47 results about "Microbial DNA" patented technology

The invention relates to the technical field of ship biological killing, in particular to an ultraviolet and ultrasonic cooperative killing control method and device for ballast water treatment, and constructs a cooperative control device which takes a central control unit as a core and integrates various sensors such as a flow sensor, a turbidity sensor, a microorganism content sensor, an ultraviolet intensity sensor, a temperature sensor and the like. The ballast water quality and the equipment operation state are monitored in real time. The ultrasonic generation unit and the ultraviolet disinfection unit cooperatively work under precise regulation and control of the central control unit, and by utilizing ultrasonic cavitation, mechanical and thermal effects and combining the destructive effect of ultraviolet rays on microorganism DNA, various microorganisms are efficiently killed, and meanwhile water scale on an ultraviolet lamp is removed. The microorganism killing efficiency is improved, the service life of the ultraviolet lamp tube is prolonged, the equipment maintenance cost and energy consumption are reduced, and it is guaranteed that ballast water discharge meets the environmental protection standard.

The invention discloses a soil microorganism carbon utilization efficiency determination method, and relates to the technical field of carbon utilization efficiency determination, and the method comprises soil sample pre-culture, multi-source 18O isotope gradient labeling, dynamic gas monitoring, microorganism respiration rate dynamic correction, and microorganism growth rate and carbon utilization efficiency acquisition. By labeling multi-source isotopes and quantifying contributions of different oxygen sources to microorganism DNA synthesis, underestimation of the carbon utilization efficiency caused by a traditional single labeling method is avoided, the problem of limitation existing in the current soil microorganism carbon utilization efficiency determination process is solved, the inhibition effect of too high local concentration on microorganism metabolism is reduced through gradient labeling, and the accuracy of soil microorganism carbon utilization efficiency determination is improved. The method has the advantages that marking uniformity is improved, multiple groups of soil samples are arranged, real-time change of microbial respiration is captured by means of dynamic monitoring, influence of isotope fractionation on carbon dioxide concentration calculation is eliminated, instantaneous errors of traditional static measurement are avoided, and accuracy of analysis results is improved to a certain extent.

The invention relates to the technical field of intelligent peanut disease monitoring, in particular to an intelligent peanut disease monitoring method based on community diversity analysis. According to the method, soil environment parameters are collected in real time through a multi-source sensor array, and rhizosphere microorganism DNA is extracted based on an improved CTAB-PEG method for high-throughput sequencing; constructing a dynamic baseline model fusing a Shannon-Wiener index, a phylogenetic diversity index and an environment correction factor; synchronously analyzing spatial distribution and time evolution characteristics of an OTU abundance matrix by adopting a deep space-time convolutional network, and decoding a microbial anomaly succession signal through a gating circulation unit; and when the disease risk index exceeds a threshold value, activating an early warning terminal and generating a resistant variety adaptation scheme. According to the method, the problems of incomplete microorganism capture, misjudgment of environmental interference, early warning lag and the like of a traditional method are solved, and collaborative optimization of precise early warning and prevention and control decision of peanut diseases is realized.

The present invention relates to the field of food processing, and discloses a weakly acidic moisturizing flour product, which comprises wheat flour and an antibacterial liquid, and the antibacterial liquid comprises tea polyphenol, a lactic acid buffer solution, ergothioneine and glucose. By adopting a dynamic biological acidification regulation and control system and accurately controlling key environmental factors in the fermentation process, specific probiotics are guided to carry out directional metabolism, so that a uniform and appropriate weak acid environment is formed in the flour product. The uniform acidity distribution not only enhances the microbial stability of the product, but also effectively protects the protein network structure of the flour product, maintains the original good elasticity and chewiness of the product, and meanwhile, integrates the microwave-ultraviolet synergistic sterilization technology, so that the product quality is improved. The body heating effect of microwaves and the photochemical damage capacity of ultraviolet rays on microorganism DNA are ingeniously combined, and the excellent sterilization effect can be achieved at the low processing temperature within the shorter processing time.

