Optimization of low aspect ratio, iron dominated dipole magnets

A study of the optimization of iron dominated dipole magnets with pole face widths comparable or less than the gap size, i.e., low aspect ratio (AR), is conducted using both theoretical and computational approaches. This regime of magnet design is particularly relevant in the context of laser plasma accelerators (LPA) due to unique beam parameters and geometric constraints, namely large energy spreads and the requirement for large apertures to accommodate drive laser passage. The breakdown of commonly employed approximations and rules of thumb in typical AR1 magnet design is examined. A library of generalized, optimized pole face geometries is provided to expedite optimization of future magnets. Finally, this methodology is used to design an electromagnetic chicane which has been fabricated, validated, and is currently in use in an x-ray free electron laser driven LPA experiment at LBNL

Symbol synchronization in convolutionally coded systems

Alternate symbol inversion is sometimes applied to the output of convolutional encoders to guarantee sufficient richness of symbol transition for the receiver symbol synchronizer. A bound is given for the length of the transition-free symbol stream in such systems, and those convolutional codes are characterized in which arbitrarily long transition free runs occur

High-sensitivity plasma density retrieval in a common-path second-harmonic interferometer through simultaneous group and phase velocity measurement

Precise measurements of the plasma density in ionized gas cells and discharged capillaries are critical to the design and operation of plasma-based accelerators, active plasma lenses, and plasma-based radiation sources. In this manuscript, a spectral-domain common-path second-harmonic interferometer is upgraded with the simultaneous measurement of the group and phase velocity, allowing for high-sensitivity density characterization (from the phase velocity advance) without the need for phase tracking from zero-density (enabled by the group velocity delay). The technique is applied to 1.5-cm-long plasma structures, without density ambiguity in parameter scans with >2π phase jumps. The single-shot sensitivity in phase retrieval is demonstrated at 63 mrad, equivalent to a density-length product of 1.8·1015 cm -2 . This is an improvement of ×45 compared to group velocity analysis alone

On the inherent intractability of certain coding problems

The fact that the general decoding problem for linear codes and the general problem of finding the weights of a linear code are both NP-complete is shown. This strongly suggests, but does not rigorously imply, that no algorithm for either of these problems which runs in polynomial time exists

Two-dimensional burst identification codes and their use in burst correction

A new class of codes, called burst identification codes, is defined and studied. These codes can be used to determine the patterns of burst errors. Two-dimensional burst correcting codes can be easily constructed from burst identification codes. The resulting class of codes is simple to implement and has lower redundancy than other comparable codes. The results are pertinent to the study of radiation effects on VLSI RAM chips, which can cause two-dimensional bursts of errors

On the existence of optimum cyclic burst-correcting codes

It is shown that for each integer b >= 1 infinitely many optimum cyclic b-burst-correcting codes exist, i.e., codes whose length n, redundancy r, and burst-correcting capability b, satisfy n = 2^{r-b+1} - 1. Some optimum codes for b = 3, 4, and 5 are also studied in detail

Femtosecond Spectroscopy with Vacuum Ultraviolet Pulse Pairs

We combine different wavelengths from an intense high-order harmonics source with variable delay at the focus of a split-mirror interferometer to conduct pump-probe experiments on gas-phase molecules. We report measurements of the time resolution (<44 fs) and spatial profiles (4 {\mu}m x 12 {\mu}m) at the focus of the apparatus. We demonstrate the utility of this two-color, high-order-harmonic technique by time resolving molecular hydrogen elimination from C2H4 excited into its absorption band at 161 nm

Agreement in dry eye management between optometrists and general practitioners in primary health care in the Netherlands

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.clae.2015.03.005 © 2015. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Purpose: To investigate the agreement in dry eye care management between general practitioners (GPs) and optometrists in the Netherlands. Methods: A web-based survey was used to investigate the agreement in symptoms associated with dry eye, causes of developing dry eye, and investigative techniques used in practice, between GPs and optometrists. Additional questions surveyed knowledge of the latest research, and co-management of dry eye disease in primary healthcare. The anonymised questionnaire contained 16 forced-choice questions with Likert scales, and was sent to 1471 general medical practitioners and 870 registered optometrists. The response data was stored on an online database, and was converted directly to text format for analysis using SPSS 21 statistical analysis software. Results: 138 optometrists and 93 GPs responded to the survey (Cronbach α = 0.885, optometrists, and 0.833, GPs). Almost no agreement was found for all the questions: a statistically significant difference (Chi-square p 0.0001), and dry eye symptoms, except for ‘burning sensation of the eye’ and ‘irritation of the eye’ as agreed symptoms, and agreement that dry eye is an age-related disease. Conclusions: As the optometrist and the GP are the gatekeepers for secondary healthcare, the fundamental differences in the methods of investigation and interpretation of dry eye-related symptoms, the possible cause of developing dry eye disease, and the therapy given by GPs and optometrists in the Netherlands, may have a significant impact on consistency of patient care.The authors extend their appreciation to the University of Applied Sciences Utrecht for funding this researc