Decrease In Stiffness Research Articles

VASCULAR WALL RIGIDITY IN PATIENTS WITH DEGENERATIVE AORTIC STENOSIS BEFORE AND AFTER AORTIC VALVE SURGICAL PROSTHESIS

Introduction. The most common cause of aortic valve surgery is aortic stenosis. So far, the focus has been on evaluating the valve itself, while increasing aortic stiffness increases the load on the left ventricle, contributing to greater impairment of cardiovascular function. Arterial stiffness is a well-established predictor of cardiovascular complications. Objective: To evaluate the dynamics of aortic stiffness in patients with degenerative aortic stenosis against the background of surgical correction of the defect. Material and methods. The study included 33 patients referred for surgical treatment of the defect. Among them, men predominated somewhat (57.6%). All patients were diagnosed with severe aortic stenosis - the area was 0.74 (0.60; 0.90) cm2, the peak and mean pressure gradients on the aortic valve were 85.5 (72.0; 98) mm Hg. Art. and 50.2 (41.0; 56.0) mm Hg. Art. respectively. 22 patients (66.7%) underwent aortic valve replacement with a mechanical prosthesis, the rest of the patients underwent operations combined with coronary artery bypass grafting or prosthetics of the ascending aorta. All patients underwent a study of aortic stiffness indicators, namely: pulse wave velocity in the carotid-radial (CR PWS) and carotid-femoral segments (CF PWS), central systolic pressure in the aorta (CSBP), central diastolic pressure in the aorta (CDAP), aortic central pulse pressure (CPAP), aortic pressure augmentation (AP), augmentation index normalized to heart rate 75 (AIx75). The parameters were measured before the operation and 7-14 days after it. The registration of the pulse wave was carried out by a non-invasive method of applanation tonometry using the SphygmoCor device (AtCor Medical Inc., Australia). Mean values are presented as median and interquartile range. Mean differences in dependent groups were assessed using the Wilcoxon test. Results. CR PWV in the postoperative period decreased and amounted to 7.2 (6.4; 7.5) m/s versus 7.9 (6.6; 9.4) m/s before surgery (p=0.03). There was no significant decrease in PWV CF after aortic valve replacement, however, there was a tendency to decrease (8.1 (6.7; 9.4) m/s before surgery versus 7.4 (6.4; 7.6) m/s). s after surgery, p=0.07). After surgery, CBP decreased and amounted to 103.8 (97; 113) mm Hg. Art. against the original 117.8 (102; 132) mm Hg. Art., (p<0.001). CDAP also decreased and amounted to 69.4 (66; 74) mm Hg. Art. after surgery, while the initial CDBP was 74.8 (70; 81) mm Hg. Art. after surgery (p=0.01). The CPA indicators decreased and amounted to 36 (27; 44) mm Hg after the operation. Art. against the initial value of 43 (31; 53) mm Hg. Art. (p=0.03). There was also a decrease in AIx75 from 31.7 (19.5; 43)% to 17.5 (7; 25)% (p < 0.001) and AR from 16.4 (7; 24.5) mm Hg. Art. up to 10.2 (6; 12) mm Hg Art. (p=0.002). Conclusion. Thus, in patients with degenerative aortic stenosis after its surgical correction, the following indicators of vascular stiffness decrease: carotid-radial pulse wave velocity, central systolic and diastolic pressure in the aorta, index and augmentation pressure. There was no statistically significant dynamics of the carotid-femoral velocity of pulse wave propagation.

