Multifractal Parameters Research Articles

A method to determine nuclear magnetic resonanceT2cutoff value of tight sandstone reservoir based on multifractal analysis

AbstractNuclear magnetic resonance (NMR)T2cutoff value is an important parameter for pore structure evaluation. It is complicated and uneconomical to obtainT2cutoff value by an experimental method; therefore, it is necessary to explore a prediction method ofT2cutoff value. In this paper, 10 samples of tight gas reservoirs in the eastern Ordos Basin were selected, and then saturation and centrifugal experiments of nuclear magnetic resonance were carried out. On this basis, multifractal theory was introduced to calculate the multifractal characteristics of the NMRT2spectrum of each sample, and the relationship between multifractal parameters andT2value was analyzed. The influencing factors of theT2cutoff value were clarified, and the prediction model of theT2cutoff value was constructed accordingly. The results show that theT2spectra of sandstones in the study area can be divided into three types: single steeple peak, double steeple peak, and irregular double peak. The pore diameter of the three types is 1 nm ~ 3×104 nm, 1 nm ~ 104 nm and 1 nm ~ 4×103 nm, respectively. TheT2cutoff value ranges from 9.72 to 35.16 ms. The correlation analysis suggests that the symmetrical fractal dimension difference and symmetrical multifractal dimension ratio (Dmin−Dmax, Dmin/Dmax) shows a positive linear correlation with theT2cutoff value. The value ofT2cutoff gradually decreases with the increase of the flow zone indicator (FZI). Therefore, three parameters, including symmetrical fractal dimension difference, symmetrical multifractal number ratio, andFZIare optimized, and the prediction model for the NMRT2cutoff value of sandstone samples in the study area is proposed. The introduction of porosity‐related parameters compensates for the shortcomings of previousT2cutoff value prediction models. At the same time, the prediction model is proven to be accurate and reliable by testing the measured data of the samples near the study area. The results of this paper can be used for further study of the NMRT2cutoff value prediction of tight sandstone reservoirs in different areas.

Investigation on pore structure and multifractal of tight sandstone reservoirs in coal bearing strata using LF-NMR measurements

In this study, pore structures of tight sandstone reservoirs in coal bearing strata were evaluated by combining the low field nuclear magnetic resonance (LF-NMR) measurements with multifractal theory. The effects of petrophysical properties, pore structure parameters, and reservoir components on multifractal parameters in different probability measure areas were then discussed. The results show that tight sandstone reservoirs in coal bearing strata have complex pore structure, low porosity (2.43%–5.18%), low permeability (0.0005–0.0125 mD), and poor pore connectivity with significant multifractal characteristics. Multifractal characteristics are well correlated with petrophysical property, pore structure, and lithology, which is useful for evaluating pore structure heterogeneity of such tight sandstone reservoirs. Moreover, the multifractal parameters of different probability measure areas are strongly associated with petrophysical parameter porosity, whereas the multifractal parameters of low probability measure areas αmax, (Dmin-D0) are weakly related to the characteristics of pore structure parameters and reservoir components. This suggests that the multifractal parameters of the high probability measure areas are more sensitive than other multifractal parameters to the pore structure, and therefore can be chosen for effective pore structure characterization. Additionally, other parameters A, (D0-D1), and (D0-D2) can also reflect the property of pore structure to a certain extent.

Fractal Analysis in Pore Size Distributions of Different Bituminous Coals

Coal bumps, coal and gas bursts are currently the main threats to coal mine safety in China. The physical properties of coal are important determining factors for the occurrence of coal bumps or coal and gas bursts. A series of experiments using mercury intrusion porosimetry (MIP), nitrogen adsorption (NA) and carbon dioxide adsorption (CA) were employed to investigate the pore size distributions (PSDs) of bump-prone coal and gas-outburst coal. Considering the influence of coal matrix compressibility on the MIP experimental data, the MIP data should be considered in combination with NA and CA testing data. The dominant pores of gas-outburst coal are different from those of bump-prone coal. The PSDs of coal samples have multifractal characteristics. However, the multifractal characteristics of two types of coal are different. (Answer to question 1, reviewer 2). A comparison of the multifractal parameters indicated that Xin Zhou Yao (XZY) coal samples have a higher spatial heterogeneity and complexity of their pore size distribution, while Zhao Ge Zhuang (ZGZ) coal samples have a lower heterogeneity and pore connectivity, which may hinder smooth gas flow and lead to a localized collection of gas in coal seams.

