Repository UNSAP (Universitas Sebelas April)
Not a member yet
1145 research outputs found
Sort by
Dual Luminescence, Interligand Decay, and Nonradiative Electronic Relaxation of Cyclometalated Iridium Complexes in Solution
No full textFemtosecond broadband photoluminescence studies are presented for Ir(ppy)(3) (Ir1), Ir(ppy)(2)(pic) (Ir2), Ir(ppy)(2)(bpy)(PF6) (Ir3), Ir(ppz)(3) (Ir4), and Ir(ppz)(2)dipy (Ir5) (where ppy = 2-phenylpyridine, pic = picolinate, bpy = 2,2'-bipyridine, ppz = 1-phenylpyrazole, and dipy = 5-phenyldipyrrinato) in solution. Upon 400-nm excitation of Ir1-Ir3, we observed a prompt population of the lowest MLCT states. The higher states decay on an ultrafast time scale (<100 fs), whereas the lowest (MLCT)-M-3 state undergoes further vibrational relaxation on a 1-ps time scale. In Ir3, this relaxation is accompanied by an interligand decay from the ppy to the bpy ligand in similar to 1.5 ps. For the ppy-containing complexes (Ir1 and Ir2), we found that, at 100 ps, the luminescence is red-shifted with respect to the steady-state emission. This is explained in terms of a time-delayed dual luminescence, which we attribute to a double-well minimum configuration of the lowest emitting triplet states involving the ppy moiety. Ir4 shows a prompt population of the lowest excited state, which then undergoes vibrational relaxation in similar to 0.5 ps. Finally, at short times, Ir5 exhibits fluorescence from the lowest (LC)-L-1 state, which decays in similar to 100 fs to the manifold of (LC)-L-3 states. Overall, this study shows that, although the ultrafast relaxation to the lowest electronic states is quite similar to that of other transition-metal complexes, most of the differences occur at the lowest emissive states, with effects such as time-delayed dual fluorescence, interligand decay, and nonradiative relaxation to the ground or lower-lying metal-centered states. Understanding these effects is crucial for obtaining optimal performances of iridium complexes, calling for further iterations between chemical synthesis and photophysical studies to optimize these complexes.LS
Ondes acoustiques à amplitude constante dans des milieux désordonnés non-Hermitiens
No full textDans un milieu acoustique, tout désordre est généralement associé à des phénomènes de diffusion multiple, créant des interférences qui empêchent généralement la transmission des ondes à certaines fréquences spécifiques. Ici, nous montrons que ces effets disparaissent lorsque l’on force les ondes à se propager avec une amplitude constante en ajoutant une distribution de perte et de gain adaptée au désordre, rendant le milieu non Hermitien. Après avoir introduit la théorie des ondes acoustiques à amplitude constante dans les milieux continus, nous présentons une démonstration expérimentale de ce concept dans un métamatériau acoustique non-Hermitien et discret, composé de haut-parleurs localement contrôlés. Les mesures démontrent sans ambiguïté la création d’une onde qui présente la même pression constante dans toute la structure désordonnée.LTS2LW
Narrow UV emission from homogeneous GaN/AlGaN quantum wells
No full textThe authors report on the achievement of narrow ultraviolet emission using GaN/AlGaN quantum wells grown by metal organic vapor phase epitaxy. The origin of the inhomogeneous broadening of the emission is explained by means of micro-photoluminescence and atomic force microscopy measurements. The effect of the well/barrier interface roughness on the linewidth is found to be marginal, while the impact of Al composition fluctuations of the barriers is highly critical. Emission linewidths as small as 5 meV at 10 K are obtained by decreasing the aluminum concentration fluctuations in the AlGaN barrier. (c) 2007 American Institute of Physics.LASP
Region-based off-heap memory for Scala
No full textThis work explores support for region-based memory in Scala through macro-based domain-specific encoding that exploits a number of extensible language features such as implicits and value classes.LAMP
Around the Corner mmWave Imaging in Practical Environments
No full textWe present the design, implementation, and evaluation of RFlect, a mmWave imaging system capable of producing around-the-corner high-resolution images in practical environments. RFlect leverages signals reflected off complex surfaces (e.g., poles, concave surfaces, or composition of multiple surfaces) to image objects that are not in the RF line-of-sight. RFlect models the reflections and introduces reconstruction algorithms for different types of surfaces. It also leverages a novel method for precisely mapping the location and geometry of the reflecting surface. We also derive the theoretical resolution and coverage for different reflecting surface geometries. We built a prototype of RFlect and performed extensive evaluations to demonstrate its ability to reconstruct the shape of objects around the corner, with an average Chamfer Distance of 2cm and 3D F-Score of 88.6%. CCS CONCEPTS • Networks → Sensor networks.SEN
Observation of Correlated Azimuthal Anisotropy Fourier Harmonics in and Collisions at the LHC
