Unimodal Frequency Distribution Research Articles

Nederlandse Baby's Gebruiken Statistische Informatie om Spraakklanken te Leren Onderscheiden

Phonemes are perceived categorically and this perception is language-specific for adult listeners. Infants initially are "universal" listeners, capable of discriminating both native and non-native speech contrasts. This ability disappears in the first year of life. Maye et al. (Cognition (2002)) propose that statistical learning is responsible for this change to language-specific perception. They were the first to show that infants of 6 and 8 months old use statistical distribution of phonetic variation in learning to discriminate speech sounds. A replication of this experiment studied 10-11-month-old Dutch infants. They were exposed to either a bimodal or a unimodal frequency distribution of an 8-step speech sound continuum based on the Hindi voiced and voiceless retroflex plosives (/da/ en /ta/). The results show that only infants in the bimodal condition could discriminate the contrast, representing the speech sounds in two categories rather than one.

Analysis of two-component mixture Weibull statistics for estimation of wind speed distributions

The typical two-parameter Weibull is a flexible distribution that is useful for describing unimodal frequency distributions of wind speeds at many sites. A two-component mixture Weibull distribution (WW-probability distribution function (pdf)) is even more useful because it is additionally able to represent heterogenous wind regimes in which there is evidence of bimodality or bitangentiality or, simply, unimodality. An analysis is made in this paper of three of the most frequently used methods in the estimation of the five parameters of the WW-pdf and the numerical methods employed are described. Hourly mean wind speed data recorded at four weather stations located in the island of Gran Canaria (Spain) are used to analyse the estimation methods. Prior identification of the sample components of the mixture is not required. The suitability of the distributions is judged from the various tests-of-fit commonly used in the specialised literature on wind energy. A comparison is also made of the ability to describe the experimental wind power density distribution. The general conclusion is that if the sample data are independent then maximum likelihood (ML) estimators should be used due to their large sampling efficiency. However, they require elaborate calculation techniques. The least-square (LS) method provides a robust and computationally efficient alternative to the techniques currently in use. The method of moments has the disadvantage that it does not always supply a feasible result and lacks the desirable optimality properties of ML and LS estimators.

Use of finite mixture distribution models in the analysis of wind energy in the Canarian Archipelago

The statistical characteristics of hourly mean wind speed data recorded at 16 weather stations located in the Canarian Archipelago are analyzed in this paper. As a result of this analysis we see that the typical two parameter Weibull wind speed distribution (W-pdf) does not accurately represent all wind regimes observed in that region. However, a Singly Truncated from below Normal Weibull mixture distribution (TNW-pdf) and a two component mixture Weibull distribution (WW-pdf) developed here do provide very good fits for both unimodal and bimodal wind speed frequency distributions observed in that region and offer less relative errors in determining the annual mean wind power density. The parameters of the distributions are estimated using the least squares method, which is resolved in this paper using the Levenberg–Marquardt algorithm. The suitability of the distributions is judged from the probability plot correlation coefficient plot R 2 , adjusted for degrees of freedom. Based on the results obtained, we conclude that the two mixture distributions proposed here provide very flexible models for wind speed studies and can be applied in a widespread manner to represent the wind regimes in the Canarian archipelago and in other regions with similar characteristics. The TNW-pdf takes into account the frequency of null winds, whereas the WW-pdf and W-pdf do not. It can, therefore, better represent wind regimes with high percentages of null wind speeds. However, calculation of the TNW-pdf is markedly slower.

