Wireless power transfer in magnetic resonance imaging at a higher-order mode of a birdcage coil

Magnetic resonance imaging (MRI) is a crucial tool for medical visualization. In many cases, performing a scanning procedure requires the use of additional equipment, which can be powered by wires as well as via wireless power transfer (WPT) or wireless energy harvesting. In this Letter, we propose a novel scheme for WPT that uses a higher-order mode of the MRI scanner's birdcage coil for energy transmission. In contrast to the existing WPT solutions, our approach does not require additional transmitting coils. Compared to the energy harvesting, the proposed method allows supplying significantly more power. We perform numerical simulations demonstrating that one can use the fundamental mode of the birdcage coil to perform a scanning procedure while transmitting the energy to the receiver at a higher-order mode without any interference with the scanning signal or violation of safety constraints, as guaranteed by the mode structure of the birdcage. Also, we evaluate the specific absorption rate along with the energy transfer efficiency and verify our numerical model by a direct comparison with an experimental setup featuring a birdcage coil of a 1.5T MRI scanner.Comment: 6 pages, 5 figures + Supplementary Material 10 pages, 7 figure

Type 2 diabetes mellitus and multiple chronic diseases

Background: Recently, there has been an increase in the number of patients with multiple chronic diseases (MCD), particularly due to obesity and ageing. The role of type 2 diabetes mellitus (T2DM) in the development of MCD, however, is still unclear. Aims: This study aimed to determine the incidence of T2DM in the structure of polymorbidity considering sex and age-related characteristics. Materials and methods: Patients with MCD (n = 2,254; 769 men/1,485 women; aged, 18–99 years) were examined. The incidence of type 2 diabetes among patients with MCD considering age and sex was determined. Results: Type 2 DM was detected in 407 patients with MCD (18.1%; male:female, 1:2.53). The polymorbidity index in male patients with type 2 diabetes was 1.5–2.0 times higher than that in male patients without diabetes. The rate of polymorbidity index increase was similar in both groups; however, its high initial value in patients with diabetes at a young age determined the burden of the comorbidity at a later age. In type 2 diabetes, hypertension was the predominant comorbidity at 18–59 years of age (p<0.05), whereas other cardiovascular diseases and liver and kidney diseases were predominant at 45–74 years of age (p<0.001) and hemiplegia at 45–89 years of age (p<0.05). Between 60 and 74 years, oncological diseases were found to be more common in patients without diabetes (p<0.001). Obesity, regardless of the presence of diabetes, was associated with a greater disease burden (p<0.05). Sex-related difference considering MCD in patients with type 2 DM was only observed for the higher incidence of myocardial infarction (p<0.001) and peptic ulcer disease in males (p<0.01). Females were more likely to have obesity, liver steatosis at a young age, or osteoarthritis than males in the general group (p<0.05); no differences were noted with respect to other diseases. Conclusions: In this study, type 2 diabetes was present in 18.1% of patients with MCD; moreover, a high initial polymorbidity index in patients with T2DM at young age was associated with a higher incidence of chronic diseases later in life than that in patients without diabetes. Based on these results, type 2 diabetes, along with ageing and obesity, can be considered as a risk factor in the development of MCD

СРАВНЕНИЕ ЛУЧЕВЫХ НАГРУЗОК НА ТОРЦЫ НЕЛИНЕЙНЫХ КРИСТАЛЛОВ В ПГС С КОЛЬЦЕВЫМ РЕЗОНАТОРОМ

It is shown that at optical parametric generation of high power pulses using a ring cavity and a nonlinear medium in each of its sections, beam load on the end face of the nonlinear medium adjacent to the output mirror is greatest when the output mirror is positioned first after the input mirror and smallest when the output mirror coincides with input one. Показано, что при параметрической генерации света (ПГС) мощных импульсов с использованием кольцевого резонатора и нелинейной среды в каждой из его секций лучевая нагрузка на торец нелинейной среды, примыкающий к выходному зеркалу, является наибольшей в случае, когда выходное зеркало расположено первым после входного зеркала, и наименьшей, когда выходное зеркало совпадает с входным зеркалом.

