Physical aging in polymer glasses     

Hodge IM 《Science (New York, N.Y.)》1995,267(5206):1945-1947

Physical aging refers to structural relaxation of the glassy state toward the metastable equilibrium amorphous state, and it is accompanied by changes in almost all physical properties. These changes, which must be taken into account in the design, manufacture, and use of glassy polymer materials and devices, present a daunting challenge to theorists.  相似文献   

Glasses and amorphous materials     

Brauman JI 《Science (New York, N.Y.)》1995,267(5206):1887

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Effects of storage time and freezing temperature on clinical chemical parameters from canine serum and heparinized plasma     

Thoresen SI  Tverdal A  Havre G  Morberg H 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1995,24(4):129-133

To assess changes in 24 blood constituents in frozen serum and heparinized plasma, blood samples were drawn from 10 clinically normal German Shepherd army dogs. The storage characteristics of nine enzymes (ALP, ALT, amylase, AST, CK, GGT, GLDH, LDH, lipase), and 15 metabolites and minerals (albumin, bile acids, bilirubin, calcium, cholesterol, creatinine, fructosamine, glucose, magnesium, phosphate, potassium, protein, sodium, triglycerides, urea) were studied. Parallel samples of serum and heparinized plasma were stored for 90 and 240 days at two different storage temperatures, -200 degrees C and -700 degrees C. Sixteen of the 24 analytes (ALP, ALT, amylase, AST, CK, GGT, GLDH, LDH, bile acids, calcium, cholesterol, creatinine, fructosamine, magnesium, phosphate, urea) showed statistically significant (p < 0.05) changes during the storage period related to storage time, storage temperature, and sample type. Seven of the analytes (amylase, GGT, GLDH, LDH, bile acids, fructosamine, magnesium) showed changes of possible clinical importance with mean differences from baseline larger than 20% for the enzymes and 10% for the metabolites and minerals during the storage periods.  相似文献   

Altered adenosine triphosphatase activities in pigs with naturally occurring hypertrophic cardiomyopathy     

K-S. Dai  C-S. Liang  Y. T. Ch'iu  P-C. Yang  I. C. Cheng 《Veterinary research communications》1995,19(2):115-125

The purpose of this study was to determine whether myocardial adenosine triphosphatase (ATPase) activities were reduced in pigs with naturally occurring hypertrophic cardiomyopathy (HCM). The selection of hearts for the HCM and the normal control groups depended on histological examination. Specific ATPase activity and 5-nucleotidase activity were measured in left ventricular myocardium obtained from HCM (n=7) and normal control (n=7) animals. The histological features of HCM included marked disorientation of muscle cells, thickening of the intramural coronary arterial wall with a narrowed lumen, endocardial fibrosis and myocardial fibrosis. The HCM group showed significant increases in both heart weight (32%) and heart weight to body weight ratio (46%). The total ATPase activity in crude homogenates from the HCM group was significantly decreased by 16%. Azide-sensitive ATPase (mitochondrial ATPase) activity, ouabain-sensitive ATPase (Na⁺,K⁺-ATPase) activity, basal Mg²⁺-ATPase activity and Ca²⁺-ATPase activity were all significantly decreased by 18%, 30%, 20% and 50%, respectively. In contrast, no significant decrease was found in the mean values for 5-nucleotidase activity. These results suggest that myocardial ATPase activities are suppressed in pigs with naturally occurring HCMAbbreviations ATP adenosine triphosphate - gww grams wet weight - HCM hypertrophic cardiomyopathy - Pi inorganic phosphate  相似文献   

Identification of tissue hypoxia in the livers of ascitic and hypoxia‐induced broilers using trypan blue     

M. H. Maxwell  I. A. Alexander  G. W. Robertson  M. A. Mitchell  C. C. McCorquodale 《British poultry science》1995,36(5):791-798

1. The perfusion of livers with the vital dye trypan blue was performed to test for evidence of tissue hypoxia in 3 groups of young broiler chickens, namely, ascitic, hypoxia‐induced and controls.

2. Hepatocytes that stained with trypan blue were considered to be dead or dying before fixation and represented damaged cells.

3. The proportion of trypan blue‐stained hepatocytes in the livers of ascitic birds was slightly less than half that observed in the hypoxia‐induced birds but significandy more than the proportion of stained cells observed in control birds.

