Static Stability Research Articles

Fabrication and evaluation of novel amphiphilic star block copolymers for increasing free water content in lignite to make coal water slurries

In order to reduce the apparent viscosity of lignite coal water slurries (CWSs) and improve its static stability, a series of three-arm amphiphilic block copolymers have been prepared through RAFT polymerization by using poly(ethylene glycol) methyl ether acrylate (PEGMA) and sodium 4-vinylbenzenesulfonate (SSNa) as hydrophilic monomers and styrene (St) as hydrophobic monomer. The chemical structure of the copolymers has been investigated, and the impact of relative molecular weight, hydrophilic/hydrophobic ratio, and ionic group content on the pulping performance of three-arm amphiphilic block copolymers has been examined. The lignite coal water slurries (CWSs) prepared from the block copolymer tri-P(St50-s-SSNa50)10K-b-PPEGMA10K exhibit a remarkably low apparent viscosity of 395 mPa·s and excellent static stability when the coal content is at 55 wt% and dispersant content is at 0.5 wt%. Moreover, these CWSs can achieve a maximum pulping concentration of up to 59 wt%. Additionally, the thermogravimetric test reveals insights into the water occurrence in CWSs, indicating that higher levels of free water content correspond to lower apparent viscosities. Suitable hydrophobicity facilitates the removal of internal water from lignite by dispersants, disrupting its flocculation structure and promoting CWSs formation. Meanwhile, the presence of ionic groups enhances the static stability of the resulting CWSs. Furthermore, the adsorption behavior of the three-arm amphiphilic block copolymer dispersant in lignite has been analyzed through XPS testing to elucidate its dispersion mechanism. The use of three-arm amphiphilic block copolymers in preparing lignite CWSs results in lower apparent viscosity and improved static stability, attributed to the amphiphilic and steric hindrance effects of dispersants. This not only expands the application range of lignite CWSs but also highlights the significant potential of this type of dispersant.

Analysis of the Voltage Stability of Power Using L-Index Voltage Stability

Voltage stability is highly dependent on the ability of the system to maintain voltage conditions throughout the bus, both under normal conditions and after a disturbance. One static analysis tool often used is the power flow completion method to determine the voltage magnitude at several points under review. This paper presents static voltage stability analysis for heavy and light load conditions on the load bus. Voltage stability analysis is performed on the IEEE-14 power system bus using the L-index voltage stability method. L-index values ranging from 0 – 1, buses with L-index voltage stability values close to 1.0 are identified as critical buses.

Three-dimensional nonlinear vibrations of slightly curved cantilevered pipes conveying fluid

In this paper, nonlinear static and dynamic behaviors of slightly curved cantilevered pipes conveying fluid under transverse base excitations are investigated. Incorporating geometrical and inertial nonlinearities, a new three-dimensional dynamic model is developed for the inextensible cantilevered pipe based on the Euler–Bernoulli beam theory. The resultant partial differential equations are discretized using the Galerkin method and solved utilizing the pseudo-arclength continuation technique and a time-integration method. The static equilibrium configuration, linear stability, and nonlinear response of the pipe are calculated for various cases, which allow us to investigate the effects of flow velocity, gravity coefficient, initial curvature amplitude and shape, and base-excitation amplitude and frequency. An emphasis is put on the importance of modal interactions on frequency-response and force-response relationships, evidencing the possible in-plane and out-of-plane transverse vibrations and identifying the preferred forms of pre- and post-instability behaviors. This study offers an efficient theoretical model for exploring the nonlinear forced response of slightly curved cantilevered pipes conveying fluid and provides a better insight for further investigations on the modal interaction in cantilevered pipe devices.

The Power-Transmission Limit of the Controlled High-Voltage Transmission Line for Modes at the Static Stability Boundary

The Power-Transmission Limit of the Controlled High-Voltage Transmission Line for Modes at the Static Stability Boundary

Predictors of static and dynamic balance control in kidney transplant recipients.

