Signal Generation Mechanism Research Articles

The Structure Design of Piezoelectric Poly(vinylidene Fluoride) (PVDF) Polymer-Based Sensor Patch for the Respiration Monitoring under Dynamic Walking Conditions.

This study reports a piezoelectric poly(vinylidene fluoride) (PVDF) polymer-based sensor patch for respiration detections in dynamic walking condition. The working mechanism of respiration signal generation is based on the periodical deformations on a human chest wall during the respiratory movements, which in turn mechanically stretch the piezoelectric PVDF film to generate the corresponding electrical signals. In this study, the PVDF sensing film was completely encapsulated within the sensor patch forming a mass-spring-damper mechanical system to prevent the noises generated in a dynamic condition. To verify the design of sensor patch to prevent dynamic noises, experimental investigations were carried out. Results demonstrated the respiration signals generated and the respiratory rates measured by the proposed sensor patch were in line with the same measurements based on a commercial respiratory effort transducer both in a static (e.g., sitting) or dynamic (e.g., walking) condition. As a whole, this study has developed a PVDF-based sensor patch which is capable of monitoring respirations in a dynamic walking condition with high fidelity. Other distinctive features include its small size, light weight, ease of use, low cost, and portability. All these make it a promising sensing device to monitor respirations particularly in home care units.

Evolution of reflexive signals using a realistic vocal tract model

We introduce a model of the evolution of reflexive primate signals that incorporates a realistic vocal tract model for generating the signals. Signaler neural networks receive signal types as inputs and produce vocal tract muscle activations as outputs. These muscle activations are input to a model of the primate vocal tract, generating real sounds. Receiver neural networks receive spectrograms of these sounds as inputs and produce signal type classifications as outputs. Incorporating a realistic vocal tract has a substantial effect on the types of signals that can evolve. Compared to a model with abstract signals, the realistic model signals are more similar and have more correlated elements. The realistic, embodied model also exhibits more variability in rate of adaptation, usually adapting more slowly. This may be explained by the more jagged fitness landscapes in the realistic model. The realistic signals also tend to be quiet. Environmental noise results in louder signals but makes the evolutionary process even slower and less robust. These results indicate that signal evolution with a more realistic genotype–phenotype mapping can differ substantially from evolution with abstract signals. Including realistic signal generation mechanisms may enable computational models to provide greater insights into natural signal evolution.

Calix[4]arene derivatives as dopamine hosts in electrochemical sensors

In this work, we introduce the use of an electrochemical sensor based on ion-channel mechanism in order to investigate the interaction between different-functionalized calixarene mercaptoalkyl derivatives and dopamine at the aqueous/organic interface. Three different calix[4]arene derivatives, functionalized with mercaptoalky groups at the upper-rim of calix[4]arene, were synthesized, and their structures were characterized by FTIR, 1H and 13C NMR spectroscopy, and elemental analysis techniques. Moreover, these calixarene-mercaptoalkyl derivatives were grafted onto gold electrode surface by covalent Au-S bound. To elucidate the functional groups’ influences on the signal generation mechanism, three different-substituted calixarene-mercaptoalkyl derivatives, with an opposite arrangement of the functional moieties and mercaptoalkyl groups at the lower and the upper rim of the calixarene, were interacted for the first time with dopamine. The formation of a supramolecular complex between the calix[4]arene host and the dopamine guest were confirmed by Osteryoung square-wave voltammetry with [Ru(NH3)6]Cl3 as an redox active marker. The proposed electrochemical sensors were suitable for the determination of dopamine in the concentration range from 1.0×10−11M to 1.0×10−6M. In order to demonstrate the applicability of the sensors proposed, the electrochemical determination of dopamine in the presence of ascorbic acid and uric acid were checked. It was proved that these interferences did not influence on dopamine determination. The detection limit was estimated as 4.9pM.

Peak‐to‐average power ratio reduction of orthogonal frequency division multiplexing systems using modified tone reservation techniques

SummaryThis paper proposed a modified tone reservation (TR) technique that can reduce the peak‐to‐average power ratio (PAPR) of the orthogonal frequency division multiplexing (OFDM) system and is able to correct errors to avoid channel interference. The TR technique is a widely used PAPR reduction technique, which divides subcarriers of the OFDM system into two sets to generate peak‐canceling signals and transmit modulated data. The subcarriers used to reduce the PAPR are called the peak reduction tone sets. The mechanism of peak‐canceling signal generation is a primary factor in determining the quality of the PAPR reduction performance of the TR technique. Currently, two signal generation mechanisms exist: TR‐gradient‐based and TR‐clipping‐based techniques. Although TR techniques can effectively reduce the high PAPR in the OFDM system, TR techniques lack the ability to correct errors. Therefore, this paper combined block coded modulation codes and TR techniques to provide the modified TR techniques with error correction abilities. From the simulation results, the modified TR techniques had a superior effect on PAPR reduction performance compared with the conventional TR technique. The modified TR technique also possessed the ability to correct errors during signal transmission. Copyright © 2015 John Wiley & Sons, Ltd.

