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As a model-free algorithm, deep reinforcement learning (DRL) agent learns and makes decisions by interacting with the environment in an unsupervised way. In recent years, DRL algorithms have been widely applied by scholars for portfolio optimization in consecutive trading periods, since the DRL agent can dynamically adapt to market changes and does not rely on the specification of the joint dynamics across the assets. However, typical DRL agents for portfolio optimization cannot learn a policy that is aware of the dynamic correlation between portfolio asset returns. Since the dynamic correlations among portfolio assets are crucial in optimizing the portfolio, the lack of such knowledge makes it difficult for the DRL agent to maximize the return per unit of risk, especially when the target market permits short selling (i.e., the US stock market). In this research, we propose a hybrid portfolio optimization model combining the DRL agent and the Black-Litterman (BL) model to enable the DRL agent to learn the dynamic correlation between the portfolio asset returns and implement an efficacious long/short strategy based on the correlation. Essentially, the DRL agent is trained to learn the policy to apply the BL model to determine the target portfolio weights. In this model, we formulate a specific objective function based on the environment's reward function, which considers the return, risk, and transaction scale of the portfolio. Our DRL agent is trained by propagating the objective function's gradient to the policy function of our DRL agent. To test our DRL agent, we construct the portfolio based on all the Dow Jones Industrial Average constitute stocks. Empirical results of the experiments conducted on real-world United States stock market data demonstrate that our DRL agent significantly outperforms various comparison portfolio choice strategies and alternative DRL frameworks by at least 42% in terms of accumulated return. In terms of the return per unit of risk, our DRL agent significantly outperforms various comparative portfolio choice strategies and alternative strategies based on other machine learning frameworks. [ABSTRACT FROM AUTHOR]

The paper Zhao et al. (Ann Oper Res 226:727–739, 2015) shows that mean-CVaR-skewness portfolio optimization problems based on asymetric Laplace (AL) distributions can be transformed into quadratic optimization problems for which closed form solutions can be found. In this note, we show that such a result also holds for mean-risk-skewness portfolio optimization problems when the underlying distribution belongs to a larger class of normal mean–variance mixture (NMVM) models than the class of AL distributions.We then study the value at risk (VaR) and conditional value at risk (CVaR) risk measures of portfolios of returns with NMVM distributions.They have closed form expressions for portfolios of normal and more generally elliptically distributed returns, as discussed in Rockafellar and Uryasev (J Risk 2:21–42, 2000) and Landsman and Valdez (N Am Actuar J 7:55–71, 2003). When the returns have general NMVM distributions, these risk measures do not give closed form expressions. In this note, we give approximate closed form expressions for the VaR and CVaR of portfolios of returns with NMVM distributions.Numerical tests show that our closed form formulas give accurate values for VaR and CVaR and shorten the computational time for portfolio optimization problems associated with VaR and CVaR considerably. [ABSTRACT FROM AUTHOR]

The Ediacaran Period (~635–539 Ma) is marked by the emergence and diversification of complex metazoans linked to ocean redox changes, but the processes and mechanism of the redox evolution in the Ediacaran ocean are intensely debated. Here we use mercury isotope compositions from multiple black shale sections of the Doushantuo Formation in South China to reconstruct Ediacaran oceanic redox conditions. Mercury isotopes show compelling evidence for recurrent and spatially dynamic photic zone euxinia (PZE) on the continental margin of South China during time intervals coincident with previously identified ocean oxygenation events. We suggest that PZE was driven by increased availability of sulfate and nutrients from a transiently oxygenated ocean, but PZE may have also initiated negative feedbacks that inhibited oxygen production by promoting anoxygenic photosynthesis and limiting the habitable space for eukaryotes, hence abating the long-term rise of oxygen and restricting the Ediacaran expansion of macroscopic oxygen-demanding animals. Using Hg isotopes, the authors find that repeated invasion of toxic, H2S-rich water into the marine photic zone of the Ediacaran ocean may have inhibited the rise of oxygen and delayed the expansion of early animals. [ABSTRACT FROM AUTHOR]

