Packing Volume Research Articles

Raman, DSC, ESR and optical properties of lithium cadmium zinc tellurite glasses

The glasses with composition 64TeO2–15ZnO–(20−x)CdO–xLi2O–1V2O5 (0≤x≤20mol%) were prepared by conventional melt quenching technique. X-ray diffraction was used to confirm the amorphous nature. The optical absorption studies revealed that the cut-off wavelength decreases while optical energy gap (Eopt) and Urbach energy (ΔE) values increase with an increase of Li2O. Refractive index (n) evaluated from Eopt was found to decrease with increase of Li2O content. The physical parameters such as density (ρ), molar volume (Vm) and oxygen packing density (OPD) have been analyzed and discussed. The electron paramagnetic resonance (EPR) spectra of VO2+ glasses have been recorded on X-band (v=9.14GHz) at room temperature. The spin Hamiltonian parameters of VO2+ ions have been calculated. It has been found that V4+ ions in these glasses exist as VO2+ in octahedral coordination with a tetragonal distortion. Raman spectroscopic studies showed that the glass network consists of TeO4, TeO3+1/TeO3 and ZnO4 units as basic structural units. The glass transition temperature (Tg), onset crystallization (To) and thermal stability (ΔT) were determined from Differential Scanning Calorimetry (DSC).

A tree search algorithm for the container loading problem

This paper presents a binary tree search algorithm for the three dimensional container loading problem (3D-CLP). The 3D-CLP is about how to load a subset of a given set of rectangular boxes into a rectangular container, such that the packing volume is maximized. In this algorithm, all the boxes are grouped into strips and layers while three constraints, i.e., full support constraint, orientation constraint and guillotine cutting constraint are satisfied. A binary tree is created where each tree node denotes a container loading plan. For a non-root each node, the layer set of its left (or right) child is obtained by inserting a directed layer into its layer set. A directed layer is parallel (or perpendicular) to the left side of the container. Each leaf node denotes a complete container loading plan. The solution is the layer set whose total volume of the boxes is the greatest among all tree nodes. The proposed algorithm achieves good results for the well-known 3D-CLP instances suggested by Bischoff and Ratcliff with reasonable computing time.

Screening, Identification and Fermentation Process Optimization of a Wild Fungus Against Pathogens

To obtain wild mushrooms having broad-spectrum antimicrobial activity and enhance the antimicrobial compounds productivity were our purpose. The active strains were screened in terms of the methods of well diffusion assay and hypha growth rate. the fermentation parameters for antimicrobial compounds productivity were optimized by response surface analysis and orthogonal test. One white-rot fungus 0331 with broad-spectrum antagonistic to pathogens was obtained,and it was identified as Cerrena sp. by ITS-5. 8 rDNA sequences analysis. The fermentation broth showed the antimicrobial activity against Staphylococcus aureus, Escherichia coli,Monilia albican,Bacillus subtilis and Rhizoctnia solani. The optimal medium for 0331 was composed of(in g / L) : potatoes 13. 99,wheat bran 7. 00,Sucrose 41. 58,KH 2 PO 4 2. 00,MgSO 4 ·7H 2 O 2. 00,VB1 0. 027. The optimal culture conditions were as follows: the initial pH value of medium 5. 0,the fermentation period 10 d,packing volume 110ml /250ml,inoculation 8mL /100ml,rotate speed 180r / min, temperature 28℃,respectively. The 0331 strain showed obvious antimicrobial activity,with an increase of 30. 37% compared to the original fermentation parameters.

Preparation of immobilized whole cell biocatalyst and biodiesel production using a packed-bed bioreactor.

Rhizopus oryzae NBRC 4697 was selected from among promising candidates as a biocatalyst for biodiesel production. This microorganism was immobilized on to polyurethane foam coated with activated carbon for reuse, and, for biodiesel production. Vacuum drying of the immobilized cells was found to be more efficient than natural or freeze-drying processes. Although the immobilized cells were severely inhibited by a molar ratio of methanol to soybean oil in excess of 2.0, stepwise methanol addition (3 aliquots at 24-h feeding intervals) significantly prevented methanol inhibition. A packed-bed bioreactor (PBB) containing the immobilized whole cell biocatalyst was then operated under circulating batch mode. Stepwise methanol feeding was used to mitigate methanol inhibition of the immobilized cells in the PBB. An increase in the feeding rate (circulating rate) of the reaction mixture barely affected biodiesel production, while an increase in the packing volume of the immobilized cells enhanced biodiesel production noticeably. Finally, repeated circulating batch operation of the PBB was carried out for five consecutive rounds without a noticeable decrease in the performance of the PBB for the three rounds.

