Lower Moments Research Articles

Performance measurement of crypto funds

Crypto funds (CFs) are a growing intermediary in cryptocurrency markets. We evaluate CF performance using metrics based on alphas, value at risk, lower partial moments, and maximum drawdown. The performance of actively managed CFs is heterogeneous: While the average fund in our sample does not outperform the overall cryptocurrency market, there seem to be some few funds with superior skills. Given the non-normal nature of fund returns, the choice of the performance measure affects the rank orders of funds. Compared to the Sharpe ratio, the most commonly applied metric in the asset management practice, performance measures based on alphas and maximum drawdown lead to diverging fund rankings. Depending on their ranking order of preferences, CF investors should consider a bundle of metrics for fund selection and performance measurement.

Theoretical Analysis of the Role of Water in Ligand Binding to Cucurbit[n]uril of Different Sizes.

The role of water in host-ligand binding was investigated using a combination of molecular dynamics simulation and three-dimensional reference interaction site model theory. Three different hosts were selected (CB6, CB7, and CB8). Six organic molecules were used as representative ligands: dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), cyclopentanone (CPN), and pyrrole. From the binding free energy and its components, we divided the ligands into two groups: those with relatively small molecular size (DMSO, DMF, acetone, and pyrrole) and those with relatively large molecular size (DBO and CPN). We established that the solvent water in the CB6 cavity can be completely displaced by small ligands, resulting in a greater binding affinity compared with larger CBs, except in the case of the small pyrrole ligand, due to outstanding intrinsic properties such as the relatively high hydrophobicity and low dipole moment. In the case of the large ligands, the solvent water can be displaced by DBO and CPN in both CB6 and CB7; there were similar tendencies in their binding affinities, with the greatest affinity in the CB7 complexes. However, the tendencies of the binding affinity components are completely different due to the difference between the complex structure and the solvation structure when a ligand binds with a CB structure. The binding affinities suggest that the size fit between the ligand and CB cannot guarantee the greatest binding affinity gain because the binding structure and intrinsic properties of CB and ligand equally play a crucial role.

A forefoot strike pattern during 18° uphill walking leads to greater ankle joint and plantar flexor loading

BackgroundThe ankle joint is one of the most involved joints in uphill walking. Furthermore, it is well known that toe walking increases the external dorsiflexion moment in the first half of stance during level walking. However, the effects of different foot-strike patterns on plantar flexor muscle forces, ankle joint forces, and other lower limb joint and muscle forces are unknown. Research questionDo foot-strike patterns during 18° uphill walking affect lower limb sagittal joint angles and moments, as well as joint contact and muscle forces? MethodsThis study was based on a data subset from previous publications, analysing uphill walking on an 18° ramp at a preset speed of 1.1 m/s in 18 male participants (34 limbs analyzed, 27 ± 5 years). Participants were divided into two groups based on their foot-strike pattern at initial contact: heel (HC) and forefoot (FC). Lower limb sagittal joint angles and moments as well as joint contact and muscle forces were assessed. Differences between the groups were assessed using two-sample t-tests. ResultsFC showed increased soleus and gastrocnemius muscle forces as well as ankle joint forces during loading response and mid stance compared to HC. The soleus muscle force impulse was 51.1% higher in the FC group than in the HC group (p < 0.001). On the other hand, FC had a lower absolute centre of mass vertical displacement and reduced knee and hip joint, as well as iliopsoas and hamstring muscle force impulses. SignificanceIn terms of plantar flexor and ankle joint loading, it is advantageous to exhibit a heel strike pattern. The current results can be used to recommend foot-strike patterns for uphill walking, particularly in the presence or prevention of musculoskeletal issues.