Retinoic acid-related orphan receptor alpha (RORA) suppression is associated with autism spectrum disorder (ASD) development, although the mechanism remains unclear. In this study, we aim to investigate the potential effect and mechanisms of RORA suppression on autism-like behavior (ALB) through maternal diabetes-mediated mouse model. Our in vitro study in human neural progenitor cells shows that transient hyperglycemia induces persistent RORA suppression through oxidative stress-mediated epigenetic modifications and subsequent dissociation of octamer-binding transcription factor 3/4 from the RORA promoter, subsequently suppressing the expression of aromatase and superoxide dismutase 2. The in vivo mouse study shows that prenatal RORA deficiency in neuron-specific RORA null mice mimics maternal diabetes-mediated ALB; postnatal RORA expression in the amygdala ameliorates, while postnatal RORA knockdown mimics, maternal diabetes-mediated ALB in offspring. In addition, RORA mRNA levels in peripheral blood mononuclear cells decrease to 34.2% in ASD patients (n = 121) compared to the typically developing group (n = 118), and the related Receiver Operating Characteristic curve shows good sensitivity and specificity with a calculated 84.1% of Area Under the Curve for ASD diagnosis. We conclude that maternal diabetes contributes to ALB in offspring through suppression of RORA and aromatase, RORA expression in PBMC could be a potential marker for ASD screening. Hong Yu, Yanbin Niu, Guohua Jia et al. integrate in vitro, in vivo, and human experiments to examine a link between RORA expression on autism-like behavior. Their results suggest that maternal diabetes may contribute to autism-like behavior via RORA suppression. [ABSTRACT FROM AUTHOR]

This paper concerns the worst-case complexity of cyclic coordinate descent (C-CD) for minimizing a convex quadratic function, which is equivalent to Gauss–Seidel method, Kaczmarz method and projection onto convex sets (POCS) in this simple setting. We observe that the known provable complexity of C-CD can be O (n 2) times slower than randomized coordinate descent (R-CD), but no example was proven to exhibit such a large gap. In this paper we show that the gap indeed exists. We prove that there exists an example for which C-CD takes at least O (n 4 κ CD log 1 ϵ) operations, where κ CD is related to Demmel's condition number and it determines the convergence rate of R-CD. It implies that in the worst case C-CD can indeed be O (n 2) times slower than R-CD, which has complexity O (n 2 κ CD log 1 ϵ) . Note that for this example, the gap exists for any fixed update order, not just a particular order. An immediate consequence is that for Gauss–Seidel method, Kaczmarz method and POCS, there is also an O (n 2) gap between the cyclic versions and randomized versions (for solving linear systems). One difficulty with the analysis is that the spectral radius of a non-symmetric iteration matrix does not necessarily constitute a lower bound for the convergence rate. Finally, we design some numerical experiments to show that the size of the off-diagonal entries is an important indicator of the practical performance of C-CD. [ABSTRACT FROM AUTHOR]

Monomethylmercury (MMHg) is a potent toxin that bioaccumulates and magnifies in marine food webs. Recent studies show abundant methylated Hg in deep oceans (>1000 m), yet its origin remains uncertain. Here we measured Hg isotope compositions in fauna and surface sediments from the Mariana Trench. The trench fauna at 7000–11000 m depth all have substantially positive mass-independent fractionation of odd Hg isotopes (odd-MIF), which can be generated only in the photic zone via MMHg photo-degradation. Given the identical odd-MIF in trench fauna and North Pacific upper ocean (<1000 m) biota MMHg, we suggest that the accumulated Hg in trench fauna originates exclusively from MMHg produced in upper oceans, which penetrates to depth by sorption to sinking particles. Our findings reveal little in-situ MMHg production in deep oceans and imply that anthropogenic Hg released at the Earth's surface is much more pervasive across deep oceans than was previously thought. Monomethylmercury is a toxin that humans can be exposed to after consumption of seafood in which it has bioaccumulated. Here the authors show that amphipods in the deepest point of the global ocean contain monomethylmercury with surface origins, suggesting rapid sinking of this toxin on particles. [ABSTRACT FROM AUTHOR]

