1,755 research outputs found

    Hall Effect in Noncommutative Coordinates

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    We consider electrons in uniform external magnetic and electric fields which move on a plane whose coordinates are noncommuting. Spectrum and eigenfunctions of the related Hamiltonian are obtained. We derive the electric current whose expectation value gives the Hall effect in terms of an effective magnetic field. We present a receipt to find the action which can be utilized in path integrals for noncommuting coordinates. In terms of this action we calculate the related Aharonov--Bohm phase and show that it also yields the same effective magnetic field. When magnetic field is strong enough this phase becomes independent of magnetic field. Measurement of it may give some hints on spatial noncommutativity. The noncommutativity parameter \theta can be tuned such that electrons moving in noncommutative coordinates are interpreted as either leading to the fractional quantum Hall effect or composite fermions in the usual coordinates.Comment: 13 pages. Some references adde

    Reciprocity and unitarity in scattering from a non-Hermitian complex PT-symmetric potential

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    In quantum scattering, Hermiticity is necessary for both reciprocity and unitarity. Reciprocity means that both reflectivity (R) and transmitivity (T) are insensitive to the direction of incidence of a wave (particle) at a scatterer from left/right. Unitarity means that R+T=1. In scattering from non-Hermitian PT-symmetric structures the (left/right) handedness (non-reciprocity) of reflectivity is known to be essential and unitarity remains elusive so far. Here we present a surprising occurrence of both reciprocity and unitarity in scattering from a complex PT-symmetric potential. In special cases, we show that this potential can even become invisible (R=0, T=1) from both left and right sides. We also find that this potential in a parametric regime enjoys a pseudo-unitarity of the type T+RleftRright=1T+\sqrt{R_{left}R_{right}}=1.Comment: 7 pages. no figures and no tables, two corrections, appeared in Phys. Lett.

    Conserved Correlation in PT -symmetric Systems: Scattering and Bound States

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    For one-dimensional PT -symmetric systems, it is observed that the non-local product obtained from the continuity equation can be interpreted as a conserved corre- lation function. This leads to physical conclusions, regarding both discrete and continuum states of such systems. Asymptotic states are shown to have necessarily broken PT -symmetry, leading to modified scattering and transfer matrices. This yields restricted boundary conditions, e.g., in- cidence from both sides, analogous to that of the proposed PT CPA laser. The interpretation of left and right states leads to a Hermitian S-matrix, resulting in the non-conservation of the flux. This further satisfies a duality condition, identical to the optical analogues. However, the non-local conserved scalar implements alternate boundary conditions in terms of in and out states, leading to the pseudo-Hermiticity condition in terms of the scattering matrix. Interestingly, when PT -symmetry is preserved, it leads to stationary states with real energy, naturally inter- pretable as bound states. The broken PT -symmetric phase is also captured by this correlation, with complex-conjugate pair of energies, interpreted as resonances.Comment: 9 page

    Advanced Pedestrian Positioning System to Smartphones and Smartwatches

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    In recent years, there has been an increasing interest in the development of pedestrian navigation systems for satellite-denied scenarios. The popularization of smartphones and smartwatches is an interesting opportunity for reducing the infrastructure cost of the positioning systems. Nowadays, smartphones include inertial sensors that can be used in pedestrian dead-reckoning (PDR) algorithms for the estimation of the user's position. Both smartphones and smartwatches include WiFi capabilities allowing the computation of the received signal strength (RSS). We develop a new method for the combination of RSS measurements from two different receivers using a Gaussian mixture model. We also analyze the implication of using a WiFi network designed for communication purposes in an indoor positioning system when the designer cannot control the network configuration. In this work, we design a hybrid positioning system that combines inertial measurements, from low-cost inertial sensors embedded in a smartphone, with RSS measurements through an extended Kalman filter. The system has been validated in a real scenario, and results show that our system improves the positioning accuracy of the PDR system thanks to the use of two WiFi receivers. The designed system obtains an accuracy up to 1.4 m in a scenario of 6000 m2

