Inflection Point Of Curve Research Articles

A simple method for estimating the optimum water content for tillage

AbstractSimple and quick determination of the optimum water content for tillage (θOPT) is helpful to guide tillage operations. Based on the definition of θOPT that is the water content at the inflection point of the soil water retention curve, a simple method was established to estimate the θOPT from saturated water content (θs) (θOPT = 0.75θs). The validation results on 132 soils with varying texture showed that the root mean squared error and mean error were 0.021 and 0.009 g g−1, respectively. These results confirmed that the θs was valuable information for estimating θOPT and the proposed method could give a reasonable estimation for θOPT.

Microscopic pore throat structures and water flooding in heterogeneous low-permeability sandstone reservoirs: A case study of the Jurassic Yan'an Formation in the Huanjiang area, Ordos Basin, Northern China

• The pore throat structure is classified based on inflection points of fractal curves. • The heterogeneity is caused by the varying proportions of micro-structure types. • The water flooding is mainly affected by the heterogeneity of pore throat structure. The complexity of the pore throat structures of heterogeneous low-permeability reservoirs causes uneven water flooding, resulting in the retention of a considerable amount of residual oil. Therefore, it is necessary to characterize pore throat structures and the effects of these structures on water flooding. Such structures and effects were investigated using scanning electron microscopy (SEM), cast thin sections (CTS), high-pressure mercury intrusion (HPMI) and microvisualization seepage experimentations. In the fractal dimension curves, there were two relatively close inflection points, corresponding to pore throat radii of approximately 3 µm and 0.02 µm. On this basis, the pore throat structures of all the samples were categorized into macrothroats, mesothroats and microthroats. All the samples contained these three types of pore throat structures. The heterogeneity of the pore throat structure was caused by the varying proportions of the different pore throat structure types. This was the first analysis of the effects of these varying proportions of pore throat structure types in one sample on water flooding. The influences of the proportions and pore throat radii of the different pore throat structures on water flooding were notable. Through this study, the effects of the pore throat structures on water flooding were found to be controlled by the proportions of the different pore throat structure types. This finding is of great significance to the efficient development of heterogeneous low-permeability reservoirs.

Mechanical properties and damage evolution of cemented coal gangue-fly ash backfill under uniaxial compression: Effects of different curing temperatures

A high geothermal heat affects the physical properties of cemented coal gangue-fly ash backfill (CGFB). The mechanical properties, damage evolution, elastic modulus, and peak strain of CGFB under uniaxial compression were investigated at different curing temperatures (20℃, 35℃, and 50℃) and curing ages (3, 7, 14, and 28 days), and the stress-strain curves were obtained. The results show that the elastic modulus and peak strain of CGFB exhibit an increasing overall trend with a rise in the curing temperature; the 14th day of curing is the inflection point of the elastic modulus curve of the CGFB specimens. The theoretical results based on the piecewise damage constitutive model are in good agreement with the experimental results, indicating that the model is reasonable. Four damage stages of the CGFB are observed: no damage, initial damage formation, accelerated damage growth, and stable damage development. The CGFB specimens cured at 35℃ and 50℃ suffer complete damage, whereas the CGFB specimens cured at 20℃ are not completely damaged, with a damage value of only 0.5409. The damage trend under uniaxial compression indicates that the damage value increases slowly from 0 at the initial stress, rapidly increases after the peak stress, and increases slowly until the damage value reaches 1, and the CGFB suffers a complete failure. This paper lays a foundation for analyzing the stability of CGFB in a high geothermal environment.

A Two-Step Polynomial and Nonlinear Growth Approach for Modeling COVID-19 Cases in Mexico

Since December 2019, the novel coronavirus (SARS-CoV-2) and its associated illness COVID-19 have rapidly spread worldwide. The Mexican government has implemented public safety measures to minimize the spread of the virus. In this paper, we used statistical models in two stages to estimate the total number of coronavirus (COVID-19) cases per day at the state and national levels in Mexico. In this paper, we propose two types of models. First, a polynomial model of the growth for the first part of the outbreak until the inflection point of the pandemic curve and then a second nonlinear growth model used to estimate the middle and the end of the outbreak. Model selection was performed using Vuong’s test. The proposed models showed overall fit similar to predictive models (e.g., time series and machine learning); however, the interpretation of parameters is simpler for decisionmakers, and the residuals follow the expected distribution when fitting the models without autocorrelation being an issue.

