This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that ...This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.展开更多
Continuous carbon fiber reinforced silicon carbide(C/SiC)composites are often subjected to low-velocity impacts when utilized as structural materials for thermal protection.However,research on in-plane impact damage a...Continuous carbon fiber reinforced silicon carbide(C/SiC)composites are often subjected to low-velocity impacts when utilized as structural materials for thermal protection.However,research on in-plane impact damage and multiple impact damage of C/SiC composites is limited.To investigate the in-plane impact damage behavior of C/SiC composites,a drop-weight impact test method was developed for strip samples,and these results were subsequently compared with those of C/SiC composite plates.Results show that the in-plane impact behavior of C/SiC strip samples is similar to that of C/SiC composite plates.Variation of the impact load with displacement is characterized by three stages:a nearly linear stage,a severe load drop stage,and a rebound stage where displacement occurs after the impact energy exceeds its peak value.Impact damage behavior under single and multiple impacts on 2D plain and 3D needled C/SiC composites was investigated at different impact energies and durations.Crack propagation in C/SiC composites was studied by computerized tomography(CT)technique.In the 2D plain C/SiC composite,load propagation between layers is hindered during impact,leading to delamination and 90°fiber brittle fracture.The crack length perpendicular to the impact direction increases with impact energy increases,resulting in more serious 0°fiber fracture and a larger area of fiber loss.In the 3D needled C/SiC composite,load propagates between the layers during impact through the connection of needled fibers.The fibers continue to provide substantial structural support,with notable instances of fiber pull-off and debonding.Consequently,the impact resistance is superior to that of 2D plain C/SiC composite.When the 3D needled C/SiC composite undergoes two successive impacts of 1.5 J,the energy absorption efficiency of the second impact is significantly lower,accompanied by a smaller impact displacement.Moreover,the total energy absorption efficiency of these two impacts of 1.5 J is lower than that of a single 3.0 J impact.展开更多
Millet [Pennisetum glaucum (L.) R. Br. (Poaceae)] is one of the most widely consumed crops in Niger. Its production, despite the efforts of farmers, is confronted with weed problems, in particular Sesbania pachycarpa ...Millet [Pennisetum glaucum (L.) R. Br. (Poaceae)] is one of the most widely consumed crops in Niger. Its production, despite the efforts of farmers, is confronted with weed problems, in particular Sesbania pachycarpa DC. (Fabaceae). The aim of the present study in this area is to assess the impact of Sesbania pachycarpa on millet growth and yield. To achieve this objective, a completely randomized Fisher block design of twenty-four elementary plots was set up with four replications. The data collected were millet plant heights and plot yields. The data collected were subjected to analysis of variance and Duncan’s test at the 5% threshold for comparisons of mean heights and yields with the control kept clean from sowing to millet harvesting. The results showed the sensitivity of millet plants to Sesbania pachycarpa. The results revealed that the threshold density for damage could be estimated at 6 Sesbania pachycarpa plants/m2 and the critical interference period at the fourth week after sowing. This study showed that the presence of Sesbania pachycarpa influences millet yield. Indeed, the best yields were obtained in plots without Sesbania pachycarpa. Millet yield decreased with increasing Sesbania pachycarpa density. The average percentage yield reduction was 36.79%, with a minimum of 21.25% and a maximum of 80%. The findings of this study complete the efforts of developing weed control techniques in pearl millet fields densely populated with Sesbania pachycarpa.展开更多
Introduction: In Africa, care during childbirth depends on routine practices to the detriment of quality. The aim of this study was to assess the quality of delivery care at the Coronthie CMC. Methods: The study was c...Introduction: In Africa, care during childbirth depends on routine practices to the detriment of quality. The aim of this study was to assess the quality of delivery care at the Coronthie CMC. Methods: The study was carried out at the Coronthie Community Medical Center. It was a cross-sectional, descriptive and analytical study lasting 6 months, from July 01 to December 31, 2021. Parturients whose term was ≥28 SA and who agreed to participate in the study were included. Excluded were those with a term Results: The frequency of quality care is 36.7%. The average age of parturients was 28.6 ± 5 years. Most parturients (89.7%) were married women with secondary education (35%) and self-employed (32%). Pauciparous women accounted for 43.80%, and most parturients (59.8%) were delivered by Caesarean section. We found that 21.5% of parturients had developed complications. These complications were perineal trauma and post-partum haemorrhage. There were no maternal deaths, and the neonatal mortality rate was 20/1000 NV. Acute fetal distress was the main cause of perinatal death. Conclusion: Correct management of factors influencing childbirth could improve maternal and neonatal prognosis.展开更多
Background: Severe acute malnutrition (SAM) is one of the major public health problems associated with increased mortality in under-five children. In low-income countries, renal dysfunction (RD) contributes to about 3...Background: Severe acute malnutrition (SAM) is one of the major public health problems associated with increased mortality in under-five children. In low-income countries, renal dysfunction (RD) contributes to about 34% mortality in under-five children with severe acute malnutrition. This study aimed to determine the impacts of severe acute malnutrition on the kidney among the admitted under-five children. Methods: In this prospective longitudinal observational study, a total of 190 children aged 6 to 59 months were enrolled from Iringa and Dodoma tertiary hospitals. Socio-demographic, clinical and laboratory data were collected using a structured questionnaire. Estimated Glomerular Filtration Rate (eGFR) and urine albumin creatinine ratio (uACR) were used to determine RD. Data analysis was done using SPSS version 26 and statistical significance was assumed for factors with p-value Results: Out of 190 children with severe acute malnutrition, 36 (19%) had renal dysfunction. Factors associated with RD in malnourished children were the history of local herbs used within one week (AOR = 5.85, 95% CI [1.41, 24.319], p = 0.0152), Acute watery diarrhea with severe dehydration (AOR = 2.15, 95% CI [1.033, 4.711], p = 0.0166), and positive urine leukocytes (AOR = 19.91, 95% CI [4.09, 96.989], p = 0.0002). At three months of follow up, out of 36 children with RD, 20 (55.56%) attained full recovery, while 4 (11.11%) developed chronic kidney disease (CKD). Children with RD had prolonged hospital stays for more than 14 days with a mean 12.25 ± 5.00 days compared to those with no RD with a mean 6.29 ± 1.68 days (p Conclusion: Renal dysfunction is common among children with severe acute malnutrition. It is associated with prolonged hospital stays and increased mortality. Further studies which can determine the burden of RD in children with severe acute malnutrition as compared to those with no severe acute malnutrition are needed.展开更多