The invention relates to the field of microbiological detection, in particular to a microbiological detection and identification device and identification method.The microbiological detection and identification device comprises a main cylinder, a bearing plate is slidably arranged in the middle of the main cylinder, a plurality of circular grooves are formed in the bearing plate, storage units are placed in the circular grooves, and a puncture assembly is arranged in a lower cavity; one side of the puncture assembly extends into the circular groove and the storage unit and is used for supplementing an extraction reagent into the circular groove and the storage unit, a limiting assembly used for limiting and plugging the storage unit is arranged at the upper end of the main cylinder, and a nanopore tester connected with the puncture assembly is mounted and inserted in the bottom of the main cylinder; through mutual cooperation of the storage unit, the puncture assembly and the adsorption assembly, when a microbial sample is detected, microbial DNA and RNA nucleic acid separation can be efficiently achieved, nucleic acid is secondarily extracted through the adsorption assembly, the purity of the nucleic acid sample is accurately improved, and the detection efficiency is improved. The problems of low extraction purity and more impurities in the traditional method are solved.

This invention relates to DNA extraction methods from soil and sediments with high humic substances content. The method focuses on the soil preparation phase; removing salts and cations with two different Tris-EDTA (TE) buffers, followed by precipitating humic substances with aluminum hydroxide solution and washing again with TE and cell lysis phase; urea is used as denaturing agents for the cell lysis phase and protein degradation phase while preventing the rediffusion of humic substances with CTAB. The purification can be performed following both the classic phenol chloroform method and using commercial DNA purification columns. This method is very accessible with operation time varying from 1h40 min to 2h30 min. The invention involves the use of TE and aluminum hydroxide solutions for soil preparation, and urea and CTAB as denaturing agents during cell lysis, in the specified concentrations, order, and incubation time, to prevent contamination of final DNA with humic substances

The invention belongs to the technical field of molecular biology, and particularly relates to a pathogenic microorganism nucleic acid co-extraction kit, an extraction method and application. The invention provides a lysis solution for nucleic acid co-extraction of pathogenic microorganisms. The lysis solution comprises a first guanidine salt, an ionic surfactant, a first sodium salt and a first nonionic surfactant. According to the splitting system, guanidine salt is adopted and matched with a certain content of sodium salt and a surfactant, a sample is split and precipitated under the grinding condition, nucleic acid cannot be damaged in the crushing process, and pathogenic microorganism DNA and RNA with high concentration and complete fragments can be extracted.

The invention discloses a method and system for synchronously detecting host chromatin openness and in-vivo microbiome based on transposase, and belongs to the technical field of biological sequencing data analysis. According to the method, transposase is used for selectively fragmenting an open chromatin region of a host, and a microbial genome is almost randomly cut, so that synchronous enrichment of host and microbial DNA is realized; after high-throughput sequencing library construction and double-end sequencing, sequencing data is split into host source and non-host source reads through bioinformatics analysis, host chromatin state and microorganism composition are analyzed respectively, and a microorganism-host epigenetic regulation network is constructed; the invention further provides a matched DNA sequencing library and an analysis system, multi-scene research of infectious diseases, intestinal microecology, tumor microenvironment and the like is supported, a public database can be reanalyzed, and potential microbial interaction signals are mined. According to the method, the host-microorganism interaction research efficiency is remarkably improved, and a high-sensitivity and integrated technical scheme is provided for epigenetic regulation mechanism analysis.

A portable extraction device consisting of a microfluidic cartridge, a magnetic bead-based cleaning system and an electronic control unit, configured for automated extraction of microbial DNA from soil samples.

The present invention relates to the technical field of oil development, and discloses a method for calculating inter-well connectivity based on the time-step response relationship, which includes collecting and sequencing the bacterial genomic DNA of the injection well and the production well of the injection-production well pair to determine the corresponding bacterial species and bacterial abundance; constructing a pulse response model, in which the measured values of the bacterial species and bacterial abundance of the injection well and the production well are used as input signals and output signals respectively in the pulse response model, introducing the Kalman filtering method to construct the response relationship based on time steps between the injection well and the production well, and using the Laplace transform to solve the response relationship to obtain the strength of the response relationship between the injection well and the production well; and using the strength of the response relationship to characterize the size of the connectivity between the injection well and the production well, and determining the connectivity between the injection well and the production well; the present invention combines the microbial DNA sequencing results and the Kalman filtering calculation method to reflect the dynamic change law of the inter-well connectivity between the injection and production wells in real time and efficiently.

