Single-Slice XRF Mapping of Light Elements in Frozen-Hydrated Allium schoenoprasum via a Self-Absorption-Corrected Hyperspectral Tomographic Reconstruction Approach.

3D and 2D-cross-sectional X-ray fluorescence analysis of biological material is a powerful tool to image the distribution of elements and to understand and quantify metal homeostasis and the distribution of anthropogenic metals and nanoparticles with minimal preparation artifacts. Using tomograms recorded on cryogenically prepared leaves of Allium schoenoprasum, the cross-sectional distribution of physiologically relevant elements like calcium, potassium, manganese, and zinc could be tomographically reconstructed by peak fitting followed by a conventional maximum-likelihood algorithm with self-absorption correction to reveal the quantitative cross-sectional element distribution. If light elements such as S and P are located deep in the sample compared to the escape depth of their characteristic X-ray fluorescence lines, the quantitative reconstruction becomes inaccurate. As a consequence, noise is amplified to a magnitude where it might be misinterpreted as actual concentration. We show that a tomographic MCA hyperspectral reconstruction in combination with a self-absorption correction allows for fitting of the XRF spectra directly in real space, which significantly improves the qualitative and quantitative analysis of the light elements compared to the conventional method as noise and artifacts in the tomographic reconstruction are reduced. This reconstruction approach can substantially improve the quantitative analysis of trace elements as it allows the fitting of summed voxel spectra in anatomical regions of interest. The presented method can be applied to XRF 2D single-slice tomography data and 3D tomograms and is particularly relevant for, but not limited to, biological material in order to help retrieve self-absorption corrected quantitative reconstructions of the spatial distribution of light elements and ultra-trace-elements.

Pump-probe X-ray holographic imaging of laser-induced cavitation bubbles with femtosecond FEL pulses.

Cavitation bubbles can be seeded from a plasma following optical breakdown, by focusing an intense laser in water. The fast dynamics are associated with extreme states of gas and liquid, especially in the nascent state. This offers a unique setting to probe water and water vapor far-from equilibrium. However, current optical techniques cannot quantify these early states due to contrast and resolution limitations. X-ray holography with single X-ray free-electron laser pulses has now enabled a quasi-instantaneous high resolution structural probe with contrast proportional to the electron density of the object. In this work, we demonstrate cone-beam holographic flash imaging of laser-induced cavitation bubbles in water with nanofocused X-ray free-electron laser pulses. We quantify the spatial and temporal pressure distribution of the shockwave surrounding the expanding cavitation bubble at time delays shortly after seeding and compare the results to numerical simulations.

Ptychographic characterisation of polymer compound refractive lenses manufactured by additive technology.

The recent success in the development of high-precision printing techniques allows one to manufacture free-standing polymer structures of high quality. Two-photon polymerization lithography is a mask-less technique with down to 100 nm resolution that provides full geometric freedom. It has recently been applied to the nanofabrication of X-ray compound refractive lenses (CRLs). In this article we report on the characterization of two sets of CRLs of different design produced by two-photon polymerization-induced lithography.

Direct imaging of ultrafast lattice dynamics.

Under rapid high-temperature, high-pressure loading, lattices exhibit complex elastic-inelastic responses. The dynamics of these responses are challenging to measure experimentally because of high sample density and extremely small relevant spatial and temporal scales. Here, we use an x-ray free-electron laser providing simultaneous in situ direct imaging and x-ray diffraction to spatially resolve lattice dynamics of silicon under high-strain rate conditions. We present the first imaging of a new intermediate elastic feature modulating compression along the axis of applied stress, and we identify the structure, compression, and density behind each observed wave. The ultrafast probe x-rays enabled time-resolved characterization of the intermediate elastic feature, which is leveraged to constrain kinetic inhibition of the phase transformation between 2 and 4 ns. These results not only address long-standing questions about the response of silicon under extreme environments but also demonstrate the potential for ultrafast direct measurements to illuminate new lattice dynamics.

Ptychographic analysis of the photorefractive effect in LiNbO3:Fe.

We present light induced refractive index changes in iron doped lithium niobate detected with a novel microscopy technique called ptychography. This method determines the change of the refractive index together with the intensity distribution of the writing beam from a single scan with a reconstructed spatial resolution of 3 µm and a sensitivity of the refractive index change of 10-5. We show that the light induced refractive index change is strongly connected to the intensity shape of the writing beam and that it shows the expected nonlocal behaviour. Applying the novel method to the investigation of the photorefractive effect offers an excellent opportunity to study this nonlocal response to the spatial distribution of the writing beam.

