Scalability and performance of an agent‐based network management middleware

Rapid growth of computer network sizes and uses necessitate analysis of network application middleware in terms of its scalability as well as performance. In this paper we analyze a distributed network management middleware based on agents that can be dispatched to locations where they can execute close to the managed nodes. The described middleware operates between the network protocol layer and the application layer and uses standard TCP protocol and SNMP probes to interface the network. By aggregating requests from many users into a single agent, our system allows multiple managers to probe problem areas with minimal management traffic overhead. We discuss and quantify the benefits of the described middleware by implementing real‐time network managers using our system. The main result of this paper is a comparison of scalability and efficiency of our agent‐based management middleware and traditional SNMP‐based data collection. To this end, we measured traffic in both real and simulated networks. In the latter case, we designed, used and described here a method of separating simulated application flow into separate subflows to simplify design of simulations. Copyright © 2004 John Wiley & Sons, Ltd.     

Predation of livestock ticks by chickens as a tick-control method in a resource-poor urban environment

The increasing prevalence of streptococci as causes of potentially fatal nosocomial bacteremia requires that antimicrobial agents used for empiric therapy in hospitalized patients include both pneumococci and viridans group streptococci as well as beta-hemolytic streptococci in their activity profile. In this study, the in vitro activity of cefepime, a new fourth-generation cephalosporin, was compared with other cephalosporins versus 197 nosocomial blood stream isolates of streptococci (20 Streptococcus pneumoniae, 104 viridans group, and 73 beta-hemolytic) isolated from patients at more than 30 medial centers from 1995 to 1997. Additional agents tested included penicillin, erythromycin, and vancomycin. Overall, cefepime inhibited 83% of the isolates at concentrations < or = 0.5 microgram/mL and 100% at < or = 8 micrograms/mL. By comparison, ceftazidime inhibited 35 and 88% of isolates at the same concentrations. Cefepime was approximately eightfold more potent than ceftazidime against S. pneumoniae, viridans group streptococci, and beta-hemolytic streptococci. Among the 42 isolates with penicillin MICs > 0.12 microgram/mL, 100% were inhibited by cefepime and only 48% by ceftazidime at < or = 8 micrograms/mL. The rank order of activity for all six agents against the 197 isolates was vancomycin > ceftriaxone > cefepime > penicillin > erythromycin > ceftazidime. Based on the results of the present study, cefepime and ceftriaxone were the superior cephalosporins in potency and spectrum for empiric coverage of patients at risk for streptococcal blood stream infections.     

On the computation of conjugacy classes of Chevalley groups

In this paper an algorithm is presented to determine the number of semisimple conjugacy classes for a given centralizertype for the Chevalley groupsSL _n(q) andSU _n(q). Moreover we give the exact number of regular semisimple classes of this groups and a summary of results on the generic classnumber of exceptional Chevalley groups of adjoint type.The first author acknowledges financial support by a grant of the Deutsche Forschungsgemeinschaft     

Hilfsmittel zum Auffinden einer ersten Gestalt beim methodischen Konstruieren: Gestaltbeeinflussung durch die Verwendung physikalischer Effekte

Zusammenfassung Ziel des Teilvorhabens, über das hier berichtet wird, was es, für eine Auswahl von physikalischen Effekten eine Zuordnung von gestaltbeeinflussenden Merkmalen auf sehr abstrakter Ebene zu erreichen und damit eine n?here Charakterisierung der Wirkfl?chen und Wirkr?ume zu erreichen die zur Umsetzung eines physikalischen Effektes notwendig sind. Die hieraus resultierenden Ergebnisse sind dem Abschlu?bericht zu entnehmen [1]. Weiterführende Themen, die basierend auf den vorliegenden Erkenntnissen bearbeitet werden, haben zum Ziel, die wesentlichen und entscheidenden Parameter einer Konstruktionsaufgabe zu erkennen und zukünftig zielgerichtet L?sungsvarianten zu erstellen, um somit für eine Neukonstruktion sinnvolle L?sungsfelder sehr frühzeitig abzugrenzen.     

Minimum spanning trees made easier via multi-objective optimization

Many real-world problems are multi-objective optimization problems and evolutionary algorithms are quite successful on such problems. Since the task is to compute or approximate the Pareto front, multi-objective optimization problems are considered as more difficult than single-objective problems. One should not forget that the fitness vector with respect to more than one objective contains more information that in principle can direct the search of evolutionary algorithms. Therefore, it is possible that a single-objective problem can be solved more efficiently via a generalized multi-objective model of the problem. That this is indeed the case is proved by investigating the computation of minimum spanning trees.This work was supported by the Deutsche Forschungsgemeinschaft (DFG) as part of the Collaborative Research Center Computational Intelligence (SFB 531) and by the German-Israeli Foundation (GIF) in the project Robustness Aspects of Algorithms.     