Investigation of spatial stratified heterogeneity of cemented paste backfill characteristics in construction demolition waste recycled aggregates

This paper discusses the application of construction demolition waste (CDW) in the field of backfill mining as an efficient way of increasing the CDW utilization rate. But much of the research on cemented paste backfill (CPB) with the CDW has been conducted in the laboratory which cannot accurately explain the spatial differentiation characteristics and mechanism of onsite CPB. To this end, this study uses fractal theory, image processing, and scanning electron microscopy (SEM) to analyze the spatial stratified heterogeneity (SSH) of recycled aggregates and the mechanical properties of the CPB under the natural flow of slurry. The spatial distribution mechanism of the CPB’s performances is also explained. The results indicate that the compressive strength reaches a maximum of 4.07 MPa on the top of the upper segment and a minimum of 1.6 MPa on the bottom of the upper segment, with a mean value of 2.4 MPa in the whole tunnel. This satisfies the requirements of field applications. The maximum and minimum mean particle sizes appear on the bottom of the upper segment and the lower segments of the tunnel, and the multifractal parameters are shown to indirectly reflect the distribution of recycled aggregate size. According to the test results of sampling point, the spatial distribution of CPB’s strength and recycled aggregate along the flow direction of slurry are regressed, allowing the tunnel to be divided into five distinct regions. Finally, the PSD of recycled aggregates and microstructures has a profound impact on the mechanical properties of CPB, but the motion characteristics of the recycled aggregates are the main reason for the SSH of the CPB properties.

Quantifying Fractal Dimension in Integrated Experimental Data of Tight Sandstones

Determining the microscopic pore structures of tight sandstones is becoming one of the most challenging efforts, and the strong heterogeneity makes the accurate assessment still a problem. In this research, we report a new criterion for pore structure typing based on the fractal geometry theory. The fractal dimension values were first accurately calculated through intrusion and nonintrusion methods. The results show that the pores in tight sandstones have multifractal distributions and different types of pore structure were divided based on various tests. The relationships between petrophysical properties and a series of multifractal parameters have been analyzed in detail. The fractal dimension values of type 1 sandstones derived from the throat curves in rate-controlled mercury intrusion methods can well characterize the porosity of the research area, while the others did not respond well. Finally, a multifractal criterion was proposed to analyze the petrological and pore structures by combined observations and experiments. The new criterion exhibits perfect performance in the prediction of the storage capacity. The multifractal model proposed in this research helps to assess the pore structures of tight sandstones and helps to characterize the reservoir quality in hydrocarbon exploration and development.

Multi‐fractal detrended fluctuation half‐spectrum analysis of HRV

Electrocardiogram is a comprehensive reflection of cardiac electrical activity on the surface of the body. It is of great research value to analyse ECG signals and diagnose heart diseases. Since the heartbeat process is a chaotic system, this study proposes a multi-fractal detrended fluctuation half-spectrum analysis method of short-term heart rate variability-y (HRV) signals from the perspective of non-linear dynamics, for patients with normal heart rate, sporadic heart rate variation and supraventricular rate, the heart rate mutation signal of patients with heart rate variation is calculated, and the statistical value distribution of multi-fractal parameter α has a certain change trend with the change of disease condition. The classification accuracy can reach >75% through box plot analysis.

