Importance Sampling Simulation of Population Overflow in Two-node Tandem Networks

In this paper we consider the application of importance sampling in simulations of Markovian tandem networks in order to estimate the probability of rare events, such as network population overflow. We propose a heuristic methodology to obtain a good approximation to the 'optimal' state-dependent change of measure (importance sampling distribution). Extensive experimental results on 2-node tandem networks are very encouraging, yielding asymptotically efficient estimates (with bounded relative error) where no other state-independent importance sampling techniques are known to be efficient The methodology avoids the costly optimization involved in other recently proposed approaches to approximate the 'optimal' state-dependent change of measure. Moreover, the insight drawn from the heuristic promises its applicability to larger networks and more general topologies

Techniques for the Fast Simulation of Models of Highly dependable Systems

With the ever-increasing complexity and requirements of highly dependable systems, their evaluation during design and operation is becoming more crucial. Realistic models of such systems are often not amenable to analysis using conventional analytic or numerical methods. Therefore, analysts and designers turn to simulation to evaluate these models. However, accurate estimation of dependability measures of these models requires that the simulation frequently observes system failures, which are rare events in highly dependable systems. This renders ordinary Simulation impractical for evaluating such systems. To overcome this problem, simulation techniques based on importance sampling have been developed, and are very effective in certain settings. When importance sampling works well, simulation run lengths can be reduced by several orders of magnitude when estimating transient as well as steady-state dependability measures. This paper reviews some of the importance-sampling techniques that have been developed in recent years to estimate dependability measures efficiently in Markov and nonMarkov models of highly dependable system

Fast simulation of the leaky bucket algorithm

We use fast simulation methods, based on importance sampling, to efficiently estimate cell loss probability in queueing models of the Leaky Bucket algorithm. One of these models was introduced by Berger (1991), in which the rare event of a cell loss is related to the rare event of an empty finite buffer in an "overloaded" queue. In particular, we propose a heuristic change of measure for importance sampling to efficiently estimate the probability of the rare empty-buffer event in an asymptotically unstable GI/GI/1/k queue. This change of measure is, in a way, "dual" to that proposed by Parekh and Walrand (1989) to estimate the probability of a rare buffer overflow event. We present empirical results to demonstrate the effectiveness of our fast simulation method. Since we have not yet obtained a mathematical proof, we can only conjecture that our heuristic is asymptotically optimal, as k/spl rarr//spl infin/

Efficient Simulation of Population Overflow in Parallel Queues

In this paper we propose a state-dependent importance sampling heuristic to estimate the probability of population overflow in networks of parallel queues. This heuristic approximates the “optimal” state-dependent change of measure without the need for difficult mathematical analysis or costly optimization involved in adaptive methodologies. Comprehensive simulations of networks with an arbitrary number of parallel queues and different traffic intensities yield asymptotically efficient estimates (with relative error increasing sub-linearly in the overflow level) where no other state-independent importance sampling techniques are known to be efficient. The efficiency of the proposed heuristic surpasses those based on adaptive importance sampling algorithms, yet it is easier to determine and implement and scales better for large networks.\u

Adaptive Importance Sampling for Performance Evaluation and Parameter Optimization of Communication Systems

We present new adaptive importance sampling techniques based on stochastic Newton recursions. Their applicability to the performance evaluation of communication systems is studied. Besides bit-error rate (BER) estimation, the techniques are used for system parameter optimization. Two system models that are analytically tractable are employed to demonstrate the validity of the techniques. As an application to situations that are analytically intractable and numerically intensive, the influence of crosstalk in a wavelength-division multiplexing (WDM) crossconnect is assessed. In order to consider a realistic system model, optimal setting of thresholds in the detector is carried out while estimating error rate performances. Resulting BER estimates indicate that the tolerable crosstalk levels are significantly higher than predicted in the literature. This finding has a strong impact on the design of WDM networks. Power penalties induced by the addition of channels can also be accurately predicted in short run-time

Spouted bed dried Rosmarinus officinalis extract: a novel approach for physicochemical properties and antioxidant activity

