Multilevel RTN Removal Tools for Dynamic FBG Strain Measurements Corrupted by Peak-Splitting Artefacts

Strain measurements using fibre Bragg grating (FBG) optical sensors are becoming ever more commonplace. However, in some cases, these measurements can become corrupted by sudden jumps in the signal, which manifest as spikes or step-like offsets in the data. These jumps are caused by a defect in the FBG itself, which is referred to as peak-splitting. The effects of peak splitting artefacts on FBG strain measurements show similarities with an additive multi-level telegraph noise process, in which the amplitudes and occurrences of the jumps are related to fibre deformation states. Whenever it is not possible to re-assess the raw spectral data with advanced peak tracking software, other means for removing the jumps from the data have to be found. The two methods presented in this article are aimed at removing additive multi-level random telegraph noise (RTN) from the raw data. Both methods are based on denoising the sample wise difference signal using a combination of an outlier detection scheme followed by an outlier replacement step. Once the difference signal has been denoised, the cumulative sum is used to arrive back at a strain time series. Two methods will be demonstrated for reconstructing severely corrupted strain time series; the data for this verification has been collected from sub-soil strain measurements obtained from an operational offshore wind-turbine. The results show that the proposed methods can be used effectively to reconstruct the dynamic content of the corrupted strain time series. It has been illustrated that errors in the outlier replacements accumulate and can cause a quasi-static drift. A representative mean value and drift correction are proposed in terms of an optimization problem, which maximizes the overlap between the reconstruction and a subset of the raw data; whereas a high-pass filter is suggested to remove the quasi static drift if only the dynamic band of the signal is of interest.

Measuring Practical Reversibility of Surface-Bound DNA for Mechanistic Insight into Folding-Based Sensors

In this paper, we characterize the mass-transport-limited response of surface-tethered redox moieties via flexible DNA linkers using measured voltammetric peak current and peak potential splitting. We demonstrate that peak splitting can be used to differentiate between reversible, quasi-reversible, and irreversible electrochemical regimes of the tethered redox molecule. Interestingly, the transition from one regime to another is dependent on the length and structure of the DNA probe. For example, as the probe length increases the transition from reversible to quasi-reversible occurs at lower scan rates. Additionally, we directly compare the dependence of the peak splitting and peak current as a function of scan rate for ssDNA, dsDNA, and other structured nucleic acids such as stem-loop and pseudoknot probes. Lastly, we find that by interrogating our surfaces with cyclic voltammetry we can observe quantitative differences in the peak splitting once the aptamer is in a bound state and correlate this to the extent of conformational change the sequence undergoes. The observations reported herein are consistent with the postulation that signaling in this class of sensor architectures is dictated by changes in nucleic acid structure and flexibility, which controls the mass transfer rate of the redox probe to the surface of the electrode.

Bonding Heterogeneity in Mixed-Anion Compounds Realizes Ultralow Lattice Thermal Conductivity

<p><a>Crystalline materials with intrinsically low lattice thermal conductivity (</a><i>κ</i>_lat) pave the way towards high performance in various energy applications, including thermoelectrics. Here we demonstrate a strategy to realize ultralow <i>κ</i>_lat using mixed-anion compounds. Our calculations reveal that locally distorted structures in chalcohalides MnPnS₂Cl (Pn = Sb, Bi) derives a bonding heterogeneity, which in turn causes a peak splitting of the phonon density of states. This splitting induces a large amount of scattering phase space. Consequently, <i>κ</i>_lat of MnPnS₂Cl is significantly lower than that of a single-anion sulfide CuTaS₃ with a similar crystal structure. Experimental <i>κ</i>_lat of MnPnS₂Cl takes an ultralow value of about 0.5 W m⁻¹ K⁻¹ at 300 K. Our findings will encourage the exploration of thermal transport in mixed-anion compounds, which remain a vast unexplored space, especially regarding unexpectedly low <i>κ</i>_lat in lightweight materials derived from the bonding heterogeneity.</p>

Bonding Heterogeneity in Mixed-Anion Compounds Realizes Ultralow Lattice Thermal Conductivity

