Constant round group key agreement protocols: A comparative study

The scope of this paper is to review and evaluate all constant round Group Key Agreement (GKA) protocols proposed so far in the literature. We have gathered all GKA protocols that require 1,2,3,4 and 5 rounds and examined their efficiency. In particular, we calculated each protocol’s computation and communication complexity and using proper assessments we compared their total energy cost. The evaluation of all protocols, interesting on its own, can also serve as a reference point for future works and contribute to the establishment of new, more efficient constant round protocols.     

Directed Evolution of Phi Class Glutathione Transferases Involved in Multiple-Herbicide Resistance of Grass Weeds and Crops

The extensive application of herbicides in crop cultivation has indisputably led to the emergence of weed populations characterized by multiple herbicide resistance (MHR). This phenomenon is associated with the enhanced metabolism and detoxifying ability of endogenous enzymes, such as phi class glutathione transferases (GSTFs). In the present work, a library of mutant GSTFs was created by in vitro directed evolution via DNA shuffling. Selected gstf genes from the weeds Alopecurus myosuroides and Lolium rigidum, and the cereal crops Triticum durum and Hordeum vulgare were recombined to forge a library of novel chimeric GSTFs. The library was activity screened and the best-performing enzyme variants were purified and characterized. The work allowed the identification of enzyme variants that exhibit an eight-fold improvement in their catalytic efficiency, higher thermal stability (8.3 °C) and three-times higher inhibition sensitivity towards the herbicide butachlor. The crystal structures of the best-performing enzyme variants were determined by X-ray crystallography. Structural analysis allowed the identification of specific structural elements that are responsible for k_cat regulation, thermal stability and inhibition potency. These improved novel enzymes hold the potential for utilization in biocatalysis and green biotechnology applications. The results of the present work contribute significantly to our knowledge of the structure and function of phi class plant GSTs and shed light on their involvement in the mechanisms of MHR.     

Bivariate semiparametric control charts for simultaneous monitoring of process mean and variance

In the present article, two semiparametric bivariate control charts are presented, which use order statistics and are effective in jointly monitoring of possible shifts in the process mean and/or variance. To achieve that both the median location (or more generally the location of a specific order statistic) and the number of specific observations of the test sample lying between the control limits are taken into account. The false alarm rate and the in-control average run length are not affected by the marginal distributions, while the effect of the dependence structure on them is negligible; therefore, they can be used as fully nonparametric charts. A performance-comparison study is carried out, and an illustrative example is provided using a real-world data set.     

NaOH treatment reduces capsaicin content and pungency of ‘Makedoniko’ pepper (Capsicum annuum L.)

Pickled peppers are preferred by certain consumer groups at reduced pungency. To investigate the reduction in pepper pungency and capsaicin content, fresh ‘Makedoniko’ hot peppers were treated with 0, 0.5 or 1% NaOH before preserved in acid brine for 60 days. Pepper physicochemical traits were monitored following NaOH treatment and during preservation. Capsaicin content was measured in the beginning and at the end of preservation, and the peppers were also tested organoleptically. Preservation in acid brine induced the typical green–yellow product colour, increased firmness and decreased the dry mass in all treatments. NaOH‐treated pepper increased phenolics, chlorophyll and antioxidant content in dry mass during preservation faster than the control. Capsaicin content was reduced by 25 or 50% following 0.5 or 1% NaOH treatment, respectively. Pepper organoleptic pungency was also decreased following 1% NaOH treatment. NaOH reduces capsaicin content and pungency of ‘Makedoniko’ pepper, with minor effects on its processed product quality.     

On the Efficient Generation of Prime-Order Elliptic Curves

We consider the generation of prime-order elliptic curves (ECs) over a prime field \mathbbF_p\mathbb{F}_{p} using the Complex Multiplication (CM) method. A crucial step of this method is to compute the roots of a special type of class field polynomials with the most commonly used being the Hilbert and Weber ones. These polynomials are uniquely determined by the CM discriminant D. In this paper, we consider a variant of the CM method for constructing elliptic curves (ECs) of prime order using Weber polynomials. In attempting to construct prime-order ECs using Weber polynomials, two difficulties arise (in addition to the necessary transformations of the roots of such polynomials to those of their Hilbert counterparts). The first one is that the requirement of prime order necessitates that D≡3mod8), which gives Weber polynomials with degree three times larger than the degree of their corresponding Hilbert polynomials (a fact that could affect efficiency). The second difficulty is that these Weber polynomials do not have roots in \mathbbF_p\mathbb{F}_{p} .     

Static and dynamic behavior of single‐edge notched glass fabric composites

This article describes the results of a series of tests conducted to support the development of a semiempirical model, for predicting the mechanical degradation of a satin weave glass fabric composite, with through‐thickness damage in the form of a crack‐like edge‐centered notch. Test specimens were subjected to loading in both static three‐point bending and dynamic mechanical thermal analysis (DMTA) tests. The effect of both notch length and displacement rate, on the static and that of notch length on the dynamic behavior of the materials tested, was evaluated and compared with respective predictions, as derived from the application of the residual property model. A satisfactory agreement between the experimental results and theoretical predictions was observed in all cases. Scanning electron microscopy was applied to observe the failure topographical characteristics of the DMTA specimens that were off‐plane loaded. POLYM. COMPOS. 27:177–183, 2006. © 2006 Society of Plastics Engineers.     

Yeast cell based feed additives: studies on aflatoxin B₁ and zearalenone

Thirty commercially available yeast cell wall products and two reference bentonites were tested for their ability to bind aflatoxin B(1) (AFB1) and zearalenone (ZON) in buffer solutions at pH 3 and pH 6.5 as well as in real gastric juice. For most products, the binding efficacy of AFB1 correlated with the ash content, which was between 2.6 and 89%, and constituted the inorganic non-volatile components, such as mineral clays, of the samples. Samples with smectite as the main ash component showed the highest binding efficacy; yet, a correlation with the content of mannanooligosaccharides (MOS) and β-glucans from yeast cell walls was not observed. Products containing >30% ash showed AFB1 adsorption values >90% at least in one of the investigated media whereas most products with <10% ash did not exceed adsorption rates of 20%. In the case of ZON, adsorption efficiency ranged between 10 and 60%. It tended to be lowest for products with MOS and β-glucan contents <10% and greatest for products with MOS and β-glucan contents >50%. However, there was no general correlation between the adsorption of ZON and the concentration of MOS and β-glucans. Different products of one brand sold in different countries were observed to bind AFB1 to different degrees, which was explained by the difference in ash contents and mineral composition. In the case of ZON, differences in adsorption between products of the same brand were less pronounced.     

Efficient generation of secure elliptic curves

In many cryptographic applications it is necessary to generate elliptic curves (ECs) whose order possesses certain properties. The method that is usually employed for the generation of such ECs is the so-called Complex Multiplication method. This method requires the use of the roots of certain class field polynomials defined on a specific parameter called the discriminant. The most commonly used polynomials are the Hilbert and Weber ones. The former can be used to generate directly the EC, but they are characterized by high computational demands. The latter have usually much lower computational requirements, but they do not directly construct the desired EC. This can be achieved if transformations of their roots to the roots of the corresponding (generated by the same discriminant) Hilbert polynomials are provided. In this paper we present a variant of the Complex Multiplication method that generates ECs of cryptographically strong order. Our variant is based on the computation of Weber polynomials. We present in a simple and unifying manner a complete set of transformations of the roots of a Weber polynomial to the roots of its corresponding Hilbert polynomial for all values of the discriminant. In addition, we prove a theoretical estimate of the precision required for the computation of Weber polynomials for all values of the discriminant. We present an extensive experimental assessment of the computational efficiency of the Hilbert and Weber polynomials along with their precision requirements for various discriminant values and we compare them with the theoretical estimates. We further investigate the time efficiency of the new Complex Multiplication variant under different implementations of a crucial step of the variant. Our results can serve as useful guidelines to potential implementers of EC cryptosystems involving generation of ECs of a desirable order on resource limited hardware devices or in systems operating under strict timing response constraints. This work was partially supported by the IST Programme of EC under contract no. IST-2001-33116 (FLAGS), and by the Action IRAKLITOS (Fellowships for Research in the University of Patras) with matching funds from ESF (European Social Fund) and the Greek Ministry of Education.