Morphologies of three-dimensional shear bands in granular media

We present numerical results on spontaneous symmetry breaking strain localization in axisymmetric triaxial shear tests of granular materials. We simulated shear band formation using three-dimensional Distinct Element Method with spherical particles. We demonstrate that the local shear intensity, the angular velocity of the grains, the coordination number, and the local void ratio are correlated and any of them can be used to identify shear bands, however the latter two are less sensitive. The calculated shear band morphologies are in good agreement with those found experimentally. We show that boundary conditions play an important role. We discuss the formation mechanism of shear bands in the light of our observations and compare the results with experiments. At large strains, with enforced symmetry, we found strain hardening.Comment: 6 pages 5 figures, low resolution figures

Feeding chicory ( Cichorium intybus ) selectively reduces Ostertagia ostertagi infection levels in cattle

Objectives: Studies were conducted to test the potential use of chicory against gastrointestinal nematode infections in cattle. Methods: In study 1, fifteen 2-4 months-old dairy calves were allocated into a chicory (CHI, n=9) or control (CTL, n=6) group. CHI and CTL were stabled and fed with chicory silage or hay, resp., ad lib for 56 days. Protein/energy intakes were equalized between groups throughout the study. After 14 days on the diet all calves were infected with 10,000 Ostertagia ostertagi and 66,000 Cooperia oncophora third-stage (L3) larvae. In study 2, twenty 4-6 months-old dairy calves grazed a second-year, pure chicory sward (CHI, n=10) or a ryegrass/white clover pasture (CTL, n=10) for 43 days. After 7 days on the diet all calves were infected with 20,000 O. ostertagi L3. In both studies, individual live weights were recorded and faecal egg counts were calculated as number of eggs per g of dried feces (FECDM). At day 56 (study 1) calves were killed for worm recovery. Live weights and log-transformed FECDM were analysed by ANOVA using repeated measurements. Log-transformed worm counts were analysed by t-test. Results: In study 1 daily live weight gains were 500 and 329 g/day in CHI and CTL animals, resp. (p=0.02). Mean FECDM were not significantly different between groups (p=0.19). O. ostertagi geo mean worm counts were 1599 (± 296) and 3752 (± 258) in CHI and CTL groups, resp. (p0.05). From this point, egg excretion in CHI calves was significantly reduced and by day 36 post-infection FECDM was decreased by 48-65% compared to CTL (P<0.05). Discussion: Feeding on a chicory diet demonstrated a marked anthelmintic effect against O. ostertagi in both trials, whereas C. oncophora in study 1 was unaffected. Apparently, chicory does not interfere with worm establishment of O. ostertagi but significantly reduces egg excretion and adult worm counts. The lower weight gains in study 2 probably reflect lower energy consumption in this group and suggest that duration of grazing of pure chicory should be limited to selectively target established O. ostertagi adult populations

Condensed tannins in the gastrointestinal tract of cattle after sainfoin (Onobrychis viciifolia) intake and their possible relationship with anthelmintic effects

The fate of condensed tannins (CTs) along the digestive tract of ruminants is not well known and may account for the variable efficacy of CTs against gastrointestinal nematodes in different locations. Here, we analyzed sainfoin CTs in the digesta of cattle from two separate experiments. When using the acetone-butanol-HCl assay, the total CTs concentrations in the digestive tract were close to those in the diets (6.3 and 1.5% of DM in Expt. 1 and 2, resp.) indicating that CTs remained largely undegraded and unabsorbed. Yet with the thiolysis assay in Expt. 1, CTs concentration was much higher in the abomasum (2.3 ± 0.4 % of DM) compared with the rumen, small and large intestines, along with increases of mean size and percentage of prodelphinidins within CTs. This corroborates the anthelmintic efficacy reported only against Ostertagia ostertagi in the abomasum. In Expt. 2, no anthelmintic effect was observed against the larval exsheathment in the rumen, probably because the dietary level of CTs was too low. Overall, the level of CTs accessible to thiolysis in the gut appears to be critical for anthelmintic activity, which is favored under the acidic conditions of the abomasum

Anthelmintic effects of forage chicory (Cichorium intybus) against gastrointestinal nematode parasites in experimentally infected cattle

