Personalized radiomics signature to screen for KIT-11 mutation genotypes among patients with gastrointestinal stromal tumors: a retrospective multicenter study

OBJECTIVES

Gastrointestinal stromal tumors (GISTs) carrying different KIT exon 11 (KIT-11) mutations exhibit varying prognoses and responses to Imatinib. Herein, we aimed to determine whether computed tomography (CT) radiomics can accurately stratify KIT-11 mutation genotypes to benefit Imatinib therapy and GISTs monitoring.

METHODS

Overall, 1143 GISTs from 3 independent centers were separated into a training cohort (TC) or validation cohort (VC). In addition, the KIT-11 mutation genotype was classified into 4 categories: no KIT-11 mutation (K11-NM), point mutations or duplications (K11-PM/D), KIT-11 557/558 deletions (K11-557/558D), and KIT-11 deletion without codons 557/558 involvement (K11-D). Subsequently, radiomic signatures (RS) were generated based on the arterial phase of contrast CT, which were then developed as KIT-11 mutation predictors using 1408 quantitative image features and LASSO regression analysis, with further evaluation of its predictive capability.

RESULTS

The TC AUCs for K11-NM, K11-PM/D, K11-557/558D, and K11-D ranged from 0.848 (95% CI 0.812-0.884), 0.759 (95% CI 0.722-0.797), 0.956 (95% CI 0.938-0.974), and 0.876 (95% CI 0.844-0.908), whereas the VC AUCs ranged from 0.723 (95% CI 0.660-0.786), 0.688 (95% CI 0.643-0.732), 0.870 (95% CI 0.824-0.918), and 0.830 (95% CI 0.780-0.878). Macro-weighted AUCs for the KIT-11 mutant genotype ranged from 0.838 (95% CI 0.820-0.855) in the TC to 0.758 (95% CI 0.758-0.784) in VC. TC had an overall accuracy of 0.694 (95%CI 0.660-0.729) for RS-based predictions of the KIT-11 mutant genotype, whereas VC had an accuracy of 0.637 (95%CI 0.595-0.679).

CONCLUSIONS

CT radiomics signature exhibited good predictive performance in estimating the KIT-11 mutation genotype, especially in prediction of K11-557/558D genotype. RS-based classification of K11-NM, K11-557/558D, and K11-D patients may be an indication for choice of Imatinib therapy.

[Clinical analysis of laparoscopic treatment of chronic traumatic diaphragmatic hernia in 29 cases]

Objective: To examine the safety and effectiveness of laparoscopic individualized surgical treatment for chronic traumatic diaphragmatic hernia (CTDH). Methods: The clinical data and follow-up data of 29 CTDH cases admitted to the Qilu Hospital of Shandong University or the First Affiliated Hospital of Shandong First Medical University from June 2015 to January 2023 were retrospectively analyzed. There were 21 males and 8 females, aged (49.4±17.8) years (range: 19 to 79 years). The main clinical manifestations were symptoms of the digestive system and respiratory system, and only 4 cases were asymptomatic. All patients received laparoscopic treatment (conversion to open surgery was not excluded). Intraoperative exploration (location of the hernia, contents of the hernia, diameter of the hernia ring), surgical conditions (surgical repair plan, operation time, blood loss, postoperative complications) and postoperative follow-up were analyzed and discussed. Results: Laparoscopic repair was successfully completed in 27 cases, including simple suture in 6 cases, suture and patch repair in 17 cases, the anterior abdominal wall muscle flap reversal suture and patch repair of in 3 cases, and patch bridge repair in 1 case. The operation time was (112.8±44.7) minutes (range: 60 to 200 minutes). The amount of bleeding (M(IQR)) was 35 (58) ml (range: 10 to 300 ml). The other 2 patients were converted to laparotomy. Except for one patient with transverse colon strangulation necrosis who died of aggravated pulmonary infection after surgery, the remaining 28 patients were discharged successfully. The follow-up time was 36 (24) months (range: 1 to 60 months). During the follow-up period, only two patients had occasional left upper abdominal discomfort. Twenty-seven patients with left diaphragmatic hernia had no recurrence, and the symptoms of 1 patient with right diaphragmatic hernia were relieved. Conclusion: Customized laparoscopic surgical repair for CTDH according to the location and size of the diaphragmatic defect can achieve good surgical results.

