2,740 research outputs found
Rb and Rc Crises
No full textThe Rb and Rc crises described by Kaoru Hagiwara in hep-ph/9512425 [2] can be resolved by the T-quark mass value of 130 GeV and the αs(MZ) value of 0.106 of the D4 − D5 − E6 model described in hep-ph/9501252 [5] and quant-ph/9503009 [6]. c○1995 Frank D. (Tony) Smith, Jr., Cartersville, Georgia USA1 Introduction. During 1995, precision electroweak data have confirmed the predictions of the Standard Model, with no new physics, with the possible exception of the two observables Rb and Rc. In his recent review, Kaoru Hagiwara [2] has described the situation i
A Box-Cox double-hurdle model of wildlife valuation: the citizen’s perspective.
No full textA stated-preference approach is used to elicit the attitudes of the general public towards coyotes conservation. The payment vehicle is presented in a way that explicitly prompts individuals to adopt a citizen perspective, rather than a consumer perspective, when responding to the survey. To deal with the large numbers of zero responses, a Box- Cox Double Hurdle specification is used to model separately individuals’ choices about whether to support conservation or not and their choice about the degree of support. The results show that simpler analyses that do not account explicitly for this two different decisions would lead to misleading conclusions in the study of nuisance wildlife. The study uses a survey conducted in Prince Edward Island (Canada).Coyotes; wildlife valuation, citizen versus consumer preferences; paymentvehicle; Box-Cox, double hurdle time-series, co- integration, Error Correction Model.
Spam on the Internet: can it be eradicated or is it here to stay?
No full textA discussion of the rise in unsolicited bulk e-mail, its effect on tertiary education, and some of the methods being used or developed to combat it. Includes an examination of block listing, protocol change, economic and computational solutions, e-mail aliasing, sender warranted e-mail, collaborative filtering, rule-based and statistical solutions, and legislation
Molecular origin of mesoderm : conservation of T-box genes in non-bilaterian animals
No full textSeveral members of the T-box gene family were characterized from cnidarians, ctenophores, sponges and placozoans, which are considered as the four metazoan phyla at the basis of animal evolution leading to bilaterians. T-box genes code for transcription factors with high sequence similarity in a region of about 180 amino acids called T-box domain, which is involved in DNA binding. T-box genes have important roles in many developmental processes such as mesoderm formation, antero-posterior axis formation, muscle and limb formation. Thus, T-box genes have been considered key genes to study developmental processes linked to evolutionary aspects. In this study it is shown that the four extant nonbilaterian phyla have members of well-defined T-box gene subfamilies such as Brachyury or Tbx2/3. These are clear homologs of higher evolved bilaterian genes, suggesting the presence of a complex T-box gene family already in the hypothetical common ancestor of all metazoans (Urmetazoa). The data collected in this study were also used to test the phylogenetic relationship of the four basal metazoan phyla in relation to bilaterian animals. Molecular phylogeny has redefined the evolutionary tree, introducing the ecdysozoa and lophotrochozoa as new clades of protostomes, but did not solve the relationship and the branching order of many phyla, especially of the four phyla at the base of animal evolution. In this study most of the investigations were done to clarify the position of the placozoan Trichoplax adhaerens, which is an enigmatic organism that has been interpreted either as a derived cnidarian or as a primitive non-bilaterian within its own phylum named Placozoa. The phylogenetic analyses reported here confirm that Trichoplax forms an own phylum, but does not really improve the knowledge about its phylogenetic position. An important improvement for the investigation of the biology of Trichoplax was achieved by adapting in situ hybridisation methods. Experiments with T-box genes such as Brachyury and Tbx2/3, homeobox genes such as Not and Trox-2, and additional reference genes suggest that Trichoplax has more than the four cell types described in the literature and that the process of regeneration could be regulated by a homeobox gene of the Not class
Identification and validation of transcription factors that regulate chromatin dynamics
No full textGene expression has to be tightly regulated during all cellular processes. During embryonic
development differentiating cells loose their developmental potential and acquire specific
functions by activating lineage-specific genes. Gene transcription programs are regulated by
transcription factors (TFs) in concert with dynamic changes in local chromatin organisation
of the DNA template. Both pathways are crucial for specific reprogramming of cells. However,
how TFs and chromatin marks exactly contribute to regulate gene expression programs
is not fully understood. For instance, the binding patterns of most mammalian TFs are still
unknown as well as how binding specificity is achieved. Chromatin modifications are highly
dynamic and cell-type specific. By regulating access to the DNA template they might guide
TF binding. As most chromatin modifications have simply been associated with gene activity,
a central remaining question is how chromatin modifications impact on gene expression
and if they are a cause or consequence of the transcriptional state of a gene.
Further it is still an open question how chromatin marks are targeted to specific loci and
how they are dynamically regulated. Trimethylation of histone 3 at lysine 27 (H3K27me3) is
set by the Polycomb group of proteins, which regulate body patterning during development.
Polycomb-mediated H3K27me3 is associated with gene repression and essential for cellular
differentiation. Further work shows that H3K27me3 targets are cell-type specific and highly
dynamic during differentiation. It is unclear how these changes are regulated. Thus, we
hypothesise that TFs, by recognising distinct DNA motifs, could contribute to the required
specificity of chromatin reprogramming. In collaboration with the group of Erik van Nimwegen
we applied an unbiased approach to model changes in H3K27me3 methylation during in vitro
neuronal differentiation in terms of predicted transcription factor binding sites. This
approach predicts many TFs to regulate H3K27me3 at specific stages of cellular differentiation.
