141 research outputs found
Standing AlfvΓ©n waves with m ? 1 in an axisymmetric magnetosphere excited by a stochastic source
International audienceIn the framework of an axisymmetric magnetospheric model, we have constructed a theory for broad-band standing AlfvΓ©n waves with large azimuthal wave number m Β» 1 excited by a stochastic source. External currents in the ionosphere are taken as the oscillation source. The source with statistical properties of "white noise" is considered at length. It is shown that such a source drives oscillations which also have the "white noise" properties. The spectrum of such oscillations for each harmonic of standing AlfvΓ©n waves has two maxima: near the poloidal and toroidal eigenfrequencies of the magnetic shell of the observation. In the case of a small attenuation in the ionosphere the maximum near the toroidal frequency is dominated, and the oscillations are nearly toroidally polarized. With a large attenuation, a maximum is dominant near the poloidal frequency, and the oscillations are nearly poloidally polarized
Standing AlfvΓ©n waves with m ? 1 in an axisymmetric magnetosphere excited by a non-stationary source
International audienceAs a continuation of our earlier paper, we consider here the case of the excitation of standing AlfvΓ©n waves by a source of the type of sudden impulse. It is shown that, following excitation by such a source, a given magnetic shell will exhibit oscillations with a variable frequency which increases from the shell's poloidal to toroidal frequency. Simultaneously, the oscillations will also switch over from poloidally (radially) to toroidally (azimuthally) polarized. With a reasonably large attenuation, only the start of this process, the stage of poloidal oscillations, will be observed in the ionosphere
The structure of standing AlfvΓ©n waves in a dipole magnetosphere with moving plasma
The structure and spectrum of standing Alfv&#233;n waves were theoretically investigated in a dipole magnetosphere with moving plasma. Plasma motion was simulated with its azimuthal rotation. The model's scope allowed for describing a transition from the inner plasmasphere at rest to the outer magnetosphere with convecting plasma and, through the magnetopause, to the moving plasma of the solar wind. Solutions were found to equations describing longitudinal and transverse (those formed, respectively, along field lines and across magnetic shells) structures of standing Alfv&#233;n waves with high azimuthal wave numbers <i>m</i>>>1. Spectra were constructed for a number of first harmonics of poloidal and toroidal standing Alfv&#233;n waves inside the magnetosphere. For charged particles with velocities greatly exceeding the velocity of the background plasma, an effective parallel wave component of the electric field appears in the region occupied by such waves. This results in structured high-energy-particle flows and in the appearance of multiband aurorae. The transverse structure of the standing Alfv&#233;n waves' basic harmonic was shown to be analogous to the structure of a discrete auroral arc
The main peculiarities of the processes of the deformation and destruction of lunar soil
The main results of study of the physical and mechanical properties of lunar soil, obtained by laboratory study of samples returned from the moon by Luna 16 and Luna 20, as well as by operation of the self-propelled Lunokhod 1 and Lunokhod 2 on the surface of the moon, are analyzed in the report. All studies were carried out by single methods and by means of unified instruments, allowing a confident comparison of the results obtained. The investigations conducted allowed the following values of the main physical-mechanical properties of lunar soil to be determined: in the natural condition the solid density corresponds to the porosity of 0.8; the modal value of the carrying capacity is 0.4 kg/square cm; adhesion is 0.04 to 0.06 kg/square cm; and the internal angle of friction is 20 to 25 degree. The main mechanisms of deformation and destruction of the soil are analyzed in the report, and the relationships between the mechanical properties and physical parameters of the soil are presented
<i>Letter to the Editor</i> Why do ultra-low-frequency MHD oscillations with a discrete spectrum exist in the magnetosphere?
