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Biomedical subjects

C R Phillips

Publications and source records attributed to C R Phillips.

At least 37 records · Page 2Linked to original sources
PubMed1989

Signals from the dorsal blastopore lip region during gastrulation bias the ectoderm toward a nonepidermal pathway of differentiation in Xenopus laevis.

Epi 1, a monoclonal antibody, was generated against an epidermal specific epithelial antigen; it does not stain neural epithelium. We have used Epi 1 as a marker to determine when the spatial patterns delineating neural from nonneural epithelium become established. We used ventral ectoderm in a sandwich assay to show that signals from the central blastopore lip region, passing through the plane of the ectoderm sheet, define the pattern and boundary characteristics of Epi 1 expression. The dorsal blastopore lip at stages 10 and 12 are the strongest in inhibiting Epi 1 expression. The involuted chordamesoderm has only a limited inhibitory effect on Epi 1 expression in ventral ectoderm recombinates and does not appear to establish pattern boundaries. We suggest that the blastopore lip region establishes a preneural bias in the adjacent ectoderm prior to the interaction of the latter with chordamesoderm.

Animals↗
PubMed1986

Expression of an epidermal antigen used to study tissue induction in the early Xenopus laevis embryo.

A monoclonal antibody (Epi 1) has been produced that recognizes an antigen expressed in epidermal cells of Xenopus laevis embryos. The Epi 1 antigen appears in embryonic epidermis at the end of gastrulation and is not expressed in nonepidermal structures derived from ectoderm (for example, neural tube or cement gland). The capacity to express the Epi 1 antigen is restricted to cells of the animal hemisphere prior to the midblastula stage of development (stage 8), and tissue interactions during gastrulation inhibit the expression of the Epi 1 antigen in neural ectoderm. This epidermal antigen will be a valuable marker for studies of ectodermal commitment.

Animals↗
PubMed1986

A simple two-count method for routine monitoring of 222Rn and 220Rn progeny working levels in U mines.

In the case of U mines containing Th, the total alpha energy will contain contributions from both 222Rn progeny and 220Rn progeny. A simple routine grab sampling monitoring scheme is therefore needed for separate measurement of the working levels of 222Rn and 220Rn progeny. The scheme presented here is based on a short delay period after sampling (2 min) for 222Rn progeny and a long delay period (340 min) before counting 220Rn progeny. An advantage of this scheme is that no corrections need to be made to the 222Rn progeny working level for the presence of 220Rn progeny. Such corrections must be made in the commonly used Kusnetz scheme.

Mathematics↗
PubMed1985

Spatial changes in poly(A) concentrations during early embryogenesis in Xenopus laevis: analysis by in situ hybridization.

The dorsal-ventral axis of the Xenopus embryo is approximately determined by the point of sperm entry, which occurs randomly about the animal-vegetal axis of the egg. Two cytoplasmic components were studied whose spatial arrangements and local concentration patterns appear to reflect the forming dorsal-ventral axis. First, three-dimensional maps depicting the rearrangements of different size classes of yolk platelets were reconstructed from serial sections. These maps provide information on the time when movements occur and the intracellular directions and distances components can travel within the early embryo. Second, local poly(A) concentrations were observed using a [3H]poly(U) in situ hybridization probe. Poly(A) concentrations were observed to change reproducibly from fertilization to late cleavage. Two cytoplasmic areas were found to undergo major, stage-specific increases in poly(A) concentration.

Animals↗
PubMed1985

Dependence of electrostatic diffusion of Rn progeny on environmental parameters.

