Propagation of extended fractures by local nucleation and rapid transverse expansion of crack-front distortion.

Fractures are ubiquitous and can lead to the catastrophic material failure of materials. Although fracturing in a two-dimensional plane is well understood, all fractures are extended in and propagate through three-dimensional space. Moreover, their behaviour is complex. Here we show that the forward propagation of a fracture front occurs through an initial rupture, nucleated at some localized position, followed by a very rapid transverse expansion at velocities as high as the Rayleigh-wave speed. We study fracturing in a circular geometry that achieves an uninterrupted extended fracture front and use a fluid to control the loading conditions that determine the amplitude of the forward jump. We find that this amplitude correlates with the transverse velocity. Dynamic rupture simulations capture the observations for only a high transverse velocity. These results highlight the importance of transverse dynamics in the forward propagation of an extended fracture.

Doppler ultrasonographic features of thoracic limb arteries in clinically normal horses.

OBJECTIVES: To determine blood flow velocities and indices from spectral waveforms obtained by use of Doppler ultrasonography of thoracic limb arteries of horses and to assess interobserver and patient variability associated with the technique. ANIMALS: 9 clinically normal adult horses. PROCEDURE: Left thoracic limb arteries of 8 nonsedated horses were examined at 5 sites by use of pulsed-wave Doppler ultrasonography to determine a range of values for peak systolic, end diastolic, and mean velocities and resistive and pulsatility indices. Interobserver and patient variabilities were determined by 2 operators repeating similar measurements on 1 horse 8 times at weekly intervals. RESULTS: A range of values for each variable measured at the 5 selected sites was obtained. For each variable, strong positive correlations (R > or = 0.7) were detected for > 70% of the site-to-site comparisons made (excluding the coronary band). Among horses, resistive index varied least, whereas over time, mean velocity varied least. Waveform characteristics were consistent with resistive (n = 5) or nonresistive (4) patterns. In the single-horse experiment, waveform characteristics were consistent throughout the 8 weeks, and operator effects were not detected. CONCLUSIONS AND CLINICAL RELEVANCE: Doppler ultrasonography of no one site resulted in more reliable measurements of blood flow characteristics in thoracic limb arteries of horses. Mean velocity and resistive index were the least variable measurements made. Pulsed-wave Doppler ultrasonography may be a useful technique for evaluating diseases that alter normal thoracic limb arterial blood flow in horses.

Effects of the naked neck (Na) gene on the sulfur-containing amino acid requirements of broilers.

Full-sibling normal (na/na) and naked neck (Na/na) chickens were fed from 28 to 42 d of age on one of five diets with different SAA contents (from 5.4 to 7.0 g/kg). The experimental diets were made by adding DL-methionine to a well-balanced corn, soybean, and cornstarch diet containing 5.4 g SAA/kg and 161 g crude protein/kg. Dietary SAA influenced the growth rate of both genotypes similarly. There were no significant differences (P > 0.125) in body weight gain due to genetics or a diet by genetics interaction. Body weight gains were maximized at 6.24 +/- 0.45 (R2 = 0.171) and 5.96 +/- 0.52 g/kg SAA (R2 = 0.107) for the na/na and Na/na stocks, respectively. There was a significant SAA by genotype interaction for feed efficiency: the na/na birds were more efficient at low SAA levels, but the Na/na birds were more efficient at high SAA levels. Feather weight gain increased in a linear manner with increasing dietary SAA and was greater in na/na than Na/na birds with high dietary SAA concentrations. Abdominal fat decreased with increasing dietary SAA; and although the Na/na birds had significantly more abdominal fat than their na/na siblings (P = 0.049), on average the difference was small and complicated by differences in body weight. Analysis of covariance showed (a significant interaction) that the relationship between abdominal fat and body weight was different for the na/na and Na/na chickens. Although the shape of the response curves of na/na and Na/na chickens to dietary SAA are different, the quantitative requirements are very similar during the growing period.

