How to address group dynamics in virtual worlds

The study of group dynamics highlights the activity in the group in terms of its performance and communication. The experience of facilitating virtual communities and teams (Eunice and Kimball in , 1997) suggests that groups go through the same stages either in face-to-face or in online mode. The paper brings together a theoretical framework based on the literature on virtual communities, Gestalt systems and online facilitation in order to address the issue of electronic togetherness, in particular from a group dynamics perspective. The empirical work on which the paper is based is an observation of a group of students in a training set playing a decision-making game. The model of Tuckman (Tuckman in Psychol Bull 63:384–399, 1965; Tuckman and Jensen in Group Organ Stud 2:419–427, 1977) is used as a framework within which to discuss the findings of the case. The paper finishes with concrete recommendations for facilitators of online communities and designers of the electronic spaces where these communities operate.     

Identification and Modeling of Permanent Deformations of Asphalt Concrete

The accumulation of permanent deformations in asphalt concrete under repeated loading, a phenomenon of great practical importance, is studied in detail and a new multidimensional nonlinear hyperelastic-nonassociative plastic model is proposed. The equations of the model are solved by using the predictor–corrector algorithm. The model’s results are compared to actual experimental data and the comparison is very favorable. A remarkable result is that the model parameters obtained from one stress level predict correctly the results for another stress level.     

Mutational Analysis of Redβ Single Strand Annealing Protein: Roles of the 14 Lysine Residues in DNA Binding and Recombination In Vivo

Redβ is a 261 amino acid protein from bacteriophage λ that promotes a single-strand annealing (SSA) reaction for repair of double-stranded DNA (dsDNA) breaks. While there is currently no high-resolution structure available for Redβ, models of its DNA binding domain (residues 1–188) have been proposed based on homology with human Rad52, and a crystal structure of its C-terminal domain (CTD, residues 193-261), which binds to λ exonuclease and E. coli single-stranded DNA binding protein (SSB), has been determined. To evaluate these models, the 14 lysine residues of Redβ were mutated to alanine, and the variants tested for recombination in vivo and DNA binding and annealing in vitro. Most of the lysines within the DNA binding domain, including K36, K61, K111, K132, K148, K154, and K172, were found to be critical for DNA binding in vitro and recombination in vivo. By contrast, none of the lysines within the CTD, including K214, K245, K251, K253, and K258 were required for DNA binding in vitro, but two, K214 and K253, were critical for recombination in vivo, likely due to their involvement in binding to SSB. K61 was identified as a residue that is critical for DNA annealing, but not for initial ssDNA binding, suggesting a role in binding to the second strand of DNA incorporated into the complex. The K148A variant, which has previously been shown to be defective in oligomer formation, had the lowest affinity for ssDNA, and was the only variant that was completely non-cooperative, suggesting that ssDNA binding is coupled to oligomerization.     

Spontaneous Crystallization in Athermal Polymer Packings

We review recent results from extensive simulations of the crystallization of athermal polymer packings. It is shown that above a certain packing density, and for sufficiently long simulations, all random assemblies of freely-jointed chains of tangent hard spheres of uniform size show a spontaneous transition into a crystalline phase. These polymer crystals adopt predominantly random hexagonal close packed morphologies. An analysis of the local environment around monomers based on the shape and size of the Voronoi polyhedra clearly shows that Voronoi cells become more spherical and more symmetric as the system transits to the ordered state. The change in the local environment leads to an increase in the monomer translational contribution to the entropy of the system, which acts as the driving force for the phase transition. A comparison of the crystallization of hard-sphere polymers and monomers highlights similarities and differences resulting from the constraints imposed by chain connectivity.     

Acute and chronic toxicity effects of silver nanoparticles (NPs) on Drosophila melanogaster

The use of nanoscaled materials is rapidly increasing, however, their possible ecotoxicological effects are still not precisely known. This work constitutes the first complex study focused on in vivo evaluation of the acute and chronic toxic effects and toxic limits of silver nanoparticles (NPs) on the eukaryotic organism Drosophila melanogaster. For the purpose of this study, silver NPs were prepared in the form of solid dispersion using microencapsulation method, where mannitol was used as an encapsulation agent. This newly prepared solid dispersion with a high concentration of silver NPs was exploited to prepare the standard Drosophila culture medium at a silver concentration range from 10 mg·L(-1) to 100 mg·L(-1) of Ag in the case of the acute toxicity testing and at a concentration equal to 5 mg·L(-1) in the case of the chronic toxicity testing. The acute toxic effect of silver NPs on Drosophila melanogaster was observed for the silver concentration equal to 20 mg·L(-1). At this silver concentration, 50% of the tested flies were unable to leave the pupae, and they did not finish their developmental cycle. Chronic toxicity of silver NPs was assessed by a long-term exposure of overall eight filial generations of Drosophila melanogaster to silver NPs. The long-term exposure to silver NPs influenced the fertility of Drosophila during the first three filial generations, nevertheless the fecundity of flies in subsequent generations consequently increased up to the level of the flies from the control sample due to the adaptability of flies to the silver NPs exposure.     

