Mechanism Of Network Formation Research Articles

Numerical Investigation on Propagation Behaviors of a Three-Dimensional Fracture Network Coupled with Microseismicity in Fractured Shale Reservoirs

The formation mechanism and propagation behaviors of a three-dimensional hydraulic fracture network in fractured shale reservoirs remain unclear, especially when the scale of hydraulic fractures is much larger than that of natural fractures. In this study, taking the well XH in the Longmaxi shale reservoir in the Sichuan Basin, China as an example, we develop a fully three-dimensional numerical model for hydraulic fracturing coupled with microseismicity based on the discrete lattice method. We introduce a randomly generated discrete fracture network into the proposed model and explore the formation mechanism of the hydraulic fracture network under the condition that the hydraulic fractures are much larger than natural fractures in scale. Moreover, microseismic events are inversely synthesized in the numerical model, which allows the evolution of the fracture network to be monitored and evaluated quantitatively. In addition, we analyze the effects of injection rate, horizontal stress difference, and fluid viscosity on fracture propagation. Our results show that when the scale of hydraulic fractures is much larger than that of natural fractures, the fracture morphology of “main hydraulic fractures + complex secondary fractures” is mainly formed. We find that a high injection rate can not only create a complex fracture network, but also improve the uniform propagation of multi-cluster fractures and enhance far-field stimulation efficiency. Optimizing the horizontal wellbore intervals with low horizontal stress differences as the sweet spots of hydraulic fracturing is also beneficial to improve the stimulation efficiency. For zones with a large number of natural fractures, it is recommended to use an injection schedule with high viscosity fluid early and low viscosity fluid late to allow the hydraulic fractures to propagate to the far-field to maximize the stimulation effect.

Effect of fatty acid composition of vegetable oils on crystallization and gelation kinetics of oleogels based on natural wax

This study aimed to understand the effect of fatty acid composition and viscosity of vegetable oils on network formation mechanism and physical properties of oleogels. To this purpose, 12 oleogels were prepared, by choosing 6 seed oils and two waxes, at a fixed oleogelator concentration (6%). The modified Avrami model correctly describes the crystallization profile (R2 > 0.98) and the oil type did not affect the Avrami index that ranged from 1.00 to 1.43. Independently from oleogelator, rice and hemp seed oils followed a 3-D network formation mechanism, while almond oil a 2-D mechanism. The strength and yield stress of carnauba wax oleogels increased with increasing saturated fatty acid amount, while in beeswax-based oleogels a more interconnected structure was associated with the length of the saturated fatty acid chain. Thus, the oleogels formation mechanism was closely related to the chemical composition of the solvent, even in highly monounsaturated or polyunsaturated oils.

Physical activity promotion in an urban district: Analyzing the mechanisms of interorganizational cooperation.

Past research has identified the importance of cooperation among community-based organizations from different sectors to address public health problems such as insufficient physical activity. However, little is known about how and why interorganizational cooperation occurs. The present study sought to analyze the structure and emergent patterns of interorganizational cooperation within a network promoting physical activity based in an urban district neighborhood of a city in Southwestern Germany. Survey data on cooperative relations among 61 network organizations and organizational attributes (e.g., possession of sport facilities) were collected. Social network analysis was applied to examine network properties and exponential random graph models were estimated to test hypotheses concerning mechanisms and conditions of cooperative tie formation. The results show that the network of cooperation is sparse but characterized by a tendency for cooperation to occur in triangular structures. Other significant mechanisms of cooperative tie formation are preferential attachment, with the community department for education and sports being the most central network actor, and heterophily regarding the cooperation of organizations from different sectors. This study provides valid and reliable findings on conditions of network formation and significant mechanisms of interorganizational cooperation in the field of physical activity promotion. Knowledge about these mechanisms can help to manage networks effectively and efficiently and reveal potentials for improvement and intensification of interorganizational cooperation in both the present and other research areas of health promotion.

