The effect of frozen soil layer thickness on thermal emission at the wavelengths 3.6–11 cm

The results of experimental investigation of temporal dynamics of radiobrightness temperature at the wavelengths 3.6, 5, and 11 cm in the course of frost penetration and thawing are presented for the soils with different humus content. Using the method of simulating emission from a horizontally stratified medium, it is shown that radiobrightness temperature variation is related to changes in the frozen soil layer thickness. It is noted that that dielectric permittivity of the frozen layer at the temperatures around 0 °C is controlled by non-frozen bound water, whose content depends on the soil type. It is also underlined that in certain cases proper interpretation of the experimental data requires inclusion of the soil moisture motion towards the cold front into consideration. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 5–10, September, 2006.     

A method for developing a moist-soil dielectric spectroscopic database in the microwave band

The method considered in this paper for developing a spectroscopic database of moist-soil dielectric properties in the microwave band is based on the generalized refractive mixing dielectric model proposed in [1, 2]. This model makes it possible to derive the Debye parameters of bound and free soil water and also the maximum bound-water fraction value for different types of soil by using dielectric-constant (DC) and loss-factor (LF) measurement data as functions of the volumetric moisture content. A set of these parameters, complemented with DC and LF values for dry soil, permits one to calculate the mentioned characteristics for moist soil in the entire microwave band. In this paper, the method developed in [1, 2] is used for deriving the spectroscopic parameters of moist soils on the basis of the DC and LF data measured in __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 4, pp. 339–349, April 2007.     

A simple model of Cs-137 profile to estimate soil redistribution in cultivated stony soils

A main issue in soil erosion studies is to calibrate ¹³⁷Cs data to provide satisfactory estimates of erosion and deposition rates. The cultivation on steep slopes in some areas of the South Central Pyrenees results in serious affections to soils due to water erosion that mobilizes soil particles down slope. In the region, the intensive soil use including deforestation, overgrazing and extensive agriculture during the last centuries together with some characteristics of the soils such as poor development, thin soil profiles and high stone contents make them prone to erosion. A model based on ¹³⁷Cs profile is proposed to calculate erosion or sedimentation rates in these cultivated soils. The model uses parameters such as the volume of the fine fraction of the soils and the depth of cultivation calculated from the values obtained just from the soil sampling. Using a computer program the annual deposit of ¹³⁷Cs is simulated for an erosion or deposition rate of soil. To test the model, ¹³⁷Cs profiles of cultivated soils were collected at sampling sites located on temperate slopes in the Sierra de la Carrodilla (South Pyrenees) and experimental results were simulated with the model. The simulation results of the model were consistent with the experimental results of ¹³⁷Cs concentrations and inventories. The model offers a potential to describe the soil redistribution in stony soils and estimates of erosion and deposition rates can be calculated easily for a range of the most common soils found in Mediterranean environments.     

Tightly bound soil water introduces isotopic memory effects on mobile and extractable soil water pools

Cryogenic vacuum extraction is the well-established method of extracting water from soil for isotopic analyses of waters moving through the soil–plant–atmosphere continuum. We investigate if soils can alter the isotopic composition of water through isotope memory effects, and determined which mechanisms are responsible for it. Soils with differing physicochemical properties were re-wetted with reference water and subsequently extracted by cryogenic water distillation. Results suggest some reference waters bind tightly to the soil and not all of this tightly bound water is removed during cryogenic vacuum extraction. Kinetic isotopic fractionation occurring when reference water binds to the soil is likely responsible for the ¹⁸O-depletion of re-extracted reference water, suggesting an enrichment of the tightly bound soil water pool. Further re-wetting of cryogenically extracted soils indicates an isotopic memory effect of tightly bound soil water on water added to the soil. The data suggest tightly bound soil water can influence the isotopic composition of mobile soil water. Findings show that soils influence the isotope composition of soil water by (i) kinetic fractionation when water is bound to the soil and (ii) equilibrium fractionation between different soil water pools. These findings could be relevant for plant water uptake investigations and complicate ecohydrological and paleohydrological studies.     

