Confinement Stress Research Articles

A machine learning based method for predicting the shear strength of Fiber-Reinforced Concrete joints in precast segmental bridges

The utilization of Fiber-reinforced concrete (FRC) in the construction of Precast segmental concrete bridges (PSCBs) is progressively increasing. The design of joints among precast members can considerably impact the overall integrity and safety of the structure. Consequently, accurately estimating the shear capacities of FRC joints has become critical for evaluating the safety of PSCBs structures. However, the effectiveness and efficiency of formulas or models intended for prediction of the shear capacities of joints with normal concrete are unknown in predicting the shear capacities of FRC joints. In this study, the machine learning (ML) algorithms are employed to predict the ultimate load of FRC joints, utilizing a database of 192 push-off test results. Three individual models (Lasso, SVM, and KNN) and three ensemble models (RF, GBDT, and XGBoost) were developed for estimating the ultimate load. The GridSearchCV technique was utilized for parameter optimization based on the training set, in conjunction with a five-fold cross-validation method. A comparative study revealed that the XGBoost ensemble model surpassed other models, with a predictive performance ranking as follows: XGBoost > GBDT > RF > KNN > SVM > Lasso. The best-performing XGBoost model achieved performance metrics of R2 = 0.964, MAE = 41.318 kN, RMSE = 56.760 kN, and MAPE = 14.228%. The superior reliability of the XGBoost ensemble model was further validated through comparisons with current design codes and existing models. As ML-based models are typically black-box models, the SHapley Additive exPlanations (SHAP) method was employed to explicitly link the predicted output to the inputs. Based on SHAP results, confining stress (CS), depth of shear key (D), compressive strength of concrete (fcu), total height of joints (H), and height of flat part (Hsm) recognized as the crucial parameters affecting ultimate load.

Experimental and numerical investigation on axial behavior of circular and square slender reinforced columns

To investigate the axial performance of slender concrete-filled steel tube (CFST) columns reinforced by outer steel tube and sandwiched concrete jackets, an axial compression test was conducted on 20 circular and square slender reinforced columns. The study aimed to examine the influence of the cross-sectional shape, steel content of the outer tube, the strength of sandwiched concrete, and slenderness ratio on the failure mode, load-displacement curves, and ultimate load. A comparative test on six slender CFST columns was also conducted. The test results showed that the local buckling degree of the outer steel tube in square reinforced columns was greater than that in circular reinforced columns, while the overall bending deformation was smaller. The influence of the sandwiched concrete strength on the load-displacement curve was weaker compared to the influence of the outer tube thickness and slenderness ratio. As the slenderness ratio increased, both the longitudinal and lateral strains of the specimens tended to decrease. The difference in strain between the tension and compression sides was more pronounced in circular reinforced columns than in square reinforced columns. The average SI values of circular and square reinforced specimens were 1.05 and 1.00, respectively, but the gap in SI values between the two types of reinforced columns is reduced as the slenderness ratio increases. Then, a numerical model on the slender reinforced columns was established by the finite element software ABAQUS. A good agreement was obtained between test results and simulation results. The mechanical mechanism of typical slender reinforced columns was further analyzed, including longitudinal stress contour map of concrete, the development of longitudinal stress of steel tube, as well as distribution of transverse confinement stress. A formula was subsequently proposed based on a design code to predict the load-bearing capacity of the retrofitted columns, the prediction results agreed well with the experimental data.

Do optimum dietary protein and early mild stress events prepare oscar (Astronotus ocellatus) for a stressful future?