NO KNEE OVERLOADING IN RATS WITH DESTABILIZATION OF THE MEDIAL MENISCUS: A STUDY BASED ON INTEGRATED MOTION CAPTURE DATA AND HIGH-THROUGHPUT MUSCULOSKELETAL WORKFLOW

Altered mechanical loading is a widely suggested, but poorly understood potential cause of cartilage degeneration in osteoarthritis. In rodents, osteoarthritis is induced following destabilization of the medial meniscus (DMM). This study estimates knee kinematics and contact forces in rats with DMM to gain better insight into the specific mechanisms underlying disease development in this widely-used model.Unilateral knee surgery was performed in adult male Sprague-Dawley rats (n=5 with DMM, n=5 with sham surgery). Radio-opaque beads were implanted on their femur and tibia. 8 weeks following knee surgery, rat gait was recorded using the 3D²YMOX setup (Sanctorum et al. 2019, simultaneous acquisition of biplanar XRay videos and ground reaction forces).10 trials (1 per rat) were calibrated and processed in XMALab (Knörlein et al. 2016). Hindlimb bony landmarks were labeled on the XRay videos using transfer learning (Deeplabcut, Mathis et al. 2019; Laurence-Chasen et al. 2020).A generic OpenSim musculoskeletal model of the rat hindlimb (Johnson et al. 2008) was adapted to include a 3-degree-of-freedom knee. Inverse kinematics, inverse dynamics, static optimization of muscle forces, and joint reaction analysis were performed.In rats with DMM, knee adduction was lower compared to sham surgery. Ground reaction forces were less variable with DMM, resulting in less variability in joint external moments. The mediolateral ground reaction force was lower, resulting in lower hip adduction moment, thus less force was produced by the rectus femoris. Rats with DMM tended to break rather than propel, resulting in lower hip flexion moment, thus less force was produced by the semimembranosus. These results are consistent with lower knee contact forces in the anteroposterior and axial directions.These preliminary data indicate no overloading of the knee joint in rats with DMM, compared with sham surgery. We are currently expanding our workflow to finite element analysis, to examine mechanical cues in the cartilage of these rats (Fig1G).

3D CFD-PBM simulation of gas–solid bubbling beds of Geldart A particles with sub-grid drag correction

The importance of bubble dynamics in fluidized beds is underscored by the efforts undertaken over the past decades through experimental and numerical studies. Nonetheless, the bubble dynamic evolution and its effects on sub-grid closures were neglected in previous coarse-grid CFD models, particularly for Geldart A particles. In this article, a population balance model with improved kernels was employed to describe the bubble dynamic evolution in three-dimensional bubbling beds, whereby the EMMS drag model was closedto be incorporated into an Eulerian continuum model . Furthermore, the Extended Quadrature Method of Moments (EQMOM) was utilized to reconstruct the number density function of bubble size once their lower moments were obtained. The simulation results showed that the hydrodynamics including bed expansion characteristics, solids concentration and bubble size distribution can be well predicted by the model, indicating its capability to capture the heterogeneous structures in three-dimensional bubbling beds of fine particles.

Verification of biomechanical factors of gait related to medial knee loading in patients 6 Months after total knee arthroplasty

BackgroundThe knee adduction moment (KAM) is considered an index for estimating the knee mechanical load, and increased KAM peak and KAM impulse are related to increased medial knee load and progression of knee joint degeneration. We aimed to verify the biomechanical factors of gait related to medial knee loading in patients 6 months after TKA. MethodsThirty-nine women who underwent TKA were enrolled. A three-dimensional gait analysis was performed 6 months postoperatively to generate data on the lower limb joint angle, moment, and power at the backward component (braking phase) and forward component (propulsion phase) peaks of the ground reaction force. Medial knee loading was evaluated using the time-integrated value of KAM during the stance period (KAM impulse). The higher the value of the KAM impulse, the higher the medial knee joint load. The relationships between the KAM impulse and the data for biomechanical factors were evaluated using partial correlation analysis with gait speed as a control factor. ResultsIn the braking phase, the KAM impulse positively correlated with the knee adduction angle (r = 0.377) and negatively correlated with the toe-out angle (r = −0.355). The KAM impulse positively correlated with the knee adduction angle (r = 0.402), the hip flexion moment (r = 0.335), and the hip adduction moment (r = 0.565) and negatively correlated with the toe-out angle (r = −0.357) in the propulsive phase. ConclusionThe KAM impulse 6 months after TKA was related to the knee adduction angle, hip flexion moment, hip adduction moment, and toe-out angle. These findings may provide fundamental data for controlling variable medial knee joint load after TKA and implementing patient management strategies to ensure implant durability.

