3,544 research outputs found
Charge instabilities and topological phases in the extended Hubbard model on the honeycomb lattice with enlarged unit cell
We study spontaneous symmetry breaking in a system of spinless fermions in
the Honeycomb lattice paying special emphasis to the role of an enlarged unit
cell on time reversal symmetry broken phases. We use a tight binding model with
nearest neighbor hopping t and Hubbard interaction V1 and V2 and extract the
phase diagram as a function of electron density and interaction within a mean
field variational approach. The analysis completes the previous work done in
Phys. Rev. Lett. 107, 106402 (2011) where phases with non--trivial topological
properties were found with only a nearest neighbor interaction V1 in the
absence of charge decouplings. We see that the topological phases are
suppressed by the presence of metallic charge density fluctuations. The
addition of next to nearest neighbor interaction V2 restores the topological
non-trivial phases
Topological Fermi liquids from Coulomb interactions in the doped Honeycomb lattice
We get an anomalous Hall metallic state in the Honeycomb lattice with nearest
neighbors only arising as a spontaneously broken symmetry state from a local
nearest neighbor Coulomb interaction V . The key ingredient is to enlarge the
unit cell to host six atoms that permits Kekul\'e distortions and supports
self-consistent currents creating non trivial magnetic configurations with
total zero flux. We find within a variational mean field approach a metallic
phase with broken time reversal symmetry (T) very close in parameter space to a
Pomeranchuk instability. Within the T broken region the predominant
configuration is an anomalous Hall phase with non zero Hall conductivity, a
realization of a topological Fermi liquid. A T broken phase with zero Hall
conductivity is stable in a small region of the parameter space for lower
values of V
Microcontrolled and networked based mobile robot electronic system
Robotics is increasingly on the agenda to perform both complex tasks in uninviting environment and also for routine actions of our day-to-day. The challenges and demands are constant. The back-office work is demanding, highly skilled and requires a lot of dedication, research and tenacity. Clearly and concisely, this work illustrates the foundations for a machine, the steps to get there, a prospect of easy and reliable use. Enjoy this auspicious and inspiring reading
Continuous-flow precipitation of hydroxyapatite at 37 °C in a meso oscillatory flow reactor
Continuous-flow precipitation of hydroxyapatite (HAp) was investigated in a meso oscillatory flow reactor (meso-
OFR) and in a scaled-up meso-OFR, obtained by associating in series eight vertical meso-ORFs. Experiments were carried out
under near-physiological conditions of temperature and pH, using fixed frequency ( f = 0.83 Hz) and amplitude (x0 = 4.5 mm),
and varying the residence time from 0.4 to 6.7 min. It has been shown that the mean particle size and the aggregation degree of
the prepared HAp particles decrease with decreasing residence time. HAp nanoparticles with a mean size (d50) of 77 nm, narrow
size distribution, and uniform morphology were obtained at the lowest residence times, Ï„ = 0.4 and 3.3 min in the meso-OFR and
the scaled-up meso-OFR, respectively. These results show the capability of the meso-OFR and the scaled-up meso-OFR for
continuous production of uniform HAp nanoparticles, while also confirming the possibility of OFR scale-up by in series
association of individual OFRs
Restoring observed classical behavior of the carbon nanotube field emission enhancement factor from the electronic structure
Experimental Fowler-Nordheim plots taken from orthodoxly behaving carbon
nanotube (CNT) field electron emitters are known to be linear. This shows that,
for such emitters, there exists a characteristic field enhancement factor (FEF)
that is constant for a range of applied voltages and applied macroscopic fields
. A constant FEF of this kind can be evaluated for classical CNT
emitter models by finite-element and other methods, but (apparently contrary to
experiment) several past quantum-mechanical (QM) CNT calculations find
FEF-values that vary with . A common feature of most such
calculations is that they focus only on deriving the CNT real-charge
distributions. Here we report on calculations that use density functional
theory (DFT) to derive real-charge distributions, and then use these to
generate the related induced-charge distributions and related fields and FEFs.
We have analysed three carbon nanostructures involving CNT-like nanoprotrusions
of various lengths, and have also simulated geometrically equivalent classical
emitter models, using finite-element methods. We find that when the
DFT-generated local induced FEFs (LIFEFs) are used, the resulting values are
effectively independent of macroscopic field, and behave in the same
qualitative manner as the classical FEF-values. Further, there is fair to good
quantitative agreement between a characteristic FEF determined classically and
the equivalent characteristic LIFEF generated via DFT approaches. Although many
issues of detail remain to be explored, this appears to be a significant step
forwards in linking classical and QM theories of CNT electrostatics. It also
shows clearly that, for ideal CNTs, the known experimental constancy of the FEF
value for a range of macroscopic fields can also be found in appropriately
developed QM theory.Comment: A slightly revised version has been published - citation below -
under a title different from that originally used. The new title is:
"Restoring observed classical behavior of the carbon nanotube field emission
enhancement factor from the electronic structure
Mobile robot electronic system with a network and micro-controller based interface
This paper describes the electronic system used to a mobile tank-robot and the network and micro-controlled based interface proceeding to drive it
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