Concentrations of mercury and other heavy metals were measured in soils surrounding the Wuda Coalfield, Inner Mongolia where underground coal fires are regarded as an important contamination source. Soil samples at the downwind direction were nearly all enriched mercury in surface layers, with their concentrations ~ 10 times higher than those from upwind soils. Mercury concentrations generally increased along soil profiles upward, indicative of increasing atmospheric mercury deposition in recent decades. We suggest that underground coal fire emissions were the potential mercury contamination source and the key factor controlling mercury enrichment in soils. Other heavy metals showed no clear spatial and vertical trends, suggesting that underground coal fire emissions may not the main factor for their enrichment in soils. Antimony showed the highest enrichment followed by tin, while chromium, mercury and cadmium only exhibited slight enrichment. Risk evaluation indicated that heavy metals in the studied soils pose no ecological threats. [ABSTRACT FROM AUTHOR]

Mercury (Hg) stable isotope is a useful tool to understand the transformation of atmospheric Hg. The observation on the enrichment of heavier isotopes in gaseous elemental Hg (GEM) relative to oxidized HgII species in atmosphere cannot be convincingly explained by isotope fractionation of Hg redox processes. This review shows that the large Hg isotope mass dependent fractionation (MDF) in coal-fired boilers is one of the underlying reasons. The reported Hg isotope data of feed coals and their combustion products are first summarized to give a general overview of how Hg isotopes fractionate before Hg discharge from coal-fired boilers. Then, predictive MDF models are discussed to simulate δ202Hg values of different Hg species in coal combustion flue gases. The discharged GEM is predicted to have the highest δ202Hg followed by gaseous HgII and particulate-bound HgII, which is in consistent with the observed MDF pattern of atmospheric Hg species. [ABSTRACT FROM AUTHOR]

To investigate the spatial and historical distributions, and source contributions of polycyclic aromatic hydrocarbon (PAHs) from the middle reach of Huai River, 15 surface sediments and two sediment cores were analyzed. The Σ16 PAHs levels in surface sediments varied from 533.15 to 1422.83 ng/g dw, and from 413.27 to 43951.56 ng/g dw in individual sediment layer of sediment cores. The temporal trends of PAHs in sediment cores are the good indicators of the anthropogenic emissions over the last 60 years. The stable carbon isotope ratios of PAHs indicate the primary PAHs sources were the combustion of wood and coal during 1950s–1970s, and automobile exhausts and the coal combustion emissions in recent decades. [ABSTRACT FROM AUTHOR]

Vanadium in coals may have potential environmental and economic impacts. However, comprehensive knowledge of the geochemistry of V in coals is lacking. In this study, abundances, distribution and modes of occurrence of V are reviewed by compiling >2900 reported Chinese coal samples. With coal reserves in individual provinces as the weighting factors, V in Chinese coals is estimated to have an average abundance of 35.81 μg/g. Large variation of V concentration is observed in Chinese coals of different regions, coal-forming periods, and maturation ranks. According to the concentration coefficient of V in coals from individual provinces, three regions are divided across Chinese coal deposits. Vanadium in Chinese coals is probably influenced by sediment source and sedimentary environment, supplemented by late-stage hydrothermal fluids. Specifically, hydrothermal fluids have relatively more significant effect on the enrichment of V in local coal seams. Vanadium in coals is commonly associated with aluminosilicate minerals and organic matter, and the modes of V occurrence in coal depend on coal-forming environment and coal rank. The Chinese V emission inventory during coal combustion is estimated to be 4906 mt in 2014, accounting for 50.55 % of global emission. Vanadium emissions by electric power plants are the largest contributor. [ABSTRACT FROM AUTHOR]