НЕПРЕРЫВНЫЙ ДИОДНО НАКАЧИВАЕМЫЙ Nd:KGdW/КTР-ЛАЗЕР С ВНУТРИРЕЗОНАТОРНЫМ УДВОЕНИЕМ ЧАСТОТЫ

A CW and quasi-CW Nd:KGd(WO4)2/KTP laser with longitudinal diode-pumping at λ ~879 nm and intracavity frequency doubling in a three-mirror linear cavity has been created. At frequency doubling, superior results are achieved with a Ng-cut crystal by virtue of a simpler character of its thermal lens. At a CW pump power of 15.6 W, the power of the second harmonic generated at a wavelength of 533.6 nm amounts to ~0.9 W. At quasi-CW pumping, the laser generates with a duty cycle of 10 % and emits 10-20 ms long pulses, whose peak power reaches 2.25 W with an optical conversion efficiency of 9%. In the case of a Nр -cut Nd:KGd(WO4)2 crystal, the peak power of the second harmonic does not exceed 2.1 W.Создан непрерывный, а также квазинепрерывный Nd:KGd(WO4)2/KTP-лазер с продольной диодной накачкой на λ ~879 нм и внутрирезонаторным удвоением частоты в трехзеркальном линейном резонаторе. При удвоении частоты более высокие результаты достигнуты с лазерным кристаллом Ng-среза в силу более простого характера его термолинзы. При мощности непрерывной накачки 15,6 Вт мощность второй гармоники, генерируемой на длине волны 533,6 нм, составляет ~0,9 Вт. В случае квазинепрерывной накачки лазер генерирует с рабочим циклом 10 % и излучает импульсы длительностью 10-20 мс, пиковая мощность которых достигает 2,25 Вт, при этом эффективность оптического преобразования составляет 9 %. В случае Nd:KGd(WO4)2-кристалла Nр-среза мгнрвенная мощность второй гармоники не превышает 2,1 Вт

ПОВЫШЕНИЕ ВЫХОДНОЙ ЭНЕРГИИ ВКР-ЛАЗЕРА ПУТЕМ ПОВТОРНОГО ИСПОЛЬЗОВАНИЯ ИСТОЩЕННОЙ НАКАЧКИ

A method for increasing the output energy of an extracavity Raman laser with a double-pass pump is proposed. The method is based on the repeated recovery of a depleted pump in the zone of SRS generation and is demonstrated by the example of eye-safe Raman lasers with a KGW crystal pumped at geometries of E Ng, and Е Nm by pulsed multimode radiation of a Nd:KGW-laser with a 4F3/2 → 4I13/2 working transition. When returning 70 % of a depleted pump in the Raman laser, an efficiency of generation of eye-safe radiation at wavelengths of 1507 and 1538 nm increases by approximately 11 %.Предложен способ увеличения выходной энергии внерезонаторного ВКР-лазера с двухпроходной накачкой. Способ основан на повторном возврате истощенной накачки в зону ВКР-генерации и демонстрируется на примере безопасных для глаз ВКР-лазеров на кристалле KGW, накачиваемом импульсным многомодовым излучением KGW:Nd-лазера с рабочим переходом 4F3/2 → 4I13/2 в геометриях E Ng, и Е Nm. При возврате в ВКР-лазер 70 % истощенной накачки КПД генерации безопасного для глаз излучения на длинах волн 1507 и 1538 нм возрастает примерно на 11 %

