Influence Of Temperature Conditions Research Articles

Ефективність амфіфільних сполук в умовах постгіпертонічного шоку еритроцитів кролика залежно від температурних умов

The influence of temperature conditions on the level of damage of rabbit erythrocytes under posthypertonic shock and the level of their protection by amphiphilic compounds was investigated. We observed the maximum cell damage at 0°C. When the temperature increased to 20°C, the level of hemolysis decreased by 1.8 times. Further increase in temperature up to 37°C did not lead to a decrease in damage. The investigated amphiphilic compounds at 0°C and 10°C effectively protected rabbit erythrocytes from posthypertonic shock. Reduction of hemolytic damage was 2–3 times. At 20°C amphiphilic compounds did not affect the level of cell damage, and at 30°C and 37°C they increased it. The existence of temperature dependence of posthypertonic damage showed the involvement of the phospholipid component of the erythrocyte membrane in the process. Lower temperature is characterized by greater orderliness of lipids, its increase is accompanied by disorder and increased fluidity, and hence elasticity of the membrane. As a result, erythrocyte damage in posthypertonic shock is less at the temperature of 20–37°C. The addition of amphiphilic compounds at 0 and 10°C acts similarly to increasing the temperature, disorganizes the bilayer, increases the elasticity of the membrane and reduces damage during the transfer from hypertonic to isotonic solution. Above 20°C, the introduction of amphiphilic compounds leads not only to disorder, but also to the formation of mixed micelles consisting of phospholipids and amphiphilic molecules. This disrupts the bilayer, gives it instability and leads to increased damage of erythrocytes.

НЕСПРИЯТЛИВІ АГРОМЕТЕОРОЛОГІЧНІ ЯВИЩА НА ТЕРИТОРІЇ УКРАЇНИ ПРОТЯГОМ 2006-2020 рр.

The article is devoted to the study of weather conditions of adverse agrometeorological phenomena (droughts) on the territory of Ukraine during the fifteen-year period of 2006-2020. The purpose of the work is to establish the peculiarities of the temperature and humidity regime in the months of the warm period of the year during certain years of the last fifteen-year period, taking into account the droughts that were observed in this period. For each year and month of the studied period, an analysis of the relevant weather conditions accompanying droughts in the territory of Ukraine was carried out. The influence of temperature conditions and features of humidification on the territorial distribution and duration of droughts has been proven. In general, during the studied period, it was established that drought phenomena were not observed only in 2012, 2016, 2018 and 2019. Droughts could start in the air or in the soil and eventually develop into air-soil droughts. In 10 years of the studied period, severe air and soil droughts were observed in large areas. Mostly droughts were observed from the end of June to the end of July, but in some years droughts could start from April and be observed with certain breaks until the beginning (mid) of autumn. In 2011, there was a case of air drought at the end of February and in March. In addition, in some years, air-soil droughts could be observed in autumn not only from its beginning, but also until its end (November 2011, 2015). For the most part, territorial droughts during 2006-2020 were observed in the east, southeast, and south, but they could also be observed in most of the country, including part of the northern territories. In some years, droughts were accompanied by droughts and dust storms. It was established that in the months of the warm period of the year, the average monthly air temperature was mostly above the norm by 1-2º C, while in some months and years the norm could be significantly exceeded, especially in the summer months from 4 to 7º. In autumn, for the most part, the average monthly air temperature was within normal limits, but in some years it was 1-3º degrees above normal. Precipitation during the studied months was extremely unevenly distributed across the territory of Ukraine. In the spring, precipitation was mostly close to normal. In the summer months, precipitation was often insufficient, sometimes less than half of the norm. In autumn, the amount of precipitation increased mostly to the norm and above, but in some years a deficit of precipitation was observed in most of the territory of Ukraine. At the end of autumn, mostly precipitation fell close to norm, and in some places even more than normal.

