Relative Density Difference Research Articles

Fabrication of green and sintered bodies prepared by centrifugal compaction process using wet-jet milled slurries

Properties of green and sintered bodies prepared by high-speed centrifugal compaction process (HCP) using wet-jet milled slurries were investigated. At 30 vol.% solids loading, the relative packing density of compacted body prepared from wet-jet milled slurry was 67%. On the other hand, the density of compacted body prepared from ball-milled slurry was 56% at the same loadings. The difference in relative densities of the top and bottom of green bodies prepared from wet-jet milled slurry was decreased to one-third of the ones prepared from ball-milled slurry. Moreover, the linear shrinkage of the sintered bodies prepared from wet-jet milled slurries was almost constant at sintering temperatures above 1400 °C; it was found to be increasing for bodies prepared from ball-milled slurries with increasing sintering temperature. Furthermore, activation energy for grain-growth was estimated. The grain-growth of green bodies prepared from wet-jet milled slurries was promoted at lower-sintering temperatures.

Relationship of densification rate and relative density for submicron α-Al2O3 green compacts during low heating rate sintering

The sintering of α-Al2O3 powder compacts with the mean particle size of 350 nm has been investigated at constant heating rates of 0˙5–5°C min–1. Curves of the instantaneous relative density differences and the temperature for different heating rates were constructed, the changing trend of which was consistent with that of densification rate v. temperature. The correlation between densification rate and the relative density was also constructed from the beginning to the end of the sintering process. Maximum densification rates occur at the same relative density of ∼73% and are independent of heating rates. For samples with the same initial relative density, the logarithm of temperature derivative of the densification rate v. the relative density fits within a single, relatively narrow band.

Vertical Centrifugal Casting of Aluminum Matrix Particle Reinforced Composites

Centrifugal casting of composites gives rise to a certain distribution of reinforcement particles due to the natural liquid flow and solidification pattern. The particle rich regions are strongly influenced by rotational speed of the mold, particle size, relative density difference between particles and melt, initial pouring temperature, initial mold temperature, and by the nature of the particles added [1—3]. In the present work zirconia, silicon carbide, and ilmenite particles have been added to an aluminum—magnesium alloy and cast using a vertical centrifugal casting machine. The particle distribution and the resultant hardness variation have been analyzed. The particles are invariably associated with porosity. In the case of ilmenite particles, there is extensive reaction with the liquid metal. The combined effect of vol % of particles, porosity, and extent of reaction gives rise to a complex hardness variation. There is a substantial increase in hardness with particle addition. The particles tend to concentrate at the middle of the casting.

The Carbon Source Analysis for Diamond Crystal Growth from Fe-C System at High Pressure-High Temperature

Despite many studies have been carried, there is no clear understanding of the growth mechanism involved in the high-pressure and high-temperature (HPHT) diamond synthesis with metal catalyst, especially the problem about carbon source. In this paper, the lattice constants of diamond, graphite and Fe3C at HPHT were calculated with the linear expansion coefficient and elastic constant. Then based on the empirical electron theory of solids and molecules (EET), the valence electron structures of them and their common crystal planes were calculated, and the boundary condition of electron movement in the Thomas-Fermi-Dirac theory modified by Cheng (TFDC) was applied to analyzing the electron density continuity of the interface. It was found that the relative electron density differences across graphite/diamond interfaces are great and discontinuous at the first order of approximation, while the relative electron density differences across Fe3C/diamond interfaces were continuous. The results show that the carbon atom cluster is easier to decompose from Fe3C than from graphite and to transform into diamond structure, so the carbon source for diamond crystal growth may come from the decomposition of Fe3C instead of graphite. Accordingly, the diamond growth mechanism was analyzed from the viewpoint of valence electron structure.

