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1.
Zhonghua Yu Fang Yi Xue Za Zhi ; 56(11): 1543-1548, 2022 Nov 06.
Artigo em Chinês | MEDLINE | ID: mdl-36372741

RESUMO

Objective: To evaluate the recognition of acute respiratory infection (ARI) by a pretrained model based on electronic medical records (EMRs). Methods: 38 581 EMRs were obtained from Chongqing University Three Gorges Hospital in December 2021. Bidirectional encoder representation from transformers (BERT) pretrained model was used to identify ARI in EMRs. The results of medical professionals were considered as the gold standard to calculate the sensitivity, specificity, Kappa value, and area under the curve of the receiver operating characteristic (AUC). Results: There were 3 817 EMRs in the test set, with 1 200 ARIs. A total of 1 205 cases were determined as ARI by the model, with a sensitivity of 92.67% (1 112/1 200) and a specificity of 96.45% (2 524/2 617). The model identified ARI with similar accuracy in males and females (AUCs 0.95 and 0.94, respectively), and was more accurate in identifying ARI cases in those aged less than 18 than in adults 18-59 and adults 60 and older (AUCs 0.94, 0.89 and 0.94, respectively). The current model had a better identification of ARIs in outpatient patients than that in hospitalized patients, with AUCs of 0.74 and 0.95, respectively. Conclusion: The use of the BERT pretrained model based on EMRs has a good performance in the recognition of ARI cases, especially for the outpatients and juveniles. It shows a great potential to be applied to the monitoring of ARI cases in medical institutions.


Assuntos
Registros Eletrônicos de Saúde , Infecções Respiratórias , Adulto , Masculino , Feminino , Humanos , Infecções Respiratórias/diagnóstico , Pacientes Ambulatoriais
2.
Radiat Environ Biophys ; 53(2): 311-20, 2014 May.
Artigo em Inglês | MEDLINE | ID: mdl-24671362

RESUMO

This paper presents the results of an interlaboratory comparison of retrospective dosimetry using the electron paramagnetic resonance method. The test material used in this exercise was glass coming from the touch screens of smart phones that might be used as fortuitous dosimeters in a large-scale radiological incident. There were 13 participants to whom samples were dispatched, and 11 laboratories reported results. The participants received five calibration samples (0, 0.8, 2, 4, and 10 Gy) and four blindly irradiated samples (0, 0.9, 1.3, and 3.3 Gy). Participants were divided into two groups: for group A (formed by three participants), samples came from a homogeneous batch of glass and were stored in similar setting; for group B (formed by eight participants), samples came from different smart phones and stored in different settings of light and temperature. The calibration curves determined by the participants of group A had a small error and a critical level in the 0.37-0.40-Gy dose range, whereas the curves determined by the participants of group B were more scattered and led to a critical level in the 1.3-3.2-Gy dose range for six participants out of eight. Group A were able to assess the dose within 20 % for the lowest doses (<1.5 Gy) and within 5 % for the highest doses. For group B, only the highest blind dose could be evaluated in a reliable way because of the high critical values involved. The results from group A are encouraging, whereas the results from group B suggest that the influence of environmental conditions and the intervariability of samples coming from different smart phones need to be further investigated. An alongside conclusion is that the protocol was easily transferred to participants making a network of laboratories in case of a mass casualty event potentially feasible.


Assuntos
Telefone Celular , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Vidro , Radiometria/métodos , Calibragem , Humanos , Estatística como Assunto
3.
J Biol Chem ; 287(42): 35260-35274, 2012 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-22923616

