Trend Curves Research Articles

Mathematical Modelling of Epidemics: Insights from Differential Equations and Stochastic Processes

Epidemic modeling is a key component in the assessment of infectious diseases transmission and guiding the public health response. This report explores two primary approaches to epidemic modeling: It has categorized the models into deterministic model where the disease spread is depicted using differential equations and stochastic models where probability forms the basis of modeling the spread of the diseases. These approaches offer essential information about the nature of epidemic behaviors, for example, the ability to forecast the trends of epidemic curves, and calculation of the basic reproduction number (R0), assessment of child and caregiver, identification of protective/environmental factors, and assessment of intervention approaches. The SIR and SEIR models based on ordinary differential equations that trace the shifting between Susceptible, Infected and Recovered populations. They are especially good in large data scenarios where randomness, or the lack of it, has negligible or no bearing and are fast in providing long-term trends. But they do not target small or more heterogenic groups and do not account for stochastic fluctuations. On the other hand, stochastic models take into consideration the variability of the disease’s transmission as well as the recovery time for disease, they are used for small population size or variable conditions. These models, frequently calibrated through computations involving Monte Carlo simulation or stochastic differential equations, allow for a wider envisaged set of outcomes and shed light on such scenarios as disease wiping out or super spread events. However, they present higher computational costs and are sensitive with parameter estimates as well. It highlights how problematic mathematical modeling is for evidence-informed decision making in public health, as evidenced by COVID-19 pandemic. This highlights the need for constant refinement of the models – data streaming, population variability, and adaptation of the model to real-world emerging issues such as climatic change and zoonotic diseases. Applying the respective strengths of deterministic and stochastic models, further research is encouraged as well as policy implications associated with the interaction between these models and infectious disease outbreaks

Study on Splitting Intensity and Acoustic Emission Characteristics of Brazilian Deep Gray Sandstone at Different Scales

In order to determine the influence of size on the mechanical properties of sandstone and acoustic emission damage characteristics, the Brazilian splitting test of 6 sandstone samples with diameters of 25mm, 37mm, 50mm, 69mm, 80mm and 100mm was carried out by using the rock weak surface direct shear instrument and acoustic emission monitoring system The effects of size change on the splitting strength, deformation, acoustic emission activity and damage characteristics of rock samples are discussed. The results show that the larger the specimen size is, the more original defects are contained in the specimen, which has a great influence on the development trend of stress-strain curve, peak strength and peak strain during loading. With the increase of sample size, the peak strength and peak strain become smaller and smaller, and the ratio of peak compressive strain to peak tensile strain remains in the range of 2~4 times. According to the development characteristics of acoustic emission signals, the whole process of rock damage is divided into four stages: micro-crack compaction stage, new crack generation and expansion stage, crack rapid expansion stage and failure stage. The diameter sample of 69mm~100mm showed almost no AE signal at the beginning of test loading, and the activity of acoustic emission signal is intense at the moment of failure.The larger the specimen size, the larger the stress value and b value corresponding to the fracture entering the instability expansion stage. Tensile microcracks are the main types of cracks in the splitting test, and with the increase of the size, the shear microcracks gradually decrease, and the tensile microcracks increase.

Study on Slipform Paving of Concrete Containing Alkali-Free Accelerators on Roadway Floor.

Aiming at the problems of collapse, deformation, and displacement in the concrete paving of roadway floors, this paper adopts the way of adding alkali-free accelerators to the concrete on both sides, through mechanical analysis, single factor experiment, orthogonal experiment, and polynomial fitting method, and determines the relevant parameters of concrete and accelerators in the sliding form paving of roadway floor from two aspects of paving material and size. The results show that the FSA-AF alkali-free liquid accelerator is more suitable for roadway floor paving than the J85 powder accelerator. When the FSA-AF accelerator dosage reaches 8%, the decreasing trend of initial setting time curve tends to be flat. The deformation resistance of concrete containing accelerator is positively correlated with the dosage of the accelerator. Concrete side pressure is positively correlated with pavement paving height. The FSA-AF accelerator can reduce the compressive strength of concrete; the compressive strength and retention rate of concrete at all ages are the highest when the dosage of FSA-AF is 7%. A water-cement ratio of 0.4 and a 9% dosage of accelerator are the optimal combination to meet the four evaluation indexes. According to the width estimation formula, the width of the side concrete should be set to 14 cm.

