Transient Response Curves Research Articles

Detection of CO 2 in solution with a Pt–NiO solid-state sensor

A metal insulator semiconductor field effect transistor (MISFET)-type sensor for the detection of CO 2 dissolved in aqueous solution is presented. This all-solid-state device is based on a Pt–NiO thin film as active sensing material on the top of a gate electrode. The fabrication of the sensor is described and its performance is characterized. In particular the transient characteristics and response curves at different biases V RS versus the amount of dissolved CO 2 are presented. The sensor shows a linear response to the logarithm of the concentration of dissolved CO 2 at room temperature.

Preparation and Characterization of One-Dimensional TiO<sub>2</sub> Nanowire Films on a Flexible Stainless Steel Substrate

We synthesized a one dimensional (1D) TiO2 nanowire with a large aspect ratio on non-Ti substrate in NaOH aqueous solution by the hydrothermal treatment of pure titanium films deposited by direct current magnetron sputtering on a flexible stainless steel substrate (50 μm). The samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoelectro- chemical methods. Results show that the density and crystallinity of the titanium film as well as the binding strength between the Ti film and the stainless steel substrate increased with an increase in substrate temperature. The optimum hydrothermal temperature for the formation of the 1D TiO2 nanowire was 130-150 ℃ when the concentration of NaOH was kept at 10 mol·L-1. TiO2 nanowires with diameters of 10-30 nm and lengths of up to several microns grow in a crosswise manner and form a 3D network structure. Moreover, linear sweep voltammetry and transient photocurrent response curves indicated that the 1D TiO2 nanowire film electrode had better photoelectrochemical performance than the TiO2 nanoparticle electrode. This technique provides a new method for the fabrication of 1D TiO2 nanowire films on different non-Ti heterogeneous substrates.

Lift Response of a Stalled Wing to Pulsatile Disturbances

The transient lift response of a low-Reynolds-number wing subjected to small amplitude pulsatile disturbances is investigated. The wing has a small aspect ratio and a semicircular planform, and it is fully stalled at a 20 deg angle of attack. Microvalve actuators distributed along the leading edge of the wing produce the transient disturbance. It is shown that the lift response to a single pulse increases with increasing actuator supply pressure and that the lift response curves are similar to each other when scaled by the total impulse. Furthermore, for fixed actuator supply pressure, the amplitude and total impulse of the transient lift response curve increases with increasing external flow speed. In this case, the lift response curves are similar when scaled by the dynamic pressure. The lift response to a single pulse can be treated as a filter kernel, and it can be used to predict the lift time history for the arbitrary actuator input signals. The kernel is similar in shape to transient measurements obtained by other investigators on two-dimensional wings and flaps. Comparisons between the model predictions and the experiments using multiple pulse inputs and square-wave modulated input signals at low frequencies are presented.

Foreign Object Damage to Fan Rotor Blades of Aeroengine Part II: Numerical Simulation of Bird Impact

Bird impact is one of the most dangerous threats to flight safety. The consequences of bird impact can be severe and, therefore, the aircraft components have to be certified for a proven level of bird impact resistance before being put into service. The fan rotor blades of aeroengine are the components being easily impacted by birds. It is necessary to ensure that the fan rotor blades should have adequate resistance against the bird impact, to reduce the flying accidents caused by bird impacts. Using the contacting-impacting algorithm, the numerical simulation is carried out to simulate bird impact. A three-blade computational model is set up for the fan rotor blade having shrouds. The transient response curves of the points corresponding to measured points in experiments, displacements and equivalent stresses on the blades are obtained during the simulation. From the comparison of the transient response curves obtained from numerical simulation with that obtained from experiments, it can be found that the variations in measured points and the corresponding points of simulation are basically the same. The deforming process, the maximum displacements and the maximum equivalent stresses on blades are analyzed. The numerical simulation verifies and complements the experiment results.

Transient Electromagnetic Response Modeling of Magnetic Source on Seafloor and the Analysis of Seawater Effect

By electromagnetic theory, for the case that the magnetic dipole source and the receiver are set in seawater, the general expressions of frequency-domain electromagnetic responses for a layered sea-floor model are deduced. From those, the transient response expressions of three common configurations–vertical magnetic dipole-dipole (HZHZ), central loop, and coincident loop, located on the surface of uniform half-space seafloor, are derived, respectively, supposing that seawater is uniform half space, or its depth is finite. These expressions connect transient response with oceanic parameters such as the conductivity of the seafloor, and provide theoretical foundation for forward modeling, and inversion and interpretation in sea-floor transient electromagnetic exploration. The modeling indicates that the presence of seawater not only changes the shape of transient response curve, but also reduces the resolution to sea-floor conductivity.

