90 results about "Method of characteristics" patented technology

The invention provides a modeling method of the characteristics of population space-time dynamic moving based on multisource data fusion. The modeling method comprises: A. inputting map data, mobile phone locating data and floating vehicle data into a system and managing data organization according to requirements; B. establishing a spatial analysis model of the characteristics of population moving based on the mobile phone locating data and the floating vehicle data; C. applying the spatial analysis model of the characteristics of the population moving to carry out multisource data fusion of the map data, the mobile phone locating data and the floating vehicle data to obtain integrated information of the characteristics of the population moving; and D. analyzing the characteristics of various population moving according to the integrated information of the characteristics of the population moving and publishing an analyzed result by the geographic information system. The modeling method can acquire data of urban population space-time dynamic distribution and moving characteristics with large data amount, high quality and space-time characteristics, obtain basis of accurate population distribution and population moving characteristics, and provide decision-making supports for urban planning, land use planning, transportation planning and the like.

The invention relates to a web page automatic classification method based on a training set. A classification process is the combination of methods of characteristic selection, characteristic weight value determination, text vector comparison, and the like. The automatic classification method based on a classification system mainly classes a document to be classified into a corresponding sort according to a beforehand established sort model, namely a training set. Along with the development of the multimedia technique, the content forms of web page information are also rich and colorful, and contents not only comprise text information but also comprise much structural information and other form information, such as sound, figures, images, and the like. However, because web pages based on texts still possess larger proportions, the classification based on web page texts still takes the precedence. The method has reliable theoretical support and favorable extensibility and accuracy and is easy to be in butt joint with application interfaces correlative to an operator.

The present invention belongs to the field of computer science and technology, in particular, it relates to a new characteristic vector weight method for text classification. Said invention provides a new weighting method (TF*IWF*DBV). It is characterized by that in TF*IWF method n-th root of DBV and TF can be introduced, the tests show that the adoption of said new method can raise FI measure by 11.8%, and can fully show its effectiveness.

The invention provides an optical fiber vibration identification system based on a phi-OTDR technology and an optical fiber vibration identification method thereof. The monitoring distance of the system is greatly enhanced through a dual-path detection structure; the adaptability of the system for environmental noise changes is enhanced by the method of characteristic threshold dynamic updating, and a vibration event is accurately positioned; background noise in signals can be greatly reduced through spectral subtraction noise reduction under the condition of maintaining the signal characteristic and energy of the vibration signals, and the signal-to-noise ratio of the signals and the sensitivity of system detection can be enhanced; and multi-characteristic parameter mode identification is performed on the vibration signals from the time domain and the wavelet domain so that the influence of other complex time-dependent interference noise can be effectively avoided, the correct rate of vibration event detection and vibration type classification can be enhanced, the false alarm rate of the system can be reduced, the detection performance of a vibration detection system based on the OTDR technology in the actual complex noise environment can be enhanced, and the national major project application requirements in the aspects of boundary safety and long-distance pipeline safety can be met.

The invention provides an asymmetric supersonic velocity spray pipe and a design method thereof. The design method of the supersonic velocity spray pipe comprises the following steps: according to an inlet coordinate and a throat area, determining a subsonic velocity segment curve; according to the subsonic velocity segment curve and a throat radius of curvature, determining a characteristic line in a transonic velocity area; according to one end point of the characteristic line and a corresponding supersonic velocity area outlet end point, determining a first wall surface curve; and according to an initial characteristic line and the Mach number distribution of the first wall surface curve, determining a second wall surface curve by mass conservation with a characteristic line method. With the design method of the asymmetric supersonic velocity spray pipe, concentrated compression wave in the flow field of the asymmetric supersonic velocity spray pipe can be reduced or eliminated, the quality of the flow field of the spray pipe is greatly improved, equipment performance is improved, and research funds can be saved. According to the asymmetric supersonic velocity spray pipe disclosed by the invention, the design method of the asymmetric supersonic velocity spray pipe is adopted.

