Highly ordered hexatic phases with large spontaneous polarization

In this article the physical properties of hexatic phases of three substances MHPNBC, FOOPP and FNHPP have been studied by differential scanning calorimetry, texture observation and dielectric spectroscopy. Experimental results are discussed from the point of view of existing theories. It is interesting that two of the substances studied, the FOOPP and FNHPP, exhibit enhanced spontaneous polarization in the highly ordered SmI* phase and show a jump of the spontaneous polarization in the vicinity of the SmC*–SmI* transition. In the SmI* phase of FOOPP a very high value of spontaneous polarization of the order of 530?nC?cm^?2 was found. Based on the results obtained the macroscopic and microscopic properties of the hexatic phases are discussed.     

Triple solutions for a nonlocal functional boundary value problem by leggett–williams theorem

The existence of triple solutions for a second-order nonlocal functional boundary value problem is proved by using a fixed-point theorem on cones in Banach spaces due to Leggett and Williams. The obtained results are new even in the ordinary case for three-point boundary value problems discussed quite recently in [Xiaoming He and Weigao Ge (2002). Triple solutions for second-order three-point boundary value problems. J. Math. Anal. Appl., 268, 256–265].     

Hydrophobic and antireflective characteristics of thermally oxidized periodic Si surface nanostructures

We reported the antireflective properties of periodic silicon (Si) subwavelength gratings and flat substrates in combination with thermal oxidation for an effective surface passivation. Moreover, theoretical calculations and analysis based on rigorous coupled-wave analysis simulation were performed. For thermally oxidized Si subwavelength grating structures, the reflectance was significantly reduced compared to that of the thermally oxidized flat Si substrates in wide ranges of wavelengths and angles of incidence. As the oxidation time increased, the reflectance became lower with increasing SiO _x thickness on Si subwavelength gratings due to the more graded effective refractive index profile from air to the Si via the thermally oxidized Si subwavelength gratings with increased height. By incorporating a thermal oxidation process into the Si subwavelength gratings, a more hydrophobic surface with good surface passivation was obtained.     

Enhanced surface plasmon resonance detection using porous ITO–gold hybrid substrates

We demonstrated enhanced surface plasmon resonance (SPR) detection by incorporating an indium tin oxide (ITO) layer on a thin gold film. Porous ITO layers were fabricated by e-beam evaporation and slanted deposition at room temperature and the ITO structure was optimized in terms of the surface roughness and the SPR curve characteristics. In sensing experiments, the results obtained by ethanol–water mixture test showed that SPR substrates with a porous ITO layer provided a notable sensitivity improvement compared to a conventional bare gold film, which is attributed to the nonlinear dispersion characteristic of surface plasmons. Our approach is intended to show the feasibility and extend the applicability of the porous ITO-mediated SPR biosensor to diverse biomolecular binding events.     

A note on Keldysh's perturbation formalism

The expansion theorem of quantum field theoy relating Heisenberg operators to asymptotic free-field operators is rewritten by means of the time-path technique, originally due to Schwinger, which to date has only found application in statistical mechanics. The theorem is combined with Bogoliubov's initial condition of vanishing correlations in the infinite past to rederive Keldysh's perturbation scheme for non-equilibrium statistical Green's functions.     

Ion equilibria in THF solutions of models of “living” methacrylonitrile oligomers with Li+ counterion

The electro-chemical characteristics of isobutyronitrile lithium (P₁Li) and 2-lithio-4-cyano-2,4-dimethylpentanenitrile (P₂Li) are studied. The dissociation constants K of P₁Li and P₂Li are of the order of 10^?11M and show that in THF mainly contact ion pairs exist. The lower value of K for P²Li is an indication for intramolecular complexation between the counterion and the cyano group, next to the active center. Both compounds tend to form ion triples. The results obtained show that in THF the nitrile group of the second monomer unit participates both in intra- and intermolecular interactions with the counterion.     

Feedback Grid Generation via Monotone Discretization for Two-point Boundary-Value Problems

We describe a uniformly enclosing discretization technique formildly nonlinear boundary-value problems. This method allowsus to derive a grid generation principle, using the distancebetween the lower and upper solutions to control the grid-generationprocedure. The convergence of the proposed feedback gridgenerationmethod is proved.     

Analyse multielementaire instrumentale des phosphates marocains par photoactivation nucleaire

Photonuclear activation and high resolution gamma-ray spectrometry have been used to determine non-destructively the concentrations of 25 trace elements in Maroccan phosphate rock. The activation was simultaneously performed for phosphate samples and multielement standards in the bremsstrahlung beam of a linear electron accelerator at 18 and 30 MeV maximum energies. Gamma-ray spectra were recorded with a 79 cm³ Ge(Li) detector and a programmable analyzer IN 96. A detailed study of interferences was carried out. Limits of detection between 0.5 and 125 μg·g^?1 were obtained.     

White light emission from nano-fibrous ZnO thin films/porous silicon nanocomposite

Nanocomposites composed of nano-fibrous ZnO thin films and porous silicon (PS) were prepared and examined by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) to investigate their structural and optical properties. PS, consisting of irregular and random nanosized-pores, was prepared by electrochemical anodization. The nano-fibrous ZnO thin films were grown on PS by the sol-gel spin-coating method. The texture coefficient (TC _(hkl)) of the nano-fibrous ZnO thin films was calculated to determine the preferred orientation. The nano-fibrous ZnO thin films were grown with a c-axis preferred orientation. The residual stress in the films was reduced in the case of PS. The observed broad PL emission peak from 460 to 598 nm was attributed to coupled emission from ZnO to PS. The results show that white light luminescence with blue, green, and red emission peaks having highly uniform intensities can be obtained from the nanocomposite via a relatively simple and low-cost sol-gel spin-coating method.     

Optimum design of InGaP/GaAs dual-junction solar cells with different tunnel diodes

We design the InGaP/GaAs dual-junction (DJ) solar cells by optimizing short-circuit current matching between top and bottom cells using the Silvaco ATLAS. The relatively thicker base layer of top cell exhibits a larger short-circuit current density (J _sc) while the thicker base layer of bottom cell allows for a smaller J _sc. The matched J _sc of 10.61±0.05 and 13.25±0.06 mA/cm ² under AM1.5G and AM0 illuminations, respectively, are obtained, leading to the increased conversion efficiency. The base thicknesses of top InGaP cells are optimized at 0.8 and 0.65 μm for AM1.5G and AM0 illuminations, respectively, and the base thicknesses of bottom GaAs cells are optimized at 2 μm. For the optimized solar cell structure, the maximum J _sc = 10.66 mA/cm ² (13.31 mA/cm ²), V _oc =  2.34 V (2.35 V), and fill factor =  87.84% (88.1%) are obtained under AM1.5G (AM0) illumination, exhibiting a maximum conversion efficiency of 25.78% (23.96%). The effect of tunnel diode structure, i.e, GaAs/GaAs, AlGaAs/AlGaAs, and InGaP/InGaP, on the characteristics of solar cells is investigated. The photogeneration rate in the DJ solar cell structure is also obtained by incident light of different wavelengths.