Search

SummaryObjective The aim of this study was to evaluate an extended protocol of the large vessels using high-frequency duplex ultrasound (DUS) for detection of vessel wall inflammation. Methods Fifty-eight patients performed a DUS examination where arteritis could not be excluded. All DUS examinations were performed using ACUSON S2000 TM ultrasound system (Siemens Medical Solutions USA, Inc.). High-frequency linear transducers were used (18L6 MHz, 9L4MHz) or curve linear for the aortic arch (6C2 MHz). Carotid, vertebral, central neck arteries (subclavian, axillary, innominate) arteries, aortic arch and femoral arteries were studied. Circumferential, homogenous wall thickening, with or without a hyperechogenic stripe lining the innermost layer, were regarded as typical signs of arteritis. Intima-media thickness (IMT) was measured in the patients and a normal control group. The latest clinical updated diagnosis was assessed at least 6 months after DUS. Results The DUS findings showed normal vessels (n = 14), arteritis and atherosclerosis (n = 13), atherosclerosis (n = 15) and arteritis (n = 16). The latter group had a significant increased IMT in the common femoral artery and the common carotid artery (mean 1·0 ± SD 0·3 mm versus 0·6 ± 0·2 mm in the normal group (n = 37), P

Two-dimensional (2D) materials are intrinsically anisotropic, and an accurate description of their out-of-plane response to an electromagnetic field is more and more important as new materials with diverse properties are proposed. Their electromagnetic properties are often modeled using a single sheet with a surface susceptibility or conductivity or by means of a thin film of finite thickness with an effective bulk permittivity. The discordances between these two approaches lead to two irreconcilable interpretations of the optical characterizations and uncertain predictions of electromagnetic responses. Here, we fully account for the particular anisotropy of 2D materials and reconcile both approaches. We propose a unified description for the electromagnetic properties that applies to 2D heterostructures for all polarizations and at all angles of incidence. In particular, we determine the class of materials for which both models can be used indifferently and when particular care should be taken to select the thickness and the tensorial response of the effective thin film. We illustrate our conclusions on extensively studied experimental quantities such as transmittance and ellipsometric data of graphene and metal dichalcogenides. We discuss similarities and discrepancies reported in the literature when single-sheet or thin-film models are used., SCOPUS: ar.j, info:eu-repo/semantics/published

The electromagnetic properties of 2D materials are modeled either as single sheets with a surface susceptibility or conductivity, or as thin films of finite thickness with an effective permittivity. Their intrinsic anisotropy, however, has to be fully described to reliably predict the optical response of systems based on 2D materials or to unambiguously interpret experimental data. In the present work, we compare the two approaches within the transfer matrix formalism and provide analytical relations between them. We strongly emphasize the consequences of the anisotropy. In particular, we demonstrate the crucial role of the choice of the thin film's effective thickness compared with the parameters of the single sheet approach and therefore the computed properties of the 2D material under study. Indeed, if the isotropic thin film model with very low thickness is similar to an anisotropic single sheet with no out-of-plane response, with larger thickness it matches with a single sheet with isotropic susceptibility, in the reasonable small phase condition. We illustrate our conclusions on extensively studied experimental quantities such as transmittance, ellipsometry and optical contrast, and we discuss similarities and discrepancies reported in the literature when using single sheet or thin film models.

