Minimum altitude variation orbits. Analysis of characteristics and stability

The article discusses the regularities of satellite motion in almost circular orbits under the influence of the second zonal harmonic of the geopotential. The aim of the research is to determine the parameters of orbits with a minimum change in radius and to study the properties of these orbits. It is shown that the problem of determining the parameters of orbits with a minimum change in radius is of theoretical and practical interest. These orbits are the closest to Keplerian circular orbits. The practical interest in such orbits is determined by the possibility of using them for scientific research and Earth observation systems. Based on the analysis of the literature, it was concluded that the solution of the problem under consideration is not complete by now: the algorithm for determining the parameters of the orbits are not well founded and unnecessarily complicated; there is no analytical analysis of the stability of the orbits of the minimum change in radius. The efficiency of application of the previously developed theory of describing the motion of satellites in almost circular orbits for determining the parameters of orbits with a minimum change in radius is shown. For this purpose, the solutions of the first approximation of the motion of satellites in almost circular orbits under the influence of the second zonal harmonic of the geopotential have been improved. These solutions make it easy to determine the parameters of the orbits of the minimum change in radius. The averaged equations of the second approximation of the influence of the second zonal harmonic on the satellite motion are constructed and, on their basis, the stability of the orbits with a minimum change in radius is proved. It is shown that the second approximation in small parameters completely describes the main regularities of the long-period satellite motion under the influence of the second zonal harmonic of the geopotential. With the help of numerical studies, the instability of orbits with a minimum change in radius is shown with allowance for the effect of higher order harmonics of the geopotential. Analysis of the area of possible application of orbits with a minimum change in radius showed that such orbits can be of practical importance for very low and ultra low orbits, where the control action on the satellite movement is carried out at least once every two days.

Investigation of multiple-stresses on mechanical and thermal properties of 9000 h Aged RTV-SiR composites for high-voltage insulation

Due to many advantages, polymer composite insulators have been extensively used for high-voltage (HV) transmission lines and substation insulations. The in-service operation, various environmental and electrical stresses degrade their mechanical and thermal characteristics. In this study, nine thousand-hour (9000 h) multi-stress (HV, heat, acid rain, salt fog, ultraviolet (UV) radiation, and humidity) accelerated lab-weathering evaluation of alumina-trihydrate (ATH) and silicon dioxide (SiO2) filled silicone rubber (SiR) composites were utilized. Moreover, to quantify the influence of multiple stresses over 9000 h lab-aging, the tensile strength, elongation at break, hardness, and thermal properties were evaluated and compared with the characterization results of neat (un-aged) composites. Winter and summer-aging cycles were designed in accordance with the actual service environment of Islamabad (Pakistan). Mechanical results of SiR blends showed a decrease in the tensile strength and the elongation at break (EAB), whereas the hardness increased over 9000 h lab-aging. The maximum deviation of ∼57.1% in tensile strength was found for hybrid samples (micro-ATH+ nano-Silica blend: SMNC), whereas the minimum change of ∼25.73% was exhibited by micro-silica-filled SiR specimen SMC3. Compared to neat blends, the maximum variation in EAB was ∼61% for a neat sample (SiR), whereas minimum change was noticed for SMC2 (of ∼31%) over 9000 h lab-aging. Additionally, after 9000 h lab-aging, the maximum (of ∼79.6%) and minimum (of ∼24.4%) variation in hardness was found for hybrid and SiR samples, respectively. Moreover, thermogravimetric (TGA) analysis showed that relative to neat samples, the thermal stability of aged specimens was decreased over weathering. Among aged specimens, only ATH filled samples (SMC1, SMC2) exhibited superior performance for a given temperature range (from 0°C to 900°C) by leaving a higher residual weight of ∼68.6% for SMC2. Hence to simulate and quantify the influence of environmental stresses over insulant performance, accelerated lab weathering can be adopted as an efficient tool.

Effects of neem leaf extract and hot water treatments on shelf life and quality of banana

A huge loss of banana occurs due to its shorter shelf life and inappropriate postharvest handling. There is a scarce of effective postharvest practices to combat this situation in Bangladesh. In this context, the current experiment was conducted to assess the effects of hot water (45°C for 2 or 5 minutes) and neem leaf extract (20% or 40%) on quality and shelf life of banana (cv. Sabri). The experiment was carried out in completely randomized design with three replications. Data on physico-chemical properties of banana were collected during storage in ambient conditions for two weeks. After two weeks of storage, the banana treated with 40% neem leaf extract showed longest shelf life (8.33 days), minimum change in color (score 4.88), minimum disease incidence (33.33%) and severity (score 2.23), lower reduction of titratable acidity (0.12%) and lower level of total soluble solid (6.90%). While the banana were treated with hot water at 45°C for 2 min, the treated banana also showed lower color change (score 4.53), longer shelf life (8.33 days), minimum loss of firmness (score 4.67), minimum change in vitamin C content (2.17mg/100g) and lower reduction in titratable acidity (0.11%). Among the combined treatments, the banana treated with the combination of hot water (at 45°C for 5 minutes)and 40% neem leaf extract also exhibited considerably longer shelf life (8.17 days), lower change in color (score 5.00), lower disease incidence (46.67%) and lower reduction in titratable acidity (0.15%). From the study it could be concluded that the fruit treated with 40% neem leaf extract retained the majority of the quality parameters for considerably longer period and thereby it could be recommended for practical use to ensure better and longer storage of banana (cv. Sabri) J.Bangladesh Agril. Univ. 16(3): 351–356, December 2018

New Decisions in Manufacturing Techniques of the Cemented Parts of Cars

The unused reserves of metal and manufacturing techniques of forgings and hardening of products promoting minimization and stabilization of deformation and a buckling of gear details are revealed. Need of rationing of size of a hardenability of steel, a regulation of speed of cooling of forgings after hot stamping and application of isothermal annealing as preliminary heat treatment is established. The rational scheme of laying and technology of low-temperature cementation of pinion gears providing the minimum change of the geometrical sizes of details in chemical and thermal processes is offered.

Recycling of Greywater (GW) through Natural Adsorbents

Reuse of water has been a popular choice toward balancing water scarcity and managing water availability in defined areas. GW which can be defined as the wastewater that comprises water from baths, showers etc, when managed and treated properly could be valuable resource for sectors like agricultural and horticultural. GW is one of the best option if treated and if not, it will mix with the sewage stream. It is possible to intercept this GW at the household level using minimum change in design, and with the primary and secondary treatment it can be recycled for garden washing, flushing and many purposes. In the present work, GW from student accommodation were collected, characterized and treated through series of natural adsorbent. Various parameters such as TDS, pH, Turbidity, BOD,COD, amount of nitrate and phosphorus were measured and it was found that most of the parameters were considerably in range after treatment. A simple method has been proposed that may be applied at individual household level.