Thermal properties of quaternary TeO2–ZnO–Nb2O5–Gd2O3 glasses

Quaternary tellurite glass systems in the form 75TeO2–15ZnO–(10−x) Nb2O5–xGd2O3 (x=0.5, 1.0, 1.5, 2.0 and 2.5mol%) have been prepared by the melt quenching technique. Density, molar volume and oxygen packing density of every glass composition have been measured and calculated. Differential thermal analyses (DTA) have been carried out on the prepared glass systems in the temperature range 300–800K at heating rate 5, 10, 15, and 20°C/min. The glass transition, Tg and crystallization, Tc temperatures values were measured by using DTA. Kinetics parameters like activation energy of relaxation structure Et, activation energy of crystallization, Ec and order of crystallization have been calculated for every glass composition. Structural parameters like number of bonds per unit volume (nb) and average stretching force constant (F¯) have been calculated to interpret the experimental data.

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

Here we present a study on the presence of physisorbed water on the surface of aligned carbon nanotubes (CNTs) in ambient conditions, where the wet CNT array mass can be more than 200% larger than that of dry CNTs, and modeling indicates that a water layer >5 nm thick can be present on the outer CNT surface. The experimentally observed nonlinear and non-monotonic dependence of the mass of adsorbed water on the CNT packing (volume fraction) originates from two competing modes. Physisorbed water cannot be neglected in the design and fabrication of materials and devices using nanowires/nanofibers, especially CNTs, and further experimental and ab initio studies on the influence of defects on the surface energies of CNTs, and nanowires/nanofibers in general, are necessary to understand the underlying physics and chemistry that govern this system.

Hydrostatic pressure effect on hydrophobic hydration and pairwise hydrophobic interaction of methane

At room temperature, the Ben-Naim standard hydration Gibbs energy of methane is a positive quantity that increases markedly with hydrostatic pressure [M. S. Moghaddam and H. S. Chan, J. Chem. Phys. 126, 114507 (2007)]. This finding is rationalized by showing that the magnitude of the reversible work to create a suitable cavity in water increases with pressure due to both the increase in the volume packing density of water and the contribution of the pressure-volume work. According to the present approach, at room temperature, the Gibbs energy of the contact-minimum configuration of two methane molecules is a negative quantity that increases in magnitude with hydrostatic pressure. This result is not in line with the results of several computer simulation studies [T. Ghosh, A. E. Garcia, and S. Garde, J. Am. Chem. Soc. 123, 10997-11003 (2001)], and emerges because pairwise association causes a decrease in solvent-excluded volume that produces a gain of configurational/translational entropy of water molecules, whose magnitude increases with the volume packing density of the liquid phase.

Effects of fuel particle size distributions on neutron transport in stochastic media

This paper presents a study of the fuel particle size distribution effects on neutron transport in three-dimensional stochastic media. Particle fuel is used in gas-cooled nuclear reactor designs and innovative light water reactor designs loaded with accident tolerant fuel. Due to the design requirements and fuel fabrication limits, the size of fuel particles may not be perfectly constant but instead follows a certain distribution. This brings a fundamental question to the radiation transport computation community: how does the fuel particle size distribution affect the neutron transport in particle fuel systems? To answer this question, size distribution effects and their physical interpretations are investigated by performing a series of neutron transport simulations at different fuel particle size distributions. An eigenvalue problem is simulated in a cylindrical container consisting of fissile fuel particles with five different size distributions: constant, uniform, power, exponential and Gaussian. A total of 15 parametric cases are constructed by altering the fissile particle volume packing fraction and its optical thickness, but keeping the mean chord length of the spherical fuel particle the same at different size distributions. The tallied effective multiplication factor (keff) and the spatial distribution of fission power density along axial and radial directions are compared between different size distributions. At low packing fraction and low optical thickness, the size distribution shows a noticeable effect on neutron transport. As high as 1.00% relative difference in keff and ∼1.50% relative difference in peak fission power density are observed. As the packing fraction and optical thickness increase, the effect gradually dissipates. Neutron channeling between fuel particles is identified as the effect most responsible for the different neutronic results. Different size distributions result in the difference in the average number of fuel particles and their average size. As a result, different degrees of neutron channeling are produced. The size effect in realistic reactor unit cells is also studied and, from the predicted values of infinite multiplication factors, it is concluded that the fuel particle size distribution effects are not negligible.

