Artificial Packs Research Articles

Formally Exact Simulations of Mesoscale Exciton Diffusion in a Light-Harvesting 2 Antenna Nanoarray.

The photosynthetic apparatus of plants and bacteria combine atomically precise pigment-protein complexes with dynamic membrane architectures to control energy transfer on the 10-100 nm length scales. Recently, synthetic materials have integrated photosynthetic antenna proteins to enhance exciton transport, though the influence of artificial packing on the excited-state dynamics in these biohybrid materials is not fully understood. Here, we use the adaptive hierarchy of pure states (adHOPS) to perform a formally exact simulation of excitation energy transfer within artificial aggregates of light-harvesting complex 2 (LH2) with a range of packing densities. We find that LH2 aggregates support a remarkable exciton diffusion length ranging from 100 nm at a biological packing density to 300 nm at the densest packing previously suggested in an artificial aggregate. The unprecedented scale of these formally exact calculations also underscores the efficiency with which adHOPS simulates excited-state processes in molecular materials.

Appeasing Pheromones for the Management of Stress and Aggression during Conservation of Wild Canids: Could the Solution Be Right under Our Nose?

Simple SummaryMany canid species are declining globally. It is important to conserve these species that often serve as important predators within ecosystems. Continued human expansion and the resulting habitat fragmentation necessitate conservation interventions, such as translocation, artificial pack formation, and captive breeding programs. However, chronic stress often occurs during these actions, and can result in aggression, and the physiological suppression of immunity and reproduction. Limited options are currently available for stress and aggression management in wild canids. Pheromones provide a promising natural alternative for stress management; an appeasing pheromone has been identified for multiple domestic species and may reduce stress and aggression behaviours. Many pheromones are species-specific, and the appeasing pheromone has been found to have slight compositional changes across species. In this review, the benefits of a dog appeasing pheromone and the need to investigate species-specific derivatives to produce more pronounced and beneficial behavioural and physiological modulation in target species as a conservation tool are examined.Thirty-six species of canid exist globally, two are classified as critically endangered, three as endangered, and five as near threatened. Human expansion and the coinciding habitat fragmentation necessitate conservation interventions to mitigate concurrent population deterioration. The current conservation management of wild canids includes animal translocation and artificial pack formation. These actions often cause chronic stress, leading to increased aggression and the suppression of the immune and reproductive systems. Castration and pharmaceutical treatments are currently used to reduce stress and aggression in domestic and captive canids. The undesirable side effects make such treatments inadvisable during conservation management of wild canids. Pheromones are naturally occurring chemical messages that modulate behaviour between conspecifics; as such, they offer a natural alternative for behaviour modification. Animals are able to distinguish between pheromones of closely related species through small compositional differences but are more likely to have greater responses to pheromones from individuals of the same species. Appeasing pheromones have been found to reduce stress- and aggression-related behaviours in domestic species, including dogs. Preliminary evidence suggests that dog appeasing pheromones (DAP) may be effective in wild canids. However, the identification and testing of species-specific derivatives could produce more pronounced and beneficial behavioural and physiological changes in target species. In turn, this could provide a valuable tool to improve the conservation management of many endangered wild canids.

The successful reintroduction of African wild dogs (Lycaon pictus) to Gorongosa National Park, Mozambique.

Large carnivores have experienced widespread extirpation and species are now threatened globally. The ecological impact of the loss of large carnivores has been prominent in Gorongosa National Park, Mozambique, after most were extirpated during the 1977-92 civil war. To remedy this, reintroductions are now being implemented in Gorongosa, initiating with endangered African wild dogs (Lycaon pictus), hereafter 'wild dogs'. We describe the first transboundary translocation and reintroduction of founding packs of wild dogs to Gorongosa over a 28-month study period and evaluate the success of the reintroduction based on five key indicator categories. We also assess how wild dog space use and diet influenced their success. We found that pre-release, artificial pack formation in holding enclosures aided group cohesion and alpha pair establishment. Post-release, we also observed natural pack formations as a result of multiple dispersal events. Founder and naturally formed packs produced pups in two of the three breeding seasons and packs successfully recruited pups. Survival rate for all wild dogs was 73% and all mortality events were from natural causes. Consequently, the population grew significantly over the study period. All indicators of success were fully achieved and this study documents the first successful reintroduction of wild dogs into a large, unfenced landscape in Mozambique and only the second on the continent. Potential mechanisms underlying these early successes were the avoidance of habitats intensively used by lions, dietary partitioning with lion, avoidance of human settlements, and Gorongosa's management strategy. We predict further population expansion in Gorongosa given that 68% of the park is still unused by wild dogs. This expansion could be stimulated by continued reintroductions over the short- to medium-term. Recovery of wild dogs in Gorongosa could aid in the re-establishment of a larger, connected population across the greater Gorongosa-Marromeu landscape.

