A spectroscopic study of the chromatic properties of GafChromicEBT3 films.

PURPOSE: This work provides an interpretation of the chromatic properties of GafChromicEBT3 films based on the chemical nature of the polydiacetylene (PDA) molecules formed upon interaction with ionizing radiation. The EBT3 films become optically less transparent with increasing radiation dose as a result of the radiation-induced polymerization of diacetylene monomers. In contrast to empirical quantification of the chromatic properties, less attention has been given to the underlying molecular mechanism that induces the strong decrease in transparency. METHODS: Unlaminated GafChromicEBT3 films were irradiated with a 6 MV photon beam to dose levels up to 20 Gy. The optical absorption properties of the films were investigated using visible (vis) spectroscopy. The presence of PDA molecules in the active layer of the EBT3 films was investigated using Raman spectroscopy, which probes the vibrational modes of the molecules in the layer. The vibrational modes assigned to PDA's were used in a theoretical vis-absorption model to fit our experimental vis-absorption spectra. From the fit parameters, one can assess the relative contribution of different PDA conformations and the length distribution of PDA's in the film. RESULTS: Vis-spectroscopy shows that the optical density increases with dose in the full region of the visible spectrum. The Raman spectrum is dominated by two vibrational modes, most notably by the ν(C≡C) and the ν(C=C) stretching modes of the PDA backbone. By fitting the vis-absorption model to experimental spectra, it is found that the active layer contains two distinct PDA conformations with different absorption properties and reaction kinetics. Furthermore, the mean PDA conjugation length is found to be 2-3 orders of magnitude smaller than the crystals PDA's are embedded in. CONCLUSIONS: Vis- and Raman spectroscopy provided more insight into the molecular nature of the radiochromic properties of EBT3 films through the identification of the excited states of PDA and the presence of two PDA conformations. The improved knowledge on the molecular composition of EBT3's active layer provides a framework for future fundamental modeling of the dose-response.

Quantification of material nonlinearity in relation to microdamage density using nonlinear reverberation spectroscopy: Experimental and theoretical study.

High amplitude vibrations induce amplitude dependence of the characteristic resonance parameters (i.e., resonance frequency and damping factor) in materials with microscopic damage features as a result of the nonlinear constitutive relation at the damage location. This paper displays and quantifies results of the nonlinear resonance technique, both in time (signal reverberation) and in frequency (sweep) domains, as a function of sample crack density. The reverberation spectroscopy technique is applied to carbon fiber reinforced plastic (CFRP) composites exposed to increasing thermal loading. Considerable gain in sensitivity and consistent interpretation of the results for nonlinear signatures in comparison with the linear characteristics are obtained. The amount of induced damage is quantified by analyzing light optical microscopy images of several cross-sections of the CFRP samples using histogram equalization and grayscale thresholding. The obtained measure of crack density is compared to the global macroscopic nonlinearity of the sample and explicitly confirms that the increase in nonlinearity is linked to an increased network of cracks. A change from 1% to 3% in crack density corresponds to a tenfold increase in the signature of nonlinearity. Numerical simulations based on a uniform distribution of a hysteretic nonlinear constitutive relation within the sample support the results.

Resonant bar simulations in media with localized damage.

As a rule, problems of wave propagation in finite media with non-uniform spatial distribution of material properties can only be tackled by numerical models. In addition, the modeling of damage features in a material requires the introduction of locally non-linear and--more important--non-unique equations of state. Using a multiscale approach, we have implemented a non-linear hysteretic stress-strain relation based on the Preisach-Mayergoyz (PM) model, into a numerical elastodynamic finite integration technique program, which has originally been developed for linearly elastic wave propagation in inhomogeneous media. The simulation results show qualitatively good agreement with data of non-linear resonant bar experiments in homogeneously non-linear and hysteretic media. When the PM density distribution of hysteretic units at the mesoscopic level is not uniform and/or confined to a finite area in stress-stress space, the response at high amplitude excitation tend to deviate from the quasi-analytical results obtained in the case of a uniform PM-space density. Localized microdamage features in an intact medium can be modeled by conceiving finite zones with pronounced hysteretic stress-strain relations within a "linear" surrounding. Forward calculations reveal a significant influence of the amplitude dependent resonance behavior on the location (edge versus center of a bar), the extend (width of the zone) and the degree (density of hysteretic units) of damage.

The influence of localized damage in a sample on its resonance spectrum.

A nonlinear version of resonance ultrasound spectroscopy (RUS) theory is presented. This is important for NDT-purposes as damage manifests itself more pronounced and in an earlier stage by changes in the nonlinear elastic constants. General equations are derived for the 1-D case, describing the interaction between the modes due to the presence of nonlinearity. An analytical solution of these equations is derived which predicts the shift of the resonance frequency versus amplitude in a bar with localized damage. The damage was modelled as a finite region, having a constant cubic nonlinearity, in an otherwise linear 1-D bar. The analytical expressions for the shifts in resonance frequency at different modes were used to infer information about the position, nonlinearity and width of the damage. Unlike other techniques, the proposed method does not require scanning to locate the defect, as it lets the different modes, each with a different vibration pattern, probe the structure.

Psammomatoid ossifying fibroma of the ethmoid.

We present a 16 year-old girl who suffered since one year of a painless slow growing mass on the left medial orbital rim causing globe displacement. CT-scan and MRI of the orbit with T1 and T2 weighted images showed the presence of a large mucocoele in the frontal sinus. This occurred secondary to the obstruction of the sinonasal tract by a bony tumour. Histopathology showed a lesion consisting of fibrous tissue and ossicles or psammomatoid bodies. The diagnosis of a psammomatoid ossifying fibroma (POF) was made.

