452 research outputs found
A Gillespie algorithm for efficient simulation of quantum jump trajectories
The jump unravelling of a quantum master equation decomposes the dynamics of
an open quantum system into abrupt jumps, interspersed by periods of coherent
dynamics where no jumps occur. Simulating these jump trajectories is
computationally expensive, as it requires very small time steps to ensure
convergence. This computational challenge is aggravated in regimes where the
coherent, Hamiltonian dynamics are fast compared to the dissipative dynamics
responsible for the jumps. Here, we present a quantum version of the Gillespie
algorithm that bypasses this issue by directly constructing the waiting time
distribution for the next jump to occur. In effect, this avoids the need for
timestep discretisation altogether, instead evolving the system continuously
from one jump to the next. We describe the algorithm in detail and discuss
relevant limiting cases. To illustrate it we include four example applications
of increasing physical complexity. These additionally serve to compare the
performance of the algorithm to alternative approaches -- namely, the
widely-used routines contained in the powerful Python library QuTip. We find
significant gains in efficiency for our algorithm and discuss in which regimes
these are most pronounced. Publicly available implementations of our code are
provided in Julia and Mathematica.Comment: 13 pages, 4 figures. Comments welcom
Economic efficiency of mobile latent heat storages
In a pilot project an optimized mobile latent heat storage based on a system available on the market has been tested at Fraunhofer Institute for Environmental, Safety and Energy Technology. Initially trials were conducted with the aim of optimizing the process of charging and discharging. A specifically constructed test rig at the incineration trials centre at the institute allowed charging and discharging procedures of the mobile latent heat storage with adjustable parameters. In addition an evaluation model was constructed to further optimize the heat exchanger systems. In conclusion the prototype of the mobile latent heat storage was tested in practical operation. The economic and technical feasibility of heat transportation was shown if not utilized waste heat is available
Dynamically Triangulated Ising Spins in Flat Space
A model describing Ising spins with short range interactions moving randomly
in a plane is considered. In the presence of a hard core repulsion, which
prevents the Ising spins from overlapping, the model is analogous to a
dynamically triangulated Ising model with spins constrained to move on a flat
surface. It is found that as a function of coupling strength and hard core
repulsion the model exhibits multicritical behavior, with first and second
order transition lines terminating at a tricritical point. The thermal and
magnetic exponents computed at the tricritical point are consistent with the
exact two-matrix model solution of the random Ising model, introduced
previously to describe the effects of fluctuating geometries.Comment: (10 pages + 4 figures), CERN-Th-7577/9
Modification of spintronic terahertz emitter performance through defect engineering
Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for
the generation of THz radiation based on spin-to-charge conversion in the
layers. The key technological and scientific challenge of THz spintronic
emitters is to increase their intensity and frequency bandwidth. Our work
reveals the factors to engineer spintronic Terahertz generation by introducing
the scattering lifetime and the interface transmission for spin polarized,
non-equilibrium electrons. We clarify the influence of the electron-defect
scattering lifetime on the spectral shape and the interface transmission on the
THz amplitude, and how this is linked to structural defects of bilayer
emitters. The results of our study define a roadmap of the properties of
emitted as well as detected THz-pulse shapes and spectra that is essential for
future applications of metallic spintronic THz emitters.Comment: 33 pages, 13 figure
Tempering simulations in the four dimensional +-J Ising spin glass in a magnetic field
We study the four dimensional (4D) Ising spin glass in a magnetic
field by using the simulated tempering method recently introduced by Marinari
and Parisi. We compute numerically the first four moments of the order
parameter probability distribution . We find a finite cusp in the
spin-glass susceptibility and strong tendency to paramagnetic ordering at low
temperatures. Assuming a well defined transition we are able to bound its
critical temperature.Comment: 6 Pages including 5 figures, Revte
Stochastic metrology and the empirical distribution
We study the problem of parameter estimation in time series stemming from
general stochastic processes, where the outcomes may exhibit arbitrary temporal
correlations. In particular, we address the question of how much Fisher
information is lost if the stochastic process is compressed into a single