The linac coherent light source single particle imaging road map.

Intense femtosecond x-ray pulses from free-electron laser sources allow the imaging of individual particles in a single shot. Early experiments at the Linac Coherent Light Source (LCLS) have led to rapid progress in the field and, so far, coherent diffractive images have been recorded from biological specimens, aerosols, and quantum systems with a few-tens-of-nanometers resolution. In March 2014, LCLS held a workshop to discuss the scientific and technical challenges for reaching the ultimate goal of atomic resolution with single-shot coherent diffractive imaging. This paper summarizes the workshop findings and presents the roadmap toward reaching atomic resolution, 3D imaging at free-electron laser sources.

Value of an automatic external defibrillator printout as a diagnostic tool after successful AED use on a child.

A 6-year-old girl without any medical history experienced a drowning incident for a duration of 2 min, according to witnesses. This was followed by cardiopulmonary resuscitation, during which the automatic external defibrillator (AED) detected a shockable rhythm and subsequently delivered a single electroshock. At the time of admission, her medical history was unclear, and as her chest had been wet, it was not clear if the AED had been capable of correctly analysing the rhythm. The AED printout, however, revealed ventricular fibrillation (VF), which proved to be a primary cardiac cause at the time of the incident. This case report confirms the assumption that the AED can adequately perform rhythm analysis on children and convert VF into sinus rhythm. Moreover, the AED printout can provide information about the rhythm that is necessary for the diagnosis of an underlying cardiac disease.

Compact x-ray microradiograph for in situ imaging of solidification processes: bringing in situ x-ray micro-imaging from the synchrotron to the laboratory.

A laboratory based high resolution x-ray radiograph was developed for the investigation of solidification dynamics in alloys. It is based on a low-power microfocus x-ray tube and is potentially appropriate for x-ray diagnostics in space. The x-ray microscope offers a high spatial resolution down to approximately 5 µm. Dynamic processes can be resolved with a frequency of up to 6 Hz. In reference experiments, the setup was optimized to yield a high contrast for AlCu-alloys. With samples of about 150 µm thickness, high quality image sequences of the solidification process were obtained with high resolution in time and space.

Structure and flow of droplets on solid surfaces.

The structure and flow of droplets on solid surfaces is investigated with imaging and scattering techniques and compared to simulations. To access nanostructures at the liquid-solid interface advanced scattering techniques such as grazing incidence small-angle x-ray scattering (GISAXS) with micro- and nanometer-sized beams, GISAXS and in situ imaging ellipsometry and GISAXS tomography are used. Using gold nanoparticle suspensions, structures observed in the wetting area due to deposition are probed in situ during the drying of the droplets. After drying, nanostructures in the wetting area and inside the dried droplets are monitored. In addition to drying, a macroscopic movement of droplets is caused by body forces acting on an inclined substrate. The complexity of the solid surfaces is increased from simple silicon substrates to binary polymer brushes, which undergo a switching due to the liquid in the droplet. Nanostructures introduced in the polymer brush due to the movement of droplets are observed.

Non-destructive and quantitative imaging of a nano-structured microchip by ptychographic hard X-ray scanning microscopy.

We used hard X-ray scanning microscopy with ptychographic coherent diffraction contrast to image a front-end processed passivated microchip fabricated in 80 nm technology. No sample preparation was needed to image buried interconnects and contact layers with a spatial resolution of slightly better than 40 nm. The phase shift in the sample is obtained quantitatively. With the additional knowledge of the elemental composition determined in parallel by X-ray fluorescence mapping, quantitative information about specific nanostructures is obtained. A significant enhancement in signal-to-noise ratio and spatial resolution is achieved compared to conventional hard X-ray scanning microscopy.

Colloidal silver nanoparticle gradient layer prepared by drying between two walls of different wettability.

A one-dimensional silver (Ag) nanoparticle gradient layer is prepared from an aqueous colloidal solution upon a polystyrene (PS) coated silicon (Si) substrate. For preparation two walls of different wettability are used. The 40 nm PS-layer exhibits a locally constant film thickness due to the strong roughness correlation with the underlying Si-substrate and is less wettable as compared to the glass plate placed above. The Ag nanoparticles have a triangular prism-like shape. The structural characterization of the obtained complex gradient formed by drying is performed with microbeam grazing incidence small-angle x-ray scattering based on compound refractive lenses. Due to the adsorption from aqueous solution in the selective geometry a double gradient type structure defined by two areas with characteristic lateral lengths and a cross-over regime between both is observed.

The fractional Talbot effect in differential x-ray phase-contrast imaging for extended and polychromatic x-ray sources.