Research of Tight Band Coiling Dynamics

Purpose of the work is to analyze tight band coiling machine dynamics for processing wire, thread, texture, paper, leatherette or other elastic bands with a steady-state tension force. Band coiling block diagram and mathematical models for cases with one and two regulators has been made for research of elastic band coiling processing using software MATLAB-SIMULINK. Transient response curves of linear speeds in the band feed section and in a coiling machine, of band tension force and of relative elongation are presented. The digital model was used for obtaining parameters of controllers when parameters of feedback and regulators have been changing.

Infrared-monitored cold response in the assessment of Raynaud's phenomenon.

Evaluation of treatments for Raynaud's phenomenon (RP) requires objective response parameters in addition to clinical activity scores. Thermographic monitoring of fingertip re-warming after cold challenge has been widely used but usually requires sophisticated equipment. We have previously shown that fingertip re-warming after cold challenge follows a first-order transient response curve that can be described by a single variable, designated tau. Here, we describe a novel device termed a duosensor, which records the tau value upon cold challenge in an automated manner. We determined tau values in healthy probands, patients with primary or secondary RP associated with autoimmune disease and patients with scleroderma-associated RP following cold challenge, to determine assay variability, sensitivity and specificity. Duosensor-based thermography exhibited low intraindividual variability in healthy probands. As expected, tau values in RP patients were significantly increased compared with controls (8.08 +/- 3.65 min vs. 3.23 +/- 1.65 min). The duosensor-determined tau value yielded a specificity of 94.6% and predictive value of 95.3% for the presence of RP in a retrospective analysis of 139 patients. Furthermore, in a cohort of scleroderma patients with RP, patient self-assessment of RP severity correlated with tau values. Taken together, the present data suggest that tau value determination provides a suitable outcome measure for clinical studies of novel RP treatments. As the duosensor is a simple stand-alone device requiring no supporting equipment and minimal personnel attention, it should allow RP activity monitoring even in clinical settings with minimal technical infrastructure.

Transient studies of the elementary steps of Fischer–Tropsch synthesis

The pulse transient method has been used to study the kinetics of several key steps of Fischer–Tropsch (FT) synthesis over cobalt supported catalysts. These elementary steps involve chemisorption of hydrogen and propene, and chemisorption and hydrogenation of carbon monoxide. It is found that at the conditions of Fischer–Tropsch synthesis, hydrogen chemisorption is reversible and quasi-equilibrated, while carbon monoxide adsorption is generally irreversible. Chemisorption of propene on cobalt metal sites results in its rapid autohydrogenation to propane and simultaneous formation of C x H y surface species. The transient response curves produced during hydrogenation of carbon monoxide pulses in a flow of hydrogen have been analyzed using the modified Kobayashi model, which involves irreversible chemisorption and dissociation of carbon monoxide, quasi-equilibrated adsorption of hydrogen and reversible adsorption of water. The kinetic analysis suggests that oxygen-containing species are probably the most abundant surface intermediates. Desorption of water from the catalysts seems to be much slower than hydrogenation of surface carbon species.

Transient parameters of a coated quartz crystal microbalance sensor for the detection of volatile organic compounds (VOCs)

A PVC blended lipid membrane coated quartz crystal microbalance has been prepared to mimic human olfaction system. Transient response curves of the sensor on exposure to methanol, ethanol, chloroform, acetone and benzene were studied. Transient parameters, viz., simple parameters consisting of peak heights, derivatives, slopes and integrals, and polynomial parameters consisting of coefficients from the curve fitting equations, were extracted from the transient response curves and used as data for the subsequent chemometric data analysis. The sensor showed good separation and classification of VOCs.

