Ambiguities in the partial-wave analysis of pseudoscalar-meson photoproduction

Ambiguities in pseudoscalar-meson photoproduction, arising from incomplete experimental data, have analogs in pion-nucleon scattering. Amplitude ambiguities have important implications for the problems of amplitude extraction and resonance identification in partial-wave analysis. The effect of these ambiguities on observables is described. We compare our results with those found in earlier studies.Comment: 12 pages of text. No figure

THE INFLUENCE OF HYDROGEN ALLOYING ON THE STRUCTURE, PHASE COMPOSITION AND TECHNOLOGICAL PLASTICITY OF THE TITANIUM ALLOY WITH ALUMINUM CONTENT EXCEEDING LIMIT SOLUBILITYABSTRACT

Установлено влияние водорода на структуру, фазовый состав и сопротивление горячей пластической деформации опытного сплава Ti–8,7Al–1,5Zr–2Mo, перспективного для изготовления силовых режущих хирургических инструментов. Установлено, что легирование водородом до 0,3 и 0,6 масс. % увеличивает объемную долю β-фазы при температурах α+α2+β-области и снижает предел текучести сплава на 115–200 МПа при температурах деформации 800–850С.The influence of hydrogen on the structure, phase composition and resistance of hot plastic deformation of the Ti–8.7Al–1.5Zr–2Moexperimental alloy, promising for the manufacture of power cutting surgical instruments, is established. It was found that doping with hydrogen to 0.3 and 0.6 wt. % increases the volume fraction of the β-phase at temperatures α+α2+β-region and reduces the yield strength of the alloy by 115–200 MPa at deformation temperatures of 800–850°C

Structure and Texture Formation behaviour in Two-Phase Titanium Alloys Billets Obtained by Additive Manufacturing

Работа выполнена с применением оборудования ресурсного центра коллективного пользования «Авиационно-космические материалы и технологии» МАИ.The effect of heat treatment on the structure, mechanical properties and texture of titanium alloy Ti–6Al–4V billets, obtained by additive manufacturing technology was investigated in this work.В рамках проведенного исследования было изучено влияние термической обработки на структуру, механические свойства и текстуру заготовок из титанового сплава ВТ6, полученных при помощи аддитивной технологии прямого лазерного нанесения материала

ВЛИЯНИЕ ТЕРМИЧЕСКОЙ ОБРАБОТКИ НА СТРУКТУРУ И СВОЙСТВА ЛИСТОВЫХ ПОЛУФАБРИКАТОВ ИЗ ЖАРОПРОЧНОГО СПЛАВА НА ОСНОВЕ ТИТАНА, ЛЕГИРОВАННОГО РЗМ

This paper is a continuation of studies on the effect of microalloying with gadolinium, a rare earth metal, on the structure formation and properties of a titanium alloy under thermal action. It was previously shown that the introduction of gadolinium into an experimental heat-resistant alloy promotes cast structure transformation and reduces the size of structural components, and affects the rate of growth and nucleation of particles. It has been established that additional alloying of gadolinium has no significant influence on the microstructure formation of hot-rolled sheets made of the heat-resistant experimental alloy after annealing at 950 °C. The structure is represented by equiaxial particles of the primary α-phase, secondary α-phase of lamellar morphology and a small amount of β-phase.It has been established that the ordering processes occur in primary α-phase particles and α2-phase particles are formed during isothermal aging at 700 °C for 100 h with the formation of silicides at the α-β interface. It is shown that the α2 phase is formed in the body of the primary α-phase particles, and its border regions are free from precipitations that is due to their aluminum depletion as a result of β→α transformation. It has been established that the silicide particle size is reduced as the gadolinium content in the alloy increases. The average particle size is 0,2–0,3 μm in the alloy with 0 % Gd, and it is reduced to 0,05–0,1 μm in the alloy with 0,2 % Gd.It was shown that the introduction of 0,2 % of gadolinium into the heat-resistant titanium alloy leads to a decrease in the gas-saturated layer depth, and to an increase in the cyclic durability and short-term strength at 700 °C by 30 %.Продолжены исследования, посвященные изучению влияния микролегирования редкоземельным металлом гадолинием на формирование структуры и свойства титанового сплава при термическом воздействии. Как установлено ранее, введение в опытный жаропрочный сплав гадолиния способствует преобразованию структуры в литом состоянии, приводит к уменьшению размера структурных составляющих, а также воздействует на скорости роста и зарождения частиц. Выявлено, что дополнительное легирование гадолинием не оказывает существенного влияния на формирование микроструктуры горячекатаных листов из жаропрочного опытного сплава после отжига при температуре 950 °С. Структура представлена равноосными частицами первичной α-фазы, вторичной α-фазы пластинчатой морфологии и небольшим количеством β-фазы. Определено, что в процессе изотермической выдержки (t = 700 °С, τ = 100 ч) в частицах первичной α-фазы протекают процессы упорядочения и отмечается выделение частиц α2-фазы, а на межфазной α/β-границе – образование химических соединений в виде силицидов. Показано, что формирование α2-фазы происходит в теле частиц первичной α-фазы, а приграничные ее области свободны от выделений, что обусловлено их обеднением алюминием вследствие протекания β→α-превращения. Установлено, что с увеличением в сплаве содержания гадолиния размеры выделяющихся частиц силицида уменьшаются. Если в сплаве с 0 % Gd средний размер частиц составляет 0,2–0,3 мкм, то в сплаве с 0,2 % Gd он снижается до 0,05–0,1 мкм. Показано, что введение в жаропрочный титановый сплав 0,2 % Gd приводит к уменьшению глубины «альфированного» слоя, повышению на 30 % циклической долговечности и кратковременной прочности при температуре 700 °С

