Quantum walk on the line: entanglement and non-local initial conditions

The conditional shift in the evolution operator of a quantum walk generates entanglement between the coin and position degrees of freedom. This entanglement can be quantified by the von Neumann entropy of the reduced density operator (entropy of entanglement). In the long time limit, it converges to a well defined value which depends on the initial state. Exact expressions for the asymptotic (long-time) entanglement are obtained for (i) localized initial conditions and (ii) initial conditions in the position subspace spanned by the +1 and -1 position eigenstates.Comment: A few mistakes where corrected. One of them leads to a factor of 2 in eq. (49), the other results remain unchanged. In this version, several figures where replaced by color version

Video elicitation of negative directives in Alaskan Dene languages: reflections on methodology

In this paper, we describe the use of video stimuli for the targeted elicitation of negative directives in Denaakk’e (Koyukon) and Nee’andeegn’ (Upper Tanana), two severely endangered Alaskan Dene languages. Negative directives are extremely rare in our previously collected data, yet they exhibit a great variety of forms. Forms further seem to depend on several factors, particularly on whether the prohibited act violates social norms known as hʉtlaanee/įįjih. To better understand the variety of on-record and off-record forms, we created video clips showing activities violating hʉtlaanee/įįjih and activities that are merely foolish or mildly dangerous. After viewing the clips, our consultants were asked to advise the actors as if they were their grandchildren. Their responses were discussed at length with the speakers. The speakers greatly enjoyed this task and produced a great variety of on-record and off-record responses including some unusual linguistic structures. In both languages, offrecord expressions were preferred over direct ones, particularly in situations where hʉtlaanee/įįjih was involved. We also identified several conventionalized off-record strategies. The emphasis on hʉtlaanee/įįjih made the task interesting and relevant for speakers. While our stimuli are designed for work with Alaskan Dene, the method can be adapted for cultural contexts around the world.National Foreign Language Resource Cente

Effects of non-local initial conditions in the Quantum Walk on the line

We report an enhancement of the decay rate of the survival probability when non-local initial conditions in position space are considered in the Quantum Walk on the line. It is shown how this interference effect can be understood analytically by using previously derived results. Within a restricted position subspace, the enhanced decay is correlated with a maximum asymptotic entanglement level while the normal decay rate corresponds to initial relative phases associated to a minimum entanglement level.Comment: 5 pages, 1 figure, Elsevier style, to appear in Physica

The EU’s Proposed Reform of Directors’ Duties and the Missing Link to Soft Law

In this paper, we investigate whether reform of EU company law is needed to make corporate governance more sustainable. We also consider some issues to which the EU proposals on company law and sustainability paid scant attention, such as the role of corporate governance codes and other types of soft law, mainly of international origin, in promoting sustainable governance. In addition, we underline that in recent years the EU has adopted several measures which offer better prospects for sustainable governance than the reform of directors' duties the EU is currently debating. We conclude that the failure to take corporate governance codes and the existing regulatory framework into account could seriously impair pending reforms of directors' duties and their link to sustainability

Simulation modeling of the long-term evolution of local malaria transmission and acquired immunity in the context of urban growth and urban-rural travel

Malaria occurrence is lower in urban versus rural areas of sub-Saharan Africa for a variety of reasons, including limitation of suitable mosquito habitat, generally improved housing standards and access to prevention and treatment, and a relative decrease in the ratio of vectors to humans. Nonetheless, empirical observation confirms that malaria cases, whether locally transmitted or imported, are frequently observed in cities in endemic areas. Theoretical considerations imply that local transmission will decrease as a city grows, transitioning from a relatively malaria-permissive state to one that encourages reduction or extinction. Using a simple deterministic systems dynamic model based on traditional malaria models, we simulate scenarios for the evolution of local transmission rates and acquired immunity in a homogenous urban area with respect to population size, growth rate, and level of suppression of mosquito breeding. In particular, we consider how the timing and extent of decreases in local transmission are mitigated by travel by city dwellers to endemic rural areas and their resulting exposure to infected mosquitoes. We explore the generalizability and sensitivity to assumptions of our results using microsimulation and analytic methods to account for various aspects of environmental (urban/rural) and demographic heterogeneity. The results of these simulation models should inform projections for long-term urban malaria trends, and have implications for the targeting of malaria prevention efforts in urban and peri-urban areas of sub-Saharan Africa

