Physical Layer Properties Research Articles

Understanding the Limiting Factors of Solvent-Annealed Small-Molecule Bulk-Heterojunction Organic Solar Cells from a Chemical Perspective.

A detailed account of the limiting factors of solvent-annealed bulk-heterojunction small-molecule organic solar cells is given. This account is based on the extensive characterisation of solar cell devices made from a library of five diketopyrolopyrole (DPP) donor dyes. Their chemical structure is designed in such a way as to provide insights into the energetics of solar cell active layer micro-structure formation. Numerous chemical and physical properties of the active layers are assessed and inter-related such as light absorption, molecular packing in the solid state, crystal-forming properties in thin films, charge carrier mobility and charge carrier recombination kinetics. A myriad of characterisation techniques are used such as UV/Vis absorption spectroscopy, photoluminescence spectroscopy, XRD, AFM and photo-induced transient measurements, which provide information on the optical properties of the active layers, morphology and recombination kinetics. Consequently, a mechanism for the solvent-vapour-annealing-assisted formation of crystalline domains of donor molecules in the active layer is proposed, and the micro-structural features are related to the J-V characteristics of the devices. According to this model, the crystalline phase in which the donor crystallise in the active layer is the key determinant to direct the formation of the micro-structure.

Seismic vulnerability indices of ground for Değirmendere (Kocaeli Province, Turkey)

It is well known that the mechanical and physical properties of subsoil layers as well as poor construction practices play an important role in determining the level of structural damage sustained from earthquakes. Thus, sufficient knowledge of these properties is essential for estimating the weak points of a region. The ground vulnerability index (Kg), an indicator of the weak points of a region, also has a substantial importance role in mitigating earthquake hazards in multidisciplinary studies. In this context, we have used engineering basement shear wave velocity (vs30), fundamental frequencies and peak amplitude values of the horizontal-to-vertical ratio (H/V) to calculate Kg values for the study area (Kocaeli Province, Turkey). Structural damage was investigated after the August 17, 1999 Kocaeli (Mw = 7.4) Earthquake and compared with the calculated Kg values. The results indicate that the Kg values decrease towards the southern part of the study area, which is in good agreement with damage distribution from this earthquake. Kg values of >10 appear to be indicative of the most vulnerable areas in the study area. Structures built along the coastlines in Degirmendere area were the mostly severely damaged or collapsed entirely; we found that the subsoil beneath them have high Kg values of between 10 and 25 In contrast, Kg values in the southern districts, which sustained little or no damage, are relatively low (Kg < 10). In our study, the Kg values and soil types showed good agreement. Potential vulnerable areas also have poor subsoil conditions. Therefore, it could be important to consider these results for the future planning and designing of urban areas. These results could also be used as a rapid way to detect potential vulnerable areas before the occurrence of a destructive earthquake.

Multilayer system of films heated from above

The paper deals with the development of convective flows in a complex system of thin liquid layers occurring under the effect of thermal load. To study this process a mathematical model which is based on the decomposition of complex problem into unitary elements (modules) with some set of rules allowing their linkage with each other was constructed. Each module represents a monotypic local model. The fluid flow and heat transfer in each of these modules are described by the Navier-Stokes and thermal conductivity equations. The boundary conditions required to solve these systems of equations are represented explicitly and written in the form of conservation laws. The numerical analysis of effect of thermal load on the characteristics of the liquid layers movement depending on the Marangoni number is carried out. It is shown that physical and thermophysical properties of liquid layers play the decisive role. It is exactly they control the convective flows in layers and determine the position and shape of interfaces. The results of model problem solutions are presented.

Impacts of inhomogeneous clamping force on local performance and liquid water formation in polymer electrolyte fuel cells

A two dimensional, half-cell, non-isothermal, multi-phase model of a polymer electrolyte fuel cell (PEFC) is developed. The model accounts for the acting clamping force on the cell with accompanying effects on gas transport properties and contact resistances. Spatial variations of anisotropic structural and physical properties of gas diffusion layers (GDLs) in both in-plane and through-plane directions are considered. Designed mechanistic model is compared and validated with the experimental data for voltage-current characteristics and channel-rib current density distribution for the first time. Significant changes are observed in local gas and water concentrations as well as current density profiles with respect to cell compression and humidity ratios of entrant gases. Compression exacerbates the liquid saturation under the rib in consequence of porosity and permeability reduction. Under compression, phase change rate increases in the cell; degree of supersaturation under the channel escalates leading to higher condensation rate while degree of undersaturation under the rib increases leading to higher evaporation rate.