Cooperative stiffening of flexible high aspect ratio nanostructures impart mechanobactericidal activity to soft substrates

Understanding how bacteria interact with surfaces with micrometer and/or sub-micrometer roughness is critical for developing antibiofouling and bactericidal topographies. A primary research focus in this field has been replicating and emulating bioinspired nanostructures on various substrates to investigate their mechanobactericidal potential. Yet, reports on polymer substrates, especially with very high aspect ratios, have been rare, despite their widespread use in our daily lives. Specifically, the role of a decrease in stiffness with an increase in the aspect ratio of nanostructures may be consequential for the mechanobactericidal mechanism, which is biophysical in nature. Therefore, this work reports on generating bioinspired high aspect ratio nanostructures on poly(ethylene terephthalate) (PET) surfaces to study and elucidate their antibacterial and antibiofouling properties. Biomimetic nanotopographies with variable aspect ratios were generated via maskless dry etching of PET in oxygen plasma. It was found that both high and low-aspect ratio structures effectively neutralized Gram-negative bacterial contamination by imparting damage to their membranes but were unable to inactivate Gram-positive cells. Notably, the clustering of the soft, flexible tall nanopillars resulted in cooperative stiffening, as revealed by the nanomechanical behavior of the nanostructures and validated with the help of finite element simulations. Moreover, external capillary forces augmented the killing efficiency by enhancing the strain on the bacterial cell wall. Finally, experimental and computational investigation of the durability of the nanostructured surfaces showed that the structures were robust enough to withstand forces encountered in daily life. Our results demonstrate the potential of the single-step dry etching method for the fabrication of mechanobactericidal topographies and their potential in a wide variety of applications to minimize bacterial colonization of soft substrates like polymers.

Effects of textile-reinforced concrete on the cyclic shear behavior of damaged confined brick masonry walls

Masonry walls are very fragile and prone to damage from the effects of earthquakes. However, after an earthquake, some of confined walls can continue to carry loads after repair and reinforcement. Strengthening is an effective measure for improving the seismic performance of damaged walls. In this study, the seismic performance of textile-reinforced concrete-strengthened damaged masonry confined walls was experimentally investigated. Apparently cracked and pre-damaged confined brick masonry walls were repaired and retrofitted with TRC (textile-reinforced concrete). The effect of anchoring on improving seismic performance was investigated, and a restoring force model of damaged confined brick masonry walls reinforced with TRC was established. The damaged masonry confined walls reinforced by TRC had better integrity and ductile behavior during the failure model, compared with unreinforced walls. Load-displacement curves of walls reinforced with TRC exhibited good postpeak behavior, and they had higher shear capacity, ductility factor, and energy dissipation. TRC surface reinforcement could provide a good restraint to damaged walls and improve the brittle failure characteristics of the walls. The number of cracks in each wall was significantly reduced, and the rate of decrease of stiffness was slowed down. For different strengthening methods, the initial stiffness, shear capacity, ductility factor, energy dissipation increased by 0.08-0.52, 0.04–0.22, 0.019–0.55, and 0.33–0.91 times, respectively, compared with unreinforced walls. Additionally, the application of anchorage measures significantly improved the shear bearing capacity and energy dissipation of the reinforced walls. Based on the experimental results, model curves of the restoring force of TRC-strengthened damaged masonry walls were given and analyzed according to the experimental results.

Classification and Mechanical Behaviors of Inner Concave Cable-Arch Structure with V-Shape Web Struts

The inner concave cable-arch structures with V-shape web struts were classified, and single-tensioning construction method and multiple-tensioning construction method for continuous cable-arch structures were described. The optimization of pretension for multiple-tensioning construction method was carried out. FE models of cable-arch structures including the single-tensioning models and the multiple-tensioning models were created. The mechanical behaviors including stress ratios, stiffness, horizontal bearing reaction force and structural stability of the two kinds of models were compared. The results show that the pretension does not significantly influence the maximum resultant displacement, horizontal bearing reaction force, and stability of the singletensioning cable-arch structures. With pretension increasing the stress ratios can be reduced. The stress ratios and stiffness decrease with the increasing of the rise-to-span ratio, and horizontal bearing reaction force slightly decreases, but structural stability has no obvious changing rules. There is no difference in mechanical behaviors between two types of cable-arch structures with the rise-to-span ratio of 0.2, it is recommended to use the singletensioning construction method. However, the mechanical behaviors of multiple-tensioning type are generally better than that of single-tensioning type with the rise-to-span ratio of 0.3 and 0.4. It is necessary to consider the cost of construction and mechanical behaviors to determine its tensioning construction method.

