Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV/c, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community

How analysts think: sense-making strategies in the analysis of temporal evolution and criminal network structures and activities

Analysis of criminal activity based on offenders’ social networks is an established procedure in intelligence analysis. The complexity of the data poses an obstacle for analysts to gauge network developments, e.g. detect emerging problems. Visualization is a powerful tool to achieve this, but it is essential to know how the analysts’ sense-making strategies can be supported most efficiently. Based on a think aloud study we identified ten cognitive strategies on a general level to be useful for designers. We also provide some examples how these strategies can be supported through appropriate visualizations

Multiple Kinase Involvement in the Regulation of Vascular Growth

The initial discovery of protein phosphorylation as a regulatory mechanism for the control of glycogen metabolism has led to intense interest of protein phosphorylation in regulating protein function (Cohen et al., 2001). Kinases play a variety of roles in many physiological processes within cells and represent one of the largest families in the human genome with over 500 members comprising protein serine/threonine, tyrosine, and dual-specificity kinases (Manning et al., 2002). Phosphorylation of proteins is one of the most significant signal transduction mechanisms which regulate intracellular processes such as transport, growth, metabolism, apoptosis, cystoskeletal arrangement and hormone responses (Bononi et al., 2011; Heidenreich et al., 1991; Manning et al., 2002; Pawson et al., 2000). As such, abnormal phosphorylation of proteins can be either a cause or a consequence of disease. Kinases are regulated by activator and inhibitor proteins, ligand binding, and phosphorylation by other proteins or via autophosphorylation (Hanks et al., 1991; Hug et al., 1993; Scott, 1991; Taylor et al., 1990; Taylor et al., 1992). Since kinases play key functions in many cellular processes, they represent an attractive target for therapeutic interventions in many disease states such as cancer, inflammation, diabetes and arthritis (Cohen et al., 2010; Fry et al., 1994; Karin, 2005; Mayers et al., 2005). In particular, the serine/threonine family of kinases comprises approximately 125 of the 500 family of kinases and includes the cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA), the cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG), and protein kinase C (PKC). These kinases are implicated in the regulation of cell growth and are the focus of this current study.We would like to acknowledge Jonathan C. Fox and Patti Shaver for assistance with isolation and culture of rat primary vascular smooth muscle cells. This project was supported by Award Number R01HL081720 from the National Institutes of Health National Heart, Lung, and Blood Institute (NHLBI), by ARRA Award Number R01HL081720-03S2, and by Post-doctoral Research Supplement Award Number R01HL081720-05S1 from the NHLBI

High current CW beam profile monitors using transisiton radiation at CEBAF

One way of measuring the profile of CEBAF`s low emittance and high power beam is to use the Optical Transition Radiation (OTR) emitted from a thin foil surface when the electron beam passes through it. We present the design of a monitor using the forward OTR emitted from a 0.25 {mu}m carbon foil. We believe that the monitor will resolve three main issues: (i) whether the max temperature of the foil stays below the melting point, (ii) whether the beam loss remains below 0. 5%, in order not to trigger the machine protection system, and (iii) whether the monitor resolution (unlike that of synchrotron radiation monitors) is better than the product {lambda}{gamma}. It seems that the most serious limitation for CEBAF is the beam loss due to beam scattering. We present results from Keil`s theory and simulations from the computer code GEANT as well as measurements with Al foils with a 45 MeV electron beam. We also present a measurement of a 3.2 GeV beam profile that is much smaller than {lambda}{gamma}, supporting Rule & Fiorito`s calculations of the OTR resolution limit due to diffraction

Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current

GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center of the photocathode, (b) limiting the photocathode active area to eliminate photoemission from regions of the photocathode that do not support efficient beam delivery, (c) using a large drive laser beam to distribute ion damage over a larger area, and (d) by applying a relatively low bias voltage to the anode to repel ions created within the downstream beam line. A combination of these techniques provided the best total charge extracted lifetimes in excess of 1000 C at dc beam currents up to 9.5 mA, using green light illumination of bulk GaAs inside a 100 kV photogun

Phosphodiesterases Regulate BAY 41-2272-Induced VASP Phosphorylation in Vascular Smooth Muscle Cells

BAY 41-2272 (BAY), a stimulator of soluble guanylyl cyclase, increases cyclic nucleotides and inhibits proliferation of vascular smooth muscle cells (VSMCs). In this study, we elucidated mechanisms of action of BAY in its regulation of vasodilator-stimulated phosphoprotein (VASP) with an emphasis on VSMC phosphodiesterases (PDEs). BAY alone increased phosphorylation of VASPSer239 and VASPSer157, respective indicators of PKG and PKA signaling. IBMX, a non-selective inhibitor of PDEs, had no effect on BAY-induced phosphorylation at VASPSer239 but inhibited phosphorylation at VASPSer157. Selective inhibitors of PDE3 or PDE4 attenuated BAY-mediated increases at VASPSer239 and VASPSer157, whereas PDE5 inhibition potentiated BAY-mediated increases only at VASPSer157. In comparison, 8Br-cGMP increased phosphorylation at VASPSer239 and VASPSer157 which were not affected by selective PDE inhibitors. In the presence of 8Br-cAMP, inhibition of either PDE4 or PDE5 decreased VASPSer239 phosphorylation and inhibition of PDE3 increased phosphorylation at VASPSer239, while inhibition of PDE3 or PDE4 increased and PDE5 inhibition had no effect on VASPSer157 phosphorylation. These findings demonstrate that BAY operates via cAMP and cGMP along with regulation by PDEs to phosphorylate VASP in VSMCs and that the mechanism of action of BAY in VSMCs is different from that of direct cyclic nucleotide analogs with respect to VASP phosphorylation and the involvement of PDEs. Given a role for VASP as a critical cytoskeletal protein, these findings provide evidence for BAY as a regulator of VSMC growth and a potential therapeutic agent against vasculoproliferative disorders

Tillage and phosphorus availability

Non-Peer Reviewe

Evaluation of Niobium as Candidate Electrode Material for DC High Voltage Photoelectron Guns

The field emission characteristics of niobium electrodes were compared to those of stainless steel electrodes using a DC high voltage field emission test apparatus. A total of eight electrodes were evaluated: two 304 stainless steel electrodes polished to mirror-like finish with diamond grit and six niobium electrodes (two single-crystal, two large-grain, and two fine-grain) that were chemically polished using a buffered-chemical acid solution. Upon the first application of high voltage, the best large-grain and single-crystal niobium electrodes performed better than the best stainless steel electrodes, exhibiting less field emission at comparable voltage and field strength. In all cases, field emission from electrodes (stainless steel and/or niobium) could be significantly reduced and sometimes completely eliminated, by introducing krypton gas into the vacuum chamber while the electrode was biased at high voltage. Of all the electrodes tested, a large-grain niobium electrode performed the best, exhibiting no measurable field emission (< 10 pA) at 225 kV with 20 mm cathode/anode gap, corresponding to a field strength of 18:7 MV/m

Photoinjector improvements at CEBAF in support of parity violation experiments

Three photoinjector modifications were undertaken at CEBAF to help ensure successful completion of the PREx and Qweak parity violation experiments: the development of a pockels cell high voltage switch that provides stable voltages at 960 Hz helicity flip rate with 60 μs rise/fall time, the installation of a two-Wien-filter spin flipper for slow spin reversal, and the installation of a new photogun with inverted insulator geometry that operates at higher bias voltage