We aimed to evaluate balance control and lower extremity muscle strength in kidney transplant recipients (KTRs) including acomparison to ahealthy control group and determine the predictors of static and dynamic balance control after kidney transplantation. In this study 40 KTRs and 40healthy controls were included. Balance control was assessed using the Biodex balance system. The static postural stability test (SPST) and clinical test of sensory integration and balance (CTSIB) were used to assess static balance control whereas the dynamic postural stability test (DPST) and limits of stability test (LOST) were used for dynamic balance control. Lower extremity muscle strength was measured with ahand-held dynamometer. Renal functions and laboratory findings of KTRs were recorded. All the stability index scores of SPST and sway index in CTSIB were significantly higher in KTRs compared to healthy controls. The right anteroposterior stability index score in DPST and the reaction time in LOST were significantly higher whereas overall score in LOST and lower extremity muscle strength were significantly lower in KTRs. The linear regression analysis revealed that hemoglobin was the predictor of static balance control accounting for 11% of the variance and body weight was the predictor of dynamic balance control accounting for 34% of the variance. Balance control, both static and dynamic, are impaired in KTRs as well as lower extremity muscle strength. Hemoglobin level is apredictor of static balance control whereas body weight is apredictor of dynamic balance control after kidney transplantation.

A comparative study of voltage stability NVSI Index and load margin index

With the development of new energy generation technologies, photovoltaic (PV) power generation has gained widespread application as a clean and sustainable source of electricity. However, the intermittency and variability of PV generation pose new challenges to power system secure and stable operation. The WSCC 9-bus system is used in this paper to investigate the effect of PV integration on static voltage stability in power systems. An improved voltage stability index (NVSI) considering the new energy was used to measure the voltage stability of the access point of PV plant. Compared with the P-V curve and the classic load margin index (ILM), even if the index value is less than 0, the NVSI index has still a better measure effect on voltage stability.

Evaluation of Voltage Variations Arising from the Increase in Photovoltaic Insertion in the Transmission Network: Case Study Coremas-PB Power Plant

The objective of this work was to analyze the impacts on the transmission network due to the increase in centralized photovoltaic (PV) generators’ incorporation. A study was carried out in a high-voltage (HV) transmission network, considering adjustments in the simulation environment for more realistic results. ANAREDE software and the static voltage stability evaluation method were used. The simulation was carried out in a steady state, considering an average load and the power of the PV generators corresponding to the base case (70.6 MW), with an increase of 100% of the predicted total (270 MW) for the future. The results showed that, under normal and contingency conditions, small disturbances caused voltage instability. It was observed that the incorporation of PV generators contributes to the improvement of the voltage stability in the bars close to their insertion. However, the greater the PV distribution and generation was, the greater the influence on the attenuations of the voltage profiles through the transmission system was.

Stability of rock-armoured mild slopes

Physical model tests have been performed to study static stability of rock-armoured mild slopes. Current stability design formulae for steeper rock-armoured slopes focus on plunging and surging waves. Slopes of 1:6 and milder usually have more spilling breakers which decreases the load. Also, on mild slopes displaced rocks more often remain present in the wave attack zone, which increases the strength. These aspects lead to an overdesigned structure when existing formulae for steep rock-armoured slopes are used. The present wave flume tests were used to understand the processes and develop a design formula for rock-armoured mild slopes with an impermeable core. These tests were performed for statically stable rock-armoured slopes of 1:6 to 1:10. The tests confirmed that not all existing damage parameters are able to accurately describe the static stability on milder slopes. For mild slopes it is more accurate to describe the damage based on the eroded depth rather than on the eroded area or number of moved stones. In this study, a design formula and guidelines are provided for practicing engineers that design or evaluate the stability of mild rock-armoured slopes.

An anthropometric study of intercondylar femur notch with MRI analysis

Background: Anterior cruciate ligament is the most common ligament injury of knee. The bony anatomy of femur and tibia is responsible for normal knee kinematics and static stability. Intercondylar notch dimensions is considered as a significant predictive risk factor for ACL tear. Narrow femoral intercondylar notch width in either sex were major correlating factors. Aim was to evaluate the intercondylar femur notch dimensions in patients of knee injury using magnetic resonance imaging at RD Gardi Medical College, Ujjain, Madhya Pradesh. Methods: This is a prospective study consist of 400 patients carried out from October 2020 to August 2022 in the Department of Orthopaedics, RDGMC Ujjain. All the patients of knee injury including ACL tear and age 18 years to 60 years are included in the study. Patient less than 18 years and more than 60 years were excluded from the study. Dicom radiant software is used as statistical tool to analyse the data. Various intercondylar notch dimensions in different sections are measured using MRI in the dicom software. Results: The cut off values of axial NWI, NSI, NDI as 0.238, 0.662, 0.472 respectively. Conclusions: We conclude that narrow femoral intercondylar notch, lower notch width index increases the risk of an ACL tear in the given population. This would help in identification of people at risk for ACL injuries. Our study provides a comprehensive analysis on the risk factor of ACL tear, which would help in betterment of the patients at danger for anterior cruciate ligament injury. People with decreased notch dimensions should be educated on the high risk of ACL tear and be given proper prophylactic precautions.

