Advances in multispectral and hyperspectral imaging for archaeology and art conservation

Multispectral imaging has been applied to the field of art conservation and art history since the early 1990s. It is attractive as a noninvasive imaging technique because it is fast and hence capable of imaging large areas of an object giving both spatial and spectral information. This paper gives an overview of the different instrumental designs, image processing techniques and various applications of multispectral and hyperspectral imaging to art conservation, art history and archaeology. Recent advances in the development of remote and versatile multispectral and hyperspectral imaging as well as techniques in pigment identification will be presented. Future prospects including combination of spectral imaging with other noninvasive imaging and analytical techniques will be discussed

A challenge to the striking genotypic heterogeneity of retinitis pigmentosa: A better understanding of the pathophysiology using the newest genetic strategies

Retinitis pigmentosa (RP) is a group of inherited retinal disorders characterized by a complex association between tremendous genotypic multiplicity and great phenotypic heterogeneity. The severity of the clinical manifestation depends on penetrance and expressivity of the disease-gene. Also, various interactions between gene expression and environmental factors have been hypothesized. More than 250 genes with ∼4500 causative mutations have been reported to be involved in different RP-related mechanisms. Nowadays, not more than the 50% of RPs are attributable to identified genes, whereas the rest of molecular defects are still undetectable, especially in populations where few genetic screenings have been performed. Therefore, new genetic strategies can be a remarkably useful tool to aid clinical diagnosis, potentially modifying treatment options, and family counseling. Genome-wide analytical techniques (array comparative genomic hybridization and single-nucleotide polymorphism genotyping) and DNA sequencing strategies (arrayed primer extension, Sanger sequencing, and ultra high-throughput sequencing) are successfully used to early make molecular diagnosis detecting single or multiple mutations in the huge heterogeneity of RPs. To date, further research needs to be carried out to better investigate the genotype/phenotype correlation, putting together genetic and clinical findings to provide detailed information concerning the risk of RP development and novel effective treatments

EPSP DISCHARGE PROPERTIES AT THE AFFERENT SYNAPSE OF THE FROG LABYRINTH POSTERIOR CANAL

The EPSP rate was intracellularly recorded from single fibres of the posterior nerve in the isolated frog labyrinth. Recordings were performed at rest and during sinusoidal canal rotation in the presence of TTX to prevent afferent spike discharge. At rest, the EPSPs are released at a considerably high rate (70-400 EPSPs/s) and their frequency consistently increases during excitation. This fact leads to a high degree of EPSP summation and fusion. To obtain a reliable estimate of both amplitude and frequency of the single EPSPs at rest and during rotation a statistical method measuring the variance, skewness and power spectrum of the fluctuations in the postsynaptic membrane potential was applied. It was observed that during rotation the change in EPSP frequency is approximately sinusoidal, indicating a dose functional relationship between stimulus and receptor response. The EPSP peak firing level during excitation and inhibition proved in some units to be linearly related to the stimulus intensity while in others it was a linear function of the stimulus logarithm. The excitatory response was larger than its inhibitory counterpart and also affected by adaptation. The present results suggest that many properties of the spike response (asymmetry, adaptation, linear or non linear intensity function) are already present in the afferent pathway earlier than at the encoder and are thus mainly due to the dynamic characteristics of the afferent synapse

The Role of the Endothelin System in the Vascular Dysregulation Involved in Retinitis Pigmentosa

Abstract Retinitis pigmentosa is a clinical and genetic group of inherited retinal disorders characterized by alterations of photoreceptors and retinal pigment epithelium leading to a progressive concentric visual field restriction, which may bring about severe central vision impairment. Haemodynamic studies in patients with retinitis pigmentosa have demonstrated ocular blood flow abnormalities both in retina-choroidal and in retroocular vascular system. Moreover, several investigations have studied the augmentation of endothelin-1 plasma levels systemically in the body and locally in the eye. This might account for vasoconstriction and ischemia, typical in vascular dysregulation syndrome, which can be considered an important factor of reduction of the ocular blood flow in subjects affected by retinitis pigmentosa

