Metal-insulator transition induced by 16O -18O oxygen isotope exchange in colossal negative magnetoresistance manganites

The effect of 16O-18O isotope exchange on the electric resistivity was studied for (La(1-y)Pr(y))0.7Ca0.3MnO3 ceramic samples. Depending on y, this mixed perovskite exhibited different types of low-temperature behavior ranging from ferromagnetic metal (FM) to charge ordered (CO) antiferromagnetic insulator. It was found that at y=0.75, the substitution of 16O by 18O results in the reversible transition from a FM to a CO insulator at zero magnetic field. The applied magnetic field (H >= 2 T) transformed the sample with 18O again to the metallic state and caused the increase in the FM transition temperature Tc of the 16O sample. As a result, the isotope shift of Tc at H = 2 T was as high as 63 K. Such unique sensitivity of the system to oxygen isotope exchange, giving rise even to the metal-insulator transition, is discussed in terms of the isotope dependence of the effective electron bandwidth which shifts the balance between the CO and FM phases.Comment: 5 pages (RevTeX), 2 eps figures included, to appear in J. Appl. Phys. 83, (1998

Cytokines and local chronic inflammation in the formation of infertility in fertile age women

The purpose of the study was to examine the characteristics of the content of cytokines in the peritoneal fluid in women of reproductive age with infertility against the background of chronic inflammatory diseases of the pelvic organs in the stage of clinical remission.Material and methods. A study was conducted of 50 patients aged 23-36 years with a verified diagnosis of infertility of tubal peritoneal genesis against a background of chronic inflammatory diseases of the reproductive sphere in the stage of clinical remission. As a control group, 15 practically healthy women aged 25-37 years were examined. Concentration of cytokines TNF-a, IL-4, IL-6, IL-10, IFN-y, MCP-1 in the peritoneal fluid was measured by enzyme-linked immunosorbent assay.Results and discussion. In the main group of patients with tubal-peritoneal infertility, the activity of local inflammatory reactions is tested in the period of clinical remission of a chronic inflammatory process. This is confirmed by a significantly higher level of TNF-a, IL-4, IL-6, IFN-y, MCP-1 in the peritoneal fluid compared to the control group. The studied biologically active substances play a significant role in the development of the immune response, as well as fibroplastic processes. The results can be regarded as the latent development of the immune response in reactions to constant antigenic stimulation from the focus of chronic inflammation, which is a significant factor in the development of adhesions in the formation of infertility, and requires the inclusion of immunotropic therapy methods in treatment

Effective String Theory Revisited

We revisit the effective field theory of long relativistic strings such as confining flux tubes in QCD. We derive the Polchinski-Strominger interaction by a calculation in static gauge. This interaction implies that a non-critical string which initially oscillates in one direction gets excited in orthogonal directions as well. In static gauge no additional term in the effective action is needed to obtain this effect. It results from a one-loop calculation using the Nambu-Goto action. Non-linearly realized Lorentz symmetry is manifest at all stages in dimensional regularization. We also explain that independent of the number of dimensions non-covariant counterterms have to be added to the action in the commonly used zeta-function regularization.Comment: 21 pages, 4 figures, v2: typo corrected, references added, published versio

