Spherical Degree Research Articles

Development and Optimization of Insulin-Chitosan Nanoparticles

Purpose: To optimize the preparation of insulin-chitosan nanoparticles (ICNS) using response surface methodology (RSM).Methods: ICNS were formulated through ionic cross linking method. The effects of the ratio between insulin and chitosan, pH of the medium and rotation speed on insulin encapsulation efficiency (EE) were investigated. Box-Behnken experimental design coupled with response surface method was employed to optimize formulation. Properties such as particle shape, size, zeta potential and release behavior were analyzed.Results: The best formulation was produced under the following conditions: the ratio between insulin and chitosan was 0.08, pH 3.0, and rotation speed 187.4 rpm. Verifying experiments were established under the optimal conditions and EE was 93.1 %. Nanoparticles showed fine degree of sphericity and homogenous distribution of particle size. The particle size of nanoparticles was between 91.3 ± 7.9 and 220.2 ± 9.5 nm and the average zeta potential was 14.4 ± 2.9 mv. More than 16.8 % of total drug was released rapidly in the first 1 h. Thereafter, the insulin trapped in ICNS was released into the medium slowly and > 93.0 % was released completely within 24 h. Ritger-Peppas model was the best-fit drugrelease from all the formulations. The diffusion exponent (n) indicates that drug release pattern was non-Fickian diffusion.Conclusion: Response surface method was a useful tool to predict the optimal formulation. ICNS showed excellent characteristics of homogenous particle size distribution, good spherical property, positive zeta potential and longer drug delivery. It could be a promising carrier for the oral administration of insulin.Keywords: Nanoparticles, Response surface methodology, Insulim release, Encapsulation efficiency, Zeta potential, Ritger-Peppas model, Box-Behnken design.

Reconstruction of the three-dimensional inclusion shapes using electrical capacitance tomography

Electrical capacitance tomography (ECT) is an industrial visualization technology that non-destructively measures the permittivity distributions within a closed vessel. Due to its advantages of good portability, high speed and low cost, ECT has been successfully applied in many industrial processes. In the paper, a shape-based method is presented to reconstruct the geometric configurations of three-dimensional inclusions using ECT. In contrast to the pixel-based methods, the presented method treats the inclusions' permittivity values as known and parameterizes their surfaces using spherical harmonics. By selecting the coefficients of the spherical harmonics as unknowns, the optimal inclusion surface shape is iteratively searched using the Levenberg–Marquardt method. To improve the computational efficiency, a fast Jacobian matrix calculation method is derived based on the reciprocity theorem. To enhance the stability, a multi-stage strategy is proposed to increase the spherical harmonics degrees gradually. Both numerical and experimental tests are conducted to test the reconstruction performance and the factors influencing the reconstruction are further discussed based on the results.

Long-term Overheating Cracking Analysis of 12Cr1MoV Boiler Superheater Tube

After running 39 840 h, a boiler superheater tube made by 12Cr1MoV steel in a plant cracked. The tube is blocked and the thick-lip-shape fracture is covered with oxides. By utilizing optical microscope(OM), X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and other methods to detect the tube, it is found that the compositions of blocking substances are Na3PO4, Fe2O3 and NaFeO2. In the unblocking position of the inner wall oxide is Fe3O4, however, in the blocking position, it is Fe2O3. In terms of the shape of the fracture morphology, it is inter granular, along with secondary cracks and pores in the grain boundary. The research results illustrate that the metallographic microstructures in samples of near crack and away from the crack are the same. With the lamellar pearlite of the initial state dissolves, the carbides gather and grow at the grain boundaries. The organization spherifies seriously, and the carbide is M23C6. According to the electric power industry standard, the spherical degree is identified as level 5. By utilizing spheroidization level and run-time to estimate the wall temperature, it can be know the tube run in over-temperature environment. To be specific, the hardness in all the samples is about 135 HV, which is relatively low. In all, the failure mode of superheater tube is high temperature creep cracking which is caused by long-term overheating resulted from the oxide layer and the blocking substances.

