We have solved the long-standing problem of the mechanism of terahertz (THz) generation by a two-color filament in air and found that both neutrals and plasma contribute to the radiation. We reveal ...that the contribution from neutrals by four-wave mixing is much weaker and higher in frequency than the distinctive plasma lower-frequency contribution. The former is in the forward direction while the latter is in a cone and reveals an abrupt down-shift to the plasma frequency. Ring-shaped spatial distributions of the THz radiation are shown to be of universal nature and they occur in both collimated and focusing propagation geometries. Experimental measurements of the frequency-angular spectrum generated by 130-fs laser pulses agree with numerical simulations based on a unidirectional pulse propagation model.
The article analyzes the foreign policy of Abe Shinzō, one of the most notable and unusual political figures of contemporary Japan, who was twice the head of Japanese government for a total of almost ...nine years. It traces how his political philosophy formed under the influence of ideological views of his relatives, prime ministers N. Kishi and E. Sato, as well as his father, Abe Shintarō. It also considers Abe’s approaches to building Japan’s relations with the countries which are most important for its interests. Abe was perceived as a devoted ally of the U.S. in Washington. He established relations of confidence with presidents Obama and Trump. For this purpose, he strengthened Japanese-American military-political cooperation, took steps to support American strategy in the Asia-Pacific region. He implemented, even if without substantial results, steps to stabilize relations with China, trying to combine policy of containing Beijing with efforts to develop bilateral ties. Abe paid substantial attention to relations with India, including for the purpose of the idea, which was put forward by him and supported by the U.S., to establish quadrilateral cooperation of “democracies” in the Indo-Pacific region – the U.S., Japan, India, and Australia. His policy on the Korean direction was not successful. The relations with Pyongyang remained in deadlock, and, with Seoul, the most acute bilateral problems were not finally solved. Abe also paid great attention to policy aiming to conclude a peace treaty with Russia on the basis of a radical improvement of Japanese-Russian ties in all spheres. The reasons for his failure in these directions are discussed in this article. The article evaluates Abe’s efforts aimed at developing governmental documents and making the Diet adopt laws determining the basic directions of the foreign and military policy of the state. The author characterizes the results of the activity of S. Abe in the sphere of foreign policy and assesses its influence on the formation of the course of the Japanese government after his resignation.
Thin Current Sheet Behind the Dipolarization Front Nakamura, R.; Baumjohann, W.; Nakamura, T. K. M. ...
Journal of geophysical research. Space physics,
October 2021, Letnik:
126, Številka:
10
Journal Article
Recenzirano
Odprti dostop
We report a unique conjugate observation of fast flows and associated current sheet disturbances in the near‐Earth magnetotail by MMS (Magnetospheric Multiscale) and Cluster preceding a positive bay ...onset of a small substorm at ∼14:10 UT, September 8, 2018. MMS and Cluster were located both at X ∼ −14 RE. A dipolarization front (DF) of a localized fast flow was detected by Cluster and MMS, separated in the dawn‐dusk direction by ∼4 RE, almost simultaneously. Adiabatic electron acceleration signatures revealed from the comparison of the energy spectra confirm that both spacecraft encounter the same DF. We analyzed the change in the current sheet structure based on multi‐scale multi‐point data analysis. The current sheet thickened during the passage of DF, yet, temporally thinned subsequently associated with another flow enhancement centered more on the dawnward side of the initial flow. MMS and Cluster observed intense perpendicular and parallel current in the off‐equatorial region mainly during this interval of the current sheet thinning. Maximum field‐aligned currents both at MMS and Cluster are directed tailward. Detailed analysis of MMS data showed that the intense field‐aligned currents consisted of multiple small‐scale intense current layers accompanied by enhanced Hall‐currents in the dawn‐dusk flow‐shear region. We suggest that the current sheet thinning is related to the flow bouncing process and/or to the expansion/activation of reconnection. Based on these mesoscale and small‐scale multipoint observations, 3D evolution of the flow and current‐sheet disturbances was inferred preceding the development of a substorm current wedge.