The invention belongs to the technical field of petroleum geology engineering, and particularly provides an analysis method for microorganism DNA sequencing and application of the analysis method in stratigraphic division. The analysis method comprises the following steps that in the drilling process, rock debris is sampled from a vibrating screen at a wellhead, and rock debris samples are collected once every 0.5 m so as to collect rock debris samples of different stratum depths; the collected rock debris is subjected to treatment and DNA sequencing, and the variety and abundance of strains contained in the rock debris are obtained; the strains are preliminarily screened, and the strains from the underground oil reservoir are reserved; the reserved strains are clustered, and the total length of the stratum where the rock debris is collected is preliminarily divided into a plurality of stratums according to the similarity and correlation of the strains in different stratum depths; and each stratum is finely divided into a plurality of small stratums by taking the characteristic strains in each stratum as main characteristics.

The present invention proposes a method for evaluating the growth of exogenous microorganisms in soil, comprising the following steps: S1, adding exogenous microorganisms and H2 to dry soil 18 O to carry out soil culture test, collect soil samples and extract soil DNA; S2, H2 16 O and H2 18 O. Preparing a liquid culture medium for culturing exogenous microorganisms, collecting the obtained exogenous microorganisms and extracting DNA; S3. Dissolving the soil DNA obtained in S1 and the bacterial DNA sample in S2 in a cesium chloride solution and performing density gradient centrifugation to obtain the distribution ratios of different DNAs along the density gradient; S4. Determining the average density of the exogenous microbial DNA in the soil based on the obtained distribution ratios of the different DNAs to achieve a quantitative evaluation of the growth degree of the exogenous microorganisms; the present invention performs quantitative PCR analysis on unique gene fragments of exogenous microorganisms, which can eliminate the interference of other microorganisms in the soil and perform highly specific analysis of the exogenous microorganisms.

The present invention is directed to methods for confirming the identity of an item or product using a segment of DNA present in a killed microorganism as a tag. In some embodiments, a food compatible microorganism containing a target nucleotide sequences not present in the item to be tagged is selected to serve as a tag and an identity unique identifier and / or other metadata for of the item is then saved for that tag in a database. The microorganism is killed to create a tag with the target nucleotide sequence and the tag is added to the item. The identity of the item can later be confirmed by extracting the DNA in the item and amplifying the target nucleotide sequence or sequences using PCR techniques, sequencing each amplified target nucleotide sequence; and then comparing them to the nucleotide sequence saved for the target nucleotide sequence.

The invention relates to the technical field of biomedicine and microorganisms, and provides an intestinal flora excrement sample preserving fluid which comprises a buffer system, a chelating agent, a reductive anaerobic protective agent, a cell lysis-bacteriostatic agent and a biomacromolecular stabilizer, wherein the buffer system is a combination of a Tris-HCl buffer solution and sodium chloride, the chelating agent is ethylenediamine tetraacetic acid disodium salt, the reductive anaerobic protective agent is L-cysteine hydrochloride, the cell lysis-bacteriostatic agent is sodium lauroyl sarcosinate, and the biomacromolecular stabilizer is a combination of trehalose and glycerin. The invention also provides a preparation method of the preserving fluid. According to the invention, the microbial DNA and community structure in the excrement can be stably preserved at room temperature for a long time without a cold chain; meanwhile, the preservation solution can effectively protect DNA of strict anaerobic bacteria from oxidative degradation, flora composition is prevented from shifting, and the reliability of subsequent molecular detection and analysis is finally ensured.

The application discloses a multi-cancer early screening method based on fragmentomics and microbiomics characteristics and application thereof, and belongs to the technical field of biomedical detection. The method comprises the following steps: extracting fragmentomics characteristics of human cfDNA and microbiomics characteristics of plasma microbial DNA based on sequencing data; inputting the two types of characteristics into a first-stage classification model after fusion, and judging whether a subject is cancer positive; and further predicting the cancer type through a second-stage classification model for the positive result. The application combines fragmentomics and microbiomics characteristics, and is used for multi-cancer early screening. Through single non-invasive blood sampling, early screening and organization tracing of eight high-incidence cancers such as lung cancer, liver cancer and colorectal cancer can be realized. The method has high sensitivity and high specificity under low sequencing depth, is low in cost, wide in coverage, and suitable for large-scale population screening.