Phase Field Simulation of Equiaxed Microstructure Formation during Semi-solid Processing of A380 Al Alloy

A phase field modelling approach is implemented in the present study towards simulation of microstructure evolution during cooling slope semi solid slurry generation process of A380 Aluminium alloy. First, experiments are performed to evaluate the number of seeds required within the simulation domain to simulate near spherical microstructure formation, occurs during cooling slope processing of the melt. Subsequently, microstructure evolution is studied employing a phase field method. Simulations are performed to understand the effect of cooling rate on the slurry microstructure. Encouraging results are obtained from the simulation studies which are validated by experimental observations. The results obtained from mesoscopic phase field simulations are grain size, grain density, degree of sphericity of the evolving primary Al phase and the amount of solid fraction present within the slurry at different time frames. Effect of grain refinement also has been studied with an aim of improving the slurry microstructure further. Insight into the process has been obtained from the numerical findings, which are found to be useful for process control.

Influence of process parameters on the characteristics of TiAl alloyed powders by fluidized bed jet milling

Micro-fine high Nb containing TiAl alloyed powders were prepared by using fluidized bed jet milling from the pre-crushed Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y(at.%) ingot. The effects of process parameters on the powder characteristics were investigated. The results show that the particle characteristics are mainly determined by classifier frequency. At or above 5600rpm, the ground powders are composed of coarse block-shaped particles and finer flaky debris, with particle number-average diameter lower than 18μm. With the increase of classifier frequency and the decrease of grinding gas pressure, the amount of flaky debris formed under abrasion mechanism gradually increases, which causes the obvious decrease of the powder number-average diameter, distribution uniformity, and sphericity degree. With the classifier frequency of 8400rpm and grinding gas pressure of 0.55MPa, the obtained powders possess the minimum particle size of 5.32μm, with a uniformity level of 0.38 and a Wadell's sphericity factor of 0.820.

Asteroseismology of DAV white dwarf stars and G29–38

Asteroseismology is a powerful tool used for detecting the inner structure of stars, which is also widely used to study white dwarfs. We discuss the asteroseismology of DAV stars. The period-to-period fitting method is discussed in detail, including its reliability in detecting the inner structure of DAV stars. If we assume that all observed modes of some DAV stars are the l = 1 cases, the errors associated with model fitting will be always large. If we assume that the observed modes are composed of l = 1 and 2 modes, the errors associated with model fitting in this case will be small. However, there will be modes identified as l = 2 that do not have observed quintuplets. G29–38 has been observed spectroscopically and photometrically for many years. Thompson et al. made l modes identifications in the star through the limb darkening effect. With 11 known l modes, we also study the asteroseismology of G29–38, which reduces the blind l fittings and is a fair choice. Unfortunately, our two best-fitting models are not in line with the previous atmospheric results. Based on factors like only a few observed modes, stability and identification of eigenmodes, identification of spherical degrees, construction of physical and realistic models and so on, detecting the inner structure of DAV stars by asteroseismology needs further development.

An Investigation into the Effects of Additives on Crystal Characteristics and Impact Sensitivity of RDX

Additives are one of the most important factors that greatly affect the crystal characteristics of the high energy compound hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX, C3H6N6O6) and they have an influence on impact sensitivity. In this article, a growth morphology method was applied to obtain the crystal habit of RDX in a vacuum as well as the morphologically important faces, and molecular dynamics simulations were applied to calculate the interaction energy between these crystal faces and additive molecules for prediction of the additive-effect crystal habits of RDX. On this basis, crystal characteristics including crystal morphology, aspect ratio, and total surface charge were investigated. Then the particle size and surface electrostatic voltage of the samples from recrystallization were analyzed experimentally. The impact sensitivity test indicated that acrylamide, which could enhance the regularity and degree of sphericity of RDX crystals and effectively reduce the surface static electricity of RDX, was successful in reducing the impact sensitivity of RDX as an additive for crystallization. The above experimental results were in good agreement with the conclusions based on the theoretical calculations.

