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Littérature scientifique sur le sujet « Hox clusters »

Auteur : Grafiati

Publié le 4 juin 2021

Mis à jour le 1 février 2022

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Articles de revues sur le sujet "Hox clusters"

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Darbellay, Fabrice, Célia Bochaton, Lucille Lopez-Delisle, Bénédicte Mascrez, Patrick Tschopp, Saskia Delpretti, Jozsef Zakany et Denis Duboule. « The constrained architecture of mammalian Hox gene clusters ». Proceedings of the National Academy of Sciences 116, n^o 27 (17 juin 2019) : 13424–33. http://dx.doi.org/10.1073/pnas.1904602116.

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In many animal species with a bilateral symmetry, Hox genes are clustered either at one or at several genomic loci. This organization has a functional relevance, as the transcriptional control applied to each gene depends upon its relative position within the gene cluster. It was previously noted that vertebrate Hox clusters display a much higher level of genomic organization than their invertebrate counterparts. The former are always more compact than the latter, they are generally devoid of repeats and of interspersed genes, and all genes are transcribed by the same DNA strand, suggesting that particular factors constrained these clusters toward a tighter structure during the evolution of the vertebrate lineage. Here, we investigate the importance of uniform transcriptional orientation by engineering several alleles within the HoxD cluster, such as to invert one or several transcription units, with or without a neighboring CTCF site. We observe that the association between the tight structure of mammalian Hox clusters and their regulation makes inversions likely detrimental to the proper implementation of this complex genetic system. We propose that the consolidation of Hox clusters in vertebrates, including transcriptional polarity, evolved in conjunction with the emergence of global gene regulation via the flanking regulatory landscapes, to optimize a coordinated response of selected subsets of target genes in cis.

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De Kumar, Bony, et Robb Krumlauf. « HOXs and lincRNAs : Two sides of the same coin ». Science Advances 2, n^o 1 (janvier 2016) : e1501402. http://dx.doi.org/10.1126/sciadv.1501402.

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The clustered Hox genes play fundamental roles in regulation of axial patterning and elaboration of the basic body plan in animal development. There are common features in the organization and regulatory landscape of Hox clusters associated with their highly conserved functional roles. The presence of transcribed noncoding sequences embedded within the vertebrate Hox clusters is providing insight into a new layer of regulatory information associated with Hox genes.

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Ruddle, Frank H., Kevin L. Bentley, Michael T. Murtha et Neil Risch. « Gene loss and gain in the evolution of the vertebrates ». Development 1994, Supplement (1 janvier 1994) : 155–61. http://dx.doi.org/10.1242/dev.1994.supplement.155.

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Homeobox cluster genes (Hox genes) are highly conserved and can be usefully employed to study phyletic relationships and the process of evolution itself. A phylogenetic survey of Hox genes shows an increase in gene number in some more recently evolved forms, particularly in vertebrates. The gene increase has occurred through a two-step process involving first, gene expansion to form a cluster, and second, cluster duplication to form multiple clusters. We also describe data that suggests that non-Hox genes may be preferrentially associated with the Hox clusters and raise the possibility that this association may have an adaptive biological function. Hox gene loss may also play a role in evolution. Hox gene loss is well substantiated in the vertebrates, and we identify additional possible instances of gene loss in the echinoderms and urochordates based on PCR surveys. We point out the possible adaptive role of gene loss in evolution, and urge the extension of gene mapping studies to relevant species as a means of its substantiation.

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Novikova, Elena L., et Milana A. Kulakova. « There and Back Again : Hox Clusters Use Both DNA Strands ». Journal of Developmental Biology 9, n^o 3 (15 juillet 2021) : 28. http://dx.doi.org/10.3390/jdb9030028.

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Bilaterian animals operate the clusters of Hox genes through a rich repertoire of diverse mechanisms. In this review, we will summarize and analyze the accumulated data concerning long non-coding RNAs (lncRNAs) that are transcribed from sense (coding) DNA strands of Hox clusters. It was shown that antisense regulatory RNAs control the work of Hox genes in cis and trans, participate in the establishment and maintenance of the epigenetic code of Hox loci, and can even serve as a source of regulatory peptides that switch cellular energetic metabolism. Moreover, these molecules can be considered as a force that consolidates the cluster into a single whole. We will discuss the examples of antisense transcription of Hox genes in well-studied systems (cell cultures, morphogenesis of vertebrates) and bear upon some interesting examples of antisense Hox RNAs in non-model Protostomia.

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Balavoine, Guillaume, Renaud de Rosa et André Adoutte. « Hox clusters and bilaterian phylogeny ». Molecular Phylogenetics and Evolution 24, n^o 3 (septembre 2002) : 366–73. http://dx.doi.org/10.1016/s1055-7903(02)00237-3.

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Krumlauf, Robb. « Hox genes, clusters and collinearity ». International Journal of Developmental Biology 62, n^o 11-12 (2018) : 659–63. http://dx.doi.org/10.1387/ijdb.180330rr.

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This year marks the 40th anniversary of the discovery by Ed Lewis of the property of collinearity in the bithorax gene complex in Drosophila. This landmark work illustrated the need to understand regulatory mechanisms that coordinate expression of homeotic gene clusters. Through the efforts of many groups, investigation of the Hox gene family has generated many fundamental findings on the roles and regulation of this conserved gene family in development, disease and evolution. This has led to a number of important conceptual advances in gene regulation and evolutionary biology. This article presents some of the history and advances made through studies on Hox gene clusters.

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Prince, V. E., L. Joly, M. Ekker et R. K. Ho. « Zebrafish hox genes : genomic organization and modified colinear expression patterns in the trunk ». Development 125, n^o 3 (1 février 1998) : 407–20. http://dx.doi.org/10.1242/dev.125.3.407.

