Stiffness Values Research Articles

Design and mechanical analysis of a novel modular bionic earthworm robot with upright functionality

With the escalating demand for exploration within confined spaces, bionic design methodologies have attracted considerable attention from researchers, primarily due to the intrinsic limitations of human access to hazardous environments. However, contemporary bionic robots primarily attain linear motion through the axial radial deformation of their body segments, thereby lacking the upright functionality that is characteristic of these organisms. In response to the limitations associated with current bionic earthworm robots concerning upright capability and stiffness modulation, we propose an innovative bionic robot that incorporates upright functionality and programmable stiffness. Initially, we present a bionic robot unit module that is capable of attaining an upright posture. A mechanical model is established in accordance with the principle of minimum potential energy to facilitate various compression and deflection functionalities. Through comprehensive simulation and experimental studies, we validate the model’s high precision in predicting compression and deformation behaviors. Furthermore, the effects of varying spring stiffness values (k) on device performance are systematically investigated, thereby enabling tailored stiffness adjustments for each module. This programmability empowers the robot to adapt to a broader spectrum of environmental demands. Ultimately, we construct a multi-module robot and successfully evaluate its upright functionality under diverse compression and deformation conditions. The proposed bionic structure, characterized by its enhanced ease of control and programmable stiffness, exhibits considerable potential for applications in complex and unstructured environments.

Sex-related differences in cardiac damage associated with severe primary mitral regurgitation: impact on surgical outcomes

Abstract Background and Aim Previous research has shown that women with primary mitral regurgitation (MPR) have worse surgical outcomes, compared with men. Our aim was to evaluate whether cardiac damage prior to intervention for severe MPR differs according to gender. Methods Retrospective analysis of a prospective cohort of patients with PMR who underwent mitral valve surgery in a tertiary care center from 2014 to 2022. Echocardiographic parameters measured prior to surgery as well as outcomes at 1-year follow-up (all-cause mortality and heart failure admissions) were analyzed, and potential differences by sex were evaluated. Results 349 patients were included. The mean age was 69 (12) years and 154 (44%) were female. Women were older and had a history of atrial fibrillation more frequently than men. Regardind morphological echocardiographic parameters, left ventricular (LV) dimensions were slightly larger in male patients, as expected, and there were no significant differences in left atrial (LA) volume index (Table). Significant differences were found in functional echocardiographic parameters: women had more impaired LV and LA strain, higher values of LA stiffness, and worse right ventricular-arterial coupling. In addition, concomitant significant tricuspid regurgitation was significantly more frequent in female patients. At one-year follow-up, the incidence of heart failure hospitalization was significantly higher in women (1% vs 7%; p=0.005) and there was a non-significant trend towards higher all-cause mortality (6.2 vs 11%; p=0.101). Conclusions In our cohort of patients with severe PMR who underwent surgery, women had worse biventricular function and more impaired LA function. At one-year follow-up, heart failure hospitalizations rates were significantly higher in female patients. Earlier indication of surgical timing in women with PMR, taking into account deformation parameters, could improve surgical outcomes in this population. Clinical and echocardiographic features

