Search PubMed⌕ Search

Biomedical subjects

J Robertson

Publications and source records attributed to J Robertson.

At least 19 recordsLinked to original sources
PubMed2006

Modelling the nucleation and chirality selection of carbon nanotubes.

The selection of chiralities of single-walled carbon nanotubes is one of the key problems of nanotube science. We suggest that the chirality-selective growth of SWNTs could be achieved using chemical vapour deposition (CVD) by controlling the type of caps that form during the nucleation stage. As the catalyst can be solid during CVD, the formation of particular caps may be favoured by an epitaxial relationship to the catalyst surface. The corresponding tubes would then grow preferentially. We show by ab-initio calculations that the formation energy of some lattice-matched caps and tubes are 1-2 eV lower than the non lattice-matched structures.

Carbon↗
PubMed2006

The preparation of liposomes using compressed carbon dioxide: strategies, important considerations and comparison with conventional techniques.

Numerous strategies are currently available for preparing liposomes, although no single method is ideal in every respect. Two methods for producing liposomes using compressed carbon dioxide in either its liquid or supercritical state were therefore investigated as possible alternatives to the conventional techniques currently used. The first technique used modified compressed carbon dioxide as a solvent system. The way in which changes in pressure, temperature, apparatus geometry and solvent flow rate affected the size distributions of the formulations was examined. In general, liposomes in the nano-size range with an average diameter of 200 nm could be produced, although some micron-sized vesicles were also present. Liposomes were characterized according to their hydrophobic drug-loading capacity and encapsulated aqueous volumes. The latter were found to be higher than in conventional techniques such as high-pressure homogenization. The second method used compressed carbon dioxide as an anti-solvent to promote uniform precipitation of phospholipids from concentrated ethanolic solutions. Finely divided solvent-free phospholipid powders of saturated lipids could be prepared that were subsequently hydrated to produce liposomes with mean volume diameters of around 5 microm.

Carbon Dioxide↗
PubMed2006

Techniques for measurement of dose width product in panoramic dental radiography.

Dose width product (DWP) is the quantity recommended for assessment of patient dose for panoramic dental radiography. It is the product of the absorbed dose in air in the X-ray beam integrated over an exposure cycle and the width of the beam, both measured at the receiving slit. A robust method for measuring the DWP is required in order to facilitate optimization of practices and enable comparison of dose levels at different centres. In this study, three techniques for measuring the DWP have been evaluated through comparison of results from 20 orthopantomographic units. These used a small in-beam semiconductor detector and X-ray film, a pencil ionization chamber and an array of thermoluminescent dosemeters (TLDs). The mean results obtained with the three techniques agreed within +/-6%. The technique employing a pencil ionization chamber of the type used for dose assessment of CT scanners is the simplest and most reliable method. The in-beam detector and film method has larger errors both from positioning the radiation detector and from measurement of X-ray beam width, which should be the full width at half maximum obtained from a scan of the film optical density. The TLD array method was accurate, but more time consuming to carry out. The mean DWP for the units studied was 65 mGy mm and the mean dose-area product was 89 mGy cm2. The DWP for 30% of the units tested exceeded the diagnostic reference dose of 65 mGy mm, recommended by the National Radiological Protection Board.

Humans↗
PubMed2005

Electron transport and hot phonons in carbon nanotubes.

We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport in metallic carbon nanotubes. In particular, we provide a simple analytic formula for the electron transport scattering length, which we validate by accurate first principles calculations on (6, 6) and (11, 11) nanotubes. The comparison of our results with the scattering lengths fitted from experimental I-V curves indicates the presence of a nonequilibrium optical phonon heating induced by electron transport. We predict an effective temperature for optical phonons of thousands Kelvin.

Journal Article↗
PubMed2005

A molecular identification system for grasses: a novel technology for forensic botany.

