The mechano-sorptive behavior of flexible water-blown polyurethane foams

Samples of flexible water-blown slabstock polyurethane foams were compressed under constant load to study the effects of cycling moisture content on creep behavior and compare this behavior with the creep response where either a constant high or low moisture environment existed at the same temperature. Three sets of foams were tested: (1) 4 pph water content slabstock foam; (2) 5 pph water content slabstock foam; and (3) 2 pph water content molded foam. As the moisture conditions were cycled from low to high humidity while maintaining constant temperature in an environmental chamber, the compressive strain increased in subsequent steps with larger increases observed during the desorption portion of the humidity cycling. All three sets of foams showed similar behavior at a given temperature. At a temperature of 40°C, the strain levels under cyclic moisture conditions surpassed those levels observed at the highest constant relative humidity. During the first absorption step, the creep level increased. During any subsequent absorption step, the creep level either increased very little or none at all. Finally, during any desorption step, the creep level increased. This overall phenomenon of enhanced creep under cyclic moisture levels is attributed to water interacting with the hydrogen bonded structure within the foam. These hydrophillic interactions, principally promoted within the hard segment regions due to high hydrogen bonding, are disrupted causing slippage and increased in strain. As the foam is rapidly dired, regions of free volume are induced by the loss of water thus causing further increases in strain Prior to the reestablishment of well ordered hydrogen bonding. Further support to this proposition was given by the results obtained at a temperature of 90° C where it is well known that hydrogen bonds are much more mobile. Here, the strain levels under cyclic moisture conditions were nearly the same as those under constant high relative humidity. Weakening of the hydrogen bonds by means such as increased temperature resulted in similar strain levels to those under cyclic moisture levels. © 1993 John Wiley & Sons, Inc.     

Laboratory study of soil acidification and leaching of nutrients from a soil amended with various surface-incorporated acidifying agents

Granular S, finely-ground S, iron sulphate and aluminium sulphate were added at two rates to the surface (0–6 cm) of a soil and acidification and leaching of nutrients were measured over 12 months in a laboratory study. Iron and aluminium sulphate both rapidly lowered soil pH in the top 0–6 cm of the soil. There was little difference in soil pH after 3 and 12 months reaction of these two amendments. In contrast, for granular S and finely-ground S there were clear decreases in soil pH between 3 and 12 months reaction with the soil. Finely-ground S was oxidized in the soil faster than granular S and therefore had a more acidifying effect. The top 0–6 cm of the soil was acidified by all the agents used but the deeper soil was less affected. The only treatments which lowered the pH of the 12–18 cm layer below pH 6 were the high rates of iron and aluminium sulphate. Soil acidification resulted in a decrease in exchangeable Ca, Mg and K, an increase in exchangeable Al and a decrease in effective CEC in the acidified soil layers.At both levels of addition, total ionic strength of percolates from the soil followed the order: aluminium sulphate = iron sulphate > finely gound S > granular S > control and was higher at the higher rate of addition. The pH values of percolates followed the order: control > granular S > finely ground S > iron sulphate = aluminium sulphate and were lower at the higher rate of addition. For the amended soils there was a very close relationship between the pattern and total amounts of SO ₄ ^2- and Ca²⁺ leached.It was concluded that granular S is not an effective acidifying agent since it is oxidized very slowly in the soil and that acidfying agents should be incorporated to the depth that acidification is required.     

Ceramers: Hybrid materials incorporating polymeric/oligomeric species with inorganic glasses by a sol-gel process

A sol-gel process has been successfully utilized to produce hybrid materials incorporating polymeric/oligomeric components of polydimethyl siloxane(PDMS) with silicon glasses. All the samples made were transparent and flexible. Dynamic mechanical studies indicate that a portion of the siloxane species is phase-separated while the remainder is well dispersed. The effect of acid content were proven to be significant on the dispersion of the siloxane components and on the structure and properties of final products.     

