Composite Likelihood Inference for Multivariate Gaussian Random Fields

In the recent years, there has been a growing interest in proposing covariance models for multivariate Gaussian random fields. Some of these covariance models are very flexible and can capture both the marginal and the cross-spatial dependence of the components of the associated multivariate Gaussian random field. However, effective estimation methods for these models are somehow unexplored. Maximum likelihood is certainly a useful tool, but it is impractical in all the circumstances where the number of observations is very large. In this work, we consider two possible approaches based on composite likelihood for multivariate covariance model estimation. We illustrate, through simulation experiments, that our methods offer a good balance between statistical efficiency and computational complexity. Asymptotic properties of the proposed estimators are assessed under increasing domain asymptotics. Finally, we apply the method for the analysis of a bivariate dataset on chlorophyll concentration and sea surface temperature in the Chilean coast.     

Nonparametric Bootstrap Confidence Intervals for Variance Components Applied to Interlaboratory Comparisons

Exact confidence intervals for variance components in linear mixed models rely heavily on normal distribution assumptions. If the random effects in the model are not normally distributed, then the true coverage probabilities of these conventional intervals may be erratic. In this paper we examine the performance of nonparametric bootstrap confidence intervals based on restricted maximum likelihood (REML) estimators. Asymptotic theory suggests that these intervals will achieve the nominal coverage value as the sample size increases. Incorporating a small-sample adjustment term in the bootstrap confidence interval construction process improves the performance of these intervals for small to intermediate sample sizes. Simulation studies suggest that the bootstrap standard method (with a transformation) and the bootstrap bias-corrected and accelerated (BC _a ) method produce confidence intervals that have good coverage probabilities under a variety of distribution assumptions. For an interlaboratory comparison of mercury concentration in oyster tissue, a balanced one-way random effects model is used to quantify the proportion of the variation in mercury concentration that can be attributed to the laboratories. In this application the exact confidence interval using normal distribution theory produces misleading results and inferences based on nonparametric bootstrap procedures are more appropriate.     

Estimation of Linear Models of Coregionalization by Residual Maximum Likelihood

Observations of ancillary soil properties spatially correlated to a soil property of interest may be used to increase the precision and reduce the sampling costs of a geostatistical survey. The relationship between such coregionalized properties must be expressed as a linear model of coregionalization but the conventional estimator of the linear model of coregionalization is biased unless the mean value of each property is constant across the study region. However, the mean value of a soil property may vary according to a spatial trend or a deterministic relationship with other factors which vary within the study region. We therefore propose that a linear mixed model should be fitted to coregionalized soil properties by residual maximum likelihood. This approach simultaneously fits spatial trends or deterministic relationships and random effects to the observations with minimum bias. We implement a residual maximum likelihood estimator for coregionalized properties and suggest a criterion to decide what order of spatial trend and which deterministic relationships should be included in the model. The effectiveness of the estimator is proved upon simulated data and upon observations of zinc and cadmium concentrations from the Swiss Jura.     

公路建设新增土壤流失预测时段探讨

新增土壤流失预测是开发建设项目水土保持方案编制的基础。根据开发建设项目的实际情况和区域水土流失特点,确定符合实际的预测时段,能提高预测结果的准确度,有利于防护措施的优化配置。探讨了高速公路建设新增土壤流失预测时段确定的有关问题。     

下拉秀剖面胡敏素组分特征

采用腐殖质组成修改法和Pallo修改法相结合的方法对下拉秀剖面的胡敏素(HM)进行了分组研究,把铁结合胡敏素(HMi)、黏粒结合胡敏素(HMc)和不溶性胡敏素(HMr)定义为胡敏素组成,同时把HMi/HMc和(HMi+HMc)/HM作为胡敏素的表征指标,研究了不同层位的胡敏素组成.结果表明:不同层位胡敏素组分含量、HMi/HMc、(HMi+ HMc)/HM、E4/E6、△lgK各不相同;多数层位HMr的含量高,HMr的最高值和最低值分别出现在剖面的上下两端;(HMi+ HMc)/HM在(0.20±0.05)～(0.60±0.03)的范围内波动,多数层位可溶性胡敏素组分低于不溶性组分;HMi/HMc在(5.42±0.34～0.46±0.03)的范围内波动,且幅度大,有5个层位＞1;除O层外,剖面各层位的E4/E6总是表现为HMc＞ HMi,但△lgK的变化情形较为复杂,并不总是表现为HMc＞ HMi;现代生草层HMi、HMc的结构较其他层位简单.     