Experimental analysis on humidification-dehumidification desalination system using different packing materials with baffle plates

The primary objective of the present work is to address the issue of the water scarcity problem facing us globally. This manuscript also attempts to incorporate a Humidification-Dehumidification Desalination Technique (HDHT) using artificial and bio-based packing materials. The thermodynamic analysis of a Humidification-Dehumidification Desalination System (HDHDS) by mathematical and experimental methods is studied in detail. To produce the maximum amount of fresh water, two configurations are developed and analyzed under weather conditions prevailing in South India (INDIA). First, the experiments were carried out with artificial packing material (Polypropylene) with and without baffle plates. Next, the second set of configurations used bio-based packing material (Paddy grass) with and without baffle plates. The present analysis inferred that the volumes of fresh water produced were 0.39, 0.46, and 0.73 kg/h without, and with artificial and bio-based packing materials. The rate of fresh water production increased to 36.30% and 46% for artificial and bio-based materials respectively. There was an increase observed in Gain Output Ratio (GOR) as well in the range of 0.28, 0.40, and 0.65 without, and with artificial, and bio-based packing material. GOR increased up to 30% and 56%, when using artificial and bio-based packing material respectively. The present study reveals that the bio-based packing material is highly advantageous in the production of fresh water and in achieving better GOR.

A Novel Technique for Artificial Pack Formation in African Wild Dogs Using Odour Familiarity

Wildlife ACT Fund, Land Rover Centurion, Richard Bosman, Investec, Vaughan de la Harpe, Q20, and Jaguar Land Rover South Africa.

African wild dogs: Genetic viability of translocated populations across South Africa

South Africa holds a viable population of the endangered African wild dog (Lycaon pictus), with almost 500 individuals divided into (1) an unmanaged population in the Kruger National Park (KNP), (2) a free-roaming population, and (3) a managed metapopulation (MTP) that originated from reintroductions. Because metapopulation reserves are geographically isolated, translocations are ongoing to mimic natural dispersal. During this study, we questioned whether the metapopulation management plan for wild dogs has been successful at maintaining healthy levels of genetic diversity and avoiding inbreeding in packs. We evaluated whether the current approach is effective for long-term population viability and assessed whether population admixture occurs between the three populations. To achieve this, we amplified 20 microsatellite loci for genetic analysis. We found high levels of genetic variation, likely resulting from translocations and artificial pack formation. Results showed that in the absence of any management intervention, the MTP would lose 48% of its heterozygosity over a 100-year trajectory, and KNP 12% heterozygosity. Under the current management scenario, the MTP will maintain 95% of its heterozygosity. We found genetic evidence that limited recent dispersal occurs between the MTP and KNP (FST = 0.06). In conclusion, the metapopulation management plan can be considered successful based on the achieved population growth and preservation of genetic diversity. Our study highlights that genetic data form a critical part of conservation management, and that translocations can be a vital tool to restore genetic variability of species.

Factors affecting the success of artificial pack formation in an endangered, social carnivore: the African wild dog

AbstractSocial integration is an important factor when reintroducing group‐living species, but examples of the formation of social groups before reintroduction are largely lacking. African wild dogs Lycaon pictus are endangered, and reintroductions have become a routine part of range expansion in South Africa. Wild dogs form packs that are essential to their reproduction and survival, and artificial pack formation is often required before reintroduction. We examined the proximate (i.e. social integration) and ultimate (i.e. reproduction) success of 43 artificial pack formation attempts in the South African managed metapopulation, between 1995 and 2018. The top (and dominant) model for proximate success included an interaction between total group size and an initial separation fence. Larger groups took longer to integrate, irrespective of initial separation, whereas smaller groups brought together immediately integrated faster than those that were initially separated. The top models for ultimate success included an interaction between the proportion of males and number of days spent in the pre‐release enclosure, the total number of days in the enclosure and an interaction between the proportion of captive‐sourced individuals and the total number of days in the enclosure. Ultimate success increased when packs spent less time in the enclosure, especially if those packs had a low proportion of males (i.e. female biased) or included >25% captive‐sourced individuals. Neither the size of the artificially created pack nor the season in which the pack was released affected ultimate success. The success of social integration and reproductive success of artificially formed packs in this study was higher than for natural pack formations. We provide guidelines for optimizing future artificial pack formation in wild dogs for reintroduction success. Our results serve as an example of the practical importance of social behavior in successfully implementing conservation measures for group‐living species.

