APPLICATION OF PLASMA ANTENNA TECHNOLOGY TO IMPROVE RADIO COMMUNICATION STEALTH IN VHF BAND

Рассматривается плазменная вибраторная антенна, которая предназначена для работы в VHF диапазоне на частоте 140 МГц. Вибраторные плазменные антенны отличаются от обычных вибраторных антенн тем, что металлический проводник заменяется плазмой в газоразрядной трубке. Плазменный вибратор, создаваемый разрядом в трубке, способен включаться и выключаться за время порядка микросекунд. Применение плазменной антенны позволяет обеспечить два режима работы: активный, когда плазма индуцирует проводящую поверхность, и скрытый, когда антенна становится практически невидимой для электромагнитных волн, а плазменное облако отсутствует. Для определения характеристик антенны использовалось электродинамическое моделирование. Полученные результаты показывают, что характеристики плазменной вибраторной антенны близки к характеристикам эквивалентного ей металлического диполя, при этом длина плазменной антенны меньше. Для определения эффективности скрытного режима антенны производилось сравнение характеристик эффективной площади рассеяния плазменной антенны с выключенным плазменным облаком и эквивалентного металлического диполя. Полученные результаты показывают, что плазменная антенна обладает высокой эффективностью излучения, диаграммами направленности, схожими с эквивалентной дипольной антенной, и значительно меньшими значениями эффективной площади рассеяния (ЭПР) в выключенном режиме The article discusses a plasma dipole antenna, which is designed to operate in the VHF band at a frequency of 140 MHz. Plasma dipole antennas differ from conventional dipole antennas in that the metal conductor is replaced by plasma in the discharge tube. The plasma dipole created by the discharge in the tube is capable of turning on and off in times of the order of microseconds. The use of a plasma antenna makes it possible to provide two modes of operation: active, when the plasma induces a conductive surface, and hidden, when the antenna becomes practically invisible to electromagnetic waves, and the plasma cloud is absent. We used electrodynamic modeling to determine the characteristics of the antenna. The results show that the characteristics of the plasma dipole antenna are close to those of the equivalent metal dipole, while the length of the plasma antenna is shorter. To determine the efficiency of the hidden mode of the antenna, we compared the characteristics of radar cross-section of the plasma antenna with the plasma cloud turned off and the equivalent metal dipole. The results obtained show that the plasma antenna has a high radiation efficiency, directional patterns similar to an equivalent dipole antenna, and significantly lower RCS values in the off mode

Syntaxonomical and ecological diversity of the class Polygono-Poetea annuae in Bulgaria

Class Polygono-Poetea annuae Rivas-Mart. 1975 includes therophyte-rich vegetation on trampled habitats. The study presents the first analysis of the syntaxonomy of this class and its ecology in Bulgaria. One hundred seventy-five relevés from this class were collected and stored in the Balkan Vegetation Database during 2017–2020. Numerical classification (hierarchical divisive) and ordination were performed by JUICE and CANOCO software packages. Diagnostic species were determined by calculating the Phi-coefficient. Four associations, Sclerochloo durae-Polygonetum arenastri, Polygonetum arenastri, Lolio-Polygonetum arenastri and Poëtum annuae, were recognized. Their floristic composition has been shaped mainly by climatic and soil conditions. Sclerochloo durae-Polygonetum arenastri association has been found at lower altitudes, occurring in fully lighted habitats with high radiation, whereas Poëtum annuae has been found at higher altitudes in wetter and cooler areas. On the other hand, stands of Polygonetum arenastri have been found on nutrient-rich soils, whereas communities of Lolio-Polygonetum arenastri were distributed in warmer and nutrient-poor areas. The Polygono-Poetea annuae class is still poorly studied in Bulgaria and much more information from all regions of the country needs to be collected and analyzed.

Asymmetric Concentric Microring Resonator Label-Free Biosensors

A study of label-free silicon nitride asymmetric double-microring resonators is presented. The use of highly accurate 3D vector modal techniques permits an extensive exploration of the parameter space defining the architecture of the proposed device in the search for optimal geometries and reaching configurations not addressed in previous studies that had been limited to symmetrical configurations. Asymmetry, on the other hand, permits to access resonances that exploit the radiation-quenching properties of the structure in an optimal way. The analysis presented also includes the effect of absorption in the sensor aqueous cladding that is generally omitted. The results of the numerical survey indicate that the optimized geometries bring about a substantive performance improvement at small microring radii that are impractical for more conventional single-ring geometries due to the high radiation losses. Therefore, lower footprint devices, and a larger scale of integration, can be attained with the proposed structure.

Sensitivity of panoramic radiographs in diagnosing maxillary sinusitis: a scoping review

Objectives: The purpose of this study was to determine the sensitivity of using this panoramic radiograph in diagnosing maxillary sinusitis. Review: Scoping Review with article searches was carried out through NCBI's PubMed database, Science Direct, and EbscoHost from January 2020 to March 2021, with the inclusion criteria being articles published in 2010-2020. Conclusion: Panoramic radiographs were found to be less sensitive for diagnosing maxillary sinusitis, but due to the low availability and accessibility of CBCT and CT, and related to their expensive cost and high radiation, panoramic radiographs are considered to be quite optimal.

