36results about How to "Less sampled data" patented technology

The invention discloses a parallel magnetic resonance imaging algorithm based on conjugation and interlayer information. The algorithm comprises the steps of carrying out the R-time undersampling of agradient positive high-frequency part and a gradient negative high-frequency part of an imaging object, taking a middle low-frequency part as a calibration region, carrying out full sampling, and obtaining a matrix F; constructing a prediction matrix A of the undersampled data; constructing a weight calculation matrix B by utilizing the calibration areas of the matrix F of the current layer and the adjacent layer; constructing a column vector matrix C of the weight calculation matrix B; obtaining the column vector matrix C according to the product of the weight calculation matrix B and a weight matrix W, and fitting by adopting a least square method to obtain the weight matrix W in an interpolation window; constructing a prediction matrix D of the undersampled row data; obtaining a columnvector E according to the product of the prediction matrix D and the weight matrix W in the interpolation window; and filling to obtain a reconstruction matrix H, and carrying out Fourier transform to obtain an image of parallel magnetic resonance imaging. The method has the advantages of being high in imaging speed, rich in prediction source matrix information amount, high in signal-to-noise ratio and the like.

The invention provides a sparse sampling-based holographic magnetic induction chest imaging method and an imaging system. A sparse sampling-based holographic magnetic induction chest imaging system isarranged. In the imaging system, a main control module controls a transceiver array module to switch the transmitting and receiving states through a switching module and controls a magnetic field signal generating module to generate a single-frequency radio-frequency signal; the single-frequency radio-frequency signal is transmitted to the transceiver array module in the form of sinusoidal alternating current through the switching module, eddy current is generated around the target area, and the eddy current generates a scattered magnetic field; the main control module controls at least threecoils to carry out sparse sampling in a random scanning mode, simultaneously measures scattered magnetic field signals from the chest cavity, and transmits the scattered magnetic field signals to animage processing module; the image processing module successively compares the scattered magnetic field signals in pairs and processes the visible scattered magnetic field function obtained by comparison in combination with a compressed sensing method to obtain a reconstructed chest image, and the reconstructed chest image is then displayed.

The invention relates to the technical field of power electronic circuit digital control, in particular to a digital control system and method for a three-level PFC circuit. The digital control system comprises an input phase current sampling module, an output voltage and current sampling module, an analog-digital conversion module, a control quantity operation module and a PWM generation module. After being converted by the analog-digital conversion module, an output voltage signal generates voltage control factors through the control quantity operation module; after being converted by the analog-digital conversion module, an output current signal generates frequency selection factors through the control quantity operation module; after being converted by the analog-digital conversion module, the input phase current generates switch tube control factors through the control quantity operation module; the voltage control factors, the frequency selection factors and the switch tube control factors form PWM control quantity through the PWM generation module. According to the digital control system and method for the three-level PFC circuit, output positive and negative bus voltage balance is achieved, and high power factors can be obtained when loads in different levels exist.

The invention relates to the technical field of power electronic circuit digital control, in particular to a digital control system and method for a three-level PFC circuit. The digital control system comprises an input phase current sampling module, an output voltage and current sampling module, an analog-digital conversion module, a control quantity operation module and a PWM generation module. After being converted by the analog-digital conversion module, an output voltage signal generates voltage control factors through the control quantity operation module; after being converted by the analog-digital conversion module, an output current signal generates frequency selection factors through the control quantity operation module; after being converted by the analog-digital conversion module, the input phase current generates switch tube control factors through the control quantity operation module; the voltage control factors, the frequency selection factors and the switch tube control factors form PWM control quantity through the PWM generation module. According to the digital control system and method for the three-level PFC circuit, output positive and negative bus voltage balance is achieved, and high power factors can be obtained when loads in different levels exist.

The invention discloses a quantitative method for the chemical exchange saturation transfer effect of a living body. The B0 distribution map of the main magnetic field is obtained by sampling; without applying a gradient, the chemical exchange sites of exchangeable protons are selectively saturated by saturation pulses, and the first is obtained by sampling. Signal intensity; applying a gradient while selectively saturating the chemical exchange sites of the exchangeable protons by a saturation pulse, sampling to obtain a second signal intensity; without applying a gradient or a saturation pulse, sampling to obtain an initial signal intensity; calculating normalization chemical exchange saturation transfer effect. The method of the invention has important practical value, can be applied to animals and human bodies, and the quantitative result is not affected by the magnetization transfer effect and the nuclear Euclidean effect in the living body.

An embodiment of the invention provides a DDoS (distributed denial of service) attack detection method and device and relates to the technical field of communications for detecting DDoS attack rapidlyand accurately. The method includes: making statistics on the total number of target messages received within various periods; calculating variation of the total number of current messages; taking the variation of the total number of the current messages as an absolute value of the difference of the total number of the target massages received in the current period and the previous period; judging whether the variation of the total number of the current massages meets a first preset condition or not, and if yes, making statistics on the proportion of the target massages sent by autonomous systems in the target massages received in the periods; calculating the variation in distribution of the current massages; taking the variation in distribution of the current massages as the sum of an absolute value of the difference of the proportion of the target massages sent in the current period or the previous period by the autonomous systems; judging whether the variation in distribution of the current massages meets a second preset condition or not, and if yes, determining existence of the DDoS attack. The DDoS attack detection method and device is applied to DDoS attack detection.

The invention relates to a baseband signal generation method and device, electronic equipment and a readable storage medium, belongs to the technical field of electronic countermeasure simulation training signal generation, and solves the problem of low baseband signal generation efficiency in the prior art. The method comprises the following steps: generating a plurality of alternative baseband sampling rates according to a final sampling rate; in the alternative baseband sampling rates, determining the baseband sampling rate corresponding to each signal feature according to the signal feature, and forming a baseband sampling group by the signals with the same baseband sampling rate; enabling each baseband sampling group to independently generate a signal. According to the technical scheme, the baseband signal generation efficiency is improved, and storage and communication resources are saved.