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The Hox genes are implicated in conferring regional identity to the anteroposterior axis of the developing embryo. We have characterized the organization and expression of hox genes in the teleost zebrafish (Danio rerio), and compared our findings with those made for the tetrapod vertebrates. We have isolated 32 zebrafish hox genes, primarily via 3′RACE-PCR, and analyzed their linkage relationships using somatic cell hybrids. We find that in comparison to the tetrapods, zebrafish has several additional hox genes, both within and beyond the expected 4 hox clusters (A-D). For example, we have isolated a member of hox paralogue group 8 lying on the hoxa cluster, and a member of hox paralogue group 10 lying on the b cluster, no equivalent genes have been reported for mouse or human. Beyond the 4 clusters (A-D) we have isolated a further 3 hox genes (the hoxx and y genes), which according to their sequence homologies lie in paralogue groups 4, 6, and 9. The hoxx4 and hoxx9 genes occur on the same set of hybrid chromosomes, hinting at the possibility of an additional hox cluster for the zebrafish. Similar to their tetrapod counterparts, zebrafish hox genes (including those with no direct tetrapod equivalent) demonstrate colinear expression along the anteroposterior (AP) axis of the embryo. However, in comparison to the tetrapods, anterior hox expression limits are compacted over a short AP region; some members of adjacent paralogue groups have equivalent limits. It has been proposed that during vertebrate evolution, the anterior limits of Hox gene expression have become dispersed along the AP axis allowing the genes to take on novel patterning roles and thus leading to increased axial complexity. In the teleost zebrafish, axial organization is relatively simple in comparison to that of the tetrapod vertebrates; this may be reflected by the less dispersed expression domains of the zebrafish hox genes.

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Drabkin, Harry, Sharvari Gadgil, Chan Zeng, Anna Baron et Olivier Bernard. « Homeodomain Expression in AML and T-ALL Cell Lines. » Blood 104, n^o 11 (16 novembre 2004) : 3369. http://dx.doi.org/10.1182/blood.v104.11.3369.3369.

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Abstract HOX genes are frequent targets of chromosomal translocations and retroviral integrations in human and murine acute leukemia, often involving genes at the 5′-end of the HOX clusters. We previously reported that HOX expression patterns in AML were related to prognostic cytogenetic subsets. We also identified a distinct subset of patients with intermediate cytogenetics based on high levels of HOX and FLT3 expression, frequent FLT3 mutations and a low incidence of C/EBPa mutations. Certain cases of T-ALL also have rearrangements of homeodomain genes and some T-ALLs express limited myeloid markers. To further explore the spectrum of homeodomain gene expression, we developed qRT-PCR assays for nearly all clustered HOXA-D genes, selected homeodomain genes on chromosomes often altered in AML, and selected polycomb (Pc) genes, FLT3 and MLL. Altogether, 52 genes were analyzed in 32 AML and T-ALL cell lines. FLT3 expression was confined to a subset of AMLs. HOX11, HOX11L2 and NKX2.5 were expressed only in cases involving rearrangements of these genes. The Pc and MLL genes were uniformly expressed. Among HOX clusters, the frequency of gene expression was HOXA>B>C>D. Genes more highly expressed in the HOXC and D clusters were those at the 5′-ends (e.g., D13, C10). Marked or selective overexpression of individual genes suggests their possible involvement in the disease process, immortalization or differentiation. Examples include EN1 (SUPT1), D13 (MEGA1, B9 (PEER). A hierarchical cluster analysis based on homeodomain genes successfully identified subsets of related cell lines. Thus, the analysis of quantitative HOX expression may provide an important new tool to better understand the biology of acute leukemia.

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Papageorgiou, Spyros. « Hox Gene Collinearity May Be Related to Noether Theory on Symmetry and Its Linked Conserved Quantity ». J — Multidisciplinary Scientific Journal 3, n^o 2 (24 avril 2020) : 151–61. http://dx.doi.org/10.3390/j3020013.

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Hox Gene Collinearity (HGC) is a fundamental property that controls the development of many animal species, including vertebrates. In the Hox gene clusters, the genes are located in a sequential order Hox1, Hox2, Hox3, etc., along the 3’ to 5’ direction of the cluster in the chromosome. During Hox cluster activation, the Hox genes are expressed sequentially in the ontogenetic units D1, D2, D3, etc., along the anterior–posterior axis (A-P) of the early embryo. This collinearity, first observed by E.B. Lewis, is surprising because the spatial collinearity of these structures (Hox clusters and embryos) correlates entities that differ by about four orders of magnitude. Biomolecular mechanisms alone cannot explain such correlations. Long-range physical interactions, such as diffusion or electric attractions, should be involved. A biophysical model (BM) was formulated, which, in alignment with the biomolecular processes, successfully describes the existing vertebrate genetic engineering data. One hundred years ago, Emmy Noether made a fundamental discovery in mathematics and physics. She proved, rigorously, that a physical system obeying a symmetry law (e.g., rotations or self-similarity) is followed by a conserved physical quantity. It is argued here that HGC obeys a ‘primitive’ self-similarity symmetry. In this case, the associated primitive conserved quantity is the irreversibly increasing ‘ratchet’-like Hoxgene ordering where some genes may be missing. The genes of a vertebrate Hox clusterare located along a finite straight line. The same order follows the ontogenetic unitsof the vertebrate embryo. Therefore, HGC is a manifestation of a primitive Noether Theory (NT). NT may be applied to other than the vertebrate case, for instance, to animals with a circular topological symmetry. For example, the observed abnormal Hox gene ordering of the echinoderm Hox clusters may be reproduced by a double-strand break of the circular Hox gene ordering and its subsequent incorporation in the flanking chromosome.

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Schiemann, Sabrina M., José M. Martín-Durán, Aina Børve, Bruno C. Vellutini, Yale J. Passamaneck et Andreas Hejnol. « Clustered brachiopod Hox genes are not expressed collinearly and are associated with lophotrochozoan novelties ». Proceedings of the National Academy of Sciences 114, n^o 10 (22 février 2017) : E1913—E1922. http://dx.doi.org/10.1073/pnas.1614501114.

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Temporal collinearity is often considered the main force preserving Hox gene clusters in animal genomes. Studies that combine genomic and gene expression data are scarce, however, particularly in invertebrates like the Lophotrochozoa. As a result, the temporal collinearity hypothesis is currently built on poorly supported foundations. Here we characterize the complement, cluster, and expression of Hox genes in two brachiopod species,Terebratalia transversaandNovocrania anomala.T. transversahas a split cluster with 10 genes (lab,pb,Hox3,Dfd,Scr,Lox5,Antp,Lox4,Post2, andPost1), whereasN. anomalahas 9 genes (apparently missingPost1). Our in situ hybridization, real-time quantitative PCR, and stage-specific transcriptomic analyses show that brachiopod Hox genes are neither strictly temporally nor spatially collinear; onlypb(inT. transversa),Hox3(in both brachiopods), andDfd(in both brachiopods) show staggered mesodermal expression. Thus, our findings support the idea that temporal collinearity might contribute to keeping Hox genes clustered. Remarkably, expression of the Hox genes in both brachiopod species demonstrates cooption of Hox genes in the chaetae and shell fields, two major lophotrochozoan morphological novelties. The shared and specific expression of Hox genes, together withArx,Zic, and Notch pathway components in chaetae and shell fields in brachiopods, mollusks, and annelids provide molecular evidence supporting the conservation of the molecular basis for these lophotrochozoan hallmarks.

