Modeling of a single-cycle current generator while forming a quasi-sinusoidal current

The paper presents the results of investigation of the influence of the output voltage magnitude on the operating frequency of the switch in the single-cycle quasi-sinusoidal current generator circuit. Analytical expressions for calculating the time parameters for transients in the circuit under given assumptions have been obtained. The results presented in the paper can be used in the design of converters of this type

Research of weldability of pipe steel X65 QS ordered for sour service

To evaluate the weldability of steel for sour service the effect of different thermal cycles of welding on toughness and resistance to sulfide stress cracking of the pipe steel X65QS was investigated. Researches were conducted by modeling the welding thermal cycles with heating to a temperature of 1300 °C followed by cooling at different rates. Also kinetics of the austenite decomposition of pipe steel X65 QS in conditions of welding thermal cycles was studied. Dilatometric studies showed bainite transformation in a wide range of cooling rates in GCHAZ. In this case, the main factor affecting both toughness and corrosion resistant is morphology of bainite transformed in GCHAZ. Found that the highest toughness and satisfactory sulfide stress cracking resistance is observed in welded joints with structure of the acicular bainite in the GCHAZ. Acicular bainite in GCHAZ forms at cooling rates 10-20 °C/sec.Для оценки свариваемости стали были проведены исследования влияния различных термических циклов сварки на вязкие свойства и стойкость к сульфидному растрескиванию под напряжением трубной коррозионностойкой стали группы прочности X65QS. Исследования проводили с помощью моделирования термических циклов сварки с нагревом до температуры 1300 °С с последующим охлаждением с различными скоростями. Так же была изучена кинетика распада аустенита стали группы прочности X65 QS в условиях термических циклов сварки. Дилатометрические исследования показали, что в области крупного зерна зоны термического влияния в широком диапазоне скоростей охлаждения присутствует бейнитное превращение. При этом основным фактором, влияющим как на вязкие, так и на коррозионные свойства, является морфология бейнита, сформированного в области крупного зерна зоны термического влияния. Установлено, что самыми высокими вязкими свойствами и удовлетворительной стойкостью к сульфидному растрескиванию под напряжением обладают сварные соединение со структурой игольчатого бейнита в области крупного зерна зоны термического влияния. Игольчатый бейнит в области крупного зерна зоны термического влияния образуется при реализации скоростей охлаждения 10-20 °С/с

Optical control of 4f orbital state in rare-earth metals

Information technology demands continuous increase of data-storage density. In high-density magnetic recording media, the large magneto-crystalline anisotropy (MCA) stabilizes the stored information against decay through thermal fluctuations. In the latest generation storage media, MCA is so large that magnetic order needs to be transiently destroyed by heat to enable bit writing. Here we show an alternative approach to control high-anisotropy magnets: With ultrashort laser pulses the anisotropy itself can be manipulated via electronic state excitations. In rare-earth materials like terbium metal, magnetic moment and high MCA both originate from the 4f electronic state. Following infrared laser excitation 5d-4f electron-electron scattering processes lead to selective orbital excitations that change the 4f orbital occupation and significantly alter the MCA. Besides these excitations within the 4f multiplet, 5d-4f electron transfer causes a transient change of the 4f occupation number, which, too, strongly alters the MCA. Such MCA change cannot be achieved by heating: The material would rather be damaged than the 4f configuration modified. Our results show a way to overcome this limitation for a new type of efficient magnetic storage medium. Besides potential technological relevance, the observation of MCA-changing excitations also has implications for a general understanding of magnetic dynamics processes on ultrashort time scales, where the 4f electronic state affects the angular momentum transfer between spin system and lattice.Comment: Manuscript (14 pages, 3 figures) and Supplementary Information (22 pages, 9 figures

The interplay of local electron correlations and ultrafast spin dynamics in fcc Ni

The complex electronic structure of metallic ferromagnets is determined by a balance between exchange interaction, electron hopping leading to band formation, and local Coulomb repulsion. The interplay between the respective terms of the Hamiltonian is of fundamental interest, since it produces most, if not all, of the exotic phenomena observed in the solid state. By combining high energy and temporal resolution in femtosecond time-resolved X-ray absorption spectroscopy with ab initio time-dependent density functional theory we analyze the electronic structure in fcc Ni on the time scale of these interactions in a pump-probe experiment. We distinguish transient broadening and energy shifts in the absorption spectra, which we demonstrate to be caused by electron repopulation and correlation-induced modifications of the electronic structure, respectively. Importantly, the theoretical description of this experimental result hence requires to take the local Coulomb interaction into account, revealing a temporal interplay between band formation, exchange interaction, and Coulomb repulsion

Photon shot-noise limited transient absorption soft X-ray spectroscopy at the European XFEL

