Optimizing communication satellites payload configuration with exact approaches

The satellite communications market is competitive and rapidly evolving. The payload, which is in charge of applying frequency conversion and amplification to the signals received from Earth before their retransmission, is made of various components. These include reconfigurable switches that permit the re-routing of signals based on market demand or because of some hardware failure. In order to meet modern requirements, the size and the complexity of current communication payloads are increasing significantly. Consequently, the optimal payload configuration, which was previously done manually by the engineers with the use of computerized schematics, is now becoming a difficult and time consuming task. Efficient optimization techniques are therefore required to find the optimal set(s) of switch positions to optimize some operational objective(s). In order to tackle this challenging problem for the satellite industry, this work proposes two Integer Linear Programming (ILP) models. The first one is single-objective and focuses on the minimization of the length of the longest channel path, while the second one is bi-objective and additionally aims at minimizing the number of switch changes in the payload switch matrix. Experiments are conducted on a large set of instances of realistic payload sizes using the CPLEX^® solver and two well-known exact multi-objective algorithms. Numerical results demonstrate the efficiency and limitations of the ILP approach on this real-world problem.     

Ultraviolet light and Ultrasound as non-thermal treatments for the inactivation of microorganisms in fresh ready-to-eat foods

The effects of two non thermal disinfection processes, Ultraviolet light (UV 254 nm) and Ultrasound (US) on the inactivation of bacteria and color in two freshly cut produces (lettuce and strawberry) were investigated. The main scope of this work was to study the efficacy of UV and US on the decontamination of inoculated lettuce and strawberries with a cocktail of four bacteria, Escherichia coli, Listeria innocua, Salmonella Enteritidis and Staphylococcus aureus. Treatment of lettuce with UV reduced significantly the population of E. coli, L. innocua, S. Enteritidis and S. aureus by 1.75, 1.27, 1.39 and 1.21 log CFU/g, respectively. Furthermore, more than a 2-log CFU/g reduction of E. coli and S. Enteritidis was achieved with US. In strawberries, UV treatment reduced bacteria only by 1–1.4 log CFU/g. The maximum reductions of microorganisms, observed in strawberries after treatment with US, were 3.04, 2.41, 5.52 and 6.12 log CFU/g for E. coli, S. aureus, S. Enteritidis and L. innocua, respectively. Treatment with UV and US, for time periods (up to 45 min) did not significantly (p > 0.05) change the color of lettuce or strawberry. Treatment with UV and US reduced the numbers of selected inoculated bacteria on lettuce and strawberries, which could be good alternatives to other traditional and commonly used technologies such as chlorine and hydrogen peroxide solutions for fresh produce industry. These results suggest that UV and US might be promising, non-thermal and environmental friendly disinfection technologies for freshly cut produce.     

Code quality analysis in open source software development

Abstract Proponents of open source style software development claim that better software is produced using this model compared with the traditional closed model. However, there is little empirical evidence in support of these claims. In this paper, we present the results of a pilot case study aiming: (a) to understand the implications of structural quality; and (b) to figure out the benefits of structural quality analysis of the code delivered by open source style development. To this end, we have measured quality characteristics of 100 applications written for Linux, using a software measurement tool, and compared the results with the industrial standard that is proposed by the tool. Another target of this case study was to investigate the issue of modularity in open source as this characteristic is being considered crucial by the proponents of open source for this type of software development. We have empirically assessed the relationship between the size of the application components and the delivered quality measured through user satisfaction. We have determined that, up to a certain extent, the average component size of an application is negatively related to the user satisfaction for this application.     

Fatty acid composition andtrans isomer content of hardened olive oil

Cooking fats and margarines prepared from olive oil were analyzed gas chromatographically for fatty acid composition andtrans isomer content. Argentation thin layer chromatography and mass spectrometry were used to assist in identifications of minor components. Olive oil margarines and cooking fats contained 70–76% monoenoic acids, of which 30–37% was in thetrans configuration, and 5% dienoic acids. Twenty percent of the dienes were in the form oftrans-trans andcis-trans octadecadienoic acid.     

