J-shaped Distribution Research Articles

The effects of machining settings on the behavior of pulse trains in the WEDM process

A pulse discrimination system has been developed to study the characteristics of pulse trains in the WEDM process under various machining conditions. The effects of on-time, off-time and feed on the variations of the proportions of short sparks, are sparks, and normal sparks in the total sparks (defined as short ratio, arc ratio, and normal ratio, respectively); the distribution of the ignition delay time of the normal sparks; the average ignition delay time; and the proportion of machining time in a specific sampling period were investigated. An approximate method for estimating the variation of the average gap width is also introduced. It is found that a short on-time, or a long off-time, or a large feed, results in the decrease of both normal ratio and average ignition delay time, and an increase of short ratio. On-time has the largest effect on the arc ratio, whilst off-time has the least effect. The ignition delay time of the normal sparks displays a reverse J-shape distribution. On-time is the most prominent factor amongst all of the machining settings under consideration affecting this distribution. In addition, the distribution becomes more left skew with a higher peak and a shorter tail under the condition of a shorter on-time setting. Based on the analysis results, the instability during the WEDM process can be attributed to an apparent increase of either arc sparks, short sparks, or both. A strategy to improve machining stability with respect to each case is proposed accordingly.

Stand structure and successional trends in virgin boreal forest reserves in Sweden

Fire history and stand structure was examined in twelve virgin forest stands situated within forest reserves in northern Sweden. The selected stands represented fire refuges as well as different successional stages after fire. Six of the stands were dominated by Norway spruce ( Picea abies L. Karst.), three were dominated by Scots pine ( Pinus sylvestris L.), and three were dominated by hairy birch ( Betula pubescens Ehrh.) or aspen ( Populus tremula L.). In 3 of the southernmost stands, the average fire interval was 34 to 65 years during the late 1600s to late 1800s, but since 1888 no fires had occurred in any of the stands. The absence of fire disturbance since 1888 is probably caused by the fire suppression in the overall landscape. The standing volume of living trees ranged between 87 and 511 m 3 ha −1 while the volume of dead trees, including both snags and logs, ranged between 27 and 201 m 3 ha −1. The volume of dead trees constituted ca. 30% of the total stem volume. In the conifer dominated stands, there was a statistically significant relationship between total stem volume, including both living and dead trees, and site productivity. A comparison between the amount of dead and living trees indicated substantial changes in tree species composition in several stands. It is suggested that data on the amount of dead trees, especially logs, and its distribution over decay classes could be used to examine the continuity of certain tree species. All stands had a multi-sized tree diameter distribution, which in most cases was similar to a reversed J-shaped distribution. In general spruce was numerous in the seedling cohort and in small diameter classes, indicating that its proportion in the stands was stable, or was increasing at the expense of pioneer tree species such as pine, aspen and silver birch ( Betula pendula Roth.). The most numerous species in the seedling cohort, rowan ( Sorbus aucuparia L.), was almost totally missing in the tree layer, indicating a high browsing pressure preventing rowan seedlings from growing into trees. The general increase of spruce and the sparse regeneration of pioneer species, in the stands previously affected by fire, are discussed in relation to natural disturbance regimes, biological diversity and nature conservation policies. It is proposed that reintroduction of fire disturbance is a necessity for future management plans of forest reserves. Other management practices to increase species diversity within forest reserves are also discussed.

Handedness Scale: How Many and Which Items?

A stepwise analysis of the Cronbach Alpha Coefficient (CAC) was performed on five large samples of adults and young children, in order to choose the “minimum” set of items of a handedness scale which gives the maximum reliability. In adults, a handedness scale with 12 items has nearly the same or even a better CAC than other scales with more items; so, a choice of 10 to 12 items seems to be adequate. For children, a scale with eight items seems to be quite reliable but it is not impossible that a scale including more items would lead to a slight increase of CAC. The controversial usefulness of a precise assessment of the “general handedness factor” (the first principal component) generated by handedness questionnaires and its J-shaped distribution in the general population are discussed.

