Post-depositional fracturing and subsidence of pumice flow deposits: Lascar Volcano, Chile.

Unconsolidated pyroclastic flow deposits of the 1993 eruption of Lascar Volcano, Chile, have, with time, become increasingly dissected by a network of deeply penetrating fractures. The fracture network comprises orthogonal sets of decimeter-wide linear voids that form a pseudo-polygonal grid visible on the deposit surface. In this work, we combine shallow surface geophysical imaging tools with remote sensing observations and direct field measurements of the deposit to investigate these fractures and their underlying causal mechanisms. Based on ground penetrating radar images, the fractures are observed to have propagated to depths of up to 10 m. In addition, orbiting radar interferometry shows that deposit subsidence of up to 1 cm/year-1 occurred between 1993 and 1996 with continued subsidence occurring at a slower rate thereafter. In situ measurements show that 1 m below the surface, the 1993 deposits remain 5°C to 15°C hotter, 18 years after emplacement, than adjacent deposits. Based on the observed subsidence as well as estimated cooling rates, the fractures are inferred to be the combined result of deaeration, thermal contraction, and sedimentary compaction in the months to years following deposition. Significant environmental factors, including regional earthquakes in 1995 and 2007, accelerated settling at punctuated moments in time. The spatially variable fracture pattern relates to surface slope and lithofacies variations as well as substrate lithology. Similar fractures have been reported in other ignimbrites but are generally exposed only in cross section and are often attributed to formation by external forces. Here we suggest that such interpretations should be invoked with caution, and deformation including post-emplacement subsidence and fracturing of loosely packed ash-rich deposits in the months to years post-emplacement is a process inherent in the settling of pyroclastic material.

NMR phase noise in bitter magnets.

We have studied the temporal instability of a high field resistive Bitter magnet through nuclear magnetic resonance (NMR). This instability leads to transverse spin decoherence in repeated and accumulated NMR experiments as is normally performed during signal averaging. We demonstrate this effect via Hahn echo and Carr--Purcell--Meiboom--Gill (CPMG) transverse relaxation experiments in a 23-T resistive magnet. Quantitative analysis was found to be consistent with separate measurements of the magnetic field frequency fluctuation spectrum, as well as with independent NMR experiments performed in a magnetic field with a controlled instability. Finally, the CPMG sequence with short pulse delays is shown to be successful in recovering the intrinsic spin--spin relaxation even in the presence of magnetic field temporal instability.

Screening for cancer and coronary risk factors through a nurse practitioner-staffed preventive health clinic.

The Preventive Health Examination (PHE) program was designed to screen for cancer of the lung, colon, skin, and prostate (or breast) and to detect the risk factors for coronary artery disease, i.e., arterial hypertension, hypercholesterolemia, cigarette smoking, and obesity. To investigate the cost-effectiveness of PHE performed by nurse practitioners, the first 176 subjects enrolled in the PHE program at a northeastern, suburban VA Medical Center were evaluated prospectively. The subjects were recruited through random mailing. The direct cost of PHEs was $80 per patient. PHEs were performed on 171 men and 5 women, mean age 57.2 years, divided into groups according to the date of evaluation. Nine percent of patients had findings highly suspicious of cancer (lung nodules in 7, skin lesions in 9). As a consequence, one patient underwent lobectomy for squamous carcinoma of the lung and another underwent prostatectomy for adenocarcinoma of the prostate. Fifty-five percent of patients had high cholesterol levels, 53% were obese, 30% were heavy cigarette smokers, and 19% were hypertensive. Nineteen percent of the patients had three or more coronary artery disease risk factors. We conclude that low cost PHEs performed by nurse practitioners have a high yield in detecting risk factors for coronary artery disease, and for detecting potentially treatable malignancies.

Effect of water deionisers on 'fracturing osteodystrophy' and dialysis encephalopathy in Plymouth.

In the Plymouth area, 95 patients with end-stage renal failure have undergone haemodialysis for 6 months or longer. Of the 47 patients beginning dialysis between 1967 and 1973, when water deionisers were not used routinely, a bone disease with multiple fractures, 'fracturing osteodystrophy', occurred in 18 patients and dialysis encephalopathy in 10. Of the 48 patients first dialysing between 1974 and 1979, when water deionisers used commonly, fracturing osteodystrophy occurred in only one and dialysis encephalopathy also in only one. Duration of dialysis without a water deioniser appeared to be the most important factor in the development of these two conditions. The use of water deionisers usually led to healing of fractures in patients with fracturing osteodystrophy and also led to improvement in 4 of the 11 patients with dialysis encephalopathy. Neither condition has occurred in any patient using a water deioniser from the first dialysis. Water deionisers, therefore, appeared to be effective in both the treatment and prevention of fracturing osteodystrophy and dialysis encephalopathy.

