Signal Generation Mechanism Research Articles

Energy-level and optical properties of nitrogen doped TiO2: An experimental and theoretical study

Photoacoustic spectroscopy was used to study nitrogen-doped titanium dioxide film. The energy positions of defect and impurity centre levels are reported. The energy levels were obtained using the excitation method and the mechanisms of the photoacoustic signal generation are discussed. The visible light absorption of the yellow film was explained considering electronic transitions between localized states within the band gap and the transitions from these states into the conduction band. Moreover, first principles calculations revealed that nitrogen doping and oxygen vacancies in titanium dioxide induce defect levels within the gap which account for the absorption in the visible light.

An Analysis Method with Equivalent Circuit for the Electrical Effect Induced by Laser Plasma

Electrical effect induced by the laser plasma was investigated with an external tiny probe during Nd:YAG high-power pulse laser ablation on copper target in air. One equivalent circuit for the electrical effect induced by laser plasma was proposed. Based on the equivalent circuit, a new theoretical explanation of the signal generation mechanism is proposed, and the reason that the distribution of electrical signal wave is strongly dependent on the probe distance was discussed. Further the observed signal peak polarity overturn was explained.

Dual Adaptive Control Properties

AbstractThe dual adaptive controls derived for a linear unknown drifting parameters plant from the Bellman equation in a semi-explicit form is analysed numerically in this paper. The probing signal generation mechanism is discussed and shown that the dual controls are dependent on certain (probing) function that drives the estimation process initially in full range of unknown parameters and then selectively with respect to the model inaccuracy. It improves the model most in this part where the model is most inaccurate (variation peak) if the drifting parameters are error-estimated compared to the average steady-state level of drift. The instantaneous cost is enhanced correspondingly in the most inaccurate part of the model and well indicates the inaccuracy of the model with respect to the past estimated trajectory.

Chemical Imaging with Frequency Modulation Coherent Anti-Stokes Raman Scattering Microscopy at the Vibrational Fingerprint Region

We present a new coherent anti-Stokes Raman scattering (CARS) method that can perform background-free microscopy and microspectroscopy at the vibrational fingerprint region. Chirped broad-band pulses from a single Ti:sapphire laser generate CARS signals over 800-1700 cm(-1) with a spectral resolution of 20 cm(-1). Fast modulation of the time delay between the pump and Stokes pulses coupled with lock-in signal detection not only removes the nonresonant background but also produces Raman-like CARS signals. Chemical imaging and microspectroscopy are demonstrated with various samples such as edible oils, lipid membranes, skin tissue, and plant cell walls. Systematic studies of the signal generation mechanism and several fundamental aspects are discussed.

Dual adaptive controls for linear system with unknown constant parameters

The semi-explicit solution of a dual adaptive control problem driven by a linear system with unknown constant parameters is given. The controls are tested in the simulation experiment and analysed in contrast to the certainty equivalent controls and cautious controls. The probing feature of dual controls is discussed and accomplished with data. The probing signal generation mechanism is investigated.

Gas cell photoacoustic detection of ultrasound absorption

The photoacoustic signal generated by a 2 MHz ultrasound transducer has been detected at 500 Hz modulation frequency by an attached photoacoustic cell. A dominant mechanism for signal generation is the ultrasound absorption in the gas of the cell, where strong acoustic resonances are excited. The periodic heating by ultrasound absorption in the transducer buffer rod and subsequent thermal diffusion into the gas is a second mechanism. Experiment and theory are in reasonable accordance.

Optical band-gap determination of nanostructured WO3 film

The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green’s function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.

Mechanisms of supported bilayer detection using field-effect devices

The adsorption of positively charged supported lipid bilayers (SLBs) on field-effect devices was studied using various salt solutions to make it possible to understand the signal generation mechanisms of the devices. The flat-band voltage change that occurred with SLB formation was dependent on the type of monovalent cations contained in the solution. Zeta potential data showed that the intrinsic charge of the bilayers was almost constant in the presence of any of the examined alkali ions. The results suggest that the lipid charge does not solely determine the flat-band voltage. The binding affinity of alkali ions to silicon nitride showed a similar trend to the dependence of the flat-band voltage change on alkali ions. The results indicate that the specific interaction of small inorganic ions with the device surface has a significant influence on the magnitude of the signal response that occurs with SLB formation. It appears that salt ions specifically bound to the device surface and the charge of the bilayers both contribute to the signal generation mechanisms.

