The performance of a-posteriori error methodology based on moving least squares(MLS)interpolation is explored in this paper by varying the finite element error recovery parameters,namely recovery points and field vari...The performance of a-posteriori error methodology based on moving least squares(MLS)interpolation is explored in this paper by varying the finite element error recovery parameters,namely recovery points and field variable derivatives recovery.The MLS interpolation based recovery technique uses the weighted least squares method on top of the finite element method’s field variable derivatives solution to build a continuous field variable derivatives approximation.The boundary of the node support(mesh free patch of influenced nodes within a determined distance)is taken as circular,i.e.,circular support domain constructed using radial weights is considered.The field variable derivatives(stress and strains)are recovered at two kinds of points in the support domain,i.e.,Gauss points(super-convergent stress locations)and nodal points.The errors are computed as the difference between the stress from the finite element results and projected stress from the post-processed energy norm at both elemental and global levels.The benchmark numerical tests using quadrilateral and triangular meshes measure the finite element errors in strain and stress fields.The numerical examples showed the support domain-based recovery technique’s capabilities for effective and efficient error estimation in the finite element analysis of elastic problems.The MLS interpolation based recovery technique performs better for stress extraction at Gauss points with the quadrilateral discretization of the problem domain.It is also shown that the behavior of the MLS interpolation based a-posteriori error technique in stress extraction is comparable to classical Zienkiewicz-Zhu(ZZ)a-posteriori error technique.展开更多
The optical and structural properties of Tb^(3+)-doped yttrium and gadolinium oxyorthosilicate(Y_(2)SiO_(5) and Gd_(2)SiO_(5)) phosphors were analyzed.The samples were synthesized via sol-gel combustion method using o...The optical and structural properties of Tb^(3+)-doped yttrium and gadolinium oxyorthosilicate(Y_(2)SiO_(5) and Gd_(2)SiO_(5)) phosphors were analyzed.The samples were synthesized via sol-gel combustion method using organic fuel.The phase purity and structural properties of the samples were determined via combined approach of powder X-ray diffraction,Fourier transformation infrared(FTIR) and transmission electron microscopy(TEM).X-ray measurements revel monoclinic crystal lattice with P_(21/c) symmetry for both M_(2)SiO_(5)(pure host) and M_(2)SiO_(5):Tb^(3+)(doped) silicates,irrespective of the nature of metal(Y or Gd),presence or absence of Tb^(3+)in lattice and change in calcination temperature up to 1050℃.FTIR analysis was applied to confirm the bonding of prepared materials.The appearance of bands corresponding to SiO_(4) tetrahedra(880-1020 cm^(-1)) suggest the layered structure and support the diffraction measurements.TEM micrographs confirm the synthesis of spherical nanoparticles with filled morphology,narrow size distribution and slightly agglomerated crystallites of the samples.The elemental composition of prepared materials was determined using energy dispersive X-ray spectroscopy.The spectra show peaks only for elements assimilated within the host framework.The photoluminescence(PL) emission spectra of Tb^(3+)-doped samples show ^(5)D_(4)→^(7)F_(J)(J=3-6) transitions under 254 nm-excitation.The dominant peak at 544 nm for ^(5)D_(4)→^(7)F_(5) transition is responsible for the emission of green light on ultraviolet-visible excitation in both the Tb^(3+)-doped host matrixes.Owing to advantageous properties like intense PL and high crystallinity,these nanophosphors could possess potential applications in the mercury free lighting sources and optoelectronic devices.展开更多
Ternary materials of europium complex with2,2,6,6-tetramethyl-3,5-heptanedione(tmhd) ligand and aqua ligand as ancillary ligands have been prepared and characterized for various optoelectronic characteristics.Reaction...Ternary materials of europium complex with2,2,6,6-tetramethyl-3,5-heptanedione(tmhd) ligand and aqua ligand as ancillary ligands have been prepared and characterized for various optoelectronic characteristics.Reactions of hydrated complex [Eu(tmhd)_(3)(H_(2)O)_(2)] proceeded with triphenylphosphine oxide(TPPO) and pyridine-N-oxide(PNO) ancillary ligands were studied to develop novel complexes. The prepared complexes show good thermal stability. A comparative investigation of