Relative Density Difference Research Articles

Measurement of powder flow in a screw feeder by x-ray penetration image analysis

A method for visualizing powder flow in a screw feeder is proposed using x-ray penetration image analysis. With this method, metal minute particle tracers with high absorption ratios are injected into the powder flow, and the motion of tracers is observed using x-ray penetration. This method yields a time series of powder flow images. It is confirmed for powder flow in a screw feeder that the tracer movement ratio agrees well with that of the powder, and a relative density difference of less than 20 times does not cause any distinct problems with tracer response. The visualization method clarified that the powder inside the feeder travels at about one-third the velocity of the screw movement rate along the transmission direction and the powder flow is highly turbulent and loses speed in the region around the screw blade edge.

Analysis of the blennioid assemblages associated with different rocky shore habitats in the Ligurian Sea

The differences among blennioid assemblages (families Blenniidae and Tripterygiidae) on different habitats were assessed at two localities of the Ligurian Sea, namely Arenzano and Riva Trigoso. The assemblage composition and species relative density were evaluated visually on four different habitats of diverse wave exposure and substratum orientation (macro‐habitat characteristics): two vertical intertidal and subtidal habitats (exposed and sheltered rockwalls) and two horizontal subtidal habitats (semi‐exposed flat rock and boulders and pebbles). Each habitat was also characterized in relation to micro‐habitat features, such as substratum complexity, heterogeneity and amount of algae cover. Patterns of differences among habitats in assemblage variables and fish density, and the influences of macro‐ and micro‐habitat features on these patterns were studied at small (within localities) and large (across localities) spatial scales. Higher values of species richness (S), diversity and evenness (J) were generally associated with vertical habitats, as a result of a positive correlation with substratum orientation. The presence of an intertidal zone in the rockwall habitats may partially explain the observed differences in assemblage variables between vertical and horizontal habitats. The strength of relationships between S, and J and the other investigated habitat variables (exposure, complexity, heterogeneity and algae cover) varied greatly depending on spatial scale. All these relationships were positive, except for complexity. Significant variation in the assemblage total density among habitats was recorded only at Arenzano, where a larger number of fishes were counted on rockwalls rather than on the horizontal habitats. The positive effect of orientation on fish total density was strictly dependent on spatial scale. Fish total density showed a negative correlation with complexity and a positive correlation with heterogeneity, both relationships being unaffected by spatial scale. The unexpected relationship with complexity was probably due to the fact that, in the most complex habitat (i.e. boulder and pebbles), the potential positive effect of high complexity on fish density might be overcome by the negative influence of other environmental features, such as horizontal orientation and low wave exposure. Complexity and heterogeneity thus seemed good predictors of fish total density, but their role needs to be carefully interpreted. The most marked differences in species composition and relative density were found between rockwalls and the other habitats, mostly due to an unbalanced distribution of some stenoecious species. Variations in species relative density were related to different combinations of both macro‐ and micro‐habitat features, and these relationships usually changed depending on spatial scale.

A Case History in Fishing Regulations in Great Smoky Mountains National Park: 1934–2004

AbstractSince the establishment of Great Smoky Mountains National Park (GRSM) in 1934, fisheries managers have utilized about every angling regulation in the toolbox to manage salmonids. Our objectives here were to summarize the regulation history of GRSM and determine whether regulations affected the age or size structure, growth, and population dynamics of wild populations of rainbow trout Oncorhynchus mykiss within GRSM. Data inconsistencies made data comparisons among regulation periods difficult; however, where feasible, comparisons revealed similar population dynamics among periods. The number of legal rainbow trout per kilometer of stream ranged from 215 to 885 throughout the 70‐year study period, regardless of regulation. There were no statistical differences in rainbow trout relative stock densities (RSDs) on Little River among the 1930s, 1950s, 1980s, and 1990s, despite liberal regulations prior to 1960. Rainbow trout mean length at age data indicate no differences among populations for age‐1 to age‐4 rainbow trout. There also was no statistical difference between the age structure data for age‐1 to age‐4 rainbow trout collected in 1945 and 1993. Water quality data indicate that GRSM streams are naturally acidic and infertile, which results in populations that exhibit fast growth with high annual mortality rates. As a result, we determined that regulations provided no discernable effect on wild rainbow trout populations in GRSM. Most regulations were put in place for social reasons and were never evaluated over long‐term periods (>5 years). Abiotic events, such as droughts and floods, have a much greater effect on salmonid abundance in GRSM than do regulations or fishing pressure.