The CEACAM1 N-terminal Ig domain mediates cis- and trans-binding and is essential for allosteric rearrangements of CEACAM1 microclusters.

Cell adhesion molecules (CAMs) sense the extracellular microenvironment and transmit signals to the intracellular compartment. In this investigation, we addressed the mechanism of signal generation by ectodomains of single-pass transmembrane homophilic CAMs. We analyzed the structure and homophilic interactions of carcinoembryonic antigen (CEA)-related CAM 1 (CEACAM1), which regulates cell proliferation, apoptosis, motility, morphogenesis, and microbial responses. Soluble and membrane-attached CEACAM1 ectodomains were investigated by surface plasmon resonance-based biosensor analysis, molecular electron tomography, and chemical cross-linking. The CEACAM1 ectodomain, which is composed of four glycosylated immunoglobulin-like (Ig) domains, is highly flexible and participates in both antiparallel (trans) and parallel (cis) homophilic binding. Membrane-attached CEACAM1 ectodomains form microclusters in which all four Ig domains participate. Trans-binding between the N-terminal Ig domains increases formation of CEACAM1 cis-dimers and changes CEACAM1 interactions within the microclusters. These data suggest that CEACAM1 transmembrane signaling is initiated by adhesion-regulated changes of cis-interactions that are transmitted to the inner phase of the plasma membrane.

Comparison Study of Three Different Image Reconstruction Algorithms for MAT-MI

In this paper, we report a theoretical study on magnetoacoustic tomography with magnetic induction (MAT-MI). According to the description of signal generation mechanism using Green's function, the acoustic dipole model was proposed to describe acoustic source excited by the Lorentz force. Using Green's function, three kinds of reconstruction algorithms based on different models of acoustic source (potential energy, vectored acoustic pressure, and divergence of Lorenz force) are deduced and compared, and corresponding numerical simulations were conducted to compare these three kinds of reconstruction algorithms. The computer simulation results indicate that the potential energy method and vectored pressure method can directly reconstruct the Lorentz force distribution and give a more accurate reconstruction of electrical conductivity.

Visualization of stochastic Ca2+ signals in the formed somites during the early segmentation period in intact, normally developing zebrafish embryos

Localized Ca(2+) signals were consistently visualized in the formed somites of intact zebrafish embryos during the early segmentation period. Unlike the regular process of somitogenesis, these signals were stochastic in nature with respect to time and location. They did, however, occur predominantly at the medial and lateral boundaries within the formed somites. Embryos were treated with modulators of [Ca(2+)](i) to explore the signal generation mechanism and possible developmental function of the stochastic transients. Blocking elements in the phosphoinositol pathway eliminated the stochastic signals but had no obvious effect, stochastic or otherwise, on the formed somites. Such treatments did, however, result in the subsequently formed somites being longer in the mediolateral dimension. Targeted uncaging of buffer (diazo-2) or Ca(2+) (NP-ethyleneglycoltetraacetic acid [EGTA]) in the presomitic mesoderm, resulted in a regular mediolateral lengthening and shortening, respectively, of subsequently formed somites. These data suggest a requirement for IP(3) receptor-mediated Ca(2+) release during convergence cell movements in the presomitic mesoderm, which appears to have a distinct function from that of the IP(3) receptor-mediated stochastic Ca(2+) signaling in the formed somites.

Simulation of spatial and energy resolution in signal for gas proportional detector

Computer simulations of charge transport and signal generation mechanism have been performed for the Aleph Inner Tracking Detector geometry. A number of factors influence the signal arising from the charge carriers generated within detector volume. In the present simulation, signal fluctuations due to changing of incident charged particle energy and position of the primary generated electron-ion pairs in the gas volume have been examined. The simulation calculations are in good agreement with experimental results. Key words: Signal generation mechanism, signal fluctuation, Monte Carlo device simulation.

