Novel approach to the microscopic inspection during laser cleaning treatments of artworks.

The present work focuses on the potential of 3D digital microscopy for assessing micro-morphological features during laser cleaning treatments of artworks. This application requires preliminary optimization studies aimed at defining operative irradiation parameters and practicable degree of cleaning, as well as in situ diagnostic assessments during the restoration work. To this goal, we developed and tested a dedicated 3D digital microscope by implementing the "shape-from-focus" technique. The significant potential of this instrument, which provides textural and chromatic information, was proven for the phenomenological characterization of black crust removal from stones, earthy concretion from bronzes and dark varnish from easel paintings. Comparative measurements using 3D digital microscopy and contact microprofilometry were performed after laser cleaning tests of prepared samples, genuine archaeological bronze artefacts and a stone sculptural element from Florence's Dome. The results achieved demonstrate the effectiveness and reliability of the novel approach and the advantages it provides with respect to alternative techniques, which will allow the methods to be used in the wider restoration community.

Characterization of copper alloys of archaeometallurgical interest using neutron diffraction: a systematic calibration study.

Neutron diffraction experiments have been performed on laboratory-prepared samples of copper alloys to determine their microscopic phase characteristics. The aim of this experiment is to set up a database that can be used in future neutron diffraction measurements on metal samples mainly of archaeological interest.

Development and application of a portable LIPS system for characterising copper alloy artefacts.

We report the development of a novel portable and low-cost laser induced plasma spectroscopy (LIPS) system and describe the application method for quantitative characterisation of quaternary copper alloy artefacts. The device was carefully calibrated and phenomenologically characterised using a set of reference samples. The reliability of the quantitative measurement of the depth profile and bulk compositions was assessed through crossed comparisons with traditional analytical techniques. Finally, the LIPS system was applied to investigate a museum figurine of unknown origin composed of several pieces, which is representative of a typical authentication problem.

Activation of cerebellar granule cells GABA(A) receptors by guanidinoacetate.

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 GABA(A) 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' GABA(A) receptors. This appears to deny an effect by this molecule on cerebellar function in the disease via interference with granule cells' GABA(A) 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 GABA(A) receptors presumably involved in granule cells' tonic inhibition. One is devoid of alpha6 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.

Automated characterization of varnishes photo-degradation using portable T-controlled Raman spectroscopy.

In this work, a portable-Raman device (excitation wavelength 1064nm) was employed for the first time for continuously monitoring the complex molecular dynamics of terpenoid resins (dammar, mastic, colophony, sandarac and shellac), which occur during their ageing under artificial light exposure. The instrumentation was equipped with a pyroelectric sensor allowing for temperature control of the sample's irradiated surface while the acquisition of spectra occurs by setting fixed maximum temperature and total radiant exposure. Resins were dropped into special pits over a dedicated rotating wheel moved by a USB motor. The rotation allowed samples sliding between the positions designated for the acquisition of the Raman spectra and that for artificial ageing. Samples were exposed to artificial light for 45-days and almost 400 spectra for each resin sample were collected. The exposure to artificial light led to significant changes allowing the characterization of the alteration process. The automated acquisition of a large number of spectra overtime during light-exposure has given the possibility to distinguish fast dynamics, mainly associated to solvent evaporation, from those slower due to resins photo-degradation processes.

Acoustic transients following excimer laser ablation of the cornea.

Pressure transients occurring inside the eyeball as a consequence of excimer laser ablation of the cornea were measured at various distances along the optical axis, on enucleated porcine eyes. Positive (compressive) pressure spikes up to 90 bars were observed, lasting 100 ns, and developing, as they propagated in the eyeball, satellite rarefaction pulses with negative pressure as high as -40 bar. Such rarefaction wavefronts can trigger the formation of cavitation bubbles, in both the anterior and posterior chamber, depending on the ablation geometry. The potential risks associated with these photoacoustic phenomena, particularly for retina and corneal endothelium, are outlined.

Prevention of corneal keratocyte apoptosis after argon fluoride excimer laser irradiation with the free radical scavenger ubiquinone Q10.