4. Liver damage in the ascitic birds was also assessed biochemically by an altered enzyme profile.

5. The study demonstrated that increased trypan blue uptake in the livers of ascitic birds reared at sea‐level may be the consequence of hypoxia stress caused by reduced oxygen utilisation.  相似文献   

Effects of air temperature, air movement and artificial rain on the heat production of brushtail possums (Trichosurus vulpecula): an exploratory study     

van den Oord QG  van Wijk EJ  Lugton IW  Morris RS  Holmes CW 《New Zealand veterinary journal》1995,43(7):328-332

Two groups of six mature brushtail possums (Trichosurus vulpeculu) were housed in two respiration chambers, and their heat production, whole body conductance and lower critical temperatures were measured under a variety of simulated weather patterns. The possums were subjected to ambient temperatures of 30, 20 and 3 degrees C. At 20 and 3 degrees C, the animals were exposed to near still air and light winds (wind speed 0.8 and 6.7 km/h), both with, and without, simulated rain every 8 hours. The lower critical temperature in near still air lies between 7 and 10 degrees C. This temperature increases by about 2, 6 and 8 degrees C respectively for a wind velocity of 6.7 km/h, simulated rain and a combination of the two factors. Weather in New Zealand, especially in the cooler part of the year, will often produce conditions below the lower critical temperature of the thermoneutral zone of possums. This will necessitate significant increases in metabolic rate and hence food consumption or mobilisation of body fat reserves, which if not sustainable will result in the death of possums. Field studies have shown that this is often the case in the wild. It is proposed that this stress may be sufficient to decrease the resistance (especially cell-mediated immunity) of some possums and allow acceleration of the disease process in those infected with Mycobacterium bovis.  相似文献   

Periodicity and gradients in dispersal ofAlternaria linicola in linseed crops     

I. Vloutoglou  B. D. L. Fitt  J. A. Lucas 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(6):639-653

Conidia ofAlternaria linicola produced on infected linseed crops were mainly dispersed by wind. The numbers of conidia in the air above linseed crops collected by a Burkard spore sampler were greatest between 1200 h and 1300 h, when the relative humidity was lowest. Although numbers of conidia collected decreased with increasing height within and above the crop canopy, air-borneA. linicola conidia were present up to 80 cm above the crop canopy. Conidia ofA. linicola were transported by wind up to at least 40 m downwind from an artificial line inoculum source, but their numbers decreased with increasing distance from the source. In 1991, 1992, and 1993, the dispersal ofA. linicola conidia above linseed crops followed a seasonal periodicity which was influenced by weather conditions and cultural practices. The greatest numbers of conidia were collected during July, August and early September and coincided with periods favourable for sporulation and with an increase in the incidence of the disease in the senescent crop. Air-borneA. linicola conidia produced on point or line inoculum sources (naturally infected linseed stem debris) were responsible for the spread of the disease in linseed crops. In 1992 and 1993, the disease was first detected downwind from the sources, but by the end of the growing seasons, it had spread in all directions and up to 20 m and 60 m from the sources, respectively. Disease gradients were initially steep near the inoculum sources but they became flatter with time due to the secondary spread of the disease.  相似文献   

Inherently safe reactors and a second nuclear era     

Weinberg AM  Spiewak I 《Science (New York, N.Y.)》1984,224(4656):1398-1402

The Swedish PIUS reactor and the German-American small modular high-temperature gas-cooled reactor are inherently safe-that is, their safety relies not upon intervention of humans or of electromechanical devices but on immutable principles of physics and chemistry. A second nuclear era may require commercialization and deployment of such inherently safe reactors, even though existing light-water reactors appear to be as safe as other well-accepted sources of central electricity, particularly hydroelectric dams.  相似文献   

Field access     

Horowitz IL 《Science (New York, N.Y.)》1984,224(4651):796-796

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The relative growth of internal organs in light and heavy breeds     

Y. Dror  I. Nir  Zafrira Nitsan 《British poultry science》1977,18(4):493-496

1. The relative weights of the gastrointestinal segments and of some other internal organs from light and heavy breed chicks from hatching to 21 days of age were compared.

2. The relative weight of the duodenum and jejunum was higher in the light breed than in the heavy one, the reverse relationship was found for the ileum and caecum.

3. The relative growth of the pancreas, heart, cerebrum and cerebellum was greater in the light breed.  相似文献