The effects of the use of weak organic acids on the improvement of oxygen storage and release properties of aged commercial three-way catalysts

The efficiency of weak organic acid solutions for improving the oxygen storage and release properties of aged commercial three-way catalysts (TWC) has been investigated. For the first time, three candidate leaching solutions, namely acetic acid (CH3COOH), oxalic acid ((COOH)2) and citric acid (C6H8O7) were tested for their efficiency in removing various contaminants, such as P, Fe, Zn, Cr, Pb, Ni and Cu that potentially reduce the oxygen storage capacity (OSC) of three-way catalysts. It was shown that over a severely aged (242,000km) commercial TWC, oxalic acid appears to be the most efficient in removing P and Cu, while citric acid in removing Zn, Fe, Cr, Pb and Ni. For all three weak organic acid solutions investigated, higher quantities of contaminants were removed with increasing aging of TWC. All regeneration procedures applied led to the partial recovery of the OSC of aged TWCs likely due to the removal of at least some of the contaminants mostly responsible for their negative effect on the processes of oxygen storage and release in CeO2 and CexZr1−xO2 “oxygen storage” materials present. It was found that oxalic acid leads to the largest improvement of OSC quantities, very likely because of its ability to remove P, the latter being known to cause severe reduction of OSC. Based on transient redox experiments in measuring the dynamic OSC of TWC (O2/He→He→CO/He), it was found that the peak maximum position of the transient response curve of CO2 obtained over the regenerated TWC samples shifts to higher reaction times compared to that of aged TWC. This behavior is very likely related to the increase of the rate constant (k) of the oxygen back-spillover step, based on mathematical simulations of the same transient experiment performed on a model Pd/CeO2 catalyst.

Study on Characteristics of Transient Electric Field by an Electrical Dipole Source on One?Cdimensional Polarizable Earth Surface

The characteristic of transient electrical field by an electrical dipole source on one-dimensional polarizable earth surface is basic knowledge for geophysicists to use electromagnetic method to explore the earth. This paper deals with involved mathematical model and numerical algorithm of the down-step transient response for the horizontal component of the electric field produced by an electric current dipole, and a series of transient response curves on some typical geoelectric section. After analyzing the computed results, some important information are provided for establishing a new branch of method which observes and utilizes induced polarization and electromagnetic effects simultaneously in time domain—time spectral resistivity.

A Two-Step Reaction Mechanism of Oxygen Release from Pd/CeO2: Mathematical Modelling Based on Step Gas Concentration Experiments

A mathematical model has been developed to study the transient release of oxygen from a 1 wt% Pd/CeO2 catalyst in the 450–550 °C range based on alternate step concentration switches between CO and O2. A two-step reaction mechanism that involves the reaction of gaseous CO with the oxygen species of PdO and of the back-spillover of oxygen from ceria to the oxygen vacant sites of surface PdO has been proven to better describe the CO and CO2 transient response curves. The proposed mathematical model allows the estimation of the transient rates of the CO oxidation reaction and of the back-spillover of oxygen process. It also allows the calculation of the intrinsic rate constant k1 (s−1) of the Eley–Rideal step for the reaction of gaseous CO with surface oxygen species of PdO to form CO2. An activation energy of 10.1 kJ/mol was estimated for this elementary reaction step. In addition, an apparent rate constant \(k_2^{app} (s^{-1})\) was estimated for the process of back-spillover of oxygen.

Multimodal Behavior in a Four Neuron Ring Circuit: Mode Switching

We study a four-neuron ring circuit comprised of oscillating burst-type neurons unidirectionally coupled via inhibitory synapses. Simple circuits of this type have been used previously to study gait patterns. The ring circuit itself is a variant of the basic reciprocal inhibition network, and it exhibits the property of multistability (multiple stable modes of behavior). That is, different gait modes can be achieved via appropriate initialization of and parameterization of this self-excited oscillatory network. We demonstrate three common gait modes with this circuit: the walk, the bound, and a slightly rotated trot mode. Attention is focused mainly on the mechanisms of rapidly and effectively switching between these modes. Our simulations suggest that neuron membrane dynamics, as well as synaptic junctional properties, strongly influence phase sensitivity in the network; each synapse is a combination of both and can be characterized by a transient phase response curve (PRC). We use the same bursting neuron model to characterize all network neurons, and shape different transient PRCs by using different synaptic properties. The characteristics of these PRCs determine the gait modes sustained in any network configuration, as well as, the ability to switch between modes. The mechanisms explored in this simple circuit, may find application in the switching of more complicated gait pattern networks, as well as, in the design of neuromorphic gait pattern circuits.

Identification of odors using a sensor array with kinetic working temperature and Fourier spectrum analysis

A method for the identification of odors using a dynamically driven sensor array has been developed, in which transient responses of the sensor array were used to recognize target odors. Fourier transformation was used to transform the transient response curves of the sensor array into Fourier spectra, and patterns composed of some of the magnitudes in the spectra were used in the pattern recognition to identify the odors. Identification of odors was performed using this method with three kinds of 10% ethanol solution of tea extract and three kinds of Japanese soy sauce. In consequence, the sample odors could be correctly recognized without any pretreatment device for separation of minor components from the main component.

