The mechanical behavior of concrete under biaxial loading condition  is one of the most important indexes to evaluate the quality of concrete. To study the mechanical behavior of concrete under biaxial compression at mesoscale, we adopted our recently developed 3D numerical model based on Voronoi tessellation and cohesive elements. A constitutive model considering the friction effect is used in the model to characterize the fracture behavior of all potential fracture surfaces inside the concrete. A series of numerical experiments with different biaxial compression stress ratios were carried out. It was found that with the increase of the biaxial compression ratio, the proportion of energy increment caused by friction stress increases. The effect of inner friction coefficient on the biaxial relative strength was also investigated, and this kind of study is hard to be carried out through laboratory experiments. The results show that the inner friction coefficient has a great influence on the biaxial relative strength of concrete, and there is a positive correlation between these two parameters. Based on the above rules, a conservative biaxial relative compression strength envelope is obtained by setting the inner friction coefficient as zero. In the design of concrete structures, the biaxial strength and fracture behavior are very important. To reveal the mechanism of the concrete biaxial fracture, researchers have carried out a series of experiments ,4,5,6,7,To study the mechanical behavior of concrete at mesoscale, we should establish an effective numerical model firstly. In recent years, many researchers have studied the meso behavior of concrete through different numerical models. The first issue to build up the numerical model is the generation of the aggregates. Two typical aggregate-generating methods have been proposed. The first method is to generate aggregates by randomly throwing the geometries ,12,13,14Besides the method mentioned above, a modified finite element method with cohesive elements is beginning to be used by more and more researchers ,42,43,44Based on our previous research works about the numerical model with cohesive element ,44, in tDue to the good shape of generated polyhedrons and the stability of calculation, Voronoi tessellation ,46 is anBased on the generated aggregates, we can easily obtain the aggregate-mortar two-phase mesostructure. However, this two-phase structure is too simple to characterize the complex fracture behavior of concrete. Thus, a more effective numerical model should be established.Cohesive element, as a special element type in the FE method, was developed to characterize the interface behavior of the traditional solid elements. This element can only transfer normal and shear stresses, and this characteristic is very suitable to characterize the mechanical behavior of fracture surfaces. The calculation thickness of cohesive element is also independent to its geometry thickness, and the geometry thickness can be set to any positive value, including zero, which means this element is very suitable to represent the components with extremely small thickness in concrete, such as ITZ. According to these characteristics, we chose zero thickness cohesive element to characterize the ITZ and potential fracture surfaces of concrete.According to the algorism proposed in references ,47,48, tTo characterize the mechanical behavior of ITZ and potential fracture surfaces (represented by cohesive elements), we adopted the modified constitutive model presented in our previous work with consideration of the friction effect between fracture surfaces , based oIn the 3D case, one normal stress (relation .6 GPa in this paper.There are two phases that exist in the stresses–displacements relation: (1) elastic phase; (2) nonlinear phase. In the elastic phase, the relation between the stresses and displacements can be expressed as: done in ,38,39, wThe nonlinear phase initiates when the following condition is met:As shown in The initial damage and failure surfaces are defined in the modified constitutive model to reflect the combined effect of normal and tangential damage. These two surfaces can be expressed as:According to the two damage surfaces mentioned above and the bilinear model, we can obtain the modified bilinear model with consideration of normal-tangential coupling effect. D can be calculated through:Based on the relation between damage factor and displacements, the damage factor lacement , and we ous work ). Thus, without considering the friction effect, the relation between stresses and displacements can be expressed as:To better understand the relation between the stresses and displacements, a 3D stresses-displacements map is shown in When the damaged area of cohesive element (fracture surfaces) is under compression, the friction occurs. The friction stress The tangential deformation displacement Thus, the orthogonal contents of friction stress can be rewritten as:Finally, the stresses of the cohesive element can be calculated through:Based on the constitutive model mentioned above, we can analyze the internal fracture situation by extracting the energies consumed inside the cohesive elements during the loading process. According to the stresses defined in the constitutive, three kinds of energy can be extracted, namely (1) the normal stress work caused by normal stress, (2) the shear stress work caused by shear stress, (3) the friction stress work caused by friction stress. These three kinds of energies can be calculated by:3. In this paper, we mainly study the fracture behavior of the concrete under biaxial compression. According to the previous works ,6,7,8,9,The loading scheme of the concrete specimen is shown in According to the previous works ,4,5,6,7,The mesh of the specimen is shown in According to the previous works about cohesive element model ,42,43,44All numerical experiments were ended when the displacement d1 = 1.5 mm, corresponding to the macro strain ε = 0.01. Since the deformation of solid elements is small, and the strains of cohesive elements are equal to their displacements , the small deformation formulation  is used. The numerical samples are solved in ABAQUS/EXPLICIT  solver with the user subroutine VUMAT . By deleIn this paper, the potential fracture surfaces are represented by the pre-inserted cohesive elements, which means the cracks are forced to propagate following the faces of solid elements. For this reason, it is important to investigate the impact of mesh density on the simulation results. A test of mesh convergence was carried out, and models with different mesh densities are shown in The simulation results of Mesh I and Mesh II are shown in To ensure the quasi-static loading condition, the smooth step  is choseThe stress–strain curves of concrete under different biaxial compression conditions are shown in The fracture pattern (d1 = 1.5 mm) of concrete specimens under different loading conditions are shown in To investigate the fracture modes, the energy analyses were carried out. To analyze the effect of the biaxial-loading ratio on the concrete fracture mode in terms of energy, we extracted the energy increments at the pre-peak stage, and these are listed in Here we investigate the effect of inner friction coefficient on the biaxial strength envelope. Since the inner friction coefficient has a great effect on the biaxial relative strength envelope, we carried out a group numerical tests with zero inner friction coefficient to find out the biaxial compressive capacity of concrete without inner friction, and this kind of test is impossible to carry out in laboratory condition. As shown in In this paper, we build up a 3D meso model of concrete based on the Voronoi tessellation and cohesive element. A modified cohesive constitutive model considering the inner friction effect is applied in the model. Based on the proposed model, the biaxial compression behavior of concrete was investigated by analyzing the fracture pattern and energy evolution. The numerical results show an agreement with the experimental one. Several conclusions can be obtained.(1) Inner friction (the friction effect which exists in the closed fracture surfaces inside the concrete) has a great effect on biaxial relative compression strength envelope. The relative strength increases with the increase of inner friction coefficient. (2) A conservative biaxial relative compression strength envelope is obtained through a group of numerical tests with zero inner friction coefficient. This biaxial relative strength envelope can be used as a reference in the design of concrete structures.In this study, we mainly investigate the effect of inner friction on the concrete biaxial compression behavior. However, there are still many issues need to be studied on the basis of this research. For example, the fracture behavior of concrete under other complex loading conditions is still worth studying, and we can carry out a series of numerical tests to reveal its meso-mechanism.


