1,046 research outputs found
Analysis and Forecasting of Trending Topics in Online Media Streams
Among the vast information available on the web, social media streams capture
what people currently pay attention to and how they feel about certain topics.
Awareness of such trending topics plays a crucial role in multimedia systems
such as trend aware recommendation and automatic vocabulary selection for video
concept detection systems.
Correctly utilizing trending topics requires a better understanding of their
various characteristics in different social media streams. To this end, we
present the first comprehensive study across three major online and social
media streams, Twitter, Google, and Wikipedia, covering thousands of trending
topics during an observation period of an entire year. Our results indicate
that depending on one's requirements one does not necessarily have to turn to
Twitter for information about current events and that some media streams
strongly emphasize content of specific categories. As our second key
contribution, we further present a novel approach for the challenging task of
forecasting the life cycle of trending topics in the very moment they emerge.
Our fully automated approach is based on a nearest neighbor forecasting
technique exploiting our assumption that semantically similar topics exhibit
similar behavior.
We demonstrate on a large-scale dataset of Wikipedia page view statistics
that forecasts by the proposed approach are about 9-48k views closer to the
actual viewing statistics compared to baseline methods and achieve a mean
average percentage error of 45-19% for time periods of up to 14 days.Comment: ACM Multimedia 201
Manipulating phenotypes by epigenetic mechanism
For many years, the plasticity and variation of phenotypes observed in CHO cell lines was attributed to genomic variation. However, while individual mutations of single genes may certainly contribute to a defined phenotype, it typically is the adaptation of the expression pattern of multiple genes which together then modulate and define cellular behavior. Such changes in the transcription pattern are defined by several layers of epigenetic regulation that act on short term and long term, serving both as rapid response mechanisms and as cellular “memory”1, 2. These include differential DNA-methylation, predominantly in promoter regions, but also in regulatory regions of the genome. These co-operate and are co-regulated with modifications of histones which change the state of chromatin and thus the accessibility for the transcriptional machinery. On top of these, there are interactions between specific genomic regions and triplex-forming long-non-coding RNAs that can both upor downregulate transcription by attracting or blocking off transcription factors. The later can serve as very rapid and very strong regulators of transcription. Such detailed understanding of the underlying mechanisms can be used to advantage to enhance our control over phenotypes both by specifically altering the expression level of individual genes (to the degree of turning them ON or OFF3) and by altering the global transcriptome to achieve enhanced cellular performance. Likewise, directed evolution and adaptation protocols also result in a new transcriptome defined by epigenic memory that lays down altered cellular behavior1. Ultimately, these tools offer new possibilities for metabolic or cellular engineering, which have the advantage of being fully reversible and dosable, as no changes in the genome sequence are required. Such epigenetic control mechanisms could be used in two directions: i) to increase the phenotypic diversity within a population, for instance during cell line development, to enable isolation of rare variants with superior properties; and ii) to stabilize an already selected phenotype such that more reproducible process outcomes are achieved. 1. Feichtinger et al. (2016) Comprehensive genome and epigenome characterization of CHO cells in response to evolutionary pressures and over time. Biotechn. Bioeng. 113:10:2241-2253 2. Hernandez et al. (2019) Epigenetic regulation of gene expression in CHO cells in response to the changing environment of a batch culture. Biotechn. Bioeng, https:\\doi.org/10.1002/bit.26891 3. Marx et al. (2018) CRISPR-based targeted epigenetic editing enables gene expression modulation of the silenced beta-galactoside alpha-2,6-sialyltransferase 1 in CHO cells. Biotechn J 13:10, 170021
To clone or not to clone? – Wrong question! An investigation on genome heterogeneity and stability and on what controls cell behavior
The most striking characteristic of CHO cells is their adaptability, which enables efficient production of proteins as well as growth under a variety of culture conditions, but also results in genomic and phenotypic instability. Potential causes include i) the high number of chromosomal rearrangements, including variation in chromosome numbers observed in CHO or any other rapidly growing cell line; ii) mutations including SNPs or InDels that change the activity or function of enzymes; iii) epigenetic changes that alter the gene expression pattern of a cell without impacting the genome sequence itself. To understand the relative contribution of these towards phenotype evolution, full genome sequences and methylomes of 6 related cell lines were analysed for changes in genome sequence and in DNA-methylation patterns. In addition, histone modifications and DNA-methylation patterns at several time points of a batch culture were determined. Finally, different methods to assess genomic stability over time were tested, including the distribution and spread of chromosome counts per cell in a population, and the analysis of large scale rearrangements by chromosome painting and amplified fragment length polymorphism (AFLP).