Vulnerability Assessment of Pelagic Sharks in the Western North Pacific by Using an Integrated Ecological Risk Assessment.

Simple SummaryA new integrated ecological risk assessment (ERA) including the IUCN Red List category, the body weight variation trend of 1989–2011 with large sample size (n > 678,000), and the inflection point of population growth curve coupled with the ERA was developed to assess the impact of longline fishery on the pelagic sharks in the western North Pacific. The intrinsic rate of population growth was used to estimate the productivity, and the susceptibility was estimated by the multiplication of the catchability, selectivity, and post-capture mortality. Five groups were identified based on the cluster analysis coupling with non-parametric multi-dimensional scaling. Rigorous management measures are recommended for the scalloped hammerhead, silky, and spinner shark at highest risk, setting total allowable catch quota is recommended for the bigeye thresher, and sandbar shark, and a consistent monitoring scheme is suggested for the smooth hammerhead, shortfin mako, pelagic thresher, oceanic whitetip, and dusky shark.The vulnerability of 11 pelagic shark species caught by the Taiwanese coastal and offshore longline fisheries in the western North Pacific were assessed by an ecological risk assessment (ERA) and 10 of the 11 species was assessed by using an integrated ERA developed in this study. The intrinsic rate of population growth was used to estimate the productivity of sharks, and the susceptibility of sharks was estimated by the multiplication of the catchability, selectivity, and post-capture mortality. Three indices namely, the IUCN Red List category, the body weight variation trend, and the inflection point of population growth curve coupled with ERA were used to conduct an integrated ERA. The results indicated that the scalloped hammerhead is at the highest risk (group 1), followed by the silky shark, and the spinner shark at high risk (group 2). The bigeye thresher, and sandbar shark fall in group 3, the smooth hammerhead falls in group 4, and the shortfin mako, pelagic thresher, oceanic whitetip, and dusky shark fall in group 5. Rigorous management measures for the species in groups 1 and 2, setting total allowable catch quota for group 3, and consistent monitoring schemes for groups 4 and 5 are recommended.

The learning curve of video-assisted thoracoscopic sleeve lobectomy in a high-volume pulmonary center.

ObjectivesTo evaluate the time course and caseload required to achieve proficiency by plotting the learning curve of video-assisted thoracoscopic sleeve lobectomy.MethodsWe reviewed 127 cases of video-assisted thoracoscopic sleeve lobectomy by a single surgeon at Shanghai Pulmonary Hospital to evaluate its learning curve using the cumulative sum (CUSUM) analysis. The changes of perioperative outcomes were assessed.ResultsThe inflection points of the CUSUM curve were around case 30 and 90, according to which 3 phases were identified: Phase I, Phase II, and Phase III. Significant downtrends were observed regarding operative time (Phase I, 194 [173-233 minutes] vs Phase II, 172 [142-215 minutes] vs Phase III, 138 [117-164 minutes], P < .05, all), blood loss (Phase I, 200 [100-238 mL] vs Phase II, 100 [50-200 mL] vs Phase III, 50 [50-100 mL]; P < .05, all), drainage duration (Phase I [5.53 ± 1.11 days] vs Phase II [4.52 ± 1.38 days]; P < .05), and length of postoperative stays (Phase I [6.60 ± 1.13 days] vs Phase II [5.68 ± 1.47 days], P < .05). The rate of severe complications significantly decreased from Phase I to Phase II (P = .03).ConclusionsThirty cases should be accumulated to lay the technical foundation, and 90 cases were required to achieve proficiency. The focus should now shift to providing sufficient training opportunities for centers wanting to implement this technique.