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Thèses sur le sujet "Hox clusters"

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Sessa, Luca. « Epigenetic control of human HOX clusters ». Thesis, Open University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402692.

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Pace, Ryan M., Miodrag Grbić et Lisa M. Nagy. « Composition and genomic organization of arthropod Hox clusters ». BioMed Central, 2016. http://hdl.handle.net/10150/615123.

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Le, Boiteux Elisa. « Altération du contrôle de H3K27me3 et dérégulation transcriptionnnelle dans les gliomes : études des clusters HOX ». Thesis, Université Clermont Auvergne‎ (2017-2020), 2019. http://www.theses.fr/2019CLFAS027.

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Il est largement documenté que les patrons épigénétiques sont altérés dans les cancers. Pour autant, l’étendue et la nature précise de ces altérations, tout comme leur impact sur l’expression des gènes, restent encore peu appréciés. Mon projet de thèse est bâti sur ce constat, et s’inscrit en particulier dans la recherche des causes et conséquences des altérations épigénétiques dans les gliomes. Ces tumeurs du système nerveux central représentent en effet un excellent modèle, car elles présentent des défauts de méthylation de l’ADN permettant de discriminer deux populations de tumeurs avec des caractéristiques cliniques différentes. Notre stratégie, basée sur des analyses moléculaires exhaustives, s’est appuyée sur une cohorte de 70 échantillons tumoraux, classés sur la base de leur statut IDH, et de six lignées de cellules souches de glioblastomes (CSG).Ces travaux ont tout d’abord permis de relativiser la contribution de la méthylation de l’ADN dans les dérégulations transcriptionnelles observées dans les gliomes. Il apparait en effet que ce sont plutôt les altérations au niveau de la chromatine bivalente, et plus spécifiquement de la marque H3K27me3, qui sont la cause principale de ces dérégulations transcriptionnelles. Spécifiquement, nos données supportent un modèle selon lequel l’altération dans le contrôle de la marque H3K27me3, et plus spécifiquement dans les interactions entre le complexe PRC2 et la machinerie de transcription spécifique au cerveau, est la cause principale des altérations transcriptionnelles dans les gliomes.Cette étude révèle également que les gènes à homéodomaine, et en particulier les gènes HOX, constituent une catégorie à part dans les gliomes les plus agressifs (IDHwt). Leur signature moléculaire, associant gain d’expression et gain de méthylation de l’ADN, est en effet atypique. Nos données révèlent que cette altération est généralisée aux quatre clusters HOX, et que la réactivation de ces gènes est liée à la perte drastique et spécifique de la marque H3K27me3 sur ces régions. Cette étude conduit également à proposer un modèle original selon lequel l’hypométhylation globale de l’ADN est un élément déclencheur de l’expression ectopique détectée au niveau de nombreux gènes, et dont l’altération des gènes HOX aurait, via un effet domino, un rôle central. L’observation de l’altération de la marque H3K27me3 dans les gliomes, et en particulier aux clusters HOX, nous a également amené à nous interroger sur le rôle des ARN non codants dans ces mécanismes. En ce sens, un transcrit non codant encore peu caractérisé, nommé HOXA-AS2 (situé en antisens au niveau du cluster HOXA), a été identifié. Ce transcrit est significativement et spécifiquement surexprimé dans les gliomes IDHwt. Des approches de sous-expression dans des lignées bien caractérisées de CSG suggèrent un rôle central de HOXA-AS2 dans la biologie de ces cellules. Il contribuerait ainsi au caractère pathologique des CSG en inhibant les voies de l’inflammation et en favorisant la capacité des cellules à proliférer.Dans son ensemble, ce travail revisite le lien entre altérations épigénétiques et défauts d’expression dans les cancers et met en évidence qu’une altération dans le contrôle de la marque H3K27me3 est la principale cause des défauts d’expression des gènes
Epigenetic alterations are a well-known signature of cancer cells. However, the causes of these defects, as well as their consequence on gene expression, remain elusive. My thesis project specifically lies in this thematic, and focuses on the causes and consequences of epigenetic alterations in gliomas. These brain tumors can be divided into two subsets, based on IDH mutation status, that are characterized by different methylation profiles. Interestingly, the mutation of IDH is also associated with a better prognosis. Our strategy, based on exhaustive molecular analyses, relies on the study of 70 glioma samples, classified according to their IDH status, and of six glioblastoma stem cell (GSC) lines.We found that most transcriptional alterations in tumor samples were DNA methylation-independent. Instead, altered histone H3 trimethylation at lysine 27 (H3K27me3) was the predominant molecular defect at deregulated genes. Our results also suggest that the presence of a bivalent chromatin signature at CpG island promoters in stem cells predisposes not only to hypermethylation, as widely documented, but more generally to all types of transcriptional alterations in transformed cells. In addition, the gene expression strength in healthy brain cells influences the choice between DNA methylation- and H3K27me3-associated silencing in glioma. Highly expressed genes were more likely to be repressed by H3K27me3 than by DNA methylation. Our findings support a model in which altered H3K27me3 dynamics, more specifically defects in the interplay between Polycomb protein complexes and the brain-specific transcriptional machinery, is the main cause of transcriptional alteration in glioma cells. Also, our study revealed that homeodomain genes, and in particular HOX genes, are characterized by an atypical defect in aggressive gliomas (IDHwt), associating a gain of expression with an aberrant gain of methylation. We determined that this alteration affect all the four HOX clusters, and that the reactivation of these genes is likely a consequence of the aberrant loss of H3K27me3 that specifically affect these clusters. This study allows to propose a model whereby global DNA hypomethylation triggers ectopic expression of numerous genes through a cascade of events, in which HOX gene alteration would have a central role.The observation that H3K27me3 is deregulated in gliomas, and particularly on HOX genes, also lead us to investigate for the role of non-coding RNA in these mechanisms. We have identified HOXA-AS2, a yet poorly characterized long non-coding RNA located at HOXA locus, that is specifically and significantly overexpressed in IDHwt gliomas. The inhibition of HOXA-AS2 in well-characterized CSG lines suggests that this transcript play a central role in the biology of these cells. Thus, it would contribute to the aggressiveness of CSG by inhibiting inflammatory pathways and promoting cell proliferation. Altogether, these works revisit the relationship between epigenetic alterations and aberrant transcription, and present the control of H3K27me3 as the main cause of transcriptionnel defects in cancer

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Cooke, Elizabeth A. « How to build a cluster : the formation and evolution of galaxies in high-redshift clusters and protoclusters ». Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/35454/.