RESUMO

Adipose phospholipase A(2) (AdPLA or Group XVI PLA(2)) plays an important role in the onset of obesity by suppressing adipose tissue lipolysis. As a consequence, AdPLA-deficient mice are resistant to obesity induced by a high fat diet or leptin deficiency. It has been proposed that AdPLA mediates its antilipolytic effects by catalyzing the release of arachidonic acid. Based on sequence homology, AdPLA is part of a small family of acyltransferases and phospholipases related to lecithin:retinol acyltransferase (LRAT). To better understand the enzymatic mechanism of AdPLA and LRAT-related proteins, we solved the crystal structure of AdPLA. Our model indicates that AdPLA bears structural similarity to proteins from the NlpC/P60 family of cysteine proteases, having its secondary structure elements configured in a circular permutation of the classic papain fold. Using both structural and biochemical evidence, we demonstrate that the enzymatic activity of AdPLA is mediated by a distinctive Cys-His-His catalytic triad and that the C-terminal transmembrane domain of AdPLA is required for the interfacial catalysis. Analysis of the enzymatic activity of AdPLA toward synthetic and natural substrates indicates that AdPLA displays PLA(1) in addition to PLA(2) activity. Thus, our results provide insight into the enzymatic mechanism and biochemical properties of AdPLA and LRAT-related proteins and lead us to propose an alternate mechanism for AdPLA in promoting adipose tissue lipolysis that is not contingent on the release of arachidonic acid and that is compatible with its combined PLA(1)/A(2) activity.


Assuntos
Modelos Moleculares , Fosfolipases A2 Independentes de Cálcio/química , Proteínas Supressoras de Tumor/química , Aciltransferases/química , Aciltransferases/genética , Aciltransferases/metabolismo , Animais , Domínio Catalítico , Cristalografia por Raios X , Humanos , Camundongos , Fosfolipases A2 Independentes de Cálcio/genética , Fosfolipases A2 Independentes de Cálcio/metabolismo , Estrutura Terciária de Proteína , Relação Estrutura-Atividade , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismo
4.
J Phys Chem A ; 116(14): 3547-55, 2012 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-22409286

RESUMO

Electron paramagnetic resonance (EPR), optical absorption, and FT-IR spectra of vanadyl ions in the sodium-lead borophosphate (Na(2)O-PbO-B(2)O(3)-P(2)O(5)) (SLBP) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO(2+) ions. The spin Hamiltonian parameters g and A are found to be independent of the V(2)O(5) content and temperature. The values of the spin Hamiltonian parameters indicate that the VO(2+) ions in SLBP glasses are present in octahedral sites with tetragonal compression. The population difference between Zeeman levels (N) is calculated as a function of temperature for an SLBP glass sample containing 1.0 mol % VO(2+) ions. From the EPR data, the paramagnetic susceptibility (χ) is calculated at different temperatures, and the Curie constant (C) is calculated from the 1/χ versus T graph. The optical absorption spectra of the glass samples show two absorption bands, and they are attributed to V(3+) and V(4+) ions. The optical band gap energy (E(opt)) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. It is observed that, as the vanadium ion concentration increases, E(opt) decreases and ΔE increases. The study of the IR absorption spectrum depicts the presence of BO(3), BO(4), PO(3), PO(4), and VO(5) structural units.


Assuntos
Materiais Biocompatíveis/química , Compostos de Boro/química , Chumbo/química , Óxidos/química , Compostos de Fósforo/química , Compostos de Sódio/química , Vanadatos/química , Espectroscopia de Ressonância de Spin Eletrônica , Vidro , Íons , Dispositivos Ópticos , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura , Termodinâmica
5.
J Bacteriol ; 193(23): 6605-13, 2011 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21965566

RESUMO

The TetR family of transcriptional regulators is ubiquitous in bacteria, where it plays an important role in bacterial gene expression. Streptococcus mutans, a gram-positive pathogen considered to be the primary etiological agent in the formation of dental caries, encodes at least 18 TetR regulators. Here we characterized one such TetR regulator, SMU.1349, encoded by the TnSmu2 operon, which appeared to be acquired by the organism via horizontal gene transfer. SMU.1349 is transcribed divergently from the rest of the genes encoded by the operon. By the use of a transcriptional reporter system and semiquantitative reverse transcription-PCR (RT-PCR), we demonstrated that SMU.1349 activates the transcription of several genes that are encoded within the TnSmu2 operon. Gel mobility shift and DNase I footprinting assays with purified SMU.1349 protein demonstrated binding to the intergenic region between SMU.1349 and the TnSmu2 operon; therefore, SMU.1349 is directly involved in gene transcription. Using purified S. mutans RpoD and Escherichia coli RNA polymerase, we also demonstrated in an in vitro transcription assay that SMU.1349 could activate transcription from the TnSmu2 operon promoter. Furthermore, we showed that SMU.1349 could also repress transcription from its own promoter by binding to the intergenic region, suggesting that SMU.1349 acts as both an activator and a repressor. Thus, unlike most of the TetR family proteins, which generally function as transcriptional repressors, SMU.1349 is unique in that it can function as both.


