72 results about "Atomic force microscopy" patented technology

The invention discloses a mixing parameter regulation and control method and system for an SBS-T modified asphalt mixture and a terminal. The method comprises the following steps: analyzing a modification mechanism through a scanning electron microscope and X-ray photoelectron spectroscopy combined technology, dividing three stages of rapid melting and the like, and establishing a temperature-viscosity model; constructing a multi-scale capture system by using an atomic force microscope, a Fourier transform infrared spectrum and a dynamic shear rheometer; designing a five-factor three-level test matrix by adopting a response surface method, and establishing a road performance prediction model in combination with a BP neural network; mixing parameters are optimized in a multi-objective mode based on a genetic algorithm, and dynamic correction is achieved through an Internet of Things sensor and Kalman filtering. The system comprises a mechanism analysis module, a multi-scale detection module, a terminal integrated storage unit, a processing unit and a man-machine interaction unit. According to the scheme, the limitation of traditional single-factor analysis is broken through, microscopic and macroscopic collaborative optimization and dynamic parameter regulation and control are achieved, and the construction adaptability and precision are improved.

The invention relates to the technical field of traditional Chinese medicine component detection and discloses a rapid detection method for traditional Chinese medicine compound components. The method comprises the following steps: performing Raman spectrum scanning on a traditional Chinese medicine compound sample to generate component spectrum distribution information, and performing fitting by adopting a partial least square algorithm to determine a local component anomaly risk area; meanwhile, atomic force microscopic imaging is carried out, a microstructure distribution map is generated, and a potential component mismatch feature region is marked through texture feature extraction and pattern recognition. And generating a detection optimization adjustment region based on the space coordinates of the region, analyzing the gradient change in the molecular arrangement direction of the region to evaluate the component distribution offset state, and analyzing the interface bonding state of the active component and the auxiliary material to evaluate the component interaction coupling strength. And finally, on the basis of an evaluation result, whether the real-time parameter calibration is started in the detection optimization adjustment area is judged through a dual-channel decision-making mechanism. According to the method, correlation analysis of component spectrums and microtopographies is realized, and the accuracy and pertinence of traditional Chinese medicine compound component detection are improved.

Disclosed herein is a device and method for measuring spatial mass distribution profiles to weigh the accumulated-aggregated mass of an analyte in a crowded bioorganic material background by employing a high frequency recognition pattern. The recognition pattern allows for the Fourier filtering of mass sensitive image data for background and noise subtraction. The device and method enables the screening of a biological fluid sample for an analyte associated with proteinopathy.

The embodiment of the invention discloses a scanning NV probe microscope which comprises an atomic force microscopy system used for detecting surface topography information of a sample and an optical detection magnetic resonance system used for detecting surface magnetic field distribution information of the sample, and the atomic force microscopy system comprises a vibration arm and a diamond probe. The optical detection magnetic resonance system comprises an NV color center, a transition excitation light path and a fluorescence detection light path; a sample to be scanned and the transition excitation light path are respectively positioned on two opposite sides of the diamond probe, and the transition excitation light path and the fluorescence detection light path are positioned on the same side of the diamond probe; a first metal coating film is arranged on one side, close to the sample, of the diamond probe and is used for blocking surface fluorescence of the sample. According to the scanning NV probe microscope provided by the embodiment of the invention, the metal coating is arranged at the bottom of the diamond probe to block stray fluorescence from the surface of the sample, so that the problems of low magnetic field imaging signal-to-noise ratio and limited measurement precision of the existing scanning NV probe microscope are solved.

The invention provides an influenza virus and cell exosome recognition method, and belongs to the technical field of microscopic imaging. The method comprises the following steps: modifying a fresh split mica sheet with a NaCl solution, adhering the mica sheet to a glass slide, respectively dripping influenza virus and cell exosome samples on the mica sheet, standing, and testing. The method comprises the following steps: selecting a nano-probe of a specific model, placing the probe in a range of dripping a sample, after the probe is placed, selecting a certain range for scanning, observing the imaging characteristics of the two samples, and analyzing the morphology, height and adhesive force of the two samples. The method comprises the following steps: scanning the surface of an influenza virus and cell exosome sample by using an atomic force microscope, selectively analyzing the morphology, height and adhesive force of the influenza virus and cell exosome in a measurement range, extracting related characteristic parameters, and then carrying out segmentation and morphological adjustment on an image to obtain the influenza virus and cell exosome sample. Analysis and recognition results of the two samples are obtained by using an image analysis and machine learning method of neural network aided prediction, and accurate and rapid intelligent distinguishing is realized.