Myocardial stiffness - not just a matter of wall thickness

Abstract Background/Introduction Heart failure, including HFpEF, is a growing global health problem. Diastolic dysfunction (DD) is a critical component of HFpEF and is mainly caused by increased myocardial stiffness(1). Current cardiac elastography methods allow the noninvasive quantification of myocardial stiffness(2, 3). Time harmonic elastography (THE) combines conventional ultrasound with continuous external vibrations(4) to generate full field-of-view stiffness maps. Novel, cost-effective cardiac THE (cTHE) with full coverage of the left ventricle (LV) in parasternal long axis view (PLAX) has recently been shown to be sensitive to increased myocardial stiffness in patients with wild-type amyloidosis (wtATTR)(5). Numerous heart diseases are linked to both myocardial stiffening and LV hypertrophy. However, they differ in the underlying pathophysiology such as reactive fibrosis due to pressure overload (hypertension (HT) or aortic stenosis (AS)) or storage disease (ATTR or Fabry disease (FD)). Purpose We aim to investigate the diagnostic value of myocardial stiffness as a quantitative parameter for the characterization of cardiac function independent of wall thickness. Methods 62 participants were enrolled in our study, including 11 healthy controls (age range 27-88 years), 19 patients with HT (age range 44-79 years), 13 patients with AS (age range 61-89 years), 11 patients with wtATTR (age range 64-86 years), 3 patients with HCM (age range 36-70 years) and 5 patients with FD (age range 50-60 years). All subjects underwent a standard echo examination before cTHE (figure 1). Multifrequency vibrations (60,70,80Hz) were induced using a custom portable vibration pillow (Elastance Imaging, Columbus, Ohio, US) underneath the subject’s thorax. A customized ultrasound scanner (GAMPT, Merseburg, Germany) was used for image acquisitions in PLAX with 15cm depth. Images were acquired in breath-hold over 4s with 100Hz frame rate. Measurements were repeated five times. Time-resolved shear wave speed maps (SWS) were generated using k-MDEV inversion(6). Diastolic frames were averaged to obtain a map of diastolic myocardial stiffness. Regions of interest for averaging were manually drawn for the septum and posterior wall. Results Using cTHE, we observed an increase in myocardial stiffness in all groups (Controls: 1.5±0.2ms/s, HT: 1.8±0.4ms/s, AS: 2.0±0.2ms/s, HCM: 2.0±x0.4ms/s, Fabry: 1.9±0.3ms/s, wtATTR: 2.1±0.3ms/s, all p<0.05). SWS correlated with wall thickness only in a pooled analysis (R=0.47, p<0.01), but not within individual groups (figure 2). Conclusions cTHE detects increased myocardial stiffness in a variety of cardiac diseases. Myocardial stiffness is known to be associated with increased wall thickness(7), however our analysis within individual groups showed independence of both parameters. Quantitative assessment of myocardial stiffness could add important diagnostic information to the detection and treatment monitoring of myocardial disease. Figure 1: Setup of cTHE Figure 2: Stiffness Maps/Correlations

A tool to measure maize root system stiffness that enables a comprehensive understanding of plant mechanics and lodging.

Plant mechanical failure, known as lodging, has detrimental impacts on the quality and quantity of maize yields. Failure can occur at stalks (stalk lodging) or at roots (root lodging). While previous research has focused on proxy measures for stalk stiffness, stalk strength, and root strength, there is a need to quantify the root system stiffness, which quantifies the force-displacement relationship. Here, we report a tool to quantify the root system stiffness of maize hybrids grown in different conditions. The results show that maize hybrids with a higher root system stiffness have a greater susceptibility to root lodging. This result is consistent with expected mechanical behavior, since higher root system stiffness values mean that the plant reaches the failure strength at lower displacements compared with a plant with lower root system stiffness. Collectively, this study describes the first tool to measure root system stiffness and enables a comprehensive understanding of the integrated plant mechanics and lodging.

Thermal buckling of composite laminates with elastic boundaries

AbstractThe investigation of thermal buckling in composite laminates holds significant theoretical and practical implications. For the commonly encountered rectangular thin plate structures in engineering, this study aims to explore their buckling characteristics under thermal loads in arbitrary elastic boundary conditions. To achieve this, a method based on the principle of minimum potential energy for calculating the buckling load during elastic instability is presented. Initially, transverse constraint springs and rotational constraint springs are set at the four boundaries of the plate structure model, with the stiffness values of these two types of elastic springs designated to simulate arbitrary elastic boundary conditions. The improved Fourier series is employed to address potential discontinuities in the boundary derivatives of displacement functions that may arise with the classical Fourier series form. Subsequently, the potential energy expression for the rectangular plate system is established. By combining this with the principle of minimum potential energy, a system of linear equations is derived through partial differentiation of the unknown Fourier coefficients. Finally, the critical buckling load and other parameters of the rectangular plate are obtained, with reasonable values for the spring stiffness under different boundary conditions provided. The critical buckling temperatures derived from the proposed method are compared with those obtained via finite element analysis. The results indicate that the buckling loads obtained using this method align closely with those from finite element analysis, affirming the validity and convergence of the research methodology.Highlights This study investigates the thermal buckling of composite laminate plates with elastic boundary conditions. Improved Fourier series techniques are employed to analyze thermal buckling in these laminates. The impact of intermediate stiffness on the thermal buckling response of composite materials is examined.