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High redshift galaxy protoclusters are the precursors of today’s massive clusters; the sites of formation of the most massive galaxies in the present-day Universe. By studying these immature structures we can directly analyse the formation of galaxies in the densest environments without relying on extrapolations from low redshift. Finding protoclusters is challenging due to the need for very wide and deep surveys. Radio-loud active galactic nuclei (RLAGN) have been shown to preferentially reside in overdense environments at z > 1. By using these bright radio sources as beacons, protoclusters may be efficiently selected, without the need for large, blind surveys. In this thesis I study the properties of galaxies in high redshift (z > 1.3) clusters and protoclusters selected around RLAGN. Using a sample of 37 clusters and protoclusters from the Clusters Around Radio-Loud AGN (CARLA) survey, I show that the protocluster galaxies have an approximately unevolving, red observed-frame i'-[3.6] colour across 1.3 < z < 3.2. This is at odds with the simple models which are commonly used to explain the cluster red sequence in the local Universe, which predict cluster galaxy colours to become more blue at higher redshifts. Taking the full cluster population into account, I show that the formation of stars within the majority of massive cluster galaxies occurs over at least 2 Gyr, and peaks at z ~ 2–3. This is consistent with the cosmic star formation history, with star formation ending in clusters at 1 < z < 2. I further show that massive galaxies at z > 2 must have assembled within 0.5 Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in z > 2 protoclusters could have formed via dry mergers. Some of the CARLA structures exhibit signs of being mature, collapsed clusters. In a pilot project, I report on the discovery of a z = 1.58 cluster with a strong red sequence around the RLAGN 7C 1753+6311. I demonstrate that the cluster has an enhanced quiescent galaxy fraction that is three times that of the control field. I also show that this enhancement is mass dependent: 91 +/- 9% of the M* > 10^10.5 Msun cluster galaxies are quiescent, compared to only 36 +/- 2% of field galaxies, whereas the fraction of quiescent galaxies with lower masses is the same in the cluster and field environments. This is in contrast to low redshift studies which have shown that mass and environmental effects on quenching star formation are separable. In the literature there is some debate as to whether RLAGN preferentially reside in clusters of a certain stage of collapse. The presence of a dense core and a well-formed, quiescent red sequence suggest that 7C1753+6311 resides within a mature cluster. This means that distant RLAGN do not solely reside in young, uncollapsed protoclusters, rather they can be found in clusters in a wide range of evolutionary states. Finally I present results from surveys of Halpha emitters in the fields around three high redshift RLAGN. I find that there is more dust-obscured star formation in protocluster galaxies than in similarly-selected control field galaxies at z ~ 2.5 and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average I do not find a difference between the star formation rate (SFR)-mass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z ~ 2.5 is governed predominantly by galaxy mass and not the host environment. The stellar mass distribution of the protocluster galaxies is also skewed towards higher masses and there is a significant lack of low mass (M < 10^10 Msun) galaxies within the protocluster core. These results have implications for future protocluster surveys. The lack of low mass galaxies affects the level of overdensity which is detected. If only high mass galaxies are considered, the density of the protocluster field may be over-estimated. This means that it is important when quantifying protoclusters to compare their mass functions, rather than simply number overdensities. I also find that some radio galaxies do not reside in the centre, or densest region of the surrounding structure, meaning the overdensity measured in an aperture centred on the RLAGN will be underestimated. This means that future studies of (proto)clusters around RLAGN should use larger fields of view in order to establish the existence of a (proto)cluster.

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Basford, Joshua E. « Colinear Expression of the Mouse HoxB Cluster : Potential Regulatory Role of Histone H4 Acetylation ». University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin997988435.

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Herrera, Úbeda Carlos. « Conservation of different mechanisms of Hox cluster regulation within chordates ». Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668561.

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In this thesis we have covered the importance of finding underlying conservation events to better understand the regulatory mechanisms of important development orchestrators like the Hox cluster. As an example of these non-evident conservation, we have shown two cases, as described below. The first case studied, after developing a software able to detect homologous long noncoding RNAs by means of microsynteny analyses, is the conservation of Hotairm1 in Chordata. For assessing the homology of this lncRNA, first we had to identify the lncRNA fraction within the B. lanceolatum transcriptome. With a reliable lincRNA dataset, we used our pipeline, LincOFinder, to identify orthologs between human and amphioxus through microsynteny. After the identification of Hotairm1 as one of the lincRNAs with conserved microsynteny, we used Xenopus as a proxy to analyse the homologies in the expression and the function. We had to proceed this way due to the difficulties associated with the inhibition of genes in B. lanceolatum, and the unavailability of expression patterns for Hotairm1 in the bibliography. After we successfully characterised Hotairm1 expression in amphioxus and Xenopus, we injected morpholino oligonucleotides to target and inhibit the splicing of Hotairm1 to promote an isoform imbalance. Through the phenotype obtained and the performing of qPCRs, we were able to deduct the mechanism of Hotairm1 and successfully relate this mechanism with the one described in human cells. With all the data obtained we were able to strongly suggest that the amphioxus Hotairm1 is homologous to the Xenopus and human Hotairm1, thus being conserved in most of the lineages within chordates. The second case studied was the conservation of the regulation of the Hox cluster mediated by Cdx. When analysing the B. floridae knockouts of Cdx and Pdx obtained using the TALEN technique, we found a severe phenotype of the developing larvae in Cdx-/- and a mild phenotype in Pdx-/-. The Cdx-/- phenotype consisted in the disruption of posterior gut development, as well as an underdevelopment of the postanal tail, coupled with a non-opening anus. When looking at changes in the expression of the Hox cluster in this Cdx-/- embryos, we found collinear misregulation of the expressed Hox genes, with the most anterior Hox cluster genes upregulated, and the most posterior ones downregulated. This is very similar to findings seen in triple morpholino knockdowns of the Cdx genes in Xenopus, indicating that in both, Xenopus and amphioxus, Cdx is regulating the Hox cluster through a homologous mechanism.

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Engerud, Martine Lien. « Constructing Clusters : How Politics Diverts Attention from Innovation ». Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for industriell økonomi og teknologiledelse, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-25444.