Development of a Pulsed-Field Differential Mobility Analyzer: A Method for Measuring Shape Parameters for Nonspherical Particles

For a nonspherical particle, a standard differential mobility analyzer (DMA) measurement yields a mobility-equivalent spherical diameter, but provides no information about the degree of sphericity. However, given that the electrical mobility for nonspheres is orientation-dependent, and that orientation can be manipulated using electric fields of varying strength, one can, in principle, extract some type of shape information through a systematic measurement of mobility as a function of particle orientation. Here, we describe the development of a pulsed-field differential mobility analyzer (PFDMA) which enables one to change the peak E-field experienced by the particle to induce orientation, while still maintaining the same time-averaged field strength as a standard DMA experiment. The instrument is validated with polystyrene latex (PSL) spheres with accurately known size, and gold rods with dimensions accurately determined by transmission electron microscopy (TEM). We demonstrate how the instrument can be used for particle separation and extraction of shape information. In particular, we show how one can extract both length and diameter information for rod-like particles. This generic approach can be used to obtain dynamic shape factors or other multivariate dimensional information (e.g., length and diameter). Copyright 2014 American Association for Aerosol Research

Study on Sedimentation Differences among Akund Fiber, its Seed and Capsule

In order to better understand the separation and cleaning of akund fibers and the potential for developing separation machinery evaluated, the sedimentation differences among single akund fiber, its seed and capsule are investigated. Based on the spherical degree, the mathematical model about free dropping velocity of single akund fiber is established and the dropping method is taken in the experiment. The dropping velocity of single akund fiber calculated by mathematical relationships is 0.0592 m/s, and the velocity calculated by dropping experiment is between 0.047 m/s~0.072 m/s, which average velocity is 0.0583 m/s. The dropping velocity of a third of capsule which is the main state after mechanical treatment calculated by dropping experiment is between 0.900~1.17 m/s. Moreover, the average dropping velocity of seed calculated by dropping experiment is 1.589 m/s. The dropping velocity of capsule and seed are much higher than that of akund fiber. And if there is no adhesion between akund fiber and capsule after mechanical treatment, the complete theoretical separation of akund fiber from its capsule and seed using airflow is possible.

Preparation and Growth Characteristics of Mesocarbon Microbeads

Mesocarbon microbeads (MCMBs) have been synthesized from coal tar pitch. Scanning electron microscopy (SEM) and laser particle size analyzer were used to evaluate the structure and partical size. The effect of process parameters on the growth and morphologies of MCMBs was investigated. The results show that the optimum temperature range is 410-430 °C and the growth time has a suitable range. The diameter and yield of MCMBs will increase and the spherical degree does not change with the extension of time.

Rosette Modes of Oscillations of Rotating Stars Caused by Close Degeneracies. I. Axisymmetric Modes

Abstract We present an analysis of unique axisymmetric eigenmodes of oscillations in rigidly rotating stars, which have been recently discovered numerically in the frequency region of low-order gravity modes of the polytropic model with index 3, and named as rosette modes after their structure of the eigenfunctions. We show that the appearance of rosette modes in the presence of slow rotation is caused by a close degeneracy in the frequency among several eigenmodes in the non-rotating case. Regarding the effect of the Coriolis force on stellar oscillations as a small perturbation, and applying quasi-degenerate perturbation theory, we can successfully reproduce the structure of rosette modes as a linear combination of several unperturbed eigenmodes, which have almost the same frequency and successive spherical degrees of the same parity. We confirm that the eigenfrequencies and the structure of the eigenfunctions that are determined by the perturbative technique are consistent with the results of more direct numerical computations, which are based on the decomposition of the eigenfunctions into a series of spherical harmonics. We discuss the characteristics of rosette modes in detail.

Porous Al2O3 microspheres prepared by a novel ice-templated spray drying technique

Abstract A novel ice-templated spray drying technique was developed for producing uniform Al 2 O 3 microspheres with controlled pore structures. Surface morphologies of microspheres demonstrated a higher sphericity degree with the increase of solid loading from 1 to 10 vol%. The pore structure of microspheres transformed from randomly distributed pores to aligned macropores, when the spray-height more than doubled using 10 vol% solid loading suspension. The thickness of the aligned pore structure was also influenced by the liquid nitrogen volume in the apparatus.

