Leggett-Garg inequalities and the geometry of the cut polytope

The Bell and Leggett-Garg tests offer operational ways to demonstrate that non-classical behavior manifests itself in quantum systems, and experimentalists have implemented these protocols to show that classical worldviews such as local realism and macrorealism are false, respectively. Previous theoretical research has exposed important connections between more general Bell inequalities and polyhedral combinatorics. We show here that general Leggett-Garg inequalities are closely related to the cut polytope of the complete graph, a geometric object well-studied in combinatorics. Building on that connection, we offer a family of Leggett-Garg inequalities that are not trivial combinations of the most basic Leggett-Garg inequalities. We then show that violations of macrorealism can occur in surprising ways, by giving an example of a quantum system that violates the new "pentagon" Leggett-Garg inequality but does not violate any of the basic "triangle" Leggett-Garg inequalities.Comment: 5 pages, 1 figur

Nonlocality as a Benchmark for Universal Quantum Computation in Ising Anyon Topological Quantum Computers

An obstacle affecting any proposal for a topological quantum computer based on Ising anyons is that quasiparticle braiding can only implement a finite (non-universal) set of quantum operations. The computational power of this restricted set of operations (often called stabilizer operations) has been studied in quantum information theory, and it is known that no quantum-computational advantage can be obtained without the help of an additional non-stabilizer operation. Similarly, a bipartite two-qubit system based on Ising anyons cannot exhibit non-locality (in the sense of violating a Bell inequality) when only topologically protected stabilizer operations are performed. To produce correlations that cannot be described by a local hidden variable model again requires the use of a non-stabilizer operation. Using geometric techniques, we relate the sets of operations that enable universal quantum computing (UQC) with those that enable violation of a Bell inequality. Motivated by the fact that non-stabilizer operations are expected to be highly imperfect, our aim is to provide a benchmark for identifying UQC-enabling operations that is both experimentally practical and conceptually simple. We show that any (noisy) single-qubit non-stabilizer operation that, together with perfect stabilizer operations, enables violation of the simplest two-qubit Bell inequality can also be used to enable UQC. This benchmarking requires finding the expectation values of two distinct Pauli measurements on each qubit of a bipartite system.Comment: 12 pages, 2 figure

Coastal dune ecology and management in the Eastern Cape

The importance of understanding the ecological functioning of coastal dune systems is emphasized as being fundamental to the correct management of the dune landscape. Dune vegetation along the Eastern Cape coastline, from Cape St Francis in the west to Kei Mouth in the east was described in terms of the distribution and phytochorological affinities of the taxa. At a regional scale species distribution was strongly influenced by both the climate, particularly rainfall, and the phytochorological affinities of the taxa. Seven communities were defined using TWINSPAN, and the interrelationships between these communities in anyone area appeared to be linked to a successional gradient. Dune Slacks are thought to play a key role in this successional sequence, and a temporal study of this community led to a conceptual model of plant succession in these dunefields. Climate, particularly rainfall and wind, are major factors influencing plant succession. Wind-borne sand causes the slacks to migrate in an easterly direction under the influence of the predominantly westerly winds, although easterly winds, mainly in summer months may reverse these trends. Autogenic changes appeared to be important in this succession, and a comparative study of a good example of a primary succession at Mtunzini in Natal was undertaken to elucidate the main mechanism of change. Eight communities that were identified here were concluded to be distnbuted along a gradient of increasing age, with successional changes predictable, linear and directional. Species were grouped in distinct zones along the continuum and edaphic changes (decrease in soil pH, increase in organic matter and exchangeable bases) were related to the community based changes in species composition. The mechanism of change supported the facilitation model of plant succession which is a modification of the original Clementsian concept. Similar results were found in the Eastern Cape, but due to the harsh environment, multiple pathways of succession exist. Data from this study lent support to the model of plant succession developed earlier, and confinned that the dune slacks played an important role in this facilitation by acting as centres of diversity. The foredunes were found to have an indirect role in protecting these slacks from salt spray and sand movement. The central theme of the management studies was to investigate the ecological consequences of recreational pressure within the dune environment. Current levels of beach utilization at East London were lower than other beaches in South Africa, but a general trend of increasing utilization due to sociopolitical changes can be expected. The suitability of questionnaire surveys to assess aspects such as the adequacy of facilities, perceptual carrying capacity and the beach users opinion of natural vegetation and preference for particular beaches was demonstrated. The dune vegetation was found to be sensitive to human trampling, but at current levels, the ecological carrying capacity will not be exceeded since results of the aerial census counts and questionnaire survey revealed that few people entered sensitive zones such as the coastal forest. More detailed long term studies on the susceptibility of dune vegetation to both trampling and off-road vehicle impacts revealed a low resilience of dune plant communities to these effects. Although susceptibility differed between the three communities tested, generally the greatest amount of damage occurred after the first few passages, and vehicles caused a more significant decrease in height when compared to trampling. Recovery rates were slow and low levels of repeated damage were sufficient to retard or prevent the recovery of the plants. Stricter control of vehicle use on beaches is therefore required, and in high use zones the ecological carrying capacity should be increased by providing access tracks if possible, or if not possible, by restricting access. A historical account of the process of dune stabilization showed that although first initiated in 1845, indigenous species were only used in the past three decades. The use of alien species has resulted in problems such as a reduction in the ecological integrity and aesthetic appeal of coastal systems. The techniques applied in the stabilization of drift sands with indigenous vegetation have been successful, as revealed by a quantitative survey of 17 sites in the Eastern Cape. Sites were grouped by multivariate analysis on the basis of their species composition, and variability between sites was dependent on the types of species planted. Selection of suitable species is therefore important and is discussed with respect to their natural distribution along the coast. The long term objective of stabilization should be the creation of functional, diverse, aesthetic ecosystems, since the intrinsic and economic value of the dune landscape for tourism lies therein. However, detailed studies should be undertaken prior to implementing a manipulative process such as dune stabilization, since ecological processes may be disrupted. An understanding of such processes is therefore important if one wishes to effectively manage the dune landscape