Removal of heavy metal ions from an aqueous solution by CS/PVA/PVP composite hydrogel synthesized using microwaved-assisted irradiation

A simple protocol of chitosan/polyvinyl alcohol/polyvinylpyrrolidone (CS/PVA/PVP) hydrogel synthesis using microwave-assisted irradiation to initiate and accelerate network formation was explored. The optimum ratio of CS:PVA:PVP was 0.3:0.6:0.3 g with epichlorohydrin as a cross-linking agent under 600 watts of irradiation for 3 min. The gel swelling degree and gel fraction of the hydrogel were approximately 1627.4% and 42.6%, respectively. The individual metal ion removal efficiency was the highest for Pb(II), followed by Cu(II), Ni(II), and Cd(II) as adsorbed by the CS/PVA/PVP hydrogel. Varying the pH of the solution containing metal ions in the range of 4.0 – 8.0 did not significantly affect the adsorption capacity. However, the order of adsorption capacity of mixed metal ions differed from that of individual ions. The maximum capacities of Pb(II), Cu(II), Ni(II), and Cd(II) ions were 80.02, 33.07, 15.13, and 8.36 mg g−1, respectively. The desorption and reusability study of the CS/PVA/PVP hydrogel revealed that 0.1 M EDTA was a suitable candidate to regenerate the hydrogel as more than 60% of metal ion removal efficiency was still achieved after five adsorption cycles. In addition, the reaction mechanism of the hydrogel network formation derived from infrared spectrometry indicated that network formations were developed through the reaction between the crosslinking agent and hydroxyl and amino functional groups of the starting materials. Adsorption mechanism based on the results obtained from x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) was also presented. This study showed that the proposed composite hydrogel could be further developed and used as a platform to efficiently adsorb metal ions.

A review of the research on externality of urban network

Urban network research has become the frontier academic field of international urban research and has gradually become a hot spot. At present, the related literature on “urban network” mostly focuses on conceptual discussion, dimension analysis, and network structure analysis. Research on the influence of network on regional economic development is relatively weak. Externality, as an essential attribute of urban network, is of great significance to the evolution of urban network and the development of cities and regions. This article starts from a comparison of agglomeration externalities with urban network externalities, focusing on the review and evaluation of the formation mechanism, utility, and measurement methods of urban network externalities.The synergy effect, integration effect, and borrowing size are considered important reasons for the formation of urban network externalities. The research on the effectiveness of urban network externalities focuses on two aspects. The first is the role of factor mobility in promoting knowledge diffusion and innovation, and the second is the impact of urban network on competitiveness and economic growth. Based on the existing literatures, the research on the measurement of urban network externalities mainly involves identification and estimation, including three common methods as correlation analysis, regression analysis, and spatial econometric analysis. The existing empirical researches on externalities are still mostly based on static analysis and lack dynamic consideration. The issues that need further attention in the future include theoretical understanding of urban network externalities, externality measurement methods, and empirical research.

Numerical Investigation of the Fracturing Effect Induced by Disturbing Stress of Hydrofracturing

Fracturing induced by disturbing stress of hydraulic fracturing is the frontier common core scientific problem of reservoir stimulation of coal bed methane and shale gas. The finite-discrete element method, numerical calculation method, is used to analyze the basic law of shear failure and tension failure of natural fractures induced by the disturbing stress of the hydraulic fracture. The simulation results show that when natural fractures and other weak structures exist on the front or both sides of hydraulic fracture, the shear stress acting on the surface of natural fracture will increase until the natural fracture failure, which is caused by the disturbing stress of hydraulic fracturing. The seepage area on the front and both sides of the hydraulic fracture did not extend to the natural fracture while the natural fracture failure occurred. It indicates that the shear failure of natural fractures is induced by the disturbing stress of hydraulic fracturing. When the hydraulic fracture propagates to the natural fracture, the hydraulic tension fracture and disturbed shear fractures are connected and penetrated. As the fluid pressure within the natural fracture surface increases, the hydraulic fracture will continue to propagate through the natural fracture. Meanwhile, due to the action of fluid pressure, a tensile stress concentration will occur at the tip of the natural fracture, which will induce the airfoil tension failure of the natural fracture. With the increase of the principal stress difference, the range of the disturbing stress area and the peak value of the disturbing stress at the front of the hydraulic fracture tip increase, as well as the shear stress acting on the natural fracture surface. During the process of hydraulic fracture approaching natural fracture, the disturbing stress is easier to induce shear failure of natural fracture. With the increase of the cohesive force of natural fracture, the ability of natural fractures to resist shear failure increases. As the hydraulic fracture approaches natural fractures, the disturbing stress is more difficult to induce shear failure of natural fracture. This study will help to reveal the formation mechanism of the fracture network during hydraulic fracturing in the natural fractures developed reservoir.

