30 results about "Pulse modulator" patented technology

The invention belongs to the technical field of atmosphere detection remote sensing, and discloses an atmosphere multi-element integrated multi-wavelength coherent differential absorption laser radar system. Lambda on1 wavelength laser generated by the first frequency stabilization seed laser, lambda on2 wavelength laser generated by the second frequency stabilization seed laser and lambda off wavelength laser generated by the third frequency stabilization seed laser are transmitted to the switching module for time domain modulation to obtain an output signal, and the output signal is decomposed into local oscillation light and a main signal by the first coupler. A main signal is modulated by the pulse modulator, amplified by the amplification module and then transmitted to the optical transceiver module, backward scattered light scattered by the atmosphere is transmitted to the second coupler and is subjected to coherent coupling and equalization with local oscillation light, and coherent electric signals are transmitted to the data analysis module through the balance detector to be analyzed. The water vapor concentration, the wind speed and the atmospheric temperature in the propagation path are obtained. Through the coherent detection technology, the signal-to-noise ratio of signals is remarkably improved, and high-precision atmospheric humidity and wind field detection is achieved.

The utility model discloses a pulse modulator comprising a housing, a circuit control board, a moving block, a semiconductor chilling plate and a driving mechanism, the housing is internally provided with the circuit control board, the circuit control board is provided with a circuit element and a first heat radiation fin, the moving block is provided with a first heat radiation fin, and the semiconductor chilling plate is provided with a second heat radiation fin. A heat conduction plate is arranged on the side, away from the circuit control board, of the first cooling fin, a moving block is arranged on the heat conduction plate in the length direction of the heat conduction plate in a reciprocating motion mode, a semiconductor chilling plate with the refrigeration face attached to the heat conduction plate is arranged in the moving block, and a power source used for powering on the semiconductor chilling plate is further arranged in the shell. Second heat dissipation fins are arranged on the heating face of the side, away from the heat conduction plate, of the semiconductor chilling plate, a fan with an outward air outlet is arranged on the side, close to the first heat dissipation fins, of the shell, and the driving mechanism is used for driving the movable block to move in a reciprocating mode.

The present invention proposes a multi-input pulse modulator circuit, which includes: an internal power supply circuit, which constitutes a linear voltage regulator circuit as a whole and provides voltage for chip operation; a signal selection circuit, which is electrically connected to the internal power supply circuit; a monostable circuit, which is electrically connected to the signal selection circuit and can adjust the output pulse width of the monostable trigger chip and the delayed output time when the signal is turned off; a pulse amplification circuit, which is electrically connected to the internal power supply circuit and the pulse amplification circuit is electrically connected to the signal selection circuit. In order to improve the amplitude and driving capability of the pulse output signal, the output signal with a fixed pulse width can be amplified, and functions such as the pulse voltage width following the input signal and the pulse voltage width being fixed can be realized.

An electronic device may include a receiver coupled to an antenna over a transmission line. The receiver may include a set of sample and hold circuits coupled in parallel between the transmission line and at least one pulse modulator. The pulse modulator(s) may be coupled between the sample and hold circuits and at least one time-to-digital converter (TDC). Each sample and hold circuit may be clocked using a different respective phase of a clock signal. During signal reception, the antenna may receive a radio-frequency signal. The sample and hold circuits may convert the radio-frequency signal into analog signals using the different phases of the clock signal. The pulse modulator(s) may convert voltages of the analog signals into pulse widths in at least one analog pulse width modulation (PWM) signal. The TDC(s) may convert the analog PWM signal(s) into digital codes.

The pulse steam type dish washing machine comprises a machine body and an adjusting mechanism, the adjusting mechanism is arranged in the machine body and comprises a connecting column, a sliding rail, a connecting shaft, a connecting pipe and a driving part, one end of the connecting column penetrates through the outer wall of the machine body and then is connected with the sliding rail, the connecting shaft is slidably connected with the sliding rail, and the connecting pipe is connected with the side wall of the connecting shaft; the driving part is arranged on the side wall of the machine body. According to the pulse steam type dish washing machine, the adjusting structure is arranged in the machine body, so that stains can be cleaned in all directions when the nozzle cleans tableware, cleaning dead angles are avoided, softened water is vaporized into supersaturated steam through the instantaneous vaporization module, and the cleaning efficiency is improved. And then the continuous steam flow is discretized into a series of pulses by an electromagnetic modulation valve, and the series of pulses are controlled by a pulse modulator to be sprayed out orderly, so that stains on the surface of the tableware are effectively impacted, and the penetrating power and the uniformity of cleaning are enhanced.