Effect of p18 on endothelial barrier function by mediating vascular endothelial Rab11a-VE-cadherin recycling

Endothelial barrier integrity requires recycling of VE-cadherin to adherens junctions. Both p18 and Rab11a play significant roles in VE-cadherin recycling. However, the underlying mechanism and the role of p18 in activating Rab11a have yet to be elucidated. Performing in vitro and in vivo experiments, we showed that p18 protein bound to VE-cadherin before Rab11a through its VE-cadherin-binding domain (aa 1-39). Transendothelial resistance showed that overexpression of p18 promoted the circulation of VE-cadherin to adherens junctions and the recovery of the endothelial barrier. Silencing of p18 caused endothelial barrier dysfunction and prevented Rab11a-positive recycling endosome accumulation in the perinuclear recycling compartments. Furthermore, p18 knockdown in pulmonary microvessels markedly increased vascular leakage in mice challenged with lipopolysaccharide and cecal ligation puncture. This study showed that p18 regulated the pulmonary endothelial barrier function in vitro and in vivo by regulating the binding of Rab11a to VE-cadherin and the activation of Rab11a.

Enhanced Production of Pterostilbene in Escherichia coli Through Directed Evolution and Host Strain Engineering

Pterostilbene is a derivative of resveratrol with a higher bioavailability and biological activity, which shows antioxidant, anti-inflammatory, antitumor, and antiaging activities. Here, directed evolution and host strain engineering were used to improve the production of pterostilbene in Escherichia coli. First, the heterologous biosynthetic pathway enzymes of pterostilbene, including tyrosine ammonia lyase, p-coumarate: CoA ligase, stilbene synthase, and resveratrol O-methyltransferase, were successively directly evolved through error-prone polymerase chain reaction (PCR). Four mutant enzymes with higher activities of in vivo and in vitro were obtained. The directed evolution of the pathway enzymes increased the pterostilbene production by 13.7-fold. Then, a biosensor-guided genome shuffling strategy was used to improve the availability of the precursor L-tyrosine of the host strain E. coli TYR-30 used for the production of pterostilbene. A shuffled E. coli strain with higher L-tyrosine production was obtained. The shuffled strain harboring the evolved pathway produced 80.04 ± 5.58 mg/l pterostilbene, which is about 2.3-fold the highest titer reported in literatures.

Cell-free Biosynthesis of Chlorogenic Acid Using a Mixture of Chassis Cell Extracts and Purified Spy-Cyclized Enzymes

A novel cell-free biosynthesis system based on a mixture of chassis cell extracts and purified Spy-cyclized enzymes (CFBS-mixture) was developed. As a demonstration, the CFBS-mixture was applied to chlorogenic acid (CGA) biosynthesis. The mix-and-match and Plackett-Burman experiments demonstrated that Lonicera japonica hydroxycinnamate-CoA quinate transferase and p-hydroxyphenylacetate 3-hydroxylase were the key enzymes for the production of CGA. After optimization of the concentrations of the biosynthetic enzymes in the CFBS-mixture reaction using the Plackett-Burman experimental design and the path of the steepest ascent, 711.26 ± 15.63 mg/L CGA was produced after 16 h, which is 71.1-fold the yield obtained using the conventional crude extract-based CFBS and 9.1-fold the reported yield obtained using the living cells. Based on the CFBS-mixture results, the production of CGA was further enhanced in engineered Escherichia coli. The CFBS-mixture strategy is highly effective and will be useful for high-level CFBS of natural products.

