Statistical Study Of Correlation Research Articles

Application of multivariate statistical analyses in the differentiation between two phosphate ores from the Nuba Mountains, Sudan

In previously published research, uranium abundance and major and trace element content were determined in phosphate ore samples from the Kurun and Uro areas of the Nuba Mountains in Sudan. The current work aims to characterise and differentiate between the phosphate ores from these two areas by subjecting the obtained geochemical data to quantitative and qualitative statistical analyses. Multivariate statistical analyses and correlation studies show several geochemical differences in the occurrence of uranium in Kurun and Uro phosphate ores. Uranium in Uro phosphate ore shows a higher degree of mobility coefficient of variability (CV% = 91) than that in Kurun phosphate ore (CV% = 48). Kurun and Uro phosphate ores are found to be good sources of titanium and strontium. The average concentrations of Ti and Sr in Uro phosphate ore are 4880 and 2780 mg kg–1, respectively. The corresponding values in Kurun phosphate ore are 7300 and 2630 mg kg–1, respectively. A cluster analysis of trace elements demonstrates that both Ti and Sr, which are the most abundant trace elements, appear in individual groups or in sub-groups. Uranium behaves in the same manner in both phosphate ores in that it associates in groups containing all the transition metals except for the most abundant trace element, titanium.

Assessment of the aerobic preparation and bottom ash addition as pretreatment steps before landfilling: Impact on methanogenesis kinetics and leachate parameters

This work focuses on assessing the impact of two types of waste pretreatment: addition of bottom ashes and aerobic pretreatment on both the onset and kinetics of methanogenesis and the evolution of different parameters in the leachate. It also studies the correlation between methane production and the different parameters measured in the leachate produced. A total of six 68-L pilots were thus used with fresh municipal solid waste (MSW) shredded to a 40-mm size. After 14months of landfilling, the control has produced less than 10NLkg−1DM, which corresponds to around 7% of its biochemical methane potential (BMP). Nevertheless, on one hand for aerobically pretreated waste, the lag phase before the onset of methanogenesis is significantly reduced to 0.9month compared to more than 1year for the control. In addition to that, on average 110NLkg−1DM (90% of the BMP) is produced within around 6.5months. On the other hand, the waste with added bottom ash shows a slight improvement of the lag phase over the control for one of the duplicate: 6.1months of lag phase. At this stage, on average of 26NLkg−1DM waste are detected (22% of the BMP) no final conclusion concerning the impact of bottom ashes could be made. The data obtained for the leachate parameters agrees with the observations on methane production. Statistical correlation study shows that the two components of the corrected PCA interpret 76% of the variability of the data: SUVA (specific UV absorbance at 254nm) and HPI* (% of hydrophilic compounds) are identified as interesting parameters for following up the biodegradation in landfill conditions.

Integrating monitoring, expert knowledge and habitat management within conservation organisations for the delivery of the water framework directive: A proposed approach

Integrating monitoring, expert knowledge and habitat management within conservation organisations for the delivery of the water framework directive: A proposed approach There is a growing necessity to better understand the nature of the relationships between environmental attributes and freshwater species/communities to enable meaningful action to take place against the impacts of environmental change in river ecosystems. Such understanding would need to be based on the investigations of causal relationships rather than the study of statistical correlations or the use of expert opinion as is generally the case. Another issue is in identifying the scale(s) at which process and features should be recorded and assessed to enable the design of relevant monitoring programs. In this paper, we present a short review of existing knowledge on species/habitat relationships and discuss the importance of adequate theoretical frameworks for identifying environmental features of importance to wildlife and determining the scale/s at which they should be assessed. We further propose an approach for eliciting those relationships within the context of monitoring and management practice in conservation organisations. We show how conceptual models of habitat-species relationships can be built using existing knowledge and expert opinion and tested on data collected as part of existing monitoring programs. We suggest such framework, if applied, could not only help identify causal relationships between species, features and processes acting at various scales, but also initiate a knowledge acquisition process within organisations responsible for the delivery of the Water Framework Directive.

