Biomedical subjects

D R Smith

Publications and source records attributed to D R Smith.

At least 19 recordsLinked to original sources

PubMed2006

Metamaterial electromagnetic cloak at microwave frequencies.

A recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. We describe here the first practical realization of such a cloak; in our demonstration, a copper cylinder was "hidden" inside a cloak constructed according to the previous theoretical prescription. The cloak was constructed with the use of artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreased scattering from the hidden object while at the same time reducing its shadow, so that the cloak and object combined began to resemble empty space.

Journal Article↗

PubMed2006

Nutrient losses from manure and fertilizer applications as impacted by time to first runoff event.

Nutrient losses to surface waters following fertilization contribute to eutrophication. This study was conducted to compare the impacts of fertilization with inorganic fertilizer, swine (Sus scrofa domesticus) manure or poultry (Gallus domesticus) litter on runoff water quality, and how the duration between application and the first runoff event affects resulting water quality. Fertilizers were applied at 35 kg P ha-1, and the duration between application and the first runoff event varied between 1 and 29 days. Swine manure was the greatest risk to water quality 1 day after fertilization due to elevated phosphorus (8.4 mg P L-1) and ammonium (10.3 mg NH4-N L-1) concentrations; however, this risk decreased rapidly. Phosphorus concentrations were 2.6 mg L-1 29 days after fertilization with inorganic fertilizer. This research demonstrates that manures might be more environmentally sustainable than inorganic fertilizers, provided runoff events do not occur soon after application.

Agriculture↗

PubMed2006

Characterization of a planar artificial magnetic metamaterial surface.

We explore the electromagnetic characterization of a planar artificial magnetic metamaterial. Because the composite structure is two- rather than three-dimensional, it does not form a medium with assignable bulk properties, such as the electric permittivity and magnetic permeability. However, we find that it is possible to characterize the expected bulk response of a structure composed of repeated layers of metamaterial planes, from a reflectance measurement of a single metamaterial surface made at an oblique angle. We present an analytical theory that relates the reflectance of a single plane to the expected bulk permeability and permeability of the composite, as well as supporting experiments and numerical simulations. Our results show that the recent use of reflectance measurements to characterize planar split ring resonator samples can reveal the presence of circulating currents in a sample--the precursor to artificial magnetism--but are insufficient to provide quantitative results unless the symmetry of the underlying metamaterial elements is carefully specified.

Journal Article↗

PubMed2006

Epidemiology of needlestick and sharps injuries among nurses in a Japanese teaching hospital.

The epidemiology of needlestick and sharps injuries (NSIs) was investigated among a complete cross-section of 1,162 nurses from a large hospital in southern Japan (response rate 74.0%). Forty-six percent had experienced an NSI in the previous year. Most were caused by ampoules or vials, which injured 32.3% of all nurses and accounted for 42.9% of all NSI events. Twenty-two percent of all NSIs involved a device that had been used on a patient prior to the NSI (contaminated device), while the usage status of a further 2.8% of devices was unknown. Logistic regression indicated that nurses younger than 25 years of age were 2.18 times more likely to have sustained a single NSI in the past 12 months [odds ratio (OR) 2.18, 95% confidence intervals (CI) 1.15-4.17] and 2.39 times more likely to have sustained multiple NSIs (OR 2.39, 95% CI 1.08-5.34). Working mixed shifts (rotating day and night, as opposed to day shifts alone) was associated with a 1.67-fold increased risk of sustaining any NSI (OR 1.67, 95% CI 1.01-2.85) and a 2.72 times greater risk of sustaining an NSI from a contaminated device (OR 2.72, 95% CI 1.71-4.44). Nurses who reported significant fatigue after work were 1.87 times more likely to sustain multiple NSIs (OR 1.87, 95% CI 1.13-3.13) and 1.94 times more likely not to report their NSIs (OR 1.94, 95% CI 1.03-3.71). Perceived high mental pressure was associated with a 1.75-fold increased risk of sustaining an NSI from a contaminated device (OR 1.75, 95% CI 1.07-2.88). Nurses who reported suboptimal staffing levels in their wards were 2.21 times more likely not to report any NSIs they sustained in the previous year (OR 2.21, 95% CI 1.06-4.89). Overall, this study suggests that NSIs represent a complex and multi-faceted problem for Japanese nurses. Intervention strategies should consider the emerging complicity of psychosocial factors on NSI among hospital staff in Japan, as elsewhere.