To study the effect of redispersible polymer emulsion powder on the mechanical properties of carbon fiber-reinforced polymer concrete (CFRPC), the compressive, flexural, and splitting tests of CFRPC specimens with different polymer–cement ratios (polymer–cement mass ratios) were performed in this study. The modification effect of emulsion powder on CFRPC was analyzed from the perspectives of the strength and deformation properties of the specimens. The results show that the static properties of CFRPC increased first and then decreased with the increase of the polymer–cement ratio, in which the splitting tensile strength had the most significant increase; the flexural strength took second place and the compressive strength had a slight increase. When the polymer–cement ratio was 8%, the flexural and splitting tensile strength of the CFRPC specimens increased significantly by 36% and 61%, respectively. According to electron microscopy images, adding emulsion powder can effectively improve the structure of fiber–matrix transition zones and enhance the bond property between fibers and the matrix. Due to the good strength and constructability, concrete is widely used in construction engineering as an important building material. However, ordinary concrete still has some limitations, such as poor crack resistance and low tensile and flexural strength . ConsideEmulsion powder is a type of powder binder with the advantages of high cohesive force, plasticity, and construction . In receAt present, there are few studies on the composite modified concrete of carbon fiber and polymer at home and abroad. Based on the above problems, redispersible emulsion powder was added into concrete to effectively increase the cementation of cement paste matrix ,14,15. TBased on this, static mechanical tests of CFRPC specimens with 0.1% carbon fiber content (volume ratio of carbon fiber to concrete) were conducted with a electro-hydraulic servo material test system. By testing the compressive, flexural, splitting tensile strength, and peak strain of specimens, different polymer–cement ratios were studied from the perspective of strength and deformation properties. The influence of the polymer–cement ratio on the compressive, splitting, and flexural properties of CFRPC was studied. The modification mechanism of emulsion powder was discussed based on the observation of the micro-morphology. In addition, concrete specimens with 0.2% carbon fiber content were performed as supplementary experiments. The reliability of the test results was verified by comparing the relationship between the static mechanical properties and polymer–cement ratio of concrete with two kinds of carbon fiber contents.The specific technical route is shown in 3, bulk density was 1600 kg/m3, and mud content was 0.2%. Ordinary river sand with a fineness modulus of 2.8, a bulk density of 1503 kg/m3, and a mud content of 1.5% was taken as the fine aggregate. A 42.5 grade ordinary Portland cement was used in the test. Running water was used to mix the cement, and the water quality met the testing standard. Well-graded limestone rubble less than 20 mm was used as coarse aggregate, and the bulk density was 2700 kg/m12H24O3) was used. Dispersant can reduce carbon fiber aggregation during concrete mixing. Hydroxyethyl cellulose (C2H6O2·x) dispersant was used, which is a white or yellowish, tasteless, non-toxic, fibrous or powdered solid, prepared by etherification of basic cellulose and ethylene oxide (or chloroethanol).Concrete additives (<5% of the cement mass) were added in the process of mixing concrete to improve its performance. Specifically, a water-reducing agent is a kind of concrete additive that can reduce the water consumption of concrete while keeping the slump of concrete basically unchanged. As a brown powder, a FDN superplasticizer water-reducing agent mother liquor was used, which was a multi-naphthalene nuclear sulfonated sodium sulphate with sulfuric acid after naphthalene sulfonation, with condensation by formaldehyde afterwards. Defoamer is a kind of concrete additive that can reduce surface tension and restrain or eliminate froth. Metal soap defoamer was used, which was composed of aluminum stearate, calcium stearate, potassium oleate, and calcium oleate. A film-forming additive can promote plastic flow and elastic deformation of polymer compounds and, thus, improve the coalescence properties. The DN-12 film-forming additive , then dispersant was added with a slow stir. When the solution became a uniform gel, the solution was cooled to room temperature without stirring. Then, chopped carbon fibers were slowly added into the dispersant solution, stirring continued for approximately 10 min. After that, a water reducing agent, defoamer, and film-forming additive were added; the solution was then stirred at low speed for 60 s. Finally, the carbon fiber dispersion with good dispersion was prepared.Redispersible polymer emulsion powder was manually mixed with cement until the powder was evenly dispersed. Fine aggregate and half of the carbon fiber dispersion liquid were poured into a concrete blender and stirred for 60 s. Coarse aggregate was added and stirred for 60 s; dispersed powder was added to the blender and stirred for 60 s; then, the remaining carbon fiber dispersion liquid was added and stirred for 60 s. The weighed defoamer was poured into the blender and stirred for 120 s. Then, the concrete was poured out of the mixer and manually poured for 60 s until the required slump was obtained. The standard curing was performed for 28 days after the model was loaded and vibrated.The static test of concrete was carried out using the HYY electro-hydraulic servo material test system. Three test methods were used, including compressive test, splitting test and flexural test of concrete. The specimen was a cube with a side length of 100 mm. Nova NanoSEM230 field emission scanning electron microscopy (produced by the American FEI Company) was used to observe the micro-morphology of specimen slices. Compressive test: the instrument was used to apply load uniformly on the cured specimens at a loading speed of 0.5–0.8 MPa/s until the specimens were damaged and the corresponding load was recorded;Splitting test: The preserved specimen, pad block, pad strip, and bracket were placed and installed in line with the requirements. Then, the hydraulic tester was used to apply load on the specimen uniformly at a loading speed of 0.05~0.08 MPa/s until the specimen failed; the corresponding failure load and displacement were recorded;Flexural test: the cured specimen, support, and hard steel cylinder were placed and installed in line with the requirements, referring to the method for the splitting test.Mechanical test details are as follows . The HYYTo reduce factors associated with accidental errors, three specimens were tested in each group.To observe the specimen’s dimension under the scanning electron microscope, certain requirements should be observed. Accordingly, cured CFRPC specimens were cut from the middle into several cubes with side lengths of no more than 15 mm . Cubic specimens were selected according to the following requirements: (1) complete shape; (2) smooth surface; and (3) aggregate and the substrate can be observed. Then these samples were further polished by the sandpaper, after which they were cleaned and sealed in the bag for later use.−3 Pa) in the sample chamber was required for the normal operation of the scanning electron microscope. However, there are many internal pores in the CFRPC sample, which increases the difficulty of vacuuming. Accordingly, these specimens were dried in the oven for 6 hours at 50 °C. Disregarding the doped chopped carbon fiber in the CFRPC material, the overall conductivity was still poor in the dry state. Therefore, gold spraying on the observation surface of the specimen was implemented to facilitate observation under the scanning electron microscope. A vacuum  is better than that of carbon fiber-reinforced concrete. It also proves the rationality of mixing two modifiers (polymer emulsion powder and carbon fiber). The test results were basically consistent with previous research ,15,21. TThus, the properties of the carbon fiber–cement interface are greatly improved. The continuous phase is formed at the interface between carbon fiber and cement, and the thickness of the substrate at the contact surface of carbon fiber is increased, which increases the bonding strength between carbon fiber and the substrate. Finally, the concrete under load carbon fiber is not easily pulled out so that the performance of carbon fiber can be fully utilized. In conclusion, when two kinds of modifiers are rationally mixed, the effect of the modifier on the compressive strength of concrete is obviously better than any single modifier; when two kinds of modifiers are unreasonably mixed , the negative effects of the modifier will be superimposed. For instance, if the carbon fibers and polymers were excessively added, the compressive strength of the specimens is lower than that of the specimens with the single modifier.When two kinds of modifiers are mixed reasonably, the effect of the carbon fiber and polymer on concrete is more significant than that of the single modifier. This can be explained from two perspectives. On the one hand, the active ingredients contained in the polymer can effectively improve the working performance of concrete, and help fibers disperse well in concrete; thus, the deformability of concrete is improved ,23. On tThe test results show that the tensile–compressive ratio and the flexural–compressive ratio of concrete increased significantly when the carbon fiber and polymer emulsion powder were added reasonably. It indicates that carbon fiber and polymer emulsion powder have a more significant effect on the tensile strength and flexural strength of concrete than the compressive strength. This can be explained as follows. The modification mechanism of short-cut carbon fibers and polymer emulsion powder for concrete is that high tensile strength materials (carbon fibers and polymer films) are used to cross the cracks and transfer stress to both ends of the cracks ,30,31. BIn this paper, compressive, flexural, and splitting tests for CFRPC specimens with different polymer–cement ratios were carried out using an HYY electro-hydraulic servo material test system. The influence of the polymer–cement ratio on the mechanical properties of CFRPC was studied from the aspects of strength and deformation performance, and the modification mechanism of emulsion powder was discussed. The main conclusions are as follows.With the increase in the polymer–cement ratio, the peak compressive strain of the specimens increased continuously, and the compressive strength of the specimens first increased first then decreased. When the polymer–cement ratio was 12%, the compressive strength of the specimens decreased, compared with specimens without emulsion powder.With the increase in the polymer–cement ratio, the flexural and splitting properties of the specimens first increased and then decreased. Within the range of raw material proportions in this paper, the optimum polymer–cement ratio was 8%.By adding emulsion powder, the splitting tensile strength of CFRPC had a most significant increase, followed by flexural strength, while the compressive strength increased slightly, even decreasing at a high dosage.Scanning electron microscopy (SEM) results show that the emulsion powder tended to form a film in CFRPC and enhanced the bond strength between the fiber and the matrix. In this way, the tensile crack resistance of the fiber can be fully utilized.


