Conical shell illumination incorporating a moving aperture for depth-resolved high-energy X-ray diffraction.

In many applications, the main limitation of X-ray absorption methods is that the signals measured are a function of the attenuation coefficient, which tells us almost nothing about the chemical or crystallographic nature of objects under inspection. To calculate fundamental crystallographic parameters requires the measurement of diffracted photons from a sample. Standard laboratory diffraction methods have been refined for well over a century and provide 'gold standard' structural models for well-prepared samples and single crystals but have little applicability for thick heterogeneous samples as demanded by many screening applications. We present a new high-energy X-ray diffraction probe, which in comparison with previous depth-resolving hollow beam techniques, requires a single beam, point detector and a simple swept aperture to resolve sample signatures at unknown locations within an inspection space. We perform Monte Carlo simulations to support experiments on both single- and multiple-material localisation and identification. The new probe is configured and tested using low-cost commercial components to provide a rapid and cost-effective solution for applications including explosives detection, process control and diagnostics.

Dual conical shell illumination for volumetric high-energy X-ray diffraction imaging.

To retrieve crystallographic information from extended sample volumes requires a high-energy probe. The use of X-rays to combine imaging with materials characterisation is well-established. However, if fundamental crystallographic parameters are required, then the collection and analysis of X-rays diffracted by the inspected samples are prerequisites. We present a new X-ray diffraction imaging architecture, which in comparison with previous depth-resolving hollow beam techniques requires significantly less X-ray power or alternatively supports significantly increased scanning speeds. Our conceptual configuration employs a pair of conical shell X-ray beams derived from a single point source to illuminate extended samples. Diffracted flux measurements would then be obtained using a pair of energy resolving point detectors. This dual beam configuration is tested using a single X-ray beam set-up employing a dual scan. The use of commercial off-the-shelf low-cost components has the potential to provide rapid and cost-effective performance in areas including industrial process control, medical imaging and explosives detection.

Formation of Au and tetrapyridyl porphyrin complexes in superfluid helium.

Binary clusters containing a large organic molecule and metal atoms have been formed by the co-addition of 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) molecules and gold atoms to superfluid helium nanodroplets, and the resulting complexes were then investigated by electron impact mass spectrometry. In addition to the parent ion H2TPyP yields fragments mainly from pyrrole, pyridine and methylpyridine ions because of the stability of their ring structures. When Au is co-added to the droplets the mass spectra are dominated by H2TPyP fragment ions with one or more Au atoms attached. We also show that by switching the order in which Au and H2TPyP are added to the helium droplets, different types of H2TPyP-Au complexes are clearly evident from the mass spectra. This study suggests a new route for the control over the growth of metal-organic compounds inside superfluid helium nanodroplets.

Preparation of ultrathin nanowires using superfluid helium droplets.

Direct preparation of long one-dimensional (1D) nanostructures with diameters <10 nm inside superfluid helium droplets is reported. Unlike conventional chemical synthetic techniques, where stabilizers, templates, or external fields are often required to induce 1D growth, here, we exploit the use of quantized vortices to guide the formation of ultrathin nanowires. A variety of elements have been added to the droplets to demonstrate that this is a general phenomenon, including Ni, Cr, Au, and Si. Control of the length and diameter of the nanowires is also demonstrated.

Vortex-induced aggregation in superfluid helium droplets.

The formation of Ag nanoparticles by the addition of Ag atoms to helium droplets has been investigated. The resulting nanoparticles were then imaged by transmission electron microscopy after being deposited on a thin solid surface. In large helium droplets chains of Ag nanorods were observed similar to recently reported track-like deposits [Gomez et al., Phys. Rev. Lett., 2012, 108, 155302]. However, by adjusting the experimental conditions chains of spherical nanoparticles could also be seen with a nearly uniform inter-particle spacing. Given that spherical Ag nanoparticles have no intrinsic anisotropy, the only viable explanation is that these particles must be guided into position by interaction with a quantized vortex spanning the diameter of the helium droplet. Furthermore, addition of Si to the droplets immediately after Ag resulted in Si inserting between the Ag nanoparticles to form continuous nanowires. This eliminates the possibility that the segmented Ag nanostructures are the result of nanowire fragmentation when the helium droplets collide with the deposition substrate. Thus segmented Ag chains are shown to be an intrinsic feature of Ag aggregation in helium droplets in the presence of a quantized vortex.