How porphyrinogenic drugs modeling acute porphyria impair the hormonal status that regulates glucose metabolism. Their relevance in the onset of this disease

This work deals with the study of how porphyrinogenic drugs modeling acute porphyrias interfere with the status of carbohydrate-regulating hormones in relation to key glucose enzymes and to porphyria, considering that glucose modulates the development of the disease. Female Wistar rats were treated with 2-allyl-2-isopropylacetamide (AIA) and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) using different doses of AIA (100, 250 and 500 mg/kg body weight) and a single dose of DDC (50 mg DDC/kg body weight). Rats were sacrificed 16 h after AIA/DDC administration. In the group treated with the highest dose of AIA (group H), hepatic 5-aminolevulinic acid synthase (ALA-S) increased more than 300%, phosphoenolpyruvate carboxykinase (PEPCK) and glycogen phosphorylase (GP) activities were 43% and 46% lower than the controls, respectively, plasmatic insulin levels exceeded normal values by 617%, and plasmatic glucocorticoids (GC) decreased 20%. GC results are related to a decrease in corticosterone (CORT) adrenal production (33%) and a significant reduction in its metabolization by UDP-glucuronosyltransferase (UGT) (62%). Adrenocorticotropic hormone (ACTH) stimulated adrenal production 3-fold and drugs did not alter this process. Thus, porphyria-inducing drugs AIA and DDC dramatically altered the status of hormones that regulate carbohydrate metabolism increasing insulin levels and reducing GC production, metabolization and plasmatic levels. In this acute porphyria model, gluconeogenic and glycogenolytic blockages caused by PEPCK and GP depressed activities, respectively, would be mainly a consequence of the negative regulatory action of insulin on these enzymes. GC could also contribute to PEPCK blockage both because they were depressed by the treatment and because they are positive effectors on PEPCK. These disturbances in carbohydrates and their regulation, through ALA-S de-repression, would enhance the porphyria state promoted by the drugs on heme synthesis and destruction. This might be the mechanism underlying the “glucose effect” observed in hepatic porphyrias. The statistical correlation study performed showed association between all the variables studied and reinforce these conclusions.

On the correlation between ionospheric perturbations as detected by subionospheric VLF/LF signals and earthquakes as characterized by seismic intensity

The long-term data during seven years from January 2001 to December 2007, as observed by the Pacific VLF/LF network consisting of several Japanese stations and one station in Kamchatka, are extensively utilized to perform a statistical correlation study between the lower ionospheric perturbations as detected by subionospheric propagation and earthquakes (EQs). In this paper, we adopt a physical parameter, the maximum seismicity intensity observed ( I) to define the strength of an EQ unlike the previously and conventionally used EQ magnitude and depth, which is a combined effect of EQ magnitude and depth, together with the Earth’s surface information and geological condition around the EQ epicenter. After considering EQs only take place on the land because of the use of seismicity and by using the superimposed epoch analysis, it is found for the larger EQs with I from 5 to 7 (we feel serious trembling and we expect serious damage) that the most important VLF/LF parameter, trend (nighttime average amplitude), shows a definite decrease about 10 days before the EQ by exceeding 2 σ ( σ: standard deviation) criterion; the dispersion shows a maximum about 10 days before the EQ but not exceeding 2 σ line and finally the nighttime fluctuation shows an enhancement about 10 days before the EQ (with exceeding the 2 σ level). A definite statistical correlation is confirmed between the ionospheric perturbations and I when I is strong enough in a range from 5 to 7. Whereas, there is no significant correlation between the two when I is in a range from 3 to 4. Finally, together with the corresponding results for EQs in the sea, but close to the land, these results are discussed in the light of lithosphere–ionosphere coupling mechanism.

Effects of Near-Fault Ground Shaking on Sliding Systems

A numerical study is presented for a rigid block supported through a frictional contact surface on a horizontal or an inclined plane, and subjected to horizontal or slope-parallel excitation. The latter is described with idealized pulses and near-fault seismic records strongly influenced by forward-directivity or fling-step effects (from Northridge, Kobe, Kocaeli, Chi-Chi, Aegion). In addition to the well known dependence of the resulting block slippage on variables such as the peak base velocity, the peak base acceleration, and the critical acceleration ratio, our study has consistently and repeatedly revealed a profound sensitivity of both maximum and residual slippage: (1) on the sequence and even the details of the pulses contained in the excitation and (2) on the direction (+ or - ) in which the shaking of the inclined plane is imposed. By contrast, the slippage is not affected to any measurable degree by even the strongest vertical components of the accelerograms. Moreover, the slippage from a specific record may often be poorly correlated with its Arias intensity. These findings may contradict some of the prevailing beliefs that emanate from statistical correlation studies. The upper-bound sliding displacements from near-fault excitations may substantially exceed the values obtained from some of the currently available design charts.

