In this paper we discuss lower bounds for convergence of convex optimization methods of high order and attainability of this bounds. We formulate a hypothesis that covers all the cases. It is ...noticeable that we provide this statement without a proof. Newton method is the most famous method that uses gradient and Hessian of optimized function. However, it converges locally even for strongly convex functions. Global convergence can be achieved with cubic regularization of Newton method Nesterov, Polyak, 2006, whose iteration cost is comparable with iteration cost of Newton method and is equivalent to inversion of Hessian of optimized function. Yu.Nesterov proposed accelerated variant of Newton method with cubic regularization in 2008 Nesterov, 2008. R.Monteiro and B. Svaiter managed to improve global convergence of cubic regularized method in 2013 Monteiro, Svaiter, 2013. Y.Arjevani, O. Shamir and R. Shiff showed that convergence bound of Monteiro and Svaiter is optimal (cannot be improved by more than logarithmic factor with any second order method) in 2017 Arjevani et al., 2017. They also managed to find bounds for convex optimization methods of p-th order for $p 2$. However, they got bounds only for first and second order methods for strongly convex functions. In 2018 Yu.Nesterov proposed third order convex optimization methods with rate of convergence that is close to this lower bounds and with similar to Newton method cost of iteration Nesterov, 2018. Consequently, it was showed that high order methods can be practical. In this paper we formulate lower bounds for p-th order methods for $p 3$ for strongly convex unconstrained optimization problems. This paper can be viewed as a little survey of state of the art of high order optimization methods.
Russia's Dead End Kovalev, Andrei A; Levine, Steven I; Reddaway, Peter
08/2017
eBook
Elite-level Soviet politics, privileged access to state secrets, knowledge about machinations inside the Kremlin-such is the environment in which Andrei A. Kovalev lived and worked. In this memoir of ...his time as a successful diplomat serving in various key capacities and as a member of Mikhail Gorbachev's staff, Kovalev reveals hard truths about his country as only a perceptive witness can do. InRussia's Dead EndKovalev shares his intimate knowledge of political activities behind the scenes at the Ministry of Foreign Affairs and the Kremlin before and after the dissolution of the USSR in December 1991, including the Russia of Vladimir Putin.Kovalev analyzes Soviet efforts to comply with international human-rights obligations, the machinations of the KGB, and the link between corrupt oligarchs and state officials. He documents the fall of the USSR, the post-Soviet explosion of state terrorism and propaganda, and offers a nuanced historical explanation of the roots of Russia's contemporary crisis under Vladimir Putin. This insider's memoir provides a penetrating analysis of late-Soviet and post-Soviet Russian politics that is pungent, pointed, witty, and accessible. It assesses the current dangerous status of Russian politics and society while illuminating the path to a more just and democratic future.
The activation of direct interspecies electron transfer (DIET) by the supplementation of conductive materials is one of the effective and available methods to enhance anaerobic digestion (AD). ...Microorganisms that colonize the surface of these materials form biofilms, the study of which could provide new insights into the character of the DIET process and its effect on AD. The present study focused on AD performance, microbial community, as well as morphological and topological features of biofilms on various materials used to promote DIET during AD of low-concentration swine manure. The best AD characteristics were observed in stainless steel mesh (SM)/digested cow manure (CM) and polyester felt (PF)/digested sewage sludge (SS) combinations used as material/inoculum, respectively. Thus, potential methane yields in CM-SM and SS-PF were up to 26.4% and 26.2% higher compared to the corresponding controls. Microbial analysis of biofilms revealed the dominance of putatively syntrophic bacteria of the MBA03 group of the Limnochordia class in CM inoculated reactors, and syntrophic proteolytic bacteria of the genus Coprothermobacter and acetogenic Clostridium sensu stricto 1, known for their ability to carry out DIET, in SS inoculated reactors. Biofilms on non-conductive materials contained pili-like structures, which were observed only in SS inoculated reactors. Polyester felt tended to biofoul better than carbon felt, resulting in up to 2.8, 3.2 and 1.8 higher nucleic acid, extracellular polymeric substances, and total biomass content, respectively, depending on the inoculum. These results provide new insights into the different types of DIET that can occur in low-loaded AD systems with attached growth.
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•Better AD characteristics correlated well with the presence of pili-like structures.•Coprothermobacter and Clostridium sensu stricto 1 play a key role in A-type DIET.•MBA03 group of the Limnochordia class dominated in biofilms on conductive mesh.•Polyester felt had denser biofilms than carbon felt regardless of the inoculum used.•DIET could take place and be beneficial to the performance of low-loaded AD systems.
•Energy intensity measure reflects consumption, not energy efficiency.•Thermodynamic indicators should describe energy efficiency at all levels.•These indicators should have no reference to economic ...or financial parameters.•A set of energy efficiency indicators should satisfy several basic principles.•There are trade-offs between energy efficiency, power and costs.
