197,133 research outputs found
Structural studies of CRISPR-associated proteins
No full textClustered regularly interspaced short palindromic repeats (CRISPRs) act to prevent viral infection and horizontal gene transfer in prokaryotes. The genomic CRISPR array contains short sequences (“spacers”) that are derived from foreign genetic elements. The CRISPR array is transcribed and processed into CRISPR RNAs (crRNAs) used in the sequence-specific degradation of foreign nucleic acids. This process is called interference and is mediated by CRISPR-associated (Cas) proteins.
This thesis has focused on the structural and functional characterisation of four Cas proteins from the CRISPR/Cas system of Sulfolobus solfataricus. The crystal structure of Cmr7 (Sso1725), a Sulfolobales-specific subunit of the ssRNA-degrading CMR complex, allowed for the identification of a putative protein-binding site, though no specific function could be ascribed to the protein. Cas6 (Sso1437) is the enzyme responsible for crRNA maturation and the characterisation of this protein allowed for the molecular rationalisation of its atypical RNA cleavage mechanism. Csa5 and Cas8a2 are subunits of the aCascade complex that targets dsDNA. Csa5 (Sso1398) was shown to have a putative role in R-loop stabilisation during interference while the role of Cas8a2 (Sso1401) was not determined. The structures of these two proteins were used to define relationships between the subunits of interference complexes from various CRISPR/Cas systems.
A second aspect of this work has been the expression and purification of eukaryotic ion channels for structural studies. The acid sensing ion channel (ASIC) and FMRFamide-gated sodium channel (FaNaC) are gated ion channels with unknown mechanisms of channel activation. These ion channels must be expressed in eukaryotic systems and so human embryonic kidney (HEK) cells and baculovirus-insect cell expression systems were developed to express ASIC and FaNaC constructs. The expression and purification protocols have been optimised to allow for the preparation of soluble protein that will in future be used for crystallography and electron paramagnetic resonance (EPR) studies
Quantification of heavy particle segregation in turbulent flows: a Lagrangian approach
No full textThe way particles suspended in a turbulent flow are transported and segregated by turbulent structures is crucial in many atmospheric and industrial applications such as powder production and formation and growth of PM10 particulate. In recent years, this phenomenon has been studied from different viewpoints; lately, Osiptsov [1] proposed an alternative approach to quantify particle segregation, later followed by [2] and [3]. This method, referred to as ‘Full Lagrangian approach (FLA)’, evaluates the size of an infinitesimally small volume of particles and its changes in the course of time along each particle trajectory. The rate of deformation of this volume is related to the compressibility of the particle velocity field (e.g. [4]) which is an indicator of particle concentration. This method presents high computational efficiency in comparison with traditional Eulerian methods such as “box-counting”, for which a large number of particles is required to obtain accurate statistics. We decided to exploit FLA in a simple two-dimension synthetic turbulent flow field Direct Numerical Simulations of homogeneous isotropic turbulence, and to compare it with the MEPFV, a method proposed by [5] et al. essentially based on box counting. Preliminary results of the spatially averaged statistics of the rate of deformation are also presented, showing that the presence of singularities increases for large St numbers. In this work, we study the dispersion of identical, rigid and spherical particles in a carrier flow of mass density ρ and kinematic viscosity ν. Particles are assumed to be heavy (i.e. ρp/ρ » 1 where ρp is the particle density) with radii aρ much smaller than the smallest length scale of the flow. Upon neglecting gravity and Brownian effects, the equations of motion are [6]: 1 where xp and v are the position and velocity of the particle respectively, and u = u(xp, t) denotes the velocity of the carrier flow at the position of the particle. All variables have been made dimensionless by a typical time scale ד and a typical velocity scale U. The parameter is the Stokes number, which represents the ratio between the inertia driving the particle and the viscous damping action of the fluid
Edvard Munchs Sfinx: Een psychologische transformatie binnen de Sfinx-reeks
No full textDe scriptie onderzoekt hoe Edvard Munchs persoonlijke ervaringen en psychische gesteldheid van invloed waren op de ontwikkeling van de Sfinx-reeks, een serie schilderijen waarin vrouwen in verschillende levensfasen centraal staan. Munch staat bekend om zijn emotioneel geladen schilderstijl en thematiek, zoals angst, liefde en dood. In de Sfinx-reeks beeldt hij vrouwen vaak af als mystieke en bedreigende figuren, wat samenhangt met zijn moeizame relaties, jeugdtrauma’s en periodes van mentale instabiliteit.