Heterogeneous node copying from hidden network structure

Node copying is an important mechanism for network formation, yet most models assume uniform copying rules. Motivated by observations of heterogeneous triadic closure in real networks, we introduce the concept of a hidden network model—a generative two-layer model in which an observed network evolves according to the structure of an underlying hidden layer—and apply the framework to a model of heterogeneous copying. Framed in a social context, these two layers represent a node’s inner social circle, and wider social circle, such that the model can bias copying probabilities towards, or against, a node’s inner circle of friends. Comparing the case of extreme inner circle bias to an equivalent model with uniform copying, we find that heterogeneous copying suppresses the power-law degree distributions commonly seen in copying models, and results in networks with much higher clustering than even the most optimum scenario for uniform copying. Similarly large clustering values are found in real collaboration networks, lending empirical support to the mechanism.

Research on the mechanism of knowledge diffusion in the MOOC learning forum using ERGMs

Research on the mechanism of knowledge diffusion in the MOOC learning forum using ERGMs

Self-Assembled 2D Networks of Metal Oxide Nanomaterials Enabling Sub-ppm Level Breathalyzers.

For extremely sensitive acetone sensors, here, we introduced an alcohol-assisted surfactant-free Langmuir-Blodgett process to rapidly assemble a single-layered two-dimensional (2D) network as a suitable percolation strategy of metal oxide semiconductor nanomaterials. The single-layered 2D network formation mechanism was investigated using zinc oxide (ZnO) nanobeads (NBs). Furthermore, the correlation between the response of the gas sensor and the average percolation number of the ZnO NBs, controlled by multi-stacking the 2D network, was investigated. It was inferred that a reduction in the number of percolations led to maximization of the response. Additionally, the versatility of the optimal percolation strategy was experimentally verified by confirming similar results to that achieved with ZnO NBs when utilizing different sizes, shapes, and compositions of metal oxides. Finally, the practical effectiveness of our extremely sensitive strategy was solidified by illustrating the response enhancement in a commercial exhalation diagnostic system that measures the amount of acetone in only 1 mL of exhalation.

Mechanisms of Single-Walled Carbon Nanotube Network Formation and Its Configuration in Polymer-Based Nanocomposites

The reinforcing and conductive performance of carbon nanotube polymer-based nanocomposites depends on the established network and its configuration. Within this study, we report on the underlying mechanisms of such network formation utilizing single-walled carbon nanotubes (SWCNTs) in low- and high-density polyethylene matrices. Mechanisms were theoretically evaluated through Doi–Edwards theory and experimentally confirmed through plasma etching coupled with electron microscopy as well as rheological flow tests. Results showed that the established network is constructed from SWCNT bundles, which geometrically entangle at a critical volume fraction Φv,crit (number of rods: β ≈ 30). Below Φv,crit, the bundles behave as individual units and may align in the flow direction. Above Φv,crit, the rotation of bundles is constrained by neighboring units, leading to a random network configuration. Moreover, the theory successfully explains SWCNT bundle behavior as a Brownian entity and predicts network formation through diminishing thermo- and hydro-dynamically driven diffusion, which can be manipulated during the production to enhance reinforcing/conductive functionality of such materials.

Analysis of influencing factors of stimulated reservoir volume (SRV) and zipper fracturing simulation in shale oil reservoirs of Hu326 Well area

Horizontal Well SRV of intensive stage and high–intensity for shale oil reservoirs of Hu326, which are different beddings and develop natural fractures locally, is conducive to the formation of complex fracture network with the intersection of main fractures, natural fractures, bedding fractures and other secondary fractures. At present, although there are systematic theories and methods for the study on the extension of hydraulic fracture after intersecting natural fractures and bedding planes, there is no quantitative research on specific parameters, and the research results are not applicable to actual exploitation. Based on the characteristics of shale oil reservoirs and combined with the theory of formation strength with weak surface, this article discusses the formation mechanism of fracture network of jimusar shale oil reservoir and improves the extension law of hydraulic fractures after intersecting with natural fractures and bedding planes. And taking the jimusar shale oil reservoir as the object, the extension law of hydraulic fracture is analysed and the geomechanical influencing factors and engineering control parameters of SRV are determined. The research results provide theoretical basis and parameter guidance for SRV of jimusar shale oil reservoir.

Polymer network formation mechanism of multifunctional poly(ethylene glycol)s in ionic liquid electrolyte with a lithium salt.

