The current thermoremendable polyurethanes (PUs) based on reversible Diels–Alder (DA) chemistry featuring both good mechanical properties and efficient macrodamage healability are up to now built ...with the DA bonds located in the hard domains with restricted mobility, which hinders the DA reversibility. Thus, the healing process in these materials requires predissociation of DA bonds via the retro reaction at high temperatures (110–180 °C) followed by DA re-formation, which may compromise the material performance integrity. Here, we show a design of thermoset PUs containing dynamic DA entities engineered at the interface between the hard and soft domains that combine high modulus and toughness with mild-temperature-triggered molecular mobility, which is a prerequisite for efficient healing capability. This concept of molecular design enables PUs to have great mechanical properties (Young’s modulus ∼80–225 MPa, ultimate tensile strength ∼16–30 MPa, and toughness ∼26–96 MJ m–3) and simultaneously remarkable healing ability at mild temperatures (60–70 °C) of macroscratches, punctures, and complete cuts. The mechanical and healing properties can be tuned by varying the DA bond content. These materials are the first reported DA-based PU materials showing excellent healing efficiency at mild temperatures without compensation of their great mechanical properties.
This study aimed to understand farmers' knowledge, attitudes, and practices regarding agricultural pest management and synthetic pesticide use in Southeast Asia. Data were used from 900 farm ...households producing leaf mustard (Brassica juncea (L.) Czern. et Coss.) and yard-long bean (Vigna unguiculata subsp. sesquipedalis (L.) Verdc.) in Cambodia, Laos and Vietnam. Farmers heavily depended on synthetic pesticides as their main method of pest control. Most farmers were aware of the adverse health effects associated with pesticide use and covered body parts while spraying, but also considered pesticides to be highly effective and indispensable farm inputs. Farmers were largely unable to distinguish between common beneficial and harmful arthropods. Greater knowledge about this was associated with less pesticide use while greater awareness of pesticide health risks was associated with fewer observed poisoning symptoms. For the average farm and while controlling for other factors, farmers who sought advice from friends and neighbors used 45% less pesticide, but those who sought advice from pesticide shopkeepers used 251% more pesticide. Pesticide use was 42% less when a woman was in charge of pest management and 31% less when farmers had adopted biopesticides. These findings suggest relevant entry points for interventions aimed at reducing pesticide dependence.
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•Vegetable farmers' pest management was studied in Cambodia, Laos, and Vietnam.•Farmers were aware of health risks from pesticides, but considered pesticides indispensable.•Low knowledge of beneficial and harmful insects was associated with more pesticide use.•Farmers who sought advice from pesticide shopkeepers tended to use more pesticides.
This paper quantifies the extent of pesticide overuse in vegetable production systems in Southeast Asia. Pesticide overuse was defined as levels of use in excess of an economic (profit-maximizing) ...optimum. A production function with an exponential damage abatement term was estimated. Data come from a representative sample of 1000 farmers producing leaf mustard and yard-long bean in Cambodia, Laos and Vietnam. The results show that 100% of the sampled farmers in Vietnam, 73% in Cambodia and 59% in Laos overused pesticides. Pesticide expenditure in excess of the economic optimum was 96% for Vietnam, 92% for Cambodia, and 42% for Laos. Pesticide overuse was positively associated with men in charge of pest management decisions, farmers seeking advice from pesticide sellers and a strong belief that pesticides are effective. It was negatively associated with the use of non-chemical methods of pest control. These results imply that farmers in Southeast Asia are spraying excessively and inefficiently and could increase their profits by applying fewer pesticides.
•We quantify pesticide overuse in vegetable production in Cambodia, Laos and Vietnam.•Production function with damage control term was estimated with data for 1000 farms.•77% of farmers overused pesticides; 77% of pesticide expenditures are overuse.•Greater overuse was observed among male applicators.•Greater overuse was also observed where pesticide sellers advised farmers.
Novel donor–acceptor (D-A) conjugated polymers containing phenothiazine and diketopyrrolopyrrole derivatives were successfully synthesized via direct arylation polymerization using the palladium ...catalyst system. The C-N coupling reaction was performed for the synthesis of 4-(10H-phenothiazin-10-yl)-N,N-diphenylaniline (PDA) and 10-(pyren-1-yl)-10H-phenothiazine (PYP) as donor monomers. The D-A conjugated polymers synthesized by polymerization of PDA/PY with diketopyrrolopyrrole have been characterized via GPC,
1
H NMR, FTIR, XRD, DSC, PL and UV-Vis spectroscopy, and used for fabrication of organic field effect transistors.
Graphical abstract
The novel D-A conjugated polymers containing phenothiazine derivatives and diketopyrrolopyrrole were successfully synthesized via direct (hetero)arylation polymerization. The obtained conjugated polymers have been applied for the fabrication of organic filed effect transistors. The conjugated polymers showed a hole mobility of 10
−5
cm2/Vs in top contact OFET devices.
A new thermoresponsive self-healing polymer thermoset ((1.5M/F)DA-PDMS-PU) based on the Diels–Alder (DA) reaction between furan and maleimide groups was developed. The material exhibited glass ...temperature induced shape memory effect that brings crack faces into intimate contact, enabling the reformation of DA bridges located in the crack surfaces. In addition, the incorporation PDMS segments and excess maleimide functional groups besides DA bridges in the network promotes the mobility of dynamic groups and the healing reaction, therefore increasing the ability of the material to heal damages at a mild temperature. Scratch healing was possible via a one-step heating process at a moderate temperature of 60 °C for 4 h, reaching a tensile strength recovery of above 85%.
