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Comment se déroule la scolarisation des enfants de migrants dans ce que l’on appelle en ce début de XXIe siècle, l’ « École inclusive » ? L’usage du mot « inclusion » dans les mondes de l’éducation, bien qu’il remonte à la loi « pour l’égalité des droits et des chances, la participation et la citoyenneté des personnes handicapées » du 11 février 2005, dite loi « handicap », s’est étendu ces dernières années à d’autres catégories d’élèves. L’inclusion est devenue une sorte d’impératif catégori...

The bulk crystals of LiTm(WO4)2 with dimensions up to 10 × 15 × 3 mm have been obtained for the first time. Crystals of the compound melts congruently at 1007 °C, however melt crystallization of high quality crystal is impossible due to phase transition at ∼920 °C. The top seeded solution method from Li2WO4-WO3 flux was successfully applied reducing the growth temperature below 900 °C. According to single crystal x-ray measurements, the crystal corresponds to the P2/n space group. Raman, luminescence and transmission spectra reveal optical features owing to the presence of thulium ions, and therefore the materials could be further studied in the scope of laser and luminescence applications.

International audience; We present a polarization-dependent pure transverse-optic (TO) Raman study of high-quality Cd x Zn 1−x Se single crystals with zincblende (cubic) structures (x 0:3) covering both the phonon and phonon-polariton variants of the TO modes, using suitable backward and near-forward scattering geometries, respectively. Insight into the native phonon regime of the phonon-polaritons is obtained at intermediate composition of the random crystal (x ¼ 0:5, 0:3) and at the (Cd,Zn)-dilute limits (x 0:1; using prototype impurity motifs) by applying ab initio codes to large supercells (64-216 atoms), with special attention to both the Raman intensities and the phonon frequencies. The experimental (Raman) and theoretical (ab initio) results converge onto a percolation-type three-phonon [1 Â (Cd-Se), 2 Â (Zn-Se)] pattern for Cd x Zn 1−x Se. On the practical side, the interplay between the oscillator strengths of the two Zn-Se Raman modes is used to diagnose a pronounced trend toward local clustering in the studied crystals, presumably an early sign of the composition-induced zincblende ⇿ wurtzite structural transition (x 0:3). The deviation from the ideal Zn ⇿ Cd random substitution is estimated by working out a zincblende-version of the percolation model equipped with a relevant order parameter κ. The model is based on a sensitivity of the Zn-Se vibration to its local environment at the second-neighbor scale, independently supported by ab initio calculation of the Raman spectra in their dependence on κ (adjusted by simulated annealing)

The bulk crystals of LiBa12(BO3)7F4 were obtained from two flux compositions by the top seeded solution growth method. Crystals grown from BaCO3:BaF2:H3BO3:Li2CO3 = 3:3:3:1 charge were found to have a distinct linear dichroism effect at 0.35–0.65 and around 0.73 μm. This suggests application of the material in the production of polarizing filters and attenuators for visible range lasers.

International audience; We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single crystals were obtained with a mirror furnace without the need for post-treatment annealing. Its properties are determined and compared with those of two commercial crystals grown by the tri-arc Czochralski method. The chemical composition was investigated using glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS), which indicate minor impurities of Sr, Hf, Ca and Ti, with maximal concentrations for Sr and Hf in the range of 0.3–0.5% at. The optical band gap determined by UV-visible spectroscopy is found to be ∼4.8 eV and indicates the high quality of the BaZrO3 crystals grown by the optical floating zone technique. Raman spectroscopy at ambient conditions and at low temperatures down to 4.2 K reveals a relatively sharp second-order spectrum and does not reveal any structural phase transition. Prospective high-temperature solution growth using BaB2O4 self-flux was investigated and led to 150–200 μm BaZrO3 crystals. This solvent opens the way to grow BaZrO3 at half its melting point by the flux method.

