94 results about "Hazard analysis" patented technology

The invention relates to the technical field of path planning, in particular to a water conservancy unmanned aerial vehicle inspection process control system and method based on big data analysis. Performing path risk assessment based on a water surface anomaly prediction result and a weather anomaly analysis result, performing unmanned aerial vehicle flight anomaly analysis based on unmanned aerial vehicle operation condition data and a historical path risk analysis result, and performing path planning selection. According to the method, the path danger is quantitatively evaluated based on the evolution condition of the weather and the wave condition on the path in the flight process of the unmanned aerial vehicle, the safety of path selection is improved, the influence of the future wind power condition on the wave danger is analyzed in the evaluation process of the wave condition, and the evaluation accuracy is improved. Therefore, the future wave danger is quantitatively predicted and evaluated, and the evaluation accuracy of the path danger is improved.

The invention provides a potential safety hazard analysis method and system based on underground cavern three-dimensional geological intelligent modeling, and the method comprises the steps: firstly, based on underground cavern three-dimensional model data, cutting the underground cavern three-dimensional model data into a plurality of sub-models according to a geological condition segmentation rule, and enabling the geological condition segmentation rule to dynamically adjust the cutting spacing according to the gradient change characteristics of a rock stratum; performing gradient analysis on the longitudinal and axial rock stratum attributes of each sub-model to generate rock stratum transition characteristic data containing the adjacent rock stratum attribute change rate and the transition area space distribution, and dynamically identifying the surrounding rock type of the sub-model according to the rock stratum transition characteristic data; and mapping and matching the surrounding rock identification result with a preset protected object space coordinate, collecting a sub-model geological parameter set in real time, finally triggering a safety early warning signal according to a geological parameter set numerical value interval, and generating an emergency disposal scheme set associated with the safety early warning signal, so that the potential safety hazard of the underground cavern can be effectively analyzed.

The invention belongs to but not limited to the technical field of safety control, and particularly relates to a quantitative risk assessment method and system for a petroleum refining device protection layer, and the method comprises the steps: S1, carrying out the harmfulness analysis of a system, and forming a system HAZOP analysis table; s2, according to a system HAZOP analysis table, fusing system process knowledge such as operation regulations, and constructing a safety knowledge graph of the system; s3, comprehensively considering the influence of the individual background of the expert and the evaluation process on the weight of the expert, determining a weight coefficient, and assisting in making a quantitative risk evaluation rule; and S4, according to the structural characteristics of the security knowledge graph, considering the path risk propagation influence and the reduction effect of the protection layer on the influence, performing rule supplementation on the RPN calculation method to obtain a quantitative risk assessment rule, and completing system risk assessment based on the rule.

The invention discloses an intelligent management system for coal mine production safety, and relates to the technical field of safety management. The invention comprises: a coal mine inspection module, a coal mine gas hazard analysis module, a coal mine flood early warning module, a coal mine safety processing module and a local database. The invention monitors the inside of the coal mine by using a drone, and uses an infrared range-finding sensor to map the inside of the coal mine, so as to accurately monitor the change of mine pressure, improve the accuracy of coal mine pressure monitoring, analyze the dust concentration and gas concentration in the coal mine according to the mine pressure and the physical condition of the staff, so as to improve the safety of the coal mine working environment, analyze the sudden threat coefficient of floods of each monitoring point belonging to the coal mine separately, merge the threatening monitoring points into a monitoring section, and estimate the monitoring point that is most likely to be a leak in the monitoring section, so as to ensure that maintenance personnel can quickly locate the leak in the coal mine, and improve the production efficiency of the coal mine.

The invention discloses an ancient site flood disaster risk assessment method coupling quantitative simulation and qualitative analysis, and the method comprises the steps: collecting related data of an ancient site flood disaster, and carrying out the preprocessing of the related data; risk analysis and vulnerability analysis are carried out on the related data, and the risk analysis comprises the steps that according to the fusion environment data and the rainfall data, a hydrodynamic model is adopted to set a rainfall scene, numerical simulation is carried out to obtain rainfall data, and a disaster is evaluated to obtain a quantitative risk level; the vulnerability analysis comprises the following steps: carrying out vulnerability grade division according to the stability, value loss and repairable ability of cultural relics in a disaster scene to obtain a qualitative vulnerability grade; and organically coupling the quantitative risk level and the qualitative vulnerability level to obtain an ancient site flood disaster risk level map. The method not only improves the accuracy of ancient site flood disaster risk assessment, but also has good interpretability, and can be directly used in an ancient site flood disaster risk assessment system.

