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Drawing on the code theory of Basil Bernstein, this study set out to examine how primary school teachers operationalize and experience their teaching practice with respect to the weak framing that may underpin teacher-pupil interaction, and how this practice is regulated by certain variables. Questionnaires were completed by 2,238 primary school teachers in China. The findings revealed that the teachers performed weak framing mainly through an invisible pedagogy in interactions with students, which was significantly affected by an interplay between student-based authority, students' linguistic codes and use of textbooks. An elaborated code generates two crucial advantages: it reduces the impact of the constraints of textbooks and traditional pedagogy on student-based teacher authority, and facilitates the teachers in implementing weak framing. Therefore, providing scaffolding resources to underachieving students to assist them in acquiring an elaborated code could be the key to ameliorating the phenomenon of cultural reproduction.

The performance of quartz crystal resonator (QXR) force sensors, which utilize symmetrical incomplete circular QXR's as indicative factors are affected by transverse force. However, the main focus of the effect of transverse force is mainly on the two types of QXR force sensors that are sensitivity and linearity.

Inverse problems are essential to imaging applications. In this letter, we propose a model-based deep learning network, named FISTA-Net, by combining the merits of interpretability and generality of the model-based Fast Iterative Shrinkage/Thresholding Algorithm (FISTA) and strong regularization and tuning-free advantages of the data-driven neural network. By unfolding the FISTA into a deep network, the architecture of FISTA-Net consists of multiple gradient descent, proximal mapping, and momentum modules in cascade. Different from FISTA, the gradient matrix in FISTA-Net can be updated during iteration and a proximal operator network is developed for nonlinear thresholding which can be learned through end-to-end training. Key parameters of FISTA-Net including the gradient step size, thresholding value and momentum scalar are tuning-free and learned from training data rather than hand-crafted. We further impose positive and monotonous constraints on these parameters to ensure they converge properly. The experimental results, evaluated both visually and quantitatively, show that the FISTA-Net can optimize parameters for different imaging tasks, i.e. Electromagnetic Tomography (EMT) and X-ray Computational Tomography (X-ray CT). It outperforms the state-of-the-art model-based and deep learning methods and exhibits good generalization ability over other competitive learning-based approaches under different noise levels. [ABSTRACT FROM AUTHOR]

Imaging the bio-impedance distribution of the brain can provide initial diagnosis of acute stroke. This paper presents a compact and non-radiative tomographic modality, i.e. multi-frequency Electromagnetic Tomography (mfEMT), for the initial diagnosis of acute stroke. The mfEMT system consists of 12 channels of gradiometer coils with adjustable sensitivity and excitation frequency. To solve the image reconstruction problem of mfEMT, we propose an enhanced Frequency-Constrained Sparse Bayesian Learning (FC-SBL) to simultaneously reconstruct the conductivity distribution at all frequencies. Based on the Multiple Measurement Vector (MMV) model in the Sparse Bayesian Learning (SBL) framework, FC-SBL can recover the underlying distribution pattern of conductivity among multiple images by exploiting the frequency constraint information. A realistic 3D head model was established to simulate stroke detection scenarios, showing the capability of mfEMT to penetrate the highly resistive skull and improved image quality with FC-SBL. Both simulations and experiments showed that the proposed FC-SBL method is robust to noisy data for image reconstruction problems of mfEMT compared to the single measurement vector model, which is promising to detect acute strokes in the brain region with enhanced spatial resolution and in a baseline-free manner. [ABSTRACT FROM AUTHOR]

