The development of structures in the aerospace industry is associated mainly with the application of advanced methods and new technologies. Promising metals include alloys containing lithium (the lightest metal, its density is 543 kg/m 3 ). The use of these alloys in welded structures reduces the weight by 20–25% in comparison with structures produced using conventional aluminium alloys such as D16, V95, etc. This article shows that alloys of aluminium with lithium of all alloying systems have metallurgical and technological special features which must be taken into account when producing welded sections by fusion welding.

(2002). Technological aspects of production of containers for liquid hydrogen and liquefied natural gas. Welding International: Vol. 16, No. 10, pp. 817-823.

(2001). Technological aspects of assembly‐welding all‐welded passenger aircraft made of aluminium alloys. Welding International: Vol. 15, No. 1, pp. 56-59.

According to the calculations of scientists of a number of the world's leading industrial countries, natural resources of oil will last 25-35 years. It is therefore very important to find a new fuel for aircraft engines. The results of investigations show that in the near future liquefied natural gas (LNG) and, in particular, liquid hydrogen may be such promising fuels. The main advantage of liquid hydrogen in comparison with kerosene is its lower mass (by a factor of three), so that it may be possible to decrease the take-off weight or increase the commercial load. However, the volume which is four times higher and the extremely low temperature ( — 253 °C) require special efficiently insulated tanks. When using LNG, the temperature in the tank sections is slightly higher than -153°C. Liquid hydrogen was used for the first time as a fuel in the Saturn-5 rocket (USA) and then in a number of other rocket systems, including the Energiya rocket system (Russia). Fuel tanks of rockets operating with liquid hydrogen are produced using aluminium alloys of the Al-Cu-Mn system (2219 alloy in the USA and France, 1201 alloy in Russia). In contrast to single-purpose rocket fuel tanks, the fuel tanks of aircraft are used for a very long period of time (20-30 years), in flights of up to 60000-80000 hr in different climatic areas over the entire world. Therefore, the requirements of their design, the materials used and the technology of production are considerably different from those for rockets. In 1985-1992-the A N Tupolev Aerospace Bureau in Russia designed, constructed and introduced into experimental service the first aircraft in the world (TU-155) where liquid hydrogen was used as fuel. The all-welded cylindrical fuel tank produced from high-strength steel with spherical dished ends was placed in the fuselage and occupied almost the entire volume of the fuselage. Therefore, the weight was almost equal to the useful load of the aircraft. This aircraft was used for the first time in the world to test liquid hydrogen engines, a system of pipelines and regulating systems. However, because of a lack of finance, all operations and work were interrupted. At present, the A N Tupolev Aerospace Bureau is carrying out investigations into the application of LNG as a fuel for commercial aircraft (types TU-154 and TU-204). It is proposed to place the all-welded fuel tank of AMg6 aluminium alloy in the tail section of the fuselage of standard aircraft. There are three design-technological variants of the tank sections for liquid nitrogen and LNG: an all-metallic structure; a compound structure with the internal thinwall plating of metal and the external plating of nonmetals (the so-called liner); a structure consisting completely of non-metals. Each of these variants has its advantages and disadvantages. The cheapest and most promising structure as regards the materials and equipment is the all-metal structure. With any distribution of all-metal tanks (outside or inside the fuselage), the most important factors are the rational selection of the type of alloy for fabrication of the tanks and the assembling-welding technology. The results of preliminary investigations show that when using liquid hydrogen as fuel, the most optimum metallic materials are aluminium deformable alloys of the systems Al-Cu-Mn and Al-Cu-Li-Sc, and in the case of LNG, in addition to these materials, alloys of the Al-Mg-Sc-Zr system. The chemical composition of these alloys is presented in Table 1, the mechanical properties in Table 2. As indicated by Table 2, with a decrease of temperature from 20 to -253 °C the strength and ductility of the alloys increase. The tensile strength and proved stress of 1460 alloy increase by 20 and 15%, respectively. The relative elongation increases by more than 40%. The notch sensitivity of 1460 alloys at low temperatures, evaluated by the <r"B/cB ratio is relatively low because this ratio is close to unity.

(2000). Rational selection of semi‐finished products made from aluminium and magnesium alloys for welded structures. Welding International: Vol. 14, No. 11, pp. 907-912.

on the geometrical distribution of the holes: the distance between them is 0.7 mm, the distance between numbers of holes is 0.6 mm, and the distribution of rows along the length and width of the panels is kO.5 mm. Taking these requirements into account and the need to produce a very large number of holes on each panel, it was necessary to develop a standard perforation technology including the method of positioning and securing the panel, determination of the start of operation of the programs, movement ofthelaser along the co-ordinates x and y along the panel and stabilisation of the co-ordinate throughout the entire perforation time of each panel. For perforation of large panels it was necessary to develop and produce special equipment moving the laser radiation source along and across the working table. The equipment has the form of a gantry moving in the longitudinal direction above a stationary sheet to be perforated (panel). A track with an LTN-101 laser and an optical system fixed to it moves along the gantry (across the sheet). The movement of the gantry and the track is realised using a gear transmission consisting of racks and pinions. The play in the transmission is removed by pressing the teeth of the gears with springs to the teeth of the racks. The longitudinal drive includes two racks for preventing misalignment of the gantry during its movement. The position sensors are in the form of rotating transformers and the travel speed is stabilised using tachogenerators. Consequently, the accuracy of positioning is around 0.01 mm. When producing single holes of the given form, it is possible to use multipass and single-pulse treatment. In the first, each hole forms during several pulses. Multipass treatment requires usually arresting the movement of the laser in relation to the panel and greatly extends the perforation cycle. Taking into account the large volume of perforations, single-pulse perforation technology was used. In perforation of the holes in the single-pulse regime, each hole forms as a result of the effect of a short laser beam pulse during several microseconds. In this highspeed process, each hole must be produced without arresting the movement ofthe laser in relation to the panel during the treatment time, because the travel speed is considerably lower than the speed of formation of each hole. This method is more suitable for the perforations of largeareas ofplating panels with a small allowance for the

(1997). Welding the structure of the Buran orbital aircraft. Welding International: Vol. 11, No. 10, pp. 826-831.

Nonlinear effects in high-T c superconducting films limit the power range of operation for linear mw devices due to generation of intermodulation distortion (IMD) products and low power handling capability [1, 2]. In these points of view measurements of IMD products in the passband of the resonant structure are important for characterization of high-T c resonance components.

The tissue components of the subendocardial, inner and outer intramural layers of the myocardium were examined by morphometry. There was no significant difference in the proportion of cardiomyocytes in the different layers of the myocardium (subendocardium 0.820 +/- 0.007; inner layer 0.713 +/- 0.100; outer intramural layers 0.727 +/- 0.008; subepicardium 0.699 +/- 0.009). The relative surface of cardiomyocytes was maximal in the subepicardium (58.62 +/- 1,18). The magnitudes of the volumetric density and surface of the capillaries decreased from the subepicardial toward the subendocardial layer. The diameter of myocytes in the test layers of the myocardium varied within a wide range.