Collective magnetism at multiferroic vortex domain walls

Topological defects have been playgrounds for many emergent phenomena in complex matter such as superfluids, liquid crystals, and early universe. Recently, vortex-like topological defects with six interlocked structural antiphase and ferroelectric domains merging into a vortex core were revealed in multiferroic hexagonal manganites. Numerous vortices are found to form an intriguing self-organized network. Thus, it is imperative to find out the magnetic nature of these vortices. Using cryogenic magnetic force microscopy, we discovered unprecedented alternating net moments at domain walls around vortices that can correlate over the entire vortex network in hexagonal ErMnO3 The collective nature of domain wall magnetism originates from the uncompensated Er3+ moments and the correlated organization of the vortex network. Furthermore, our proposed model indicates a fascinating phenomenon of field-controllable spin chirality. Our results demonstrate a new route to achieving magnetoelectric coupling at domain walls in single-phase multiferroics, which may be harnessed for nanoscale multifunctional devices.Comment: 18 pages, 10 figure

Towards Sonification in Multimodal and User-friendly Explainable Artificial Intelligence

We are largely used to hearing explanations. For example, if someone thinks you are sad today, they might reply to your "why?"with "because you were so Hmmmmm-mmm-mmm". Today's Artificial Intelligence (AI), however, is - if at all - largely providing explanations of decisions in a visual or textual manner. While such approaches are good for communication via visual media such as in research papers or screens of intelligent devices, they may not always be the best way to explain; especially when the end user is not an expert. In particular, when the AI's task is about Audio Intelligence, visual explanations appear less intuitive than audible, sonified ones. Sonification has also great potential for explainable AI (XAI) in systems that deal with non-audio data - for example, because it does not require visual contact or active attention of a user. Hence, sonified explanations of AI decisions face a challenging, yet highly promising and pioneering task. That involves incorporating innovative XAI algorithms to allow pointing back at the learning data responsible for decisions made by an AI, and to include decomposition of the data to identify salient aspects. It further aims to identify the components of the preprocessing, feature representation, and learnt attention patterns that are responsible for the decisions. Finally, it targets decision-making at the model-level, to provide a holistic explanation of the chain of processing in typical pattern recognition problems from end-to-end. Sonified AI explanations will need to unite methods for sonification of the identified aspects that benefit decisions, decomposition and recomposition of audio to sonify which parts in the audio were responsible for the decision, and rendering attention patterns and salient feature representations audible. Benchmarking sonified XAI is challenging, as it will require a comparison against a backdrop of existing, state-of-the-art visual and textual alternatives, as well as synergistic complementation of all modalities in user evaluations. Sonified AI explanations will need to target different user groups to allow personalisation of the sonification experience for different user needs, to lead to a major breakthrough in comprehensibility of AI via hearing how decisions are made, hence supporting tomorrow's humane AI's trustability. Here, we introduce and motivate the general idea, and provide accompanying considerations including milestones of realisation of sonifed XAI and foreseeable risks.acceptedVersionPeer reviewe

Dispersive charge density wave excitations and temperature dependent commensuration in Bi2Sr2CaCu2O8+{\delta}

Experimental evidence on high-Tc cuprates reveals ubiquitous charge density wave (CDW) modulations, which coexist with superconductivity. Although the CDW had been predicted by theory, important questions remain about the extent to which the CDW influences lattice and charge degrees of freedom and its characteristics as functions of doping and temperature. These questions are intimately connected to the origin of the CDW and its relation to the mysterious cuprate pseudogap. Here, we use ultrahigh resolution resonant inelastic x-ray scattering (RIXS) to reveal new CDW character in underdoped Bi2Sr2CaCu2O8+{\delta} (Bi2212). At low temperature, we observe dispersive excitations from an incommensurate CDW that induces anomalously enhanced phonon intensity, unseen using other techniques. Near the pseudogap temperature T*, the CDW persists, but the associated excitations significantly weaken and the CDW wavevector shifts, becoming nearly commensurate with a periodicity of four lattice constants. The dispersive CDW excitations, phonon anomaly, and temperature dependent commensuration provide a comprehensive momentum space picture of complex CDW behavior and point to a closer relationship with the pseudogap state

Doping the holographic Mott insulator

Mott insulators form because of strong electron repulsions, being at the heart of strongly correlated electron physics. Conventionally these are understood as classical "traffic jams" of electrons described by a short-ranged entangled product ground state. Exploiting the holographic duality, which maps the physics of densely entangled matter onto gravitational black hole physics, we show how Mott-insulators can be constructed departing from entangled non-Fermi liquid metallic states, such as the strange metals found in cuprate superconductors. These "entangled Mott insulators" have traits in common with the "classical" Mott insulators, such as the formation of Mott gap in the optical conductivity, super-exchange-like interactions, and form "stripes" when doped. They also exhibit new properties: the ordering wave vectors are detached from the number of electrons in the unit cell, and the DC resistivity diverges algebraically instead of exponentially as function of temperature. These results may shed light on the mysterious ordering phenomena observed in underdoped cuprates.Comment: 27 pages, 9 figures. Accepted in Nature Physic

