Are probability estimates from the permutation model of Mantel's test stable?

1989 ◽  
Vol 67 (3) ◽  
pp. 766-769 ◽  
Author(s):  
Donald A. Jackson ◽  
Keith M. Somers
Keyword(s):  
Null Distribution ◽  
Statistical Distribution ◽  
Quadratic Assignment ◽  
Considerable Error ◽  
Probability Estimates ◽  
Permutation Model ◽  
The Stability ◽  
Mantel’S Test

Matrix comparison tests (i.e., Mantel's test or quadratic assignment) are employed with increasing frequency to measure the concordance between genetic, behavioural, morphological, ecological, and geographic distances. Such tests compare an observed measure of matrix association with a null distribution derived from a randomly generated subset of all possible permutations of one of the original matrices. Typically, 500–2000 randomly permutated matrices are used to generate the statistical distribution and thereby estimate the probability of obtaining an observed association between two matrices. We demonstrate that a considerable error (i.e., 5–6%) may be associated with probability estimates based on such low numbers of permutations. To ensure the stability of the probability estimates (i.e., increase the reliability of the test), we recommend the use of a minimum of 10 000 permutations, and 100 000 permutations if the observed probability approaches a critical significance value (e.g., 0.05).

Determination of the size and charge of dye aggregates in aqueous electrolyte solution

1975 ◽  
Vol 28 (9) ◽  
pp. 1971 ◽  
Author(s):  
BR Craven ◽  
JC Griffith ◽  
JG Kennedy
Keyword(s):  
Electrolyte Solution ◽  
Diffusion Coefficients ◽  
Aqueous Electrolyte ◽  
Aqueous Electrolyte Solution ◽  
Particle Sizes ◽  
Considerable Error ◽  
Electrophoretic Mobilities ◽  
Dye Aggregation ◽  
The Stability

The stability of two dyes in the presence of electrolyte has been investigated over the period required for measurement of diffusion coefficients in glass sinter diaphragm cells, and the results indicate that particle sizes remain constant over such times. The effect of concentration differences within the cell during a run has been measured and was found to give rise to considerable error. Corrected diffusion coefficients have been used together with electrophoretic mobilities to calculate aggregation numbers and the extent of counter- ion uptake into the aggregates. The results are shown to be consistent with the ?stack of coins? model for dye aggregation.

scholarly journals STABILITY AGAINST WAVES AND CURRENTS OF GRAVEL RUBBLE MOUNDS OVER PIPELINES AND FLAT GRAVEL BEDS

2011 ◽  
Vol 1 (32) ◽  
pp. 59
Author(s):  
Alf Tørum ◽  
Øivind Arntsen ◽  
Colin Kuester
Keyword(s):  
Shear Stress ◽  
Laboratory Tests ◽  
Statistical Distribution ◽  
Irregular Waves ◽  
Bed Shear Stress ◽  
Gas Pipelines ◽  
Gravel Beds ◽  
Waves And Currents ◽  
The Stability ◽  
Oil Gas

For different reasons oil/gas pipelines or parts of oil/gas pipelines have to be covered with rubble mounds. The question is then what the size of the stones/gravel in the mound should be to withstand waves and currents of the area. In order to obtain more information on the stability of gravel mounds over pipelines, laboratory tests in a wave/current flume have been carried out and are summarized herein. In addition data from other similar investigations elsewhere are discussed. A brief analysis of the stability of a flat gravel bed subjected to irregular waves has also been included, using the concept of the statistical distribution of the bed shear stress.

scholarly journals The expediency of vertical integration: synergy approach arguments

2014 ◽  
Vol 36 (3) ◽  
pp. 627-633
Author(s):  
Vasyl Shukalovych
Keyword(s):  
Vertical Integration ◽  
Value Added ◽  
Added Value ◽  
Market System ◽  
Market Evolution ◽  
Probability Estimates ◽  
Micro Level ◽  
The Stability ◽  
Definition Of ◽  
Transformation Processes

