82results about How to "Engineering practicability" patented technology

The invention discloses a method for estimating the modulation frequency and starting frequency of a linear frequency-modulated signal. The method comprises the following steps of: I, acquiring a data sequence x(n), wherein n=0, 1, 2, ellipsis , N-1; II, initializing parameters; III, calculating the power spectrum Yi(12) of a data sequence xi(m) in an ith short time window; IV, estimating the instant frequency estimated value fi of the data sequence in the short time window by adopting a Rife interpolation algorithm; V, judging whether the data sequences of all short time windows are processed, if not, returning to the step III, otherwise, turning to a step VI; VI, calculating a kth iteration weight; VII, judging whether an iteration weight least square linear fitting stop condition is met, if not, returning to the step VI, otherwise, turning to a step VIII; and VIII, calculating modulation frequency and starting frequency parameters. Due to the adoption of the method, the accuracy ofparameter estimation can be increased on the premise of ensuring rapid estimation without performing complex calculation and parameter search.

The invention relates to a method for estimating the residual magnetism of a transformer core based on the slope of a local hysteresis loop, which comprises the following steps: S1, measuring the saturation hysteresis loop of a transformer core material; S2, using a JA model to simulate the hysteresis characteristic of the transformer coil; S3, getting the relation between the residual magnetism and the slope of a local hysteresis loop near a residual magnetism point based on the JA model, and fitting the relation to get a corresponding formula relation; and S4, powering on and testing a transformer coil under test, getting the positive and negative slope near the residual magnetism point through electromagnetic relation conversion, and calculating the residual magnetism value according tothe formula obtained in the previous step. The method of the invention is simple. There is only the need to apply small positive and negative excitation and record the voltage and current in the residual magnetism calculation experiment. No complicated online experiment is needed. The test power is low, and the experimental cost is low.

The invention discloses a simulation method for an open type array signal. The method includes the following steps of firstly, obtaining the real-time target movement path of an underwater sound target; secondly, obtaining an underwater sound target radiation noise signal; thirdly, calculating coordinates of all array elements of linear arrays arrayed at equal intervals after array form distortion; fourthly, generating a real-time ocean channel pulse response sequence; fifthly, generating array element signals under the condition that no array element random shaking exists; sixthly, obtaining an array element signal, practically generated, of the i7th array element when random shaking occurs; seventhly, obtaining real-time ocean environment noise signals of the array elements; eighthly, obtaining a passive sonar array signal. By means of the simulation method, openness of an array signal simulation system can be achieved.

The invention discloses an acquiring method for a dynamic random optimal power flow of a power system for a wind-containing power field. According to the acquiring method, the dynamic random optimal power flow of the power system under the influence of the randomness of wind speed and load as well as temporal and spatial correlation is realized. The acquiring method comprises the following steps: firstly, establishing a dynamic probability model of wind speed, and analyzing the temporal and spatial correlation of the wind speed; secondly, calculating by adopting a deterministic dynamic optimal power flow based on an original dual and decoupling interior point method to obtain an optimal dispatching scheme; secondly, under the guidance of the dispatching scheme, solving the dynamic random optimal power flow considering the correlation based on a cumulants method to obtain probability distribution of a state variable, and adjusting the upper and lower bound of chance constraint according to the probability distribution; finally, performing iterative computation to solve a group of optimal dispatching schemes meeting all the chance constraints. According to the acquiring method disclosed by the invention, the optimal power flow of the power system under the random influence of an input variable can be effectively processed. The acquiring method has the advantages of accurate result and convenience for realization. The obtained result has certain guiding significance for dispatching persons.

The present invention provides a method and a system for detecting and distinguishing a passive synthetic aperture target signal, wherein the method comprises the following steps: step 101) constructing a motion doppler receiving model for a target signal under motion of a towed array sonar; step 102) respectively performing cross correlation averaging on target signals which are received by a hydrophone at an overlapping part on spatial position according to a passive synthetic aperture sonar algorithm when the array performs two successive motions in a fixed time interval, and then performing frequency domain wave beam forming treatment on the target signals which are received by array elements at different time periods; step 103) performing energy integration on the output sub-frequency-bands after forming of the frequency domain wave beam for obtaining wave beam output of each time interval; step 104) performing phase estimation on time delay and spatial position movement according to the doppler receiving model, and acquiring a phase correction factor according to the phase estimation; and step 105) compensating the wave beam output through each phase correction factor of time interval, and performing cross combined accumulation on the compensated wave beam output and realizing detection on the target through a time orientation process map.