Polarisation insensitive semiconductor optical amplifier withintegrated electroabsorption modulators

The authors demonstrate a 1.55 μm wavelength multiquantum well semiconductor optical amplifier, integrated with bulk layer electroabsorption modulators and passive waveguide beam expanders at the input and output ports. The device has a fibre to fibre gain of 9 dB, an extinction ratio of 15 dB per modulator, a spectral range >35 nm, and polarisation sensitivity <1 dB     

Microcalorimetry for characterization of film formation and cure of coatings and adhesives

A new microcalorimeter with eight parallel channels using robust, low cost sensors for characterization of coatings and adhesives is described and first experiments on coatings and adhesives are presented. The calorimetric sensors are based on thin glass plates (20 mm × 20 mm, thickness 150 μm) with heater and thermocouple sputtered on the surfaces (calorimetric active area of about 9 mm²). The setup allows heating and cooling experiments as well as isothermal measurements in the temperature-modulated mode with up to eight sensors in parallel. The measured quantities are the real (C^′_p) and imaginary part (C^″_p) of the complex heat capacity (), the related absolute value of the heat capacity () and the heat flow . An industrial computer (NI PXI system) with specific software for calibration and data recording controls the electronic components. Sensors can be embedded in a temperature controlled oven (heating and cooling by Peltier elements) or alternatively in a climatic cabinet with controlled temperature and humidity.

The method has been applied successfully to monitoring of film formation of aqueous polymer dispersions (styrene-acrylate copolymer) and curing of coatings.     

Geographic variations in the composition of ivory of the African elephant (Loxodonta africana)

OBJECTIVES: The purpose of the present study was to compare the inclination of the occlusal plane with occlusal guidance as a contributing factor to masticatory movement. METHODS: Masticatory movements of 41 young adults were measured using a 3-D mandibular movement analysing system. The inclination of the occlusal plane was measured in the sagittal plane using a 3-D digitizer. The contribution of the occlusal guidance and the inclination of the occlusal plane to the direction of the masticatory path of closure was evaluated at various closing levels. RESULTS: The masticatory path of closure outside the intercuspal range was influenced mainly by the inclination of the occlusal plane, and the masticatory path of closure near the intercuspal range was only influenced by occlusal guidance. The so-called gliding type masticatory pattern was observed predominantly in subjects with a posteriorly inclined occlusal plane. In contrast, a chopping type masticatory pattern was observed predominantly in subjects with an anteriorly inclined occlusal plane. CONCLUSIONS: The contribution of the inclination of the occlusal plane to masticatory movement was greater than that of occlusal guidance throughout the closing phase except near the intercuspal range.     

XPS investigation on AISI 420 stainless steel corrosion in oil and gas well environments

The corrosion behaviour of 13Cr-martensitic stainless steel (AISI 420) was investigated in CO₂-H₂S-Cl^– environments typical of oil and gas wells under different CO₂ and H₂S partial pressures. The corrosion tests indicated that the AISI 420 steel was highly corrosion resistant to CO₂-induced phenomena (general corrosion and carbonate S.C.C.), while in the H₂S environment a high S.S.C.C. (Sulphide Stress Corrosion Cracking) susceptibility and high corrosion rates were found. Moreover, CO₂ in CO₂-H₂S-Cl^– systems inhibited general corrosion and S.S.C.C. phenomena by favouring the formation of a protective film. By means of X-ray photoelectron spectroscopy (XPS) the chemical nature of the films grown on AISI 420 in different environmental conditions was investigated and the following statements were drawn out:

Dynamic light scattering and ultrasonic investigations during the cure reaction of an epoxy resin

Brillouin scattering (BS), photon correlation spectroscopy (PCS), and ultrasonic (US) measurements were conducted to study the curing process of diglycidyl ether of bisphenol A with butane-1,4-diol at a curing temperature of 100°C. The experimental techniques probe the primary glass-rubber transition during the curing reaction. The primary relaxation time τ obtained from the BS and US velocity and absorption increases with curing time and hence the BS experiment measures τ at earlier stages of cure than the US experiment. The relaxation times at a different extent of reaction and for different measuring temperatures are consistent with BS, US, PCS, and DSC measurements and conform to a single reduced Vogel–Fulcher–Hesse–Tamann equation. Furthermore, the US experiments show evidence of secondary relaxations in the epoxy system.