Influence of Na in Cu2SnS3 film on its physical properties and photovoltaic performances

Cu2SnS3 (CTS) is the promising absorber of thin-film solar cell due to earth-abandant and non-toxic element. Influence of sodium (Na) on physical properties of CTS layers is investigated. In this work, CTS films with different Na concentrations are fabricated by sulfurizations of NaF/Cu/SnS2 and Cu/SnS2 stacked precursors on both soda-lime glass (SLG) and quartz substrates. The Na from NaF precursor layer and SLG substrate is introduced into CTS films. It is demonstrated that Na in forms of NaxCuSnS3 (x: 0.5–1.0) and Na2S is segregated in the large grain regions of CTS films. The crystal grains are significantly enlarged by Na addition into CTS films. As a result, the carrier lifetime, examined by time-resolved photoluminescence, is enhanced. From Raman scattering measurement, CTS films possess the peaks of monoclinic CTS structure. In addition, Cu2Sn3S7 and NaxCuSnS3 peaks are clearly observed in CTS films with high Na content. Finally, conversion efficiency of CTS thin-film solar cell is strongly enhanced from 0.61 (without Na addition) to 2.01% (with Na addition), mainly attributed to the increases in open-circuit voltage and fill factor through the decrease in carrier recombination.

Low-Temperature Synthesis of Vertically Align ZnO Layer on ITO Glass: The Role of Seed Layer and Hydrothermal Process

ZnO thin layer has a broad potential application in optoelectronic devices. In the present study, vertically align ZnO layers on ITO glass were synthesized using wet chemical method. The seed layers were prepared using electrodeposition method at 3°C. After that, the growing process was carried out using chemical bath deposition (CBD) at 90°C. To improve the structural property of the ZnO layers, hydrothermal technique was used subsequently. Results showed that seeding layer has a great influence on the physical properties of the ZnO layers. Moreover, hydrothermal process conducted after the ZnO growth can enhance the morphological property of the layers. From the experiments, it is found that the ZnO layers has diameter of ∼60 nm with increasing thickness from ∼0.8 to 1.2 μm and band-gap energies of ∼3.2 eV.

Mixing and trapping of dissolved CO2 in deep geologic formations with shale layers

For dissolution trapping, the spatial variability of the geologic properties of naturally complex storage formations can significantly impact flow patterns and storage mechanisms of dissolved CO2. The significance of diffusive mixing that occurs in low permeability layers embedded between relatively higher permeability materials was highlighted by Agartan et al. (2015) using a highly controlled laboratory experimental study on trapping of dissolved CO2 in multilayered systems. In this paper, we present a numerical modeling study on the impacts of low permeability layers on flow and storage of dissolved CO2 in realistic field-scale settings. The simulator of variable-density flow used in this study was first verified using the experimental data in Agartan et al. (2015) to capture the observed processes. The simulator was then applied to a synthetic, field-scale multilayered system, with 19 sensitivity cases having variable permeability and thickness of the shale layers as well as the source strength and geometry of the source zone of dissolved CO2. Simulation results showed that the presence of continuous shale layers in the storage system disrupts the convective mixing by enhancing lateral spreading of dissolved CO2 in sandstone layers and retarding the vertical mixing of dissolved CO2. The effectiveness of trapping of dissolved CO2 depends on the physical properties of the shale layers and configurations of the source zone. The comparison to homogeneous cases with effective vertical permeability shows that it is important to capture these continuous thin shale layers in a storage formation and include them in the models to enhance dissolution trapping.

Monolayer alkali and transition-metal monoxides: MgO, CaO, MnO, and NiO

Two-dimensional crystals with strong interactions between layers has attracted increasing attention in recent years in a variety of fields. In particular, the growth of a single layer of oxide materials (e.g., MgO, CaO, NiO, and MnO) over metallic substrates were found to display different physical properties than their bulk. In this study, we report on the physical properties of a single layer of metallic oxide materials and compare their properties with their bulk and other two-dimensional (2D) crystals. We found that the planar structure of metallic monoxides are unstable whereas the buckled structures are thermodynamically stable. Also, the 2D-MnO and NiO exhibit different magnetic (ferromagnetic) and optical properties than their bulk, whereas band-gap energy and linear stiffness are found to be decreasing from NiO to MgO. Our findings provide insight into oxide thin-film technology applications.

