Biomedical subjects

R A Hancock

Publications and source records attributed to R A Hancock.

17 recordsLinked to original sources

PubMed2003

Use of DSC to detect the heterogeneity of hydrothermal stability in the polyphenol-treated collagen matrix.

The hydrothermal stability of the collagen matrixes treated with plant polyphenols (tannins) depends on not only the strength of the polyphenol-collagen interactions but also the distribution uniformity of polyphenolic molecules within the collagen fibrils. Traditional methods of uniformity tests rely heavily on the expertise of workers and are thus subjective. This paper describes a differential scanning calorimetry (DSC) study of the sheepskin collagen samples treated with hydrolyzable tannins, including two commercial tannins' extracts (chestnut and valonea), two pure ellagitannins (vescalagin and castalagin), and six synthetic gallotannins (di-galloyl-ethylene glycol (DGE), tri-galloyl-glycerol, tetra-galloyl-meso-erythritol, penta-galloyl-adonitol, penta-galloyl-glucose, and hexa-galloyl-ducitol). The collagen sample without polyphenol treatment and the sample treated with DGE showed a single sharp peak in their DSC thermogram with a full peak width at half height (fwhh) of 3-4 degrees C. The samples treated with other tannins all showed multiple peak DSC profiles with the fwhh of each peak at about 3-4 degrees C. These multiple peak profiles imply that in these polyphenol-treated samples, there is a distribution of collagen molecules having different hydrothermal stability. The results have demonstrated that DSC offers an objective method to detect the stability heterogeneity of collagen matrixes in the solid state, providing a useful tool for the leather industry to evaluate the uniformity of leather tanning.

Animals↗

PubMed2003

Structure-activity relationships in the hydrophobic interactions of polyphenols with cellulose and collagen.

Polyphenol interactions with both cellulose and collagen in the solid state have been studied by using chromatography on cellulose and by evaluating the hydrothermal stability of the polyphenol treated sheepskin collagen. Twenty-four polyphenolic compounds were studied, including seven glucose-based gallotannins, five polyalcohol-based gallotannins, and twelve ellagitannins. In the cellulose-polyphenols systems, the polyphenol's affinity to cellulose is positively correlated with their molecular masses, the number of galloyl groups, and their hydrophobicity (logP). The polyphenol treatment increased the hydrothermal stability of collagen samples, and such effects are also positively correlated with the molecular masses, total number of galloyl groups and the hydrophobicity of polyphenols. Ellagitannins showed much weaker interactions with both biopolymers than gallotannins having similar molecular mass, the same number of galloyl groups, and the same number of phenolic hydroxyl groups. It is concluded that, for the polyphenol interactions with both cellulose and collagen, (1) the galloyl group of polyphenols is the functional group; (2) the strength of interactions are positively correlated with molecular size, the number of galloyl groups and the hydrophobicity of polyphenols; (3) the hydrophobic interactions are of great significance; and (4) the interactions are strongly dependent on the flexibility of galloyl groups.

Animals↗

PubMed1996

Predictors of thought rebound.

Individual differences in the paradoxical thought rebound effect (increased thought expression following attempted thought suppression) were examined in two studies. In these two studies, the majority of Ss did not evidence thought rebound and, in both studies, it was found that a measure of thought rebound was correlated with other variables. In Study 1, a four-factor regression model predicted thought rebound (R2 = 0.1477). The significant predictors were: (1) ACT Composite (higher ACT predicted more rebound); (2) gender, (3) thought intrusion frequency during suppression; and (4) the interaction of gender and thought intrusion frequency (for male Ss only, more thought intrusions during suppression predicted more rebound). In Study 2, a replication regression model (R2 = 0.1408) cross-validated the ACT effect observed in Study 1. A Study 2 extension model (R2 = 0.2154) found the following significant predictors of thought rebound: (1) obsessionality (less obsessionality predicted more rebound); (2) trait anxiety (less anxiety predicted more rebound); (3) race (whites rebounded more than blacks); (4) gender; (5) 16 PF independence; and (6) the interaction of gender and 16 PF independence (for male Ss only, more independence predicted more rebound). The implications of these results for thought rebound theory are discussed.

Adult↗

PubMed1993

Individual differences in the Wegner rebound effect: evidence for a moderator variable in thought rebound following thought suppression.