The invention provides a random production analog method of an electric system with a large-scale photovoltaic power station. The method includes the following steps that conventional unit data, light resource data and time sequence load data are acquired; the equivalent effective capacity cumulant of all orders of a system unit without the photovoltaic power station is determined; time sequence effective capacity probability distribution Beta models and parameters of photovoltaic power generation at corresponding time frames are sequentially acquired; equivalent effective capacity distribution probability models and parameters of the system unit with the photovoltaic power station at corresponding time frames and reliability indexes under the corresponding load levels are sequentially obtained; and the reliability indexes of the system under the total load level are obtained in a hop-by-hop accumulation mode. The method relates to correlation on the time sequence between photovoltaic power station output and the load change, random fluctuation of the photovoltaic power station output is contained in system equivalent effective capacity probability distribution through cumulant correction, and the method is used for acquiring the reliability indexes of the system under the corresponding running modes.

The invention discloses a method for estimating the cycle slope and the starting frequency of hyperbolic frequency modulated signals. The method comprises the following steps of first, acquiring a data sequence, second, initializing parameters, third, calculating the power spectrum of data in the ith short time window, fourth, estimating the instantaneous frequency fi of the data in the ith short time window by using a maximum gammagraphy method, fifth, estimating the zero crossing point interval gi = 1 / fi of the data in the ith short time window, sixth, judging whether the data of all the short time windows are processed, executing the third step if not processed, otherwise executing the seventh step, seventh, sliding median filtering is conducted on a zero crossing point interval estimating sequence {gi, i = 1, 2, ..., I}, eighth, calculating the kth time interation weight, ninth, judging whether an interation stopping condition is met or not, if not, executing the eighth step again, otherwise executing the tenth step, and tenth, calculating the cycle slope and the starting frequency. According to the method, complex calculating and parametric search are of no need, the stability is strong, and quick and high-precision estimation of the parameters can be achieved.

An acceleration and scanning integrated structure of fully impervious high vacuum electron beam belongs to the fields of radiation processing technology. It includes accelerating tube, drift tube, scanning electromagnet and scanning box equipped with ion pump, the scanning electromagnet is mounted on top of the scanning box and is connected with the drift tube by the ring flange two, and the top end of the drift tube is connected with the accelerating tube by the ring flange one. It characterized in that the accelerating tube and the scanning box are located and fixed by bracket, the ring flange two and the ring flange one are connected with each other by welding mode with featheredge flange, the accelerating tube adopts the standing wave acceleration structure equipped with exhaust orifice. Compared with current technology, the invention improves the stability and tightness of the accelerator and makes whole volume smaller; it can discharge air in high-temperature discharging furnace directly and leave out the endless vacuum exhaust cause of accelerating tube. It possesses engineering practicability.

The invention relates to a multidimensional joint nonuniformity correction method for an infrared imaging system, which belongs to the technical field of infrared imaging. Multidimensional informationis obtained through different temperature and different integration time of a reference radiation source, a correction parameter is calculated for nonuniformity adaptive correction for working of theinfrared imaging system under different integration time. An image through actual target acquisition is subjected to base image deduction before correction, offset errors are eliminated automaticallyin real time, the imaging system does not need to use devices such as a shutter and a shield, and the nonuniformity can be effectively corrected under different environment and bias voltage conditions. The method requires less storage capacity and less computation, and is easy to be implemented by hardware. Moreover, only a set of correction parameters can be used to complete correction on targetimaging with different integration time, which has engineering practicability.

The invention relates to a design method for a linear active-disturbance-rejection controller based on a prediction tracking differentiator, and the method comprises the following steps: a, designingthe prediction tracking differentiator, and performing the filtering of an obtained state signal through the prediction tracking differentiator to obtain a filter value; b, obtaining an extension state of the system through an extension state observer based on the filter value; c, correcting a PD control law through the extension state to obtain the linear active-disturbance-rejection controller.The method provided by the invention can inhibit the impact on the closed-loop characteristics of a system from the noise pollution, can effectively inhibit the phase delay phenomenon caused by the filtering, solves a problem of noise pollution amplification caused by a high-gain observer, and improves the robustness of a controller. The method improves the robustness of the active-disturbance-rejection controller to the high-frequency noise, and has the engineering practicality.