PURPOSE: To assess in vitro the potential of the free radical scavenger ubiquinone Q10 in preventing keratocyte apoptosis after argon fluoride (ArF) excimer laser irradiation. METHODS: Cultured rabbit keratocytes were irradiated at very low single-pulse laser fluences. The cumulative effects generated by three total fluence doses between 12 and 45 mJ/cm2, representative of single-pulse subablative doses during photorefractive keratectomy (PRK) in humans, were evaluated. We employed the following parameters to compare pretreated (10 microM ubiquinone Q10) and untreated samples: 1) number and morphology of living cells by Trypan blue test and ultramicroscopy, respectively; 2) level of free-radical formation assessed by malonaldehyde quantitation; 3) cellular energy level evaluated by ATP assay. RESULTS: Excimer laser irradiation kills cultured keratocytes by inducing apoptosis. The effect increases with the cumulative fluence dose. In the samples pretreated with ubiquinone Q10 there were significantly fewer cumulative apoptotic events than in the untreated ones. Quantitative analysis of malonaldehyde cellular levels suggested this protective action of ubiquinone Q10 was connected with its ability to scavenge laser-generated free radicals. ATP assay also confirmed that it raised cellular energy levels. CONCLUSIONS: The treatment of corneal keratocytes with relatively low concentrations of ubiquinone Q10 can prevent apoptosis after ArF excimer laser irradiation. If these findings are confirmed on human keratocytes this treatment could be usefully exploited in the PRK surgical procedure. That might lead to a reduction in the occurrence of haze and curvature regression triggered by programmed cell death.

Use of the abiotic proton balance for determining linear relations among net conversion rates of primary metabolites in fermentation processes.

Linear relations among net conversion rates of primary metabolites in fermentation processes can be determined by using the macroscopic or pathway balancing methods. It is shown that the process observability can be improved by incorporating both the abiotic proton balance and the pH control reagent addition rate measurement into the balancing methods. (c) 1996 John Wiley & Sons, Inc.

Biomass measurement by inductive permittivity.

An electrodeless, inductive permittivity probe is shown to reliably indicate fermentation biomass. By designing the probe based on electromagnetic induction, the electrode polarization artifact-common to electrode-based permittivity measurements of conductive solutions-is eliminated. The measurement of viable biomass concentration (X(V)) is precise and linear, with negligible interference, as shown for two bacteria, two yeasts, and two mammalian cells. The permittivity spectra often can be described by the three parameters of the Cole-Cole equation: the maximum (low-frequency) permittivity, the characteristic frequency (f(C)), and the Cole-Cole alpha. The f(C) and alpha have potential as relative indicators of cell size and morphology, respectively. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 289-304, 1997.

A simple method of correction for forward Rayleigh scattering in turbidity measurements.

A simple method is developed to correct for primary light scattered forward to the detector in turbidity measurements of Rayleigh scatterers. The relative measurement error, Δτ(err)/τ is shown to be independent of turbidity and specific absorbance, unlike the error calculated by use of a more involved model in the literature. In addition, although both methods address the presence of absorbing components in the sample, only the simple method can be used when absorbing components and/or scattering components of any size (Rayleigh, Rayleigh-Gans-Debye, or Mie scatterers) are present in the blank.

On the use of the pH control reagent addition rate for fermentation monitoring.

The linear relation between the pH control reagent addition rate, the net conversion rates of metabolites, the carbon dioxide mass transfer rate and the feed rates is developed and shown to have the same form for batch, fed-batch, and continuous reactors, regardless of the number of feeds. The magnitudes of various biological and solution chemistry effects on the pH control reagent addition rate are estimated to be negligible, facilitating the use of the pH control reagent addition rate as a straightforward indicator of primary metabolism. Finally, application of the linear relation, termed the abiotic proton balance, is discussed for a number of fermentation processes. (c) 1995 John Wiley & Sons, Inc.

Use of the abiotic proton balance for describing the pH-auxostat.

A new description of the pH-auxostat is obtained by using the abiotic proton balance in the mathematical model. The new model shows how the stoichiometry of metabolism affects the steady-state and stability characteristics of the pH-auxostat. The model can also be used to determine the amount of ammonium salts to include in the medium, and can be applied to the pH-stat modal fed-batch reactor and the bistat.