Changes in lower extremity joint moments one-year following osseointegration in individuals with Transfemoral lower-limb amputation: A case series

BackgroundDissatisfaction with socket prostheses has led to the development of bone-anchored prostheses through osseointegration for people with transfemoral amputation, eliminating the need for a prosthetic socket. Gait deviations of transfemoral prosthesis users may be linked to increased risk of osteoarthritis, and it remains unknown if gait biomechanics change following osseointegration. The purpose of this case series was to evaluate the longitudinal changes in joint kinetics one year post-osseointegration in patients with transfemoral amputation during walking. MethodsKnee, hip, and trunk internal moments were evaluated in the prosthetic and intact limbs during walking at a self-selected speed in four participants pre- and one-year post-osseointegration. Longitudinal changes were quantified using the percent change (%∆) in peak joint moments between the two time points and Cohen's d (d) effect size was used to determine the magnitude of effect on joint moments during walking one year following osseointegration. FindingsParticipants demonstrated increased peak knee extension moment (224 ± 308%∆, d = −1.31) in the prosthetic limb, while demonstrating reduced peak knee extension moment (−43 ± 34%∆, d = 1.82) in the intact limb post-osseointegration. Participants demonstrated bilateral reduction of peak hip extension moment (prosthetic: −22 ± 37%∆, d = 0.86; intact: −29 ± 10%∆, d = 1.27) and bilateral increase of peak hip abduction moment (prosthetic: 45 ± 40%∆, d = 1.20; intact: 23 ± 44%∆, d = 0.74) post-osseointegration. Participants demonstrated reduced peak trunk moments on both the prosthetic (extension: −31 ± 16%∆, d = 1.51; lateral flexion: −21 ± 20%∆, d = 0.63) and intact side (extension: −7 ± 22%∆, d = 0.38; lateral flexion: −22 ± 18%∆, d = 1.12) post-osseointegration. InterpretationThis case series suggests improved gait symmetry in individuals with transfemoral amputation one year following osseointegration, justifying future investigation.

Design and simulation experiment of ridge planting strawberry picking manipulator

Strawberry picking robot arm is an important part of strawberry picking operation. The narrow and complex working environment of ridged strawberry is a great challenge for strawberry picking. Aiming at the problems of narrow working space and complex working environment for strawberry picking in ridge farming, a P-R-R-P-R-R strawberry picking arm is proposed to realize automatic picking of strawberries in ridge farming. By establishing the kinematics model of the strawberry picking manipulator, the Jacobian condition number and operability index of the strawberry picking manipulator are solved to analyze the dexterity of the manipulator. In order to analyze the performance of each joint of the strawberry picking manipulator in the picking operation, a dynamic model of the strawberry picking manipulator was established. The strawberry picking arm has no singular position within the set strawberry picking point range, and the operability indexes are all greater than 0.38. According to the growing environment of strawberry, the simulation route of strawberry picking and the picking operation cycle were set and tested by experiments. Compared with the S-curve motion mode, the motion of each joint of the strawberry picking robotic arm is less smooth in the uniform acceleration-uniform speed-uniform deceleration motion mode. However, the peak velocity of each joint in the uniform acceleration-uniform velocity-uniform deceleration motion mode is lower than that in the S-curve motion mode, Taking three-joint as an example, the peak velocity of S-curve is 19.8° per second, higher than that of the uniform acceleration-uniform speed-uniform deceleration motion mode, which is 16.6° per second. Since joint 4 needs to overcome the influence of gravity, its peak force exceeds 15.5 N. It did not reach the farthest point of its own stroke during the picking process, resulting in a low moment of inertia at the three joints to the end which caused the peak moment of joint 3 to range from 0.2 N·M to 0.31 N·M. The peak torque of joint 5 is all under 0.1 N·M. The total power consumption of the strawberry picking robotic arm is 0.1622 J in a single picking operation using the uniform acceleration-uniform speed-uniform deceleration motion mode. In conclusion, the strawberry picking manipulator designed in this study has good dexterity and can adapt to a ridge environment.