Experimental and numerical analysis of quasi-static bubble size and shape characteristics at detachment

When investigating the physical mechanisms responsible for pool boiling heat transfer, individual bubbles are commonly assumed to be spherical. This is done in order to ease the computational expense when solving the Navier–Stokes equations. However, bubbles are observed to deviate from spherical depending on fluid properties, cavity sizes and gravitational field strengths. Since it is bubble detachment volume that dictates ebullition frequency, improvements in detachment size and shape predictions would improve nucleate pool boiling heat and mass transfer models.Recent studies have shown that a numerical treatment of the capillary equation’s detachment criterion – which is a result of an interfacial pressure balance analysis – generates profiles corresponding to axis-symmetric quasi-static bubbles for adiabatic conditions. In the present work, this criterion is validated for heat induced bubbles providing the basis for a full analysis of size and shape characteristics of a detaching vapour bubble. A volume detachment correlation is validated for heat induced vapour bubbles and detachment correlations for other size and shape characteristics such as bubble height, width, apex principal radius of curvature, contact angle, and degree of sphericity are developed. Furthermore, a local stress analysis reveals detachment regimes and bubble profile regions.

Minimum Sobolev norm interpolation with trigonometric polynomials on the torus

Let q⩾1 be an integer, y1,…,yM∈[-π,π]q, and η be the minimal separation among these points. Given the samples {f(yj)}j=1M of a smooth target function f of q variables, 2π-periodic in each variable, we consider the problem of constructing a q-variate trigonometric polynomial of spherical degree O(η-1) which interpolates the given data, remains bounded in the Sobolev norm (independent of η or M) on [-π,π]q, and converges to the function f on the set where the data becomes dense. We prove that the solution of an appropriate optimization problem leads to such an interpolant. Numerical examples are given to demonstrate that this procedure overcomes the Runge phenomenon when interpolation at equidistant nodes on [-1,1] is constructed, and also provides a respectable approximation for bivariate grid data, which does not become dense on the whole domain.

One-step syntheses and properties of carbon microspheres with amino groups

This paper proposes a method that can be used to synthesize carbon microspheres with controllable sizes, rich amino groups and oxygen-containing groups. The synthesized materials are portrayed by various methods including SEM, FT-IR, XRD, and EDX. The resulting carbon spheres presented an amorphous characteristic, which displayed a broad range in diameter, high degree of sphericity, and smoothness with amino groups and oxygen-containing groups. Pyknotic and smooth silver shells were deposited on carbon spheres by electroless silver plating. Moreover, it could directly reduce Ag+ to Ag in aqueous silver nitrate. These materials can potentially be used as adsorbents for heavy-metal removal from aqueous solutions.

Theoretical calculation and analysis of ZrO2 spherical nanometer powders

ZrO2 spherical nanometer powders containing 3.5 mol% Y2O3 have been prepared via the coupling route of water/oil (W/O) emulsion with dimethyl oxalate homogenous precipitation. ZrO2 powders and their precursor powders have been characterized by XRD, TEM and SEM. According to the XRD result, phase volume fractions of powders were calculated by comparing the peaks’ intensities of spectrum. Furthermore, phase crystal lattice constants were obtained using crystal interplanar spacing formula and Bragg equation. With these results, the theoretical density of powders was analyzed. Finally, powders’ spherical degree was revealed via the method of comparison between theoretical density and actual density.

THE QUASI-BIENNIAL PERIODICITY AS A WINDOW ON THE SOLAR MAGNETIC DYNAMO CONFIGURATION

Manifestations of the solar magnetic activity through periodicities of about 11 and 2 years are now clearly seen in all solar activity indices.In this paper, we add information about the mechanism driving the 2 year period by studying the time and latitudinal properties of acoustic modes that are sensitive probes of the subsurface layers. We use almost 17 years of high quality resolved data provided by the Global Oscillation Network Group (GONG) to investigate the solar cycle changes in p-mode frequencies for spherical degrees l from 0 to 120 and 1.6 mHz < nu < 3.5 mHz. For both periodic components of solar activity, we locate the origin of the frequency shift in the subsurface layers and put in evidence for a sudden enhancement in amplitude just in the last few hundred kilometers. We also show that, in both cases, the size of the shift increases towards equatorial latitudes and from minimum to maximum of solar activity, but, in agreement with previous findings,the quasi-biennial periodicity (QBP) causes a weaker shift in mode frequencies and a slower enhancement than the one caused by the 11 year cycle. We compare our observational findings with the features predicted by different models that try to explain the origin of this QBP and conclude that the observed propertiescould result from the beating between a dipole and quadrupole magnetic configuration of the dynamo.