The invention discloses a nanoscale saw blade shape optimization and production method adopting a neural network. The nanoscale saw blade shape optimization and production method comprises the following steps: S1, performing high-resolution imaging and modeling on an initial shape of a nanoscale saw blade by utilizing a scanning electron microscope and a three-dimensional confocal microscopic measurement technology; s2, constructing a shape optimization model based on a convolutional neural network; s3, generating a virtual saw blade shape data set by using the generative adversarial network, and training an optimization model in combination with experimental data; s4, performing multi-scale performance verification on the optimized saw blade shape by adopting a finite element analysis and molecular dynamics simulation technology; s5, realizing high-precision manufacturing based on a femtosecond laser nano processing technology; s6, performing shape measurement and surface roughness evaluation on the processed saw blade by using an optical interferometer and an atomic force microscope; and S7, integrating an automatic shape detection and feedback adjustment module through the programmable logic controller, and correcting the machining deviation in real time. The method has the advantages of being high in design precision, high in machining consistency and high in production efficiency.

This disclosure provides an electronic control readout system and method for quantum diamond atomic force microscopy. The system includes: a system control readout module, a magnetic measurement algorithm module, and a magnetic measurement control and readout module. The magnetic measurement control and readout module is used to respond to the control signal of the system control readout module by emitting a laser pulse sequence and a microwave pulse sequence of a preset frequency to the quantum diamond probe located at the i-th pixel position of the sample to be tested, and then acquiring the analog fluorescence signal of the quantum diamond probe at the i-th pixel position and outputting the digital fluorescence signal of the i-th pixel. The magnetic measurement algorithm module is used to respond to the control signal of the system control readout module by obtaining the resonance frequency at the i-th pixel position and the preset frequency at the i+1-th pixel position according to the fluorescence photon number of the i-th pixel corresponding to the digital fluorescence signal of the i-th pixel, the resonance frequency at the (i-1)-th pixel position, and a microwave frequency lookup table.

The present invention discloses a polyporus badius polysaccharide and its preparation method and application, belonging to the technical field of polysaccharide extraction. The polyporus badius polysaccharide (PPP-0A) includes galactose, fucose, glucose, mannose and xylose, and the molar ratios are 62.26%, 16.96%, 15.23%, 4.68% and 0.87% respectively. The present invention uses techniques such as methylation, scanning electron microscopy, thermogravimetric analysis, nuclear magnetic resonance and atomic force microscopy to determine the structural characteristics of PPP-0A, analyze its composition and properties, and its inhibitory effects on the activities of α-glucosidase and α-amylase. In addition, an in vitro HepG2 cell model induced by high blood glucose and high insulin levels was used to study the hypoglycemic effect of PPP-0A. The present invention provides a theoretical basis for clarifying the relationship between the hypoglycemic activity of PPP-0A and its hypoglycemic effect on type 2 diabetic mice.

The invention provides a method for predicting fiber yield stress based on monomolecular mechanics, and relates to the technical field of monomolecular level determination of interaction among chain tracks, lacing molecules and chains in fibers, the method comprises the steps of preparing a fiber sample, preparing a functionalized atomic force microscope probe, and testing atomic force microscope (AFM) imaging and monomolecular force spectrum (SMFS). The method comprises the following steps of: verifying a single molecule signal, reconstructing a fiber medium chain track by utilizing a force-distance curve of a single molecule, quantifying the interaction between fiber medium chains, establishing a quantitative relationship between the single molecule and macromechanics, carrying out a static tensile experiment of polymer fibers, and verifying the quantitative relationship by utilizing the dependency of the molecular density and the utilization rate of a lace on tensile orientation. According to the method, the chain track in the fiber can be reconstructed, the molecular density of the lace and the strength of interaction between the chains are quantified, then the ultimate yield stress (sigma SMFS) of the fiber is calculated, and the quantitative relation between single molecules and macromechanics is established.

