Model for the low-temperature magnetic phases observed in doped YBa_2Cu_3O_{6+x}

A classical statistical model for the antiferromagnetic (AFM) ordering of the Cu-spins in the CuO_2 planes of reduced YBa_2Cu_3O_{6+x} type materials is presented. The magnetic phases considered are the experimentally observed high-temperature AFI phase with ordering vector Q_I=(1/2,1/2,0), and the low-temperature phases: AFII with Q_II=(1/2,1/2,1/2) and intermediate TA (Turn Angle) phases TAI, TAII and TAIII with components of both ordering vectors. It is shown that the AFII and TA phases result from an effective ferromagnetic (FM) type coupling mediated by free spins in the CuO_x basal plane. Good agreement with experimental data is obtained for realistic model parameters.Comment: 11 pages, 2 Postscript figures, Submitted to Phys.Rev.Let

Mass and charge transport in micro and nano-fluidic channels

We consider laminar flow of incompressible electrolytes in long, straight channels driven by pressure and electro-osmosis. We use a Hilbert space eigenfunction expansion to address the general problem of an arbitrary cross section and obtain general results in linear-response theory for the mass and charge transport coefficients which satisfy Onsager relations. In the limit of non-overlapping Debye layers the transport coefficients are simply expressed in terms of parameters of the electrolyte as well as the hydraulic radius R=2A/P with A and P being the cross-sectional area and perimeter, respectively. In articular, we consider the limits of thin non-overlapping as well as strongly overlapping Debye layers, respectively, and calculate the corrections to the hydraulic resistance due to electro-hydrodynamic interactions.Comment: Invited paper presented at the Second International Conference on Transport Phenomena in Micro and Nanodevices, Il Ciocco Hotel and Conference Center, Barga, Italy, 11-15 June 2006. Accepted for publication in a special issue of Nanoscale and Microscale Thermophysical Engineering (Taylor & Francis

First-Order Melting of a Moving Vortex Lattice: Effects of Disorder

We study the melting of a moving vortex lattice through numerical simulations with the current driven 3D XY model with disorder. We find that there is a first-order phase transition even for large disorder when the corresponding equilibrium transition is continuous. The low temperature phase is an anisotropic moving glass.Comment: Important changes from original version. Finite size analysis of results has been added. Figure 2 has been changed. There is a new additional Figure. To be published in Physical Review Letter

Universality in edge-source diffusion dynamics

We show that in edge-source diffusion dynamics the integrated concentration N(t) has a universal dependence with a characteristic time-scale tau=(A/P)^2 pi/(4D), where D is the diffusion constant while A and P are the cross-sectional area and perimeter of the domain, respectively. For the short-time dynamics we find a universal square-root asymptotic dependence N(t)=N0 sqrt(t/tau) while in the long-time dynamics N(t) saturates exponentially at N0. The exponential saturation is a general feature while the associated coefficients are weakly geometry dependent.Comment: 4 pages including 4 figures. Minor changes. Accepted for PR

Defensin-rich granules of human neutrophils: characterization of secretory properties

AbstractThe various granule subtypes of the human neutrophil differ in propensity for exocytosis. As a rule, granules formed at late stages of myelopoiesis have a higher secretory potential than granules formed in more immature myeloid cells. Neutrophils contain four closely related α-defensins, which are stored in a subset of azurophil granules. These defensin-rich azurophil granules (DRG) are formed later than defensin-poor azurophil granules, near the promyelocyte/myelocyte transition. In order to characterize the secretory properties of DRG, we developed a sensitive and accurate ELISA for detection of the neutrophil α-defensins HNP 1–3. This allowed us to quantify the exocytosis of α-defensins and markers of azurophil (myeloperoxidase), specific (lactoferrin) and gelatinase (gelatinase) granules from neutrophils stimulated with different secretagogues. The release pattern of α-defensins correlated perfectly with the release of myeloperoxidase and showed no resemblance to the exocytosis of lactoferrin or gelatinase. This finding was substantiated through subcellular fractionation experiments. In conclusion, despite a distinct profile of biosynthesis, DRG are indistinguishable from defensin-poor azurophil granules with respect to exocytosis. Thus, in contrast to peroxidase-negative granules, azurophil granules display homogeneity in their availability for extracellular release

miRConnect: Identifying Effector Genes of miRNAs and miRNA Families in Cancer Cells

micro(mi)RNAs are small non-coding RNAs that negatively regulate expression of most mRNAs. They are powerful regulators of various differentiation stages, and the expression of genes that either negatively or positively correlate with expressed miRNAs is expected to hold information on the biological state of the cell and, hence, of the function of the expressed miRNAs. We have compared the large amount of available gene array data on the steady state system of the NCI60 cell lines to two different data sets containing information on the expression of 583 individual miRNAs. In addition, we have generated custom data sets containing expression information of 54 miRNA families sharing the same seed match. We have developed a novel strategy for correlating miRNAs with individual genes based on a summed Pearson Correlation Coefficient (sPCC) that mimics an in silico titration experiment. By focusing on the genes that correlate with the expression of miRNAs without necessarily being direct targets of miRNAs, we have clustered miRNAs into different functional groups. This has resulted in the identification of three novel miRNAs that are linked to the epithelial-to-mesenchymal transition (EMT) in addition to the known EMT regulators of the miR-200 miRNA family. In addition, an analysis of gene signatures associated with EMT, c-MYC activity, and ribosomal protein gene expression allowed us to assign different activities to each of the functional clusters of miRNAs. All correlation data are available via a web interface that allows investigators to identify genes whose expression correlates with the expression of single miRNAs or entire miRNA families. miRConnect.org will aid in identifying pathways regulated by miRNAs without requiring specific knowledge of miRNA targets