Crystal Chemistry and Magnetic Properties of Gd-Substituted Aurivillius-Type Bi5FeTi3O15 Ceramics

Aurivillius-phase ferroelectrics can be turned into multiferroic materials by incorporating magnetic ions. The four-layer Aurivillius-type system Bi5FeTi3O15 is well-known to show a strong magnetoelectric effect; however, much controversy exists on its magnetic state and the possible multiferroicity at room temperature. In this paper, we report a detailed investigation on the interconnections between crystal chemistry and magnetic properties of Bi5FeTi3O15 ceramics chemically modified by the A-site gadolinium substitution. The structural studies showed that all Bi5–xGdxFeTi3O15 (0 ≤ x ≤ 1) samples adopt the polar orthorhombic space group symmetry A21am at room temperature. The unit cell volume and the orthorhombic distortion decrease alongside the reduction of octahedral tilts by increasing the amount of Gd added. The decrease in tilting distortion of the [Ti/Fe]O6 octahedra was further evidenced by the suppression of the Raman A1[111] tilt mode at 233 cm–1. By using superconducting quantum interference and vibrating sample magnetometry, it was demonstrated that all the ceramics are paramagnetic from 5 K up to 700 K. It was thus concluded that the A-site substitution of Bi5FeTi3O15 with magnetic Gd ions brings about a slight structural relaxation of the parental orthorhombic lattice, but it is not an effective way to induce multiferroic properties in the Aurivillius compound. We suggest that the room-temperature (ferri/ferro/antiferro-) magnetism in Bi5FeTi3O15 previously reported in the literature might be due to the presence of magnetic impurities or local short-range magnetic ordering formed during material processing under different conditions

Active suppression of dephasing in Josephson-junction qubits

Simple majority code correcting $k$ dephasing errors by encoding a qubit of information into $2k+1$ physical qubits is studied quantitatively. We derive an equation for quasicontinuous evolution of the density matrix of encoded quantum information under the error correction procedure in the presence of dephasing noise that in general can be correlated at different qubits. Specific design of the Josephson-junction circuit implementing this scheme is suggested.Comment: 4 pages, 1 figur

Pulse Control of Decoherence with Population Decay

The pulse control of decoherence in a qubit interacting with a quantum environment is studied with focus on a general case where decoherence is induced by both pure dephasing and population decay. To observe how the decoherence is suppressed by periodic pi pulses, we present a simple method to calculate the time evolution of a qubit under arbitrary pulse sequences consisting of bit-flips and/or phase-flips. We examine the effectiveness of the two typical sequences: bb sequence consisting of only bit-flips, and bp sequence consisting of both bit- and phase-flips. It is shown that the effectiveness of the pulse sequences depends on a relative strength of the two decoherence processes especially when a pulse interval is slightly shorter than qubit-environment correlation times. In the short-interval limit, however, the bp sequence is always more effective than, or at least as effective as, the bb sequence.Comment: 11 pages, 7 figure

The Multidisciplinary Approach for the Diagnosis of Laryngohyoid Lesions: a Systematic Literature Review and Meta-Analysis

Background: The diagnosis of neck lesions remains a medico-legal diagnostic challenge because of the complexity of the anatomical relationship of the neck's organs and their anthropometric morphological variability. We compared the multidisciplinary approach using autopsy and postmortem computed tomography (PMCT), postmortem fine preparation (PMFP), postmortem micro-computed tomography (micro-CT), and postmortem magnetic resonance (PMMR) with the performance of a single diagnostic method among them evaluating the significance of different results. The multidisciplinary approach significantly reduced the number of unidentified neck lesions. The analysis demonstrates the need to better define the scan protocols and compose forensic guidelines for radiological application. The results of this study point out the need to compare the different diagnostic approaches in deceased subjects to better define the radiological scan protocol based on a multidisciplinary approach, including autopsy and radiological methods and the radiological scan protocols. Methods: We performed a systematic electronic search of retrospective scientific articles in PubMed, the Scopus database, and the Cochrane Library. The following combinations of words were used: "hyoid fracture"; "comparison between PMCT AND autopsy"; "hyoid fracture PMCT AND autopsy"; "hyoid bone fracture AND forensic imaging"; "hyoid fracture AND PMCT"; "neck fracture PMCT AND autopsy"; "laryngohyoid lesions"; "postmortem CT AND autopsy in strangulation"; "postmortem AND strangulation Signs "; "strangulation virtopsy"; and "strangulation AND MRI". We selected 16 articles that were published between March 2003 and June 2020. We conducted a meta-analysis with R software to evaluate the rates. We obtained related confidence intervals and a forest plot. Results: Thyroid cartilage damages were significantly more common than hyoid bone fractures (61.7% vs 42.2%) in a sample of 128 subjects. The synergic uses of autopsy/PMCT, autopsy/PMFP, autopsy/microCT, and autopsy/PMMR revealed significantly higher rates than a single investigation. We analyzed the PMCT scan data. The scan parameters evaluated were as follows: row, scan sample, reconstruction, kernel, slice thickness, kVp, and mAs. A lack of uniformity in the application of the protocol was observed. Conclusion: Further studies are needed to better define the radiological scan protocols and to draw guidelines to identify the appropriate radiological methods in relation to the specific case

Iron metabolism and lymphocyte characterisation during Covid-19 infection in ICU patients: An observational cohort study