ΠΠ°Π½ΠΎΡΠΈΠ±ΡΠΎΠ±Π΅ΡΠΎΠ½: ΠΌΠ½ΠΎΠ³ΠΎΡΡΠΎΠ²Π½Π΅Π²ΠΎΠ΅ Π°ΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅
Concrete is the most commonly used building material worldwide. One of its main disadvantages is the fragility of fracture and low crack resistance. The use of dispersed reinforcement of concrete composites is a promising direction in solving this type of problem. Dispersed fibers, evenly distributed over the entire volume of the material, create a spatial frame and contribute to the inhibition of developing cracks under the action of destructive forces. In order to increase the fracture toughness of concrete, dispersed fiber reinforcement is increasingly used in practice. The beginning of crack nucleation occurs at the nanoscale in the cement matrix. Thus, the use of nano-reinforcement with dispersed nanofibers can have a positive effect on the crack resistance of the cement composite. It is proposed to consider carbon nanotubes as such nanofibers. The presence of carbon nanofibers changes the microstructure and nanostructure of cement modified with carbon nanotubes. The result of the processes occurring in capillaries and cracks are deformations in the intergranular matrix, the free flow of which is prevented by rigid clinker grains and nanocarbon tubes, which creates a certain stress intensity at the tips of the separation cracks. The working hypothesis is confirmed that the required fracture toughness of structural concrete is provided by multi-level reinforcement: at the level of the crystalline aggregate of cement stone β carbon nanotubes, and at the level of fine-grained concrete β various macro-sized fibers (steel, polymer). Reinforcement of a crystalline joint with carbon nanotubes leads to an increase in the fracture toughness of the matrix (cement stone) by 20 %, compressive strength by 12 %, and tensile strength in bending by 20 %. When reinforcing at the level of fine-grained concrete, we obtain a composite β nanofibre-reinforced concrete with fracture toughness.