Behavioural Cues Can be Used to Predict the Outcome of Artificial Pack Formation in African Wild Dogs (Lycaon pictus)

The managed metapopulation of African wild dogs (Lycaon pictus) in South Africa consists of a number of subpopulations in geographically isolated reserves. These subpopulations are managed as one metapopulation through direct human intervention. Central to the success of the managed metapopulation is the artificial formation of packs by bonding groups of unrelated male and female wild dogs prior to release. Here, we provide data from both a failed and a successful bonding attempt in the De Beers Venetia Limpopo Nature Reserve and identify two variables which may be used to determine the probability of a successful artificial bonding attempt: distance to partitioning fence and frequency of ‘hoo-calls’. Both variables decreased significantly with time for the successful bonding attempt but not for the unsuccessful one. Based on our observations we suggest that behavioural observations can provide important cues to predict the success of bonding attempts, and that such cues may be used to terminate bonding a...

Sand pumping and well design in consolidated and semi-consolidated sandstone aquifers

Ingress of sand usually occurs in wells abstracting from sandstone aquifers that are poorly cemented. Impacts can be serious and may add significantly to production costs. They include loss of yield and continuity of supply, a reduction in the efficiency and operational life of wells and pumps, more frequent maintenance of wells and ultimately well replacement. The design of high-capacity sand-free wells in sandstone aquifers is often problematical. This is partly because a substantial proportion of the flow is through fractures, which means that well design criteria of screen slot size and artificial pack grain size and grading that have been developed for unconsolidated granular aquifers are not generally applicable. Also, many sandstone aquifers are multi-layered. Interbedded fine-grained and friable sandstone layers or loose sands are often responsible for sand entering a well. Excluding them is often difficult in practice without blocking productive fracture zones, and, therefore, risking a reduction of well yield. Well design alone is not always capable of controlling sand pumping. Pumping at a lower discharge rate, regulating flow at start-up, and the use of sand traps at the ground surface or inside wells are other measures that can assist in alleviating the problem.

Effect of Crystal Packing on Cro Dimer Conformation

X-ray crystallography is the primary method in structural biology for providing information about protein conformation. However, artificial packing forces in the crystal lattice select just a snapshot of a protein’s conformational ensemble, whereas proteins are flexible and may adopt different conformations in order to function. This raises the question, how accurately do X-ray structures describe the solution state of a protein? To address this critical issue, we have established protocols for performing Molecular Dynamics (MD) simulation in solution as well as the crystalline environment and for using network analysis to study the conformational ensembles1-3.As a model system, we consider the λ Cro repressor, whose solved X-ray structures range from a closed to an open global conformation. The fully open form is observed both bound and unbound to DNA. Network analysis and a free energy surface constructed from Replica Exchange MD reveal that closed and semi-open conformations are stable in solution, with a modest barrier separating these two states3. Yet the fully open conformation, while accessible, lies higher in free energy, indicating it requires stabilization by DNA or crystal contacts. Since a semi-open state is among the low energy conformations sampled in simulation, we propose that this form may initiate DNA recognition and only minor adjustments are needed to achieve the fully open conformation as observed in the functional complex. Subsequent crystal MD simulations estimated the strength of packing interfaces in the lattice, showing the influence of crystal form and mutation in stabilizing different dimer conformations. Our quantitative results will aid analysis of X-ray data in establishing protein structure-function relationships. [1] Vorontsov, I. I. and Miyashita, O. (2009) Biophys. J., 97, 2532-2540. [2] Campbell, Z. T., et al. (2010) Biophys. J. 99, 4012-4019. [3] Ahlstrom, L. S. and Miyashita, O., submitted.

