2331results about How to "Not affected" patented technology

The invention relates to a non-excavation tube pulling construction method which comprises the following steps: (1) preparation work: understanding stratum and underground condition, calculating the number of chambering and the size of a return compandor, and formulating the control data of a pipeline midline and elevation and correction measures; (2) measuring plane surface, controlling payingoff, and measuring the elevation of each pile; (3) setting an active well, and receiving and setting a drilling machine; (4) preparing drilling fluid; (5) drilling pilot holes,; (6) adopting the compandor to chambering, cleaning the hole at the same time, and protecting walls with slurry; (7) welding the pipeline; (8) pulling the tube, and simultaneously pulling a steel tube with the same length as that of the tube; (9) casting slip and fixing; (10) mounting tubes; (11) testing pressure and flushing. The invention can effectively increases economical benefit and social benefit, and has the advantages of environmental protection and energy saving.

The invention provides an electric bus integrated control hardware in-loop test platform and a test method. The electric bus integrated control hardware in-loop test platform is formed by an air source component, a line control air brake system, a conventional brake component, a driving control component, a signal simulation component, a target machine, and a host computer based on line control air brake, and the electric bus integrated control hardware in-loop test method comprises an acceleration test, a brake test and a steering test. According to the test platform and the test method, accurate adjustment of the brake pressure of four wheels is realized through front and rear axle proportion relay valves and four ABS solenoid valves in a line control air brake system, and integrated control of electric buses is realized with the combination of signal simulation components including a two-degree-of-freedom rotation platform and a wheel speed simulation motor and the corresponding test method.

The invention discloses a hermetia illucens breeding system and belongs to the technical field of green cultivation. The hermetia illucens breeding system comprises a culture pond and a ceiling arranged at the upper part of the culture pond; the culture pond is sequentially provided with a water absorption layer, a heating device and a grid layer from bottom to top; the heating device comprises a heating tape and a fixing frame for fixing the heating tape; a compost is put on the upper part of the water absorption layer; the heating device is located in the compost; the grid layer is located on a surface layer of the compost; a lifting device is arranged on the side of the culture pond; the lifting device drives the heating device to lift; and a heat preservation cover is arranged at the top of the culture pond. Hermetia illucens is bred by using the hermetia illucens breeding system, so that the survival rate of hermetia illucens larvae is high and the hermetia illucens is not affected by an external environment; furthermore, the hermetia illucens is easily separated from the compost and insect feces do not need to be cleaned, so that the cost of manpower and material resources is greatly reduced. In addition, the compost in the culture pond is digested and fermented in the hermetia illucens breeding process and can be directly returned to the field as an organic fertilizer, so that the hermetia illucens breeding system is economical and environmentally friendly.

The invention provides a 3D human face quick identity authentication method and apparatus. The method comprises the following steps of S1, obtaining a depth image and a two-dimensional image comprising a current user face; S2, obtaining the depth image and the two-dimensional image of the current user face; S3, performing identity authentication primary screening on the current user face to obtaincandidate reference data sets; S4, extracting feature information of the current user face, and determining a pose orientation vector of the current user face; and S5, performing identity authentication. The functions of input, detection, identification and the like of a face identity are realized by utilizing the depth image and the two-dimensional image, and the primary screening of the reference data sets is performed in combination with the depth image and the two-dimensional image, so that the identification efficiency is improved, the influence of an external complex environment is avoided, and absolute front face of a user is not required.

The invention discloses wearable equipment, an unmanned plane control device and a control realization method, the wearable equipment comprises a gesture configuration identification module, a ground control station module and a wireless transmission module, wherein the gesture configuration identification module can collect to-be-identified characteristic data of a wearer by a sensor, present gesture of the wearer is identified, a corresponding relation between a pre-configured and saved gesture and an unmanned plane control command are searched, and the unmanned plane control command corresponding to the gesture is transmitted to the ground control station module; the ground control station module receives the unmanned plane control command through a data interface, codes the control command, converts the control command into a control message and transmits the message to the wireless transmission module; and the wireless transmission module receives the control message and wirelessly transmits the message to the unmanned plane to realize that the flight state of the unmanned plane is controlled according to the control message. According to the invention, the wireless connection between the wearable equipment and the unmanned plane is established, when a user makes a gesture through the wearable equipment, the unmanned plane is controlled, and intelligentize interactive operation is conveniently and intuitively realized.