The Acute Effects of Theragun™ Percussive Therapy on Viscoelastic Tissue Dynamics and Hamstring Group Range of Motion

Handheld percussive therapy (PT) massage guns have seen a rapid rise in use and with-it increased attention within injury prevention and sport performance settings. Early studies have proposed beneficial effects upon range of motion (ROM), however the mechanism behind these increases remains unreported. This study aimed to determine the influence of a minimal frequency PT dose upon ROM and myotonometry outcomes. Twenty participants (N = 20; 13 males and 7 females, height 1.78cm ± 9.62; weight 77.35kg ± 8.46) participants were allocated to either a PT group receiving 2 x 60-seconds (plus 30-seconds rest) via a Theragun™ Pro4 to the hamstrings covering a standardised 20 lengths from proximal to distal via the standard ball attachment at 1 bar of pressure or a control group (CON) of 2-minutes 30-seconds passive supine rest. Pre and post intervention outcomes were measured for ROM via passive straight leg raise (PSLR) and tissue dynamics via MyotonPro (Tone, Stiffness, Elasticity, Relaxation Time). Results showed significant within-group increases (p < 0.0001, ηp2 0.656, +11.4%) in ROM following PT and between group difference against CON (P < 0.026). Significant within-group differences in stiffness (p < 0.016, ηp2 0.144, -6%), tone (p < 0.003, ηp2 0.213, +2%) and relaxation time (p < 0.002, ηp2 0.232, +6.3%) were also reported following PT. No significant difference was reported in elasticity (P > 0.05) or any other between group outcomes. PT therapy can provide an acute increase in hamstring group ROM following a resultant decrease in tissue stiffness.

Acute Passive Stretching-induced Decrease In Joint And Arterial Stiffness: Does A Correlation Exist?

Acute Passive Stretching-induced Decrease In Joint And Arterial Stiffness: Does A Correlation Exist?

The Acute Effects of Theragun™ Percussive Therapy on Viscoelastic Tissue Dynamics and Hamstring Group Range of Motion.

Handheld percussive therapy (PT) massage guns have seen a rapid rise in use and with-it increased attention within injury prevention and sport performance settings. Early studies have proposed beneficial effects upon range of motion (ROM), however the mechanism behind these increases remains unreported. This study aimed to determine the influence of a minimal frequency PT dose upon ROM and myotonometry outcomes. Twenty participants (N = 20; 13 males and 7 females, height 1.78cm ± 9.62; weight 77.35kg ± 8.46) participants were allocated to either a PT group receiving 2 x 60-seconds (plus 30-seconds rest) via a Theragun™ Pro4 to the hamstrings covering a standardised 20 lengths from proximal to distal via the standard ball attachment at 1 bar of pressure or a control group (CON) of 2-minutes 30-seconds passive supine rest. Pre and post intervention outcomes were measured for ROM via passive straight leg raise (PSLR) and tissue dynamics via MyotonPro (Tone, Stiffness, Elasticity, Relaxation Time). Results showed significant within-group increases (p < 0.0001, ηp2 0.656, +11.4%) in ROM following PT and between group difference against CON (P < 0.026). Significant within-group differences in stiffness (p < 0.016, ηp2 0.144, -6%), tone (p < 0.003, ηp2 0.213, +2%) and relaxation time (p < 0.002, ηp2 0.232, +6.3%) were also reported following PT. No significant difference was reported in elasticity (P > 0.05) or any other between group outcomes. PT therapy can provide an acute increase in hamstring group ROM following a resultant decrease in tissue stiffness.

