1,696 research outputs found
Atomic step motion during the dewetting of ultra-thin films
We report on three key processes involving atomic step motion during the
dewetting of thin solid films: (i) the growth of an isolated island nucleated
far from a hole, (ii) the spreading of a monolayer rim, and (iii) the zipping
of a monolayer island along a straight dewetting front. Kinetic Monte Carlo
results are in good agreement with simple analytical models assuming
diffusion-limited dynamics.Comment: 7 pages, 5 figure
Exploring daily time-use patterns: ATUS-X data extractor and online diary visualization tool
Time-use data can often be perceived as inaccessible by non-specialists due to their unique format. This article introduces the ATUS-X diary visualization tool that aims to address the accessibility issue and expand the user base of time-use data by providing users with opportunity to quickly visualize their own subsamples of the American Time Use Survey Data Extractor (ATUS-X). Complementing the ATUS-X, the online tool provides an easy point-and-click interface, making data exploration readily accessible in a visual form. The tool can benefit a wider academic audience, policy-makers, non-academic researchers, and journalists by removing accessibility barriers to time use diaries
Multi-graviton theory, a latticized dimension, and the cosmological constant
Beginning with the Pauli-Fierz theory, we construct a model for
multi-graviton theory. Couplings between gravitons belonging to
nearest-neighbor ``theory spaces'' lead to a discrete mass spectrum. Our model
coincides with the Kaluza-Klein theory whose fifth dimension is latticized.
We evaluate one-loop vacuum energy in models with a circular latticized extra
dimension as well as with compact continuous dimensions. We find that the
vacuum energy can take a positive value, if the dimension of the continuous
space time is . Moreover, since the amount of the vacuum energy can
be an arbitrary small value according to the choice of parameters in the model,
our models is useful to explain the small positive dark energy in the present
universe.Comment: 10 pages, No figure. Needs REVTeX4. citations are corrected and minor
correction
Electronic and Magnetic Properties of Partially-Open Carbon Nanotubes
On the basis of the spin-polarized density functional theory calculations, we
demonstrate that partially-open carbon nanotubes (CNTs) observed in recent
experiments have rich electronic and magnetic properties which depend on the
degree of the opening. A partially-open armchair CNT is converted from a metal
to a semiconductor, and then to a spin-polarized semiconductor by increasing
the length of the opening on the wall. Spin-polarized states become
increasingly more stable than nonmagnetic states as the length of the opening
is further increased. In addition, external electric fields or chemical
modifications are usable to control the electronic and magnetic properties of
the system. We show that half-metallicity may be achieved and the spin current
may be controlled by external electric fields or by asymmetric
functionalization of the edges of the opening. Our findings suggest that
partially-open CNTs may offer unique opportunities for the future development
of nanoscale electronics and spintronics.Comment: 6 figures, to appear in J. Am. Chem. So
Ramond-Ramond Cohomology and O(D,D) T-duality
In the name of supersymmetric double field theory, superstring effective
actions can be reformulated into simple forms. They feature a pair of vielbeins
corresponding to the same spacetime metric, and hence enjoy double local
Lorentz symmetries. In a manifestly covariant manner --with regard to O(D,D)
T-duality, diffeomorphism, B-field gauge symmetry and the pair of local Lorentz
symmetries-- we incorporate R-R potentials into double field theory. We take
them as a single object which is in a bi-fundamental spinorial representation
of the double Lorentz groups. We identify cohomological structure relevant to
the field strength. A priori, the R-R sector as well as all the fermions are
O(D,D) singlet. Yet, gauge fixing the two vielbeins equal to each other
modifies the O(D,D) transformation rule to call for a compensating local
Lorentz rotation, such that the R-R potential may turn into an O(D,D) spinor
and T-duality can flip the chirality exchanging type IIA and IIB
supergravities.Comment: 1+37 pages, no figure; Structure reorganized, References added, To
appear in JHEP. cf. Gong Show of Strings 2012
(http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/Talks/Thursday/Gongshow/Lee.pdf
"Narrow" Graphene Nanoribbons Made Easier by Partial Hydrogenation
It is a challenge to synthesize graphene nanoribbons (GNRs) with narrow
widths and smooth edges in large scale. Our first principles study on the
hydrogenation of GNRs shows that the hydrogenation starts from the edges of
GNRs and proceeds gradually toward the middle of the GNRs so as to maximize the
number of carbon-carbon - bonds. Furthermore, the partially
hydrogenated wide GNRs have similar electronic and magnetic properties as those
of narrow GNRs. Therefore, it is not necessary to directly produce narrow GNRs
for realistic applications because partial hydrogenation could make wide GNRs
"narrower"
Photo- and Electro-Disintegration of 3He at Threshold and pd Radiative Capture
The present work reports results for: pd radiative capture observables