Radiation-Induced Heart Disease

Cancer incidence and survivorship have had a rising tendency over the last two decades due to better treatment modalities. One of these is radiation therapy (RT), which is used in 20–55% of cancer patients, and its basic principle consists of inhibiting proliferation or inducing apoptosis of cancer cells. Classically, photon beam RT has been the mainstay therapy for these patients, but, in the last decade, proton beam has been introduced as a new option. This newer method focuses more on the tumor and affects less of the surrounding normal tissue, i.e., the heart. Radiation to the heart is a common complication of RT, especially in patients with lymphoma, breast, lung, and esophageal cancer. The pathophysiology is due to changes in the microvascular and macrovascular milieu that can promote accelerated atherosclerosis and/or induce fibrosis of the myocardium, pericardium, and valves. These complications occur days, weeks, or years after RT and the risk factors associated are high radiation doses (>30 Gy), concomitant chemotherapy (primarily anthracyclines), age, history of heart disease, and the presence of cardiovascular risk factors. The understanding of these mechanisms and risk factors by physicians can lead to a tailored assessment and monitorization of these patients with the objective of early detection or prevention of radiation-induced heart disease. Echocardiography is a noninvasive method which provides a comprehensive evaluation of the pericardium, valves, myocardium, and coronaries, making it the first imaging tool in most cases; however, other modalities, such as computed tomography, nuclear medicine, or cardiac magnetic resonance, can provide additional value.

CHARGE DISTRIBUTION IN THE AlO - SiO SYSTEM EXPOSED TO IONIZING RADIATION

Полупроводниковые МДП (металл - диэлектрик - полупроводник) структуры являются ключевыми элементами современной электронной техники, в том числе устройств работающих в условиях воздействия проникающих излучений. Одним из возможных подходов к уменьшению радиационных эффектов в МДП структурах является использование диэлектриков, которые уменьшают генерацию и накопление избыточного пространственного заряда в объеме диэлектрика. В работе исследована система диэлектриков AlO - SiO. Исследование показывает пригодность использования МДП структур, на основе системы диэлектриков, для формирования приборов с высокой радиационной стойкостью. Нанесение слоя AlO поверх слоя SiO улучшает рабочие характеристики МДП структур за счет повышения однородности параметров. Основной эффект влияния слоя AlO на параметры структур заключается в уменьшении механических напряжений на границе SiO-подложка. Захват ловушками электронов в AlO, компенсирует заряд захваченных дырок в AlO, и снижает паразитный ток через AlO. Metal-insulator-semiconductor (MIS) structures are key elements of modern electronic technology, including devices operating under conditions of exposure to penetrating radiation. One of the possible approaches to reducing radiation effects in MIS structures is the use of dielectrics, which reduce the generation and accumulation of excess space charge in the bulk of the dielectric. We investigated the system of dielectrics AlO - SiO. The study shows the suitability of using MIS structures based on a system of dielectrics for formation of devices with high radiation resistance. Applying a AlO layer on top of the SiO layer improves the performance of MIS structures by increasing the uniformity of parameters. The main effect of the influence of the AlO layer on the parameters of the structures is to reduce the mechanical stresses at the interface SiO -substrate. The trapping of electrons in AlO, compensates for the charge of the trapped holes in SiO, and reduces the parasitic current through AlO.

Lettuce Production under Mini-PV Modules Arranged in Patterned Designs

The growing need for clean energy and food production are favoring the use of underused spaces, such as rooftops. This study aims to demonstrate the compatibility of the use of rooftops both for the production of photovoltaic energy and for the production of food, despite the fact that both compete for the same resource, sunlight (rooftop agrivoltaic). In the experiment reported in this study, which was carried out in Almería (Spain) during the spring and summer of 2021, three shade treatments were tested for a lettuce crop, produced by photovoltaic modules with different arrangements: concentrated shade (CS), scattered shade (SS) and full sun (FS). This experiment was repeated in two seasons with high radiation levels and temperature. The results show that in these environmental conditions, the cultivation of plants that demand little sunlight, such as lettuce, is compatible with the shading produced by photovoltaic panels. In addition, it is shown that the same percentage of the area covered with shade (22%), but using mini-PV modules arranged in patterns, improves the productivity (fresh weight, dry matter, number of leaves, maximum length and dry matter of roots) of lettuce cultivation, both in spring and summer.

Radiation Protection in Interventional Radiology/Cardiology—Is State-of-the-Art Equipment Used?

Interventional radiology/cardiology is one of the fields with the highest radiation doses for workers. For this reason, the International Commission on Radiological Protection (ICRP) published new recommendations in 2018 to shield staff from radiation. This study sets out to establish the extent to which these recommendations are observed in Germany. For the study, areas were selected which are known to have relatively high radiation exposure along with good conditions for radiological protection—interventional cardiology, radiology and vascular surgery. The study was advertised with the aid of an information flyer which was distributed via organisations including the German Cardiac Society (Deutsche Gesellschaft für Kardiologie- Herz- und Kreislaufforschung e. V.). Everyone who participated in our study received a questionnaire to record their occupational medical history, dosimetry, working practices, existing interventional installations and personal protective equipment. The results were compared with international recommendations, especially those of the ICRP, based on state-of-the-art equipment. A total of 104 respondents from eight German clinics took part in the survey. Four participants had been medically diagnosed with cataracts. None of the participants had previously worn an additional dosimeter over their apron to determine partial-body doses. The interventional installations recommended by the ICRP have not been fitted in all examination rooms and, where they have been put in place, they are not always used consistently. Just 31 participants (36.6%) stated that they “always” wore protective lead glasses or a visor. This study revealed considerable deficits in radiological protection—especially in connection with shielding measures and dosimetric practices pertaining to the head and neck—during a range of interventions. Examination rooms without the recommended interventional installations should be upgraded in the future. According to the principle of dose minimization, there is considerable potential for improving radiation protection. Temporary measurements should be taken over the apron to determine the organ-specific equivalent dose to the lens of the eye and the head.