Synergy and specificity of two Na+–aromatic amino acid symporters in the model alimentary canal of mosquito larvae

The nutrient amino acid transporter (NAT) subfamily is the largest subdivision of the sodium neurotransmitter symporter family (SNF; also known as SLC6; HUGO). There are seven members of the NAT population in the African malaria mosquito Anopheles gambiae, two of which, AgNAT6 and AgNAT8, preferably transport indole- and phenyl-branched substrates, respectively. The relative expression and distribution of these aromatic NATs were examined with transporter-specific antibodies in Xenopus oocytes and mosquito larval alimentary canal, representing heterologous and tissue expression systems, respectively. NAT-specific aromatic-substrate-induced currents strongly corresponded with specific accumulation of both transporters in the plasma membrane of oocytes. Immunolabeling revealed elevated expressions of both transporters in specific regions of the larval alimentary canal, including salivary glands, cardia, gastric caeca, posterior midgut and Malpighian tubules. Differences in relative expression densities and spatial distribution of the transporters were prominent in virtually all of these regions, suggesting unique profiles of the aromatic amino acid absorption. For the first time reversal of the location of a transporter between apical and basal membranes was identified in posterior and anterior epithelial domains corresponding with secretory and absorptive epithelial functions, respectively. Both aromatic NATs formed putative homodimers in the larval gut whereas functional monomers were over-expressed heterologously in Xenopus oocytes. The results unequivocally suggest functional synergy between substrate-specific AgNAT6 and AgNAT8 in intracellular absorption of aromatic amino acids. More broadly, they suggest that the specific selectivity, regional expression and polarized membrane docking of NATs represent key adaptive traits shaping functional patterns of essential amino acid absorption in the metazoan alimentary canal and other tissues.

Dispersion enhancement and damping by buoyancy driven flows in 2D networks of capillaries

The influence of a small relative density difference on the displacement of two miscible liquids is studied experimentally in transparent 2D networks of micro channels. Both stable displacements in which the denser fluid enters at the bottom of the cell and displaces the lighter one and unstable displacements in which the lighter fluid is injected at the bottom and displaces the denser one are realized. Except at the lowest mean flow velocity U, the average $C(x,t)$ of the relative concentration satisfies a convection-dispersion equation. The dispersion coefficient is studied as function of the relative magnitude of fluid velocity and of the velocity of buoyancy driven fluid motion. A model is suggested and its applicability to previous results obtained in $3D$ media is discussed.

Dispersion enhancement and damping by buoyancy driven flows in two-dimensional networks of capillaries

The influence of a small relative density difference (Δρ∕ρ≃3×10−4) on the displacement of two miscible Newtonian liquids is studied experimentally in transparent two-dimensional square networks of microchannels held vertically; the channel width distribution is log normal with a mean value of a=0.33mm. Maps of the local relative concentration are obtained by an optical light absorption technique. Both stable displacements in which the denser fluid enters at the bottom of the cell and displaces the lighter one and unstable displacements in which the lighter fluid is injected at the bottom and displaces the denser one are realized. Except at the lowest mean flow velocity U, the average C(x,t) of the relative concentration satisfies a convection-dispersion equation. The relative magnitude of ∣U∣ and of the velocity Ug of buoyancy driven fluid motions is characterized by the gravity number Ng=Ug∕∣U∣. At low gravity numbers ∣Ng∣<0.01 (or equivalently high Péclet numbers Pe=Ua∕Dm>500), the dispersivities ld in the stable and unstable configurations are similar to ld∝Pe0.5. At low velocities such that ∣Ng∣>0.01, ld increases like 1/Pe in the unstable configuration (Ng<0), while it becomes constant and close to the length of individual channels in the stable case (Ng>0). Isoconcentration lines c(x,y,t)=0.5 are globally flat in the stable configuration, while in the unstable case, they display spikes and troughs with a rms amplitude σf parallel to the flow. For Ng>−0.2, σf increases initially with the distance and reaches a constant limit, while it keeps increasing for Ng<−0.2. A model taking into account buoyancy forces driving the instability and the transverse exchange of tracer between rising fingers and the surrounding fluid is suggested and its applicability to previous results obtained in three-dimensional media is discussed.

Fountains impinging on a density interface

We present an experimental study of an axisymmetric turbulent fountain in a two-layer stratified environment. Interacting with the interface, the fountain is observed to exhibit three regimes of flow. It may penetrate the interface, but nonetheless return to the source where it spreads as a radially propagating gravity current; the return flow may be trapped at the interface where it spreads as a radially propagating intrusion or it may do both. These regimes have been classified using empirically determined regime parameters which govern the relative initial momentum of the fountain and the relative density difference of the fountain and the ambient fluid. The maximum vertical distance travelled by the fountain in a two-layer fluid has been theoretically determined by extending the theory developed for fountains in a homogeneous environment. The theory compares favourably with experimental measurements. We have also developed a theory to analyse the initial speeds of the resulting radial currents. The spreading currents exhibited two different flow regimes: a constant-velocity regime and an inertia-buoyancy regime in which the front position,R, scales with time,t, asR∼t3/4. These regimes were classified using a critical Froude number which characterized the competing effects of momentum and buoyancy in the currents.

