Self-ratcheting Stokes drops driven by oblique vibrations

We develop and analyze a minimal hydrodynamic model in the overdamped limit to understand why a drop climbs a smooth homogeneous incline that is harmonically vibrated at an angle different from the substrate normal [Brunet, Eggers and Deegan, Phys. Rev. Lett. 99, 144501 (2007)]. We find that the vibration component orthogonal to the substrate induces a nonlinear (anharmonic) response in the drop shape. This results in an asymmetric response of the drop to the parallel vibration and, in consequence, in the observed net motion. Beside establishing the basic mechanism, we identify scaling laws valid in a broad frequency range and a flow reversal at high frequencies.Comment: 4 pages, 7 figure

Performance and carcass quality of fully on partly outdoor reared pigs in organic production

Outdoor rearing of finishers can be considered a relevant option in organic pig production. The performance and carcass characteristics of 245 organically produced and free-range born crossbred pigs allocated to five treatments were compared. The five treatments were: transfer to a barn with free access to feed (1) at weaning and until slaughter, (2) at a live weight of 40 kg and until slaughter, (3) at live weight of 80 kg and until slaughter, or reared at pasture (4) with free or (5) limited access to concentrates until slaughter. Pigs fed ad libitum fed indoor compared to pigs fed ad libitum outdoor had a significant lower feed consumption (5 MJ ME /kg gain), lower lean percentage (2.3%), and a higher backfat depth (1.1 mm)(all P < 0.05). Compared with outdoor pigs fed ad libitum, restricted feeding outdoor resulted in a significantly lower daily gain (107 g), a lower feed consumption (6.3 MJ ME/kg gain), higher lean percentage (2.1% units), and a reduced backfat (1.8 mm) (all P < .001). Pigs, which at a live weight of 40 kg, were transferred to indoor facilities with free access to feed compensated almost completely before slaughter, while pigs transferred at 80 kg live weight only compensated little. Although the housing environment (in- or outdoor) seems to affect performance and carcass traits, the length of energy restriction appears to be of greater importance

From a thin film model for passive suspensions towards the description of osmotic biofilm spreading

Biofilms are ubiquitous macro-colonies of bacteria that develop at various interfaces (solid-liquid, solid-gas or liquid-gas). The formation of biofilms starts with the attachment of individual bacteria to an interface, where they proliferate and produce a slimy polymeric matrix - two processes that result in colony growth and spreading. Recent experiments on the growth of biofilms on agar substrates under air have shown that for certain bacterial strains, the production of the extracellular matrix and the resulting osmotic influx of nutrient-rich water from the agar into the biofilm are more crucial for the spreading behaviour of a biofilm than the motility of individual bacteria. We present a model which describes the biofilm evolution and the advancing biofilm edge for this spreading mechanism. The model is based on a gradient dynamics formulation for thin films of biologically passive liquid mixtures and suspensions, supplemented by bioactive processes which play a decisive role in the osmotic spreading of biofilms. It explicitly includes the wetting properties of the biofilm on the agar substrate via a disjoining pressure and can therefore give insight into the interplay between passive surface forces and bioactive growth processes

Spontaneous polarization in an interfacial growth model for actin filament networks with a rigorous mechano-chemical coupling

Many processes in eukaryotic cells, including cell motility, rely on the growth of branched actin networks from surfaces. Despite its central role the mechano-chemical coupling mechanisms which guide the growth process are poorly understood, and a general continuum description combining growth and mechanics is lacking. We develop a theory that bridges the gap between mesoscale and continuum limit and propose a general framework providing the evolution law of actin networks growing under stress. This formulation opens an area for the systematic study of actin dynamics in arbitrary geometries. Our framework predicts a morphological instability of actin growth on a rigid sphere, leading to a spontaneous polarization of the network with a mode selection corresponding to a comet, as reported experimentally. We show that the mechanics of the contact between the network and the surface plays a crucial role, in that it determines directly the existence of the instability. We extract scaling laws relating growth dynamics and network properties offering basic perspectives for new experiments on growing actin networks.Comment: 7 pages, 4 figure

Modelling of surfactant-driven front instabilities in spreading bacterial colonies

The spreading of bacterial colonies at solid-air interfaces is determined by the physico-chemical properties of the involved interfaces. The production of surfactant molecules by bacteria is a widespread strategy that allows the colony to efficiently expand over the substrate. On the one hand, surfactant molecules lower the surface tension of the colony, effectively increasing the wettability of the substrate, which facilitates spreading. On the other hand, gradients in the surface concentration of surfactant molecules result in Marangoni flows that drive spreading. These flows may cause an instability of the circular colony shape and the subsequent formation of fingers. In this work, we study the effect of bacterial surfactant production and substrate wettability on colony growth and shape within the framework of a hydrodynamic thin film model. We show that variations in the wettability and surfactant production are sufficient to reproduce four different types of colony growth, which have been described in the literature, namely, arrested and continuous spreading of circular colonies, slightly modulated front lines and the formation of pronounced fingers

Full or partial outdoor rearing of slaughter pigs – effects on performance, carcass quality and nutrient load

