Solution of the transfer equation in a moving medium

The integral transfer equation for resonance radiation in a semi-infinite medium expanding with a constant velocity gradient is considered. A method for the numerical-analytical solution of this problem is presented, together with an estimation of the associated errors. This method is based on a discretization in optical depth and the application of non-linear equation factorization equations.     

Polarization in resonance lines: Diffuse reflection

The linear polarization of resonance radiation diffusely reflected from a semi-infinite atmosphere is analyzed, including a full account of the azimuthal dependence. The radiating atom is assumed to have two levels and the radiation to be fully redistributed in frequency. A new approach to the transformation of the equations of polarized radiative transport is proposed based on factorization of the full (3×3) Rayleigh phase matrix. The emergent radiation field is expressed in terms of a matrix analog for the Chandrasekhar H function. The polarization properties of radiation at the frequencies of resonance lines diffusely reflected from a scattering atmosphere are discussed. The degree of polarization of the reflected radiation can be very high.     

Anaerobic oxidation of methane (AOM) in marine sediments from the Skagerrak (Denmark): I. Geochemical and microbiological analyses

The organic rich sediments of the Skagerrak contain high quantities of shallow gas of mostly biogenic origin that is transported to the sediment surface by diffusion. The sulfate methane transition zone (SMTZ), where anaerobic oxidation of methane (AOM) and sulfate reduction occur, functions as a methane barrier for this upward diffusing methane.To investigate the regulation of AOM and sulfate reduction rates (SRR) and the controls on the efficiency of methane consumption, pore water concentrations, and microbial rates of AOM, sulfate reduction and methanogenesis were determined in three gravity cores collected along the slope of the Norwegian Trench in the Skagerrak. SRR occurred in two distinct peaks, at the sediment surface and the SMTZ, the latter often exceeding the peak AOM rates that occurred at the bottom of the SMTZ. Highest rates of both AOM and SRR were observed in a core from a pockmark, where advective methane transport occurred, generating high methane and sulfate fluxes. But even at this site with a shallow SMTZ, the entire flux of methane was oxidized below the sediment surface. AOM, SRR and methanogenesis seem to be closely associated and strongly regulated by sulfate concentrations, which were, in turn, regulated by the methane flux. Rate measurements of SRR, AOM and methanogenesis revealed a tight coupling of these processes. Bicarbonate-based methanogenesis occurred at moderate sulfate concentrations (>5 mM) above the AOM zone but seemed to be inhibited in the depth where AOM occurred. The unbalanced stoichiometry of AOM and SRR in the SMTZ was more pronounced in rate measurements than in methane and sulfate fluxes, and seemed more likely be related to enhanced SRR in this zone than an underestimation of methane fluxes.     

Light regulation of benthic sulfate reduction rates mediated by seagrass (Thalassia testudinum) metabolism

The effects of light reduction on community metabolism and sediment sulfate reduction rates (SRR) were assessed experimentally in a shallow (<2.0 m) seagrass (Thalassia testudinum) meadow along Florida's north-central Gulf coast. Nine experimental plots (1.5 m×1.5 m) were shaded differentially to achieve a 0–90% gradient in light reduction within the seagrass meadow. Gross primary production and net community production (NCP), estimated with in situ benthic chamber incubations, decreased with increasing light reduction. The compensation irradiance for community metabolism, i.e., the shading level at which NCP shifted from net autotrophic to net heterotrophic, was determined to be 52.5% of the incoming irradiance at canopy height in the seagrass bed (308.7 μE m⁻² s⁻¹ PAR at noon). Sediment SRR, determined with the use of a³⁵S−SO₄ ²⁻ radiotracer technique, increased quickly (within 5 d) and markedly with increased shade, i.e., simulated light reduction. SRR increased 50-fold when shading exceeded the light compensation point for the seagrass community, rendering the community net heterotrophic. Five days after restoring ambient light conditions, SRR had decreased sharply for all shading treatments. The observed decrease in NCP, coincident with the increase in the SRR with light reduction, suggests that light reduction has an indirect influence on sediment SRR mediated through its effect on seagrass metabolism.     

