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21.
A study of standardization of variables in cluster analysis 总被引:2,自引:2,他引:0
A methodological problem in applied clustering involves the decision of whether or not to standardize the input variables prior to the computation of a Euclidean distance dissimilarity measure. Existing results have been mixed with some studies recommending standardization and others suggesting that it may not be desirable. The existence of numerous approaches to standardization complicates the decision process. The present simulation study examined the standardization problem. A variety of data structures were generated which varied the intercluster spacing and the scales for the variables. The data sets were examined in four different types of error environments. These involved error free data, error perturbed distances, inclusion of outliers, and the addition of random noise dimensions. Recovery of true cluster structure as found by four clustering methods was measured at the correct partition level and at reduced levels of coverage. Results for eight standardization strategies are presented. It was found that those approaches which standardize by division by the range of the variable gave consistently superior recovery of the underlying cluster structure. The result held over different error conditions, separation distances, clustering methods, and coverage levels. The traditionalz-score transformation was found to be less effective in several situations. 相似文献
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Pancreatic amylin and calcitonin gene-related peptide cause resistance to insulin in skeletal muscle in vitro 总被引:21,自引:0,他引:21
Insulin resistance occurs in a variety of conditions, including diabetes, obesity and essential hypertension, but its underlying molecular mechanisms are unclear. In type 2 (non-insulin-dependent) diabetes mellitus, it is insulin-resistance in skeletal muscle, the chief site of insulin-mediated glucose disposal in humans, that predominantly accounts for the low rates of glucose clearance from the blood, and hence for impaired glucose tolerance. Human type 2 diabetes is characterized by a decrease in non-oxidative glucose storage (muscle glycogen synthesis), and by the deposition of amyloid in the islets of Langerhans. Amylin is a 37-amino-acid peptide which is a major component of islet amyloid and has structural similarity to human calcitonin gene-related peptide-2 (CGRP-2; ref. 8). CGRP is a neuropeptide which may be involved in motor activity in skeletal muscle. We now report that human pancreatic amylin and rat CGRP-1 are potent inhibitors of both basal and insulin-stimulated rates of glycogen synthesis in stripped rat soleus muscle in vitro. These results may provide a basis for a new understanding of the molecular mechanisms that cause insulin resistance in skeletal muscle. 相似文献
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Stereochemical requirements of the mescaline receptor 总被引:1,自引:0,他引:1
26.
Zusammenfassung Die durch Röntgenstrahlen (1 R/sec) erzeugten elektrischen Impulse einzelner Nervenzellen der Geruchszwiebel wurden in narkotisierten Katzen, Kaninchen und Hunden gemessen. Als typische Reaktion wurde eine kurzfristige Erhöhung der elektrischen Impulse gefunden. Somit sind die von Röntgenstrahlen ausgelösten elektrischen Impulse des Geruchsystems kein artspezifisches, sondern vielmehr ein allgemeines Phänomen.
This study was supported through funds provided by the Bureau of Medicine and Surgery, U.S. Navy, and the Defense Atomic Support Agency. The opinions and assertions contained herein are those of the authors and are not to be construed as the official views of the Navy Department. 相似文献
This study was supported through funds provided by the Bureau of Medicine and Surgery, U.S. Navy, and the Defense Atomic Support Agency. The opinions and assertions contained herein are those of the authors and are not to be construed as the official views of the Navy Department. 相似文献
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Clayton DG Walker NM Smyth DJ Pask R Cooper JD Maier LM Smink LJ Lam AC Ovington NR Stevens HE Nutland S Howson JM Faham M Moorhead M Jones HB Falkowski M Hardenbol P Willis TD Todd JA 《Nature genetics》2005,37(11):1243-1246
The main problems in drawing causal inferences from epidemiological case-control studies are confounding by unmeasured extraneous factors, selection bias and differential misclassification of exposure. In genetics the first of these, in the form of population structure, has dominated recent debate. Population structure explained part of the significant +11.2% inflation of test statistics we observed in an analysis of 6,322 nonsynonymous SNPs in 816 cases of type 1 diabetes and 877 population-based controls from Great Britain. The remainder of the inflation resulted from differential bias in genotype scoring between case and control DNA samples, which originated from two laboratories, causing false-positive associations. To avoid excluding SNPs and losing valuable information, we extended the genomic control method by applying a variable downweighting to each SNP. 相似文献
30.
Diversity of immunoglobulin expression in leukaemic cells resembling B-lymphocyte precursors 总被引:3,自引:0,他引:3
L B Vogler J L Preud'homme M Seligmann W E Gathings W M Crist M D Cooper F J Bollum 《Nature》1981,290(5804):339-341
Approximately 20% of patients with acute lymphocytic leukaemia (ALL) have leukaemic blasts with features of pre-B cells which are the recently characterized precursors of B lymphocytes in normal development (for a review, see ref. 2). Pre-B cells isolated from normal bone marrow or fetal liver, and malignant cells from patients with pre-B cell leukaemia, are rapidly dividing lymphoid cells that contain cytoplasmic immunoglobulin mu heavy chains, but have no detectable surface immunoglobulin. The resemblance of immunoglobulin-containing ALL cells to normal precursors of B lymphocytes and their availability in relatively pure preparations allowed us to explore them as models of early stages in the differentiation of the B-lymphocyte line. We report here observations on the occurrence of intermediate pre-B/B-cell phenotypes, immunoglobulin isotype switching and the asynchrony of immunoglobulin heavy and light chain expression in 30 cases of ALL and 3 cases of chronic myelogenous leukaemia in lymphoblastic crisis (CML-BC). 相似文献