The invention discloses a vehicle safety fusion hazard analysis method and device, electronic equipment and a medium, and the method comprises the steps: carrying out the hazard and operability analysis of each vehicle function operation scene, and obtaining a hazard analysis result corresponding to each safety analysis type in each vehicle function operation scene; performing hazard fusion analysis on the hazard analysis result corresponding to each safety analysis type in each vehicle function operation scene to obtain a hazard fusion analysis result corresponding to each vehicle function operation scene, and performing hazard analysis and risk assessment according to the hazard fusion analysis result of each vehicle function operation scene to obtain a risk assessment result corresponding to each vehicle function operation scene. And determining a hazard triggering condition corresponding to each vehicle function operation scene and a hazard processing scheme corresponding to the hazard triggering condition. The method can achieve vehicle safety fusion hazard analysis, improves the comprehensiveness of vehicle safety hazard analysis, improves the reliability and safety of an automobile intelligent driving system, and can be widely applied to the technical field of automobiles.

The invention belongs to the technical field of reliability analysis of aviation products, and particularly relates to a method for determining the service life of an aviation mechanical-electrical-hydraulic product based on performance model simulation, which comprises the following steps: S1, collecting information of the aviation mechanical-electrical-hydraulic product, and completing failure mechanism analysis of the aviation mechanical-electrical-hydraulic product according to product failure mode, influence and criticality analysis; s2, determining a load profile of each lowest agreed level according to the one-dimensional performance control model of the aviation electromechanical hydraulic product, and carrying out stress analysis on the aviation electromechanical hydraulic product; s3, the durability index of the aviation electromechanical liquid product is analyzed through a linear cumulative damage method, and the wear-type failure time is obtained; and S4, determining a weak link of the aviation electromechanical hydraulic product according to the lowest agreed level with the shortest service life in the aviation electromechanical hydraulic product, and obtaining the service life of the aviation electromechanical hydraulic product. According to the method, through full-life periodic performance simulation, load information and boundary conditions of the lowest agreed level of the electromechanical hydraulic product are obtained, and stress analysis and loss type failure time calculation are achieved.

The invention provides an intelligent launching pad management system based on AI visual auxiliary supervision. The system carries out target identification through a YOLO model, carries out behavior sequence analysis in combination with an LSTM model, and carries out cross-modal dynamic feature fusion through spatio-temporal feature alignment, time sequence and spatial feature enhancement and a graph convolution network and graph attention mechanism to generate globally optimized feature representation. And further utilizing a knowledge reasoning engine to combine with the case database and the equipment knowledge graph to generate an intelligent emergency processing scheme. And finally, generating a preliminary potential safety hazard analysis report based on a Transform technology, and performing semantic calibration in combination with the central control module and the domain knowledge base to generate an accurate and normalized alarm analysis report. The system also has the functions of adaptive algorithm optimization, multi-modal data fusion processing and real-time alarm and feedback, realizes the intelligent and automatic management of the launching pad, improves the safety supervision efficiency and fault processing capability, and effectively improves the intelligent level of the safety management of the launching pad.

The invention discloses a coal mine underground unmanned aerial vehicle autonomous inspection method, and relates to the technical field of image analysis, and the method comprises the steps: S1, importing a to-be-inspected coal mine internal trend map into an intelligent inspection terminal of an unmanned aerial vehicle; and S2, the intelligent inspection terminal performs real-time image acquisition on the interior of the coal mine well according to the to-be-inspected coal mine well interior trend graph. The method comprises the following steps: firstly, carrying out feature analysis on an internal color image and an internal depth image of a coal mine well, and determining obstacle position information, obstacle actual shape information and obstacle actual size information; the method comprises the following steps: acquiring obstacle position information, obstacle actual shape information and obstacle actual size information, performing risk degree analysis on the obstacle position information, the obstacle actual shape information and the obstacle actual size information to determine the obstacle risk level, and finally performing distance analysis on the obstacle and the surrounding well wall of the coal mine well to determine that the unmanned aerial vehicle can cross the obstacle to perform subsequent inspection, thereby shortening the inspection period of the coal mine well, and meanwhile, improving the inspection efficiency. And the potential safety hazard of the inspection personnel is reduced to a certain extent.

