Abstract
Preparing materials which simultaneously exhibit spontaneous magnetic and electrical polarisations is challenging as the electronic features which are typically used to stabilise each of ...these two polarisations in materials are contradictory. Here we show that by performing low-temperature cation-exchange reactions on a hybrid improper ferroelectric material, Li
2
SrTa
2
O
7
, which adopts a polar structure due to a cooperative tilting of its constituent TaO
6
octahedra rather than an electronically driven atom displacement, a paramagnetic polar phase, MnSrTa
2
O
7
, can be prepared. On cooling below 43 K the Mn
2+
centres in MnSrTa
2
O
7
adopt a canted antiferromagnetic state, with a small spontaneous magnetic moment. On further cooling to 38 K there is a further transition in which the size of the ferromagnetic moment increases coincident with a decrease in magnitude of the polar distortion, consistent with a coupling between the two polarisations.
Octahedral distortion in ABO3 perovskite materials is ubiquitous because of the ionic size mismatch between A and B cations, leading to various kinds of crystal symmetry. However, such a distortion ...always results in centrosymmetric structures except for the covalent bond formation because of the second-order Jahn–Teller (SOJT) effect that occurs with d0 or lone-pair cations. Here, we report that an unusual combination of the layered A-site cation ordering and B-site rock salt ordering in NaYNiWO6 prepared under high-pressure and high-temperature conditions results not only in a polar (P21) structure, as revealed by the neutron diffraction analysis, but exhibits multiferroic properties below the magnetic ordering of Ni2+ ions (T N = 21 K). Analysis of the neutron diffraction data at 20 K reveals an incommensurate sinusoidal spin ordering with the propagation vector, k i = (0.471(2), 0, 0.491(4)), and a commensurate collinear spin structure with k c = (0.5, 0, 0.5) below 18 K. X-ray diffraction data confirm the polar structure in Dy, Ho, and Yb compounds. All four compounds exhibit a switchable change in electric polarization (ΔP) at the magnetic ordering temperatures, demonstrating coupling between ferroelectricity and magnetism.
Nonalcoholic fatty liver disease (NAFLD) ranges from simple steatosis (SS) to nonalcoholic steatohepatitis (NASH). Though liver‐related risk seems confined to NASH, it is currently unclear whether ...NASH has a higher risk of cardiovascular disease (CVD) and diabetes than SS as a result of the coexistence of obesity and other cardiometabolic confounders. Adipose tissue is an emerging modulator of liver disease in NAFLD and of cardiometabolic disease in the general population. We evaluated in SS and NASH (1) glucose homeostasis and cardiovascular risk profile and (2) the effect of adipose tissue dysfunction, assessed in fasting conditions and postprandially, on liver injury, glucose and lipoprotein metabolism, and markers of early atherosclerosis. Forty nonobese, nondiabetic, normolipidemic biopsy‐proven NAFLD patients (20 with SS and 20 with NASH) and 40 healthy subjects, matched for overall/abdominal adiposity and metabolic syndrome, underwent an oral fat load test, with measurement of plasma triglyceride‐rich lipoproteins, oxidized low‐density lipoproteins, adipokines, and cytokeratin‐18 fragments, and an oral glucose tolerance test with minimal model analysis to yield glucose homeostasis parameters. Circulating endothelial adhesion molecules were measured, and adipose tissue insulin resistance (adipose IR) index and visceral adiposity index were calculated. Despite similar fasting values, compared to SS, NASH showed a more atherogenic postprandial lipoprotein profile, an altered adipokine response (i.e., higher resistin increase and an adiponectin fall), and hepatocyte apoptosis activation after fat ingestion. Adipose IR index, endothelial adhesion molecules, and hepatic insulin resistance progressively increased across NAFLD stages. NASH, but not SS, showed an impaired pancreatic β‐cell function. On multiple regression analysis, adipose IR index and postprandial adiponectin independently predicted liver histology and altered cardiometabolic parameters. Conclusion: Adipose tissue dysfunction, including a maladaptive adipokine response to fat ingestion, modulates liver injury and cardiometabolic risk in NAFLD. (HEPATOLOGY 2012;56:933–942)
Emergent helical texture of electric dipoles Khalyavin, Dmitry D.; Johnson, Roger D.; Orlandi, Fabio ...