Freshwater Mussel (Bivalvia: Unionidae) Assemblages of the Lower Cache River, Arkansas

Abstract Freshwater mussel beds of the lower 68 km of the Cache River, AR, were delineated and sampled using diving and stratified random sampling methodology to determine species richness, density, size structure, and population and community numerical standing crop (CNSC). A total of 38 mussel beds were delineated, including 14 major beds (Mbeds) and 24 minor beds (mbeds). Twenty six species were collected, four of which were previously unknown from the Cache River. Amblema plicata, Megalonaias nervosa, and Plectomerus dombeyanus were the most abundant. Estimates of CNSC ranged from 3705 ± 1908 to 122,115 ± 24,194 individuals in Mbeds with mean densities ranging from 6.2 to 44.1 mussels/m2. Nine of 16 species with > 10 individuals had a unimodal size frequency distribution and the other seven had multi-modal distributions. This study found impressive mussel assemblages in the lower Cache River, previously thought to contain only refugial pockets of mussel assemblages. Further monitoring of some species ...

Variability of the 3′ApoB Minisatellite Locus in Eastern Slavonic Populations

Objective: To describe and compare the 3′ apolipoprotein (Apo) B minisatellite allele frequency distributions of Eastern Slavonic populations and their Uralic, Altaic, and Caucasian speaking neighbors. Methods: Healthy individuals of 10 populations among Russians, Byelorussians, Komis and Bashkirs were studied for variable number tandem repeats (VNTRs) in the 3′ApoB minisatellite region. Data were analyzed with other results reported for this polymorphism in eastern Europeans and Siberians. Results: Allele frequency spectra in Eastern Slavonic, Northern Caucasian and Finno-Ugric speaking populations are bimodal with the main peak in alleles 34–36 and a secondary mode around allele 48, whereas Altaic speaking populations have a unimodal allele frequency distribution with a peak of around 34–36 VNTRs. Population relationships were revealed using both multidimensional scaling analysis (based on Nei’s genetic distance estimate) and testing for genetic heterogeneity. Eastern Slavonic populations (Russians, Ukrainians, Byelorussians) were most closely related to each other and formed a separate tight clusterwhen plotted. Testing for genetic heterogeneity among the Eastern Slavonic ethnic groups revealed maximum diversity among Byelorussians, followed by Russians, then Ukrainians.The 3′ApoB minisatellite variability reveals little heterogeneityamong the Eastern Slavonic ethnic groups, whereas there wassignificant heterogeneity for Northern Caucasian and Altaic speakers. Conclusion: For this 3′ApoB polymorphism the Eastern Slavonic populations, despite their wide geographical distribution, appear to be much more homogenous than other ethnic groups of the region. Multidimensional scaling analysis of these data allowed for differentiation between individual populations from an ethnic group even if there is little heterogeneity.

Validation of an ovarian biopsy method for monitoring oocyte development in the fat snook, Centropomus parallelus Poey, 1860 in captivity

The validation of an ovarian biopsy method for in vivo assessment of oocyte maturation in Centropomus parallelus was studied. Diameters of intra-ovarian oocytes siphoned with cannula were analyzed fresh and preserved with 1% formalin in 0.7% NaCl solution. Oocytes in different stages were present along the ovaries, up to the tertiary yolk globule stage, which had a unimodal diameter frequency distribution. The oocyte diameter means were not significantly different at four sites along the ovaries (P > 0.05). Samples obtained with cannula were representative of the ovary central portion, in vivo and in vitro samples of the seven females examined were not significantly different (P > 0.05). An estimate of the coefficient of variation corrected for bias (P < 0.05) for 8 repeated in vivo samples was 1.9 ± 0.6. The results demonstrated that for the species, the biopsy method was satisfactory, providing representative samples of the ovaries.

