In Situ Imaging of the Conducting Filament in a Silicon Oxide Resistive Switch

The nature of the conducting filaments in many resistive switching systems has been elusive. Through in situ transmission electron microscopy, we image the real-time formation and evolution of the filament in a silicon oxide resistive switch. The electroforming process is revealed to involve the local enrichment of silicon from the silicon oxide matrix. Semi-metallic silicon nanocrystals with structural variations from the conventional diamond cubic form of silicon are observed, which likely accounts for the conduction in the filament. The growth and shrinkage of the silicon nanocrystals in response to different electrical stimuli show energetically viable transition processes in the silicon forms, offering evidence to the switching mechanism. The study here also provides insights into the electrical breakdown process in silicon oxide layers, which are ubiquitous in a host of electronic devices.Comment: 7 pages, 7 figure

Mechanical Deformation Induced in Si and GaN Under Berkovich Nanoindentation

Details of Berkovich nanoindentation-induced mechanical deformation mechanisms of single-crystal Si(100) and the metal-organic chemical-vapor deposition (MOCVD) derived GaN thin films have been systematic investigated by means of micro-Raman spectroscopy and cross-sectional transmission electron microscopy (XTEM) techniques. The XTEM samples were prepared by using focused ion beam (FIB) milling to accurately position the cross-section of the nanoindented area. The behaviors of the discontinuities displayed in the loading and unloading segments of the load-displacement curves of Si and GaN thin films performed with a Berkovich diamond indenter tip were explained by the observed microstructure features obtained from XTEM analyses. According to the observations of micro-Raman and XTEM, the nanoindentation-induced mechanical deformation is due primarily to the generation and propagation of dislocations gliding along the pyramidal and basal planes specific to the hexagonal structure of GaN thin films rather than by indentation-induced phase transformations displayed in Si

Vitamin D status in irritable bowel syndrome and the impact of supplementation on symptoms: what do we know and what do we need to know?

BACKGROUND: Low vitamin D status is associated with risk of colorectal cancer and has been implicated in inflammatory bowel disease. Irritable bowel syndrome (IBS) is a chronic, relapsing, functional bowel disorder. A nascent literature suggests a role for vitamin D in IBS, but this has not been collated or critiqued. To date, seven studies have been published: four observational studies and three randomised controlled trials (RCTs). All observational studies reported that a substantial proportion of the IBS population was vitamin D deficient. Two intervention studies reported improvement in IBS symptom severity scores and quality of life (QoL) with vitamin D supplementation. There are limited data around the role of vitamin D in IBS. CONCLUSIONS: The available evidence suggests that low vitamin D status is common among the IBS population and merits assessment and rectification for general health reasons alone. An inverse correlation between serum vitamin D and IBS symptom severity is suggested and vitamin D interventions may benefit symptoms. However, the available RCTs do not provide strong, generalisable evidence; larger and adequately powered interventions are needed to establish a case for therapeutic application of vitamin D in IBS

Bioactive epoxides and hydroperoxides derived from naturally monoterpene geranyl acetate

Geranyl acetate (1) was oxidized thermally and photochemically using (mcpba, H2O2) respectively to obtain (E)-5-(3, 3-dimethyloxiran-2-yl)-3-methylpent-2-enyl acetate (2) and 3-(2-(3, 3-dimethyloxiran-2-yl) ethyl)-3-methyloxiran-2-yl) methyl acetate (3). On the other hand, photooxygenation of 1 with tetraphenyl porphin (TPP) as a photo sensitizer gave corresponding acitic acid 2,6-bis-hydroperoxy-7-methyl-3-methylene-oct-7-enyl-ester (4), acitic acid 7-hydroperoxy-3,7-dimethyl-octa-2,5-dienyl ester (5) and Acitic acid 3-hydroperoxy-7-methyl-3,7-dimethyl-octa-1,6-dienyl ester (6). Antifungal studies were carried out on geranyl acetate and its derivatives. Studies on the antifungal activity especially Microsporum gypsum, Trichophyton vercossum and Candida tropicalis showed that geranyl acetate, its epoxide and hydroperoxide derivatives have good antifungal action. Keywords: Medicinal plants, Geranyl acetate, Hydroperoxide, epoxide, Photooxygenation, antifungal activit

Coaxial Alginate Hydrogels : From Self-Assembled 3D Cellular Constructs to Long-Term Storage

Alginate as a versatile naturally occurring biomaterial has found widespread use in the biomedical field due to its unique features such as biocompatibility and biodegradability. The ability of its semipermeable hydrogels to provide a favourable microenvironment for clinically relevant cells made alginate encapsulation a leading technology for immunoisolation, 3D culture, cryopreservation as well as cell and drug delivery. The aim of this work is the evaluation of structural properties and swelling behaviour of the core-shell capsules for the encapsulation of multipotent stromal cells (MSCs), their 3D culture and cryopreservation using slow freezing. The cells were encapsulated in core-shell capsules using coaxial electrospraying, cultured for 35 days and cryopreserved. Cell viability, metabolic activity and cell–cell interactions were analysed. Cryopreservation of MSCs-laden core-shell capsules was performed according to parameters pre-selected on cell-free capsules. The results suggest that core-shell capsules produced from the low viscosity high-G alginate are superior to high-M ones in terms of stability during in vitro culture, as well as to solid beads in terms of promoting formation of viable self-assembled cellular structures and maintenance of MSCs functionality on a long-term basis. The application of 0.3 M sucrose demonstrated a beneficial effect on the integrity of capsules and viability of formed 3D cell assemblies, as compared to 10% dimethyl sulfoxide (DMSO) alone. The proposed workflow from the preparation of core-shell capsules with self-assembled cellular structures to the cryopreservation appears to be a promising strategy for their off-the-shelf availability