Improved EEMD-based standardization method for developing long tree-ring chronologies

Long tree-ring chronologies can be developed by overlapping data from living trees with data from fossil trees through cross-dating.However,low-frequency climate signals are lost when standardizing tree-ring series due to the"segment length curse".To alleviate the segment length curse and thus improve the standardization method for developing long tree-ring chronologies,here we first calculated a mean value for all the tree ring series by overlapping all of the tree ring series.The growth trend of the mean tree ring width(i.e.,cumulated average growth trend of all the series)was determined using ensemble empirical mode decomposition.Then the chronology was developed by dividing the mean value by the growth trend of the mean value.Our improved method alleviated the problem of trend distortion.Long-term signals were better preserved using the improved method than in previous detrending methods.The chronologies developed using the improved method were better correlated with climate than those developed using conservative methods.The improved standardization method alleviates trend distortion and retains more of the low-frequency climate signals.

Straw layer burial to alleviate salt stress in silty loam soils: Impacts of straw forms

Salt stress can be alleviated by straw layer burial in the soil, but little is known of the appropriate form of the straw layer for optimal regulation of soil water and salinity because of the uncontrollability of field tests. Here, the following four straw forms with compaction thickness of 5 cm buried 40–45 deep were studied: no straw layer(CK), segmented straw(SL, 5 cm in length), straw pellet(SK), and straw powder(SF). The three straw forms(SL, SK and SF) significantly delayed the infiltration of irrigation water down the column profile by 71.20–134.3 h relative to CK and the migration velocity of the wetting front under SF was the slowest. It took longer for the wetting front to transcend SK than SL but shorter for it to reach the bottom of soil column after water crossed the straw layer. Compared with CK, the average volumetric water content in the 0–40 cm soil layer increased by 6.45% under SL, 1.77% under SK and 5.39% under SF. The desalination rates at the 0–40 and 0–100 cm soil layers increased by 5.85 and 3.76% under SL, 6.64 and 1.47% under SK and 5.97 and 4.82% under SF. However, there was no significant difference among straw forms in the 0–40 cm soil layer. Furthermore, the salt leaching efficiency(SLE, g mm^–1 h^–1) above the 40 cm layer under SL was 0.0097, being significantly higher than that under SF(0.0071) by 37.23%. Salt storage under SL, SK and SF in the 40–45 cm layer accounted for 4.50, 16.92 and 7.43% of total storage in the 1-m column profile. Cumulative evaporation under SL and SF decreased significantly by 41.20 and 49.00%, with both treatments having the most significant inhibition of salt accumulation(resalinization rate being 36.06 and 47.15% lower than CK) in the 0–40 cm soil layer. In conclusion, the different forms of straw layers have desalting effects under high irrigation level(446 mm). In particular, SL and SF performed better than SK in promoting deep salt leaching and inhibiting salt accumulation on the soil surface. However, SL was simpler to implement and its SLE was higher. Therefore, the segmented 5 cm straw can be recommended as an optimum physical form for establishing a straw layer for managing saline soils for crop production.

STRUCTURAL CHARACTERIZATION OF POLYETHYLENES BY DSC ANALYSIS AFTER CRYSTALLIZATION SEGREGATION

The molecular structure of polyethylene (PE) samples with various comonomers including propylene, I-butane and 1-hexene was investigated by DSC and C-13-NMR techniques. The density of the samples varies from 0.948 g/cm(3) to 0.917 g/cm(3), and the molecular weight determined by the GPC method is in the range of 1 similar to2 x 10(5). The branch paint content of the samples was determined by C-13-NMR measurements and was found to be less than 20 per 1000 C atoms along the main chain. Crystallization segregation DSC technique (CSDSC) was used to characterize the branch point distribution or the segment length distribution of PEs. The crystallization segregation was performed in a successive annealing process at decreasing temperatures. The interval of two successive annealing temperatures was 6 K, and the time length of each annealing step was 2.5 h. The CSDSC results clearly indicate that all the PE samples used, including some metallocene PEs, more or less exhibit their non-uniformity in segment length distribution, and bimodal or multimodal CSDSC curves were usually observed. For quantitative characterization of the CSDSC curves and the segment length distribution two parameters, the average melting point, T-mAV, and the root-mean-square deviation of melting temperature, (DeltaT(m)(AV)(2))(1/2), were proposed. TmAV is corresponding to the average segment length due to branching and (DeltaT(m)(AV)(2))(1/2) gives information about the: width of the segment length distribution. Experimental results show that both the degree of average melting temperature depression and the width of the distribution seem to increase with increasing the branching content and are dependent on the type of comonomers. Very good reproducibility and additivity of the CSDSC method were evidenced experimentally. It was concluded that the CSDSC technique is a sensitive and convenient method for characterizing the segment length distribution of branched polyethylenes and will be of great interest in structure-property relationship studies of crystalline polymers.