Photoacoustic Spectrum Analysis for Microstructure Characterization in Biological Tissue: Analytical Model

Photoacoustic spectrum (PA) analysis (PASA) has been found to have the ability to identify the microstructures in phantoms and biological tissues. PASA adopts the procedures in ultrasound spectrum analysis, although the signal generation mechanisms related to ultrasound backscatter and PA wave generation differ. The purpose of this study was to theoretically validate PASA. The analytical solution to the power spectrum of PA signals generated by identical microspheres following discrete uniform random distribution in space was derived. The simulation and experiment validation of the analytical solution include: (i) the power spectrum profile of a single microsphere with a diameter of 300 μm, and (ii) the PASA parameters of the PA signals generated by randomly distributed microspheres 100, 200, 300, 400 and 500 μm in diameter, at concentrations of 30, 60, 120, 240, 480 per 1.53 cm3 in the observation range 0.5–13 MHz.

A plasmonic aptasensor for ultrasensitive detection of thrombin via arrested rolling circle amplification.

A sensitive signal generation mechanism for gold nanoparticle growth by reducing gold ions with hydrogen peroxide is applied in a plasmonic aptasensor, achieving naked-eye detection of thrombin at the single-molecule level based on the specific interaction of aptamer-thrombin via an arrested rolling circle amplification to yield horseradish peroxidase (HRP)-mimicking DNAzymes as biocatalysts.

Mechanism for laser-induced fluorescence signal generation in a nanoparticle-seeded flow for planar flame thermometry

The mechanism of atomic indium generation for laser-induced fluorescence (LIF) of indium from laser ablation seeding was investigated in a hydrogen/nitrogen non-premixed flame. The morphology and particle size distributions of the ablation products were examined with scanning electron microscopy and transmission electron microscopy. These investigations show that the ablation products comprise complex agglomerates of nano-sized primary particles of indium compounds and micron-sized spherical indium beads. Images of the atomic indium LIF, Mie scattering of ablation products and natural fluorescence emission of indium in the flame were recorded to investigate the mechanism of fluorescence signal generation. The relative contribution of natural fluorescence emission of indium towards the total indium fluorescence signal was assessed by comparing these images. These images also reveal the evolution of ablation products through the flame structure and the correlation between LIF signal and ablation products. It is found that the LIF signal generation is associated with the vapourisation of indium nanoparticles into the gas phase by thermal decomposition in the flame. A further mechanism for thermal decomposition of the nanoparticles was also identified, that of heating the ablation products by in situ laser ablation. This was assessed by means of a second laser, introduced prior to the excitation laser, to reveal that the LIF signal can be enhanced by in situ laser ablation, particularly in the upstream regions of the flame. These findings supersede the mechanism deduced previously by the authors that neutral atomic indium can survive a convection time of the order of tens of seconds and be directly seeded into reacting or non-reacting flows. The possible influences of laser ablation seeding on the nonlinear two-line atomic fluorescence thermometry technique were also assessed.

A new model of the signal generation mechanism on magnetostrictive position sensor

Magnetostrictive waveguide position sensor (MPS) is widely used in industry for position measurement and monitoring. Generally, the generation mechanism of MPS signal is just roughly attributed to the inverse magnetostrictive effect. In this paper, we introduce a novel model of MPS signal generation mechanism which consists of the magnetic domain rotation free (MRF) effect and the magnetic source fluctuation (MSF) effect. Based on this model, the signal intensity is influenced by external magnetic field and the status of magnetostrictive waveguide wire (MPS wire). A series of experiments have been performed to verify the validity of MRF and MSF. The results showed that the signal mechanism model presented here is reasonable. Finally, the practical application of this study is also discussed. As a conclusion, in the application of MPS, the receiving coil must be shielded by ferromagnetic material rather than non-ferrous metal, and the MPS wire cannot be restricted and it must be placed in the center of coil. Otherwise, the signal intensity will be weakened rapidly. The research results indicate that the findings lay a foundation for designing the reasonable structure of MPS, so the new explanation for the signal generation mechanism in this study is of great practical value.

