16 research outputs found
Fight Fire with Fire: Combating Adversarial Patch Attacks using Pattern-randomized Defensive Patches
Object detection has found extensive applications in various tasks, but it is
also susceptible to adversarial patch attacks. Existing defense methods often
necessitate modifications to the target model or result in unacceptable time
overhead. In this paper, we adopt a counterattack approach, following the
principle of "fight fire with fire," and propose a novel and general
methodology for defending adversarial attacks. We utilize an active defense
strategy by injecting two types of defensive patches, canary and woodpecker,
into the input to proactively probe or weaken potential adversarial patches
without altering the target model. Moreover, inspired by randomization
techniques employed in software security, we employ randomized canary and
woodpecker injection patterns to defend against defense-aware attacks. The
effectiveness and practicality of the proposed method are demonstrated through
comprehensive experiments. The results illustrate that canary and woodpecker
achieve high performance, even when confronted with unknown attack methods,
while incurring limited time overhead. Furthermore, our method also exhibits
sufficient robustness against defense-aware attacks, as evidenced by adaptive
attack experiments
An optimized three-dimensional time-space domain staggered-grid finite-difference method
Numerical simulation of three-dimensional (3D) seismic wavefields forms the basis of the research on the migration methods of 3D seismic data based on wave equations. Because the simulation precision of wavefield extrapolation determines the imaging accuracy to a certain extent, it is very important to study how to enhance the forward modeling precision of 3D seismic wavefields. Thus, we build on an optimized 3D staggered-grid finite-difference (SFD) method with high simulation precision based on two-dimensional (2D) seismic modeling. Since it generates the corresponding difference coefficients by utilizing the least square (LS) method to minimize the objective function constructed by the time-space domain dispersion relation of the 3D acoustic wave equation, our optimized time-space domain LS-based 3D SFD method can effectively enhance the modeling precision of the 3D seismic wavefields in theory compared with the 3D SFD methods based on the Taylor-series expansion (TE), especially for the large wavenumber range. Examining the numerical dispersion, algorithm stability and computational cost, we compare our optimized time-space domain LS-based 3D SFD method with three conventional TE-based and LS-based 3D SFD methods to illustrate and demonstrate its effectiveness and feasibility. The numerical examples from different 3D models suggest that our optimized time-space domain LS-based 3D SFD method can generate less numerical dispersion and higher simulation accuracy for 3D seismic wavefields than three other conventional 3D SFD methods, but its stability condition is stricter and its computational cost is slightly higher
Potential Applications of Remote Limb Ischemic Conditioning for Chronic Cerebral Circulation Insufficiency
Chronic cerebral circulation insufficiency (CCCI) refers to a chronic decrease in cerebral blood perfusion, which may lead to cognitive impairment, psychiatric disorders such as depression, and acute ischemic stroke. Remote limb ischemic conditioning (RLIC), in which the limbs are subjected to a series of transient ischemic attacks, can activate multiple endogenous protective mechanisms to attenuate fatal ischemic injury to distant organs due to acute ischemia, such as ischemic stroke. Recent studies have also reported that RLIC can alleviate dysfunction in distant organs caused by chronic, non-fatal reductions in blood supply (e.g., CCCI). Indeed, research has indicated that RLIC may exert neuroprotective effects against CCCI through a variety of potential mechanisms, including attenuated glutamate excitotoxicity, improved endothelial function, increased cerebral blood flow, regulation of autophagy and immune responses, suppression of apoptosis, the production of protective humoral factors, and attenuated accumulation of amyloid-β. Verification of these findings is necessary to improve prognosis and reduce the incidence of acute ischemic stroke/cognitive impairment in patients with CCCI
Vector Decomposition of Elastic Seismic Wavefields Using Self-Attention Deep Convolutional Generative Adversarial Networks
Vector decomposition of P- and S-wave modes from elastic seismic wavefields is a key step in elastic reverse-time migration (ERTM) to effectively improve the multi-wave imaging accuracy. Most previously developed methods based on the apparent velocities or the polarization characteristics of different wave modes are unable to accurately achieve the vector decomposition of P- and S-wave modes. To effectively overcome the shortcomings of conventional methods, we develop a vector decomposition method of P- and S-wave modes using self-attention deep convolutional generative adversarial networks (SADCGANs) to effectively separate the horizontal and vertical components of P- and S-wave modes from elastic seismic wavefields and accurately preserve their amplitude and phase characteristics for isotropic elastic media. For an elastic model, we use many time slices for a given source position to train the neural network, and use other time slices not in this training dataset to test the neural network. Numerical examples of different models demonstrate the effectiveness and feasibility of our developed method and indicate that it provides an effective intelligent data-driven vector decomposition method of P- and S-wave modes
