142 research outputs found
Meissner response of a bulk superconductor with an embedded sheet of reduced penetration depth
We calculate the change in susceptibility resulting from a thin sheet with
reduced penetration depth embedded perpendicular to the surface of an isotropic
superconductor, in a geometry applicable to scanning Superconducting QUantum
Interference Device (SQUID) microscopy, by numerically solving Maxwell's and
London's equations using the finite element method. The predicted stripes in
susceptibility agree well in shape with the observations of Kalisky et al. of
enhanced susceptibility above twin planes in the underdoped pnictide
superconductor Ba(Fe1-xCox)2As2 (Ba-122). By comparing the predicted stripe
amplitudes with experiment and using the London relation between penetration
depth and superfluid density, we estimate the enhanced Cooper pair density on
the twin planes, and the barrier force for a vortex to cross a twin plane. Fits
to the observed temperature dependence of the stripe amplitude suggest that the
twin planes have a higher critical temperature than the bulk, although stripes
are not observed above the bulk critical temperature.Comment: 16 pages, 9 figure
Interpreting the sense of home through a self-built housing experiment in Madras, India
Typescript (photocopy)
Generalized Lévy walks and the role of chemokines in migration of effector CD8+ T cells.
Chemokines have a central role in regulating processes essential to the immune function of T cells, such as their migration within lymphoid tissues and targeting of pathogens in sites of inflammation. Here we track T cells using multi-photon microscopy to demonstrate that the chemokine CXCL10 enhances the ability of CD8+ T cells to control the pathogen Toxoplasma gondii in the brains of chronically infected mice. This chemokine boosts T-cell function in two different ways: it maintains the effector T-cell population in the brain and speeds up the average migration speed without changing the nature of the walk statistics. Notably, these statistics are not Brownian; rather, CD8+ T-cell motility in the brain is well described by a generalized Lévy walk. According to our model, this unexpected feature enables T cells to find rare targets with more than an order of magnitude more efficiency than Brownian random walkers. Thus, CD8+ T-cell behaviour is similar to Lévy strategies reported in organisms ranging from mussels to marine predators and monkeys, and CXCL10 aids T cells in shortening the average time taken to find rare targets
Innovations in Information Systems Education - Reflections of AIS Award Winners
AIS Council monitors social and technical trends that might affect the timeliness and relevance of IS curricula. Consequently, AIS Council charged the AIS VP for Education with developing a process to highlight the importance of these trends and to stimulate the development of education innovations to address them. The result is an AIS-sponsored awards competition (http://www.aisnet.org/award/awards.asp), first held in 2004. The call for submissions focused on the two themes of offshore outsourcing and software development innovations. A panel of expert judges made six awards— three awards of excellence and three honorable mentions. Members of five of the six winning teams appear on this panel. Panelists will address the following questions: · What was the origin of the innovation idea? · What support did you receive upfront for developing your innovation? · What barriers did you encounter in developing your innovation and how did you overcome them? · What learning or other benefits did you, your students, and your program experience from the innovation? · What other areas do you see where innovation in the IS curriculum is required? · What advice do you have for other IS educational innovators
Enhanced superfluid density on twin boundaries in Ba(Fe1-xCox)2As2
Superconducting quantum interference device (SQUID) microscopy shows stripes
of increased diamagnetic susceptibility in underdoped, but not overdoped,
single crystals of Ba(Fe1-xCox)2As2. These stripes of increased diamagnetic
susceptibility are consistent with enhanced superfluid density on twin
boundaries. Individual vortices avoid pinning on or crossing the stripes, and
prefer to travel parallel to them. These results indicate a relationship
between superfluid density, local strain, and frustrated magnetism, and
demonstrate two mechanisms for enhancing critical currents.Comment: 16 pages, 4 figure
Measurements of the gate tuned superfluid density in superconducting LaAlO3/SrTiO3
The interface between the insulating oxides LaAlO3 and SrTiO3 exhibits a
superconducting two-dimensional electron system that can be modulated by a gate
voltage. While gating of the conductivity has been probed extensively and
gating of the superconducting critical temperature has been demonstrated, the
question whether, and if so how, the gate tunes the superfluid density and
superconducting order parameter is unanswered. We present local magnetic
susceptibility, related to the superfluid density, as a function of
temperature, gate voltage and location. We show that the temperature dependence
of the superfluid density at different gate voltages collapse to a single curve
characteristic of a full superconducting gap. Further, we show that the dipole
moments observed in this system are not modulated by the gate voltage
Analysis of Behavior and Trafficking of Dendritic Cells within the Brain during Toxoplasmic Encephalitis
Under normal conditions the immune system has limited access to the brain; however, during toxoplasmic encephalitis (TE), large numbers of T cells and APCs accumulate within this site. A combination of real time imaging, transgenic reporter mice, and recombinant parasites allowed a comprehensive analysis of CD11c+ cells during TE. These studies reveal that the CNS CD11c+ cells consist of a mixture of microglia and dendritic cells (DCs) with distinct behavior associated with their ability to interact with parasites or effector T cells. The CNS DCs upregulated several chemokine receptors during TE, but none of these individual receptors tested was required for migration of DCs into the brain. However, this process was pertussis toxin sensitive and dependent on the integrin LFA-1, suggesting that the synergistic effect of signaling through multiple chemokine receptors, possibly leading to changes in the affinity of LFA-1, is involved in the recruitment/retention of DCs to the CNS and thus provides new insights into how the immune system accesses this unique site
Local measurement of the penetration depth in the pnictide superconductor Ba(FeCo)As
We use magnetic force microscopy (MFM) and scanning SQUID susceptometry to
measure the local superfluid density in
Ba(FeCo)As single crystals from 0.4 K to the critical
temperature K. We observe that the penetration depth
varies about ten times more slowly with temperature than previously published,
with a dependence that can be well described by a clean two-band fully gapped
model. We demonstrate that MFM can measure the important and hard-to-determine
absolute value of , as well as obtain its temperature dependence and
spatial homogeneity. We find to be uniform despite the highly
disordered vortex pinning
Tests for Genetic Interactions in Type 1 Diabetes: Linkage and Stratification Analyses of 4,422 Affected Sib-Pairs
OBJECTIVE - Interactions between genetic and environmental factors lead to immune dysregulation causing type 1 diabetes and other autoimmune disorders. Recently, many common genetic variants have been associated with type 1 diabetes risk, but each has modest individual effects. Familial clustering of type 1 diabetes has not been explained fully and could arise from many factors, including undetected genetic variation and gene interactions. RESEARCH DESIGN AND METHODS - To address this issue, the Type 1 Diabetes Genetics Consortium recruited 3,892 families, including 4,422 affected sib-pairs. After genotyping 6,090 markers, linkage analyses of these families were performed, using a novel method and taking into account factors such as genotype at known susceptibility loci. RESULTS - Evidence for linkage was robust at the HLA and INS loci, with logarithm of odds (LOD) scores of 398.6 and 5.5, respectively. There was suggestive support for five other loci. Stratification by other risk factors (including HLA and age at diagnosis) identified one convincing region on chromosome 6q14 showing linkage in male subjects (corrected LOD = 4.49; replication P = 0.0002), a locus on chromosome 19q in HLA identical siblings (replication P = 0.006), and four other suggestive loci. CONCLUSIONS - This is the largest linkage study reported for any disease. Our data indicate there are no major type 1 diabetes subtypes definable by linkage analyses; susceptibility is caused by actions of HLA and an apparently random selection from a large number of modest-effect loci; and apart from HLA and INS, there is no important susceptibility factor discoverable by linkage methods
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