Key Points
Evolution of localized fast flows and dipolarization front is obtained from multi‐scale multi‐point observations in near‐Earth magnetotail
Current sheet thinning accompanied by intense field‐aligned currents is detected following the passage of the dipolarization front
From signatures of adiabatic electron acceleration it is confirmed that the same flow front was detected by the multi‐point measurements
The reasons for the creation of the Japanese–American Military–Political Alliance and the factors that were conductive for its existence after the conclusion in 1951 of the first Treaty on Security ...Guarantees between Japan and the Unites States are analyzed. The present successor of this treaty, the Treaty on Mutual Cooperation and Security between Japan and the Unites States, which was concluded in 1960, constitutes the foundation of alliance relations between Tokyo and Washington. The content of these treaties, the obligations of the participants according the articles of the treaties, and the evolution of the interpretations of these mutual obligations in accordance with changes in the international situation and in relations in the Asia-Pacific region are considered. Finally, the growing possibilities for Japan to play a more independent role in this bilateral alliance and the reasons why Tokyo has not taken steps to explore them are evaluated.
Supercharacter theories are constructed for the finite groups obtained by parabolic contraction from simple groups of A,B,C,D Lie types. Supercharacters and superclasses are classified in terms of ...rook placements in root systems.
•β-solidifying TiAl-based alloy subjected to N ion implantation with low (40 keV) energy.•TiN, Ti2N, Ti3AlN, and Ti3Al2N2 particles nitrides formed in the modified layer.•Annealing at 550 or 750 °C ...resulted in dissolution of the Ti2N phase.•N ion implantation significantly enhanced oxidation resistance of the alloy.•Thin, continuous, and stable oxide layer is formed during oxidation tests.
Oxidation behavior and thermal stability of a β-solidifying γ-TiAl alloy after plasma source nitrogen ion implantation were studied. Nano-sized TiN, Ti2N, Ti3AlN, and Ti3Al2N2 particles were found in the modified layer. The microhardness of the modified layer was 2.5 times higher than that of the as-cast condition. Nitrogen ion implantation increased the oxidation resistance significantly in comparison to the as-cast condition. Thin inner and outer TiO2, dense protective Al2O3 and fine-grained mixed Al2O3+TiO2 layers were found on the surface after oxidation. The effect of nitrogen ion implantation on phase stability and oxidation mechanisms is analyzed.
The paper reveals the possibility for obtaining excellent strength-ductility combination under both tension and compression in a fully lamellar β-solidified γ-TiAl based alloy by controlling the ...interlamellar spacing. Ingots of the alloy were subjected to multi-axial forging, quenching and further aging at 800–1050 °C to produce microstructures with the colony size of 25 μm and interlamellar spacing (λ) in the range from 10 to 1500 nm. A good balance between ductility and strength was found at λ ∼100 nm under both tension (elongation to fracture of 2.9%; ultimate strength - 875 MPa) and compression (peak strain and stress of 39% and 2700 MPa, respectively) due to a strain transfer by transverse twin/slip bands that improved strain hardening capacity. Both coarser and thinner lamellae caused pronounced strain localization and early crack nucleation resulting in failure. Meanwhile, the Hall-Petch relationship was observed between the yield strength and interlamellar spacing above λ ∼20–50 nm. At a lower interlamellar spacing the yield strength stabilized at the values of 820 and 1150 MPa upon tensile and compression loading, respectively. The dependences of deformation and fracture mechanisms on the interlamellar spacing and loading scheme are discussed.
•Interlamellar spacing (λ) of Ti-43.2Al-1.9V-1.1Nb-1.0Zr-0.2Gd-0.2B alloy varies from 10 to 1500 nm.•Tensile-compression asymmetry is derived.•Maximum of ductility and ultimate strength is observed at λ∼100 nm under both tension and compression.•Yield strength and interlamellar spacing obey to the Hall-Petch relationship above the critical interlamellar spacing.•Yield strength stabilized below the critical interlamellar spacing.
We construct a supercharacter theory for the finite groups of triangular type. Its special case is the supercharacter theory for algebra groups of Diaconis and Isaacs. The supercharacter analog of ...the Kirillov formula for irreducible characters of unipotent groups is proved.
A supercharacter theory is constructed for the parabolic subgroups of the group GL(
n
, F
q
) with blocks of orders less or equal to two. The author formulated the hypotheses on construction of a ...supercharacter theory for an arbitrary parabolic subgroup in GL(
n
, F
q
).
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