Great house, poor food: effects of exotic leaf litter on shredder densities and caddisfly growth in 6 subtropical Australian streams

Exotic plants have invaded the riparian zones of many streams worldwide, but their consequences for stream fauna are seldom fully appreciated, especially when effects are sublethal. In northern New South Wales, Australia, the exotic tree camphor laurel (Cinnamomum camphora) has aggressively invaded riparian zones of many subtropical streams, often forming monocultures and outcompeting native vegetation. In forested streams, leaf litter provides a major source of food for some stream fauna and is broken down by shredding invertebrates. We hypothesized that shredder densities would be reduced in streams where the riparian zone was dominated by camphor laurel because of the reputed chemical toxicity of the leaf litter. We also investigated the sublethal effects of camphor laurel litter by comparing growth rates of larvae of the common shredding caddisfly Anisocentropus (Calamoceratidae:Trichoptera) reared on a diet of camphor laurel vs native leaf litter. Shredder densities were significantly lower in streams where camphor laurel constituted >38% of the benthic leaf litter than in streams with a lower percentage of camphor laurel litter (0.43 ± 0.13 vs 1.43 ± 0.28 individuals/g dry mass of litter; mean ± SE). Shredder densities were greater on artificial packs of native leaf litter than on packs of camphor laurel litter in camphor laurel–infested streams (3.37 ± 1.01 vs 1.40 ± 0.46 ind./g dry mass of litter). However, shredder densities did not differ between leaf-litter types in streams lined with native vegetation. Anisocentropus growth was retarded when larvae were fed only camphor laurel compared to those reared on native leaf litter. This native caddisfly used camphor laurel leaves for case construction, but impaired larval growth in infested streams implies a sublethal impact that has repercussions for energy transfer to higher trophic levels (e.g., predatory fish). Our findings suggest effects similar to those often reported for shredder assemblages in temperate streams subject to invasion by exotic riparian plants, indicating that the tropical–temperate differences in this aspect of leaf breakdown might not be as marked as previously suspected. Carefully managed river restoration to remove camphor laurel to allow recovery by native vegetation is recommended in these streams. Population dynamics of Anisocentropus could provide a useful indicator of the ecological success of such restoration.

Solute dilution under imbibition and drainage conditions in a heterogeneous structure: Modeling of a sand tank experiment

This study aims at modeling the transport of a conservative tracer in two dimensions, as experimentally observed in a strongly heterogeneous medium under conditions of variable water saturation during drainage and imbibition. Solute transport experiments were conducted in a sand tank containing an artificial packing of three quartz sands of different particle sizes. The packing was characterized by the presence of numerous homogeneous layers (0.5 × 5 × 5 cm) inclined at 45° and randomly distributed in a tank. Six different stationary flow conditions were sequentially established during imbibition and drainage. When a stationary flow regime was reached, several solute pulses were applied at different positions at the upper surface of the sand structure. The transport regime was studied by monitoring the tracer plumes injected as point-like pulses at the surface, as they travelled through the sand bedding. A textural map was generated from a digital image of the sand bedding. The Richards equation was solved with the experimental boundary conditions assuming homogeneity of the individual sand layers. The hydraulic properties of the three quartz sands were deduced from multistep-outflow column experiments [Ursino N, Gimmi T. Combined effect of heterogeneity, anisotropy and saturation on steady state flow and transport: structure recognition and numerical simulation. Water Resour Res 2004;40. doi:10.1029/2003WR002180]. The convection–dispersion equation was solved on the resulting flow fields for solute pulses of given solute mass applied onto the top boundary at the same positions as in the experiment. The simulated and observed solute concentration distributions were then compared. In agreement with the experimental observations, the simulations reproduced the existence of preferential pathways in those stationary flow fields at low saturation degrees. The values of the vertical and horizontal macroscopic dispersivities obtained from the simulations are smaller than experimentally observed, especially at low flow rates. The simulated solute concentration distributions show a realistic degree of solute dilution quantified as reactor ratio.

