Large-scale Decomposition Research Articles

Evolution of S/N containing compounds in pyrolysis of highly oily petroleum sludge

Pyrolysis of oily sludge in inert environment has a strong potential for energy recovery, in which the transformation of S/N containing compounds is a key to influence the quality of various products. This work addresses the evolution of S/N containing compounds in pyrolysis process of two oily sludge samples with high oil content by comparing the species and distribution of S/N containing compounds in origin samples and char. The results demonstrate that aromatic and saturated completed volatilize or react completely at 500 °C while the resin completed the reaction at 750 °C–800 °C. The S-containing compounds are mainly Sulfate-S. At 500 °C, most sulfate remained unchanged, and continued heating led to a large-scale decomposition. After condensation and cyclization, the S/N compounds were transformed into components with high thermal stability. Sulfoxide-S, Thiophenic-S and Aromatic-S with more stable thermal stability held the main position at higher temperature. The transformation of N-containing compounds was almost based on Proteins-N. As the temperature rising from 500 °C to 700 °C and 900 °C, the content of protein-N decreased continuously and transformed into high thermal stability Pyridine-N, Pyrrole-N and Quaternary graphic-N, which could account for more than 90%. This work provides a theoretical basis for the distribution and transformation of S/N in char, the deep application of char and the pollution prevention in subsequent treatment.

Large-scale decomposition of green ammonia for pure hydrogen production

It is acknowledged that Hydrogen has a decisive role to play in insuring a reliable and efficient penetration of renewable electricity in the energy mix. Nonetheless, building a sustainable Hydrogen Economy is faced with numerous challenges across the value chain. Namely, large-scale production and storage are still open issues that need to be addressed. A promising solution is to store renewable H2 in the form of green ammonia often referred to as Power-to-Ammonia. Thus unlocking all available infrastructure for ammonia to effectively store and export hydrogen in bulk. In this value chain, the missing link is ammonia cracking to recover back hydrogen at high purities. The present work explores a technical solution to recover hydrogen from ammonia at large-scale. Through an exhaustive technoeconomic analysis, we have demonstrated the feasibility of large-scale production of pure H2 from ammonia. The designed Ammonia-to-H2 plant operates at a thermal efficiency of 68.5% to produce 200 MTPD of pure hydrogen at 250 bar. Furthermore, this study has established a final estimation of the Levelized Cost of Hydrogen (LCOH) from green ammonia. It was revealed that LCOH is mostly dependent on green ammonia cost, which in turn varies with renewable electricity cost.

Mechanism for the enrichment of organic matter in the Liushagang Formation of the Weixinan Sag, Beibuwan Basin, China

Eocene lacustrine organic-rich shales, mudstones and shales in the middle member of Liushagang Formation (designated as LS2) are the most important source rocks in the Beibuwan Basin located in the northwest of the South China Sea. In this study, we explored the mechanisms responsible for the accumulation of organic matter in source rocks from LS2 of Weixinan Sag by investigating the paleoclimate, paleoredox, paleoproductivity and lithological characteristics of the parent rocks using biomarkers and elemental geochemistry data. Based on our analytical data, the deposition of the source rocks from LS2 occurred in a warm, humid paleoclimate with moderate chemical weathering, as indicated by CIA indexes and Sr/Cu ratios. The Sr/Ba ratios and gammacerane indexes indicated that the source rocks from LS2 were deposited in a freshwater paleolake. The Corg/P ratios and Redox Sensitive Elements (RSEs) -TOC bivariate diagrams demonstrated that the organic-rich shales and mudstones/shales deposited under anoxic and oxic-suboxic conditions, respectively. The levels of TOC, copper (Cu), molybdenum (Mo) and C30 4-methylsterance index in the organic-rich shales were higher than those of the mudstones and shales, indicating greater algae bloom and paleoproductivity during the deposition of the organic-rich shales compared to during the sedimentation of the mudstones and shales. Combined with La/Yb-∑REE, SiO2–TiO2, Al2O3/TiO2, Nb/Ta and Cr/Co ratios, it is considered that the parent rocks of the organic-rich shales were granite of relatively intermediate lithological compositions, with greater levels of nutrients such as phosphorus (P), Mo, Cu, compared to those of the mudstones and shales. Large-scale decomposition of dead algae led to oxygen depletion, which created favorable conditions for the preservation of organic matter and the release of P from the sediments to water. The increased content of P in water subsequently aggravated algal blooms. Such a positive feedback loop was conducive to the formation of organic-rich shales. The inter-relationships of algal blooms (controlled by P), paleoproductivity and paleoredox conditions play an important role in the accumulation of organic matter in organic-rich shales from LS2 of Weixinan Sag, Beibuwan Basin.