The invention relates to the technical field of biomedical imaging and terahertz detection, in particular to a terahertz near-field imaging quality analysis system and method. According to the technical scheme, the system comprises an atomic force microscope system, a terahertz source, an image acquisition module, an image scoring module and a data processing module, and the atomic force microscope system adopts a tapping mode based on the terahertz scattering type scanning near-field optical microscope technology and comprises a Z voltage control unit used for adjusting the probe insertion depth; the terahertz source is used for providing terahertz waves required by imaging, and the terahertz source and the probe module of the atomic force microscope system are coaxially arranged. By quantifying the association rule of the probe insertion depth and the imaging quality, the core pain points of blind parameter adjustment and unstable quality in terahertz near-field imaging are solved at one stroke, the imaging consistency is greatly improved, the detection process and the quality evaluation system are exclusive, the method is particularly suitable for undyed paraffin sections, and the detection accuracy is improved. And the pathological characteristics of papillary carcinoma cells can be clearly presented.

Exemplary embodiments of the present disclosure can include, for example, an atomic force microscopy (AFM) system, including a cantilever(s), an optical pickup unit(s) (OPU(s)) including a laser positioned over the cantilever(s), and a power source providing noise with a noise level that is below 300 Picometers. The noise level of the power source can be below 200 Picometers. A digitizing arrangement can be included which can be associated with the OPU. The digitizing arrangement(s) can have a bandwidth of about 2 MHZ. The OPU(s) can have a detection bandwidth of at least 80 MHZ. The exemplary apparatus can be combined with a chemical protocol and statistical signal processing and image analysis procedures to map DNA at high speed and accuracy.

The invention discloses a method for rapidly detecting aspergillus conidia in a label-free manner through terahertz near-field imaging, and belongs to the technical field of microbiological detection. The method comprises the following steps: synchronously acquiring atomic force microscope morphology images and terahertz near-field signals of spores through a scattering type terahertz time-domain spectrum near-field scanning system, and jointly extracting morphology features, multi-order harmonic signal intensity and a local near-field amplitude spectrum peak value after phase-locked amplification and demodulation processing; and combining into a feature set for spore type identification. The method provided by the invention solves the problem that high-resolution, label-free and rapid detection cannot be realized at the same time in the prior art, and is mainly used for rapid label-free accurate detection and type identification of the aspergillus conidia.

A method of evaluating a region of interest of a sample with a sample evaluation tool that includes a focused ion beam (FIB) column, a scanning electron microscope (SEM) column, and an atomic force microscope (AFM) instrument, the method comprising: transferring the sample into in a vacuum chamber of the sample evaluation tool; acquiring a plurality of two-dimensional images of the region of interest over a plurality of iterations of a delayering process by: (a) positioning the region of interest under a field of view of the FIB column; (b) milling a layer of material from the region of interest with the FIB column; (c) moving the region of interest under a field of view of the SEM column; (d) imaging the region of interest with the SEM column and measuring a depth of the milled layer in the region of interest with the AFM instrument; and repeating steps (a)-(d) a plurality of times without removing the sample from the vacuum chamber.

The present invention discloses an atomic force microscope in-situ electrolytic cell device for measuring the molecular force spectrum of a solid-liquid interface. The structure includes a working electrode, a reference electrode, a counter electrode, and an electrolytic cell. The cell body is sequentially composed of an optical glass window, a flange top cover, a Teflon substrate, a sealing ring, a metal sample support sheet, a central through-hole Teflon support sheet, a magnetic coil plate, a spring gasket, and a flange base from top to bottom. The center of the Teflon substrate is provided with an opening, and the top is sequentially fixed with a flange top cover and an optical glass window from bottom to top. The bottom is respectively composed of a sealing ring, a metal sample support sheet, a central through-hole Teflon support sheet, a magnetic coil plate, and a flange base from top to bottom. An external signal source drives the magnetic coil, and the interaction between the magnetic probe and the molecular / ion clusters inside the interface double layer is used to realize sub-nanometer real-space imaging of the solid-liquid interface structure in the electrochemical process. The present invention can assist in the needs of material electrochemical testing and atomic force microscope data acquisition.