Performance of the 2017 and 2010 Revised McDonald Criteria in Predicting MS Diagnosis After a Clinically Isolated Syndrome: A MAGNIMS Study

BACKGROUND AND OBJECTIVES: To compare the performance of the 2017 revisions to the McDonald criteria with the 2010 McDonald criteria in establishing MS diagnosis and predicting prognosis in patients with clinically isolated syndrome (CIS) suggestive of multiple sclerosis (MS). METHODS: CSF examination, brain and spinal cord MRI obtained ≤5 months from CIS onset, and a follow-up brain MRI acquired within 15 months from CIS onset were evaluated in 785 CIS patients from 9 European centers. Date of second clinical attack and of reaching Expanded Disability Status Score (EDSS) ≥ 3.0, if they occurred, were also collected. Performance of the 2017 and 2010 McDonald criteria for dissemination in space (DIS), time (DIT) (including oligoclonal bands assessment) and DIS + DIT for predicting a second clinical attack (clinically definite [CD] MS) and EDSS ≥ 3.0 at follow-up was evaluated. Time to MS diagnosis for the different criteria was also estimated. RESULTS: At follow-up (median = 69.1 months), 406/785 CIS patients developed CDMS. At 36 months, the 2017 DIS + DIT criteria had higher sensitivity (0.83 vs 0.66), lower specificity (0.39 vs 0.60) and similar area under the curve values (0.61 vs 0.63). Median time to MS diagnosis was shorter with the 2017 vs the 2010 or CDMS criteria (2017 revision = 3.2; 2010 revision = 13.0; CDMS = 58.5 months). The 2 sets of criteria similarly predicted EDSS ≥ 3.0 milestone. Three periventricular lesions improved specificity in patients ≥45 years. DISCUSSION: The 2017 McDonald criteria showed higher sensitivity, lower specificity and similar accuracy in predicting CDMS compared to 2010 McDonald criteria, while shortening time to diagnosis of MS. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that the 2017 McDonald Criteria more accurately distinguish CDMS in patients early after a CIS when compared to the 2010 McDonald criteria

Safety, pharmacodynamics, and potential benefit of omaveloxolone in Friedreich ataxia

OBJECTIVE: Previous studies have demonstrated that suppression of Nrf2 in Friedreich ataxia tissues contributes to excess oxidative stress, mitochondrial dysfunction, and reduced ATP production. Omaveloxolone, an Nrf2 activator and NF-kB suppressor, targets dysfunctional inflammatory, metabolic, and bioenergetic pathways. The dose-ranging portion of this Phase 2 study assessed the safety, pharmacodynamics, and potential benefit of omaveloxolone in Friedreich ataxia patients (NCT02255435). METHODS: Sixty-nine Friedreich ataxia patients were randomized 3:1 to either omaveloxolone or placebo administered once daily for 12 weeks. Patients were randomized in cohorts of eight patients, at dose levels of 2.5–300 mg/day. RESULTS: Omaveloxolone was well tolerated, and adverse events were generally mild. Optimal pharmacodynamic changes (noted by changes in ferritin and GGT) were observed at doses of 80 and 160 mg/day. No significant changes were observed in the primary outcome, peak work load in maximal exercise testing (0.9 ± 2.9 W, placebo corrected). At the 160 mg/day dose, omaveloxolone improved the secondary outcome of the mFARS by 3.8 points versus baseline (P = 0.0001) and by 2.3 points versus placebo (P = 0.06). Omaveloxolone produced greater improvements in mFARS in patients that did not have musculoskeletal foot deformity (pes cavus). In patients without this foot deformity, omaveloxolone improved mFARS by 6.0 points from baseline (P < 0.0001) and by 4.4 points versus placebo (P = 0.01) at the 160 mg/day. INTERPRETATION: Treatment of Friedreich ataxia patients with omaveloxolone at the optimal dose level of 160 mg/day appears to improve neurological function. Therefore, omaveloxolone treatment is being examined in greater detail at 150 mg/day for Friedreich ataxia

Photo-enhanced antinodal conductivity in the pseudogap state of high-T-c cuprates

