Vulnerable Location Research Articles

Seismic Response and Collapse Analysis of a Transmission Tower Structure: Assessing the Impact of the Damage Accumulation Effect

This paper delves into the impact of the damage accumulation effect, which leads to the degradation of material strength and stiffness, on the seismic resistance of transmission towers. Building upon the elastic–plastic finite element theory, a mixed hardening constitutive model is derived for circular steel tubes, standard elements in transmission towers, incorporating the damage accumulation effect. A user material subroutine, UMAT, is created within the LS–DYNA framework. The program’s validity and reliability are established through axial constant–amplitude loading tests on single steel tubes. The subroutine is employed to conduct the incremental dynamic analysis (IDA) of an individual transmission tower and to contrast it with the structure utilizing the Plastic Kinematic material model, assessing the discrepancies in tower top displacements and segment damage indices (SDIs) at both macroscopic and microscopic scales. The results shows that the Plastic Kinematic model inflates the seismic performance of the transmission tower. When considering the damage accumulation effect in structural failure, the damage index of the members increases, leading to a reduction in both the structural strength and stiffness. The dynamic response in the plastic phase becomes more pronounced, and the onset of structural failure is accelerated. Consequently, structural analysis under seismic conditions should account for the damage accumulation process. Through the delineation of member and segment damage, the extent of damage to transmission tower segments can be quantitatively assessed. Subsequently, the ultimate load–bearing capacity and the most vulnerable location of the transmission tower can be ascertained. Finally, this paper provides a detailed analysis of the transmission tower collapse process under seismic action and summarizes the mechanism of collapse for the structure.

Banking on Optimism: Why do Some Dutch Delta Engineers Resist the New Water and Soil System Policy?

Engineers, long accustomed to finding technological solutions for any vulnerable location regardless of water and soil conditions, fear that a new Dutch spatial planning policy that takes the impacts of climate change into account will place limits on the scope of their activity. The concept of Water en Bodem Sturend (WBS), approximately translated in English as “water and soil as governing principles,” is considered a continuation of earlier proposals such as Meebewegen. This ecological and climate-informed policy transition has in fact been in development for at least three decades. Engineers resist the legal anchoring of this policy by downplaying the threat of sea level rise. Anchoring the concept of WBS in law is needed to create a break with technological solutions that are not well adapted and are based on complacency and optimism about sea level rise.

Enhanced Typhoon-Induced Design Wave Height Estimation for Ocean Engineering Applications Using High Performance Computing

Coastal construction heavily depends on accurately estimating design wave parameters. This paper presents a technique for calculating ocean engineering design wave heights that addresses the challenges of inadequate wind speed and measured wave data in the field using High Performance Computing (HPC). The proposed method combines the Simulating WAves Nearshore (SWAN) wave model driven by wind with two different wind field models: the NCEP/NCAR reanalysis wind field and the Jelesnianski typhoon model wind field. By combining these models, the study reduces the underestimation of wind speed and inaccurate depiction of typhoon-related details. The method's effectiveness is demonstrated by applying it to calculate the design wave elements of the deep-sea breeding platform in Dongluo Island, Fujian. The study results show that the platform can experience a maximum wave height of 9.42 m during a 50-year recurrence period. The research shows that the platform's southwest corner is the most vulnerable location. This new calculation method is a significant improvement in ocean engineering design since it overcomes the limitations that come with the lack of wind speed and measured waves. By utilizing multiple wind field models, the calculated wave heights' accuracy and reliability is considerably enhanced. The application of this method to the breeding platform in Dongluo Island has yielded valuable insights for designing resilient structures in similar oceanic environments. This study demonstrates the important application of computational numerical simulations in the field of ocean engineering, providing high-precision predictive capabilities for structural design and risk assessment.

Estimation of Injury Limits at Vulnerable Impact Locations Along the Forearm Via THUMS AM50 Finite Element Model at Airbag Loading Rates.