An effective and versatile strategy for the synthesis of structurally diverse heteroarylsilanes via Ir(iii)-catalyzed C-H silylation

A versatile silylation of heteroaryl C–H bonds is accomplished under the catalysis of a well-defined spirocyclic NHC Ir(iii) complex (SNIr), generating a variety of heteroarylsilanes. A significant advantage of this catalytic system is that multiple types of intermolecular C–H silylation can be achieved using one catalytic system at α, β, γ, or δ positions of heteroatoms with excellent regioselectivities. Mechanistic experiments and DFT calculations indicate that the polycyclic ligand of SNIr can form an isolable cyclometalated intermediate, which leaves a phenyl dentate free and provides a hemi-open space for activating substrates. In general, favorable silylations occur at γ or δ positions of chelating heteroatoms, forming 5- or 6-membered C–Ir–N cyclic intermediates. If such an activation mode is prohibited sterically, silylations would take place at the α or β positions. The mechanistic studies would be helpful for further explaining the reactivity of the SNIr system.

A versatile silylation of heteroaryl C–H bonds is accomplished under the catalysis of a well-defined spirocyclic NHC Ir(iii) complex (SNIr), generating a variety of heteroarylsilanes.

ATP and NADPH engineering of Escherichia coli to improve the production of 4-hydroxyphenylacetic acid using CRISPRi

BACKGROUND

4-Hydroxyphenylacetic acid (4HPAA) is an important raw material for the synthesis of drugs, pesticides and biochemicals. Microbial biotechnology would be an attractive approach for 4HPAA production, and cofactors play an important role in biosynthesis.

RESULTS

We developed a novel strategy called cofactor engineering based on clustered regularly interspaced short palindromic repeat interference (CRISPRi) screening (CECRiS) for improving NADPH and/or ATP availability, enhancing the production of 4HPAA. All NADPH-consuming and ATP-consuming enzyme-encoding genes of E. coli were repressed through CRISPRi. After CRISPRi screening, 6 NADPH-consuming and 19 ATP-consuming enzyme-encoding genes were identified. The deletion of the NADPH-consuming enzyme-encoding gene yahK and the ATP-consuming enzyme-encoding gene fecE increased the production of 4HPAA from 6.32 to 7.76 g/L. Automatically downregulating the expression of the pabA gene using the Esa-P_esaS quorum-sensing-repressing system further improved the production of 4HPAA. The final strain E. coli 4HPAA-∆yfp produced 28.57 g/L of 4HPAA with a yield of 27.64% (mol/mol) in 2-L bioreactor fed-batch fermentations. The titer and yield are the highest values to date.

CONCLUSION

This CECRiS strategy will be useful in engineering microorganisms for the high-level production of bioproducts.

Sleeve gastrectomy ameliorates endothelial function and prevents lung cancer by normalizing endothelin-1 axis in obese and diabetic rats

BACKGROUND

Previous evidence has implied that obesity is an independent risk factor for developing cancer. Being closely related to obesity, type 2 diabetes mellitus provides a suitable environment for the formation and metastasis of tumors through multiple pathways. Although bariatric surgeries are effective in preventing and lowering the risk of various types of cancer, the underlying mechanisms of this effect are not clearly elucidated.

AIM

To uncover the role and effect of sleeve gastrectomy (SG) in preventing lung cancer in obese and diabetic rats.

METHODS

SG was performed on obese and diabetic Wistar rats, and the postoperative transcriptional and translational alterations of the endothelin-1 (ET-1) axis in the lungs were compared to sham-operated obese and diabetic rats and age-matched healthy controls to assess the improvements in endothelial function and risk of developing lung cancer at the postoperative 4^th, 8^th, and 12^th weeks. The risk was also evaluated using nuclear phosphorylation of H2A histone family member X as a marker of DNA damage (double-strand break).

