Vitamin E supplementation in healthy persons.
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Dietary Supplements↗
Biomedical subjects
J A Dixon
Publications and source records attributed to J A Dixon.
Fas mRNA expression in blood is reduced during episodes of human corneal graft rejection.
BACKGROUND: Our purpose is to examine levels of Fas mRNA expression in blood during human corneal transplant rejection. METHODS: Fas mRNA expression was detected by reverse transcription-PCR in blood from normal controls, corneal recipients at the time of transplantation and during episodes of rejection. RESULTS: Samples taken at the time of a corneal rejection episode showed Fas mRNA levels were significantly lower in these patients than either normal controls (P = 0.017) or corneal transplant recipients not undergoing graft rejection (P = 0.00052). Serial samples from five patients who suffered an episode of rejection showed that the level of Fas mRNA is reduced during the rejection episode and subsequently recovers. CONCLUSIONS: These results indicate low levels of Fas mRNA in blood may have a role in corneal transplant rejection.
Adult↗
Generating initial models for reasoning.
Much of the knowledge that children and adults have about the world resides in intuitive models. Previous work shows that intuitive models allow for computation of specific outcomes given information about the system, but little is known about how such models are acquired. The current study tested three hypotheses about how children and adults construct intuitive models when they encounter a new property: (1) intuitive models are constructed by transferring principles from familiar properties; (2) with development, children shift from applying a default model to constructing specialized models; and (3) younger children's model construction is constrained by the domain, but becomes increasingly domain independent with development. Participants from three age groups (10, 13, and 19 years) made a series of judgments about two familiar properties and one novel property. Causal models showed that all age groups transferred principles from the familiar properties to the novel property. None of the age groups used a default model. There was developmental change in the effect of domain; younger, but not older, children's models were affected by domain. These findings suggest that the transfer process is developmentally invariant but that constraints on the process (i.e., domain dependence and understanding of base models) change with development.
Adolescent↗
The representations of the arithmetic operations include functional relationships.
Current theories of mathematical problem solving propose that people select a mathematical operation as the solution to a problem on the basis of a structure mapping between their problem representation and the representation of the mathematical operations. The structure-mapping hypothesis requires that the problem and the mathematical representations contain analogous relations. Past research has demonstrated that the problem representation consists of functional relationships, or principles. The present study tested whether people represent analogous principles for each arithmetic operation (i.e., addition, subtraction, multiplication, and division). For each operation, college (Experiments 1 and 2) and 8th grade (Experiment 2) participants were asked to rate the degree to which a set of completed problems was a good attempt at the operation. The pattern of presented answers either violated one of four principles or did not violate any principles. The distance of the presented answers from the correct answers was independently manipulated. Consistent with the hypothesis that people represent the principles, (1) violations of the principles were rated as poorer attempts at the operation, (2) operations that are learned first (e.g., addition) had more extensive principle representations than did operations learned later (multiplication), and (3) principles that are more frequently in evidence developed more quickly. In Experiment 3, college participants rated the degree to which statements were indicative of each operation. The statements were either consistent or inconsistent with one of two principles. The participants' ratings showed that operations with longer developmental histories had strong principle representations. The implications for a structure-mapping approach to mathematical problem solving are discussed.
Adolescent↗
Serious liver disease in a patient receiving methotrexate and leflunomide.
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Anti-Inflammatory Agents, Non-Steroidal↗
The logic of interpreting evidence of developmental ordering: strong inference and categorical measures.
Developmental ordering is a fundamental prediction of developmental theories and a central issue in developmental research. However, logically sound evidence of developmental ordering is difficult to obtain. This article analyzes the logical basis of testing developmental order hypotheses with categorical measures. Depending on whether saltatory (i.e., discrete) or continuous developmental changes are being assessed, the observed relationship between categorical measures yields very different types of information about developmental ordering. When change is continuous, the relationship between the measures does not confirm any one ordering hypothesis, but rather, disconfirms one or more hypotheses. Whether an underlying variable undergoes saltatory or continuous development has long been recognized as an important theoretical issue, but its impact on the interpretation of developmental ordering has not previously been explicated.
