Effect of an amorphous precursor macrostructure on the size of NaA and NaX zeolites

The effect of an amorphous precursor macrostructure on size of NaA and NaX zeolites is studied. NaA and NaX zeolites grown in dense aluminosilicate gels reach sizes of 6?C8 ??m, while NaA and NaX zeolites grown in gels with loose particles reach sizes of 20?C30 ??m. Gel density is controlled by adding organic compounds to the initial solutions.     

Modeling of nanomaterial structure based on quantum-sized mesoparticles

Some fundamental aspects of the three-level (micro-, meso-, and macrolevel) scheme of modeling nanomaterial structure based on physics of quantum-sized mesoparticles are considered. Within the framework of quantum-field chemistry, the mesoparticles provide the basis for the construction of mesoquanta and macrodefects of nanomaterials. The microstructure is described by the method of quantum density topology, and the macrostructure is described by the method of thermal field dynamics of quantum-sized mesoparticles. Based on an analysis of quantum-sized nanoparticle motion, a strict mathematical classification of physical and chemical mesoprocesses in nanomaterials is given. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 66–68, July, 2006.     

Multi-parametric function of differential backscattering in 3D biological media with heterogeneities

A model scheme for spectral visualization of biological media macrostructure is presented. Superficial tissue with heterogeneities was chosen as a basic investigation object. 3D Monte Carlo simulation of laser radiation propagation in multiple scattered media was used for computation of differential spectral backscattering density which may characterize the state of the irradiated tissue. Numerical results allow to determine differential backscattering intensity as the multi-parametric function of media and heterogeneities features. The data are basic for diagnostic scheme software implementation.     

Cone-like bubble formation in ultrasonic cavitation field

A new phenomenon in ultrasonic cavitation field is reported. Cavitation bubbles are observed to self-arrange in a cone-like macrostructure in the vicinity of transducer radiating surface. The cone-like macrostructure is stable while its branch-like pattern microstructure changes rapidly. The structure is constituted by moving bubbles which undergo attractive and repulsive Bjerknes forces caused by high acoustic pressure gradients and strongly nonlinear oscillations of cavitation bubbles. The cone-like bubble structure is a chemically active formation. Its remarkably high activity is confirmed by chemiluminescence experiments.     

Macrostructure of high-temperature superconducting YBaCuO thin films grown by laser ablation

The superconducting parameters and macrostructure of YBaCuO thin films grown by laser ablation on SrTiO₃ substrates are influenced by the substrate temperature during growth. In a study of this influence it is found that the macrostructure has significant bearing on the superconducting parameters of the films and on the critical current, in particular. For J _c⩽10⁵ A/cm² the films have a distinctly pronounced granular structure, while for J _c>10⁵ A/cm² the films do not have any kind of block structure. Zh. Tekh. Fiz. 68, 48–51 (February 1998)     

Structure analysis of electrically conductive polymers filled with agglomerated components

An analysis of macrostructure topology of electrically conductive polymer composites with agglomerated fillers is performed. Parameters that allow the value of volume electrostatic resistance and agglomeration of the filler are determined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 13–18, November, 2006.     

The blow-off and transient characteristics of co-firing ammonia/methane fuels in a swirl combustor

Recent studies have demonstrated that ammonia could be one of the most promising hydrogen carrier candidates which can be used in large-scale power plants. However, it is challenging to burn ammonia in gas turbines due to its narrow flame stabilization limits. This study investigates the blow-off characteristics and flame macrostructure transition behavior of ammonia/air flame (i.e. NH₃ flame) and ammonia/methane/air flame (i.e. 50%NH₃ flame) in a swirl combustor. Methane/air flame (i.e. CH₄ flame) is also demonstrated for comparative purposes. The flow field and instantaneous OH profile are measured with PIV and OH-PLIF technique, respectively. Large eddy simulation (LES) is conducted to extend understandings of the experimental findings. The results show that the NH₃ flame possesses a poor lean flame stability limit which can be largely extended by adding CH₄ in the fuel. Moreover, changing swirl number (S) shows no apparent effect on the lean blow-off limit (?_b) for the NH₃ flame. On the contrary, a clear extension on ?_b is found for the 50%NH₃ flame when increasing S. Four flame macrostructure modes can be identified when decreasing equivalence ratio (?). The transition from flame II to flame III (?_t describes the transition equivalence ratio) can be considered as the early warning of blow-off for a swirl stabilized flame. It is found that for the NH₃ flame, there is no clear flame macrostructure transition at small inlet velocities (U < 3.8 m/s), i.e., ?_b ≈ ?_t, while the difference between ?_b and ?_t will be observed as the inlet velocity increases. However, for the 50%NH₃ and CH₄ flames, a clear flame macrostructure transition from flame II to flame III is observed even for a lower inlet velocity. The LES results show that the NH₃ flame has a faster blow-off process compared to the CH₄ flame, which is mainly attributed to the excessive stretch causing local extinction during the blow-off process.     