<p><a>Crystalline materials with intrinsically low lattice thermal conductivity (</a><i>κ</i>_lat) pave the way towards high performance in various energy applications, including thermoelectrics. Here we demonstrate a strategy to realize ultralow <i>κ</i>_lat using mixed-anion compounds. Our calculations reveal that locally distorted structures in chalcohalides MnPnS₂Cl (Pn = Sb, Bi) derives a bonding heterogeneity, which in turn causes a peak splitting of the phonon density of states. This splitting induces a large amount of scattering phase space. Consequently, <i>κ</i>_lat of MnPnS₂Cl is significantly lower than that of a single-anion sulfide CuTaS₃ with a similar crystal structure. Experimental <i>κ</i>_lat of MnPnS₂Cl takes an ultralow value of about 0.5 W m⁻¹ K⁻¹ at 300 K. Our findings will encourage the exploration of thermal transport in mixed-anion compounds, which remain a vast unexplored space, especially regarding unexpectedly low <i>κ</i>_lat in lightweight materials derived from the bonding heterogeneity.</p>

Structure of GeO2 Glass under Compression Using Molecular Dynamics Simulation

We have investigated the behavior of GeO2 at the temperature of 300 K and the pressure from 0 to 100GPa by using the molecular dynamics simulation (the model with 5499 atoms). The results show that the Ge-Ge, Ge-O bond distance increase but O-O bond distance decreases when increasing the pressure. We find that the peak splitting of Ge-Ge at high pressure corresponds with the Ge-O-Ge and O-Ge-O bond angles. We also find that O-Ge-O bond angle decreases, and Ge-O-Ge bond angle increases with pressure. The core-sharing-bond is major at ambient pressure, but fractions of edge and face-sharing-bonds increase with pressure.

Nanoscopic live electrooptic imaging

A door to the nanoscopic domain is opened regarding real-time visualization of electric field distributions and dynamics. Through the use of a live electrooptic imaging system with an oil-immersion objective lens and a highly thinned electrooptic sensor film, a minimum linewidth of 330 nm and a minimum peak splitting of 650 nm in real-time electric field video images have been successfully demonstrated. In addition, room to improve the resolution is noted, while a few problems that need to be solved are discussed, including an effect caused by optical interference.

Strain measurements with fibre Bragg grating sensors under inhomogeneous deformations

Bragg grating sensors are fibre optic sensors for strain and temperature investigations with many advantages: the sensors can be embedded in plastic materials or composites and several gratings can be inscribed in one sensor. However, inhomogeneous deformation or transversal loading cause widening and splitting of the reflected wavelength peak of a fibre Bragg grating (FBG) sensor. These effects are shown in a residual stress analysis, in which the hole drilling method is adapted for FBG sensors. Additionally, a four-point bending test on three different notched aluminium beams is used to investigate the widening and splitting of the reflected peaks and their effects on the strain analysis. At each sample, a reference strain gauge sensor and two FBG sensors are applied. The two FBG sensors are loaded with different strain gradients. The unnotched beam and the beam with small strain gradient show the accuracy and reproducibility of the experiment. The beam with medium strain gradient shows no peak splitting, but the widening does influence the strain analysis. The results of the beam with high strain gradient demonstrate the peak splitting and the failure of the strain analysis methods. Initial approaches on how to deal with this widening and splitting are discussed.

Hydrogen Intramolecular Stretch Redshift in the Electrostatic Environment of Type II Clathrate Hydrates from Schrödinger Equation Treatment

The one-dimensional Schrödinger equation, applied to the H2 intramolecular stretch coordinate in singly to quadruply occupied large cages in extended Type II (sII) hydrogen clathrate hydrate, was solved numerically herein via potential-energy scans from classical molecular dynamics (MD), employing bespoke force-matched H2–water potential. For both occupation cases, the resultant H–H stretch spectra were redshifted by ~350 cm−1 vis-à-vis their classically sampled counterparts, yielding semi-quantitative agreement with experimental Raman spectra. In addition, ab initio MD was carried out systematically for different cage occupations in the extended sII hydrate to assess the effect of differing intra-cage intrinsic electric field milieux on H–H stretch frequencies; we suggest that spatial heterogeneity of the electrostatic environment is responsible for some degree of peak splitting.