Carbon-film-based Zernike phase plates with smooth thickness gradient for phase-contrast transmission electron microscopy with reduced fringing artefacts.

Phase plates (PPs) in transmission electron microscopy (TEM) improve the contrast of weakly scattering objects under in-focus imaging conditions. A well-established PP type is the Zernike (Z)PP, which consists of a thin amorphous carbon (aC) film with a microscaled hole in the centre. The mean inner potential of the aC film is exploited to shift the phase of the scattered electrons while the unscattered electrons in the zero-order beam propagate through the hole and remain unaffected. However, the abrupt thickness increase at the hole edge induces an abrupt change of the phase-shift distribution and leads to fringing, that is, intensity oscillations around imaged objects, in TEM images. In this work, we have used focused-ion-beam milling to fabricate ZPPs with abrupt and graded thickness profiles around the centre hole. Depending on the thickness gradient and inner hole radius, graded-ZPP-TEM images of an aC/vacuum interface and bundles of carbon nanotubes (CNTs) show strongly reduced fringing. Image simulations were performed with ZPP-phase-shift distributions derived from measured thickness profiles of graded ZPPs, which show good agreement with the experimental images. Fringing artefacts, that is, intensity oscillations around imaged objects, are strongly reduced for Zernike phase plates with a graded thickness profile around the centre hole. Focused-ion-beam milling is used to fabricate graded Zernike phase plates with specific inner hole radius and thickness gradients. The phase-shift distribution is obtained from measured thickness profiles around the centre hole. Image simulations based on experimentally measured thickness/phase-shift distributions show good agreement with experimental Zernike phase-plate TEM images.

Bridging the gap between public health and primary care in prevention of cardiometabolic diseases; background of and experiences with the Prevention Consultation in The Netherlands.

BACKGROUND: There is an increasing need for programmatic prevention of cardiometabolic diseases (cardiovascular disease, type 2 diabetes and chronic kidney disease). Therefore, in the Netherlands, a prevention programme linked to primary care has been developed. This initiative was supported by the national professional organizations of GPs and occupational physicians as well as three large health foundations. OBJECTIVES: To describe and discuss the content, structure of and first experiences with this initiative. METHODS: Description of context, risk assessment tool, guideline, content of the Prevention Consultation and pilot studies. RESULTS: Preceding surveys revealed a need for proactive disease prevention, linked to primary care. An evidence-based guideline was developed using a validated eight-question screening list. According to the guideline, high-risk participants were advised to attend two consultations at the general practice, for completing the risk assessment and for tailored advice. Three pilot studies revealed that the programme was feasible and that (sufficient) participants with a condition requiring treatment were detected. We learned that with a 'passive' recruitment (with only posters and brochures), screening uptake is limited. A more active approach with a personal invitation from the GP is more effective. Both an Internet as written questionnaire should be available and reminders are necessary. The need for a consultation with the GP practice after a high-risk test result should be emphasized. The first consultation can be performed by a practice nurse. CONCLUSIONS: A national systematic screening programme for cardiometabolic diseases linked to primary care is feasible. The cost-effectiveness still has to be established.

Experimental realization of a π/2 vortex mode converter for electrons using a spherical aberration corrector.

In light optics, beams with orbital angular momentum (OAM) can be produced by employing a properly-tuned two-cylinder-lens arrangement, also called π/2 mode converter. It is not possible to convey this concept directly to the beam in an electron microscope due to the non-existence of cylinder lenses in commercial transmission electron microscopes (TEMs). A viable work-around are readily-available electron optical elements in the form of quadrupole lenses. In a proof-of-principle experiment in 2012, it has been shown that a single quadrupole in combination with a Hilbert phase-plate produces a spatially-confined, transient vortex mode. Here, an analogue to an optical π/2 mode converter is realized by repurposing a CEOS DCOR probe corrector in an aberration corrected TEM in a way that it resembles a dual cylinder lens using two quadrupoles. In order to verify the presence of OAM in the output beam, a fork dislocation grating is used as an OAM analyser. The possibility to use magnetic quadrupole fields instead of, e.g., prefabricated fork dislocation gratings to produce electron beams carrying OAM enhances the beam brightness by almost an order of magnitude and delivers switchable high-mode purity vortex beams without unwanted side-bands.

Oxygen consumption during functional electrical stimulation-assisted exercise in persons with spinal cord injury: implications for fitness and health.

