Influence of Crystallization Kinetics and Flow Behavior on Structural Inhomogeneities in 3D-Printed Parts Made from Semi-Crystalline Polymers.

We report the results of a study focusing on the influence of crystallization kinetics and flow behavior on structural inhomogeneities in 3D-printed parts made from polyamide 12 (PA12) and poly(lactic acid) (PLA) by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and wide-angle X-ray diffraction (WAXD). Temperature-dependent WAXD measurements on the neat PLA filament reveal that PLA forms a single orthorhombic α phase during slow cooling and subsequent 2nd heating. The PA12 filament shows a well pronounced polymorphism with a reversible solid-solid phase transition between the (pseudo)hexagonal γ phase near room temperature and the monoclinic α' phase above the Brill transition temperature TB = 140 °C. The influence of the print bed temperature Tb on structure formation, polymorphic state, and degree of crystallinity χc of the 3D-printed parts is investigated by height and depth-dependent WAXD scans and compared with that of 3D-printed single layers, used as a reference. It is found that the heat transferred from successive layers has a strong influence on the polymorphic state of PA12 since a superimposed mixture of γ and α phases is present in the 3D-printed parts. In the case of PLA, a single α phase is formed. The print bed temperature has, in comparison to PA12, a major influence on the degree of crystallinity χc and thus the homogeneity of the 3D-printed parts, especially close to the print bed. By comparing the obtained results from WAXD, DMA, DSC, and FSC measurements with relevant printing times, guidelines for 3D-printed parts with a homogeneous structure are derived.

The whole blood DNA methylation of RAB8A and RAP1A in autoimmune thyroiditis: evidence and validation of iodine exposure in a population from different water iodine areas.

Our study aimed to identify and verify G protein-related methylated genes in AIT patients, while also investigate those genes in AIT patients exposed to iodine in different water iodine areas. Different areas were classified by median water iodine (MWI) concentrations: Iodine-Fortified Areas (IFA, MWI<10µg/L), Iodine-Adequate Areas (IAA, 40≤MWI≤100 µg/L), and Iodine-Excessive Areas (IEA, MWI>100 µg/L). We studied 176 AIT cases and 176 controls, with 89, 40, and 47 pairs in IFA, IAA, and IEA, respectively. Using the Illumina Human Methylation 850k BeadChip, we identified candidate methylated genes. MethylTargetTM and QRT-PCR validated DNA methylation and mRNA expression. Results showed hypomethylation and high expression of RAB8A and RAP1A in all 176 AIT cases. RAB8A's CpG sites were mainly hypomethylated in IFA and IEA, while RAP1A's sites were primarily hypomethylated in IEA. This study underscores how water iodine exposure may influence RAB8A and RAP1A methylation in AIT.

Synthesis and Characterization of Quadrupolar-Hydrogen-Bonded Polymeric Ionic Liquids for Potential Self-Healing Electrolytes.

Within the era of battery technology, the urgent demand for improved and safer electrolytes is immanent. In this work, novel electrolytes, based on pyrrolidinium-bistrifluoromethanesulfonyl-imide polymeric ionic liquids (POILs), equipped with quadrupolar hydrogen-bonding moieties of ureido-pyrimidinone (UPy) to mediate self-healing properties were synthesized. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was employed using S,S-dibenzyl trithiocarbonate as the chain transfer agent to produce precise POILs with a defined amount of UPy and POIL-moieties. Kinetic studies revealed an excellent control over molecular weight and polydispersity in all polymerizations, with a preferable incorporation of UPy monomers in the copolymerizations together with the ionic monomers. Thermogravimetric analysis proved an excellent thermal stability of the polymeric ionic liquids up to 360 °C. By combining the results from differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS), and rheology, a decoupled conductivity of the POILs from glass transition was revealed. While the molecular weight was found to exert the main influence on ionic conductivity, the ultimate strength and the self-healing efficiency (of up to 88%) were also affected, as quantified by tensile tests for both pristine and self-healed samples, evidencing a rational design of self-healing electrolytes bearing both hydrogen bonding moieties and low-molecular-weight polymeric ionic liquids.

