共找到 20 条结果
The k-means method is a widely used clustering technique that seeks to minimize the average squared distance between points in the same cluster. Although it offers no accuracy guarantees, its simplicity and speed are very appealing in practice. By augmenting k-means with a simple, randomized seeding technique, we obtain an algorithm that is O(log k)-competitive with the optimal clustering. Experiments show our augmentation improves both the speed and the accuracy of k-means, often quite dramatically. 1
暂无摘要（点击查看原文获取完整内容）
暂无摘要（点击查看原文获取完整内容）
暂无摘要（点击查看原文获取完整内容）
暂无摘要（点击查看原文获取完整内容）
Introduction. Ecologically Meaningful Germination Studies. Types of Seed Dormancy. Germination Ecology of Seeds with Nondeep Physiological Dormancy. Germination Ecology of Seeds with Morphophysiological Dormancy. Germination Ecology of Seeds with Physical Dormancy. Germination Ecology of Seeds in the Persistent Seed Bank. Causes of Within-Species Variations in Seed Dormancy and Germination Characteristics. A Geographical Perspective on Germination Ecology: Tropical and Subtropical Zones. A Geographical Perspective on Germination Ecology: Temperate and Arctic Zones. Germination Ecology of Plants with Specialized Life Cycles and/or Habitats. Biogeographical and Evolutionary Aspects of Seed Dormancy. Subject Index.
We report studies on the synthesis of gold nanorods by a three-step seeding protocol method using a variety of different gold seeds. The synthetic method is adapted from one we published earlier (Jana et al. J. Phys. Chem. B 2001, 105, 4065). The seeds chosen for these studies have average diameters in the range from 4 to 18 nm, with positively charged as well as negatively charged surface groups. In all the cases, along with a large concentration of long rods, a small number of different shapes such as triangles, hexagons, and small rods are observed. The proportion of small rods increases with an increase in the seed size used for nanorod synthesis. For long nanorods synthesized by different seeds a comparison of various parameters such as length, width, and aspect ratio has been made. A dependence of the nanorod aspect ratio on the size of the seed is observed. Increasing the seed size results in lowering of the gold nanorod aspect ratios for a constant concentration of reagents. The charge on the seed also plays a role in determining the nanorod aspect ratio. For positively charged seeds variation in the aspect ratio is not as pronounced as that for negatively charged seeds. The gold nanorods synthesized were characterized by transmission electron microscopy (TEM), UV−vis spectroscopy, and Fourier transform infrared spectroscopy. The role of seed size in the size and shape evolution of the nanocrystal, at different growth stages, has been studied by TEM.
A method is used for preparing gold NRs with aspect ratios ranging from 1.5 to 10 for which the surface plasmon absorption maxima are between 600 and 1300 nm. This method has been adapted from a previously published seed-mediated growth method (Jana et al. Adv. Mater. 2001, 13, 1389). The disadvantages and limitations of the earlier method (i.e., formation of noncylindrical NRs, φ-shaped particles, and formation of a large fraction of spherical particles) have been overcome by use of a hexadecyltrimethylammonium bromide (CTAB)-capped seed instead of a citrate-capped one. In a single-component surfactant system, the silver content of the growth solution was used to grow NRs to a desired length. This results in reproducible formation of NRs with aspect ratios ranging from 1.5 to 4.5. To grow longer NRs with aspect ratios ranging from 4.6 to 10, a binary surfactant mixture composed of benzyldimethylhexadecylammoniumchloride (BDAC) and CTAB was used. NRs are grown in this mixture either by aging or by addition of a growth solution suitable to shorter NRs. Effects of the silver ion and the cosurfactant along with the growth mechanism of NRs are discussed.