非负矩阵分解及在地学中的应用

非负矩阵分解（NMF）是重要的矩阵分解算法与数据降维工具。介绍了NMF的背景、定义、原理及特征。在已有NMF算法分类的基础上,总结当前流行的NMF算法及研究进展,综述NMF在地学领域中的应用,主要包括高光谱图像的处理与矿产资源预测。对NMF算法的研究方向进行了预测和展望。     

Computationally efficient generation of gaussian conditional simulations over regular sample grids

The generation over two-dimensional grids of normally distributed random fields conditioned on available data is often required in reservoir modeling and mining investigations. Such fields can be obtained from application of turning band or spectral methods. However, both methods have limitations. First, they are only asymptotically exact in that the ensemble of realizations has the correlation structure required only if enough harmonics are used in the spectral method, or enough lines are generated in the turning bands approach. Moreover, the spectral method requires fine tuning of process parameters. As for the turning bands method, it is essentially restricted to processes with stationary and radially symmetric correlation functions. Another approach, which has the advantage of being general and exact, is to use a Cholesky factorization of the covariance matrix representing grid points correlation. For fields of large size, however, the Cholesky factorization can be computationally prohibitive. In this paper, we show that if the data are stationary and generated over a grid with regular mesh, the structure of the data covariance matrix can be exploited to significantly reduce the overall computational burden of conditional simulations based on matrix factorization techniques. A feature of this approach is its computational simplicity and suitability to parallel implementation.     

Seasonal variations in sediment sulfur cycling in the Ballastplaat mudflat, Belgium

Sulfate reduction rate (SRR) and pools of reduced inorganic sulfur, acid volatile sulfide (AVS), chromium reducible sulfur (CRS), and elemental sulfur (S^o), were studied from June 1990 till March 1992 at two locations on the Ballastplaat mudflat in the Scheldt estuary. The sediment composition at station A was mainly sand with low organic content whereas sediments at station B were dominated by silt and clay with high organic content. SRR was positively related to temperature; more pronounced at station B (Ea=190 kJ mol⁻¹) than at station A (Ea=110 kJ mol⁻¹). The maximum SRR values observed equalled 14 μmol cm⁻³ d⁻¹ at station B and 1 μmol cm⁻³ d⁻¹ at station A. AVS was the dominant radiolabelled end product of the sulfate reduction reaction, except in surface sediments where pyrite and S^o were more dominant. However, CRS was the predominant reduced inorganic sulfur pool in the sediments. Both AVS and CRS pools showed temporal variations out of phase with SRR. SRR peaked in summer, while the concentrations of AVS and CRS were highest in fall. The accumulation of AVS and CRS started late summer after depletion of oxidants, which had accumulated during winter and spring. The estimated annual SRR and thus sulfide production in the upper 15 cm of station B was of the order of 100 mol m⁻² yr⁻¹, and at station A of the order of 12 mol m⁻² yr⁻¹. The sulfur mass balance shows that only a very small fraction, if any, of the produced sulfide is retained as reduced inorganic sulfur in the sediment.     

S/S fractionation by sulfate-reducing microbial communities in estuarine sediments

Sulfur isotope fractionation during microbial sulfate reduction in brackish estuarine sediments was studied using an experimental flow-through reactor approach designed to preserve the in situ physical, geochemical and microbial structure of the sediment. Concurrent measurements of potential sulfate reduction rates and ³⁴S/³²S fractionations were carried out using intact sediment slices (2 cm thick, 4.2 cm diameter) from unvegetated, intertidal sites adjoining a salt marsh along the Scheldt estuary, The Netherlands. A total of 30 reactor experiments were performed with sediments collected in February, May and October 2006. The effects of incubation temperature (10, 20, 30 and 50 °C) and sediment depth (0-2, 4-6 and 8-10 cm) were investigated. Sulfate was supplied in non-limiting concentrations via the reactor inflow solutions; no external electron donor was supplied. Isotope fractionations (ε values) were calculated from the measured differences in sulfate δ³⁴S between in- and outflow solutions of the reactors, under quasi-steady state conditions. Potential sulfate reduction rates (SRR) varied over one order of magnitude (5-49 nmol cm⁻³ h⁻¹) and were highest in the 30 °C incubations. They decreased systematically with depth, and were highest in the sediments collected closest to the vegetated marsh. Isotope fractionations ranged from 9‰ to 34‰ and correlated inversely with SRR, as predicted by the standard fractionation model for enzymatic sulfate reduction of Rees (1973). The ε versus SRR relationship, however, varied between sampling times, with higher ε values measured in February, at comparable SRRs, than in May and October. The observed ε versus SRR relationships also deviated from the previously reported inverse trend for sediments collected in a marine lagoon in Denmark (Canfield, 2001b). Thus, isotope fractionation during sulfate reduction is not uniquely determined by SRR, but is site- and time-dependent. Factors that may affect the ε versus SRR relationship include the structure and size of the sulfate-reducing community, and the nature and accessibility of organic substrates. Whole-sediment data such as those presented here provide a link between isotopic fractionations measured with pure cultures of sulfate-reducing prokaryotes and sulfur isotopic signatures recorded in sedimentary deposits.     