Femtosecond transient soft X-ray Absorption Spectroscopy (XAS) is a very promising technique that can be employed at X-ray Free Electron Lasers (FELs) to investigate out-of-equilibrium dynamics for material and energy research. Here we present a dedicated setup for soft X-rays available at the Spectroscopy & Coherent Scattering (SCS) instrument at the European X-ray Free Electron Laser (EuXFEL). It consists of a beam-splitting off-axis zone plate (BOZ) used in transmission to create three copies of the incoming beam, which are used to measure the transmitted intensity through the excited and unexcited sample, as well as to monitor the incoming intensity. Since these three intensity signals are detected shot-by-shot and simultaneously, this setup allows normalized shot-by-shot analysis of the transmission. For photon detection, the DSSC imaging detector, which is capable of recording up to 800 images at 4.5 MHz frame rate during the FEL burst, is employed and allows approaching the photon shot-noise limit. We review the setup and its capabilities, as well as the online and offline analysis tools provided to users

Electron population dynamics in resonant non-linear x-ray absorption in nickel at a free-electron laser

Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray–matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the L3-edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm2. We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale

Ultrafast manipulation of the NiO antiferromagnetic order via sub gap optical excitation

Wide band gap insulators such as NiO offer the exciting prospect of coherently manipulating electronic correlations with strong optical fields. Contrary to metals where rapid dephasing of optical excitation via electronic processes occurs, the sub gap excitation in charge transfer insulators has been shown to couple to low energy bosonic excitations. However, it is currently unknown if the bosonic dressing field is composed of phonons or magnons. Here we use the prototypical charge transfer insulator NiO to demonstrate that 1.5 eV sub gap optical excitation leads to a renormalised NiO band gap in combination with a significant reduction of the antiferromagnetic order. We employ element specific X ray reflectivity at the FLASH free electron laser to demonstrate the reduction of the upper band edge at the O 1s 2p core valence resonance K edge whereas the antiferromagnetic order is probed via X ray magnetic linear dichroism XMLD at the Ni 2p 3d resonance L2 edge . Comparing the transient XMLD spectral line shape to ground state measurements allows us to extract a spin temperature rise of 65 5 K for time delays longer than 400 fs while at earlier times a non equilibrium spin state is formed. We identify transient mid gap states being formed during the first 200 fs accompanied by a band gap reduction lasting at least up to the maximum measured time delay of 2.4 ps. Electronic structure calculations indicate that magnon excitations significantly contribute to the reduction of the NiO band ga

Megahertz-rate ultrafast X-ray scattering and holographic imaging at the European XFEL

The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range

A New Method for Treating Burn Wounds Using Targeted Delivery of Medicinal Substances by Magnetic Nanocarrier (Experimental Part)

Проведено экспериментальное исследование на лабораторных животных по изучению эффективности адресной доставки мази левомеколь с помощью магнитных наночастиц и внешнего магнитного поля при термических ожогах. В исследовании принимало участие 20 крыс с двумя очагами ожога. Крысы были разделены на 4 группы: без лечения, терапия с использованием мази левомеколь, лечение с использованием наночастиц, мази левомеколь и внешнего магнитного поля и только магнитотерапии. При гистологическом исследовании на 14-е сутки во всех группах в зоне термического повреждения кожи были отмечены признаки глубокого ожога III и IV степени с распространением некроза на всю глубину дермы и на мышцы. В группе с наночастицами, мазью левомеколь и магнитным полем на фоне уменьшения воспаления отмечалось очаговое появление грануляционной ткани. Таким образом, гистологические исследования ожогового раневого процесса лабораторных животных показали, что использование инновационного биологически активного ранозаживляющего средства на основе наночастиц в сочетании с мазью левомеколь улучшает регенерацию тканей и приводит к ускорению эпителизации, что в целом повышает результаты лечения ожоговой раны. Использование внешнего магнитного поля способствует адресной доставке лечебного нанокомплекса и поддержанию оптимальной концентрации препарата в ранеExperimental studies have been carried out on laboratory animals to investigate the effectiveness of targeted delivery of levomekol ointment using magnetic nanoparticles and an external magnetic field for treatment of thermal burns. The study involved 20 rats, with two burns on each. The rats were divided into 4 groups: untreated; treated with levomekol ointment; treated with levomekol ointment associated with nanoparticles and an external magnetic field; and treated with magnetic field alone. Histological examination was conducted on Day 14, and in all groups, in the thermal burn zone of the skin there were signs of deep three- and four-degree burns with necrosis spread through the dermis, reaching the muscle. In the group with levomekol ointment associated with nanoparticles and magnetic field, inflammation was decreased, and focal granulation tissue formation was observed. Thus, histological studies of the burn wound process in laboratory animals showed that the use of an innovative biologically active wound healing agent based on nanoparticles in combination with the levomecol ointment improved tissue regeneration and accelerated epithelialization, which enhanced the effectiveness of burn wound treatment. The use of an external magnetic field facilitated targeted delivery of the therapeutic nanosystem and maintenance of the optimal concentration of the drug in the woun