Disentangling surface atomic motions from surface field effects in ultrafast low-energy electron diffraction

Ultrafast low-energy electron diffraction holds potential to provide atomic level details to the surface dynamics controlling processes from surface chemistry to exotic collective effects. Accessing the primary timescales requires subpicosecond excitation pulses to prepare the corresponding nonequilibrium state. The needed excitation for maximum contrast above background invariably leads to photoinduced electron emission with the creation of surface fields that affect diffraction and must be quantified to recover the key structural dynamics. Using 2 keV ultrashort low-energy electron bunches, we investigate this field effect on the ensuing electron distribution in projection imaging and diffraction as a function of excitation intensity. Using a structural model, we demonstrate a quantitative separation of the surface field effect on electron diffraction, enabling isolation of the structural dynamics of interest. Particle trajectory simulations provide insight into the correlation between geometrical characteristics of the charge separated region and the corresponding intensity modulation at the detector

The Agricultural Economy of South Africa

Broadly speaking, this paper consists of three main parts. Firstly, a historical perspective; secondly, an analysis of the present situation and thirdly, a consideration of the future

Impact of echo contrast agents on ventricular assist devices (vad) hemodynamics: Are they safe to use?

Background: Ventricular assist devices (VADs) areapproved therapy in advanced heart failure population as a bridge to transplant or destination therapy. Echocardiography plays a crucial role in evaluation of VAD function. Echo contrast (EC) agentsare commonly used adjuncts for better visualization of cardiac chambers. The safety of EC use and their affect on VAD hemodynamics has not been well studied to our knowledge. Methods: Retrospective review of 130 patients with VAD who were hospitalized at our institution between 2010-2015. Changes in vital signs, speed, power, pulsatility index (PI) and flow were recorded within 24 hours and also 24-48 hours after EC use. Baseline characteristics, alarms, death, new arrhythmias or worsening heart failure were also recorded. Results: Our sample patients had 99 Heart Mate II, 26 Heart Ware and 5 Heart Mate III. Median age was 57 + 12.6 and median amount of contrast used was 1.5 + 0.7. There was no statistically significant changes in hemodynamics or VAD interrogation within 24 hours of contrast use. 24-48 hours post contrast was only statistically significant for changes in VAD speed. Results aredescribed in table 1. No significant new arrhythmias or worsening heart failure noted Conclusions: EC use has no adverse hemodynamic influence on VADhemodynamics. The mean change in VAD speed was likely related to changes in patient medical condition that is not related to worsening heart failure or new arrhythmias. EC use should follow standard echoindications in VAD patients (Table Presented)

Optical fiber-based photocathode

We present the design of a back-illuminated photocathode for electron diffraction experiments based on an optical fiber, and experimental characterization of emitted electron bunches. Excitation light is guided through the fiber into the experimental vacuum chamber, eliminating typical alignment difficulties between the emitter metal and the optical trigger and position instabilities, as well as providing reliable control of the laser spot size and profile. The in-vacuum fiber end is polished and coated with a 30 nm gold (Au) layer on top of 3 nm of chromium (Cr), which emits electrons by means of single-photon photoemission when femtosecond pulses in the near ultraviolet (257 nm) are fed into the fiber on the air side. The emission area can be adjusted to any value between a few nanometers (using tapered fibers) and the size of a multi-mode fiber core (100 μm or larger). In this proof-of-principle experiment, two different types of fibers were tested, with emission spot diameters of 50 μm and 100 μm, respectively. The normalized thermal electron beam emittance (TE) was measured by means of the aperture scan technique, and a TE of 4.0 π nm was measured for the smaller spot diameter. Straightforward enhancements to the concept allowed to demonstrate operation in an electric field environment of up to 7 MV/m

The Potential Role of Renal Denervation in the Management of Heart Failure

Sympathetic nervous system activation in patients with heart failure is one of the main pathophysiologic mechanisms associated with the worse outcomes. Pharmacotherapies targeting neurohormonal activation have been at the center of heart failure management. Despite the advancement of therapies and the available treatments, heart failure continues to have an overall poor prognosis. Renal denervation was originally developed to lower systemic blood pressure in patients with poorly controlled hypertension, by modulating sympathetic outflow. However, more recently, multiple studies have investigated the effect of renal denervation in heart failure patients with both preserved (HFpEF) and reduced ejection fractions (HFrEF). This paper provides an overview of the potential effect of renal denervation in altering the various pathophysiologic, sympathetically mediated pathways that contribute to heart failure, and reviews the literature that supports its future use in those patients

Fiber tip-based electron source

The authors report on the first experimental characterization of a fiber tip-based electron source, where electron emission can be triggered by both electric field and optical excitation. Our approach consists of coating the open aperture of a commercial 100 nm apex size near-field scanning optical microscopy fiber tip with a 10 nm thick tungsten (W) layer, which is back-illuminated by a 405 nm continuous-wave laser beam in the presence of an extraction electric field. Despite the very low optical transmission of the fiber due to the subwavelength aperture size, measurements show a clearly enhanced emission when photoexciting the W layer with respect to pure field emission. The emission response time is slower than the optical trigger time, suggesting that thermal effects are predominant in the studied regime. To back up this hypothesis, the authors fabricated a nanometric thermocouple probe based on a Pt/Au junction and measured the temporal response of the tip temperature. The measured switch-on time for the tip temperature is consistent with the switch-on time of the optically enhanced electron emission

A novel fiber tip based electron source

In this paper we report on the first experimental characterization of a fiber tip-based electron source where the electron emission is triggered by both, electric field and optical excitation. Our approach consists of coating a commercial 100 nm apex size NSOM multi-mode fiber tip with a 10 nm thick tungsten layer, which is back-illuminated in the presence of an extraction electric field. The measurements show a clear enhancement of the emission by the incident light, but the emission response time is slower than the optical trigger time, suggesting that thermal effects are predominant. This hypothesis is backed up by the temporal response measurements of the tip temperature