Deciding on vertical integration is caused by the need to increase the company's competitiveness in the market. At the same time, under conditions of intense transformation processes in the market environment, the choice of organizational strategy is very complicated. This requires the development of recommendations on its feasibility taking into account the stage of market evolution. Accordingly, the aim of the work is the definition of expediency of vertical integration by use methodological instruments of synergetic approach. Results of the study were obtained using a methodology that includes theoretical synchronization of synergy tools and economic phenomena at the macro and micro level; simulative modeling stages of development of the market system which includes parameters of the value added, value of enterprises, number of enterprises; forming conclusions based on a comparison of probability estimates. As a result, it is determined that vertical integration is more doomed to success in conditions close to the stability of the market, rather than in terms of active transformations on it.

scholarly journals Stability Analysis of Company Co-Mention Network and Market Graph Over Time Using Graph Similarity Measures

2019 ◽  
Vol 5 (3) ◽  
pp. 55
Author(s):  
Alexey Faizliev ◽  
Vladimir Balash ◽  
Vladimir Petrov ◽  
Alexey Grigoriev ◽  
Dmitriy Melnichuk ◽  
...  
Keyword(s):  
Time Windows ◽  
Similarity Measures ◽  
Quadratic Assignment ◽  
News Item ◽  
Sharp Change ◽  
Graph Similarity ◽  
Market Graph ◽  
The Stability ◽  
The Impact ◽  
Over Time

The aim of the paper is to provide an analysis of news and financial data using their network representation. The formation of network structures from data sources is carried out using two different approaches: by building the so-called market graph in which nodes represent financial assets (e.g., stocks) and the edges between nodes stand for the correlation between the corresponding assets, by constructing a company co-mention network in which any two companies are connected by an edge if a news item mentioning both companies has been published in a certain period of time. Topological changes of the networks over the period 2005–2010 are investigated using the sliding window of six-month duration. We study the stability of the market graph and the company co-mention network over time and establish which of the two networks was more stable during the period. In addition, we examine the impact of the crisis of 2008 on the stability of the market graph as well as the company co-mention network. The networks that are considered in this paper and that are the objects of our study (the market graph and the company co-mention network) have a non-changing set of nodes (companies), and can change over time by adding/removing links between these nodes. Different graph similarity measures are used to evaluate these changes. If a network is stable over time, a measure of similarity between two graphs constructed for two different time windows should be close to zero. If there was a sharp change between the graphs constructed for two adjacent periods, then this should lead to a sharp increase in the value of the similarity measure between these two graphs. This paper uses the graph similarity measures which were proposed relatively recently. In addition, to estimate how the networks evolve over time we exploit QAP (Quadratic Assignment Procedure). While there is a sufficient amount of works studying the dynamics of graphs (including the use of graph similarity metrics), in this paper the company co-mention network dynamics is examined both individually and in comparison with the dynamics of market graphs for the first time.

Open discussion

1982 ◽  
Vol 99 ◽  
pp. 605-613
Author(s):  
P. S. Conti
Keyword(s):  
Buenos Aires ◽  
Large Mass ◽  
List Type ◽  
Common Phenomenon ◽  
Open Discussion ◽  
The Stability ◽  
Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

Symmetric Multistep Methods Revisited: II. Numerical Experiments

1999 ◽  
Vol 173 ◽  
pp. 309-314 ◽  
Author(s):  
T. Fukushima
Keyword(s):  
Multistep Methods ◽  
Computational Time ◽  
Integration Time ◽  
Implicit Methods ◽  
Symmetric Methods ◽  
Celestial Bodies ◽  
The Stability ◽  
Predictor Corrector ◽  
Symmetric Multistep Methods ◽  
Integration Errors

AbstractBy using the stability condition and general formulas developed by Fukushima (1998 = Paper I) we discovered that, just as in the case of the explicit symmetric multistep methods (Quinlan and Tremaine, 1990), when integrating orbital motions of celestial bodies, the implicit symmetric multistep methods used in the predictor-corrector manner lead to integration errors in position which grow linearly with the integration time if the stepsizes adopted are sufficiently small and if the number of corrections is sufficiently large, say two or three. We confirmed also that the symmetric methods (explicit or implicit) would produce the stepsize-dependent instabilities/resonances, which was discovered by A. Toomre in 1991 and confirmed by G.D. Quinlan for some high order explicit methods. Although the implicit methods require twice or more computational time for the same stepsize than the explicit symmetric ones do, they seem to be preferable since they reduce these undesirable features significantly.

