Mechanical Rippling for Diverse Ferroelectric Topologies in Otherwise Nonferroelectric SrTiO_{3} Nanofilms.

Polar topological structures such as skyrmions and merons have become an emerging research field due to their rich functionalities and promising applications in information storage. Up to now, the obtained polar topological structures are restricted to a few limited ferroelectrics with complex heterostructures, limiting their large-scale practical applications. Here, we circumvent this limitation by utilizing a nanoscale ripple-generated flexoelectric field as a universal means to create rich polar topological configurations in nonpolar nanofilms in a controllable fashion. Our extensive phase-field simulations show that a rippled SrTiO_{3} nanofilm with a single bulge activates polarizations that are stabilized in meron configurations, which further undergo topological transitions to Néel-type and Bloch-type skyrmions upon varying the geometries. The formation of these topologies originates from the curvature-dependent flexoelectric field, which extends beyond the common mechanism of geometric confinement that requires harsh energy conditions and strict temperature ranges. We further demonstrate that the rippled nanofilm with three-dimensional ripple patterns can accommodate other unreported modulated phases of ferroelectric topologies, which provide ferroelectric analogs to the complex spin topologies in magnets. The present study not only unveils the intriguing nanoscale electromechanical properties but also opens exciting opportunities to design various functional topological phenomena in flexible materials.

Emergent ultrasmall multiferroics in paraelectric perovskite oxide by hole polarons.

Ultimately small multiferroics with coupled ferroelectric and ferromagnetic order parameters have drawn considerable attention for their tremendous technological potential. Nevertheless, these ferroic orders inevitably disappear below the critical size of several nanometers in conventional ferroelectrics or multiferroics. Here, based on first-principles calculations, we propose a new strategy to overcome this limitation and create ultrasmall multiferroic elements in otherwise nonferroelectric CaTiO3 by engineering the interplay of oxygen octahedral rotations and hole polarons, though both of them are generally believed to be detrimental to ferroelectricity. It is found that the hole doped in CaTiO3 spontaneously forms a localized polaronic state. The lattice distortions associated with a hole polaron interacting with the intrinsic oxygen octahedral rotations in CaTiO3 effectively break the inversion symmetry and create atomic-scale ferroelectricity beyond the critical size limitation. The hole polaron also causes highly localized magnetism attributed to the associated spin-polarized electric state and thus manifests as a multiferroic polaron. Moreover, the hole polaron exhibits high hopping mobility accompanied by rich switching of polarization and magnetic directions, indicating strong magnetoelectric coupling with a mechanism dissimilar from that of conventional multiferroics. The present work provides a new mechanism to engineer inversion symmetry and opens avenues for designing unusual multifunctional materials.

Time course changes in insulin sensitivity during cardiac surgery: A retrospective study on intraoperative glycemic management using an artificial pancreas.

INTRODUCTION: Glycemic control is essential for improving the prognosis of cardiac surgery, although precise recommendations have not yet been established. Under a constant blood glucose level, the insulin infusion rate correlates with insulin resistance during glycemic control using an artificial pancreas (AP). We conducted this retrospective study to elucidate changes in intraoperative insulin sensitivity as a first step to creating glycemic control guidelines. METHODS: Fifty-five cardiac surgery patients at our hospital who underwent intraoperative glycemic control using an AP were enrolled. Twenty-three patients undergoing surgical procedures requiring cardiac arrest under hypothermic cardiopulmonary bypass (CPB) with minimum rectal temperatures lower than 32°C, 13 patients undergoing surgical procedures requiring cardiac arrest under hypothermic CPB with minimum rectal temperatures of 32°C, eight patients undergoing on-pump beating coronary artery bypass grafting and 11 patients undergoing off-pump coronary artery bypass were assigned to groups A, B, C and D, respectively. We analyzed the time course of changes in the data derived from glycemic control using the AP. RESULTS: Significant time course changes were observed in groups A and B, but not in groups C and D. Insulin resistance was induced after the start of hypothermic CPB in groups A and B, and the induced change was not resolved by the rewarming procedure, remaining sustained until the end of surgery. CONCLUSIONS: Hypothermia is the predominant factor of the induced insulin resistance during cardiac surgery. Thus, careful glycemic management during hypothermic CPB is important. Prospective clinical studies are required to confirm the findings of this study.