A better understanding on the partitioning behavior of mercury (Hg) during coal combustion in large-scale coal-fired power plants is fundamental for drafting Hg-emission control regulations. Two large coal-fired utility boilers, equipped with electrostatic precipitators (ESPs) and a wet flue gas desulfurization (WFGD) system, respectively, in coal energy-dominant Huainan City, China, were selected to investigate the distribution and fate of Hg during coal combustion. In three sampling campaigns, we found that Hg in bottom ash was severely depleted with a relative enrichment (RE) index <7 %, whereas the RE index for fly ash (9-54 %) was comparatively higher and variable. Extremely high Hg was concentrated in gypsum (≤4500 ng/g), which is produced in the WFGD system. Mass balance calculation shows that the shares of Hg in bottom ash, fly ash, WFGD products (gypsum, effluents, sludge), and stack emissions were <2, 17-32, 7-22, and 54-82 %, respectively. The Hg-removal efficiencies of ESPs, WFGD, and ESPs + WFGD were 17-32, 10-29, and 36-46 %, respectively. The Hg-emission factor of studied boilers was in a high range of 0.24-0.29 g Hg/t coal. We estimated that Hg emissions in all Huainan coal-fired power plants varied from 1.8 Mg in 2003 to 7.3 Mg in 2010. [ABSTRACT FROM AUTHOR]

A better understanding on geochemistry of elements in coal has both environmental and geological implications. In this study, 53 coal samples were collected from No. 8 coal seam of the Zhuji coal mine, Huainan Coalfield. The concentrations of 49 elements, ash yield, and total organic compound (TOC), as well as mineralogical phases in coal were determined. As compared with Chinese, the USA, and world coals, Si, K, Se, Cd, Sn, Sb, and W in studied coal seam are higher, whereas Zn, As, and Lu are lower. The enrichment factor and concentration coefficient show that Se, Cd, Sn, Sb, and W are preferably enriched in studied coals. The enrichment of Se and Cd is probably attributed to their higher proportions of organic forms. Most major and trace elements tend to concentrate in either the upper or lower sections of coal seams, which suggest that depositional micro-environment was important in controlling elements migration and enrichment. The correlation analysis of elements with ash yield shows that the behavior of elements in coal follows the periodic change of metallic activity. The modes of occurrence of major and trace elements are elaborated by statistical methods. Silicon is mainly in form of montmorillonite or presents as free quartz. Iron is associated with chlorite, siderite, lepidocrocite, and other iron-bearing minerals. Ti shows obviously organic association. Three groups of elements are divided in accordance with the cluster dendrogram: Group 1 (Sc–HREE–Be–Y–V–Co–Cu–P–Sr–B–Sn–Se–Bi–TOC–S–Ba–As), Group 2 (LREE–Zn–Al–Mn–Li–Na–Th–Cr–Fe–Mg) and Group 3 (Ca–Mo–Si–W–Ad–Ti–Pb–K). Many trace elements, including Li, Sc, V, Cr, Zn, Sr, La, Ce, Nd, Sm, Eu, Gd, Tb, Lu, Pb, Bi, and Th, correlate positively with Al, suggesting their occurrence mainly in clay such as kaolinite and chlorite. REE in the studied coalfield was primarily supplied by terrestrial clastics coming from North China Coal Basin. The differentiation of LREE and HREE is probably attributable to their different physicochemical characterisitcs and specific paleo-sedimentary environment. Various indexes (e.g., B content, Ash Index, C-value) and the existence of certain minerals suggest a reducing and anoxic sedimentary environment of coal swamp with a stable supply of terrigenous detrital materials in a moist environment. The origins of enriched elements are primarily derived from the source rock, sedimentary environment, and thermally contact metamorphism or possibly magmatic–hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Based on 1625 data collected from the published literature, the geochemistry of tin (Sn) in Chinese coals, including the abundance, distribution, modes of occurrence, genetic types and combustion behavior, was discussed to make a better understanding. Our statistic showed the average Sn of Chinese coal was 3.38 mg/kg, almost two times higher than the world. Among all the samples collected, Guangxi coals occupied an extremely high Sn enrichment (10.46 mg/kg), making sharp contrast to Xinjiang coals (0.49 mg/kg). Two modes of occurrence of Sn in Chinese coals were found, including sulfide-bounded Sn and clay-bounded Sn. In some coalfields, such as Liupanshui, Huayingshan and Haerwusu, a response between REEs distribution and Sn content was found which may caused by the transportation of Sn including clay minerals between coal seams. According to the responses reflecting on REEs patterns of each coalfield, several genetic types of Sn in coalfields were discussed. The enrichment of Sn in Guangxi coals probably caused by Sn-rich source rocks and multiple-stage hydrothermal fluids. The enriched Sn in western Guizhou coals was probably caused by volcanic ashes and sulfide-fixing mechanism. The depletion of Sn in Shengli coalfield, Inner Mongolia, may attribute to hardly terrigenous input and fluids erosion. As a relative easily volatilized element, the Sn-containing combustion by-products tended to be absorbed on the fine particles of fly ash. In 2012, the emission flux of Sn by Chinese coal combustion was estimated to be 0.90 × 10 g. [ABSTRACT FROM AUTHOR]

