96 results about "Polarizability" patented technology

The invention discloses an SERF atom magnetometer double-axis magnetic field detection method and device based on pulsed magnetic field modulation, relates to the technical field of magnetic field precision measurement, and compresses the action time of a modulation magnetic field additionally applied in the same unit period on a hot atom ensemble by replacing conventional continuous sinusoidal magnetic field modulation with pulsed magnetic field modulation. The pulse magnetic field with the duty ratio of d can reduce the spin exchange relaxation rate to 2d times of that of a conventional method under the same modulation amplitude and frequency, due to the fact that the spin exchange relaxation rate is effectively restrained, the collected polarizability response signal is obviously improved, and the polarizability response signal can be obtained through the pulse magnetic field with the duty ratio of d and the pulse magnetic field with the duty ratio of d. Low-relaxation-rate sensitivity-enhanced double-axis magnetic field measurement under a pulse modulation scheme is realized, the double-axis measurement sensitivity of a miniaturized SERF atom magnetometer is further improved, and the method has great significance in supporting leap-type development of a future array type extremely-weak magnetic imaging system and medical application thereof.

The invention discloses a non-contact geomagnetic coil single-frequency and multi-frequency combined stratum exploration method. The method comprises the following steps that S1, observation parameters are calculated according to exploration requirements; s2, transmitting a single-frequency vertical coil, and moving and scanning a three-component coil; s3, the apparent resistivity and the apparent polarizability of the earth are quickly found through transverse and longitudinal table look-up; s4, quickly identifying a regional stratum, and dividing abnormal sections; s5, abnormal section multi-frequency static data acquisition; s6, multi-frequency data longitudinal underground layering inversion is carried out; and S7, performing combined output of plane quick sweeping and section layering results. According to the method, the precision of the exploration result and the data accuracy are guaranteed, the final exploration result is combined with the plane section and the longitudinal section, the exploration efficiency is guaranteed, the exploration precision can be guaranteed, and the exploration cost is greatly reduced on the premise that the exploration precision is guaranteed.

The invention discloses a deep underground multi-physical field detection method and system, and particularly relates to the technical field of underground detection, and the method comprises the following steps: S1, obtaining seismic wave field data; s2, based on a multi-physics field original data set; s3, according to the basic characteristic parameter set; s4, calling a comprehensive feature fusion matrix; in the deep underground multi-physics field detection process, waveform, wave velocity and amplitude parameters contained in seismic wave field data and electromagnetic field intensity, resistivity and polarizability parameters contained in electromagnetic field data are collected by adopting a monitoring instrument sensor to generate a multi-physics field original data set, so that comprehensive basic data are provided for subsequent processing; based on the data set, the wave velocity and amplitude characteristics of each waveform segment of seismic wave field data and the resistivity and polarizability characteristics of electromagnetic field data are determined, a basic characteristic parameter set is obtained through integration, and key characteristics of different physical fields are accurately grasped.

The invention discloses an SERF atomic gyro signal detection device and method based on an optical heterodyne method, and belongs to the technical field of atomic polarization stability control, after magnetic fields with x-axis frequency and y-axis frequency are applied to atoms in a sensitive unit air chamber, x-axis electron polarizability information under respective modulation frequencies comprises longitudinal polarizability information and longitudinal magnetic field information, and x-axis electron polarizability information and y-axis electron polarizability information under respective modulation frequencies comprise longitudinal polarizability information and longitudinal magnetic field information; the value of the longitudinal polarizability is obtained by resolving information contained in the two, and effective longitudinal polarizability closed-loop control is achieved through a liquid crystal phase delayer power stabilizing rate system. Based on the biaxial magnetic field modulation technology, interference of longitudinal magnetic field fluctuation on polarizability closed-loop control is effectively avoided, and effective polarizability in-situ closed-loop control is achieved.

The invention belongs to the technical field of earth and rockfill dam deep burying disease identification and positioning, and discloses an earth and rockfill dam leakage channel comprehensive detection method and system, and the method comprises the steps: determining the distribution of detection points detected by an electrical method, and collecting the apparent resistivity data and the apparent polarizability data of the detection points; inverting apparent resistivity and apparent polarizability data to obtain a resistivity profile and a polarizability profile, and obtaining a normalized polarizability profile based on the resistivity profile and the polarizability profile; performing stratum zoning on the to-be-detected area based on the section, determining the soil cation exchange capacity and the cementation index of the zoned stratum, and calculating the soil water content and the permeability of the measured section according to the normalized polarizability, the soil cation exchange capacity and the cementation index; and determining an earth and rockfill dam leakage channel according to a water content and permeability judgment mechanism. According to the method, the uncertainty of a single physical property threshold value method is overcome, and the accuracy and precision of the leakage hidden danger of the earth and rockfill dam are improved.