Effects of Asphaltene Content and Temperature on Viscosity of Iranian Heavy Crude Oil: Experimental and Modeling Study

Heavy and extra heavy crude oils usually have a high weight percentage of asphaltene, which could induce many problems during production to refining processes. Also, asphaltene has the main role on the high viscosity of the heavy and extra heavy crude oils. In this paper, the effects of asphaltene characteristics on the crude oil rheological properties have been experimentally and theoretically investigated using different classes of the suspension models. For experimental investigation, the asphaltene was first precipitated from the original heavy crude oil and then 10 well-defined reconstituted heavy oil samples are made by dispersing the asphaltene into the maltene (i.e., deasphalted heavy crude oil) for measuring viscosity at a wide range of temperatures from 25 to 85 °C. Then, the viscosity of the prepared reconstituted heavy oil samples was measured using a rotational rheometer at seven different temperatures. Moreover, for modeling the viscosity behavior of the heavy oil samples versus different asphaltene contents (0–12.22 vol %) at different temperatures (25–85 °C), six equations from three groups of suspension models are used, including Pal–Rhodes (with parameters of the shape factor ν and solvation constant K), Mooney, Krieger–Dougherty, and Brouwers (with parameters of the intrinsic viscosity [η] and the maximum packing volume fraction φmax), and Bicerano et al. and Santamaria-Holek and Mendoza (with parameters of the intrinsic viscosity [η] and the critical volume fraction φc). The results of experimental study indicate that the viscosity of the reconstituted heavy oil samples increases exponentially as the asphaltene content increases at a constant temperature. Also, the viscosity of the heavy oil samples decreases significantly with increasing the temperatures from 25 to 85 °C at a constant asphaltene volume fraction.

Thermostabilization ofBacillus subtilislipase A by minimizing the structural deformation caused by packing enhancement

Enzyme thermostabilization is a critical research topic due to potential industrial benefits. Among the various reasons to increase enzyme thermostability, enhancement of residual packing at the core of the enzyme structure has been commonly accepted as a successful strategy. However, structural changes that occur with residual packing enhancement may decrease enzyme activity. In this study, a strategy to minimize structural deformation by calculating the overlapping packing volume of a single-point mutation followed by applying a double-point mutation was suggested. Four double mutants, A38V_K23A, A75V_T83A, G80A_N106A, and G172A_V100A, were selected for the in vitro experiment; three of the four showed enhancements in both thermostability and catalytic activity. In particular, G80A_N106A showed 2.78 times higher catalytic activity compared with wild type.

The Limitations of an Exclusively Colloidal View of Protein Solution Hydrodynamics and Rheology

Proteins are complex macromolecules with dynamic conformations. They are charged like colloids, but unlike colloids, charge is heterogeneously distributed on their surfaces. Here we overturn entrenched doctrine that uncritically treats bovine serum albumin (BSA) as a colloidal hard sphere by elucidating the complex pH and surface hydration-dependence of solution viscosity. We measure the infinite shear viscosity of buffered BSA solutions in a parameter space chosen to tune competing long-range repulsions and short-range attractions (2 mg/mL ≤ [BSA] ≤ 500 mg/mL and 3.0 ≤ pH ≤ 7.4). We account for surface hydration through partial specific volume to define volume fraction and determine that the pH-dependent BSA intrinsic viscosity never equals the classical hard sphere result (2.5). We attempt to fit our data to the colloidal rheology models of Russel, Saville, and Schowalter (RSS) and Krieger-Dougherty (KD), which are each routinely and successfully applied to uniformly charged suspensions and to hard-sphere suspensions, respectively. We discover that the RSS model accurately describes our data at pH 3.0, 4.0, and 5.0, but fails at pH 6.0 and 7.4, due to steeply rising solution viscosity at high concentration. When we implement the KD model with the maximum packing volume fraction as the sole floating parameter while holding the intrinsic viscosity constant, we conclude that the model only succeeds at pH 6.0 and 7.4. These findings lead us to define a minimal framework for models of crowded protein solution viscosity wherein critical protein-specific attributes (namely, conformation, surface hydration, and surface charge distribution) are addressed.

등가 구형입자를 이용한 DEM에서의 골재 슬럼프 실험 모사

PURPOSES: Simulation of aggregate slump test using equivalent sphere particle in DEM and its validity evaluation against lab aggregate slump test METHODS : In this research, aggregate slump tests are performed and compared with DEM simulation. To utilize spheric particles in YADE, equivalent sphere diameter concept is applied. As verification measures, the volume in slump cone filled with aggregate is used and it is compared with volume in slump cone filled with equivalent sphere particle. Slump height and diameter are also used to evaluate the suggested numerical method with equivalent concept RESULTS : Simulation test results show good agrement with lab test results in terms of loose packing volume, height and diameter of slumped particle clump. CONCLUSIONS : It is concluded that numerical simulation using DEM is applicable to evaluate the effect of aggregate morphological property in loose packing and optimum gradation determination based on the aggregate slump test simulation result.

