An efficient Schottky-varactor frequency multiplier at millimeter waves. Part IV. Quintupler

The multiplication efficiency of a millimeter-wave Schottky-varactor quintupler with fixed idler terminations was studied. The highest efficiency measured was 4.2% at 168 GHz with 10 mW input power and 3.3% with 40 mW input power. Over the range from 165 GHz to 170 GHz the output power was 0.7–1.3 mW withp _in =40 mW.     

First direct kinetic measurement of i-C4H5 (CH2CHCCH2) + O2 reaction: Toward quantitative understanding of aromatic ring formation chemistry

The kinetics of the i-C₄H₅ (buta-1,3-dien-2-yl) radical reaction with molecular oxygen has been measured over a wide temperature range (275–852 K) at low pressures (0.8–3 Torr) in direct, time-resolved experiments. The measurements were performed using a laminar flow reactor coupled to photoionization mass spectrometer (PIMS), and laser photolysis of either chloroprene (2-chlorobuta-1,3-diene) or isoprene was used to produce the resonantly stabilized i-C₄H₅ radical. Under the experimental conditions, the measured bimolecular rate coefficient of i-C₄H₅ + O₂ reaction is independent of bath gas density and exhibits weak, negative temperature dependency, and can be described by the expression k₃ = (1.45 ± 0.05) × 10^?12 × (T/298 K)^{?(0.13±0.05)} cm³ s^?1. The measured bimolecular rate coefficient is surprisingly fast for a resonantly stabilized radical. Under combustion conditions, the reactions of i-C₄H₅ radical with ethylene and acetylene are believed to play an important role in forming the first aromatic ring. However, the current measurements show that i-C₄H₅ + O₂ reaction is significantly faster under combustion conditions than previous estimations suggest and, consequently, inhibits the soot forming propensity of i-C₄H₅ radicals. The bimolecular rate coefficient estimates used for the i-C₄H₅ + O₂ reaction in recent combustion simulations show significant variation and are up to two orders of magnitude slower than the current, measured value. All estimates, in contrast to our measurements, predict a positive temperature dependency. The observed products for the i-C₄H₅ + O₂ reaction were formaldehyde and ketene. This is in agreement with the one theoretical study available for i-C₄H₅ + O₂ reaction, which predicts the main bimolecular product channels to be H₂CO + C₂H₃ + CO and H₂CCO + CH₂CHO.     

Nanotextured multicrystalline Al‐BSF solar cells reaching 18% conversion efficiency using industrially viable solar cell processes

We report recent achievements in adapting industrially used solar cell processes on nanotextured surfaces. Nanostructures were etched into c‐Si surfaces by dry exothermic plasma‐less reaction of F species with Si in atmospheric pressure conditions and then modified using a short post‐etching process. Nanotextured multicrystalline wafers are used to prepare Al‐BSF solar cells using industrially feasible solar cell proc‐ essing steps. In comparison to the reference acidic textured solar cells, the nanostructured cells showed gain in short circuit current (J_sc) of up to 0.8 mA/cm² and absolute gain in conversion efficiency of up to 0.3%. The best nanotextured solar cell was independently certified to reach the conversion efficiency of 18.0%. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A duality theorem for Tate–Shafarevich groups of curves over algebraically closed fields

In this note, we prove a duality theorem for the Tate–Shafarevich group of a finite discrete Galois module over the function field K of a curve over an algebraically closed field: there is a perfect duality of finite groups Open image in new window for F a finite étale Galois module on K of order invertible in K and with \(F' = {{\mathrm{Hom}}}(F,\mathbf{Q}/\mathbf {Z}(1))\). Furthermore, we prove that \(\mathrm {H}^1(K,G) = 0\) for G a simply connected, quasisplit semisimple group over K not of type \(E_8\).     

Optical aperture area determination for accurate illuminance and luminous efficacy measurements of LED lamps

The measurement uncertainty of illuminance and, consequently, luminous flux and luminous efficacy of LED lamps can be reduced with a recently introduced method based on the predictable quantum efficient detector (PQED). One of the most critical factors affecting the measurement uncertainty with the PQED method is the determination of the aperture area. This paper describes an upgrade to an optical method for direct determination of aperture area where superposition of equally spaced Gaussian laser beams is used to form a uniform irradiance distribution. In practice, this is accomplished by scanning the aperture in front of an intensity-stabilized laser beam. In the upgraded method, the aperture is attached to the PQED and the whole package is transversely scanned relative to the laser beam. This has the benefit of having identical geometry in the laser scanning of the aperture area and in the actual photometric measurement. Further, the aperture and detector assembly does not have to be dismantled for the aperture calibration. However, due to small acceptance angle of the PQED, differences between the diffraction effects of an overfilling plane wave and of a combination of Gaussian laser beams at the circular aperture need to be taken into account. A numerical calculation method for studying these effects is discussed in this paper. The calculation utilizes the Rayleigh–Sommerfeld diffraction integral, which is applied to the geometry of the PQED and the aperture. Calculation results for various aperture diameters and two different aperture-to-detector distances are presented.     

Selective dispersion of single-walled carbon nanotubes with specific chiral indices by poly(N-decyl-2,7-carbazole)

Physico-chemical methods to sort single-walled carbon nanotubes (SWNTs) by chiral index are presently lacking but are required for in-depth experimental analysis and also for potential future applications of specific species. Here we report the unexpected selectivity of poly(N-decyl-2,7-carbazole) to almost exclusively disperse semiconducting SWNTs with differences of their chiral indices (n - m) ≥ 2 in toluene. The observed selectivity complements perfectly the dispersing features of the fluorene analogue poly(9,9-dialkyl-2,7-fluorene), which disperses semiconducting SWNTs with (n - m) ≤ 2 in toluene. The dispersed samples are further purified by density gradient centrifugation and analyzed by photoluminescence excitation spectroscopy. All-atom molecular modeling with decamer model compounds of the polymers and (10,2) and (7,6) SWNTs suggests differences in the π-π stacking interaction as origin of the selectivity. We observe energetically favored complexes between the (10,2) SWNT and the carbazole decamer and between the (7,6) SWNT and the fluorene decamer, respectively. These findings demonstrate that subtle structural changes of polymers lead to selective solvation of different families of carbon nanotubes. Furthermore, chemical screening of closely related polymers may pave the way toward simple, low-cost, and index-specific isolation of SWNTs.     

Versatile wet-chemical synthesis of non-agglomerated CaCO3 vaterite nanoparticles

Calcium carbonate (vaterite) nanoparticles of 20-60 nm size were obtained without stabilizing tensides by heating a dispersion of calcium bicarbonate (CaHCO(3)) in ethylene glycol for 30 minutes at 40 to 100 °C.