261 research outputs found
Critical natural frequency: an improved empirical effectiveness criterion in vibration stress relief of rectangle welded plates
Decreasing of natural frequency of the treated structure is the most frequently used empirical effectiveness criteria in vibration stress relief (VSR). However, dependability and reliability of this criteria is still far from sufficient. In this study, a covert negative treatment phenomenon was investigated, i.e. natural frequency of welded structures decreased after VSR but residual stress in one direction increased. Relationship between natural frequency and residual stresses was studied by mathematical deduction and finite element method. “Natural Frequency Function” and “Natural Frequency Surface (NFS)” was proposed to describe that relationship. “Critical Natural Frequency” (CNF) was proposed to depict possible situations after VSR. A quantitative natural frequency criterion for VSR effectiveness estimation was proposed
Self-Paced Multi-Task Learning
In this paper, we propose a novel multi-task learning (MTL) framework, called
Self-Paced Multi-Task Learning (SPMTL). Different from previous works treating
all tasks and instances equally when training, SPMTL attempts to jointly learn
the tasks by taking into consideration the complexities of both tasks and
instances. This is inspired by the cognitive process of human brain that often
learns from the easy to the hard. We construct a compact SPMTL formulation by
proposing a new task-oriented regularizer that can jointly prioritize the tasks
and the instances. Thus it can be interpreted as a self-paced learner for MTL.
A simple yet effective algorithm is designed for optimizing the proposed
objective function. An error bound for a simplified formulation is also
analyzed theoretically. Experimental results on toy and real-world datasets
demonstrate the effectiveness of the proposed approach, compared to the
state-of-the-art methods
Neural Polarizer: A Lightweight and Effective Backdoor Defense via Purifying Poisoned Features
Recent studies have demonstrated the susceptibility of deep neural networks
to backdoor attacks. Given a backdoored model, its prediction of a poisoned
sample with trigger will be dominated by the trigger information, though
trigger information and benign information coexist. Inspired by the mechanism
of the optical polarizer that a polarizer could pass light waves with
particular polarizations while filtering light waves with other polarizations,
we propose a novel backdoor defense method by inserting a learnable neural
polarizer into the backdoored model as an intermediate layer, in order to
purify the poisoned sample via filtering trigger information while maintaining
benign information. The neural polarizer is instantiated as one lightweight
linear transformation layer, which is learned through solving a well designed
bi-level optimization problem, based on a limited clean dataset. Compared to
other fine-tuning-based defense methods which often adjust all parameters of
the backdoored model, the proposed method only needs to learn one additional
layer, such that it is more efficient and requires less clean data. Extensive
experiments demonstrate the effectiveness and efficiency of our method in
removing backdoors across various neural network architectures and datasets,
especially in the case of very limited clean data
Shared Adversarial Unlearning: Backdoor Mitigation by Unlearning Shared Adversarial Examples
Backdoor attacks are serious security threats to machine learning models
where an adversary can inject poisoned samples into the training set, causing a
backdoored model which predicts poisoned samples with particular triggers to
particular target classes, while behaving normally on benign samples. In this
paper, we explore the task of purifying a backdoored model using a small clean
dataset. By establishing the connection between backdoor risk and adversarial
risk, we derive a novel upper bound for backdoor risk, which mainly captures
the risk on the shared adversarial examples (SAEs) between the backdoored model
and the purified model. This upper bound further suggests a novel bi-level
optimization problem for mitigating backdoor using adversarial training
techniques. To solve it, we propose Shared Adversarial Unlearning (SAU).
Specifically, SAU first generates SAEs, and then, unlearns the generated SAEs
such that they are either correctly classified by the purified model and/or
differently classified by the two models, such that the backdoor effect in the
backdoored model will be mitigated in the purified model. Experiments on
various benchmark datasets and network architectures show that our proposed
method achieves state-of-the-art performance for backdoor defense
Microscopic and endoscopic “chopstick” technique removal of choroid plexus papilloma in the third ventricle of an infant: a case report with systematic review of literature
BackgroundChoroid plexus papilloma (CPP) is rare and even rarer in infants and young children, and it usually occurs in the ventricles. Due to the physical peculiarities of infants, tumor removal by microscopic or endoscopic surgery alone is difficult.Case PresentationA 3-month-old patient was found to have an abnormally enlarged head circumference for 7 days. Cranial magnetic resonance imaging (MRI) examination revealed a lesion in the third ventricle. The patient underwent combined microscopic and endoscopic “chopstick” technique to remove the tumor. He recovered well after the surgery. Postoperative pathological examination revealed CPP. Postoperative MRI suggested total resection of the tumor. Follow-up for 1 month showed no recurrence or distant metastasis.ConclusionsCombined microscopic and endoscopic “chopstick” technique may be a suitable approach to remove tumors in infant ventricles
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