363 research outputs found
Polaronic distortion and vacancy-induced magnetism in MgO
The electronic structure of the neutral and singly charged Mg vacancy in MgO
is investigated using density functional theory. For both defects, semilocal
exchange correlation functionals such as the local spin density approximation
incorrectly predict a delocalized degenerate ground state. In contrast
functionals that take strong correlation effects into account predict a
localized solution, in agreement with spin resonance experiments. Our results,
obtained with the HSE hybrid, atomic self-interaction corrected and LDA+U
functionals, provide a number of constraints to the possibility of
ferromagnetism in hole doped MgO
Ab initio study of electron transport in dry poly(G)-poly(C) A-DNA strands
The bias-dependent transport properties of short poly(G)-poly(C) A-DNA
strands attached to Au electrodes are investigated with first principles
electronic transport methods. By using the non- equilibrium Green's function
approach combined with self-interaction corrected density functional theory, we
calculate the fully self-consistent coherent I-V curve of various double-strand
polymeric DNA fragments. We show that electronic wave-function localization,
induced either by the native electrical dipole and/or by the electrostatic
disorder originating from the first few water solvation layers, drastically
suppresses the magnitude of the elastic conductance of A-DNA oligonucleotides.
We then argue that electron transport through DNA is the result of
sequence-specific short-range tunneling across a few bases combined with
general diffusive/inelastic processes.Comment: 15 pages, 13 figures, 1 tabl
Analysis of the Worst Case Space Complexity of a PR Quadtree
We demonstrate that a resolution-r PR quadtree containing n points has, in the worst case, at most nodes. This captures the fact that as n tends towards 4r, the number of nodes in a PR quadtree quickly approaches O(n). This is a more precise estimation of the worst case space requirement of a PR quadtree than has been attempted before
Room-temperature ferromagnetism in nanoparticles of superconducting materials
Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit
ferromagnetism at room temperature while the bulk YBCO, obtained by heating the
nanoparticles at high temperature (940 degree C), shows a linear magnetization
curve. Across the superconducting transition temperature, the magnetization
curve changes from that of a soft ferromagnet to a superconductor. Furthermore,
our experiments reveal that not only nanoparticles of metal oxides but also
metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit
room-temperature ferromagnetism.Comment: 11 pages, 6 figure
An Improved Bound for First-Fit on Posets Without Two Long Incomparable Chains
It is known that the First-Fit algorithm for partitioning a poset P into
chains uses relatively few chains when P does not have two incomparable chains
each of size k. In particular, if P has width w then Bosek, Krawczyk, and
Szczypka (SIAM J. Discrete Math., 23(4):1992--1999, 2010) proved an upper bound
of ckw^{2} on the number of chains used by First-Fit for some constant c, while
Joret and Milans (Order, 28(3):455--464, 2011) gave one of ck^{2}w. In this
paper we prove an upper bound of the form ckw. This is best possible up to the
value of c.Comment: v3: referees' comments incorporate
Magnetic interaction of Co ions near the {10\bar{1}0} ZnO surface
Co-doped ZnO is the prototypical dilute magnetic oxide showing many of the
characteristics of ferromagnetism. The microscopic origin of the long range
order however remains elusive, since the conventional mechanisms for the
magnetic interaction, such as super-exchange and double exchange, fail either
at the fundamental or at a quantitative level. Intriguingly, there is a growing
evidence that defects both in point-like or extended form play a fundamental
role in driving the magnetic order. Here we explore one of such possibilities
by performing {\it ab initio} density functional theory calculations for the
magnetic interaction of Co ions at or near a ZnO \{100\} surface. We
find that extended surface states can hybridize with the -levels of Co and
efficiently mediate the magnetic order, although such a mechanism is effective
only for ions placed in the first few atomic planes near the surface. We also
find that the magnetic anisotropy changes at the surface from an hard-axis
easy-plane to an easy axis, with an associated increase of its magnitude. We
then conclude that clusters with high densities of surfacial Co ions may
display blocking temperatures much higher than in the bulk
Social Media and the Adolescent and Young Adult (AYA) Patient with Cancer
Over 70,000 adolescent and young adults aged 15 to 39 years (AYA) are diagnosed with cancer each year in the US. The National Cancer Institute (NCI) has identified AYA cancer patients as a unique population. The most common cancers in this age group include tumors typically seen in pediatric patients such as acute lymphoblastic leukemia (ALL) and brain tumors, as well as cancers more typically seen in adult patients such as breast cancer and melanoma. In addition, some cancers have their highest incidence in AYA patients, such as Hodgkin Lymphoma, testicular cancer and bone tumors. AYA patients face additional unique issues due to their age, not just questions about treatment choices due to lack of data, but also questions about fertility, relationships, loss of autonomy, and interruptions in school/work with potentially significant financial complications. This age group also has very high rates of social media usage with up to 90% of adults aged 18 to 29 using social networking sites. In this review, we will describe the use of social media in AYAs with cancer and highlight some of the online resources for AYAs
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