Relevant bibliographies by topics / Optimal clusters

Academic literature on the topic 'Optimal clusters'

Author: Grafiati
Published: 10 December 2022
Last updated: 28 January 2023

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Contents

Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Optimal clusters.'

Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.

You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.

Journal articles on the topic "Optimal clusters"

1

GREKOUSIS, GEORGE. "GIVING FUZZINESS TO SPATIAL CLUSTERS: A NEW INDEX FOR CHOOSING THE OPTIMAL NUMBER OF CLUSTERS." International Journal on Artificial Intelligence Tools 22, no. 03 (June 2013): 1350009. http://dx.doi.org/10.1142/s0218213013500097.

Full text
Abstract:
Choosing the optimal number of clusters is a key issue in cluster analysis. Especially when dealing with more spatial clustering, things tend to be more complicated. Cluster validation helps to determine the appropriate number of clusters present in a dataset. Furthermore, cluster validation evaluates and assesses the results of clustering algorithms. There are numerous methods and techniques for choosing the optimal number of clusters via crisp and fuzzy clustering. In this paper, we introduce a new index for fuzzy clustering to determine the optimal number of clusters. This index is not another metric for calculating compactness or separation among partitions. Instead, the index uses several existing indices to give a degree, or fuzziness, to the optimal number of clusters. In this way, not only do the objects in a fuzzy cluster get a membership value, but the number of clusters to be partitioned is given a value as well. The new index is used in the fuzzy c-means algorithm for the geodemographic segmentation of 285 postal codes.
APA, Harvard, Vancouver, ISO, and other styles
2

Zhong, Yanfei, and Liangpei Zhang. "A New Fuzzy Clustering Algorithm Based on Clonal Selection for Land Cover Classification." Mathematical Problems in Engineering 2011 (2011): 1–21. http://dx.doi.org/10.1155/2011/708459.

Full text
Abstract:
A new fuzzy clustering algorithm based on clonal selection theory from artificial immune systems (AIS), namely, FCSA, is proposed to obtain the optimal clustering result of land cover classification withouta prioriassumptions on the number of clusters. FCSA can adaptively find the optimal number of clusters and is designed as a two-layer system: the classification layer and the optimization layer. The classification layer of FCSA, inspired by clonal selection theory, generates the optimal classification result with a fixed cluster number by utilizing the clone, mutation, and selection of immune operators. The optimization layer of FCSA evaluates the optimal solutions according to performance measures for cluster validity and then adjusts the cluster number to output the final optimal cluster number. Two experiments with different types of image evince that FCSA not only finds the optimal number of clusters, but also consistently outperforms the traditional clustering algorithms, such as K-means and Fuzzy C-means. Hence, FCSA provides an effective option for performing the task of land cover classification.
APA, Harvard, Vancouver, ISO, and other styles
3

Rosing, K. E., and C. S. ReVelle. "Optimal Clustering." Environment and Planning A: Economy and Space 18, no. 11 (November 1986): 1463–76. http://dx.doi.org/10.1068/a181463.

Full text
Abstract:
Cluster analysis can be performed with several models. One method is to seek those clusters for which the total flow between all within-cluster members is a maximum. This model has, until now, been viewed as mathematically difficult because of the presence of products of integer variables in the objective function. In another optimization model of cluster analysis, the p-median, a central member is found for each cluster, so that relationships of cluster members with the various central members are maximized (or minimized). This problem, although mathematically tractable, is a less realistic formulation of the general clustering problem. The formulation of the maximum interflow problem is here transformed in stages into a linear analogue which is economically solvable. Computation experience with the several transformed stages is reported and a practical example of the analysis demonstrated.
APA, Harvard, Vancouver, ISO, and other styles
4

Ren, Min, Peiyu Liu, Zhihao Wang, and Jing Yi. "A Self-Adaptive Fuzzyc-Means Algorithm for Determining the Optimal Number of Clusters." Computational Intelligence and Neuroscience 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/2647389.

Full text
Abstract:
For the shortcoming of fuzzyc-means algorithm (FCM) needing to know the number of clusters in advance, this paper proposed a new self-adaptive method to determine the optimal number of clusters. Firstly, a density-based algorithm was put forward. The algorithm, according to the characteristics of the dataset, automatically determined the possible maximum number of clusters instead of using the empirical rulenand obtained the optimal initial cluster centroids, improving the limitation of FCM that randomly selected cluster centroids lead the convergence result to the local minimum. Secondly, this paper, by introducing a penalty function, proposed a new fuzzy clustering validity index based on fuzzy compactness and separation, which ensured that when the number of clusters verged on that of objects in the dataset, the value of clustering validity index did not monotonically decrease and was close to zero, so that the optimal number of clusters lost robustness and decision function. Then, based on these studies, a self-adaptive FCM algorithm was put forward to estimate the optimal number of clusters by the iterative trial-and-error process. At last, experiments were done on the UCI, KDD Cup 1999, and synthetic datasets, which showed that the method not only effectively determined the optimal number of clusters, but also reduced the iteration of FCM with the stable clustering result.
APA, Harvard, Vancouver, ISO, and other styles
5

Feng, Xue Bo, Fang Yao, Zhi Gang Li, and Xiao Jing Yang. "Improved Fuzzy C-Means Based on the Optimal Number of Clusters." Applied Mechanics and Materials 392 (September 2013): 803–7. http://dx.doi.org/10.4028/www.scientific.net/amm.392.803.

Full text
Abstract:
According to the number of cluster centers, initial cluster centers, fuzzy factor, iterations and threshold, Fuzzy C-means clustering algorithm (FCM) clusters the data set. FCM will encounter the initialization problem of clustering prototype. Firstly, the article combines the maximum and minimum distance algorithm and K-means algorithm to determine the number of clusters and the initial cluster centers. Secondly, the article determines the optimal number of clusters with Silhouette indicators. Finally, the article improves the convergence rate of FCM by revising membership constantly. The improved FCM has good clustering effect, enhances the optimized capability, and improves the efficiency and effectiveness of the clustering. It has better tightness in the class, scatter among classes and cluster stability and faster convergence rate than the traditional FCM clustering method.
APA, Harvard, Vancouver, ISO, and other styles
6

Jollyta, Deny, Syahril Efendi, Muhammad Zarlis, and Herman Mawengkang. "Optimasi Cluster Pada Data Stunting: Teknik Evaluasi Cluster Sum of Square Error dan Davies Bouldin Index." Prosiding Seminar Nasional Riset Information Science (SENARIS) 1 (September 30, 2019): 918. http://dx.doi.org/10.30645/senaris.v1i0.100.

