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Blind Source Separation Exploiting Higher-Order Frequency Dependencies
Taesu Kim,Attias, H.T.,Soo-Young Lee,Te-Won Lee IEEE 2007 IEEE transactions on audio, speech, and language p Vol.15 No.1
<P>Blind source separation (BSS) is a challenging problem in real-world environments where sources are time delayed and convolved. The problem becomes more difficult in very reverberant conditions, with an increasing number of sources, and geometric configurations of the sources such that finding directionality is not sufficient for source separation. In this paper, we propose a new algorithm that exploits higher order frequency dependencies of source signals in order to separate them when they are mixed. In the frequency domain, this formulation assumes that dependencies exist between frequency bins instead of defining independence for each frequency bin. In this manner, we can avoid the well-known frequency permutation problem. To derive the learning algorithm, we define a cost function, which is an extension of mutual information between multivariate random variables. By introducing a source prior that models the inherent frequency dependencies, we obtain a simple form of a multivariate score function. In experiments, we generate simulated data with various kinds of sources in various environments. We evaluate the performances and compare it with other well-known algorithms. The results show the proposed algorithm outperforms the others in most cases. The algorithm is also able to accurately recover six sources with six microphones. In this case, we can obtain about 16-dB signal-to-interference ratio (SIR) improvement. Similar performance is observed in real conference room recordings with three human speakers reading sentences and one loudspeaker playing music</P>
Patterning of pH sensitive fluorescent bipyridazine derivatives.
Do, Jaekwon,Kim, Yuna,Attias, André,-Jean,Kreher, David,Kim, Eunkyoung American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.10
<P>A pH sensitive pipeprazine substituted bipyridazine fluorophore, DPP-BPDZ was explored as a pH sensor in solution and thin film state. Greenish highly fluorescent solution of the DPP-BPDZ with fluorescence quantum yield of 0.63 showed fluorescence decrease as the acetic acid concentration of the media was increased. The fluorescence quenching was correlated linearly with the content of acetic acid dose and attributed to the protonation at the terminal piperazine group. An acid sensitive film was fabricated using a transparent polymeric host (PMMA) and the DPP-BPDZ dye molecules as a guest. The resultant bright green fluorescent film (1.4 microm thick) showed exponential decrease of the fluorescence intensity as the pH of the dipping solution was decreased. In the range of pH below 4.5, the film sensitivity to pH was higher than the pH range over 4.5. A patternable film sensor was fabricated by introducing a photo acid generator (PAG) layer on the dye layer. Fluorescence patterns was formed on the film sensor through a photo-mask by relatively weak power of UV light (0.4 mW/cm2). Fluorescent line patterns having 10 microm line width were obtained with high fluorescence contrast between the patterns.</P>
Sosa-Vargas, Lydia,Kim, Eunkyoung,Attias, André,-Jean The Royal Society of Chemistry 2017 Materials horizons Vol.4 No.4
<▼1><P>Designing new molecular building blocks for functional supramolecular self-assembly at surfaces.</P></▼1><▼2><P>2D supramolecular self-assembly has emerged as a powerful tool in nanoscience for bottom-up fabrication of well-defined and long-range ordered two-dimensional (2D) molecular nanostructures at surfaces. Following an overview of the principles of this distinctive self-assembly process, this review focuses on recent strategies developed to go beyond surface nanopatterning and to provide functional surfaces. With an emphasis on the chemical engineering of the molecular building blocks constituting the adlayer, we show that besides supported nanoporous networks, a more promising approach lies in the upstanding 3D functional building blocks mounted on the substrate. We highlight the opportunities offered by graphene, a substrate for which non-covalent functionalization by supramolecular self-assembly represents a way to either control its electronic properties or provide a new functionality. Finally, future perspectives are addressed.</P></▼2>