The invention discloses a chiral supramolecular nano assembly as well as a preparation method and application thereof, and belongs to the technical field of biomedical nano materials. The nano assembly (ZnO2 (at) CDP / Fc-DA) is constructed by taking zinc peroxide as a core, modifying a supramolecular ligand CDP through ligand exchange and combining D-alanine functionalized ferrocene guest molecules (Fc-DA) by virtue of interaction of a host and a guest. According to the assembly, the specific targeting effect of D-alanine on tumor tissues and gram-positive bacteria in tumors is utilized, Zn < 2 + > and H2O2 are decomposed and released in an acid lysosome environment of tumor cells, hydroxyl free radicals are generated under the catalysis of ferrocene, and the bacteria and the tumor cells are synchronously induced to generate ferroptosis. The microbial DNA released by bacterial ferroptosis can further activate the cGAS-STING innate immune pathway, reverse the immunosuppression microenvironment and synergistically enhance the anti-tumor immune response. According to the invention, the collaborative treatment of precise removal and immune activation of bacteria in the tumor is successfully realized, and a new effective strategy is provided for treating the breast tumor with bacteria colonization.

The invention discloses an ultraviolet and hydrogen peroxide synergistic sterilization method. According to the method, an ultraviolet light source is arranged, a microbial DNA structure is directly destroyed by utilizing ultraviolet rays to realize primary inactivation, and meanwhile, a hydrogen peroxide solution is excited to be decomposed to generate high-activity oxidizing substances such as hydroxyl free radicals and the like. Through a dual action mechanism of physical irradiation and chemical oxidation, a multi-dimensional synergistic sterilization system is formed, and various microorganisms with cellular structures, such as fungi, bacteria and spores, can be efficiently killed. Compared with a traditional single sterilization technology, the sterilization method has the application advantages that the sterilization blind area is eliminated through a multi-effect synergistic mechanism, and sterilization thoroughness is improved; a low-concentration hydrogen peroxide solution is adopted, so that the chemical residue risk is reduced. The method is realized through a special ultraviolet and hydrogen peroxide synergistic sterilization device, and is suitable for object surface treatment.

The application discloses a kind of determination methods of soil microbial carbon utilization efficiency, it is related to the determination field of carbon utilization efficiency, the application includes pre-culturing soil sample, multi-source 18 O Isotope gradient labeling, dynamic gas monitoring, dynamic correction of microbial respiration rate, microbial growth rate and carbon utilization efficiency acquisition, by multi-source isotope labeling, the contribution of different oxygen sources to microbial DNA synthesis is quantified, the low estimation of carbon utilization efficiency caused by traditional single labeling method is avoided, the limitation problem existing in the current soil microbial carbon utilization efficiency determination process is solved, gradient labeling reduces the inhibitory effect of local concentration on microbial metabolism, improves the uniformity of labeling, sets multiple soil samples, simultaneously uses dynamic monitoring to capture the real-time change of microbial respiration, eliminates the influence of isotope fractionation on carbon dioxide concentration calculation, avoids the instantaneous error of traditional static measurement, to a certain extent, the accuracy of analysis result is improved.

The utility model relates to the technical field of boards, and discloses a plasma antibacterial board which comprises a wood board base material, surface layer boards are arranged at the upper end and the lower end of the wood board base material, the surface layer boards are antibacterial boards processed through the plasma technology, the surface layer boards are hot-pressed on the wood board through high temperature and high pressure generated by ionized gas, and antibacterial factors are contained in the surface layer boards. After the antibacterial factors are catalyzed by high temperature and high pressure generated by ionized gas, quadruple antibacterial effective components including zinc ions, hydroxyl radicals, superoxide ions and hydrogen peroxide are formed. The antibacterial effective components can destroy the protein structure of bacteria and interfere the DNA synthesis of microorganisms, so that the efficient antibacterial effect is realized. The efficient and lasting antibacterial property is realized, and the bacterium breeding can be effectively inhibited.

The present invention is directed to methods for confirming the identity of an item or product using a segment of DNA present in a killed microorganism as a tag. In some embodiments, a food compatible microorganism containing a target nucleotide sequences not present in the item to be tagged is selected to serve as a tag and an identity unique identifier and / or other metadata for of the item is then saved for that tag in a database. The microorganism is killed to create a tag with the target nucleotide sequence and the tag is added to the item. The identity of the item can later be confirmed by extracting the DNA in the item and amplifying the target nucleotide sequence or sequences using PCR techniques, sequencing each amplified target nucleotide sequence; and then comparing them to the nucleotide sequence saved for the target nucleotide sequence.