The invention discloses a method for improving star sensor-gyro federated filtering. The method comprises the following steps: step 1, constructing an extended Kalman filter and implementing an extended Kalman filtering algorithm; step 2, determining the jumping time of a measured quaternion value q<s>, i.e., an input of the xtended Kalman filtering algorithm, wherein the scalar part of the measured quaternion value is smaller than a threshold, and the current beat and the previous beat of a vector part with a greatest absolute value in the measured quaternion value have opposite signs; step 3, resetting a reference quaternion value q<^><R> at the jumping time so as to obtain a reference quaternion value fitting with the measured quaternion value at the jumping time; and step 4, continuing implementation of the extended Kalman filtering algorithm by using the reset q<^><R>. According to the invention, the reference quaternion value at the jumping time is reset so as to overcome the problem that an estimated quaternion value needs convergence anew caused by jumping of the measured quaternion value, so stable continuous high-precision attitude information is provided for an attitude determination system; and the method is simple in the algorithm, can be easily implemented by spaceborne software and has high reliability.

The invention provides a method and system for determining low-voltage line loss of a transformer area and operation errors of electric energy meters. According to the method and the system, based onthe tree topology of the transformer area and a total score mathematic relation, a transformer area low-voltage line loss model is built by using the Kirchhoff law, and an electric energy meter operation error mathematic model is built according to the energy conservation law; collected total meter power supply data and sub-meter freezing power consumption data are substituted into the operation error mathematical model to obtain a group of equations; the equations are solved to determine the equivalent resistance of each branch of the transformer area and the calculation error of each metering point; and the loss of a low-voltage line and the operation error of each metering point are determined according to the branch equivalent resistance and the calculation errors. According to the method and the system, the accurate values of the low-voltage line loss and the fixed loss of the transformer area can be obtained by utilizing big data and only knowing the total meter and the sub-meterof the transformer area, the power supply quantity of the total meter of the transformer area and the freezing power consumption of the sub-meters without knowing the real power topology of the transformer area, so operation is simple, and efficiency is extremely high.

The invention provides a nuclear power plant reactor core damage evaluation method. The method comprises the following steps of: in an accident, if a state parameter monitoring system of a power plantis located in an effective healthy state, taking a result obtained through evaluating a reactor core damage by adoption of a temperature at the outlet of a reactor core, a radiation level in a containment, a temperature of a hot section of a main loop, a water level of a pressure container and a response of a source range detector as a reference for damage evaluation; or if the whole power plantis de-energized or the state parameter monitoring system loses efficacy, carrying out monitoring by adoption of an off-site radiation level, and taking a result obtained through evaluating the reactorcore damage by combining a source item inversion technology as the reference for damage evaluation. According to the nuclear power plant reactor core damage evaluation method provided by the invention, an advanced method which is capable of providing round-the-clock effective reactor core damage evaluation under any state of the power plant is created on the basis of a comprehensive and mature reactor core damage evaluation way.

The invention discloses an agglomerate fog monitoring method based on big data. A big data technology is used to process and analyze massive video data (the data of multiple cameras in continuous timeperiods), and the agglomerate fog monitoring method based on a time sequence is established. Massive image information and the change rule of background pixels when agglomerate fog bursts are fully used so that a monitoring result is accurate and engineering practicality is possessed.

The invention discloses a cascade hydropower station peak regulating method based on a random continuous optimization strategy. The cascade hydropower station peak regulating method comprises the following steps: (1) generating an initial solution, selecting water levels in front of a dam from hydropower stations from upstream to downstream as discrete state quantities; taking a minimum power grid residual load mean square error as a target to carry out single reservoir peak regulating optimization calculation; (2) randomly and continuously carrying out optimized search step by step; and (3) updating iteration judgment: if reaching the tail of a time period, finishing a regulating process when a stopping condition of a successive optimization algorithm is reached, and outputting a final result, if the stopping condition of the successive optimization algorithm is not reached, setting a time period number to be a starting time period and turning into the step (2) to carry out the next time of iteration optimization, and if not reaching the tail of the time period, adding one to the time period number and turning into the step (2) to carry out two-phase regulation of the next time period. With the adoption of a constraint handling method provided by the invention, complicated cascade hydropower station coupling operation constraint of the cascade hydropower stations can be completely decoupled, and a constraint handling process of the algorithm is simplified; and a decision-making variable dimension is reduced, a reasonable optimization space is found and the method is suitable for solving a peak regulating problem of a large-scale cascade hydropower station group.