Full text
Abstract:
The clusters number optimization problem is a problem that still requires continuous research so that the information produced can be a consideration. Cluster evaluation techniques with Sum of Square Error (SSE) and Davies Bouldin Index (DBI) are techniques that can evaluate the number of clusters from a data test. Research with these two techniques utilizes Stunting data from a number of regions in Indonesia. The result is information on stunting data which is formed from the optimal number of clusters where the largest SSE is formed at k = 5 and the smallest DBI is formed at k = 5, with values of 23.403 and 1,178 respectively. Changes in the number of clusters also influence the information produced and DBI is proven to produce optimal number of clusters that contain information with a better pattern because it has a small intra-cluster value. It is expected that the results of this study can show the performance of the two evaluation techniques in producing the optimal number of clusters so that grouping information is in accordance with the expected pattern.
APA, Harvard, Vancouver, ISO, and other styles
7

Danilova, Natalia V., and Daniil I. Zhitnikov. "Dichotomous Clustering Method аnd Optimal Portfolio." UNIVERSITY NEWS. NORTH-CAUCASIAN REGION. NATURAL SCIENCES SERIES, no. 2 (214) (June 30, 2022): 15–20. http://dx.doi.org/10.18522/1026-2237-2022-2-15-20.

Full text
Abstract:
The problem of optimal portfolio finding is considered in the paper. Many papers are devoted to the solving of this problem in various its formulations, that is why the problem is relevant. For the solving of the problem the methods of robust optimization and machine learning are used, namely, the splitting of the sample of the random asset returns into clusters and subsequent construction of an ellipsoid in each cluster. The method of maximal likelihood is used for dividing on two clusters, the method of dichotomous clustering is used for dividing on several clusters. The sample average and the sample covariance matrix are used for the constructing of the ellipsoid; the radius is calculated based on the assumption that the sample elements have a normal distribution. The example of calculating the optimal portfolio is given. It uses the real values of the return vectors. In this case part of the sample is used to calculate the sample means and the sample covariance matrices of the clusters, the rest part of the sample is used for verification of the portfolio. The tables show the dependence of the optimal portfolio return on the model parameter and on the number of clusters (ellipsoids). The comparing of results is considered; there are cases in which there is an increase in the income of the investor.
APA, Harvard, Vancouver, ISO, and other styles
8

Jorio, Ali, Sanaa El Fkihi, Brahim Elbhiri, and Driss Aboutajdine. "An Energy-Efficient Clustering Routing Algorithm Based on Geographic Position and Residual Energy for Wireless Sensor Network." Journal of Computer Networks and Communications 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/170138.

Full text
Abstract:
Recently wireless sensor network (WSN) has become one of the most interesting networking technologies, since it can be deployed without communication infrastructures. A sensor network is composed of a large number of sensor nodes; these nodes are responsible for supervision of the physical phenomenon and transmission of the periodical results to the base station. Therefore, improving the energy efficiency and maximizing the networking lifetime are the major challenges in this kind of networks. To deal with this, a hierarchical clustering scheme, called Location-Energy Spectral Cluster Algorithm (LESCA), is proposed in this paper. LESCA determines automatically the number of clusters in a network. It is based on spectral classification and considers both the residual energy and some properties of nodes. In fact, our approach uses theK-ways algorithm and proposes new features of the network nodes such as average energy, distance to BS, and distance to clusters centers in order to determine the clusters and to elect the cluster's heads of a WSN. The simulation results show that if the clusters are not constructed in an optimal way and/or the number of the clusters is greater or less than the optimal number of clusters, the total consumed energy of the sensor network per round is increased exponentially.
APA, Harvard, Vancouver, ISO, and other styles
9

Nenashev, Vadim A., Igor G. Khanykov, and Mikhail V. Kharinov. "A Model of Pixel and Superpixel Clustering for Object Detection." Journal of Imaging 8, no. 10 (October 6, 2022): 274. http://dx.doi.org/10.3390/jimaging8100274.

Full text
Abstract:
The paper presents a model of structured objects in a grayscale or color image, described by means of optimal piecewise constant image approximations, which are characterized by the minimum possible approximation errors for a given number of pixel clusters, where the approximation error means the total squared error. An ambiguous image is described as a non-hierarchical structure but is represented as an ordered superposition of object hierarchies, each containing at least one optimal approximation in g0 = 1,2,..., etc., colors. For the selected hierarchy of pixel clusters, the objects-of-interest are detected as the pixel clusters of optimal approximations, or as their parts, or unions. The paper develops the known idea in cluster analysis of the joint application of Ward’s and K-means methods. At the same time, it is proposed to modernize each of these methods and supplement them with a third method of splitting/merging pixel clusters. This is useful for cluster analysis of big data described by a convex dependence of the optimal approximation error on the cluster number and also for adjustable object detection in digital image processing, using the optimal hierarchical pixel clustering, which is treated as an alternative to the modern informally defined “semantic” segmentation.
APA, Harvard, Vancouver, ISO, and other styles
10

Shaffer, Kris, Esther Vasiete, Brandon Jacquez, Aaron Davis, Diego Escalante, Calvin Hicks, Joshua McCann, Camille Noufi, and Paul Salminen. "A cluster analysis of harmony in the McGill Billboard dataset." Empirical Musicology Review 14, no. 3-4 (July 6, 2020): 146. http://dx.doi.org/10.18061/emr.v14i3-4.5576.