Acousto-optic lens for pulsed lasers.

Theoretical predictions of the acousto-optic interaction under Raman-Nath conditions of ultrasound and laser light with a beam width w comparable to or smaller than the ultrasonic wavelength lambda are experimentally investigated, and good agreement between experiment and prediction is found. The experimental setup consists of a pulsed laser, emitting pulses that are synchronized with the sound frequency by means of a controllable delay time. When w approximately lambda, strong focusing is obtained for most delay times. The lensing properties of this configuration are carefully investigated.

Ophthalmologic and systemic features of the Alström syndrome: report of 9 cases.

The Alström syndrome is a rare autosomal recessive disorder characterized by pigmentary retinopathy, diabetes mellitus, sensorineural deafness and obesity. A normal intelligence is often present. We report 9 patients.

Electromyography in relation to end-plate acetylcholinesterase in rats poisoned by different organophosphates.

Organophosphate (OP) poisoning produces various forms of acute, subacute, or delayed neurotoxicity. We investigated in vivo the relationship between clinical, histochemical and electromyographic (EMG) parameters in rats at various stages of poisoning by paraoxon or fenthion. Paraoxon is acutely toxic, whereas fenthion produces more sustained AChE inhibition. Fenthion has been involved in a subacute type of OP-related neurotoxicity in patients, the so-called intermediate syndrome. The animals underwent serial EMGs, with single and repetitive nerve stimulation, and concomitant contralateral muscle biopsies to determine the end-plate acetylcholinesterase (AChE) activity. Repetitive activity (RA) after single nerve stimulation and decrements on repetitive nerve stimulation (RNS) were the major EMG findings in either type of poisoning, occurring in the initial and later stages of the poisoning, respectively. RA was highly correlated to fasciculations in acute, but not in prolonged intoxication. Amplitude decrements provoked by RNS occurred only in weak rats with severe end-plate AChE inhibition. The smallest amplitude occurred either at the second response with gradual improvement in the subsequent responses (decrement-increment phenomenon), or the amplitude decrease progressed up to the last response (decrement phenomenon). The decrement-increment phenomenon preceded the decrement phenomenon and occurred at a slightly less severe degree of AChE inhibition. Various types of impairment of neuromuscular transmission coexist, probably to a different extent at distinct stages of anticholinesterase poisoning.

Acute and subacute organophosphate poisoning in the rat.

The intermediate syndrome in organophosphate poisoning is clinically characterized by weakness in the territory of cranial nerves, weakness of respiratory, neck and proximal limb muscles, and depressed deep tendon reflexes. It occurs between the acute cholinergic crisis and the usual onset of organophosphate-induced delayed neurotoxicity. The weakness has been ascribed to muscle fiber necrosis. Fenthion has been the most common cause. This study assesses the occurrence of the necrotizing myopathy in rats in relation to the clinical course and the acetylcholinesterase (AChE) inhibition after poisoning with organophosphates representative for each of the major types of organophosphate-related neurotoxicity. Marked differences are noted in the duration of cholinergic symptoms and of AChE inhibition after either paraoxon and mipafox, or fenthion poisoning. The necrotizing myopathy begins shortly after the initial decline in AChE activity with all organophosphates studied. Maximal muscle involvement occurs within the first 2 days of the poisoning with all organophosphates studied. The myopathy is not aggravated by a further decline in AChE activity in fenthion poisoning. Our data argues against the monophasic necrotizing myopathy being the cause of the intermediate syndrome, and is suggestive of persistent AChE inhibition being involved.

Are Wistar rats not susceptible to organophosphate-induced delayed neurotoxicity?

Male Wistar rats were sacrificed 12 weeks after single exposure to various organophosphate compounds. Peripheral nerves and skeletal muscles were examined light microscopically for the occurrence of a delayed polyneuropathy. Although unequivocal morphological hallmarks of OPIDN had been demonstrated in other rat strains using similar doses of TOCP or mipafox, we were unable to demonstrate any abnormality with these compounds. Normal findings were also obtained with fenthion, the delayed neuropathic potential of which is debated, and with paraoxon or parathion, which are both highly unlikely to cause OPIDN. These data indicate that the Wistar rat strain is highly likely to be resistant to OPIDN.

Variable involvement of rat skeletal muscles in paraoxon-induced necrotizing myopathy.

We studied the incidence of paraoxon-induced myopathy in several rat skeletal muscles in relation to the morphometric properties and oxidative metabolism of their fibers. The necrosis was most pronounced in the predominantly oxidative-rich fiber-composed diaphragm. The purely oxidative-rich masseter and soleus muscles were also severely affected. All 7 mixed muscles with oxidative-poor fiber predominance were far less involved. A high correlation between oxidative capacity and the extent of the muscle fiber necrosis was evidenced in mixed muscles. No relation was found between the muscle fiber diameter and the susceptibility to necrosis. We conclude that muscles predominantly composed of highly oxidative fiber types are more susceptible to organophosphate-induced necrotizing myopathy. Oxidative capacity alone is not the only factor, however, as the mixed diaphragm was more involved than the purely oxidative-rich masseter and soleus. Several features of the distinct fiber types could be responsible for the variable vulnerability.

Brain abscess after esophageal dilatation for stenosis.

The case is presented of a 28-year-old female with a brain abscess after esophageal dilatation for stricture, secondary to an acute necrotizing esophagitis. Other causes of brain abscess were excluded. To our knowledge this is the first documented case of brain abscess after dilatation for esophageal stricture in adult life. Some reports in the pediatric literature have been published previously.