Marker, myth and monolith: A Sculpture garden

In my thesis proposal I said I wanted to make four large scale works, relative as a group but individual. As the work evolved in the design stage, it became obvious to me that what I was doing was designing a sculpture garden. I have referred to my thesis work as The Sculpture Garden since, and refer to it as such throughout this paper. The individual sculpture pieces I refer to as \u27markers\u27. After much critical discourse with Rick Hirsch, I determined that the sculptures I wanted to create were in fact markers or signposts, beacons to whatever audience they might attract, with a message - some meaning for those who pass. The Sculpture Garden turned out to be seven sculptures, varying in size from 18 to 6\u274 , composed around a ceramic block path 16\u27 x 16\u27. The work took 2800 pounds of clay and eight weeks to build. The scale of the work and it\u27s composition had the impact I was looking for. It seemed to catch the attention and curiosity of the viewer. I watched people walk around The Sculpture Garden examining individual pieces and then the work as a whole. The work represented two years worth of experimentation in graduate school, and years of being influenced by a love of ancient Mayan art and architecture. It was my intention in creating The Sculpture Garden to take the pedestal out from under ceramic sculpture, to flirt with architecture by magnifying scale thus magnifying the \u27presence\u27 of the piece; to create the feeling of being in a place where something incredible had or could happen. This paper is an autobiographical account of what lead up to the creation of The Sculpture Garden and a discussion of what the work means

Simulating Brownian suspensions with fluctuating hydrodynamics

Fluctuating hydrodynamics has been successfully combined with several computational methods to rapidly compute the correlated random velocities of Brownian particles. In the overdamped limit where both particle and fluid inertia are ignored, one must also account for a Brownian drift term in order to successfully update the particle positions. In this paper, we present an efficient computational method for the dynamic simulation of Brownian suspensions with fluctuating hydrodynamics that handles both computations and provides a similar approximation as Stokesian Dynamics for dilute and semidilute suspensions. This advancement relies on combining the fluctuating force-coupling method (FCM) with a new midpoint time-integration scheme we refer to as the drifter-corrector (DC). The DC resolves the drift term for fluctuating hydrodynamics-based methods at a minimal computational cost when constraints are imposed on the fluid flow to obtain the stresslet corrections to the particle hydrodynamic interactions. With the DC, this constraint need only be imposed once per time step, reducing the simulation cost to nearly that of a completely deterministic simulation. By performing a series of simulations, we show that the DC with fluctuating FCM is an effective and versatile approach as it reproduces both the equilibrium distribution and the evolution of particulate suspensions in periodic as well as bounded domains. In addition, we demonstrate that fluctuating FCM coupled with the DC provides an efficient and accurate method for large-scale dynamic simulation of colloidal dispersions and the study of processes such as colloidal gelation

Protein engineering of cytochrome c by semisynthesis: substitutions at Glutamic acid 66

We have used protein semisynthesis to prepare four analogues of horse cytochrome c, in which the glutamic acid residue at position 66 has been removed and replaced by norvaline, glutamine, lysine and, as a methodological control, glutamic acid. This residue is quite strongly conserved in mitochondrial cytochrome c, and forms part of a cluster of acidic residues that occurs in all cytochromes c but whose function is obscure. Comparative studies of the physical and biochemical properties of the analogues have now disclosed two specific roles for Glu66 in the protein. It contributes significantly to the stabilization of the active conformation of the protein, probably by salt bridge formation, and it appears to participate in the redox-state-dependent ATP-binding site of cytochrome c. Our results also support two general views of the role of surface charged residues in cytochrome c, namely that their disposition influences both redox potential, through the electrostatic field felt at the redox centre, and the kinetics of electron transfer, through the dipole moment they generat

Findings Consistent with Nonselective Feeding in Tetrahymena pyriformis

In amoeboid cells, food particles are engulfed only after receptors on the phagocytic cell’s membrane bind to ligands on a particle’s surface. Ciliates also feed via phagocytosis but, instead of enveloping particles, some ciliates take them up through a complex, permanent, funnel-shaped, feeding apparatus. It is unclear whether receptor-ligand interactions are needed to trigger the process. If ciliates were shown to feed selectively on certain particles over others, based on the particles’ surface properties, then receptor-ligand interactions would likely play a role in phagocytosis. The literature includes few reports of such selectivity. To further investigate this issue, we chose to study feeding preference in the ciliate Tetrahymena pyriformis. We fed Tetrahymena mixtures of orange and green, fluorescent, 3 µm, polystyrene beads at two concentrations. One of the two types of beads was coated with bovine serum albumin. Authors were blinded to experimental conditions. We found no evidence of a preference for coated or uncoated beads at either concentration. We also found no trend toward the development of selective feeding as cells acquired more beads over time. Although we cannot rule out the possibility that Tetrahymena feeds selectively, we did not find convincing evidence of such selectivity when T. pyriformis is given a choice between uncoated beads and those coated with albumin. Our results failed to demonstrate a role for molecular recognition when Tetrahymena engages in phagocytosis