Establishment and Application of an Elastic-Plastic Damage Constitutive Model for Ceramic Fiber Insulation Tiles.

A thermal protection system is critical for ensuring the safe take-off and return of various aircraft. A key heat-resistant material within this system is the ceramic fiber insulation tile (CFIT), which is a porous three-dimensional network material with density ranges from 0.3 to 0.4 g/cm3 that exhibits complex mechanical behaviors. Due to the complexity of the service environment, experimental methods cannot accurately capture the mechanical behavior of a CFIT. Although simulation-based methods can provide insights, an accurate constitutive model for CFITs has yet to be established. To predict its complex mechanical behavior, an elastic-plastic damage constitutive model was established for CFITs. Based on the Hashin criteria and four fundamental assumptions, a yield rule was modified by introducing a damage factor in the TTT direction. The model was encoded into a user-material subroutine (UAMT) integrated within ABAQUS to capture the mechanical responses under four typical working conditions. The change trend of the simulation curve closely aligned with that of the experiment curve, better characterizing the stress-strain relationship of the CFIT under different working conditions such as compression, tension, and shear and the error was less than 18%. The proposed approach was validated by designing a millimeter-level indentation experiment. The results in this paper demonstrate that the maximum loading depths of the simulation and experiment were consistent, and the relative errors were within 12%, respectively. The research provides a reliable elastic-plastic damage constitutive model to predict the mechanical behavior of CFITs under complex working conditions.

Comparison of laser diffractometry and pipetting methods for particle size determination: A pilot study on the implications of result discrepancies on soil classification

AbstractIn recent decades, the determination of particle size distribution (PSD) using the laser diffraction method (LDM) has become increasingly common, supplanting traditional sedimentation techniques. Advances in everything from sample preparation to software settings have been realized globally, whether through recommendations from laser diffraction (LD) manufacturers or through user experiences. These developments seek to enhance accuracy and diminish the uncertainties associated with new methodologies. Particularly in the determination of PSD using LDM on various LD instruments and in comparison with the sieve–pipette method (SPM), discrepancies in PSD frequently arise. This article aims to mitigate these discrepancies by predefining parameters, specifically through the adjustment of LD software settings and sample preparation (employing a uniform set of dispersed samples in potassium hydroxide) on two widely used LD instruments for soil measurements: Mastersizer 3000 and Analysette 22. Additionally, these samples were analyzed using the traditional SPM (ISO 11277, 1998), with the results from LDM and SPM subsequently compared. The paper also explores the impact, range of user options, and limitations of predefined software settings on both LD instruments. Eighty soil samples were analyzed for PSD, collected from arable land in the cadastral area of Hrušky, district of Břeclav (Czech Republic), in spring 2022, from depths of 0‐ to 10‐cm and 10‐ to 20‐cm. Significant differences in PSD were confirmed, although the trends of the grain size distribution curves were very similar to those of LDM. Results from the Mastersizer underestimated the clay fraction by an average of 17% compared to SPM, at the expense of the sand fraction, whereas the silt fraction was underestimated by a maximum of 4%. Conversely, Analysette 22 overestimated the silt fraction by an average of 37% at the expense of the sand fraction, confirming only a slight difference in the clay fraction: 3%. Moreover, the quantity of sample entering the dispersion unit was identified as a significant issue when comparing LD instruments, despite the obscuration value being nearly identical, that is, 20%–30%. Therefore, it was not possible to achieve the same or similar weight when introducing suspension into circulation. The robustness of the obtained results underscores the importance of understanding input parameters when interpreting results between different methods.

Mechanical Properties and Damage Constitutive Model of Saturated Sandstone Under Freeze-Thaw Action.

