Parkland trees on smallholder farms ameliorate soil physical-chemical properties in the semi-arid area of Tigray,Ethiopia

Proposed agroforestry options should begin with the species that farmers are most familiar with,which would be the native multipurpose trees that have evolved under smallholder farms and socioeconomic conditions.The African birch(Anogeissus leiocarpa(DC.)Guill.&Perr.)and pink jacaranda(Stereospermum kunthianum Cham.)trees are the dominant species in the agroforestry parkland system in the drylands of Tigray,Ethiopia.Smallholder farmers highly value these trees for their multifunctional uses including timber,firewood,charcoal,medicine,etc.These trees also could improve soil fertility.However,the amount of soil physical and chemical properties enhanced by the two species must be determined to maintain the sustainable conservation of the species in the parklands and to scale up to similar agroecological systems.Hence,we selected twelve isolated trees,six from each species that had similar dendrometric characteristics and were growing in similar environmental conditions.We divided the canopy cover of each tree into three radial distances:mid-canopy,canopy edge,and canopy gap(control).At each distance,we took soil samples from three different depths.We collected 216 soil samples(half disturbed and the other half undisturbed)from each canopy position and soil depth.Bulk density(BD),soil moisture content(SMC),soil organic carbon(SOC),total nitrogen(TN),available phosphorus(AP),available potassium(AK),p H,electrical conductivity(EC),and cation exchange capacity(CEC)were analysed.Results revealed that soil physical and chemical properties significantly improved except for soil texture and EC under both species,CEC under A.leiocarpus,and soil p H under S.kunthianum,all the studied soils were improved under both species canopy as compared with canopy gap.SMC,TN,AP,and AK under canopy of these trees were respectively 24.1%,11.1%,55.0%,and 9.3% higher than those soils under control.The two parkland agroforestry species significantly enhanced soil fertility near the canopy of topsoil through improving soil physical and chemical properties.These two species were recommended in the drylands with similar agro-ecological systems.

Microvascular alterations of the ocular surface and retina in connective tissue disease-related interstitial lung disease

AIM:To examine the disparities in macular retinal vascular density between individuals with connective tissue disease-related interstitial lung disease(CTD-ILD)and healthy controls(HCs)by optical coherence tomography angiography(OCTA)and to investigate the changes in microvascular density in abnormal eyes.METHODS:For a retrospective case-control study,a total of 16 patients(32 eyes)diagnosed with CTD-ILD were selected as the ILD group.The 16 healthy volunteers with 32 eyes,matched in terms of age and sex with the patients,were recruited as control group.The macular retina’s superficial retinal layer(SRL)and deep retinal layer(DRL)were examined and scanned using OCTA in each individual eye.The densities of retinal microvascular(MIR),macrovascular(MAR),and total microvascular(TMI)were calculated and compared.Changes in retinal vascular density in the macular region were analyzed using three different segmentation methods:central annuli segmentation method(C1-C6),hemispheric segmentation method[uperior right(SR),superior left(SL),inferior left(IL),and inferior right(IR)],and Early Treatment Diabetic Retinopathy Study(ETDRS)methods[superior(S),inferior(I),left(L),and right(R)].The data were analyzed using Version 9.0 of GraphPad prism and Pearson analysis.RESULTS:The OCTA data demonstrated a statistically significant difference(P<0.05)in macular retinal microvessel density between the two groups.Specifically,in the SRL and DRL analyses,the ILD group exhibited significantly lower surface density of MIR and TMI compared to the HCs group(P<0.05).Furthermore,using the hemispheric segmentation method,the ILD group showed notable reductions in SL,SR,and IL in the superficial retina(P<0.05),as well as marked decreases in SL and IR in the deep retina(P<0.05).Similarly,when employing the ETDRS method,the ILD group displayed substantial drops in superficial retinal S and I(P<0.05),along with notable reductions in deep retinal L,I,and R(P<0.05).In the central annuli segmentation method,the ILD group exhibited a significant decrease in the superficial retinal C2-4 region(P<0.05),whereas the deep retina showed a notable reduction in the C3-5 region(P<0.05).Additionally,there was an observed higher positive likelihood ratio in the superficial SR region and deep MIR.Furthermore,there was a negative correlation between conjunctival vascular density and both deep and superficial retinal TMI(P<0.001).CONCLUSION:Patients with CTD-ILD exhibits a significantly higher conjunctival vascular density compared to the HCs group.Conversely,their fundus retinal microvascular density is significantly lower.Furthermore,CTD-ILD patients display notably lower superficial and deep retinal vascular density in comparison to the HCs group.The inverse correlation between conjunctival vascular density and both superficial and deep retinal TMI suggests that detecting subtle changes in ocular microcirculation could potentially serve as an early diagnostic indicator for connective tissue diseases,thereby enhancing disease management.