T, B and K cells in autoimmune thyroid disease.

The K-cell cytotoxic activity of peripheral blood lymphoid cells from 104 patients with autoimmune thyroid disease and from age and sex matched control subjects was measured using chicken erythrocytes as target cells. Patients with Hashimoto thyroiditis,primary hypothyroidism and thyrotoxicosis who were either newly diagnosed and untreated or had received therapy for less than or equal to 1 year showed a significant increase in K-cell cytotoxic activity. Patients who had received treatment for greater than 1 year and less than or equal to 5 years showed no such comparable increase in cytotoxic activity. Within the group of patients with untreated thyrotoxicosis it was found that K-cell cytotoxic activity was related to both goitre size and serum antibody titre. Thus patients with little or no goitre showed a highly significant elevation of cytotoxic activity whereas patients with moderate to large goitres gave values within the normal range. Similarly patients with no detectable serum thyroid autoantibodies showed high K-cell activity while patients with positive antibody titres did not. It was also shown that neither the absolute number nor the proportion of circulating T and B lymphocytes in patients with autoimmune thyroid disease as assessed by the sheep red cell rosette method and by indirect immunofluorescence was significantly different from that observed in the normal control population. No correlation was found between peripheral blood K-cell cytotoxic activity and the percentage of circulating null cells, i.e. 100-(percentage T + percentage B) in either patients or control subjects.

K cell cytotoxicity against antibody-coated chicken erythrocytes in tumor-bearing mice: its development with progressively growing tumor and the effect of immunization against the tumor.

Antibody-dependent (K cell) cytotoxic activity of spleen cells from mice bearing a chemically induced fibrosarcoma has been studied by using antibody-coated chicken erythrocytes as target cells. Spleen cells from tumor-bearing animals caused a significantly greater degree of target cells destruction than did those from control animals. The elevated cytotoxic activity in tumor-bearing animals increased with time after the tumor inoculation and correlated directly with the size of the tumor. The development of increased cytotoxic activity could be circumvented by surgical removal of the tumor. Mice that received x-irradiated tumor cells of x-irradiated tumor cells followed by a live challenge did not show a tumor growth and also failed to show increased K cell cytotoxic activity. It has been concluded that the increased K cell activity results directly from the active growth of tumor. The role of K cells in immunosurveillance has been discussed.

The effect of anti-alpha2-macroglobulin on K-cell cytolysis and T- and B-cell rosette formation.

The effect of antisera to human alpha2-macroglobulin (alpha2M) on the ability of human peripheral blood lymphoid cells to lyse antibody coated target cells (exert a K-cell effect) and form T(E) and B(EAC) rosettes has been investigated. Pretreatment of lymphoid cells with these antisera inhibited their K-cell activity but had no effect on their capacity to form T or B rosettes. The inhibitory activity of the anti-alpha2M sera was always reduced following absorption on a CnBr column to which human alpha2M had been coupled. The absorbed antibody, recovered by acid elution reacted strongly with human alpha2M in gel diffusion precipitin analysis and caused a highly significant inhibition of K-cell cytotoxicity. It was further shown that the inhibitory activity of the anti-alpha2M was localized exclusively in the IgG fraction and was greatly reduced following pepsin digestion.

K-cell cytotoxic activity in the spleen and lymph nodes of tumour-bearing mice.

The cytotoxic activity of spleen and lymph node cells from female CBA mice bearing a methylcholanthrene-induced fibrosarcoma on target cells coated with anti-target cell antibody has been investigated. Spleen cells from tumour-bearing mice caused a significantly greater degree of target cell lysis than did spleen cells from control mice. This increase in cytotoxicity was most apparent when a ratio of ten lymphoid cells to one target cell was used. With control mice, the mean cytotoxic index was 13.54 +/- 1.05 (s.e.m.) as compared to 55.00 +/- 6.11 with tumour-bearing mice. An increase in the cytotoxic activity of lymph node cells was also noted. In control mice, the cytotoxic index, using a ratio of 100:1 was 8.55 +/- 2.27. In tumour-bearing mice, the mean cytotoxic activity of the draining lymph node was 21.66 +/- 4.96, and of the contralateral lymph node, 13.00 +/- 3.46.

Evidence for circulating immune complexes in thyroid disease.

Anti-complementary activity was detected in the sera of 23 (59%) out of 39 patients with Hashimoto thyroiditis; in 10 (29%) out of 34 patients with primary hypothyroidism; in six (17%) out of 36 patients with thyrotoxicosis; and in only six (8%) out of 78 control subjects. Fractionation of Hashimoto sera by Sephadex G-200 chromatography showed that the anti-complementary activity was founding fractions of larger molecular size than monomeric IgG, being localized predominantly in the ascending limb of the second elution peak, suggesting that it was in the form of small immune complexes.