Comparison of Density Difference Measurements at PTB and NMIJ

Silicon single crystals are used as density standards and to determine the Avogadro constant. Density comparisons by the flotation method can check the homogeneity of the silicon crystals and determine the absolute density of silicon samples by comparison to primary density standards. Results of the two flotation apparatuses at NMIJ (Japan) and PTB (Germany) were compared with each other and with density determinations from other methods. For this purpose, three small silicon samples from the crystals WASO 04 and NRLM4 were measured in both institutes. These measurements show that the flotation method is able to detect and measure density differences with uncertainties of 0.02/spl middot/10/sup -6//spl rho/. Additionally, the density of the 1-kg silicon sphere AVO#1 was determined by flotation comparisons to primary standards of the institutes and compared with density values obtained by different methods. With one exception, all results are consistent within the combined uncertainties, the largest relative density difference being only 0.18/spl middot/10/sup -6/.

Sensitivity and cost considerations for the detection and eradication of marine pests in ports

Port surveys are being conducted in Australia, New Zealand and around the world to confirm the presence or absence of particular marine pests. The most critical aspect of these surveys is their sensitivity—the probability that they will correctly identify a species as present if indeed it is present. This is not, however, adequately addressed in the relevant national and international standards. Simple calculations show that the sensitivity of port survey methods is closely related to their encounter rate—the average number of target individuals expected to be detected by the method. The encounter rate (which reflects any difference in relative pest density), divided by the cost of the method, provides one way to compare the cost-effectiveness of different survey methods. The most cost-effective survey method is site- and species-specific but, in general, will involve sampling from the habitat with the highest expected population of target individuals. A case study of Perna viridis in Trinity Inlet, Cairns, demonstrates that plankton trawls processed with gene probes provide the same level of sensitivity for a fraction of the cost associated with the next best available method—snorkel transects in bad visibility (secchi depth = 0.72 m). Visibility and the adult/larvae ratio, however, are critical to these arguments. If visibility were good (secchi depth = 10 m), the two approaches would be comparable. Diver deployed quadrats were at least three orders of magnitude less cost-effective in this case study. It is very important that environmental managers and scientists perform sensitivity calculations before embarking on port surveys to ensure the highest level of sensitivity is achieved for any given budget.

Density peaking in low collisionality ELMy H-mode in JET

Low collisionality, low particle source, ELMy H-modes (type-III) with sawteeth are produced in JET in order to address the question of density profile evolution in the reference q95 = 3 ITER scenario. The paper focuses on particle transport in the core zone around the mid-radius. The pedestal region including ELMs and the region affected by sawteeth are not considered. By replacing a significant part of the neutral beam heating by RF power the beam particle flux at mid-radius has been reduced to ΓBeam/ne = 0.07 m s−1. The additional flux due to wall neutrals is estimated as ΓWall/ne ⩽ 0.12 m s−1. Density profiles are found to be modestly peaked under these conditions with a relative density difference of Δn/⟨n⟩ = 0.23 across the zone not affected by sawteeth and ELMs. In a region around the mid-radius the ratio of effective particle diffusivity to electron thermal diffusivity is found to be De,eff/χe ≈ 0.2, which might indicate an anomalous pinch provided the particle diffusivity De is sufficiently large. The measured values of De,eff/χe are at the lower end of the range used in ITER models.