RESULTS

Compared to obese and diabetic sham-operated rats, SG brought a significant reduction to body weight, food intake, and fasting blood glucose while improving oral glucose tolerance and insulin sensitivity. In addition, ameliorated levels of gene and protein expression in the ET-1 axis as well as reduced DNA damage indicated improved endothelial function and a lower risk of developing lung cancer after the surgery.

CONCLUSION

Apart from eliminating metabolic disorders, SG improves endothelial function and plays a protective role in preventing lung cancer via normalized ET-1 axis and reduced DNA damage.

Recent Advances in Metabolically Engineered Microorganisms for the Production of Aromatic Chemicals Derived From Aromatic Amino Acids

Aromatic compounds derived from aromatic amino acids are an important class of diverse chemicals with a wide range of industrial and commercial applications. They are currently produced via petrochemical processes, which are not sustainable and eco-friendly. In the past decades, significant progress has been made in the construction of microbial cell factories capable of effectively converting renewable carbon sources into value-added aromatics. Here, we systematically and comprehensively review the recent advancements in metabolic engineering and synthetic biology in the microbial production of aromatic amino acid derivatives, stilbenes, and benzylisoquinoline alkaloids. The future outlook concerning the engineering of microbial cell factories for the production of aromatic compounds is also discussed.

Combining directed evolution of pathway enzymes and dynamic pathway regulation using a quorum-sensing circuit to improve the production of 4-hydroxyphenylacetic acid in Escherichia coli

BACKGROUND

4-Hydroxyphenylacetic acid (4HPAA) is an important building block for synthesizing drugs, agrochemicals, biochemicals, etc. 4HPAA is currently produced exclusively via petrochemical processes and the process is environmentally unfriendly and unsustainable. Microbial cell factory would be an attractive approach for 4HPAA production.

RESULTS

In the present study, we established a microbial biosynthetic system for the de novo production of 4HPAA from glucose in Escherichia coli. First, we compared different biosynthetic pathways for the production of 4HPAA. The yeast Ehrlich pathway produced the highest level of 4HPAA among these pathways that were evaluated. To increase the pathway efficiency, the yeast Ehrlich pathway enzymes were directedly evolved via error-prone PCR. Two phenylpyruvate decarboxylase ARO10 and phenylacetaldehyde dehydrogenase FeaB variants that outperformed the wild-type enzymes were obtained. These mutations increased the in vitro and in vivo catalytic efficiency for converting 4-hydroxyphenylpyruvate to 4HPAA. A tunable intergenic region (TIGR) sequence was inserted into the two evolved genes to balance their expression. Regulation of TIGR for the evolved pathway enzymes further improved the production of 4HPAA, resulting in a 1.13-fold increase in titer compared with the fusion wild-type pathway. To prevent the toxicity of a heterologous pathway to the cell, an Esa quorum-sensing (QS) circuit with both activating and repressing functions was developed for inducer-free productions of metabolites. The Esa-P_esaR activation QS system was used to dynamically control the biosynthetic pathway of 4HPAA in E. coli, which achieved 17.39 ± 0.26 g/L with a molar yield of 23.2% without addition of external inducers, resulting in a 46.4% improvement of the titer compared to the statically controlled pathway.

CONCLUSION

We have constructed an E. coli for 4HPAA production with the highest titer to date. This study also demonstrates that the combination of directed evolution of pathway enzymes and dynamic pathway regulation using a QS circuit is a powerful strategy of metabolic engineering for the productions of metabolites.

Deactivation of the NLRP3 inflammasome in infiltrating macrophages by duodenal-jejunal bypass surgery mediates improvement of beta cell function in type 2 diabetes

OBJECTIVE

Bariatric surgery could improve pancreatic beta cell function, thereby leading to the remission of the type 2 diabetes mellitus (T2DM). However, the specific mechanism underlying this phenomenon is yet to be revealed. The aim of this study is to test the hypothesis that Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome in infiltrating macrophages plays an important role in the modulation of beta cell function after duodenal-jejunal bypass (DJB) surgery.