Plasmonic ELISA for the detection of analytes at ultralow concentrations with the naked eye

This protocol describes a signal-generation mechanism for the naked-eye detection of analytes at low concentrations with ELISA. The key step is to generate solutions of desired tonality by growing gold nanoparticles with a particular state of aggregation. This is accomplished by linking the growth of gold nanoparticles with the biocatalytic cycle of the enzyme label. The protocol adapts a conventional ELISA procedure with catalase-labeled antibodies. The enzyme consumes hydrogen peroxide, and then gold (III) ions are added to generate gold nanoparticles. The concentration of hydrogen peroxide dictates the state of aggregation of gold nanoparticles. This allows for the naked-eye detection of analytes by observing the generation of blue- or red-colored gold nanoparticle solutions. When coupled with conventional ELISA, this signal-generation procedure allows for the naked-eye detection of analytes within 1 h.

Proximate and ultimate causes of signal diversity in the electric fishGymnotus

A complete understanding of animal signal evolution necessitates analyses of both the proximate (e.g. anatomical and physiological) mechanisms of signal generation and reception, and the ultimate (i.e. evolutionary) mechanisms underlying adaptation and diversification. Here we summarize the results of a synthetic study of electric diversity in the species-rich neotropical electric fish genus Gymnotus. Our study integrates two research directions. The first examines the proximate causes of diversity in the electric organ discharge (EOD) - which is the carrier of both the communication and electrolocation signal of electric fishes - via descriptions of the intrinsic properties of electrocytes, electrocyte innervation, electric organ anatomy and the neural coordination of the discharge (among other parameters). The second seeks to understand the ultimate causes of signal diversity - via a continent-wide survey of species diversity, species-level phylogenetic reconstructions and field-recorded head-to-tail EOD (ht-EOD) waveforms (a common procedure for characterizing the communication component of electric fish EODs). At the proximate level, a comparative morpho-functional survey of electric organ anatomy and the electromotive force pattern of the EOD for 11 species (representing most major clades) revealed four distinct groups of species, each corresponding to a discrete area of the phylogeny of the genus and to a distinct type of ht-EOD waveform. At the ultimate level, our analyses (which emphasize the ht-EOD) allowed us to conclude that selective forces from the abiotic environment have had minimal impact on the communication component of the EOD. In contrast, selective forces of a biotic nature - imposed by electroreceptive predators, reproductive interference from heterospecific congeners, and sexual selection - may be important sources of diversifying selection on Gymnotus signals.

Deep-penetration photoacoustic array imaging of calcifications

Calcifications are one of the most important indicators for early breast cancer detection. We explore the feasibility of deep-penetration photoacoustic (PA) imaging of calcifications based on a medical ultrasound array imaging platform. Intralipid and chicken breast phantoms embedded with different-sized hydroxyapatite (HA) particles, which are the major components of calcifications, were imaged to verify the equipment's capability and penetration depth for the visualization of calcifications. An optimal near-infrared excitation wavelength was selected to maximize PA signals of HAs, resulting in a better HA signal-to-blood ratio. We demonstrated that PA imaging is capable of visualizing 0.5-mm HA particles at a depth of 3 cm in chicken breast phantoms. The noise-equivalent penetration depth of the system for visualizing 0.5-mm HA particles in the human breast was estimated to be about 2.9 to 3.5 cm, which is clinically relevant as calcifications are usually found at a depth of 0.6 to 3.0 cm. Moreover, the feasibility of differentiating HA from blood by the PA spectroscopic technique was presented and the mechanism of the HA signal generation was discussed. The results show that PA imaging is a promising technique for real-time visualization of breast calcifications.