ANALYSIS ON THE TIME-FREQUENCY CHARACTERISTICS OF ULTRASONIC WAVEFORM OF COAL UNDER UNIAXIAL LOADING

Ultrasonic receiving wave can reflect physical properties and damage degree of coal samples. Therefore, it is of great significance to deeply study the parameters of ultrasonic. In this paper, time-domain characteristics of receiving wave are analyzed systematically, which present good correlation with stress. The frequency spectrum of receiving wave is obtained using Fast Fourier Transform (FFT), and peak frequency and centroid frequency are calculated. During the entire loading process, peak frequency fluctuates around 110[Formula: see text]kHz, but corresponding centroid frequency decreases obviously at the end stage of loading. According to multifractal theory, the multifractal spectrum of wavelet packet energy characteristics is calculated. The results show that wavelet packet energy distribution has obvious multifractal characteristics, and multifractal parameter [Formula: see text] presents downward trend before coal samples buckling failure. Based on damage process of the coal samples, the reason of change in [Formula: see text] value is related to damage degree of coal samples. This research is of great significance for understanding the deformation and failure process of coal samples using ultrasonic technology.

Multifractal analysis to study break points in temperature data sets.

Since the last century, the air surface temperature has increased at a global scale, showing trends and inhomogeneities that vary from place to place. Many statistical methods can be used to analyze whether or not an inhomogeneity or break point exists in a meteorological data series, and even to detect the time of the break. Sometimes, there is no agreement in the year at which the inhomogeneity occurs detected by different tests. The scale invariance of a process can be studied through its multifractal properties that can be related to the existence of break points in it. In this work, the multifractal properties of monthly temperature data series are used to test what is the right break point year in those situations at which different dates are found by two different tests: the Pettitt and the Standard Normal Homogeneity tests. The comparison of the fractal dimension function Dq and the multifractal spectrum obtained by the box counting method for both the original data sets and for those obtained by splitting the original into two considering the break point years was made. When different multifractal functions and parameters were obtained, a break point was confirmed. Whereas, if equal values appeared, the break point year was discarded. These results let to select the most suitable test to be applied to detect inhomogeneities in a certain data set that will be very useful for climate change studies.

RESEARCH ON THE FRACTAL STATISTICAL CHARACTERISTICS AS POSSIBLE PROGNOSTIC PARAMETERS FOR EARTHQUAKES, GENERATED IN THE SEISMIC ZONE OF VRANCEA, IN THE PERIOD BETWEEN 01.08.2016 AND 30.12.2016


 
 
 Using fractal analysis is an excellent alternative method for decode the seismic noise structure. Fractal analysis of microseismic noise could also be an appropriate method to detect earthquake indicators. The scientific goal is to detect standard signals, based on different earthquakes’ focal mechanisms, separating the "individual" behavior of the elements of the monitoring systems.The method for describing low-frequency microseismic noise from the network of seismic stations in a seismically active region of the Vrancea used. Seismic records of twenty-three broadband stations were analyzed, situated at distances of 20 to 500 km from the Vrancea earthquakes whit magnitudes Mw=5.7 and Mw=5.6 on September 23 and December 27, 2016, respectively. The daily assessment values of three multifractal parameters (characteristics of the multifractal singularity spectra of the waveform) from each station used for the description.The present paper is a continuation of previous work [Oynakov et al., 2019], where the effects of synchronization in the low-frequency microseismic field were found before the Vrancea earthquake with magnitude Mp=5.6 on October 28, 2019.The study shows that the noise coherence measure increased for stations, closer to the epicenter. However, the question of the source of this coherence remains open.
 
 

Multifractal characteristics of the pore structures of physically amended sandy soil and the relationship between soil properties and multifractal parameters

ABSTRACT Pore structures of physically amended sandy soils exhibit significant multifractal characteristics, which are influenced by many soil physical properties. This study investigated the influences of adding fly ash and Montmorillonite-enriched sandstone (MS) on the physical properties and multifractal characteristics of pore structures in a sandy soil. Scanning electron microscope (SEM) was used to obtain the pore structures. MATLAB scripts were developed for calculating the Hölder index (αq) and generalized dimensions (Dq) of binary SEM images. The results showed that particle compositions and water retention capacity are improved after adding the two materials. The amplitudes of Dq (ΔD) was reduced by 6.9% to 35.6% in the amended soils, which means smaller scaling diversities of pore structures. The right branches of multifractal spectrum (αr) showed higher amplitudes than that of left branches (αl), indicating that smallest pores were more diverse than the largest pores after adding the two materials. Multifractal parameters showed significant linear relationships with the sand and silt content, bulk density and total porosity. The result indicate that multifractal parameters could be used to describe the changes of pore characteristics and to quantify the characteristics of pore structures in the amended sandy soils.

