Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Catalysis & Coupling constant. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

Complete integrability of nonlocal nonlinear Schrödinger equation

Abstract: Based on the completeness relation for the squared solutions of the Lax operator L, we show that a subset of nonlocal equations from the hierarchy of nonlocal nonlinear Schrodinger equations (NLS) is a completely integrable system. The spectral properties of the Lax operator indicate that there are two types of soliton solutions. The relevant action-angle variables are parametrized by the scattering data of the Lax operator. The notion of the symplectic basis, which directly maps the variations of the potential of L to the variations of the action-angle variables has been generalized to the nonlocal case. We also show that the inverse scattering method can be viewed as a generalized Fourier transform. Using the trace identities and the symplectic basis, we construct the hierarchy Hamiltonian structures for the nonlocal NLS equations.

Sleep problems and their effect in ADHD

Abstract: Sleep problems are common in attention-deficit/hyperactivity disorder (ADHD) to the extent that they mimic or exacerbate daytime symptoms expression. In this review, we advocate the need for a better understanding of sleep alterations in youths with ADHD and their impact on neurobehavioral functions including learning, memory and emotional regulation. An in-depth exploration of existing data showed that although extensively studied, the actual nature of sleep problems in ADHD and their effects on daytime behavior are still less well understood. Important issues, among which developmental changes in sleep architecture and role of subtle sleep electroencephalogram signatures, are generally neglected. Future research of sleep effects on behavior in ADHD would benefit from considering developmental aspects and links between brain activation patterns during sleep and wake.

Electrochromic properties of atmospheric CVD MoO3 and MoO3–WO3 films and their application in electrochromic devices

Abstract: The transition metal oxides exhibit electrochromism, defined as color change caused by applied voltage. The electrochromic (EC) effect can be stronger in mixed oxides because of the higher optical absorption, due to electron transitions between two kinds of metal sites with different valences. Thin films of MoO3 and mixed Mo/W oxides were obtained by atmospheric pressure chemical vapor deposition (CVD), using pyrolytic decomposition of metal hexacarbonyls. IR and Raman spectra are presented and compared with data for WO3 from previous investigation. Sputter auger spectroscopy was used to determine the chemical composition of the mixed films. The visible transmittance of films deposited on glass substrate was about 80%; on conductively coated glass (i.e. SnO2:Sb/glass) the visible transmittance drops to around 60%. After annealing, the optical transmittance of the single oxide films slightly improves, while for the mixed films it slightly decreases. The electrochromic properties of MoO3 and mixed Mo/W oxide films were investigated by cyclic voltammetry performed in a conventional potentiostatic three-electrode configuration. Current and transmittance were measured simultaneously during the potential sweep at different wavelengths over the spectral range of 400–800 nm. Deep blue coloring of all the electrochromic films (MoO3, WO3 or Mo/WO3) appears only in the cathodic range, minimizing visible light transmittance. At positive potentials, the EC film starts bleaching (for about 3 min) and the film returns its initial transparency. It was found that the CVD deposited MoO3 and Mo0.07W0.93O3 thin films performed well as electrodes in electrochromic devices. We made devices based on Mo0.07W0.93O3/LiClO4 + propylene carbonate + polyvinyl alcohol + PVA/SnO2:Sb. The devices exhibited good cyclic reversibility (colored/bleached state) and good coloration efficiencies. We measured a transmittance change (600 nm) of 48.4% switching to 17.4% for our best device.

Ni-Nb-O catalysts for ethane oxidative dehydrogenation

Abstract: Ni–Nb–O catalysts with various Nb contents (0–19%) have been studied as catalysts for the oxidative dehydrogenation of ethane. An optimum ethane conversion of 33% with 78% of selectivity to ethylene was obtained for a Ni–Nb–O catalyst containing 15% of Nb at 350 °C with a weight to flow W/F ratio of 0.54 g s mL−1. The catalysts have been characterized using various techniques allowing to show that the efficiency of the catalysts was related to a surface interaction between the NiO active phase and an amorphous Nb2O5 phase. Because ammonium oxalato niobate was used as niobium precursor, oxalate ions were present; concomitantly to the surface interaction described, the thermal decomposition of these oxalate ions induced a reduction in NiO oxygen over-stoichiometry which also influences the catalytic properties. It was demonstrated that only a small percent of Nb was necessary to have these effects and the optimal activity observed for 15% of Nb had to be related to another process which corresponds to the decrease in the active phase particle size induced by the amorphous Nb2O5 phase; this phase prevents the sintering of the active phase particles during the thermal transformation of the catalysts precursors. It was also shown that the thermal decomposition of oxalates limits NiO crystal growth. Above 15% of Nb the amorphous phase reacted with the nickel oxide to form an inactive mixed niobium and nickel oxide phase NiNb2O6. The study of the catalytic properties over long periods of time showed that the Ni–Nb–O catalysts underwent a slow but systematic deactivation. This deactivation has been attributed both to the continuous reduction of the NiO oxygen over-stoichiometry in the reaction conditions and to the formation of the NiNb2O6 phase thermodynamically stable at the catalytic reaction temperature. Attempt to regenerate the catalysts has failed.