We experimentally focus on the validation of the RE-1 silencing transcription factor (REST)
and the family of SNAIL TFs, which are both predicted to regulate a gain of H3K27me3 levels
as stem cells differentiate to neuronal progenitor cells. We determine genome-wide binding
sites of REST at these two cellular stages and show that measured binding sites of REST show
a high overlap with predicted ones. Mapping H3K27me3 in stem cells and progenitor cells of
wild type and REST knock out (RESTko) cells shows a specific loss of H3K27me3 at
promoter-proximal REST binding sites in neuronal progenitors, validating the computational
prediction. Moreover, short promoter fragments containing either REST or SNAIL binding sites
are sufficient to recruit H3K27me3, whereas deletion of the respective binding sites results
in a significant loss of H3K27me3. These results suggest that TFs are important contributors
in the regulation of chromatin dynamics. However, further experiments are required to test if
this is a general feature of TFs or a specialised role for REST and SNAIL proteins. In this
context the extension of TF binding maps is crucial, as binding preferences for only 20-30%
of all TFs are known at present. Extending this list, together with further perturbation
experiments, will elucidate to what extent TF binding patterns can explain both changes in
chromatin state as well as transcription
Quenched invariance principles for random walks and elliptic diffusions in random media with boundary
No full textVia a Dirichlet form extension theorem and making full use of two-sided heat kernel estimates, we establish quenched invariance principles for random walks in random environments with a boundary. In particular, we prove that the random walk on a supercritical percolation cluster or amongst random conductances bounded uniformly from below in a half-space, quarter-space, etc., converges when rescaled diffusively to a reflecting Brownian motion, which has been one of the important open problems in this area. We establish a similar result for the random conductance model in a box, which allows us to improve existing asymptotic estimates for the relevant mixing time. Furthermore, in the uniformly elliptic case, we present quenched invariance principles for domains with more general boundaries
Planetary stewardship in an urbanizing world: beyond city limits
No full textCities are rapidly increasing in importance as a major factor shaping the Earth system, and as such must take corresponding responsibility. With currently over half of the world population, cities are supported by resources originating from primarily rural regions that are often located around the world far distant from the urban loci of use. The multiple and complex environmental and social challenges the world faces require interconnected solutions and a coordinated governance approach to planetary stewardship. There is a new opportunity to conceptualize a key component of planetary stewardship as a global system of cities that develop sustainable processes and policies in concert with its non-urban areas. The potential for cities to cooperate as a system and with rural connectivity could not only increase their capacity to effect change and foster stewardship at the planetary scale but also increase their resource security
Exact Travelling wave solutions for Cattaneo’s reaction diffusion for prisoner’s dilemma game
No full textMathematics Department
King Saud University
Women Students Medical Studies & Sciences Sections
P. O. Box 22452, Riyadh 11495,, Saudi Arabia
e-mail: [email protected]
2) Mathematics Department
College of Science
Kingdom of Saudi Arabia
P. O. Box 2455, Riyadh 11451, Saudi Arabia
e-mail: [email protected]
AbstractIn this work, we use factorization method to find explicit exact particular
travelling wave solutions for or Cattaneo’s reaction diffusion for
Prisoner’s dilemma (PD) game. Using the particular solutions for these
equations we find the two-parameter solutions for the equation
A framework to identify epigenome and transcription factor crosstalk
No full textWhile changes in chromatin are integral to transcriptional reprogramming during cellular differentiation, it is currently unclear how chromatin modifications are targeted to specific loci. To systematically identify transcription factors (TFs) that can direct chromatin changes during cell fate decisions, we model the genome-wide dynamics of chromatin marks in terms of computationally predicted TF binding sites. By applying this computational approach to a time course of Polycomb-mediated H3K27me3 marks during neuronal differentiation of murine stem cells, we identify several motifs that likely regulate dynamics of this chromatin mark. Among these, the motifs bound by REST and by the SNAIL family of TFs are predicted to transiently recruit H3K27me3 in neuronal progenitors. We validate these predictions experimentally and show that absence of REST indeed causes loss of H3K27me3 at target promoters in trans, specifically at the neuronal progenitor state. Moreover, using targeted transgenic insertion, we show that promoter fragments containing REST or SNAIL binding sites are sufficient to recruit H3K27me3 in cis, while deletion of these sites results in loss of H3K27me3. These findings illustrate that the occurrence of TF binding sites can determine chromatin dynamics. Local determination of Polycomb activity by Rest and Snail motifs exemplifies such TF based regulation of chromatin. Furthermore, our results show that key TFs can be identified ab initio through computational modeling of epigenome datasets using a modeling approach that we make readily accessible
HMD versus PDA: A comparative study of the user out-of-box experience
No full textThe out-of-box experience (OOBE) has been identified as a significant factor contributing to user perception and acceptance of products and technologies. Whilst there has been considerable emphasis placed on formalising methodological procedures for evaluating the OOBE and on the creation of positive user experiences through appropriate interfaces and applications, relatively little work has been undertaken examining how the OOBE is impacted when the experience itself covers a range of (possibly interconnected) devices. In this paper we report the results of an empirical study which examined the OOBE when a Personal Digital Assistant (PDA) and Head Mounted Device (HMD) were configured and then connected for inter-operability purposes. Our findings show that type of device has a considerable impact on the OOBE, with the ask of interconnecting devices having a detrimental effect on the OOBE. The OOBE, however, is in main unaffected by user type and gender
- …
