Real time plasma equilibrium reconstruction in a Tokamak

The problem of equilibrium of a plasma in a Tokamak is a free boundary problemdescribed by the Grad-Shafranov equation in axisymmetric configurations. The right hand side of this equation is a non linear source, which represents the toroidal component of the plasma current density. This paper deals with the real time identification of this non linear source from experimental measurements. The proposed method is based on a fixed point algorithm, a finite element resolution, a reduced basis method and a least-square optimization formulation

A likely role for anoxygenic photosynthetic microbes in the formation of ancient stromatolites

Although cyanobacteria are the dominant primary producers in modern stromatolites and other microbialites, the oldest stromatolites pre-date geochemical evidence for oxygenic photosynthesis and cyanobacteria in the rock record. As a step towards the development of laboratory models of stromatolite growth, we tested the potential of a metabolically ancient anoxygenic photosynthetic bacterium to build stromatolites. This organism, Rhodopseudomonas palustris, stimulates the precipitation of calcite in solutions already highly saturated with respect to calcium carbonate, and greatly facilitates the incorporation of carbonate grains into proto-lamina (i.e. crusts). The appreciable stimulation of the growth of proto-lamina by a nonfilamentous anoxygenic microbe suggests that similar microbes may have played a greater role in the formation of Archean stromatolites than previously assumed

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

Microbial Kinetic Controls on Calcite Morphology in Supersaturated Solutions

Recognizing microbial imprints in the morphology of calcium carbonate minerals that form in very supersaturated solutions containing a high level of dissolved inorganic carbon (DIC) is challenging. To better define criteria for this purpose, we have analyzed the influence of sulfate-reducing bacterium Desulfovibrio desulfuricans strain G20 on the morphology of calcite in such solutions. G20 does not induce large shifts of pH or alkalinity under these conditions, but its uptake of millimolar sulfate and lactate decreases the number of anhedral crystals and stimulates growth of subhedral spar crystals relative to the abiotic controls. In addition, organic compounds associated with the basal growth medium, purified exopolymeric substances produced by G20 and lypopolysaccharide, stimulate the growth of anhedral crystals and crystals with rounded edges at low supersaturation index (SI) of calcite. The effect of organic compounds is reduced at higher SI, where rhombohedral habits dominate. Our results suggest that the local production and uptake of kinetic inhibitors within microbial biofilms may be an important control on calcite morphology in supersaturated solutions

