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Clustering of earthquake magnitudes is still actively debated, compared to well-established spatial and temporal clustering. Magnitude clustering is not currently implemented in earthquake forecasting but would be important if larger magnitude events are more likely to be followed by similar sized events. Here we show statistically significant magnitude clustering present in many different field and laboratory catalogs at a wide range of spatial scales (mm to 1000 km). It is universal in field catalogs across fault types and tectonic/induced settings, while laboratory results are unaffected by loading protocol or rock types and show temporal stability. The absence of clustering can be imposed by a global tensile stress, although clustering still occurs when isolating to triggered event pairs or spatial patches where shear stress dominates. Magnitude clustering is most prominent at short time and distance scales and modeling indicates >20% repeating magnitudes in some cases, implying it can help to narrow physical mechanisms for seismogenesis. Clustering of earthquake magnitudes is actively debated. Here, the authors show statistically significant magnitude clustering present in many different field and laboratory catalogs at a wide range of spatial scales (mm to 1000 km).

What follows is an apology for drama as a university study. I hope, however, that it avoids the thinly disguised plea for the status of the drama faculty which most such endeavors are. My concern here is with the undergraduate student who elects a major concentration in the field of drama in the expectation of achieving that increasingly more elusive academic amalgam, a simultaneous degree and education. If changing approaches in the university disciplines, rapid growth in content and techniques as well as changes in student attitudes are makingsuch an expectation difficult to fulfill in other areas, they make it doubly so in the study of drama.

Villus epithelial cells of mice that had received daily injections of nitrogen mustard for 4 days showed a progressive loss of ribosomes, reduction in terminal web material, and failure to absorb and transport lipid in normal amounts from the gut lumen to the lamina propria. There was also a progressive shortening of crypts and villi and occasional loss of epithelium by day 4. These results parallel to a large extent conditions existing in the intestinal epithelium in mice at 3 to 4 days posttreatment with 3 krads of X-rays.

C57Br/cdj mice were exposed to 1500 R whole-body X irradiation and sacrificed 1, 2, 3, 3.5, and 4 days postirradiation. Thirty minutes prior to sacrifice each mouse received 0.2 ml of safflower $\\text{oil-}{}^{3}{\\rm H}\\text{-palmitic}$ acid. Specimens of ileum, jejunum, and liver were examined with light and electron microscopes. Through 2 days postexposure, absorption and transport of lipid in both ileum and jejunum were essentially normal and liver glycogen and lipid content were stable. Beginning on day 3 ileal function began to fail rapidly but the jejunum functioned near normal. On day 3.5 jejunal absorption declined somewhat and hepatocytes were virtually depleted of glycogen and of intracellular lipid. Changes in absorption paralleled subcellular changes in epithelial cells, e.g., mitochondria were abnormal in appearance and reduced in number, ribosomes were depleted and only remnants of endoplasmic reticulum and Golgi membranes remained. The cellular effects observed are in accord with the time of onset of inhibition of protein synthesis in epithelial cells exposed to X rays, suggesting that irradiated cells lost the ability to synthesize the protein necessary to maintain the intracellular enzyme systems required for normal metabolism and the exportable protein components of chylomicrons. Failure of protein synthesis is attributed to inhibition of ribonucleoprotein synthesis or of ribosomal assembly rather than a direct effect on existing ribosomes.

Mice were exposed to 1500-R x-radiation and injected with horseradish peroxidase 2 minutes prior to sacrifice on days 1, 2, 3, 3.5, and 4 postexposure. Kidney damage in the form of increased tubular permeability to peroxidase was detected as early as day 1, suggesting that functional damage occurred before morphologic lesions became apparent. Changes were observed in glomeruli on day 2, mainly involving capillary endothelium and some focal thickening of the basement membrane.

Within 10 minutes after intravenous injection, horseradish peroxidase has been found in the lamina propria and in the intestinal epithelium, both in intercellular spaces and within the cytoplasm of epithelial cells. Examination of intestines of mice subjected to 3 krads of X-irradiation and sacrificed at 24-hour intervals up to 4 days revealed that most intact capillaries remained patent and were permeable to peroxidase. It was not possible to characterize damage to endothelial cells on a morphological basis alone, but definite changes in permeability to peroxidase were demonstrated. Neither capillary nor epithelial basement membranes seemed to constitute a significant barrier to the extravascular diffusion of peroxidase, but at the time of villus denudation, on day 4, epithelial basement membranes were disrupted in the denuded areas. Diffuse staining of epithelial cell cytoplasm by peroxidase reaction product and less accumulation of it in intercellular spaces within the epithelium was observed on days 3 and 4 postirradiation. Neither evidence of leakage through, nor secretion by, epithelial cells of peroxidase into the gut lumen nor localization within lacteals was detected. Some of the enzyme probably was secreted or diffused into the lumen before denudation occurred but escaped detection by being washed away by the tissue fixative.