Solution structure of glutathione bound to human glutathione transferase P1-1: comparison of NMR measurements with the crystal structure

The conformation of the bound glutathione (GSH) in the active site of the human glutathione transferase P1-1 (EC 2.5.1.18) has been studied by transferred NOE measurements and compared with those obtained by X-ray diffraction data. Two-dimensional TRNOESY and TRROESY experiments have been performed under fast-exchange conditions. The family of GSH conformers, compatible with TRNOE distance constraints, shows a backbone structure very similar to the crystal model. Interesting differences have been found in the side chain regions. After restrained energy minimization of a representative NMR conformer in the active site, the sulfur atom is not found in hydrogen-bonding distance of the hydroxyl group of Tyr 7. This situation is similar to the one observed in an "atypical" crystal complex grown at low pH and low temperature. The NMR conformers display also a poorly defined structure of the glutamyl moiety, and the presence of an unexpected intermolecular NOE could indicate a different interaction of this substrate portion with the G-site. The NMR data seem to provide a snapshot of GSH in a precomplex where the GSH glutamyl end is bound in a different fashion. The existence of this precomplex is supported by pre-steady-state kinetic experiments [Caccuri, A. M., Lo Bello, M., Nuccetelli, M., Nicotra, M., Rossi, P., Antonini, G., Federici, G., and Ricci, G. (1998) Biochemistry 37, 3028-3034] and preliminary time-resolved fluorescence data.     

Speech perception performance in experienced cochlear-implant patients receiving the SPEAK processing strategy in the Nucleus Spectra-22 cochlear implant

Sixteen experienced cochlear implant patients with a wide range of speech-perception abilities received the SPEAK processing strategy in the Nucleus Spectra-22 cochlear implant. Speech perception was assessed in quiet and in noise with SPEAK and with the patients' previous strategies (for most, Multipeak) at the study onset, as well as after using SPEAK for 6 months. Comparisons were made within and across the two test sessions to elucidate possible learning effects. Patients were also asked to rate the strategies on seven speech recognition and sound quality scales. After 6 months' experience with SPEAK, patients showed significantly improved mean performance on a range of speech recognition measures in quiet and noise. When mean subjective ratings were compared over time there were no significant differences noted between strategies. However, many individuals rated the SPEAK strategy better for two or more of the seven subjective measures. Ratings for "appreciation of music" and "quality of my own voice" in particular were generally higher for SPEAK. Improvements were realized by patients with a wide range of speech perception abilities, including those with little or no open-set speech recognition.     

Multidimensionality of oral health in dentate adults

OBJECTIVES: An understanding of the validity and usefulness of self-reported measures (as distinct from clinically determined measures) of oral health is emerging. These self-reported measures include self-rated oral health (SROH). Three objectives were to: (1) describe self-rated oral health in dentate adults, (2) quantify associations between self-rated oral health and other measures of oral health (oral disease and tissue damage, pain and discomfort, functional limitation, and disadvantage), and (3) assess the construct validity of a model of oral health proposed herein. METHODS: The Florida Dental Care Study is a longitudinal study of oral health, which included at baseline 873 subjects who had at least one tooth, were 45 years or older, and who participated for an interview and clinical examination. RESULTS: The prevalence of self-rated oral health decrements was substantial; approximately one fourth of subjects reported their oral health as only fair or poor. Bivariate and multivariate results provided consistent evidence of the construct validity of the proposed model of oral health. Additionally, the salience of one measure of dental appearance suggests that persons may use esthetic cues when rating their oral health. CONCLUSIONS: The proposed multidimensional model of oral health has construct validity. Self-rated oral health is affected by oral disease and tissue damage, oral pain and discomfort, oral functional limitation, and oral disadvantage. These self-reported measures and the proposed model should provide useful information for dental care effectiveness research. General health status has been disaggregated into the "physical" and the "mental;" an additional separation into the "oral" aspects of health seems warranted.     