This study aimed to investigate the effects of dietary protein (380 vs 510 g/kg) and duration of early mild stress (0, 2 and 4 weeks) on growth, haematology, serum biochemistry, immunological response, antioxidant system, liver enzymes, and stress responsiveness of oscar (Astronotus ocellatus; 4.7 ± 0.6 g). After the nine-week feeding trial, all fish were exposed to final acute AC stress (acute confinement stress) and sampled for serum and haematological parameters. Fish fed dietary 510 g/kg protein grew faster (gain 54.21 g vs 42.98 g) and had a higher condition factor (2.22 vs 1.81) than those fed diets containing 380 g/kg protein after ten weeks feeding ad libitum. After AC stress, oscars subjected to four-time stress (4EMS) had a higher survival rate than the 0EMS group (77.08% vs 64.59%). Additionally, white blood cells, blood performance, total protein, high-density lipoproteins, immunoglobulin M, complement component 4, complement component 3, superoxide dismutase, and glutathione peroxidase were significantly greater in the two-time stress (2EMS) group than the 0EMS treatments. Although fish welfare must be considered, mild stress during the trial can reduce glucocorticoid feedback sensitivity in fish, resulting in greater survival after the acute stress reaction at the end of the study.

Size effect on axial behavior of stub CFST columns strengthened with square steel tube and sandwiched concrete jackets

The size effect of CFST columns strengthened with square steel tube and sandwiched concrete jackets subjected to axial compression was investigated. Test parameters included specimen size, outer steel ratio and sandwiched concrete grade. The test results showed that the peak nominal stress and ductility index of both CFST and strengthened columns presented a decreasing tendency with the increase of the specimen size. Compared with traditional CFST columns, the size effect on peak stress of retrofitted columns was found to be more significant, while the size effect on ductility index was weaker. The analysis revealed that the level of confinement stress decreased as the size of the confined concrete increased at the peak load. The size effect on the confining stress was much greater than that on the material strength of the sandwiched concrete. Comparison results with four design codes indicated that the existing specifications overestimated the load-bearing capacity of large-size specimens. A formula for calculating the reduction coefficient related to confinement ratio was proposed to consider the size effect on the compressive strength of inner and sandwiched concrete. By introducing the reduction coefficients into formulas of design codes, the trend of overestimating the load-bearing capacity of large-size columns was weakened.

Confining Stress Response to Hydraulic Fracturing Volumetric Opening on the Representative Volume Element (RVE) Scale

Confining stress response is considered an accompanying behavior of hydraulic fracturing. Along these lines, an evaluation model of confining stress response was presented in this work. It was established on a rock representative volume element (RVE) and based on the hydraulic volumetric opening model, which stems from the theories of poroelasticity, breakdown damage, and hydraulic fracture mechanics. From the extracted outcomes, it was demonstrated that the confinement of the stress response depends on the matching among the characteristic parameters (εb,εs,m) of the rock breakdown, the volumetric opening, and channel flow regimes of the fracturing fluid. Examples in four limiting fracturing regimes show that (1) the confinement of the stress response is strongly determined by the existence of various fracturing regimes and takes place in a different manner during fracture initiation and opening. More specifically, during fracturing initiation, the ratio of the confining stress response to the far-field stress (Pcmax/σh) is 2.0500 in the M regime, 1.9600 in the M˜ regime, 2.7126 in the K regime, and 1.7448 in the K˜ regime, while when the fracture is opened, these values (PC/σh) are 1.8994, 1.8314, 1.6378, and 1.2846, respectively. (2) The impact of the confined stress response to the fluid pressure is also affected by the fracturing regimes; e.g., in both M and M˜ regimes, the peak confinement stress responses lag behind peak pore pressures, but in the K and K˜ regimes, lag off disappears. (3) The pore volumetric opening (Vpe) leads to an increase in the confining stress response, while the fracture opening (Vpd) leads to a reduction in the confining stress response.