The invention relates to the field of the identification method, and particularly relates to a personnel reidentification method based on deep learning and distance metric learning. The identificationmethod comprises the steps that (1) a pedestrian target detection method based on the convolutional neural network is adopted to process the video data so as to detect the pedestrian target in the video; (2) the initial characteristics of the pedestrian target are coded by using an unsupervised RBM network through the bottom-up mode so as to obtain a visual dictionary having sparsity and selectivity; (3) supervised fine adjustment is performed on the initial visual dictionary by using error back propagation so as to obtain the new image expression mode of the video image, i.e. the image deeplearning representation vector; and (4) the metric space closer to the real semantics is acquired by using the distance metric learning method of characteristic grouping and characteristic value optimization, and the pedestrian target is identified by using a linear SVM classifier. The essential attributes of the image can be more accurately expressed so as to greatly enhance the accuracy of pedestrian reidentification.

The invention discloses a design method for a three-dimensional internal rotary inlet based on complete flow direction suction, and relates to inlet boundary layer suction. The method comprises the following steps of solving an axial symmetric basic flow field by adopting a characteristic line method according to design requirements; generating a three-dimensional internal rotary inlet compression profile by applying a streamline tracing method; calculating displacement thicknesses of conical sections of different positions of the shoulder of the three-dimensional internal rotary inlet according to a displacement thickness formula; designing a complete flow direction suction opening based on the inlet compression profile and the displacement thicknesses; constructing a new inlet exit shape by the complete flow direction suction opening, and performing unidiameter backward stretching to obtain a three-dimensional internal rotary inlet separation section; and obtaining the three-dimensional internal rotary inlet which is capable of eliminating low-speed and low-energy airflow of a boundary layer completely in a flow direction and does not influence flowing characteristics of high-speed and high-energy airflow in the inlet. The self-opening performance of the three-dimensional internal rotary inlet can be remarkably improved. The low-energy flow of the boundary layer can be completely eliminated and the flowing characteristics in the inlet are not influenced.

The invention relates to a detection system and method of a characteristic substance. The method comprises: step 1, analyzing tested samples by mass spectrometry to obtain mass spectrometric data of each sample point and determining areas of interest of tested samples; step 2, for the substances characterized by the same m / z, respectively calculating the total ion strength of all sample points inside and outside the areas of interest, the mean strength of all sample points inside and outside the areas of interest and / or the spatial aggregation of the substance characterized by m / z inside the areas of interest, and judging whether the substance characterized by m / z is the characteristic substance according to pre-set rules. Researchers can accurately and precisely analyze and detect which substances are specific substances of the samples and which substances are background noises inside the areas of interest, relative contents of all characteristic substances and spatial distribution within the samples.

The invention discloses a mixing spray pipe runner wall face determination method, a mixing spray pipe and a supersonic speed mixing wind tunnel. The mixing spray pipe runner wall face determination method includes following steps: providing a figure of an outlet section of a spray pipe to be determined and determining a circum-circle of the figure; taking the circum-circle as the outlet section of an imaginary round spray pipe, and determining a curve shaped surface of the round spray pipe by using a characteristics method; extracting filament line races of a runner according to the curve shaped surface of the round spray pipe; and determining filament lines in the filament line race corresponding to each point on the figure, wherein the filament lines of all points on the figure form a runner wall face of the spray pipe to be determined. According to the supersonic speed mixing wind tunnel, a three-dimensional mixing flow field is achieved, mixing efficiency is improved, quality of the flow field is comparable to quality of a two-dimensional flow field or an axisymmetric flow field, and a square outer spray pipe and a square experimental section facilitate implementation of observation technology.

The invention discloses a testing method of characteristics of sound vibration and point vibration of a piano sound board and special equipment thereof. The testing method of sound vibration and point vibration comprises the steps of applying the modern technologies, such as magnetostriction, audio measurement, vibration measurement, computer frequency spectrum analysis and the like in the manufacturing process of the piano sound board, utilizing a sound sensor and a vibration sensor for respectively detecting an integral sound vibration signal of the sound board and a point vibration signal of a local area, then analyzing the comprehensive vibration characteristics of the sound board through a computer frequency spectrum system, and further realizing the oriented tuning of the sound board. The method has the advantages of high sensitivity, fast and accurate measurement and strong intuition, and can effectively control the sound of the sound board and provide the scientific method andmeans for objective identification, evaluation and tuning of the acoustic quality of the piano sound board.The special equipment for testing of the characteristics of the sound vibration and the point vibration of the piano sound board mainly comprises an audio sweep signal generator, a magnetostrictive audio transducer, a measurement microphone, an accelerometer, a data acquisition card, professional frequency spectrum analysis software, a computer and the like.

