Optimization of evaporative fluid coolersOptimisation des refroidisseurs de liquide évaporatifs

In the paper the optimization of geometrical and operating parameters for evaporative fluid coolers has been presented. The algorithm of optimizational calculations contains:

• the mathematical model of heat and mass transfer in evaporative fluid coolers;

• model of operating costs based, among others, on the Zalewski–Gryglaszewski relations developed by the authors for evaluation of air pressure drops in the heat exchanger;

• model of evaporative heat exchangers production costs.

Optimization problem formulated for non-linear objective functions with inequality and equality constraints has been solved using Schittkowski's method based on quadratic programming. Two optimization problems have been considered. A solution to the first problem consists in the design of a heat exchanger with such geometrical parameters which ensure its maximum heat capacity at minimal total costs. A result to the second optimization problem are such thermal and flow parameters which will ensure minimum operating costs.The results of optimization calculations presented in the paper are accompanied by their experimental verification.     

The EuQoS system: a solution for QoS routing in heterogeneous networks [Quality of Service based Routing Algorithms for Heterogeneous Networks]

EuQoS is the acronym for "end-to-end quality of service support over heterogeneous networks", which is a European research project aimed at building an entire QoS framework, addressing all the relevant network layers, protocols, and technologies. This framework, which includes the most common access networks (xDSL, UMTS, WiFi, and LAN) is being prototyped and tested in a multidomain scenario throughout Europe, composing what we call the EuQoS system. In this article we present the novel QoS routing mechanisms that are being developed and evaluated in the framework of this project. The preliminary performance results validate the design choices of the EuQoS system, and confirm the potential impact this project is likely to have in the near future     

The use of Path Tracking Method for determining the tortuosity field in a porous bed

The article is related to a computational method of obtaining the geometric tortuosity in granular beds, i.e. polydisperse beds consisting of spherical or quasi-spherical particles, freely distributed in the 3D space. The main aim is to show a new way of calculating two-dimensional tortuosity distribution in the plane perpendicular to the chosen direction in the space (interpreted as the main flow direction) by the use of own computational algorithm, the so-called Path Tracking Method (PTM). This way links the ability of the PTM to analyze relatively large granular beds due to low demand for computing power and the possibility of obtaining the tortuosity distribution in the space. Although this distribution is only 2D (there is only one value for every discrete point in the plane perpendicular to the main flow direction), it may be useful for estimation of the local pressure drops in fluid flows through granular bed. To reach the aim, the PTM has been improved and its application here is shown in a new context.     

Positive real control of two-dimensional systems: Roesser models and linear repetitive processes

This paper considers the problem of positive real control for two-dimensional (2-D) discrete systems described by the Roesser model and also discrete linear repetitive processes, which are another distinct sub-class of 2-D linear systems of both systems theoretic and applications interest. The purpose of this paper is to design a dynamic output feedback controller such that the resulting closed-loop system is asymptotically stable and the closed-loop system transfer function from the disturbance to the controlled output is extended strictly positive real. We first establish a version of positive realness for 2-D discrete systems described by the Roesser state space model, then a sufficient condition for the existence of the desired output feedback controllers is obtained in terms of four LMIs. When these LMIs are feasible, an explicit parameterization of the desired output feedback controllers is given. We then apply a similar approach to discrete linear repetitive processes represented in their equivalent 1-D state-space form. Finally, we provide numerical examples to demonstrate the applicability of the approach.     

Extruded tellurite glass optical fiber preforms

The extrusion behavior of tellurite glass in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at various temperatures in the glass transformation region investigated. Tube and holey fiber (HF) preforms were fabricated from tellurite glass billets using a laboratory press. In particular, the results for three-spoke HF design and round tube preforms with composition 75TeO₂·20ZnO·5Na₂O (TZN) are presented. The extruded preforms with precise geometrical features, an excellent surface quality and no crystallization were achieved in the temperatures range from 344 to 360 °C and at ram speeds ranging from 0.002 to 0.01 mm/s. Discrete shear bands were observed in the preforms, increasing in number and/or becoming better defined with increasing load and ram speed. Fewer shear bands were present when increasing the extrusion temperature from 344 to 360 °C. Thus, subsequent extrudates were successfully fabricated free of shear bands, providing good optical homogeneity that yielded solid and holey fibers that could provide much improved optical performance.     