Diamond-like carbon layers modified by ion bombardment during growth and researched by Resonant Ultrasound Spectroscopy

Biocompatible Diamond-Like Carbon (DLC) films were prepared by Pulsed Laser Deposition technique using the laser energy density of 10Jcm−2 on the graphite target. The surface of the grown film was modified during the deposition by bombardment with argon, xenon, nitrogen or oxygen ions. The ion energy (up to 150eV) was changed by gun voltage and by ionic current. The films with high and low diamond/graphite content were prepared. Physical and mechanical properties of biocompatible DLC thin layers prepared by hybrid laser technology were studied. The composition of layers and the content trace elements were determined by the methods of Rutherford Backscattering Spectrometry and Particle Induced X-ray Emission. The content of sp2 and sp3 bonds was measured using X-ray Photoelectron Spectroscopy. For different energy of argon and oxygen ions the maximum of sp3 bonds content was found (83.63% of sp3 bonds for argon ions). All films were smooth, which was confirmed by profilometry and Atomic Force Microscopy measurements. Maximum roughness Ra and RMS was did not exceed 1nm. The Younǵs and shear moduli were studied by Resonant Ultrasound Spectroscopy. The Young’s Modulus attained the value of 601GPa and the shear Modulus attained the value of 253GPa at the energy of 30eV of Ar ions. The influence of ion bombardment on DLC film properties is discussed.

Weakly doped InP layers prepared by liquid phase epitaxy using a modulated cooling rate

Epitaxial structures based on InP are widely used to manufacture a number of devices such as microwave transistors, light-emitting diodes, lasers and Gunn diodes. However, their temporary instability caused by heterogeneity of resistivity along the layer thickness and the influence of various external or internal factors prompts the need for the development of a new reliable technology for their preparation. Weak doping by Yb, Al and Sn together with modulation of the cooling rate applied to prepare InP epitaxial layers is suggested to be adopted within the liquid phase epitaxy (LPE) method. The experimental results confirm the optimized conditions created to get a uniform electron concentration in the active n-InP layer. A sharp profile of electron concentration in the n+-InP(substrate)/n-InP/n+-InP epitaxial structure was observed experimentally at the proposed modulated cooling rate of 0.3 °С–1.5 °С min−1. The proposed technological method can be used to control the electrical and physical properties of InP epitaxial layers to be used in Gunn diodes.

Optical permittivity, thermo-optical and electrical properties of nickel oxide nanostructures with heavy cupper doping

In this research, physical properties of nickel oxide nano-structured layers doped with various amount of Cu atoms (20–60 at.%) is studied using spray pyrolysis method on the glass substrate. The FESEM images show formations of nanostructures of about 20–60 nm and the XRD patterns show layers have a polycrystalline cubic structure nature with (111) as the preferred direction that its intensity reduces as the doping density increases. Analyzing transmittance UV. Vis spectra shows the variations of optical band gap of the samples are due to occurrence of doping atoms and quantum confined effects. Optical permittivity of different doped films have been compared using new numerical method and show the prominent effect of doping percent to real and imaginary parts of electrical permittivity. Also Hall effect results shows that Cu atoms substituted by Ni atoms sites play as acceptor atoms in the crystalline lattice. Finally, thermo-optical properties of the films have been studied using Nd–YAG laser illumination.

Heterogeneity analysis of geophysical well-log data using Hilbert–Huang transform

