Photosystem I (PSI)/Photosystem II (PSII)‐Based Photo‐Bioelectrochemical Cells Revealing Directional Generation of Photocurrents

Layered assemblies of photosystem I, PSI, and/or photosystem II, PSII, on ITO electrodes are constructed using a layer‐by‐layer deposition process, where poly N,N′‐dibenzyl‐4,4′‐bipyridinium (poly‐benzyl viologen, PBV²⁺) is used as an inter‐protein “glue”. While the layered assembly of PSI generates an anodic photocurrent only in the presence of a sacrificial electron donor system, such as dichlorophenol indophenol (DCPIP)/ascorbate, the PSII‐modified electrode leads, upon irradiation, to the formation of an anodic photocurrent (while evolving oxygen), in the absence of any sacrificial component. The photocurrent is generated by transferring the electrons from the PSII units to the PBV²⁺ redox polymer. The charge‐separated species allow, then, the injection of the electrons to the electrode, with the concomitant evolution of O₂. A layered assembly, consisting of a PSI layer attached to a layer of PSII by the redox polymer PBV²⁺, leads to an anodic photocurrent that is 2‐fold higher, as compared to the anodic photocurrent generated by a PSII‐modified electrode. This observation is attributed to an enhanced charge separation in the two‐photosystem assembly. By the further nano‐engineering of the two photosystems on the electrode using two different redox polymers, vectorial electron transfer to the electrode is demonstrated, resulting in a ca. 6‐fold enhancement in the photocurrent. The reversed bi‐layer assembly, consisting of a PSII layer linked to a layer of PSI by the PBV²⁺ redox polymer, yields, upon irradiation, an inefficient cathodic current. This observation is attributed to a mixture of photoinduced electron transfer reactions of opposing effects on the photocurrent directions in the two‐photosystem assembly.     

AFM characterization of the structure of Au-colloid monolayers and their chemical etching

Modification of a glass support with triethoxy propylaminosilane yields an active interface for the assembly of Au colloids. The colloids are imaged by AFM using a low applied load (0.5–0.7 nN). The lateral Au-colloid dimensions, 33±3 nm, deviate from the particle dimensions determined by TEM (19±2 nm) and absorption spectroscopy (15 nm). This deviation is attributed to the intrinsic curvature of the AFM tip. Application of higher loads on the tip (3 nN) results in the sweeping of Au colloids from the monolayer. The Au colloid monolayer is etched in the presence of CN⁻. The etching proceeds by the initial coincidental etching of Au particles followed by the kinetically favored etching of particles at the edges of the etched domains. This provides means for the micro machining and the chemical manipulation of Au colloids of controlled spatial arrangement.     

Optical switching speed requirements for terabit/second packet overWDM networks

Optical dynamics requirement for packet-over-WDM networks is analyzed. Optimization among optical switching speed, global resource availability, and local queuing considerations is performed, yielding multiterabit/second throughput capability by employing submicrosecond switching technology     

Differential weighting of common and distinctive components.

We investigated possible explanations of the finding that the relative weight (W) of common components in similarity judgments is higher for verbal than for pictorial stimuli. A serial presentation of stimulus components had no effect on verbal stimuli; it increased the impact of both common and distinctive components of pictorial stimuli but did not affect their relative weight. On the other hand, W was increased by manipulations that reduced the cohesiveness of composite pictures, such as separating, scrambling, and mixing their components. Furthermore, W was decreased by manipulations that enhanced the cohesiveness of composite verbal stimuli by imposing structure on their components. Verbal and pictorial representations of the same stimuli yielded no systematic differences in W. (PsycINFO Database Record (c) 2010 APA, all rights reserved)