83 research outputs found
Ultra-Fast Relaxation, Decoherence and Localization of Photoexcited States in -Conjugated Polymers: A TEBD Study
The exciton relaxation dynamics of photoexcited electronic states in
poly(-phenylenevinylene) (PPV) are theoretically investigated within a
coarse-grained model, in which both the exciton and nuclear degrees of freedom
are treated quantum mechanically. The Frenkel-Holstein Hamiltonian is used to
describe the strong exciton-phonon coupling present in the system, while
external damping of the internal nuclear degrees of freedom are accounted for
by a Lindblad master equation. Numerically, the dynamics are computed using the
time evolving block decimation (TEBD) and quantum jump trajectory techniques.
The values of the model parameters physically relevant to polymer systems
naturally lead to a separation of time scales, with the ultra-fast dynamics
corresponding to energy transfer from the exciton to the internal phonon modes
(i.e., the C-C bond oscillations), while the longer time dynamics correspond to
damping of these phonon modes by the external dissipation. Associated with
these time scales, we investigate the following processes that are indicative
of the system relaxing onto the emissive chromophores of the polymer: 1)
Exciton-polaron formation occurs on an ultra-fast time scale, with the
associated exciton-phonon correlations present within half a vibrational time
period of the C-C bond oscillations. 2) Exciton decoherence is driven by the
decay in the vibrational overlaps associated with exciton-polaron formation,
occurring on the same time scale. 3) Exciton density localization is driven by
the external dissipation, arising from `wavefunction collapse' occurring as a
result of the system-environment interactions. Finally, we show how
fluorescence anisotropy measurements can be used to investigate the exciton
decoherence process during the relaxation dynamics.Comment: 16 pages, 15 figure
Ultracold atoms in an optical lattice with dynamically variable periodicity
The use of a dynamic "accordion" lattice with ultracold atoms is
demonstrated. Ultracold atoms of Rb are trapped in a two-dimensional
optical lattice, and the spacing of the lattice is then increased in both
directions from 2.2 to 5.5 microns. Atoms remain bound for expansion times as
short as a few milliseconds, and the experimentally measured minimum ramp time
is found to agree well with numerical calculations. This technique allows an
experiment such as quantum simulations to be performed with a lattice spacing
smaller than the resolution limit of the imaging system, while allowing imaging
of the atoms at individual lattice sites by subsequent expansion of the optical
lattice.Comment: 4 pages, 3 figures. Minor changes made and references update
Observation of vortex nucleation in a rotating two-dimensional lattice of Bose-Einstein condensates
We report the observation of vortex nucleation in a rotating optical lattice.
A 87Rb Bose-Einstein condensate was loaded into a static two-dimensional
lattice and the rotation frequency of the lattice was then increased from zero.
We studied how vortex nucleation depended on optical lattice depth and rotation
frequency. For deep lattices above the chemical potential of the condensate we
observed a linear dependence of the number of vortices created with the
rotation frequency,even below the thermodynamic critical frequency required for
vortex nucleation. At these lattice depths the system formed an array of
Josephson-coupled condensates. The effective magnetic field produced by
rotation introduced characteristic relative phases between neighbouring
condensates, such that vortices were observed upon ramping down the lattice
depth and recombining the condensates.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let
Automatic pelvis segmentation from x-ray images of a mouse model
The automatic detection and quantification of skeletal structures has a variety of different applications for biological research. Accurate segmentation of the pelvis from X-ray images of mice in a high-throughput project such as the Mouse Genomes Project not only saves time and cost but also helps achieving an unbiased quantitative analysis within the phenotyping pipeline. This paper proposes an automatic solution for pelvis segmentation based on structural and orientation properties of the pelvis in X-ray images. The solution consists of three stages including pre-processing image to extract pelvis area, initial pelvis mask preparation and final pelvis segmentation. Experimental results on a set of 100 X-ray images showed consistent performance of the algorithm. The automated solution overcomes the weaknesses of a manual annotation procedure where intra- and inter-observer variations cannot be avoided
Automatic Spine Curvature Estimation from X-ray Images of a Mouse Model
Automatic segmentation and quantification of skeletal structures has a variety of applications for biological research. Although solutions for good quality X-ray images of human skeletal structures are in existence in recent years, automatic solutions working on poor quality X-ray images of mice are rare. This paper proposes a fully automatic solution for spine segmentation and curvature quantification from X-ray images of mice. The proposed solution consists of three stages, namely preparation of the region of interest, spine segmentation, and spine curvature quantification, aiming to overcome technical difficulties in processing the X-ray images. We examined six different automatic measurements for quantifying the spine curvature through tests on a sample data set of 100 images. The experimental results show that some of the automatic measures are very close to and consistent with the best manual measurement results by annotators. The test results also demonstrate the effectiveness of the curvature quantification produced by the proposed solution in distinguishing abnormally shaped spines from the normal ones with accuracy up to 98.6%
Heat transport in the spin chain: from ballistic to diffusive regimes and dephasing enhancement
In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain
with homogeneous magnetic field, incoherently driven out of equilibrium by
reservoirs at the boundaries. We focus on the effect of bulk dephasing
(energy-dissipative) processes in different parameter regimes of the system.
