Dangerous Regions Research Articles

Stress Evolution and Rock Burst Prevention in Triangle Coal Pillars under the Influence of Penetrating Faults: A Case Study

The occurrence of rock bursts due to penetrating faults are frequent in China, thereby limiting the safe production of coal mines. Based on the engineering background of a 501 working face in a TB coal mine, this paper investigates stress and energy evolution during the excavation of this working face due to multiple penetrating faults. Utilizing both theoretical analysis and numerical simulations, this study reveals the rock burst mechanism within the triangular coal pillar influenced by the penetrating faults. Based on the evolution of stress within the triangular coal pillar, a stress index has been devised to categorize both the rock burst danger regions and the levels of rock burst risks associated with the triangular coal pillar. Furthermore, targeted stress relief measures are proposed for various energy accumulation areas within the triangular coal pillar. The results demonstrate that: (1) the superimposed tectonic stress resulting from the T6 and T5 penetrating faults exhibits asymmetric distribution and has an influence range of about 90 m in the triangular coal pillar, reaching a peak value of 11.21 MPa at a distance of 13 m from the fault plane; (2) affected by the barrier effect of penetrating faults, the abutment stress of the working face is concentrated in the triangular coal pillar, and the magnitude of the abutment stress is positively and negatively correlated with the fault plane barrier effect and the width of the triangular coal pillar, respectively; (3) the exponential increase in abutment stress and tectonic stress as the width of the triangular coal pillar decreases leads to a high concentration of static stress, which induces pillar burst under the disturbance of dynamic stress from fault activation; (4) the numerical simulation shows that when the working face is 150 m away from the fault, the static stress and accumulated energy in the triangle coal pillar begins to rise, reaching the peak at 50 m away from the fault, which is consistent with the theoretical analysis; (5) the constructed stress index indicates that the triangular coal pillar exhibits moderate rock burst risks when its width is between 73 to 200 m, and exhibits high rock burst risks when the width is within 0 to 73 m. The energy accumulation pattern of the triangular coal pillar reveals that separate stress relief measures should be implemented within the ranges of 50 to 150 m and 0 to 50 m, respectively, in order to enhance the effectiveness of stress relief. Blasting stress relief measures for the roof and coal are proposed, and the effectiveness of these measures is subsequently verified.

A complete course of photodynamic therapy reduced the risk of malignant transformation of oral leukoplakia

BackgroundPhotodynamic therapy (PDT) has shown good short-term efficacy in the treatment of oral leukoplakia (OLK). However, the malignant transformation of OLK was seldom evaluated in most PDT studies. Therefore, this study evaluated the effect of PDT on the risk of malignant transformation of OLK. MethodsKaplan-Meier survival analysis, COX regression, and sensitivity analysis were used to evaluate the effects of PDT on the risk of malignant transformation of OLK. Subgroup analyses were performed to explore the role of PDT in OLK patients with different clinical characteristics. ResultsOLK patients with older age (HR=1.032, P = 0.018) and non-homogeneous lesion (HR=2.104, P = 0.044) had higher risk of malignant transformation. Patients who had finished a complete course of PDT (HR=0.305, P = 0.006) had a significant lower risk of malignant transformation, while those who hadn't finished a complete course of PDT (HR=0.692, P = 0.352) cannot be considered to have such a protective effect. In the subgroup analyses, complete PDT course showed a significant protective effect on malignant transformation of OLK in patients with female sex, no smoking or drinking habits, non-homogeneous lesions, lesions on oral mucosa outside the dangerous region, and any grade of epithelial dysplasia. ConclusionsA complete course of PDT could significantly reduce the risk of malignant transformation of OLK, especially in those patients with risk factors of malignant transformation.

Vision-Based obstacle detection in dangerous region of coal mine driverless rail electric locomotives

In order to solve the problem of inaccurate obstacle detection as well as frequent start-stops caused by oversensitive obstacle detection in existing driverless rail electric locomotives in underground coal mines, the YOLO-Region model is proposed to realize regional obstacle detection. First, the model backbone uses InceptionNeXt block and the developed New Spatial Pyramid Pooling (NSPP) module; the model neck extends the FPN+PAN architecture; the model head uses improved task-specific context decoupling (Impro-TSCODE) head. In addition, repulsion loss is introduced to improve the detection ability of partially occluded targets. The experimental results show that the YOLO-Region achieves competitive detection performance with mAP of 98.0 % and an average detection speed of 94.5 FPS. Second, a vision-based method for defining dangerous region based on pixel coordinate points is developed and integrated into YOLO-Region, which allows the model to detect obstacles only within a specific region, thereby reducing frequent start-stops of driverless electric locomotives.