Semivariance below the maximum: Assessing the performance of economic and financial prospects

This paper examines the ordering of economic and financial prospects using a rescaled semivariance below the maximum (SVBMax). This indicator is consistent with stochastic dominance (SD) until order three, but is distinct from any expected utility framework, both in terms of construction and in terms of economic implications, despite an apparent formal similarity with the quadratic expected utility framework. SVBMax is able to deal with economic puzzles such as the restaurant puzzle or Rabin’s paradox. SVBMax also provides a consistent alternative performance measure to popular measures such as the Sharpe ratio, the Omega ratio, or lower partial moments with exogenous thresholds. Compared to almost stochastic dominance, SVBMax is devoid of the drawbacks associated with the determination of violation areas. SVBMax can also replace the Aumann-Serrano and Foster-Hart riskiness indicators, which do not conform to third order SD. Further, SVBMax can provide a way of reaching an optimal diversification of stock portfolios. Besides, we also show that SVBMax is consistent with mean-variance-skewness preferences.

Association Between the Medial-Lateral Quadriceps and Hamstring Muscle Thickness and the Knee Kinematics and Kinetics During Single-Leg Landing.

Muscle thickness can influence the joint kinematics and/or kinetics during dynamic activities. The relationship between the muscle thickness of individual quadriceps and hamstrings or medial-to-lateral thigh muscle thickness ratio and the knee kinematics/kinetics with respect to anterior cruciate ligament (ACL) injury risk remains unclear. Higher medial-to-lateral thigh muscle thickness ratio would be associated with lower knee valgus angle/moment and lower tibial internal rotation angle/moment during single-leg landing. Cross-sectional. Level 4. Muscle thickness of the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and semitendinosus (ST) of 30 healthy participants (16 males and 14 females) were measured using ultrasound. Knee joint kinematics and kinetics during single-leg landing were obtained. Stepwise multiple regression analysis, a follow-up Fisher's r to z test to examine the sex as a moderator, and independent t tests to evaluate sex difference were performed. Both knee valgus moment (R2 = 0.466, P < 0.001) and tibial external rotation moment (R2 = 0.330, P < 0.001) at peak anterior tibial shear force during single-leg landing were negatively correlated with medial-to-lateral (ie, (VM+ST):(VL+BF)) thickness ratio regardless of sex, whereas medial-to-lateral thigh muscle thickness ratio was not correlated with knee valgus and tibial external rotation angles. Male participants exhibited higher (VM+ST):(VL+BF) thickness ratio than female participants (P = 0.005), and lower knee valgus moment (P = 0.04) and tibial external rotation moment (P = 0.05), as well. The knee joint moments in frontal and transverse planes during single-leg landing were associated with the medial-to-lateral thigh muscle thickness ratio; thus, the medial-lateral thigh muscle thickness could be a potential contributor to frontal and transverse plane knee joint loading during dynamic movement. Strength training that aims to selectively strengthen the medial/lateral thigh muscles might be considered in a new ACL injury prevention training program to alter the biomechanical parameters associated with ACL injuries.

Lower Extremity Support Moment and Distribution of Joint Moments during Sloped Running

The existing literature often exhibits inconsistent findings regarding lower extremity kinetics during sloped running, likely due to high variability of typical individual joint moments between and within runners. A better understanding of the kinetic effects of sloped running may be achieved by comparing the support moment and joint contributions among level, upslope, and downslope running. Twenty recreational runners (10 females) ran on three different conditions (level, 6° upslope and 6° downslope). Total support moment and joint contributions of the hip, knee, and ankle joints were compared among the three slope conditions using a one-way ANOVA with repeated measures and post-hoc pairwise comparisons. Our results showed that peak total support moment was highest during upslope running and was lowest during downslope running. The joint contribution to total support moment was similar in upslope and level running where the ankle joint has highest contribution followed by the knee and hip joints. During downslope running, highest knee joint contribution but least ankle and hip joint contributions were found when compared to level and upslope running.

Tuning Perovskite Surface Polarity via Dipole Moment Engineering for Efficient Hole-Transport-Layer-Free Sn-Pb Mixed-Perovskite Solar Cells.