均衡纵剖面形态的实验研究

均质地层和定流量条件下均衡纵剖面的形成过程与最速滑降问题类似.从最小耗能原理出发,用大量的室内实验成果验证了理想的均衡纵剖面应最接近于一条摆线,从而证实了理论推求的结论,并为均衡纵剖面理论的实践应用打下了坚实的基础.     

WRKY转录因子表达谱的研究进展

环境胁迫对植物的生长发育造成重大影响,因此,提高植物的抗逆性是农业面临的重要问题。自然界中存在多种抗逆基因,如抗盐基因、抗旱基因、抗寒基因等。利用植物基因工程和分子生物学技术提高植物对逆境的适应性及其抗逆分子机制的研究已成为当今热点。WRKY转录因子是一类参与多种胁迫反应的诱导型转录因子,本文综述了WRKY转录因子家族的结构特点、WRKY转录因子在非生物胁迫（高温、低温、干旱、盐）、外源物质（激素及O3）处理及生物胁迫下的表达模式。各种胁迫下的表达谱均呈现不同特点,这些差异表达可能与它们所行使的不同生物学功能有关。     

Unit and Internal Chain Profile of Millet Amylopectin

The unit chain compositions of debranched foxtail, proso, pearl, and finger millet amylopectins and their ϕ,β‐limit dextrins were analyzed by high‐performance anion‐exchange chromatography. The ϕ,β‐limit dextrins reflected amylopectin internal chain profiles. The amylopectins had average chain lengths ranging from 17.94 to 18.12. The ranges of external chain length, internal chain length, and total internal chain length of the millet amylopectins were 11.85–12.33, 4.75–5.09, and 11.64–12.28, respectively. The relative molar concentration of B‐chains in the amylopectins was close to 50% in all samples. Significant differences were, however, observed in the proportions of very short “fingerprint” B‐chains (B_fp, degree of polymerization 3–7) and the major group of short B‐chains (BS_major): foxtail and proso millets possessed high amounts of B_fp‐chains, whereas finger and pearl millets had higher amounts of BS_major‐chains, suggesting possible differences in the fine structure of the clusters and building blocks of the amylopectins. Millet amylopectin can be classified structurally as type 2.     

黄土剖面水文地质特性的初步研究

对黄土剖面中不同层次的土壤结构特征进行了分析,表明黄土土体的多层次有序网状水文通道体系是黄土地下水补给主要通道;在黄土性古土壤层与红褐色古土衷肠支互相间成的巨厚黄土剖面内,黄土层和古土壤层的结构、颗粒组成、孔隙组合等特征具有较大的变化,形成水文地质特性差异较大的互层,古土壤中部的粘化层及钙质结核层和黄土层中相对较细密的层次,构成区域的相对隔水层,有效的阻止了地表水的渗成为地下水,而这些隔水层的形成     

不同开垦年限土壤剖面盐分变化

通过对不同开垦年限土壤剖面盐分调查,进行北疆典型残余盐土的变化特征研究.以玛纳斯河流域包家店镇典型地块为研究区,运用统计学和空间置换时间相结合的方法探讨土壤盐分的动态变化及其影响因素.结果表明,随着开垦年限的延长土壤剖面盐分均呈现相对减少的趋势,8年后土壤剖面的平均盐分降低到4 g/kg左右,年均脱盐率达到10.6%;该残余盐土区域土壤剖面盐分主要聚集在中底层(30-100cn),呈底聚型;开垦6年后土壤盐分的活跃范围集中在0-60 cm;开垦年限影响土壤盐分的同时土壤质地也是影响土壤盐分大小的重要因素.该研究结果将对残余盐土的发生演变及改良培肥提供科学依据.     