The invention provides a light-induced force microscope system and an application method thereof. The system comprises a first laser, an atomic force microscope probe, a photosensitive detector, a first lock-in amplifier, a control box, piezoelectric ceramic, a second lock-in amplifier, a semiconductor laser, a light path system, a sample table, a piezoelectric scanning tube and a host. According to the light-induced force microscope system, the semiconductor laser is used, sine wave modulation is directly carried out on the semiconductor laser through the oscillator in the lock-in amplifier, and the light-induced force microscope system can accurately measure light force information at a needle point-sample position by using a common silicon needle point probe in the atmosphere. By analyzing the light force information, the light-induced force component can be qualitatively identified, and the rigidity, polarizability and other property information of the material can be reflected. According to the invention, accurate measurement of the light force signal on the surface of the two-dimensional material is realized, and a technology which is economical, simple in structure and convenient to operate is provided for identifying components and defects of the two-dimensional material in electronic devices, optoelectronic elements and sensors.

The present invention provides a full-decay induced polarization (FDIP) detection system and method for water inrush in tunnels, comprising: through instructions for controlling constant-current high-power transmitting module and multi-channel parallel data acquisition and receiving module, receiving observation data and performing inversion by replacing minimum gradient support constraint to traditional smooth constraint, introducing data shape as prior information into inversion objective function, and constructing and solving focusing inversion formula of FDIP detection for water inrush in tunnels based on data shape constraint, to update model parameters; completing multi-source information acquisition of apparent resistivity, polarizability and the like and multi-parameter inversion imaging of zero-frequency resistivity, relaxation time, chargeability and frequency correlation coefficient, effectively reduce electromagnetic interference and improve detection efficiency, greatly meet the urgent requirement for detecting sudden water inrush disaster sources in front of tunnel face under construction, and having strong research significance and application value.

According to the vector vortex beam generation method applied to the SERF magnetic field measurement device, a vector vortex beam is generated according to a light field distribution formula of the vortex beam in combination with a computer-generated holography method and a polarization mode decomposition method, then iterative optimization is carried out on parameters such as the phase, the amplitude and the polarization direction in the beam in a global NSGA-II algorithm and local SPGD algorithm combination mode, and finally the vector vortex beam is generated. And then judging whether the electron steady-state polarizability uniformity meets the expectation or not, if so, ending the optimization, taking the optimized light beam as a pumping light beam to pump alkali metal atoms, and carrying out subsequent magnetic field measurement, and if not, changing parameters and continuing optimization until the electron steady-state polarizability uniformity meets the expectation. Compared with a traditional Gaussian beam, the atomic polarizability in the air chamber is stabilized at a required value, the atomic spin gradient field of the device is effectively inhibited, the differential performance of the device is enhanced, and the sensitivity of the SERF magnetic field measurement device is improved.

The application provides a nonlinear optical effect generation method, relates to the field of optoelectronic technology, and comprises the following steps: fixing and placing a polar ion crystal as a nonlinear medium, the polar ion crystal being a diatomic crystal or a polyatomic crystal with an optical phonon mode; using a modulated terahertz wave to excite a stimulated phonon polariton in the nonlinear medium, so as to enhance the nonlinear efficiency of signal light incident on the nonlinear medium; and adjusting the polarization angle and the incident angle of the signal light and / or the modulated terahertz wave, so as to generate a nonlinear optical effect. The application is based on the characteristics of the interaction between light and matter modulated by the stimulated phonon polariton, and the nonlinear polarizability is greatly improved by using the stimulated phonon polariton, so that the weak light nonlinear effect of most wavelengths of light can be realized efficiently; and the nonlinear optical effect has the advantages of high refresh rate, wide spectral response, low threshold and low power consumption.

