Atomic level defects such as dislocations play key roles in determining the macroscopic properties of crystalline materials 1,2. Their effects range from increased chemical reactivity 3,4 to enhanced mechanical properties 5,6. Dislocations have been widely studied using traditional techniques such as X-ray diffraction and optical imaging. Recent advances have enabled atomic force microscopy to study single dislocations 7 in two-dimensions (2D), while transmission electron microscopy (TEM) can now visualise strain fields in three-dimensions (3D) with near atomic resolution 8–10. However, these techniques cannot offer 3D imaging of the formation or movement of dislocations during dynamic processes. Here, we describe how Bragg Coherent Diffraction Imaging (BCDI) 11,12 can be used to visualize in 3D, the entire network of dislocations present within an individual calcite crystal during repeated growth and dissolution cycles. These investigations demonstrate the potential of BCDI for studying the mechanisms underlying the response of crystalline materials to external stimuli.

Purpose To study the risk factors for radiation-induced lung toxicity (RILT) after stereotactic body radiotherapy (SBRT) of the thorax. Methods Published studies on lung toxicity in patients with early stage non-small cell lung cancer (NSCLC) or metastatic lung tumors treated with SBRT were pooled and analyzed. The primary endpoint was RILT including pneumonitis and fibrosis. Data of RILT and risk factors were extracted from each study, and rates of grade 2-5 (G2+) and grade 3-5 (G3+) RILT were computed. Patient, tumor and dosimetric factors were analyzed for their correlation with RILT. Results Eighty-eight studies (7752 patients), that reported RILT incidence, were eligible. The pooled rates of G2+ and G3+ RILT from all 88 studies were 9.1% (95% CI: 7.15-11.4) and 1.8% (95% CI: 1.3-2.5), respectively. The median of median tumor sizes was 2.3 (range 1.4-4.1) cm. Among the factors analyzed, older patient age (P= 0.044) and larger tumor size (the greatest diameter) were significantly correlated with higher rates of G2+ (P= 0.049) and G3+ RILT (P= 0.001). Patients with stage IA vs. stage IB NSCLC had significantly lower risks of G2+ RILT (8.3% vs 17.1%, OR= 0.43, 95% CI: 0.29-0.64, P<0.0001). Among studies that provided detailed dosimetric data, the pooled analysis demonstrated a significantly higher mean lung dose (MLD) (P= 0.027) and V20 (P= 0.019) in patients with G2+ RILT comparing to that of grade 0-1 RILT. Conclusions The overall rate of RILT is relatively low after thoracic SBRT. Older age and larger tumor size are significant adverse risk factors for RILT. Lung dosimetry, specifically lung V20 and MLD also significantly affect RILT risk. Summary Risk factors for radiation-induced lung toxicity (RILT) after stereotactic body radiotherapy (SBRT) were analyzed from 88 published studies (7752 patients). The overall rate of RILT is relatively low after thoracic SBRT. Adverse risk factors for RILT after SBRT include older age, larger tumor size and greater lung dose-volume exposure as measured by mean lung dose and volume of lung receiving greater than 20 Gy.

Heterogeneous nucleation is vital to a wide range of areas as diverse as ice nucleation on atmospheric aerosols and the fabrication of high-performance thin films. There is excellent evidence that surface topography is a key factor in directing crystallization in real systems; however, the mechanisms by which nanoscale pits and pores promote nucleation remain unclear. Here, we use natural cleavage defects on Muscovite mica to investigate the activity of topographical features in the nucleation from vapor of ice and various organic crystals. Direct observation of crystallization within surface pockets using optical microscopy and also interferometry demonstrates that these sharply acute features provide extremely effective nucleation sites and allows us to determine the mechanism by which this occurs. A confined phase is first seen to form along the apex of the wedge and then grows out of the pocket opening to generate a bulk crystal after a threshold saturation has been achieved. Ice nucleation proceeds in a comparable manner, although our resolution is insufficient to directly observe a condensate before the growth of a bulk crystal. These results provide insight into the mechanism of crystal deposition from vapor on real surfaces, where this will ultimately enable us to use topography to control crystal deposition on surfaces. They are also particularly relevant to our understanding of processes such as cirrus cloud formation, where such topographical features are likely candidates for the "active sites" that make clay particles effective nucleants for ice in the atmosphere.nucleation | confinement | topography | pores | active sites T he growth of a new phase is almost always dependent on a nucleation event. Nucleation is therefore fundamental to a number of processes including crystallization, freezing, condensation, and bubble formation and is typically described in terms of classical nucleation theory. However, because this theory was developed to describe the nucleation of liquid droplets in vapor it cannot give a complete understanding of all nucleation processes, and in particular the formation of crystalline materials. Nucleation in the real world is also usually heterogeneous, occurring on seeds, impurities, or container surfaces. Although simple models consider nucleation to occur on perfectly flat, uniform surfaces, it is clear that real surfaces inevitably vary in chemistry and topography. We focus here on the effects of surface topography. Classical nucleation theory predicts a lower free energy barrier to nucleation in surface cracks or pores on the length scale of a critical nucleus (1). The extent of the reduction is contact-angle-dependent, such that nuclei with a low contact angle experience a more significant reduction from topography.Topography is known to promote crystallization directly from a vapor (2-5), because these systems typically exhibit low contact angles. Crystallization from the melt, in contrast, is associated with very high contact angles such that topography is usually ineff...