Precision engineering of nano-assemblies in superfluid helium by the use of van der Waals forces.

The ability to precisely engineer nanostructures underpins a wide range of applications in areas such as electronics, optics, and biomedical sciences. Here we present a novel approach for the growth of nanoparticle assemblies that leverages the unique properties of superfluid helium. Unlike viscous solvents at or near room temperature, superfluid helium provides an unperturbed and cold environment in which weak van der Waals interactions between molecular templates and metal atoms become significant and can define the spatial arrangement of nanoparticles. To demonstrate this concept, diol and porphyrin-based molecules are employed as templates to grow gold nanoparticle assemblies in superfluid helium droplets. After soft-landing on a solid surface to remove the helium, transmission electron microscopy (TEM) imaging shows the growth of gold nanoparticles at specific binding sites within the molecular templates where the interaction between gold atoms and the molecular template is at its strongest.

Electronic spectroscopy of toluene in helium nanodroplets: evidence for a long-lived excited state.

Optical excitation of toluene to the S1 electronic state in helium nanodroplets is found to alter the rate of production of the fragment ions C7H7(+) and C5H5(+) when the droplets are subjected to subsequent electron ionization. The optical excitation process reduces the abundance of C7H7(+) ions delivered into the gas phase, whereas C5H5(+) ions become more abundant beyond a minimum droplet size. This process contrasts with normal optical depletion spectroscopy, where the optical absorption of a molecular dopant in a helium nanodroplet shrinks the helium droplet, and thus, the electron impact cross-sections because of dissipation of the absorbed energy by evaporative loss of helium atoms. The observations here are interpreted in terms of formation of an excited state in the neutral molecule, which survives for several hundred µs. This long-lived excited state, which is assumed to be the lowest triplet electronic state, shows different cross-sections for production of C7H7(+) and C5H5(+) relative to the S0 state.

Exploring the origin of pain subclassification, with emphasis on low back pain: a scoping review.

OBJECTIVE: This scoping review aimed to explore the different working definitions for the duration of acute, subacute, and chronic pain, with emphasis on low back pain, and to establish where these definitions originated and the rationale provided for the time frames used. INTRODUCTION: From a global perspective, low back pain is a major social and economic problem. One of the most commonly used methods to stratify and manage low back pain is the traditional duration-based classification (acute, subacute, and chronic). Where these time points lie to differentiate these transitions continues to be debated within the scientific community, which may engender a degree of heterogeneity in study findings. Therefore, applying these findings to clinical practice may be somewhat challenging. This review encapsulates the historical origins of the different duration categories to provide an understanding of how these variations were derived. INCLUSION CRITERIA: Studies that included participants with low back pain were the focus of this review. Sources that included children or other specific pain pathologies, such as cancer pain, were excluded. The main concept of interest was that the publication proposed an original definition of the duration of acute, subacute, or chronic low back pain. All study designs were included provided they gave a rationale for the duration that they used. METHODS: The following databases were searched: MEDLINE, Embase, CINAHL, and PsycINFO, from the inception of each database until September 18, 2019. This review was limited to studies published in English. Two independent reviewers screened the retrieved articles against the eligibility criteria. Additional studies were searched from the reference lists of studies to find the original source. Some original sources overlapped with general pain duration literature. This led to a deviation from the scoping review protocol, which originally intended to focus on definitions of low back pain duration only. Data extraction was undertaken using a charting table developed specifically for the review objectives. The findings were presented using narrative synthesis. RESULTS: Nineteen records were included in this review, and comprised three book chapters, four review articles, four articles that arose following pain expert group discussions, seven primary research studies, and a spinal guideline. Data were extracted from the included studies and categorized into four themes based on the origin of the classification of the duration. The themes included i) work/employment setting, ii) empirical studies, iii) expert reasoning, and iv) pathophysiological explanation. CONCLUSIONS: This scoping review compiled the existing literature on the working definitions of the duration of acute, subacute, and chronic low back pain and found a wide variation. These ranged from seven days, 14 days, and seven weeks for the acute and subacute transition points, and seven weeks to three years for chronic low back pain. The duration definitions specifically referring to the general pain literature focused on three and/or six months for the transition to chronic. Better integration of reasoning between the identified themes could facilitate the establishment of more ideal duration definitions in the future. Although inconclusive, the definition most commonly cited, with most consensus, was three months for the transition to chronic low back pain.