The influence of different physical parameters, such as the source size and the energy spectrum, on the functional capability of a grating interferometer applied for phase-contrast imaging is discussed using numerical simulations based on Fresnel diffraction theory. The presented simulation results explain why the interferometer could be well combined with polychromatic laboratory x-ray sources in recent experiments. Furthermore, it is shown that the distance between the two gratings of the interferometer is not in general limited by the width of the photon energy spectrum. This implies that interferometers that give a further improved image quality for phase measurements can be designed, because the primary measurement signal for phase measurements can be increased by enlargement of this distance. Finally, the mathematical background and practical instructions for the quantitative evaluation of measurement data acquired with a polychromatic x-ray source are given.

Coherent x-ray diffraction imaging with nanofocused illumination.

Coherent x-ray diffraction imaging is an x-ray microscopy technique with the potential of reaching spatial resolutions well beyond the diffraction limits of x-ray microscopes based on optics. However, the available coherent dose at modern x-ray sources is limited, setting practical bounds on the spatial resolution of the technique. By focusing the available coherent flux onto the sample, the spatial resolution can be improved for radiation-hard specimens. A small gold particle (size <100 nm) was illuminated with a hard x-ray nanobeam (E=15.25 keV, beam dimensions approximately 100 x 100 nm2) and is reconstructed from its coherent diffraction pattern. A resolution of about 5 nm is achieved in 600 s exposure time.

Successful percutaneous balloon valvuloplasty in a preterm infant weighing 1500 g with critical pulmonary valve stenosis.

We describe a successful cardiac intervention in an infant, born at 32 weeks of gestation, with a birth weight of 1040 g, who had a critical pulmonary valve stenosis with the right ventricular pressure twice the systemic pressure. Continuous prostaglandin E infusion kept the arterial duct open and at the age of four weeks and a weight of 1500 g a balloon valvuloplasty was performed, which reduced the systolic right ventricular pressure to below the systemic pressure. Two weeks later the procedure was repeated because of increasing right ventricular pressure. At two months of age the mean systolic transpulmonary Doppler gradient was 30 mmHg with an adequate right ventricular volume. The neurological status of the infant was normal and the femoral vein was patent. Timely interventional heart catheterisation is a successful method of treatment in critical pulmonary valve stenosis in infants with a low birth weight. (Neth Heart J 2008;16:264-6.).

Compact x-ray microtomography system for element mapping and absorption imaging.

We have designed and built a compact x-ray microtomography system to perform element mapping and absorption imaging by exploiting scanning fluorescence tomography and full-field transmission microtomography, respectively. It is based on a low power microfocus tube and is potentially appropriate for x-ray diagnostics in space. Full-field transmission tomography yields the three-dimensional inner structure of an object. Fluorescence microtomography provides the element distribution on a virtual section through the sample. Both techniques can be combined for appropriate samples. Microradiography as well as fluorescence mapping are also possible. For fluorescence microtomography a small and intensive microbeam is required. It is generated using a polycapillary optic. Operating the microfocus tube with a molybdenum target at 12 W, a microbeam with a full width at half maximum lateral extension of 16 microm and a flux of about 10(8) photonss is generated. As an example of application, this beam is used to determine the element distribution inside dried plant samples. For full-field scanning tomography, the x-ray optic is removed and the sample is imaged in magnifying projection onto a two-dimensional position sensitive detector. Depending on the sample size, a spatial resolution down to about 10 microm is possible in this mode. The method is demonstrated by three-dimensional imaging of a rat humerus.

Organizational characteristics as predictors of work disability: a prospective study among sick employees of for-profit and not-for-profit organizations.

INTRODUCTION: This article reports a prospective study that focused on the influence of organizational structure and organizational culture on the outcome of sickness absence, return to work or work disability. Former studies of determinants of work disability hardly have given attention to organizational characteristics and, if so, not following a appropriate prospective design. METHODS: The study population consisted of 455 employees of 45 for-profit and not-for-profit companies participating in the Maastricht Cohort Study on fatigue at work who were on sick leave for at least 6 weeks. Both independent variables which were type of company, size, centralization of decision making and organizational culture, and covariates, which were sex, age, educational level, fatigue, and chronic illness, were all measured before employees reported sick. The dependent variable outcome of the sickness absence, mainly return to work or work disability, was measured 15 months after reporting sick. RESULTS: Multilevel logistic regression analysis, with organizational characteristics as level 2 independent variables and demographic and health characteristics as covariates, suggested that the type of company (for-profit/private or not-for-profit/public) is predictive of the outcome of sickness absence (crude OR = 2.21; CI: 1.16-4.20), but this may be partially due to a higher proportion of fatigued and chronically ill employees in not-for-profit companies (adjusted OR = 2.09; CI: 0.93-4.37). Findings about the role of some other organizational characteristics, like organizational culture, were inconclusive. CONCLUSIONS: Organizational characteristics should next to health characteristics be included in the models of studies which aim at predicting which sick employees are at risk for work disability. To prevent work disability not-for-profit companies might be stimulated to more active return-to-work policy by charging them with the costs of it.

