Biomedical subjects

T L Ferrell

Publications and source records attributed to T L Ferrell.

9 recordsLinked to original sources

PubMed2003

Thermal transpiration at the microscale: a Crookes cantilever.

Local temperature inhomogeneities in systems containing micron and submicron objects can result in unexpected consequences. If the mean free path of the host gas constituents is comparable to a characteristic length of the system, then a net exchange of momentum occurs between the constituents and the involved surfaces. For a given temperature gradient and a given pressure range, this results in the presence of Knudsen and Knudsen-like forces (KF). The pressure dependence of these forces has been studied using a microelectromechanical system composed of a microcantilever near a substrate surface. Nano-Newton scale KF are observed by the bending of the microcantilever as monitored by the charge variation on the microcantilever-substrate assembly in a capacitive mode.

Journal Article↗

PubMed2001

Telesensor integrated circuits.

Progress in personal computing has recently permitted small research programs to design and simulate application-specific integrated circuits (ASICs). Inexpensive fabrication of silicon chips can then be obtained using chip foundries, and quite complex circuits can be greatly reduced in size with an accompanying increase in certain performance characteristics. Within the past 5 years it has also become possible to design ASICs which can transmit and receive radio signals and which thus may be employed in applications in which wired connections for input and output of signals are not practicable. We are currently developing research-grade prototype ASICs for the monitoring of human vital signs. In this case one or more sensors placed on an ASIC provides a signal to be transmitted a distance of 2-3 meters to a receiver/display unit. The use of ASIC telesensors provides the possibility of wireless monitoring, including long-term monitoring, with inexpensive and unencumbering devices. Their self-contained nature permits a number of potential uses in future biomedical applications as new sensors are devised which are amenable to deployment on silicon.

Arsenicals↗

PubMed1992

Electrostatic spraying of DNA molecules for investigation by scanning tunneling microscopy.

We have investigated electrostatic spraying of DNA onto gold surfaces as an alternative sample-preparation technique for STM studies. Preliminary results show that a higher distribution of isolated strands as well as well ordered aggregates can be obtained with this technique when compared with electrodeposition or drop evaporation. In many places, the well ordered aggregates were found to cleave in a direction perpendicular to their length after repeated scanning in the same direction.

DNA↗

PubMed1992

Scanning tunneling microscopy of DNA: a novel technique using radiolabeled DNA to evaluate chemically mediated attachment of DNA to surfaces.

pBS+ plasmid deoxyribonucleic acid (DNA) was imaged by scanning tunneling microscopy (STM) after mounting microdroplets by aerosol deposition onto heated epitaxial gold surfaces. However, the instability of the adsorbate to forces exerted by the tunneling tip points out the need for more aggressive bonding of molecules to surfaces. We describe a sensitive assay for the qualitative and quantitative evaluation of chemical agents to influence binding of DNA to surfaces using 32P-labeled pBS+ plasmid DNA. We propose that such an assay can make an important contribution to immobilization techniques prior to STM imaging.

DNA↗

PubMed1992

Imaging isolated strands of DNA molecules by atomic force microscopy.

We have employed an atomic force microscope (AFM) to image in air isolated strands of pBS+ plasmid DNA adsorbed onto freshly cleaved mica. At a DNA concentration below 0.3 micrograms/ml isolated strands of the plasmid DNA are usually seen, while for concentrations higher than 3 micrograms/ml a uniform coverage of interconnected DNA strands was observed. We found that the contrast and the width of DNA were dependent upon humidity. When the relative humidity exceeds 60%, negative contrast images with strand widths 20 times the width of DNA are found, while positive contrast images with 7 to 10 times the width of DNA are found when the humidity is below 30%. By placing the AFM in an environment where the humidity could be controlled, we were able to switch between positive and negative contrasts.

Adsorption↗

PubMed1992

Atomic force microscopy of DNA on mica and chemically modified mica.

Atomic force microscopy (AFM) was used to image circular DNA adsorbed on freshly cleaved mica and mica chemically modified with Mg(II), Co(II), La(III), and Zr(IV). Images obtained on unmodified mica show coiling of DNA due to forces involved during the drying process. The coiling or super twisting appeared to be right handed and the extent of super twisting could be controlled by the drying conditions. Images of DNA observed on chemically modified surfaces show isolated open circular DNA that is free from super twisting, presumably due to strong binding of DNA on chemically modified surfaces.

Adsorption↗

PubMed1990

Scanning tunneling microscopy and spectroscopy of plasmid DNA.

We present scanning tunneling microscope (STM) images of uncoated deoxyribonucleic acid (DNA) electrochemically mounted on highly-oriented pyrolytic graphite (HOPG) and imaged in air. Images of linear abnormalities inherent to HOPG surfaces that can be confused with DNA are also presented. Scanning tunneling spectroscopic (STS) images generated by superimposing a small, high frequency ac bias onto the dc tunnel bias and recording the ac current signal were taken simultaneously with the topographic images. These spectroscopic images reveal contrast due to local conductivity variations and can be used to differentiate DNA molecules from graphite artifacts.

Carbon↗

PubMed1979

A spontaneous outbreak of polychlorinated biphenyl (PCB) toxicity in rhesus monkeys (Macaca mulatta): clinical observations.

A spontaneous, progressive disease occurred in a large domestic breeding colony of rhesus monkeys (Macaca mulatta). The disease was characterized by slow but continuous weight loss, alopecia, acne, facial edema, diarrhea and trauma from other monkeys. Breeding efficiency was impaired with a high incidence of abortions and stillbirths. Live offspring were small and unthrifty contributing to a high infant mortality rate. The cause of this disease was polychlorinated biphenyls (PCSs) which were present in the concrete sealant on the cage floors. Removing the sealant and resurfacing the floors alleviated the problem.

Aggression↗

PubMed1978

Suspected ascorbic acid deficiency in a colony of squirrel monkeys (Saimiri sciureus).

Subperiosteal cranial hematomas were observed in five female squirrel monkeys. The absence of trauma in the clinical history, the characteristic clinical changes, and the pathological lesions suggested that the animals were scorbutic. Analysis of feed which was soaked in water, or left on the ground for varying time periods at different temperatures, indicated that there was loss of ascorbic acid. During the manufacture of monkey feed, ascorbic acid is dusted on as a final process. The practice of soaking feed resulted in the "washing off" or the destruction of ascorbic acid. This disease outbreak emphasized the important of management practices in a primate colony.

Animals↗