The ferrite core of a sensing coil enhances its magnetic field, thereby improving its detection sensitivity in eddy current testing (ECT). Due to the hysteresis caused by the ferrite core, the lumped impedance of a coil–target system is essentially nonlinear. In this article, the impedance nonlinearity is used and a dual-parameter oscillation method for ECT is proposed. By utilizing the nonlinear impedance of the coil–target system in the oscillating circuit, a self-oscillation signal can be generated. Subsequently, the dual parameters of oscillation, i.e., the amplitude and the frequency are obtained by the detection circuit. The amplitude reflects the nonlinear resistance of the coil–target system, while the frequency reflects the nonlinear inductance. A negative resistor is used to ensure the oscillation and adjust the amplitude to the appropriate range and a capacitor is used to adjust the frequency. This method is capable of real-time defect detection. The correlation of dual parameters is analyzed and used, and a synthesis parameter is proposed to suppress the lift-off effect and noise, therefore the performance of detection for small defects is enhanced. The proposed dual-parameter maps provide a graphical observation of the location and the depth of defects in real-time scanning. The proposed method is applied to detect the surface and subsurface defects of the metal sample as well as of a ferromagnetic target behind the nonferromagnetic shield. [ABSTRACT FROM AUTHOR]

Biopotential signals captured by wearable devices are generally corrupted by different kinds of noises. Singular Spectrum Analysis (SSA) algorithm can be utilized for processing such signals by reconstructing the signal from the sum of a small number of independent and interpretable components. However, in case of extremely lower signal-to-ratio (SNR) signals, the components to be extracted are often located at the back of the eigentriple list. By analyzing the filtering characteristics of the SSA algorithm, a target component advancing method based on template addition is proposed. The template is constructed based on the frequency features of the processed signal. By splicing the template at the starting point of the processed signal, the energy of the components to be extracted is enhanced and therefore the eigentriples of interest can be effectively advanced to the front of the list. This method is applied to denoising and feature extraction of human physiologic signals with lower SNRs, such as non-contact Electrocardiogram (ECG), Ballistocardiogram (BCG) and Electroencephalogram (EEG). Experimental results show that, with the aid of the proposed method, the computational cost of the eigentriple selection in SSA can be effectively reduced. [ABSTRACT FROM AUTHOR]

When implementing temporary vibration monitoring of mechanical equipment, it is hoped that the installation and disassembly of the sensor will not change the original structure of the equipment. In that case, non-intrusive vibration sensors are preferable. This paper presents a motion induced eddy current sensor that can non-intrusively acquire vibration signal from the surface of metal objects. The sensor consists of a cylindrical permanent magnet and a pancake coil coaxially placed under it. The permanent magnet is used to generate a static magnetic field and the coil is used to pick up the eddy current signal induced by vibration. The results of principle experiments indicate that the output signal of the sensor has a linear relationship with the vibration acceleration/velocity when the measured object is a non-ferromagnetic/ferromagnetic metallic specimen. Two application measurement experiments are also done. When the sensor is placed on the metallic panel of a weighting scale, the ballistocardiogram (BCG) of the human body can be effectively obtained. Another experiment is carried out on a rotor test bed. When the sensor is placed above the bearing support with a fixed lift distance, satisfying vibration signals can be obtained compared with that from the conventional piezoelectric accelerometer. The present works show that the simple-structure, low-cost, non-intrusive vibration sensor (MIECS) can be applied in various fields. [ABSTRACT FROM AUTHOR]

In this paper, the human body communication (HBC) and level crossing sampling (LCS) are combined to design electronics for a wearable electrocardiograph (ECG). The ECG signals acquired by capacitively coupled electrodes are sampled with LCS in place of conventional synchronous sampling. In order to transmit signals through HBC at low frequencies (100 kHz, 1 MHz), an electric field sensor with high input impedance is adopted as the front end of the HBC receiver. The HBC channel gain is enhanced by more than 30 dB with the electric field sensor. An LCS structure based on the send-on-delta concept is implemented with discrete components to convert the ECG signals into binary impulses. The converted impulses are modulated by an on–off keying modulator and then transmitted via the human body to the receiver. A prototype ECG waist belt is developed with commercially available components and experimentally evaluated. The results indicate that the acquired ECG waveforms exhibit good agreement with regular Ag/AgCl ECG methods. The heartbeat detection using a technique based on the Kadane's algorithm and the power consumption performance of the proposed system are also discussed. [ABSTRACT FROM AUTHOR]

