346 research outputs found
A Functional Limit Theorem for Limit Order Books with State Dependent Price Dynamics
We consider a stochastic model for the dynamics of the two-sided limit order
book (LOB). Our model is flexible enough to allow for a dependence of the price
dynamics on volumes. For the joint dynamics of best bid and ask prices and the
standing buy and sell volume densities, we derive a functional limit theorem,
which states that our LOB model converges in distribution to a fully coupled
SDE-SPDE system when the order arrival rates tend to infinity and the impact of
an individual order arrival on the book as well as the tick size tends to zero.
The SDE describes the bid/ask price dynamics while the SPDE describes the
volume dynamics.Comment: 43 page
A functional limit theorem for limit order books
We consider a stochastic model for the dynamics of the two-sided limit order book (LOB). For the joint dynamics of best bid and ask prices and the standing buy and sell volume densities, we derive a functional limit theorem, which states that our LOB model converges to a continuous-time limit when the order arrival rates tend to infinity, the impact of an individual order arrival on the book as well as the tick size tend to zero. The limits of the standing buy and sell volume densities are described by two linear stochastic partial differential equations, which are coupled with a two-dimensional reflected Brownian motion that is the limit of the best bid and ask price processes
Four-wave mixing in coupled semiconductor quantum dots
We present a theoretical analysis of four-wave mixing in coupled quantum dots
subject to inhomogeneous broadening. For the biexciton transitions a clear
signature of interdot-coupling appears in the spectra. The possibility of
experimental observation is discussed
Correlated Photon-Pair Emission from a Charged Single Quantum Dot
The optical creation and recombination of charged biexciton and trion
complexes in an (In,Ga)As/GaAs quantum dot is investigated by
micro-photoluminescence spectroscopy. Photon cross-correlation measurements
demonstrate the temporally correlated decay of charged biexciton and trion
states. Our calculations provide strong evidence for radiative decay from the
excited trion state which allows for a deeper insight into the spin
configurations and their dynamics in these systems.Comment: 5 pages, 3 figures, submitted for publicatio
Practical Attacks Against Graph-based Clustering
Graph modeling allows numerous security problems to be tackled in a general
way, however, little work has been done to understand their ability to
withstand adversarial attacks. We design and evaluate two novel graph attacks
against a state-of-the-art network-level, graph-based detection system. Our
work highlights areas in adversarial machine learning that have not yet been
addressed, specifically: graph-based clustering techniques, and a global
feature space where realistic attackers without perfect knowledge must be
accounted for (by the defenders) in order to be practical. Even though less
informed attackers can evade graph clustering with low cost, we show that some
practical defenses are possible.Comment: ACM CCS 201
Massive creation of entangled exciton states in semiconductor quantum dots
An intense laser pulse propagating in a medium of inhomogeneously broadened
quantum dots massively creates entangled exciton states. After passage of the
pulse all single-exciton states remain unpopulated (self-induced transparency)
whereas biexciton coherence (exciton entanglement) is generated through
two-photon transitions. We propose several experimental techniques for the
observation of such unexpected behavior
Non-resonant dot-cavity coupling and its applications in resonant quantum dot spectroscopy
We present experimental investigations on the non-resonant dot-cavity
coupling of a single quantum dot inside a micro-pillar where the dot has been
resonantly excited in the s-shell, thereby avoiding the generation of
additional charges in the QD and its surrounding. As a direct proof of the pure
single dot-cavity system, strong photon anti-bunching is consistently observed
in the autocorrelation functions of the QD and the mode emission, as well as in
the cross-correlation function between the dot and mode signals. Strong Stokes
and anti-Stokes-like emission is observed for energetic QD-mode detunings of up
to ~100 times the QD linewidth. Furthermore, we demonstrate that non-resonant
dot-cavity coupling can be utilized to directly monitor and study relevant QD
s-shell properties like fine-structure splittings, emission saturation and
power broadening, as well as photon statistics with negligible background
contributions. Our results open a new perspective on the understanding and
implementation of dot-cavity systems for single-photon sources, single and
multiple quantum dot lasers, semiconductor cavity quantum electrodynamics, and
their implementation, e.g. in quantum information technology.Comment: 17 pages, 4 figure
Multiple CaMKII Binding Modes to the Actin Cytoskeleton Revealed by Single-Molecule Imaging.
Localization of the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) to dendritic spine synapses is determined in part by the actin cytoskeleton. We determined binding of GFP-tagged CaMKII to tag-RFP-labeled actin cytoskeleton within live cells using total internal reflection fluorescence microscopy and single-molecule tracking. Stepwise photobleaching showed that CaMKII formed oligomeric complexes. Photoactivation experiments demonstrated that diffusion out of the evanescent field determined the track lifetimes. Latrunculin treatment triggered a coupled loss of actin stress fibers and the colocalized, long-lived CaMKII tracks. The CaMKIIα (α) isoform, which was previously thought to lack F-actin interactions, also showed binding, but this was threefold weaker than that observed for CaMKIIβ (β). The βE' splice variant bound more weakly than α, showing that binding by β depends critically on the interdomain linker. The mutations βT287D and αT286D, which mimic autophosphorylation states, also abolished F-actin binding. Autophosphorylation triggers autonomous CaMKII activity, but does not impair GluN2B binding, another important synaptic protein interaction of CaMKII. The CaMKII inhibitor tatCN21 or CaMKII mutations that inhibit GluN2B association by blocking binding of ATP (βK43R and αK42M) or Ca(2+)/calmodulin (βA303R) had no effect on the interaction with F-actin. These results provide the first rationale for the reduced synaptic spine localization of the αT286D mutant, indicating that transient F-actin binding contributes to the synaptic localization of the CaMKIIα isoform. The track lifetime distributions had a stretched exponential form consistent with a heterogeneously diffusing population. This heterogeneity suggests that CaMKII adopts different F-actin binding modes, which is most easily rationalized by multiple subunit contacts between the CaMKII dodecamer and the F-actin cytoskeleton that stabilize the initial weak (micromolar) monovalent interaction
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