A grade of a specific microbial disease in a biological sample of a subject is determined. In one example, masked microbial reference genomes are used to determine the amount of free DNA molecules corresponding to a particular microbial species associated with a particular microbial disease. The masking may remove an area shared with another. In another example technique, end motifs are used for free DNA fragments from a subject and from a particular microbial species. A correlation between a subject and an amount of a set of terminal sequence motifs of a particular microbial species may be determined. The two groups of quantities of positive subjects are substantially more correlated than negative subjects.

This invention provides a method and system for assessing the development of infant gut microbiota, involving a set of judgment models and standards, including a classification model for the maturity of infant gut microbiota development, a regression model for the developmental age of infant gut microbiota development, and a developmental curve and reference range for microbiota age. This invention extracts and sequences microbial DNA from infant feces, and based on statistical analysis, determines that 27 months of age is a critical node for the maturity of infant gut microbiota development in China. Using this as a dividing line, a machine learning classification model is constructed to determine whether the microbiota development is mature, with an AUC exceeding 97%. Furthermore, based on this, a machine learning regression model is used to predict the developmental age of infant gut microbiota. The regression prediction model is applied to large-scale datasets to predict and set reference ranges for developmental judgment standards, providing a new reference standard for assessing the maturity of infant gut microbiota development.

The invention belongs to the technical field of forensic medicine and biological medicine, discloses a method for forensic medicine identification of corpses in water based on metagenomics markers and application, and aims to solve the problems that existing drowning diagnosis is insufficient in accuracy and the deduction of post-death submerging time (PMSI) is limited. The method comprises the following steps: collecting a corpse lung tissue in water and a water sample in a corresponding water area, and obtaining a microbial DNA sequence by adopting a metagenome sequencing technology; the method comprises the following steps: processing data through bioinformatics analysis (such as fastp quality control, host sequence removal by KneadData and Kraken2 species annotation), and selecting and screening species level microbial markers in combination with a random forest algorithm and Boruta characteristics; and respectively establishing a drowning diagnosis model and a PMSI inference model based on the screened markers, and verifying the performance of the models through indexes such as AUC and MAE. Complete microbial communities of bacteria, eukaryotes (including fungi), archaea and viruses in lung tissues of corpses in water are comprehensively analyzed for the first time, 17 bacterial markers and 9 eukaryote markers are screened out for drowning diagnosis (verification experiment bacterial model AUC = 1, the accuracy rate is 89.29%, eukaryote model AUC = 0.95, the accuracy rate is 87.5%), and 17 markers are screened out for PMSI inference (integrated model MAE = 0.66 days). According to the method, the species resolution reaches the species level, the method is not influenced by amplification bias, the method is suitable for different water area environments, and an efficient and objective forensic medicine tool is provided for identifying the cause of the dead body in water and deducing the submerged time after the dead body.

The invention discloses a gastric cancer risk assessment and diagnosis method based on gastric mucosa micro-ecological change, relates to the technical field of medical diagnosis and biology, and provides the gastric cancer risk assessment and diagnosis method based on the gastric mucosa micro-ecological change. The method comprises the following steps: collecting gastric mucosa tissues or gastric juice samples, extracting total DNA (deoxyribonucleic acid) of microorganisms, performing high-throughput sequencing by using an Illumina MiSeq platform, analyzing the diversity of the microorganisms, and identifying key flora. And inputting a random forest model by combining the concentration of metabolites such as short-chain fatty acid and clinical information, outputting a gastric cancer risk score, and dividing risk grades. The model is trained based on a large number of samples, and high accuracy is ensured. High-risk persons suggest gastroscope precise examination within three months, and personalized intervention suggestions are provided, so that early warning and precise health management are realized.

