109 research outputs found
Persistence of Kardar-Parisi-Zhang Interfaces
The probabilities that a growing Kardar-Parisi-Zhang interface
remains above or below the mean height in the time interval are
shown numerically to decay as with and . Bounds on are
derived from the height autocorrelation function under the assumption of
Gaussian statistics. The autocorrelation exponent for a
--dimensional interface with roughness and dynamic exponents and
is conjectured to be . For a recently proposed
discretization of the KPZ equation we find oscillatory persistence
probabilities, indicating hidden temporal correlations.Comment: 4 pages, 3 figures, uses revtex and psfi
Strong coupling probe for the Kardar-Parisi-Zhang equation
We present an exact solution of the {\it deterministic} Kardar-Parisi-Zhang
(KPZ) equation under the influence of a local driving force . For substrate
dimension we recover the well-known result that for arbitrarily small
, the interface develops a non-zero velocity . Novel behaviour is
found in the strong-coupling regime for , in which must exceed a
critical force in order to drive the interface with constant velocity. We
find for . In particular,
the exponent for , but saturates at
for , indicating that for this simple problem, there exists a finite upper
critical dimension . For the surface distortion caused by the
applied force scales logarithmically with distance within a critical radius
, where . Connections
between these results, and the critical properties of the weak/strong-coupling
transition in the noisy KPZ equation are pursued.Comment: 18 pages, RevTex, to appear in J. Phys. I Franc
Conserved Growth on Vicinal Surfaces
A crystal surface which is miscut with respect to a high symmetry plane
exhibits steps with a characteristic distance. It is argued that the continuum
description of growth on such a surface, when desorption can be neglected, is
given by the anisotropic version of the conserved KPZ equation (T. Sun, H. Guo,
and M. Grant, Phys. Rev. A 40, 6763 (1989)) with non-conserved noise. A
one--loop dynamical renormalization group calculation yields the values of the
dynamical exponent and the roughness exponent which are shown to be the same as
in the isotropic case. The results presented here should apply in particular to
growth under conditions which are typical for molecular beam epitaxy.Comment: 10 pages, uses revte
A SYSTEMATIC EXPLORATION OF INSULIN-DEPENDENT PROTEIN NETWORKS BY QUANTITATIVE MASS SPECTROMETRY
The highly conserved peptide hormone insulin functions as a central regulator of
metabolic homeostasis in the human body. So far, several large-scale-omics studies
based on proteomics approaches have been performed to investigate intracellular
insulin signaling, including glucose uptake, gene regulation, and differentiation. These
studies uncovered a plethora of insulin-dependent effectors and revealed complex
mechanisms of how these signaling molecules interact. However, detailed functions of
large numbers of signaling molecules remained entirely unclear. It became further
evident that interactions between signaling pathways are much more complex than
initially assumed.
This thesis aims to generate large-scale insulin-dependent protein-protein
interactomes and phosphoproteomes to decipher the complex mechanisms of insulin
signaling pathways in brown adipocytes. For the global protein-protein interactome
analysis, nearly 100 proteins were selected which either have known functions in
insulin signaling pathways or show insulin-dependent phosphorylation. Bait
expression experiments in brown adipocytes were performed for the selected
candidates by transient transfection of FLAG-tagged expression constructs and
enrichment of bait-specific protein interactors. After immuno-precipitation and highresolution
mass spectrometric analysis, samples were analyzed by comprehensive
statistical and bioinformatics methods. In a semi-automated workflow, 4,197 binary
interactions with 95 baits were identified, and a total of 3,815 interactors showed
dynamic interaction behavior in response to insulin. The study uncovered various
insulin-dependent interactions, and the enrichment of different protein motifs after
insulin stimulation demonstrated a dynamic remodeling of protein interaction
communities. In addition, an insulin-dependent phosphoproteomics screen in brown
adipocytes discovered 2,334 differentially regulated phosphorylation sites, including
sites on 46 bait and 319 prey proteins. A comparative analysis of interaction and
phosphorylation kinetics revealed 2,010 interaction-phosphosite pairs with either
positively or negatively correlating dynamics indicating activating or inhibiting effects
of phosphorylation on protein-protein interactions after insulin stimulation. The
correlation of insulin-dependent interactions and phosphorylation kinetics allowed
the placement of previously unknown proteins within the insulin signaling pathway.