Thermal Effects of Microwave Energy in Agricultural Soil Radiation

The thermal treatment by millimeter waves for the soil disinfection can be one possible alternative to chemical treatments. This physical method is based on incrementing the soil temperature and its pathogens irradiating with high frequency electromagnetic waves. So the previous knowledge of the temperature distribution in the irradiated soil is essential for achieving an effective bad microorganism and weed seeds elimination. This report analyse the heating kinetic and spatial distribution of the maximum temperatures reached by the soil. It is presented a mathematic model about how are distributed the reached temperatures in the depth of the irradiated soil. This model concludes that when an orchard soil is irradiated superficially by microwaves, the microwaves have a big attenuation due to the soil dielectric properties and the water located in the pores of the most superficial layer. This fact causes a shield effect blocking the waves penetration in few centimetres. The heating by radiation is reduced to the superficial layer. The heating propagation in the depth is occurred by conduction following the Fourier equations.     

The spalling of overgrowths during experimental freeze-thaw of a quartz sandstone as a mechanism of quartz silt production

The experimental frost weathering of a quartz sandstone is being carried out as part of a series of laboratory simulations to investigate geomorphic mechanisms capable of producing loess-sized quartz silt. The preliminary results are reported in this paper. Frost weathering simulations involved two different temperature regimes: (a) −5°C–+15°C, and (b) −12°C–+15°C. Debris production was observed for both temperature regimes with the blocks subjected to the more intense freezing regime experiencing the most disintegration. Scanning electron microscopic (SEM) examination and particle size analysis revealed that the debris produced by both these experiments included a significant silt sized fraction. Further SEM examinations of this debris demonstrated the presence of silt sized fragments of quartz overgrowths among the debris. It is suggested that overgrowth detachment occurs during frost weathering by either the penetration into and subsequent freezing of water in the gaps between overgrowths and host grains, or pressures applied to the outer surfaces of overgrowths during frost cycles causes them to collapse onto the underlying grain.     

土介质对低速弹丸的抗侵彻性能实验研究

 通过低速条件下弹丸对硬土、中硬土和中软土不同土介质侵彻性能的实验研究,得到了弹丸对土介质垂直侵彻的弹道特点和不同弹丸速度对不同性能参数土介质的侵彻深度,拟合得到了不同土介质中侵彻深度随弹丸动压增加呈线性增加的无量纲关系式;基于低速弹丸对不同土介质具有不同侵彻性能的实验研究方法,可有效标定不同土介质抗侵彻性能和弹丸侵彻不同土介质性能;通过实验数据与Young侵彻公式计算结果的比较分析,验证了Young公式在侵彻深度小于弹丸直径3倍时的有效性。     

Water–heat migration and frost-heave behavior of a saturated silty clay with a water supply

In this study, a large-scale one-directional freezing experiment with water supply was performed to investigate the water–heat migration and frost-heave behavior of the saturated silty clay. The results indicate that the temperature gradient is larger in the frozen zone than that in the unfrozen zone because of the heat release of the supplied water and its water–ice phase change during the freezing process. Furthermore, the different parts of the total frost heave are evaluated, respectively, and it is also found that the frost heave can be reduced if the advance rate of the freezing front is effectively controlled even if external water is sufficient.     

