Hemolysin toxin produced and secreted by pathogenic Escherichia coli is one of a family of cytolytic, structurally homologous protein toxins known as RTX (repeats in toxin) toxins. RTX toxins are products of a gene cluster, CABD . The A gene product, nontoxic hemolysin (proHlyA) is made toxic by post-translational fatty acylation of two internal lysine residues. HlyC, C gene product, is essential for acylation, and acyl-acyl carrier protein (ACP) is the acyl donor. HlyB and HlyD are involved in secretion of the toxin. HlyC was thought to serve as an internal protein acyltransferase and remained uncharacterized until now. ProHlyA and HlyC were separately subcloned, expressed, and purified, and acyl-ACPs with diverse radioactive acyl groups were synthesized. With these proteins, the conversion of proHlyA to HlyA by acyltransfer was assayed. Acyl-ACP was the obligate acyl donor. Acyltransfer was catalyzed by HlyC monomer, and an acyl-enzyme intermediate was detected and shown to catalyze the reverse reaction. The reaction mechanism was examined by steady state kinetics, and the nature of inhibitions by reaction products was determined. The kinetic mechanism of the internal protein acylation was compatible with an uni uni iso uni uni ping pong with isomerization of the F form of the enzyme. Clues to the chemical mechanism for the acyltransferase were elucidated by both chemical modification studies and site directed mutagenesis of the enzyme. Chemical modification experiments ruled out any critical cysteines, serines, and lysine residues, but suggested a role for histidine(s) and tyrosine(s) in acyltransferase function. In order to examine the function of specific residues and possibly corroborate the chemical findings, site directed mutagenesis studies of the acyltransferase were employed. Seventeen residues that were conserved among 13 different RTX toxin acyltransferases were individually mutated, and the respective HlyCs expressed, and characterized. Residues that were critical for acyltransferase function included Gly 11, His 23, Tyr 70, and Gly 85. As with chemical modification data, mutagenesis ruled out any conserved, essential, cysteines or serines critical for HlyC acyltransferase activity.

<p>Vi har i vårt samhälle idag en hög skilsmässostatistik. Individerna i parrelationer har problem att fungera tillsammans på ett tillfredställande sätt. Denna studie baseras på intervjuer med familjerådgivare som hanterar par som har problem i relationen. I undersökningen har jag valt att försöka svara på vad som familjerådgivaren anser kunna skapa höga förväntningar på relationen samt hur dessa förväntningar påverkar relationen. Den belyser även de aspekter som är viktiga för att en relation skall fungera och vad familjerådgivaren kan göra för par som har problem i relationen. Som teoretisk utgångspunkt till undersökningen har Giddens teori om den rena relationen använts. Resultatet visar att par som söker hjälp hos familjerådgivarna har svårt att få tid till att arbeta och underhålla sin relation. Slitningar som barn och ekonomiska bekymmer är vanliga. Undersökningen visar även att jämställdhet är att eftersträva för att relationen skall hålla en god balans. Den mans och kvinnoroll som finns i samhället påverkar också mannens och kvinnans förväntningar på varandra. Resultatet visar att par framför allt har svårigheter att kommunicera med varandra.</p><p>Nyckelord: relationer, ”rena relationer”, problem, kommunikation, familjerådgivare.</p>

Vi har i vårt samhälle idag en hög skilsmässostatistik. Individerna i parrelationer har problem att fungera tillsammans på ett tillfredställande sätt. Denna studie baseras på intervjuer med familjerådgivare som hanterar par som har problem i relationen. I undersökningen har jag valt att försöka svara på vad som familjerådgivaren anser kunna skapa höga förväntningar på relationen samt hur dessa förväntningar påverkar relationen. Den belyser även de aspekter som är viktiga för att en relation skall fungera och vad familjerådgivaren kan göra för par som har problem i relationen. Som teoretisk utgångspunkt till undersökningen har Giddens teori om den rena relationen använts. Resultatet visar att par som söker hjälp hos familjerådgivarna har svårt att få tid till att arbeta och underhålla sin relation. Slitningar som barn och ekonomiska bekymmer är vanliga. Undersökningen visar även att jämställdhet är att eftersträva för att relationen skall hålla en god balans. Den mans och kvinnoroll som finns i samhället påverkar också mannens och kvinnans förväntningar på varandra. Resultatet visar att par framför allt har svårigheter att kommunicera med varandra. Nyckelord: relationer, ”rena relationer”, problem, kommunikation, familjerådgivare.

