Elastic distortion determining conduction in BiFeO3 phase boundaries

It is now well-established that boundaries separating tetragonal-like (T) and rhombohedral-like (R) phases in BiFeO₃ thin films can show enhanced electrical conductivity. However, the origin of this conductivity remains elusive. Here, we study mixed-phase BiFeO₃ thin films, where local populations of T and R can be readily altered using stress and electric fields. We observe that phase boundary electrical conductivity in regions which have undergone stress-writing is significantly greater than in the virgin microstructure. We use high-end electron microscopy techniques to identify key differences between the R–T boundaries present in stress-written and as-grown microstructures, to gain a better understanding of the mechanism responsible for electrical conduction. We find that point defects (and associated mixed valence states) are present in both electrically conducting and non-conducting regions; crucially, in both cases, the spatial distribution of defects is relatively homogeneous: there is no evidence of phase boundary defect aggregation. Atomic resolution imaging reveals that the only significant difference between non-conducting and conducting boundaries is the elastic distortion evident – detailed analysis of localised crystallography shows that the strain accommodation across the R–T boundaries is much more extensive in stress-written than in as-grown microstructures; this has a substantial effect on the straightening of local bonds within regions seen to electrically conduct. This work therefore offers distinct evidence that the elastic distortion is more important than point defect accumulation in determining the phase boundary conduction properties in mixed-phase BiFeO₃.

The localized crystallography of conducting and non-conducting phase boundaries in mixed-phase BiFeO₃ is directly compared using scanning transmission electron microscopy techniques.

The complexity of electrical conductivity in domain walls in BiFeO₃ (and in ferroics in general) is as multifaceted as ever. Various influences such as point defect accumulation, octahedral rotations, magnetic interactions and electrostatic discontinuities are thought to be possible mechanisms at play,^1–8 either alone or in combination. The research area of domain wall conductivity is currently flourishing and the view that domain walls offer exciting prospects in terms of engineering systems in which the domain walls act as distinct identities to the domains which they separate is now widely accepted. We believe that it is pertinent timing to address a lack of experimental investigations providing meaningful direct comparison of the localised crystallography and defect structure responsible for observed enhanced electrical conductivity. This study is stimulated by the interesting discoveries of conductive phase boundaries, specifically, in mixed-phase BiFeO₃.^9,10 By tuning the local populations of the tetragonal-like (T) and rhombohedral-like (R) phases in BiFeO₃ thin films via electric and stress fields, we demonstrate that electrical conductivity along phase boundaries is significantly greater after stress-writing. We probe the key crystallographic differences between the R–T boundaries created via stress, compared to those already present in the as-grown microstructures, to disentangle the mechanism determining electrical conduction in mixed-phase BiFeO₃.The growth of BiFeO₃ on substrates enforcing a large in-plane compressive strain drives the formation of monoclinic phases that are approximately rhombohedral (R) and tetragonal (T). Similar to materials such as PbZr_0.53Ti_0.47O₃ that straddle a morphotropic phase boundary, highly strained BiFeO₃ can readily undergo phase transitions between the R and T phases (and vice versa). The high-strain T phase exhibits a tetragonal-like symmetry (almost P4mm) with a c/a ratio of ∼1.2; the Fe displacement towards one of the apical oxygens along [001]_pc results in fivefold oxygen coordinated Fe, and an enhanced polarisation roughly 1.5 times that of the bulk single crystal.^7,11 The R phase, on the other hand, resembles the rhombohedral bulk phase (almost R3c), where the Fe is octahedrally coordinated, with a ferroelectric distortion along the pseudocubic [111]_pc axis, and antiferrodistortive rotations of the FeO₆ octahedra around [111]_pc occur. The crystal structure and misfit strain associated with the native (as-grown) R and T phases is reported elsewhere, both theoretically^12–15 and experimentally,^6,7,16–21 making it well-known that the ferroelectric and the antiferrodistortive degrees of freedom in mixed-phase BiFeO₃ set it apart from other typical perovskites. Notably, despite the ample evidence provided on phase reversal and characterisation of the as-grown phases, most of the literature (especially regarding electric field cycling of the mixed-phase state) has been primarily concerned with X-ray diffraction (XRD) i.e. global measurements that will not necessarily pick up on the more subtle, atomic-scale aspects of structure local to the phase boundaries. The importance of the study described herein resides in the uniqueness of creating microstructures such that both the as-grown and stress-induced R–T phase boundaries can be included within one single cross-sectional transmission electron microscopy (TEM) lamella; this gives the best possible scenario to allow meaningful direct comparison of the localised crystallography and defect structure responsible for the observed enhanced electrical conductivity found at stress-induced phase boundaries.     