Eddy current testing technique is widely used in nondestructive testing area. A novel eddy current testing scheme by transient oscillation and nonlinear impedance evaluation is proposed in this paper. A sensing coil with a ferrite core is used as the eddy current probe. The probe is connected in series with a capacitor and a simulated negative resistor to establish a second-order circuit. A square-wave voltage signal is utilized as the excitation source. By adjusting the value of the negative resistor within an appropriate range, the response signal will exhibit free damped oscillations within the transient durations. The transient oscillations are sampled as the response signal and first processed by singular spectrum analysis to remove noises. Then, Hilbert transform is further used to calculate the instantaneous frequency and the instantaneous damping coefficient of the transient oscillation. After that the nonlinear impedance carrying the defect information of the specimen under test can be finally obtained. Subsurface defects of 304 stainless steel specimens are experimentally detected. The results indicate that the proposed scheme is competent to detect subsurface defects. An interesting phenomenon is that the impedance nonlinearity of the probe-specimen system can be extracted from the transient oscillations. The nonlinear impedance causes critical damping in theory. Therefore, an online defect detection can be implemented by simply measuring the envelope of the transient oscillations. [ABSTRACT FROM PUBLISHER]

In order to detect the QRS complexes locally in the microcontroller-based embedded system, a novel algorithm with lower computation burden is proposed by phase space reconstruction and box-scoring calculation. The method depends on the geometrical property of the ECG signal phase portraits. According to the time-delay method, one segment of the sampled 1-D ECG signal is embedded into a 2-D phase space. The phase space is divided into 2^M\times 2^M grids, and each grid is called a box. The box gridding is implemented by numerically truncating the high $M$ -bits from the digital data. The phase portraits of the sampled ECG signal in the phase space are therefore divided by these boxes. Since the trajectory points corresponding to the R-waves are located relatively far away from the diagonal line, boxes that crossed by the trajectory are flagged and valued according to its distance to the diagonal line. Correspondingly, the box-scoring of the ECG segment is obtained by summarizing the values of the flagged boxes. The location of the R-waves can then be found by finding peak values in the box-scoring time series. The proposed algorithm is suitable for real-time QRS complex detection in microcontroller-based wearable ECG acquisition devices. [ABSTRACT FROM PUBLISHER]

A microprocessor measurement system is developed for simultaneously capturing electrocardiography (ECG) and impedance plethysmogram (IPG) signals. All the measurement electrodes are coupled with human skin in a non-contact capacitive way. A capacitive coupled pickup circuit is used for obtaining the original ECG and IPG signals. Three differences of electrode configurations are experimentally tested for picking up the ECG signals, i.e., from the plantar area of the feet, from the instep area of the feet, and from a single hand and a single foot. Two different configurations (i.e., two-electrode IPG and four-electrode IPG) are tested to get IPG signals. A singular spectrum analysis (SSA)-based algorithm is embedded in a microprocessor system for signal processing. It is found that the original signals, especially the IPG signals, are quite noisy and can only be used after SSA processing. When both the ECG and IPG signals are measured simultaneously, the ECG signal will be severely ruined by the interference from the excitation current signal of IPG measurement. Relatively satisfied signals can only be simultaneously obtained when one ECG electrode is placed in a hand. The time difference between the ECG R-peak and IPG C-peak (the peak point in IPG) is experimentally tested for its potential application in blood pressure measurement. [ABSTRACT FROM PUBLISHER]

To measure the nonlinear impedance of interdigital electrode-solution system, a novel method based on free damped oscillation is proposed. A high valued active inductance with adjustable negative resistance is constructed by an operational amplifier. A second order oscillation system for measurement is then set up by connecting the active inductance with the device under test. The active inductance is designed to be around 470H to meet the measurement requirements of low frequency. The negative resistor is utilized to adjust damping coefficient of the oscillation system in order to obtain enough number of ring-down oscillation cycles for parameter estimation. The free damped oscillation signal of the oscillation system is obtained under square wave voltage excitation. After processed by Hilbert transform, the instantaneous capacitance and resistance can be calculated simultaneously to implement nonlinear impedance measurement. The operational availability of the proposed method is verified by experimental results of commercial available resistors and capacitors. The impedance nonlinearity of a gold interdigital electrode immersed in KCl solutions of different concentration is tested and compared with that obtained by sweep-amplitude sinusoidal excitation methods. The results indicate that the proposed method can successfully obtain impedance nonlinearity in half of the square wave period. [ABSTRACT FROM PUBLISHER]