Lee, Kwang Jin,Xiao, Yiming,Woo, Jae Heun,Kim, Eunsun,Kreher, David,Attias, André,-Jean,Mathevet, Fabrice,Ribierre, Jean-Charles,Wu, Jeong Weon,André,, Pascal Nature Publishing Group, a division of Macmillan P 2017 NATURE MATERIALS Vol.16 No.7
<P>Charge transfer (CT) is a fundamental and ubiquitous mechanism in biology, physics and chemistry. Here, we evidence that CT dynamics can be altered by multi-layered hyperbolic metamaterial (HMM) substrates. Taking triphenylene: perylene diimide dyad supramolecular self-assemblies as a model system, we reveal longer-lived CT states in the presence of HMM structures, with both charge separation and recombination characteristic times increased by factors of 2.4 and 1.7-that is, relative variations of 140 and 73%, respectively. To rationalize these experimental results in terms of driving force, we successfully introduce image dipole interactions in Marcus theory. The non-local effect herein demonstrated is directly linked to the number of metal-dielectric pairs, can be formalized in the dielectric permittivity, and is presented as a solid analogue to local solvent polarity effects. This model and extra PH3T:PC60BM results show the generality of this non-local phenomenon and that a wide range of kinetic tailoring opportunities can arise from substrate engineering. This work paves the way toward the design of artificial substrates to control CT dynamics of interest for applications in optoelectronics and chemistry.</P>
Madathil, Pramod Kandoth,Heinrich, Benoî,t,Donnio, Bertrand,Mathevet, Fabrice,Fave, Jean-Louis,Guillon, Daniel,Attias, Andre-Jean,Lee, Changjin,Kim, Tae-Dong,Lee, Kwang-Sup American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.10
<P>We report here the synthesis and characterization of novel diethynylbenzene-based liquid crystalline semiconductor (P1) for organic thin-film transistors (OTFTs). Compound P1 was synthesized by the Sonogashira coupling reaction between 2-bromo-5-(4-hexylthiophen-2-yl)thieno[3,2-b]thiophene and 1,4-bis(dodecyloxy)-2,5-diethynylbenzene. Top contact OTFTs were fabricated by spin casting with 2 wt% solution of P1 in chloroform and their best performance, which exhibited a hole mobility of 4.5 x 10(-5) cm2/Vs, was showed after annealing of the films at liquid crystalline temperature. Time-of-flight (TOF) mobility measured at liquid crystalline phase was observed to be 1.5 x 10(-6) cm2/Vs for both positive and negative carriers. These results indicate that the liquid crystallinity helps to improve the molecular packing and enhance charge mobility for P1. These advantages can be applicable to design and construct solution-processable OTFT materials for electronic applications.</P>
Lee, K. J.,Woo, J. H.,Kim, E.,Xiao, Y.,Su, X.,Mazur, L. M.,Attias, A.-J.,Fages, F.,Cregut, O.,Barsella, A.,Mathevet, F.,Mager, L.,Wu, J. W.,D'Alé,o, A.,Ribierre, J.-C. The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.11
<P>We investigate the photophysical properties of organic donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units linked by a non-conjugated flexible bridge in solution using complementary optical spectroscopy techniques. When these molecules are diluted in dichloromethane solution, energy transfer from the triphenylene to the perylene diimide excited moieties is evidenced by time-resolved fluorescence measurements resulting in a quenching of the emission from the triphenylene moieties. Simultaneously, another quenching process that affects the emission from both donor and acceptor units is observed. Solution ultrafast transient absorption measurements provide evidence of photo-induced charge transfer from either the donor or the acceptor depending upon the excitation. Overall, the analysis of the detailed time-resolved spectroscopic measurements carried out in the dyad and triad systems as well as in the triphenylene and perylene diimide units alone provides useful information both to better understand the relations between energy and charge transfer processes with molecular structures, and for the design of future functional dyad and triad architectures based on donor and acceptor moieties for organic optoelectronic applications.</P>
Choi, E. Y.,Mazur, L.,Mager, L.,Gwon, M.,Pitrat, D.,Mulatier, J. C.,Monnereau, C.,Fort, A.,Attias, A. J.,Dorkenoo, K.,Kwon, J. E.,Xiao, Y.,Matczyszyn, K.,Samoc, M.,Kim, D.-W.,Nakao, A.,Heinrich, B.,Ha The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.32