Geophysical well-log data manifest nonlinear behaviour of their respective physical properties of the subsurface layers as a function of depth. Therefore, nonlinear data analysis techniques must be used to understand and characterize the nature of the subsurface lithologies, vis-à-vis their degree of heterogeneity. One such nonlinear technique is the fully data adaptive Hilbert–Huang Transform (HHT), which constitutes two independent techniques, namely, the empirical mode decomposition technique (EMDT) and the Hilbert spectral analysis (HSA). While EMDT facilitates to decompose the well-log data into oscillatory signals of different wavelengths called intrinsic mode functions (IMFs), which represent different frequency characteristics of the signal and which in turn helps to calculate the degree of heterogeneity in the subsurface, the HSA facilitates to determine the instantaneous amplitudes and frequencies of the IMFs, which can be used to characterize the heterogeneity in the signals. In this study, HHT has been applied to gamma-ray log of the thickest limestone reservoir zones of two different wells: Well B and Well C, located in the western offshore basin of India to determine the respective IMFs. The estimated instantaneous amplitudes and frequencies of the derived IMFs by HSA qualitatively suggested well C to be more heterogeneous than well B. By establishing a relationship between the IMF number (m) and its mean wavelength (Im), a heterogeneity index (ρ) associated with subsurface layers was determined using Im=kρm, where ‘k’ is a constant. ρ bears an inverse relation with the heterogeneity of the subsurface. The estimated ρ values confirm our observations from HSA. We attribute the higher degree of heterogeneity in Well C to high average shale volume in the limestone reservoir zone in Well C than in Well B. Interpretation of the results together with those of the heterogeneity analysis of the gas zone in limestone reservoir of Well C is made by comparing with the results of multifractal analysis of the same data carried out earlier.

Mimicking Cortex Convolutions Through the Wrinkling of Growing Soft Bilayers

Brain convolutions are a specificity of mammals. Varying in intensity according to the animal species, it is measured by an index called the gyrification index, ratio between the effective surface of the cortex compared to its apparent surface. Its value is close to 1 for rodents (smooth brain), 2.6 for newborns and 5 for dolphins. For humans, any significant deviation is a signature of a pathology occurring in fetal life, which can be detected now by magnetic resonance imaging (MRI). We propose a simple model of growth for a bilayer made of the grey and white matter, the grey matter being in cortical position. We analytically solved the neo-Hookean approximation in the short and large wavelength limits. When the upper layer is softer than the bottom layer, the selection mechanism is shown to be dominated by the physical properties of the upper layer. When the anisotropy favors the growth tangentially as for the human brain, it decreases the threshold value for gyri formation. The gyrification index is predicted by a post-buckling analysis and compared with experimental data. We also discuss some pathologies in the model framework.

Stabilization of peat soil using locally admixture

Peat has considerable negative geotechnical properties such as high water content, low shear strength, high organic matter, and low bearing capacity and consequently a significant severing high compressibility takes place that makes it as one of the most difficult soils for constructing structures over its natural state. Because of these geotechnical problems of peat soil, improvement mechanism is so essential when the peat soil exists to deal with it as a soil foundation. In this paper, the physical and mechanical properties of the peat are discussed. Also, the two creative mixtures were prepared to study their effect on the properties of peat and to what extent can these new mixtures improve both the physical and mechanical properties of peat layers to bear stresses as the soil foundation, the first one consisted of clayey diatomite which is widespread in Egypt, calcium carbonate, lime and water. On the other hand, the prepared second mixture has the same ingredients of the first one except to replace the clayey diatomite by the cement. For both mixtures two systems of cubes were prepared, and peat was added to the two prepared mixtures. Then the all cubes were submerged in clean water, and also in sewage water for forty-five days for the sake of studying their durability against submergence and environmental changes, and the cubes’ resistances were measured. The obtained results in this study were compared by other currently used mixtures for stabilizing peat soils to date for focusing clearly on the performance magnitude of this study.

Determination of the Physical Properties of Near Surface Layers of Omerulu Area, Nigeria, Using Seismic Refraction Method

Seismic refraction method is a geophysical technique used to study physical properties of the subsurface such as layer thicknesses, travel times and velocities of seismic signals through the layers. The process of turning seismic refraction data to useful information involves use of first arrival times and offsets. In this study, the near surface investigation of the physical properties of the unconsolidated and consolidated layers was carried out in Omerelu, Rivers State of Nigeria. Omerelu lies between latitude 050 08’N and 050 13’N and longitude 060 51’E and 060 58’E. Previous investigations were based on refection method in which the near surface effect caused misalignment in the deeper horizons observed in the final stack of the reflection data. This problem was solved by running a seismic refraction survey over the area. The study involved identification of points at which data would be acquired to give a good overview of the area under consideration. Twelve sampling points were picked with a grid of approximately 4 × 4 km. A 100 m line with two source points at each end was cleared at each data acquisition point after which the coordinates were taken using Leica Total station (TC 1203 survey equipment). Seismic signals were recorded using OYO McSeis 160M coupled with a 12-geophone harness along with a blasting unit. Upsphere processing software was used to plot time - offset graphs to determine the velocities of the unconsolidated and consolidated layers. The intercept times were also graphically obtained and used to determine the thickness of the unconsolidated layer. Results show that the thickness of unconsolidated/weathered layer in the study area varies between 12.25 and 13.60 m, while the velocities of the unconsolidated and the consolidated layers vary between 500 – 550 m/s and 1790 – 1875 m/s respectively. The results obtained when applied to the reflection data, were able to resolve the static problems; thereby increasing and improving the quality of data available on the lithology of the study area.