After oxidation, pearlites in the vermicular graphite cast iron are decomposed into ferrite and cementite at high temperatures.The oxidation mechanism of vermicular graphite cast iron was studied. The oxidation reaction starts from graphites and diffused slowly. Graphites in vermicular graphite are interconnected, coral-like clusters, providing the main oxidation core and channel. The worm-like graphites on the surface are mostly oxidized and form oxide affected zones. The oxide films are composed of a loose oxide layer with the phases of Fe Vermicular graphite cast iron is a kind of transition state cast iron with transition forms between flake and spheroidal graphite. It is a new engineering material with fine mechanical properties, thermal conductivity, and section conductivity. Its strength, plasticity, and toughness are superior to that of gray iron. Its castability, thermal fatigue properties, and heat conductivity are better than those of ductile iron ,2,3. TheHowever, at high temperatures, vermicular iron is badly oxidized, sometimes causing serious economic loss and security risks. Its application conditions are more and more severe with the rapid development of modern industry. Oxidation has become a significant apparent danger in the application of vermicular iron. According to Ref. , the autThe compositions of vermicular graphite cast iron were C (wt%): 3.8%, Si (wt%): 2.1%, Mn (wt%): <0.2%, Mo (wt%): 0.2%, S (wt%): <0.03%, P (wt%): <0.05%, Fe (wt%): residual.Mg-Re alloys were the vermiculizer. Their compositions were Re (wt%): 14%, Si (wt%): 39%, Fe (wt%): 41.9%, Mg (wt%): 2.5%, Ca (wt%): 1.9%.Since the work temperature of a cylinder head is 530 °C, in order to be close the operating conditions, the oxidation experiment was performed in a muffle furnace set at 530 °C. The size of the test bars was Φ15 mm × 30 mm; they were washed in acetone. The microstructure of the vermicular graphite cast iron was observed via JSM-6700F scanning electron microscopy . The phase compositions of the oxide films were tested via XRD-7000S X-ray diffraction (XRD) diffractometer . Three-dimensional XRT morphology of graphite in vermicular graphite was determined by Xradia Versa XRM-500 . Before oxidation, when the vermicular rate was 89%, the surface of vermicular graphite cast iron was composed of vermicular graphite and spherical graphite without oxidation, as shown in An analysis of element area distributions is shown in In order to determine the growth process of the oxidation layer, the cross-section morphologies of vermicular graphite cast iron at different oxidation times were observed, as shown in 2) of the passivation layer is slightly increased compared with the original size (L0) of the sample, as shown in When vermicular iron was oxidized for 500 h, the oxidation layer thickness reached about 40 μ m. As shown in (a) The cross section of the passivation layer and the oxidation layer does not migrate significantly with the extension of time, so it can be considered that this cross section is the original surface before oxidation.2+ diffuses to the outside, being oxidized to form FexOy on the interface between the oxide film and the atmosphere, which leads to the oxide film growing outwards gradually and the size of the sample increasing. Meanwhile, as O2− diffuses inward through the oxide layer and Fe2+ and Si4+ diffuse outward, FeO and Fe2SiO4 are generated at the metal-oxide film interface, so the passivation layer can gradually grow inward [(b) The oxide film grows outwards and inwards simultaneously, with the oxide layer growing outwards and the passive layer growing inwards. This is because the Few inward ,11,12,13It can be seen from Except for some small graphites, the volumes of individual coral graphites are difficult to detect, and the 2-dimensional structure of an isolated graphite eutectic cell form is difficult to evaluate in 3- dimensional structure. Therefore, the greater the interface area, the greater the diffusion rate of oxygen, leading to a high oxidation rate ,18,19,20Meanwhile, concerning graphite, much more oxidation product appears, as shown in 2O3 is dense and exhibits flakes and needle-like structures. Fe3O4 shows a grain-shape, but is difficult to observe on the surface microstructure since it is dispersed under the needle-shapes and flakes of Fe2O3.2O3, Fe3O4, and Fe2SiO4. The oxidation reactions are as follows: 2Fe + O2 = 2FeO, 3Fe + 2O2 = Fe3O 4, and FeO + O2 = Fe2O3. 2Fe + O2 + SiO2 = Fe2SiO4. The inside closing to the vermicular iron matrix is the passivation layer with dense FeO and Fe2SiO4 [The phase compositions of vermicular iron were studied at different times, as shown in  Fe2SiO4 ,29,30,313O4, Fe2O3, and FeO, and a passivation layer with FeO and Fe2SiO4. Graphites in vermicular graphite are interconnected, coral-like clusters, providing the oxygen channel. After oxidation, pearlites are decomposed into ferrite and cementite at high temperatures. Meanwhile, regarding graphite, many more oxidation products appeared.The oxidation mechanism of vermicular graphite cast iron was studied in this paper. The oxidation reaction started from graphite and diffused slowly to the Fe substrate. The worm-like graphites on the surface were mostly oxidized, and there were oxide affected zones with serious oxidation from the edge to the center. The oxidation reaction started from graphites and diffused slowly. From the exterior to the interior, the oxide layers were mostly composed of Fe


Escherichia coli exposed to long-term low-shear modeled microgravity and background antibiotic exposure” (I read with interest the paper recently published by Tirumalai et al. entitled “Evaluation of acquired antibiotic resistance in xposure” . That paxposure” , 2. Undexposure” . If infeMy colleagues and I have previously shown that exposure to both ionizing  and noniIn summary, although the paper by Tirumalai et al. addresses an important topic, its conclusions must be evaluated in terms of the issues noted in this letter. Extrapolating the results obtained in the very specific environment addressed in that study to other environments is not likely to yield credible results in view of the issues summarized in my comments.


