PubMed Health⌕ Search

Biomedical subjects

David J Smith

Publications and source records attributed to David J Smith.

10 recordsLinked to original sources

Mapping of electrostatic potential in deep submicron CMOS devices by electron holography.

Quantitative two-dimensional maps of electrostatic potential in device structures are obtained using off-axis electron holography with a spatial resolution of 6 nm and a sensitivity of 0.17 V. Estimates of junction depth and variation in electrostatic potential obtained by electron holography, process simulation, and secondary ion mass spectroscopy show close agreement. Measurement artifacts due to sample charging and surface "dead layers" do not need to be considered provided that proper care is taken with sample preparation. The results demonstrate that electron holography could become an effective method for quantitative 2D analysis of dopant diffusion in deep-submicron devices.

Journal Article↗

Application of a monoclonal antibody-based enzyme-linked immunosorbent assay for the determination of ractopamine in incurred samples from food animals.

A monoclonal antibody-based ractopamine immunoassay has been applied to incurred samples from sheep and cattle. Results obtained by immunoassay were compared with those from high-performance liquid chromatography (HPLC). Three sets of sample extracts containing primarily unmetabolized ractopamine were analyzed. Correlation of HPLC with enzyme-linked immunosorbent assay (ELISA) for beef liver samples gave an r(2) = 0.98 despite rather low ractopamine concentrations (range 1.1-13.4 ng/mL, n = 6). Ractopamine concentrations in cow urine samples treated by solid phase extraction, to remove ractopamine metabolites, also showed a high correlation between the HPLC and the ELISA results (r(2) = 0.95, range 1.0-275 ng/mL, n = 61). In contrast, HPLC and ELISA analyses of ractopamine in sheep urine were not well-correlated (r(2) = 0.58, range 0.85-51 ng/mL, n = 34). When ractopamine conjugates in urine samples were hydrolyzed with hydrolytic enzymes, ELISA and HPLC methods were highly correlated [r(2) = 0.94 for sheep (range 123-10 554 ppb, n = 60) and an r(2) = 0.98 for cattle (range 14-8159 ppb, n = 62)]. Tissues contained only minute amounts of ractopamine, and after 7-day withdrawal periods, less than 1 ppb of free ractopamine was detected. Ractopamine was rapidly metabolized in both cattle and sheep. The difference in ractopamine concentration of urine samples before and after hydrolysis indicated that only 1-5% of ractopamine was excreted unmetabolized. Results from this study indicate that the monoclonal antibody-based ELISA could be useful for a sensitive, quantitative, or qualitative ractopamine screening assay.

Animal Feed↗

Primary hyperparathyroidism in an elderly woman: surgical reversibility of profound mental state problems due to mild hypercalcaemia.

BACKGROUND: Clinical case of primary hyperparathyroidism in an 89 year old woman causing profound neuropsychiatric symptoms associated with relatively mild increases in serum calcium levels. OBJECTIVES: To demonstrate that lowering of serum calcium levels by medical treatment (biphosphonate), provided a scientific basis from which to treat a very elderly woman with neuropsychiatric symptoms with definitive surgery. METHOD: Case report. RESULTS: The use of biphosphonate therapy led to marked but temporary improvements in her mental state. CONCLUSION: A trial of reducing serum calcium levels with biphosphonate appears to be indicated in elderly patients with mild primary hyperparathyroidism and neuropsychiatric disorders.

Aged↗

Liquid chromatography/electrospray tandem mass spectrometric analysis of incurred ractopamine residues in livestock tissues.

Ractopamine HCl is a beta-adrenergic agonist (beta-agonist) recently approved by the U.S. Food and Drug Administration, but not other governmental agencies, for use in finishing swine. For these reasons, it was important to develop and validate mass spectrometric methods for the detection and confirmation of ractopamine residues in livestock marker tissues. Incurred tissues in cattle, sheep, turkeys, and ducks were generated during 7-day ractopamine feeding (20 ppm in diets) periods. Disposition of ractopamine residues in liver and pigmented retinal epithelium was determined in animals slaughtered with withdrawal periods of 0, 3, and 7 days. Ractopamine residues, purified using solid-phase extraction, were measured using liquid chromatography (LC) and electrospray with detection by tandem mass spectrometry (MS/MS) in the multiple reaction-monitoring (MRM) mode. Total ractopamine residues (parent ractopamine + hydrolyzed conjugates) in liver were detected in all species on withdrawal day 0 (2-97 ppb) and were greatly diminished in all species by withdrawal day 7 (<1 ppb). Bovine and ovine retina had lower levels of ractopamine (0.5-3 ppb) than liver, and occular residues increased with withdrawal time, suggesting redistribution into this tissue. Lower limits of quantification were found to be approximately 0.1 ppb in liver and retina. Incurred ractopamine residues were confirmed by the precise and accurate agreement of MRM intensity ratios of diagnostic fragment ions (m/z 284, 164, and 121) from the protonated molecule between ractopamine residues in incurred samples and an authentic ractopamine standard. The limits of confirmation in liver and retina using recognized acceptance criteria were below 1 ppb. The high sensitivity and specificity for measurement and confirmation of ractopamine residues suggests this method will be applicable for regulatory residue surveillance programs.

Animals↗

Performance evaluation of swimmers: scientific tools.

