In blockchain networks driven by Proof of Work, clients spend a certain amount of cryptocurrency (called fees) to control the speed of confirmation of the transactions that they generate. In fact, ...transactions are confirmed according to a strong priority policy that favors those offering the highest fees. The problem of determining the optimal fee to offer to satisfy certain delay requirements is still widely open and, at the state of the art, mainly reactive methods based on historical data are available. In this work, we propose a queueing model based on the exact transient analysis of a M/MB/1 system to address this problem. The model takes into account (i) the state of the Mempool (the backlog of pending work) when the transaction is generated, (ii) the current transaction arrival intensity and (iii) the distribution of the fees offered by other transactions to the miners. We apply the model to study the performance of the Bitcoin blockchain. Its parameterization is based on an extensive statistical analysis of the transaction characteristics. To this aim, we collected data from over 1.5 million of pending transactions observed in the Mempool of our Bitcoin node. The outcome of our analysis allows us to provide an algorithm to quickly compute the expected transaction confirmation time given the blockchain state, and to highlight new insights on the relations between the transaction fees and confirmation time in BTC blockchain.
•Analysis of confirmation time in blockchains based on proof-of-work.•Transient solution of the M/Mx/1 model conditioned to initial buffer occupancy.•Study of bitcoin blockchain transaction auction.•Validation of the model with Monte Carlo trace-driven simulation.
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Sesame seeds have economic interest owing to their oil content (45%–60%, dry basis). A multilevel factorial design was created in order to analyze the effects of air temperature (120, 150, and 180°C) ...and roasting time (20, 25, and 30 min) in a laboratory‐scale fluidized‐bed dryer. All treatments showed oil recovery values higher than 70%, except for roasting at 180°C for 25 and 30 min. The roasting treatment at 180°C for 20 min yielded oils with the best sensory properties and with acceptable values for chemical quality parameters: acid value (1.82 mg KOH/g oil), peroxides (not detected), oxidative stability index (11.58 hr), and antioxidants' content (total tocopherols: 410 ppm; total lignans: 9.54 g/kg oil). The combination of the seeds' roasting by fluidized‐bed drying and oil extraction by screw‐pressing, allowed obtaining high oil recoveries and products with high oxidative stability and sensory acceptability.
Practical applications
Sesame oil is popular among healthy‐food consumers given its bioactive components, mainly tocopherols and lignans, which confer a relatively high oxidative stability. Sesame seeds are roasted to change their microstructure for oil accumulation, to intensify flavor, and to increase the levels of antioxidants in the oil. Regarding the production of high‐quality roasted oil, the roasting of sesame seeds in fluidized‐bed dryers and the subsequent oil extraction in screw‐presses have never been reported together. High oil recoveries and roasted sesame oils with a healthy physico‐chemical composition, great oxidative stability, and sensory acceptability would be achieved by the oilseed industry through the use of two widely known technologies. First, fluidized‐bed drying offers a high degree of mixing, and uniform heat and mass transfer over conventional direct heating methods for seed roasting. Second, screw‐pressing of roasted seeds represents a green alternative to solvent extraction, mainly for specialty oils, because only mechanical power input is necessary to expel the oil.
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This book constitutes the refereed proceedings of the 18th International Conference on Analytical and Stochastic Modeling Techniques and Applications, ASMTA 2011, held in Venice, Italyin June ...2011.The 24 revised full papers presented were carefully reviewed and selected from many submissions.The papers are organized in topical sections on queueing theory, software and computer systems, statistics and inference, telecommunication networks, and performance and performability.
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Difficult airway is a clinical situation in which a trained anesthesiologist experiences trouble with facemask ventilation and/or laryngoscopy and/or intubation. Poor identification of at-risk ...patients has been identified as one of the causes of difficult airway management.
We aimed to review the literature regarding the use of wristbands to identify adult patients with known or predicted difficult airway in hospitals.
We searched Web of Science (WoS), Scopus, MEDLINE and OVID following the stages described by the PRISMA Extension for Scoping Reviews (PRISMA-ScR). We used a combination of MeSH terms and non-controlled vocabulary regarding the use of difficult airway wristbands in adults. Three researchers independently reviewed the full texts and selected the papers to be included based on the inclusion criteria.
Our search generated 334 articles after removing duplicates. After reviewing full text articles, only seven studies were included. Here we found that most were from the United States, in which the authors report the use of in-patients’ wristbands in adults. According to the authors, the use of wristbands is being implemented as a measure of improved quality and safety of in-patients with difficult airway either known or suspected.
The identification with wristbands of a difficult airway at an appropriate time is an identification strategy can have a low cost but a high impact on morbidity. It is pertinent to develop a methodology such as the use of wristbands, that allows a good classification and identification of patients with difficult airway in hospitals from Latin America.
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PRODUCT-FORM IN G-NETWORKS Marin, Andrea
Probability in the engineering and informational sciences,
07/2016, Volume:
30, Issue:
3
Journal Article
Peer reviewed
Open access
The introduction of the class of queueing networks called G-networks by Gelenbe has been a breakthrough in the field of stochastic modeling since it has largely expanded the class of models which are ...analytically or numerically tractable. From a theoretical point of view, the introduction of the G-networks has lead to very important considerations: first, a product-form queueing network may have non-linear traffic equations; secondly, we can have a product-form equilibrium distribution even if the customer routing is defined in such a way that more than two queues can change their states at the same time epoch. In this work, we review some of the classes of product-forms introduced for the analysis of the G-networks with special attention to these two aspects. We propose a methodology that, coherently with the product-form result, allows for a modular analysis of the G-queues to derive the equilibrium distribution of the network.