Bulk Enthalpy of Melting of Poly (l-lactic acid) (PLLA) Determined by Fast Scanning Chip Calorimetry.

The bulk enthalpy of melting of α-crystals of poly (L-lactic acid) (PLLA) is evaluated by fast scanning calorimetry (FSC), by correlating the melting enthalpy of samples of different crystallinity with the corresponding heat capacity at 90 °C, that is at a temperature higher than the glass transition temperature of the bulk amorphous phase and lower than the melting temperature. Extrapolation of this relationship for crystals formed at 140 °C towards the heat capacity of fully solid PLLA yields a value of 104.5±6 J g-1 when melting occurs at 180-200 °C. The analysis relies on a two-phase structure, that is, absence of a vitrified rigid amorphous fraction (RAF) at the temperature of analysis the solid fraction (90 °C). Formation and vitrification of an RAF are suppressed by avoiding continuation of primary crystallization and secondary crystallization during cooling the system from the crystallization temperature of 140 °C to 90 °C, making use of the high cooling capacity of FSC. Small-angle X-ray scattering (SAXS) confirmed thickening of initially grown lamellae which only is possible if these lamellae are not surrounded by a glassy RAF. Linear crystallinity values obtained by SAXS and calorimetrically determined enthalpy-based crystallinities agree close to each other.

The Association of Suicidal Ideation With Family Characteristics and Social Support of the First Batch of Students Returning to a College During the COVID-19 Epidemic Period: A Cross Sectional Study in China.

Objective: To investigate the prevalence of suicidal ideation among the first batch of students returning to a college during the COVID-19 epidemic, and to explore the correlation of suicidal ideation with family characteristics and social support. Methods: A cluster sampling survey with a self-designed questionnaire was conducted among the first batch of students returning to a college in Wuhu, China. The Positive and Negative Suicidal ideation (PANSI) and Social Support Scale (SSRS) were used to define students' suicidal ideation and social support, respectively. The influence of family characteristics and social support on the students' suicidal ideation was investigated using multivariate unconditional logistic regression analysis. Results: Two thousand seven hundred valid questionnaires were collected, including 673 males (24.9%) and 2,027 females (75.1%), in this study. A total of 146 students (5.4%) showed suicidal ideation. Male respondents reported higher rates (7.9%) than females (4.6%). Multivariate logistic regression analysis showed that a higher risk level of residence before returning to school and lower objective support were the risk factors for suicidal ideation in males. In contrast, a higher level of maternal education, a poorer relationship with the mother, and lower scores for subjective support and support availability had significant effects on females' suicidal ideation. Limitations: This is a cross-sectional study, and lacks comparison to the time point unaffected by COVID-19. Moreover, it was limited by COVID-19 epidemic prevention and control restrictions, and the differences in returning to school in different regions. Only one college was investigated in this study, and all of the respondents were sophomores, so there may be some limitations in the representativeness of the sample and extrapolation of the results. Conclusion: Family characteristics and social support have had an important influence on suicidal ideation among students returning to school during the COVID-19 epidemic. Some gender differences were identified. Targeted interventions are needed for early prevention and control.

Surface Crystal Nucleation and Growth in Poly (ε-caprolactone): Atomic Force Microscopy Combined with Fast Scanning Chip Calorimetry.

By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was placed on the active/heatable area of the FSC chip, melted, and then rapidly cooled to 330 K, which is 13 K below the equilibrium melting temperature. Subsequent isothermal crystallization at this temperature was initiated by a soft-tapping AFM-tip nucleation event. Crystallization starting at such surface nucleus led to formation of a single spherulite within the FSC sample, as concluded from the radial symmetry of the observed morphology. The observed growth rate in the sub-micron thin FSC sample, nucleated at its surface, was found being much higher than in the case of bulk crystallization, emphasizing a different growth mechanism. Moreover, distinct banding/ring-like structures are observed, with the band period being less than 1 µm. After crystallization, the sample was melted for gaining information about the achieved crystallinity and the temperature range of melting, both being similar compared to much slower bulk crystallization at the same temperature but for a much longer time.

Effect of Molar Mass on Critical Specific Work of Flow for Shear-Induced Crystal Nucleation in Poly (l-Lactic Acid).

