4,965 research outputs found
Design And Analysis Of Reconfigurable Sensing Antennas For Wireless Sensing Applications
Reconfiguration sensing antenna (rsa) is a novel antenna concept, which not only can transmit or receive radio waves but also can sense the surrounding environment. The environment sensing is realized by reconfiguring the antenna\u27s characteristics, such as resonant frequency, and radar cross section (rcs). The rsas possess the advantages of passive and low cost, which make them suitable for the large-scale wireless sensing networks (wsns) deployment. In this dissertation, the rsas concept is demonstrated, and two sensing mechanisms performed in the rsas are investigated. In order to verify these sensing mechanisms, four rsas are designed, analyzed, and measured. All the rsa designs in this dissertation are temperature monitoring rsas, and they realize the temperature sensing by reconfiguring the antenna resonant frequency. About the two sensing mechanisms, one utilizes the electrical properties of materials, and the other utilizes thermal properties of the materials. For each sensing mechanism, there are two rsa designs using different sensing materials. As sensing antennas, sensitivity is a crucial factor in the rsa designs. Thus, a sensitivity evaluation method is also defined in this dissertation. There are three factors used to evaluate the rsa performance, which are realized gain, and realized gain bandwidth. For the sensing mechanism using electrical properties of materials, water and high density polyethylene-ba0.3sr0.7tio3 (hdpe-bst) are investigated and selected as the sensing materials. Patch antennas are properly designed to easily implement these sensing materials as their substrate. Simulation and measurement results show that these two designs provide 4mhz/10â°c and 8mhz/10â°c frequency shift with temperature, respectively. Their realized gain is -3.2db with 4.33
Electronic Highways in Bilayer Graphene
Bilayer graphene with an interlayer potential difference has an energy gap
and, when the potential difference varies spatially, topologically protected
one-dimensional states localized along the difference's zero-lines. When
disorder is absent, electronic travel directions along zero-line trajectories
are fixed by valley Hall properties. Using the Landauer-B\"uttiker formula and
the non-equilibrium Green's function technique we demonstrate numerically that
collisions between electrons traveling in opposite directions, due to either
disorder or changes in path direction, are strongly suppressed. We find that
extremely long mean free paths of the order of hundreds of microns can be
expected in relatively clean samples. This finding suggests the possibility of
designing low power nanoscale electronic devices in which transport paths are
controlled by gates which alter the inter-layer potential landscape.Comment: 8 pages, 5 figure
Microscopic theory of quantum anomalous Hall effect in graphene
We present a microscopic theory to give a physical picture of the formation
of quantum anomalous Hall (QAH) effect in graphene due to a joint effect of
Rashba spin-orbit coupling and exchange field . Based on a
continuum model at valley or , we show that there exist two distinct
physical origins of QAH effect at two different limits. For ,
the quantization of Hall conductance in the absence of Landau-level
quantization can be regarded as a summation of the topological charges carried
by Skyrmions from real spin textures and Merons from \emph{AB} sublattice
pseudo-spin textures; while for , the four-band low-energy
model Hamiltonian is reduced to a two-band extended Haldane's model, giving
rise to a nonzero Chern number at either or . In the
presence of staggered \emph{AB} sublattice potential , a topological phase
transition occurs at from a QAH phase to a quantum valley-Hall phase. We
further find that the band gap responses at and are different when
, , and are simultaneously considered. We also show that the
QAH phase is robust against weak intrinsic spin-orbit coupling ,
and it transitions a trivial phase when
. Moreover, we use a tight-binding
model to reproduce the ab-initio method obtained band structures through doping
magnetic atoms on and supercells of graphene, and explain
the physical mechanisms of opening a nontrivial bulk gap to realize the QAH
effect in different supercells of graphene.Comment: 10pages, ten figure
Assigning personality/identity to a chatting machine for coherent conversation generation
Endowing a chatbot with personality or an identity is quite challenging but
critical to deliver more realistic and natural conversations. In this paper, we
address the issue of generating responses that are coherent to a pre-specified
agent profile. We design a model consisting of three modules: a profile
detector to decide whether a post should be responded using the profile and
which key should be addressed, a bidirectional decoder to generate responses
forward and backward starting from a selected profile value, and a position
detector that predicts a word position from which decoding should start given a
selected profile value. We show that general conversation data from social
media can be used to generate profile-coherent responses. Manual and automatic
evaluation shows that our model can deliver more coherent, natural, and
diversified responses.Comment: an error on author informatio
Stabilizing topological phases in graphene via random adsorption
We study the possibility of realizing topological phases in graphene with
randomly distributed adsorbates. When graphene is subjected to periodically
distributed adatoms, the enhanced spin-orbit couplings can result in various
topological phases. However, at certain adatom coverages, the intervalley
scattering renders the system a trivial insulator. By employing a finite-size
scaling approach and Landauer-B\"{u}ttiker formula, we show that the
randomization of adatom distribution greatly weakens the intervalley
scattering, but plays a negligible role in spin-orbit couplings. Consequently,
such a randomization turns graphene from a trivial insulator into a topological
state.Comment: 5 pages and 3 figure
Unbalanced edge modes and topological phase transition in gated trilayer graphene
Gapless edge modes hosted by chirally-stacked trilayer graphene display
unique features when a bulk gap is opened by applying an interlayer potential
difference. We show that trilayer graphene with half-integer valley Hall
conductivity leads to unbalanced edge modes at opposite zigzag boundaries,
resulting in a natural valley current polarizer. This unusual characteristic is
preserved in the presence of Rashba spin-orbit coupling that turns a gated
trilayer graphene into a topological insulator with an odd number of
helical edge mode pairs.Comment: 5 pages, 4 figure
- …