HEMOGLOBIN BINDING TO PHOSPHOLIPID MEMBRANES AS REVEALED BY PYRENE FLUORESCENCE STUDY

In this work hemoglobin (Hb) association with lipid bilayers was investigated using fluorescent probe pyrene. Model membranes were prepared from zwitterionic lipid phosphatidylcholine (PC), anionic lipid phosphatidylglycerol (PG) and cholesterol (Chol). Hb-lipid binding was followed by the pyrene fluorescence quenching. Hb-induced decrease of pyrene monomer fluorescence was followed by the increase of relative intensities of vibronic bands. Presumably, Hb penetration into the bilayer increases the space between neighbouring lipids and promotes water penetration into the membrane core. Pyrene excimer emission quenching was interpreted in terms of resonance energy transfer. The greatest depth of Hb penetration into the lipid bilayer was observed in PC vesicles. In Chol-containing liposomes sterol condensing effect prevents deep protein penetration into the membrane. PG has an ability to stabilize lipid bilayers due to the ordered state of its lipid tails and H-bonding interactions between lipid molecules. This also can prevent Hb access to the inner membrane regions. KEY WORDS: hemoglobin, model membranes, protein-lipid complexes, pyrene, fluorescence spectroscopy. ДОСЛІДЖЕННЯ ЗВ'ЯЗУВАННЯ ГЕМОГЛОБІНУ З ФОСФОЛІПІДНИМИ МЕМБРАНАМИ ЗА ДОПОМОГОЮ ПІРЕНУ O.К. Куценко, Г.П. Горбенко, В.М. Трусова Харківський національний університет імені В.Н. Каразіна, пл. Свободи, 4, Харків, 61077 В даній роботі комплексоутворення гемоглобіну (Hb) з ліпідними бішарами різного складу досліджувалось за допомогою флуоресцентного зонду пірену. Зв'язування Hb з ліпідами характеризувалось гасінням флуоресценції зонда, що супроводжувалось зростанням відносної інтенсивності вібронних смуг. Можливо, Hb, проникаючи у бішар, розсуває сусідні молекули ліпідів, сприяючи проникненню води у мембрану. Гасіння випромінювання ексимерів інтерпретувалось у термінах резонансного переносу енергії. Найбільша глибина проникнення білка спостерігалась у РС везикулах. У ліпосомах, які містили Chol, конденсуючий ефект стерола перешкоджав проникненню білка у мембрану. Структурні властивості PG сприяють стабілізації ліпідного бішару, що також може перешкоджати проникненню Hb у внутрішні регіони мембрани. КЛЮЧОВІ СЛОВА: гемоглобін, модельні мембрани, білок-ліпідні комплекси, пірен, флуоресцентна спектроскопія. ИССЛЕДОВАНИЕ СВЯЗЫВАНИЯ ГЕМОГЛОБИНА С ФОСФОЛИПИДНЫМИ МЕМБРАНАМИ С ПОМОЩЬЮ ПИРЕНА O.К. Куценко, Г.П. Горбенко, В.М. Трусова Харьковский национальный университет имени В.Н. Каразина, пл. Свободы, 4, Харьков, 61077 В данной работе комплексообразование гемоглобина (Hb) с липидными бислоями различного состава исследовалось с помощью флуоресцентного зонда пирена. Связывание Hb с липидами характеризовалось тушением флуоресценции пирена, что сопровождалось увеличением относительной интенсивности вибронных полос пирена. Возможно, Hb, проникая в бислой, раздвигает соседние молекулы липидов, способствуя проникновению воды в мембрану. Тушение испускания эксимеров интерпретировалось в терминах резонансного переноса энергии. Наибольшая глубина проникновения белка наблюдалась в РС везикулах. В липосомах, содержащих Chol, конденсирующий эффект стерола препятствовал проникновению белка в мембрану. Структурные свойства PG способствуют стабилизации липидного бислоя, что также может препятствовать проникновению Hb во внутренние области мембраны. КЛЮЧЕВЫЕ СЛОВА: гемоглобин, модельные мембраны, белок-липидные комплексы, пирен, флуоресцентная спектроскопия

Phase diagram and isotope effect in (PrEu)_0.7Ca_0.3CoO_3 cobaltites exhibiting spin-state transitions

We present the study of magnetization, thermal expansion, specific heat, resistivity, and a.c. susceptibility of (Pr$_{1-y}$Eu$_y$)$_{0.7}$Ca$_{0.3}$CoO$_3$ cobaltites. The measurements were performed on ceramic samples with $y = 0.12 - 0.26$ and $y = 1$. Based on these results, we construct the phase diagram, including magnetic and spin-state transitions. The transition from the low- to intermediate-spin state is observed for the samples with $y > 0.18$, whereas for a lower Eu-doping level, there are no spin-state transitions, but a crossover between the ferromagnetic and paramagnetic states occurs. The effect of oxygen isotope substitution along with Eu doping on the magnetic/spin state is discussed. The oxygen-isotope substitution ($^{16}$O by $^{18}$O) is found to shift both the magnetic and spin-state phase boundaries to lower Eu concentrations. The isotope effect on the spin-state transition temperature ($y > 0.18$) is rather strong, but it is much weaker for the transition to a ferromagnetic state ($y < 0.18$). The ferromagnetic ordering in the low-Eu doped samples is shown to be promoted by the Co$^{4+}$ ions, which favor the formation of the intermediate-spin state of neighboring Co$^{3+}$ ions.Comment: 13 pages, including 11 figures, to be published in Phys. Rev.

Термометричні дослідження полімеризації 2-гідроксіетилметакрилату в присутності полівінілпіролідону з одночасним відновленням йонів нікелю

