The early bee catches the flower - circadian rhythmicity influences learning performance in honey bees, Apis mellifera

Circadian rhythmicity plays an important role for many aspects of honey bees’ lives. However, the question whether it also affects learning and memory remained unanswered. To address this question, we studied the effect of circadian timing on olfactory learning and memory in honey bees Apis mellifera using the olfactory conditioning of the proboscis extension reflex paradigm. Bees were differentially conditioned to odours and tested for their odour learning at four different “Zeitgeber” time points. We show that learning behaviour is influenced by circadian timing. Honey bees perform best in the morning compared to the other times of day. Additionally, we found influences of the light condition bees were trained at on the olfactory learning. This circadian-mediated learning is independent from feeding times bees were entrained to, indicating an inherited and not acquired mechanism. We hypothesise that a co-evolutionary mechanism between the honey bee as a pollinator and plants might be the driving force for the evolution of the time-dependent learning abilities of bees

A Fear-Inducing Odor Alters PER2 and c-Fos Expression in Brain Regions Involved in Fear Memory

Evidence demonstrates that rodents learn to associate a foot shock with time of day, indicating the formation of a fear related time-stamp memory, even in the absence of a functioning SCN. In addition, mice acquire and retain fear memory better during the early day compared to the early night. This type of memory may be regulated by circadian pacemakers outside of the SCN. As a first step in testing the hypothesis that clock genes are involved in the formation of a time-stamp fear memory, we exposed one group of mice to fox feces derived odor (TMT) at ZT 0 and one group at ZT 12 for 4 successive days. A separate group with no exposure to TMT was also included as a control. Animals were sacrificed one day after the last exposure to TMT, and PER2 and c-Fos protein were quantified in the SCN, amygdala, hippocampus, and piriform cortex. Exposure to TMT had a strong effect at ZT 0, decreasing PER2 expression at this time point in most regions except the SCN, and reversing the normal rhythm of PER2 expression in the amygdala and piriform cortex. These changes were accompanied by increased c-Fos expression at ZT0. In contrast, exposure to TMT at ZT 12 abolished the rhythm of PER2 expression in the amygdala. In addition, increased c-Fos expression at ZT 12 was only detected in the central nucleus of the amygdala in the TMT12 group. TMT exposure at either time point did not affect PER2 or c-Fos in the SCN, indicating that under a light-dark cycle, the SCN rhythm is stable in the presence of repeated exposure to a fear-inducing stimulus. Taken together, these results indicate that entrainment to a fear-inducing stimulus leads to changes in PER2 and c-Fos expression that are detected 24 hours following the last exposure to TMT, indicating entrainment of endogenous oscillators in these regions. The observed effects on PER2 expression and c-Fos were stronger during the early day than during the early night, possibly to prepare appropriate systems at ZT 0 to respond to a fear-inducing stimulus

Special Issue: Papers presented at EuroResidue VI 2008 Preface

We have investigated the structural and defect characteristics of GaAs and Al xGa 1-xAs grown at low substrate temperature (250°C) by molecular beam epitaxy. Using x-ray diffraction we have observed an increase in lattice parameter for all as-grown layers, with the Al xGa 1-xAs layers showing a smaller expansion than the GaAs layer. However, infrared absorbtion measurements revealed that the concentration of neutral arsenic antisite defect, [As Ga] 0, was not significantly affected by aluminum content (x), with only a small reduction for x=0.36. Positron beam studies showed that the low temperature layers had a higher concentration of vacancy-related defects (∼10 17 cm -3) than the semi-insulating substrate, with the Al xGa 1-xAs layers having the highest values. After annealing (600°C, 15 min) the lattice constants relaxed to those of conventionally grown material and [As Ga] 0 was reduced in all cases, with the smallest reduction occurring for the x=0.36 layer, indicating that the Al atoms strengthen the lattice against excess arsenic incorporation and hold the arsenic antisite atoms more strongly in position. X-ray photoelectron spectroscopy showed that arsenic diffused out of the surface region and was replaced by oxygen, possibly due to an insufficient overpressure of forming gas during the anneal. This oxygen penetration was greater for the GaAs layer than for the Al xGa 1-xAs layers. Extra Raman peaks at 200 and 257 cm -1 confirmed that the surface was very disordered. There was, nevertheless, a large increase (4%) in the positron S parameter in the bulk of the annealed layers, suggesting the formation of vacancy clusters, whereas in the surface region we find evidence that As Ga diffusion proceeded at a faster rate in the x=0.36 than the x=0.2, in agreement with the vacancy-enhanced As Ga diffusion model. © 1997 American Institute of Physics.published_or_final_versio

Hochratige optische Empfänger für 80/160 Gbit/s: MultiTeraNet, Projekt HIGHREC, Abschlußbericht. Laufzeit: 1. Oktober 2002 - 30. September 2005

Die Weiterentwicklung von wellenleiter-integrierten Photodetektoren für Bitraten von 80/100 Gbit/s und höher und die Steigerung der Bandbreite der Photoempfänger bei 160 Gbit/s unter Anwendung des monolithischen Integrationskonzepts einer wellenleiter-integrierten Photodiode mit einem elektrischen Wanderwellenverstärker auf InP-Basis im optischen Langwellenbereich um 1,55 Mikrometer stehen hier im Mittelpunkt der Betrachtungen. Dabei wird auch eine Weiterentwicklung der Modultechnik für 80 Gbit/s und höher und durch die Anwendung einer Chip-Board- Verbindungstechnologie in Form der Flip-Chip-Bond-Technik für Datenraten im 160 Gbit/s-Bereich vorgenommen. Unter Beibehaltung des pinTWA- Integrationskonzepts werden die vertikalen Schichtenfolgen der Bauelemente (Photodiode und HEMT) und auch deren laterale Designs optimiert. Für die höhere Bitratenstufe wird die Photodiode in einer micro-pin-Photodiodenform und die Wanderwellendetektorform innerhalb des Integrationskonzepts weiterentwickelt (Bandbreiten um 120 GHz) und mit einem optimierten Wanderwellenverstärker monolithisch integriert. Als Ergebnisse werden unter anderem ein Integrationskonzept für einen 160- Gbit/s-Empfänger und ein Technologiedemonstrator dafür beschrieben. Hervorzuheben ist die erzielte direkte optisch-elektrische Konversion für die Datenrate von 160 Gbit/s

Highly efficient InP-based narrowband photodetectors for 40 to 85 GHz linear high power applications

The fabrication and characterization of InP-based narrowband photodetector OEICs and modules, covering the frequency range 38-90 GHz, is reported. The reverse bias tuneable detectors exhibit 0.55A/W peak responsivities at 80 GHz, equal to the DC value

Organisation des OEPNV im Grossraum Braunschweig Schlussbericht. Gefoerdert mit Forschungsmitteln des Landes Niedersachsen

SIGLEDEGerman