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Klynge- og innovasjonsteorier har i de senere årene fått økt oppmerksomhet, noe som har bidratt til en oppblomstring av offentlig strategier for innovasjon og næringsutvikling. Klyngeinitiativ er blitt promotert som regionale utviklingsverktøy for offentlige myndigheter, med en forventning om at de skal påvirke konkurransekraften positivt gjennom økt produktivitet og innovasjonstakt. Næringsklynger defineres som “geografiske konsentrasjoner av tilknyttede selskaper, spesialiserte leverandører, serviceselskaper, selskaper fra relaterte industrier og omkringliggende institusjoner (som for eksempel universiteter, virkemiddelapparat og handelsorganisasjoner.” (Porter 2000:15) Denne studien argumenterer for at klynger initiert for å promotere regional utvikling, sjelden innfrir forventningene. Det er få utvetydige bevis for en sammenheng mellom initiert klyngesamarbeid og innovasjon. I slike miljøer er det stor sannsynlighet for at politiske egenskaper, i form av konkurrerende interesser og oppfatninger, fører til politisk oppførsel, slik som konflikter, strategiutvikling og maktspill. Fraværet av innovasjonsresultater i denne type samarbeid, kan potensielt forklares med den sterke tilstedeværelsen av politikk. Politikk påvirker feltet, koster tid og tar energi fra de involverte aktørene. Dette avleder fokus fra den opprinnelige intensjonen om samarbeid knyttet til næringsutvikling. Politikk må derfor tas med i betraktningen nå man snakker om, planlegger og gjennomfører klyngesamarbeid. Debatter om konkrete resultater av klyngestrategier og regionale klyngeinitiativ er nesten fraværende i den offentlige debatten. Den presenterte casestudien avslører et felt hvor politikk og rivalisering mellom ulike organisasjoner og konkurrerende klyngeinitiativer er sterkt tilstedeværende. Over tid, og som følge av åpenbar konkurranse, ser det ut til at enkelte klyngeinitiativ vokser, noen slår seg sammen, mens en tredje gruppe tvinges til å legge ned. I denne studien kalles dette fenomenet ”klyngekannibalisme”. Siden politikk dominerer både etablering og utvikling av klynger, ser klyngestrategiene ut til å ha blitt strategier for å organisere det politiske innovasjonsfeltet, snarere enn et verktøy for å øke innovasjonstakten
The popularization of cluster and innovation theories has led to the development of public strategies for innovation enhancement. Cluster initiatives have been promoted as a regional development tool for public governments, proposed to lead to innovation and economic development. Clusters can be defined as “geographical concentrations of interconnected companies, specialized suppliers, service providers, firms in related industries, and associated institutions (e.g. universities, standards agencies, trade associations) in a particular field that compete but also cooperate.” (Porter, 2000:15) They are expected to affect competition by increasing productivity and drive innovation through business development. This study argues that cluster cooperation initiated to promote regional innovation seldom is successful in doing so. There is little unambiguous evidence for correlation between initiated clusters and innovation. In cluster environments, political features of actors in the form of diverging interests and perceptions often lead to political behavior such as conflicts, strategy development and power play. The lack of innovative output of initiated cluster efforts may be explained by the strong orientation towards political features and behavior. Politics influence the field, consume time and energy of involved stakeholders and deflect the original intention of cooperation related to business development. Consequently, politics must be taken into account when speaking of, planning and carrying out cluster cooperation. Debates on the outcomes of cluster strategies and cluster initiation have been almost absent in the public sphere. The case presented reveals a field where politics and rivalry both among inter-agencies and competing cluster initiatives are present. Eventually, some initiatives are enlarged, some join forces, while others die out. In this study, these phenomena are called cluster cannibalism. As politics come to dominate clusters, cluster strategies seem to have become strategies for organizing the policy field of innovation, rather than a way of actually achieving innovation.

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Croft, Rupert Alfred Charles. « Galaxy clusters and the formation of large-scale structures in the universe ». Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308751.

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Wood, Angela Clare. « Expression of the HOX A gene cluster in acute myeloid leukaemia ». Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300219.

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Fuiten, Allison. « Hox Cluster Evolution in the Highly Derived Pipefish & ; Seahorse Family ». Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24552.

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A central question in evolutionary biology is how organisms evolve highly derived and novel morphologies. More specifically, what changes to conserved developmental genes lead to the evolution of divergent morphologies? Here, I investigate the genetic and genomic changes to the developmentally important Hox genes using comparative genomics, gene expression and gene editing approaches. Hox genes code for homeodomain transcription factors that are responsible for determining the body plan of an embryo along the anterior-posterior axis, and changes to these genes have paralleled the rise of morphological diversity in the vertebrate animals. I focus my studies in a group of fish that exhibit a striking departure from the typical fish body plan: the pipefish and seahorse family, Syngnathidae. The evolution of syngnathid fish involved major modifications to their vertebrate body plan, but the developmental genetic basis of those changes is largely unknown. I describe the genomic organization of Hox clusters in a species of syngnathid pipefish—the Gulf pipefish (Syngnathus scovelli). I present an initial investigation on phenotypic consequences to the loss of hox7 genes in teleost fish—a group of Hox genes that are missing in syngnathids—using of the CRISPR/Cas9 system to induce indels in all hox7 genes (hoxa7a, hoxb7a) in the threespine stickleback (Gasterosteus aculeatus). In the second half of my thesis, I investigate noncoding changes in the syngnathid Hox clusters. I use syngnathid representative species and compared their conserved noncoding sequences within the Hox clusters to other teleost fish, non-teleost fish, and non-fish vertebrates. I present a detailed study regarding the nature of the loss of one conserved non-coding element. Results from this research indicate that the divergent syngnathid body plan is not due to rampant change in throughout Hox clusters. Also, these data do not argue for the absence of any role of genetic changes in Hox clusters. Instead, the findings presented here support the intermediate hypothesis that certain key changes to the Hox genes, microRNAs, and regulatory elements have probably contributed to their body plan developmental evolution in this unique family of fish. This work includes published co-authored material.

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Livres sur le sujet "Hox clusters"

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Renzulli, Joseph S. How to develop an authentic enrichment cluster. [Storrs, CT : National Research Center on the Gifted and Talented, 1997.

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Geada, AntÆnio Moreno Colao. Analysis of the two most 3' genes of the Hox-c cluster. Manchester : University of Manchester, 1993.

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Nidia, Morrell, Niemela Virpi et Barbá Rodolfo H, dir. Workshop on Hot Stars in Open Clusters of the Galaxy and the Magellanic Clouds : La Plata, Argentina, diciembre 1-5, 1997. México, D.F : Instituto de Astronomiá, Universidad Nacional Autónoma de México, 1999.

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United Nations Institute for Disarmament Research, dir. Unacceptable harm : A history of how the treaty to ban cluster munitions was won. New York : United Nations, 2009.

