Frequency Density Distribution Research Articles

Effect of plasma electrolytic oxidation process on surface characteristics and tribological behavior

Plasma electrolytic oxidation (PEO) produces oxide ceramic coatings on lightweight Al alloys with high hardness, low thermal conductivity and dimple-like surface morphology. By changing PEO process parameters, coating surface morphology can be manipulated for friction reduction. This study uses both unipolar and bipolar current modes to prepare oxide coatings on Al-Si alloy samples with different durations in order to obtain surface textures with different dimple sizes and densities. The results indicate that decreasing actual contact areas of the coating surfaces and their counterparts lowers the coefficient of friction. The real contact areas, which can be observed in the frequency density distribution histograms and curves of the surface profile data, were different initially and then varied during the sliding tests in progress. More negatively and downwardly shifted maximum values on the probability density distribution function curve of a coating surface profile indicate less real contact area and thus a smaller coefficient of friction. Hardness also plays a factor in frictional behavior.

Semi-empirical seismic relations of A-F stars from COROT and Kepler legacy data

Asteroseismology is witnessing a revolution thanks to high-precise asteroseismic space data (MOST, CoRoT, Kepler, BRITE), and their large ground-based follow-up programs. Those instruments have provided an unprecedented large amount of information, which allows us to scrutinize its statistical properties in the quest for hidden relations among pulsational and/or physical observables. This approach might be particularly useful for stars whose pulsation content is difficult to interpret. This is the case of intermediate-mass classical pulsating stars (i.e. gamma Dor, delta Scuti, hybrids) for which current theories do not properly predict the observed oscillation spectra. Here we establish a first step in finding such hidden relations from Data Mining techniques for these stars. We searched for those hidden relations in a sample of delta Scuti and hybrid stars observed by CoRoT and Kepler (74 and 153, respectively). No significant correlations between pairs of observables were found. However, two statistically significant correlations emerged from multivariable correlations in the observed seismic data, which describe the total number of observed frequencies and the largest one, respectively. Moreover, three different sets of stars were found to cluster according to their frequency density distribution. Such sets are in apparent agreement with the asteroseismic properties commonly accepted for A-F pulsating stars.

Nano-mechanical behavior of the interfacial transition zone between steel-polypropylene fiber and cement paste

The fiber-matrix interfacial transition zone (ITZ) at nanoscale plays an important role in determining the mechanical performance of hybrid steel-polypropylene fiber reinforced concrete at upper scales. This paper investigates the elastic behavior of the ITZ between steel/polypropylene fiber and pure cement paste through nanoindentation for different water/cement ratios. The microstructure mapping and gradient of ITZ were analyzed based on the elastic modulus (E) and hardness (H) distributions. The morphology of ITZs was observed with the help of Scanning Electron Microscope. In addition, to probe into the formation mechanism of ITZ, distinct phases in ITZ were statistically determined from the frequency density distributions of E and H values through the deconvolution technique. Results show that the thickness of fiber-matrix ITZ mainly depends on the fiber type, where the steel fiber and polypropylene fiber ITZ are about 30μm and 15μm in thickness respectively. It is also found from E distribution that a trough in the steel fiber ITZ exists at lower w/c ratios, whereas a gradual growth of E and H values is demonstrated away from polypropylene fiber surface for all cases shown. The ITZ’s chemical compositions at nanoscale suggest that the volume fractions of HD C-S-H, CH/C-S-H and porosity are noted to be the main determinants for the overall properties of ITZ. In comparison with steel fiber samples, a larger amount of porosity exists in the vicinity of polypropylene fiber surface. Finally, based on the test data, the ITZ formation mechanism was discussed with water/cement ratio effect considered.

Mean Particle Diameters. Part VIII. Computer Program to Decompose Mixtures of (Truncated) Lognormal Particle Size Distributions Using Differential Evolution to Generate Starting Values for Nonlinear Least Squares

Multimodal size distributions can result from a mixing of two or more component distributions and arise in quite different application areas. Physical and statistical approaches are described for decomposition of a multimodal particle size distribution into a number of lognormal components. These approaches, incorporated in the Fortran computer program FitDist, use a nonlinear least-squares (NLLS) optimization, requiring initial parameter estimates. A hybrid deconvolution method has been developed. Differential Evolution (DE), is used for generation of initial parameter values, followed by an NLLS optimization to derive precise parameter values at the local optimum. The DE algorithm is required to decide on the proper number of modes to be fitted. Mathematical relationships have been derived to convert the parameter values of one multimodal lognormal moment distribution, e.g., a number distribution, to those of another moment distribution, e.g., a volume distribution. Moreover, mathematical relationships have been derived to compute mean diameters (Moment-Ratio notation) from the parameters of a multimodal lognormal size distribution. Fitting a 1.5th moment distribution, being just in between a number and a volume distribution, has been introduced as an instrument to balance inaccuracies in both tails of a distribution due to sampling inaccuracies or truncation of these tails. The program fits a truncated size distribution by fitting its frequency density distribution, whereas a complete size distribution is fitted by fitting the cumulative distribution. Some guidelines are given for fitting Number, Diameter, Surface area, and Volume distributions to measured size distributions. Although fitting of multimodal normal distributions is an option, higher moment distributions will not be fitted as these distributions are not normally distributed. Practical examples demonstrate the validity of the method to decompose multimodal particle size distributions by use of DE.

