273 research outputs found
Fire Performance of Steel Reinforced Concrete (SRC) Structures
AbstractThis paper summarizes some of the recent research published on steel reinforced concrete (SRC) structures under or after exposure to fire. The contents include: 1) Fire resistance and post-fire behavior of SRC columns; 2) Fire performance of SRC column to beam joints, by adopting a loading sequence including initial loading, heating, cooling and post-fire loading; 3) Fire resistance and post-fire behavior of SRC composite frames
Threshold current of field-free perpendicular magnetization switching using anomalous spin-orbit torque
Spin-orbit torque (SOT) is a candidate technique in next generation magnetic
random-access memory (MRAM). Recently, experiments show that some material with
low-symmetric crystalline or magnetic structures can generate anomalous SOT
that has an out-of-plane component, which is crucial in switching perpendicular
magnetization of adjacent ferromagnetic (FM) layer in the field-free condition.
In this work, we analytically derive the threshold current of field-free
perpendicular magnetization switching using the anomalous SOT. And we
numerically calculate the track of the magnetic moment in a FM free layer when
an applied current is smaller and greater than the threshold current. After
that, we study the applied current dependence of the switching time and the
switching energy consumption, which shows the minimum energy consumption
decreases as out-of-plane torque proportion increases. Then we study the
dependences of the threshold current on anisotropy strength, out-of-plane
torque proportion, FM free layer thickness and Gilbert damping constant, and
the threshold current shows negative correlation with the out-of-plane torque
proportion and positive correlation with the other three parameters. Finally,
we demonstrate that when the applied current is smaller than the threshold
current, although it cannot switch the magnetization of FM free layer, it can
still equivalently add an effective exchange bias field H_{bias} on the FM free
layer. The H_{bias} is proportional to the applied current J_{SOT}, which
facilitates the determination of the anomalous SOT efficiency. This work helps
us to design new spintronic devices that favor field-free switching
perpendicular magnetization using the anomalous SOT, and provides a way to
adjust the exchange bias field, which is helpful in controlling FM layer
magnetization depinning
On Penalty-based Bilevel Gradient Descent Method
Bilevel optimization enjoys a wide range of applications in hyper-parameter
optimization, meta-learning and reinforcement learning. However, bilevel
optimization problems are difficult to solve. Recent progress on scalable
bilevel algorithms mainly focuses on bilevel optimization problems where the
lower-level objective is either strongly convex or unconstrained. In this work,
we tackle the bilevel problem through the lens of the penalty method. We show
that under certain conditions, the penalty reformulation recovers the solutions
of the original bilevel problem. Further, we propose the penalty-based bilevel
gradient descent (PBGD) algorithm and establish its finite-time convergence for
the constrained bilevel problem without lower-level strong convexity.
Experiments showcase the efficiency of the proposed PBGD algorithm.Comment: Improved Section 4 by removing a critical assumption; Added Section 5
and citation
A Region-Shrinking-Based Acceleration for Classification-Based Derivative-Free Optimization
Derivative-free optimization algorithms play an important role in scientific
and engineering design optimization problems, especially when derivative
information is not accessible. In this paper, we study the framework of
classification-based derivative-free optimization algorithms. By introducing a
concept called hypothesis-target shattering rate, we revisit the computational
complexity upper bound of this type of algorithms. Inspired by the revisited
upper bound, we propose an algorithm named "RACE-CARS", which adds a random
region-shrinking step compared with "SRACOS" (Hu et al., 2017).. We further
establish a theorem showing the acceleration of region-shrinking. Experiments
on the synthetic functions as well as black-box tuning for
language-model-as-a-service demonstrate empirically the efficiency of
"RACE-CARS". An ablation experiment on the introduced hyperparameters is also
conducted, revealing the mechanism of "RACE-CARS" and putting forward an
empirical hyperparameter-tuning guidance
Utopia point method based robust vector polynomial optimization scheme
In this paper, we focus on a class of robust vector polynomial optimization
problems (RVPOP in short) without any convex assumptions. By
combining/improving the utopia point method (a nonlinear scalarization) for
vector optimization and "joint+marginal" relaxation method for polynomial
optimization, we solve the RVPOP successfully. Both theoratical and
computational aspects are considered
- …