Cerebral Ischemic Postconditioning Plays a Neuroprotective Role through Regulation of Central and Peripheral Glutamate
Following cerebral ischemia/reperfusion (I/R) injury, a series of pathophysiological processes are stimulated in both the central nervous system (CNS) and the periphery, including, but not limited to, the peripheral immune and endocrine systems and underregulation of the neuroendocrine-immune network. Glutamate (Glu) is an important excitatory neurotransmitter in the CNS; its excitotoxicity following cerebral ischemia has been a focus of study for several decades. In addition, as a novel immunoregulator, Glu also regulates immune activity in both the CNS and periphery and may connect the CNS and periphery through regulation of the neuroendocrine-immune network. Ischemic postconditioning (IPostC) is powerful and activates various endogenous neuroprotective mechanisms following cerebral I/R, but only a few studies have focused on the mechanisms associated with Glu to date. Given that Glu plays an important and complex pathophysiological role, the understanding of Glu-related mechanisms of IPostC is an interesting area of research, which we review here
Alkali Solution Erodes Shale: Influencing Factors and Structural Damage Characteristics
High-pH drilling fluids are often used for drilling shale gas wells. Alkali erosion of shale is one of the important factors of wellbore instability. Alkali erosion experiments of different kinds of minerals and shale were conducted in this paper. Experimental results show that the corrosion rate of kaolinite is the highest when the pH is 9, the corrosion rate of smectite is the highest when the pH is 10 or 11, and the corrosion rate of the quartz is the highest when the pH is 12. Both shale particle size and concentration of hydroxide ion all affect the reaction rate, and the former has a negative correlation with the reaction rate, and the latter has a positive correlation with the reaction rate. In addition, alkaline erosion can lead to the fracture propagation along the bedding planes of shale, which can easily result in wellbore instability. This study may offer some theoretical basis for wellbore instability induced by high-pH drilling fluids
Depth Migration Based on Two-Way Wave Equation to Image OBS Multiples: A Case Study in the South Shetland Margin (Antarctica)
With the development of marine seismic exploration, the ocean bottom seismometer (OBS) as a new seismic acquisition technology has been widely concerned. Although multiple waves are frequently viewed as noises, they may carry a wealth of subsurface information and produce a broader illumination than primary waves. To perform multiple wave imaging, we propose to utilize a two-way wave equation depth wavefield extrapolation method which is rarely used in this field. A simple dipping model is imaged by using primary and multiple waves, which proves the superiority of multiple waves in imaging over the primary waves and lays a foundation for practical application. Moreover, the comparison of multiple imaging results by reverse time migration and those by our proposed method demonstrates that our proposed method requires less storage space. In this study, we apply this migration method to actual OBS data collected in the South Shetland margin (Antarctica), where gas hydrates have been well documented. Firstly, the wavefield separation method is adopted to process the OBS data, so as to produce reliable primary and multiples waves; secondly, the ray-tracing method is used to derive the velocity field; and finally, the depth wavefield extrapolation method based on the two-way wave equation is applied to image primary and multiple waves. Migration results show that multiple waves provide a broader illumination and a clearer sediment structure than primary waves, especially for the highly shallow reflections
Amplitude-Preserved Wave Equation: An Example to Image the Gas Hydrate System