DYNAMIC IDENTIFICATION OF WEAR STATE BASED ON NONLINEAR PARAMETERS

This paper presents a new methodology of wear state recognition by using fractal parameters, multifractal parameters and recurrence parameters. The relationship between these nonlinear parameters is analyzed. A nonlinear state point of worn surface is established by fractal dimension, average diagonal length and spectrum width. Further, a steady state sphere is obtained by the nonlinear state point and [Formula: see text]-means clustering algorithm. Results show that fractal, multifractal and recurrence parameters characterize the worn surface from different perspectives. They should be used simultaneously to comprehensively characterize the integral structures, partial structures and internal structures of worn surface. The proposed nonlinear state point shows a variation process of concentration–stabilization–separation during the wear process. The wear states can be identified effectively by the relationship between nonlinear state points and steady state sphere.

Multifractality of meteorological time series for Poland on the base of MERRA-2 data

• Retrospective meteorological time series from MERRA-2 exhibit multifractality. • Highest variability of multifractal spectra parameters was observed for the air temperature. • Maps of the multifractal parameters can be used to analyse differences in climate dynamics. • Correlation of the multifractal parameters with a number of statistical parameters describing the series was observed. • Geo-statistical analysis delivered important information about the range of influence, sill and nugget variance of singularity spectra parameters. Spatial variability of the multifractal properties of a 36-year-long meteorological time series for Poland coming from the MERRA-2 database was analysed. It constitute a very valuable source of meteorological data, as high similarity with ground data recorded at meteorological stations in the region of interest was stated by the analysis of similarity measures. The highest variability of multifractal spectra parameters was observed for the air temperature, whereas the lowest was for the air pressure. Spatial analysis of multifractal spectra parameters enabled to select the regions vulnerable to the occurrence of extreme events, correlated or uncorrelated processes, etc. Obtained maps of multifractal parameters give a new insight into climate dynamics in the region and are a valuable source of information for comparative analyses. The spatial variation of the parameters of multifractal spectra was also confirmed by geo-statistical analysis, which delivered important information about the range of influence, sill and nugget variance. The paper is the first attempt to use geo-statistical analysis in regard to multifractal properties of meteorological quantities.

INVESTIGATING THE LOCAL DISTORTION OF THE FRACTAL COMPLEXITY OF THE RETINAL VASCULAR ALTERATIONS IN COGNITIVELY IMPAIRED PATIENTS

We investigated whether multifractal dimension and lacunarity analyses performed in sectoral regions of the retina may reveal local distortion in cognitive impaired (CI) patients that may be masked in the analysis considering the whole retinal branching pattern. Quantification of the retinal vasculature and function were conducted for every subject (19 healthy controls (HC) and 20 CI's patients) using advanced retinal imaging, full-field electroretinogram (ERG) and visual performance exams. The Montreal Cognitive Assessment (MoCA) was used to measure CI. The skeletonized vasculature network that comprised the whole branching pattern was obtained for each image and divided into nine equal regions (superotemporal, superior, superonasal, macular, optic disc, nasal, inferotemporal, inferior, inferonasal). The multifractal behavior was analyzed by calculating the generalized dimensions (Do, D1, D2), lacunarity parameter and singularity spectrum f(α) in the regions and whole retina. Statistical analyses were performed to find associations between all parameters in both groups (p< 0.05, statistically significant). The Do, D1 and D2 values in the HC individuals were significantly greater in the optic disc region (1.59 ± 0.05, 1.57 ± 0.05, 1.56 ± 0.05) vs. CI's participants (1.52 ± 0.08, 1.50 ± 0.08, 1.49 ± 0.08); p<0.05. Similar trends were observed in the optic disc region for the f(α). The lacunarity values were greater for CI's participants (0.329 ± 0.035) than controls (0.307 ± 0.024), p = 0.026 in the optic disc region but this difference was absent in the whole retina, p = 0.45. The Do and αo values were significantly associated with MoCA scores in the macular region, r = 0.47, p = 0.039; r = 0.46, p = 0.043; respectively but these associations were absent in the whole retina. Also, significant correlations between multifractal and lacunarity parameters with the MoCA and ERG's parameters were observed in the regional analysis; a trend was not found in the whole retina analysis. The regional analysis uncovered significant differences in CI's patients vs. HCs that were masked in the whole retinal analysis. Regional multifractal and lacunarity analyses may add additional diagnostic value to the use of retinal biomarkers for early diagnosis of CI.