Study of Screw Pump Stator and Rotor Working Capacity to Increase the Output

For pumping fluid with high viscosity and high content of mechanical impurities and the installations of the screw pumps that allow us to control and regulate the technological parameters of production gas are used. The research of efficiency of screw pump revealed that the failure of the cage (stator) and wear of the stator – rotor, accompanied by a decrease in performanceThe wear of the pair of stator and rotor, extended condition normal operation of the screw pump are studied, taking into account the orientation of the working screw, the effect of inertial and hydraulic forces, physical and mechanical properties of the contact layers. This considerably improves the durability and manufacturability of the screw pumps.

PREPARATION AND STUDY OF CERAMIC MEMBRANE REACTOR FOR HYDROGEN SULFIDE CATALYTIC DECOMPOSITION

The paper studies a number of alumina ceramic membrane catalysts of various design and composition for high temperature H 2 S decomposition. The design of two types of catalytic membranes used consists of sandwich-like structure including (1) “catalytic layer”/”membrane support”/”membrane layer” and (2) “catalytic layer”/”membrane support”/”intermediate layer”/”membrane layer”. The paper describes: the physical and chemical properties (pore structure, specific surface area and phase composition) of membrane supports and membrane layers calcined at different temperatures; the methods of various composition membrane reactors preparation; the data on membrane permeability on H 2 and H 2 S; the test results of prepared membranes in the reaction of H 2 S decomposition. The introduction of La 2 O 3 modifying additions in a membrane layer is shown to lead to the increase of thermal stability of a membrane. The effective diameter of pores of membrane layer having 5%La 2 O 3 -γ-Al 2 O 3 composition and calcined at 900ºC is three times lower than of the unmodified γ-Al 2 O 3 . The presence of pure γ-Al 2 O 3 phase in the modified membrane layer is observed while the δ-Al 2 O 3 phase is formed in the unmodified sample. The pore structure and the thickness of the membrane layer are demonstrated to significantly influence permeability of H 2 and H 2 S. There has been observed a significant improvement of the catalytic activity in the H 2 S decomposition reaction compared with a granulated catalyst because the separation coefficient of H 2 /H 2 S is higher than 2.5. It has been determined that the introduction an intermediate layer, which has different effective pore diameter in comparison with the membrane layer, to the membrane composition increases significantly the H 2 S conversion. The membrane reactor consisting of the membrane layer (6 m thickness, pore diameter 45 Å) and the intermediate layer (9 m thickness, pore diameter 110 Å) has been found to exhibit maximal efficiency in the H 2 S decomposition reaction. The H 2 S conversion reaches 65% at 900ºC on the membrane catalyst of optimal composition.

