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排序方式: 共有3485条查询结果,搜索用时 15 毫秒
61.
D R Sumner C L Olson P M Freeman J J Lobick T P Andriacchi 《Journal of biomechanics》1989,22(6-7):649-653
In this study digital images of bone cross-sections obtained by computed tomography were analyzed with an automated outlining method. It was shown that unbiased cross-sectional geometric measurements of cortical bone could be obtained if the periosteal and endosteal surfaces were defined at separate thresholds. Use of different threshold levels for these two surfaces resulted in errors of 2.6% for periosteal diameters, 7.4% for endosteal diameters and 7.3% for cortical area. If incorrect thresholds were used, cortical thickness measurements can have errors as high as 30%. In addition, simulated variation in medullary fat content did not affect measurement of medullary dimensions. 相似文献
62.
Oral administration of methyltestosterone (MT) at 50 mg/dog/day to intact adult male greyhounds for 90 d resulted in decreased (P < 0.05) mean daily sperm output and mean testicular length. Additionally, the mean diameter of seminiferous tubules in MT-treated dogs tended to decrease (P = 0.08). Mean concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) and concentrations of testosterone in serum were also decreased or tended to decrease (P = 0.0003 to 0.059) at various sampling periods during MT treatment, suggesting alterations in spermatogenesis resulted from decreased serum concentrations of gonadotropins and steroids. Mean daily sperm output, mean testicular length, mean seminiferous tubule diameter and mean concentrations of FSH in serum were not decreased (P > 0.05) at the end of a 90-d recovery period. However, mean concentrations of serum LH and concentrations of testosterone were still lower (P < 0.05) during five of six and one of six sampling times, respectively, during the recovery period than the pretreatment levels, suggesting a prolonged effect of MT treatment on the pituitary/gonadal axis. 相似文献
63.
Detection of virulence factors in culturable Escherichia coli isolates from water samples by DNA probes and recovery of toxin-bearing strains in minimal o-nitrophenol-beta-D-galactopyranoside-4-methylumbelliferyl-beta-D-g luc uronide media. 总被引:1,自引:1,他引:0 下载免费PDF全文
A total of 449 Escherichia coli isolates in treated and raw water sources were submitted to DNA-DNA hybridization using seven different DNA probes to detect homology to sequences that code for Shiga-like toxins I and II; heat-stabile and heat-labile toxins, adherence factors EAF and eae, and the fimbrial antigen of entero-hemorrhagic E. coli. Fifty-nine (13%) of the isolates demonstrated homology with one or more specific DNA probes. More than 50% of the isolates in treated water were not recovered in MMO-4-methylumbelliferyl-beta-D-glucuronide media designed for detection of this indicator. 相似文献
64.
Physiological studies of chloramine resistance developed by Klebsiella pneumoniae under low-nutrient growth conditions. 总被引:1,自引:1,他引:0 下载免费PDF全文
This study investigated the physiological mechanisms of resistance to chloramines developed by Klebsiella pneumoniae grown in a nutrient-limited environment. Growth under these conditions resulted in cells that were smaller than cells grown under high-nutrient conditions and extensively aggregated. Cellular aggregates ranged from 10 to more than 10,000 cells per aggregate, with a mean population aggregate size of 90 cells. This aggregation may have been facilitated by the presence of extracellular polymer material. By using glucose as a reference of capsule content, it was determined that growth under low-nutrient conditions produced cells with 8 x 10(-14) to 41 x 10(-14) g of carbohydrate per cell, with a mean +/- standard deviation of 27 x 10(-14) +/- 16 x 10(-14) g of carbohydrate per cell. In comparison, growth under high-nutrient conditions resulted in 2.7 x 10(-14) to 5.9 x 10(-14) g of carbohydrate per cell, with a mean and standard deviation of 4.3 x 10(-14) +/- 1.2 x 10(-14) g of carbohydrate per cell. Cell wall and cell membrane lipids also varied with growth conditions. The ratio of saturated to unsaturated fatty acids in cells grown under low-nutrient conditions was approximately five times greater than that in cells grown under high-nutrient conditions, suggesting possible differences in membrane permeability. An analysis of sulfhydryl (-SH) groups revealed no quantitative difference with respect to growth conditions. However, upon exposure to chloramines, only 33% of the -SH groups of cells grown under low-nutrient conditions were oxidized, compared with 80% oxidization of -SH groups in cells grown under high-nutrient conditions. The reduced effectiveness of chloramine oxidization of -SH groups in cells grown under low-nutrient conditions may be due to restricted penetration of chloramines into the cells, conformational changes of enzymes, or a combination of both factors. The results of this study suggest that chloramine resistance developed under low-nutrient growth conditions may be a function of multiple physiological factors, including cellular aggregation and protection of sulfhydryl groups within the cell. 相似文献
65.
