5,356 research outputs found
Spin Chains as Perfect Quantum State Mirrors
Quantum information transfer is an important part of quantum information
processing. Several proposals for quantum information transfer along linear
arrays of nearest-neighbor coupled qubits or spins were made recently. Perfect
transfer was shown to exist in two models with specifically designed strongly
inhomogeneous couplings. We show that perfect transfer occurs in an entire
class of chains, including systems whose nearest-neighbor couplings vary only
weakly along the chain. The key to these observations is the Jordan-Wigner
mapping of spins to noninteracting lattice fermions which display perfectly
periodic dynamics if the single-particle energy spectrum is appropriate. After
a half-period of that dynamics any state is transformed into its mirror image
with respect to the center of the chain. The absence of fermion interactions
preserves these features at arbitrary temperature and allows for the transfer
of nontrivially entangled states of several spins or qubits.Comment: Abstract extended, introduction shortened, some clarifications in the
text, one new reference. Accepted by Phys. Rev. A (Rapid Communications
Boundary field induced first-order transition in the 2D Ising model: numerical study
In a recent paper, Clusel and Fortin [J. Phys. A.: Math. Gen. 39 (2006) 995]
presented an analytical study of a first-order transition induced by an
inhomogeneous boundary magnetic field in the two-dimensional Ising model. They
identified the transition that separates the regime where the interface is
localized near the boundary from the one where it is propagating inside the
bulk. Inspired by these results, we measured the interface tension by using
multimagnetic simulations combined with parallel tempering to determine the
phase transition and the location of the interface. Our results are in very
good agreement with the theoretical predictions. Furthermore, we studied the
spin-spin correlation function for which no analytical results are available.Comment: 12 pages, 7 figures, 2 table
Global Diffusion of the Internet VII- Teledensity Growth Strategies for Latin America: The Case of Colombia and Ecuador
The Internet in developing countries grew substantially in recent years. Given the large income disparities and low telephone penetration. rates in most Latin American countries, only about 4% of the region\u27s population can access the Internet. The International Telecommunication Union reports that teledensity (the number of telephone land-lines per 100 people) in Latin America is currently at about 10.8%. Prior research identified specific factors that hinder growth of teledensity in developing countries and specific strategies used to overcome such limitations. This study investigates Latin American telecommunication stakeholders\u27 perspective of how these strategies can be used to address teledensity growth in the region. Survey participants (Latin America\u27s telecommunications stakeholders) analyzed the strategies critically and modified, enhanced, or added new insights. Using appropriate statistical procedures we examined the telecommunications stakeholders\u27 perceptions to find potential solutions the low teledensity problem. Qualitative comments to support the stakeholders\u27 responses are reported, together with future research implications
State and Local Anti-Predatory Lending Laws: The Effect of Legal Enforcement Mechanisms
Subprime mortgage lending has grown rapidly in recent years and with it, so have concerns about predatory lending. In response to evidence of predatory lending, most states have enacted new laws or expanded existing laws to address abuses in the subprime home loan market. The effect of these statutes is a matter of debate. This paper seeks to improve the understanding of this increasingly important issue and pays particular attention to the role that legal enforcement mechanisms play in this context. The results of the analysis are consistent with the view that anti-predatory lending laws influence subprime lending markets and that disaggregating the details of the overall legal framework into its component parts is essential for understanding subprime market dynamics. The restrictions, coverage, and enforcement components all have significant relationships with subprime market outcomes, with the coverage relationship found to be broadly consistent with the reverse lemons hypothesis put forward by Ho and Pennington-Cross (2007). The results also suggest that the newer mini-HOEPA laws have had an impact on the subprime market above and beyond the older preexisting laws, particularly for subprime originations. Broader coverage through these new laws is associated with higher origination likelihoods, while increased restrictions through the mini-HOEPA laws are associated with lower origination propensities
The Impact of State Anti-Predatory Lending Laws: Policy Implications and Insights
The subprime mortgage market, which consists of high-cost loans designed for borrowers with weak credit, has grown tremendously over the past ten years. Between 1993 and 2005, the subprime market experienced an average annual growth rate of 26 percent. As this market emerged, so did allegations that subprime loans contained predatory features or were the result of predatory sales practices.3 In the worst cases, brokers deceived borrowers about the meaning of loan terms or falsely promised to assist them in obtaining future refinance loans with better terms. In other situations, borrowers entered into loans with low teaser rates, not aware how high their monthly payments could go when their interest rates reset
