334 research outputs found
Model-Free Sure Screening via Maximum Correlation
We consider the problem of screening features in an ultrahigh-dimensional
setting. Using maximum correlation, we develop a novel procedure called MC-SIS
for feature screening, and show that MC-SIS possesses the sure screen property
without imposing model or distributional assumptions on the response and
predictor variables. Therefore, MC-SIS is a model-free sure independence
screening method as in contrast with some other existing model-based sure
independence screening methods in the literature. Simulation examples and a
real data application are used to demonstrate the performance of MC-SIS as well
as to compare MC-SIS with other existing sure screening methods. The results
show that MC-SIS outperforms those methods when their model assumptions are
violated, and it remains competitive when the model assumptions hold.Comment: 38 pages, 5 table
Holomorphic Curves into Algebraic Varieties Intersecting Divisors in Subgeneral Position
Recently, there are many developments on the second main theorem for
holomorphic curves into algebraic varieties intersecting divisors in general
position or subgeneral position. In this paper, we refine the concept of
subgeneral position by introducing the notion of the index of subgeneral
position. With this new notion we give some surprising improvement of the
previous known second main theorem type results. Moreover, via the analogue
between Nevanlinna theory and Diophantine approximation, the corresponding
Schmidt's subspace type theorems are also established in the final section.Comment: to appear in Math. An
Computation Load Balancing Real-Time Model Predictive Control in Urban Traffic Networks
Owing to the rapid growth number of vehicles, urban traffic congestion has
become more and more severe in the last decades. As an effective approach,
Model Predictive Control (MPC) has been applied to urban traffic signal control
system. However, the potentially high online computation burden may limit its
further application for real scenarios. In this paper, a new approach based on
online active set strategy is proposed to improve the real-time performance of
MPC-based traffic controller by reducing the online computing time. This
approach divides one control cycle into several sequential sampling intervals.
In each interval, online active set method is applied to solve quadratic
programming (QP) of traffic signal control model, by searching the optimal
solution starting at the optimal solution of previous interval in the feasible
region. The most appealing property of this approach lies in that it can
distribute the computational complexity into several sample intervals, instead
of imposing heavy computation burden at each end of control cycle. The
simulation experiments show that this breakthrough approach can obviously
reduce the online computational complexity, and increase the applicability of
the MPC in real-life traffic networks
Sample-Efficient Policy Learning based on Completely Behavior Cloning
Direct policy search is one of the most important algorithm of reinforcement
learning. However, learning from scratch needs a large amount of experience
data and can be easily prone to poor local optima. In addition to that, a
partially trained policy tends to perform dangerous action to agent and
environment. In order to overcome these challenges, this paper proposed a
policy initialization algorithm called Policy Learning based on Completely
Behavior Cloning (PLCBC). PLCBC first transforms the Model Predictive Control
(MPC) controller into a piecewise affine (PWA) function using multi-parametric
programming, and uses a neural network to express this function. By this way,
PLCBC can completely clone the MPC controller without any performance loss, and
is totally training-free. The experiments show that this initialization
strategy can help agent learn at the high reward state region, and converge
faster and better
Compact Model of Nanowire Tunneling FETs Including Phonon-Assisted Tunneling and Quantum Capacitance
A physics-based compact model for silicon gate-all-around (GAA) nanowire
tunneling FETs (NW-tFETs) with good accuracy has been developed by considering
Phonon-Assisted Tunneling (PAT) and transition from Quantum Capacitance Limit
(QCL) to Classical Limit (CL) during the device-size scaling. The impact of PAT
results in the broadening of a single electron-energy level to an energy band
with density-of-states (DOS) distribution of Lorentzian shape. As a
consequence, the tunneling probability at the edge of tunneling window no
longer changes abruptly from zero to having a finite value. By adjusting the
parameters in the Lorentzian function, an accurate fitting to the measured
transfer characteristics in the subthreshold region is made possible. Besides,
with an analytical formula to calculate the channel potential, the model is
able to cover naturally the transition from QCL to CL regime when the device
size is scaled. Furthermore, on-voltage is defined to facilitate the modeling
and fitting processes. Comparisons with the experimental data demonstrate the
model accuracy across all device operation regions and the flexibility in model
parameter extraction is also shown
Structured Pruning for Efficient ConvNets via Incremental Regularization
Parameter pruning is a promising approach for CNN compression and
acceleration by eliminating redundant model parameters with tolerable
performance degrade. Despite its effectiveness, existing regularization-based
parameter pruning methods usually drive weights towards zero with large and
constant regularization factors, which neglects the fragility of the
expressiveness of CNNs, and thus calls for a more gentle regularization scheme
so that the networks can adapt during pruning. To achieve this, we propose a
new and novel regularization-based pruning method, named IncReg, to
incrementally assign different regularization factors to different weights
based on their relative importance. Empirical analysis on CIFAR-10 dataset