IRNA-PseU: Identifying RNA pseudouridine sites

As the most abundant RNA modification, pseudouridine plays important roles in many biological processes. Occurring at the uridine site and catalyzed by pseudouridine synthase, the modification has been observed in nearly all kinds of RNA, including transfer RNA, messenger RNA, small nuclear or nucleolar RNA, and ribosomal RNA. Accordingly, its importance to basic research and drug development is self-evident. Despite some experimental technologies have been developed to detect the pseudouridine sites, they are both time-consuming and expensive. Facing the explosive growth of RNA sequences in the postgenomic age, we are challenged to address the problem by computational approaches: For an uncharacterized RNA sequence, can we predict which of its uridine sites can be modified as pseudouridine and which ones cannot? Here a predictor called “iRNA-PseU” was proposed by incorporating the chemical properties of nucleotides and their occurrence frequency density distributions into the general form of pseudo nucleotide composition (PseKNC). It has been demonstrated via the rigorous jackknife test, independent dataset test, and practical genome-wide analysis that the proposed predictor remarkably outperforms its counterpart. For the convenience of most experimental scientists, the web-server for iRNA-PseU was established at http://lin.uestc.edu.cn/server/iRNA-PseU, by which users can easily get their desired results without the need to go through the mathematical details.

基于非参数方法的频率密度分布计算及其并行优化

基于非参数方法的频率密度分布计算及其并行优化

Computational Analyses of Simple Sequence Repeats on Human Tissue Specific Genes Promoters

Promoter region of gene closely related with tissue specific expression and SSRs (simple sequence repeats) have been shown to have a variety of effects on an organism. This paper used a heuristic method to find SSRs and compared the most frequently SSRs on promoter region of both human tissues specific genes and human housekeeping genes. We used kidney and testis tissue as examples to show the final results. Especially, we found that (AGG)n is kidney specific SSR and (GCG)n is testis specific SSR. We also analyzed the SSRs frequency density distribution on different promoter regions of both tissue specific genes and housekeeping genes, and we found the density of housekeeping genes on core-promoter region is much higher than on other promoter regions.

Fast changes of the solar irradiance

The results of special measurements of solar irradiance with high resolution in time domain are compared with results of traditional measurements. Three possible characteristic parameters are studied to describe the dynamic quality of the recorded dataset: standard deviation, frequency density distribution law of increments and the number of fronts of the solar radiation per time unit. Recording traditionally one-minute average values of the solar irradiance, most of the changes cannot be registered in the condition of clouds cumulus humilis.

Development of a virtual active fire product for Africa through a synthesis of geostationary and polar orbiting satellite data

We explore the ability to enhance landscape fire detection and characterization by constructing a ‘virtual’ fire product from a synthesis of geostationary and polar orbiting satellite data. Active fire pixels detected by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) were spatially and temporally collated across Africa between February 2004 and January 2005. Coincident fire pixels detected by SEVIRI and MODIS were used to populate an empirical database of frequency density (f-D) distributions of fire radiative power (FRP). Frequency density distributions of FRP measured by SEVIRI at 5.0° grid cell resolution and 15-minute temporal resolution were then cross referenced in the database to a set of counterpart f-D distributions of FRP measured by MODIS. This procedure resulted in the first generation of a ‘virtual’ fire product that exhibits the full continental coverage and high temporal resolution of SEVIRI whilst quantifying fire pixel counts and FRP with accuracies approaching those of MODIS. Diurnal cycles extracted from the virtual fire product indicate that SEVIRI measures a greater proportion of the active fire pixels and FRP potentially detectable by MODIS during the day due to the increased prevalence and stronger radiant contribution of highly energetic fire pixels. On a daily basis (sample size n = 365) the peak magnitude in the diurnal cycle of the virtual FRP occurred within the same 15-minute timeslot as in the native SEVIRI fire product. Continental-scale ignition and extinction events, however, were detected on average 44 min earlier (standard deviation s.d. = 40 min) and 137 min later (s.d. = 92 min), respectively. It is anticipated that the methodology developed here can be used to cross-calibrate active fire products between a variety of different satellite platforms.