Seismic performance of precast columns strengthened with prestressed CFRP

To address the issue of poor seismic performance in precast columns compared to cast-in-place columns during service, a wedge-type anchor was designed to apply prestress to multi-layer carbon fiber reinforced polymer (CFRP) and strengthen the precast columns. Eight specimens were designed and fabricated to validate the strengthening effect of the proposed method. The seismic performance indicators, including ductility, energy dissipation, and load-bearing capacity of each specimen, were analyzed based on parameters such as the use of strengthening, axial compression ratio, and longitudinal reinforcement diameter (equivalent reinforcement ratio). The results showed that the ductility coefficient and energy dissipation of the strengthened specimens increased by up to 240% and 640% respectively, and the ultimate bearing capacity increased by up to 34.5%. With the increase in axial compression ratio, the ductility coefficient and energy dissipation capacity of the specimens decreased, but the load-bearing capacity increased. Increasing the diameter of the longitudinal reinforcement at an equivalent reinforcement ratio resulted in a decrease in the ductility and energy dissipation capacity of the specimens, but improved their load-bearing capacity and stiffness. This is because there is a stiffness transition in the connection area between the grouting sleeve and the top, and plastic hinges form at the upper part of the sleeve, resulting in a reduction in the effective height of the specimen. However, prestressed CFRP provides sufficient lateral active confinement stress to the specimen, greatly reducing the bond slip between the longitudinal reinforcement and concrete, and improving the stiffness transition in the grouting sleeve area of the precast column, thereby enhancing the seismic performance and overall integrity of the precast column. Finally, a calculation method for the flexural capacity of strengthened specimens considering the constraint effect of CFRP on concrete was proposed, and the effective height of the specimens was calculated based on the upward mechanism of plastic hinges in precast columns. The final calculation results had small errors, indicating that the proposed method has high accuracy and good applicability.

Failure characterization of fully grouted rock bolts under triaxial testing

Confining stresses serve as a pivotal determinant in shaping the behavior of grouted rock bolts. Nonetheless, prior investigations have oversimplified the three-dimensional stress state, primarily assuming hydrostatic stress conditions. Under these conditions, it is assumed that the intermediate principal stress (σ2) equals the minimum principal stress (σ3). This assumption overlooks the potential variations in magnitudes of in situ stress conditions along all three directions near an underground opening where a rock bolt is installed. In this study, a series of push tests was meticulously conducted under triaxial conditions. These tests involved applying non-uniform confining stresses (σ2 ≠ σ3) to cubic specimens, aiming to unveil the previously overlooked influence of intermediate principal stresses on the strength properties of rock bolts. The results show that as the confining stresses increase from zero to higher levels, the pre-failure behavior changes from linear to nonlinear forms, resulting in an increase in initial stiffness from 2.08 kN/mm to 32.51 kN/mm. The load-displacement curves further illuminate distinct post-failure behavior at elevated levels of confining stresses, characterized by enhanced stiffness. Notably, the peak load capacity ranged from 27.9 kN to 46.5 kN as confining stresses advanced from σ2 = σ3 = 0 to σ2 = 20 MPa and σ3 = 10 MPa. Additionally, the outcomes highlight an influence of confining stress on the lateral deformation of samples. Lower levels of confinement prompt overall dilation in lateral deformation, while higher confinements maintain a state of shrinkage. Furthermore, diverse failure modes have been identified, intricately tied to the arrangement of confining stresses. Lower confinements tend to induce a splitting mode of failure, whereas higher loads bring about a shift towards a pure interfacial shear-off and shear-crushed failure mechanism.

Experimental Wave-Based Assessment of Liquefaction Resistance for Different Degrees of Saturation

Abstract This paper presents the results of an experimental program carried out in the laboratory aimed at assessing the liquefaction resistance by correlations between longitudinal wave (P-wave) and shear wave (S-wave) velocities (VP and VS) and cyclic stress ratio from triaxial testing (CSRCTx) for different degrees of saturation (Sr). The liquefaction resistance was assessed using a cyclic triaxial apparatus equipped with Hall-effect transducers and bender elements, combining stress-based (large-strain level) and wave-based (small-strain level) approaches. These tests were carried out in soil specimens at relatively high degrees of saturation, which were estimated during testing by VP measurements interpreted using Biot’s theory. The results revealed that, for the same relative density and confinement stress, the S-wave-based approach did not predict the liquefaction resistance well because of the negligible variation in the stress state and soil stiffness for the assessed Sr values, which were above the air-entry value. In turn, the P-wave-based approach effectively predicted the liquefaction resistance increment of the TP-Lisbon sand for different Sr conditions because of the strong dependency of P-wave propagation on the degree of saturation in granular media. This is a consequence of the most relevant factor conditioning the pore pressure buildup in partially saturated sands, e.g., the compressibility of the occluded air bubbles, which can be detected by VP but not by VS.