广东省生态环境与土壤研究所简介

广东省生态环境与土壤研究所成立于1958年。原名为“中国科学院广州土壤研究所”，1978年恢复建所后定名为“广东省土壤研究所”，随着科研业务与学科建设的发展，1996年更名为“广东省生态环境与土壤研究所”，现隶属于广东省科学院。研究所位于广州市天河区天源路808号，所部占地4．7公顷，另有一个面积20公顷的亚热带坡地生态试验站和五个分布在广东省各地的水土保持试验台站。“广东农业环境综合治理重点实验室”与“广东省环境科学与技术公共实验室”设在该所。     

水库纵向淤积形态分类研究

我国江河泥沙含量大小不一，北方河流含沙量大，尤其是西北地区含沙量很高，南方地区江河含沙量一般较小。河流上修建的水库都要淤积，但根据水库所处地理位置及所处流域的自然条件的不同、水库运用方式不同，其淤积纵剖面不同。对我国水库淤积纵剖面形态分类研究状况和成果进行了全面的综述。内容包括公式的形式、公式采用的资料范围、公式的判别标准及对每个公式的简单评价。     

下拉秀剖面有机碳赋存特征

以位于青藏高原三江源地区的下拉秀剖面为对象,按剖面自然分异的颜色层次分层采集样品,研究了三江源腹地沉积土壤的有机碳。结果表明:各层位有机碳含量差异显著(P<0.05),现代生草层总有机碳(TOC)、易氧化碳(LOC)、胡敏素(HM)碳含量最高。全剖面可见LOC和水溶性物质(WSS)存在,WSS和45cm以下的LOC的相对含量随剖面深度的增加总体呈上升趋势。富里酸(FA)和HM含量在各层位间差异显著(P<0.05),胡敏酸(HA)在个别层位存在绝对含量差异不显著(P>0.05)的现象。HA/FA在0.14～2.72范围内变化,总体表现为剖面上半部分大于1,下半部分小于1,最大值未出现在现代生草层。FA的E4/E6变化幅度大,HA的E4/E6波动小。综合表现为剖面有机物质腐殖化程度各层异质各向的特征,现代生草层的腐殖质化程度所代表的年代在剖面各层位当中既不是最高的时期亦不是最低的时期。     

银川平原草甸湿地盐土及其盐分分布特征

通过野外观测和室内分析,研究银川平原草甸湿地盐土及其盐分的分布特征,根据土壤表层全盐含量将研究区土壤划分为5个等级,分别为Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ,不同土壤等级的植被类型不同,在土壤Ⅰ中主要分布盐生草本草甸和盐生小灌木草甸,在土壤Ⅱ中主要分布盐生草甸和丛生禾草草甸,在Ⅲ、Ⅳ中主要分布根茎禾草草甸,在Ⅴ中主要分布杂类草草甸和一些低湿草甸;研究区草甸土壤全盐含量在垂直方向上表现出明显的表聚现象,在0~30 cm土层,随着土壤深度的增加,土壤全盐含量急剧下降,在30~70 cm土壤全盐含量的下降则较为平缓;各盐分离子除了HCO_3~–以外,其余各离子均表现出明显的表聚现象,但在不同的土壤等级中,只有Na~+、K~+、Cl~–和土壤全盐的表现一致,均为ⅠⅡⅢⅣⅤ。草甸湿地植物体中也有一定的盐分累积,在植物体中,主要盐分为NaCl、NaHCO_3;在土壤中主要盐分为NaCl、NaHCO_3、Na_2CO_3。     

