High-temperature heat capacity and thermodynamic properties for end-member titanite (CaTiSiO5)     

J. Tangeman  D. Xirouchakis 《Physics and Chemistry of Minerals》2001,28(3):167-176

 The heat capacity of end-member titanite and (CaTiSiO₅) glass has been measured in the range 328–938 K using differential scanning calorimetry. The data show a weak λ-shaped anomaly at 483 ± 5 K, presumably associated with the well-known low-pressure P2₁/a ⇆ A2/a transition, in good agreement with previous studies. A value of 0.196 ± 0.007 kJ mol⁻¹ for the enthalpy of the P2₁/a ⇆ A2/a transition was determined by integration of the area under the curve for a temperature interval of 438–528 K, bracketing the anomaly. The heat capacity data for end-member titanite and (CaTiSiO₅) glass can be reproduced within <1% using the derived empirical equations (temperature in K, pressure in bars): The available enthalpy of vitrification (80.78 ± 3.59 kJ mol⁻¹), and the new heat capacity equations for solid and glass can be used to estimate (1) the enthalpy of fusion of end-member titanite (122.24 ± 0.2 kJ mol⁻¹), (2) the entropy of fusion of end-member titanite (73.85 ± 0.1 J/mol K⁻¹), and (3) a theoretical glass transition temperature of 1130 ± 55 K. The latter is in considerable disagreement with the experimentally determined glass transition temperature of 1013 ± 3 K. This discrepancy vanishes when either the adopted enthalpy of vitrification or the liquid heat content, or both, are adjusted. Calculations using Eq. (2), new P−V−T data for titanite, different but also internally consistent thermodynamic data for anorthite, rutile, and kyanite, and experimental data for the reaction: anorthite + rutile = titanite + kyanite strongly suggest: (1) the practice to adjust the enthalpy of formation of titanite to fit phase equilibrium data may be erroneous, and (2) it is probably the currently accepted entropy of 129.2 ± 0.8 J/mol K⁻¹ that may need revision to a smaller value. Received: 30 December 1999 / Accepted: 23 June 2000  相似文献   

Multifractal and entropic properties of landslides in Japan   总被引：4，自引：0，他引：4  

C. Goltz 《International Journal of Earth Sciences》1996,85(1):71-84

Landslide distributions in two major areas of northern Japan, Tohoku and Hokkaido, are analysed for multifractal properties. For the latter data set, also the multifractal spectrum for the spatial landslide size distribution is determined and compared to the probability distribution. It is concluded that the fields possess definite multifractal character. This finding is supported by the known multifractality of the main triggering processes, rain and earthquakes. Further support comes from a configuration entropy analysis which is found to be a useful complimentary tool to multifractal analysis. Models leading to multifractality are briefly reviewed. Careful attention is paid to the algorithms used and to the verification of the numerical results. Some general suggestions concerning numerical methods are made.  相似文献   

APPLICATION OF MEM SPECTRAL ESTIMATION TO MU RADAR OBSERVATION   总被引：1，自引：0，他引：1       下载免费PDF全文

Li Wei  L&#;Daren  Shoichiro Fukao  Mamoru Yamamoto  Toshitaka Tsu  Susumu Kato 《Acta Meteorologica Sinica》1991,5(3):293-298

Preliminary results of the wind velocity estimation using the Maximum Entropy Method (MEM) to MUradar observation data sets are presented. The comparison of the results from the periodogram method and theMEM shows that the MEM estimation is reliable, and has higher accuracy, resolution and detectability than theestimation from periodogram method. The high accuracy power spectrum obtained by the MEM is veryuseful to studying the atmospheric turbulence structure. However. the MEM needs the longer computingtime for obtaining the high accuracy spectrum. Particularly, the estimation of MEM will bring serious devia-tion at lower signal-to-noise ratio.  相似文献   

超谱遥感图像快速聚类无损压缩算法   总被引：1，自引：0，他引：1  

王朝晖  周佩玲 《遥感学报》2003,7(5):400-406

K-means聚类要求每个像素要和所有聚类中心求欧氏距离，当聚类数很多时，这是一个相当耗时的工作。改进的K—meam聚类算法根据历史聚类结果进行初始类分割，即节约初始聚类时间，又能使历史聚类过程中形成的类间稳定关系得以保持；类内像素只和相邻的聚类中心计算距离进行聚类，随着算法的迭代进行，大量类的状态基本固定，使得聚类速度不断加快。基于改进K-means聚类的无损压缩算法具有充分利用历史聚类成果和收敛速度快的特点，通过提高类内像素冗余度，最大限度消除谱间冗余和空间冗余。采用多次聚类压缩的结果预测最佳聚类数的方法，可实现最小熵无损压缩。通过和DPCM算法概率模型的熵值比较及实验数据的分析，验证了基于聚类无损压缩效率比不聚类无损压缩效果更优。  相似文献   

The solar magnetic flux mid-term periodicities and the solar dynamo     

J.F. Valds-Galicia  A. Lara  B. Mendoza 《Journal of Atmospheric and Solar》2005,67(17-18):1697

We investigate here the fluctuations in the total, open and closed solar magnetic flux (SMF) for the period 1971–1999 by means of the maximum entropy method in the frequency range 5×10⁻⁹–10⁻⁷ Hz (6 yr to 120 days). We use monthly data for the total, open and closed magnetic solar fluxes. Periodicities found in the series are similar showing that there is some relationship between the fluxes. The most important finding of this work is the existence of fluctuations at around 1.3 and 1.7 yr in the SMF with alternating importance during consecutive even and odd solar cycles. These fluctuations are directly related with variations present in cosmic rays, solar wind parameters and geomagnetic activity indexes. A quasi-triennial periodicity previously found in sunspots and other solar phenomena is also of importance. The SMF is generated by the action of the solar dynamo; therefore, it is through the magnetic flux that the solar dynamo influences several heliospheric phenomena.  相似文献   