Ultrasmall-Scale Brittle Fracture Initiated from a Dislocation in SrTiO3.

Crystal defects often lead to an intriguing variety of catastrophic failures of materials and determine the mechanical properties. Here we discover that a dislocation, which was believed to be a source of plasticity, leads to brittle fracture in SrTiO3. The fracture mechanism, i.e., bond breaking at the dislocation core triggers crack initiation and subsequent fracture, is elucidated from an atomic view by hybrid quantum and molecular simulations and in situ nanomechanical experiments. The fracture strength of the dislocation-included SrTiO3 was theoretically evaluated to be 8.8-10.7 GPa, which was eminently lower than that of the pristine one (21.7 GPa). The experimental results agree well with the simulated ones. Moreover, the fracture toughness of the ultrasmall crack initiating from the dislocation is quantitatively evaluated. This study reveals not only the role of dislocations in brittle fracture but also provides an in-depth understanding of the fracture mechanism of dislocations at the atomic scale.

Topological ferroelectric nanostructures induced by mechanical strain in strontium titanate.

Ferroelectric materials exhibit novel topological polarization configurations due to geometric confinements originating from the material shapes and interfaces at the nanoscale. In this study, we demonstrate that those nontrivial topological ferroelectric nanostructures can be tailored in paraelectric nanoporous materials by mechanical loads using phase-field modeling. That is, in nanoporous strontium titanate, periodically-arrayed ferroelectric nanostructures in the shape of networks are formed due to strain concentrations by mechanical loads, and topological polarization configurations, such as hierarchical vortices, woven fabrics and nested structures of spiral like Hopf fibration, are stabilized in the structures strongly affected by the pore arrangements. Our work indicates that various ferroelectric nanostructures with novel shapes and topologies can be designed by controlling the pore arrangements and strain conditions in nanoporous SrTiO3, and thus provides a new pathway to realize novel topological ferroelectric nanostructures, which are essential for future nanodevices.

Periodically-arrayed ferroelectric nanostructures induced by dislocation structures in strontium titanate.

A dislocation induces ferroelectricity around it in incipient ferroelectric SrTiO3 due to some reasons such as electro-mechanical coupling and it being a one-dimensional ferroelectric nanostructure. Furthermore, this microstructure is arrayed periodically in the material and dislocation structures such as a dislocation wall are formed. Due to these facts, periodically-arrayed ferroelectric nanostructures, which show various intriguing polarization configurations and functionalities depending on the internal periodic structure, may be fabricated by dislocations. The phase-field simulation exhibits that a ferroelectric nano-region induced by the strain concentration and incidental electric field around a dislocation connects with each other in a dislocation wall. As a result, a periodic ferroelectric nano-region, which is a periodically-arrayed ferroelectric nanostructure embedded in paraelectric matrices, is formed. Our findings provide a new pathway for the fabrication of novel functional nanodevices in ferroelectric systems.

Intrinsic and extrinsic effects on the electrotoroidic switching in a ferroelectric notched nanodot by a homogeneous electric field.

The control of topological defects in ferroelectrics, in particular by a homogeneous electric field, has emerged as an active research direction. A polarization vortex, which is a fundamental topological defect formed in ferroelectric nanodots, has recently been demonstrated to be switchable by a homogeneous electric field through the control of the built-in electrical distribution using low-symmetry nanodots. Such electrotoroidic switching is investigated for nearly ideal systems, e.g., free-standing nanodots. However, the electrotoroidic switching may be impacted by several factors, for instance, the nanoscale effect of flexoelectricity (intrinsic effect), epitaxial strain and the frequency of the applied field (extrinsic effects). In the present study, the switching of the polarization vortex in a notched nanodot under a homogeneous electric field is investigated. The emphasis is put on a comparison between intrinsic and extrinsic effects on the vortex switching. The results show that the vortex switching takes place through alternate vortex-to-polar and polar-to-vortex transformations due to the appearance of the notch. Although the flexoelectricity breaks the symmetry of the polarization field in the notched nanodot during the polarization transformation and gives rise to an unusual behavior of the vortex core, which departs from the symmetry axis of the notched nanodot, this intrinsic effect plays a relatively insignificant role in the switching behavior of the polarization vortex. In comparison to the intrinsic effect, interestingly, the extrinsic effects strongly influence the vortex switching behavior. Specifically, the frequency of the applied electric field can alter both the shape of the toroidal hysteresis loop and the domain transformation process of the vortex switching. In addition, under substrate constraints, the magnitude of the coercive electric fields at which the vortex-to-polar and polar-to-vortex transformations occur linearly decreases with the increase of strain. The present study provides instructive information on the efficient control of a polarization vortex, which is dominated by extrinsic factors rather than intrinsic ones.