Direct measurement of the three-dimensional distribution of leaf area density and light conditions in a mature oak stand by the cube method

Although the distributions of foliage and light play major roles in various forest functions,accurate,nondestructive measurement of these distributions is difficult due to the complexity of the canopy structure.To evaluate the foliage and light distributions directly and nondestructively in a mature oak stand,we used the cube method by dividing the forest canopy into small cubes(50 cm per side)and directly measured leaf area density(LAD,the total one-sided leaf area per unit volume,i.e.,cube)and relative irradiance(RI)within each cube.The distribution of LAD and of RI was highly heterogeneous,even at the same canopy height.This heterogeneity reflected the presence of foliage clusters associated with multiple forking branches.The relationship between cumulative LAD at the canopy surface and average RI followed the Beer-Lambert law.The mean light extinction coefficient(K)was 0.32.However,K was overestimated by more than double(0.80)when calculated based on the classical method using RI at the forest floor.This overestimation was caused by the lower RI due to light absorption by nonleaf plant parts below the canopy.Our findings on the complex foliage and light distributions in canopy layers should help improve the accuracy of RI and K measurements and thus more accurate predictions of environmental responses and forest functions.

First principles study on the charge density and the bulk modulus of the transition metals and their carbides and nitrides

A first principles study of the electronic properties and bulk modulus （B0） of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.

Using the Dual Energy Gamma-Ray Transmission Technique to Measure Soil Bulk Density and Water Content of Central Southwestern Nigerian Soils

In this work, a radiological technique which simultaneously measures soil bulk density and water contents accurately and quickly in a non-destructive manner at different depths of the soil profile of the major soil series of Central Southwestern Nigeria is developed. Undisturbed samples from Iwo, Ondo, Egbeda, Itagunmodi, Okemessi, Mamu, Origo and Jago soil series of Southwestern Nigeria were collected on monthly intervals from June 2006 to May 2007. Using gamma-ray energy pairs of 122 and 1112 keV;and 344 and 1408 keV obtained from europium-152 (152Eu) radionuclide, the attenuation coefficients for soil and water, μs, μw and consequently ρs and θv at varying soil depths of these series were calculated. Comparative gravimetric measurements of these soil parameters were carried out. Using the XCOM computer algorithm with the soil elemental concentrations obtained using the Energy Dispersive X-Ray Fluorescence analysis (EDXRF) technique, theoretical estimates of μs for the various soil series were obtained and compared with the experimental values. The result of the developed dual energy gamma-ray transmission technique was compared with the gravimetric measurement method and Pearson correlation coefficient (0.987, p s and (0.996, p θv. The results of the measurements showed that θv minima with values 0.1931, 0.1987, 0.2377, 0.2111, 0.1738, 0.1701, 0.2334, 0.2341 and minima ρs values of 1.21 g/cm3, 1.20 g/cm3, 1.02 g/cm3, 1.38 g/cm3, 1.12 g/cm3, 1.14 g/cm3, 0.64 g/cm3, 1.33 g/cm3 were obtained respectively for the soil series stated above in January. The maxima θv with values 0.3621, 0.4212, 0.3962, 0.3794, 0.3049, 0.2811, 0.4415, 0.4416 and maxima ρs values of 1.52 g/cm3, 1.67 g/cm3, 1.74 g/cm3, 1.69 g/cm3, 1.70 g/cm3, 1.68 g/cm3, 1.08 g/cm3, 1.54 g/cm3 occurred for these soil series respectively in July except for Mamu soil series which occurred in May. These correlated very well with the occurrence of the Dry and Rainy seasons in the study area. The results of the EDXRF analysis showed that maxima Iron, Fe concentrations of 5.0890 ppm at the depth of 90 - 120 cm into the soil profile, was obtained for Iwo series, 4.4691 ppm at 50 - 70 cm for Ondo, 6.3438 ppm at 15 - 30 cm for Egbeda, 6.6845 ppm at 30 - 50 cm for Itagunmodi, 5.0252 ppm at 90 - 120 cm for Okemessi, 3.4996 ppm at 30 - 50 cm for Mamu, 5.1191 ppm at 50 - 70 cm for Jago and 4.7193 ppm at 90 - 120 cm for Origo. Maxima Potassium, K concentrations of 2.9613 ppm at the depth of 50 - 70 cm, was obtained for Iwo soil series, 2.3315 ppm at 0 - 15 cm for Egbeda, 2.2763 ppm at 70 - 90 cm for Okemessi and 3.3636 ppm at 50 - 70 cm for Mamu. Maxima Ti concentrations of 1.4822 ppm at 0 - 15 cm was obtained for Ondo soil series, 2.5159 ppm at 15 - 30 cm for Egbeda, 1.8690 ppm at 90 - 120 cm for Itagunmodi, 2.2975 ppm at 15-30 cm for Okemessi, 1.6453 ppm at 0 - 15 cm for Jago and 1.0513 ppm at 30 - 50 cm for Origo.