The effect of silicon on the structure and properties of Fe-Cr-Co permanent magnet alloys

The influence of silicon in amounts of up to 4.33 wt% was studied in terms of its effect on micro- and macrostructure, on non-metallic inclusions, on mechanical hardening and on magnetic properties of Fe-28Cr-24Co alloy of equiaxial grain structure and of partially ordered structure-the so-called semicolumnar structure. Optimum magnetic properties in the examined alloy are attained with silicon content Si = 1.04 wt%. Magnetic properties of an alloy of semicolumnar structure are markedly superior to those of the alloy devoid of that structure. With up to 1.04 wt% of silicon, the macrostructure of the alloy remains practically unchanged, while with higher contents of silicon a refinement of the structure takes place. The stereometric parameters of non-metallic inclusions (Al₂O₃, SiO₂, Al₂O₃·SiO₂) increase with silicon contents Si > 1.04 wt%. The hardness of the alloy after homogenizing is practically constant up to silicon content Si = 1.65 wt%, but it increases slightly with Si > 1.65 wt%. The examined alloy with silicon up to 1.65 wt% is ductile in the quenched state and could also be cold-worked.     

Fragmentation of primary coarse macrostructure of AISI 321 steel

Fragmentation of primary grains in an ingot of AISI 321 steel was studied under common hammer forging conditions, i.e. at a temperature gradient existing in the cross-section of the ingot. It has been found that recrystallization in the surface zone starts by deformation induced migration of large subgrains observed inside primary grains, that static recrystallization takes place by intragranular twinning and that the fragmentation of the primary macrostructure is conditioned by static recrystallization.     

Enhancing carrot convective drying by combining ethanol and ultrasound as pre-treatments: Effect on product structure,quality, energy consumption,drying and rehydration kinetics

Ultrasound was combined with ethanol to improve different aspects of carrot convective drying, evaluating both processing and product quality. The ultrasound in water treatment resulted in cellular swelling and small impact on texture. Differently, the ultrasound in ethanol and ethanol treatments modified both carrot microstructure (cell wall modifications of parenchymatic tissue) and macrostructure (shrinkage and resistance to perforation). Pre-treatments with ultrasound in ethanol and ethanol improved the drying kinetics, reducing the processing time (~50%) and the energy consumption (42–62%). These pre-treatments also enhanced rehydration, whose initial rate and water retention were higher than the control. In addition, the carotenoid content was preserved after drying, for all the treatments. Any impact on shrinkage was observed. A mechanistic discussion, based on structural modification (microstructure and macrostructure) and physical properties of water and ethanol, was provided. As conclusion, this work not only described positive aspects of combining the technologies of ultrasound and ethanol as pre-treatments to convective drying, but also proposed mechanisms to explain the phenomena.     

From hexagonally arrayed nanorods to ordered porous film through controlling the morphology of ZnO crystals

The macrostructure can be changed by changing the morphology of its units. In this article, we use a colloidal template route, combined with hydrothermal growth method, to get the hexagonally arrayed ZnO nanorods on the polycrystalline ZnO substrate. More significantly, through controlling the morphology of ZnO crystals by adding structure-directing agent in the precursor solution, the highly ordered porous ZnO films were obtained instead of ZnO nanorods. This templated solvent-thermal method has great potential in micro/nano-fabrication.     

Investigation of the properties of filled polyethylene by the texture pattern of macrostructure images

The results of an investigation of the structure of polymer composite materials are presented. The materials were produced with the use of the texture analysis and mathematical methods of processing of macrostructure images. The approach proposed to measure texture parameters allows one to investigate the effect of the type and concentration of the filler on the properties of the material.     