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Rimkus, Manuel. Wissenstransfer in Clustern : Eine Analyse am Beispiel des Biotech-Standorts Martinsried. Wiesbaden : Gabler, 2008.

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Heffernon, Rick. Destination Flagstaff : How important is the Flagstaff-area tourism cluster ? Tempe, Ariz : Morrison Institute for Public Policy, School of Public Affairs, College of Public Programs, Arizona State University, 2000.

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Campbell, Michael J. How to design, analyse and report cluster randomised trials in medicine and health related research. Chichester, West Sussex : John Wiley & Sons, 2014.

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Campbell, Michael J., et Stephen J. Walters. How to Design, Analyse and Report Cluster Randomised Trials in Medicine and Health Related Research. Chichester, UK : John Wiley & Sons, Ltd, 2014. http://dx.doi.org/10.1002/9781118763452.

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Dina, Brulles, dir. The cluster grouping handbook : A schoolwide model : how to challenge gifted students and improve achievement for all. Minneapolis, MN : Free Spirit Pub., 2008.

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Winebrenner, Susan. The cluster grouping handbook : A schoolwide model : how to challenge gifted students and improve achievement for all. Minneapolis, MN : Free Spirit Pub., 2008.

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Chapitres de livres sur le sujet "Hox clusters"

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Matharu, Navneet Kaur, et Rakesh K. Mishra. « Mining the Cis-Regulatory Elements of Hox Clusters ». Dans Methods in Molecular Biology, 121–31. New York, NY : Springer New York, 2014. http://dx.doi.org/10.1007/978-1-4939-1242-1_8.

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Spitz, François. « Control of Vertebrate Hox Clusters by Remote and Global Cis-Acting Regulatory Sequences ». Dans Advances in Experimental Medicine and Biology, 63–78. New York, NY : Springer New York, 2010. http://dx.doi.org/10.1007/978-1-4419-6673-5_4.

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Cardona, Charles A. « How to Use This Book ». Dans Star Clusters, 17. New York, NY : Springer New York, 2010. http://dx.doi.org/10.1007/978-1-4419-7040-4_3.

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Renzulli, Joseph S., Marcia Gentry et Sally M. Reis. « How to Develop Your Own Enrichment Cluster ». Dans Enrichment Clusters, 61–83. 2^e éd. New York : Routledge, 2021. http://dx.doi.org/10.4324/9781003234999-4.

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Koltcov, Sergei, Vera Ignatenko et Sergei Pashakhin. « How Many Clusters ? An Entropic Approach to Hierarchical Cluster Analysis ». Dans Advances in Intelligent Systems and Computing, 560–69. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-52243-8_40.

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Cavaliere, A., et S. Colafrancesco. « Intergalactic Plasma in Clusters : Evolution ». Dans Hot Thin Plasmas in Astrophysics, 315–33. Dordrecht : Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-3065-0_22.

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Jones, C., et W. Forman. « Imaging the Hot Intracluster Medium ». Dans Clusters and Superclusters of Galaxies, 49–70. Dordrecht : Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2482-9_4.

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Makarov, Sergey N., Jyrki Ahveninen, Matti Hämäläinen, Yoshio Okada, Gregory M. Noetscher et Aapo Nummenmaa. « Multiscale Modeling of EEG/MEG Response of a Compact Cluster of Tightly Spaced Pyramidal Neocortical Neurons ». Dans Brain and Human Body Modeling 2020, 195–211. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-45623-8_11.

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AbstractIn this study, the boundary element fast multipole method or BEM-FMM is applied to model compact clusters of tightly spaced pyramidal neocortical neurons firing simultaneously and coupled with a high-resolution macroscopic head model. The algorithm is capable of processing a very large number of surface-based unknowns along with a virtually unlimited number of elementary microscopic current dipole sources distributed within the neuronal arbor.The realistic cluster size may be as large as 10,000 individual neurons, while the overall computation times do not exceed several minutes on a standard server. Using this approach, we attempt to establish how well the conventional lumped-dipole model used in electroencephalography/magnetoencephalography (EEG/MEG) analysis approximates a compact cluster of realistic neurons situated either in a gyrus (EEG response dominance) or in a sulcus (MEG response dominance).

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Tsuru, Takeshi Go. « ASCA Observations of Distant Clusters of Galaxies ». Dans The Hot Universe, 65–68. Dordrecht : Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-4970-9_15.

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Bowyer, S., R. Lieu et J. P. Mittaz. « Diffuse EUV Emission from Clusters of Galaxies ». Dans The Hot Universe, 185–88. Dordrecht : Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-4970-9_43.

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Actes de conférences sur le sujet "Hox clusters"

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Sekachev, Mikhail, Cheng-Xian Lin, Zhiyu Hu et Don Dareing. « A Computational Study of Catalytic Platinum Nanoparticles With and Without OH Chemisorption During Reactions ». Dans ASME 2008 3rd Energy Nanotechnology International Conference collocated with the Heat Transfer, Fluids Engineering, and Energy Sustainability Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/enic2008-53029.

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In this paper, various energies and geometries of pure platinum nanoparticles and those of platinum nanoparticles with adsorbed OH were investigated. Ten different platinum clusters of up to 28 atoms were studied using spin-unrestricted density functional theory (DFT) with a double numerical plus polarization basis set. Three different shapes were presented, and the effect of cluster size on binding energy, total energy, and HOMO-LUMO energy gap was investigated. The same set of calculations was performed for selected clusters with OH adsorbate on the Pt(111) surface. The results show that the stability of both the pure clusters and the clusters with adsorbed OH molecule increases with an increase of cluster size. This fact indicates that direct influence of the size of Pt cluster on the reaction rate is possible, and the understanding of how cluster size would affect binding energy is important. The effect of cluster size on total energy of molecule was shown to be a linear function independent of cluster type, as expected. We also found that optimized (stable) Pt clusters were bigger in size than that of the initial clusters, or clusters with bulk geometry.

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Wa¨rmefjord, Kristina, Johan S. Carlson et Rikard So¨derberg. « A Measure of the Information Loss for Inspection Point Reduction ». Dans ASME 2008 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/detc2008-49708.

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Since the vehicle program in automotive industry gets more and more extensive, the costs related to inspection increase. Therefore, there are needs for more effective inspection preparation. In many situations, a large number of inspection points are measured, despite the fact that only a small subset of points is needed. A method, based on cluster analysis, for identifying redundant inspection points has earlier been successfully tested on industrial cases. Cluster analysis is used for grouping the variables into clusters, where the points in each cluster are highly correlated. From every cluster only one representing point is selected for inspection. In this paper the method is further developed and multiple linear regression is used for evaluating how much of the information that is lost when discarding an inspection point. The information loss can be quantified using an efficiency measure based on linear multiple regression, where the part of the variation in the discarded variables that can be explained by the remaining variables is calculated. This measure can be illustrated graphically and that helps to decide how many clusters that should be formed, i.e. how many inspection points that can be discarded.

