Genus Two Surface and Quarter BPS Dyons: The Contour Prescription

Following the suggestion of hep-th/0506249 and hep-th/0612011, we represent quarter BPS dyons in N=4 supersymmetric string theories as string network configuration and explore the role of genus two surfaces in determining the spectrum of such dyons. Our analysis leads to the correct contour prescription for integrating the partition function to determine the spectrum in different domains of the moduli space separated by the walls of marginal stability.Comment: LaTeX file, 25 page

The nature of static and dynamic correlation in nearly degenerate singlet and triplet states of N-heterocyclic chromophores

In this paper we investigate the role of electron correlation in predicting the S$_1$-S$_0$ and T$_1$-S$_0$ excitation energies and hence, the singlet-triplet gap ($\Delta$E$_{ST}$) in a set of cyclazines which act as templates for potential candidates for 5th generation Organic Light Emitting Diode (OLED) materials. This issue has recently garnered much interest with the focus being on the inversion of the $\Delta$E$_{ST}$, although experiments have indicated near degenerate levels with both positive and negative being within the experimental error bar (J. Am. Chem. Soc., 102: 6068 , J. Am. Chem. Soc., 108: 17 ). We have carried out a systematic and exhaustive study of various excited state electronic structure methodologies and identified the strengths and shortcomings of the various approaches and approximations in view of this challenging case. We have found that near degeneracy can be achieved either with a proper balance of static and dynamic correlation in multireference theories or with state-specific orbital corrections including its coupling with correlation. The role of spin contamination is also discussed. Eventually, this paper seeks to produce benchmark numbers for establishing cheaper theories which can then be used for screening derivatives of these templates with desirable optical and structural properties. Additionally we would like to point out that the use of DLPNO-STEOM-CCSD as the benchmark for $\Delta$E$_{ST}$ (as used in J. Phys. Chem. A, 126: 8: 1378, Chem. Phys. Lett., 779: 138827) is not a suitable benchmark for this class of molecules.Comment: 13 pages, 10 figures, submitted for revie

Constraining gravity using entanglement in AdS/CFT

We investigate constraints imposed by entanglement on gravity in the context of holography. First, by demanding that relative entropy is positive and using the Ryu-Takayanagi entropy functional, we find certain constraints at a nonlinear level for the dual gravity. Second, by considering Gauss-Bonnet gravity, we show that for a class of small perturbations around the vacuum state, the positivity of the two point function of the field theory stress tensor guarantees the positivity of the relative entropy. Further, if we impose that the entangling surface closes off smoothly in the bulk interior, we find restrictions on the coupling constant in Gauss-Bonnet gravity. We also give an example of an anisotropic excited state in an unstable phase with broken conformal invariance which leads to a negative relative entropy.Comment: 36 pages, 3 figures, v4: fig 1 modifie

Isoform-Specific Contributions of α-Actinin to Glioma Cell Mechanobiology

Glioblastoma Multiforme (GBM) is a malignant astrocytic tumor associated with low survival rates because of aggressive infiltration of tumor cells into the brain parenchyma. Expression of the actin binding protein α-actinin has been strongly correlated with the invasive phenotype of GBM in vivo. To probe the cellular basis of this correlation, we have suppressed expression of the nonmuscle isoforms α-actinin-1 and α-actinin-4 and examined the contribution of each isoform to the structure, mechanics, and motility of human glioma tumor cells in culture. While subcellular localization of each isoform is distinct, suppression of either isoform yields a phenotype that includes dramatically reduced motility, compensatory upregulation and redistribution of vinculin, reduced cortical elasticity, and reduced ability to adapt to changes in the elasticity of the extracellular matrix (ECM). Mechanistic studies reveal a relationship between α-actinin and non-muscle myosin II in which depletion of either α-actinin isoform reduces myosin expression and maximal cell-ECM tractional forces. Our results demonstrate that both α-actinin-1 and α-actinin-4 make critical and distinct contributions to cytoskeletal organization, rigidity-sensing, and motility of glioma cells, thereby yielding mechanistic insight into the observed correlation between α-actinin expression and GBM invasiveness in vivo

Synergistic Modulation of Cellular Contractility by Mixed Extracellular Matrices

The extracellular matrix (ECM) is known to provide various physicochemical cues in directing cell behavior including composition, topography, and dimensionality. Physical remodeling of the ECM has been documented in a variety of cancers. In breast cancer, the increased deposition of matrix proteins, their crosslinking, and alignment create a stiffer microenvironment that activates cell contractility and promotes cancer invasion. In this paper, we sought to study the collective influence of ECM composition and density on the contractile mechanics of human MDA-MB-231 cells making use of the recently established trypsin deadhesion assay. Using collagen and fibronectin-coated surfaces of varying density, we show that cell contractility is tuned in a density-dependent manner, with faster deadhesion on fibronectin-coated surfaces compared to collagen-coated surfaces under identical coating densities. The deadhesion responses are significantly delayed when cells are treated with the myosin inhibitor blebbistatin. By combining collagen and fibronectin at two different densities, we show that mixed ligand surfaces synergistically modulate cell contractility. Finally, we show that on fibroblast-derived 3D matrices that closely mimic in vivo matrices, cells are strongly polarized and exhibit faster deadhesion compared to the mixed ligand surfaces. Together, our results demonstrate that ECM composition, density, and 3D organization collectively regulate cell contractility