Disclosed is an on-satellite configuration layout determining method of multi-field-of-view star sensors. Firstly, all possible optical axis orientations of the three star sensors are traversed according to a satellite Pro / E three-dimensional model, and then feasible solution sets which meet the requirement of a star stray radiation suppression angle of the star sensors are obtained; then feasible solution sets meeting the requirements of a sunlight suppression angle and a geogas light suppression angle at a zero attitude are obtained according to the feasible solution sets meeting the requirement of the star stray radiation suppression angle of the star sensors; and finally feasible solution sets meeting the requirements of the sunlight suppression angle and the geogas light suppression angle at a non-zero attitude are figured out, and therefore ultimate on-satellite configuration layout orientations of the multi-field-of-view star sensors are finished. Compared with the prior art, the method has the engineering practicability, is better than manual experience trial assembly in directivity and effectiveness and is excellent in practical effect.

The invention relates to a method for extracting a nonlinear behavior model of a radio-frequency microwave two-port device, which comprises the following steps of: measuring the radio-frequency microwave two-port device under different excitation powers by using a conventional vector network analyzer, and then converting a specific value S parameter of a power-related reflected wave and an incident wave obtained by measurement; and selecting the forward transmission coefficient S21 under the minimum excitation power as a reference value, performing normalization processing on the amplitude and phase of the S21 under different excitation powers, and generating a behavior model capable of representing the nonlinear characteristic of the tested piece. The model extraction method provided by the invention directly converts an actual measurement result, and has compatibility for vector network analyzers of different models. When the method provided by the invention is used for extracting the nonlinear behavior model of the two-port tested piece, only a vector network analyzer and a small number of accessories need to be used, and special test equipment does not need to be additionally purchased, so that the modeling cost can be reduced.

The invention discloses a multi-power-grid-oriented hydropower station short period peak load regulation characteristic value searching method, and belongs to the technical field of hydroelectric energy optimized operation and electrical power system electricity generation optimized dispatching. With the maximal and minimal values of each electricity receiving power grid residual load as a characteristic value, the output at the period of time of the characteristic value is adjusted gradually in a characteristic value limit range, and the electricity receiving process of each power grid is corrected gradually in order to meet the hydropower station operation limit requirement. Multi-power-grid short period peak regulation is divided into two scheduling modes of a non-abandoned water mode and an abandoned water mode according to available water quantity of a scheduling period. Under the non-abandoned water mode, based on the consideration of power grid typical load characteristic and peak regulation requirement, under the precondition that a lower course comprehensive water usage demand is met, hydropower station peak regulation capacity gain is exerted as much as possible, more electricity is generated at electricity utilization peak and less electricity is generated at electricity utilization valley; under the abandoned water mode, the hydropower station is in fully loaded running, under the requirement of appointed power grid distribution ratio, with minimal rest load variance as a target, a power grid electricity receiving plan is made by a classical particle swarm optimization algorithm.

A method for consolidating collapsible loess foundation includes laying out water-submerging holes on construction job site, sealing site by seal diaphragm and vacuuming sealed site to let soil be consolidated after is water fully injected in said holes.

The invention belongs to the field of engine rotor performance testing, and particularly relates to a measuring system and method of a torsion angle of rotor blades in an operating state of an engine.The measuring system comprises two or more first sensors, a signal processing and collecting module, a rotating speed sensor and a torsion angle processing module; the two or more first sensors are arranged on the inner ring face of a casing and arranged at the front edge and the tailing edge of the axial position of the same to-be-measured rotor blade; the signal processing and collecting moduleis used for receiving sensor data and converting the data into the blade tip arrival time data of the front edge and the tailing edge of the to-be-measured rotor blade; the rotating speed sensor is used for detecting the rotating speed of the to-be-measured rotor blade; and the torsion angle processing module is used for calculating the torsion angle of the rotor blades. According to the measuring system and method of the torsion angle of the rotor blades in the operating state of the engine, on the basis of first-order torsion and measurement thereof, the feasible measuring method, a feasible measuring model and a feasible measuring formula are provided, the measuring points are arranged easily, calculated related parameters are easy to obtain, the measuring system and method are easy toimplement on the engine, and guiding significance is achieved in torsion angle measuring.