Natural gas hydrate is an important energy source. Therefore, it is extremely important to provide a clear imaging profile to determine its distribution for energy exploration. In view of the problems existing in conventional migration methods, e.g., the limited imaging angles, we proposed to utilize an amplitude-preserved one-way wave equation migration based on matrix decomposition to deal with primary and multiple waves. With respect to seismic data gathered at the Chilean continental margin, a conventional processing flow to obtain seismic records with a high signal-to-noise ratio is introduced. Then, the imaging results of the conventional and amplitude-preserved one-way wave equation migration methods based on primary waves are compared, to demonstrate the necessity of implementing amplitude-preserving migration. Moreover, a simple two-layer model is imaged by using primary and multiple waves, which proves the superiority of multiple waves in imaging compared with primary waves and lays the foundation for further application. For the real data, the imaging sections of primary and multiple waves are compared. We found that multiple waves are able to provide a wider imaging illumination while primary waves fail to illuminate, especially for the imaging of bottom simulating reflections (BSRs), because multiple waves have a longer travelling path and carry more information. By imaging the actual seismic data, we can make a conclusion that the imaging result generated by multiple waves can be viewed as a supplementary for the imaging result of primary waves, and it has some guiding values for further hydrate and in general shallow gas exploration
Astrocytic gap junction inhibition by carbenoxolone enhances the protective effects of ischemic preconditioning following cerebral ischemia
Abstract Background Stroke is the second leading cause of death worldwide and the most common cause of adult-acquired disability in many nations. Thus, attenuating the damage after ischemic injury and improving patient prognosis are of great importance. We have indicated that ischemic preconditioning (IP) can effectively reduce the damage of ischemia reperfusion and that inhibition of gap junctions may further reduce this damage. Although we confirmed that the function of gap junctions is closely associated with glutamate, we did not investigate the mechanism. In the present study, we aimed to clarify whether the blockade of cellular communication at gap junctions leads to significant reductions in the levels of glutamate released by astrocytes following cerebral ischemia. Methods To explore this hypothesis, we utilized the specific blocking agent carbenoxolone (CBX) to inhibit the opening and internalization of connexin 43 channels in an in vitro model of oxygen-glucose deprivation/re-oxygenation (OGD/R), following IP. Results OGD/R resulted in extensive astrocytic glutamate release following upregulation of hemichannel activity, thus increasing reactive oxygen species (ROS) generation and subsequent cell death. However, we observed significant increases in neuronal survival in neuron-astrocyte co-cultures that were subjected to IP prior to OGD/R. Moreover, the addition of CBX enhanced the protective effects of IP during the re-oxygenation period following OGD, by means of blocking the release of glutamate, increasing the level of the excitatory amino acid transporter 1, and downregulating glutamine expression. Conclusions Our results suggest that combined use of IP and CBX represents a novel therapeutic strategy to attenuate damage from cerebral ischemia with minimal adverse side effects
Nursing undergraduates' media competence in the context of health communication and its relationship to professionalism
Abstract Aims To investigate the association between professionalism and social media competence among Chinese mainland nursing undergraduates. Design This study employed a cross‐sectional descriptive correlation design. Participants From June to July 2021, 797 nursing students from four nursing colleges in Jiangsu Province, China, were chosen using stratified cluster sampling. Methods The questionnaire included the Chinese version of the Nursing Professionalism Scale and the Social Media Competency Scale. The association between professionalism and social media competency was examined using Pearson's correlation analysis. Results The professionalism of nursing undergraduates (average scores:70.44 ± 8.82) was at a medium level. Social media self‐efficacy, performance expectancy, facilitating conditions and social influence (3.76 ± 0.75, 3.87 ± 0.60, 3.53 ± 0.69, 3.41 ± 0.76) were at a medium–high level, while social media experience and effort expectancy (3.03 ± 0.72, 2.60 ± 0.59) were at medium and low levels. Among nursing undergraduates, professionalism was related to social media competence, among which, professionalism was positively correlated with social media self‐efficacy (r = 0.40, p < 0.01), social media experience (r = 0.50, p < 0.01), performance expectancy (r = 0.34, p < 0.01), facilitating conditions (r = 0.41, p < 0.01), but negatively correlated with effort expectancy (r = −0.10, p < 0.01). Conclusion The professionalism of nursing undergraduates is related to social media. The scores of social media self‐efficacy, social media experience, performance expectancy and facilitating conditions of nursing students with high professionalism were higher than those of nursing students with low professionalism. Impact This study suggests that developing a course on health communication on social media can help nursing students improve their professionalism. Patient or Public Contribution Participants completed a survey via the online survey platform Wenjuangxing