Wegner, Schneider, Carter, and White in 1987 found that attempts to suppress thoughts of a white bear produced even greater preoccupation with that stimulus--a rebound effect. This effect was investigated in Exp. 1 using both Wegner's white bear stimulus and a more personally meaningful stimulus (an upcoming test). The rebound effect was not observed with either stimulus. Exp. 2 was conducted to examine the hypothesis that this failure to replicate Wegner, et al.'s rebound effect reflected individual differences in the respective subject pools. A within-subjects design was used to classify subjects as rebounders or nonrebounders by comparing each subject's expression of a thought following suppression to their own baseline expression of that thought. Subjects classified as rebounders had significantly higher ACT Mathematics subtest scores than did the subjects classified as nonrebounders. This suggests that there is a moderator variable related to mathematics ability for the rebound effect.

Aptitude↗

PubMed1992

Study on the composition and structure of commercial chestnut tanning agent.

Current research has focused on the composition of commercially used chestnut tannin extracts so as to provide a quantitative basis for studies of reactions, structure-property relationships, and applications of chestnut tannin extract. Two chestnut tannins, vescalagin and castalagin, have been isolated using chromatography on Sephadex LH-20 and cellulose. The structures of these compounds have been established by means of nuclear magnetic resonance and fast atom bombardment mass spectroscopy. Some other components have been found and analyzed by chromatography and spectroscopy, but their structures have not as yet been completely defined. These structural features, together with quantitative results for each component, provide a better understanding of the mode of action of complex commercial chestnut tannin extracts.

Chromatography↗

PubMed1984

Polyorchidism.

A review of the English literature has yielded 39 cases of polyorchidism suitable for consideration in this review, and we add one more. The patients may be grouped according to the location of the aberrant testicular mass or the anatomic arrangement of their collecting systems.

Adolescent↗

PubMed1984

The prone position for transurethral resection of anterior bladder-wall tumours.

Transurethral resection of tumours of the anterior bladder wall may be technically difficult. The resectoscope must be held with an awkward upside-down grip and the surgeon assume an uncomfortable position, particularly as the bladder fills and causes the tumour to drift away from the surgeon. There is a risk of intraperitoneal perforation as the surgeon cuts more deeply to resect the tumour. When the patient is in the prone position the tumour is more accessible. This allows it to be resected more easily, more thoroughly and more comfortably. The technique may be used in men as well as in women.

Female↗

PubMed1976

Retroperitoneal cyst and congenital absence of ipsilateral kidney.

The case report of a patient in whom a cystic retroperitoneal mass and the congenital absence of the ipsilateral kidney, ureter, ureteral orifice, and trigone is presented. The embryology and literature are noted. We can find only 2 similar cases in the literature.

Adult↗

PubMed1976

Structure of the levan elaborated by Streptococcus salivarius strain 51: an application of chemical-ionisation mass-spectrometry.

The polysaccharide elaborated by Streptococcus salivarius strain 51 contains beta-D-fructofuranose residues linked through positions 2 and 6, as well as 1, 2, and 6. The approximate numbers of terminal, non-reducing D-fructofuranose residues and those linked through positions 2 and 6, and through 1, 2, and 6 in the average repeating-unit are 1, 7, and 1, respectively. The branches through the beta-(2 leads to 1)-linkage contain up to at least four D-fructofuranose residues. Chemical-ionisation mass-spectrometry aids the assignment of structures to O-acetyl-O-methylalditols obtained in methylation analysis.

Chromatography, Gas↗

PubMed1975

Some variables affecting rate of key pecking during response-independent procedures (autoshaping).

Rate of key pecking by pigeons subjected to response-independent procedures in which a stimulus on the response key preceded food presentation was investigated in eight experiments. Color and shape of the stimulus, duration of the stimulus, probability of food following the stimulus, duration of the intertrial interval, and duration of food presentation were varied separately and in combination. All variables studied, except color and shape of the stimulus, had a reliable effect on pecking rate, but some variables had stronger effects than others. Rapid key pecking may be obtained with a variety of response-independent procedures, as well as by response-dependent reinforcement. The results of experiments in which food is both dependent on key pecking and correlated with stimulus conditions are not representative of simple operant effects. Key pecking is an ideal response for studying the simultaneous operation of response-reinforcer and stimulus-reinforcer effects.

Journal Article↗

PubMed1973