The invention relates to a method for solving the aerodynamic effect of a long tunnel or a tunnel group. The method comprises the following steps: the method of one-dimensional characteristic is adopted to simulate the aerodynamic effect in a tunnel, a three-dimensional compressible SIMPLE algorithm is adopted to simulate the flow fields at the tunnel exit and between the two adjacent tunnels in the tunnel group; the results of the two algorithms are used for performing data exchange in a place in which the three-dimensional effect can be ignored far away from the tunnel exit, and the air pressure changes of the flow field in the tunnel and the micro-pressure wave at the tunnel exit can be simulated. The efficiency and precision of the calculation of the aerodynamic effect of the long tunnel or the tunnel group can be both considered; and when a high-speed train passes through a tunnel or two trains intersect in the tunnel, the air pressure change amplitude, micro-pressure wave and train wind in the tunnel can be solved.

The invention provides an ultrasonic nonuniform flow nozzle and a design method thereof. The design method for the ultrasonic nonuniform flow nozzle comprises the following steps of: determining a subsonic speed section curve according to the diameter of an inlet of a subsonic speed section; determining a left characteristic line boundary and a right characteristic line boundary of an outlet dependence domain according to Mach number distribution of an outlet and a method of characteristics; determining an initial characteristic line from a throat; determining an equi-flow line of the nonuniform flow nozzle; and determining upper and lower wall curves by using the initial characteristic line and the equi-flow line according to conservation of mass and the method of characteristics. By thedesign method for the ultrasonic nonuniform flow nozzle, the ultrasonic nonuniform flow nozzle can be designed, so that the ultrasonic nonuniform flow nozzle generates the required nonuniform flow, and can continuously eliminate waves, eliminate or reduce centralized compression or expansion waves and ensure the quality of a flow field. According to the ultrasonic nonuniform flow nozzle, the design method for the ultrasonic nonuniform flow nozzle is used.

The invention provides an annular supersonic velocity spray pipe and a design method thereof. The design method for the annular supersonic velocity spray pipe comprises the following steps of: predicting a flow field parameter in a transonic velocity segment area, and extracting an initial characteristic line from the flow field parameter; determining the mach number distribution of a supersonic velocity upright wall of the spray pipe according to design requirements; and determining a supersonic velocity curved wall molded surface of the spray pipe by a characteristic line method according to the initial characteristic line and the mach number distribution of the supersonic velocity upright wall. According to the design method for the annular supersonic velocity spray pipe, compression waves are not concentrated in a flow field of the designed annular supersonic velocity spray pipe, the distribution of the flow field parameter can be optimized according to actual application, and thequality of the flow field of the annular supersonic velocity spray pipe can be greatly improved. According to the annular supersonic velocity spray pipe, the design method for the annular supersonic velocity spray pipe is utilized.

The invention provides a supersonic velocity spray pipe with a shared throat part and a design method of the supersonic velocity spray pipe. The design method of the supersonic velocity spray pipe with the shared throat part comprises the following steps of: determining a subsonic velocity segment curve according to an entrance geometric parameter and the area of the throat part; determining an initial characteristic line emitted from the throat part according to the subsonic velocity segment curve and the maximum divergence angle; determining a curve of a wall surface in the shared segment of the throat part by a characteristic line method according to the initial characteristic line and the mach number of the wall surface in the shared segment of the throat part; and setting the mach number distribution of an axial line in the downstream of the curve on the wall surface in the shared segment of the throat part according to the structural design requirement of the supersonic velocitysegment of the spray pipe, and determining a non-throat part curve in an iteration way by the characteristic line method. By the design method, the parameter of an exit flow field of the spray pipe can be changed by sharing the throat part and exchanging an expansion segment; the processing cost of the throat part of a wind tunnel spray pipe is saved; and the uniformity of the exit flow field of the spray pipe can be ensured and the quality of a wind tunnel flow field can be improved while the throat part is shared. According to the supersonic velocity spray pipe with the shared throat part, the design method of the supersonic velocity spray pipe with the shared throat part is utilized.

