Polyimide(PI)synthesized from aromatic diamine and dianhydrides via two-step poly-condensation method was highly soluble in TGDDM(MY-720)and DGEBA(E-51)at desirable temperature.TGDDM-PI(M-PI)and DGEBA-PI(E-PI)composit...Polyimide(PI)synthesized from aromatic diamine and dianhydrides via two-step poly-condensation method was highly soluble in TGDDM(MY-720)and DGEBA(E-51)at desirable temperature.TGDDM-PI(M-PI)and DGEBA-PI(E-PI)composites within 0.5%-3%PI loading could be prepared without organic solvent.On the cryogenically fractured surfaces of M-PI and E-PI composites,no obvious heterogeneous phase was observed by SEM.The mechanical properties were promoted significantly by PI,especially for impact strength.Adding 2%PI-2W into MY-720 and E-51 composites,the impact strength increased to 21 and 51 kJ/m2,the tensile strength increased by 62%and 19%,and the flexural strength by 18%and 13%,respectively,with slight increases in tensile modulus.These results were related to the promotion in plasticity of composites and changes in fragile→ductile fracture mode.Moreover,Tg and thermal stability of M-PI and E-PI were increased effectively.展开更多
The curing behavior of diglycidyl ether of bisphenol-A(DGEBA) with aromatic diamide-diimide-diamines having aryl ether,sulfone and methylene linkages was studied by differential scanning calorimetry(DSC).Nine diamide-...The curing behavior of diglycidyl ether of bisphenol-A(DGEBA) with aromatic diamide-diimide-diamines having aryl ether,sulfone and methylene linkages was studied by differential scanning calorimetry(DSC).Nine diamide-diimide-diamines of varying structure were synthesized by reacting 1 mole of dianhydride with 2 moles of L-cysteine(S) in a mixture of acetic acid and pyridine(3:2 V/V) followed by activation with thionyl chloride(SOCl_2) and then condensation with excess of diamines.Structural characterization...展开更多
Here, dielectric spectroscopy is used in the fre- quency range from 10-2 Hz up to 107 Hz and we found dynamics of the primary α-and intermolecular Johari–Goldstein β-processes are strongly correlated in diglycidyl-...Here, dielectric spectroscopy is used in the fre- quency range from 10-2 Hz up to 107 Hz and we found dynamics of the primary α-and intermolecular Johari–Goldstein β-processes are strongly correlated in diglycidyl-ether of bis-phenol-A and poly phenyl glycidyl-ether (PPGE) over a wide temperature from 193 to 345 K and pressure P range from 0.1 to 600 MPa. In contrast with the widespread opinion of statistical independence of these processes the α-β mutual dependence is quantitatively confirmed in [1] analysing the temperature and pressure behavior of the α-and (JG) β-processes the investigation of the ratio of dielectric strength of two processes close to Tg evidence that the importance of secondary dy namics in relaxing external electric stresses increase in glass formers at high pressures with respect to that of the structural relaxation. We suggest that the thermal agitation, acting above Tg is at the basis of the observed result.展开更多
AIM： To examine the prevalence of dyslexia and Meares-Irlen syndrome（MIS） among female students and determine their level of visual stress in comparison with normal subjects.·METHODS： A random sample of 450 f...AIM： To examine the prevalence of dyslexia and Meares-Irlen syndrome（MIS） among female students and determine their level of visual stress in comparison with normal subjects.·METHODS： A random sample of 450 female medical students of King Saud University Riyadh（age range, 18-30y） responded to a wide range of questions designed to accomplish the aims of this study. The detailed questionnaire consisted of 54 questions with 12 questions enquiring on ocular history and demography of participants while 42 questions were on visual symptoms. Items were categorized into critical and non-critical questions（CQ and NCQ） and were rated on four point Likert scale. Based on the responses obtained, the subjects were grouped into normal（control）, dyslexic with or without MIS（Group 1） and subjects with MIS only（Group 2）. Responses were analysed as averages and mean scores were calculated and compared between groups using one way analysis of variance to evaluate total visual stress score（TVSS =NCQ ＋CQ）, critical and non-critical visual stress scores. The relationship between categorical variables such as age, handedness and condition were assessed with Chi-square test.·RESULTS： The completion rate was 97.6% and majority of the respondents（92%） were normal readers, 2%dyslexic and 6% had MIS. They were age-matched. More than half of the participants had visited an eye care practitioner in the last 2y. About 13% were recommendedeye exercises and one participant experienced pattern glare. Hand preference was not associated with any condition but Group 1 subjects（3/9, 33%） were significantly more likely to be diagnosed of lazy eye than Group 2（2/27, 7%） and control（27/414, 7%） subjects. The mean±SD of TVSS responses were 63±14 and it was 44±9for CQ and 19 ±5 for NCQ. Responses from all three variables were normally distributed but the CQ responses were on the average more positive（82%） in Group 2 and less positive（46%） in Group 1 than control. With NCQ,the responses were equally less positive in Group 1 and2 than control. Group 2 subjects showed significantly higher TVSS（P =0.002）, NCQ（P =0.006） and CQ（P =0.008）visual stress scores than control but no difference between Group 1 and control subjects, was observed for all scores（P 〉0.05, for all comparisons）.·CONCLUSION： The prevalence of dyslexia and MIS among Saudi female students was 2% and 6%,respectively. Critical questions performed best for assessing visual stress symptoms in dyslexic and MIS subjects. Generally, students with MIS were more sensitive to visual stress than normal students but dyslexics were more likely to present with a lazy eye than MIS and normal readers.展开更多
基金This work was financially supported by the National Key Research and Development Program of China(No.2016YFC0204300)the National Natural Science Foundation of China(Nos.21777043,21976056).