Spontaneous curling of freestanding Janus monolayer transition-metal dichalcogenides.

In this paper, using molecular dynamics simulations we report spontaneous curling behaviors of freestanding Janus monolayer S-Mo-Se (MoSeS) structures. Density functional theory calculations are performed to obtain the phonon dispersion and phonon spectra of the Janus monolayer MoSeS for analyzing its structural stability. The results show that the Janus monolayer MoSeS is structurally stable. Due to the lattice mismatch between MoS and MoSe domains, the Janus monolayer MoSeS at the freestanding state always spontaneously rolls up in a constant temperature and pressure system. The direction of curling is preferred along the armchair orientation. Specifically, as for the Janus monolayer MoSeS whose size is larger than ∼30 nm, it can spontaneously roll up into a nanotube structure. The underlying physical mechanisms of these phenomena are well uncovered by using classical Timoshenko plate theory and the minimum energy principle.

Multiferroic Dislocations in Ferroelectric PbTiO3.

Ultrathin multiferroics with coupled ferroelectric and ferromagnetic order parameters hold promise for novel technological paradigms, such as extremely thin magnetoelectric memories. However, these ferroic orders and their functions inevitably disappear below a fundamental size limit of several nanometers. Herein, we propose a novel design strategy for nanoscale multiferroics smaller than the critical size limit by engineering the dislocations in nonmagnetic ferroelectrics, even though these lattice defects are generally believed to be detrimental. First-principles calculations demonstrate that Ti-rich PbTiO3 dislocations exhibit magnetism due to the local nonstoichiometry intrinsic to the core structures. Highly localized spin moments in conjunction with the host ferroelectricity enable these dislocations to function as atomic-scale multiferroic channels with a pronounced magnetoelectric effect that are associated with the antiferromagnetic-ferromagnetic-nonmagnetic phase transitions in response to polarization switching. The present results thus suggest a new field of dislocation (or defect) engineering for the fabrication of ultrathin magnetoelectric multiferroics and ultrahigh density electronic devices.

Strain-induced ferroelectricity and lattice coupling in BaSnO3 and SrSnO3.

Perovskite stannates such as BaSnO3 and SrSnO3 exhibit promising photovoltaic properties, and hold promise for application in solar cell devices. However, the lack of ferroelectricity and the wide band gap in these materials limit their potential for photovoltaic applications. Here, by first-principles calculations, we demonstrate the realization of a primary ferroelectric polarization in non-ferroelectric BaSnO3 and SrSnO3 through strain engineering. In addition to the appearance of polarization, the band gaps of the materials are greatly narrowed when the paraelectric to ferroelectric phase transition takes place under compressive strain. Furthermore, an intriguing Q2 mode triggered by lattice coupling with the polar mode is found in the stannates subjected to a sufficient tensile strain and this mode has a significant effect on the band gap, which suggests another pathway to narrow the band gap through the electric field control of the Q2 mode. The fruitful electronic, structural, and energetic properties are discussed in detail to achieve a fundamental understanding of the strain-induced ferroelectricity, tunable band gap, and lattice couplings between the Q2 mode and different polar/rotational distortions in the perovskite stannates.

Outstanding Elastic Limit of a Thin Film Composed of Nickel Nanosprings.

This paper presents experimental results of vertical loading using an atomic force microscope (AFM) performed on a thin film consisting of nickel helical nanoelements (nanosprings) formed by glancing angle deposition (GLAD) technique. As a helical element has large reversible deformation limit in general, a characteristic behavior is expected on the yielding of the film. From the load versus displacement curves, we find the outstanding elastic limit of nickel nanosprings film. The apparent yield strain is evaluated as ε' Y = 5.2˜6.2 × 10−2, which is around 200 times of that in bulk nickel (ε Y = 0.29˜0.44 × 10−3). However, comparing the maximum shear stress in the helical spring and the solid film, the shape effect (helical shape) is only around 10˜20 times stemmed from the difference in the stress condition (torsion). The origin of difference is attributed to the size effect of nanosprings, as nano-scale metals have higher yield strain than that of bulk counterpart because of the difference in the understructure morphology. The combination of shape effect and size effect brings about the giant elastic limit on the film.