Cyclic axial compression stress-strain model for FRP-confined concrete-encased cross-shaped steel columns

FRP-confined concrete-encased cross-shaped steel columns (FCCSCs) are novel composite columns developed in recent years. For the bearing capacity design and seismic design of FCCSCs, the development of an accurate cyclic axial compression stress–strain model is necessary. Considering such a demand, this paper presents the cyclic axial stress–strain model for FCCSCs. The model is informed by physical observation and test measurements from a series of experimental investigations conducted by the authors and other researchers. The proposed cyclic model consists of two main components, namely (1) the monotonic stress–strain envelope curve and (2) the cyclic rules and equations to describe the unloading and reloading paths. Moreover, the hybrid confinement effect of FRP tube and cross-shaped steel is considered in the stress–strain model through the effective confinement stress model, in addition to their influence on the transition and ultimate point of the envelope curve. Finally, the accuracy of the proposed model is verified with the current test results.

Compressive–Flexural Failure Mechanism and Bearing Capacity Calculation of Over-Ranging Tapered CFDST Members for Support Structures of Offshore Wind Turbines

Upon the higher requirement on high-performance structures of large-scale supporting structures of offshore wind turbines, the systematic analysis on the compressive-flexural behavior and ultimate bearing capacity of tapered concrete-filled double skin steel tubular (CFDST) members designed by over-ranging parameters was performed. Investigating the entire-process mechanism, e.g., the moment–deformation response, stress development, interaction stress, and subassembly contribution, was based on the finite element (FE) analysis, where the moment–deformation curve can be distinguished by four characteristic points, and the transverse local buckling of outer tube partly weakens distribution height of interface pressure in compression zone compared to that in tension zone. Influences of material strengths and geometric parameters were examined by the parametric study, e.g., increasing tapered angle (ψ) slightly reduces the bearing capacity; the higher axial compression ratio (n) contributes a noteworthy action on the post-peak behavior and carrying capacity, e.g., the bearing capacities at n = 0.9 and n = 0.5 reduce by 64.14% and 18.44% compared to capacity at n = 0.1, respectively; influence of Do/to ratio is more significant than Di/ti ratio. Subsequently, the modified cross-sectional stress integration (CSI) method was proposed to predict the moment–strain (M-ε) curves of tapered CFDST members; meanwhile, a confined concrete model with transverse confinement stress as an explicit parameter was modified, and influences of different confined concrete models on predicting M-ε curves were compared. Finally, design methods based on the modified CSI method and limit state method were proposed as a simplified calculation method to determine the correlative relationship of axial compressive strength and moment-resisting capacity (N-M curve).

Compression behavior of concrete columns combinedly confined by FRP externally wrapped Fe-SMA strips

Compared to the traditional passive confinement to strengthen concrete columns, previous studies testified that the active confinement provided by prestressed materials not only can improve certainly the material utilization rate, but also alleviate the hysteresis of confinement stress. Meanwhile, the iron-based shape memory alloy (Fe-SMA), that performs the shape memory effect, can be utilized as an innovative strengthening method to rapidly apply the active confinement on concrete columns. In this paper, an innovative active strengthening method by using Fe-SMA strips was proposed, which can provide the potential to make emergency repairing for the damaged columns after the earthquake or impact. The compressive behavior of concrete columns separately confined by the passive confinement, the active confinement, and the hybrid confinement was researched by the compression test, and the different net-spacing strips and different layers of FRP strips were considered as well. The compression test was used to explore the compressive behavior of concrete columns that were confined by three different methods: passive confinement, active confinement, and hybrid confinement, and the test also considered different spacing distance strips and different FRP layers. According to the results, these three confinement types can effectively enhance the load carrying capacity and corresponding deformation of stub columns, especially the hybrid confinement. Finally, a verifying calculation was proposed to predict the peak compressive stress of these specimens, serving as a reference for selecting appropriate methods to strengthen concrete columns.