Assuntos
Proteínas de Bactérias/metabolismo , Regulação Bacteriana da Expressão Gênica , Streptococcus mutans/metabolismo , Transcrição Gênica , Proteínas de Bactérias/genética , Óperon , Regiões Promotoras Genéticas , Ligação Proteica , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Streptococcus mutans/genética , Transativadores/genética , Transativadores/metabolismo
6.
Appl Biochem Biotechnol ; 150(2): 205-19, 2008 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-18443744

RESUMO

alpha-Amylases reported from various microbial sources have been shown to be moderately thermostable and Ca2+ dependent. The bacterial strain used in this investigation is an extremely thermophilic bacterium Geobacillus thermoleovorans that produces a novel alpha-amylase (26 kDa; alpha-amylase gt), which is hyperthermostable (Topt 100 degrees C) and does not require Ca2+ for its activity/stability. These special features of alpha-amylase gt make it applicable in starch saccharification process. The structural aspects of alpha-amylase gt are, therefore, of significant interest to understand its structure-function relationship. The circular dichroism spectroscopic data revealed the native alpha-amylase gt to contain 25% alpha-helix, 21% beta-sheet, and 54% random coils. The addition of urea, at high concentration (8 M), appeared to expose the buried Trp residues of the native alpha-amylase gt to the aqueous environment and thus showed low fluorophore. Fluorescence-quenching experiments using KI, CsCl, N-bromosuccinimide, and acrylamide revealed interesting features of the tryptophan microenvironment. Analysis of Ksv and fa values of KI, CsCl, and acrylamide suggested the overall Trp microenvironment in alpha-amylase to be slightly electropositive. Fluorescence-quenching studies with acrylamide revealed the occurrence of both collisional as well as static quenching processes. There was no change in the alpha-helix content or the enzyme activity with an increase in temperature (60-100 degrees C) that suggested a critical role of the alpha-helix content in maintaining the catalytic activity.


Assuntos
Bacillaceae/enzimologia , Cálcio/metabolismo , alfa-Amilases/metabolismo , Bacillaceae/genética , Bacillaceae/metabolismo , Estabilidade Enzimática , Temperatura
7.
Spectrochim Acta A Mol Biomol Spectrosc ; 71(3): 809-13, 2008 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-18372211

RESUMO

EPR spectral investigations of some commonly available vegetables in south India, which are of global importance like Daucus carota (carrot), Cyamopsis tetragonoloba (cluster beans), Coccinia indica (little gourd) and Beta vulgaris (beet root) have been carried out. In all the vegetable samples a free radical corresponding to cellulose radical is observed. Almost all the samples under investigation exhibit Mn ions in different oxidation states. The temperature variation EPR studies are done and are discussed in view of the paramagnetic oxidation states. The radiation-induced defects have also been assessed by using the EPR spectra of such irradiated food products.


Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Irradiação de Alimentos , Minerais/análise , Verduras/química , Verduras/efeitos da radiação , Beta vulgaris/química , Beta vulgaris/efeitos da radiação , Celulose/química , Celulose/efeitos da radiação , Cucurbitaceae/química , Cucurbitaceae/efeitos da radiação , Cyamopsis/química , Cyamopsis/efeitos da radiação , Daucus carota/química , Daucus carota/efeitos da radiação , Radicais Livres/análise , Temperatura Alta , Índia , Manganês/análise , Manganês/química , Oxirredução
8.
Bioresour Technol ; 98(2): 345-52, 2007 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-16473003

RESUMO

By cultivating Geobacillus thermoleovorans in shake flasks containing cane molasses medium at 70 degrees C, the fermentation variables were optimized by 'one variable at a time' approach followed by response surface methodology (RSM). The statistical model was obtained by central composite design (CCD) using three variables (cane-molasses, urea and inoculum density). An overall 1.6- and 2.1-fold increase in enzyme production was achieved in the optimized medium in shake flasks and fermenter, respectively. The alpha-amylase titre increased significantly in cane-molasses medium (60 U ml(-1)) as compared to that in the synthetic medium (26 U ml(-1)). Thus the cost of enzyme produced in cane molasses medium (0.823 euros per million U) was much lower than that produced in the synthetic starch-yeast extract-tryptone medium (18.52 euros per million U). The shelf life of bread was improved by supplementing dough with alpha-amylase, and thus, the enzyme was found to be useful in preventing the staling of bread. Reducing sugars liberated from 20% and 30% raw pearl millet starch were fermented to ethanol; ethanol production levels attained were 35.40 and 28.0 g l(-1), respectively.


Assuntos
Bacillaceae/enzimologia , Maltose/metabolismo , alfa-Amilases/metabolismo , Pão , Cálcio/metabolismo , Culinária , Estabilidade Enzimática , Fermentação , Temperatura Alta , Pennisetum/química , Amido/química , Amido/metabolismo , alfa-Amilases/química
9.
Appl Biochem Biotechnol ; 142(2): 179-93, 2007 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-18025579

RESUMO

The purified alpha-amylase of Geobacillus thermoleovorans had a molecular mass of 26 kDa with a pI of 5.4, and it was optimally active at 100 degrees C and pH 8.0. The T 1/2 of alpha-amylase at 100 degrees C increased from 3.6 to 5.6 h in the presence of cholic acid. The activation energy and temperature quotient (Q 10) of the enzyme were 84.10 kJ/mol and 1.31, respectively. The activity of the enzyme was enhanced strongly by Co2+ and Fe2+; enhanced slightly by Ba2+, Mn2+, Ni2+, and Mg2+; inhibited strongly by Sn2+, Hg2+, and Pb2+, and inhibited slightly by EDTA, phenyl methyl sulfonyl fluoride, N-ethylmaleimide, and dithiothreitol. The enzyme activity was not affected by Ca2+ and ethylene glycol-bis (beta-amino ethyl ether)-N,N,N,N-tetra acetic acid. Among different additives and detergents, polyethylene glycol 8000 and Tween 20, 40, and 80 stabilized the enzyme activity, whereas Triton X-100, glycerol, glycine, dextrin, and sodium dodecyl sulfate inhibited to a varied extent. alpha-Amylase exhibited activity on several starch substrates and their derivatives. The K m and K cat values (soluble starch) were 1.10 mg/ml and 5.9 x 10(3)/min, respectively. The enzyme hydrolyzed raw starch of pearl millet (Pennisetum typhoides) efficiently.


Assuntos
Bacillaceae/enzimologia , Glicosídeo Hidrolases/química , Glicosídeo Hidrolases/isolamento & purificação , Temperatura , Bacillaceae/classificação , Bacillaceae/ultraestrutura , Ativação Enzimática , Estabilidade Enzimática , Glicosídeo Hidrolases/ultraestrutura , Concentração de Íons de Hidrogênio , Hidrólise , Cinética , Metais/metabolismo , Microscopia Eletrônica de Varredura , Pennisetum/metabolismo , Amido/metabolismo , Especificidade por Substrato
10.
J Nanosci Nanotechnol ; 16(1): 789-96, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27398524