Impact of Epinephrine Contained in Local Anesthetic Solution on Serum Lactate Level During Orthognathic Surgery.

PURPOSE: There have been many discussions of a relation between endogenous and exogenous epinephrine and hyperlactatemia. This study aimed to identify the impact of epinephrine contained in a local anesthetic solution on serum lactate levels in patients who underwent orthognathic surgery. MATERIALS AND METHODS: This study was a retrospective record review of cases of maxillary and mandibular osteotomy at the Tokyo University Hospital (Tokyo, Japan) from January 2006 through December 2014. One hundred ninety-three patients were enrolled in this study. RESULTS: The maximum intraoperative serum lactate level was 22.3 ± 14.7 mg/dL. Of 193 patients, 91 showed an intraoperative serum lactate level that was higher than the normal maximum of 19.8 mg/dL (2.2 mmol/L), and 16 of these had a level that was at least 40 mg/dL (≥4.49 mmol/L). Multiple logistic regression analysis showed 2 factors that could increase the serum lactate level: the amount of epinephrine contained in the local anesthetic solution injected into the oral cavity (odds ratio [OR] = 1.014; 95% confidence interval [CI], 1.006-1.022; P = .0001) and the absence of intraoperative treatment with propranolol (OR, 0.105; 95% CI, 0.019-0.434; P = .0013). Patients with severe serum lactate concentrations (ie, ≥40 mg/dL [≥4.49 mmol/L]) had slight metabolic acidosis. All patients survived 90 days. The number of postoperative hospitalization days for patients with severe serum lactate concentrations was 12.8 ± 2.6 days and that for patients without severe serum lactate concentration was 16.0 ± 8.6 days. CONCLUSION: Increases in intraoperative serum lactate levels during orthognathic surgery are associated, at least in part, with increased aerobic glycolysis because of ß2-adrenergic signaling. Lactate increase caused by epinephrine contained in a local anesthetic solution does not result in a poor postoperative outcome.

Multiferroic Domain Walls in Ferroelectric PbTiO3 with Oxygen Deficiency.

Atomically thin multiferroics with the coexistence and cross-coupling of ferroelectric and (anti)ferromagnetic order parameters are promising for novel magnetoelectric nanodevices. However, such ferroic order disappears at a critical thickness in nanoscale. Here, we show a potential path toward ultrathin multiferroics by engineering an unusual domain wall (DW)-oxygen vacancy interaction in nonmagnetic ferroelectric PbTiO3. We demonstrate from first-principles that oxygen vacancies formed at the DW unexpectedly bring about magnetism with a localized spin moment around the vacancy. This magnetism originates from the orbital symmetry breaking of the defect electronic state due to local crystal symmetry breaking at the DW. Moreover, the energetics of defects shows the self-organization feature of oxygen vacancies at the DW, resulting in a planar-arrayed concentration of magnetic oxygen vacancies, which consequently changes the deficient DWs into multiferroic atomic layers. This DW-vacancy engineering opens up a new possibility for novel ultrathin multiferroic.

Unusual Multiferroic Phase Transitions in PbTiO3 Nanowires.

Unconventional phases and their transitions in nanoscale systems are recognized as an intriguing avenue for both unique physical properties and novel technological paradigms. Although the multiferroic phase has attracted considerable attention due to the coexistence and cross-coupling of electric and magnetic order parameters, mutually exclusive mechanism between ferroelectricity and ferromagnetism leaves conventional ferroelectrics such as PbTiO3 simply nonmagnetic. Here, we demonstrate from first-principles that ultrathin PbTiO3 nanowires exhibit unconventional multiferroic phases with emerging ferromagnetism and coexisting ferroelectric/ferrotoroidic ordering. Nanometer-scale and nonstoichiometric effects intrinsic to the nanowires bring about nonzero and nontrivial magnetic moments that coexist with the host ferroelectricity. The multiferroic order is susceptible to surface termination and nanowire morphology. Furthermore, calculations suggest that the nanowires undergo size-dependent ferroelectric-multiferroic-ferromagnetic phase transitions. This work therefore provides a route to multiferroic transitions in conventional nonmagnetic ferroelectric oxides.