The present invention belongs to the field of millimeter wave radiation detection technology, and discloses a complex dielectric constant measurement method and system based on reflection polarization, comprising: keeping the physical temperature of the material to be tested unchanged within the test time [0, t], so that the current incident angle θ i The ambient radiation incident on the surface of the material to be tested is in a changing state, and the current incident angle θ is measured. i Calculate the estimated value of the emission voltage of the material to be tested based on the horizontal polarization output and the vertical polarization output to estimate the current incident angle θ i Reflection polarization RDoP: Change the current incident angle θ i , and repeat the above steps to obtain the incident angles θ1, θ2, ..., θ M The reflection polarization RDoP under each incident angle θ1, θ2, ..., θ M The complex dielectric constant of the material to be measured at the current physical temperature is estimated by using the reflection polarization RDoP under the condition of φ(R)=1. The present invention can reduce the error and complexity of complex dielectric constant measurement.

The application provides a method for homogenizing the polarizability of an atomic sensor based on a singular point super surface, which can effectively improve the spatial uniformity of the pumping light intensity in a micro-nano nuclear magnetic resonance gyroscope, thereby enhancing the uniformity of the atomic polarizability along the propagation direction and improving the average value, so as to reduce the light frequency shift error. While realizing the reflection enhancement of the pumping light, the reflected light has the opposite rotation direction and propagation direction compared with the incident light, and the pumping effect on the alkali metal atoms in the gas chamber is equivalent. Compared with the traditional scheme and the reflection mirror enhancement scheme, the application can significantly improve the detection sensitivity and signal-to-noise ratio of the sensor while keeping the element miniaturized.

A method includes receiving image data of a person passing through an inspection volume and samples including a combination of a first magnetic field and a second magnetic field resulting from interaction of the first magnetic field and an object passing through the inspection volume. The object can be classified as threat or non-threat based on the received second data and a polarizability index characterizing a magnetic polarizability property of the object. The method can further include determining third data characterizing an indication of the object overlaid atop the first data. The method can also include comparing the polarizability index determined for the object and the indication of the object in the third data and determining, based on the comparing, an alarm status associated with the object and / or the person and providing the determined alarm status. Related apparatus, systems, techniques, and articles are also described.

There is described a device (100) for analyzing particles of a sample, the device (100) comprising: i) an electromagnetic radiation source to illuminate the sample with electromagnetic radiation to thereby generate a scattered signal; ii) a detector to detect a first component (Ivh) of the scattered signal (101), and a second component (Ivv) of the scattered signal (102); and iii) a control device configured to: a) determine (110) the depolarization ratio (Ivh / Ivv) of the sample based on the detected first component (Ivv) and the detected second component (Ivh); b) calculate (122) a polarizability (α) associated with the sample, and c) determine (120) a shape characteristic (p) of the sample particles based on the depolarization ratio (Ivh / Ivv) and the polarizability (α).

The invention relates to the technical field of computational electromagnetism, in particular to a metasurface scattering behavior analysis method and device, equipment and a storage medium. The method comprises the following steps: tracking an incident wave emitted into the metasurface based on geometrical optics; for the tracked incident wave, determining a first relationship between the equivalent surface current and the scattered field based on physical optics; determining an equivalent surface current based on the generalized boundary condition and a surface polarizability model; and determining a scattering field by combining the equivalent surface current and the first relationship by adopting Gordon integral. According to the metasurface scattering behavior analysis method provided by the embodiment of the invention, the surface polarizability model is combined with physical optics and geometrical optics, so that the scattering behavior related to the metasurface target can be effectively analyzed, and meanwhile, the calculation amount is reduced.

The invention records a fluorenyl polyimide film with a low dielectric constant and a preparation method and application thereof, and the polyimide is prepared by taking 9, 9-bis (4-(4-aminophenoxy) phenyl) fluorene and 4, 4 '-diaminodiphenyl ether diamine as diamine and aromatic dianhydride as dianhydride, and carrying out thermal imidization on the diamine and the dianhydride to obtain the PI film. The PI film provided by the invention has an asymmetric molecular structure, a fluorine-containing group and a fluorene group. The fluorine group has smaller dipole and lower polarizability, and can increase the free volume, and the free volume of the polymer material is increased, so that the number of polar groups in unit volume can be reduced, and the dielectric constant of the PI film can be reduced. The method can be applied to the high-tech fields of low-dielectric materials, gas separation membranes, fuel cell proton exchange membranes, outer space and the like.