Although hunting in the north-eastern Atlantic forest of Brazil began more than 500 years ago, no study to date has evaluated its impacts on the region’s mammalian fauna. For one year we carried out diurnal and noctu...Although hunting in the north-eastern Atlantic forest of Brazil began more than 500 years ago, no study to date has evaluated its impacts on the region’s mammalian fauna. For one year we carried out diurnal and nocturnal surveys using the Line Transect method in seven forest fragments varying from 7.32 ha to 469.76 ha, within a 4000 ha forest island archipelago, in Pernambuco State, Atlantic forest of northeastern Brazil. We calculated species density, population size, biomass and synergetic biomass, and recorded direct and indirect human impacts along the study transects. We recorded 44 mammalian species, of which 45.5% (n = 20) went extinct through hunting. The smallest forest fragment had the lowest richness, diversity, population size, and total biomass. It also had no synergetic biomass. The largest fragment had the highest richness, total density, and population size. There was a statistically significant relationship between fragment area and number of gunshots heard and suspended hunting platforms found;between population size and gunshots heard, suspended hunting platforms, free-roaming and feral dogs, and between total density and free-roaming and feral dogs. After more than 500 years of colonization hunting is still devastating, with larger fragments being linked to more hunters. Higher mammal abundances attracted more free-roaming and feral dogs, which have adapted to hunt wildlife on their own. Unless we protect every single forest fragment and create sustainable landscapes, we will not be able to save this hotspot’s hotspot.展开更多
Coronavirus is a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) caused by a novel coronavirus belonging to the family Coronaviridae. The disease was first discovered in December 2019 in Wuhan City, Hubei...Coronavirus is a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) caused by a novel coronavirus belonging to the family Coronaviridae. The disease was first discovered in December 2019 in Wuhan City, Hubei Province, China. A few months later, the disease spread all over the world and became an epidemic. The infection for most people is mild to moderate but in Vulnerable groups, if they have the infections, they might experience severe COVID-19. Saudi Arabia initiated its response plan early, and all sectors and agencies worked in an integrated way to combat the disease. It has maintained proper communication during the pandemic and ensured community involvement, epidemiologic surveillance, and activation of rapid response teams. The COVID-19 pandemic significantly affected daily lives. Schools and daycares were closed, education was online, traveling stopped, work was suspended, gathering in social activities and practicing religious rituals, like praying or doing Umrah or Hajj, were banded. Changing lifestyles as a response to COVID-19 impacted whole communities with different categories of children, parents, and families. Women usually take the majority of daily responsibilities. The sudden change in lifestyle during COVID-19 put pressure on mothers, especially those who are working to balance work and family obligations. This study aims to identify the impact of Coronavirus disease 2019 on working mothers in Saudi Arabia. Method: Data of the study was collected through survey posted on social media and analyzed through Excel. It focuses on five aspects: health, lifestyle, social relations, work production and financial status. Our target population was working mothers in Saudi Arabia aged at least 25 years. Results: In this study, all factors affected working mothers categorized under two groups: Social Economic Status and Work suspension. For Social Economic Status factors, we find five factors which are monthly income, main breadwinner, number of children at school age, type of housing, and type of work. Almost all mothers include spiritual activities to their routine to cope with stress during this period. About half of our sample have negative impact on their mental health because they are the main breadwinner, and mothers with a smaller number of children at school age have more challenges to cope up. We found that mothers who own a house or work at governmental sector have better outcome of health. After analyzing data related to Work suspension, we found that mothers who have work support have better management for life circumstances, however their health outcomes were negatively affected. In addition, mothers working at education sector have the highest positive impact among other sectors. Our data shows that working mothers’ abilities to follow up with their children decreased. This study recommends that there is need to invest more in working mothers’ research and supportive programs and ensure collaboration globally to address working mothers’ needs and share experiences.展开更多
This article is descriptive research that takes into account the growing concerns of the authorities of the municipality of Coyah regarding waste management, as well as our desire to contribute to improving the living...This article is descriptive research that takes into account the growing concerns of the authorities of the municipality of Coyah regarding waste management, as well as our desire to contribute to improving the living conditions of the inhabitants of this region. The main objective is to assess the environmental impacts of uncontrolled waste collection points on the receiving environments, by characterizing and evaluating them. This will make it possible to propose appropriate measures for rational and sustainable management of the environment in Coyah. The study addresses the characterization and assessment of pollution of receiving environments, including water, soil and air. Environmental analyses were carried out according to standard methods of EPA (1997), adapted to the equipment of the companies Hach, Millipore and Verlan. During the environmental impact assessment, we identified the sources of pollution and assessed the potential impacts. This research highlighted the pollution of receiving environments by waste located in the vicinity of collection points, while considering solutions for efficient and sustainable waste management.展开更多