A non-contact electrolyte solution measurement system is developed based on inductive coupling coils fabricated on printed circuit boards (PCBs). The basic sensing system is made up of a readout coil and the electrolyte solution under test. A passive coil is composed by a coil printed on the PCB substrate, and a capacitance element to make an $LC$ resonator. When it is placed in the basic sensing system, the measurement performance is enhanced because of the strong coupling around its resonant frequency. Sodium chloride solution with 0%–5% massed fraction concentration in a plastic container is adopted as the target to be detected. Impedance spectrums are experimentally analyzed for the cases of that the passive coil is placed in front and at the back of the target solutions, respectively. The results indicate that, when the target is located at the same distance, a measurement system with a passive coil performs a higher sensitivity to solution concentration than that without one. Furthermore, when the target solution is located beyond the sensing range of the basic sensing system, the solution concentration can also be effectively measured with the aid of a passive coil. Such an enhancement effect of the passive coil can efficiently promote the performances of non-contact measurement systems for low conductivity targets, such as electrolyte solutions or biological tissues. This is especially true when the passive coil is fabricated on a flexible circuit substrate, since the flexible coil can be attached to the non-planar surface of the target to ensure a stronger magnetic coupling. [ABSTRACT FROM PUBLISHER]

A portable tester for accessing human skin status quantitatively at home is reported. An interdigital electrode (IDE) that contacts directly with human skin is used as the sensing element. The electrode-skin model is simplified as a resistance and a capacitance in series. Using square wave signal for excitation, impedance of the IDE is measured in a charging/discharging way. During one measurement cycle, the response voltages at two excitation frequencies, i.e., 10 kHz and 600 Hz, are measured successively. Equivalent resistance and capacitance of skin are then resolved from the measured values. Both the numerical and experimental simulation results indicate that the proposed circuit and corresponding algorithms work well for resistors and capacitors. The performance of the tester is experimentally tested with human skin in cases of different status. Obvious relationship between the measured values and the skin status is observed. Moreover, distinctive results are obtained between hydrating and emollient cosmetics smeared skins. The tester can be potentially used to give a quantitative guidance for individual skin care, such as cosmetics selection. [ABSTRACT FROM PUBLISHER]

A wearable electrocardiogram (ECG) measuring system is designed based upon capacitively coupled biopotential sensing electrodes. The sensing electrodes are made from the standard printed-circuit board. Using a reversely connected diode to provide the required high-value bias resistance, the pickup circuit for biopotential sensing is implemented by a high-input-impedance instrumentation amplifier. Two different configurations of the ECG measuring system are constructed and experimentally tested. One is a floating ground configuration in which only two sensing electrodes are used for ECG signal acquisition. Another is the passive ground configuration in which an additional grounding electrode is employed as the reference for common-mode noise suppression. The ECG signal can be obtained through thin clothes for both cases but performs lower signal-to-noise ratio. In order to improve the quality of the obtained signal, an algorithm based on a singular spectrum analysis is designed for noise reduction. A matching template is introduced to pick out the critical principal components automatically. Experimental results show that, with the aid of the proposed algorithm, satisfied ECG and respiration signals can be effectively obtained outside cotton-fiber clothing. [ABSTRACT FROM PUBLISHER]

Abstract: Detecting the new or anomalous signal sequences in the observed time series data is a problem of great practical interest for many applications. The bio-inspired negative selection algorithm, whose main idea is to discriminate the non-self pattern from self pattern, has drawn much attention because only normal information is needed for training. Most of the proposed algorithms are based on binary-valued string matching. A real-valued negative selection algorithm for novelty detection in vibration signal is implemented in this paper. The vector set for calculation is constructed by sampling the discrete time series from a moving time window. The matching affinity between two vectors is measured by cosine similarity. The calculated results show that the cosine similarity-based algorithm is more practical for potential applications in online signal monitoring. [Copyright &y& Elsevier]