International audience; β-BaB2O4 is an interesting material for the generation of VUV sources. It has good physical properties such as a large birefringence, a wide transparent waveband (190 to 3500 nm), a low dispersion, and high damage thresholds. Moreover, BaB2O4 is present in two crystalline solid phases usually indicated as α-BaB2O4 and β-BaB2O4 distinguished as the high-temperature phase and the low-temperature phase, respectively. The β-BaB2O4 is non-centrosymmetric and important for harmonic generation devices. Traditionally, the crystals of β-BaB2O4 are grown both by top-seeded solution growth and Czochralski melt-growth methods. In this work, we obtain single-crystal fiber of β-BBO by micro-pulling down (μ-PD) technique. The crystal fibers are formed from supercooled melt, using oriented seed with 0.1 mm/min as pulling rate.Further, characterizations by Optical microscopy and Raman spectroscopy have been performed to identify the crystal fibers quality.

International audience

Many of our medical procedures are conditioned by beliefs or experiences by our mentors, which we pass on to the younger, for example: gradually emptying a full bladder to avoid hypotension or haemorrhage, hydrating the alcoholic so that the blood alcohol level decreases faster, always obtaining an arterial blood gas instead of a venous one and not injecting iodinated intravenous contrast in patients allergic to shellfish.Un bon nombre de nos actes médicaux sont conditionnés par les croyances ou les expériences enseignées par nos mentors que nous transmettons à notre tour aux plus jeunes : vider progressivement un globe urinaire pour éviter une hypotension artérielle ou une hémorragie, hydrater les alcoolisés pour que leur alcoo-lémie baisse plus vite, toujours réaliser une gazométrie artérielle au lieu de veineuse et ne pas injecter de produits de contraste iodés chez les allergiques aux crustacés sont des exemples.

International audience; The apparently universal 1-bond2-mode percolation behavior in the Raman spectra of zincblende semiconductor alloys is generally observed for the short bond only, and not for the long one. In this work we perform a combined high-pressure-backward/near-forward Raman study of the leading percolation-type (Zn,Be)Se alloy (50at.% Be), which exhibits a distinct percolation doublet in the spectral range of its short Be?Se bond, in search of a Zn?Se analogue. The high-pressure-backward insight is not conclusive per se, but clarifies the perspective behind the near-forward Raman study. The latter reveals an unique Zn?Se phonon-polariton. Its fair contour modeling depending on the scattering angle is achieved within the linear dielectric approach, based on ellipsometry measurement of the ZnBeSe refractive index. Somewhat surprisingly this reveals that the phonon-polariton in question is a fractional' one in that it carries only half of the available Zn?Se oscillator strength, as ideally expected in case of a BeSe-like bimodal Raman behavior of the long Zn?Se bond.

International audience; For the first time, Ca5(BO3)3F (CBF) fiber crystals were grown by the micro-pulling down technique from LiF-based flux. Regular and transparent fibers were obtained with good optical quality. Characterization by Raman spectroscopy and EDX microprobe showed fibers compositionally homogeneous. The specific heat capacity of the fibers was measured indicating a laser damage threshold slightly lower, at room temperature, than for crystals belonging to the related rare earth calcium oxoborate family.

International audience; We perform,a combined backward/near-forward Raman study of the multi-oscillator Zn(Se,S) zincblende alloy with particular attention to the transverse optical modes. Besides the three [1 x (Zn-Se), 2 x (Zn-S)] known modes apparent in backscattering, one novel Zn-Se mode is revealed in near-forward scattering, suggesting a four-mode [2 x (Zn-Se), 2 x (Zn-S)] percolation behavior (1-bond -> 2-mode) for Zn(Se,S). The latter four-mode pattern appears to violate most admitted rules behind the current version of the percolation scheme for a zincblende- or diamond-type alloy, in reference to Ga(As,P) and (Ge,Si), respectively, concerning (i) the number of Raman modes, and the composition dependence of their (ii) frequencies and (iii) intensities. It is explained within a refined version of the percolation scheme, now suggested, in which the 1-bond 2-mode behavior is echoed among all constituent bonds of an alloy - referring to (i), the phonon dispersion is taken into account besides the local strain - referring to (ii), and both the Zn-Se and Zn-S bonds exhibit an unusual Sensitivity to their local environment at the second-neighbor scale - referring to (iii). The discussion is supported by ab initio phonon calculations using prototype (S,Se)-impurity motifs, and by a contour modeling of the multi-phonon-polariton Zn(Se,S) near-forward Raman spectra within the formalism of the linear dielectric response, based on ellipsometly measurement of the Zn(Se,S) refractive index. Particular attention is awarded to the coupling of neighboring transverse optical modes viatheir developing transverse electric field when entering the phonon-polariton regime.