Side and frontal airbag deployment represents the main injury mechanism to the upper extremity during automotive collisions. Previous dynamic injury limit research has been limited to testing the forearm at either the assumed most vulnerable location to fracture, the distal 1/3rd, or the midpoint. Studies have varied the surface to which impacts were applied, with no clear consensus on the site of greatest vulnerability. The unpredictability of airbag impact location, especially with altered hand positioning, limits the effectiveness of existing forearm injury limits determined from impacts at only one location. The current study quantified the effect of impacts at alternative locations on injury risk along the forearm using the THUMS FE model. Airbag-level impacts were simulated along the forearm on all four anatomical surfaces. Results showed the distal 1/3rd is not the most vulnerable location (for any side), indicating forearm fracture is not solely driven by area moment of inertia (as previously assumed). The posterior forearm was the weakest, suggesting that current test standards underestimate the fracture risk of the forearm. Linear regression models showed strong correlation between forearm fracture risk and bone geometry (cross-sectional area and area moment of inertia) as well as soft-tissue depth, potentially providing the ability to predict forearm injury tolerances for any location or forearm size. This study demonstrated the forearm's vulnerability to fracture from airbag deployments, indicating the need for safety systems to better address injury mechanisms for the upper limb to effectively protect drivers.

Urban heat island phenomenon in Istanbul: A comprehensive analysis of land use/land cover and local climate zone effect

The relationship between urban heat island (UHI) and land use/land cover (LULC), and local climate zone (LCZ) is apparent and takes rising attention in the current literature. This study aimed to investigate the relationship between meteorological data collected from 30 stations between 2016 and 2022 and Istanbul’s LULCs and LCZs. Several notable findings were uncovered, providing light on the UHI phenomenon and its consequences for the city’s characteristics. The stations in urban areas (typology A) had higher temperatures than stations in rural/suburban (typology B) and forested landscape (typology C). Those yearly values were ∼1°C for monthly mean temperatures and ∼1.5°C for monthly minimum temperatures. Moreover, urban areas possessed +4 and +2 hot days (35°C and above) for typologies B and C, respectively. Another remarkable result was that stations situated close to water surfaces exhibited a lower tendency to exceed temperatures of 35°C. Furthermore, built-type LCZs wind velocity achieved a lower value than land cover type, and humidity in typology A was 5% and 10% less than the typologies B and C, respectively. Consequently, the southern part of Istanbul emerged as the most vulnerable location to the UHI phenomena, suffering greater temperatures.

Numerical Analysis of Hybrid Fibre-Reinforced Concrete Beam-Column Joint

Beam-column joint is the most vulnerable location of a moment-resisting reinforced concrete frame structure. The joint region experiences the maximum shear stress both in vertically and horizontally which is generated due to the shear transfer mechanism from the adjoining beams and columns. The shear capacity and bond stress capacity are the two major factors affecting the strength of a joint core in RC structure. An important discovery recently is the ductile behaviour of the whole structure under repeated loading. The behaviour of the concrete beyond elastic limit which is in the concrete hardening zone can drastically influence the ductility of the concrete. The non-linear stress-strain behaviour after the onset of the initial crack and up to ultimate compressive strength plays an important role in improving ductility. Beyond the ultimate compressive strength, concrete will undergo softening which is neglected in this study as once concrete reaches ultimate stress it is unsafe for service. This material ductility can be fulfilled with the application of high-strength fibres with ductile behaviour. However, the hybridization of two or more fibres can incorporate two different characteristics of the fibre used. The use of ordinary-grade of concrete moreover reduces the shear-resisting capacity of the joint. A hybrid mix of hooked-end steel fibre with basalt fibre and crimpled steel fibre with polypropylene fibre are used with a volume fraction of 1% to 1.4% of the concrete. In this study, ordinary M25 grade concrete and fibre mixed M25 grade concrete is employed under static and cyclic loading. The laboratory tests are also conducted to evaluate the compressive strength, split-tensile strength, and flexural strength of the hybrid mix fibre-reinforced concrete at the age of 28th days. Five full-scale models of the beam-column joint are designed as per the Bureau of Indian Standards. Numerical models of concrete and steel reinforcement are developed. Numerical analysis is carried out using finite element software ANSYS-v21. The behaviours of the beam-column joint are observed under static as well as cyclic loading. Crack patterns, first crack load, initial displacement, ultimate load, and ultimate displacement are observed under static conditions. And under cyclic loading, hysteresis load vs displacement, energy dissipation, and stiffness degradation are observed. The hybridization of hooked steel with basalt fibre gives better results in mechanical strengths and the hybrid effect of crimpled steel with polypropylene fibre gives better results in mechanical strengths. And also under numerical study, the above specimens show an improvement in energy dissipation capacity. Keywords beam-column joint, hybrid fibre reinforced concrete, numerical concrete model, ANSYS, static, reverse cyclic, energy dissipation, stiffness, crack

