2,001 research outputs found
Helical modes in carbon nanotubes generated by strong electric fields
Helical modes, conducting opposite spins in opposite directions, are shown to
exist in metallic armchair nanotubes in an all-electric setup. This is a
consequence of the interplay between spin-orbit interaction and strong electric
fields. The helical regime can also be obtained in chiral metallic nanotubes by
applying an additional magnetic field. In particular, it is possible to obtain
helical modes at one of the two Dirac points only, while the other one remains
gapped. Starting from a tight-binding model we derive the effective low-energy
Hamiltonian and the resulting spectrum
Hyperplane arrangements of Torelli type
We give a necessary and sufficient condition in order for a hyperplane
arrangement to be of Torelli type, namely that it is recovered as the set of
unstable hyperplanes of its Dolgachev sheaf of logarithmic differentials.
Decompositions and semistability of non-Torelli arrangements are investigated.Comment: 2 Figue
Insertions Yielding Equivalent Double Occurrence Words
A double occurrence word (DOW) is a word in which every symbol appears
exactly twice; two DOWs are equivalent if one is a symbol-to-symbol image of
the other. We consider the so called repeat pattern () and the
return pattern (), with gaps allowed between the 's.
These patterns generalize square and palindromic factors of DOWs, respectively.
We introduce a notion of inserting repeat/return words into DOWs and study how
two distinct insertions into the same word can produce equivalent DOWs. Given a
DOW , we characterize the structure of which allows two distinct
insertions to yield equivalent DOWs. This characterization depends on the
locations of the insertions and on the length of the inserted repeat/return
words and implies that when one inserted word is a repeat word and the other is
a return word, then both words must be trivial (i.e., have only one symbol).
The characterization also introduces a method to generate families of words
recursively
The Stripe 82 Massive Galaxy Project III: A Lack of Growth Among Massive Galaxies
The average stellar mass (Mstar) of high-mass galaxies (Mstar > 3e11 Msun) is
expected to grow by ~30% since z~1, largely through ongoing mergers that are
also invoked to explain the observed increase in galaxy sizes. Direct evidence
for the corresponding growth in stellar mass has been elusive, however, in part
because the volumes sampled by previous redshift surveys have been too small to
yield reliable statistics. In this work, we make use of the Stripe 82 Massive
Galaxy Catalog to build a mass-limited sample of 41,770 galaxies (Mstar >
1.6e11) with optical to near-IR photometry and a large fraction (>55%) of
spectroscopic redshifts. Our sample spans 139 square degrees, significantly
larger than most previous efforts. After accounting for a number of potential
systematic errors, including the effects of Mstar scatter, we measure galaxy
stellar mass functions over 0.3 < z < 0.65 and detect no growth in the typical
Mstar of massive galaxies with an uncertainty of 9%. This confidence level is
dominated by uncertainties in the star formation history assumed for Mstar
estimates, although our inability to characterize low surface-brightness
outskirts may be the most important limitation of our study. Even among these
high-mass galaxies, we find evidence for differential evolution when splitting
the sample by recent star formation (SF) activity. While low-SF systems appear
to become completely passive, we find a mostly sub-dominant population of
galaxies with residual, but low rates of star formation (~1 Msun/yr) number
density does not evolve. Interestingly, these galaxies become more prominent at
higher Mstar, representing ~10% of all galaxies at Mstar ~ 1e12 Msun and
perhaps dominating at even larger masses.Comment: Accepted in Ap
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