In order to investigate the impact of freeze-thaw damage on sandstone under the coupling of ground stress and pore water pressure, three types of porous sandstone were subjected to freezing at different negative temperatures (-5 °C, -10 °C, -15 °C, and -20 °C). Subsequently, hydraulic coupling triaxial compression tests were conducted on the frozen and thawed sandstone. We analyzed the effects of porosity and freezing temperature on the mechanical properties of sandstone under hydraulic coupling and performed nuclear magnetic resonance tests on sandstone samples before and after freezing and thawing. The evolution of the pore structure in sandstone at various freezing and thawing stages was studied, and a statistical damage constitutive model was established to validate the test results. The results indicate that the stress-strain curves of sandstone samples under triaxial compression after a freeze-thaw cycle exhibit minimal changes compared to those without freezing at normal temperature. The peak deviator stress shows a decreasing trend with decreasing freezing temperature, particularly between -5 °C and -10 °C, and then gradually stabilizes. The elastic modulus of sandstone with different porosity decreases with the decrease in freezing temperature, and the decrease is more obvious in the range of -5 °C~-10 °C, decreasing by 2.33%, 6.11%, and 10.5%, respectively. Below -10 °C, the elastic modulus becomes similar to that at -10 °C, and the change tends to stabilize. The nuclear magnetic porosity of sandstone samples significantly increases after freezing and thawing. The smaller the initial porosity, the greater the rate of change in nuclear magnetic porosity after a freeze-thaw cycle. The effects of freeze-thaw damage on the T2 distribution of sandstone with different porosity levels vary. We established a statistical damage constitutive model considering the combined effects of freeze-thaw damage, ground stress, and pore water pressure. The compaction coefficient K was introduced into the constitutive model for optimization. The change trend of the theoretical curve closely aligns with that of the test curve, better characterizing the stress-strain relationship of sandstone under complex pressure environments. The research findings can provide a scientific basis for wellbore wall design and subsequent maintenance in complex environments.

In vivo quantitative assessment of proximal femoral cortical bone microstructure using double-echo ultrashort echo time magnetic resonance imaging.

Quantitative assessment of cortical bone microstructure is crucial for the evaluation of osteoporosis, yet current clinical methods such as dual-energy X-ray absorptiometry (DXA) have many limitations. The in vivo quantitative assessment without radiation can be achieved by ultrashort echo time (UTE) magnetic resonance imaging (MRI), where double-echo UTE has high clinical feasibility. However, related studies have mainly focused on distal extremities, and there is a lack of in vivo studies on the proximal femur. This cross-sectional study, as a preliminary study for in vivo quantitative assessment of proximal femoral cortical bone in healthy adults by double-echo UTE MRI, aimed to evaluate the repeatability and explore the impact of potential influencing factors on UTE measurements, thereby providing a reference for the further clinical application of this technique. Healthy volunteers without osteoporosis risk factors were enrolled and underwent double-echo UTE MRI of the proximal femur. Porosity index (PI) and cortical bone thickness (CbTh) were obtained manually by two radiologists independently on double-echo UTE images using image processing software. Repeatability of PI and CbTh measurements were evaluated using intra-class correlation coefficient (ICC) analysis. PI and CbTh of different limbs and sexes were compared, and P<0.05 indicated statistical significance for these analyses. Correlations of PI and CbTh with age and body mass index (BMI) were assessed by Pearson or Spearman correlation coefficient as well as the partial Pearson correlation coefficient. Curve estimation was used to assess non-monotonic variable correlations in scatterplots. For these analyses, P<0.025 indicated statistical significance according to the Bonferroni correction. A total of 52 healthy cases (33 males, 19 females) aged 22-55 years were included for analysis, where no statistical difference in age was found between sexes (P=0.586) and BMI of males was greater than that of females (P=0.007). The repeatability of PI and CbTh measurements was excellent (ICC 0.985 and 0.943, respectively). The proximal femoral cortical PI was greater on the non-dominant side (P<0.001). PI was greater in males than in females (non-dominant: P<0.001, dominant: P=0.032) and CbTh was greater on the non-dominant side in males than in females (P=0.036) after excluding the effect of confounding factor (BMI). PI on the dominant side was positively correlated with BMI in males (r=0.535, P=0.001), and CbTh on the non-dominant side was positively correlated with BMI in males (r=0.482, P=0.005). There was a U-shaped curve trend between dominant side cortical PI and age in females (y = 65.32 - 1.88x + 0.02x2, R2=0.348, P=0.033), although there was no statistical significance after Bonferroni correction. Double-echo UTE MRI enables in vivo quantitative assessment of proximal femoral cortical microarchitecture with excellent repeatability. We identified the effects of limb dominance, sex, age, and BMI on UTE measurements in healthy adults, which can serve as a reference for future in vivo studies on proximal femoral cortical bone and is essential before clinical application.