De reeks toont drie vrouwen die levensfasen vertegenwoordigen, gescheiden van een mannelijke figuur in contemplatie. Dit benadrukt de ongrijpbaarheid van vrouwen voor Munch. De scriptie analyseert stilistische en thematische veranderingen in de reeks, zoals kleurgebruik en symboliek, en koppelt deze aan gebeurtenissen in Munchs leven. De evolutie van de reeks weerspiegelt Munchs groeiende obsessie met de dood en zijn complexe kijk op vrouwen. Door een combinatie van biografische en kunsthistorische analyse biedt de scriptie inzicht in Munchs visie en psyche
Hollandia-reeks 367
No full textAanpassing eerder uitgevoerd booronderzoek in 2004 (hollandia reeks 64). Boringen 4 en 6 zullen worden doorgezet
Statistics of velocity and preferential accumulation of micro-particles in boundary layer turbulence
No full textThe distribution of inertial particles in turbulent flows is strongly non-homogeneous and is driven by the structure of the underlying carrier flow field. In this work, we use DNS combined with Lagrangian particle tracking to characterize the effect of inertia on particle preferential accumulation. We compare the Eulerian statistics computed for fluid and particles of different size, and observe differences in terms of distribution patterns and deposition rates which depend on particle inertia. Specifically, different statistics are related to the selective interaction occurring between particles and coherent flow structures. This selective response causes a preferential sampling of the flow field by the particles and eventually leads to the well-known phenomenon of long-term particle accumulation in the boundary layer. We try to measure particle preferential accumulation with a Lagrangian parameter related to the rate of deformation of an elemental volume of the particle phase along a particle trajectory. In the frame of the Lagrangian approach, this parameter is mathematically defined as the particle position Jacobian, J(t), computed along a particle path. This quantity is related to the local compressibility/divergence of the particle velocity field. Lagrangian statistics of J(t) show that compressibility increases for increasing particle response times τp+ (up to τp+=25 and within the time span covered by the simulation). \ua9 2005 Elsevier B.V. All rights reserved
Growth of nano- and micro-scale ZnO particles as a platform for studies of antibacterial action in ZnO
No full textAntimicrobial action of micro- and nanoscale ZnO particles has been documented, but the fundamental physical mechanisms driving this action is still relatively unknown. We hypothesize that antibacterial action of ZnO is rooted in interactions between ZnO surfaces and extracellular material. This study builds a platform upon which a study of unique surface properties of micro- and nanoscale ZnO can be studied in conjunction with antibacterial action. Using a bottom-up hydrothermal chemical method we established the ability to grow morphologically different ZnO micro-crystals to isolate and study the two characteristically different surfaces (polar and nonpolar) in crystalline ZnO. SEM and EDX studies confirmed the growth of ZnO microcrystals of different morphologies based on chemical precursor. Photoluminescence revealed changes in emission spectra as reaction parameters change. To build on this platform, various optoelectronic methods and antibacterial testing techniques will be used to connect different morphologies, surface polarity, optoelectronic properties, and antibacterial activities
Schols (Ch.-M.). — De half-convergente Reeks ter Berekening van de integraal ψ(Ζ) (Verslagen der K. Akademie van Wetenschappen, Naturkunde, 3, II). Amsterdam, 1885
No full textRadau Rodolphe. Schols (Ch.-M.). — De half-convergente Reeks ter Berekening van de integraal ψ(Ζ) (Verslagen der K. Akademie van Wetenschappen, Naturkunde, 3, II). Amsterdam, 1885. In: Bulletin astronomique, tome 2, 1885. pp. 573-577
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
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