There is a widespread assumption in energy statistics and econometrics that energy intensity and energy efficiency are equivalent measures of energy performance of economies. The paper points to the discrepancy between the engineering concept of energy efficiency and the energy intensity as it is understood in macroeconomic statistics. This double discrepancy concerns definitions (while engineering concept of energy efficiency is based on the thermodynamic definition, energy intensity includes economic measures) and use. With regard to the latter, the authors conclude that energy intensity can only provide indirect and delayed evidence of technological and engineering energy efficiency of energy conversion processes, which entails shortcomings for management and policymaking. Therefore, we suggest to stop considering subsectoral, sectoral and other levels of energy intensities as aggregates of lower-level energy efficiency. It is suggested that the insufficiency of energy intensity indicators can be compensated with the introduction of thermodynamic indicators describing energy efficiency at the physical, technological, enterprise, sub-sector, sectoral and national levels without references to any economic or financial parameters. Structured statistical data on thermodynamic efficiency is offered as a better option for identifying break-through technologies and technological bottle-necks that constrain efficiency advancements. It is also suggested that macro-level thermodynamic indicators should be based on the thermodynamic first law efficiency and the energy quality problem may be left to enterprise-level thermoeconomic optimization.
Gasification technology often requires the use of modeling approaches to incorporate several intermediate reactions in a complex nature. These traditional models are occasionally impractical and ...often challenging to bring reliable relations between performing parameters. Hence, this study outlined the solutions to overcome the challenges in modeling approaches. The use of machine learning (ML) methods is essential and a promising integration to add intelligent retrieval to traditional modeling approaches of gasification technology. Regarding this, this study charted applied ML-based artificial intelligence in the field of gasification research. This study includes a summary of applied ML algorithms, including neural network, support vector, decision tree, random forest, and gradient boosting, and their performance evaluations for gasification technologies.
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•Batch test is a useful tool for predicting H2 potential and hydrolysis constant.•Maximum H2 production rate has been underestimated in batch test.•Thermoanaerobacterium is an ...effective thermophilic H2 producer at a very low pH.•Both batch and semi-continuous experiments are needed to predict dark fermentation.
The performance and kinetics response of thermophilic semi-continuous dark fermentation (DF) of simulated complex carbohydrate-rich waste was investigated at various hydraulic retention times (HRT) (2, 2.5, and 3 d) and compared with data obtained from biochemical hydrogen potential assay (BHP). A culture of Thermoanaerobacterium thermosaccharolyticum was used as the inoculum and dominated both in BHP and semi-continuous reactor. Both the modified Gompertz and first-order models described the DF kinetics well (R2 = 0.97–1.00). HRT of 2.5 d was found to be optimal in terms of maximum hydrogen production rate and hydrogen potential, which were 3.97 and 1.26 times higher, respectively, than in BHP. The hydrolysis constant was highest at HRT of 3 d and was closest to the value obtained in the BHP. Overall, BHP has been shown to be a useful tool for predicting H2 potential and the hydrolysis constant, while the maximum H2 production rate is greatly underestimated.
Biogas production involves various types of intricate microbial populations in an anaerobic digester (AD). To understand the anaerobic digestion system better, a broad-based study must be conducted ...on the microbial population. Deep understanding of the complete metagenomics including microbial structure, functional gene form, similarity/differences, and relationships between metabolic pathways and product formation, could aid in optimization and enhancement of AD processes. With advancements in technologies for metagenomic sequencing, for example, next generation sequencing and high-throughput sequencing, have revolutionized the study of microbial dynamics in anaerobic digestion. This review includes a brief introduction to the basic process of metagenomics research and includes a detailed summary of the various bioinformatics approaches, viz., total investigation of data obtained from microbial communities using bioinformatics methods to expose metagenomics characterization. This includes (1) methods of DNA isolation and sequencing, (2) investigation of anaerobic microbial communities using bioinformatics techniques, (3) application of the analysis of anaerobic microbial community and biogas production, and (4) restriction and prediction of bioinformatics analysis on microbial metagenomics. The review has been concluded, giving a summarized insight into bioinformatic tools and also promoting the future prospects of integrating humungous data with artificial intelligence and neural network software.
Tribological behavior of polymers is reviewed since the mid-20
th century to the present day. Surface energy of different coatings is determined with new contact adhesion meter. Adhesion and ...deformation components of friction are discussed. It is shown how load, sliding velocity, and temperature affect friction. Different modes of wear of polymers and friction transfer are considered.
Spatial separation into acidogenic and methanogenic stages is considered a viable option to ensure process stability, energy efficiency and the better control of key anaerobic digestion (AD) ...parameters. The elucidation of the optimal modes of two-stage AD for the maximization of the recovery of biofuels (H2 and CH4) is still an urgent task, the main optimization criteria being the highest energy yield (EY) and energy production rate (EPR). In this work, a response surface methodology was used for an optimization of energy production from the two-stage mesophilic–thermophilic AD of cheese whey (CW). Three dilution rates of CW, providing values of 10.9, 14.53 and 21.8 g for the chemical oxygen demand (COD)/L in the influent and three hydraulic retention times (HRTs) (1, 2 and 3 days) in methanogenic biofilters at a constant HRT in an acidogenic biofilter of 0.42 days, were tested to optimize the EY and EPR. The desirability approach produced combined optimum conditions as follows: the dilution rate of the CW provided 17.58 g COD/L (corresponding to OLR of 6.5 g COD/(L·day)) in the influent and a HRT in the methanogenic biofilter of 2.28 days, both of which provided a maximum EPR of 80.263 kJ/(L·day) and EY of 9.56 kJ/g COD, with an overall desirability value of 0.883.
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