Structure, stability and electronic properties of zirconium nitride nanoclusters

Zirconium nitride (ZrN) is an industrial material having very high melting point, hardness and chemical stability. Compared to the bulk ZrN, its nanoclusters (NCs) are rarely explored. In this report, we generate a few ZrN NCs using ab initio molecular dynamics simulation. We investigate their electronic properties in terms of Bader charge, electron localization function and density of states. The obtained results are compared with their bulk counterpart. We also study the static and dynamical stability of the NCs with the help of binding energy, density of states and phonon dispersion spectra. The electron localization function of bulk ZrN is reported here for the first time to better understand its often confusing bonding behaviour.

A Parameter Investigation on Static Stability of Tunnel in Hilly Region

A Parameter Investigation on Static Stability of Tunnel in Hilly Region

Winkler‐Pasternak foundation effect on the buckling loads of arbitrarily rigid or restrained supported nonlocal beams made of different FGM and porosity distributions

AbstractThe present research investigates lateral stability of a functionally graded nanobeam using Eringen's differential nonlocal elasticity model under rigid (clamped, pinned, free) and deformable (lateral, rotational restraints) boundary conditions. Sigmoid and power law have been employed as grading laws to study the influence of the material distribution on the snap‐buckling analysis of a nanobeam with arbitrary boundary conditions. Moreover, Fourier sine series with Stokes’ transformation are employed to investigate the effects of boundary conditions on the stability response of nanobeams embedded in a Pasternak foundation. A parametric study has been performed to investigate the effect of deformable boundaries, Pasternak foundation and small‐scale parameters on the stability response of the nanobeam and the results have been presented in a series of tables and figures. It has been observed that consideration of the small‐scale parameter, Pasternak foundation, deformable boundaries and functionally grading index (of sigmoid and power‐law) are essential while analyzing the static stability response. The obtained analytical results may be used as benchmarks in future researches of functionally graded nanobeams embedded in an elastic medium.

Enhanced flame retardancy and thermal stability of zinc borate and magnesium carbonate as a promising alternative for Sb2O3 toward polyvinyl chloride

AbstractInorganic zinc compounds such as zinc carbonate (ZC) and zinc borate (ZB) are considered as promising alternatives for harmful antimony trioxide in the future, but may result in poor thermal stability for flexible polyvinyl chloride (PVC). To enhance the flame retardancy and static thermal stability of flexible PVC, zinc compounds with environmentally friendly magnesium carbonate (MC) were introduced into PVC matrix. Findings reveal that the simultaneous use of 5 phr ZB and 5 phr MC for flexible PVC exhibits satisfactory properties containing pronounced flame retardancy with a limiting oxygen index of 30.2% and a UL‐94 V‐0 rating without dripping, enhanced static thermal stability with high color stability by discoloration tests, reduced smoke emission, and decent mechanical properties, which are advantageous over the standalone use of ZC, ZB, and MC. The enhancement mainly due to that the incorporation of ZB can accelerate the dehydrochlorination and promote the charring of flexible PVC in the early stage of flame burning, and MC can perform the long‐term static thermal stability due to the HCl absorption capacity.

