Packing Volume Research Articles

Modelling the relative permittivity of anisotropic insulating composites

Three models have been developed for predicting the dielectric permittivity of insulating composites with inclusions of different lengths (from nm and larger) and different shapes. Firstly, for approximately periodic materials, a finite element model based on a smallest repeating box method was used in order to mimic frameworks with fibres, crystals, clay platelets, foams and lamellar layers. The introduction of parameters for relative aspect ratio, overlap, rotation and packing density made the model very flexible while maintaining its simplicity. Secondly, a finite element composite model with oriented, randomly positioned particles of different shapes was constructed. Thirdly, an analytical relationship to approximate the effective permittivity of two- or three-phase insulators with brick-shaped inclusions was derived. For a wide range of volume fractions, permittivity ratios and packing conditions, this model gave solutions very close to corresponding finite element simulation data for lamellae, much closer than all the other analytical relationships found in the literature. Results obtained by simulation were in agreement with experimental data from the literature for composites of micrometre-sized hollow glass spheres in epoxy and nanocomposites of mica platelets in polyimide, provided that a third (interfacial) component was introduced.

New fuel rod design based on LEU/Th fuel and an assessment on in-core fuel cycle length of the MHR core

The current Modular Helium Reactor (MHR) fuel cycle uses fissile LEU (19.8 wt% U-235) and depleted uranium in separate TRISO particles, in a single fuel rod within a graphite matrix. The TRISO particle volume packing fraction (PF) in the fuel rods is 29%, of which the LEU particle PF is 62%. The lifetime between refuelings is about 476 effective full power days (EFPD). In this paper we assess the possibility of replacing the depleted uranium TRISO particles with thorium TRISO particles, and evaluate the impact of such replacement on fuel cycle length. A preliminary scoping study was performed to determine the most promising fuel rod/zoning configurations. The scoping study indicates that there is advantage to separating the thorium TRISO particles from the LEU particles at the fuel rod level instead of mixing them within a single rod. An axial checkerboard distribution of the fuel rods where all uranium and all thorium rods are interchangeable along the axial direction within the graphite block is the most promising configuration that was identified in this study and can be lead to a fuel cycle length extension of 50–80% relative to the current design, with only a modest increase in the fissile material loading (15–20%). To this advantage can be added the benefit of a significant reduction in nuclear waste and in health risk. This study also lays the foundation for improving the fuel rod arrangement within the graphite block and the graphite blocks within the entire reactor core. The analysis is limited to a once – through fuel cycle based on in situ fissioning of the U-233, without further separation and reprocessing. The preliminary heat transfer analysis indicates that the maximum temperature in the fuel will be raised by about 10–15% over that of current MHR design.

Vibrational spectral analysis of structural modifications of Cr 2O 3 containing oxyfluoroborate glasses

Infrared and Raman spectra of oxyfluoroborate glasses of the compositions 20CaF 2–20 ZnO–(60-x) B 2O 3-x Cr 2O 3 with 0 ≤ × ≤ 0.10 mol% (x = 0, 0.02, 0.04, 0.05, 0.06, 0.07, 0.08 and 0.1) have been analyzed in order to explain the role of Cr 2O 3 on the structure of these glasses. Density, molar volume, oxygen molar volume and oxygen packing density are determined to explain the packing of the atoms in the glasses. From these studies, the existence of different borate groups like di-, tri-, tetra-, penta-, ortho-, pyro- and metaborates in these glasses is established. With the increase in the concentration of Cr 2O 3 up to 0.06 mol%, conversion of BO 3 units into BO 4 units and above this mole fraction the reconversion of BO 4 units into BO 3 units is observed. The breaking and reforming of the boroxol ring is explained from the Raman spectral studies of these glasses.

Glass Formation and Shear Elasticity in Dense Suspensions of Repulsive Anisotropic Particles

Kinetic vitrification, shear elasticity, and the approach to jamming are investigated for repulsive nonspherical colloids and contrasted with their spherical analog. Particle anisotropy dramatically increases the volume fraction for kinetic arrest. The shear modulus of all systems increases roughly exponentially with volume fraction, and a universal collapse is achieved based on either the dynamic crossover or random close packing volume fraction as the key nondimensionalizing quantity. Quantitative comparisons with recent microscopic theories are performed and good agreement demonstrated.