The analysis of fork-join queueing systems has played an important role for the performance evaluation of distributed systems where parallel computations associated with the same job are carried out ...and a job is considered served only when all the parallel tasks it consists of are served and then joined. The fork-join nodes that we consider consist of K≥2 parallel servers each of which is equipped with two First Come First Served queues, namely the service-queue and the join-queue. The former stores the tasks waiting to be served while the latter stores the served tasks waiting to be joined. Under heavy load conditions, the variance of the service times associated with the tasks tends to cause long join-queue lengths. In this work, we propose an algorithm to dynamically control the servers’ speeds (e.g., via frequency scaling), that aims at reducing the power consumption of the servers whose join-queue lengths are longer than the others’. Under Markovian assumptions, we provide a model for the performance evaluation of the system in saturation that allows us to derive the expression for the steady-state distribution, the system’s throughput and balance index. Finally, we derive the analytical expression for the marginal state probabilities of each server and provide upper and lower bounds for the expected power consumption.
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In many theoretical works, the benefits of size-based scheduling disciplines have been proved. The Foreground–Background discipline (or Least Attained Service (LAS)) and the multi-level processor ...sharing discipline are two examples of scheduling algorithms that provide an improvement of the expected flow completion time for heavily-tailed TCP flows with respect to the widely adopted Processor Sharing (PS) discipline.
In this work, we provide an implementation of the 2-level processor sharing queue (2LPS) for a Linux kernel and we measure its performance with TCP flow sizes taken from real-world datasets. 2LPS is the simplest implementation of a size-based scheduling and is parametrised with a threshold a: at each epoch, flows which received less than a service have hard priority on those that have crossed the threshold.
We give a numerical procedure to solve the 2LPS queue which allows for the computation of the optimal threshold for arbitrary job size distributions (approximated arbitrary well by generalised hyper-exponential distributions) and compare the results with those obtained by other disciplines (LAS and Shortest Remaining Processing Time (SRPT)).
Finally, we measure the performance of its implementation. Our findings show that the benefits of 2LPS, although slightly lower than those predicted by the theoretical model, are still significant and that using just two levels with optimal threshold seems the best trade-off between the complexity and resource demand of the implementation of a size-based scheduler and the improvements in the expected response time.
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The increased penetration of renewable energy sources into existing power systems induces challenges in supply–demand balancing. Demand-side flexibility is seen as an option to accommodate ...variability and limited predictability from renewable energy generation. Heat pumps at residential level, if well coordinated, can be one of those flexibility sources. The complexity involved is high though, since their coordinated operation combines control, population effects and the fact agents may actually not behave as rational decision-makers. We describe here a coordinated control framework that accounts for those aspects altogether. Decentralized model predictive control for large populations of heterogeneous agents is employed. As the cost to be minimized is affected by the population behaviour as a whole through the electricity price, the decentralized control is re-thought as a mean-field game. Existence and uniqueness of a Nash equilibrium are discussed while the Picard–Banach algorithm is used as a solution approach. It is extended to the case of bounded-rational agents. The impact on system dynamics of modelling agents as bounded rational is illustrated through numerical simulations.
This article is part of the theme issue ‘The mathematics of energy systems’.
The continued increase in human populations and use of chemical fertilizers remain a threat to the health and stability of human–ecological systems worldwide. To ameliorate this problem and achieve ...long-term food security, a variety of ecofriendly technologies have been developed, including the production of cyanobacteria-based biofertilizers. This technology can be optimized through experiments that assess how plant growth is enhanced under different biofertilizer concentrations (g L−1). In this study, the biofertilizer capabilities of various concentrations of sonicated biomass (0, 2.5, 5, 10, 20, and 40 g L−1) derived from the cyanobacteria Arthrospira maxima on the growth of basil (Ocimum basilicum, Lamiaceae) were assessed, comparing their effectiveness with that of a positive control, a commercial biofertilizer (OptiMar Algas Marinas®) administered at 4 mL L−1. Generally, increased concentrations led to enhanced growth parameters; however, discernible differences from the negative control (0 g L−1) were often observed only when concentrations exceeded 5 g L−1. Surprisingly, the negative and positive controls often yielded similar results. A chemical composition analysis of A. maxima revealed high concentrations of the phytohormones, macronutrients, and essential amino acids that likely explain how our A. maxima sample enhanced growth in basil. Further research is required to determine how other crop plants respond to different concentrations of A. maxima. Additionally, assessing the feasibility of creating an economically accessible product with a higher concentration of A. maxima is crucial for practical applications.
Non-Interference is an information flow security property which aims to protect confidential data by ensuring the complete absence of any information flow from high level entities to low level ones. ...However, this requirement is too demanding when dealing with real applications: indeed, no real policy ever guarantees a total absence of information flow. In order to deal with real applications, it is often necessary to allow mechanisms for downgrading or declassifying information such as information filters and channel control.
In this paper we introduce the notion of Delimited Persistent Stochastic Non-Interference (D_PSNI) that allows information to flow from a higher to a lower security level through a downgrader. We provide two algebraic characterizations of D_PSNI and prove some compositionality properties. Finally, we present a decision algorithm and discuss its time complexity.
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