Handedness Scale: How Many and Which Items?

A stepwise analysis of the Cronbach Alpha Coefficient (CAC) was performed on five large samples of adults and young children, in order to choose the “minimum” set of items of a handedness scale which gives the maximum reliability. In adults, a handedness scale with 12 items has nearly the same or even a better CAC than other scales with more items; so, a choice of 10 to 12 items seems to be adequate. For children, a scale with eight items seems to be quite reliable but it is not impossible that a scale including more items would lead to a slight increase of CAC. The controversial usefulness of a precise assessment of the “general handedness factor” (the first principal component) generated by handedness questionnaires and its J-shaped distribution in the general population are discussed.

76P J-shaped compliance distribution: Revised

76P J-shaped compliance distribution: Revised

Dynamics of the forest vegetation of the Umtiza Nature Reserve, East London

The forest community at the Umtiza Nature Reserve near East London was surveyed using 24 plots (0.04 ha) in which all woody stems 0.5 m tall were enumerated. Based on a classification using numbers of stems of canopy species, it was assumed that basically only one forest community was sampled. Further multivariate analyses suggest that this forest is fine-grained. Sample plots were similarly placed in ordination space irrespective of whether woody species occurrence was used as importance value or if species occurrence per size class was used separately [seedlings (0.5-1.0 m), saplings (1-5 m) or canopy individuals ( 5 m)). An analysis of size-class distributions of the most common canopy species indicated that the majority of species exhibited inverse J-shaped size-class distributions. This is the expected pattern for a fine-grained forest. In these measures of dynamics, this forest is not fundamentally different to the more temperate Afromontane forests.

Predicting Crown Sizes and Diameter Distributions of Tanoak, Pacific Madrone, and Giant Chinkapin Sprout Clumps

Abstract Crown size and stem diameters were measured on a total of 908 sprout clumps of tanoak (Lithocarpus densiflorus), Pacific madrone (Arbutus menziesii), and giant chinkapin (Castanopsis chrysophylla). The clumps, age 1 to 16 years, were located at 23 sites in southwestern Oregon and 20 sites in northwestern California. Regression equations were developed for predicting individual-clump crown size and stem-diameter distributions of dominant sprouts from the total basal area (dm² at 1.37 m) in stems of the parent tree (PBA) and number of growing seasons since burning (AGE). Variables of PBA, AGE, and species in combination accounted for over 75% of the total variation in hardwood crown width and height and for 62% of the variation in sprout number. Variables describing site characteristics and competing vegetation abundance did not explain more than 2% of additional variation in hardwood crown size or sprout diameter distribution. On the basis of the Kolmogorov-Smirnoff test (α = 0.05), the Weibull function adequately described the reverse J-shaped distribution of stem diameters for individual sprout clumps. The goodness of fit for each of the predictive models for tanoak and madrone was verified with independent data. West. J. Appl. For. 7(4):103-108.

The J-shaped relationship between coronary heart disease and achieved blood pressure level in treated hypertension: further analyses of 12 years of follow-up of treated hypertensives in the Primary Prevention Trial in Gothenburg, Sweden

The relationship between the blood pressure level achieved through antihypertensive treatment and the incidence of coronary heart disease (CHD) was studied in 686 middle-aged hypertensive men. The patients studied came from a random population sample and were followed-up for 12 years, yielding a total of 6563 patient-years for the study. Eighty-seven patients suffered a non-fatal myocardial infarction or died from CHD. The incidence of CHD showed a J-shaped distribution in relation to achieved treated systolic and diastolic blood pressure levels. The incidence of CHD, adjusted for entry characteristics, age, serum cholesterol, blood pressure and smoking habits, decreased with reductions in blood pressure achieved through treatment, to a level of about 150/85 mmHg, below which the incidence rate again increased. This J-shaped pattern was also observed when data from patients with pre-existing signs or symptoms of ischemic heart disease at entry were excluded. Using a quadratic term as the best fit to the observed relationship between achieved treated diastolic blood pressure level and the incidence of CHD, a Cox regression analysis showed that the nadir of the J-shaped incidence curve was at a diastolic blood pressure value of 81 mmHg. There did not seem to be any association between the absolute size of the blood pressure reduction during treatment and the incidence of CHD. Although we cannot exclude the possibility that the increased incidence of CHD in patients with a low treated blood pressure is due primarily to pre-existing but subclinical ischemic heart disease, our findings indicate that an excessive lowering of blood pressure in hypertensive patients may be harmful.(ABSTRACT TRUNCATED AT 250 WORDS)

Does hand proficiency determine hand preference?