Serological diagnosis of bovine, caprine, and ovine mastitis caused by Listeria monocytogenes by using an enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay for detecting Listeria monocytogenes antibodies in bovine (n = 35), caprine (n = 27), and ovine (n = 30) milk samples was evaluated by comparison with bacteriological examination. Microtiter plates were coated with proteins obtained from culture supernatant, and antibodies were revealed with a monoclonal antibody able to react with the immunoglobulins belonging to the three animal species. The arithmetic mean optical density (OD) of milk samples infected with L. monocytogenes was above that of uninfected milk samples or milk samples infected with pathogens others than L. monocytogenes. With an OD threshold of 0.2 for goat and ewe milk samples, the sensitivity and specificity of the test were 100 and 88%, respectively. The choice of a different OD threshold (0.5) for cows allowed the discrimination of all of the infected cows and yielded no false positives, and both sensitivity and specificity were 100%.

Comparative responses of genetically lean and fat chickens to lysine, arginine and non-essential amino acid supply. I. Growth and body composition.

1. Three experiments were performed to study the effects of amino acid imbalance on the growth of genetically lean (LL) or fat (FL) male chickens from 28 to 42 d of age. In experiment 1, five concentrations of digestible lysine were compared (4.75, 6.75, 7.75, 8.75 and 9.75 g/kg). In experiment 2, four concentrations of digestible arginine were compared (6.53, 7.69, 8.84 and 10.0 g/kg). In experiment 3, three diets were compared: a high-protein diet (189 g CP/kg), a low-protein diet containing added essential amino acids (EAA) (144 g CP/kg) and this low-protein diet supplemented with 40 g/kg of non-essential amino acids (NEAA) (glutamic acid+aspartic acid). 2. LL birds exhibited a lower growth rate than the FL when the diet was deficient in either lysine or arginine. Plotting weight gain against lysine or arginine intake suggested that most of this effect was caused by variations in food intake. 3. When protein gains (body or total proteins) were plotted against lysine or arginine intake, LL chickens appeared more efficient than FL chickens. 4. Similar growth rates, although slightly lower in FL, were obtained with low- and high-protein diets. However, NEAA supplementation of the low-protein diet reduced adiposity of LL and did not modify that of FL. Increasing crude protein content (all amino acids) was more effective than NEAA supplementation in decreasing the adiposity of both lines.

Effect of extreme walking conditions for dairy cows on milk yield, chemical composition, and somatic cell count.

Thirty-two cows (16 Montbeliardes and 16 Tarentaises) in midlactation were used in an experiment utilizing a 2 x 2 factorial arrangement of treatments. Throughout the trial, cows received first-cutting cocksfoot hay for ad libitum intake supplemented with a fixed amount of concentrate that was individually adapted to the milk yield of each cow. During a 23-d experimental period, one group of cows walked 9.6 km/d; the other group of cows remained in the barn. Cows that walked daily ate less hay (-1.3 and -2.1 kg/d of dry matter for Tarentaise and Montbeliarde cows, respectively) and yielded less milk (-1.7 and -2.5 kg/d for Tarentaise and Montbeliarde cows, respectively) than did cows that did not walk daily. A residual effect of walking on milk yield was observed during the 10 d following the experimental period. For both breeds, fat content and, to a lesser extent, protein content were higher (+6.4 and +1.0 g/kg, respectively) for cows that walked. Somatic cell count was also higher for cows that walked (+115,000 cells/ml). This difference was more marked in cows that were initially infected by a minor or major pathogen (+185,000 cells/ml) than in uninfected cows (+47,000 cells/ml) and on the 1st d of walking when walking was linked to increases in pH, bovine serum albumin, and immunoglobulin G1 contents of milk (+0.08 unit, +0.16 g/L, and +0.19 g/L, respectively). Throughout the experimental period, walking induced a rise in body temperature (+1 degree C) and in plasma nonesterified fatty acids (+0.63 mM/L). On the 1st d of walking, plasma glucose, lactic acid, and cortisol contents were significantly higher for cows that walked (+0.25 g/L, +0.64 g/L, and +28.8 ng/ml, respectively).

Comparative utilisation of sulphur-containing amino acids by genetically lean or fat chickens.