Steel‑aluminum clinched joints mechanical properties and strength prediction under different geometric parameters

With the evolution of modularization and prefabrication in construction, there is a growing adoption of prefabricated thin-wall steel and aluminum structures for lightweight buildings and interior decoration. Clinching emerges as a proficient method for achieving heterogeneous metal connections, offering benefits such as streamlined processes, reduced material usage, environmental friendliness, and potential for automation. This study focuses on high-strength steel DP590 and aluminum alloy AW5754-H22, exploring various process parameters (including punch diameter, punch fillet radius, extensible die diameter, and extensible die depth) tailored for clinching experiments on thin steel and aluminum plates. The research analyzes how these process parameters affect the geometric characteristics of the joints and investigates their mechanical properties through static shear tests. Findings indicate that interlocks exceeding 0.29 mm lead to neck cracks during the clinching process. Additionally, the energy absorption of the specimens in button separation exceeds that in neck fracture by 44 % under comparable maximum failure loads in static shear. Optimal process parameters identified are SR5605-SR60310, achieving a maximum failure load of 4.14kN and an energy absorption value of 12.37 J in static shear tests. Finally, a method is proposed to calculate the shear strength of steel‑aluminum clinched joints based on the transmission dynamics of infectious diseases model (SIR model), accounting for the influence of geometric parameters on the static performance of the joints. This approach accurately describes the load-displacement curve trend and predicts the static shear strength of steel‑aluminum clinched joints effectively.

The impact of herd age structure on the performance of commercial sow-breeding farms

BackgroundThe herd age structure, i.e., distribution of sows within a farm based on their parity number, and its management are essential to optimizing farm reproductive efficiency. The objective of this study is to define different types of herd age structure using data from 623 Spanish commercial sow farms. Additionally, this study aims to determine which type of herd age structure can enhance reproductive efficiency at the farm level.ResultsFarms are classified into three groups according to the quadratic function fitted to the percentage of sows by parities. This classification unveils three types of herd structures: type 1 (HS1) exhibits a concave-downward trend, with a higher percentage of sows in intermediate parities (mean of 45.5% sows between the 3rd to 5th parity); type 2 (HS2) presents a trend curve that is close to a straight line, with a gradual decrease in the percentage of sows per parity (approximately 2% loss of sows census per parity); and type 3 (HS3) shows an upward concave trend curve, with an increase in the percentage of sows in later parities (19.0% of sows between 7th and ≥ 8th parity). Parametric tests assess productivity differences between the three types of herd structures (p < 0.01). HS1 farms have the best productive outcomes over a year, with 31.2 piglets weaned per sow and year (PWSY) and a farrowing rate of 87%, surpassing HS2 and HS3 farms (30.1 and 28.7 PWSY; 85.3% and 83.4% farrowing rates, respectively). HS1 also have the lowest percentage of sows returning to oestrus (11.8%) and the highest number of weaned piglets per litter (12.8), compared to HS2 (13.2% and 12.4 piglets weaned) and HS3 (15.1%, 11.9 piglets weaned). These differences show a medium effect size (η2 between 0.06 to < 0.14).ConclusionsThis study shows the importance of herd age structure on sow-breeding farms as a factor of reproductive efficiency. The results endorse the proposed classification based on the curvature of the trend parabola obtained with the quadratic function to categorize herd structures into three groups. Additionally, these findings highlight the importance of considering the herd age structure in farm decision-making.

