Channeling in helium ion microscopy: Mapping of crystal orientation

Background: The unique surface sensitivity and the high resolution that can be achieved with helium ion microscopy make it a\ud competitive technique for modern materials characterization. As in other techniques that make use of a charged particle beam, channeling\ud through the crystal structure of the bulk of the material can occur.\ud Results: Here, we demonstrate how this bulk phenomenon affects secondary electron images that predominantly contain surface\ud information. In addition, we will show how it can be used to obtain crystallographic information. We will discuss the origin of\ud channeling contrast in secondary electron images, illustrate this with experiments, and develop a simple geometric model to predict\ud channeling maxima.\ud Conclusion: Channeling plays an important role in helium ion microscopy and has to be taken into account when trying to achieve\ud maximum image quality in backscattered helium images as well as secondary electron images. Secondary electron images can be\ud used to extract crystallographic information from bulk samples as well as from thin surface layers, in a straightforward manner

Effectiveness of cognitive and physical training in slowing progression to dementia: a clinical and experimental study. Focus on relationship with cardiovascular fitness

Physical activity is beneficial to vascular health; on the other hand, vascular damage is associated with cognitive impairment. Both physical activity and a cognitively stimulating environment are known to delay the onset of dementia. The Train The Brain study evaluated the effectiveness of a comprehensive program of physical training and mental activity in delaying cognitive decline in elderly people with initial cognitive impairment, at the same time investigating the relationship between physical, vascular, neurological, and cognitive fitness. Elders age 65-89 with were recruited with the help of family physicians and territorial services. All participants underwent a neurological and cardiologic evaluation. Carotid-femoral pulse wave velocity and carotid pressure were measured with the SphygmoCor system (AtCor, Australia). Longitudinal ultrasound scans of the common carotid were performed and 10-second video clips were recorded to be analysed offline through the Cardiovascular Suite software (Quipu srl, Italy), with the computation of diameter, intima-media thickness, wall cross-sectional area, distensibility coefficient, and elastic modulus. The latter software was used also to measure endothelial function through flow mediated dilation (FMD) of the brachial artery. Subjects classified as mild cognitive impairment at the neurological examination were randomized either to standard care, or a 7-month program of physical training and environmental stimulation (lectures, games, music, social activities) three hours a week. The evaluation was then repeated. Data were obtained for 54 patients who underwent training and 36 controls. The intervention was successful in improving cognitive function as measured through the ADAS-Cog score: 11.95 (3.86) to 13.00 (4.73) for no training, 14.32 (4.27) to 12.85 (4.03) for training, time x treatment p<0.001. Pulse wave velocity showed no significant effect (p=0.5). FMD improved with intervention (no training: 3.20 (2.03) to 2.50 (1.77) %; training: from 2.82 (2.19) to 3.42 (1.82); p=0.014). All selected carotid parameters were influenced by the combination of time and treatment, in a diverging trend, at a statistically significant level, with intervention determining less dilated, less thick and less stiff vessels. None of the parameters measured analysing the vessels showed a correlation The proposed 7-months program improved cognitive function in elders with initial cognitive impairment. There was a significant difference in behaviour in time of the two groups as for endothelial function and carotid enlargement, wall thickening and arterial stiffening. The intervention seems to oppose the typical harmful effects of aging on vessels; at the same time, the positive effects on cognition and vascular health do not appear as directly correlated

Spinodal decomposition driven formation of Pt-nanowires on Ge(001)

Using low energy electron microscopy, we have found that the deposition of Pt on Ge(001) leads to the formation of a surface confined eutectic liquid when the system is heated above 980 K. From the bulk phase diagram we derive the composition of the eutectic phase: Ge$_{0.78}$Pt$_{0.22}$. Upon solidification and further cooling down, two distinct types of terrace emerge, the so-called α and β terraces, which have been assigned previously as relatively Pt-poor and Pt-rich, respectively. Immediately after solidification β terraces fully cover the surface, while further cooling leads to their partial transformation into α terraces. Subsequently, Pt nanowire domains nucleate and grow exclusively on β terraces at about 600 K. The results are discussed using spinodal decomposition concepts and reveal a new pathway for nanowire formation

Hydrophobic surfaces with tunable dynamic wetting properties via colloidal assembly of silica microspheres and gold nanoparticles

Hierarchically structured surfaces have been fabricated using a simple colloidal bottom-up approach. The substrates exhibit a wide range of wettability properties, expressed by water contact angles ranging from 110 ∘ to 166 ∘ . The liquid–solid adhesive characteristics vary from very sticky to non-sticky, exhibited by very large and negligible sliding angles, respectively. Silica spheres with diameters in the range 130–850 nm comprise the larger length scale entities in the hierarchical superstructures, while gold nanoparticles with diameters 13–45 nm are included as the smaller length scale features. Surfaces are derivatized with suitable chemical agents to render them (super)hydrophobic. Dynamic wetting properties in terms of contact angle hysteresis and sliding angles are discussed in relation to the surface morphology

Imaging ultra thin layers with helium ion microscopy: Utilizing the channeling contrast mechanism

Background: Helium ion microscopy is a new high-performance alternative to classical scanning electron microscopy. It provides superior resolution and high surface sensitivity by using secondary electrons.\ud \ud Results: We report on a new contrast mechanism that extends the high surface sensitivity that is usually achieved in secondary electron images, to backscattered helium images. We demonstrate how thin organic and inorganic layers as well as self-assembled monolayers can be visualized on heavier element substrates by changes in the backscatter yield. Thin layers of light elements on heavy substrates should have a negligible direct influence on backscatter yields. However, using simple geometric calculations of the opaque crystal fraction, the contrast that is observed in the images can be interpreted in terms of changes in the channeling probability.\ud \ud Conclusion: The suppression of ion channeling into crystalline matter by adsorbed thin films provides a new contrast mechanism for HIM. This dechanneling contrast is particularly well suited for the visualization of ultrathin layers of light elements on heavier substrates. Our results also highlight the importance of proper vacuum conditions for channeling-based experimental methods\u

Le determinanti nella scelta del sistema di costing: analisi di un caso aziendale.

La tesi è incentrata sullo studio delle variabili interne all'azienda e dei fattori esterni che possono esercitare un'influenza significativa sulla scelta del sistema di costing da implementare. Tale studio si avvale del contributo di un'ampia letteratura sulla materia. Nello specifico,viene concentrata l'attenzione sull'analisi della struttura organizzativa, del processo decisionale, delle finalità di utilizzo del sistema di costing e dell'ambiente competitivo in cui l'azienda muove i propri passi, al fine di valutare come tali fattori influenzano la scelta e l'adozione di sistemi di costing più o meno sofisticati. Le nozioni teoriche acquisite e argomentate sono poi impiegate per la valutazione dell'adeguatezza del sistema di costing adottato nell'azienda Alfa Srl (nome di fantasia), una società di progettazione e consulenza ingegneristica con sede a Pisa

Inversion of Randomly Corrugated Surfaces Structure from Atom Scattering Data

The Sudden Approximation is applied to invert structural data on randomly corrugated surfaces from inert atom scattering intensities. Several expressions relating experimental observables to surface statistical features are derived. The results suggest that atom (and in particular He) scattering can be used profitably to study hitherto unexplored forms of complex surface disorder.Comment: 10 pages, no figures. Related papers available at http://neon.cchem.berkeley.edu/~dan