Copper influences the electrical and optical properties of zinc oxide to a high degree. Previously this has been explained within the frame of a model assuming Cu++ ions to be substitutional for divalent zinc. The observation of additional signals in the Electron Spin Resonance spectrum, however, proved this assumption to be wrong. Satisfying quantitative agreement with experiment is obtained assuming neutral copper atoms at an interstitial site having 3d9 4s2 electron configuration and a2D3/2 ground state. The infrared absorption bands as well as the spin lattice relaxation mechanism give further confirmation of Cu
i0
. 相似文献
Erstmals wurden, in einen intermetallischen Vorläuferansatz, durch In‐situ‐Elektrokonversion von Mangangallid (MnGa4) hochleistungsfähige und langzeitstabile MnOx‐basierte Elektrokatalysatoren für die Wasseroxidation in alkalischem Medium hergestellt. Überraschend führt seine Elektrokorrosion, unter gleichzeitigem Verlust von Ga, gleichzeitig zu drei kristallinen Typen von MnOx‐Mineralien mit verschiedenen Strukturen und induzierten Defekten: Birnessit δ‐MnO2, Feitknechtit β‐MnOOH und Hausmannit α‐Mn3O4. Das Vorkommen und die intrinsische Stabilität von aktiven MnIII/MnIV‐Zentren in den drei gebildeten MnOx‐Phasen erklärt die hervorragende Effizienz und Stabilität des Systems für die elektrokatalytische Wasseroxidation. Nach der elektrophoretischen Abscheidung des MnGa4‐Vorläufers auf elektrisch leitfähigem Nickelschaum wurde ein niedriges Überpotential von 291 mV bei der Stromdichte von 10 mA cm?2 erreicht, das praktisch den Überpotentialen von edelmetallbasierten Katalysatoren entspricht und für mehr als fünf Tage beständig ist. 相似文献
Fast methods for the extraction and analysis of various secondary metabolites from cocoa products were developed and optimized regarding speed and separation efficiency. Extraction by pressurized liquid extraction is automated and the extracts are analyzed by rapid reversed‐phase ultra high‐performance liquid chromatography and normal‐phase high‐performance liquid chromatography methods. After extraction, no further sample treatment is required before chromatographic analysis. The analytes comprise monomeric and oligomeric flavanols, flavonols, methylxanthins, N‐phenylpropenoyl amino acids, and phenolic acids. Polyphenols and N‐phenylpropenoyl amino acids are separated in a single run of 33 min, procyanidins are analyzed by normal‐phase high‐performance liquid chromatography within 16 min, and methylxanthins require only 6 min total run time. A fourth method is suitable for phenolic acids, but only protocatechuic acid was found in relevant quantities. The optimized methods were validated and applied to 27 dark chocolates, one milk chocolate, two cocoa powders and two food supplements based on cocoa extract. 相似文献
Microalgae are expected to play a significant role in greenhouse gas mitigation because they can utilize CO2 from power plant flue gases directly while producing a variety of renewable carbon-neutral biofuels. In order for such a
microalgal climate change mitigation strategy to become economically feasible, it will be necessary to significantly improve
biomass productivities. One approach to achieve this objective is to reduce, via mutagenesis, the number of light-harvesting
pigments, which, according to theory, should significantly improve the light utilization efficiency, primarily by increasing
the light intensity at which photosynthesis saturates (Is). Employing chemical (ethylmethylsulfonate) and UV mutagenesis of a wild-type strain of the diatom Cyclotella, approximately 10,000 pigment mutants were generated, and two of the most promising ones (CM1 and CM1-1) were subjected to
further testing in both laboratory cultures and outdoor ponds. Measurements of photosynthetic oxygen production rates as a
function of light intensity (i.e., P–I curves) of samples taken from laboratory batch cultures during the exponential and linear growth phase indicated that the
light intensity at which photosynthesis saturates (Is) was two to three times greater in the pigment mutant CM1-1 than in the wild type, i.e., 355–443 versus 116–169 μmol/m2 s, respectively. While theory, i.e., the Bush equation, predicts that such a significant gain in Is should increase light utilization efficiencies and thus biomass productivities, particularly at high light intensities, no
improvements in biomass productivities were observed in either semi-continuous laboratory cultures or outdoor ponds. In fact,
the maximum biomass productivity in semi-continuous laboratory culture was always greater in the wild type than in the mutant,
namely 883 versus 725 mg/L day, respectively, at low light intensity (200 μmol/m2 s) and 1,229 versus 1,043 mg/L day, respectively, at high light intensity (1,000 μmol/m2 s). Similarly, the biomass productivities measured in outdoor ponds were significantly lower for the mutant than for the
wild type. Given that these mutants have not been completely characterized in these initial studies, the exact reasons for
their poor performance are not known. Most likely, it is possible that the mutation procedure affected other photosynthetic
or metabolic processes. This hypothesis was partially validated by the observation that the pigment mutant had a longer lag
period following inoculation, a lower maximum specific growth rate, and poorer stability than the wild type. 相似文献
Functionalized nanodiamonds : Various functional groups have been incorporated into the structures of the naturally occurring diamondoids [1(2)3]tetramantane and [12312]hexamantane (cyclohexamantane), which represent hydrogen‐terminated prism‐shaped nanodiamonds (see picture). The attachment points define the use of these diamond‐like molecules as geometric building blocks for a variety of applications.