Our present inability to rapidly, accurately and cost-effectively identify trace botanical evidence remains the major impediment to the routine application of forensic botany. Grasses are amongst the most likely plant species encountered as forensic trace evidence and have the potential to provide links between crime scenes and individuals or other vital crime scene information. We are designing a molecular DNA-based identification system for grasses consisting of several PCR assays that, like a traditional morphological taxonomic key, provide criteria that progressively identify an unknown grass sample to a given taxonomic rank. In a prior study of DNA sequences across 20 phylogenetically representative grass species, we identified a series of potentially informative indels in the grass mitochondrial genome. In this study we designed and tested five PCR assays spanning these indels and assessed the feasibility of these assays to aid identification of unknown grass samples. We confirmed that for our control set of 20 samples, on which the design of the PCR assays was based, the five primer combinations produced the expected results. Using these PCR assays in a 'blind test', we were able to identify 25 unknown grass samples with some restrictions. Species belonging to genera represented in our control set were all correctly identified to genus with one exception. Similarly, genera belonging to tribes in the control set were correctly identified to the tribal level. Finally, for those samples for which neither the tribal or genus specific PCR assays were designed, we could confidently exclude these samples from belonging to certain tribes and genera. The results confirmed the utility of the PCR assays and the feasibility of developing a robust full-scale usable grass identification system for forensic purposes.

Botany↗
PubMed2005

Surface diffusion: the low activation energy path for nanotube growth.

We present the temperature dependence of the growth rate of carbon nanofibers by plasma-enhanced chemical vapor deposition with Ni, Co, and Fe catalysts. We extrapolate a common low activation energy of 0.23-0.4 eV, much lower than for thermal deposition. The carbon diffusion on the catalyst surface and the stability of the precursor molecules, C2H2 or CH4, are investigated by ab initio plane wave density functional calculations. We find a low activation energy of 0.4 eV for carbon surface diffusion on Ni and Co (111) planes, much lower than for bulk diffusion. The energy barrier for C2H2 and CH4 dissociation is at least 1.3 eV and 0.9 eV, respectively, on Ni(111) planes or step edges. Hence, the rate-limiting step for plasma-enhanced growth is carbon diffusion on the catalyst surface, while an extra barrier is present for thermal growth due to gas decomposition.

Journal Article↗
PubMed2005

Emotional and behavioural needs of children and adolescents with intellectual disabilities in an urban conurbation.

BACKGROUND: Over the past decade, increased attention has been paid to identifying and responding to the emotional and behavioural needs of children and adolescents with intellectual disability (ID). The aims of the present study were to add to this body of knowledge by identifying factors associated with emotional and behavioural needs among a sample of children with ID drawn from a large urban conurbation. METHOD: Information was collected by postal questionnaire (or interview for family carers who did not have English as their first language) from teachers and from family carers of 615 children administratively identified as having ID (47% of all children with ID). RESULTS: Results indicated that: (1) the administrative prevalence of moderate but not severe ID was associated with social deprivation whereas the prevalence of severe but not moderate ID appeared to be associated with ethnicity; (2) 54% of children scored above the threshold on the Developmental Behaviour Checklist (DBC)-primary family carer, and 37% of children scored above the threshold on the DBC-teacher; (3) social deprivation, male gender, less severe ID and having fewer physical or sensory impairments were associated with antisocial and disruptive behaviour; and (4) more severe ID and additional impairments were associated with anxiety, communication disturbance, social relating and self-absorbed behaviours. CONCLUSIONS: These results identify a range of risk factors associated with behavioural and emotional problems experienced by children with ID.

Adolescent↗
PubMed2005

Treatment and management of challenging behaviours in congregate and noncongregate community-based supported accommodation.

OBJECTIVES: To compare the nature and prevalence of use of procedures employed to treat and manage challenging behaviours across two approaches to providing community-based supported accommodation for people with intellectual disabilities (ID) and severe challenging behaviour: noncongregate settings where the minority of residents have challenging behaviour, and congregate settings where the majority of residents have challenging behaviour. SETTING: Community-based supported accommodation for people with ID and challenging behaviour. DESIGN: Longitudinal matched groups design. MAIN OUTCOME MEASURES: The nature and prevalence of use of procedures employed to treat and manage challenging behaviours. Observed and reported severity of challenging behaviours. RESULTS: Both types of settings were associated with low prevalence of use of behavioural technologies for the reduction of challenging behaviour (less than 15% of participants). In contrast, high proportions of participant received antipsychotic medication in both noncongregate (56%) and congregate (80%) settings. Congregate settings were associated with the increased use of physical restraint as a reactive management strategy, with over half of participants being in receipt of physical restraint by two or more members of staff. DISCUSSION: Changes in reported and observed challenging behaviour over a 10-month period were slight. The use of evidence-based behavioural technologies for the reduction of challenging behaviour may have led to better outcomes.