P.127: The Influence of Temperature Conditions and Reconstruction of the Extracellular Matrix Environment on the Viability of Pancreatic Islets

Introduction: Pancreatic islet transplantation is one of the methods of treating patients with T1D. However, for the procedure to be successful, the high quality of the implanted islets is of key importance for a successful islet transplant. Following islet isolation, it has been shown that mainly β-cells undergo apoptosis due to vascular loss and hypoxia. The cellular stresses to which islets are subjected during isolation (for example disturbance of the cell-matrix relationship). Appropriate storage conditions for insulated islands are of key importance for their functionality. The most common method of islet storage is the introduction into a suspension culture. However, because these are micro organs, the storage of pancreatic islets is a more accurate term. Therefore, this study aimed to demonstrate whether for pancreatic islets it is better to cultivate them in standard conditions (37oC; 5% CO2), or maybe stored them at 4oC. Material: The research material was porcine pancreatic islets. Islets were isolated from the native organ using collagenase and a Ricordi chamber. After isolation, the material was divided into 4 research groups: 1. control (islands suspended in CMRL 1066 medium) - traditional breeding conditions (temperature 37oC; 5% CO2); 2. CMRL 1066 suspended islets stored at 4oC; 3. Islets in CMRL 1066 medium with the addition of dECM (decellularized extracellular matrix) - in traditional culture conditions; 4. Islets in CMRL 1066 supplemented with dECM stored at 4oC. Each variant was tested in 3 replicates and each trial was 3000iEq. Additionally, each tested variant was tested on pancreatic islets that were cleaned or not immediately after isolation. Results: The research showed that the storage temperature, reduced to 4oC, and the addition of ECM significantly influenced the functionality of the islets. This variant tested (uncleaned islands) showed functionality even 5 days after isolation. On the other hand, islets incubated at 37°C without the addition of dECM showed no functionality after 2 days of the experiment. The remaining variants showed a gradual loss of functionality. However, the 4oC variant was better in each case. Conclusion: Pancreatic islets, as micro organs with their vascularization, need appropriate storage conditions after isolation to ensure their proper functioning. Based on these studies, it was shown that the islands should be stored and not cultivated as single-cell lines. In addition, the addition of dECM allows for the recreation of the matrix-cell environment, which is appropriate storage conditions - corresponding to the native environment. This study was financially supported by The National Centre for Research and Development STRATEGMED3/305813/2/NCBR/2017.

Influence of temperature conditions on seasonal development of Cydalima Perspectalis Walker, 1859 (lepidoptera: crambidae) in the Crimea

In 2018-2020 phenological observations of Cydalima perspectalis Walker were carried out in two agroclimatic regions of the Crimea. The pest, both on the Southern Coast of the Crimea and in the central foothill zone, develops in three generations. The sum of effective temperatures required for the development of generations varies over the years in a wide range, which is due to the asynchronous development of the caterpillars of C. perspectalis . The beginning of summer of the adults of the overwintered generation over the years of research in both regions differed insignificantly and was noted with the accumulation of the sums of effective air temperatures above 10°С on the Southern Coast of the Crimea from 210 to 297 degree days, and in Simferopol - from 222 to 299 degree days. It was found that in the summer months in the central foothill zone of the Crimea, in terms of temperature indicators, more favorable conditions are created for the development of boxwood firewood than on the Southern Coast of the Crimea. The combination of hydrothermal conditions, in which air temperatures exceed 33-36°C, and the relative humidity drops below 19-49%, cause the death of up to 20-28% of Cydalima perspectalis egg embryos at an early stage of embryogenesis. From the embryos of eggs of later stages of embryogenesis, under these conditions, the hatching of caterpillars occurred by 100%.

Influence of Temperature Conditions during Growth on Bioactive Compounds and Antioxidant Potential of Wheat and Barley Grasses.

Wheat and barley grasses are freshly sprouted leaves of wheat and barley seeds, and are rich sources of phytochemicals. This study was conducted to investigate the effects of day and night temperatures on the growth, bioactive compounds, and antioxidant potential of wheat and barley grasses. Briefly, each grass was cropped in an organic growing medium at 10/5 °C, 20/15 °C, and 30/25 °C (day/night temperature) in a growth chamber by maintaining specific light (12/12 h light/dark; light intensity 150 µmol photons m−2 s−1) and humidity (60%) conditions for 8 days. The highest growth parameters (height, weight, and yield) were observed at the 20/15 °C growth conditions in both types of grass. Conversely, the lowest growth parameters were observed at 10/5 °C. However, the low growth temperature of 10/5 °C resulted in increased levels of bioactive compounds (total phenol, total flavonoid, and total vitamin C), antioxidant activities (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid and 2,2-Diphenyl-1-picrylhydrazyl radical-scavenging activity)), and antioxidant enzymes (guaiacol peroxidase activity, catalase activity, and glutathione reductase) in both types of grass. Therefore, proper temperature growth conditions of wheat and barley grasses may be a convenient and efficient method to increase bioactive compounds and antioxidant potential in our diet to exploit the related health benefits.