Adult↗

PubMed2006

Controlling electromagnetic fields.

Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-electric displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed volume of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.

Journal Article↗

PubMed2006

Functional categories of TP53 mutation in colorectal cancer: results of an International Collaborative Study.

BACKGROUND: Loss of TP53 function through gene mutation is a critical event in the development and progression of many tumour types including colorectal cancer (CRC). In vitro studies have found considerable heterogeneity amongst different TP53 mutants in terms of their transactivating abilities. The aim of this work was to evaluate whether TP53 mutations classified as functionally inactive (< or=20% of wildtype transactivation ability) had different prognostic and predictive values in CRC compared with mutations that retained significant activity. MATERIALS AND METHODS: TP53 mutations within a large, international database of CRC (n = 3583) were classified according to functional status for transactivation. RESULTS: Inactive TP53 mutations were found in 29% of all CRCs and were more frequent in rectal (32%) than proximal colon (22%) tumours (P < 0.001). Higher frequencies of inactive TP53 mutations were also seen in advanced stage tumours (P = 0.0003) and in tumours with the poor prognostic features of vascular (P = 0.006) and lymphatic invasion (P = 0.002). Inactive TP53 mutations were associated with significantly worse outcome only in patients with Dukes' stage D tumours (RR = 1.71, 95%CI 1.25-2.33, P < 0.001). Patients with Dukes' C stage tumours appeared to gain a survival benefit from 5-fluorouracil-based chemotherapy regardless of TP53 functional status for transactivation ability. CONCLUSIONS: Mutations that inactivate the transactivational ability of TP53 are more frequent in advanced CRC and are associated with worse prognosis in this stage of disease.

Adenocarcinoma↗

PubMed2006

A flexible instrument control and image acquisition system for a scanning electron microscope.

We have developed an instrument control and image acquisition system for use with scanning electron microscopes. By making the system flexible over a wide range of operating voltages, scan generation and image acquisition modes can be easily accommodated to a wide range of instruments. We show the implementation of this system for use with a custom-built low-voltage scanning electron microscope. We then explore the simple modifications that are required for control of two instruments intended for use as free electron lasers.

Journal Article↗

PubMed2006

Prevalence of percutaneous exposure incidents amongst dentists in Queensland.

BACKGROUND: Percutaneous exposure incidents (PEI) represent an important occupational health issue in dentistry, and one that can incur severe consequences from blood-borne infections. Given the importance of this topic, we considered it necessary to investigate the distribution and cause of PEI among Queensland dentists. METHODS: In 2004, a self-reporting questionnaire was mailed to a random sample of 400 dentists on the register of the Queensland Branch of the Australian Dental Association. RESULTS: A total of 285 questionnaires (73.1 per cent) were completed and returned. Of the respondents, 73.3 per cent were male and 26.7 per cent female, with a mean age of 45.2 years (SD = 11.9 years). Most were general dentists (89.1 per cent) with the remainder being specialists (10.9 per cent). More than three-quarters (78.5 per cent) reported damaging their gloves at least once during a clinical procedure in the previous 12-month period. Roughly one-quarter (27.7 per cent) had experienced at least one 'sharps' or needlestick injury in the previous 12 months, 16.1 per cent of which involved a contaminated instrument that had been previously used on a patient. The most common devices to cause 'sharps' injury in the previous 12 months were needles (14.4 per cent) and burs (10.2 per cent). CONCLUSIONS: Although PEI clearly remains a major occupational health problem for Queensland dentists, the prevalence of needlestick injuries appears to be lower than other studies from developed countries. The identification of needlestick injuries as a common cause of PEI again stresses the importance of preventive strategies with respect to potential blood-borne infections. Further research is now needed to more carefully identify effective measures for reducing PEI among dental personnel.

Adult↗

PubMed2006

Intraspinal synovial cysts: a retrospective study.