Bond shear modulus in reinforced concrete at high temperature: General trends from test results

The scanty attention devoted so far to bond shear modulus (secant or tangent slope of the loading branch of the bond-slip curve) limits the ability to numerically model such phenomena as tension stiffening, that controls the stiffness of cracked RC structures even past a fire. To improve the knowledge of bond shear modulus at high temperature, the bond stress-bar slip curves resulting from the tests of eleven selected experimental campaigns spanning a forty-year period are re-examined in this paper. Bond shear modulus is derived as the initial slope of the bond stress-bar slip curves of stressed or unstressed specimens in either hot or residual conditions. The criteria to compare the test results coming from very different experimental campaigns are discussed at length. Bond shear modulus is shown to be a decreasing function of the residual compressive strength of the concrete (at high temperature or past cooling). The envelopes of the test data allow to assess the roles of bar diameter and concrete grade. Trend curves are derived for normal-strength and high-strength/high-performance concretes, as a first necessary step for the formulation of parametric design-oriented laws, that may be useful to model tension stiffening and to describe the distribution of the bond stresses in long anchored bars. A numerical example is also developed and the consistency with EuroCode EC2 is checked.

Estimating soil strength using ultra high resolution seismic: A case study from a shallow water windfarm

The increasing global reliance on offshore wind farms as a sustainable energy source necessitates precise soil assessment for foundation design, due to their high foundation costs and complex integration into marine environments. This study explores the utilization of ultra-high-resolution seismic data in conjunction with cone penetration test data for soil strength estimation in offshore wind farm development. We propose a convolutional neural network-based approach that leverages ultra-high-resolution seismic data for direct soil strength estimation, aiming to address the challenges of limited cone penetration test measurements and potential overfitting in complex geological settings. Our methodology involves preprocessing ultra-high-resolution seismic and cone penetration test data, interpreting and integrating geological unit information, and applying repeated k-fold cross-validation to evaluate model performance. The field data results demonstrate the model's efficacy in accurately predicting cone penetration test curve trends, albeit with some amplitude discrepancies. We highlight the significance of geological interpretation in predicting soil strength and identify the dependency on valid data within each geological unit as a limitation.

Rainfall Variability, Flood Hazards and Adaptation Strategies in Douala IV and V Municipalities, Littoral Region of Cameroon

Excessive rainfall resulting to floods remain a thorny problem in developing countries including Cameroon. This follows the negative impacts of floods on the population, infrastructure and public services. This study examines rainfall variability, population vulnerability to floods and measures put in place by the population and other stakeholders to adapt to the situation in the Douala IV and V municipalities in Littoral Cameroon. The study exploits both primary and secondary sources data for its realization. Heads of households, quarter’s heads, municipal authorities and its personnel, and public administrative officials were contacted for data collection. The data focused on floods manifestation, their effects on the city, and adaptation strategies put in place to mitigate the negative outcomes. Data from semi structured interview conducted were analyzed using content analysis methods. Sociological and spatial data also collected were analyzed using remotely sensed techniques and statistical tools such as SPSS and Microsoft excel. Climatic data were collected from the urban council, the meteorological units in the town and the National Observatory on Climate Change of Cameroon. Sequential analyses (linear trend curves, standard deviations, and cumulative balances) were used to evaluate the evolution of rainfall and correlation to floods events. The result revealed that floods in Douala IV and V result from rainfall variability, characterized by deficit and excessive rains in the months of June, July, August and September. These heavy rains accompanied by human induced factors such as uncontrolled urbanization, anarchy in construction and occupation of wetlands, poor waste management, pollution of water ways and lack of drains for stagnant water evacuation leads to floods. Also, natural drivers such as the low relief of the area, a dense hydrographic network and contact with the Atlantic Ocean via the Wouri estuary result to floods. These floods are a problem to the health of the population, public services and infrastructure and sustainability of the city. Faced with the numerous damages caused by floods, remediation strategies such as: the construction of traditional dikes, solid house foundations, water embankments, and periodic weather forecasting by the National Observatory on Climate Change of Cameroon to reduce the negative outcomes of flooding has been ineffective in reduction of floods outcomes. Consequently, floods still remains a concern in Douala town. Good environmental practices such as civil education on hygiene and sanitation, periodic cleaning of drains, combats on deforestation of mangroves and afforestation campaigns, government investment on decentralization of waste collection and management will be productive in reducing the effects of floods in Douala. The implementation of all these remedial measures will not only ensure the safety of vulnerable civilian populations but the protection of their activities.

