EVALUATION OF BIOLOGICAL ACTIVITIES OF NANOCRYSTALLINE TETRAGONAL ZIRCONIA SYNTHESIZED VIA SOL-GEL METHOD

Objective: The objective of the following study was a synthesis of nanocrystalline tetragonal zirconia (ZrO2) using simple sol–gel method and evaluation of its structural and biological properties.Methods: The sample was characterized by X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and evaluated for cell growth study using 3T3 mouse fibroblast cells and for degradation using Phosphate Buffered Saline (PBS) solution. The synthesized materials were also evaluated for their antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacterial strains.Results: The XRD pattern shows that the tetragonal phase of nanocrystalline zirconia was obtained at relatively low temperature i.e. 300 °C. The FESEM images showed that the prepared sample consists of particles in the range of 35-69 nm and homogenous particle size distribution. The TEM images confirmed the results shown by FESEM images. The sample of zirconia has excellent tissue biocompatibility, higher cell growth and does not show the toxicity towards normal 3T3 mouse fibroblast cells. The result of qualitative antibacterial tests revealed that the nanocrystalline zirconia had an important inhibitory activity on E. coli and S. aureus. The sample shows stability at the physiological condition and does not show degradation.Conclusion: Nanocrystalline tetragonal zirconia shows higher cell growth and efficient antibacterial activity against E. coli and S. aureus bacterial pathogen and also it is stable at the physiological condition. Hence, it can be used for various biomedical applications.Keywords: Nanocrystalline zirconia, Sol-gel route, Antimicrobial action, Biomedical applicatio

On Protection by Layout Randomization

Layout randomization is a powerful, popular technique for software protection. We present it and study it in programming-language terms. More specifically, we consider layout randomization as part of an implementation for a high-level programming language; the implementation translates this language to a lower-level language in which memory addresses are numbers. We analyze this implementation, by relating low-level attacks against the implementation to contexts in th

Individual rules for trail pattern formation in Argentine ants (Linepithema humile)

We studied the formation of trail patterns by Argentine ants exploring an empty arena. Using a novel imaging and analysis technique we estimated pheromone concentrations at all spatial positions in the experimental arena and at different times. Then we derived the response function of individual ants to pheromone concentrations by looking at correlations between concentrations and changes in speed or direction of the ants. Ants were found to turn in response to local pheromone concentrations, while their speed was largely unaffected by these concentrations. Ants did not integrate pheromone concentrations over time, with the concentration of pheromone in a 1 cm radius in front of the ant determining the turning angle. The response to pheromone was found to follow a Weber's Law, such that the difference between quantities of pheromone on the two sides of the ant divided by their sum determines the magnitude of the turning angle. This proportional response is in apparent contradiction with the well-established non-linear choice function used in the literature to model the results of binary bridge experiments in ant colonies (Deneubourg et al. 1990). However, agent based simulations implementing the Weber's Law response function led to the formation of trails and reproduced results reported in the literature. We show analytically that a sigmoidal response, analogous to that in the classical Deneubourg model for collective decision making, can be derived from the individual Weber-type response to pheromone concentrations that we have established in our experiments when directional noise around the preferred direction of movement of the ants is assumed.Comment: final version, 9 figures, submitted to Plos Computational Biology (accepted

Control of antiferromagnetic spin axis orientation in bilayer Fe/CuMnAs films

Using x-ray magnetic circular and linear dichroism techniques, we demonstrate a collinear exchange coupling between an epitaxial antiferromagnet, tetragonal CuMnAs, and an Fe surface layer. A small uncompensated Mn magnetic moment is observed which is antiparallel to the Fe magnetization. The staggered magnetization of the 5 nm thick CuMnAs layer is rotatable under small magnetic fields, due to the interlayer exchange coupling. This allows us to obtain the x-ray magnetic linear dichroism spectra for different crystalline orientations of CuMnAs in the (001) plane. This is a key parameter for enabling the understanding of domain structures in CuMnAs imaged using x-ray magnetic linear dichroism microscopy techniques

Friends and Foes from an Ant Brain's Point of View – Neuronal Correlates of Colony Odors in a Social Insect

Background: Successful cooperation depends on reliable identification of friends and foes. Social insects discriminate colony members (nestmates/friends) from foreign workers (non-nestmates/foes) by colony-specific, multi-component colony odors. Traditionally, complex processing in the brain has been regarded as crucial for colony recognition. Odor information is represented as spatial patterns of activity and processed in the primary olfactory neuropile, the antennal lobe (AL) of insects, which is analogous to the vertebrate olfactory bulb. Correlative evidence indicates that the spatial activity patterns reflect odor-quality, i.e., how an odor is perceived. For colony odors, alternatively, a sensory filter in the peripheral nervous system was suggested, causing specific anosmia to nestmate colony odors. Here, we investigate neuronal correlates of colony odors in the brain of a social insect to directly test whether they are anosmic to nestmate colony odors and whether spatial activity patterns in the AL can predict how odor qualities like ‘‘friend’’ and ‘‘foe’’ are attributed to colony odors. Methodology/Principal Findings: Using ant dummies that mimic natural conditions, we presented colony odors and investigated their neuronal representation in the ant Camponotus floridanus. Nestmate and non-nestmate colony odors elicited neuronal activity: In the periphery, we recorded sensory responses of olfactory receptor neurons (electroantennography), and in the brain, we measured colony odor specific spatial activity patterns in the AL (calcium imaging). Surprisingly, upon repeated stimulation with the same colony odor, spatial activity patterns were variable, and as variable as activity patterns elicited by different colony odors. Conclusions: Ants are not anosmic to nestmate colony odors. However, spatial activity patterns in the AL alone do not provide sufficient information for colony odor discrimination and this finding challenges the current notion of how odor quality is coded. Our result illustrates the enormous challenge for the nervous system to classify multi-component odors and indicates that other neuronal parameters, e.g., precise timing of neuronal activity, are likely necessary for attribution of odor quality to multi-component odors

Foraging behavior as a determinant of asymmetric competitive interaction between two ant species in a tropical agroecosystem

This work is concerned with elucidating competitive interactions between two neotropical ants, Solenopsis geminata and Pheidole radoszkowskii , focusing on their foraging behavior. When released from competition from P. radoszkowskii, S. geminata increased its foraging activity. On the other hand, when released from competition from S. geminata, P. radoszkowskii did not respond, demonstrating asymmetric competition between the two species. Foraging experiments showed that P. radoszkowskii is more efficient at finding food resources, whereas S. geminata is better at defending the resources once they are encountered. These differences in foraging behavior appear to permit the coexistence of these two species. The practical implications of the results for the management of ant communities in tropical agroecosystems is discussed with respect to the potential use of ants as natural enemies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47804/1/442_2004_Article_BF00341471.pd