RESUMO

By adopting a facile solution combustion synthesis, crystallized europium doped blue phosphors were successfully prepared. These phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared absorption (FT-IR), energy dispersive analysis of X-ray, Electron Paramagnetic Resonance (EPR) and Photoluminescence (PL) experimental methods. The photoluminescence spectrum indicates Eu²âº and Eu³âº ions in these phosphors. The band at around 442 nm is attributed to the spin-allowed 4f65d¹ (2D) --> 4f7(8S7/2) transition of Eu²âº ions. The sharp bands at 591 (5D0 --> 7F1) and 616 (5D0 --> 7F2) nm are attributed to the spin-forbidden transitions of Eu³âº ions. The EPR spectra of as-prepared and post-treated LaAl11O18:Eu phosphors exhibit signals characteristic of La²âº and Eu²âº ions. The number of spins, Gibbs energy, magnetic susceptibility, Curie constant and effective magnetic moment values were calculated and compared at 296 and 110 K.

11.
Spectrochim Acta A Mol Biomol Spectrosc ; 61(9): 2169-79, 2005 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-15911407

RESUMO

An investigations of the optical absorption and fluorescence spectra of 0.2 mol% Er2O3 in mixed alkali borate glasses of the type 67.8B2O3 x xLi2O(32-x)Na2O, 67.8B2O3 x xLi2O(32-x)K2O and 67.8B2O3 x xNa2O(32-x)K2O (where x = 8, 12, 16, 20 and 24) are presented. The glasses were obtained by quenching melts consisting of H3BO3, Li2CO3, Na2CO3, K2CO3 and Er2O3 (950-1100 degrees C, 1.5-2 h) between two brass plates. Spectroscopic parameters like Racah (E1, E2 and E3), spin-orbit (xi(4f)) and configuration interaction (alpha) parameters are deduced as function of x. Using Judd-Ofelt theory, Judd-Ofelt intensity parameters (omega2, omega4 and omega6) are obtained. Radiative and non-radiative transition rates (A(T) and W(MPR)), radiative lifetimes (tauR), branching ratios (beta) and integrated absorption cross-sections (sigma) have been computed for certain excited states of Er3+ in these mixed alkali borate glasses. Emission spectra have been studied for all the three Er3+ doped mixed alkali borate glasses. The present paper throws light on the trends observed in the intensity parameters, radiative lifetimes, branching ratios and emission cross-sections as a function of x in these borate glasses, keeping in view the effect of mixed alkalies in borate glasses.


Assuntos
Álcalis/química , Boratos/química , Érbio/química , Vidro/química , Absorção , Cátions/química , Concentração de Íons de Hidrogênio , Medições Luminescentes , Óptica e Fotônica , Fotoquímica , Espectrofotometria
12.
Artigo em Inglês | MEDLINE | ID: mdl-25546490

RESUMO

The gadolinium doped CaAl12O19 phosphor has been prepared by a low temperature solution combustion method in a short time and characterized using powder X-ray diffraction, energy dispersive analysis of X-ray mapping, electron paramagnetic resonance (EPR) and photoluminescence spectroscopic techniques. EPR and optical analysis of the sample confirm the presence of Gd(3+) in the CaAl12O19 matrix.


Assuntos
Compostos de Alumínio/química , Compostos de Cálcio/química , Cálcio/química , Gadolínio/química , Luminescência , Substâncias Luminescentes/química , Óxidos/química , Espectroscopia de Ressonância de Spin Eletrônica , Íons , Espectrometria por Raios X , Difração de Raios X
13.
Spectrochim Acta A Mol Biomol Spectrosc ; 56A(7): 1345-53, 2000 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-10888440

RESUMO

The electron paramagnetic resonance (EPR) and infrared (IR) spectral studies have been employed on the periostracum, the prismatic layer and the nacre of the shell of the marine bivalve molluscan Mytilus conradinus of the South Indian origin. All the layers of this shell show Fe3+ ion spin resonance signals in common. The inner layer namely nacre at room temperature shows EPR signals of Fe3+ ions and the heated one exhibits a sextet hyperfine pattern characteristic of Mn2+ ions. The prismatic layer of the shell also exhibits a similar spectrum, but of distinct pattern. The spin-Hamiltonian parameters have been evaluated for the prismatic and nacreous layers of this shell. Infrared spectra of the two main layers of the shell namely prismatic and the nacre exhibit the characteristic bands of CO3(2-) molecular ion in different symmetries of CaCO3.