Abstract 115: An Action Plan To Improve Biochemically Detected Non-adherence To Antihypertensive Treatment Results In A Short-term Reduction In Arterial Stiffness And A Long-term Reduction In Albuminuria (the ATHAN Clinical Trial)

We previously shown that a specific 3-months(m) intervention improved therapeutic adherence in patients with non-controlled hypertension (HT) decreases blood pressure (BP). We aim to evaluate if there is also a decrease in HT-mediated organ damage (HMOD) at short- and long-term. We conducted a prospective, randomized clinical trial in a HT Unit. Consecutively attended patients with 24h-BP &gt;or=130/80 mmHg despite receiving at least 2 antihypertensive drugs and with therapeutic non-adherence confirmed by determination of antihypertensives in urine (n=47) were randomized (1:1) to receive a specific 3m program to improve adherence (INT=intervention) or routine follow-up (C=control). Antihypertensive treatment was not changed. Prior to randomization, and at 3m and 12m, the presence of antihypertensives in urine and albuminuria were determined. BP and pulse wave velocity (PWV) were evaluated by 24h- ambulatory monitoring in all periods. After 3m, all patients received usual care. At 3m, the adjusted BP differences (mean; 95% CI) from baseline (INT vs. C) were -14.3 mmHg (-5.1 to -23.5), p=0.003, and -10, 0 mmHg (-4.0 to -16.0), p=0.002, for 24h-SBP and 24h-DBP, respectively. The INT group maintained the decrease in BP at 12m. vs baseline: mean change (95% CI) of 24h-SBP = -16.1 mmHg (-22.8 to -9.4), p &lt;0.001 and 24h-DBP change = -7.8 (-12, 8 to -2.7), p=0.002. In the INT group, the percentage of undetected antihypertensive drugs decreased from baseline (median [interquartile range]): 40% [20-100], 0% [0-25], and 18.3% [0-40] at baseline, 3m and 12m, respectively; Z= -3.426 (p&lt;0.001) and Z= -3.055 (p=0.002) for changes at 3m and 12m, respectively. PWV decreased at 3m only in the INT group: mean difference (95% CI) -0.402 m/sec (-0.054 to -0.749), p=0.025, but not at 12m. Albuminuria (median [IQR]) decreased in the INT group at 12m: 27.1 mg/g [11.1-116.2] and 22.4 mg/g [6.4-91.9] at baseline and 12 m, respectively (Z=-2.207, p=0.027). In conclusion, urine biochemical detection of therapeutic non-adherence and a specific 3m-intervention to improve adherence lead to better BP control, which maintains in the long term. In addition, there is a decrease in arterial stiffness in the short term and a regression of albuminuria in the long term, thus reducing the HMOD.

Experimental study on flexural behavior of precast ultra-lightweight ECC plank with lattice girder at construction stage

During the construction of precast concrete (PC) structures, concrete composite slabs are commonly used, employing PC planks with lattice girders as permanent formwork to enhance assembly efficiency while ensuring structural performance. However, traditional PC planks suffer from heavy weight and susceptibility to cracking, adversely affecting construction efficiency and quality. This paper proposes the incorporation of ultra-lightweight engineered cementitious composite (ULECC) into PC planks. The research aims to investigate the flexural behavior of precast ULECC planks with lattice girders during the construction stage. Four-point bending tests were conducted to study the effects of lattice girders and ULECC layer. The introduction of ULECC reduced the self-weight of precast planks by 24%, while resulting in a decrease in strength and stiffness due to ULECC's lower elastic modulus. Remarkably, precast ULECC planks exhibited excellent crack width control. Even at a deflection-span ratio of approximately 4%, precast ULECC planks were capable of maintaining crack widths below 0.2 mm. The combination of ULECC and lattice girders significantly improved the structural performance of precast ULECC planks, allowing them to meet construction requirements without requiring temporary support.

Three-dimensional finite element analysis of the effect of soil liquefaction on the seismic response of a single pile

