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U Wanderlingh

Publications and source records attributed to U Wanderlingh.

6 recordsLinked to original sources
PubMed2006

The fragile-to-strong dynamic crossover transition in confined water: nuclear magnetic resonance results.

By means of a nuclear magnetic resonance experiment, we give evidence of the existence of a fragile-to-strong dynamic crossover transition (FST) in confined water at a temperature T(L)=223+/-2 K. We have studied the dynamics of water contained in 1D cylindrical nanoporous matrices (MCM-41-S) in the temperature range 190-280 K, where experiments on bulk water were so far hampered by crystallization. The FST is clearly inferred from the T dependence of the inverse of the self-diffusion coefficient of water (1D) as a crossover point from a non-Arrhenius to an Arrhenius behavior. The combination of the measured self-diffusion coefficient D and the average translational relaxation time tau(T), as measured by neutron scattering, shows the predicted breakdown of Stokes-Einstein relation in deeply supercooled water.

Journal Article↗
PubMed2005

Elastic neutron scattering study of water dynamics in ion-exchanged type-A zeolites.

With the aim to investigate, by means of elastic neutron scattering, the effects produced by the cation substitution on the dynamics of water in zeolites, we measured, using a neutron backscattering spectrometer, the temperature dependence of mean-square atomic displacements [u2] derived from window integrated quasielastic spectra of fully and partially hydrated Na-A and Mg50-A zeolites. The results, collected in the 20-273 K temperature range, reveal that, at low temperature, the [u2] shows a harmonic trend independent of hydration and cation substitution, and, at higher temperatures, the onset of a non-Gaussian dynamics of the elastic intensity. This latter takes place at T approximately 200 K and approximately 150 K for fully and partially hydrated samples, respectively. This behavior has been interpreted in terms of reorientational jumps of H atoms described by two-site processes within an asymmetric double-minimum potential. In spite of its simplicity, the model seems to reproduce the rearrangement of the hydrogen bond network of zeolitic water. The fit results indicate a reduced proton mobility by diminishing the water content and by the induced Na+-->Mg2+ ion exchange, in agreement with previous incoherent quasielastic neutron scattering results at higher temperatures.

Journal Article↗
PubMed2003

A FT-IR absorption analysis of vibrational properties of water encaged in NaA zeolites: evidence of a "structure maker" role of zeolitic surface.

We performed, in the O-H stretching region, Fourier-transform Infrared (FT-IR) Absorption measurements for investigating the vibrational dynamics on water confined in NaA zeolite, vs. temperature and for different hydration percentages. The spectral substructure of the O-H stretching band is explained postulating the existence of three major components centred at approximately 3290 cm(-1) (omega(1)), approximately 3470 cm(-1) (omega(2)), approximately 3590 cm(-1) (omega(3)), with different dynamical properties traced over the full T-range investigated.

Journal Article↗
PubMedDate not supplied

Free radical erythrocyte damage in tumoral disease assessed by He-Ne laser and optical microscope through "Heinz Bodies" method.

Results obtained from blood sample readings by optical microscopy and He-Ne laser (lambda = 630.1 mW), have confirmed the reduction in Heinz Bodies (HB) formation time and the Transmittance Reduction Degree (TRD), in malignancies. The results of spectrometric readings in colorectum polyposis, (TRD = 0.07) and fibrocystic mastopathy (TRD = 0.08) gave results overlapping with controls (TRD = 0.08). In neoplasias, the early HB formation in erythrocytes observed by optical microscope corresponded to TRD increase = 0.17 (P < 0.01). TRD increase was statistically significant (P < 0.01), as well as the reduction in the time of HB appearance (< 0.01). The relationship between optical and laser readings was exponential in tumors, while it was linear in controls, in polyposis and mastopathies. The values of the correlation coefficients obtained by both methods were significant (P < 0.01) for all the studied groups. Moreover, these research data further support the existence, even in the earlier stages of the disease, of the labile state of the red cell membrane due to strong lipid peroxidation by FRs.

Erythrocytes↗