Deciphering solar turbulence from sunspots records

It is generally believed that sunspots are the emergent part of magnetic flux tubes in the solar interior. These tubes are created at the base of the convection zone and rise to the surface due to their magnetic buoyancy. The motion of plasma in the convection zone being highly turbulent, the surface manifestation of sunspots may retain the signature of this turbulence, including its intermittency. From direct observations of sunspots, and indirect observations of the concentration of cosmogenic isotopes $^{14}$C in tree rings or $^{10}$Be in polar ice, power spectral densities in frequency are plotted. Two different frequency scalings emerge, depending on whether the Sun is quiescent or active. %magnetic activity is maximum or minimum. From direct observations we can also calculate scaling exponents. These testify to a strong intermittency, comparable with that observed in the solar wind.Comment: 5 pages, 6 figures, accepted for publication in MNRAS Letter

PP-Wave / CFT_2 Duality

We investigate the pp-wave limit of the AdS_3\times S^3\times K3 compactification of Type IIB string theory from the point of view of the dual Sym_N(K3) CFT. It is proposed that a fundamental string in this pp-wave geometry is dual to the c=6 effective string of the Sym_N(K3) CFT, with the string bits of the latter being composed of twist operators. The massive fundamental string oscillators correspond to certain twisted Virasoro generators in the effective string. It is shown that both the ground states and the genus expansion parameter (at least in the orbifold limit of the CFT) coincide. Surprisingly the latter scales like J^2/N rather than the J^4/N^2 which might have been expected. We demonstrate a leading-order agreement between the pp-wave and CFT particle spectra. For a degenerate special case (one NS 5-brane) an intriguing complete agreement is found.Comment: JHEP3 LaTeX, 20 pages; discussion of WZW levels clarified, reference adde

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

Dependent Types for Pragmatics

This paper proposes the use of dependent types for pragmatic phenomena such as pronoun binding and presupposition resolution as a type-theoretic alternative to formalisms such as Discourse Representation Theory and Dynamic Semantics.Comment: This version updates the paper for publication in LEU

Squashed Giants: Bound States of Giant Gravitons

We consider giant gravitons in the maximally supersymmetric type IIB plane-wave, in the presence of a constant NSNS B-field background. We show that in response to the background B-field the giant graviton would take the shape of a deformed three-sphere, the size and shape of which depend on the B-field, and that the giant becomes classically unstable once the B-field is larger than a critical value B_{cr}. In particular, for the B-field which is (anti-)self-dual under the SO(4) isometry of the original giant S^3, the closed string metric is that of a round S^3, while the open string metric is a squashed three-sphere. The squashed giant can be interpreted as a bound state of a spherical three-brane and circular D-strings. We work out the spectrum of geometric fluctuations of the squashed giant and study its stability. We also comment on the gauge theory which lives on the brane (which is generically a noncommutative theory) and a possible dual gauge theory description of the deformed giant.Comment: Latex file, 32 pages, 6 .eps figures; v3: typos correcte

On massless 4D Gravitons from 5D Asymptotically AdS Space-times

We investigate the conditions for obtaining four-dimensional massless spin-2 states in the spectrum of fluctuations around an asymptotically $AdS_5$ solution of Einstein-Dilaton gravity. We find it is only possible to have normalizable massless spin-2 modes if the space-time terminates at some IR point in the extra dimension, far from the UV AdS boundary, and if suitable boundary conditions are imposed at the ``end of space.'' In some of these cases the 4D spectrum consists only of a massless spin-2 graviton, with no additional massless or light scalar or vector modes. These spin-2 modes have a profile wave-function peaked in the interior of the 5D bulk space-time. Under the holographic duality, they may be sometimes interpreted as arising purely from the IR dynamics of a strongly coupled QFT living on the AdS boundary.Comment: 40 pages, 1 figure. Revised version, to appear in Nuclear Physics B. Typos corrected, one reference adde

Intersecting Flavor Branes

We consider an instance of the AdS/CFT duality where the bulk theory contains an open string tachyon, and study the instability from the viewpoint of the boundary field theory. We focus on the specific example of the AdS_5 X S^5 background with two probe D7 branes intersecting at general angles. For generic angles supersymmetry is completely broken and there is an open string tachyon between the branes. The field theory action for this system is obtained by coupling to N =4 super Yang-Mills two N =2 hyper multiplets in the fundamental representation of the SU(N) gauge group, but with different choices of embedding of the two N=2 subalgebras into N=4. On the field theory side we find a one-loop Coleman-Weinberg instability in the effective potential for the fundamental scalars. We identify a mesonic operator as the dual of the open string tachyon. By AdS/CFT, we predict the tachyon mass for small 't Hooft coupling (large bulk curvature) and confirm that it violates the AdS stability bound.Comment: 36 page

Glueballs of Super Yang-Mills from Wrapped Branes

In this paper we study qualitative features of glueballs in N=1 SYM for models of wrapped branes in IIA and IIB backgrounds. The scalar mode, 0++ is found to be a mixture of the dilaton and the internal part of the metric. We carry out the numerical study of the IIB background. The potential found exhibits a mass gap and produces a discrete spectrum without any cut-off. We propose a regularization procedure needed to make these states normalizable.Comment: 22 pages plus a appendixes, 2 figure

Noncommutative geometry, Quantum effects and DBI-scaling in the collapse of D0-D2 bound states

We study fluctuations of time-dependent fuzzy two-sphere solutions of the non-abelian DBI action of D0-branes, describing a bound state of a spherical D2-brane with N D0-branes. The quadratic action for small fluctuations is shown to be identical to that obtained from the dual abelian D2-brane DBI action, using the non-commutative geometry of the fuzzy two-sphere. For some of the fields, the linearized equations take the form of solvable Lam\'e equations. We define a large-N DBI-scaling limit, with vanishing string coupling and string length, and where the gauge theory coupling remains finite. In this limit, the non-linearities of the DBI action survive in both the classical and the quantum context, while massive open string modes and closed strings decouple. We describe a critical radius where strong gauge coupling effects become important. The size of the bound quantum ground state of multiple D0-branes makes an intriguing appearance as the radius of the fuzzy sphere, where the maximal angular momentum quanta become strongly coupled.Comment: 34 pages, Latex; v2: Minor correction in conformal transformation of couplings, references adde