A method for selecting near-source strong motion records considering fling-step effects includes the following steps: introducing a permanent displacement as a conditional parameter into ground motion selection based on generalized conditional intensity measures, and giving a target permanent displacement by extended probabilistic fault displacement hazard analysis; characterizing a frequency content component of a ground motion with a spectral displacement instead of spectral acceleration in a target ground motion intensity measure set; further calculating an empirical correlation coefficient suitable for near-source strong motion records with permanent displacement, constructing a corresponding target conditional distribution, and finally obtaining a data set of near-source strong motion records with permanent displacement most consistent with a target conditional distribution by optimizing selection from a near-source strong motion database. A reasonable ground motion selection method is provided for seismic response analysis of near-source engineering structures under a strong motion-fault dislocation coupled effect.

The invention belongs to the technical field of multi-level RCM, and discloses a multi-level RCM analysis and reliability structure construction method and a related device. The multi-level RCM analysis and reliability structure construction method comprises the following steps: establishing a unit system function model after constructing a unit system database, performing multi-level classification on equipment of a unit system in combination with a fuzzy clustering algorithm, and then determining levels and weights of various types of equipment in the unit system function model, analyzing a failure mode of each type of equipment after multi-level classification through a harmfulness analysis method in combination with a fault tree analysis technology, establishing a correlation model between the equipment failure mode and a unit system function, determining an influence weight of the equipment failure mode on the reliability of the unit system, and establishing a unit system reliability model; inputting the unit system database into the unit system reliability model to obtain a unit system maintenance strategy library; the analysis result accuracy and the system reliability can be greatly improved.

A method for automated monitoring of a passenger transport system with a monitoring system. The monitoring system has a hazard analysis module and a motion-sensing module. The motion-sensing module is configured to capture real motion sequence recordings. The method comprises: receiving real motion sequence recordings and data of a digital double of the passenger transport system in the hazard analysis module, wherein the data comprise information relating to physical properties of the passenger transport system, which allow determination of a visual appearance of the passenger transport system; determining dynamic objects information on the passenger transport system with the hazard analysis module based on the received recordings and data; determining a current hazardous situation on the passenger transport system with the hazard analysis module based on an analysis of the determined dynamic objects; and outputting a warning with the hazard analysis module based on the current hazardous situation.

The disclosure relates to a method for monitoring the travel operation of a person-transporting installation with a monitoring system. The at least one motion-sensing module transmits its motion sequence images to an interaction module and to a hazard analysis module; the motion sequence images are displayed on a screen of the interaction module and, at the same time, in the hazard analysis module the motion sequence images are examined for critical situations with analysis algorithms. As soon as a critical situation is recognized, a warning signal is sent to the interaction module. As a result of the warning signal, the interaction module visually and / or acoustically emphasizes the corresponding motion sequence image on the screen and generates a confirmation input field. The travel operation of the person-transporting installation can be influenced based on a manual tapping on the confirmation input field.

The invention provides a safety early warning method, system and equipment for a galvanizing process production line and a medium. The safety early warning method comprises the following steps: acquiring multi-source data of the galvanizing process production line; performing multi-modal analysis and vectorization processing on the multi-source data, constructing a galvanizing process production line knowledge graph, and storing the knowledge graph to an AI data lake; reading a knowledge graph from an AI data lake to adjust the general large model; transversely splitting the galvanization process into a plurality of process thinking chain nodes according to a process sequence; longitudinally splitting each process thinking chain node into an analysis node and an auxiliary node executed by the potential safety hazard analysis model to form a tree structure thinking chain; traversing the tree structure thinking chain based on a preset sequence, and analyzing the potential safety hazard of each process; and summarizing the potential safety hazard analysis results of all the processes, and generating a potential safety hazard report and rectification measures for safety early warning. The method helps managers to master potential safety hazards possibly existing after operation of a production line and corresponding rectification measures in the galvanization industry.

Systems and methods is provided for road hazard analysis. The method includes obtaining sensor data of a road environment including a road and observable surroundings, and applying labels to the sensor data. The method further includes training a first neural network model to identify road hazards, training a second neural network model to identify faded lane markings, and training a third neural network model to identify overhanging trees and blocking foliage. The method further includes implementing the trained neural network models to detect road hazards in a real road setting.