The concept of specific work of flow has been applied for the analysis of critical shearing conditions for the formation of crystal nuclei in poly (l-lactic acid) (PLLA). Systematic variation in both time and rate of shearing the melt in a parallel-plate rheometer revealed that these parameters are interconvertible regarding the shear-induced formation of crystal nuclei; that is, low shear rate can be compensated for by increasing the shear time and vice versa. This result supports the view that critical shearing conditions can be expressed by a single quantity, providing additional options for tailoring polymer processing routes when enhanced nuclei formation is desired/unwanted. Analysis of PLLA of different mass-average molar masses of 70, 90, 120, and 576 kDa confirmed improved shear-induced crystal nucleation for materials of higher molar mass, with critical specific works of flow, above which shear-induced nuclei formation occurs, of 550, 60, 25, and 5 kPa, respectively.

Depression and anxiety and assciated factors among college students returned to campus during the outbreak of COVID-19 / 中国学校卫生

Objective@#The purpose of this study was to investigate the state of depression and anxiety and assciated factors of back to school college students during the outbreak of COVID-19, so as to provide theoretical basis for emotional counseling and psychological crisis intervention after long term school closure due to epidemic outbreak.@*Methods@#Cluster sampling was used to select the first batch of 2 697 back to school students in a high vocational college. The survey content includes basic information questionnaire, Depression Self rating Scale (SDS) and Anxiety Self rating Scale(SAS).@*Results@#The detection rate of depression and anxiety was 31.8% and 10.4% respectively. Multivariate Logistic regression analysis showed that the risk of depression in female college students was 1.28 times higher than that in male students. The risk of depression among college students with family loss experience caused by the outbreak of COVID-19 was 1.30 times that of those without family loss experience caused by the outbreak of COVID-19. Outgoing personality(OR=0.62), neutral (OR=0.55) and mild temper(OR=0.46), moderate frequency of physical exercise per week(1-2 times:OR=0.73, 3-4 times:OR=0.65) were protective effects for depression in college students.Low frequency of breakfast were the risk effects for depression in college. The risk of anxiety among college students who was the only child in the family was 1.61 times higher than that who was not the only child in the family. The risk of anxiety among college students with family loss experience caused by the outbreak of COVID-19 was 1.45 times higher than that college students without family loss experience caused by the outbreak of COVID-19. Neutral temper, mild temper and physical exercise 1-2 times a week were associated with lower level of anxiety in college students(OR=0.67,0.56,0.67). Breakfast skipping (OR=2.03) was associated with higher levvel of anxiety in college students.@*Conclusion@#During the outbreak of COVID-19, the first batch of back to school college students presented high level of depression. Colleges are suggested to promptly carry out effective emotional relief and psychological intervention for students, especially those whose family suffered in COVID-19, the only child in the family, with poor breakfast eating habits, as well as breakfast skipping and lack of physical exercise.

Sleep quality and influencing factors of college students returning to school during COVID-19 epidemic / 中国学校卫生

Objective@#To investigate the sleep quality and influencing factors of the first batch of college students returning to school during COVID-19 epidemic, so as to provide scientific basis for taking corresponding measures.@*Methods@#An anonymous self-administered questionnaire survey was conducted among the first batch of college students returning from a certain university by cluster sampling, which included general demographic characteristics, Trait Coping Style Questionnaire (TCSQ) and Pittsburgh Sleep Quality Index(PSQI).@*Results@#The detection rate of sleep disorders was 19.33%(522/2 701). The mother s education level was high school or technical secondary school or below(OR=2.24, 95%CI=1.47-3.41), never eat breakfast(OR=3.25, 95%CI=1.86-5.68), families were damaged during the outbreak (OR=1.48, 95%CI=1.17-1.87) and negative coping (OR=1.15, 95%CI=1.12-1.17) were risk factors for sleep disorders(P<0.05). Compared to having a very poor relationship with parents, the relationship between parents was average(OR=0.23, 95%CI=0.06-0.89), better(OR=0.23, 95%CI=0.06-0.87), very good (OR=0.19, 95%CI=0.05-0.74) were protective factors for sleep disorders(P<0.05). Exercise once or twice a week during the epidemic(OR=0.76, 95%CI=0.58-1.00), positive coping (OR=0.93, 95%CI=0.91-0.96) were protective factors for sleep disorders(P<0.05).@*Conclusion@#In this COVID-19 epidemic, the sleep quality of returning college students was affected to different extent, and the relationship between parents, sports, mother s education, breakfast habits, and family damage during the COVID-19 were factors affecting their sleep quality. Targeted psychological intervention measures should be given to returning college students in the early stage.