By the near-field measurement of the electric field distribution inside the finite width THz parallel plate waveguide, we find the transition from conventional diffractive TEM-like mode to plasmonic mode. This mode transition depends on the geometry of the waveguide. The measurement is conducted on THz-TDS system with scattering probe-technique. We present the simulation which agrees with our experimental data

Composite fibers comprised of 5:95 wt ratio of ultra-short single walled carbon nanotubes (US-SWCNT):polyacrylonitrile (PAN) were spun using a dry-jet wet-spinning method followed by oxidative stabilization at 285 °C. The as-spun and stabilized composite fibers exhibited a 50 and 40 % increase, respectively, in modulus when compared to neat PAN. The vacuum pressure impregnation (VPI) method was employed to reinforce SWCNT fibers. SWCNT fibers were impregnated with polyamic acid (PAA) solution at 100 psi followed by thermal imidization to obtain fibers reinforced with polyimide (PI). The tensile strength was increased form 68 to 215 MPa for SWCNT fibers after VPI and imidization. Surfactant-wrapped chemically converted graphene (CCG) sheets obtained from the hydrazine reduction of GO were functionalized by treatment with aryl diazonium salts. The functionalized nanosheets disperse readily in polar aprotic solvents. A one-pot method has also been developed for reducing GO and simultaneously functionalizing it with alkyl and aryl groups. The alkyl functionalized reduced GO shows higher solubility in organic solvents when compared to GO. Graphene-filled PI composite films were prepared by solution blending of GO and PAA, casting the mixture and imidizing the films by heating up to 400 °C resulting in composite films that exhibit up to a ∼75 % increase in modulus and low moisture uptake. At 2 wt % loading GO, the composite films exhibit a conductivity of 1.25 × 10 -5 S/cm. The layer-by-layer (LbL) assembly technique was also employed in the fabrication of thin film composites of CCG and PI. The assembly was driven by the acid-base interaction between the aniline moieties on functionalized CCG and the carboxyl groups of the PAA. A simple fluid-phase processing method to obtain single to few layers of graphene without the aid of sonication has been developed. Graphene is spontaneously exfoliated from graphite and dissolved at isotropic concentrations as high as ∼1000 ppm in chlorosulfonic acid. The dissolution mechanism in superacids is protonation and electrostatic repulsion. The utility of this simple exfoliation process is further extended to diazonium functionalization of graphene allowing access to edge-functionalized graphenes with a minimal disruption of the graphitic network on the basal plane.

This thesis presents spectroscopic results using semiconductor heterostructures important for both applied and fundamental physics. First, we studied short-period superlattices of InAs and GaSb that suggest a promising alternative to mercury cadmium telluride for mid-infrared detection. Our time-domain measurements help sample growers optimize growth conditions to maximize the carrier lifetime and determine the superlattice period and interface quality. The second area of research has a more fundamental focus. Here, we study the time-integrated emission and time-resolved population and emission properties of high-density excitons in an InGaAs quantum well sample in strong perpendicular magnetic field. Our time-integrated results indicate that two-dimensional magneto-excitons can appear to be stable against a Mott transition with the application of magnetic field. Our time-resolved results provide the first direct observation of superfluorescence using a semiconductor showing the population inversion of magneto-excitons suddenly drop from fully excited to completely unexcited emitting an intense pulse of coherent radiation.