Study of Indoor Ventilation Based on Large-Scale [DNS by a Domain Decomposition Method

This paper presents a large-scale Domain Decomposition Method (DDM) based Direct Numerical Simulation (DNS) for predicting the behavior of indoor airflow, where the aim is to design a comfortable and efficient indoor air environment of modern buildings. An analogy of the single-phase convection problems is applied, and the pressure stabilized domain decomposition method is used to symmetrize the linear systems of Navier-Stokes equations and the convection-diffusion equation. Furthermore, a balancing preconditioned conjugate gradient method is utilized to deal with the interface problem caused by domain decomposition. The entire simulation model is validated by comparing the numerical results with that of recognized experimental and numerical data from previous literature. The transient behavior of indoor airflow and its complexity in the ventilated room are discussed; the velocity and vortex distribution of airflow are investigated, and its possible influence on particle accumulation is classified.

Permafrost-carbon mobilization in Beringia caused by deglacial meltwater runoff, sea-level rise and warming

During the last deglaciation (18–8 kyr BP), shelf flooding and warming presumably led to a large-scale decomposition of permafrost soils in the mid-to-high latitudes of the Northern Hemisphere. Microbial degradation of old organic matter released from the decomposing permafrost potentially contributed to the deglacial rise in atmospheric CO2 and also to the declining atmospheric radiocarbon contents (Δ14C). The significance of permafrost for the atmospheric carbon pool is not well understood as the timing of the carbon activation is poorly constrained by proxy data. Here, we trace the mobilization of organic matter from permafrost in the Pacific sector of Beringia over the last 22 kyr using mass-accumulation rates and radiocarbon signatures of terrigenous biomarkers in four sediment cores from the Bering Sea and the Northwest Pacific. We find that pronounced reworking and thus the vulnerability of old organic carbon to remineralization commenced during the early deglaciation (∼16.8 kyr BP) when meltwater runoff in the Yukon River intensified riverbank erosion of permafrost soils and fluvial discharge. Regional deglaciation in Alaska additionally mobilized significant fractions of fossil, petrogenic organic matter at this time. Permafrost decomposition across Beringia’s Pacific sector occurred in two major pulses that match the Bølling-Allerød and Preboreal warm spells and rapidly initiated within centuries. The carbon mobilization likely resulted from massive shelf flooding during meltwater pulses 1A (∼14.6 kyr BP) and 1B (∼11.5 kyr BP) followed by permafrost thaw in the hinterland. Our findings emphasize that coastal erosion was a major control to rapidly mobilize permafrost carbon along Beringia’s Pacific coast at ∼14.6 and ∼11.5 kyr BP implying that shelf flooding in Beringia may partly explain the centennial-scale rises in atmospheric CO2 at these times. Around 16.5 kyr BP, the mobilization of old terrigenous organic matter caused by meltwater-floods may have additionally contributed to increasing CO2 levels.

To a Question of Predicting Model Stability on the Basis of Multiple Scale Wavelet Transformation

Purpose of research. The article is devoted to the development of production predicting models and their stability conditions.Methods: Predicting models are actively used in modern control systems, in information support intellectual systems of decision-making. They have a huge role in any activity connected with signals' processing including anomalies detection of various technological processes and assessment of risk potential of critical information infrastructure objects. They can also be used in monitoring systems of security threats. Special class among predicting models is represented by the models based on experiences of proceeding processes (for example, regularities taken from the data which are saved up as a result of an object work).Results. Virtual "instant" model of an object belonging to this class is described in the article. It is presented taking into account multiple and large-scale decomposition of entrance influences vectors and the forecast of an object output. The described model gives the forecast without possible future conditions of an expected background. The approach based on the wavelet-analysis which is characterized by a unique opportunity of detailed frequency analysis in time is developed for stability study of virtual "instant" model. Stability conditions of the predicting model are received on the basis of this approach. This model has allocation conditions for approximating and detailing components for four types of ratios between memory depth on input and output.Conclusion: Predicting model of oil processing in which memory depth on an input is more than memory depth on output is described in the article. It is shown that the accuracy of virtual "instant" model forecast is higher than linear predicting model has at rare data of laboratory analysis. One of stability conditions depending on decomposition depth is shown for the constructed model. On the basis of received results analysis it is possible to draw a conclusion on applicability of received stability conditions for risk potential assessment of process development forecast implementation in monitoring systems of security threats.

