Conservation and co-option in developmental programmes: the importance of homology relationships

One of the surprising insights gained from research in evolutionary developmental biology (evo-devo) is that increasing diversity in body plans and morphology in organisms across animal phyla are not reflected in similarly dramatic changes at the level of gene composition of their genomes. For instance, simplicity at the tissue level of organization often contrasts with a high degree of genetic complexity. Also intriguing is the observation that the coding regions of several genes of invertebrates show high sequence similarity to those in humans. This lack of change (conservation) indicates that evolutionary novelties may arise more frequently through combinatorial processes, such as changes in gene regulation and the recruitment of novel genes into existing regulatory gene networks (co-option), and less often through adaptive evolutionary processes in the coding portions of a gene. As a consequence, it is of great interest to examine whether the widespread conservation of the genetic machinery implies the same developmental function in a last common ancestor, or whether homologous genes acquired new developmental roles in structures of independent phylogenetic origin. To distinguish between these two possibilities one must refer to current concepts of phylogeny reconstruction and carefully investigate homology relationships. Particularly problematic in terms of homology decisions is the use of gene expression patterns of a given structure. In the future, research on more organisms other than the typical model systems will be required since these can provide insights that are not easily obtained from comparisons among only a few distantly related model species

Sedimentological, geomorphological and geochronological studies on Holocene tsunamis in the Lefkada / Preveza area (NW Greece) and their implications for coastal evolution

Research on palaeo-tsunami and palaeo-extreme wave events aims to provide new data about former events and is of remarkable importance in the eastern Mediterranean. In general, coastal geomorphology and fine-grained near-coast geological archives store information about coastal changes over medium to long timescales, as well as short, episodic processes such as palaeo-tsunami events. In the eastern Mediterranean and particularly for the Ionian Sea and the Lefkada / Preveza coastal zone (NW Greece), strong seismic activity and a high tsunamigenic potential are evident. Thus, comprehensive geo-scientific investigations were carried out in the Lefkada / Preveza coastal zone in order to decipher coastal change throughout time, and thereby detect, verify and date the influence of tsunami events on the coastal system and coastal evolution. Herein, particular focus was set on the distinguishability of event deposits in the geological record and the evaluation of event recurrence rates - an issue of major importance in extreme wave event research. In a first step, detailed analysis of the geomorphological and geomorphodynamic situation in the study area revealed several major disturbances of the coastal system, which mark episodically occurring major impulses of coastal evolution, entailing the recurrent reorganization of coastal balance. In a second step, comprehensive geo-scientific investigations on the main near-coast geological archives provided insight into the palaeogeographical evolution and the palaeo-event history of the Lefkada / Preveza area. In the sedimentary record of the Phoukias sand spit and the washover-dominated northern Lefkada Lagoon, distinct event deposits were identified. These event deposits provide a linkage to the inferred disturbances of the coastal system and allow the dating of the main impulses in coastal evolution. Detailed analyses of the event deposits - comprising sedimentological, microfaunal and geochemical investigations as well as the interpretation of the regional geomorphologic and geographic context - strongly suggest a tsunamigenic origin of the encountered event deposits, proving the significant impact of tsunamis on the coastal system. Moreover, numerous block and boulder fields were mapped along the coastline and equally point to the impact of high energy wave events. Altogether, four major tsunamigenic disturbances were identified throughout the late Holocene. These disturbances were dated to ~1000 BC, to at around or after 300 BC and, for the main washover structures in the northern Lagoon of Lefkada, to at around or after 300 AD, the latter event most likely triggered by the 365 AD earthquake off western Crete and the related tsunami. During the younger history of coastal evolution a fourth disturbance occurred sometime before 1850 AD. In addition to the detected 365 AD event, the presented findings fit well to previous investigations in adjacent coastal zones. From a geomorphological and geomorphodynamic point of view, the major tsunami events involved the breakdown of former coastlines (the Plaka), the formation of the Phoukias sand spit and the onset of intense coastal erosion in western Aktium Headland. Moreover, the inferred tsunami events contributed to the formation of block and boulder fields, induced the evolution of ridge structures in the northern part of the Phoukias sand spit and triggered the formation of at least one, probably two washover generations in the northern Lefkada Lagoon. The episodic occurrence of tsunami events was thus responsible for the formation of major geomorphological structures and modifications of the coastal system, which are recurrently masked and mimicked by long term, gradually operating coastal processes. These marked geomorphic changes provide clear evidence that tsunami-induced disturbances exert a major control on the evolution of the coastal system in the study area. In conclusion, this study presents new geo-scientific evidence of extreme wave event deposits and will thereby expand the regional and global data pool of palaeo-event and particularly palaeo-tsunami deposits. Moreover, it contributes to ongoing research concerned with the detection of extreme wave event deposits in near-coast geological archives, ultimately enabling an improved understanding of type and degree of their impact on the evolution of coastal systems

