576 research outputs found
Age-associated epigenetic modifications in human DNA increase its immunogenicity
Chronic
inflammation, increased reactivity to self-antigens and incidences of
cancer are hallmarks of aging. However, the underlying mechanisms are not
well understood. Age-associated alterations in the DNA either due to
oxidative damage, defects in DNA repair or epigenetic modifications such as
methylation that lead to mutations and changes in the expression of genes
are thought to be partially responsible. Here we report that epigenetic
modifications in aged DNA also increase its immunogenicity rendering it
more reactive to innate immune system cells such as the dendritic cells. We
observed increased upregulation of costimulatory molecules as well as
enhanced secretion of IFN-α from dendritic cells in response to
DNA from aged donors as compared to DNA from young donors when it was
delivered intracellularly via Lipofectamine. Investigations into the
mechanisms revealed that DNA from aged subjects is not degraded, neither is
it more damaged compared to DNA from young subjects. However, there is
significantly decreased global level of methylation suggesting that age-associated
hypomethylation of the DNA may be the cause of its increased
immunogenicity. Increased immunogenicity of self DNA may thus be another
mechanism that may contribute to the increase in age-associated chronic
inflammation, autoimmunity and cancer
Atomic-scale visualization of quasiparticle interference on a type-II Weyl semimetal surface
We combine quasiparticle interference simulation (theory) and atomic
resolution scanning tunneling spectro-microscopy (experiment) to visualize the
interference patterns on a type-II Weyl semimetal MoWTe for
the first time. Our simulation based on first-principles band topology
theoretically reveals the surface electron scattering behavior. We identify the
topological Fermi arc states and reveal the scattering properties of the
surface states in MoWTe. In addition, our result reveals
an experimental signature of the topology via the interconnectivity of bulk and
surface states, which is essential for understanding the unusual nature of this
material.Comment: To appear in Phys. Rev. Let
Ultraquantum magnetoresistance in Kramers Weyl semimetal candidate -Ag2Se
The topological semimetal -Ag2Se features a Kramers Weyl node at the
origin in momentum space and a quadruplet of spinless Weyl nodes, which are
annihilated by spin-orbit coupling. We show that single crystalline
-Ag2Se manifests giant Shubnikov-de Haas oscillations in the
longitudinal magnetoresistance which stem from a small electron pocket that can
be driven beyond the quantum limit by a field less than 9 T. This small
electron pocket is a remainder of the spin-orbit annihilatedWeyl nodes and thus
encloses a Berry-phase structure. Moreover, we observed a negative longitudinal
magnetoresistance when the magnetic field is beyond the quantum limit. Our
experimental findings are complemented by thorough theoretical band structure
analyses of this Kramers Weyl semimetal candidate, including first-principle
calculations and an effective k*p model.Comment: A new version based on arXiv:1502.0232
Mirror protected Dirac fermions on a Weyl semimetal NbP surface
The first Weyl semimetal was recently discovered in the NbP class of
compounds. Although the topology of these novel materials has been identified,
the surface properties are not yet fully understood. By means of scanning
tunneling spectroscopy, we find that NbPs (001) surface hosts a pair of Dirac
cones protected by mirror symmetry. Through our high resolution spectroscopic
measurements, we resolve the quantum interference patterns arising from these
novel Dirac fermions, and reveal their electronic structure, including the
linear dispersions. Our data, in agreement with our theoretical calculations,
uncover further interesting features of the Weyl semimetal NbPs already exotic
surface. Moreover, we discuss the similarities and distinctions between the
Dirac fermions here and those in topological crystalline insulators in terms of
symmetry protection and topology
Unconventional transformation of spin Dirac phase across a topological quantum phase transition
The topology of a topological material can be encoded in its surface states.
These surface states can only be removed by a bulk topological quantum phase
transition into a trivial phase. Here we use photoemission spectroscopy to
image the formation of protected surface states in a topological insulator as
we chemically tune the system through a topological transition. Surprisingly,
we discover an exotic spin-momentum locked, gapped surface state in the trivial
phase that shares many important properties with the actual topological surface
state in anticipation of the change of topology. Using a spin-resolved
measurement, we show that apart from a surface band-gap these states develop
spin textures similar to the topological surface states well-before the
transition. Our results offer a general paradigm for understanding how surface
states in topological phases arise and are suggestive for future realizing Weyl
arcs, condensed matter supersymmetry and other fascinating phenomena in the
vicinity of topological quantum criticality.Comment: 20 pages, 5 Figures, Related papers at
http://physics.princeton.edu/zahidhasangroup/index.html, Accepted for
publication in Nature Commun.(2015
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