Effect of sintering on the relative density of Cr-coated diamond/Cu composites prepared by spark plasma sintering

Cr-coated diamond/Cu composites were prepared by spark plasma sintering. The effects of sintering pressure, sintering temperature, sintering duration, and Cu powder particle size on the relative density and thermal conductivity of the composites were investigated in this paper. The influence of these parameters on the properties and microstructures of the composites was also discussed. The results show that the relative density of Cr-coated diamond/Cu reaches ~100% when the composite is gradually compressed to 30 MPa during the heating process. The densification temperature increases from 880 to 915℃ when the diamond content is increased from 45vol% to 60vol%. The densification temperature does not increase further when the content reaches 65vol%. Cu powder particles in larger size are beneficial for increasing the relative density of the composite.

The effects of relative density of metal foams on the stresses and deformation of beam under bending

The exact analytic solution of the pure bending beam of metallic foams is given. The effects of relative density of the material on stresses and deformation are revealed with the Triantafillou and Gibson constitutive law （TG model） taken as the analysis basis. Several examples for individual foams are discussed, showing the importance of compressibility of the cellular materials. One of the objects of this study is to generalize Hill＇s solution for incompressible plasticity to the case of compressible plasticity, and a kinematics parameter is brought into the analysis so that the velocity field can be determined.

Reproductive Components of Safflower Genotypes Submitted of Bulk Density Levels in the Brazilian Cerrado

Nutrient absorption in crops can decline and their development can be hindered by increased bulk density. This study aimed at assessing the manner in which bulk density levels affect the reproductive structures of the safflower genotypes in the Brazilian Cerrado. The completely randomized design was adopted with four replications for the experiment, which was conducted in a greenhouse using Oxisol collected from 0.0 to 0.2 m depth from the region supporting Cerrado vegetation. The treatments included ten safflower genotypes (PI 237538, PI 248385, PI 250196, PI 301049, PI 305173, PI 305205, PI 306520, PI 306603, PI 560202 and PI 613366) and five bulk density levels (1.0, 1.2, 1.4, 1.6 and 1.8 Mg·m-3). Evaluations were done at 90 days after emergence, in terms of the number, diameter and dry mass of the heads. The data were submitted to the analysis of variance. The means were grouped using the Scott-Knott test at 5% probability. The diameter and dry mass of the chapters were influenced by the mean bulk density of 1.10 Mg·m-3. A notable interaction was evident between the safflower genotypes and bulk density levels for the diameter and dry mass of the head alone, revealing the high degree of genetic variability that environmental changes induce among the genotypes. The PI 250196, PI 301049, PI 305173 and PI 305205 genotypes exhibited greater stability to the bulk density variations compared with the others. Mean bulk density of 1.2 Mg·m-3 was found to impair the development of the reproductive components of the safflower genotypes.

Effect of Crystallinity of Fullerene Derivatives on Doping Density in the Organic Bulk Heterojunction Layer in Polymer Solar Cells

Polymer solar cells （PSCs） based on poly（3-hexylthiophene） （P3HT） and [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） are fabricated by using 1,8-diiodooctane （DIO） as a solvent additive to control the doping density of the PSCs. It is shown that the processing of DIO does not change the doping density of the P3HT phase, while it causes a dramatic reduction of the doping density of the PCBM phase, which decreases the doping density of the whole blend layer from 3.7 × 10^16 cm-3 to 1.2 ×10^16 cm-3. The reduction of the doping density in the PCBM phase originates from the increasing crystallinity of PCBM with DIO addition, and it leads to a decreasing doping density in the blend film and improves the short circuit current of the PSCs.