Assuntos
Bivalves/química , Animais , Espectroscopia de Ressonância de Spin Eletrônica , Minerais/química , Espectroscopia de Luz Próxima ao Infravermelho
14.
Spectrochim Acta A Mol Biomol Spectrosc ; 60(11): 2441-8, 2004 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-15294226

RESUMO

Electron paramagnetic resonance (EPR), optical, infrared and Raman spectral studies have been performed on a natural Actinolite mineral. The room temperature EPR spectrum reveals the presence of Mn(2+) and Fe(3+) ions giving rise to two resonance signals at g = 2.0 and 4.3, respectively. The resonance signal at g = 2.0 exhibits a six line hyperfine structure characteristic of Mn(2+) ions. EPR spectra have been studied at different temperatures from 123 to 433 K. The number of spins (N) participating in the resonance at g = 2.0 has been calculated at different temperatures. A linear relationship is observed between log N and 1/T in accordance with Boltzmann law and the activation energy was calculated. The paramagnetic susceptibility (chi) has been calculated at different temperatures and is found to be increasing with decreasing temperature as expected from Curie's law. From the graph of 1/chi versus T, the Curie constant and Curie temperature have been evaluated. The optical absorption spectrum exhibits bands characteristic of Fe(2+) and Fe(3+) ions. The crystal field parameter Dq and the Racah parameters B and C have been evaluated from the optical absorption spectrum. The infrared spectral studies reveal the formation of Fe(3+)--OH complexes due to the presence of higher amount of iron in this mineral. The Raman spectrum exhibits bands characteristic of Si--O--Si stretching and Mg?OH translation modes.


Assuntos
Amiantos Anfibólicos/química , Interpretação Estatística de Dados , Espectroscopia de Ressonância de Spin Eletrônica , Espectrofotometria Infravermelho , Análise Espectral Raman , Temperatura
15.
Spectrochim Acta A Mol Biomol Spectrosc ; 59(13): 2955-65, 2003 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-14583272

RESUMO

Electron Paramagnetic Resonance (EPR), optical and infrared (IR) spectral studies have been performed on the pure and Cu-adsorbed exoskeletons of marine environment. The EPR spectrum of exoskeletons at room temperature exhibits a sharp signal at g approximately 1.9970. The possible redox mechanisms have been noticed on heating these exoskeletons in which the low spin Mn(3+) reduces to Mn(2+). The optical absorption spectra also give the evidence of the presence of Mn(3+) ions. The effects of thermal sintering on the EPR spectra have been studied and discussed in detail. The Cu-adsorbed samples clearly showed the adsorption of the Cu(2+) ions over CaCO(3) and the redox mechanism in these samples have been monitored by EPR.


Assuntos
Carbonato de Cálcio/química , Cobre , Crustáceos/química , Moluscos/química , Animais , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Oxirredução , Água do Mar , Espectrofotometria Infravermelho/métodos
16.
Artigo em Inglês | MEDLINE | ID: mdl-24607471