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•A thermoresponsive Diels-Alder crosslinked self-healing polymer thermoset was prepared.•PDMS segments and excess maleimide groups were incorporated to promote the healing ability.•The material exhibited glass transition induced shape memory that assists crack closure.•Scratch healing was possible via a one-step heating process at a moderate temperature of 60 °C.
This paper is an original empirical attempt to explain the outcome of collective action in the domain of food safety. We examine conditions and institutions that influence pesticide residue levels in ...vegetables using econometric analysis on data gathered from 60 farmer organisations in Vietnam. Findings suggest that collective action affects safety in that it provides members with technical assistance and monitoring for pest management at the farming level. They confirm the U-shape hypothesis of the effect of group size on safety performance which derives from the trade-off that exists between economies of scale and free-riding. The contribution of public authorities and ecological conditions to food safety remains controversial, while market forces do not yet seem able to drive the production of safer vegetables.
A total of 1,318 wild geckos were collected in Cambodia, Thailand and Vietnam (Hue and the Mekong Delta) from 2012 to 2015 to determine the prevalence of Salmonella Weltevreden. Those geckos belong ...to three species: common house gecko (Hemidactylus frenatus), flat‐tailed house gecko (Hemidactylus platyurus) and four‐clawed gecko (Gehyra mutilata). Of 1,318 gecko samples, 293 (22.2%) samples were positive for Salmonella in this study. The prevalence of Salmonella in geckos was 46.0% in Thailand, 17.3% in Cambodia and 16.3% in Vietnam. Among the Salmonella isolates, S. Weltevreden was the most predominant serovar (32.1%) isolated from wild geckos in these countries. There was no significant difference in the prevalence of Salmonella among gecko species. All S. Weltevreden isolates (100%) were susceptible to the nine antibiotics examined in this study. The PFGE assay by XbaI enzyme identified 19 different patterns from 75 S. Weltevreden isolates. These isolates showed high genetic heterogenicity, and there were specific types prevalent in each region. Furthermore, S. Weltevreden has been prevalent since the ancient times in this region. The results indicate that wild gecko seems to be an important natural reservoir for S. Weltevreden as well as a source of Salmonella infections in humans in Southeast Asian countries.
This study was conducted to identify the diversity of feather color and to determine the relationship between plumage color and egg yield as well as eggshell patterns and internal egg quality traits ...of Japanese quails.
For investigating phenotypic diversity, a total of 600 quails from five breeding farms were evaluated to record head feather, shank, and plumage color. An on-station experiment was also conducted on 360 laying quails to examine the relationship between plumage color and egg production and egg weight during 24 weeks of laying. Eggs collected during this period were also used for identifying eggshell patterns and examining their relationship with internal egg quality characteristics.
Plumage color was primarily wild-type, with the highest proportion being 56.3% (p<0.001). Brown color was also found at a relatively high proportion in the population (16.7%), followed by black color (11.3%). The egg production and laying rate of quails with wild-type and brown plumage colors also significantly (p=0.001) differed from those of quails with other plumage types. Egg weight was also higher in these quail groups, especially than that of quails with yellow plumage color. Four patterns of eggshell were identified, among which spotted and dark eggshells were predominant (45.2% and 43.1%, respectively); however, patterns did not affect internal egg quality characteristics.
Plumage color was primarily wild-type in both male and female quails. Egg yield over a 24-week laying period was superior in quails with wild-type and brown plumage colors, whereas a relationship between eggshell patterns and egg quality traits could not be established.
Recent research has shown writing strategies to have a substantial impact on language learners' writing performance but little is known about what strategies EFL learners use and how they use them in ...writing academic texts such as reports, final assignments, and project papers. The study reported in this paper extends this line of research by investigating the strategies Vietnamese EFL pre-service teachers use in academic writing. Data included document analysis of 17 pre-service teachers' final assignment papers (one paper per teacher) and individual semi-structured interviews with ten teachers. The study adopted a content-based approach to qualitative data analysis with reference to a comprehensive research-based taxonomy for L2 academic writing strategies, including rhetorical, metacognitive, cognitive, and social affective strategies. The results show that rhetorical, metacognitive, and cognitive strategies were most frequently used by the teacher participants. The results further show that self-efficacy and self-regulation determined the teachers' use of strategies during the writing process. Implications for the L2 writing classroom focused on academic writing strategies to enhance pre-service teachers’ writing quality will be discussed.
Recent studies have sought to describe and understand English as a second/foreign language (ESL/EFL) teachers’ pronunciation teaching practices in different contexts, but much less research has ...examined how teachers and learners perceive pronunciation instruction at tertiary level, especially in EFL settings. The qualitative study reported in this paper extends this line of research by investigating the beliefs of teachers and learners with regard to pronunciation instruction in tertiary EFL education in Vietnam. Data were collected from individual semi-structured interviews with six EFL teachers and focus group interviews with 24 students (four students per group) at a Vietnamese university. The study adopted a content-based approach to qualitative data analysis. The findings show that both the teachers and students considered pronunciation instruction an important component in tertiary EFL programs, which deserves explicit and systematic delivery. The findings suggest that both groups of participants believed communicative pronunciation teaching to have the potential to improve learners’ pronunciation and facilitate their general communicative purposes. The study has implications for language curriculum design and L2 pronunciation teaching and learning.
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