A lesion in the spinal cord leads in most cases to a significant reduction in active muscle mass, whereby the paralysed muscles cannot contribute to oxygen consumption (VO2) during exercise. Consequently, persons with spinal cord injury (SCI) can only achieve high VO2 values by excessively stressing the upper body musculature, which might increase the risk of musculoskeletal overuse injury. Alternatively, the muscle mass involved may be increased by using functional electrical stimulation (FES). FES-assisted cycling, FES-cycling combined with arm cranking (FES-hybrid exercise) and FES-rowing have all been suggested as candidates for cardiovascular training in SCI. In this article, we review the levels of VO2 (peak [VO2peak] and sub-peak [VO2sub-peak]) that have been reported for SCI subjects using these FES exercise modalities. A systematic literature search in MEDLINE, EMBASE, AMED, CINAHL, SportDiscus and the authors' own files revealed 35 studies that reported on 499 observations of VO2 levels achieved during FES-exercise in SCI. The results show that VO2peak during FES-rowing (1.98 L/min, n = 17; 24.1 mL/kg/min, n = 11) and FES-hybrid exercise (1.78 L/min, n = 67; 26.5 mL/kg/min, n = 35) is considerably higher than during FES-cycling (1.05 L/min, n = 264; 14.3 mL/kg/min, n = 171). VO2sub-peak values during FES-hybrid exercise were higher than during FES-cycling. FES-exercise training can produce large increases in VO2peak; the included studies report average increases of +11% after FES-rowing training, +12% after FES-hybrid exercise training and +28% after FES-cycling training. This review shows that VO2 during FES-rowing or FES-hybrid exercise is considerably higher than during FES-cycling. These observations are confirmed by a limited number of direct comparisons; larger studies to test the differences in effectiveness of the various types of FES-exercise as cardiovascular exercise are needed. The results to date suggest that FES-rowing and FES-hybrid are more suited for high-intensity, high-volume exercise training than FES-cycling. In able-bodied people, such exercise programmes have shown to result in superior health and fitness benefits. Future research should examine whether similar high-intensity and high-volume exercise programmes also give persons with SCI superior fitness and health benefits. This kind of research is very timely given the high incidence of physical inactivity-related health conditions in the aging SCI population.

Electron-beam broadening in amorphous carbon films in low-energy scanning transmission electron microscopy.

Resolution in scanning transmission electron microscopy (STEM) is ultimately limited by the diameter of the electron beam. The electron beam diameter is not only determined by the properties of the condenser lens system but also by electron scattering in the specimen which leads to electron-beam broadening and degradation of the resolution with increasing specimen thickness. In this work we introduce a new method to measure electron-beam broadening which is based on STEM imaging with a multi-segmented STEM detector. We focus on STEM at low electron energies between 10 and 30 keV and use an amorphous carbon film with known thickness as test object. The experimental results are compared with calculated beam diameters using different analytical models and Monte-Carlo simulations. We find excellent agreement of the experimental data with the recently published model by Gauvin and Rudinsky [1] for small t/λel (thickness to elastic mean free path) values which are considered in our study.

Oxide-free aC/Zr0.65Al0.075Cu0.275/aC phase plates for transmission electron microscopy.

Thin-film phase plates (PP) have become a valuable tool for the imaging of organic objects in transmission electron microscopy (TEM). The thin film usually consists of amorphous carbon (aC), which undergoes rapid aging under intense illumination with high-energy electrons. The limited lifetime of aC film PPs calls for alternative PP materials with improved material stability. This work presents thin-film PPs fabricated from the metallic glass alloy Zr0.65Al0.075Cu0.275 (ZAC), which was identified as a promising PP material with beneficial properties, such as a large inelastic mean free path. An adverse effect of the ZAC alloy is the formation of a surface oxide layer in ambient air, which reduces the electrical conductivity and causes electrostatic charging in the electron beam. To avoid surface oxidation, the ZAC alloy is enclosed by thin aC layers. The resulting aC/ZAC/aC layer system is used to fabricate Zernike and Hilbert PPs. Phase-contrast TEM imaging is demonstrated for a sample of carbon nanotubes, which show strong contrast enhancement in PP TEM images.

A nanocrystalline Hilbert phase-plate for phase-contrast transmission electron microscopy.