The invention discloses a whole-process steam turbine modeling and recognizing method of actual characteristics of parameters changing with working conditions. The method mainly includes: 1), applying a mechanism analyzing method to build a whole-process steam turbine mathematical model in consideration of characteristics of parameters changing with unit running conditions; 2), putting forward an acquiring method of characteristics of key parameters changing with working conditions on the basis of an on-site experiment method; 3), putting forward a steam turbine system model parameter recognizing method based on a particle swarm algorithm-steam turbine system model. A solution is provided for the problem that a steam turbine model under the condition of dynamic stimulation great disturbance of a power system is difficult to reflect actual unit active power response characteristics, power output characteristics of a steam turbine under the condition of great disturbance in whole-process dynamic stimulation of the power system can be stimulated, analysis accuracy of the power system is improved, and safe and stable running of a power grid is guaranteed.

The invention discloses a characteristic description method of a plane geometry plane, which belongs to the basic technique in the pattern recognition field. The method comprises extracting geometric figure outline characteristic points through the mode of simulating an image thinking memory geometric figure, utilizing a characteristic point polar coordinate vector and an additional curvature information as a core to form characteristic information for describing a plane geometry shape. The characteristic description method achieves the correct description to the main characteristics of plane geometry shapes. The calculating method of characteristic information is simple, and calculating quantity is greatly reduced. Characteristic information which is accurately described can be got under the complex circumstance of rotating, translating and scaling.

The invention relates to a reverse method of characteristic parameters of the material of an automobile body stamped steel plate. The method is characterized in that the method comprises the following steps: 1, carrying out area division on the automobile body stamp-formed steel plate; 2, arranging test points on the surface of the stamp-formed steel plate; 3, carrying out tensile tests on the stamp-formed steel plate; 4, establishing a direct problem simulation model of the tensile tests of the stamp-formed steel plate; 5, researching a stress strain curve of the material, and converting an enhancement coefficient K and a hardening exponent n of the reverse material to reverse parameters epsilon p and delta K; 6, comparing test response data with simulation response data to form an objective function, thereby forming a reverse problem model; and 7, optimizing the reverser problem model to acquire the materials parameters K and n of each subarea. The subarea calibration method for describing the stamp-formed body steel plate provided in the invention allows a plurality of areas to be simultaneously tested, and only a less amount of tests to be needed to obtain all the materials parameters of each subarea of the stamped steel pate

The invention discloses a method for dividing and sticking horizons by using X-ray fluorescence spectral characteristics of rock debris. The method comprises the following steps: a, familiarizing stratigraphic characteristics of a working area and division standards of stratum; b, determining a marker bed or an auxiliary marker bed for dividing and sticking horizons; c, determining characteristic elements with different lithologies; d, establishing an XRF (X-ray Fluorescence) section model in the working area; e, performing lithological horizon homing by using XRF spectral characteristics of the rock debris; f, drawing an XRF profile map of the rock debris according to analyzed XRF data of the rock debris at a well section; g, dividing horizons by using a curve characteristic method of characteristic elements with different lithologies, a curve intersection method, an element ratio method and a characteristic element method. According to the method, the conditions that a new drilling process and a new drilling technology limit an existing lithology identification technology and affect drilling fluid materials are avoided, change characteristics of formulation lithology can be objectively and accurately reflected, and microscopic verification and quantification of the lithologic interpretation are realized.

The invention discloses a method for classifying texts. The method comprises: establishing a training text set, generating a first text classifier and a second text classifier; preprocessing to-be-classified texts, using a replacement string to replace text noise in the texts; counting the probability of the replacement string, when the probability is larger than or equal to a filtering threshold value of the first text classifier, the to-be-classified texts being divided into common texts; when the probability is smaller than the filtering threshold value, performing word segmentation on the to-be-classified texts which is preprocessed; establishing a first text representation, a second text representation, and a third text representation of the to-be-classified texts; based on a method of characteristic representation, calculating first text characteristic representation of the first text representation, second text characteristic representation of the second text representation, and third text characteristic representation of the third text representation; and based on the first text characteristic representation, the second text characteristic representation, and the third text characteristic representation, using a second classifier to classify the to-be-classified texts. Also disclosed is a device for classifying texts.

