277 research outputs found
Diamond biocompatible coatings for medical implants
New carbon (diamond-like) nanocomposite coatings deposited from a C60 ionic beam can be used as a wear-resistant protective coating for implants. It was found that these coatings enhance resistance to тelectrochemical corrosion processes due to a shift of the material’s electrode potential to a zone of positive values. They also promote a complex of reparative, adaptative and compensatory reorganization that accelerates the healing processes in the vicinity of the implant
Stimulation of calcium phosphate crystal formation by implant surfaces with electret properties
Oxide coatings with electret properties are investigated. The possibility of stimulation of the formation of calcium phosphate sediments near the electroactive surface is discussed. The exposure of implants with such coatings to solutions imitating blood plasma showed their high efficiency of biointegration due to activation of an exchange processes in living tissues by a negative superficial charge. The revealed effect amplifies with the growth of the thickness of the anodic oxide film
Features of medical implant passivation using anodic oxide films
The passivation ability of metals from groups IV and V of the Periodic Table is considered. Anodic treatment is able to neutralize the increase of metal hardening when comminuting grains to nanometre sizes. The deposition of metal oxide film coatings on a cobalt–chromium alloy surface results in substantial passivation of its surface and prevents cobalt and chromium accumulation in bone tissues. The decrease of surface activity of titanium implants can be achieved both by cleaning the surface during vacuum annealing before oxidation and by the increase of the anodic oxide film thickness, which limits mass and charge transfer through the implant surface. Recommended titanium implant treatment regimens are vacuum annealing at 650 °C and anodic oxidation to attain an oxide thickness less or equal to 300 nm
Properties of magnetron hydroxyapatite coatings deposited on oxidized substrates
Hydroxyapatite (HA) coating were formed on oxidized niobium surfaces by the highfrequency magnetron sputtering method using hydroxyapatite and tricalcium phosphate targets. The structure, substructure and mechanical properties of the Nb–Nb2O5–HA system were investigated by X-ray diffraction, atomic force microscopy and nanoindentation and the stress state was assessed. The synthesized hydroxyapatite film had the following characteristics: thermal expansion coefficient 10–5 K–1; modulus of elasticity 120 GPa; adhesive strength not less than 0.45 kg/mm2; density 2900 kg/m3. The stress magnitude in the metal oxide substrate was from 11 to 14 MPa after hydroxyapatite film deposition
Theoretical prediction of perfect spin filtering at interfaces between close-packed surfaces of Ni or Co and graphite or graphene
The in-plane lattice constants of close-packed planes of fcc and hcp Ni and
Co match that of graphite almost perfectly so that they share a common two
dimensional reciprocal space. Their electronic structures are such that they
overlap in this reciprocal space for one spin direction only allowing us to
predict perfect spin filtering for interfaces between graphite and (111) fcc or
(0001) hcp Ni or Co. First-principles calculations of the scattering matrix
show that the spin filtering is quite insensitive to amounts of interface
roughness and disorder which drastically influence the spin-filtering
properties of conventional magnetic tunnel junctions or interfaces between
transition metals and semiconductors. When a single graphene sheet is adsorbed
on these open -shell transition metal surfaces, its characteristic
electronic structure, with topological singularities at the K points in the two
dimensional Brillouin zone, is destroyed by the chemical bonding. Because
graphene bonds only weakly to Cu which has no states at the Fermi energy at the
K point for either spin, the electronic structure of graphene can be restored
by dusting Ni or Co with one or a few monolayers of Cu while still preserving
the ideal spin injection property.Comment: 12 pages, 11 figure
Multiple-charge transfer and trapping in DNA dimers
We investigate the charge transfer characteristics of one and two excess
charges in a DNA base-pair dimer using a model Hamiltonian approach. The
electron part comprises diagonal and off-diagonal Coulomb matrix elements such
a correlated hopping and the bond-bond interaction, which were recently
calculated by Starikov [E. B. Starikov, Phil. Mag. Lett. {\bf 83}, 699 (2003)]
for different DNA dimers. The electronic degrees of freedom are coupled to an
ohmic or a super-ohmic bath serving as dissipative environment. We employ the
numerical renormalization group method in the nuclear tunneling regime and
compare the results to Marcus theory for the thermal activation regime. For
realistic parameters, the rate that at least one charge is transferred from the
donor to the acceptor in the subspace of two excess electrons significantly
exceeds the rate in the single charge sector. Moreover, the dynamics is
strongly influenced by the Coulomb matrix elements. We find sequential and pair
transfer as well as a regime where both charges remain self-trapped. The
transfer rate reaches its maximum when the difference of the on-site and
inter-site Coulomb matrix element is equal to the reorganization energy which
is the case in a GC-GC dimer. Charge transfer is completely suppressed for two
excess electrons in AT-AT in an ohmic bath and replaced by damped coherent
electron-pair oscillations in a super-ohmic bath. A finite bond-bond
interaction alters the transfer rate: it increases as function of when
the effective Coulomb repulsion exceeds the reorganization energy (inverted
regime) and decreases for smaller Coulomb repulsion
Graphite and graphene as perfect spin filters
Based upon the observations (i) that their in-plane lattice constants match
almost perfectly and (ii) that their electronic structures overlap in
reciprocal space for one spin direction only, we predict perfect spin filtering
for interfaces between graphite and (111) fcc or (0001) hcp Ni or Co. The spin
filtering is quite insensitive to roughness and disorder. The formation of a
chemical bond between graphite and the open -shell transition metals that
might complicate or even prevent spin injection into a single graphene sheet
can be simply prevented by dusting Ni or Co with one or a few monolayers of Cu
while still preserving the ideal spin injection property
A New Multiscale Approach to Nuclear Fuel Simulations: Atomistic Validation of Kinetic Method
A key issue for fuel behavior codes is their sensitivity to values of various materials properties, many of which have large uncertainties or have not been measured. Kinetic mesoscale models, such as those developed at Argonne National Laboratory within the past decade, are directly comparable to data obtained from in-reactor experiments. In the present paper, a new multiscale concept is proposed that consists of using atomistic simulation methods to verify the kinetic approach. The new concept includes kinetic rate-equations for radiation damage, energetics and kinetics of defects, and gas/defect-driven swelling of fuels as a function of temperature and burnup. The quantum and classical atomistic simulation methods are applied to increase our understanding of radiation damage and defect formation and growth processes and to calculate the probabilities of elemental processes and reactions that are applicable to irradiated nuclear materials
Anti-corrosion ceramic coatings on the surface of Nd-Fe-B repelling magnets
The results of vacuum-arc deposition of thin ZrO₂coatings to protect the surface of Nd-Fe-B permanent magnets used as repelling devices in orthodontics are presented. The structure, phase composition and mechanical properties of zirconium dioxide films have been investigated by means of SEM, XRD, EDX, XRF and nanoindentation method. It was revealed the formation of polycrystalline ZrO₂ films of monoclinic modification with average grain size 25 nm. The influence of the ZrO₂ coating in terms of its barrier properties for corrosion in quasi-physiological 0.9 NaCl solution has been studied. Electrochemical measurements indicated good barrier properties of the coating on specimens in the physiological solution environment
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