Small Packing Research Articles

African Wild Dogs (Lycaon pictus) Can Subsist on Small Prey: Implications for Conservation

In mammalian predators, prey size typically increases with body size, such that most carnivores weighing .21.5 kg specialize on prey weighing� 45% of their own mass. By hunting in packs, endangered African wild dogs (Lycaon pictus) are able to feed primarily on ungulates weighing .100% of their own individual mass and, in most populations, wild dogs specialize on such large prey. However, we show that wild dogs living outside protected areas in northern Kenya fed primarily on Kirk’s dikdiks (Madoqua kirkii), small antelope weighing just 15% of wild dog body mass. We estimated that dikdiks constituted 70% of the prey biomass consumed by wild dogs. Despite feeding on small prey, pack size, home-range size, and vital rates in this population were similar to those recorded in protected areas where wild dogs specialize on much larger ungulates. The energy content of a dikdik was about one-tenth that of the 2nd most important prey, impala (Aepyceros melampus). However, because dikdiks occurred at high population densities, the 2 prey species had apparently comparable hunting profitabilities. Wild dog packs ate more small (,10-kg) prey when confined to a breeding den. Also, packs living on commercial ranches consumed fewer small prey than did those living on community lands where larger prey were depleted. However, demographic parameters were similar in the 2 land uses. Although livestock occupy virtually the whole area, wild prey have persisted because local Masai and Samburu pastoralists do not traditionally hunt wild ungulates. This tradition has helped wild dogs to recolonize successfully and to reach densities comparable with those recorded in protected areas. The apparent ability of wild dogs to persist on small prey, in a livestock-dominated ecosystem, suggests that other important populations might occur, or be recoverable, in Africa’s unprotected rangelands.

Modeling of agglomerate behavior under shear deformation: effect of velocity field of a high shear mixer granulator on the structure of agglomerates

Abstract -High shear mixer granulators are typically found in pharmaceutical and detergent industries, and are capable of reducing processing time and producing agglomerates with high strength and density. Generally, several granulation scaling-up stages are involved before reaching the production level. This is conducted to exert better understanding, control and optimization at the smaller scales before proceeding to the larger scales in terms of geometric, kinematic and/or dynamic similarities. During granulation scaling-up stages, the mechanics of particle interactions and the prevailing level of compressive stresses and strains within the granulator are affected by the variation in hydrodynamics of the granulator as a result of different scales. This in turn affects the final structure of the agglomerates. In this paper we analyze the effect of velocity field of two different scales of high shear mixer granulator (1 and 5 l) on the structure of the evolved agglomerates. The study is based on computer simulation using the discrete element method (DEM). A single agglomerate is generated using DEM computer code and is placed in a bed of primary particles. A velocity field is then superimposed on the surrounding particles. This velocity field corresponds to that obtained experimentally from a separate study using Positron Emission Particle Tracking analysis on 1- and 5-l granulators which were scaled up based on the condition of constant shear stress. The results show that when the velocity profile of the 1-l granulator is used the agglomerate becomes more elongated and it has a smaller packing fraction. Therefore the agglomerate would be weaker.

Interactions of 1-Methylimidazole with UO2(CH3CO2)2 and UO2(NO3)2: Structural, Spectroscopic, and Theoretical Evidence for Imidazole Binding to the Uranyl Ion

The first definitive high-resolution single-crystal X-ray structure for the coordination of the 1-methylimidazole (Meimid) ligand to UO2(Ac)2 (Ac = CH3CO2) is reported. The crystal structure evidence is confirmed by IR, Raman, and UV-vis spectroscopic data. Direct participation of the nitrogen atom of the Meimid ligand in binding to the uranium center is confirmed. Structural analysis at the DFT (B3LYP) level of theory showed a conformational difference of the Meimid ligand in the free gas-phase complex versus the solid state due to small energetic differences and crystal packing effects. Energetic analysis at the MP2 level in the gas phase supported stronger Meimid binding over H2O binding to both UO2(Ac)2 and UO2(NO3)2. In addition, self-consistent reaction field COSMO calculations were used to assess the aqueous phase energetics of combination and displacement reactions involving H2O and Meimid ligands to UO2R2 (R = Ac, NO3). For both UO2(NO3)2 and UO2(Ac)2, the displacement of H2O by Meimid was predicted to be energetically favorable, consistent with experimental results that suggest Meimid may bind uranyl at physiological pH. Also, log(Knitrate/KAc) calculations supported experimental evidence that the binding stoichiometry of the Meimid ligand is dependent upon the nature of the reactant uranyl complex. These results clearly demonstrate that imidazole binds to uranyl and suggest that binding of histidine residues to uranyl could occur under normal biological conditions.