INVESTIGATION OF THE RHEOLOGICAL CHARACTERISTICS AND LEVEL OF SYNTHESIS OF EXOPOLYSACCHARIDES (EPS) BY THE CONSORTIUM OF STREPTOCOCCUS SALIVARIUS SUBSP. THERMOPHILUS AND LACTOBACILLUS DELBRUECKII SUBSP. BULGARICUS AT DIFFERENT TEMPERATURE IN PROCESS OF MILK FERMENTATION

The article provides the results of studies on the influence of temperature conditions of milk fermentation in the manufacture of yogurt on the characteristics of milk clots and the level of EPS production. The characteristics of the samples of reconstituted skim milk fermented by consortia of lactic acid microorganisms for the manufacture of
 starter and viscous consistency yoghurt starter cultures under temperature conditions are determined: (43 ± 1)°С, (38 ± 1)°С, (35 ± 1)°С and ( 30 ± 1)°С. It was noted that with a decrease in the fermentation temperature from (43±1)°C to (30±1)°С, the organoleptic characteristics of the formed clot are evaluated differently. At the fermentation temperature of (30±1)°С, the lowest
 degree of syneresis was noted: 45% for the consortium, during the fermentation of milk raw materials forming clumps of inviscid consistency, 29% for the consortium, during the fermentation of
 milk raw materials forming clumps of viscous consistency. At the same time, it was found that at fermentation temperatures of (43±1)°С and (30±1)°С, the highest level of EPS synthesis for consortia was noted: (2107 ST-A+2674 TL-AV) – 874.6 and 667.9 μg / ml, (1141 ST-AV+2674 TLAV) – 683.9 and 541.3 μg / ml.

Influence of temperature conditions on the shrinkage of wax patterns for investment casting

The study of free linear shrinkage of unfilled (PS50-50, MBC 3-T, Romocast 105, Romocast 152) and filled (Romocast 252, Romocast 325) model compositions for investment casting depending on the ambient temperature was carried out. It has been shown that unfilled model compositions have the greatest free linear shrinkage, and filled ones have the smallest. Moreover, the processes associated with free linear shrinkage proceeded in the samples for a long time (up to 24 h). This is probably caused by the duration of the polymerization processes and the low thermal conductivity of the model compositions. A change in the ambient temperature in the range from –5 to +35 °C has a significant effect on the linear dimensions of the samples from the studied model compositions. The length of samples from unfilled model compositions varies from +0.3 to –0.4%, and from filled ones from +0.2 to –0.15%. When samples from unfilled compositions cooled to –5 °C and subsequently heated to +20 °C, their initial length decreases on average by 0.2 mm, and at heating to +35 °C and subsequent cooling to +20 °C, it increases on average by 0.2–0.3 mm. At similar changes in ambient temperature, the dimensional change of samples from filled model compositions is not more than 0.1 mm.

Influence of reactor temperature conditions on the recycle flow rate

Objectives. The problem of optimizing chemical flow sheets according to energy costs associated with recycling flows is at present quite relevant. The current article investigates the influence of temperature conditions on the recycle flow rate, securing the specified conversion of the recycled flow sheet “reactor – separation unit.”Methods. The study’s main method is the mathematical simulation of a recycled flow sheet based on material balance and chemical kinetics equations. This model assumes that the separation unit can form the recycle and outlet flows of any specified compositions.Results. The mathematical model recycle flows provides the full reagent conversion of recycled flow sheet depends on the reactor type and the temperature conditions in it. It was established that the dependence of the recycle flow rate on the reactor temperature for endothermic reactions has monotonously decreasing shape. The most interesting are exothermic reactions for which the dependence of the recycle flow rate on the reactor temperature curve has a minimum. It is proved that the “reactor – separation unit” system with the plug flow reactor has lower optimal recycle flow rate than the recycled system with the continuous stirred tank reactor. For the adiabatic reactor the dependence of total conversion recycle flow rate on the inlet reactor temperature was investigated. It has been proven that the optimal recycle flow rate is equal to the minimum recycle flow rate for total conversion in the “reactor – separation unit” system.Conclusions. It has been established that isothermal operation conditions are the best in terms of the recycle flow rate, securing the specified conversion for the system.