METHODS

DJB and sham surgery were performed in diabetic Sprague-Dawley (SD) rats induced by high-fat diet (HFD) and streptozotocin (STZ). Body weight, food intake, and glucose tolerance test (GTT) were measured at indicated time points. Apoptosis of the beta cells was measured by Terminal deoxynucleotidyl transferase mediated dUTP Nick End Labeling (TUNEL) assay. We also assessed the macrophage content and NLRP3 expression in the rat model. Furthermore, macrophage reconstitution was performed after DJB surgery. Beta cell function and NLRP3 inflammasome pathway were re-evaluated in wild-type macrophage reconstitution group and NLRP3-knockdown macrophage reconstitution group.

RESULTS

DJB surgery group rats displayed rapid and sustained improvement in glucose tolerance. Decreased apoptosis and improved secretion function of the beta cells were observed in DJB surgery group. NLRP3 inflammasome pathway in infiltrating macrophages was also suppressed after DJB surgery. Moreover, diabetic remission acquired by DJB sustained in NLRP3-knockdown macrophage reconstitution group, while extinguished in group reconstituted with wild-type macrophage.

CONCLUSIONS

NLRP3 inflammasome deactivation in infiltrating macrophages is involved in marked beta cell function improvement after DJB surgery.

Understanding the multiferroicity in TmMn2O5 by a magnetically induced ferrielectric model

The magnetically induced electric polarization behaviors in multiferroic TmMn₂O₅ in response to varying temperature and magnetic field are carefully investigated by means of a series of characterizations including the high precision pyroelectric current technique. Here polycrystalline rather than single crystal samples are used for avoiding the strong electrically self-polarized effect in single crystals, and various parallel experiments on excluding the thermally excited current contributions are performed. The temperature-dependent electric polarization flop as a major character is identified for different measuring paths. The magneto-current measurements indicate that the electric polarization in the low temperature magnetic phase region has different origin from that in the high temperature magnetic phase. It is suggested that the electric polarization does have multiple components which align along different orientations, including the Mn³⁺-Mn⁴⁺-Mn³⁺ exchange striction induced polarization P_MM, the Tm³⁺-Mn⁴⁺-Tm³⁺ exchange striction induced polarization P_TM, and the low temperature polarization P_LT probably associated with the Tm³⁺ commensurate phase. The observed electric polarization flop can be reasonably explained by the ferrielectric model proposed earlier for DyMn₂O₅, where P_MM and P_TM are the two antiparallel components both along the b-axis and P_LT may align along the a-axis. Finally, several issues on the unusual temperature dependence of ferroelectric polarizations are discussed.

High stability of electro-transport and magnetism against the A-site cation disorder in SrRuO3

It is known that the electro-transport and magnetism of perovskite alkaline-earth ruthenate oxides are sensitive to the lattice distortion associated with the A-site cation size. Orthorhombic CaRuO3 and cubic BaRuO3 exhibit distinctly different electro-transport and magnetic properties from orthorhombic SrRuO3. It has been suggested that SrRuO3 can be robust against some intrinsic/external perturbations but fragile against some others in terms of electro-transport and magnetism, and it is our motivation to explore such stability against the local site cation disorder. In this work, we prepare a set of SrRuO3-based samples with identical averaged A-site size but different A-site cation disorder (size mismatch) by Ca and Ba co-substitution of Sr. It is revealed that the electro-transport and magnetism of SrRuO3 demonstrate relatively high stability against this A-site cation disorder, characterized by the relatively invariable electrical and magnetic properties in comparison with those of SrRuO3 itself. A simple electro-transport network model is proposed to explain quantitatively the measured behaviors. The present work suggests that SrRuO3 as an itinerant electron ferromagnetic metal possesses relatively high robustness against local lattice distortion and cation occupation disorder.

