43 research outputs found
Ab initio simulations of the kinetic properties of the hydrogen monomer on graphene
The understanding of the kinetic properties of hydrogen (isotopes) adatoms on
graphene is important in many fields. The kinetic properties of
hydrogen-isotope (H, D and T) monomers were simulated using a composite method
consisting of density functional theory, density functional perturbation theory
and harmonic transition state theory. The kinetic changes of the magnetic
property and the aromatic bond of the hydrogenated graphene during the
desorption and diffusion of the hydrogen monomer was discussed. The vibrational
zero-point energy corrections in the activation energies were found to be
significant, ranging from 0.072 to 0.205 eV. The results obtained from
quantum-mechanically modified harmonic transition state theory were compared
with the ones obtained from classical-limit harmonic transition state theory
over a wide temperature range. The phonon spectra of hydrogenated graphene were
used to closely explain the (reversed) isotope effects in the prefactor,
activation energy and jump frequency of the hydrogen monomer. The kinetic
properties of the hydrogen-isotope monomers were simulated under conditions of
annealing for 10 minutes and of heating at a constant rate (1.0 K/s). The
isotope effect was observed; that is, a hydrogen monomer of lower mass is
desorbed and diffuses more easily (with lower activation energies). The results
presented herein are very similar to other reported experimental observations.
This study of the kinetic properties of the hydrogen monomer and many other
involved implicit mechanisms provides a better understanding of the interaction
between hydrogen and graphene.Comment: Accepted by J. Phys. Chem.
Gauge fields and curvature in graphene
The low energy excitations of graphene can be described by a massless Dirac
equation in two spacial dimensions. Curved graphene is proposed to be described
by coupling the Dirac equation to the corresponding curved space. This
covariant formalism gives rise to an effective hamiltonian with various extra
terms. Some of them can be put in direct correspondence with more standard
tight binding or elasticity models while others are more difficult to grasp in
standard condensed matter approaches. We discuss this issue, propose models for
singular and regular curvature and describe the physical consequences of the
various proposals.Comment: Proceedings of the International Conference on Theoretical Physics:
Dubna-Nano2008 to be published online in Journal of Physics: Conference
serie
The influence of size effect on the electronic and elastic properties of diamond films with nanometer thickness
The atomic structure and physical properties of few-layered oriented
diamond nanocrystals (diamanes), covered by hydrogen atoms from both sides are
studied using electronic band structure calculations. It was shown that energy
stability linear increases upon increasing of the thickness of proposed
structures. All 2D carbon films display direct dielectric band gaps with
nonlinear quantum confinement response upon the thickness. Elastic properties
of diamanes reveal complex dependence upon increasing of the number of
layers. All theoretical results were compared with available experimental data.Comment: 16 pages, 5 figures, 3 table
Plasma lipids are altered in Gaucher disease: Biochemical markers to evaluate therapeutic intervention
Enzyme replacement therapy has been in clinical practice for the non-neuronopathic form of Gaucher disease for 15 years. However, the wide phenotypic variability in this disorder poses challenges to clinicians to assess patient severity and disease progression in order to effectively manage patients. Once therapy is initiated, methods to monitor the complex biochemical changes associated with the disease, and the response of these changes to therapy, are required in order to tailor therapy regimens to individual patients. We have evaluated the suitability of plasma sphingolipids and phospholipids as biochemical markers of disease burden and the efficacy of therapy to reduce that burden. Over 60 lipid species were measured using electrospray ionization-tandem mass spectrometry in plasma from controls and Gaucher patients, pre- and post-therapy. Glucosylceramide, molecular species of phosphatidylglycerol and G(M3) ganglioside were elevated in Gaucher disease, whereas species of ceramide, dihexosylceramide and sphingomyelin were decreased. Multivariate analysis enabled us to calculate the combined response of these lipids to therapy in Gaucher patients and correlate them with patient severity. Plasma lipids are proposed to be useful biomarkers for Gaucher disease.Peter J. Meikle, Philip D. Whitfield, Tina Rozaklis, David Blacklock, Stephen Duplock, Deborah Elstein, Ari Zimran, Eugen Mengel, Paul Cannell, John J. Hopwood and Maria Fullerhttp://www.elsevier.com/wps/find/journaldescription.cws_home/622796/description#descriptio
Chemical functionalization of graphene with defects
Contains fulltext :
71901.pdf (preprint version ) (Open Access)7 p