No full textThe azimuthal anisotropy Fourier coefficients (vn) in 8.16 TeV p+Pb data are extracted via long-range two-particle correlations as a function of the event multiplicity and compared to corresponding results in pp and PbPb collisions. Using a four-particle cumulant technique, vn correlations are measured for the first time in pp and p+Pb collisions. The v2 and v4 coefficients are found to be positively correlated in all collision systems. For high-multiplicity p+Pb collisions, an anticorrelation of v2 and v3 is observed, with a similar correlation strength as in PbPb data at the same multiplicity. The new correlation results strengthen the case for a common origin of the collectivity seen in p+Pb and PbPb collisions in the measured multiplicity range.LPH
Effect of the choice of the tunnelling path on semi-classical numerical simulations of TFET devices
No full textIn this work a non-local band-to-band tunnelling model has been successfully implemented into a fullband Monte Carlo simulator and applied to Tunnel-FET devices. No stability or statistical noise problems were encountered in spite of particle weights ranging over many orders of magnitude (due to vastly different generation rates at different positions inside the device and biases) so that Tunnel-FET I-V curves could be traced over the whole on-off range. Different approaches for the choice of the tunnelling path have been compared and relevant differences are observed in both the current levels and the spatial distribution of the generated carriers. (C) 2011 Elsevier Ltd. All rights reserved.NANOLA
Design and exploration of externally post-tensioned structures using graphic statics
No full textFunicular structures, which follow the shapes of hanging chains, work in pure tension (cables) or pure compression (arches), and offer a materially efficient solution compared to structures that work through bending action. However, the set of geometries that are funicular under common loading conditions is limited. Non-structural design criteria, such as function, program, and aesthetics, often prohibit the selection of purely funicular shapes, resulting in large bending moments and excess material usage. In response to this issue, this paper explores the use of a new design approach that converts non-funicular planar curves into funicular shapes without changing the geometry; instead, funicularity is achieved through the introduction of new loads using external post-tensioning. The methodology is based on graphic statics, and is generalized for any two-dimensional shape. The problem is indeterminate, meaning that a large range of allowable solutions is possible for one initial geometry. Each solution within this range results in different internal force distributions and horizontal reactions. The method has been implemented in an interactive parametric design environment, empowering fast exploration of diverse axial-only solutions. In addition to presenting the approach and tool, this paper provides a series of case studies and numerical comparisons between new post-tensioned structures and classical bending solutions, demonstrating that significant material can be saved without compromising on geometrical requirementsSX
Graphene Nanoplatelet Cathode for Co(III)/(II) Mediated Dye-Sensitized Solar Cells
No full textGraphene nanoplatelets (GNP) in the form of thin semitransparent film on F-doped SnO2 (FTO) exhibit high electrocatalytic activity for Co(L)(2); where L is 6-(1H-pyrazol-1-yl)-2,2'-bipyridine. The exchange current densities for the Co(2+/)3(+)(L)(2) redox reaction scaled linearly with the GNP film's optical absorbance, and they were by 1-2 orders of magnitude larger than those for the l(3-)/l(-) couple on the same electrode. The electrocatalytic activity of GNP films with optical transmission below 88% is outperforming the activity of platinized FTO for the CO2+/3+(L)(2) redox reaction. Dye-sensitized solar cells with Y123 dye adsorbed on TiO2 photoanode achieved energy conversion efficiencies between 8 and 10% for both GNP and Pt-based cathodes. However, the cell with GNP cathode is superior to that with Pt-FTO cathode particularly in fill factors and in the efficiency at higher illumination intensities.LP
Mechanical and chemical mechanisms in the tribocorrosion of a Stellite type alloy
No full textThe tribocorrosion of a Stellite 21 type alloy sliding against alumina in sulfuric acid was investigated in order to identify relevant degradation mechanisms. Tribocorrosion tests were performed using a reciprocating motion pin-on-plate system operating under potentiostatic conditions as well as open circuit potential under different loadings. Scanning electron microscopy, optical microscopy, laser profilometry and focus ion beam (FIB) were used for characterizing wear pattern and subsurface deformation. Results show that the prevailing electrochemical conditions, and in particular the presence or not of a passive film, crucially affect the tribocorrosion behavior of this alloy. The passive film was found to significantly enhance tribocorrosion damage and this for two reasons: (i) abrasion of the passive film induces wear accelerated corrosion, (ii) the presence of the passive film significantly increases subsurface deformation in the metal and thus mechanical wear. The effect of electrode potential and normal load on the overall degradation by tribocorrosion could be accurately described by the Archard's wear law (taking into consideration the effect of the passive film) and existing models for wear accelerated corrosion.SCI-STI-S