First-Principles Approach to Nonlinear Lattice Dynamics: Anomalous Spectra in PbTe

published_or_final_versio

Collective decision-making on triadic graphs

Many real-world networks exhibit community structures and non-trivial clustering associated with the occurrence of a considerable number of triangular subgraphs known as triadic motifs. Triads are a set of distinct triangles that do not share an edge with any other triangle in the network. Network motifs are subgraphs that occur significantly more often compared to random topologies. Two prominent examples, the feedforward loop and the feedback loop, occur in various real-world networks such as gene-regulatory networks, food webs or neuronal networks. However, as triangular connections are also prevalent in communication topologies of complex collective systems, it is worthwhile investigating the influence of triadic motifs on the collective decision-making dynamics. To this end, we generate networks called Triadic Graphs (TGs) exclusively from distinct triadic motifs. We then apply TGs as underlying topologies of systems with collective dynamics inspired from locust marching bands. We demonstrate that the motif type constituting the networks can have a paramount influence on group decision-making that cannot be explained solely in terms of the degree distribution. We find that, in contrast to the feedback loop, when the feedforward loop is the dominant subgraph, the resulting network is hierarchical and inhibits coherent behavior

Balanced electric-magnetic dihole in Kaluza-Klein theory

We present a four-dimensional double-black-hole (or dihole) solution in Kaluza-Klein theory, describing a superposition of an electrically charged and a magnetically charged black hole. This system can be balanced for appropriately chosen parameters, and the resulting space-time is completely regular on and outside the event horizons. This solution was constructed using the inverse-scattering method in five-dimensional vacuum gravity, in which it describes a rotating black ring surrounding a static black hole on a Taub-NUT background space. Various properties of this solution are studied, from both a four- and five-dimensional perspective.Comment: 33 pages, 6 figures; v2: expanded discussion of phase space, published versio

Observation of pseudogap behavior in a strongly interacting Fermi gas

Ultracold atomic Fermi gases present an opportunity to study strongly interacting Fermi systems in a controlled and uncomplicated setting. The ability to tune attractive interactions has led to the discovery of superfluidity in these systems with an extremely high transition temperature, near T/T_F = 0.2. This superfluidity is the electrically neutral analog of superconductivity; however, superfluidity in atomic Fermi gases occurs in the limit of strong interactions and defies a conventional BCS description. For these strong interactions, it is predicted that the onset of pairing and superfluidity can occur at different temperatures. This gives rise to a pseudogap region where, for a range of temperatures, the system retains some of the characteristics of the superfluid phase, such as a BCS-like dispersion and a partially gapped density of states, but does not exhibit superfluidity. By making two independent measurements: the direct observation of pair condensation in momentum space and a measurement of the single-particle spectral function using an analog to photoemission spectroscopy, we directly probe the pseudogap phase. Our measurements reveal a BCS-like dispersion with back-bending near the Fermi wave vector k_F that persists well above the transition temperature for pair condensation

Global minimum estimates of children affected by COVID-19-associated orphanhood and deaths of caregivers: a modelling study

BACKGROUND: The COVID-19 pandemic priorities have focused on prevention, detection, and response. Beyond morbidity and mortality, pandemics carry secondary impacts, such as children orphaned or bereft of their caregivers. Such children often face adverse consequences, including poverty, abuse, and institutionalisation. We provide estimates for the magnitude of this problem resulting from COVID-19 and describe the need for resource allocation. METHODS: We used mortality and fertility data to model minimum estimates and rates of COVID-19-associated deaths of primary or secondary caregivers for children younger than 18 years in 21 countries. We considered parents and custodial grandparents as primary caregivers, and co-residing grandparents or older kin (aged 60–84 years) as secondary caregivers. To avoid overcounting, we adjusted for possible clustering of deaths using an estimated secondary attack rate and age-specific infection–fatality ratios for SARS-CoV-2. We used these estimates to model global extrapolations for the number of children who have experienced COVID-19-associated deaths of primary and secondary caregivers. FINDINGS: Globally, from March 1, 2020, to April 30, 2021, we estimate 1 134 000 children (95% credible interval 884 000–1 185 000) experienced the death of primary caregivers, including at least one parent or custodial grandparent. 1 562 000 children (1 299 000–1 683 000) experienced the death of at least one primary or secondary caregiver. Countries in our study set with primary caregiver death rates of at least one per 1000 children included Peru (10·2 per 1000 children), South Africa (5·1), Mexico (3·5), Brazil (2·4), Colombia (2·3), Iran (1·7), the USA (1·5), Argentina (1·1), and Russia (1·0). Numbers of children orphaned exceeded numbers of deaths among those aged 15–50 years. Between two and five times more children had deceased fathers than deceased mothers. INTERPRETATION: Orphanhood and caregiver deaths are a hidden pandemic resulting from COVID-19-associated deaths. Accelerating equitable vaccine delivery is key to prevention. Psychosocial and economic support can help families to nurture children bereft of caregivers and help to ensure that institutionalisation is avoided. These data show the need for an additional pillar of our response: prevent, detect, respond, and care for children. FUNDING: UK Research and Innovation (Global Challenges Research Fund, Engineering and Physical Sciences Research Council, Medical Research Council), UK National Institute for Health Research, US National Institutes of Health, and Imperial College London

Comparative differences in musculoskeletal pain consultation and analgesic prescription for people with dementia

