9,621 research outputs found
Super-pixel cloud detection using Hierarchical Fusion CNN
Cloud detection plays a very important role in the process of remote sensing
images. This paper designs a super-pixel level cloud detection method based on
convolutional neural network (CNN) and deep forest. Firstly, remote sensing
images are segmented into super-pixels through the combination of SLIC and
SEEDS. Structured forests is carried out to compute edge probability of each
pixel, based on which super-pixels are segmented more precisely. Segmented
super-pixels compose a super-pixel level remote sensing database. Though cloud
detection is essentially a binary classification problem, our database is
labeled into four categories: thick cloud, cirrus cloud, building and other
culture, to improve the generalization ability of our proposed models.
Secondly, super-pixel level database is used to train our cloud detection
models based on CNN and deep forest. Considering super-pixel level remote
sensing images contain less semantic information compared with general object
classification database, we propose a Hierarchical Fusion CNN (HFCNN). It takes
full advantage of low-level features like color and texture information and is
more applicable to cloud detection task. In test phase, every super-pixel in
remote sensing images is classified by our proposed models and then combined to
recover final binary mask by our proposed distance metric, which is used to
determine ambiguous super-pixels. Experimental results show that, compared with
conventional methods, HFCNN can achieve better precision and recall
Anderson localization in the Non-Hermitian Aubry-Andr\'e-Harper model with physical gain and loss
We investigate the Anderson localization in non-Hermitian
Aubry-Andr\'e-Harper (AAH) models with imaginary potentials added to lattice
sites to represent the physical gain and loss during the interacting processes
between the system and environment. By checking the mean inverse participation
ratio (MIPR) of the system, we find that different configurations of physical
gain and loss have very different impacts on the localization phase transition
in the system. In the case with balanced physical gain and loss added in an
alternate way to the lattice sites, the critical region (in the case with
p-wave superconducting pairing) and the critical value (both in the situations
with and without p-wave pairing) for the Anderson localization phase transition
will be significantly reduced, which implies an enhancement of the localization
process. However, if the system is divided into two parts with one of them
coupled to physical gain and the other coupled to the corresponding physical
loss, the transition process will be impacted only in a very mild way. Besides,
we also discuss the situations with imbalanced physical gain and loss and find
that the existence of random imaginary potentials in the system will also
affect the localization process while constant imaginary potentials will not.Comment: 6 pages, 4 figure
Generalized Aubry-Andr\'e-Harper model with p-wave superconducting pairing
We investigate a generalized Aubry-Andr\'e-Harper (AAH) model with p-wave
superconducting pairing. Both the hopping amplitudes between the nearest
neighboring lattice sites and the on-site potentials in this system are
modulated by a cosine function with a periodicity of . In the
incommensurate case [], due to the modulations on the
hopping amplitudes, the critical region of this quasiperiodic system is
significantly reduced and the system becomes more easily to be turned from
extended states to localized states. In the commensurate case (),
we find that this model shows three different phases when we tune the system
parameters: Su-Schrieffer-Heeger (SSH)-like trivial, SSH-like topological, and
Kitaev-like topological phases. The phase diagrams and the topological quantum
numbers for these phases are presented in this work. This generalized AAH model
combined with superconducting pairing provides us with a useful testfield for
studying the phase transitions from extended states to Anderson localized
states and the transitions between different topological phases.Comment: 9 pages, 5 figure
A lossless metamaterial with tunable permittivity and its application as a compact phase shifter
In this Letter, we propose a new type of lossless metamaterial whose
effective permittivity is tunable from negative to positive values. Its optical
response is studied analytically and numerically. We further demonstrate that
this tunable metamaterial can significantly modulate the phase of an incident
pulse with negligible reflection loss, functioning as an efficient phase
shifter.Comment: 9 pages, 2 figure
Quench dynamics in the Aubry-Andr\'e-Harper model with \textit{p}-wave superconductivity
The Anderson localization phase transition in the Aubry-Andr\'e-Harper (AAH)
model with \textit{p}-wave superconducting (SC) pairing is numerically
investigated by suddenly changing the on-site potential from zero to various
finite values which fall into the extended, critical and localized phase
regimes shown in this model. The time evolutions of entanglement entropy (EE),
mean width of wave packets and Loschmidt echo of the system exhibit distinct
but consistent dynamical signatures in those three phases. Specifically, the EE
grows as a power function of time with the exponent of which varies in the
extended phase but keeps almost unchanged in the critical phase for different
quench parameters. However, if the system is in the localized phase after a
quench, the EE grows much slower and will soon get saturated. The
time-dependent width of wave packets in the system shows similar behaviors as