Full text
Abstract:
We set out to perform a cluster analysis of harmonic structures (specifically, chord-to-chord transitions) in the McGill Billboard dataset, to determine whether there is evidence of multiple harmonic grammars and practices in the corpus, and if so, what the optimal division of songs, according to those harmonic grammars, is. We define optimal as providing meaningful, specific information about the harmonic practices of songs in the cluster, but being general enough to be used as a guide to songwriting and predictive listening. We test two hypotheses in our cluster analysis — first that 5–9 clusters would be optimal, based on the work of Walter Everett (2004), and second that 15 clusters would be optimal, based on a set of user-generated genre tags reported by Hendrik Schreiber (2015). We subjected the harmonic structures for each song in the corpus to a K-means cluster analysis. We conclude that the optimal clustering solution is likely to be within the 5–8 cluster range. We also propose that a map of cluster types emerging as the number of clusters increases from one to eight constitutes a greater aid to our understanding of how various harmonic practices, styles, and sub-styles comprise the McGill Billboard dataset.
APA, Harvard, Vancouver, ISO, and other styles
More sources

Dissertations / Theses on the topic "Optimal clusters"

1

Peng, Shuyue. "Optimal Semantic Labeling of Social Network Clusters." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406821134.

Full text
APA, Harvard, Vancouver, ISO, and other styles
2

Adams, Daniel Alan. "Optimal Load Balancing in a Beowulf Cluster." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-050205-135758/.

Full text
APA, Harvard, Vancouver, ISO, and other styles
3

Frigui, Hichem. "New approaches for robust clustering and for estimating the optimal number of clusters /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9842528.

Full text
APA, Harvard, Vancouver, ISO, and other styles
4

Panebianco, Gabriele. "A new implementation of an optimal filter for the detection of galaxy clusters through weak lensing." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24444/.

Full text
Abstract:
We developed a new version of a C++ code, Get the Halo 2021, that implements the optimal linear matched filter presented in Maturi et al.(2005). Our aim is to detect dark matter haloes of clusters of galaxies through their weak gravitational lensing signatures applying the filter to a catalogue of simulated galaxy ellipticities. The dataset represents typical data that will be available thanks to the Euclid mission, thus we are able to forecast the filter performances on weak lensing data obtained by Euclid. The linear matched filter is optimised to maximise the signal-to-noise ratio (S/N) of the detections and minimise the number of spurious detections caused by superposition of large-scale structures; this is achieved by suppressing those spatial frequencies dominated by the large-scale structure contamination. We compared our detections with the true population of dark matter haloes used to produce the catalogue of ellipticities. We confirmed the expectations on the filter performance raised by Maturi et al.(2005) and Pace et al.(2007). We found that S/N 7 can be considered as a reliable threshold to detect haloes through weak lensing as 83% of our detections with S/N>7 were matched to the haloes; this is consistent with Pace et al.(2007). The purity of our catalogues of detections increases as a function of S/N and reaches 100% at S/N 10.5-11. We also confirmed that the filter selects preferentially haloes with redshift between 0.2 and 0.5, that have an intermediate distance between observer and background sources, condition that maximises the lensing effects. The completeness of our catalogues is a steadily growing function of the mass until 4-5Msun/h, where it reaches values 58-68%. Our algorithm might be used to enhance the reliability of the detections of the AMICO code (Bellagamba et al.2018), the optimal linear matched filter implemented in the Euclid data analysis pipeline to identify galaxy clusters in photometric data (Euclid Collaboration et al.2019).
APA, Harvard, Vancouver, ISO, and other styles
5

Vanišová, Adéla. "Shluková analýza jako nástroj klasifikace objektů." Master's thesis, Vysoká škola ekonomická v Praze, 2012. http://www.nusl.cz/ntk/nusl-114191.

Full text
Abstract:
The aim of this thesis is to examine the cluster analysis ability segment the data set by selected methods. The data sets are consisting of quantitative variables. The basic criterion for the data sets is that the number of classes has to be known and the next criterion is that the membership of all object to each class has to be known too. Execution of the cluster analysis was based on knowledge about the number of classes. Classified objects to individual clusters were compared with its original classes. The output was the relative success of classification by selected methods. Cluster analysis methods are not able to determine an optimal number of clusters. Estimates of the optimal number of clusters were the second step in analysis for each data set. The ability of selected criteria identify the original number of classes was analyzed by comparing numbers of original classes and numbers of optimal clusters. The main contribution of this thesis is the validation of the ability of selected cluster analysis methods to identify similar objects and verify the ability of selected criteria to estimate the number of clusters corresponding to the real file distribution. Moreover, this work provides a structured overview of the basic cluster analysis methods and indicators for estimating the optimal number of clusters.
APA, Harvard, Vancouver, ISO, and other styles
6

Novák, Miroslav. "Hodnocení úspěšnosti koeficientů pro stanovení optimálního počtu shluků ve shlukové analýze." Master's thesis, Vysoká škola ekonomická v Praze, 2014. http://www.nusl.cz/ntk/nusl-193328.

Full text
Abstract:
The objective of this thesis is the evaluation of selected coefficients of the cluster analysis when determining the optimal number of clusters. The analytical evaluation is performed on 20 independent real datasets. The analysis is made in statistical SYSTAT 13.1 Software. The application of coefficients RMSSTD, CHF, PTS, DB and Dunn's index on real datasets is the main part of this thesis, because the issue of evaluating the results of clustering is not devoted sufficient attention in scientific publications. The main goal is whether the selected coefficients of clustering can be applied in the real situations. The second goal is to compare selected clustering methods and their corresponding metrics when determining the optimal number of clusters. In conclusion, it is found that the optimal number of clusters determined by the coefficients mentioned above cannot be considered to be correct since, after application to the real data, none of the selected coefficients overcome the success rate of 40%, hence, the use of these coefficients in practice is very limited. Based on the practical analysis, the best method in identifying the known number of clusters is the average linkage in connection with the Euclidean distance, while the worst is the Ward's method in connection with the Euclidean distance.
APA, Harvard, Vancouver, ISO, and other styles
7

Ouaalaya, El Hassane. "Phénotypes et trajectoires des patients BPCO, données issues de la cohorte PALOMB." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0295.

