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(2006)Journal Article
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(1995)Journal ArticleNormal-state reentrant behavior is observed in the resistive transition for Bi-2212/2223 intergrowth single crystals. It is found that for a small driving current of 50 μA the resistivity for the intergrowth system exhibits a superconducting transition with zero values at 105 K, which returns to the resistive state at a lower temperature. With a further temperature decrease, the system again becomes superconducting at 92 K. In the case of large driving currents, the reentrant behavior is not found and only a two-step resistive transition is observed. The normal-state reentrant behavior is interpreted using a model where the Josephson coupling between the CuO2 trilayers is weakened by thermally activated resistance between these layers. The two-step transition can be explained by the proximity effect along the ab plane. Our results suggest that due to thermally activated resistance between the superconducting layers in the layered superconductors like Bi-Sr-Ca-Cu-O, the three- to two-dimensional crossover of superconducting behavior may be induced at temperatures much lower than Tc by applying magnetic or electric fields.
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(1995)Journal ArticleAn anomalously broad foot structure is observed in the zero-field resistive transition for the ab plane of Bi2Sr2CaCu2O8+y single crystals, which are found to have a high density of dislocations. However, this anomalous behavior is not apparent for resistive measurements along the c axis. The foot structure can be treated as a superposition of a long resistance tail and a dissipation peak, in which the long resistance tail obeys the theory of KT scaling behavior of resistivity. The dissipation peak is related to the fluxon transition in Josephson-coupled layered superconductors as detailed by Horovitz [Phys. Rev. Lett. 72, 1569 (1994)].
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(1995)Journal ArticleSr-based 123 compounds R1-xCaxSr2Cu2.7Mo0.3Oy with R = Pr, Nd, and Y are successfully stabilised by partial substitution of Mo for Cu. A tetragonal-orthorhomic-tetragonal transition is observed for R = Y and Nd, which is induced by different oxygen content in the samples. Tc of the samples is sensitive to the oxygen content other than the structure. For Pr-contained samples the resistivity decreases systematically with increasing the Ca dopant and oxygen content. The results show that the hybridisation of the conduction electrons with the 4f band of Pr in Sr-based 123 compounds is weaker than that in Ba-based 123 compounds.
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(1996)Journal ArticleThe effects of contact area as well as the weight fraction of Y2BaCuO5 (211) substrate on the melt textured growth (MTG) of YBa2Cu3O7- (123) crystals are investigated. It is found that the 123 grain size and its orientation have been greatly improved by a well designed 211 substrate with maximized number of contact points. The size of the 123 single domain has been extended up to 2.7 cm with no porosity and cracks by applying 50% of contact area and 35% of absorbed liquid weight into 211 substrate. Magnetization and levitation measurements show that the MTG 123 crystals have a high Jc and a good performance in high magnetic fields.
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(2009)Journal ArticleHuman embryonic stem cells (hESCs) have previously been cultured on three dimensional (3D) biodegradable polymer scaffolds. Although complex structures were formed from the hESCs, very little is known about the mechanism of adhesion of these cells to the surfaces of the scaffolds. In this study, we achieved the efficient adhesion of pluripotent hESCs to 3D poly(lactic-co-glycolic acid) (PLGA) scaffolds based on our data from a novel two dimensional (2D) model that imitates the surface properties of the scaffolds. In the 2D model, single cell preparations of pluripotent hESCs adhered efficiently and predominantly to PLGA surfaces coated with laminin in comparison to collagen I, collagen IV, or fibronectin-coated surfaces. Flow cytometry analysis revealed that almost all of the pluripotent single cells expressed the integrin 6, with a small percentage also expressing 3ß1, which facilitates adhesion to laminin. This data was then translated into the 3D environment, with the efficient binding of single pluripotent hESCs to PLGA scaffolds coated with laminin. The utility of this system was shown by the directed differentiation of single hESCs seeded within laminin-coated scaffolds toward the endoderm lineage.
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(2004)Journal ArticleThe accurate partitioning of Ig H chain V(H)DJ(H) junctions and L chain V(L)J(L) junctions is problematic. We have developed a statistical approach for the partitioning of such sequences, by analyzing the distribution of point mutations between a determined V gene segment and putative Ig regions. The establishment of objective criteria for the partitioning of sequences between V(H), D, and J(H) gene segments has allowed us to more carefully analyze intervening putative nontemplated (N) nucleotides. An analysis of 225 IgM H chain sequences, with five or fewer V mutations, led to the alignment of 199 sequences. Only 5.0% of sequences lacked N nucleotides at the V(H)D junction (N1), and 10.6% at the DJ(H) junction (N2). Long N regions (>9 nt) were seen in 20.6% of N1 regions and 17.1% of N2 regions. Using a statistical analysis based upon known features of N addition, and mutation analysis, two of these N regions aligned with D gene segments, and a third aligned with an inverted D gene segment. Nine additional sequences included possible alignments with a second D segment. Four of the remaining 40 long N1 regions included 5` sequences having six or more matches to V gene end motifs, which may be the result of V gene replacement. Such sequences were not seen in long N2 regions. The long N regions frequently seen in the expressed repertoire of human Ig gene rearrangements can therefore only partly be explained by V gene replacement and D-D fusion.
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(2004)Journal ArticleBACKGROUND: Immunoglobulin rearrangement involves random and imprecise processes that act to both create and constrain diversity. Two such processes are the loss of nucleotides through the action of unknown exonuclease(s) and the addition of P nucleotides. The study of such processes has been compromised by difficulties in reliably aligning immunoglobulin genes and in the partitioning of nucleotides between segment ends, and between N and P nucleotides. RESULTS: A dataset of 294 human IgM sequences was created and partitioned with the aid of a probabilistic model. Non-random removal of nucleotides is seen between the three IGH gene types with the IGHV gene averaging removals of 1.2 nucleotides compared to 4.7 for the other gene ends (p < 0.001). Individual IGHV, IGHD and IGHJ gene subgroups also display statistical differences in the level of nucleotide loss. For example, within the IGHJ group, IGHJ3 has average removals of 1.3 nucleotides compared to 6.4 nucleotides for IGHJ6 genes (p < 0.002). Analysis of putative P nucleotides within the IgM and pooled datasets revealed only a single putative P nucleotide motif (GTT at the 3` D-REGION end) to occur at a frequency significantly higher then would be expected from random N nucleotide addition. CONCLUSIONS: The loss of nucleotides due to the action of exonucleases is not random, but is influenced by the nucleotide composition of the genes. P nucleotides do not make a significant contribution to diversity of immunoglobulin sequences. Although palindromic sequences are present in 10% of immunologlobulin rearrangements, most of the `palindromic` nucleotides are likely to have been inserted into the junction during the process of N nucleotide addition. P nucleotides can only be stated with confidence to contribute to diversity of less than 1% of sequences. Any attempt to identify P nucleotides in immunoglobulins is therefore likely to introduce errors into the partitioning of such sequences. [Journal Article; In English;