On the Effects of Flow Swirl on Static Stability Limits and Flow/Flame Characteristics of Premixed Oxy-Methane Flames: An Experimental Study

ABSTRACT An experimental study was performed to investigate the effects of flow swirl on flow/flame characteristics and stability of atmospheric premixed oxy-methane (CH4/O2/CO2) flames. The flames generated by two swirlers of 55° and 45° swirl angles were tested on a test stand for a dry low emission (DLE) model gas turbine combustor at constant inlet flow velocity of 5.2 m/s and over ranges of operating oxygen fraction (OF: 21% to 70% - by volume in the O2/CO2 mixture) and equivalence ratio (: 0.2 to 1.0). Combustor static stability limits (flashback and blow-out) were determined experimentally in the -OF domain to identify the operational ranges of the combustor while varying inlet flow swirl. To understand the mechanisms for flashback and blow-out, the lines representing the stability limits were displayed in the -OF domain against the contours of combustor power density (PD: MW/m3/atm), adiabatic flame temperature (AFT), and inlet flow Reynolds (Re). Comparison of flame macrostructure and measurements of local flame temperatures were performed for the two swirlers over ranges of , OF, and AFT to determine the effects of such operational parameters on flow/flame interactions and flame stability and to serve as a database for validating numerical models for such flames. The results show that, for both swirlers, the flames blow-out at a very similar AFT of ~1600 K indicating the dominant role of AFT in controlling premixed oxy-flame stability near the blow-out limit. Compared to the same combustor with a 55° swirler, the 45° swirler has a wider stable combustion zone. Comparing the flames of the same AFT, at fixed inlet flow velocity, shows almost identical flame macrostructure whatever the operating inlet flow swirl, OF and φ.

Large-Scale Stability and the Greater Horn of Africa Long and Short Rains

Abstract The societies of the coastal regions of the Greater Horn of Africa (GHA) experience two distinct rainy seasons: the generally wetter “long” rains in the boreal spring and the generally drier “short” rains in the boreal fall. The GHA rainfall climatology is unique for its latitude in both its aridity and for the dynamical differences between its two rainy seasons. This study explains the drivers of the rainy seasons through the climatology of moist static stability, estimated as the difference between surface moist static energy hs and midtropospheric saturation moist static energy . In areas and at times when this difference, , is higher, rainfall is more frequent and more intense. However, even during the rainy seasons, on average and the atmosphere remains largely stable, in line with the GHA’s aridity. The seasonal cycle of , to which the unique seasonal cycles of surface humidity, surface temperature, and midtropospheric temperature all contribute, helps explain the double-peaked nature of the regional hydroclimate. Despite tropospheric temperature being relatively uniform in the tropics, even small changes in can have substantial impacts on instability; for example, during the short rains, the annual minimum in GHA lowers the threshold for convection and allows for instability despite surface humidity anomalies being relatively weak. This framework can help identify the drivers of interannual variability in GHA mean rainfall or diagnose the origin of biases in climate model simulations of the regional climate.

Effects of dual-task training on chronic ankle instability: a systematic review and meta-analysis

BackgroundDual-task training has been a popular intervention for individuals with balance impairments. However, the effects of dual-task training on chronic ankle instability (CAI) have not been comprehensively analyzed and reliable clinical evidence is scarce. The purpose of this systematic review and meta-analysis is to evaluate the effectiveness of dual-task training on postural stability and functional ability in individuals with CAI.MethodsPubMed, Web of Science, EBSCO, Cochrane Library, Physiotherapy Evidence Database (PEDro), and China National Knowledge Infrastructure (CNKI) were researched from inception to November 2022. This study was conducted by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Two reviewers assessed the studies for inclusion and extracted data. The Cochrane Risk of Bias list was used to assess the risk of bias in included studies. Mean differences (MD) with a 95% confidence interval (CI) were calculated with the RevMan 5.3 software.ResultsA total of 7 randomized controlled trials with 192 CAI met the inclusion criteria. The meta-analysis results showed that compared with the control group, dual-task training significantly improved the Y-balance test (MD = 1.60, 95% CI: −0.00 to 3.21, P = 0.050) and reduced COP-area (MD = − 0.94, 95% CI: −1.62 to − 0.26, P = 0.007) in individuals with CAI. However, there is no significant difference between dual-task training and the control group on COP-velocity (MD = − 0.26, 95% CI: −0.70 to 0.17, P = 0.240), hop test (MD = − 0.20, 95% CI: −0.66 to 0.26, P = 0.386) and BESS (MD = − 1.24, 95% CI: −2.95 to 0.48, P = 0.157) in individuals with CAI.ConclusionThis meta-analysis showed that dual-task training may be effective in improving static and dynamic postural stability. However, more high-quality randomized controlled trials are needed to verify the short and long-term effectiveness of dual-task training on CAI.