Структура и свойства композитных TiN–Pb-покрытий, напыленных на сплав вт6 магнетронным распылением постоянного тока

DC reactive magnetron sputtering of two separate single-element Ti and Pb targets was used to deposit a TiN–Pb composite coating onto a substrate made of the VT6 titanium alloy. The studies were carried out at Pb cathode currents of 0.2 and 0.1 A and two fixed argon flow rate values of 6.0 or 8.5 cm3/min, and the flow rate of nitrogen supplied to the chamber varying from experiment to experiment. The composition of coatings was determined by energy dispersive analysis. It was shown that the amount of lead in the coatings ranged from 0.5 to 16 wt.% depending on the Pb cathode current and reactive nitrogen consumption. Coating microhardness and wear were determined for each deposition mode. It was found that coating thicknesses varied from 1.9 to 5.2 μm depending on the ratio of argon and nitrogen fluxes. The effect of TiN–Pb magnetron coating deposition parameters on the structure and phase composition was investigated by X-ray diffraction method. It was shown that the coating consists of Pb and PbO at the Pb cathode current of 0.2 A, and of TiN, Pb, and PbO at the current of 0.1 A, while an increase in the ratio of argon and nitrogen fluxes leads to an increase in the fraction of TiN, the intensity of titanium substrate surface saturation with nitrogen, as well as microhardness and wear resistance. Under all deposition conditions the TiN coating features by a typical texture (111), the intensity of which varies nonmonotonically.Методом реакционного магнетронного распыления постоянного тока двух раздельных моноэлементных мишеней Ti и Pb напыляли композитное покрытие состава TiN–Pb на подложку из титанового сплава ВТ6. Исследования проводили при токах на Pb-катоде 0,2 и 0,1 А и двух фиксированных значениях расхода аргона: 6,0 либо 8,5 см3/мин, меняя от опыта к опыту расход подаваемого в камеру азота. Состав покрытий определяли энергодисперсионным анализом. Показано, что количество свинца в покрытиях составляло от 0,5 до 16 мас.% в зависимости от тока на Pb-катоде и расхода реактивного азота. Для каждого режима напыления оценивали микротвердость и износ покрытий. Установлено, что в зависимости от отношения потоков аргона и азота толщина покрытий менялась от 1,9 до 5,2 мкм. Рентгеноструктурным методом исследовали влияние параметров нанесения магнетронных TiN–Pb-покрытий на их структуру и фазовый состав. Выявлено, что при значениях тока на Pb-катоде, равном 0,2 А, покрытие состоит из Pb и PbO, а при токе 0,1 А – из TiN, Pb и PbO. При этом увеличение отношения потоков аргона и азота приводит к росту доли TiN, повышению интенсивности насыщения поверхности титановой подложки азотом, а также увеличению микротвердости и износостойкости. При всех условиях напыления TiN-покрытие характеризуется типичной текстурой (111), интенсивность которой меняется немонотонно