SUMMARY The recurrent debate between Braudel and Gurvitch was given a new development in 1958, when both of them clarified their definition of time. In Braudel's mind the distinction he made between three different historical times (long, middle, short) offered a common epistemological and methodological framework for social sciences, including sociology. For Braudel, Gurvitch's typification of time in terms of social times seemed to be unoperative : it is too qualitative. Gurvitch replied to him that historical reality and historical times referred to specific types of social times : qualitative-quantitative, discon- tinuous-continuous... The study of these types would confirm that the historian and the sociologist do not conceive their object and their method in the same way. The article sketches a critical analysis of the question.

A complete Raman scattering study on a lithium tetraborate single crystal is reported. The frequency and scattered intensity of Raman modes are carefully determined in the various geometrical configurations. These Raman data are then used to relate to the electro-optical and non-linear optical properties. Raman scattering efficiencies of A1(a), A1(b) and E phonons are consistent with the values of the EO coefficients r13, r33 and r51 respectively.

We present absolute measurements of the effective non-linear optical coefficients d eff of cesium lithium borate crystals (CsLiB 6 O 10 , CLBO) by second harmonic generation using a continuous Nd-YAG laser source. The experiments were carried out at room temperature, on crystals cut perpendicular to type I or type II phase matching directions, with two different crystal lengths along the propagation direction. The d 36 and d 14 non-linear coefficients involved in d eff developments are deduced and are shown to be equal as it is predicted by the Kleinman symmetry. Two different compositions prepared by the Czochralski technique from melt with compositions of 1:1:6 and 1:1:5.5 molar ratios of Cs 2 O, Li 2 O and B 2 O 3 are comparatively studied.

La generation d'U.V. a partir de cristaux de metaborate de Baryum en phase basse temperature (β-BBO, β-BaB 2 O 4 ) necessite l'obtention de cristaux de bonne qualite exempts d'impurete. Afin d'obtenir des cristaux de haute purete, nous proposons de realiser la croissance dans un bain en surfusion dont la composition est celle de BBO sans ajout de solvant tel que Na 2 O. Un ensemble de parametres est propose pour assurer la croissance de la phase β, presentant les proprietes non lineaires requises. Cette methode de croissance de β-BBO s'apparente a celle decrite par Kouta [1]. L'interpretation differente de la comprehension de la croissance dans un bain en surfusion nous permet de proposer des parametres beaucoup moins extremes que ceux de l'equipe japonaise Ainsi les gradients de temperature sont divises par deux, passant de 1200°/cm a 600°/cm. De ce fait les conditions extremes sont ramenees a des conditions de croissance plus classiques.

We report second harmonic generation measurements of a continuous Nd-YAG laser beam propagating in a β barium metaborate (β-BaB 2 O 4 ) crystals cut in the type I and type II phase matching directions. The absolute values of the effective non-linear optical coefficients d eff I and d eff II are determined by measuring conversion efficiency and the d 22 and d 31 coefficients involved in d eff developments coefficients are deduced. Experimental and theoretical investigations of the BBO angular acceptance for different focusing conditions, lengths of crystal and phase matching conditions are comparatively presented. On the basis of the perfect agreement reached, an extrapolation of the angular acceptance is proposed for crystal lengths from 0.1 to 10 mm and waist sizes from 20 to 200 μm.

