Towards a perfect fixed point action for SU(3) gauge theory

We present an overview of the construction and testing of actions for SU(3) gauge theory which are approximate fixed points of renormalization group equations (at $\beta\rightarrow \infty$). Such actions are candidates for use in numerical simulations on coarse lattices.Comment: 6 pages, uuencoded compressed postscript file, contribution to LAT9

Topological structure in the SU(2) vacuum

We study the topological content of the vacuum of SU(2) pure gauge theory using lattice simulations. We use a smoothing process based on the renormalization group equation. This removes short distance fluctuations but preserves long distance structure. The action of the smoothed configurations is dominated by instantons, but they still show an area law for Wilson loops with an unchanged string tension. The average radius of an instanton is about 0.2 fm, at a density of about 2 fm${}^{-4}$.Comment: 3 pages, LaTeX, 3 figures, uses espcrc2.sty, Talk given at LATTICE9

Lipid-bilayer coated nanosized bimodal mesoporous carbon spheres for controlled release applications

Highly mesoporous nanosized carbon spheres (MCS) equipped with an active lipid bilayer demonstrate pronounced molecular release behavior, and excellent potential for drug delivery applications. We report a facile synthesis route for the creation of colloidal MCS with a bimodal pore size distribution, featuring a high BET surface area combined with high pore volume. Bimodal mesoporosity was achieved by a simultaneous co-assembly of a polymer resin (resol), tetraethyl orthosilicate (TEOS) and a block copolymer (Pluronic F127). The spherical geometry originates from casting the precursor mixture into a macroporous silica hard template, having a mean pore size of 60 nm, followed by thermopolymerization and final carbonization at 900 °C in nitrogen atmosphere. The final bimodal mesoporous MCS were obtained after removal of inorganic compounds by etching with hydrofluoric acid. Colloidal suspensions of MCS were prepared by oxidation with ammonium persulfate. MCS were loaded with calcein as a model drug. Efficient sealing of the MCS was achieved with a supported lipid bilayer (SLB). The SLB acts as a diffusion barrier against the uncontrolled release of encapsulated dye molecules until the release is triggered via the addition of a surface active agent. The high surface area and pore volume and the excellent release characteristics make the SLB-coated MCS a promising release-on-demand system

Lipid-bilayer coated nanosized bimodal mesoporous carbon spheres for controlled release applications

Highly mesoporous nanosized carbon spheres (MCS) equipped with an active lipid bilayer demonstrate pronounced molecular release behavior, and excellent potential for drug delivery applications. We report a facile synthesis route for the creation of colloidal MCS with a bimodal pore size distribution, featuring a high BET surface area combined with high pore volume. Bimodal mesoporosity was achieved by a simultaneous co-assembly of a polymer resin (resol), tetraethyl orthosilicate (TEOS) and a block copolymer (Pluronic F127). The spherical geometry originates from casting the precursor mixture into a macroporous silica hard template, having a mean pore size of 60 nm, followed by thermopolymerization and final carbonization at 900 °C in nitrogen atmosphere. The final bimodal mesoporous MCS were obtained after removal of inorganic compounds by etching with hydrofluoric acid. Colloidal suspensions of MCS were prepared by oxidation with ammonium persulfate. MCS were loaded with calcein as a model drug. Efficient sealing of the MCS was achieved with a supported lipid bilayer (SLB). The SLB acts as a diffusion barrier against the uncontrolled release of encapsulated dye molecules until the release is triggered via the addition of a surface active agent. The high surface area and pore volume and the excellent release characteristics make the SLB-coated MCS a promising release-on-demand system

Fixed point actions for SU(3) gauge theory

We summarize our recent work on the construction and properties of fixed point (FP) actions for lattice $SU(3)$ pure gauge theory. These actions have scale invariant instanton solutions and their spectrum is exact through 1--loop, i.e. in their physical predictions there are no $a^n$ nor $g^2 a^n$ cut--off effects for any $n$. We present a few-parameter approximation to a classical FP action which is valid for short correlation lengths. We perform a scaling test of the action by computing the quantity $G = L \sqrt{\sigma(L)}$, where the string tension $\sigma(L)$ is measured from the torelon mass $\mu = L \sigma(L)$, on lattices of fixed physical volume and varying lattice spacing $a$. While the Wilson action shows scaling violations of about ten per cent, the approximate fixed point action scales within the statistical errors for $1/2 \ge aT_c$.Comment: 11 pages, uuencoded compressed postscript fil

The classically perfect fixed point action for SU(3) gauge theory

In this paper (the first of a series) we describe the construction of fixed point actions for lattice $SU(3)$ pure gauge theory. Fixed point actions have scale invariant instanton solutions and the spectrum of their quadratic part is exact (they are classical perfect actions). We argue that the fixed point action is even 1--loop quantum perfect, i.e. in its physical predictions there are no $g^2 a^n$ cut--off effects for any $n$. We discuss the construction of fixed point operators and present examples. The lowest order $q {\bar q}$ potential $V(\vec{r})$ obtained from the fixed point Polyakov loop correlator is free of any cut--off effects which go to zero as an inverse power of the distance $r$.Comment: 34 pages (latex) + 7 figures (Postscript), uuencode

Local control of globally competing patterns in coupled Swift--Hohenberg equations