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For example, several bait proteins were strongly associated with cytoskeletal
remodeling and vesicle translocation, including RAI14, SHC3, NCK1, and SH3BP4.
Other overrepresented pathways included candidates involved in fatty acid
metabolism (CERS1), mRNA translocation, and translation (ZC3H11A).
Overall, the workflow presented here can be used to analyze any cellular system after
stimulation and therefore provides an unbiased platform to study protein-protein
interactions. The data collected in this thesis serves as a repository for exploring
insulin-dependent dynamics in brown adipocytes and functionally characterizes
several proteins so far not known to be involved in insulin signaling
Island Distance in One-Dimensional Epitaxial Growth
The typical island distance in submonlayer epitaxial growth depends on
the growth conditions via an exponent . This exponent is known to
depend on the substrate dimensionality, the dimension of the islands, and the
size of the critical nucleus for island formation. In this paper we study
the dependence of on in one--dimensional epitaxial growth. We
derive that for and confirm this result
by computer simulations.Comment: 5 pages, 3 figures, uses revtex, psfig, 'Note added in proof'
appende
Damping of Oscillations in Layer-by-Layer Growth
We present a theory for the damping of layer-by-layer growth oscillations in
molecular beam epitaxy. The surface becomes rough on distances larger than a
layer coherence length which is substantially larger than the diffusion length.
The damping time can be calculated by a comparison of the competing roughening
and smoothening mechanisms. The dependence on the growth conditions,
temperature and deposition rate, is characterized by a power law. The
theoretical results are confirmed by computer simulations.Comment: 19 pages, RevTex, 5 Postscript figures, needs psfig.st
Evaporation and Step Edge Diffusion in MBE
Using kinetic Monte-Carlo simulations of a Solid-on-Solid model we
investigate the influence of step edge diffusion (SED) and evaporation on
Molecular Beam Epitaxy (MBE). Based on these investigations we propose two
strategies to optimize MBE-growth. The strategies are applicable in different
growth regimes: during layer-by-layer growth one can reduce the desorption rate
using a pulsed flux. In three-dimensional (3D) growth the SED can help to grow
large, smooth structures. For this purpose the flux has to be reduced with time
according to a power law.Comment: 5 pages, 2 figures, latex2e (packages: elsevier,psfig,latexsym
Persistence exponents for fluctuating interfaces
Numerical and analytic results for the exponent \theta describing the decay
of the first return probability of an interface to its initial height are
obtained for a large class of linear Langevin equations. The models are
parametrized by the dynamic roughness exponent \beta, with 0 < \beta < 1; for
\beta = 1/2 the time evolution is Markovian. Using simulations of
solid-on-solid models, of the discretized continuum equations as well as of the
associated zero-dimensional stationary Gaussian process, we address two
problems: The return of an initially flat interface, and the return to an
initial state with fully developed steady state roughness. The two problems are
shown to be governed by different exponents. For the steady state case we point
out the equivalence to fractional Brownian motion, which has a return exponent
\theta_S = 1 - \beta. The exponent \theta_0 for the flat initial condition
appears to be nontrivial. We prove that \theta_0 \to \infty for \beta \to 0,
\theta_0 \geq \theta_S for \beta
1/2, and calculate \theta_{0,S} perturbatively to first order in an expansion
around the Markovian case \beta = 1/2. Using the exact result \theta_S = 1 -
\beta, accurate upper and lower bounds on \theta_0 can be derived which show,
in particular, that \theta_0 \geq (1 - \beta)^2/\beta for small \beta.Comment: 12 pages, REVTEX, 6 Postscript figures, needs multicol.sty and
epsf.st
Spatial distribution of persistent sites
We study the distribution of persistent sites (sites unvisited by particles
) in one dimensional reaction-diffusion model. We define
the {\it empty intervals} as the separations between adjacent persistent sites,
and study their size distribution as a function of interval length
and time . The decay of persistence is the process of irreversible
coalescence of these empty intervals, which we study analytically under the
Independent Interval Approximation (IIA). Physical considerations suggest that
the asymptotic solution is given by the dynamic scaling form
with the average interval size . We show
under the IIA that the scaling function as and
decays exponentially at large . The exponent is related to the
persistence exponent through the scaling relation .
We compare these predictions with the results of numerical simulations. We
determine the two-point correlation function under the IIA. We find
that for , where , in agreement
with our earlier numerical results.Comment: 15 pages in RevTeX, 5 postscript figure
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