Extension Length Research Articles

Method for identifying the position of crack tip by displacement distribution based on digital image correlation

Determining the position of crack tip is crucial for rock fracture characteristic analysis. This study aims to establish a quantitative standard for determining crack tip positions in crystalline rocks based on digital image correlation (DIC). Semi-circular bending (SCB) tests were conducted on four types of rocks under three-point bending. Optical microscopy and DIC were used to investigate characteristics of the horizontal displacement fields around the crack tips. A significant disparity in the displacement gradient was observed across the crack tips, with the internal gradient being approximately 3–5.1 times higher than the external gradient. A critical value ranging from 0.41%–0.64% was determined for the high internal displacement gradient (∂u/∂x) at a 20 pixel resolution equivalent to 1 mm. Furthermore, a novel DIC-based method was proposed that used three patterns of opening displacement gradients to classify SCB specimens into non-cohesive, cohesive, and elastic zones, providing a quantitative determination of Type I crack tip positions. This study offers valuable insights and a crack tip determination method based on DIC gradients, applicable for assessing parameters such as the crack extension length and fracture process zone length.

Role of elasticity on polymeric droplet generation and morphology in microfluidic cross-junctions

Recently, our direct numerical simulations [Duan et al., Phys. Fluids 36, 033112 (2024)] showed that fluid elasticity affects the extension length and pinch-off time of the droplet formation process, thus changing the flow pattern. However, the effect of fluid elasticity on the morphology and properties of polymeric droplets is not yet fully understood. In this work, by analyzing the stretched state of the polymer macromolecule and the velocity distribution of the flow process, we find that the increase in fluid elasticity (characterized by the relaxation time) inhibits the contraction of the dispersed phase during droplet pinching and resists the effect of surface tension after droplet generation, which significantly affects the droplet geometry, volume, and generation frequency. The results demonstrate that the length and volume of polymeric droplets increase with the relaxation time of the polymer fluid, while the generation frequency decreases. Meanwhile, the effects of polymer viscosity and the superficial velocity ratio of the continuous to the dispersed phase on the droplets' morphology are investigated. The semi-empirical models for the length, volume, and generation frequency of polymeric droplets are developed for the first time by considering the elastic interaction. The purpose of our work is to provide a better understanding and experimental guidance for controlling the parameters of polymeric droplets with viscoelasticity of different shapes and sizes.

Comparison of the environmental impacts of heating systems in Chile by life cycle assessment

The present study conducts a Life Cycle Assessment (LCA) to evaluate the environmental impacts of heating technologies commonly used in Chile based on six environmental indicators: Climate Change (CC), Human Toxicity (HT), Formation of Particulate Matter (PM), Formation of Photochemical Oxidants (PO), Ozone Destruction (OD), and Water Depletion (WD). Due to the extensive length of the territory studied, it is demonstrated that the environmental impacts depend on the geographical location where the heating equipment is used. Stoves that use wet firewood presented the highest environmental impact in CC, PM, HT, and PO. Using dry firewood could reduce pollution by 14%–81%, compared to wet firewood. Replacing wood heating with natural gas, LPG, and kerosene stoves reduces the CC and HT indicators. On the other hand, switching to electric heating, such as split inverter heat pumps, could transfer these impacts to areas where electricity is generated using coal. When the pellet is a byproduct of the forestry industry and transportation distances are not very high, the pellet stove stands out for its lower CC. In Magallanes, electric heating appears environmentally attractive due to using natural gas for electricity generation.

Investigation of the fracture behavior of cemented waste rock-tailing backfill by digital image correlation technique and discrete element modeling

Cemented waste rock-tailing backfill (CWTB), as an artificial false roof in the downward-filling mining method, with its fracture mechanical properties, directly affects the safety of workers. However, few studies have been conducted on CWTB. Therefore, in this study, three-point bending tests and digital image correlation were used to systematically investigate the effects of waste rock aggregate content (10, 20, 30, 40, and 50 %) on the bending mechanical properties (bending strength, post-peak toughness, and fracture toughness) and deformation characteristics (crack extension length and crack opening length) of CWTB. In addition, based on the partition modelling method, a mesoscopic DEM model of CWTB was proposed to reveal the crack extension mechanism and contact force evolution trends of CWTB beams. The results showed that increasing the waste rock aggregate content decreased the flexural strength and increased the post-peak toughness of CWTB. The waste rock aggregate content affected the contact force distribution characteristics and contact force variation was the mesoscopic reason for the evolution of the mechanical properties of CWTB. This study provided important experimental data and simulation basis for the engineering application of CWTB.