Painful musculoskeletal conditions are common in older adults, however pain identification, assessment, and management are reported to be suboptimal for people with dementia. Adequate pain management is an integral aspect of care for people with dementia to prevent or delay negative outcomes, such as behavioural and psychological changes, emergency department attendance, and premature nursing home admission. This study aims to examine musculoskeletal consultations and analgesic prescriptions for people with dementia compared to people without dementia. A dementia cohort (n=36,582) and matched cohort were identified in the Clinical Practice Research Datalink (a UK wide primary care database). Period prevalence for musculoskeletal consultations and analgesic prescriptions were described and logistic regression applied to estimate associations between dementia and musculoskeletal consultation/analgesic prescription from time of dementia diagnosis to 5 years post diagnosis. People with dementia had a consistently (over time) lower prevalence and odds of musculoskeletal consultation and analgesic prescription compared to people without dementia. The evidence suggests that pain management may be suboptimal for people with dementia. These results highlight the need to understand more about practical methods to increase awareness of pain and to employ better methods of pain assessment, evaluation of treatment response and acceptable and effective management for people with dementia, in primary care

Isotope effect on the transition temperature TcT_c in Fe-based superconductors: the current status

The results of the Fe isotope effect (Fe-IE) on the transition temperature $T_c$ obtained up to date in various Fe-based high temperature superconductors are summarized and reanalyzed by following the approach developed in [Phys. Rev. B 82, 212505 (2010)]. It is demonstrated that the very controversial results for Fe-IE on $T_c$ are caused by small structural changes occurring simultaneously with the Fe isotope exchange. The Fe-IE exponent on $T_c$ [$\alpha_{\rm Fe}=-(\Delta T_c/T_c)/(\Delta M/M)$, $M$ is the isotope mass] needs to be decomposed into two components with the one related to the structural changes ($\alpha_{\rm Fe}^{\rm str}$) and the genuine (intrinsic) one ($\alpha_{\rm Fe}^{\rm int}$). The validity of such decomposition is further confirmed by the fact that $\alpha_{\rm Fe}^{\rm int}$ coincides with the Fe-IE exponent on the characteristic phonon frequencies $\alpha_{\rm Fe}^{\rm ph}$ as is reported in recent EXAFS and Raman experiments.Comment: 7 pages, 4 figures. The paper is partially based on the results published in [New J. Phys. 12, 073024 (2010) = arXiv:1002.2510] and [Phys. Rev. B 82, 212505 (2010) = arXiv:1008.4540

Magnetically induced metal-insulator transition in Pb2CaOsO6

We report on the structural, magnetic, and electronic properties of two new double-perovskites synthesized under high pressure, Pb2CaOsO6 and Pb2ZnOsO6. Upon cooling below 80 K, Pb2CaOsO6 simultaneously undergoes a metal-to-insulator transition and develops antiferromagnetic order. Pb2ZnOsO6, on the other hand, remains a paramagnetic metal down to 2 K. The key difference between the two compounds lies in their crystal structures. The Os atoms in Pb2ZnOsO6 are arranged on an approximately face-centered cubic lattice with strong antiferromagnetic nearest-neighbor exchange couplings. The geometrical frustration inherent to this lattice prevents magnetic order from forming down to the lowest temperatures. In contrast, the unit cell of Pb2CaOsO6 is heavily distorted up to at least 500 K including antiferroelectriclike displacements of the Pb and O atoms despite metallic conductivity above 80 K. This distortion relieves the magnetic frustration, facilitating magnetic order which, in turn, drives the metal-insulator transition. Our results suggest that the phase transition in Pb2CaOsO6 is spin driven and could be a rare example of a Slater transition

A novel algorithm for dynamic student profile adaptation based on learning styles

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.E-learning recommendation systems are used to enhance student performance and knowledge by providing tailor- made services based on the students’ preferences and learning styles, which are typically stored in student profiles. For such systems to remain effective, the profiles need to be able to adapt and reflect the students’ changing behaviour. In this paper, we introduce new algorithms that are designed to track student learning behaviour patterns, capture their learning styles, and maintain dynamic student profiles within a recommendation system (RS). This paper also proposes a new method to extract features that characterise student behaviour to identify students’ learning styles with respect to the Felder-Silverman learning style model (FSLSM). In order to test the efficiency of the proposed algorithm, we present a series of experiments that use a dataset of real students to demonstrate how our proposed algorithm can effectively model a dynamic student profile and adapt to different student learning behaviour. The results revealed that the students could effectively increase their learning efficiency and quality for the courses when the learning styles are identified, and proper recommendations are made by using our method

L-Carnitine and extendin-4 improve outcomes following moderate brain contusion injury

© 2018, The Author(s). There is a need for pharmaceutical agents that can reduce neuronal loss and improve functional deficits following traumatic brain injury (TBI). Previous research suggests that oxidative stress and mitochondrial dysfunction play a major role in neuronal damage after TBI. Therefore, this study aimed to investigate two drugs known to have antioxidant effects, L-carnitine and exendin-4, in rats with moderate contusive TBI. L-carnitine (1.5 mM in drinking water) or exendin-4 (15 µg/kg/day, ip) were given immediately after the injury for 2 weeks. Neurological function and brain histology were examined (24 h and 6 weeks post injury). The rats with TBI showed slight sensory, motor and memory functional deficits at 24 h, but recovered by 6 weeks. Both treatments improved sensory and motor functions at 24 h, while only exendin-4 improved memory. Both treatments reduced cortical contusion at 24 h and 6 weeks, however neither affected gliosis and inflammatory cell activation. Oxidative stress was alleviated and mitochondrial reactive oxygen species was reduced by both treatments, however only mitochondrial functional marker protein transporter translocase of outer membrane 20 was increased at 24 h post injury. In conclusion, L-carnitine and exendin-4 treatments immediately after TBI can improve neurological functional outcome and tissue integrity by reducing oxidative stress