94,342 research outputs found
Classification of multidimensional inflationary models
We define under which circumstances two multi-warped product spacetimes can
be considered equivalent and then we classify the spaces of constant curvature
in the Euclidean and Lorentzian signature. For dimension D=2, we get
essentially twelve representations, for D=3 exactly eighteen. More general, for
every even D, 5D+2 cases exist, whereas for every odd D, 5D+3 cases exist. For
every D, exactly one half of them has the Euclidean signature. Our definition
is well suited for the discussion of multidimensional cosmological models, and
our results give a simple algorithm to decide whether a given metric represents
the inflationary de Sitter spacetime (in unusual coordinates) or not.Comment: 21 pages, LaTeX, no figures, J. Math. Phys. in prin
Creation and Manipulation of Anyons in the Kitaev Model
We analyze the effect of local spin operators in the Kitaev model on the
honeycomb lattice. We show, in perturbation around the isolated-dimer limit,
that they create Abelian anyons together with fermionic excitations which are
likely to play a role in experiments. We derive the explicit form of the
operators creating and moving Abelian anyons without creating fermions and show
that it involves multi-spin operations. Finally, the important experimental
constraints stemming from our results are discussed.Comment: 4 pages, 3 figures, published versio
Asymptotic Freedom in Curvature-Satured Gravity
For a spatially flat Friedmann model with line element , the 00-component of the Einstein field equation
reads containing no derivative. For a nonlinear
Lagrangian , we obtain a second--order differential equation for
instead of the expected fourth-order equation. We discuss this equation for
the curvature-saturated model proposed by Kleinert and Schmidt. Finally, we
argue that asymptotic freedom is fulfilled in
curvature-saturated gravity.Comment: 9 pages, World Scientific LATEX, to appear in "Fluctuating Paths and
Fields", WSPC Singapore 2001, Eds: W. Janke, A. Pelster, H.-J. Schmidt, M.
Bachman
How to measure spatial distances?
The use of time--like geodesics to measure temporal distances is better
justified than the use of space--like geodesics for a measurement of spatial
distances. We give examples where a ''spatial distance'' cannot be
appropriately determined by the length of a space--like geodesic.Comment: 4 pages, latex, no figure
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote ER stress resistance
Misfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (U PR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress
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