ΠΠ΅ΡΠΎΠ½ ΡΠ²Π»ΡΠ΅ΡΡΡ Π½Π°ΠΈΠ±ΠΎΠ»Π΅Π΅ ΡΠ°ΡΠΏΡΠΎΡΡΡΠ°Π½Π΅Π½Π½ΡΠΌ ΡΡΡΠΎΠΈΡΠ΅Π»ΡΠ½ΡΠΌ ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠΌ Π²ΠΎ Π²ΡΠ΅ΠΌ ΠΌΠΈΡΠ΅. ΠΡΠ½ΠΎΠ²Π½ΡΠΌΠΈ Π΅Π³ΠΎ Π½Π΅Π΄ΠΎΡΡΠ°ΡΠΊΠ°ΠΌΠΈ ΡΠ²Π»ΡΡΡΡΡ Ρ
ΡΡΠΏΠΊΠΎΡΡΡ ΠΏΡΠΈ ΡΠ°ΡΡΡΠΆΠ΅Π½ΠΈΠΈ ΠΈ Π½ΠΈΠ·ΠΊΠ°Ρ ΡΡΠ΅ΡΠΈΠ½ΠΎΡΡΠΎΠΉΠΊΠΎΡΡΡ. ΠΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ Π΄ΠΈΡΠΏΠ΅ΡΡΠ½ΠΎΠ³ΠΎ Π°ΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π±Π΅ΡΠΎΠ½Π½ΡΡ
ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠΎΠ² β ΠΏΠ΅ΡΡΠΏΠ΅ΠΊΡΠΈΠ²Π½ΠΎΠ΅ Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½ΠΈΠ΅ Π² ΡΠ΅ΡΠ΅Π½ΠΈΠΈ ΡΠ°ΠΊΠΎΠ³ΠΎ ΡΠΎΠ΄Π° Π·Π°Π΄Π°Ρ. ΠΠΈΡΠΏΠ΅ΡΡΠ½ΡΠ΅ Π²ΠΎΠ»ΠΎΠΊΠ½Π°, ΡΠ°Π²Π½ΠΎΠΌΠ΅ΡΠ½ΠΎ ΡΠ°ΡΠΏΡΠ΅Π΄Π΅Π»Π΅Π½Π½ΡΠ΅ ΠΏΠΎ Π²ΡΠ΅ΠΌΡ ΠΎΠ±ΡΠ΅ΠΌΡ ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»Π°, ΡΠΎΠ·Π΄Π°ΡΡ ΠΏΡΠΎΡΡΡΠ°Π½ΡΡΠ²Π΅Π½Π½ΡΠΉ ΠΊΠ°ΡΠΊΠ°Ρ ΠΈ ΡΠΏΠΎΡΠΎΠ±ΡΡΠ²ΡΡΡ ΡΠΎΡΠΌΠΎΠΆΠ΅Π½ΠΈΡ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΡΠ΅ΡΠΈΠ½ ΠΏΠΎΠ΄ Π΄Π΅ΠΉΡΡΠ²ΠΈΠ΅ΠΌ ΡΠ°Π·ΡΡΡΠ°ΡΡΠΈΡ
ΡΠΈΠ». ΠΠ»Ρ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΡ ΡΡΠ΅ΡΠΈΠ½ΠΎΡΡΠΎΠΉΠΊΠΎΡΡΠΈ Π±Π΅ΡΠΎΠ½Π° Π½Π° ΠΏΡΠ°ΠΊΡΠΈΠΊΠ΅ Π²ΡΠ΅ ΡΠ°ΡΠ΅ ΠΏΡΠΈΠΌΠ΅Π½ΡΡΡ Π°ΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ Π΄ΠΈΡΠΏΠ΅ΡΡΠ½ΡΠΌΠΈ Π²ΠΎΠ»ΠΎΠΊΠ½Π°ΠΌΠΈ. ΠΠ°ΡΠ°Π»ΠΎ Π·Π°ΡΠΎΠΆΠ΄Π΅Π½ΠΈΡ ΡΡΠ΅ΡΠΈΠ½Ρ ΠΏΡΠΎΠΈΡΡ
ΠΎΠ΄ΠΈΡ Π½Π° Π½Π°Π½ΠΎΡΡΠΎΠ²Π½Π΅ Π² ΡΠ΅ΠΌΠ΅Π½ΡΠ½ΠΎΠΉ ΠΌΠ°ΡΡΠΈΡΠ΅. Π’Π°ΠΊΠΈΠΌ ΠΎΠ±ΡΠ°Π·ΠΎΠΌ, ΠΏΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ Π½Π°Π½ΠΎΠ°ΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π΄ΠΈΡΠΏΠ΅ΡΡΠ½ΡΠΌΠΈ Π½Π°Π½ΠΎΠ²ΠΎΠ»ΠΎΠΊΠ½Π°ΠΌΠΈ ΠΌΠΎΠΆΠ΅Ρ ΠΏΠΎΠ»ΠΎΠΆΠΈΡΠ΅Π»ΡΠ½ΠΎ ΡΠΊΠ°Π·Π°ΡΡΡΡ Π½Π° ΡΡΠ΅ΡΠΈΠ½ΠΎΡΡΠΎΠΉΠΊΠΎΡΡΠΈ ΡΠ΅ΠΌΠ΅Π½ΡΠ½ΠΎΠ³ΠΎ ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠ°. Π ΠΊΠ°ΡΠ΅ΡΡΠ²Π΅ ΡΠ°ΠΊΠΈΡ
