Stochastic Ultralow-Frequency Oscillations of the Luminescence Intensity from the Surface of a Polymer Membrane Swelling in Aqueous Salt Solutions.

Photoluminescence from the surface of a Nafion polymer membrane upon swelling in isotonic aqueous solutions and Milli-Q water has been studied. Liquid samples were preliminarily processed by electric pulses with a duration of 1 μs and an amplitude of 0.1 V using an antenna in the form of a flat capacitor; experiments on photoluminescent spectroscopy were carried out 20 min after this treatment.

Interfacial ferroelectricity in marginally twisted 2D semiconductors.

Twisted heterostructures of two-dimensional crystals offer almost unlimited scope for the design of new metamaterials. Here we demonstrate a room temperature ferroelectric semiconductor that is assembled using mono- or few-layer MoS. These van der Waals heterostructures feature broken inversion symmetry, which, together with the asymmetry of atomic arrangement at the interface of two 2D crystals, enables ferroelectric domains with alternating out-of-plane polarization arranged into a twist-controlled network.

A Scalable Network Model for Electrically Tunable Ferroelectric Domain Structure in Twistronic Bilayers of Two-Dimensional Semiconductors.

Moiré structures in small-angle-twisted bilayers of two-dimensional (2D) semiconductors with a broken-symmetry interface form arrays of ferroelectric (FE) domains with periodically alternating out-of-plane polarization. Here, we propose a network theory for the tunability of such FE domain structure by applying an electric field perpendicular to the 2D crystal. Using multiscale analysis, we derive a fully parametrized string-theory-like description of the domain wall network (DWN) and show that it undergoes a qualitative change, after the arcs of partial dislocation (PD) like domain walls merge (near the network nodes) into streaks of perfect screw dislocations (PSD), which happens at a threshold displacement field dependent on the DWN period.

Graphene-based plasmonic metamaterial for terahertz laser transistors.

This paper reviews recent advances in the research and development of graphene-based plasmonic metamaterials for terahertz (THz) laser transistors. The authors' theoretical discovery on THz laser transistors in 2007 was realized as a distributed-feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) in 2018, demonstrating ∼0.1 µW single-mode emission at 5.

Modification of thermally expanded graphite and its effect on the properties of the amperometric biosensor.

The work considered the properties of a biosensor based on a novel nanomaterial-modified thermally expanded graphite (TEG). The main focus was on whether the procedure of additional graphite thermal expansion would affect the electrochemical properties of biosensors based on membrane fractions of acetic acid bacteria . Raman spectroscopy, scanning electron microscopy and electrochemical analysis were used for the study.

Synchronization of the Processes of Autonomic Control of Blood Circulation in Humans Is Different in the Awake State and in Sleep Stages.

The influence of higher nervous activity on the processes of autonomic control of the cardiovascular system and baroreflex regulation is of considerable interest, both for understanding the fundamental laws of the functioning of the human body and for developing methods for diagnostics and treatment of pathologies. The complexity of the analyzed systems limits the possibilities of research in this area and requires the development of new tools. Earlier we propose a method for studying the collective dynamics of the processes of autonomic control of blood circulation in the awake state and in different stages of sleep.

Hypersonic magnetoelastic waves in inhomogeneous structures.

This work focuses on the propagation of surface magnetoelastic waves in a inhomogeneous structure containing ferromagnetic layer of smooth and slowly variable thickness. The dispersion relation of magnetoelastic waves and the wave attenuation due to the thickness variation in the studied structure were analytically obtained. We found that the magnetoelastic resonance frequency is changed at different positions in this structure.

Enhanced terahertz detection of multigate graphene nanostructures.

Terahertz (THz) waves have revealed a great potential for use in various fields and for a wide range of challenging applications. High-performance detectors are, however, vital for exploitation of THz technology. Graphene plasmonic THz detectors have proven to be promising optoelectronic devices, but improving their performance is still necessary.

Impact of PN junction inhomogeneity on the piezoelectric fields of acoustic waves in piezo-semiconductive fibers.

