On the problem of the “effective” secondary nuclei

Introducing an “on-line” Coulter Counter measurement technique in a stirred fluidized bed of KAl(SO₄)₂·12H₂O crystals in order to observe the generated secondary nuclei leads to results. But even these results still do not give an answer to the complicated phenomena of birth and growth of the secondary nuclei.The results are the following:Secondary nuclei of sizes smaller than 2 μm are generated and the smaller the size the higher the number of the generated nuclei.Nuclei below about 3 μm seem not to be “effective”. The high number of particles in the unfiltered “pure” solution prior to the experiment does not grow in the sampling cells. The number of nuclei grown in the sampling cells corresponds to the number of nuclei above 3 μm counted by the Coulter Counter. There are particles growing more slowly in the sampling cells, but the number is much smaller than the number of particles below 3 μm counted by the Coulter Counter. This means some of these particles do not grow or they grow at very slow rates or something else happens to them.The higher the supersaturation the more nuclei are generated. The effect of supersaturation at high stirrer speeds is the least with the small nuclei, but the strongest with the larger nuclei sizes. That means more nuclei can be found in larger size ranges at high supersaturations and high stirrer speeds.The higher the stirrer speed the more nuclei are generated.The power number found for the supersaturation 1.3 fits well into the range of 1.3–1.6 given by former work.     

Theoretical and Experimental Study of Freeze-Drying of “loco” (Concholepas concholepas)

The “loco” is a mollusk somewhat similar to abalone that exists exclusively in Chile and Peru. Given the high commercial value of loco, preservation through freeze-drying seems economically viable. In this work, the freeze-drying process of loco meat was analyzed theoretically and experimentally. The effects of particle size, freeze-drying pressure, and intermittent use or not of microwave in the secondary drying stage, on the extent of the freeze-drying period, rehydration properties, shrinkage and texture were investigated by using a 2³ factorial design. Drying and rehydration kinetics were adjusted to phenomenological models in order to determine mass transfer parameters.

Freeze-drying pressure significantly affects the extent of the drying process. Freeze-drying pressure results in shrinkage, while microwave produces a volume increase. The effective moisture diffusivity (D_eff) estimated form drying curves fluctuated between 10^?10 and 10^?11 (m²/s), agreeing with values reported for other meat products. The adjustment of the rehydration kinetics to the Constant Diffusivity Model gave the best fit, resulting in D_eff in the order of 10^?10 (m²/s). Particle size and freeze-drying pressure significantly affected rehydration capacity.     

Experimental Study of Ignition of a Gasoline–Air Mixture in a Constant‐Volume Combustion Chamber

The characteristics of flamekernel development in a premixed gasoline–air mixture in a cylindrical constantvolume combustion chamber are measured. The experiments are performed with an initial temperature of 393 K, pressure of 6 bar, and equivalence ratio = 0.8 with the use of various ignition systems and spark plugs. The schlieren pictures of the process are presented, and the measured results for flame velocity, heatrelease rate, and mass fraction of the burnt fuel are analyzed.     

Experimental Study of the Disperse Composition of Condensed Products of Aluminum‐Particle Combustion in Air

The particle shape and structure and also the disperse composition of condensed products of combustion of ASD1, ASD4 and ASD6 aluminumbased powders in air with oxidizertofuel ratios of 0.12–0.4 and initial pressures of 0.05–0.30 MPa are examined. The mass of submicron particles of aluminum oxide amounts to 90% of the total mass of condensed combustion products. The mean mass diameter of particles is 0.15–0.18 m and increases with increasing pressure. Under atmospheric pressure, the initial disperse composition of aluminum powders and the proportion between the components in the combustor volume have little or no effect on the disperse composition of the condensed phase. A comparative analysis is performed of the disperse composition of condensed phase particles formed due to aluminum combustion in various propellant mixtures and various combustors. It is shown that the main factors affecting the disperse composition are the type of the propellant mixture, the gasdynamic combustion process, and the conditions determining the interaction of aluminum particles with each other and with the gas phase.     