Timothy P. Causgrove Daniel C. Brune Robert E. Blankenship John M. Olson 《Photosynthesis research》1990,25(1):1-10
Fluorescence lifetimes have been measured for bacteriochlorophyll (BChl) c isolated from Chlorobium limicola in different states of aggregation in non-polar solvents. Two different homologs of BChl c were used, one with an isobutyl group at the 4 position, the other with n-propyl. Species previously identified as dimers (Olson and Pedersen 1990, Photosynth Res, this issue) decayed with lifetimes of 0.64 ns for the isobutyl homolog, 0.71 ns for n-propyl. Decay-associated spectra indicate that the absorption spectrum of the isobutyl dimer is slightly red-shifted from that of the n-propyl dimer. Aggregates absorbing maximally at 710 nm fluoresced with a principal lifetime of 3.1 ns, independent of the homolog used. In CCl4, only the isobutyl homolog forms a 747-nm absorbing oligomer spectrally similar to BChl c in vivo. This oligomer shows non-exponential fluorescence decay with lifetimes of 67 and 19 ps. Because the two components show different excitation spectra, the higher oligomer is probably a mixture of more than one species, both of which absorb at 747 nm.Abbreviations BChl
bacteriochlorophyll
- Chl
chlorophyll
- % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGGipm0dc9vqaqpepu0xbbG8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Xdm2aaW% baaSqabeaacaaIYaaaaaaa!3777!\[\chi ^2 \]
chi-square
- FWHM
full-width at half-maximum 相似文献
66.
D. J. Conklin H. B. Lillywhite K. R. Olson R. E. Ballard A. R. Hargens 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,165(7):518-526
The effects of vasoactive agonists on systemic blood vessels were examined with respect to anatomical location and gravity acclimation in the semi-arboreal snake, Elaphe Obsoleta. Major blood vessels were reactive to putative neurotransmitters, hormones or local factors in vessel specific patterns. Catecholamines, adenosine triphosphate, histamine and high potassium (80 mM) stimulated significantly greater tension per unit vessel mass in posterior than anterior arteries. Anterior vessels were significantly more sensitive to catecholamines than midbody and posterior vessels. Angiotensin II stimulated significantly greater tension in carotid artery than in midbody and posterior dorsal aorta. Arginine vasotocin strongly contracted the left and right aortic arches and anterior dorsal aorta. Veins were strongly contracted by catecholamines, high potassium and angiotensin II, but less so by adenosine triphosphate, arginine vasotocin and histamine. Precontracted vessels were relaxed by acetylcholine and sodium nitroprusside, but not by atrial natriuretic peptide or bradykinin. Chronic exposure of snakes to intermittent hypergravity stress (+1.5 Gz at tail) did not affect the majority of vessel responses. These data demonstrate that in vitro tension correlates with known patterns of sympathetic innervation and suggest that catecholamines, as well as other agonists, are important in mediating vascular responses to gravitational stresses in snakes.Abbreviations
ACH
acetylcholine
-
ADA
anterior dorsal aorta
-
ANG II
salmon asn1-val5-angiotensin II
-
ANP
rat ile26-atrial natriuretic peptide
-
ATP
adenosine triphosphate
-
AVT
arginine vasotocin
-
BK
human bradykinin
-
BL
total body length
-
CA
carotid artery
-
CONT
control
-
EC
50
effective concentration producing 50% maximal response
-
EPI
epinephrine
- + G
z
earth's gravity force
-
HI-G
high gravity acclimation
-
HI K
+
80 mM high potassium
-
JV
jugular vein
-
LAA
left aortic arch
-
MDA
midbody dorsal aorta
-
MPV
midbody portal vein
-
MS
Mackenzie's solution
-
NEPI
norepinephrine
-
pD
2
log EC50
-
PDA
posterior dorsal aorta
-
PPV
posterior portal vein
-
RAA
right aortic arch
-
SNP
sodium nitroprusside 相似文献
67.
68.
A Mef2 gene that generates a muscle-specific isoform via alternative mRNA splicing. 总被引:26,自引:11,他引:15 下载免费PDF全文
J F Martin J M Miano C M Hustad N G Copeland N A Jenkins E N Olson 《Molecular and cellular biology》1994,14(3):1647-1656
69.
70.
A. Randall Olson 《American journal of botany》1994,81(6):718-725
Monotropsis odorata Elliott. is one of the most cryptic and relatively rare North American endemic species of the Monotropaceae; therefore, information concerning the biology of this achlorophyllous, mycotrophic angiosperm is limited. Bright field and fluorescence microscopic investigations of postpollination gynoecia reveal that pollen tubes follow a continuous pathway from the receptive surface of the stigma to micropyles of the ovules. The pollen tube pathway is characterized by discrete strands of transmitting tissue connecting an exudate-coated stigma to an exudate-filled, stylar canal that leads directly to exudate-coated placentae. Pollen tube growth appears restricted to those areas associated with an exudate. The gynoecial pathway for pollen tube growth in this taxon conforms to those described from other monotropàceous species. 相似文献