Two experiments studied the effects of dietary chicory against gastrointestinal nematodes in cattle. In Experiment (Exp.) 1, stabled calves were fed chicory silage (CHI1; n = 9) or ryegrass/clover hay (CTL1; n = 6) with balanced protein/energy intakes between groups. After 16 days, all calves received 10 000 Ostertagia ostertagi and 66 000 Cooperia oncophora third-stage larvae (L3) [day (D) 0 post-infection (p.i.)]. In Exp. 2, calves were assigned to pure chicory (CHI2; n=10) or ryegrass/clover (CTL2; n = 10) pastures. After 7 days, animals received 20 000 O. ostertagi L3/calf (D0 p.i.) and were moved regularly preventing pasture-borne infections. Due to poor regrowth of the chicory pasture, CHI2 was supplemented with chicory silage. At D40 p.i. (Exp. 1) and D35 p.i. (Exp. 2) calves were slaughtered for worm recovery. In Exp.1, fecal egg counts (FEC) were similar between groups. However, O. ostertagi counts were significantly reduced in CHI1 by 60% (geometric mean; P &lt; 0·01), whereas C. oncophora burdens were unaffected (P = 0·12). In Exp. 2, FEC were markedly lowered in CHI2 from D22 p.i onwards (P &lt; 0·01). Ostertagia ostertagi adult burdens were significantly reduced in CHI2 by 66% (P &lt; 0·001). Sesquiterpene lactones were identified only in chicory (fresh/silage). Chicory shows promise as an anti-Ostertagia feed for cattle and further studies should investigate its on-farm use

Feeding chicory (Cichorium intybus) selectively reduces Ostertagia ostertagi infection levels in cattle

Objectives: Studies were conducted to test the potential use of chicory against gastrointestinal nematode infections in cattle. Methods: In study 1, fifteen 2-4 months-old dairy calves were allocated into a chicory (CHI, n=9) or control (CTL, n=6) group. CHI and CTL were stabled and fed with chicory silage or hay, resp., ad lib for 56 days. Protein/energy intakes were equalized between groups throughout the study. After 14 days on the diet all calves were infected with 10,000 Ostertagia ostertagi and 66,000 Cooperia oncophora third-stage (L3) larvae. In study 2, twenty 4-6 months-old dairy calves grazed a second-year, pure chicory sward (CHI, n=10) or a ryegrass/white clover pasture (CTL, n=10) for 43 days. After 7 days on the diet all calves were infected with 20,000 O. ostertagi L3. In both studies, individual live weights were recorded and faecal egg counts were calculated as number of eggs per g of dried feces (FECDM). At day 56 (study 1) calves were killed for worm recovery. Live weights and log-transformed FECDM were analysed by ANOVA using repeated measurements. Log-transformed worm counts were analysed by t-test. Results: In study 1 daily live weight gains were 500 and 329 g/day in CHI and CTL animals, resp. (p=0.02). Mean FECDM were not significantly different between groups (p=0.19). O. ostertagi geo mean worm counts were 1599 (± 296) and 3752 (± 258) in CHI and CTL groups, resp. (p0.05). From this point, egg excretion in CHI calves was significantly reduced and by day 36 post-infection FECDM was decreased by 48-65% compared to CTL (P<0.05). Discussion: Feeding on a chicory diet demonstrated a marked anthelmintic effect against O. ostertagi in both trials, whereas C. oncophora in study 1 was unaffected. Apparently, chicory does not interfere with worm establishment of O. ostertagi but significantly reduces egg excretion and adult worm counts. The lower weight gains in study 2 probably reflect lower energy consumption in this group and suggest that duration of grazing of pure chicory should be limited to selectively target established O. ostertagi adult populations

Contact dynamics in a gently vibrated granular pile

We use multi-speckle diffusive wave spectroscopy (MSDWS) to probe the micron-scale dynamics of a granular pile submitted to discrete gentle taps. The typical time-scale between plastic events is found to increase dramatically with the number of applied taps. Furthermore, this microscopic dynamics weakly depends on the solid fraction of the sample. This process is strongly analogous to the aging phenomenon observed in thermal glassy systems. We propose a heuristic model where this slowing down mechanism is associated with a slow evolution of the distribution of the contact forces between particles. This model accounts for the main features of the observed dynamics.Comment: 4 pages, 4 figure

Anti-parasitic activity of pelleted sainfoin (Onobrychis viciifolia) against Ostertagia ostertagi and Cooperia oncophora in calves

