2,038 research outputs found
Polaritonic characteristics of insulator and superfluid phases in a coupled-cavity array
Recent studies of quantum phase transitions in coupled atom-cavity arrays
have focused on the similarities between such systems and the Bose-Hubbard
model. However, the bipartite nature of the atom-cavity systems that make up
the array introduces some differences. In order to examine the unique features
of the coupled-cavity system, the behavior of a simple two-site model is
studied over a wide range of parameters. Four regions are identified, in which
the ground state of the system may be classified as either a polaritonic
insulator, a photonic superfluid, an atomic insulator, or a polaritonic
superfluid.Comment: 7 pages, 9 figures, 1 table, REVTeX 4; published versio
A method to identify differential expression profiles of time-course gene data with Fourier transformation
BACKGROUND: Time course gene expression experiments are an increasingly popular method for exploring biological processes. Temporal gene expression profiles provide an important characterization of gene function, as biological systems are both developmental and dynamic. With such data it is possible to study gene expression changes over time and thereby to detect differential genes. Much of the early work on analyzing time series expression data relied on methods developed originally for static data and thus there is a need for improved methodology. Since time series expression is a temporal process, its unique features such as autocorrelation between successive points should be incorporated into the analysis. RESULTS: This work aims to identify genes that show different gene expression profiles across time. We propose a statistical procedure to discover gene groups with similar profiles using a nonparametric representation that accounts for the autocorrelation in the data. In particular, we first represent each profile in terms of a Fourier basis, and then we screen out genes that are not differentially expressed based on the Fourier coefficients. Finally, we cluster the remaining gene profiles using a model-based approach in the Fourier domain. We evaluate the screening results in terms of sensitivity, specificity, FDR and FNR, compare with the Gaussian process regression screening in a simulation study and illustrate the results by application to yeast cell-cycle microarray expression data with alpha-factor synchronization. The key elements of the proposed methodology: (i) representation of gene profiles in the Fourier domain; (ii) automatic screening of genes based on the Fourier coefficients and taking into account autocorrelation in the data, while controlling the false discovery rate (FDR); (iii) model-based clustering of the remaining gene profiles. CONCLUSIONS: Using this method, we identified a set of cell-cycle-regulated time-course yeast genes. The proposed method is general and can be potentially used to identify genes which have the same patterns or biological processes, and help facing the present and forthcoming challenges of data analysis in functional genomics
Dynamics in a coupled-cavity array
The dynamics of a system composed of two coupled optical cavities, each
containing a single two-level atom, is studied over a wide range of detuning
and coupling values. A description of the field in terms of delocalized modes
reveals that the detuning between the atoms and these modes is controlled by
the coupling between the cavities; this detuning in turn governs the nature of
the dynamics. If the atoms are highly detuned from both delocalized field
modes, the dynamics becomes dispersive and an excitation may be transferred
from the first atom to the second without populating the field. In the case of
resonance between the atoms and one of the delocalized modes, state transfer
between the atoms requires intermediate excitation of the field. Thus the
interaction between the two atoms can be controlled by adjusting the coupling
between the cavities.Comment: 11 pages, 3 figure
Cross-Kerr-based information transfer processes
The realization of nonclassical states is an important task for many
applications of quantum information processing. Usually, properly tailored
interactions, different from goal to goal, are considered in order to
accomplish specific tasks within the general framework of quantum state
engineering. In this paper we remark on the flexibility of a cross-Kerr
nonlinear coupling in hybrid systems as an important ingredient in the
engineering of nonclassical states. The general scenario we consider is the
implementation of high cross-Kerr nonlinearity in cavity-quantum
electrodynamics. In this context, we discuss the possibility of performing
entanglement transfer and swapping between a qubit and a continuous-variable
state. The recently introduced concept of entanglement reciprocation is also
considered and shown to be possible with our scheme. We reinterpret some of our
results in terms of applications of a generalized Ising interaction to systems
of different nature.Comment: 8 pages, 4 figures, RevTeX
Concentration and purification of entanglement for qubit systems with ancillary cavity fields
We propose schemes for entanglement concentration and purification for qubit
systems encoded in flying atomic pairs. We use a cavity-quantum electrodynamics
setting as the paradigmatic scenario within which our proposals can be
implemented. Maximally entangled pure states of qubits can be produced as a
result of our protocols. In particular, the concentration protocol yields Bell
states with the largest achievable theoretical probability while the
purification scheme produces arbitrarily pure Bell states. The requirements for
the implementation of these protocols are modest, within the state of the art,
and we address all necessary steps in two specific set-ups based on
experimentally mature microwave technology.Comment: 10 pages, 6 figure
An affine continuum mechanical model for cross-linked F-actin networks with compliant linker proteins
Cross-linked actin networks are important building blocks of the cytoskeleton. In order to gain deeper insight into the interpretation of experimental data on actin networks, adequate models are required. In this paper we introduce an affine constitutive network model for cross-linked F-actin networks based on nonlinear continuum mechanics, and specialize it in order to reproduce the experimental behavior of in vitro reconstituted model networks. The model is based on the elastic properties of single filaments embedded in an isotropic matrix such that the overall properties of the composite are described by a free-energy function. In particular, we are able to obtain the experimentally determined shear and normal stress responses of cross-linked actin networks typically observed in rheometer tests. In the present study an extensive analysis is performed by applying the proposed model network to a simple shear deformation. The single filament model is then extended by incorporating the compliance of cross-linker proteins and further extended by including viscoelasticity. All that is needed for the finite element implementation is the constitutive model for the filaments, the linkers and the matrix, and the associated elasticity tensor in either the Lagrangian or Eulerian formulation. The model facilitates parameter studies of experimental setups such as micropipette aspiration experiments and we present such studies to illustrate the efficacy of this modeling approach
ACCOUNTING FOR PRIVATISATION IN BANGLADESH: TESTING WORLD BANK CLAIMS
The World Bank and the IMF have encouraged many less developed countries (LDCs) to pursue privatisation policies. Development economists and World Bank reports claim this facilitates development by improving controls within enterprises and external regulation of financial markets acting on external accounting reports. This paper questions these beliefs. It compares the post-privatisation performance of companies in Bangladesh examined in a World Bank report with the authors' own research on the same companies. The World Bank report reported that the success of the privatisations established the case for more. In the research reported here, only one of the privatised companies was judged a commercial success, though the unavailability and dubious accuracy of accounting reports prevented any definitive assessment. Above all, the paper questions the narrow criteria adopted by the World Bank report - namely profitability - and the neglect of employment conditions, trade union and individual rights; social returns; and financial transparency and accountability to external constituents. Our evidence suggested that privatisation has not increased returns to society: privatised companies' contributions to state revenue declined in real terms and as a proportion of value added. Transparent external reports failed to materialise as required by law and there was evidence of untoward transactions affecting minority shareholders, creditors, and tax collecting institutions. Internal controls may have become more commercial but at the cost of declining employment, wages, quality of working life, and employee rights. The World Bank claims rest upon efficiency benefits trickling down to all but the effects of privatisation may have been a redistribution of power and wealth to the new owners. This paper argues that the IMF, the World Bank, and Western capitalist states have not provided the technical infrastructure and organisational capacity to execute their neo-liberal privatisation agenda, which rests on dubious socio-economic assumptions. Our unfavourable evaluation of privatisation in Bangladesh is not unique. It has been happening again and again around the world. © 2003 Published by Elsevier Science Ltd
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