Soil liquefaction is considered as one of the most significant issues that leads to failure of shallow and deep foundations. However, the effect of liquefaction on the seismic response of piles still poorly understood. Therefore, this research examines the seismic response of a pile embedded in soil stratum of saturated fine-grained soils. Midas GTS/NX is used to carry out the number assessment. In addition, the modified UBCSAND soil constitutive model is used to depict the nonlinear features of saturated sand during earthquake waves. The developed three-dimensional model is first validated using the results of a shaking table test of a pile embedded in coarse-grained soil, where good agreement is obtained between the finite element model and the experimental results for the displacement, acceleration, and liquefaction ratio demonstrated good agreement. Furthermore, the orientations of the vectors produced by the numerical study, that matched a global circular flow characteristic, reflected the movement of the liquefied soil all around pile. The findings showed a considerable decrease in the pile frictional resistance during the seismic events as a consequence of increasing the pore water pressure and subsequent liquefaction. Regarding this, before the soil was entirely softened, resistance due to friction was observed near the ground, in correspondence with the loose sand layer. In addition, the pile showed excessive settling, which is due to the decrease of the soil stiffness caused by the increase of the pore water pressure. The results of this research provide an insight into the mechanism of the behavior of pile in saturated coarse-grained soils and thus, it helps to improve future research on the topic and also achieve better design of piles embedded in saturated coarse-grained soils.

Dynamic responses of a waste sludge modified by magnesium-cement-based multiphase cementitious material under influences of temperature and moisture cycles

This paper explores the influences of external stress and moisture and temperature cycles on the microstructure and dynamic responses (including the dynamic shear modulus G, damping ratio λ, and accumulative plastic strain εp) of a waste sludge that is modified by magnesium-cement-based multiphase cementitious material. Experimental results show that (i) freeze–thaw (FT), wet-dry (WD), and wet-dry-freeze–thaw (WD-FT) cycles significantly change the soil’s pore system. Intra-aggregate pores gradually evolve into inter-aggregate pores and cracks develop during moisture and temperature cycles. This leads to the degradation of the pore structure and decrease in the soil stiffness; (ii) during the progress of moisture and temperature cycles, the G decreases, and the λ increases. The effects of WD and WD-FT cycles on the G and λ are more significant compared to FT cycles. The G increases with the confining pressure σc while the λ is not sensitive to the σc. The relationships of the G and λ to the deviator stress σd are generally non-monotonic and the turning point of such relationships is influenced by the moisture and temperature cycles; (iii) the εp increases after moisture and temperature cycles and the development of the εp during cyclic loading gradually evolve from plastic shakedown to plastic creep. Predictive models based on decay laws considering stress states are developed to describe the changes in dynamic shear modulus and accumulative plastic strain.

Warping deformation of the track slab and their influence on the interlayer stiffness and vibration transmission characteristics of the unit ballastless track

The unit ballastless track partially segments the concrete track bed in the longitudinal direction, and relieves the concrete temperature stress by isolating the upper and lower layers. However, the layer isolation leads to the incompatible deformation of the upper and lower track structures under the effect of the temperature gradient. A large temperature gradient on the track slab will cause local contact between layers, the contact area between layers will then decrease, thus leading to “stiffness softening” between layers. When the vehicle passes, the contact area between layers will gradually increase, which, in turn, leads to “stiffness hardening”. The analysis results show that the greater the design stiffness between layers, the more significant the “stiffness softening” effect will be under the temperature gradient. When k0 = 400 × 106 (N·m−1)·m−2 and Tg = 90 °C·m−1, the interlayer stiffness decreases by 88%.The simulation analysis results of the wheel-drop impact test show that under a positive temperature gradient, the peak value of rail vibration acceleration increases, and the peak value of the track slab and base plate vibration acceleration decreases. The greater the stiffness designed between layers, the more obvious the influence will be. With the increase of the positive temperature gradient, the vibration acceleration of the rail and the track slab will be reduced in the 1–30 Hz and 40–100 Hz frequency domains. With the increase of the negative temperature gradient, the vibration acceleration of the rail in the 4–10 Hz, 20–50 Hz frequency domains, and the vibration acceleration of the track slab in the 70–200 Hz frequency domains will be increased. A large positive temperature gradient inhibits the transmission of high-frequency vibrations above 40 Hz to the substructure, while a negative temperature gradient inhibits the transmission of low-frequency vibrations within 30 Hz and 70–200 Hz to the substructure. A positive temperature gradient is beneficial to restrain the downward transmission of low-frequency vibration. When k0 = 200 × 106 (N·m−1)·m−2, the low-frequency vibration transmission loss of the track slab to the base plate is close to 0 dB without temperature gradient, but the positive temperature gradient increases the transmission loss by about 10 dB, the greater the temperature gradient, the higher the transmission loss of the track slab to the base plate under high stiffness.