Study on Loading Leaves Density with Cage Clamp on Quality of Cured Tobaccos in Bulk-Curing Barn

In order to determine the best loading density of tobacco leaf with cage clamp in bulk-curing barns, a curing test was conducted on middle-part tobacco leaves. The results showed that for good appearance quality of cured tobacco, the loading density at 59.52 kg/m2 （4 000 kg/barn） was the best, fol owed by 66.96 kg/m2 （4 500 kg/barn） and 74.40 kg/m2 （5 000 kg/barn）. As leaf loading density increased, the contents of leaf nicotine and total nitrogen increased, sugar content had smal changes, the ratio of sugar to nicotine decreased and tended to be balanced and the content of neutral aroma substances was decreasing, but the difference among treatments was not significant. With the increase of loading density, the sensory quality of cured leaf was better. When leaf loading density was 66.96 kg/m2 （4 500 kg/barn）, apperance quality of cured leaf improved considerably, with prominent aro-ma. Therefore, the best loading density of tobacco leaf in cage clamp of bulk-curing barn would be 66.96 kg/m2 （4 500 kg/barn） .

Spatial variability of soil bulk density and its controlling factors in an agricultural intensive area of Chengdu Plain,Southwest China

Soil bulk density is a basic but important physic soil property related to soil porosity,soil moisture and hydraulic conductivity,which is crucial to soil quality assessment and land use management.In this study,we evaluated the spatial variability of soil bulk density in the 0–20,20–40,40–60 and 60–100 cm layers as well as its affecting factors in Southwest China’s agricultural intensive area.Results indicated the mean value of surface soil bulk density(0–20 cm)was 1.26 g cm^(–3),significantly lower than that of subsoil(20–100 cm).No statistical difference existed among the subsoil with a mean soil bulk density of 1.54 g cm^(–3).Spatially,soil bulk density played a similar spatial pattern in soil profile,whereas obvious differences were found in details.The nugget effects for soil bulk density in the 0–20 and 20–40 cm layers were 27.22 and27.02%while 12.06 and 3.46%in the 40–60 and 60–100 cm layers,respectively,gradually decreasing in the soil profile,indicating that the spatial variability of soil bulk density above 40 cm was affected by structural and random factors while dominated by structural factors under 40 cm.Soil organic matter was the controlling factor on the spatial variability of soil bulk density in each layer.Land use and elevation were another two dominated factor controlling the spatial variability of soil bulk density in the 0–20 and 40–60 cm layers,respectively.Soil genus was one of the dominated factors controlling the spatial variability of soil bulk below 40 cm.

Density Functional Study on Structures and Relative Stability of Gd（H2O）n^3＋ （n=8,9）

Density functional theory calculations were performed to study the structures and relative stability of the gadolinium complexes, Gd（H2O）n^3＋ （n=8,9）, in vacuo and in aqueous solution. The polarizable continuum model with various radii for the solute cavity was used to study the relative stability in aqueous solution. The calculated molecular geometries for n=8 and 9 obtained in vacuo are consistent with those observed in experiments. It was found that while the nona-aqua complex is favored in the gas phase, in aqueous solution the octa-aqua conformation is preferred. This result, independent of the types of cavities employed, is in agreement with the experimental observation. The reliability of the present calculation was also addressed by comparing the calculated and experimental free energy of hydration, which revealed that the UA0, UAHF, and UAKS cavities are most appropriate when only the first solvation shell is treated explicitly.

Dynamic monitoring of soil bulk density and infiltration rate during coal mining in sandy land with different vegetation

To investigate the effects of coal mining on soil physical properties,sandy lands with three major vegetation types(Salix psammophila,Populus simonii,and Artemisia ordosica)were investigated by the ring knife method and double-ring infiltrometer.Specifically,variations in soil bulk density and water infiltration rate and the influences of coal mining and vegetation type on the properties during different subsidence stages were studied at the Shendong Bulianta mine.The results showed that,in the period before mining,soil bulk density occurred in the order A.ordosica>P.simonii>S.psammophila,with a negative correlation between the initial infiltration rate and steady infiltration rate being observed.In the period during mining and 3 months after mining,there were no significant differences in soil bulk density and water infiltration rate among vegetation types.At 1 year after mining,the soil bulk density occurred in the order A.ordosica>S.psammophila>P.simonii,having a negative correlation with the steady infiltration rate.The water infiltration depths of the S.psammophila,P.simonii and A.ordosica were 50,60,and 30 cm,respectively.The infiltration characters were simulated by the Kostiakov equations,and the simulated and experimental results were consistent.Linear regression revealed that vegetation types and soil bulk density had significant effects on soil initial infiltration rate during the four study periods,and the infiltration rate of the period 1 year after mining was mainly influenced by the soil bulk density of the period before mining.The results indicated that vegetation types had significant effects on soil bulk density,and that the tree-shrub-grass mode was better than one single plantation for water conversation and vegetation recovery in sandy land subjected to mining.

