167 research outputs found
Self-Organisation of Neural Topologies by Evolutionary Reinforcement Learning
In this article we present EANT, "Evolutionary Acquisition of Neural Topologies", a method that creates neural networks (NNs) by evolutionary reinforcement learning. The structure of NNs is developed using mutation operators, starting from a minimal structure. Their parameters are optimised using CMA-ES. EANT can create NNs that are very specialised; they achieve a very good performance while being relatively small. This can be seen in experiments where our method competes with a different one, called NEAT, "NeuroEvolution of Augmenting Topologies", to create networks that control a robot in a visual serving scenario
What drives stocks during the Corona-crash? News attention vs. rational expectation
We explore if the corona-crash 2020 was driven by news attention or rational expectations about the pandemicâs economic impact. Using a sample of 64 national stock markets covering 94% of the worldâs GDP, we find the stock marketsâ decline to be mainly associated with higher news attention and less with rational expectation. We estimate the economic cost from the news hype to amount to USD 3.5 trillion for the US and USD 200 billion on average for the rest of the G8 countries
Untersuchung von Helikonwellen zur Plasmaheizung im Torsatron TJ-K
Helikonwellen eignen sich zur Erzeugung von magnetisierten Plasmen hoher Dichte. Die Arbeit stellt die technischen Details, die mit der Heizung des Plasmas verbunden sind, dar. Die physikalischen Aspekte der Wellenpropagation der Helikonwelle werden in toroidaler Geometrie hergeleitet und experimentell im Torsatron TJ-K untersucht. Die Welle wird dabei als geschlossener Wellenzug im toroidalen Umlauf interpretiert. Ergebnisse der Messungen sind Daten zur Dispersionsrelation, zum Wellenfeld und zu den erreichten Plasmaparametern. Der theoretische Verlauf der Dispersionsrelation ist dabei in sehr guter Ăbereinstimmung mit den experimentellen Ergebnissen
Atomistic Insight into the Role of Threonine 127 in the Functional Mechanism of Channelrhodopsin-2
Channelrhodopsins (ChRs) belong to the unique class of light-gated ion channels. The structure of channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2) has been resolved, but the mechanistic link between light-induced isomerization of the chromophore retinal and channel gating remains elusive. Replacements of residues C128 and D156 (DC gate) resulted in drastic effects in channel closure. T127 is localized close to the retinal Schiff base and links the DC gate to the Schiff base. The homologous residue in bacteriorhodopsin (T89) has been shown to be crucial for the visible absorption maximum and darkâlight adaptation, suggesting an interaction with the retinylidene chromophore, but the replacement had little effect on photocycle kinetics and proton pumping activity. Here, we show that the T127A and T127S variants of CrChR2 leave the visible absorption maximum unaffected. We inferred from hybrid quantum mechanics/molecular mechanics (QM/MM) calculations and resonance Raman spectroscopy that the hydroxylic side chain of T127 is hydrogen-bonded to E123 and the latter is hydrogen-bonded to the retinal Schiff base. The C=NâH vibration of the Schiff base in the T127A variant was 1674 cmâ1, the highest among all rhodopsins reported to date. We also found heterogeneity in the Schiff base ground state vibrational properties due to different rotamer conformations of E123. The photoreaction of T127A is characterized by a long-lived P2380 state during which the Schiff base is deprotonated. The conservative replacement of T127S hardly affected the photocycle kinetics. Thus, we inferred that the hydroxyl group at position 127 is part of the proton transfer pathway from D156 to the Schiff base during rise of the P3530 intermediate. This finding provides molecular reasons for the evolutionary conservation of the chemically homologous residues threonine, serine, and cysteine at this position in all channelrhodopsins known so far
Plastid located WHIRLY1 enhances the responsiveness of Arabidopsis seedlings toward abscisic acid
WHIRLY1 is a protein that can be translocated from the plastids to the nucleus, making it an ideal candidate for communicating information between these two compartments. Mutants of Arabidopsis thaliana lacking WHIRLY1 (why1) were shown to have a reduced sensitivity toward salicylic acid (SA) and abscisic acid (ABA) during germination. Germination assays in the presence of abamine, an inhibitor of ABA biosynthesis, revealed that the effect of SA on germination was in fact caused by a concomitant stimulation of ABA biosynthesis. In order to distinguish whether the plastid or the nuclear isoform of WHIRLY1 is adjusting the responsiveness toward ABA, sequences encoding either the complete WHIRLY1 protein or a truncated form lacking the plastid transit peptide were overexpressed in the why1 mutant background. In plants overexpressing the full-length sequence, WHIRLY1 accumulated in both plastids and the nucleus, whereas in plants overexpressing the truncated sequence, WHIRLY1 accumulated exclusively in the nucleus. Seedlings containing recombinant WHIRLY1 in both compartments were hypersensitive toward ABA. In contrast, seedlings possessing only the nuclear form of WHIRLY1 were as insensitive toward ABA as the why1 mutants. ABA was furthermore shown to lower the rate of germination of wildtype seeds even in the presence of abamine which is known to inhibit the formation of xanthoxin, the plastid located precursor of ABA. From this we conclude that plastid located WHIRLY1 enhances the responsiveness of seeds toward ABA even when ABA is supplied exogenously
Proton transfer in the quinol-dependent nitric oxide reductase from Geobacillus stearothermophilus during reduction of oxygen
Bacterial nitric oxide reductases (NOR) are integral membrane proteins that
catalyse the reduction of nitric oxide to nitrous oxide, often as a step in
the process of denitrification. Most functional data has been obtained with
NORs that receive their electrons from a soluble cytochrome c in the periplasm
and are hence termed cNOR. Very recently, the structure of a different type of
NOR, the quinol-dependent (q)-NOR from the thermophilic bacterium Geobacillus
stearothermophilus was solved to atomic resolution [Y. Matsumoto, T. Tosha,
A.V. Pisliakov, T. Hino, H. Sugimoto, S. Nagano, Y. Sugita and Y. Shiro, Nat.
