cot1: a regulator of Arabidopsis trichome initiation

In Arabidopsis, the timing and spatial arrangement of trichome initiation is tightly regulated and requires the activity of the GLABROUS1 (GL1) gene. The COTYLEDON TRICHOME 1 (COT1) gene affects trichome initiation during late stages of leaf development and is described in this article. In the wild-type background, cot1 has no observable effect on trichome initiation. GL1 overexpression in wild-type plants leads to a modest number of ectopic trichomes and to a decrease in trichome number on the adaxial leaf surface. The cot1 mutation enhances GL1-overexpression-dependent ectopic trichome formation and also induces increased leaf trichome initiation. The expressivity of the cot1 phenotype is sensitive to cot1 and 35S::GL1 gene dosage, and the most severe phenotypes are observed when cot1 and 35S::GL1 are homozygous. The COT1 locus is located on chromosome 2 15.3 cM north of er. Analysis of the interaction between cot1, try, and 35S::GL1 suggests that COT1 is part of a complex signal transduction pathway that regulates GL1-dependent adoption of the trichome cell fate.     

Ion source brightness and nuclear microprobe applications

The ion source used to provide beams for nuclear microprobe systems must ideally satisfy several demands. Of primary importance is the beam brightness. It is clearly desirable to employ the brightest possible source in order to focus the smallest possible probe size on the specimen, with the highest possible beam current. Also important is the need for minimal maintenance, particularly for ion sources used inside single ended accelerators.

We report here on measurements conducted on the beam from the RF ion source in our 5U Pelletron accelerator. We have found that the beam brightness is highly heterogenous, with the paraxial rays about an order of magnitude brighter than the surrounding rays. This is desirable for nuclear microprobe operation because probe forming lens systems optimised for large demagnification magnitude can exploit the high brightness of the paraxial region. We find several other accelerators around the world also exhibit this characteristic.     

Experiments with simple neural networks for real-time control

We demonstrate the practical ability of neural networks (NNs) trained in a supervised mode to extract useful control “knowledge” from a large, high-dimensional empirical database, and then to deliver almost optimal control in “real time”. In particular, this paper describes experiments with NN-based controllers for allocating bandwidth capacity in a telecommunications network (SDH). This system was proposed in order to overcome a “real time” response constraint. Two basic architectures, each consisting of a combination of two methods, are evaluated: (1) a feedforward network-heuristic combination and (2) a feedforward network-recurrent network combination. These architectures are compared against a linear programming (LP) optimizer as a benchmark. This LP optimizer was also used as a teacher to label the data samples for the feedforward NN training algorithm. NN-based solutions are very accurate (~98% of optimal throughput) and, in contrast to the algorithmic approach, can be delivered in “real time”. It is found that while the “human” generated heuristics (greedy search optimization) fail to find a solution in approximately 30% of cases, the best NN fails only in 4.9% of cases. Moreover, it has been found that in spite of the very high dimensionality of the problem (55 inputs and 126 outputs), the solution can be delivered by surprisingly compact NNs, with as little as around 1000 synaptic weights. This proves that on this occasion the NNs were able to extract simple but powerful “heuristics” hidden in the complex sets of numerical data     

Signal-detection, threshold, and dual-process models of recognition memory: ROCs and conscious recollection

Threshold- and signal-detection-based models have dominated theorizing about recognition memory. Building upon these theoretical frameworks, we have argued for a dual-process model in which conscious recollection (a threshold process) and familiarity (a signal-detection process) contribute to memory performance. In the current paper we assessed several memory models by examining the effects of levels of processing and the number of presentations on recognition memory receiver operating characteristics (ROCs). In general, when the ROCs were plotted in probability space they exhibited an inverted U shape; however, when they were plotted in z space they exhibited a U shape. An examination of the ROCs showed that the dual-process model could account for the observed ROCs, but that models based solely on either threshold or signal-detection processes failed to provide a sufficient account of the data. Furthermore, an examination of subjects' introspective reports using the remember/know procedure showed that subjects were aware of recollection and familiarity and were able to consistently report on their occurrence. The remember/know data were used to accurately predict the shapes of the ROCs, and estimates of recollection and familiarity derived from the ROC data mirrored the subjective reports of these processes.     

Social loafing and self-evaluation with a social standard.

Social loafing has been described as the phenomenon in which participants who work together generate less effort than do participants who work alone (e.g., Latané, Williams, & Harkins, 1979). Subsequent research (Harkins & Jackson, 1985; Williams, Harkins, & Latané, 1981) has shown that a particular aspect of this paradigm leads to the loafing effect. In those studies, the evaluation potential of the experimenter has been emphasized. However, when the experimenter could not evaluate individual outputs, neither could the participants evaluate themselves. In this study we tested the possibility that the opportunity for the participants to evaluate themselves would be sufficient to eliminate the loafing effect. In 2 experiments, the evaluation potential of the experimenter (experimenter evaluation vs. no experimenter evaluation) was crossed with the potential for self-evaluation (self-evaluation vs. no self-evaluation). Consistent with previous loafing research, the potential for evaluation by the experimenter was sufficient to increase motivation, whether participants could self-evaluate or not. However, when the experimenter could not evaluate the participants' outputs, the potential for self-evaluation reliably improved participant performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recent applications of particle image velocimetry in aerodynamic research

Particle image velocimetry (PIV) is increasingly used to investigate unsteady velocity fields instantaneously. For the first time the PIV technique allows the recording of a complete velocity field in a plane of the flow within a few microseconds. The PIV technique thereby provides information about unsteady flow fields which is difficult to obtain with other experimental techniques. The short acquisition times and fast availability of data reduce the operational time, and hence cost, in large scale wind tunnels and test facilities.

At DLR a variety of PIV systems for use in industrial wind tunnels has been developed in the past decade. The flexibility of these portable systems is illustrated by presenting several results of recent PIV applications. More recently the original photographic means of PIV image recording has been partially replaced by high resolution electronic imaging which can provide PIV data nearly on-line. Images recorded by either system use the same multiple-pass, cross-correlation analysis software, whose algorithms are briefly described. Several examples of actual applications are given: the flow issuing from a jet nozzle was imaged by a specially developed high-speed video camera at close proximity. A high resolution dual-frame digital camera was applied in the study of helicopter rotor aerodynamics and wake vortex measurements of an airplane model. Further, large image sequences exceeding 100 PIV recordings provided detailed information on the structure of a turbulent boundary layer.