Some notes on entropy measures. II. The relative entropy matrix and the positivity constraint     

Ian Lerche 《Mathematical Geology》1989,21(8):843-852

Based on the maximum entropy concept with the number of bins (class intervals), N, maximized in terms of residual errors in sampling of the system, the residual entropy matrix (REM), which is intrinsically positive definite, is sampled uniformly at N equal intervals in entropy space. The mandatory constraint of positivity shows that the finitely sampled REM then provides estimates on the magnitudes of missing components of the autocorrelation sequence describing REM. If the mandatory constraint is relaxed to its limit, the resulting prediction for REM is identical to Burg's (1967) maximum entropy algorithm. The advantages are that assessments can be made: (i) whether the missing components are known accurately enough that no further measurements are needed; (ii) the N equal intervals of the entropy measure are sufficient to provide resolution on the REM for each and every sample; or (iii) whether finer interval resolution is needed to extract information for a particular sample.  相似文献   

新疆及其邻区M≥7强震的预测研究   总被引：2，自引：0，他引：2       下载免费PDF全文

门可佩 《地震工程学报》1994,16(4):29-36

新疆及其邻近地区Ｍ≥７强震活动在时间分布上具有明显的有序性。自１７１６年以来的２１次Ｍ≥７强震存在着时间间隔为１１、２５、３０、４１和６０年的有序值。利用强震活动时间的有序性结构，可对该区７级强震进行预测探索。本文同时还应用熵和经验分布函数，讨论了下次强震发生的地点和概率。  相似文献   

Revisiting prior distributions,Part II: Implications of the physical prior in maximum entropy analysis     

Rafi Baker  George Christakos 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):435-446

The well-known “Maximum Entropy Formalism” offers a powerful framework for deriving probability density functions given a relevant knowledge base and an adequate prior. The majority of results based on this approach have been derived assuming a flat uninformative prior, but this assumption is to a large extent arbitrary (any one-to-one transformation of the random variable will change the flat uninformative prior into some non-constant function). In a companion paper we introduced the notion of a natural reference point for dimensional physical variables, and used this notion to derive a class of physical priors that are form-invariant to changes in the system of dimensional units. The present paper studies effects of these priors on the probability density functions derived using the maximum entropy formalism. Analysis of real data shows that when the maximum entropy formalism uses the physical prior it yields significantly better results than when it is based on the commonly used flat uninformative prior. This improvement reflects the significance of the incorporating additional information (contained in physical priors), which is ignored when flat priors are used in the standard form of the maximum entropy formalism. A potentially serious limitation of the maximum entropy formalism is the assumption that sample moments are available. This is not the case in many macroscopic real-world problems, where the knowledge base available is a finite sample rather than population moments. As a result, the maximum entropy formalism generates a family of “nested models” parameterized by the unknown values of the population parameters. In this work we combine this formalism with a model selection scheme based on Akaike’s information criterion to derive the maximum entropy model that is most consistent with the available sample. This combination establishes a general inference framework of wide applicability in scientific/engineering problems.  相似文献   

1961—2016年祁连山区季节性干旱综合指数特征分析     

郭小芹  罗永忠 《气象与环境学报》2019,35(1):88-93

采用Z指数和熵权理论,构建了干旱综合指数作为干旱强度评价标准,对祁连山区季节性干旱特征及其空间分布规律进行了深入剖析。结果表明:1961—2016年季节性干旱强度普遍减弱,其中春秋两季显著减弱,夏季明显减弱;尽管20世纪60—70年代、90年代为季节性干旱频发与重发时段,但从2000年以来夏旱与冬旱却比较频繁,不容忽视。干旱强度由强到弱依次为冬季、夏季、春季和秋季,冬季干旱程度最强;在干旱波动性上秋季最强,冬季次之,春季最弱。春夏秋三季南侧比北侧干旱,冬季北侧比南侧干旱,其中冬季干旱范围最为广泛,尤以酒泉为中心的北侧区域最为显著。在研究时段内祁连山南北两侧干旱强度逐渐减弱,南侧明显减弱,枯草期干旱强度减弱程度尤为显著。本研究为祁连山区干旱评价提供了参考依据。  相似文献   

The relationship between obesity and socioeconomic status among Texas school children and its spatial variation     

《Applied geography (Sevenoaks, England)》2017

Understanding the relationships between obesity and socioeconomic status (SES) among school children and the spatial variation of such relationship is essential for developing appropriate intervention strategies. In this study, we employed Local Entropy Map (LEM) to explore the spatial patterns of the relationship at school district level in Texas. Children's obesity was measured by Body Mass Index (BMI). The BMI data for this study were obtained from Physical Fitness Assessment Initiative (PFAI) program that has been coordinated by Texas Education Agency (TEA). SES was described by six variables, which were further reduced into two factors, namely Household SES and Neighborhood SES. The study period was 2012–2013 academic year. LEM analyses revealed clear spatial variation of the relationship between obesity and SES at school-district level. In particular, the prevalence of obesity among school children was found to be significantly related to Household SES and Neighborhood SES in four regions in Texas. These four regions are centered in major metropolitan areas in Texas, including San Antonio, Dallas-Fort Worth, Houston, and Lubbock. Further regression analyses showed variation of the relationship across these four regions. Obesity among school children in Texas was found to be more related to Household SES than Neighborhood SES; the relationship was strongest in San Antonio region. These findings may suggest the presence of obesogenic environment in the low SES school districts in these regions. Further studies to examine the particular nature of the obesogenic environment in these school districts are needed in order to support the development of regionalized policy and practice that can be more effective in addressing locale specifics.  相似文献