Factors affecting juvenile survival in African wild dogs (Lycaon pictus) in Kruger National Park, South Africa

AbstractAfrican wild dog Lycaon pictus populations are declining due to persecution as well as habitat destruction and fragmentation. Understanding the natural mechanisms driving population dynamics is important for conservation management as it clarifies natural from human‐induced factors. Therefore, this understanding is essential to compensate for disadvantaging ecological factors and successfully apply conservation actions. Juvenile survival is important in driving wild dog population dynamics, and therefore this study investigated the influence of rainfall and pack size on the survival of juveniles up to the age of 12 months. We found that past rainfall significantly influenced pup survival up to 9 months of age, such that pups benefited from preceding dry periods. The positive effects of pack size on juvenile survival only became evident for pups older than 9 months and, despite this delayed Allee effect, we found no evidence of reproductive failure in small packs as compared with larger ones.

Injector‐internal thermal desorption from edible oils performed by programmed temperature vaporizing (PTV) injection

Injector-internal thermal desorption is a promising technique for the analysis of a wide range of food components (e.g., flavors) or food contaminants (e.g., solvent residues, pesticides, or migrants from packaging materials) in edible oils and fats or fatty food extracts. Separation from the fatty matrix occurs during injection. Using programmed temperature vaporizing (PTV) injection, the oily sample or sample extract was deposited on a small pack of glass wool from which the components of interest were evaporated and transferred into the column in splitless mode, leaving behind the bulk of the matrix. Towards the end of the analysis, the oil was removed by heating out the injector and backflushing the precolumn. The optimization dealt with the gas supply configuration enabling backflush, the injector temperature program (sample deposition, desorption, and heating out), separation of the sample liquid from the syringe needle and positioning it on a support, deactivation of the support surface, holding the plug of fused silica wool by a steel wire, and the analytical sequence maintaining adsorptivity at the desorption site low. It was performed for a mixture of poly(vinyl chloride) (PVC) plasticizers in oil or fatty food. Using MS in SIM, the detection limit was below 0.1 mg/kg for plasticizers forming single peaks and 1 mg/kg for mixtures like diisodecyl phthalate. For plasticizers, RSDs of the concentrations were below 10%; for the slip agents, oleamide and erucamide, it was 12%. The method of incorporating PTV injection was used for about one year for determining the migration from the gaskets of lids for glass jars into oily foods.

Non-intrinsic contribution to the partial molar volume of cavities in water

In general the partial molar volume of a cavity in a liquid or that of a solute in a solvent can be dissected in an intrinsic contribution and a non-intrinsic one. It is shown that, if the intrinsic contribution is given by the van der Waals volume of the cavity, the non-intrinsic contribution is always a positive quantity in water, increasing with cavity size. This result has a general validity, being in line with the basic notion that there is a lot of void volume in liquids, and water, in particular, has a small volume packing density. In addition, it is pointed out that the recent claim [F.M. Floris, J. Phys. Chem. B 108 (2004) 16244] that the non-intrinsic contribution changes sign, passing from negative to positive values for sufficiently large cavities, is simply due to the choice of using the excluded volume of the cavity instead of the van der Waals volume as the intrinsic contribution.