ЕКОЛОГІЧНА ХАРАКТЕРИСТИКА РІЧОК У СЛАВСЬКОМУ ЛЬВІВСЬКОЇ ОБЛАСТІ

Introduction. The problem and deterioration of the water quality the source of drinking water and the basis of life on the planet which is becoming threatening today – is the threat to humanity. In 30 years, half of the Earth's population will suffer from water scarcity. In Ukraine it may occur much earlier, and for residents of 1,228 cities and town of Ukraine that use imported water, it is already come. Today in Ukraine there is almost no water reservoirs that meet the requirements of water quality, ecological state and basic sanitary-chemical and microbiological indicators for making pure drinking water. Now, the problem of pollution of water bodies (rivers, lakes, seas, groundwater) is the most urgent, because everyone knows that water is a life. A sharp deterioration in the quality of water in the country's reservoirs was the result of pol-lution by chemicals waste, poisons, synthetic fertilizers and sewage. During plants operation, industrial wastewater is discharged into fresh water. The wasterwater content is rich in all kinds of heavy metals (zinc, cadmium, mercury, lead, copper). In fact, in all reservoirs the concentration of pollutants exceeds the pollution standards. The annual data obtained by the bodies of the State Agency for Water Resources of Ukraine indicate that the content of highly oxidizable pollutants in water is high. Therefore, the study of environmental factors of pollution of reservoirs is currently a topical issue. Purpose. The purpose of the work is the ecological characterization of the water quality of the Slavka and the Opri rivers in Slavske of Lviv region. Methods. Hydrochemical investigations of the river Slavka and the Opir were used in the work. Results. The results indicate that surface waters are pH neutral of calcium carbonate content, which is characteristic for the investigated area. No significant changes in the water content are observed along the river, except for a slight increase in the Na + and Cl– content. All samples of the river Opir showed the high content of ammonium, indicating that the sewage flows into the river. The amounts of inorganic compounds of nitrogen, phosphorus, organic matter do not ex-ceed the MPC, are sufficiently saturated with oxygen. The low concentrations of the studied components are apparently due to the fact that the river flows over a long distance in the mountainous area and has a high self-cleaning ability. Conclusion. The waters of the rivers Slavka and the Opir of Slavske cannot be the collectors of pollution of an-thropogenic origin. Chemicals accumulating in reservoirs cause significant environmental changes that ultimately affect humans. Among the problems the humanity facing today are social, environmental, food, energy and water problems.Постановка проблеми. Проблемою для усього людства, яка сьогодні набуває загрозливого характеру, є виснаження і погіршення якості водних ресурсів − джерела питної води і основи життєдіяльності на планеті. Через 30 років близько половини населення Землі буде потерпати від нестачі води. Для України цей час може настати значно раніше, а для жителів 1228 міст, населених пунктів України, які користуються привозною водою, він уже настав. На сьогодні в Україні практично жодної поверхневої водойми за ступенем забруднення води, екологічним станом та основними санітарно-хімічними та мікробіологічними показниками не можна віднести до водойм першої категорії, з яких можна приготувати чисту питну воду. Зараз проблема забруднення водних об’єктів (річок, озер, морів, ґрунтових вод) є найбільш актуальною, оскільки всім відомо, що вода – це життя. Різке погіршення якості води у водоймах країни відбулося в результаті забруднення її хімічними відходами, отрутохімікатами, синтетичними добривами і каналізаційними стоками. В процесі діяльності великих заводів в прісну воду скидаються промислові стоки, склад яких рясніє різного роду важкими металами (цинк, кадмій, ртуть, свинець, мідь). Фактично у кожній з водойм можна легко зафіксувати перевищення допустимих норм забруднення. Середньорічні дані лабораторних вимірювань, які проводять органи Державного агентства водних ресурсів України, свідчать про підвищений вміст у воді контрольованих створів важко та легкоокисних забруднюючих речовин. Тому, вивчення екологічних чинників забруднення водойм на сьогодні є актуальним питанням.Мета. Метою роботи є екологічна характеристика якості води річок Славка та Опір селища Славське Львівської області. Методи. У роботі використано гідрохімічні обстеження річки Славка та Опір.Результати. Отримані результати свідчать, що поверхневі води є нейтральними, гідрокарбонатного кальцієвого складу, що характерно для району досліджень. Уздовж течії річки відчутних змін у складі вод не спостерігається, окрім незначного зростання вмісту Na+ та Cl–. У всіх пробах річки Опір зафіксовано підвищений вміст амонійних солей, що свідчить про потрапляння у річку стоків каналізації. Кількості неорганічних сполук азоту, фосфору, органічних речовин не перевищують ГДК, є достатньо насичені киснем. Низькі концентрації досліджуваних компонентів, очевидно, зумовлені тим, що ріка протікає на великій відстані в гірській місцевості та має високу здатність до самоочищення.Висновки. Води річок Славка та Опір смт. Славське не можуть бути нескінченними накопичувачами за-бруднень антропогенного походження. Хімічні речовини, накопичуючись у водоймах, викликають істотні екологічні зміни, які зрештою негативно впливають на людину. Серед безлічі проблем, що стоять сьогодні перед людством найбільш актуальними є соціальна, екологічна, продовольча, енергетична та водна

Weak localization competes with the quantum oscillations in a natural electronic superlattice: the case of Na1.5(PO2)4(WO3)20

We report an investigation of the combined structural and electronic properties of the bronze Na1.5 (PO2 )4 (WO3 )20 . Its low-dimensional structure and possible large reconstruction of the Fermi surface due to charge density wave instability make this bulk material a natural superlattice with a reduced number of carriers and Fermi energy. Signatures of multilayered two-dimensional (2D) electron weak localization are consequently reported, with an enhanced influence of quantum oscillations. A crossover between these two antagonistic entities, previously observed only in genuine low-dimensional materials and devices, is shown to occur in a bulk crystal due to its hidden 2D nature

Microstructural analysis of phase separation in iron chalcogenide superconductors

The interplay between superconductivity, magnetism and crystal structure in iron-based superconductors is a topic of great interest amongst the condensed matter physics community as it is thought to be the key to understanding the mechanisms responsible for high temperature superconductivity. Alkali metal doped iron chalcogenide superconductors exhibit several unique characteristics which are not found in other iron-based superconducting materials such as antiferromagnetic ordering at room temperature, the presence of ordered iron vacancies and high resistivity normal state properties. Detailed microstructural analysis is essential in order to understand the origin of these unusual properties. Here we have used a range of complementary scanning electron microscope based techniques, including high-resolution electron backscatter di raction mapping, to assess local variations in composition and lattice parameter with high precision and sub-micron spatial resolution. Phase separation is observed in the Csx Fe2-ySe2 crystals, with the minor phase distributed in a plate-like morphology throughout the crystal. Our results are consistent with superconductivity occurring only in the minority phase.Comment: Accepted for publication in a special edition of Supercond. Sci. Techno

Vibrational properties of hexagonal boron nitride by Inelastic X-ray scattering and ab initio calculations

The phonon dispersion relations of bulk hexagonal boron nitride have been determined from inelastic x-ray scattering measurements and analyzed by ab initio calculations. Experimental data and calculations show an outstanding agreement and reconcile the controversies raised by recent experimental data obtained by electron-energy loss spectroscopy and second-order Raman scattering