by 31 % (p < 0.05). Conclusions. We established the absence of hepatotoxic properties of pyrimidine derivatives 3-[2-(1-naphthyl)-2-oxoethyl]-6-bromoquinazoline-4(3H)- oh and 3-(2-tert-butyl-2-oxoethyl)quinazoline-4(3H)-oh. Compound 3-(2-isopropyloxy-2-oxoethyl)quinazoline-4(3H)- oh has a hepatotoxic effect, accompanied by a decrease in protein-synthesizing and detoxifying liver function

Magnetic Properties Of The Quasi-Two-Dimensional S=1/2 Heisenberg Antiferromagnet [Cu(Pyz)(2)(Hf2)]Pf6

We report on high-field magnetization, specific heat, and electron-spin-resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet [Cu(pyz)(2)(HF2)]PF6. The frequency-field diagram of ESR modes below T-N=4.38 K is described in the frame of the mean-field theory, confirming a collinear magnetic structure with an easy-plane anisotropy. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J=0.003, and the upper limit for the interplane/intraplane exchange interaction ratio, J\u27/J=1/16. It is argued that despite the onset of three-dimensional long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and nonmonotonic field dependence of the Neel temperature) are strongly affected by two-dimensional spin correlations

Synchronization of breathing and aiming skills as a Basis for training rifle shooters at a moving target

Objective of the study was to develop a pedagogical model for training rifle shooters at a moving target based on the synchronization of breathing and aiming skill

Screening studies of antimicrobial activity of pyrimidine derivative

Aim of the study was to screen the antimicrobial activity of pyrimidine derivative 3-[2-(1-naphthyl)-2-oxoethyl]-6-bromoquinazoline-4(3H)-oh with laboratory cipher VMA–13–06 in relation to pathogenic and opportunistic flora. Material and methods. Antimicrobial activity of VMA–13–06 was established in vitro against strains of Staphylococcus aureus, Klebsiella pneumonia, Streptococcus pyogenes, Escherichia coli, Acinetobacter baumannii and Citrobacter freundii by the method of serial dilutions, by forming rows with different concentrations of the compound under study. Results. VMA–13–06 was found to exhibit high antibacterial activity against S. aureus, S. pyogenes, E. coli and K. pneumonia at concentrations of 128 and 64 μg/ml comparable to the activity of the comparison drug norfloxacin. At a concentration of 32 μg/ml, the studied derivative is highly active against S. aureus and S. pyogenes and shows average activity against E. coli and K. pneumonia. The compound VMA–13–06 in dilution from 16 to 4 μg/ml is moderately active against the above-mentioned microorganisms. At concentrations from 2 to 0.25 μg/ml, the pyrimidine derivative is inactive against S. aureus, S. pyogenes, E. coli and K. pneumonia, in all dilutions – against C. freundii and A. baumannii. Conclusions. The results of a screening study indicate a pronounced bactericidal effect of VMA–13–06 against S. aureus, S. pyogenes, E. coli и K. pneumonia comparable to the comparison drug norfloxacin

Versatile Coordination of Cyclopentadienyl-Arene Ligands and Its Role in Titanium-Catalyzed Ethylene Trimerization

Cationic titanium(IV) complexes with ansa-(η5-cyclopentadienyl,η6-arene) ligands were synthesized and characterized by X-ray crystallography. The strength of the metal-arene interaction in these systems was studied by variable-temperature NMR spectroscopy. Complexes with a C1 bridge between the cyclopentadienyl and arene moieties feature hemilabile coordination behavior of the ligand and consequently are active ethylene trimerization catalysts. Reaction of the titanium(IV) dimethyl cations with CO results in conversion to the analogous cationic titanium(II) dicarbonyl species. Metal-to-ligand backdonation in these formally low-valent complexes gives rise to a strongly bonded, partially reduced arene moiety. In contrast to the η6-arene coordination mode observed for titanium, the more electron-rich vanadium(V) cations [cyclopentadienyl-arene]V(NiPr2)(NC6H4-4-Me)+ feature η1-arene binding, as determined by a crystallographic study. The three different metal-arene coordination modes that we experimentally observed model intermediates in the cycle for titanium-catalyzed ethylene trimerization. The nature of the metal-arene interaction in these systems was studied by DFT calculations.