histogram, known as the empirical distribution. As we show, the answer is
non-trivial due to the correlations between outcomes. We derive practical
formulas for the resulting Fisher information for various scenarios, from
generic stationary processes to discrete-time Markov chains to continuous-time
classical master equations. The results are illustrated with several examples.Comment: 16 pages, 8 figures, 1 tabl
A Coupled Mathematical Model of the Intracellular Replication of Dengue Virus and the Host Cell Immune Response to Infection
Dengue virus (DV) is a positive-strand RNA virus of the Flavivirus genus. It is one of the most prevalent mosquito-borne viruses, infecting globally 390 million individuals per year. The clinical spectrum of DV infection ranges from an asymptomatic course to severe complications such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), the latter because of severe plasma leakage. Given that the outcome of infection is likely determined by the kinetics of viral replication and the antiviral host cell immune response (HIR) it is of importance to understand the interaction between these two parameters. In this study, we use mathematical modeling to characterize and understand the complex interplay between intracellular DV replication and the host cells' defense mechanisms. We first measured viral RNA, viral protein, and virus particle production in Huh7 cells, which exhibit a notoriously weak intrinsic antiviral response. Based on these measurements, we developed a detailed intracellular DV replication model. We then measured replication in IFN competent A549 cells and used this data to couple the replication model with a model describing IFN activation and production of IFN stimulated genes (ISGs), as well as their interplay with DV replication. By comparing the cell line specific DV replication, we found that host factors involved in replication complex formation and virus particle production are crucial for replication efficiency. Regarding possible modes of action of the HIR, our model fits suggest that the HIR mainly affects DV RNA translation initiation, cytosolic DV RNA degradation, and naïve cell infection. We further analyzed the potential of direct acting antiviral drugs targeting different processes of the DV lifecycle in silico and found that targeting RNA synthesis and virus assembly and release are the most promising anti-DV drug targets
Critical Slowing Down of Cluster Algorithms for Ising Models Coupled to 2-d Gravity
We simulate single and multiple Ising models coupled to 2-d gravity using
both the Swendsen-Wang and Wolff algorithms to update the spins. We study the
integrated autocorrelation time and find that there is considerable critical
slowing down, particularly in the magnetization. We argue that this is
primarily due to the local nature of the dynamical triangulation algorithm and
to the generation of a distribution of baby universes which inhibits cluster
growth.Comment: 7 pages including 5 postscript figures, epsf.sty late
Topology and phase transitions: a paradigmatic evidence
We report upon the numerical computation of the Euler characteristic \chi (a
topologic invariant) of the equipotential hypersurfaces \Sigma_v of the
configuration space of the two-dimensional lattice model. The pattern
\chi(\Sigma_v) vs. v (potential energy) reveals that a major topology change in
the family {\Sigma_v}_{v\in R} is at the origin of the phase transition in the
model considered. The direct evidence given here - of the relevance of topology
for phase transitions - is obtained through a general method that can be
applied to any other model.Comment: 4 pages, 4 figure
Type I and type II interferon responses in two human liver cell lines (Huh-7 and HuH6)
AbstractMost studies investigating the biology of Hepatitis C virus (HCV) have used the human hepatoma cell line Huh-7 or subclones thereof, as these are the most permissive cell lines for HCV infection and replication. Other cell lines also support replication of HCV, most notably the human hepatoblastoma cell line HuH6. HCV replication in cell culture is generally highly sensitive to interferons (IFNs) and differences in the IFN-mediated inhibition of virus replication may reflect alterations in the IFN-induced antiviral response inherent to different host cells. For example, HCV replication is highly sensitive to IFN-γ treatment in Huh-7, but not in HuH6 cells. In this study, we used microarray-based gene expression profiling to compare the response of Huh-7 and HuH6 cells to stimulation with IFN-α and IFN-γ. Furthermore, we determined whether the resistance of HCV replication in HuH6 cells can be linked to differences in the expression profile of IFN-regulated genes. Although both cells lines responded to IFNs with rapid changes in gene expression, thereby demonstrating functional type I and type II signaling pathways, differences were observed for a number of genes. Raw and normalized expression data have been deposited in GEO under accession number GSE68927
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