449 research outputs found
Interference of diffraction and transition radiation and its application as a beam divergence diagnostic
We have observed the interference of optical diffraction radiation (ODR) and
optical transition radiation (OTR) produced by the interaction of a
relativistic electron beam with a micromesh foil and a mirror. The production
of forward directed ODR from electrons passing through the holes and wires of
the mesh and their separate interactions with backward OTR from the mirror are
analyzed with the help of a simulation code. By careful choice of the micromesh
properties, mesh-mirror spacing, observation wavelength and filter band pass,
the interference of the ODR produced from the unperturbed electrons passing
through the open spaces of the mesh and OTR from the mirror are observable
above a broad incoherent background from interaction of the heavily scattered
electrons passing through the mesh wires. These interferences (ODTRI) are
sensitive to the beam divergence and can be used to directly diagnose this
parameter. We compare experimental divergence values obtained using ODTRI,
conventional OTRI, for the case when front foil scattering is negligible, and
computed values obtained from transport code calculations and multiple screen
beam size measurements. We obtain good agreement in all cases.Comment: 40 pages 18 Figures. accepted for publication in PRSTA
Synaptic Therapy in Alzheimer’s Disease: A CREB-centric Approach
Therapeutic attempts to cure Alzheimer’s disease (AD) have failed, and new strategies are desperately needed. Motivated by this reality, many laboratories (including our own) have focused on synaptic dysfunction in AD because synaptic changes are highly correlated with the severity of clinical dementia. In particular, memory formation is accompanied by altered synaptic strength, and this phenomenon (and its dysfunction in AD) has been a recent focus for many laboratories. The molecule cyclic adenosine monophosphate response element-binding protein (CREB) is at a central converging point of pathways and mechanisms activated during the processes of synaptic strengthening and memory formation, as CREB phosphorylation leads to transcription of memory-associated genes. Disruption of these mechanisms in AD results in a reduction of CREB activation with accompanying memory impairment. Thus, it is likely that strategies aimed at these mechanisms will lead to future therapies for AD. In this review, we will summarize literature that investigates 5 possible therapeutic pathways for rescuing synaptic dysfunction in AD: 4 enzymatic pathways that lead to CREB phosphorylation (the cyclic adenosine monophosphate cascade, the serine/threonine kinases extracellular regulated kinases 1 and 2, the nitric oxide cascade, and the calpains), as well as histone acetyltransferases and histone deacetylases (2 enzymes that regulate the histone acetylation necessary for gene transcription)
Multi-component measurements of the Jefferson Lab energy recovery linac electron beam using optical transition and diffraction radiation
High brightness electron accelerators, such as energy recovery linacs (ERL),
often have complex particle distributions that can create difficulties in beam
transport as well as matching to devices such as wigglers used to generate
radiation from the beam. Optical transition radiation (OTR), OTR interferometry
(OTRI) and optical diffraction-transition radiation interferometry (ODTRI) have
proven to be effective tools for diagnosing both the spatial and angular
distributions of charged particle beams. OTRI and ODTRI have been used to
measure rms divergences and optical transverse phase space mapping has been
demonstrated using OTRI. In this work we present the results of diagnostic
experiments using OTR and ODR conducted at the Jefferson Laboratory 115 MeV ERL
which show the presence of two separate components within the spatial and
angular distributions of the beam. By assuming a correlation between the
spatial and angular features we estimate an rms emittance value for each of the
two components.Comment: 25 pages, 10 figures; accepted for publication in PRSTAB; minor
formatting errors correcte
In-Situ Growth and Characterization of Highly Textured La0.9Sr0.1MnO3 Films on LaAlO3(100) Substrates
Union effectiveness: In Search of the Holy Grail
YesThis article revisits the concept of union effectiveness and proposes a conceptual model to inform its study and application. Previous conceptual and empirical work is examined to identify key strengths and weaknesses, and to relate the union effectiveness concept to union renewal and other key concepts. This leads to the proposal of a Goal-System framework that builds and improves on prior research
Determination of pharmaceuticals in surface waters by an electro-activated glassy-carbon electrode
Vector electromagnetic theory of transition and diffraction radiation with application to the measurement of longitudinal bunch size
We have developed a novel method based on vector electromagnetic theory and
Schellkunoff's principles to calculate the spectral and angular distributions
of transtion radiation (TR) and diffraction radiation (DR) produced by a
charged particle interacting with an arbitrary target. The vector method
predicts the polarization and spectral angular distributions of the radiation
at an arbitrary distance form the source, i.e. in both the near and far fields,
and in any direction of observation. The radiation fields of TR and DR
calculated with the commonly used scalar Huygens model are shown to be limiting
forms of those predicted by the vector theory and the regime of validity of the
scalar theory is explicitly shown. Calculations of TR and DR done using the
vector model are compared to results available in the literature for various
limiting cases and for cases of more general interest. Our theory has important
applications in the design of TR and DR diagnostics particularly those that
utilize coherent TR or DR to infer the longitudinal bunch size and shape. A new
technique to determine the bunch length using the angular distribution of
coherent TR or DR is proposed.Comment: 47 pages, 16 figures, accepted for publication in Phys. Rev. ST.
Accel. and Beam
Contested resources: unions, employers, and the adoption of new work practices in US and UK telecommunications
The pattern of adoption of high-performance work practices has been explained in terms of strategic contingency and in terms of union presence. We compare the post-deregulation/privatization changes in work practice at AT&T, Bell Atlantic and British Telecom. On the basis of these cases, we argue that the choice of new work practices should be understood as a consequence not only of the company's resources or changes in its environment, nor of a simple union presence, but also as a consequence of the practices' effects on union power, the nature of the union's engagement, and the union's strategic choices
Beam Halo Imaging with a Digital Optical Mask
Beam halo is an important factor in any high intensity accelerator. It can
cause difficulties in the control of the beam, emittance growth, particle loss
and even damage to the accelerator. It is therefore essential to understand the
mechanisms of halo formation and its dynamics in order to control and minimize
its effects. Experimental measurement of the halo distribution is an important
tool for such studies. In this paper, we present a new adaptive masking method
that we have developed to image beam halo, which uses a digital
micro-mirror-array device (DMD). This method has been thoroughly investigated
in the laboratory using laser and white light sources, and with real beams
produced by the University of Maryland Electron Ring (UMER). A high dynamic
range ~10(5) has been demonstrated with this new method and recent studies
indicate that this number can be exceeded for more intense beams by at least an
order of magnitude. The method is flexible, easy to setup and can be used at
any accelerator or light source. We present the results of our measurements of
the performance of the method and images of beam halos produced under various
experimental conditions.Comment: 44 pgs.; submitted to Phys. Rev. ST Accel. and Beams, 3/9/201
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