Confined steady simple shear flow of polymeric liquids

In a confined simple shear flow, the macromolecules of a polymeric liquid reorient near the walls so that the measured viscosity decreases. For instance, in a small-amplitude oscillatory shear flow, the real part of the complex viscosity decreases with confinement, and macromolecular orientation explains this. These effects in oscillation have been explained analytically for a rigid dumbbell suspension and, for a confined small-amplitude oscillatory shear flow, the summation coefficients have been determined. By contrast, for the confined steady shear flow, the summation coefficients are undetermined. In this paper, we determine these coefficients and use them to evaluate the steady shear (i) viscosity and (ii) normal stress coefficients for a rigid dumbbell suspension. We find that the zero-shear viscosity and the zero-shear first normal stress coefficients decrease with confinement. We further find that the dimensionless (i) steady shear viscosity curve increases with confinement and (ii) first normal stress coefficient first decreases with light confinement and then increases with greater confinement. We confirm our theory, at low confinement, by comparing with our new measurements of the confined zero-shear viscosity of a polystyrene solution.

Genetic heterogeneity in p53-null leukemia increases transiently with spindle assembly checkpoint inhibition and is not rescued by p53.

Chromosome gains or losses often lead to copy number variations (CNV) and loss of heterozygosity (LOH). Both quantities are low in hematologic "liquid" cancers versus solid tumors in data of The Cancer Genome Atlas (TCGA) that also shows the fraction of a genome affected by LOH is ~ one-half of that with CNV. Suspension cultures of p53-null THP-1 leukemia-derived cells conform to these trends, despite novel evidence here of genetic heterogeneity and transiently elevated CNV after perturbation. Single-cell DNAseq indeed reveals at least 8 distinct THP-1 aneuploid clones with further intra-clonal variation, suggesting ongoing genetic evolution. Importantly, acute inhibition of the mitotic spindle assembly checkpoint (SAC) produces CNV levels that are typical of high-CNV solid tumors, with subsequent cell death and down-selection to novel CNV. Pan-cancer analyses show p53 inactivation associates with aneuploidy, but leukemias exhibit a weaker trend even though p53 inactivation correlates with poor survival. Overexpression of p53 in THP-1 does not rescue established aneuploidy or LOH but slightly increases cell death under oxidative or confinement stress, and triggers p21, a key p53 target, but without affecting net growth. Our results suggest that factors other than p53 exert stronger pressures against aneuploidy in liquid cancers, and identifying such CNV suppressors could be useful across liquid and solid tumor types.

The Recovery Time between Early Mild Stress and Final Acute Stress Affects Survival Rate, Immunity, Health, and Physiology of Oscar (Astronotus ocellatus).

This study investigated how the time interval between the last EMS (netting) and the acute confinement stress (AC stress) at the end of the experiment can influence growth, haematology, blood biochemistry, immunological response, antioxidant system, liver enzymes, and stress response of oscar (Astronotus ocellatus; 5.7 ± 0.8 g). Nine experimental treatments were tested, as follows: Control, Stress28 (EMS in weeks two and eight), Stress27 (EMS in weeks two and seven), Stress26 (EMS in weeks two and six), Stress25 (EMS in weeks two and five), Stress24 (EMS in week two and four), Stress23 (EMS in week two and three), Stress78 (EMS in week seven and eight), and Stress67 (EMS in week six and seven). After the nine-week experimental period, while it was not significant, fish exposed to Stress78 (26.78 g) and Stress67 (30.05 g) had the lowest growth rates. After AC stress, fish exposed to Stress78 (63.33%) and Control (60.00%) showed the lowest survival rate. The Stress78 fish displayed low resilience, illustrated by values of blood performance, LDL, total protein, lysozyme, ACH50, immunoglobin, complement component 4, complement component 3, cortisol, superoxide dismutase, catalase, and alanine aminotransferase. In conclusion, gathering consecutive stress and not enough recovery time in the Stress78 group negatively affected stress responsiveness and the health of oscar.