BACKGROUND: We report the clinical presentation, radiographic studies, intraoperative findings, histopathological analysis, and post-treatment outcome in 26 patients diagnosed with spinal synovial cysts (SSCs). AIMS: To describe the clinical presentation, radiographic studies, operative findings, and postoperative follow-up in 26 patients with SSCs. SETTINGS AND DESIGN: The study was retrospective in design, involving chart review. Individual patient data was tabulated and patterns were recognized. MATERIALS AND METHODS: The charts for 26 patients who underwent surgical extirpation of SSC between April 1993 and October 2002 were retrospectively reviewed. Specifically, initial clinical presentation, pertinent radiographs (X-rays, magnetic resonance imaging, computed tomography), intraoperative findings, histopathology, and postoperative follow-up were noted. STATISTICAL ANALYSIS USED: Patient data was tabulated and analyzed for patterns in demographics, symptoms and histopathology. RESULTS: SSCs were more common in females than males (17:9 ratio). Presenting symptoms were back pain with radiculopathy in 13 (50%), radicular pain in the absence of back pain in 10 (38%), and back pain without radicular pain in three (11%). In addition, 17 patients (65%) had sensory deficit, and 9 (35%) had motor deficit. Most SSCs occurred at the lumbar (19/26) or lumbosacral (5/26) regions, with only 2 (2/26) in the thoracic region. One patient had bilateral SSC at the L4-5 level. Intraoperatively, each cyst was located adjacent to a degenerated facet joint. These lesions could grossly be identified intraoperatively and histopathological confirmation was achieved in all the cases. CONCLUSIONS: SSCs are important lesions to consider in the differential diagnosis of lumbar epidural masses and surgical resection leads to significant improvement in the majority of cases.

Humans↗

PubMed2005

Pleistocene to recent dietary shifts in California condors.

We used carbon and nitrogen isotopes to investigate changes in the diet of California condors from the Pleistocene to the recent. During the Pleistocene, condors from California fed on both terrestrial megafauna and marine mammals. Early accounts reported condors feeding on the carcasses of marine mammals, but by the late 1700s, condor diets had shifted predominantly to terrestrial animals, following the commercial harvesting of marine mammals and the development of cattle ranching on land. At present, dairy calves provided by humans significantly augment condor diet, constituting an artificial support of the current population. Reestablishing a marine mammal component in the condor diet may be an effective strategy for fostering viable condor populations independent of direct human subsidies.

Analysis of Variance↗

PubMed2005

Electromagnetic parameter retrieval from inhomogeneous metamaterials.

We discuss the validity of standard retrieval methods that assign bulk electromagnetic properties, such as the electric permittivity epsilon and the magnetic permeability mu, from calculations of the scattering (S) parameters for finite-thickness samples. S-parameter retrieval methods have recently become the principal means of characterizing artificially structured metamaterials, which, by nature, are inherently inhomogeneous. While the unit cell of a metamaterial can be made considerably smaller than the free space wavelength, there remains a significant variation of the phase across the unit cell at operational frequencies in nearly all metamaterial structures reported to date. In this respect, metamaterials do not rigorously satisfy an effective medium limit and are closer conceptually to photonic crystals. Nevertheless, we show here that a modification of the standard S-parameter retrieval procedure yields physically reasonable values for the retrieved electromagnetic parameters, even when there is significant inhomogeneity within the unit cell of the structure. We thus distinguish a metamaterial regime, as opposed to the effective medium or photonic crystal regimes, in which a refractive index can be rigorously established but where the wave impedance can only be approximately defined. We present numerical simulations on typical metamaterial structures to illustrate the modified retrieval algorithm and the impact on the retrieved material parameters. We find that no changes to the standard retrieval procedures are necessary when the inhomogeneous unit cell is symmetric along the propagation axis; however, when the unit cell does not possess this symmetry, a modified procedure--in which a periodic structure is assumed--is required to obtain meaningful electromagnetic material parameters.

Journal Article↗

PubMed2005

Gradient index metamaterials.