During times of war, it is rare to find a government willing and able to require the military to fund and support environmental impact studies. In the 1960s, many United States scientists expressed concerns about the ...During times of war, it is rare to find a government willing and able to require the military to fund and support environmental impact studies. In the 1960s, many United States scientists expressed concerns about the use of herbicides during the Vietnam War. This protest was led by Dr. Arthur Galston and eventually included scientists with the National Academy of Science. By 1970, the Department of Defense (DoD) was ordered to permit the scientists to visit South Vietnam during the war to document these impacts. In all 1500 scientist days were spent in South Vietnam. In addition, the US government and military funded research studies on the impact of herbicides on animals. The goal of military use of herbicides, as chemical weapons, was to defoliate jungle forests and destroy food crops as a strategy to win battles and the war. The primary objective of this research study is to describe how it is possible for a country to fund and carry out scientific studies during the conduct of a war rather than decades later. The environmental impact study findings often lack boots on the ground validation and can be inaccurate or misleading in some situations. The United States (US) and other countries, including Russia and Ukraine, need to learn the historical lessons from the US use of herbicides, containing dioxin TCDD and/or arsenic (As), as chemical weapons during the Vietnam War.展开更多
Purpose:For a set of 1,561 Open Access(OA)and non-OA journals in business and economics,this study evaluates the relationships between four citation metrics-five-year Impact Factor(5IF),CiteScore,Article Influence(AI)...Purpose:For a set of 1,561 Open Access(OA)and non-OA journals in business and economics,this study evaluates the relationships between four citation metrics-five-year Impact Factor(5IF),CiteScore,Article Influence(AI)score,and SCImago Journal Rank(SJR)-and the journal ratings assigned by expert reviewers.We expect that the OA journals will have especially high citation impact relative to their perceived quality(reputation).Design/methodology/approach:Regression is used to estimate the ratings assigned by expert reviewers for the 2021 CABS(Chartered Association of Business Schools)journal assessment exercise.The independent variables are the four citation metrics,evaluated separately,and a dummy variable representing the OA/non-OA status of each journal.Findings:Regardless of the citation metric used,OA journals in business and economics have especially high citation impact relative to their perceived quality(reputation).That is,they have especially low perceived quality(reputation)relative to their citation impact.Research limitations:These results are specific to the CABS journal ratings and the four citation metrics.However,there is strong evidence that CABS is closely related to several other expert ratings,and that 5IF,CiteScore,AI,and SJR are representative of the other citation metrics that might have been chosen.Practical implications:There are at least two possible explanations for these results:(1)expert evaluators are biased against OA journals,and(2)OA journals have especially high citation impact due to their increased accessibility.Although this study does not allow us to determine which of these explanations are supported,the results suggest that authors should consider publishing in OA journals whenever overall readership and citation impact are more important than journal reputation within a particular field.Moreover,the OA coefficients provide a useful indicator of the extent to which anti-OA bias(or the citation advantage of OA journals)is diminishing over time.Originality/value:This is apparently the first study to investigate the impact of OA status on the relationships between expert journal ratings and journal citation metrics.展开更多
The pressure and temperature increase resulting from the impact of different threats onto target materials is analyzed with a unified laboratory-scale setup.This allows deriving qualitative information on the occurrin...The pressure and temperature increase resulting from the impact of different threats onto target materials is analyzed with a unified laboratory-scale setup.This allows deriving qualitative information on the occurring phenomenology as well as quantitative statements about the relative effects sizes as a function of target material and threat.The considered target materials are steel,aluminum,and magnesium.As threats,kinetic energy penetrator,explosively formed projectile,and shaped charge jet are used.For the investigated combinations,the measured overpressures vary by a factor of up to 5 for a variation of the material,by a factor of up to 7 for a variation of the threat,and by a factor larger than 15for a simultaneous variation of both.The obtained results as well as the experimental approach are relevant for the basic understanding of impact effects and risks due to material reactivity.The paper combines two main aims.Firstly,to provide a summary of own prior work in a coherent journal article and,secondly,to review and discuss these earlier results with a new perspective.展开更多
Climate change significantly affects environment,ecosystems,communities,and economies.These impacts often result in quick and gradual changes in water resources,environmental conditions,and weather patterns.A geograph...Climate change significantly affects environment,ecosystems,communities,and economies.These impacts often result in quick and gradual changes in water resources,environmental conditions,and weather patterns.A geographical study was conducted in Arizona State,USA,to examine monthly precipi-tation concentration rates over time.This analysis used a high-resolution 0.50×0.50 grid for monthly precip-itation data from 1961 to 2022,Provided by the Climatic Research Unit.The study aimed to analyze climatic changes affected the first and last five years of each decade,as well as the entire decade,during the specified period.GIS was used to meet the objectives of this study.Arizona experienced 51–568 mm,67–560 mm,63–622 mm,and 52–590 mm of rainfall in the sixth,seventh,eighth,and ninth decades of the second millennium,respectively.Both the first and second five year periods of each decade showed accept-able rainfall amounts despite fluctuations.However,rainfall decreased in the first and second decades of the third millennium.and in the first two years of the third decade.Rainfall amounts dropped to 42–472 mm,55–469 mm,and 74–498 mm,respectively,indicating a downward trend in precipitation.The central part of the state received the highest rainfall,while the eastern and western regions(spanning north to south)had significantly less.Over the decades of the third millennium,the average annual rainfall every five years was relatively low,showing a declining trend due to severe climate changes,generally ranging between 35 mm and 498 mm.The central regions consistently received more rainfall than the eastern and western outskirts.Arizona is currently experiencing a decrease in rainfall due to climate change,a situation that could deterio-rate further.This highlights the need to optimize the use of existing rainfall and explore alternative water sources.展开更多