    A emigração cubana e saariana. Entre a “traição” e a esperança

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    Despite the scarcity of comparative academic literature, there exists a close relationship between Cuba and the Western Sahara. is connection was carved during the Cold War, by means of the assistance, respect and shared position oered in the face of social emancipation processes. is article reects on the implications of the mobility and migratory control policies of these two experiences that, despite their geographic separation and distinct histories, developed political projects based on the construction of egalitarian societies under the socialist ideology. e established migration discourses and regulations in the two cases show clear connections between both political projects and their steadfastness.A pesar de la escasez de trabajos académicos comparativos, existe una estrecha relación entre Cuba y el Sáhara Occidental. Dicho vínculo fue labrándose durante la Guerra Fría, desde la ayuda, el respeto y una postura compartida frente a procesos de emancipación social. El presente artículo reflexiona sobre las implicaciones de la movilidad y las políticas de control migratorio de estas dos experiencias que, a pesar de sus distancias geográficas y diferencias históricas, desarrollaron proyectos políticos basados en la construcción de sociedades igualitarias bajo la ideología socialista. Los discursos y regulaciones establecidos sobre la migración en uno y otro caso muestran evidentes conexiones entre ambos proyectos políticos y sus pretensiones de perdurabilidad. Apesar da escassez de trabalhos acadêmicos comparativos, existe uma estreita relação entre Cuba e o Saara Ocidental. Dito vínculo foi sendo construído durante a Guerra Fria, desde a ajuda, o respeito e uma postura compartilhada diante de processos de emancipação social. O presente artigo reete sobre as implicações da mobilidade e as políticas de controle migratório destas duas experiências que, apesar de suas distâncias geográcas e diferenças históricas, desenvolveram projetos políticos baseados na construção de sociedades igualitárias sob a ideologia socialista. Os discursos e regulamentos estabelecidos sobre a migração em ambos os casos mostram evidentes conexões entre ambos os projetos políticos e suas pretensões de durabilidade

    Balancing near-field enhancement and hot carrier injection: plasmonic photocatalysis in energy-transfer cascade assemblies

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    Photocatalysisstands as a very promisingalternativeto photovoltaicsin exploitingsolar energyand storingit inchemicalproductsthrougha single-stepprocess.A centralobstacleto its broad implementationis its low conversionefficiency,motivatingresearchin differentfields to bring about a breakthroughin this technology.Using plasmonicmaterialsto photosensitizetraditionalsemiconductorphotocatalystsis a popularstrategywhose full potentialis yet to be fully exploited.In this work, we useCdS quantumdots as a bridge system,reapingenergyfrom Au nanostructuresand deliveringit to TiO2nanoparticlesservingascatalyticcenters.The quantumdots can do this by becomingan intermediatestep in a charge-transfercascadeinitiatedin theplasmonicsystemor by creatingan electron−holepair at an improvedrate due to their interactionwith the enhancednear-fieldcreatedby the plasmonicnanoparticles.Our results show a significantaccelerationin the reactionupon combiningthese elementsinhybrid colloidalphotocatalyststhat promotethe role of the near-fieldenhancementeffect, and we show how to engineercomplexesexploitingthis approach.In doing so, we also explorethe complexinterplaybetweenthe differentmechanismsinvolvedin thephotocatalyticprocess,highlightingthe importanceof the Au nanoparticles’morphologyin their photosensitizingcapabilitiesMinisterio de Universidades | Ref. 33.50.460A.752Ministerio de Ciencia e Innovación | Ref. PDC2021-121787-I00Ministerio de Ciencia e Innovación | Ref. PID2020-113704RB-I00Ministerio de Ciencia e Innovación | Ref. PID2020-118282RA-I00Ministerio de Ciencia e Innovación | Ref. PID2020-120306RB-I00Ministerio de Ciencia e Innovación | Ref. RYC2021-033818-IMinisterio de Ciencia e Innovación | Ref. TED2021-130038A-I00Ministerio de Ciencia e Innovación | Ref. TED2021-132101B-I00Xunta de Galicia | Ref. IN607A 2018/5Generalitat de Catalunya | Ref. 2020SGR00166Centro Singular de Investigación de Galicia | Ref. ED431G 201906National Natural Science Foundation of China | Ref. 22250610200Universitat Rovira i Virgili | Ref. 2021PFR-URV-B2-02United States-Israel Binational Science Foundation | Ref. 2018050Universidade de Vigo/CISU

    Global Spillovers of a China Hard Landing

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    Hand washing promotion for preventing diarrhoea.