Cost and energy sensitivity analysis of absorber design in CO2 capture with MEA

Amine-based CO2 capture processes appear to be the near-term technology for post-combustion CO2 removal from fossil fuel power plants. However, there is no experience with large-scale application of CO2 capture on power plants. A good absorber design is necessary to handle the large volumes of dilute flue gas with high performance, low cost and energy requirement of the plant. In the present work, multi-scale simulations of the absorber were investigated using Aspen RateSep, and a cost estimation model was developed based on mass and energy balances produced by the Aspen Plus simulations, and data from Turton et al. (2012) were applied for cost estimation. Investment costs (CAPEX) and energy requirements of the lean amine circulation pump and absorber blower for variations in the absorber design were compared for two cases: CO2 absorption from a coal-fired power plant, and CO2 absorption from a gas-fired power plant both with a net power output of 400MWe. The flue gas flow rate in the gas-fired power plant case is higher than for the coal-fired power plant, over the same net power output. In the gas-fired power plant case the absorber needs to be designed to process high volumes of flue gas and the pressure drop will often be higher than for a coal-fired power plant due to higher gas velocity. This results in higher capital and operatingcosts. Possible re-design of the absorber is studied and the results show that large electrical energy savings in the feed gas blower can be obtained when a design is chosen giving reduced absorber pressure drop. This can be achieved if the column cross sectional area is increased. This is offset by extra capital cost by a need for slightly more volume of packing. The operational design flexibility in a CO2 capture plant for a gas-fired power plant is higher than for a coal-fired power plant.

Analytical Dancoff factor evaluations for reactor designs loaded with TRISO particle fuel

A new mathematical model, the dual-sphere model, is proposed to analytically evaluate Dancoff factors of TRISO fuel kernels based on the chord method. The accurate evaluation of fuel kernel Dancoff factors is needed when one analyzes nuclear reactors loaded with TRISO particle fuel. In these reactor designs, fuel kernels are randomly distributed and shield each other, causing a shadowing effect. The Dancoff factor is a quantitative measure of this effect and is determined by the spatial distribution of fuel kernels. A TRISO fuel particle usually consists of four layers that form a coating region outside the fuel kernel. When fuel particles are loaded in the reactor, the spatial distribution of fuel kernels can be affected by the thickness of the coating region. Therefore, the coating region should be taken into account in the calculation of Dancoff factors. However, the previous model, the single-sphere model, assumes no coating regions in the Dancoff factor predictions. To address this model deficiency, the dual-sphere model is proposed by deriving a new chord length distribution function between two fuel kernels that explicitly accounts for coating regions. The new model is employed to derive analytical solutions of infinite medium, intra-fuel pebble and intra-fuel compact/pin Dancoff factors over a wide range of volume packing fractions of TRISO fuel particles, varying from 2% to 60%. Comparisons are made with the predictions from the single-sphere model and reference Monte Carlo simulations. A significant improvement of the accuracy, over the ranges of packing fractions under current investigation, has been observed. The new model provides a reliable numerical evaluation of Dancoff factors for TRISO particle fuel and can be used as a routine method for the neutronic design and analysis of reactors loaded with TRISO particle fuel.

On the interpretation of viscosity data of suspensions of asphaltene nano‐aggregates

The viscous behaviour of suspensions of asphaltene nano‐aggregates is often described in terms of the Pal and Rhodes model (Pal, Rhodes, J. Rheol. 1989, 33, 1021). The model assumes particles to be spherical in shape and takes into account the solvation or hydration of particles. However, the solvation coefficient estimated from the Pal and Rhodes model for asphaltene particles is generally too high to be realistic. Furthermore, the model does not consider the packing limitations (maximum packing volume fraction) of the asphaltene particles. A large body (14 sets) of the available viscosity data for asphaltene suspensions are reinterpreted in terms of the Krieger–Dougherty model. The data analysis indicates that asphaltene nano‐aggregates are non‐spherical disk‐shaped particles with low aspect ratio (ratio of particle thickness to particles diameter). The aspect ratio depends on the nature of the asphaltene/oil system. For a given system, it increases with the increase in the temperature. Interestingly, the maximum packing volume fraction (φm) of asphaltene particles is found to be nearly constant , independent of the nature of the asphaltene/oil system and temperature. Also the values of φm predicted from the viscosity data are in reasonable agreement with the values predicted from a percolation model. Based on the analysis carried out in this work, the following model is proposed for accurate estimation and correlation of the viscosity of asphaltene suspensions: ηr = [1 − (φ/0.37)]−0.37[η], where ηr is the relative viscosity, [η] is the intrinsic viscosity and φ is the volume fraction of asphaltene particles.

