Quasi-non-linear fracture mechanics analysis of splitting failure in simply supported beams loaded perpendicular to grain by dowel joints

A quasi-non-linear fracture mechanics model based on beam on elastic foundation theory is applied for analysis of the splitting failure of dowel joints loaded perpendicular to grain. Simply supported beams symmetrically loaded by two dowels are considered, and the effects of edge distance, dowel spacing, and distance between dowels and supports are accounted for. The foundation modulus used in the beam on elastic foundation model is chosen so that the perpendicular-to-grain tensile strength and fracture energy properties of the wood are correctly represented. This ensures that a conventional stress analysis and failure criterion lead to the same solution as the compliance method of fracture mechanics. A semiempirical efficiency factor is proposed to account for the influence of the total beam depth, which does not enter the beam on elastic foundation model, but the effect of which is evident from tests. It is shown that the so-called Van der Put/Leijten model, which recently has been adopted in Eurocode 5, appears as a special case of the model presented. Tests on simply supported beams with a single dowel joint at midspan are compared with the theoretical predictions. Various edge distances, beam depths, and spans were tested.     

Comparative infectivity for axenic and specific-pathogen-free chickens of O2 Escherichia coli strains with or without virulence factors

Adhesion to epithelial respiratory cells, iron acquisition, and production of K1 polysaccharide capsules have been proposed as potential virulence factors of avian Escherichia coli. These factors were studied by inoculating groups of axenic or specific-pathogen-free (SPF) chickens intratracheally with O2 E. coli strains after previous challenge with a wild strain of infectious bronchitis virus (IBV). In all experiments, the association between IBV and an E. coli strain endowed with the three virulence factors previously mentioned resulted in the most severe pathological effects, as measured by mortality, weight gains, lesions, and reisolation of E. coli from internal organs. An E. coli strain devoid of virulence factors was able only to induce mild pathological effects restricted to the respiratory tract when combined with IBV. Both E. coli strains were more invasive in axenic chickens than in SPF chickens. These results confirm the probable involvement of the three factors studied in the pathogenic properties of avian E. coli. This model can be used to assess the role of virulence factors, by comparing pairs of positive and negative isogenic strains.     

The antimicrobial susceptibility of Staphylococcus species isolated from canine dermatitis

In a retrospective study, 1538 strains of -haemolysin-producing Staphylococcus species isolated from dermatitis in dogs at three veterinary clinical microbiology laboratories in Norway during 1986–87 and 1993–94 were investigated for their antimicrobial susceptibility. None of the strains was resistant to cloxacillin, cephalexin or the quinolones enrofloxacin and ciprofloxacin. More than 96% of the strains were susceptible to trimethoprim-sulphonamide, bacitracin and fucidic acid. Between 67% and 89% of the strains were susceptible to erythromycin, lincosamides, tetracycline, neomycin and chloramphenicol. Only 37.9% of the strains were susceptible to penicillin. The frequency of penicillin resistance increased significantly between the first and second periods, from 46.0% to 58.6%. The frequency of resistance to lincomycin, clindamycin and erythromycin also increased significantly between the first and second periods, from 3.0%, 2.1% and 3.3% to 25.5%, 19.5% and 24.8%, respectively. A moderate increase in resistance to tetracycline was also noted, from 20.4% in the first to 27.6% in the second period. On the other hand, the frequency of resistance to trimethoprim-sulphonamide decreased significantly from 4.1% in the first to 0.9% in the second period. Many different resistance patterns were observed in each period. However, the proportion of multiresistant strains increased from 2.1% in the first to 10.2% in the second period. There was a decrease in resistance to the combination of trimethoprim-sulphonamide and penicillin from the first to the second period. Resistance to the combination of lincosamides and pencillin increased. For the combinations penicillin-tetracycline-lincosamides, pencillin-lincosamides-erythromycin, and pencillin-tetracycline-lincosamides-erythromycin, there was a striking increase in resistance between the first and the second periods.Abbreviations CVL Central Veterinary Laboratory - NCVM Norwegian College of Veterinary Medicine - NVL Norwegian Veterinary Laboratory     

Tentative description of Hippeastrum latent virus in Hippeastrum hybridum plants and differentiation from Hippeastrum mosaic virus