Full-scale mud pumping test of ballastless trackbed under train loading

This paper presents a full-scale physical modeling investigation on the mud pumping in ballastless trackbed. The physical model was equipped with a rainfall device to simulate the in situ precipitation and various testing sensors were installed to monitor the dynamic response of the track-subgrade system. Results showed that the whipping of the track structure induced by high-speed train passages caused a separation between the track structure and the underlying roadbed, which allowed rainwater to intrude into the roadbed. The intruded rainwater infiltrated vertically and then permeated laterally from the bottom of the roadbed, eventually saturating the entire roadbed. Train moving loads partially promoted this rainwater infiltration. The excess pore water pressure (EPWP) was formed in the saturated roadbed caused by train moving loads, and it increased with train speeds and loading carriages. A noticeable upward EPWP gradient and a slight longitudinal EPWP gradient towards the expansion gap were also created in the saturated roadbed. Accordingly, both the vertical hydraulic gradient (HG) and longitudinal HG increased with train speeds and loading carriages, most of which, especially the vertical HG, exceeded the critical HG for particle migration with a diameter smaller than 7.1 mm. It caused severe upward particle migration and slight longitudinal particle migration towards the expansion gap. This spatial fine particle migration process, known as mud pumping, was driven by the HG-induced seepage force and further promoted by the EPWP amplification induced by high-speed train passages. Mud pumping resulted in a significant decrease in stiffness of the trackbed and a noticeable increase in vibration velocity of the track slab.

Efficacy of γ-linolenic acid, Vitis vinifera extract, and acetyl-L-carnitine combination therapy for improving arterial stiffness in Korean adults: Real-world evidence.

Atherosclerosis is associated with various cardiovascular diseases (CVDs). Measurement of arterial stiffness using pulse wave velocity (PWV) enables assessment of atherosclerosis progression in individuals. The authors screened patients with asymptomatic atherosclerosis, based on the PWV findings, to evaluate appropriate early interventions and assess the efficacy of γ-linolenic acid, Vitis vinifera extract, and acetyl-L-carnitine triple combination therapy in atherosclerosis prevention. This retrospective study analyzed the medical records of adult patients between March 2007 and April 2019, with presenting complaints of fatigue and lethargy. Among patients with vascular stiffness beyond their biological age on brachial-ankle PWV (baPWV) testing, those with ≥80% compliance for three drugs were allocated to the experimental group. Those with compliance of <80% for any one drug were allocated to the control group to assess changes in arterial stiffness, fasting plasma glucose (FPG), lipid level, and blood pressure (BP). After 1year of triple-combination therapy, there were significant decreases in right and left baPWV (1537.16±274.84 and 1519.00±289.32cm/s, respectively) as compared to baseline (1633.15±271. 20 and 1598.64±267.95cm/s, respectively; p<.001). There was no difference in baPWV between sexes. Moreover, neither group showed significant changes in FPG and lipid levels. When triple-combination therapy combining γ-linolenic acid, V. vinifera extract, and acetyl-L-carnitine was administered to patients with high arterial stiffness relative to their age, as assessed by baPWV, the experimental group showed a decrease in arterial stiffness in both sexes.

Copolyarylates containing phthalazinone and cardo moieties: An attempt toward the balance between thermal resistance and solubility

