On GPR signal polarity: a comparison between theoretical findings and real case-studies

<p>Signal polarity is an attribute that can be used as additional key element to reduce ambiguities and pitfalls in the data interpretation step.</p><p>A theoretical analysis of the reflection and transmission phenomena for parallel and perpendicular polarization of the electric field was carried out highlighting that polarity changes (180-degree phase shifts) are caused only by reflection phenomena in specific conditions.</p><p>Numerical modelling, through the Finite Difference Time Domain (FDTD) method, helped visualize the theoretical findings and was employed to reproduce the GPR response in two simple contexts (high permittivity layer embedded in a lower permittivity material and vice versa). The findings showed the expected theoretical polarity of multiple reflections providing a tool to effectively recognise them along with travel time information and reflection shapes.</p><p>The FDTD technique was also used to analyse the polarity response of regular geometrical shaped air-filled cavities (circle, square and arched roof square), in lossless and lossy conditions. The output was then compared with real radargrams concluding that A-scan assessment should be considered when pronounced scattering and attenuation phenomena are experienced (although polarity analysis may not be possible in very complex environments) and that the shape of the target may affect the resulting signal polarity due to interference with other wave fields.</p><p>Polarity analysis should be carried out by comparing the direct wavelet with the signal pattern of interest to assess if a phase shift occurred: attention should be paid to the GPR system used as not all the GPR antennas record the direct wavelet.</p>

Study on Bias Control of Memristor Multistablity System

In this paper, we study a memristor chaotic system with bias control. Based on the analysis of basic dynamic behavior, the hidden attractor coexistence and multi-stability of the non-equilibrium memristor chaotic system are verified, the bias control based on DC power control is studied, and the polarity control of the output variable is realized by using the change of parameters. The sinusoidal function is introduced as the bias periodic function, so that the system can realize signal polarity control only by changing the initial conditions. The analog circuit of memristor chaotic system is designed and verified by simulation..

A general approach to engineer positive-going eFRET voltage indicators

We engineered electrochromic fluorescence resonance energy transfer (eFRET) genetically encoded voltage indicators (GEVIs) with “positive-going” fluorescence response to membrane depolarization through rational manipulation of the native proton transport pathway in microbial rhodopsins. We transformed the state-of-the-art eFRET GEVI Voltron into Positron, with kinetics and sensitivity equivalent to Voltron but flipped fluorescence signal polarity. We further applied this general approach to GEVIs containing different voltage sensitive rhodopsin domains and various fluorescent dye and fluorescent protein reporters.

Segmented independent component analysis for improved separation of fetal cardiac signals from nonstationary fetal magnetocardiograms

Fetal magnetocardiograms (fMCGs) have been successfully processed with independent component analysis (ICA) to separate the fetal cardiac signals, but ICA effectiveness can be limited by signal nonstationarities due to fetal movements. We propose an ICA-based method to improve the quality of fetal signals separated from fMCG affected by fetal movements. This technique (SegICA) includes a procedure to detect signal nonstationarities, according to which the fMCG recordings are divided in stationary segments that are then processed with ICA. The first and second statistical moments and the signal polarity reversal were used at different threshold levels to detect signal transients. SegICA effectiveness was assessed in two fMCG datasets (with and without fetal movements) by comparing the signal-to-noise ratio (SNR) of the signals extracted with ICA and with SegICA. Results showed that the SNR of fetal signals affected by fetal movements improved with SegICA, whereas the SNR gain was negligible elsewhere. The best measure to detect signal nonstationarities of physiological origin was signal polarity reversal at threshold level 0.9. The first statistical moment also provided good results at threshold level 0.6. SegICA seems a promising method to separate fetal cardiac signals of improved quality from nonstationary fMCG recordings affected by fetal movements.

Polarity Switchable Photovoltages in Miscut La0.67Ca0.33MnO3Films

We report the transient laser-induced anomalous photovoltaic effect in the La0.67Ca0.33MnO3film grown on miscut LaSrAlO4(001) substrate under 248 nm pulsed laser irradiation at ambient temperature without any applied bias. A photovoltaic pulse signal was observed when the La0.67Ca0.33MnO3film was irradiated directly, and the signal polarity was reversed when the sample was irradiated through the LaSrAlO4substrate, while the signal recorded between the two electrodes on the surface of LaSrAlO4was not reversed when the sample was irradiated through La0.67Ca0.33MnO3film rather than at the surface of LaSrAlO4. The switchable signal polarity provides a potential application of miscut manganite films as optical components. A possible mechanism is introduced to explain the experiment results.

Resistive Electrical Switching of Nonvolatile Memories from Electrodeposited Copper Tetracyanoquinodimethane (CuTCNQ)

CuTCNQ is a charge transfer complex displaying resistive electrical switching when sandwiched between Cu and Al contacts. Corresponding memory cells switch from a native high resistive OFF state (HRS) to a low resistive ON state (LRS) by applying a negative voltage to the Al with respect to the Cu. Inversion of the signal polarity leads to switching from the LRS to the HRS. Typical CuTCNQ preparation occurs by a chemical reaction of a Cu substrate with TCNQ, involving (partial) corrosion of the metal. In this contribution we present electrodeposition of CuTCNQ on Au and Pt substrates, leading – in contrast to previously published dendritically crystal growth – to relatively smooth, micrometer thick layers. Corresponding large area cross-bar memory arrays (200€m by 200€m, with Al top contacts) exhibited up to several thousand write/erase cycles with an ON/OFF current ratio of 5-10. Furthermore preliminary growth experiments with blanket tungsten bottom contact Metal–Oxide–Semiconductor (CMOS) wafers with 250 nm diameter contact holes showed that electrodeposition is a suitable method for CuTCNQ integration.