Antibiotic resistance is a global problem that threatens human and animal health and has increased in recent years. Although many factors are responsible for the development of resistance, antibiotics used in animals for preventive, therapeutic, and other purposes play a major role. Conscious and rational antibiotic use in animals will contribute to decreases in resistance. It is therefore important to determine knowledge, attitudes, and behaviors of farmers working in the livestock sector with regard to antibiotic knowledge, use, and resistance in order to develop communication strategies accordingly. The aim of this study was to measure the knowledge of livestock farmers about antibiotics by conducting a questionnaire survey. As a result of the survey, it was found that knowledge of the participants on antibiotics and resistance was very low. It was concluded that periodic training programs can be employed to overcome this problem and raise awareness among farmers.The aim of this study was to determine knowledge, attitudes, and behaviors of farmers dealing with animal husbandry in eastern Turkey with regard to antibiotic knowledge, use, and resistance. A face to face questionnaire survey, consisting of five sections with 42 questions in total, was applied to 360 farmers located in the region. The questions in the first and fifth sections were closed-ended while those in other sections were prepared using the Likert scale. It was determined that knowledge of the farmers about antibiotic use, duration, storage, and resistance was well below desired levels. This was particularly remarkable in the participants with a low level of education, living in rural areas, and those at 48 years of age or over. In contrast, younger and highly educated participants living in urban areas were more knowledgeable about antibiotic use and they were well aware of the fact that resistance might pose a great risk for public health. Providing appropriate antibiotic use in animals through systematic training of livestock farmers is crucial in tackling the resistance problem. The discovery of antibiotics commonly used in the treatment and control of infectious diseases caused by microorganisms has been an important milestone for human health. Many infections, especially epidemics that have been a major threat to human life in the past and have caused high mortality, have been brought under control following the use of antibiotics . SimilarAs in many countries, intensive efforts such as legal arrangements are being made in Turkey to combat antibiotic resistance. Although e-prescription and a drug tracking system for veterinary drugs was officially established in 2018, the system is not fully settled down due to the lack of adequate infrastructure. Veterinarians working both in public and private clinics continue to make prescriptions without entering the e-prescription system and animal owners continue to receive the drugs they wish from the clinics.Campylobacter, Escherichia coli, Salmonella, Enterococcus spp., etc.) in the intestines of animals can be transferred to humans [The increase in drug resistant bacterial infections in humans has led to studies on monitoring and controlling of all possibly responsible factors. In this context, animal products are another important factor with a role in resistance. Antimicrobial drugs are used extensively for the prevention, control, and treatment of diseases in animals ,11. AntiEthical approval was obtained from Scientific Research and Publication Ethics Committee, Bingol University. The consent of selected farmers were sought and obtained after explaining the purpose of the study (with protocol 11.07.2019-E.13913).2 surface area. Bingol province is suitable for cattle breeding due to its geographical structure and most of the local people live work in livestock production. In the study region, both beef and dairy cattle breeding are common and most of the animals are mixed breeds. Approximately 1% of the national cattle population of the country (n = 17 million) is present in Bingol. Most of the enterprises in the province are family type managements and the average number of animals in each enterprise is 12.A questionnaire survey was carried out in cattle farms located in Bingol province and its central villages, in eastern Turkey, covering 1814 kmThe sample size was calculated by using Raosoft sample volume calculation method based on a 5% error rate, 95% reliability level, and 50% response distribution . The samBefore conducting the survey in the field, a pilot study was carried out with 25 randomly selected animal owners who applied to the clinics of Bingol Veterinary Faculty in order to test the clarity, reliability, and validity of the questionnaire. Following this study, the questionnaire was revised and finalized in accordance with suggestions and data were collected in the study population. The questionnaire, which consisted of five sections and 42 questions, was constructed by taking into consideration the questions of the WHO organization and previous similar studies ,14,15,16The first part of the questionnaire includes five questions concerning demographic information, the second part includes nine questions measuring general information about antibiotics, the third part includes 10 questions in relation to antibiotic use, the fourth part includes 10  questions with respect to antibiotic resistance, and the final part includes eight questions about duration of antibiotic use and storage. While the questions in the first and fifth sections were closed-ended, the questions in the second, third, and fourth sections were prepared using five point Likert scale response options. The questionnaire was applied to the farmers by the face to face survey method by trained and experienced researchers.The internal consistency of answers given to the questions which were prepared according to the 5-point Likert scale was measured with reliability analysis. The Cronbach’s α, which is a numerical coefficient of reliability, was determined as 0.68, 0.64, and 0.73, respectively for the questions asked in the second (antibiotic knowledge level), third (antibiotic use), and fourth (antibiotic resistance) sections.t test was used for comparison of “place of residence”. The Levene test was performed to determine the homogeneity of variances. The results were presented as mean ± standard deviation (SD) and p < 0.05 was considered as statistically significant. Pearson correlation analysis was performed to determine the direction and degree of the relationship between the mean scores of the second, third, and fourth sections. IBM SPSS 22.0 for Windows  was used for statistical analyses. GraphPad Prism for Windows version 5.0  was used to create charts. The stacked bar charts for Likert scales were created using Tableau 8.2 .The scores  obtained from the answers given by the participants to the questions in the second, third, and fourth sections were collected and the section scores were calculated. The participant scores taken from each section were compared with one-way analysis of variance (ANOVA) for “educational status”, “age”, and “the time spent as farmer” while an independent Analysis of demographic parameters showed that the vast majority of the participants were male, primary school graduates, at the age of 48 years or more, and were engaged with animal breeding for at least 11 years. On the other hand, the percentages of female, university graduate, and younger (18–32 years old) cattle farmers were rather low .p < 0.001). Antibiotic knowledge of the participants with associate degrees and/or bachelor degrees was also significantly higher when compared to those without education (p < 0.001). Antibiotic knowledge level of the residents in urban areas was detected to be significantly higher than those living in rural areas (p < 0.05)  .p < 0.001). Also, younger farmers (18–22 years old) had higher knowledge level on antibiotic use than older ones (48 years or older) (p < 0.001)  .p < 0.001). There was a moderately positive correlation between mean scores of antibiotic knowledge and antibiotic use (r (359) = 0.55, p < 0.001) (p < 0.001)  A. Also, < 0.001) B.The vast majority (41%) of the participants stated that they stored antibiotics in the barn/farm. The highest duration of antibiotic use among the farmers was three days with approximately 66%. The rate of residual antibiotic use for treatment of other sick animals was 67%. Interestingly more than 90% of the respondents expressed that they did not receive any training about antibiotic use, residues, and resistance .https://www.fda.gov/animal-veterinary/development-approval-process/fact-sheet-veterinary-feed-directive-final-rule-and-next-steps) there was no legal obstacle toward the use of antibiotics in animals as a growth factor in the US, the use of antibiotics in animals for this purpose was prohibited in 2016 in the European Union countries. Within the framework of the harmonization laws of the European Union, Turkey started to apply this ban on the same date. For this reason, antibiotics used as growth factors are not produced or imported in the country. However, it is interesting to note that some farmers (41%) participating in this study believed that antibiotics can be used to improve weight gain in animals. This finding indicated that although antibiotics for growth promotion are not marketed, other antibiotics are likely to be used for this purpose. It is therefore necessary for the authorized institutions to apply stricter rules in order to prevent the use of antibiotics for growth promotion.Many factors play a role in the increasing development of antibiotic resistance, thus threatening public health by becoming a national and global problem. Prophylactic and therapeutic antibiotics commonly used in animals draw attention as one of the most important factors. Knowledge, attitudes, and behaviors of livestock farmers regarding the use of antibiotics in animals play a significant role in the development of antibiotic resistance. However, previous reports indicated that a significant portion of the farming community do not have sufficient information about antibiotic knowledge, antibiotic use, and resistance ,16,17,18In this study, in addition to the knowledge on antibiotic use, the participants were observed to have insufficient awareness in terms of rational use of antibiotics. Approximately half of the respondents stated that when their animals became ill they used antibiotics they had readily available before they contacted the veterinarian. In a study conducted by Sudershan et al.,  the rateAs a matter of fact, the practices in dairy farms in India show that knowledge and beliefs are transferred from one generation to another . ChauhanAfter antibiotic resistance has reached serious levels, many organizations and countries, especially WHO, have spent great efforts to develop strategies for the prevention of resistance and raising awareness. For this purpose, many activities such as posters, informational advertisements, and meetings have been organized to educate the public and health workers. In fact, studies showed that healthcare workers were quite aware of the resistance problem ,21,22. HOne of the factors that facilitates antibiotic resistance is the use of antibiotics below the treatment dose and the failure to comply with the duration of treatment. It has been demonstrated by previous studies that people in the community have stopped and adjusted the antibiotic dose on their own initiative . In our A significant relationship between knowledge of antibiotic use and the level of education and other demographic factors such as the region of residence has been shown in previous studies ,26,27. OIn conclusion, this survey revealed viewpoints of cattle breeders located in eastern Turkey on antibiotic knowledge, use, and resistance which may help the authorities to draw a direction toward taking necessary steps in order to minimize antibiotic resistance. Periodic educational programs are urgently needed to train farmers in order to raise awareness about antibiotics, rational drug use, and resistance with particular attention to public health as well as alternative approaches such as vaccination, environmental protection, and preventive medicine. In addition, necessary measures should be taken by the authorities to limit and control the use of veterinary drugs. It is suggested that many aspects of the problem of antibiotic resistance can be overcome by identifying and communicating effectively with all stakeholders. In addition, there may be a need for some surveillance of antibiotic use and antimicrobial resistance.