Significance of shear wave ultrasound elastography in predicting one-year posthospital outcomes of lower extremity deep vein thrombosis

The aim of the study was to analyze the results of shear wave elastography data of iliac and femoral vein thrombi in the acute period of the disease to identify ultrasound parameters that are prognostically significant for posthospital outcomes.Material and Methods. At the hospitalization stage, 153 patients with iliac and femoral vein thrombosis underwent venous ultrasound with shear wave elastography. Depending on the outcome of the disease 6–12 months after discharge from the hospital, the examined patients were divided into 3 groups: with recanalization, venous retrombosis and death.Results. In those with the outcome “retrombosis” the thrombus stiffness during inpatient treatment was higher than in the groups with the outcomes “recanalization” and “death”. According to the Accuracy and Gini coefficients for iliac vein thrombosis, the values of maximum and mean Young’s moduli of iliac vein thrombus on the first, third and sixth days of hospitalization, whereas in femoral vein thrombosis – maximum, average and minimum Young’s moduli of femoral vein thrombus on the mentioned days and minimum Young’s modulus of sural vein thrombus on the first day of hospitalization. The variables separating the posthospital outcomes “recanalization” and “death” in iliac vein thrombosis were the maximum Young’s modulus of femoral vein thrombus on the first day of hospitalization and the length of the floating part of the thrombus; in femoral vein thrombosis – the maximum Young’s modulus of the saphenous vein on the first day of hospitalization, the PE mass and the duration of the period from the first symptoms to hospitalization.Conclusion. The results of shear wave elastography at the hospital stage of management of patients with DVT allow predicting the recurrence of thrombosis in the following year based on the stiffness values of the proximal part of the venous thrombus and lethal outcome based on the stiffness of the thrombus in the inferior vein of the affected limb.

Barrier Properties Against UV Radiation of Woven Fabrics Coated With Micronized Pumice

Abstract This research primarily investigates the UV properties obtained in woven fabrics with different properties coated with micronized pumice. Most of the studies in the textile industry are based on the search for new technologies and materials to produce functional products. In this study, three different types of fabrics woven from polyamide/viscose, polyamide/linen and cotton/silk yarns were covered with 50-μm pumice material at 5%, 10%, and 15% ratios. At these rates, the effect of pumice coating on the physical and UV properties of the mentioned fabrics was investigated. SEM/EDS analysis, tear strength, fabric stiffness (bending length) and air permeability values of the coated fabrics were evaluated. According to the results of the study, it was observed that the UPF values of fabrics coated with 15% pumice were improved by 5.08 times in cotton/silk, 8.7 times in polyamide/viscose and 34.9 times in polyamide/linen compared to control uncoated fabrics.

Spleen stiffness in a healthy pediatric population undergoing liver magnetic resonance elastography.

