141 results about "Crystal morphology" patented technology

The present invention belongs to the field of catalysts and relates to an α-alumina carrier and a preparation method thereof, a silver catalyst for ethylene epoxidation and an ethylene oxidation method. The α-alumina carrier has an α-A12O3 content of more than 90% by weight; a crushing strength of 80 to 350 N / particle; and a specific surface area of ​​1.5 to 3.0 m 2 / g; water absorption rate is 30-70%; pore volume is 0.30-0.75mL / g; the crystal morphology of the α-alumina carrier includes two sizes of flake crystals, wherein the size of the larger flake crystals is 1.0-8.0μm, and the size of the smaller flake crystals is less than 1μm. Compared with the prior art, the silver catalyst made of the α-alumina carrier provided by the present invention is used for the reaction of ethylene oxidation to produce ethylene oxide, while ensuring selectivity, and has the advantages of higher activity and stability.

The invention discloses an energetic crystal surface hydrophobicity evaluation method based on an improved adhesion energy model. The energetic crystal surface hydrophobicity evaluation method comprises the steps that 1, crystal habit information of a specified CL-20-based energetic eutectic in vacuum is simulated and predicted through molecular dynamics; 2, cutting a surface structure corresponding to the crystal habit, and constructing a molecular scale eutectic-solvent interface model; step 3, correcting the crystal face adhesion energy by using the correction adhesion energy model, and simulating and predicting the crystal morphology of the eutectic crystal in a specified solvent; 4, constructing a molecular scale eutectic-water interface model, and evaluating hydrophobicity of different surfaces according to the corrected adhesion energy model; and 5, synthesizing the surface hydrophobicity and the simulated and predicted crystal morphology under different solvents, and screening a proper solvent to realize the energy-containing eutectic hydrophobicity regulation and control. According to the method, accurate quantification of hydrophobicity is realized by dynamically simulating interface energy change.

The invention relates to analcime with an ANA structure and a preparation method of the analcime, the chemical molecular formula of a unit cell of the analcime with the ANA structure is Na < x > [SiyAlzO96], x is equal to 6-15, y is equal to 30-37, and z is equal to 10-16; the analcime with the ANA structure has a spherical crystal morphology. The analcime with the ANA structure disclosed by the invention has a spherical crystal morphology, shows excellent molecular diffusion performance, and has a good application prospect in the fields of small molecular acid catalytic reaction, small molecular gas adsorption separation, ion adsorption purification and the like.

The invention belongs to the technical field of materials, and particularly relates to a multi-component compounded stable extrusion insulating material and a preparation method thereof. The invention relates to a multi-component compounded stable extrusion insulating material which is prepared from the following raw materials in percentage by weight: 70-99 parts of low-density polyethylene; 5-20 parts of modified resin; 0.8 to 1.5 parts of a cross-linking agent; 0.2 to 0.6 part of a cross-linking agent auxiliary agent; and 0.5 part of an antioxidant. Through cooperation of binary base material blending, low-crosslinking multi-component additive system optimization and a flexible mixing stable extrusion process, the synergistic effect of the binary base material blending, the low-crosslinking multi-component additive system optimization and the flexible mixing stable extrusion process can be brought into full play, the crystal form of the compound insulation material is improved, the phonon transmission free path is enhanced, the content of a crosslinking agent is reduced, the melt flow stability of the insulation material is enhanced, and low-temperature stable extrusion is achieved; product defects are reduced, and production efficiency and sample quality are improved. Impurities and scorching melting points are effectively filtered, the product quality stability and the production process are greatly improved, the comprehensive electrical mechanical and heat-conducting properties of the cable are systematically improved, and effective preparation of the large-length cable is achieved.

The invention discloses a treatment method of an ammonium paratungstate sieve head material. The treatment method comprises the following steps: S1, preparing a solution; step S2, dissolving; s3, filtering and washing; step S4, drying and screening; according to the process disclosed by the invention, the ammonium paratungstate sieve head material is adjusted and treated, the consumption of auxiliary materials is reduced, the energy consumption is low, and the open crystal appearance of the original ammonium paratungstate crystal is kept; compared with the original undersize ammonium paratungstate product, the ammonium paratungstate product recovered and treated by the method has the advantages that the impurity element content is lower, the total impurity content is 20-30ppm lower than that before treatment, and the product quality is integrally improved.