Selenium, a toxic element, is highly enriched in the coals of the Huaibei coal deposit, China. For this study, Se content along with rock-forming and trace element abundances was determined in 123 coal and 19 rock samples collected from the main coal seams in seven coal mines in the Huaibei coalfield. This was done to investigate the Se geochemistry in the Huaibei coals. Compared with average Chinese coal and other coals around the world, the Huaibei coals are enriched in Se by a factor of five. Differences in the boron content in the sequence of Huaibei coal seams show that the depositional environment of the formations hosting the coal seams evolved from a delta front to a prodelta setting and then to a delta plain environment. Selenium is distributed unevenly both horizontally and vertically in the Huaibei coal deposit. Pearson correlation coefficients between Se with several elements (Ca, Fe, and S) indicate that iron-bearing clay minerals and carbonates are the dominant carriers of Se in coals of the Lower Shihezi Formation. Selenium in coals from No. 3 and No. 10 coal seams are mainly associated with sulfide minerals. The well-developed faults in Huaibei coalfield may have contributed to the enrichment of Se in Huaibei coals. [ABSTRACT FROM AUTHOR]

Perhydrous bituminous coal has multi-purpose industrial applications established by its distinctive thermal behavior. The Huainan coalfield in China has a large volume of these types of coals. Nevertheless, little information is obtainable with respect to their thermodynamic characteristics. In this study, one representative coal sample, selected from Zhuji Coal Mine, was scrutinized using thermogravimetry/mass spectrometry at different heating rates. The observed results indicate that the process of thermal decomposition of this sample can be partitioned into three evident stages associated with its mass loss rates and the releasing of gaseous species. The secondary pyrolysis step (300-600 °C), in particular, was affected by means of the alterations of heating rate. The maximum mass loss rate and the releasing rate of gaseous species increased related with the increase of heating rate. To achieve reliable kinetic parameters, the Coats-Redfern and Flynn-Wall-Ozawa methods are integrated. The activation energy is applicable in the range of 108-224 kJ mol. [ABSTRACT FROM AUTHOR]

Coal is one of the major energy resources in China, accounting for approximately 70 % of primary energy consumption. Many environmental problems and human health risks arise during coal exploitation, utilization, and waste disposal, especially in the remote mountainous areas of western China (e.g., eastern Yunnan, western Guizhou and Hubei, and southern Shaanxi). In this paper, we report a thorough review of the environmental and human health impacts related to coal utilization in China. The abundance of the toxic trace elements such as F, As, Se, and Hg in Chinese coals is summarized. The environmental problems (i.e., water, soil, and air pollution) that are related to coal utilization are outlined. The provenance, distributions, typical symptoms, sources, and possible pathways of endemic fluorosis, arsenism, and selenosis due to improper coal usage (briquettes mixed with high-F clay, mineralized As-rich coal, and Se-rich stone coal) are discussed in detail. In 2010, 14.8, 1.9 million, and 16,000 Chinese people suffered from dental fluorosis, skeletal fluorosis, and arsenism, respectively. Finally, several suggestions are proposed for the prevention and treatment for endemic problems caused by coal utilization. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is an element of environmental and geological significance. Quantification of different Hg-binding forms is crucial to understand geological Hg provenances and associated geochemical processes during coal formation. In this study, seven coal samples were selected, according to coal rank (i.e., middle volatile bituminous, C-3; low volatile bituminous, C-2; anthracite, C-1), chemical anomalies (high S coal, IBC-105; high Cl coal, C22650) and sampling environment (fresh coal, LH; weathered coal LHW), to determine their Hg-binding forms using well-established sequential extraction procedures coupled with sink-float experiment. In the thermally metamorphosed samples C-1 and C-2, a comparative enrichment of total Hg relative to C-3 is observed. Silicate- and organic-bound Hg are the dominant Hg-binding forms in C-1, suggesting possible Hg sources from magma silicate and secondary Hg enrichment by adsorption. Sulfide- and organic-bound Hg are the most abundant Hg-binding forms in IBC-105, whereas only organic-bound Hg dominates in CC22650. Weathering processes are suggested to transform the abundant sulfide-bound Hg in LH to silicate- and organic-bound Hg in its weathering product LHW. [ABSTRACT FROM AUTHOR]