Failure analysis of non-rotating control rod of a helicopter

The paper presents findings of the failure analysis of a control rod that resulted in accident to a helicopter during a routine flight. The helicopter crashed due to several events that led to loss of control. Post-accident wreckage examination showed that failure in the non-rotating control rod connecting the swash plate and bell crank was the primary component that led to the accident. The control rod was manufactured from Ti-6Al-4V alloy. Fractography studies revealed that the control rod failed by fatigue mechanism. The fatigue crack initiated at the rod-to-eye-end transition fillet. Fatigue crack initiation was associated with presence of deep machining marks on the fillet surface. After initiation at the machining marks, the crack propagated through the thickness as well as along the machining mark over a length on either side of the crack origin. Study revealed presence of multiple fatigue cracks on the machining marks on the fillet surface. Analysis showed that the primary cause of the fatigue failure of the non-rotating control rod was the stress concentration effect arising from the deep machining marks at vulnerable location, which is the rod–to–eye transition fillet surface. Issues related to the fitment of the bearing in the control rod led to fretting on the inner bearing surface, and this damage contributed to the initiation of the fatigue cracks.

Development of a health monitoring framework: Application to a supercritical pulverized coal-fired boiler

This work details the development of a physics-based equipment health monitoring framework for a supercritical boiler, using first-principles models to estimate the remaining useful life (RUL) of its components. The framework accounts for fatigue and creep life consumption, generating spatio-temporal variations in mechanical and thermal stress. Analysis of the stress profile throughout the boiler highlights the finishing superheater inlet steam header as a vulnerable location susceptible to damage from cycling operation. The framework also yields quantified uncertainty in the RUL projection for specific locations, accounting for uncertainties in material properties and boiler operation. Results indicate that operational uncertainties (e.g., seasonal variation and operational strategy) and material properties (e.g., rupture time coefficients, Young's modulus, yield strength, and coefficient of thermal expansion) significantly impact the RUL of the finishing superheater inlet steam header. Additionally, case studies demonstrate the use of the health monitoring framework as a predictive tool for operational planning under uncertainty, including scenarios with and without updates on the operation of the boiler.

Adverse Cosmetic Reactions in a Pediatric Population Reported to the Chongqing Drug Administration in China From 2017 to 2021.

Background: Despite their ubiquitous use and several safety incidents involving cosmetics for children in China, there is little research on adverse reactions to cosmetics in children. Objectives: We assessed the cosmetic adverse reactions (CARs) reports submitted to the Chongqing Drug Administration in China for children, to understand the characteristics of CARs in a pediatric population and determine whether useful insights can be derived. Methods: We extracted the data file of the Chongqing Drug Administration's cosmetic adverse events reporting system from 2017 to 2021, and screened the information of people under the age of 18 years for analysis. Results: A total of 589 children were reported; of them, 475 female children and 114 male children, aged 1-17 years, and 89.6% were diagnosed with cosmetic contact Dermatitis. Itching and burning were the most prominent symptoms and accounted for 83.4% and 40.2%, respectively. The most frequently reported clinical sign was erythema (73.3%) followed by papule (37.9%). The face is the most vulnerable location to lesions, accounting for 80.8% of all areas, with girls having a significantly higher rate of facial and scalp damage than boys. The majority of the CARs were reported with cream, lotion, and toner for the skin (45.9%) and facial or body cleansing products (15.4%), and most of these products were purchased from authoritative shops. Conclusion: Although adults are the main group of people who use cosmetics, due to the special physiological structure of children, the safety of children's cosmetics should be given more attention. In addition, pediatricians and dermatologists should be active in submitting reports of adverse cosmetic events and encouraging consumers to do so likewise in situations in which a product adversely affects a child's health.