There is much evidence that nucleation of liquid droplets from vapour as well as nucleation of crystals from both solution and vapour occurs preferentially in surface defects such as pits and grooves. In the case of nucleation of solid from liquid (freezing) the situation is much less clear-cut. We have therefore carried out a study of the freezing of 50 µm diameter water drops on silicon, glass and mica substrates, and made quantitative comparisons for smooth substrates and those roughened by scratching with three diamond powders of different size distributions. In all cases, freezing occurred close to the expected homogeneous freezing temperature, and the nucleation rates were within the range of literature data. Surface roughening had no experimentally significant effect on any of the substrates studied. In particular, surface roughening of mica -which has been shown to cause dramatic differences in crystal nucleation from organic vapours -has an insignificant effect on ice nucleation from supercooled water. The results also show that glass, silicon and mica have at best only a marginal ice-nucleating capability which does not differ appreciably between the substrates.The lack of effect of roughness on freezing can be rationalised in terms of the relative magnitudes of interfacial free energies and the lack of a viable two-step mechanism, which allows vapour nucleation to proceed via a liquid intermediate.

Patients who underwent implantation of dorsal column stimulators from 1970 to 1973 were reviewed 7–10 years following stimulation. The number who achieved satisfactory pain relief was not significant. The criteria for selecting these patients were reviewed utilizing those now used in 1980. 50% of the patients originally selected would now be rejected for psychological or drug-related reasons. This long-term evaluation indicates no benefit to the patients treated with spinal cord stimulation. However, it appears that psychological factors were the most important reasons for failure. A smaller group of patients studied for 3–5 years following implantation of epidural spinal cord stimulators achieved a 70% pain control rate. Selection factors that explain these differences are discussed.

Nucleation of ice from vapor on atmospheric aerosols has been attributed to the condensation and freezing of supercooled water in small pores. Here we use wedge pores on mica to directly observe the growth of ice in confinement prior to the growth of bulk crystals. We report a transition in behavior with a decreasing temperature: At low temperatures, the limiting step is not nucleation but a free energy barrier associated with the growth of ice through a narrow pore mouth to become a bulk phase.

Surface topography is here investigated as a route to controlling crystal nucleation. The nucleation from vapor of crystals of neo-pentanol and tetrabromomethane was studied on flat surfaces of glass and mica, and on identical substrates scratched with diamond powders of varying particle size. The result is a study which presents a systematic comparison of the nucleating ability of surfaces with the same chemistry and wettability, but varying surface topography. An increase in nucleation density of up to an order of magnitude was observed on scratched mica surfaces compared to unscratched ones, and there was a decrease in the induction time by up to 60%. Larger diamond particles led to enhanced effects, particularly on the nucleation density. Although the nucleation density and induction time on unscratched glass were similar to those on mica, the surface scratches on glass had no significant effect on nucleation density or induction time. The results suggest that a high density of nanoscale features of the surface topography, such as those produced as the diamond particles fracture the mica, is necessary for an enhancement of nucleation. The apparent length scale of the topographical features on mica is discussed with reference to classical nucleation theory and other models. These results show that both a quantitative reduction in induction time and an increase in nucleation density can be achieved as a result of mechanically produced topographical surface defects, which suggests that the engineering of nanoscale topographical features has real potential for control of heterogeneous nucleation.

The nucleation of ice crystals in clouds is poorly understood, despite being of critical importance for our planet’s climate. Nucleation occurs largely at rare “active sites” present on airborne particles such as mineral dust, but the nucleation pathway is distinct under different meteorological conditions. These give rise to two key nucleation pathways where a particle is either immersed in a supercooled liquid water droplet (immersion freezing mode) or suspended in a supersaturated vapor (deposition mode). However, it is unclear if the same active sites are responsible for nucleation in these two modes. Here, we directly compare the sites that are active in these two modes by performing immersion freezing and deposition experiments on the same thin sections of two atmospherically important minerals (feldspar and quartz). For both substrates, we confirm that nucleation is dominated by a limited number of sites and show that there is little correlation between the two sets of sites operating in each experimental method: across both materials, only six out of 73 sites active for immersion freezing nucleation were also active for deposition nucleation. Clearly, different properties determine the activity of nucleation sites for each mode, and we use the pore condensation and freezing concept to argue that effective deposition sites have size and/or geometry requirements not of relevance to effective immersion freezing sites. Hence, the ability to nucleate is pathway dependent, and the mode of nucleation has to be explicitly considered when applying experimental data in cloud models.