In the quest for ultrathin materials compatible with CMOS technology for all-optical signal processing applications in integrated photonics, graphene appears to be a promising candidate, with broadband1 optical properties and a high and broadband optical nonlinearity. However, researchers do not agree on the value of its nonlinear refractive index, and commonly used characterization methods do not provide a clear picture of the optical nonlinearity, in terms of its tensor nature or relaxation time. In the first part of this thesis, apart from the previously used Z-scan method, we have also used the ultrafast Optical Kerr Effect method coupled to Optical Heterodyne Detection (OHD-OKE) for the characterization of the third order optical nonlinearity of monolayer CVD graphene at telecom wavelengths. This method allows to separately measure the real and the imaginary part of the third-order nonlinearity, as well as their dynamics. With respect to the Z-scan method, OHD-OKE presents the major advantage of being robust against inhomogeneities of the sample. As such, we have demonstrated that graphene has a negative nonlinear refractive index, contrary to previously reported results. In addition, we have studied the real and imaginary part of graphene’s nonlinearity, when electrostatic gating is applied to change the chemical potential of graphene. Furthermore, we have proposed an enhanced version of the OHD-OKE method, together with the appropriate theoretical framework, in order to extract the tensor elements of the nonlinearity including the out-of-plane tensor elements. In particular, we have measured separately the time response of the two main tensor elements of the nonlinear susceptibility and we have experimentally verified that the out-of-plane tensor components are negligible. In the second part of this thesis, we have investigated, from an experimental point of view, the use of the nonlinear optical response of graphene for all-optical switching applications in integrated photonics. Namely, we have designed simple silicon nitride waveguide structures that constitute basic building blocks of switching devices, which were then fabricated and covered by graphene patches. Finally, we have experimentally tested the graphene-covered structures at low and high power levels and discussed the results., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Fungi are common spoilers of intermediate moisture foods such as bakery products. Brioche are bakery products prone to fungal spoilage due to their pH (5.8-6.2) and water activity (aw) (0.82-0.84). The aims of the present study were: (i) the identification of fungal species occurring in brioche products, (ii) the in vitro assessment of their growth potential, and (iii) the development of a validated growth model following the gamma concept. A total of 102 fungal strains were isolated, with Penicillium sp., Cladosporium sp., and Aspergillus sp. being the main genera, representing 90% of the isolates. Given the isolation frequency, any potential fungal prevalence throughout the bakery processs and/or the results of in vitro assessment of fungal growth potential under conditions mimicking brioche (pH, aw, temperature), Aspergillus flavus, Aspergillus fumigatus, and Penicillium sp. were selected for the development of the gamma model. According to in vitro validation, the model successfully predicted fungal growth, while on in situ experiments, the intrinsic parameters (aw and/or level of used preservative) of brioche in combination with packaging conditions (modified atmosphere) did not allow fungal growth.

Using an enhanced optically heterodyned optical Kerr effect method and a theoretical description of the interactions between an optical beam, a single layer of graphene, and its substrate, we provide experimental answers to questions raised by theoretical models of graphene third-order nonlinear optical response. In particular, we measure separately the time response of the two main tensor components of the nonlinear susceptibility, we validate the assumption that the out-of-plane tensor components are small, and we quantify the optical impact of the substrate on the measured coefficients. Our method can be applied to other two-dimensional materials, as it relies mainly on the small ratio between the thickness and the wavelength., SCOPUS: ar.j, info:eu-repo/semantics/published

Formic and acetic acid levels were determined in 15 display cases and 5 cabinets of the National Archaeological Museum and the Numismatic Museum of Athens after both active and passive sampling. Low volume air samplers with solid sorbent silica gel tubes and activated charcoal personal passive samplers were used. The organic acids were analysed by Reverse Phase High Performance Liquid Chromatography with phosphate buffer (pH = 2.5) as the mobile phase and UV detection at 210nm. Formic acid concentrations in display cases and cabinets ranged from 0.03 to 0.18mg·m−3, and acetic acid concentrations ranged from 0.06 to 2.42mg·m−3.

The present paper aims at investigating the indoor air quality in fifteen school buildings located in the greater Athens area. Experimental investigations were performed in fifteen different school classrooms and the concentration levels of various pollutants such as CO, CO, TVOC, HCHO, and radon, were measured. Moreover, the experimental investigation included measurements of several environmental parameters such as temperature, relative humidity and air velocity inside each classroom, while ventilation was examined by estimating the air changes using the tracer gas technique. From the above investigation, it was found that the indoor air quality inside the classrooms is strongly related to the number of occupants and their activities. The toxic pollutants such as CO, HCHO, TVOC and radon, measured inside the classrooms, present concentrations that are lower than their relative limit values and hence, they do not create any problem for the occupants. However, frequently, the CO concentration leve...