The invention provides an atomic force microscope operation method. The method comprises the following steps: selecting a sample, and setting an atomic force microscope detection mode; setting initial scanning parameters; scanning the surface topography, and calculating the resolution of a scanning result; scanning parameters are modified, scanning is carried out for multiple times, the abrasion loss of the probe is calculated, and scanning is ended when a certain duration is reached; according to the resolution ratio and the probe abrasion loss, the better scanning parameters are obtained, the corresponding scanning parameter combination can be determined according to the requirements of the resolution ratio and the probe abrasion loss, the high resolution ratio and the high detection effect are achieved, meanwhile, the abrasion of the probe is reduced, and the service life of the probe is prolonged.

The invention provides an extreme ultraviolet collection mirror grating hybrid measurement system and method, and relates to the technical field of extreme ultraviolet (EUV) lithography and nanometer metrology, and the system comprises an atomic force microscopic module which is in communication connection with a data processing module and is used for carrying out high-resolution morphology detection on an abnormal morphology according to position information, and obtaining image data; the shared precision positioning platform module is connected with the optical scattering measurement module and the atomic force microscopy module and used for controlling movement of the optical scattering measurement module and the atomic force microscopy module so that the atomic force microscopy module can accurately move to the position where the abnormal morphology is located; wherein the data processing module is also used for generating a comprehensive detection report based on the geometric structure parameters reconstructed by the optical scattering measurement module and the image data acquired by the atomic force microscopic module. According to the invention, high-precision, high-efficiency, cross-scale and lossless comprehensive characterization of the grating on the surface of the EUV collecting mirror can be realized.

This application provides an atomic force microscopy system, relating to the field of optical detection. In the atomic force microscopy system provided by this application, the focusing lens structure and the reflective surface of the cantilever constitute a tilt-invariant retroreflection system, adjusting the reflected beams from the cantilever at different tilt angles to be spatially staggered but along the same direction. Therefore, when detecting this reflected beam, the relevant sensors can be set based on the modulated direction of the reflected beam, enabling the sensors to receive the beam reflected from the cantilever at a stable angle, reducing the detection difficulty for the sensors. Furthermore, to avoid multiple reflections of the resulting beam between the reflective interface and the reflective surface affecting the detection results of the position-sensitive detector, the atomic force microscopy system provided by this application also includes an anti-interference structure. This anti-interference structure introduces additional deflection into the resulting beam, ensuring the detection accuracy of the position-sensitive detector.

Technologies for atomic force microscopy (AFM)-based photothermal two-dimensional infrared (2DIR) spectroscopy are disclosed. Techniques may comprise providing pulsed light from an infrared (IR) laser source. A pulse sequence may be generated from the IR light. The pulse sequence may comprise one or more time delays among constituent pulses. The pulsed IR light may be focused on matter in a sample region. The pulsed IR light may interact with the matter in the sample region. One or more photothermal expansion mechanical actions in the matter of the sample region may be measured. One or more signals corresponding to the one or more measured photothermal expansion actions may be created and may be recorded as a function of the one or more time delays. A photothermal two-dimensional (2D) spectrum may be extracted from the one or more signals as recorded as a function of the one or more time delays.

The present invention relates to a method for measuring the dielectric properties of a sample with a scanning probe microscope. In particular, the invention relates to highly-localized optical imaging and spectroscopy on a sample surface using an atomic force microscope (AFM) probe mechanically driven at two oscillation frequencies, referred to herein as “active bimodal operation”, and a modulated source of electromagnetic radiation.

The invention discloses phlebopus portentosus polysaccharide as well as a preparation method and application thereof, and belongs to the technical field of polysaccharide extraction. The phlebopus portentosus polysaccharide (PP-0A) comprises galactose, fucose, glucose, mannose and xylose, and the molar ratios of the galactose, the fucose, the glucose, the mannose and the xylose are 62.26%, 16.96%, 15.23%, 4.68% and 0.87% respectively. According to the invention, the structural characteristics of PPP-0A are measured by using methylation, a scanning electron microscope, thermogravimetric analysis, nuclear magnetic resonance, an atomic force microscope and other technologies, and the composition and properties of PPP-0A and the inhibition effect of PPP-0A on the activity of alpha-glucosidase and alpha-amylase are analyzed. In addition, the hypoglycemic effect of the PPP-0A is researched by using an in-vitro HepG2 cell model induced by hyperglycemia and high insulin level. The invention provides a theoretical basis for clarification of the relationship between the hypoglycemic activity of the PPP-0A and the hypoglycemic effect of the PPP-0A on type 2 diabetes mellitus mice.

