Piezoelectric and optical setup to measure an electrical field: Application to the longitudinal near-field generated by a tapered coax

We propose a new setup to measure an electrical field in one direction. This setup is made of a piezoelectric sintered lead zinconate titanate film and an optical interferometric probe. We used this setup to investigate how the shape of the extremity of a coaxial cable influences the longitudinal electrical near-field generated by it. For this application, we designed our setup to have a spatial resolution of 100 um in the direction of the electrical field. Simulations and experiments are presented

NucTools: analysis of chromatin feature occupancy profiles from high-throughput sequencing data

Background: Biomedical applications of high-throughput sequencing methods generate a vast amount of data in which numerous chromatin features are mapped along the genome. The results are frequently analysed by creating binary data sets that link the presence/absence of a given feature to specific genomic loci. However, the nucleosome occupancy or chromatin accessibility landscape is essentially continuous. It is currently a challenge in the field to cope with continuous distributions of deep sequencing chromatin readouts and to integrate the different types of discrete chromatin features to reveal linkages between them. Results: Here we introduce the NucTools suite of Perl scripts as well as MATLAB- and R-based visualization programs for a nucleosome-centred downstream analysis of deep sequencing data. NucTools accounts for the continuous distribution of nucleosome occupancy. It allows calculations of nucleosome occupancy profiles averaged over several replicates, comparisons of nucleosome occupancy landscapes between different experimental conditions, and the estimation of the changes of integral chromatin properties such as the nucleosome repeat length. Furthermore, NucTools facilitates the annotation of nucleosome occupancy with other chromatin features like binding of transcription factors or architectural proteins, and epigenetic marks like histone modifications or DNA methylation. The applications of NucTools are demonstrated for the comparison of several datasets for nucleosome occupancy in mouse embryonic stem cells (ESCs) and mouse embryonic fibroblasts (MEFs). Conclusions: The typical workflows of data processing and integrative analysis with NucTools reveal information on the interplay of nucleosome positioning with other features such as for example binding of a transcription factor CTCF, regions with stable and unstable nucleosomes, and domains of large organized chromatin K9me2 modifications (LOCKs). As potential limitations and problems we discuss how inter-replicate variability of MNase-seq experiments can be addressed

The Perfect Boundary Approximation Technique Facing the Big Challenge of High Precision Field Computation”,

Abstract Computational tools for the design of accelerating structures are in use since decades. While highly accurate methods exist for quasi two dimensional cavities, fully three dimensional modeling with high precision is still a 'big challenge'. The most widely used computer code in this area is MAFIA, basing on the Finite Integration Theory (FIT, In this paper we present two recently developed algorithms, facing this challenge within FIT: the usage of generalized non-orthogonal computational grids (NO-FIT), and the so-called Perfect Boundary Approximation (PBA) technique. Both methods represent consistent extensions of FIT, preserving all important properties as second order accuracy and stability of the transient solver. Especially the PBA technique reveals to be a highly efficient method, as it combines easy-to-use Cartesian grids with a perfect approximation of boundaries. We compare MAFIA with the PBA technique for typical accelerator components, and it turns out, that the PBA technique is more than one order of magnitude faster than the conventional method if many non Cartesian metallic boundaries appear inside the modeled structure

SPURIOUS osCILL,ATIONS IN HIGH POWER KLYSTRONS*

Spurious oscillations in high power Mystrons are found to occur in tbe gun region, in the cavities in the main body of the tube, or in the drift tunnel. The criteria that determine whether a mode will oscillate is that its beam loading be negative, and that the power it extracts from the beam exceeds its losses to external loading and wall dissipation. Using the electromagnetic and particlcin-cell modules of MAFIA, we have devised numerical techniques with which the quality factors & Q. and Q, can be evaluated and compared. Simulations involving a gun oscillation observed in the SLAC/DESY S-Band klystron will be reported. I

High power conditioning of the 202 MHZ IH tank 2 at the CERN LINAC3

High accelerating gradients are very interesting for future machines, and, in particular, for high-current heavy-ion linac projects like the "Inertial Fusion Driver". In order to explore the maximum field achievable in an Interdigital-H type structure (IH), an experiment has been carried out at CERN with the Lead Ion Linac (Linac3). After the 1997 run, the RF amplifiers were rearranged in order to allow the feeding of the IH Tank number 2 (1.54 m long, 28 gaps, frequency of 202.56 MHz) with up to 2 MW pulsed RF power. After two weeks of conditioning at pulse lengths varying between 200 ms and 1 ms with a constant pulse repetition rate of 0.8 Hz, the maximum effective accelerating gradient achieved was 10.7 MV/m. This corresponds to a local field maximum of 75 MV/m, and to fields in excess of 50 MV/m (3.5 times the Kilpatrick limit) on large portions of the drift tube surfaces. This paper reports the conditioning procedure used, the measurements of field emission current at different voltages and pulse lengths, the determination of the surface field enhancement factor as well as the calculation of the electric field distribution for the gap with the highest surface fields