Struct. Mol. Biol. 19 (2012) 238â246]. In this study, we have investigated the
reaction between this qNOR and oxygen. Our results show that, like some cNORs,
the G. stearothermophilus qNOR is capable of O2 reduction with a turnover of ~
3 electrons sâ 1 at 40 °C. Furthermore, using the so-called flow-flash
technique, we show that the fully reduced (with three available electrons)
qNOR reacts with oxygen in a reaction with a time constant of 1.8 ms that
oxidises the low-spin heme b. This reaction is coupled to proton uptake from
solution and presumably forms a ferryl intermediate at the active site. The pH
dependence of the reaction is markedly different from a corresponding reaction
in cNOR from Paracoccus denitrificans, indicating that possibly the proton
uptake mechanism and/or pathway differs between qNOR and cNOR. This study
furthermore forms the basis for investigation of the proton transfer pathway
in qNOR using both variants with putative proton transfer elements modified
and measurements of the vectorial nature of the proton transfer. This article
is part of a Special Issue entitled: 17th European Bioenergetics Conference
(EBEC 2012)
Proton transfer in the quinol-dependent nitric oxide reductase from Geobacillus stearothermophilus during reduction of oxygen
Bacterial nitric oxide reductases (NOR) are integral membrane proteins that
catalyse the reduction of nitric oxide to nitrous oxide, often as a step in
the process of denitrification. Most functional data has been obtained with
NORs that receive their electrons from a soluble cytochrome c in the periplasm
and are hence termed cNOR. Very recently, the structure of a different type of
NOR, the quinol-dependent (q)-NOR from the thermophilic bacterium Geobacillus
stearothermophilus was solved to atomic resolution [Y. Matsumoto, T. Tosha,
A.V. Pisliakov, T. Hino, H. Sugimoto, S. Nagano, Y. Sugita and Y. Shiro, Nat.
Struct. Mol. Biol. 19 (2012) 238â246]. In this study, we have investigated the
reaction between this qNOR and oxygen. Our results show that, like some cNORs,
the G. stearothermophilus qNOR is capable of O2 reduction with a turnover of ~
3 electrons sâ 1 at 40 °C. Furthermore, using the so-called flow-flash
technique, we show that the fully reduced (with three available electrons)
qNOR reacts with oxygen in a reaction with a time constant of 1.8 ms that
oxidises the low-spin heme b. This reaction is coupled to proton uptake from
solution and presumably forms a ferryl intermediate at the active site. The pH
dependence of the reaction is markedly different from a corresponding reaction
in cNOR from Paracoccus denitrificans, indicating that possibly the proton
uptake mechanism and/or pathway differs between qNOR and cNOR. This study
furthermore forms the basis for investigation of the proton transfer pathway
in qNOR using both variants with putative proton transfer elements modified
and measurements of the vectorial nature of the proton transfer. This article
is part of a Special Issue entitled: 17th European Bioenergetics Conference
(EBEC 2012)
Self-Organisation of Neural Topologies by Evolutionary Reinforcement Learning
In this article we present EANT, "Evolutionary Acquisition of Neural Topologies", a method that creates neural networks (NNs) by evolutionary reinforcement learning. The structure of NNs is developed using mutation operators, starting from a minimal structure. Their parameters are optimised using CMA-ES. EANT can create NNs that are very specialised; they achieve a very good performance while being relatively small. This can be seen in experiments where our method competes with a different one, called NEAT, "NeuroEvolution of Augmenting Topologies", to create networks that control a robot in a visual serving scenario
- âŠ