Chlorhexidine rinsing inhibits biofilm formation and causes biofilm disruption on dental enamel in situ

Clinical Oral Investigations - This in situ study aims to evaluate the effects of chlorhexidine (CHX) mouth rinsing on biofilm formation and moreover on the disruption of existing mature dental...     

Musicians show general enhancement of complex sound encoding and better inhibition of irrelevant auditory change in music: an ERP study

Using electrophysiology, we have examined two questions in relation to musical training – namely, whether it enhances sensory encoding of the human voice and whether it improves the ability to ignore irrelevant auditory change. Participants performed an auditory distraction task, in which they identified each sound as either short (350 ms) or long (550 ms) and ignored a change in timbre of the sounds. Sounds consisted of a male and a female voice saying a neutral sound [a], and of a cello and a French Horn playing an F3 note. In some blocks, musical sounds occurred on 80% of trials, while voice sounds on 20% of trials. In other blocks, the reverse was true. Participants heard naturally recorded sounds in half of experimental blocks and their spectrally‐rotated versions in the other half. Regarding voice perception, we found that musicians had a larger N1 event‐related potential component not only to vocal sounds but also to their never before heard spectrally‐rotated versions. We therefore conclude that musical training is associated with a general improvement in the early neural encoding of complex sounds. Regarding the ability to ignore irrelevant auditory change, musicians' accuracy tended to suffer less from the change in timbre of the sounds, especially when deviants were musical notes. This behavioral finding was accompanied by a marginally larger re‐orienting negativity in musicians, suggesting that their advantage may lie in a more efficient disengagement of attention from the distracting auditory dimension.     

Defining the Epsilon‐Sarcoglycan (SGCE) Gene Phenotypic Signature in Myoclonus‐Dystonia: A Reappraisal of Genetic Testing Criteria

Mutations or exon deletions of the epsilon‐sarcoglycan (SGCE) gene cause myoclonus‐dystonia (M‐D), but a subset of M‐D patients are mutation‐negative and the sensitivity and specificity of current genetic testing criteria are unknown. We screened 46 newly enrolled M‐D patients for SGCE mutations and deletions; moreover, 24 subjects previously testing negative for SGCE mutations underwent gene dosage analysis. In our combined cohorts, we calculated sensitivity, specificity, positive and negative predictive values, and area under the curve of 2 published sets of M‐D diagnostic criteria. A stepwise logistic regression was used to assess which patients' characteristics best discriminated mutation carriers and to calculate a new mutation predictive score (“new score”), which we validated in previously published cohorts. Nine of 46 (19.5%) patients of the new cohort carried SCGE mutations, including 5 novel point mutations and 1 whole‐gene deletion; in the old cohort, 1 patient with a complex phenotype carried a 5.9‐Mb deletion encompassing SGCE. Current diagnostic criteria had a poor ability to discriminate SGCE‐positive from SGCE‐negative patients in our cohort; conversely, age of onset, especially if associated with psychiatric features (as included in the new score), showed the best discriminatory power to individuate SGCE mutation carriers, both in our cohort and in the validation cohort. Our results suggest that young age at onset of motor symptoms, especially in association with psychiatric disturbance, are strongly predictive for SGCE positivity. We suggest performing gene dosage analysis by multiple ligation‐dependent probe amplification (MLPA) to individuate large SGCE deletions that can be responsible for complex phenotypes. © 2013 Movement Disorder Society     

Bilateral ectopic pregnancy

Bilateral simultaneous ectopic pregnancy is a very rare clinical condition. Two different subsets of patients can be distinguished: women presenting with the disease as a result of spontaneous conception and those with the condition after undergoing assisted reproduction procedures. This article reviews and analyzes 42 cases of bilateral ectopic pregnancies reported in the last 10 years, proposes a new classification of the disease, and presents some data that should be useful for the clinician who confronts this difficult entity.     