Post-treatment has been recognized as one of the effective methods for passivating the underlying defects in perovskite solar cells (PSCs), but little attention has been paid to how to pick suitable passivation agents with diverse isomers for efficient PSCs, particularly for the tin-lead (Sn-Pb) mixed PSCs. Here, we introduce the dependence of the power conversion efficiency (PCE) on a dipole moment for surface passivator screening, in which we chose three trifluoromethyl-phenylethylamine hydroiodide (CF3-PEAI) isomers as surface-treatment materials for hole-transport-layer-free (HTL-free) Sn-Pb mixed PSCs. The different positions of the -CF3 group for the CF3-PEAI isomer result in different dipole moments, which influences the interaction between CF3-PEAI and lead iodide. The para position CF3 with the highest dipole moment exhibits a higher PCE than the ortho-position with a lower dipole moment, which is attributed to the large dipole moment on the surface that could tune the surface polarity from p-type to n-type, facilitating electron charge transport in the HTL-free Sn-Pb mixed PSCs. An ultrathin 2D layer is formed on the perovskite surface to passivate the surface defects, which is responsible for the enhancement of the PCE and stability of the PSCs. As a result, the open-circuit voltage (VOC) of the device is improved from 0.775 to 0.824 V, yielding a champion PCE of 20.17%, which is one of the highest PCEs among the reported HTL-free Sn-Pb mixed PSCs. The device also shows improved stability with remaining 75% of its initial PCEs after storage in N2 for 700 h.

Definition of High-Risk Motion Patterns for Female ACL Injury Based on Football-Specific Field Data: A Wearable Sensors Plus Data Mining Approach.

The aim of the present study was to investigate if the presence of anterior cruciate ligament (ACL) injury risk factors depicted in the laboratory would reflect at-risk patterns in football-specific field data. Twenty-four female footballers (14.9 ± 0.9 year) performed unanticipated cutting maneuvers in a laboratory setting and on the football pitch during football-specific exercises (F-EX) and games (F-GAME). Knee joint moments were collected in the laboratory and grouped using hierarchical agglomerative clustering. The clusters were used to investigate the kinematics collected on field through wearable sensors. Three clusters emerged: Cluster 1 presented the lowest knee moments; Cluster 2 presented high knee extension but low knee abduction and rotation moments; Cluster 3 presented the highest knee abduction, extension, and external rotation moments. In F-EX, greater knee abduction angles were found in Cluster 2 and 3 compared to Cluster 1 (p = 0.007). Cluster 2 showed the lowest knee and hip flexion angles (p < 0.013). Cluster 3 showed the greatest hip external rotation angles (p = 0.006). In F-GAME, Cluster 3 presented the greatest knee external rotation and lowest knee flexion angles (p = 0.003). Clinically relevant differences towards ACL injury identified in the laboratory reflected at-risk patterns only in part when cutting on the field: in the field, low-risk players exhibited similar kinematic patterns as the high-risk players. Therefore, in-lab injury risk screening may lack ecological validity.

Driving skyrmions with low threshold current density in Pt/CoFeB thin film

Magnetic skyrmions are topologically stable spin swirling particle like entities which are appealing for next generation spintronic devices. The expected low critical current density for the motion of skyrmions makes them potential candidates for future energy efficient electronic devices. Several heavy metal/ferromagnetic (HM/FM) systems have been explored in the past decade to achieve faster skyrmion velocity at low current densities. In this context, we have studied Pt/CoFeB/MgO heterostructures in which skyrmions have been stabilized at room temperature (RT). It has been observed that the shape of the skyrmions are perturbed even by the small stray field arising from low moment magnetic tips while performing the magnetic force microscopy (MFM), indicating presence of low pinning landscape in the samples. This hypothesis is indeed confirmed by the low threshold current density to drive the skyrmions in our sample, at velocities of few ∼10 m s−1.