measured at center-of-mass (c.m.) energies in the range 0--100 keV and at 2 MeV
by the TUNL and Wisconsin groups, respectively; contributions to the
Gerasimov-Drell-Hearn (GDH) integral in 3He from the two- up to the three-body
breakup thresholds, compared to experimental determinations by the TUNL group
in this threshold region; longitudinal, transverse, and interference response
functions measured in inclusive polarized electron scattering off polarized 3He
at excitation energies below the threshold for breakup into ppn, compared to
unpolarized longitudinal and transverse data from the Saskatoon group. The
calculations are based on a realistic Hamiltonian with two- and three-nucleon
interactions and a realistic current operator, including one- and two-body
components. The theoretical predictions obtained by including only one-body
currents are in violent disagreement with data. These differences between
theory and experiment are, to a large extent, removed when two-body currents
are taken into account, although some rather large discrepancies remain in the
c.m. energy range 0--100 keV, particularly for the pd differential cross
section and tensor analyzing power at small angles, and contributions to the
GDH integral. A rather detailed analysis indicates that these discrepancies
have, in large part, a common origin, and can be traced back to an excess
strength obtained in the theoretical calculation of the E1 reduced matrix
element associated with the pd channel having L,S,J=1,1/2,3/2. It is suggested
that this lack of E1 strength observed experimentally might have implications
for the nuclear interaction at very low energies. Finally, the validity of the
long-wavelength approximation for electric dipole transitions is discussed.Comment: 47 pages RevTex file, 10 PostScript figures, submitted to Phys. Rev.
Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions
We investigate the optical properties of edge-functionalized graphene
nanosystems, focusing on the formation of junctions and charge transfer
excitons. We consider a class of graphene structures which combine the main
electronic features of graphene with the wide tunability of large polycyclic
aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we
show that, upon convenient choice of functional groups, low energy excitations
with remarkable charge transfer character and large oscillator strength are
obtained. These properties can be further modulated through an appropriate
width variation, thus spanning a wide range in the low-energy region of the
UV-Vis spectra. Our results are relevant in view of designing all-graphene
optoelectronic nanodevices, which take advantage of the versatility of
molecular functionalization, together with the stability and the electronic
properties of graphene nanostructures.Comment: J. Phys. Chem. Lett. (2011), in pres
Towards Graphene Nanoribbon-based Electronics
The successful fabrication of single layer graphene has greatly stimulated
the progress of the research on graphene. In this article, focusing on the
basic electronic and transport properties of graphene nanoribbons (GNRs), we
review the recent progress of experimental fabrication of GNRs, and the
theoretical and experimental investigations of physical properties and device
applications of GNRs. We also briefly discuss the research efforts on the spin
polarization of GNRs in relation to the edge states.Comment: 9pages,10figure
Mechanisms controlling anaemia in Trypanosoma congolense infected mice.
Trypanosoma congolense are extracellular protozoan parasites of the blood stream of artiodactyls and are one of the main constraints on cattle production in Africa. In cattle, anaemia is the key feature of disease and persists after parasitaemia has declined to low or undetectable levels, but treatment to clear the parasites usually resolves the anaemia. The progress of anaemia after Trypanosoma congolense infection was followed in three mouse strains. Anaemia developed rapidly in all three strains until the peak of the first wave of parasitaemia. This was followed by a second phase, characterized by slower progress to severe anaemia in C57BL/6, by slow recovery in surviving A/J and a rapid recovery in BALB/c. There was no association between parasitaemia and severity of anaemia. Furthermore, functional T lymphocytes are not required for the induction of anaemia, since suppression of T cell activity with Cyclosporin A had neither an effect on the course of infection nor on anaemia. Expression of genes involved in erythropoiesis and iron metabolism was followed in spleen, liver and kidney tissues in the three strains of mice using microarrays. There was no evidence for a response to erythropoietin, consistent with anaemia of chronic disease, which is erythropoietin insensitive. However, the expression of transcription factors and genes involved in erythropoiesis and haemolysis did correlate with the expression of the inflammatory cytokines Il6 and Ifng. The innate immune response appears to be the major contributor to the inflammation associated with anaemia since suppression of T cells with CsA had no observable effect. Several transcription factors regulating haematopoiesis, Tal1, Gata1, Zfpm1 and Klf1 were expressed at consistently lower levels in C57BL/6 mice suggesting that these mice have a lower haematopoietic capacity and therefore less ability to recover from haemolysis induced anaemia after infection
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