Self-written waveguides in photopolymerizable resins

We study the optically induced growth and interaction of self-written waveguides in a photopolymerizable resin. We investigate experimentally how the interaction depends on the mutual coherence and the relative power of the input beams and suggest an improved analytical model that describes the growth of single waveguides and the main features of their interaction in photosensitive materials.     

Detection and evaluation of the depth of surface cracks in conductive materials by using a loop antenna

A new method is developed for detection and evaluation of the depth of surface cracks in conductive materials. The main components of the measurement equipment are a conductive wire and a loop antenna, both of which are located as close as possible to the surface of the investigated material, while the antenna loop is perpendicular to the surface and parallel to the wire. Supplying of electrical potential with microwave frequency f and amplitude |_s| to the wire results in spreading of induced current close beneath the surface of the material. The induced current redistributes in the vicinity of surface cracks, and some of the current paths flow along the crack walls. This leads to generation of a time-variable magnetic field mostly within the volume of the crack, which is detected by the loop antenna. A theoretical analysis is presented of the contributions of the different types of generated magnetic fields to the potential drop with amplitude |U_s| measured by the antenna. The distribution of the ratio R(dB)=|U|/|U_s| is measured for specimens of paramagnetic and ferromagnetic steel which contain three artificial cracks with depths of 0.5 mm, 1 mm, and 2 mm, and frequency f=300 MHz of the supplied electrical potential. It turns out that artificial cracks with a depth of d 0.5 mm, located at distances from x=3 mm to x=15 mm from the wire, can be detected. The largest sensitivity of crack detection is achieved for x4 mm when the long axis of a crack is perpendicular to the wire. The crack response of the measured ratio R is proportional to the crack depth when the loop of the antenna is located above or slightly outside an artificial crack, and at least 4 mm from the wire. This relation could be used for evaluation of the depth of real surface cracks. The notable decrement of the crack response outside the crack can indicate the location of the crack tips on the surface of the specimen. It is shown that a loop antenna with a diameter of 7 mm provides the largest crack response, as well as that the developed method can be applied to both paramagnetic and ferromagnetic materials. An example of the detection of a real crack by an antenna is reported for the first time. PACS 81.70.Ex; 84.40.Ba; 84.32.Ff     

Application of high pressure induced by water-freezing to the direct catalytic asymmetric three-component List-Barbas-Mannich reaction

High pressure induced by water-freezing has been successfully applied to the direct catalytic asymmetric-three component List-Barbas-Mannich reaction, in which higher yield and better enantioselectivity can be realized than those from the reaction at room temperature under 0.1 MPa.     

Observation of the "self-healing" of an error field island in the large helical device

It was observed that the vacuum magnetic island produced by an external error magnetic field in the large helical device shrank in the presence of plasma. This was evidenced by the disappearance of flat regions in the electron temperature profile obtained by Thomson scattering. This island behavior depended on the magnetic configuration in which the plasmas were produced.     

Synthesis of donor-acceptor chromophores by the [2 + 2] cycloaddition of arylethynyl-2H-cyclohepta[b]furan-2-ones with 7,7,8,8-tetracyanoquinodimethane

Arylethynyl-2H-cyclohepta[b]furan-2-ones reacted with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a formal [2 + 2] cycloaddition reaction, followed by ring opening of the initially formed cyclobutene derivatives, to afford the corresponding dicyanoquinodimethane (DCNQ) chromophores in excellent yields. The intramolecular charge-transfer (ICT) interactions between the 2H-cyclohepta[b]furan-2-one ring and DCNQ acceptor moiety were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behavior of the novel DCNQ derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties depended on the number of DCNQ units in the molecule. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.     

Annealing behavior of a void network in amorphous silicon

A void network in a-Si films prepared by vacuum deposition was studied. A close relationship in annealing behavior has been observed between the changes in surface area of voids and in the ESR signal strength.