The invention relates to the technical field of electron accelerators, and particularly provides a modular electron accelerator pulse modulator device. The device comprises a cabinet, a system main controller, a central dynamic energy pool and a power module cluster composed of N power modules. The power modules are installed in a pluggable mode through the backboard slots and form a hybrid cascade Marx topology through the series busbars. The system main controller is integrated with a digital twinborn calculation module, coordinates the central dynamic energy pool to execute non-uniform energy distribution on each power module through a control bus, and controls each module to pre-shape an output pulse waveform. And each power module comprises a module energy storage unit, a module power switch unit and a module fine tuning unit formed by a GaN FET, and is used for realizing nanosecond precision correction of a pulse waveform. According to the invention, through modularized and intelligent control, the problems of pulse waveform distortion, low energy efficiency and insufficient reliability of a traditional device are effectively solved.

The invention discloses a multi-treatment-head accelerator and a control method thereof. The multi-treatment-head accelerator comprises a rotating rack, at least two independent treatment heads and a beam control device, the treatment heads are installed on the rotating rack and distributed in the circumferential direction of the rotating rack, and each treatment head is provided with an electron gun, an accelerating tube, a pulse modulator, a magnetron and an electron gun power source; the beam control device comprises a main controller, a trigger control unit and a multi-path pulse generator, the main controller is connected with the trigger control unit through a real-time communication signal, and the trigger control unit is connected with the multi-path pulse generator. According to the invention, at least two independent treatment heads are arranged on the rotating rack, so that the treatment efficiency is obviously improved; and each treatment head is correspondingly provided with an independent image acquisition device, so that the image guide treatment process is further optimized.

The application belongs to the field of distributed optical fiber sensing detection, and discloses a distributed strain and temperature sensing device and method based on chaotic laser Rayleigh scattering. The device comprises a chaotic laser. Chaotic laser emitted by the chaotic laser enters a pulse modulator after an isolator, is modulated into pulsed laser, then enters a sensing optical fiber through a first optical circulator after a light amplifier and a polarization scrambler. Rayleigh scattering occurs along the sensing optical fiber, backward Rayleigh scattering light signals are output after returning to the first optical circulator, and are converted into electric signals by a photoelectric detector. The electric signals enter a data processing system after a data acquisition card. Quantitative measurement of strain is realized through linear relationship between cross-correlation frequency shift and strain or temperature. The application uses chaotic laser with low coherence state as detection light pulse, which can ensure wide measurement range under medium sensitivity.

The embodiment of the invention provides a microwave generating device and radiotherapy equipment. The microwave generating device comprises a microwave source used for generating microwave energy; the pulse modulator is used for providing pulse power for the microwave source; and an impedance matching circuit connected between the microwave source and the pulse modulator. Wherein the impedance matching circuit comprises an instantaneous matching unit, and the instantaneous matching unit is used for performing impedance matching at the moment when the pulse modulator applies the high-voltage pulse. The instantaneous matching unit comprises a resistor element and a capacitor element which are connected in series, the first end of the instantaneous matching unit is connected with the first output end of the pulse modulator and the anode of the microwave source, and the second end of the instantaneous matching unit is connected with the second output end of the pulse modulator and the cathode of the microwave source.

The invention relates to the technical field of pulse modulators, and discloses a circuit for improving the stability of a modulator system and a control method. The pulse width of a synchronous trigger signal of the synchronous switch is greater than that of a trigger signal of the solid-state modulator; in the charging stage of the solid-state modulator, the synchronous switch is switched on, the front-stage high-voltage power supply charges the solid-state modulator, and in the discharging stage of the solid-state modulator, the synchronous switch is switched off, so that the front-stage high-voltage power supply is isolated from the solid-state modulator; and the sampling circuit is used for sampling at the flat top part of the output pulse of the solid-state modulator, generating a feedback signal and sending the feedback signal to the preceding-stage high-voltage power supply so as to realize closed-loop control. According to the invention, the stability of a modulator system can be obviously improved, the power resistance requirement of a charging resistor of a high-power switching power supply is reduced, the inherent instability of the system at the moment of high-current pulse discharging can be effectively avoided, and the consistency and short-term stability of different pulses are improved.

