Random distribution of topological defects in mesoscopic superconducting samples

In the present work we analyze the effect of topological defects at different temperatures in a mesoscopic superconducting sample in the presence of an applied magnetic field H. The time-dependent Ginzburg-Landau equations are solved with the method of link variables. We study the magnetization curves M(H), number of vortices N(H) and Gibbs G(H) free energy of the sample as a applied magnetic field function. We found that the random distribution of the anchor centers for the temperatures used does not cause strong anchor centers for the vortices, so the configuration of fluxoids in the material is symmetrical due to the well-known Beam-Livingston energy barrier.

The Ongoing Quest for the it Artifact: Looking Back, Moving Forward

More than 10 years ago, Orlikowski and Iacono (2001) examined the conceptualization of Information Technology (IT) in Information Systems Research (ISR) articles published in the 1990s. Their main conclusion was that the majority of these articles did not properly conceptualize the IT artifact. They recommended that IS researchers start to theorize about the IT artifact and employ rich conceptualizations of IT. The Orlikowski and Iacono paper provides a strong anchor point from which to analyze the evolution of the IS discipline. In order to obtain an up-to-date image of contemporary IS research, and to assess how the IS field has evolved since the 1990s, we carried out a similar analysis on a more recent and broader set of articles, that is, the full set (N = 644) of papers published between 2006 and 2009 by six top North American (ISR, MISQ, JAIS) and European (JIT, ISJ, EJIS) journals. The statistics in our results reveal no drastic advance in terms of deeper engagement with the IT artifact; more than 39% of the articles in our set are virtually mute about the artifact, and less than 16% employ an ensemble view of IT. Moreover, we note differences among the North American and European journals. Implications of the findings for two perspectives central to the IS research legitimacy debate are discussed.

Alloreactive cytotoxic T lymphocytes recognize epitopes determined by both the alpha helices and beta sheets of the class I peptide binding site.

A chimeric class I glycoprotein was created to investigate the functional contribution of the alpha helices and the beta-pleated sheets in forming the antigen recognition site (ARS) of antigen-presenting molecules. This novel molecule was generated by replacing the DNA sequences encoding the alpha helices of the Ld gene with the corresponding sequences from the Kb gene. Serologic analysis of transfected L cells that expressed the chimeric molecule (Kb alpha Ld beta) revealed that the engineered class I glycoprotein retains two conformational epitopes associated with the alpha helices of Kb, as defined by monoclonal antibodies K10.56 and 28-13-3. These results demonstrate that the alpha helices of Kb can associate with the beta-pleated sheets of Ld to form a stable structure, which is expressed on the cell surface. To address the role of the alpha helices of the ARS in determining T cell crossreactivity, alloreactive cytotoxic T lymphocytes (CTL) were used to analyze L cells expressing Kb alpha Ld beta. CTL raised against Kb or Ld as alloantigens showed little, if any, ability to lyse L cells expressing Kb alpha Ld beta. Thus, alloreactive CTL did not recognize structures determined by the alpha helices alone or by the beta sheets of the ARS alone. However, bulk and cloned alloreactive CTL that were generated against the mutant Kb glycoprotein Kbm8 reacted strongly with Kb alpha Ld beta. In addition to the Kb alpha helices, the Kbm8 ARS shares a single polymorphic amino acid at position 24 with Kb alpha Ld beta. Amino acid 24 is located on the beta 2 strand that forms part of the floor of the ARS and has been identified as a component of pocket B in the HLA class I ARS. The substitution of Glu to Ser at this position was shown previously to be the central determinant of the Kbm8 mutant alloantigenicity. The functional significance of this position in determining crossreactivity between bm8 and Kb alpha Ld beta identifies pocket B as a strong anchor for allogenic self-peptides. These findings demonstrate that determinants recognized by CTL on class I alloantigens are formed by interactions involving both the alpha helices and beta sheets of the ARS. These interactions are best explained by the influence of the alpha helices and beta sheets on the peptide-binding properties of these antigen-presenting molecules.