Engineering plastics from lignin. VI. Structure–property relationships of PEG-containing polyurethane networks

Hydroxypropyl lignin-based thermosetting polyurethanes were synthesized with excess hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI) by solution casting. Four polyethylene glycols (PEG) of molecular weight 400, 600, 1000, and 4000 were mixed with lignin polyol to incorporate different proportions of soft segment into the network prior to crosslinking. Neither thermal nor mechanical and limited small angle x-ray scattering (SAXS) analysis provided distinct evidence for phase separation and microstructure formation. The study examines the effect of the soft segment in relation to chain length and weight contribution on the thermal and mechanical properties of the final networks. A significant sensitivity of glass transition temperature (T_g), of swelling in DMF, and of the mechanical properties to soft segment content was observed. Some of this sensitivity must, however, be attributed to differences in crosslink density since the polyol to diisocyanate weight ratio was kept constant throughout the synthesis series. The magnitude of the change of the different properties was found to be influenced by both glycol content and glycol molecular weight. The T_g of the network decreased from 105°C to as low as 38°C (HDI), and from 158°C to 70°C (TDI), with incorporation of up to 17.8% glycol, and it was greater with lower molecular weight glycols than with higher ones at any weight fraction. Swelling in DMF increased as expected with soft segment content. Mechanical properties were affected most if HDI and lower molecular weight glycols were used. The uniformity in structure, reduction in brittleness, and considerable improvement in mechanical properties with inclusion of minor PEG contents indicates that lignin-based network polyurethanes can be synthesized with controllable performance characteristics.     

The general practitioner as sports physician

General practitioners must become more knowledgeable about sports medicine in order both to treat the injured athlete and to provide better rehabilitative treatment and advice on fitness and exercise to other patients. Close involvement with young amateur athletes also helps to keep the older physician "in tune" with the younger generation. Finances remain a major problem for amateur sporting events and sports medicine groups, as well as for the individual physician volunteering his time.     

Big and little forms of osteoclast activating factor

We have further characterized osteoclast activating factor (OAF) using a bioassay for bone resorption which utilizes the release of previously incorporated (45)Ca from fetal rat long bones in organ culture. When supernatant media from activated leukocyte cultures were concentrated on Amicon PM10 membranes (assigned molecular weight cutoff 10,000 daltons) and chromatographed on Sephadex G-50 columns, the bone-resorbing activity eluted between the molecular weight markers chymotrypsinogen (25,000 daltons) and cytochrome c (12,500 daltons). This peak of biological activity has been called big OAF. When filtrates from the PM10 membranes were concentrated on Amicon UM2 membranes (assigned molecular weight cutoff 1,000 daltons) and chromatographed on Sephadex G-50 columns, some of the biological activity eluted between the molecular weight markers chymotrypsinogen and cytochrome c (big OAF), but there was a separate peak of biological activity which eluted with [(3)H]proline (140 daltons). This second peak has been called little OAF. Little OAF was eluted from Bio-Gel P6 columns between the molecular weight markers calcitonin (approximately 3,500 daltons) and vitamin B(12) (1,330 daltons), but was retained by Spectrapor dialysis tubing (nominal molecular weight cutoff 3,500 daltons). Big OAF was converted to little OAF by equilibration in 1 M NaCl or 2 M urea. Little OAF was self-associated back to big OAF by equilibration in buffers of low ionic strength (Tris-HCl 10-50 mM). Little OAF was extracted into the organic phase in ethyl acetate after acidification of the sample to pH 3.5. The biological activity remained in the aqueous phase after ethyl acetate extraction at pH 7.5-8.4. Little OAF has been purified more than 6,000-fold compared with the original material so that bone-resorbing activity is maximal in a sample with a protein concentration of 80 ng/ml.     

Quantitative determination of spleen added to ground beef

Simultaneous measurement of cardiac output distribution with 86Rubidium and 57Cobalt-tagged microspheres in rats implanted with liver tumors by intraportal injection of sarcoma cells enables quantitation of arterial and portal tumor circulation. The portal circulation was found to be increased in small tumors as compared to the liver, but as the tumor grew there was a decrease in the portal tumor circulation. When the tumor growth became massive even the total liver circulation was reduced, as measured with 133Xenon wash-out. All the tumors had increased arterial circulation. This arterial hyperperfusion was changed into ischemia when the liver artery was occluded through embolization with degradable microspheres.     

