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R Righini

Publications and source records attributed to R Righini.

9 recordsLinked to original sources
PubMed2003

Experimental studies of the ortho-toluidine glass transition.

The thermodynamic and dynamics proprieties of ortho-toluidine, in the vicinity of a glass transition, have been studied by calorimetric and by two light scattering techniques, depolarized light scattering and time-resolved optical Kerr effect. Differential scanning microcalorimetry clearly detects a glass transition in o-toluidine and it measures some thermodynamics critical parameters, in particular, the transition temperature. The light scattering data have been analyzed according to the mode-coupling theory. This theory gives a good interpretation of our data and it allows to extract safely the critical parameters of the o-toluidine dynamics. We found a fair agreement between the analysis outputs performed in the frequency domain and in the time domain. Finally, we compared the glass transition features of o-toluidine with that of its isomer meta-toluidine, looking for some general idea about the molecular aspects of the glass transition.

Journal Article↗
PubMed2000

Three-wave mixing in chiral liquids

Second-order nonlinear optical frequency conversion in isotropic systems is only dipole allowed for sum- and difference-frequency generation in chiral media. We develop a single-center chiral model of the three-wave mixing (sum-frequency generation) nonlinearity and estimate its magnitude. We also report results from ab initio calculations and from three- and four-wave mixing experiments in support of the theoretical estimates. We show that the second-order susceptibility in chiral liquids is much smaller than previously thought.

Journal Article↗
PubMed2000

Time-resolved experiments on light diffusion in anisotropic random media

Multiple light scattering in isotropic and anisotropic media is studied experimentally with an optical gating technique, as commonly used in fluorescence spectroscopy. The experimental setup permits an accurate analysis of the propagation of a short light pulse through disordered or partially ordered media. The diffusion constant of some isotropic systems is reported, and the anisotropy in the diffusion constant for light diffusion through liquid crystals is observed. For the time-resolved data, good agreement with diffusion theory is found in all cases, including the liquid crystal in the nematic phase.

Journal Article↗
PubMed2000

The photochemical behavior of colchicone and thiocolchicone.

The irradiation of colchicone 5 led to the formation of lumicolchicone 7. The same reaction cannot be obtained by using thiocolchicone 6 as substrate. Transient absorption spectroscopy of colchicone and beta-lumicolchicone showed that probably the photoisomerization occurred on colchicone in its first excited singlet state. The spectroscopic data are in agreement with the hypothesis that lumicolchicone was generated in the ground state from the S1 state of colchicone without the presence of any intermediate. Semiempirical calculations on colchicone and thiocolchicone showed that the highest single occupied molecular orbital and the lowest unoccupied molecular orbital of the singlet excited colchicone can give a disrotatory ring closure to 7, while thiocolchicone cannot give the same type of process.

Colchicine↗
PubMed1985

Pilot study of multiple-fraction daily radiotherapy alternating with chemotherapy in patients with stage IV non-oat cell lung cancer.

From March 1982, 31 patients with stage IV non-oat cell lung cancer have been treated. Radiotherapy was given as three 2.00-Gy fractions on Days 1 and 2, 8 and 9, 22 and 23, and 29 and 30, for a total dose of 48 Gy over a 30-32-day treatment period. A three-drug combination of cyclophosphamide (400 mg/m2), doxorubicin (17 mg/m2), and methotrexate (15 mg/m2) was given on Days 3 and 24 and repeated thereafter every 21 days. Three of 31 evaluable patients (10%) achieved objective complete response and 18 of 31 (58%) achieved partial response (ie, regression of 50%-90%), while no change or disease progression was observed in ten of 31 (32%). The overall response rate in our study was 68%, which is a response much higher than other results in extensive disease. However, controlled trials will be necessary to definitively establish the superiority of this regimen to conventional trials. There was a significant shift of performance status towards higher values after treatment: 12 of the 27 patients classified in the 70-80 Karnofsky category before treatment moved to the higher category, 13 remained in the same status, and only two shifted to the worst category, indicating that the treatment had been effective in giving patients a better quality of life during their survival. The median survival was 35 weeks for the entire group of patients and 44 and 15 weeks for the responders and nonresponders, respectively. One of the primary findings of this pilot study was the ability to give one course of 12 Gy of radiation as multiple fractions per day during each of the first 2 weeks of treatment alternated with one course of chemotherapy, with most patients having very mild or no side effects. Giving multiple daily fractions greater than or equal to 4 hours apart permits the delivery of a large amount of irradiation over a short time period (ie, 1-2 days) within the limits of normal tissue toxicity. Increasing the recovery time of radiotherapy by alternation with chemotherapy offers the possibility of increasing the total radiation dose beyond the upper limits now considered feasible by conventional radiation schedules for induction therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenocarcinoma↗
PubMed1983

Combined radiation and drugs: the effect of intra-arterial chemotherapy followed by radiotherapy in head and neck cancer.

This study was designed to ascertain whether a prior reduction of tumor size by drugs could affect the final outcome of tumors treated with radiation. 142 patients with head and neck cancer (oropharynx, maxillary antrum and intra-oral) were randomized for the study. In 72 cases, irradiation was preceded by a continuous intra-arterial infusion of 3-5 mg/day methotrexate to a total dose of 90-120 mg; the other 70 patients were treated with radiotherapy alone. Chemotherapy, given prior to radiotherapy, caused a shift in the tumor stage (i.e. a reduction in tumor size) in more than one third of the cases. The overall 5-year survival was 43% in the combined treatment group and 25% in the group treated with radiation alone (statistical difference: p less than .05). However, when analysed separately the difference was statistically significant only in oral cavity tumors (5-year survival of 54% in the combined modality group vs. 27% in the control group), although local control rates after both single and combined modalities were not statistically different from those of oropharynx and maxillary antrum tumors. In these last lesions, however, the dissemination of disease was more frequent; therefore, the lack of improvement of cure rate with the combined modality in these cases seems to be related to both the higher tendency of these tumors to disseminate and the low effectiveness of intra-arterial chemotherapy in controlling distant metastases. Mild and transient local and systemic toxicities were observed during chemotherapy infusion, but no radiosensitising effect on normal skin and mucosa was seen during radiotherapy in patients who had received pre-irradiation chemotherapy.

Combined Modality Therapy↗
PubMedDate not supplied

[Transitory hypersecretion of light chains (IgG k) of probable para-infectious nature in childhood. Description of 2 cases].

The idiopathic monoclonal gammapathy is frequent in adult. In this age the gammopathy is persistent due to either malignant disorders or so called benign monoclonal gammopathy. This condition in infants and children is uncommon, but not exceptional and is usually of a transient nature. We describe two cases during infectious diseases.

Arthritis, Infectious↗