The Temporal Variations of PM10 Concentration in Taipei: A Fractal Approach

A one-year series of hourly average PM10 observations, which was obtained from the urban and national park air monitoring station at Taipei (Taiwan), was analyzed by descriptive statistics and fractal methods to examine the temporal structures of PM10 concentrations. It was found that all PM10 measurements exhibited the characteristic right-skewed unimodal frequency distribution and long-term memory. A monodimensional fractal analysis was performed by transferring the PM10 concentration time series into a useful compact form: the box-dimension (D(subscript B))-threshold (T(subscript h)) and critical scale (C(subscript S))-threshold (T(subscript h)) plots. Scale invariance was found in these time series and the box dimension was shown to be a decreasing function of the threshold PM10 level, implying multifractal characteristics, (i.e., the weak and intense regions scale differently). To test this hypothesis, the PM10 concentration time series were transferred into multifractal spectra, i.e, the π(q)-q polts. The analysis confirmed the existence of multifractal characteristics. A simple two-scale Cantor set with unequal scales and weights was then used to fit the calculated π(q)-q plots. This model fits well with the entire spectrum of scaling exponents for the examined PM10 time series. The relationship between the fractal parameters and classical statistical characteristics, as well as some problems concerning the applicability of fractal methods on air pollution, are discussed.

Local plant species richness increases with regional habitat commonness across a gradient of forest productivity

We tested the prediction that forest habitat types with relatively high productivity are not only relatively low in species richness but are also regionally uncommon. This relationship was supported by an analysis of data from 146 forest communities in southern Ontario, Canada. Potential forest habitat productivity was determined based on a classification scheme developed for the Canadian Land Inventory (CLI) project. Vascular plant species richness approximated a unimodal distribution across forest productivity classes with the lowest mean species richness recorded for the two most productive classes. The contemporary regional commonness of forest habitat productivity classes were also displayed as a unimodal frequency distribution. Hence, mean species richness per CLI class was positively correlated with the regional area of land encompassing each of these productivity classes and this relationship was increasingly significant at increasingly larger spatial scales of regional CLI class land areas. These results are consistent with the species pool hypothesis, which postulates that species richness is relatively low in highly productive habitats because such habitats have been relatively uncommon in both space and time and hence, have had relatively little historical opportunity for the origination of adapted species.

Use of hydrodynamic and hydrochemistry to characterise carbonate aquifers. Case study of the Blanca-Mijas unit (Málaga, southern Spain)

To validate the geological and piezomet- ric subdivision of two carbonate massifs in southern Spain, and to carry out a characterisation of aquifer behaviour, 23 representative springs and wells were monitored at the end of the dry season. Tempera- ture, pH and electrical conductivity and major ions were measured. Calcite (SIc) and dolomite (SId) saturation indexes, PCO2 and cation exchange index (CEI) were calculated with the SOLUTEQ code. Water flow and electrical conductivity were also monitored at the eight main springs. Sierra Blanca and Sierra Mijas constitute an important carbonate hydrogeological unit in southern Spain, supplying water to 250,000 people on the Costa del Sol. Hy- drochemically, two basic types of aquifer behaviour can be distinguished: conduit and diffuse flow sys- tems. The former are found in the calcareous mar- bles of the western Sierra Blanca. They present a calcium-bicarbonate hydrochemical facies with low mineralization, and with quick outflow and water chemistry variations in response to rainfall; hydro- chemical time series present frequency distributions with several modes. The diffuse flow systems are characteristic of the dolomitic marbles of eastern Sierra Blanca and Sierra Mijas. These waters are more highly mineralised and present a calcium- magnesium bicarbonate facies. They are character- ised by slight discharge fluctuations, with nearly unimodal frequency distributions. Aquifer beha- viour affects groundwater exploitation in terms of the success of boreholes and the specific yield of the pumping wells, which are less in the conduit flow systems in western Sierra Blanca.

Multifractal Characteristics in Air Pollutant Concentration Time Series

One-year series of hourly average air pollutant concentration(APC) observations, including O3, CO, SO2 and NO2,were analyzed by means of statistical tools: histogram, variancemethod, and multifractal analysis, to examine the possible scale-invariant behavior and the clustering characteristics. It was found that all APC measurements exhibit the characteristicright-skewed unimodal frequency distribution and long term memory. A monodimensional fractal analysis was performed by thebox counting method. Scale invariance was found in these time series and the box dimension was shown to be a decreasing function of the threshold APC level, implying multifractal characteristics, i.e., the weak and intense regions scaledifferently. To test this hypothesis, the APC time series weretransferred into a useful compact form through the multifractalformalism, namely, the τ(q)-q and f(α)-α plots. The analysis confirmed the existence of multifractal characteristics in the investigated APC time series. It wasconcluded that the origin of both the pronounced right-skewnessand multifractal phenomena in APC time series may be interpretedin terms of the Ott (1995) proposed successive random dilution (SRD) theory and the dynamics of APC distribution process can bedescribed as a random multiplicative process.

