Observation of polymer conformation hysteresis in extensional flow

Highly extensible Escherichia coli DNA molecules in planar extensional flow were visualized in dilute solution by fluorescence microscopy. For a narrow range of flow strengths, the molecules were found in either a coiled or highly extended conformation, depending on the deformation history of the polymer. This conformation hysteresis persists for many polymer relaxation times and is due to conformation-dependent hydrodynamic forces. Polymer conformational free-energy landscapes were calculated from computer simulations and show two free-energy minima for flow strengths near the coil-stretch transition. Hysteresis cycles may directly influence bulk-solution stresses and the development of stress-strain relations for dilute polymer flows.     

Comparison of metrizamide and iohexol for cisternal myelographic examination of dogs

A double-blind study, using metrizamide, iohexol, or Ringer's solution (control) as cisternal myelographic agents, was performed on 25 dogs. Before myelographic examination was done, each dog was subjected to physical, clinical pathologic, and neurologic examinations, as well as examinations by electroencephalography and computerized tomography. These were repeated 24 hours after completion of the myelographic examination. The group of dogs given metrizamide (group II) had a significantly greater occurrence of seizure activity (6 of 10) than did the control dogs (group I; 0 of 5) or dogs given iohexol (group III; 0 of 10; P less than 0.003). In group II, the CSF microprotein concentration was significantly greater 24 hours after myelography was done than were the values in groups I and III (P less than 0.003). Myelograms of the group II dogs (metrizamide) and group III dogs (iohexol) had similar diagnostic qualities. At 24 hours after myelographic examination was done, computerized tomography scan revealed that each dog given metrizamide and iohexol had myelographic contrast material in the brain and cervical spinal cord parenchyma. Seemingly, iohexol has good diagnostic quality, but is less epileptogenic than metrizamide when used in cervical myelographic examinations of dogs.     

Spatial structure of shell polychromatism in <Emphasis Type="Italic">Cepaea hortensis</Emphasis> in relation to a gradient of landscape fragmentation in Western France

Because of their highly polymorphic shell patterns, Cepaea land snails have been the subject of numerous studies in ecological genetics. Here, we investigated the spatial structure of polychromatism in Cepaea hortensis in agricultural landscapes with zones from low to high hedgerow densities. Our main purpose was to search for a relationship between landscape composition and spatial structuring of chromatism. Despite significant spatial heterogeneity in the three landscapes sampled, only the high hedgerow density landscape showed a significant spatial structuring of shell polymorphism. In order to understand this result, an investigation of daily movement patterns in relation to habitat form was carried out on a mark-release experiment under semi-artificial conditions. This experiment revealed a strong influence of a linear corridor on snail dispersal. In the field, spatial heterogeneity of shell polymorphism, related to the effects of genetic drift, was shaped by restricted dispersal in narrow corridors. In the more enclosed one, i.e. where hedgerow density was the highest, the significant spatial structure we detected involved a balance between local genetic drift and environmentally mediated gene flow. This isolation-by-distance pattern resulted from direct gene exchange through fields between neighbouring populations. When applying landscape distances based on hedgerow length, no significant spatial correlation with polychromatism was found. In the more fragmented sites, random genetic drift seemed to be the prevailing force and, at the scale of the whole sampled area, selective pressures potentially interfere with these genetic drift-dispersal events.     

Magnetic resonance imaging features of feline intracranial neoplasia: retrospective analysis of 46 cats

The purpose of this retrospective study was to determine the magnetic resonance imaging (MRI) characteristics of feline brain tumors and to determine whether these characteristics can be used to accurately predict the histologic diagnosis. MRI scans of 46 cats with histologically confirmed brain tumors were reviewed, including 33 meningiomas, 6 lymphomas, 4 gliomas, 2 olfactory neuroblastomas, and 1 pituitary tumor. MRI features including axial origin, shape, location, signal intensity, contrast enhancement, peritumoral edema, and mass effect were reviewed and characterized for each tumor type. Tumor shape, axial origin, contrast enhancement, and degree of peritumoral edema aided in the identification of tumor type. Meningiomas were always extra-axial and were most often ovoid with marked contrast enhancement and mild peritumoral edema. Gliomas were always intra-axial with ring enhancement and generally caused more peritumoral edema than other tumors. The brain tumor was detected on MRI in 45 (98%) cats. Two blinded independent reviewers correctly identified 82% of all of the tumor types on the basis of MRI appearance alone. Thus, MRI is an excellent diagnostic tool for the detection of brain tumors in cats, and it provides important information to aid in the diagnosis of tumor type.     