Analysis of network usage and influencing factors among college students returning to a vocational college during COVID-19 epidemic / 中国学校卫生

Objective@#To understand the current situation and influencing factors of Internet addiction among college students after returning to school during the COVID-19 epidemic, and to provide scientific basis for timely intervention measures to adjust the risk factors of Internet addiction.@*Methods@#A cluster sampling method was adopted to conduct a questionnaire survey among 2 700 college students who firstly returned to college using general condition questionnaire and Internet Addiction scale.@*Results@#The detection rate of Internet addiction disorder was 32.4% among returning college students, moreover, the detection rate of Internet addiction in male students(36.0%) was higher than that in female students (31.2%) (χ 2=5.42,P<0.05). The degree of Internet addiction was negatively correlated with the physical health score (r-s=-0.20) and mental health score (r-s=-0.24) of college students (P<0.01). Multivariate Logistic regression analysis showed that compared with introversion, neutral (OR=0.67, 95%CI=0.55-0.82) and extroverted college students (OR=0.59, 95%CI=0.48-0.74) were protective factors for Internet addiction; compared with no exercise, physical exercise ≥3 times or more per week (exercise 3-4 times：OR=0.67, 95%CI=0.51-0.87; ≥5 times：OR=0.67, 95%CI=0.50-0.90) were the protective factors for Internet addiction among college students; family loss during the epidemic was a risk factor for Internet addiction among college students (OR=1.34, 95%CI=1.12-1.60); the risk of Internet addiction was 2.13 times higher for college students who actively sought psychological help than for those who did not seek psychological help (95%CI=1.14-3.96); college students who did not want to go back to school had 1.50 times the risk of Internet addiction as those who did (95%CI=1.26-1.77).@*Conclusion@#The current situation of college students online behaviors during COVID-19 is not optimistic, and should arouse sufficient attention from society and universities. In addition, college students returning to school should take more physical exercises and psychological counseling to detect and intervene in psychological problems in time, reduce their psychological burden, and enhance their psychological quality.

School adaptation and behavior of the first batch of college students returning to school during the COVID-19 epidemic / 中国学校卫生

Objective@#To analyze the school adaptation and behavioral performance of the first batch of students who return to school during the COVID-19 epidemic, and to provide a theoretical basis for further development of corresponding intervention measures.@*Methods@#The method of cluster sampling was adopted to conduct anonymous questionnaire survey on the first batch of college students who have returned to a certain university. The survey contents included the basic information of the students, the adaptability of the school after returning to school and the corresponding behavior performance.@*Results@#Male students reported high lever of satisfaction than female students on the dormitory environment health (t=10.28, P<0.01), but low satisfaction on school security and logistical support (t=2.26, P=0.02), rural students marked higher score than urban students for the school closed management system (t=2.82, P=0.01), in terns of school security, Logistics, the degree of school s attention to the epidemic prevention and epidemic prevention, non only-child gave high score than the only children; In terms of their own behavior, the rate of seek medical treatment immediately when they develop COVID-19 related symptoms (68.1%) was lower than that of others (81.3%)(χ 2=223.88，P<0.01)；In addition, the percentage of respondents who chose to report COVID-19 related symptoms (79.5%) was lower than that of others (88.7%)(χ 2=97.49，P<0.01). A total of 2 671 college students (98.9%) were able to wear masks every day and 2 457 (90.9%) chose to improve their diet to improve their immunity.@*Conclusion@#The first batch of college students who return to school have a high level of satisfaction on school management, and can take active measures to adapt to the life back to school and commit self-protection, however targeted measures to are still needed further strengthen students health education.