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Biomedical subjects

R E Stark

Publications and source records attributed to R E Stark.

14 recordsLinked to original sources
PubMed1992

Quantitation of model digestive mixtures by 13C NMR.

13C nuclear magnetic resonance (NMR) spectra were obtained at 50.3 and 100.5 MHz for methanolic and aqueous mixtures of sodium taurocholate, 1-monocapryloyl-rac-glycerol, and caprylic acid. Distortionless Enhancement by Polarization Transfer (DEPT) was used to improve spectral sensitivity and resolution, and to generate calibration curves for quantitative determinations of each lipid in methanol. Alternatively, the heights for nonoverlapping peaks in a 13C NMR spectrum acquired with inverse-gated decoupling provide reliable quantitative estimates for each component of the mixture, particularly when the data are obtained in methanol. These experiments also demonstrate the feasibility of detailed NMR structural investigations in model systems for glyceride digestion.

Carbon Isotopes↗
PubMed1991

Speech-language habilitation of hearing-impaired children: basis for assessment and training.

Spoken language assessment and training for profoundly deaf children should be based on normal developmental sequences. However, existing models of normal speech/language development have not been able to account for shifts from one developmental level to another. The implications of more recent theories of the development of expressive communication are reviewed. The concept of levels of spoken language development is reevaluated in terms of these theories. It is proposed that the developmental landmarks that initiate each level are a product of changes with growth in underlying subsystems. Some of these changes are specific to motor subsystems, but in addition, the interaction of motor, cognitive, linguistic, and social domains is stressed. The implications of these findings for development of assessment procedures and speech/language training programs is summarized.

Child Behavior↗
PubMed1990

Magic-angle spinning NMR studies of molecular organization in multibilayers formed by 1-octadecanoyl-2-decanoyl-sn-glycero-3-phosphocholine.

Magic-angle spinning 1H and 13C nuclear magnetic resonance (NMR) have been employed to study 50%-by-weight aqueous dispersions of 1-octadecanoyl-2-decanoyl-sn-glycero-3-phosphocholine (C[18]:C[10]PC) and 1-octadecanoyl-2-d19-decanoyl-PC (C[18]:C[10]PC-d19), mixed-chain phospholipids which can form interdigitated multibilayers. The 1H NMR linewidth for methyl protons of the choline headgroup has been used to monitor the liquid crystalline-to-gel (LC-to-G) phase transition and confirm variations between freezing and melting temperatures. Both 1H and 13C spin-lattice relaxation times indicate unusual restrictions on segmental reorientation at megahertz frequencies for C(18):C(10)PC as compared with symmetric-chain species in the LC state; nevertheless each chemical moiety of the mixed-chain phospholipid exhibits motional behavior that may be classified as liquidlike. Two-dimensional nuclear Overhauser spectroscopy (NOESY) on C(18):C(10)PC and C(18):C(10)PC-d19 reveals cross-peaks between the omega-methyl protons of the C18 chain and the N-methyl protons of the phosphocholine headgroup, and several experimental and theoretical considerations argue against an interpretation based on spin diffusion. Using NMR relaxation times and NOESY connectivities along with a computational formalism for four-spin systems (Keepers, J. W., and T. L. James. 1984. J. Magn. Reson. 57:404-426), an estimate of 3.5 A is obtained for the average distance between the omega-methyl protons of the C18 chain and the N-methyl protons of the phosphocholine headgroup. This finding is consistent with a degree of interdigitation similar to that proposed for organized assemblies of gel-state phosphatidylcholine molecules with widely disparate acyl-chain lengths (Hui, S. W., and C.-H. Huang. 1986. Biochemistry. 25:1330-1335); however, acyl-chain bendback or other intermolecular interactions may also contribute to the NOESY results. For multibilayers of C(18):C(10)PC in the gel phase, 13C chemical-shift measurements indicate that trans conformers predominate along both acyl chains. 13C Spin-lattice relaxation times confirm the unusual motional restrictions noted in the LC state; nevertheless, 13C and 1H rotating-frame relaxation times indicate that the interdigitated arrangement enhances chain or bilayer motions which occur at mid-kilohertz frequencies.

