Plasmonic enhancement of the two photon absorption cross section of an organic chromophore using polyelectrolyte-coated gold nanorods

The effect of plasmonic enhancement on the two-photon absorption cross section of organic chromophores attached to polyelectrolyte-coated gold nanorods was investigated. The magnitudes of such enhancements were confirmed using single and two photon excitations of the chromophore molecules bound to polyelectrolyte-coated gold nanorods. By synthesizing two-, four-, six-, and eight-polyelectrolyte layer coated nanorods of a particular aspect ratio, the distance dependence of the evanescent electromagnetic field on molecular two-photon absorption was observed. Enhancements of 40-fold were observed for the chromophores nearest to the surface.     

Uniquely <Emphasis Type="Italic">C</Emphasis><Subscript>4</Subscript>-Saturated Graphs

For a fixed graph H, a graph G is uniquely H-saturated if G does not contain H, but the addition of any edge from [`(G)]{\overline{G}} to G completes exactly one copy of H. Using a combination of algebraic methods and counting arguments, we determine all the uniquely C ₄-saturated graphs; there are only ten of them.     

Topological Field Theories and Harrison Homology

Tools and arguments developed by Kevin Costello are adapted to families of “Outer Spaces” or spaces of graphs. This allows us to prove a version of Deligne’s conjecture: the Harrison homology associated with a homotopy commutative algebra is naturally a module over a cobordism category of 3-manifolds.     

Time reversal and the neutron

We have measured the triple correlation $D\langle\vec J_n\rangle/J_n\cdot (\vec\beta_e\times\hat p_\nu)$ with a polarized cold-neutron beam (Mumm et al., Phys Rev Lett 107:102301, 2011; Chupp et al., Phys Rev C 86:035505, 2012). A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation. Final-state effects also contribute to D at the level of 10^???5 and can be calculated with precision of 1 % or better. The D coefficient is uniquely sensitive to the imaginary part of the ratio of axial-vector and vector beta-decay amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D?=?[???0.94±1.89 (stat)±0.97(sys)]×10^???4. Assuming only vector and axial vector interactions in beta decay, our result can be interpreted as a measure of the phase of the axial-vector coupling relative to the vector coupling, $\phi_{\rm AV}= 180.012^\circ \pm 0.028^\circ$ . This result also improves constrains on certain non-VA interactions.     

Properties of segmented polyurethane zwitterionomer elastomers

Four series of polyurethane zwitterionomers based on different soft segment polyols [polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), and polybutadiene (PBD)] were synthesized, and their properties were investigated using differential scanning calorimetry, dynamic mechanical spectroscopy, infrared dichroism, and stress-strain testing. Two different molar ratios of hard segment [4,4′-diphenylmethane diisocyanate (MDI)] to chain extender [N-methyl diethanol-amine (MDEA)] to soft segment polyol, each with three different levels of ionization, were prepared based on the four different polyols. Zwitterionization was accomplished by quaternizing the tertiary amine of MDEA with γ-propane sultone. For the PBD materials, the un-ionized samples exhibited a high degree of phase separation, and ionization served mainly to improve domain cohesion. Increasing ionic content improved material strength while sacrificing extensibility. For the polyether materials the un-ionized samples were not highly phase separated, and ionization improved both the degree of phase separation and hard segment domain cohesion. These morphological changes led to greatly improved mechanical properties. The tensile properties of the ionized PEO and PTMO materials were superior to the tensile properties of the PPO and PBD materials. This was attributed to the ability of the PEO and PTMO segments to crystallize under strain. The effects of segment length (by comparison with a previous study) and hard segment content on mechanical properties are also discussed.     

Exfoliation of Crystalline 2D Carbon Nitride: Thin Sheets,Scrolls and Bundles via Mechanical and Chemical Routes

The carbon nitride poly(triazine imide) with intercalated bromide ions is a layered, graphitic material of 2D covalently bonded molecular sheets with an exceptionally large gallery height of 3.52 Å due to the intercalated bromide anions. The material can be cleaved both mechanically and chemically into thin sheets and scrolls analogous to the carbon‐only systems graphite and graphene.

     

Bistability in the chemical master equation for dual phosphorylation cycles

Dual phospho/dephosphorylation cycles, as well as covalent enzymatic-catalyzed modifications of substrates are widely diffused within cellular systems and are crucial for the control of complex responses such as learning, memory, and cellular fate determination. Despite the large body of deterministic studies and the increasing work aimed at elucidating the effect of noise in such systems, some aspects remain unclear. Here we study the stationary distribution provided by the two-dimensional chemical master equation for a well-known model of a two step phospho/dephosphorylation cycle using the quasi-steady state approximation of enzymatic kinetics. Our aim is to analyze the role of fluctuations and the molecules distribution properties in the transition to a bistable regime. When detailed balance conditions are satisfied it is possible to compute equilibrium distributions in a closed and explicit form. When detailed balance is not satisfied, the stationary non-equilibrium state is strongly influenced by the chemical fluxes. In the last case, we show how the external field derived from the generation and recombination transition rates, can be decomposed by the Helmholtz theorem, into a conservative and a rotational (irreversible) part. Moreover, this decomposition allows to compute the stationary distribution via a perturbative approach. For a finite number of molecules there exists diffusion dynamics in a macroscopic region of the state space where a relevant transition rate between the two critical points is observed. Further, the stationary distribution function can be approximated by the solution of a Fokker-Planck equation. We illustrate the theoretical results using several numerical simulations.