Techniques are described for decoding a pulse-width modulation (PWM) signal transmitted across an isolation barrier, such as within a gate driver. The techniques utilize a PWM modulation scheme that uses four or more stages for encoding and decoding data to ensure accurate and efficient communication across the isolation barrier. Using these techniques, the pulse modulator generates a PWM signal with four or more different modulation stages, each representing different combinations of AC and DC components, enabling the encoding of two data bits per modulation cycle.

The invention discloses an anti-electromagnetic interference shielding structure of a pulse modulator cabinet, relates to the technical field of pulse modulator cabinets, and solves the problems that the pulse modulator cabinet in the prior art is poor in anti-electromagnetic interference shielding effect and the heat dissipation effect is reduced due to the fact that a dustproof net of a heat dissipation mechanism is not cleaned in time. Comprising a cabinet body, and a backboard of the cabinet body is provided with heat dissipation ports; the heat dissipation assembly is used for heat dissipation of equipment modules in the cabinet body, and the heat dissipation assembly comprises a heat dissipation pipe fixedly installed in the heat dissipation opening, a heat dissipation fan fixedly connected in the heat dissipation pipe, an electric valve fixedly connected to the side face of the heat dissipation pipe and a dustproof net fixedly connected to the outer side of a port of the electric valve; the device further comprises a shielding assembly. By means of the design, the shielding requirements of high frequency and low frequency can be met at the same time, and the interference problem is effectively avoided by installing the core modules in a partitioned mode. In addition, dust adhering to the dustproof net can be automatically cleaned before each time of use, the heat dissipation effect is ensured, and the problem that manual cleaning is not timely is effectively avoided.

A kind of quick weak light fiber grating array demodulation device and method based on reflection enhancement point belong to optical fiber sensing technical field, the present application is to solve the problem of wavelength grating reflection signal segmentation inaccuracy in prior art high-speed dynamic demodulation, make system demodulation error big.This application includes fast scanning laser, electric pulse signal generator, optical pulse modulator, fiber amplifier, fiber circulator, reflection enhancement point, weak grating array sensing unit, photoelectric conversion module, acquisition module, data analysis processing module and control module.Reflection enhancement point and weak grating array sensing unit are reflected to fast scanning optical pulse signal and obtain reflected signal, the reflected signal of reflection enhancement point is segmented to weak grating array reflected optical pulse signal of any wavelength, after data processing, grating position and center wavelength are obtained.The system uses reflection enhancement point to obtain the grating reflected signal of each wavelength, realizes the high-speed dynamic demodulation of weak grating array sensing unit.

The invention discloses a multi-channel pseudo-random code modulation laser interference source device. The device comprises a pseudo-random code modulator, an external modulation laser group, an optical fiber beam splitter group, an optical fiber buncher and a two-dimensional galvanometer which are arranged in sequence, according to the invention, laser modulation is carried out through the pseudo-random code pulse modulator, pseudo-random pulse codes are generated, and optical interference pulses with different coded signals are generated; two-dimensional galvanometer light beam deflection control is adopted, and control over laser interference signals in different directions can be achieved; a multi-path 1 * 2 optical fiber beam splitter and a multi-path 1 * 8 optical fiber beam splitter are adopted, beam splitting of coding signals of the same type is achieved, and the function of transmitting multi-channel interference light beams at the same time is established. According to the invention, emission of light interference signals of different codes is realized, a function of simulating laser radar light signals of unmanned vehicles produced by different manufacturers is realized, a function of simultaneously emitting multiple paths of light interference signals is realized, and a problem of simulating complex light interference environment signals in practical application of the unmanned vehicles is solved.

The invention particularly relates to a high-power dual-mode solid-state microwave amplifier which is characterized in that a control and pulse modulator is used for generating pulse signals with different widths, amplitudes and frequencies according to external control signals and outputting the pulse signals to a microwave power amplification link; and the microwave power amplification link is used for switching accessed links according to the external control signal and the pulse signal, and amplifying the input microwave small signal so as to output microwave signals with different duty ratios, peak powers and pulse widths. The device can be used for a phased array microwave weapon integrating detection, guidance and striking functions, and has the capability of outputting pulse waveforms meeting different functional requirements.

