23,572 research outputs found
Effect of many modes on self-polarization and photochemical suppression in cavities
The standard description of cavity-modified molecular reactions typically involves a single (resonant) mode, while in reality, the quantum cavity supports a range of photon modes. Here, we demonstrate that as more photon modes are accounted for, physicochemical phenomena can dramatically change, as illustrated by the cavity-induced suppression of the important and ubiquitous process of proton-coupled electron-transfer. Using a multi-trajectory Ehrenfest treatment for the photon-modes, we find that self-polarization effects become essential, and we introduce the concept of self-polarization-modified Born–Oppenheimer surfaces as a new construct to analyze dynamics. As the number of cavity photon modes increases, the increasing deviation of these surfaces from the cavity-free Born–Oppenheimer surfaces, together with the interplay between photon emission and absorption inside the widening bands of these surfaces, leads to enhanced suppression. The present findings are general and will have implications for the description and control of cavity-driven physical processes of molecules, nanostructures, and solids embedded in cavities
Stochastic analysis of ocean wave states with and without rogue waves
This work presents an analysis of ocean wave data including rogue waves. A
stochastic approach based on the theory of Markov processes is applied. With
this analysis we achieve a characterization of the scale dependent complexity
of ocean waves by means of a Fokker-Planck equation, providing stochastic
information of multi-scale processes. In particular we show evidence of Markov
properties for increment processes, which means that a three point closure for
the complexity of the wave structures seems to be valid. Furthermore we
estimate the parameters of the Fokker-Planck equation by parameter-free data
analysis. The resulting Fokker-Planck equations are verified by numerical
reconstruction. This work presents a new approach where the coherent structure
of rogue waves seems to be integrated into the fundamental statistics of
complex wave states.Comment: 18 pages, 13 figure
Dark solitons, modulation instability and breathers in a chain of weakly non-linear oscillators with cyclic symmetry
In the aerospace industry the trend for light-weight structures and the
resulting complex dynamic behaviours currently challenge vibration engineers.
In many cases, these light-weight structures deviate from linear behaviour, and
complex nonlinear phenomena can be expected. We consider a cyclically symmetric
system of coupled weakly nonlinear undamped oscillators that could be
considered a minimal model for different cyclic and symmetric aerospace
structures experiencing large deformations. The focus is on localised
vibrations that arise from wave envelope modulation of travelling waves. For
the defocussing parameter range of the approximative nonlinear evolution
equation, we show the possible existence of dark solitons and discuss their
characteristics. For the focussing parameter range, we characterise modulation
instability and illustrate corresponding nonlinear breather dynamics.
Furthermore, we show that for stronger nonlinearity or randomness in initial
conditions, transient breather-type dynamics and decay into bright solitons
appear. The findings suggest that significant vibration localisation may arise
due to mechanisms of nonlinear modulation dynamics
Super rogue waves in simulations based on weakly nonlinear and fully nonlinear hydrodynamic equations
The rogue wave solutions (rational multi-breathers) of the nonlinear
Schrodinger equation (NLS) are tested in numerical simulations of weakly
nonlinear and fully nonlinear hydrodynamic equations. Only the lowest order
solutions from 1 to 5 are considered. A higher accuracy of wave propagation in
space is reached using the modified NLS equation (MNLS) also known as the
Dysthe equation. This numerical modelling allowed us to directly compare
simulations with recent results of laboratory measurements in
\cite{Chabchoub2012c}. In order to achieve even higher physical accuracy, we
employed fully nonlinear simulations of potential Euler equations. These
simulations provided us with basic characteristics of long time evolution of
rational solutions of the NLS equation in the case of near breaking conditions.
The analytic NLS solutions are found to describe the actual wave dynamics of
steep waves reasonably well.Comment: under revision in Physical Review
Multistability and localization in forced cyclic symmetric structures modelled by weakly-coupled Duffing oscillators
Many engineering structures are composed of weakly coupled sectors assembled
in a cyclic and ideally symmetric configuration, which can be simplified as
forced Duffing oscillators. In this paper, we study the emergence of localized
states in the weakly nonlinear regime. We show that multiple spatially
localized solutions may exist, and the resulting bifurcation diagram strongly
resembles the snaking pattern observed in a variety of fields in physics, such
as optics and fluid dynamics. Moreover, in the transition from the linear to
the nonlinear behaviour isolated branches of solutions are identified.
