Dynamic susceptibility and dynamic correlations in spin ice

Here we calculate the dynamic susceptibility and dynamic correlation function in spin ice using the model of emergent magnetic monopoles. Calculations are based on a method originally suggested for the description of dynamic processes in water ice (non-equilibrium thermodynamics approach). We show that for zero temperature the dynamic correlation function reproduces the transverse dipole correlations (static correlation function) characteristic of spin ice in its ground state. At non-zero temperatures the dynamic correlation function includes an additional longitudinal component which decreases as the temperature decreases. Both terms (transverse and longitudinal) exhibit identical Debye-like dependences on frequency but with different relaxation times: the magnetic Coulomb interaction of monopoles reduces the longitudinal relaxation time with respect to the transverse one. We calculate the dielectric function for the magnetic monopole gas and discuss how the non-equilibrium thermodynamics approach exposes corrections to the Debye-Huckel theory of magnetic monopoles and the concept of "entropic charge".Comment: 5 pages, 2 figure

Dynamic susceptibility of a spin ice near the critical point

We consider spin ice magnets (primarily, $\mathrm{Dy_2Ti_2O_7}$) in the vicinity of their critical point on the $(H,T)$ plane. We find that the longitudinal susceptibility diverges at the critical point, leading to the behaviour qualitatively similar to the one which would result from non-zero conductance of magnetic charges. We show that dynamics of critical fluctuations belongs to the universality class of easy-axis ferroelectric and calculate logarithmic corrections (within two-loop approximation) to the mean-field critical behavior.Comment: 5 pages, 3 figures. Some misprints are corrected, among them are the formula (20) and the estimation for $\Gamma_c

Maritime trade by Chinese Junks between Van Don of Northeast Coastal Vietnam and China

In the latter half of the 17th century, after the Qing dynasty permitted Chinese coastal folk to trade with foreign countries, those living on the coast actively advanced overseas using Chinese junks. One of their maritime trade partners was Vietnam. China and Vietnam are connected by land, and since ancient times China has maintained neighborly relations with Vietnam via overland routes. However, people of the Huanan coastal region still conducted maritime trade with Vietnam using Chinese junks. This paper traces the history of maritime trade by Chinese junks between Van Don and China, through filed research in Van Don, a port town in northeastern Vietnam, close to the border with China

Specifics of self-organization and properties of highly dilute aqueous solutions of polyoxidonium

© 2016, Springer Science+Business Media New York.Using a combination of physicochemical methods (dynamic and electrophoretic light scattering (DLS and ELS, respectively), nanoparticle tracking analysis, atomic force and transmission electron microscopy (AFM and TEM, respectively), UV spectroscopy, conductometry, pH-metry, dielcometry), it was found that dilute solutions of a multicomponent drug immunomodulator polyoxidonium (PO) are nanoheterogeneous disperse systems, with their disperse phase undergoing considerable restructurings when diluting the solution in the range of calculated concentrations from 1∙10–1 to 1∙10–16 mg mL–1, which is reflected in the non-monotonous concentration dependencies of specific electroconductivity, dielectric permittivity, and pH of the solutions. Using ELS, AFM, TEM, and UV spectroscopy methods, it was found that the disperse phase with a size of hundreds of nanometers which forms at concentrations of ≤1∙10–5 mg mL–1, contains organized water structures substantiating the negative values of ζ-potential, which vary non-monotonously from–5 to–16 mV. Radioprotective properties of dilute solutions of PO (1∙10–1 and 1∙10–9 mg mL–1) were demonstrated for the first time when exposing the test mutant bacterial strain Salmonella typhimurium TA 100 (Ames test) to X-ray radiation in a dose of 7.50 mGy used for medical diagnostics

High pressure route to generate magnetic monopole dimers in spin ice

The gas of magnetic monopoles in spin ice is governed by one key parameter: the monopole chemical potential. A significant variation of this parameter could access hitherto undiscovered magnetic phenomena arising from monopole correlations, as observed in the analogous electrical Coulomb gas, like monopole dimerization, critical phase separation, or charge ordering. However, all known spin ices have values of chemical potential imposed by their structure and chemistry that place them deeply within the weakly correlated regime, where none of these interesting phenomena occur. Here we use high-pressure synthesis to create a new monopole host, Dy2Ge2O7, with a radically altered chemical potential that stabilizes a large fraction of monopole dimers. The system is found to be ideally described by the classic Debye–Huckel–Bjerrum theory of charge correlations. We thus show how to tune the monopole chemical potential in spin ice and how to access the diverse collective properties of magnetic monopoles

