Tunnelling Characteristics of Stone-Wales Defects in Monolayers of Sn and Group-V Elements

Topological defects in ultrathin layers are often formed during synthesis and processing, thereby, strongly influencing their electronic properties . In this paper, we investigate the role of Stone-Wales (SW) defects in modifying the electronic properties of the monolayers of Sn and group-V elements. The calculated results find the electronic properties of stanene (monolayer of Sn atoms) to be strongly dependent on the concentration of SW-defects e.g., defective stanene has nearly zero band gap (~ 0.03 eV) for the defect concentration of 2.2 x 10^13 cm^-2 which opens up to 0.2 eV for the defect concentration of 3.7 x 10^13 cm^-2. In contrast, SW-defects appear to induce conduction states in the semiconducting monolayers of group-V elements. These conduction states act as channels for electron tunnelling, and the calculated tunnelling characteristics show the highest differential conductance for the negative bias with the asymmetric current-voltage characteristics. On the other hand, the highest differential conductance was found for the positive bias in stanene. Simulated STM topographical images of stanene and group-V monolayers show distinctly different features in terms of their cross-sectional views and distance-height profiles which can serve as fingerprints to identify the topological defects in the monolayers of group-IV and group-V elements in experiments.Comment: 18 pages, 5 figures, 1 tabl

Response surface and artificial neural network simulation for process design to produce L-lysine by Corynebacterium glutamicum NCIM 2168

269-279The L-lysine is one of the most important essential amino acid used in food and pharmaceutical industries. The present investigation was conducted to optimize the L-lysine production by Corynebacterium glutamicum (NCIM 2168). The production parameters such as the temperature, pH and glucose concentration (g/l) were optimised and evaluated by simulation method to develop a suitable model. The experimental design was done using central composite design (CCD). Total 20 set of experiments were performed according to the CCD. The factors and their responses were analysed by using the statistical tools: response surface methodology (RSM) and artificial neural network (ANN) linked with genetic algorithm (GA). The predicted optimum production of L-lysine was 19.003 g/l and 28.363 g/l by CCD-RSM and ANN-GA respectively. During validation by GA under optimized conditions, the L-lysine production was found to be 27.25 ± 1.15 g/l, which was significantly high than that obtained using CCD-RSM optimization method. The ANN coupled with GA was found to be a powerful tool for optimizing production parameters with high level of accuracy. This technique may be used for other fermentation products to optimize the important process parameters before scaling up the process to industrial level

Designing a bottom-up professional development programme

Ashok Pandey describes a recent professional development activity undertaken at his school

Shipping route optimization in ice

Technological advances and changing climatic conditions provide commercial opportunities and some unique challenges for the Arctic region this century. Emerging trans-Arctic shipping routes in the Northwest Passage are a direct consequence of progressively receding sea ice in the Canadian Arctic archipelagic waters. This study conceptualized and developed a Computer-aided Arctic Route Optimization Model (CAROM) in the framework of a Geographical Information System (GIS) for ship voyage planning and tactical ice navigation. The model optimizes shipping routes in ice based on the charted depth of water, appropriate structural strengthening (Ice Class notation), and predicted and observed sea-ice conditions, with the latest available navigational and ice data in digital format. An incorporated ship transit-model provides speed-in-ice input to the route model essential to estimating the transit time critical for vessel scheduling and fuel cost estimation. The CAROM is operational, tactical in nature, and intended to act as a decision-making tool for the ice navigator. The presence of diminishing sea ice is an existential threat to surface navigation in the ecologically sensitive Arctic region, and ship-sourced oil pollution is a threat to Arctic marine ecology. Access to reliable satellite communication in the Arctic, the adoption of the Polar Code and the proposed e- Navigation framework of the IMO has opened new doors to implement and operationalize tactical navigation tools that may help in decision-making and risk mitigation in ice navigation. A seamless integration of the route optimization tool in the e-Navigation architecture is the desired objective that evolving technology may be able to achieve in future for the Mariners onboard. This research underscores the current limitations on the spatial resolution of ice data, electronic navigation chart coverage, and hydrographic surveys in the Canadian Arctic, to mention but a few. The transit time in ice predicted by the CAROM provides a comparative cost-benefit evaluation between a trans-Arctic route and the Panama Canal route for container ships of two different sizes trading between Rotterdam and Tokyo. The last few years have witnessed the arrival of mega container ships (Neo-Panamax type) primarily driven by economy of scale considerations, global trade dynamics, and expansion of the Panama Canal locks to accommodate such ships. The Cost Benefit Analysis reveals some interesting aspects of the container shipping business via the Northwest Passage and the difference a large container vessel of the Neo- Panamax type may result in assessing the overall cost comparison

Proizvodnja α-amilaze na podlozi od poljoprivrednih otpadaka s pomoću bakterije Bacillus amyloliquefaciens

The productivity of enzyme fermentations depends critically on maintaining a high oxygen transfer rate to satisfy the optimal oxygen demand of the microorganism for product formation. Among the several factors that affect oxygen transfer rates in a fermentor are the air flow rate and agitation. The production of α-amylase by Bacillus amyloliquefaciens was performed in 600-mL and 5-litre fermentor with a working volume of 300 mL and 3 L, respectively. The experiments indicated a requirement of high rates of aeration to enhance the enzyme yield. The biomass yield and productivity of the enzyme were found to have a linear relationship with the air flow rate, and the highest productivity was observed at 1.0 vvm. A maximum productivity of 41.4 U/(mL·h) was obtained after 14 h of fermentation in 600-mL fermentor system and a comparable productivity of 40 U/(mL·h) was obtained after 12 h in the 5-litre fermentor.Učinkovitost fermentacijske proizvodnje enzima ponajprije ovisi o optimalnoj opskrbi mikroorganizma kisikom, tj. dobrom prijenosu kisika. Protok zraka i miješanje su neki od čimbenika koji utječu na opskrbu reaktora kisikom. S pomoću Bacillus amyloliquefaciens proizvedena je α-amilaza u reaktoru zapremnine 600 mL, radnog volumena od 300 mL, i u reaktoru od 5 L, s radnim volumenom od 3 L. Utvrđeno je da je često prozračivanje reaktora povećalo prinos enzima. Prinos biomase i produktivnost enzima bili su u linearnom odnosu s protokom zraka, a najveća je produktivnost bila pri 1 vvm. Maksimalna je produktivnost od 41,4 U/(mL·h) postignuta nakon 14 h u fermentoru od 600 mL, dok je u onom od 5 L najveća produktivnost bila 40 U/(mL·h) nakon 12 sati fermentacije

Purification and Characterization of Tannin Acyl Hydrolase from Aspergillus niger ATCC 16620

Tannin acyl hydrolase produced extracellularly by the fungal strain Aspergillus niger ATTC 16620 in solid state fermentation was purified from the cell free culture broth by ammonium sulphate fractionation followed by DEAE–Sephadex A-50 chromatography. SDS-PAGE analysis indicated that the enzyme protein molecular mass was 168 kDa. Enzyme activity was stable up to the temperature of 40 °C and the enzyme activity was optimal at pH=6. Tannase activity was maximal at 0.01 M concentration of the substrate. The addition of metal ions like Zn2+, Mn2+, Cu2+, Ca2+, Mg2+and Fe2+ inhibited the enzyme activity. Only K+ ions enhanced tannase activity, and an activity of 4.31 U/mL was reported here. Enzyme activity was maximal after 15–20 min of incubation time, with an activity of 3.9 U/mL. Km was found to be 1.03 mM and Vmax=4.25 mmol/min. Since the enzyme is active over a wide range of pH and temperature it could find potential use in the food-processing industry