Valley symmetry breaking and gap tuning in graphene by spin doping

We study graphene with an adsorbed spin texture, where the localized spins create a periodic magnetic flux. The latter produces gaps in the graphene spectrum and breaks the valley symmetry. The resulting effective electronic model, which is similar to Haldane's periodic flux model, allows us to tune the gap of one valley independently from that of the other valley. This leads to the formation of two Hall plateaux and a quantum Hall transition. We discuss the density of states, optical longitudinal and Hall conductivities for nonzero frequencies and nonzero temperatures. A robust logarithmic singularity appears in the Hall conductivity when the frequency of the external field agrees with the width of the gap.Comment: 14 pages, 7 figure

Branching: the Essence of Constraint Solving

This paper focuses on the branching process for solving any constraint satisfaction problem (CSP). A parametrised schema is proposed that (with suitable instantiations of the parameters) can solve CSP's on both finite and infinite domains. The paper presents a formal specification of the schema and a statement of a number of interesting properties that, subject to certain conditions, are satisfied by any instances of the schema. It is also shown that the operational procedures of many constraint systems including cooperative systems) satisfy these conditions. Moreover, the schema is also used to solve the same CSP in different ways by means of different instantiations of its parameters.Comment: 18 pages, 2 figures, Proceedings ERCIM Workshop on Constraints (Prague, June 2001

Dust and Gas in the disc of HL Tauri: Surface density, dust settling, and dust-to-gas ratio

The recent ALMA observations of the disc surrounding HL Tau reveal a very complex dust spatial distribution. We present a radiative transfer model accounting for the observed gaps and bright rings as well as radial changes of the emissivity index. We find that the dust density is depleted by at least a factor 10 in the main gaps compared to the surrounding rings. Ring masses range from 10-100 M$_{\oplus}$ in dust, and, we find that each of the deepest gaps is consistent with the removal of up to 40 M$_{\oplus}$ of dust. If this material has accumulated into rocky bodies, these would be close to the point of runaway gas accretion. Our model indicates that the outermost ring is depleted in millimetre grains compared to the central rings. This suggests faster grain growth in the central regions and/or radial migration of the larger grains. The morphology of the gaps observed by ALMA - well separated and showing a high degree of contrast with the bright rings over all azimuths - indicates that the millimetre dust disc is geometrically thin (scale height $\approx$ 1 au at 100 au) and that a large amount of settling of large grains has already occurred. Assuming a standard dust settling model, we find that the observations are consistent with a turbulent viscosity coefficient of a few $10^{-4}$. We estimate the gas/dust ratio in this thin layer to be of the order of 5 if the initial ratio is 100. The HCO$^+$ and CO emission is consistent with gas in Keplerian motion around a 1.7 $M_\odot$ star at radii from $\leq 10 - 120\,$au.Comment: 12 pages, 8 figures, published in ApJ, same version as before but with slightly extended discussion on temperature and masses to account for literature published since initial submissio

The Chemical Enrichment History of the Small Magellanic Cloud and Its Gradients

We present stellar metallicities derived from Ca II triplet spectroscopy in over 350 red giant branch stars in 13 fields distributed in different positions in the SMC, ranging from $\sim$1\arcdeg\@ to $\sim$4\arcdeg\@ from its center. In the innermost fields the average metallicity is [Fe/H] $\sim -1$. This value decreases when we move away towards outermost regions. This is the first detection of a metallicity gradient in this galaxy. We show that the metallicity gradient is related to an age gradient, in the sense that more metal-rich stars, which are also younger, are concentrated in the central regions of the galaxy.Comment: 30 pages, 13 figures, accepted for publication in Astronomical Journa

The CARESSES study protocol: testing and evaluating culturally competent socially assistive robots among older adults residing in long term care homes through a controlled experimental trial