Localization is caused by the hardening effect introduced by the nonlinear
stiffness, and occurs at large excitation levels. Contrary to the case of
mistuning, the presented localization mechanism is triggered by the
nonlinearities and arises in perfectly homogeneous systems
Non-LTE models for synthetic spectra of type Ia supernovae. III. An accelerated lambda iteration procedure for the mutual interaction of strong spectral lines in SN Ia models with and without energy deposition
Context. Spectroscopic analyses to interpret the spectra of the brightest
supernovae from the UV to the near-IR provide a powerful tool with great
astrophysical potential for the determination of the physical state of the
ejecta, their chemical composition, and the SNe distances even at significant
redshifts.
Methods. We report on improvements of computing synthetic spectra for SNIa
with respect to i) an improved and sophisticated treatment of thousands of
strong lines that interact intricately with the "pseudo-continuum" formed
entirely by Doppler- shifted spectral lines, ii) an improved and expanded
atomic database, and iii) the inclusion of energy deposition within the ejecta.
Results. We show that an accelerated lambda iteration procedure we have
developed for the mutual interaction of strong spectral lines appearing in the
atmospheres of SNeIa solves the longstanding problem of transferring the
radiative energy from the UV into the optical regime. In detail we discuss
applications of the diagnostic technique by example of a standard SNIa, where
the comparison of calculated and observed spectra revealed that in the early
phases the consideration of the energy deposition within the spectrum-forming
regions of the ejecta does not qualitatively alter the shape of the spectra.
Conclusions. The results of our investigation lead to an improved
understanding of how the shape of the spectrum changes radically as function of
depth in the ejecta, and show how different emergent spectra are formed as a
result of the particular physical properties of SNe Ia ejecta and the resulting
peculiarities in the radiative transfer. This provides an important insight
into the process of extracting information from observed SNIa spectra, since
these spectra are a complex product of numerous unobservable SNIa spectral
features which are thus analyzed in parallel to the observable spectral
features.Comment: 27 pages, 19 figures. Submitted to A&A, revised versio
Quantum-dot thermometry
We present a method for the measurement of a temperature differential across
a single quantum dot that has transmission resonances that are separated in
energy by much more than the thermal energy. We determine numerically that the
method is accurate to within a few percent across a wide range of parameters.
The proposed method measures the temperature of the electrons that enter the
quantum dot and will be useful in experiments that aim to test theory which
predicts quantum dots are highly-efficient thermoelectrics.Comment: 3 pages, 4 Figure
Aspirations as reference points: an experimental investigation of risk behavior over time
This paper examines the importance of aspirations as reference points in a multi-period decision-making context. After stating their personal aspiration level, 172 individuals made six sequential decisions among risky prospects as part of a choice experiment. The results show that individuals make different risky-choices in a multi-period compared to a single-period setting. In particular, individuals’ aspiration level is their main reference point during the early stages of decision-making, while their starting status (wealth level at the start of the experiment) becomes the central reference point during the later stages of their multi-period decision-making.Arvid O. I. Hoffmann; Sam F. Henry; Nikos Kalogera
Exploiting Macro-actions and Predicting Plan Length in Planning as Satisfiability
The use of automatically learned knowledge for a planning domain can significantly improve the performance of a generic planner when solving a problem in this domain. In this work, we focus on the well-known SAT-based approach to planning and investigate two types of learned knowledge that have not been studied in this planning framework before: macro-actions and planning horizon. Macro-actions are sequences of actions that typically occur in the solution plans, while a planning horizon of a problem is the length of a (possibly optimal) plan solving it. We propose a method that uses a machine learning tool for building a predictive model of the optimal planning horizon, and variants of the well-known planner SatPlan and solver MiniSat that can exploit macro actions
and learned planning horizons to improve their performance. An experimental analysis illustrates the effectiveness of the proposed techniques
Lineshape of the thermopower of quantum dots
Quantum dots are an important model system for thermoelectric phenomena, and
may be used to enhance the thermal-to-electric energy conversion efficiency in
functional materials. It is therefore important to obtain a detailed
understanding of a quantum-dot's thermopower as a function of the Fermi energy.
However, so far it has proven difficult to take effects of co-tunnelling into
account in the interpretation of experimental data. Here we show that a
single-electron tunnelling model, using knowledge of the dot's electrical
conductance which in fact includes all-order co-tunneling effects, predicts the
thermopower of quantum dots as a function of the relevant energy scales, in
very good agreement with experiment.Comment: 10 pages, 5 figure
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