627 research outputs found
11-Dimensional Supergravity Compactified on Calabi-Yau Threefolds
We consider generic features of eleven dimensional supergravity compactified
down to five dimensions on an arbitrary Calabi-Yau threefold.Comment: TeX, harvmac, 8 pg
Space-Time Distribution of G-Band and Ca II H-Line Intensity Oscillations in Hinode/SOT-FG Observations
We study the space-time distributions of intensity fluctuations in 2 - 3 hour
sequences of multi-spectral, high-resolution, high-cadence broad-band
filtergram images (BFI) made by the SOT-FG system aboard the Hinode spacecraft.
In the frequency range 5.5 < f < 8.0 mHz both G-band and Ca II H-line
oscillations are suppressed in the presence of magnetic fields, but the
suppression disappears for f > 10 mHz. By looking at G-band frequencies above
10 mHz we find that the oscillatory power, both at these frequencies and at
lower frequencies too, lies in a mesh pattern with cell scale 2 - 3 Mm, clearly
larger than normal granulation, and with correlation times on the order of
hours. The mesh pattern lies in the dark lanes between stable cells found in
time-integrated G-band intensity images. It also underlies part of the bright
pattern in time-integrated H-line emission. This discovery may reflect
dynamical constraints on the sizes of rising granular convection cells together
with the turbulence created in strong intercellular downflows.Comment: 24 pages, 15 figure
Novel Human Embryonic Stem Cell Regulators Identified by Conserved and Distinct CpG Island Methylation State
Human embryonic stem cells (hESCs) undergo epigenetic changes in vitro which may compromise function, so an epigenetic pluripotency "signature" would be invaluable for line validation. We assessed Cytosine-phosphate-Guanine Island (CGI) methylation in hESCs by genomic DNA hybridisation to a CGI array, and saw substantial variation in CGI methylation between lines. Comparison of hESC CGI methylation profiles to corresponding somatic tissue data and hESC mRNA expression profiles identified a conserved hESC-specific methylation pattern associated with expressed genes. Transcriptional repressors and activators were over-represented amongst genes whose associated CGIs were methylated or unmethylated specifically in hESCs, respectively. Knockdown of candidate transcriptional regulators (HMGA1, GLIS2, PFDN5) induced differentiation in hESCs, whereas ectopic expression in fibroblasts modulated iPSC colony formation. Chromatin immunoprecipitation confirmed interaction between the candidates and the core pluripotency transcription factor network. We thus identify novel pluripotency genes on the basis of a conserved and distinct epigenetic configuration in human stem cells
N=2 Heterotic Superstring and its Dual Theory in Five Dimensions
We study quantum effects in five dimensions in heterotic superstring theory
compactified on K_3 x S_1 and analyze the conjecture that its dual effective
theory is eleven-dimensional supergravity compactified on a Calabi-Yau
threefold. This theory is also equivalent to type II superstring theory
compactified on the same Calabi-Yau manifold, in an appropriate large volume
limit. In this limit the conifold singularity disappears and is replaced by a
singularity associated to enhanced gauge symmetries, as naively expected from
the heterotic description. Furthermore, we exhibit the existence of additional
massless states which appear in the strong coupling regime of the heterotic
theory and are related to a different type of singular points on Calabi-Yau
threefolds.Comment: 26 pages, LaTe
On the Geometry of Moduli Space of Vacua in N=2 Supersymmetric Yang-Mills Theory
We consider generic properties of the moduli space of vacua in
supersymmetric Yang--Mills theory recently studied by Seiberg and Witten. We
find, on general grounds, Picard--Fuchs type of differential equations
expressing the existence of a flat holomorphic connection, which for one
parameter (i.e. for gauge group ), are second order equations. In the
case of coupling to gravity (as in string theory), where also ``gravitational''
electric and magnetic monopoles are present, the electric--magnetic S duality,
due to quantum corrections, does not seem any longer to be related to
as for supersymmetric theory.Comment: 10 pgs (TeX with harvmac), POLFIS-TH.07/94, CERN-TH.7384/9
Recent Efforts in the Computation of String Couplings:
We review recent advances towards the computation of string couplings.
Duality symmetry, mirror symmetry, Picard-Fuchs equations, etc. are some of the
tools.Comment: Talk hold at the `International Conference on Modern Problems in
Quantum Field Theorie, Strings and Quantum Gravity', Kiev, June 1992, 18
page
Interaction of Variable Bacterial Outer Membrane Lipoproteins with Brain Endothelium
Previously we reported that the variable outer membrane lipoprotein Vsp1 from the relapsing fever spirochete Borrelia turicatae disseminates from blood to brain better than the closely related Vsp2 [1]. Here we studied the interaction between Vsp1 and Vsp2 with brain endothelium in more detail.We compared Vsp1 to Vsp2 using human brain microvascular endothelial cell (HBMEC) association assays with aminoacid radiolabeled Vsp-expressing clones of recombinant Borrelia burgdorferi and lanthanide-labeled purified lipidated Vsp1 (LVsp1) and Vsp2 (LVsp2) and inoculations of the lanthanide-labeled proteins into mice. The results showed that heterologous expression of LVsp1 or LVsp2 in B. burgdorferi increased its association with HBMEC to a similar degree. Purified lanthanide-labeled lipidated Vsp1 (LVsp1) and LVsp2 by themselves were capable of associating with HBMEC. The association of LVsp1 with brain endothelium was time-dependent, saturable, and required the lipidation. The association of Vsp1 with HBMEC was inhibited by incubation at lower temperature or with excess unlabeled LVsp1 or LVsp2 but not with excess rVsp1 or mouse albumin or an anti Vsp1 monoclonal antibody. The association of LVsp2 with HBMEC and its movement from blood to brain parenchyma significantly increased in the presence of LVsp1.Variable bacterial outer membrane lipoproteins interact with brain endothelium differently; the lipidation and variable features at the protein dome region are key modulators of this interaction
Bianchi Type I Cosmology in N=2, D=5 Supergravity
The dynamics and evolution of Bianchi type I space-times is considered in the
framework of the four-dimensional truncation of a reduced theory obtained from
the N=2,D=5 supergravity. The general solution of the gravitational field
equations can be represented in an exact parametric form. All solutions have a
singular behavior at the initial/final moment, except when the space-time
geometry reduces to the isotropic flat case. Generically the obtained
cosmological models describe an anisotropic, expanding or collapsing, singular
Universe with a non-inflationary evolution for all times.Comment: revised version to appear in PR
R^4 Couplings in M and Type II Theories
We discuss several implications of R^4 couplings in M theory when
compactified on Calabi-Yau (CY) manifolds. In particular, these couplings can
be predicted by supersymmetry from the mixed gauge-gravitational Chern-Simons
couplings in five dimensions and are related to the one-loop holomorphic
anomaly in four-dimensional N=2 theories. We find a new contribution to the
Einstein term in five dimensions proportional to the Euler number of the
internal CY threefold, which corresponds to a one-loop correction of the
hypermultiplet geometry. This correction is reproduced by a direct computation
in type II string theories. Finally, we discuss a universal non-perturbative
correction to the type IIB hyper-metric.Comment: 21 pages, harvmac, misprints corrected, version to appear in Nuclear
Physics
- …