1. Genetically lean (LL) or fat (FL) male chickens were fed from 28 to 47 days of age on 5 experimental diets differing by their methionine+cystine content (5.4, 5.8, 6.2, 6.6 and 7.0 g/kg, respectively). 2. Growth rate of LL chickens was reduced by the lower sulphur-containing amino acid (SAA) concentrations whereas that of FL was not modified. 3. LL chickens exhibited a larger feather protein gain than FL, which was stimulated by SAA intake. 4. SAA retention, when plotted against SAA consumption, was always greater in LL than in FL. 5. Large differences were observed between genotypes for plasma-free amino acids. Lysine, glutamic acid, histidine and serine were found at significantly higher concentrations in LL birds. Branched amino acids, aromatic amino acids, SAA and arginine were found at higher concentrations in FL. No differences were observed for aspartic acid, glycine, alanine and total amino acids. Methionine supplementation decreased free amino acid concentrations, with the exceptions of arginine and leucine. 6. It is concluded that lean chickens require a higher dietary concentration of SAA than FL. This is mainly caused by their lower food consumption and their greater feather synthesis. However, LL use SAA more efficiently than FL.

Comparative responses of genetically lean and fat chickens to lysine, arginine and non-essential amino acid supply. II. Plasma amino acid responses.

1. Three experiments performed to study the effects of amino acid imbalances on the growth of genetically lean (LL) and fat (FL) male chickens from 28 to 42 d of age were described by Leclercq et al. (1994). The plasma amino acid concentrations of birds on selected treatments from that paper are reported here. In experiment 1, three dietary concentrations of digestible lysine were compared (4.75, 6.75 and 7.75 g/kg). In experiment 2, two dietary concentrations of digestible arginine were compared (6.53 and 10.00 g/kg). In experiment 3, three diets were compared: a high-protein diet (189 g CP/kg), a low-protein diet containing added essential amino acids (144 g CP/kg), and this low-protein diet supplemented with 40 g/kg of non-essential amino acids (NEAA; glutamic and aspartic acids). 2. The present results are compared with two earlier reports on the same genotypes. The LL consistently had lower plasma concentrations of methionine, cystine, phenylalanine, isoleucine and valine, and higher concentrations of histidine, than the FL chickens. In 4 of 5 experiments, LL leucine concentrations were lower, and glutamic acid, tyrosine, glutamine and alanine were higher, than in the FL. The other amino acids measured; arginine, lysine, aspartic acid, glycine and serine, exhibited variable responses among the experiments. 3. When the limiting essential amino acids, lysine and arginine, were added to a deficient diet, the plasma concentration of the supplemented amino acid increased while the others remained constant or decreased. 4. When glutamic and aspartic acids were added to the low protein diet, plasma amino acid responses were similar to those of adding a limiting amino acid to a deficient diet, except that alanine exhibited a dramatic increase. 5. Although there were genotype by diet interactions for several amino acids, the interactions were caused by differences in the degree of the responses, not in their direction. 6. These results suggest that the FL and LL genotypes do not utilise various amino acids with the same efficiency and, as a consequence, the ideal profile of dietary amino acids should not be the same for both lines. The results support the hypothesis that selection for fatness and leanness changed the amino acid requirements independently of the effects of food intake.

Characterization of Staphylococcus aureus strains isolated from cystic fibrosis patients by conventional and molecular typing.

The phenotypic and genotypic characteristics of Staphylococcus aureus strains isolated from respiratory tract of cystic fibrosis (CF) patients were investigated. Slime production, cell-surface hydrophobicity, type of capsular polysaccharide, profile of heteroresistance to methicillin and Sma I restriction profiles were evaluated. S. aureus CF strains have been shown to be heterogeneous in respect to several important features. All of them were slime producing with variation in colony morphology. High or moderate cell-surface hydrophobicity (CSH) was found for, respectively, 16.2% and 83.8% strains. Thirty strains were resistant to methicillin, 60% of them showed heteroresitance and 40% were homoresistant. It was found that 59.6% of strains produced capsular polysaccharides (CP) of 5 or 8 type. Among CP5/CP8 strains, CP8 was the predominant type (81.1%). Typing of 62 CF strains by macrorestriction analysis of chromosomal DNA revealed several major types, differing in their SmaI profiles with a similarity coefficient lower than 0.4. Some of the strains isolated from the same patient at different times of hospitalization, as well as strains isolated at the same time from the relatives, were identical in their PFGE pattern.