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581.
The 200-300 microm soft zone of dentin, found beneath enamel in crowns of human teeth, is thought to fulfill important roles in tooth function, but little is known about its structure-mechanical relations. Scanning electron microscopy images of fracture surfaces showed that near the dentino-enamel junction (DEJ), a porous reticulate matrix of intertubular-dentin contains tubules with no peritubular lining. Peritubular-dentin however is found at some distance from the DEJ, and it gradually thickens with increasing depth into the bulk dentin. Concurrently, tighter packing of the collagen fibers is observed with a gradual increase in mineral deposits on and between the fibers. This structurally graded zone is known to be softer when tested for micro-hardness. It undergoes greater strain compared to bulk dentin, when measured using Moiré interferometry. We investigated the deformation and stiffness of this zone by means of non-contact laser-speckle interferometry (ESPI), and nanometer-scale deformations were tracked during compression-testing performed in water. We report a significantly reduced stiffness of this zone compared to bulk dentin, with mid-buccal regions of teeth averaging 3.5 GPa compared with 9.7 GPa in mid-lingual regions. Our results support and expand upon the hypothesis that the durability of the whole tooth relies upon a bucco-lingual asymmetric matching of stiffness by means of an interphase: a cushioning soft layer between enamel and bulk dentin. 相似文献
582.
Due in part to scarcity of material, no published study has yet cladistically addressed the systematics of living and fossil Tenrecidae (Mammalia, Afrotheria). Using a noninvasive technique for sampling nuclear DNA from museum specimens, we investigate the evolution of the Tenrecidae and assess the extent to which tenrecids fit patterns of relationships proposed for other terrestrial mammals on Madagascar. Application of several tree-reconstruction techniques on sequences of the nuclear growth hormone receptor gene and morphological data for all recognized tenrecid genera supports monophyly of Malagasy tenrecids to the exclusion of the two living African genera. However, both parsimony and Bayesian methods favor a close relationship between fossil African tenrecs and the Malagasy Geogale, supporting the hypothesis of island paraphyly, but not polyphyly. More generally, the noninvasive extraction technique can be applied with minimal risk to rare/unique specimens and, by better utilizing museum collections for genetic work, can greatly mitigate field expenses and disturbance of natural populations. 相似文献
583.
584.
Background: The relationship between H. pylori infection and anemia in childhood is still unclear. The aim of the study was to examine the association between H. pylori infection and anemia or iron deficiency in school‐age children and in infants. Materials and Methods: Six‐ to 9‐ year‐old Israeli Arab children (N = 202) and infants (N = 197) were examined for hemoglobin and ferritin levels. ELISA was used to detect H. pylori antigens in stool specimens collected from the participants. Household characteristics were obtained through personal interviews with the mothers. Results: The prevalence of anemia was 15.5 versus 5.5% in H. pylori‐positive and ‐negative school‐age children, respectively and 34.5 versus 29.8% in H. pylori‐positive and ‐negative infants, respectively. The Mantel–Haenszel age‐adjusted prevalence ratio (PR) and 95% confidence intervals (CIs) were 1.6 (95%CI 1.0, 2.6). In multivariate analysis controlling for socioeconomic variables, H. pylori infection was associated with 2.8 higher prevalence of anemia only in school‐age children: adjusted PR 2.8 (95% CI 0.9, 9.3). The adjusted mean difference in hemoglobin levels between H. pylori infected school‐age children and uninfected ones was ?0.372 gr/dL (95% CI ?0.704, ?0.039) (p = .04). The respective mean ferritin difference was ?6.74 μg/L (95% CI ?13.38, ?.011) (p = .04). Such differences were not found in infants. Conclusions: H. pylori infection is associated with higher prevalence of anemia in school‐age children independently of socioeconomic variables. Such association was not observed in infants. These findings are of clinical and public health importance. 相似文献
585.
Wesley B Asher Kara L Bren 《Protein science : a publication of the Protein Society》2010,19(10):1830-1839
We report a novel affinity‐based purification method for proteins expressed in Escherichia coli that uses the coordination of a heme tag to an L ‐histidine‐immobilized sepharose (HIS) resin. This approach provides an affinity purification tag visible to the eye, facilitating tracking of the protein. We show that azurin and maltose binding protein are readily purified from cell lysate using the heme tag and HIS resin. Mild conditions are used; heme‐tagged proteins are bound to the HIS resin in phosphate buffer, pH 7.0, and eluted by adding 200–500 mM imidazole or binding buffer at pH 5 or 8. The HIS resin exhibits a low level of nonspecific binding of untagged cellular proteins for the systems studied here. An additional advantage of the heme tag‐HIS method for purification is that the heme tag can be used for protein quantification by using the pyridine hemochrome absorbance method for heme concentration determination. 相似文献
586.