The ferroelectric polarization of Y2CoMnO6 aligns along the b-axis: the first-principles calculations

Double-perovskite A2BB'O6 oxides with magnetic B and B' ions and E*-type antiferromagnetic order (E*-AFM, i.e. the ↑↑↓↓ structure) are believed to exhibit promising multiferroic properties, and Y2CoMnO6 (YCMO) is one candidate in this category. However, the microscopic origins for magnetically induced ferroelectricity in YCMO remain unclear. In this study, we perform detailed symmetry analysis on the exchange striction effect and lattice distortion, plus the first-principles calculations on YCMO. The E*-AFM state as the ground state with other competing states such as ferromagnetic and A-antiferromagnetic orders is confirmed. It is observed that the ferroelectricity is generated by the exchange striction associated with the E*-AFM order and chemically ordered Mn/Co occupation. Both the lattice symmetry consideration and first-principles calculations predict that the electric polarization aligns along the b-axis. The calculated polarization reaches up to 0.4682 μC cm(-2), mainly from the ionic displacement contribution. The present study presents a comprehensive understanding of the multiferroic mechanisms in YCMO and is of general significance for predicting emergent multiferroicity in other double-perovskite magnetic oxides.

Ferroelectricity driven magnetism at domain walls in LaAlO3/PbTiO3 superlattices

Charge dipole moment and spin moment rarely coexist in single-phase bulk materials except in some multiferroics. Despite the progress in the past decade, for most multiferroics their magnetoelectric performance remains poor due to the intrinsic exclusion between charge dipole and spin moment. As an alternative approach, the oxide heterostructures may evade the intrinsic limits in bulk materials and provide more attractive potential to realize the magnetoelectric functions. Here we perform a first-principles study on LaAlO₃/PbTiO₃ superlattices. Although neither of the components is magnetic, magnetic moments emerge at the ferroelectric domain walls of PbTiO₃ in these superlattices. Such a twist between ferroelectric domain and local magnetic moment, not only manifests an interesting type of multiferroicity, but also is possible useful to pursuit the electrical-control of magnetism in nanoscale heterostructures.

Low-field Switching Four-state Nonvolatile Memory Based on Multiferroic Tunnel Junctions

Multiferroic tunneling junction based four-state non-volatile memories are very promising for future memory industry since this kind of memories hold the advantages of not only the higher density by scaling down memory cell but also the function of magnetically written and electrically reading. In this work, we demonstrate a success of this four-state memory in a material system of NiFe/BaTiO₃/La_0.7Sr_0.3MnO₃ with improved memory characteristics such as lower switching field and larger tunneling magnetoresistance (TMR). Ferroelectric switching induced resistive change memory with OFF/ON ratio of 16 and 0.3% TMR effect have been achieved in this multiferroic tunneling structure.

Magnetic phase transitions and monopole excitations in spin ice under uniaxial pressure: A Monte Carlo simulation

In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition. Furthermore, the domain walls in such ferromagnetic state are the hotbed of the excitations of magnetic monopoles, thus indicating that the uniaxial pressure can greatly increase the monopole density.

Unusual ferromagnetism enhancement in ferromagnetically optimal manganite La0.7-yCa0.3+yMn1-yRuyO3 (0≤y<0.3): the role of Mn-Ru t2g super-exchange

The e_g-orbital double-exchange mechanism as the core of physics of colossal magnetoresistance (CMR) manganites is well known, which usually covers up the role of super-exchange at the t_2g-orbitals. The role of the double-exchange mechanism is maximized in La_0.7Ca_0.3MnO₃, leading to the concurrent metal-insulator transition and ferromagnetic transition as well as CMR effect. In this work, by a set of synchronous Ru-substitution and Ca-substitution experiments on La_0.7–yCa_0.3+yMn_1–yRu_yO₃, we demonstrate that the optimal ferromagnetism in La_0.7Ca_0.3MnO₃ can be further enhanced. It is also found that the metal-insulator transition and magnetic transition can be separately modulated. By well-designed experimental schemes with which the Mn³⁺-Mn⁴⁺ double-exchange is damaged as weakly as possible, it is revealed that this ferromagnetism enhancement is attributed to the Mn-Ru t_2g ferromagnetic super-exchange. The present work allows a platform on which the electro-transport and magnetism of rare-earth manganites can be controlled by means of the t_2g-orbital physics of strongly correlated transition metal oxides.

