24,652 research outputs found
The Classification of Dimensional Reduced Hopf Insulators
The Hopf insulators are characterized by a topological invariant called Hopf
index which classifies maps from three-sphere to two-sphere, instead of a Chern
number or a Chern parity. In contrast to topological insulator, the Hopf
insulator is not protected by any kind of symmetry. By dimensional reduction,
we argue that there exists a new type of index for 2D
Hamiltonian with vanishing Chern number. Specific model Hamiltonian with this
nontrivial index is constructed. We also numerically calculate
the topological protected edge modes of this dimensional reduced Hopf insulator
and show that they are consistent with the classification.Comment: 6 pages, 3 figure
CamSwarm: Instantaneous Smartphone Camera Arrays for Collaborative Photography
Camera arrays (CamArrays) are widely used in commercial filming projects for
achieving special visual effects such as bullet time effect, but are very
expensive to set up. We propose CamSwarm, a low-cost and lightweight
alternative to professional CamArrays for consumer applications. It allows the
construction of a collaborative photography platform from multiple mobile
devices anywhere and anytime, enabling new capturing and editing experiences
that a single camera cannot provide. Our system allows easy team formation;
uses real-time visualization and feedback to guide camera positioning; provides
a mechanism for synchronized capturing; and finally allows the user to
efficiently browse and edit the captured imagery. Our user study suggests that
CamSwarm is easy to use; the provided real-time guidance is helpful; and the
full system achieves high quality results promising for non-professional use.
A demo video is provided at https://www.youtube.com/watch?v=LgkHcvcyTTM
PanoSwarm: Collaborative and Synchronized Multi-Device Panoramic Photography
Taking a picture has been traditionally a one-persons task. In this paper we
present a novel system that allows multiple mobile devices to work
collaboratively in a synchronized fashion to capture a panorama of a highly
dynamic scene, creating an entirely new photography experience that encourages
social interactions and teamwork. Our system contains two components: a client
app that runs on all participating devices, and a server program that monitors
and communicates with each device. In a capturing session, the server collects
in realtime the viewfinder images of all devices and stitches them on-the-fly
to create a panorama preview, which is then streamed to all devices as visual
guidance. The system also allows one camera to be the host and to send direct
visual instructions to others to guide camera adjustment. When ready, all
devices take pictures at the same time for panorama stitching. Our preliminary
study suggests that the proposed system can help users capture high quality
panoramas with an enjoyable teamwork experience.
A demo video of the system in action is provided at
http://youtu.be/PwQ6k_ZEQSs
An Optimal LiDAR Configuration Approach for Self-Driving Cars
LiDARs plays an important role in self-driving cars and its configuration
such as the location placement for each LiDAR can influence object detection
performance. This paper aims to investigate an optimal configuration that
maximizes the utility of on-hand LiDARs. First, a perception model of LiDAR is
built based on its physical attributes. Then a generalized optimization model
is developed to find the optimal configuration, including the pitch angle, roll
angle, and position of LiDARs. In order to fix the optimization issue with
off-the-shelf solvers, we proposed a lattice-based approach by segmenting the
LiDAR's range of interest into finite subspaces, thus turning the optimal
configuration into a nonlinear optimization problem. A cylinder-based method is
also proposed to approximate the objective function, thereby making the
nonlinear optimization problem solvable. A series of simulations are conducted
to validate our proposed method. This proposed approach to optimal LiDAR
configuration can provide a guideline to researchers to maximize the utility of
LiDARs.Comment: Conferenc
On the Relationship Between Coronal Magnetic Decay Index and CME Speed
Numerical simulations suggest that kink and torus instabilities are two
potential contributors to the initiation and prorogation of eruptive events. A
magnetic parameter named decay index (i.e., the coronal magnetic gradient of
the overlying fields above the eruptive flux ropes) could play an important
role in controlling kinematics of eruptions. Previous studies have identified a
threshold range of the decay index that distinguishes between eruptive and
confined configurations. Here we advance the study by investigating if there is
a clear correlation between the decay index and CME speed. 38 CMEs associated
with filament eruptions and/or two-ribbon flares are selected using the Halpha
data from the Global Halpha Network. The filaments and flare ribbons observed
in Halpha associated with the CMEs help to locate the magnetic polarity
inversion line, along which the decay index is calculated based on the
potential field extrapolation using MDI magnetograms as boundary conditions.
