Helen F Kemp

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Many field experiments have indicated that litter decomposition in semi-arid areas may be partly or fully controlled by photodegradation. We devised a study to test our hypothesis that light exposure makes plant litter more degradable. Dry, senescent, aboveground plant litter from Miscanthus x giganteus was exposed to light including ultraviolet (UV)(More)
Stable oxygen isotope compositions (δ(18)O values) of two commercial and one synthesized silver orthophosphate reagents have been determined on the VSMOW scale. The analyses were carried out in three different laboratories: lab (1) applying off-line oxygen extraction in the form of CO(2) which was analyzed on a dual inlet and triple collector isotope ratio(More)
Variations in natural abundance of carbon (C) and nitrogen (N) stable isotopes are widely used as tools for many aspects of scientific research. By examining variations in the ratios of heavy to light stable isotopes, information can be obtained as to what physical, chemical and biological processes may be occurring. The spatial heterogeneity of soil(More)
We have identified both N-ethylmaleimide (NEM)-resistant (system T) and NEM-sensitive (system L1) L-[3H]tryptophan transporters in sinusoidal membrane vesicles (SMVs) from euthyroid, hypothyroid (propylthiouracil-treated), and hyperthyroid [L-3,5,3'-triiodothyronine (L-T3)-injected] rats. L-[125I]T3 associates with SMVs largely by surface binding. Kinetic(More)
Glucose transport activity ([3H]D-glucose uptake) in liver sinusoidal membrane vesicles (SMVs) from hyperthyroid rats was significantly higher than that from euthyroid controls (2.1-times increase in V(max) with K(m) unchanged at approximately 18 mM), associated with increased GLUT2 expression. In contrast, glucose transport V(max) into SMVs from(More)
Stable isotope analysis of organic materials for their hydrogen ((2)H), carbon ((13)C), nitrogen ((15)N) or oxygen ((18)O) isotopic composition using continuous flow isotope ratio mass spectrometry (CF-IRMS) is an increasingly used tool in forensic chemical analysis. (2)H isotopic analysis can present a huge challenge, especially when dealing with exhibits(More)
Observations made during the (13)C isotope analysis of gaseous CO(2) in the simultaneous presence of argon in the ion source of the isotope ratio mass spectrometer prompted us to investigate what influence the simultaneous presence of nitrogen would have on both accuracy and precision of bulk (2)H isotope analysis of nitrogen-rich organic compounds.(More)
Several recent deaths in the U.K. have been attributed to "legal high" drugs and in particular to (±)-4-methylmethcathinone ((±)-mephedrone). Recent literature has begun to focus on the chemical analysis of mephedrone and related substituted cathinones and methcathinones; however, no studies involving the application of stable isotope analysis to these(More)
Hair is a keratinous tissue that incorporates hydrogen from material that an animal consumes but it is metabolically inert following synthesis. The stable hydrogen isotope composition of hair has been used in ecological studies to track migrations of mammals as well as for forensic and archaeological purposes to determine the provenance of human remains or(More)
Stable isotope analysis of biogenic tissues such as tooth enamel and bone mineral has become a well-recognised and increasingly important method for determining the provenance of human remains, and it has been used successfully in bio-archaeological studies as well as forensic investigations. In particular, (18)O and (2)H stable isotope signatures of bone(More)