Full text
Abstract:
La BPCO est une pathologie hétérogène responsable d’une morbidité et d’une mortalité importante. La classification GOLD de la sévérité de la BPCO introduit des incertitudes, son applicabilité dans la pratique est plus que douteuse. Les exacerbations et les comorbidités contribuent à la sévérité globale de l'affection, au complexe des symptômes et à l'évolution de la maladie. L’évaluation de la dyspnée en pratique clinique n’est pas chose aisée, et il est difficile d’apprécier la part attribuable respiratoire de la dyspnée chez des patients ayant des comorbidités. Les données actuelles restent insuffisantes pour affirmer ou infirmer l’importance de la majorité des candidats phénotypes. Principalement, ce travail a pour buts de caractériser l’évolution des trajectoires des patients BPCO et d’identifier des candidats phénotypes chez des patients BPCO. Secondairement, ce travail a pour buts : d’identifier les clusters stables de comorbidités, de caractériser les déterminants de la dyspnée, de déterminer les facteurs associés aux phénotypes des Exacerbateurs fréquents et d'évaluer l'impact des symptômes, des fonctions pulmonaires et des comorbidités sur la mortalité. Les patients BPCO (VEMS/CVF<70% post-BD) ont été inclus depuis Janvier 2014 par leur pneumologue en utilisant le questionnaire de la cohorte PALOMB. Ce questionnaire comprenait les domaines suivants : les critères démographiques, les symptômes cliniques, les tests fonctionnels, les comorbidités, les vaccinations et les traitements inhalés. Après cinq ans de suivi, les données sur leur statut vital ont été obtenues en utilisant le RNIPP. L’identifier des clusters stables de comorbidités a été réalisé à partir des modèles de classification supervisée sur les composantes principales. L’analyse de sensibilité et l’estimateur des moindres carrés pénalisé (modèle LASSO) ont ensuite été utilisés afin d’évaluer les déterminants de la dyspnée. Le suivi longitudinal de la fréquence des exacerbations a permis d’identifier trois phénotypes à partir d’une classification non-supervisée. De plus, Le modèle de Cox a été utilisé afin d’identifier les facteurs associés à la mortalité toute cause. Les arbres de classification et de régression (CART) ont été utilisés pour répartir les patients dans des sous-groupes et la pertinence clinique a été déterminée en comparant la mortalité à 5 ans. L’analyse en cluster la plus optimale (supervisé vs non-supervisé) a été utilisée pour identifier de façon robuste les phénotypes cliniques. L’analyse en cluster a permis de différencier 5 clusters de comorbidités : cardiovasculaire ; syndrome métabolique et SAOS ; dénutrition ; patients avec bronchectasie et un cluster de patients ayant moins de comorbidités. Nos résultats suggèrent que la dyspnée est liée à la sévérité de la BPCO, au sexe, aux exacerbations, aux comorbidités et à l'hyperinflation statique. Révélant que l'hyperinflation statique définie par le rapport IC/TLC était un meilleur déterminant de l'échelle de dyspnée mMRC comparativement aux rapports RV/TLC et FRC/TLC. Sur la base de notre hypothèse, nous avons pu déterminer quatre phénotypes : le phénotype A (Exacerbateurs non fréquents), B (exacerbations fréquentes chez les patients en sous poids), C (transitoires) et D (exacerbations fréquentes chez les patients obèses). Les déterminants les plus importants du phénotype exacerbateur fréquent sont les antécédents d’exacerbations, l’absence de vaccination antigrippale annuelle et l’anxiété. Le cancer et les comorbidités cardiovasculaires contribuent à l’augmentation de la mortalité, en plus des critères connus en rapport avec la sévérité de la maladie. Nos résultats montrent que la multimorbidité est fréquente, hétérogène et varie en fonction du stade de sévérité de la BPCO. Ils illustrent l’aspect plurifactoriel de la dyspnée chez les patients BPCO, confirment l’existence et la pertinence clinique d’un phénotype d’Exacerbateurs fréquents de patients BPCO
COPD is a heterogeneous and multisystemic disease with progressive increasing morbidity and mortality. The GOLD classification introduces uncertainties, its validity in predicting mortality is still uncertain, and its applicability in practice is more than questionable. Our understanding of the longitudinal determinants of COPD exacerbations remains unclear. COPD patients frequently suffer from comorbidities, with a significant impact on mortality. Evaluating dyspnea in clinical practice is not easy, and it is difficult to assess the respiratory attributable part of dyspnea in patients with comorbidities. Current data remains insufficient to confirm the importance of the majority of candidate phenotypes. Mainly, this work aims to characterize the evolution of the trajectories of COPD patients and to identify candidate phenotypes in COPD patients. Secondly, this work aims to: identify stable clusters of comorbidities, characterize the determinants of dyspnoea, determine the factors associated with the phenotypes of frequent exacerbators and assess the impact of symptoms, pulmonary functions and comorbidities on mortality. Diagnosis of COPD was made using spirometry with post-BD FEV1/FVC <70%. Since January 2014, pulmonologists have been using the PALOMB web site questionnaire to include COPD patients. This questionnaire included the following domains: demographic criteria, clinical symptoms, lung function, comorbidities and therapeutic management. After 5 years of follow-up, vital status was recorded through the RNIPP. Stable clusters of comorbidities were identified using the supervised classification models on the principal components. The sensitivity analysis and the least absolute shrinkage and selection operator (LASSO) were then used to assess the determinants of dyspnea. The unsupervised classification was used to identify three phenotypes by modelling the longitudinal changes in the frequency of COPD exacerbations. In addition, the Cox model was used to identify factors associated with all-cause mortality. Classification and regression trees (CART) were used for allocating patients to the subgroups and clinical relevance was determined by comparing 5-year mortality. The most optimal cluster analysis (supervised vs unsupervised) was used to robustly identify clinical phenotypes. The cluster analysis showed five phenotypes of comorbidities: cluster 1 included cardiac profile; cluster 2 included less comorbidities; cluster 3 included metabolic syndrome, apnea and anxiety-depression; cluster 4 included malnutrition and osteoporosis and cluster 5 included bronchiectasis. Regardless of the cut-off values set to identify higher dyspnoea, our results suggested that dyspnoea is related to the severity of airflow limitation, gender, exacerbations, comorbidities and hyperinflation. Revealing that the hyperinflation defined by IC/TLC ratio was a better determinant of the mMRC dyspnoea scale in comparison to both RV/TLC and FRC/TLC ratio. Based on our hypothesis, we were able to determine four phenotypes: A (infrequent), B (frequent in underweight patients), C (transient), and D (frequent in obese patients). The most important determinants of the frequent exacerbating phenotype are: the presence of anxiety, chronic sputum, and unvaccinated against influenza. In addition to known criteria related to COPD severity, cancer and cardiovascular comorbidities contribute to increased mortality in COPD patients. Our results show that within the Palomb cohort (a large clinic-based cohort) multimorbidity is frequent, heterogeneous and varies according to the stage of COPD severity. The presence of comorbidities should therefore be included in any assessment of COPD severity. These cohort results illustrate in real-life the multifactorial aspect of dyspnoea in COPD patients, confirm the existence and clinical relevance of two frequent exacerbators’ phenotypes and the currently used threshold to define this phenotype
APA, Harvard, Vancouver, ISO, and other styles
8