Based on the investigation of mechanical response and microstructure evolution of a commercial 7003 aluminum alloy under high-speed impact,a new simple and effective method was proposed to determine the critical strai...Based on the investigation of mechanical response and microstructure evolution of a commercial 7003 aluminum alloy under high-speed impact,a new simple and effective method was proposed to determine the critical strain required for the nucleation of adiabatic shear band(ASB).The deformation results of cylindrical and hat-shaped samples show that the critical strain required for ASB nucleation corresponds to the strain at the first local minimum after peak stress on the first derivative curve of true stress−true strain.The method of determining the critical strain for the nucleation of ASB through the first derivative of the flow stress curve is named the first derivative method.The proposed first derivative method is not only applicable to the 7003 aluminum alloy,but also to other metal materials,such as commercial purity titanium,WY-100 steel,and AM80 magnesium alloy.This proves that it has strong universality.展开更多
Purpose:This study investigates key factors contributing to research impact and their interactions with the Research Impact Quintuple Helix Model by Arsalan et al.(2024).Design/methodology/approach:Using data from a g...Purpose:This study investigates key factors contributing to research impact and their interactions with the Research Impact Quintuple Helix Model by Arsalan et al.(2024).Design/methodology/approach:Using data from a global survey of 630 scientists across diverse disciplines,genders,regions,and experience levels,Structural Equation Modelling(SEM)was employed to assess the influence of 29 factors related to researcher characteristics,research attributes,publication strategies,institutional support,and national roles.Findings:The study validated the Quintuple Helix Model,uncovering complex interdependencies.Institutional support significantly affects research impact by covering leadership,resources,recognition,and funding.Researcher attributes,including academic experience and domain knowledge,also play a crucial role.National socioeconomic conditions indirectly influence research impact by supporting institutions,underscoring the importance of conducive national frameworks.Research limitations:While the study offers valuable insights,it has limitations.Although statistically sufficient,the response rate was below 10%,suggesting that the findings may not fully represent the entire global research community.The reliance on self-reported data may also introduce bias,as perceptions of impact can be subjective.Practical implications:The findings have a significant impact on researchers aiming to enhance their work’s societal,economic,and cultural significance,institutions seeking supportive environments,and policymakers interested in creating favourable national conditions for impactful research.The study advocates for a strategic alignment among national policies,institutional practices,and individual researcher efforts to maximise research impact and effectively address global challenges.Originality/value:By empirically validating the Research Impact Quintuple Helix Model,this study offers a holistic framework for understanding the synergy of factors that drive impactful research.展开更多
This letter presents a multi-frequency proportional-resonant （MFPR） current controller developed for PWM voltage source converter （VSC） under the unbalanced supply voltage conditions. The delta operator is used in...This letter presents a multi-frequency proportional-resonant （MFPR） current controller developed for PWM voltage source converter （VSC） under the unbalanced supply voltage conditions. The delta operator is used in place of the shift operator for the implementation of MFPR by using a low-cost fixed-point DSE The experimental results with an alternative control strategy validated the feasibility of the proposed MFPR current controller for the PWM VSC during voltage unbalance.展开更多
For radar targets flying at low altitude, multiple pathways produce fade or enhancement relative to the level that would be expected in a free-space environment. In this paper, a new detec- tion method based on a wide...For radar targets flying at low altitude, multiple pathways produce fade or enhancement relative to the level that would be expected in a free-space environment. In this paper, a new detec- tion method based on a wide-ranging multi-frequency radar for low angle targets is proposed. Sequential transmitting multiple pulses with different frequencies are first applied to decorrelate the cohe- rence of the direct and reflected echoes. After receiving all echoes, the multi-frequency samples are arranged in a sort descending ac- cording to the amplitude. Some high amplitude echoes in the same range cell are accumulated to improve the signal-to-noise ratio and the optimal number of high amplitude echoes is analyzed and given by experiments. Finally, simulation results are presented to verify the effectiveness of the method.展开更多
Based on the complexity of mine stratum and coupling of the multi-frequency for the damage of mine stratum,using the method of on-site inspection and mathematical statistics,the regulation and nonlinear characteristic...Based on the complexity of mine stratum and coupling of the multi-frequency for the damage of mine stratum,using the method of on-site inspection and mathematical statistics,the regulation and nonlinear characteristics of strata collapse in mine stratum's multi-frequency mining were put forward and systemically studied.Study result shows that the influence of multi-frequency mining in mine stratum has the feature of multi-frequency incontinuity,multi-characteristic and multi-type nonlinear collapse,strata collapse activa- tion turned worse,presenting an accumulation effect of multi-frequency mining for the strata damage.With the example of multi-frequency mining in the mine,the real characte- ristics of strata collapse by multi-frequency mining and nonlinear characteristics of accu- mulative response damage were analyzed.Research achievements about the surface re- cover and controlling of strata collapse by the multi-frequency mining have instruction meaning.展开更多
The chaotic dynamics of the softening-spring Duffing system with multi-frequency external periodic forces is studied. It is found that the mechanism for chaos is the transverse heteroclinic tori. The Poincaré map...The chaotic dynamics of the softening-spring Duffing system with multi-frequency external periodic forces is studied. It is found that the mechanism for chaos is the transverse heteroclinic tori. The Poincaré map, the stable and the unstable manifolds of the system under two incommensurate periodic forces were set up on a two-dimensional torus. Utilizing a global perturbation technique of Melnikov the criterion for the transverse interaction of the stable and the unstable manifolds was given. The system under more but finite incommensurate periodic forces was also studied. The (Melnikov's) global perturbation technique was therefore generalized to higher dimensional systems. The region in parameter space where chaotic dynamics may occur was given. It was also demonstrated that increasing the number of forcing frequencies will increase the area in parameter space where chaotic behavior can occur.展开更多
基金supported by the National Natural Science Foundation of China(No.52271089)the financial support from the C hina Postdoctoral Science Foundation(No.2023M732192)。
文摘This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched highstrength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher transformation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(BS),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.