Real-space anisotropic dielectric response in a multiferroic skyrmion lattice

A magnetic skyrmion lattice is a microstructure consisting of hexagonally aligned skyrmions. While a skyrmion as a topologically protected carrier of information promises a number of applications, an easily accessible probe of the skyrmion and skyrmion lattice at mesoscopic scale is of significance. It is known that neutron scattering, Lorentz transmission electron microscopy, and spin-resolved STM as effective probes of skyrmions have been established. In this work, we propose that the spatial contour of dielectric permittivity in a skyrmion lattice with ferromagnetic interaction and in-plane (xy) Dzyaloshinskii-Moriya (DM) interaction can be used to characterize the skyrmion lattice. The phase field and Monte Carlo simulations are employed to develop the one-to-one correspondence between the magnetic skyrmion lattice and dielectric dipole lattice, both exhibiting the hexagonal symmetry. Under excitation of in-plane electric field in the microwave range, the dielectric permittivity shows the dumbbell-like pattern with the axis perpendicular to the electric field, while it is circle-like for the electric field along the z-axis. The dependences of the spatial contour of dielectric permittivity on external magnetic field along the z-axis and dielectric frequency dispersion are discussed.

Coupled ferroelectric polarization and magnetization in spinel FeCr2S4

One of the core issues for multiferroicity is the strongly coupled ferroelectric polarization and magnetization, while so far most multiferroics have antiferromagnetic order with nearly zero magnetization. Magnetic spinel compounds with ferrimagnetic order may be alternative candidates offering large magnetization when ferroelectricity can be activated simultaneously. In this work, we investigate the ferroelectricity and magnetism of spinel FeCr₂S₄ in which the Fe²⁺ sublattice and Cr³⁺ sublattice are coupled in antiparallel alignment. Well defined ferroelectric transitions below the Fe²⁺ orbital ordering termperature T_oo = 8.5 K are demonstrated. The ferroelectric polarization has two components. One component arises mainly from the noncollinear conical spin order associated with the spin-orbit coupling, which is thus magnetic field sensitive. The other is probably attributed to the Jahn-Teller distortion induced lattice symmetry breaking, occuring below the orbital ordering of Fe²⁺. Furthermore, the coupled ferroelectric polarization and magnetization in response to magnetic field are observed. The present work suggests that spinel FeCr₂S₄ is a multiferroic offering both ferroelectricity and ferrimagnetism with large net magnetization.

Electric field control of ferroelectric domain structures in MnWO4

Competing interactions make the magnetic structure of MnWO4 highly frustrated, and only the AF2 phase of the three magnetically ordered phases (AF1, AF2, AF3) is ferroelectric. The high frustration may thus allow a possibility to tune the magnetic structure by means of an electric field via magnetoelectric coupling. By using the pyroelectric current method, we measure the remnant ferroelectric polarization in MnWO4 upon application of a poling electric field via two different roadmaps. It is demonstrated that an electric field as low as 10 kV cm(-1) is sufficient to enhance the stability of a ferroelectric AF2 phase at the expense of a non-ferroelectric AF1 phase. This work suggests that electric field induced electrostatic energy, although small due to weak magnetically induced electric polarization, may effectively tune ferroelectric domain structures, and thus the magnetic structure of highly frustrated multiferroic materials.

