Titanium-assisted growth of silica nanowires: from surface-matched to free-standing morphologies

We report on an oxide-assisted growth technique for silica nanowires which allows tuning the growth from surface-matched nanowires to free-standing morphologies based on growth control by Ti in the role of a catalyst and surfactant. Using an adjustable Ti concentration, we grew silica nanowires with lengths ranging from 100 nm up to several millimetres whose defect chemistry was analysed by electron microscopy tools, monochromatic cathodoluminescence imaging and time resolved photoluminescence spectroscopy. The knowledge of the luminescence properties and the related defect occurrence along with their spatial distribution is pivotal for advancing silica nanowire growth in order to realize successful device designs based on self-assembled Si/SiO(x) nanostructures. We demonstrate a core-shell structure of the grown nanowires with a highly luminescent 150 nm thick shell and outstandingly fast decaying dynamics (≈1 ns) for glass-like materials. The conjunction of the observed efficient and stable luminescences with their attributed decaying behaviours suggests applications for silica nanowires such as active and passive optical interconnectors and white light phosphors. The identification of a time domain difference for the spectral regime from 2.3 to 3.3 eV, within the confined spatial dimensions of a single nanowire, is very promising for future, e.g. data transmission applications, employing silica nanowires which exhibit achievable compatibility with commonly applied silicon-based electronics. A qualitative growth model based on silica particle diffusion and Ti-assisted seed formation is developed for the various types of segregated silica nanowires which extends commonly assumed oxide-assisted growth mechanisms.     

Fin-line PIN-diode attenuators and switches for 94 GHz range

The letter reports new results of fin-line PIN-diode attenuators and switches for the 94 GHz range. Design and performance of SPST and SPDT switches?single-pole single-throw and single-pole double-throw, respectively?will be presented. The attenuation of the SPST switch, for example, can be adjusted between 2 and 35 dB over the entire waveguide band from 75 to 110 GHz.     

p-i-n diode control devices in E-plane technique

The status of the use of p-i-n diode control devices in the E -plane technique, especially in integrated finline configurations, is reviewed. The circuit topologies, operating principles, and design considerations for state-of-the-art switches, attenuators, and digital modulators are discussed, and typical performance characteristics are presented. The superior performance of these components confirms that finline is the appropriate transmission medium for the realization of millimeter-wave p-i-n diode switches and attenuators in the low-power regime (up to some 10 W of CW power), where beam-lead diode devices can be used. By properly matching these devices to their finline embedding network, excellent broadband characteristics can be achieved     

Fermi Level Control of Point Defects During Growth of Mg-Doped GaN

In this study, Fermi level control of point defects during metalorganic chemical vapor deposition (MOCVD) of Mg-doped GaN has been demonstrated by above-bandgap illumination. Resistivity and photoluminescence (PL) measurements are used to investigate the Mg dopant activation of samples with Mg concentration of 2 × 10¹⁹ cm^?3 grown with and without exposure to ultraviolet (UV) illumination. Samples grown under UV illumination have five orders of magnitude lower resistivity values compared with typical unannealed GaN:Mg samples. The PL spectra of samples grown with UV exposure are similar to the spectra of those grown without UV exposure that were subsequently annealed, indicating a different incorporation of compensating defects during growth. Based on PL and resistivity measurements we show that Fermi level control of point defects during growth of III-nitrides is feasible.     

Quasiplanar 3 dB hybrid for millimetre-wave integrated circuits

A quasiplanar 3 dB hybrid suitable for integration in millimetre-wave fin-line circuits is presented. The performance of the device is characterised by 0.5 dB insertion loss, less than 0.5 dB imbalance and 20?25 dB isolation over the entire Ka-band (26.5?40 GHz).     

Assessment of compatibilization role of nanoclay in immiscible polystyrene/ethylene–octene copolymer blends via wide-angle X-ray scattering,microstructure, rheological analyses,and mechanical properties

Polystyrene (PS)/ethylene–octene copolymer (EOC) blends with 80/20 wt % composition containing different amounts (0, 1.0, 2.5, 5.0 and 7.5 wt %) of an organically modified nanoclay were prepared by one-step melt-mixing method. Also, the EOC-rich blends with 80 wt % EOC content loaded with 0 and 5.0 wt % of the nanoclay were prepared under the similar processing conditions. Presence of both PS and EOC chains in between clay layers localized at the interface of the blends could be deduced by X-ray diffraction analysis, which suggested formation possibility of PS-EOC physical structures at the blend interface. Transmission electron microscopy results confirmed that clay nanoparticles were mainly localized at the interface of the blends and also partly in the PS and EOC components of the systems. The localization of the nanoclay was also described by the linear viscoelastic melt rheological studies. It is also revealed that nanoclay had stronger interactions with PS than EOC. This is reflected in the higher tensile properties in the PS-rich system. The analysis of morphology of the developed systems by emulsification curve revealed that the optimum amount of nanoclay to modify PS-rich blend is 2.5 wt %. At this clay loading, the blend exhibited the highest impact resistance. According to the overall results, suitability of nanoclay was confirmed for compatibilization of the PS/EOC blends. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48748.     

Open Heterogeneous Computing in Actorspace

A number of efforts in heterogeneous computing involve the development of basic architecture independent communication primitives. We present a new programming paradigm, called ActorSpace, which provides a new communication model based on destination patterns. An actorspace is a computationally passive container of actors which acts as a context for matching patterns. Patterns are matched against listed attributes of actors and actorspaces that are visible in the actorspace. Both visibility and attributes are dynamic. Messages may be sent to one or all members of a group defined by a pattern. The paradigm provides powerful support for component-based construction of heterogeneous scalable distributed applications. In particular, it supports open interfaces to servers and pattern-directed access to software repositories.     

NF-kappaB and AP-1 activation by nitric oxide attenuated apoptotic cell death in RAW 264.7 macrophages

A toxic dose of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO; 1 mM) promoted apoptotic cell death of RAW 264.7 macrophages, which was attenuated by cellular preactivation with a nontoxic dose of GSNO (200 microM) or with lipopolysaccharide, interferon-gamma, and NG-monomethyl-L-arginine (LPS/IFN-gamma/NMMA) for 15 h. Protection from apoptosis was achieved by expression of cyclooxygenase-2 (Cox-2). Here we investigated the underlying mechanisms leading to Cox-2 expression. LPS/IFN-gamma/NMMA prestimulation activated nuclear factor (NF)-kappaB and promoted Cox-2 expression. Cox-2 induction by low-dose GSNO demanded activation of both NF-kappaB and activator protein-1 (AP-1). NF-kappaB supershift analysis implied an active p50/p65 heterodimer, and a luciferase reporter construct, containing four copies of the NF-kappaB site derived from the murine Cox-2 promoter, confirmed NF-kappaB activation after NO addition. An NF-kappaB decoy approach abrogated not only Cox-2 expression after low-dose NO or after LPS/IFN-gamma/NMMA but also inducible protection. The importance of AP-1 for Cox-2 expression and cell protection by low-level NO was substantiated by using the extracellular signal-regulated kinase inhibitor PD98059, blocking NO-elicited Cox-2 expression, but leaving the cytokine signal unaltered. Transient transfection of a dominant-negative c-Jun mutant further attenuated Cox-2 expression by low-level NO. Whereas cytokine-mediated Cox-2 induction relies on NF-kappaB activation, a low-level NO-elicited Cox-2 response required activation of both NF-kappaB and AP-1.