基金Aeronautical Science Foundation of China(2021Z057053001)。
文摘Continuous carbon fiber reinforced silicon carbide(C/SiC)composites are often subjected to low-velocity impacts when utilized as structural materials for thermal protection.However,research on in-plane impact damage and multiple impact damage of C/SiC composites is limited.To investigate the in-plane impact damage behavior of C/SiC composites,a drop-weight impact test method was developed for strip samples,and these results were subsequently compared with those of C/SiC composite plates.Results show that the in-plane impact behavior of C/SiC strip samples is similar to that of C/SiC composite plates.Variation of the impact load with displacement is characterized by three stages:a nearly linear stage,a severe load drop stage,and a rebound stage where displacement occurs after the impact energy exceeds its peak value.Impact damage behavior under single and multiple impacts on 2D plain and 3D needled C/SiC composites was investigated at different impact energies and durations.Crack propagation in C/SiC composites was studied by computerized tomography(CT)technique.In the 2D plain C/SiC composite,load propagation between layers is hindered during impact,leading to delamination and 90°fiber brittle fracture.The crack length perpendicular to the impact direction increases with impact energy increases,resulting in more serious 0°fiber fracture and a larger area of fiber loss.In the 3D needled C/SiC composite,load propagates between the layers during impact through the connection of needled fibers.The fibers continue to provide substantial structural support,with notable instances of fiber pull-off and debonding.Consequently,the impact resistance is superior to that of 2D plain C/SiC composite.When the 3D needled C/SiC composite undergoes two successive impacts of 1.5 J,the energy absorption efficiency of the second impact is significantly lower,accompanied by a smaller impact displacement.Moreover,the total energy absorption efficiency of these two impacts of 1.5 J is lower than that of a single 3.0 J impact.
文摘Millet [Pennisetum glaucum (L.) R. Br. (Poaceae)] is one of the most widely consumed crops in Niger. Its production, despite the efforts of farmers, is confronted with weed problems, in particular Sesbania pachycarpa DC. (Fabaceae). The aim of the present study in this area is to assess the impact of Sesbania pachycarpa on millet growth and yield. To achieve this objective, a completely randomized Fisher block design of twenty-four elementary plots was set up with four replications. The data collected were millet plant heights and plot yields. The data collected were subjected to analysis of variance and Duncan’s test at the 5% threshold for comparisons of mean heights and yields with the control kept clean from sowing to millet harvesting. The results showed the sensitivity of millet plants to Sesbania pachycarpa. The results revealed that the threshold density for damage could be estimated at 6 Sesbania pachycarpa plants/m2 and the critical interference period at the fourth week after sowing. This study showed that the presence of Sesbania pachycarpa influences millet yield. Indeed, the best yields were obtained in plots without Sesbania pachycarpa. Millet yield decreased with increasing Sesbania pachycarpa density. The average percentage yield reduction was 36.79%, with a minimum of 21.25% and a maximum of 80%. The findings of this study complete the efforts of developing weed control techniques in pearl millet fields densely populated with Sesbania pachycarpa.
文摘Introduction: In Africa, care during childbirth depends on routine practices to the detriment of quality. The aim of this study was to assess the quality of delivery care at the Coronthie CMC. Methods: The study was carried out at the Coronthie Community Medical Center. It was a cross-sectional, descriptive and analytical study lasting 6 months, from July 01 to December 31, 2021. Parturients whose term was ≥28 SA and who agreed to participate in the study were included. Excluded were those with a term Results: The frequency of quality care is 36.7%. The average age of parturients was 28.6 ± 5 years. Most parturients (89.7%) were married women with secondary education (35%) and self-employed (32%). Pauciparous women accounted for 43.80%, and most parturients (59.8%) were delivered by Caesarean section. We found that 21.5% of parturients had developed complications. These complications were perineal trauma and post-partum haemorrhage. There were no maternal deaths, and the neonatal mortality rate was 20/1000 NV. Acute fetal distress was the main cause of perinatal death. Conclusion: Correct management of factors influencing childbirth could improve maternal and neonatal prognosis.