Numerical Study of Functionally Graded Materials

One-dimensional comprehensive mathematical model coupling particle movement and thermal conduction in the casting mould system is developed. A formula for pressure in liquid metal during the centrifuge process is derived. The model takes into consideration the propagation of solidification front and movement of particles due to centrifugal acceleration which takes place either in the same or in opposite direction to that of the solidification front depending on the relative density difference between the particles and melts. In the force balance expression, repulsive force term is incorporated for the particles that are at the vicinity of the solid/liquid interface to calculate the particle segregation pattern in the casting region The effects of various process parameters such as, rotational speed of the mold, size of the reinforcing material, relative density difference between the particle and melt, initial pouring temperature of the liquid melt, mold pre-heating temperature, heat transfer coefficient between the casting/mold interface are studied. It is noted that for a given set of operating conditions, the thickness of the particle rich region in the composite decreases with increase in rotational speed, particle size, relative density difference between the particle and melt, initial pouring temperature and initial mold temperature. With decrease in the heat transfer coefficient between the casting/mold interface, the solidification time increases which, in turn, results in more intense segregation of solid particulates. Again, with increase in the initial volume fraction of the solid particulates, both the solidification time as well as the final thickness of the particulate rich region increase.

Relationship between the orientation of texture and heteroepitaxy of diamond and related materials films on silicon single crystal and the valence electron structure of the interface

Diamond and cubic boron nitride films have already been applied practically because of their excellent properties. The specific orientations of the films have special meaning on their application in optics and microelectronics fields. In this paper, the relative electron density differences of the interface between the different crystal planes of silicon substrate and those of diamond and cubic boron films are calculated with the empirical electron theory in solids and molecules. Analyses on the calculation results show that in the range of the researched films, the smaller the relative electron density difference between the film and the substrate is, the stabler the film is in thermodynamics. Therefore, the electron density difference is the essential factor of determining the orientation of the texture and heteroepitaxy of the films. The deductions accord well with the experimental facts. The calculation methods and the theory not only provide a new angle of view for the research of the growth mechanism of diamond film and cubic boron nitride film on the silicon substrate, but also provide a possible direction for the prediction of the orientation of other films.

Comparison of opioid receptor binding in horse, guinea pig, and rat cerebral cortex and cerebellum

ObjectiveTo compare the density and binding characteristics of opioid receptor subtypes in horse, rat, and guinea pig cerebral cortex and cerebellum. Study designProspective receptor binding study. AnimalsWhole brains were obtained from four neurologically normal adult horses during necropsy. Rat and guinea pig brains were obtained commercially. MethodsThe cerebellum and cerebral cortex were dissected from each brain, and tissue homogenates prepared. A radioligand binding technique with the highly selective ligands [3H]-DAMGO, [3H]-U69593, and [3H]-DPDPE was used to identify the mu- (μ), kappa- (κ) and delta- (δ) opioid receptors, respectively. Competitive binding assays were performed with these ligands and varying concentrations of one of multiple unlabeled ligands. ResultsWhile there were marked species differences in relative densities of opioid receptors, all radioligands interacted with their binding sites with high, nanomolar affinity in both the cerebral cortex and cerebellum. In the horse cerebral cortex, the percentages of total opioid binding sites for the μ-, κ- and δ-receptors were 71%, 14% and 15%, respectively. In the rat and guinea pig cerebral cortex, the corresponding values were 56%μ-, 4%κ- and 40%δ-receptors, and 25%μ-, 37%κ- and 38%δ-receptors, respectively. In horse and guinea pig cerebellum, the binding was 37%μ-, 59%κ- and 4%δ-receptors, and 15%μ-, 76%κ- and 10%δ-receptors, respectively. For competitive analysis, all competitors of the μ-, κ- and δ-receptors completely displaced [3H]-DAMGO, [3H]-U69593, and [3H]-DPDPE and had inhibitory constants in the nanomolar range. Conclusion and clinical relevanceHorses used in this study had a greater density of μ-receptors in the cerebral cortex compared with rats and guinea pigs but without further characterization of the functional role of these receptors it is impossible to determine the clinical significance of these data.

