Food safety concerns have been raised over vegetables and herbs grown in aquaponics and hydroponics due to the reuse of wastewater and spent nutrient solutions. This study was conducted to determine the occurrence of foodborne pathogens in greenhouse-based aquaponic and hydroponic systems. Fish feces, recirculating water, roots, and the edible portions of lettuce, basil, and tomato were collected at harvest, and microbiological analyses were conducted for the bacterial pathogens Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes, and Salmonella spp. Enrichments and selective media were used for the isolation, and presumptive positive colonies were confirmed by PCR. STEC was found in fish feces, in the water of both systems, and on the surface of the roots of lettuce, basil, and tomato regardless of the system. However, contaminated water did not lead to the internalization of STEC into the roots, leaves, and/or fruit of the plants. Meanwhile, L. monocytogenes and Salmonella spp. were not present in any samples examined. Our results demonstrated that there are potential food safety hazards for fresh produce grown in aquaponic and hydroponic production systems.
Purpose Information technology is widely applied for completing group tasks and enhancing learning in computer-supported collaborative learning (CSCL) environment. Group members not only complete tasks but also learn ideas from other members of the group. These ideas can be better than what individual could come up with. As these ideas are referred as an upward comparison in the perspective of social comparison theory. However, there are limited studies that provide evidence in investigating how social comparison orientation (SCO) perceived by individual learner impacts on learning and group performance. The paper aims to discuss these issues. Design/methodology/approach This study experimentally tackles this problem at both individual and group level. An experimental study was applied in this study. Structural equation modeling and hierarchical linear modeling approaches are used to validate the data. Findings Results of 168 subjects reveal that SCO does have associations with group performance and learning performance respectively. Discussions and implications for literature and practice are given at the end of the paper. Originality/value This study confirms that the social genesis occurs more effectively through social interactions in CSCL. It also extends our understandings about the impacts of SCO. Results reveal that the higher level of SCO adopted by group members, the higher level of social interactions at group level can be triggered. As a result, the group performance can be enhanced. On one hand, these findings bridge the research gap in terms of investigating the notion of SCT on CSCL. On the other hand, it provides a possible solution in alleviating the problem of social loafing as commonly observed in CSCL. Therefore, these findings fulfilled the two research objectives.
This paper describes synthesis of ultrathin pinhole-free insulating aluminum oxide layers for electronic device protection in corrosive liquid environments, such as phosphate buffered saline (PBS) or clinical fluids, to enable emerging biomedical applications such as biomolecular sensors. A pinhole-free 25-nm thick amorphous aluminum oxide layer has been achieved using ultra-high vacuum DC magnetron reactive sputtering of aluminum in oxygen/argon plasma followed by oxygen plasma post-processing. Deposition parameters were optimized to achieve the best corrosion protection of lithographically defined device structures. Electrochemical deposition of copper through the aluminum oxide layers was used to detect the presence (or absence) of pinholes. FTIR, XPS, and spectroscopic ellipsometry were used to characterize the material properties of the protective layers. Electrical resistance of the copper device structures protected by the aluminum oxide layers and exposed to a PBS solution was used as a metric to evaluate the long-term stability of these device structures.
Ion Beam Aperture Array Lithography was applied to top-down fabrication of large dense (108–109 particles/cm2) arrays of uniform micron-scale particles at rates hundreds of times faster than electron beam lithography. In this process, a large array of helium ion beamlets is formed when a stencil mask containing an array of circular openings is illuminated by a broad beam of energetic (5–8 keV) ions, and is used to write arrays of specific repetitive patterns. A commercial 5-micrometer metal mesh was used as a stencil mask; the mesh size was adjusted by shrinking the stencil openings using conformal sputter-deposition of copper. Thermal evaporation from multiple sources was utilized to form magnetic particles of varied size and thickness, including alternating layers of gold and permalloy. Evaporation of permalloy layers in the presence of a magnetic field allowed creation of particles with uniform magnetic properties and pre-determined magnetization direction. The magnetic properties of the resulting particles were characterized by Vibrating Sample Magnetometry. Since the orientation of the particles on the substrate before release into suspension is known, the orientation-dependent magnetic properties of the particles could be determined.
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