Splenic stiffness is a potential imaging marker of portal hypertension. Normative spleen stiffness values are needed to define diagnostic thresholds. To report stiffness measurements of the spleen in healthy children undergoing liver magnetic resonance (MR) elastography across MRI vendors and field strengths. This was a post-hoc analysis of data collected under a prospective multicenter cross-sectional study. Volunteers aged 7-17.9years without a known history of liver or spleen disease were recruited for a research MRI between February 2018 and October 2019. Gradient recalled echo (GRE) or spin-echo-echo-planar imaging (SE-EPI) MR elastography was performed on a total of three vendor platforms and at two field strengths (1.5T (T) and 3T) with standard right upper quadrant passive driver placement (frequency of 60Hz). Two independent reviewers measured spleen stiffness, length, and volume. Descriptive statistics, independent sample t-tests or Mann-Whitney test, and Pearson's or Spearman's correlation were used. From 101 study volunteers, 72 (34 female) had measurable splenic stiffness. Median age was 12years (interquartile range [IQR], 9.9-14.9years). Mean (± SD) spleen stiffness was 4.7 ± 0.9kPa (IQR, 3.8-5.4kPa) with 6.1kPa reflecting the 95th percentile. Strong correlation was observed between reviewers (ICC = 0.89 [95%CI, 0.71-0.93; P < 0.001]). Male volunteers had slightly higher splenic stiffness compared to females: 4.9 ± 0.9 vs. 4.3 ± 0.8kPa (P = 0.014). There was significant correlation between spleen stiffness and body mass index (r = 0.33 [95%CI, 0.06-0.56; P = 0.024]) but no other measure of patient size (r = 0.15-0.29). No significant difference in spleen stiffness was observed across vendors (P = 0.089) or field strengths (P = 0.236). MR elastography-based spleen stiffness, measured as part of a liver MR elastography acquisition, is < 6.1kPa in a healthy pediatric population and does not vary with MRI vendor or field strength.

Identifying the current penetration depth in high-Tc superconducting bulks through levitation force measurements

Abstract High-Tc superconducting REBa2Cu3O7−x (REBCO) bulks are actively researched&amp;#xD;for use in superconducting magnetic bearings. Superconducting magnetic bearings are&amp;#xD;attractive in applications which require zero friction, ultra high speeds, or integration&amp;#xD;within crygoenic environments. However, superconducting magnetic bearings are&amp;#xD;limited by low stiffness values compared to mechanical bearings, prohibiting their use&amp;#xD;in turbulent environments such as rocketry or aviation. To improve the performance&amp;#xD;of superconducting magnetic bearings, a comprehensive understanding of the precise&amp;#xD;distribution of currents and magnetic fields within the material during magnetic&amp;#xD;suspension is required. Hence, the results of vertical and lateral levitation force&amp;#xD;measurements between a single directional melt growth REBCO bulk and an NdFeB&amp;#xD;magnet are reported. The measurements are carried out between 77 K and 90 K and&amp;#xD;for bulk thickness between 0.5 mm to 4.5 mm. By reducing the bulk thickness, the&amp;#xD;depth to which the induced currents penetrate the bulk is identified in zero-field cooling&amp;#xD;conditions. At 77 K, the current and magnetic field occupy the top 1 mm, closest to&amp;#xD;the magnet. By reducing the bulk thickness further, the levitation force profiles vary&amp;#xD;significantly. Field-cooling results are similarly impacted; reducing the bulk thickness&amp;#xD;below 1 mm dramatically reduces the lateral stiffness. The above results are interpreted&amp;#xD;using finite element simulations employing experimentally measured J c(B,θ) data&amp;#xD;from the bulk, following the completion of the levitation force measurement routine.&amp;#xD;These results are relevant for future bearing designs, helping to inform the optimal&amp;#xD;distribution of superconducting material for a given application.