Effects of virtual heights, dual-tasking, and training on static postural stability

Working at altitudes, dual-tasking (DT), and lack of experience cause falls. This study aimed to investigate the impact of virtual heights, DT, and training on static postural stability. Twenty-eight volunteers' balance at seven virtual environments [VE; ground (G), altitude 1 (A1), edge 1 (E1), altitude 2 (A2), edge 2 (E2), altitude 3 (A3), and edge 3 (E3)] were recorded during single-tasking (ST) and DT over three days. Independent variables were analyzed using a 7 (VE) x 3 (DAY) x 2 (TASK) factorial repeated measures ANOVA. Greater postural sway was observed in A3 and E1, on DAY 1, and during DT. The study demonstrated static postural stability deteriorates at higher virtual altitudes and during DT and improves with training. The findings of the study suggest that virtual reality is a great altitude simulator, which could be used as a potential balance training tool in ergonomic settings.

Novel Compact Polarized Martian Wind Imaging Interferometer

The Mars Atmospheric Wind Imaging Interferometer offers several advantages, notably its high throughput, enabling the acquisition of precise and high vertical resolution data on the temperature and wind fields in the Martian atmosphere. Considering the current absence of such an Interferometer, this paper introduces a novel Mars wind field imaging interferometer. In analyzing the photochemical model of O2 (a1Δg) 1.27 μm molecular airglow radiation in the Martian atmosphere and considering the impact of instrument signal-to-noise ratio (SNR), we have chosen an optical path difference (OPD) of 8.6 cm for the interferometer. The all-solid-state polarized wind imaging interferometer is miniaturized by incorporating two arm glasses as the compensation medium in its construction, achieving the effects of field-widening and temperature compensation. Additionally, an F-P Etalon is designed to selectively filter the desired three spectral lines of O2 dayglow, and its effect is evaluated through simulations. The accuracy of the proposed compact Mars polarized wind imaging interferometer for detecting Mars’ wind field and temperature field has been validated through rigorous theoretical derivation and comprehensive computer simulations. The interferometer boasts several advantages, including its compact and small size, static stability, minimal stray light, and absence of moving parts. It establishes the theoretical, technological, and instrumental engineering foundations for future simultaneous static measurement of Martian global atmospheric wind fields, temperature fields, and ozone concentrations from spacecraft, thereby significantly contributing to the dataset for investigating Martian atmospheric dynamics.

Static stability of partially crystalline emulsions stabilized by milk proteins: Effects of κ-carrageenan, λ-carrageenan, ι-carrageenan, and their blends

In addition to good whippability, partially crystallized emulsions (PCEs) represented by whipping creams and ice creams must also have prolonged long shelf-life. Carrageenan, the most commonly used thickener for production of PCEs, mainly comes in three commercial forms that may exert different effects on storage stability. In the present study, κ-carrageenan (κ-C), λ-carrageenan (λ-C), ι-carrageenan (ι-C), and their blends (κ-C + λ-C, κ-C + ι-C, λ-C + ι-C, and κ-C + λ-C + ι-C) were included as stabilizers of PCEs to investigate effects of such carrageenans on their static stability. The results indicated that in comparison with λ-C and ι-C, κ-C formed stronger three-dimensional networks with casein micelles, and effectively inhibited droplet flocculation of PCEs by improving zeta potentials (−19.93 mV) and reducing contribution of hydrophobic interactions (0.34 mg/mL) and disulfide bonds (0.34 mg/mL). Interestingly, combination of different types of carrageenans (especially κ-C + λ-C, λ-C + ι-C, and κ-C + λ-C + ι-C) also enhanced the electronegativity (−19.73 to −21.43 mV) and reduced the hydrophobic interactions (0.44–0.53 mg/mL) and disulfide bonds (0.03–0.34 mg/mL), which contributed to preventing fat droplets from flocculation during storage. After a storage of 2 months, the emulsions formulated with κ-C, κ-C + λ-C, λ-C + ι-C, and κ-C + λ-C + ι-C exhibited low levels of watering-off (10.03–11.35% of creaming index) and agglomeration (676.00–1012.50 mPa·s of viscosity).

Recent Advancements in Static and Seismic Stability Analysis of Caissons

Recent Advancements in Static and Seismic Stability Analysis of Caissons