Hysteresis in Trickle-Bed Reactors: A Review

A concise review of the hysteresis in cocurrent down-flow trickle-bed reactors (TBRs) is presented. The effects of several factors on the hysteresis, such as the type of particles (porous/nonporous), the size of the particles, the operating flow ranges, and the start-up conditions (wet/dry) are described. Also, some limited information that is available about the effects of other factors, such as addition of wetting agents (surfactants) and inlet liquid distribution, are also discussed. Empirical and theoretical models developed to predict hysteresis are briefly described. Most of the studies have reported an appreciable amount of hysteresis in key hydrodynamic parameters such as pressure drop, liquid holdup, and wetting efficiency, especially with small packing material (∼1.6−3.5 mm). The hysteresis is attributed to the different degrees of wetting, which occurs because of the flowing of liquid in two different modes, such as film and rivulet. The hysteresis behavior of a packed bed with porous particles...

Backpack Moment of Inertia Affects Oxygen Consumption During Walking

Prior research on the metabolic energy cost of carrying backpack loads has focused primarily on the effects of weight carried on the rate of oxygen consumption during walking. However, less research has been done on the effects of manipulating backpack mass center location or moment of inertia (MOI) on oxygen consumption. PURPOSE: The purpose of this study was to examine the effects of manipulating the MOI (distribution of mass about an axis of rotation) of a backpack load on the rate of oxygen consumption during walking. We hypothesized that varying the relationships among MOI values for the principal axes would differentially affect oxygen consumption. METHODS: Fourteen male volunteers participated in the study. Steel weights (26 kg total mass) were positioned in each of three military backpacks to produce different MO Is, but with the same mass (35 kg, inclusive of the backpack) and mass center locations (0.3 m posterior to the pack frame and 0.3 m superior to the bottom of the pack). The three packs differed in that each had the MOI of a unique principal axis (Ixx, Iyy, Izz) set at a small value (< 1.0 kg.m2), while the other two principal axes had large moments of inertia (> 2.0 kg.m2). Relative to the load carrier's body, Ixx, Iyy, and Izz defined the MOI about the anterior-posterior axis, the medial-lateral axis, and the vertical axis, respectively. The volunteers walked on a level treadmill at 4.8 km/h for 10 min carrying each of the packs. The rate of oxygen consumption (VO2) was recorded (COSMED K4b2, COSMED, Rome, Italy) during the last 90 sec of the walking period and was scaled to body plus load mass. A repeated measures ANO VA with three levels of MOI and follow-up comparisons were used to assess differences in the mean mass specific VO2. RESULTS: A significant difference (p < .05) in mean mass specific VO2 was found between the small Ixx value pack (15.04 ml/kg/min (SD 1.96)) and the small Iyy value pack (16.27 ml/kg/min (SD 2.09)). Mean differences approached statistical significance (p = .061) between the small Ixx pack and the small Izz pack (16.15 ml/kg/min (SD 2.23)). The small Iyy value and small Izz value packs did not statistically differ. CONCLUSION: The mean mass specific rate of oxygen consumption was 7.6% lower when Ixx was minimized relative to Iyy. Therefore, the metabolic energy cost of carrying backpack loads is not solely dependent on the amount of mass carried. The manner in which items are stowed in the backpack also affects metabolic energy expenditure and thus the physical endurance of the load carrier.

Pair formation and global ordering of strongly interacting ferrocolloid mixtures: An integral equation study

Using the reference hypernetted chain (RHNC) integral equation theory and an accompanying stability analysis we investigate the structural and phase behaviors of model bidisperse ferrocolloids based on correlations of the homogeneous isotropic high-temperature phase. Our model consists of two species of dipolar hard spheres (DHSs) which dipole moments are proportional to the particle volume. At small packing fractions our results indicate the onset of chain formation, where the (more strongly coupled) A species behaves essentially as a one-component DHS fluid in a background of B particles. At high packing fractions, on the other hand, the RHNC theory indicates the appearance of isotropic-to-ferromagnetic transitions (volume ratios close to one) and demixing transitions (smaller volume ratios). However, contrary with the related case of monodisperse DHS mixtures previously studied by us [Phys. Rev. E 70, 031201 (2004)], none of the present bidisperse systems exhibit demixing within the isotropic phase, rather we observe coupled ferromagnetic/demixing phase transitions.