Background: Iron metabolism and immune response to SARS-CoV-2 have not been described yet in intensive care patients, although they are likely involved in Covid-19 pathogenesis. Methods: We performed an observational study during the peak of pandemic in our intensive care unit, dosing D-dimer, C-reactive protein, troponin T, lactate dehydrogenase, ferritin, serum iron, transferrin, transferrin saturation, transferrin soluble receptor, lymphocyte count and NK, CD3, CD4, CD8 and B subgroups of 31 patients during the first 2 weeks of their ICU stay. Correlation with mortality and severity at the time of admission was tested with the Spearman coefficient and Mann-Whitney test. Trends over time were tested with the Kruskal-Wallis analysis. Results: Lymphopenia is severe and constant, with a nadir on day 2 of ICU stay (median 0.555 109/L; interquartile range (IQR) 0.450 109/L); all lymphocytic subgroups are dramatically reduced in critically ill patients, while CD4/CD8 ratio remains normal. Neither ferritin nor lymphocyte count follows significant trends in ICU patients. Transferrin saturation is extremely reduced at ICU admission (median 9%; IQR 7%), then significantly increases at days 3 to 6 (median 33%, IQR 26.5%, p value 0.026). The same trend is observed with serum iron levels (median 25.5 μg/L, IQR 69 μg/L at admission; median 73 μg/L, IQR 56 μg/L on days 3 to 6) without reaching statistical significance. Hyperferritinemia is constant during intensive care stay: however, its dosage might be helpful in individuating patients developing haemophagocytic lymphohistiocytosis. D-dimer is elevated and progressively increases from admission (median 1319 μg/L; IQR 1285 μg/L) to days 3 to 6 (median 6820 μg/L; IQR 6619 μg/L), despite not reaching significant results. We describe trends of all the abovementioned parameters during ICU stay. Conclusions: The description of iron metabolism and lymphocyte count in Covid-19 patients admitted to the intensive care unit provided with this paper might allow a wider understanding of SARS-CoV-2 pathophysiology

Targeting qubit states using open-loop control

We present an open-loop (bang-bang) scheme which drives an open two-level quantum system to any target state, while maintaining quantum coherence throughout the process. The control is illustrated by a realistic simulation for both adiabatic and thermal decoherence. In the thermal decoherence regime, the control achieved by the proposed scheme is qualitatively similar, at the ensemble level, to the control realized by the quantum feedback scheme of Wang, Wiseman, and Milburn [Phys. Rev. A 64, #063810 (2001)] for the spontaneous emission of a two-level atom. The performance of the open-loop scheme compares favorably against the quantum feedback scheme with respect to robustness, target fidelity and transition times.Comment: 27 pages, 7 figure

The Equivalence Postulate of Quantum Mechanics

The Equivalence Principle (EP), stating that all physical systems are connected by a coordinate transformation to the free one with vanishing energy, univocally leads to the Quantum Stationary HJ Equation (QSHJE). Trajectories depend on the Planck length through hidden variables which arise as initial conditions. The formulation has manifest p-q duality, a consequence of the involutive nature of the Legendre transform and of its recently observed relation with second-order linear differential equations. This reflects in an intrinsic psi^D-psi duality between linearly independent solutions of the Schroedinger equation. Unlike Bohm's theory, there is a non-trivial action even for bound states. No use of any axiomatic interpretation of the wave-function is made. Tunnelling is a direct consequence of the quantum potential which differs from the usual one and plays the role of particle's self-energy. The QSHJE is defined only if the ratio psi^D/psi is a local self-homeomorphism of the extended real line. This is an important feature as the L^2 condition, which in the usual formulation is a consequence of the axiomatic interpretation of the wave-function, directly follows as a basic theorem which only uses the geometrical gluing conditions of psi^D/psi at q=\pm\infty as implied by the EP. As a result, the EP itself implies a dynamical equation that does not require any further assumption and reproduces both tunnelling and energy quantization. Several features of the formulation show how the Copenhagen interpretation hides the underlying nature of QM. Finally, the non-stationary higher dimensional quantum HJ equation and the relativistic extension are derived.Comment: 1+3+140 pages, LaTeX. Invariance of the wave-function under the action of SL(2,R) subgroups acting on the reduced action explicitly reveals that the wave-function describes only equivalence classes of Planck length deterministic physics. New derivation of the Schwarzian derivative from the cocycle condition. "Legendre brackets" introduced to further make "Legendre duality" manifest. Introduction now contains examples and provides a short pedagogical review. Clarifications, conclusions, ackn. and references adde

Electric field-induced transformations in bismuth sodium titanate-based materials

Electric field-induced transformations occur in a myriad of systems with a variegated phenomenology and have attracted widespread scientific interest due to their importance in many applications. The present review focuses on the electric field-induced transformations occurring in bismuth sodium titanate (BNT)-based materials, which are considered an important family of lead-free perovskites and represent possible alternatives to lead-based compounds for several applications. BNT-based systems are generally classified as relaxor ferroelectrics and are characterized by complex structures undergoing various electric field-driven phenomena. In this review, changes in crystal structure symmetry, domain configuration and macroscopic properties are discussed in relation to composition, temperature and electrical loading characteristics, including amplitude, frequency and DC biases. The coupling mechanisms between octahedral tilting with polarization and strain, and other microstructural features are identified as important factors mediating the local and overall electric field-induced response. The role of field-induced transformations on electrical fatigue is discussed by highlighting the effects of ergodicity on domain evolution and fatigue resistance in bipolar and unipolar cycles. The relevance of field-induced transformations in key applications, including energy storage capacitors, actuators, electrocaloric systems and photoluminescent devices is comprehensively discussed to identify materials design criteria. The review is concluded with an outlook for future research

Universal dynamical control of quantum mechanical decay: Modulation of the coupling to the continuum

We derive and investigate an expression for the dynamically modified decay of states coupled to an arbitrary continuum. This expression is universally valid for weak temporal perturbations. The resulting insights can serve as useful recipes for optimized control of decay and decoherence.Comment: 4 pages, 2 figures. Rewritten, changed figures, added reference