On-line calibration for linear time-base error correction of terahertz spectrometers with echo pulses

Error compensation is one of effective and economical means to improve the machining accuracy of machine tools. The measurement accuracy of kinematic errors has great impact on the accuracy of machine tool error modeling. Some measurement errors are inevitably generated due to the distortion of the slide table and the limit of local measuring stroke. To solve these problems, an improved machine tool volumetric error compensation method is proposed in this paper, based on linear and squareness error correction method. The linear errors, including position errors and straightness errors, are corrected by considering the distance effect between optical mirror groups and the surface of worktable. The squareness errors are corrected through modifying local squareness errors measured with double ball bar to global squareness errors, with the aid of straightness errors measured with multi-laser calibrator. Then volumetric errors are obtained based on multi-body system theory, and volumetric diagonal errors are measured with laser interferometer. It is illustrated that the bidirectional systematic deviation of positioning of four volumetric diagonals reduced about 81.3%, 35.2%, 29.2%, and 4.5% respectively by using this improved machine tool volumetric error compensation method, and it is of obvious advantages in contrast with traditional compensation method with direct measurement data. The improved error compensation method proposed in this paper has universal applicability and has great significance on machine tool accuracy improvement.

In this paper, we study basic properties of linear network error correction codes, their construction and error correction capability for various kinds of errors. Our discussion is restricted to the single-source multicast case. We define the minimum distance of a network error correction code. This plays the same role as it does in classical coding theory. We construct codes that can correct errors up to the full error correction capability specified by Singleton bound for network error correction codes recently established by Cai and Yeung. We propose a decoding principle for network error correction codes, based on which we introduce two decoding algorithms and analyze their performance. We formulate the global kernel error correction problem and characterize the error correction capability of codes for this kind of error.

This paper presents a novel technique for on-line calibration and digital correction of the mismatches among the elements of the digital-to-analog converter (DAC) used in the feedback loop of multi-bit sigma---delta (ΣΔ) modulators. The proposed method, with an extremely limited amount of additional circuitry, allows the mismatches among the elements of the DAC to be accurately measured and corrected in the digital domain, thus improving the linearity performance of the modulator. A switched capacitor (SC) 4-bit second-order ΣΔ modulator has been implemented to validate the proposed solution. The experimental results confirm that the proposed technique allows us to achieve an improvement in the spurious-free dynamic range of the ΣΔ modulator as large as 26 dB.

Online calibration technique for a long-baseline laser interferometer has been studied, which can be used for nanoscale displacement and vibration measurement. The method combined laser interferometer calibration with measurement to meet the needs of online calibration and state detection of long-baseline laser interferometer. Based on Phase Generated Carrier (PGC) demodulation technique, we add a calibration signal which we have already known to phase-modulated carrier, and according to the amplitude variations of calibration signal, we can achieve work condition monitoring of laser interferometer and measurement of environmental changes and the instruction of fluctuations. In the paper, a laser interferometer with 22-meter-long arm, resolution of 20pm and frequency range of DC ~ 200Hz used for displacement and vibration measurement was constructed, completed the online calibration software and hardware design, experimental results show that: by adding a calibration signal with frequency of 400Hz, amplitude 600nm, online condition monitoring of the laser interferometer can be realized. The advantages of this method is,that it can achieve online calibration for laser interferometer without increase burden in hardware, simplify the interferometer debugging process, improve operational efficiency, at the same time, it is of great significance and value to practical application of long-baseline laser interferometer .

With the development of fiber-optic gyroscopes, strapdown inertial navigation system has become a trend in the development of inertial navigation system (INS), and strapdown inertial system error calibration technique has become one of the key technologies. This paper combined engineering practice with study an on-line calibration method of INS, which based on the high-precision multi-functional three-axis turntable. First of all, aim at the actual system used in fiber-optic gyroscopes, accelerometers quartz flexible components, set up corresponding system error model respectively. Then, take the high-precision three-axis turntable as platform to design the calibrate path, through the on-line combination calibration .Use Kalman filter algorithm to process data on-line, completed the corresponding experiments, and verified by tests. Experimental results show that the calibration method is feasible in project and effective, and increased level of automation.

Active phase stabilisation in electronic speckle pattern interferometry without additional optical components

Robotic CT systems offer several advantages over conventional systems due to their high flexibility. They can perform almost any CT trajectory and are particularly well suited for region-of-interest (ROI) scans of objects that exceed the size limitations of conventional CT systems. However, robot-based manipulators have a significantly lower absolute positioning accuracy compared to conventional manipulators, necessitating additional calibration methods to refine the geometric information about the spatial position and orientation of the X-ray source and detector for each projection for higher resolution reconstructions. We propose a geometric calibration method for CT systems with twelve degrees of freedom that does not require additional calibration scans. The method is easy to use, computationally efficient, and supports continuous CT trajectories. It utilises spheres with unknown positions that are attached to the specimen. The calibration process is divided into two stages. First, the spatial positions of the spheres are estimated using the initial geometric information and the acquired projections. Second, these estimates serve as input to an iterative optimisation that calibrates each projection individually. The applicability of the proposed method is demonstrated through simulations and real-world scans using a twin robotic CT system. Both quantitative and qualitative evaluations show a significant improvement in scan quality, comparable to results obtained via offline calibration. Moreover, evaluations on simulated data confirm the method’s robustness even for systems with positioning errors in the millimetre range. This novel online calibration technique is computationally efficient, compatible with highly flexible CT systems, and holds promise for enabling future mobile CT applications.