There is debate in the handedness literature over proficiency and preference measures are indicators of common underlying factors, or separate dimensions of behavior with different causes. It has been argued that hand preference has different origins from hand proficiency on the grounds that (i) the two types of measure are imperfectly correlated and (ii) distributions of relative hand proficiency are normal or nearly so, whereas distributions of hand preference are J-shaped. A model is described in which the probability that one hand will be preferred for a given activity is directly proportional to the relative proficiency of the two sides, the latter being normally distributed. It is shown that imperfect correlations between proficiency and preference measures, and J-shaped distributions of preference, can be predicted by such a model. These facts about hand preference and proficiency do not, therefore, go against the view that preference is determined by proficiency.

EVOLUTION OF ATLANTIC AND PACIFIC COD: LOSS OF GENETIC VARIATION AND GENE EXPRESSION IN PACIFIC COD

An allozyme investigation of 41 protein-coding loci in two morphologically similar fishes, Atlantic and Pacific cod, indicates that Pacific cod experienced a severe population bottleneck that led to the loss of gene diversity and gene expression. Pacific cod possesses a significantly lesser amount of gene diversity (H = 0.032) than Atlantic cod (H = 0.125) and lacks gene expression for Me-3. Allele-frequency distributions differ between species as predicted by neutral theory: Atlantic cod has a U-shaped distribution, which is expected for populations in drift-mutation equilibrium, whereas Pacific cod has a J-shaped distribution with an excess of low-frequency alleles. This excess may be explained by the appearance of new alleles through mutation which have not yet reached intermediate frequencies through drift. The population bottleneck in Pacific cod was most likely associated with founder populations that dispersed into the Pacific Ocean after the Bering Strait opened. Under the molecular-clock hypothesis a Nei genetic distance of 0.415 (based on 41 loci) suggests that Pacific cod dispersed into the Pacific Ocean soon after the Bering Strait opened in the mid-Pliocene, 3.0 to 3.5 million years ago.

Tests of Significance for Differences in Counts of Rare Events in Two Treatment Groups

Counts of rare events tend to have Poisson or J-shaped distributions that render parametric assumptions questionable. Six different methods for testing the significance of the difference between location parameters for two such distributions are evaluated in this article. A binomial test for the difference between means is known to be the most powerful unbiased test when population distributions are truly Poisson; however, it appears extremely non-robust against departures from the distributional assumption. Robust enough to provide appropriate protection against Type I error, Student's t test was among the most powerful of the tests when applied to counts of rare events in two treatment groups. The Mann-Whitney sum of ranks test also provided superior alpha protection and power even where a large number of tied ranks occurred in the zero-count category of a J-shaped distribution. Finally, a 1 df chi-square test for linear shift in proportional representation across frequency categories of one group as opposed to the other was the most powerful of three chi-square tests that were evaluated.

Use of multivariate measures of disability in health surveys.

It has been claimed that the aggregation of information from several areas of life into a small set of global measures has certain advantages for describing disability. Global measures of disability were constructed from a modified version of an existing health survey instrument and the sickness impact profile (SIP) and their properties were tested. The disability items grouped satisfactorily into five global measures (physical, psychosocial, eating, communication, and work). All disability measures (global and original category scores) were poor predictors of service use by individuals but were related as expected to age and number of medical conditions. The global measures generally had lower standard errors and better repeatability. All scores exhibit J-shaped distributions for cross sectional data but the change in global measures over time was consistent with the normal distribution. Preferably, both global and category measures should be used for comparing changes over time between groups of individuals.