Fast transmission CT for determining attenuation maps using a collimated line source, rotatable air-copper-lead attenuators and fan-beam collimation

We describe a technique using a line source and a rotatable air-copper-lead assembly to acquire gamma transmission computed tomographic (TCT) data for determining attenuation maps to compensate SPECT emission scans. The technique minimizes problems associated with discriminating 99mTc transmission and 201Tl emission photons and requires only a modest increase in total study time. A 99mTc line source and a stacked foil ("multislat") collimator are placed near the focal line of a fan-beam collimator (114 cm focal length) mounted on one detector of a triple-camera SPECT system. We acquired TCT data of plastic rod and anthropomorphic thorax phantoms to investigate the capability of the line source and rotatable air-copper-lead attenuators to determine attenuation maps. The data were acquired with and without 5.4 MBq (145 microCi) of 201Tl placed in the myocardial chamber of the thorax phantom. Phantoms also were scanned using a curved transmission slab source mounted to a parallel-hole collimator. Fan-beam TCT images have improved resolution compared with parallel-beam TCT images. Two patient scans also were performed to evaluate the clinical usefulness of fan-beam TCT. The rotatable air-copper-lead attenuator method eliminates contamination of emission data by transmission photons and reduces spill-over of emission data into the transmission energy window for some cases. Results show the feasibility of using fast, sequential or interlaced transmission scans of a line source within a rotatable air-copper-lead attenuator assembly to obtain accurate attenuation maps for SPECT attenuation compensation.     

Overcoming challenges in the study of nitrided microalloyed steels using atom probe

Nitrided steels are widely used in the engineering field due to their superior hardness and other attractive properties. Atom probe tomography (APT) was employed to study two Nb-microalloyed CASTRIP steels with different N contents. A major challenge of using APT to study this group of materials is the presence of tails after Fe peaks in the mass spectra, which overestimates the composition for alloying elements such as Nb and Cu in the steels. One important factor that contributes to the tails is believed to be delayed field evaporation from Fe²⁺. This artefact of the mass spectrum was observed to be the most severe when voltage pulsing was used. The application of laser pulses with energy ranging from 0.2 to 1.2 nJ successfully reduced the tails and lead to better compositional measurement accuracy. Spatial resolution in the z-direction (along the tip direction) was observed to be less affected by changing laser energy but deteriorates in x-y direction with increasing laser energy. This investigation suggests that pulsed-laser atom probe with ∼0.4 nJ laser energy can be used to study this group of materials with improved mass resolution while still maintaining high spatial resolution.     

Relaxation of the distribution function branch imbalance Q * in Sn and Sn-In alloys

We have used double tunnel junctions M₁-S₂-N₃ to measure the detector junction (S₂-N₃) voltage at zero detector current V _d(0) vs. generator junction (M₁-S₂) current I _g for samples cooled by helium exchange gas. We find terms both symmetric V _d ^S(0; I _g ²) and asymmetric V _d ^A(0; I _g) in I _g. The term V _d ^S is attributed to a thermoelectric voltage generated in the sample; V _d ^A is produced by Q ^*, the distribution function branch imbalance, in S₂. We have analyzed Q ^* relaxation in these samples and have compared the results with those obtained earlier by Paterson. For Sn and Sn : In alloys we find % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqiXdq3aaS% baaSqaaGqaaiaa-ffacaWFQaaabeaakiabg2da9Gqaciaa+fdacaGF% UaGaa4xmaiaa+flacaGFWaGaa4Nlaiaa+jdacaGFxdGaa4xmaiaa+b% dadaahaaWcbeqaaiaa+1cacaGFXaGaa4hmaaaakiabfs5aejaacIca% caGFWaGaaiykaiaac+cacqqHuoarcaGGOaGaa8hvaiaacMcaaaa!4C83!\[\tau _{Q*} = 1.1 \pm 0.2 \times 10^{ - 10} \Delta (0)/\Delta (T)\] sec for T - T _c; the data at all temperatures have been compared with the calculations by Chang. The attempt to measure % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqiXdq3aaS% baaSqaaGqaaiaa-ffacaWFQaaabeaaaaa!3964!\[\tau _{Q*} \] in Pb near T _c is discussed and data are presented for V _d ^S for Pb.Supported by grants from the Research Corporation and the National Science Foundation (DMR 74-23661).     