Study on wind load characteristics of stadium under tornado

The stadium is a wind-sensitive structure, and the tornado has a greater damage to the stadium. The Ward tornado generating device was used to simulate the wind load characteristics of the stadium during tornado action in order to investigate the wind load characteristics of the stadium. The results of this paper are compared with the experimental results to verify the accuracy of the simulation method. The wind load characteristics of the stadium and its most vulnerable location during a tornado are ascertained by examining the wind pressure coefficient and wind speed distribution law of the stadium’s upper and lower surfaces with different swirl ratio. The influence of uniform wind and wind profile on the wind load of the stadium is explored by comparing and analyzing the wind pressure coefficient of the stadium surface with and without wind profile at the entrance of the wind field. The impact of varying ground roughness on the stadium is compared in order to ascertain how it affects the wind speed, stadium wind pressure, and vortex core radius. The vorticity of the stadium in the tornado wind field with different swirl ratios was compared and analyzed, and the influence of the stadium on the vorticity development of the wind field was explored. This study reveals the effects of swirl ratio, ground roughness and wind profile on the wind pressure, wind speed and vorticity of the stadium under tornadoes, and determines the most vulnerable location and the most unfavorable factors. The above research is helpful to provide reference for disaster prevention and mitigation of stadium structure design.

Chance-constrained vulnerability assessment of smart water distribution systems against stealthy false data injection attacks

Smart water distribution systems (SWDSs) have not only enhanced the monitoring and control of the entire water infrastructure but have also jeopardized its security and resilience. The state-of-the-art examined the uncertainties in the water supply network to obtain optimal design parameters to ensure hydraulic integrity. However, the investigations of uncertainties in SWDSs from the cybersecurity perspective remain unexplored. To address this limitation, this paper utilizes a robust chance-constrained optimization strategy to scrutinize the vulnerable location of SWDSs against False Data Injection (FDI) attacks. This is achieved by factoring in the probabilistic behavior of water demand at junctions that can potentially facilitate stealthy FDI attacks on the hourly measurements of the pump’s flow rate. The proposed nonlinear model is validated with several case studies reflecting the real-world cyberattack consequences including cutoff water supply of the network, enhanced power consumption of the pump, and the undesirable pressure surge in the system at strategic locations of SWDSs. As a result of the studied cases, the cyberattack consequences on the entire water supply network are obtained while highlighting the threat-prone regions of the network. This paper contributes to embedding additional security layers to the existing water infrastructure at the vulnerable links and junctions.

Enhancing Urban Resilience to Flood in Chennai : Strategies for Sustainable and Adaptive Cities

Chennai, the capital of Tamil Nadu is located in the South East of India and lies at a mere 6.7m above mean sea level and well developed and highly vulnerable city in India especially to floods. Chennai is in a vulnerable location due to storm surges as well as tropical cyclones that bring about heavy rains and yearly floods. The 2004 tsunami had a significant impact on the shoreline, and increasing urbanization together with the ground's declining natural drainage capacity as a result of encroachment on wetlands, marshes, and other ecologically delicate and permeable places have contributed to have more floods in the city. Canals and rivers that have been filtered through the Waste and informal settlements have made the situation worse. Organic and artificial water systems, such as those for collecting and storing monsoon water infrastructure like the reservoirs and tanks at Temple have been contaminated and have fallen into abuse. This dissertation involves the study of various geographical contexts that are similar to Chennai context and to analyze urban flood resilience. The various case studies that are discussed and analyzed. The outputs can be recommended to city Chennai to become better urban resilience to floods.

The pattern of maxillofacial fractures associated with rollover accidents: A 7-year retrospective study.

This study aimed to assess the incidence and pattern of maxillofacial fractures and related demographic data in the victims of rollover crashes. This retrospective study was based on medical records of patients who sustained maxillofacial injuries following rollover accidents. Investigated data included age, gender, accident date and time, accident cause, seat belt usage, airbag deployment, road type, anatomical location of the facial fracture, and treatment approach. Among the 147 patients who met the inclusion criteria, the most prevalent age groups were 20-30 (36.7%) and 30-40 (32.7%) years, with a mean age of 33.6 ± 9.7 years. The male-to-female ratio was 6:1. Most crashes occurred in March, August, and July. These accidents involved 69.4% light vehicles and 39.6% heavy vehicles. The leading causes of rollover crashes were speeding (58.5%) followed by distracted driving (21.1%) and traffic rule violations (13.6%). The most prevalent injuries were fractures of the maxillary sinus wall (40.8%), nasal bones (39.5%), zygomaticomaxillary complex (36.1%), and the mandible (32.6%). Surgical intervention was necessary for 44.2% of patients, while 12.9% of cases underwent close reduction, and 42.9% did not require any surgical intervention. The occurrence of nasal bone fractures was significantly lower in cases where seat belts were worn and zygomatic arch fractures were less frequent in incidents with airbag deployment. In rollover crashes, the midface is the most vulnerable anatomical location. Utilization of seat belts and airbag deployment has the potential to prevent nasal bone and zygomatic arch fractures.