The invention discloses a halide-assisted single-crystal-morphology high-nickel ternary layered positive electrode material and a preparation method thereof. The chemical formula of the material is shown in the specification. Li < 1-alpha > Ni < x > Co < y > Mn < z > A < alpha > O < 2-beta > X < beta >, 1, 0lt; y is less than or equal to 0.2, 0lt; z < = 0.2, 0lt; alpha is less than or equal to 0.05, 0lt; beta is less than or equal to 0.05, x + y + z = 1, A is at least one of Li, Na, K, Rb and Cs, X is at least one of F, Cl, Br and I, and the material has a monodisperse morphology. The temperature rise time of the low-temperature section is prolonged by controlling the temperature rise rate of the multiple sintering stages, the halide salt with the low melting point is introduced in the sintering process, adhesion and agglomeration of single crystal particles are reduced, the structural stability of the material is enhanced, and the electrochemical performance of the material is improved.

The invention provides a production device and process for increasing the content of magnesium citrate crystals. The problems that in the prior art, the impurity co-crystallization rate is high, and crystal forms are difficult to control are solved. The device comprises a gradient temperature control multi-stage crystallization device and a crystal form directional regulation and self-adaptive separation system. The gradient temperature control multi-stage crystallization device is composed of a main crystallizer, a gradient temperature control system, an ultrasonic-assisted system and a liquid phase partition circulating system, and the crystallization environment is accurately controlled through the temperature gradients of five independent temperature zones. The crystal form directional regulation and self-adaptive separation system is composed of a seed crystal dynamic inoculation device, an electric field auxiliary directional crystallization system, a real-time crystal morphology analysis system and a self-adaptive separation system, and the crystal morphology and particle size distribution can be accurately controlled. According to the process disclosed by the invention, the main content of magnesium citrate is increased to 98.8 + / -0.3%, heavy metal impurities and organic impurities are respectively reduced by 70% and 75%, the crystal form consistency is increased to 96 + / -2%, the production period is shortened by 33%, and the process has remarkable economic benefits and social benefits.

The invention belongs to the technical field of automatic control, and discloses a cyclopropylamine (R)-mandelate crystallization process feedback control method, which comprises the following steps: acquiring the concentration, solvent temperature, stirring speed and pH value of cyclopropylamine (R)-mandelate in a solvent in real time, and forming a state parameter set reflecting the real-time state of a cyclopropylamine (R)-mandelate crystallization system; based on the state parameter set, deriving a solute supersaturation degree change rate, a nucleation rate and a crystal growth rate by adopting an explicit kinetic relationship to obtain a kinetic feature set of the cyclopropylamine (R)-mandelate; collecting the grain size, the shape and the crystallization uniformity of the crystal, and constructing a corresponding crystal quality prediction function in combination with the kinetic feature set of the cyclopropylamine (R)-mandelate to obtain a predicted crystal quality index; comparing the actually detected crystal morphology index with the predicted crystal quality index, and calculating to obtain a deviation value; the crystal quality of the cyclopropylamine (R)-mandelate is improved.

The invention discloses a liquid phase growth method of n-type silicon carbide crystals, and belongs to the technical field of semiconductors. By changing the formula of a growth raw material for silicon carbide growth, the growth raw material is configured to be SixCryMz, the molar ratio x of Si to the raw material is 40-70%, the molar ratio y of Cr to the raw material is 20-60%, and the molar ratio z of M to the raw material is 1-10%; m is one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ce, La, Tb, Nd, Ta and Pr. According to the method, other elements M are doped on the basis of a Si-Cr system, the liquid growth method is matched to replace an Al element to improve the crystal morphology, meanwhile, evaporation of solution components can be inhibited, and the growth system can be kept stable for a longer time, so that the n-type silicon carbide crystal with more uniform surface steps can be grown.