Strain glass transition in Nb nanowire toughened NiTiHf shape memory alloy composite wires

In this work, we successfully prepared Nb nanowire toughened NiTiHf composite wires with different diameters. The strain glass transition was found in the as-drawn 0.1 mm diameter wire characterized by the Vogel-Fulcher type frequency-dependent modulus anomaly. However, the strain glass transition was not detected in 0.3 mm diameter wires. Microstructural characterization reveals that densely distributed Nb nanowires with small diameter and discontinuous orientation impose both physical confinement and heterogeneous stress fields on the matrix, which interrupt the long-range ordered martensitic transformation, leading to a continuous, high-order like strain glass transition. This work provides a new design strategy for searching new strain glass systems.

Study of Strain-rate Effect in Two-dimensional Biaxial Test on Granular Material using Discrete Element Method

Numerical study to investigate the effect of various strain rates on global friction angle in the sand has been performed. Granular material behavior is influenced by several factors, among others: pack configuration, grain macro and micro roughness, confinement pressure, loading rate, etc. Sand is a granular material composed of discrete particles that the most refined microscopic techniques are needed to study its mechanical properties. In Indonesia, research related to the Discrete Element Method is still very limited. The two-dimensional discrete element method is capable to calculate the motion and interparticle contacts of large number of small particles, and each particle is modeled as a rigid circular element. The study started with the validation of the DEM model using YADE. Particles with a local friction angle of 35° are arranged in a closed rectangular box (frictionless wall). The number of particles used in this model validation simulation is 1000 sphere-type particles with monodisperse particle gradations. The simulation was done by a drained biaxial test with confinement stress of 100 kPa, thereafter varying strain rate are applied. Based on the deviatoric stress–axial strain curve from YADE, the result can be depicted on the Mohr circle to obtain the value of the global friction angle. It is found that the different value of strain rate affects its global friction angle. Increasing the value of the strain rate can increase the material global friction angle, which increases the strain rate from 1% to 5%, 10%, 25%, and 50% will increase its global friction angle by 5%, 5%, 14%, and 18%, respectively.

Bond-slip performance of seawater sea sand concrete filled filament wound FRP tubes under cyclic and static loads

Adequate bond strength of concrete filled tubes is required to ensure full composite action and prevent premature bond failure before ultimate bending capacity is reached. This study investigates the bond strength and bond slip mechanisms of FRP tubes filled with seawater sea sand concrete (SWSSC) under static and cyclic axial loads using a push-out test. Glass and carbon fibre reinforced polymer (FRP) and two different diameters (100 mm and 165 mm) were tested to investigate the effect of changing parameters on the bond strength. Each group of specimen was tested under static load (SL) and various different cyclic loading (CL) regimes. An ANSYS FE model was created to simulate a static pushout test for FRP SWSSC composites under varying parameters to quantify the induced tube and confinement stress. Confinement and accumulated damage were found to be the two main factors determining the change in bond strength between cyclic and static load conditions. The high active confinement of the smaller diameter GFRP tubes resulted in a slight increase in bond strength for most samples under CL. The larger diameter CFRP tubes generally exhibited a slight drop in bond strength under CL due to the more pronounced effects of accumulated interface damage.

Fish Meal Replacement and Early Mild Stress Improve Stress Responsiveness and Survival of Fish after Acute Stress.

