431 research outputs found
Role of crystallizational differention in the origin of island-arc andesitic melts: evidence from data on melt inclusions and oxygen isotopes
Enhanced longitudinal mode spacing in blue-violet InGaN semiconductor laser
A novel explanation of observed enhanced longitudinal mode spacing in InGaN
semiconductor lasers has been proposed. It has been demonstrated that e-h
plasma oscillations, which can exist in the laser active layer at certain
driving conditions, are responsible for mode clustering effect. The resonant
excitation of the plasma oscillations occurs due to longitudinal mode beating.
The separation of mode clusters is typically by an order of magnitude larger
that the individual mode spacing.Comment: 3 pages, 2 figure
Bundling up carbon nanotubes through Wigner defects
We show, using ab initio total energy density functional theory, that the
so-called Wigner defects, an interstitial carbon atom right besides a vacancy,
which are present in irradiated graphite can also exist in bundles of carbon
nanotubes. Due to the geometrical structure of a nanotube, however, this defect
has a rather low formation energy, lower than the vacancy itself, suggesting
that it may be one of the most important defects that are created after
electron or ion irradiation. Moreover, they form a strong link between the
nanotubes in bundles, increasing their shear modulus by a sizeable amount,
clearly indicating its importance for the mechanical properties of nanotube
bundles.Comment: 5 pages and 4 figure
Magmatic evolution of Avachinsky volcano (Kamchatka) during the Holocene revealed from composition of tephra, their matrix glasses and melt inclusions in minerals
Embedding Transition-Metal Atoms in Graphene: Structure, Bonding, and Magnetism
We present a density-functional-theory study of transition-metal atoms (Sc–Zn, Pt, and Au) embedded in single and double vacancies (SV and DV) in a graphene sheet. We show that for most metals, the bonding is strong and the metal-vacancy complexes exhibit interesting magnetic behavior. In particular, an Fe atom on a SV is not magnetic, while the Fe@DV complex has a high magnetic moment. Surprisingly, Au and Cu atoms at SV are magnetic. Both bond strengths and magnetic moments can be understood within a simple local-orbital picture, involving carbon sp2 hybrids and the metal spd orbitals. We further calculate the barriers for impurity-atom migration, and they agree well with available experimental data. We discuss the experimental realization of such systems in the context of spintronics and nanocatalysis.Peer reviewe
Irradiation-Induced Magnetism in Graphite: A Density Functional Study
Recent experiments indicate that proton irradiation triggers ferromagnetism in originally nonmagnetic graphite samples while He ion bombardment has a much smaller effect. To understand the origin of irradiation-induced magnetism, we have performed spin-polarized density functional theory calculations of the magnetic properties of the defects which are most likely to appear under irradiation vacancies and vacancy-hydrogen complexes. Both defects are magnetic, but as for the latter we find that H adsorption on one of the vacancy dangling bonds gives rise to a magnetic moment double that of the naked vacancy. We show that for small irradiation doses vacancy-hydrogen complexes result in a macroscopic magnetic signal which agrees well with the experimental values.Peer reviewe
Resonant electron transfer between quantum dots
An interaction of electromagnetic field with a nanostructure composed of two
quantum dots is studied theoretically. An effect of a resonant electron
transfer between the localized low-lying states of quantum dots is predicted. A
necessary condition for such an effect is the existence of an excited bound
state whose energy lies close to the top of the barrier separating the quantum
dots. This effect may be used to realize the reversible quantum logic gate NOT
if the superposition of electron states in different quantum dots is viewed as
the superposition of bits 0 and 1.Comment: 8 pages, 1 EPS-figure, submitted to Phys. Rev.
Magnetic Properties and Diffusion of Adatoms on a Graphene Sheet
We use ab initio methods to calculate the properties of adatom defects on a graphite surface. By applying a full spin-polarized description to the system we demonstrate that these defects have a magnetic moment of about 0.5 myy B and also calculate its role in diffusion over the surface. The magnetic nature of these intrinsic carbon defects suggests that it is important to understand their role in the recently observed magnetism in pure carbon systems.Peer reviewe
Mantle melting conditions under the eastern volcanic front of Kamchatka estimated from melt inclusions in olivine
Here we present new data on the composition of olivine phenocrysts, melt inclusions and inclusions of chromium spinel in olivine from high Mg# basalts of the Eastern Volcanic Front in Kamchatka
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