The present invention relates to the technical field of digital control of power electronic circuits, in particular to a digital control system and control method of a three-phase three-level PFC circuit. The digital control system includes an input phase current sampling module, an output voltage sampling module, and a PID regulator. Turn-on time calculator, PWM module; the turn-on time calculator calculates the input phase current ia, ib, ic and the output voltage Uo adjusted by the PID regulator to obtain the turn-on time of the switch, and limit the comparator to obtain the corresponding turn-on time change The PWM module updates the comparator value of the PWM module according to the change value of the turn-on time that limits the output of the comparator, and controls the corresponding switching tubes of each phase. The digital control system and control method only need to sample the three-phase input current and output voltage, the calculation of the control quantity is simple and time-saving, the unit power factor of the circuit is realized, and the harmonic pollution is small.

The invention discloses a method and a device for self-adaptive sampling of an analog signal. The method comprises the steps of: acquiring analog signals output by a sensor, and performing signal conditioning; determining a digital quantity obtained by sampling of the analog signals under a designated analog-to-digital conversion frequency and an acquisition timestamp; determining a threshold value for analog-to-digital conversion frequency adjustment of acquired signals; determining difference degrees between the currently acquired signal and the signals acquired at a plurality of previous sampling moments; and determining a new sampling frequency according to the determined difference degrees, the analog-to-digital conversion frequency at the moment, and the threshold value of the analog-to-digital conversion frequency adjustment. Through adoption of the method and the device of the invention, a sampling rate of a data acquisition device is dynamically adjusted according to a relative variation ratio of sampling data, and a sampling frequency is iteratively adjusted on the condition of not measuring the sampling frequency, therefore, accuracy of sampling is ensured, and unnecessary sampling data is reduced.

The present invention discloses and proposes a three-dimensional SAR sparse imaging method based on the decomposition and fusion of coprime arrays. In the method, the coprime array and the subarrays of the coprime array are firstly reconstructed by compressive sensing iterative minimization of sparse Bayesian reconstruction. The (SBRIM) imaging algorithm performs imaging separately to obtain three synthetic aperture radar images, and then fuses the obtained imaging results to obtain the final 3D SAR sparse imaging result based on array decomposition and fusion. The present invention combines the advantages of the coprime sampling method and the compressed sensing sparse reconstruction method. The coprime sampling method can not only reduce the sampling data, but also is easier to realize systematically than the traditional random sampling method; compared with the traditional sparse imaging method, the method of the present invention can Effectively suppress grating lobes and false targets and improve imaging quality.

The invention discloses a method for predicting the porosity of carbonate rocks and a method for constructing a prediction model. The construction method includes the following steps: obtaining carbonate rock samples in a research block and drying them; obtaining the quality of carbonate rock samples in different Factor Q and porosity; according to the quality factor Q and porosity of different carbonate rock samples, a porosity prediction model is constructed. Its prediction reliability is high.

The invention provides a periodic interference torque identification and compensation method, which is used for phase identification and torque compensation of the periodic interference torque received by the satellite, applying a control torque with a fixed amplitude and a known period to the satellite, and compensating the moment on the satellite. The flywheel sends a feedforward compensation torque command to arbitrarily specify the initial phase of the compensation torque, including: measuring the satellite angular velocity in real time and extracting the angular velocity fluctuation range; when the angular velocity fluctuation range is greater than the first preset threshold, it is determined that phase shift control is required , carry out phase scanning with the initial phase as the starting point, during the phase scanning process, update the feedforward compensation torque according to the current phase; when the angular velocity fluctuation range is reduced to the second preset threshold, it is determined to end the phase movement control, and the current phase is For the disturbance torque phase, the feedforward compensation torque is updated according to the disturbance torque phase. The invention can realize the identification and compensation of the periodic interference moment of the satellite, and improve the control precision of the satellite.

The invention belongs to the field of structural health monitoring, and relates to a data compression reconstruction and structural damage identification method and equipment based on piezoelectric admittance. This method collects the original conductance data, and performs maximum and minimum normalization processing on it; uses compressed sensing theory to compress the processed sampling data, and implements linear transformation on the data through a random matrix, transforming the problem of restoring the original signal into a residual The difference iteration problem; the adaptive orthogonal matching pursuit algorithm based on the optimal sparsity parameter analysis is used to reconstruct the conductance data; the root mean square deviation and correlation coefficient obtained from the reconstructed data are used to diagnose the damage of the structure. This method can effectively combine the damage identification based on piezoelectric admittance technology with the data compression algorithm based on orthogonal matching pursuit algorithm, and can effectively identify different types of damage in the structure, and it is still effective in the case of sensor damage.

The invention discloses a laser radar imaging system based on compressed sensing. A unit APD is adopted for the system, so that the bottleneck that large-scale integration of domestic line array APDs cannot be achieved at present is effectively broken through. The system is formed by a laser emission module, a telescope imaging module, a DMD, a control module, the APD, a synchronization module, a data acquisition module and an image reconstruction module. In the system, pulse laser is emitted to a target through the laser emission module, target reflection echoes are modulated through the DMD, sampling of the unit APD on a time series is achieved through a convergence lens, and finally a three-dimensional image of the target is reconstructed on the basis of a compressed sensing theory by means of related algorithms. The laser radar imaging system based on compressed sensing has the advantages that scanning is not needed, the structure is simple, the data size needed for image reconstruction is small, and detection sensitivity is high.