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Biomedical subjects

S D Kelly

Publications and source records attributed to S D Kelly.

13 recordsLinked to original sources
PubMed2002

Survey of stable sulfur isotope ratios (34S/32S) of sulfite and sulfate in foods.

A study was conducted to determine the natural abundance sulfur isotope ratios in foods containing sulphite preservatives. This involved determining (1) the accuracy and repeatability of sulfur isotope ratios measured using an elemental analyser (EA) coupled to an isotope ratio mass spectrometer (IRMS); and (2) the isotope ratios of 21 samples of commercially available S(IV) oxo-anion compounds, nine samples of S(VI) sulfate salts and the isotope ratios of the sulfate obtained by modified Monier-Williams distillation of SO(2) from 33 retail foods containing sulfite preservatives. The sulfur isotope ratio data for SO(2) recovered from foodstuffs showed a large spread of results, which suggested that the SO(2) derived from sulfite preservatives does not have a distinctive sulfur signature ratio. The range of results (3.1-52.1) overlapped with that found for a range of commercially available sulfite and sulfate reagents commonly used to preserve food (sulfites 2.5-13.7, sulfates 10.0-16.9). Whilst the variability in isotope ratios originated from the food samples themselves, evidence from the analysis of SO(2) gas suggested that isotope fractionation during dissolution, reaction and recovery was also a confounding factor.

Barium Sulfate↗
PubMed2001

Determining crystalline atomic positions using XAFS, a new addition to the UWXAFS analysis package.

XAFS and x-ray diffraction (XRD) are complementary structure determination techniques. The combination of XAFS and XRD can be used to determine the complete crystal structure when diffraction can not be refined. This is often the case at high pressures or high temperatures where there is limited access to the samples and energy dispersive x-ray diffraction is used. A new method to determine the atomic positions within the unit cell using EXAFS data with the programs RUNFIT and MKFIT is described. These programs systematically produce and test models for the XAFS data that are consistent with the diffraction results. The programs were written to solve the structure of two intermediate high pressure phases of AgCl, and are distributed with a working example.

Crystallization↗
PubMed2001

X-ray absorption fine structure spectroscopy determination of the binding mechanism of tetrahedral anions to self assembled monolayers on mesoporous support.

X-ray absorption fine structure (XAFS) spectroscopy is used to investigate the chemical interaction between the end member [Cu(NH2)6] of self-assembled monolayers on mesoporous supports (SAMMS) and the tetrahedral anion SO4. The local structure about Cu indicates monodentate bonding between the SO4 anion and the SAMMS.

Journal Article↗
PubMed2001

XAFS determination of the bacterial cell wall functional groups responsible for complexation of Cd and U as a function of pH.

Bacteria, which are ubiquitous in near-surface geologic systems, can affect the distribution and fate of metals in these systems through adsorption reactions between the metals and bacterial cell walls. Recently, Fein et al. (1997) developed a chemical equilibrium approach to quantify metal adsorption onto cell walls, treating the sorption as a surface complexation phenomenon. However, such models are based on circumstantial bulk adsorption evidence only, and the nature and mechanism of metal binding to cell walls for each metal system have not been determined spectroscopically. The results of XAFS measurements at the Cd K-edge and U L3-edge on Bacillus subtilis exposed to these elements show that, at low pH, U binds to phosphoryl groups while Cd binds to carboxyl functional groups.

Adsorption↗
PubMed2001

XAS investigations of Fe(VI).

Recent attention has been given to a reexamination of results from the early Viking missions to Mars that suggested the presence of one or more strong oxidants in Martian soil. Since Fe is one of the main constituents of the Martian surface and Fe(VI) is known to be a highly reactive, strong oxidant, we have made XANES and EXAFS measurements of Fe(II), Fe(III), Fe(IV), and Fe(VI) in solid and solution forms. Results from these studies indicate a preedge XANES feature from Fe(VI) samples similar to that commonly seen from Cr(VI) samples. Results of first shell analysis indicate a linear relationship between the Fe-O bondlength and Fe valence state.

Journal Article↗
PubMed2001

Deuterium/hydrogen isotope ratio measurement of water and organic samples by continuous-flow isotope ratio mass spectrometry using chromium as the reducing agent in an elemental analyser.

A rapid continuous-flow technique for quantitative determination of hydrogen isotope ratios in water and organic materials at natural abundance levels is described. Water and organic samples were reduced in a helium stream at temperatures in excess of 1000 degrees C over chromium metal. delta(2)H per thousand values of water and organic samples were determined by calibration against International Atomic Energy Agency reference materials V-SMOW and SLAP water. The accuracy of the method was demonstrated through the analysis of the intermediate water standard GISP and IAEA water intercomparison materials OH-1, OH-2 and OH-3. Values obtained using this technique compared well with reference values (maximum difference 2.2 per thousand). The precision of water analyses was less than 2.3 per thousand (1 sigma or 1 standard deviation) in all cases. No apparent memory effect was observed when measuring samples at the natural abundance level. The application of the technique to organic molecules and the salts of organic acids was successfully demonstrated by measuring the delta(2)H per thousand values of an n-hexadecane laboratory reference and anhydrous calcium formate versus water calibration materials.

