Search

Neutrons can be produced in nuclear reactions and used as very versatile probes for condensed matter research. Since their introduction in the 1950s neutron scattering techniques have evolved to be very powerful tools for investigating the properties of condensed matter. Here we present the concept of neutron diffraction and how this technique can be used to address problems in archaeology facilitated by accelerator-based neutron sources like ISIS at the Rutherford Appleton Laboratory in Oxfordshire. The great beauty of neutrons for the archaeologist is that they allow non-destructive testing of intact and original archaeological artifacts and museum objects.

In this work, warm white (3,000 K) LEDs were used for investigating accelerated ageing of different classes of natural terpenoid compounds. In particular, colophony, sandarac, shellac, and mastic resins were considered. Maximum total irradiance of 80 Mlxh was used, which can be compared to about 130 years of exposure in recommended museum conditions. Moreover, another set of the same resins was kept in darkness conditions in order to assess kinetic differences. Raman spectroscopy was employed to assess molecular changes occurring in resins structures during both dark and light ageing. Spectroscopic information was achieved through a portable Raman scanner provided with a narrow-b and CW diode-pumped Nd:YAG (1,064 nm) laser and an NIR spectrometer equipped with an InGaAs linear array. Vis-LED light appears to be suitable to avoid yellowing in the case of mastic and colophony resins suggesting that it is advisable to use this light with respect to traditional halogen lamps for illuminating museums and art galleries. Conversely, the ageing process of sandarac and shellac appears not to be particularly affected by the UV radiation. Raman spectroscopy in combination with multivariate analysis (principal component analysis) was able to provide information about the ageing process of colophony both in light and dark conditions. [ABSTRACT FROM AUTHOR]

We report the results of an analytical investigation on the bronze alloys of the Porta del Paradiso by Lorenzo Ghiberti using a portable X-ray fluorescence instrument. The study was carried out on five panels of the bronze artwork. It provided information on the artist’s selection of the sculptural alloys and on some manufacturing details of interest for understanding the development of the art foundry during the early Renaissance. [ABSTRACT FROM AUTHOR]

Non-destructive neutron diffraction techniques were applied to determine composition and microstructure data, and hence to derive information on manufacturing techniques of Picenum bronze artefacts. Furthermore, texture analyses were carried out on standards and suitable ancient artefacts to investigate their potential role in archaeometallurgical studies. This is a first step towards an overall characterization of the bronze collection of the Marches National Museum of Archaeology, Italy, and the analytical demonstration of relations with and differences compared to Etruscan metallurgy. The work is also an example application of the powerful non-destructive archaeometrical approaches provided by time-of-flight neutron diffraction. [ABSTRACT FROM AUTHOR]

Investigates the stress generation associated with xenon-chloride (XeCl) excimer laser ablation of polyimide. Adaption of variable blast theory in the condition of laser-target interaction in air; Measurement of acoustic transients propagating inside the irradiated target; Evaluation of the alpha fraction of laser energy transferred to the blast wave.

Focusing, as well as diffraction effects experienced by the stress wave produced by the argon–fluoride excimer laser ablation of corneal tissue have been studied in artificial and real eye samples. The evolution of the laser-induced acoustic front was imaged by means of fast shadowgraphy in an artificial eye model, while the absolute temporal profile of the pressure transient along the optical axis was directly measured in enucleated porcine eyes by a needle hydrophone inserted into the eyeball. Observations pointed out that the finite size of the acoustic source gave rise to diffraction effects during propagation, as the development of a negative tensile phase in the pulse shape, while the spherical shape of the acoustic source produced focusing of the wave front, causing pressure enhancements up to a factor of 3 in real eyes. The implications to surgical laser procedures as photorefractive keratectomy are discussed. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The extracellular concentration of guanidinoacetate (GAA) in the brain increases in guanidino acetate methyl transferase (GAMT) deficiency, an inherited disorder. We tested whether the levels which this substance can reach in the brain in GAMT deficiency are able to activate GABAA receptors in key cerebellar neurons such as the cerebellar granules. GAA in fact activates these receptors in rat cerebellar granules in culture although at quite high concentrations, in the millimolar range. However, these millimolar GAA levels are not reached extracellularly in the brain in GAMT deficiency. In addition, GAA does not act as a partial agonist on granules’ GABAA receptors. This appears to deny an effect by this molecule on cerebellar function in the disease via interference with granule cells’ GABAA receptors. Study of partial blockage by furosemide of chloride currents activated by GABA and GAA in granule cells allowed us to distinguish two populations of GABAA receptors presumably involved in granule cells’ tonic inhibition. One is devoid of α6 subunit and another one contains it. The latter when activated by GABA has a decay kinetics much slower than the former. GAA does not distinguish between these two populations. In any case, the very high extracellular GAA concentrations able to activate them are not likely to be reached in GAMT deficiency. [Copyright &y& Elsevier]