The invention relates to a method for decoupling the morphology and resonant frequency of a contact resonance atomic force microscope. The method comprises the following steps: S1, preparing a microscope, a probe, a lock-in amplifier, a to-be-tested sample, a sapphire sheet and a PC (Personal Computer) upper computer; step S2, probe parameter calibration; s3, establishing a resonant frequency measurement device; s4, fixing the sample; s5, detecting the resonant frequency, collecting the test results of the appearance and the resonant frequency of the surface of the to-be-tested sample, and transmitting the test results to the PC upper computer; s6, data processing is carried out, and an inclination angle corresponding to a morphology result is calculated; drawing the corresponding relation between the resonance frequency # imgabs0 # and the inclination angle, and then solving the ratio # imgabs1 # of the lateral rigidity to the normal rigidity by adopting a probe-sample contact model; and then the # imgabs2 # is substituted into the probe-sample contact model, and each pixel point of a test result is reduced into an indentation modulus, so that decoupling of morphology coupling is completed.

The invention discloses a self-adaptive scanning method of a scanning probe microscope, and belongs to the technical field of atomic force microscopes. The invention aims to solve the problem that the scanning operation mode cannot be adjusted according to real-time requirements in the existing probe scanning method. Comprising the following steps: in a scanning process, triggering monitoring after completing signal acquisition of each pixel point so as to obtain a current concerned signal; setting a trigger condition of the current concerned signal, and executing a preset trigger operation under the condition that the trigger condition is met; and then signal acquisition of a next pixel point is carried out. According to the invention, the self-adaptability and efficiency of AFM scanning can be improved.

The present invention discloses an atomic force microscopy imaging device and method for a Josephson probe microscope, belonging to the field of atomic force microscopy imaging technology. The device includes a sample stage, a second displacement component, a first displacement component, a superconducting Josephson probe component, a first controller, a second controller, a lock-in amplifier, a current amplifier, and a high-speed data acquisition device. The superconducting Josephson probe component includes a probe module and a tuning fork module. The probe module includes a probe and a probe box. The tuning fork module includes a tuning fork wafer and a substrate. The probe is connected to the tuning fork wafer. The lock-in amplifier is connected to the tuning fork wafer to monitor the amplitude change of the tuning fork wafer in real time. The lock-in amplifier controls the second controller to drive the sample up and down to achieve closed-loop regulation of the distance between the probe and the sample. The present invention adjusts the distance between the probe and the sample surface in real time, ensuring high stability during imaging and further improving resolution. It can also effectively extend the service life of the probe and reduce the cost of use.

A method for inspecting and reviewing defects in a substrate using a scanning probe microscope comprising a plurality of scanning heads and a substrate carrier, wherein each of the plurality of scanning heads comprises a probe including a probe tip positioned for scanning the substrate surface, the method comprising: - providing a substrate on a substrate carrier, wherein the substrate carrier is positioned to position the substrate for at least one of the plurality of scanning heads; - scanning the substrate surface in a first scanning mode using at least one first scanning head of the plurality of scanning heads; - scanning the substrate surface in a second scanning mode using at least one second scanning head of the plurality of scanning heads, wherein at least one first scanning head and at least one second scanning head are different scanning heads of the plurality of scanning heads, the method for inspecting and reviewing defects, wherein the first scanning mode has a lower scanning resolution than the second scanning mode.

The invention provides an atomic force microscopy system, and relates to the field of optical detection. According to the atomic force microscopy system provided by the invention, the focusing lens structure and the reflective surface of the cantilever form an inclined invariant retroreflection system, and different-angle reflected light beams reflected by the cantilevers with different inclined angles are adjusted into light beams which are staggered in space and are in the same direction. Therefore, when the reflected light beam is detected, the related sensor can be arranged based on the modulated direction of the reflected light beam, so that the related sensor can receive the light beam reflected by the cantilever at a stable angle, and the detection difficulty of the sensor is reduced. Besides, in order to prevent multiple reflections of the result light beam between the reflection interface and the light reflection surface from influencing the detection result of the position sensitive detector on the result light beam, the atomic force microscopic system provided by the invention is also provided with an anti-interference structure, and the anti-interference structure introduces additional deflection for the result light beam, so that the detection result of the result light beam is more accurate. And the detection precision of the position sensitive detector on the result light beam is ensured.