Abstract: Since the detected molecule may probably attach to the uncovered surface, the coverage of the immobilized sensing film is very important for electrochemical biosensors. This is especially true for gold electrodes. One electrochemical quartz crystal microbalance (EQCM) approach is investigated for characterizing the coverage. A 5MHz QCM element is used together with an electrochemical system. During the electrochemical experiments, the frequency response of the QCM is recorded simultaneously with the electrochemical parameters. Three cases, the bare, the 6-mecapto-1-hexanol modified and the 16-mer oligonucleotide probe (with a mercaptohexyl group at the 5′-phosphate end) modified gold electrodes are investigated. The results indicate that the frequency is more sensitive than the electrochemical response to the surface coverage. It could be used to evaluate the clearness of the electrode surface before immobilization, or the surface coverage after immobilization. [Copyright &y& Elsevier]

A prototype of an electrocardiogram (ECG) signal acquisition system with multiple unipolar capacitively coupled electrodes is designed and experimentally tested. Capacitively coupled electrodes made of a standard printed circuit board (PCB) are used as the sensing electrodes. Different from the conventional measurement schematics, where one single lead ECG signal is acquired from a pair of sensing electrodes, the sensing electrodes in our approaches operate in a unipolar mode, i.e., the biopotential signals picked up by each sensing electrodes are amplified and sampled separately. Four unipolar electrodes are mounted on the backrest of a regular chair and therefore four channel of signals containing ECG information are sampled and processed. It is found that the qualities of ECG signal contained in the four channel are different from each other. In order to pick up the ECG signal, an index for quality evaluation, as well as for aggregation of multiple signals, is proposed based on phase space reconstruction. Experimental tests are carried out while subjects sitting on the chair and clothed. The results indicate that the ECG signals can be reliably obtained in such a unipolar way.

In order to measure the nonlinear features of micromechanical resonators, a free damped oscillation method based on stair-stepped frequency sinusoidal pulse excitation is investigated. In the vicinity of the resonant frequency, a frequency stepping sinusoidal pulse sequence is employed as the excitation signal. A set of free vibration response signals, containing different degrees of nonlinear dynamical characteristics, are obtained. The amplitude-frequency curves of the resonator are acquired from the forced vibration signals. Together with a singular spectrum analysis algorithm, the instantaneous amplitudes and instantaneous frequencies are extracted by a Hilbert transform from the free vibration signals. The calculated Backbone curves, and frequency response function (FRF) curves are distinct and can be used to characterize the nonlinear dynamics of the resonator. Taking a Duffing system as an example, numerical simulations are carried out for free vibration response signals in cases of different signal-to-noise ratios (SNRs). The results show that this method displays better anti-noise performance than FREEVIB. A vibrating ring microgyroscope is experimentally tested. The obtained Backbone and FRF curves agree with those obtained by the traditional frequency sweeping method. As a test technique, the proposed method can also be used to for experimentally testing the dynamic characteristics of other types of micromechanical resonators., Competing Interests: The authors declare no conflict of interest.

In order to measure the impedance variation process in electrolyte solutions, a method of triangular waveform voltage excitation is investigated together with principal component analysis (PCA). Using triangular waveform voltage as the excitation signal, the response current during one duty cycle is sampled to construct a measurement vector. The measurement matrix is then constructed by the measurement vectors obtained from different measurements. After being processed by PCA, the changing information of solution impedance is contained in the loading vectors while the response current and noise information is contained in the score vectors. The measurement results of impedance variation by the proposed signal processing method are independent of the equivalent impedance model. The noise-induced problems encountered during equivalent impedance calculation are therefore avoided, and the real-time variation information of noise in the electrode-electrolyte interface can be extracted at the same time. Planar-interdigitated electrodes are experimentally tested for monitoring the KCl concentration variation process. Experimental results indicate that the measured impedance variation curve reflects the changing process of solution conductivity, and the amplitude distribution of the noise during one duty cycle can be utilized to analyze the contact conditions of the electrode and electrolyte interface.