The application discloses a kind of control method and system of industrial park energy storage device, it is related to energy storage device control technical field.This application is based on production plan and real-time electricity price, dynamically senses load demand fluctuation, and distributes distribution unit accordingly dynamic adjustment;Further through real-time current signal analysis, actively identify potential hazards, guarantee the reliability of distribution unit hazard analysis result;While comprehensive multidimensional data assesses the overall health status of distribution unit, provides basis for maintenance and replacement decision, solves the limitations existing in current energy storage device control feasibility analysis;Once hidden danger or state anomaly occurs, immediately give early warning, improve system security and reliability;From demand calculation, resource matching and operation monitoring to abnormal early warning form complete closed loop, realize the intelligentization, safety and high efficiency management of energy storage device control.

The invention discloses a coal mine goaf unmanned aerial vehicle detection system and method, relates to the technical field of unmanned aerial vehicle detection, solves the problem that drilling detection can only be carried out at a known goaf boundary during current coal mine goaf detection, and comprises an image analysis module, a gas detection module, a settlement analysis module and a hazard analysis module, the image analysis module is used for analyzing a coal mine image of a coal mine area to obtain a crack influence area and latitude and longitude information of the crack influence area, and the gas detection module is used for analyzing real-time gas concentration data of the crack influence area. The settlement analysis module is used for analyzing the ground surface settlement amount of the suspected goaf area to obtain the average settlement amount of the goaf area, the hazard analysis module is used for analyzing the hazard level of the goaf area, and intelligent detection of the coal mine goaf and intelligent analysis of the hazard condition of the coal mine goaf are achieved.

This invention relates to the field of geological hazard analysis technology, and particularly to a geological hazard early warning method based on active detection and spectral response variation. The method includes: deploying active signal excitation devices and signal receiving sensors in the monitoring area to apply active detection signals to the geological body and collect response signals; filtering and adaptive time window segmentation of the response signals to obtain stable-period spectral data; establishing a benchmark spectral model through Fourier transform and phase spectrum analysis; periodically transmitting active signals and collecting real-time responses, calculating real-time spectral characteristic parameters, and comparing them with the benchmark spectral model to obtain spectral variability; determining an early warning threshold using a decision tree model based on historical monitoring data; and calculating the geological hazard risk level and outputting early warning information when the real-time spectral variability exceeds the threshold, combined with environmental variables.

The invention discloses an energy storage system hazard analysis method and system based on full-link fault sorting, and relates to the technical field of energy storage systems, and the method comprises the steps: defining a hazard scene of an energy storage system; establishing a safety control system of the energy storage system; taking a safety control loop of the whole link of the energy storage system as an object, performing fault sorting on the safety control system, and identifying a problem control behavior of the safety control system; and determining an energy storage system hazard scene corresponding to the problem control behavior of the safety control system. According to the method, key failure events can be identified, and harmful events possibly caused by unsafe fault protection decisions when the failure events occur can be analyzed and obtained from the perspective of component interaction. Meanwhile, safety function classification is carried out on all the components, sorting is carried out from the whole link based on the interaction relation, potential safety hazards still existing in a complex system can be avoided, and the possibility of accidents caused by decision errors is relieved from the mechanism.

The invention discloses a vehicle hazard analysis and risk assessment method, device and equipment and a vehicle, and relates to the technical field of vehicles. The whole vehicle hazard analysis and risk assessment method comprises the following steps: obtaining function case information of a whole vehicle; performing security correlation analysis on the function case information to obtain function case security indication information; if the function case safety indication information indicates that the function case information is related to the safety of the whole vehicle, associating the function case information with a failure mode of the whole vehicle to obtain function abnormal information; then, performing security correlation analysis on the functional abnormality information to obtain functional abnormality security indication information; and if the functional abnormity safety indication information indicates that the functional abnormity information is related to the safety of the whole vehicle, performing hazard analysis and risk assessment on the whole vehicle based on the functional abnormity information. According to the embodiment of the invention, the analysis and evaluation efficiency of vehicle hazard analysis and risk evaluation can be improved.