Determination of ammonia removal from aqueous solution and volumetric mass transfer coefficient by microwave-assisted air stripping

In this study, the removal of ammonia from synthetically prepared ammonia solution at pH 11 was investigated by using microwave radiation heating. Initially, conventional and microwave radiation heating were compared with respect to ammonia removal efficiency and overall volumetric mass transfer coefficient at five different temperatures. Overall volumetric mass transfer coefficient was calculated from the material balance for ammonia at unsteady-state condition. The effects of temperature, initial ammonia concentration, air flow rate, stirring speed, and microwave radiation power on both ammonia removal efficiency and overall volumetric mass transfer coefficient in liquid phase were also examined. The results of the experiments revealed that microwave-assisted air stripping allowed to the higher ammonia removal efficiency and overall volumetric mass transfer coefficient value compared to the conventional heating air stripping. Additionally, temperature and air flow rate were determined as the most substantial parameters affecting both ammonia removal efficiency and overall volumetric mass transfer coefficient value.     

A point source of radiation in the early Universe: Solution in a one-dimensional approximation

The radiation field of a point source with a specified power in the early Universe acting for a specified time in the radiation-dominated epoch after the annihilation of electron-positron pairs is considered. A three-component model for this period is adopted. The equations of radiative transfer for the source are formulated, taking into account polarization arising during scattering of the radiation by free electrons. Analytical, numerical, and asymptotic solutions of the transfer equation are obtained for a flat model in a one-dimensional approximation, which describe the evolution of the intensity and flux of scattered radiation of the source in periods close to the onset of its action. Intervals of redshift corresponding to these periods are estimated. The behavior of the linear polarization near the source is traced. It is shown that the source radiation can be comparable to the thermal background only if the source energy is very high or we consider regions in its immediate vicinity. More optimistic estimates will require that we take into account the decrease in the degree of ionization of matter in the epoch of recombination.     

Kinetics of microbial sulfate reduction in estuarine sediments

Kinetic parameters of microbial sulfate reduction in intertidal sediments from a freshwater, brackish and marine site of the Scheldt estuary (Belgium, the Netherlands) were determined. Sulfate reduction rates (SRR) were measured at 10, 21, and 30 °C, using both flow-through reactors containing intact sediment slices and conventional sediment slurries. At the three sites, and for all depth intervals studied (0-2, 2-4, 4-6 and 6-8 cm), the dependence of potential SRR on the sulfate concentration followed the Michaelis-Menten rate equation. Apparent sulfate half-saturation concentrations, K_m, measured in the flow-through reactor experiments were comparable at the freshwater and marine sites (0.1-0.3 mM), but somewhat higher at the brackish site (0.4-0.9 mM). Maximum potential SRR, R_max, in the 0-4 cm depth interval of the freshwater sediments were similar to those in the 0-6 cm interval of the marine sediments (10-46 nmol cm⁻³ h⁻¹ at 21 °C), despite much lower in situ sulfate availability and order-of-magnitude lower densities of sulfate-reducing bacteria (SRB), at the freshwater site. Values of R_max in the brackish sediments were lower (3.7-7.6 nmol cm⁻³ h⁻¹ at 21 °C), probably due to less labile organic matter, as inferred from higher C_org/N ratios. Inflow solutions supplemented with lactate enhanced potential SRR at all three sites. Slurry incubations systematically yielded higher R_max values than flow-through reactor experiments for the freshwater and brackish sediments, but similar values for the marine sediments. Transport limitation of potential SRR at the freshwater and brackish sites may be related to the lower sediment porosities and SRB densities compared to the marine site. Multiple rate controls, including sulfate availability, organic matter quality, temperature, and SRB abundance, modulate in situ sulfate-reducing activity along the estuarine salinity gradient.     

