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Mixture Analysis (mixture + analysis)
Selected AbstractsResearch Submission: Mixture Analysis of Age at Onset in Migraine Without Aura: Evidence for Three SubgroupsHEADACHE, Issue 8 2010Carlo Asuni MD (Headache 2010;50:1313-1319) Objective. , To verify the presence of different age at onset (AAO) subgroups of patients in a sample of patients with migraine without aura (MWA) and compare clinical correlates among them. Background., MWA is a long-lasting disease whose prognosis has not yet been fully investigated. Patients may present complete remission, partial clinical remission, persistence and progression (migraine attack frequency and disability may increase over time leading to chronic migraine). Limited evidence exists regarding the identification of risk factors or predictors which might influence migraine prognosis. AAO has been proven a useful tool in the investigation of the clinical, biological, and genetic characteristics able to influence the prognosis of a number of neuropsychiatric disorders. AAO distribution was studied using mixture analysis, a statistical approach that breaks down the empirical AAO distribution observed into a mixture of normal components. Methods., A sample of 334 outpatients affected by MWA, recruited in a clinical genetic study at our Headache Center from 2004 to 2008, was enrolled for this study. Diagnosis was made according to International Headache Society criteria 2004. AAO distribution in patients was studied using mixture analysis. Chi-square test was used to compare clinical correlates among identified subgroups. Logistic regression was performed in order to correct for effect of possible confounders. Results., Mixture analysis broke up the observed distribution of AAO into 3 normal theoretical distributions. Informational criteria clearly showed a better 3-component model rather than the 2-component one. An early-onset (,7 years of age), an intermediate-onset (,8 and ,22), and a late-onset group (,23) were identified. Comparison of clinical correlates among subgroups by means of chi-square test showed a statistically significant result for migraine frequency (,2 = 7.41, P = .02). Considering the frequency of migraine attacks as a main outcome, the regression model showed a higher AAO is associated with low frequency (odds ratio = 0.95; P = .02). Conclusions., The significant association between AAO and attack frequency found in our study supports the hypothesis that AAO could act as a predictor factor able to influence prognosis. AAO could represent a phenotype suitable for identifying MWA susceptibility genes. [source] The genetic structure of cattle populations (Bos taurus) in northern Eurasia and the neighbouring Near Eastern regions: implications for breeding strategies and conservationMOLECULAR ECOLOGY, Issue 18 2007MENG-HUA LI Abstract We investigated the genetic structure and variation of 21 populations of cattle (Bos taurus) in northern Eurasia and the neighbouring Near Eastern regions of the Balkan, the Caucasus and Ukraine employing 30 microsatellite markers. By analyses of population relationships, as well as by a Bayesian-based clustering approach, we identified a genetic distinctness between populations of modern commercial origin and those of native origin. Our data suggested that northern European Russia represents the most heavily colonized area by modern commercial cattle. Further genetic mixture analyses based on individual assignment tests found that native Red Steppe cattle were also employed in the historical breeding practices in Eastern Europe, most probably for incorporating their strong and extensive adaptability. In analysis of molecular variance, within-population differences accounted for ~90% of the genetic variation. Despite some correspondence between geographical proximity and genetic similarity, genetic differentiation was observed to be significantly associated with the difference in breeding purpose among the European populations (percentage of variance among groups and significance: 2.99%, P = 0.02). Our findings give unique genetic insight into the historical patterns of cattle breeding practices in the former Soviet Union. The results identify the neighbouring Near Eastern regions such as the Balkan, the Caucasus and Ukraine, and the isolated Far Eastern Siberia as areas of ,genetic endemism', where cattle populations should be given conservation priority. The results will also be of importance for cost-effective management of their future utilization. [source] Using pulsed gradient spin echo NMR for chemical mixture analysis: How to obtain optimum resultsCONCEPTS IN MAGNETIC RESONANCE, Issue 4 2002Brian Antalek Abstract Pulsed gradient spin echo NMR