The invention discloses an online training cerebellar neural network controller and a control method for a single-inductor multi-output switching power supply. The method comprises the following steps: performing difference operation on reference voltage and output voltage through a logical operation unit to obtain an output voltage error, an error integral quantity and an error differential quantity; each PID controller is configured to enable an input signal to correspond to each path of output voltage error, and is used for carrying out proportional-integral-differential adjustment on the PID controller based on each error integral quantity and error differential quantity; the cerebellar neural network is configured to update the weight of the cerebellar neural network in real time through online training based on a local learning rule and output a digital control signal carrying duty ratio adjustment information; the digital pulse modulator generates a complementary switching signal based on the duty ratio adjustment information and forms a switching signal to drive a power switching tube of the single-inductor multi-output switching power supply, the disturbance recovery time and overshoot of the digital power supply can be effectively reduced, and the transient performance is remarkably improved.

The invention provides a time phase domain random modulation ultra-long distance Brillouin optical time domain reflectometer, and belongs to the technical field of time phase domain random modulation Brillouin optical time domain reflectometers. In order to solve the technical problem that the spatial resolution and the sensing distance of an existing Brillouin optical time domain reflectometer cannot be increased at the same time, the adopted technical scheme is as follows: the output end of a narrow linewidth laser is connected to the input end a of a first optical fiber coupler; the output end b of the first optical fiber coupler is connected to the input end d of the pulse modulator; the output end f of the pulse modulator is connected to the input end g of the phase modulator; the output end A of the arbitrary waveform generator is connected to the input end e of the pulse modulator, and the output end B of the arbitrary waveform generator is connected to the input end h of the phase modulator; the output end i of the phase modulator is connected to the input end of the pulsed light amplifier; the output end of the pulse optical amplifier is connected to the input end of the first optical filter; the method is applied to the Brillouin optical time domain reflectometer.

The application discloses a circuit breaker and automatic transfer switch integrated power supply continuity guarantee system and a method thereof. The system comprises a controlled pulse modulator circuit, which changes the output pulse sequence frequency of a driving switching actuator in response to a voltage regulation signal; a period extender circuit, which performs integer multiple expansion on the pulse sequence; a phase deviation discriminator circuit, which detects the time deviation between the expanded pulse sequence and a power supply reference synchronization signal, generates a compensated deviation voltage through a loop dynamic compensation filter; a tunable time base generator circuit, which generates a time base reference pulse based on a series magnetostrictive delay line element and a piezoelectric adjustable capacitor, and is controlled by the compensated deviation voltage; and a transient time error sampler circuit, which determines the time error signal between the output pulse sequence and the time base reference pulse through a charge holding integral sampling mode, and forms the voltage regulation signal through negative feedback closed loop.

This application discloses a voice assistance system based on phased array focusing, its manufacturing method, and its usage method, relating to the field of voice-assisted speaking technology. The system includes: a glottal pulse modulator, a phased array drive control system, and an acoustic parametric array; the glottal pulse modulator is used to modulate the original vocal glottal wave signal with a carrier signal that excites an ultrasonic transducer to obtain a modulated signal; the acoustic parametric array includes several ultrasonic transducers; the transmission phase of each ultrasonic transducer is set to the ultrasonic phase emitted by the virtual sound source it receives; the virtual sound source is located at the focusing position; the phased array drive control system is used to control the transmission phase of each ultrasonic transducer when emitting the modulated signal. This application controls the transmission phase of each ultrasonic transducer to the ultrasonic phase emitted by the virtual sound source located at the focusing position, thereby enabling the information emitted by these ultrasonic transducers to be focused at that focusing position.

Techniques for decoding a pulse width modulation (PWM) signal transmitted across an isolation barrier, such as within a gate driver, are described. The techniques utilize a PWM modulation scheme that uses four or more levels to encode and decode data, ensuring accurate and efficient communication across the isolation barrier. Using these techniques, the pulse modulator generates a PWM signal with four or more distinct modulation levels, where each level represents different combinations of AC and DC components, allowing the encoding of two bits of data per modulation cycle.