The non-equilibrium steady state of the chain is obtained by simulating its
evolution under the corresponding Lindblad master equation, using the time
evolving block decimation method. In the absence of dephasing, the heat
transport is ballistic for weak interactions, while being diffusive in the
strongly-interacting regime, as evidenced by the heat-current scaling with the
system size. When bulk dephasing takes place in the system, diffusive transport
is induced in the weakly-interacting regime, with the heat current
monotonically decreasing with the dephasing rate. In contrast, in the
strongly-interacting regime, the heat current can be significantly enhanced by
dephasing for systems of small size
On the Discrimination Power of Dynamic Features for Online Signature
The mobile market has taken huge leap in the last
two decades, re-defining the rules of communication, networking, socializing and transactions among individuals and organizations.
Authentication based on verification of signature on mobile
devices, is slowly gaining popularity. Most online signature verification algorithms focus on computing the global Equal Error Rate across all users for a dataset. In this work, contrary to such a representation, it is shown that there are user-specific differences on the combined features and user-specific differences on each feature of the Equal Error Rate(EER) values. The experiments to test the hypothesis is carried out on the two publicly available dataset using the dynamic time warping algorithm. From the experiments, it is observed that for the MCYT-100 dataset, which yields an overall EER of 0.08, the range of user-specific EER is between 0 and 0.27
oBiometrics: A Software protection scheme using biometric-based obfuscation
This paper proposes to integrate biometric-based key generation into an obfuscated interpretation algorithm to protect authentication application software from illegitimate use or reverse-engineering. This is especially necessary for mCommerce because application programmes on mobile devices, such as Smartphones and Tablet-PCs are typically open for misuse by hackers. Therefore, the scheme proposed in this paper ensures that a correct interpretation / execution of the obfuscated program code of the authentication application requires a valid biometric generated key of the actual person to be authenticated, in real-time. Without this key, the real semantics of the program can not be understood by an attacker even if he/she gains access to this application code. Furthermore, the security provided by this scheme can be a vital aspect in protecting any application running on mobile devices that are increasingly used to perform business/financial or other security related applications, but are easily lost or stolen. The scheme starts by creating a personalised copy of any application based on the biometric key generated during an enrolment process with the authenticator as well as a nuance created at the time of communication between the client and the authenticator. The obfuscated code is then shipped to the client’s mobile devise and integrated with real-time biometric extracted data of the client to form the unlocking key during execution. The novelty of this scheme is achieved by the close binding of this application program to the biometric key of the client, thus making this application unusable for others. Trials and experimental results on biometric key generation, based on client's faces, and an implemented scheme prototype, based on the Android emulator, prove the concept and novelty of this proposed scheme
Topological pumping of photons in nonlinear resonator arrays
We show how to implement topological or Thouless pumping of interacting
photons in one dimensional nonlinear resonator arrays, by simply modulating the
frequency of the resonators periodically in space and time. The interplay
between interactions and the adiabatic modulations enables robust transport of
Fock states with few photons per site. We analyze the transport mechanism via
an effective analytic model and study its topological properties and its
protection to noise. We conclude by a detailed study of an implementation with
existing circuit QED architectures.Comment: 5 pages, 4 figures, and Supplemental Material. Comments are welcom
The Tensor Network Theory
In this technical paper we introduce the Tensor Network Theory (TNT) library - an open-source software project aimed at developing robust, easy to use and highly optimised code for TNT calculations, available at http://www.tensornetworktheory.org. The aims of this paper are threefold: to (i) give a brief but broad introduction to TNT, (ii) give an overview of the structure of TNT library, and (iii) describe in detail the core tensor features of the library
- …