Service-Learning (SL) has become a teaching methodology that promotes social and personal skills while helping groups in need and at risk of social exclusion. This paper is a systematic review of the literature on SL experiences and research on college subjects in the area of health-care promotion in settings for older adults. After an exhaustive search, 43 peer-reviewed publications were classified according to frequency and geographical distribution, sample and duration of the programs, research methodologies, data collection instruments used, and main outcomes investigated. The results indicate that the research methodologies used tended to be qualitative and mixed, while the variety of samples and duration of interventions was very broad. The instruments used were mainly interviews and questionnaires, and the programs were developed specially in the United States of America. The groups receiving most SL were healthy older adults and older adult populations with aging disabilities and illnesses. The articles in the present review highlight that SL can have a positive effect on older adults’ health promotion and can enhance their community participation. The World Population Ageing report  concludeThis might be alleviated with the increase of general knowledge related to gerontology, as well as supporting issues related with well-being, active aging, and physical and mental health in aged people . IntergeSL is a pedagogical methodology that establishes a genuinely operational relationship between theory and practice and provides students with the opportunity to learn while contributing to the community. SL combines learning and community service, based on the application of skills and reflective understanding of curriculum content in real contexts, experientially, and with the aim of improving students’ critical skills while offering a social benefit .The increase in SL has roused great interest in educators at all levels and academic disciplines. Consequently, a multitude of studies examining its impact have been implemented, particularly in higher education . Due to SL requires great deal of effort and attention in the specific field of health-care promotion and community participation. It is important to note that the American College of Sports Medicine highlights the need to have some basic knowledge in working with different collectives while focusing on health promotion and community participation . For thiThis study presents a systematic review of the literature focused on higher education SL aimed at achieving benefits associated with health promotion and community participation among older adults. There is substantial literature on the beneficial impact of volunteering on older adults, much of which helps older adults . HoweverConcerning the conjunction of work among older adults and SL, Roodin et al.  have preThe present review is therefore structured around the following descriptive categories: Frequency with which SL articles on older adult populations are published, geographical distribution of papers, sample and duration of the programs, research methodologies employed, data collection instruments used, and the main outcomes investigated. Knowing the main advantages and disadvantages involved in these dimensions before starting a program can be critical for SL success.Because there have been some critiques of previous reviews that have not adopted a transparent and reproducible search protocol , we wereAfter identifying the problem, two main search strategies were used. The first step consisted of a search in two of the most respected databases in the field of social sciences and education: (ISI)-Thomson Reuters and Scopus-Elsevier. From these, we considered all peer-reviewed publications from the 21st century, that is, between 2001 and July 2019. Due to the variety of the terminology used in the literature, we sought to identify multiple terms to capture the intersection of ideas for our review. All of the publications therefore had to contain at least one term related to the following concepts: ‘Service-learning’ ; ‘health’ ; ‘higher education’ ; and ‘older adults’ . The search strings consisted of a combination of the terms for each concept, which were scanned for in titles, keywords, and abstracts.Finally, as a second step, the reference lists of all retrieved articles were reviewed to identify the possible existence of other interesting publications on the subject of SL in the field of health and higher education with older adults. The reason for choosing articles from the last 19 years was to highlight selected existing studies and trends from the current century.The selection of the literature to be reviewed was based on four general criteria: Quality, relevance, educational level, and topicality. Papers that did not meet these criteria were excluded from further consideration. Regarding quality and relevance, the first filter was the academic nature of the database where the articles were found and the accomplishment of the PRISMA literature search procedure. The format of each item also had to meet the standardized scientific criteria by being empirical, narrative, or reasoned, with well-defined objectives, methodologies, and designs containing valid and recognized studies. Regarding educational level and topicality, the search was directed solely at SL programs in the field of health care that had college students as the learners and older adults as service receivers.The results of the search for the selected articles should also respond to the type of research and/or application carried out through the SL experience in a field related to the subjects of health with older adults, excluding internships, scholarships, or volunteering. A team of four researchers applied the inclusion criteria. To ensure reliability in the application of the criteria, this research occurred after a one-day moderation. For the most part, the decision to include articles was relatively straightforward, because there was clear evidence of whether the papers were aligned (or not) with the review’s purpose.The initial search within the two databases yielded 753 potentially relevant articles. After reviewing title, keyword, and abstract information, the sample of potential articles was reduced to 141. No other interesting publications were found among their reference lists. There were 38 repeated publications, 16 records were excluded because they were abstracts that did not provide enough data, and 44 articles did not meet the inclusion criteria, leaving 43 articles for review. Each of the papers in the final sample was classified according to the following descriptive categories: Frequency and geographical distribution, sample and duration of the program, research methodology, data collection instruments used, and main outcomes investigated. The PRISMA literature search methodology is graphically represented in According to the publication dates, the results do not show clear patterns in terms of frequency . The mosAnother aspect that should be noted is the geographical distribution of the programs, because this will reveal the world’s leading research centers for college SL involving health promotion among aged people. The majority of articles (83.7%) were developed in the United States. Apart from this, the rest of the sample does not show more relevant patterns.SL programs may vary widely depending on features such as aim, service learners, scope of action, or service receivers. We may note a disparity in both the number of students giving service and the number of elders receiving it. In terms of the former, this number of individuals ranges from 16 in the works of Fruhauf et al.  and SingIn terms of the length of the programs and sessions involved in the investigations, it is worth noting the complexity of classification and analysis due to the varying information provided in each text. The majority of papers present studies or experiences that are part of larger programs, as in the cases of Timmermans et al.  or LynchSeveral differences appeared among the research methodologies. In this sense, Creswell  differenRegarding our sample, 34.8% of the publications employed a qualitative method, whereas 13.9% used a quantitative approach. In addition, nearly half of the sample (46.5%) used a mixed approach. The remaining two papers (4.8%) do not evince any type of methodology because they are devoted to a description of experiences  and a piMoreover, in this field it is important to analyze whether the effects of SL remain or disappear over time for both populations, service providers and service receivers. In this sense, only four out of 43 articles  used long-term designs.The instruments used to gather the data are another relevant aspect. A total of 30 articles employed surveys and/or questionnaires. Specifically, there were four articles that only used standardized questionnaires ,29,42,43The main objectives addressed by researchers can be principally divided into two areas of interest: The effects of SL on the students who provide the service and the impact on the older adults who receive it. The majority of the articles (65.1%) generated results related to the college students. A wide range of aspects was considered, for example, Andreoletti and Howard , AugustiIn addition, 25.6% of the sample examines both older adults and college students ,31,38,41At this point, it is important to note that only four studies used long-term designs (4.6%), two analyzed community service involvement and positive attitudes on students ,33, and It is noteworthy that one of the articles examines the particular effects of SL on the program as a pedagogical process , and twoFinally, seven articles (16.3%) refer to the general satisfaction with the SL program, four of them (9.3%) indicate that college students were satisfied, whereas three (7%) refer to the older adults’ general satisfaction. The synthesis of all of papers that met the inclusion criteria for this review is presented in According to the data obtained in this systematic review, higher education SL has been used on a number of occasions for health-care promotion among older adults and to encourage community participation. The experiences that constitute the sample enabled both