Child↗
Effect of inhibitors on the ubiquinone binding capacity of the primary energy conversion site in the Rhodobacter capsulatus cytochrome bc(1) complex.
A key issue concerning the primary conversion (Q(O)) site function in the cytochrome bc(1) complex is the stoichiometry of ubiquinone/ubihydroquinone occupancy. Previous evidence suggests that the Q(O) site is able to accommodate two ubiquinone molecules, the double occupancy model [Ding, H., Robertson, D. E., Daldal, F., and Dutton, P. L. (1992) Biochemistry 31, 3144-3158]. In the recently reported crystal structures of the cytochrome bc(1) complex, no electron density was identified in the Q(O) site that could be ascribed to ubiquinone. To provide further insight into this issue, we have manipulated the cytochrome bc(1) complex Q(O) site occupancy in photosynthetic membranes from Rhodobacter capsulatus by using inhibitor titrations and ubiquinone extraction to modulate the amount of ubiquinone bound in the site. The nature of the Q(O) site occupants was probed via the sensitivity of the reduced [2Fe-2S] cluster electron paramagnetic resonance (EPR) spectra to modulation of Q(O) site occupancy. Diphenylamine (DPA) and methoxyacrylate (MOA)-stilbene are known Q(O) site inhibitors of the cytochrome bc(1) complex. Addition of stoichiometric concentrations of MOA-stilbene or excess DPA to cytochrome bc(1) complexes with natural levels of ubiquinone elicits the same change in the [2Fe-2S] cluster EPR spectra; the g(x)() resonance broadens and shifts from 1. 800 to 1.783. This is exactly the same signal as that obtained when there is only one ubiquinone present in the Q(O) site. Furthermore, addition of MOA-stilbene or DPA to the cytochrome bc(1) complex depleted of ubiquinone does not alter the [2Fe-2S] cluster EPR spectral line shapes, which remain indicative of one ubiquinone or zero ubiquinones in the Q(O) site, with broad g(x)() resonances at 1. 783 or 1.765, respectively. The results are quite consistent with the Q(O) site double occupancy model, in which MOA-stilbene and DPA inhibit by displacing one, but not both, of the Q(O) site ubiquinones.
Diphenylamine↗
Detection of canine distemper virus in 100% of Paget's disease samples by in situ-reverse transcriptase-polymerase chain reaction.
Previous evidence implicating paramyxoviruses in the aetiopathology of Paget's disease of bone has been controversial. While several groups have demonstrated the presence of paramyxoviruses using electron microscopy, immunohistochemistry, and molecular biological techniques, others have found no evidence of viruses using reverse transcriptase-polymerase chain reaction (RT-PCR). We have previously provided evidence that canine distemper virus (CDV) is present in approximately 65% of samples of pagetic bone, using in situ hybridization and RT-PCR; however, these results have been criticized. To further investigate the possible Role of CDV, we have now developed the technique of in situ-RT-PCR (IS-RT-PCR) to examine for the presence of CDV-nucleocapsid (CDV-N) ribonucleic acid (RNA) in pagetic bone. Control samples consisted of uninvolved sites from patients with the disease, normal bone, and several active remodeling states. IS-RT-PCR was optimized to detect CDV-N using distemper-infected vero cells. The specificity of the technique was confirmed using vero cells infected with CDV, which showed amplified signal following IS-RT-PCR, and cells infected with measles virus (MV), in which no positive signal for CDV was detected by IS-RT-PCR. Following conventional in situ hybridization, CDV-N was detectable in 10 of 15 pagetic bone samples. However, after five, and particularly 10, cycles of IS-RT-PCR, CDV-N was found in all 15 samples. There was no evidence of CDV in four samples from uninvolved sites from pagetic patients, or in any of the other control samples. In this study, using the novel technique of IS-RT-PCR, CDV was found to be present in 100% of pagetic samples examined. There was no evidence of the virus in any of the control samples, including samples of bone from uninvolved sites from patients with Paget's disease. These results provide additional proof that CDV is present within pagetic bone and further support the hypothesis that paramyxoviruses are involved in the etiopathology of Paget's disease.
Animals↗
Developmental ordering, scale types, and strong inference.