Detecting spatial and temporal patterns in NDVI time series using histograms

The aim of this study was to analyse bimodal histogram patterns of monthly National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) normalized difference vegetation index (NDVI) global area coverage (GAC) data and their relation to vegetation dynamics and climatic conditions for the period 1982‐1991 in Argentina. The proposed method was to split up bimodal histograms by the median criterion and to study each mode as a separate unimodal frequency distribution. Modes were analysed based on their histogram shape and statistical parameters, geographical distribution and dynamics, and climatic significance. For the latter, a multinomial statistical analysis was used. The split-up criterion yielded coherent results. Histogram shapes and statistical parameters changed according to season. For geographical dynamics, 84% of pixels remained in the same mode through the seasons, and 16% shifted temporarily to the other mode. Changes from low-NDVI mode to high-NDVI mode were caused by an improvement in water supply, rainfall or irrigation, and higher temperatures. Changes in the opposite direction were due to a reduction in vegetation cover produced by drought, harvest, or autumn effects. The low-NDVI mode was strongly related to the arid zone with 74.6% probability (α = 0.05), and the high-NDVI mode was related to humid (58.8%) and semiarid zones (38.4%). This contribution helps explain the dynamics of vegetation cover along the latitudinal range from 22° to 55°S, for nine growing cycles, with a simple methodology. Improving the knowledge of multimodal histograms may allow a better understanding of difficult classification results.

Infant sensitivity to distributional information can affect phonetic discrimination

For nearly two decades it has been known that infants' perception of speech sounds is affected by native language input during the first year of life. However, definitive evidence of a mechanism to explain these developmental changes in speech perception has remained elusive. The present study provides the first evidence for such a mechanism, showing that the statistical distribution of phonetic variation in the speech signal influences whether 6- and 8-month-old infants discriminate a pair of speech sounds. We familiarized infants with speech sounds from a phonetic continuum, exhibiting either a bimodal or unimodal frequency distribution. During the test phase, only infants in the bimodal condition discriminated tokens from the endpoints of the continuum. These results demonstrate that infants are sensitive to the statistical distribution of speech sounds in the input language, and that this sensitivity influences speech perception.

Bifurcations and global stability of synchronized stationary states in the Kuramoto model for oscillator populations

Bistability between synchronized stationary states is shown to occur in large populations of nonlinearly coupled random oscillators (Kuramoto model), governed by trimodal natural frequency distributions. Numerical simulations and a numerical investigation of bifurcating states provide evidence of global stability of such states, subject to unimodal, bimodal, and trimodal frequency distributions. All this may be important in the framework of large superconducting Josephson junctions arrays, as well as of neural networks.

Validation of an ovarian biopsy method in a sea bass, Centropomus medius Günther

In the present study, the establishment and validation of an ovarian biopsy method for in vivo assessment of oocyte maturation in the snook, Centropomus medius Günther, is described. Diameter and morphological characteristics of intra-ovarian oocytes siphoned with a polyethylene cannula were analysed fresh, preserved with 1% formalin in 0.7% NaCl solution and also cleared with Serra solution. There were no effects detected of the preservative solution on the opaque oocytes within the 24-h interval of the test. The clearing solution allowed excellent visibility of the membrane thickness, yolk appearance and germinal vesicle. Oocytes from each of the five ovarian sites of all examined females were in different prematuration stages and those on the tertiary yolk globule stage had a unimodal diameter frequency distribution and their diameter means were not significantly different among sites (P > 0.01) on eight females. In vivo and in vitro samples of the eight females examined were not significantly different (P > 0.05). As samples obtained with the polyethylene cannula are representative of the ovary central portion, an estimate of the coefficient of variation corrected for bias (P < 0.05) for 20 means of repeated in vivo samples was 1.4 ± 0.47. The results obtained demonstrate that for the species studied, the biopsy method is satisfactory, providing representative samples of the ovaries with the required precision.