Optimizing Efficiency of Tea Harvester Leaf-Collection Pipeline: Numerical Simulation and Experimental Validation

To address the challenges of missed and disorderly picking in tea harvesters, this study focused on the leaf-collection pipeline and utilized Fluent simulation 19.0 software. A single-factor test identified key parameters affecting airflow velocity. An orthogonal test evaluated the main pipe taper, number of branch pipes, and branch pipe outlet diameter, with average outlet wind speed and wind speed non-uniformity as indicators. The optimal parameters were a main pipe taper of 25.5 mm, 10 branch pipes, and an inner diameter of 17.10 mm for the outlet, resulting in 10.73 m/s average wind speed and 8.24% non-uniformity. Validation tests showed errors under 1%. Further optimization on the internal structure’s extension length led to 11.02 m/s average wind speed and 8.04% non-uniformity. Field experiments demonstrated a 3.40% stalk leakage rate and 90.36% bud leaf integrity rate; the optimized structure of the leaf-collecting pipeline significantly improved the uniformity of airflow and the picking efficiency. These findings offer valuable insights and practical benefits for enhancing the efficiency of tea harvesters.

Multiscale simulations of viscoelastic fluids in complex geometries using a finitely extensible nonlinear elastic transient network model

This paper presents a novel implementation of a numerical scheme for predicting complex flows of viscoelastic fluids using a finitely extensible nonlinear elastic (FENE) transient network model. This model extends the FENE model by incorporating chain interactions and accounting for the way in which the maximum chain length, drag, and relaxation time are influenced by entanglement and disentanglement processes. Three different initial networks are considered (disentanglement, entanglement, and aleatory), and the influence of variables such as the kinetic rate constants, elasticity, and chain length on the microstate concentration, stresses, and drag force is investigated. It is shown that although the concentrations of the microstates are independent of the Weissenberg number and the maximum extension length, the stresses and hence the drag are influenced by them.

On Improving the Noise Reduction Performance of Trailing Edge Serrations by Extension

Trailing edge serration is an effective method to reduce broadband noise generation by an airfoil. However, the noise reduction performance can be significantly reduced when there is flow misalignment at the serration. This experimental study investigates the impact of a shift in the serration position downstream of the airfoil trailing edge on the noise reduction performance, referred to in this paper as serration extension. Experiments were performed on a 100-mm-chord NACA 0012 wing model with sawtooth trailing edge serrations. The serration performance was studied at 0° and 7° flap-down configurations at various angles of attack. The serrations with three different extension lengths of 5, 10, and 15 mm were tested and compared with the baseline case without extension. The emitted noise was measured with a phased microphone array. The results show a significant reduction in broadband high-frequency noise by extension under loading conditions. Particle image velocimetry measurements of root flow along the wall-normal plane reveal diminished crossflow across the serration after extension. Furthermore, the extensions cause an up-to-25% increase in the maximum lift coefficient and improved or unaltered lift-to-drag ratios.

Quantifying the impact of geological and construction factors on hydraulic fracture dynamics in heterogeneous rock layers using the phase field method