Loadable TiO 2 scaffolds—A correlation study between processing parameters, micro CT analysis and mechanical strength

It was shown in the present study that it is possible to produce TiO 2 scaffolds with both high mechanical strength and high porosity by using the polymer sponge method. TiO 2 scaffolds with porosity above 85% exceeded 1 MPa in compressive strength. TiO 2 scaffolds with equally high compressive strength having a fully open porosity close to 90% is not previously been reported in the literature. Reduction of porosity leads to even further reinforce the scaffolds’ mechanical structure. A statistical correlation study with 160 tested scaffolds defined the most important manufacturing steps and the governing morphological characteristics for the scaffold's increased mechanical strength. The key manufacturing factors were a holding phase during sintering time for more than 30 h (at 1500 °C) and multiple coatings of the scaffold's structure. The crucial parameters for high mechanical strength were the fractal dimensions of the struts, object surface/volume ratio, density and overall porosity.

GALEX-SDSS CATALOGS FOR STATISTICAL STUDIES

We present a detailed study of the Galaxy Evolution Explorer’s (GALEX) photometric catalogs with special focus on the statistical properties of the All-sky and Medium Imaging Surveys. We introduce the concept of primaries to resolve the issue of multiple detections and follow a geometric approach to define clean catalogs with well understood selection functions. We cross-identify the GALEX sources (GR2+3) with Sloan Digital Sky Survey (SDSS; DR6) observations, which indirectly provides an invaluable insight into the astrometric model of the UV sources and allows us to revise the band merging strategy. We derive the formal description of the GALEX footprints as well as their intersections with the SDSS coverage along with analytic calculations of their areal coverage. The crossmatch catalogs are made available for the public. We conclude by illustrating the implementation of typical selection criteria in SQL for catalog subsets geared toward statistical analyses, e.g., correlation and luminosity function studies.

MT+, Integrating Magnetotellurics to Determine Earth Structure, Physical State, and Processes

As one of the few deep-earth imaging techniques, magnetotellurics provides information on both the structure and physical state of the crust and upper mantle. Magnetotellurics is sensitive to electrical conductivity, which varies within the earth by many orders of magnitude and is modified by a range of earth processes. As with all geophysical techniques, magnetotellurics has a non-unique inverse problem and has limitations in resolution and sensitivity. As such, an integrated approach, either via the joint interpretation of independent geophysical models, or through the simultaneous inversion of independent data sets is valuable, and at times essential to an accurate interpretation. Magnetotelluric data and models are increasingly integrated with geological, geophysical and geochemical information. This review considers recent studies that illustrate the ways in which such information is combined, from qualitative comparisons to statistical correlation studies to multi-property inversions. Also emphasized are the range of problems addressed by these integrated approaches, and their value in elucidating earth structure, physical state, and processes.

Characterization, Source Identification and Apportionment of Selected Metals in TSP in an Urban Atmosphere

To understand the metal distribution characteristics in the atmosphere of urban Islamabad, total suspended particulate (TSP) samples were collected on daily 12 h basis, at Quaid-i-Azam University campus, using high volume sampler. The TSP samples were treated with HNO(3)/HClO(4) based wet digestion method for the quantification of eight selected metals; Fe, Zn, Pb, Mn, Cr, Co, Ni and Cd by FAAS method. The monitoring period ran from June 2001 to January 2002, with a total of 194 samples collected on cellulose filters. Effects of different meteorological conditions such as temperature, relative humidity, wind speed and wind direction on selected metal levels were interpreted by means of multivariate statistical approach. Enhanced metal levels for Fe (930 ng/m(3)), Zn (542 ng/m(3)) and Pb (210 ng/m(3)) were found on the mean scale while Mn, Cr, Co and Ni emerged as minor contributors. Statistical correlation study was also conducted and a strong correlation was observed between Pb-Cr (r=0.611). The relative humidity showed some significant influence on atmospheric metal distribution while other meteorological parameters showed weak relationship with TSP metal levels. Regarding the origin of sources of heavy metals in TSP, the statistical procedure identified three source profiles; automobile emissions, industrial/metallurgical units, and natural soil dust. The metal levels were also compared with those reported for other parts of the world which showed that the metal levels in urban atmosphere of Islamabad are in exceedence than those of European industrial and urban sites while comparable with some Asian sites.