Theory of Superconductive Traveling-Wave Photodetectors

This paper studies the theory of traveling-wave photodetection in superconductive multilayer optical waveguides, as a general platform for ultrafast, ultrasensitive, and ultralow-noise optoelectronics. The kinetic inductance theory of superconductive thin films and the modified transmission line theory are employed to investigate the distributed photodetection and signal generation mechanisms in superconductive traveling-wave devices. A general model for calculation of the optical responsivity of superconductive traveling-wave photodetectors is developed and operation regimes of interest are highlighted. Moreover, the inclusion of a photoconductive layer in the device structure and some important loading schemes are discussed and their effects on the device performance, such as quantum efficiency and electrical bandwidth, are addressed.

Thoracic vibrations in stingless bees (Melipona seminigra):resonances of the thorax influence vibrations associated with flight but not those associated with sound production

Bees generate thoracic vibrations with their indirect flight muscles in various behavioural contexts. The main frequency component of non-flight vibrations, during which the wings are usually folded over the abdomen, is higher than that of thoracic vibrations that drive the wing movements for flight. So far, this has been concluded from an increase in natural frequency of the oscillating system in association with the wing adduction. In the present study, we measured the thoracic oscillations in stingless bees during stationary flight and during two types of non-flight behaviour, annoyance buzzing and forager communication, using laser vibrometry. As expected, the flight vibrations met all tested assumptions for resonant oscillations: slow build-up and decay of amplitude; increased frequency following reduction of the inertial load; and decreased frequency following an increase of the mass of the oscillating system. Resonances, however, do not play a significant role in the generation of non-flight vibrations. The strong decrease in main frequency at the end of the pulses indicates that these were driven at a frequency higher than the natural frequency of the system. Despite significant differences regarding the main frequency components and their oscillation amplitudes, the mechanism of generation is apparently similar in annoyance buzzing and forager vibrations. Both types of non-flight vibration induced oscillations of the wings and the legs in a similar way. Since these body parts transform thoracic oscillations into airborne sounds and substrate vibrations, annoyance buzzing can also be used to study mechanisms of signal generation and transmission potentially relevant in forager communication under controlled conditions.

Field-resolved measurement of reaction-induced spectral densities by polarizability response spectroscopy

The experimental design and theoretical description of a novel five-pulse laser spectroscopy is presented with an application to a pyridinium charge transfer complex in acetonitrile and methanol. In field-resolved polarizability response spectroscopy (PORS), an electronically resonant laser pulse first excites a solvated chromophore (reactant) and off-resonant Raman spectra of the resulting nuclear motions are measured as a function of the reaction time. The present apparatus differs from our earlier design by performing the Raman probe measurement (with fixed pulse delays) in the frequency domain. In addition, the full electric fields of the signals are measured by spectral interferometry to separate nonresonant and Raman responses. Our theoretical model shows how the PORS signal arises from nuclear motions that are displaced/driven by the photoinduced reaction. The field-resolved off-resonant (of the solute's electronic transitions) probing favors detection of solvent (as opposed to solute) dynamics coupled to the reaction. The sign of the signal represents the relative strengths of polarization responses associated with the ground and photoexcited solutions. Signatures of nonresonant and PORS signal contributions to the experimental results are analyzed with numerical calculations based on a theoretical model we have developed for reaction-induced PORS. Our model identifies two mechanisms of PORS signal generation: (i) structural relaxation induced resonance; (ii) dephasing induced resonance. In the charge transfer reaction investigated, the solvent-dependent and time-evolving (solvent) polarizability spectral density (PSD) is readily obtained. The general trend of an initial broadband inertial nuclear response followed by a decrease in the linewidth of the PSD establishes that the measured PSD is inconsistent with the approximation of a linear response. Furthermore, the explicit time evolution of the PSD is important for properly describing solvent control of reactions that do not satisfy the time-scale separability inherent to nonadiabatic kinetic models.