The invention discloses a leakage detection method for a large complex natural gas pipeline network system. The method comprises the steps of 1, performing static simulation to obtain a pressure along a line, flow and initial distribution of temperature in a pipeline; 2, performing online simulation to obtain a pressure along the line, flow and real-time distribution of temperature in the pipeline; 3, performing parameter learning, and proposing a pipeline transient flow state space model-based pipeline parameter real-time online estimation and learning model based on an implicit method and characteristic line method-based gas pipeline dynamic simulation state space model according to a sensitivity analysis theory; and 4, performing leakage detection, calculating a deviation between a simulated pressure and an actually measured pressure of each pressure measurement point, and realizing leakage state identification and diagnosis of the large complex oil and gas pipeline system through correlation analysis of simulated and actually measured pressure deviation distribution. The limitation of sectional detection is broken through, and a leakage detection system for the CPM (Computational Pipeline Monitoring)-based large complex natural gas pipeline system is established.

The present invention concerns a method of providing a wet deposition process with a shutter driven in one axis direction in order to produce a thin film or powder array various in composition on a wafer or in a reactor having apertures as many as the number of sample to be produced. A material having various compositions is transferred to an area predetermined by means of a mask on the wafer to form an array having minimum 16 to about 20000 different compositions by mixture or reaction of at least two or more materials to a minimum in a liquid state. By the process, it is possible to develop materials for various use, e.g., ferroelectrics and inorganic material including fluorescencers, organic polymers, organic metals, ionic solids and metal alloys, more efficiently than by the current experiment. The invention also comprises a method of characteristic analysis of the aforementioned array within a short time, in addition to development of the array having aforementioned various compositions.

The invention discloses an axisymmetric continuous variable Mach spray pipe and a wall determining method thereof. The wall determining method comprises the steps as follows: a rotation axis, a known wall curve, a plug wall curve matched with the known wall curve and the relation curve of the precession distance of a plug mechanism and Mach are determined according to the structural design requirements of the spray pipe; the corresponding wall curve to be obtained is determined by utilizing a characteristic method according to the relation curve of the precession distance of a plug mechanism and Mach when the plug mechanism is in the current position; the position of the plug mechanism on the rotation axis is changed, and the wall curves to be obtained in various sections are determined step by step; in addition, a wall of the axisymmetric continuous variable Mach spray pipe is determined according to the known wall curve, the plug wall curve matched with the known wall curve and the wall curves to be obtained in various sections. By adopting the wall determining method, the fluid field homogeneity degree of the determined axisymmetric continuous variable Mach spray pipe is less than 1 percent, and is increased by one order of magnitude as compared with the traditional technology; and the sensitivity of Mach on the precession distance can be controlled.

The invention discloses a water body modeling method for a shallow water equation model with optimized parameters. According to the method, first, a three-dimensional dynamic coordinate system is constructed, and the shallow water equation model with optimized parameters is derived; when the model is solved, a reverse path tracking method and a method of characteristics are combined to solve an advective item in an equation, a vector projection method and a Fourier transformation method are combined to solve the effect of external acting force on a water body, and therefore a velocity field and a height field are updated; next, boundary check is performed, a boundary truncation method is adopted to process mesh points beyond a boundary; and last, the height field is drawn, and a next time period is processed cyclically. Compared with a traditional shallow water equation, when the contact surface between the water body and a solid is excessively steep, a water body model can be constructed more vividly and accurately, and the velocity of average 24.9 frame / second can be reached in the water body modeling simulation process; compared with a traditional method, the velocity is increased by 29.016%, and real-time simulation can be realized basically.

The invention discloses an on-line fitting method of the characteristic function of a discrete control system based on data mining, and belongs to the technical field of industrial control. The on-line fitting method comprises: step one, obtaining relevant to-be-fitted data and carrying out preprocessing of the data; step two, establishing an artificial neural network model and calculating to obtain a characteristic function curve after training the model; step three, carrying out fold line fitting of the curve obtained in step two to obtain the fold line fitting result of the characteristic function; and step four, according to a new characteristic function curve, carrying out on-line correction of the fitting fold line of the current characteristic function, and ensuring that the correction method can meet the requirements of generating no disturbance during the operation of the discrete control system. The on-line fitting method combines an artificial intelligence method with a numerical calculation method, and has high calculation speed and ideal fitting effects; moreover, the method effectively solves the problems of the characteristic function of the prior discrete control system needs manual calculation and has difficult precise fitting and on-line correction.

