Positive Feedback Regulation Results in Spatial Clustering and Fast Spreading of Active Signaling Molecules on a Cell Membrane

Positive feedback regulation is ubiquitous in cell signaling networks, often leading to binary outcomes in response to graded stimuli. However, the role of such feedbacks in clustering, and in spatial spreading of activated molecules, has come to be appreciated only recently. We focus on the latter, using a simple model developed in the context of Ras activation with competing negative and positive feedback mechanisms. We find that positive feedback, in the presence of slow diffusion, results in clustering of activated molecules on the plasma membrane, and rapid spatial spreading as the front of the cluster propagates with a constant velocity (dependent on the feedback strength). The advancing fronts of the clusters of the activated species are rough, with scaling consistent with the Kardar-Parisi-Zhang (KPZ) equation in one dimension. Our minimal model is general enough to describe signal transduction in a wide variety of biological networks where activity in the membrane-proximal region is subject to feedback regulation.Comment: 37 pages, 8 figures. Journal of Chemical Physics (in press

A 0.5 MW/10 Hz option of the spallation source AUSTRON

In 1993-94 a feasibility study for AUSTRON, a neutron spallation source, was made on behalf of the Austrian Ministry of Science and Research. At that time, the machine was synchrotron cycling at 25 Hz and delivering an average beam power of 205 kW at 1.6 GeV. An option to double the power by doubling the frequency was foreseen. Now a more ambitious development of the original concept is proposed that aims at 0.5 MW at 1.6 GeV, pulsed at either 50 Hz or 10 Hz. The slow repetition rate is achieved by the addition of a storage ring holding four consecutive (single bunch) pulses from the 50 Hz synchrotron until a fifth pulse is accelerated and transferred to the target with the four stored ones. In this way, an energy per pulse of 50 kJ (one half of the pulse energy of the 5 MW ESS) is obtained, yielding about 3.5*10/sup 16/ thermal neutrons/(s cm/sup 2/). This peak flux matches well a number of innovative instruments and allows unprecedented resolution for some more conventional ones. On August 20, 1998, the Austrian Government has unanimously decided to contribute one third of the total cost of the facility and invites international partners to participate. (13 refs)

Significance of gene variants for the functional biogeography of the near-surface Atlantic Ocean microbiome

Microbial communities are major drivers of global elemental cycles in the oceans due to their high abundance and enormous taxonomic and functional diversity. Recent studies assessed microbial taxonomic and functional biogeography in global oceans but microbial functional biogeography remains poorly studied. Here we show that in the near-surface Atlantic and Southern Ocean between 62°S and 47°N microbial communities exhibit distinct taxonomic and functional adaptations to regional environmental conditions. Richness and diversity showed maxima around 40° latitude and intermediate temperatures, especially in functional genes (KEGG-orthologues, KOs) and gene profiles. A cluster analysis yielded three clusters of KOs but five clusters of genes differing in the abundance of genes involved in nutrient and energy acquisition. Gene profiles showed much higher distance-decay rates than KO and taxonomic profiles. Biotic factors were identified as highly influential in explaining the observed patterns in the functional profiles, whereas temperature and biogeographic province mainly explained the observed taxonomic patterns. Our results thus indicate fine-tuned genetic adaptions of microbial communities to regional biotic and environmental conditions in the Atlantic and Southern Ocean

Exact Results on e+ e- --> e+ e- + 2 Photons at SLC/LEP Energies

We use the spinor methods of the CALKUL collaboration, as realized by Xu, Zhang and Chang, to calculate the differential cross section for e+ e- --> e+ e- + 2 photons for c.m.s. energies in the SLC/LEP regime. An explicit complete formula for the respective cross section is obtained. The leading log approximation is used to check the formula. Applications of the formula to high precision luminosity calculations at SLC/LEP are discussed.Comment: 16 pages(LaTeX), UTHEP-92-0601 (contains corrected figures

IMECE2004-60039 IMPLEMENTATION OF HIGH BANDWIDTH SENSOR ARRAYS USING FEEDBACK MECHANISMS

ABSTRACT Proposed in this paper is a new method to implement the high operating bandwidth sensor arrays. In certain control applications, it is necessary that a high bandwidth sensor be used to improve the efficiency of feedback. The design of a single sensor with the desired high bandwidth may not be easy and economically feasible. It is shown that the idea of sensor arrays can be utilized to obtain a cost effective and efficient solution to the problem posed. It is discussed that an effective data fusion scheme is necessary in order to implement the proposed sensor array that consists of low bandwidth pass-band sensors with possible overlapping operating regions. Moreover, we point out that obtaining accurate sensor models may not be always easy in practice and this may make the proposed sensor arrays inapplicable for certain applications. To address this issue, a new implementation scheme that utilizes feedback mechanisms to combine multi-sensor data is developed. The proposed framework is validated using simulation examples

Cruciform specimens used for determination of the influence of T-stress on fatigue crack growth with overloads on aluminum alloy Al 6061 T651

The publication presents a cruciform specimen for the determination of cyclic crack growth data under biaxial loading. The design of the specimen with slotted loading arms allows good decoupling between the two loading directions. For different initial crack geometries, the solutions for the stress intensity factors KI and KII as well as the crack-parallel T-stress are calculated by linear elastic finite element analysis (FEA) with the program ABAQUS. For two specimens with the same geometry made of aluminium alloy 6061 T651, the crack growth behaviour is measured at different T-stresses at a stress ratio of R=0.7 and overloads. It is shown that the crack retardation after an overload with crack-parallel tensile stress is less than without it. The reason for this behaviour is considered to be the reduced plasticity at the crack tip due to the higher triaxiality of the stress state

Putative degraders of low-density polyethylene-derived compounds are ubiquitous members of plastic associated bacterial communities in the marine environment

Research articleIt remains unknown whether and to what extent marine prokaryotic communities are capable of degrading plastic in the ocean. To address this knowledge gap, we combined enrichment experiments employing low-density polyethylene (LDPE) as the sole carbon source with a comparison of bacterial communities on plastic debris in the Pacific, the North Atlantic and the northern Adriatic Sea. A total of 35 operational taxonomic units (OTUs) were enriched in the LDPE-laboratory incubations after 1 year, of which 20 were present with relative abundances > 0.5% in at least one plastic sample collected from the environment. From these, OTUs classified as Cognatiyoonia, Psychrobacter, Roseovarius and Roseobacter were found in the communities of plastics collected at all oceanic sites. Additionally, OTUs classified as Roseobacter, Pseudophaeobacter, Phaeobacter, Marinovum and Cognatiyoonia, also enriched in the LDPE-laboratory incubations, were enriched on LDPE communities compared to the ones associated to glass and polypropylene in in-situ incubations in the northern Adriatic Sea after 1 month of incubation. Some of these enriched OTUs were also related to known alkane and hydrocarbon degraders. Collectively, these results demonstrate that there are prokaryotes capable of surviving with LDPE as the sole carbon source living on plastics in relatively high abundances in different water masses of the global ocean.Austrian Academy of Sciences, Austrian Sciences Fund, University of Viena, German Federal Ministry of Education and Science (BacGeoPac project (03G0248A) and IEO (RADPROF project)Versión del editor5,84