Exploring simple ancillary ligands in copper-based dye-sensitized solar cells: effects of a heteroatom switch and of co-sensitization

The copper( I ) complexes [Cu(1) 2 ][PF 6 ], [Cu(2) 2 ][PF 6 ], [Cu(3) 2 ][PF 6 ] and [Cu(4) 2 ][PF 6 ] (1 . 2-(1H-imidazol-2-yl)- 6-methylpyridine, 2 . 2-(6-methylpyridin-2-yl)oxazole, 3 . 2-(6-methylpyridin-2-yl)thiazole and 4 . 2- methyl-6-(1-methyl-1H-imidazol-2-yl)pyridine) are reported. The crystal structures of [Cu(2) 2 ][PF 6 ]$ 0.5CH 2 Cl 2 and [Cu(3) 2 ][PF 6 ] confirm N,N 0 -chelation modes for 2 and 3, and tetrahedral copper( I ). In the solution absorption spectra, the MLCT band shifts to lower energy with a change in heteroatom (O, 424 nm; NH, 435 nm; NMe, 446 nm; S, 465 nm). [Cu(1) 2 ][PF 6 ] and [Cu(4) 2 ][PF 6 ] undergo copper-centred oxidative processes at lower potential than the complexes with O or S heteroatoms. Heteroleptic complexes [Cu(5)(L)] + (5 . ((6,6 0 -dimethyl-[2,2 0 -bipyridine]-4,4 0 -diyl)bis(4,1-phenylene)bis(phosphonic acid)), L . 1–4) were assembled on FTO/TiO 2 electrodes. The shift in the MLCT band (O NH < NMe < S) in the solid-state absorption spectra of the dye-functionalized electrodes parallels that of solution. The photoconversion efficiencies (h) of masked, dye-sensitized solar cells (DSCs) containing [Cu(5)(L)] + (L . 1– 4) dyes and an I/I 3 redox shuttle follow the order [Cu(5)(1)] + (3.03%) > [Cu(5)(3)] + (2.88%) > [Cu(5)(4)] + (2.71%) > [Cu(5)(2)] + (2.62%) relative to 7.55% for N719. Ancillary ligand 1 (with NH) leads to the highest open-circuit voltage (V OC . 608 mV) whilst 3 (S-heteroatom) gives the highest short-circuit current density (J SC . 7.76 mA cm 2 ). The performances of [Cu(5)(1)] + and [Cu(5)(3)] + are understood with the aid of electrochemical impedance spectroscopy (EIS). The DSC with [Cu(5)(1)] + exhibits a high chemical capacitance (C m ) and a low recombination resistance (R rec ); since the latter is offset by a low transport resistance (R tr ), a high J SC and V OC are observed for [Cu(5)(1)] + . DSCs with [Cu(5)(3)] + have the lowest R tr of all four devices. The performance of DSCs sensitized by a combination of [Cu(5)(1)] + and [Cu(5)(3)] + were assessed in order to capitalize upon the high V OC of [Cu(5)(1)] + and the high J SC of [Cu(5)(3)] + . After FTO/ TiO 2 functionalization with anchor 5, the electrodes were treated with a 1 : 1 mix of [Cu(5)(1)] + and [Cu(5)(3)] + or sequentially with [Cu(5)(3)] + then [Cu(5)(1)] + , or [Cu(5)(1)] + then [Cu(5)(3)] + . The DSC performances and the EIS parameters are consistent with competition between 1 and 3 for surface binding-sites; 1 dominates over 3, both in binding and in contribution to the overall photoresponse

Phytoplasmas in Australian grapevines - detection, differentiation and associated diseases

Phytoplasmas associated with Australian grapevine yellows (AGY) symptoms were detected using the polymerase chain reaction (PCR). To optimise the diagnostic, nested PCRs were compared with single PCRs using different primer pairs. Grapevine DNA known to be AGY phytoplasma positive was serially diluted and subjected to nested and single round PCR tests to determine which was the most sensitive. Samples taken over two growing seasons were used to determine the optimum sampling time for phytoplasma detection. The specificity of primer pairs was determined using phytoplasmas detected in Australian grapevines and overseas reference grapevine phytoplasmas. DNA extracted from grapevine exhibiting a range of symptoms was screened for phytoplasmas. Two different phytoplasmas were amplified in the PCR and they were identified using specific PCR primers and by restriction fragment length polymorphism (RFLP) analysis of the 16S rRNA gene and 16S rRNA/23S rRNA spacer region. RFLP analysis confirmed that one phytoplasma was the AGY phytoplasma and the other phytoplasma was indistinguishable from the tomato big bud (TBB) phytoplasma. The AGY phytoplasma was associated with AGY symptoms but was occasionally detected in asymptomatic vines and those with late season leaf curl (LSLC) and restricted growth (RG) symptoms. The TBB phytoplasma was detected in some vines with LSLC symptoms and very occasionally in vines with AGY symptoms. A 'variant' of the AGY phytoplasma was also detected in vines showing typical AGY symptoms