Degradation of methylparathion in aqueous solution by electrochemical oxidation

The electrochemical degradation of methylparathion has been investigated by using Ti/Pt as anode, Stainless Steel 304 as cathode, and sodium chloride as electrolyte. The pesticide is rapidly degraded, but full mineralization is not observed. Degradation products have been monitored through gas chromatography and mass spectrometry, and the overall degradation process has been monitored through dissolved and particulate organic carbon, sulfur, and phosphorus measurements. Several intermediates have been identified, and oxalic, formic, and acetic acids as well as tetraphosphorus trisulfide have been recognized as final products of the degradation process. A proposed mechanism of the process is presented.     

Exploiting Context-Awareness for the Autonomic Management of Mobile Ad Hoc Networks

Mobile Ad Hoc Networks (MANETs) are characterized by a degree of dynamicity that can result in significant drawbacks regarding their useful deployment. The fact they are formed spontaneously, comprising possibly heterogeneous devices, hinders further their wide adoption. In this paper we present the design and implementation of a system that exploits context-awareness and couples it with policy-based management in order to enable the self-management of MANETs. The key idea is to support self-configuration by being adaptive to varying conditions modeled as context, with high-level management policies driving self-configuration towards particular goals. We propose the management of the MANET in a hierarchical but also distributed manner through a dynamically constructed set of manager nodes. We present and evaluate our work on context-awareness and context dissemination in MANETs through simulation and also by deploying the prototype system in our experimental MANET testbed for a proof-of-concept application scenario.     

Applying systolic multiplication–inversion architectures based on modified extended Euclidean algorithm for GF(2) in elliptic curve cryptography

Elliptic curve cryptography is a very promising cryptographic method offering the same security level as traditional public key cryptosystems (RSA, El Gamal) but with considerably smaller key lengths. However, the computational complexity and hardware resources of an elliptic curve cryptosystem are very high and depend on the efficient design of EC point operations and especially point multiplication. Those operations, using the elliptic curve group law, can be analyzed in operations of the underlined GF(2^k) Field. Three basic GF(2^k) Field operations exist, addition–subtraction, multiplication and inversion–division. In this paper, we propose an optimized inversion algorithm that can be applied very well in hardware avoiding well known inversion problems. Additionally, we propose a modified version of this algorithm that apart from inversion can perform multiplication using the architectural structure of inversion. We design two architectures that use those algorithms, a two-dimensional multiplication/inversion systolic architecture and an one-dimensional multiplication/inversion systolic architecture. Based on either one of those proposed architectures a GF(2^k) arithmetic unit is also designed and used in a EC arithmetic unit that can perform all EC point operations required for EC cryptography. The EC arithmetic unit’s design methodology is proposed and analyzed and the effects of utilizing the one or two-dimensional multiplication/inversion systolic architecture are considered. The performance of the system in all its design steps is analyzed and comparisons are made with other known designs. We manage to design a GF(2^k) arithmetic unit that has the space and time complexity of an inverter but can perform all GF(2^k) operations and we show that this architecture can apply very well to an EC arithmetic unit required in elliptic curve cryptography.     

Quantity discounts in single-period supply contracts with asymmetric demand information

We investigate how a supplier can use a quantity discount schedule to influence the stocking decisions of a downstream buyer that faces a single period of stochastic demand. In contrast to much of the work that has been done on single-period supply contracts, we assume that there are no interactions between the supplier and the buyer after demand information is revealed and that the buyer has better information about the distribution of demand than does the supplier. We characterize the structure of the optimal discount schedule for both all-unit and incremental discounts and show that the supplier can earn larger profits with an all-unit discount.     

Tooling and binder design for sheet metal forming processes compensating springback error

Part shape error due to springback can be a manufacturing defect in sheet metal forming processes. This manufacturing problem can be corrected by using appropriate designs of the tooling and the binder shape together with a binder constraint. In the present work a methodology for tool and binder design based on inverse springback calculations is developed and demonstrated. The design procedure invokes finite element analysis of the manufacturing process. The proposed method was demonstrated for two cases of forming of channel geometries (two-dimensional and three-dimensional) with an aluminum alloy sheet. The tooling needed to form the desired parts was numerically designed using the proposed algorithm then constructed with the aid of CNC machining. The designed tooling was found to produce the desired part shapes demonstrating both the accuracy of the numerical simulations and the success of the proposed tooling design algorithm.