Use of social media by self-help and mutual aid groups

This paper explores the use of social media by self-help/mutual aid groups that meet on a regular face-to-face basis. It draws on data from the ESTEEM project, which ran from 2010 to 2013 with the overall aim of developing a range of resources for health and social care practitioners on how to support self-help/mutual aid groups. A re-examination of the interviews and discussions that were undertaken with 21 groups in two UK sites indicated that groups’ use of social media was becoming an increasingly important resource. The findings highlight a range of benefits and limitations with self-help/mutual aid groups using social media and suggest a blurring of boundaries between online and face-to-face groups. For groupworkers involved with self-help/mutual aid groups opportunities in developing groups’ online presence are raised

Being a ‘Self-Help Supporter’: Recognising the roles that community practitioners can adopt in supporting self-help groups

Recent policies on self-care and personalisation have a strong focus on the value of peers as a means through which understanding and knowledge can be conveyed. This opens up new opportunities for community practitioners to work with groups run for and by peers who share the same health or social situation. Selected findings are presented from a three year Big Lottery funded project ‘ESTEEM’ (2010-13) conducted in two locations in England, focussing on the ways in which community practitioners can best support the ethos and practice of peer led self-help groups in the community. The study involved a sample of 21 SHGs and 26 practitioners who contributed to semi-structured interviews, group interviews and workshops which shaped online national resources and subsequent training programmes. The findings explore the types of relationships and core activities that practitioners have with SHGs. suggesting a nuanced picture of practitioner support to groups in three main areas of activity: organisational development; nurturing members and processes and enhancing and sharing expertise. Building on the findings the discussion considers how practitioners can best support SHGs, whilst crucially respecting the autonomy and integrity of the groups. Five roles that practitioners as a ‘self-help supporter’ can adopt are identified

Noise Thresholds for Higher Dimensional Systems using the Discrete Wigner Function

For a quantum computer acting on d-dimensional systems, we analyze the computational power of circuits wherein stabilizer operations are perfect and we allow access to imperfect non-stabilizer states or operations. If the noise rate affecting the non-stabilizer resource is sufficiently high, then these states and operations can become simulable in the sense of the Gottesman-Knill theorem, reducing the overall power of the circuit to no better than classical. In this paper we find the depolarizing noise rate at which this happens, and consequently the most robust non-stabilizer states and non-Clifford gates. In doing so, we make use of the discrete Wigner function and derive facets of the so-called qudit Clifford polytope i.e. the inequalities defining the convex hull of all qudit Clifford gates. Our results for robust states are provably optimal. For robust gates we find a critical noise rate that, as dimension increases, rapidly approaches the the theoretical optimum of 100%. Some connections with the question of qudit magic state distillation are discussed.Comment: 14 pages, 1 table; Minor changes vs. version

Verpleegkunde en Internationale Mobiliteit: Attitudes van Laatstejaarsstudenten Verpleegkunde in drie Europese Onderwijsinstellingen