Empirical modelling and dual-performance optimisation of a hydrogen sulphide removal process for biogas treatment

This study was conducted in order to investigate the use of a simple, low-cost technology for the removal of hydrogen sulphide (H(2)S) from biogas, consisting of an anoxic biotrickling filter. Modelling and optimisation of the process was achieved by studying two independent variables (H(2)S concentration and biogas flowrate) and two simultaneous performance criteria (H(2)S removal efficiency (%) and H(2)S loading rate (g/(m(3) bed day)), which were inversely related. The experiments were carried out on a bioreactor with a 12 L packing volume. H(2)S concentration and biogas flowrate were varied in the range of 2000-4000 ppm(v) and 10-70 L/h, respectively. A model sensitivity analysis indicated the influence of the process variables on the bioreactor performance. Process optimisation was undertaken on a H(2)S removal efficiency basis, while maintaining a target H(2)S loading rate, depending on the desired quality for the biogas use and the technological requirements.

E-039 Coil packing volume in the treatment of ruptured intracranial aneurysms and the rate of recurrence

IntroductionThe recanalization rate of cerebral aneurysms treated by coil embolization has been reported to be as high as 60%. Several characteristics have been shown to correlate with coil compaction and...

Optical band gap, glass transition temperature and structural studies of (100 − 2 x)TeO 2– xAg 2O– xWO 3 glass system

Optical absorption, differential scanning calorimetry (DSC) and Raman studies have been carried out on (100 − 2 x)TeO 2– xAg 2O– xWO 3 (7.5 ≤ x ≤ 30) glass system. The Raman spectra showed that the structure of glass network consists of [TeO 4], [TeO 3]/[TeO 3+1], [WO 4] units. The glass transition temperature ( T g ) values were measured from DSC thermogram and the variation in T g has been discussed in terms of physical parameters like number of bonds per unit volume ( n b ), average cross-link density ( n c ¯ ), average stretching force constant ( F ¯ ), oxygen molar volume ( V o ) and oxygen packing density (OPD) values. The cut-off wavelength ( λ c), optical band gap ( E opt ), Urbach energy (Δ E) and refractive index ( n) values were calculated from optical absorption data. The observed decrease in optical band gap ( E opt ), Urbach energy (Δ E) and increase in refractive index ( n) values have been discussed in terms of structural changes brought about by WO 3 and Ag 2O incorporation in to TeO 2 network.

Vortex magnetic field mixing with anisometric particles

Recently, we reported a vigorous, scale-adaptive mixing technique suitable for microfluidic applications, wherein a suspension of spherical magnetic particles is subjected to a vortex magnetic field, which induces the formation of dynamic particle chains that efficiently stir the solution. Here we explore the dependence of the mixing torque on particle shape, and show that increasing degrees of shape anisometry (i.e., spheres, platelets, rods) give increased mixing torque at the same particle volume fraction. Moreover, all particles, regardless of shape, exhibit similar dependencies of the mixing torque on the vortex field parameters: the torque is maximized in a balanced vortex magnetic field, is proportional to the square of the field strength, and is independent of the field frequency. However, the torque advantage of anisometric particles is somewhat offset by their increased packing volume, which can make the removal of trapped fluid difficult.

Selective Absorption of H2S from a Gas Mixture with CO2 by Aqueous N-Methyldiethanolamine in a Rotating Packed Bed

In this work, selective absorption of H2S from a gas mixture with CO2 into N-methyldiethanolamine (MDEA) is investigated experimentally and theoretically in a rotating packed bed (RPB). In the RPB, various rotating speeds, gas flow rates, liquid flow rates, and concentrations of MDEA aqueous solutions were studied by means of the evaluation of removal efficiency, selectivity, and overall volumetric mass transfer coefficient. The reaction−diffusion mass transfer model based on penetration theory for the selective absorption process is developed, accordingly. The results of experiment and model show that the uppermost function of RPB in selective absorption of H2S is to restrain the CO2 removal efficiency but sharply intensify the absorption of H2S. The mass transfer coefficient of CO2 absorption is enhanced in RPB. However, the total amount of CO2 mass transfer virtually is low because of the short gas−liquid contact time, small volume of packing, and large gas−liquid ratio within the RPB, and the CO2 remo...

Control of Morphological and Rheological Properties of Carrot Cell Wall Particle Dispersions through Processing

A range of thermal and mechanical processes were used to create dispersions with different particle morphologies, i.e., systems that contain primarily plant cell wall clusters with an average particle size (d(0.5)) of ∼200 µm, single cells ((d(0.5) = ∼70 µm) or cell fragments (d(0.5) = ∼40 µm). The small and large deformation rheology (viscoelastic properties and flow properties) of these dispersions, with a range of total solid contents covering textures varying from a fluid to a paste, were determined. The particle dispersions showed weak gel-like behaviour. Their elastic modulus (G′) as a function of total solid content exhibited three regions of different rheological behaviours. The particles formed particulate colloidal networks at relatively low solid content. The interaction of particles contributed to the sharp increase in the elastic modulus of the dispersion in the concentrated region. Further packing of particles beyond the critical packing volume fraction, caused the G′ for the ‘cluster-cell’ and the ‘single-cell’ dispersions to reach a plateau value. This is due to particle deformation resulting in changes in their microstructure and their ability to pack closely. Plant particle dispersions displayed abrupt yielding at the critical stress with a 3–4 order decrease in viscosity and high yield stress at low solids due to the formation of particulate colloidal network.