We report a controlled polymer network gel electrolyte based on a multifunctional poly(ethylene glycol) (PEG) prepolymer (herein, tetrafunctional PEGs (tetra-PEGs) and bisfunctional linear PEGs (linear-PEGs)) and an ionic liquid (IL)-based electrolyte solution containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSA) salt. The gel electrolyte was obtained via a gelation reaction, i.e., the Michael addition reaction between maleimide (MA)-terminated tetra-PEGs and thiol (SH)-terminated tetra- or linear-PEGs (termed tetra/tetra-PEG gel or tetra/linear-PEG gel systems), in a LiTFSA/IL solution under noncatalytic conditions at room temperature. For the tetra/linear-PEG system, the gelation reaction depended on the ratio of tetra-PEG-MA and linear-PEG-SH; an optimum terminal MA/SH ratio of 1 : 1 yielded a reaction efficiency (p) of ∼98% (an ideal polymer network structure). The tetra/tetra-PEG system with an MA/SH ratio of 1 : 1 also achieved a reaction efficiency of ∼98%. Time-resolved rheological measurements revealed that the network formation process can be categorized into three steps: (I) oligomer formation at an early stage of the reaction, (II) formation of a roughly linked polymer network with a large mesh size as the reaction proceeded, and (III) full network formation also at the local scale near the gelation completion time. The resulting tetra/linear-PEG ion gel with an optimum MA/SH ratio of 1 : 1 exhibited high stretchability, enduring approximately 10-fold elongation, and superior ion-conducting properties compared with the corresponding IL-based electrolyte solution.

The formation mechanism of the player transfer network among football clubs

ABSTRACT Clubs compete for talented players to succeed in the global football industry. Drawing on a network analytical framework, this research explores how endogenous and exogenous factors influence the partner selection process in the player transfer market. The boundary of the transfer network consists of 98 football clubs from the top five European leagues. Using exponential random graph models (ERGMs), the current study confirms that clubs have a significantly high propensity of exchanging players. Player transactions often occur through closed triads, such that clubs tended to make a deal with those who shared the same third partners. Additionally, league type and match performance produce stable and significant effects on the formation of transfer ties. Practical implications are also discussed.

A Facile Synthesis of Self-Catalytic Hydrogel Films and Their Application as a Wound Dressing Material Coupled with Natural Active Compounds.

A simple and economical method for polyvinyl alcohol/polyvinylpyrrolidone/citric acid (PVA/PVP/CA) hydrogel preparation using microwave-assisted irradiation was presented. The synthesized hydrogels embedded with berberine or chlorogenic acid were investigated as a wound dressing agent. This study showed that the optimum condition for the hydrogel synthesis based on gel fraction and a degree of swelling values was 6:6:3% (w/v) of PVA/PVP/CA under 600 W at 120 °C for 3 min of microwave irradiation. Herbal active compounds, berberine and chlorogenic acid, were loaded onto the hydrogel (4% (w/v)), and both were able to inhibit the growth of Staphylococcus aureus. Additionally, the anti-inflammatory study revealed that 700 μg/mL berberine and 2500 μg/mL chlorogenic acid could inhibit protein degradation equivalent to a 200 μg/mL aspirin solution. The drug release study demonstrated that both compounds showed a more sustained release into PBS than water. The mechanism for the three-dimensional network formation based on esterification and the hydrogen-bonding interaction was also proposed. The ionic liquid-like structure of PVP-CA possibly played an important role in the cross-linking process. In addition, sodium bicarbonate applied to the synthesized hydrogel also had a significant effect in enhancing gel formation. The proposed approach showed a potential of the loaded hydrogels to protect wounds from infection and enhance the healing process.

Research on Formation and Control Method of Volume Fracturing Network in Tight Reservoir Based on Computer

With the maturity and application of the concept of volume fracturing, the development of tight reservoirs has gradually become a strategic goal of unconventional oil and gas resources development. However, there are still some difficulties and problems in the theory of volume fracturing fracture opening. Based on this, this paper first studies the feasibility evaluation of volume fracturing in tight reservoir, then analyses the formation mechanism of volume fracturing network in tight reservoir, and finally gives the formation control method of volume fracturing network in tight reservoir based on computer.