A kind of narrow linewidth single frequency high energy 1064nm laser for space-based wind lidar, using seed injection-based master oscillator power amplifier (MOPA) scheme, using narrow linewidth continuous single frequency distributed feedback laser (DFB) as seed source, two-stage semiconductor optical amplifier (SOA) modulated pulse width, single-end pumped crystal as preamplifier stage, two double-end pumped Nd:YAG slab as main amplifier stage;Two DFB seed sources are used to lock the frequency difference and correct the Doppler shift;Two-stage cascaded SOA pulse modulator has the advantages of narrow linewidth, high extinction ratio and small volume. Using 885nm LD end-pumping, good thermal management performance, helps to improve beam quality;End-pumping has high optical coupling efficiency, high Stokes efficiency under 885nm LD pumping, no intermediate relaxation heat, which helps to improve optical-optical conversion efficiency and save pumping.

The present application discloses an all-fiber pull-string switch and a transmission equipment fault location and warning system. The all-fiber pull-string switch includes a single-wavelength laser, an optical pulse modulator, a light detector, a fiber coupler, a signal processor, and a microstructured optical fiber. The single-wavelength laser is connected to one end of the optical pulse modulator, the other end of the optical pulse modulator is connected to the input end of the fiber coupler, the first output end of the fiber coupler is connected to the microstructured optical fiber, and the second output end is connected to one end of the light detector. The other end of the light detector is connected to the signal processor. The microstructured optical fiber is arranged on both sides of the transmission equipment along the transmission direction. The present invention uses microstructured optical fiber to reduce the complexity and cost of the system. It has good stability and corrosion resistance, can be used in extreme environments, and does not require electrical transmission, so it is not prone to safety risks. It can quickly determine the operating status of the transmission equipment and accurately locate the fault point.

The invention discloses a rapid scanning system and method based on YTO, and belongs to the technical field of microwave signal source and frequency synthesis. In order to solve the problem that the scanning speed is limited due to the fact that lock losing is prone to occurring in the start-stop stage due to the hysteresis effect in an existing YTO simulation frequency sweeping scheme, the invention provides a method combining extended scanning and precise gating. According to the method, a wider extended scanning frequency band (F1 to F2) is calculated according to YTO hysteresis characteristics outside a target scanning frequency band (Fstart to Fstop) set by a user. The system controls the YTO to execute high-speed analog scanning in an extended frequency band, meanwhile, the FPGA accurately controls a pulse modulator in a radio frequency channel, signal output is started only when the scanning frequency is in a target frequency band (Fstart to Fstop), and output is closed in extended start-stop transition sections (F1 to Fstart and Fstop to F2). The influence of the hysteresis effect on the stability of the phase-locked loop is effectively avoided, the simulation scanning speed is increased from the traditional hundreds of MHz / ms magnitude to the GHz / ms magnitude, and the test efficiency is remarkably improved.

The invention discloses a TLTs-based multi-stage floating superposition high-voltage narrow pulse modulator, which comprises M floating power supplies, M single pulse forming circuits, a driving circuit of the floating power supplies, a high-voltage isolation transformer and a power supply controller, and is characterized in that the driving circuit and the high-voltage isolation transformer supply power to the M floating power supplies; the multi-level floating superposition is formed by superposing W-level transmission line transformers to form a W-time high-voltage pulse amplitude, each single pulse forming circuit outputs a W-time Vin pulse voltage, Vin is a power supply voltage of each single pulse forming circuit and is provided by a corresponding floating power supply, and each single pulse forming circuit outputs a W-time Vin pulse signal; and the amplitude of a pulse signal formed by isolating and superposing the M groups of single pulse forming circuits is N times of Vin. According to the invention, a combined design is adopted, and pulse signals with different high-voltage requirements can be generated by adopting flexible combination of different numbers of single pulse circuits and different numbers of TLTs according to performance and index requirements.

The invention discloses a method for adjusting the output front edge of a multi-primary pulse modulator, and the method comprises the steps: controlling the conduction time sequence of each primary winding of the multi-primary pulse modulator, and adjusting the conduction time of each primary winding in real time, thereby adjusting the output pulse front edge through the influence of the conduction of the primary windings on the loop impedance. According to the scheme, software is adopted to control the conduction time sequence of the primary windings, that is, the conduction time of each group of primary windings can be adjusted through the software, the opening time of each path is adjusted in real time, loop impedance is affected through the method, and then the leading edge is affected to achieve the adjustment purpose.