Lima, Ana Isabel Lage Figueiredo. "Alargamento da UEM : choques assimétricos e identificação de clusters." Master's thesis, Instituto Superior de Economia e Gestão, 2004. http://hdl.handle.net/10400.5/4165.

Full text
Abstract:
Mestrado em Economia
Com a aproximação da data de adesão formal dos dez Países em Adesão à União Europeia, muitos autores têm-se debruçado sobre a questão da adesão prospectiva destes países à Zona Euro. À luz da teoria das Zonas Monetárias Óptimas, a perda da autonomia na condução da política monetária e cambial constitui o principal custo económico associado à adopção do euro por parte destes países, ao limitar os instrumentos disponíveis aos Estados-membros para acomodar eventuais choques assimétricos. Neste trabalho, considerei um modelo vector autoregressivo (VAR) estrutural para identificar e comparar os choques de procura e de oferta entre os Estados-membros da Zona Euro e os Países em Adesão. De forma a avaliar o grau de simetria entre os choques da Zona Euro e dos Países em Adesão, considerei duas abordagens distintas: o cálculo das correlações dos choques de procura e oferta entre os vários países e a UEM e a análise de clusters. Recorrendo ainda à análise de clusters, procurei também identificar grupo homogéneos de países dentro da futura UE e analisar a sua evolução ao longo do tempo. Os resultados obtidos neste estudo relativamente ao período 1996-2002 revelam que os Países em Adesão estão, em geral, menos correlacionados com os choques de oferta e de procura da Zona Euro que os actuais Estados-membros da UEM. No entanto, o cenário em termos individuais é bastante heterogéneo. Em particular, alguns Países em Adesão mais avançados, a Hungria e a Polónia, já se encontram ao nível dos países de menor dimensão da UEM (nomeadamente Portugal e a Grécia). Em contrapartida, em países como Lituânia e a Eslováquia, a correlação entre os choques permanece baixa, o que implica que um avanço rápido para a adopção do euro traria eventualmente elevados custos de estabilização para estes países.
On the eve of the formal accession of the ten Accession Countries into the European Union, many authors have been discussing the implications of the upcoming integration of these countries in the Euro Area. Under the Optimum Currency Areas (OCA) theory, the loss of monetary autonomy and exchange rate flexibility constitutes the main economic cost associated with the adoption of the euro, thus limiting the instruments for adjusting asymmetric shocks available to member countries. In this paper, I used a structural vector autoregression model to identify and compare demand and supply shocks between euro area countries and the accession countries. In order to assess the degree of symmetry between euro area and accession countries shocks, 1 considered two ditterent approaches: the correlation between shocks and cluster analysis. With the help of cluster analysis, I also tried to identify homogenous groups of countries within the future EU, and analyse their evolution through time. Focusing on the period 1996-2002, the results show that the accession countries are generally less correlated with euro area supply and demand shocks than the EMU Member Countries. However, when considering individual countries, a different picture emerges. The more advanced Accession Countries (namely Hungary and Poland) are hardly different in the correlation of their shocks vis-a-vis the euro area than the smaller countries of the EMU (i.e. Portugal and Greece). At the same time, countries like Lithuania and Slovakia show a low correlation with euro area shocks, implying that moving fast towards the adoption of the euro may eventually generate high stabilization costs for these countries.
APA, Harvard, Vancouver, ISO, and other styles
9

Girish, Deeptha S. "Thresholded K-means Algorithm for Image Segmentation." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1479815784173769.

Full text
APA, Harvard, Vancouver, ISO, and other styles
10

Hammerbauer, Jiří. "Hodnocení úspěšnosti metod a koeficientů využívaných ve shlukové analýze." Master's thesis, Vysoká škola ekonomická v Praze, 2014. http://www.nusl.cz/ntk/nusl-193440.

Full text
Abstract:
The diploma thesis explores with the evaluation of the success of selected indices for determining the number of clusters used in cluster analysis. The aim of this thesis is on the basis of various combinations of clustering methods and distances verify whether, alternatively using which clustering methods and distances is it possible to rely on the results of indices for determining the number of clusters. The results of success rate presented in the third chapter suggest that not all of indices for determining the number of clusters can be used universally. The most successful index is Dunn index, which was able to determine the correct number of clusters in 37 % of cases, respectively Davies-Bouldin index with the share of 70 % when including deviation of one cluster. The success rate is affected by both used method and selected distance.
APA, Harvard, Vancouver, ISO, and other styles
More sources

Books on the topic "Optimal clusters"

1

Kreibig, Uwe, and Michael Vollmer. Optical Properties of Metal Clusters. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-662-09109-8.

Full text
APA, Harvard, Vancouver, ISO, and other styles
2

1957-, Vollmer Michael, ed. Optical properties of metal clusters. Berlin: Springer, 1995.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
3

Canada, Canada Agriculture, ed. Optimal set covering for biological classification. Ottawa: Agriculture Canada, 1993.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
4

Goncharov, Vladimir. Non-Linear Optical Response in Atoms, Molecules and Clusters. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-08320-9.