EKC and carbon footprint of cross-border waste transfer: Evidence from 134 countries

Many developing countries, such as China, Malaysia, Vietnam, India, etc., choose to prohibit waste import. Does this mean the inflection point of the Environmental Kuznets Curve (EKC) in these countries has arrived? In this paper, we first calculate the carbon dioxide emission and energy consumption in major resource-based wastes of 134 countries using the Life Cycle Assessment (LCA) method. Second, we test whether the relationship between CO2 (energy consumption) and GDP per capita confirms an EKC's inverted U-shaped curve. Empirical results show that: (1) the relationship between embodied CO2 emissions (energy consumption) of imported wastes and GDP per capita of a country confirms EKC in various robustness checks, including using an alternative, dependent variable and using sub-sample data. (2) The EKC's inflection point on the average embodied carbon dioxide emissions of imported wastes is 36623.88 USD (37181.3 USD for energy). (3) EKC appears in 68 countries out of 134 countries. Most of these 68 countries have crossed the turning point. This research is novel in describing the EKC of waste trade's carbon footprint using the LCA model. This is the first research that provides empirical evidence to the “Waste Haven Hypothesis”. This result empirically explains the evolution of the global waste trade network. That is, waste first transfers from the “North” to the “South” (from US to Europe, and from Europe to Japan and Korea), and then it moves again from the “South” to the “South” (from China to other Asian countries). It reflects the evolution of global pollution haven transfer in the pollution-intensitive sector. Previous research failed to do it because the indicators used for waste transfer limits to trade value (weight) that can not correctly measure waste transfer's environmental pollution. An advantage of using LCA is that it better estimates the pollution generated by the recycling sectors.

Hyperbolic‐Like Structure with Negative Poisson's Ratio: Deformation Mechanism and Structural Design

Mechanical metamaterials with negative Poisson's ratio (NPR) effect possess important practical applications in aerospace, nanotechnology, and other fields. The microstructure and its deformation mode directly determine the NPR ability and mechanical performance of auxetic metamaterials. Herein, inspired by the double‐negative‐index ceramic aerogels, a novel NPR structural model is proposed in which symmetric reentrant oblique ligaments and short transversal ligaments constitute the main framework inside a square, which is different from the traditional reentrant structure due to the hyperbolic‐like skeleton and deformation modes. The influence of structural parameters on the NPR effect is investigated using the Timoshenko beam model and finite element simulations. The structural model is then extended to design multiple reentrant structures and assembled structures, respectively. The multiple reentrant structures include multiple pairs of symmetrically hyperbolic‐like skeletons, and the distribution of horizontal ligaments can be regulated to achieve a better NPR effect. For assembled structures under compression, the local rotational deformation and buckling result in structural instability, demonstrated by inflection points in the NPR curves. Moreover, one special assembled structure is found for which there is a linear relationship between the compressive strain and NPR value. The insights should be significant for designing mechanical metamaterials with the NPR effect.

A Damage Model to Trabecular Bone and Similar Materials: Residual Resource, Effective Elasticity Modulus, and Effective Stress under Uniaxial Compression

Experimental research of bone strength remains costly and limited for ethical and technical reasons. Therefore, to predict the mechanical state of bone tissue, as well as similar materials, it is desirable to use computer technology and mathematical modeling. Yet, bone tissue as a bio-mechanical object with a hierarchical structure is difficult to analyze for strength and rigidity; therefore, empirical models are often used, the disadvantage of which is their limited application scope. The use of new analytical solutions overcomes the limitations of empirical models and significantly improves the way engineering problems are solved. Aim of the paper: the development of analytical solutions for computer models of the mechanical state of bone and similar materials. Object of research: a model of trabecular bone tissue as a quasi-brittle material under uniaxial compression (or tension). The new ideas of the fracture mechanics, as well as the methods of mathematical modeling and the biomechanics of bone tissues were used in the work. Compression and tension are considered as asymmetric mechanical states of the material. Results: a new nonlinear function that simulates both tension and compression is justified, analytical solutions for determining the effective and apparent elastic modulus are developed, the residual resource function and the damage function are justified, and the dependences of the initial and effective stresses on strain are obtained. Using the energy criterion, it is proven that the effective stress continuously increases both before and after the extremum point on the load-displacement plot. It is noted that the destruction of bone material is more likely at the inflection point of the load-displacement curve. The model adequacy is explained by the use of the energy criterion of material degradation. The results are consistent with the experimental data available in the literature.