ТЕПЛОВЫЕ ЭФФЕКТЫ В БЕЗОПАСНОМ ДЛЯ ГЛАЗ КОЛЬЦЕВОМ ПАРАМЕТРИЧЕСКОМ ГЕНЕРАТОРЕ СВЕТА НА КРИСТАЛЛАХ KTiOPO4

For an eye-safe optical parametric oscillator (OPO) built on the basis of a three-mirror ring cavity, each section of which (the space between adjacent plane mirrors) contains a x-cut KTiOPO4 (KТР) crystal having a size of 15(х) × 7(y) × 7(z) mm3, the thermal effects due to idler wave absorption in KTP crystals were investigated. These thermal effects were evaluated by means of experimental measurement of the change in the OPO performance (divergence of the output beam and pulse energy) when transferring the OPO from the mode of generation of occasional single pulses to the mo de of generation of periodically repetitive pulses. It was found when the eye-safe OPO pumped by multimode YAG: Nd laser radiation generates 8-ns pulses with a repetition rate of 10 Hz and an energy of 30–35 mJ, thermal distortions of KTP crystals placed in metal holders at their natural air-cooling, are moderate. The total effect of positive thermolenses induced in nonlinear crystals leads to an increase in the divergence of the beam of the eye-safe OPO by 10 % and to a decrease in the efficiency of the OPO by 0.76 %, by virtue of fact that the induced thermal lenses are not ideal and thereby introduce additional aberration losses into the OPO cavity. The theoretical simulation of the OPO operation in the plane-wave approximation with the use of a system of three coupled first-order abridged differential equations showed that among three KTP crystals the KTP crystal placed first in the path of pump radiation in the OPO is the largest thermal load and the action of the most intense beams.Для безопасного для глаз параметрического генератора света (ПГС), выполненного на основе трехзеркального кольцевого резонатора, каждая секция которого (пространство между плоскими соседними зеркалами) содержит кристалл KTiOPO4 (KТР) х-среза размером 15(х) × 7(y) × 7(z) мм3, проведено исследование тепловых эффектов, обусловленных поглощением холостой волны в кристаллах KТР. Оценка тепловых эффектов проводилась посредством экспериментального определения изменений в рабочих характеристиках параметрического генератора света (расходимости выходного пучка и энергии импульса) при его переводе из режима генерации редко повторяющихся одиночных импульсов в режим генерации периодически повторяющихся импульсов. Выявлено, что в случае, когда безопасный для глаз ПГС, накачиваемый многомодовым излучением YAG:Nd-лазера, генерирует 8-наносекундные импульсы с частотой следования 10 Гц и энергией 30–35 мДж, термоискажения кристаллов KТР, помещенных в металлические держатели при их естественном воздушном охлаждении, носят умеренный характер. Суммарное действие положительных термолинз, наведенных в нелинейных кристаллах, вызывает увеличение расходимости пучка безопасного для глаз параметрического генератора света на 10 % и снижение эффективности ПГС на 0,76 % в силу того, что наведенные термолинзы не являются идеальными и поэтому вносят в резонатор ПГС дополнительные аберрационные потери. Теоретическое моделирование работы кольцевого параметрического генератора света в плосковолновом приближении с использованием системы трех связанных укороченных дифференциальных уравнений первого порядка показало, что среди трех кристаллов наиболее сильной тепловой нагрузке и воздействию наиболее интенсивных пучков подвергается кристалл KТР, расположенный первым по ходу излучения накачки в ПГС

Spectroscopic and photoluminescence characterization of Eu 3+-doped monoclinic KY(WO4)2 crystal

Monoclinic 2 at% Eu-doped KY(WO4)2 is grown by top-seeded solution growth method. Polarizationresolved absorption and stimulated-emission cross-section spectra are determined for this crystal. Spectroscopic properties of Eu:KY(WO4)2 are modeled within conventional Judd–Ofelt theory, as well as theory of f–f transition intensities for systems with anomalously strong configuration interaction, yielding absorption oscillator strengths, luminescence branching ratios and radiative lifetime of 5D0 state. The impact of excited-state absorption from this state on possibility of laser operation is discussed. Photoluminescent properties of Eu:KY(WO4)2 are determined. This crystal provides intense red emission with CIE coordinates x¼0.670, y¼0.329

Spectroscopy of tetragonal Eu:NaGd(WO4)2 crystal

We report on growth and detailed spectroscopic study of Eu3ю-doped tetragonal sodium gadolinium double tungstate, Eu:NaGd(WO4)2, a new promising crystal for deep-red lasers. Large-volume crystal doped with 4.9 at.% Eu is grown by Czochralski method along the [001] crystallographic direction. Absorption of Eu3ю ions is studied at room temperature (RT) and at 6 K. For the absorption band related to the 7F1 / 5D1 transition suitable for pumping of Eu:NaGd(WO4)2, the maximum cross-section is sabs ј 1.2 _ 10_21 cm2 at 535.5 nm with the full width at half maximum (FWHM) of 3.1 nm (at RT, for E jj a polarization). For the 5D0 / 7F4 transition, the maximum stimulated-emission cross-section is sSE ј 1.6 _ 10_21 cm2 at 698.3 nm (RT, E jj c polarization). Lifetime of the 5D0 state is 490 ± 10 ms (at RT). Under UV excitation, Eu:NaGd(WO4)2 provides intense red emission with CIE coordinates (x ј 0.671, y ј 0.329)