The costs and benefits of animal predation: An analysis of Scandinavian wolf re-colonization

After coming close to extinction, the grey wolf ( Canis lupus) has re-colonized Scandinavia during the last two decades. The current population numbers some 100–120 individuals, and is distributed in small packs along the Swedish-Norwegian border. However, with wolf re-colonization, several conflicts have arisen. One conflict is due to wolf predation on livestock, especially sheep and reindeer. Another is predation on wild ungulates. As the wolves have shown a strong preference for moose ( Alces alces) in this respect, a smaller moose population is available for game hunting. The cost of increased moose predation by wolves is examined using a two-step process. First, we analyse the costs to landowners, comprising the loss of animals potentially available for hunting less the reduction in browsing damage associated with a smaller moose population. Second, we examine the problem from a broader point of view, where costs external to landowners and local communities are included. By far the most important cost here is damage related to collisions between moose and motor vehicles.

European legal limits for migration from food packaging materials: 1. Food should prevail over simulants; 2. More realistic conversion from concentrations to limits per surface area. PVC cling films in contact with cheese as an example

For small packs with a high ratio of contact surface area/volume, present European legislation tolerates extremely high migration in terms of concentration in the food, since limits apply as migration per surface area. Overall migration (OM) may exceed 1000 mg/kg, which is orders of magnitude above the tolerance for any other type of food contaminant. With the present rules for specific migration (SM), the tolerable daily intake (TDI) may be exceeded with less than 100 g food, particularly when a fat consumption reduction factor (FRF) is applied. The OM and the SM of di(2-ethylhexyl) adipate (DEHA) from PVC cling films into cheese demonstrate that such high migration is not just a theoretical extrapolation, but is encountered in reality. Another problem concerns possible inaccuracy of migration testing with simulants. Even when the migration into the food is known to be almost complete, simulant D reduction factors (DRFs) are applied. The following measures are suggested: 1. The legal limits in terms of concentration in food should be converted to migration per contact surface area by a ratio which no longer focuses on the 1 l cube, but on the current smaller packs. It is proposed to assume 20 dm 2 contact surface area per liter of packaging volume, i.e. the OML of 60 mg/kg should correspond to 3 mg/dm 2. 2. Legal limits should apply in terms of concentrations down to a contact surface area/volume ratio of 20 dm 2/l, below which they should be calculated per surface area. 3. For compliance testing, migration into food should explicitly prevail over migration into simulants. These modifications will ensure that the overall migration exceeds the 60 mg/kg in food only for packagings with a high surface area to volume ratio and that with normal consumption, the TDI can still be approached rather easily, but not strongly exceeded.

Characterization of electrode structures and the related performance of direct methanol fuel cells

The performance of membrane electrode assemblies (MEAs) in fuel cells is substantially affected by the structures of the electrodes. An increase of about 25% in power performance was achieved merely by controlling the pressure of hot press in the MEA fabrication process for a given Pt loading, instead of by employing pore formers and heat treatment-a widely accepted method-to modify the structures of the electrode. The microstructures of the different hot-pressed electrodes were examined by transmission electron microscopy, scanning electron microscopy, and small angle X-ray scattering to assess the effect of the pressure on the structures of the electrodes. Based on experimental observations, the improved performance of the MEA is attributed to the porosity of the cathode electrode, in which a network of macrofissures and sub-microfissures allows air to penetrate the electrode. Emphasis is also placed on the relationship between the total porosity of the electrodes and the MEA performance. Results of this study demonstrate that the specific power density nearly doubles when the total porosity increased from 57% to 76%. Also, the MEAs mounted in an air-breathing DMFC small pack were fabricated in-house to supply power for a mobile phone.