Hydrophilic silicon and germanium quantum dots were synthesized by a "bottom-up" method utilizing micelles to control particle size. Liquid phase deposition of silica on these quantum dots was successful with and without DTAB (dodecyltrimethylammonium bromide) as a surfactant to yield uniform spheres. Coating the quantum dots in the presence of DTAB allowed for better size control. The silica coated quantum dots were then arrayed in three dimensions using a vertical deposition technique on quartz slides or ITO glass. UV-vis absorbance, AFM, SEM, and TEM images were used to analyze the particles at every stage. The photoconductivity of the arrays was tested, and the cells were found to be conductive in areas.

The current chemical industry produces a diverse array of industrial chemicals from a handful of highly reduced byproducts (termed "platform chemicals") derived from oil refining. However, petroleum is a non-renewable resource, and increases in its cost have created pressure to convert the chemical industry into one that is renewable to ensure its long-term viability. To complete this objective, one approach is the conversion of biomass to platform chemicals through fermentation by Escherichia coli . One such platform chemical is methyl ketone, which can be readily converted to dienes that can directly replace existing platform chemicals such as ethylene. To bestow non-native methyl ketone production capability to E. coli from glucose, the polyketide biosynthesis pathway was exploited in conjunction with grafting in a heterologous methyl ketone synthesis pathway found in wild tomato species Solanum habrochaites to produce the methyl ketones. Cultivation under microaerobic conditions improved titers and yields, and further engineering to knock out the native competitive pathways that become activated under microaerobic conditions led to significantly improved strains. The final strain, ΔadheΔldhaΔptaΔpoxB [pTrcHis2A-shmks2-mks1], produced up to 450 mg/L of methyl ketones at 17 mg of methyl ketones produced per gram of glucose consumed under optimized operating conditions in minimal media supplemented with glucose.

The major pathway for O 2 binding to mammalian myoglobins (Mbs) and hemoglobins (Hbs) involves transient outward movements of the distal histidine (HisE7), which allows ligand migration into the distal portion of the heme pocket. This E7 gate pathway appears dominant in vertebrate Hbs and Mbs. However, a number of invertebrate globins, including the dimeric hemoglobin from the blood clam Scapharca inaequivalvis (ScHbI), have an inverted quaternary structure in which an EF:FE dimer interface appears to block the HisE7 gate. Another set of globins, including the mini-hemoglobin from the Nemertean sea worm Cerebratulus lacteus (CerHb), are missing the N-terminal A-helix, which results in an internal tunnel between the E- and H-helices. This apolar channel has been suggested to represent an alternative to the HisE7 gate pathway. To determine the roles of the E7 gate and alternative pathways, we have systematically examined the effects of mutations at the E7 position in ScHbI and CerHb and at 21 other positions along the polar channel in CerHb. As was observed for SwMb and HbA, there is a progressive decrease in the bimolecular rate constants for O 2 binding to ScHbI as the size of the amino acid at position E7 is increased from Ala to Trp. This pattern is unaffected when ScHbI is completely converted to the R- or high affinity quaternary state by the F97Y mutation or when the dimer interface is completely disrupted by the K30D mutation. In contrast, E7 mutations have little affect on the rates of ligand entry and escape in CerHb. Instead, ligands diffuse through the apolar channel between the E- and H-helices as judged by decreases in both overall association and dissociation rate constants and increases in the extent of geminate recombination when the channel is blocked by small to large amino acid mutations. In SwMb, these trends are only observed when the small to large mutations are constructed at or near the E7 gate or directly in the distal pocket where ligands are captured. Thus, it is clear that globins have evolved more than one pathway for rapid O 2 uptake and release.

In this paper we establish the existence and partial regularity of a (d-2)-dimensional edge-length minimizing polyhedron in [Special characters omitted.] . The minimizer is a generalized convex polytope of volume one which is the limit of a minimizing sequence of polytopes converging in the Hausdorff metric. We show that the (d-2)-dimensional edge-length ζ d -2 is lower-semicontinuous under this sequential convergence. Here the edge set of the limit generalized polytope is a closed subset of the boundary whose complement in the boundary consists of countably many relatively open planar regions.