the EE. In addition, from the perspective of dynamical phase transition, we
find that the Loschmidt echo oscillates and always keeps finite when the system
is quenched in the extended phase. In contrast, in the critical or localized
phase, the echo will reach to zero at some time intervals or will decay almost
to zero after a long-time evolution. The universal features of these quantities
in the critical phase of the system with various SC pairing amplitudes are also
observed.Comment: 9 pages, 6 figure
Topological Phases in Non-Hermitian Aubry-Andr\'e-Harper Models
Topological phases have recently witnessed a rapid progress in non-Hermitian
systems. Here we study a one-dimensional non-Hermitian Aubry-Andr\'e-Harper
model with imaginary periodic or quasiperiodic modulations. We demonstrate that
the non-Hermitian off-diagonal AAH models can host zero-energy modes at the
edges. In contrast to the Hermitian case, the zero-energy mode can be localized
only at one edge. Such a topological phase corresponds to the existence of a
quarter winding number defined by eigenenergy in momentum space. We further
find the coexistence of a zero-energy mode located only at one edge and
topological nonzero energy edge modes characterized by a generalized Bott
index. In the incommensurate case, a topological non-Hermitian quasicrystal is
predicted where all bulk states and two topological edge states are localized
at one edge. Such topological edge modes are protected by the generalized Bott
index. Finally, we propose an experimental scheme to realize these
non-Hermitian models in electric circuits. Our findings add a new direction for
exploring topological properties in Aubry-Andr\'e-Harper models.Comment: 10 pages, 3 figures, including Supplementar
Transport through a quantum dot coupled to two Majorana bound states
We investigate electron transport inside a ring system composed of a quantum
dot (QD) coupled to two Majorana bound states confined at the ends of a
one-dimensional topological superconductor nanowire. By tuning the magnetic
flux threading through the ring, the model system we consider can be switched
into states with or without zero-energy modes when the nanowire is in its
topological phase. We find that the Fano profile in the conductance spectrum
due to the interference between bound and continuum states exhibits markedly
different features for these two different situations, which consequently can
be used to detect the Majorana zero-energy mode. Most interestingly, as a
periodic function of magnetic flux, the conductance shows periodicity
when the two Majorana bound states are nonoverlapping (as in an infinitely long
nanowire) but displays periodicity when the overlapping becomes nonzero
(as in a finite length nanowire). We map the model system into a QD--Kitaev
ring in the Majorana fermion representation and affirm these different
characteristics by checking the energy spectrum.Comment: 8 pages, 8 figure
16-qubit IBM universal quantum computer can be fully entangled
Entanglement is an important evidence that a quantum device can potentially
solve problems intractable for classical computers. In this paper, we prepare
connected graph states involving 8 to 16 qubits on ibmqx5, a 16-qubit
superconducting quantum processor accessible via IBM cloud,using low-depth
circuits. We demonstrate that the prepared state is fully entangled, i.e. the
state is inseparable with respect to any fixed partition.Comment: 23 pages, 9 figures, 2 tables; The full entanglement is clarified; a
new section is added on the localized entanglement with distance 3 and 4,
accepted versio
Learning Personalized End-to-End Goal-Oriented Dialog
Most existing works on dialog systems only consider conversation content
while neglecting the personality of the user the bot is interacting with, which
begets several unsolved issues. In this paper, we present a personalized
end-to-end model in an attempt to leverage personalization in goal-oriented
dialogs. We first introduce a Profile Model which encodes user profiles into
distributed embeddings and refers to conversation history from other similar
users. Then a Preference Model captures user preferences over knowledge base
entities to handle the ambiguity in user requests. The two models are combined
into the Personalized MemN2N. Experiments show that the proposed model achieves
qualitative performance improvements over state-of-the-art methods. As for
human evaluation, it also outperforms other approaches in terms of task
completion rate and user satisfaction.Comment: Accepted by AAAI 201
An Auto-Encoder Matching Model for Learning Utterance-Level Semantic Dependency in Dialogue Generation
Generating semantically coherent responses is still a major challenge in
dialogue generation. Different from conventional text generation tasks, the
mapping between inputs and responses in conversations is more complicated,
which highly demands the understanding of utterance-level semantic dependency,
a relation between the whole meanings of inputs and outputs. To address this
problem, we propose an Auto-Encoder Matching (AEM) model to learn such
dependency. The model contains two auto-encoders and one mapping module. The
auto-encoders learn the semantic representations of inputs and responses, and
the mapping module learns to connect the utterance-level representations.
Experimental results from automatic and human evaluations demonstrate that our
model is capable of generating responses of high coherence and fluency compared
to baseline models. The code is available at https://github.com/lancopku/AMMComment: Accepted by EMNLP 201
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