RESUMO

A simple and inexpensive combustion method was used to prepare Fe(3+) doped YAlO3 perovskite within few minutes at low temperature (400±10°C). This might be useful in lowering the cost of the material. The final products were well characterized by various spectroscopic techniques such as PXRD, SEM, TEM, FTIR and UV-Visible. The average crystallite size was estimated from the broadening of the PXRD peaks and found to be in the range 45-90nm, the results were in good agreement with the W-H plots and TEM. The crystallites show dumbbell shape, agglomerated particles with different size. The TL glow curves of 1-5kGy γ-irradiated YAlO3:Fe(3+) (0.1mol%) nanopowder warmed at a heating rate of 3°Cs(-1) records a single glow peak at ∼260°C. The kinetic parameters namely activation energy (E), order of kinetics (b) and frequency factor (s) were determined at different gamma doses using the Chens glow peak shape method and the results were discussed in detail. The photoluminescence spectra for Fe(3+) (0.1-0.9mol%) doped YAlO3 records the lower energy band at 720nm ((4)T1 (4G)→(6)A1 (6S)) and the intermediate band located at 620nm ((4)T2 ((4)G)→(6)A1 (6S)) with the excitation of 378nm. The higher energy band located at 514nm was associated to (4)E+(4)A1 ((4)G)→(6)A1 (6S) transition. The resonance signals at g values 7.6, 4.97, 4.10, 2.94, 2.33 and 1.98 were observed in EPR spectra of Fe(3+) (0.1-0.9mol%) doped YAlO3 recorded at room temperature. The g values indicate that the iron ions were in trivalent state and distorted octahedral site symmetry was observed.


Assuntos
Compostos de Alumínio/química , Ferro/química , Substâncias Luminescentes/química , Ítrio/química , Compostos de Alumínio/síntese química , Compostos de Cálcio/síntese química , Compostos de Cálcio/química , Cátions/síntese química , Cátions/química , Espectroscopia de Ressonância de Spin Eletrônica , Luminescência , Substâncias Luminescentes/síntese química , Medições Luminescentes , Nanopartículas/química , Nanopartículas/ultraestrutura , Óxidos/síntese química , Óxidos/química , Pós , Espectrofotometria Ultravioleta , Espectroscopia de Infravermelho com Transformada de Fourier , Titânio/química , Difração de Raios X
17.
Artigo em Inglês | MEDLINE | ID: mdl-23291114

RESUMO

α-Fe(2)O(3) nanoparticles were synthesized by a low temperature solution combustion method. The structural, magnetic and luminescence properties were studied. Powder X-ray diffraction (PXRD) pattern of α-Fe(2)O(3) exhibits pure rhombohedral structure. SEM micrographs reveal the dumbbell shaped particles. The EPR spectrum shows an intense resonance signal at g≈5.61 corresponding to isolated Fe(3+) ions situated in axially distorted sites, whereas the g≈2.30 is due to Fe(3+) ions coupled by exchange interaction. Raman studies show A(1g) (225 cm(-1)) and E(g) (293 and 409 cm(-1)) phonon modes. The absorption at 300 nm results from the ligand to metal charge transfer transitions whereas the 540 nm peak is mainly due to the (6)A(1)+(6)A(1)→(4)T(1)(4 G)+(4)T(1)(4 G) excitation of an Fe(3+)-Fe(3+) pair. A prominent TL glow peak was observed at 140°C at heating rate of 5 °Cs(-1). The trapping parameters namely activation energy (E), frequency factor (s) and order of kinetics (b) were evaluated and discussed.


Assuntos
Compostos Férricos/química , Fenômenos Magnéticos , Nanopartículas/química , Fenômenos Ópticos , Espectroscopia de Ressonância de Spin Eletrônica , Cinética , Medições Luminescentes , Nanopartículas/ultraestrutura , Espectrofotometria Ultravioleta , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman , Temperatura , Difração de Raios X
18.
Artigo em Inglês | MEDLINE | ID: mdl-22579331

RESUMO

Nanocrystalline Nd(2)O(3):Cu(2+) (2mol %) phosphors have been prepared by a low temperature solution combustion technique. Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd(2)O(3) (900°C, 3h) and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of as-formed and Cu(2+) doped Nd(2)O(3) phosphors show that the particles are irregular in shape and porous in nature. TEM results also confirm the nature and size of the particles. The EPR spectrum exhibits two resonance signals with effective g values at g(ǀǀ)≈2.12 and g(⊥)≈2.04. The g values indicate that the site symmetry of Cu(2+) ions is octahedral symmetry with elongated tetragonal distortion. Raman studies show major peaks, which are assigned, to F(g) and combination of A(g)+E(g) modes. It is observed that the Raman peaks and intensity have been reduced in Cu(2+) doped samples. UV-Visible absorption spectra exhibit a strong and broad absorption band at ∼240nm. Further, the absorption peak shifts to ∼14nm in Cu(2+) doped samples. The optical band gap is estimated to be 5.28eV for Cu doped Nd(2)O(3) nanoparticles which are higher than the bulk Nd(2)O(3) (4.7eV). This can be attributed to the quantum confinement effect of the nanoparticles.