Science (American Association for the Advancement of Science),
08/2020, Letnik:
369, Številka:
6504
Journal Article
Recenzirano
Odprti dostop
A helix of dipoles
In magnetic materials, magnetic dipoles typically line up parallel or antiparallel to each other. However, more complex orderings, such as helical, can also occur. Khalyavin
et al.
...found that in the material BiCu
0.1
Mn
6.9
O
12
, a helical order can be formed out of electric rather than magnetic dipoles. The material also harbors an associated structural helical order, which symmetry analysis suggests might be switchable with an applied electric field.
Science
, this issue p.
680
Light hole doping of the quadruple perovskite BiMn
7
O
12
results in an unusual ordering.
Long-range ordering of magnetic dipoles in bulk materials gives rise to a broad range of magnetic structures, from simple collinear ferromagnets and antiferromagnets, to complex magnetic helicoidal textures stabilized by competing exchange interactions. In contrast, dipolar order in dielectric crystals is typically limited to parallel (ferroelectric) and antiparallel (antiferroelectric) collinear alignments of electric dipoles. Here, we report an observation of incommensurate helical ordering of electric dipoles by light hole doping of the quadruple perovskite BiMn
7
O
12
. In analogy with magnetism, the electric dipole helicoidal texture is stabilized by competing instabilities. Specifically, orbital ordering and lone electron pair stereochemical activity compete, giving rise to phase transitions from a nonchiral cubic structure to an incommensurate electric dipole and orbital helix via an intermediate density wave.
Artefact conditions need to be continuously monitored to avoid degradation effects naturally caused by time and public exploitation in order to increase the value of cultural assets. In this way, the ...atmospheric analysis of both biological and chemical pollutants potentially present inside conservation environments represents valid support for the adoption of preventive conservation actions by evaluating periodically the presence of risk for the same artefacts. The aim of the present study was to analyze the fungal particles, potentially biodeteriogen, through aerobiological volumetric monitoring, particularly inside valuable historical, artistic, and cultural sites. Different exposition and conservation typologies of the artefacts with different flows of visitors were considered. The applied methodologies have furnished a reliable description of biological air pollution due to the presence of fungal spores-moreover, they have allowed for the prevention of risk situations and the measurement of their evolution in order to limit degradation processes. Through aerobiological monitoring, it was possible to provide important indications for interventions of prevention, conservation and restoration of cultural heritage in indoor environments.
In order to estimate the impact of climate change on the phenological parameters and to compare them with the historical record, a decision support system (DSS) has been applied employing a ...Phenological Modelling Platform. Biological observations of two willow species (
Salix acutifolia
and
smithiana
Willd) in 3 gardens at different altitudes located in Central Italy were utilized to identify suitable phenological models related to four main vegetative phase timings (BBCH11, BBCH91, BBCH 94, BBCH95), and male full flowering (BBCH 65) clearly identifiable in these species. The present investigation identifies the best phenological models for the main phenophases allowing their practical application as real-time monitoring and plant development prediction tools. Sigmoid model revealed high performances in simulating spring vegetative phases, BBCH11 (First leaves unfolded), and BBCH91 (Shoot and foliage growth completed).
Salix acutifolia
Willd. development appeared to be more related to temperature amount interpreted by phenological models in comparison to
Salix smithiana
Willd. above all during spring (BBCH11 and 91), probably due to a different grade of phenotypic plasticity between the 2 considered species.