Hybrid improper ferroelectricity in SrZrO3/BaZrO3 superlattice.

Incipient ferroelectrics, which show a unique dielectric property, arouse tremendous interests due to their potential application in microwave dielectric devices. However, ferroelectric transition in incipient ferroelectrics is suppressed entirely by quantum fluctuation. Here, by means of first-principles calculations, we demonstrate that there exists hybrid improper ferroelectricity in a layered artificial superlattice composed of the incipient ferroelectrics of SrZrO3 and BaZrO3. The hybrid improper ferroelectric polarization stems from oxygen octahedral rotation and coexists with the strain-induced ferroelectric distortion. The coexistence of oxygen octahedral rotation and ferroelectric distortion results in an enhanced polarization in the superlattice. It is further found that the total polarization in the superlattice is mainly contributed by the oxygen octahedral rotation for zero or small strain, whereas the contribution from strain-induced ferroelectric distortion gradually becomes predominant as the strain increases. The phonon dispersion, energy surface and atomic displacements are calculated to shed light on the underlying mechanism of the hybrid improper ferroelectricity in the SrZrO3/BaZrO3 superlattice.

Multiferroic grain boundaries in oxygen-deficient ferroelectric lead titanate.

Ultimately thin multiferroics arouse remarkable interest, motivated by the diverse utility of coexisting ferroelectric and (anti)ferromagnetic order parameters for novel functional device paradigms. However, the ferroic order is inevitably destroyed below a critical size of several nanometers. Here, we demonstrate a new path toward realization of atomically thin multiferroic monolayers while resolving a controversial origin for unexpected "dilute ferromagnetism" emerged in nanocrystals of nonmagnetic ferroelectrics PbTiO3. The state-of-the-art hybrid functional of Hartree-Fock and density functional theories successfully identifies the origin and underlying physics; oxygen vacancies interacting with grain boundaries (GBs) bring about (anti)ferromagnetism with localized spin moments at the neighboring Ti atoms. This is due to spin-polarized defect states with broken orbital symmetries at GBs. In addition, the energetics of oxygen vacancies indicates their self-assembling nature at GBs resulting in considerably high concentration, which convert the oxygen-deficient GBs into multiferroic monolayers due to their atomically thin interfacial structure. This synthetic concept that realizes multiferroic and multifunctional oxides in a monolayered geometry through the self-assembly of atomic defects and grain boundary engineering opens a new avenue for promising paradigms of novel functional devices.

Multiferroic Vacancies at Ferroelectric PbTiO(3) Surfaces.

Multiferroics in nanoscale dimensions are promising for novel functional device paradigms, such as magnetoelectric memories, due to an intriguing cross-coupling between coexisting ferroelectric and (anti)ferromagnetic order parameters. However, the ferroic order is inevitably destroyed below the critical dimension of several nanometers. Here, we demonstrate a new path towards atomic-size multiferroics while resolving the controversial origin of dilute ferromagnetism that unexpectedly emerges in nanoparticles of nonmagnetic ferroelectric PbTiO(3). Systematic exploration using predictive quantum-mechanical calculations demonstrates that oxygen vacancies formed at surfaces induce ferromagnetism due to local nonstoichiometry and orbital symmetry breaking. The localized character of the emerged magnetization allows an individual oxygen vacancy to act as an atomic-scale multiferroic element with a nonlinear magnetoelectric effect that involves rich ferromagnetic-antiferromagnetic-nonmagnetic phase transitions in response to switching of the spontaneous polarization.

Mechanical control of magnetism in oxygen deficient perovskite SrTiO3.