The SERF gyroscope multi-parameter in-situ measurement method based on transverse magnetic field resonance first measures the amplitude-frequency characteristic curve of SERF atomic spin gyroscope Bx, By alternating current magnetic field response, then finds the resonance frequency and resonance amplitude value corresponding to the alkali metal electron resonance peak in x and y directions respectively, and finally constructs an equation through the ratio of the resonance frequency and resonance amplitude value corresponding to the alkali metal electron resonance peak in x and y directions, and obtains the accurate values of the electron magnetic field, the slowing factor and the electron transverse relaxation rate through the global optimization function algorithm. The present application can realize the in-situ accurate measurement of the electron magnetic field, the nuclear magnetic field, the electron polarizability, the nuclear polarizability, the slowing factor and the electron transverse relaxation rate of the SERF atomic spin gyroscope without changing the system state.

The invention discloses a method and system for testing key performance parameters of environment-friendly insulating gas, and relates to the technical field of gas performance test.The method comprises the following steps that a dynamic space-time mapping model based on gas molecule polarization response is established, and electric field gradient distribution in the high-voltage rapid rising stage serves as input parameters; generating a corresponding multi-scale polarizability evolution curve, and constructing a dynamic prediction baseline for identifying a nonlinear polarizability mutation precursor according to the multi-scale polarizability evolution curve; and constructing a micro-scale discharge channel constraint field according to polarizability abrupt change precursor parameters output by the dynamic prediction baseline, and performing vector rotation and energy amplitude limiting control on an electric field gradient, so that local electric field energy is absorbed through a spatial redistribution mechanism. According to the invention, real-time sensing and active regulation and control of the polarization behavior of the environment-friendly insulating gas are realized, through multi-stage energy redistribution and electric field dynamic balance, the formation of a discharge channel is effectively inhibited, the breakdown voltage is stabilized, the steady state duration is prolonged, and the safety and reliability of a test system are improved.

The application provides a low-refractive-index cover layer material, which is a carbazolyl-oxazole derivative and benzene as a mother nucleus, and a plurality of steric groups and electron-withdrawing groups are introduced to regulate the packing density and electron density of the molecule to adjust the polarizability of the molecule, so as to obtain a low-refractive-index cover layer material with a chemical structure shown in formula 1. By matching the low-refractive-index cover layer material with a high-refractive-index material, the light interference effect can be utilized to further improve the light extraction efficiency of an organic electroluminescent device. The refractive index of the compounds in examples 1-155 is 1.411-1.519 in each color gamut, which is lower than the refractive index of the comparative examples Ref1-Ref11, and the extinction coefficient k value is almost 0 in each color gamut, which does not affect the light emission of the light-emitting layer. The device performance of the device examples 1-155 prepared by combining the compounds prepared in examples 1-155 with the high-refractive-index CPL is better than the device performance of the device prepared by only containing the high-refractive-index CPL.

The present invention provides a starting material coordination compound for forming a metal thin film, the starting material coordination compound having a central metal and a ligand coordinated to the central metal, (i) the atomic polarizability of the central metal being 45-51, and the starting material coordination compound for forming a metal thin film satisfying the following conditions: a polarization volume < = 200 and a relative dielectric constant < = 2.20; or (ii) the atomic polarizability of the central metal is 52-90, and the raw material coordination compound for forming a metal thin film satisfies the following conditions: polarization volume < = 240 and relative permittivity < = 2.50.

The application discloses a kind of based on aeromagnetic three-component polarizability method and system, it is related to the field of magnetic prospecting, including: obtaining target area aeromagnetic three-component data and carrying out anomaly extraction;The three-component anomaly data extracted is grid processing, and equivalent rectangular body data is constructed;Based on the equivalent rectangular body data, inversion is carried out using pre-trained inversion model, and the total magnetization intensity three-component data of each rectangular body is obtained;According to the total magnetization intensity three-component data, aeromagnetic three-component polar calculation is carried out, and the final polar result is obtained.The application greatly improves the reliability and engineering applicability of magnetic anomaly polarizability, and provides more efficient and stable technical support for mineral exploration, geological structure analysis and deep geological exploration.