文摘Polyimide(PI)synthesized from aromatic diamine and dianhydrides via two-step poly-condensation method was highly soluble in TGDDM(MY-720)and DGEBA(E-51)at desirable temperature.TGDDM-PI(M-PI)and DGEBA-PI(E-PI)composites within 0.5%-3%PI loading could be prepared without organic solvent.On the cryogenically fractured surfaces of M-PI and E-PI composites,no obvious heterogeneous phase was observed by SEM.The mechanical properties were promoted significantly by PI,especially for impact strength.Adding 2%PI-2W into MY-720 and E-51 composites,the impact strength increased to 21 and 51 kJ/m2,the tensile strength increased by 62%and 19%,and the flexural strength by 18%and 13%,respectively,with slight increases in tensile modulus.These results were related to the promotion in plasticity of composites and changes in fragile→ductile fracture mode.Moreover,Tg and thermal stability of M-PI and E-PI were increased effectively.
文摘The curing behavior of diglycidyl ether of bisphenol-A(DGEBA) with aromatic diamide-diimide-diamines having aryl ether,sulfone and methylene linkages was studied by differential scanning calorimetry(DSC).Nine diamide-diimide-diamines of varying structure were synthesized by reacting 1 mole of dianhydride with 2 moles of L-cysteine(S) in a mixture of acetic acid and pyridine(3:2 V/V) followed by activation with thionyl chloride(SOCl_2) and then condensation with excess of diamines.Structural characterization...
文摘Here, dielectric spectroscopy is used in the fre- quency range from 10-2 Hz up to 107 Hz and we found dynamics of the primary α-and intermolecular Johari–Goldstein β-processes are strongly correlated in diglycidyl-ether of bis-phenol-A and poly phenyl glycidyl-ether (PPGE) over a wide temperature from 193 to 345 K and pressure P range from 0.1 to 600 MPa. In contrast with the widespread opinion of statistical independence of these processes the α-β mutual dependence is quantitatively confirmed in [1] analysing the temperature and pressure behavior of the α-and (JG) β-processes the investigation of the ratio of dielectric strength of two processes close to Tg evidence that the importance of secondary dy namics in relaxing external electric stresses increase in glass formers at high pressures with respect to that of the structural relaxation. We suggest that the thermal agitation, acting above Tg is at the basis of the observed result.
基金Supported by the Research Centre,College of Applied Medical Sciences and the Deanship of Scientific Research at King Saud University
文摘AIM： To examine the prevalence of dyslexia and Meares-Irlen syndrome（MIS） among female students and determine their level of visual stress in comparison with normal subjects.·METHODS： A random sample of 450 female medical students of King Saud University Riyadh（age range, 18-30y） responded to a wide range of questions designed to accomplish the aims of this study. The detailed questionnaire consisted of 54 questions with 12 questions enquiring on ocular history and demography of participants while 42 questions were on visual symptoms. Items were categorized into critical and non-critical questions（CQ and NCQ） and were rated on four point Likert scale. Based on the responses obtained, the subjects were grouped into normal（control）, dyslexic with or without MIS（Group 1） and subjects with MIS only（Group 2）. Responses were analysed as averages and mean scores were calculated and compared between groups using one way analysis of variance to evaluate total visual stress score（TVSS =NCQ ＋CQ）, critical and non-critical visual stress scores. The relationship between categorical variables such as age, handedness and condition were assessed with Chi-square test.·RESULTS： The completion rate was 97.6% and majority of the respondents（92%） were normal readers, 2%dyslexic and 6% had MIS. They were age-matched. More than half of the participants had visited an eye care practitioner in the last 2y. About 13% were recommendedeye exercises and one participant experienced pattern glare. Hand preference was not associated with any condition but Group 1 subjects（3/9, 33%） were significantly more likely to be diagnosed of lazy eye than Group 2（2/27, 7%） and control（27/414, 7%） subjects. The mean±SD of TVSS responses were 63±14 and it was 44±9for CQ and 19 ±5 for NCQ. Responses from all three variables were normally distributed but the CQ responses were on the average more positive（82%） in Group 2 and less positive（46%） in Group 1 than control. With NCQ,the responses were equally less positive in Group 1 and2 than control. Group 2 subjects showed significantly higher TVSS（P =0.002）, NCQ（P =0.006） and CQ（P =0.008）visual stress scores than control but no difference between Group 1 and control subjects, was observed for all scores（P 〉0.05, for all comparisons）.·CONCLUSION： The prevalence of dyslexia and MIS among Saudi female students was 2% and 6%,respectively. Critical questions performed best for assessing visual stress symptoms in dyslexic and MIS subjects. Generally, students with MIS were more sensitive to visual stress than normal students but dyslexics were more likely to present with a lazy eye than MIS and normal readers.