Metamaterials--artificially structured materials with tailored electromagnetic response--can be designed to have properties difficult or impossible to achieve with traditional materials fabrication methods. Here we present a structured metamaterial, based on conducting split ring resonators (SRRs), which has an effective index of refraction with a constant spatial gradient. We experimentally confirm the gradient by measuring the deflection of a microwave beam by a planar slab of the composite metamaterial over a range of microwave frequencies. The gradient index metamaterial may prove an advantageous alternative approach to the development of gradient index lenses and similar optics, especially at higher frequencies. In particular, the gradient index metamaterial we propose may be suited for terahertz applications, where the magnetic resonant response of SRRs has recently been demonstrated.

Journal Article↗

PubMed2005

Use of rope devices to describe and explain the feedlot ecology of Escherichia coli O157:H7 by time and place.

Escherichia coli O157:H7 is an important pathogen of humans, and cattle populations serve as an important reservoir for human exposure. The organism is ubiquitous to feedlot cattle populations, although the nature of its occurrence is quite dynamic. Why E. coli O157:H7 varies by time and place in fed cattle is poorly understood. This study was designed to describe and explain the occurrence of E. coli O157:H7 by pen-level factors of time and place. From each pen, we cultured seven ropes placed within pens for cattle to rub and chew (ROPES), in order to classify the pens as high or low prevalence in longitudinal studies conducted during the summer and winter feeding periods of 2 full years. We observed differences in occurrence of ROPES-positive pens by season, weeks within season, and feedyard. ROPES-positive pens clustered temporally. Factors associated with ROPES-positive pen-weeks during both the summer and winter feeding periods were feedyard, prior 7-day mean air temperature, recovery of E. coli O157:H7 from the composite fecal sample, and recovery of E. coli O157:H7 from the water tank. Pens of summer-fed cattle were less likely to be ROPES-positive for E. coli O157:H7 if the ROPES were positive for Salmonella spp. The condition of the pen surface was associated with the likelihood for winter-fed pens of cattle to be ROPES-positive. We were able to monitor these pens of cattle using ROPES at minimal cost and without disturbing individual cattle. These observations improve our understanding of the ecology of E. coli O157:H7 in fed cattle, and also illustrate the importance of designing and analyzing observational studies and clinical trials to account for time- and place-dependent variables that affect the probability of detecting E. coli O157:H7.

Animal Husbandry↗

PubMed2005

Use of rope devices to describe and explain the feedlot ecology of Salmonella by time and place.

Salmonella spp. are important zoonotic pathogens, and cattle can serve as an important source of this organism for human exposure through food. This study was designed to describe and explain the occurrence of Salmonella spp. by pen-level factors of time and place using a pen-level test-method previously validated for E. coli O157:H7. From each pen, we cultured seven ropes placed within the pen for cattle to rub and chew (ROPES), in order to classify the pens as ROPES-positive or ROPES-negative each week in longitudinal studies conducted during the summer and winter feeding periods of 2 full years. We observed differences in occurrence of ROPES-positive pens by week within each season such that, at times, a high proportion of pens were of the same ROPES-status even though feedyards were separated by 50-200 km. Factors associated with ROPES-positive pen-weeks during both the summer and winter feeding periods were the condition of the pen surface and recovery of Salmonella spp. from the water tank. The probability for pens of summer-fed cattle to be ROPES-positive for Salmonella spp. increased as the number of cattle in the pen increased and decreased when the pen was ROPES-positive for E. coli O157:H7. Pens of winter-fed cattle differed by feedyard in the probability of their being ROPES-positive for Salmonella spp. We were able to monitor these pens using ROPES at minimal expense, without disturbing individual cattle, and observe important time and place relationships of Salmonella spp. in fed cattle. These observations illustrate the importance of accounting for time- and place-dependent variables that affect the probability of detecting Salmonella spp. when designing and analyzing observational studies and clinical trials.

Animal Husbandry↗

PubMed2005

A randomized blinded trial of combination therapy with cyclophosphamide in patients-with active multiple sclerosis on interferon beta.