Hydraulic fracturing, a pivotal practice for optimizing development in tight oil reservoirs, encounters challenges in accurately predicting propagation paths within heterogeneous rock formations. Existing phase models often overlook the influence of complex formations, especially in porous media with heterogeneous characteristics. Addressing this gap, we present a novel phase field method aligned with on-site practices. This innovative approach considers cracks, bedding planes, and faults as heterogeneous structures, integrating directional physical and mechanical properties. The key innovation lies in constructing assignment functions to characterize mechanical and seepage parameters of the rock matrix. Anchored in pore elasticity theory and the principle of energy minimization, we establish and validate a hydraulic coupled phase field model through plaster experiments. This model not only corrects the oversight of formation heterogeneity but also provides a comprehensive analysis of the impact of physical and construction parameters on crack propagation. The study extends to numerical simulation studies on three typical heterogeneous rock layers—natural fractures, bedding planes, and faults. Utilizing indicators like fracture pressure, crack extension length, and damage area, a random forest algorithm quantifies the degree of influence of each factor on fracturing. Our results underscore varying impacts from geological factors (natural fractures, bedding angle, stress difference, elastic modulus, matrix porosity, and permeability) and construction factors (cluster spacing, perforation length, fracturing fluid viscosity, displacement, well spacing, and perforation opening) on the fracturing effect of heterogeneous rock layers. In conclusion, our proposed phase field framework demonstrates predictive capability across diverse heterogeneous situations. This innovative model not only rectifies past oversights but also offers insights unattainable through traditional experimental testing, significantly advancing our understanding of hydraulic fracture dynamics.

Models of Video Feedback for Youth Athletes Performing an American Football Tackle.

Video feedback is an expeditious method for improving athlete safety when performing activities with an inherent risk of injury. Providing appropriate and validated feedback during tackling training in American football may be a mechanism for athletes to learn safe tackling performance. To determine the effect of video feedback in the instruction of tackling form. Controlled laboratory study. Laboratory. A total of 32 youth football athletes (28 boys, 4 girls; age = 11.8 ± 0.8 years) participated in 1 day of training. Of those, 14 participants completed 2 additional days of training and a 48-hour retention and transfer test. Video feedback using self as model, expert as model, combined self and expert model, and oral feedback to promote safe tackling performance in a laboratory environment. Shoulder extension, cervical extension, trunk angle, pelvis height, and step length by training block and over time. For the 1-day training group, main effects for time were observed for shoulder extension (P < .01), cervical extension (P = .01), pelvis height (P < .01), and step length (P < .01), with better performance for pelvis height and step length after combined feedback. For the 3-day training group, main effects of time were identified in pelvis height (P < .01) and step length (P < .01), with combined feedback showing better performance than other methods in shoulder extension and pelvis height. Combined feedback resulted in better performance compared with its component parts and oral feedback alone. In the combined model, participants viewed both their performance and the expert model, enabling them to see the difference between current and required performance. Combined feedback may be superior to other forms of feedback in improving movement performance. This effect can be generalized across disciplines that provide instruction and feedback in movement.

Polymeric droplet formation and flow pattern evolution in capillary microchannels: Effect of fluid elasticity

Polymeric droplets are widely employed in fields such as chemical, biomedical, and materials engineering. However, the study of polymeric droplet formation is still insufficient due to the complex elasticity. In this work, the effect of fluid elasticity on the flow patterns for polymeric droplet formation in cross-junction microchannels is investigated by means of finite-volume direct numerical simulations. The volume of fluid method with cell-based adaptive mesh refinement technique is used to capture the interface. Additionally, the rheological behavior of polymeric fluids is described using the exponential Phan-Thien–Tanner constitutive model. The simulated flow behaviors are highly consistent with the experimental observations. The results indicate that three typical flow patterns of dripping, jetting, and threading flows are obtained at different fluid elasticities (denoted by the Weissenberg number Wi) and viscosities (denoted by the Capillary number Ca). Meanwhile, the elastic effect is found to be greater in the dripping flow, significantly reducing the axial tensile stress. It is demonstrated that changes in the stretched state of polymer macromolecules with the same Wi at different Ca lead to variations in the strength of elastic action, which, in turn, affects the extension length and the pinch-off time of droplets. Finally, a relationship equation between the extension length and time of the polymer fluid is established. This present study aims to provide important insight into the preparation of polymeric droplets in microchannels.