BACKGROUND: Increasing anthelmintic-resistance in nematodes of ruminants emphasises the need for sustainable parasite control. Condensed tannin-containing legume forages such as sainfoin (Onobrychis viciifolia) have shown promising anthelmintic properties in small ruminants but this has never been explored in cattle. Therefore, our aim was to examine the efficacy of sainfoin against cattle nematodes in vivo. METHODS: Fifteen Jersey male calves (2–4 month-old) were allocated into two groups and fed isoproteic and isoenergetic diets mainly composed of sainfoin pellets (Group SF; n = 9, three pens) or concentrate and grass-clover hay (Group CO; n = 6, two pens). After 16 days of adaptation, all animals were experimentally infected with 10,000 and 66,000 third-stage larvae of Ostertagia ostertagi and Cooperia oncophora, respectively. Egg excretion, blood parameters and bodyweights were recorded throughout the study. Worms were harvested by sieving for quantification and scanning electron microscopy (SEM) 42 days post-infection (dpi) when the calves were necropsied. RESULTS: The number of O. ostertagi adults in the abomasum was reduced by 50 % in Group SF compared with Group CO (P < 0.05). This was further reflected in higher albumin (P < 0.1) and lower pepsinogen levels (P < 0.05) in Group SF at 21 dpi, and structural damage of the worm cuticle could be visualised by SEM. Yet, the nematode egg excretion in Group SF was not significantly different from that of the controls (P > 0.05). Likewise, no statistical difference in total worm burdens of C. oncophora was found between the groups. Weight gains were lower for Group SF (P < 0.05), which may reflect lower digestibility and phosphorus levels in the SF diet, despite similar feed intake at pen-level. CONCLUSIONS: Overall, the effect of sainfoin on abomasal nematodes corroborates results from studies with small ruminants and encourages further investigations of the use of this crop for control of cattle nematodes

Impact of chemical structure of flavanol monomers and condensed tannins on in vitro anthelmintic activity against bovine nematodes

Plants containing condensed tannins (CT) may have potential to control gastrointestinal nematodes (GIN) of cattle. The aim was to investigate the anthelmintic activities of four flavan-3-ols, two galloyl derivatives and 14 purified CT fractions, and to define which structural features of CT determine the anti-parasitic effects against the main cattle nematodes. We used in vitro tests targeting L1 larvae (feeding inhibition assay) and adults (motility assay) of Ostertagia ostertagi and Cooperia oncophora. In the larval feeding inhibition assay, O. ostertagi L1 were significantly more susceptible to all CT fractions than C. oncophora L1. The mean degree of polymerization of CT (i.e. average size) was the most important structural parameter: large CT reduced larval feeding more than small CT. The flavan-3-ols of prodelphinidin (PD)-type tannins had a stronger negative influence on parasite activity than the stereochemistry, i.e. cis- vs trans-configurations, or the presence of a gallate group. In contrast, for C. oncophora high reductions in the motility of larvae and adult worms were strongly related with a higher percentage of PDs within the CT fractions while there was no effect of size. Overall, the size and the percentage of PDs within CT seemed to be the most important parameters that influence anti-parasitic activity

Anomalous acoustic reflection on a sliding interface or a shear band

We study the reflection of an acoustic plane wave from a steadily sliding planar interface with velocity strengthening friction or a shear band in a confined granular medium. The corresponding acoustic impedance is utterly different from that of the static interface. In particular, the system being open, the energy of an in-plane polarized wave is no longer conserved, the work of the external pulling force being partitioned between frictional dissipation and gain (of either sign) of coherent acoustic energy. Large values of the friction coefficient favor energy gain, while velocity strengthening tends to suppress it. An interface with infinite elastic contrast (one rigid medium) and V-independent (Coulomb) friction exhibits spontaneous acoustic emission, as already shown by M. Nosonovsky and G.G. Adams (Int. J. Ing. Sci., {\bf 39}, 1257 (2001)). But this pathology is cured by any finite elastic contrast, or by a moderately large V-strengthening of friction. We show that (i) positive gain should be observable for rough-on-flat multicontact interfaces (ii) a sliding shear band in a granular medium should give rise to sizeable reflection, which opens a promising possibility for the detection of shear localization.Comment: 13 pages, 10 figure

Plastic Flow in Two-Dimensional Solids

A time-dependent Ginzburg-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables are the displacement field \bi u and the lattice velocity {\bi v}=\p {\bi u}/\p t. Damping is assumed to arise from the shear viscosity in the momentum equation. The elastic energy density is a periodic function of the shear and tetragonal strains, which enables formation of slips at large strains. In this work we neglect defects such as vacancies, interstitials, or grain boundaries. The simplest slip consists of two edge dislocations with opposite Burgers vectors. The formation energy of a slip is minimized if its orientation is parallel or perpendicular to the flow in simple shear deformation and if it makes angles of $\pm \pi/4$ with respect to the stretched direction in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow is stopped. Thus large applied strains give rise to metastable, structurally disordered states. We divide the elastic energy into an elastic part due to affine deformation and a defect part. The latter represents degree of disorder and is nearly constant in plastic flow under cyclic straining.Comment: 16pages, Figures can be obtained at http://stat.scphys.kyoto-u.ac.jp/index-e.htm