We present absolute measurements of the effective non-linear optical coefficients d eff of two lithium niobate crystals by second harmonic generation using a continuous Nd-YAG laser source. The experiments were carried out at room temperature, on crystals containing 49.6 and 49.96 mol% Li 2 O respectively and cut perpendicular to type I phase matching directions. For each composition, two configurations were studied with light propagating in the xz and yz planes, respectively, characterized by different combinations d eff of the non-linear optical coefficients. The d 31 and d 22 values, deduced from these d eff measurements are shown to be very sensitive to the crystal composition.

The absorption spectrum of BaTiO 3 :Rh is measured from 400 nm to 1100 nm, there is strong absorption peak (α = 7 cm -1 at 633 nm) while at 850 nm the absorption is rather weak: α = 2 cm -1 .Then, we propose an experimental investigation of the EO coefficients, for two different wavelengths corresponding to strong and weak absorption, based on an interferometric and ellipsometric assembly using application of a static electric field and leading to the measurement of the coefficients r 13 and r 33 separately and the linear combination r c .

We propose in the present work second harmonic generation (SHG) measurements on near stoichiometric crystals with a composition of 49.96 mol% Li2O. These experiments are carried out with a continuous Nd-YAG laser, at room temperature. Samples are cut perpendicular to the type I phase matching direction, with two different configurations of light propagation planes and with two different lengths. The corresponding absolute non-linear effective coefficients and therefore the d31 and d22 coefficients, are deduced from SHG efficiency measurements. By recording the SHG efficiency as function of the variation of angle around the phase matching direction, the angular acceptance measured for the different crystal lengths and incident beam waist sizes is shown to be dependent on experimental conditions. A theoretical interpretation is given and an extrapolation to other crystal lengths and beam waist sizes is proposed.

An investigation of the dielectric constant according to the frequency (20 Hz and 1 GHz) for as-grown and reduced samples of lithium tetraborate (LTB) is done. Anisotropy of e' and e at low frequency decreases by reducing crystal then at frequency higher the 104 Hz the reduced state does not affect e. The disappearance of relaxations in both real and imaginary part of e x in as-grown LTB, shows the unidirectional conductivity of the lithium ions along the 'Z' axis. When the samples are reduced we notice the appearance of relieving in the imaginary and real parts of e x and an increase in these relaxations for the two components of e z , that shows the appearance of a new mechanism of conduction in two directions X and Z other than that of lithium.

The non-linear optical properties of pure and MgO-doped lithium tetraborate (Li 2 B 4 O 7 , LTB) are studied by second harmonic generation (SHG) using a continuous Nd:YAG laser. The non-linear effective coefficients, d eff , are measured absolutely and compared for pure and MgO doped LTB crystals both cut for type I phase matching. The d 31 coefficient of both crystals are deduced. The dependence of the frequency conversion efficiency is measured as function of the deviation from the phase matching direction. The angular acceptance is deduced from these experimental data and discussed on the basis of theoretical calculation implying the gaussien beam approximation.

In this article, we report how the growth method used for barium beta-borate β-BaB 2 O 4 (BBO) impacts its high power second harmonic generation properties in the deep-UV. We compared a BBO crystal grown by flux (Top Seeded Solution Growth or TSSG) and a BBO crystal grown by the Czochralski (CZ) method. We first characterized their transparency properties, then we measured their single-pass second harmonic conversion efficiencies with both a low average power and a high average power nanosecond pulsed lasers. We show that both crystals have comparable linear absorption and conversion efficiencies at low power, whereas in a high power experiment, the CZ-grown BBO yields higher conversion efficiency than the TSSG grown BBO. With a 30 W, 150 kHz, 8 ns green laser, the use of a CZ BBO led at best to a 40% increase in available average output power at 257 nm.

Une chapelle pres de la gare de Lyon, bâtiments flambant neuf de bois et de verre surgis de la renovation de l’ancienne zone de l’ilot Chalon. C’est sans ceremonial que le pere de La Morandais nous accueille, « en civil », le tutoiement rapide, nous fait asseoir en allant chercher son CV… Eminence grise surexposee mediatiquement, homme de tradition et de conviction, de l’aumonier des hommes politiques au cure des SDF, ce theologien telegenique se definit lui-meme avant tout comme « un homme l...