AbstractA series of copolyarylates containing phthalazinone and cardo moieties are synthesized by interfacial polymerization of terephthaloyl dichloride with bisphenol monomers including 2,4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one, 9,9‐bis(4‐hydroxyphenyl) fluorene, and phenolphthalein. The intrinsic viscosity and number average molecular weight of copolyarylates are in the range of 0.71–1.01 dL g−1 and 16.3–28.4 kDa, respectively, indicating the formation of medium molecular weight copolymers. The effects of phthalazinone and cardo moieties on the solubility and thermal resistance of copolyarylates are discussed in detail. With only phthalazinone moieties, the polyarylate has high thermal resistance with the glass transition temperature (Tg) of 335 °C, but poor solubility. The introduction of cardo moieties enables the produced copolyarylates readily soluble in chloroform, 1,1,2,2‐tetrachloroethane, and N‐methyl‐2‐pyrrolidone, for they not only increase the free volume of intermolecular chains but also lead to a fractional reduction in the structural stiffness of copolymers. Although the decrease in structural stiffness is related to a decrease in Tg value, fortunately, the rigid cardo and phthalazinone moieties allow the thermal resistance of copolyarylate to reach the leading level among (co)polyarylates. In addition, the resulting copolyarylates have good tensile properties. These copolyarylates have important application prospects in the high thermal‐resistant material industry.

Experimental and numerical studies on shear stud connectors under combined shear and tension force

Shear stud connections have been widely used in steel–concrete composite bridges, while research on shear studs under combined shear and tension force is still lacking. In this research, 18 specimens, including sixteen push–out specimens under different tension force ratios and two pull–out specimens were tested to study the failure modes, load–slip curves and shear capacity of shear stud connectors under combined shear and tension force. The experimental results show that both the shear capacity and shear stiffness decrease remarkably as the tension force ratio rises. The maximum reduction in shear capacity and in shear stiffness are 37.0% and 68.9%, respectively, when tension force ratio rises from 0 to 0.6. Shear slip and necking are both demonstrated in the failure mode of shear stud connectors when shear and tension forces are coupled. Numerical models were established using ABAQUS and verified by the experimental data to investigate the influence of concrete strength, reinforcement ratio and stud diameter thoroughly via parametric analysis. The results indicate that the shear capacity of shear stud connectors increases as concrete strength and stud diameter rise. Higher concrete strength and closer reinforcement spacing offer better collaborative deformation ability between the studs and the surrounding concrete, and also develop the ratio of the shear capacity under combined shear and tension force to the shear capacity under uniaxial shear force ( Vu/ Vuu). Equations to give prediction of the shear capacity integrated with concrete strength enhancement factor and to describe the load–slip curves of shear stud connectors under combined shear and tension force were proposed and proved to be more accurate.

The stability, electronic, thermal, and optical properties of silver halide (AgX: X = F, Cl, Br, and I) semiconductors: Ab-initio study

The structural properties, mechanical and dynamic stability, electronic, thermal and optical properties of silver halide AgX (X = F, Cl, Br, and I) compounds in the rock-salt phase within GGA and HSE approximations have been studied. The calculations are performed using the QUANTUM-ESPRESSO package which is based on the density functional theory (DFT) and the pseudo-potential method. The calculated elasticity parameters illustrated that the rock-salt phase complies with the mechanical stability conditions at ambient pressure. Based on the results of the mechanical calculations, it can be concluded that AgI is more rigid than other silver halide compounds, while the AgF compound is more malleable than other silver halide compounds. Also, against other examined silver halides, the AgI compound has an isotropic nature. The phonon scattering diagram has proved the dynamic stability of silver halide compounds in the studied rock-salt phase. Evaluation of the electronic results indicates that silver halide compounds in both GGA and HSE approximations have an indirect bandgap in the L−Γ path. In comparison to GGA, the HSE calculation improves the amount of bandgap toward a better agreement with experimental results. At room temperature, the hole mobility of silver halides is much less than the electron mobility. The decreasing trend of the effective mass of electrons in silver halides with the atomic radius of halide in the rock-salt phase leads to a faster carrier transfer rate in AgI, AgBr, AgCl, and AgF compounds, respectively. Moreover, by increasing the atomic radius of halide atom X, the Debye temperature θD and stiffness decrease, and inversely the heat capacity Cv increases. The increasing entropy relative to temperature refers to the endothermic properties of silver halide compounds. In both GGA and HSE approximations, the AgF compound has the highest absorption coefficient peak with the maximum optical absorption in the ultraviolet regime of the electromagnetic spectrum. The absorption coefficients of the silver halide compounds are of the order of 105 cm−1 which is comparable to the absorption coefficient of silicon crystals. The latter property along with a high stability and high electron mobility, makes silver halides attractive photocatalytic materials in the NaCl structure.