Experimental investigation of effects of the feed flow rate and “tail scoop-wall” clearance on the performance of a gas centrifuge by feeding a Freon mixture

Experimental study of the performance of a gas centrifuge can be appreciably simplified if instead of isotopic mixtures, a binary mixture of gases with large molecular weight difference is used. The current study undertook this approach by injecting a 53%–47% (w/w) mixture of “Freon12-Freon22” into a gas centrifuge. The two parameters, whose investigation was the objective of the current study were: the feed flow rate (F), and the clearance between tail scoop and the rotor wall (d). The results demonstrated that changing the scoop-wall clearance has the most significant effect on the cut (θ), so that by fixing “d”, “θ” becomes nearly invariant. The head separation factor (α) exhibited the same dependency, but it was more influenced by the “F” than the “d”. Apparently the following regression exists between the inspected parameters:

Decreasing “d” → Decreasing “θ” → Increasing “α”.

Variations of the tail separation factor (β) with “F” or “d” was quite slight, even though similar to “α”, it was lowered with increasing of the “F”. The separation capacity (δU) as the most significant parameter of a centrifuge was optimised at the highest value of “F = 40.5 g/h”, and lowest value of “d = 3 mm”. The study achieved a separation capacity and an overall separation factor equal to 195.53 kg Freon/y and 16.87, respectively. These values are several times larger than those of the isotopic mixtures, demonstrating that application of Freons is a useful mean for magnifying the features of a gas centrifuge.     

Experimental Study of Laser Initiation of a Light-Sensitive Explosive Charge over a ≈1000 mm2Surface

Combustion, Explosion, and Shock Waves - This paper presents the results of a study of the initiation of explosive transformation of flat charges 40 mm in diameter and 5 mm thick,...     

Determination of Copper,Iron, Nickel,and Zinc in Ethanol Fuel by Flame Atomic Absorption Spectrometry Using On‐Line Preconcentration System

Abstract

In this work, an on‐line system for preconcentration and determination of copper, iron, nickel, and zinc at µg L^?1 level by flame atomic absorption spectrometry (FAAS) has been developed. Amberlite XAD‐4 functionalized with 3,4‐dihydroxybenzoic acid packed in a minicolumn was used as metal sorbent. The retained metals can be quickly eluted from sorbent material, with the eluent stream consisting of hydrochloric acid solution, directly to the nebulizer burner system of the FAAS. Analytical parameters were evaluated and the results demonstrated that all studied metals can be determined, using borate buffer to adjust the sample pH at 8.0. The results showed that the proposed method is simple and rapid. The limits of detection were estimated as 2.3, 5.0, 7.8, and 0.1 µg L^?1 for copper, iron, nickel, and zinc, respectively, using a preconcentration time of 60 s and a sample flow rate of 5.5 mL min^?1. Enrichment factors of 22, 15, 12, and 54 and coefficients of variations of 3.5, 4.4, 4.4, and 3.2% were obtained in the determination of copper, iron, nickel, and zinc, respectively. The system presented an analytical throughput of 10 samples per hour and was successfully applied in the determination of metals in ethanol fuel.     

On the results of the First All-Russian Conference “Sol-Gel Synthesis and Study of Inorganic Compounds,Hybrid Functional Materials,and Disperse Systems”

Chronicle

On the results of the First All-Russian Conference “Sol-Gel Synthesis and Study of Inorganic Compounds, Hybrid Functional Materials, and Disperse Systems”     

On the nature of “functional groups” in non-functionalized hypercrosslinked polystyrenes

The paper discusses the assignment of the absorbance band at 1700 cm⁻¹ in FTIR spectra of hypercrosslinked polystyrenes. This band is exceptionally intensive in the spectra of networks obtained by post-crosslinking styrene-0.5% DVB copolymer, swollen in ethylene dichloride, with monochlorodimethyl ether up to the maximum possible crosslinking degrees of 300%, 400% and 500% in the presence of non-oxidizing catalyst SnCl₄. Theoretically, in these networks each phenyl ring binds to neighboring phenyls through three, four or five methylene groups, respectively. Elemental analysis of the products seems to be deficient in C and H, thus allowing expectation of a surprisingly high percentage of oxygen. However, the traditional attribution of both the suspected high content of oxygen and the band at 1700 cm⁻¹ to aromatic carbonyl groups is incorrect. Treatment of hypercrosslinked polystyrenes with hydroxylamine, sodium bisulfite, ethyl orthoformiate or LiAlH₄ do not result in disappearance of the absorbance at 1700 cm⁻¹ in FTIR spectra and emergence of corresponding characteristic new bands. Solid state ¹³C NMR spectroscopy also confirms the absence of CO moieties in the above hypercrosslinked polystyrenes. The absorbance at 1700 cm⁻¹ disappears, while new bands in the range of 1670–1650 cm⁻¹ emerge, in the spectrum of the sample with 500% crosslinking degree after the reduction of its benzene rings via Birch reaction. This allows suggesting that the band at 1700 cm⁻¹ and its shoulders are caused by hindered vibrations of carbon–carbon bonds and valence angles in the aromatic fragments composing the rigid network with extremely high extent of mutual connectivity.     