Methods for constraint violation suppression in the numerical simulation of constrained multibody systems – A comparative study

Multibody systems are frequently modeled as constrained systems, and the arising governing equations incorporate the closing constraint equations at the acceleration level. One consequence of accumulation of integration truncation errors is the phenomenon of violation of the lower-order constraint equations by the numerical solutions to the governing equations. The constraint drift usually tends to increase in time and may spoil reliability of the simulation results. In this paper a comparative study of three methods for constraint violation suppression is presented: the popular Baumgarte’s constraint violation stabilization method, a projective scheme for constraint violation elimination, and a novel scheme patterned after that proposed recently by Braun and Goldfarb [D.J. Braun, M. Goldfarb, Eliminating constraint drift in the numerical simulation of constrained dynamical systems, Comput. Meth. Appl. Mech. Engrg., 198 (2009) 3151–3160]. The methods are confronted with respect to simplicity in applications, numerical effectiveness and influence on accuracy of the constraint-consistent motion.     

Surface grain structure evolution in hot rolling of 6061 aluminum alloy

During hot deformation of Al–Mg–Si alloys, a non-uniform microstructure is developed due to differences in localized strain. Physical simulations were performed to examine the effects of processing parameters such as deformation temperature, total reduction, rolling schedule and alloying additions on the grain structure evolution. Overall, the kinetics of recrystallization followed the traditional trends predicted by JMAK kinetics. Electron backscatter diffraction (EBSD) was used to quantify the difference in recrystallization kinetics at the sample surface and mid-thickness. The results showed that the surface showed elevated kinetics when compared to the sample mid-thickness.     

Inflammasome NLRP3 Potentially Links Obesity-Associated Low-Grade Systemic Inflammation and Insulin Resistance with Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common form of neurodegenerative dementia. Metabolic disorders including obesity and type 2 diabetes mellitus (T2DM) may stimulate amyloid β (Aβ) aggregate formation. AD, obesity, and T2DM share similar features such as chronic inflammation, increased oxidative stress, insulin resistance, and impaired energy metabolism. Adiposity is associated with the pro-inflammatory phenotype. Adiposity-related inflammatory factors lead to the formation of inflammasome complexes, which are responsible for the activation, maturation, and release of the pro-inflammatory cytokines including interleukin-1β (IL-1β) and interleukin-18 (IL-18). Activation of the inflammasome complex, particularly NLRP3, has a crucial role in obesity-induced inflammation, insulin resistance, and T2DM. The abnormal activation of the NLRP3 signaling pathway influences neuroinflammatory processes. NLRP3/IL-1β signaling could underlie the association between adiposity and cognitive impairment in humans. The review includes a broadened approach to the role of obesity-related diseases (obesity, low-grade chronic inflammation, type 2 diabetes, insulin resistance, and enhanced NLRP3 activity) in AD. Moreover, we also discuss the mechanisms by which the NLRP3 activation potentially links inflammation, peripheral and central insulin resistance, and metabolic changes with AD.     

Optimal routing to parallel heterogeneous servers-small arrivalrates

Consider a set of k(⩾2) heterogeneous and exponential servers that operate in parallel. Customers arrive into a single infinite capacity buffer according to a Poisson process, and are routed to available servers in accordance with some routing policy. It is shown that for arrival rates in some possible interval (0,λ₀), ever routing policy which minimizes the long-run expected holding cost is contained in the set of routing policies that minimize the expected flow time for a system with fixed initial population and no new arrivals     

Wetting Behavior and Reactivity of Molten Silicon with h-BN Substrate at Ultrahigh Temperatures up to 1750 °C

For a successful implementation of newly proposed silicon-based latent heat thermal energy storage systems, proper ceramic materials that could withstand a contact heating with molten silicon at temperatures much higher than its melting point need to be developed. In this regard, a non-wetting behavior and low reactivity are the main criteria determining the applicability of ceramic as a potential crucible material for long-term ultrahigh temperature contact with molten silicon. In this work, the wetting of hexagonal boron nitride (h-BN) by molten silicon was examined for the first time at temperatures up to 1750 °C. For this purpose, the sessile drop technique combined with contact heating procedure under static argon was used. The reactivity in Si/h-BN system under proposed conditions was evaluated by SEM/EDS examinations of the solidified couple. It was demonstrated that increase in temperature improves wetting, and consequently, non-wetting-to-wetting transition takes place at around 1650 °C. The contact angle of 90° ± 5° is maintained at temperatures up to 1750 °C. The results of structural characterization supported by a thermodynamic modeling indicate that the wetting behavior of the Si/h-BN couple during heating to and cooling from ultrahigh temperature of 1750 °C is mainly controlled by the substrate dissolution/reprecipitation mechanism.