Experimental study of flame extension lengths and fire pattern lengths induced by the turbulent jet fire impinging on inclined wooden boards

The safety of producing and transporting flammable gas may be compromised by the occurrence of jet fires resulting from pipeline leakage. During such incidents, combustible obstacles can impede the development of vertical jet fires, leading to impingement. Wood, a typical building material, was chosen as a combustible solid for the experiment due to its ability to produce regular fire patterns on its surface when heated, making it useful for fire investigation. A series of experiments were conducted to examine the flame extension length and fire pattern length resulting from a jet fire impinging on inclined wooden boards with different nozzle diameters, inclination angles, and heat release rates. This work showed that, unlike non-combustible boards, the rate of increase in flame extension length beneath a wooden board continues to rise as the heat release rate increases. Additionally, the boards' ability to absorb heat during the initial stages of combustion affects the flame extension length at low heat release rates. This work introduces a new correlation that can predict the length of flame extension under wooden boards, addressing a gap in research on jet fire impingement on combustible ceilings. For the regular fire patterns left by jet fires impinging on wooden boards, a new correlation of fire pattern length with flame extension length for different inclination angles of wooden boards is proposed. Considering the characteristics of turbulence, a novel model for fire pattern length is introduced, incorporating the Karlovitz flame stretch factor, nozzle inner diameter, and fire source-wooden board spacing.

Controls of Multi-Scale Fractures in Tight Sandstones: A Case Study in the Second Member of Xujiahe Formation in Xinchang Area, Western Sichuan Depression

Abstract Different scales of fractures affect the reservoir quality in tight sandstone. There are more studies on macroscopic tectonic fractures but less on bedding fractures and microfractures. The control factors of multi-scale fractures are unclear. In this paper, we analyzed the types and controls of fractures in the second member of the Xinchang region in Western Sichuan. We use core and outcrops observations, imaging logging, scanning energy spectra, and rock slices. Natural fractures can be classified into tectonic, bedding, and microscopic types. The tectonic fractures are mainly low- to medium-angle tensile fractures. The bedding fractures are nearly horizontally distributed along the bedding surface, including parallel, dark mineral interface, and carbonaceous fragments interface bedding fractures. The microfractures develop intra-grain, edge-grain, and inter-grain types. The intra-grain microfractures are inside quartz or feldspar grains, whereas inter-grain types penetrate multiple grains with larger extension lengths. The tectonic fractures are related to the stress, grain size, mineral component, argillaceous content, and lithologic thickness. Parallel bedding fractures are controlled by the coupling of water depth and flow velocity. Bedding fractures at the interface are controlled by rock component. The microfractures are controlled by the length-width axis ratio of the grain, grain element content, and brittleness index. Fractures of different scales form a three-dimensional fracture system that has a substantial impact on the gas production.

The Impact of Activating Agents on Non-Enzymatic Nucleic Acid Extension Reactions.

Non-enzymatic template-directed primer extension is increasingly being studied for the production of RNA and DNA. These reactions benefit from producing RNA or DNA in an aqueous, protecting group free system, without the need for expensive enzymes. However, these primer extension reactions suffer from a lack of fidelity, low reaction rates, low overall yields, and short primer extension lengths. This review outlines a detailed mechanistic pathway for non-enzymatic template-directed primer extension and presents a review of the thermodynamic driving forces involved in entropic templating. Through the lens of entropic templating, the rate and fidelity of a reaction are shown to be intrinsically linked to the reactivity of the activating agent used. Thus, a strategy is discussed for the optimization of non-enzymatic template-directed primer extension, providing a path towards cost-effective in vitro synthesis of RNA and DNA.

Revealing the Effect of the Length of Chains on Rubber Mechanical Properties by the Two‐Component Quantum Mechanical Gaussian Model

AbstractThe special mechanical properties of natural rubber originate from the stretching of the network chains (i.e., cis‐1,4‐polyisoprene chains) in the rubber network. The chains with various lengths exhibit various relative extensions, leading to various normalized energy contributions to the mechanical properties of rubber. However, the stretching behaviors of cis‐1,4‐polyisoprene chains with different lengths are not studied clearly. Here, the stretching behavior, which is the basis for analyzing the normalized energy contribution, is obtained by the modified freely jointed chain model. Next, using a new statistical model, i.e., the two‐component quantum‐mechanics Gaussian (TCQMG) model, the relative extension–length relationship of network chains is determined. Combining the above results, the energy contributions of network chains with different lengths are analyzed. The results show that long and short chains show different stretching states. The following can be explained by these results: short chains play an important role in the mechanical properties of rubber. As the network chain density increases, the average length of the chains decreases, leading to the variation of the normalized extensions. It is found that the variation of the normalized extensions is responsible for both the effects of the network chain density and network chain length on the mechanical properties of rubber.