The invention discloses a method for real-time simulation of an unstable target motion trail based on B spline fitting. The method for real-time simulation includes the following steps that firstly, an actual measurement underwater sound target motion trail sequence m(n) with the sampling rate being fs is acquired; secondly, actual measurement underwater sound target motion trail sub-sequences are acquired; thirdly, control vertexes for reverse determination of a three-time B spline curve by all the sub-sequences are acquired; fourthly, target motion trails of the sub-sequences in the sampling rate fs are acquired; fifthly, the real-time target motion trails are acquired. According to the method for real-time simulation, curve fitting is conducted on target motion trail data in the actual measurement sampling rate fs through a mathematical method that a smooth parameter curve section approaches a polyline polygon, the target motion trails in the sampling rate fs are simulated, and then the motion trails in which inflection points are probably generated due to the change of a target motion state are smoother.

The invention discloses a self-adaptive action control method of an alternating current contactor and belongs to the technical field of electrical intelligent control. According to the self-adaptive action control method of the alternating current contactor, the fault ride-through capability of a motor can be given to full play, so that the alternating current contactor can realize self-adaptive action according to a fault type, duration time and the magnitude of load torque; off-line calculation and on-line analysis are combined, so that the alternating current contactor under voltage sag canmake a quick response, the production continuity under most voltage sag can be guaranteed, the alternating current contactor under severe voltage sag can trip off the motor in time, and the safe operation of the motor is guaranteed; a motor double-cage rotor model is adopted, changes of rotor parameters along with the rotating speed are considered, and dynamic behaviors of the induction motor inthe stall and acceleration process can be well represented. In the self-adaptive control process, the original structure and functions of the alternating current contactor are not damaged, only simplecapacitor type energy storage delay elements need to be additionally arranged, an economic effect is remarkable, and engineering practicability is achieved.

The invention discloses a reduced-order model-based aerodynamic-heat-structure optimization method and belongs to the field of aerospace. The method comprises the steps of building an aircraft analysis model; building an initial aerodynamic heat reduced-order model; verifying an overall average relative error of the built aerodynamic heat reduced-order model; building an aerodynamic heat reduced-order model meeting a design precision requirement; obtaining a change condition of a structural internal temperature field of an aircraft in a whole ballistic flight process; performing aeroelasticityanalysis considering temperature influence in a whole ballistic trajectory for the aircraft; and by taking aircraft aeroelasticity characteristics obtained by analysis as constraints, optimizing design variables in the aircraft by adopting an optimization algorithm with a global optimization capability, thereby improving comprehensive performance of the hypersonic aircraft. The aerodynamic-heat-structure multidisciplinary optimization design efficiency of the hypersonic aircraft can be improved; the design cost can be reduced; the engineering practicality of the multidisciplinary design optimization method in hypersonic aircraft design can be improved; and the method has the advantage of high universality.

The present invention provides a reservoir water supply scheduling method based on an SEM algorithm. The method comprises the following steps of: the step 1, determining a water supply mode of a hydraulic project; the step 2, determining an initial multi-way water diversion and scheduling process of the hydraulic project; the step 3, searching a feature value: when [Delta]S is not equal to 0, increasing or decreasing water supply according to a certain step length, dividing the [Delta]S into G parts according to a diversion and scheduling water quantity ratio, dividing the G parts to corresponding water receiving users, and recalculating a reservoir total water supply; the step 4, calculating water quantity balance: performing scheduling calculation according to the total water supply process, determining the water level and the discharged volume process of the reservoir in each time period, allowing parameters of each time period to meet constraint conditions, determining whether a calculation end water level Zc is equal to an end water level control value Zg of a scheduling period in a hydropower station or not, if not, turning to a step 5, or else, turning to a step 6; the step5, correcting the end water level until Zc=Zg; and the step 6, according to the diversion and scheduling water quantity ratio requirement and the determined water receiving users, employing the SEM algorithm to perform solution, and taking the globally optimal solution of the SEM algorithm as the diversion and scheduling water process result of each water receiving user.