Forest Regrowth on the Cumberland Plateau and Implications for Productive Management

Abstract An old-growth forest and a 35-year-old, second-growth forest on the Cumberland Plateau were studied to compare species composition and structure. Species composition and total basal area of the two stands did not differ, although total stand density was 19 percent lower and basal area of commercial species was 25 percent higher in the old-growth than in the second-growth stand. Analysis of size-class distributions showed that both stands were best represented by an inverse J-shaped distribution, which best describes old-age stands. The rapid regeneration of the second-growth stand seems to be the result of minimal disturbance to accumulated nutrient pools in the soil. The importance of these accumulated nutrient pools and implications for forest management on the Cumberland Plateau are discussed.

Infant mortality differentials in an Indian setting: follow-up of hospital deliveries.

Using data collected through follow-up home visits to a sample of mothers, whose singleton babies were born at the Dufferin Hospital, Lucknow, September 1976—August 1977, estimates are made of infant mortality in Lucknow city, and its differentials by socioeconomic, demographic and health care characteristics of the infants and their families. Infant mortality was 74·5 per 1000 births during the year 1976–77 and there is evidence of some recent decline in it.Among socioeconomic factors considered, infant mortality is found to be inversely related with caste status among Hindus, education of mother, father's monthly income, and father's occupation. Infant mortality exhibits a J-shaped distribution in relation to maternal age and parity and a reversed J-shaped distribution in relation to maternal age at marriage. Among health and health care factors, antenatal care of the mother appears to exercise a negative influence on infant mortality, which also shows a marked negative relationship with birth weight and feeding index of the child. The findings suggest important policy implications, which, if followed, would help to reduce infant mortality, and would thus remove a serious obstacle in the way of acceptance of the small family norm and its achievement through the adoption of family planning.

An Evaluation of the Briggs-Nebes Modified Version of Annett's Handedness Inventory

The Briggs-Nebes (1975) modified version of Annett's (1967) handedness inventory was administered to 59 female and 51 male undergraduates and 101 nursing students. J-shaped distributions of scores in the dextral direction and significant sex differences such that males were more sinistral than females were found. The inventory was found to be multi-dimensional with up to three factors, power, skill, and rhythm in order of importance. The utility of the modified inventory was supported and recommendations were made concerning the use of subscale or factor scores in addition to overall scores.

Workers' Arrivals and Departures: An Informal Look

Wieland and Uhich (1976, pp. 57-58) suggest that employees tend to arrive at work just before the scheduled starting time. Further, the arrival array approximates Allport's (1934) J-shaped distribution. Tate, et al. (1978, pp. 25-37) imply that owner-managers, too, arrive before the starting time. However, their arrivals are normally earlier and their departures later. To examine these thoughts, the arrival and departure of cars at a parking area in a surburban industrial site were noted. Sampling observations were made of two time intervals: 30 min. before through 30 min. after the common starting and quitting times for the plants using the space. Further, note was made as to whether the residual cars (those there at the beginning or remaining at the end) were luxury or economy class. Cadillacs, Lincolns, and Chrys1e.r~ were considered luxury; Chevrolets, Fords, and Plymouths economy. Generally, 30 min. before the starting time about 6% of the arriving cars were in place; 25 rnin., 11%; 20 min., 20%; 15 min., 34%; 10 min., 62%; and 5 rnin., 96%. At the starting time, 97% were there. Five min. later the number increased by 1%, with the remaining 2% arriving during the last 25 min. As for departures, normally about 1% of the cars left during the first 15 min. By 10 min. prior to quitting time, 2% of the cars were gone; and 5 min., 3%. At quitting time, 5% had departed. Five min. later, 36% were gone; 10 min., 63%; 15 min., 79%; 20 rnin., 87%; 25 rnin., 91%; and 30 rnin., 93%. The pattern of arrivals tends to support both parts of the Wieland and Ullrich contention. Further, the distribution of the departures suggests that the involved frequency pattern is an approximate mirror-image of the arrival display. The average ratio of luxury to economy cars at the beginning of the arrival and the end of the departure intervals was about 2 to 1, as contrasted with approximately a 1 to 20 ratio at the end of the arrival and the beginning of the departure intervals. Assuming that most of the luxury class cars belonged to the owner-managers, the economy cars to the employees, the findings sugge& support of the thinking of Tate, et al. ( 1978).