Evaluation of the core muscles of children and adolescents with nocturnal enuresis using shear wave elastography: a preliminary study

The purpose of this study was to determine any changes in the rectus abdominis and diaphragm muscles, which are core muscles, in children and adolescents with nocturnal enuresis (NE) using the shear wave elastography (SWE). In this case-control study, the rectus abdominis and diaphragm muscles of 40 children and adolescents with NE and 40 healthy controls were evaluated. The rectus abdominis muscle was examined at the right supra- and subumbilical levels, and the diaphragm at the right 9th-10th intercostal space. The thickness of both muscles was measured by gray scale ultrasound and muscle stiffness was measured by SWE. The demographic characteristics of the patients such as sex and age and their anthropometric measurements including height, weight, and BMI were recorded. Compared to the control group, the NE group had significantly lower mean rectus abdominis muscle stiffness values on both the supraumbilical and subumbilical levels (p < 0.05). There was no significant difference in mean rectus abdominis thickness and diaphragm thickness-stiffness values between the groups (p > 0.05). According to the results of the study, it is thought that NE children have problems with core stabilization and that children with NE should be directed to appropriate treatment. However, future studies are needed with larger sample sizes and other factors that are thought to affect muscle architecture.

Elastographic evaluation for fatty liver disease in north Indian children and adolescents with type 1 diabetes.

The prevalence and predisposing factors to metabolic dysfunction-associated fatty liver disease (MAFLD) in children with type 1 Diabetes (T1D) living in developing countries are unknown. A cross-sectional study was conducted in children with T1D. The presence of liver fat and tissue stiffness were assessed by ultrasonography and shear-wave elastography (SWE), respectively. The SWE values were correlated to body mass index (BMI), glycemic control, disease duration, and gamma-glutamyl transferase (GGT). Healthy non-obese children (n=36) were recruited as controls. One hundred children with T1D were grouped (Group A-C) according to the disease duration (<5, 5-10, and >10 years, respectively). The mean diabetes duration and glycated hemoglobin were 5.9±4.0 years and 8.2±0.55 %, respectively. The mean SWE values were significantly higher in the patient groups compared to controls (5.07±0.67, 5.27±0.65, 5.16±0.50, vs. 4.80±0.82 kPa, p-value 0.006). The liver stiffness based on SWE showed a positive but weak relationship with BMI, diabetes duration, glycemic control, and GGT levels. A significantly higher number of children with T1D had MAFLD [9(20 %), 7(24.1 %), 7(26.9 %), vs. 1(3 %), p-value <0.001] based on ultrasonography. Children with T1D showed higher liver stiffness values than controls. A weakly positive relationship of liver stiffness was observed with BMI, duration of diabetes, glycemic control, and serum GGT. Approximately one-fourth of children with diabetes showed sonographic evidence of hepatic steatosis. Larger studies are needed to ascertain the effects of obesity, diabetes duration, and metabolic control on the prevalence and progression of MAFLD in children with T1D.

Evaluation of hepatic steatosis in obese children and adolescents using immune-inflammatory markers and shear wave elastography.

To investigate the changes in liver stiffness and immune-inflammatory markers associated with obesity and the degree of hepatic steatosis in obese children and adolescents. A total of 76 obese children and adolescents aged 6-18 years, with body mass index percentiles >95th, were included in the study. Patients with metabolic syndrome, diabetes mellitus, and chronic liver disease were excluded. A control group of 44 patients of healthy and normal-weight children was included. Laboratory values from the past month were analyzed using patient records. Shear wave elastography and ultrasound examinations were performed on a single device by the same experienced radiologist. The systemic immune-inflammation index and pan-immune inflammation values were significantly higher in obese patients with hepatic steatosis compared to obese patients without hepatic steatosis (p <0.001). Liver stiffness values were significantly higher in steatotic patients compared to nonsteatotic patients (p <0.001). A significant difference was observed between hepatic steatosis grades in terms of immune-inflammation index and pan-immune inflammation value values (p <0.001). There was a strong, positive, statistically significant correlation between liver stiffness and immune-inflammation index and pan-immune inflammation value (p <0.05). Immune-inflammatory biomarkers and shear wave elastography may provide valuable insights into the diagnosis and follow-up of inflammation and fibrosis in the evaluation of hepatic steatosis in obese children and adolescents.

Hepatoscope 2DTE's image-based quality index enhances applicability and repeatability of liver stiffness measurement.

