Main systems development of K-band linac

The main purpose of our work is the creation of the small-sized linear electron accelerator on the energy up to 5 MeV on the base of such low-power Х- and K-bands sources. In this paper the results on development of main systems for such an accelerator are represented: two versions of an injector system and accelerating section. The operating frequency of the accelerator is 12500 MHz

Electron injector based on resonance system with evanescent oscillations

The article presents the design and simulated performances of an electron gun and a bunching system of the Sband injector based on a coupled cavity chain. Amplitude of the on-axis field varies substantially from the cell to the cell in the bunching system. The cell lengths are chosen to get the effective bunching and accelerating of the beam from the initial energy of 25 keV to the energy of about 1 MeV with the current up to 300 mA. The bunching system can be used in electron linacs both for fundamental researches and for radiation technologies.Приведено конструкцію та розрахункові характеристики інжектора 10-см діапазону, основаного на ланцюжку зв’язаних резонаторів. Амплітуда поля суттєво змінюється вздовж осі системи, що дозволяє одержати ефективне групування та прискорення пучка від початкової енергії 25 кеВ до енергії біля 1 МеВ при струмі до 300 мА. Інжектор може бути використаний як в лінійних прискорювачах електронів для фундаментальних досліджень, так і в прискорювачах для радіаційних технологій.Приведены конструкция и расчетные характеристики инжектора 10-cм диапазона, основанного на цепочке связанных резонаторов. Амплитуда поля существенно изменяется вдоль оси системы, что позволяет получить эффективную группировку и ускорение пучка от начальной энергии 25 кэВ до энергии около 1 МэВ с током до 300 мА. Инжектор может использоваться в ускорителях электронов как для фундаментальных исследований, так и для радиационных технологий

Accelerating section for technological electron linac

The construction parameters and electrodynamic characteristics of the accelerating section with phase advance of 120° at the operating frequency of 2856 MHz are presented. This section is designed to upgrade the electron LINAC LU-10 at NSC KIPT. Experimental results are compared with calculated ones.Приведены параметры конструкции и результаты исследования электродинамических характеристик ускоряющей секции с набегом фазы 120° на рабочей частоте 2856 МГц, предназначенной для модернизации ускорителя электронов ЛУ-10 ННЦ ХФТИ. Полученные экспериментальные данные сравниваются с расчётными.Наведено параметри конструкції і результати дослідження електродинамічних характеристик прискорювальної секції з набігом фази 120° на робочій частоті 2856 МГц, яка призначена для модернізації прискорювача електронів ЛУ-10 ННЦ ХФТІ. Отримано експериментальні дані, які порівнюються з розрахунковими

Phenomenological description of quantum gravity inspired modified classical electrodynamics

We discuss a large class of phenomenological models incorporating quantum gravity motivated corrections to electrodynamics. The framework is that of electrodynamics in a birefringent and dispersive medium with non-local constitutive relations, which are considered up to second order in the inverse of the energy characterizing the quantum gravity scale. The energy-momentum tensor, Green functions and frequency dependent refraction indices are obtained, leading to departures from standard physics. The effective character of the theory is also emphasized by introducing a frequency cutoff. The analysis of its effects upon the standard notion of causality is performed, showing that in the radiation regime the expected corrections get further suppressed by highly oscillating terms, thus forbiding causality violations to show up in the corresponding observational effects.Comment: 14 pages, to be published in Obregon Festschrift 2006, Gen. Rel. and Gra

Loop Quantum Gravity: An Inside View

This is a (relatively) non -- technical summary of the status of the quantum dynamics in Loop Quantum Gravity (LQG). We explain in detail the historical evolution of the subject and why the results obtained so far are non -- trivial. The present text can be viewed in part as a response to an article by Nicolai, Peeters and Zamaklar [hep-th/0501114]. We also explain why certain no go conclusions drawn from a mathematically correct calculation in a recent paper by Helling et al [hep-th/0409182] are physically incorrect.Comment: 58 pages, no figure