NADH fluorescence and oxygen uptake responses of hybridoma cultures to substrate pulse and step changes.

A fiber-optic probe was interfaced to an analytical spectrofluorophotometeru and used to measure NAD(P)H fluorescence of hybridoma cells in a bioreactor. NAD(P)H fluorescence was found to qualitatively represent metabolic state during various induced metabolic transitions. NAD(P)H fluorescence increased immediately following aerobic-anaerobic transitions, and decreased immediately upon transition back to aerobic metabolism. Pulsing of glucose to glucose-depleted cultures caused NAD(P)H fluorescence to first increase immediately after the pulse, and then decrease gradually before reaching a constant level. Pulsing of glutamine to glutamine-depleted cultures resulted in a gradual increase in NAD(P)H fluorescence which lagged a simultaneous increase in oxygen uptake. ATP production and oxygen uptake also varied with metabolic state. The decrease in oxidative phosphorylation following transition from aerobic to anaerobic metabolism was found to be only partially compensated by the concomitant increase in substrate-level phosphorylation, as shown by decreases of 35-52% in calculated total specific ATP production rates. The specific oxygen uptake rate decreased by 6-38% following glucose pulses of between 0.2 and 0.5 g/L, respectively, and by 50% following glutamine depletion. Subsequent pulsing of glutamine after depletion caused oxygen uptake to increase by 50%.

NADH and flavin fluorescence responses of starved yeast cultures to substrate additions.

Model experiments were performed with starved yeast (Saccharomyces cerevisiae) cultures in a batch reactor in order to develop a better understanding of NAD(P)H and flavin culture fluorescence. Fluorescence was monitored during aerobic-anaerobic-aerobic transitions and ethanol and glucose substrate addition experiments. Interpretations of the fluorescence responses obtained are provided, with consideration given to redox compartmentation and the formation of ethanol shortly after a glucose addition. An analytical spectrofluorophotometer was interfaced to a personal computer and adapted to measure fluorescence in a bioreactor. This was achieved by the use of quartz fiber-optic waveguides to convert the right-angle cuvette geometry of the analytical spectrofluorophotometer to an open-ended fluorescence probe geometry, resulting in a flexible culture fluorescence apparatus. Features of the apparatus include variable excitation and emission wavelengths, allowing for detection of NAD(P)H or flavin fluorescence, as well as small slit widths, a variable sampling rate, excitation and emission scanning capabilities, and good sensitivity.

Cleaning processes of encrusted marbles by Nd:YAG lasers operating in free-running and Q-switching regimes.

The removal process of degraded superficial layers from marble samples by Nd:YAG lasers was studied while simulating operative conditions of stone artwork restoration. The effects of laser irradiation at 1064 nm with three different pulse durations of 6 ns, 20 micros, and 200 micros were investigated by time-resolved shadowgraphy and emission spectroscopy of the ejection plume to characterize the specific interaction regimes, with particular concern given to the occurrence of side effects, such as thermal and mechanical damages to the substrate, that could affect the laser cleaning procedure.

Intraocular measurements of pressure transients induced by excimer laser ablation of the cornea.

BACKGROUND AND OBJECTIVE: The evolution of pressure waves induced by argon-fluoride laser ablation of the cornea in the typical operative conditions of clinical laser keratectomy has been studied experimentally and analyzed. MATERIALS AND METHODS: Freshly enucleated porcine eyes were irradiated at a laser fluence of 180 mJ/cm2 with various spot diameters in the range 1-6.5 mm. Pressure transients were detected by a fast rise time needle hydrophone inserted into the eyeball from the posterior pole and moved along the eye optical axis toward the cornea. RESULTS: Pressure peaks as high as 90 bar and 50 ns pulse duration (FWHM) were measured in the anterior chamber. Observation of the pulse shape evolution during propagation put in evidence the onset of a marked rarefaction phase following the compressional spike, with intense negative peaks (up to -40 bar) located at increasing distances from the corneal surface for increasing spot diameters. CONCLUSIONS: This behavior was explained by means of simplified models describing pressure pulse generation and diffraction effects occurring during its propagation. Implications to clinical procedures, as possible damages due to tissue stretching and cavitation formation, are also discussed.