OBJECTIVE: To evaluate the efficacy and safety of combination therapy with pulse cyclophosphamide given with methylprednisolone (MP) and interferon beta (IFNbeta)-Ia in multiple sclerosis (MS) patients with active disease during IFNbeta monotherapy. METHODS: This was a randomized, single-blind, parallel-group, multicenter trial in MS patients with a history of active disease during IFNbeta treatment. Patients were randomized to either cyclophosphamide 800 mg/m2 plus methylprednisolone 1 g IV (CY/MP) or methylprednisolone once a month for six months and then followed for an additional 18 months. All patients received three days of methylprednisolone 1 g IV at screening and 30 mcg IFNbeta-Ia IM weekly for the entire 24 months. The primary endpoint was change from baseline in the mean number of gadolinium-enhancing (Gd+) lesions. Secondary clinical endpoints included time to treatment failure. RESULTS: Fifty-nine patients were randomized to treatment: 30 to CY/MP and 29 to MP Change from baseline in the number of Gd+ lesions was significantly different between treatment groups at three (P =0.01), six (P =0.04) and 12 months (P =0.02), with fewer lesions in the CY/MP group. The cumulative rate of treatment failure was significantly lower in the CY/MP group compared with the MP group (rate ratio =0.30; 95% confidence interval, 0.12-0.75; P =0.011). CY/MP treatment was well tolerated. CONCLUSION: Combination therapy with CY/MP and IFNbeta-Ia decreased the number of Gd+ lesions and slowed clinical activity in patients with previously active disease on IFNbeta alone.

Adjuvants, Immunologic↗

PubMed2004

Negative index lens aberrations.

We examine the Seidel aberrations of thin spherical lenses composed of media with refractive index not restricted to be positive. We find that consideration of this expanded parameter space allows for the reduction or elimination of more aberrations than is possible with only positive index media. In particular, we find that spherical lenses possessing real aplanatic focal points are possible only with a negative index. We perform ray tracing, using a custom code that relies only on Maxwell's equations and conservation of energy, that confirms the results of the aberration calculations.

Journal Article↗

PubMed2004

Manganese oxidation state mediates toxicity in PC12 cells.

The role of the manganese (Mn) oxidation state on cellular Mn uptake and toxicity is not well understood. Therefore, undifferentiated PC12 cells were exposed to 0-200 microM Mn(II)-chloride or Mn(III)-pyrophosphate for 24 h, after which cellular manganese levels were measured along with measures of cell viability, function, and cytotoxicity (trypan blue exclusion, medium lactate dehydrogenase (LDH), 8-isoprostanes, cellular ATP, dopamine, serotonin, H-ferritin, transferrin receptor (TfR), Mn-superoxide dismutase (MnSOD), and copper-zinc superoxide dismutase (CuZnSOD) protein levels). Exposures to Mn(III) >10 microM produced 2- to 5-fold higher cellular manganese levels than equimolar exposures to Mn(II). Cell viability and ATP levels both decreased at the highest Mn(II) and Mn(III) exposures (150-200 microM), while Mn(III) exposures produced increases in LDH activity at lower exposures (> or =50 microM) than did Mn(II) (200 microM only). Mn(II) reduced cellular dopamine levels more than Mn(III), especially at the highest exposures (50% reduced at 200 microM Mn(II)). In contrast, Mn(III) produced a >70% reduction in cellular serotonin at all exposures compared to Mn(II). Different cellular responses to Mn(II) exposures compared to Mn(III) were also observed for H-ferritin, TfR, and MnSOD protein levels. Notably, these differential effects of Mn(II) versus Mn(III) exposures on cellular toxicity could not simply be accounted for by the different cellular levels of manganese. These results suggest that the oxidation state of manganese exposures plays an important role in mediating manganese cytotoxicity.

Adenosine Triphosphate↗

PubMed2004

Enhanced diffraction from a grating on the surface of a negative-index metamaterial.

We show by numerical simulation as well as by measurements on negative-index metamaterial wedge samples, that the unavoidable stepping of the refraction interface-due to the finite unit-cell size inherent to metamaterials-can give rise to a well-defined diffracted beam in addition to the negatively refracted beam. The direction of the diffracted beam is consistent with elementary diffraction theory; however, the coupling to this higher order beam is much larger than would be the case for a positive index material. The results confirm recent theoretical predictions of enhanced diffraction for negative-index grating surfaces.

Journal Article↗