Decoupling relationship between haze pollution and economic growth: A new decoupling index

Economic development is accompanied by the production of pollutants. Coordinating the relationship between economic development and haze pollution is of great significance to future development in China. Based on the original decoupling index (Tapio decoupling index), this study developed a new decoupling index that overcomes some of the original defects and highlights the trends to a better extent. It also analyzes the transformation relationship among the new decoupling index, the original decoupling index and the EKC curve. Firstly, we compared the changing trends of the two decoupling indexes and then derived the factors that influence the new and original decoupling indexes based on C-D-Kaya equation. Finally, we compared the factors influencing the two decoupling indexes from the perspective of decomposition analysis and measurement. The conclusions are as follows: (1) Based on the limit theory, the boundary point for relative decoupling and absolute decoupling derived from the original decoupling index can be used to determine the inflection point of the EKC curve. The new decoupling index can also reflect this property. At the inflection point of the EKC curve, the ratio of the new decoupling index of two adjacent periods satisfies equation (12), which is only related to GDP. (2) In 2003, the new decoupling index showed a downward trend, and the fluctuation was smaller than that of the original decoupling index. The original decoupling index is more sensitive to short-term policies than the new decoupling index, but the new decoupling index is more conducive to the comprehensive analysis of China’s decoupling trend. (3) After decomposing the new decoupling index and the original decoupling index, per capita GDP and the emission coefficient are the largest positive and negative driving forces, respectively. However, the trend of the contribution made by each factor was more obvious when the new decoupling index was used. The emission coefficient for Shandong made the largest negative contribution, and the per capita GDP for Shanxi made the greatest positive contribution. (4) The geographically and temporally weighted regression (GTWR) analysis showed that the fitting degree of the new decoupling index is much higher than that of the original decoupling index. The analysis of the influencing factors affecting the new decoupling index showed that there was temporal and spatial heterogeneity among the factors in east, middle, and west China, and there were significant differences in the impacts due to energy structure, energy intensity, technological progress, and urban population factors, respectively. These findings will significantly improve the formulation of efficient and pertinent policies for energy conservation and haze reduction.

Accelerated Locati method for testing machine parts for fatigue resistance

The results of testing specimens and machine parts for fatigue resistance according to the standard method with the construction of the Wöhler curve and the determination of the endurance limit and the accelerated method with the determination of the endurance limit are presented. As an accelerated test method, the method of step-increasing loads (the Locati method) was used, as the conditional fatigue curves — oblique fatigue curves parallel to the oblique fatigue curves obtained during standard tests of specimens with the construction of the Wöhler curve. For all conventional curves, the same inflection point of the fatigue curve in semilogarithmic coordinates was taken. Keywords: fatigue resistance, endurance limit, Wöhler curve, accelerated tests. valpal-1938@mail.ru

Correlation between convection requirement and carotid body responses to hypoxia and hemoglobin affinity: comparison between two rat strains.

