排序方式: 共有52条查询结果,搜索用时 15 毫秒
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J. M. Bloomfield J. A. Sherratt K. J. Painter G. Landini 《Journal of the Royal Society Interface》2010,7(52):1525-1535
Mosaic tissues are composed of two or more genetically distinct cell types. They occur naturally, and are also a useful experimental method for exploring tissue growth and maintenance. By marking the different cell types, one can study the patterns formed by proliferation, renewal and migration. Here, we present mathematical modelling suggesting that small changes in the type of interaction that cells have with their local cellular environment can lead to very different outcomes for the composition of mosaics. In cell renewal, proliferation of each cell type may depend linearly or nonlinearly on the local proportion of cells of that type, and these two possibilities produce very different patterns. We study two variations of a cellular automaton model based on simple rules for renewal. We then propose an integrodifferential equation model, and again consider two different forms of cellular interaction. The results of the continuous and cellular automata models are qualitatively the same, and we observe that changes in local environment interaction affect the dynamics for both. Furthermore, we demonstrate that the models reproduce some of the patterns seen in actual mosaic tissues. In particular, our results suggest that the differing patterns seen in organ parenchymas may be driven purely by the process of cell replacement under different interaction scenarios. 相似文献
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A THEORETICAL SOLUTION FOR THE ESTIMATION OF "RAINFLOW" RANGES FROM POWER SPECTRAL DENSITY DATA 总被引:2,自引:0,他引:2
N. W. M. Bishop Frank Sherratt 《Fatigue & Fracture of Engineering Materials & Structures》1990,13(4):311-326
Abstract— This report outlines a theoretical solution for the estimation of rainflow range density functions using statistics computed directly from power spectral density data. The rainflow range mechanism is broken down into a set of events which can be analyzed using Markov process theory. The dependence between extremes in this instance is modelled using an approximation of the joint distribution of peaks and troughs first proposed by Kowalewski. 相似文献
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MJ Sherratt DF Holmes CA Shuttleworth CM Kielty 《Canadian Metallurgical Quarterly》1997,29(8-9):1063-1070
We have applied scanning transmission electron microscopy to intact native fibrillin-containing microfibrils isolated from foetal bovine elastic tissues in order to derive new insights into microfibril organisation. This technique provides quantitative data on the mass per unit length and axial mass distribution of unstained, unshadowed macromolecules. Scanning transmission electron microscopy of microfibrils from aorta, skin and nuchal ligament revealed that the beads corresponded to peaks of mass and the interbead regions to troughs of mass. These major features of axial mass distribution were characteristic of all microfibrils examined. Tissue-specific and age-dependent variations in mass were identified in microfibrils that were structurally comparable by rotary shadowing electron microscopy. Increased microfibril mass correlated with increasing gestational age. The additional mass was associated predominantly at, or close to, the bead. Some microfibril populations exhibited pronounced assymetry in their axial mass distribution. These data indicate that intact native microfibrillar assemblies from developing elastic tissues are heterogeneous in composition. Loss of mass following chondroitinase ABC or AC lyase treatment confirmed the presence of chondroitin sulphate in nuchal ligament microfibrillar assemblies. 相似文献
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Back Cover: Hydrophobic Triaryl‐Substituted β‐Lactams as Activity‐Based Probes for Profiling Eukaryotic Enzymes and Host–Pathogen Interactions (ChemBioChem 15/2014) 下载免费PDF全文
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SG Williams RM Cranenburgh AM Weiss CJ Wrighton DJ Sherratt JA Hanak 《Canadian Metallurgical Quarterly》1998,26(9):2120-2124