Dynamics of Fine Particulate Organic Matter (FPOM) and Macroinvertebrates in Natural and Artificial Leaf Packs

This paper provides data on fine particulate organic matter (FPOM) and macroinvertebrates associated to natural and artificial leaf packs in a small woodland stream (Schlaube, Brandenburg). Macroinvertebrate colonisation and the dynamics of FPOM were studied in oven-dried alder leaf packs, air-dried alder leaf packs and packs with artificial leafshaped substrate exposed in the stream during a 68-day period. The importance of FPOM as a potential food source for macroinvertebrates especially in artificial leaf packs was evaluated. Changes in the quantity as well as in the chemical composition of the accumulating FPOM (>63 and 63 μm and decreased in both size-fractions with length of exposure. Referring to leaf area the abundance of macroinvertebrates continually increased in all packs till the end of exposure, whereas the numbers in artificial packs remained below that in alder leaf packs. The taxonomic composition of all treatments was very similar with Gammarus pulex being the most abundant taxon in all packs until day 42, while afterwards the caddis fly genus Hydropsyche gained in importance. The amphipod Gammarus pulex in general did not show a preference for air-dried alder leaf packs compared to oven-dried alder leaf and artificial packs. Corresponding dynamics of macroinvertebrate colonisation and FPOM content in artificial packs support the hypothesis that FPOM functions not only as an important food source for macroinvertebrates including gammarideans but also as a control mechanism of macroinvertebrate abundance in stream habitats. Even if the accumulation of FPOM and drifting macroinvertebrates might be influenced by the same abiotic factor (e.g. by reduction in stream velocity inside the packs) it is quite unlikely that only physical properties caused the invertebrates to stay.

The variability of soil moisture diffusivity of loamy to silty soils on marl, determined by the hot air method

Various attempts have been made to estimate hydraulic characteristics from textural soil properties, often by testing models on materials with artificial packing. The latter approach prevented soil structure and the arrangement and orientation of soil particles from being taken into account. In this paper the moisture diffusivity (in short “diffusivity”) characteristics of loamy to silty soils with intermediate soil moisture contents are examined. The relationship between diffusivity and soil moisture content was determined by the hot air method on undistributed soil cores from eight different sites in the Ardeche Basin, France. Our objectives were: (1) to obtain reproducible diffusivity values; (2) to distinguish between the natural and procedural variability; (3) to examine the spatial variability; and (4) to discuss whether soil texture can be used to distinguish between the diffusivities of different loamy soils. As for problems of regionalization, it was found that the diffusivity of these soils can be related to the physiographic diversity of the area, rather than to soil texture.

Leaf‐pack dynamics in a southern African mountain stream

SUMMARY 1. The occurrence, composition and invertebrate fauna of naturally‐occurring leaf packs were studied over 24 months in Langrivier, a second‐order mountain stream in the south‐western Cape, South Africa. Langrivier is shallow and fast‐flowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year.2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall from riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7–10−5 m3) in winter when discharge was high, and largest (maximum dry mass 191 g, maximum volume 4.2–10−3 m3) in spring when discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % of the stream bed and had a mean abundance of 0.46 packs m−2 of stream bed. They were ephemeral, lasting on average <1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year.3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002–0.030), presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December).4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,

Differential Decomposition of Leaves in Grassland and Gallery Forest Reaches of Kings Creek