We tested the hypothesis that differences in ventilatory ([Formula: see text]) or convection requirement ([Formula: see text]/[Formula: see text]O2) response to hypoxia would be correlated with differences in hemoglobin (Hb) oxygen affinity between two strains of rats, as they have been shown to be among several species of mammals, birds and reptiles. Brown Norway (BN) rats reduce metabolism more than they increase ventilation in response to hypoxia and both the ventilatory and convection requirement responses to hypoxia are lower in the BN than the Sprague-Dawley (SD) rat. The lower threshold of the ventilation/convection requirement responses of the BN to hypoxia are associated with a higher affinity Hb than the SD rats, (P50 values of 32.4 (± 0.6) versus 34.4 (± 0.5), respectively (P < 0.05), and P75 values of 46.1 (± 0.5) for BN versus 50.7 (± 0.8) for SD (P < 0.001). This significant difference, particularly near the inflection point of the dissociation curve, supported our hypothesis. A reduced sensitivity of BN compared to SD carotid bodies was found. BN carotid bodies (from 36 20-60-day-olds) had a mean estimated volume of 26.64 ± 1.47 × 106 μm3, significantly (P < 0.0001) smaller than SD carotid bodies (from 46 16-40-day-olds) at 50.66 ± 3.41 × 106 μm3. Both genetic and epigenetic/developmental mechanisms may account for the observed inter-strain differences.

Predicting the Postoperative Addition Power of a Multifocal Intraocular Lens at the Spectacle Plane.

To establish a simple clinical method of predicting addition power achieved with a multifocal intraocular lens (IOL). In this prospective cohort study, 41 patients were bilaterally implanted with the Bi-Flex MY multifocal IOL (Medicontur) with +3.50 diopters (D) near addition power. Monocular defocus curves were plotted for each patient and effective addition power was calculated as the dioptric difference between the distance and near inflection points of the defocus curve. Six biometry formulas (Haigis, Holladay, SRK/T, Hill RBF, Barrett Universal II, and Holladay 2) were used to predict the addition power at the spectacle plane. Mean effective addition power was 2.60 ± 0.29 D, with significant (P < .01) differences between the prediction methods. Significant differences were found between predicted and effective addition when the Holladay, SRK/T, Hill RBF, and Holladay 2 formulas were used. A moderate but significant correlation (r = 0.342, P = .033) was found with the Barrett formula, and this was also the method to show the least proportional bias with Bland-Altman analysis. The study demonstrates that the effective addition power can be predicted using the proposed simple clinical method derived using the Barrett Universal II formula. The proposed technique may have significant clinical value in screening for patients where ocular biometry may lead to aberrant addition power. [J Refract Surg. 2021;37(5):318-323.].

A Novel Thyroid Ultrasound Proficiency Metric Designed Through a Multidisciplinary Delphi Approach.

Thyroid ultrasounds extend surgeons' outpatient capabilities and are essential for operative planning. However, most residents are not formally trained in thyroid ultrasound. The purpose of this study was to create a novel thyroid ultrasound proficiency metric through a collaborative Delphi approach. Clinical faculty experienced in thyroid ultrasound participated on a Delphi panel to design the thyroid Ultrasound Proficiency Scale (UPS-Thyroid). Participants proposed items under the categories of Positioning, Technique, Image Capture, Measurement, and Interpretation. In subsequent rounds, participants voted to retain, revise, or exclude each item. The process continued until all items had greater than 70% consensus for retention. The UPS-Thyroid was pilot tested across 5 surgery residents with moderate ultrasound experience. Learning curves were assessed with cumulative sum. Three surgeons and 4 radiologists participated on the Delphi panel. Following 3 iterative Delphi rounds, the panel arrived at >70% consensus to retain 14 items without further revisions or additions. The metric included the following items on a 3-point scale for a maximum of 42 points: Positioning (1 item), Technique (4 items), Image Capture (2 items), Measurement (2 items), and Interpretation (5 items). A pilot group of 5 residents was scored against a proficiency threshold of 36 points. Learning curve inflection points were noted at between 4 to 7 repetitions. A multidisciplinary Delphi approach generated consensus for a thyroid ultrasound proficiency metric (UPS-Thyroid). Among surgery residents with moderate ultrasound experience, basic proficiency at thyroid ultrasound is feasible within 10 repetitions.