Influence of temperature conditions on wood polymer-sand composite

The subject of this research is new wood polymer-sand composite and the study of its frost resistance using computer experiment. Industrial waste in the form of sawdust, chips, lumpy waste and polyethylene terephthalate are used as the filler. A computer program has been developed for modelling the structure and physical properties of building blocks from wood polymer-sand composite. The program enables to set (in the windows of the interface form in the program code) geometric and physical parameters of building block and material components, as well as test conditions for cyclic heating and cooling to the maximum temperature during operation. It explores the effect of parameters on internal and surface destruction of building blocks. The program is applicable for a wide range of composite component concentrations, building blocks’ geometric parameters, variety of mechanical and thermal cycling tests. The influence of wood polymer-sand composite formulation on the structure has been studied during thermocyclic testing. The dependences of broken bonds on wood concentration, cartograms of bond breaking of wood polymer-sand composite with a wood concentration from 20 to 80% have been obtained. Recommendations for optimizing the formulation of wood polymer-sand composite blocks are given to minimize bond breaking during thermal cycling.

Термогравіметричні дослідження двокомпонентних епоксидних смол для виготовлення об’ємних етикеток

There was investigated the influence of temperature conditions on the stability of a polymer coating based on epoxy resins, which is used in the manufacture of volume labels by thermogravimetry.Objects of research were volumetric labels printed on a digital printing machine using transparent (glossy and matte) PVC films filled with different thicknesses of polymer coating. As a polymer coating, a soft and hard epoxy resin of 0.84 to 1.95 mm in thickness was used.The process of manufacturing volume labels included the preparation of an epoxy resin before applying a full-color printed image to the surface.Taking into account that for the production of volume labels we use multicomponent polymeric composite materials that are subject to heat treatment, for the study used thermogravimetric analysis, which involves studying the thermal stability of samples; with the registration of a similar signal of mass loss and thermal effects using a computer.It is proved that the sample of a volume label with soft epoxy resin demonstrates higher thermal stability. In the process of its heating during the studied temperature range there is less intensive mass lost compared with a label sample made of solid resin. The highs of exothermic effects of this sample shifted into higher temperatures range.Within the operating temperature range of 20–60° C samples of epoxy coating are heat resistant. In the process of heating the mass loss of samples does not exceed 0.5 % due to the allocation volatile compounds, which are present in them.The research allows to make the right choice of temperature conditions of polymer coatings formation based on of two-component epoxy resins in the manufacture of volume labels and conditions of their use.

Electrochemical Approach to Investigate the Electrolyte Wetting Process of Lithium-Ion Cells

Expanding life time as well as lowering production costs of a lithium-ion cell are two important subjects, which are addressed in the current research of lithium-ion batteries. One approach to reach these aims is an optimization of the electrolyte filling and formation process of the lithium-ion cells. This process steps have a major contribution to the production costs, since it requires high investments to provide a sufficient amount of formation equipment. Furthermore, since this processes can take up to 3 weeks, quite a lot of stock capacity is necessary [1]. After filling the cell with electrolyte, the formation process starts with different aging and charging steps with different durations, charging conditions (e.g. c-rate, voltage cut-off) and atmosphere conditions (e.g. pressure and temperature profiles). The aging steps during the formation process are applied to ensure a proper saturation of all the pores of the electrodes with electrolyte. This is of particular importance for graphite based anodes since a SEI film is built on the graphite particles during the charging steps, which greatly influences the cell’s specific values (e.g. lifetime and safety) [2]. To ensure a good and homogenous quality of the SEI film, there should be no significant amount of electrolyte-dry graphite particles, when the first charging step is applied to the cell. So it’s of relevant importance, to know when this state is reached. Commonly, the optimization of the formation process is an empirical process. For a systematical optimization of the formation process of lithium ion cells, amongst others, a detailed knowledge of the electrolyte wetting process is necessary. First of all, the wetting process is of course greatly influenced by the choice of the materials of the cell components (primarily electrodes and separator) and material parameters (e.g. porosity and torosity). The wettability of single components can be evaluated by tracking the wetting progress of individual components visually or with gravimetric techniques, but there is no generally established test [3]. Beside, since the interface between electrodes and separator has a strong influence on the electrolyte wetting behavior, findings about the wettability of the individual components are not easily transferable to the wetting behavior in a full cell geometry. Furthermore the cell geometry itself has a great impact to the electrolyte wetting behavior, since it can favor or limit the electrolyte supply to the edges of the cell and as a consequence the wetting speed within the cell. This is of particular importance for bigger cell designs (e.g. PHEV 1). Based on electrochemical measurements we propose a novel method, which is performed in situ, to investigate the electrolyte wetting process in lithium-ion full cells. The experiments were executed with a modified pouch-bag cell design enabling us to initiate electrical measurement simultaneous to the start of the filling process under controlled conditions in a climate chamber. The reliability of the method is demonstrated by investigating the electrolyte wetting behavior of cells with different commercially available separators, including polyolefin, ceramic and ceramic coated polyolefin separators. Measurements on the separator by visual methods were executed to validate our novel electrochemical method. To demonstrate the potential of the method, the influence of temperature conditions during the wetting process was investigated. By using the method the wetting speed and degree can be measured in situ on full cell level for the first time. In this presentation, the method’s principals will be presented and the results will be discussed. Furthermore the potential of this method will be illustrated, for example, how and which modification of the components can be realized and how they can help to optimize the electrolyte wetting behavior of lithium-ion cells.