is a powerful technique for measuring diffusion coefficients. When coupled with appropriate data processing schemes, the technique becomes an exceptionally valuable tool for mixture analysis, the separation of which is based on the molecular size. Extremely fine differentiation may be possible in the diffusion dimension but only with high-quality data. For fully resolved resonances, components with diffusion coefficients that differ by less than 2% may be distinguished in mixtures. For highly overlapped resonances, the resolved spectra of pure components with diffusion coefficients that differ by less than 30% may be obtained. In order to achieve the best possible data quality one must be aware of the primary sources of artifacts and incorporate the necessary means to alleviate them. The origin of these artifacts are described, along with the methods necessary to observe them. Practical solutions are presented. Examples are shown that demonstrate the effects of the artifacts on the acquired data set. Many mixture analysis problems may be addressed with conventional high resolution pulsed field gradient probe technology delivering less than 0.5 T m,1 (50 G cm,1). © 2002 Wiley Periodicals, Inc. Concepts Magn Reson 14: 225,258, 2002. [source] Parallel heterogeneous CBIR system for efficient hyperspectral image retrieval using spectral mixture analysisCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 9 2010Antonio J. Plaza Abstract The purpose of content-based image retrieval (CBIR) is to retrieve, from real data stored in a database, information that is relevant to a query. In remote sensing applications, the wealth of spectral information provided by latest-generation (hyperspectral) instruments has quickly introduced the need for parallel CBIR systems able to effectively retrieve features of interest from ever-growing data archives. To address this need, this paper develops a new parallel CBIR system that has been specifically designed to be run on heterogeneous networks of computers (HNOCs). These platforms have soon become a standard computing architecture in remote sensing missions due to the distributed nature of data repositories. The proposed heterogeneous system first extracts an image feature vector able to characterize image content with sub-pixel precision using spectral mixture analysis concepts, and then uses the obtained feature as a search reference. The system is validated using a complex hyperspectral image database, and implemented on several networks of workstations and a Beowulf cluster at NASA's Goddard Space Flight Center. Our experimental results indicate that the proposed parallel system can efficiently retrieve hyperspectral images from complex image databases by efficiently adapting to the underlying parallel platform on which it is run, regardless of the heterogeneity in the compute nodes and communication links that form such parallel platform. Copyright © 2009 John Wiley & Sons, Ltd. [source] Research Submission: Mixture Analysis of Age at Onset in Migraine Without Aura: Evidence for Three SubgroupsHEADACHE, Issue 8 2010Carlo Asuni MD (Headache 2010;50:1313-1319) Objective. , To verify the presence of different age at onset (AAO) subgroups of patients in a sample of patients with migraine without aura (MWA) and compare clinical correlates among them. Background., MWA is a long-lasting disease whose prognosis has not yet been fully investigated. Patients may present complete remission, partial clinical remission, persistence and progression (migraine attack frequency and disability may increase over time leading to chronic migraine). Limited evidence exists regarding the identification of risk factors or predictors which might influence migraine prognosis. AAO has been proven a useful tool in the investigation of the clinical, biological, and genetic characteristics able to influence the prognosis of a number of neuropsychiatric disorders. AAO distribution was studied using mixture analysis, a statistical approach that breaks down the empirical AAO distribution observed into a mixture of normal components. Methods., A sample of 334 outpatients affected by MWA, recruited in a clinical genetic study at our Headache Center from 2004 to 2008, was enrolled for this study. Diagnosis was made according to International Headache Society criteria 2004. AAO distribution in patients was studied using mixture analysis. Chi-square test was used to compare clinical correlates among identified subgroups. Logistic regression was performed in order to correct for effect of possible confounders. Results., Mixture analysis broke up the observed distribution of AAO into 3 normal theoretical distributions. Informational criteria clearly showed a better 3-component model