Characteristics of limb kinematics in the gait disorders of post-stroke patients

Post-stroke gait disorders involve altered lower limb kinematics. Recently, the endpoint of the lower limb has been used as a control variable to understand gait kinematics better. In a cross-sectional study of sixty-seven post-stroke patients, the limb extension angle and effective limb length during gait were used as input variables with a mixed Gaussian model-based probabilistic clustering approach to identify five distinct clusters. Each cluster had unique characteristics related to motor paralysis, spasticity, balance ability, and gait strategy. Cluster 1 exhibited high limb extension angle and length values, indicating increased spasticity. Cluster 2 had moderate extension angles and high limb lengths, indicating increased spasticity and reduced balance ability. Cluster 3 had low limb extension angles and high limb length, indicating reduced balance ability, more severe motor paralysis, and increased spasticity. Cluster 4 demonstrated high extension angles and short limb lengths, with a gait strategy that prioritized stride length in the component of gait speed. Cluster 5 had moderate extension angles and short limb lengths, with a gait strategy that prioritized cadence in the component of gait speed. These findings provide valuable insights into post-stroke gait impairment and can guide the development of personalized and effective rehabilitation strategies.

Extending the usefulness of the Stryker Growing Prosthesis in pediatric patients.

Osteosarcoma is a highly invasive primary bone tumor that predominantly occurs in childhood and adolescence. The Stryker Growing Prosthesis provides a means of reconstructing large bone defects resulting from bone resection in skeletally immature patients. This device can be expanded as the patient grows. The possible length of extension depends on the length of the prosthesis. Because further expansion was not possible, by turning the adjustable part of the extension back to zero and adding a new permanent extension allow the prosthesis to be further adjusted as growth ensues. Using this method/device only, a separate endoprosthesis was required to be attached onto the extension. Therefore, the applicable cases are limited, because of the fact that extensive resection usually means total femoral replacement is best indicated. However, this method is still useful for reducing the number of revision surgeries in such cases. This reduces costs and increases savings for insurers/countries.

Use of a Candida albicans SC5314 PacBio HiFi reads dataset to close gaps in the reference genome assembly, reveal a subtelomeric gene family, and produce accurate phased allelic sequences.

Candida albicans SC5314 is the most-often used strain for molecular manipulation of the species. The SC5314 reference genome sequence is the result of considerable effort from many scientists and has advanced research into fungal biology and pathogenesis. Although the resource is highly developed and presented in a phased diploid format, the sequence includes gaps and does not extend to the telomeres on its eight chromosome pairs. Accurate SC5314 genome assembly is complicated by the presence of extensive repeated sequences and considerable allelic length variation at some loci. Advances in genome sequencing technology provide the tools to obtain highly accurate long-read data that span even the most-difficult-to-assemble genome regions. Here, we describe derivation of a PacBio HiFi data set and creation of a collapsed haploid telomere-to-telomere assembly of the SC5314 genome (ASM3268872v1) that revealed previously unknown features of the strain. ASM3268872v1 subtelomeric distances were up to 19 kb larger than in the reference genome and revealed a family of highly conserved DNA helicase-encoding genes at 10 of the 16 chromosome ends. We also describe alignments of individual HiFi reads to deduce accurate diploid sequences for the most notoriously difficult-to-assemble C. albicans genes: the agglutinin-like sequence (ALS) gene family. We provide a tutorial that demonstrates how the HiFi reads can be visualized to explore any region of interest. Availability of the HiFi reads data set and the ASM3268872v1 comparative guide assembly will streamline research efforts because accurate diploid sequences can be derived using simple in silico methods rather than time-consuming laboratory-bench approaches.