Non-uniform mechanical strain can be easily induced at the interface of a piezoelectric semiconductive (PS) PN junction with variable cross sections by using piezoactive acoustic waves, and thus produces a giant piezoelectric field to significantly enhance the piezotronic effect. For revealing the piezotronic performance modulation in the non-uniform PS PN junction, the electromechanical field under a pair of applied end mechanical forces is studied from perspectives of theoretical analysis and numerical simulations. A one-dimensional linearized model for the PS fiber is established, which is applied for the mechanical analysis of a selected profile with the cross section varying in a specific quadratic function.

Bifurcation analysis of multistability of synchronous states in the system of two delay-coupled oscillators.

Systems of mutually coupled oscillators with delay coupling are of great interest for various applications in electronics, laser physics, biophysics, etc. Time delay usually originates from the finite speed of propagation of the coupling signal. In this paper, we present the results of detailed bifurcation analysis of two delay-coupled limit-cycle (Landau-Stuart) oscillators.

Microbial acoustic sensor test-system based on a piezoelectric resonator with a lateral electric field for kanamycin detection in liquid.

A microbial test-system for real-time determination of low/residual concentrations of kanamycin in a liquid without the need for special labels is presented. The main element of the system was a piezoelectric resonator excited by a lateral electric field based on an X-cut lithium niobate plate 0.5 mm thick with two rectangular electrodes on one side.

Morphology of Mixed Langmuir and Langmuir-Schaefer Monolayers with Covered CdSe/CdS/ZnS Quantum Dots and Arachidic Acid.

The process of formation of a Langmuir-Schaefer (LS) matrix based on a mixed monolayer of arachidic acid (AA) and 8 nm CdSe/CdS/ZnS quantum dots (QDs) stabilized by molecules of trioctylphosphine oxide (TOPO) was investigated. The change in the morphology, monolayer compressibility, and area per elementary cell of the created mixed monolayers, depending on the ratio of the components, was studied. It is shown that the change in the morphology of Langmuir-Blodgett (LB) monolayers begins to occur at a ratio between the number of QDs and AA molecules of 1:24.

Simulation of the Transmission Spectrum of Long-Period Fiber Gratings Structures with a Propagating Acoustic Shock Front.

In this paper, we investigate modification of transmission spectra of long-period fiber grating structures with an acoustic shock front propagating along the fiber. We simulate transmission through inhomogeneous long-period fiber gratings, π-shift and reflective π-shift gratings deformed by an acoustic shock front. Coupled mode equations describing interaction of co-propagating modes in a long-period fiber grating structures with inhomogeneous deformation are used for the simulation.

A new liquid sensor based on a piezoelectric resonator with a radial electric field.

The possibility of development a liquid sensor based on a piezoelectric resonator with radial concentric electrodes is shown. The specified resonator has a large number of resonance peaks corresponding to different vibrational modes. The influence of two types of liquid container with distilled water on the resonance characteristics of these vibrational modes is experimentally investigated.

Magnetic domain wall motion driven by an acoustic wave.

Dynamic interaction of acoustic and magnetic systems is of strong current interest, triggered by the promises of almost lossless new concepts of magnet-based information technology. In such concepts, a significant role is often given to domain walls (DW). Therefore, here we investigate how launching an acoustic shear wave, we can control the DW motion.

Wavelet Ridges in EEG Diagnostic Features Extraction: Epilepsy Long-Time Monitoring and Rehabilitation after Traumatic Brain Injury.

Interchannel EEG synchronization, as well as its violation, is an important diagnostic sign of a number of diseases. In particular, during an epileptic seizure, such synchronization occurs starting from some pairs of channels up to many pairs in a generalized seizure. Additionally, for example, after traumatic brain injury, the destruction of interneuronal connections occurs, which leads to a violation of interchannel synchronization when performing motor or cognitive tests.

The influence of the Sc dopant on the transmittance of (Y, Er)AlO ceramics.

