Improving temporal resolution of ultrafast electron diffraction by eliminating arrival time jitter induced by radiofrequency bunch compression cavities

The temporal resolution of sub-relativistic ultrafast electron diffraction (UED) is generally limited by radio frequency (RF) phase and amplitude jitter of the RF lenses that are used to compress the electron pulses. We theoretically show how to circumvent this limitation by using a combination of several RF compression cavities. We show that if powered by the same RF source and with a proper choice of RF field strengths, RF phases and distances between the cavities, the combined arrival time jitter due to RF phase jitter of the cavities is cancelled at the compression point. We also show that the effect of RF amplitude jitter on the temporal resolution is negligible when passing through the cavity at a RF phase optimal for (de)compression. This will allow improvement of the temporal resolution in UED experiments to well below 100 fs

Energy spread of ultracold electron bunches extracted from a laser cooled gas

Ultrashort and ultracold electron bunches created by near-threshold femtosecond photoionization of a laser-cooled gas hold great promise for single-shot ultrafast diffraction experiments. In previous publications the transverse beam quality and the bunch length have been determined. Here the longitudinal energy spread of the generated bunches is measured for the first time, using a specially developed Wien filter. The Wien filter has been calibrated by determining the average deflection of the electron bunch as a function of magnetic field. The measured relative energy spread $\frac{\sigma_{U}}{U} = 0.64 \pm 0.09\%$ agrees well with the theoretical model which states that it is governed by the width of the ionization laser and the acceleration length

Theory and particle tracking simulations of a resonant radiofrequency deflection cavity in TM110_{110} mode for ultrafast electron microscopy

We present a theoretical description of resonant radiofrequency (RF) deflecting cavities in TM$_{110}$ mode as dynamic optical elements for ultrafast electron microscopy. We first derive the optical transfer matrix of an ideal pillbox cavity and use a Courant-Snyder formalism to calculate the 6D phase space propagation of a Gaussian electron distribution through the cavity. We derive closed, analytic expressions for the increase in transverse emittance and energy spread of the electron distribution. We demonstrate that for the special case of a beam focused in the center of the cavity, the low emittance and low energy spread of a high quality beam can be maintained, which allows high-repetition rate, ultrafast electron microscopy with 100 fs temporal resolution combined with the atomic resolution of a high-end TEM. This is confirmed by charged particle tracking simulations using a realistic cavity geometry, including fringe fields at the cavity entrance and exit apertures

A 340/380 nm light emitting diode illuminator for Fura-2 AM ratiometric Ca2+ imaging of live cells with better than 5 nM precision

We report the first demonstration of a fast wavelength-switchable 340/380 nm light emitting diode (LED) illuminator for Fura-2 ratiometric Ca2+ imaging of live cells. The LEDs closely match the excitation peaks of bound and free Fura-2 and enables the precise detection of cytosolic Ca2+ concentrations, which is only limited by the Ca2+ response of Fura-2. Using this illuminator, we have shown that Fura-2 acetoxymethyl ester (AM) concentrations as low as 250 nM can be used to detect induced Ca2+ events in tsA-201 cells and while utilizing the 150 µs switching speeds available, it was possible to image spontaneous Ca2+ transients in hippocampal neurons at a rate of 24.39 Hz that were blunted or absent at typical 0.5 Hz acquisition rates. Overall, the sensitivity and acquisition speeds available using this LED illuminator significantly improves the temporal resolution that can be obtained in comparison to current systems and supports optical imaging of fast Ca2+ events using Fura-2

Narratives of Undiagnosability:Chronic Fatigue Syndrome Life-Writing and the Indeterminacy of Illness Memoirs

There is a distinct tendency within the field of psychological and psychiatric literature to cite illness memoirs as exemplary sources of insight into the subjective dimension of how illness is experienced. However, the epistemological reliability of such sources remains open to question: Do such sources indeed offer meaningful insights into the authentic experiences of patients and in doing so, provide effective coping and self-management strategies, or are they merely literary and/or popular constructs, the value and meaning of which are fundamentally indeterminate? In this contribution, I analyze three such memoirs: Floyd Skloot’s (1996) The Night-side; Rik Carlson’s (2004) We’re Not in Kansas Anymore; and Julie Rehmeyer’s (2017) Through the Shadowlands—all describing individual experiences of the symptoms of chronic fatigue syndrome (CFS). As CFS remains a puzzling and contested illness, an analysis of these narratives offers the opportunity to explore the presupposed values as well as the limitations of illness life-writing. In this article, I map the academic debate on the epistemological value of illness narratives and chart the discussion on CFS since the early 1990s. Subsequently, I propose a double reading—a “medical” reading and a “literary” reading—of the memoirs considered. Finally, I suggest that the inherent indeterminacy of CFS life-writing is an important quality that contributes to a deeper understanding of living and coping with chronic, as yet medically unexplained illnesses. Reading illness memoirs, I conclude, reveals the rhetorical and cultural dimensions, as well as the ambiguities and uncertainties of such experiences

Versterking van het diergezondheidsmanagement in de varkenshouderij: belemmeringen en oplossingsinrichtingen

This report presents barriers and possible solutions to strengthen the animal health management on pig farms