Focusing hard x rays to nanometer dimensions by adiabatically focusing lenses.

We address the question of what is the smallest spot size that hard x rays can be focused to using refractive optics. A thick refractive x-ray lens is considered, whose aperture is gradually (adiabatically) adapted to the size of the beam as it converges to the focus. These adiabatically focusing lenses are shown to have a relatively large numerical aperture, focusing hard x rays down to a lateral size of 2 nm (FWHM), well below the theoretical limit for focusing with waveguides [C. Bergemann, Phys. Rev. Lett.912003204801].

Fatigue as a predictor of sickness absence: results from the Maastricht cohort study on fatigue at work.

OBJECTIVES: To investigate whether there is a relationship between fatigue and sickness absence. Two additional hypotheses were based on the theoretical distinction between involuntary, health related absence and voluntary, attitudinal absence. In the literature, the former term is usually used to describe long term sickness absence, the latter relates to short term sickness absence. In line with this, the first additional hypothesis was that higher fatigue would correspond with a higher risk of long term, primarily health related absence. The second additional hypothesis was that higher fatigue would correspond with a higher risk of short term, primarily motivational absence. METHODS: A multidimensional fatigue measure, as well as potential sociodemographic and work related confounders were assessed in the baseline questionnaire of the Maastricht cohort study on fatigue at work. Sickness absence was objectively assessed on the basis of organisational absence records and measured over the six months immediately following the baseline questionnaire. In the first, general hypothesis the effect of fatigue on time-to-onset of first sickness absence spell during follow up was investigated. For this purpose, a survival analysis was performed. The effect of fatigue on long term sickness absence was tested by a logistic regression analysis. The effect of fatigue on short term sickness absence was investigated by performing a survival analysis with time-to-onset of first short absence spell as an outcome. RESULTS: It was found that higher fatigue decreased the time-to-onset of the first sickness absence spell. Additional analyses showed that fatigue was related to long term as well as to short term sickness absence. The effect of fatigue on the first mentioned outcome was stronger than the effect on the latter outcome. Potential confounders only weakened the effect of fatigue on long term absence. CONCLUSIONS: Fatigue was associated with short term but particularly with long term sickness absence. The relation between fatigue and future sickness absence holds when controlling for work related and sociodemographic confounders. Fatigue as measured with the Checklist Individual Strength can be used as a screening instrument to assess the likelihood of sickness absence in the short term.

The Demand-Control-Support model as a predictor of return to work.

The present study investigated work-related determinants of return to work. Our hypothesis was based on the strain hypothesis of the Demand-Control-Support model, which postulates a relation between job demands, job control and support at work on the one hand, and the aetiology of health complaints on the other hand. High demands were hypothesized to obstruct return to work, whereas high control and high support were thought to have a positive effect on return to work. This hypothesis was tested in a population of employees who were sick-listed for 6-8 weeks. Return to work, as operationalized by the categories (i) not working; (ii) return to work with adjustments; and (iii) full return to work, was determined 4 months after the onset of the sick leave. The hypothesis was tested by logistic regression analyses. High job demands were the least predictive of full return to work. However, the likelihood of employees with high job demands returning to work with adjustments was higher than the likelihood of them not working. Therefore, job demands might also work as a pressure to return to work (compare this with Smulders and Nijhuis, 1999). Furthermore, high skill discretion in combination with high job demands predicted working with adjustments in comparison with not working. Finally, high supervisor support was the most predictive of return to work without adjustments, and the least predictive of not working.

Fatigue as a predictor of work disability.

The objective of this study was to assess the predictive value of fatigue for work disability on medical grounds within the framework of a large prospective cohort study. Analyses were carried out on the data of 10 927 employees with a follow up of 32 months. We found that fatigue, as measured with the Checklist Individual Strength, was a strong predictor of subsequent permanent work disability. The for age, gender, presence of a chronic medical condition, and educational level adjusted relative risks were, for the 2nd, 3rd, and 4th fatigue score quartile against the first, respectively: 2.17 (1.17-4.03), 3.30 (1.67-6.52), and 12.8 (5.14-32.1).