rather than the 2-component one. An early-onset (,7 years of age), an intermediate-onset (,8 and ,22), and a late-onset group (,23) were identified. Comparison of clinical correlates among subgroups by means of chi-square test showed a statistically significant result for migraine frequency (,2 = 7.41, P = .02). Considering the frequency of migraine attacks as a main outcome, the regression model showed a higher AAO is associated with low frequency (odds ratio = 0.95; P = .02). Conclusions., The significant association between AAO and attack frequency found in our study supports the hypothesis that AAO could act as a predictor factor able to influence prognosis. AAO could represent a phenotype suitable for identifying MWA susceptibility genes. [source] Sexual dimorphism in limb bones of ibex (Capra ibex L.): mixture analysis applied to modern and fossil dataINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 5 2007H. Fernández Abstract Estimating sex ratios of fossil bone assemblages is an important step in the determination of demographic profiles, which are essential for understanding the palaeobiology and palaeoethology of any particular species, as well as its exploitation patterns by humans. This is especially true for ibex (Capra ibex), which was a main source of food for hominids during Pleistocene times. Classical methods for determining sexual dimorphism and sex ratio, such as analyses using uni- and bivariate plots, are based on an arbitrary fixing of limits between sexes. Here we use a more robust statistical method termed mixture analysis (MA) to determine the sex of postcranial remains (long bones, metapodials and tarsals) from ibex. For the first time, we apply MA to both a modern and a fossil sample of one species, by using metric data taken from (i) a collection of present-day ibex skeletons and (ii) a Palaeolithic sample of the same species. Our results clearly show that the forelimb (humerus and radius) is more dimorphic than the hindlimb (femur and tibia) and is therefore better suited for sexing ibex. It also appears that metapodials should be used carefully for estimating sex ratios. On the basis of these results, we propose a classification of bone measurements that are more or less reliable for sexing ibex. The results of MA applied to the ibex fossil bones from the Upper Palaeolithic site of the Observatoire (Monaco) lead us to the conclusion that this assemblage consists of a majority of males. The quantitative estimations calculated by the MA make it possible to compare the size of Pleistocene and modern ibex for the whole set of variables used in this study. Copyright © 2006 John Wiley & Sons, Ltd. [source] Relationships between expanding pinyon,juniper cover and topography in the central Great Basin, NevadaJOURNAL OF BIOGEOGRAPHY, Issue 5 2008Bethany A. Bradley Abstract Aim, Increasing geographical range and density of conifers is a major form of land-cover change in the western United States, affecting fire frequency, biogeochemistry and possibly biodiversity. However, the extent and magnitude of the change are uncertain. This study aimed to quantify the relationship between changing conifer cover and topography. Location, The central Great Basin in the state of Nevada, USA. Methods, We used a series of Landsat Thematic Mapper satellite images from 1986, 1995 and 2005 to map change in pinyon,juniper woodlands (Pinus monophylla, Juniperus spp.) in the montane central Great Basin of Nevada. We derived fractional greenness for each year using spectral mixture analysis and identified all areas with an above average increase in greenness from 1986 to 1995 and 1995 to 2005. Results, Areas with high fractional greenness in 2005 were most likely to occur at elevations between 2200 and 2600 m a.s.l. Increases in fractional greenness between 1986 and 2005 were most likely to occur at elevations below 2000 m a.s.l. and on south-facing slopes. However, relationships between elevation and increasing greenness for individual mountain ranges varied considerably from the average trend. Fractional greenness values measured by Landsat suggest that the majority of pinyon,juniper woodlands have not reached their maximum potential tree cover. Main conclusions, Expansion of pinyon,juniper at low elevations and on south-facing slopes probably reflects increasing precipitation in the 20th century, higher water use efficiency caused by increasing atmospheric CO2 in the late 20th century and livestock grazing at the interface between shrubland and woodland. Identification of the spatial relationships between changing fractional greenness of pinyon,juniper woodland and topography can inform regional land management and improve projections of long-term ecosystem change. [source] Web