Fluctuaciones recientes del glaciar Alerce (1953-2020), Andes de Patagonia norte

In recent decades, glacier retreat has been observed in all the world’s mountain ranges. Over the last 20 years, glaciers in the Andes have lost mass at one of the highest rates on record. Particularly, glaciers in the northern Patagonian Andes show the highest rate of loss of all the Andean regions for the last decade. Detailed records of long-term variations in glacier extent are crucial to put current climate change into context and quantify its impact on mountain areas. In the present study, a reconstruction of the extension (length and area) of the Alerce glacier (41.15° S-71.81° W) for the last 70 years was carried out. By means of historical documents and satellite images (Landsat and Pléiades), detailed maps of glacier fluctuations were generated for the period 1953-2020. Four methodologies were evaluated to measure the front position: i) central flow line; ii) curvilinear box; iii) multiline; and iv) variable box. The magnitude of the front position variations depends on the methodology applied. The method that best addresses glacier front variations over the period analyzed is the variable box method. Between 1953 and 2020, the Alerce glacier lost 35% of its area (1.1±0.1 km2) and 67% of its total length (1.49±0.04 km). It is possible to distinguish periods with different rates of retreat. A stage of slight retreat (-11.3±0.5 ma-1) between 1953 and 1976, followed by a period of stability (-6.7±0.5 ma-1) between 1977 and 1983, then a strong retreat (-58.7±0.5 ma-1) between 1984 and 1999, followed by another period of stability (-5.4±0.5 ma-1) between 2000 and 2009 and, finally, another retreat (-8.7±0.5 ma-1) between 2010 and 2020. The retreat rates for the Alerce glacier mimic those observed in other glaciers in the region, possibly representing a regional climatic signal.

The Relationship of Socio-Economic Characteristics with the Implementation of the main Tasks of Agricultural Extension Workers

Individual characteristics are personal factors related to all aspects of life that are influenced by behavior, environment, and individual interaction. Socioeconomic characteristics indicate the resources owned by agricultural extension workers to carry out extension services in accordance with their abilities that can affect the main tasks of agricultural extension workers. The purpose of this study is to analyze the correlation between the socioeconomic characteristics of extension workers and the implementation of the main tasks of agricultural extension workers. The research method used is the survey method. Sampling using saturated sample method or census with 48 respondents. The data collection method uses a questionnaire with reference to the Likert scale. The research data were analyzed using Partial Least Square (PLS). The results showed that the socioeconomic characteristics of agricultural extension workers have diversity including; productive age, education, work experience, income, and expenses. The implementation of the main duties of agricultural extension workers in carrying out their duties is quite visible from the average result of the Work Performance Value of 68.70. There is a positive correlation between the social characteristics of agricultural extension workers, age background, and length of time as extension workers with the implementation of the main duties of agricultural extension workers.

Synchronous Fracture Expansion Pattern of Hydraulic Fracturing with Different Perforation Spacing

Using the self-developed “TCHFSM-I” large-size true triaxial fracturing seepage simulation device and fluid injection flow dynamic monitoring device, we studied the crack initiation and expansion law of multi-fractures under different perforation spacing conditions and revealed the mechanism of multi-fractures expanding from non-equilibrium to equilibrium on the basis of the evolution law of the injection pressure and characteristics of the distribution of the injection flow. The results show that when the perforation spacing is small (&lt;60 mm), the central injection fracturing cracks are affected by the extension of the upper and lower injection cracks, and their extension lengths are shorter; on the contrary, the extension lengths of the upper, central and lower injection cracks are basically the same, and the three hydraulically fractured cracks shift from non-equilibrium to equilibrium extension. When the perforation spacing is small, the fracture initiation pressure of the middle perforation is much larger than that of the upper and lower perforations. However, as the perforation spacing increases, the fracture initiation pressure of the middle perforation gradually decreases. Its fracture initiation pressure is basically the same as that of the upper and lower perforations. The expansion of the three hydraulically fractured cracks is independent of each other. In addition, the evolution law of the injection flow rate can better reflect the multi-fracture fracture initiation and expansion pattern, and the evolution pattern of the injection flow rate can better reflect the synchronous fracture initiation and expansion mechanism of multi-fracture fracture. The results of the study can provide technical guidance for efficient coalbed methane extraction.