preparedmaterials[Eu(tmhd)_(3)(H_(2)O)_(2)],[Eu(tmhd)_(3)(TPPO)_(2)] and [Eu(tmhd)_(3)(PNO)_(2)] was conducted for their luminescent behaviors in order to obtain the role of ancillary ligand in the enhancement of illumination amount generated from europium(Eu^(3+)) ion. Color coordinates of prepared ternary complexes such as[Eu(tmhd)_(3)(H_(2)O)_(2)]with(x = 0.54,y = 0.32),[Eu(tmhd)_(3)(TPPO)_(2)] with(x = 0.56, y = 0.32) and[Eu(tmhd)_(3)(PNO)_(2)] with(x = 0.57, y = 0.33) indicated that these materials exhibited bright red emission in visible region spectrum. The complexes show a proficient energy transport pathway from the ligands to the innermost Eu^(3+)by means of an ancillary ligand-sensitized luminescence process. Interaction between the metal and ligand results in a distinguished effect on quantum efficiency(η) as well as on Judd–Ofelt intensity factor(Ω_(2)) of the prepared materials.展开更多
To explore the silicate lattice-based nanophosphors, a series of Eu3+-doped Z_(2)Si_(3)O_(8)(Z = Mg, Ca and Sr) materials were prepared by sol–gel procedure. The metal nitrates and silica powder were used as precurso...To explore the silicate lattice-based nanophosphors, a series of Eu3+-doped Z_(2)Si_(3)O_(8)(Z = Mg, Ca and Sr) materials were prepared by sol–gel procedure. The metal nitrates and silica powder were used as precursor components for the synthesis of these luminescent materials. Photoluminescence(PL) emission spectra, powder X-ray diffraction(PXRD), energy-dispersive X-ray spectroscopy(EDS), Fourier transform infrared spectroscopy(FTIR) and transmission electron microscopy(TEM)spectroscopic techniques were applied for the characterization of the fabricated materials. Three peaks were observed at 589, 613 and 650–652 nm corresponding to ^(5)D_(0)→^(7)F_(1-3) transition in PL emission spectra. Upon395 nm excitation and at 0.03 mol Eu3+, these nanophosphors displayed optimum photoluminescence with the most intense peak analogous to ^(5)D_(0)→^(7)F_(2)transition of dopant ion. The as-prepared phosphor materials were re-heated at1050 and 1150 ℃ to observe the consequences of higher temperatures on the emission intensity and crystal lattice.XRD analysis confirmed that all the synthesized materials were of crystalline nature, and the crystallinity was observed to be improved by increasing the temperature. In the FTIR spectrum, peaks at 483 and 610 cm^(-1) proved the existence of SiO_(4)group in Ca_(2)Si_(3)O_(8), and the peak centered at 417 cm^(-1) confirmed the presence of MgO6 octahedral in Mg_(2)Si_(3)O_(8) materials. TEM images were used to determine the particle size(13–35 nm) and to study the threedimensional structure of nanophosphor materials. The experimental studies indicate that these materials may be promising as red-emitting nanophosphors for white lightemitting diodes.展开更多
基金The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through General Research Project under Grant No.(R.G.P2/73/41).
文摘The performance of a-posteriori error methodology based on moving least squares(MLS)interpolation is explored in this paper by varying the finite element error recovery parameters,namely recovery points and field variable derivatives recovery.The MLS interpolation based recovery technique uses the weighted least squares method on top of the finite element method’s field variable derivatives solution to build a continuous field variable derivatives approximation.The boundary of the node support(mesh free patch of influenced nodes within a determined distance)is taken as circular,i.e.,circular support domain constructed using radial weights is considered.The field variable derivatives(stress and strains)are recovered at two kinds of points in the support domain,i.e.,Gauss points(super-convergent stress locations)and nodal points.The errors are computed as the difference between the stress from the finite element results and projected stress from the post-processed energy norm at both elemental and global levels.The benchmark numerical tests using quadrilateral and triangular meshes measure the finite element errors in strain and stress fields.The numerical examples showed the support domain-based recovery technique’s capabilities for effective and efficient error estimation in the finite element analysis of elastic problems.The MLS interpolation based recovery technique performs better for stress extraction at Gauss points with the quadrilateral discretization of the problem domain.It is also shown that the behavior of the MLS interpolation based a-posteriori error technique in stress extraction is comparable to classical Zienkiewicz-Zhu(ZZ)a-posteriori error technique.