Study of the color detection of a-Si:H by transient response in the visible range

A new technique of color detection based on time-resolved charge collection during transient response measurement using a hydrogenated amorphous silicon detector has been proposed and experimentally demonstrated. The method based on the material intrinsic wavelength-filtering properties is implemented in color sensing by transient response of a detector to a combination of basic color light and voltage pulse. Resulting transient responses under different illumination and bias voltage conditions confirm considerable accuracy of proposed method. In particular, the best agreement of measured and calculated transient response curves has been obtained by using the spectral response of all three primary colors in calculations. It was observed that the presence of blue light drastically reduces the transient response to a chromatic light illumination. Finally, a voltage pulse influence to the basic colors transient response was found.

On the modeling of the transient thermal behavior of semiconductor devices

A mathematical model of the transient temperature response of integrated devices is presented which takes into account the three-dimensional (3-D) nature of heat flow and the physical structure of the device. Simple analytical relations for the transient thermal impedance and thermal time constants are derived for the first time. The impact of device geometry on the transient thermal response curve is discussed, and simple guidelines for the thermal design of solid-state devices operated in transient or pulsed regime are given.

Investigation of the catalytic decomposition of NO and N 2O on supported Rh with transient techniques

The adsorption of NO, the self-decomposition of N 2O and the catalytic reduction of NO with H 2 were investigated with transient step-response experiments over an alumina-supported Rh monolith. The experiments were carried out under atmospheric pressure at a temperature range of 150–350°C. The experiments revealed the self-decomposition of N 2O to N 2 and O 2 as well as the reduction of NO with H 2. The reduction of NO gave N 2 as a main product and N 2O as a by-product. Based on the experimentally recorded transient response curves, “oxidation–reduction” surface reaction mechanisms were discussed for the NO–H 2 reaction system. The mechanism assumes a common surface intermediate for the formation of N 2 and N 2O.

Electrical fluctuations and photoinduced current transients in CdxHg1−xTe long wavelength epilayers

Measurements are described of I-V characteristics, resistance versus T−1, noise spectra and photoresponse for frequencies of 10 Hz-1 MHz in the temperature range 300–50 K for cadmium-mercury telluride long-wavelength infrared detectors having 12μ epitaxial layers on wide band gap material. The noise consists of 1/f noise and one or two Lorentzians, attributed to shallow hole traps, probably associated with Hg vacancies. The results are discussed and analyzed after a brief resume of generation-recombination noise. The photoinduced current transient spectroscopy response curves are attributed to tunneling to interface states.

Starting transients of three phase reluctance motors as affected by torsional dynamics

In this paper, a rigorous mathematical model describing the transient behavior of three-phase reluctance motors under the effect of torsional dynamics is developed. Provisions are made to allow the analysis of both the three-phase balanced mode of operation and the single-phase mode of operation of such motors. The resulting state-space equations are then solved numerically in order to yield the required transient response curves. The outcome of this study will help in devising techniques to deal with the dangerous consequences of the electromechanical resonance phenomenon that may arise.

Calibration of glucose biosensors by using pre-steady state kinetic data

A new method for biosensor calibration and data processing, allowing the prediction of steady state parameters from the analysis of transient response curves ( Rinken et al., 1996. Analytical Letters 29, 859), has been evaluated in the case of an oxygen sensor based two-substrate enzyme electrode for glucose determination. The electrochemical glucose biosensor was prepared by covering the surface of oxygen sensor with glucose oxidase (EC 1.1.3.4) immobilized in nylon mesh. This decreased the oxygen flow to the sensor in the presence of glucose and resulted in time-dependent decrease of the biosensor signal. Except the lag period of the response in the beginning of the assay, the oxygen consumption by the immobilized enzyme was described by an exponential function: [ O 2] c bulk O 2 =A exp(−Bt)+C . The parameter C, which corresponded to the steady state output of the biosensor, was found to be the most suitable for glucose determination. The non-linear fitting for data of over 1000 independent experiments to the equation above always revealed correlation coefficients greater than 0.97. The calculation of the steady state parameter from the transient phase data makes the analysis fast and precise, especially for sensors with thick membranes, being convenient to use in the case of enzyme electrodes. The theoretical essence of the parameter C also gives valuable information for the optimal design of biosensors.