Optimasi Waktu Tunggu Lampu Lalu Lintas dengan Mengaplikasikan Teori Graf dan Metode Webster

Mobility in the city of Manado is a trigger for the occurrence of traffic volume density, leading to congestion at several points, particularly at intersections. The Toar-Lumimuut intersection is one such vulnerable location where congestion often occurs, despite the presence of traffic lights controlling the flow of vehicles. In fact, many drivers still have to wait for the red light more than once at the Toar-Lumimuut intersection. Based on these findings, it indicates that the waiting time for traffic lights at the Toar-Lumimuut intersection is still inefficient. This study aims to determine the synchronized waiting time for traffic lights according to the traffic situation, in order to achieve a more optimal waiting time for traffic lights. This problem can be addressed using graph theory and the Webster method. The research yielded results, with the optimum cycle time increasing to 285 seconds, accompanied by an increase in green light duration and a decrease in red light duration as a percentage for each road segment. Therefore, the research concludes that this provides a more effective waiting duration.

Seismic fragility analysis of containment structure subjected to near fault ground motions

This study presents seismic fragility analysis of the containment structure subjected to near fault ground motion. Prior to perform seismic fragility analysis, 20 near fault ground motion records with pulse characteristics are selected PEER database. Nonlinear dynamic analysis of the containment structure is performed automatically using Matlab scripts and Batch files. To quantify the global damage behavior of the containment structure subjected to near fault ground motion, energy-based global damage index is proposed. The evolution of global damage behavior and tensile damage of the containment structure are analyzed in depth. Goodness of fit for two widely used fragility fitting methods is compared. To quantify the uncertainty in fragility function parameters, Bootstrap resampling procedure and analytical statistical inference method are adopted to estimate the confidence interval of the fragility function parameters. Results indicated that the bottom of containment structure suffered from severe tensile damage and it is most vulnerable location of the containment structure. With the increase of peak ground motion intensity level, tensile damage increases rapidly and extends to higher elevations of the containment structure. The relative error for fragility function parameter x˜m is not more than 4%, and the error of fragility function parameter β˜R is more than 12%. In general, analytical statistical method provides good estimation for the confidence interval of fragility function parameter x˜m, while overestimate the confidence interval of fragility function parameter β˜R.

Interhemispheric transfer time and concussion in adolescents: A longitudinal study using response time and event-related potential measures.

Concussion in children and adolescents is a public health concern with higher concussion incidence than adults and increased susceptibility to axonal injury. The corpus callosum is a vulnerable location of concussion-related white matter damage that can be associated with short- and long-term effects of concussion. Interhemispheric transfer time (IHTT) of visual information across the corpus callosum can be used as a direct measure of corpus callosum functioning that may be impacted by adolescent concussion with slower IHTT relative to matched controls. Longitudinal studies and studies testing physiological measures of IHTT following concussion in adolescents are lacking. We used the N1 and P1 components of the scalp-recorded brain event-related potential (ERP) to measure IHTT in 20 adolescents (ages 12-19 years old) with confirmed concussion and 16 neurologically-healthy control participants within 3 weeks of concussion (subacute stage) and approximately 10 months after injury (longitudinal). Separate two-group (concussion, control) by two-time (3 weeks, 10 months) repeated measures ANOVAs on difference response times and IHTT latencies of the P1 and N1 components showed no significant differences by group (ps ≥ 0.25) nor by time (ps ≥ 0.64), with no significant interactions (ps ≥ 0.15). Results from the current sample suggest that measures of IHTT may not be strongly influenced at 3 weeks or longitudinally following adolescent concussion using the current IHTT paradigm.