Adult↗
PubMed2004

Kohn anomalies and electron-phonon interactions in graphite.

We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E(2g) and K-A'1 modes. The anomalies are revealed by two sharp kinks. By an exact analytic derivation, we show that the slope of these kinks is proportional to the square of the electron-phonon coupling (EPC). Thus, we can directly measure the EPC from the experimental dispersions. The Gamma-E(2g) and K-A'1 EPCs are particularly large, while they are negligible for all the other modes at Gamma and K.

Journal Article↗
PubMed2004

Bonding, energies, and band offsets of Si-ZrO2 and HfO2 gate oxide interfaces.

New oxides with high dielectric constant are required for gate oxides. ZrO2 is a typical example with ionic bonding. We give the rules for bonding at interfaces between Si and ionic oxides, to satisfy valence requirements and give an insulating interface. Total energies and band offsets are calculated for various (100)Si:ZrO(2) and HfO2 interface structures. The oxygen-terminated interface is found to be favored for devices, because it has no gap states and has a band offset which is rather independent of interfacial bonding.

Journal Article↗
PubMed2004

Intra-arterial cisplatin and concomitant radiation therapy followed by surgery for advanced paranasal sinus cancer.

OBJECTIVE: To report the long-term efficacy of a combined regimen of intra-arterial high-dose cisplatin chemotherapy and concomitant radiation therapy followed by organ-sparing surgery when possible in the treatment of advanced paranasal sinus cancer. DESIGN: Review of prospectively collected data. SETTING: Academic referral center. Patients Nineteen patients with advanced paranasal sinus malignancies with a minimum follow-up of 2 years. Malignancies included 14 squamous cell carcinomas (74%), 2 adenocarcinomas (10%), 2 adenoid cystic carcinomas (10%), and 1 undifferentiated carcinoma (5%). Sixteen patients (84%) had T4 disease. Intervention Treatment consisted of preoperative radiation therapy (2.0 Gy/fraction per day; total dose, 50 Gy in 5 weeks) given concomitantly with 3 to 4 weekly infusions of intra-arterial cisplatin (150 mg/m(2) per week) and systemic sodium thiosulfate neutralization. The regimen included planned surgery performed approximately 8 weeks after completion of radiation therapy. Ten patients underwent a transcranial anterior craniofacial resection; 1, a medial maxillectomy; and 1, an endoscopic restaging only. RESULTS: After a median follow-up of 53 months, actuarial overall survival at 2 and 5 years was 68% and 53%, respectively. One patient died of myocardial infarction during treatment. No other treatment-limiting toxic effect was noted. Although 3 patients had persistence of disease, delayed local failure occurred only in 2 and distant metastasis in 3. Except for cataract in 2 patients, no visual loss developed. CONCLUSION: Despite the advanced stage and unfavorable nature of cancer in this cohort, our results indicate that this regimen holds promise and merits further study.

Antineoplastic Agents↗
PubMed2004

The Resident Choice Scale: a measure to assess opportunities for self-determination in residential settings.

BACKGROUND: A 26-item Resident Choice Scale was designed to assess service practices for promoting resident choice. METHOD: The staff working with 560 UK/Irish adults with intellectual disability were interviewed. Specific examples of practices promoting resident choice were requested and independently rated by the interviewer. RESULTS: The interrater reliability of Resident Choice items was found to be acceptable (subsample n = 50). The psychometric properties of the Resident Choice Scale total score and scores on eight subscales were also acceptable. Consistently strong associations were found between greater resident choice and greater resident ability and, to a lesser extent, fewer resident challenging behaviours. Few associations were found between resident choice and autism or mental health problems. Even when controlling for resident ability and challenging behaviour, consistent associations were found between greater resident choice and the concurrent variables of greater community presence, fewer institutional practices, and greater user self-reported satisfaction (subsample n = 50). CONCLUSIONS: Taken together, this pattern of results indicates that the Resident Choice Scale shows promise as a measure of the environmental opportunities available for adults with intellectual disability to exercise self-determination. Areas for future research testing the reliability and validity of the Resident Choice Scale are outlined.