Hepatoscope® is an ultraportable ultrasound system with 50 Hz two-dimensional transient elastography (2DTE) for liver stiffness measurement (LSM). It provides a quality index (QI) for individual stiffness values that is based on imaging features. This study evaluated the 2DTE intra- and inter-user repeatability in patients with chronic liver diseases (CLD) for novice and expert operators across various QI conditions. We compared the performances with other imaging and non-imaging elastography techniques. This investigation was a prospective cross-sectional single-center study. One hundred CLD patients underwent LSMs with vibration-controlled transient elastography (VCTE™), two-dimensional shear wave elastography (2DSWE) and 2DTE. Expert and novice operators each performed two consecutive exams with 2DTE, blinded to any output. Intra-class correlation coefficient for intra-, and inter-user repeatability were calculated as well as applicability for various QI conditions, and Spearman's correlations against VCTE and 2DSWE were assessed. Computing LSM as the median of 10 stiffness values with a QI>85 % yielded the best compromise between reliability and applicability. In this setting, expert and inter-operator repeatability showed significant improvement over the condition with no QI threshold (ICC = 0.81 and 0.79, respectively) and 95 % applicability. Novice repeatability was excellent with a more restrictive QI (ICC = 0.80). LSM with 2DTE demonstrated strong and moderate correlation with VCTE and 2DSWE (r = 0.63 and 0.55, respectively). Hepatoscope 2DTE provides a promising and reliable alternative for non-invasive liver stiffness assessment in patients with CLD. The application of the image-based QI enhances LSM reliability and consistency across novice and expert operators.

Investigating Stability and Structural Behavior of Steel Pipe Column-Berger Beam Systems

The steel pipe column-Berger beam support system is widely utilized in bridge construction due to its simple structure, convenient installation, high load-bearing capacity, and excellent stability. Stability research on this system is therefore essential. This study employs ANSYS finite element software to conduct a comprehensive analysis, including buckling behavior, node stiffness, and initial defects in the Berger beam support system. The research identifies the first four buckling modes, examines load-displacement curves corresponding to node stiffness values ranging from 0 to 400 kN·m/rad, and evaluates load-displacement curves under varying initial defect ratios. These findings contribute to improving the design and application of the support system. This study not only addresses gaps in current research but also serves as a valuable reference for scholars in related fields. Additionally, it provides practical guidance for engineers involved in bracket design, significantly enhancing their efficiency and effectiveness. In conclusion, the research presented in this paper holds considerable importance for both academic and practical advancements in the field.

A Hysteresis Model Incorporating Varying Pinching Stiffness and Spread for Enhanced Structural Damage Simulation

The widely used Bouc–Wen–Baber–Noori (BWBN) hysteresis model, although effective in simulating hysteresis behaviors, does not account for variations in the pinching region of hysteretic behaviors. This can negatively impact the accuracy of the BWBN model in simulating structural responses and damage mechanisms in structures such as reinforced concrete (RC) and timber, which exhibit highly pinched hysteresis behavior when damaged by earthquakes. This paper introduces a BWBN model with varying pinching region characteristics (BWBN-VP model) which can degrade pinching stiffness and increase pinching effects under seismic loads. Unlike the original BWBN model using constant pinching stiffness (kp), this modified new model, inspired by real-world structural damage, improves structural damage detection, identifiability, and analysis in real-world scenarios. Model validation uses experimental data from three RC column tests with different failure modes and hysteresis loop shapes, resulting in an ~0.98 correlation coefficient between the experimental and simulated responses. Further validation uses real-world seismic data from a six-story RC building and achieves an average correlation of ~0.97 with a minor 2.5% difference in the peak restoring forces compared to direct measurements. The proposed BWBN-VP model also accurately and realistically captures damage to both the elastic and pinching stiffness values of the building, with an average difference of ~4%. Results confirm that the BWBN-VP model, compared to the original, more accurately predicts hysteretic responses, especially in Shear Failure (SF) modes. Therefore, the BWBN-VP model, superior in simulating highly pinched behaviors in RC and timber structures, would be an advanced tool for resilient seismic design and Structural Health Monitoring (SHM).