Lead (Pb) has gained much attention since the 1970s because of its potential and cumulative toxicity. As one of the most hazardous elements in coals, Pb can be released into the environment during coal mining, processing, and utilization. This study presents a synthesis on the abundance, distribution, modes of occurrence, and environmental impacts of Pb in Chinese coals. Using the expected coal reserves as the weighting factor and based on the previously published Pb content in 4,304 coal samples (including results obtained in our laboratory) from main coalfields or coal mines in China, the weighted mean Pb content in Chinese coals is 13.0 μg/g, which is higher than that of the American coals (11 μg/g) and average world coals (7.8 μg/g). With respect to regional distribution of Pb in Chinese coals, Pb content can be arbitrarily divided into three groups (<20, 20-40, >40 μg/g). Following this classification, coals from Tibet have the highest average Pb content (128.94 μg/g). The abundance of Pb in coals varies with coal-forming periods and coal ranks, with the late Triassic and higher rank coals having the highest Pb content, which could be ascribed to regional geochemical differences and later geological evolution as well as magma hydrothermal activities. The enrichment of Pb in coals is influenced by several geological factors, including coal-forming plants, source rocks, hydrothermal fluid, and depositional environment. Pb, dominantly associates with sulfide minerals, especially galena in coals. During coal combustion or pyrolysis, Pb is partly emitted into the atmosphere and partly partitioned to solid residues. Accumulation of Pb from coal utilization in human body could lead to a range of health problems and increase the risk of cancer. [ABSTRACT FROM AUTHOR]

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1-20 ng/g) by wet chemistry is challenging. Combustion-trapping techniques have been shown to be an appropriate alternative []. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into HO, CO, SO, etc. The O carrier gas, including combustion products and elemental Hg, is then purged into a 40 % ( v/ v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO/1HCl ( v/ v), 25 mL/min O flow rate, and a dynamic temperature ramp rate (15 °C/min for 25-150 and 600-900 °C; 2.5 °C/min for 150-600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81-102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80-120 %. This protocol has the advantages of a short sample processing time (∼3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis. [ABSTRACT FROM AUTHOR]

Twenty-nine low sulfur coal samples were selected to determine the magnitude and variability of mercury (Hg) content in a well-documented stratigraphy system including ten continuous coal seams in Zhuji Coal Mine, Huainan Coalfield, Anhui Province, North China. Mercury content of samples was measured on a direct mercury analyzer and confident results were obtained as evaluated by standard references, sample replicates and procedural blanks. The calculated overall mine average Hg content is 71.19 ± 9.28 ng/g based on seam averages and weighting by the estimated reserve of each coal seam. The estimated Hg emission potential for Huainan coalfield is obviously lower than that calculated from coal emission factor in industrial use. An increasing trend of Hg content with the evolution of depositional environment was observed from Nos. 3 to 11-2 coal seams. Combining the evidence of sedimentology and paleontology, a better understanding was gained of the mechanism of Hg sequestration in specific coal benches. A large portion of Hg residing in the low sulfur coals presumably integrated to the functional groups of organic constitution, whereas pyrite was generally abundant in the high sulfur coals. [ABSTRACT FROM AUTHOR]