The speeds of CMEs are obtained from the LASCO C2 CME catalog available online.
We find that the mean decay index increases with CME speed for those CMEs with
a speed below 1000 km/s, and stays flat around 2.2 for the CMEs with higher
speeds. In addition, we present a case study of a partial filament eruption, in
which the decay indexes show different values above the erupted/non-erupted
part.Comment: ApJ, accepte
Service Provisioning and Profit Maximization in Network-assisted Adaptive HTTP Streaming
Adaptive HTTP streaming with centralized consideration of multiple streams
has gained increasing interest. It poses a special challenge that the interests
of both content provider and network operator need to be deliberately balanced.
More importantly, the adaptation strategy is required to be flexible enough to
be ported to various systems that work under different network environments,
QoE levels, and economic objectives. To address these challenges, we propose a
Markov Decision Process (MDP) based network-assisted adaptation framework,
wherein cost of buffering, significant playback variation, bandwidth management
and income of playback are jointly investigated. We then demonstrate its
promising service provisioning and maximal profit for a mobile network in which
fair or differentiated service is required.Comment: ICIP 2015 submissio
Reinforcement Learning for Learning Rate Control
Stochastic gradient descent (SGD), which updates the model parameters by
adding a local gradient times a learning rate at each step, is widely used in
model training of machine learning algorithms such as neural networks. It is
observed that the models trained by SGD are sensitive to learning rates and
good learning rates are problem specific. We propose an algorithm to
automatically learn learning rates using neural network based actor-critic
methods from deep reinforcement learning (RL).In particular, we train a policy
network called actor to decide the learning rate at each step during training,
and a value network called critic to give feedback about quality of the
decision (e.g., the goodness of the learning rate outputted by the actor) that
the actor made. The introduction of auxiliary actor and critic networks helps
the main network achieve better performance. Experiments on different datasets
and network architectures show that our approach leads to better convergence of
SGD than human-designed competitors.Comment: 7 pages, 9 figure
Predicting Depression Severity by Multi-Modal Feature Engineering and Fusion
We present our preliminary work to determine if patient's vocal acoustic,
linguistic, and facial patterns could predict clinical ratings of depression
severity, namely Patient Health Questionnaire depression scale (PHQ-8). We
proposed a multi modal fusion model that combines three different modalities:
audio, video , and text features. By training over AVEC 2017 data set, our
proposed model outperforms each single modality prediction model, and surpasses
the data set baseline with ice margin.Comment: Thirty-Second AAAI Conference on Artificial Intelligence (AAAI-18
Engineering entangled microwave photon states via multiphoton interactions between two cavity fields and a superconducting qubit
It has been shown that there are not only transverse but also longitudinal
couplings between microwave fields and a superconducting qubit with broken
inversion symmetry of the potential energy. Using multiphoton processes induced
by longitudinal coupling fields and frequency matching conditions, we design a
universal algorithm to produce arbitrary superpositions of two-mode photon
states of microwave fields in two separated transmission line resonators, which
are coupled to a superconducting qubit. Based on our algorithm, we analyze the
generation of evenly-populated states and NOON states. Compared to other
proposals with only single-photon process, we provide an efficient way to
produce entangled microwave states when the interactions between
superconducting qubits and microwave fields are in the ultrastrong regime
Field induced quantum spin liquid with spinon Fermi surfaces in the Kitaev model
Recent experimental evidence for a field-induced quantum spin liquid (QSL) in
-RuCl calls for an understanding for the ground state of honeycomb
Kitaev model under a magnetic field. In this work we address the nature of an
enigmatic gapless paramagnetic phase in the antiferromagnetic Kitave model,
under an intermediate magnetic field perpendicular to the plane. Combining
theoretical and numerical efforts, we identify this gapless phase as a
QSL with spinon Fermi surfaces. We also reveal the nature of continuous quantum
phase transitions involving this QSL, and obtain a phase diagram of the
Kitaev model as a function of bond anisotropy and perpendicular magnetic field.Comment: 6+15 pages, 7 figures, 1 table, references update
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