Biomedical subjects

F Sweeney

Publications and source records attributed to F Sweeney.

5 recordsLinked to original sources

PubMed2002

Characterization of nitride thin films by electron backscatter diffraction.

Thin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light-emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90 degrees rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tiltedby 13 +/- 1 degrees towards [1010]GaN), where the tilt is due to the inclination of the sapphire substrate (cut off-axis by 10 degrees from (0001)sapphire towards (1010)sapphire). We compare EBSD patterns obtained from As-doped GaN films grown by plasma-assisted molecular beam epitaxy (PA-MBE) with low and high As4 flux, respectively. Higher As4 flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled.

Journal Article↗

PubMed1994

Identification, partial sequence and genetic analysis of mlpA, a novel gene encoding a myosin-related protein in Physarum polycephalum.

Studies of motility in Physarum polycephalum have concentrated on the well-defined actomyosin system in plasmodia. It is clear from recent genetic studies in lower eukaryotes that myosin is involved in a number of physiological processes in addition to the contractile functions previously ascribed to the classical type II myosins. Moreover, the myosin protein family has proved to be more complex than anticipated, with an increasing number of reported specialized isoforms. Although a myosin type II activity has been identified in both amoebae and plasmodia of P. polycephalum, and it has been inferred that these proteins undergo a phase-specific isoform switch during development, this phenomenon has not been analysed genetically. In an effort to understand the putative developmental expression of actomyosin-associated proteins, we isolated a 180-kDa protein from amoebae which is highly enriched, along with actin and myosin, in actomyosin preparations in the presence of mM concentrations of Mg++ ions and 10 mM of ATP. Using polyclonal antisera raised against pl80 we have cloned and sequenced a partial cDNA encoding a protein whose predicted amino-acid sequence indicates some similarity with the Dictyostelium discoideum myosin heavy-chain tail domain. Southern-blot and RFLP analyses indicate that the gene involved, designated mlpA (myosin-like protein), occurs in a single copy in the genome, is a novel Physarum gene and is expressed during amoebal and plasmodial growth and in the dormant forms of both these cell types.

Amino Acid Sequence↗

PubMed1994

Estimation of ambient chronic toxicity in a polluted creek system.

Ambient water toxicity estimations were conducted in Piles Creek as part of an ecological risk assessment study. This creek is part of a highly polluted estuarine system located near Linden, New Jersey. An upstream and a downstream site in the creek were evaluated for effects on survival, growth and sexual maturity of the estuarine mysid, Mysidopsis bahia. Manasquan Inlet, Manasquan, New Jersey, served as the reference site. Seven-day screening toxicity tests were conducted once a month over a three month period. Results indicate that survival of mysids was not affected in any toxicity test. Mysid growth was significantly reduced at both of the test sites, in two out of three trials. Sexual maturity was shown to be adversely affected in mysids exposed to ambient waters from both test sites throughout the duration of the study.

Journal Article↗

PubMed1983

Variable susceptibility to NK activity of cloned cell lines derived from a primary rat rhabdomyosarcoma: relationship to metastatic potential.

In vitro cloned lines derived from a primary nickel-induced rat rhabdomyosarcoma exhibited diverse levels of susceptibility to spontaneous NK activity. The presence of NK target structures was revealed by competition assays on all cloned cell lines, and the NK susceptibility of the tumour lines varied according to their osmotic fragility. Tumour cell lines derived from metastatic lung nodules presented similar NK susceptibilities to cells originating from the primary tumour. However, cloned cell lines differed in their capacity to form lung colonies after i.v. injection, and in their potential for invading lungs after s.c. primary tumour development. No correlation was found between lung colonization potential and NK resistance. Studies of the correlation between metastatic potential and NK sensitivity revealed that (1) all the NK resistant tumour cells were highly metastatic; (2) NK susceptible tumour cells could be either highly or weakly metastatic. Therefore, highly metastatic tumour cells could be either resistant or susceptible to NK lysis. We conclude that the property of resistance to NK contributes to a high metastatic potential. However, other properties could counterbalance and finally prevail over NK susceptibility thus enabling NK susceptible cell lines to be also highly metastatic.

Animals↗

PubMed1982

Alterations of spontaneous quantal transmitter release at the mammalian neuromuscular junction induced by divalent and trivalent ions.

The present studies have demonstrated that Ca and Sr have a similar ability to support the release of spontaneous quanta of transmitter at the rat neuromuscular junction. The foreign ions Co, Pb, Zn and La have also been shown to support spontaneous release, although the time course of the increase in miniature end-plate potentials (m.e.p.p.s) caused by these ions is much slower than that caused by Ca and Sr. However, Sr, Co, Pb and Zn were unable to sustain m.e.p.p.s for prolonged periods. High extracellular K (10--15 mM) inhibited the steady state m.e.p.p. frequency in Ca and Sr concentrations above 1 mM, and also delayed the m.e.p.p. frequency increase induced by 1 mM Pb. It is suggested that K ions directly inhibit divalent ion entry into the nerve terminal.

Animals↗