Detonation spray method: features of technical implementation of the process and technology for obtaining ultrathin layers of semiconductor oxides

The design has been developed and the main components of the equipment for detonation growth have been modernized, which allows conducting the synthesis of semiconductor ultrathin films. The equipment was modernized taking into account the features of the thermodynamic properties of semiconductor materials. The data on the main adapted elements of the equipment are given, their functional purpose is indicated. Special attention is paid to the principles of operation of both the modified units of equipment and their functional interrelations in managing the process of the synthesis of layers. The conditions for the functioning and burning of gaseous hydrogen - oxygen mixture to obtain a high-energy shock wave, which provided the process of mass transfer of matter from source to substrate during the synthesis of ultrathin oxide semiconductor layers, are found. Particular attention is paid to ensuring optimal gas-dynamic conditions for the propagation of the zone of increased pressure in the process of transferring the substance from the source to the growth substrate. The design has been developed and systems of check valves have been manufactured that provide a given rate of switching gas flows during the synthesis of semiconductor oxides. The detonation spray method was used to synthesize ultrathin layers of the PbO and ZnO systems. The crystallographic and morphological properties of the surface of layers synthesized by detonation growth were investigated by optical methods. The obtained photographic images were analyzed by the method of multifractal analysis. It is proved that the multifractal parameters of the spectrum of the nanoform surface area formed on the growth surface of the layers are comparable in size with the corresponding parameters for the spectra from the surface of the layers synthesized by vacuum technologies.

Assessing the Wet Deposition Mechanism of Benzo(a)pyrene in the Atmosphere by MF-DCCA

Based on the 19 year observation from 1998 to 2016 at the Tsuan Wan and Central/Western District monitoring stations in Hong Kong, the aim of this paper was to assess the wet deposition pathway of Benzo(a)pyrene (BaP) on a large time-scale. In order to achieve this goal, multi-fractal detrended cross-correlation analysis (MF-DCCA) was used to characterize the long-term cross-correlations behaviors and multi-fractal temporal scaling properties between BaP (or PM2.5) and precipitation. The results showed that the relationships between BaP and precipitation (or PM2.5) displayed long-term cross-correlation at the time-scale ranging from one month to one year; no cross-correlation between each other was observed in longer temporal scaling regimes (greater than one year). These results correspond to the atmospheric circulation of the Asian monsoon system and are explained in detail. Similar dynamic processes of the wet deposition of BaP and PM2.5 suggested that the main removal process of atmospheric BaP was rainfall deposits of PM2.5-bound BaP. Furthermore, cross-correlations between BaP (or PM2.5) and precipitation at the long time-scale have a multi-fractal nature and long-term persistent power-law decaying behavior. The temporal evolutions of the multi-fractality were investigated by the approach of a sliding window. Based on the evolution curves of multi-fractal parameters, the wet deposition pathway of PM2.5-bound BaP is discussed. Finally, the contribution degree of wet deposition to PM2.5-bound BaP was derived from the coefficient of determination. It was demonstrated that about 45% and 60% of atmospheric BaP removal can be attributed to the wet deposition pathway of PM2.5-bound BaP for the Tsuan Wan and Central/Western District areas, respectively. The findings in this paper are of great significance for further study on the removal mechanism of atmospheric BaP in the future. The MF-DCCA method provides a novel approach to assessing the geochemical cycle dynamics of BaP.