The invention provides a control method for image generation in a crystal growth process, and relates to the technical field of crystal growth image.The control method comprises the following steps that axial acceleration, temperature gradient and interface morphology data in the crystal growth process are collected in real time, the current growth stage of a crystal is judged, and if the crystal enters a transition stage, the crystal is subjected to image generation; if yes, historical rotating speed data and historical temperature field distribution characteristics of the crystal are called to carry out time sequence prediction, a multi-parameter data stream of the crystal in a future preset time period is generated, and shooting parameters of corresponding imaging units are obtained and comprise a shooting sequence and adjacent imaging intervals; the shooting sequence comprises a shooting sequence and a shooting angle of each imaging unit; and controlling each imaging unit to image the crystal growth process under the shooting parameters in a future preset time period so as to realize multi-view image splicing. According to the method, image missing in a key deformation stage is avoided, the crystal image splicing success rate and splicing efficiency are improved, and then the real-time monitoring effect on the crystal morphology is guaranteed.

The invention relates to a micro-fluidic chip pour point depressant intelligent screening and optimizing device and method integrating multi-parameter detection, and the micro-fluidic chip pour point depressant intelligent screening and optimizing device integrating multi-parameter detection comprises an experiment module, a data acquisition module and a data analysis and control module, the experimental module comprises a power area, a conveying area, a temperature control area, an imaging area and a recovery area, the imaging area comprises a polarizing microscope and a micro-fluidic chip, the micro-fluidic chip comprises a sample introduction channel, a storage chamber, a micro-mixing chamber, a wax precipitation chamber and a temperature control system, and the micro-mixing chamber realizes efficient mixing of a pour point depressant and crude oil; the wax precipitation chamber simulates the complex flow state environment of a real oil pipeline, a wax crystal morphology observation area, a wax crystal motion behavior observation area and a wax crystal dynamic behavior observation area are arranged, the wax crystal flow state is observed, and wax crystal dynamic parameters are collected; through dynamic time sequence modeling of LSTM and strategy gradient optimization of PPO, efficient dynamic adjustment of a pour point depressant formula is realized.

The present invention relates to the technical field of waste recovery, and provides a method for preparing a hemihydrate gypsum powder from phosphogypsum by means of an atmospheric salt solution process, and a hemihydrate gypsum powder. The method comprises: preparing a slurry from a mixed liquid of a salt and a crystal modifier and purified phosphogypsum, wherein the crystal modifier is a betaine compound with pH responsiveness; and adjusting the pH value of the slurry on the basis of the isoelectric point of the crystal modifier and the required length-diameter ratio of hemihydrate gypsum crystals, subjecting the slurry to a constant-temperature dynamic reaction, and filtering same, thereby obtaining a hemihydrate gypsum powder, wherein when the pH value of the slurry is greater than the isoelectric point of the crystal modifier, the length-diameter ratio of the hemihydrate gypsum crystals increases, and when the pH value of the slurry is less than the isoelectric point of the crystal modifier, the length-diameter ratio of the hemihydrate gypsum crystals decreases. By using the betaine compound as the crystal modifier, hemihydrate gypsum crystals with different length-diameter ratios can be obtained by adjusting the pH value of the slurry, and therefore the regulation and control of the crystal morphology of hemihydrate gypsum are achieved and exhibit a certain pattern.

The application belongs to the technical field of inorganic fine chemical phosphate purification, and provides a high-purity trisodium phosphate and a preparation method thereof. The preparation method comprises the following steps: (1) preparing a trisodium phosphate saturated crude slurry; (2) adjusting the quality of the slurry: after the trisodium phosphate saturated crude slurry is warmed, it is placed and kept warm; (3) purification: the temperature of the adjusted slurry is controlled and kept; then, anhydrous trisodium phosphate homologous slow-release seeds are added into the slurry; the system supersaturation is adjusted in two stages; the stirring is stopped to perform normal-pressure static crystal growth, and the purified slurry is obtained; and (4) post-treatment. The prepared high-purity trisodium phosphate has extremely low impurity contents of heavy metals and anion by-products, and has regular crystal morphology and strong crystal form stability, and is not prone to problems such as caking and hydrolysis during storage.

The present disclosure relates to the field of pharmaceutical chemistry, and specifically relates to a crystal form of a selective PARP-1 inhibitor, i.e. a crystal form of a compound represented by formula (I), a preparation method therefor and the use thereof. The crystal form of the compound represented by formula (I) provided by the present disclosure has at least one of the following excellent characteristics: good stability, high purity, good solubility, good dissolution, high bioavailability, low hygroscopicity, good fluidity, good mechanical stress stability, good processability, such as good compressibility, good crystal morphology, good pressure resistance, capability of stable storage, capability of avoiding crystal transformation of a drug during development and storage processes, a simple and reliable preparation method and high development value.