Topology by Design in Magnetic nano-Materials: Artificial Spin Ice

Artificial Spin Ices are two dimensional arrays of magnetic, interacting nano-structures whose geometry can be chosen at will, and whose elementary degrees of freedom can be characterized directly. They were introduced at first to study frustration in a controllable setting, to mimic the behavior of spin ice rare earth pyrochlores, but at more useful temperature and field ranges and with direct characterization, and to provide practical implementation to celebrated, exactly solvable models of statistical mechanics previously devised to gain an understanding of degenerate ensembles with residual entropy. With the evolution of nano--fabrication and of experimental protocols it is now possible to characterize the material in real-time, real-space, and to realize virtually any geometry, for direct control over the collective dynamics. This has recently opened a path toward the deliberate design of novel, exotic states, not found in natural materials, and often characterized by topological properties. Without any pretense of exhaustiveness, we will provide an introduction to the material, the early works, and then, by reporting on more recent results, we will proceed to describe the new direction, which includes the design of desired topological states and their implications to kinetics.Comment: 29 pages, 13 figures, 116 references, Book Chapte

СОВРЕМЕННЫЕ ОСОБЕННОСТИ ФОРМИРОВАНИЯ УРОВНЕЙ МЕДИЦИНСКОГО ОБЛУЧЕНИЯ НАСЕЛЕНИЯ РЕСПУБЛИКИ ТАТАРСТАН ПРИ ВЫПОЛНЕНИИ РЕНТГЕНОЛОГИЧЕСКИХ ПРОЦЕДУР