Gels↗
PubMed1990

Cognitive processing in specifically language-impaired children.

Eighteen language-impaired children and 25 non-language-impaired children were evaluated to investigate the relationship between language ability and selected aspects of the five-component problem-solving process defined by Kagan and Kogan (1970). Non-impaired children performed better than language-impaired children on nearly all components of the problem-solving process. Language-impaired children had particular difficulties in the areas of coding and hypothesis generation. In fact, coding ability was inversely related to the number of errors made in hypothesis evaluation. Coding ability was also positively correlated with language ability. The exact causal relationship between coding ability, language ability, and error-making in hypothesis evaluation is unclear; however, improving coding skills through training may increase automaticity and lead to improved performance in the higher levels of the problem-solving process.

Attention↗
PubMed1985

The relationship between auditory temporal analysis and receptive language development: evidence from studies of developmental language disorder.

The relationship between sensory, perceptual and motor abilities and receptive language abilities was studied in developmental dysphasic children. The tests administered included experimental auditory, visual and cross-modal perceptual tests. In addition, a battery of neurodevelopmental "soft sign" sensory, perceptual and motor tests were also given. Demographic and case history data were collected. Receptive language was derived based upon a battery of standardized language tests. Multivariate analyses were employed to examine the relationship between receptive language and sensory, perceptual and motor abilities. Results demonstrated that auditory perceptual variables, specifically those requiring rapid temporal analysis, were most highly correlated with the degree of receptive language deficit of the dysphasic children.

Aphasia↗
PubMed1985

Identification of language-impaired children on the basis of rapid perception and production skills.

Discriminant function analysis was used to determine whether performance on temporal perception and production tasks alone could correctly classify children as language-impaired or normal. The analysis identified six variables, all of which assessed temporal perceptual and production abilities, which taken in combination correctly classified 98% of participating subjects. None of these variables assess the higher-level linguistic abilities (semantic, syntactic, pragmatic) that have classically been considered to be deficient in language-impaired children, or have been used to diagnose them clinically.

Aphasia↗
PubMed1979

Analysis of stop consonant production errors in developmentally dysphasic children.

The speech production skills of 12 dysphasic children and of 12 normal children were compared. The dysphasic children were found to have significantly greater difficulty than the normal children in producing stop consonants. In addition, it was found that seven of the dysphasic children, who had difficulty in perceiving initial stop consonants, had greater difficulty in producing stop consonants than the remaining five dysphasic children who showed no such perceptual difficulty. A detailed phonetic analysis indicated that the dysphasic children seldom omitted stops or substituted nonstop for stop consonants. Instead, their errors were predominantly of voicing or place of articulation. Acoustic analyses suggested that the voicing errors were related to lack of precise control over the timing of speech events, specifically, voice onset time for initial stops and vowel duration preceding final stops. The number of voicing errors on final stops, however, was greater than expected on the basis of lack of differentiation of vowel duration alone. They appeared also to be related to a tendency in the dysphasic children to produce final stops with exaggerated aspiration. The possible relationship of poor timing control in speech production in these children and auditory temporal processing deficits in speech perception is discussed.

Aphasia↗
PubMed1975

Nuclear magnetic resonance spectroscopy: reinvestigation of carbon-13 spin-lattice relaxation time measurements of amino acids.

The carbon-13 spin-lattice relaxation times (T1) of glycine have been measured as a function of pD and concentration. Contrary to previously reported findings, no significant dependence was observed on either pD or concentration. In addition, the T1 values reported here are much longer than those published earlier. The discrepancies arise from the presence of paramagnetic impurities in the earlier samples. For the carboxyl carbon, dipole-dipole relaxation is dominant in both D2O and H2O solution, and in H2O there is a significant intermolecular dipolar contribution. Proton and oxygen relaxation times have also been measured. These, along with the carbon relaxation data, allow a discussion of the dynamics of glycine in solution.

Amino Acids↗