Enhancing machine learning-based seismic facies classification through attribute selection: application to 3D seismic data from the Malay and Sabah Basins, offshore Malaysia

Over the past few years, the use of machine learning has gained considerable momentum in many industries, including exploration seismic. While supervised machine learning is increasingly being used in seismic data analysis, some obstacles hinder its widespread application. Seismic facies classification—a crucial aspect in this field—particularly faces challenges such as the selection of appropriate input attributes. Plethora of seismic attributes have been created over the years, and new ones are still coming out. Yet, several have been deemed redundant or geologically meaningless. In the context of machine learning, it is crucial to avoid these redundant and irrelevant attributes as they can result in overfitting, building unnecessary complex models, and prolonging computational time. The current study incorporates an attribute selection approach to seismic facies classification and evaluates the importance of several available seismic attributes. Two datasets from the AN Field and the Dangerous Grounds region offshore Malaysia were utilized. Several attribute selection techniques were evaluated, with most of them yielding perfect attribute subsets for the AN dataset. However, only the wrapper and embedded methods could produce optimal subsets for the more complex Dangerous Grounds dataset. In both datasets, distinguishing the targeted seismic facies was mainly dependent on amplitude, spectral, and gray-level co-occurrence matrix attributes. Furthermore, spectral magnitude components played a significant role in classifying the facies of the Dangerous Grounds broadband data. The study demonstrated the importance of attribute selection, established a workflow, and identified significant attributes that could enhance seismic facies classification in Malaysian basins and similar geologic settings.

Thermal-fluid-structure coupling simulation of piston in large marine diesel engine

Abstract Traditionally, most simulation approaches for pistons are conducted based on thermal-structure coupling, where the cooling boundary conditions are determined by empirical formulas. However, these approaches often suffer some decreases in the accuracy of the simulation results. Aiming at the problem, this paper conducts a thermal-fluid-structure coupling simulation method for the piston of a large marine diesel engine, which employs computational fluid dynamics to identify the cooling boundary conditions. Firstly, the solid and fluid models are established. Then, the cooling process of the piston chamber is simulated, with the temperature and heat transfer coefficients being mapped onto the solid component. Finally, loads and constraints are imposed on the solid component to accomplish the simulation. Under the presumed simulation conditions, the obtained coupling stresses are within the permissible range, with a maximum value of 419.68 MPa, and the dangerous region occurs at the junction of the piston head and the cooling chamber.

Parsimonious statistical techniques for the detection of drifts toward dangerous operational conditions in tokamaks

The approaching initial operation of major new tokomaks is rendering more pressing the need for effective disruption prediction techniques. The required tools should be not only accurate but also capable of operating with a minimum number of signals, because in the first campaigns of new devices typically only a very limited number of diagnostics is available. The present work reports the results obtained with two advanced statistical techniques, chaos onset and concept drift (CD). These methods are capable of detecting the plasma drifting towards dangerous regions of the operational space using only global signals such as the plasma current or the locked mode amplitude. The obtained performances meet the requirements of mitigation in devices such as JT60-SA and ITER at the beginning of their operation. The computational times of the chaos onset approach are already of the order of 1 ms on laptop computers, whereas the CD technique requires implementation on FPGAs or GPUs to be compatible with real time requirements.

How the brain can be trained to achieve an intermittent control strategy for stabilizing quiet stance by means of reinforcement learning

The stabilization of human quiet stance is achieved by a combination of the intrinsic elastic properties of ankle muscles and an active closed-loop activation of the ankle muscles, driven by the delayed feedback of the ongoing sway angle and the corresponding angular velocity in a way of a delayed proportional (P) and derivative (D) feedback controller. It has been shown that the active component of the stabilization process is likely to operate in an intermittent manner rather than as a continuous controller: the switching policy is defined in the phase-plane, which is divided in dangerous and safe regions, separated by appropriate switching boundaries. When the state enters a dangerous region, the delayed PD control is activated, and it is switched off when it enters a safe region, leaving the system to evolve freely. In comparison with continuous feedback control, the intermittent mechanism is more robust and capable to better reproduce postural sway patterns in healthy people. However, the superior performance of the intermittent control paradigm as well as its biological plausibility, suggested by experimental evidence of the intermittent activation of the ankle muscles, leaves open the quest of a feasible learning process, by which the brain can identify the appropriate state-dependent switching policy and tune accordingly the P and D parameters. In this work, it is shown how such a goal can be achieved with a reinforcement motor learning paradigm, building upon the evidence that, in general, the basal ganglia are known to play a central role in reinforcement learning for action selection and, in particular, were found to be specifically involved in postural stabilization.