By means of the ultrafast optical Kerr effect method coupled to optical heterodyne detection (OHD-OKE), we characterize the third-order nonlinear response of graphene and compare it to experimental values obtained by the Z-scan method on the same samples. From these measurements, we estimate a negative nonlinear refractive index for monolayer graphene, n2=−1.1×10−13 m2/W. This is in contradiction to previously reported values, which leads us to compare our experimental measurements obtained by the OHD-OKE and the Z-scan method with theoretical and experimental values found in the literature and to discuss the discrepancies, taking into account parameters such as doping., SCOPUS: ar.j, info:eu-repo/semantics/published

Students with specific developmental learning disorders (dyslexia) may be examined orally in university entrance examination providing they have a certificate to that effect from a public child psychiatric or psychoeducational centre. The aim of this study was to investigate the success rate of dyslexic students in the university entrance examinations. Our hypothesis was, firstly, that these students will have the same success rate as other students and secondly, that they will mainly enter schools of science or technology. Our sample consisted of 420 dyslexic students who had sat for university entrance exams in 2006. Data was collected anonymously from Ministry of Education's files and consisted of the number of dyslexic students who were examined, their success rate, their choice of school and their grade. This data was derived from three examination centres in Athens and from five examination centres in an equal number of large provincial towns. Results showed that the success rate of dyslexic students in university entrance examinations was 39.76%, which was statistically lower than that of the general population of candidates which was 65.36%. Our hypothesis that these students would have a similar university entrance rate was not confirmed. Our second hypothesis concerning the preferred school of these candidates was confirmed since the majority of dyslexic students chose to study schools of sciences or technology. The dyslexic students' grades reveal a similar pattern to those of the general student population in the university entrance examinations, as long as these grades are greater than 9 on a score from 1-20. However dyslexic students entered technological colleges twice as often as the general student population. Our results are representative since our data was collected from 25% of university candidates throughout Greece. The anonymous nature of our data does not allow us to draw conclusions concerning socio-economic status, IQ levels or the quality and quantity of psycho-educational intervention, which would have led us to a more detailed analysis of the parameters leading to success or failure. Further investigation of the academic progress of dyslexic students would give us a more complete view of their educational achievements.

The reversed-flow gas chromatography (RF-GC) method has been applied to measure the time separation of adsorption entropies and their probability density functions, when acetic and formic acid vapors, responsible for artifacts degradation inside museums, are adsorbed on various heterogeneous surfaces. The solid materials studied were Penteli marble and solid metals (lead, copper and iron), which are commonly used for the construction of the artifacts. Physicochemical measurements were performed at various temperatures in the range 353-473 K, the surface coverage theta being also calculated over time. A new mathematical model, based on well known equations was used in order to extract the above quantities. (C) 2007 Elsevier B.V. All rights reserved.

Formic and acetic acid levels were determined in 15 display cases and 5 cabinets of the National Archaeological Museum and the Numismatic Museum of Athens after both active and passive sampling. Low volume air samplers with solid sorbent silica gel tubes and activated charcoal personal passive samplers were used. The organic acids were analysed by Reverse Phase High Performance Liquid Chromatography with phosphate buffer (pH=2.5) as the mobile phase and UV detection at 210nm. Formic acid concentrations in display cases and cabinets ranged from 0.03 to 0.18mg(.)m(-3), and acetic acid concentrations ranged from 0.06 to 2.42 mg(.)m(-3).

© 2016 Optical Society of America.By means of the ultrafast optical Kerr effect method coupled to optical heterodyne detection (OHD-OKE), we characterize the third-order nonlinear response of graphene and compare it to experimental values obtained by the Z-scan method on the same samples. From these measurements, we estimate a negative nonlinear refractive index for monolayer graphene, n2 = -1.1 × 10-13 m2/W. This is in contradiction to previously reported values, which leads us to compare our experimental measurements obtained by the OHD-OKE and the Z-scan method with theoretical and experimental values found in the literature and to discuss the discrepancies, taking into account parameters such as doping.