Adult↗
PubMed2003

The persistence of human scalp hair on clothing fabrics.

This study reports the persistence behaviour of human scalp hairs under a number of different circumstances. The effects of artificial dyeing of hairs, the presence or absence of roots and different types of fabrics on the persistence of hair on a variety of garments were investigated. The garments were made from cotton, polycotton, cotton/acrylic, polyester and wool. The results indicated that neither artificial dyes nor the presence or absence of roots had statistically significant effects on the persistence of hair. In contrast, the type of fabric had a major impact and it was found that, generally, hairs persist longer on rougher fabrics. The rate of loss of hairs from non-woollen fabrics during normal wear was found to follow an exponential decay curve. In contrast, the rate of loss from the woollen garments was quite linear, indicating a constant, even loss, and thus suggests that a different process is involved in the persistence of hairs on woollen garments from that on non-woollen garments. The speed at which hair was lost from fabrics decreased in the order polyester, cotton/acrylic, polycotton, cotton, smooth wool, rough wool, so that wool gives the best chance of recovering samples of hair. Due to the uniqueness of each case, it is advised that caution be used when making any interpretations and before drawing any conclusions.

Clothing↗
PubMed2003

Dynamic roughening of tetrahedral amorphous carbon.

The roughness of tetrahedral amorphous carbon (ta-C) films grown at room temperature is measured as a function of film thickness by atomic force microscopy, to extract roughness and growth exponents of alpha approximately 0.39 and beta approximately 0-0.1, respectively. This extremely small growth exponent shows that some form of surface diffusion and relaxation operates at a homologous temperature of 0.07, much lower than in any other material. This is accounted for by a Monte Carlo simulation, which assumes a smoothening during a thermal spike, following energetic ion deposition. The low roughness allows ta-C to be used as an ultrathin protective coating on magnetic disk storage systems with approximately 1 Tbit/in.(2) storage density.

Journal Article↗
PubMed2003

Use of pharmacoeconomics in prescribing research. Part 1: costs--moving beyond the acquisition price for drugs.

This paper addresses pharmacoeconomics in prescribing research and reflects the increasing use of techniques of economic evaluation to aid drug purchasing decisions in a variety of settings -- for national drug subsidization programmes, provincial purchasing plans, insurance programmes, and for hospital and area health authority formulary decisions. First, we focus on the cost component of an economic evaluation and discuss methodological issues that are relevant to all pharmacoeconomic analyses.

Cost Control↗
PubMed2003

Clinical experience with porous tantalum cervical interbody implants in a prospective randomized controlled trial.

A prospective randomized study was undertaken to evaluate the radiological appearance and clinical effectiveness of two porous tantalum (Hedrocel) implants in achieving a stable cervical interbody fusion. A prerandomization protocol was used to allocate patients to the three arms of the study: a ring implant containing autologous cancellous bone graft, a solid block implant or autologous tricortical iliac crest bone graft. Patients were followed for 2 years with plain radiological studies, SF-36, and Neck Disability Index questionnaires and neurological assessment. Early in the study the postoperative radiographs of four patients receiving Hedrocel implants showed inferior end-plate lucency raising concerns about delayed or non-fusion. Recruitment to the study was halted by the investigators to allow longer-term follow-up of the implanted patients when only 24 patients had been recruited to the study. Although fusion was subsequently noted in all patients at 12 months there was no further enrolment to the study. At 2 years the radiological and clinical outcomes of the three groups appeared comparable, but the study numbers were too small for any statistical analysis. This study highlights the difficulties that can arise when clinical caution takes precedence over objective measures of clinical progress during a study. In the absence of an independent safety monitoring committee, the investigators were under an ethical obligation to suspend recruitment to this study, until it was clear that the radiological features were not associated with poor clinical outcomes. The use of safety monitoring committees and the clarification of stopping criteria in relation to outcome measures should be considered in open randomized trials of spinal surgical techniques and implants.

Adult↗