The invention discloses a system for detecting a driving state and generating a path of an AGV (Automatic Guided Vehicle) based on RFID (Radio Frequency Identification). Passive RFID tag arrays are embedded in a container wharf and a storage yard and used for establishing position coordinate systems of the wharf and the storage yard; by virtue of RGID reading antennas mounted under the front and the back of an AGV body, RFID tags, which are embedded in the storage yard, in a sensing range of the antennas are read in the driving process of the AGV, so that state information such as the current position, speed and direction of the driving AGV can be obtained; then a real-time driving path of the AGV is generated according to the current position of the AGV and an AGV driving instruction (target position) from a central control system, thereby achieving the path driving control of the AGV through a driving controller of the AGV. The system is simple to implement, reliable in performance, practical and free from influence of the environment, can be applied to unmanned automatic navigation of the AGV at the intelligent container wharf and also can be applied to the unmanned automatic navigation of a cargo carrying vehicle at a large automatic logistics warehouse.

The present invention discloses a full-autonomous underground pipeline measurement system based on an inertia technology, and the system consists of an in-pipe measurement unit, an external control unit, and a data information processing unit. The in-pipe measurement unit is arranged into a pipeline being measured and is caused to move along the central axle line of the pipeline, the three dimensional information of the pipeline can be completely gotten through measuring the moving track of the in-pipe measurement unit. The system adopts a strapped-down inertial navigation technology to measure the course heading and the attitude angle of the in-pipe measurement unit (carrier), the angular motion information of the carrier is measured according to the gyro output angle rate, each instant accurate location of the carrier can be analyzed according to the integrated angle and the displacement information, thereby the three dimensional information of the pipeline can be obtained. The operation of the in-pipe measurement unit is irrelevant to the external factor such as depth, location, peripheral electromagnetic field, etc., not limited by other conditions, the integrated course angle, the attitude angle, and the instant location information of a navigation principle are applied to any depth, and the three dimensional information of the pipeline waiting for measuring can be independently measured.

The invention provides a method for realizing the cross-platform performance monitoring of a J2EE architecture enterprise application system, which is a real-time monitoring method with a B / S structure for a J2EE architecture. The method divides the realization of performance monitoring to the application system into three layers: a data acquisition layer, a data processing layer, and a data exhibition layer; an enterprise can define key performance indices (KPI) of the enterprise according to the demand of IT operation and maintenance management of the enterprise; the realization method also internally defines a set of key performance indices which meet the demand of a plurality of enterprises at the same time; a data analysis engine is used to analyze acquired data through the acquisition to needed performance data of the key performance indices, and an analysis result is sent for alarm notification. Most enterprise-level application systems are deployed under the complex environment of various platforms, such as Unix, Windows and linux; and the development of different monitoring softwares aiming at different platforms is a complex and huge job. The data acquisition layer of the method adopts universal interface technology, and can realize the performance monitoring to multi-platform databases and application middlewares.

The invention relates to a device for detecting snaking motion instability of a high speed train bogie, which is used for monitoring on-line whether snaking motion instability of the bogie appears during the travel of a high speed train. The device provided by the invention comprises a main controller system and a sub-detection system. The main controller system mainly comprises a man-machine interaction module, a GPS (global position system) module, a data analysis record module and a field bus control module. The sub-detection system mainly comprises a sensor module, a data acquisition module, a data analysis module, a field bus control module and a data storage module. A main controller and the sub-detection system are subjected to data communication through a field bus. The sub-detection system monitors the transverse vibration state of the bogie in real time to judge whether the snaking motion instability appears and transmits instability information to the main controller through a field bus; and the main controller completes analysis of the instability information, combines with the GPS module and a clock module to correctly provide time and space synchronizing information at the moment of the occurrence of instability, then gives out a warning signal and stores the fault information.

The invention discloses a shift register, a driving method thereof, a driving control circuit, a display panel and a display device. Through arranging a third control module, stable signal of a firstnode is kept through controlling by the signal of the first node. In floating connection of the first node, the signal at a third clock signal end is coupled with the first node. When a signal outputend outputs an effective pulse signal, the signal of the first node is not affected by the signal at the third clock signal end, and influence of a second control module to the signal of a third nodeis prevented. Furthermore through arranging a transmission control module, the level of the signal of a second node is same with the level of the signal of the third node through controlling by the signal of a second node. The signal can be directly and quickly transmitted to the third node, thereby preventing a risk of signal transmission competition, and further preventing an output competitionrelation of the shift register so that the shift register can stably outputs the signal in a shifted manner.