Interferometry with coherent Gaussian illumination for roughness and shape measurement

In recent days, polar codes have attracted the attention of Industry and Academia. It is one of a linear block error correction codes. Polar codes are one of the capacity achieving algorithms over a wide range of channels, making them very attractive from a theoretical perspective. Polar codes are shown to be instances of concatenated codes. It has been shown that the effect of a polar code can be enhanced by showing the multistage decoding algorithm with log-likelihood based Successive List decoding (SCL). However, SCL decoders are no longer optimal in terms of frame error rate. It is believed that the machine learning based algorithm can improve the FER for the decoded bit. Thus, the logistic regression algorithm is proposed in this paper. The proposed method offers an optimized solution to the decoded bits. The simulation result shows that with sufficient training, this method can provide a lower frame error rate for different code lengths.

This paper aims to provide preliminary evidence about the existence of horizontal integration between the rapeseed markets in Ukraine (UA) and the European Union (EU). To this end, both a trade analysis and a price analysis were carried out. In particular, the trade analysis was performed using yearly trade flows between the UA and EU, whereas price co-movement was assessed by means of linear vector error correction model (VECM) applied to weekly prices for rapeseed from 2008 to 2018. Our findings provide evidence of strong integration between the UA and EU markets in terms of the trade of rapeseeds, rape cake, and rape oil, as well as high horizontal rapeseed price transmission between the two economies.

Low x-ray dose is desirable in x-ray computed tomographic (CT) imaging due to health concerns. But low dose comes with a cost of low signal artifacts such as streaks and low frequency bias in the reconstruction. As a result, low signal correction is needed to help reduce artifacts while retaining relevant anatomical structures. Low signal can be encountered in cases where sufficient number of photons do not reach the detector to have confidence in the recorded data. X-ray photons, assumed to have Poisson distribution, have signal to noise ratio proportional to the dose, with poorer SNR in low signal areas. Electronic noise added by the data acquisition system further reduces the signal quality. In this paper we will demonstrate a technique to combat low signal artifacts through adaptive filtration. It entails statistics-based filtering on the uncorrected data, correcting the lower signal areas more aggressively than the high signal ones. We look at local averages to decide how aggressive the filtering should be, and local standard deviation to decide how much detail preservation to apply. Implementation consists of a pre-correction step i.e. local linear minimum mean-squared error correction, followed by a variance stabilizing transform, and finally adaptive bilateral filtering. The coefficients of the bilateral filter are computed using local statistics. Results show that improvements were made in terms of low frequency bias, streaks, local average and standard deviation, modulation transfer function and noise power spectrum.

We propose an explicit construction of full-diversity space-time block codes, under the constraint of an error correction capability. Furthermore, these codes are constructed in order to be suitable for a serial concatenation with an outer linear forward error correcting (FEC) code. We apply the binary rank criterion, and we use the threaded layering technique and an inner linear FEC code to define a space-time error-correcting code. When serially concatenated with an outer linear FEC code, a product code can be built at the receiver, and adapted iterative receiver structures can be applied. An optimized hybrid structure mixing MMSE turbo equalization and turbo product code decoding is proposed. It yields reduced complexity and enhanced performance compared to previous existing structures.

This study aims to determine the effect of domestic investment, foreign investment and transportation infrastructure on economic growth in Indonesia. This type of research is quantitative research. The data used are secondary data from 1980 to 2019 collected through documentation and related agencies. . This study uses multiple linear regression analysis and Error Correction Model (ECM). The results of this study indicate that: (1) domestic investment has no significant effect on economic growth in Indonesia; (2) foreign investment has a significant effect in increasing economic growth in Indonesia; (3) Transportation infrastructure has a significant effect in increasing economic growth in Indonesia.

The purpose of this study is to determine how the influence of monetary policy instruments on economic stability in Indonesia. Monetary policy instruments as exogenous variables are policies in the money supply M2 (X1) and Bank Indonesia interest rates (X2) while indicators of economic stability as endogenous variables can be seen from price stability (Y1) and exchange rate stability (Y2). This research is descriptive and associative research. The data used in this study is monthly secondary data from January 2001 to December 2020 which was collected through documentation from the relevant agencies. The data analysis used in this research is descriptive analysis and inductive analysis. In the inductive analysis there are several tests, namely (1) Stationarity Test; (2) Cointegration Test; (3) Multiple Linear Regression Test and Error Correction Model (ECM); (4) Classical Assumption Test; (5) T test and F test. The results of this study is: (1) in the long term and short term the money supply M2 has a negative effect on price stability in Indonesia; (2) Bank Indonesia interest rates in the long term and short term have a positive influence on price stability in Indonesia; (3) in the long term and short term The money supply M2 has a positive influence on the stability of the exchange rate in Indonesia; (4) Bank Indonesia interest rates in the long term and short term have a positive influence on exchange rate stability in Indonesia.

In this paper, a linear-prediction maximum power point tracking (MPPT) algorithm for photovoltaic (PV) power generation is presented. This allows rapid tracking without step-size reference. The new methodology has two parts: linear prediction and error correction. The first part estimates the maximum power point (MPP); this improves the MPPT response speed. The second part calibrates the error after the linear prediction; this enhances the calculation accuracy which leads to a faster MPP convergence. Theoretical analysis and simulations are put forward to validate the feasibility of the linear prediction method. Convergence, error correction, and steady and dynamic state evaluations are made. The results show that the algorithm can work effectively and have the advantages of fast response and high efficiency when compared to the Perturbation and Observe (P&O) algorithm.