college students and older adults to overcome stereotypes and biases to gain multigenerational perspectives, which triggered an improvement of mutual understanding and cohesion while favoring older adults’ wellness. However, there are many alternatives through which this area of study might be improved by future researchers and to provide better SL programs addressing issues related with the health of aged people.The analysis of the literature shows that the frequency with which SL articles on older adult populations have been published does not follow a gradual development, although it is a recurring topic since the beginning of the 21st century. The programs described may vary widely depending on features such as study methodology, duration and intensity of the SL program, location, service learners or service receivers, and scope of action. There is great diversity in terms of program length, but the most repeated ones were programs lasting one semester and providing 20 hours of service, which is a result consistent with the reviews made by Chiva-Bartoll et al.  or CopacRegarding the type of research methodology employed in settings that opt for SL as a way to promote health care among older adults, there is a clear predisposition towards qualitative or mixed approaches. This result is in line previous literature on SL ,60 and rIn the pedagogical context it is important to know the lasting effects of the SL programs implemented. This systematic review found four long-term studies published, two referring to attitudes of college students ,33, one The main issues investigated in the papers analyzed in this systematic review may be classified into two categories: Those relating to students and those relating to older adults. Some studies reported positive results in learning outcomes related to the personal perceptions of students, as well as the acquisition of professional skills. The benefits to college students are positive and well documented : The knoIn general, the majority of published results report better social stimulation and understanding of young people after a SL intervention and the general satisfaction of older adults. In addition, a program managed by Zucchero  with a pThe literature review shows that the United States is a country with a great tradition and proven experience in SL. Indeed, the term SL was first used in the United States by Ramsay et al. in 1967 , and theAccording to the political dimension of civic activities, college students might become more quickly and profoundly aware of the benefits of voluntary service among older adults thanks to their own SL experience. The result may be a progressive increase of college students implementing SL with older adults and, consequently, developing social cohesion between these two groups of people. Another important aspect is the wide variety of differentiating aspects among SL programs and the scope of action in which are implemented ,9, incluTo conclude, consistent with Novak et al.  and Warr


Eonset) in CV is observed with Ru-POSS compared to trisruthenium(II) complex (Ru(bpy)32+). From the series of mechanistic studies, it was shown that adsorption of Ru-POSS onto the ITO electrode enhances TPrA oxidation and subsequently the efficiency of ECL with lower voltage. Moreover, oxygen quenching of ECL was suppressed, and it is proposed that the enhancement to the production of the TPrA radical could contribute to improving oxygen resistance. Finally, the ECL-based detection for water pollutant is demonstrated without the degassing treatment. The commodity system with Ru(bpy)32+ is not applicable in the absence of degassing with the sample solutions due to critical signal suppression, meanwhile the present system based on Ru-POSS was feasible for estimating the amount of the target even under aerobic conditions by fitting the ECL intensity to the standard curve. One of critical disadvantages of ECL can be solved by the hybrid formation with POSS.We report the oxygen-resistant electrochemiluminescence (ECL) system from the polyhedral oligomeric silsesquioxane (POSS)-modified trisruthenium(II) complex (Ru-POSS). In electrochemical measurements, including cyclic voltammetry (CV), it is shown that electric current and ECL intensity increase in the mixture system containing Ru-POSS and tripropylamine (TPrA) on the indium tin oxide (ITO) working electrode. The lower onset potential ( ECL hed state . Meanwhied state ,8,9, foled state ,11,12. TPolyhedral oligomeric silsesquioxane (POSS) attracted attention as an “element-block” which is the minimum unit containing heteroatoms for constructing functional materials ,14. We rInspired by the enhancement of environmental resistance of POSS without losses of stimuli responsiveness, we presume that oxygen resistance in ECL systems might be reinforced. On the basis of this assumption, we synthesize the modified POSS tethered to the trisruthenium(II) complex (Ru-POSS) and evaluate the influence of dissolved oxygen on the ECL properties in the aqueous mixture system containing tripropylamine . Initially it is shown that ECL intensity and electric current can be enlarged by the connection to POSS. Moreover, from the comparison studies, it is clearly indicated that ECL quenching by oxygen is suppressed in the Ru-POSS/TPrA system. We elucidate how this phenomenon could originate from the improvement of TPrA oxidation by Ru-POSS adsorption onto the ITO electrode. Finally, we also accomplish the ECL-based detection for the water pollutant without the degassing pretreatment. The oxygen-resistance enhancement and target detection which tend to show the trade-off relationship are compatible by employing the POSS element-block.1H NMR spectrum. Purification with Ru-POSS was only precipitation and Ru-POSS was obtained as mixtures containing variable numbers of the Ru complex. The structures of synthesized compounds were confirmed by 1H, 13C and 29Si NMR spectroscopies and high-resolution mass spectrometry (HRMS). The detailed procedures are shown in the 32+, Ru(bpy)2(dmbpy)2+ (dmbpy = dimethylbipyridine) and tripropyl amine (TPrA), are listed in The chemical structures and preparation of the Ru(II)-containing materials involving Ru-POSS and the model compound, Ru-Model are shown in 3MLCT) in the Ru(II) complex moiety [32+, critical reduction of electric currents was obtained  in the oxidative wave of the CV curves 32+. Although it was reported that the substituent effect can decrease Eonset [Eonset could exist. Additionally, even in the absence of TPrA, lower Eonset values were obtained from the Ru(II)-containing materials except for Ru(bpy)32+ 32+ and Ru-Model. To understand the roles of POSS in these changes, further experiments were executed.The cyclic voltammograms and corresponding ECL profiles in the TPrA co-reactant system are shown in V curves . Obviouse Eonset , the deg(bpy)32+ , proposi32+ and Ru-Model 32+ in the presence of Amino-POSS under the same condition as above -containing molecular species in the solution  at 1.2 V vs. Ag/AgCl, it was also observed that a larger current was able to be generated from Ru-POSS than those of Ru(bpy)Ru-Model . In partas above . It was solution . The rednolayers ,28,29, pl-lysine ,31,32, al-lysine . It is lEonset, it was reported that modification of ITO electrodes with CNT [Regarding the lowering with CNT , poly generated by the TPrA oxidation can contribute to reducing of the amount of DO near the ECL reaction layer and subsequently can suppress ECL quenching [To obtain further insight regarding the detailed mechanism and the role of POSS in enhanced oxygen resistance, we performed measurements under various conditions. It was shown that the connection of the Ru(II) complex was necessary for expressing oxygen resistance in the former section . From thA system  [12,40,432+/TPrA system was too small to discriminate the target, meanwhile critical decrease in emission intensity was detected from the Ru-POSS sample, meaning that the existence of OTC was able to be detected even in the aerobic sample. In particular, the linear relationship between ΔIECL and the concentration in the range from 1.3 × 10−5 to 2.0 × 10−4 M (R2 = 0.993) was obtained when using Ru-POSS. The limit of detection was 9.8 × 10−6 M (S/N = 3). It was suggested that ECL quenching may be caused by oxidized OTC at the electrode, which is a benzoquinone derivative [−6 and 10−9 M order [Because ECL is usually obtained from the triplet-excited state, most conventional ECL systems always suffer from emission quenching by DO in the pristine sample. Therefore, degassing for lowering DO levels in the sample was previously needed in practical usage. To demonstrate the advantage of oxygen-resistant ECL based on Ru-POSS, we finally performed the detection without degassing as a pre-treatment. By evaluating the decrease in ECL intensity, the target concentration was determined ,47,48,49rivative . Benzoqu M order , howeverEonset in CV was lowered compared to Ru(bpy)32+. Moreover, ECL quenching by oxygen was suppressed in the Ru-POSS/TPrA system. From our mechanistic studies, adsorption of Ru-POSS to the ITO electrode, followed by efficient TPrA oxidation on the ITO electrode were suggested. Finally, oxygen quenching was compensated by generation of the TPrA radical. Our findings and materials could be a scaffold for developing future sensing technologies based on ECL, such as real-time monitoring for small molecular pollutants which it is difficult to detect with conventional environment sensors. Furthermore, compared to the conventional system, the oxygen-resistance can be improved by connecting to POSS at this stage. As mentioned in the introduction, POSS has significant properties for capturing hydrophobic molecules under aerobic conditions. In combination with the unique capturing property of the POSS unit, improvement of sensitivity and selectivity for the target detection might be proposed.We demonstrate the Ru(II) complex-modified POSS and its application for oxygen-resistant ECL system. By employing POSS, various beneficial effects were obtained. Electronic currents and ECL intensities were enhanced in the electro- and optical measurements, and


