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1.
Aluminum based metal matrix composites are offering o utstanding properties in a number of automotive and aircraft components and body structures. The major advantages of these composite materials are their high st rength to weight ratio, high stiffness, high hardness, wear resistance, low coef ficient of thermal expansion, superior dimensional stability and versatility to designer. In addition to these their isotropic properties, good forming characte ristics, easy availability of cheaper reinforcements... 相似文献
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Most bony fishes rely on suction mechanisms to capture and transport prey. Once captured, prey are carried by water movement inside the oral cavity to a second set of jaws in the throat, the pharyngeal jaws, which manipulate the prey and assist in swallowing. Moray eels display much less effective suction-feeding abilities. Given this reduction in a feeding mechanism that is widespread and highly conserved in aquatic vertebrates, it is not known how moray eels swallow large fish and cephalopods. Here we show that the moray eel (Muraena retifera) overcomes reduced suction capacity by launching raptorial pharyngeal jaws out of its throat and into its oral cavity, where the jaws grasp the struggling prey animal and transport it back to the throat and into the oesophagus. This is the first described case of a vertebrate using a second set of jaws to both restrain and transport prey, and is the only alternative to the hydraulic prey transport reported in teleost fishes. The extreme mobility of the moray pharyngeal jaws is made possible by elongation of the muscles that control the jaws, coupled with reduction of adjacent gill-arch structures. The discovery that pharyngeal jaws can reach up from behind the skull to grasp prey in the oral jaws reveals a major innovation that may have contributed to the success of moray eels as apex predators hunting within the complex matrix of coral reefs. This alternative prey transport mode is mechanically similar to the ratcheting mechanisms used in snakes--a group of terrestrial vertebrates that share striking morphological, behavioural and ecological convergence with moray eels. 相似文献
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Döring A Gieger C Mehta D Gohlke H Prokisch H Coassin S Fischer G Henke K Klopp N Kronenberg F Paulweber B Pfeufer A Rosskopf D Völzke H Illig T Meitinger T Wichmann HE Meisinger C 《Nature genetics》2008,40(4):430-436
Serum uric acid concentrations are correlated with gout and clinical entities such as cardiovascular disease and diabetes. In the genome-wide association study KORA (Kooperative Gesundheitsforschung in der Region Augsburg) F3 500K (n = 1,644), the most significant SNPs associated with uric acid concentrations mapped within introns 4 and 6 of SLC2A9, a gene encoding a putative hexose transporter (effects: -0.23 to -0.36 mg/dl per copy of the minor allele). We replicated these findings in three independent samples from Germany (KORA S4 and SHIP (Study of Health in Pomerania)) and Austria (SAPHIR; Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk), with P values ranging from 1.2 x 10(-8) to 1.0 x 10(-32). Analysis of whole blood RNA expression profiles from a KORA F3 500K subgroup (n = 117) showed a significant association between the SLC2A9 isoform 2 and urate concentrations. The SLC2A9 genotypes also showed significant association with self-reported gout. The proportion of the variance of serum uric acid concentrations explained by genotypes was about 1.2% in men and 6% in women, and the percentage accounted for by expression levels was 3.5% in men and 15% in women. 相似文献
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Pravenec M Churchill PC Churchill MC Viklicky O Kazdova L Aitman TJ Petretto E Hubner N Wallace CA Zimdahl H Zidek V Landa V Dunbar J Bidani A Griffin K Qi N Maxova M Kren V Mlejnek P Wang J Kurtz TW 《Nature genetics》2008,40(8):952-954
To identify renally expressed genes that influence risk for hypertension, we integrated expression quantitative trait locus (QTL) analysis of the kidney with genome-wide correlation analysis of renal expression profiles and blood pressure in recombinant inbred strains derived from the spontaneously hypertensive rat (SHR). This strategy, together with renal transplantation studies in SHR progenitor, transgenic and congenic strains, identified deficient renal expression of Cd36 encoding fatty acid translocase as a genetically determined risk factor for spontaneous hypertension. 相似文献
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A sound epistemological foundation for biological inquiry comes, in part, from application of valid statistical procedures. This tenet is widely appreciated by scientists studying the new realm of high-dimensional biology, or 'omic' research, which involves multiplicity at unprecedented scales. Many papers aimed at the high-dimensional biology community describe the development or application of statistical techniques. The validity of many of these is questionable, and a shared understanding about the epistemological foundations of the statistical methods themselves seems to be lacking. Here we offer a framework in which the epistemological foundation of proposed statistical methods can be evaluated. 相似文献
7.
Polyamine-dependent gene expression 总被引:15,自引:0,他引:15
The polyamines spermidine and spermine along with the diamine putrescine are involved in
many cellular processes, including chromatin condensation, maintenance of DNA structure, RNA
processing, translation and protein activation. The polyamines influence the
formation of compacted chromatin and have a well-established role in DNA aggregation. Polyamines
are used in the posttranslational modification of eukaryotic initiation factor 5A, which regulates
the transport and processing of specific RNA. The polyamines also participate in a
novel RNA-decoding mechanism, a translational frameshift, of at least two known genes, the TY1
transposon and mammalian antizyme. Polyamines are crucial for their own regulation and are involved
in feedback mechanisms affecting both polyamine synthesis and catabolism. Recently, it has become
apparent that the polyamines are able to influence the action of the protein kinase
casein kinase 2. Here we address several roles of polyamines in gene expression.Received 27 November 2002; received after revision 9 January 2003; accepted 31 January 2003 相似文献
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A. R. Mehta 《Cellular and molecular life sciences : CMLS》1966,22(5):300-300
Zusammenfassung Organisation und Differenzierung trachealer Elemente im Kallusgewebe von Wurzeln vonLycopersicum esculentum Mill- undLinum usitatissimum L. hängen von der Auxinkonzentration der Nährlösung ab. Der Effekt der untersuchten Auxine in Gewebekulturen (2,4-D, NES) deutet auf eine negative Korrelation zwischen Auxinwirkung und Differenzierung hin. 相似文献
9.
Extracellular electron transfer via microbial nanowires 总被引:8,自引:0,他引:8
Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(iii) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(iii) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(iii) reducers in many environments, must directly contact Fe(iii) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, to aid in establishing contact with the Fe(iii) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(iii) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell-cell interactions, and for bioengineering of novel conductive materials. 相似文献
10.
Myosin-V is a processive actin-based motor. 总被引:25,自引:0,他引:25
Class-V myosins, one of 15 known classes of actin-based molecular motors, have been implicated in several forms of organelle transport, perhaps working with microtubule-based motors such as kinesin. Such movements may require a motor with mechanochemical properties distinct from those of myosin-II, which operates in large ensembles to drive high-speed motility as in muscle contraction. Based on its function and biochemistry, it has been suggested that myosin-V may be a processive motor like kinesin. Processivity means that the motor undergoes multiple catalytic cycles and coupled mechanical advances for each diffusional encounter with its track. This allows single motors to support movement of an organelle along its track. Here we provide direct evidence that myosin-V is indeed a processive actin-based motor that can move in large steps approximating the 36-nm pseudo-repeat of the actin filament. 相似文献