The invention discloses an SQP (sequence quadratic program) based allocation method for avionics system failure detection rate. The method mainly solves the problems of low failure diagnosis efficiency, long failure recovery time, high test cost and the like caused by unreasonable allocation of failure detection rate indexes in the upgrading and refitting process of an airborne avionics system. The method comprises the following implementation process: firstly, performing structure level dividing on an upgraded and refitted avionics system, and defining the level of testability allocation; secondly, analyzing various factors affecting the testability allocation, solving influence coefficients of the various factors, and obtaining constraint conditions so as to build a model of the avionicssystem failure detection rate allocation problem; finally, performing optimization allocation on failure detection rate indexes of the avionics system with an SQP method. Compared with traditional methods of experience distribution, distribution based on failure rate, weighted distribution and the like, the method has the advantages that the influence of personal subjective factors in the actualtestability distribution of the project is reduced, so that the distribution process is more reasonable and efficient.

The invention belongs to the field of power systems, and particularly relates to a power supply capacity configuration and layout planning method considering large-scale high-proportion new energy. Based on comprehensive analysis of technical and economic characteristics of a multi-energy power system consisting of wind power, photovoltaic power, photo-thermal power, hydropower, thermal power andenergy storage, a power supply planning model is provided based on an evolutionary game theory. The model takes each power supply node as a game main body, accumulates experience through time sequenceproduction simulation, continuously changes behavior rules of the power supply nodes, adjusts installed capacities of various types of power supplies to adapt to the environment, finally solves an optimal layout scheme of various power supply capacities of each node, and verifies that the proposed method has a remarkable effect on improvement of new energy consumption, so the efficient operationof a power system is ensured.

The invention provides a data-driven power distribution network distributed new energy consumption capability assessment method. The method comprises the following steps: 1) recording data accumulated by actual production and operation of a power system; 2) establishing a maximum new energy consumption capability evaluation model of the power distribution network; 3) calculating a maximum new energy output value as a label set by solving the model, and further forming a complete data set; 4) establishing a graph convolutional neural network model for power distribution network consumption capability evaluation, processing the data set in the step 3), and training the deep network by using the data set; and 5) quantizing a to-be-solved power grid operation mode, quickly and accurately calculating a maximum new energy output value through the trained network, and further calculating to obtain an annual power distribution network new energy output duration curve and the maximum new energy consumption electric quantity of the system. Compared with a traditional time sequence simulation method, the method has the advantages that the calculation efficiency is improved, and application innovation and engineering practicability are achieved.

The invention provides a multi-channel feature based high speed related filtering object tracking method. The method includes (1) constructing an object feature model through weight fusion of three channels of an HOG feature, a CN feature and an angular point feature so as to perform long term stable tracking on the object; (2) utilizing the HOG feature to overcome a problem of influence on objectfeature extraction due to luminance change; (3) utilizing the CN feature to overcome a problem of texture information rapid change due to dimension change of the object; (4) utilizing the angular point feature to overcome a problem of object tracking failure due to partial shielding of the object; (5) converting each feature to frequency domain through Fourier transform for relevance calculationand convolution operation is converted to point multiplication operation so as to reduce the calculation volume and accelerate the calculation speed; (6) adopting the MPR (Maximal Peak Ratio) to judgewhether an weight coefficient of the object feature model requires update or not and adjusting the leading role of a specific feature channel in a specific environment factor in a self-adaptive manner; (7) utilizing online learning to select a fixed learning factor to update the weight coefficient and implementing and the object model updating process.

The invention discloses a power transmission line harmonic parameter estimation method for power grid harmonic analysis. The method comprises the steps that a power transmission line is monitored to obtain harmonic voltage effective values, harmonic active power and harmonic reactive power at the two ends; based on a power transmission line distribution parameter model, a relational expression between power transmission line harmonic parameters and the harmonic voltage effective values, the harmonic active power and the harmonic reactive power at the two ends is established; a plurality of point data is selected from each data segment, and an equation set is obtained by using multi-point estimation; and the equation set is solved through a nonlinear optimization algorithm to obtain harmonic parameters of the power transmission line. More accurate harmonic modeling is carried out by utilizing the harmonic parameters obtained by the method, and the method has significance in harmonic power flow calculation, state estimation, harmonic source positioning and the like of the power grid.