Mechanical control of magnetism in perovskite oxides is an important and promising approach in spintronics. Based on the first-principles calculations, we demonstrate that a negative pressure leads to a great enhancement of magnetic moment in deficient SrTiO3 with oxygen vacancies, whereas a positive pressure results in the gradual disappearance of magnetism. Spin charge density, Bader charge analysis and electronic density of states successfully elucidate the origin and underlying physics of the enhancement and disappearance of magnetism. It is found that the split electronic states of dz(2), dyz and dzx in the 3d orbitals of Ti atoms remarkably contribute to the occupancy of majority spin states under negative pressure, which induces a large magnetic moment. Under positive pressure, however, the equal occupancy of both majority and minority t2g and eg states leads to the disappearance of magnetization. In addition, both negative and positive pressures can largely lower the vacancy formation enthalpy, suggesting that the oxygen vacancy is preferable with pressure. Our findings may provide a mechanism to achieve the pressure control of magnetization in nonmagnetic perovskite oxides.

Quality assurance monitoring of a citywide transportation protocol improves clinical indicators of intravenous tissue plasminogen activator therapy: a community-based, longitudinal study.

BACKGROUND: Stroke-bypass transportation to the stroke center by paramedics is important to maximize the efficiency of intravenous tissue plasminogen activator (iv-tPA) therapy. To improve access to stroke thrombolysis, a citywide protocol was launched on January 2007 in Kawasaki City (population 1.4 million) using the Maria Prehospital Stroke Scale (MPSS), and quality assurance monitoring has been performed every 6 months. The aim was to identify whether the citywide quality assurance monitoring improves the process and outcome of iv-tPA therapy. METHODS: All of the MPSS-based transportation data prospectively recorded by the Kawasaki City Fire Department and the associated clinical data in the 11 hospitals that accept stroke-bypass transfers were merged every 6 months for the quality assurance monitoring. Clinical indicators such as ambulance call-to-door time, onset-to-needle time, door-to-needle time, frequency of thrombolytic use, and outcome of thrombolytic therapy were analyzed. These clinical indicators were also compared between patients transferred on weekdays and on weekends. RESULTS: A total of 2049 patients was registered from April 2009 to March 2013. Their mean age was 70.4 ± 13.2 (range, 24-98) years, and 64.3% were male. Ambulance call-to-door time decreased gradually from 37.5 ± 12.5 minutes to 33.9 ± 11.7 minutes over 4 years (P = .000, analysis of variance with the post hoc Dunnett test). Onset-to-needle time and door-to-needle time were similar over the 4 years. Good outcome (modified Rankin Scale score <2) after iv-tPA therapy increased from 24.1% to 35.3% (P = .045, 2010 vs. 2012). No deleterious effect of weekend admission was observed based on these clinical indicators. CONCLUSIONS: A citywide MPSS-based transportation protocol significantly decreased the delay in the ambulance call-to-door time. The implementation of standardized cross-institutional quality assurance programs for acute stroke therapy may improve the process and outcome of iv-tPA therapy in the community.

Pathophysiology and management of intracranial arterial stenosis around the circle of Willis associated with hyperthyroidism: case reports and literature review.

Cases of moyamoya disease or intracranial arterial stenosis around the circle of Willis (M/IAS) associated with hyperthyroidism have been reported. However, most of these previous reports were of the ischemic form of M/IAS and primary hyperthyroidism. To the best of our knowledge, no studies have documented therapy for M/IAS associated with hyperthyroidism. We discuss four previously unreported cases, including those involving the intracerebral hemorrhage form and thyroid-stimulating hormone (TSH) secretion from a pituitary adenoma (secondary hyperthyroidism). We analyzed data from 52 previously reported cases, including the 4 cases presented here, and discuss M/IAS associated with hyperthyroidism, treatment options, pathophysiology, the ischemic and hemorrhagic forms, secondary hyperthyroidism, and the relevant literature. Hyperthyroidism results in thyrotoxicosis and the stimulation of the superior cervical ganglion by TSH antibodies and f-T3/f-T4. Consequently, hypercoagulability and stenosis of the cerebral artery can occur. There are many reports of ischemic M/IAS associated with hyperthyroidism. A conservative approach to treatment is important in such cases; for example, antithyroid therapy should be the first choice to treat ischemic M/IAS. There have been only a limited number of reports on hemorrhagic M/IAS. We presume that hemorrhagic M/IAS tears the weakened vasculature in a manner similar to that of normal M/IAS (with no complicating hyperthyroidism). The authors also reported M/IAS associated with secondary hyperthyroidism due to pituitary thyroid secreting hormone secreting adenoma.