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    BACKGROUND: Diarrhoea accounts for 1.8 million deaths in children in low- and middle-income countries (LMICs). One of the identified strategies to prevent diarrhoea is hand washing. OBJECTIVES: To assess the effects of hand washing promotion interventions on diarrhoeal episodes in children and adults. SEARCH METHODS: We searched the Cochrane Infectious Diseases Group Specialized Register (27 May 2015); CENTRAL (published in the Cochrane Library 2015, Issue 5); MEDLINE (1966 to 27 May 2015); EMBASE (1974 to 27 May 2015); LILACS (1982 to 27 May 2015); PsycINFO (1967 to 27 May 2015); Science Citation Index and Social Science Citation Index (1981 to 27 May 2015); ERIC (1966 to 27 May 2015); SPECTR (2000 to 27 May 2015); Bibliomap (1990 to 27 May 2015); RoRe, The Grey Literature (2002 to 27 May 2015); World Health Organization (WHO) International Clinical Trial Registry Platform (ICTRP), metaRegister of Controlled Trials (mRCT), and reference lists of articles up to 27 May 2015. We also contacted researchers and organizations in the field. SELECTION CRITERIA: Individually randomized controlled trials (RCTs) and cluster-RCTs that compared the effects of hand washing interventions on diarrhoea episodes in children and adults with no intervention. DATA COLLECTION AND ANALYSIS: Three review authors independently assessed trial eligibility, extracted data, and assessed risk of bias. We stratified the analyses for child day-care centres or schools, community, and hospital-based settings. Where appropriate, incidence rate ratios (IRR) were pooled using the generic inverse variance method and random-effects model with 95% confidence intervals (CIs). We used the GRADE approach to assess the quality of evidence. MAIN RESULTS: We included 22 RCTs: 12 trials from child day-care centres or schools in mainly high-income countries (54,006 participants), nine community-based trials in LMICs (15,303 participants), and one hospital-based trial among people with acquired immune deficiency syndrome (AIDS) (148 participants).Hand washing promotion (education activities, sometimes with provision of soap) at child day-care facilities or schools prevents around one-third of diarrhoea episodes in high income countries (rate ratio 0.70; 95% CI 0.58 to 0.85; nine trials, 4664 participants, high quality evidence), and may prevent a similar proportion in LMICs but only two trials from urban Egypt and Kenya have evaluated this (rate ratio 0.66, 95% CI 0.43 to 0.99; two trials, 45,380 participants, low quality evidence). Only three trials reported measures of behaviour change and the methods of data collection were susceptible to bias. In one trial from the USA hand washing behaviour was reported to improve; and in the trial from Kenya that provided free soap, hand washing did not increase, but soap use did (data not pooled; three trials, 1845 participants, low quality evidence).Hand washing promotion among communities in LMICs probably prevents around one-quarter of diarrhoea episodes (rate ratio 0.72, 95% CI 0.62 to 0.83; eight trials, 14,726 participants, moderate quality evidence). However, six of these eight trials were from Asian settings, with only single trials from South America and sub-Saharan Africa. In six trials, soap was provided free alongside hand washing education, and the overall average effect size was larger than in the two trials which did not provide soap (soap provided: rate ratio 0.66, 95% CI 0.56 to 0.78; six trials, 11,422 participants; education only: rate ratio: 0.84, 95% CI 0.67 to 1.05; two trials, 3304 participants). There was increased hand washing at major prompts (before eating/cooking, after visiting the toilet or cleaning the baby's bottom), and increased compliance to hand hygiene procedure (behavioural outcome) in the intervention groups than the control in community trials (data not pooled: three trials, 3490 participants, high quality evidence).Hand washing promotion for the one trial conducted in a hospital among high-risk population showed significant reduction in mean episodes of diarrhoea (1.68 fewer) in the intervention group (Mean difference 1.68, 95% CI 1.93 to 1.43; one trial, 148 participants, moderate quality evidence). There was increase in hand washing frequency, seven times per day in the intervention group versus three times in the control in this hospital trial (one trial, 148 participants, moderate quality evidence).We found no trials evaluating or reporting the effects of hand washing promotions on diarrhoea-related deaths, all-cause-under five mortality, or costs. AUTHORS' CONCLUSIONS: Hand washing promotion probably reduces diarrhoea episodes in both child day-care centres in high-income countries and among communities living in LMICs by about 30%. However, less is known about how to help people maintain hand washing habits in the longer term
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