Untersuchungen zur Bedeutung der intrazellulären Ca2+ Konzentration für die Chemotaxis von Seeigel- und Seestern-Spermien

The events that occur during chemotaxis of sperm are only partly known. As an essential step toward determining the underlying mechanism, we developed a sensitive laser-stroboscopic technique that allows the recording of changes in intracellular Ca$^{2+}$-concentration in swimming sperm of the sea urchin Arbacia punctulata and starfish Asterias amurensis. Stimulation of the sea urchin Arbacia punctulata by the themoattractant or by intracellular cGMP evokes Ca$^{2+}$ spikes in the flagellum. These Ca$^{2+}$ spikes control the swiming behaviour of sperm. A Ca$^{2+}$ spike elicits a turn in the trajectory followed by a period of straight swimming (‘turn-andrun’). The train of Ca$^{2+}$ spikes gives rise to repetitive loop-like movements. When sperm swim in a concentration gradient of the attractant, the Ca$^{2+}$ spikes and the stimulus function are synchronized, suggesting that precise timing of Ca$^{2+}$ spikes controls navigation. We identified the peptide asterosap as a chemotactic factor of the starfish Asterias amurensis. The similarities in first, the cGMP-induced Ca$^{2+}$ spikes in the flagellum, second, the motor response and third the swimming behavior of sperm from starfish and sea urchin imply that the signaling pathway of chemotaxis has been conserved in species, which diverged almost 500 million years ago. A cGMP-gated ion channel (CNG-channel), which might be involved in hyperpolarisation or Ca$^{2+}$ entry, could not yet be identified in Arbacia punctulata. Voltage-sensitive Ca$^{2+}$- channels, which are only said to have a function in the acrosome reaction, however, seem to play a more important role for the Ca$^{2+}$ entry during sperm chemotaxis

Carbon nanotubes: innovative heterogeneous gas phase catalysts

Since the coke deposition on the inorganic oxide in the course of ODEB to styrene has been considered as the true catalytically active substance, various carbonaceous materials have shown to be active and selective catalysts for this reaction. It has been confirmed that oxygenated surface functional groups of catalyst, especially carbonyl/quinoid and hydroxyl groups, are responsible for the catalytic performance. Therefore, the focus in this study is in the creation of oxygen-containing functional groups on the surface of carbon nanotubes by partial oxidation using high potential oxidizing agents, including hydroxyl radicals, and ozone in gas phase followed by investigating the influences of these groups on the ODEB catalytic behavior. The effects of the oxidative treatment methods on the textural, structural and chemistry surface of MWCNTs, as well as comparative investigations on the catalysts before and after the ODEB have been conducted by using a series of analytical techniques including TGA, BET surface area, Raman spectroscopy, TEM, FTIR and XPS. It is found that as-received MWCNTs possessed a number of oxygenated surface groups, as a result of CVD method. Further oxidation treatment with highly active hydroxyl radicals generated via UV/H2O2 process increased substantially the formation of oxygenated surface functional groups compared to as-received MWCNTs, particularly hydroxyl and carbonyl groups. Using hydrogen peroxide solutions with concentrations higher than 35 wt.% for the radical oxidation of MWCNTs did not enhance the surface oxygen content as expected. The effectiveness of the oxidation could be declined by the scavenging of radicals instead. As a result, the catalytic performance of UV/H35 catalyst is better than that of UV/H50 or UV/H60. At 400 oC and molar ratio EB/O2 of 1:1, ethylbenzene conversion and styrene selectivity of UV/H35 catalyst achieved 47% and 91%, respectively, for several hours time on stream. The styrene yield of UV/H35 is two times higher than that of as-received MWCNTs. Purification of as-received MWCNTs followed by ozone corona discharge oxidation of samples generated various oxygenated functional groups on the MWCNTs as identified by FT-IR. The surface oxygen content of the ozonated MWCNT increased significantly with increasing ozone concentration in gas flow, leading to highly stable ethylbenzene conversion and styrene selectivity reaching up to 80 and 92%, respectively, at 450 oC, and EB/O2 molar ratio of 1:2 in long-term experiments under conventional heating. That is the best result for the ODEB community to the best of our knowledge. The catalyst performance does not depend on the porosity of the MWCNTs. At the same reaction conditions (EB/O2 molar ratio of 1:1, 400 °C), the catalytic activity/ selectivity of the MWCNTs treated with ozone is better than that of the MWCNTs oxidized with hydroxyl radicals. The catalytic performance is substantially affected by the supplied heating mode for the reaction. A comparative investigation on catalyst performance under conventional and microwave heating indicated that the conversion difference between both heating methods is negligible, but conventional heating results in higher styrene selectivity than the microwave-assisted process. Generally, coke deposit has been observed for all the tested catalysts after the ODEB. However, the extent of coke formation depends strongly the oxidative treatment of nanotubes. For conventional heating, an increase in coke weight incorporated with oxygenated groups has been occurred, while for microwave heating coke deposit has been observed but the oxygenated groups are reduced after the ODEB. This fact could be the reason for the lower selectivity under microwave heating. In order to investigate the contribution of carboxylic groups on the nanotubes to the catalytic behavior, Boehm’s titration has been employed. By selective neutralization of carboxylic groups on the MWCNTs with NaHCO3 solution, and by comparison of the catalytic activity/selectivity with that of untreated samples, it has been shown that the styrene yield of neutralized MWCNTs is 16% lower than that of non-neutralized catalysts. Examining both catalysts after the reaction indicated that oxygenated coke is not deposited on carboxylic neutralized MWCNTs after the reaction test. This result demonstrates that carboxylic surface groups improve the catalytic performance indirectly. After the ODEB reaction, it is found that an enhancement of oxygen-containing groups on the surface of MWCNTs, particularly hydroxyl and carbonyl groups, have been observed, suggesting that these oxygenated groups could be able to be the main active phases in the reaction

