The Effect of Ketone Defects on the Charge Transport and Charge Recombination in Polyfluorenes

The effect of on‐chain ketone defects on the charge transport of the polyfluorene derivative poly(9,9‐dioctylfluorene) (PFO) is investigated. Using MoO₃ as ohmic hole contact, the hole transport in a pristine PFO diode is observed to be limited by space‐charge, whereas fluorenone contaminated PFO (PFO‐F) is shown to be trap limited by the occurrence of an exponential trap distribution with a trap depth of 0.18 eV. The electron transport in PFO is also observed to be trap limited, but in order to describe the electron transport of PFO‐F, an additional trap level with a depth of 0.46 eV must be introduced. The obtained energy levels of the fluorenone trapping sites are in close agreement with cyclic voltammetry (CV) measurements reported in literature. As a result, the fluorenone defects are shown to simultaneously act as hole‐ and electron trap. Moreover, through ideality factor measurements, the green emission associated with these defects is observed to originate from trap‐assisted recombination.     

An animal-as-client (AAC) theory for zoo exhibit design

The enthusiasm for the use of so-called native plants and the rejection of so-called exotic plants in 20th-century garden and landscape design is explored. The underlying ideas and ideology are discussed using examples in Germany, particularly from the time of National Socialism, and the United States.     

VLSI Implementation of Fuzzy Adaptive Resonance and Learning Vector Quantization

We present a mixed-mode VLSI chip performing unsupervised clustering and classification, implementing models of Fuzzy Adaptive Resonance Theory (ART) and Learning Vector Quantization (LVQ), and extending to variants such as Kohonen Self-Organizing Maps (SOM). The parallel processor classifies analog vectorial data into a digital code in a single clock, and implements on-line learning of the analog templates, stored locally and dynamically using the same adaptive circuits for on-chip quantization and refresh. The unit cell performing fuzzy choice and vigilance functions, adaptive resonance learning and long-term analog storage, measures 43 m×43 m in 1.2 m CMOS technology. Experimental learning results from a fabricated 8-input, 16-category prototype are included.     

High-velocity transport of nanoparticles through 1-D nanochannels at very large particle to channel diameter ratios

We explore the possibility of generating high-velocity flows of nanoparticles through flat-rectangular nanochannels, which are only 50% deeper than the diameter of the particles. Using the shear-driven flow principle, 200-nm particles can, for example, be transported through a 300-nm-deep channel at velocities up to 35 mm/s (upper limit of our current setup). Working under high-pH conditions, the velocity of the carboxylated nanoparticles still respects the small-molecule velocity law, despite the high degree of confinement to which the particles are subjected. The high degree of confinement is also found to lead to a reduced band broadening. When injecting sharply delimited particle plugs, the plate heights observed for the flow of 0.2-microm particles through a 0.3-microm channel (with plate heights of the order of 1-2 microm) are, for example, approximately 1 order of magnitude smaller than for the flow of 1.0-microm particles through a 1.4-microm channel. It is also found that the band broadening is, within its statistical variation, independent of the fluid velocity over a large range of particle velocities (5-35 mm/s). The flow method distinguishes itself from pressure-driven field-flow fractionation and hydrodynamic chromatography in that the mean particle velocity is independent of the particle size over the entire range of possible particle to channel diameter ratios.     

Importance and reduction of the sidewall-induced band-broadening effect in pressure-driven microfabricated columns

The influence of the detailed design of the sidewall region upon the over-all band-broadening in microfabricated packed-bed or collocated monolithic support structure (COMOSS) columns has been investigated using computational fluid dynamics (CFD) simulation techniques. It is shown that, under unretained solute conditions, very small structural variations of the order of only 5% of the particle diameter can give rise to a 4-fold increase of the band-broadening. A comprehensive study has been made to quantify this effect as a function of the fluid velocity, the particle diameter, the channel widths, and of course, the sidewall region design. Because the sidewall effect can be fully attributed to a mismatch between the flow rates in the column center and in the sidewall region, it is fortunately also quite straightforward to avoid it. A very simple design, yielding band-broadening values identical to that of a hypothetical sidewall-less column for all possible values of the flow velocity, the particle diameter, or the channel width is proposed.     

Stabilization of a chitinase from Serratia marcescens by Gly->Ala and Xxx->Pro mutations

This paper describes attempts to increase the kinetic stabilityof chitinase B from Serratia marcescens (ChiB) by the introductionof semi-automatically designed rigidifying mutations of theGlyAla and XxxPro type. Of 15 single mutants, several displayedsignificant increases in thermal stability, whereas most mutantsshowed minor effects. All mutations with non-marginal effectson stability clustered in a limited, surface-exposed regionof the enzyme, indicating that this region is involved in apartial unfolding process that triggers irreversible thermalinactivation (aggregation). A double mutant containing two stabilizingmutations in this region (G188A, A234P) displayed a 10-foldincrease in half-life at 57°C and a 4.2°C increase inapparent T_m. These results show that entropic stabilizationworks well for ChiB and they pinpoint a region whose unfoldingmay be crucial for the kinetic stability of this enzyme. Received June 18, 2003; revised September 3, 2003; accepted September 12, 2003.     

Using matrix peaks to map topography: increased mass resolution and enhanced sensitivity in chemical imaging

It is well known in secondary ion mass spectrometry (SIMS) that sample topography leads to decreased mass resolution. Specifically, the ion's time of flight is dependent on where it was generated. Here, using matrix-enhanced SIMS, it is demonstrated that, in addition to increasing the yield of intact pseudomolecular ions, the matrix allows the user to semiquantitatively record the topography of a sample. Through mapping the topography-related mass shifts of the matrix (which leads to decreased mass resolution), the analogous mass shifts of higher mass ions can be deconvoluted and higher resolution and greater sensitivity obtained. Furthermore, the semiquantitative topographical map obtained can be compared with any chemical images obtained, allowing the user to quickly ascertain whether local intensity maximums are due to topological features or represent genuine features of interest.     

Youth crowds and substance use: The impact of perceived group norm and multiple group identification.

The impact of group identity on adolescent tobacco, alcohol, and marijuana use was examined through a postal survey. The study included adolescents who identified with 1 subgroup (n = 1425) as well as adolescents who identified with 2 (n = 895) or 3 (n = 339) subgroups. The results showed that identification with the pop, skate/hip-hop, techno, and hippie subgroups was associated with higher risks of substance use, whereas identification with the sporty, quiet, computer nerd, and religious subgroups was associated with lower risks. Perceived group norm mediated the group identity-substance use relationship. Furthermore, identification with multiple groups with corresponding norm increased norm-consistent substance use, whereas identification with multiple groups with opposing norms reduced normative behavior. Implications for health promotion are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bubble chamber for fixed-target experiments at multi-TeV accelerators

A tentative layout for a huge argon bubble chamber/calorimeter/scintillation detector, to be used for neutrino experiments at a multi-TeV accelerator, is described. Such a detector can be operated in beams with various spill duration and it combines the features of a bubble chamber with properties of counter detectors.