Using multi-fractal and joint multi-fractal methods to characterize spatial variability of reconstructed soil properties in an opencast coal-mine dump in the Loess area of China

Opencast coal mining activities have significant effects on the reconstructed soil properties, including its physical, chemical and biological properties. To assess the effects of opencast mining and associated dumping activities on reconstructed soil properties, the spatial variability of soil properties, i.e., soil particle size distribution (PSD), organic matter (OM) and total nitrogen (TN), in an inner dump after dumping and before reclamation in Antaibao opencast coal-mine of Shanxi Pingshuo was analyzed using multi-fractal and joint multi-fractal methods. Soil samples at 78 sampling sites at the depths of 0–20 cm and 20–40 cm were collected using an auger. The singularity spectra of soil properties in the study area were analyzed, and three multi-fractal parameters (i.e., D1, D2 and ∆α) were calculated. The singularity spectra and multi-fractal parameters can quantitatively characterize the spatial variability of soil PSD, OM and TN. The variability of soil PSD, OM and TN at the depth of 20–40 cm was higher than that at the depth of 0–20 cm. At same soil depth, the sand and clay contents showed relatively high spatial variability, and the silt content, OM and TN exhibited relatively low spatial variability. The spatial variability in sand content, OM and TN between 0 and 20 cm and 20–40 cm depths had a relatively high correlation, while the clay and silt contents at the depths of 0–20 cm and 20–40 cm showed a relatively low correlation. Multi-fractal and joint multi-fractal methods exhibited more advantages in characterizing spatial variability of reconstructed soil properties. This study provided a theoretical basis for the soil sampling optimization of in the opencast coal-mine dump in the Loess area of China.

Assessment of fractal and multifractal features of sol-gel spin coated ZnO thin film surface

Scaling property of the atomic force microscopic (AFM) images of the annealed sol-gel spin coated ZnO thin film at different scales along with the glass substrate has been studied explicitly using fractal and multifractal formalism. Accordingly, the thin film surface growth and roughening are discussed. Polycrystalline Hexagonal wurtzite structure with preferential c-axis orientation and very little microcrystalline stress have been found from the glancing angle x-ray diffraction (GAXRD) pattern analysis of the annealed ZnO film on Glass substrate. Presence of statistical self-similarity in the surface micrographs is realized. Consequently, the fractal dimensions and Hurst exponents have been computed using the Higuchi’s algorithm and the correlation properties of the surfaces are quantified by these parameters. Values of the Hurst exponent indicate that the nature of overall surface growth is anti-correlated or anti-persistent, and while zoomed first it appears random or Brownian, having no ultimate correlation then seems to be positively correlated while further zoomed. The height and width of the singularity spectrum computed using box-counting multifractal formalism can quantify surface complexity both vertically and spatially. The multifractal analysis illustrates that the larger scan sized images have less overall surface complexity. Also, the multifractal parameters are found to be more universal than any other surface complexity measuring parameters. The fractal and multifractal behavior of both the glass substrate and the ZnO film on it reveal that the surface complexity of the ZnO thin film is originated from the complexity of the glass substrate. Furthermore, it has been understood that the proper choice of scan size is necessary to assess the actual complexity of a rough surface. Further investigation of the fractal and multifractal character of residual surface micrographs by varying various deposition conditions in sol-gel derived films could depict film growth and roughening mechanism in a scale-independent, precise, complete and generalized manner by avoiding an excessive number of parameters in conventional roughness and symmetry analysis methods.