The invention belongs to the technical field of power system relay protection, and discloses a circuit single-end ranging method based on phase aberration characteristic of positioning function. The method deduces an operating voltage of reference positions and a fault point voltage based on distribution parameters by using electric quantity of a single end, and constructs a positioning function. When the reference positions are positioned on the left side and the right side of fault point, the positioning function has different phase characteristics; and when the reference positions are changed in front and back of the fault point, the phase of the positioning function has a unique stepped aberration. A circuit is subjected to N equal distribution, the equal distribution area containing the fault point is determined by using the phase characteristics, the step length is further reduced to determine the phase aberration position in the area, and then quick fault positioning of the single end can be realized. The method overcomes the defects of the traditional single-end ranging method, and theoretically is not affected by the factors such as distributed capacitance, transition resistance, opposite side running mode, communication facilities, load current and the like. The algorithm is simple, reliable and easy to realize, and the use value of the method is strong.

The invention discloses an aseismatic structure of a high earth-rock dam and a construction method thereof, and an aseismatic structure is constituted by steel bars, geogrids, stainless steel meshes, precast concrete anchoring sections and geogrid wrapping sections. In rockfill in an upstream dam shell and a downstream dam shell within the range from the dam top to 1 / 5-1 / 4 of the height of the dam, a layer of the steel bars is laid every three layers of the rockfill according to the number of the compacted layers of the rockfill material, asphalt is further top-poured for performing anti-rusting treatment, one end of each steel bar is fixedly connected with the precast concrete anchoring section and the other end of each steel bar is hinged with the stainless steel mesh on the dam surface; and the geogrid is laid on the rockfill in each layer after compaction, and each geogrid is reserved on the dam surface for being turned and rolled onto the rockfill of the upper layer after roller compaction for forming the geogrid wrapping section; and the steel bars on the top surface of a core wall penetrate through the whole rockfill for connecting the stainless steel meshes on the upstream dam surface and the downstream dam surface. The aseismatic structure of the high earth-rock dam absorbs the advantages of flexible material and rigid material in the aseismatic aspect, the aseismatic performance is good, the construction is convenient, the construction progress is not affected, the size of a dam body is not increased and the aseismatic structure of the high earth-rock dam is economic and practical.

The invention discloses a molecular marking method of an indica rice variety subjected to anti-brown planthopper host gene Bph27 transfer. The developed and designed gene Bph27 is closely interlocked with molecular marking primers B471 and B58, and differential fragments can be amplified from an anti-brown planthopper donor Balamawee and a susceptible indica rice variety; the anti-brown planthopper host gene Bph27 is genetically transferred through molecular marking of a gene Bph27 locus, the required fragments can be accurately and quickly guided, the selection efficiency of the gene Bph27 is greatly improved, and a new anti-brown planthopper indica rice variety 991RB is developed.

The invention provides a color histogram based vehicle body color identification method. The method comprises three main steps of license plate positioning, vehicle body color feature region positioning and vehicle body color identification. The method particularly comprises: firstly, determining a license plate position through a license plate identification technology, and detecting a coarse region of vehicle body color through the height, width and position coordinate information of a license plate; preprocessing the region of the vehicle body color to reduce external environment interferences; further searching the preprocessed coarse region of the vehicle body color to obtain an accurate feature region of the vehicle body color; and converting the feature region into a Lab color space, extracting a color histogram from the Lab space, and performing vehicle body color training and identification by using a nonlinear SVM. The method is capable of intelligently processing traffic vehicle videos and images and automatically identifying the vehicle body color. Compared with other schemes in the same field, the method has very high identification accuracy and is high in robustness in a complicated environment.

