Dielectric response of KCN crystal at ultralow frequencies

The dielec. response of pure KCN crystals (ƒÃ\u27, ƒÃ", and tan ƒÂ) was measured as a function of temp. in the frequency range 10-2 to 104 Hz. In the antiferroelec. phase the width of the loss peak is found practically independent of temp. and close to Debye behavior; the relaxation time of the CN- dipoles is characterized by an Arrhenius behavior ƒÑ = ƒÑ0exp (U/KT) with ƒÑ3 = 7.26 \u27~ 10-15 s and U = 0, 147 eV confirming a classical temp. activated reorientation of the dipoles

Pre-resonant Raman effect of CrO2-4 in a metasilicate glass

Pre-resonant Raman effect of chromate ion, CrO42-, was observed in a metasilicate glass with molar composition 2Na2O · 1CaO · 3SiO2 containing 1.0 wt% of Cr2O3. Raman spectra were measured by the conventional 90° scattering geometry and by the microprobe Raman spectroscopic techniques. The presence of chromate ions in the glass is favoured by the glass composition and oxidizing conditions during the glass melting, and they are responsible for optical absorption bands at 370 and 250 nm. Raman spectrum of the undoped glass presents bands at 625, 860 and 980 cm-1, and the presence of chromate ions gives rise to additional bands at 365, 850 and a shoulder at 890 cm-1. An enhancement of the 850 cm-1 Raman band is observed with decreasing laser exciting wavelength. The exciting frequency dependence of the intensity of this band is discussed in terms of theoretical models given in the literature

Reorganização dos ajustes posturais antecipatórios em indivíduos após AVE: influência de um programa de intervenção em fisioterapia no registo electromiográfico do tibial anterior e solear

Introdução: As dificuldades encontradas em individuos após Acidente Vascular Encefálico, ao nível da marcha, influenciam significativamente o retorno ao trabalho, a participação na comunidade ou o desempenho nas actividades da vida diária. Objectivo: Neste trabalho, procurou-se verificar qual o efeito de um programa de intervenção em fisioterapia nos ajustes posturais antecipatórios que ocorrem previamente ao movimento voluntário e assim pré-determinar a sua contribuição para a estabilidade postural e o equilíbrio. Material e Métodos: Para testar os pressupostos inerentes, relatam-se dois casos clínicos de sujeitos do sexo masculino com diagnóstico de Acidente Vascular Encefálico. Estes foram submetidos a um programa de intervenção em fisioterapia, durante 10 semanas consecutivas, baseado no Conceito de Bobath e que teve em conta o principal problema de cada indivíduo. Foi monitorizada a actividade electromiográfica do ventre medial do Tibial Anterior e Solear na fase de pré-activação da marcha, em dois momentos distintos, no início e no fim da intervenção. Resultados: Dos resultados obtidos evidenciam-se as diferenças entre os tempos médios de pré-activação, bem como as diferenças entre a percentagem da contracção isométrica voluntária máxima atingida pelos músculos Tibial Anterior e Solear, direito e esquerdo, entre os dois momentos de avaliação, em ambos os sujeitos. Verificou-se, no entanto, que a actividade electromiográfica dos referidos músculos possui grande variabilidade. Conclusão: Os resultados sugerem que o programa de intervenção em fisioterapia parece ter tido influência no recrutamento da actividade muscular do TA e do SO, uma vez que, em termos médios absolutos, ocorreram diferenças após a implementação das estratégias e procedimentos da intervenção.Introduction: The difficulties found in individuals after stroke, on the basis of walking independently, are a huge influence in the ability to return to work, participate in the community or perform other activities of daily living. Purpose: Whith this research, it is aimed to verify the effect of a program of physiotherapy intervention in the anticipatory postural adjustments which occur previously to the voluntary movement and by this pre-determinate its contribution to the postural stability and equilibrium. Methods and Materials: To test the inerent assumptions, it is described two clinical cases of two male individuals with stroke diagnosis. Both were submitted to an intervention program of Physioterapy, for ten consecutives weeks, based in the Bobath Concept which had in focus the main problem of the individuals. In each individual it was monitorize the electromyography activity of the Tibialis Anterior and Soleus in the phase of pre-activation of the gait, in two distinguish moments, at the beginning and at the end of the intervention. Results: From the results obtained, it is verified the diferences between the medium times of pre-activation, and also the diferences between the percentage of the maximum voluntary isometric contraction achieved by the Tibialis Anterior and Soleus muscles, right and left, between the two moments of evaluation, in both individuals. Although, it was verify that the electromiographic activity of the refered muscles, has a high variability. Conclusion: The results obtained let us suggest that the intervention in physiotherapy established seams to have influence in the muscular activity recruitement of the Tibialis Anterior and Soleus because, in absolutes medium terms, occured differences after the implementation of the procedures and strategies of the intervention