Assessing the Efficacy of Lokomat Training in Pediatric Physiotherapy for Cerebral Palsy: A Progress Evaluation.

Background: Gait disturbances in children with cerebral palsy can increase the hindrance caused by loss of independence and social engagement. The Lokomat, developed by Hocoma, shows promise as a supplementary tool for gait rehabilitation. This study investigates the impact of Lokomat training on gait parameters and trends observed during training. Methods: A total of 26 children (13 male individuals) with a diagnosis of cerebral palsy (CP), aged 4 to 23 years, were enrolled in the study. Patients participated in a standard comprehensive rehabilitation program with additional Lokomat training sessions. Gait function was assessed using the Timed Up and Go Test (TUG) and the 10 m walking test (10mWT) at the beginning and end of the rehabilitation period. Changes in Lokomat parameters (step number, session duration, speed, body weight support, and guidance force) were also analysed. Results: The median duration of the 10mWT and TUG significantly decreased across the groups after the treatment program. The highest increases were observed for the number of steps taken. Across the entire cohort, the linear trend curves for distance and number of steps exhibited near-perpendicular alignment with the horizontal axis, suggesting significant improvement in these parameters. A consistent trend was noted for speed, with the trend line aligned parallel with the horizontal axis. Decreasing trends were observed for body weight support and guidance force. Conclusions: Therapy with the Lokomat functioning as the active gait orthosis can be used as a form of support to the standard rehabilitation protocol for patients with CP.

Assessing Watershed Flood Resilience Based on a Grid-Scale System Performance Curve That Considers Double Thresholds

Enhancing flood resilience has become crucial for watershed flood prevention. However, current methods for quantifying resilience often exhibit coarse spatiotemporal granularity, leading to insufficient precision in watershed resilience assessments and hindering the accurate implementation of resilience enhancement measures. This study proposes a watershed flood resilience assessment method based on a system performance curve that considers thresholds of inundation depth and duration. A nested one- and two-dimensional coupled hydrodynamic model, spanning two spatial scales, was utilized to simulate flood processes in plain river network areas with detailed and complex hydraulic connections. The proposed framework was applied to the Hangjiahu area (Taihu Basin, China). The results indicated that the overall trend of resilience curves across different underlying surfaces initially decreased and then increase, with a significant decline observed within 20–50 h. The resilience of paddy fields and forests was the highest, while that of drylands and grasslands was the lowest, but the former had less recovery ability than the latter. The resilience of urban systems sharply declined within the first 40 h and showed no signs of recovery, with the curve remaining at a low level. In some regions, the flood tolerance depth and duration for all land use types exceeded the upper threshold. The resilience of the western part of the Hangjiahu area was higher than that of other regions, whereas the resilience of the southern region was lower compared to the northern region. The terrain and tolerance thresholds of inundation depth were the main factors affecting watershed flood resilience. The findings of this study provide a basis for a deeper understanding of the spatiotemporal evolution patterns of flood resilience and for precisely guiding the implementation and management of flood resilience enhancement projects in the watershed.

Does acupuncture treatment reduce temporomandibular dysfunction symptoms?