In this study, a conical-cylindrical spouted bed dryer with Teflon® beads as spouting material was used for producing powdered rosemary (Rosmarinus officinalis L.) extract. The influence of the inlet drying gas temperature (Tgi) and the percentage ratio between the feed rate of concentrated liquid extract by the maximum evaporation capacity of the spouted bed (Ws/Wmax) on selected physicochemical properties of the finished products were investigated. Antioxidant properties of the concentrated liquid extract and dried extracts were also evaluated by the 2.2-diphenyl-1-picrylhydrazyl radical scavenging (DPPH) and lipid peroxidation induced by Fe2+/citrate (LPO) methods; and compared with the values obtained for a lyophilized extract (used as a control). Colloidal silicon dioxide (Tixosil® 333) and maltodextrin (DE 14) at a 2:1 ratio was added to the concentrated extract before drying (4.4% w/w) to improve the drying performance. The drying variables Ws/Wmax and Tgi have statistically significant influence on total polyphenols and total flavonoid contents of the dried powders. The concentrated extract (on dry basisbeing absolute solid content) showed superior antioxidant activity (AA) compared to both the spouted bed dried and the lyophilized extracts; exhibiting IC50 values of 0.96 ± 0.02, 2.16 ± 0.04 and 3.79 ± 0.05 µg mL1 (DPPH method) and 0.22 ± 0.01, 1.31± 0.01 and 2.54 ± 0.02 µg mL1 (LPO method), respectively. These results of AA are comparable to values obtained for quercetin, a flavonoid compound often used as a reference standard due to its potent antioxidant activity; with IC50 of 1.17 µg mL1 (DPPH) and 0.22 µg mL1 (LPO). However, the dried rosemary extracts are about 13.5 times more concentrated than the initial concentrated extract (dry weight), with a concentration of total flavonoids and polyphenols compounds ranging from 4.3 to 12.3 and from 1.2 to 4.7 times higher than the concentrated extract values (wet basis). The AA per dry product mass was thus significantly higher than the values measured for concentrated extractive solution, irrespective of some losses of AA apparently due to the drying process.Foundation of Research Support of the São Paulo State (FAPESP) for the funded projects 2011/10333-1, 2012/03427-2 and 2018/26069-0 and for the National Council for Scientific and Technological Development (CNPq) for the financial support. E.B.S. acknowledges the Portuguese Science and Technology Foundation (FCT) for the funded projects M-ERA-NET/0004/2015 (PAIRED) and UIDB/04469/2020 (strategic fund)info:eu-repo/semantics/publishedVersio

Bronchogenic cyst associated with pericardial defect: Case report and review of the literature

Partial defect of the pericardium combined with bronchogenic cyst is a very rare congenital anomaly. We describe the case of a 32-year-old man with a partial defect of the left pericardium and a bronchogenic cyst arising from the border of the pericardial defect. The cyst was successfully resected with the harmonic scalpel by three-port videothoracoscopic approach

Ernst Freund as Precursor of the Rational Study of Corporate Law

Gindis, David, Ernst Freund as Precursor of the Rational Study of Corporate Law (October 27, 2017). Journal of Institutional Economics, Forthcoming. Available at SSRN: https://ssrn.com/abstract=2905547, doi: https://dx.doi.org/10.2139/ssrn.2905547The rise of large business corporations in the late 19th century compelled many American observers to admit that the nature of the corporation had yet to be understood. Published in this context, Ernst Freund's little-known The Legal Nature of Corporations (1897) was an original attempt to come to terms with a new legal and economic reality. But it can also be described, to paraphrase Oliver Wendell Holmes, as the earliest example of the rational study of corporate law. The paper shows that Freund had the intuitions of an institutional economist, and engaged in what today would be called comparative institutional analysis. Remarkably, his argument that the corporate form secures property against insider defection and against outsiders anticipated recent work on entity shielding and capital lock-in, and can be read as an early contribution to what today would be called the theory of the firm.Peer reviewe

Free-standing graphene oxide and carbon nanotube hybrid papers with enhanced electrical and mechanic performance and their synergy in polymer laminates

Hybrid nanomaterials fabricated by the heterogeneous integration of 1D (carbon nanotubes) and 2D (graphene oxide) nanomaterials showed synergy in electrical and mechanical properties. Here, we reported the infiltration of carboxylic functionalized single-walled carbon nanotubes (C-SWNT) into free-standing graphene oxide (GO) paper for better electrical and mechanical properties than native GO. The stacking arrangement of GO sheets and its alteration in the presence of C-SWNT were comprehensively explored through scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The C-SWNTs bridges between different GO sheets produce a pathway for the flow of electrical charges and provide a tougher hybrid system. The nanoscopic surface potential map reveals a higher work function of the individual functionalised SWNTs than surrounded GO sheets showing efficient charge exchange. We observed the enhanced conductivity up to 50 times and capacitance up to 3.5 times of the hybrid structure than the GO-paper. The laminate of polystyrene composites provided higher elastic modulus and mechanical strength when hybrid paper is used, thus paving the way for the exploitation of hybrid filler formulation in designing polymer composites