Feasibility of a cognitive strategy training intervention for people with Parkinson's disease.

PURPOSE: To investigate the feasibility of a novel client-centered cognitive strategy training intervention for people with Parkinson's disease (PD). MATERIALS AND METHODS: This was a case series of seven people with PD without dementia but with subjective cognitive decline. The intervention involved ≥5 treatment sessions at the participant's home. Participant acceptance and engagement were assessed by the Credibility/Expectancy Questionnaire (CEQ), Client Satisfaction Questionnaire (CSQ), enjoyment and effort ratings, and homework completion. Logistical information was tracked, and the Canadian Occupational Performance Measure (COPM) was an exploratory outcome measure. Data analysis was descriptive. RESULTS: CEQ scores were positive and increased over time. CSQ scores were high (M = 30.8, SD = 0.75), with all participants rating all items positively. Almost all (95%) effort and enjoyment ratings were ≥3 (Much), and homework completion rates averaged 84% (SD = 18). Intervention duration was 6-15 weeks (M = 9.2, SD = 2.8), with treatment sessions averaging 1.7 h (SD = 0.5). Group and most individual COPM ratings improved ≥2 points. CONCLUSIONS: These findings support the feasibility of the intervention for people with PD. It was acceptable, engaging, and promising in terms of its effect on self-identified functional cognitive problems. Implications for Rehabilitation People with Parkinson's disease (PD) without dementia can experience cognitive decline that negatively impacts function and quality of life. Strategy-based interventions that explicitly train for transfer may mitigate the negative functional consequences of cognitive decline in this population. We developed a client-centered cognitive strategy training intervention for people with PD. This small case series supports its feasibility, indicating that it is acceptable and engaging for people with PD and promising in terms of its effect on self-identified functional cognitive problems.

Robust Ferromagnetism of Chromium Nanoparticles Formed in Superfluid Helium.

Chromium nanoparticles are formed using superfluid helium droplets as the nanoreactors, which are strongly ferromagnetic. The transition from antiferromagentism to ferromagnetism is attributed to atomic-scale disorder in chromium nanoparticles, leading to abundant unbalanced surface spins. Theoretical modeling confirms a frustrated aggregation process in superfluid helium due to the antiferromagnetic nature of chromium.

Helium droplets: a new route to nanoparticles.

Helium droplets are large helium clusters that are capable of picking up individual atoms and molecules and show promise as nano-reactors for the synthesis of unique nanoparticles. In particular, the sequential addition of materials of different types offers opportunities for the fabrication of novel core-shell nanoparticles that cannot be synthesised by other methods. To exploit this potential, here we have carried out a mass spectrometry investigation on metal clusters in order to establish how to control the doping conditions for the fabrication of nanoparticles in superfluid helium droplets, and in particular to develop a recipe to control core and shell ratios in the case of core-shell nanoparticles. Several types of metal nanoparticles, including pure Ag, Au and Ni nanoparticles, and Ag/Au and Ni/Au core-shell systems, have been synthesised and then removed from the helium droplets by deposition on substrates for ex situ investigations using high-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM imaging has been used to estimate the sizes of nanoparticles, which show a bimodel distribution under the conditions employed. We also present the first evidence that crystalline metal nanoparticles are formed by self-assembly of metal atoms in helium droplets. The XPS investigation of Ni/Au core-shell nanoparticles shows an absence of any Au 4f core-level shift that would occur on alloying of Au and Ni, which provides the first direct evidence for the successful formation of core-shell nanoparticles using superfluid helium droplets.

Growing metal nanoparticles in superfluid helium.

Helium droplets provide a cold and confined environment where atomic and/or molecular dopants can aggregate into clusters and nanoparticles. In particular, the sequential addition of different materials to helium droplets can lead to the formation of a wide range of nanoparticles, including core-shell nanoparticles, which can then be deposited onto a surface. Here we briefly discuss the fundamental properties of helium droplets and then address their implications for the formation of clusters and nanoparticles. Several key experiments on atomic and molecular clusters will be highlighted and new results obtained for nanoparticles formed in this way will be presented. Finally, the versatility, the limitations and new possibilities provided by superfluid helium droplets in nanoscience and nanotechnology will be addressed.