Diffusion of Chloride Ions in Soils:I.Influences of Soil Moisture, Bulk Density and Temperature

Diffusion coefficients of chloride ions in four soils of different texture with varying effective moisture content and varying bulk density from 1.1 to 1.6 g cm3 under three different temperatures were determined by the diffusion-cell method using 36Cl-labelled CaCl2 solution. The results showed that activation energy decreased with water content, which indicated that the threshold for diffusion was lower at a higher soil moisture rate. Therefore, the diffusion coefficient (D) of chloride ions in soil increased consistently with soil moisture. Although a near linear increase in the diffusion coefficient with increasing soil moisture or bulk density in all the soils was observed, the increase rate in different soils was not the same. The D value increased with temperature, and with temperature increased by 10℃ in the range from 5 "C to 45℃ theD valve increased by 10%～30%, averaging about 20%.

Change in relative density of WC-Co cemented carbides in spark plasma sintering process

The relative density of WC-Co cemented carbides during spark plasma sintering（SPS） was analyzed.Based on the change in displacement of the ram in the SPS system,the relative densities in the sintering process can be achieved at different temperatures.The results indicated that densification of the samples started at near 900°C,the density rapidly reached its maximum at the increasing temperature stage,in which the temperature was lower than the sintering temperature of 1200°C,and most of the densification took place in the stage.Besides,the theoretical values were consistent with the experimental results.

Monitoring of Soil Bulk Density in Context with Its Small-Scale Spatial Heterogeneity

The main aim of soil monitoring system is to obtain the knowledge of the most current state and development of soil properties according to concrete threats to soil. To determine the significant changes of soil properties in time, it is important to know spatial variability of concrete soil parameter for concrete site. Only those time changes of the soil parameter are significant, which exceed its spatial variability at the site. The main aim of the study has been focused on the evaluation of small-scale site heterogeneity of equilibrium soil bulk density and the integration of impact of this heterogeneity in evaluation of degradation process of soil compaction in time. As site variation coefficients have considerably varied at standard sampling with five repetitions during monitoring period, one-time detail spatial variability mapping of soil bulk density was realized at 17 repetitions on five selected monitoring sites with different soil type, texture and use. This increase in the number of sampling points helped us to specify and stabilize the values of variation coefficients (between minimum and maximum by standard sampling) as well as the extent of confidence intervals. Standard deviations at the chosen monitoring sites moved from 0.039 to 0.118 g·cm-3 in topsoil and from 0.031 to 0.067 g·cm-3 in subsoil and expressed as variation coefficient 2.9% - 9.2% and 2.0% - 4.9%, respectively. The intervals of significant time changes of soil bulk density for the sites and depths were determined on the base of its site confidence interval (95%) and uncertainty rate of its measure methodology. The time changes of bulk density values between single year-to-year sampling were overlapped by this interval of significant changes to obtain significant bulk density changes in time. This method allowed us to distinguish significant time changes in soil bulk density from insignificant ones. The bulk density value changes on the monitoring sites were significant in the range of six to nine years within observed period 2002-2014 in both depths.

Charge density at the nucleus and radial behavior of ground state for lithium-like ions with Z=21 to 30

By using the full-core plus correlation （FCPC） type wave functions, the accurate charge densities p（0） at the nucleus and the radial expectation values of the ground states for the lithium-like systems with Z =- 21 to 30 are obtained. The determinantal conditions and the electron-nucleus cusp condition are used to calculate the inequalities of the upper and the lower bounds to p（0） with two or more expectation values. These inequalities, derived by Angulo and Dehesa [Phys. Rev. A 44 1516 （1991）], are verified to be also valid for these ions with higher nuclear charge. The present results show that the wave functions used in this paper are satisfactory in the whole configuration space for these ions with higher nuclear charge.

