Origin of nonlinear magnetoelectric response in rare-earth orthoferrite perovskite oxides

We report a theoretical study of the non-linear magnetoelectric response of GdFeO$_3$ through an analytical approach combined with a Heisenberg model which is fitted against first-principles calculations. Our theory reproduces the non-linear change of polarization under applied magnetic field reported experimentally such that it allows to analyze the origin of the large responses in the different directions. We show that the non-linear character of the response in these materials originates from the fact that the antiferromagnetic order of Gd atoms changes non-linearly with respect to the applied magnetic field. Our model can be generalized to other materials in which the antiferromagnetic ordering breaks inversion symmetry

Complication Rate after Percutaneous Liver Biopsy Using a Real-time Ultrasound Approach and Introducing a Uniform Methodology: A Brief Report

Following the initial liver biopsy attempts, several techniques using a wide range of methodologies and materials were developed. Many studies on the evaluation of post-liver biopsy complications were conducted. However, their fundamental limitation was significant variance in patient demographics and methodology, which might account for the inconsistent outcomes. Therefore, a uniform methodology to perform percutaneous liver biopsies that result in comparable outcomes around the world is required. This study aimed to determine the precise complication rate following percutaneous liver biopsy using a consistent method in all individuals. It also aimed to establish a consistent operating procedure for a percutaneous liver biopsy that yielded comparable outcomes. Between July 2018 and July 2019, 116 patients were enrolled in this retrospective study for percutaneous liver biopsy. All individuals underwent a biopsy using the same procedure. There was an attempt to exclude elements that could have an impact on the complication rate. For this purpose, the same type and size of needle were utilized. Moreover, a single needle pass, a subcostal approach, deep inspiration breath holding, identical pre- and post-biopsy preparation, real-time ultrasonography guidance, the use of a single operator, and the absence of sedation or general anesthesia were the other approaches that were used to minimize the impact of variables that could raise complication rates. The overall complication rate was 19.8%, of which 18.9% of patients experienced pain and mild bleeding, and one patient (0.9%) experienced hematoma necessitating precautionary hospitalization. The overall percentage of patients who experienced pain was 13.8%. No further complications were observed. The findings of this study could provide an accurate estimate of the post-liver biopsy complication rate. Furthermore, due to a lower complication rate than other practiced procedures, this uniform methodology could be an attractive alternative in clinical practice. However, more research is required to confirm these results

Lattice dynamics and Raman spectrum of supertetragonal PbVO3

Lead vanadate PbVO3 is a polar crystal with a P4mm space group at ambient conditions. It is isostructural with the model soft-mode driven ferroelectric PbTiO3, but differs from it by the so-called 'supertetragonal' elongation of its unit cell. In this paper, we report a combined study of the lattice dynamics of PbVO3 by Raman spectroscopy at room temperature and first-principle calculations. All zone-center transverse optical (TO) phonon modes are identified by polarized, angle-dependent Raman spectroscopy and assigned as follows: E modes at 136, 269, 374 and 508 cm-1, A1 modes at 188, 429 and 874 cm-1 and B1 mode at 319 cm-1. The calculations confirm the experimental symmetry assignment and allow to obtain the longitudinal (LO) phonons wavenumbers. Besides, we analyze the mode eigenvectors in detail, in order to identify the atomic displacements associated with each mode and compare them with PbTiO3. In spite of their differences in chemistry and strain, the phonon eigenvectors are found to be remarkably comparable in both compounds. We discuss the position of the ferroelectric soft mode in PbVO3 as compared to PbTiO3. A sizeable splitting of the B1+E modes appears as a characteristic feature of supertetragonal phases. The peculiarity of the vanadyl V-O bond frequency in PbVO3 is also addressed.Comment: 11 pages, 8 figures, 6 Tables, Supplemental Information 3 figures and 6 Tables, under revie

Lattice dynamics and Raman spectrum of supertetragonal PbVO3

Lead vanadate PbVO3 is a polar crystal with a P4mm space group under ambient conditions. PbVO3 is isostructural with the model soft mode-driven ferroelectric PbTiO3, but it differs due to the so-called “supertetragonal” elongation of its unit cell. In this study, we investigated the lattice dynamics of PbVO3 based on Raman spectroscopy at room temperature and first-principle calculations. All zone-center transverse optical phonon modes were identified by polarized, angle-dependent Raman spectroscopy and assigned as follows: E modes at 136, 269, 374, and 508 cm−1; A1 modes at 188, 429, and 874 cm−1, and B1 mode at 319 cm−1. The calculations confirmed the experimental symmetry assignment and allowed us to obtain the longitudinal optical phonon wavenumbers. In addition, we analyzed the mode eigenvectors in detail in order to identify the atomic displacements associated with each mode and compare them with PbTiO3. Despite differences in chemistry and strain, the phonon eigenvectors were found to be highly comparable in both compounds. We investigated the position of the ferroelectric soft mode in PbVO3 compared with PbTiO3. Sizeable splitting of the B1+E modes appeared as a characteristic feature of supertetragonal phases. The peculiarity of the vanadyl V–O bond frequency in PbVO3 was also addressed