Abstract
Mixed-valent transition metal compounds display complex structural, electronic and magnetic properties which can often be exquisitely tuned. Here the charge-ordered state of stoichiometric ...CaFe
3
O
5
is probed using neutron powder diffraction, Monte Carlo simulation and symmetry analysis. Magnetic ordering is dominated by the formation of ferromagnetic Fe
3+
–Fe
2+
–Fe
3+
trimers which are evident above the magnetic ordering transition. Between
T
N
= 289 K and 281 K an incommensurate magnetically ordered phase develops due to magnetic frustration, but a spin Jahn-Teller distortion lifts the frustration and enables the magnetic ordering to lock in to a charge-ordered commensurate state at lower temperatures. Stoichiometric CaFe
3
O
5
exhibits single phase behaviour throughout and avoids the phase separation into two distinct crystallographic phases with different magnetic structures and Fe valence distributions reported recently, which likely occurs due to partial Fe
2+
for Ca
2+
substitution. This underlines the sensitivity of the magnetism and chemistry of these mixed-valent systems to composition.
Tetrahedrite, Cu12Sb4S13, is an abundant mineral with excellent thermoelectric properties owing to its low thermal conductivity. The electronic and structural origin of the intriguing physical ...properties of tetrahedrite, including its metal‐to‐semiconductor transition (MST), remains largely unknown. This work presents the first determination of the low‐temperature structure of tetrahedrite that accounts for its unique properties. Contrary to prior conjectures, the results show that the trigonal–planar copper cations remain in planar coordination below the MST. The atomic displacement parameters of the trigonal–planar copper cations, which have been linked to low thermal conductivity, increase by 200% above the MST. The phase transition is a consequence of the orbital degeneracy of the highest occupied 3d cluster orbitals of the copper clusters found in the cubic phase. This study reveals that a Jahn–Teller electronic instability leads to the formation of “molecular‐like” Cu57+ clusters and suppresses copper rattling vibrations due to the strengthening of direct copper–copper interactions. First principles calculations demonstrate that the structural phase transition opens a small band gap in the electronic density of states and eliminates the unstable phonon modes. These results provide insights on the interplay between phonon transport, electronic properties, and crystal structure in mixed‐valence compounds.
Direct copper–copper interactions in tetrahedrite result in the formation of pentameric Cu57+ clusters below the metal‐to‐semiconductor transition. The enhancement of copper–copper interactions in these “molecular‐like” clusters “locks” the trigonal–planar copper cations in place, suppressing the out‐of‐plane rattling vibrations to which low thermal conductivity is attributed.
Background and purpose
Ketogenic diet (KD) is based on restriction of carbohydrate intake. Metabolism is forced to obtain energy starting from β-oxidation of fatty acids which, turned into ketone ...bodies, can also be used by central nervous system (CNS). KD use in treatment of chronic migraine has recently been considered. We set out to verify modification of symptoms in patients with refractory chronic migraine in response to KD.
Methods
Fifty patients were enrolled of which 38 completed the procedures the study and 23 were considered in the statistics. All of the patients considered in our study were affected by medication overuse headache (MOH). They were on a KD for 3 months. The following parameters have been checked at
t
= 0 and every 30 days for 6 months: migraine episode length (
n
. hours/day), frequency (
n
. days/month), level of pain of every episode measured on a scale from 1 to 3 (1 = mild; 2 = moderate; 3 = severe), and
n
. analgesic drugs taken/month.
Results
Days with symptoms decreased from 30 (median value) to 7.5 with
p
< 0.0001. The duration of the migraine episodes decreased from 24 h (median value) to 5.5 h with
p
< 0.0016. The patients’ pain level, initially at maximum value for 83% of the participants, improved for 55% of them (
p
< 0.0024). The number of drugs taken in a month decreased from 30 doses (median value) to 6 doses.
Conclusions
It can be stated that a 3-month KD resulted in a reduction of painful symptoms of drug refractory chronic migraine. This result may suggest an improvement in quality of life of the patients, even without a tabulated data collection.
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