In summary, our results reveal the following picture: On the epigenetic level, short term adaptation of gene expression patterns to alterations in the environment (such as changes in nutrient availability or waste concentrations during a process) are predominantly controlled by modifications of histones and resulting changes in chromatin states. Long term adaptation to altered culture conditions, such as the transition from adherent to suspension culture, adaptation to different media or selection of specific phenotypes, are controlled by more stable changes in DNA-methylation patterns which are largely inherited by daughter cells as long as conditions remain constant. Genomic variants including SNPs, InDels, translocations, copy number variation and inversions, occur (and disappear) on a continuous basis, even over time. These variants happen on a random basis, they may contribute to phenotype if they provide a growth advantage, however, due to their continuous occurrence they are difficult to stabilize and/or control and may well be unavoidable. The majority of SNPs (99%) have no impact on coding sequence. All populations analysed, whether subclone or pool, contained a comparable absolute number of variants and at a similar frequency distribution within the population. The effect of subcloning on genome homogeneity is thus lost by the time cells are expanded to sufficient numbers for an MCB. Due to the variation present in each population, methods to assess genomic identity or stability are severely hampered by background noise, making the use of AFLP and probably other methods such as STR or DNA fingerprinting difficult. Nevertheless, genomic changes can be followed and semi-quantified by these methods in combination with rigid statistic tests. Counting the number of chromosomes per nucleus reveals a large spread in numbers, with typically only 30-50% of cells forming a peak at a dominant chromosome count. Again, cells with aberrant chromosome counts appear and disappear on a continuous basis, as subcloning does not lead to more homogenous count distributions. Over time, chromosome counts become more divergent, frequently near-tetraploid counts appear. Chromosome painting reveals frequent, large scale rearrangements, with aberrant chromosomes present from start, and/or appearing and disappearing over time.
In view of these results, the question arises whether subcloning is a suitable step to ensure genomic homogeneity and stability and whether, rather than proving that a clone is actually derived from a single cell, efforts should not be directed towards developing tools and methods that enable reliable and rapid characterization of subclones/cell lines in terms of homogeneous behavior rather than genome. While subcloning may be required for assurance of a single gene integration site or for selection of specific behavior that may be energetically more demanding and thus requires protection from outgrowth by faster growing cells, the common expectation that subclones are genomically homogenous needs to be challenged for a rapidly growing mammalian cell line
Junior Recital: Gillian Borth
Kemp Recital HallApril 25, 2012Wednesday Evening6:00 p.m
Municipal Tort Liability for Erroneous Issuance of Building Permits: A National Survey
Actions alleging municipal tort liability for negligent administration of building and zoning codes are part of the current judicial and legislative trend to abolish municipal tort immunity. In surveying how such actions are treated, this Comment briefly examines the historical background of governmental immunity. It then categorizes the states according to the scope of governmental tort immunity currently recognized. After establishing these categories, this Comment applies the law under each category to the facts of Preston v. City of Daniellville, the hypothetical case. It then analyzes the public duty defense raised by the municipality, focusing on the origin of the defense and on its continued use as a municipal defense to negligence actions. This Comment concludes by recommending one type of governmental tort claims act which best balances the equities between the injured individual and the municipality
Bamboo mosaic
This article describes the symptoms of bamboo mosaic, the viral pathogen, and integrated management practices that can effectively reduce disease occurance
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