A Comparative Study of the Two Isomers of Bicalicene

Two isomers of bicalicene are possible. The trans-isomer is a stable aromatic compound, known since the 1980s. The cis-isomer has never been experimentally prepared and has so far attracted little attention of theoretical chemists. The properties of cis-bicalicene are now studied theoretically, using the B3LYP/6-311G(d,p) quantum-chemical method. All data obtained (geometric, energetic, as well as those based on harmonic oscillator model of aromaticity and nucleus-independent chemical shift indices of local aromaticity) unequivocally indicate that the “missing” isomer of bicalicene is an unstable antiaromatic species, and that the lack of its existence is no surprise whatsoever.     

Analytics of time management strategies in a flipped classroom

This paper aims to explore time management strategies followed by students in a flipped classroom through the analysis of trace data. Specifically, an exploratory study was conducted on the dataset collected in three consecutive offerings of an undergraduate computer engineering course (N = 1,134). Trace data about activities were initially coded for the timeliness of activity completion. Such data were then analysed using agglomerative hierarchical clustering based on Ward's algorithm, first order Markov chains, and inferential statistics to (a) detect time management tactics and strategies from students' learning activities and (b) analyse the effects of personalized analytics-based feedback on time management. The results indicate that meaningful and theoretically relevant time management patterns can be detected from trace data as manifestations of students' tactics and strategies. The study also showed that time management tactics had significant associations with academic performance and were associated with different interventions in personalized analytics-based feedback.     

A New Method for Pore Pressure Prediction on Malfunctioning Cells Using Artificial Neural Networks

Embankment rockfill dams are the most common dam construction types used in the world today. One third of all embankment dam failures are caused by dam slope instability. The dam is stable when the slopes are stable. Slope safety of the dam is assessed through pore and total pressure data analysis registered on pressure measurement cells installed in the dam. During the service life of a dam, one or more cells may malfunction after years of operation. Cell replacement implies economically unjustified high costs and is usually technically impossible and high risk. In this paper, the problem of a malfunctioning cell with a small available dataset is analysed. A new method for pore pressure prediction on malfunctioning cells has been developed using several successive artificial neural networks (ANNs) to obtain high accuracy of the predicted values. The results show that these predicted values are more precise than values we could have obtained using only one artificial neural network for prediction.

     

Parameters optimization of a vertical ground heat exchanger based on response surface methodology

Vertical ground heat exchangers are one of the most important parts of geothermal utilization systems. In order to understand the effect of simultaneous variation of design parameters; a three dimensional computational fluid dynamics simulation was carried out. Based on the effective parameters on the heat exchanger efficiency and the total heat transfer efficiency in cooling mode, and with the aid of the second-order Response Surface Model, two functions for the total heat transfer efficiency and the heat exchanger efficiency were derived. The effects of different design parameters on the response variables were examined. Based on the Response Surface Model, it was found that the dimensionless inlet fluid temperature and the dimensionless pipe diameter significantly affect the response variables, while the response variables are weakly affected by dimensionless depth. Finally, an optimization was performed and the optimum heat exchanger is defined using the model equations.     

Elastic liposomes-in-vehicle formulations destined for skin therapy: the synergy between type of liposomes and vehicle

Objective: The present study is focused on optimization of elastic liposomes-in-vehicle formulations in respect to drug release and formulation properties. By combining penetration potential of elastic liposomes containing high ratio of entrapped drug and physicochemical properties of vehicles, both affecting the release and texture properties, optimal formulation could be achieved.

Materials and methods: Deformable, propylene glycol-containing or conventional liposomes with hydrophilic model drug (diclofenac sodium) were incorporated into the following vehicles appropriate for skin application: a hydrogel, a cream base and derma membrane structure base cream (DMS base). Each formulation was assessed for in vitro drug release and mechanical properties.

Results and discussion: The composition and type of both liposomes and the vehicle affected the rate and amount of the released drug. The cream base exhibited the slowest release, followed by the hydrogel and DMS base. Similar release profiles were achieved with both types of elastic vesicles (deformable and propylene glycol liposomes); the slowest release was observed for conventional liposomes, regardless of the vehicle used. The drug release profiles from different liposomes-in-vehicle formulations were in agreement with the physicochemical properties of the formulations. All of the liposomes were found to be compatible with the hydrogel preserving its original textures, whereas a significant decrease in all texture parameters was observed for liposomes-in-DMS base, regardless of liposome type.

Conclusion: Propylene glycol liposomes-in-hydrogel is considered as the optimal formulation for improving skin delivery of hydrophilic drug. Further investigations involving in vivo animal studies are necessary to confirm its applicability in skin therapy.     

