6,841 research outputs found
Short periodic orbits theory for partially open quantum maps
We extend the semiclassical theory of short periodic orbits [Phys. Rev. E
{\bf 80}, 035202(R) (2009)] to partially open quantum maps. They correspond to
classical maps where the trajectories are partially bounced back due to a
finite reflectivity . These maps are representative of a class that has many
experimental applications. The open scar functions are conveniently redefined,
providing a suitable tool for the investigation of these kind of systems. Our
theory is applied to the paradigmatic partially open tribaker map. We find that
the set of periodic orbits that belong to the classical repeller of the open
map () are able to support the set of long-lived resonances of the
partially open quantum map in a perturbative regime. By including the most
relevant trajectories outside of this set, the validity of the approximation is
extended to a broad range of values. Finally, we identify the details of
the transition from qualitatively open to qualitatively closed behaviour,
providing an explanation in terms of short periodic orbits.Comment: 6 pages, 4 figure
Reaction rate calculation with time-dependent invariant manifolds
The identification of trajectories that contribute to the reaction rate is
the crucial dynamical ingredient in any classical chemical reactivity
calculation. This problem often requires a full scale numerical simulation of
the dynamics, in particular if the reactive system is exposed to the influence
of a heat bath. As an efficient alternative, we propose here to compute
invariant surfaces in the phase space of the reactive system that separate
reactive from nonreactive trajectories. The location of these invariant
manifolds depends both on time and on the realization of the driving force
exerted by the bath. These manifolds allow the identification of reactive
trajectories simply from their initial conditions, without the need of any
further simulation. In this paper, we show how these invariant manifolds can be
calculated, and used in a formally exact reaction rate calculation based on
perturbation theory for any multidimensional potential coupled to a noisy
environment
Phosphonium dicyanamide ionogel incorporating bromophenol blue dye as a versatile platform for monitoring pH in solution
Online monitoring of pH levels in different environments such as bio-engineering and chemistry is vital for effective control of many critical industrial processes. The most common chemical parameter monitored is pH, and there is an increasing interest in the fabrication of robust, cheap and versatile pH sensing materials
that can be easily integrated within existing industrial technologies. Ideally these materials present low fouling and do not require calibration, thus minimising manual attention over long operational intervals. In this work we present an innovative material (ionogel) that integrates pH-sensing capabilities for continuously measuring pH during chemical or biological processes. The ionogel is a solid, flexible and easily to pattern material generated using tetrabutylphosponium dicyanamide ionic liquid, hydrogel polymer (N-isopropylacrylamide and N,N-methylene-bis(acrylamide)) and a pH sensitive dye (Bromophenol Blue). Figure 1 shows the UV spectra of the ionogel-dye in an acidic and a basic pH environment as well as the pictures of the ionogels.
A substantial colour variation is observed as the pH changes that can be monitored visually or optically. We incorporated the photoresponsive dye during photo-polymerisation of the monomer to improve stability, for example, by preventing leaching of the dye from the ionogel into the sample phase. This strategy was not found to inhibit the sensitivity of the optical response
The scar mechanism revisited
Unstable periodic orbits are known to originate scars on some eigenfunctions
of classically chaotic systems through recurrences causing that some part of an
initial distribution of quantum probability in its vicinity returns
periodically close to the initial point. In the energy domain, these
recurrences are seen to accumulate quantum density along the orbit by a
constructive interference mechanism when the appropriate quantization (on the
action of the scarring orbit) is fulfilled. Other quantized phase space
circuits, such as those defined by homoclinic tori, are also important in the
coherent transport of quantum density in chaotic systems. The relationship of
this secondary quantum transport mechanism with the standard mechanism for
scarring is here discussed and analyzed.Comment: 6 pages, 6 figure
The role of short periodic orbits in quantum maps with continuous openings
We apply a recently developed semiclassical theory of short periodic orbits
to the continuously open quantum tribaker map. In this paradigmatic system the
trajectories are partially bounced back according to continuous reflectivity
functions. This is relevant in many situations that include optical
microresonators and more complicated boundary conditions. In a perturbative
regime, the shortest periodic orbits belonging to the classical repeller of the
open map - a cantor set given by a region of exactly zero reflectivity - prove
to be extremely robust in supporting a set of long-lived resonances of the
continuously open quantum maps. Moreover, for step like functions a significant
reduction in the number needed is obtained, similarly to the completely open
situation. This happens despite a strong change in the spectral properties when
compared to the discontinuous reflectivity case.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1604.0181
Real-space study of the growth of magnesium on ruthenium
The growth of magnesium on ruthenium has been studied by low-energy electron
microscopy (LEEM) and scanning tunneling microscopy (STM). In LEEM, a
layer-by-layer growth is observed except in the first monolayer, where the
completion of the first layer in inferred by a clear peak in electron
reflectivity. Desorption from the films is readily observable at 400 K.