S-band electron linac with beam energy of 30…100 MeV

The S-band electron linac has been designed at NSC KIPT to cover an energy range from 30 to 100 MeV. The linac consists of the injector based on evanescent oscillations and the two four-meter long piecewise homogeneous accelerating sections. Each section is supplied with RF power from the KIU-12AM klystron. Variation of mean energy of the beam over a wide range is produced by placing bunches out of the wave crest in the second accelerating section. The report presents layout of the linac as well as simulation results of self-consistent particle dynamics in the linac and its present status.Лінійний прискорювач електронів 10 см - діапазону було розроблено в ННЦ ХФТІ з метою перекрити діапазон енергій 30…100 MeВ. Прискорювач складається з інжектора, основаного на коливаннях, що не розповсюджуються, і двох шматково-однорідних чотириметрових прискорювальних секцій. Кожна секція забезпечується НВЧ-потужністю від клістрона KІУ-12AM. Зміна середньої енергії пучка в широких межах забезпечується прискоренням згустків не на гребені хвилі в другій прискорювальній секції. Представлено структурну схему прискорювача, результати моделювання динаміки частинок в прискорювачі і його поточний стан.Линейный ускоритель электронов 10 см - диапазона был разработан в ННЦ ХФТИ с целью перекрытия диапазона энергий 30…100 MэВ. Ускоритель состоит из инжектора, основанного на не распространяющихся колебаниях и двух кусочно-однородных четырехметровых ускоряющих секций. Каждая секция питается СВЧ-мощностью от клистрона KИУ-12AM. Изменение средней энергии пучка в широких пределах обеспечивается ускорением сгустков не на гребне волны во второй ускоряющей секции. Представлены структурная схема ускорителя, результаты моделирования динамики частиц в ускорителе и его текущее состояние

Opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes

Iron is a scarce but essential micronutrient in the oceans that limits primary productivity in many regions of the surface ocean. The mechanisms and rates of Fe supply to the ocean interior are still poorly understood and quantified. Iron isotope ratios of different Fe pools can potentially be used to trace sources and sinks of the global Fe biogeochemical cycle if these boundary fluxes have distinct signatures. Seafloor hydrothermal vents emit metal rich fluids from mid-ocean ridges into the deep ocean. Iron isotope ratios have the potential to be used to trace the input of hydrothermal dissolved iron to the oceans if the local controls on the fractionation of Fe isotopes during plume dispersal in the deep ocean are understood. In this study we assess the behaviour of Fe isotopes in a Southern Ocean hydrothermal plume using a sampling program of Total Dissolvable Fe (TDFe), and dissolved Fe (dFe). We demonstrate that δ56Fe values of dFe (δ56dFe) within the hydrothermal plume change dramatically during early plume dispersal, ranging from −2.39 ± 0.05‰ to −0.13 ± 0.06‰ (2 SD). The isotopic composition of TDFe (δ56TDFe) was consistently heavier than dFe values, ranging from −0.31 ± 0.03‰ to 0.78 ± 0.05‰, consistent with Fe oxyhydroxide precipitation as the plume samples age. The dFe present in the hydrothermal plume includes stabilised dFe species with potential to be transported to the deep ocean. We estimate that stable dFe exported from the plume will have a δ56Fe of −0.28 ± 0.17‰. Further, we show that the proportion of authigenic iron-sulfide and iron-oxyhydroxide minerals precipitating in the buoyant plume exert opposing controls on the resultant isotope composition of dissolved Fe passed into the neutrally buoyant plume. We show that such controls yield variable dissolved Fe isotope signatures under the authigenic conditions reported from modern vent sites elsewhere, and so ought to be considered during iron isotope reconstructions of past hydrothermalism from ocean sediment records

Global impact of COVID-19 on stroke care and IV thrombolysis

Objective To measure the global impact of COVID-19 pandemic on volumes of IV thrombolysis (IVT), IVT transfers, and stroke hospitalizations over 4 months at the height of the pandemic (March 1 to June 30, 2020) compared with 2 control 4-month periods. Methods We conducted a cross-sectional, observational, retrospective study across 6 continents, 70 countries, and 457 stroke centers. Diagnoses were identified by their ICD-10 codes or classifications in stroke databases. Results There were 91,373 stroke admissions in the 4 months immediately before compared to 80,894 admissions during the pandemic months, representing an 11.5% (95% confidence interval [CI] -11.7 to -11.3, p < 0.0001) decline. There were 13,334 IVT therapies in the 4 months preceding compared to 11,570 procedures during the pandemic, representing a 13.2% (95% CI -13.8 to -12.7, p < 0.0001) drop. Interfacility IVT transfers decreased from 1,337 to 1,178, or an 11.9% decrease (95% CI -13.7 to -10.3, p = 0.001). Recovery of stroke hospitalization volume (9.5%, 95% CI 9.2-9.8, p < 0.0001) was noted over the 2 later (May, June) vs the 2 earlier (March, April) pandemic months. There was a 1.48% stroke rate across 119,967 COVID-19 hospitalizations. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was noted in 3.3% (1,722/52,026) of all stroke admissions. Conclusions The COVID-19 pandemic was associated with a global decline in the volume of stroke hospitalizations, IVT, and interfacility IVT transfers. Primary stroke centers and centers with higher COVID-19 inpatient volumes experienced steeper declines. Recovery of stroke hospitalization was noted in the later pandemic months.Paroxysmal Cerebral Disorder