Probleemstelling Het Europese onderwijsbeleid pleit voor meer mobiliteit van studenten met het oog op de verdere harmonisering van het Hoger Onderwijs (cfr. Bologna verklaring). Opdat onze studenten het tijdelijk of blijvend werken in het buitenland zouden overwegen dienen zowel de mogelijkheid tot studeren en werken in het buitenland alsook de potentiële persoonlijke voordelen ervan gekend te zijn. Met uitzondering van het werk van Wihlborg1 is onderzoek naar de attitudes van studenten verpleegkunden ten aanzien van internationale mobiliteit, beperkt. Onderzoeksvragen 1. Hoe worden begrippen zoals ‘internationalisering’ alsook ‘internationale mobiliteit’ gepercipieerd door laatstejaarsstudenten verpleegkunde in de drie deelnemende Europese onderwijsinstellingen? 2. Welke zijn, met het oog op een toename van internationale mobiliteit, de implicaties van deze percepties en attitudes voor de organisatie van het verpleegkundig onderwijs? Onderzoeksdesign Deze exploratieve pilootstudie werd kwalitatief opgevat en startte in januari 2008 met het vastleggen van de te bevragen concepten. Deze concepten werden peer-discussed in het Engels door alle deelnemers ter verbetering van de inhouds- en begripsvaliditeit. De methodologie en de vragen voor het interview werden vertaald in de plaatselijke brontaal, gecontroleerd op logica en samenhang en vervolgens terug in het Engels vertaald (‘backward translation’). Tussen januari en september 2008 verzamelden de drie Europese onderwijsinstellingen hun kwalitatieve data door middel van focus group interviews. Bij de praktische uitwerking werd een strikte procedure gevolgd met het oog op een vergelijkbare methodologie en hoge betrouwbaarheid. In september 2008 kwamen de deelnemers opnieuw samen voor een thematische analyse van de data bekomen uit de verschillende interviews. In eerste instantie werden de resultaten voor elke partner afzonderlijk besproken en geïnterpreteerd, nadien werden deze data onder algemene thema’s verzameld. Opnieuw werden alle begrippen eerst in het Engels gedefinieerd en nadien wederom vertaald naar de brontaal. Aanvullende mondelinge discussie stond de onderzoekers toe om indien nodig bepaalde thema’s inhoudelijk te verduidelijken. Resultaten Voor de bevraagde studenten leidt internationalisering tot een aantal persoonlijke ‘opportuniteiten’ zoals reizen en het ontwikkelen van een brede visie. Internationalisering kan heel wat persoonlijke aspiraties helpen ontwikkelen. Het leren en werken in het buitenland brengt zowel risico’s als uitdagingen met zich mee maar ook het ervaren van avontuur, onafhankelijkheid, zelfvertrouwen en vrijheid. Ook in het importeren van kennis en vaardigheden uit het buitenland zien de studenten een meerwaarde, net zoals in het exporteren van hun eigen kennis en leerervaringen naar het buitenland. Er werd eveneens gediscusieerd over complexe politieke en ethische dilemma’s. Voor sommige studenten is werken noch studeren in het buitenland aantrekkelijk, doch deze studenten ervaarden wel reeds algemene voordelen bij het leren van mensen met een buitenlandse studie- of werkervaring. De studenten opperden tot slot enkele vernieuwende ideeën die binnen het huidige verpleegkundig onderwijs (meer bepaald het curriculum) kunnen worden geïntroduceerd met het oog op het verlagen van bestaande barrières. Discussie Deze pilootstudie bij laatstejaarsstudenten verpleegkunde uit drie verschillende Europese landen identificeerde een aantal kwesties met betrekking tot internationalisering die meer aandacht vragen. In een volgende fase zal deze studie dan ook op grote schaal worden uitgevoerd. Om gedetailleerde informatie te bekomen over de gedragsdeterminanten alsook de persoonlijke motivaties en barrières die internationale mobiliteit beïnvloeden, zullen toekomstige studies bijkomende focus groups bevatten. Zo dienen zeker studenten met een uitwisselingservaring te worden geïncludeerd, net zoals studenten die nooit in internationale mobiliteit zullen participeren. 1Wihlborg, M (1999) Student nurses’ conceptions of internationalization: a phenomenographic study. Nurse Education Today 19, 533–542. Bologna Proces