Experimental Study of Thrust Characteristics of a Model Air‐Breathing Ejector‐Type Combustor with Vibrational Burning of Hydrogen

The dependence of thrust of an airbreathing ejectortype combustor on its geometric parameters are experimentally determined in the case of vibrational burning of hydrogen in the combustor. The combustor is a cylindrical tube with a confuser at the entrance and a diffuser at the exit. It is shown that there is a certain limiting size of the confuser and a certain limiting length of the combustor, which ensure the maximum thrust.     

Comprehensive Characterization of an “Off/On” Rhodol-Based Lysosomal Tracker for Orthogonal Cellular Analysis by Confocal Imaging

Two florescent xanthene-cyanamide lysosomal trackers emitting strongly at ∼525 nm were prepared from fluorescein and rhodol methyl esters in microwave-assisted reactions. Both forms named “off” (nonfluorescent lactam) and “on” (strongly fluorescent ring-opened amide) have been comprehensively characterized out by using a combination of NMR spectroscopy, X-ray analysis, fluorimetry and confocal microscopy. Known rhodamines bearing electron-withdrawing groups (EWGs) exhibit an equilibrium between non-fluorescent (off) and fluorescent (on) depending on the dielectric constant of the medium. Here, cyanamide was introduced as EWG amine into the fluorescein and rhodol framework. Unlike rhodamine-type dyes, the ring-opened forms of fluorescein- and rhodol-cyanamides are stable in protic solvents under circumneutral and basic pH conditions. The osteoblastic cell line MC3T3-E1 from C57BL/6 mouse calvaria was used for confocal imaging where the different organelles and nuclei were distinguished by using an orthogonal combination of fluorescent dyes.     

Study of the Dynamic Modes of the Operation of Flowsheets for the Extractive Distillation of a Benzene–Cyclohexane–Toluene Mixture

Theoretical Foundations of Chemical Engineering - This work considers four extractive distillation flowsheets of a benzene–cyclohexane–toluene mixture with different structures: one of...     

Numerical Study of the Problem of Thermal Ignition in a Thick‐Walled Container

A problem of thermal ignition of an exothermic mixture with an inert filler in a thickwalled container is formulated. It was found that synthesis can be performed under conditions of a weakly changing temperature if an inert filler is added to the mixture. Variation of critical conditions separating different thermal regimes with different values of model parameters is examined: ignition and extinction or ignition and slow transformation.     

Fibrous Particle Deposition in a Turbulent Channel Flow—An Experimental Study

The deposition rate of glass cylinders and dust paper fibers in a turbulent duct flow was studied experimentally. The glass fibers with a minimum diameter of 5 μm and the paper fibers with a minimum diameter of 1–20 μm and aspect ratios from 4 to 20 were deposited on a flat gold plate. The particle concentration at the test section was measured with the aid of an isokinetic probe in conjunction with a digital image processing technique. An oil lubricant was used on the plate to reduce the effect of particle bounce from the surface. The experimental data show that the deposition rate increases with an increase in fiber length and size. For a fixed minimum diameter or a fixed equivalent relaxation time, the deposition rate increases rapidly with fiber aspect ratio. When the equivalent spherical particle relaxation time is used, the deposition rate of the fibers was found to increase only slightly with aspect ratio and resemble those of spherical particles. The measured deposition velocities were in good agreement with the empirical model predictions and previous data.     

Experimental Study of Effect of Class Ⅲ Fly Ash on Rolled Concrete Performance

通过对掺Ⅲ级粉煤灰的碾压混凝土的拌合物性能和硬化混凝土性能研究,分析碾压混凝土中掺加Ⅲ级粉煤灰的可行性.研究表明,在碾压混凝土中掺加Ⅲ级粉煤灰,碾压混凝土的各项性能指标均可满足设计要求.