Degradation in soil behavior of artificially aged polyethylene films with pro‐oxidants

Bio‐based, biodegradable in soil, as well as degradable polyethylene mulching films with pro‐oxidants, have been introduced in the market in an effort to deal with the serious problem of managing plastic waste streams generated from conventional mulching films. In a previous experimental investigation, a series of naturally degraded under water melon cultivation conditions linear low density polyethylene (LLDPE) mulching films with pro‐oxidants, buried in the field for 8.5 years, were recovered intact even though undergoing a continuous slow abiotic degradation in soil. The aim of the present article was to simulate the behavior of the LLDPE mulching films with pro‐oxidants under a much longer time‐scale (e.g. some decades). Toward this purpose, samples of LLDPE with pro‐oxidants film were artificially degraded to simulate severe degradation/fragmentation of these films while been buried in the soil for many years, following the end of the cultivation season. Further degradation of these severely degraded samples was investigated by burying them in the soil over a period of seven years. During this burial period, all degradation parameters and their evolution with time were measured. The artificially degraded LLDPE film samples with pro‐oxidants, in contrast to the naturally degraded film that remained intact for 8.5 years, were gradually transformed into tiny micro‐fragments in the soil. These fragments, through a continuing abiotic degradation process under natural soil conditions are eventually transformed into invisible micro‐fragments. The fate of these micro‐fragments and their long‐term impact to the environment and human health is unpredictable. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42289.     

Gender issues in technology use: Perceived social support,computer self-efficacy and value beliefs,and computer use beyond school

In this study, we examined relations between outside school computer experiences, perceived social support for using computers, and self-efficacy and value beliefs about computer learning for 340 Greek elementary school boys and girls. Participants responded to a questionnaire about their access to computer use outside school (e.g. frequency of use and nature of activities), perceived parental and peer support, and computer self-efficacy and value beliefs. Although almost all students used computers outside school, there were significant gender differences in frequency and type of computer use. Also, boys reported more perceived support from their parents and peers to use computers and more positive computer self-efficacy and value beliefs than girls. Parental support and, to a lesser extent, peer support were the factors more strongly associated with boys’ and girls’ computer self-efficacy and value beliefs, while home computer access was not related to students’ motivation. Our findings highlight the role of socialization in the gender gap in computing and the need for research and educational interventions that focus on the social practices that communicate gendered expectations to young boys and girls.     

Precipitation Forecast Using Artificial Neural Networks in Specific Regions of Greece

In recent years, significant changes in precipitation regimes have been observed and these manifest in socio economic and ecological problems especially in regions with increased vulnerability such as the Mediterranean region. For this reason, it is necessary to estimate the future projected precipitation on short and long-term basis by analyzing long time series of observed station data. In this study, an effort was made in order to forecast the monthly maximum, minimum, mean and cumulative precipitation totals within a period of the next four consecutive months, using Artificial Neural Networks (ANNs). The precipitation datasets concern monthly totals recorded at four meteorological stations (Alexandroupolis, Thessaloniki, Athens, and Patras), in Greece. For the evaluation of the results and the ability of the developed prognostic models, appropriate statistical indexes such as the coefficient of determination (R ²), the index of agreement (IA) and the root mean square error (RMSE) were used. The findings from this analysis showed that the ANN’s methodology provides satisfactory precipitation totals in four consecutive months and these results are better results, than those obtained using classical statistical methods. A fairly good consistency between the observed and the predicted precipitation totals at a statistical significance level of p < 0.01 for the most of the examined cases has been revealed. More specifically, the Index of Agreement (IA) ranges between 0.523 and 0.867 and the coefficient of determination (R ²) ranges between 0.141 and 0.603. The most accurate forecasts concern the mean monthly and the cumulative precipitation for the next four consecutive months.     

Transforming communicating X-machines into P systems

Tissue P systems (tPS) represent a class of P systems in which cells are arranged in a graph rather than a hierarchical structure. On the other hand, communicating X-machines (XMs) are state-based machines, extended with a memory structure and transition functions instead of simple inputs, which communicate via message passing. One could use communicating XMs to create models built out of components in a rather intuitive way. There are investigations showing how various classes of P systems can be modelled as communicating XMs. In this paper, we define a set of principles to transform communicating XMs into tPS. We describe the rules that govern such transformations, present an example to demonstrate the feasibility of this approach and discuss ways to extend it to more general models, such as population P systems, which involve dynamic structures.     