Full text
APA, Harvard, Vancouver, ISO, and other styles
5

Thurston, Mark Robert. X-ray & optical observations of the young open cluster NGC 2516. Birmingham: University of Birmingham, 2000.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
6

Strobel, Andrzej. On some properties of the local galactic disk as determined by star clusters. Warszawa: Państwowe Wydawn. Nauk., 1986.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
7

Ehrhardt, H. Electron Collisions with Molecules, Clusters, and Surfaces. Boston, MA: Springer US, 1994.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
8

Antoine, Rodolphe, and Vlasta Bonačić-Koutecký. Liganded silver and gold quantum clusters. Towards a new class of nonlinear optical nanomaterials. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-64743-2.

Full text
APA, Harvard, Vancouver, ISO, and other styles
9

Pittner, Jiří. Ab initio study of optical properties of neutral and charged pure and mixed alkali metal clusters. Berlin: VMF Verlag für Wissenschaft und Forschung, 1997.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
10

P, Jena, Khanna S. N, Rao B. K, and NATO Advanced Research Workshop on Physics and Chemistry of Finite Systems: From Clusters to Crystals (1991 : Richmond, Va.), eds. Physics and chemistry of finite systems: From clusters to crystals. Dordrecht: Kluwer Academic Publishers, 1992.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
More sources

Book chapters on the topic "Optimal clusters"

1

Maulik, Ujjwal, Sanghamitra Bandyopadhyay, and Anirban Mukhopadhyay. "Combining Pareto-Optimal Clusters Using Supervised Learning." In Multiobjective Genetic Algorithms for Clustering, 123–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-16615-0_6.

Full text
APA, Harvard, Vancouver, ISO, and other styles
2

Cleofas-Sanchez, L., A. Pineda-Briseño, and J. S. Sanchez. "Identifying Optimal Clusters in Purchase Transaction Data." In Advances in Computational Intelligence, 3–22. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-89817-5_1.

Full text
APA, Harvard, Vancouver, ISO, and other styles
3

Träff, Jesper Larsson, and Andreas Ripke. "An Optimal Broadcast Algorithm Adapted to SMP Clusters." In Recent Advances in Parallel Virtual Machine and Message Passing Interface, 48–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 2005. http://dx.doi.org/10.1007/11557265_11.

Full text
APA, Harvard, Vancouver, ISO, and other styles
4

Zhuang, Zhenyun, Min Shen, Haricharan Ramachandra, and Suja Viswesan. "Choosing Optimal Maintenance Time for Stateless Data-Processing Clusters." In Job Scheduling Strategies for Parallel Processing, 252–73. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-61756-5_14.

Full text
APA, Harvard, Vancouver, ISO, and other styles
5

Buhmann, J. M., and M. Held. "On the Optimal Number of Clusters in Histogram Clustering." In Studies in Classification, Data Analysis, and Knowledge Organization, 37–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 2002. http://dx.doi.org/10.1007/978-3-642-55991-4_4.

Full text
APA, Harvard, Vancouver, ISO, and other styles
6

Barraza, Juan, Fevrier Valdez, Patricia Melin, and Claudia González. "Optimal Number of Clusters Finding Using the Fireworks Algorithm." In Hybrid Intelligent Systems in Control, Pattern Recognition and Medicine, 83–93. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-34135-0_7.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Palmer, J., and I. Mitrani. "Optimal Server Allocation in Reconfigurable Clusters with Multiple Job Types." In Computational Science and Its Applications – ICCSA 2004, 76–86. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-540-24709-8_9.

Full text
APA, Harvard, Vancouver, ISO, and other styles
8

Broda, Bartosz, and Paweł Kędzia. "Finding the Optimal Number of Clusters for Word Sense Disambiguation." In Text, Speech and Dialogue, 388–94. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-23538-2_49.

Full text
APA, Harvard, Vancouver, ISO, and other styles
9

Boudjeloud-Assala, Lydia, and Ta Minh Thuy. "Determine Optimal Number of Clusters with an Elitist Evolutionary Approach." In Advances in Knowledge Discovery and Data Mining, 324–35. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-06605-9_27.

Full text
APA, Harvard, Vancouver, ISO, and other styles
10

Rosenberg, Arnold L. "Greedy “Exploitation” Is Close to Optimal on Node-Heterogeneous Clusters." In Euro-Par 2011 Parallel Processing, 155–66. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-23400-2_16.

Full text
APA, Harvard, Vancouver, ISO, and other styles

Conference papers on the topic "Optimal clusters"

1

Rao, K. V. S. N. Rama, and B. Manjula Josephine. "Exploring the Impact of Optimal Clusters on Cluster Purity." In 2018 3rd International Conference on Communication and Electronics Systems (ICCES). IEEE, 2018. http://dx.doi.org/10.1109/cesys.2018.8724114.

Full text
APA, Harvard, Vancouver, ISO, and other styles
2

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

Full text
Abstract:
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.
APA, Harvard, Vancouver, ISO, and other styles
3

Lapshina, S. Yu. "The Optimal Processor Cores' Number choice for the Parallel Cluster Multiple Labeling Technique on HighPerformance Computing Systems." In Всероссийская научная конференция "Единое цифровое пространство научных знаний: проблемы и решения". Москва, Берлин: Директмедиа Паблишинг, 2021. http://dx.doi.org/10.51218/978-5-4499-1905-2-2021-311-319.

Full text
Abstract:
The article is about the research of a optimum number of processor cores for launching the Parallel Cluster Multiple Labeling Technique on modern supercomputer systems installed in the JSCC RAS. This technique may be used in any field as a tool for differentiating large lattice clusters, because it is given input in a format independent of the application. At the JSCC RAS, this tool was used to study the problem of the spread of epidemics, for which an appropriate multiagent model was developed. In the course of imitation experiments, a variant of the Parallel Cluster Multiple Labeling Technique for percolation Hoshen-Kopelman clusters related to the tag linking mechanism, which can also be used in any area as a tool for differentiating large-size lattice clusters, was used to be improved on a multiprocessor system.
APA, Harvard, Vancouver, ISO, and other styles
4

Deogun, J., and V. Raghavan. "Optimal determination of user-oriented clusters." In the 10th annual international ACM SIGIR conference. New York, New York, USA: ACM Press, 1987. http://dx.doi.org/10.1145/42005.42021.

