Once More About the Possibility of Determining the Local Electron Concentration by the Dispersion Method with the Help of AES and on New Ionization Maxima in the Ionosphere

Reliability of ionospheric density measurements by satellites using dispersion metho

Terahertz Spectroscopy System of Gas Mixtures Based on a Solid State Superconducting Source and a Terahertz Receiver

Abstract: The application of a Josephson generator of the terahertz range based on a long superconductor–insulator–superconductor tunnel junction matched with a transmitting antenna and emitting a signal into open space is demonstrated for gas spectroscopy. The generator is used as an active source, the signal of which is absorbed by a sample of a gas mixture in a cell with a length of 60 cm and then recorded by a spectrometer based on a superconductor–insulator–superconductor receiver with a spectral resolution better than 100 kHz. In the experiment, the absorption lines of ammonia and water in the terahertz range were recorded, and the dependence of the spectral characteristics of the absorption lines on the pressure of the gas mixture in a wide range (from 0.005 to 10 mbar) was demonstrated

An Antenna with a Feeder for a Superconducting Terahertz Josephson Oscillator with Phase Locking

A principal layout of a Josephson terahertz radiation oscillator integrated with a transmitting antenna-lens system and a harmonic mixer (HM) for phase locking of radiation has been proposed and was successfully implemented. Two antenna-feeder systems designed for the central frequencies of 0.3 and 0.6 THz and located on the same chip with the oscillator are numerically simulated and fabricated. A microstrip transmission line between the oscillator and the antenna is used as the feeder. A study was carried out on matching the oscillator power and HM for two designs; the frequency range of pumping HM was 0.25-0.45 and 0.5-0.68 THz for the designs at 0.3 and 0.6 THz, respectively. Good agreement was obtained between experimental results and numerical simulations. A study of the spectral characteristics of the radiation of the oscillator into the external space for the 0.6 THz design using a superconducting integrated spectrometer was carried out. The linewidth of an emission line in free-running regime was of the order of several megahertz; in the phase locking regime down to tens of kilohertz with a signal-to-noise ratio of more than 20 dB was obtained

Comparing the performance of 850 GHz integrated bias-tee superconductor-insulator-superconductor (SIS) mixers with single- and parallel-junction tuner

We present and compare the design and performance of two 850 GHz radial probe fed superconductor-insulator-superconductor mixers, where the antenna is aligned perpendicular to the E-Plane of the input full-height rectangular waveguide connected to a multiple flare-angles smooth-walled horn. Both designs are comprised of 0.5 µm2 hybrid niobium/aluminium-nitride/niobium-nitride tunnel junction, fabricated on top of a niobium titanium nitride ground plane with an Al wiring layer. The entire superconducting circuit is supported with a 40 µm thick quartz substrate. The major difference between the two designs is the method used to cancel out the parasitic junction capacitance for broadband performance. The first design utilises two identical junctions connected in parallel with a short transmission line to convert the capacitance of one junction into the equivalent inductance of the other junction, commonly known as the twin-junction tuning scheme; whilst the second design employs an end-loaded scheme with only one tunnel junction. We found that both methods offer similar radio frequency performances, with close to 2× the double sideband quantum noise temperature, but the twin-junction design is more resilient to fabrication tolerances. However, the end-loaded design offers a much better intermediate frequency (IF) bandwidth performance, made possible by the sub-micron and high current density tunnel junction technology. The improved IF performance is important for many millimetre (mm) and sub-mm observatories, such as future upgrades of Atacama Large Millimetre/sub-mm Array receivers, as well as forthcoming space-borne far-infrared missions. Therefore, we conclude that the single-junction mixer design is the preferred option for THz applications, as long as the fabrication error can be minimised within a certain limit