Pump and probe spectroscopy of A Cr+3-doped glass

Probe beam modulation in Cr+3-doped glasses induced by a high intensity pump laser is reported. A non-degenerate pump and probe geometry is used. Laser induced clearing and darkening effects and non-linear switching were observed. The effective relaxation time for this system was measured

Surface corrosion of soda-lime metasilicate glasses

-Metasilicate glasses have a mean of 2 non-bridging oxigens per SiO4 tetrahedron, so that its structure is constituted essentially by (SiO3(2-))n chains. Due to the low polymerization degree of the SiO4 tetrahedra, the surface of such glasses undergoes pronounced physico-chemical changes in contact with water, acid solutions and with the surrounding atmosphere. Surfaces of a 2Na2O∙1CaO∙2SiO2 glass were submitted to corrosion by a weak HCl and HF solution. Infrared reflection spectroscopy measurements show that the characteristic bands of the glass change with leaching time. The prolonged corrosion by the acid solution gives spectra which approach that of a porous silica glass (Vycor). This leads to the conclusion that the acid corrosion produces a thin silica gel layer at the metasilicate glass surface

Raman spectroscopy of 2Na(2)0.1Ca0.3SiO(2) glass and glass-ceramics

2Na(2)0.1Ca0.3SiO(2) glass and glass-ceramics are investigated by conventional and microprobe Raman spectroscopy. The glass spectrum can be deconvolved into 6 gaussian bands located at 860, 920, 975, 1030 cm(-1) attributed to stretching of Si-nonbridging oxygen (NBO) bond and at 625, 660 cm(-1) attributed to Si-O-Si bond vibrations. Partially crystallized glass is formed as spherulites imbedded in the amorphous phase. Their Raman activities show that during crystallization the number of SiO4 tetrahedra having 2 NBO increases and that the Si-O-Si bonds soften. Highly crystallized samples still contain a small amount of amorphous phase

Raman and infrared investigations of glass and glass-ceramics with composition 2Na2O·1CaO·3SiO2

Precursor glass and glass-ceramics with molar composition 2Na2O·1CaO·3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm-1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975 and 1030 cm-1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm-1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented

Dielectric response of KCN crystals at ultra-low frequencies

We describe an ultra low frequency equipment employing programmable digital technique. The system is used to measure the dielectric parameters et, en and tg d or pure KCN crystals as a function of temperature in the frequency range 10-2 Hz to 40 Hz. The relaxation time of the Cn dipoles presents a classical temperature activated reorientation behaviour characterized by an Arrhenius law t=to exp (U/kT) with t0=7,26 x 10-15 s and U = 0,147 eV

Dielectric response of KCN crystals at ultra-low frequencies

We describe an ultra low frequency equipment employing programmable digital technique. The system is used to measure the dielectric parameters et, en and tg d or pure KCN crystals as a function of temperature in the frequency range 10-2 Hz to 40 Hz. The relaxation time of the Cn dipoles presents a classical temperature activated reorientation behaviour characterized by an Arrhenius law t=to exp (U/kT) with t0=7,26 x 10-15 s and U = 0,147 eV

Electrical conductivity of Ag-Na ion exchanged soda-lime glass

This paper reports on a study of the influence of silver on the electrical conductivity of Ag-Na ion exchanged soda-lime-silica glass. A glass of 22Na(2)O.8CaO.70SiO(2) (mol %) composition was prepared and silver was introduced into its samples by Ag-Na ion exchange at 350 degrees C for 1 h. The ion exchanged samples were further subjected to a thermal treatment at 500 degrees C for 24 h. Complex impedance diagrams (-Z '' vs. Z' plots) at several temperatures were obtained to calculate the activation energy for the dc electrical conductivity, Ea. The electrical conductivity of the ion exchanged sample is close to that of the pristine sample. The complex impedance plots of this sample show a tail in the low frequency range assigned to the non-uniform distribution of silver in the surface layers and stresses produced by the thermal and chemical temperings. The electrical conductivity of the layers was lower than that of the pristine glass. The further thermal treatment reduced the conductivity of the sample due to the formation of metallic silver nanopartides in the glass matrix and the lower concentration of the mobile Na+ ions. UV-visible optical absorption spectra showed an absorption band at 420 nm attributed to the presence of silver nanoparticles in the thermally treated sample. (C) 2014 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP