7,675 research outputs found
Performance of the coupled cluster singles and doubles method on two-dimensional quantum dots
An implementation of the coupled-cluster single- and double excitations
(CCSD) method on two-dimensional quantum dots is presented. Advantages and
limitations are studied through comparison with other high accuracy approaches
for two to eight confined electrons. The possibility to effectively use a very
large basis set is found to be an important advantage compared to full
configuration interaction implementations. For the two to eight electron ground
states, with a confinement strength close to what is used in experiments, the
error in the energy introduced by truncating triple excitations and beyond is
shown to be on the same level or less than the differences in energy given by
two different Quantum Monte Carlo methods. Convergence of the iterative
solution of the coupled cluster equations is, for some cases, found for
surprisingly weak confinement strengths even when starting from a
non-interacting basis. The limit where the missing triple and higher
excitations become relevant is investigated through comparison with full
Configuration Interaction results.Comment: 11 pages, 1 figure, 5 table
Effects of screened Coulomb impurities on autoionizing two-electron resonances in spherical quantum dots
In a recent paper (Phys. Rev. B {\bf 78}, 075316 (2008)), Sajeev and Moiseyev
demonstrated that the bound-to-resonant transitions and lifetimes of
autoionizing states in spherical quantum dots can be controlled by varying the
confinment strength. In the present paper, we report that such control can in
some cases be compromised by the presence of Coulomb impurities. It is
demonstrated that a screened Coulomb impurity placed in the vicinity of the dot
center can lead to bound-to-resonant transitions and to avoided crossings-like
behavior when the screening of the impurity charge is varied. It is argued that
these properties also can have impact on electron transport through quantum dot
arrays
Amy Sternberg’s Historical Pageant (1927): The Performance of IODE Ideology during Canada’s Diamond Jubilee
In 1927, sixty-five chapters of the Imperial Order Daughters of the Empire (IODE) staged Amy Sternberg’s Historical Pageant in Toronto to celebrate Canada’s Diamond Jubilee. Accessing primary source documentation, this article argues that Sternberg’s production constructed and conveyed IODE ideology by placing female agency in the service of liberal imperialism. Specifically, the female allegorical and historical characters in the pageant provide an index of values that emphasized the role of women in creating a strong Canada closely aligned with a venerated British Empire. Beyond the script and the stage, the program for the production and press clippings suggest that the IODE used Historical Pageant to promote itself as a modern organization in which female leadership fostered civically engaged action while simultaneously and subtly re-inscribing the traditional hierarchical social structure of the British Empire within Canada. In these ways, Historical Pageant reminds historians of the necessity to consider how theatre has been used by Canadian women to assert their political views publicly even when those views espouse ideology that is no longer acceptable.
Résumé
En 1927, soixante-cinq sections locales de l’Ordre impérial des filles de l’Empire (IODE) ont mis en scène le Historical Pageant de Amy Sternberg à Toronto pour célébrer le jubilé de diamant du Canada. Dans cet article, l’auteure fait valoir, à partir de références documentaires de première main, que le défilé historique de Steinberg a servi à construire et à communiquer l’idéologie de l’IODE en mettant l’action des femmes au service de l’impérialisme libéral. Plus précisément, les personnages allégoriques et historiques de sexe féminin mis en scène dans la production constituent un répertoire de valeurs qui met l’accent sur le rôle des femmes dans la création d’un Canada fort, en conformité avec le vénérable Empire britannique. Au-delà du scénario et de la mise en scène, le programme de la pièce et les articles parus dans les journaux laissent entendre que l’IODE s’est servi du Historical Pageant afin de se promouvoir en tant qu’organisme moderne au sein duquel les leaders de sexe féminin invitaient la population à l’engagement civique tout en reproduisant subtilement la hiérarchie sociale traditionnelle de l’Empire britannique au Canada. Ainsi, le Historical Pageant rappelle aux historiens qu’il faut voir comment les Canadiennes se sont servies du théâtre pour affirmer publiquement leurs opinions politiques, même quand ces dernières endossent une idéologie devenue désuète
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Simple devices for concentration of microbial life: Experiments in Haughton impact structure
Simple devices that create environments with high levels of light and moisture could attract extant microbial life on a planetary surface and hence enhance the detection of it. Experience in the Haughton crater shows that this can occur readily
Dynamic Response of a fast near infra-red Mueller matrix ellipsometer
The dynamic response of a near infrared Ferroelectric Liquid Crystal based
Mueller matrix ellipsometer (NIR FLC-MME) is presented. A time dependent
simulation model, using the measured time response of the individual FLCs, is
used to describe the measured temporal response. Furthermore, the impulse
response of the detector and the pre-amplifier is characterized and included in
the simulation model. The measured time-dependent intensity response of the MME
is reproduced in simulations, and it is concluded that the switching time of
the FLCs is the limiting factor for the Mueller matrix measurement time of the
FLC-based MME. Based on measurements and simulations our FLC based NIR-MME
system is estimated to operate at the maximum speed of approximately 16 ms per
Mueller matrix measurement. The FLC-MME may be operated several times faster,
since the switching time of the crystals depends on the individual crystal
being switched, and to what state it is switched. As a demonstration, the
measured temporal response of the Mueller matrix and the retardance of a thick
liquid crystal variable retarder upon changing state is demonstrated.Comment: to be published in Journal of Modern Optics 20 pages, 6 figure
A streamwise-constant model of turbulent pipe flow
A streamwise-constant model is presented to investigate the basic mechanisms
responsible for the change in mean flow occuring during pipe flow transition.