The embodiment of the invention discloses a liquid crystal device, and belongs to the technical field of display. The liquid crystal display device comprises an array substrate, a color filter substrate, a liquid crystal layer and frame glue, wherein the array substrate comprises a plurality of scanning lines in parallel, insulated layers arranged on the surfaces of the scanning lines, a plurality of parallel data lines arranged on the surfaces of the insulated layers, a plurality of pixel electrodes arranged on the surfaces of the insulated layers and distributed in a matrix, passivation layers covering the surfaces of the pixel electrodes and the surfaces of the data lines, and a plurality of first common electrodes which cover the surfaces of the passivation layers and are parallel with the data lines and crossed with the scanning lines; the color filter substrate comprises a black matrix, a color resistance layer, a flat layer and a second common electrode covering the surface of the flat layer, and the second common electrode is of a net-shaped structure, the net-shaped structure is a certain distance away from the data lines and the scanning lines in the vertical direction and the net-shaped structure is relatively overlapped with the data lines and the scanning lines. The penetration rate of the liquid crystal display device rises, and the response speed is improved.

The invention discloses a bandgap reference voltage source which comprises a starting circuit, a core bandgap reference circuit and a high-order compensation circuit. The core bandgap reference circuit comprises PMOS tubes M1, M2 and M3, NPN triodes Q1 and Q2 and resistance units R1, RB1, RB2 and RA; and the high-order compensation circuit comprises PMOS tubes M4, M5, M6, M7, M8, M9, M10 and M11, NPN triodes Q3, Q4, Q5, Q6, Q7 and Q8 and resistance units R2 and R3. The bandgap reference voltage source disclosed by the invention adopts the high-order compensation circuit, thereby the temperature coefficient is reduced greatly; the circuits adopt the resistance ratio, thus the circuits can not be affected by the absolute value of the resistance, and the influence of the temperature coefficient of the resistance to the output quantity can be reduced. The bandgap reference voltage source has high power supply rejection ratio and can ensure that the circuits can resist the interference of a power supply.

The invention discloses a consistency-based edge detection method. The consistency-based edge detection method comprises the steps of (1) utilizing the image gray scale gradient magnitude for screening out an initial edge set, (2) calculating an image gray scale gradient direction sum, (3) extracting the edge set according to the gradient direction sum, and (4) conducting edge refining. According to the consistency-based edge detection method, the index of the gray scale gradient direction sum is introduced, the correlation of the gray scale gradient directions near edges is utilized for analyzing the edge occurrence rationality, the new imaging noise determination method is provided, gray scale gradient changes caused by actual edges and noise can be effectively distinguished, and the edge extracting effect can be improved by combining the index with other methods.

The invention relates to a Raman optical fiber amplifier and a detection method of loss of a transmission optical fiber connector of the Raman optical fiber amplifier. A transmission end (with a pumping signal multiplexer) of the amplifier is connected with a public end (with an out-of-band ASE (amplification of spontaneous emission) optical filter) of the amplifier, an out-of-band ASE output end of the out-of-band ASE optical filter is connected with a photoelectric detector, an output end of the photoelectric detector is connected with an input end of a control unit, an output end of the control unit is connected with an input end of a pumping laser device group, the pumping laser device group is connected with a pumping end of the pumping signal multiplexer, and a public end of the pumping signal multiplexer is connected with an input end of an erbium-doped fiber amplifier through a transmission optical fiber. The detection method comprises the following steps of: outputting a group of pumping light with determined power; determining a mathematic relation of out-of-band ASE optical power and pumping light power, and determining a mathematic relation of joint loss and the out-of-band ASE optical power; and determining a loss value of a joint. According to the Raman optical fiber amplifier and the detection method of the loss of the transmission optical fiber connector of the Raman optical fiber amplifier, disclosed by the invention, the gain and the gradient of the gain can be exactly controlled, the relative insertion loss of a transmission optical fiber line is known in real time, and performances of products can be improved.

The invention relates to a position identification and guide method based on bluetooth and a two-dimension code. The method comprises a bluetooth 4.0 terminal, a user hand-held terminal and a server end, wherein the bluetooth 4.0 terminal, the user hand-held terminal and the server end are connected through wireless communications, and the user hand-held terminal is provided with a bluetooth 4.0 module. The method includes the following steps: step one, conducting regional division and enabling the bluetooth 4.0 terminal to be mounted in a region; step two, conducting subregion division; step three, appointing a destination; step four, appointing an original place; step five, guiding a path from the original place to the destination; and step six, guiding the position of a subregion of the destination. By means of the position identification and guide method based on the bluetooth and the two-dimension code, position guiding can be achieved swiftly.