Comparison of stem volume estimates from terrestrial point clouds for mature Douglas-fir(Pseudotsuga menziessi(Mirb.)Franco)

As a complement to traditional estimates of stem dimensions from numerical models,terrestrial light detection and ranging(Lidar)provides direct stem diameter and volume values using cylindrical models constructed from point clouds.This study used two approaches to estimate total stem volume using Lidar and compared them with two empirical equations,one used by the Forest Inventory Analysis in the Pacific Northwest(FIA-PNW)and one based on a taper equation.We fitted point clouds of 10 Douglas-fir with three sets of cylinder models that are distinguished by their segment length(i.e.0.5 m,1 m,and 2 m),then developed three taper equations based on the point-cloud-based diameter estimated previously.We estimated the total stem volume of the tree with eight models:six-point cloudbased(i.e.three taper and three cylinders)and two empirical.Finally,we used simulations to extrapolate the volume estimations of various methods for different diameters at breast height(DBH)classes.We found that all the point-cloud-based taper equations were similar in their performance(R2¼0:94,RMSE=4.6 cm)and produced mean volume estimates greater than mean estimates of the existing models.The cylinder models produced 11–16%greater mean volume estimates than the FIA-PNW estimate,with the 0.5 m segment length producing the greatest values,followed by the 1 m and 2 m segment length.The simulated data suggested that the mean volume estimates of a given DBH class are different when using different computation methods.ANOVA revealed a combined effect of the computation methods and the DBH class on the mean volume estimates.We conclude that the point-cloud-based taper equations,after being symmetrically calibrated,would be consistent with the regional stem volume estimates,whereas the cylinder models would be better in estimating individual stem volume.When constructing Lidar-based cylinder models in future applications,cylinder segment length would need to be adjusted to the length and DBH of the stem,as well as to the objectives of the research.

Quantifying microstructural changes in retinitis pigmentosa using spectral domain – optical coherence tomography

Background:Most patients of established retinitis pigmentosa(RP)have subnormal peripheral vision and heavily rely on central vision for their daily activities.Central visual acuity is dependent on photoreceptor survival at the macula.Identification of structural changes that precede visual loss is essential.The aim of this study was to correlate the Spectral Domain-Optical Coherence Tomography(SD-OCT)characteristics with visual acuity in patients with typical RP.Methods:This was a retrospective,observational case series of 224 eyes of 113 RP patients conducted a tertiary eye care center.SD-OCT imaging was done for all eyes.Central retinal thickness(CRT),photoreceptor outer segment length(PROS),foveal outer segment pigment epithelial thickness(FOSPET)and ellipsoid zone(EZ)extent were measured.A new variable,FOSPET-PROS ratio(FPR),obtained by dividing FOSPET by PROS is defined and correlated to corrected distance visual acuity(CDVA)in logMAR using linear regression.Results:Out of 113 patients,71 were males and 42 females.Mean age of the patients was 35.4±15.1 years.Mean CDVA was 0.33±0.25 logMAR with no difference between the genders.Mean CRT(218.74±83.5μm)and FPR(1.63±0.22)significantly correlated to CDVA with a correlation coefficient of r=−0.139(p=0.048)and r=0.842(p=0.0001),respectively.FOSPET(mean=71.15±13.8μm)and PROS(mean=44.85±12.5μm)did not show a significant correlation to CDVA,independent of FPR.Conclusions:Retinal microstructural changes on SD-OCT,especially the FPR,can be used as a surrogate marker to monitor disease progression in the central retina in degenerative diseases like RP.