Predicting Hemiwicking Dynamics on Textured Substrates

The ability to predict liquid transport rates on textured surfaces is key to the design and optimization of devices and processes such as oil recovery, coatings, reaction-separation, high-throughput screening, and thermal management. In this work we develop a fully analytical model to predict the propagation coefficients for liquids hemiwicking through micropillar arrays. This is carried out by balancing the capillary driving force and a viscous resistive force and solving the Navier–Stokes equation for representative channels. The model is validated against a large data set of experimental hemiwicking coefficients harvested from the literature and measured in-house using high-speed imaging. The theoretical predictions show excellent agreement with the measured values and improved accuracy compared to previously proposed models. Furthermore, using lattice Boltzmann (LB) simulations, we demonstrate that the present model is applicable over a broad range of geometries. The scaling of velocity with texture geometry, implicit in our model, is compared against experimental data, where good agreement is observed for most practical systems. The analytical expression presented here offers a tool for developing design guidelines for surface chemistry and microstructure selection for liquid propagation on textured surfaces

Synthesis and characterisation of pyrene-labelled polydimethylsiloxane networks: towards the in situ detection of strain in silicone elastomers

Pyrene-substituted polyhydromethylsiloxanes (PHMS-Py-x) were synthesised by the hydrosilylation reaction of prop-3-enyloxymethylpyrene with polyhydromethylsiloxane (M-n = 3700). The ratio of pyrene substituent to Si-H unit was varied to afford a range of pyrene-functionalised polysiloxanes. These copolymers were subsequently incorporated into polydimethylsiloxane (PDMS) elastomers by curing via either Pt(0) catalysed hydrosilylation with divinyl-terminated PDMS (M-n = 186) and tetrakis(dimethylsiloxy) silane, or Sn(II) catalysed condensation with alpha,omega-dihydroxyPDMS (M-n = 26 000) and tetraethoxysilane. An alternative method involving the synthesis and integration of [3-(pyren-1-ylmethoxy)propyl]triethoxysilane (Py-TEOS) into PDMS elastomers was also investigated: a mixture of alpha,omega-dihydroxyPDMS (M-n = 26 000), tetraethoxysilane, and Py-TEOS was cured using an Sn( II) catalyst. Certain of the resulting fluorescent pyrene-labelled elastomers were studied by differential scanning calorimetry and dynamic mechanical analysis. No significant changes were observed in the thermal or mechanical properties of the elastomers containing pyrene when compared to otherwise identical samples not containing pyrene. All of the pyrene-containing elastomers were demonstrated to be fluorescent under suitable excitation in a photoluminescent spectrometer. Two of the elastomers were placed in a photoluminescence spectrometer and subjected to cycles of extension and relaxation (strain = 0-16.7%) while changes in the emission spectra were monitored. The resulting spectra of the elastomer containing the PHMS-Py-50 copolymers were variable and inconsistent. However, the emission peaks of elastomers containing Py-TEOS displayed clear and reproducible changes in fluorescence intensity upon stretching and relaxation. The intensity of the monomer and excimer emission peaks was observed to increase with elongation of the sample and decrease upon relaxation. Furthermore, the ratio of the intensities of the excimer : monomer peak decreased with elongation and increased with relaxation. In neither case was there appreciable hysteresis, suggesting that fluorescent labelling of elastomers is a valid approach for the non-invasive in situ monitoring of stress and strain in such materials

Explicit finite-difference time-domain scheme for the simulation of 1-3 piezoelectric effect in axisymmetrical configurations

[EN] Numerical simulations are useful in the processes of design, development and optimization of transducers for non-destructive testing. In this work, a three-dimensional velocity-stress finite-difference model is presented for the elastic wave propagation in the piezoelectric substrate of a transducer excited by applying an impulsive voltage signal to the transducer electrodes. The allocation of the stress, velocity and electric field components on a staggered grid leads to a stable scheme. The different time scales of both mechanical and electromagnetic waves have leaded previous FDTD models to choose between significant physical simplifications or complicated implicit equations. The model presented here is explicit in all its time domain equations, contains only first order derivatives and is centered in time and space. The results of simulations show remarkable accuracy and stability for the different transducers studied. © 2012 Elsevier B.V.The authors want to thank Miquel Ardid, Víctor Sánchez and Bernardino Roig for their cooperation and fruitful discussions. This study was supported by the Programa de Apoyo a la Investigación y Desarrollo PAID-06-10-002-295 of Universidad Politécnica de Valencia.Ferri García, M.; Camarena Femenia, F.; Redondo, J.; Picó Vila, R.; Avis, MR. (2012). Explicit finite-difference time-domain scheme for the simulation of 1-3 piezoelectric effect in axisymmetrical configurations. Wave Motion. 49(6):569-584. https://doi.org/10.1016/j.wavemoti.2012.03.007S56958449