The Effect of Muscles Fatigue on the Knee’s Kinetics and Kinematics Characteristics

Badminton is very popular on college campuses. In badminton, the anterior cruciate ligament of the players has a higher risk of injury. There are many studies investigating the impact of fatigue on the injury of professional athletes, but few studies focused on college students. We hypothesized that the knee joint would experience greater ground reaction forces, valgus moments, and flexion moments of lunge contact in amateur after fatigue than those indicators before fatigue. Ten male badminton amateurs were enrolled in this study. They performed a lunge to hit the shuttlecock at the designated position and then quickly returned to the starting position before and after fatigue. Fatigue was induced by repeated isokinetic flexion/extension of the knee. Lower body kinematics and ground reaction force (GRF) were collected and further used to calculate the lower body joint moments from initial contact to maximum knee flexion. Compared to the pre-fatigue condition, the peak flexion moment (p = 0.012) and peak abduction moment of knee joint (p = 0.01), and maximum horizontal ground reaction force (p = 0.027) increased significantly at the initial contact (p = 0.01). After muscle fatigue, the knee buckling moment and valgus moment increased significantly at initial contact, and the horizontal backward maximum GRF also increased significantly. These changes might increase the injury risk of anterior cruciate ligament (ACL). The fatigue of the muscles around the knee joint did not change the maximum GRF in the vertical direction at the moment of contact. Combined with the results of our study, badminton coaches and teachers should increase the training of lower extremity muscle strength and endurance in our daily class and training, and also should pay special attention to the coordinated development of muscles.

A Statistical Parametric Mapping Analysis Approach for the Evaluation of a Passive Back Support Exoskeleton on Mechanical Loading During a Simulated Patient Transfer Task

This study assessed the effectiveness of a passive back support exoskeleton during a mechanical loading task. Fifteen healthy participants performed a simulated patient transfer task while wearing the Laevo (version 2.5) passive back support exoskeleton. Collected metrics encompassed L5-S1 joint moments, back and abdominal muscle activity, lower body and back kinematics, center of mass displacement, and movement smoothness. A statistical parametric mapping analysis approach was used to overcome limitations from discretization of continuous data. The exoskeleton reduced L5-S1 joint moments during trunk flexion, but wearing the device restricted L5-S1 joint flexion when flexing the trunk as well as hip and knee extension, preventing participants from standing fully upright. Moreover, wearing the device limited center of mass motion in the caudal direction and increased its motion in the anterior direction. Therefore, wearing the exoskeleton partly reduced lower back moments during the lowering phase of the patient transfer task, but there were some undesired effects such as altered joint kinematics and center of mass displacement. Statistical parametric mapping analysis was useful in determining the benefits and hindrances produced by wearing the exoskeleton while performing the simulated patient transfer task and should be utilized in further studies to inform design and appropriate usage.

Assessing Effectiveness of Shape Memory Alloys on the Response of Bolted T-Stub Connections Subjected to Cyclic Loading

This study presents finite element analysis of double split tee (DST) connections with high-strength steel bolts and coupled split tee sections, to evaluate various cyclic response parameters and elements. The investigation included quantifying connection behavior and hysteretic response, damage indexes, and failure modes. Over 40 specimens were simulated in ABAQUS under cyclic loading, including shape memory alloy (SMA)-built specimens. In the post-analysis phase, the T-stub thickness, the T-stub yield strength, the bolt preload and bolt number, and the stiffener type and stiffener material for the most significant parts of the DST connection were calculated. Simulation results showed that a lower ultimate moment yielded fewer needed stem bolts. The energy dissipation (ED) capacity increased as the horizontal distance between the stem bolts decreased. Additionally, increasing the strength of the bolt and T-stub by 15% resulted in a 3.86% increase in residual displacement (RD) for the bolt and a 1.73% decrease in residual displacement for the T-stub. T-stub stiffeners enhanced ED capacity by 31.7%. SMA materials were vulnerable to mode 1 failure when used in T-stubs, bolts, or stiffeners. However, the use of SMA increased the rate of energy dissipation. Adding stiffeners to the T-stubs altered the failure indexes and improved the pattern of failure modes. In addition, stiffeners decreased the rupture and pressure indexes. As a result, the failure index of a T-stub shifted from brittle failure to ductile failure.