In mosaic-diseased plants ofHippeastrum hybridum two viruses were found. One virus with a normal length of 706 nm caused local lesions onHyoscyamus niger test plants and mosaic symptoms in the leaves ofH. hybridum. This virus was identified with theHippeastrum mosaic virus (HMV) (*/*∶*/*∶E/E∶S/*) and had a dilution end point between 10^?3 and 10^?4, a thermal inactivation point between 55–60°C and a longevity at room temperature of 28–32 hours. The second virus had a normal length between 584 and 611 nm depending on the method used. It caused local lesions onGomphrena globosa andChenopodium quinoa leaves, and after inoculation ofH. hybridum was found to be present without showing symptoms. It was readily purified from inoculated leaf tissue ofC. quinoa andNicotiana clevelandii by differential centrifugation and ofH. hybridum by density-gradient centrifugation. Purified virus had an absorption minimum at 242 nm, a maximum at 262 nm and a 260/280 absorption ratio of 1.19. The dilution end point was between 10^?3 and 10^?4, the thermal inactivation point between 70 and 80°C and the longevity in vitro at room temperature 28–32 hours. Although no direct comparisons have been made with other members of the potexvirus group, the virus seems to be a new one now namedHippeastrum latent virus. Both viruses were not seed-borne.     

Bedeutung von Regenwurmröhren für die Verlagerung des Herbizids Diuron in Böden von Obstanlagen

Herbicide translocation was investigated in a Haplic Luvisol from loess (clayey silt; Klein-Altendorf near Bonn, Germany) and a Eutric Cambisol (sandy loam; fluvial sediments on the lower Rhine terrace north of Bonn) using the herbicide diuron as an example. diuron was applied once a year in May at the recommended dose of 2.4 kg/ha. It rapidly degraded in the topsoil: the “time for 50% disappearance” (DT₅₀) was 14–30 days. A population of adapted soil micro-organisms, which is repeatedly exposed to applications of the same compound every year, is thought to be responsible for this fast degradation. Remaining Diuron residues were largely degraded in the loess soil during the subsequent summer and became less mobile due to increasing binding strength. As a result, residue levels and leaching in the loess soil during the winter were negligible, with diuron traces of less than 10 µg/kg below the topsoil 11 months after application. Comparison of the translocation in a sandy loam soil showed—as expected—that diuron was leached to the subsoil to a higher extent than in clayey silt (loess). However, in the loess soil, diuron leached to the subsoil via macropores after 20 mm of natural precipitation within 1 week after herbicide application due to macropore flow. Colour tracer and analysis of the linings of earthworm burrows identified these macropores as preferred pathways of herbicide leaching. Macropore flow occurred in wet soil and moist soil with a sealed surface or crust but not in dry soil. Superficial mechanical soil cultivation before the herbicide application is discussed as one possibility to interrupt macropore entries and reduce herbicide leaching after its application in the spring.     

Resistance to Botrytis cinerea in Solanum lycopersicoides is Dominant in Hybrids with Tomato, and Involves induced Hyphal Death

Botrytis cinerea causes gray mold disease and affects hundreds of plant species, including tomato (Lycopersicon esculentum). The wild nightshade, Solanum lycopersicoides, is cross compatible with tomato and is more resistant to B. cinerea, thus representing a potential source for crop improvement. Tests involving droplet inoculation of detached leaves and spray inoculation of entire seedlings demonstrated that resistance to B. cinerea varies among S. lycopersicoides accessions, with S. lycopersicoides LA2951 being the most resistant accession tested. Expression of resistance in the intergeneric hybrid (L. esculentum cv. 'VF36' × S. lycopersicoides LA2951) suggested that resistance is at least partially dominant in tomato. A green fluorescent protein-tagged B. cinerea strain was used for confocal microscopic comparison of infection in leaves of S. lycopersicoides and tomato. Even though S. lycopersicoides supported spore germination, there was evidence for hyphal lysis and death 3 days after inoculation, at a time when lesions were expanding on susceptible tomato plants. The reduced frequency of B. cinerea lesion spread on S. lycopersicoides explains why this fungus produced fewer spores in this wild nightshade than in tomato.     

Finding best exotic breed proportion in crossbred lactating sheep kept under farmers’ conditions in Ethiopia determined by use of nested Legendre polynomials with limited data

ABSTRACT

The present study was conducted to estimate milk production performance and fit lactation curves for groups of ewes of Local and of Awassi crosses, with a variable blood level, reared under farmer’s environment. The Weigh-Suckle-Weigh method plus hand milking was used to estimate milk yield for ewes. A total of 466 observations from 115 ewes were used. Estimated least-squares adjusted means for the milk production over 120 days were 0.56?kg day^?1 (Local), 0.67 (<30% Awassi), 0.86 (30–50% Awassi), and 0.96 (>50% Awassi). Groups with 30–50% Awassi and >50% Awassi ewes produced significantly (p?<?0.05) more milk than Local ewes. Significant differences were observed between <30% Awassi and >50% Awassi crossbred groups. The best crosses (>50% Awassi) produced over 70% more milk than the local ewes which demonstrates the potential that exists in increasing milk production through the initiated crossbreeding programme with sheep in Ethiopia.