The kinetics of heat release during the processes of 2-hydroxyethyl methacrylate (HEMA) polymerization in the presence of polyvinylpyrrolidone (PVP) and the copolymerization of HEMA with PVP with simultaneous reduction of Ni2+ has been investigated. Nickel sulphate/sodium hypophosphite redox system in alkaline medium was used for Ni2+ reduction. The kinetic regularities of polymerization have been evaluated by thermometric method. The temperature change of the reaction medium during polymerization has been investigated by means of developed equipment, based on the reactor with properties like adiabatic one. The characteristic parameters that correspond to the time of gel formation, the time of exothermic maximum temperature reach, the range of gel effect and maximum temperature of the exotherm are identified on the obtained thermometric curves. It is determined that in the case of HEMA/PVP compositions, polymerization in the presence of benzoyl peroxide occurs with high rate already at 50 °C.&nbsp;The time of the gel effect start and maximum exothermic temperature mainly depend on the initial composition formula, solvent content, initial polymerization temperature, and also the simultaneous reduction of Ni2+ in the polymerization process. The presence of even a small content of oxidizing agent and reducing agent causes an increase of the time of gel formation start, time of maximum exothermic temperature reach and a decrease of the maximum exothermic temperature. It is determined that use of benzoyl peroxide in combination with iron (II) sulfate for initiating of HEMA copolymerization with PVP enables the process to be performed at room temperature and with a maximum exothermic temperature, which provides chemical reduction of Ni2+. The time and temperature parameters of polymerization determined in the work, as well as the main factors on which these parameters depend, will provide an opportunity to substantiate the technological parameters of metal-filled HEMA/PVP copolymers obtaining.За допомогою термометричного методу досліджено кінетику виділення тепла під час полімеризації композицій на основі 2-гідроксіетилметакрилату (ГЕМА) та полівінілпіролідону (ПВП), ініційованої пероксидом бензоїлу з одночасним відновленням Ni2+. Для відновлення Ni2+ використано окисно-відновну систему нікелю сульфат натрію гіпофосфіт у лужному середовищі. Оцінено вплив складу вихідної композиції, вмісту розчинника, початкової температури полімеризації, концентрації окисника та відновника на кінетичні параметри полімеризації&nbsp;– час початку гелеутворення, час досягнення максимальної температури екзотермії, область гель-ефекту та максимальну температуру екзотермії. Встановлено, що у випадку ГЕМА/ПВП композицій полімеризація у присутності пероксиду бензоїлу відбувається з високою швидкістю вже за температури 50°С.&nbsp;Доведено, що використання комплексного ініціатора, який складається з сульфату заліза (ІІ) та пероксиду бензоїлу, дає можливість здійснювати полімеризацію ГЕМА/ПВП композицій за кімнатної температури та з максимальною температурою екзотермії, яка забезпечує хімічне осадження металу. Виявлено, що температура, до якої нагрівається реакційне середовище, може бути достатньою для перебігу хімічної реакції відновлення Ni2+

Features of the immune response in children with acute respiratory infections caused by DNA and RNA viruses

The issues of immunopathogenesis of acute respiratory viral infections (ARVI) remain relevant, despite a long history of study. The aim of the study was to investigate the characteristics of the content of some cytokines in the blood serum of children with ARVI caused by DNA and RNA-containing viruses. Material and methods. We examined 92 children with ARVI at the age from 1 to 15 years, hospitalized in the hospital of the Children’s Clinical Hospital No. 6 (Novosibirsk). In order to determine the etiological factor, a study was carried out using the RT-PCR method (test systems AmpliSensORVI-screen-FL, “InterLabService”, Russia) of mucus from the nose and throat for the presence of genetic material of viruses that cause ARVI. Determination of the content of IL-8, IL-17, IFN-γ in the blood serum in children of all groups was carried out by the method of solid-phase ELISA using commercial test systems of LLC “Cytokin” (Russia). Results and discussion. 4 groups were formed: group I (n = 20) children with ARVI caused by DNA-containing viruses (group B, C, E adenoviruses, bocaviruses); group II (n = 53) children with ARVI caused by RNA viruses (RS virus, metapneumovirus, parainfluenza viruses 1, 2, 3, 4, rhinovirus and coronoviruses); group III (n = 12) children with ARVI caused by mixed infection; group IV (n = 7) – the genetic material of the pathogen has not been isolated. Concentration of IL-8, IL-17, IFN-γ was significantly increased in all groups compared to the normative values. Higher values of IFN-γ and IL-8 were revealed in patients with DNA viruses compared with the group with RNA-containing viruses, although the excess of IFN-γ was not statistically significant. Differences in the content of IFN-γ, IL-8 and IL-17 were noted for various etiological viral agents, but they were not significant. Conclusions. The results obtained can serve as confirmation that the functional characteristics of the response of the immune system in children with ARVI are determined not so much by the etiological factor as by its individual state. With ARVI in children, the presence of genetic material from more than one virus, apparently, is not a significant potentiating factor in the activation of the immune response. At the same time, a negative PCR result with a detailed clinical picture of ARVI does not exclude the viral genesis of the disease

Ultrafast photoinduced reflectivity transients in (Nd0.5Sr0.5)MnO3(Nd_{0.5}Sr_{0.5})MnO_3

The temperature dependence of ultrafast photoinduced reflectivity transients is reported in Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ thin film. The photoinduced reflectivity shows a complex response with very different temperature dependences on different timescales. The response on the sub-ps timescale appears to be only weakly sensitive to the 270K-metal-insulator phase transition. Below $\sim 160$ K the sub-ps response displays a two component behavior indicating inhomogeneity of the film resulting from the substrate induced strain. On the other hand, the slower response on the 10-100 ps timescale is sensitive only to the metal-insulator phase transition and is in agreement with some previously published results. The difference in the temperature dependences of the responses on nanosecond and $\mu$s timescales indicates that thermal equilibrium between the different degrees of fredom is established relatively slowly - on a nanosecond timescale