Research on the Economic Development Threshold Effect of the Employment Density of the Shanghai Consumer Goods Industry in the Context of New Manufacturing, Based on the Experience Comparison with International Metropolis

With the rise of a new generation of technology and industrial changes, the service-oriented manufacturing industry has become the direction of future development. With the background of new manufacturing, this paper constructs an economic development threshold model of employment density of consumer goods industry based on data from Shanghai and Tokyo from 2007 to 2016, and empirically analyzes the impact of the employment density of the consumer goods industry on urban economic development under different population densities. At the same time, by comparing the experience of Tokyo, the development status and prospects of Shanghai’s consumer goods industry are explored. The study found that the threshold of Tokyo’s consumer goods industry is 0.608. When population density is lower than this threshold, the consumer goods industry continues to promote the economic development of Tokyo; however, when the population density is higher than this threshold, the consumer goods industry begins to inhibit the economic development of Tokyo. The Shanghai consumer goods industry threshold is 0.329. Under the threshold, most of the consumer goods industry contributions to the economy are negative, but above the threshold, they begin to show a positive trend. The inflection point of the effect curve of Tokyo’s consumer goods industry on economic development has appeared, but the inflection point of Shanghai’s consumer goods industry has not yet appeared. Compared with Tokyo, the economic vitality of Shanghai’s consumer goods industry has not yet been fully released. With the continued increase of population density in Shanghai, the growth potential of the consumer goods industry is huge, and it is expected to reshape the flourishing age of Shanghai’s light industry brand.

Crack initiation stress of brittle rock with different porosities

Accurately determining the crack initiation stress (CI) is of great importance to evaluate the stability of deep underground openings and the permeability of host rock in the near field. For this paper, uniaxial compression tests and increasing amplitude cyclic stressing tests were performed on four kinds of rocks with different porosities. The stress-strain data and acoustic emission (AE) data of these tests are analyzed to evaluate the applicability and accuracy of the existing methods for determining the CI. The results demonstrate that for marble and Beishan granite with low porosity, the lateral strain (LS) method is the simplest and most direct method to obtain the CILS. For high porosity sandstone, the result of lateral strain response (LSR) method is significantly smaller than that obtained by AE. The cumulative AE hits (CAEH) method heavily depends on the “S-shaped” characteristic of the cumulative AE hits curve, which limits its scope of application. The cumulative AE hits curve slope (CAHS) method, which determines the key inflection point of the cumulative AE hits curve by slope variation to determine the CICAHS, possesses the widest applicability and highest accuracy. The CI/UCS ratios of rocks with similar grain sizes decreases with increasing porosity. For Beishan granite, the average CICAHS is less than that of CILS. They are 0.43 UCS and 0.53 UCS, respectively. According to the residual strain data from the cyclic loading tests, the two crack initiation thresholds of Beishan granite can be clearly identified. These two crack initiation thresholds represent different crack initiation sequences in grain boundaries and different minerals.

From nanotubes to nanoholes: Scaling of selectivity in uniformly charged nanopores through the Dukhin number for 1:1 electrolytes.

Scaling of the behavior of a nanodevice means that the device function (selectivity) is a unique smooth and monotonic function of a scaling parameter that is an appropriate combination of the system's parameters. For the uniformly charged cylindrical nanopore studied here, these parameters are the electrolyte concentration, c, voltage, U, the radius and the length of the nanopore, R and H, and the surface charge density on the nanopore's surface, σ. Due to the non-linear dependence of selectivities on these parameters, scaling can only be applied in certain limits. We show that the Dukhin number, Du=|σ|/eRc∼|σ|λD 2/eR (λD is the Debye length), is an appropriate scaling parameter in the nanotube limit (H → ∞). Decreasing the length of the nanopore, namely, approaching the nanohole limit (H → 0), an alternative scaling parameter has been obtained, which contains the pore length and is called the modified Dukhin number: mDu ∼ Du H/λD ∼ |σ|λDH/eR. We found that the reason for non-linearity is that the double layers accumulating at the pore wall in the radial dimension correlate with the double layers accumulating at the entrances of the pore near the membrane on the two sides. Our modeling study using the Local Equilibrium Monte Carlo method and the Poisson-Nernst-Planck theory provides concentration, flux, and selectivity profiles that show whether the surface or the volume conduction dominates in a given region of the nanopore for a given combination of the variables. We propose that the inflection point of the scaling curve may be used to characterize the transition point between the surface and volume conductions.