The propagation of recombinant plasmids in bacterial hosts, particularly in Escherichia coli, is essential for the amplification and manipulation of cloned DNA and the production of recombinant proteins. The isolation of bacterial transformants and subsequent stable plasmid maintenance have traditionally been accomplished using plasmid-borne selectable marker genes. Here we describe a novel system that employs plasmid-mediated repressor titration to activate a chromosomal selectable marker, removing the requirement for a plasmid-borne marker gene. A modified E.coli host strain containing a conditionally essential chromosomal gene (kan) under the control of the lac operator/promoter, lac O/P, has been constructed. In the absence of an inducer (allolactose or IPTG) this strain, DH1 lackan , cannot grow on kanamycin-containing media due to the repression of kan expression by LacI protein binding to lac O/P. Transformation with a high copy-number plasmid containing the lac operator, lac O, effectively induces kan expression by titrating LacI from the operator. This strain thus allows the selection of plasmids without antibiotic resistance genes (they need only contain lac O and an origin of replication) which have clear advantages for use as gene therapy vectors. Regulation in the same way of an essential, endogenous bacterial gene will allow the production of recombinant therapeutics devoid of residual antibiotic contamination. 相似文献
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Multiple-input multiple-output (MIMO) systems offer significant enhancements in terms of their data rate and channel capacity compared to traditional systems. However, correlation degrades the system performance and imposes practical limits on the number of antennas that can be incorporated into portable wireless devices. The use of switched parasitic antennas (SPAs) is a possible solution, especially where it is difficult to obtain sufficient signal decorrelation by conventional means. The covariance matrix represents the correlation present in the propagation channel, and has significant impact on the MIMO channel capacity. The results of this work demonstrate a significant improvement in the MIMO channel capacity by using SPA with the knowledge of the covariance matrix for all pattern configurations. By employing the “water-pouring algorithm” to modify the covariance matrix, the channel capacity is significantly improved compared to traditional systems, which spread transmit power uniformly across all the antennas. A condition number is also proposed as a selection metric to select the optimal pattern configuration for MIMO-SPAs. 相似文献
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Prasenjit Chanak Indrajit Banerjee R. Simon Sherratt 《International Journal of Communication Systems》2020,33(9)
In wireless sensor networks (WSNs), clustering has been shown to be an efficient technique to improve scalability and network lifetime. In clustered networks, clustering creates unequal load distribution among cluster heads (CHs) and cluster member (CM) nodes. As a result, the entire network is subject to premature death because of the deficient active nodes within the network. In this paper, we present clustering‐based routing algorithms that can balance out the trade‐off between load distribution and network lifetime “green cluster‐based routing scheme.” This paper proposes a new energy‐aware green cluster‐based routing algorithm to preventing premature death of large‐scale dense WSNs. To deal with the uncertainty present in network information, a fuzzy rule‐based node classification model is proposed for clustering. Its primary benefits are flexibility in selecting effective CHs, reliability in distributing CHs overload among the other nodes, and reducing communication overhead and cluster formation time in highly dense areas. In addition, we propose a routing scheme that balances the load among sensors. The proposed scheme is evaluated through simulations to compare our scheme with the existing algorithms available in the literature. The numerical results show the relevance and improved efficiency of our scheme. 相似文献
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Wireless Sensor Networks (WSNs) are usually formed with many tiny sensors
which are randomly deployed within sensing field for target monitoring. These sensors
can transmit their monitored data to the sink in a multi-hop communication manner.
However, the ‘hot spots’ problem will be caused since nodes near sink will consume
more energy during forwarding. Recently, mobile sink based technology provides an
alternative solution for the long-distance communication and sensor nodes only need to
use single hop communication to the mobile sink during data transmission. Even though
it is difficult to consider many network metrics such as sensor position, residual energy
and coverage rate etc., it is still very important to schedule a reasonable moving trajectory
for the mobile sink. In this paper, a novel trajectory scheduling method based on
coverage rate for multiple mobile sinks (TSCR-M) is presented especially for large-scale
WSNs. An improved particle swarm optimization (PSO) combined with mutation
operator is introduced to search the parking positions with optimal coverage rate. Then
the genetic algorithm (GA) is adopted to schedule the moving trajectory for multiple
mobile sinks. Extensive simulations are performed to validate the performance of our
proposed method. 相似文献