The invention relates to a construction method of a high-spin-selectivity photoelectric detector, and the method comprises the steps: setting a scattering region in the middle of a photoelectric detector model constructed by an armchair type Janus WSSe lattice, and enabling the regions at the two ends to serve as a left electrode and a right electrode respectively; the method comprises the following steps: introducing a vacancy defect of a single atomic level into a scattering region of a photoelectric detector, carrying out electronic local state analysis and impurity doping analysis on the scattering region after the defect is introduced, and screening out transition metal elements meeting preset conditions as doping elements; and performing bias voltage regulation and control on the photoelectric detector doped with the elements to construct a cooperative regulation and control strategy so as to complete construction of the photoelectric detector. According to the invention, through atomic scale defect introduction and transition metal doping modes, the photo-generated spinning current intensity, the spinning polarizability and the selective response ability to polarized light are significantly improved.

The invention discloses an optical response electromagnetic simulation method and system for dynamic evolution of a nano-array structure, and the method comprises the following steps: carrying out the geometric modeling of the nano-array structure, dispersing the periodic units in the nano-array structure into dipole arrays at equal intervals, and distributing a corresponding polarizability to each dipole; initializing a simulation condition, and setting an incident light condition, a medium environment and a periodic boundary condition; establishing a dipole interaction matrix meeting a periodic boundary condition, calculating an inverse matrix, and further calculating a polarization vector of a dipole; updating the inverse matrix based on a rank-one or low-rank inverse updating method; and calculating an optical response parameter of the nano array based on the updated polarization vector. On the premise of ensuring the calculation accuracy, the optical response change of the nano array structure in the dynamic evolution process can be efficiently tracked, and the method is suitable for electromagnetic simulation and optical optimization calculation scenes involving a large number of intermediate states.

The application belongs to the technical field of radio frequency electromagnetic field measurement, and particularly discloses a quantum field intensity measurement method and system of offset electric field regulation, which comprises the following steps: selecting a Rydberg atomic energy level close to resonance according to the microwave frequency of a measured signal; determining a coupling light wavelength according to the Rydberg atomic energy level, preparing a Rydberg atom, simultaneously obtaining a difference value between the microwave frequency of the measured signal and a resonance transition frequency, and obtaining an energy level offset value according to the difference value; obtaining a polarizability of the Rydberg atomic energy level, obtaining an offset electric field value to be applied according to the energy level offset value and the polarizability; and starting the offset electric field according to the offset electric field value, so that the relevant energy level of the Rydberg atom produces a movement in the offset electric field; when the energy difference between the offset Rydberg energy level and the adjacent energy level resonates with the microwave frequency of the measured signal, the offset sub-energy level forms an energy level splitting, and a frequency splitting is generated, and the electric field of the measured signal is measured according to the interval between the frequency splittings.

The present application relates to the technical field of new high-end polyolefin, in particular to a kind of cycloolefin copolymer and its preparation method, the use in optical material.The cycloolefin copolymer has the structure shown in formula I: The present application introduces high polarizability sulfur-containing group in polymer molecular structure, so that the prepared cycloolefin copolymer realizes high refractive index of 1.62~1.66, while having abbe number of 22~25, and exhibits excellent optical performance.The light transmittance of the material is more than 90%, the moisture absorption is lower, and has glass transition temperature of 130 DEG C~175 DEG C, and shows good thermal stability.With these excellent properties, the material has wide application prospect in high refractive index optical element, optical coating and high-end optical equipment.

This invention relates to a miniaturized triaxial SERF atomic magnetometer device with dual-pump light semi-transparent and semi-reflective beams. A single pump light is guided into the probe by a polarization-maintaining fiber. Then, using a half-wave plate, a polarization beam splitter, a right-angle mirror, and a quarter-wave plate, the pump light is split into two circularly polarized pump lights of equal intensity, which then pass perpendicularly through the same alkali metal gas cell. The pump light passing through the gas cell is then split by a semi-transparent and semi-reflective planar beam splitter; half of the pump light is detected by a photodetector to extract magnetic field information, while the other half returns along the same path and passes through the alkali metal gas cell a second time. This invention achieves high-sensitivity simultaneous measurement of triaxial magnetic fields in a miniaturized triaxial SERF atomic magnetometer, enhances atomic spin polarizability, and improves the uniformity of atomic spin polarizability within the gas cell. It addresses the technical challenge of achieving uniform spin polarizability in miniaturized SERF atomic magnetometer applications, and is beneficial for applications of array-type triaxial SERF atomic magnetometers in fields such as magnetocardiography and magnetoencephalography.