紫色土坡耕地土壤属性差异对耕层土壤质量的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 紫色土坡耕地土壤属性差异对耕层土壤质量的影响 DOI: 10.5846/stxb201607181460 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 公益性行业（农业）科研专项（201503119-01-01）；重庆市水利局项目（2016）。 Effect of different soil properties on plow-layer soil quality of sloping farmland in purple hilly areas Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:坡耕地是一个区域最易发生水土流失的土地利用类型，其严重的水土流失、面源污染和耕层退化现象直接威胁着坡耕地持续利用以及当地粮食安全、生态安全；耕层土壤质量对自然因素和人为耕作活动的影响较为敏感。以南方3个地点紫色土坡耕地耕层土壤质量为研究对象，从土壤属性角度，对比分析了重庆合川、江西兴国、云南楚雄不同耕层垂直深度土壤养分特征、土壤物理性质、土壤水库特征、耕作性能差异性及其形成原因。结果表明：（1）坡耕地耕层土壤有机质表现为云南楚雄（28.80 g/kg）>江西兴国（9.03 g/kg）>重庆合川（8.80 g/kg）；除全钾含量外，土壤全量养分和速效养分的含量表现为云南楚雄 > 江西兴国 > 重庆合川；坡耕地耕层速效养分垂直分布变化规律基本一致，主要表现为土壤速效养分主要在0-20 cm土层富集，而20-40 cm和40-60 cm土层无显著差异。（2）不同地点紫色土坡耕地耕层土壤物理性质差异明显，以重庆合川坡耕地土壤物理质量最差，表现为土壤砂粒含量 > 60 %、土壤容重最大（1.43 g/cm3）、土壤总孔隙度（45.97%）和毛管孔隙度（34.36%）最小；从坡耕地耕层土壤物理性质垂直变化特征看，耕作层（0-20 cm）优于心土层（20-40 cm）和底土层（40-60 cm）。（3）紫色土坡耕地耕层土壤初始入渗率以江西兴国坡耕地耕层最大（0.32 mm/min），而以重庆合川坡耕地耕层最小（0.19 mm/min）；土壤稳定入渗率和平均入渗率均表现为云南楚雄 > 重庆合川 > 江西兴国；坡耕地耕层土壤最大有效库容以云南楚雄最好（873.311 t/hm2），说明云南楚雄紫色土坡耕地耕层土壤具有较好的抵御季节性干旱能力；不同地点坡耕地耕层土壤总库容、死库容、兴利库容、滞洪库容、最大有效库容在垂直方向变化表现为耕作层（0-20 cm）大于心土层（20-40 cm）和底土层（40-60 cm）。（4）不同地点紫色土坡耕地耕层土壤抗剪强度和贯入阻力均呈现出相同变化规律，土壤抗剪强度表现为重庆合川（15.39 kg/cm2）>云南楚雄（14.74 kg/cm2）> 江西兴国（10.66 kg/cm2），而土壤贯入阻力值为重庆合川（424.83 kPa）> 云南楚雄（252.50 kPa）> 江西兴国（188.87 kPa），这种土壤力学性能的变化说明重庆合川紫色土坡耕地耕层土壤具有较好抵抗剪切破坏的能力和较大耕作阻力。上述研究结果可为不同地点紫色土坡耕地耕层土壤质量诊断、坡耕地合理耕层评价提供理论依据和数据支持。 Abstract:As the most easily eroded land-use type, severe soil degradation of the plow layer (as a shallow soil layer), deterioration of soil properties, and gravel process, could restrict the sustainable utilization of slope farmland, which also directly threatens local food security and ecological security. Plow-layer soil quality is highly sensitive to both natural factors and artificial farming tillage. Taking the plow-layer soil quality of three slope farmlands in the southern purple hilly area (Hechuan-Chongqing, Xingguo-jiangxi, and Chuxiong-Yunnan) as examples, this study mainly analyzed the differences in soil physical properties, soil reservoir characteristics, and soil nutrient characteristics of slope farmlands, and their vertical distribution characteristics, from the perspective of soil properties, so did the forming causes at the same time. The results indicated the following. (1) The soil organic matter of the plow-layer in the three locations in decreasing order was as follows: Chuxiong-Yunnan (28.80 g/kg) > Xingguo-jiangxi (9.03 g/kg) > Hechuan-Chongqing (8.80 g/kg). With the exception of total soil potassium content, other contents such as total soil nutrients and available soil nutrients, could be arranged in the following order: Chuxiong-Yunnan > Hechuan-Chongqing > Xingguo-jiangxi. The vertical characteristics of available soil nutrients in the plow-layer of slope farmland showed the same distribution, being mainly concentrated in the 0-20-cm soil layer. However, there were no significant differences between the 20-40-cm soil layer and the 40-60-cm soil layer. (2) The soil physical properties of the plow-layer of slope farmlands among the three purple hilly locations showed significant differences. The soil physical quality of the plow-layer in Hechuan-Chongqing was the worst, with the characteristic of soil sand content > 60%, maximum soil bulk density of 1.43 g/cm3, minimum soil total porosity of 45.97%, and capillary porosity of 34.36%. From the viewpoint of the plow-layer vertical characteristics of slope farmland, the soil physical properties of the tillage layer (0-20 cm) were better than those of the subsoil (20-40 cm) and bottom layer (40-60 cm). (3) The initial soil infiltration rate of the plow-layer in the Xingguo-jiangxi slope farmland was the largest (0.32 mm/min), and the initial soil infiltration rate in Hechuan-Chongqing plow-layer was the lowest (0.19 mm/min). The soil infiltration rate and the average soil infiltration rate both showed the same order of Chuxiong-Yunnan > Xingguo-jiangxi > Hechuan-Chongqing. The soil maximum effective capacity of the plow-layer in Chuxiong-Yunnan slope farmland was the best (873.311 t/hm2), which indicated that such plow-layers of slope farmland have better resistance to seasonal drought. Plow-layer vertical characteristics, such as the total storage capacity, dead storage capacity, active storage capacity, flood detention storage capacity, and maximum effective capacity, all showed the same order: tillage layer (0-20 cm) > subsoil layer (20-40 cm) > bottom layer (40-60 cm). (4) The soil shear strength and the soil penetration resistance of the plow-layer among the three slope farmland locations showed the same regular changes. The soil shear strengths of the plow-layer were Hechuan-Chongqing (15.39 kg/cm2) > Chuxiong-Yunnan (14.74 kg/cm2) > Xingguo-jiangxi (10.66 kg/cm2), whereas the soil penetration resistances of the plow-layer were Hechuan-Chongqing (424.83 kPa) > Chuxiong-Yunnan (252.50 kPa) > Xingguo-jiangxi (188.87 kPa), which indicated that the plow-layer soil of slope farmland in the Hechuan-Chongqing purple hilly area has better resistance to shear stress and greater resistance to farming tillage. These results could provide a theoretical basis and supporting data not only for soil quality diagnosis but also for rational plow-layer evaluation for slope farmlands in different purple hilly areas. 参考文献 相似文献 引证文献