Algorithms↗
PubMed2001

Broadening the units of analysis in communication: speech and nonverbal behaviours in pragmatic comprehension.

Recently, much research has explored the role that nonverbal pointing behaviours play in children's early acquisition of language, for example during word learning. However, few researchers have considered the possibility that these behaviours may continue to play a role in language comprehension as children develop more sophisticated language skills. The present study investigates the role that eye gaze and pointing gestures play in three- to five-year-olds understanding of complex pragmatic communication. Experiment 1 demonstrates that children (N = 29) better understand videotapes of a mother making indirect requests to a child when the requests are accompanied by nonverbal pointing behaviours. Experiment 2 uses a different methodology in which children (N = 27) are actual participants rather than observers in order to generalize the findings to naturalistic, face-to-face interactions. The results from both experiments suggest that broader units of analysis beyond the verbal message may be needed in studying children's continuing understanding of pragmatic processes.

Child, Preschool↗
PubMed2001

Explaining math: gesturing lightens the load.

Why is it that people cannot keep their hands still when they talk? One reason may be that gesturing actually lightens cognitive load while a person is thinking of what to say. We asked adults and children to remember a list of letters or words while explaining how they solved a math problem. Both groups remembered significantly more items when they gestured during their math explanations than when they did not gesture. Gesturing appeared to save the speakers' cognitive resources on the explanation task, permitting the speakers to allocate more resources to the memory task. It is widely accepted that gesturing reflects a speaker's cognitive state, but our observations suggest that, by reducing cognitive load, gesturing may also play a role in shaping that state.

Adult↗
PubMed2000

Formation of sphalerite (ZnS) deposits in natural biofilms of sulfate-reducing bacteria.

Abundant, micrometer-scale, spherical aggregates of 2- to 5-nanometer-diameter sphalerite (ZnS) particles formed within natural biofilms dominated by relatively aerotolerant sulfate-reducing bacteria of the family Desulfobacteriaceae. The biofilm zinc concentration is about 10(6) times that of associated groundwater (0.09 to 1.1 parts per million zinc). Sphalerite also concentrates arsenic (0.01 weight %) and selenium (0.004 weight %). The almost monomineralic product results from buffering of sulfide concentrations at low values by sphalerite precipitation. These results show how microbes control metal concentrations in groundwater- and wetland-based remediation systems and suggest biological routes for formation of some low-temperature ZnS deposits.

Arsenic↗
PubMed1999

Determination of the oxygen-18/oxygen-16 isotope ratios of sugar, citric acid and water from single strength orange juice.

The ratio of the stable isotopes of oxygen (18O/16O) has been measured in the sugar, citric acid and water from authentic single strength orange juices, originating from a number of different countries. The sugars and citric acid were recovered from the juices and their 18O/16O ratios were determined by pyrolysis/continuous flow-isotope ratio mass spectrometry (Py/CF-IRMS). The 18O/16O ratio of the fruit juice water was determined by the carbon dioxide/water equilibration method. The delta 18O/1000 values of 45 different sugars ranged from +29.1 to +38.8/1000 and 15 citric acids ranged from +18.9 to +25.4/1000. The delta 18O/1000 value of the water present in the same samples ranged from -2.1 to +7.8/1000. A correlation was evident between the delta 18O/1000 values of the sugar, citric acid and water from the juices. This information can be used to improve the assessment of the authenticity of commercial 'freshly squeezed' orange juices. The detection of the presence of reconstituted orange juice concentrate in 'freshly squeezed' orange juices was improved by 37% using regression analysis of the combined water and sugar delta 18O/1000 ratios when compared to the use of delta 18O/1000 ratios of fruit juice water alone.

Beverages↗
PubMed1998

A comparison between children's and adults' ability to detect conceptual information conveyed through representational gestures.

The present study compares children's and adults' ability to detect information that is conveyed through representational hand gestures. Eighteen children (M = 10 years, 1 month) and 18 college undergraduates watched videotaped stimuli of children verbally and gesturally explaining their reasoning in a problem-solving situation. A recall procedure was used to assess whether children and adults could detect information conveyed in the stimulus children's gesture and speech. Results showed that children and adults recalled information that was conveyed through representational gestures. In addition, "mismatching" gesture negatively affected the precision of speech recall for adults. However, this negative effect on speech recall was absent for children.

Adult↗