Identification of internal properties of fibres and micro-swimmers

In this paper, we address the identifiability of constitutive parameters of passive or active micro-swimmers. We first present a general framework for describing fibres or micro-swimmers using a bead-model description. Using a kinematic constraint formulation to describe fibres, flagellum or cilia, we find explicit linear relationship between elastic constitutive parameters and generalized velocities from computing contact forces. This linear formulation then permits one to address explicitly identifiability conditions and solve for parameter identification. We show that both active forcing and passive parameters are both identifiable independently but not simultaneously. We also provide unbiased estimators for generalized elastic parameters in the presence of Langevin-like forcing with Gaussian noise using a Bayesian approach. These theoretical results are illustrated in various configurations showing the efficiency of the proposed approach for direct parameter identification. The convergence of the proposed estimators is successfully tested numerically

Characterization of Antibody Bipolar Bridging Mediated by the Human Cytomegalovirus Fc receptor gp68

The human cytomegalovirus glycoprotein gp68 functions as an Fc receptor for host IgGs and can form antibody bipolar bridging (ABB) complexes in which gp68 binds the Fc region of an antigen-bound IgG. Here we show that gp68-mediated endocytosis transports ABB complexes into endosomes, after which the complex is routed to lysosomes, presumably for degradation. These results suggest gp68 contributes to evasion of IgG-mediated immune responses by mediating destruction of host IgG and viral antigens

Resonance ionization spectroscopy of thorium isotopes - towards a laser spectroscopic identification of the low-lying 7.6 eV isomer of Th-229

In-source resonance ionization spectroscopy was used to identify an efficient and selective three step excitation/ionization scheme of thorium, suitable for titanium:sapphire (Ti:sa) lasers. The measurements were carried out in preparation of laser spectroscopic investigations for an identification of the low-lying Th-229m isomer predicted at 7.6 +- 0.5 eV above the nuclear ground state. Using a sample of Th-232, a multitude of optical transitions leading to over 20 previously unknown intermediate states of even parity as well as numerous high-lying odd parity auto-ionizing states were identified. Level energies were determined with an accuracy of 0.06 cm-1 for intermediate and 0.15 cm-1 for auto-ionizing states. Using different excitation pathways an assignment of total angular momenta for several energy levels was possible. One particularly efficient ionization scheme of thorium, exhibiting saturation in all three optical transitions, was studied in detail. For all three levels in this scheme, the isotope shifts of the isotopes Th-228, Th-229, and Th-230 relative to Th-232 were measured. An overall efficiency including ionization, transport and detection of 0.6 was determined, which was predominantly limited by the transmission of the mass spectrometer ion optics

Candidate molecular ions for an electron electric dipole moment experiment

This paper is a theoretical work in support of a newly proposed experiment (R. Stutz and E. Cornell, Bull. Am. Soc. Phys. 89, 76 2004) that promises greater sensitivity to measurements of the electron's electric dipole moment (EDM) based on the trapping of molecular ions. Such an experiment requires the choice of a suitable molecule that is both experimentally feasible and possesses an expectation of a reasonable EDM signal. We find that the molecular ions PtH+, HfH+, and HfF+ are suitable candidates in their low-lying triplet Delta states. In particular, we anticipate that the effective electric fields generated inside these molecules are approximately of 73 GV/cm, -17 GV/cm, and -18 GV/cm respectively. As a byproduct of this discussion, we also explain how to make estimates of the size of the effective electric field acting in a molecule, using commercially available, nonrelativistic molecular structure software.Comment: 25 pages, 3 figures, submitted to Physical Review

The Herpes Virus Fc Receptor gE-gI Mediates Antibody Bipolar Bridging to Clear Viral Antigens from the Cell Surface

The Herpes Simplex Virus 1 (HSV-1) glycoprotein gE-gI is a transmembrane Fc receptor found on the surface of infected cells and virions that binds human immunoglobulin G (hIgG). gE-gI can also participate in antibody bipolar bridging (ABB), a process by which the antigen-binding fragments (Fabs) of the IgG bind a viral antigen while the Fc binds to gE-gI. IgG Fc binds gE-gI at basic, but not acidic, pH, suggesting that IgG bound at extracellular pH by cell surface gE-gI would dissociate and be degraded in acidic endosomes/lysosomes if endocytosed. The fate of viral antigens associated with gE-gI–bound IgG had been unknown: they could remain at the cell surface or be endocytosed with IgG. Here, we developed an in vitro model system for ABB and investigated the trafficking of ABB complexes using 4-D confocal fluorescence imaging of ABB complexes with transferrin or epidermal growth factor, well-characterized intracellular trafficking markers. Our data showed that cells expressing gE-gI and the viral antigen HSV-1 gD endocytosed anti-gD IgG and gD in a gE-gI–dependent process, resulting in lysosomal localization. These results suggest that gE-gI can mediate clearance of infected cell surfaces of anti-viral host IgG and viral antigens to evade IgG-mediated responses, representing a general mechanism for viral Fc receptors in immune evasion and viral pathogenesis