The Variable Frequency Conductivity of Geopolymers during the Long Agieng Period

The variable frequency conductivity was applied to characterize the process of solidification of geopolymers based on fly ash with sand additives. XRD qualitative and quantitative analysis, porosity measurements, and sorption analysis of specific surface area were performed. The conductivity was correlated with porosity and specific surface area of geopolymer concretes. Both values of conductivity, real and imaginary parts, decreased during polymerization processing time. Characteristic maximum on graphs describing susceptance vs. frequency curve was observed. The frequency of this maximum depends on time of polymerization and ageing, and can also indicate porosity of material. Low-porous geopolymer concrete shows both low-conductivity values, and susceptance maximum frequency peak occurs more in the higher frequencies than in high-porous materials.

USE OF ULTRASOUND FOR EXTRACTION OF BIOLOGICALLY ACTIVE SUBSTANCES FROM TAMARIX HISPI-DA WILLD.

The extractions of biologically active substances from aerial part of Tamarix hispida Willd. over ultrasound have been studied. The results showed that the output of extractive substances using ultrasound was increased to 37.34% under the following conditions: 10% ethyl alcohol in a raw-extractant ratio (1 : 6) for 25 minutes at a 20–25 °С temperature and an ultrasound frequency of 35 kHz. The extraction was compared with maceration by yield and chemical composition. As a result of optimization, the output of components from the raw material is increased by 3–4 times at ultrasound frequency from 20 to 35 kHz and extraction time is significantly reduced from 48 hours to 30 minutes. It was found that the major substances were hydrolyzable tannins, the content of which are 10% (ultrasonic extraction) and 8% (maceration), respectively. Using UV-spectrometry, it was confirmed that the appearance of a characteristic maximum in the spectrum of the substance to be analyzed corresponds to the area of absorption of gallic acid and its derivatives, which indicates the content of these in the structure of hydrolyzable tannins. The substance shown significant antidiabetic activity (in vitro) at IC 50 = 3.94±0.14 μg/ml.

16Cr-19Ni steel swelling at dose rates from 1×10-8 to 1.6×10-6 dpa/s

The article presents the first data on EK-164ID steel swelling after operational irradiation in a fast nuclear reactor in the temperature range of 370–630 °C and maximum damaging doses of 66–77 dpa. The dose accumulation rate along the cladding tubes made of this material was 1×10-8–1.6×10-6 dpa/s. The swelling was determined by the hydrostatic weighing method with an error of no more than 0.5%. The results obtained were analyzed depending on the irradiation parameters and in comparison with the 16Cr-15Ni grade material. The objectives of the study were to estimate the characteristic values of the maximum swelling temperature and dose as well as to calculate the average material swelling rate at the working temperature of irradiation, the incubation period for the onset of swelling, and the stationary swelling rate. It was found that the tube samples, characterized with austenite grain sizes of 9–12 µm before irradiation, have an average swelling rate of 0.035–0.05 %/dpa after reaching the maximum damaging doses of 66–77 dpa (at a rate of (1–1.5)×10-6 dpa/s) and not more than 0.035%/dpa at doses less than 20 dpa (at a rate of 5×10-7 dpa/s). The characteristic maximum swelling temperature of the studied material is in the range of 430–500 °C. The characteristic maximum swelling dose is in the range of 61–72.5 dpa or 70–80% of the maximum accumulated dose. The incubation stationary swelling period for the material is 30 dpa. The stationary swelling rate is 0.1% /dpa. The radiation resistance characteristics of the studied material have an advantage over those for 16Cr-15Ni grade cladding materials under similar irradiation conditions and a similar structural state, which inherits grain sizes of 9–14 μm during the tube processing.