Cyclic Oxidation Behaviors of MoSi_2 with Different Relative Density

The influence of different relative density on the cyclic oxidation behaviors of MoSi2 at 1 273 K were studied. ＂Pesting＂ was not found in all MoSi2 materials after being oxidized for 480 h. All samples exhibited continuous mass gain during the oxidation process. The mass gains of MoSi2 with the lowest relative density （78.6%） and the highest relative density （94.8%） are increased by 8.15 mg·cm^-2 and 3.48 mg·cm^-2, respectively. The surface of the material with lower relative density formed a loose, porous and discontinuous oxidation scale, which accelerated oxygen diffusion and aggravated the oxidation process. However, a dense scale in the material with higher relative density is formed, which acts a diffusion barrier to the oxygen atoms penetrating into the matrix. The high temperature oxidation resistance of MoSi2 can be improved by increasing its relative density.

Species Richness, Diversity and Density of Understory Vegetation along Disturbance Gradients in the Himalayan Conifer Forest

We investigated whether species richness, diversity and density of understory herbaceous plants differed along logging(gap) and grazing(primarily by cattle) disturbance gradients, and sought to identify drivers of richness, diversity and density of understory vegetation of logged sites. A factorial experiment was conducted in the mixed conifer forest of Gidakom in Western Bhutan. Levels of the logging treatment included small(0.15 – 0.24 ha), medium(0.25 – 0.35 ha) and large(0.36 – 1.31 ha) gaps. The grazing treatment included grazed(primarily by cattle) and ungrazed(where herbivores were excluded by a fence) plots nested within each gap. Data were collected from 12 gaps(4 replicates at each level of logging) using the point intercept method. Shannon Weaver Diversity and Margalef's indices were used to estimate species diversity and describe species richness, respectively. Soil samples were analyzed for pH and nutrients. The interaction effect of logging and grazing was significant(p≤0.001) only on species diversity. Relative to ungrazed areas, species diversity was significantly higher(0.01≤p≤0.05) in medium grazed gaps. Under grazed conditions, soil P was negatively correlated with gap size and species diversity. While species diversity was positivelycorrelated(0.01≤p≤0.05) with soil N in grazed plots species richness was positively correlated(0.001≤p≤0.01) with soil N in ungrazed plots. Relative density of Yushania microphylla and Carex nubigena were higher under ungrazed conditions. Our study suggests that the combined effect of cattle grazing and logging results in higher species diversity of understory vegetation in medium and grazed gaps in mixed conifer forests of Bhutan,whereas increase or decrease in relative density of major species is determined primarily by the independent effects of grazing and logging. From management perspective, forest managers must refrain from creating large gaps to avoid loss of nutrients(mainly P and N), which may eventually affect tree regeneration. Managers intending to maintain understory vegetation diversity must consider the combined effects of grazing and logging, ensuring low to moderate grazing pressure.

Studies of Structural and Thermodynamic Properties for Polychlorinated Thianthrenes by Density Functional Theory

The structural and thermodynamic （PCTAs） in the ideal gas state at 298.15 K and 1.013 properties of 75 polychlorinated thianthrenes ×10^5 Pa have been calculated at the B3LYP/6- 31G＊ level using Gaussian 98 program. Based on the output data of Gaussian, the isodesmic reactions were designed to calculate standard enthalpy of formation （△fH^θ） and standard free energy of formation （△fH^θ） of PCTAs congeners. The relations of these thermodynamic parameters with the number and position of C1 atom substitution （Npcs） were discussed, and it was found that there exists high correlation between thermodynamic parameters （total energy （TE）, zero-point vibrational energy （ZPE）, thermal correction to energy （Eth）, heat capacity at constant volume （Cv^θ）, entropy （S^θ）, enthalpy （H^θ）, free energy （G^θ）, standard enthalpies of formation （△fH^θ） and standard Gibbs energies of formation （△fG^θ）） and Npcs. On the basis of the relative magnitude of their △fG^θ, the order of relative stability of PCTA congeners was theoretically proposed. In addition, the correlations between structural parameters and Npcs were also discussed. The good correlations were found between molecular average polarizability （α）, energy of the highest occupied molecular orbital （EHOMO）, molecular volume （Vm） and Npcs, and all R^2 values are larger than 0.95. Moreover, it was supposed that the isomer groups with higher toxicity should be Tri-CTA and TCTA.