Redundancy Strategies for a High Splitting Optically Amplified Passive Optical Network

Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.High splitting, optically amplified, passive optical networks (SuperPONs) are investigated in terms of redundancy provision and protection mechanisms. Options for redundancy, including the important special case of dual homing, are detailed, and it is determined as to which of these options (duplication of the feeder and first distribution section, and N+1 protection of the optical amplifiers in the amplified splitter) would be required to be provided to all attached users to facilitate appropriate availability of the basic telephony service. The distributed amplified splitter dual homing solution is found to outperform the single amplified splitter solution in terms of its survivability. The protection mechanisms necessary to automatically switch to the redundant provision are discussed and it is seen that with the aid of suitable regular precautionary procedures protection switching can generally be provided rapidly (<50 ms). Finally, an availability, and cost versus availability, study confirms the aforementioned redundancy assessment for fiber-to-the-home (FTTH) implementations, but shows fiber-to-the-curb (FTTC) as needing additional redundancyPeer reviewe

Finite Element Analysis to Estimate Bearing Capacity of Strip Footing in Coastal Sandy Soils in Bengkulu City, Indonesia

This study presents results of bearing capacity analysis for strip footing in coastal sandy soils. Three sites located at coastal area are investigated. The site investigation and laboratory tests are conducted to obtain soil properties. Variations on depth and width of strip footing are considered. Finite element analysis is conducted to observe failure mechanism and bearing capacity of strip footing. Several results such as relationship between ultimate bearing capacity and foundation dimensions, factor of safety, displacement, and failure mechanism are discussed. The comparison between finite element results and exact solutions is also presented. The results show that variations of dimension tend to influence the bearing capacity and failure mechanism. The results also shows that finite element result is generally consistent with the exact solution. The results states that the footing dimension of 1.1. m embedded at 1.0 m below ground surface as the suitable strip footing in the study area. This study can also benefit local engineers designing strip footing for the coastal sandy soils

Applications of Mach-Zehnder Interferometry to Studies on Local Deformation of Polymers Under Photocuring

A Mach‐Zehnder interferometer (MZI) was built and modified to in situ monitor the deformation of polymers during the photocuring process. In this review, the working principle and method of operation of this MZI were explained together with the method of data analysis. As the examples for the utilization of this modified MZI, measurements of the deformation induced by photopolymerization was demonstrated for three different types of samples: homopolymer in the bulk state, miscible polymer blends and phase‐separated polymer blends. Finally, a concluding remark is provided for the usage of MZI in polymer research

Revisiting the role of H+ in chemotactic signaling of sperm

© 2004 Solzin et al. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License. The definitive version was published in Journal of General Physiology 124 (2004): 115-124, doi:10.1085/jgp.200409030.Chemotaxis of sperm is an important step toward fertilization. During chemotaxis, sperm change their swimming behavior in a gradient of the chemoattractant that is released by the eggs, and finally sperm accumulate near the eggs. A well established model to study chemotaxis is the sea urchin Arbacia punctulata. Resact, the chemoattractant of Arbacia, is a peptide that binds to a receptor guanylyl cyclase. The signaling pathway underlying chemotaxis is still poorly understood. Stimulation of sperm with resact induces a variety of cellular events, including a rise in intracellular pH (pHi) and an influx of Ca2+; the Ca2+ entry is essential for the chemotactic behavior. Previous studies proposed that the influx of Ca2+ is initiated by the rise in pHi. According to this proposal, a cGMP-induced hyperpolarization activates a voltage-dependent Na+/H+ exchanger that expels H+ from the cell. Because some aspects of the proposed signaling pathway are inconsistent with recent results (Kaupp, U.B., J. Solzin, J.E. Brown, A. Helbig, V. Hagen, M. Beyermann, E. Hildebrand, and I. Weyand. 2003. Nat. Cell Biol. 5:109–117), we reexamined the role of protons in chemotaxis of sperm using kinetic measurements of the changes in pHi and intracellular Ca2+ concentration. We show that for physiological concentrations of resact (<25 pM), the influx of Ca2+ precedes the rise in pHi. Moreover, buffering of pHi completely abolishes the resact-induced pHi signal, but leaves the Ca2+ signal and the chemotactic motor response unaffected. We conclude that an elevation of pHi is required neither to open Ca2+-permeable channels nor to control the chemotactic behavior. Intracellular release of cGMP from a caged compound does not cause an increase in pHi, indicating that the rise in pHi is induced by cellular events unrelated to cGMP itself, but probably triggered by the consumption and subsequent replenishment of GTP. These results show that the resact-induced rise in pHi is not an obligatory step in sperm chemotactic signaling. A rise in pHi is also not required for peptide-induced Ca2+ entry into sperm of the sea urchin Strongylocentrotus purpuratus. Speract, a peptide of S. purpuratus may act as a chemoattractant as well or may serve functions other than chemotaxis.This work was supported by a grant from the Deutsche Forschungsgemeinschaft