Daniel Hayes Michael Jones Nigel Lester Cindy Chu Susan Doka John Netto Jason Stockwell Bradley Thompson Charles K. Minns Brian Shuter Nicholas Collins 《Reviews in Fish Biology and Fisheries》2009,19(3):295-312
One of the major challenges facing fishery scientists and managers today is determining how fish populations are influenced
by habitat conditions. Many approaches have been explored to address this challenge, all of which involve modeling at one
level or another. In this paper, we explore a process-oriented model approach whereby the critical population processes of
birth and death rates are explicitly linked to habitat conditions. Application of this approach to five species of Great Lakes
fishes including: walleye (Sander vitreus), lake trout (Salvelinus namaycush), smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens), and rainbow trout (Onchorynchus mykiss), yielded a number of insights into the modeling process. One of the foremost insights is that processes determining movement
and transport of fish are critical components of such models since these processes largely determine the habitats fish occupy.
Because of the importance of fish location, an individual-based model appears to be a nearly inescapable modeling requirement.
There is, however, a paucity of field-based data directly relating birth, death, and movement rates to habitat conditions
experienced by individual fish. There is also a paucity of habitat information at a fine temporal and spatial scale for many
important habitat variables. Finally, the general occurrence of strong ontogenetic changes in the response of different life
stages to habitat conditions emphasizes the need for a modeling approach that considers all life stages in an integrated fashion. 相似文献
587.
Osnat Segev Wolfram Meusel Melanie Friedenberger Asher Brenner Ariel Kushmaro 《Biodegradation》2009,20(5):621-627
Halogenated organic compounds constitute one of the largest and most diverse groups of chemicals in the environment. Many
of these compounds are toxic, persistent and, as a result of their often limited biodegradability, tend to bioaccumulate in
the environment. Dibromoneopentyl glycol (DBNPG) and tribromoneopentyl alcohol (TBNPA) are brominated flame retardants commonly
used as additives during the manufacture of plastic polymers and as chemical intermediates in the synthesis of other flame
retardants. Both are classified as not readily biodegradable. In this paper, we demonstrate the biodegradation of both DBNPG
and TBNPA by a common bacterial consortium under aerobic conditions in enrichment cultures containing yeast extract. DBNPG
and TBNPA biodegradation is accompanied by a release of bromide into the medium, due to a biological debromination reaction.
Molecular analysis of the clone library PCR amplified 16S rRNA gene was used to characterize the bacterial consortium involved
in the biodegradation. 相似文献
588.
589.
Carbon and Electron Flow in Mud and Sandflat Intertidal Sediments at Delaware Inlet, Nelson, New Zealand 总被引:4,自引:22,他引:4 下载免费PDF全文
Douglas O. Mountfort Rodney A. Asher Edward L. Mays James M. Tiedje 《Applied microbiology》1980,39(4):686-694
An investigation of carbon and electron flow in mud and sandflat intertidal sediments showed that the terminal electron acceptor was principally sulfate and that the carbon flow was mainly to CO2. Studies with thin layers of sediment exposed to H2 showed that methane production accounted for virtually none of the H2 utilized, whereas sulfate reduction accounted for a major proportion of the gas uptake. At all sampling sites except one (site B7), rates of methanogenesis were low but sulfate concentrations in the interstitial water were high (>18 mM). At site B7, the sulfate concentrations declined with depth from 32 mM at 2 cm to <1 mM at 10 cm or below, and active methanogenesis occurred in the low-sulfate zone. Sulfate-reducing activity at this site initially decreased and then increased with depth so that elevated rates occurred in both the active and nonactive methanogenic zones. The respiratory index (RI) [RI = 14CO2/(14CO2 + 14CH4)] for [2-14C]acetate catabolism at site B7 ranged from 0.98 to 0.2 in the depth range of 2 to 14 cm. Addition of sulfate to sediment from the low-sulfate zone resulted in an increase in RI and a decrease in methanogenesis. At all other sites examined, RI ranged from 0.97 to 0.99 and was constant with depth. The results suggested that although methanogenesis was inhibited by sulfate (presumably through the activity of sulfate-reducing bacteria), it was not always limited by sulfate reduction. 相似文献
590.
Anna E. Sarfaty Robert K. Fulbright Susan R. Compton Jennifer L. Asher Caroline J. Zeiss 《Journal of medical primatology》2020,49(2):103-106
A 16-year-old rhesus macaque presented with progressive, ascending quadriparesis following measles vaccination. He was diagnosed with transverse myelitis following MRI, gross necropsy, and histopathology. This is the first report of transverse myelitis in a rhesus macaque following measles vaccination. 相似文献