Effects of image artifacts on gray-value density in limited-volume cone-beam computerized tomography

An in vitro study was designed to investigate the influence of projection data discontinuity-related artifacts in limited-volume cone-beam computerized tomography (CBCT) imaging of the jaws. Test objects were positioned in 4 patterns in a water-filled phantom as follows: bimandible and vertebrae, bimandible, left mandible and vertebrae, and left mandible. The CT imaging of the left molar region was performed using image intensifier (II)- and flat panel detector (FPD)-based CBCT scanners. The CT value of the mandible and the adjacent soft tissue region were analyzed for density by means of an 8-bit grayscale. The effects of artifacts were scored as the difference in relative density between the lingual and buccal soft tissue. The intensity of artifacts increased when more objects were presented outside the area being imaged. Fewer artifacts were noted in images produced by the particular FPD CBCT used in this investigation. The CBCT system using an FPD resulted in fewer artifacts than the CBCT system using an II in this particular study.

Similarity solutions of vertical plane wall plume based on finite analytic method

The turbulent flow of vertical plane wall plume with concentration variation was studied with the finite analytical method. The k-epsilon model with the effect of buoyancy on turbulent kinetic energy and its dissipation rate was adopted. There were similarity solutions in the uniform environment for the system of equations including the equation of continuity, the equation of momentum along the flow direction and concentration, and equations of k, epsilon. The finite analytic method was applied to obtain the similarity solution. The calculated data of velocity, relative density difference, the kinetic energy of turbulence and its dissipation rate distribution for vertical plane plumes are in good agreement with the experimental data at the turbulent Schmidt number equal to 1.0. The variations of their maximum value along the direction of main flow were also given. It shows that the present model is good, i.e., the effect of buoyancy on turbulent kinetic energy and its dissipation rate should be taken into account, and the finite analytic method is effective.

Density Determination of a Small Isotopically Enriched Silicon Single Crystal

For a new determination of the Avogadro constant using small crystals of isotopically enriched silicon, the density of a sample was determined at Physikalisch-Technische Bundesanstalt. The sample has a mass of 58 g and a 28Si enrichment of about 99.98%. Its density was compared by the pressure-of-flotation method to the density of a large hollow transfer standard that was manufactured from natural silicon, to have the same density. The flotation measurement yielded a relative density difference of 0.64(10) 10-6. The density of the transfer standard was then measured by hydrostatic weighing, which is traceable to a primary density standard. Thus, the density of the small 28Si sample was determined to be 2320.08031(40) kg/m 3, i.e., with a relative standard uncertainty of 0.17 10-6

VALENCE ELECTRON STRUCTURE ANALYSIS OF INTERFACE OF FeAl/TiN COMPOSITES

Based on Pauling's nature of chemical bond, the valence electron structures of TiN and FeAl have been constructed, and the relative electron density differences (REDD) between the low index plane of TiN and FeAl , respectively, have been calculated. [110] FeAl //[110] TiN crystallography orientation has been set up from the minimization of the electron density difference across the interface. From the viewpoint of improving the mechanical properties of composites, the formation of such structures must been engineered in the fabrication processing.

Low Density Sub-Critical CO2-Blown Solid-State PLA Foams

This paper presents a characterization of the PLA-CO2 system for solid-state foaming process with a particular goal of producing low density foams. The diffusivity of CO2 in PLA increases with increasing saturation pressures. The results show that low relatively density (lower than 10%) can be achieved in a wide processing window. The cell size can vary from tens of microns to several hundreds of microns depending on the solid-state foaming process parameters. There are significant differences in relative density and cell size for 2 and 3 MPa saturation cases, which are likely due to the much higher crystallinity at 3 MPa (26.4%) compared to 2 MPa (9.7%). Foams with cell size of around 300 μm and relative density of 3% were produced at 2 MPa saturation. It was observed that the higher the gas pressure, the higher the rate of gas-induced crystallization. Further, the gas-induced crystallization as well as the gas concentration in PLA during sorption reach their respective maximum values at approximately the same time for all gas pressures explored. For specimens saturated at 2 MPa, there is a substantial jump in crystallinity (from 5.2% to 23.4%) after foaming.