激光熔覆TiC-Ni复合涂层的摩擦磨损性能和磨损机制研究

利用光学显微镜和扫描电镜观察了钛合金表面TiC-Ni激光熔覆层的宏观形貌和微观组织,测试了激光熔覆层的硬度、摩擦系数和磨损量。利用SEM观察了磨损的表面形貌和磨屑的形貌,分析了激光熔覆层的磨损机制。结果表明:激光熔覆层组织致密,无气孔和裂纹,硬度为基材的3倍;激光熔覆层的摩擦系数随环境压力的降低而提高,磨损量随环境压力的降低、法向载荷的增加而增加;低载时为轻微的磨粒磨损,高载时为严重的剥层磨损。     

High-temperature tests of fine-grained dense graphite composites to predict the lifetime of a neutron target converter

The conductivity of graphite composite samples MPG-6 and MPG-7 has been measured before and after 1.4 MeV electron irradiation and heating by alternating current up to temperatures higher than 2500°C, causing the fracture of the samples. It has been shown that both heating and electron irradiation result in a shift of the temperature dependence of the conductivity of the samples, namely, in an increase in conductivity. The measurements of the relative magnetoresistance at helium temperature in fields of ±1.15 T have shown that the imperfection of the macrostructure increases. The noticeable changes in the x-ray phase diagram do not observed up to the fracture of the samples. All the obtained data make it possible to suppose that the ultimate strength and the lifetime of graphite composites are limited by intercrystalline or grain boundaries.     

Optimization of the efficiency and cycling performance of Na0.1CrS2 electrodes in nonaqueous secondary lithium cells

The effect of the macrostructure (grain size) and the microstructure (crystal lattice parameters) factors on the coulombic efficiency of Na_0.1CrS₂ cathodes in secondary Li cells is studied. An attempt is made to employ Atlung's model in assessing the chemical diffusion coefficient of Li⁺ in the host structure leading to more realistic values with respect to effective interface area. The possibility of enhancing the mobility rate of Li⁺ by intercalation of water in the host structure is revealed. Using Atlung's model as a guideline it was possible to improve considerably the performance of the Na_0.1CrS₂ cathodes, while retaining their good cycling stability.     

Minimum fluctuations in nanostructures

The properties of the Bose gas in traps have been experimentally and theoretically investigated. The main results of these investigations were discussed in L. Pitaevskii’s review. In this study, we consider excitations of low-lying levels in a disk-shaped magnetic trap. In contrast to the macrostructure, the excitation spectrum in the traps is a set of quasi-Bogolyubov modes with the gaps, which can be interpreted as a discrete breathing mode spectrum.     

Structure optimization of structured corrugation foam packing by computational fluid dynamics method

A computational fluid dynamic method is developed to predict the pressure losses within the newly developed foam SiC ceramic structured packing. The present work simulates the flow pattern in a macrostructure model and the typical REU mechanisms. Vertical pulse structure districts are added in one corrugated packing to aid the optimization of structured packing designs while minimizing the pressure drop. The simulations are carried out and the results are validated to obtain optimization structured packings with good pressure drop performance.     

Assessing severity of obstructive sleep apnea by fractal dimension sequence analysis of sleep EEG

Different sleep stages are associated with distinct dynamical patterns in EEG signals. In this article, we explored the relationship between the sleep architecture and fractal dimension (FD) of sleep EEG. In particular, we applied the FD analysis to the sleep EEG of patients with obstructive sleep apnea-hypopnea syndrome (OSAHS), which is characterized by recurrent oxyhemoglobin desaturation and arousals from sleep, a disease which received increasing public attention due to its significant potential impact on health. We showed that the variation of FD reflects the macrostructure of sleep. Furthermore, the fast fluctuation of FD, as measured by the zero-crossing rate of detrended FD (zDFD), is a useful indicator of sleep disturbance, and therefore, correlates with apnea-hypopnea index (AHI), and hourly number of blood oxygen saturation (SpO₂) decreases greater than 4%, as obstructive apnea/hypopnea disturbs sleep architecture. For practical purpose, a modified index combining zDFD of EEG and body mass index (BMI) may be useful for evaluating the severity of OSAHS symptoms.