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Ohama, Iku, Takuya Kida et Hiroki Arimura. « Discovering Relevance-Dependent Bicluster Structure from Relational Data ». Dans Twenty-Sixth International Joint Conference on Artificial Intelligence. California : International Joint Conferences on Artificial Intelligence Organization, 2017. http://dx.doi.org/10.24963/ijcai.2017/359.

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In this paper, we propose a statistical model for relevance-dependent biclustering to analyze relational data. The proposed model factorizes relational data into bicluster structure with two features: (1) each object in a cluster has a relevance value, which indicates how strongly the object relates to the cluster and (2) all clusters are related to at least one dense block. These features simplify the task of understanding the meaning of each cluster because only a few highly relevant objects need to be inspected. We introduced the Relevance-Dependent Bernoulli Distribution (R-BD) as a prior for relevance-dependent binary matrices and proposed the novel Relevance-Dependent Infinite Biclustering (R-IB) model, which automatically estimates the number of clusters. Posterior inference can be performed efficiently using a collapsed Gibbs sampler because the parameters of the R-IB model can be fully marginalized out. Experimental results show that the R-IB extracts more essential bicluster structure with better computational efficiency than conventional models. We further observed that the biclustering results obtained by R-IB facilitate interpretation of the meaning of each cluster.

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Sperry, Ben, et Curtis Morgan. « Case Study of Cluster Analysis in Intercity Passenger Rail Planning and Marketing ». Dans 2011 Joint Rail Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/jrc2011-56025.

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Recent policy and regulatory initiatives have established new momentum for intercity passenger rail among planners, policymakers, and the general public. As a result, there is a great interest in developing new passenger rail lines and expanding existing routes in intercity corridors across the country. Moving forward, there exists a need to understand how current passenger rail services are being utilized, who is riding them, and what changes could be implemented to existing routes to attract ridership — as well as to document lessons learned from existing lines that can aid service development planning for newly proposed routes. In this paper, cluster analysis is applied to passenger survey data obtained in 2007 from riders of three Amtrak routes in the state of Michigan, USA. Cluster analysis is a multivariate data analysis method used extensively in marketing and customer profile research which seeks to identify similarities among potential customers that are not immediately evident using traditional grouping techniques. Data used in the formation of the passenger clusters include traveler alternatives to the passenger rail service and the importance of service attributes, on-board activities, and station amenities. These variables and other data from the passenger survey are then used to characterize the identified clusters in terms of what kinds of passengers are in each cluster and how these passengers benefit from the rail service. The passenger clusters are also analyzed for their potential response to service improvements such as reduced travel time, increased service frequencies, or improved intermodal connections. The findings of this case study can be applied in a number of activities related to intercity passenger rail service planning for existing as well as proposed routes. The findings provide valuable insight into the needs and preferences of current passengers and can be used to formulate strategies for equipment investments or the development of new on-board amenities. From a policy perspective, passengers’ preferences for alternative travel modes in the absence of the rail service reveal how the rail service supports intercity mobility for each of the clusters. Finally, from the cluster profile, potential strategies to attract new riders can be identified. The results show that clustering analysis methodology applied in this case study is a valuable tool for intercity passenger rail planning.

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Evans, Emmeline, Jessica Menold et Christopher McComb. « Critical Thinking in the Design Classroom : An Analysis of Student Design Reflections ». Dans ASME 2019 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/detc2019-97533.

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Abstract Within the domain of education, the term “critical thinking” is widely understood to mean the various skills that comprise an individual’s logical and reasoning abilities. It is critical that designers possess these abilities so that they can solve the complex problems of an increasingly interconnected world. In order to better understand patterns in engineering students’ critical thinking, this research applies the classifications of the 2001 revision of Bloom’s Taxonomy to 49 reflections written by first-year engineering students on a two-hour design practicum. Reflections were thematically coded to identify when students operated in different levels of the cognitive process and knowledge dimensions. Using k-means clustering analysis, genres of reflection were then determined. Four unique clusters of responses were identified. Notable trends in clusters included application and evaluation of procedural knowledge. Additionally, a difference was observed between the two largest clusters regarding deviance from the design process. While one cluster of responses generally minimized discussion of deviance, the second largest cluster emphasized this deviance, highlighting it as an opportunity for future growth. This work provides insight into how students learn design and how they communicate their learning, providing insight for instructors hoping to encourage deeper critical thinking in design courses.

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Qin, Zhi-Chang, et Jian-Qiao Sun. « Cluster Analysis and Switching Control : A Post-Processing of Multi-Objective Optimal Designs ». Dans ASME 2016 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/dscc2016-9633.

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The multi-objective optimal control design usually generates hundreds or thousands of Pareto optimal solutions. How to assist an user to select an appropriate controller to implement is a post-processing issue. In this paper, we develop a method of cluster analysis of the Pareto optimal designs to discover the similarity of the optimal controllers. After we identify the clusters of optimal controllers, we then develop a switching strategy to select controls from different clusters to improve the performance. Numerical results show that the switching control algorithm is quite promising.

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Hallac, David, Sagar Vare, Stephen Boyd et Jure Leskovec. « Toeplitz Inverse Covariance-based Clustering of Multivariate Time Series Data ». Dans Twenty-Seventh International Joint Conference on Artificial Intelligence {IJCAI-18}. California : International Joint Conferences on Artificial Intelligence Organization, 2018. http://dx.doi.org/10.24963/ijcai.2018/732.

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Subsequence clustering of multivariate time series is a useful tool for discovering repeated patterns in temporal data. Once these patterns have been discovered, seemingly complicated datasets can be interpreted as a temporal sequence of only a small number of states, or clusters. However, discovering these patterns is challenging because it requires simultaneous segmentation and clustering of the time series. Here we propose a new method of model-based clustering, which we call Toeplitz Inverse Covariance-based Clustering (TICC). Each cluster in the TICC method is defined by a correlation network, or Markov random field (MRF), characterizing the interdependencies between different observations in a typical subsequence of that cluster. Based on this graphical representation, TICC simultaneously segments and clusters the time series data. We solve the TICC problem through a scalable algorithm that is able to efficiently solve for tens of millions of observations. We validate our approach by comparing TICC to several state-of-the-art baselines in a series of synthetic experiments, and we then demonstrate on an automobile dataset how TICC can be used to learn interpretable clusters in real-world scenarios.