The invention discloses an unexpected electric braking fault control method and related equipment, and the method comprises the steps: determining a risk level and a fault cause corresponding to an unexpected electric braking fault of a vehicle, the unexpected electric braking fault being used for representing unexpected deceleration exceeding a quantitative safety boundary generated by the abnormal electric braking function of the vehicle, and determining the risk level and the fault cause corresponding to the unexpected electric braking fault; the quantitative safety boundary is a threshold value of unexpected deceleration and duration related to each risk level, the risk level is determined based on hazard analysis and risk assessment, and the fault cause is obtained through analysis and tracing of an architecture-level fault tree; safety requirements are determined based on the risk level and the fault reason, and the safety requirements comprise generation control of an electric braking request, execution process monitoring of the electric braking request and management and degradation when an unexpected electric braking fault occurs; an actual execution electric braking force of the vehicle is configured based on the safety demand to limit an unexpected electric braking force within a quantified safety boundary.

The invention relates to the technical field of cable management, in particular to a thermal insulation type fire-resistant cable potential safety hazard analysis sniffing method and system.The method comprises the steps that in the cable manufacturing stage, a memory metal wire is embedded in a protection sleeve on the outermost layer of a cable; constructing a cable distribution model according to the cable distribution information; real coordinates are configured for the cable distribution model, after the real coordinates are configured, the cable distribution model is amplified, and a hidden danger sniffing path is planned by applying the amplified cable distribution model; a cable surface wide image is acquired based on unmanned aerial vehicle aerial photographing equipment, and an acquisition period is synchronously set and applied; according to the invention, the memory metal wire is embedded into the outermost protection sleeve of the cable, the operation heating condition of the cable is represented, and the unmanned aerial vehicle aerial photography equipment is further matched to collect the cable surface image, so that the position of the cable surface where potential safety hazards easily exist is analyzed based on continuous cable surface image collection; and reference is provided for cable management users.

The invention relates to the field of clinical nursing equipment, in particular to a clinical nursing potential safety hazard analysis and early warning device which comprises a storage supporting box, a fixing plate is fixedly connected to the rear end of the storage supporting box, and an overall fixing supporting piece is fixedly connected to the outer side of the fixing plate through bolts. The front end of the overall fixing supporting piece is connected with a plurality of sets of hanging storage assemblies, the interior of the storage supporting box is connected with an article storage assembly, and the front end of the storage supporting box is connected with an infusion monitoring assembly. By using the infusion monitoring assembly, the situation of liquid medicine is monitored in real time, and air embolism caused by air entering blood vessels is avoided; the monitoring watch is arranged on the wrist of a patient in a sleeving mode, the body temperature, the blood pressure and the heart rate of the patient are monitored in real time, and potential safety hazards can be analyzed and early warned in time; through the design that the limiting disc is detachably connected to the outer side of the mounting block, the patient can conveniently move, and the use flexibility of the patient is improved.

The present application relates to the technical field of local structure damage detection, and particularly relates to a local structure hazard analysis method using digital twinning. The method acquires measured strain signals and vehicle parameters when a standard vehicle passes over a bridge, and extracts a normalized measured feature vector. At the same time, an isomorphic simulation feature vector is generated based on the vehicle parameters and a finite element model. An optimal transmission coupling matrix between the two is calculated using the Sinkhorn algorithm, and a distribution pattern transmission cost and an adaptive sparse weight are obtained, solving the recognition error caused by the phase shift in the waveform space. By minimizing the transmission cost and applying sparse constraints, the equivalent cross-section reduction coefficient of each unit is inverted, and the precise positioning of local stiffness damage is realized. Finally, the model material parameters are updated synchronously, and the load bearing capacity reduction rate of the structure is calculated through nonlinear whole-process analysis. The present application can accurately quantify the influence of local damage on the overall safety of the structure under the conditions of unknown vehicle weight and waveform shift.

The invention provides a construction potential safety hazard analysis system and method based on image recognition, and relates to the technical field of potential safety hazard analysis, and the method comprises the steps: obtaining an excavation video of excavated earthwork and a three-dimensional point cloud model of unexcavated earthwork; determining a plurality of initial safety excavation points based on the three-dimensional point cloud model of the unexcavated earthwork; determining a plurality of preliminary excavation lines based on the plurality of initial safe excavation points and the three-dimensional point cloud model of the unexcavated earthwork, wherein each preliminary excavation line passes through each initial safe excavation point; generating a simulation excavation video of each preliminary excavation line based on the preliminary excavation lines, the three-dimensional point cloud model of the unexcavated earthwork and the excavation video of the excavated earthwork; and determining a target excavation line based on the simulated excavation video of each preliminary excavation line. The method can accurately determine the target excavation line of the earthwork excavation operation.