Appraisal of elevated fluoride concentration in ground water using statistical correlation and regression study

In order to predict the suitability of water for different purposes viz. drinking, irrigation etc. and protect the environment determination of a large number of water parameters becomes evident. Statistical analysis has gained the popularity in overcoming such laborious and tedious operation. The water quality, with special reference to fluoride, of the area of Nalhati and Rampurhat block of the Birbhum district was assessed. Correlation between fluoride and other significant water quality parameters was made in order to find out their mutual dependence. It is found that an appreciable correlation holds for fluoride with pH, E.C., sodium, alkalinity, hardness and calcium and low correlation for fluoride with chloride, phosphate, iron and sulphate. Interestingly, fluoride is found to bear a positive correlation with pH and sodium while a negative correlation exists for fluoride with both potassium and alkalinity which is explained considering the local geological condition and mineralogical phase like secondary mineral depositions through weathering, companion ions, pH and properties of clay minerals.

Laser surface treatment of grey cast iron for automotive applications

The surface of pearlitic grey cast iron was treated using a 2 kW Nd:YAG laser beam with the final aim to improve its surface properties, mainly for automotive applications. Two kinds of laser surface treatments were experimentally applied. In the laser surface hardening approach the surface of cast iron was hardened simply by passing a laser beam at travel speeds 1-50 mm/s keeping the surface temperature constant in the irradiated area. Detailed structural analysis of the layer modified by the laser treatment was performed by optical and scanning electron microscopy, EDS and orientation imaging microscopy with the electron back scattered diffraction and microhardness profiles were measured. Conclusions concerning the mechanism and kinetics of pearlite-austenite transformation during the laser surface hardening were drawn. The size of the transformed zone was calculated using a three dimensional model for a Gaussian beam distribution in accordance with direct observations of laser beam energy densities. In the laser surface cladding experiments a thick Co-based alloy coating was created on the cast iron surface using so-called side-cladding set-up when the powder of additional material is locally molten together with a small amount of substrate and then rapidly solidified creating a coating with the metallurgical bond to the substrate. A gradual change of a single processing parameter was used for an appropriate experimental analysis and statistical correlation study between main processing parameters and geometrical characteristics of an individual laser track.

Study of statistical correlations in DNA sequences

Here we present a study of statistical correlations among different positions in DNA sequences and their implications by directly using the autocorrelation function. Such an analysis is possible now because of the availability of large sequences or even complete genomes of many organisms. After describing the way in which the autocorrelation function can be applied to DNA-sequence analysis, we show that long-range correlations, implying scale independence, appear in several bacterial genomes as well as in long human chromosome contigs. The source for such correlations in bacteria, which may extend up to 60 kb in Bacillus subtilis, may be related to massive lateral transfer of compositionally biased genes from other genomes. In the human genome, correlations extend for more than five decades and may be related to the evolution of the ’neogenome’, a modern evolutionary acquisition composed by GC-rich isochores displaying long-range correlations and scale invariance.

Chemometric studies of chemical compounds in five cultivars of potatoes from Tenerife.

A statistical study of correlation and multivariate analysis on the chemical composition of five cultivars of potatoes harvested in Tenerife was carried out to establish the relationships between the chemical compounds and, therefore, to differentiate the samples according to traditional and recent importation potatoes, cultivars, and species/subspecies. A large number of significant correlations between the chemical compounds were found, which suggests biochemical relationships among them. After factor analysis, the dimension space was reduced from 24 variables to eight factors, accounting for 77.2% of the total variance. Starch, moisture, organic acids, and metals are the variables that make it possible to characterize the system without losing very much information. Total differentiation of potato samples according to the criteria species/subspecies and cultivars was obtained using discriminant analysis with all the variables. However, with only four variables (weight of tuber, starch, amylose, and glucose + fructose) it is possible to differentiate between the traditional and recent importation potatoes.

Does Frequency of Visits to the Writing Center Increase Student Satisfaction? A Statistical Correlation Study - or Story

Does Frequency of Visits to the Writing Center Increase Student Satisfaction? A Statistical Correlation Study - or Story

Prognostic Evaluation of Legg–Calvé–Perthes Disease by MRI Part I: The Role of Physeal Involvement