Evaluation of the wood degradation in the underground fort Goli vrh

Before the Second World War, a large underground fortress was built around Goli vrh. Some wood remains in the fort from the time of construction, and some wooden objects have been exhibited in the fort. Several years after the opening of the fort, large scale decomposition was observed on the wood. A sensor for monitoring the relative air humidity and temperature was installed. In addition, a few samples of wood were isolated and examined by X-ray fluorescence spectroscopy and laser confocal linear microscopy. The analysis confirmed the high humidity of the wood and the presence of wood decay fungi on all wood objects, with the exception of wooden ammunition boxes.

Early stage litter decomposition across biomes

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from −9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.

Distributed Model Predictive Control for Hybrid Energy Resource System With Large-Scale Decomposition Coordination Approach

Due to the large-scale and distributed characteristics of increasing renewable energy resources, dynamic economic emission dispatch (DEED) of hybrid energy resource system becomes more and more important in the power system operation. This paper proposes a distributed model predictive control (DMPC) method for hybrid energy resources system of dynamic economic optimal dispatch with large-scale decomposition coordination approach. First, the DEED model of hybrid energy resources is converted into predictive control model, which can provide rolling optimization mechanism for dealing with intermittent energy resources optimization. Second, predictive control model is decomposed into several subsystems with Lagrangian multipliers for coordinating those subsystems, which can greatly decrease the computational complexity. Third, due to the randomness or uncertainty of intermittent power generation, model predictive control can dynamically optimize random or uncertainty problem with rolling optimization mechanism. Furthermore, adaptive dynamic programming is utilized to solve those subsystem optimization problems, which can optimize the random or uncertain problem in real-time condition. In the optimization process, probability constraint is converted into deterministic constraint with its probability density function, and system load balance can be properly handled with coupled coarse-fine constraint-handling technique. According to the obtained results in the case studies, the proposed DMPC can optimize the DEED of hybrid energy resources well combining with the large-scale decomposition-coordination approach, while greatly decreasing the optimization complexity and computation time, which reveals that the proposed method can provide an alternative way for solving the DEED problem of hybrid energy resources.

L₁-Norm Low-Rank Matrix Decomposition by Neural Networks and Mollifiers.

The L1-norm cost function of the low-rank approximation of the matrix with missing entries is not smooth, and also cannot be transformed into a standard linear or quadratic programming problem, and thus, the optimization of this cost function is still not well solved. To tackle this problem, first, a mollifier is used to smooth the cost function. High closeness of the smoothed function to the original one can be obtained by tuning the parameters contained in the mollifier. Next, a recurrent neural network is proposed to optimize the mollified function, which will converge to a local minimum. In addition, to boost the speed of the system, the mollifying process is implemented by a filtering procedure. The influence of two mollifier parameters is theoretically analyzed and experimentally confirmed, showing that one of the parameters is critical to computational efficiency and accuracy, while the other not. A large number of experiments on synthetic data show that the proposed method is competitive to the state-of-the-art methods. In particular, the experiments on large matrices and a real application in the structure from motion indicate that the memory requirement of the proposed algorithm is mild, making it suitable for real applications that often involve large-scale matrix decomposition.

Climate and litter quality differently modulate the effects of soil fauna on litter decomposition across biomes

Climate and litter quality have been identified as major drivers of litter decomposition at large spatial scales. However, the role played by soil fauna remains largely unknown, despite its importance for litter fragmentation and microbial activity. We synthesised litterbag studies to quantify the effect sizes of soil fauna on litter decomposition rates at the global and biome scales, and to assess how climate, litter quality and soil fauna interact to determine such rates. Soil fauna consistently enhanced litter decomposition at both global and biome scales (average increment ~ 37%). [corrected]. However, climate and litter quality differently modulated the effects of soil fauna on decomposition rates between biomes, from climate-driven biomes to those where climate effects were mediated by changes in litter quality. Our results advocate for the inclusion of biome-specific soil fauna effects on litter decomposition as a mean to reduce the unexplained variation in large-scale decomposition models.

