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

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

Monolayer, Bilayer and Heterostructures of Green Phosphorene for Water Splitting and Photovoltaics

We report the results of density functional theory (DFT) based calculations on monolayer and bilayer green phosphorene and their heterostructures with MoSe2. Both monolayer and bilayer green phosphorene are direct band gap semiconductors and possess anisotropic carrier mobility as high as 10^{4} cm^{2}V^{-1}s^{-1}. In bilayers, pressure of about 9 GPa induces the semiconductor-metal transition. Moreover, the band gap depends strongly on the thickness of the films and the external electric field. By employing strain-engineering under suitable solution conditions, monolayer and AC-stacked bilayer green phosphorene offer the band edge alignments which can be used for water splitting. The upper limit of the power conversion efficiencies for monolayer, AB- and AC-stacked bilayer green phosphorene heterostructures with MoSe_{2} is calculated to be 18-21 %. Our results show the possibility of green phosphorene to be used as photocatalytic and photovoltaic material in the energy-related applications.Comment: 23 pages, 7 figures, 2 table

Adaptation and human migration, and evidence of agriculture coincident with changes in the Indian summer monsoon during the Holocene

Human societies have evolved through a complex system of climate and ecological interactions. Known records suggest intimate relationship of adaptations, mitigations and migrations to climate extremes leaving their impacts on human societies. The northwestern part of India provides such an example, where human civilizations flourished in the early Holocene along the major fluvial systems when the Indian summer (southwest) monsoon was much stronger and rainfall was higher over the Indian land mass. Summers were thus wetter, conducive to agriculture and ecodiversity. Changes in the early civilizations in the Indian subcontinent had a close relation to changes in the monsoon climate over the past 10,000 years. The summer monsoon has weakened over the last 7000 years since its peak intensification in the early Holocene (10,000-7000 cal yrs BP). Discrete intervals of dry phases in the summer monsoon are visible in the proxy record of the monsoon winds from the marine sediments of the Arabian Sea, which had significant impact on human settlements in South Asia. The strongest aridity in the Indian subcontinent and extended periods of droughts at ca 5000- 4000 cal yrs BP seems to have triggered eastward human migrations towards the Ganga plain. Other times of monsoon weakening during the Holocene are coincident with the initial development of ponds, reservoirs and other rainwater harvesting structures that may have served as an adaptation to climate change

Two Dimensional Allotropes of Arsenene with Wide Range of High and Anisotropic Carrier Mobility

Considering the rapid development of experimental techniques for fabricating 2D materials in recent years, various monolayers are expected to be experimentally realized in the near future. Motivated by the recent research activities focused on the honeycomb arsenene monolayers, stability and carrier mobility of non-honeycomb and porous allotropic arsenene are determined using first principles calculations. In addition to five honeycomb structures of arsenene, a total of eight other structures are considered in this study. An extensive analysis comprising energetics, phonon spectra and mechanical properties confirms that these structures are energetically and dynamically stable. All these structures are semiconductors with a broad range of band gap varying from ~1 eV to ~2.5 eV. Significantly, these monolayer allotropes possess anisotropic carrier mobilities as high as several hundred cm^{2}V^{-1}s^{-1} which is comparable with the well-known 2D materials such as black phosphorene and monolayer MoS_{2}. Combining such broad band gaps and superior carrier mobilities, these monolayer allotropes can be promising candidates for the superior performance of the next generation nanoscale devices. We further explore these monolayer allotropes for photocatalytic water splitting and find that arsenene monolayers have potential for usage as visible light driven photocatalytic water splitting.Comment: 31 pages, 8 figures, 3 table

Determination of precise crystallographic directions for mask alignment in wet bulk micromachining for MEMS

In wet bulk micromachining, the etching characteristics are orientation dependent. As a result, prolonged etching of mask openings of any geometric shape on both Si{100} and Si{110} wafers results in a structure defined by the slowest etching planes. In order to fabricate microstructures with high dimensional accuracy, it is vital to align the mask edges along the crystal directions comprising of these slowest etching planes. Thus, precise alignment of mask edges is important in micro/nano fabrication. As a result, the determination of accurate crystal directions is of utmost importance and is in fact the first step to ensure dimensionally accurate microstructures for improved performance. In this review article, we have presented a comprehensive analysis of different techniques to precisely determine the crystallographic directions. We have covered various techniques proposed in the span of more than two decades to determine the crystallographic directions on both Si{100} and Si{110} wafers. Apart from a detailed discussion of each technique along with their design and implementation, we have provided a critical analysis of the associated constraints, benefits and shortcomings. We have also summed up the critical aspects of each technique and presented in a tabular format for easy reference for readers. This review article comprises of an exhaustive discussion and is a handy reference for researchers who are new in the field of wet anisotropic etching or who want to get abreast with the techniques of determination of crystal directions

Estimation of plant nitrogen content using digital image processing

A manually operated four wheel test trolley was designed and developed for acquiring outdoor color images of plant under controlled illumination to predict crop nitrogen content in field.  This set up consists of a camera to capture the plant image, four lights to control illumination and a laptop for processing the signal.  The developed unit was evaluated rigorously for paddy crop for four observations at fifteen days interval after transplantation.  The results were compared with the chlorophyll content of the crop measured by SPAD meter and the chemical analysis of plant leaf.  The processing of the color plant image was done in MATLAB 7.0 program.  Various features such as R, G, B, normalized ‘r’ and normalized ‘g’ were analyzed for both the processes.  Regression models were developed and evaluated between various image feature and the plant nitrogen content and observed that, the minimum accuracy was found to be 65% with an average accuracy of 75% (Standard Deviation +1.9), actual and predicted values of nitrogen percent were linearly correlated with R2 value (0.948), this showed that the plant nitrogen content can be successfully estimated by its color image feature.   Keywords: precision agriculture, digital image processing, site specific nitrogen applicatio

Study of ambient air pollutants over Rishikesh at foothills of north-western Indian Himalaya

49-60Air quality parameters measured over Rishikesh city of Uttarakhand, where a large number of visitors and pilgrimage stay and pass by throughout the year are analyzed and studied. Such intensive human activities lead to the impacts and its manifestation on regional scale environment. Due to consistent infrastructure development and the increased vehicular emission due to transport, a large amount of particulate matters is added to the ambient environment and affects the air quality adversely. Here an attempt is made to understand the growth in level of ambient air pollutants through available measurement. In this study particulate matter (PM10), suspended particulate matters (SPMs) and the concentration of gaseous pollutants (SO2 and NO2) from 2011 to 2014 are measured and analyzed. It is observed that concentrations of the pollutants increase during pre-monsoon season as compared to the winter and monsoon seasons. In addition, PM10 and SPM concentrations are found about two times higher than the prescribed national standard. SO2 and NO2 levels are found within the limits as proposed by the Central Pollution Control Board (CPCB) New Delhi, India. A detailed statistical analysis is carried out on the basis of monthly mean values of the observed pollutants. The PM10 exhibits a significant positive correlation with SO2 and NO2 concentrations. In addition, back trajectories show partly long-term transport from North Africa, Saudi Arabia and central Asian region in contributing over the region with local emission that is considered to be the main and direct cause of increasing trend of the pollutants