684 research outputs found
Coherence creation in an optically thick medium by matched propagation of a chirped laser pulse pair
We consider the simultaneous propagation of a pair of Raman-resonant,
frequency-modulated (chirped) laser pulses in an optically thick medium,
modeled by an ensemble of -atoms. A self-organization ('matching`)
effect is shown for the chirped pulse pair, which leads to a quasi-lossless
propagation. Furthermore, we demonstrate that a well-defined coherent
superposition of the atomic ground states and, correspondingly, a coherence is
robustly created in the medium that can be controlled by amplitudes of the
laser pulses. The proposed scheme can be applied to substantially increase the
efficiency of the optical wave mixing processes, as well as in other nonlinear
processes where the initial preparation of a spatially extended medium in a
coherent superposition state is required
Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals
We study theoretically the instabilities induced by a linearly polarized
ordinary light wave incident at a small oblique angle on a thin layer of
homeotropically oriented nematic liquid crystal with special emphasis on the
dye-doped case. The spatially periodic Hopf bifurcation that occurs as the
secondary instability after the stationary Freedericksz transition is analyzed.Comment: 8 pages, 7 figures, LaTeX, accepted to Phys. Rev.
Miniaturization of molecular conjugated systems for organic solar cells: towards pigmy donors
Organic solar cells with short-circuit current densities and conversion efficiencies of ca. 7.0 mA cm(-2) and 2.0%, respectively, have been fabricated with a very small molecular donor based on substituted triarylamines
Organic dye for dye-sensitized solar cell
Organic dye for a dye-sensitized solar cell (DSSC) comprising at least one electron-acceptor unit and at least one π-conjugated unit. Said organic dye is particularly useful in a dye-sensitized photoelectric transformation element which, in its turn, can be used in a dye-sensitized solar cell (DSSC)
Strain induced pressure effect in pulsed laser deposited thin films of the strongly correlated oxide V2O3
V2O3 thin films about 10 nm thick were grown on Al2O3 (0001) by pulsed laser
deposition. The XRD analysis is in agreement with R-3c space group. Some of
them exhibit the metal / insulator transition characteristic of V2O3 bulk
material and others samples exhibit a metallic behavior. For the latter, the
XPS analysis indicates an oxidation state of +III for vanadium. There is no
metal / insulator transition around 150 K in this sample and a strongly
correlated Fermi liquid rho = AT2 behavior of the resistivity at low
temperature is observed, with a value of A of 1.2 10-4 ohm cm, 3 times larger
than the bulk value at 25 kbar
Poly(thiophenes) derivatized with linear and macrocyclic polyethers: from cation detection to molecular actuation
The association of linear or macrocyclic polyethers with the electronic properties of the π-conjugated polythiophene backbone leads to functional conducting polymers that exhibit metal cation dependent electronic properties. Based on this concept, various classes of cation sensors have been proposed and investigated for almost two decades. The interactions of metal cations with linear or macrocyclic polyether functional groups lead to modifications of the electronic properties of the π-conjugated backbone through various mechanisms including direct electronic effects on a single conjugated chain, collective electrochemical processes, or conformational changes. Conjugated polymers and oligomers representative of these various processes are discussed with an emphasis on recent examples of derivatized conjugated systems in which the interactions between metal cations and polyether groups serve as driving force to create molecular motion in conjugated systems
Organic dye for dye-sensitized solar cells
Organic dye for a dye-sensitized solar cell (DSSC) comprising at least one electron-acceptor unit and at least one π-conjugated unit. Said organic dye is particularly useful in a dye-sensitized photoelectric transformation element which, in its turn, can be used in a dye-sensitized solar cell (DSSC)
The situation of horticultural family farms in Hajdu-Bihar County
The main aim of this research work is to study horticultural farms in HajdĂş-Bihar County, that mobilize labour and capital for thesake of agricultural production, namely family farms. During this study work we tried to chart the main characters, the conditions offunctioning, their profitability and its use possibilities, their external contacts and the resource of information of these farms, beside this toinvestigate the relationships between these parameters. Parallel to this we tried to compensate the relatively high deficiency of information byempirical research work. This deficiency is the characterization of farmers and the inducement of farming and its conditions both on the levelof county and state. By our empirical research work we have made a comprehensive position paper that shows the conditions of farms andfarmer populations, as well. Two hundred questionnaires were evaluated. The percentages of horticultural farms were 25% from allquestionnaires. Above all this paper is looking for the answer to the following questions: How and by which sources do farmers develop andextent their farms? How do farmers see their own future, what kind of aims do they have?Who will stop and who will go on producing? Thecollected information on the whole may help to make much more flexible legislatives and administrative regulations, although the surveycovered only one county
Structure-properties relationships in triarylamine-based donor-acceptor molecules containing naphtyl groups as donor material for organic solar cells
The effects of replacing the phenyl rings of triphenylamine (TPA) by naphtyl groups are analysed on a series of push-pull molecules containing a 2-thienyl-dicyanovinyl acceptor group. UV-Vis absorption spectroscopy and cyclic voltammetry show that the introduction of one or two naphtyl groups in the structure has limited effects on the optical properties and energy levels of the molecule. On the other hand, the evaluation of the compounds as donor material in bi-layer solar cells with C60 as acceptor shows that the number and mode of linkage of the naphtyl groups exert a marked influence on the power conversion efficiency (PCE) of the cell. Two naphtyl groups lead to a decrease of PCE with respect to TPA, while a single naphtyl group produces opposite effects depending on the linking mode. Compared to TPA, an alpha-naphtyl group leads to a small decrease of PCE while in contrast a beta-naphtyl leads to a ~35% increase of PCE due to improved short-circuit current density (Jsc) and fill-factor. The determination of the hole-mobility of these two donors by the space-charge-limited current method shows that these effects are correlated with the higher hole-mobility of the β-naphtyl compound
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