To analyze the pain, the muscle profile of some muscles actively and passively involved in the stomatognathic system, and stress traits. A clinical, randomized and double-blind study (n = 35) was performed analyzed by the Research Diagnostic Criteria/Temporomandibular Dysfunction (RDC/TMD), with subjects allocated in experimental group (EG) which received acupuncture at the meridian points according to Traditional Chinese Medicine, and another placebo group (PG) which received acupuncture at random points. The degree of discomfort was evaluated by the Visual Analog Scale (VAS), tissue sensitivity, somatic and psychic anxiety level, salivary cortisol levels, electrical activity of the masseter, anterior temporal, sternocleidomastoid (SCM) and trapezoid muscles before and after the proposed treatment. The Wilcoxon test, Chi-squared test, Signal test, Mann-Whitney U-test, paired and independent Student’s t-test, Pearson’s correlation test and the symmetry index of the muscles were used for statistical analysis, considering a significance level equal to 0.05. There was a reduction of physical non-specific TMD symptoms, and the degree of discomfort decreased by fifty percent in the EG, with a trend curve pointing to an evolution in the repair process. Tissue sensitivity decreased in the EG and increased in the PG. The treated group presented a reduction of physical and psychological manifestations in the anxiety situation, while the reduction was only for physical manifestations in the PG. Salivary cortisol levels did not change. The masticatory musculature presented an increase in the temporal activity and a decrease in the masseter/temporal ratio in the PG. The EG showed a better relationship between the trapezium and sternocleidomastoid muscles. Therefore, acupuncture treatment was efficient for reducing the pain symptoms and the physical and mental conditions of anxiety in people with TMD, as well as to improve the relationship of postural muscles.

Measurements and analysis of the radar cross section of chaff dipoles

AbstractA free space test method to measure the Radar Cross Section (RCS) of single dipole elements is presented. The method is such that dipoles can be measured over a large range of frequencies, in free space and without the need of an anechoic chamber. The setup employs with a Vector Network Analyser (VNA) synchronised to a rotating turntable that controls the position of the transmitting and receiving antennas and the polarisation of the irradiated electric field. Measurements are collected for chaff dipoles made of copper wire, microwire and aluminised glass, from 5 to 11 GHz, to allow a comparison of chaff RCS properties with respect to chaff material and method of fabrication. Measurements of the copper wire chaff also allowed a comparison with existing theoretical predictions of chaff reflectivity. An analysis and a comparison of the results is presented. Results show that the experimental trends of the chaff RCS curves agree with the theoretical RCS curves for perfectly conducting wires. They also show that copper wire provides the strongest reflective chaff followed by the aluminised glass and the microwire.

Coupling and Coordination Analysis of High-Quality Agricultural Development and Rural Revitalization: Spatio-Temporal Evolution, Spatial Disparities, and Convergence

The coupling and coordination of high-quality agricultural development (HQAD) and rural revitalization is an inevitable choice to accelerate the realization of Chinese-style agricultural and rural modernization. Based on system theory, this study reconstructs the indicator systems of both and conducts measurements by applying the improved AHP–entropy weight method. This study has extended the analytical methods of kernel density estimation, Dagum Gini coefficient, σ convergence, and spatial β convergence to further investigate the spatio-temporal evolution, regional disparities, and convergence effect of the coupling coordination degree (CCD) of HQAD and rural revitalization in China from 2010 to 2020. The results show that the CCD has a tendency to increase year by year, presenting the characteristics of ‘high coupling degree–low comprehensive development level–low coupling coordination degree’, and also has the spatial distribution pattern of ‘high in the east and low in the west’. In addition, most of the provinces have a tendency to jump to a higher stage of coupling coordination; the overall trend of the kernel density curves is favorable; the results of Dagum’s Gini coefficient show that inter-regional disparities contribute the most to regional spatial disparities; and there is a significant tendency towards σ convergence and spatial β convergence of the CCD in China and the four regions. This study stimulates a broader discussion of rural revitalization, with potential implications for decision making in practice.

