Dynamics of the Exponential Population Growth System with Mixed Fractional Brownian Motion

This paper examines the dynamics of the exponential population growth system with mixed fractional Brownian motion. First, we establish some useful lemmas that provide powerful tools for studying the stochastic differential equations with mixed fractional Brownian motion. We offer some explicit expressions and numerical characteristics such as mathematical expectation and variance of the solutions of the exponential population growth system with mixed fractional Brownian motion. Second, we propose two sufficient and necessary conditions for the almost sure exponential stability and the k th moment exponential stability of the solution of the constant coefficient exponential population growth system with mixed fractional Brownian motion. Furthermore, we conduct some large deviation analysis of this mixed fractional population growth system. To the best of the authors’ knowledge, this is the first paper to investigate how the Hurst index affects the exponential stability and large deviations in the biological population system. It is interesting that the phenomenon of large deviations always occurs for addressed system when 1 / 2 < H < 1 . Moreover, several numerical simulations are reported to show the effectiveness of the proposed approach.

Accumulation and Combined Effect of Salinity and Heavy Metals on Growth, Yield and Uptake of Green Pea Grown in Piped Hydroponics

This research is to study the accumulation and combined effect of three salinity levels (750, 1500 and 3750 ppm) and of heavy metals (3.26, 3.2, 2 ppm, 2, and 0.2 of Zn, Cu, Fe, Mn, and Mo, respectively) on growth, yield, and uptake of green pea plants grown in piped hydroponic. Due to freshwater shortages, the use of hydroponic growth system was encouraged and used. The experiment consists of planting green peas from seeds into a 6” PVC piped system. After 2.5 months of growing, the experiment was stopped and plants parts were separated and divided into pods, leaves, stems, and roots, Then, physical, and chemical measurements conducted on them. Results indicated that (1) Salt concentration above 1500 mg/l was detrimental on the growth of green pea, (2) the best growth, yield, and biomass weight were observed at salinity of 750 mg/l, (3) heavy metals had positive effect on stems and roots of plants, but declined effect plant growth in general, (4) lines with nutrient deficiency were deficient in growth too, (5) sodium increased in plant’s organs in response to increased salinity in the feed solution, (6) the largest concentration of copper and zinc were found at the roots of the highest salinity level lines (36.05 and 211.58 mg/kg dry plant, respectively), (7) the hydroponic system proved to be efficient and economical and therefore, it is recommended for use for Palestinian farmers, and (8) results obtained in this study agree with previously published research with extent differences.

The Effect of the Crucible on the Temperature Distribution for the Growth of a Large Size AlN Single Crystal

The appropriate distribution of temperature in the growth system is critical for obtaining a large size high quality aluminum nitride (AlN) single crystal by the physical vapor transport (PVT) method. As the crystal size increases, the influence of the crucible on the temperature distribution inside the growth chamber becomes greater. In order to optimize the field of temperature and study the specific effects of various parts of the crucible on the large size AlN single crystal growth system, this study carried out a series of numerical simulations of the temperature field of two crucibles of different materials and put forward the concept of a composite crucible, which combines different materials in the crucible parts. Four composite crucible models were established with different proportions and positions of tantalum carbide (TaC) parts and graphite parts in the crucible. Calculations reveal that different parts of the crucible have different effects on the internal temperature distribution. The axial temperature gradient at the crystal was mainly governed by the crucible wall, whereas the temperature gradient was determined by the integrated effect of the crucible lid and the crucible wall in the radial direction. One type of composite crucible was chosen to minimize the thermal stress in grown AlN crystal, which is applicable to the growth of large sized AlN crystals in the future; it can also be used to grow AlN single crystals at present as well.

Several Yeast Species Induce Iron Deficiency Responses in Cucumber Plants (Cucumis sativus L.)

