To lay background for studying rejection mechanisms in xenotransplantation and developing the strategies for intervention, class I genes of swine leukocyte antigens (SLA) of three Chinese pig strains Bm, Gz and Yn were cloned and sequenced. The cDNA of the class I loci P1 and P14 were amplified by RT-PCR and subjected to insert into sequencing vectors. All six allelic sequences we examined, each two for one Chinese strain, are not identical to those reported, which allows these novel sequences receiving their accession numbers AY102467-AY102472 from GenBank. This study further reveals that the homologies of MHC class I genes in their primary structures and the deduced amino acids between Chinese pigs (SLA) and human (HLA-A*0201) are better than those between pigs and mice (H-2Db/H-2Kb). The comparison also indicates that the amino acid residues critical for recognition by human KIRs are altered in the swine class I molecules. The amino acids responsible for binding human CD8 coreceptor are largely conserved although there are two critical residues substituted. A functional test indicated that the human T cells specific for the prokaryotically expressed SLA P1protein could respond quite well in vitro to the class I-positive swine chondrocytes and PBMCs in presence of human APCs. This implies that, due to the substitution of two critical residues, the inaccessibility of human CD8 coreceptor to swine class I molecule might be contributable to the indirect pathway that the human T cells have to use for recognizing the SLA class I xenogeneic antigens.
the aging existing in use and construction of bituminous pavement will directly resulting in shortening of the pavement’s service life. It is provide the theoretical basis of the design and construction of the SBS modified asphalt mixture to analyze the influence of aging to the rheological property of SBS modified asphalt under high temperature. The testing for the rheological property of three kinds SBS modified asphalt under high temperature has been finished before and after the aging in construction by Brookfield DV Ⅱ+ type of rotation viscometer. The results indicated that viscosity will be increased and the sensitivity of SBS modified asphalt to viscosity will also be lowered along with increase of aging degree. The testing for the rheological property of three kinds of SBS modified asphalt has been finished before and after aging in usage period by the dynamic shear rheometer (DSR). The results shown that G* will be continually increased along with increase of aging degree and this is consistent with change of base asphalt. And this shown that the increase of G* can only come down to oxidation and aging of base asphalt contained in the modified asphalt and also, asphaltene in SBS modified asphalt will be changing in the mode same with that of base asphalt.
This article studies the low-temperature anti-cracking properties of plain asphalt mixtures and rubber-modified asphalt mixtures at different aging condition. Laboratory flexural test was conducted on the beam specimens of plain asphalt mixtures and rubber-modified asphalt mixtures. Experiment results indicate that rubber-modified asphalt mixtures have superior low-temperature anti-cracking performance than that of plain asphalt mixtures. Compared with the short term oven aging test, the long term oven aging test has more significant effect on the low-temperature anti-cracking of the mixture. In order to better represent the low-temperature anti-cracking of in-service aging asphalt pavement, the long term oven aging test should be used to appraise the low-temperature anti-cracking of asphalt pavements in china.
During the service of asphalt pavement, the aging makes asphalt binder become brittle, gradually lose flexibility and adhesion. All these result in the low-temperature properties of asphalt pavement to be poor. This paper conducts the rolling thin film oven test (RTFOT) and pressure aging vessel (PAV) test on base asphalt and rubber-modified asphalt respectively. The bending beam rheometer (BBR) test was conducted on original asphalts, rolling thin film oven test (RTFOT) residuals and RTFOT + pressure aging vessel (PAV) residuals of base asphalt and rubber-modified asphalt respectively. Results indicate that the low-temperature properties of all aged asphalts were declined. The attenuation of low-temperature properties of RTFOT + PAV residuals is larger than that of the RTFOT residuals. The attenuation of different types of asphalt is different. From the overall trend, effect of aging on the low-temperature properties of asphalt binder reduced as the test temperature reduction. The rubber-modified asphalt has superior low-temperature performance than that of base asphalt, and its low-temperature performance decreases more slowly than the base asphalt.
Ice layer on pavement surface was a serious problem for highway traffic safety. Crumbed rubber asphalt mixture was an effective way to drive ice layer away from surface. Through wheel test asphalt mixture specimen with ice layer at negtive temperature, the paper studied ice breaking performance of asphalt mixtures containing different amount crumbed rubber. Pendulumlike friction test BPN after wheel test was taken as an performance index of crumber rubber asphalt breaking ice. Results shown that the quantity of crumbed rubber and the performance of ice breaking had good linear relationship and more rubber content had better slide resistance recover speed at same wheel arround number.Through numerial model of pavement covered ice based on FEM method, the paper had analyzed the relationship between elastic modulus of crumbed rubber pavement and ice stress-strain on pavement, and put forward the mechanism of ice breaking.
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