This invention discloses a method for preparing a lysosome-targeted polar fluorescent probe and its application in bioimaging, belonging to the field of chemical analysis and detection technology. The structure of the polar fluorescent probe is as follows: The lysosome-targeted polar fluorescent probe of this invention exhibits excellent polar sensing properties and significant aggregation-induced emission characteristics. With increasing solvent polarity, the fluorescence emission of the probe PHPT shows a significant redshift and a marked increase in fluorescence intensity. Within the polarizability range of 0.214–0.353, the maximum emission wavelength of the probe PHPT shows a good linear relationship with the solvent polarizability. The probe also exhibits good photostability. More importantly, the polarity detection properties of the probe PHPT are unaffected by pH and various small biological molecules. The probe PHPT has low cytotoxicity and is suitable for bioimaging. PHPT has the ability to precisely target lysosomes and can be used to detect decreased cell polarity and increased polarity during autophagy, and can be used to monitor physiological activities related to changes in intracellular polarity.

A method for measuring alkali metal atom equilibrium spin polarizability based on three-axis magnetic field steady-state response comprises the following steps: firstly, adjusting a device to a normal working state, then applying direct-current magnetic fields in x, y, y and z directions, changing the size of the magnetic field in the z direction, fitting the ratio of two outputs of the device with the square of the magnetic field applied in the z direction to obtain the size of the total relaxation rate, and finally measuring the alkali metal atom equilibrium spin polarizability. Obtaining the pressure broadening of the alkali metal air chamber by using the optical depth of the detection light at a low temperature, then changing the power of the detection light at a normal working temperature, establishing a transfer coefficient by using the pressure broadening and a fitting slope, and finally applying a direct-current magnetic field on a y axis and changing the size of the direct-current magnetic field, and fitting the relationship between the output of the device and the By-fit, so as to obtain the alkali metal air chamber. The final balance spin polarizability is obtained by combining the transfer coefficient, the SERF state required by normal work of the system is not damaged, the influence of temperature is avoided, the measurement error is small, and a more accurate measurement means is provided for further optimizing an SERF magnetic field measurement device to improve the sensitivity of the SERF magnetic field measurement device.

A method includes receiving, from a plurality of magnetic field receivers including magnetic sensors, data characterizing samples obtained by the plurality of magnetic field receivers, the samples of a combination of a first magnetic field and a second magnetic field resulting from interaction of the first magnetic field and an object; determining, using the received data, a polarizability index of the object, the polarizability index characterizing a magnetic polarizability property of the object; classifying, using the determined polarizability index, the object as threat or non-threat; and providing the classification. Related apparatus, systems, techniques, and articles are also described.

Embodiments of the present disclosure relate to a method, apparatus, electronic device, computer-readable storage medium, and computer program product for determining the polarization of a solid system. The method includes: inputting the electronic coordinates of a periodic unit of the solid system into a neural network, and determining the wave function of the solid system by minimizing an objective function, where the objective function is determined based on the enthalpy in the presence of an electric field; and determining the polarizability of the solid system based on the wave function of the solid system. This solution takes into account the periodicity of the solid system, reduces the computational amount of processing, and improves the processing efficiency; and by using a neural network to determine the wave function, the accuracy of determining the polarizability can be improved.

The application discloses a kind of based on the measurement method of geologic hazard body slip surface of induced polarization effect, comprising: drilling N work drill holes in the rear end of potential landslide body to be detected;High polarizability and lower viscosity slurry are injected into work drill hole;Using the werner device with equal electrode distance, apparent polarizability under several first electrode distances along the direction of landslide body is obtained;The distance of electrode is increased, and apparent polarizability under several second electrode distances along the direction of landslide body is repeatedly obtained;Apparent polarizability dataset is formed, and apparent polarizability pseudo-section is drawn according to apparent polarizability dataset;According to apparent polarizability pseudo-section, high polarizability distribution law is analyzed, and preliminary slip surface position is obtained;The apparent polarizability dataset is inverted, and apparent polarizability inversion section is obtained;According to apparent polarizability pseudo-section and apparent polarizability inversion section, the accurate slip surface position is obtained.