Biomedical subjects

Scott Robertson

Publications and source records attributed to Scott Robertson.

8 recordsLinked to original sources

PubMed2006

Method to find the electron distribution function from cylindrical probe data.

Druyvesteyn's method finds the distribution of electron speeds from the second derivative of probe data using the assumption that the distribution is spherically symmetric. For the disk probe, the data are more directly related to the velocity distribution projected onto the direction normal to the probe surface. The projected distribution is less sensitive to noise because it is related to the first derivative of the data rather than the second. For the cylindrical probe, the data are more directly related to the distribution of energies projected onto the plane perpendicular to the probe axis. A method is developed for recovering this projected distribution from digitized probe data. The method is mathematically more complex than Druyvesteyn's method, but has the advantage of being less sensitive to noise. The methods are compared using noise-free simulated data and using noisy data from a double-plasma device with multidipolar magnetic confinement.

Journal Article↗

PubMed2005

Model for the density, temperature, and plasma potential of low-density hot-filament discharges.

A theoretical model is developed for the density and temperature of confined electrons and the plasma potential in low-density hot-filament discharges. These three parameters are found from a simultaneous solution of the equations for ion particle balance, electron particle balance, and electron energy balance. In the model, electrons are lost by diffusion in velocity over the potential barrier determined by the plasma potential. The confined electrons are heated by the unconfined electrons that are the secondaries from the wall and, to a lesser extent, by the primary electrons from the filaments. The plasma parameters calculated from the model agree with parameters measured in a double plasma device that has been modified to have a clean wall that gives a single value for the confining potential.

Journal Article↗

PubMed2004

Effect of candesartan and verapamil on exercise tolerance in diastolic dysfunction.

Diastolic dysfunction may be exacerbated by increased systolic blood pressure (SBP) during exercise. Ang II may contribute to this process. We performed a randomized, double-blind, crossover study of two weeks of candesartan (16 mg) and verapamil (SR 160 mg). The 21 subjects were 64 +/- 10 years old with ejection fraction greater than 50%, no ischemia, mitral flow velocity E/A less than 1, normal resting SBP (< 150 mm Hg), and SBP greater than 200 mm Hg during exercise. Exercise tolerance was assessed using a Modified Bruce Protocol at baseline and after each two-week treatment period, separated by a two-week washout period. Quality of life (QOL) was assessed using the Minnesota Living with Heart Failure questionnaire. During exercise, Ang II levels increased from 29 +/- 18 to 33 +/- 18 pg/ml (P < 0.05). SBP during exercise was 213 +/- 9 mm Hg at baseline and similarly reduced by candesartan (198 +/- 18, P < 0.01) and verapamil (197 +/- 14, P < 0.01). With candesartan, exercise time increased from 793 +/- 182 seconds to 845 +/- 163 seconds (P < 0.05), and QOL improved from 11 +/- 14 to 5 +/- 6 (P < 0.05). In contrast, verapamil did not significantly improve exercise time or QOL. In patients with mild diastolic dysfunction at rest and a hypertensive response to exercise, both Ang II receptor blockade and verapamil blunted the hypertensive response to exercise. Ang II blockade increased exercise tolerance and improved QOL.

Antihypertensive Agents↗

PubMed2003

Monte Carlo model of ion mobility and diffusion for low and high electric fields.

A Monte Carlo method is described to model the mobility and diffusion of ions drifting in response to an electric field in a neutral gas. The model uses a collision frequency that is dependent upon the ion velocity and neutral gas thermal velocity. When implemented with a constant collision cross section for momentum transfer, the model gives a mobility that is constant for small electric fields (those giving a subsonic drift velocity) and that for larger fields falls inversely with the square root of the electric field. For argon ions drifting in argon, the model gives a close agreement with experimental data for the mobility for a wide range of electric fields when implemented with an energy-dependent cross section. For modeling of transverse diffusion, agreement with data is improved if the collisions are a combination of idealized charge-exchange collisions and hard-sphere collisions.

Journal Article↗

PubMed2003

Tracking mesoderm induction and its specification to the hemangioblast during embryonic stem cell differentiation.

