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At least 649 records · Page 36Linked to original sources
PubMed2006

An ESR spin-label study on molecular mobility in the interface between microphases of a diblock copolymer: effects of admixture of homopolymers that are miscible with one of the blocks.

Molecular mobility in the interfacial region of a microphase-separated structure was studied in binary mixtures of AB-type diblock copolymers and homopolymers (miscible with only A) by the spin-label technique. In this study, we prepared (a) binary blends of polystyrene-block-poly(methyl acrylate) (PS-block-PMA) and homopolymer poly(cyclohexyl acrylate)'s having the number-averaged molecular weight (Mn) of 1000 (PCHA-S) and (b) having the Mn of 17300 (PCHA-L), and (c) binary mixtures of the PS-block-PMA and homopolymer PS with the Mn of 900 (PS-1). Emphasis was placed on effects of the molecular weight and the miscibility of added homopolymers on the mobility in the interfacial region of the microphase separation. Selective incorporation of the added PCHA-S, PCHA-L, and PS-1 into the PS phase of the PS-block-PMA was confirmed by modulated-temperature differential scanning calorimetry (MDSC) measurement as a decrease in the glass transition temperature of the PS phase. Moreover, the MDSC and small-angle X-ray scattering (SAXS) measurements suggested that the spatial distributions of the PCHA-S and PS-1 in the PS phase were relatively uniform because of their small Mn. On the other hand, the distribution of the PCHA-L in the PS phase was somewhat heterogeneous because of the large Mn of the PCHA-L. The spin-label at the junction point of the PS-block-PMA allowed us to estimate the mobility in the interfacial region of the microphase separation. Influence of the PCHA-S and PCHA-L on the mobility in the interfacial region was negligible even though the relatively uniform distribution of the PCHA-S in the PS phase was suggested by the SAXS and MDSC. More uniform distribution of the PS-1 than that of the PCHA-S in the PS phase was suggested by the SAXS, and the mobility in the interfacial region was slightly enhanced by the addition of the PS-1. However, the mobility was almost constant against an increase in the PS-1. The PS-1 was considered to be penetrated into the interfacial region and activated the mobility, but the fraction of the PS-1 in the interfacial region was constant irrespective of the blended amount of the PS-1. These results suggest that effects of homopolymers on the mobility in the interface are significantly related to their spatial distribution in the host phase.

Journal Article↗
PubMed2000

Effect of several additives and their admixtures on the physico-chemical properties of a calcium phosphate cement.

Combinations of citrate (C6H5O(7)3-), pyrophosphate (P2O(7)4-) and sulfate (SO(4)2-) ions were used to modify the physico-chemical properties of a calcium phosphate cement (CPC) composed of beta-tricalcium phosphate (beta-TCP) and phosphoric acid (PA) solution. The results obtained with only one additive at a time are similar to those previously published. New facts are: the positive effect of C6H5O(7)3- ions on cement failure strain and their negative effect on cement pH. The position of the setting time maximum measured at an SO(4)2- concentration of 0.09 M was not displaced by the addition of C6H5O(7)3- and P2O(7)4- ions. However, the effect of SO(4)2- ions on the setting time was depressed by C6H5O(7)3- ions. Moreover, no increase in tensile strength was observed when increasing amounts of SO(4)2- were added into a C6H5O(7)3--containing cement. The latter results suggest a competitive effect of C6H5O(7)3- and SO(4)2- on setting time and tensile strength. Anhydrous dicalcium phosphate (DCP; CaHPO4) appeared in cement samples dried just after setting, but not in cement samples incubated for 24 h in deionized water before the drying step. It is believed that the setting reaction is stopped by the drying step, leaving a low internal pH in the sample, hence providing favorable conditions for the transformation of dicalcium phosphate dihydrate (DCPD) into DCP. Interestingly, even though C6H5O(7)3- ions dramatically lowered the equilibrium pH of the cement with 5 ml of deionized water, they still prevented the occurrence of the transformation of DCPD into DCP.

Journal Article↗
PubMed2026

Genomic consequences of admixture in an experimentally founded sand lizard population.

Conservation interventions are increasingly required for species threatened by population declines and isolation due to anthropogenic pressures. Small, isolated populations are particularly vulnerable to the loss of genetic diversity, increased inbreeding, and the accumulation of deleterious mutations. Translocations or supplementation of allopatric individuals for genetic rescue may be the only way to increase genetic diversity and increase population persistence via increased adaptive potential. Here, we use an experimentally admixed population of sand lizards on a small island in Sweden as a valuable model of genetic rescue. This population was established approximately 20 years ago (5-6 generations), resulting in increased fecundity and hatchling viability. This population was founded from crossings between individuals from an inbred population from the nearby mainland and individuals sourced from populations in southern Sweden. Low-coverage whole-genome sequencing revealed elevated genetic diversity and reduced realized genetic load in this admixed population relative to the source populations. Ancestry analyses indicated a greater contribution of southern Swedish genetic variation, potentially reflecting the contribution of beneficial adaptive variation from this region that may underlie the positive population effects. This system provides valuable empirical insights into the long-term genomic consequences of genetic rescue in this model vertebrate population.

Journal Article↗
PubMed1976

Gas exchange during exercise in healthy people II. Venous admixture.