A superconducting flux-flow oscillator of terahertz range

We have elaborated, fabricated and tested a THz source radiating to open space based on the superconducting flux-flow oscillator (FFO). In this concept, the oscillator is integrated with the transmitting lens antenna based on a slot structure in Nb film with a thickness of ∼200 nm located on the same chip. The slot planar antenna is matched to the oscillator (by input) and to the semielliptical Si lens with a diameter of 10 mm (by output) providing a narrow output beam of THz emission. A harmonic mixer based on the superconductor-insulator-superconductor junction embedded in the "FFO and antenna" integrated structure has been used for the phase locking of the oscillator. Several designs of antenna coupled with the oscillator by microstrip lines have been numerically simulated, and the batches of experimental samples based on Nb-AlN-NbN superconducting trilayers with Rn •A ∼ 20 Ω•μm2 (jc ∼ 10 kA/cm2) have been fabricated and tested. Two different setups were used for experimental study: A THz spectrometer based on the SIS receiver with a high spectral resolution (better than 0.1 MHz) and a Si bolometer. The overall operating range of 250 to 700 GHz is covered by all the developed designs

Low-Noise Sis Receivers for New Radio-Astronomy Projects

We have developed, manufactured, and tested a waveguide mixer in the range 211-275 GHz on the basis of the superconductor-insulator-superconductor (SIS) tunnel structures. The methods of manufacturing high-quality tunnel structures on quartz substrates have been worked out. To extend the receiver band, the Nb/AlOx/Nb and Nb/AlN/NbN tunnel junctions with a high current density of up to 20 kA/cm2 are employed. The dependence of the characteristics of the receiving elements on the signal frequency is simulated for the intermediate-frequency band 4-12 GHz. The measurements demonstrate a good agreement of the input band of the receiving structures with the calculated results. The uncorrected noise temperature of the receiver amounts to 24 K at a frequency of 265 GHz, which is only two times higher than the quantum limit. The receivers under development are intended for a number of newly-built ground-based radio telescopes ("Suffa" and LLAMA), as well as for the "Millimetron" space program

Physical and mathematical modelling of the conditions of coal and gas outbursts

Purpose. Experimental study and theoretical modeling of conditions initiating destructive processes and development of gas generation in coals. Methods. Analysis, generalization and statistical processing of experimental data and results of analytical studies followed by the identification of patterns, and numerical solution of equations in partial derivatives. Findings. Experimental studies of changes in properties of mechanically activated samples of gas coal and fat coal in weak electric fields have been performed. The experimental results were compared with the characteristics of coals taken from the zones of different outburst hazard probability, which enabled to formulate new ideas about the causes of gas generation in coals. A mathematical model has been elaborated for gas outburst development taking into consideration the solid phase porosity changes due to the transition of coal organic mass to gas. Originality. The treated samples with the broken microstructure demonstrated a significant increase (1.5 – 3 times) in the characteristic time of methane desorption and manifestation of electret properties identified by the value of the evoked potential and electrochemical activity, while qualitative and quantitative changes in the treated coal properties were identical to the natural analogues. It is for the first time that the developed mathematical model of gas flow during the outburst reproduces the changes in porosity and permeability of the rock caused by chemical reactions of gas generation by coal organic mass. Practical implications. The improvement of the proposed outburst model can be used for predictive estimations of instantaneous outbursts taking into account the changes in thermodynamic and kinetic stability parameters of the “coal – gas” system.Цель. Экспериментальные исследования и теоретическое моделирование условий инициирования деструктивных и развития газогенерирующих процессов в каменных углях. Методика. Анализ, обобщение и статистическая обработка экспериментальных показателей и результатов аналитических исследований с последующим выделением закономерностей, численное решение уравнений в частных производных. Результаты. Выполнены экспериментальные исследования изменения свойств механоактивированных образцов угля марок Г и Ж в слабых электрических полях. Экспериментальные результаты сопоставлены с характеристиками углей, отобранных из зон с разной вероятностью выбросоопасности, на основе чего сформулированы новые представления о причинах газогенерации в углях. Разработана математическая модель развития выброса газа при изменении пористости твердой фазы вследствие перехода органической массы угля в газ. Научная новизна. Установлено, что для обработанных образцов с нарушенной микроструктурой наблюдается значительное увеличение (в 1.5 – 3 раза) характерного времени десорбции метана и проявление электретных свойств по величине вызванного потенциала и электрохимической активности, при этом, качественные и количественные изменения свойств в обработанных углях идентичны природным аналогам. Разработанная математическая модель течения газа во время выброса впервые отражает изменения пористости и проницаемости породы, обусловленные химическими реакциями генерации газа органической массой угля. Практическая значимость. Совершенствование предложенной модели выброса может быть использовано в прогнозных оценках внезапных выбросов с учетом изменения параметров термодинамической и кинетической устойчивости системы “уголь – газ”.Мета. Експериментальні дослідження та теоретичне моделювання умов ініціювання деструктивних і розвитку газогенеруючих процесів у кам’яному вугіллі. Методика. Аналіз, узагальнення та статистична обробка експериментальних показників і результатів аналітичних досліджень з подальшим виділенням закономірностей, чисельне рішення рівнянь у частинних похідних. Результати. Виконано експериментальні дослідження зміни властивостей механоактивованих зразків вугілля марок Г і Ж у слабких електричних полях. Експериментальні результати зіставлені з характеристиками вугілля, відібраних із зон з різною ймовірністю небезпеки викиду, на основі чого сформульовані нові уявлення про причини газогенерації у вугіллі. Розроблено математичну модель розвитку викиду газу при зміні пористості твердої фази внаслідок переходу органічної маси вугілля в газ. Наукова новизна. Встановлено, що для оброблених зразків з порушеною мікроструктурою спостерігається значне збільшення (у 1.5 – 3 рази) характерного часу десорбції метану і прояв електретних властивостей за величиною викликаного потенціалу та електрохімічної активності; при цьому якісні та кількісні зміни властивостей в обробленому вугіллі ідентичні природним аналогам. Розроблена математична модель течії газу під час викиду вперше відображає зміни пористості й проникності породи, які зумовлені хімічними реакціями генерації газу органічною масою вугілля. Практична значимість. Удосконалення запропонованої моделі викиду може бути використано у прогнозних оцінках раптових викидів з урахуванням зміни параметрів термодинамічної і кінетичної стійкості системи “вугілля – газ”.Данная работа выполнена при поддержке и финансировании Министерством образования и науки Украины проекта ГП-491 “Исследование наноструктуры ископаемых углей как источника метана угольных месторождений”. Авторы благодарят доктора технических наук Е.В. Ульянову за помощь в проведении физических исследований углей, обработанных слабыми электрическими полями