Development of high energy density small flat spiral cells and battery pack based on lithium/carbon monofluoride (Li/CF x)

Small spiral-wound lithium–carbon monofluoride (Li/CF x ) cells, which were discharged at the C/40 rate, had a nominal capacity of 300 mAh and a gravimetric energy density of about 464 Wh kg −1. These cells delivered pulse current loads (>22 mA) with good capacity (>200 mAh) if they were subjected to a pre-discharge step. A 17 V, 2.2 kW battery based on Li/CF x flat cell technology has also been fabricated and tested. The battery had gravimetric and volumetric energy densities of 360 Wh kg −1 and 700 Wh dm −3, respectively. This compares with a value of 330 Wh kg −1 and 522 Wh dm −3 for an equivalent battery based on Li/SOCl 2.

DrugScoreCSDKnowledge-Based Scoring Function Derived from Small Molecule Crystal Data with Superior Recognition Rate of Near-Native Ligand Poses and Better Affinity Prediction

Following the formalism used for the development of the knowledge-based scoring function DrugScore, new distance-dependent pair potentials are obtained from nonbonded interactions in small organic molecule crystal packings. Compared to potentials derived from protein-ligand complexes, the better resolved small molecule structures provide relevant contact data in a more balanced distribution of atom types and produce potentials of superior statistical significance and more detailed shape. Applied to recognizing binding geometries of ligands docked into proteins, this new scoring function (DrugScore(CSD)) ranks the crystal structures of 100 protein-ligand complexes best among up to 100 generated decoy geometries in 77% of all cases. Accepting root-mean-square deviations (rmsd) of up to 2 angstroms from the native pose as well-docked solutions, a correct binding mode is found in 87% of the cases. This translates into an improvement of the new scoring function of 57% with respect to the retrieval of the crystal structure and 20% with respect to the identification of a well-docked ligand pose compared to the original Protein Data Bank-based DrugScore. In the analysis of decoy geometries of cross-docking studies, DrugScore(CSD) shows equivalent or increased performance compared to the original PDB-based DrugScore. Furthermore, DrugScore(CSD) predicts binding affinities convincingly. Reducing the set of docking solutions to examples that deviate increasingly from the native pose results in a loss of performance of DrugScore(CSD). This indicates that a necessary prerequisite to successfully resolving the scoring problem with a more discriminative scoring function is the generation of highly accurate ligand poses, which approximate the native pose to below 1 angstroms rmsd, in a docking run.

Fluctuation Flows in Random Fibrous Media and Their Influence on the Efficiency of Aerosol Particle Deposition

The distribution function of random velocities in the fibrous medium of parallel fibers and the generating functional of correlation functions in a 3D fibrous medium are calculated. It is shown that the velocity fluctuations are Gaussian in the rarefied medium at a small packing density. The influence of 3D fluctuation hydrodynamic gas flows on the efficiency of aerosol particle deposition is studied.

Mass transfer in liquid–liquid membrane-based extraction at small fiber packing fractions

Results are presented of carefully controlled mass transfer experiments, complemented by theoretical analysis. A simple test section is employed, comprised of five microporous nearly parallel fibers (fixed within a tubular glass shell), to study mass transfer when the shell-side resistance is controlling. The feed phase, flowing in the shell side, is an aqueous solution of either benzaldehyde or 2-hexanal, whereas n-hexane is used as the organic solvent (in the lumen); the respective partition coefficients at 25 °C are 10 and 57. Accurate data are obtained by using ‘once-through’ flow of both fluids. For the class of problems studied here (i.e. small fiber packing fraction Φ and high Sc number at shell side), a boundary layer solution is obtained for the mass transfer rate to the outer fiber surface. This expression, model variations thereof, as well as similar theoretical results recently reported in the literature, are assessed by comparison with the new data. By combining the analytical solution for the shell with a known expression for mass transfer at the lumen side, a closed-form expression is derived for the solute concentration variation in the organic solvent along the fiber/module. Very good agreement is obtained between experimental data and theoretical predictions, with no recourse to adjustable parameters. An important conclusion of this work, concerning shell-side mass transfer, is the dependence of Sh· Sc −1/3 on Reynolds number to the 1/3 power. Furthermore, the flow rate in the lumen (though not controlling) is shown to be a significant parameter affecting process efficiency.