Penile shear-wave elastography predicts the outcome of botulinum neurotoxin (Botox) in the management of non-responders to phosphodiesterase-5-inhibitors: A pilot study

ABSTRACT Objective Botulinum neurotoxin (BoNT) was introduced as a minimally invasive treatment option for erectile dysfunction (ED). However, there is no proven method that predicts improvement after BoNT injection. Shear wave elastography is an emerging imaging modality that evaluates tissue stiffness. This study aims to assess the reliability of SWE in predicting BoNT response in patients with ED and phosphodiesterase 5 inhibitors (PDE-5i) non-responders. Methods This study comprised 20 men presenting with ED and PDE-5i non-responders. Mean tissue stiffness values (TSVs) were measured by SWE, international index of erectile function (IIEF-5), erection hardness score (EHS), sexual encounter profile questions 2 and 3 (SEP-2 and SEP-3), and global assessment questionnaire (GAQ) were evaluated before and after 100 IU of BoNT injection by 6 and 12 weeks. Results In comparison with baseline, there was a significant improvement in IIEF-5 and EHS scores after BoNT injection at 6- and 12 weeks (p < 0.001). Similar improvements were observed in SEP-2&3 (p < 0001 & p = 0.001, respectively) and GAQ-1&2 (p = 0.008 & p = 0.006, respectively). We found that mean SWE in a penile flaccid state can predict failure of clinically significant improvement after BoNT injection using a cutoff point of 12.7 kPa (sensitivity = 100%, specificity = 54%, AUC = 0.86, p = 0.014). Conclusion This finding could be applied to avoid unnecessary BoNT injections in men with ED and PDE-5i non-responders.

Vibration Energy Color Doppler Imaging (VECDI) in Evaluating the Effect of Screw Fixation on Sacroiliac Joint Stiffness: A Prospective Pilot Study

BackgroundThe sacroiliac joints (SIJ) are specialized articulations in the pelvis that allow load transfer between the upper and lower body. Traumatic pelvic disruption often requires surgical fixation of at least one of these joints. Subsequent SIJ pain is associated with asymmetries in joint laxity or stiffness. This pilot study examines SIJ stiffness in patients with intact sacroiliac screw fixation after posterior pelvic ring injuries. This information will prove valuable to informing surgeons about technique efficacy in SIJ injury stabilization.Questions/purposesThis pilot study examined SIJ stiffness in patients with intact sacroiliac screw fixation to: (1) establish vibration energy color Doppler imaging (VECDI) SIJ intra-rater reliability; (2) measure SIJ stiffness in subjects following surgical fixation using VECDI; (3) compare stiffness data between post-surgical and healthy control subjects; (4) evaluate the relationship between stiffness data and pain and disability scores.Methods13 reliability and 19 experimental subjects were tested using VECDI. Subjects were placed into a side-lying position on top of a shaker apparatus that transmitted vibration energy to the pelvic ring while color Doppler images were taken from the bilateral posterior SIJ. One investigator performed SIJ measurements on healthy subjects to establish reliability and then evaluated post SIJ fixation stiffness in experimental subjects at four-weeks (T1) and eight-weeks (T2). Visual analog scales were used to collect subjective pain scores at each time point.ResultsHealthy subject VECDI values suggested good intra-rater reliability (ICC = 0.819; CI 95% = 0.405–0.945). No significant differences in SIJ stiffness (ΔTU) were observed between healthy and experimental subjects at both time points (p > .05). Pearson correlation coefficients highlighted relationships between current pain at T1 and T2 (p = .004, r = .879), and Oswestry Disability Index (ODI) values at T1 and T2 (p = .003, r = .890).ConclusionsAsymmetric laxity through the SIJ can be associated with pain resulting from either trauma or inherent physiologic variations. Prior to this study, the mainstay of evaluation was subjective indexes, such as the ODI. Here we propose VECDI as a potentially objective tool in SIJ assessment. Following surgical fixation necessitated by trauma, fixation using SI screws demonstrated similar stiffness values through the SIJ at four- and eight-weeks post-operatively when compared to healthy controls. Direct inferences regarding VECDI’s exact sensitivity to SIJ dysfunction cannot be concluded from our investigation due to small sample sizes. Future investigations should include a larger sample size to enhance our understanding of stiffness measurements obtained using VECDI, validate the technique, and determine the time-course of healing from SIJ surgical stabilization.