非均匀月壤介质的被动微波辐射传输模拟

基于非均匀月壤物理模型和辐射传输方程,模拟月壤介质中的微波辐射传输特性,探讨频率、月壤厚度等与月表亮温的关系。结果表明:在低频段,月壤微波辐射亮温的动态变化范围较大,可探测的月壤厚度大,3 GHz时的最大可探测月壤厚度达12.4 m;在高频段对应的可探测月壤厚度较小,特别是从50GHz往后的频率段内,最大可探测月壤厚度均小于2 m。不同频率的亮温-厚度变化曲线没有交叉点,且频率越高,所能探测的月壤厚度越小。根据模拟结果,建立了月壤厚度与亮温的查找表。基于查找表,利用单个波段的亮温数据即可得到月壤厚度信息。     

基于SPH方法的非饱和多孔介质相变耦合研究

在考虑相变的热能平衡方程和非饱和水分迁移质量控制方程的基础上,建立温度场-水分场的耦合模型,并采用一种无网格粒子算法（SPH）进行数值求解。其中,耦合方程中考虑了水流传热以及温度势对水流的直接驱动,在不考虑相变的情况下,该耦合模型可退化为常温下的水-热耦合模型,故可用于模拟冻融循环的相关问题。从求解热能平衡方程中的含冰量出发,实现解耦并对半无限单向冻结条件下介质内非稳态温度场和体积含水率分布场进行模拟,将耦合作用下的温度场与不耦合的解析解进行对比,反映出水分迁移对温度场存在较大影响。最后,求解了路基边坡在季节性周期温度边界下,温度场、水分场分布的演变规律,并评估了边坡阴阳面受热不均对水热两场分布的影响。计算结果基本能反映土冻结相变的实际物理过程,光滑粒子算法可以用于尝试解决冻土领域的其他相关问题。     

大气校正方法及其在高光谱影像Hyperion中的应用

利用遥感影像反演地物反射率,大气校正必不可少。对于高光谱影像,其信噪比与多波段遥感影像相比非常低,消除大气的影响显得尤为重要。在大气辐射传输模型Modtran4.0基础上,给出了一种直接、有效的大气校正参数计算方法。结合MODIS/TERRA大气温湿度廓线产品,使用此方法计算了高光谱影像Hyperion大气校正参数,并用于Hyperion影像的部分波段的反射率反演,与卫星过境时地面同步实测的典型地物反射率以及高光谱大气校正软件ACORN的计算结果进行比较,获得了比较好的结果。研究表明,大气辐射传输模型和卫星遥感大气参数产品相结合用于遥感影像的大气校正是可行的。     

2009/2010年黄河源区高寒草甸下垫面能量平衡特征分析

以青藏高原黄河源玛多为实验区, 基于TRM-ZS1气象生态环境监测仪2009年11月1日至2010年10月31日辐射及能量通量观测数据, 采用波文比能量平衡法, 进行了该区域潜热和感热通量的估算, 分析了黄河源区高寒草甸下垫面辐射收支, 潜热、 感热和土壤热通量在不同季节的分配, 对该区域冬季地面加热场强度的变化进行了研究.结果表明: 该区域总辐射、 净辐射较强, 总辐射平均日积分值为18.06 MJ·m^-2·d^-1, 净辐射平均日积分值5.95 MJ·m^-2·d^-1, 曾观测到高达979.5 W·m^-2的净辐射通量.全年地表平均反射率为0.30, 接近于荒漠和半荒漠下垫面的反射率.植物生长季土壤湿度和冬、 春季地面积雪是影响该区域地表反射率的两个最主要因素.该区域感热通量年积分值为742.68 MJ·m^-2·a^-1, 潜热通量年积分值为1 388.58 MJ·m²·a^-1, 全年中地表以潜热方式传递热量为主.分季节分析, 冬季感热潜热强度相当, 春季以感热为主, 夏秋季则以潜热为主.土壤热通量年积分值为38.06 MJ·m^-2·a^-1, 全年热通量在热量平衡中约占1.8%, 但季节分配不平衡, 在冬季, 有|G|>H+LE, 土壤热通量是热平衡最大的分量.该区域地表全年向大气释放热量, 地表对大气而言是热源.     