Π½Π°Π½ΠΎΠ²ΠΎΠ»ΠΎΠΊΠΎΠ½ ΠΏΡΠ΅Π΄Π»Π°Π³Π°Π΅ΡΡΡ ΡΠ°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°ΡΡ ΡΠ³Π»Π΅ΡΠΎΠ΄Π½ΡΠ΅ Π½Π°Π½ΠΎΡΡΡΠ±ΠΊΠΈ. ΠΡΠΈΡΡΡΡΡΠ²ΠΈΠ΅ ΡΠ³Π»Π΅ΡΠΎΠ΄Π½ΡΡ
Π½Π°Π½ΠΎΠ²ΠΎΠ»ΠΎΠΊΠΎΠ½ ΠΈΠ·ΠΌΠ΅Π½ΡΠ΅Ρ ΠΌΠΈΠΊΡΠΎΡΡΡΡΠΊΡΡΡΡ ΠΈ Π½Π°Π½ΠΎΡΡΡΡΠΊΡΡΡΡ ΡΠ΅ΠΌΠ΅Π½ΡΠ°, ΠΌΠΎΠ΄ΠΈΡΠΈΡΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠ³ΠΎ ΡΠ³Π»Π΅ΡΠΎΠ΄Π½ΡΠΌΠΈ Π½Π°Π½ΠΎΡΡΡΠ±ΠΊΠ°ΠΌΠΈ. Π Π΅Π·ΡΠ»ΡΡΠ°ΡΠΎΠΌ ΠΏΡΠΎΡΠ΅ΡΡΠΎΠ², ΠΏΡΠΎΠΈΡΡ
ΠΎΠ΄ΡΡΠΈΡ
Π² ΠΊΠ°ΠΏΠΈΠ»Π»ΡΡΠ°Ρ
ΠΈ ΡΡΠ΅ΡΠΈΠ½Π°Ρ
, ΡΠ²Π»ΡΡΡΡΡΒ Π΄Π΅ΡΠΎΡΠΌΠ°ΡΠΈΠΈ Π² ΠΌΠ΅ΠΆΠ·Π΅ΡΠ½ΠΎΠ²ΠΎΠΉ ΠΌΠ°ΡΡΠΈΡΠ΅, ΡΠ²ΠΎΠ±ΠΎΠ΄Π½ΠΎΠΌΡ ΡΠ΅ΡΠ΅Π½ΠΈΡ ΠΊΠΎΡΠΎΡΡΡ
ΠΏΡΠ΅ΠΏΡΡΡΡΠ²ΡΡΡ ΠΆΠ΅ΡΡΠΊΠΈΠ΅ Π·Π΅ΡΠ½Π° ΠΊΠ»ΠΈΠ½ΠΊΠ΅ΡΠ° ΠΈ Π½Π°Π½ΠΎΡΠ³Π»Π΅ΡΠΎΠ΄Π½ΡΠ΅ ΡΡΡΠ±ΠΊΠΈ, ΡΡΠΎ ΡΠΎΠ·Π΄Π°Π΅Ρ Π² Π²Π΅ΡΡΠΈΠ½Π°Ρ
ΡΠ°Π·Π΄Π΅Π»ΠΈΡΠ΅Π»ΡΠ½ΡΡ
ΡΡΠ΅ΡΠΈΠ½ Π½Π΅ΠΊΠΎΡΠΎΡΡΡ ΠΈΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΡ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ. ΠΠΎΠ΄ΡΠ²Π΅ΡΠΆΠ΄Π΅Π½Π° ΡΠ°Π±ΠΎΡΠ°Ρ Π³ΠΈΠΏΠΎΡΠ΅Π·Π°, ΡΡΠΎ ΡΡΠ΅Π±ΡΠ΅ΠΌΠ°Ρ ΡΡΠ΅ΡΠΈΠ½ΠΎΡΡΠΎΠΉΠΊΠΎΡΡΡ ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ Π±Π΅ΡΠΎΠ½Π° ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°Π΅ΡΡΡ ΠΌΠ½ΠΎΠ³ΠΎΡΡΠΎΠ²Π½Π΅Π²ΡΠΌ Π°ΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ: Π½Π° ΡΡΠΎΠ²Π½Π΅ ΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π·Π°ΠΏΠΎΠ»Π½ΠΈΡΠ΅Π»Ρ ΡΠ΅ΠΌΠ΅Π½ΡΠ½ΠΎΠ³ΠΎ ΠΊΠ°ΠΌΠ½Ρ β ΡΠ³Π»Π΅ΡΠΎΠ΄Π½ΡΠΌΠΈ Π½Π°Π½ΠΎΡΡΡΠ±ΠΊΠ°ΠΌΠΈ, Π½Π° ΡΡΠΎΠ²Π½Π΅ ΠΌΠ΅Π»ΠΊΠΎΠ·Π΅ΡΠ½ΠΈΡΡΠΎΠ³ΠΎ Π±Π΅ΡΠΎΠ½Π° β ΡΠ°Π·Π»ΠΈΡΠ½ΡΠΌΠΈ Π²ΠΈΠ΄Π°ΠΌΠΈ ΠΌΠ°ΠΊΡΠΎΡΠ°Π·ΠΌΠ΅ΡΠ½ΠΎΠΉ ΡΠΈΠ±ΡΡ (ΡΡΠ°Π»ΡΠ½ΡΠ΅, ΠΏΠΎΠ»ΠΈΠΌΠ΅ΡΠ½ΡΠ΅). ΠΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΡΠ³Π»Π΅ΡΠΎΠ΄Π½ΡΠΌΠΈ Π½Π°Π½ΠΎΡΡΡΠ±ΠΊΠ°ΠΌΠΈ ΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΡΠΎΡΡΠΊΠ° ΠΏΡΠΈΠ²ΠΎΠ΄ΠΈΡ ΠΊ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΡ ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»Ρ Π²ΡΠ·ΠΊΠΎΡΡΠΈ ΡΠ°Π·ΡΡΡΠ΅Π½ΠΈΡ ΠΌΠ°ΡΡΠΈΡΡ (ΡΠ΅ΠΌΠ΅Π½ΡΠ½ΠΎΠ³ΠΎ ΠΊΠ°ΠΌΠ½Ρ) Π½Π° 20 %, ΠΏΡΠΎΡΠ½ΠΎΡΡΠΈ Π½Π° ΡΠΆΠ°ΡΠΈΠ΅ Π½Π° 12 %, ΠΏΡΠΎΡΠ½ΠΎΡΡΠΈ Π½Π° ΡΠ°ΡΡΡΠΆΠ΅Π½ΠΈΠ΅ ΠΏΡΠΈ ΠΈΠ·Π³ΠΈΠ±Π΅ Π½Π° 20 %. ΠΡΠΈ Π°ΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ Π½Π° ΡΡΠΎΠ²Π½Π΅ ΠΌΠ΅Π»ΠΊΠΎΠ·Π΅ΡΠ½ΠΈΡΡΠΎΠ³ΠΎ Π±Π΅ΡΠΎΠ½Π° ΠΏΠΎΠ»ΡΡΠ°Π΅ΠΌ ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡ β Π½Π°Π½ΠΎΡΠΈΠ±ΡΠΎΠ±Π΅ΡΠΎΠ½ Ρ Π²ΡΠ·ΠΊΠΎΡΡΡΡ ΡΠ°Π·ΡΡΡΠ΅Π½ΠΈΡ
Comparative Study of Fiber Glass Reinforced Polymer and Carbon Fiber Reinforced Polymer on Cube and Cylinder
A comparative analysis of polymers reinforced with glass fiber and polymers reinforced with carbon fiber was carried out on a cube and a cylinder in the laboratories of Baghdad. 36 samples were taken with fiber percentages of 1.0, 2.5 and 5.0 % by weight of cement. The methodology of this study included the use of composite polymer fibers in the external reinforcement of concrete beams for the purpose of improving their performance when bending by gluing polymer fibers to the surface. Group A tests of non-reinforced concrete beams with other reinforced polymer fibers were also implemented. Excellent results were obtained by adding two types of polymer fibers to a concrete sample. It was found that the polymer reinforced with glass fiber showed better results than the polymer reinforced with carbon fiber when testing samples for bending strength. However, in splitting strength, the carbon fiber reinforced polymer achieved higher performance than the glass fiber reinforced polymer. Whereas the results of a group of previous studies conducted to study the effect of fiber additives on the mechanical properties of concrete proved that their addition led to an increase in compression, tensile and bending resistance at rates that reached 25, 75 and 80 %, respectively
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