New Achievements in the Field of Intramolecular Phenolic Coupling Reactions,Using Hypervalent (III) Iodine Reagent: Synthesis of Galanthamine

Our investigations on the oxidative possibilities of the hypervalent iodine(III) reagent established that phenyliodine(III)bis(trifluoroacclate) (PIFA) can provide one-pot contiguous coupling-cyclization reaction giving a product with narwedine skeleton, when used in a phenolic coupling reaction of p'-bromonorbelladine derivatives. A suitably selected precursor gave up to 60% yield of the coupled product.     

Tunable subnanosecond laser pulse generation using an active mirror concept

We report (theory, experimental check) an improved approach for generation of a tunable, subnanosecond pulse (0.1–0.4 ns), based on a single pulsation (“spike”) separation from the transient oscillations in a dye laser with active mirror (AMIR). A pumping by 20–50 ns pulses from Q-switched Nd:YAG laser is considered. The separation is in original, two-spectral selective channels cavity, where the forced by AMIR quenched generation at one of the wavelength stops initially started spiking generation at the other wavelength after the first spike development. The AMIR quickly starts the quenching generation at a precisely controlled moment and with necessary intensity thus assuring the desired separation. An advantage is a high reproducibility of the separation for high (~250%) pump power fluctuations combined with tuning in large range (~20 nm). To obtain such an operation we form ~1 ns leading front pump pulse by electrooptical temporal cutting of the input pump pulse and use an optical delay line. This increases also a few times the power in the separated spike (to be ~100 kW). Our approach widens the combinations of lasers for effective applications of spike separation technique (dye lasers excited by Q-switched solid-state or Cu-vapor lasers).     

Equilibrium for a combinatorial Ricci flow with generalized weights on a tetrahedron

Chow and Lou [2] showed in 2003 that under certain conditions the combinatorial analogue of the Hamilton Ricci flow on surfaces converges to Thruston’s circle packing metric of constant curvature. The combinatorial setting includes weights defined for edges of a triangulation. A crucial assumption in [2] was that the weights are nonnegative. We have recently shown that the same statement on convergence can be proved under weaker conditions: some weights can be negative and should satisfy certain inequalities. In this note we show that there are some restrictions for weakening the conditions. Namely, we show that in some situations the combinatorial Ricci flow has no equilibrium or has several points of equilibrium and, in particular, the convergence theorem is no longer valid.     

Simulation of Mean Curvature Flows on Surfaces of Revolution

Computational Mathematics and Mathematical Physics - This paper is devoted to the simulation of the mean curvature flow on a surface of revolution. The surface is discretized using the icosahedral...     

New Results About Weakly Equivalent MAP 2 and MAP 3 Processes

In Ramírez-Cobo et?al.?(J Appl Probab 47(3):630?C649, 2010b), weakly equivalent second order Markovian arrival processes (noted MAP ₂s) are introduced and partially characterized. In this work we look into weak equivalence in detail and provide a complete characterization of weakly equivalent MAP ₂s. The analogous problem for the MAP ₃ case is partially solved.     

Time series interpolation via global optimization of moments fitting

Most time series forecasting methods assume the series has no missing values. When missing values exist, interpolation methods, while filling in the blanks, may substantially modify the statistical pattern of the data, since critical features such as moments and autocorrelations are not necessarily preserved.     

Identifiability of the MAP 2/G/1 queueing system

In this paper, we study how the lack of a unique representation for the two-state Markovian arrival process (MAP ₂) can influence statistical estimation for the MAP ₂/G/1 queueing system. In particular, given two equivalent representations of the same MAP ₂, we find that the steady-state distributions of the queuing system can be identified.     

New Convenient Reagents for Chemoselective N‐Alkoxycarbonylation of (S)‐Isoserine: Application in the Isepamicin Synthesis

A synthesis of a series of N‐alkoxycarbonyl mercaptobenzothiazoles (MBTs) and their application as reagents for chemoselective protection of amino group are presented herein. It was shown that all new reagents, Z‐MBT, Fmoc‐MBT, Phoc‐MBT, and Tec‐MBT, are highly effective in the selective N‐alkoxycarbonylation of (S)‐isoserine. The transformation is a simple, fast, and low‐cost protocol, which is applicable in scale‐up experiments. The starting MBT was fully recovered at the end of the process, which is an additional advantage of the method. The efficiency of the Z‐reagent was also demonstrated by the selective protection of both gentamicin B and (S)‐isoserine before their peptide‐type coupling in the synthesis of the aminoglycoside antibiotic isepamicin.     

Protons colliding with crystalline ice: proton reflection and collision induced water desorption at low incidence energies

We present results of classical trajectory (CT) calculations on the sticking of protons to the basal plane (0001) face of crystalline ice, for normal incidence at a surface temperature (Ts) of 80 K. The calculations were performed for moderately low incidence energies (Ei) ranging from 0.05 to 4.0 eV. Surprisingly, significant reflection is predicted at low values of Ei (< or = 0.2 eV) due to repulsive electrostatic interactions between the incident proton and the surface water molecules with one of their H-atoms pointing upward toward the gas phase. The sticking probability increases with Ei and converges to unity for Ei > or = 0.8 eV. In the case of sticking, the proton is trapped in the ice forming a Zundel complex (H5O2+), with an average binding energy of 9.9 eV with a standard deviation of 0.5 eV, independent of the value of Ei. In nearly all sticking trajectories, the proton is implanted into the ice surface, with a penetration depth that increases with Ei. The strong interaction with the neighboring water molecules leads to a local rupture of the hydrogen bonding network, resulting in collision induced desorption of water (puffing), a process that occurs with significant probability even at the lowest Ei considered. The probability of water desorption increases with Ei. In nearly all trajectories in which water desorption occurs, a single three-coordinated water molecule is desorbed from the topmost monolayer.