Ultrathin Tropical Tropopause Clouds (UTTCs) : I. Cloud morphology and occurrence

Subvisible cirrus clouds (SVCs) may contribute to dehydration close to the tropical tropopause. The higher and colder SVCs and the larger their ice crystals, the more likely they represent the last efficient point of contact of the gas phase with the ice phase and, hence, the last dehydrating step, before the air enters the stratosphere. The first simultaneous in situ and remote sensing measurements of SVCs were taken during the APE-THESEO campaign in the western Indian ocean in February/March 1999. The observed clouds, termed Ultrathin Tropical Tropopause Clouds (UTTCs), belong to the geometrically and optically thinnest large-scale clouds in the Earth´s atmosphere. Individual UTTCs may exist for many hours as an only 200--300 m thick cloud layer just a few hundred meters below the tropical cold point tropopause, covering up to 105 km2. With temperatures as low as 181 K these clouds are prime representatives for defining the water mixing ratio of air entering the lower stratosphere

Characterization of superconducting NbTiN films using a dispersive Fourier transform spectrometer

We have built a Terahertz Dispersive Fourier Transform Spectrometer \cite{Birch1987} to study frequency properties of superconducting films used for fabrication of THz detectors. The signal reflected from the tested film is measured in time domain, which allows to separate it from the other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in the superconducting state (temperature is below $T_c$) with the reflection of the normal state, we characterise the film quality at terahertz frequencies. The method was applied to 70 and 200nm thick Nb films on a silicon wafer and to 360nm thick NbTiN films on silicon and quartz wafers. The strong-coupling coefficient, $\alpha$, was found to be 3.52 for Nb, and 3.71-4.02 for the NbTiN films. The experimental results were fitted using extended Mattis-Bardeen theory \cite{Noguchi2012} and show a good agreement.Comment: The following article has been accepted by Applied Physics Letters. After it is published, it will be found at https://aip.scitation.org/journal/ap