Carbon cycling in tropical ecosystems

The diverse assemblage of ecosystems in tropical regions of the Earth holds a large fraction of the terrestrial biosphere’s carbon (C) stock (Bonan, 2008), and the annual exchange between tropical ecosystems (plants and soils) and the atmosphere is a critical controller of the CO2 concentration of the atmosphere, and hence of climate. Large-scale changes in the structure and function of tropical ecosystems, whether from the pressures of development or the impacts of drought (Meir & Woodward, 2010), can alter the balance in the annual exchange of carbon with far-reaching implications for the pace of climate change. Global models that couple the Earth’s climate system to the C cycle must, therefore, characterize well the biogeochemical and ecophysiological processes of tropical ecosystems and their sensitivity to atmospheric and climatic change. However, major uncertainties about fundamental C cycle processes in tropical ecosystems continue to hinder our progress (Dolman et al., 2010). Diverse aspects of C cycling in tropical ecosystems – from plant physiology and plant–soil interactions to human interactions and regional and global analyses – were discussed at the 23rd New Phytologist Symposium, ‘Carbon cycling in tropical ecosystems’, convened in Guangzhou, China, in November 2009, and summarized by Douglas Schaefer and Matthew Warren (http://www.newphytologist.org/carbon/23rdreport.pdf). In this issue of New Phytologist, we present four papers that emerged from that symposium. They cover the full range of topics discussed – plant physiology, soil processes, human interactions and global analysis – and, from their different perspectives, they all present analyses of C uptake, storage and release in tropical ecosystems. Hättenschwiler et al. (this issue, pp. 950–965) review the literature on leaf litter chemistry in a nutrient-poor Amazonian rainforest. They start with the recognition that, although several large-scale decomposition experiments have been invaluable for parameterizing biogeochemical and global C models, they generally do not include consideration of the influence of soil meso- and macrofauna, which may be particularly important in wet tropical ecosystems, and they often do not incorporate local variation in leaf traits, which are especially important in highly diverse tropical rainforests. Their analysis challenges the commonly held view that litter decomposition in the tropics is fast – decomposition of native litter at their site in French Guiana, and elsewhere in the tropics as shown in a literature survey, was comparatively slow. The authors speculate that natural selection favoured a leaf litter trait syndrome that leads to starvation and inhibition of decomposers, thereby altering competitive dynamics for limiting nutrients, particularly phosphorus. Salinas et al. (this issue, pp. 967–977) carried out an ambitious and comprehensive litter translocation experiment to evaluate the influence of environmental factors on decay rates of multiple species. They conducted their experiment over an elevational gradient from the tropical Andes in Peru to the adjacent Amazon lowlands in what was probably the largest-scale tropical leaf decomposition study to date. Despite the logistical challenges, this gradient had the advantages of the consistently high annual rainfall and the absence of substantial seasonality in temperature and a dormant season that would confound interpretation. They found that soil temperature explained most of the variation in decomposition of a variety of species, and concluded that recent warming in the region may have increased decomposition and nutrient mineralization by c. 10%. This increase in litter mineralization, coupled with rising atmospheric CO2, may partially explain accelerated growth and increased biomass in lowland Amazon forests. Ruiz-Jaen & Potvin (this issue, pp. 978–987) explored whether functional trait diversity or species diversity inform analyses of tree C storage in a mixed-species plantation and a natural forest in Panama. They were motivated by the potential value of using information on functional traits from different natural forests to design tree plantations for C sequestration. They concluded that the C storage capacity of natural forests could not be predicted using data from experimental plantations and, conversely, that forest managers need to be cautious when applying functional traits measured in natural populations when they design plantations for C management. Prentice et al. (this issue, pp. 988–998) approached C cycling questions from a very different temporal and spatial perspective. They assessed the realism of models of the changes in vegetation distribution and C cycling between the last glacial maximum (LGM, c. 21 000 yr ago) to the pre-industrial Holocene (PIH) using stable isotope and pollen data. They concluded that tropical forests accounted for a greater proportion of land C storage at LGM than PIH. Both model results and palaeodata supported the hypothesis that ecophysiological effects of atmospheric CO2 concentration influence tree–grass competition and plant productivity – effects that are assumed still to be in play today.