Carbon Turnover in a Sorghum-cultivated Semi-arid Mediterranean Soil Profile

ABSTRACT

Organic carbon storage in soils is a key factor for agriculture sustainability and future climate control. Nevertheless, this issue has been insufficiently studied in the semi-arid context of northern Africa. Our aim was to quantify carbon dynamics in a Tunisian Calcaric Cambisol profile, using the natural ¹³C labeling offered by the continuous C4 crop forage sorghum. Our results show that in the topsoil 0–30 cm, the amount of crop-derived carbon accounted for 20% of the cumulated input from crops after 12 years, and half of it was retrieved as organic matter with particule size < 50 µm. Such values could be model-predicted with no particular adaptation to the specific calcareous environment using the RothC model. However, soils were additionally characterized by a very high subsoil organic carbon stock (170 t C ha^?1 between 30 and 140 cm), and we demonstrated that crop rooting highly contributed to this subsoil organic matter. Indeed, an unusually large proportion of new crop-derived carbon (one third) was found below the upper 30 cm. Our results show an increase in carbon content in the deep layers of this soil under semi-arid Mediterranean climate.     

Bibliometric Profile of an Agbioscience Research Enhancement Grant Program

This study is a bibliometric analysis of journal articles generated from an intramural grant program in the agbiosciences. Using citation analysis and bibliometric mapping, the study analyzes 515 journal articles published from 1999 to 2017. Results show the growth of journal article output, identify the major research fields and topics, describe national and international authorial and institutional collaborations, and quantify the performance and impact of the article output. The grant program’s journal article output presents a multi-disciplinary range of scholarly publications that reflect the disciplines of The Ohio State University’s College of Food, Agricultural, and Environmental Sciences, which houses the grant program.     

食品挤压机模头温度分布的研究

为了估计食品挤压机模头的温度分布,基于挤压机柱的热传导和流动能量的散发,该文做了一些必要的假设,并给出了相应的方程,计算热传导所需的参数、温度分布估计的数学方法及曲线。     

矿化垃圾中植物大量营养元素含量的剖面分布特征

对经长期填埋后已稳定化的垃圾进行开采和资源化利用,能增加现有填埋场库容,对解决城市生活垃圾填埋场紧张的现状具有重要意义。以一个已运行10a以上的垃圾填埋场为研究对象,对已填埋6、8、10a的矿化垃圾中一些植物大量营养元素的剖面分布进行了测定。结果表明：（1）矿化垃圾中氮、磷、钾养分的浓度总和已达到国家有机肥养分含量标准,有机质含量也明显高于土壤的有机质含量,从植物养分供应的角度看,矿化垃圾可具有资源化利用的价值;（2）矿化垃圾中养分主要以氮素为主,磷、钾营养元素的总量较低,但速效态含量相对较高;（3）不同填埋深度的矿化垃圾中,主要营养元素的含量大部分在填埋8~10a后达到相对稳定的状态,但受矿化垃圾组成成分复杂性的影响,部分形态营养元素的变化规律不明显。     

Comparing mapping approaches at subcatchment scale in northern Thailand with emphasis on the Maximum Likelihood approach

This study compares different soil mapping approaches in three different petrographic areas in order to test their suitability for regional mapping in northern Thailand. Sampling was based on transects or grid-based randomization. Maps were created based on expert knowledge (eye fitting) or using Classification Tree (CART algorithm) or the Maximum Likelihood approach. In addition, local knowledge-based-soil maps were created. Validation was performed using soil reference maps and independent sampling points. The mapping approaches based on transects and grid-based randomization showed a very high correspondence with the respective reference soil map and a very high degree of matching with independent sampling points. Both methods are best suited for sub-watershed scale. Mapping larger areas is difficult due to the inaccessibility of the mountainous regions. The soil maps based on Maximum Likelihood showed a high correlation with the respective reference soil maps and the individual sampling points. Maximum Likelihood maps and Classification Tree maps showed similar levels of accuracy. The Maximum Likelihood approach is applicable to upscaling procedures; therefore, a calibration area is required which represents the target area. Local knowledge-based-soil mapping is very cheap and fast, but is restricted to village areas where classification often varies even within a village. Despite this, local knowledge is very useful for soil reconnaissance surveys, as well as to acquire an overview of the major distribution of soils and their properties. Upscaling of local knowledge due to its inherent inconsistency is not realistic.