The effect of hydrogen, tritium and decay helium on the fracture toughness of a stainless steel superalloy

The effect of tritium and helium-3 on tensile properties, fracture toughness properties and fracture mechanisms was studied in a modified A-286 alloy, and compared to the effects of hydrogen. The yield strength and work hardening rate showed no sensitivity to helium-3 in the concentration range studied, but the tensile ductility decreased with increased helium concentration. Fracture toughness with tritium plus helium decreased below that obtained with hydrogen alone. Helium-3 caused a decrease in tensile ductility and fracture toughness because it precipitates on and induces failure at grain boundaries.     

A semantic framework for automatic generation of computational workflows using distributed data and component catalogues

Computational workflows are a powerful paradigm to represent and manage complex applications, particularly in large-scale distributed scientific data analysis. Workflows represent application components that result in individual computations as well as their interdependences in terms of dataflow. Workflow systems use these representations to manage various aspects of workflow creation and execution for users, such as the automatic assignment of execution resources. This article describes an approach to automating a new aspect of the process: the selection of application components and data sources. We present a novel approach that enables users to specify varying degrees of detail and amount of constraints in a workflow request, including the specification of constraints on input, intermediate or output data in the workflow, abstract workflow component classes rather than specific component implementations, and generic reusable workflow templates that express a pre-defined combination of components. The algorithm elaborates the user request into a set of fully ground workflows with specific choices of data sources and codes to be used so that they can be submitted for mapping and execution. The algorithm searches through the space of possible candidate workflows by creating increasingly more specialized versions of the original template and eliminating candidates that violate constraints cumulated in the candidate workflow as components and data sources are selected. A novel feature of our approach is that it assumes a distributed architecture where data and component catalogues are separate from the workflow system. The algorithm explicitly poses queries to external catalogues, and therefore any reasoning regarding data or component properties is not assumed to occur within the workflow system. We describe our implementation of this approach in the Wings workflow system. This implementation uses the W3C Web Ontology Language and associated reasoners to implement the workflow system as well as the data and component catalogues. This research demonstrates the use of artificial intelligence techniques to support the kinds of automation envisioned by the scientific community for large-scale distributed scientific data analysis.     

Impact of intervention strategies on Listeria contamination patterns in crawfish processing plants: a longitudinal study

Two ready-to-eat crawfish processing plants were monitored for 2 years to study the impact of Listeria control strategies, including employee training and targeted sanitation procedures, on Listeria contamination. Environmental, raw material, and finished product samples were collected weekly during the main processing months (April to June) and tested for Listeria spp. and Listeria monocytogenes. Before implementation of control strategies (year 1), the two processing plants showed Listeria spp. prevalences of 29.5% (n = 78) in raw, whole crawfish, 5.2% (n = 155) in the processing plant environment, and 0% (n = 78) in finished products. In year 2, after plant-specific Listeria control strategies were implemented, Listeria spp. prevalence increased in raw crawfish (57.5%, n = 101), in the processing plant environment (10.8%, n = 204), and in the finished product (1.0%, n = 102). Statistical analysis showed a significant increase in Listeria spp. prevalence (P < 0.0001) and a borderline nonsignificant increase in L. monocytogenes prevalence (P = 0.097) on raw material in year 2. Borderline nonsignificant increases were also observed for Listeria spp. prevalence in environmental samples (P = 0.082). Our data showed that Listeria spp. prevalence in raw crawfish can vary significantly among seasons. However, the increased contamination prevalence for raw materials only resulted in a limited Listeria prevalence increase for the processing plant environment with extremely low levels of finished product contamination. Heat treatment of raw materials combined with Listeria control strategies to prevent cross-contamination thus appears to be effective in achieving low levels of finished product contamination, even with Listeria spp. prevalences for raw crawfish of more than 50%.