Analysis of shimming performance and clearance influence under manipulation state

During the roll control process of an aircraft, shimmy often occurs, usually manifested as high-frequency and low amplitude vibrations. In order to better analyze the essential causes of landing gear shimmy, this paper establishes a flexible shimmy dynamics model for the nose landing gear and analyzes the influence of the hydraulic stiffness of the control actuator. The analysis shows that a decrease in stiffness will reduce the stability of the system, and the shimmy frequency will decrease, but the frequency will be higher than the reduced shimmy state. Finally, the system damping ratio is compared to evaluate the stability of the system. Based on the above model and combined with clearance theory, a set of shimmy dynamics model considering the influence of clearance was established. The results show that radial clearance has almost no effect on shimmy; The presence of axial clearance can cause equal amplitude vibration in the system, and increasing the clearance value can cause an increase in amplitude; When the initial swing angle of the system is different, the system will gradually swing to the same amplitude of vibration; There is a coupling effect between system stiffness and clearance values, and as the system stiffness decreases, its amplitude will increase nonlinearly.

Functionally graded sustainable lattice structures: Insights into material grading and lattice hybridization

This novel work presents the investigation of functionally graded lattice structures (FGLS) based on polylactic acid (PLA) and wood-reinforced PLA (WPLA) composite. The synergistic effect of a multi-material system and hybridization of two different primitive lattices (Gyroid and Schwarz primitive (SP)) on compressive strength, specific energy absorption (SEA) and stiffness was studied. The findings of the study revealed that the hybrid FGLS fabricated combining the Gyroid lattice of PLA and SP lattice of WPLA (PLA-G/WPLA-SP) exhibits the highest values of stiffness, SEA, and compressive strength.

Establishing thresholds for swing transparency at the knee during gait to inform exoskeleton design.

Knee exoskeletons have been developed to assist, stabilize, or improve human movement or recovery. However, exoskeleton designers must implement transparency (i.e., get out of the way) modes during the swing phase of locomotor tasks to avoid impeding movement. The problem is that it is not understood how sensitive people are to small knee torques or what level of knee impedance is acceptable (sufficiently transparent) during swing phase. Here, we (i) characterized the biomechanical consequences of knee stiffness and damping during swing, and (ii) leveraged user perceptions of being impeded and toe clearance to define transparency thresholds, below which the participants were sufficiently unimpeded during the swing phase of gait. We conducted a series of human subject experiments that involved walking and stair ascent/descent while wearing a modified knee brace with five stiffness values ranging from 0 to 4 Nm/rad and five damping values ranging from 0 to 0.77 Nm/rad/s. We measured changes to lower limb kinematics, knee flexor muscle activity, and participants' perception of being impeded during swing. Kinematics, muscle activity, and perceived impedance all changed in response to added stiffness and damping. For stiffness, we found the median transparency thresholds for walking and stairs to be 1.76 Nm/rad and 2.95 Nm/rad, respectively, which corresponds to peak knee moments during swing of around 2.3 and 5 Nm. For damping, we found the median transparency threshold for walking and stairs to be about the same, 0.29 Nm/rad/s, which corresponds to peak knee moments during swing of around 2.3 Nm. These values provide useful benchmarks for defining quantitative design requirements for knee exoskeletons intended for locomotor activities.