Enhanced magnetoelectric properties in three-phase composites with 2-1-2 connectivity

An investigation is reported on a 2-1-2 magnetoelectric (ME) laminate composite having Metglas/PZNT/Metglas configuration with ferrite pillars embedded in the PZNT phase. The piezoelectric layer with composition 0.2Pb(Zn_1/3Nb_2/3)O₃–0.8Pb(Zr_0.5Ti_0.5)O₃ (PZNT) consisted of co-fired (Ni_0.6Cu_0.2Zn_0.2)Fe₂O₃ (NCZF) pillars. The top and bottom Metglas layers in the sandwich structure had a thickness of 100 µm, whereas the middle piezoelectric layer had thickness of 800 µm. This 2-1-2 composite was found to exhibit a ME coefficient of the order of 352 mV/cm Oe. Interestingly, the performance of the 2-1-2 composite is 15% higher than that of conventional 2-2 laminate composite.     

n-Type microcrystalline silicon oxide layer and its application to high-performance back reflectors in thin-film silicon solar cells

Light trapping is a key issue in improving the efficiency of thin-film Si solar cells, and using a back reflector material plays a critical role in improving a cell's light-trapping efficiency. In this study, we developed n-type microcrystalline silicon oxide (n-μc-SiO_x) films that are suitable for use as back reflectors in thin-film silicon solar cells. They exhibit a lower refractive index and lower absorption spectra, especially at long wavelengths of >700 nm, than conventional ZnO:Al materials, which are beneficial for this application. The n-μc-SiO_x films were prepared by the PECVD (plasma-enhanced chemical vapor deposition) method and applied to the fabrication of back reflectors in μc-Si:H solar cells. We also characterized the changes in cell performance with respect to the refractive index, conductivity, and thickness of the n-μc-SiO_x back reflectors. The novel back reflector boosts the total current density by up to 3.0% with the help of the enhanced long-wavelength response. It also improves open circuit voltage (V_oc) and fill factor (FF), which may be attributed to the reduced shunt current caused by the anisotropic electrical characteristics of the n-μc-SiO_x layer. Finally, we could achieve a conversion efficiency for the hydrogenated microcrystalline silicon (μc-Si:H) solar cells of up to 9.3% (V_oc: 0.501 V, J_sc: 27.4 mA/cm², FF: 0.68) using the n-μc-SiO_x back reflector.     

Resonant transmission of terahertz waves through metallic slot antennas on various dielectric substrates

We report on terahertz electromagnetic field transmission through metallic slot antennas supported on various dielectric substrates. The substrate effect strongly modifies the transmission resonance compared to the free-standing case, while the resonance can be determined systematically by introducing an effective refractive index. The relative contribution of the substrate index to the effective index has been measured for various substrates, and shows a good agreement with theoretical calculations based on a coupled mode method. In addition, the slot antenna arrays embedded in a flexible substrate show a transmission resonance governed by a substrate refractive index.     

Reduction of surface defects on the GaP window layer of 630 nm AlGaInP LED using post-Zn diffusion process

We have investigated the characteristics of the surface of the GaP window layer of 630 nm AlGaInP LED, which was improved by post-Zn diffusion process. The measured resistance and the amount of hole concentration of the post-Zn-diffused GaP window layer have remarkably decreased and increased, respectively. Moreover, the ECV system showed that the amount of doping concentrations on the surface of the GaP window layer was significantly increased because of the diffusion of Zn atoms. The amount of surface defects observed on the post-Zn-diffused GaP window layer was also reduced. Furthermore, it was found out that the efficiency of 630 nm AlGaInP LED chip was increased due to the surface improvement of the GaP window layer. At an injection current of 40 mA, the LED chip with a Zn diffusion layer obtained a higher output power of 11 mW compared to the 7.5 mW output of the conventional LED chip.     

Spectroscopic characterization,photoinduced processes and cytotoxic properties of substituted N‐ethyl selenadiazoloquinolones

