Emittance Growth and Energy Loss due to Coherent Synchrotron Radiation in a bunch compressor

Bunches of high charge (10 nC) are compressed in length in the CTF II bunch compressor from 1.2 mm rms to less than 0.4 mm. The short bunches start to radiate coherently, thus affecting the horizontal and longitudinal phase spaces of the beam. This paper reports the results of measurements and simulations concerning the increase of the beam emittance and the impact on the energy distribution. Beam emittances were measured for different bunch compression factors and bunch charges. For each compressor setting, the energy spectrum of the beam was recorded in order to measure the energy loss due to coherent synchrotron radiation. For bunch charges of 10 nC a maximum increase of the horizontal emittance of 50% was observed at full compression, while the mean beam energy decreased by 5% from 39 MeV to 37 MeV. Both effects are correlated with an increase of the energy spread from 2.3% to 8.5% rms. The experimental results are compared with simulations

<i>In situ</i> investigation of controlled polymorphism in mechanochemistry at elevated temperature†

Mechanochemistry routinely provides solid forms (polymorphs) that are difficult to obtain by conventional solution-based methods, making it an exciting tool for crystal engineering. However, we are far from identifying the full scope of mechanochemical strategies available to access new and potentially useful solid forms. Using the model organic cocrystal system of nicotinamide (NA) and pimelic acid (PA), we demonstrate with variable temperature ball milling that ball milling seemingly decreases the temperature needed to induce polymorph conversion. Whereas Form I of the NA:PA cocrystal transforms into Form II at 90 °C under equilibrium conditions, the same transition occurs as low as 65 °C during ball milling: a ca 25 °C reduction of the transition temperature. Our results indicate that mechanical energy provides a powerful control parameter to access new solid forms under more readily accessible conditions. We expect this ‘thermo-mechanical’ approach for driving polymorphic transformations to become an important tool for polymorph screening and manufacturing

Research on information systems failures and successes: Status update and future directions

The final publication is available at Springer via http://dx.doi.org/10.1007/s10796-014-9500-yInformation systems success and failure are among the most prominent streams in IS research. Explanations of why some IS fulfill their expectations, whereas others fail, are complex and multi-factorial. Despite the efforts to understand the underlying factors, the IS failure rate remains stubbornly high. A Panel session was held at the IFIP Working Group 8.6 conference in Bangalore in 2013 which forms the subject of this Special Issue. Its aim was to reflect on the need for new perspectives and research directions, to provide insights and further guidance for managers on factors enabling IS success and avoiding IS failure. Several key issues emerged, such as the need to study problems from multiple perspectives, to move beyond narrow considerations of the IT artifact, and to venture into underexplored organizational contexts, such as the public sector. © 2014 Springer Science+Business Media New York

Three-dimensional organization of nascent rod outer segment disk membranes

The vertebrate photoreceptor cell contains an elaborate cilium that includes a stack of phototransductive membrane disks. The disk membranes are continually renewed, but how new disks are formed remains poorly understood. Here we used electron microscope tomography to obtain 3D visualization of the nascent disks of rod photoreceptors in three mammalian species, to gain insight into the process of disk morphogenesis. We observed that nascent disks are invariably continuous with the ciliary plasma membrane, although, owing to partial enclosure, they can appear to be internal in 2D profiles. Tomographic analyses of the basal-most region of the outer segment show changes in shape of the ciliary plasma membrane indicating an invagination, which is likely a first step in disk formation. The invagination flattens to create the proximal surface of an evaginating lamella, as well as membrane protrusions that extend between adjacent lamellae, thereby initiating a disk rim. Immediately distal to this initiation site, lamellae of increasing diameter are evident, indicating growth outward from the cilium. In agreement with a previous model, our data indicate that mature disks are formed once lamellae reach full diameter, and the growth of a rim encloses the space between adjacent surfaces of two lamellae. This study provides 3D data of nascent and mature rod photoreceptor disk membranes at unprecedented z-axis depth and resolution, and provides a basis for addressing fundamental questions, ranging from protein sorting in the photoreceptor cilium to photoreceptor electrophysiology

Ectopic synaptic ribbons in dendrites of mouse retinal ON- and OFF-bipolar cells

The ectopic distribution of synaptic ribbons in dendrites of mouse retinal bipolar cells was examined by using genetic ablation of metabotropic glutamate receptor subtype 6 (mGluR6), electron microscopy, and immunocytochemistry. Ectopic ribbons were observed in dendrites of rod and ON-cone bipolar cells in the mGluR6-deficient mouse but not in those of wild-type mice. The number of rod spherules facing the ectopic ribbons in mGluR6-deficient rod bipolar dendrites increased gradually during early growth and reached a plateau level of about 20% at 12 weeks. These ectopic ribbons were immunopositive for RIBEYE, a ribbon-specific protein, but the associated vesicles were immunonegative for synaptophysin, a synaptic-vesicle-specific protein. The presence of ectopic ribbons was correlated with an increase in the roundness of the invaginating dendrites of the rod bipolar cells. We further confirmed ectopic ribbons in dendrites of OFF-cone bipolar cells in wild-type retinas. Of the four types of OFF-cone bipolar cells (T1–T4), only the T2-type, which had a greater number of synaptic ribbons at the axon terminal and a thicker axon cylinder than the other types, had ectopic ribbons. Light-adapted experiments revealed that, in wild-type mice under enhanced-light adaptation (considered similar to the mGluR6-deficient state), the roundness in the invaginating dendrites and axon terminals of rod bipolar cells increased, but no ectopic ribbons were detected. Based on these findings and known mechanisms for neurotransmitter release and protein trafficking, the possible mechanisms underlying the ectopic ribbons are discussed on the basis of intracellular transport for the replenishment of synaptic proteins