Scattering of cyclotron radiation in a moving plasma

We consider the scattering of cyclotron radiation in a plasma moving along a homogeneous magnetic field. The equation of radiation transfer in a co-moving frame is derived and two limiting cases are pointed out. In the first case of a “small” velocity gradient, the total Doppler frequency shift due to variations in the plasma velocity over the flow is much smaller than the width of the line. The second, opposite, case of a “large” velocity gradient is analogous to the Sobolev approximation in the theory of moving stellar envelopes. The solution of the transfer equation for a wind-type flow illuminated by radiation of a given intensity is obtained in the latter case, when the influence of the plasma motion on cyclotron scattering is most important. It is shown that cyclotron scattering in a moving plasma differs from the known (and qualitatively similar) problems of resonance scattering in moving stellar envelopes and cyclotron scattering in a motionless plasma permeated by an inhomogeneous magnetic field. In particular, a symmetric absorption band with residual intensity proportional to the velocity gradient appears in the spectrum of the outgoing radiation, while in these two other problems, the depth of the corresponding spectral features cannot exceed half the continuum level. Detailed qualitative analysis reveals that this difference is due to the particular form of the frequency redistribution for cyclotron scattering.     

利用地基微波辐射计验证积雪微波辐射传输模型

积雪雪水当量参数是水文、气候、水资源利用与管理模型中非常重要的输入参数,积雪辐射理论模型可以模拟积雪物理参数与微波辐射的关系.因此,准确模拟积雪辐射信息,验证积雪辐射模型显得尤为重要.采用改进的基于能量守恒的干雪微波辐射传输理论模型(DMRT-AIEM-MD),利用2008年3月24 日黑河地区联合实验获取的地面测量数据以及车载辐射计18.7 GHz和36.5 GHz两个频率的辐射亮温值,考虑地形的影响,分析积雪辐射散射特性以及验证该模型.结果表明:该模型模拟值与地面实测值吻合的比较好,该模型能较好的模拟中国地区自然地表积雪辐射信号.分析了部分模型模拟值和地面实测值偏差的可能原因,该积雪区是多次堆积形成,积雪垂直剖面的密度、温度不规则变化可能会引起偏差.     

Restoration of the Parameters of a Gas-Dust Disk Based on Its Synthetic Images

Astronomy Reports - The topic of the present study is combining a dynamic model of a protoplanetary disk with the computations of radiation transfer for obtaining synthetic spectra and disk images...     

基于快速应力释放的深埋隧洞岩爆防治对策研究

大型地下工程开挖中,高地应力环境下高储能脆性岩体通常会通过脆性破裂快速释放应变能而产生岩爆。岩爆作为常见的一类动力失稳地质灾害现象,极大地威胁着现场施工人员和设备的安全。作为雅砻江锦屏二级水电站的主要工程,千米级埋深的引水隧洞也面临高地应力下硬岩岩爆问题。针对锦屏二级引水隧洞岩爆的特点,提出采用快速应力释放的方法防治岩爆,并采用数值模拟的方法优选了倾斜辐射爆破孔方案。数值模拟结果表明：该方法能使岩体内的初始应力快速卸荷,同时使应力集中区向岩体深部转移。通过在锦屏二级引水隧洞工程中的试验与运用,采用声波测试法对实施快速应力释放方案的效果进行检验,验证了快速应力释放方法防治岩爆的有效性。研究成果为解决类似工程岩爆防治问题提供了理论依据和借鉴。     

井地直流电法三维数值模拟中若干问题研究

讨论了地下垂直线源分段计算和场叠加的方法,并实现了在套管上供直流电的三维数值模拟。讨论了大型容量矩阵的压缩存储方式,采用数组和结构体相结合的方法实现容量矩阵的一维链表式压缩存储。在求解超大型稀疏线形方程组时引入不完全Cholesky分解稳定化的双共轭梯度算法(ICBG),通过与均匀半空间垂直线源解析解的对比,证明了该算法是准确可靠的。