Mass spectrometry studies on meso‐substituted corroles and their photochemical decomposition products

Corroles, ring-contracted analogs of porphyrins, are an important class of compounds which have attracted the attention of many researchers in the fields of organic, coordination and physical chemistry. In the present work, the stability and the decomposition pathways of a diverse set of meso-substituted corroles have been studied using mass spectrometry (MS), UV-Vis absorption and preparative methods combined with NMR spectroscopy. Four different ionization methods (electrospray ionization, field desorption, atmospheric pressure photoionization and atmospheric pressure chemical ionization) were utilized to investigate light- and oxygen-induced decomposition in various solvents. It was found that the rate of decomposition in MeCN is significantly higher than in CH(2)Cl(2), hexane, MeOH and ethyl acetate. HR-MS combined with CID-MS/MS enabled us to identify the products of initial decomposition. Surprisingly, numerous smaller open-chain compounds were also detected. Large-scale decomposition of a corrole bearing sterically hindered substituents at positions 5 and 15 allowed us to isolate mg quantities of three decomposition products: isocorrole and isomeric biliverdin-type species. These are formed as a result of oxygen attack on the meso-10 position.

Thermal decomposition of chrysotile-containing wastes in a water vapor atmosphere

A simple thermal decomposition technique to convert asbestos-containing wastes (ACWs) into non-asbestos products has been developed by heating ACWs in a water vapor atmosphere. It was confirmed that cement slates containing 18 mass % chrysotile were converted into non-asbestos products by the thermal treatment in a water vapor atmosphere at 800°C for 2 h. In contrast, the thermal treatments in air required temperatures as high as 900°C to convert the cement slates into non-asbestos products. It should be noted that any chrysotile particles were not detected by the phase-contrast microscopic observation in the products after the thermal treatments in a water vapor atmosphere at temperatures beyond 800°C but three or less chrysotile particles remained after the thermal treatments in air at high temperatures beyond 900°C. In a water vapor atmosphere, ACWs were successfully converted into non-asbestos products at low temperatures below 800°C for 2 h by accelerated solid-state reactions between decomposed products of chrysotile and cement components to form calcium magnesium silicates. This technique may contribute to large-scale decomposition of ACWs with low energy consumption in comparison with the traditional melting method.

Property A and uniform embeddability of metric spaces under decompositions of finite depth

Property A and uniform embeddability are notions of metric geometry which imply the coarse Baum-Connes conjecture and the Novikov conjecture. In this paper, the authors prove the permanence properties of property A and uniform embeddability of metric spaces under large scale decompositions of finite depth.

Optimized Scheduled Multiple Access Control for Wireless Sensor Networks

We consider wireless sensor networks with multiple sensor modalities that capture data to be transported over multiple frequency channels to potentially multiple gateways. We study a general problem of maximizing a utility function of achievable transmission rates between communicating nodes. Decisions involve routing, transmission scheduling, power control, and channel selection, while constraints include physical communication constraints, interference constraints, and fairness constraints. Due to its structure the formulation grows exponentially with the size of the network. Drawing upon large-scale decomposition ideas in mathematical programming, we develop a cutting-plane algorithm and show that it terminates in a finite number of iterations. Every iteration requires the solution of a subproblem which is NP-hard. To solve the subproblem we i) devise a particular relaxation that is solvable in polynomial time and ii) leverage polynomial-time approximation schemes. A combination of both approaches enables an improved decomposition algorithm which is efficient for solving large problem instances.

Characterizing the zonally asymmetric component of the SH circulation

Much research concerning the Southern Hemisphere (SH) zonally asymmetric circulation has focused on the Pacific-South American mode (PSA) or the major zonal waves. However, these large-scale decompositions may mask important local variability. In this paper the month-to-month variability explained by the zonal waves 1 and 3 is examined, and an alternative representation of the SH circulation is presented based on two quasi-stationary anticyclones in the sub-Antarctic western hemisphere. These anticyclones are related to the zonal waves, but features of their variability are masked by the zonal wave decomposition; in particular, the anticyclones’ strengths are not positively covariant. They are also compared with the leading Principal Components of the SH atmosphere. We show that they capture variance independent of the Southern Annular Mode. Additionally, they explain a generally greater fraction of the variability than the PSA, and in a manner that also includes information regarding spatial variability. These results have implications for analysis of the atmospheric-forcing of western Antarctic climate.