文摘Background: Severe acute malnutrition (SAM) is one of the major public health problems associated with increased mortality in under-five children. In low-income countries, renal dysfunction (RD) contributes to about 34% mortality in under-five children with severe acute malnutrition. This study aimed to determine the impacts of severe acute malnutrition on the kidney among the admitted under-five children. Methods: In this prospective longitudinal observational study, a total of 190 children aged 6 to 59 months were enrolled from Iringa and Dodoma tertiary hospitals. Socio-demographic, clinical and laboratory data were collected using a structured questionnaire. Estimated Glomerular Filtration Rate (eGFR) and urine albumin creatinine ratio (uACR) were used to determine RD. Data analysis was done using SPSS version 26 and statistical significance was assumed for factors with p-value Results: Out of 190 children with severe acute malnutrition, 36 (19%) had renal dysfunction. Factors associated with RD in malnourished children were the history of local herbs used within one week (AOR = 5.85, 95% CI [1.41, 24.319], p = 0.0152), Acute watery diarrhea with severe dehydration (AOR = 2.15, 95% CI [1.033, 4.711], p = 0.0166), and positive urine leukocytes (AOR = 19.91, 95% CI [4.09, 96.989], p = 0.0002). At three months of follow up, out of 36 children with RD, 20 (55.56%) attained full recovery, while 4 (11.11%) developed chronic kidney disease (CKD). Children with RD had prolonged hospital stays for more than 14 days with a mean 12.25 ± 5.00 days compared to those with no RD with a mean 6.29 ± 1.68 days (p Conclusion: Renal dysfunction is common among children with severe acute malnutrition. It is associated with prolonged hospital stays and increased mortality. Further studies which can determine the burden of RD in children with severe acute malnutrition as compared to those with no severe acute malnutrition are needed.
文摘Although hunting in the north-eastern Atlantic forest of Brazil began more than 500 years ago, no study to date has evaluated its impacts on the region’s mammalian fauna. For one year we carried out diurnal and nocturnal surveys using the Line Transect method in seven forest fragments varying from 7.32 ha to 469.76 ha, within a 4000 ha forest island archipelago, in Pernambuco State, Atlantic forest of northeastern Brazil. We calculated species density, population size, biomass and synergetic biomass, and recorded direct and indirect human impacts along the study transects. We recorded 44 mammalian species, of which 45.5% (n = 20) went extinct through hunting. The smallest forest fragment had the lowest richness, diversity, population size, and total biomass. It also had no synergetic biomass. The largest fragment had the highest richness, total density, and population size. There was a statistically significant relationship between fragment area and number of gunshots heard and suspended hunting platforms found;between population size and gunshots heard, suspended hunting platforms, free-roaming and feral dogs, and between total density and free-roaming and feral dogs. After more than 500 years of colonization hunting is still devastating, with larger fragments being linked to more hunters. Higher mammal abundances attracted more free-roaming and feral dogs, which have adapted to hunt wildlife on their own. Unless we protect every single forest fragment and create sustainable landscapes, we will not be able to save this hotspot’s hotspot.
文摘Coronavirus is a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) caused by a novel coronavirus belonging to the family Coronaviridae. The disease was first discovered in December 2019 in Wuhan City, Hubei Province, China. A few months later, the disease spread all over the world and became an epidemic. The infection for most people is mild to moderate but in Vulnerable groups, if they have the infections, they might experience severe COVID-19. Saudi Arabia initiated its response plan early, and all sectors and agencies worked in an integrated way to combat the disease. It has maintained proper communication during the pandemic and ensured community involvement, epidemiologic surveillance, and activation of rapid response teams. The COVID-19 pandemic significantly affected daily lives. Schools and daycares were closed, education was online, traveling stopped, work was suspended, gathering in social activities and practicing religious rituals, like praying or doing Umrah or Hajj, were banded. Changing lifestyles as a response to COVID-19 impacted whole communities with different categories of children, parents, and families. Women usually take the majority of daily responsibilities. The sudden change in lifestyle during COVID-19 put pressure on mothers, especially those who are working to balance work and family obligations. This study aims to identify the impact of Coronavirus disease 2019 on working mothers in Saudi Arabia. Method: Data of the study was collected through survey posted on social media and analyzed through Excel. It focuses on five aspects: health, lifestyle, social relations, work production and financial status. Our target population was working mothers in Saudi Arabia aged at least 25 years. Results: In this study, all factors affected working mothers categorized under two groups: Social Economic Status and Work suspension. For Social Economic Status factors, we find five factors which are monthly income, main breadwinner, number of children at school age, type of housing, and type of work. Almost all mothers include spiritual activities to their routine to cope with stress during this period. About half of our sample have negative impact on their mental health because they are the main breadwinner, and mothers with a smaller number of children at school age have more challenges to cope up. We found that mothers who own a house or work at governmental sector have better outcome of health. After analyzing data related to Work suspension, we found that mothers who have work support have better management for life circumstances, however their health outcomes were negatively affected. In addition, mothers working at education sector have the highest positive impact among other sectors. Our data shows that working mothers’ abilities to follow up with their children decreased. This study recommends that there is need to invest more in working mothers’ research and supportive programs and ensure collaboration globally to address working mothers’ needs and share experiences.
文摘This article is descriptive research that takes into account the growing concerns of the authorities of the municipality of Coyah regarding waste management, as well as our desire to contribute to improving the living conditions of the inhabitants of this region. The main objective is to assess the environmental impacts of uncontrolled waste collection points on the receiving environments, by characterizing and evaluating them. This will make it possible to propose appropriate measures for rational and sustainable management of the environment in Coyah. The study addresses the characterization and assessment of pollution of receiving environments, including water, soil and air. Environmental analyses were carried out according to standard methods of EPA (1997), adapted to the equipment of the companies Hach, Millipore and Verlan. During the environmental impact assessment, we identified the sources of pollution and assessed the potential impacts. This research highlighted the pollution of receiving environments by waste located in the vicinity of collection points, while considering solutions for efficient and sustainable waste management.