ТЕМПЕРАТУРНІ РЕЖИМИ ЗОН ЗВОРОТНИХ ТОКІВ У БЛИЖНЬОМУ СЛІДІ ЦИЛІНДРИЧНИХ СТАБІЛІЗАТОРІВ ПОЛУМ'Я

The results of experimental studies of the temperature regimes of the back flow zones behind the cylindrical flame stabilizers of microjet burners are presented. The authors have considered a burner device, which is a circular channel with a cylindrical stabilizer placed in it. Circular openings for feeding fuel gas (propane-butane) into the blowing air flow off are located in a circle on the stabilizer. To determine the sizes of the back flow zones in the regions astern of the stabilizer, a method of visualizing the flow using sodium salts was used. The temperature measurement in the back flow zone was carried out by the chromel-alumel thermocouple. The regularities of the influence on the length of the back flows zones and the temperatures in these zones of such regime parameters of the combustion process as the value of the air flow velocity at the inlet to the channel and the air excess coefficient are analysed. Particular attention is paid to the study of the features of the change in the heat state and the length of the back flow zones as a function of the magnitude of the relative pitch of disposition of the gas-supply openings. An increase in the relative pitch of the gas-supplying openings and the air excess coefficient is shown to lead to a decrease in the length of the back flow zones, and an increase in the airflow velocity, on the contrary, increases this length. The influence of the relative pitch of disposition of the gas is noted to supply openings related to the fact that its growth leads to an increase in the injecting action of the fuel gas jets, which consists in a greater attraction of ambient air to the fuel jets. This in turn leads to an additional increase in the degree of rarefaction in the back flows zone beyond the stabilizer, and then to a decrease in the length of this zone. The dependence of the length of the back flow zone on the magnitude of the relative pitch of the gas supply openings is observed to be significant only at relatively high values of the air excess coefficient. With an increase in this pitch and the air-flow velocity, the maximum values of the temperatures are defined to increase. An increase in the air excess coefficient is considered to lead to a drop in maximum temperatures in the back flows zone. The results of the completed studies can be used in energy practice in the design of burner devices for fuel combustion equipment with relatively low power, when it is necessary to ensure the uniformity of heat supply over the fire space.Наведено результати експериментальних досліджень теплового стану мікрофакельних пальникових пристроїв з циліндричними стабілізаторами полум'я. Встановлено особливості формування температурних режимів і геометричних характеристик зон зворотних токів у закормовій ділянці циліндричних стабілізаторів. Проаналізовано закономірності впливу конструктивних і режимних чинників на основні параметри процесу спалювання в розглядуваних пальникових пристроях. Наведено дані щодо залежності довжини зон зворотних токів у закормових ділянках циліндричних стабілізаторів полум'я та величини температур у них від таких режимних параметрів процесу спалювання, як величина швидкості потоку повітря на вході в канал і коефіцієнт надлишку повітря. Встановлено, що зі збільшенням швидкості повітряного потоку протяжність зони зворотних токів зростає, вплив же коефіцієнта надлишку повітря має протилежний характер: довжина зони зворотних токів і рівень температур у них зменшуються зі зростанням коефіцієнта надлишку повітря. Певну увагу приділено дослідженню особливостей зміни теплового стану і протяжності зон зворотних токів за стабілізаторами полум'я від величини відносного кроку розташування газоподавальних отворів. Зазначено, що з огляду на інжектуючу дію струмин паливного газу відбувається скорочення довжини зон зворотних токів зі збільшенням вказаного відносного кроку