The invention provides a multi-view-angle spatial positioning danger early warning device and method for crane lifting and supporting operation, and relates to the technical field of computer vision. The device comprises a horizontal camera, a vertical camera, a first wireless bridge transmitting end, a second wireless bridge transmitting end, a wireless bridge receiving end, a video server, a video switch, an inference server and an alarm module. A front image and a top image are acquired through a horizontal camera and a vertical camera, and are sent to a reasoning server through a first wireless network bridge sending end, a second wireless network bridge sending end, a wireless network bridge receiving end, a video server and a video switch; and the reasoning server processes the image by adopting a visual method, carries out danger analysis and identification, and controls the alarm module to start and stop according to an analysis result. According to the method and the device, the technical problem of insufficient danger prediction precision caused by a single view angle space error in the prior art is solved, and the technical effect of improving the accuracy and the reliability of danger identification and prediction in the operation process is achieved.

To allow a plurality of management companies for managing a space object flying in space to efficiently perform sharing execution of danger analysis.SOLUTION: Each of space transportation management devices 100 includes all of space transportation management rule information, a space information recorder 101, a danger alarm device 102, and a danger analysis device 103. Further, each of the plurality of space transportation management devices 100 includes all of a danger avoidance behavior support device 104 for displaying role sharing of an avoidance behavior of a space object, a danger avoidance behavior execution plan, a measurement error scrutiny device, and a security device 105 for preventing information falsification. The danger alarm device 102 notifies an approach or a collision of the space object, and even an anybody of a plurality of management companies quickly shares information among related companies with minimal effort in the case of foreseeing danger.SELECTED DRAWING: Figure 11

The invention relates to a monitoring system and method for monitoring a personnel transportation device. The monitoring system comprises at least one hazard analysis module, an interaction module, a control module and at least one motion detection module, which components are connected to one another via a data network. As soon as the hazard analysis module recognizes a critical situation in the motion sequence recording of the motion detection module, the hazard analysis module sends an alarm signal to the interaction module and the control module, wherein the motion sequence recording associated with the alarm signal is reproduced on the display of the interaction module immediately after receipt of the alarm signal and the control module exerts an influence on the operation in the personnel transportation device associated with the alarm signal. By manually operating an input device, the monitoring personnel can revoke the initiated influence on the operation.

The invention relates to the technical field of electric vehicle fire simulation, and discloses an underground parking lot electric vehicle whole vehicle fire simulation and hazard analysis method comprising the following steps: carrying out a thermal runaway test on an electric vehicle power battery monomer to obtain related data; building a three-dimensional geometric model of the underground parking lot and the electric vehicle according to the actual structure size, simplifying a vehicle body of the electric vehicle and reserving combustible parts, restoring the structure of the parking lot and considering the influence of beam columns, and carrying out hierarchical modeling on surrounding vehicles; pyrosim software is used for simulation, multiple parameters are set, and test data are used as boundary conditions to obtain a result; after simulation, based on multi-dimensional analysis of monitoring data, an evaluation model is constructed by using a specific method to quantitatively evaluate fire hazard; the objective of the invention is to solve the technical problem of lack of simulation of multi-vehicle coupling and large-space fire spreading behaviors in the existing simulation multi-focus single-vehicle scene.

The present application relates to the technical field of inspection planning, and particularly relates to a UAV low-altitude inspection planning system and method based on danger analysis, which performs detailed evaluation on the route of the UAV, combines environmental abnormal influence and dangerous area influence, and considers building collision danger, performs multi-dimensional calculation on flight complexity evaluation, flight height danger and building density danger, comprehensively calculates dynamic and static risks, finally, comprehensively obtains global route danger evaluation result by combining building collision danger of each area and risk evaluation result, and selects the route with the minimum danger according to the global route danger evaluation result, so that the whole scheme realizes multi-dimensional and comprehensive risk evaluation, considers various factors such as environment and building, meets relevant standard requirements, and can effectively reduce UAV flight risk.