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Biomedical subjects

A Borghesi

Publications and source records attributed to A Borghesi.

At least 19 recordsLinked to original sources
PubMed2006

Effect of static and dynamic disorder on exciton mobility in oligothiophenes.

The polarized optical absorption spectra of different quaterthiophene single crystals in the energy region of the exciton bands originating from the first molecular transition are reported as measured in the temperatures ranging from 7 to 140 K. The intrinsic higher mobility of the b-polarized 0-0 a(u) exciton both with respect to its replicas and to the a-polarized structures is demonstrated in high quality crystals at the lowest temperatures. The influence of structural disorder on mobility is discussed considering, for the different samples, the measured lineshape and linewidth of the absorption peaks, and the relative lineshift and intensity ratio between the 0-0 a(u) line and its first replica at the lowest temperature. The influence of dynamic disorder is discussed considering the lineshape and linewidth of the measured peaks as a function of temperature for both polarizations in the framework of the exciton-phonon coupling theory.

Absorption↗
PubMed2006

Measured Davydov splitting in oligothiophene crystals.

The polarized absorption spectra of single crystals of oligothiophenes in a wide spectral range are reported. The experimental procedure is discussed, underlying several details which are relevant to obtain reliable spectra particularly for samples of increasing thickness. On the basis of these considerations, it has been possible to fully detect the transition to the upper Davydov exciton originating from the first molecular state. The position and shape of the main exciton peak in these materials are compared and discussed, taking into consideration the molecular arrangement and the longitudinal contribution which depends on the transition moment orientation. The Davydov splitting values as deduced from the experimental data at room temperature are also reported either for the first vibronic replica or for the electronic transition as a whole. The difference between the purely transverse and the measured Davydov splitting is discussed.

Journal Article↗
PubMed2005

Magnetically driven growth of anthracene thin films by organic molecular beam deposition.

The possible use of a static magnetic field during organic molecular beam deposition of thin molecular films for inducing some preferential growth is discussed and the magnetic properties of diamagnetic molecules and molecular crystals are recalled. Considering prototypical materials, namely anthracene molecules and potassium phthalate substrates, which interact and may give rise to polycrystalline films with specific orientations, we show that in the presence of a magnetic field the films display a macroscopic preferential orientation as a result of minimization of the magnetic energy contribution. A very good agreement between the results of optical spectroscopy, atomic force microscopy, and predictions made on the basis of the anisotropic magnetic susceptibility of anthracene is found.

Journal Article↗
PubMed2005

Optical transverse excitation in quaterthiophene crystals by ultraviolet-visible internal and attenuated total reflection.

We report internal and attenuated total reflection of light at the interface between glass and a quaterthiophene crystal in the spectral region of the electronic transitions. The bands corresponding to the absorption of the a(u) and b(u) Frenkel exciton states are detected for different polarization of the incident light. In particular, the wave-normal vector being almost perpendicular to the b(u) transition dipole moment allows its transverse component to be accessed, whose excitation in conventional external reflection or transmission spectroscopies is forbidden.

Journal Article↗
PubMed2005

Directional dispersion in absorbance spectra of oligothiophene crystals.

Due to the large oscillator strength of the first molecular transition in oligothiophenes, a strong directional dispersion of the b(u) exciton transition is expected originating from the macroscopic polarization field. Examining such dispersion unambiguously usually requires different faces to be accessible for the optical measurements. Alternatively, measurements carried out at different angles of incidence are met with intrinsic limits due to the peculiarities of wave propagation in such anisotropic systems. In order to demonstrate these limits along with the experimental difficulties involved, we examine refraction and absorption of light in these crystals and discuss the effects of directional dispersion on the absorbance spectra of quaterthiophene crystals.

Computer Simulation↗
PubMed2004

Polarized absorption of quaterthiophene single crystals.

Polarized optical spectra of quaterthiophene single crystals are reported over a wide spectral range for different planes and angles of incidence corresponding to either transverse or mixed longitudinal/transverse wave propagation. From the absorbance and reflectance spectra the corresponding absorption coefficients are deduced. In the region of the first molecular transition, polarized exciton states of Frenkel origin are found to be responsible for a strong optical anisotropy and for the modification of the state of polarization during light propagation in the crystal. Transmission measurements with crossed polarizer and analyzer allow to clearly identify Frenkel replica of the principal transition.

Journal Article↗
PubMed2004

Reflectivity and anisotropic optical functions of quaterthiophene single crystals.

Polarized reflectance spectra of quaterthiophene single crystals are reported with different angles and planes of incidence. The strong dependence of the spectral features on the experimental configuration is described by an orthorhombic model and the components of the complex diagonal dielectric tensor are given.

Journal Article↗
PubMed2002

Intrinsic excitonic luminescence in odd and even numbered oligothiophenes.

The emission properties of crystalline oligothiophenes (OTs) are investigated and related to the different selection rules arising from the number of rings. In odd OT crystals the purely electronic emission is absent since the molecular A1-1B(1) transition dipoles cancel at the bottom of the excitonic band. On the contrary, in crystals of even OTs this transition is allowed due to the constructive interference of the off-axis components of the molecular transition dipole. It possesses a polarization in the herringbone plane and exhibits superradiant behavior.