The decomposition of autumn shed leaves of hackberry (Celtis occidentalis L.) and elm (Ulmus americana L.) in a gallery forest reach and a grassland reach of Kings Creek was examined by placing 24 artificial leaf packs of each species at the two stream sites. Sampling was done after 24 hours and weekly thereafter for a seven week period. No differences between elm and hackberry leaf decomposition rates were measured. The mean percentage weight loss of elm leaves during the sampling period was 90.3% of their ash-free dry weight in the gallery forest reach and 88.9% in the grassland reach. The decay coefficients were -0.0211 and -0.0199 respectively. Hackberry leaves lost 93.8% of their ash-free dry weight at both sites (decay coefficient of -0.02 5). Larvae of the leaf shredding insect, Tipula, were found to influence the decomposition process in the grassland reach but not in the gallery forest reach. The Tipula larvae were estimated to exert their greatest influence on the elm leaves. Headwater streams in forested ecosystems are characterized by the import of allochthonous organic matter, usually in the form of leaf litter (Fisher and Likens, 1973; Petersen and Cummins, 1974; and others). The decomposition of terrestrial leaf material is a major pathway of energy flow through such stream ecosystems (Anderson and Sedell, 1979). The rate of decomposition is controlled by a variety of factors including stream microbial populations (Suberkropp and Klug, 1976), stream water temperatures (Bott, 1975; Suberkropp and Klug, 1976; Paul et al., 1978), chemical composition of the leaf material (Benfield et al., 1979), invertebrate populations (Anderson and Sedell, 1979; Wallace et al., 1982; Kirby et al., 1983), and current velocity (Boling et al., 1982; Gurtz et al., 1982). However, the initial fragmentation of the leaf material is dependent upon mechanical breakage in conjunction with microbial decomposition (Benfield et al., 1979). Rounick and Winterbourne (1983) observed that differences in leaf decomposition rates were associated primarily with differences in the benthic invertebrates related to the physical characteristics of the streambed. There are several mechanisms This content downloaded from 157.55.39.151 on Fri, 29 Jul 2016 04:00:56 UTC All use subject to http://about.jstor.org/terms 18 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE involved in the degradation of allochthonous organic matter in streams. The interactions among them, while various, are associated with watershed characteristics. Kings Creek is a stream with its headwaters in grassland rather than in forest. The riparian vegetation changes to forest downstream. The upper reaches are bordered by riparian vegetation dominated by grasses. The stream side vegetation of the middle reaches is comprised of small trees, shrubs and grasses. The vegetation change to gallery forest in the lower reaches is abrupt and dramatic. The purpose of this study was to determine the decomposition rates of artificial packs of leaves from elm (Ulmus americana L.) and hackberry (Celtis occidentalis L.) in two of these distinctly different riparian reaches of Kings Creek. The hypothesis tested was that autumn shed leaves of elm and hackberry trees would decompose more rapidly in a gallery forest reach of Kings Creek than in a grassland reach because these leaves form a part of the natural organic input and stream microbes would be more adapted to decomposing the leaves. Additionally, the microbes in the grassland reaches were hypothesized to be less active on substrates not experienced naturally.

Effect of the Addition of Certain Chemicals On Oil Recovery During Waterflooding

Abstract A laboratory study was conducted to determine the recovery of high-viscosity crude oil from natural unconsolidated sand by wate1flooding with a number of chemical solutions. Displacement tests were run using chemical solutions to displace a high-viscosity crude oil from artificial packs of unconsolidated core sand. Results of the displacement tests showed that oil recovery was increased by a number of chemical solutions. Sodium hydroxide in bTi.ne at concentrations less than 0.01 per cent by weight had little effect on recovery as compared to brine floods. Sodium hydroxide concentrations of 0.1 per cent OT greater increased recovery significantly. The interfacial tension between Lloydminster crude oil and various aqueous solutions was greatly reduced by the addition of a number of chemicals to the aqueous solutions. The presence of sodium chloride in the aqueous solution reduced the a1nount of chemical required for the reduction of the interfacial tension between crude oil and the solution to a given level. The reduction in interfacial tension influenced the recovery of oil. The production of a very stable emulsion and evidence of reduced water mobility during displacement tests suggested that emulsification may have occurred within the core. The formation of an emulsion may have increased oil recovery. Introduction THERE ARE large known reserves of heavy oil in Western Canada. However, the nature of the reservoirs and oils involved are such that primary recovery is estimated at 5 to 6 per cent(l), with a possibility of increasing total recovery to about 10 per cent of the oil in place by means of conventional water-flooding. In order that these recoveries be increased to a more acceptable value) new secondary recovery techniques must be developed. This study represents a continuation of a series of investigations conducted at the University of Alberta(2,3) into the effect of chemical additives on water-flood recovery from heavy oil reservoirs. It is well known that the preferential wettability of the solid surfaces in porous media influences their relative permeability, capillary pressure and waterflood ability characteristics. These properties can be altered by introducing any one of a variety of liquids which alter the contact angle. However, if a surface is oil-wet, the contact angle (conventionally measured through the denser phase) cannot be reduced below 90 degrees, so that further reductions in adhesion tension and therefore energy requirements for oil displacement can only be realized through reductions in interfacial tension. Reductions in interfacial tension also serve to reduce capillary forces, thereby further reducing the amount of energy required for oil displacement. Similarly, changing a system from an oil-wet to a water-wet state improves the relative permeability to oil and increases the efficiency of the oil displacement process. Several investigators(4,5,6) have reported obtaining higher waterflood recoveries from preferentially water-wet systems than from corresponding oil-wet systems. The ability of some oils to preferentially wet silica sand surfaces has been noted and the use of chemicals or "flooding agents" to increase recovery from such sands has been considered by a number of investigators.