Effect of acid tolerance response (ATR) on attachment of Listeria monocytogenes Scott A to stainless steel under extended exposure to acid or/and salt stress and resistance of sessile cells to subsequent strong acid challenge

The aim of this study was to investigate the potential effect of adaptive stationary phase acid tolerance response (ATR) of Listeria monocytogenes Scott A cells on their attachment to stainless steel (SS) under low pH or/and high salt conditions and on the subsequent resistance of sessile cells to strong acid challenge. Nonadapted or acid-adapted stationary-phase L. monocytogenes cells were used to inoculate (ca. 10? CFU/ml) Brain Heart (BH) broth (pH 7.4, 0.5% w/v NaCl) in test tubes containing vertically placed SS coupons (used as abiotic substrates for bacterial attachment). Incubation was carried out at 16 °C for up to 15 days, without any nutrient refreshment. L. monocytogenes cells, prepared as described above, were also exposed to low pH (4.5; adjusted with HCl) or/and high salt (5.5% w/v NaCl) stresses, during attachment. On the 5th, 10th and 15th day of incubation, cells attached to SS coupons were detached (through bead vortexing) and enumerated (by agar plating). Results revealed that ATR significantly (p<0.05) affected bacterial attachment, when the latter took place under moderate acidic conditions (pH 4.5, 0.5 or 5.5% w/v NaCl), with the acid-adapted cells adhering slightly more than the nonadapted ones. Regardless of acidity/salinity conditions during attachment, ATR also enhanced the resistance of sessile cells to subsequent lethal acid challenge (exposure to pH 2 for 6 min; pH adjusted with either hydrochloric or lactic acid). The trend observed with viable count data agreed well with conductance measurements, used to indirectly quantify remaining attached bacteria (following the strong acid challenge) via their metabolic activity. To sum, this study demonstrates that acid adaptation of L. monocytogenes cells during their planktonic growth enhances their subsequent attachment to SS under extended exposure (at 16 °C for up to 15 days) to mild acidic conditions (pH 4.5), while it also improves the resistance of sessile cells to extreme acid treatment (pH 2). Therefore, the ATR of bacterial cells should be carefully considered when applying acidic decontamination strategies to eradicate L. monocytogenes attached to food processing equipment.     

Resource provision ego-networks in small Greek construction firms

The prominence of small professional service providers in a fragmented construction sector in part relates to the ability to provide competitive advantage through the provision of a personalized service in a context where diseconomies of scale prevail. The Greek construction industry is particularly representative of this trend towards the dominance of small businesses. The small business owner relies upon their ability to secure critical resources through personal networks which provide information, advice, funding and brokerage. Resource provision ego-networks are investigated structurally using social network analysis. A multiple case study approach is employed with comparative social network analysis, focusing on the density of ego-networks and the prominence of resource providers and associated subgroups. Findings show that commercial development activity is promoted through high-density networks, which infers that higher levels of connectivity characterize networks operating in environments of uncertainty. As these critical resource networks mature, they appear to rely less on strong ties and temporary formal project networks. Contractual relationships appear to co-exist with reciprocal flows of resources outside the contract's scope.