Methods are provided for detecting disease in liquid biopsy samples by identifying microbial rRNA. The methods include isolating nucleic acids from extracellular vesicles, treating the nucleic acids with DNase to remove DNA including human cfDNA, mcfDNA, and contaminating microbial DNA, and then amplifying a region of a microbial phylogenetic rRNA. To further reduce contaminating DNA, the amplifying step can include reverse transcription to translate the phylogenetic region into cDNA and extend the cDNA ends with a T7 promoter and sequencing adaptors. The translated region is amplified with primers to the extended ends of the cDNA and sequenced. The resulting phylogenetic microbial sequences are useful for diagnosis and monitoring of diseases including cancer. The method can further include amplification of other human or bacterial DNA or RNA sequences to augment disease diagnosis. The method results in a very low contribution of contaminating microbial DNA and RNA to the overall microbial signature.

The present disclosure provides systems and methods for detection of microbial DNA and RNA. In an aspect, a system or method for detection of microbial DNA or RNA comprises metagenomic next-generation sequencing of clinical samples (e.g., cerebral spinal fluid) to detect the microbial composition of the sample to diagnose a microbial infection (e.g., of the central nervous system).

The present application relates to the technical field of ship biological killing, in particular to a UV and ultrasonic synergistic killing control method and device for ballast water treatment, which is constructed with a central control unit as the core, integrates a synergistic control device of multiple sensors such as flow, turbidity, microbial content, ultraviolet intensity and temperature, and realizes real-time monitoring of the ballast water quality and the equipment operation state. The ultrasonic generating unit and the ultraviolet disinfection unit work synergistically under the precise regulation and control of the central control unit, utilize the ultrasonic cavitation, mechanical and thermal effects, combine the ultraviolet damage to the microbial DNA, efficiently kill various microorganisms and remove the scale on the ultraviolet lamp. The present application improves the microbial killing efficiency, prolongs the service life of the ultraviolet lamp, reduces the equipment maintenance cost and energy consumption, and ensures that the ballast water discharge meets the environmental protection standards.

The invention discloses disinfection equipment for a root canal file. The disinfection equipment consists of a box body, a cleaning device, a disinfection and drying device and an intelligent control module, the box body is divided into an upper layer and a lower layer, and the cleaning device cleans the root canal file at 360 degrees through a nozzle. And the lower layer is a disinfecting and drying device which comprises a chemical disinfecting device, a high-temperature steam disinfecting device, an ultraviolet disinfecting device and a drying device. The chemical disinfection device adopts an environment-friendly disinfectant; the high-temperature steam sterilization device utilizes an efficient electric heating pipe and a steam-water separation device to generate steam to kill microorganisms; the ultraviolet form device destroys microorganism DNA by using a high-efficiency ultraviolet lamp tube; the drying device forms hot air circulation to evaporate moisture through a fan and a hot-air blower. The intelligent control module can automatically select programs and parameters, monitor the operation state, give an alarm and record data. The equipment integrates various technologies and realizes comprehensive, efficient and safe disinfection of the root canal file.

The present invention relates to the field of biomedical technologies, and discloses a data verification and processing method for feline chronic inflammatory bowel disease, including the following steps: Sample collection and pretreatment: Collect feline fecal samples and tissue samples, extract microbial DNA and host RNA, and record the sample sources and detailed clinical information; Microbiota analysis: Perform 16S rRNA sequencing on the extracted microbial DNA. Also disclosed is a data verification and processing system for feline chronic inflammatory bowel disease, including: A data collection and storage module: Used to record sample sources, save sample information, and manage the DNA and RNA extraction results of samples. Through a comprehensive technical solution combining microbiota analysis and functional prediction based on 16S rRNA sequencing with qPCR verification and ELISA detection, a dynamically optimized feline IBD microbiota database is constructed, and personalized treatment suggestions are generated, forming a complete closed-loop system from data collection to treatment plan generation.

This invention belongs to the field of plant rhizosphere research and discloses a method for determining the regulatory effect of exogenous selenium application on the rhizosphere microecology of Amorphophallus bulbifera. The method includes: experimental design and sample collection; soil microbial DNA extraction and amplicon sequencing; and quality control and analysis of the microbiome data. This invention utilizes Illumina MiSeq high-throughput sequencing technology to analyze the changes in the composition and diversity of rhizosphere soil bacteria communities in Amorphophallus bulbifera under exogenous selenium treatment, and further analyzes the functions of related communities through PICRUSt functional prediction analysis. The conclusions are as follows: exogenous selenium treatment induces significant changes in the rhizosphere soil bacterial community of Amorphophallus bulbifera, which is beneficial for creating a stable and more diverse rhizosphere microbial community structure.