Passive mode locking of fiber lasers upon doubling the period of repetition of ultrashort pulses in the output radiation

The dynamics of the output radiation of fiber lasers with nonlinear losses caused by an intracavity polarizer and by nonlinear optical activity due to the Kerr nonlinearity of the fiber is studied by numerical simulation. It is shown that the model of lasing that takes into account the concentration of nonlinear losses in the intracavity polarizer describes the characteristic transient regimes of the passive mode locking, connected with a nonstationarity of the parameters of the output radiation: doubling of the period of repetition of the field structure in the output radiation, appearance of slow periodic changes of the parameters of light pulses in the regimes with the doubled period, and transitions to the regimes with chaotic change of the characteristics of ultrashort pulses.     

Synthesis of chiral nopinane annelated 3-methyl-1-aryl-1H-pyrazolo[3,4-b]pyridines by condensation of pinocarvone oxime with 1-aryl-1H-pyrazol-5-amines

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Distribution function for relativistic charges in the vicinity of cyclotron resonance

The function of charge distribution over the momentum projections in a preset field of a circularly polarized rf transverse electromagnetic wave propagating along a constant uniform magnetic field with phase velocity u > c is obtained by solving the relativistic collisionless kinetic equation. The peculiarities in energy associated with the nonlinearity of the cyclotron resonance for various values of the phase velocity are analyzed in the limits of single-valuedness of the resonance curve. Some distribution functions are considered.     

Consecutive recovery of uranium oxides from uranyl-containing molten alkali metal sulfate electrolytes

The oxygen coefficient (atomic ratio O/U) of a cathode product and the cathode current yield in consecutive recovery of uranium oxides from molten salt mixtures (nLi₂SO₄ + (1 ? n)Cs₂SO₄) + UO₂SO₄ and (Li,Na,K)₂SO₄ + UO₂SO₄ in air were analyzed as dependent on the electrolyte and the mean solvent-salt cation radius. The increasing mean solvent-salt cation radius and decreasing UO₂SO₄ concentration in the electrolyte during long-term electrolysis suppress the solvolysis of uranyl ions and decrease the oxygen coefficient in the cathode product. The cathode current yield decreases systematically during electrolysis and drops to zero long before the uranium is completely recovered from the melt. The ultimate uranium recovery increases as the mean solvent-salt cation radius increases.     

Direct Phosphorylation of N-Protected Imidazoles and Benzoimidazoles-A Route to 1H-Imidazol(benzoimidazol)-2-yl Phosphonic and Phosphinic Acids and Their Derivatives

Synthetic approaches to 1H-imidazol-2-yl and 1H-benzoimidazol-2-yl phosphinic and phosphonic acids and their derivatives are reported, based on phosphorylation of N-protected heterocylcles by PhPOCl₂ or MePOCl₂. Reaction of N-alkylbenzoimidazoles with POCl₃ did not lead to C-phosphorylated products in a reasonable yield, [2,2′]-bis-benzoimidazolyles being formed instead.     

Epoxy-amine composites with ultralow concentrations of single-layer carbon nanotubes

The physical and mechanical properties of composite materials based on epoxy-amine systems—diglycidyl ether of diphenylolpropane-eutectic mixture of aromatic amines (40 wt % m-phenylenediamine-60 wt % 4,4′-diaminodiphenylmethane) and epoxy-diane resin ED-20-eutectic mixture of aromatic diamines with ultralow contents (≤0.1 wt %) of single-layer carbon nanotubes—are studied. It is shown that, for the concentration dependence of the modulus of elasticity during tension, the additivity rule is obeyed only at the lowest concentrations of carbon nanotubes. In this case, the presence of near-surface layers of a matrix with an increased elastic modulus should be considered.     

μSR study of the properties of Fe3O4-based nanostructured magnetic systems

A ferrofluid based on Fe₃O₄ nanoparticles dispersed in heavy water D₂O is studied using the μSR method. The experiment has been carried out at temperatures 26–300 K. It is found that the diamagnetic (muon) fraction is formed in the ferrofluid in about the same amount as in D₂O, but the muon-spin relaxation rate in the ferrofluid is much higher than in D₂O. A significant shift of the muon-spin precession frequency in the ferrofluid is observed. It is shown that the shift of the muon precession frequency as a function of the external magnetic field is described by the Langevin function typical of paramagnetic magnetization. The mean magnetic field in the medium due to magnetic-nanoparticle polarization in an external field is experimentally determined. The nanoparticle sizes are estimated.     

Ultrahigh-repetition-rate bound-soliton harmonic passive mode-locked fiber lasers

On the basis of numerical simulation results, we put forward a way to realize harmonic passive mode locking of fiber lasers with an ultrahigh-repetition-rate pulse train. The equidistant distribution of ultrashort pulses filling the total laser cavity is due to bound-soliton mechanisms. In the case of large bound energy, such long soliton trains are very stable and have the ideal periodic structure as a soliton crystal.     

Topological Insulator State in Thin Bismuth Films Subjected to Plane Tensile Strain

The results of experimental examination of galvanomagnetic properties of thin bismuth films subjected to plane tensile strain resulting from the difference in thermal expansion coefficients of the substrate material and bismuth are presented. The resistivity, the magnetoresistance, and the Hall coefficient were studied at temperatures ranging from 5 to 300 K in magnetic fields as strong as 0.65 T. Carrier densities were calculated. A considerable increase in carrier density in films thinner than 30 nm was observed. This suggests that surface states are more prominent in thin bismuth films on mica substrates, while the films themselves may exhibit the properties of a topological insulator.     

Effect of ionic impurities on the primary nucleation of potassium sulphate solutions

A technique is described for rapidly assessing the effect of impurities on primary nucleation in solutions. The influence of Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Pb²⁺, Cr³⁺ and Ni²⁺ on the nucleation of potassium sulphate solutions is discussed. It is generally observed that a discontinuity in the behaviour of the impurity occurs at an impurity concentration corresponding to the solubility of the “impurity sulphate” in the solution under investigation.