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R Ho

Publications and source records attributed to R Ho.

59 records · Page 4Linked to original sources
PubMedDate not supplied

Optimization of quantitative electron energy loss spectroscopy in the low loss region: phosphorus L-edge.

The purpose of this study was to optimize quantitative electron energy loss spectroscopy (EELS) of elements that have characteristic edges in the low energy loss region and are components of organic matrices. The optimum parameters for phosphorus L2,3-edge (at 135 eV) detection were determined by numerical analysis of computer-generated, Poisson-noisy spectra and by experimental measurements (at 80 keV) of films of the phosphoprotein, phosvitin. When the first, second and third valence electron/plasmon scatterings are included in the multiple least-squares (MLS) fit, the background subtraction of (first-difference) spectra is significantly more accurate than that obtained with the "inverse power law" method, even for a specimen thickness of only 0.25 lambda. Taking into account the effects of plural scattering, the optimal thickness for P quantitation is approximately 0.3 lambda. Signal-to-noise (S/N) ratio decreases rapidly with thickness, and at 1.0 lambda, it is only about 60% of the optimum S/N. The combined effects of the statistical uncertainty of measurements and of the systematic error due to gain variations of the parallel detector were evaluated, and the relative sensitivities of the no-difference (raw spectrum), first-difference and second-difference methods were compared. For channel-to-channel gain variations greater than 0.1% and up to 0.8%, the first-difference method results in the lowest uncertainty of P measurements. In the absence of gain variations, direct fitting provides the greatest sensitivity (least uncertainty), whereas at larger gain variations it may be necessary to use the second-difference method. The optimum energy shift for collecting a first-difference spectrum, approximately 15 eV, did not show any great variation between 5 and 25 eV, and is, in general, specimen dependent. Quantitation with EELS showed excellent correlation with simultaneous electron probe X-ray microanalysis, but, for the detection of P in a 0.25 lambda thick specimen, EELS was approximately five to six times more sensitive than X-ray. The minimal detectable P concentration, with 0.5 nA beam current for 100 s in a 0.25 lambda thick specimen, was 8.4 mmol/kg (0.01 at%) at the 99% confidence level, equivalent to 34 phosphorus atoms for a 15 nm probe. This value is close to the theoretical prediction of 7.5 mmol/kg, and can be improved only by further reducing the gain variation and directly fitting the non-difference spectrum. Appropriate reduction of the gain variations to less than 0.1% would result in a further, approximately two-fold, improvement in the parallel EELS detection system.(ABSTRACT TRUNCATED AT 400 WORDS)

Computer Simulation↗
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American Cancer Society guideline for the early detection of prostate cancer: update 1997.

In summary, the 1997 revision of the ACS guideline for the early detection of prostate cancer is based on knowledge gained by a critical analysis of experience since the original version of 1992. This is only a milestone along a continuous journey rather than being the final destination. Other revisions will be considered when new knowledge becomes available, but for the present, this guideline is offered to health care professionals seeking to provide optimal care to asymptomatic men at risk for prostate cancer.

Aged↗
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Disparities in cancer treatment outcomes among asian americans: implications for the asian american network for cancer awareness, research and training.

PURPOSE: The purpose of this paper is to describe the scope of concern of Asian Americans in cancer treatment. METHODS: AANCART, the Asian American Network for Cancer Awareness, Research and Training, is a project whose goal includes promoting the well-being of Asian Americans through educating the public, increasing data on cancer, and helping health care providers better treat their Asian American patients. FINDINGS: In many instances, Asian Americans have the highest cancer rate compared with other ethnic groups. Knowledge gaps exist for both the patient and the health professional, preventing proper assessment of the patient's needs. CONCLUSIONS: Asian Americans are difficult to reach because of bipolar population distributions, cultural barriers, and lack of patient care data. With the efforts of AANCART, this racial group should be able to reduce some of the cancer treatment disparities that currently exist.

Journal Article↗