Acoustic Emission Multi-Parameter Analysis of Dry and Saturated Sandstone with Cracks under Uniaxial Compression

In order to study the mechanics and acoustic emission (AE) characteristics of fractured rock under water-rock interaction, dried and saturated sandstone samples with prefabricated double parallel cracks were prepared. Then, uniaxial compression experiments were performed to obtain their AE signals and crack propagation images. The results show that water reduces the strength and fracture toughness of fractured sandstone and enhances plasticity. After saturation, the samples start to crack earlier; the cracks grow slowly; the failure mode is transformed from shear failure along the prefabricated cracks to combined shear and tensile failure; more secondary cracks are produced. The saturated samples release less elastic energy and weaker AE signals in the whole failure process. However, their AE precursor information is more obvious and advanced, and their AE sources are more widely distributed. Compared with dry specimens, the AE frequencies of saturated specimens in the early stage of loading are distributed in a lower frequency domain. Besides, the saturated samples release less complex AE signals which are dominated by small-scale signals with weaker multi-fractal characteristics. After discussion and analysis, it is pointed out that this may be because water makes rock prone to inter-granular fracture rather than trans-granular fracture. The water lubrication also may reduce the amplitude of middle-frequency band signals produced by the friction on the fracture surface. Multi-fractal parameters can provide more abundant precursory information for rock fracture. This is of great significance to the stability of water-bearing fractured rock mass and its monitoring, and is conducive to the safe exploitation of deep energy.

The impact of the surface morphology on optical features of the green emitting InGaN/GaN multiple quantum wells

AFM study of surface morphology in green LED structures and multifractal analysis allowed us to reveal a relationship between step-meandering morphology quantitatively characterized by a multifractal parameter, the degree of disorder, and features of In incorporation in InGaN/GaN MQW structures. These features manifest themselves in a shape of the distribution of peak external quantum efficiency values with wavelengths (DPEW) in the current range of 0.1–1000 mA. High values of degree of disorder result in spinodal alloy decomposition and/or local In enriched regions in InGaN alloy and in a twofold decrease in EQE values in green LEDs.

Effects of checkerboard barriers on the distribution of aeolian sandy soil particles and soil organic carbon

Sand-barrier setup is an important measure to protect the topsoil against wind erosion. Salix psammophila checkerboard barriers are used widely in the Mu Us Sandy Land in order to ensure the safety of life and agricultural production. To measure variations in soil structure and quality caused by barriers with different duration (7 years and 2 years), the composition of aeolian sandy soil particles and the soil organic carbon (SOC) distributions are studied; the dunes with no barrier are used as controls (CK). Analyzed by multi-fractal parameters, the topsoil samples are collected in the field and tested in the laboratory.The predominant soil particles are fine sand, medium coarse sand and clay, and the contents of silt and very fine sand increase with extending barrier duration, which shows a wider distribution range, greater dispersion degree and larger soil particle heterogeneity. The aeolian sandy particles, particularly fine granular grains, are deposited and accumulate at the bottom and top of dunes because of the barrier blocking effect.The particle size distribution (PSD) heterogeneity is the highest in 7-year barrier dunes and the lowest in the no barrier dunes. The mean values of D0 (Capacity dimension) of 7-year barrier dunes, D1 (entropy dimension) of the no barrier dunes and D1/D0 of 2-year barrier dunes are maxima. In addition, the PSD range and distribution increased with prolonged dune barrier duration, as well as the changes of Δf(∂) (shape of the multi-fractal spectrum) and Δ∂ (width of multi-fractal spectrum).SOC content increased with increasing barrier duration and decreasing D1/D0. The average SOC contents of 7-year barrier dunes were the maximum and one of no barrier dunes had the minimum SOC content, and their difference was significant (P < 0.05). In both the PSD and SOC distribution, the 7-year barrier showed better results on the topsoil than that of 2-year and no barrier situation.Correlations between the SOC content and the PSD multi-fractal parameters of both 7-year and 2-year barrier dunes are significantly different (P < 0.01). The multi-fractal parameters can be used to indicate soil nutrient contents, which provide fundamental knowledge for evaluating the effectiveness of ecological engineering to restore soil quality and structure to sandy ecosystems. Salix psammophila checkerboard sand barriers play a role in increasing the fine particles and soil organic carbon in surface dune soil, which is helpful in restoring the Mu Us sand ecosystem. The early use of sand barriers is therefore recommended.