Нелинейное просветление InAs нитевидных нанокристаллов в видимом диапазоне

The spectral and nonlinear optical properties of InAs nanowires suspensions in isopropanol were studied at room temperature. InAs nanowires were synthesized by molecular beam epitaxy. The absorption spectra of suspensions with a characteristic maximum at a wavelength of 235 nm were obtained, as well as Raman spectra in the range 180–280 cm – 1. The nonlinear transmission of InAs nanowires with a diameter less than the Bohr radius of the exciton upon two-photon excitation in the transparency region in the visible range (λ = 468 nm) was studied firstly. The effect of cumulative bleaching was discovered, the manifestation of which is associated with the dynamic Stark effect.

Электрические характеристики термовольтаического элемента на основе сульфида самария

The converter of thermal energy into electrical energy based on the thermovoltaic effect is considered. Samarium sulfide (SmS) samples obtained by high-temperature sintering were used as working material. The main electrical characteristics of the thermovoltaic element based on the thermovoltaic effect are determined: volt-ampere characteristic, maximum power, internal resistance. It is shown that the optimal load to obtain maximum power is equal to the internal resistance of the element.

Stochastic Description of Loads on the Steel Storage Capacities

This paper deals with the study of stochastic parameters of external loads, which are used in the tasks of determining the level of reliability of steel storage capacities. To describe the random load process, the normal law and the double exponential distribution of Gumbel were used. It was formulated the technique of transition from the study of the entire random process to the consideration of its maximums. It was obtained quantitative values of the stochastic characteristics of snow and wind loads on the territory of Ukraine, without reference to the zoning maps. A general procedure for determining the probability of failure was formulated, depending from a given characteristic maximum. This index corresponds to the basic level of load. The average intersection of this level by a random load process is equal to one. Analytical formulas are obtained to determine the scale and position of the double exponential distribution of Gumbel, which depend on the characteristic maximum, as well as formulas, which help to calculate the statistical characteristics (standard, expected value and coefficient of variation) of the random value of the load maximums. The possibility of using this approach is theoretically confirmed when the density distribution of the ordinate of a random process follows the normal law. It was proposed expressions for the parameters of the distribution maximums of the random processes, which are described by the polynomial exponent and the Weibull law.