1. Venous admixture/cardiac output ratio (Qva/Qt) has been measured in twenty-four healthy volunteer subjects of both sexes aged 20-71 years, at rest and during the steady state of treadmill exercise at two rates of work, and breathing air and breathing oxygen. 2. With oxygen breathing, Qva/Qt was considerably less during exercise than during the time subjects were taking either normal or deep breaths of oxygen at rest, and did not significantly increase with the intensity of exercise. It is postulated that the increase in ventilation during exercise opens most or all of those alveoli which, during oxygen breathing at rest, close because of critically low ventilation/perfusion (V/Q) ratios. 3. With air breathing, Qva/Qt fell from rest to exercise (especially in older subjects), presumably due to improved ventilation of alveoli at the lung bases. With an increase in work rate Qva/Qt increased in all age groups. This increase was not due to increase in the shunt fraction (Qs/Qt), nor to limitation of diffusing capacity; it arose from an increase in V/Q variance. 4. Equations have been derived for the prediction of normal Qva/Qt during exercise, with or without correction for the effects of increasing pulmonary capillary temperature. These effects do not materially influence the accuracy of prediction, but may be relevant to some of the interpretations. In particular, they provide a further indication that Qs/Qt probably cannot be measured by breathing oxygen at rest, even in deep breathing.

Adult↗
PubMed1998

Compatibility and stability of fentanyl admixtures in polypropylene syringes.

OBJECTIVE: To determine the physicochemical stability of fentanyl in combination with midazolam and either hyoscine butylbromide or metoclopramide, and stored in 30 ml polypropylene syringes. METHODS: Solutions containing approximately 40 microg/ ml of fentanyl in combination with midazolam (approximately 600 microg/ml) and either metoclopramide (approximately 700 microg/l) or hyoscine (approximately 850 microg/ml) were prepared from commercial ampoules of the drugs. The solutions were stored, in triplicate, in the dark at 32 degrees C (to simulate usage conditions) for 10 days, and the concentration of each constituent drug was periodically determined using a stability-indicating high-performance liquid chromatography assay. RESULTS: The combinations were relatively stable, with all drugs maintaining over 90% of their initial chemical potency for at least 1 week. There were no evident changes in either the physical appearance or pH values of the solutions over the course of the study. CONCLUSIONS: On the basis of physicochemical stability, polypropylene syringes containing fentanyl with midazolam and either hyoscine butylbromide or metoclopramide can be safely prepared and stored at or below 32 degrees C for periods of up to 1 week prior to use by palliative care patients receiving the drugs via a portable subcutaneous infusion device.

Adjuvants, Anesthesia↗
PubMed2000

Genetic divergence between Atlantic and Indo-Pacific stocks of bigeye tuna (Thunnus obesus) and admixture around South Africa.

Two mitochondrial DNA segments of the bigeye tuna (Thunnus obesus) were amplified by polymerase chain reaction (PCR), and restriction fragment length polymorphism (RFLP) analyses of these segments were used for the genetic stock study. The variation in a segment flanking the ATPase and COIII genes was low; only two genotypes (alpha and beta) were detected by RsaI digestion. Yet a large difference in the genotype distribution was observed between ocean basin samples. The alpha type predominated in four Atlantic samples, where 178 of 244 individuals were the alpha type. In contrast, only one of 195 individuals collected in the Indo-Pacific was the alpha type? The frequency of the alpha type varied considerably from 0 to 80% among seven samples collected off the Cape of Good Hope. The variation found in the other segment, containing the D-loop region, was much higher; two endonucleases (DpnII and RsaI) detected five genotypes each and 15 composite genotypes. A highly significant difference in genotype frequencies was observed between the Atlantic and Indo-Pacific samples, but no heterogeneity was observed among the four Atlantic or among four Indo-Pacific samples. These results clearly indicate that not only gene flow, but also fish migration, between the Atlantic and Indian Oceans are severely restricted, and that fishes from these distinct stocks are intermingling around South Africa. The simple and diagnostic genetic marker found in this study can be used to estimate mixing ratios between Atlantic and Indian stocks around South Africa.

Animals↗
PubMedDate not supplied

Red cell tolerance of admixture with heated saline.

Red cell stability in the face of thermal stress has been evaluated only in the setting of prolonged incubation. This study was conducted to determine red cell tolerance of rapid mixture with heated saline, which exposes red cells to heat only until thermal equilibration, which is a matter of seconds. Half-units of 35-day-old red cells stored in CPDA-1 were mixed at 6 to 10 degrees C in the blood container with an equal weight of 60, 70, or 80 degrees C saline. This resulted in mean mixture temperatures of 30.9, 37.5, and 42.6 degrees C, respectively. Controls consisted of the same mixture, but with 6 to 10 degrees C saline. The red cells in the mixtures were assessed for osmotic fragility, and the supernatant was examined for plasma hemoglobin and potassium. Neither osmotic fragility curves nor supernatant hemoglobin or potassium changed significantly with saline temperatures of 60 or 70 degrees C. When 80 degrees C saline was used, osmotic fragility, supernatant hemoglobin, and potassium all increased significantly (p less than 0.01) over control values. Red cells tolerate rapid mixture with 70 degrees C saline without hemolysis or change in osmotic fragility.

Erythrocyte Transfusion↗