Molecular Genetic Analysis of the DXS52Polymorphism in Populations of the Volga–Ural Region

The DXS52polymorphic locus mapping to the 5"-region of the blood-clotting factor VIII gene on the X chromosome was genotyped in seven Volga–Ural ethnic groups (Bashkirs, Tatars, Chuvashes, Maris, Mordovians, Udmurts, and Komis). A total of 47 different genotypes and 15 allelic variants of this locus were described. Substantial intra- and interpopulation heterogeneity of the ethnic groups studied in respect to frequency and distribution of the DXS52alleles and genotypes was demonstrated. The unimodal DXS52allele frequency distribution pattern with the peak at 1690 bp was typical to Mordovians and Komis. Chuvashes and Maris, as well as Udmurts, were characterized by bimodal frequency distribution patterns, with the peaks at 1690 and 670 bp, and 1690 and 1390 bp, respectively. Moreover, Bashkirs and Tatars displayed trimodal DXS52allele frequency distribution patterns with the peaks at 1690, 1390, and 670 bp. The DXS52allele frequency distribution patterns described in populations of the Volga– Ural region were found to be remarkably different from those established for the mixed Moscow population and the population of Western Europe. These data indicate that the DXS52locus is highly informative, and this polymorphic system can serve as a molecular marker for population genetic studies.

Schizophrenic symptoms as clues to the neural basis of language (also poster A38)

Previous research has shown that infants match vowel sounds to facial displays of vowel articulation [Kuhl, P. K., & Meltzoff, A. N. (1982). The bimodal perception of speech in infancy. Science, 218, 1138–1141; Patterson, M. L., & Werker, J. F. (1999). Matching phonetic information in lips and voice is robust in 4.5-month-old infants. Infant Behaviour & Development, 22, 237–247], and integrate seen and heard speech sounds [Rosenblum, L. D., Schmuckler, M. A., & Johnson, J. A. (1997). The McGurk effect in infants. Perception & Psychophysics, 59, 347–357; Burnham, D., & Dodd, B. (2004). Auditory-visual speech integration by prelinguistic infants: Perception of an emergent consonant in the McGurk effect. Developmental Psychobiology, 45, 204–220]. However, the role of visual speech in language development remains unknown. Our aim was to determine whether seen articulations enhance phoneme discrimination, thereby playing a role in phonetic category learning. We exposed 6-month-old infants to speech sounds from a restricted range of a continuum between /ba/ and /da/, following a unimodal frequency distribution. Synchronously with these speech sounds, one group of infants (the two-category group) saw a visual articulation of a canonical /ba/ or /da/, with the two alternative visual articulations, /ba/ and /da/, being presented according to whether the auditory token was on the /ba/ or /da/ side of the midpoint of the continuum. Infants in a second (one-category) group were presented with the same unimodal distribution of speech sounds, but every token for any particular infant was always paired with the same syllable, either a visual /ba/ or a visual /da/. A stimulus-alternation preference procedure following the exposure revealed that infants in the former, and not in the latter, group discriminated the /ba/–/da/ contrast. These results not only show that visual information about speech articulation enhances phoneme discrimination, but also that it may contribute to the learning of phoneme boundaries in infancy.