Characterization of electrode structures and the related performance of direct methanol fuel cells

The performance of membrane electrode assemblies (MEAs) in fuel cells is substantially affected by the structures of the electrodes. An increase of about 25% in power performance was achieved merely by controlling the pressure of hot press in the MEA fabrication process for a given Pt loading, instead of by employing pore formers and heat treatment-a widely accepted method-to modify the structures of the electrode. The microstructures of the different hot-pressed electrodes were examined by transmission electron microscopy, scanning electron microscopy, and small angle X-ray scattering to assess the effect of the pressure on the structures of the electrodes. Based on experimental observations, the improved performance of the MEA is attributed to the porosity of the cathode electrode, in which a network of macrofissures and sub-microfissures allows air to penetrate the electrode. Emphasis is also placed on the relationship between the total porosity of the electrodes and the MEA performance. Results of this study demonstrate that the specific power density nearly doubles when the total porosity increased from 57% to 76%. Also, the MEAs mounted in an air-breathing DMFC small pack were fabricated in-house to supply power for a mobile phone.

Effect of raven Corvus corax scavenging on the kill rates of wolf Canis lupus packs

During late winter 1991 and 1992, we investigated the influence of raven Corvus corax scavenging on the predation rate by different-sized wolf Canis lupus packs on moose Alces alces in the Yukon Territory, Canada. To assess the magnitude of scavenging, we presented 10 ungulate carcasses, pre-warmed to simulate the flesh temperature of freshly-killed prey, to scavengers and measured their daily consumption. Ravens were by far the main scavengers and on average, we counted 18.5 ± 12.7 (SD) ravens and documented removal of 14.1 ± 1.3 (SE) kg biomass each day (N = 53 observation days). However, assuming a daily scavenging rate of 14 kg by ravens fails to explain the almost equally short handling times for moose carcasses of small, medium and large packs. Only when raven consumption rate varies with pack size can we match the observed pattern. Assuming complete consumption, daily raven scavenging has to be 43 kg for ravens feeding on the kills of small wolf packs, 21 kg for ravens feeding on the kills of medium packs and close to zero for ravens feeding on the kills of large packs. Thus raven-wolf competition is highest for small packs, where ravens manage to remove up to 75% of the edible biomass and very low for large packs where ravens hardly manage to remove any edible biomass. Large packs seem to leave less opportunity for ravens to feed on carcasses, possibly because some wolves are always present at the kill and either actively chase away ravens or inhibit access to the carcass.

On instabilities and migration phenomena in cone and plate geometry

This paper reports experimental observations on suspensions of glass spheres in a viscoelastic polymer solution. The fluid is submitted to shear flows at constant stress in a cone and plate geometry. After shearing, for sufficiently high stress, one observes, on the plate and on the cone, that the beads are located on concentric rings. In each ring, they regroup in regularly spaced small packs. This migration phenomenon is related to the viscoelasticity of the suspending medium but the mechanism of formation of the packs is not yet elucidated.

Fabrication of electrocatalyst layers for direct methanol fuel cells

To optimize the performance of the membrane electrode assembly (MEA), a manufacturing process for electrocatalyst layers is systematically studied by controlling physical parameters such as electrocatalyst loadings at each electrode, electrocatalyst compositions, and layer thickness. The MEA is evaluated in an air-breathing direct methanol fuel cell (DMFC) with various methanol concentrations. The investigation focuses on finding the best compromise between electrocatalyst loadings and utilization of methanol concentration. Surprisingly, the power density is influenced more by the Pt loading than by the Pt–Ru loading, and can be increased further by using a methanol concentration above 3 wt.% for a certain level of electrocatalyst loading. Current–voltage characteristics indicate that increasing Pt and Pt–Ru loadings at each electrode can reduce the activation overpotentials, but the respective variation of current density with cell voltage differs in the voltage range (0.3–0.8 V). Although MEA performance can be improved by increasing the Pt (and Pt–Ru) concentration, a penalty is paid due to the tendency towards increased nanoparticle aggregation. The MEAs are also applied to a small pack of air-breathing DMFCs to assess their operability in mobile phones.