Twenty-eight unselected hips affected by Legg-Calvé-Perthes disease (LCPD) in 24 patients from 1987 to 1994 had magnetic resonance imaging (MRI) performed. The patients were retrospectively reviewed at a mean follow-up of 5.4 years. An interobserver blind analysis was made to establish the reliability of four MRI parameters: extent of epiphyseal necrosis (EXT), lateral extrusion of the femoral head (LAT), physeal involvement (PHY), and metaphyseal changes (MET). The interobserver analysis resulted in a good reliability for all MRI parameters (concordance, >80%; K index, >0.45). A statistical correlation study (Spearman test) was then done between each MRI parameter and the condition of the hips at follow-up evaluated by Stulberg class and a personal scored system (total score) of clinical-radiographic condition. All MRI parameters appeared well correlated to the Stulberg class and to the total score (S > 0.66; p < 0.05). PHY resulted the strongest correlated parameter (S = 0.84 for Stulberg class; S = 0.91 for total score). Finally our statistical correlation study demonstrates physis involvement to have a high predictive value in LCPD; therefore it can be assumed as the main risk factor in formulating prognosis.

Chemometric studies of several minerals in milks.

A statistical study of correlation, factorial, and discriminant analysis on the metal composition (Se, Fe, Cu, Zn, Na, K, Ca, Mg) of different types of milks (human, cow, goat, pasteurized, and powdered infant formula) was carried out to establish the relationships between the metal concentrations and, therefore, differentiate the samples according to the type of milk. A large number of significant intermetallic correlations were found in all samples, which could be due to biological relationships between the metals studied. After the factorial analysis, the dimension space was reduced from eight variables to two factors, accounting for approximately 71.4% of the total variance. After an orthogonal rotation, the first factor was positively correlated with Ca and the second factor with Fe. The representation of the scores makes it possible to separate not only human milk from powdered infant formula but also to separate both of these from the other milks. In the discriminant analysis, four discriminant functions were obtained, which are linear combinations of the quantitative variables that best explain the differences among the different milks analyzed. These functions make it possible to classify 98% of the samples analyzed within each type of milk correctly. Therefore, discriminant functions obtained here can be used to identify the origin of any milk sample.

A statistical study of the correlation between k′ or log k′ and log Pow for a group of benzene and naphthalene derivatives in micellar liquid chromatography using a C-18 column

It is shown that the logarithm of the capacity factor (log k′) for fifteen benzene and naphthalene derivatives in micellar liquid chromatography with forty nine different mobile phases generally correlates better with the logarithm of the octanol-water partition coefficient (log Pow) than the capacity factor (k′). Optimum conditions are established to obtain the best linear correlations of log k′-log Pow.

A comprehensive study of physical parameters, biomechanical properties, and statistical correlations of iliac crest bone wedges used in spinal fusion surgery. II. Mechanical properties and correlation with physical parameters.

Iliac crest wedges have been the most frequently used bone graft in spinal fusion procedures since the 1970s. Physical parameters and correlations among physical parameters of allogeneic iliac crest wedges have been described in part I of this series. This article discusses the mechanical properties, as well as their correlations with physical parameters, of iliac crest wedges. A total of 250 frozen-thawed, freeze-dried, and rehydrated iliac crest wedges were used in this study. The axial load-bearing capacities for wedges in the three subgroups showed no statistically significant differences, however, rehydrated wedges appeared to have the greatest load bearing capacity and compressive strength. In addition, rehydrated wedges were more deformable than either the frozen-thawed or freeze-dried wedges. Based on biomechanical properties, it is suggested that rehydrated (1 hour in vacuo), or frozen-thawed iliac crest wedge should be used in spinal fusion procedures, and the direct clinical application of nonrehydrated freeze-dried wedges should be avoided.

A Comprehensive Study of Physical Parameters, Biomechanical Properties, and Statistical Correlations of Iliac Crest Bone Wedges Used in Spinal Fusion Surgery

Iliac crest wedges are commonly used in spinal fusion procedures and must be capable of withstanding considerable mechanical stress during the healing process. Physical parameters, mechanical properties, correlations among physical parameters, and correlations of mechanical properties versus physical parameters have been presented by the authors in companion papers. In this study, mathematical formulas have been developed, using multi-variable regression analysis, which permit calculation of the axial load-bearing capacity and compressive strength of a wedge, provided donor age, cortical bone cross-sectional area, total cross-sectional area, and wedge "width" are available. The formulas proposed are simple, easy to use, and provide acceptable accuracy. For the predicted load-bearing capacity, experimentally determined data illustrated that 59% of the calculated values had either less than 10% error or their predicted values were smaller than the observed values, 75% of the calculated values had either less than 20% error or their predicted values were smaller than the observed values. Similar accuracies were estimated for calculation of compressive strengths. Charts are generated from the established formulas, which permit a visual determination of load-bearing capacity and compressive strength of a wedge.