A Tree Search Algorithm for Solving the Container Loading Problem

This paper presents a tree search algorithm for the three-dimensional container loading problem (3D-CLP). The 3D-CLP is the problem of loading a subset of a given set of rectangular boxes into a rectangular container so that the packing volume is maximized. The method includes two variants: the full-support variant guarantees full support from below for all packed boxes, although this constraint is not taken into account by the nonsupport variant. The guillotine cut constraint is considered by both variants. The method is mainly based on two concepts. On the one hand, the block building approach is generalized. Not only are blocks of identical boxes in the same spatial orientation applied but also blocks of different boxes with small inner gaps. On the other hand, the tree search is carried out in a special fashion called a partition-controlled tree search. This makes the search both efficient and diverse, enabling a sufficient search width as well as a suitable degree of foresight. The approach achieves excellent results for the well-known 3D-CLP instances suggested by Bischoff and Ratcliff [Bischoff, E. E., M. S. W. Ratcliff. 1995. Issues in the development of approaches to container loading. Omega 23(4) 377–390] with reasonable computing time.

Lipid second messengers and related enzymes in vertebrate rod outer segments

Rod outer segments (ROSs) are specialized light-sensitive organelles in vertebrate photoreceptor cells. Lipids in ROS are of considerable importance, not only in providing an adequate environment for efficient phototransduction, but also in originating the second messengers involved in signal transduction. ROSs have the ability to adapt the sensitivity and speed of their responses to ever-changing conditions of ambient illumination. A major contributor to this adaptation is the light-driven translocation of key signaling proteins into and out of ROS. The present review shows how generation of the second lipid messengers from phosphatidylcholine, phosphatidic acid, and diacylglycerol is modulated by the different illumination states in the vertebrate retina. Findings suggest that the light-induced translocation of phototransduction proteins influences the enzymatic activities of phospholipase D, lipid phosphate phosphatase, diacylglyceride lipase, and diacylglyceride kinase, all of which are responsible for the generation of the second messenger molecules.

Spectral responses in granular compaction

The slow compaction of a tapped granular packing is reminiscent of the low-temperature dynamics glasses. Here, I study the dynamics of granular compaction by means of a volumetric spectroscopy. While the specific packing volume v displays glassy aging and memory effects at low tapping amplitudes Gamma, the dynamic volumetric susceptibility chi(v)= partial differentialv/ partial differentialGamma displays minimal glassy effects, and its frequency spectrum gives no indication of a rapidly growing time scale. These features are contrast sharply with that found in the dielectric and magnetic susceptibilities of structural and spin glasses. Instead, chi(v) appears to exhibit the behavior of a dynamic configurational specific heat, such as that obtained from computer simulations of spin-glass models. This suggests that the glassy dynamics of granular compaction is controlled by statistically rare processes that diverge from the typical dynamics of the system. From modifications of the dynamical spectrum by finite system size, I suggest that these glassy processes derive from large-scale collective particle rearrangements.

Evaluation of a hybrid upflow anaerobic sludge-filter bed reactor: effect of the proportion of packing medium on performance

The aim of this study was to determine the effects of the volume occupied by the filter bed zone on the behavior of an anaerobic hybrid UASFB reactor. This configuration contains a sludge bed in the lower part of the reactor and a filter bed in the upper part. Three such reactors, each with a working volume of 9.8-L, were studied; these differed in proportion of packing medium occupying 50, 35 and 20% of the working volume of the reactors, respectively. All the reactors were fed with wine distillery vinasse and were operated for a period of 232 days at 33+/-1 degrees C with increasing OLRs. No significant differences were observed between the reactors for the range of OLRs studied. Indeed, relatively high OLRs could be reached for all the three reactors with an average OLR of about 18 g COD/L d towards the end of the experiment, while maintaining a constant HRT of 26 h. COD(t) and COD(s) removal efficiencies were always more than 80 and 86%, respectively, even for the highest OLR. High quantities of VS were accumulated in the reactors with an average value of 438+/-17 g per reactor. Most of the biomass was in the sludge bed zone suggesting that this part was playing a major role in COD removal. The internal packing medium on the top of the reactor had a key role in retaining the small flocculated particles inside the reactor, while minimizing the escape of solids in the effluent. This study suggests that low packing volume ratios can be used in the design of UASFB reactors, which allows a reduction in the costs of packing medium required as the supports are expensive.