Adiabatic perturbation theory and geometry of periodically-driven systems

We give a systematic review of the adiabatic theorem and the leading non-adiabatic corrections in periodically-driven (Floquet) systems. These corrections have a two-fold origin: (i) conventional ones originating from the gradually changing Floquet Hamiltonian and (ii) corrections originating from changing the micro-motion operator. These corrections conspire to give a Hall-type linear response for non-stroboscopic (time-averaged) observables allowing one to measure the Berry curvature and the Chern number related to the Floquet Hamiltonian, thus extending these concepts to periodically-driven many-body systems. The non-zero Floquet Chern number allows one to realize a Thouless energy pump, where one can adiabatically add energy to the system in discrete units of the driving frequency. We discuss the validity of Floquet Adiabatic Perturbation Theory (FAPT) using five different models covering linear and non-linear few and many-particle systems. We argue that in interacting systems, even in the stable high-frequency regimes, FAPT breaks down at ultra slow ramp rates due to avoided crossings of photon resonances, not captured by the inverse-frequency expansion, leading to a counter-intuitive stronger heating at slower ramp rates. Nevertheless, large windows in the ramp rate are shown to exist for which the physics of interacting driven systems is well captured by FAPT.The authors would like to thank M. Aidelsburger, M. Atala, E. Dalla Torre, N. Goldman, M. Heyl, D. Huse, G. Jotzu, C. Kennedy, M. Lohse, T. Mori, L. Pollet, M. Rudner, A. Russomanno, and C. Schweizer for fruitful discussions. This work was supported by AFOSR FA9550-16-1-0334, NSF DMR-1506340, ARO W911NF1410540, and the Hungarian research grant OTKA Nos. K101244, K105149. M. K. was supported by Laboratory Directed Research and Development (LDRD) funding from Berkeley Lab, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors are pleased to acknowledge that the computational work reported in this paper was performed on the Shared Computing Cluster which is administered by Boston University's Research Computing Services. The authors also acknowledge the Research Computing Services group for providing consulting support which has contributed to the results reported within this paper. The study of the driven non-integrable transverse-field Ising model was carried out using QuSpin [185] - an open-source state-of-the-art Python package for dynamics and exact diagonalization of quantum many body systems, available to download here. (FA9550-16-1-0334 - AFOSR; DMR-1506340 - NSF; W911NF1410540 - ARO; K101244 - Hungarian research grant OTKA; K105149 - Hungarian research grant OTKA; DE-AC02-05CH11231 - Laboratory Directed Research and Development (LDRD) funding from Berkeley Lab)https://arxiv.org/pdf/1606.02229.pd

Determination of the E2/M1 Ratio in the \gamma N \to \Delta(1232) Transition from a Simultaneous Measurement of p(\vec{\gamma},p)\pi^0 and p(\vec{\gamma},\pi^+)n

Tagged linearly polarized photons have been used at the Mainz Microtron MAMI for simultaneous measurements of the p(\vec{\gamma},p)\pi^0 and p(\vec{\gamma},\pi^+)n reaction channels to study the \gamma N \to \Delta(1232) transition. The energy dependence of the magnetic dipole M_{1+}^{3/2} and electric quadrupole E_{1+}^{3/2} amplitudes have been extracted from these data in the photon energy range from 270 to 420 MeV. The E2/M1 ratio for the \gamma N \to \Delta(1232) transition has been determined to be - (2.5+-0.1_{stat}+-0.2_{sys}) % at the resonance position delta_{33}=90^0.Comment: 25 pages Latex including 13 postscript figures submitted for publication in Phys. Rev.

The formation of human populations in South and Central Asia

By sequencing 523 ancient humans, we show that the primary source of ancestry in modern South Asians is a prehistoric genetic gradient between people related to early hunter-gatherers of Iran and Southeast Asia. After the Indus Valley Civilization’s decline, its people mixed with individuals in the southeast to form one of the two main ancestral populations of South Asia, whose direct descendants live in southern India. Simultaneously, they mixed with descendants of Steppe pastoralists who, starting around 4000 years ago, spread via Central Asia to form the other main ancestral population. The Steppe ancestry in South Asia has the same profile as that in Bronze Age Eastern Europe, tracking a movement of people that affected both regions and that likely spread the distinctive features shared between Indo-Iranian and Balto-Slavic languages