Characterization of Yellow Seahorse Hippocampus kuda feeding click sound signals in a laboratory environment: an application of probability density function and power spectral density analyses

Do the sounds generated by different-sized fish of different sexes differ from each other in temporal, spectral or intensity patterns? Such differences would enable the development of passive acoustic techniques to locate seahorses in open water bodies. On the basis of this perspective, we characterize and present in this study Yellow Seahorse Hippocampus kuda (Syngnathidae) feeding click sounds, recorded in a controlled laboratory environment. The characterization involved analysis of the “probability density function” (PDF) and the “power spectral density” (PSD) of the seahorse feeding click sound signals of different sizes and sexes. The PDF describes the general distribution of the magnitude of a random process, and such analysis, using recorded seahorse clicks, points towards a multimodal statistical distribution, which is the existence of more than one fitting component for the majority of seahorse click signals above the tank ambient noise level. This fact has been appraised towards the involvement of more than one process in the seahorse click signal generation mechanism. However, lack of prior knowledge about the individual PDF components of the data leads towards the mismatch between the data of PDFs. The PDF gives no information on the time and frequency content of the processes as provided by the PSD. Under such conditions, curve fitting of the “power law” expressions to the PSD functions estimates “slope” and “intercept” parameters of the seahorse click signal. Striking differences in the feeding click characteristics of various sizes of the H. kuda and between the sexes were discernable based on the clustering pattern among the estimated “slope” and “intercept” parameters. Further studies using the seahorse body sizes and weight (wet) with respect to the peak frequencies estimated from the PSD distribution show results equivalent to those from previous studies.

Luminescent Noble Metal Nanoclusters as an Emerging Optical Probe for Sensor Development

In the past few years, highly luminescent noble metal nanoclusters (e.g., Au and Ag NCs or Au/Ag NCs in short) have emerged as a class of promising optical probes for the construction of high-performance optical sensors because of their ultrasmall size (<2 nm), strong luminescence, good photostability, excellent biocompatibility, and unique metal-core@ligand-shell structure. In this Focus Review, we briefly summarize the common syntheses for water-soluble highly-luminescent thiolate- and protein-protected Au/Ag NCs and their interesting luminescence properties, highlight recent progress in their use as optical sensors with an emphasis on the mechanisms underlying their selectivity, and finally discuss approaches to improving their sensitivity. The scope of the works surveyed is confined to highly luminescent thiolate- and protein-protected Au/Ag NCs.

Detection of DNA hybridization by field-effect DNA-based biosensors: mechanisms of signal generation and open questions

We model theoretically the electrostatic effects taking place upon DNA hybridization in dense DNA arrays immobilized on a layer of Au nano-particles deposited on the surface of a field-effect-based DNA capacitive biosensor. We consider the influence of separation of a charged analyte from the sensor surface and the salinity of electrolyte solution, in the framework of both linear and nonlinear Poisson–Boltzmann theories. The latter predicts a substantially weaker sensor signals due to electrostatic saturation effects that is the main conclusion of this paper. We analyze how different physical parameters of dense DNA brushes affect the magnitude of hybridization signals. The list includes the fraction of DNA charge neutralization, the length and spatial conformations of adsorbed DNA molecules, as well as the discreteness of DNA charges. We also examine the effect of Donnan ionic equilibrium in DNA lattices on the sensor response. The validity of theoretical models is contrasted against recent experimental observations on detection of DNA hybridization via its intrinsic electric charge. The sensitivity of such biochemical sensing devices, their detection limit, and DNA hybridization efficiency are briefly discussed in the end.

Biomedical detection via macro- and nano-sensors fabricated with metallic and semiconducting oxides.

Originally developed as gas sensors, the benefits of metallic and semiconducting oxide materials are now being realized in other areas of sensing, such as chemical, environmental, and biomedical monitoring and detection. Metallic and semiconducting oxides have continuously expanded their roles to date, and have also established their significance in biosensing by utilizing a variety of modes for signal generation and detection mechanism. These sensors are typically based either on their optical, electrochemical, electrical, gravimetric, acoustic, and magnetic properties for signal transduction. This article reviews such biosensors that employ metallic and semiconducting oxides as active sensing elements to detect nucleic acids, proteins, cells, and a variety of important biomarkers, both in thin film and one-dimensional forms. Specific oxide materials (M(x)O(y)) examined comprehensively in this article include M = Fe, Cu, Si, Zn, Sn, In. The derivatives of these oxide materials resulting from incorporation of dopants are examined as well. The crystalline structures and unique properties that may be exploited for various biosensing applications are discussed, and recent efforts investigating the feasibility of using these oxide materials in biosensor technology are described. Key biosensor characteristics resulting from reduced dimensionality are overviewed under the motif of planar and one-dimensional sensors. This article also provides insight into current challenges facing biosensor applications for metallic and semiconducting oxides. In addition, future outlook in this particular field as well as different impacts on biology and medicine are addressed.