Z dependence of mass attenuation coefficient at 59.54 keV photon energy: Experimental assessment of binding energy effects

Mass attenuation coefficients of 59.54 keV photons were measured in elements with atomic number ranging from low to high, and including lanthanides whose K-shell binding energies were close to those of incident photons. Comparison with the most reliable data from tabulations in current use reveals some disagreement in the interval of binding energy values close to 59.54 keV. The significant disagreement reported by other authors for certain elements was not confirmed by the present investigation. (C) 1998 Elsevier Science Ltd. All rights reserved

Updating of form factor tabulations for coherent scattering of photons in tissues

An updating of photon transport modelling in tissues is carried out by including the effect of molecular interference in the coherent (Rayleigh) scattering. To this end, the present tabulations-which permit us to obtain the linear differential scattering coefficient of compounds from a simple weighted sum of the elemental components-are integrated by adding files for a limited set of molecular interference functions. This set originates from a four-component model which is found to be capable of reproducing human tissues in situations involving bony and soft tissues. The proposed procedure overcomes, in the computation, the hindrance that the dependence on molecular interference effects leads every tissue to have its own diffraction pattern, which is not easily obtained by means of measurements or calculations

Costruzione degli integrali formali del moto per un sistema di particelle con interazione Lennard-Jones

Per una catena lineare di molecole interagenti con il potenziale di Lennard-Jones tra primi vicini si costruiscono gli integrali formali del sistema che riducono la funzione di Hamilton in forma normale

New measurements and observations on aged NaI detectors

The dead layer near the front surface of aged or damaged NaI detectors produces both an energy dependent diminution in counting efficiency and a characteristic iodine K X-Ray peak which interferes with the registered radiation spectra. In this paper the exploitation of this peak as an internal reference to assess the dead layer thickness and the relative loss of detector quality is proved by means of a comparison between experiments and Monte Carlo simulations. Investigations with different NaI based equipments and photon transport simulations are carried out in order to assess the detector degradation in terms of peak interference, efficiency and resolution

THE SEMICIRCULAR CANAL TRANSFER FUNCTION ANALYZED AT THE mEPSP LEVEL IN THE ISOLATED FROG LABYRINTH

mEPSPs were intracellularly recorded in the presence of TTX from single fibres of the posterior nerve at rest and during sinusoídal rotation (0.02-0.5 Hz). To define the frequency response of the cytoneural junction the canal was subjected either to fixed (18 deg.s-2) or increasing peak accelerations (2.5-63 deg.s-2). The mEPSP waveform was evaluated by power spectral analysis; the mEPSP amplitude and rate of occurrence were determined by a fluctuation analysis procedure with a fast time resolution such that rotation frequencles up to 0.5 Hz could be studied. A response asymmetry (increase in mEPSP rate during excitation larger than the corresponding decrease during inhibition) was observed at all rotation frequencies and the time course of the mEPSP rates was analytically well described by asymmetrical sinusoids. For each unit the frequency response was computed in terms of: gain (peak to peak swing in mEPSP rate per unit peak acceleration); phase (phase lead with respect to angular velocity); asymmetry (ratio between excitatory and inhibitory responses). With fixed acceleration the gain vs. frequency relations were systematically described by one-pole low-pass filter functions (corner frequency 0.04-0.24 Hz), in agreement with the kinetics of the cupula-endolymph system. The same behaviour (corner frequency 0.1-0.24 Hz) was exhibited by the units where peak accelerations were changed. When the response of each of these units was corrected for attenuation at the corresponding frequency, linear stimulus-response relations were obtained and a static gain was defined for each unit. Unit phase leads were in agreement with the predictions of the fits obtained from gain data. A decrease in the response to successive cycles of rotation (adaptation) was observed when the EPSP rate during the first cycle exceeded the typical value, strictly related in each unit to its own static gain. No well defined pattems (tuning) could be identified in the fluctuations in EPSP rate at rest or ín the residuals from fits during rotation. These results indicate that most of the properties previously described in the spike firing pattern directly follow from the properties of the transmitter release by the hair cells