Patterns in the development of collective immunity to SARS-CoV-2 during the COVID-19 pandemic

The ongoing coronavirus disease (COVID-19) pandemic over the past three years has caused close attention to the problem of herd immunity, which is understood as: "resistance to the spread of a contagious disease within a population or herd". Collective immunity is formed both as a result of infection (natural spread of the pathogen in a population of susceptible individuals) and as a result of the use of specific vaccines. During the COVID-19 pandemic, both mechanisms for the formation of collective immunity were realized. In the first wave, there was a natural formation of collective immunity to the virus following recoveries from COVID-19 caused by pandemic spread of SARS-CoV-2. Starting from December 2020, the widespread use of specific vaccines against SARS-CoV-2 began in the USA, Great Britain, China, Russia, and a number of other countries. This launched the process of post-vaccination collective immunity formation; its features have depended on the vaccine types implemented. Currently, in those countries where vaccination and revaccination of recovered patients is widely carried out, immunity is "hybrid" in nature. Several commonalities should be noted in the pandemic experience: a somewhat regular, periodic (wavelike) nature of the COVID-19 epidemic process; changes in pathogen genetics in variants in all countries; and expansive mass vaccination programs in many populations. From these, we can draw some conclusions about the general trend for all countries in the formation of collective immunity during the pandemic: At the beginning of the pandemic in 2020, overall population seroprevalence did not exceed 20%. Other findings were: the highest seroprevalence rates were noted in the children's age group; pronounced regional differences were revealed; and the highest indicators were noted among medical workers. Collective immunity developed as a result of infection or illness, and in the majority of seropositive volunteers, it was represented by antibodies to both antigens. At the height of the pandemic in the summer of 2021, population seroprevalence reached 50%. This was due to both a significant number of convalescents and the start of mass vaccination campaigns. In all countries, specific differences in seroprevalence (by age, region, profession) leveled out, leading to more uniformity. During this period, the formation of "hybrid" immunity is clearly prominent, and the proportion of individuals with antibodies to RBD alone increased (due to vaccination with vector vaccines).  Later, mass vaccination, as well as involvement of most of the population in the epidemic process due to the emergence of the highly contagious Omicron strain, raised the level of collective immunity to 80-90%. This led to a sharp decrease in COVID-19 incidence in the second half of 2022 in all countries participating in the study. In the later stages of the pandemic (2022-2023), almost 90% of seropositive volunteers had hybrid immunity, reflected as antibodies to both antigens (Nc, RBD)

Параметрическая генерация света в двуосном кристалле KTA при накачке излучением YAG:Nd-лазера в произвольных направлениях

Herein, on the basis of expressions for the refractive indices of isonormal waves, the possibility of performing collinear phase matching for optical parametric generation in arbitrary directions of a biaxial KTA crystal under pumping by radiation of a YAG:Nd laser is analyzed. The tuning curves that determine the tuning range of the signal and idler for type-I and II-type phase-matching and arbitrary angles θ and φ in cases where the tuning is carried out along the angle θ at a fixed angle φ and vice versa are calculated. The effective nonlinear coefficient is determined. It is shown that their maximum value is achieved аt a polar angle θ = 90° and type-II phase-matching. For the case of generation of eye-safe radiation the spectral and angular phase matching widths were estimated, as well as gain widths of KTA-OPO under monochromatic pumping.На основе выражений для показателя преломления изонормальных волн проанализирована возможность выполнения коллинеарного фазового синхронизма для параметрической генерации света в произвольных направлениях двуосного кристалла KTA при накачке излучением YAG:Nd-лазера. Рассчитаны перестроечные кривые, определяющие диапазон перестройки сигнальной и холостой волн для синхронизма типов I и II и произвольных углов q и j в случаях, когда перестройка осуществляется по углу q при фиксированном угле j и наоборот. Определены эффективные нелинейные коэффициенты. Показано, что их максимальное значение обеспечивается при 90-градусном по углу q фазовом синхронизме типа II. Для случая генерации безопасного для глаз излучения произведена оценка спектральной и угловой ширины синхронизма, а также ширины полосы усиления ПГС при монохромной накачке