The synthesis and photophysical properties of several porphyrin (P)-phthalocyanine (Pc) conjugates (P-Pc; 1-3) are described, in which the phthalocyanines are directly linked to the β-pyrrolic position of a meso-tetraphenylporphyrin. Photoinduced energy- and electron-transfer processes were studied through the preparation of H(2)P-ZnPc, ZnP-ZnPc, and PdP-ZnPc conjugates, and their assembly through metal coordination with two different pyridylfulleropyrrolidines (4 and 5). The resulting electron-donor-acceptor hybrids, which were formed by axial coordination of compounds 4 and 5 with the corresponding phthalocyanines, mimicked the fundamental processes of photosynthesis; that is, light harvesting, the transduction of excited-state energy, and unidirectional electron transfer. In particular, photophysical studies confirmed that intramolecular energy-transfer resulted from the S(2) excited state as well as from the S(1) excited state of the porphyrins to the energetically lower-lying phthalocyanines, followed by an intramolecular charge-transfer to yield P-Pc(.+)?C(60)(.-). This unique sequence of processes opens the way for solar-energy-conversion processes. 相似文献
We developed a fused fiber coupler (FFC) capable of multiplexing wavelengths in the range of 795 nm and 2 μm. A simple 2D simulation model to calculate the pretaper length for matching the propagation constants in the coupling region was established. Based on the numerical data, we fabricated an asymmetric FFC consisting of two different fibers with single-mode guidance for the respective wavelength, achieving a transmission of 90% in the signal fiber for both wavelengths. In order to demonstrate the application, we integrated the FFC into a core pumped thulium-doped fiber amplifier. 相似文献
An all-fiber-integrated linear chirped-pulse amplifier system generating microjoule pulse energies is reported. It is seeded by an all-fiber dissipative-soliton laser and incorporates a newly developed fiber stretcher, whose dispersive properties match that of the grating compressor. Pulse durations of 189 fs with energies of 2.2 μJ were achieved after compression. The average power was 9.8 W at the repetition rate of 4.5 MHz. 相似文献
A study of bound states of the fourth-generation quarks in the range of 500?C700 GeV is presented, where the binding energies are expected to be mainly of Yukawa origin, with QCD subdominant. Near degeneracy of their masses exhibits a new ??isospin??. The production of a colour-octet, isosinglet vector meson via $q\bar q \to \omega_8$ is the most interesting. Its leading decay modes are $\pi_8^\pm W^\mp$, $\pi_8^0Z^0$, and constituent quark decay, with $q\bar q$ and $t\bar t'$ and $b\bar b'$ subdominant. The colour octet, isovector pseudoscalar ??8 meson decays via constituent quark decay, or to Wg. This work calls for more detailed study of fourth-generation phenomena at LHC. 相似文献
A novel method for mass measurements of short-lived exotic nuclides is presented. Exotic nuclides were produced and separated
in flight at relativistic energies with the fragment separator (FRS) and were injected into the experimental storage ring
(ESR). Operating the ESR in the isochronous mode we performed mass measurements of neutron deficient fragments of 84Kr with half-lives larger than 50 ms. However, this experimental technique is applicable in a half-life range down to a few
μs. A mass resolving power of 110000 (FWHM) has been achieved. Results are presented for the masses of 68As, 70,71Se and 73Br.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献