The invention discloses a nano NON molecular sieve as well as a preparation method and application thereof. The crystal morphology of the nano NON molecular sieve is a nano particle, and the average diameter of the crystal is 50-140 nm. The molecular sieve has the advantages of nano-particle morphology, uniform particle size and small size; the molecular sieve can be used as an adsorbent or a catalyst for conversion of organic compounds, and has good performance.

The invention provides a blank molding assembly block of diamond large single crystals and a plastic growth method, and belongs to the technical field of superhard material synthesis. The blank molding assembly block comprises a mutually-embedded metal catalyst layer formed by mutually embedding a plurality of prismatic table metal catalyst structures, the whole mutually-embedded metal catalyst layer is in a prismatic table shape, one of the upper end face and the lower end face of each prismatic table metal catalyst structure is in contact with the high-purity graphite carbon source layer, and the other one of the upper end face and the lower end face of each prismatic table metal catalyst structure is in contact with the seed crystal; the adjacent prismatic table metal catalyst structures are separated by an insulating layer, and the insulating layer is a Ca coating or a BN coating. A mutually-embedded prismatic-table-shaped metal catalyst structure with an axial temperature gradient and a carbon diffusion channel is constructed in a blank assembly block, diamond is induced to grow in a preset direction in an HPHT environment, directional shaping growth of the diamond is achieved under the condition that the process complexity is not improved, and the quality of the diamond is improved. The crystal morphology controllability, the catalytic agent utilization efficiency and the final drilling rate are remarkably improved, and the single-cavity yield is increased.

The application discloses a nano aluminophosphate molecular sieve and a synthesis method thereof. The crystal structure of the aluminophosphate molecular sieve is an aluminophosphate-A type crystal structure, the crystal morphology is similar to a cube, and the crystal edge length is 30-110 nm. The crystal outer surface has irregular step lines, and with the decrease of the crystal size, the crystal morphology tends to be a sphere. The synthesis method of the nano aluminophosphate molecular sieve comprises the following steps: (1) preparing initial gel materials; (2) performing crystallization treatment on the gel obtained in the step (1) under crystallization reaction conditions; (3) further separating after the crystallization treatment, and then treating under drying conditions and calcination conditions to obtain the nano aluminophosphate molecular sieve. The synthesis method adopts a novel structure directing agent to synthesize the nano aluminophosphate molecular sieve, and the synthesis process is simple and operable, and the target product can be obtained without harsh conditions.

The waterproof multi-layer display device comprises a main display module, the main display module comprises a substrate, a liquid crystal layer, a conductive layer, a first base layer and a second base layer, the liquid crystal layer is arranged between the first base layer and the second base layer, the substrate is attached to the first base layer, the surface of the substrate is covered with a layer of flat conductive adhesive, and the conductive layer is arranged between the first base layer and the second base layer. The liquid crystal layer is injected between the first base layer and the second base layer in a filling manner, the second liquid crystal layer is filled between the conductive layer and the polarizing plate and is arranged between the conductive layer and the conductive adhesive, and the conductive adhesive and the conductive layer are separated from each other; the second liquid crystal layer is arranged between the conductive layer and the conductive adhesive, the conductive adhesive and the conductive layer are separated from each other, the conductive layer and the conductive adhesive are covered with a moisture-proof agent, the conductive layer applies voltage to the liquid crystal layer to change the crystal form of the liquid crystal layer, and the conductive layer covers the conductive adhesive to ensure the overall conductive sensitivity; the moisture-proof agent covering the surface of the conductive adhesive and hydrophobic groups of the moisture-proof agent form double barriers.

The invention belongs to the technical field of ardealite treatment, and particularly relates to a method for preparing high-strength alpha-semi-hydrated gypsum from ardealite. The method comprises the following steps: fully dissolving an organic acid salt and a crystal modifier in deionized water by adopting a normal-pressure organic acid salt solution method to obtain an organic acid salt solution system; heating the organic acid salt solution system to a dehydration conversion reaction temperature, and then adding ardealite for reaction; and filtering the reaction liquid, and cleaning and drying a filter cake to obtain the high-strength alpha-semi-hydrated gypsum. By controlling various factors such as the variety and concentration of the organic acid salt, the dosage of the crystal modifier, the reaction temperature and the addition amount of the phosphogypsum, the conversion of the phosphogypsum to the alpha-semi-hydrated gypsum is realized in multiple ways, and the crystal morphology of the alpha-semi-hydrated gypsum is effectively regulated and controlled, so that the alpha-semi-hydrated gypsum forms a short columnar crystal of which the length-diameter ratio is close to 2.2; therefore, the high-strength gypsum with the compressive strength reaching 25MPa is prepared.