Application of piezoelectric resonance enables determination of the complex coefficient s = s ' m is " by means of measurements of the complex admittance. The coefficients s ' and s " can be calculated from the parameters characterising behaviour of the dumped harmonic oscillator in the vicinity of piezoelectric resonance. This method has been used in the determination of phase transition points in a Li 2 B 4 O 7 single crystal. In respect of the temperature dependence of the elastic coefficient $ s_{11}^E $ several anomalies in the range of 20-180°C have been found. In the vicinity of the critical temperatures the imaginary part $ s''^E_{11} $ reveals a more distinct anomaly than the real part $ s'^E_{11} $ .

Bulk crystals of new huntite type borates were grown by TSSG method using eutectic LiBO2–LiF as a flux. Chemical composition, X-ray diffraction, optical absorption and fluorescence spectra of the grown samples were studied.

We report here a characterisation of non-linear single β BaB2O4(BBO) crystals by Second Harmonic Generation (SHG). Due to high damage thresholds and a wide transparency range, BBO is one of most widely used crystals in non-linear optical devices. In spite of the great number of publications on this subject, the magnitude of the non-linear optical coefficients in BBO is still the subject of controversy. We propose room temperature absolute measurements of the effective non-linearity, deff, for type I and type II phase matched BBO crystals, with an accuracy estimated to be better than 10%. The d22 and d31 coefficients are deduced. The variation of the frequency conversion efficiency is measured as function of the deviation from the phase- matching direction. The angular bandwidths are deduced from these experimental data and interpreted.

A Raman-scattering study performed on (-BBO) at room temperature allows us to assign all the vibrational modes detected in the Raman spectra. The internal and external vibration modes are properly obtained by taking account of the light polarization, mode contamination and isotope effects. A correspondence between the lattice and the free-ring modes is also presented.

Theoretical efficiencies and angular acceptances of β BaB2O4 crystals cut in the phase matching direction are calculated as function of crystal lengths, focusing conditions, phase matching types, for second and fourth harmonic generation processes.

International audience; A search for compounds of the NaBaR(BO3)2 composition (where R = La3+, Nd3+, Gd3+, or Yb3+) is performed by solid state synthesis and spontaneous crystallization. A new compound, NaBaYb(BO3)2, is found in this series. It crystallizes in space group R3¯ and belongs to the family of sublayer complex orthoborates with isolated BO3 groups NaBaR(BO3)2 (R = Y, Sc, and Yb). Theoretical X-ray powder diffraction patterns of NaBaY(BO3)2, NaBaSc(BO3)2, and NaBaYb(BO3)2 are calculated based on single-crystal data.

LYSB, NdYSB, and PrYSB borate crystals show interesting optical non linear properties, optical quality for theses three crystal is studied then we report absorption spectra, and second harmonic generation coefficients deff for type I phase matching.

International audience; We study the bulk and surface phonon-polaritons of the Zn0.67Be0.33Se zincblende alloy by near-forward Raman scattering. The short (Be-Se) bond exhibits a distinct percolation doublet in the conventional backscattering Raman spectra, corresponding to a three-mode behavior in total [1××(Zn-Se), 2××(Be-Se)] for Zn0.67Be0.33Se. This offers an opportunity to achieve a refined understanding of the phonon-polariton modes of a zincblende alloy beyond the current two-mode approximation, corresponding to a [1××(Zn-Se), 1××(Be-Se)] description in the present case. The discussion is supported by contour modeling of the Raman signals of the multi-mode bulk and surface phonon-polaritons within the formalism of the linear dielectric response.