Comparative analysis of balsam fir wetwood, heartwood, and sapwood properties

Physical, anatomical, chemical, and microbiological properties of wetwood in heartwood were compared with those of sapwood and normal heartwood in balsam fir (Abies balsamea (L.) Mill.). Wetwood found only in heartwood of balsam fir had significantly higher moisture content (MC) than normal heartwood but not significantly higher MC than sapwood. No differences in relative density or shrinkage properties were found among tissue types. Wetwood tissue needed longer times to dry to an equilibrium MC of 15%, not only because of its high initial MC, but also because of its lower moisture permeability (diffusion coefficient) in this particular MC range (from initial MC to 15% equilibrium MC). However, there were no significant differences in drying rates for the different tissues when drying from 15% MC to 8% MC. Anatomically, wetwood is similar to normal heartwood, and it has no distinctive characteristics except a greater frequency of bacteria. Energy dispersive X-ray analysis showed that all of the tissues contained the same inorganic elements. Both high-performance liquid chromatography and ash analysis showed that wetwood is chemically closer to normal heartwood than to sapwood. Wetwood was significantly more acidic than either normal heartwood or sapwood. A large number of bacterial genera were found in all three tissues, but there were no consistent or significant differences in bacterial presence or activity among tissue types.

Sea Level Variations in the Western Mediterranean Studied by a Numerical Tidal Model of the Strait of Gibraltar

Aspects of the sea level changes in the western Mediterranean Sea are investigated using a numerical tidal model of the Strait of Gibraltar. As a prerequisite, the performance of this model, that is, a two-dimensional, nonlinear, two-layer, boundary-fitted coordinate numerical model based on the hydrostatic approximation on an f plane, is assessed in the simulation of mean and tidal circulation of the Strait of Gibraltar. The model is forced by imposing mean interface and surface displacements as well as M2, S2, O1, and K1 tidal components along the Atlantic and Mediterranean model open boundaries. Model results are compared with observations and with results obtained from a tidal inverse model for the eastern entrance of the Strait of Gibraltar. In general, good agreement is found. A sensitivity study performed by varying different model parameters shows that the model behaves reasonably well in the simulation of the averaged circulation. The model is then used to investigate the climatological sensitivity of the simulated dynamics in the Strait of Gibraltar to changes in the density difference between Atlantic and Mediterranean waters. For this purpose, given a certain density difference between Atlantic and Mediterranean waters, the authors iteratively searched for that sea level drop between the Atlantic and the Mediterranean that fulfills the mass balance of the Mediterranean. It is found that an increase of the density difference leads to an increase of the exchange flow and to an increase of the sea level drop between the two basins. A trend in the sea level drop of O(1 cm yr21), such as the one observed between 1994 and 1997, is explained by the model as the result of a trend of O(10 24 yr21) in the relative density difference between the Mediterranean and Atlantic waters. The observed north‐south asymmetry in this trend is also captured by the model, and it is found to arise from changes in the along-strait velocity. Results suggest that the dynamics within the Strait of Gibraltar cannot be neglected when sea level changes in the western Mediterranean basin are investigated.

Electro-acupuncture preconditioning abrogates the elevation of c-Fos and c-Jun expression in neonatal hypoxic-ischemic rat brains induced by glibenclamide, an ATP-sensitive potassium channel blocker

This study aimed to clarify the neuroprotective mechanism of electro-acupuncture (EA) preconditioning on hypoxic-ischemic brain injury (HIBI). Using Western blot, the expression of c-fos protein (c-Fos) and c-jun protein (c-Jun) induced by glibenclamide, an ATP-sensitive potassium (K ATP) channel blocker was examined from cerebral cortical and hippocampal samples in neonatal hypoxic-ischemic rats, with or without EA preconditioning. EA was performed on Hegu (LI4), a well-known acupoint commonly used in Oriental medicine for the treatment of neuronal injury resulting from hypoxia–ischemia (HI). Preconditioned rats were treated with either diazoxide, a K ATP channel opener, glibenclamide, or sterile saline injected into the left lateral ventricle (i.c.v.), with or without EA administration before HI insult. Interestingly, low c-Fos and c-Jun expressions were found both in diazoxide and EA groups, 24 h after HI. Furthermore, significant differences in relative optical density (ROD) were found between glibenclamide and HI control groups ( P≤0.05), as well as between the group administered glibenclamide after EA and the HI control group ( P≤0.05). However, the level of c-Fos and c-Jun expression in the group administered glibenclamide after EA was significantly lower than in the glibenclamide group ( P≤0.05). The present findings indicate that the effectiveness of EA preconditioning against HIBI may be mediated via the opening of K ATP channels.