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Razminienė, Kristina, et Manuela Tvaronavičienė. « Clusters’ Role in Globalization ». Dans Contemporary Issues in Business, Management and Education. Vilnius Gediminas Technical University, 2017. http://dx.doi.org/10.3846/cbme.2017.028.

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The purpose of this study is to review globalization literature and cluster literature to see how these two phenomena are understood, which perspective scholars refer to when analysing globalization and clusters, how can the approaches explain each other. The attention was focused more on the outcomes of globalization for the countries that are a part of the ongoing proccess rather than theoretical aspects, while cluster literature was chosen to address globalization and the attempt was to see the links between these phenomena. Bibliometrical analysis is used for the purpose, articles selected from the Emerald Insight database. The findings suggest that the main concern caused by globalization is inequality of income and wage which can be reduced by education for people can gain skills and knowledge which would make them competitive in demanding environment. Competitiveness is emphasized in cluster definition and the processes of globalization are seen as advantageous for cluster development. This literature review needs further analysis with more articles taken into consideration. The concept is advanced and developed, so there are many studies made regarding this topic. In this paper a certain aspect is observed to see how far the concept has advanced and how scholars view it.

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Li, Yong, et Ping Wang. « Cluster Cache Based K-Hop Clustered MANET Routing Protocol ». Dans 2010 6th International Conference on Wireless Communications, Networking and Mobile Computing (WiCOM). IEEE, 2010. http://dx.doi.org/10.1109/wicom.2010.5601204.

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Alajmei, Shabeeb, et Jennifer Miskimins. « Limited Entry Perforation Configurations Effect on Proppant Transport and Distribution in Fresh Water ». Dans SPE Hydraulic Fracturing Technology Conference and Exhibition. SPE, 2021. http://dx.doi.org/10.2118/204163-ms.

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Abstract Proppant transport in horizontal wellbores has received significant industry focus over the past decade. One of the most challenging tasks in the hydraulic fracturing of a horizontal well is to predict the proppant concentration that enters each perforation cluster within the same stage. The main objective of this research is to investigate the effect of different limited-entry perforation configurations on proppant transport, settling, and distribution across different perforation clusters in multistage horizontal wells. To simulate a fracturing stage in a horizontal wellbore, a laboratory-based 30-foot horizontal clear apparatus with three perforation clusters is used. Fresh water (~1 cp) is utilized as the carrier fluid to transport the proppant. This research incorporates the effect of testing three different injection rates each at four different proppant concentrations on proppant transport. Different limited-entry perforation configurations are also used to test the perforation effect on proppant transport using similar injection rates and proppant concentrations for the same proppant size. The proppant is mixed with fresh water in a 200-gallon tank for at least 10 minutes to ensure the consistency of the slurry mixture. The mixture is then injected into the transparent horizontal wellbore through a slurry pump. This laboratory apparatus also includes a variable frequency drive, a flow meter, and two pressure transducers located right before the first two perforation clusters. Sieve analysis is conducted to understand the ability of fresh water to carry bigger particles of the mixture at different injection rates, proppant concentrations, and perforation configurations. The results show different fluid and proppant distributions occur when altering the perforation configurations, injection rates, and proppant concentrations. The effect of gravity is extreme when using a limited entry configuration at each cluster (1 SPF) located at the bottom of the pipe, especially at low injection rates, resulting in uneven proppant distribution with a heal-biased distribution. However, even proppant distribution is observed by changing the limited entry perforation configuration to the top of the horizontal pipe at similar injection rates and low proppant concentration. Increasing the proppant concentration reduces the void spaces between the particles and pushes them away toward the toe cluster. Even proppant distribution is also observed across the three perforation clusters when using high flow rates and a 2 SPF perforation configuration located at both the top and the bottom of the pipe. The results of the sieve analyses show different size distributions of the settled and exited proppant through different perforations and clusters. This illustrates the ability of fresh water to transport different percentages of different proppant sizes to different perforations and clusters within a single stage. Frequently, the injected proppant is assumed to be distributed evenly across the perforation clusters and that the distribution of fluid and proppant is identical. However, this research adds data to the portfolio that this assumption is generally not valid. Additionally, the distribution of the transported proppant is observed to be different across individual clusters and different perforations within each cluster. Such information is beneficial to understanding transport in horizontal, multi-stage completions and how such impacts the overall treatment efficiency, especially when employing limited-entry perforation techniques.

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Rapports d'organisations sur le sujet "Hox clusters"

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Shumaker, Justin L. Diskless Linux Cluster How-To. Fort Belvoir, VA : Defense Technical Information Center, septembre 2005. http://dx.doi.org/10.21236/ada439528.

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Mazumdar, S., F. Guo, D. Guo, K.-C. Ung et J. T. Gammel. Infinite Volume Extrapolations of Finite Cluster Calculations-How Correct Are These. Fort Belvoir, VA : Defense Technical Information Center, mai 1993. http://dx.doi.org/10.21236/ada265648.

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Smalley, Rebecca, Emmanuel Sulle, Ngala Chome, Ana Duarte et Euclides Gonçalves. Agricultural Investment Corridors in Africa : Does Smallholder and Women's Participation Count ? Institute of Development Studies (IDS), août 2021. http://dx.doi.org/10.19088/apra.2021.021.

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Agricultural development corridors and clusters are highly complex projects that have been driven in Africa by agribusiness and mining corporations, host governments, international donors and development finance institutions. There is interest in whether these projects can support inclusive agribusiness. Evidence shows that involvement of small-scale economic actors in such initiatives is often impeded by a failure to grant them participation or a voice. We therefore investigated if and how recent corridors and clusters in Africa have been able to achieve the meaningful engagement of small-scale economic actors, with a focus on smallholders, including pastoralists, and the women among them.

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Kott, Phillip S. The Degrees of Freedom of a Variance Estimator in a Probability Sample. RTI Press, août 2020. http://dx.doi.org/10.3768/rtipress.2020.mr.0043.2008.

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Inferences from probability-sampling theory (more commonly called “design-based sampling theory”) often rely on the asymptotic normality of nearly unbiased estimators. When constructing a two-sided confidence interval for a mean, the ad hoc practice of determining the degrees of freedom of a probability-sampling variance estimator by subtracting the number of its variance strata from the number of variance primary sampling units (PSUs) can be justified by making usually untenable assumptions about the PSUs. We will investigate the effectiveness of this conventional and an alternative method for determining the effective degrees of freedom of a probability-sampling variance estimator under a stratified cluster sample.

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