Effects of axial torsion on sp carbon atomic nanowires

Ab-initio calculations within Density Functional Theory combined with experimental Raman spectra on cluster-beam deposited pure carbon films provide a consistent picture of sp-carbon chains stabilized by sp^3 or sp^2 terminations, the latter being sensitive to torsional strain. This unexplored effect promises many exciting applications since it allows one to modify the conductive states near the Fermi level and to switch on and off the on-chain pi-electron magnetism.Comment: in print in Phys Rev Let

The development of complex verb constructions in British Sign Language

This study focuses on the mapping of events onto verb-argument structures in British Sign Language (BSL). The development of complex sentences in BSL is described in a group of 30 children, aged 3;2–12;0, using data from comprehension measures and elicited sentence production. The findings support two interpretations: firstly, in the mapping of concepts onto language, children acquiring BSL overgeneralize the use of argument structure related to perspective shifting;secondly, these overgeneralizations are predicted by the typological characteristics of the language and modality. Children under age 6;0, in attempting to produce sentences encoded through a perspective shift, begin by breaking down double-verb constructions (AB verbs) into components, producing only the part of the verb phrase which describes the perspective of the patient. There is also a prolonged period of development of non-manual features, with the full structure not seen in its adult form until after 9;0. The errors in the use of AB verbs and the subsequent protracted development of correct usage are explained in terms of the conceptual–linguistic interface

A Pedagogical Evaluation of Intra-Sentential Code-Switching Patterns in L2 Classroom Talk

The paper is concerned with teachers' and students' alternation between L1 and L2 within the same utterance, i.e. uses of intra-sentential code-switching which in classroom discourse tends to be less accepted by modern language pedagogy than its inter-sentential counterpart. The rationale for the study is the universal nature of the phenomenon known to occur in the first place in interactions among natural bilinguals and multilinguals. The data analysis sections of the article review eight different patterns which are evaluated pedagogically. It transpires that the category most likely to arouse methodological controversy is code-mixing

Droplet traffic in microfluidic networks: A simple model for understanding and designing

We propose a simple model to analyze the traffic of droplets in microfluidic ``dual networks''. Such functional networks which consist of two types of channels, namely those accessible or forbidden to droplets, often display a complex behavior characteristic of dynamical systems. By focusing on three recently proposed configurations, we offer an explanation for their remarkable behavior. Additionally, the model allows us to predict the behavior in different parameter regimes. A verification will clarify fundamental issues, such as the network symmetry, the role of the driving conditions, and of the occurrence of reversible behavior. The model lends itself to a fast numerical implementation, thus can help designing devices, identifying parameter windows where the behavior is sufficiently robust for a devices to be practically useful, and exploring new functionalities.Comment: accepted for publication in PR

Quantum Alternation: Prospects and Problems

We propose a notion of quantum control in a quantum programming language which permits the superposition of finitely many quantum operations without performing a measurement. This notion takes the form of a conditional construct similar to the IF statement in classical programming languages. We show that adding such a quantum IF statement to the QPL programming language simplifies the presentation of several quantum algorithms. This motivates the possibility of extending the denotational semantics of QPL to include this form of quantum alternation. We give a denotational semantics for this extension of QPL based on Kraus decompositions rather than on superoperators. Finally, we clarify the relation between quantum alternation and recursion, and discuss the possibility of lifting the semantics defined by Kraus operators to the superoperator semantics defined by Selinger.Comment: In Proceedings QPL 2015, arXiv:1511.0118

Resonant effects in a SQUID qubit subjected to non adiabatic changes

By quickly modifying the shape of the effective potential of a double SQUID flux qubit from a single-well to a double-well condition, we experimentally observe an anomalous behavior, namely an alternance of resonance peaks, in the probability to find the qubit in a given flux state. The occurrence of Landau-Zener transitions as well as resonant tunneling between degenerate levels in the two wells may be invoked to partially justify the experimental results. A quantum simulation of the time evolution of the system indeed suggests that the observed anomalous behavior can be imputable to quantum coherence effects. The interplay among all these mechanisms has a practical implication for quantum computing purposes, giving a direct measurement of the limits on the sweeping rates possible for a correct manipulation of the qubit state by means of fast flux pulses, avoiding transitions to non-computational states.Comment: 6 pages and 6 figures. The paper, as it is, has been accepted for publication on PRB on March 201

Non-linear macroscopic polarization in III-V nitride alloys

We study the dependence of macroscopic polarization on composition and strain in wurtzite III-V nitride ternary alloys using ab initio density-functional techniques. The spontaneous polarization is characterized by a large bowing, strongly dependent on the alloy microscopic structure. The bowing is due to the different response of the bulk binaries to hydrostatic pressure, and to internal strain effects (bond alternation). Disorder effects are instead minor. Deviations from parabolicity (simple bowing) are of order 10 % in the most extreme case of AlInN alloy, much less at all other compositions. Piezoelectric polarization is also strongly non-linear. At variance with the spontaneous component, this behavior is independent of microscopic alloy structure or disorder effects, and due entirely to the non-linear strain dependence of the bulk piezoelectric response. It is thus possible to predict the piezoelectric polarization for any alloy composition using the piezoelectricity of the parent binaries.Comment: RevTex 7 pages, 7 postscript figures embedde