An optimal spectrum-efficient routing protocol for multi-hop 802.11s networks

Routing in multi-hop wireless networks is a vital aspect to sustain acceptable performance. Standard routing schemes, such as ad-hoc on-demand vector routing (AODV) and dynamic source routing (DSR), use the number of hops from source to destination as the routing metric without paying attention to the physical layer properties of the wireless links. This paper, however, presents a new routing protocol for finding the path with maximum end-to-end spectral efficiency in real-world IEEE 802.11s networks. In contrast to previous work, our protocol fully considers the physical layer characteristics of the wireless channel, the interaction between network layer route computation and medium access control (MAC) contention resolution, in addition to all necessary information gathering and exchange performed by the wireless nodes. Furthermore, we provide a full NS-2 simulation comparison between spectrum-efficient routing and standard routing protocols using various performance metrics such as end-to-end data rate, delay, packet loss and overhead time.

Chemical and physical properties of an anthropogenic dark earth soil from Bragança, Para, Eastern Amazon

ABSTRACT Although anthropogenic dark earth (ADE) is generally found in non-floodable land, it also occurs on floodplains but, there is no information about the chemical and physical characteristics of ADE in this environment. In this study, we propose to check the hypothesis that a Gleysol, classified as ADE, presents improved chemical and physical conditions than an adjacent soil, no anthropogenic. Thus, the objective of this study was to characterize the chemical and physical properties of the top layer of two ADE profiles in a Gleysol and compare them with an adjacent soil. Samples were taken from two areas classified as ADE in Bragança, Pará State, Brazil, at the "Jabuti" archaeological site, and from an adjacent non-anthropogenic site. Disturbed and undisturbed soil samples were collected at the soil depth of 0.05-0.10 m for chemical (pH, potential acidity, exchangeable cations, and soil organic carbon) and physical (soil particle size distribution, particles density, water retention curve, total porosity, microporosity, macroporosity, and bulk density) analysis. The two areas of ADE in a Gleysol, showed improved soil chemical properties compared to the adjacent soil, particularly in relation to phosphorus and calcium levels that contributed to higher cation exchange capacity which, in turn, was positively related to organic carbon content. Changes in soil physical properties were less noticeable but both areas of ADE presented higher water retention capacity, particularly at low tension. The improved conditions of the ADE soil under Gleysols shows that these areas are adequate for soil cultivation, especially with plants adapted to floodplain.