USE OF THE PURIFIED APPLE PECTIN FOR STABILIZATION OF ASCORBIC ACID IN FRESH JUICES

Исследована возможность применения очищенных пектинов для стабилизации аскорбиновой кислоты (АК) в фреш-соках с концентрацией 10–6–10–4г/мл. В работе использованы: АК, щавелевая кислота (ЩК), свекловичный (СП), цитрусовый (ЦП) и яблочный (ЯП) пектины с высокой молярной массой 61000–87500 г/моль и степенью этерификации 46,5–76,3%, предназначенные для фармацевтического применения. Фреш-соки получены посредством отжима ягод, плодов и овощей (18 видов). Установлено отсутствие мешающего влияния пектинов на определение АК методом дифференциальной спектроскопии в УФ-области – характеристический максимум поглощения АК 264 нм. По серии растворов АК (0,25–1,25) · 10–3% определен удельный показатель поглощения АК 727, в соответствии с которым оценено содержание АК в модельных растворах со вспомогательными веществами при хранении. Устойчивость АК составляет, сут: в присутствии ЩК 5, СП 4, ЦП 6, ЯП 10. Установлено оптимальное массовое соотношение АК : ЯП как 1 : 16, что использовано для купажирования фреш-соков, в которых предварительно определена концентрация АК 0,40–19,99 мг % методом титрования 2,6-дихлорфенолиндофенолятом натрия. Сравнительная оценка соков до и после купажирования ЯП при хранении (20°С, 10 сут) показала, что ЯП способствует смещению рН в оптимальную для АК область рН 4,5–8,0; увеличению вязкости соков на 5–148% и сроков хранения в 3,3–59 раз. Относительная погрешность различных определений (n = 5, P = 95%, t = 2,57) составила ± (0,7–5,6)%. Доказана возможность применения очищенного ЯП в качестве стабилизатора АК в фреш-соках с концентрацией АК 10–6–10–4 г/мл, что создает перспективы безопасного «продления жизни» соков. The possibility of using purified pectins to stabilize ascorbic acid (AA) in fresh juices with a concentration of 10–6–10–4g/ml was investigated. In the work were used: АA, oxalic acid (OA), beetroot, citrus and apple pectins (BP, CP and AP) with high molar mass (61000–87500 g/mol) and the degree of etherification (46,5–76,3%), intended for pharmaceutical use. Fresh juices were obtained by pressing berries, fruits and vegetables (18 kinds). Absence of interfering effect of pectins on the determination of AA by differential spectroscopy in the UV region (characteristic maximum absorption of AA – 264 nm) was established. According to the series of AA solutions (0,25–1,25) · 10–3%, the specific absorption rate of AA 727 was determined, according to which the content of AA in model solutions with auxiliary substances during storage was estimated. The stability of AA in the presence of OA is 5 days, BP – 4 days, CP – 6 days, AP – 10 days. The optimal mass ratio of AA : AP 1 : 16 was established, which was used for blending fresh juice, in which the concentration of AA (0,40–19,99 mg %) was previously determined by the method of titration with 2,6-dichlorphenolindophenol sodium. A comparative assessment of juices before and after blending during storage (20°C, 10 days) showed that AP contributes to the displacement of pH in the optimal for AA area of pH 4,5–8,0; increase in the viscosity of juices by 5–148% and shelf life of 3,3–59 times. The relative error of different definitions (n = 5, P = 95%, t = 2,57) was ± (0,7–5,6)%. Thus, the possibility of using purified AP as an AA stabilizer in fresh juices with the concentration of AA 10–6–10–4g/ml is proved, which creates prospects for safe prolonging the life of juices.

Contact-Patch-Size Distribution and Limits of Self-Affinity in Contacts between Randomly Rough Surfaces

True contact between solids with randomly rough surfaces tends to occur at a large number of microscopic contact patches. Thus far, two scaling regimes have been identified for the number density n ( A ) of contact-patch sizes A in elastic, non-adhesive, self-affine contacts. At small A, n ( A ) is approximately constant, while n ( A ) decreases as a power law at large A. Using Green’s function molecular dynamics, we identify a characteristic (maximum) contact area A c above which a superexponential decay of n ( A ) becomes apparent if the contact pressure is below the pressure p cp at which contact percolates. We also find that A c increases with load relatively slowly far away from contact percolation. Results for A c can be estimated from the stress autocorrelation function G σ σ ( r ) with the following argument: the radius of characteristic contact patches, r c , cannot be so large that G σ σ ( r c ) is much less than p cp 2 . Our findings provide a possible mechanism for the breakdown of the proportionality between friction and wear with load at large contact pressures and/or for surfaces with a large roll-off wavelength.

Contact-Patch-Size Distribution and Limits of Self-Affinity in Contacts between Randomly Rough Surfaces

True contact between solids with randomly rough surfaces tends to occur at a large number of microscopic contact patches.  So far, two scaling regimes have been identified for the number density n(A) of contact-patch sizes A in elastic, non-adhesive, self-affine contacts.  At small A, n(A) is approximately constant,  while  n(A)  decreases as a power law at large  A.  Using Green’s function molecular dynamics, we identify a characteristic (maximum) contact area Ac above which a superexponential decay of n(A) becomes apparent if the contact pressure is below the pressure pcp at which contact percolates.  We  also find that  Ac increases with load relatively slowly far away from contact percolation. Results for Ac  can be estimated from the stress autocorrelation function Gσσ (r) with the following argument: the radius of characteristic contact patches, rc, cannot be so large that Gσσ (rc) is much less than pc2. Our findings provide a possible mechanism for the breakdown of the proportionality between friction and wear with load at large contact pressures and/or for  surfaces with a large roll-off wavelength.