反射光谱特征的土壤分类模型

土壤反射光谱综合反映了土壤的理化性质和内部结构,高光谱遥感已被用于基于土壤反射光谱特性的土壤分类。已有研究一般利用土壤反射光谱一阶微分主成分作为输入量进行光谱分类模型构建,但主成分数据缺乏物理意义,且缺乏对比性、适用范围也有限。与反射率一阶微分数据相比,基于去包络线提取具有明确物理意义的特征参数,能够提高土壤分类的精度,并寻找到一种高精度土壤分类模型。选取吉林省农安县的四种典型土壤（风砂土、草甸土、黑土、黑钙土）,将采集后的土壤样本进行风干、研磨、过2 mm筛处理,采用ASD FiledSpec®3便携式光谱仪对处理后的土壤样本的可见光近红外光谱区进行测试,从而获得土壤样本的光谱数据。对光谱数据进行九点平滑、10 nm重采样处理进行降噪,将处理后的数据分别进行一阶微分主成分以及去包络线处理。利用土壤样本的去包络线提取光谱特征参数。以一阶微分主成分数据和光谱特征参数为输入量分别代入Logistic聚类模型（LR）、人工神经网络聚类模型（ANN）、K-均值聚类模型（K-means）。首先明确了不同土类之间的反射光谱曲线、去包络线的差异大小,以及相同土壤的反射率曲线、去包络线进行土壤分类的优劣,并且在去包络线的基础上提取能够区分不同土类的光谱特征参数;其次,比较一阶微分主成分与光谱特征参数作为输入量时,三种光谱分类模型精度差异并分析不同模型精度差异的原因。结果表明：（1）四种土壤的反射光谱曲线差异较小,去包络线可以极大的增强四种土壤在430～1 210 nm之间的光谱差异,并在去包络线的基础上构建具有明确物理意义的光谱特征参数。（2）将一阶微分主成分和光谱特征参数分别代入三种聚类模型可知,以光谱特征参数为输入量的土壤光谱分类模型均超过了以一阶微分主成分为输入量的模型精度,由于光谱特征参数保留了原数据的物理意义、更准确的体现了不同土壤类型之间的差异性,而一阶微分主成分数据带有一定的模糊性不同范围之间缺乏对比性,在土壤分类中以光谱特征参数作为输入量更具有优势。（3）在三类土壤分类模型中,LR的分类精度最高为76.67%,Kappa系数为0.56;ANN的分类精度中等为72.50%,Kappa系数为0.48;K-means的分类精度最低,只有65.00%,Kappa系数为0.33。研究成果可为土壤精细制图、以及土壤分类仪器的研制提供技术支持。     

Effect of atomic disorder and temperature on incommensurate helical spin waves in the Anderson–Hubbard model

Based on the single-band t–t' Anderson–Hubbard model, the effect of disorder on the parameters and ranges of existence of incommensurate helical spin waves is studied. The problem is solved within the functional integration theory in static approximation, taking into account longitudinal fluctuations of the magnetic moment. Magnetic phase diagrams and parameters of incommensurate helical spin waves are obtained as functions of temperatures and electron and impurity concentrations. It is shown that disorder can lead to the first-order transition from the antiferromagnetic phase to the (Q, π) phase and the metal–dielectric transition from antiferromagnetic metal to antiferromagnetic dielectric far from the half-filled band. The results obtained are used to explain the incommensurate magnetic order observed in cuprates in the overdoped mode.     

Fluids of polarizable hard spheres with dipoles and tetrahedral quadrupoles Integral equation results with application to liquid water

The mean spherical, linearized hypernetted chain and quadratic hypernetted chain approximations are solved for a fluid of hard spheres with embedded point dipoles and tetrahedral quadrupoles and this system is shown to be quite similar to the dipole-linear quadrupole case previously studied. However, tetrahedral quadrupoles have a larger influence upon the structural and thermodynamic properties and are slightly more effective in decreasing the dielectric constant from the purely dipolar value. Also we describe a simple self-consistent mean field theory which allows molecular polarizability to be taken into account. This approximation together with the integral equation methods is applied to a polarizable dipole-tetrahedral quadrupole fluid with water-like parameters. The dielectric constant of this system is found to be in good agreement with the experimental results for liquid water for temperatures ranging from 25°C to 300°C. The influence of molecular polarizability is shown to be very large. At 25°C the mean dipole moment is ～2·56 D compared with ～1·85 D in the gas phase and the dielectric constant increases from ～25 for non-polarizable particles to ～80 for the polarizable model.     