In previous work it was established that electrostatic diffusion of Rn progeny attached to aerosols can be used for passive dosimetry by replacing the pump-filter assembly in an active dosimeter by an electret. In the present work, results are presented on the dependence of activity collected by an electret on aerosol concentration, aerosol diameter, attachment rate of Rn progeny to aerosols, unattached fraction of Rn progeny, and Rn progeny concentrations. The electrostatic flow rate of Rn progeny is defined and all relationships analyzed in terms of this flow rate. The electrostatic flow rate is found to be reasonably constant for 0.03 micron less than particle diameter less than 0.09 micron, unattached fraction of 218Po less than 0.40 and 70,000/cm3 less than aerosol concentration less than 180,000/cm3; experimentally obtained data outside these limits are too few to draw any definite conclusions. The results are useful from a practical point of view because typical U mine conditions are described by these limits.

Aerosols↗
PubMed1985

The application of electrets to passive Rn progeny dosimeters.

The theoretical and experimental bases are presented for development of a passive electret dosimeter for Rn progeny. The mechanism of aerosol collection is described, and experiments to develop a suitable aerosol collecting element (electret) for a passive Rn progeny dosimeter are reported.

Air Pollutants↗
PubMed1984

Electrets for passive radon daughter dosimetry.

Electrets are demonstrated to collect radon-daughter aerosols with efficiencies which are similar to the efficiencies of aluminum discs held at a potential equal to the surface potential of the electrets. The properties of the electrets are suitable for incorporation of an electret into a radon-daughter dosimeter as the passive collecting element.

Aerosols↗
PubMed1982

The regional distribution of poly (A) and total RNA concentrations during early Xenopus development.

Xenopus laevis embryos were oriented and sectioned into six regions along one of three axes: animal-vegetal, dorsal-ventral, or right-left. Total RNA (predominantly ribosomal RNA) and poly riboadenylate [poly (A)] were measured for each region during early embryogenesis. The concentrations of both total RNA and poly(A) are nonuniformly distributed during early development. Total RNA is approximately four-fold more concentrated in the more animal portions than the more vegetal portions of the embryo. The dorsal-most region contains a 1.5-fold higher concentration than in the other five regions of the four-celled embryo along the dorsal-ventral axis. Poly(A) concentrations show temporal and regional specific changes in concentration during early development with higher concentrations more generally found in the animal-most regions.

Animals↗
PubMed1982

Development of a continuous monitor for 226Ra in water.

Continuous 226Ra in water monitoring has wide application in uranium mining and milling areas, particularly since present practice is to use grab sampling. In this work, a continuous monitor based on 222Rn de-emanation and alpha scintillation counting is developed and tested. The critical parameters associated with the method are identified, and optimum operating conditions determined. For the laboratory scale proto-type constructed, the lower limit of detection is 0.5 pCi Ral-1 at an overall sensitivity of 2 counts per hr per pCi Ra per l. and a response time fo about 2 hr.

Mining↗
PubMed1982

An evaluation of unattached radon (and thoron) daughter measurement techniques.

The collection efficiencies of parallel plate, inertial impactor and wire screen devices reported in the literature for measurement of the unattached fraction of radon (or thoron) daughters are calculated for collection of the attached fraction of the aerosol, using real uranium mine aerosol activity-size distributions. The attached activity collection efficiencies may be as much as 4.3%, which, given the typically low values of the unattached fraction (a few per cent), results in a very substantial error in the measurement of the latter. Published unattached fraction measurements in the environment may therefore be high and should be interpreted with care.

Air Pollutants, Radioactive↗
PubMed1982

An optimized scheme for measurement of the concentrations of the decay products of radon and thoron.

Radon daughter measurement methods have not previously been fully optimized in the presence of thoron daughters, the presence of which leads to an increase in the total potential alpha energy. Taking into account the fluctuations associated with flow rate and concentration as well as the statistics of decay, optimized counting schemes were determined for the daughters of radon and thoron for different sampling times over a wide range of counting intervals. The counting schemes examined were optimized for maximum precision. Counting schemes corresponding to impractically long counting intervals, and counting times which required measurements beyond an 8 hr working shift were rejected. Under these constraints the most appropriate sampling time was found to be 10 min.

Air Pollutants, Radioactive↗