<P>We investigate the photophysical and amplified spontaneous emission properties of a series of monodisperse solution-processable oligofluorenes functionalized with hexyl chains at the C9 position of each fluorene unit. Thin films of these oligofluorenes are then used in organic field-effect transistors and their charge transport properties are examined. We have particularly focused our attention on the influence of oligofluorene length on the absorption and steady-state fluorescence spectra, on the HOMO/LUMO energy levels, on the photoluminescence lifetime and quantum yield as well as on the amplified spontaneous emission properties and the charge carrier mobilities. Differential scanning calorimetry and X-ray diffraction measurements demonstrate that, among all oligofluorene derivatives used in this study, only the structure and morphology of the pentafluorene film is significantly modified by a thermal treatment above the glass transition temperature, resulting in a 9 nm blue-shift of the fluorescence spectrum without significant changes in the photoluminescence quantum yield and in the amplified spontaneous emission threshold. In parallel, hole field-effect mobility is significantly increased from 8.6 × 10<SUP>−7</SUP> to 3.8 × 10<SUP>−5</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> upon thermal treatment, due to an increase of crystallinity. This study provides useful insights into the morphological control of oligofluorene thin films and how it affects their photophysical and charge transport properties. Moreover, we provide evidence that, because of the low threshold, the tunability of the amplified spontaneous emission and the photostability of the films, these oligofluorenes are promising candidates for organic solid-state laser applications.</P> <P>Graphic Abstract</P><P>We investigate the charge transport, photophysical and amplified spontaneous emission properties of a series of monodisperse solution-processable oligofluorenes functionalized with hexyl chains at the C9 position of each fluorene unit. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp01134a'> </P>
Yoon, Seong‐,Jun,Kim, Jong H.,Kim, Kil Suk,Chung, Jong Won,Heinrich, Benoî,t,Mathevet, Fabrice,Kim, Pyosang,Donnio, Bertrand,Attias, André,‐,Jean,Kim, Dongho,Park, Soo Young WILEY‐VCH Verlag 2012 Advanced Functional Materials Vol.22 No.1
<P><B>Abstract</B></P><P>A new dicyanodistyrylbenzene‐based phasmidic molecule, (2Z,2′Z)‐2,2′‐(1,4‐phenylene)bis(3‐(3,4,5‐tris(dodecyloxy)phenyl)acrylonitrile), GDCS, is reported, which forms a hexagonal columnar liquid crystal (LC) phase at room temperature (RT). GDCS molecules self‐assemble into supramolecular disks consisting of a pair of molecules in a side‐by‐side disposition assisted by secondary bonding interactions of the lateral polar cyano group, which, in turn, constitute the hexagonal columnar LC structure. GDCS shows very intense green/yellow fluorescence in liquid/solid crystalline states, respectively, in contrast to the total absence of fluorescence emission in the isotropic melt state according to the characteristic aggregation‐induced enhanced emission (AIEE) behavior. The AIEE and two‐color luminescence thermochromism of GDCS are attributed to the peculiar intra‐ and intermolecular interactions of dipolar cyanostilbene units. It was found that the intramolecular planarization and restricted molecular motion associated with a specific stacking situation in the liquid/solid crystalline phases are responsible for the AIEE phenomenon. The origin of the two‐color luminescence was elucidated to be due to the interdisk stacking alteration in a given column driven by the specific local dipole coupling between molecular disks. These stacking changes, in turn, resulted in the different degree of excited‐state dimeric coupling to give different emission colors. To understand the complicated photophysical properties of GDCS, temperature‐dependent steady‐state and time‐resolved PL measurements have been comprehensively carried out. Uniaxially aligned and highly fluorescent LC and crystalline microwires of GDCS are fabricated by using the micromolding in capillaries (MIMIC) method. Significantly enhanced electrical conductivity (0.8 × 10<SUP>−5</SUP> S•cm<SUP>−1</SUP>/3.9 × 10<SUP>−5</SUP> S•cm<SUP>−1</SUP>) of the aligned LC/crystal microwires were obtained over that of multi‐domain LC sample, because of the almost perfect shear alignment of the LC material achieved in the MIMIC mold.</P>