分形理论结合相变动力学的冷表面结霜过程模拟

运用分形理论并结合相变动力学模拟冷表面上结霜过程.在相变动力学基础上成功模拟了结霜初始阶段水蒸气在冷表面上凝结、液滴生长及冻结过程,随后运用分形理论的有限制的扩散凝聚(diffusion limited aggregation,DLA) 模型模拟了霜晶在冻结液滴表面上的形成生长过程.模拟结果与实验结果取得良好的一致,模拟过程中凝结液滴出现及冻结的时间与实验结果几乎完全符合;液滴冻结之前其表面接触半径随时间变化的模拟结果与实验结果基本一致,同时模拟霜层厚度与实验测得霜层厚度也非常接近.研究结果对于探讨分形理 关键词： 分形 相变动力学 结霜 模拟     

利用土壤的近红外光谱特征测定土壤含水量

以新疆玛纳斯县不同质地土壤(砂壤土、粉粘壤土和粘土)室内光谱反射率作为研究对象,采用包络线去除法对土壤光谱曲线进行处理,与土壤含水量进行相关分析并建立模型。结果表明：不同质地土壤光谱反射率大小依次为：粘土>粉粘壤土>砂壤土;砂壤土、粉粘壤土和粘土分别以田间持水量20.01%,24.10%和30.43%为临界点,在低于该临界点范围内含水量与反射率呈反比,在高于该临界点范围内含水量与反射率呈正比;在1 390～1 623 nm波段内,土壤含水量与光谱归一化反射率有较好的负相关,并达到显著水平,所建立的土壤含水量预测模型R2值达到0.8以上,模型平均相对误差为10%。结果表明,建立不同质地土壤含水量光谱预测模型可以较准确反映土壤含水量,其快速、无损、准确的优点,为测定土壤含水量提供了一种新方法。     

分形大地土壤表面与部分埋藏目标复合散射特性

采用土水混合物介电常数的Topp方程模型表示大地土壤的介电特性,应用带限Weierstrass-Mandelbrot分形粗糙面模型和Monte Carlo方法模拟大地土壤表面,运用矩量法研究了带限分形大地土壤表面与部分埋藏矩形截面柱复合模型的电磁散射,得出了复合散射系数的角分布曲线;计算了复合散射系数随带限分形大地土壤表面分维、空间基频、高度起伏均方根、土壤含水率、矩形截面柱几何参数、埋藏深度、倾角、入射波频率等的变化情况,并做了详细分析与讨论;结果表明,土壤表面分维等参数对复合散射系数的影响是非常复杂的,镜像附近的角分布曲线具有明显的分形特征。     

分形大地土壤表面与部分埋藏目标复合散射特性

采用土水混合物介电常数的Topp方程模型表示大地土壤的介电特性,应用带限Weierstrass-Mandelbrot分形粗糙面模型和Monte Carlo方法模拟大地土壤表面,运用矩量法研究了带限分形大地土壤表面与部分埋藏矩形截面柱复合模型的电磁散射,得出了复合散射系数的角分布曲线;计算了复合散射系数随带限分形大地土壤表面分维、空间基频、高度起伏均方根、土壤含水率、矩形截面柱几何参数、埋藏深度、倾角、入射波频率等的变化情况,并做了详细分析与讨论;结果表明,土壤表面分维等参数对复合散射系数的影响是非常复杂的,镜像附近的角分布曲线具有明显的分形特征。     

结合有效介质理论的乳状液太赫兹光谱分析

原油乳状液对原油的长距离输运具有重要影响,乳状液的油、水状态及相互作用机制还需新理论和新方法获得新认识,基于有效介质理论,本文研究了原油乳状液太赫兹光谱响应特征.通过太赫兹时域光谱系统测试得到了含水率为0～28％的原油乳状液的太赫兹时域光谱,结合傅里叶变换计算了吸收系数和介电常数等光学参数,同一频率下吸收系数等光学参数...     

