Black String Entropy from Anomalous D-brane Couplings

The quantum corrections to the counting of statistical entropy for the 5+1-dimensional extremal black string in type-IIB supergravity with two observers are studied using anomalous Wess-Zumino actions for the corresponding intersecting D-brane description. The electric-magnetic duality symmetry of the anomalous theory implies a new symmetry between D-string and D-fivebrane sources and renders opposite sign for the RR charge of one of the intersecting D-branes relative to that of the black string. The electric-magnetic symmetric Hilbert space decomposes into subspaces associated with interior and exterior regions and it is shown that, for an outside observer, the expectation value of a horizon area operator agrees with the deviation of the classical horizon area in going from extremal to near-extremal black strings.Comment: 12 pages, LaTeX; Corrections and clarifying comments adde

Cryogenic shutter

A magnetically operated shutter mechanism is provided that will function in cryogenic or cryogenic zero gravity environments to selectively block radiation such as light from passing through a window to a target object such as a mirror or detector located inside a cryogenic container such as a dewar. The mechanism includes a shutter paddle blade that is moved by an electromagnetically actuated torquing device between an open position where the target object is exposed to ambient radiation or light and a closed position where the shutter paddle blade shields the ambient radiation or light from the target object. The purpose of the shuttering device is to prevent the mirror or other target object from being directly exposed to radiation passing through the window located on the side wall of the dewar, thereby decreasing or eliminating any temperature gradient that would occur within the target object due to exposure to the radiation. A special nylon bearing system is utilized to prevent the device from binding during operation and the paddle blade is also thermally connected to a reservoir containing cryogen to further reduce the internal temperature

Double quiver gauge theory and nearly Kahler flux compactifications

We consider G-equivariant dimensional reduction of Yang-Mills theory with torsion on manifolds of the form MxG/H where M is a smooth manifold, and G/H is a compact six-dimensional homogeneous space provided with a never integrable almost complex structure and a family of SU(3)-structures which includes a nearly Kahler structure. We establish an equivalence between G-equivariant pseudo-holomorphic vector bundles on MxG/H and new quiver bundles on M associated to the double of a quiver Q, determined by the SU(3)-structure, with relations ensuring the absence of oriented cycles in Q. When M=R^2, we describe an equivalence between G-invariant solutions of Spin(7)-instanton equations on MxG/H and solutions of new quiver vortex equations on M. It is shown that generic invariant Spin(7)-instanton configurations correspond to quivers Q that contain non-trivial oriented cycles.Comment: 42 pages; v2: minor corrections; Final version to be published in JHE

The properties of Msh2-Msh6 ATP binding mutants suggest a signal amplification mechanism in DNA mismatch repair.

DNA mismatch repair (MMR) corrects mispaired DNA bases and small insertion/deletion loops generated by DNA replication errors. After binding a mispair, the eukaryotic mispair recognition complex Msh2-Msh6 binds ATP in both of its nucleotide-binding sites, which induces a conformational change resulting in the formation of an Msh2-Msh6 sliding clamp that releases from the mispair and slides freely along the DNA. However, the roles that Msh2-Msh6 sliding clamps play in MMR remain poorly understood. Here, using Saccharomyces cerevisiae, we created Msh2 and Msh6 Walker A nucleotide-binding site mutants that have defects in ATP binding in one or both nucleotide-binding sites of the Msh2-Msh6 heterodimer. We found that these mutations cause a complete MMR defect in vivo The mutant Msh2-Msh6 complexes exhibited normal mispair recognition and were proficient at recruiting the MMR endonuclease Mlh1-Pms1 to mispaired DNA. At physiological (2.5 mm) ATP concentration, the mutant complexes displayed modest partial defects in supporting MMR in reconstituted Mlh1-Pms1-independent and Mlh1-Pms1-dependent MMR reactions in vitro and in activation of the Mlh1-Pms1 endonuclease and showed a more severe defect at low (0.1 mm) ATP concentration. In contrast, five of the mutants were completely defective and one was mostly defective for sliding clamp formation at high and low ATP concentrations. These findings suggest that mispair-dependent sliding clamp formation triggers binding of additional Msh2-Msh6 complexes and that further recruitment of additional downstream MMR proteins is required for signal amplification of mispair binding during MMR

Quiver Gauge Theory of Nonabelian Vortices and Noncommutative Instantons in Higher Dimensions

We construct explicit BPS and non-BPS solutions of the Yang-Mills equations on the noncommutative space R^{2n}_\theta x S^2 which have manifest spherical symmetry. Using SU(2)-equivariant dimensional reduction techniques, we show that the solutions imply an equivalence between instantons on R^{2n}_\theta x S^2 and nonabelian vortices on R^{2n}_\theta, which can be interpreted as a blowing-up of a chain of D0-branes on R^{2n}_\theta into a chain of spherical D2-branes on R^{2n} x S^2. The low-energy dynamics of these configurations is described by a quiver gauge theory which can be formulated in terms of new geometrical objects generalizing superconnections. This formalism enables the explicit assignment of D0-brane charges in equivariant K-theory to the instanton solutions.Comment: 45 pages, 4 figures; v2: minor correction

Quiver Gauge Theory and Noncommutative Vortices

We construct explicit BPS and non-BPS solutions of the Yang-Mills equations on noncommutative spaces R^{2n}_theta x G/H which are manifestly G-symmetric. Given a G-representation, by twisting with a particular bundle over G/H, we obtain a G-equivariant U(k) bundle with a G-equivariant connection over R^{2n}_theta x G/H. The U(k) Donaldson-Uhlenbeck-Yau equations on these spaces reduce to vortex-type equations in a particular quiver gauge theory on R^{2n}_theta. Seiberg-Witten monopole equations are particular examples. The noncommutative BPS configurations are formulated with partial isometries, which are obtained from an equivariant Atiyah-Bott-Shapiro construction. They can be interpreted as D0-branes inside a space-filling brane-antibrane system.Comment: talk by O.L. at the 21st Nishinomiya-Yukawa Memorial Symposium, Kyoto, 15 Nov. 200