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(394) Production(s) de l'année 2014
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The universal photoluminescence behaviour of yellow light emitting (Ga,In)N/GaN heterostructures
Auteur(s): Rosales D., Ngo T. H., Valvin P., Lekhal K, Damilano B., Demierry P, Gil B., Bretagnon T.
(Article) Publié:
Superlattices And Microstructures, vol. 76 p.9 (2014)
Ref HAL: hal-01101061_v1
DOI: 10.1016/j.spmi.2014.09.017
WoS: 000347264700002
Exporter : BibTex | endNote
8 Citations
Résumé: Time-resolved photoluminescence spectra of orange light emitting (Ga,In)N-based devices have been grown by metal-organic vapour phase epitaxy on C plane sapphire for indium compositions ranging up to 23 percents. The temperature dependent time resolved photoluminescence spectra collected through the 8K-300K range are found to exhibit behaviours that are found to be very similar to what is reported in literature in samples with different designs (well width, indium composition in the well layer). However, our quantum devices always exhibit a two-mode exponential decay with a long decay time about 4 to five times longer than the short one, which was not reported so far.The photoluminescence decay times are wavelength-dependent as always found for indium rich quantum well, a behaviour that is interpreted in terms of carrier localization in indium-rich regions of the alloy active layers. The spectral dependence of the decay time, which were fitted using sigmoidal function, give access to an average decay time, centred at a given energy, with a phenomenological broadening constant. The average splitting between characteristic energies for long and short decay times, the broadening constants both increase with the indium composition. Radiative and non-radiative recombination times are deduced in the whole temperature range. The average decay time increase exponentially with the product of the well width to indium composition. This quantity is found to be an excellent indicator of the device performance.
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Correlation of local order with particle mobility in supercooled liquids Is highly system dependent
Auteur(s): Hocky Glen M, Coslovich D., Ikeda A., Reichman David R.
(Article) Publié:
Physical Review Letters, vol. 113 p.157801 (2014)
Texte intégral en Openaccess :
Ref HAL: hal-01072203_v1
DOI: 10.1103/PhysRevLett.113.157801
WoS: 000342797100016
Exporter : BibTex | endNote
75 Citations
Résumé: We investigate the connection between local structure and dynamical heterogeneity in supercooled liquids. Through the study of four different models, we show that the correlation between a particle's mobility and the degree of local order in nearby regions is highly system dependent. Our results suggest that the correlation between local structure and dynamics is weak or absent in systems that conform well to the mean-field picture of glassy dynamics and strong in those that deviate from this paradigm. Finally, we investigate the role of order-agnostic point-to-set correlations and reveal that they provide similar information content to local structure measures, at least in the system where local order is most pronounced.
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Index from Twistors
Auteur(s): Alexandrov S.
Conférence invité: Autumn Symposium on String/M-theory (Seoul, KR, 2014-09-22)
Ref HAL: hal-01071271_v1
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Résumé: I propose to consider a new function on the moduli space of N=2 supersymmetruic gauge theories in 4 dimensions. It encodes the BPS spectrum of the theory and possesses many intersting properties which make it unique and one of the most natural objects to be studied.
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AC-magnetotransport of a 2DEG in the quantum Hall regime
Auteur(s): Hernandez Carlos, Consejo C., Chaubet C.
Conference: 7TH INTERNATIONAL CONFERENCE ON LOW DIMENSIONAL STRUCTURES AND DEVICES: (LDSD 2011) (Telchac, MX, 2011-05-22)
Actes de conférence: AIP Proceedings, vol. 1598 p.218 (2014)
Ref HAL: hal-01071270_v1
DOI: 10.1063/1.4878312
WoS: 000341459700047
Exporter : BibTex | endNote
Résumé: In this paper we present an ac-magneto-transport study of a two-dimensional electron gas (2DEG) in the quantum Hall effect (QHE) regime, for frequencies in the range [100Hz, 1MHz]. We present a new approach to understand admittance measurements based in the Landauer-Buttiker formalism for QHE edge channels and taking into account the capacitance and the topology of the cables connected to the contacts used in the measurements. Our model predicts an universal behavior with the a-dimensional parameter RCω where R is the 2 wires resistance of the 2DEG, C the capacitance cables and the angular frequency, in agreement with experiments
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Novel gels from wheat gluten proteins
Auteur(s): Ramos L.
(Séminaires)
Laboratoire Gulliver ESPCI (Paris, FR), 2014-09-29
Résumé: Wheat storage gluten proteins are among the most complex proteins families comprising at
least fifty different proteins, with extremely broad polymorphisms. Wheat gluten proteins
are moreover largely insoluble in water, rendering their study difficult. Gluten proteins are
responsible for the remarkable viscoelastic properties of dough. However despite extensive
studies over more than 200 years, in order to provide structural and mechanistic basis for
the improvement of the viscoelastic properties of dough and of the quality of resulting food
products, there is still a crucial need to understand supramolecular organization of gluten
proteins.
We have proposed a novel extraction protocol that allows for the first time careful structural
and rheological analysis of gluten protein suspensions over a wide range of protein
concentrations. Our system appears therefore as a unique model system to investigate the
supramolecular organization of gluten proteins and its impact on the viscoelastic properties
of gluten gels.
Rheological measurements show a spontaneous and very slow and concentration-dependent
gelation of the samples which can be rationalized using percolation models. Consistently,
scattering data highlight a hierarchical structure strikingly similar to that of polymeric gels,
thus providing some factual knowledge to rationalize the viscoelastic properties of wheat
gluten and their assemblies.
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Polymeric Assembly of Gluten Proteins in an Aqueous Ethanol Solvent
Auteur(s): Dahesh M., Banc A., Duri Agnès, Morel Marie-Hélène, Ramos L.
(Article) Publié:
Journal Of Physical Chemistry B, vol. 118 p.11065 (2014)
Texte intégral en Openaccess :
Ref HAL: hal-01071076_v1
Ref Arxiv: 1409.0744
DOI: 10.1021/jp5047134
WoS: 000342396000005
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
34 Citations
Résumé: The supramolecular organization of wheat gluten proteins is largely unknown due to the intrinsic complexity of this family of proteins and their insolubility in water. We fractionate gluten in a water/ethanol (50/50 v/v) and obtain a protein extract which is depleted in gliadin, the monomeric part of wheat gluten proteins, and enriched in glutenin, the polymeric part of wheat gluten proteins. We investigate the structure of the proteins in the solvent used for extraction over a wide range of concentration, by combining X-ray scattering and multi-angle static and dynamic light scattering. Our data show that, in the ethanol/water mixture, the proteins display features characteristic of flexible polymer chains in a good solvent. In the dilute regime, the protein form very loose structures of characteristic size 150 nm, with an internal dynamics which is quantitatively similar to that of branched polymer coils. In more concentrated regimes, data highlight a hierarchical structure with one characteristic length scale of the order of a few nm, which displays the scaling with concentration expected for a semi-dilute polymer in good solvent, and a fractal arrangement at much larger length scale. This structure is strikingly similar to that of polymeric gels, thus providing some factual knowledge to rationalize the viscoelastic properties of wheat gluten proteins and their assemblies.
Commentaires: J. Phys. Chem. B 2014, 118, 11065
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