Thin-film-based phase-plates are applied to enhance the contrast of weak-phase objects in transmission electron microscopy. In this work, metal-film-based phase-plates are considered to reduce contamination and electrostatic charging, which up to now limit the application of phase-plates fabricated from amorphous C-films. Their crystalline structure requires a model for the simulation of the effect of crystallinity on the phase-plate properties and the image formation process. The model established in this work is verified by experimental results obtained by the application of a textured nanocrystalline Au-film-based Hilbert phase-plate. Based on the model, it is shown that monocrystalline and textured nanocrystalline phase-plate microstructures of appropriate thickness and crystalline orientation can be a promising approach for phase-contrast transmission electron microscopy.

Object-wave reconstruction by carbon film-based Zernike- and Hilbert-phase plate microscopy: a theoretical study not restricted to weak-phase objects.

Transmission electron microscopy phase-contrast images taken by amorphous carbon film-based phase plates are affected by the scattering of electrons within the carbon film causing a modification of the image-wave function. Moreover, image artefacts are produced by non-centrosymmetric phase plate designs such as the Hilbert-phase plate. Various methods are presented to correct phase-contrast images with respect to the scattering of electrons and image artefacts induced by phase plates. The proposed techniques are not restricted to weak-phase objects and linear image formation. Phase-contrast images corrected by the presented methods correspond to those taken by an ideal centrosymmetric, matter-free phase plate and are suitable for object-wave reconstruction.

Object wave reconstruction by phase-plate transmission electron microscopy.

A method is described for the reconstruction of the amplitude and phase of the object exit wave function by phase-plate transmission electron microscopy. The proposed method can be considered as in-line holography and requires three images, taken with different phase shifts between undiffracted and diffracted electrons induced by a suitable phase-shifting device. The proposed method is applicable for arbitrary object exit wave functions and non-linear image formation. Verification of the method is performed for examples of a simulated crystalline object wave function and a wave function acquired with off-axis holography. The impact of noise on the reconstruction of the wave function is investigated.

Using consensus methods in developing clinical guidelines for exercise in managing persistent low back pain.

OBJECTIVES: To generate expert consensus evidence for the purpose of developing more complete guidelines for people with persistent low back pain than is possible using current research evidence alone. Gaps in research evidence lead to incomplete practice recommendations unless a scientific process can provide supplementary consensus evidence that is a basis for additional recommendations. DESIGN: A modified Nominal Group Technique (NGT). This followed a systematic review indicating incomplete research evidence. SETTING: UK-wide coordinated by the Chartered Society of Physiotherapy. PARTICIPANTS: Twenty-three individuals selected for their expertise as clinicians, researchers, managers and patients. METHODS: Three stages: a first-round questionnaire of clinical questions unanswered by the systematic review; an electronic conference for outstanding questions unanswered by the first questionnaire; and a second-round questionnaire for these outstanding questions. All three stages were carried out electronically. RESULTS: Of 17 clinical questions unanswered by the systematic review, consensus evidence was generated for 14 questions by the modified NGT and this led to 14 recommendations for practice. Consensus was not reached for the remaining three questions. CONCLUSIONS: The modified NGT was a practical and cost-effective way of generating consensus evidence from a UK-wide group. The consensus evidence was the basis of appropriately graded recommendations for effective care of people with persistent low back pain. Consensus methods have been little used in physiotherapy to date but are likely to be valuable in developing clinically useful, evidence-based tools for future practice.

The feasibility of functional electrical stimulation indoor rowing for high-energy training and sport.

Objectives. To explore the potential of functional electrical stimulation (FES)-assisted indoor rowing to enable spinal cord individuals to participate in indoor rowing competitions and to achieve high exercise intensities and volumes. Materials and Methods. Six spinal cord injured subjects used a newly developed four-channel, manually controlled, FES-rowing system for training and competition. Results. Four paraplegics and two quadriplegics used the newly developed FES-rowing system for long-term training. Moreover, they competed successfully with able-bodied rowers in major indoor rowing events; the 2004-2006 British and 2006 World Indoor Rowing Championships. The current best FES-rowing time for the official 2000 meter distance is 10:28. Steady state VO(2) values of 2.5 L/min (> 35 mL/kg/min) and weekly training volumes of 1150 kcal/week (4814 kJ/week) have been achieved. Conclusions. For the first time, individuals with spinal cord injury have participated, on an equal basis, in major indoor rowing events using FES. The FES-rowers attained high levels of exercise volume and intensity. These levels are higher than have been previously reported for FES exercise and are similar to those that have been associated with significant health benefits in the general population.