Effect of age and sex on the prevalence of intestinal parasitism in dogs

The effects of age, sex, and neutering on the prevalence of canine intestinal parasitism were evaluated by fecal examination of 1,468 pet dogs admitted to the University of Missouri Veterinary Teaching Hospital during 1975. Evidence of hookworm infection was encountered in 35.8% of the dogs examined, whipworms in 18.5%, ascarids in 17.9%, tapeworms in 5.2%, and coccidia in 4.5%. Evidence of intestinal parasitism was not detected in 653 (44.4%) dogs. Whipworm infections were detected less often in young dogs than in older ones, whereas ascarid and coccidial infections were more prevalent in pups that in mature dogs. In dogs more than 6 months old, hookworm infections were the most common parasitism. Tapeworm infections were diagnosed sporadically in all age groups. For most of these parasites, castrated males and spayed females had decreased prevalence of infection, compared with their respective intact counterparts. There were significant (P less than 0.05) differences in the prevalence of both ascarid and hookworm infections between intact and spayed female dogs. Also, there were significant (P less than 0.001) differences between age categories for all parasites observed. Overall, parasitism tended to decrease with age.     

Specificity of amphetamine induced release of norepinephrine and serotonin from rat brain in vitro

Incubation of normal rat cortical or brain stem tissue with 3H-NE or 3H-5-HT and subsequent exposure to amphetamine produced a concentration-related release of the transmitters from tissue stores into the incubation media. Although pretreatment with the catecholamine neurotoxin in 6-hydroxydopamine (6-OHDA) reduced the retention of 3H-NE in both of these tissues, the proportion of 3H-NE released by amphetamine was attenuated only in cortical tissue. Pretreatment with the serotonergic neurotoxin, 5,6-dihydroxytryptamine (5,6-DHT) had no effect on the retention or release of 3H-NE in cortical or brain stem tissue. Pretreatment with 5,6-DHT reduced the retention of 3H-5-HT in the cortex and brain stem, but the release of 3H-5-HT was significantly attenuated only in the latter tissue. 6-OHDA pretreatment increased the retention and proportion of cortical 3H-5-HT released by amphetamine but reduced the release of brain stem 3H-5-HT in the absence of an effect on retention. It appears that the in vitro release of 3H-NE from the cerebral cortex occurs primarily from catecholamine and not serotonergic neurons whereas the cortical release of 3H-5-HT is not an event specific to serotonergic nerve terminals. The release of 3H-5-HT from brain stem does not appear to be restricted to the serotonergic cell bodies since its release was attenuated by 5,6-DHT and 6-OHDA.     

Cryosurgery of bronchopulmonary structures. An approach to lesions inaccessible to the rigid bronchoscope

Cryonecrosis of the upper lobe of the lung and bronchi was safely inudced in healthy dogs by application of the cryoprobe to serosal surfaces or, through a bronchotomy, to the mucosal surfaces under direct vision. Seven days after cryosurgery, hyperemia of the bronchus was seen. By 14 days the bronchus at the target site was covered with cuboidal epithelium. Reappearance of normal ciliated epithelium occurred by 180 days after cryosurgery. Cartilage remained intact, and there was no evidence of formation of a stricture or other gross alteration of bronchial architecture. In the lung there was coagulation necrosis; and by 14 days after cryosurgery, there was fibrosis in the target area. There were no complications of the pleural space. Cryosurgery of tissues at the margins of the bronchotomy does not impair healing. Cryosurgery may reduce the necessity for extensive surgery in selected patients with bronchopulmonary tumors, including those inaccessible to the rigid bronchoscope. Clinically, eight patients with recurrent bronchogenic tumors have received palliation by transbronchoscopic cryosurgery.