Tuning the energy landscape of CaTiO3 into that of antiferroelectric PbZrO3

peer reviewedTSARPDR PromospanIPD Stem

Proven pulmonary aspergillosis in a COVID-19 patient: A case report

Background and Purpose: Coronavirus disease 2019 (COVID-19) has become a significant clinical challenge in healthcare settings all over the world. Critically ill COVID-19 patients with acute respiratory distress syndrome may be at increased risk of co-infection with pulmonary aspergillosis. This study aimed to describe a clinical case of proven pulmonary aspergillosis caused by Aspergillus tubingensis in a 59-year-old man with a history of hospitalization due to COVID-19 infection.Case report: The Covid-19 infection was confirmed by positive nasopharyngeal polymerase chain reaction. He had a cavitary lesion measured 20 mm in diameter with intracavitary soft tissue density in the left lung in the first chest computerized tomography scan. After 25 days, he showed two cavitary lesions in both lungs which raised suspicion of fungal infection; hence, the patient underwent a trans-thoracic biopsy of the cavitary lesion. The direct examination and culture of the biopsy material revealed Aspergillus species. To confirm the Aspergillus species identification, the beta-tubulin region was sequenced. The patient was treated with oral voriconazole.Conclusion: This report underlined the importance of early diagnosis and management of invasive fungal infections in severe COVID-19 patient

First and second principles study of magnetic and multiferroic properties of rare-earth orthoferrites

Rare-earth orthoferrite perovskites (RFeO3, where R is a rare-earth element, i.e., La, Gd, Dy, …) are a family of materials that have attracted a lot of attention due to their original magnetic properties and large nonlinear magnetoelectric responses (ME). A large magnetoelectric response will allow controlling magnetic properties using an electric field which can bring in a plethora of applications and improvements of the current technologies. In my thesis, I have studied magnetic properties of rare-earth orthiferrites and I have made a Heisenberg model to explain the origin of different unique magnetic behaviors (spin reorientation and magnetization reversal) present in these rare-earth orthoferrites. We have then used the model to explain large ME responses observed in these materials. We have shown that the nonlinear response present in these materials arises from the fact that the antiferromagnetic ordering changes nonlinearly with an applied magnetic field. Through a collaboration with experimentalists, we have also studied ultrafast manipulation of the magnetic phase of DyFeO3 using laser pulses in an ultrafast time scale which allows the use of these materials in memories with ultrafast time responses.Magnele

Magnetic phase diagram of rare-earth orthorhombic perovskite oxides

peer reviewedSpin reorientation and magnetization reversal are two important features of the rare-earth orthorhombic perovskites (RMO3) that have attracted a lot of attention, though their exact microscopic origin has eluded researchers. Here, using density functional theory and classical atomistic spin dynamics we build a general Heisenberg magnetic model that allows to explore the whole phase diagram of the chromite and ferrite compounds and to scrutinize the microscopic mechanism responsible for spin reorientations and magnetization reversals. We show that the occurrence of a magnetization reversal transition depends on the relative strength and sign of two interactions between rare-earth and transition-metal atoms: superexchange and Dzyaloshinskii- Moriya. We also conclude that the presence of a smooth spin reorientation transition between the so-called G4 and the G2 phases through a coexisting region, and the temperature range in which it occurs, depends on subtle balance of metal-metal (superexchange and Dzyaloshinskii-Moriya) and metal–rare-earth (Dzyaloshinsky-Moriya) couplings. In particular, we show that the intermediate coexistence region occurs because the spin sublattices rotate at different rates

Origin of nonlinear magnetoelectric response in rare-earth orthoferrite perovskite oxides

peer reviewedWe report a theoretical study of the nonlinear magnetoelectric response of GdFeO3 through an analytical approach combined with a Heisenberg model, which is fitted against first-principles calculations. Our theory reproduces the nonlinear change of polarization under applied magnetic field reported experimentally such that it allows us to analyze the origin of the large responses in different directions. We show that the nonlinear character of the response in these materials originates from the fact that the antiferromagnetic order of Gd atoms changes nonlinearly with respect to the applied magnetic field. Our model can be generalized to other materials in which the antiferromagnetic ordering breaks inversion symmetry

Brain activity characteristics of RGB stimulus: an EEG study

Abstract The perception of color is a fundamental cognitive feature of our psychological experience, with an essential role in many aspects of human behavior. Several studies used magnetoencephalography, functional magnetic resonance imaging, and electroencephalography (EEG) approaches to investigate color perception. Their methods includes the event-related potential and spectral power activity of different color spaces, such as Derrington-Krauskopf-Lennie and red-green-blue (RGB), in addition to exploring the psychological and emotional effects of colors. However, we found insufficient studies in RGB space that considered combining all aspects of EEG signals. Thus, in the present study, focusing on RGB stimuli and using a data-driven approach, we investigated significant differences in the perception of colors. Our findings show that beta oscillation of green compared to red and blue colors occurs in early sensory periods with a latency shifting in the occipital region. Furthermore, in the occipital region, the theta power of the blue color decreases noticeably compared to the other colors. Concurrently, in the prefrontal area, we observed an increase in phase consistency in response to the green color, while the blue color showed a decrease. Therefore, our results can be used to interpret the brain activity mechanism of color perception in RGB color space and to choose suitable colors for more efficient performance in cognitive activities