Self-consistent simulation of quantum wires defined by local oxidation of Ga[Al]As heterostructures

We calculate the electronic width of quantum wires as a function of their lithographic width in analogy to experiments performed on nanostructures defined by local oxidation of Ga[Al]As heterostructures. Two--dimensional simulations of two parallel oxide lines on top of a Ga[Al]As heterostructure defining a quantum wire are carried out in the framework of Density Functional Theory in the Local Density Approximation and are found to be in agreement with measurements. Quantitative assessment of the influence of various experimental uncertainties is given. The most influential parameter turns out to be the oxide line depth, followed by its exact shape and the effect of background doping (in decreasing order).Comment: 5 pages, 6 figures; revised figures, clarified tex

Corrections to "Modulation Strategies for Anisotropy-Based Position Estimation of PMSMs Using the Neutral Point Voltage"

In the above article [1], there are a few errors that are corrected in the following

Modulation Strategies for Anisotropy-Based Position Estimation of PMSMs Using the Neutral Point Voltage

Information obtained about magnetic anisotropy via neutral point voltage measurements can be used to estimate the position of synchronous and induction machines at all speeds including standstill. Due to its usually high signal-to-noise ratio, this estimation method can be an attractive alternative to approaches that acquire anisotropy information via current measurements. The position estimation method looked at in this paper relies on anisotropy information in the form of position-dependent inductance ratios. These are obtained through measurement of the voltage between the machine’s neutral point and an artificial neutral point during the application of different voltage vectors via a two-level switching inverter. We analyze the conditions placed on and the consequences of implementing necessary modifications to a standard space vector modulation. Five different modified modulation strategies are compared and investigated, including two newly proposed strategies which use only a minimal set of active and zero voltage vectors for measurement of the inductance ratios and therefore allow high utilization of available voltage and a high update rate of the estimated position. Experimental results for three low-power threephase permanent magnet synchronous machines are presented which suggest that modulation strategies that use active measurement vectors in all three instead of only two axes of the machine are less susceptible to systematic deviations in the position estimation that presumably result from nonlinear machine properties. As part of the machine model, a normalizing inductance variation ratio is introduced, which simplifies expressions and supports the comparison of motors

Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure

Photosynthesis is nature’s route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators

Time-resolved Monitoring of Enzyme Activity with Ultrafast Hyper-CEST Spectroscopy

We propose a method to dynamically monitor the progress of an enzymatic reaction using NMR of hyperpolarized ^(129)Xe in a host-guest system. It is based on a displacement assay originally designed for fluorescence experiments that exploits the competitive binding of the enzymatic product on the one hand and a reporter dye on the other hand to a supramolecular host. Recently, this assay has been successfully transferred to NMR, using xenon as a reporter, cucurbit[6]uril as supramolecular host, and Hyper-CEST as detection technique. Its advantage is that the enzyme acts on the unmodified substrate and only the product is detected through immediate inclusion into the host. We here apply a method that drastically accelerates the acquisition of Hyper-CEST spectra in vitro using magnetic field gradients. This allows monitoring the dynamic progress of the conversion of lysine to cadaverine with a temporal resolution of ~30 s. Moreover, the method only requires to sample the very early onset of the reaction (<0.5 % of substrate conversion where the host itself is required only at μM concentrations) at comparatively low reaction rates, thus saving enzyme material and reducing NMR acquisition time. The obtained value for the specific activity agrees well with previously published results from fluorescence assays. We furthermore outline how the Hyper-CEST results correlate with xenon T_2 measurements performed during the enzymatic reaction. This suggests that ultrafast Hyper-CEST spectroscopy can be used for dynamically monitoring enzymatic activity with NMR