Support-studies for the coronagraph contamination experiment, 1 September 1968 - 31 August 1969

Calculation of Mie scattering function

Supporting studies for the coronagraph contamination experiment

Calculations of Mie scattering functions involved individual as well as mixed scattering of particles. In particular, computations were completed for a 15A particle and for particles subjected to incident light of ultraviolet wavelengths. Calculations of contaminant atmospheres for Gemini, Apollo, and Skylab considered leakage rates for the respective vehicles and the mass column density of the atmospheres surrounding them. Atmospheres for these vehicles have been computed for a uniform particle size distribution, and for a particle size distribution in which size varied

Assembly and Certification of ATLAS Muon Stations for the Middle and Outer Barrel at CERN

Roughly 400 of the approximately 700 muon stations of the ATLAS barrel belong to the middle and outer layer. Barrel Middle and Barrel Outer stations consist of both an MDT chamber and one or two RPC planes delivering the level-1 trigger information. While MDT chambers and individual RPC units are constructed at their home institutes, the assembly of the RPCs into planes, including the final cabling and the mounting of the trigger electronics, as well as the integration of MDTs and RPCs into muon stations takes place at CERN. MDT chambers, RPC planes and the completed stations have to pass a series of tests before being declared 'ready-for-installation'. Final certification criteria is the passing of a one-day cosmic ray test, for which a special setup has been built in building 899 (BB5). This note gives an overview over the work carried out in BB5, with emphasis on the cosmic ray test. Examples of abnormal chamber behavior will be discussed and a summary of common mistakes in station assembly or chamber cabling will be given. A second focus of the note is on the statistical analysis of the certification results

Filament Nucleation Tunes Mechanical Memory in Active Polymer Networks

Incorporating growth into contemporary material functionality presents a grand challenge in materials design. The F‐actin cytoskeleton is an active polymer network that serves as the mechanical scaffolding for eukaryotic cells, growing and remodeling in order to determine changes in cell shape. Nucleated from the membrane, filaments polymerize and grow into a dense network whose dynamics of assembly and disassembly, or “turnover,” coordinates both fluidity and rigidity. Here, the extent of F‐actin nucleation is varied from a membrane surface in a biomimetic model of the cytoskeleton constructed from purified protein. It is found that nucleation of F‐actin mediates the accumulation and dissipation of polymerization‐induced F‐actin bending energy. At high and low nucleation, bending energies are low and easily relaxed yielding an isotropic material. However, at an intermediate critical nucleation, stresses are not relaxed by turnover and the internal energy accumulates 100‐fold. In this case, high filament curvatures template further assembly of F‐actin, driving the formation and stabilization of vortex‐like topological defects. Thus, nucleation coordinates mechanical and chemical timescales to encode shape memory into active materials

Effects of Grazing Management on Sediment and Phosphorus Losses in Run-off (A Progress Report)

In 2001 and 2002, pastures at the ISU Rhodes Research and Demonstration Farm were grazed to determine the effects of stocking treatment on nutrient and sediment loss from pastureland. Treatments included an ungrazed control (UG), summer hay harvest with winter stockpiled grazing (HS), continuous stocking to a residual height of 2 inches (2C), rotational stocking to a residual height of 2 inches (2R), and rotational stocking to a residual height of 4 inches (4R). At three times in 2001 (late spring, mid-summer, and fall) and four times in 2002 (early spring, late spring, mid-summer, and fall), rainfall simulations were conducted at 6 sites within each paddock and 6 sites in a buffer zone down slope from each paddock. Run-off was collected and analyzed for total sediment, total phosphorus, and dissolved phosphorus. Simultaneous to each rainfall simulation, ground cover, penetration resistance, surface roughness, slope, contents of phosphorus and moisture of the soil, and the sward height and mass of forage were measured. In years 1 (late spring 2001 through early spring 2002) and 2 (late spring 2002 through fall 2002), mean concentrations of sediment in runoff did not differ between ungrazed or grazed paddocks. Mean concentrations of total P in the run-off were greater (P \u3c .05) in paddocks grazed to 2 inches by continuous or rotational stocking than in paddocks that were ungrazed, grazed to 4 inches by rotational stocking or harvested as hay and grazed as stockpiled forage. In year 1, mean losses of sediment, total P, and soluble P were greater (P \u3c .1) from paddocks grazed to 2 inches by continuous or rotational stocking than other treatments. In year 2, mean losses of sediment and total P in paddocks grazed to 2 inches by continuous stocking and mean losses of soluble P from paddocks grazed to 2 inches by rotational stocking were greater (P \u3c .05) than the other treatments

Near-infrared molecular imaging of tumors via chemokine receptors CXCR4 and CXCR7

The chemokine CXCL12/SDF-1 and its receptors CXCR4 and CXCR7 play a major role in tumor invasion, proliferation and metastasis. Since both receptors are overexpressed on distinct tumor cells and on the tumor vasculature, we evaluated their potential as targets for detection of cancers by molecular imaging. We synthesized conjugates of CXCL12 and the near-infrared (NIR) fluorescent dye IRDye®800CW, tested their selectivity, sensitivity and biological activity in vitro and their feasibility to visualize tumors in vivo. Purified CXCL12-conjugates detected in vitro as low as 500 A764 human glioma cells or MCF-7 breast cancer cells that express CXCR7 alone or together with CXCR4. Binding was time- and concentration-dependent, and the label could be competitively displaced by the native peptide. Control conjugates with bovine serum albumin or lactalbumin failed to label the cells. In mice, the conjugate distributed rapidly. After 1–92 h, subcutaneous tumors of human MCF-7 and A764 cells in immunodeficient mice were detected with high sensitivity. Background was observed in particular in liver within the first 24 h, but also skull and hind limbs yielded some background. Overall, fluorescent CXCL12-conjugates are sensitive and selective probes to detect solid and metastatic tumors by targeting tumor cells and tumor vasculature

Multi-monoubiquitylation controls VASP-mediated actin dynamics Icon for The Forest of Biologists

The actin cytoskeleton performs multiple cellular functions, and as such, actin polymerization must be tightly regulated. We previously demonstrated that reversible, non-degradative ubiquitylation regulates the function of the actin polymerase VASP in developing neurons. However, the underlying mechanism of how ubiquitylation impacts VASP activity was unknown. Here, we show that mimicking multi-monoubiquitylation of VASP at K240 and K286 negatively regulates VASP interactions with actin. Using in vitro biochemical assays, we demonstrate the reduced ability of multi-monoubiquitylated VASP to bind, bundle, and elongate actin filaments. However, multi-monoubiquitylated VASP maintained the ability to bind and protect barbed ends from capping protein. Finally, we demonstrate the electroporation of recombinant multi-monoubiquitylated VASP protein altered cell spreading morphology. Collectively, these results suggest a mechanism in which ubiquitylation controls VASP-mediated actin dynamics