Moscow State University

About: Moscow State University is a education organization based out in Moscow, Russia. It is known for research contribution in the topics: Laser & Population. The organization has 66747 authors who have published 123358 publications receiving 1753995 citations. The organization is also known as: MSU & Lomonosov Moscow State University.

Photoluminescence of singlet oxygen in pigment solutions

Abstract: — Luminescence of 1O2 (1270 nm) accompanying energy transfer to oxygen from photoexcited (triplet) molecules of sensitizers in air saturated solutions has been investigated. The luminescence was observed in CC14, CS2 and freon with the use of porphyrins, chlorophylls, pheophytins and aromatic hydrocarbons as sensitizers. The lifetime and quantum yield of the luminescence depended on the nature of the solvents. pigments and their concentrations. The maximum values of these parameters were equal to 28 ± 5 ms and 5 ± 4 times 10--5, respectively. The quantum yield of 1O2 generation by pigments has been measured and the results used for determining the quantum yields of intersystem crossing in the pigment molecules. The rate constants of 1O2 reaction with different substances have been determined with the aid of luminescence quenching. It has been shown that along with β-carotene. Chls, pheophytins, and some porphyrins are also very active quenchers of 1O2, The quenching effect depends on their molecular structure and on the presence and nature of the central metal atom. Quenching 1O2 by the pigments is due mainly to a “physical” mechanism (without destruction of the pigments). The destructive “chemical” quenching is by 1–4 orders of magnitude less effective and is accompanied with photochemiluminescence of the pigments. The experiments on 1O2 generation and quenching indicate that energy of triplet states of bacteriochlorophyll and bacteriopheophytin is somewhat higher than that of 1Δg oxygen. The data demonstrate wide possibilities of the luminescence studied as a method for investigating 1O2 reactivity and photophysical properties of sensitizers.

Estimates for the number of sums and products and for exponential sums in fields of prime order

Abstract: Our first result is a ‘sum-product’ theorem for subsets A of the finite field Fp, p prime, providing a lower bound on max(|A + A|, |A · A|). The second and main result provides new bounds on exponential sums ∑ x1,...,xk∈A exp(2πix1 . . . xkξ/p), where A ⊂ Fp.

On regularity of transition probabilities and invariant measures of singular diffusions under minimal conditions

Abstract: Let A = (aij ) be a matrix-valued Borel mapping on a domain Ω ⊂ R d , let b = (bi ) be a vector field on Ω, and let LA, b ϕ = a ij ∂ x i ∂ xj ϕ + bi ∂ xi ϕ. We study Borel measures μ on Ω that satisfy the elliptic equation LA, b *μ = 0 in the weak sense: ∫ LA, b ϕ dμ = 0 for all ϕ ∈ C 0 ∞ (Ω). We prove that, under mild conditions, μ has a density. If A is locally uniformly nondegenerate, A ∈ H loc p, 1 and b ∈ L loc p for some p > d, then this density belongs to H loc p, 1. Actually, we prove Sobolev regularity for solutions of certain generalized nonlinear elliptic inequalities. Analogous results are obtained in the parabolic case. These results are applied to transition probabilities and invariant measures of diffusion processes.

Optical-damage-resistant impurities in lithium niobate

Abstract: We analyzed the properties of damage-resistant LiNbO3 crystals doped with Mg, Zn, or In. Damage resistance is due to an essential increase in the photoconductivity σp. In the first two compounds the increase in σp is most pronounced at concentrations exceeding certain thresholds (5.5 mol. % MgO or 7 mol. % ZnO in the congruent melt), whereas in In-doped crystals it occurs at any In concentration. The increase in σp is directly related to the reduction of the intrinsic defects NbLi because of their substitution by damage-resistant impurities. If an iron impurity is present, then an abrupt decrease in the capture cross section of Fe3+ acceptors at Mg or Zn concentrations higher than the threshold is responsible for the observed increase in σp.