Uniformity of Magnification from Different Electron Microscopes

1967 ◽  
Vol 25 ◽  
pp. 32-33
Author(s):  
Godfrey C. Hoskins ◽  
V. Williams ◽  
V. Allison
Keyword(s):  
Diffraction Grating ◽  
The Other ◽  
Carbon Replica ◽  
Electron Microscopes ◽  
The Stability

The method demonstrated is an adaptation of a proven procedure for accurately determining the magnification of light photomicrographs. Because of the stability of modern electrical lenses, the method is shown to be directly applicable for providing precise reproducibility of magnification in various models of electron microscopes.A readily recognizable area of a carbon replica of a crossed-line diffraction grating is used as a standard. The same area of the standard was photographed in Phillips EM 200, Hitachi HU-11B2, and RCA EMU 3F electron microscopes at taps representative of the range of magnification of each. Negatives from one microscope were selected as guides and printed at convenient magnifications; then negatives from each of the other microscopes were projected to register with these prints. By deferring measurement to the print rather than comparing negatives, correspondence of magnification of the specimen in the three microscopes could be brought to within 2%.

Effect of Improved ThO2 Particle Dispersion in Nickel on High-Temperature Strength

1970 ◽  
Vol 28 ◽  
pp. 444-445
Author(s):  
E. R. Kimmel ◽  
H. L. Anthony ◽  
W. Scheithauer
Keyword(s):  
High Temperature ◽  
Metal Matrix ◽  
Oxide Particle ◽  
Oxide Phase ◽  
Dislocation Motion ◽  
Particle Dispersion ◽  
High Temperature Strength ◽  
Strengthening Effect ◽  
Oxide Particles ◽  
The Stability

The strengthening effect at high temperature produced by a dispersed oxide phase in a metal matrix is seemingly dependent on at least two major contributors: oxide particle size and spatial distribution, and stability of the worked microstructure. These two are strongly interrelated. The stability of the microstructure is produced by polygonization of the worked structure forming low angle cell boundaries which become anchored by the dispersed oxide particles. The effect of the particles on strength is therefore twofold, in that they stabilize the worked microstructure and also hinder dislocation motion during loading.

An Analysis of Dissociation of Molecules in a High Resolution Electron Microscope

1973 ◽  
Vol 31 ◽  
pp. 486-487
Author(s):  
Mihir Parikh
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Cross Sections ◽  
Resolving Power ◽  
Peak Intensity ◽  
Molecular Film ◽  
Resolution Electron ◽  
Dissociation Cross Section ◽  
High Resolution Electron Microscope ◽  
The Stability

It is well known that the resolution of bio-molecules in a high resolution electron microscope depends not just on the physical resolving power of the instrument, but also on the stability of these molecules under the electron beam. Experimentally, the damage to the bio-molecules is commo ly monitored by the decrease in the intensity of the diffraction pattern, or more quantitatively by the decrease in the peaks of an energy loss spectrum. In the latter case the exposure, EC, to decrease the peak intensity from IO to I’O can be related to the molecular dissociation cross-section, σD, by EC = ℓn(IO /I’O) /ℓD. Qu ntitative data on damage cross-sections are just being reported, However, the microscopist needs to know the explicit dependence of damage on: (1) the molecular properties, (2) the density and characteristics of the molecular film and that of the support film, if any, (3) the temperature of the molecular film and (4) certain characteristics of the electron microscope used

Formation and Structure of Casein Micelles in Lactating Mammary Tissue

1970 ◽  
Vol 28 ◽  
pp. 150-151
Author(s):  
Robert J. Carroll ◽  
Marvin P. Thompson ◽  
Harold M. Farrell
Keyword(s):  
Size Distribution ◽  
G Protein ◽  
Milk Proteins ◽  
Mammary Tissue ◽  
Colloidal System ◽  
Casein Micelles ◽  
The Stability

Milk is an unusually stable colloidal system; the stability of this system is due primarily to the formation of micelles by the major milk proteins, the caseins. Numerous models for the structure of casein micelles have been proposed; these models have been formulated on the basis of in vitro studies. Synthetic casein micelles (i.e., those formed by mixing the purified αsl- and k-caseins with Ca2+ in appropriate ratios) are dissimilar to those from freshly-drawn milks in (i) size distribution, (ii) ratio of Ca/P, and (iii) solvation (g. water/g. protein). Evidently, in vivo organization of the caseins into the micellar form occurs in-a manner which is not identical to the in vitro mode of formation.

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