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M Allegrini

Publications and source records attributed to M Allegrini.

At least 19 recordsLinked to original sources
PubMed2003

Near-field Raman imaging of morphological and chemical defects in organic crystals with subdiffraction resolution.

In this study we report on the application of an aperture near-field optical microscope for Raman imaging of organic materials. Spectral analysis and detailed Raman imaging are performed with integration times of 100 ms per point, without the aid of field enhancement effects. The studied samples consist of two high Raman-efficiency molecular samples: a 7,7',8,8'-tetracyanoquinodimethane crystal showing surface defects and a 7,7',8,8'-tetracyanoquinodimethane thin film characterized by the presence of submicrometre-sized organometallic copper-salt complexes. In the first case, the effect of the surface deformation was studied, whereas in the second sample we were able to chemically image the formation of salt complexes. Subdiffraction resolution was achieved in both studies.

Crystallization↗
PubMed2003

A versatile multipurpose scanning probe microscope.

A combined scanning probe microscope has been developed that allows simultaneous operation as a non-contact/tapping mode atomic force microscope, a scattering near-field optical microscope, and a scanning tunnelling microscope on conductive samples. The instrument is based on a commercial optical microscope. It operates with etched tungsten tips and exploits a tuning fork detection system for tip/sample distance control. The system has been tested on a p-doped silicon substrate with aluminium depositions, being able to discriminate the two materials by the electrical and optical images with a lateral resolution of 130 nm.

Journal Article↗
PubMed2001

Optical near-field harmonic demodulation in apertureless microscopy.

Spatial derivatives of the optical fields scattered by a surface can be investigated by apertureless near-field optical microscopy by modulating sinusoidally the probe to sample distance and detecting the optical signal at the first and higher harmonics. Demodulation up to the fifth harmonic order has been accomplished on a sample of close-packed latex spheres by means of the silicon tip of a scanning interference apertureless microscope. The working principles of such microscope are reviewed. The experimental configuration used comprises a tuning-fork-based tapping-mode atomic force microscope for the distance stabilization, and a double-modulation technique for complete separation of the topography tracking from the optical detection. Simple modelling provides first indications for the interpretation of experimental data. The technique described here provides either artefact-free near-field optical imaging, or detailed information on the structure of the near fields scattered by a surface.

Journal Article↗
PubMed2000

Photoassociative spectroscopy as a self-sufficient tool for the determination of the Cs triplet scattering length

In photoassociation spectroscopy, the line intensities of a given vibrational progression exhibit zero-signal modulation reflecting the node structure of the s-wave ground state wave function of two free colliding atoms. This leads to the determination of the scattering length. We performed photoassociation of cold Cs atoms polarized in the Zeeman sublevel f = 4, m(f) = 4. We analyzed the intensities of the lines associated with the Cs2 0(-)(g) state dissociating to the 6s(1/2)+6p(3/2) asymptote. This yields a value of the Cs triplet state scattering length, a(T) = -530a(0), while consistency requirements impose a value of the multipole ground state molecular coefficient, C6 = 6510 a.u.

Journal Article↗
PubMed1990

Availability of selenium in dough and biscuit in comparison to wheat meal.

We studied the availability of selenium in processed foods and whole wheat diets for restoring the Se content and glutathione peroxidase (GSHPx) activity in the blood and liver of selenium-depleted rats. The Se content in the rat diets ranged from 225 to 342 micrograms Se/kg diet. Different selenium sources and different Se amounts had little influence on the Se levels in the blood and liver of repleted rats. Se from processed foods did not completely restore the GSHPx activity in whole blood and liver as happened with Se coming from wheat. These results indicate that it is the milling processes of the flour production, and not the cooking, which decrease the availability of Se for GSHPx synthesis in rats.

Animals↗
PubMed1987

Effects of various dietary selenium intakes on the levels of blood glutathione-peroxidase and selenium in long-term fed rats.

Female Sprague-Dawley rats were fed a torula diet or wheat diets containing 4 levels of Se partially supplemented (24-402 ppb) for 120 days. Selenium content and glutathione-peroxidase (GSH-Px) activity in plasma and erythrocytes were measured every 20 days. In rats fed torula diet or basal wheat diet, plasma Se (P-Se) increased for up to 60 days, then remained constant, while erythrocytes Se (E-Se) and E-GSH-Px decreased in basal-diet rats during the first 40-60 days, then increased. In rats fed supplemented diets, P-Se and P-GSH-Px increased more rapidly than E-Se and E-GSH-Px, plateauing at 60-80 days. The best correlation was found between P-GSH-Px and dietary Se indicating that this index is the most sensitive for evaluating changes resulting from different Se intakes. In addition, correlations became more significant with time. The results from rats fed a low Se diet suggest the existence of regulatory mechanisms working in different ways and at different times in plasma and erythrocytes.

Animals↗
PubMed1983

Blood cells glutathione peroxidase activity and selenium in multiple sclerosis.

In the present study, the plasma and erythrocyte Se concentration and the erythrocyte and leukocyte glutathione peroxidase (GSH-Px) activity in 20 patients affected by multiple sclerosis (MS) were compared with those of a group of healthy controls. The Se concentration in the food was also studied and found to be less than the minimum values suggested by the US Food and Nutrition Board. The erythrocyte Se levels were found to be similar in both MS patients and in controls, while the plasma Se values were higher in the MS patients. The Se-dependent GSH-Px activity in the erythrocytes was found to be lower in the MS patients while no difference was found in the two groups as far as the leukocytes were concerned. Our data confirm that of other authors and indicate that the modified GSH-Px activity found in erythrocytes of MS patients is independent from the Se concentration and probably due to genetic factors.

Adult↗