Role of Genetic Variation in Cytochromes P450 in Breast Cancer Prognosis and Therapy Response

Breast cancer is the most frequent cancer in the female population worldwide. The role of germline genetic variability in cytochromes P450 (CYP) in breast cancer prognosis and individualized therapy awaits detailed elucidation. In the present study, we used the next-generation sequencing to assess associations of germline variants in the coding and regulatory sequences of all human CYP genes with response of the patients to the neoadjuvant cytotoxic chemotherapy and disease-free survival (n = 105). A total of 22 prioritized variants associating with a response or survival in the above evaluation phase were then analyzed by allelic discrimination in the large confirmation set (n = 802). Associations of variants in CYP1B1, CYP4F12, CYP4X1, and TBXAS1 with the response to the neoadjuvant cytotoxic chemotherapy were replicated by the confirmation phase. However, just association of variant rs17102977 in CYP4X1 passed the correction for multiple testing and can be considered clinically and statistically validated. Replicated associations for variants in CYP4X1, CYP24A1, and CYP26B1 with disease-free survival of all patients or patients stratified to subgroups according to therapy type have not passed a false discovery rate test. Although statistically not confirmed by the present study, the role of CYP genes in breast cancer prognosis should not be ruled out. In conclusion, the present study brings replicated association of variant rs17102977 in CYP4X1 with the response of patients to the neoadjuvant cytotoxic chemotherapy and warrants further research of genetic variation CYPs in breast cancer.     

Anticonvulsant Effects of Topiramate and Lacosamide on Pilocarpine-Induced Status Epilepticus in Rats: A Role of Reactive Oxygen Species and Inflammation

Background: Status epilepticus (SE) is a neurological disorder characterized by a prolonged epileptic activity followed by subsequent epileptogenic processes. The aim of the present study was to evaluate the early effects of topiramate (TPM) and lacosamide (LCM) treatment on oxidative stress and inflammatory damage in a model of pilocarpine-induced SE. Methods: Male Wistar rats were randomly divided into six groups and the two antiepileptic drugs (AEDs), TPM (40 and 80 mg/kg, i.p.) and LCM (10 and 30 mg/kg, i.p.), were injected three times repeatedly after pilocarpine administration. Rats were sacrificed 24 h post-SE and several parameters of oxidative stress and inflammatory response have been explored in the hippocampus. Results: The two drugs TPM and LCM, in both doses used, succeeded in attenuating the number of motor seizures compared to the SE-veh group 30 min after administration. Pilocarpine-induced SE decreased the superoxide dismutase (SOD) activity and reduced glutathione (GSH) levels while increasing the catalase (CAT) activity, malondialdehyde (MDA), and IL-1β levels compared to the control group. Groups with SE did not affect the TNF-α levels. The treatment with a higher dose of 30 mg/kg LCM restored to control level the SOD activity in the SE group. The two AEDs, in both doses applied, also normalized the CAT activity and MDA levels to control values. In conclusion, we suggest that the antioxidant effect of TPM and LCM might contribute to their anticonvulsant effect against pilocarpine-induced SE, whereas their weak anti-inflammatory effect in the hippocampus is a consequence of reduced SE severity.     

Enzyme-assisted physicochemical enantioseparation processes—Part II: Solid-liquid equilibria, preferential crystallization, chromatography and racemization reaction

This contribution addresses the design and investigation of two hybrid enantioseparation processes including an enzymatic racemization step in order to enhance the overall performance. Complementary to part I where the manufacturing and the characterization of an amino acid racemase (EC 5.1.1.10) was emphasized [Würges, K., Petrusevska, K., Serci, S., Wilhelm, S., Wandrey, C., Seidel-Morgenstern, A., Elsner, M.P., Lütz, S., 2009. Enzyme-assisted physicochemical enantioseparation processes—part I: production and characterization of a recombinant amino acid racemase. J. Mol. Cat. B (in print), online available: doi:10.1016/j.molcatb.2008.10.006.], the work presented in this paper tends more towards developing a data base for potential process schemes for the manufacture of selected amino acids.The first proposed process concept (P-I) couples preferential crystallization (PC) and racemization for the production of l-asparagine (l-Asn) using racemic mixture of dl-asparagine (conglomerate-forming system) as a starting material, while the second concept (P-II) integrates chromatography and racemization for the preparation of l-methionine (l-Met) starting with racemic mixture of dl-methionine (compound-forming system). As mentioned in part I, a racemization unit, where the unwanted enantiomer will be converted into racemate, is incorporated into the hybrid processes for the sake of 100% yield, theoretically. Besides the basic investigation according to the solid-liquid equilibria, PC and chromatography, the focus of this paper is mainly on the kinetic studies of the racemization reaction. Initially, the solubility ternary phase diagrams of both examined systems were determined, leading into the idea of combination of the proposed process schemes. For P-I the concept of PC of l-Asn was experimentally proven and the kinetics of the racemization was examined for d- and l-Asn in water using purified lyophilizate (PL). Concerning P-II, for the chromatographic unit the impact on the separation of dl-Met on eremomycin based stationary phase using KPi buffer and MeOH as mobile phase was evaluated in terms of resolution and selectivity at three different temperatures by varying the content of methanol (MeOH) in the mobile phase and the pH. The experiments for determination of the racemization kinetics were done for a compromised parameter set using crude lyophilizate (CL). In both cases a Michaelis-Menten three-step model was used to describe the enzymatic reaction.