The Rožná uranium deposit (Bohemian Massif, Czech Republic): shear zone-hosted, late Variscan and post-Variscan hydrothermal mineralization

Three major mineralization events are recorded at the Rožna uranium deposit (total mine production of 23,000 t U, average grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium quartz-carbonate-sulfide mineralization. (1) K–Ar ages for white mica from wall rock alteration of the pre-uranium mineralization style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of low-salinity aqueous inclusions, together with H2O-CO2-CH4, CO2-CH4, and pure CH4 inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into the pre-ore, ore, and post-ore substages. K–Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C. During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K–Ar ages of illite from ore substage alteration range from 277.2 ± 5.5 to 264.0 ± 4.3 Ma and roughly correspond with the results of chemical U–Pb dating of authigenic monazite (268 ± 50 Ma). The uranium ore deposition was accompanied by large-scale decomposition of biotite and pre-ore chlorite to Fe-rich illite and iron hydrooxides. Therefore, it is proposed that the deposition of uranium ore was mostly in response to the reduction of the ore-bearing fluid by interaction with ferrous iron-bearing silicates (biotite and pre-ore chlorite). The Th data on primary, mostly aqueous, inclusions trapped in carbonates of the ore substage range between 152°C and 174°C and total salinity ranges over a relatively wide interval of 3.1 to 23.1 wt% NaCl eq. Gradual reduction of the fluid system during the post-ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite. Chlorite thermometry yielded temperatures of 150°C to 170°C. Solid bitumens that post-date uranium mineralization indicate radiolytic polymerization of gaseous and liquid hydrocarbons and their derivatives. The origin of the organic compounds can be related to the diagenetic and catagenetic transformation of organic matter in Upper Stephanian and Permian sediments. (3) K–Ar ages on illite from post-uranium quartz-carbonate-sulfide mineralization range from 233.7 ± 4.7 to 227.5 ± 4.6 Ma and are consistent with the early Tethys-Central Atlantic rifting and tectonic reactivation of the Variscan structures of the Bohemian Massif. A minor part of the late Variscan uranium mineralization was remobilized during this hydrothermal event.

Asymptotically Optimal Transmission Policies for Large-Scale Low-Power Wireless Sensor Networks

We consider wireless sensor networks with multiple gateways and multiple classes of traffic carrying data generated by different sensory inputs. The objective is to devise joint routing, power control and transmission scheduling policies in order to gather data in the most efficient manner while respecting the needs of different sensing tasks (fairness). We formulate the problem as maximizing the utility of transmissions subject to explicit fairness constraints and propose an efficient decomposition algorithm drawing upon large-scale decomposition ideas in mathematical programming. We show that our algorithm terminates in a finite number of iterations and produces a policy that is asymptotically optimal at low transmission power levels. Furthermore, we establish that the utility maximization problem we consider can, in principle, be solved in polynomial time. Numerical results show that our policy is near-optimal, even at high power levels, and far superior to the best known heuristics at low power levels. We also demonstrate how to adapt our algorithm to accommodate energy constraints and node failures. The approach we introduce can efficiently determine near-optimal transmission policies for dramatically larger problem instances than an alternative enumeration approach.

Continental weathering in the Early Precambrian: Specific features of mineral transformations and composition of supergene solutions

The paper presents a detailed description of the geological structure, mineralogy, and chemical composition of the Archean weathering profile of granitoids in the Baltic Shield. Based on model calculations, the primary composition of granites in the substrate and weathering profile, as well as elemental composition of solutions draining the supergene profile, are determined. Model calculations for the Proterozoic weathering profile of analogous granitoids testify to the similarity of supergene alterations in the Early Precambrian. Mineral transformations during the weathering of granitoids are mainly expressed in the formation of minerals of new micas of the illite group against the background of large-scale decomposition of plagioclase. The composition of solutions in the hypergenesis zone of Precambrian weathering profiles sharply differs from the modern composition by lower contents of Ca2+ and K+ and the higher content of Fe2+. This is only possible under reducing conditions at high acidity of the diagenetic environment (pH < 6.5). The results obtained are essential for understanding the nature of unique Precambrian rocks (sedimentary iron ore rocks). The subordinate amount of carbonate sequences in Precambrian sedimentary sequences can be related to the specific composition of continental runoff primarily governed low-Ca supergene solutions.