Iron (Fe) deficiency is a first-order agronomic problem that causes a significant decrease in crop yield and quality. Paradoxically, Fe is very abundant in most soils, mainly in its oxidized form, but is poorly soluble and with low availability for plants. In order to alleviate this situation, plants develop different morphological and physiological Fe-deficiency responses, mainly in their roots, to facilitate Fe mobilization and acquisition. Even so, Fe fertilizers, mainly Fe chelates, are widely used in modern agriculture, causing environmental problems and increasing the costs of production, due to the high prices of these products. One of the most sustainable and promising alternatives to the use of agrochemicals is the better management of the rhizosphere and the beneficial microbial communities presented there. The main objective of this research has been to evaluate the ability of several yeast species, such as Debaryomyces hansenii, Saccharomyces cerevisiae and Hansenula polymorpha, to induce Fe-deficiency responses in cucumber plants. To date, there are no studies on the roles played by yeasts on the Fe nutrition of plants. Experiments were carried out with cucumber plants grown in a hydroponic growth system. The effects of the three yeast species on some of the most important Fe-deficiency responses developed by dicot (Strategy I) plants, such as enhanced ferric reductase activity and Fe2+ transport, acidification of the rhizosphere, and proliferation of subapical root hairs, were evaluated. The results obtained show the inductive character of the three yeast species, mainly of Debaryomyces hansenii and Hansenula polymorpha, on the Fe-deficiency responses evaluated in this study. This opens a promising line of study on the use of these microorganisms as Fe biofertilizers in a more sustainable and environmentally friendly agriculture.

Designing a Teacher's Horizontal Career based on Additional Types of Pedagogical Activities and Professional Achievements: Russian and International Experiences

The relevance of developing approaches to the formation of organizational and regulatory conditions for teachers professional careers is determined by the goals of implementing the Russian Federal project Teacher of the Future and the necessity to provide the quality of Russian education by improving teachers professional competence. The aim of the present study is to develop a model of a teachers career based on the institutionalization of the professional roles of mentor and methodologist as additional types of pedagogical acti- vities and professional achievements. The official concept of the National Teacher Growth System (NTGS) was based in different periods on the research of different scholar teams that proposed the formation of a vertical teachers career by introducing from two to five new positions, and has changed several times in recent years, but has not been implemented. Based on the analysis and theoretical comprehension of Russian and international practices of stimulating the professional growth of teachers, a project of a diversified professional career trajectory in relation to the teachers position (horizontal career) is proposed; framework requirements for the amount and quality of additional types of pedagogical activities are identified for their differentiated assessment at each stage of a teachers career. The proposed model can be used as an intermediate one and developed at the next stages of the implementation of the federal project Teacher of the Future towards the introduction of new positions, new qualification categories, new opportunities to form teachers professional growth trajectories for career-building and professional development.

Assessment on the oil accumulation by knockdown of triacylglycerol lipase in the oleaginous diatom Fistulifera solaris

Microalgae are promising producers of biofuel due to higher accumulation of triacylglycerol (TAG). However, further improvement of the lipid metabolism is critical for feasible application of microalgae in industrial production of biofuel. Suppression of lipid degradation pathways is a promising way to remarkably increase the lipid production in model diatoms. In this study, we established an antisense-based knockdown (KD) technique in the marine oleaginous diatom, Fistulifera solaris. This species has a capability to accumulate high content of lipids. Tgl1 KD showed positive impact on cell growth and lipid accumulation in conventional culture in f/2 medium, resulting in higher oil contents compared to wild type strain. However, these impacts of Tgl1 KD were slight when the cells were subjected to the two-stage growth system. The Tgl1 KD resulted in slight change of fatty acid composition; increasing in C14:0, C16:0 and C16:1, and decreasing in C20:5. This study indicates that, although Tgl1 played a certain role in lipid degradation in F. solaris, suppression of only a single type of TAG lipase was not significantly effective to improve the lipid production. Comprehensive understanding of the lipid catabolism in this microalga is essential to further improve the lipid production.

Reduction of impurity sources in Si crystal growth system with electron gun beam heating

A new series of experiments was conducted to determine the source of impurities in the process of silicon crystal growth with electron beam heating. A gas-dynamic window was placed between the electron gun and growth chamber. Also positively-charged traps were placed along the crucible to reduce the number of electrons hitting the chamber and the crucible. Five experiments were conducted: two with the window, two with charge traps, and one with both the window and charge traps. The analysis of obtained samples showed that the gas-dynamic window decreases the content of Al, Cu, Fe, Cr and O2, and the trap, used in the experiments, decreases the content of Fe, Cr and Cu in residues of the melt. The content of all impurities, except Al, is close to the goal level. Al impurities come only from the gun, but the gas-dynamic window cannot eliminate them completely. It seems that Al impurities come either as neutral atoms carried by the gas or as positively charged ions. To reduce these impurities, a separation of the Al flow from the beam by the magnetic field is proposed.