Optical study of parameters of the passage of a shock wave from air to water

A study is made of the penetration of shock waves from air into water. The shock wave in air is generated as a result of dielectric breakdown induced by pulsed CO₂-laser radiation. A combination of the double-exposure shadow method and holographic interferometry is used to measure the shock-wave parameters. Density and pressure profiles behind the wave front are obtained at different times after onset of breakdown. It is shown experimentally that as the wave passes through the interface from the air to the water, there is a fourfold amplification of the pressure in the shock wave front. Estimates of the width of the shock wave front formed in the water are given in the context of studies of large-scale explosion processes. It is shown that simple empirical dependences, established in the course of studies of large-scale explosions, are also valid with certain corrections for microscopic laboratory experiments. Zh. Tekh. Fiz. 68, 39–43 (August 1998)     

Application of the two-liquid model for the interpretation of the observed electrophysical properties of supercooled water in nanopores

We propose a model combining the first-order liquid-liquid and the second-order ferroelectric phase transitions phenomenology to explain various features of the λ-point of liquid water. We suggest that the long-range dipole-dipole interaction of water molecules leads to a ferroelectric phase transition, which occurs only in the low-density component of the liquid and is the origin of the singularity of the dielectric constant recently observed in experiments with supercooled liquid water in nanoporous materials. Finally, we establish the model parameters and prove the consistency of the combined model by comparing its predictions with experimental data and the results of recent molecular-dynamics simulations.     

高功率微波作用下介质窗表面电子运动2维仿真

建立了真空中高功率微波作用下介质窗表面电子运动2维仿真模型,充分考虑了微波电磁场及介质表面静电场等影响因素。通过对不同电子出射初始角度和微波场参数（电场幅值、频率及电子出射时电场相位）对电子运动状态影响的仿真分析,得到了二次电子倍增过程中电子在复合场下的运动轨迹、电子重新返回介质表面的撞击能量及返回时间等状态参数,获得了电子运动状态参数随电子出射角度和微波场参数的变化规律。研究发现：电子出射角度对其运动状态有显著影响,电子存在运动轨迹最大的某一出射角度,该角度下电子拥有最大的撞击能量;微波电场幅值的增加将使电子撞击能量增加,返回时间减小,微波电场相位的变化使电子的撞击能量和返回时间呈周期振荡,这从本质上解释了电子数量在二次电子倍增过程中以微波频率两倍周期振荡的原因;随着微波频率的增加电子将由简单的类抛物线运动转变为复杂的振荡运动。     

Effect of electric field on the dielectric permittivity of betaine phosphite crystals in the paraelectric phase

Temperature dependences of the dielectric permittivity of betaine phosphite crystals are studied both without and under application of an electric bias. It is shown that, in view of the fact that the high-temperature improper ferroelastic (antiferrodistorsive) phase transition at T _c1=355 K is nearly tricritical, the nonlinear temperature dependence of inverse dielectric permittivity in the paraelectric phase and the effect of the field on the dielectric permittivity can be described within a phenomenological model containing two coupled (polar and nonpolar) order parameters with a negative coupling coefficient. An analysis of the model revealed that, in the case where two phase transitions, a nonpolar and a ferroelectric one, can occur in the crystal, all of its dielectric properties, including the polarization response in a field, can be described by one dimensionless parameter a. For the crystal under study, we have a=?2.5. This value of the parameter corresponds to a second-order ferroelectric transition far from the tricritical point, at which a=?1. It is shown that the polarization response in the paraelectric phase in an electric field calculated within this model differs radically from that in the ferroelectric phase-transition model for which the Curie-Weiss law holds in the paraelectric phase.