Effects of spaceflight on the proliferation of jejunal mucosal cells

The purpose of this project was to test the hypothesis that the generalized, whole body decrease in synthetic activity due to microgravity conditions encountered during spaceflight would be demonstrable in cells and tissues characterized by a rapid rate of turnover. Jejunal mucosal cells were chosen as a model since these cells are among the most rapidly proliferating in the body. Accordingly, the percentage of mitotic cells present in the crypts of Lieberkuhn in each of 5 rats flown on the COSMOS 2044 mission were compared to the percentage of mitotic cells present in the crypts in rats included in each of 3 ground control groups (i.e., vivarium, synchronous and caudal-elevated). No significant difference (p greater than .05) was detected in mitotic indices between the flight and vivarium group. Although the ability of jejunal mucosal cells to divide by mitosis was not impaired in flight group, there was, however, a reduction in the length of villi and depth of crypts. The concommitant reduction in villus length and crypth depth in the flight group probably reflects changes in connective tissue components within the core of villi

Planck Fluctuations, Measurement Uncertainties and the Holographic Principle

Starting from a critical analysis of recently reported surprisingly large uncertainties in length and position measurements deduced within the framework of quantum gravity, we embark on an investigation both of the correlation structure of Planck scale fluctuations and the role the holographic hypothesis is possibly playing in this context. While we prove the logical independence of the fluctuation results and the holographic hypothesis (in contrast to some recent statements in that direction) we show that by combining these two topics one can draw quite strong and interesting conclusions about the fluctuation structure and the microscopic dynamics on the Planck scale. We further argue that these findings point to a possibly new and generalized form of quantum statistical mechanics of strongly (anti)correlated systems of degrees of freedom in this fundamental regime.Comment: 19 pages, Latex, no figures, some new references, to appear ModPhysLett

Spatial distribution of cell-cell and cell-ECM adhesions regulates force balance while main-taining E-cadherin molecular tension in cell pairs.

Mechanical linkage between cell-cell and cell-extracellular matrix (ECM) adhesions regulates cell shape changes during embryonic development and tissue homoeostasis. We examined how the force balance between cell-cell and cell-ECM adhesions changes with cell spread area and aspect ratio in pairs of MDCK cells. We used ECM micropatterning to drive different cytoskeleton strain energy states and cell-generated traction forces and used a Förster resonance energy transfer tension biosensor to ask whether changes in forces across cell-cell junctions correlated with E-cadherin molecular tension. We found that continuous peripheral ECM adhesions resulted in increased cell-cell and cell-ECM forces with increasing spread area. In contrast, confining ECM adhesions to the distal ends of cell-cell pairs resulted in shorter junction lengths and constant cell-cell forces. Of interest, each cell within a cell pair generated higher strain energies than isolated single cells of the same spread area. Surprisingly, E-cadherin molecular tension remained constant regardless of changes in cell-cell forces and was evenly distributed along cell-cell junctions independent of cell spread area and total traction forces. Taken together, our results showed that cell pairs maintained constant E-cadherin molecular tension and regulated total forces relative to cell spread area and shape but independently of total focal adhesion area

Generalized Sagnac Effect

Experiments were conducted to study light propagation in a light waveguide loop consisting of linearly and circularly moving segments. We found that any segment of the loop contributes to the total phase difference between two counterpropagating light beams in the loop. The contribution is proportional to a product of the moving velocity v and the projection of the segment length Deltal on the moving direction, Deltaphi=4pivDeltal/clambda. It is independent of the type of motion and the refractive index of waveguides. The finding includes the Sagnac effect of rotation as a special case and suggests a new fiber optic sensor for measuring linear motion with nanoscale sensitivity.Comment: 3 pages (including 3 figures

Ghost Kinetic Operator of Vacuum String Field Theory

Using the data of eigenvalues and eigenvectors of Neumann matrices in the 3-string vertex, we prove analytically that the ghost kinetic operator of vacuum string field theory obtained by Hata and Kawano is equal to the ghost operator inserted at the open string midpoint. We also comment on the values of determinants appearing in the norm of sliver state.Comment: 19 pages, 1 figure, lanlmac; v2: typos correcte

Quantum Monte Carlo calculation of the finite temperature Mott-Hubbard transition

We present clear numerical evidence for the coexistence of metallic and insulating dynamical mean field theory(DMFT) solutions in a half-filled single-band Hubbard model with bare semicircular density of states at finite temperatures. Quantum Monte Carlo(QMC) method is used to solve the DMFT equations. We discuss important technical aspects of the DMFT-QMC which need to be taken into account in order to obtain the reliable results near the coexistence region. Among them are the critical slowing down of the iterative solutions near phase boundaries, the convergence criteria for the DMFT iterations, the interpolation of the discretized Green's function and the reduction of QMC statistical and systematic errors. Comparison of our results with those of other numerical methods is presented in a phase diagram.Comment: 4 pages, 5 figure

Ratio of Tensions from Vacuum String Field Theory

We show analytically that the ratio of the norm of sliver states agrees with the ratio of D-brane tensions. We find that the correct ratio appears as a twist anomaly.Comment: 13 pages, lanlmac; version to appear in JHE

Disk Partition Function and Oscillatory Rolling Tachyons

An exact cubic open string field theory rolling tachyon solution was recently found by Kiermaier et. al. and Schnabl. This oscillatory solution has been argued to be related by a field redefinition to the simple exponential rolling tachyon deformation of boundary conformal theory. In the latter approach, the disk partition function takes a simple form. Out of curiosity, we compute the disk partition function for an oscillatory tachyon profile, and find that the result is nevertheless almost the same.Comment: 17 pages, 2 figures. v4: discussion clarified, appendix added, conclusions unchanged; version to appear in J.Phys.