Microstructure and Interface of TiC &lt;i&gt;In Situ&lt;/i&gt; Synthesized Reinforced Steel-Based Surface Composite Prepared by V-EPC Infiltrating Method

In order to optimize the processing parameters of TiC/steel composite materials, in-situ TiC particle reinforced steel-based surface composites were prepared by vacuum evaporative pattern casting (V-EPC) infiltration process, and the structure and interface of the composites were investigated. The results show that, TiC particle size with Ti-C-20wt%Fe reaction system was much smaller than the composite with Ti-C reaction system in the same location of the composites. In the composites, the TiC particle size and volume fraction increased and spherical degree dropped from the tradition layers (interface between the substrate and the composite layer) to the outer surface. But the increase of TiC particle size (1-3μm) and volume fractions (25.8%-43.5%) in the composite with Ti-C-20wt%Fe reaction system was obviously lower than that of TiC particle size (1-10μm) and volume fractions (12.3%- 67.7%) in the composite with Ti-C reaction system. The bond zone between TiC particles and the matrices was totally metallurgical bonding without apparent interface. Comparing with the composite with Ti-C-xFe reaction system, the tradition layer with Ti-C reaction system has a poorer internal quality. The forming process of TiC in situ synthesized reinforced steel substrate surface composites prepared by V-EPC infiltrating process was infiltrating of the melting and carbothermal reactions of C and Ti powder the result of joint action.

Melt granulation in fluidized bed: a comparative study of spray-on versus in situ procedure

Objective: The aim of this study was to investigate the influence of process parameters, binder content and binder addition method on characteristics of the granules obtained by melt granulation (MG) in fluidized bed.Methods: Spray-on experiments were performed according to 23 full factorial design. The effect of binder content, molten binder feed rate, and spray air pressure on granule size and size distribution, granule shape, flowability and drug release rate was investigated. In the in situ experiments, the influence of binder particle size and binder content was evaluated. Solid-state characterization was performed by means of differential scanning calorimetry, X-ray powder diffraction and Fourier transform infrared spectroscopy.Results: Size of the granules obtained by spray-on procedure was significantly influenced by binder content and spray air pressure, while the width of particle size distribution was mainly affected by binder feed rate. Spray air pressure showed the most significant influence on granule shape. It was shown that smooth and spherical particles with good flow properties may be obtained by both procedures, spray-on and in situ MG. The results obtained indicated the influence of agglomeration mechanism on granule sphericity, with higher degree of granule sphericity observed when immersion and layering was the dominant mechanism. Paracetamol release from granulates was very rapid, but after compression of the granules into tablets, drug release was considerably slower. Solid-state analysis confirmed that the physical form of the granulate components remained unaffected after the MG process.Conclusion: The results presented indicate that MG in fluidized bed could be a good alternative to conventional granulation techniques.

Study on the Fabrication of Carbon Nanotube - Mesocarbon Microbead Composites

Carbon nanotube-Mesocarbon microbead composites were synthesized from coal tar pitch with carbon nanotubes (CNTs) as additive. The effect of CNTs addition and process parameters on the growth and morphologies of Mesocarbon microbeads (MCMBs) was investigated. The results show that adding CNTs enhances the nucleation and inhibits the growth and coalescence of MCMBs. Under the same thermal condensation conditions, the MCMBs made in the presence of CNTs tend to have smaller size, lower yield and more uniform size distribution, but more CNTs can lead to poor spherical degrees. Compared with the raw CNTs, the CNTs treated with blended acid can achieve better sphere and more uniform MCMBs with increasing CNTs ratio.