verifies the merits of IncReg. Further extensive experiments with popular CNNs
on CIFAR-10 and ImageNet datasets show that IncReg achieves comparable to even
better results compared with state-of-the-arts. Our source codes and trained
models are available here: https://github.com/mingsun-tse/caffe_increg.Comment: IJCNN 201
Unitary-Coupled Restricted Boltzmann Machine Ansatz for Quantum Simulations
Neural-Network Quantum State (NQS) has attracted significant interests as a
powerful wave-function ansatz to model quantum phenomena. In particular, a
variant of NQS based on the restricted Boltzmann machine (RBM) has been adapted
to model the ground state of spin lattices and the electronic structures of
small molecules in quantum devices. Despite these progresses, significant
challenges remain with the RBM-NQS based quantum simulations. In this work, we
present a state-preparation protocol to generate a specific set of
complex-valued RBM-NQS, that we name the unitary-coupled RBM-NQS, in quantum
circuits. This is a crucial advancement as all prior works deal exclusively
with real-valued RBM-NQS for quantum algorithms. With this novel scheme, we
achieve (1) modeling complex-valued wave functions, (2) using as few as one
ancilla qubit to simulate hidden spins in an RBM architecture, and (3)
avoiding post-selections to improve scalability.Comment: 21 pages, 6 figure
Deficiency of the Bulk Spin Hall Effect Model for Spin-Orbit Torques in Magnetic Insulator/Heavy Metal Heterostructures
Electrical currents in a magnetic insulator/heavy metal heterostructure can
induce two simultaneous effects, namely, spin Hall magnetoresistance (SMR) on
the heavy metal side and spin-orbit torques (SOTs) on the magnetic insulator
side. Within the framework of the pure spin current model based on the bulk
spin Hall effect (SHE), the ratio of the spin Hall-induced anomalous Hall
effect (SH-AHE) to SMR should be equal to the ratio of the field-like torque
(FLT) to damping-like torque (DLT). We perform a quantitative study of SMR,
SH-AHE, and SOTs in a series of thulium iron garnet/platinum or Tm3Fe5O12/Pt
heterostructures with different Tm3Fe5O12 thicknesses, where Tm3Fe5O12 is a
ferrimagnetic insulator with perpendicular magnetic anisotropy. We find the
ratio between measured effective fields of FLT and DLT is at least 2 times
larger than the ratio of the SH-AHE to SMR. In addition, the bulk SHE model
grossly underestimates the spin torque efficiency of FLT. Our results reveal
deficiencies of the bulk SHE model and also address the importance of
interfacial effects such as the Rashba and magnetic proximity effects in
magnetic insulator/heavy metal heterostructures
Strong Rashba-Edelstein Effect-Induced Spin-Orbit Torques in Monolayer Transition-Metal Dichalcogenide/Ferromagnet Bilayers
The electronic and optoelectronic properties of two dimensional materials
have been extensively explored in graphene and layered transition metal
dichalcogenides (TMDs). Spintronics in these two-dimensional materials could
provide novel opportunities for future electronics, for example, efficient
generation of spin current, which should enable the efficient manipulation of
magnetic elements. So far, the quantitative determination of charge current
induced spin current and spin-orbit torques (SOTs) on the magnetic layer
adjacent to two-dimensional materials is still lacking. Here, we report a large
SOT generated by current-induced spin accumulation through the Rashba-Edelstein
effect in the composites of monolayer TMD (MoS or WSe)/CoFeB bilayer.
The effective spin conductivity corresponding to the SOT turns out to be almost
temperature-independent. Our results suggest that the charge-spin conversion in
the chemical vapor deposition-grown large-scale monolayer TMDs could
potentially lead to high energy efficiency for magnetization reversal and
convenient device integration for future spintronics based on two-dimensional
materials.Comment: accepted versio
Deep Learning for Optoelectronic Properties of Organic Semiconductors
Atomistic modeling of energetic disorder in organic semiconductors (OSCs) and
its effects on the optoelectronic properties of OSCs requires a large number of
excited-state electronic-structure calculations, a computationally daunting
task for many OSC applications. In this work, we advocate the use of deep
learning to address this challenge and demonstrate that state-of-the-art deep
neural networks (DNNs) are capable of predicting the electronic properties of
OSCs at an accuracy comparable with the quantum chemistry methods used for
generating training data. We extensively investigate the performances of four
recent DNNs (deep tensor neural network, SchNet, message passing neural
network, and multilevel graph convolutional neural network) in predicting
various electronic properties of an important class of OSCs, i.e.,
oligothiophenes (OTs), including their HOMO and LUMO energies, excited-state
energies and associated transition dipole moments. We find that SchNet shows
the best performance for OTs of different sizes (from bithiophene to
sexithiophene), achieving average prediction errors in the range of 20-80meV
compared to the results from (time-dependent) density functional theory. We
show that SchNet also consistently outperforms shallow feed-forward neural
networks, especially in difficult cases with large molecules or limited
training data. We further show that SchNet could predict the transition dipole
moment accurately, a task previously known to be difficult for feed-forward
neural networks, and we ascribe the relatively large errors in transition
dipole prediction seen for some OT configurations to the charge-transfer
character of their excited states. Finally, we demonstrate the effectiveness of
SchNet by modeling the UV-Vis absorption spectra of OTs in dichloromethane and
a good agreement is observed between the calculated and experimental spectra.Comment: comments are welcom
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