Changes in the elemental composition of Asterionella formosa during the diatom spring bloom

Changes in the elemental composition of the diatom Asterionella formosa within mixed phytoplankton samples were determined over the spring bloom period using energy dispersive X-ray microanalysis. Using a 10 kV electron microprobe, X-ray information from the top 1-2 µm of the cell revealed overall mean concentrations of: Si (4636 mmol kg -1 dry wt), P (82), S (54), Cl (71) K (94) and Ca (90). Concentrations of all elements showed wide variation within each date sample, with unimodal frequency distributions approximating to a Normal distribution. Correlation of the entire data set demonstrated clear statistical associations between elements, including Si, P and K. Uptake of Si during the course of the diatom bloom led to a major fall in lake water concentration (1.0 to 0.07 mg l -1 ), which correlated with a decrease in the mean cell Si concentration (6735 to 3107 mmol kg -1 dry wt) during the final phase of the bloom. Mean cell concentrations of P and K also showed marked decreases with time, in close parallel with cell Si. These changes in P and K were attributed to the high level of internal correlation with Si and not to any significant decrease in P and K availability in the environment.

Seriation, Superposition, and Interdigitation: A History of Americanist Graphic Depictions of Culture Change

Histories of Americanist archaeology regularly confuse frequency seriation with a technique for measuring the passage of time based on superposition—percentage stratigraphy—and fail to mention interdigitation as an important component of some percentage-stratigraphic studies. Frequency seriation involves the arrangement of collections so that each artifact type displays a unimodal frequency distribution, but the direction of time's flow must be determined from independent evidence. Percentage stratigraphy plots the fluctuating frequencies of types, but the order of collections is based on their superposition, which in turn illustrates the direction of time's flow. Interdigitation involves the integration of sets of percentage-stratigraphy data from different horizontal proveniences under the rules that (1) the order of superposed collections cannot be reversed and (2) each type must display a unimodal frequency distribution. Ceramic stratigraphy is similar to occurrence seriation, as both focus on the presence-absence of types with limited temporal distributions—index fossils—but the former uses the superposed positions of types to indicate the direction of time"s flow, whereas occurrence seriation does not.

A proposed approach for evaluating expert wine judge performance using descriptive statistics

Descriptive statistics were used to evaluate the performance of five expert wine judges using a 20‐point quality scorecard in a wine competition environment. For each judge, frequency distributions were used to assess scorecard usage, and deviation font‐means were calculated as an index of consistency with the group. Differences in curve shapes were described using means, skewness and kurtosis values. Four of the five judges showed unimodal frequency distributions that were slightly skewed to lower scores. This information was believed to be useful for identifying expert judges whose use of a 20‐point quality scorecard and perspective of wine quality are consistent with the group.

Correlation of Thyrotropin Secretion with Morphometric Data of Secretory Granules from Individual Thyrotropes. An Ultrastructural Study on Rat Cells Identified by Reverse Hemolytic Plaque Assay.

We investigated the existence of functional subpopulations of thyrotropes in pituitary glands of male rats, also seeking to establish any correlation of thyrotropin secretion with morphometric data of secretory granules. Pituitary cells secreting thyrotropin were detected using a reverse hemolytic plaque assay. Population analysis of the plaque sizes (TSH secreted) of individual thyrotropes in control cultures from male rats revealed a unimodal frequency distribution. TRH added to the medium resulted in a shift to a bimodal distribution of sizes, consisting of small and large modes, but did not alter the fraction of plaque-forming thyrotropes. The plaque size of control cultures was the same as that of the fraction of TRH-stimulated thyrotropes forming small plaques. Because the extent of hemolysis is related to the amount of thyrotropin secreted by each individual thyrotrope, these results suggest that: a) all thyrotropes secrete thyrotropin even in the absence of a stimulatory dose of TRH; b) the thyrotrope subpopulation secreting small amounts of thyrotropin when incubated with TRH may be unresponsive to this stimulatory factor. After performing reverse hemolytic plaque assay, plaque-forming cells were subsequently processed for electron microscopy. Morphometric analysis of the secretory granules correlated well with plaque size (TSH secreted). It is thus concluded that the functional subtypes of thyrotropes can be recognized on the basis of their ultrastructural images.