On the partitioning of benzene between water and n-alkanes

The magnitude of the work of cavity creation increases with the n-alkane chain-length due to the volume packing density increase, in line with expectations based on correlations with surface tension, cohesive energy density, and the inverse of isothermal compressibility. Also the magnitude of the Gibbs energy gain to turn on benzene–alkane attractive interactions increases with the n-alkane chain-length, but to a lesser extent than the work of cavity creation, thus benzene solubility, under Ben-Naim standard conditions, slightly decreases on lengthening the alkyl chain, in line with experimental data. It is unjustified to apply a Flory–Huggins correction to the Ben-Naim standard Gibbs energy of transfer.

Disordered jammed packings of frictionless spheres

At low volume fraction, disordered arrangements of frictionless spheres are found in un--jammed states unable to support applied stresses, while at high volume fraction they are found in jammed states with mechanical strength. Here we show, focusing on the hard sphere zero pressure limit, that the transition between un-jammed and jammed states does not occur at a single value of the volume fraction, but in a whole volume fraction range. This result is obtained via the direct numerical construction of disordered jammed states with a volume fraction varying between two limits, $0.636$ and $0.646$. We identify these limits with the random loose packing volume fraction $\rl$ and the random close packing volume fraction $\rc$ of frictionless spheres, respectively.

Loose packings of frictional spheres

We have produced loose packings of cohesionless, frictional spheres by sequential deposition of highly-spherical, monodisperse particles through a fluid. By varying the properties of the fluid and the particles, we have identified the Stokes number (St)—rather than the buoyancy of the particles in the fluid—as the parameter controlling the approach to the loose packing limit. The loose packing limit is attained at a threshold value of St at which the kinetic energy of a particle impinging on the packing is fully dissipated by the fluid. Thus, for cohesionless particles, the dynamics of the deposition process, rather than the stability of the static packing, defines the random loose packing limit. We have made direct measurements of the interparticle friction in the fluid, and present an experimental measurement of the loose packing volume fraction, ϕRLP, as a function of the friction coefficient μs.

Ovine Prion Polymorphisms Investigated by Threading to a Model Left Handed Beta Helical Structure using Molecular Dynamics Simlation

We use AMBER all atom molecular dynamics (MD) to assess the stability of a model of the prion protein in its disease-causing conformation, PrPsc. The model is based upon threading the ovine prion sequence onto a template left-handed beta-helical (LHBH) structure with 18 residues per turn. Five polymorphisms in the sheep prion protein, VRQ, ARQ, ARH, AHQ, and ARR, have been identified at residues 136, 154, and 171 respectively, which are roughly 18 amino acids apart which thus align approximately on the LHBH. Threading of the sequence was thus done with an emphasis on the locations of these special sites as a means to investigate their possible role in disease susceptibility as well as investigating the overall viability of the LHBH as a structural candidate for PrPsc. In comparison to known left handed beta-helical proteins, the resulting model for VRQ is shown in all atom MD to 10 ns to exhibit similar stability as indicated by a low root mean square deviation, the presence of substantial side-chain to side-chain hydrogen bonding, and volume packing fraction. Interestingly, and in corroboration with experimental data that it is a disease resistant variant, the same model for ARR exhibits much less stability. Each polymorphic site was also investigated individually by comparing results from models with only one site different and showed a good correlation to experimental data regarding the relation of the variants to disease susceptibility.

Volumetric Properties of Aqueous Solutions of Tetramethyl-bis-urea between 278.15 and 338.15 K at Atmospheric Pressure

Densities of aqueous solutions of tetramethyl-bis-urea (TMbU) with solute mole fractions ranging up to 7.0×10−2 have been measured with an uncertainty of 1.5×10−5 g⋅cm−3, at 278.15, 298.15, 318.15, and 338.15 K using a vibrating-tube densimeter. The partial molar volumes and expansibilities of TMbU (down to the infinite dilution) and water have been computed. The effects of solute concentration and temperature on the volume packing changes, caused by dissolution (and hydration) of TMbU in an aqueous medium, have been considered.

Measurement of granular entropy

Recently, Dean and Lefèvre [Phys. Rev. Lett. 90, 198301 (2003)] developed a method for testing the statistical mechanical theory of granular packings proposed by Edwards and co-workers [Physica A 157, 1080 (1989); Phys. Rev. E 58, 4758 (1998)]. The method relies on the prediction that the ratio of two overlapping volume histograms should be exponential in volume. We extend the method by showing that one can also calculate the entropy of the packing and also that the method can yield false positive results when the histograms are Gaussians with nearly identical variances. We then apply the method to simulations and experiments of granular compaction. The distribution of global volumes (the volume of the entire packing) is nearly Gaussian and it is difficult to conclude if the theory is valid. On the other hand, the distribution of Voronoï volumes clearly obeys the theoretical prediction.