Full text
APA, Harvard, Vancouver, ISO, and other styles
5

Yu, Lei, and Hao Li. "Toward Optimal Selection of Feature Clusters." In Sixth International Conference on Machine Learning and Applications (ICMLA 2007). IEEE, 2007. http://dx.doi.org/10.1109/icmla.2007.108.

Full text
APA, Harvard, Vancouver, ISO, and other styles
6

Yu, Lei, and Hao Li. "Toward optimal selection of feature clusters." In Sixth International Conference on Machine Learning and Applications (ICMLA 2007). IEEE, 2007. http://dx.doi.org/10.1109/icmla.2007.93.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Shoeb, Md Asaduzzaman, Farhad Shahnia, and G. M. Shafiullah. "Optimal Coupling of Multiple Microgrid Clusters." In 2019 IEEE Innovative Smart Grid Technologies - Asia (ISGT Asia). IEEE, 2019. http://dx.doi.org/10.1109/isgt-asia.2019.8881386.

Full text
APA, Harvard, Vancouver, ISO, and other styles
8

Kadam, S., D. Kolluru, A. Vaidya, and A. Viswanadhuni. "Optimal Clusters and Architectures in Complex Networks." In 2010 International Conference on Advances in Recent Technologies in Communication and Computing (ARTCom). IEEE, 2010. http://dx.doi.org/10.1109/artcom.2010.26.

Full text
APA, Harvard, Vancouver, ISO, and other styles
9

Jalali, M., and A. R. Ohadi. "Optimal Placement of Sensors and Actuators in Cluster Control of Acoustic Potential Energy in a Cavity." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-38142.

Full text
Abstract:
This paper aims the cluster control of acoustic potential energy in a structural/acoustic cavity. The cavity consists of five rigid walls and one flexible panel with clamped boundary conditions on all four edges. It is desired to suppress the acoustic noise within the cavity, produced by a disturbing force or plane wave. In order to perform noise suppression, both acoustic and structural actuators can be used, while only acoustic sensors are necessary for measurement. Cluster control approach classifies acoustic and structural modes such that they interfere if and only if they belong to the same cluster. Providing methods to actuate and measure each of these clusters individually, cluster control enables us to implement a multi-SISO system as opposed to a MIMO system, which can significantly reduce computational load on the controller. This paper also investigates the optimal placement of sensors and actuators for further noise suppression. It is shown that optimization is critically important when cluster control method is used. Optimal placement of sensors and actuators helps to improve the noise suppression, without increasing the cost of control system equipments. In order to locate the optimum positions, the genetic algorithm (GA) is employed. The effect of optimization on acoustic potential energy suppression is discussed using numerical simulations.
APA, Harvard, Vancouver, ISO, and other styles
10

Odonkor, Philip, and Kemper Lewis. "Designing Optimal Arbitrage Policies for Distributed Energy Systems in Building Clusters Using Reinforcement Learning." In 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/detc2019-97190.

Full text
Abstract:
Abstract In the wake of increasing proliferation of renewable energy and distributed energy resources (DERs), grid designers and operators alike are faced with several emerging challenges in curbing allocative grid inefficiencies and maintaining operational stability. One such challenge relates to the increased price volatility within real-time electricity markets, a result of the inherent intermittency of renewable energy. With this challenge, however, comes heightened economic interest in exploiting the arbitrage potential of price volatility towards demand-side energy cost savings. To this end, this paper aims to maximize the arbitrage value of electricity through the optimal design of control strategies for DERs. Formulated as an arbitrage maximization problem using design optimization, and solved using reinforcement learning, the proposed approach is applied towards shared DERs within multi-building residential clusters. We demonstrate its feasibility across three unique building cluster demand profiles, observing notable energy cost reductions over baseline values. This highlights a capability for generalized learning across multiple building clusters and the ability to design efficient arbitrage policies towards energy cost minimization. Finally, the approach is shown to be computationally tractable, designing efficient strategies in approximately 5 hours of training over a simulation time horizon of 1 month.
APA, Harvard, Vancouver, ISO, and other styles

Reports on the topic "Optimal clusters"

1

Rantala, Tapio T., Mark I. Stockman, Daniel A. Jelski, and Thomas F. George. Optical (Hyper) Polarizabilities of Small Silicon Clusters. Fort Belvoir, VA: Defense Technical Information Center, November 1990. http://dx.doi.org/10.21236/ada229383.

Full text
APA, Harvard, Vancouver, ISO, and other styles
2

Rantala, Tapio T., Mark I. Stockman, Daniel A. Jelski, and Thomas F. George. Linear and Nonlinear Optical Properties of Small Silicon Clusters. Fort Belvoir, VA: Defense Technical Information Center, August 1990. http://dx.doi.org/10.21236/ada225495.

Full text
APA, Harvard, Vancouver, ISO, and other styles
3

Markel, Vadim A., Leonid S. Muratov, Mark I. Stockman, and Thomas F. George. Scale-Invariant Theory of Optical Properties of Fractal Clusters. Fort Belvoir, VA: Defense Technical Information Center, September 1990. http://dx.doi.org/10.21236/ada227031.

Full text
APA, Harvard, Vancouver, ISO, and other styles
4

Hao, Jiangang. Optical galaxy cluster detection across a wide redshift range. Office of Scientific and Technical Information (OSTI), April 2009. http://dx.doi.org/10.2172/971005.

Full text
APA, Harvard, Vancouver, ISO, and other styles
5

Tolbert, Sarah Helen. High pressure studies on nanometer sized clusters: Structural, optical, and cooperative properties. Office of Scientific and Technical Information (OSTI), May 1995. http://dx.doi.org/10.2172/110667.

Full text
APA, Harvard, Vancouver, ISO, and other styles
6

Stubbs, Christopher. Developing the Optimal Technique for Cluster Photometric Redshift Determination: An Essential Ingredient in Measuring Dark Energy with Cluster Abundances. Office of Scientific and Technical Information (OSTI), April 2009. http://dx.doi.org/10.2172/951183.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Boatz, Jerry A., Jeffery A. Sheehy, and Peter W. Langhoff. Monte Carlo Simulations of the Structures and Optical Absorption Spectra of AlAr(sub N) Clusters. Fort Belvoir, VA: Defense Technical Information Center, April 1998. http://dx.doi.org/10.21236/ada408581.