7‐R‐9‐ethyl‐6,9‐dihydro‐6‐oxo‐[1,2,5]selenadiazolo[3,4‐h]quinolines (R = H, COOC₂H₅, COOCH₃, COOH and COCH₃, E1h , E2h , E3h , E4h , E5h ) and 6‐ethyl‐6,9‐dihydro‐9‐oxo‐[1,2,5]selenadiazolo[3,4‐f]quinoline ( E1f ) were characterized by UV/vis, FT‐IR and fluorescence spectroscopy. The electronic absorption spectra of the derivatives E1h , E2h , E3h and E5h in the aprotic solvents dimethylsulfoxide (DMSO) and acetonitrile (ACN) reveal low‐energy absorption maxima with λ_max > 400 > nm, shifted hypsochromically in water. In DMSO, N‐ethyl selenadiazoloquinolones behave as strong fluorescent agents (λ_em ≥ 550 nm) with the exception of the carboxylic acid derivative E4h which shows only poor emission. Photoinduced reactions of N‐ethyl selenadiazoloquinolones were investigated by means of electron paramagnetic resonance (EPR) spectroscopy. Photoexcitation of N‐ethyl selenadiazoloquinolones in aerated DMSO with either 385 nm or 400 nm wavelengths, monitored by EPR spin trapping technique, results in the generation of superoxide radical anions; under an inert atmosphere, the generation of methyl radicals originating from the solvent predominates. Upon exposure at either 365 nm, 385 nm or 400 nm, aerated ACN solutions of selenadiazoloquinolones in the presence of sterically hindered amines produce nitroxide radicals via a reaction with photogenerated singlet oxygen. The 7‐substituted derivatives of 9‐ethyl‐6,9‐dihydro‐6‐oxo‐[1,2,5]selenadiazolo[3,4‐h]quinoline behave as photosensitizers activating molecular oxygen upon photoexcitation and possess the sufficient photochemical stability under the given experimental conditions. The cytotoxic effects of non‐photoactivated and UVA photoactivated N‐ethyl substituted selenadiazoloquinolones on cancer (human HeLa and murine L1210) and non‐cancer (NIH‐3T3) cell lines were monitored by the MTT test. The derivative E2h demonstrates the highest cytotoxic/photocytotoxic activity on the neoplastic cell lines. Copyright © 2013 John Wiley & Sons, Ltd.     

Moment inequalities for sums of random matrices and their applications in optimization

In this paper, we consider various moment inequalities for sums of random matrices—which are well-studied in the functional analysis and probability theory literature—and demonstrate how they can be used to obtain the best known performance guarantees for several problems in optimization. First, we show that the validity of a recent conjecture of Nemirovski is actually a direct consequence of the so-called non-commutative Khintchine’s inequality in functional analysis. Using this result, we show that an SDP-based algorithm of Nemirovski, which is developed for solving a class of quadratic optimization problems with orthogonality constraints, has a logarithmic approximation guarantee. This improves upon the polynomial approximation guarantee established earlier by Nemirovski. Furthermore, we obtain improved safe tractable approximations of a certain class of chance constrained linear matrix inequalities. Secondly, we consider a recent result of Delage and Ye on the so-called data-driven distributionally robust stochastic programming problem. One of the assumptions in the Delage–Ye result is that the underlying probability distribution has bounded support. However, using a suitable moment inequality, we show that the result in fact holds for a much larger class of probability distributions. Given the close connection between the behavior of sums of random matrices and the theoretical properties of various optimization problems, we expect that the moment inequalities discussed in this paper will find further applications in optimization.     

NHC-catalyzed oxidative cyclization reactions of 2-alkynylbenzaldehydes under aerobic conditions: synthesis of O-heterocycles

An NHC-catalyzed, regio- and stereoselective oxidative cyclization of o-alkynylbenzaldehydes bearing an unactivated alkyne moiety as an internal electrophile has been developed to afford phthalides and isocoumarins. A single organocatalytic system enabled two sequential C-O bond formations to take place in an atom economical manner via highly efficient dual activation. Molecular oxygen in air could be utilized as a source of an oxygen atom for the oxidation of aldehydes to the corresponding benzoic acids under our newly developed reagent system.     

Empty pseudo-triangles in point sets

We study empty pseudo-triangles in a set P of n points in the plane, where an empty pseudo-triangle has its vertices at the points of P, and no points of P lie inside. We give bounds on the minimum and maximum number of empty pseudo-triangles. If P lies inside a triangle whose corners must be the convex vertices of the pseudo-triangle, then there can be between Θ(n²) and Θ(n³) empty pseudo-triangles. If the convex vertices of the pseudo-triangle are also chosen from P, this number lies between Θ(n³) and Θ(n⁶). If we count only star-shaped pseudo-triangles, the bounds are Θ(n²) and Θ(n⁵). We also study optimization problems: minimizing or maximizing the perimeter or the area over all empty pseudo-triangles defined by P. If P lies inside a triangle whose corners must be used, we can solve these problems in O(n³) time. In the general case, the running times are O(n⁶) for the maximization problems and O(nlogn) for the minimization problems.