An experiment with slaughter pigs from weaning to slaughter including five treatments and five replicates was carried out at the Danish organic experimental station, Rugballegård. Treatments included full or partial outdoor rearing of the pigs, and the replicates covered the seasonal effects. Pigs fed ad libitum indoors had a significantly lower feed consumption (5 MJ ME /kg gain), a lower lean percentage (2.3% points), and a higher backfat depth (1.1 mm, P < 0.05) than pigs fed ad libitum outdoors. Compared with outdoor pigs fed ad libitum, restricted feeding outdoors resulted in a significantly lower daily gain (107 g), a lower feed consumption (6.3 MJ ME/kg gain), higher lean percentage (2.1% points), and a reduced backfat (1.8 mm) (P <0.001). The content of soil nitrogen was considerably higher than for the soil outside the paddocks. Despite a considerable variation within the paddocks, N was distributed throughout the paddock. The present investigation highlights the fact that outdoor rearing of organic finishers may be a competitive option even in a temperate climate and all year round

Integration of organic animal production intor land use with special reference to swine and poultry

The development in organic livestock production can be attributed to an increased consumer interest in organic products while, at the same time, increased farmers' interest in converting to organic production methods—often stimulated by governmental support or subsidies. It is important that organic production systems can fulfil the expectations of each of these stakeholders if organic livestock production is to increase further. This is of particular importance if organic pig and poultry production (other than egg) is to move from the present niche-production to a significant place in the food market, as in the case of beef and milk. It can be argued that the limited organic pork and poultry production is related to the fact that it is far more difficult for farmers to change the existing production systems for pig and poultry compared to production systems for cattle and other ruminants in a way that gives a harmonious balance between the different aims of organic farming. Conflicts may occur as to the most appropriate rearing practice in considerating the basic aspects of the innate behaviour of animals on one hand, the risk of pollution from the production on the other and, in addition, the aim of producing in sufficient quantities. These possible conflicts are reflected in the compromises made in national or EU regulations on organic farming. In the regulations for organic farming, the aspect of allowing a high degree of natural behaviour of the livestock is, among others, translated in the requirement that livestock, in certain periods of their life or of the year, should be allowed to graze or have access to an outdoor area. The most common outdoor systems for pig and poultry used in intensively managed organic production have some significant drawbacks in relation to environmental impact (risk of N-leaching and ammonia volatilisation), animal welfare (nose-ringed sows), high mortality in poultry and workload and management constraints. From recent experience of such systems, it is argued that there is a need for a radical development of the systems. There is a need for outdoor/free range systems (for the sake of the livestock), which are constructed and managed in such a way that the livestock, at the same time, exert a positive influence on other parts of the farming system. There is evidence that pregnant sows can fulfil their nutritional needs to a large extent by grazing, that co-grazing sows with heifers can diminish the parasite burden of the heifers, and that the pig inclination for rooting can be managed in a way that makes ploughing and other heavy land cultivation more or less superfluous. As regard poultry, there is an indication that quite big flocks can be managed efficiently in a way where the flock act as weeders in other crops or fight pests in orchards. These elements need to be further explored as a basis for future system development

Complex wave patterns in an effective reaction–diffusion model for chemical reactions in microemulsions

An effective medium theory is employed to derive a simple qualitative model of a pattern forming chemical reaction in a microemulsion. This spatially heterogeneous system is composed of water nanodroplets randomly distributed in oil. While some steps of the reaction are performed only inside the droplets, the transport through the extended medium occurs by diffusion of intermediate chemical reactants as well as by collisions of the droplets. We start to model the system with heterogeneous reaction–diffusion equations and then derive an equivalent effective spatially homogeneous reaction–diffusion model by using earlier results on homogenization in heterogeneous reaction–diffusion systems [ S. Alonso, M. Bär, and R. Kapral, J. Chem. Phys. 134, 214102 (2009)]. We study the linear stability of the spatially homogeneous state in the resulting effective model and obtain a phase diagram of pattern formation, that is qualitatively similar to earlier experimental results for the Belousov–Zhabotinsky reaction in an aerosol OT (AOT)-water-in-oil microemulsion [ V. K. Vanag and I. R. Epstein, Phys. Rev. Lett. 87, 228301 (2001)]. Moreover, we reproduce many patterns that have been observed in experiments with the Belousov–Zhabotinsky reaction in an AOT oil-in-water microemulsion by direct numerical simulations.Peer ReviewedPostprint (published version

Metabolic and cometabolic degradation of herbicides in the fine material of railway ballast

Microbial degradation of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) and mineralization of 4-chloro-2-methylphenoxyacetic acid (MCPA) were studied in soil samples taken from the ballast layers of three Swedish railway embankments. The degradation of diuron followed first-order kinetics and half-lives ranged between 122 and 365 days. The half-lives correlated strongly with microbial biomass estimated by substrate-induced respiration (SIR; R=-0.85; p<0.05) and with the amount of organic matter measured as loss on ignition (R=-0.87; p<0.05). Accumulation of the metabolites 1-(3,4-dichlorophenyl)-3-methyl urea (DCPMU) and 1-(3,4-dichlorophenyl) urea (DCPU) was observed in all samples and these were only detectably degraded in the sample with the highest SIR. Addition of ground lucerne straw to the ballast samples stimulated microbial activity and led to increased formation of metabolites, but further transformation of DCPMU and DCPU was not enhanced. Mineralization of MCPA followed growth-linked kinetics and the time for 50% mineralization was 44.5±7.1 days in samples of previously untreated ballast. In samples of ballast that had been previously treated with the herbicide formulation MCPA 750, the time for 50% mineralization was reduced to 13.7±11.3 days. The number of MCPA degraders, quantified using an MPN technique, was clearly increased but highly variable. An average yield of 0.18 cells pg−1 of MCPA was estimated from the kinetic data. The yield estimates correlated with the amount of nitrogen in the ballast, indicating that mineralization of MCPA was nitrogen-limited in the railway embankments studied. This has practical implications for weed control using herbicides on railways