Real-space STM and low-energy electron diffraction confirm that sub-monolayer
coverage presents a moir\'e pattern with a 1.2 nm periodicity, which evolves
with further Mg deposition by compressing the Mg layer to a 2.2 nm periodicity.
Layer-by-layer growth is followed in LEEM up to 10 ML. On films several ML
thick a substantial density of stacking faults are observed by dark-field
imaging on large terraces of the substrate, while screw dislocations appear in
the stepped areas. The latter are suggested to result from the mismatch in
heights of the Mg and Ru steps. Quantum size effect oscillations in the
reflected LEEM intensity are observed as a function of thickness, indicating an
abrupt Mg/Ru interface.Comment: 21 pages, 10 figure
Maximum population transfer in a periodically driven two-level system
We study the dynamics of a two-level quantum system under the influence of
sinusoidal driving in the intermediate frequency regime. Analyzing the Floquet
quasienergy spectrum, we find combinations of the field parameters for which
population transfer is optimal and takes place through a series of well defined
steps of fixed duration. We also show how the corresponding evolution operator
can be approximated at all times by a very simple analytical expression. We
propose this model as being specially suitable for treating periodic driving at
avoided crossings found in complex multi-level systems, and thus show a
relevant application of our results to designing a control protocol in a
realistic molecular modelComment: 7 pages, 6 figure
- A COMPUTATIONAL APPROACH TO THE FUNDAMENTAL THEOREM OF ASSET PRICING IN A SINGLE-PERIOD MARKET.
In this paper we provide a new approach to the Fundamental Theorem of As-set Pricing. The proofof this result is usually based on Projection (Separation) Theorems and is far more intuitive. Ourapproach follow the relation between the projection problem an equivalent least squares problem.More precisely, we will use and iterative procedure in order to obtain solutions of a bounded leastsquare problem. This solutions will give, under some conditions, either the state price vector orthe arbitrage opportunity of the problem under consideration.Asset Pricing; Arbitrage; Mathematical Finance
Concept and development of an autonomous wearable micro-fluidic platform for real time pH sweat analysis
In this work the development of an autonomous, robust and wearable micro-fluidic platform capable of performing on-line analysis of pH in sweat is discussed. Through the means of an optical detection system based on a surface mount light emitting diode (SMD LED) and a light photo sensor as a detector, a wearable system was achieved in which real-time monitoring of sweat pH was performed during 55 minutes of cycling activity. We have shown how through systems engineering, integrating miniaturised electrical components, and by improving the micro-fluidic chip characteristics, the wearability, reliability and performance of the micro-fluidic platform was significantly improved
Early forest fire detection by vision-enabled wireless sensor networks
Wireless sensor networks constitute a powerful technology particularly suitable for environmental monitoring. With regard to wildfires, they enable low-cost fine-grained surveillance of hazardous locations like wildland-urban interfaces. This paper presents work developed during the last 4 years targeting a vision-enabled wireless sensor network node for the reliable, early on-site detection of forest fires. The tasks carried out ranged from devising a robust vision algorithm for smoke detection to the design and physical implementation of a power-efficient smart imager tailored to the characteristics of such an algorithm. By integrating this smart imager with a commercial wireless platform, we endowed the resulting system with vision capabilities and radio communication. Numerous tests were arranged in different natural scenarios in order to progressively tune all the parameters involved in the autonomous operation of this prototype node. The last test carried out, involving the prescribed burning of a 95 x 20-m shrub plot, confirmed the high degree of reliability of our approach in terms of both successful early detection and a very low false-alarm rate. Journal compilationMinisterio de Ciencia e Innovación TEC2009-11812, IPT-2011-1625-430000Office of Naval Research (USA) N000141110312Centro para el Desarrollo Tecnológico e Industrial IPC-2011100
- …