Developmental ordering, 1 item preceding another in development, is a primary piece of evidence in developmental research. However, testing developmental ordering hypotheses is remarkably difficult; the problem is that researchers rarely have absolute measures (ratio scales). Therefore, directly comparing 2 measures is often not sensible. This article demonstrates that, depending on the type of scale, the observed data pattern is constrained by the underlying relationship. Although the observed data pattern may not reflect the exact relationship, it does limit the possible relationships. Researchers can use this information to reject potential underlying relationships. An application of the method of strong inference (J. R. Platt, 1964) is outlined whereby researchers can use observed data patterns to systematically reject competing developmental ordering hypotheses. The approach requires only standard statistical methods and assumptions.
Age Factors↗
Gender, social context, and backchannel responses.
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Adolescent↗
Gender and hedging: from sex differences to situated practice.
In a reanalysis of women's language, Holmes (1995) has argued that women's use of hedges expresses interpersonal warmth and not, as many researchers have maintained, linguistic tentativeness. It is typically men, she suggests, who employ hedges to convey imprecision and incertitude. In this study, we investigated the use of the hedges sort of and you know in a sample of South African students. Holmes's method of analysis was applied to hedging behavior in 52 dyadic conversations. The study consisted of a 2 (Speaker Gender: Male/Female) x 2 (Audience Gender: Male/Female) x 2 (CONDITION: Competitive/Noncompetitive) between-subjects experimental design. The results showed that contextual influences eclipsed the effects of gender: in fact, no main effects were found for speaker gender. Fewer hedges were deployed in the competitive condition than in the noncompetitive condition. Moreover, perhaps reflecting differences in social status, both sexes used sort of to express tentativeness more frequently when talking to male addressees. When speaking to female addressees, on the other hand, men deployed facilitative you know hedges more readily than women.
Adolescent↗
Characterizing the intuitive representation in problem solving: evidence from evaluating mathematical strategies.
Two experiments were conducted to investigate the nature of the intuitive problem representation used in evaluating mathematical strategies. The first experiment tested between two representations: a representation composed of principles and an integrated representation. Subjects judged the correctness of unseen math strategies based only on the answers they produced for a set of temperature mixture problems. The distance of the given answers from the correct answers and whether the answers violated one of the principles of temperature mixture were manipulated. The results supported the principle representation hypothesis. In the second experiment we manipulated subjects' understanding of an acid mixture task with a brief paragraph of instruction on one of the principles. Subjects then completed an estimation task intended to measure their understanding of the problem domain. The evaluation task from the first experiment was then presented, but with acid mixture instead of temperature mixture. The results showed that intuitive understanding of the domain mediates the effect of instruction on evaluating problems. Additionally, the results supported the hypothesis that subjects perform a mapping process between their intuitive understanding and math strategies.
Analysis of Variance↗
rel-(1R,6S,7S,8R,9S)-9-methyl-8-phenyl-6-[(1s,2R)-(2-phenylcyclohexyl) oxy]-4-aza-3,5-dioxatricyclo[5.2.1.0(4,9)]decane.
The structure of the title compound, C26H31NO3, was determined by X-ray crystallography. It was found to be a unique bridged tricyclic nitroso acetal. Notable features include a chair conformation of the tetrahydro-1,2-oxazine ring and a highly pyramidalized N atom [sigma angles = 314.2 (6) degrees]. The configurations of the five contiguous stereogenic centers in the nitroso acetal establish that the tandem cycloaddition sequence proceeded via an exo-[4 + 2] endo-[3 + 2] pathway.
Crystallography, X-Ray↗
Physical knowledge of sugar water solutions: cross-cultural data.
Children's understanding of sugar water solutions may progress through universal stages: from nonpreservation to preservation to liquefaction to atomism. This claim was investigated in the current study; the claim was originally prefigured in the work of Piaget and Inhelder (1974) and more recently consolidated by Slone (1987). Our sample consisted of 270 South African children drawn from three cultural groups and ranging in age from 4 to 14 years. Children watched a demonstration in which a sugar lump was dissolved in water. Then, using structured interviews, we explored their understanding of this phenomenon. The results generally confirmed the hypothesized developmental sequence. Moreover, because the sequence was consistent across cultural groups, the claim that physical knowledge evolves through universal stages also was supported. Perhaps significantly, however, the progression of knowledge development did not unequivocally lead to the concept of atomism. Developmental implications of these findings are discussed.
