Discrete solitons and nonlinear surface modes in semi-infinite waveguide arrays

We discuss the formation of self-trapped localized states near the edge of a semi-infinite array of nonlinear optical waveguides. We study a crossover from nonlinear surface states to discrete solitons by analyzing the families of odd and even modes centered at finite distances from the surface and reveal the physical mechanism of the nonlinearity-induced stabilization of surface modes.     

Electrochemical properties and radical anions of carbocycle‐fluorinated quinoxalines and their substituted derivatives

Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline ( 1 ) and its derivatives bearing various substituents R (7‐H ( 2 ), 7,8‐H₂ (3 ), 6‐CF₃ ( 4 ), 6‐Cl ( 5 ), 5,7‐Cl₂ ( 6 ), 5‐NH₂ ( 7 ), 6‐OCH₃ ( 8 ), 6,7‐(OCH₃)₂ ( 9 ), 6,7,8‐(OCH₃)₃ ( 10 ), 5,6,7,8‐(OCH₃)₄ ( 11 ), 6‐OCH₃,7‐N(CH₃)₂ ( 12 ), 6‐N(CH₃)₂ ( 13 ), 6,7‐(N(CH₃)₂)₂ ( 14 ), 5,6,7‐(N(CH₃)₂)₃ ( 15 ), and 7,8‐cyclo‐(=CF‐CF = CF‐CF=) ( 16 )) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1 – 4 and 7 – 15 , the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4 – 6 and 15 , 16 . Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H₂ derivative of 1 ( 17 ) at the next steps. Electrochemically generated RAs of 1 – 3 , 7 – 14 , and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1 – 15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1 – 15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1 – 5 and 7 – 14 has been found to be irreversible.     

High-speed electronics of the T0 detector for the ALICE experiment (CERN)

The design and special features of the main units of high-speed electronics for the trigger subsystem of the T0 detector of the ALICE experiment are considered. Its characteristic time resolution is 50 ps. The dead time does not exceed 25 ns.     

Translational cooling of doped nanocrystals by Raman pulses: Towards macroscopic quantum state

One of the most interesting problems of modern physics is the realization of nanoparticles in macroscopic quantum states, in which they behave as a quantum objects. These states can only be implemented at ultra-low translational temperatures that have not been achieved so far. Here we develop a novel method for optical cooling of CaF₂:Yb³⁺ nanocrystals, which is based on the coherent population transfer induced in the impurity ions by ultraviolet Raman pulses. A doped nanocrystal localized in a radio-frequency trap is cooled due to the photon recoil from the pulses of varied intensity. The proposed method allows to obtain nanocrystals with translational temperatures of the order of 10^?9 K, which indicates that the nanocrystal approaches a macroscopic quantum state.     

On the Possibility of using Vertical Receiving Arrays for Underwater Acoustic Communication on the Arctic Shelf

Acoustical Physics - Numerical simulation is applied to analyze the possibilities of using vertical receiving arrays covering the entire waveguide for underwater acoustic communication on the...     

N‐Methylbenzoazacrown ethers with the nitrogen atom conjugated with the benzene ring: the improved synthesis and the reasons for the high stability of complexes with metal and ammonium cations

An improved method for the synthesis of formyl derivatives of N‐methylbenzoazacrown ethers is proposed. They are prepared in up to 68% yields over fewer steps and with a much shorter time required for the last step. The stability constants of complexes formed by N‐methylbenzoazacrown ethers and their structural analogs with alkali metal, alkaline‐earth metal and ammonium cations were determined by ¹H NMR titration in CD₃CN. High stability of complexes of N‐methyl derivatives of benzoazacrown ethers is demonstrated, comparable with or even exceeding the stability of benzocrown‐ether complexes and markedly exceeding the stability of complexes of phenylazacrown ethers with the same macrocycle size. The structures of azacrown ethers and their complexes with Ba(ClO₄)₂ were studied by X‐ray diffraction. A high degree of pre‐organization of N‐methylbenzoazacrown ethers toward the formation of complexes with metal and ammonium cations was noted, which is due to the clear‐cut pyramidal geometry of the nitrogen atom and the orientation of the lone electron pairs (LEPs) of most heteroatoms towards the centre of the macroheterocycle. Copyright © 2009 John Wiley & Sons, Ltd.     

Large Deviation Probabilities for Square-Gaussian Stochastic Processes

We investigate properties of square-Gaussian stochastic processes. These processes are formed by quadratic forms of Gaussian processes or by limits in the mean square of quadratic forms of Gaussian processes. Special classes of these processes are determined and investigated. For processes from these classes estimates of large deviation probability are obtained. These estimates we use to estimate the probability that Gaussian vector-valued process leave some region on some interval of time. We construct asymptotic confidence regions for estimates of covariance functions of vector-valued Gaussian processes. Criterion of hypothesis testing on covariance functions of these processes is constructed.     

Choiceless polynomial time

Turing machines define polynomial time (PTime) on strings but cannot deal with structures like graphs directly, and there is no known, easily computable string encoding of isomorphism classes of structures. Is there a computation model whose machines do not distinguish between isomorphic structures and compute exactly PTime properties? This question can be recast as follows: Does there exist a logic that captures polynomial time (without presuming the presence of a linear order)? Earlier, one of us conjectured a negative answer. The problem motivated a quest for stronger and stronger PTime logics. All these logics avoid arbitrary choice. Here we attempt to capture the choiceless fragment of PTime. Our computation model is a version of abstract state machines (formerly called evolving algebras). The idea is to replace arbitrary choice with parallel execution. The resulting logic expresses all properties expressible in any other PTime logic in the literature. A more difficult theorem shows that the logic does not capture all of PTime.