The invention discloses a calculation method for an electric field under the crossing area of an alternating current-direct current power transmission line, and relates to the field of the high-voltage power transmission technology and electromagnetic field calculation. The calculation method comprises the following steps that: calculating the nominal electric field of each space joint at a certain moment, initializing space charge density, calculating a synthesis electric field, applying a method of characteristics to update space charge density distribution on an electric field line, calculating space charge density corresponding to different moments on the space node, and carrying out convergence judgment so as to obtain the electric field under the crossing area of the alternating current-direct current power transmission line. The calculation method disclosed by the invention has the characteristics of accurate calculation result and small calculation workload.

The invention provides a slider type Mach-number-variable spray pipe and a wall determination method thereof. The wall determination method of the slider type Mach-number-variable spray pipe comprises according to structural design requirements of the spray pipe, determining partial wall curve as a fixed wall curve, and determining a slider guide rail wall line, a slider wall curve, and a relation curve between a procession distance and an exit Mach number; according to the relation curve between the procession distance and the exit Mach number, using a characteristics method to determine a corresponding wall curve to be solved when the slider is located in a current position; changing the slider position on the slider guide rail to enable a currently designed Mach number value interval to cover all values of the exit Mach number in the relation curve between the procession distance and the exit Mach number, and determining each section of the wall curve to be solved; and determining the wall curve of the spray pipe according to the slider guide rail wall line, a fixed wall curve, the slider wall curve, and each section of the wall curve to be solved. The exit fluid field of the spray pipe determined with the method is high in uniformity, and the exit Mach number can well accord with an exit Mach number given in advance.

Disclosed in the invention is a thin interbed analytical method of a characteristic slice. The method comprises: step 1, extracting a continuous stratum slice from a seismic section; step 2, carrying out pretreatment on the continuous stratum slice; step 3, analyzing the number of sand bodies, a distribution range of the sand bodies, and a superposition relation of the sand bodies by using an in-phase method; step 4, in the distribution range of the certain determined sand body, determining the characteristic slice position of the sand body by using a characteristic slice zero value method and determining the apparent thickness of the sand body; step 5, carrying out traversal processing on each determined sand body; and step 6, calculating actual time thicknesses of all sand bodies by using the apparent thickness of the characteristic slice. The method has the following beneficial effects: the -90-degree seismic continuous slice study is used as the core; only the seismic amplitude information is needed during the analysis process and the sand body can be predicted directly and effectively; and an error caused by involvement of methods of frequency extraction and time frequency analysis and the like can be avoided.

The invention discloses a high-supersonic-speed internal contraction air intake channel gradually changed from the convex shape into the round shape and a design method thereof. According to the high-supersonic-speed internal contraction air intake channel gradually changed from the convex shape into the round shape, the middle of a lip plate of the air intake channel gradually changed from the convex shape into the round shape is provided with an upward protruding part, an inlet of the air intake channel is in the convex shape, and the air intake channel contracts towards an outlet, is gradually changed into the round shape and then is connected with a circular-cross-section equal straight isolation section equal to the air intake channel in area; an internal conical surface controllablein compression surface Mach number, a central body of a uniform flow movable angle variable cross section, and a datum flow field are obtained through a characteristic line method, and reverse streamline tracing is conducted according to the round outlet of the air intake channel; the upward protruding part is additionally arranged at the inlet based on the original rectangle and extends to the central body, accordingly, matching is conducted on the natural outlet area obtained through convex inlet streamline tracing, and a round outlet of which the area is equal to that of the convex inlet isobtained; and after streamline fitting and boundary layer correcting are conducted, the final air intake channel changed from the convex shape into the round shape is obtained. According to the high-supersonic-speed internal contraction air intake channel gradually changed from the convex shape into the round shape and the design method thereof, on the premise that design point shock wave sealingis ensured, starting of the internal contraction air intake channel is substantially improved through the upper convex overflow design measure designed by the streamline tracing technology.

The construction of an internal / external single expansion ramp nozzle (nxSERN), and method of designing the same, is provided. Initial design parameters for primary stream construction are selected and additional parameters are determined by isentropic relations using the selected design parameters and Prandtl-Meyer function. The nozzle throat input and output angles are determined and used to define an initial portion of the nozzle primary stream lower expansion surface. The nozzle primary stream upper expansion surface and an aft portion of the primary stream lower expansion surface are defined using a method of characteristics. Initial and aft portions of the primary stream lower expansion surface are then connected by a straight line to define the primary stream nozzle.