Tuning the Structure of Nylon 6,6 Electrospun Bundles to Mimic the Mechanical Performance of Tendon Fascicles.

Tendon and ligament injuries are triggered by mechanical loading, but the specific mechanisms are not yet clearly identified. It is well established however, that the inflection and transition points in tendon stress-strain curves represent thresholds that may signal the onset of irreversible fibrillar sliding. This phenomenon often results in a progressive macroscopic failure of these tissues. With the aim to simulate and replace tendons, electrospinning has been demonstrated to be a suitable technology to produce nanofibers similar to the collagen fibrils in a mat form. These nanofibrous mats can be easily assembled in higher hierarchical levels to reproduce the whole tissue structure. Despite the fact that several groups have developed electrospun tendon-inspired structures, an investigation of the inflection and transition point mechanics is missing. Comparing their behavior with that of the natural counterpart is important to adequately replicate their behavior at physiological strain levels. To fill this gap, in this work fascicle-inspired electrospun nylon 6,6 bundles were produced with different collector peripheral speeds (i.e., 19.7 m s–1; 13.7 m s–1; 7.9 m s–1), obtaining different patterns of nanofibers alignment. The scanning electron microcopy revealed a fibril-inspired structure of the nanofibers with an orientation at the higher speed similar to those in tendons and ligaments (T/L). A tensile mechanical characterization was carried out showing an elastic-brittle biomimetic behavior for the higher speed bundles with a progressively more ductile behavior at slower speeds. Moreover, for each sample category the transition and the inflection points were defined to study how these points can shift with the nanofiber arrangement and to compare their values with those of tendons. The results of this study will be of extreme interest for the material scientists working in the field, to model and improve the design of their electrospun structures and scaffolds and enable building a new generation of artificial tendons and ligaments.

Novel method for determining the lower producing limits of pore-throat radius and permeability in tight oil reservoirs

Determination of the lower limit of flowing porosity for oil recovery from tight oil reservoirs is the key to promoting scientific and economic development of tight oil reservoirs. This study performed a comprehensive analysis based on pore-throat radius distribution measurements, low-temperature nitrogen adsorption measurements, and centrifugation and nuclear magnetic resonance measurements to establish a method for calculating the bound water film thickness and, in turn, the lower limits of pore-throat radius and permeability. The method was applied on rock samples from typical tight oil reservoirs in the Daqing and Changqing oil regions in China. The results indicated that for a given reservoir, bound water film thickness tends to be constant. With decreasing permeability, bound water film thickness showed an L-shaped distribution curve due to the changes in the pore-throat structure and the impact of molecular forces. The flat segment of the distribution curve corresponded to the lower limit of pore-throat radius, while the curve inflection point corresponded to the lower limit of permeability. The pore-throat radius and permeability limits were 22 nm and 0.08 mD for the Daqing tight oil reservoir and 18 nm and 0.03 mD for the Changqing tight oil reservoir, respectively.

Identifying characteristic changes in club convergence of China's urban pollution emission: A spatial-temporal feature analysis

We explore China's pollution emission convergence through theoretical deduction and empirical test using a spatial Green Solow model. First, the extended theoretical analysis results show that an economy will pass the inflection point of Environmental Kuznets Curve when growth rate of pollution reduction technology exceeds that of output, which supports the existence of pollution emission convergence. Secondly, estimation results of a dynamic spatial panel data model show that China's urban pollution emission has convergence properties in which club convergence will come true first. Thirdly, China's low-pollution urban cluster has entered a benign pattern of pollution prevention; the medium-pollution club characterized by pollution transfer shows beggar-thy-neighbor effects; while the high-pollution club with a typical positive feedback mechanism of pollution still faces risks of escalating pollution. Hence, the government should pay great attention to pollution prevention of the medium- and high-pollution clubs by strengthening regional coordination and accelerating industrial upgrading, which promotes the shift of pollution prevention from club convergence to absolute convergence and provides an environmental guarantee for high-quality development.