Digital postcolonialism and NGO accountability during COVID-19: Evidence from the Gaza Strip

Drawing from a digital postcolonialism perspective, this paper explores how the leftover technology available in the colonised space shapes the landscape of NGOs’ accountability to beneficiaries and funders during the COVID-19 lockdown. The context of the study is the Gaza Strip, a socially and politically vulnerable geographic location with heavy reliance on support from NGOs. We conducted 20 semi-structured interviews with Palestinian and international NGOs during and after the lockdown to enhance our understanding of the challenges and opportunities they faced in adopting technology to discharge accountability during a major disruptive event. Three main themes emerged from our analysis. First, the biggest challenge is downward accountability to the most deprived and marginalised beneficiaries due to implications of the digital occupation which caused digital unaffordability and illiteracy, voluntary digital resistance to counter suspicion of surveillance, and female digital disempowerment. Second, upward accountability was less problematic as funders accepted ad hoc technology-based accountability practices, but some concerns remained over the efficacy and sustainability of digital adoption in the long run. Finally, the pandemic granted NGOs new opportunities in utilising technology, which successfully changed their process and practice of accountability.

FaultMeter: Quantitative Fault Attack Assessment of Block Cipher Software

Fault attacks are a potent class of physical attacks that exploit a fault njected during device operation to steal secret keys from a cryptographic device. The success of a fault attack depends intricately on (a) the cryptographic properties of the cipher, (b) the program structure, and (c) the underlying hardware architecture. While there are several tools that automate the process of fault attack evaluation, none of them consider all three influencing aspects.This paper proposes a framework called FaultMeter that builds on the state-of-art by not just identifying fault vulnerable locations in a block cipher software, but also providing a quantification for each vulnerable location. The quantification provides a probability that an injected fault can be successfully exploited. It takes into consideration the cryptographic properties of the cipher, structure of the implementation, and the underlying Instruction Set Architecture’s (ISA) susceptibility to faults. We demonstrate an application of FaultMeter to automatically insert optimal amounts of countermeasures in a program to meet the user’s security requirements while minimizing overheads. We demonstrate the versatility of the FaultMeter framework by evaluating five cipher implementations on multiple hardware platforms, namely, ARM (32 and 64 bit), RISC-V (32 and 64 bit), TI MSP-430 (16-bit) and Intel x86 (64-bit).

Flood adaptation decision‐making for vulnerable locations using expectation–quantile–investment analysis

AbstractFloods represent one of the major challenges facing human societies. The impacts caused by them are extensive, and efficient flood adaptation will play a key role in the current century. The present work proposes a new approach to decision‐making in flood adaptation aimed at achieving robust adaptation decisions. It consists in evaluating decisions on a triaxial basis that considers expectation, probability quantile and investment in a so‐called expectation–quantile–investment (EQI) evaluation. With such approach it is possible to understand the influence of uncertainties in the probabilistic response of adaptation. While adaptation should minimise expected total costs, it needs also to be robust for competitive levels of investment. Transfer curves that relate events with outcomes are used to infer on the probabilistic character of decisions in a case study of a vulnerable location. Results show that EQI‐informed decisions can distinguish optimality in apparently competitive measures. It is shown that decisions based on one‐dimensional or two‐dimensional aspects of this triaxial rationale may fail to identify important probabilistic outcomes of adaptation, such as, the possibility of large losses with relevant probability of occurrence; and that are of high relevance when uncertainty considerations need to be enclosed in the analysis of adaptation.

Finite element based interfacial failure analysis of PVC and laminated FRP composite pipe socket joints subjected to internal pressure

Present study reports a comparison of stress, failure and failure growth behaviour of polyvinyl chloride (PVC) and fiber reinforced plastic (FRP) made pipe socket joints. Finite element based Ansys codes have been developed and validated with experiment and literature based analytical results. Various stress based failure criteria (parabolic yield criterion, and Tsai-Wu failure criteria), and Strain Energy Release Rates (SERRs) as the fracture parameters determined using Virtual Crack Closure Technique (VCCT) have been used to simulate the onset of failure and its growth, respectively. Stress and failure analysis suggested, the pipe-adhesive interface at the junction of the joints to be the most vulnerable location for failure under internal pressure. Pre‐embedded adhesion failure growth along the axial length and circumferential width has been simulated. Adhesion failure growth in axial direction was found more susceptible to mode I failure whereas mode III was dominating in circumferential direction. It was also evident from the studies that axial direction is the dominating direction for adhesion failure growth. Unidirectional ply [90]4 was observed to be the optimum stacking sequence for adhesion failure growth resistance.