Synthesis of poly-L-ornithine

Summary The syntheses of poly-L-ornithine hydrobromides and poly-N⁵-(benzyloxycarbonyl)-L-ornithines of various molecular weights are described.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2153–2156, December, 1966.We are very grateful to S. A. Pavlova for help rendered in the determination of the molecular weights of thepolymers by the light-scattering method.     

Magnetic properties of Fe2P-type R6CoTe2 compounds (R=Gd-Er)

The magnetic structure of the Fe₂P-type R₆CoTe₂ phases (R=Gd-Er, space group P6¯2m) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: T_C=220 K and T_CN=180 K for Gd₆CoTe₂, T_C=174 K and T_CN=52 K for Tb₆CoTe₂, T_C=125 K and T_CN=26 K for Dy₆CoTe₂, T_CN=60 K and T_N=22 K for Ho₆CoTe₂ and T_CN∼30 K and T_N∼14 K for Er₆CoTe₂.Between 174 and 52 K Tb₆CoTe₂ has a collinear magnetic structure with K₀=[0, 0, 0] and with magnetic moments along the c-axis, whereas below 52 K it adopts a non-collinear ferromagnetic one.Below 60 K the magnetic structure of Ho₆CoTe₂ is that of a non-collinear ferromagnet. The holmium magnetic components with a K₀=[0, 0, 0] wave vector are aligned ferromagneticaly along the c-axis, whereas the magnetic component with a K₁=[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22 K coincides with the reorientation of the Ho magnetic component with the K₀ vector from the collinear to the non-collinear state.Below 30 K Er₆CoTe₂ shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K₀=[0, 0, 0] and K₁=[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14 K corresponds to the variation in the magnitudes of the M_Er^K0 and M_Er^K1 magnetic components.In these phases, no local moment was detected on the cobalt site.The magnetic entropy of Gd₆CoTe₂ increases from ΔS_mag=−4.5 J/kg K at 220 K up to ΔS_mag=−6.5 J/kg K at 180 K for the field change Δμ₀H=0-5 T.     

Development of a High-Power Continuous-Wave Gyrotron for High-Efficiency Technological K-Band Microwave Complexes

Radiophysics and Quantum Electronics - We analyze the possibility to create new generation continuous-wave gyrotrons operating in the Kband (at frequencies of 28-30 GHz) at the fundamental...     

Understanding the magnetic ground state of rare-earth intermetallic compound Ce4Sb3: Magnetization and neutron diffraction studies

Magnetization and neutron diffraction studies have been performed on Ce₄Sb₃ compound (cubic Th₃P₄-type, space group I4¯3d, no. 220). Magnetization of Ce₄Sb₃ reveals a ferromagnetic transition at ∼5 K, the temperature below which the zero-field-cooled and field-cooled magnetization bifurcate in low applied fields. However, a saturation magnetization (M_S) value of only ∼0.93μ_B/Ce³⁺ is observed at 1.8 K, suggesting possible presence of crystal field effects and a paramagnetic/antiferromagnetic Ce³⁺ moment. Magnetocaloric effect in this compound has been computed using the magnetization vs. field data obtained in the vicinity of the magnetic transition, and a maximum magnetic entropy change, −ΔS_M, of ∼8.9 J/kg/K is obtained at 5 K for a field change of 5 T. Inverse magnetocaloric effect occurs at ∼2 K in 5 T indicating the presence of antiferromagnetic component. This has been further confirmed by the neutron diffraction study that evidences commensurate antiferromagnetic ordering at 2 K in zero magnetic field. A magnetic moment of ∼1.24μ_B/Ce³⁺ is obtained at 2 K and the magnetic moments are directed along Z-axis.     

The magnetic structure of the compound Ho5Sb3

We have investigated the magnetic behavior of Ho₅Sb₃ compound (Mn₅Si₃-type, hexagonal; a=0.8865(1) nm, c=0.6232(1) nm, as derived from X-ray Guinier powder pattern) by using the techniques of magnetization, electrical resistivity, heat capacity and neutron diffraction. We find that Ho₅Sb₃ exhibits a ferrimagnetic type (Ferrimagnet I) ordering below 60 K with propagation vectors K₀=[0, 0, 1] and K₁=[±K_x, 0, 0]. Below 40 K, the thermal variation of magnetic reflections and the appearance of an additional magnetic component with propagation vector K₂=[0, 1/2, 0] show the onset of an antiferromagnetic type of ordering in the magnetic structure; which evolves into yet another ferrimagnetic structure (Ferrimagnet II) as the temperature is lowered down to 2 K. The magnetic moments of the Ho atoms at the (4d) and (6g) sites with magnitudes of nearly 7.4 and 6.3 μ_B at 2 K, respectively, are inclined approximately at 70° to the c-axis.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Separation of energy fractions of an electron beam by a localized nonuniformity of magnetic field in the collector region of gyrodevices

To separate the energy fractions of an electron beam, we propose that a ferromagnetic ring coaxial to the solenoid is inserted in the collector region, which can increase the efficiency of energy recovery in the case of electron deposition onto the multistage collector. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 10, pp. 900–905, October 2006.