To provide a compound for use as a medicine.SOLUTION: Provided are a compound of formula (1) as an anhydrate which is in a crystalline Form 2, characterized by having a powder X-ray diffractogram presenting peaks expressed as degree 2θ angles at about 9.5, 11.8, 14.1, 14.6, 17.7, and 18.5, and a solid form thereof.SELECTED DRAWING: None

The invention belongs to the technical field of medicine separation, and discloses a coupling crystallization method for preparing a dicloxacillin sodium premium-grade product, which comprises the following steps: taking 6-aminopenicillanic acid (6-APA) as an initial raw material, carrying out acylation reaction and salt forming reaction, and finally carrying out evaporation-elution coupling crystallization to obtain the dicloxacillin sodium premium-grade product. The dicloxacillin sodium premium-grade product with regular crystal morphology, large particle size (greater than 200 [mu] m), high crystallinity, high purity (up to 99.4%), process yield greater than or equal to 80% and good stability can be obtained. The method is simple in required equipment, large in treatment scale, simple and convenient to operate and easy for industrial production, and has better technical economy and higher industrial application value.

The invention relates to the technical field of regulation and control of ethylene glycol antimony, in particular to a preparation method for conveniently regulating and controlling the morphology of ethylene glycol antimony crystals, which comprises the following steps: adding an antimony source and ethylene glycol into a reaction kettle according to a mass ratio of 1: (3-8), and stirring until the antimony source is completely dissolved to obtain an antimony source-ethylene glycol solution; and adding a crystal morphology regulating agent into the obtained solution, and uniformly stirring and mixing. By selecting different types of regulating agents and adjusting the dosage, flaky (1-5 microns), columnar (length-diameter ratio is (3-5): 1) or spherical (0.5-2 microns) ethylene glycol antimony crystals can be stably prepared, and the requirements of different polyester synthesis scenes are met.

The invention provides a preparation method of micro-nano anhydrous gypsum with various crystal forms, and belongs to the technical field of recycling of inorganic non-metallic materials and solid wastes. The method comprises the following steps: by taking phosphogypsum as a raw material, firstly washing and drying the phosphogypsum; then, selecting different reaction medium systems and corresponding crystal form / morphology control agent combinations, and regulating and controlling corresponding reaction temperature, time and stirring rate to directionally prepare a micro-nano anhydrous gypsum precursor with spherical, short columnar, layered or cubic morphology; and finally, filtering, washing, drying and calcining to obtain a final micro-nano anhydrous gypsum product. According to the invention, through precise regulation and control of process conditions, controllable preparation of the morphology of the anhydrous gypsum crystal is realized, the added value of the product is high, and a new way is provided for high-quality utilization of phosphogypsum.

The application relates to the field of molecular sieves, and discloses a ZSM-5 molecular sieve, a preparation method and application thereof, and a catalytic cracking method of triisopropylbenzene. The ZSM-5 molecular sieve has a cross-assembled aggregate crystal morphology formed by sheet-shaped nanocrystals, and the sheet-shaped nanocrystals adjacent to each other in the molecular sieve have a cross-assembled aggregate crystal morphology formed by 90 DEG + / -10 DEG rotation symbiosis and 30 DEG + / -5 DEG rotation symbiosis.