Atomistic study of Positive Exchange Bias in Hard/Soft ferromagnetic bilayer nanosystem

We present calculations for the Exchange spring nano-bilayer with intermixing of high and low anisotropic moments at the interface, where we study the unusual phenomenon of positive exchange bias. The results are well reproducible at different simulation temperatures. However, the amount of shift as well as the width of M-H loop is greatly influenced by the temperature itself. We illustrate interface roughness as an important cause for the shift of Hysteresis loop in Ferromagnetic Hard/Soft nano bilayer systems.

Influence of eccentricity on the thermomechanical performance of a bayonet tube of a central solar receiver

This work numerically evaluates the thermal and mechanical behaviors of eccentric bayonet tubes to be used in external central receivers of solar power tower plants. A bayonet tube is composed of two tubes, one inside the other, creating circular and annular sections, through which the molten salt of the receiver sequentially flows. Eccentricity in the annular section is achieved by displacing the axis of the interior tube with regard to the exterior one. For comparative purposes, two examples of conventional tubes (single tubes with circular cross-sections with diameters of 25mm and 50mm) are also investigated in this work to compare their performances with those of bayonet tubes. The results obtained with the eccentric configurations show an enhancement of the heat transfer to the molten salt and a reduction of the tube wall overheating compared with the concentric bayonet tubes and the largest simple tube. For conditions representative of the normal operation of a solar power tower, eccentric bayonet tubes could reduce the pressure drop by 30.8% and increase the convective heat transfer achieved in a concentric configuration of the bayonet tube by 26.1%. Nevertheless, this pressure drop was considerably higher than those obtained in the smallest and largest simple tubes, which were 1.28 bar and 0.13 bar, respectively. To investigate whether the enhancement of the convection heat transfer experienced by bayonet tubes compensates for their higher pressure drop or not, a Performance Evaluation Criterion (PEC) was proposed and used to compare the global performance of bayonet tubes with that of conventional tubes. The bayonet tubes with eccentricity 0.45 obtained the largest PEC, which was up to 13% higher than reference conventional tubes. Enhancement of the tube wall refrigeration produced when increasing the eccentricity is reflected in the maximum tube temperature and thermal stresses, which are found to diminish by approximately 8.8% with the highest eccentricity. In addition, the largest eccentric bayonet tube layout obtains the smallest peak temperatures compared to conventional tubes. The lower inertial moment of the smallest conventional tube indicates that its thermal stress is 2.1% lower than the stress obtained in the most eccentric layout analyzed in this work. Nevertheless, the time to rupture associated with creep damage of the eccentric bayonet tube is 1.04 times higher than that obtained in the smallest simple tube, demonstrating that bayonet tubes could be a potential alternative to the current tubes of external tubular receivers.

Effect of foot strike patterns and cutting angles on knee kinematics and kinetics during side-cutting maneuvers

Purpose Cutting maneuvers are important actions in multidirectional sports but associated with noncontact anterior cruciate ligament (ACL) injuries. This study aimed to investigate the effect of different foot strike patterns and cutting angles on knee kinematics and kinetics. Methods Twenty healthy male team sports athletes performed cuts with maximum speed at three angles (45°, 90°, and 135°) with different foot strike patterns (rearfoot strike [RFS] and forefoot strike [FFS]). A three-dimensional motion capture system combined with a force plate was used to collect makers trajectory and ground reaction force (GRF). Vertical GRF, and knee joint angles and moments were compared among these cutting tasks. Results Regardless of foot strike patterns, increased knee flexion angle, knee valgus moment, and knee internal rotation moment were observed during cutting to sharper angles (p &lt; 0.001). At 90° and 135°, the FFS condition remained in a varus position and showed lower knee flexion moment than the RFS condition (p ≤ 0.004). However, no significant differences in knee kinematic and kinetic variables were found between foot strike patterns during cutting to 45°. Conclusions These findings suggest that sharper cutting angles potentially increase the risk of ACL injury. Compared with the RFS pattern, the FFS pattern induces a slight knee varus angle and a lower knee flexion moment at sharper angles, which might further reduce the load placed on the knee.