Evaluating Single Fiber and Fiber Bundle Tensile Curves

Most research on estimations of fiber bundle tensile curves from single fiber tensile properties is based on knowledge of the frequency density distribution of fiber breaking extension and the linear elastic spring constant. Such research focuses on cotton fibers and fiber bundles. On the other hand, there are few methods to predict the tenacity of single wool fibers from fiber bundle tensile curves. Using characteristics of specific stress-strain curves from both single fiber and fiber bundle tensile testing, new theoretical calculations to estimate the tenacity and breaking extension distribution of single fibers from bundle tensile curves are described in detail for wool fibers. The experimental results show that these algorithms are effective and reliable for such evaluations, the experimental and estimated results obtained from the TENSOR fiber bundle tests and the SIFAN single fiber measurements agree with each other, and single fiber tenacity or even its urve can be evaluated using the tail of the bundle tensile curve.

Statistical extreme value modeling of particle size distributions: experimental grain size distribution type estimation and parameterization of sintered zirconia

The grain size distribution of a sintered zirconia is investigated in detail. Microstructural evidence in combination with X-ray diffraction (XRD) data reveal a bimodal microstructure consisting of a polycrystalline matrix of retained untransformed tetragonal zirconia, containing clusters of smaller transformed monoclinic zirconia grains. This necessitates a comparison between the size measurements for the untransformed zirconia and the full set of measurements made on the sintered zirconia microstructure. A statistically consistent, graphical representation of grain size density distributions is shown. The experimental frequency density distributions are compared with the Log Normal and the Gumbel model. Traditional statistical tools are used to estimate the probability of observing the experimental data set from the expected model functions. Parameter estimations for the model functions are made according to a quantile approach, an R 2 fit, a χ 2 fit and a non-linear simplex optimization routine. The bimodality of the experimentally obtained grain size distribution influences the likelihood probabilities of the model functions in accordance with their respective boundary conditions. The Gumbel function is shown to provide the best correspondence to the experimental data, with a slightly higher probability for a unimodal distribution as compared with the bimodal dataset. The Log Normal function is less likely than the Gumbel function in both instances, but has a slightly higher probability for the bimodal data set. It is shown that the quantile estimation is fast and straightforward to implement and allows a full evaluation of the expectation ranges on the estimated parameters.

The Stochastics of the Positive Ion Penumbra

Statistical analysis of Monte Carlo simulations of positive ion track structure is presented for 1 MeV protons passing outside an absorbing region of interest. Energy deposition and production of ionization within the region occur only by delta-ray transport from the ion's path. Depositions in spherical absorber regions of 2 to 100 nm diameter in unit density tissue were scored. It is shown that production of delta rays sufficiently energetic to reach the region is infrequent and the delta rays are therefore relatively far apart along the ion path compared to their average range. The probability for any delta-ray energy deposition in a distant site is small and proportional to the solid angle intercepted by the site. The functional dependence of the frequency density distributions in energy imparted and in ionization number, conditional on there being some interaction, is approximately exponential, and the first and second moments of the distributions are largely independent of distance from the ion path. These findings confirm similar conclusions from experimental measurements on the track structure of germanium, iron and uranium ions.

Economics of Drilling for Cretaceous Oil on East Flank of Denver-Julesburg Basin

After a brief review of the results of the past drilling activity and the production history of the Denver-Julesburg basin to date, the merits of this play are discussed from an economic viewpoint. An analysis of the relative importance of stratigraphy and structure in forming the Lower Cretaceous traps is presented. The cost of drilling dry holes and producers in the basin is discussed and its effect on the economics of producing marginal wells analyzed. The Denver-Julesburg basin at present with its hundreds of Lower Cretaceous fields and thousands of wells represents a unique opportunity for statistical analysis. A of 5,700,000 acres was chosen on the east flank and a statistical correlation prepared of the estimated ultimate recovery per field and the number of delineating dry holes per field as a function of the productive field area. This correlation shows some well defined trends from which significant conclusions can be drawn. A frequency-density distribution of the fields found was then prepared and plotted versus ultimate field recovery, which again indicated a well defined pattern. A mathematical relation is presented, relating the number of fields of a given size found after drilling a known number of wildcats to the total number of fields of that size originally occurring in the sample area for the assumptions of: (a) random drilling in the productive trend; (b) pattern drilling in the productive trend; and (d) drilling on geophysical and geological leads in the trend. After computing the frequency-density of occurrence from the frequency-density distribution of fields found, it is shown how this mathematical relation can also be used to make a forecast of the average results to be expected from future drilling.