Alzheimer's disease and diet: a systematic review

Purpose/Aim: Approximately 44 million people worldwide have Alzheimer's disease (AD). Numerous claims have been made regarding the influence of diet on AD development. The aims of this systematic review were to summarize the evidence considering diet as a protective or risk factor for AD, identify methodological challenges and limitations, and provide future research directions. Methods: Medline, PsycINFO and PsycARTICLES were searched for articles that examined the relationship between diet and AD. Results: On the basis of the inclusion and exclusion criteria, 64 studies were included, generating a total of 141 dietary patterns or “models”. All studies were published between 1997 and 2015, with a total of 132 491 participants. Twelve studies examined the relationship between a Mediterranean (MeDi) diet and AD development, 10 of which revealed a significant association. Findings were inconsistent with respect to sample size, AD diagnosis and food measures. Further, the majority of studies (81.3%) included samples with mean baseline ages that were at risk for AD based on age (>65 years), ranging from 52.0 to 85.4 years. The range of follow-up periods was 1.5–32.0 years. Conclusions: The mean age of the samples poses a limitation in determining the influence of diet on AD; given that AD has a long prodromal phase prior to the manifestation of symptoms and decline. Further studies are necessary to determine whether diet is a risk or protective factor for AD, foster translation of research into clinical practice and elucidate dietary recommendations. Despite the methodological limitations, the finding that 50 of the 64 reviewed studies revealed an association between diet and AD incidence offers promising implications for diet as a modifiable risk factor for AD.     

Chemistry of the Fe2O3/BiFeO3 Interface in BiFeO3 Thin Film Heterostructures

We investigate the interfacial chemistry of secondary Fe₂O₃ phases formed in a BiFeO₃ (BFO) layer in BFO/ La_0.67Sr_0.33MnO₃ (LSMO)/SrTiO₃ (STO) heterostructures. A combination of high-resolution spherical aberration corrected scanning TEM and spectroscopy results, reveals that specific chemical and crystallographic similarities between Fe₂O₃ and BFO, enable the BFO layer to form a facile host for Fe₂O₃.     

Effect of a mediterranean-style diet on endothelial dysfunction and markers of vascular inflammation in the metabolic syndrome: a randomized trial

Context  The metabolic syndrome has been identified as a target for dietary therapies to reduce risk of cardiovascular disease; however, the role of diet in the etiology of the metabolic syndrome is poorly understood. Objective  To assess the effect of a Mediterranean-style diet on endothelial function and vascular inflammatory markers in patients with the metabolic syndrome. Design, Setting, and Patients  Randomized, single-blind trial conducted from June 2001 to January 2004 at a university hospital in Italy among 180 patients (99 men and 81 women) with the metabolic syndrome, as defined by the Adult Treatment Panel III. Interventions  Patients in the intervention group (n = 90) were instructed to follow a Mediterranean-style diet and received detailed advice about how to increase daily consumption of whole grains, fruits, vegetables, nuts, and olive oil; patients in the control group (n = 90) followed a prudent diet (carbohydrates, 50%-60%; proteins, 15%-20%; total fat, <30%). Main Outcome Measures  Nutrient intake; endothelial function score as a measure of blood pressure and platelet aggregation response to L-arginine; lipid and glucose parameters; insulin sensitivity; and circulating levels of high-sensitivity C-reactive protein (hs-CRP) and interleukins 6 (IL-6), 7 (IL-7), and 18 (IL-18). Results  After 2 years, patients following the Mediterranean-style diet consumed more foods rich in monounsaturated fat, polyunsaturated fat, and fiber and had a lower ratio of omega-6 to omega-3 fatty acids. Total fruit, vegetable, and nuts intake (274 g/d), whole grain intake (103 g/d), and olive oil consumption (8 g/d) were also significantly higher in the intervention group (P<.001). The level of physical activity increased in both groups by approximately 60%, without difference between groups (P = .22). Mean (SD) body weight decreased more in patients in the intervention group (–4.0 [1.1] kg) than in those in the control group (–1.2 [0.6] kg) (P<.001). Compared with patients consuming the control diet, patients consuming the intervention diet had significantly reduced serum concentrations of hs-CRP (P = .01), IL-6 (P = .04), IL-7 (P = 0.4), and IL-18 (P = 0.3), as well as decreased insulin resistance (P<.001). Endothelial function score improved in the intervention group (mean [SD] change, +1.9 [0.6]; P<.001) but remained stable in the control group (+0.2 [0.2]; P = .33). At 2 years of follow-up, 40 patients in the intervention group still had features of the metabolic syndrome, compared with 78 patients in the control group (P<.001). Conclusion  A Mediterranean-style diet might be effective in reducing the prevalence of the metabolic syndrome and its associated cardiovascular risk.