The Selection of Class Intervals

The selection of class intervals, which can strongly affect the visual impression given by a map, is currently a totally anarchic branch of cartography. While practising cartographers have barely accustomed themselves to the routine techniques of class selection, recent work has widened the choice available and extended the opportunity to produce a desired bias. Systems of class intervals, apart from those fixed exogenously or in arbitrary fashion, are classified into idiographic or serial types, the latter being recommended here. Scale transformations leading towards symmetrical frequency distribu- tions are important and are required for proportional as well as graded symbolization. It is suggested that class intervals should not be optimized in relation to details of the statistical frequency distribution, but should be selected according to the overall shape of this distribution. For rectangular distributions, equal division of the range is appropriate: for dominantly unimodal distributions, intervals related to the standard deviation (on a scale which makes the distribution symmetrical): and for J-shaped distributions, geometric progressions to bases which are greater as skewness increases. Techniques are given for calibrating geometric progressions relative to the median, and for dealing with the special characteristics of percentages. An analysis of maps prepared by authors in various academic disciplines fails to show any rational or standardized procedures for the selection of class intervals. Evidently intuition, inspiration, revelation, mystical hunches, prejudices, legerdemain and predetermined ideas of what the class intervals should be have characterized the work of most map-makers ... Apparently many authors believe that maps are an art-form which allow liberties not admissible in verbal or tabular presentation. (Jenks and Coulson, 1963, p. 120)

A Generalization of the Poisson Distribution

A new generalization of the Poisson distribution, with two parameters λ1 and λ2, is obtained as a limiting form of the generalized negative binomial distribution. The variance of the distribution is greater than, equal to or smaller than the mean according as λ2 is positive, zero or negative. The distribution gives a very close fit to supposedly binomial, Poisson and negative-binomial data and provides with a model suitable to most unimodel or reverse J-shaped distributions. Diagrams showing the variations in the form of the distribution for different values of λ1 and λ2 are given.

A Generalization of the Poisson Distribution

A new generalization of the Poisson distribution, with two parameters λ1 and λ2, is obtained as a limiting form of the generalized negative binomial distribution. The variance of the distribution is greater than, equal to or smaller than the mean according as λ2 is positive, zero or negative. The distribution gives a very close fit to supposedly binomial, Poisson and negative-binomial data and provides with a model suitable to most unimodel or reverse J-shaped distributions. Diagrams showing the variations in the form of the distribution for different values of λ1 and λ2 are given.

Concentration of Dominance and Adaptive Zones

Ecologists have long recognized that temperate communities generally exhibit a characteristic pattern of species abundances few species boasting many individuals and relatively many species each represented by few individuals (Fisher et al. 1943). This phenomenon of concentration of dominance (generally regarded as the inverse of species diversity) is obviously characteristic of many natural communities. Because of its ubiquity, however, the classic J-shaped distribution may reasonably be expected to be of some evolutionary significance. Thus, Gause (1936) considered the quantitative relation between the numbers of rare and abundant species to be the most important aspect of a community's structure. Hutchinson (1953) commented is likely that something very important is involved here and then added, (significantly) but for the present what it may be is a mystery. In addition, Williams (1964) has reported numerous instances of equivalent concentration of dominance among animal taxa, generally revealing a species (represented by many individuals) with many relatively rare congenors. It thus appears that the Jshaped pattern goes beyond community structure in its relevance, reflecting something in the taxonomic as well as local ecologic affinities of organisms. Further, this distribution also appears among higher taxonomic categories, where many large taxa reveal a dominant sub-taxon (considering number of species rather than