Stress responsiveness and fish meal (FM) replacement are two of the most important concerns toward achieving sustainable aquaculture. The purpose of this study was to see how early mild stress (netting) and FM replacement with meat and bone meal (MBM) affected oscar (Astronotus ocellatus; 5.2 ± 0.9 g) growth, hematology, blood biochemistry, immune responses, antioxidant system, liver enzymes, and stress responses. Oscars were subjected to a 3 × 3 experimental design (three fish meal replacement levels: 250, 180 and 110 g/kg of FM in diets; three stress periods: 0-, 2- and 3-times early mild stress). After ten weeks of the experiment, FM levels in diets did not affect growth data, but the survival rate after the acute confinement (AC) stress was lower in 11FM treatments (47.7% compared to 67.7%) than others. Fish exposed to the 3Stress schedule had a lower growth (31.03 ± 6.50 g) and survival rate (55.5%) after the AC stress than the 2Stress group (38.92 ± 6.82 g and 70.0%). Lower survival and growth rate in the 3Stress and 11FM groups coincided with the lowest blood performance, total protein, lysozyme, complement C4, complement C3, immunoglobulin, superoxide dismutase, catalase, glutathione peroxidase, and the highest glucose, cortisol, low-density lipoprotein and aspartate aminotransferase serum levels. Altogether, this study revealed that it is possible to replace FM with MBM up to 28% (180 g/kg of FM) without negative effects on the growth and health of juvenile oscar as dietary 110 g/kg of FM impaired fish health. While fish welfare should be considered, we can conclude that mild stress (2Stress) during the farming period, but without adding excessive alternative protein sources, can improve the stress responsiveness of oscar.

Pandemic and precocious puberty - a Google trends study.

Recent publications from several countries have reported that more young people (mainly girls) are experiencing precocious puberty (PP)/menarche during the coronavirus disease 2019 pandemic compared to the past. This variation is attributed to the stress of confinement, lack of exercise, obesity and disturbed sleep patterns. A common feature of the relevant papers, however, is the small number of reported cases of PP. Studies have shown that searches for diseases on the internet also reflect to some extent the epidemiology of these diseases. To estimate, through internet searches for PP, any changes in the epidemiology of PP. We assessed in Google Trends searches for 21 PP-related terms in English internationally (which practically dwarf searches in other languages), in the years 2017-2021. Additionally, we assessed local searches for selected terms, in English and local languages, in countries where a rise in PP has been reported. Searches were collected in Relative Search Volumes format and analyzed using Kendall's Tau test, with a statistical significance threshold of P < 0.05. Internationally, searches for three PP-related terms showed no noticeable change over the study period, while searches for eight terms showed a decrease. An increase was found over time in searches for nine PP-related terms. Of the 17 searches in English and local languages, in countries where a rise in PP has been reported, 5 showed a significant increase over time. Over the study period, more than half of the search terms showed little change or declined. The discrepancy between internet searches for PP and the reported increase in the literature is striking. It would be expected that a true increase in the incidence of PP would also be aptly reflected in Google trends. If our findings are valid, the literature may have been biased. The known secular trend of decreasing age of puberty may also have played a role.

Scalable microfluidic fabrication of vertically aligned two-dimensional nanosheets for superior thermal management.

Two-dimensional (2D) nanosheets have been assembled into various macroscopic structures for wide engineering applications. To fully explore their exceptional thermal, mechanical, and electrical properties, 2D nanosheets must be aligned into highly ordered structures due to their strong structural anisotropy. Structures stacked layer by layer such as films and fibers have been readily assembled from 2D nanosheets due to their planar geometry. However, scalable manufacturing of macroscopic structures with vertically aligned 2D nanosheets remains challenging, given their large lateral size with a thickness of only a few nanometers. Herein, we report a scalable and efficient microfluidics-enabled sheet-aligning process to assemble 2D nanosheets into a large-area film with a highly ordered vertical alignment. By applying microchannels with a high aspect ratio, 2D nanosheets were well aligned vertically under strong channel size confinement and high flow shear stress. A vertically aligned graphene sheet film was obtained and applied to effectively improve the heat transfer of thermal interfacial materials (TIMs). Superior through-plane thermal conductivity of 82.7 W m-1 K-1 at a low graphene content of 11.8 vol% was measured for vertically aligned TIMs. Thus, they demonstrate exceptional thermal management performance for switching power supplies with high reliability.