基金financially supported by the Senior Research Fellowship (SRF) from CSIR,New Delhi,India (No.09/382(0194)/2017-EMR-1)。
文摘The optical and structural properties of Tb^(3+)-doped yttrium and gadolinium oxyorthosilicate(Y_(2)SiO_(5) and Gd_(2)SiO_(5)) phosphors were analyzed.The samples were synthesized via sol-gel combustion method using organic fuel.The phase purity and structural properties of the samples were determined via combined approach of powder X-ray diffraction,Fourier transformation infrared(FTIR) and transmission electron microscopy(TEM).X-ray measurements revel monoclinic crystal lattice with P_(21/c) symmetry for both M_(2)SiO_(5)(pure host) and M_(2)SiO_(5):Tb^(3+)(doped) silicates,irrespective of the nature of metal(Y or Gd),presence or absence of Tb^(3+)in lattice and change in calcination temperature up to 1050℃.FTIR analysis was applied to confirm the bonding of prepared materials.The appearance of bands corresponding to SiO_(4) tetrahedra(880-1020 cm^(-1)) suggest the layered structure and support the diffraction measurements.TEM micrographs confirm the synthesis of spherical nanoparticles with filled morphology,narrow size distribution and slightly agglomerated crystallites of the samples.The elemental composition of prepared materials was determined using energy dispersive X-ray spectroscopy.The spectra show peaks only for elements assimilated within the host framework.The photoluminescence(PL) emission spectra of Tb^(3+)-doped samples show ^(5)D_(4)→^(7)F_(J)(J=3-6) transitions under 254 nm-excitation.The dominant peak at 544 nm for ^(5)D_(4)→^(7)F_(5) transition is responsible for the emission of green light on ultraviolet-visible excitation in both the Tb^(3+)-doped host matrixes.Owing to advantageous properties like intense PL and high crystallinity,these nanophosphors could possess potential applications in the mercury free lighting sources and optoelectronic devices.
基金financially supported by the program from the SERB-DST,New Delhi(No.EMR/2016/006,135)。
文摘Ternary materials of europium complex with2,2,6,6-tetramethyl-3,5-heptanedione(tmhd) ligand and aqua ligand as ancillary ligands have been prepared and characterized for various optoelectronic characteristics.Reactions of hydrated complex [Eu(tmhd)_(3)(H_(2)O)_(2)] proceeded with triphenylphosphine oxide(TPPO) and pyridine-N-oxide(PNO) ancillary ligands were studied to develop novel complexes. The prepared complexes show good thermal stability. A comparative investigation of preparedmaterials[Eu(tmhd)_(3)(H_(2)O)_(2)],[Eu(tmhd)_(3)(TPPO)_(2)] and [Eu(tmhd)_(3)(PNO)_(2)] was conducted for their luminescent behaviors in order to obtain the role of ancillary ligand in the enhancement of illumination amount generated from europium(Eu^(3+)) ion. Color coordinates of prepared ternary complexes such as[Eu(tmhd)_(3)(H_(2)O)_(2)]with(x = 0.54,y = 0.32),[Eu(tmhd)_(3)(TPPO)_(2)] with(x = 0.56, y = 0.32) and[Eu(tmhd)_(3)(PNO)_(2)] with(x = 0.57, y = 0.33) indicated that these materials exhibited bright red emission in visible region spectrum. The complexes show a proficient energy transport pathway from the ligands to the innermost Eu^(3+)by means of an ancillary ligand-sensitized luminescence process. Interaction between the metal and ligand results in a distinguished effect on quantum efficiency(η) as well as on Judd–Ofelt intensity factor(Ω_(2)) of the prepared materials.
文摘To explore the silicate lattice-based nanophosphors, a series of Eu3+-doped Z_(2)Si_(3)O_(8)(Z = Mg, Ca and Sr) materials were prepared by sol–gel procedure. The metal nitrates and silica powder were used as precursor components for the synthesis of these luminescent materials. Photoluminescence(PL) emission spectra, powder X-ray diffraction(PXRD), energy-dispersive X-ray spectroscopy(EDS), Fourier transform infrared spectroscopy(FTIR) and transmission electron microscopy(TEM)spectroscopic techniques were applied for the characterization of the fabricated materials. Three peaks were observed at 589, 613 and 650–652 nm corresponding to ^(5)D_(0)→^(7)F_(1-3) transition in PL emission spectra. Upon395 nm excitation and at 0.03 mol Eu3+, these nanophosphors displayed optimum photoluminescence with the most intense peak analogous to ^(5)D_(0)→^(7)F_(2)transition of dopant ion. The as-prepared phosphor materials were re-heated at1050 and 1150 ℃ to observe the consequences of higher temperatures on the emission intensity and crystal lattice.XRD analysis confirmed that all the synthesized materials were of crystalline nature, and the crystallinity was observed to be improved by increasing the temperature. In the FTIR spectrum, peaks at 483 and 610 cm^(-1) proved the existence of SiO_(4)group in Ca_(2)Si_(3)O_(8), and the peak centered at 417 cm^(-1) confirmed the presence of MgO6 octahedral in Mg_(2)Si_(3)O_(8) materials. TEM images were used to determine the particle size(13–35 nm) and to study the threedimensional structure of nanophosphor materials. The experimental studies indicate that these materials may be promising as red-emitting nanophosphors for white lightemitting diodes.
