Reducing the risk of human immunodeficiency virus type 1 (HIV-1) transmission is still a public health priority. The development of effective control strategies relies on the quantification of the effects of prophylactic and therapeutic measures in disease incidence. Although several assays can be used to estimate HIV incidence, these estimates are limited by the poor performance of these assays in distinguishing recent from long-standing infections. To address such limitation, we have developed an assay to titrate p24-specific IgG3 antibodies as a marker of recent infection. The assay is based on a recombinant p24 protein capable to detect total IgG antibodies in sera using a liquid micro array and enzyme-linked immunosorbent assay. Subsequently, the assay was optimised to detect and titrate anti-p24 IgG3 responses in a panel of sequential specimens from seroconverters over 24 months. The kinetics of p24-specific IgG3 titres revealed a transient peak in the 4 to 5-month period after seroconversion. It was followed by a sharp decline, allowing infections with less than 6 months to be distinguished from older ones. The developed assay exhibited a mean duration of recent infection of 144 days and a false-recent rate of ca. 14%. Our findings show that HIV-1 p24-specific IgG3 titres can be used as a tool to evaluate HIV incidence in serosurveys and to monitor the efficacy of vaccines and other transmission control strategies.

In this work we mainly report on the analyses of polycrystalline silicon carbide films grown by Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) on Si (100) and Si (111) substrates. Structural properties of the films have been analyzed by X-ray diffractometry, transmission electron microscopy and micro-Raman spectroscopy. Samples deposited with optimized deposition conditions, show a polycrystalline columnar structure with lateral crystal dimensions ranging from 300 up to 1400 Å and an orientation close to that of the Si substrates.

In this work we report some results concerning Raman characterisation of covalently bonded amorphous carbon based thin films (∼ 100 nm) of binary alloys, obtained by ion implantation of carbon ions into silicon and germanium matrices. It will be shown that compositional disorder is present in our samples even below the stoichiometric concentration (∼50 carbon at.%) as deduced by the presence of three vibrational features in the Raman spectra. A quantitative measure of the compositional disorder will be also given by using either Raman or infrared spectroscopies in samples with different carbon content.

Amorphous hydrogenated silicon carbon alloys were synthesized by C2H2 ions implantation in a silicon substrate at different fluences to obtain samples with different carbon atomic concentrations (10−50 at. %). As-implanted and subsequently annealed samples were investigated by using Rutherford backscattering, infrared, and Raman spectroscopies in order to follow the crystallization process. It was found that crystallization of stoichiometric SiC phase starts at 1000 °C both in low and high containing carbon films, while at the stoichiometric composition silicon (or carbon) was found to clusterize into homonuclear islands even at lower temperatures. The analysis of the fundamental absorption edge reveals the presence of an optical energy gap of about 1.3 eV independently on the film composition in the as-implanted samples, while after the thermal process at 1000 °C it increases to 2 eV for a carbon concentration below 0.5 and up to 1.8 eV for all those samples with a carbon excess.

Cross-links among long chains have been observed in ion bombarded hydrocarbon polymers like polystyrene or polyethylene. Irradiation of fluoropolymers, instead, produces a strong sample erosion with emission of fragments produced along the ion track. Polytetrafluoroethylene foils of thickness ranging from 50 μm up to 2 mm were exposed to MeV helium and proton beams. The ion erosion rate was investigated by changing the target temperature and observing surface topography modifications, using the scanning electron microscopy technique. Etching was measured as removed thickness per irradiation time in the range values of 102−104 μm/h, corresponding to about 104−106 CF2 emitted group/ion. Target temperature (200–400 K), ion mass, and ion energy are the key parameters to follow the evolution of ion erosion of polytetrafluoroethylene.

Rheological and optical properties of polystyrene are modified by 200 keV He irradiation because of new molecular bonds induced by ion energy deposition. Total amount of bonds, as calculated by optical measurements, increases linearly with ion fluence without any dependence on the initial molecular weight. Density of interchain bonds or crosslinks, as calculated by rheological measurements, increases linearly at low fluence (∼1013 ions/cm2), while for high values shows a saturation behaviour.

Correlation between optical and rheological measurements allows us to calculate the fractions of interchain and intrachain bonds of ion irradiated 9000, 35000 and 100000 initial molecular weight samples.

The incidence and evolution of patent ductus arteriosus (PDA) was evaluated in twins and preterm singletons with birth weight ≤ 1750 g admitted to our Department in 1987 for respiratory distress syndrome (RDS). Screening by echocardiography and Doppler-flow studies (AT MK 600) was performed on the third day of life. Out of 91 neonates who needed intubation and ventilation during this 12-month period (23.8% of admissions), 40 weighed less than 1750 g and of these 40, 14 were twins (35%). Hemodynamically significant PDA was documented in 13 patients; of these, only 5 were preterm singletons and 8 were twins. Two twins weighing < 1000 g received no therapy for ductus closure; one ductus closed spontaneously, the other had an early demise. Three twins and 2 preterm singletons received indomethacin; one of the twins needed a second cycle for definitive ductus closure. Three twins and three preterm singletons underwent surgery, while one twin died on the 10th postoperative day. Screening and early therapy of PDA during RDS could be of great clinical importance. Twinning seems to play a role in the incidence and evolution of PDA and this needs to be evaluated in further studies.