Assuntos
Cobre/química , Luminescência , Nanopartículas/química , Neodímio/química , Óxidos/química , Análise Espectral Raman , Espectroscopia de Ressonância de Spin Eletrônica , Nanopartículas/ultraestrutura , Tamanho da Partícula , Pós , Espectrofotometria Ultravioleta , Propriedades de Superfície , Termodinâmica , Difração de Raios X
19.
Artigo em Inglês | MEDLINE | ID: mdl-22673389

RESUMO

YAlO(3):Cr(3+) (0.1 mol%) nanophosphor has been synthesized by low temperature solution combustion method. The X-ray diffraction studies reveal an orthorhombic structure. Transmission electron microscopy reveals that the particles are spherical in shape with nano-size ~40-65 nm. Electron paramagnetic resonance (EPR) spectrum shows a resonance signal with effective g value at g=1.978 which can be attributed to the exchange coupled Cr(3+) ion pairs in weakly distorted sites. The photoluminescence spectrum shows an intense doublet at 677 nm and 694 nm (R lines) assigned to spin-forbidden (2)E(g)→(4)A(2)(g) transition of Cr(3+) ions. EPR and PL studies reveal that the Cr(3+) ions occupy Al(3+) sites in YAlO(3). The interesting feature reported in this work concerns the linearity with gamma dose in the wide range (0.1-6 kGy). Prominent TL glow peaks at 226 °C and 346 °C were observed for both γ and UV-rays respectively. It is observed that the peaks at 226 °C and 346 °C eventually show a linear response up to 5 kGy which makes them a candidate for high dose dosimetry of ionizing radiation. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped and Cr doped samples were determined using Chens glow peak shape method and the results are discussed in detail.


Assuntos
Compostos de Alumínio/química , Cromo/química , Medições Luminescentes/métodos , Nanopartículas/química , Dosimetria Termoluminescente/métodos , Ítrio/química , Relação Dose-Resposta à Radiação , Espectroscopia de Ressonância de Spin Eletrônica , Raios gama , Temperatura Alta , Cinética , Espectrofotometria Ultravioleta , Espectroscopia de Infravermelho com Transformada de Fourier , Raios Ultravioleta , Difração de Raios X
20.
Artigo em Inglês | MEDLINE | ID: mdl-22484256

RESUMO

Nanocrystalline Nd(2)O(3):Ni(2+) (2 mol%) phosphor has been prepared by a low temperature (∼400°C) solution combustion method, in a very short time (<5 min). Powder X-ray diffraction results confirm the single hexagonal phase of nanopowders. Scanning electron micrographs show that nanophosphor has porous nature and the particles are agglomerated. Transmission electron microscopy confirms the nanosize (20-25 nm) of the crystallites. The electron paramagnetic resonance (EPR) spectrum exhibits a symmetric absorption at g≈2.77 which suggests that the site symmetry around Ni(2+) ions is predominantly octahedral. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) has been evaluated. Raman study show major peaks, which are assigned to F(g) and combination of A(g)+E(g) modes. Thermoluminescence (TL) studies reveal well resolved glow peaks at 169°C along with shoulder peak at around 236°C. The activation energy (E in eV), order of kinetics (b) and frequency factor (s) were estimated using glow peak shape method. It is observed that the glow peak intensity at 169°C increases linearly with γ-dose which suggest that Nd(2)O(3):Ni(2+) is suitable for radiation dosimetry applications.


Assuntos
Neodímio/química , Níquel/química , Óxidos/química , Cristalização , Espectroscopia de Ressonância de Spin Eletrônica , Raios gama , Luminescência , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Dosimetria Termoluminescente , Difração de Raios X
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