High erbium content yttrium aluminum garnet (Er:YAG) and yttrium scandium aluminum garnet (Er:YSAG) ceramics have been fabricated from Er:YAG and Er:YSAG powders, respectively. The powders have been synthesized a reverse precipitation technique, processed by uniaxial pressing followed by cold isostatic pressing, and sintered in a vacuum. TEOS (tetraethoxysilane) was used as a sintering additive.

Hypothesis of macroscopic quantum state in biological systems and discussion on the possibility of its experimental verification.

Earlier it was noted that the functioning of biological systems is accompanied by a very low level of energy dissipation, and it was assumed that a physical mechanism similar to that which works in superconductivity can operate here. The paper proposes a hypothesis that the phenomenon of life is not based on superconductivity, but on some so far unexplored macroscopic quantum state of organic structures making up the cell. It is assumed that this state is also characterized by the presence of an energy gap in the electronic spectrum, which makes the state stable and provides a low level of energy dissipation.

Arc-Induced Long-Period Fiber Gratings at INESC TEC. Part II: Properties and Applications in Optical Communications and Sensing.

In this work, we review the most important achievements of INESC TEC related to the properties and applications of arc-induced long-period fiber gratings. The polarization dependence loss, the spectral behavior at temperatures ranging from cryogenic up to 1200 °C and under exposure to ultraviolet and gamma radiation is described. The dependence of gratings sensitivity on the fabrication parameters is discussed.

Thalamo-Cortical and Thalamo-Thalamic Coupling During Sleep and Wakefulness in Rats.

The thalamus, a heterogeneous brain structure, is involved in the generation of sleep-related thalamo-cortical oscillations. Higher order nuclei might possess a distinct function compared with first-order nuclei in brain communication. Here it is investigated whether this distinction can also be found during the process of falling asleep and deepening of slow-wave sleep.

Arc-Induced Long-Period Fiber Gratings at INESC TEC. Part I: Fabrication, Characterization and Mechanisms of Formation.

In this work, we reviewed the most important achievements of INESC TEC related to the fabrication of long-period fiber gratings using the electric arc technique. We focused on the fabrication setup, the type of fiber used, and the effect of the fabrication parameters on the gratings' transmission spectra. The theory was presented, as well as a discussion on the mechanisms responsible for the formation of the gratings, supported by the measurement of the temperature reached by the fiber during an electric arc discharge.

A Statistical Method for Exploratory Data Analysis Based on 2D and 3D Area under Curve Diagrams: Parkinson's Disease Investigation.

A statistical method for exploratory data analysis based on 2D and 3D area under curve (AUC) diagrams was developed. The method was designed to analyze electroencephalogram (EEG), electromyogram (EMG), and tremorogram data collected from patients with Parkinson's disease. The idea of the method of wave train electrical activity analysis is that we consider the biomedical signal as a combination of the wave trains.

New modification of the acoustic Lamb waves and its application for liquid and ice sensing.

Using quartz plates as an example existance of the new modification of the Lamb waves is demonstrated. The waves have small vertical displacement, large shear-horizontal and longitudinal components, and elliptic polarization which is oriented parallel to the plate faces. Numerical calculations of the surface displacements and depth profiles show the particular polarization is maintained at any depth from free faces and for all plate thickness in the range h/λ = 0-1.

Artificial radio lighting with sources of microwave dynamic chaos.

Application of dynamic chaos for the illumination of the surrounding space by artificial incoherent sources of microwave radiation with the purpose of its subsequent observation using special receiving equipment is considered. An incoherent broadband microwave radiation field is provided by "radio light lamps" based on dynamic chaos generators. The radio light is received with specially designed sensitive elements that combine the properties of an envelope detector in communication systems and a radiometer.

The Peculiarities of the Acoustic Waves of Zero-Order Focusing in Lithium Niobate Plate.

In this research, beam focusing in lithium niobate plate was studied for fundamental anti-symmetric (A) and symmetric (S) Lamb waves, and the shear-horizontal (SH) wave of zero-order. Using the finite element method, appropriate configuration of the interdigital transducer with arc-like electrodes was modeled accounting for the anisotropy of the slowness curves and dispersion of the modes in the plate. Profiles of the focalized acoustic beams generated by the proposed transducer were theoretically analyzed.