The formation and decomposition of inclusion compounds with a solid-solid phase transition may be very selective to the guest molecular structure. This selectivity may function in essentially different ways than defined by the classical concept of molecular recognition, which implies the preferential binding of complementary molecules. Solid inclusion compounds may take part as an initial or/and final state in several processes of different types summarized in this review, which selectivity is boosted by cooperativity of participating molecular crystals. Some of these processes resemble switching electronic devices and can be called smart giving practically absolute molecular recognition. Molecular recognition of neutral molecules is one of the key problems in chemical technologies and in analytical and biotechnological applications  component has an ability to induce the host crystallization. The mixture should have the concentration of this guest above a certain threshold value for this crystallization to be apparent, A vs. relative vapor pressure P/P0” coordinates  in mol of guest per 1 mol of host, C is a sorption constant, N is a cooperativity parameter, which in ideal case of phase transition should have an infinitely high value, N → ∞. The integration of sigmoidal sorption isotherms fitted by this equation gives the inclusion Gibbs energy ΔGc of guest transfer from its pure liquid or solid state to the saturated inclusion compound  means the stepwise selectivity of guest inclusion. If two guests have very small difference in molecular structure, but the first guest has sorption constant S at the variation of the guest molecular structure, tert-butylcalix[4]arene including a lot of guests inside its molecular cavity  may give another type of selectivity. This is the selective formation of stable intermediate clathrates, An example of absolute molecular recognition of benzene by a number of guest inclusion steps was observed for tetra(ethoxycarbonyl)methoxy thiacalix[4]arene carbamoylmethoxy) tert-butylthiacalix[4]arene .An ideal case for molecular recognition is the host ability to form two polymorphs: stable and metastable ones, tert-butylcalix[6]arene is less selective breaking the studied guest compounds into two groups: (1) remembered guests inducing formation of metastable polymorphs, and (2) non-remembered guests without such ability (Yakimov et al., tert-butylcalix[6]arene may be used in the analysis of binary mixtures if at least one of their components is from the first group. The efficiency of this analysis was demonstrated using DSC for the binary mixtures with one (Safina et al., For comparison, Guest-induced metastable polymorphs of calixarenes capable of an exothermic solid-phase transition have also a potential in 100% separation of binary mixtures of close homologs (Morohashi et al., The phenomenon of polymorphism is more variable than the examples given in this review. In many cases, metastability of a polymorph is in its lower melting point than that of the stable form. Such polymorphs may have more than one melting point with an intermediate exothermic cold crystallization to the more stable forms (Gataullina et al., Cooperativity of guest inclusion by solid host with phase transition provides specific types of selectivity for neutral guest compounds that cannot be observed in liquid solutions. In some cases, this selectivity gives practically absolute molecular recognition and may be called smart because it uses the host polymorphism with a very selective and easily detectable memory of the guest included and released. Besides, of the same molecular recognition level is the very selective formation of stable intermediate inclusion compounds, which may be detected by mass-sensitive sensor and in thermogravimetric curves. This process resembles a smart switch of the initial host crystals recognizing only one guest or few guest compounds.The specific types of structure-property relationships and molecular recognition caused by phase transition at guest inclusion and release may be expected for any solid host capable of clathrate formation. Still, discovery of the host-guest systems with a genuine selectivity for neutral molecules requires an extensive screening, which success cannot be predicted.VG supervised the project and mainly wrote the paper. AG and MZ co-wrote the paper. All authors discussed the reviewed results and commented on the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


MVC_backf, body weight, walking speed, and ramp angle was established. This model may be used to determine the work/rest allowance for backpacking tasks under conditions similar to this study.Manual material handling (MMH) tasks create a burden for workers which could result in musculoskeletal injuries. Assessments of the decrease of muscular strength and the maximum endurance time (MET) for MMH tasks are essential in studying the ergonomic risk of MMH tasks. A backpacking experiment was conducted for measuring the MET for MMH tasks. Human participants carried a load on their back and walked on a treadmill under various load, walking speed, and ramp angle conditions until they coud no longer do so. It was found that the participants were able to walk for approximately 15 min to two hours before they needed to have a pause. Their back and leg strengths declined moderately due to performing the tasks. These tasks resulted in an increase in heart rate and elevated perceived physical exertion. The rating of perceived exertion (RPE)/heart rate ratio in our backpacking tasks was 31% higher than that in the literature, implying the calibration of the RPE may be required for such tasks. A MET model incorporating the  Body pain and discomfort due to undesirable conditions such as overexertion and unnatural postures are common at work. Based on labor insurance claim data, reported injuries in the neck, shoulder, and upper extremity of workers in Taiwan increased 5.2 times in a twelve-year period 2001–2013), while lower back injuries increased 1.7 times [–2013, whManual material handling (MMH) tasks are major contributors of musculoskeletal injuries in workplaces ,4,5. DetMuscular fatigue is a common phenomenon for physical activities. It may be defined as the reduction in the ability to exert muscle force or power ,9,10,11,k) for an individual or for a certain population should be incorporated when predicting the progress of muscular fatigue. The reciprocal of this parameter, or 1/k, was termed fatigue resistance [p < 0.0001) higher k than female participants. Muscular decrease models incorporating the concept of fatigue rate have also been employed in both one- and two-handed carrying tasks [Ma et al.  suggestesistance . Zhang esistance  assessedng tasks ,22. MVCf = %MVC/100), as independent variable [In addition to the study of muscular strength, assessment and modeling of maximum endurance time (MET) have also been beneficial to studying muscular fatigue. The MET represents the maximum time during which a static muscular load can be maintained . It has variable ,35,36,37MVCf. Their results indicated that both body weight and walking speed were important parameters in predicting the MET when walking was considered, especially when the MVCf was 0.3 or lower. Most MET models in the literature were developed for static contractions. However, most tasks involving static contractions for certain body segments in industry are accompanied by dynamic or cyclic activities of other body parts. Li et al.  conducteMuscular fatigue issues for one- and two-handed carrying tasks have been discussed ,22,35. BA carrying experiment was performed in a laboratory. The temperature and relative humidity were 21.1 (±2.4) °C and 65.1 (±9.7)%, respectively. A total of 16 adults  participated in the experiment. The participants were healthy without self-reported history of musculoskeletal disorders within a year. Their age, stature, and body weight (BW) were 21.7 (±2.6) years, 169.5 (±5.6) cm, and 63.0 (±11.4) kg, respectively. Signed informed consent was obtained from every participant before participating in the study. The participants were compensated 150 NTD per hour for their participation in the experiment. This study has been reviewed and approved by an external IRB .A treadmill which allows adjustment of inclination was used. In addition, an isometric strength measurement unit was adopted. This unit contains a platform, a chain with a handle, and a loadcell. It allows measurements of isometric back strength and isometric leg strength. This unit had been adopted in previous studies ,22. A BoCarrying a load weighing 25% of their BW is common for firefighters, police officers in special missions , and eveThree walking speeds were tested, including 2 km/h, 4 km/h, and 6 km/h. The walking speed was controlled by the settings on the treadmill. The inclination of the treadmill can be adjusted. Two levels of treadmill inclination were tested. The first one was flat or a 0° ramp angle condition. The second was a 10° uphill condition. backMVC. For the isometric leg strength, the participant bent his/her knee with upper body straight to grasp the handle 38 cm above the platform and pulled upward with maximum force. This force was the legMVC. The procedure performing these strengths measurements followed those in Ayoub and Mital [Before the trial, the isometric back, and leg strengths were measured. For these measurements, the participant stood on a platform and pulled a handle connected to the platform upward. A loadcell was hooked between the handle and the platform to measure the force. The participant applied his/her maximum force for 4 to 6 seconds. The peak force was displayed and recorded. For isometric back strength, the participant stood and bent his/her waist to grasp the handle 38 cm above the platform and pulled upward with maximum force see . This fond Mital . The parbHR) and immediately after the walk (aHR) were recorded. The time of walking was recorded as the maximum endurance time (MET). After the walk, the participant’s RPE was immediately recorded. He or she then unloaded the backpack and was tested for his/her isometric back and leg strengths. These back and leg strengths were termed backaMVC and legaMVC, respectively. The participant joined the test only once per day to avoid the effects of fatigue. In the