暂无摘要（点击查看原文获取完整内容）
In 2004, the SEED (http://pubseed.theseed.org/) was created to provide consistent and accurate genome annotations across thousands of genomes and as a platform for discovering and developing de novo annotations. The SEED is a constantly updated integration of genomic data with a genome database, web front end, API and server scripts. It is used by many scientists for predicting gene functions and discovering new pathways. In addition to being a powerful database for bioinformatics research, the SEED also houses subsystems (collections of functionally related protein families) and their derived FIGfams (protein families), which represent the core of the RAST annotation engine (http://rast.nmpdr.org/). When a new genome is submitted to RAST, genes are called and their annotations are made by comparison to the FIGfam collection. If the genome is made public, it is then housed within the SEED and its proteins populate the FIGfam collection. This annotation cycle has proven to be a robust and scalable solution to the problem of annotating the exponentially increasing number of genomes. To date, >12 000 users worldwide have annotated >60 000 distinct genomes using RAST. Here we describe the interconnectedness of the SEED database and RAST, the RAST annotation pipeline and updates to both resources.
暂无摘要（点击查看原文获取完整内容）
暂无摘要（点击查看原文获取完整内容）
(Uploaded by Plazi for the Bat Literature Project) No abstract provided.
Seeds: Germination, Structure, and Composition. Seed Development and Maturation. Development-Regulation and Maturation. Cellular Events during Germination and Seedling Growth. Dormancy and the Control of Germination. Some Ecophysiological Aspects of Germination. Mobilization of Stored Seed Reserves. Control of the Mobilization of Stored Reserves. Seeds and Germination: Some Agricultural and Industrial Aspects. Index.
Read alignment is an ongoing challenge for the analysis of data from sequencing technologies. This article proposes an elegantly simple multi-seed strategy, called seed-and-vote, for mapping reads to a reference genome. The new strategy chooses the mapped genomic location for the read directly from the seeds. It uses a relatively large number of short seeds (called subreads) extracted from each read and allows all the seeds to vote on the optimal location. When the read length is <160 bp, overlapping subreads are used. More conventional alignment algorithms are then used to fill in detailed mismatch and indel information between the subreads that make up the winning voting block. The strategy is fast because the overall genomic location has already been chosen before the detailed alignment is done. It is sensitive because no individual subread is required to map exactly, nor are individual subreads constrained to map close by other subreads. It is accurate because the final location must be supported by several different subreads. The strategy extends easily to find exon junctions, by locating reads that contain sets of subreads mapping to different exons of the same gene. It scales up efficiently for longer reads.
Summary Seed dormancy is an innate seed property that defines the environmental conditions in which the seed is able to germinate. It is determined by genetics with a substantial environmental influence which is mediated, at least in part, by the plant hormones abscisic acid and gibberellins. Not only is the dormancy status influenced by the seed maturation environment, it is also continuously changing with time following shedding in a manner determined by the ambient environment. As dormancy is present throughout the higher plants in all major climatic regions, adaptation has resulted in divergent responses to the environment. Through this adaptation, germination is timed to avoid unfavourable weather for subsequent plant establishment and reproductive growth. In this review, we present an integrated view of the evolution, molecular genetics, physiology, biochemistry, ecology and modelling of seed dormancy mechanisms and their control of germination. We argue that adaptation has taken place on a theme rather than via fundamentally different paths and identify similarities underlying the extensive diversity in the dormancy response to the environment that controls germination. Contents Summary 501 I. Introduction 502 II. What is dormancy and how is it related to germination? 502 III. How is nondeep physiological dormancy regulated within the seed at the molecular level? 509 IV. How is nondeep physiological seed dormancy regulated by the environment? Ecophysiology and modelling 514 V. Conclusions and perspectives 518 Acknowledgements 519 References 519 Supplementary material 523
We present here a new algorithm for segmentation of intensity images which is robust, rapid, and free of tuning parameters. The method, however, requires the input of a number of seeds, either individual pixels or regions, which will control the formation of regions into which the image will be segmented. In this correspondence, we present the algorithm, discuss briefly its properties, and suggest two ways in which it can be employed, namely, by using manual seed selection or by automated procedures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
暂无摘要（点击查看原文获取完整内容）
Nearly a century has been spent collecting and preserving genetic diversity in plants. Germplasm banks-living seed collections that serve as repositories of genetic variation-have been established as a source of genes for improving agricultural crops. Genetic linkage maps have made it possible to study the chromosomal locations of genes for improving yield and other complex traits important to agriculture. The tools of genome research may finally unleash the genetic potential of our wild and cultivated germplasm resources for the benefit of society.