Optical portable biosensors based on stabilized lipid membrane for the rapid detection of doping materials in human urine

Abstract This work reports a technique for the construction of portable devices that are based on stabilized lipid membrane with an incorporated artificial receptor that can be used for the rapid optical detection of doping materials in human urine. The artificial receptors are incorporated within the lipid mixture prior to polymerization. Microporous filters composed of glass fibers were used as supports for the stabilization of these sensors. The lipid film was formed on the filter by polymerization using UV irradiation prior its use. Methacrylic acid was the functional monomer, ethylene glycol dimethacrylate was the crosslinker and 2,2′-azobis-(2-methylpropionitrile) was the initiator. The polymerization is completed within 4 h and the artificial receptors retain their activity. These devices can be used as portable sensors because they provided a simple screening sensitive spot optical test for the rapid one-shot detection of dopamine and ephedrine in human urine. It was now possible to have quantitative data based on a calibration graph. A quantitative method for the detection of dopamine or ephedrine in real samples of urine that can be complimentary to HPLC methods is provided in the present paper. An investigation of the mechanism of signal generation for the “switch on” and “switch off” the fluorescence signal is made herein. The construction of these devices will allow the practical use of the techniques for chemical sensing based on lipid membranes to prepare portable chips/biosensors for the detection of toxicants in foods or pollutants in the field and commercialization of these devices.

A surface photovoltage spectroscopy study of GaAs∕AlAs complicated nanostructures with graded interfaces

We present a surface photovoltage (SPV) spectroscopy study of the optical properties and the bound states of graded interface AlAs∕GaAs superlattices (SLs) containing two GaAs embedded quantum wells (EQWs) with different widths. SPV spectra are measured in the metal-insulator-semiconductor operation mode under super-band-gap optical excitation at room temperature. In spite of the relatively large absorption of the GaAs substrate, the SPV spectra exhibit clearly resolved features superimposed on the substrate smooth background. These features have been identified as free exciton transitions in the EQWs and in the SL. This interpretation is based on a detailed comparison of the SPV results with those of electronic structure calculations and photoluminescence spectral measurements. The calculations are performed in frames of the envelope function approximation, employing a model structure very similar to the real one and taking into account the interface grading. The mechanisms of the SPV signal generation have been discussed. An experimental confirmation is given to the theoretical model developed by others, about the SPV behavior in quantum wells. Our study demonstrates further the SPV spectroscopy powerful potentialities for nondestructive contactless characterization at room temperature of complicated nanostructures with graded interfaces.

Label-free detection of charged macromolecules by using a field-effect-based sensor platform: Experiments and possible mechanisms of signal generation

The possibilities and limitations of a direct electrical detection of charged macromolecules using a field-effect-based sensor platform is evaluated, mainly focusing on capacitive EIS (electrolyte-insulator-semiconductor) devices. The experimentally obtained results on the detection of DNA immobilisation and hybridisation as well as the monitoring of layer-by-layer adsorbed charged polyelectrolyte (PE) multilayers have been discussed by using two basic possible mechanisms of signal generation, namely the intrinsic charge of the macromolecules and the charge redistribution within the intermolecular spaces or in the multilayer. The effects of the layer-by-layer adsorption conditions (unbuffered and pH buffer solution), and the number and polarity of charged layers on the sensor response have been systematically investigated by means of capacitance–voltage (C–V), constant–capacitance (ConCap) and impedance spectroscopy (IS) methods.

Time Resolved Analysis of Molecular Interactions Using Nanomechanical Cantilever Sensors

Cantilever sensors have created a widespread interest in recent years due to their unique nanomechanical signal generation mechanism. Their applications range from sensing of small molecules, chemicals and biomolecules to on-line monitoring of surface-associated phenomena, such as molecular reorganization and formation of self assembled monolayers (SAMs). Cantilever sensors allow real-time monitoring, which is the basis for the kinetic description of interactions at the sensor surface. In this paper, we present examples of cantilever sensor measurements in continuous liquid flow using a commercially available instrument (Cantisens® Research, Concentris GmbH, Switzerland) and demonstrate successful approaches fora) the description of molecular interaction kinetics,b) the improvement of calibration curves of cantilever biosensors andc) the study of SAM formation, protein immobilization and surface-related conformational changes.

Spontaneous activity of living cells

The purpose of this article is to give a theoretical framework to describe the mechanism of internal signal generation and discuss the physiological significance of spontaneous activities of certain living cells [Oosawa, F., 2001. Spontaneous signal generation in living cells. Bull. Math. Biol. 63, 643].