Zero--Temperature Quantum Phase Transition of a Two--Dimensional Ising Spin--Glass
We study the quantum transition at in the spin- Ising
spin--glass in a transverse field in two dimensions. The world line path
integral representation of this model corresponds to an effective classical
system in (2+1) dimensions, which we study by Monte Carlo simulations. Values
of the critical exponents are estimated by a finite-size scaling analysis. We
find that the dynamical exponent, , and the correlation length exponent,
, are given by and . Both the linear
and non-linear susceptibility are found to diverge at the critical point.Comment: RevTeX 10 pages + 4 figures (appended as uuencoded, compressed
tar-file), THP21-9
Monte Carlo study of the evaporation/condensation transition on different Ising lattices
In 2002 Biskup et al. [Europhys. Lett. 60, 21 (2002)] sketched a rigorous
proof for the behavior of the 2D Ising lattice gas, at a finite volume and a
fixed excess \delta M of particles (spins) above the ambient gas density
(spontaneous magnetisation). By identifying a dimensionless parameter \Delta
(\delta M) and a universal constant \Delta_c, they showed in the limit of large
system sizes that for \Delta < \Delta_c the excess is absorbed in the
background (``evaporated'' system), while for \Delta > \Delta_c a droplet of
the dense phase occurs (``condensed'' system).
To check the applicability of the analytical results to much smaller,
practically accessible system sizes, we performed several Monte Carlo
simulations for the 2D Ising model with nearest-neighbour couplings on a square
lattice at fixed magnetisation M. Thereby, we measured the largest minority
droplet, corresponding to the condensed phase, at various system sizes (L=40,
>..., 640). With analytic values for for the spontaneous magnetisation m_0, the
susceptibility \chi and the Wulff interfacial free energy density \tau_W for
the infinite system, we were able to determine \lambda numerically in very good
agreement with the theoretical prediction.
Furthermore, we did simulations for the spin-1/2 Ising model on a triangular
lattice and with next-nearest-neighbour couplings on a square lattice. Again,
finding a very good agreement with the analytic formula, we demonstrate the
universal aspects of the theory with respect to the underlying lattice. For the
case of the next-nearest-neighbour model, where \tau_W is unknown analytically,
we present different methods to obtain it numerically by fitting to the
distribution of the magnetisation density P(m).Comment: 14 pages, 17 figures, 1 tabl
Narrative Financial Therapy: Integrating a Financial Planning Approach with Therapeutic Theory
The article serves as one of the first attempts to develop an integrated theoretical approach to financial therapy that can be used by practitioners from multiple disciplines. The presented approach integrates the components of the six-step financial planning process with components of empirically-supported therapeutic methods. This integration provides the foundation for a manualized approach to financial therapy, shaped by the writings of narrative theorists and select cognitive-behavioral interventions that can be used both by mental health and financial professionals
Factors Relating to Gender Specificity of Unloading-Induced Declines in Strength
Introduction: This investigation aimed to: (1) confirm whether women were more vulnerable to the negative neuromuscular adaptations elicited by muscle unloading and if so, (2) determine which physiological mechanism(s) explain those gender-related differences. Methods: Healthy young men (20.7 +/- 0.3 years) and women (20.3 +/- 0.3 years)-(N = 12/group)-participated by completing neuromuscular functional tests before and after 7 days of unloading. Results: During isokinetic testing of peak torque, work performed, and power, women displayed significantly (P \u3c = 0.05) greater declines in performance than men at 1.05 and 2.09, but not 0.53 rads/s. During maximal isometric contractions, women experienced greater strength decrements. Similar gender-specific adaptations to unloading were found in EMG activity, but not muscle mass, neuromuscular transmission, or force relative to EMG. Conclusions: Women are more susceptible to the adaptations of muscle unloading, and disturbances in neural drive from the central nervous system are probably responsible. Muscle Nerve 46: 210-217, 201
Droplets in the coexistence region of the two-dimensional Ising model
The two-dimensional Ising model with fixed magnetization is studied using
Monte Carlo techniques. At the coexistence line, the macroscopic, extensive
droplet of minority spins becomes thermally unstable by breaking up into
microscopic clusters. Intriguing finite--size effects as well as singularities
of thermal and cluster properties associated with the transition are discussed.Comment: 7 pages, 3 figures included, submitted to J. Phys. A: Math. Ge
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