Mechanisms of Network Formation in the Public Sector: A Systematic Review of the Literature

AbstractThis article provides a systematic review of the network formation literature in the public sector. In particular, we code and categorize the theoretical mechanisms used in empirical network research to motivate collaboration and tie formation. Based on a review of the 107 articles on network formation found in 40 journals of public administration and policy from 1998 to 2019, we identify 15 distinct theoretical categories. For each category, we describe the theory, highlight its use in the literature, and identify limitations and concerns with current applications. Overall, we find that most studies rely on a similar set of general theories of network formation. More importantly, we find that most theoretical mechanisms are not well specified, and empirical tests are often unable to directly assess the specific underlying mechanism. The results of our review highlight the need for our field to embrace experimental designs, develop panel network datasets, and engage in more network-level research.

Research progresses in formation mechanism of complex fracture network for unconventional reservoir

The practice of oilfield development promotes the development theory, and the breakthrough of development theory brings about the revolution of development technology. Using horizontal wells and volume fracturing technology, volume fracturing has been applied in unconventional reservoir, and the formation mechanism of complex fracture network will bring innovation to development technology. At present, the research on the formation mechanism mainly focuses on theoretical research, experimental research, and numerical simulation. Theoretically, the mechanical model of the intersection of HF and NF is established, and some judgment criteria are put forward. Activation of NF by HF is a necessary condition for the formation of complex fracture networks; the activation conditions of NF are verified by true triaxial experiment in terms of horizontal stress difference, approximation angle, and fracturing fluid viscosity; finite element method, finite difference method, boundary element method, and discontinuous displacement method have their own advantages and disadvantages on simulation. Using digital speckle correlation technique, the authors explained the mechanism of shear action on the formation of fracture network, established a macro-meso two-scale non-uniform damage constitutive model, and formed a computing method for dynamic expansion of fractured network in tight reservoir. A field well example is calculated using this method.

Tantalum network nanoparticles from a Ta2O5+kMg system by liquid magnesium controlled combustion

In this study, tantalum network nanoparticles are prepared from a Ta2O5+kMg system via a liquid magnesium-controlled combustion reaction. Super-stoichiometric amounts of magnesium are used in the preparation of a reaction mixture to produce a liquid magnesium pool capable of lowering the combustion temperature and leading to the formation of Ta network structures. The heat transfer kinetics from the hot reaction zone of ‘cold’ Mg particles is determined using heat transfer-coupled fluid dynamics simulation software. The formation of network structures is characterized through SEM, TEM, XRD, and BET analysis techniques. The mechanism of network formation is explained based on solid particle collisions in liquid media. Our method is able to produce Ta network structures in which the size of individual particles ranges between 50 and 700 nm.

PCA likelihood ratio test approach for attributed social networks monitoring

One of the most important factors in building and changing communication mechanisms in social networks is considering features of the members of social networks. Most of the existing methods in network monitoring don’t consider effects of features in network formation mechanisms and others don’t lead to reliable results when the features abound or when there are correlations among them. In this article, we combined two methods principal component analysis (PCA) and likelihood method to monitor the underlying network model when the features of individuals abound and when some of them have high correlations with each other.

Comparing Gender Homophily among the Multilayer Media Social Networks of Face-to-Face, Instant Messenger and Social Networking Services: A Case Study of a High School Classroom

Abstract In which social worlds does gender homophily operate more strongly – offline or online? To address this question, the following two aspects must be considered. First, people currently use many types of online communication media. Second, to examine the homophily effects exclusively, it is necessary to control for other network formation mechanisms such as ‘foci’ and ‘triadic closure.’ For this study, I conducted a mixed-method research in a high school in rural Japan. I asked students about who they interacted with face-to-face (F2F), through instant messenger (IM), and social networking services (SNS) and then analyzed the social networks using exponential random graph models (ERGMs). Subsequently, I conducted semi-structured interviews to uncover the practices and social contexts of each communication media and explain the results of the quantitative analysis. The results showed that SNS was more gender heterogeneous than offline. In the IM network, a small gender homophily effect was initially observed. However, three months later, its strength decreased to almost the same as that in the SNS networks. From the qualitative research, some key mechanisms producing the difference in gender homophily are specified, such as precedence of F2F communication to IM interaction, independence of SNS communication from F2F, recommending functions, and hobby homophily. Overall, this study implies that considering offline or online alone may cause misunderstanding regarding homophily in organizations because the observed strength of homophily effects depends on whether the space is examined offline or online, what kind of media is examined, and when the online social network data are collected.