Thermal, structural and transport properties of the fast oxide-ion conductors La 2−xR xMo 2O 9 (R=Nd, Gd, Y)

The thermal evolution of the crystal structure of the new fast oxide-ion conductor La 2Mo 2O 9 across its structural α to β first order transition at 580 °C has been followed using synchrotron X-ray diffraction (XRD). The influence on the transition, structure and oxide-ion conductivity of partial substitution by other rare earths (Nd, Gd, Y) is studied. For Nd substitution the monoclinic α form is retained at room temperature in the whole compositional range. For Gd and Y substitutions, above a certain doping level, the suppression of the phase transition and stabilization at room temperature of the cubic β form are achieved. The cubic structures of La 1.9Y 0.1Mo 2O 9 at room temperature and of β-La 2Mo 2O 9 at 670 °C (revisited), both refined from neutron powder diffraction patterns, are very similar. Despite the cell volume reduction, lanthanide substitution results above 500 °C in an increase of the anion conductivity compared to that of β-La 2Mo 2O 9, which might result from differences in samples' relative density.

The Rheology of Liquids: A Comparison of Clinicians? Subjective Impressions and Objective Measurement

Texture-modified diets are commonly prescribed for patients with dysphagia; it is therefore important to demonstrate that clinicians form accurate impressions of the rheological (flow) properties of the items that they recommend for their clients. We explored the correlation between objective rheological measurement and clinicians' subjective impressions of liquid consistency, rated on the bases of product labeling and sampling. Ten liquids, ranging from thin through nectar-thick and honey-thick to spoon-thick consistencies, were selected for study. Rheological analysis was conducted using a CarriMed CSL Controlled Stress Rheometer. Fifty speech-language pathologists ranked the liquids in order of perceived viscosity, based on their interpretation of the product packaging and label. Product nomenclature proved insufficient to accurately represent the consistency class to which each liquid belonged. A second group of 16 speech-language pathologists rated the perceived relative viscosity and density of nectar-thick and honey-thick juice items in blinded two-point discrimination tests of stirring-resistance, oral manipulation, and vessel weight. Physical sampling of these two products enabled clinicians to reliably perceive relative viscosity and density differences between the nectar- and honey-thick items.

Gravitational instability in suspension flow

The gravity-driven flow of non-neutrally buoyant suspensions is shown to be unstable to spanwise perturbations when the shearing motion generates a density profile that increases with height. The instability is simply due to having heavier material over light – a Rayleigh–Taylor-like instability. The wavelength of the fastest growing disturbance is on the order of the thickness of the suspension layer. The parameters important to the problem are the angle of inclination of the layer relative to gravity, the relative density difference between the particles and the fluid, the ratio of the particle size to the thickness of the layer and the bulk volume fraction of particles. The instability is illustrated for a range of these parameters and shown to be most pronounced at intermediate values thereof. This instability mechanism may play an important role in pattern formation in multiphase flows.

Stratified flow over topography: bifurcation fronts and transition to the uncontrolled state

A distinguishing feature of controlled stratified flows over topography is the formation of a wedge of partly mixed fluid downstream of a bifurcation or plunge point. We describe observations acquired over a sill in a coastal inlet under progressively increased tidal forcing. This wedge of partly mixed fluid is displaced downstream as the flow undergoes a continuous transition from control over the obstacle crest to an uncontrolled state. The effects of changing barotropic forcing and relative density difference between the plunging flow and partly mixed layer above combine to determine the fluid dynamical response. The relative density difference in turn is determined by the prior history of the flow as well as small–scale mixing. In general it decreases with time as denser fluid is entrained into the intermediate layer, thus increasing the effective forcing. For sufficiently strong tidal velocities and small relative density difference, the wedge of partly mixed fluid is displaced downstream of the crest and topographic control is lost. Such flows occur naturally in the ocean over sills and ridges, and in the atmosphere as severe downslope winds.