server suite for complex mixture analysis by covariance NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2009Fengli Zhang Abstract Elucidation of the chemical composition of biological samples is a main focus of systems biology and metabolomics. Their comprehensive study requires reliable, efficient, and automatable methods to identify and quantify the underlying metabolites. Because nuclear magnetic resonance (NMR) spectroscopy is a rich source of molecular information, it has a unique potential for this task. Here we present a suite of public web servers (http://spinportal.magnet.fsu.edu), termed COLMAR, which facilitates complex mixture analysis by NMR. The COLMAR web portal presently consists of three servers: COLMAR covariance calculates the covariance NMR spectrum from an NMR input dataset, such as a TOCSY spectrum; COLMAR DemixC method decomposes the 2D covariance TOCSY spectrum into a reduced set of nonredundant 1D cross sections or traces, which belong to individual mixture components; and COLMAR query screens the traces against a NMR spectral database to identify individual compounds. Examples are presented that illustrate the utility of this web server suite for complex mixture analysis. Copyright © 2009 John Wiley & Sons, Ltd. [source] The design of a multi-dimensional LC-SPE-NMR system (LC2 -SPE-NMR) for complex mixture analysis,MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2006A. J. Alexander Abstract In this communication, we describe the design of an online multi-chromatographic approach to the routine NMR analyses of low-level components (,0.1%) in complex mixtures. The technique, termed LC2 -SPE-NMR, optimally combines multi-dimensional liquid chromatography with SPE technology for isolating, enriching and delivering trace analytes to the NMR probe. The fully automated LC2 -SPE-NMR system allows for maximal loading capacity (in the first, preparative LC dimension), close to optimal peak resolution (in the second, analytical LC dimension) and enhanced sample concentration (through SPE). Using this system, it is feasible to conveniently conduct a wide range of NMR experiments on, for example, drug impurities at the low microgram per milliliter level, even for components poorly resolved in the first dimension. Such a sensitivity gain significantly elevates the analytical power of online NMR technology in terms of the level at which substances of pharmaceutical significance can be structurally characterized. Copyright © 2006 John Wiley & Sons, Ltd. [source] Impact desolvation of electrosprayed microdroplets , a new ionization method for mass spectrometry of large biomoleculesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2001Sergei A. Aksyonov Impact desolvation of electrosprayed microdroplets (IDEM) is a new method for producing gas-phase ions of large biomolecules. Analytes are dissolved in an electrolyte solution which is electrosprayed in vacuum, producing highly charged micron and sub-micron sized droplets (microdroplets). These microdroplets are accelerated through potential differences ,5,,,10,kV to velocities of several km/s and allowed to impact a target surface. The energetic impacts vaporize the droplets and release desolvated gas-phase ions of the analyte molecules. Oligonucleotides (2- to 12-mer) and peptides (bradykinin, neurotensin) yield singly and doubly charged molecular ions with no detectable fragmentation. Because the extent of multiple charging is significantly less than in atmospheric pressure electrospray ionization, and the method produces ions largely free of adducts from solutions of high ionic strength, IDEM has some promise as a method for coupling to liquid chromatographic techniques and for mixture analysis. Ions are produced in vacuum at a flat equipotential surface, potentially allowing efficient ion extraction. Copyright © 2001 John Wiley & Sons, Ltd. [source] Evaluation of DNA Mixtures from Database SearchBIOMETRICS, Issue 1 2010Yuk-Ka Chung Summary With the aim of bridging the gap between DNA mixture analysis and DNA database search, a novel approach is proposed to evaluate the forensic evidence of DNA mixtures when the suspect is identified by the search of a database of DNA profiles. General formulae are developed for the calculation of the likelihood ratio for a two-person mixture under general situations including multiple matches and imperfect evidence. The influence of the prior probabilities on the weight of evidence under the scenario of multiple matches is demonstrated by a numerical example based on Hong Kong data. Our approach is shown to be capable of presenting the forensic evidence of DNA mixtures in a comprehensive way when the suspect is identified through database search. [source] | |||||||||||||