The chaotic solar cycle II. Analysis of cosmogenic 10Be data

Context. The variations of solar activity over long time intervals using a solar activity reconstruction based on the cosmogenic radionuclide 10Be measured in polar ice cores are studied. Methods. By applying methods of nonlinear dynamics, the solar activity cycle is studied using solar activity proxies that have been reaching into the past for over 9300 years. The complexity of the system is expressed by several parameters of nonlinear dynamics, such as embedding dimension or false nearest neighbors, and the method of delay coordinates is applied to the time series. We also fit a damped random walk model, which accurately describes the variability of quasars, to the solar 10Be data and investigate the corresponding power spectral distribution. The periods in the data series were searched by the Fourier and wavelet analyses. The solar activity on the long-term scale is found to be on the edge of chaotic behavior. This can explain the observed intermittent period of longer lasting solar activity minima. Filtering the data by eliminating variations below a certain period (the periods of 380 yr and 57 yr were used) yields a far more regular behavior of solar activity. A comparison between the results for the 10Be data with the 14C data shows many similarities. Both cosmogenic isotopes are strongly correlated mutually and with solar activity. Finally, we find that a series of damped random walk models provides a good fit to the 10Be data with a fixed characteristic time scale of 1000 years, which is roughly consistent with the quasi-periods found by the Fourier and wavelet analyses.Comment: 8 pages, 11 figure

Kampala Trauma Score (KTS): Is it a new triage tool?

In North America, injury surveillance has generated an accumulation of data regarding trauma events and outcomes through the implementation of trauma registries. Trauma registries have been predominantly instituted in response to the desire to be accredited by the American College of Surgeons (ACS). Committee on Trauma as an ACS Trauma Center1. These registries play a key role in research that determines epidemiological patterns of injury, advances injury prevention actions and finally, measures outcomes2. For example, they have been used extensively in the US to monitor reductions in mortality which has been attributed to the institution of “trauma systems”, coordinated hospital-based systems for the management of injured patients3. As interventions to reduce and prevent injuries are sought, registries allow the calculation of injury rates, identification of causes and measurement of outcomes produced by implementation of interventions4. Trauma registry data is made universally comparable across different strata through the routine use of trauma scores, such as the revised trauma score (RTS) and injury severity score (ISS)

Electro-optic time profile monitors for femtosecond electron bunches at the soft x-ray free-electron laser FLASH

Precise measurements of the temporal profile of ultrashort electron bunches are of high interest for the optimization and operation of ultraviolet and x-ray free-electron lasers. The electro-optic (EO) technique has been applied for a single-shot direct visualization of the time profile of individual electron bunches at FLASH. This paper presents a thorough description of the experimental setup and the results. An absolute calibration of the EO technique has been performed utilizing simultaneous measurements with a transverse-deflecting radio-frequency structure that transforms the longitudinal bunch charge distribution into a transverse streak. EO signals as short as 60 fs (rms) have been observed using a gallium-phosphide (GaP) crystal, which is a new record in the EO detection of single electron bunches and close to the physical limit imposed by the EO material properties. The data are in quantitative agreement with a numerical simulation of the EO detection process

Strong-field vacuum polarisation with high energy lasers

When photons propagate in vacuum they may fluctuate into matter pairs thus allowing the vacuum to be polarised. This \emph{linear} effect leads to charge screening and renormalisation. When exposed to an intense background field a \emph{nonlinear} effect can arise when the vacuum is polarised by higher powers of the background. This nonlinearity breaks the superposition principle of classical electrodynamics, allowing for light-by-light scattering of probe and background photons mediated through virtual pairs dressed by the background. Vacuum polarisation is a \emph{strong-field} effect when all orders of interaction between the virtual pair and the background must be taken into account. In this investigation we show that multiple scattering processes of this type may be observed by utilising high-energy laser pulses with long pulse duration, such as are available at facilities like ELI Beamlines. In combination with appropriate sources of high-energy probe photons, multiple probe-background light-by-light scattering allows for testing the genuine nonlinear regime of strong-field QED. This provides access to the uncharted nonperturbative regime beyond the weak-field limit.Comment: 42 pages, 8 figure

Single shot longitudinal bunch profile measurements by temporally resolved electro-optical detection

For the high gain operation of a SASE FEL, extremely short electron bunches are essential to generate sufficiently high peak currents. At the superconducting linac of FLASH at DESY, we have installed an electro- optic measurement system to probe the time structure of the electric field of single ~100 fs electron bunches. In this technique, the field induced birefringence in an electro-optic crystal is encoded on a chirped picosecond laser pulse. The longitudinal electric field profile of the electron bunch is then obtained from the encoded optical pulse by a single shot cross correlation with a 35 fs laser pulse using a second harmonic crystal (temporal decoding). An electro-optical signal exhibiting a feature with 118 fs FWHM was observed, and this is close to the limit of resolution due to the material properties of the particular electro-optic crystal used. The measured electro-optic signals are compared to bunch shapes simultaneously measured with a transverse deflecting cavity

Benchmarking of electro-optic monitors for femtosecond electron bunches

The longitudinal profiles of ultrashort relativistic electron bunches at the soft x-ray free-electron laser FLASH have been investigated using two single-shot detection schemes: an electro-optic (EO) detector measuring the Coulomb field of the bunch and a radio-frequency structure transforming the charge distribution into a transverse streak. A comparison permits an absolute calibration of the EO technique. EO signals as short as 60 fs (rms) have been observed, which is a new record in the EO detection of single electron bunches and close to the limit given by the EO material properties

Electro-optic techniques for longitudinal electron bunch diagnostics

Electro-optic techniques are becoming increasingly important in ultrafast electron bunch longitudinal diagnostics and have been successfully implemented at various accelerator laboratories. The longitudinal bunch shape is directly obtained from a single-shot, non-intrusive measurement of the temporal electric field profile of the bunch. Further- more, the same electro-optic techniques can be used to measure the temporal profile of terahertz / far-infrared opti- cal pulses generated by a CTR screen, at a bending magnet (CSR), or by an FEL. This contribution summarizes the re- sults obtained at FELIX and FLASH