experiment, the participant was requested to carry a backpack with a predetermined weight and walk on the treadmill under a predetermined ramp angle and walking speed see . The ordMVCf [MVCf, BW, walking speed, and ramp angle:v is walking speed (km/h) and θ is ramp angle (degree). Backpacking tasks involve both load carrying and walking. Load carrying on the back requires static contraction mainly on the back. Walking, on the other hand, involves dynamic contractions especially on the lower limbs. For static muscular contraction, the MET is dependent on the fMVC ,31,36,37fMVC ,44,45. TMVCf considering ramp angle and multiplicative effects of BW and walking speed, as in Equation (2): MVC_backf is the MVCf on back muscles; β1, β2, β3, and β4 are coefficients to be determined. Both power and exponential functions have been proposed in MET modeling ,37,46,47Equation (2) may be converted to a linear equation by taking natural logarithm on both sides:MVC_backf was calculated by dividing the weight carried by the backMVC. The following equations were adopted to calculate the decline (%) of isometric back and leg strengths:There was a total of 288 trials . The aHR, MET, RPE, and declines of both back and leg strengths. Regression analysis was performed to determine the regression coefficients in Equation (3). The statistical analyses were performed using the SAS 9.4 software . Descriptive statistics and analyses of variance (ANOVA) were performed for the bHR and aHR were 85.5 (±10.3) bpm and 112.3 (±21.1) bpm, respectively. The difference between these two was statistically significant (p < 0.0001). This corresponds to an increase of 26.8 bpm on average. Walking and carrying depletes our energy. Theoretically, the energy expenditure for such an activity results in increase of heart rate and decrease of muscular strength. Sixteen participants joined our backpacking experiment. Their anthropometric characteristics are shown in The RPE values averaged for each weight carried, walking speed, and ramp angle were between 11.9 and 17.6, with an overall average of 15.1 (±2.9). An RPE of 15 corresponds to “hard” on the RPE scale. The decreases of the back strengths, averaged over each weight carried, walking speed, and ramp angle condition were between −1.1% and 9.9%. The corresponding leg strength decreases were between −1.7% and 9.1%. The strength decreases (%) on the back and the leg for performing the backpacking tasks are shown in p < 0.0001), ramp angle (p < 0.05), and walking speed (p < 0.0001). The effects of gender were not statistically significant. The mean MET values for the 0, 12.5% and 25% BW conditions were 89.3, 61.3, and 31.6 mins, respectively. The Duncan’s multiple range test results indicated that the MET without load carrying was significantly (p < 0.05) higher than those of the carrying 12.5% and 25% BW conditions. The MET of the 12.5% BW condition was significantly (p < 0.05) higher than that of the 25% BW conditions. The MET decreased when the walking speed increased. The mean MET values for the 2, 4, and 6 km/h walking speed were 82.8, 65.2, and 34.2 mins, respectively. The MET of the 2 km/h was significantly (p < 0.05) higher than those of the 4 and 6 km/h conditions. The MET of the 4 km/h was significantly (p < 0.05) higher than that of the 6 km/h condition. In addition, the MET for the 0° and 10° ramp conditions were 65.3 and 56.2 mins, respectively. They were significantly (p < 0.05) different. The ANOVA results indicated that the MET were significantly affected by the weight carried (aHR were significantly affected by the weight carried (p < 0.001), walking speed (p < 0.0001) and ramp angle (p < 0.001). The Duncan’s multiple range test results indicated that aHR of the 25%BW condition (116.9 bpm) was significantly (p < 0.05) higher than those of the 12.5%BW (112.1 bpm) and 0%BW (107.9 bpm) conditions. The aHR of the 12.5%BW condition and that of the 0%BW were not significantly different. The aHR for the 2 km/h (98.4 bpm) condition was significantly (p < 0.05) lower than those of the 4 km/h (108.1 bpm) and 6 km/h (130.3 bpm) conditions. The aHR for the 4 km/h condition was significantly (p < 0.05) lower than that of the 6 km/h conditions. The aHR of the 0° ramp angle condition (108.7 bpm) was significantly (p < 0.05) lower than that of the 10° condition (115.8 bpm). The ANOVA results indicated that t-test results indicated that back strength decrease was significantly (p < 0.05) higher than that of leg strength decrease. The ANOVA results indicated that both the decrease (%) of the back and leg strengths were insignificant to the weight carrying condition, walking speed, and the ramp angle of the treadmill. A pairwise p < 0.0001) and walking speed (p < 0.0001). The Duncan’s multiple range test results indicated that the RPE without load carrying (13.5) was significantly (p < 0.05) lower than those of the 12.5% (15.0) and 25% (16.8) BW conditions. The RPE for the 12.5% BW condition was significantly (p < 0.05) lower than that of the 25% BW condition. The RPE when walked at 2 km/h (14.0) was significantly (p < 0.05) lower than those of the 4 km/h (15.1) and 6 km/h (16.2) conditions. The RPE for the 4 km/h condition was significantly (p < 0.05) lower than that of the 6 km/h conditions. The effects of ramp angle on RPE were not significant. The ANOVA results indicated that the RPE were significantly affected by the weight carried  with an Radj2 = 0.97. Equation (6) may be converted to Equation (7):This equation was statistically significant (A mean absolute deviation (MAD) was calculated using the following equation to compare the actual MET and predicted MET:The MAD of Equation (8) in estimating the MET in our backpacking tasks were 29.7 (mins).Muscular strength decrease has been adopted to quantify the progress of muscular fatigue ,36,37. Ap < 0.05) higher than that on the leg, as back muscles experienced less dynamic contractions than those of the leg muscles. It was hypothesized that the strengths of the back and leg would decrease upon performing the backpacking tasks. However, both the back and leg strengths decreased only moderately (<10%). In addition, to our further surprise, the decreases of these two strengths after the trial were not affected by any of the three factors tested. An explanation of these phenomena may be that muscular strength decrease due to performing physical tasks is more likely to occur under static muscular contraction conditions. Muscular contractions on the leg were dynamic. Such dynamic contractions facilitate blood circulation, and hence slow down the onset of muscular fatigue. On the other hand, back muscle contractions were required to support the backpacking tasks. These muscles might; however, provide only partial contributions to the tasks. Many other muscles in the trunk, such as those in abdomen and shoulders, might also play a role. Unfortunately, muscular strength for those muscles could not be measured due to technical difficulties and the limitations of our apparatus. Decrease of both of the back and leg strengths were, therefore, less prominent than what we had expected. Strength decrease in the back was significantly ) was then fitted. In Equation (8), predictive MET was established considering MVC_backf, BW, ramp angle, and walking speed. The MVC_backf, ramp angle, and walking speed were associated with physical burdens or job demand of the tasks. MVC_backf was getting higher. The effects of walking speed on the MET were more prominent at low MVC_backf than were at a high one. This was consistent with the findings in the literature [It is well known that g of MET ,37,46,47g of MET ,32 indic as 0.05 . A powerterature . The METThere were limitations in the study. First of all, the participants were not allowed to drink or listen to music. Instead of being physically exhausted, they might have given up walking because of thirst, boredom, or some other reasons. In other words, their MET values could be higher than what were recorded if they were allowed to replenish water when they were thirsty or if they were allowed to listen to their favorite music. Replenishment of water and music listening may be important factors affecting the decrease of muscular strength, RPE, and MET. Effects of such factors will be interesting topics in the future. Secondly, the experiment was conducted in the laboratory where the temperature and relative humidity were controlled at 21.1 (±2.4) °C and 65.1 (±9.7)%, respectively. It is well known that temperature and humidity do affect the physiological strain of people performing physical tasks. We believe that the MET should be lower than our prediction if the task was performed in an environment with higher temperature or humidity than ours. Thirdly, age was not considered in the modeling of MET due to the nature of our participants. Our MET model may not be applicable to people in other age groups, especially school-aged children. This is because the ranges of the body weight and walking speed of our participants are much higher than those of children. Other MET models should be established for backpacking for school-aged children in the future. Finally, the sample size of this study was not large. This was due to our budget constraint. However, a sample size of 16 was believed to be acceptable as it was larger than some of the studies in the literature ,49. MVC_backf, body weight, walking speed, and ramp angle was established. This model may be used to determine the work/rest allowance for backpacking tasks under conditions similar to this study.The participants carried a backpack and walked until they could no longer do so. The endurance time for the backpacking tasks under different weight carried, walking speed, and ramp angle conditions ranged from approximately 15 min to more than two hours. These tasks resulted in an increase of heart rate and elevated perceived exertion. Our data support the hypotheses that both the MET and heart rate are affected by the weight carried, walking speed, and ramp angle. The RPE was also affected by the weight carried and walking speed significantly. The effects of ramp angle were not significant on RPE. The RPE/heart rate ratio for our backpacking tasks was 31% higher than that in the literature  implying