文摘During times of war, it is rare to find a government willing and able to require the military to fund and support environmental impact studies. In the 1960s, many United States scientists expressed concerns about the use of herbicides during the Vietnam War. This protest was led by Dr. Arthur Galston and eventually included scientists with the National Academy of Science. By 1970, the Department of Defense (DoD) was ordered to permit the scientists to visit South Vietnam during the war to document these impacts. In all 1500 scientist days were spent in South Vietnam. In addition, the US government and military funded research studies on the impact of herbicides on animals. The goal of military use of herbicides, as chemical weapons, was to defoliate jungle forests and destroy food crops as a strategy to win battles and the war. The primary objective of this research study is to describe how it is possible for a country to fund and carry out scientific studies during the conduct of a war rather than decades later. The environmental impact study findings often lack boots on the ground validation and can be inaccurate or misleading in some situations. The United States (US) and other countries, including Russia and Ukraine, need to learn the historical lessons from the US use of herbicides, containing dioxin TCDD and/or arsenic (As), as chemical weapons during the Vietnam War.
文摘Purpose:For a set of 1,561 Open Access(OA)and non-OA journals in business and economics,this study evaluates the relationships between four citation metrics-five-year Impact Factor(5IF),CiteScore,Article Influence(AI)score,and SCImago Journal Rank(SJR)-and the journal ratings assigned by expert reviewers.We expect that the OA journals will have especially high citation impact relative to their perceived quality(reputation).Design/methodology/approach:Regression is used to estimate the ratings assigned by expert reviewers for the 2021 CABS(Chartered Association of Business Schools)journal assessment exercise.The independent variables are the four citation metrics,evaluated separately,and a dummy variable representing the OA/non-OA status of each journal.Findings:Regardless of the citation metric used,OA journals in business and economics have especially high citation impact relative to their perceived quality(reputation).That is,they have especially low perceived quality(reputation)relative to their citation impact.Research limitations:These results are specific to the CABS journal ratings and the four citation metrics.However,there is strong evidence that CABS is closely related to several other expert ratings,and that 5IF,CiteScore,AI,and SJR are representative of the other citation metrics that might have been chosen.Practical implications:There are at least two possible explanations for these results:(1)expert evaluators are biased against OA journals,and(2)OA journals have especially high citation impact due to their increased accessibility.Although this study does not allow us to determine which of these explanations are supported,the results suggest that authors should consider publishing in OA journals whenever overall readership and citation impact are more important than journal reputation within a particular field.Moreover,the OA coefficients provide a useful indicator of the extent to which anti-OA bias(or the citation advantage of OA journals)is diminishing over time.Originality/value:This is apparently the first study to investigate the impact of OA status on the relationships between expert journal ratings and journal citation metrics.
文摘The pressure and temperature increase resulting from the impact of different threats onto target materials is analyzed with a unified laboratory-scale setup.This allows deriving qualitative information on the occurring phenomenology as well as quantitative statements about the relative effects sizes as a function of target material and threat.The considered target materials are steel,aluminum,and magnesium.As threats,kinetic energy penetrator,explosively formed projectile,and shaped charge jet are used.For the investigated combinations,the measured overpressures vary by a factor of up to 5 for a variation of the material,by a factor of up to 7 for a variation of the threat,and by a factor larger than 15for a simultaneous variation of both.The obtained results as well as the experimental approach are relevant for the basic understanding of impact effects and risks due to material reactivity.The paper combines two main aims.Firstly,to provide a summary of own prior work in a coherent journal article and,secondly,to review and discuss these earlier results with a new perspective.
文摘Climate change significantly affects environment,ecosystems,communities,and economies.These impacts often result in quick and gradual changes in water resources,environmental conditions,and weather patterns.A geographical study was conducted in Arizona State,USA,to examine monthly precipi-tation concentration rates over time.This analysis used a high-resolution 0.50×0.50 grid for monthly precip-itation data from 1961 to 2022,Provided by the Climatic Research Unit.The study aimed to analyze climatic changes affected the first and last five years of each decade,as well as the entire decade,during the specified period.GIS was used to meet the objectives of this study.Arizona experienced 51–568 mm,67–560 mm,63–622 mm,and 52–590 mm of rainfall in the sixth,seventh,eighth,and ninth decades of the second millennium,respectively.Both the first and second five year periods of each decade showed accept-able rainfall amounts despite fluctuations.However,rainfall decreased in the first and second decades of the third millennium.and in the first two years of the third decade.Rainfall amounts dropped to 42–472 mm,55–469 mm,and 74–498 mm,respectively,indicating a downward trend in precipitation.The central part of the state received the highest rainfall,while the eastern and western regions(spanning north to south)had significantly less.Over the decades of the third millennium,the average annual rainfall every five years was relatively low,showing a declining trend due to severe climate changes,generally ranging between 35 mm and 498 mm.The central regions consistently received more rainfall than the eastern and western outskirts.Arizona is currently experiencing a decrease in rainfall due to climate change,a situation that could deterio-rate further.This highlights the need to optimize the use of existing rainfall and explore alternative water sources.