The Raman selection rules of the (Zn-Se, Be-Se)-mixed phonon-polariton ( PP) created by “alloying” in the three-mode [1 × (Zn-Se), 2 × (Be-Se)] Zn1−xBexSe system, whose dramatic S-like dispersion (∼200 cm−1) covers the large frequency gap between the Zn-Se and Be-Se spectral ranges, are studied in its wave vector ( q) dependence by near-forward Raman scattering. Both the “collapse” regime away from the Γ point (q = 0) and the “reinforcement” regime near Γ are addressed, using appropriate laser lines and Be contents. We find that in both regimes the considered PP, in fact a transverse mode with the mixed mechanical-electrical character, obeys the same nominal Raman selection rules as its purely mechanical variant observed in the standard backscattering geometry. The discussion is supported by contour modeling of the multi- PP Raman lineshapes in their q-dependence within the linear dielectric approach.

International audience; We report second and fourth harmonic generation measurements in β-BaB2O4 single crystals (β-BBO) cut in the type I phase matching direction for the conversions from 1064 to 532 nm and from 532 to 266 nm.The absolute values of the effective non-linear optical coefficients deff are determined by measuring the conversion efficiency towards the visible and the UV.Crystals grown by the Czochralski method (directly pulled from a supercooled pure melt) are compared with crystals produced by the usual high temperature top seeded solution growth method. No difference in the effective non-linear optical coefficients was observed for the conversion from 1064 to 532 nm. In contrast, a systematically slightly higher deff value of crystal grown by the Czochralski method is obtained for the conversion from 532 to 266 nm.

In this work the influence of the vacancies concentration in pure BaTiO3 single crystals is studied. It is shown that the oxidation and the reduction do not change the electrooptic coefficients. The reduction modifies the nature of the majority carriers. An evaluation of the trap density N is done.

International audience; Recent site seeing testing campaigns conducted by our team from University of Nice1 show that Dome C represents the best site on Earth for astronomical high angular resolution (HAR) observations at optical and IR wavelengths. The dramatic gain over relevant HAR parameters r0, L0, θ0 and τ0, added to very low temperatures during the polar winter nights (-70°C), the dry atmosphere and the possibility of continuous observations during several nights make Dome C the ideal site for deploying a kilometric optical interferometer before the 2015 horizon. Here we describe the concept of Kiloparsec Explorer for Optical Planet Search (KEOPS) that is studied by our group at LUAN. KEOPS is an interferometric array of 36 off-axis telescopes, each 1.5m in diameter. Its kilometric baselines open sub-mas snap-shot imaging possibilities to detect and characterize extra-solar planetary systems, especially exo-Earths out to 300 parsecs from the visible to the thermal IR. KEOPS can be considered as a DARWIN/TPF challenger but at a much lower cost.

International audience; We investigate by near-forward Raman scattering a presumed reinforcement of the (A-C,B-C)-mixed phonon-polariton of a A(1-x)B(x)C zincblende alloy when entering its longitudinal optical-like (LO-like) regime near the Brillouin zone centre Gamma, as predicted within the formalism of the linear dielectric response. A choice system to address such issue is ZnSe0.68S0.32 due to the moderate dispersion of its refractive index in the visible range, a sine qua non condition to bring the phonon-polariton insight near Gamma. The LO-like reinforcement regime is actually accessed by using the 633.0 nm laser excitation, testified by the strong emergence of the (Zn-Se,Zn-S)-mixed phonon-polariton at ultimately small scattering angles.

Alain Maillard, The Communist Generation of 1840 and the Memory of Gracchus Babeuf The emergence of a communist movement in 1840 is in part linked to the generational situation of neo-babeufist theorists of the time. The intervention of Buonarroti, the executor of Babeuf's legacy, was decisive during their years of intellectual and political formation. As young romantic revolutionaries, they learned that regeneration must be the work of their generation. But the work of memory does not only allow an orientation in time, it helps the young generation to define its identity in political space as it differentiates itself from competing forces. In this way the conflict between Cabet and the neo-babeufists was a generational conflict., Maillard Alain. La génération communiste de 1840 et la mémoire de Gracchus Babeuf . In: L'Homme et la société, N. 111-112, 1994. Générations et mémoires. pp. 89-100.