万年历还剩93年

手表显示日期看上去是一个基础简单的功能。但是每当碰到闰年、闰月的情况，大部分的机械手表都需要手动调整日期来纠正显示错误。为了解决这个技术上的难题，万年历手表诞生了。[编者按]     

Effect of profound hearing loss on a central auditory nucleus

The present study was designed to investigate the type and extent of degeneration occurring in the human central auditory system subsequent to profound hearing loss. The authors have examined the size of one population of neurons in the ventral cochlear nucleus in seven subjects with profound hearing loss (audiometric responses poorer than 90-100 dB HL). Six normal subjects, ages 35-78, were used as controls. Cell size in the hearing-impaired subjects ranged from normal to reduced by more than 50 percent. Two factors appear to contribute to the variability in cell size reduction. The correlation coefficient (Spearman rs) of cell size with duration of profound deafness was -0.48, indicating a moderate tendency for neurons to become smaller with longer periods of deafness. The correlation coefficient of cell size with number of surviving cochlear ganglion cells was 0.73, indicating a stronger tendency for neurons to be larger with greater eighth nerve innervation of the cochlear nucleus. Two cases of Scheibe degeneration showed the most severe degenerative change in the central auditory system.     

Prophylactic efficacy of tilmicosin for bovine respiratory tract disease

The prophylactic administration of injectable tilmicosin for pneumonia in weaned beef calves was investigated in 1,806 animals. Comparisons were made among calves receiving an "on-arrival" injection of tilmicosin, calves receiving a single injection of long-acting oxytetracycline, and calves receiving no prophylaxis. Morbidity and mortality attributable to pneumonia, morbidity and mortality attributable to all causes, and case fatality were significantly lower in the group of calves that received tilmicosin, compared with calves that received long-acting oxytetracycline and calves that received no prophylactic antibiotic. Mean time to initial pneumonia treatment was significantly extended in calves that received prophylaxis, compared with those that received no antibiotic on arrival at the feedlot. Calves that received tilmicosin gained significantly more weight than calves that received oxytetracycline. Calves that were not treated for pneumonia during the trial period gained significantly more weight than did those calves that were treated for pneumonia regardless of experimental group. The majority of mortalities were attributable to fibrinous pneumonia (31/34). Important bacterial isolates (Pasteurella spp, Haemophilus somnus, Actinomyces pyogenes) obtained at necropsy did not have resistance to tilmicosin in association with administration of tilmicosin as prophylaxis for pneumonia. However, bacterial resistance to trimethoprim/sulfonamide and to oxytetracycline were commonly found in these postmortem isolates.     

Large shift in source of fine sediment in the upper Mississippi river

Although sediment is a natural constituent of rivers, excess loading to rivers and streams is a leading cause of impairment and biodiversity loss. Remedial actions require identification of the sources and mechanisms of sediment supply. This task is complicated by the scale and complexity of large watersheds as well as changes in climate and land use that alter the drivers of sediment supply. Previous studies in Lake Pepin, a natural lake on the Mississippi River, indicate that sediment supply to the lake has increased 10-fold over the past 150 years. Herein we combine geochemical fingerprinting and a suite of geomorphic change detection techniques with a sediment mass balance for a tributary watershed to demonstrate that, although the sediment loading remains very large, the dominant source of sediment has shifted from agricultural soil erosion to accelerated erosion of stream banks and bluffs, driven by increased river discharge. Such hydrologic amplification of natural erosion processes calls for a new approach to watershed sediment modeling that explicitly accounts for channel and floodplain dynamics that amplify or dampen landscape processes. Further, this finding illustrates a new challenge in remediating nonpoint sediment pollution and indicates that management efforts must expand from soil erosion to factors contributing to increased water runoff.     

Levels of prostaglandins in the small intestine of rats during primary and secondary infection with Nippostrongylus brasiliensis

The level of PGE is increased 10-fold in intestinal tissues during primary infection of the rat with Nippostrongylus brasiliensis. Peak levels (ca. 7,000 pg/cm) were assayed in the jejunal site of infection on day 7 of infection and similar levels were recorded in 'post-infection' (ileal) segments at this time. The level of PGE in 'post-infection' segments showed further increase to 12,000 pg/cm on day 10. The level of PGE also increased in 'pre-infection' (duodenal) but this was delayed by 4-5 days. The level of PGF also increased during primary infection (from about 100 to 950 pg/cm) but this occurred after expulsion. Increase in the level of PGE occurred earlier (at 3-4 days) during secondary challenge given 19 days after primary infection, but the PGE levels followed the primary response when challenge was given 10 weeks after primary infection. It is suggested that PGE plays a dual role in parasite immunity. (1) PGE may directly affect metabolism of the parasite. In this event it is also suggested that protective antibodies cause the release of PG. (2) Elevated levels of PGE act indirectly by affecting gastrointestinal function which alters the microenvironment at the site of infection. The duodenal migration of parasites may be due to this effect of PGE.