Adolescent↗
Evaluation of sensibility in leprosy--comparison of various clinical methods.
In order to determine whether various sensibility tests, not in common use at our hospital, are appropriate for the neurological screening of leprosy patients, an extended nerve function assessment (NFA) was done on 50 in- and outpatients who had been diagnosed as suffering from leprosy (100 hands and feet). The nerve function assessment battery consisted of Semmes-Weinstein monofilament testing (SWMT), moving 2-point discrimination (M2PD). Pinprick (PP), position sense (PS), vibration sense (VS) and voluntary muscle testing (VMT). In addition the SWMT was performed on 637 hands and 634 feet of field patients' in order to get a better indication of the prevalence of sensory impairment as measured with the SWMT. The SWMT has been shown to be a sensitive test of peripheral nerve function, therefore the other tests were compared with the SWMT. Results are reported separately for the ulnar, median and posterior tibial nerve. Test sites were the pulp of the distal phalanx of the index finger, the little finger and the big toe. Correlation between the SWMT and each of the other tests proved statistically significant; the closest correlations were between the SWMT, M2PD and PP for both ulnar and median nerves (r > 0.7, F test > 100, p < 0.0001). It is argued that the first tests to show nerve function impairment (NFI) are the M2PD and the SWMT. VS and PS were also absent in a significant proportion of patients. Arguments are presented that this may indicate advanced NFI. Results are compared with other data currently available in the literature.
Adolescent↗
Application of charge-coupled device technology for measurement of laser light and fluorescence distribution in tumors for photodynamic therapy.
Laser and fluorescence light distributions with applications for photodynamic therapy were measured in mouse tumors using a non-invasive electronic optical imaging system. The system consists of a liquid-nitrogen-cooled, charge-coupled-device (CCD) array camera under computer control with 576 x 384 detection elements having dimensions of 23 microns x 23 microns. The available dynamic range of the array is approx. 10(3), and the effective wavelength range is 400-1000 nm. An interstitially placed cylindrical diffusing optical fiber was used to provide tumor illumination. The light distribution pattern from the fiber was determined by immersing the cylindrical diffusing tip in a fluorescing solution and recording the emission image. Fluorescence imaging facilitates an accurate measurement of light intensity distribution while avoiding problems associated with the directional nature of other detection methods used with diffusing fibers. Radiation-induced fibrosarcoma tumors on C3H mice were grown to about 1 cm diameter for in vivo recording of light distribution from the tumor volume and for determination of effective light penetration distance at 18 wavelengths in the range 458-995 nm. Endogenous tumor fluorescence and Photofrin II fluorescence intensity were measured over the wavelength range 585-725 nm to investigate the possible application of CCD imaging technology for drug distribution measurements. Model experiments were begun to evaluate the relative importance of potential distortions of light distribution measurements using this approach.
Animals↗
The development of perspective taking: understanding differences in information and weighting.
2 separate aspects of perspective taking are that judgments attributed to another should depend on the information available to the other (Information effect) and on how the other's use of information differs from one's own (Weighting effect). These 2 aspects of perspective taking were studied in a moral judgment task with preschoolers, and second and fifth graders. Subjects were read a series of stories about a little boy transgressing and asked to make judgments from both their own perspective and that of a mother character in the stories. The mother story character had either the same information as the subject or only partial information. Valence of intention and consequence and the amount of mother's knowledge varied factorially. Subjects were clustered using scores derived from the judgements. 3 clusters were found that showed different levels of perspective-taking ability. There was a developmental progression in the 3 levels of perspective taking. Subjects in the Harshness cluster attributed harsher judgments to the mother perspective. Subjects in the Weighting cluster weighted information differently depending on the perspective from which they judged. Subjects in the Information-and-Weighting cluster weighted information differently depending on perspective, and also considered the amount of information available to the mother character in attributing judgments. The findings are compared to current theory on the development of perspective taking. Future research and theory need to consider the influence of both information and weighting differences on performance in perspective-taking tasks.
Affect↗
Managing the third-party payers.
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Health Maintenance Organizations↗