The flowability of bentonite bonded green molding sand

This paper investigates the properties of green molding sands, and a new model to evaluate the flowability of sand compact is developed. Controlling the flowability of the molding sand is extremely important in the sand casting process. Although several flowability indices have been proposed to measure this property, none of them has been universally adopted as a reliable indicator of the flowability. In this study, experimental results are presented to show how the flowability of silica sand is affected by water content, bentonite and sea-coal content. The equation proposed by Shapiro and Kolthoff can well fit the relationship between the compacting pressure and the relative density. The coefficients of S–K equation were substituted into the strength equation proposed by Sheppard and McShane. The S–M equation matches the green compaction strength data, with an error less than 5%. The model reported here correlates a one-dimensional compaction model with the S–M and S–K equations, and derives the relative density difference and the compression strength difference of the compact. The experimental results showed that the green strength reached the maximum at the ratio of moisture-to-bentonite of around 0.33. The hardness deviation on the central plane of the compact was taken as the reference to test the estimated strength difference. The results indicated that the flowability increased as the water content decreased. The model can explain the experimental results and directly predicts the uniformity of the compact. The estimated relative density difference Δ D r can be a new index of the flowability. For lowest Δ D r, the best water content occurs at around w%=3.0.

Identification of birds as biological markers along a neotropical urban–rural gradient (Cayenne, French Guiana), using co-inertia analysis

This article examines the utility of particular bird species and guilds as bioindicators in a complex habitat mosaic, namely that of the tropical city of Cayenne (French Guyana). For this purpose, an urbanization gradient was divided up into nine classes based on 576 standard bird counts (using the point-count method) conducted in and around Cayenne between 1992 and 1995. Each point-count location was characterized by 10 habitat variables. A multiple correspondence analysis of this data set, followed by a cluster analysis, was used to establish a classification of eight habitats, according to level of anthropogenic disturbance and diversity of vegetation. 13667 birds, belonging to 136 species, were recorded. A co-inertia analysis linking the point-counts and the 72 most common bird species and the urban–rural gradient classes showed that the bird populations were distributed along an anthropogenic gradient extending from second-growth forest to the old city center. The bird species fell into 11 trophic guilds. Six of these guilds, which had a high relative density or were homogenous in distribution, were not used in the characterization of the habitats. The large differences in relative density among the five other guilds allowed them to serve as habitat indicators. The eight dominant species were wide-ranging, and could not be used as biological markers. The co-inertia analysis brought out associations with some habitats of 64 other species. Each omnivorous marker was specific of an anthropogenic step in the gradient, while each insectivorous marker was associated with an increased diversity in vegetation structure. With an investment of just 10 sampling points, it was possible to characterize these habitats using a combination of observations on a maximum of 11 species. The Cayenne case shows a methodology to understand the relationships between environmental changes and avifaunal responses. The conclusions will be useful for the management of open spaces in growing towns along the tropical belt.

Mathematical Modeling of Centrifugal Casting of Metal Matrix Composites

Centrifugal casting of Aluminum melts containing suspended ceramic particles has been studied. One dimensional heat transfer model coupled with equations for force balance on particles is formulated and analysed to predict the particles distribution in the casting region, the temperature distribution in the casting and mold regions, and solidification time of the casting. The model takes into consideration propagation of solid-liquid interface and movement of particles due to centrifugal acceleration. The solution of the model equations has been obtained by pure implicit finite difference technique with modified variable time step approach. The effect of various parameters like particle size, mold rotational speed, relative density difference between melt and particle, etc. on segregation of particles and solidification time have been examined. For a given set of operating conditions, the thickness of the particle rich region decreases with increase in rotational speed of the mold, particle size, relative density difference between the particle and melt, and the melt superheat. Solidification time increases as the heat transfer coefficient at the metal-mold interface decreases.