Kinetics of 90° domain wall motions and high frequency mesoscopic dielectric response in strained ferroelectrics: a phase-field simulation

The dielectric and ferroelectric behaviors of a ferroelectric are substantially determined by its domain structure and domain wall dynamics at mesoscopic level. A relationship between the domain walls and high frequency mesoscopic dielectric response is highly appreciated for high frequency applications of ferroelectrics. In this work we investigate the low electric field driven motion of 90°-domain walls and the frequency-domain spectrum of dielectric permittivity in normally strained ferroelectric lattice using the phase-field simulations. It is revealed that, the high-frequency dielectric permittivity is spatially inhomogeneous and reaches the highest value on the 90°-domain walls. A tensile strain favors the parallel domains but suppresses the kinetics of the 90° domain wall motion driven by electric field, while the compressive strain results in the opposite behaviors. The physics underlying the wall motions and thus the dielectric response is associated with the long-range elastic energy. The major contribution to the dielectric response is from the polarization fluctuations on the 90°-domain walls, which are more mobile than those inside the domains. The relevance of the simulated results wth recent experiments is discussed.

Experimental observation of ferrielectricity in multiferroic DyMn2O5

One of the major breakthroughs associated with multiferroicity in recent years is the discovery of ferroelectricity generated by specific magnetic structures in some magnetic insulating oxides such as rare-earth manganites RMnO3 and RMn2O5. An unresolved issue is the small electric polarization. Relatively large electric polarization and strong magnetoelectric coupling have been found in those manganites of double magnetic ions: magnetic rare-earth R ion and Mn ion, due to the strong R-Mn (4f-3d) interactions. DyMn2O5 is a representative example. We unveil in this work the ferrielectric nature of DyMn2O5, in which the two ferroelectric sublattices with opposite electric polarizations constitute the ferrielectric state. One sublattice has its polarization generated by the symmetric exchange striction from the Mn-Mn interactions, while the polarization of the other sublattice is attributed to the symmetric exchange striction from the Dy-Mn interactions. We present detailed measurements on the electric polarization as a function of temperature, magnetic field, and measuring paths. The present experiments may be helpful for clarifying the puzzling issues on the multiferroicity in DyMn2O5 and other RMn2O5 multiferroics.

Wang-Landau sampling with logarithmic windows for continuous models

We present a modified Wang-Landau sampling (MWLS) for continuous statistical models by partitioning the energy space into a set of windows with logarithmically shrinking width. To demonstrate its necessity and advantages, we apply this sampling to several continuous models, including the two-dimensional square XY spin model, triangular J1-J2 spin model, and Lennard-Jones cluster model. Given a finite number of bins for partitioning the energy space, the conventional Wang-Landau sampling may not generate sufficiently accurate density of states (DOS) around the energy boundaries. However, it is demonstrated that much more accurate DOS can be obtained by this MWLS, and thus a precise evaluation of the thermodynamic behaviors of the continuous models at extreme low temperature (kBT<0.1) becomes accessible. The present algorithm also allows efficient computation besides the highly reliable data sampling.

Ferroelectricity and ferromagnetism of La(0.5)Lu(0.5)Ni(0.5)Mn(0.5)O(3) thin films on Nb:SrTiO(3) substrates

Epitaxial orthorhombic La(0.5)Lu(0.5)Ni(0.5)Mn(0.5)O(3) (LLNMO) thin films deposited on Nb:SrTiO(3) (NSTO) substrates are prepared by pulsed laser deposition and their ferroelectricity and magnetism are investigated using various techniques. It is revealed that the as-prepared thin films are ferromagnetic (FM) insulators. The FM transition occurring at ∼ 125 K is evidenced by the well defined hysteresis at low temperature, with a saturated magnetic moment as high as 1.8 µ(B)/f.u. at ∼ 5 K. A reversible ferroelectric polarization of ∼ 0.2 µC cm(-2) below ∼ 140 K is also observed. The magnetism can be understood by the FM ordering associated with a partially ordered major Ni(2 +)-Mn(4 +) plus minor Mn(3+)-Ni(3+) configuration, while the ferroelectricity is argued to originate from the A-site disordering of La(3+) and Lu(3+).