Post-disaster housing reconstruction in conflict affected Sri Lanka

Purpose This paper is an account of a study to critically analyse the role of housing reconstruction projects in post conflict Sri Lanka and discuss their implications on conflict prevention. Method Using four housing reconstruction projects in Batticaloa, Kilinochchi and Jaffna Districts, Sri Lanka, as case studies, and a novel methodological framework, the study explores the causal relations among the independent variables associated with housing reconstruction and dependent variables related to conflict prevention. The data, gathered from interviews and project reports, were analysed using propositions from a literature review, adopting a thematic analytical approach. Findings This study finds that reconstruction has created new forms of conflicts and tensions for the people who came to live in the newly constructed houses. The people, already vulnerable due to years of civil war, had to adopt strategies in order to survive in the new environment, which in return increased local tensions. The hostile relations that existed among different ethnic groups during the conflict were continued, and to some extent, exacerbated by the reconstruction undertaken after the war. Practical implications It is important to account for the war dynamics and the relationships that existed among different ethnic groups during war, when implementing reconstruction projects in a conflict sensitive environment. Originality/value This study examines post disaster housing reconstruction in Sri Lanka in a post-tsunami and post-conflict environment, a subject not adequately addressed by previous studies that have tended on the reconstruction in the immediate aftermath of the tsunami. The results reveal concerns in housing and infrastructure development that have implications for future research and practice in post-conflict environments

Dynamical Localization in Quasi-Periodic Driven Systems

We investigate how the time dependence of the Hamiltonian determines the occurrence of Dynamical Localization (DL) in driven quantum systems with two incommensurate frequencies. If both frequencies are associated to impulsive terms, DL is permanently destroyed. In this case, we show that the evolution is similar to a decoherent case. On the other hand, if both frequencies are associated to smooth driving functions, DL persists although on a time scale longer than in the periodic case. When the driving function consists of a series of pulses of duration $\sigma$, we show that the localization time increases as $\sigma^{-2}$ as the impulsive limit, $\sigma\to 0$, is approached. In the intermediate case, in which only one of the frequencies is associated to an impulsive term in the Hamiltonian, a transition from a localized to a delocalized dynamics takes place at a certain critical value of the strength parameter. We provide an estimate for this critical value, based on analytical considerations. We show how, in all cases, the frequency spectrum of the dynamical response can be used to understand the global features of the motion. All results are numerically checked.Comment: 7 pages, 5 figures included. In this version is that Subsection III.B and Appendix A on the quasiperiodic Fermi Accelerator has been replaced by a reference to published wor

High binding yet accelerated guest rotation within a cucurbit[7]uril complex. Toward paramagnetic gyroscopes and rolling nanomachines †

International audienceThe (15-oxo-3,7,11-triazadispiro[5.1.5.3]hexadec-7-yl)oxidanyl, a bis-spiropiperidinium nitroxide derived from TEMPONE, can be included in cucurbit[7]uril to form a strong (K a ∼ 2 × 10 5 M −1) CB[7]@bPTO complex. EPR and MS spectra, DFT calculations, and unparalleled increased resistance (a factor of ∼10 3) toward ascorbic acid reduction show evidence of deep inclusion of bPTO inside CB[7]. The unusual shape of the CB[7]@bPTO EPR spectrum can be explained by an anisotropic Brownian rotational diffusion, the global tumbling of the complex being slower than rotation of bPTO around its " long molecular axis " inside CB[7]. The CB[7] (stator) with the encapsulated bPTO (rotator) behaves as a supramolecular para-magnetic rotor with increased rotational speed of the rotator that has great potential for advanced nano-scale machines requiring wheels such as cucurbiturils with virtually no friction between the wheel and the axle for optimum wheel rotation (i.e. nanopulleys and nanocars)

Quantum random walk on the line as a markovian process

We analyze in detail the discrete--time quantum walk on the line by separating the quantum evolution equation into Markovian and interference terms. As a result of this separation, it is possible to show analytically that the quadratic increase in the variance of the quantum walker's position with time is a direct consequence of the coherence of the quantum evolution. If the evolution is decoherent, as in the classical case, the variance is shown to increase linearly with time, as expected. Furthermore we show that this system has an evolution operator analogous to that of a resonant quantum kicked rotor. As this rotator may be described through a quantum computational algorithm, one may employ this algorithm to describe the time evolution of the quantum walker.Comment: few typos corrected, 13 pages, 2 figures, to appear in Physica