Using a single forced momentum balance equation, we show that the shape of the
velocity profile is robust to changes in the forcing profile and that both
linear non-normal and nonlinear effects are required to capture the change in
mean flow associated with transition to turbulence. The particularly simple
form of the model allows for the study of the momentum transfer directly by
inspection of the equations. The distribution of the high- and low-speed
streaks over the cross-section of the pipe produced by our model is remarkably
similar to one observed in the velocity field near the trailing edge of the
puff structures present in pipe flow transition. Under stochastic forcing, the
model exhibits a quasi-periodic self-sustaining cycle characterized by the
creation and subsequent decay of "streamwise-constant puffs", so-called due to
the good agreement between the temporal evolution of their velocity field and
the projection of the velocity field associated with three-dimensional puffs in
a frame of reference moving at the bulk velocity. We establish that the flow
dynamics are relatively insensitive to the regeneration mechanisms invoked to
produce near-wall streamwise vortices and that using small, unstructured
background disturbances to regenerate the streamwise vortices is sufficient to
capture the formation of the high- and low-speed streaks and their segregation
leading to the blunting of the velocity profile characteristic of turbulent
pipe flow
Fermionization of two-component few-fermion systems in a one-dimensional harmonic trap
The nature of strongly interacting Fermi gases and magnetism is one of the
most important and studied topics in condensed-matter physics. Still, there are
many open questions. A central issue is under what circumstances strong
short-range repulsive interactions are enough to drive magnetic correlations.
Recent progress in the field of cold atomic gases allows to address this
question in very clean systems where both particle numbers, interactions and
dimensionality can be tuned. Here we study fermionic few-body systems in a one
dimensional harmonic trap using a new rapidly converging effective-interaction
technique, plus a novel analytical approach. This allows us to calculate the
properties of a single spin-down atom interacting with a number of spin-up
particles, a case of much recent experimental interest. Our findings indicate
that, in the strongly interacting limit, spin-up and spin-down particles want
to separate in the trap, which we interpret as a microscopic precursor of
one-dimensional ferromagnetism in imbalanced systems. Our predictions are
directly addressable in current experiments on ultracold atomic few-body
systems.Comment: 12 pages, 6 figures, published version including two appendices on
our new numerical and analytical approac
Statistical Models of Reconstructed Phase Spaces for Signal Classification
This paper introduces a novel approach to the analysis and classification of time series signals using statistical models of reconstructed phase spaces. With sufficient dimension, such reconstructed phase spaces are, with probability one, guaranteed to be topologically equivalent to the state dynamics of the generating system, and, therefore, may contain information that is absent in analysis and classification methods rooted in linear assumptions. Parametric and nonparametric distributions are introduced as statistical representations over the multidimensional reconstructed phase space, with classification accomplished through methods such as Bayes maximum likelihood and artificial neural networks (ANNs). The technique is demonstrated on heart arrhythmia classification and speech recognition. This new approach is shown to be a viable and effective alternative to traditional signal classification approaches, particularly for signals with strong nonlinear characteristics
Resolving all-order method convergence problems for atomic physics applications
The development of the relativistic all-order method where all single,
double, and partial triple excitations of the Dirac-Hartree-Fock wave function
are included to all orders of perturbation theory led to many important results
for study of fundamental symmetries, development of atomic clocks, ultracold
atom physics, and others, as well as provided recommended values of many atomic
properties critically evaluated for their accuracy for large number of
monovalent systems. This approach requires iterative solutions of the
linearized coupled-cluster equations leading to convergence issues in some
cases where correlation corrections are particularly large or lead to an
oscillating pattern. Moreover, these issues also lead to similar problems in
the CI+all-order method for many-particle systems. In this work, we have
resolved most of the known convergence problems by applying two different
convergence stabilizer methods, reduced linear equation (RLE) and direct
inversion of iterative subspace (DIIS). Examples are presented for B, Al,
Zn, and Yb. Solving these convergence problems greatly expands the
number of atomic species that can be treated with the all-order methods and is
anticipated to facilitate many interesting future applications
Time-Domain Isolated Phoneme Classification Using Reconstructed Phase Spaces
This paper introduces a novel time-domain approach to modeling and classifying speech phoneme waveforms. The approach is based on statistical models of reconstructed phase spaces, which offer significant theoretical benefits as representations that are known to be topologically equivalent to the state dynamics of the underlying production system. The lag and dimension parameters of the reconstruction process for speech are examined in detail, comparing common estimation heuristics for these parameters with corresponding maximum likelihood recognition accuracy over the TIMIT data set. Overall accuracies are compared with a Mel-frequency cepstral baseline system across five different phonetic classes within TIMIT, and a composite classifier using both cepstral and phase space features is developed. Results indicate that although the accuracy of the phase space approach by itself is still currently below that of baseline cepstral methods, a combined approach is capable of increasing speaker independent phoneme accuracy
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