A major challenge in understanding the cuprate superconductors is to clarify the nature of the fundamental electronic correlations that lead to the pseudogap phenomenon. Here we use ultrashort light pulses to prepare a non-thermal distribution of excitations and capture novel properties that are hidden at equilibrium. Using a broadband (0.5-2 eV) probe, we are able to track the dynamics of the dielectric function and unveil an anomalous decrease in the scattering rate of the charge carriers in a pseudogap-like region of the temperature (T) and hole-doping (p) phase diagram. In this region, delimited by a well-defined T*(neq)(p) line, the photoexcitation process triggers the evolution of antinodal excitations from gapped (localized) to delocalized quasiparticles characterized by a longer lifetime. The novel concept of photo-enhanced antinodal conductivity is naturally explained within the singleband Hubbard model, in which the short-range Coulomb repulsion leads to a k-space differentiation between nodal quasiparticles and antinodal excitations. \ua9 2014 Macmillan Publishers Limited. All rights reserved

Prediction of a multiple sclerosis diagnosis in patients with clinically isolated syndrome using the 2016 MAGNIMS and 2010 McDonald criteria: a retrospective study

BACKGROUND: In 2016, the Magnetic Resonance Imaging in Multiple Sclerosis (MAGNIMS) network proposed modifications to the MRI criteria to define dissemination in space (DIS) and time (DIT) for the diagnosis of multiple sclerosis in patients with clinically isolated syndrome (CIS). Changes to the DIS definition included removal of the distinction between symptomatic and asymptomatic lesions, increasing the number of lesions needed to define periventricular involvement to three, combining cortical and juxtacortical lesions, and inclusion of optic nerve evaluation. For DIT, removal of the distinction between symptomatic and asymptomatic lesions was suggested. We compared the performance of the 2010 McDonald and 2016 MAGNIMS criteria for multiple sclerosis diagnosis in a large multicentre cohort of patients with CIS to provide evidence to guide revisions of multiple sclerosis diagnostic criteria. METHODS: Brain and spinal cord MRI and optic nerve assessments from patients with typical CIS suggestive of multiple sclerosis done less than 3 months from clinical onset in eight European multiple sclerosis centres were included in this retrospective study. Eligible patients were 16-60 years, and had a first CIS suggestive of CNS demyelination and typical of relapsing-remitting multiple sclerosis, a complete neurological examination, a baseline brain and spinal cord MRI scan obtained less than 3 months from clinical onset, and a follow-up brain scan obtained less than 12 months from CIS onset. We recorded occurrence of a second clinical attack (clinically definite multiple sclerosis) at months 36 and 60. We evaluated MRI criteria performance for DIS, DIT, and DIS plus DIT with a time-dependent receiver operating characteristic curve analysis. FINDINGS: Between June 16, 1995, and Jan 27, 2017, 571 patients with CIS were screened, of whom 368 met all study inclusion criteria. At the last evaluation (median 50·0 months [IQR 27·0-78·4]), 189 (51%) of 368 patients developed clinically definite multiple sclerosis. At 36 months, the two DIS criteria showed high sensitivity (2010 McDonald 0·91 [95% CI 0·85-0·94] and 2016 MAGNIMS 0·93 [0·88-0·96]), similar specificity (0·33 [0·25-0·42] and 0·32 [0·24-0·41]), and similar area under the curve values (AUC; 0·62 [0·57-0·67] and 0·63 [0·58-0·67]). Performance was not affected by inclusion of symptomatic lesions (sensitivity 0·92 [0·87-0·96], specificity 0·31 [0·23-0·40], AUC 0·62 [0·57-0·66]) or cortical lesions (sensitivity 0·92 [0·87-0·95], specificity 0·32 [0·24-0·41], AUC 0·62 [0·57-0·67]). Requirement of three periventricular lesions resulted in slightly lower sensitivity (0·85 [0·78-0·90], slightly higher specificity (0·40 [0·32-0·50], and similar AUC (0·63 [0·57-0·68]). Inclusion of optic nerve evaluation resulted in similar sensitivity (0·92 [0·87-0·96]), and slightly lower specificity (0·26 [0·18-0·34]) and AUC (0·59 [0·55-0·64]). AUC values were also similar for DIT (2010 McDonald 0·61 [0·55-0·67] and 2016 MAGNIMS 0·61 [0·55-0·66]) and DIS plus DIT (0·62 [0·56-0·67] and 0·64 [0·58-0·69]). INTERPRETATION: The 2016 MAGNIMS criteria showed similar accuracy to the 2010 McDonald criteria in predicting the development of clinically definite multiple sclerosis. Inclusion of symptomatic lesions is expected to simplify the clinical use of MRI criteria without reducing accuracy, and our findings suggest that needing three lesions to define periventricular involvement might slightly increase specificity, suggesting that these two factors could be considered during further revisions of multiple sclerosis diagnostic criteria. FUNDING: UK MS Society, National Institute for Health Research University College London Hospitals Biomedical Research Centre, Dutch MS Research Foundation