We propose a variant of a slitted cavity for gyrotrons based on spatial synchronization of TE-type modes with azimuthal indexes equal to multiples of the slit number and close eigenfrequencies. A ...simplified theory of such a cavity is presented demonstrating its basic properties. High selectivity of the novel cavity was confirmed by 3-D PIC simulation of a 0.3-THz gyrotron energized by a helical electron beam with an energy of 500 keV and a current of 2 kA. This simulation demonstrates that, using the slit-type cavity, stable single-frequency operation at TE 6,4 -TE 12,2 mode combined with an output power of more than 80 MW and an efficiency of about 8%. The same arrangement with a conventional solid-wall cavity demonstrates no single-frequency regimes at all.
Reaction of 5,5-dimethyl-3-(2-chloroethyl)- and 5,5-diphenyl-3-(2-bromoethyl)- hydantoins with potassium 4-aminobenzoate in dimethylformamide in the presence of triethylbenzylammonium chloride leads ...to the formation of 2-5,5-dimethyl(diphenyl)-2,4-dioxo-1,3-diazolidin-2-ylethyl-4-aminobenzoates. The latter were used for synthesis of new types of maleimides, namely 2-5,5-dimethyl(diphenyl)-2,4-dioxo-1,3-diazolidin-2-ylethyl-4-(2,5-dioxo-1-azolin-1-yl) benzoates. Reactions of 5,5-dimethyl-1,3-di(2-chloroethyl) hydantoin with potassium 4-aminobenzoate or sodium 4-
N
-acetylaminophenolate at a molar ratio of 1:2 also lead to 3-monosubstituted products.
The main principles of using wires with tungsten nanopowder for arc cladding are considered. Special features of production and application of tungsten-modified wires are analyzed. The microstructure ...of the high-strength layer obtained by cladding wires with different tungsten nanopowder contents is investigated. Microhardness of clad specimens is determined.
Layered lanthanide nickelates of the first order with a K2NiF4-type structure, including Nd2NiO4, are considered as prospective oxygen electrode materials for different high-temperature ...electrochemical devices, membrane materials and catalysts. The presence of highly-mobile over-stoichiometric oxygen in their structure, the content of which depends on the synthesis and ambient conditions, strongly influences their functional properties. In this study, the materials of the Nd2-xCaxNiO4+δ (x = 0–1.0) series were obtained via a citrate-nitrate method. The Ca substitution limit was found to be equal to 30 mol %. The high-temperature structural, thermo-mechanical and electrical properties of the materials obtained were investigated in close relation with their oxygen over-stoichiometry. It was found that the absolute oxygen content decreased with Ca doping, which resulted in a transition from an orthorhombic structure (Fmmm sp. gr.) at x = 0, 0.1 to a tetragonal structure (I4/mmm sp. gr.) at x = 0.2, 0.3 and then, with further increase in Ca doping, to an orthorhombic structure (Bmab sp. gr.). Dilatometric curves for all the samples possessed high-temperature breaks corresponding to the structural changes caused by oxygen release upon heating, which was revealed in the HT-XRD and TGA-DSC experiments. There was a tendency for the thermal expansion coefficient to decrease both in the low and high temperature range with Ca doping. The minimum average TEC values were found for the samples with x = 0.4 (12.1 × 10−6 K−1) and with x = 0.6 (11.8 × 10−6 K−1) according to the HT-XRD and dilatometry data, respectively. There was a maximum at x = 0.4 (135 S cm−1) on the concentration dependence of the total conductivity obtained in the dc four-probe measurements. Materials with a medium Ca content (0.3–0.4), possessing moderate CTE values (∼12 × 10−6 K−1), close to those of the majority of solid-state electrolytes, and showing a high level of total conductivity, can be recommended as promising materials for various electrochemical applications.
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•Nd2-xCaxNiO4 (x = 0–1) were obtained by a citrate-nitrate combustion method.•Solubility limit was found to be equal to 30 mol % of Ca.•High-temperature structural, thermo-mechanical and electrical properties were studied.•Materials with medium Ca content are promising for electrochemical applications.
An analysis of the dependence of the
F
2-layer critical frequency on solar activity indices that has been started earlier based on the Juliusruh station data is continued. The data of six stations in ...the Northern Hemisphere and five stations in the Southern Hemisphere are analyzed in this paper. The determination coefficient
R
2
for the
foF
2 dependence on solar activity in each particular situation (station, month, local time) is taken as a measure of the quality of that dependence. The conclusion that a well-pronounced diurnal variation in
R
2
is observed in the winter months is confirmed for four solar activity proxies: this value is maximum and changes weakly in the daytime but decreases substantially to the nighttime hours. It is found that the
F
30 proxy is the best solar proxy to describe the
foF
2 behavior in the solar cycle, whereas the sunspot number
Rz
is the worst. Based on a comparison of the changes in
R
2
with LT in the same months at stations of the Northern and Southern hemispheres, it is shown that the aforementioned well-pronounced diurnal behavior in
R
2
is observed only in winter and is absent in summer.
Trends in the
F
2-layer critical frequency
foF
2 are calculated based on the vertical sounding data at Juliusruh station over a period of 1996–2022. Four solar activity indices:
Ly-
α,
MgII
,
F
...10.7mon, and
Rz
were used. The conclusion drawn previously is confirmed: seasonal (stronger in winter than in summer) and diurnal (stronger in the daytime than at night) variations exist in the
foF
2 negative trends. It is shown that the results for the first three indices agree very well, whereas the results using
Rz
provide slightly different results. It has been found that during the recent 5–7 years, the maximum (winter, daytime) negative trends in
foF
2 became stronger than for the entire considered interval by a factor of 2–3.
A description of the ionospheric
F
2-layer critical frequency
foF
2 dependence on solar activity by various indices (proxies) has been analyzed. The results of the vertical ionospheric sounding at ...the Juliusruh station during 2 winter months (January and February), 2 equinox months (March and October), and a summer month (June) are considered. Five solar proxies:
Ly-
α,
MgII
,
Rz
,
F
30, and
F
10.7 have been analyzed. The changes in
foF
2 are compared to the corresponding changes in 1957–1980. The determination coefficient
R
2
according to the Fisher F-test is used as a measure of the quality of the description of the
foF
2 dependence on SA by each of the proxies. It has been found that a well-pronounced diurnal variation in the
R
2
value is observed in winter months: this is higher at the near-noon hours than at night. In other words, all indices describe the
foF
2 behavior better in the daytime than at night. A well-pronounced diurnal variation in
R
2
is also observed for four proxies in the equinoctial months, whereas that variation is pronounced much less for
Rz
: a strong scatter of the
R
2
values is seen. A diurnal variation in the
R
2
is absent completely in June: jumps from one hour to another are observed. This analysis allows us to conclude that the most reliable SA proxies for description of the
foF
2 dependence on SA at all LT hours are
MgII
,
F
30, and
Ly-
α.
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