Atomic force microscope (AFM) device and its operating method An atomic force microscope (AFM) apparatus 1 is disclosed that includes at least one scanning head for scanning a sample 9. A cantilever deflection detector 30 measures the deflection d of the probe relative to the scanning head during scanning and provides an output signal indicative of the measured deflection. A controller 40 of the AFM apparatus receives and analyzes the output signal from the cantilever deflection detector to measure the deflection of the probe, and automatically adjusts one or more imaging parameters during scanning in response to information about sample characteristics near the location of the sample currently being scanned. The information about the sample characteristics includes one or more of information from a specification of the sample, a recipe for manufacturing the sample.

The invention provides a micro-cantilever, a probe and an atomic force microscopy, the micro-cantilever is applied to the atomic force microscopy, the micro-cantilever comprises a first area, a second area and a third area, the first area and the third area are respectively arranged at two ends of the micro-cantilever, the second area is arranged between the first area and the third area, the first area is used for fixing one end of the micro-cantilever, a needle point used for detecting a detected sample is arranged in the third area, and the second area comprises more than two micro-channels. In the embodiment of the invention, the second region of the micro-cantilever comprises at least one micro-channel so as to divide the micro-cantilever into smaller cantilevers, each cantilever has respective resonant frequency, and the superposition of the at least two smaller cantilevers can reduce the overall Q value of the micro-cantilever, so that the micro-cantilever has a wider frequency amplitude peak and responds to a wider-frequency signal, and therefore, the overall performance of the micro-cantilever is improved. Therefore, the requirement of detecting vibration signals with different frequencies can be met.

The invention discloses a high-sensitivity positioning atomic force microscope detection device and method. The high-sensitivity positioning atomic force microscope detection device comprises a dark field oblique incidence light source module, an open atomic force scanning module, a microscopic imaging system and a high-precision motion platform for placing a sample, the dark field oblique incidence light source module provides a multi-angle oblique incidence light source for a sample to form a dark field effect, so that scattered light of micro-nano defects on the surface of the sample is captured by a microscopic imaging system, and high-sensitivity positioning is realized; the atomic force scanning module comprises a radio frequency modulation laser, a probe assembly and a photoelectric detector; the laser output by the laser irradiates the probe assembly and then is reflected into the photoelectric detector; the sample is a transparent element, and the relationship among the incident angle of the dark field oblique incidence light source module, the refractive index of the sample and the numerical aperture NA of the microscopic imaging system is constrained, so that the imaging of the center and the edge of the sample meets the dark field condition. By utilizing the method, the micro-nano scale surface defect can be accurately positioned in the AFM detection process.

The utility model provides a general atomic force microscope probe clamp device for multiple environmental atmospheres, which comprises a main body and a quartz baffle plate, the quartz baffle plate is detachably connected to the lower end of the main body, the interior of the main body is provided with a through conical cavity from top to bottom, and the conical cavity is gradually shrunk from top to bottom; the upper end of the main body is embedded into the scanning head, the upper side edge of the main body and the scanning head are fixedly installed, a stainless steel metal clamping piece is installed on one side below the main body, and the lower portion of the stainless steel metal clamping piece is used for pressing an atomic force probe. According to the utility model, the atmospheric environment imaging resolution can be obviously improved, the submerged diving depth can be increased, the test range is expanded, and the device has the advantages of convenience in processing, low cost, easiness in maintenance and repair and no dependence on expensive accessories of foreign original factories.

The invention is suitable for the technical field of image processing and biomedical analysis, and provides an atomic force microscope chromosome image fusion and detection method and system, and the system comprises an image loading module which is used for loading a chromosome image file scanned by an atomic force microscope from a specified folder; and the image splicing module is used for splicing the loaded image files into a panoramic image and comprises an automatic splicing sub-module and a manual splicing sub-module. According to the method, automatic splicing and intelligent detection of chromosome images can be realized, the stability and accuracy of image processing are greatly improved, high-quality panoramic image construction can still be realized in a complex scene, the image utilization rate is improved, a chromosome extraction result is more accurate and reliable, the whole scheme is high in automation degree and strong in robustness, manual intervention can be reduced, and the efficiency is improved. The method improves the processing efficiency and detection accuracy of the chromosome image of the atomic force microscope, and has a remarkable practical value.