Full text
APA, Harvard, Vancouver, ISO, and other styles
8

Dissanayake, Sahan T., Hayri Onal, James D. Westervelt, and Harold E. Balbach. Optimum Selection of Clustered Conservation Areas Within Military Installations. Fort Belvoir, VA: Defense Technical Information Center, October 2011. http://dx.doi.org/10.21236/ada553526.

Full text
APA, Harvard, Vancouver, ISO, and other styles
9

Boatz, Jerry A., Jeffrey A. Sheehy, Robert J. Hinde, and Peter W. Langhoff. Quantum and Classical Monte Carlo and Molecular Dynamics Simulations of the Structures, Photoionization-Induced Fragmentation, and Optical Absorption Spectra of AlArN Clusters. Fort Belvoir, VA: Defense Technical Information Center, May 1999. http://dx.doi.org/10.21236/ada408622.

Full text
APA, Harvard, Vancouver, ISO, and other styles
10

Prusky, Dov, Nancy P. Keller, and Amir Sherman. global regulation of mycotoxin accumulation during pathogenicity of Penicillium expansum in postharvest fruits. United States Department of Agriculture, January 2014. http://dx.doi.org/10.32747/2014.7600012.bard.

Full text
Abstract:
Background to the topic- Penicilliumas a postharvest pathogen and producer of the mycotoxin PAT. Penicilliumspp. are destructive phytopathogens, capable of causing decay in many deciduous fruits, during postharvest handling and storage; and the resulting losses can amount to 10% of the stored produce and the accumulation of large amounts of the mycotoxinpatulin. The overall goal of this proposal is to identify critical host and pathogen factors that modulate P. expansummycotoxin genes and pathways which are required for PAT production and virulence. Our preliminary results indicated that gluconic acid are strongly affecting patulin accumulation during colonization. P. expansumacidifies apple fruit tissue during colonization in part through secretion of gluconic acid (GLA). Several publications suggested that GLA accumulation is an essential factor in P. expansumpathogenicity. Furthermore, down regulation of GOX2 significantly reduced PAT accumulation and pathogenicity. PAT is a polyketide and its biosynthesis pathway includes a 15-gene cluster. LaeA is a global regulator of mycotoxin synthesis. It is now known that patulin synthesis might be subjected to LaeA and sometimes by environmental sensing global regulatory factors including the carbon catabolite repressor CreA as well as the pH regulator factor PacC and nitrogen regulator AreA. The mechanisms by which LaeA regulates patulin synthesis was not fully known and was part of our work. Furthermore, the regulatory system that controls gene expression in accordance with ambient pH was also included in our work. PacC protein is in an inactive conformation and is unable to bind to the promoter sites of the target genes; however, under alkaline growth conditions activated PacC acts as both an activator of alkaline-expressed genes and a repressor of acid-expressed genes. The aims of the project- This project aims to provide new insights on the roles of LaeA and PacC and their signaling pathways that lead to GLA and PAT biosynthesis and pathogenicity on the host. Specifically, our specific aims were: i) To elucidate the mechanism of pH-controlled regulation of GLA and PAT, and their contribution to pathogenesis of P. expansum. We are interested to understanding how pH and/or GLA impact/s under PacC regulation affect PAT production and pathogenesis. ii) To characterize the role of LaeA, the global regulator of mycotoxin production, and its effect on PAT and PacC activity. iii) To identify the signaling pathways leading to GLA and PAT synthesis. Using state- of-the-art RNAseq technologies, we will interrogate the transcriptomes of laeAand pacCmutants, to identify the common signaling pathways regulating synthesis of both GLA and PAT. Major conclusions, solutions, achievements- In our first Aim our results demonstrated that ammonia secreted at the leading edge of the fungal colony induced transcript activation of the global pH modulator PacC and PAT accumulation in the presence of GLA. We assessed these parameters by: (i) direct exogenous treatment of P. expansumgrowing on solid medium; (ii) direct exogenous treatment on colonized apple tissue; (iii) growth under self-ammonia production conditions with limited carbon; and (iv) analysis of the transcriptional response to ammonia of the PAT biosynthesis cluster. Ammonia induced PAT accumulation concurrently with the transcript activation of pacCand PAT biosynthesis cluster genes, indicating the regulatory effect of ammonia on pacCtranscript expression under acidic conditions. Transcriptomic analysis of pH regulated processes showed that important genes and BARD Report - Project 4773 Page 2 of 10 functionalities of P. expansumwere controlled by environmental pH. The differential expression patterns of genes belonging to the same gene family suggest that genes were selectively activated according to their optimal environmental conditions to enable the fungus to cope with varying conditions and to make optimal use of available enzymes. Concerning the second and third Aims, we demonstrated that LaeA regulates several secondary metabolite genes, including the PAT gene cluster and concomitant PAT synthesis invitro. Virulence studies of ΔlaeAmutants of two geographically distant P. expansumisolates (Pe-21 from Israel and Pe-T01 from China) showed differential reduction in disease severity in freshly harvested fruit ranging from no reduction for Ch-Pe-T01 strains in immature fruit to 15–25% reduction for both strains in mature fruit, with the ΔlaeAstrains of Is-Pe-21 always showing a greater loss in virulence. Results suggest the importance of LaeA regulation of PAT and other secondary metabolites on pathogenicity. Our work also characterized for the first time the role of sucrose, a key nutritional factor present in apple fruit, as a negative regulator of laeAexpression and consequent PAT production in vitro. This is the first report of sugar regulation of laeAexpression, suggesting that its expression may be subject to catabolite repression by CreA. Some, but not all of the 54 secondary metabolite backbone genes in the P. expansumgenome, including the PAT polyketide backbone gene, were found to be regulated by LaeA. Together, these findings enable for the first time a straight analysis of a host factor that potentially activates laeAand subsequent PAT synthesis.
APA, Harvard, Vancouver, ISO, and other styles
You might also be interested in the extended bibliographies on the topic 'Optimal clusters' for particular source types:
Journal articles Dissertations / Theses Books
We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!

To the bibliography