The purpose. The purpose of the investigation is an assessment of the peculiarities of forming and registration of the collective doses of patients and the population of the Tatarsatan Republic (RT) from medical exposure and the development of measures for optimization of this radiation factor.Materials and methods. The analysis is based on the forms of the Federal statistical observation № 3-DOZ «Data on the exposure doses to patients obtained during medical radiological examination» (form № 3-DOZ) and radiation-hygienic passports of RT for the period from 2006 to 2013.The results. Annually in RT there is an increase of the number of performed X-ray procedures, which reached the value of 6279696 (1.64 procedures per resident per year) in 2013. During the reporting period (from 2006 to 2013) the structure of the performed X-ray procedures has also changed. It is observed that the percentage of fluorography procedures in the overall structure decreased from 41.3% to 31.3% at the same time the level of absolute value of annually performed fluorography procedures is stable. There is an increase in the absolute number of radiographic procedures performed during the period from 2578754 to 4072810 X-rays per year, that is 1.58 times higher. Absolute and relative values related to X-ray fluoroscopy examinations decreased from 1.1% to 0.7%. In contrast, the absolute number of annually performed X-ray computed tomography examinations (CT) has increased over the period by 3.3 times and percentage of CT in overall structure of X-ray procedure is 2.7%. The number of special investigations has increased in 2.1 times, but the relative value remained at average level of 0.4% on general background of the increasing of X-ray activity in the region. This fact influenced the change in the radiation-hygienic indexes of medical radiation exposure of the population of RT. According to №3-DOZ forms and radiation-hygienic passports of the territories, the levels of the annual collective effective dose from medical exposure to the patients and population increases in the period from 2006 to 2012. The structure of the medical exposure has been significantly changed. If the dominant role in the formation of the annual collective effective dose in 2006 performed the fluorography procedures (609.17 person-Sv; 34.03% in the structure of the total collective dose from medical exposure), then the primary importance passed to СТ in 2013 (748.18 person-Sv; 50.04%). The article considers the peculiarities of the formation and recording of exposure doses to patients when performing various types of x-ray procedures.Conclusion. The widespread use of the digital technologies of producing and processing of the X-ray images, an adjust instrumental control and registration of patient exposure doses, routine control of operational parameters of the equipment used for the fluorographic, X-ray and fluoroscopic procedures allowed to objectify and reduce correspondent indicators of the collective effective exposure doses to patients and population. There exists the reserve for organizational, technical measures for the further reduction of patient exposure doses during the performance of the routine X-ray procedures, namely the standardization of the performed examinations, further transition to the digital X-ray technologies of the image obtaining. The use of calculation methods of the patient dose registration continues to provide the significant influence on the statistical reporting when the performing of CT and special examinations. Taking into account the fact that CT provides the greatest contribution to the annual collective effective dose in the region in recent years (more than 50%, the first place in the structure of medical exposure), and special examinations of a high clinical efficient, are also accompanied by a significant radiation exposure it is necessary to apply the measures fore the objectification of the exposure doses for these types of examinations in order to develop scientifically justified measures to reduce adverse effects on the exposed population categories.Цель. Установление особенностей формирования и учета коллективных доз облучения пациентов и населения Республики Татарстан (РТ) от медицинского облучения и разработка мероприятий по оптимизации данного радиационного фактора.Материалы и методы. Для анализа использованы формы федерального государственного статистического наблюдения № 3-ДОЗ «Сведения о дозах облучения пациентов при проведении медицинских рентгенорадиологических исследований» (формы № 3-ДОЗ) и радиационно-гигиенические паспорта территории РТ за период с 2006 по2013 г.Результаты. Ежегодно в РТ наблюдается увеличение количества выполняемых рентгенологических процедур, которое в2013 г. достигло значения 6 279 696 (1,64 процедуры на жителя в год). За рассматриваемый период времени (с 2006 по2013 г.) изменилась также и структура выполняемых рентгено-диагностических процедур. Отмечается относительное снижение доли флюорографических процедур в общей структуре с 41,3% до 31,3% при сохранении стабильного уровня абсолютных значений выполняемых ежегодно флюорограмм. Наблюдается увеличение абсолютного количества выполняемых рентгенографических процедур за рассматриваемый период с 2 578 754 до 4 072 810 рентгенографий в год, то есть в 1,58 раза. Абсолютные и относительные значения, относящиеся к рентгеноскопическим исследованиям, уменьшились с 1,1% до 0,7%. Напротив, абсолютное количество выполняемых ежегодно рентгеновских компьютерно-томографических исследований (РКТ) возросло за рассматриваемый период в 3,3 раза и в общей структуре РКТ уже составляет 2,7%. Количество специальных исследований возросло в 2,1 раза, но на общем фоне увеличения рентгенодиагностической работы в регионе относительное значение сохранилось на среднемноголетнем уровне и составило 0,4%. Это не могло не повлиять на изменение радиационно-гигиенических показателей медицинского облучения населения РТ. Согласно формам № 3-ДОЗ и радиационно-гигиеническим паспортам территорий, за период с 2006 по2012 г. отмечался рост уровней годовых коллективных эффективных доз медицинского облучения пациентов и населения. Значительно изменилась структура медицинского облучения. Если в2006 г. доминирующее значение в формировании годовой коллективной эффективной дозы представляли флюорографические процедуры (609,17 чел.-Зв; 34,03% в общей структуре коллективной дозы медицинского облучения), то в2013 г. первостепенное значение стала занимать РКТ (748,18 чел.-Зв; 50,04%). В статье рассматриваются особенности формирования и учета доз облучения пациентов при выполнении различных видов рентгенологических процедур.Заключение. Широкое использование цифровых технологий получения и обработки рентгенологических изображений, налаженный инструментальный контроль и учет доз облучения пациентов, рутинный контроль эксплуатационных параметров используемого оборудования для флюорографических, рентгенографических и рентгеноскопических процедур позволили объективизировать и снизить соответствующие показатели коллективных эффективных доз облучения пациентов и населения. Существует резерв организационных, технических мероприятий по дальнейшему снижению доз облучения пациентов при выполнении рутинных рентгенографических процедур, а именно: стандартизация выполняемых исследований, дальнейший переход на цифровые технологии получения изображения. Существенное влияние на статистическую отчетность продолжает оказывать использование расчетных методов учета доз облучения пациентов при выполнении РКТ и специальных исследований. Учитывая то, что РКТ в последние годы обеспечивает наибольший вклад в годовую коллективную эффективную дозу облучения региона (более 50%, первое место в структуре медицинского облучения), а специальные исследования, обладающие высокой клинической эффективностью, также сопровождаются значительной лучевой нагрузкой, необходимы меры по объективизации доз облучения при данных видах исследований в целях разработки научно обоснованных мероприятий по снижению неблагоприятного воздействия на облучаемые категории населения