Adaptive control of femtosecond soliton self-frequency shift in fibers

The Raman shift of a subpicosecond soliton in 100 m of fiber is controlled adaptively by pulse shaping before launching into the fiber. We use a deformable-mirror-based shaper to control the spectral phase of the input pulse.     

Magnetic resonance imaging of objects with dipolar-broadened spectra using soft excitation pulses

Feasibility of acquiring high-resolution 3D NMR images of objects with dipolar-broadened spectra by using soft excitation pulses is experimentally demonstrated. The models are liquid-crystalline phantoms and a pencil eraser. The pulse sequence is a standard 3D gradient-echo sequence.     

Restrictions on arrangements of ovals of projective algebraic curves of odd degree

This paper investigates the first part of Hilbert's 16th problem which asks about topology of the real projective algebraic curves. Using the Rokhlin-Viro-Fiedler method of complex orientation, we obtain new restrictions on the arrangements of ovals of projective algebraic curves of odd degree , , with nests of depth .

     

Reaction of ortho-palladated dimethylbenzylamine with styrene: Unexpected salt effect

Treatment of ortho-palladated complex $\text{I}$ with styrene in benzene - acetic acid mixture gives complex $\text{IV}$. The reaction is strongly accelerated in the presence of NaClO₄ or LiClO₄.     

A delicate universe: compactification obstacles to D-brane inflation

We investigate whether explicit models of warped D-brane inflation are possible in string compactifications. To this end, we study the potential for D3-brane motion in a warped conifold that includes holomorphically embedded D7-branes involved in moduli stabilization. The presence of the D7-branes significantly modifies the inflaton potential. We construct an example based on a very simple and symmetric embedding due to Kuperstein, z1= const, in which it is possible to fine-tune the potential so that slow-roll inflation can occur. The resulting model is rather delicate: inflation occurs in the vicinity of an inflection point, and the cosmological predictions are extremely sensitive to the precise shape of the potential.     

Modified coulomb law in a strongly magnetized vacuum

We study the electric potential of a charge placed in a strong magnetic field B>B(0) approximately 4.4x10(13) G, as modified by the vacuum polarization. In such a field the electron Larmour radius is much less than its Compton length. At the Larmour distances a scaling law occurs, with the potential determined by a magnetic-field-independent function. The scaling regime implies short-range interaction, expressed by the Yukawa law. The electromagnetic interaction regains its long-range character at distances larger than the Compton length, the potential decreasing across B faster than along. Correction to the nonrelativistic ground-state energy of a hydrogenlike atom is found. In the limit B = infinity, the modified potential becomes the Dirac delta function plus a regular background. With this potential the ground-state energy is finite--the best pronounced effect of the vacuum polarization.     

Channel-facilitated molecular transport across membranes: attraction, repulsion, and asymmetry

Transport of molecules across membrane channels is investigated theoretically using exactly solvable discrete stochastic site-binding models. It is shown that the interaction potential between molecules and the channel has a strong effect on translocation dynamics. The presence of attractive binding sites in the pore accelerates the particle current for small concentrations outside the membrane, while for large concentrations, surprisingly, repulsive binding sites yield the most optimal transport. In addition, the asymmetry of the interaction potential also strongly influences the channel transport. The mechanism underlying these phenomena is discussed using the details of particle dynamics at the binding sites.     

Electrocatalytic multicomponent one-pot approach to tetrahydro-2′H,4H-spiro[benzofuran-2,5′-pyrimidine] scaffold

The new electrocatalytic multicomponent transformation has been found: the electrolysis of arylaldehydes, N,N′-dimethylbarbiturate, and cycloxehane-1,3-diones in alcohols in the presence of sodium bromide as a mediator in an undivided cell results in the formation of substituted unsymmetric spirobarbituric dihydrofurans in 62%–76% yields. The optimized reaction conditions and a mechanistic rationale for this electrocatalytic multicomponent transformation are presented. This new electrocatalytic process is a facile and efficient way to produce substituted unsymmetric spirobarbituric dihydrofurans containing both barbituric and 3,5,6,7-tetrahydro-1-benzofuran-4(2H)-one fragments, which are promising compounds for different biomedical applications, among them are anticonvulsants, anti-AIDS agents, and antiinflammatory remedies. The scaffold approach was employed to find a protein, which may be influenced by the synthesized compounds—human aldose reductase was proposed. It was shown by molecular docking studies that such a scaffold search is beneficial and tetrahydro-2′H,4H-spiro[benzofuran-2,5′-pyrimidines] used in this approach are promising for the development of novel aldose reductase inhibitors.     

Optimal separation sequence for three-component mixtures

In this paper, the problem of finding the optimal separation sequence for a three-component mixture in a cascade of two binary separation stages is considered. The minimal energy that is needed for a separation in a two-stage mechanical separation subject to a given flow rate of the input mixture is obtained. Optimization is achieved by selecting the optimal sequence of binary separations and by distributing mass-exchange surfaces between separation stages optimally. For a heat-driven two-stage separation system, it is shown that the rate of flow of the input mixture cannot be higher than some bound. This bound (the maximal possible rate of heat-driven separation) and the separation sequence when it is achieved are derived.