A new grapevine yellows phytoplasma from the Buckland Valley of Victoria, Australia

A new phytoplasma detected in grapevines with grapevine yellows disease from the Buckland Valley of Victoria, Australia was characterized. Buckland Valley grapevine yellows phytoplasma (BVGYp) could not be amplified by PCR using primers specific for the stolbur (STOL, 16SrXII) group of phytoplasmas indicating that it was unlikely to be a STOL group phytoplasma. BVGYp was amplified by PCR using primers specific for both the aster yellows (AV, 16Sr I) and STOL phytoplasma groups, indicating that it may be more closely related to the AY group phytoplasmas. Sequence analysis of 16SrRNA gene sequences showed that BVGYp clustered with AY and STOL groups of phytoplasmas. Sequence similarities were determined by pairwise comparisons of the 16S rDNA sequence of BVGYp WAY and STOL group phytoplasmas and BVGYp was more closely related to the AY group phytoplasmas. Although the data indicate BVGYp may form a newAY subgroup, the similarity coefficients between BVGYp and phytoplasmas from the AY, STOL and Mexican periwinkle virescence groups, derived from putative RFLP patterns, were less than 90%, so BVGYp may actually form a new phytoplasma group.

DLCQ String Spectrum from N=2{\cal N}=2 SYM Theory

We study non planar corrections to the spectrum of operators in the ${\mathcal N}=2$ supersymmetric Yang Mills theory which are dual to string states in the maximally supersymmetric pp-wave background with a {\em compact} light-cone direction. The existence of a positive definite discrete light-cone momentum greatly simplifies the operator mixing problem. We give some examples where the contribution of all orders in non-planar diagrams can be found analytically. On the string theory side this corresponds to finding the spectrum of a string state to all orders in string loop corrections.Comment: 35 pages, no figure

Dynamical Stability of Six-Dimensional Warped Brane-Worlds

We study a generalization of the Randall-Sundrum mechanism for generating the weak/Planck hierarchy, which uses two rather than one warped extra dimension, and which requires no negative tension branes. A 4-brane with one exponentially large compact dimension plays the role of the Planck brane. We investigate the dynamical stability with respect to graviton, graviphoton and radion modes. The radion is shown to have a tachyonic instability for certain models of the 4-brane stress-energy, while it is stable in others, and massless in a special case. If stable, its mass is in the milli-eV range, for parameters of the model which solve the hierarchy problem. The radion is shown to couple to matter with gravitational strength, so that it is potentially detectable by submillimeter-range gravity experiments. The radion mass can be increased using a bulk scalar field in the manner of Goldberger and Wise, but only to order MeV, due to the effect of the large extra dimension. The model predicts a natural scale of 10^{13} GeV on the 4-brane, making it a natural setting for inflation from the ultraviolet brane.Comment: 28 pages, 7 figure

Reversals in nature and the nature of reversals

The asymmetric shape of reversals of the Earth's magnetic field indicates a possible connection with relaxation oscillations as they were early discussed by van der Pol. A simple mean-field dynamo model with a spherically symmetric $\alpha$ coefficient is analysed with view on this similarity, and a comparison of the time series and the phase space trajectories with those of paleomagnetic measurements is carried out. For highly supercritical dynamos a very good agreement with the data is achieved. Deviations of numerical reversal sequences from Poisson statistics are analysed and compared with paleomagnetic data. The role of the inner core is discussed in a spectral theoretical context and arguments and numerical evidence is compiled that the growth of the inner core might be important for the long term changes of the reversal rate and the occurrence of superchrons.Comment: 24 pages, 12 figure

Bulk Filling Branes and the Baryon Density in AdS/QCD with gravity back-reaction

We consider the gravity back reaction on the metric due to the baryon density in effective ads/qcd model by reconsidering the role of the charged AdS black hole. Previously it has been known that the U(1) charge is dual to the R-charge. Here we point out that if we consider the case where $AdS_5$ is completely filled with $N_f$ flavor branes, the gravity back reaction produces charged AdS black hole where the effect of charge on the metric is proportional to $N_f/N_c$. As a consequence, phase diagram changes qualitatively if we allow $N_f/N_c$ finite: it closes at the finite density unlike the probe brane embedding approach. Another issue we discuss here is the question whether there is any chemical potential dependence in the confining phase. We consider this problem in the hard wall model with baryon charge. We conclude that there is a non-trivial dependence on the chemical potential in this case also.Comment: 17 pages 3x2 figures, v2: references added;v3 published version, title change and reference adde

Rolling to the tachyon vacuum in string field theory

We argue that the rolling-tachyon solution in cubic OSFT proceeds at late times to precisely the analytic tachyon-vacuum solution constructed by Schnabl. In addition, we demonstrate the relationship between the rolling-tachyon solution and the standard BCFT description by showing that there is a finite gauge transformation which relates the two.Comment: 16 pages, 5 figures, References and comments adde