NiSi and Ni2Si layers on silicon substrates as well as high fluence Si(As) ion implanted layers,have been rapidly melted by 30 ns Nd laser pulse irradiation.The energy density ranged between 0.4 and 1.2 J/cm2. Bilayer structures have been observed when the energy density has been chosen properly.

Buried epitaxial layers together with an amorphous or a policrystalline layer on top,have been detected by RBS and TEM measurements.

Damage formation during hot implants of 600 keV As or Ge ions into Si was investigated by changing the target temperature (>150 °C) and the ion fluence. The defect distributions, as obtained by channeling analysis, are characterized by a gaussian shape whose maximum coincide with the peak of the energy density deposition and with a width of 200 nm. The amount of damage is a factor of two higher for Ge than for As ion implants, and a similar result was found for the damage created by Ge implants into bare Si or Si doped with a near constant As concentration of 2×10 20/cm3. The transition to amorphous formation is quite sharp for As (around 120 °C) and quite broad for Ge implants. The different amount and kind of extended defects is probably due to an interaction of the mobile point defects, vacancies and interstitials, with As. The interaction probably increases the defects annihilation rate.

The synthesis of polymeric films under ion bombardment of frozen benzene has been investigated for the dependence of the thickness on the fluence and beam energy of keV proton and argon ions. Chemical analyses have been performed to characterize the films.

We propcoe a novel technique to convert polymer films into useful inorganic films by ion beam irradiation. Along the track of an ion the polymer is dissociated into smaller fragments. volatile fragments diffuse through the film and escape. Any element which is not removed in the form of volatile species is subsequently enriched with respect to the other elements. We demonstrate this effect in a polymer poly(dimethylsilylene-co-methylphenylsilylene), which initially has a C:Si ratio of 45:1. Upon irradiation with 2 MeV Ar+ ions at a dose of 1015 ions/cm2 the C:Si ratio changes to 3.4:1 as verified by Rutherford backscattering spectrometry. We believe that the effect of the ion beam irradiation is to produce more Si-C bonds at the expeme of the C-H and Si-Si bonds, with ≲10% of the original hydrogen being present in the film at high doses. The loss of the H atoms is further confirmed by a nuclear reaction technique. The IR spectra of the film as a function of the irradiation dose shows a progressive loss of fine molecular features with significant increase of the refractive index. The IR spectrum at the high doses appears to be due to a mixture of various Si and C bonds. However, the irradiated films are very hard and scratch resistant (knoop value ≳1300) suggesting an increase in the number of silicon carbide bonds

Narrow-band spectrophotometry observations (Cohen, 1975) showed that the extremely young star HL Tau has an absorption feature at 3.1 μm well matched by extinction from pure ice solid grains (radius a≈0.3μm, mice ≈10-4 gr cm-2). This feature, not present in others (more evolved) T Tau stars, suggests that ice may be only found around the very youngest T Tau stars and progressively disappears as starsbecome increasingly visible through their circumstellarshells (Cohen, 1975).

The interaction of energetic particles with frozen gas layers plays a relevant role in a variety of astrophysical scenarii and also in T Tau nebulae because of the large fluxes of particles ejected by these stars during their continuous flaring activity and the observed presence of ice grains at least around the very young star KL Tau (Cohen, 1975).

The crystallization onset and the annealing thresholds have been nmeasured as a function of the absorbed energy density in ion implanted amorphous silicon irradiated with nanosecond Nd pulse. Thin amorphous layers (∼500 Å) require higher thresholds ccapared with thick (∼4000 Å) amorphous layers. This result can be explained in terms of balance between absorbed energy and heat flow. For a given thickness of the amorphous layer the thresholds depend on the absorption coefficient of the amorphous material. This last parameter has been varied frcm 104 to 102 CM−1 by low temperature (T<400°C) pre-treatment of the ion implanted sample. The observed drastic variations of both crystallizazion and annealing thresholds agree well with nunerical evaluation of heat flow.

Amorphous, implanted, Si layers have been melted by pulsed electron irradiation. Implanted As has been used as a marker for determining melt duration. Systematic differences between As diffusion in initially amorphous or crystalline Si are interpreted in terms of different enthalpies of melting between amorphous (1220 J/g) and crystalline (1790 J/g) Si. The amorphous Si layers melt and crystallize at significantly lower electron energies than those required to melt crystalline Si, indicating that amorphous Si melts at 1170K compared to 1685 K for crystalline Si. We have used these thermodynamic parameters to successfully predict some of the phenomena associated with the laser induced melting and crystallization of amorphous Si.

Laser processing of amorphous thin films of amorphous Ge often results in an explosive or self-sustaining crystallization reaction. The reaction is sustained by the heat liberated during crystallization. In a theoretical analysis of the process that was presented at this symposium last year, Gilmer and Leamy postulated the existence of a thin layer of liquid at the propagating interface. The liquid layer forms at temperatures above Ta, the melting point of amorphous Ge, and is predicted to be ~ 0.02 – 0.1 of the film thickness in width. We have obtained experimental confirmation of the presence of this liquid layer.