A baited underwater video system for the determination of relative density of carnivorous reef fish

Estimates of the relative density of fishes form the basis of many marine ecological studies as well as the assessment of effects of fishing or pollution. Plasticity in the behavioural response of large reef fishes to SCUBA divers means that commonly used underwater visual census (UVC) techniques do not always provide reliable estimates of relative density. The paper describes the system configuration, deployment methods, testing and use of a remotely deployed baited underwater video (BUV) system for the survey of carnivorous reef fishes (snapper, Pagrus auratus and blue cod,Parapercis colias) in marine reserves of northern New Zealand. Concurrent UVC and BUV surveys inside and outside a marine reserve showed that, whereas UVC detected few snapper in either area (resulting in little confidence in statistically significant results), BUV demonstrated significant differences in relative density. Conversely, blue cod were found to occur at significantly higher densities within the reserve by UVC, but not by BUV. The provision of accurate estimates of fish size (<20 mm error) from video footage also illustrated differences in size structure between protected and fished populations. The data suggest that a combination of survey techniques is likely to be necessary where multispecies assemblages are being assessed.

A geostrophic adjustment model of shelfward intrusion of oceanic upper water across a depth discontinuity: implication to the Kuroshio region

The dynamics of gravity-forced intrusion of the oceanic upper water onto the shelf across a depth discontinuity is considered by using a simple geostrophic adjustment model with application to the Kuroshio region bordering the East China Sea Shelf in mind. The external parameters affecting the intrusion of the oceanic upper water are found to be the difference in surface elevation between the shelf and the oceanic regions, the relative density difference between two water masses and the bottom depth of the shelf. The sea level difference moves the frontal system shelfward through barotropic effect whereas the density difference increases the frontal width through baroclinic effect. Both effects favorably act upon the intrusion of the oceanic upper water. The barotropic and baroclinic effects are pronounced relatively more, respectively, for the larger and smaller depth changes across the slope. For the oceanic upper water initially in motion in the same direction as that due to the adjustment and conserving the potential vorticity of the resting state, the intrusion is greatly hindered.

Theobroma bicolor Humb. & Bonpl. (Sterculiaceae, "Cuapataxtle") en el Municipio de Ayutla de los Libres, Guerrero. Composición Florística de los huertos y aspectos etnobotánicos

El presente trabajo tuvo como objetivos: 1] describir la composición florística de los huertos donde crece Theobroma bicolor; en el municipio de Ayutla de los Libres, Guerrero; 2] describir los aspectos etnobotánicos relacionados con los usos de T. bicolor y 3] reportar la presencia de T. bicolor en el estado de Guerrero, específicamente en el Municipio de Ayutla de Los Libres-: Se muestrearon 9 huertos ubicados en diferentes localidades con diferente composición étnica. Se obtuvo el número total de especies por área muestreada, número de individuos por especie y densidad relativa de cada especie. La descripción de los usos de T. bicolor se obtuvo mediante encuestas a indígenas y mestizos. Se observa una heterogeneidad en la riqueza de especies presentes en los huertos, en el tipo de especies y en las densidades relativas. En general, los huertos cercanos a la cabecera municipal, conservan una composición florística variable y una alta densidad relativa de diversas especies frutales y del cuapataxtle. Los huertos alejados de la cabecera municipal y manejados por indígenas mixtecos también presentan una heterogeneidad alta pero las densidades relativas en general son bajas, incluyendo la de cuapataxtle. Se concluye que la composición florística variable en los huertos, así como las diferencias en las densidades relativas de las especies, incluyendo el cuapataxtle, reflejan la concepción tradicional de manejo de los huertos, la ubicación de los huertos con respecto a la cabecera municipal de Ayutla, y la importancia de la cercanía con sitios de comercialización de productos.

Brine transport in porous media: self-similar solutions

In this paper we analyze a model for brine transport in porous media, which includes a mass balance for the fluid, a mass balance for salt, Darcy's law and an equation of state, which relates the fluid density to the salt mass fraction. This model incorporates the effect of local volume changes due to variations in the salt concentration. Density variations affect the compressibility of the fluid, which in turn cause additional fluid flow. Two specific situations are investigated that lead to self similarity. We study the relative importance of the compressibility effect in terms of the relative density difference. Semi-analytical solutions are obtained as well as asymptotic expressions in terms of the relative density difference. It is found that the volume changes have a small but noticeable effect on the mass transport only when the salt concentration gradients are large. Some results on the simultaneous transport of brine and dissolved (radioactive) tracers are presented.