Solid-phase extraction for HPLC analysis of dietary folates

Phenyl and cyclohexyl bonded silicas used for the solid-phase extraction (SPE) of dietary folates were studied and compared in terms of their retention capacities and recoveries. The SPE procedure was optimised to achieve the maximum recovery. The stabilities of folates in elution buffers and during the SPE procedure were also studied. The use of ascorbic acid throughout the SPE procedure was found to be important for the stabilisation of tetrahydrofolate – the most labile folate compound, whereas the use of both ascorbic acid and 2-mercaptoethanol was necessary to stabilise tetrahydrofolate during the storage of the eluates in the autosampler until analysis. Two purification methods, using phenyl endcapped (PH EC) cartridges or the combination of strong anion-exchange (SAX) and PH EC cartridges, were applied to the determination of folates in different food extracts, and verified by correlation with the usual purification method that uses SAX cartridges. The combination of SAX and PH EC cartridges was found to give the cleanest extracts.     

Characterization and antimicrobial activity of bacteriocin 217 produced by natural isolate Lactobacillus paracasei subsp. paracasei BGBUK2-16

The strain Lactobacillus paracasei subsp. paracasei BGBUK2-16. which was isolated from traditionally homemade white-pickled cheese, produces bacteriocin 217 (Bac217; approximately 7 kDa). The onset of Bac217 biosynthesis was observed in the logarithmic phase of growth, and the production plateau was reached after 9 or 12 h of incubation at 37 and 30 degrees C, respectively, when culture entered the early stationary phase. Biochemical characterization showed that Bac217 retained antimicrobial activity within the range of pH 3 to 12 or after treatment at 100 degrees C for 15 min. Bac217 antimicrobial activity also remained unchanged after storage at 4 degrees C for 6 months or -20 degrees C for up to 12 months. However, Bac217 activity was completely lost after treatment with different proteolytic enzymes. BGBUK2-16 contains only one plasmid about 80 kb in size. Plasmid curing indicated that genes coding for Bac217 synthesis and immunity seem to be located on this plasmid. Bac217 exhibited antimicrobial activity against some pathogenic bacteria, such as Staphylococcus aureus and Bacillus cereus. Interestingly, Bac217 showed activity against Salmonella sp. and Pseudomonas aeruginosa ATCC27853. The inhibitory effect of BGBUK2-16 on the growth of S. aureus in mixed culture was observed. S. aureus treatment with Bac217 led to a considerable decrease (CFU/ml) within a short period of time. The mode of Bac217 action on S. aureus was identified as bactericidal. It should be noted that the strain BGBUK2-16 was shown to be resistant to bacteriocin nisin, which is otherwise widely used as a food additive for fermented dairy products.     

Impact of priority differentiation on the bridged WBAN/WLAN healthcare networks

In this work, we develop a prioritized bridging mechanism between the IEEE 802.15.6‐based wireless body area networks (WBANs) and the IEEE 802.11e enhanced distributed channel access (EDCA)‐based wireless local area network (WLAN) to convey the medical data to the medical center. We map the eight WBAN user priorities (UPs) into the four WLAN access categories (ACs) to provide the required quality of service and prioritization for the health variables generated by the WBAN nodes. By assignment of WBAN UPs with default medium access control parameters to eight different medical data streams and under the presence of ordinary nodes, we investigate the impact of WLAN AC differentiation by arbitrary inter‐frame space (AIFS) and contention window (CW) on performance of medical and regular nodes’ data streams. The results of this work indicate that the AC differentiation by AIFS outperforms the differentiation by CW in the sense that it does not deteriorate the end‐to‐end delay of relayed WBAN traffic and ordinary WLAN traffic.Copyright © 2012 John Wiley & Sons, Ltd.     

Closed‐Form Expressions for Selection Combining System Statistics over Correlated Generalized‐K Fading Channels in the Presence of Interference

This paper considers the effects of simultaneous correlated multipath fading and shadowing on the performances of a signal‐to‐interference ratio (SIR)‐based dual‐branch selection combining (SC) diversity receiver. This analysis includes the presence of cochannel interference. A generalized fading/shadowing channel model in an interference‐limited correlated fading environment is modeled by generalized‐K distribution. Closed‐form expressions are obtained for probability density function and cumulative distribution function of the SC output SIR, as well as for the outage probability. Based on this, the influence of various fading and shadowing parameter values and the correlation level on the outage probability is examined.     

Aqua regia extracted metals in sediments from the industrial area and surroundings of Pančevo, Serbia

Surface and buried sediments were analyzed for Ba, Ca, Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn and V, as well as for total carbon and hydrogen to assess the distribution of sediment pollution due to the vicinity of the petrochemical complex. The samples, collected from 20 locations within the petrochemical complex and from 16 locations outside the complex, were aqua regia extracted and analyzed by ICP/OES. Metals were determined with an acceptable accuracy for certified metals of 82-113%. The precision for the aqua regia extraction was satisfactory, less than 20%, except for Cd where it was 28%. Comparison of the data from the petrochemical with those from the non-petrochemical areas showed different distributions of the metals. Metals that exceeded the baseline range; Ba, Cd, Cu, Zn and Pb, were detected in higher concentrations in sediments that were under the influence of the chlor-alkali plant within the petrochemical complex. Comparison with data from the petrochemical complex and its surroundings and their distribution demonstrated that the metal compositions of the sediments were modified by anthropogenic activities.