基金National Natural Science Foundation of China (No. U20A20275)Natural Science Foundation of Hunan Province,China (No. 2021JJ40096)。
文摘Based on the investigation of mechanical response and microstructure evolution of a commercial 7003 aluminum alloy under high-speed impact,a new simple and effective method was proposed to determine the critical strain required for the nucleation of adiabatic shear band(ASB).The deformation results of cylindrical and hat-shaped samples show that the critical strain required for ASB nucleation corresponds to the strain at the first local minimum after peak stress on the first derivative curve of true stress−true strain.The method of determining the critical strain for the nucleation of ASB through the first derivative of the flow stress curve is named the first derivative method.The proposed first derivative method is not only applicable to the 7003 aluminum alloy,but also to other metal materials,such as commercial purity titanium,WY-100 steel,and AM80 magnesium alloy.This proves that it has strong universality.
基金approved by our institutional Research Ethics Committee(HREC Approval Number H13554).
文摘Purpose:This study investigates key factors contributing to research impact and their interactions with the Research Impact Quintuple Helix Model by Arsalan et al.(2024).Design/methodology/approach:Using data from a global survey of 630 scientists across diverse disciplines,genders,regions,and experience levels,Structural Equation Modelling(SEM)was employed to assess the influence of 29 factors related to researcher characteristics,research attributes,publication strategies,institutional support,and national roles.Findings:The study validated the Quintuple Helix Model,uncovering complex interdependencies.Institutional support significantly affects research impact by covering leadership,resources,recognition,and funding.Researcher attributes,including academic experience and domain knowledge,also play a crucial role.National socioeconomic conditions indirectly influence research impact by supporting institutions,underscoring the importance of conducive national frameworks.Research limitations:While the study offers valuable insights,it has limitations.Although statistically sufficient,the response rate was below 10%,suggesting that the findings may not fully represent the entire global research community.The reliance on self-reported data may also introduce bias,as perceptions of impact can be subjective.Practical implications:The findings have a significant impact on researchers aiming to enhance their work’s societal,economic,and cultural significance,institutions seeking supportive environments,and policymakers interested in creating favourable national conditions for impactful research.The study advocates for a strategic alignment among national policies,institutional practices,and individual researcher efforts to maximise research impact and effectively address global challenges.Originality/value:By empirically validating the Research Impact Quintuple Helix Model,this study offers a holistic framework for understanding the synergy of factors that drive impactful research.
基金Project (No. 50577056) supported by the National Natural Science Foundation of China
文摘This letter presents a multi-frequency proportional-resonant （MFPR） current controller developed for PWM voltage source converter （VSC） under the unbalanced supply voltage conditions. The delta operator is used in place of the shift operator for the implementation of MFPR by using a low-cost fixed-point DSE The experimental results with an alternative control strategy validated the feasibility of the proposed MFPR current controller for the PWM VSC during voltage unbalance.
基金supported by the National Natural Science Foundation of China(6137213661372134+2 种基金61172137)the Fundamental Research Funds for the Central Universities(K5051202005)the China Scholarship Council(CSC)
文摘For radar targets flying at low altitude, multiple pathways produce fade or enhancement relative to the level that would be expected in a free-space environment. In this paper, a new detec- tion method based on a wide-ranging multi-frequency radar for low angle targets is proposed. Sequential transmitting multiple pulses with different frequencies are first applied to decorrelate the cohe- rence of the direct and reflected echoes. After receiving all echoes, the multi-frequency samples are arranged in a sort descending ac- cording to the amplitude. Some high amplitude echoes in the same range cell are accumulated to improve the signal-to-noise ratio and the optimal number of high amplitude echoes is analyzed and given by experiments. Finally, simulation results are presented to verify the effectiveness of the method.
基金the National Natural Science Foundation of China(50604009)Open Research Project of State Key Laboratory of Coal Resources & Safe Mining(CUMTB)(2007-09)+3 种基金Liaoning Technical University Science Research Foundation(04A01009)Natural Science Research Foundation of Liaoning Province(20022158202183392)Liaoning Technical University Open Research Foundation Program of the Geomantics & Application Provincial Level Key Laboratory(2004014)
文摘Based on the complexity of mine stratum and coupling of the multi-frequency for the damage of mine stratum,using the method of on-site inspection and mathematical statistics,the regulation and nonlinear characteristics of strata collapse in mine stratum's multi-frequency mining were put forward and systemically studied.Study result shows that the influence of multi-frequency mining in mine stratum has the feature of multi-frequency incontinuity,multi-characteristic and multi-type nonlinear collapse,strata collapse activa- tion turned worse,presenting an accumulation effect of multi-frequency mining for the strata damage.With the example of multi-frequency mining in the mine,the real characte- ristics of strata collapse by multi-frequency mining and nonlinear characteristics of accu- mulative response damage were analyzed.Research achievements about the surface re- cover and controlling of strata collapse by the multi-frequency mining have instruction meaning.
文摘The chaotic dynamics of the softening-spring Duffing system with multi-frequency external periodic forces is studied. It is found that the mechanism for chaos is the transverse heteroclinic tori. The Poincaré map, the stable and the unstable manifolds of the system under two incommensurate periodic forces were set up on a two-dimensional torus. Utilizing a global perturbation technique of Melnikov the criterion for the transverse interaction of the stable and the unstable manifolds was given. The system under more but finite incommensurate periodic forces was also studied. The (Melnikov's) global perturbation technique was therefore generalized to higher dimensional systems. The region in parameter space where chaotic dynamics may occur was given. It was also demonstrated that increasing the number of forcing frequencies will increase the area in parameter space where chaotic behavior can occur.
