355 research outputs found
Importance of carbon solubility and wetting properties of nickel nanoparticles for single wall nanotube growth
Optimized growth of Single Wall Carbon Nanotubes requires a full knowledge of
the actual state of the catalyst nanoparticle and its interface with the tube.
Using Tight Binding based atomistic computer simulations, we calculate carbon
adsorption isotherms on nanoparticles of nickel, a typical catalyst, and show
that carbon solubility increases for smaller nanoparticles that are either
molten or surface molten under experimental conditions. Increasing carbon
content favors the dewetting of Ni nanoparticles with respect to sp2 carbon
walls, a necessary property to limit catalyst encapsulation and deactivation.
Grand Canonical Monte Carlo simulations of the growth of tube embryos show that
wetting properties of the nanoparticles, controlled by carbon solubility, are
of fundamental importance to enable the growth, shedding a new light on the
growth mechanisms
Understanding amorphous phase-change materials from the viewpoint of Maxwell rigidity
Phase-change materials (PCMs) are the subject of considerable interest
because they have been recognized as potential active layers for
next-generation non-volatile memory devices, known as Phase Change Random
Access Memories (PRAMs). By analyzing First Principles Molecular Dynamics
simulations we develop a new method for the enumeration of mechanical
constraints in the amorphous phase and show that the phase diagram of the most
popular system (Ge-Sb-Te) can be split into two compositional regions having a
well-defined mechanical character: a Tellurium rich flexible phase, and a
stressed rigid phase that encompasses the known PCMs. This sound atomic scale
insight should open new avenues for the understanding of PCMs and other complex
amorphous materials from the viewpoint of rigidity.Comment: 5 pages, 4 figures in EP
Topological Origin of Fracture Toughening in Complex Solids: the Viewpoint of Rigidity Theory
In order to design tougher materials, it is crucial to understand the
relationship between their composition and their resistance to fracture. To
this end, we investigate the fracture toughness of usual sodium silicate
glasses (NS) and complex calcium--silicate--hydrates (CSH), the binding phase
of cement. Their atomistic structure is described in the framework of the
topological constraints theory, or rigidity theory. We report an analogous
rigidity transition, driven by pressure in NS and by composition in CSH.
Relying both on simulated and available experimental results, we show that
optimally constrained isostatic systems show improved fracture toughness. The
flexible to stressed--rigid transition is shown to be correlated to a
ductile-to-brittle transition, with a local minimum of the brittleness for
isostatic system. This fracture toughening arises from a reversible molecular
network, allowing optimal stress relaxation and crack blunting behaviors. This
opens the way to the discovery of high-performance materials, designed at the
molecular scale
A randomised feasibility study of serial magnetic resonance imaging to reduce treatment times in Charcot neuroarthropathy in people with diabetes (CADOM): A protocol
Background Charcot neuroarthropathy is a complication of peripheral neuropathy associated with diabetes which most frequently affects the lower limb. It can cause fractures and dislocations within the foot, which may progress to deformity and ulceration. Recommended treatment is immobilisation and offloading, with a below knee non-removable cast or boot. Duration of treatment varies from six months to more than one year. Small observational studies suggest that repeated assessment with Magnetic Resonance Imaging improves decision making about when to stop treatment, but this has not been tested in clinical trials. This study aims to explore the feasibility of using serial Magnetic Resonance Imaging without contrast in the monitoring of Charcot neuroarthropathy to reduce duration of immobilisation of the foot. A nested qualitative study aims to explore participants’ lived experience of Charcot neuroarthropathy and of taking part in the feasibility study. Methods We will undertake a two arm, open study, and randomise 60 people with a suspected or confirmed diagnosis of Charcot neuroarthropathy from five NHS, secondary care multidisciplinary Diabetic Foot Clinics across England. Participants will be randomised 1:1 to receive Magnetic Resonance Imaging at baseline and remission up to 12 months, with repeated foot temperature measurements and x-rays (standard care plus), or standard care plus with additional three-monthly Magnetic Resonance Imaging until remission up to 12 months (intervention). Time to confirmed remission of Charcot neuroarthropathy with off-loading treatment (days) and its variance will be used to inform sample