The invention belongs to the technical field of solar energy application, in particular relates to an automatic sun tracking system of a solar collector. The system consists of a motor which drives the solar collector to track the sun, a mechanical transmission mechanism and a tracking control circuit which controls the mechanical transmission mechanism to operate; the system is characterized in that a GPS receiver arranged on the solar collector and an attitude sensor are used for outputting the signals of the position, the orientation, and the like, of the collector to a microprocessor; the microprocessor outputs control signals to the motor, so as to control the mechanical transmission mechanism to drive the solar collector to face the sun directly after working out the difference value of the orientation of the collector and the position of the sun. The system can realize the accurate all-round sun tracking in real time by adopting the GPS location finding technique without the influence of weather and environment, and is suitable for the solar collector which has the fixed position on the earth or the solar collector which is arranged on the moving car body and a transocean vessel to track the sun.

The invention discloses a gene TaSnRK2.10 relevant to the wheat thousand seed weight, a molecular marker TaSnTK2.10-4A-caps relevant to the gene and application of the marker. The DNA of a wheat variety to be detected is subjected to PCR (polymerase chain reaction) multiplication through a marker primer TaSnTK2.10-4A-caps; a multiplication product is subjected to cleavage through SalI incision enzyme and is also subjected to electrophoretic separation; for example, PCR products are two bands with the sizes of 793bp and 316bp; the wheat variety is a variety with haplotype with high thousand grain weight of the gene; the PCR product is only a band with the size of 106bp; the wheat variety is a variety which is not provided with the haplotype with high thousand grain weight of the gene. According to the gene TaSnRK2.10 relevant to the wheat thousand seed weight and the molecular marker TaSnTK2.10-4A-caps thereof, the wheat variety or strain with high thousand grain weight can be conveniently detected or screened, and the selection process of the high-yield variety of wheat can be greatly accelerated.

The method comprises: according to the QoS parameters, automatically sending Ping request message at main and standby interfaces or at main interface on time, and receiving the Ping response message; making calculation for each parameters of QoS in the Ping request message in order to decide if there is failure in network and there is a parameter of QoS over the threshold; if there is a network failure or a parameter of QoS over the threshold, then making a changeover between the main and standby interfaces, and giving a alarm to the main interface.

The invention discloses a method for transmitting real-time data and non-real time data by an Ad Hoc web radio station, comprising the following steps of: (1) dividing data time slots provided for users into static time slots, competition time slots and preserve time slots, wherein the static time slots are distributed to various users in the web, are only used by corresponding users and adopt astatic TDMA (Time Division Multiple Address) occupied mode, the competition time slots can be used by various users and adopt a time slot ALOHA occupied mode, and the preserve time slots can be used by various users and adopt an end-to-end control packet handing occupied mode; (2) transmitting real-time data in the static time slots; (3) transmitting competition data during competition; and (4) transmitting preserve data during preservation. By using the method, the real-time data are transmitted at the static time slots and the non-real time data are transmitted at the completion time slots and the preserve time slots; and on the basis of maintaining a static TDMA access protocol to the maximum extent, the method provides a more flexible access means for the users.

The invention discloses a soft cabin isolator which comprises a soft cabin hung in a cabin frame, an operation platform, an air supply filtering unit, an exhaust filtering unit, a control unit, a sterilizing unit and a glove operation port unit positioned on the side surface of the soft cabin, wherein the operation platform is positioned at the bottom of the soft cabin and is in soft sealing connection with the soft cabin. The soft cabin isolator can completely isolate materials from operation staff, thereby fundamentally solving the pollution of the materials caused by people, providing a more reliable guarantee for aseptic performance of products and simultaneously preventing the operation staff from being affected by toxic materials; compared with the stainless steel hard cabin in the existing isolation operation device, the soft cabin isolator is lower in cost and small in mounting difficulty, and can provide a controllable purified environment for laboratory QC (quality control) inspection and small batch production.