A Bayesian belief data mining approach applied to rice and shrimp aquaculture

In many parts of the world, conditions for small scale agriculture are worsening, creating challenges in achieving consistent yields. The use of automated decision support tools, such as Bayesian Belief Networks (BBNs), can assist producers to respond to these factors. This paper describes a decision support system developed to assist farmers on the Mekong Delta, Vietnam, who grow both rice and shrimp crops in the same pond, based on an existing BBN. The BBN was previously developed in collaboration with local farmers and extension officers to represent their collective perceptions and understanding of their farming system and the risks to production that they face. This BBN can be used to provide insight into the probable consequences of farming decisions, given prevailing environmental conditions, however, it does not provide direct guidance on the optimal decision given those decisions. In this paper, the BBN is analysed using a novel, temporally-inspired data mining approach to systematically determine the agricultural decisions that farmers perceive as optimal at distinct periods in the growing and harvesting cycle, given the prevailing agricultural conditions. Using a novel form of data mining that combines with visual analytics, the results of this analysis allow the farmer to input the environmental conditions in a given growing period. They then receive recommendations that represent the collective view of the expert knowledge encoded in the BBN allowing them to maximise the probability of successful crops. Encoding the results of the data mining/inspection approach into the mobile Decision Support System helps farmers access explicit recommendations from the collective local farming community as to the optimal farming decisions, given the prevailing environmental conditions

Bearing Capacity of Ring Foundations on Anisotropic and Heterogenous Clays: FEA, NGI‑ADP, and MARS

Axisymmetric solutions for the bearing capacity of ring foundation resting on anisotropic and heterogenous clays are presented in this paper using finite element analysis (FEA). The NGI-ADP model in PLAXIS FEA, a widely used anisotropic soil model, is adopted to study the stability responses of ring foundations, with special consideration given to the effects of increasing undrained shear strength with the depth. Numerical results are formulated in terms of a dimensionless stability number (bearing capacity ratio) that is a function of three dimensionless input parameters: namely, the ratio of inner and outer radius, the increasing strength gradient ratio, and the anisotropic shear strength ratio. The influence of each dimensionless input parameter on the bearing capacity ratio is investigated using design charts and failure mechanisms, and they are scored by relative importance indexes in multivariate adaptive regression splines (MARS) model—a machine learning approach. A highly accurate equation generated from the MARS model is proposed as an effective tool for engineering practitioners

An adaptive grid refinement strategy for the simulation of negative streamers

The evolution of negative streamers during electric breakdown of a non-attaching gas can be described by a two-fluid model for electrons and positive ions. It consists of continuity equations for the charged particles including drift, diffusion and reaction in the local electric field, coupled to the Poisson equation for the electric potential. The model generates field enhancement and steep propagating ionization fronts at the tip of growing ionized filaments. An adaptive grid refinement method for the simulation of these structures is presented. It uses finite volume spatial discretizations and explicit time stepping, which allows the decoupling of the grids for the continuity equations from those for the Poisson equation. Standard refinement methods in which the refinement criterion is based on local error monitors fail due to the pulled character of the streamer front that propagates into a linearly unstable state. We present a refinement method which deals with all these features. Tests on one-dimensional streamer fronts as well as on three-dimensional streamers with cylindrical symmetry (hence effectively 2D for numerical purposes) are carried out successfully. Results on fine grids are presented, they show that such an adaptive grid method is needed to capture the streamer characteristics well. This refinement strategy enables us to adequately compute negative streamers in pure gases in the parameter regime where a physical instability appears: branching streamers.Comment: 46 pages, 19 figures, to appear in J. Comp. Phy

Oseltamivir resistance during treatment of influenza A (H5N1) infection

Influenza A (H5N1) virus with an amino acid substitution in neuraminidase conferring high-level resistance to oseltamivir was isolated from two of eight Vietnamese patients during oseltamivir treatment. Both patients died of influenza A (H5N1) virus infection, despite early initiation of treatment in one patient. Surviving patients had rapid declines in the viral load to undetectable levels during treatment. These observations suggest that resistance can emerge during the currently recommended regimen of oseltamivir therapy and may be associated with clinical deterioration and that the strategy for the treatment of influenza A (H5N1) virus infection should include additional antiviral agents. Copyright © 2005 Massachusetts Medical Society.published_or_final_versio