Influence of temperature conditions on grain refinement of pure Cu solidified with low-voltage pulsed magnetic field

The influence of temperature conditions on the grain refinement of pure Cu solidified with low-voltage pulsed magnetic field (LVPMF) was investigated. With the pouring temperature (Tp) and mould temperature (Tm) increasing, the solidified microstructure of pure Cu was gradually changed from fine equiaxed grains to coarse columnar grains and then to the mixed structure of coarse equiaxed grains and columnar grains. Little change was observed from the microstructure of pure Cu solidified with and without LVPMF for the low Tp and Tm. But for the high Tp and Tm, applying LVPFM remarkably reduced the coarse columnar grains and obtained fine equiaxed grains. The grain refinement by LVPFM is considered to be caused by the electromagnetic flow. The smaller cooling rate resulted by higher Tp and Tm offers much acting time for LVPMF and thus better grain refinement can be achieved.

Influence of temperature conditions of forming nanosized SnO2-based materials on hydrogen sensor properties

Semiconductor sensors are widely used to detect toxic and flammable gases, and nanosized SnO2 is usually applied as material for gas-sensitive layers of the sensors. Sensor nanomaterial has to provide appropriate value of the electrical resistance of the sensor in air and high sensor response to analyzed gas. Sol–gel synthesis is the most promising to obtain SnO2 nanomaterial because it enables to rich high chemical homogeneity of the obtaining material, to control its particle size and structure at different stages of the material synthesis. These characteristics of the nanomaterials have to determine the sensor properties. To obtain SnO2 sensor nanomaterial, synthesis of xerogel by a sol–gel method via SnCl4·5H2O dissolved in the ethylene glycol was carried out. To provide optimal values of the sensor electrical resistance in air, decomposition of the xerogel was studied by DTA–DTG analysis. This study was carried out by heating the xerogel to 1000 °C in air with heating rates of 2.5, 5 and 10 °C min−1. It was found that decomposition of the xerogel was performed in several stages: water desorption, removing ethanediol-1,2, HCl and CO2. Using the selected heating mode with isothermal holding at 280, 350, 390 and 600 °C, optimized SnO2 nanomaterial was obtained. It was found that sensors based on this material had suitable values of their electrical resistances (150–400 kΩ) and possessed high responses to very small concentration of hydrogen.

Mechanical characterization of clay reinforced polypropylene nanocomposites at high temperature

This paper focuses on the influence of temperature conditions and the clay contents on enhancement of mechanical characterization of polypropylene (PP) nanocomposites. The nanocomposites were prepared using the melt mixing technique in a co-rotating intermeshing twin screw extruder followed by injection moulding. Nanocomposites properties such as impact strength and ultimate tensile strength, yield strength, failure strain, Young’s modulus and toughness are calculated. The addition of clay to PP matrix was showed remarkable enhancement in mechanical properties at the temperature of 25 oC and 120 °C. Nearly 36 % and 160 % increase in the Young’s modulus and about 45 % and 62 % increase in the impact strength were observed at both room temperature (RT) and high temperature (HT), respectively. But, the tensile strength was not affected much. The basal spacing of clay in the composites was measured by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to assess the surface morphology of the fractured surfaces and dispersion of the nanoclay.