Background : This article describes the design of an intervention study that focuses on whether and to what degree culturally competent social robots can improve health and well-being related outcomes among older adults residing long-term care homes. The trial forms the final stage of the international, multidisciplinary CARESSES project aimed at designing, developing and evaluating culturally competent robots that can assist older people according to the culture of the individual they are supporting. The importance of cultural competence has been demonstrated in previous nursing literature to be key towards improving health outcomes among patients. Method : This study employed a mixed-method, single-blind, parallel-group controlled before-and-after experimental trial design that took place in England and Japan. It aimed to recruit 45 residents of long-term care homes aged ≥65 years, possess sufficient cognitive and physical health and who self-identify with the English, Indian or Japanese culture (n = 15 each). Participants were allocated to either the experimental group, control group 1 or control group 2 (all n = 15). Those allocated to the experimental group or control group 1 received a Pepper robot programmed with the CARESSES culturally competent artificial intelligence (experimental group) or a limited version of this software (control group 1) for 18 h across 2 weeks. Participants in control group 2 did not receive a robot and continued to receive care as usual. Participants could also nominate their informal carer(s) to participate. Quantitative data collection occurred at baseline, after 1 week of use, and after 2 weeks of use with the latter time-point also including qualitative semi-structured interviews that explored their experience and perceptions further. Quantitative outcomes of interest included perceptions of robotic cultural competence, health-related quality of life, loneliness, user satisfaction, attitudes towards robots and caregiver burden. Discussion : This trial adds to the current preliminary and limited pool of evidence regarding the benefits of socially assistive robots for older adults which to date indicates considerable potential for improving outcomes. It is the first to assess whether and to what extent cultural competence carries importance in generating improvements to well-being

A tripartite filter design for seamless pedestrian navigation using recursive 2-means clustering and Tukey update

Mobile devices are desired to guide users seamlessly to diverse destinations indoors and outdoors. The positioning fixing subsystems often provide poor quality measurements with gaps in an urban environment. No single position fixing technology works continuously. Many sensor fusion variations have been previously trialed to overcome this challenge, including the particle filter that is robust and the Kalman filter which is fast. However, a lack exists, of context aware, seamless systems that are able to use the most fit sensors and methods in the correct context. A novel adaptive and modular tripartite navigation filter design is presented to enable seamless navigation. It consists of a sensor subsystem, a context inference and a navigation filter blocks. A foot-mounted inertial measurement unit (IMU), a Global Navigation Satellite System (GNSS) receiver, Bluetooth Low Energy (BLE) and Ultrawideband (UWB) positioning systems were used in the evaluation implementation of this design. A novel recursive 2-means clustering method was developed to track multiple hypotheses when there are gaps in position fixes. The closest hypothesis to a new position fix is selected when the gap ends. Moreover, when the position fix quality measure is not reliable, a fusion approach using a Tukey-style particle filter measurement update is introduced. Results show the successful operation of the design implementation. The Tukey update improves accuracy by 5% and together with the clustering method the system robustness is enhanced

High Levels of Recombination among Streptococcus pneumoniae Isolates from the Gambia

We carried out multilocus sequence typing (MLST) on 148 pneumococcal carriage isolates collected from children <24 months old in the Upper River Division, the Gambia. MLST revealed a diverse population. Seventy-six different sequence types (STs) were found, the most common of which were 802 and 919, associated with 23F and 6A serotypes, respectively. Comparison with the MLST database showed that only 11 of the STs found in the present sample had been reported outside Africa. Six STs showed evidence of capsular switching (172, 802, 847, 1730, 1736, and 1737). Serotype switches were confirmed by microarrays that detected capsule genes. Of isolates analyzed by using microarrays, 40/69 (58%) harbored the tetM resistance determinant. A statistical genetic analysis to detect recombination found that 49/144 (34%) isolates showed significant (P < 0.05) evidence of admixture, which is greater than that observed in similar samples from the United Kingdom (5%) and Finland (2%). We hypothesize that large amounts of admixture could reflect the high prevalence of multiple carriage in this region, leading to more opportunities for homologous recombination between strains. This could have consequences for the population response to conjugate vaccination