We present analytical and numerical investigations of two anti-symmetrically coupled 1D Swift--Hohenberg equations (SHEs) with cubic nonlinearities. The SHE provides a generic formulation for pattern formation at a characteristic length scale. A linear stability analysis of the homogeneous state reveals a wave instability in addition to the usual Turing instability of uncoupled SHEs. We performed weakly nonlinear analysis in the vicinity of the codimension-two point of the Turing-wave instability, resulting in a set of coupled amplitude equations for the Turing pattern as well as left and right traveling waves. In particular, these complex Ginzburg--Landau-type equations predict two major things: there exists a parameter regime where multiple different patterns are stable with respect to each other; and that the amplitudes of different patterns interact by local mutual suppression. In consequence, different patterns can coexist in distinct spatial regions, separated by localized interfaces. We identified specific mechanisms for controlling the position of these interfaces, which distinguish what kinds of patterns the interface connects and thus allow for global pattern selection. Extensive simulations of the original SHEs confirm our results

Immune response to functionalized mesoporous silica nanoparticles for targeted drug delivery

Multifunctional mesoporous silica nanoparticles (MSN) have attracted substantial attention with regard to their high potential for targeted drug delivery. For future clinical applications it is crucial to address safety concerns and understand the potential immunotoxicity of these nanoparticles. In this study, we assess the biocompatibility and functionality of multifunctional MSN in freshly isolated, primary murine immune cells. We show that the functionalized silica nanoparticles are rapidly and efficiently taken up into the endosomal compartment by specialized antigen-presenting cells such as dendritic cells. The silica nanoparticles showed a favorable toxicity profile and did not affect the viability of primary immune cells from the spleen in relevant concentrations. Cargo-free MSN induced only very low immune responses in primary cells as determined by surface expression of activation markers and release of pro-inflammatory cytokines such as Interleukin-6, -12 and -1β. In contrast, when surface-functionalized MSN with a pH-responsive polymer capping were loaded with an immune-activating drug, the synthetic Toll-like receptor 7 agonist R848, a strong immune response was provoked. We thus demonstrate that MSN represent an efficient drug delivery vehicle to primary immune cells that is both non-toxic and non-inflammagenic, which is a prerequisite for the use of these particles in biomedical applications

Multifunctional polymer-capped mesoporous silica nanoparticles for pH-responsive targeted drug delivery

Supramolecular templating techniques have been widely used to direct the formation of porous materials with the goal of introducing permanent mesoporosity. While surfactant-directed self-assembly has been exploited for inorganic materials such as titania, silica, organosilica, and zeolites, it has rarely been applied to metal-organic frameworks (MOFs) and coordination polymers. Here we introduce a new family of gemini surfactant-directed zinc imidazolates, referred to as mesostructured imidazolate frameworks (MIFs), and present a detailed study on the influence of different gemini-type surfactants on the formation mechanism and structures of the resulting zinc imidazolates. The proposed formation mechanism for MIF-type materials involves co-assembly and crystallization processes that yield lamellar mesostructured imidazolate frameworks. Understanding and controlling such processes also has implications for the syntheses of microporous zinc imidazolate framework (ZIF) materials, whose formation can be suppressed in surfactant-rich solutions, whereas formation of MIF materials is favored in the presence of surfactants and triggered by the addition of halogenides. Solid-state 2D 13C1H HETCOR NMR measurements on prototypic CTAB-directed MIF-1 establish that the head group moieties of the surfactant molecules interact strongly with the zinc-imidazolate-bromide sheets. Additionally, the NMR analyses suggest that MIF-1 has a significant fraction of surfactant molecules that are interdigitated between the zinc-imidazolate-bromide sheets with an antiparallel stacking arrangement, consistent with the high thermal and chemical stability of the MIF hybrid materials

Multifunctional polymer-capped mesoporous silica nanoparticles for pH-responsive targeted drug delivery

Supramolecular templating techniques have been widely used to direct the formation of porous materials with the goal of introducing permanent mesoporosity. While surfactant-directed self-assembly has been exploited for inorganic materials such as titania, silica, organosilica, and zeolites, it has rarely been applied to metal-organic frameworks (MOFs) and coordination polymers. Here we introduce a new family of gemini surfactant-directed zinc imidazolates, referred to as mesostructured imidazolate frameworks (MIFs), and present a detailed study on the influence of different gemini-type surfactants on the formation mechanism and structures of the resulting zinc imidazolates. The proposed formation mechanism for MIF-type materials involves co-assembly and crystallization processes that yield lamellar mesostructured imidazolate frameworks. Understanding and controlling such processes also has implications for the syntheses of microporous zinc imidazolate framework (ZIF) materials, whose formation can be suppressed in surfactant-rich solutions, whereas formation of MIF materials is favored in the presence of surfactants and triggered by the addition of halogenides. Solid-state 2D 13C1H HETCOR NMR measurements on prototypic CTAB-directed MIF-1 establish that the head group moieties of the surfactant molecules interact strongly with the zinc-imidazolate-bromide sheets. Additionally, the NMR analyses suggest that MIF-1 has a significant fraction of surfactant molecules that are interdigitated between the zinc-imidazolate-bromide sheets with an antiparallel stacking arrangement, consistent with the high thermal and chemical stability of the MIF hybrid materials