Numerical Simulation of Pressure Influence on Workpiece Properties during Thixoforging

Numerical simulation of pressure influence on the relative densities of both solid and hollow cylindrical workpieces during Thixoforging was carried out by using ANSYS software. The results showed that there was a big difference in relative density between different points within the workpiece during Thixoforging with the use of a single punch. Therefore, partial feeding with the help of assembly punches was proposed to improve workpiece density uniformity and properties, and the effectiveness of this approach was well-demonstrated by numerical simulation.

Wolbachia transinfection in Aedes aegypti: a potential gene driver of dengue vectors.

The endosymbiotic bacteria in the genus Wolbachia are capable of inducing a wide range of reproductive abnormalities in their hosts, including cytoplasmic incompatibility (CI), which could lead to the replacement of uninfected host populations with infected ones. Because of this, Wolbachia have attracted considerable interest as a potential mechanism for spreading disease-blocking transgenes through vector populations. Here we report the establishment of double Wolbachia transinfection by direct adult microinjection of Wolbachia from naturally double-infected Aedes albopictus to Aedes aegypti, the most important mosquito vector of infectious viral diseases, and a mosquito in which natural Wolbachia infections are not known to occur. We further demonstrate that incomplete CI is induced in these double-transinfected mosquitoes. Comparisons of fitness traits between naturally uninfected and transinfected Ae. aegypti lines indicated one significant difference in favor of the latter, namely, an increased number of eggs laid. Levels of CI expression corresponded to the Wolbachia density. There were large differences in relative Wolbachia density between reproductive and nonreproductive tissues in both Ae. albopictus and transinfected Ae. aegypti, except Malpighian tubule, which implied the preferred establishment of Wolbachia within reproductive tissue. Results from a simulation model confirm that population replacement by transinfected Ae. aegypti is possible over time. The establishment of Wolbachia double infections in Ae. aegypti by direct adult microinjection and the demonstration of CI expression in this new host suggest that Wolbachia could be experimentally transferred into vector species and could also be used as a gene-driving system to genetically manipulate vector populations.

Peri-prosthetic bone mineral density after total knee arthroplasty

We compared peri-prosthetic bone mineral density between identical cemented and cementless LCS rotating platform total knee arthroplasties. Two matched cohorts had dual energy x-ray absorptiometry scans two years post-operatively using a modified validated densitometric analysis protocol, to assess peri-prosthetic bone mineral density. The knee that was not operated on was also scanned to enable the calculation of a relative bone mineral density difference. Oxford Knee and American Knee Society scores were comparable in the two cohorts. Statistical analysis revealed no significant difference in absolute, or relative peri-prosthetic bone mineral density with respect to the method of fixation. However, the femoral peri-prosthetic bone mineral density and relative bone mineral density difference were significantly decreased, irrespective of the method of fixation, particularly in the anterior distal portion of the femur, with a mean reduction in relative bone mineral density difference of 27%. There was no difference in clinical outcome between the cemented and cementless LCS total knee arthroplasty. However, both produce stress-shielding around the femoral implants. This leads us to question the use of more expensive cementless total knee components.

Mathematical modeling of particle segregation during centrifugal casting of metal matrix composites

A one-dimensional transient heat-transfer model coupled with an equation for force balance on particles is developed to predict the particle segregation pattern in a centrifugally cast product, temperature distribution in the casting and the mold, and time for complete solidification. The force balance equation contains a repulsive force term for the particles that are in the vicinity of the solid/liquid interface. The solution of the model equations has been obtained by the pure implicit finite volume technique with modified variable time-step approach. It is seen that for a given set of operating conditions, the thickness of the particle-rich region in the composite decreases with an increase in rotational speed, particle size, relative density difference between particles and melt, initial pouring temperature, and initial mold temperature. With reduced heat-transfer coefficient at the casting/mold interface, the solidification time increases, which, in turn, results in more intense segregation of solid particulates. Again, with increased initial volume fraction of the solid particulates in the melt, both the solidification time and the final thickness of the particulate-rich region increase. It is noted that for Al-Al2O3 and Al-SiC systems, in castings produced using finer particles, lower rotational speeds, and an enhanced heat-transfer coefficient at the casting/mold interface, the volume fraction of particles in the outer layer of the casting remains more or less the same as in the initial melt. However, for castings produced with coarser particles at higher rotational speeds and reduced heat-transfer coefficients at the casting/mold interface, intense segregation is predicted even at the outer periphery of the casting. In the case of the Al-Gr system, however, intense segregation is predicted at the innermost layers.