This application provides a mechanical optical pulse modulator and modulation method. The mechanical optical pulse modulator includes: a light source; a motor flywheel; at least one wedge mirror disposed on the outer edge of the motor flywheel, the wedge mirror being configured to reflect light emitted from the light source when the wedge mirror is rotated to a position where the center of the motor flywheel and the light source are aligned and facing the light source; and a micro-reflector located in the direction of the reflected light emission from the wedge mirror, used to reflect the light reflected by the wedge mirror, wherein the micro-reflector includes a light reflecting component and a light absorbing component, the light absorbing component being used to absorb light around the light reflecting component. The mechanical optical pulse modulator provided by this application solves the problems of high cost and complex adjustment methods in existing optical pulse modulation devices.

The application discloses an ultrasonic transducer driving circuit and an electronic artificial larynx, and relates to the field of medical devices. In the ultrasonic transducer driving circuit, a power module is used for providing power supply for the whole driving circuit; a glottal wave pulse modulator is used for amplitude modulating a glottal wave signal of normal speech of a patient and a carrier signal for exciting the ultrasonic transducer to generate a modulated signal; a differential output power amplifier is used for signal conditioning and power amplification of the modulated signal, and the amplified driving signal is output in a differential mode; a transformer is used for boosting the amplified driving signal to generate a boosted driving signal; and a matching circuit is used for realizing impedance matching between the boosted driving signal and the ultrasonic transducer, so that the power of the boosted driving signal is maximized and loaded on the ultrasonic transducer to drive the ultrasonic transducer to emit ultrasonic waves. The ultrasonic transducer driving circuit can reduce the overall volume of the driving circuit and meet the portable requirement of a handheld electronic artificial larynx device.

The present invention discloses an interferometric fiber optic hydrophone phase-shift PGC demodulation method and demodulation system. First, a laser is used to generate an optical signal, which is then sinusoidally frequency modulated to output a sinusoidally frequency-modulated light wave. The sinusoidally frequency-modulated light wave is input into an optical pulse modulator for processing to output periodic light pulses. The light pulses are subjected to fiber splitting, fiber delay, and fiber beam combining to obtain a light pulse sequence. The light pulse sequence is phase-modulated by a phase modulator and then input into an optical fiber interferometer for interference processing, outputting an interference light pulse sequence. The interference light pulse sequence is input into an optoelectronic converter for optoelectronic conversion and digital sampling. The sampled signal is input into a signal processing system for PGC demodulation processing and high-pass filtering. The demodulated phase signals after high-pass filtering are summed and averaged to obtain the final demodulated phase signal. This method can obtain a stable, low-noise demodulated phase signal without adding additional optoelectronic detection and signal acquisition hardware.

The utility model belongs to a klystron structure of a high-voltage pulse modulator in the technical field of high-voltage pulse modulators. Comprising an anode tubular pile (1) and a cathode tubular pile (3), the anode tubular pile (1) is connected with a klystron anode, the cathode tubular pile (3) is connected with a klystron cathode, the anode tubular pile (1) is provided with an anode contact terminal (2), the cathode tubular pile (3) is provided with a cathode contact terminal (7), the anode tubular pile (1) and the cathode tubular pile (3) are installed on an insulating plate (4), and the anode tubular pile (1) is located on the inner ring of the cathode tubular pile (3). The klystron structure of the high-voltage pulse modulator is simple in structure, and ensures that the klystron is convenient to install above a pulse transformer and reliable in contact.

The utility model discloses a general compact HPM source device, include: combined cabinet, be assembled from first cabinet and second cabinet, be provided with high pressure pulse modulator unit, control unit, solid state amplifier excitation source unit, distribution unit and standing wave protection unit from below to above in proper order in first cabinet, be provided with high -power klystron in second cabinet, high pressure pulse modulator unit is used for changing 380V alternating current into the pulse high pressure required by high -power klystron cathode, solid state amplifier excitation source unit is used for providing the microwave excitation of high -power klystron when working, standing wave protection unit has two microwave detection mouth outward, is respectively used for monitoring the forward power and reverse power of high -power klystron output, high -power klystron is used for connecting microwave transmission link outward through microwave output mouth, control unit is used for receiving the control instruction of host computer issue, and the device state information is reported to host computer, the utility model discloses compact structure, convenient operation.