Efficient approximation of stochastic turning process based on power spectral density

Turning is one of the most important material removal processes in manufacturing, where the proper understanding of the process is crucial for the quality of the final product. In this study, the stochastic cutting force is utilized to enhance the existing 1-degree-of-freedom turning model. A stochastic model is adopted to address the stochastic resonance phenomenon occurring near stability boundaries. Additionally, a novel simplified stochastic model is introduced with additive noise only. The comparison of the two models reveals that, with the recommended noise intensity of 0.1 to 1%, there is no significant difference in the stability charts and mean square characteristics between the two models. As a result, the time-consuming numerical methods can be bypassed, as the simplified model offers a computationally more efficient analytical approach to compute variance based on power spectral density (PSD). By combining techniques such as D-separation to determine stability boundaries and the PSD-based variance calculation, it only takes a minute instead of hours to construct a heatmap using the introduced simplified stochastic turning model that clearly outlines dangerous stochastic resonance regions inside the stable domain.

Multiscale modeling on the multi-physical behaviors of high temperature superconducting magnets based on a combined global homogenization and local refinement scheme

The safe and stable operation is a crucial issue in the development of high-field high temperature superconducting (HTS) magnets. In this paper, we construct a multiscale model which couples the homogenized global (macroscopic) behavior and the refined local (mesoscopic) characteristics to simulate the coupled electromagnetic-mechanical-thermal behaviors of the HTS magnets. In the model, the numerical homogenization method is adopted to simulate the macroscopic behavior of the magnets and identify the ‘dangerous region’ of the magnet which are prone to damage or quench. Then, a refined local sub-model which coupling with the macroscopic homogenization model is established by considering the microstructure and physical parameters of each components of the HTS tapes in the ‘dangerous region’. Thus, a combined global homogenization and local refinement scheme which balances the computational efficiency and numerical accuracy is developed to simulate the coupled multi-physical behaviors of the HTS magnets including the quench and its propagation. Our results show that the refined local sub-model can simulate the electromagnetic field and the stress-strain at the scale of the tape more accurately. Characteristics, such as the discontinuous stress distribution across the interfaces between different layers and the current shunt from the HTS layer to metallic layers during the quench process of HTS tapes, which are beyond the capability of the homogenization model, have also been well depicted by the refined sub-model.

Simple Design Criterion for High-Intensity Hadron Linacs

Abstract A simple procedure is established to optimize fundamental design parameters of a high-intensity hadron linac where interparticle Coulomb interaction plays a crucial role. Based on the recently proposed semi-empirical resonance condition, a stability map is constructed which reveals potentially dangerous operating regions in tune space. The map is shown to be consistent with numerical data obtained from more complicated approaches. The effectiveness of the new design scheme is demonstrated through systematic particle-in-cell simulations assuming the most typical structure of an Alvarez-type drift tube linac. The present results suggest that the so-called equipartitioning condition, which has often been taken very seriously in high-intensity linac designs, does not need to be met to guarantee the best machine performance. The basic design concept described here can be applied not only to linacs but also to circular machines.

Three-Dimensional Location of the Facial Artery in Relation to the Nasolabial Fold in Asian People: A Cadaveric CTA Study.

Injection cosmetics have become popular in recent years. The nasolabial fold is one of the most important and dangerous regions in the midface, and its three-dimensional relationship with the facial artery remains unclear. Fifty-two cadavers infused with lead oxide contrast medium via the external carotid arteries were scanned by computed tomography (CT). The three-dimensional model was reconstructed using Mimics and Origin software, and the relevant data were calculated using validated algorithms. There were three facial artery types according to its course in relation to the nasolabial fold. In the most common type, accounting for 83.7% of specimens, the facial artery evolves into an angular artery, with a horizontal distance between facial artery and nasolabial fold of - 1.90 ± 2.40, - 3.90 ± 2.95, - 5.18 ± 3.42, - 5.59 ± 3.53, - 5.59 ± 3.83, - 6.07 ± 4.10, - 6.92 ± 3.70, - 6.79 ± 3.37, - 4.52 ± 3.20, and - 2.76 ± 3.60 (mm) from the nasal ala to the oral commissure and a vertical distance of - 4.03 ± 2.56,- 3.27 ± 2.27,- 2.81 ± 2.57, - 2.1 ± 2.64,- 1.5 ± 3.32,- 0.71 ± 3.99,0.92 ± 4.43,0.4 ± 5.31,- 4.14 ± 5.14,- 7.05 ± 4.74 (mm). The facial artery is vulnerable to damage when injecting filler in the nasolabial fold. For the upper 1/3 of the nasolabial fold, the supraperiosteal layer is recommended for injection, while for the lower 2/3 of the nasolabial fold, the dermal layer along the nasolabial fold is recommended. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Table-top ion-trap experiment on the stability of intense short bunches in linear hadron accelerators