Control of landing flight by laying hens: implications for the design of extensive housing systems

(1) Ten domestic hens (Lohmann Brown) were video-recorded while moving between perches at a horizontal distance of 0.6, 0.8 or 1.15 m apart. The take-off perch was either 0.2 m above or below the landing perch. (2) Weight and wing area of the hens were measured at the end of the experiment. The same measures where taken from 10 jungle fowls. (3) Clumsy or missed landings were observed on some downward flights over 0.8 and 1.15 m. (4) Hens' trajectories on take-off were closely related to the position of the target perch, and variation in take-off trajectory decreased as the distance between perches increased. (5) The standard deviation of the horizontal distance between head and perch, at the point when the feet first contacted the perch, did not vary with flight distance, suggesting that timing of foot extension was equally accurate at all distances. (6) The standard deviation of the vertical distance between head and perch, at the point when the feet first contacted the perch, did increase with distance, suggesting increasing difficulty in controlling the height of the flight trajectory above the landing perch. (7) Wing loading of the hens (mean 213 N/m2) was approximately twice that of the jungle fowl (mean 111 N/m2). (8) Loss of accuracy in hens' landings at greater distances can be attributed specifically to the effects of high wing loading on the ability to generate and control lift.     

Learning performances of honeybees (Apis mellifera L) are differentially affected by imidacloprid according to the season

To establish the sublethal concentrations domain, acute and chronic oral tests were conducted on caged honeybee workers (Apis mellifera L) using imidacloprid and a metabolite, 5-OH-imidacloprid, under laboratory conditions. The latter showed a 48-h oral LD50 value (153 ng per bee) five times higher than that of imidacloprid (30 ng per bee). Chronic feeding tests indicated that the lowest observed effect concentrations (LOEC) of imidacloprid and of 5-OH-imidacloprid on mortality of winter bees were 24 and 120 microg kg(-1) respectively. Behavioural effects of imidacloprid and 5-OH-imidacloprid were studied using the olfactory conditioning of proboscis extension response at two periods of the year. Winter bees surviving chronic treatment with imidacloprid and 5-OH-imidacloprid had reduced learning performances. The LOEC of imidacloprid was lower in summer bees (12 microg kg(-1)) than in winter bees (48 microg kg(-1)), which points to a greater sensitivity of honeybees behaviour in summer bees, compared to winter bees.     

Vapour pressure of permethrin

The vapour pressures of the separate isomers of permethrin have been determined over a range of temperatures by two laboratories using different versions of the gas saturation method. A statistical analysis of the sets of data from the two laboratories shows no significant differences for the cis isomers but a small difference in the 20°C extrapolated values for the trans isomer exists. However, this difference is discounted as arising from experimental error and the mean values of the estimated vapour pressures at 20°C are given as 2.5 μPa (cis) and 1.5 μPa (trans).     

Microscopic analysis of the effect of azoxystrobin treatments on Mycosphaerella graminicola infection using green fluorescent protein (GFP)‐expressing transformants

Green fluorescent protein (GFP)‐expressing transformants were used to investigate the effects of strobilurin fungicide azoxystrobin on Mycosphaerella graminicola infection. Azoxystrobin treatments (125 or 250 g AI ha^?1) were applied at various stages of the infection process under controlled conditions. GFP transformants showed conserved in vitro sensitivity to azoxystrobin and pathogenicity. Azoxystrobin controlled over 90% of M graminicola infections when applied before or during penetration of the pathogen (15% of the incubation phase). Azoxystrobin also impaired the growth of intercellular hyphae in M graminicola post‐penetration infection stages when applied at up to 50% of the incubation phase. Incubating infections observed in treated leaves were viable, but their growth was impaired and they did not induce necrosis under controlled conditions. Reduction by half of azoxystrobin dosage had little or no effect on azoxystrobin efficiency in controlling M graminicola. The contribution of post‐penetration fungistatic effect to azoxystrobin curative properties toward M graminicola in a field situation is discussed. © 2001 Society of Chemical Industry     

Attaching and effacing lesions in the large intestine of an eight-month-old heifer associated with Escherichia coli O26 infection in a group of animals with dysentery

Escherichia coli O26:K60, with genetic attributes consistent with a potentially human enterohaemorrhagic E. coli was isolated from the faeces of an eight-month-old heifer with dysentery. Attaching and effacing lesions were identified in the colon of a similarly affected heifer examined postmortem, and shown to be associated with E. coli O26 by specific immunolabelling.