The invention discloses a battery grade ferrous sulfate continuous cooling crystallization method and system based on a crystal form directing agent, and the method comprises the following steps: mixing a purified ferrous sulfate solution with a nanoscale CHA / MOR molecular sieve crystal form directing agent, feeding the mixture into a multi-stage continuous crystallization kettle, carrying out temperature control crystallization, and finally carrying out solid-liquid separation to obtain a product, the system correspondingly comprises a crystallization kettle, a crystal form guiding agent and a seed crystal adding unit which are connected in sequence, the crystal morphology is actively regulated and controlled by utilizing the specific crystal form guiding agent, and the high-tap-density columnar crystal is obtained; an electric field is arranged in a crystallization transition area, so that in-situ directional migration and deep removal of foreign ions are realized; a crystal form memory elimination module is integrated, impurity circulation is broken through rapid freezing-instantaneous heating, efficient and energy-saving deep purification is achieved, the problems that in battery-grade ferrous sulfate production, the crystal morphology is uncontrollable, the impurity content is high, the technological process is long, and energy consumption is large are synchronously solved, and the product is high in purity and good in physical performance; the method is especially suitable for preparing a lithium ion battery positive electrode material precursor.

The invention belongs to the field of scale inhibitor performance evaluation, and particularly relates to a scale inhibitor dynamic evaluation method which comprises the following specific steps: firstly, taking an actual water sample or a configured water sample as an experimental water sample; putting the heating element into an experimental water sample, operating a water sample circulating system, and continuously supplementing scale anions, cations and a to-be-evaluated scale inhibitor into the system in the operation process; after the operation is finished, analyzing the scale sample to obtain the results of the scale inhibition rate, the dispersion rate of the scale inhibitor and the crystal form of the scale sample; and finally, re-preparing the scale inhibitor according to the results of the scale inhibition rate, the dispersion rate of the scale inhibitor and the crystal form of the scale sample, and repeating the steps 1-3 until the scale inhibition requirement is met. By analyzing the scale inhibition rate, the dispersion rate of the scale inhibitor and the crystal form of a scale sample, comprehensive and efficient evaluation on the performance of the scale inhibitor in the fields of pulping and papermaking is realized, the scale inhibitor is re-prepared according to an evaluation result, and the most suitable scale inhibitor is prepared for different water samples. Meanwhile, the invention further discloses the scale inhibitor prepared according to the result of the evaluation method.

The present disclosure relates to an ANA-structure faujasite zeolite and a preparation method thereof, a unit cell chemical formula of the ANA-structure faujasite zeolite being |Na x |[Si y Al z O 96 ] wherein x = 6-15, y = 30-37, and z = 10-16; the ANA-structure faujasite zeolite has a spherical crystal morphology. The ANA-structure faujasite zeolite of the present disclosure has a spherical crystal morphology and exhibits excellent molecular diffusion performance, and has good application prospects in the fields of small molecule acid catalytic reactions, small molecule gas adsorption separation, ion adsorption purification, and the like.

This invention provides a radially temperature-adjustable crystal growth apparatus and method, relating to the field of silicon carbide crystal growth technology, to improve the technical problem of inconvenient radial temperature gradient adjustment of the crystal to be grown in the prior art. It includes a heating furnace, a crucible, and a radial temperature gradient adjustment device; the crystal to be grown and silicon carbide powder are respectively arranged inside the crucible; the radial temperature gradient adjustment device is disposed on the top wall, and includes a driving component and multiple heat reflectors connected to the driving component; the multiple heat reflectors selectively move above the crystal to be grown under the action of the driving component to reflect at least a portion of the heat above the crystal to be grown to the crystal, thereby adjusting the radial temperature gradient at the growth interface of the crystal. This invention can effectively reduce crystal defects, improve substrate yield, and obtain the desired crystal morphology.

The present invention provides omadacycline crystalline free base and a method for synthesizing the same. The present invention also provides pharmaceutical compositions containing omadacycline crystalline free base and methods for using the same to treat bacterial infections. The present invention also provides a method for purifying crude omadacycline free base, including crystallization to produce crystalline omadacycline free base. The omadacycline crystalline free base can also be used to prepare salts of omadacycline, such as the tosylate salt.

The embodiment of the invention provides a corrosion device for crystal treatment. The corrosion device comprises a corrosion crucible and a lifting structure arranged on the corrosion crucible, the corrosion crucible is used for filling corrosive liquid, the corrosive liquid is used for leveling crystal morphology and / or corroding target substances, and the target substances comprise volatile matters and / or cosolvents at the bonding positions of the crystals and the crystal tray; the lifting structure is used for placing a crystal, a protrusion is arranged at the bottom of the lifting structure and used for making contact with the surface of the crystal, and the contact area of contact is smaller than a first preset threshold value.