The influence of temperature conditions on position control of fluidic muscle

Pneumatic artificial muscles (PAMs) are of special importance in the field of pneumatic drives and in robotics. Different designs have been developed, but the McKibben muscle is the most popular and is made commercially available by different companies, e.g. Fluidic Muscle manufactured by Festo Company. There are a lot of advantages of PAMs like the high strength, good power/weight ratio, good power/volume ratio, low price, little maintenance needed, great compliance, compactness, flexibility, inherent safety and usage under rough environments. The objective of this research note is to determine the error of positioning with a Fluidic Muscle at cold and at normal operating temperature of the system with sliding mode control. The results of the experiments showed that the positioning error of the Fluidic Muscle under the experimental conditions was 0.01 mm.

Influence of temperature conditions in outer space on the macrokinetic characteristics of ignition and combustion of the solid-fuel charge of the microthruster of a microelectromechanical system

On the basis of macrokinetic calculations, the influence of the initial temperature on the impulse responses of the processes of ignition and combustion of the solid-fuel charge of the microelectromechanical system (MEMS) microthruster burning the solid fuel glycidyl azide polymer (GAP)/RDX has been investigated. It has been established that fuel heating/cooling in a wide range of temperature values from 150 to 450 K characteristic of the conditions of a satellite in orbital flight markedly affects both the thrust and the total impulse of the MEMS microthruster. In so doing, an increase in the initial temperature leads to a marked decrease in the induction period and an increase in the critical flux of fuel ignition. The influence of the change in the initial temperature on the self-ignition temperature of GAP can be neglected. To obtain stable characteristics of the microthruster, it seems expedient to use a thermostating system.

The effect of indole-3-acetylaspartic acid on adventitious root formation on bean cuttings

The influence of indole-3-acetylaspartic acid (IAAsp) on rooting of stem cuttings from bean plants (Phaseolus vulgaris L.) of different ages, cultivated at different temperatures (17°, 21° and 25°C) was studied and compared to that of indole-3-acetic acid (IAA). At a concentration of 10−4 M, IAAsp only nonsignificantly stimulated adventitious root formation, approximately to the same level as IAA in all treatments. IAAsp at 5×10−4 M further enhanced rooting, by up 200% of control values, with little influence of temperature conditions and stock plant age. This concentration of IAA usually stimulated rooting more than the conjugate. The largest differences between the effects of IAAsp and IAA occured at the highest cultivation temperature of 25°C where stock plant age also influenced the response. The number of roots produced in comparison with the control, was enhanced from 350% on cuttings from the youngest plants to more than 600% on cuttings from the oldest. In contrast to the conjugate, 5×10−4 M IAA induced hypocotyl swelling and injury of the epidermis at the base of cuttings, in all treatments.

Influence of temperature conditions in formation of end moraines in Fennoscandia and Svalbard

In the Finnmark region of northern Norway, end from Younger Drays and earlier periods appear as irregular mounds and ridges in a broad zone with a distinct distal margin. These moraines are similar in shape to end moraines formed in Svalbard today by melting of ice‐cored moraines in front of subpolar glaciers under permafrost conditions. The end moraines in Finnmark were mkost likely formed in the same way in a permafrost climate during deglaciation. This might also be the case for moraines in the southernmost parts of Fennoscandia, in Denmark and southernmost Sweden. Cold‐based ice during deglaciation in central parts of Fennoscandia is due to climatic conditions tens of thousands of years earlier. The period with climatic improvement after the Weicheselian maximum was too short to have any influence on the thermal conditions at the base of the ice‐cap in the central areas.

Influence of temperature conditions in horizontal Bridgman furnace on crystal growth of GaAs

AbstractThe experimental investigation of the boat shape and boat position in the furnace in the case of unseeded horizontal Bridgman growth of GaAs single crystals was carried out. The relation between axial and radial temperature gradients in the furnace was also studied. On the basis of experimental results the optimum conditions for the growth of low dislocation density GaAs single crystals were derived.

The influence of temperature conditions in the preparation of polyurethanes on branching and properties of the polymers

An equation has been derived giving the number-average amount of branchings per macromolecule for slightly branched polyurethanes in relation to degrees of conversion of functional groups. Experimental findings are taken as a basis for calculating kinetic parameters of propagation and branching reactions taking place in the system polyethylenebutyleneglycol adipate-2,4-toluylene diisocyanate, and theoretical temperature conditions have been calculated for the synthesis of the slightly branched prepolymer formed in the first stage of formation of network polyurethane. Two network polyurethanes were synthesized: the first under a regime approximating to theory, and the second under isothermal conditions. It is shown that the degree of branching of the prepolymer can have a marked influence on several properties of the polyurethanes.