FIM: A fatigued-injured muscle model based on the sliding filament theory

Skeletal muscle modeling has a vital role in movement studies and the development of therapeutic approaches. In the current study, a Huxley-based model for skeletal muscle is proposed, which demonstrates the impact of impairments in muscle characteristics. This model focuses on three identified ions: H+, inorganic phosphate Pi, and Ca2+. Modifications are made to actin-myosin attachment and detachment rates to study the effects of H+ and Pi. Additionally, an activation coefficient is included to represent the role of calcium ions interacting with troponin, highlighting the importance of Ca2+. It is found that maximum isometric muscle force decreases by 9.5% due to a reduction in pH from 7.4 to 6.5 and by 47.5% in case of the combination of a reduction in pH and an increase of Pi concentration up to 30 mM, respectively. Then the force decline caused by a fall in the active calcium ions is studied. When only 15% of the total calcium in the myofibrillar space is able to interact with troponin, up to 80% force drop is anticipated by the model. The proposed fatigued-injured muscle model is useful to study the effect of various shortening velocities and initial muscle-tendon lengths on muscle force; in addition, the benefits of the model go beyond predicting the force in different conditions as it can also predict muscle stiffness and power. The power and stiffness decrease by 40% and 6.5%, respectively, due to the pH reduction, and the simultaneous accumulation of H+ and Pi leads to a 50% and 18% drop in power and stiffness.

Hydraulic variable stiffness mechanism for swimming locomotion optimization of soft robotic fish

In this paper, we describe the development of a soft robotic fish with Hydraulic Variable Stiffness (HVS), a simple and light mechanism that actively controls the tail stiffness. Modal analysis model using PRBM was developed to predict the tendency of optimal tail stiffness which maximizes the forward swimming speed in response to driving frequency. The forward swimming locomotion experiment demonstrated that the optimal tail stiffness which maximizes swimming speed exists for each driving frequency, and that optimal stiffness increases as the frequency increases. The turning locomotion experiment showed that, as the tail stiffness decreases, the turning radius decreases and the turning angular velocity increases significantly. By controlling the tail stiffness to its optimal for specific locomotion, the robot can increase its swimming speed by 118% on average, reduce its turning radius to almost a quarter, and increase its turning angular velocity by almost three times. These results demonstrate that the HVS soft robotic fish can optimize its swimming locomotion more effectively compared to conventional robots by optimizing its tail stiffness depending on its required swimming situation with only one actuator to oscillate the tail using the HVS device.

Carotid Stiffness After Transcatheter Aortic Valve Replacement.

The present study aimed to analyze common carotid artery strain properties in patients (n = 59) with severe aortic valve stenosis who underwent transcatheter aortic valve replacement (TAVR). Arterial compliance of the common carotid artery was assessed by ultrasound speckle-tracking before and after TAVR. For sub-analysis the study cohort was divided according to aortic valve area <.75cm2 (n = 30) vs ≥.75cm2 (n = 29). Comparison of pre- and post-procedural strain variables showed an improvement in median radial velocity (P < .0001), radial displacement (P = .007), circumferential strain (P = .004), radial strain rate (P = .023), and circumferential strain rate (P < .0001), while the increase of radial strain showed a trend (P = .082). Analysis of aortic valve area revealed an inverse correlation between aortic valve area and the differences (post-procedural-pre-procedural values) for radial strain rate, and circumferential strain. Moreover, sub-analysis revealed that the increase of carotid strain variables before and after TAVR were more pronounced in the sub-group of aortic valve area .75 vs ≥.75cm2. TAVR led to a reduction of arterial wall stiffness of the common carotid artery assessed by ultrasound speckle-tracking. The decrease of arterial wall stiffness after TAVR was more pronounced in more severe aortic valve stenosis.