The invention relates to the current conducting ployaniline composite membrane having the framework of the lotus leaf genus. It is the cancellated film composed by the nm fibre with microsphere and has the tuber on the surface of the fibre and the microsphere. The producing process of the composite includes the below steps: the eigenstate polyaniline is dissolved into the solvent; the insoluble substance is rejected, the adulterating acid is added; then, the polystyrene is added; the current conducting polyaniline mixed liquor is gained; finally, the petrified urrent conducting ployaniline composite membrance is gained one the receiving system using the electrostatic spinning technique. The composite membrane is indicative of the contact angle of 160 degree and the roll angle of below 5 degree to the pure water, the acid and the alkaline solution in the range of the entirely PH value and express the sky high ability of self purging; at the same time, the conductivity of the conducting macromolecule composite membrane don't change with the acid and alkaline solution. The conducting composite membrane can be used for producing the resisting electromagnetic shielding material, the antistatic stuff, the anticorrosion stuff, the anti fouling stuff of the shipping and the airplane, the latent stuff, the liquid transmission without the loss and the micro-flow stuff.

The invention discloses a digital colourimetry method based on an imaging device. According to application needs, two to three illumination bodies or light sources are selected, and a color card with the same medium as a shooting target sample is designed to serve as a training sample color card; a 45o / 0o illumination shooting environment is built, and parameters of the imaging device are set manually; digital images of the training sample color card and the target sample are obtained respectively on the basis, and illumination evenness and repeatability correction are carried out; by means of polynomials and other models, prediction from an RGB value of the target sample to CIEXYZ tri-stimulus values under the selected illumination bodies or the light sources is achieved, and prediction of a spectrum value is achieved by means of pseudo-inverse and other methods. The method can be widely used in the application fields with high color precision requirements for color image obtaining such as textiles, printing and dyeing, printing, leather, plastics, coating, paint, cultural relics, medical care, machine vision and artwork digital repositories and reproduction.

The invention relates to a molecular marking method for detecting a tobacco mosaic resistance gene (N gene), which comprises primer design, genome DNA extracting, PCR amplification and electrophoresis detection, and comprises the following specific steps: designing a specific primer according to the nucleotide sequence of the tobacco TMV resistance gene (N gene), amplifying a tobacco variety (strain) containing the TMV resistance gene (N gene)by a PCR reaction to obtain a feature band of 1200bp or so, and thus achieving the purpose of detecting whether the tobacco variety (strain) has TMV resistance. 84 cured tobacco materials are detected by the molecular markers of the invention, and the results are in accordance with the TMV resistance of the variety (strain). The method has the advantages of convenient operation, reliable result and high detection speed, and is not influenced by growth and development periods of plants. When the method is used for the seed selection of cured tobacco TMV resistant varieties, the selection efficiency can be greatly improved.

The invention provides a U-shaped pipe underground fluid multilayer sampling device. The U-shaped pipe underground fluid multilayer sampling device comprises a ground auxiliary system, a supporting system, a gas getting unit, water getting units and interlayer packers. The gas getting unit, the water getting units and the packers are arranged on a supporting connection rod of the supporting system. The gas getting unit is arranged in an aeration zone above a water table, the water getting units are arranged below the water table, the packers are mixed with the gas getting unit and the water getting units, waterpower incontinuity of upper parts and lower parts of sampling units in sampling layers of different aquifers or the same aquifer is achieved, and underwater of the different aquifers is sealed and cannot be mutually disturbed by drilled channels. The U-shaped pipe underground fluid multilayer sampling device is simple and novel in structural design and free of starting pressure, the service life of equipment is prolonged, the sample introduction speed is increased, the cost is reduced, and the application range is wider.

The invention discloses a 3D printing-based bionic artificial tooth and a manufacturing method thereof. The 3D printing-based bionic artificial tooth comprises a bionic dentin main body, a bionic enamel layer coating the upper end surface of the bionic dentin main body and a bionic cementum layer coating the bionic dentin main body, the bionic enamel layer is connected to the bionic cementum layer through a transition region, the outer surface of the bionic cementum layer is covered with a microstructure layer, and the microstructure layer comprises porous structures and barb structures staggered or irregularly distributed on the bionic cementum layer. According to bionic characteristics, solids with different gradient strength are molded in different implantation material areas so that stress interference between an implantation material and an alveolar bone is reduced. Through combination with a high freedom degree molding capability of the 3D printing technology, a completely personalized bionic dental implant is directly molded so that wearing comfort is improved. The barb structures and the porous structures are conducive to cell adhesion, growth and fixation, improve a bonding capacity of an implant and an alveolar bone and reduce adverse effects such as a dental implant falling risk after an operation.