Approximate controllability for semilinear retarded systems

This paper deals with the approximate controllability for the semilinear retarded control system. We will also derive the equivalent relation between controllability and stabilizability of the solution for the corresponding linear control system.     

Single-mode Raman fiber laser based on a multimode fiber

Single-mode operation of a Raman fiber laser based on a multimode fiber has been demonstrated for what is to our knowledge the first time. Single-mode operation was achieved through the beam cleanup effect of stimulated Raman scattering in multimode fibers. The Raman laser, consisting of a 50-microm-core multimode fiber and a multimode Nd:YAG laser pump, produced an output beam corresponding to the fundamental mode of the fiber.     

Experimental test and modeling of hollow-core composite insulators

Hollow-core composite post insulators, used in high voltage electrical equipment, are important parts of the power substation systems. In many applications the composite insulators are considered as slender cantilever columns, fixed at one end and connecting to a conductor at the other end. During earthquakes the post insulators are damaged and sometimes fail near their base connection. When the post is pulled laterally, the tube dislocates from the walls in the end flange, and slips in and out the flange. Subsequently the composite tube sticks in the flange and slips again if the load is reversed, as it is occurring during earthquakes. In this study, an analytical model is developed using a combination of linear and nonlinear springs, viscous and frictional dampers and inertial masses. The developed macroscopic model is governed by a third-order differential equation which is derived in a state-space and solved by using Runge?CKutta integration in MATLAB. Several prototype insulators have been tested at the University at Buffalo??s Structural Engineering and Earthquake Simulation Laboratory (SEESL). Through a methodical identification of the stiffness, mass, friction, and damping properties, the analytical model is verified to produce reliable estimates of strength, damping and global behavior.     

The dynamics of unfolded versus folded tRNA: the role of electrostatic interactions

The dynamics of RNA contributes to its biological functions such as ligand recognition and catalysis. Using quasielastic neutron scattering spectroscopy, we show that Mg(2+) greatly increases the picosecond to nanosecond dynamics of hydrated tRNA while stabilizing its folded structure. Analyses of the atomic mean-squared displacement, relaxation time, persistence length, and fraction of mobile atoms showed that unfolded tRNA is more rigid than folded tRNA. This same result was found for a sulfonated polystyrene, indicating that the increased dynamics in Mg(2+) arises from improved charge screening of the polyelectrolyte rather than specific interactions with the folded tRNA. These results are opposite to the relationship between structural compactness and internal dynamics for proteins in which the folded state is more rigid than the denatured state. We conclude that RNA dynamics are strongly influenced by the electrostatic environment, in addition to the motions of local waters.     

Identification of indoline-2-thione analogs as novel potent inhibitors of α-melanocyte stimulating hormone induced melanogenesis

Based on the hits, 3,4-dihydroquinazoline-2-thione (1) and benzimidazole-2-thione (2), a series of indole-2-thione (3) and indole-2-thiol inhibitors (4) of melanogenesis were designed, synthesized and evaluated in melanoma B16 cells under the stimulant of α-melanocyte stimulating hormone (α-MSH). The indole-2-thione compounds (3a-g) exhibited an effective inhibitory activity on melanin synthesis. The Structure-Activity Relationship (SAR) studies of 2 have revealed that in potent inhibitor 3a (>100% inhibition at 30 μM, IC50=1.40 μM) the role of nitrogen (3-N) at 3-position is insignificance. In addition, the hydrophobic substituents of 3 were better than the hydrophilic one. However, conversion of thione (-C=S, 3) to thiol (-C-SH, 4) led to decrease in the potency.     

Investigation of the effects of graphite flake alignment on thermal emissivity by applying a magnetic field during coating of an aluminum sheet

In this study we investigated the effects of graphite flake alignment on thermal emissivity by applying a magnetic field during coating of aluminum sheets with graphite. The coating paste was prepared by ball milling graphite flakes with an organic binder. The graphite flake content was 9.1, 13.0, 16.7, 20.0, or 23.1 wt.%. After coating of aluminum sheets with the paste by dipping, a magnetic field was applied vertically to the coated aluminum sheet by use of neodymium magnets. It was observed that the graphite flakes were aligned at an angle to the surface by application of the magnetic field. In contrast, in the absence of the magnetic field the graphite flakes were aligned horizontally on the aluminum sheets. The surface roughness of specimens prepared by use of a magnetic field (MF; R _a = 10.172–14.654 μm) was more than twofold that of specimens for which no magnetic field was applied (NMF; R _a = 4.564 μm). The thermal emissivity of MF9 (9.1 wt.% graphite; ε = 0.80) was higher than that of NMF9 (9.1 wt.% graphite; ε = 0.77). The thermal emissivity of MF20 (20.0 wt.% graphite) was 0.91, the highest in this study. It was shown that flakes aligned at an angle to the surface contribute to enhanced thermal emissivity. Well aligned graphite flakes are therefore expected to enable high thermal dissipation from electronic components.     

Class number 2 problem for certain real quadratic fields of Richaud-Degert type

In this paper we will apply Biró's method in [A. Biró, Yokoi's conjecture, Acta Arith. 106 (2003) 85-104; A. Biró, Chowla's conjecture, Acta Arith. 107 (2003) 179-194] to class number 2 problem of real quadratic fields of Richaud-Degert type and will show that there are exactly 4 real quadratic fields of the form with class number 2, where n²+1 is a even square free integer.