size in a full-scale trial. We will look for opportunities to improve the protocols for monitoring techniques and the clinical, patient centred, and health economic measures used in a future study. For the nested qualitative study, we will invite a purposive sample of 10-14 people able to offer maximally varying experiences from the feasibility study to take part in semi-structured interviews to be analysed using thematic analysis. Discussion The study will inform the decision whether to proceed to a full-scale trial. It will also allow deeper understanding of the lived experience of Charcot neuroarthropathy, and factors that contribute to engagement in management and contribute to the development of more effective patient centred strategies. Trial registration ISRCTN, ISRCTN, 74101606. Registered on 6 November 2017, http://www.isrctn.com/ISRCTN74101606?q=CADom&filters=&sort=&offset=1&totalResults=1&page=1&pageSize=10&searchType=basic-searc
Los determinantes de la IED española en Iberoamerica
This article thoroughly analyses the main determinants of the process of intemationalisation of Spanish firms in Latin America during the second half of the nineties when Spain became one of the main foreign investor in this region. The results of the interviews that have been carried out firstly remark that the process of intemationalisation of Spanish firms reflects both, the stage of maturity of Spanish economic growth and the structural changes that the country has experienced since its integration to the European Union. Interviews also show that the intemationalisation of Spanish firms is as well a consequence of certain strengths related to the existence of a group of ownership advantages, on the part of some Spanish firms, and location advantages, specially those related to market access, which determine the decision to invest in Latin America. The context where this process in taking place and its characteristics lead the authors to conclude that Spanish firms are staking on Latin America as a launching pad for a competitive intemationalisation process in the world market
El paro juvenil no es el principal desequilibrio del mercado laboral. Informe de coyuntura sobre el mercado de trabajo en España y Andalucía (cuarto trimestre de 2011)
El artículo analiza la evolución de las principales variables laborales españolas y andaluzas en el cuarto trimestre de 2011. En primer lugar, se plantea el contexto de la evolución de la actividad económica en el ámbito internacional y nacional señalándose un cierto deterioro en el crecimiento económico especialmente en la segunda parte del año. A continuación se analiza con mayor detenimiento la evolución de las principales variables laborales relativas a la oferta y demanda de trabajo y desempleo. Esta misma estructura se sigue para el análisis del mercado de trabajo en Andalucía. Se presta especial atención a los trabajadores más jóvenes para indicar el impacto de la crisis económica sobre este grupo social
Endophytic fungi of Paullinia cupana and its antimicrobial potential.
The objective of this study is to characterize P. cupana endophytic fungi and evaluate their antibiotic potential by agar diffusion test. Fruits and root fragments from 6 individuals were collected and sterilized with 70% ethanol and 2% sodium hypochlorite
Basal-plane Incommensurate Phases in HCP Structures
An Ising model with competing interaction is used to study the appearance of
incommensurate phases in the basal plane of an hexagonal closed-packed
structure. The calculated mean-field phase diagram reveals various
1q-incommensurate and lock-in phases. The results are applied to explain the
basal-plane incommensurate phase in some compounds of the A'A"BX_4 family, like
K_2MoO_4, K_2WO_4, Rb_2WO4 and to describe the sequence of high-temperature
phase transitions in other compounds of this family.Comment: 8 pages, RevTeX + 4 ps figure
A tight-binding potential for atomistic simulations of carbon interacting with transition metals: Application to the Ni-C system
We present a tight-binding potential for transition metals, carbon, and
transition metal carbides, which has been optimized through a systematic
fitting procedure. A minimal basis, including the s, p electrons of carbon and
the d electrons of the transition metal, is used to obtain a transferable
tight-binding model of the carbon-carbon, metal-metal and metal-carbon
interactions applicable to binary systems. The Ni-C system is more specifically
discussed. The successful validation of the potential for different atomic
configurations indicates a good transferability of the model and makes it a
good choice for atomistic simulations sampling a large configuration space.
This approach appears to be very efficient to describe interactions in systems
containing carbon and transition metal elements
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