50 research outputs found
First-principles study of phenyl ethylene oligomers as current-switch
We use a self-consistent method to study the distinct current-switch of
-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol, from
the first-principles calculations. The numerical results are in accord with the
early experiment [Reed et al., Sci. Am. \textbf{282}, 86 (2000)]. To further
investigate the transport mechanism, we calculate the switching behavior of
p-terphenyl with the rotations of the middle ring as well. We also study the
effect of hydrogen atom substituting one ending sulfur atom on the transport
and find that the asymmetry of I-V curves appears and the switch effect still
lies in both the positive and negative bias range.Comment: 6 pages, 6 figure
Polarization Induced Switching Effect in Graphene Nanoribbon Edge-Defect Junction
With nonequilibrium Green's function approach combined with density
functional theory, we perform an ab initio calculation to investigate transport
properties of graphene nanoribbon junctions self-consistently. Tight-binding
approximation is applied to model the zigzag graphene nanoribbon (ZGNR)
electrodes, and its validity is confirmed by comparison with GAUSSIAN03 PBC
calculation of the same system. The origin of abnormal jump points usually
appearing in the transmission spectrum is explained with the detailed
tight-binding ZGNR band structure. Transport property of an edge defect ZGNR
junction is investigated, and the tunable tunneling current can be sensitively
controlled by transverse electric fields.Comment: 18 pages, 8 figure
Ab initio study of single molecular transistor modulated by gate-bias
We use a self-consistent method to study the current of the single molecular
transistor modulated by the transverse gate-bias in the level of the
first-principles calculations. The numerical results show that both the
polyacene-dithiol molecules and the fused-ring oligothiophene molecules are the
potential high-frequency molecular transistor controlled by the transverse
field. The long molecules of the polyacene-dithiol or the fused-ring thiophene
are in favor of realizing the gate-bias controlled molecular transistor. The
theoretical results suggest the related experiments.Comment: 14 pages, 7 figure
Density functional calculations of nanoscale conductance
Density functional calculations for the electronic conductance of single
molecules are now common. We examine the methodology from a rigorous point of
view, discussing where it can be expected to work, and where it should fail.
When molecules are weakly coupled to leads, local and gradient-corrected
approximations fail, as the Kohn-Sham levels are misaligned. In the weak bias
regime, XC corrections to the current are missed by the standard methodology.
For finite bias, a new methodology for performing calculations can be
rigorously derived using an extension of time-dependent current density
functional theory from the Schroedinger equation to a Master equation.Comment: topical review, 28 pages, updated version with some revision
Developments in the negative-U modelling of the cuprate HTSC systems
The paper deals with the many stands that go into creating the unique and
complex nature of the HTSC cuprates above Tc as below. Like its predecessors it
treats charge, not spin or lattice, as prime mover, but thus taken in the
context of the chemical bonding relevant to these copper oxides. The crucial
shell filling, negative-U, double-loading fluctuations possible there require
accessing at high valent local environment as prevails within the mixed valent,
inhomogeneous two sub-system circumstance of the HTSC materials. Close
attention is paid to the recent results from Corson, Demsar, Li, Johnson,
Norman, Varma, Gyorffy and colleagues.Comment: 44 pages:200+ references. Submitted to J.Phys.:Condensed Matter, Sept
7 200
Green electrochemical template synthesis of CoPt nanoparticles with tunable size, composition, and magnetism from microemulsions using an ionic liquid (bmimPF6)
Altres ajuts: Substrates have been prepared in IMB-CNM (CSIC),supported by the (CSIC) NGG-258 project.Electrodeposition from microemulsions using ionic liquids is revealed as a green method for synthesizing magnetic alloyed nanoparticles, avoiding the use of aggressive reducing agents. Microemulsions containing droplets of aqueous solution (electrolytic solution containing Pt(IV) and Co(II) ions) in an ionic liquid (bmimPF) define nanoreactors in which the electrochemical reduction takes place. Highly crystalline hcp alloyed CoPt nanoparticles, in the 10-120 nm range with a rather narrow size distribution, have been deposited on a conductive substrate. The relative amount of aqueous solution to ionic liquid determines the size of the nanoreactors, which serve as nanotemplates for the growth of the nanoparticles and hence determine their size and distribution. Further, the stoichiometry (PtCo) of the particles can be tuned by the composition of the electrolytic solution inside the droplets. The control of the size and composition of the particles allows tailoring the room-temperature magnetic behavior of the nanoparticles from superparaparamagnetic to hard magnetic (with a coercivity of H = 4100 Oe) in the as-obtained state. © 2014 American Chemical Society
Report from the EPAA workshop: In vitro ADME in safety testing used by EPAA industry sectors
AbstractThere are now numerous in vitro and in silico ADME alternatives to in vivo assays but how do different industries incorporate them into their decision tree approaches for risk assessment, bearing in mind that the chemicals tested are intended for widely varying purposes? The extent of the use of animal tests is mainly driven by regulations or by the lack of a suitable in vitro model. Therefore, what considerations are needed for alternative models and how can they be improved so that they can be used as part of the risk assessment process? To address these issues, the European Partnership for Alternative Approaches to Animal Testing (EPAA) working group on prioritisation, promotion and implementation of the 3Rs research held a workshop in November, 2008 in Duesseldorf, Germany. Participants included different industry sectors such as pharmaceuticals, cosmetics, industrial- and agro-chemicals. This report describes the outcome of the discussions and recommendations (a) to reduce the number of animals used for determining the ADME properties of chemicals and (b) for considerations and actions regarding in vitro and in silico assays. These included: standardisation and promotion of in vitro assays so that they may become accepted by regulators; increased availability of industry in vivo kinetic data for a central database to increase the power of in silico predictions; expansion of the applicability domains of in vitro and in silico tools (which are not necessarily more applicable or even exclusive to one particular sector) and continued collaborations between regulators, academia and industry. A recommended immediate course of action was to establish an expert panel of users, developers and regulators to define the testing scope of models for different chemical classes. It was agreed by all participants that improvement and harmonization of alternative approaches is needed for all sectors and this will most effectively be achieved by stakeholders from different sectors sharing data