Photonic generation of high-frequency microwave signals utilizing a multi-transverse-mode vertical-cavity surface-emitting laser subject to two-frequency orthogonaloptical injection

We study photonic microwave signal generation obtained when single- and multi-transverse-mode vertical-cavity surface-emitting lasers (VCSELs) are subject to two-frequency orthogonal optical injection. Our calculations show that broadly tunable microwave signals can be obtained in these systems. The response of the multi-transverse-mode VCSEL is enhanced with respect to that obtained with a similar single-transverse-mode VCSEL subject to the same two-frequency orthogonal optical injection. The extra degree of freedom given by the multi-transverse-mode operation of the VCSEL under two-frequency orthogonal optical injection enhances the performance of the photonic microwave generation system, because the higher-order transverse mode is excited with a much larger amplitude than that of the fundamental transverse mode. Periodic oscillations are obtained for a very wide range of frequency detunings between the optical injections and transverse modes. A relative maximum of the microwave signal amplitude is obtained when the frequency of one of the optical injections is very close to the frequency of the orthogonally polarized fundamental mode of the VCSEL. Periodic oscillations are demonstrated for symmetric and asymmetric values of the injection strengths. Wide tuning ranges, extended into the THz band, are obtained in our system. Our results show that the proposed microwave signal generation mechanism is independent of the polarization of the master lasers.

Plasmonic ELISA for the ultrasensitive detection of disease biomarkers with the naked eye

In resource-constrained countries, affordable methodologies for the detection of disease biomarkers at ultralow concentrations can potentially improve the standard of living. However, current strategies for ultrasensitive detection often require sophisticated instruments that may not be available in laboratories with fewer resources. Here, we circumvent this problem by introducing a signal generation mechanism for biosensing that enables the detection of a few molecules of analyte with the naked eye. The enzyme label of an enzyme-linked immunosorbent assay (ELISA) controls the growth of gold nanoparticles and generates coloured solutions with distinct tonality when the analyte is present. Prostate specific antigen (PSA) and HIV-1 capsid antigen p24 were detected in whole serum at the ultralow concentration of 1×10(-18)gml(-1). p24 was also detected with the naked eye in the sera of HIV-infected patients showing viral loads undetectable by a gold standard nucleic acid-based test.

Analysis of nonharmonic oscillations in Schottky diodes

We investigate damped nonharmonic oscillations at terahertz frequencies observed in the current response of Schottky diodes simulated with the Monte Carlo method under applied signals of a few hundred GHz. From Monte Carlo simulations of different diode structures, two kinds of nonharmonic oscillations have been identified. The first kind of oscillations is due to the coupling of the nonlinear performance of the Schottky junction with the inertial motion of the carriers in the non-depleted region of the epilayer. The second kind of oscillations is due to the modulation of the n+–n junction when high electric fields are induced in the non-depleted region of the epilayer. These oscillations constitute a promising mechanism for THz signal generation.

Plasmonic nanosensors with inverse sensitivity by means of enzyme-guided crystal growth

Lowering the limit of detection is key to the design of sensors needed for food safety regulations, environmental policies and the diagnosis of severe diseases. However, because conventional transducers generate a signal that is directly proportional to the concentration of the target molecule, ultralow concentrations of the molecule result in variations in the physical properties of the sensor that are tiny, and therefore difficult to detect with confidence. Here we present a signal-generation mechanism that redefines the limit of detection of nanoparticle sensors by inducing a signal that is larger when the target molecule is less concentrated. The key step to achieve this inverse sensitivity is to use an enzyme that controls the rate of nucleation of silver nanocrystals on plasmonic transducers. We demonstrate the outstanding sensitivity and robustness of this approach by detecting the cancer biomarker prostate-specific antigen down to 10(-18) g ml(-1) (4 × 10(-20) M) in whole serum.

Membrane dynamics shape TCR-generated signaling

Despite intensive investigation, the mechanisms of T cell receptor (TCR)-mediated signal generation remain poorly understood. Here we review various dynamic processes at the cell membrane that might critically control this signaling. Firstly, we summarize recent reports providing new information on the sensitivity of TCR/ligand interaction to the membrane environment and particularly to applied forces. Secondly, we review recent evidence that forces and displacements are continuously generated at cell surfaces. Thirdly, we summarize recent experimental evidence demonstrating the capacity of forces to generate signals. Lastly, we provide a quantitative model to exemplify the capacity of dynamic processes to modulate TCR properties such as specificity that were previously difficult to explain with conventional models. It is concluded that the described dynamic processes must be integrated into current models of TCR signaling.