Branching Defects in Dendritic Molecules: Coupling Efficiency and Congestion Effects

An analytical model supplemented by Monte Carlo simulations specifies the statistics of branching defects in dendritic molecules as a function of the generation g as well as the maximal g for which defect-free synthesis is possible, gmax. The defects arise because of (i) imperfect coupling efficiency characterized by a constant fraction P ≤ 1 of successful add-on reactions in the absence of excluded volume effects and (ii) packing constraints associated with steric congestion at high g when the maximal density is approached. The model specifies ng, the number of junctions, and the number of defects for both g ≤ gmax and g > gmax, as well as gmax and its dependence on P. The branching polydispersity is characterized by the average number of junction–junction bonds, Xgeff. For g < gmax and efficient synthesis Xgeff is weakly reduced with respect to X, its value in defect-free molecules, and ng ∼ (Xeff – 1)g increases exponentially. In the congested regime, at g > gmax, branching is strongly reduced, and Xgeff slowly approaches 2 as Xgeff – 2 ∼ 1/g while ng eventually exhibits power law growth: ng ∼ g3 for dendrimers and ng ∼ g2 for dendronized polymers. The branching defects can be interrogated by different forms of end-group analysis utilizing the theory framework proposed.

Radiative transfer theory verified by controlled laboratory experiments

We report the results of high-accuracy controlled laboratory measurements of the Stokes reflection matrix for suspensions of submicrometer-sized latex particles in water and compare them with the results of a numerically exact computer solution of the vector radiative transfer equation (VRTE). The quantitative performance of the VRTE is monitored by increasing the volume packing density of the latex particles from 2% to 10%. Our results indicate that the VRTE can be applied safely to random particulate media with packing densities up to ∼2%. VRTE results for packing densities of the order of 5% should be taken with caution, whereas the polarized bidirectional reflectivity of suspensions with larger packing densities cannot be accurately predicted. We demonstrate that a simple modification of the phase matrix entering the VRTE based on the so-called static structure factor can be a promising remedy that deserves further examination.

Gel point behavior of colloidal unimolecular polymer (CUP) particles

The gel point of a colloidal unimolecular polymer (CUP) aqueous suspension was determined. The zero-shear viscosities of suspensions were measured by capillary viscometer and cone-and-plate rheometer. The relative viscosities were fit to the Krieger-Dougherty equation $$ {\upeta}_{\mathrm{r}}={\left[1-\frac{\phi }{\phi_{\max }}\right]}^{-\left[\upeta \right]{\phi}_{\max }} $$ to determine the maximum packing volume fraction ϕmax. The gel point was found to be much lower than the anticipated random close packing (~0.63) or hexagonal packing (~0.74). The gel point was attributed to the effect of surface water, and subsequently the thickness and density of water layer were calculated. The CUP results were compared with the rheological behavior of commercial waterborne suspension with particle size 25 and 77 nm. The packing volume fraction of colloids with different particle sizes was predicted considering the effect of surface water.

E-008 Packing Volume Densities by Coated vs Non-coated Coils in Endovascular treatment of Cerebral Aneurysms

IntroductionHydrogel coils have been introduced to efficiently increase the aneurysmal packing volumes which may, in turn, decreases the recurrence rate of the endovasularly treated cerebral aneurysms. There is no definite...

Changes in solid particle fractions of coating color in low- and high-speed blade coating

Changes in coating color composition in a recirculation loop of a coater can cause runnability and paper quality variability. Besides an increase in the coating color solids content, the average size of the solid particles increases as a result of depletion of fine materials or shear-induced aggregation. The mechanisms for changes in solid particle fractions of coating colors and control parameters are not well understood or documented. Previous work has investigated the role of coating color solids content and cohesion energy in particle segregation tendencies by using a low-speed laboratory coater. The current work extends the study to high-speed pilot-scale coating and compares the results to the laboratory-scale coater. It is proposed that similar results in regard to particle size segregation can be observed with both a low-speed laboratory coater and a high-speed pilot coater. The same parameters, such as solids volume fraction, control the particle size segregation regardless of the speed and the applicator type. If the solids volume fraction and the packing volume are high, the coating color cohesion energy is not of importance for particle segregation.