The hematopoietic and endothelial lineages derive from mesoderm and are thought to develop through the maturation of a common progenitor, the hemangioblast. To investigate the developmental processes that regulate mesoderm induction and specification to the hemangioblast, we generated an embryonic stem cell line with the green fluorescent protein (GFP) targeted to the mesodermal gene, brachyury. After the in vitro differentiation of these embryonic stem cells to embryoid bodies, developing mesodermal progenitors could be separated from those with neuroectoderm potential based on GFP expression. Co-expression of GFP with the receptor tyrosine kinase Flk1 revealed the emergence of three distinct cell populations, GFP(-)Flk1(-), GFP(+)Flk1(-) and GFP(+)Flk1(+) cells, which represent a developmental progression ranging from pre-mesoderm to prehemangioblast mesoderm to the hemangioblast.

Animals↗

PubMed2003

3D visualization methods to guide surgery for Parkinson's disease.

In this paper we present 2D and 3D visualization techniques that are part of our ongoing effort to improve the accuracy of neurosurgical procedures such as 'Pallidotomy' and 'Deep Brain Stimulation' (DBS), which are performed to alleviate the symptoms of Parkinson's disease. The precise targeting and mapping of structures in the Basal Ganglia particularly the internal Globus Pallidus (GPi) using a combination of stereotactic frame- registered Magnetic Resonance Imaging (MRI) and intraoperative microelectrode recording (IMR) is key to the success of these procedures. We have designed a set of software components, including a knowledge-based system (KBS), a digital signal processing module and a 2D/3D imaging system with automated mapping paradigm, which will work in combination to improve upon the standards currently in use. The imaging system will be the focus of this publication.

Humans↗

PubMed2002

The development of an interactive game-based tool for learning surgical management algorithms via computer.

BACKGROUND: We have previously demonstrated the potential efficacy of a computer-assisted board game as a tool for medical education. The next logical step was to transfer the entire game on to the computer, thus increasing accessibility to students and allowing for a richer and more accurate simulation of patient scenarios. METHODS: First, a general game model was developed using Microsoft Visual Basic. A breast module was then created using 3-D models, radiographs, and pathology and cytology images. The game was further improved by the addition of an animated facilitator, who directs the players via gestures and speech. Thirty-three students played the breast module in a variety of team configurations. After playing the game, the students completed surveys regarding its value as both an educational tool and as a form of entertainment. 10-question tests were also administered before and after playing the game, as a preliminary investigation into its impact on student learning. RESULTS: After playing the game, mean test scores increased from 6.43 (SEM +/- 0.30) to 7.14 (SEM +/- 0.30; P = 0.006). The results of the five-question survey were extremely positive. Students generally agreed that the game concept has value in increasing general knowledge regarding the subject matter of breast disease and that the idea of following simultaneously the work-up of numerous patients with similar problems is a helpful way to learn a work-up algorithm. CONCLUSIONS: Postgame surveys demonstrate the efficacy of our computer game model as a tool for surgical education. The game is an example of problem based learning because it provides students with an initial set of problems and requires them to collect information and reason on their own in order to solve the problems. Individual game modules can be developed to cover material from different diagnostic areas.

Algorithms↗

PubMed2002

The heart LIM protein gene (Hlp), expressed in the developing and adult heart, defines a new tissue-specific LIM-only protein family.

In a subtraction designed to identify transcripts accompanying mesodermal lineage specification in mouse ES differentiation cultures, we identified a gene encoding a two LIM-domain protein which we named heart LIM protein (Hlp). Hlp is most closely related to thymus LIM protein, and these two genes comprise a new gene family related to the cysteine-rich protein (CRP) gene family. In the embryo, Hlp expression is primarily restricted to the developing heart. In situ hybridization showed expression at E7.75 in the paired heart-forming primordia prior to linear heart-tube formation. At E8.5, strong expression is detected in the heart, with equal expression in both heart chambers. Hlp expression is detected in both myocardium and endocardium, and in vascular endothelium. Later in fetal development low levels of Hlp expression are detected outside the heart, including dorsal root ganglia and the spinal cord. In the adult, Hlp is expressed at highest levels in the heart, and at lower levels in the brain, skeletal muscle and aorta. Hlp expression is unchanged in hypertrophic hearts induced by aortic constriction. These data suggest a role for the two LIM-domain gene Hlp in the very earliest stages of heart differentiation and development.

Amino Acid Sequence↗