L'importance des petits prestataires de services professionnels dans un secteur du bâtiment qui est fragmenté tient pour partie à la capacité à assurer un avantage concurrentiel par la fourniture d'un service personnalisé dans un contexte où les déséconomies d'échelle prévalent. L'industrie grecque du bâtiment est particulièrement représentative de cette tendance à la dominance des petites entreprises. Le propriétaire d'une petite entreprise s'appuie sur sa capacité à garantir des ressources critiques par des réseaux personnels qui fournissent des informations, des conseils, du financement et des services de courtage. Les ego-réseaux prestataires de ressources sont examinés d'un point de vue structurel en utilisant une analyse des réseaux sociaux. Il est employé une approche basée sur une étude de cas multiples s'accompagnant d'une analyse comparative des réseaux sociaux, centrée sur la densité des ego-réseaux et sur l'importance des prestataires de ressources et des sous-groupes associés. Les résultats constatés montrent que la promotion des activités de développement commercial se fait par les réseaux haute densité, ce qui induit que des niveaux supérieurs de connectivité caractérisent les réseaux fonctionnant dans des contextes marqués par l'incertitude. Au fur et à mesure que ces réseaux de ressources critiques mûrissent, ils semblent moins s'appuyer sur des liens forts et des réseaux temporaires en rapport avec des projets formels. Il apparaît que les relations contractuelles coexistent avec des flux de ressources réciproques en dehors du champ du contrat.

ego-réseaux ou réseaux personnels, activité entrepreneuriale, réseaux prestataires de ressources, PME du bâtiment, analyse des réseaux sociaux     

Effect of acid adaptation on growth during storage at 10 degrees C and resistance to simulated gastric fluid of Listeria monocytogenes inoculated onto bologna formulated with or without antimicrobials

The fate of acid-adapted and nonadapted Listeria monocytogenes inoculated onto bologna slices (formulated with or without antimicrobials) was examined during storage and after exposure to in vitro gastric challenge. Bologna slices formulated with no antimicrobials (control), 3% sodium lactate (SL), or 1.8% SL plus 0.25% sodium diacetate (SD) were inoculated (2 log CFU/cm2) with a 10-strain composite of acid-adapted or nonadapted L. monocytogenes strains. Growth or survival of the two inocula on bologna was evaluated during vacuum-packaged storage (10 degrees C) for up to 36 days. Survival of previously acid-adapted or nonadapted L. monocytogenes on stored bologna exposed to simulated gastric fluid (adjusted to pH 1.0 with HCl) for 20, 40, and 60 min also was determined. As expected, inclusion of antimicrobials in the product formulation inhibited growth of L. monocytogenes during storage of vacuum-packaged bologna compared with growth on control samples. Acid adaptation of L. monocytogenes prior to product inoculation did not affect subsequent survival or growth on bologna or resistance to simulated gastric fluid (P > 0.05). Survival of L. monocytogenes exposed to simulated gastric fluid during storage increased with product age, growth phase of the cells, and possibly age of the cells, particularly for control samples (no antimicrobials), in which the pathogen grew uninhibited to approximately 6 log CFU/cm2 by day 8 of storage. Inhibition of L. monocytogenes growth on product formulated with antimicrobials was associated with only sporadic and small numbers of survivors following exposure of these samples to simulated gastric fluid, especially in samples stored longer. However, cell numbers in these treatment groups before the gastric challenge did not exceed 3.8 log CFU/cm2. Inhibition of growth on product with antimicrobials precluded detection of survivors resistant to the effects of simulated gastric fluid.     

Effect of different iron compounds on wheat and gluten‐free breads

BACKGROUND: Iron fortification of bread often results in sub‐optimal quality of the final product due to undesirable changes in the physical characteristics and sensory properties of the bread. In this study both the form of iron (soluble, insoluble or encapsulated) and the type of bread (wheat or gluten‐free) were varied in order to investigate the effect of iron and gluten on the product characteristics. RESULTS: The effect of iron on the quality characteristics of the breads investigated depended on iron type, but not on iron solubility. Colour, crust firmness, specific volume, cell number and uniformity as well as aroma were the attributes that were mainly affected in iron‐enriched wheat bread. In some cases, specific volume was 30% lower than that of the control sample, while cell uniformity was significantly lower, as low as 50% of the control sample in some fortified samples. In gluten‐free breads, differences between unfortified and fortified samples included colour, crust firmness, cell number, ‘moisture’ odour, metallic taste and stickiness. In some cases, the sensory scores were better for fortified samples. CONCLUSIONS: Differences due to iron fortification were less pronounced in gluten‐free compared to wheat breads. The choice of the appropriate iron compound which will not cause adverse quality changes is still a challenge. Copyright © 2010 Society of Chemical Industry