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71.
James E. Boggan Julian T. Hoff Edwin B. Boldrey William M. Wara 《The Western journal of medicine》1980,133(2):108-114
Thirty cases of intraspinal neoplasms occurring during the first two decades of life are reviewed. Histologic examination showed 13 of these to be astrocytomas, 6 neuroblastomas, 5 sarcomas, 3 ependymomas, 2 neurofibromas and 1 a schwannoma. Orthopedic deformities developed or worsened in 60 percent of patients surviving longer than a year after diagnosis. In five patients some form of endocrine deficiency developed after irradiation. For treatment of radiosensitive extradural malignant lesions, biopsy followed by irradiation is advocated. 相似文献
72.
It is generally perceived that landscape patterns or textures in a given protected area are spatially stationary. The findings
of this study suggest that this common perception is only partially correct. Over the course of 52 years, equilibrium in landscape
shifting was detected using digital data for the Lassen Volcanic National Park (USA). Vertical aerial photographs taken of
the park in 1941 were geo-referenced with the digital orthophoto quarter quadrangle (DOQQ) images of the same area from 1993
to identify landscape compositions and to measure change. Spatial analysis was used to observe pattern changes over time.
The results suggested that landscape development maintained equilibrium while patches were in various stages of a successional
sequence. The total area of each landscape component held steady, although over time patches throughout the landscape changed—a
shifting-mosaic steady state (SMSS). These findings reflect the limitations of contemporary environmental conservation theory.
They also suggest the importance of considering landscape change in policies that currently govern park planning and management. 相似文献
73.
James A. Simmons Andrea Megela Simmons 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(5):585-594
Widely divergent vertebrates share a common central temporal mechanism for representing periodicities of acoustic waveform
events. In the auditory nerve, periodicities corresponding to frequencies or rates from about 10 Hz to over 1,000 Hz are extracted
from pure tones, from low-frequency complex sounds (e.g., 1st harmonic in bullfrog calls), from mid-frequency sounds with
low-frequency modulations (e.g., amplitude modulation rates in cat vocalizations), and from time intervals between high-frequency
transients (e.g., pulse-echo delay in bat sonar). Time locking of neuronal responses to periodicities from about 50 ms down
to 4 ms or less (about 20–300 Hz) is preserved in the auditory midbrain, where responses are dispersed across many neurons
with different onset latencies from 4–5 to 20–50 ms. Midbrain latency distributions are wide enough to encompass two or more
repetitions of successive acoustic events, so that responses to multiple, successive periods are ongoing simultaneously in
different midbrain neurons. These latencies have a previously unnoticed periodic temporal pattern that determines the specific
times for the dispersed on-responses. 相似文献
74.
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76.
Anne M. Berry Eric M. Glare David Hansman James C. Paton 《FEMS microbiology letters》1989,65(3):275-278
Twenty-four of 63 enteric Gram-negative organisms (38.1%) which were isolated from 35 apparently healthy Nigerian students were found to have low trimethoprim resistance (MIC less than 1000 mg/l). These isolates were also found to be resistant to several other antibiotics and trimethoprim resistance was found to be transferable from 15 (62.5%) of the trimethoprim resistant organisms into E. coli EC 1005. It is likely that the high percentage of trimethoprim resistance encountered in this study is related to the high rate of resistance transfer which was observed. 相似文献
77.
78.
Incubation of [14C] caffeine with hepatic microsomes from male AKR/J mice resulted in the formation of several metabolites including 1, 3, 7-trimethylurate and 6-amino-5-(N-formylmethyl-amino)-1, 3-dimethyluracil. These two compounds comprised about 60% of products and are major urinary metabolites in several animals. When cytosol was included during incubation, there was a 14-fold increase in yield of the uracil at the expense of the urate; the combination of the two metabolites remained about 60% of total products. Cytosol alone was catalytically inert. Glutathione and other sulfhydryl compounds reproduced the effect of cytosol, and the action of cytosol was accounted for quantitatively by its sulfhydryl content. We propose that an oxidized intermediate of caffeine en route to trimethylurate is reduced by glutathione to the ring-opened uracil derivative. 相似文献
79.
Mutations in Aprataxin cause the neurodegenerative syndrome ataxia oculomotor apraxia type 1. Aprataxin catalyzes removal of adenosine monophosphate (AMP) from the 5′ end of a DNA strand, which results from an aborted attempt to ligate a strand break containing a damaged end. To gain insight into which DNA lesions are substrates for Aprataxin action in vivo, we deleted the Saccharomyces cerevisiae HNT3 gene, which encodes the Aprataxin homolog, in combination with known DNA repair genes. While hnt3Δ single mutants were not sensitive to DNA damaging agents, loss of HNT3 caused synergistic sensitivity to H2O2 in backgrounds that accumulate strand breaks with blocked termini, including apn1Δ apn2Δ tpp1Δ and ntg1Δ ntg2Δ ogg1Δ. Loss of HNT3 in rad27Δ cells, which are deficient in long-patch base excision repair (LP-BER), resulted in synergistic sensitivity to H2O2 and MMS, indicating that Hnt3 and LP-BER provide parallel pathways for processing 5′ AMPs. Loss of HNT3 also increased the sister chromatid exchange frequency. Surprisingly, HNT3 deletion partially rescued H2O2 sensitivity in recombination-deficient rad51Δ and rad52Δ cells, suggesting that Hnt3 promotes formation of a repair intermediate that is resolved by recombination. 相似文献
80.