The purpose of this article is to provide a critical commentary of the physiological and psychological tools used in the evaluation of swimmers. The first-level evaluation should be the competitive performance itself, since it is at this juncture that all elements interplay and provide the 'highest form' of assessment. Competition video analysis of major swimming events has progressed to the point where it has become an indispensable tool for coaches, athletes, sport scientists, equipment manufacturers, and even the media. The breakdown of each swimming performance at the individual level to its constituent parts allows for comparison with the predicted or sought after execution, as well as allowing for comparison with identified world competition levels. The use of other 'on-going' monitoring protocols to evaluate training efficacy typically involves criterion 'effort' swims and specific training sets where certain aspects are scrutinised in depth. Physiological parameters that are often examined alongside swimming speed and technical aspects include oxygen uptake, heart rate, blood lactate concentration, blood lactate accumulation and clearance rates. Simple and more complex procedures are available for in-training examination of technical issues. Strength and power may be quantified via several modalities although, typically, tethered swimming and dry-land isokinetic devices are used. The availability of a 'swimming flume' does afford coaches and sport scientists a higher degree of flexibility in the type of monitoring and evaluation that can be undertaken. There is convincing evidence that athletes can be distinguished on the basis of their psychological skills and emotional competencies and that these differences become further accentuated as the athlete improves. No matter what test format is used (physiological, biomechanical or psychological), similar criteria of validity must be ensured so that the test provides useful and associative information concerning current or future performance. The practical worth of any proposed testing or monitoring protocol should be carefully evaluated. In addition, the developmental stage of the athlete(s) in question should be reflected in the testing/monitoring programme. Finally, increasing technological innovations will bring to the pool deck or dry-land training area simple, fast and advanced diagnostic tools, particularly in the areas of blood-borne markers of training response and neuromuscular excitability.

Heart Rate↗

Ketamine analgesia is not related to an opiate action in the periaqueductal gray region of the rat brain.

Ketamine is an injectable anesthetic agent that has been shown to interact as an agonist at opiate receptors. In addition, its antinociceptive action in rats is antagonized by the narcotic receptor antagonist naloxone. Thus it was assumed that the anesthetic may activate the pain inhibitory pathway, originating in the periaqueductal gray (PAG) and descending into the spinal cord, in a manner similar to that of narcotics like morphine. In the present study, it was verified that the systemic administration of naloxone (3 mg/kg i.p.) antagonized the elevation in tail-flick latency produced by an anesthetic dose of ketamine (160 mg/kg i.p.), but did not alter the duration of anesthesia (defined as duration of the loss of the righting reflex). However, when naloxone (3 micrograms/0.5 microliter/30 sec) was given by microinjection into the PAG it was found to be ineffective against the ketamine-induced elevation of the tail-flick latency. In contrast, the microinjection of the antagonist significantly attenuated (halved) the elevated latency in response to systemically administered morphine (4 mg/kg s.c.). It was also shown that ketamine was unable to elicit an increase in the latency of the tail-flick reflex when administered directly into the PAG over a wide range (0.10-100 micrograms) of doses. On the other hand, a local anesthetic-like effect of ketamine, known to occur when the drug is used in high concentration, was observed when doses exceeding 0.1 microgram were injected into the PAG. This action interfered with opiate actions in the PAG and made data from the microinjection studies difficult to interpret. The descending, pain inhibitory neuronal system originating in the PAG does not appear to participate in the antinociceptive action of ketamine measured by the tail-flick reflex. Perhaps the drug's effects are associated with alternative opiate mechanisms and/or opiate receptor subtypes not present on the cells of origin of the descending nerves within the PAG.

Animals↗

Semiconductor dopant profiling by off-axis electron holography.

Silicon wafers with a complex but known dopant profile were used to explore possible methods for improving the reliability of off-axis electron holography for quantitative determination of electrostatic potential profiles in doped semiconductor devices. The variability of results from nominally identical structures was attributed to local charging and associated external fields, forcing the development of a more robust approach to hologram analysis that incorporated an additional phase correction factor rather than rely on vacuum for phase flattening. Consistent results in close agreement with simulated profiles based on measured dopant distributions could then be obtained. Carbon coating was shown to be effective in reducing accumulation of charge caused by emission of secondary electrons. Overall, this work demonstrates that reliable potential profiles from unbiased samples should be obtainable on a routine basis provided that regions suitable for flattening of the phase profile can be identified.

Journal Article↗

Immunoaffinity column as sample cleanup method for determination of the beta-adrenergic agonist ractopamine and its metabolites.

A monoclonal antibody-based immunoaffinity column (RAC-IAC) was developed as a cleanup method for the determination of ractopamine and ractopamine glucuronides. [14C]Ractopamine (5 microg) and [14C]ractopamine glucuronides (5 microg) were fortified into 10 mL cattle urine, and loaded onto an RAC-IAC (5 mg IgG/mL) column. The column was washed and the bound analytes were eluted. In the initial loading and washing, 22% of the radioactivity was washed off and the subsequent elution step recovered 78%. A blank column prepared from nonspecific IgG retained <10% of the radioactivity. The RAC-IACs were damaged by high methanol concentrations, preventing reuse. Elution of the analytes with 50mM glycine buffer, pH 2.8, prevented damage, and the columns could be reused at least 20 times with no change in performance. They were stored >3 months in phosphate-buffered saline with 0.02% sodium azide at 4 degrees C. The method was used with fortified cattle muscle, liver, and kidney samples with recoveries of 82.1+/-7.6, 87.8+/-1.9, and 92.5+/-0.4%, respectively (n = 3). Similar studies with sheep muscle, liver, and kidney samples gave recoveries of 91.8+/-0.2, 91.7+/-0.3, and 92.3+/-0.3, respectively (n = 3). Liver and kidney samples were diluted to prevent column plugging, but all of the eluants were suitable for liquid chromatography analysis. This IAC is a selective, efficient, and economical cleanup method in a variety of matrixes for ractopamine determination.

Adrenergic beta-Agonists↗