Experimental study on the rock breaking effect of different tooth shapes of inserted teeth in a hobbing-cone hybrid PDC bit under complex stress environment

The hobbing-cone hybrid PDC bit has emerged with the increasing exploitation of deep oil and gas resources. As an important component of new bits, studying the mechanism of toothed fracturing of deep rocks is crucial for improving rock-breaking efficiency. In this paper, the spherical teeth and conical teeth were used to intrude sandstone under different confining pressures, and the brittleness index (BIm), specific energy (SE), and average fragment size (dm) were used to analyze the rock-breaking effect. The 3D contour scanner quantitatively analyzed the crushing pit area. Finally, the in-situ CT scanning and discrete element numerical simulation were used to summarize the crack propagation law. The results show that with the increase of confining pressure, the BIm of inserted teeth increases continuously, and the growth rate of conical teeth increases, while that of spherical teeth decreases. The SE and dm exhibit a symmetrical distribution with a confining pressure of 10MPa as the axis of symmetry. When the difference in principal stress is 5MPa, the SE is the lowest point, the rock-breaking efficiency is the highest, and the corresponding dm is at the highest point, but the curve trend is the opposite. When the stress difference is 5MPa, it is conducive to propagating surface cracks, thus forming a larger crushing area and the highest rock-breaking efficiency. Based on CT results, the dense particle core is formed near the inserted teeth, and that of the spherical teeth is located below. In contrast, that of the conical teeth is located on the side, which is also the reason for the difference in crack propagation between different tooth shapes.

Arthroscopic meniscal surgery in Norway from 2010 to 2020: A paradigmatic shift.

Meniscal injuries in the knee are usually treated surgically with arthroscopic partial resection (APR) or arthroscopic repair (AR). APR has been shown to increase the risk of osteoarthritis and the focus has shifted to repairing the meniscus with AR. The extent of this shift is yet to be established and an analysis of incidence rates (IR) of APR and AR for meniscal injuries could highlight this. Data from the Norwegian Patient Registry (NPR) and Statistics Norway (SN) from 2010 to 2020 were collected. The number of procedures, demographics and facilities providing meniscal surgery were obtained from NPR, while population size and catchment area were collected from SN. IR of APR and AR and APR/AR rate ratios were estimated and compared. A total of 119,528 knee arthroscopies were performed, 89.6% of which were APR. The number of APR performed nationally decreased by 72%, while AR procedures increased by 178%. The national IR of APR decreased from 298 to 82/100,000 inhabitants (p < 0.001). For AR, the national IR increased annually from 13/100,000 inhabitants to a peak in 2019 of 32/100,000 inhabitants (p < 0.001). The APR/AR rate ratio decreased from 22 to below five and the APR/AR trend curves showed a statistically significant decrease (p < 0.001). Surgical treatment of meniscal injuries has changed, with a substantial reduction in APR and a strong increase in AR. The reduction in APR, especially in older patients, suggests that meniscal surgery in Norway has undergone a paradigmatic shift, in line with recent literature. Level IV.

Research on Rock Energy Constitutive Model Based on Functional Principle

The essence of rock fracture can be broadly categorized into four processes: energy input, energy accumulation, energy dissipation, and energy release. From the perspective of energy consumption, the failure of rock materials must be accompanied by energy dissipation. Dissipated energy serves as the internal driving force behind rock damage and progressive failure. Given that the process of rock loading and deformation involves energy accumulation and dissipation, the rock constitutive model theory is expanded by incorporating energy principles. By introducing the dynamic energy correction coefficient, according to the law of the conservation of energy, the total energy exerted by external loads on rocks is equal to the energy dissipated through the dynamic energy inside the rocks. A new type of energy constitutive model is established through the functional principle and momentum principle. To validate the model’s accuracy, a triaxial compression test was conducted on sandstone to examine the stress–strain behavior of the rock during the failure process. A sensitivity analysis of the parameters introduced into the model was conducted by comparing the model results, which helped to clarify the innate laws of significance of these parameters. The results indicated that the energy model more accurately captures the non-linear mechanical behavior of sandstone under high-stress loading conditions. The model curve fits the test data to a high degree. The fitting curve was basically consistent with the changing trend of the test curve, and the correlation coefficients were all above 0.90. Compared with other models, the model based on the energy principle not only accurately reflects the rock’s stress–strain curve, but also reflects the energy change law of rock. This has reference value for the safety analysis of rock mass engineering under loading conditions and aids in the development of anchoring and support schemes. The research results can fill in the blanks that exist in the energy method in terms of rock deformation and failure and provide a theoretical basis for deep rock engineering. Moreover, this research can further improve and extend the rock mechanics research system based on energy.