Journal Article↗
PubMed1996

AIDS and tuberculosis control programmes: an integrated approach at educational level.

In developing countries with a high prevalence of individuals co-infected by human immunodeficiency virus (HIV) and tuberculosis (TB), urgent public health measures should be implemented to prevent the spread of both diseases. This study was performed by a combined acquired immune deficiency syndrome (AIDS)-TB health team with the following aims: 1) to assess knowledge, attitudes and practice towards AIDS; 2) to identify target groups for health education (HE); 3) to evaluate HE impact; 4) to circulate correct information on AIDS and TB through target groups; and 5) to evaluate integration of AIDS and control TB activities. Secondary school students of Arua District, Uganda, participated in a standardized HE session (covering the key-points of AIDS and TB control) preceded by a pretest (multiple choice) questionnaire and followed 3 months later by the same questionnaire (post-test). The impact of HE on AIDS control was evaluated by comparing answers to pre- and post-test questionnaires and its influence on the TB programme by evaluating case-finding performances in the period preceding and following the survey. We analysed 1,478 questionnaires. The results of our study gave information on knowledge about AIDS, identified females and students < 16 yrs of age as good targets for HE, revealed that the impact of HE was significantly associated with improved knowledge, contributed to improved TB case-finding and offered suggestions for the integration of programmes. The survey represented an opportunity to create a stable AIDS/TB health team at district level.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Determinants of stunting and recovery from stunting in northwest Uganda.

BACKGROUND: Socioeconomic deprivation is associated with unhealthy living conditions and insufficient nutrient intake which affect linear growth. This study investigates the major risk factors which influence stunting in Northwest Uganda, the age range at which growth failure is more likely to occur, and the age at which chances of recovery are higher. METHODS: In February-March 1987, 1072 children < 5 years, were selected from 30 villages in Arua district (Northwest Uganda) and included in a longitudinal study. The children were measured for length and height; household socioeconomic and environmental variables were collected in order to assess risk factors for the future development of stunting. Two years after baseline, the height of the children was measured again. RESULTS: Children who were < 29 months old at baseline were at higher risk for linear growth faltering in the following 2 years; income, mother's education and presence of stunting at baseline were significant predictors of stunting. However, being stunted at age < 6 months or between 54 and 59 months old carried the same risk of remaining stunted after 2 years, and the probability of recovering from stunting was the same in every age group. CONCLUSIONS: These results suggest that, in this population, linear growth is influenced by environmental factors. It is a dynamic process continuing beyond the first 2-3 years of life, and the probability of catching up is very similar across all age groups < 5 years old. Recovery from stunting is more associated with mother's education than with income.

Age Factors↗
PubMed1994

Risk of infection and estimated incidence of tuberculosis in northern Uganda.

The main goals of our study were to evaluate: 1) the annual risk of tuberculosis infection (ARTI) and its annual decrease in Uganda; 2) the expected incidence of new tuberculosis cases and the notification rate; and 3) the role of incentives given to children tested in increasing compliance with the survey procedures. The methodology is based on performing the standard World Health Organization (WHO) tuberculin test on children of the same age groups at intervals of 10-15 yrs, identifying infected persons by induration distribution analysis, and converting the prevalence rates detected into risk rates according to the ARTI model. Two thousand six hundred and twenty one school children aged 10 yrs old and bacilli Calmette-Guérin (BCG) nonvaccinated, in six study areas, were injected with two tuberculin units (TU) of purified protein derivative (PPD) RT 23 Copenhagen. The detected prevalence was 14 +/- 1.4% (prevalence +/- 95% confidence interval (95% CI)) and the ARTI value 1.2 +/- 0.9%, with an estimated annual decrease of 0.83% from 1958 to 1970 and 2.9% in the 1970-1987 period. The estimated expected incidence of new cases in Uganda was 59 smear positive and 75 smear negative/extrapulmonary cases per 100,000 population in 1987, and 53 and 65, respectively, in 1990, with an overall 68% notification coverage. No significant improvement in children returning for reading was observed in the group receiving incentives. We conclude that the average decrease (2.9%) probably represents the natural decline of tuberculosis in Uganda. The coverage appears encouraging, although the ARTI detected could be underestimated, since the existing ARTI model was developed and validated before the human immunodeficiency virus (HIV) era.(ABSTRACT TRUNCATED AT 250 WORDS)

BCG Vaccine↗
PubMed1993

Anthropometry and childhood mortality in northwest and southwest Uganda.

Two longitudinal studies were carried out in northwest and southwest Uganda to examine the relationship between anthropometry and childhood mortality. Although the prevalence of malnutrition was significantly different between the two geographic areas, the relative risk for mortality associated with low levels of anthropometry was similar. When the anthropometric parameters were compared among each other, mid-upper arm circumference was found to be the most powerful predictor of mortality. The findings of this study confirm that mid-upper arm circumference is the indicator of choice to identify children at higher risk of death.

Anthropometry↗