The novel experimental system “S-POD” (Simulator of Particle Orbit Dynamics) is employed to explore the stability of short hadron bunches in high-intensity linacs. In a previous study with the S-POD [M. Goto et al., ], a static potential was used to focus the bunch in the longitudinal direction. We here make a step forward to include the possibility of pure synchrotron resonance, introducing periodic modulation to the longitudinal potential well. The modulation period was taken a half of the transverse alternating-gradient focusing period, which reflects the most typical lattice condition of a drift-tube linac. Detailed stability maps are constructed to reveal dangerous parameter regions where serious beam loss may occur due to resonance. We reconfirm the existence of various betatron and synchrobetatron resonance stop bands whose widths and locations change in tune space depending on the bunch intensity. It turns out that the periodicity of the longitudinal focusing potential brings about no pronounced effect on the resonance feature; the result is very similar to what we obtained in the previous study with a static longitudinal potential. As long as the lattice periodicity mentioned above is maintained, no serious noncoupling synchrotron resonance appears even with a high synchrotron phase advance above 90° per unit alternating-gradient cell. Severe envelope instability may, however, be excited in the longitudinal direction if the axial focusing force includes error components that affect the original lattice periodicity. The experimental observations can be explained with the free from the concept of incoherent tune spread. Published by the American Physical Society 2024

ПРИМЕНЕНИЕ НЕИЗВЛЕКАЕМЫХ ТРУБЧАТЫХ ПУСТОТООБРАЗОВАТЕЛЕЙ И ЛЁГКИХ БЕТОНОВ ДЛЯ СНИЖЕНИЯ СЕЙСМИЧЕСКОГО ВОЗДЕЙСТВИЯ НА ЗДАНИЯ

Annotation. The article gives examples of buildings and structures, successfully and unsuccessfully designed and built, shows their characteristic features, analyzes publications that justify the need to reduce the weight of structures; reducing the location of the center of gravity of the masses, the use of constructive solutions of the building itself capable of counteracting seismic effects. An example of the design and calculation of two design options for a twelve-story residential building of various weights using heavy and lightweight concrete and non-removable cardboard-polyethylene void formers with a circular cross section with a diameter of 159 mm is given as one of the methods aimed at reducing seismic impact. Based on the studies performed, it was concluded that it is expedient to use non-removable void formers in combination with lightweight concrete to reduce the mass of reinforced concrete structures and heavy concrete to reduce the center of gravity of the building, and as a result, reduce the seismic impact.
 Subject of study. The subject of the study is to reduce the mass of reinforced concrete structures of high-rise buildings and their center of gravity, as well as the construction of the building itself in seismic zones.
 Materials and methods. To reduce the mass of reinforced concrete structures, the frame was designed and the center of gravity of a twelve-story residential building was calculated in two options - the first option: the use of heavy reinforced concrete completely 2.5 t/m3 and solid floor slabs 22 cm thick; the second option is the use of heavy reinforced concrete with a density of 2.5 t/m3 to cover the basement and the lower four floors, the rest of the upper floors using light reinforced concrete with a density of 1.7 t/m3 and non-removable cardboard-polyethylene void formers with a diameter of 159 mm for floor slabs. The possibility, expediency and application of building design according to the second option are substantiated.
 Results.
 1) Reducing the center of gravity of the building by 16.3%.
 2) Reducing the mass of the building while maintaining the standard loads: 20.5%.
 3) The cumulative reduction in the mass of reinforced concrete elements is 30.7%.
 Conclusions. The proposed design of a monolithic twelve-story residential building using heavy concrete on the lower floors and lightweight concrete in combination with non-removable cardboard-polyethylene tubular hollow formers of circular cross section with a diameter of 159 mm on the upper floors, providing a significant reduction in the mass and center of gravity of the building, is a possible and expedient way to build in seismically dangerous regions

COMPLEX ASSESSMENT AND FORMATION OF SCENARIOS ENSURING THE BUSINESS ENTITIES INVESTMENT ATTRACTIVENESS IN THE GLOBAL CHALLENGES CONDITIONS

The new global challenges that Ukraine has faced have an ambiguous effect on the process of attracting investments in the development of the economy. The key negative factors are war and related violations of international logistics due to the destruction and closure of airports, ports, closed borders; liquidation of vital infrastructure; mass displacement of the population, which is caused by active hostilities, which creates economic threats for investing in any projects of the country due to the risks of their freezing or disruption; the annexation of certain regions, as a result of which the process of business relocation from dangerous regions became more active, causing the emergence of additional risks and losses; decrease in economic indicators and the potential of economic development, lack of a system of guaranteeing and protecting foreign investments at the state level. Therefore, ensuring investment attractiveness at the macro and micro levels is complicated by existing global challenges and requires special attention, taking into account the fact that the post-war recovery of Ukraine's economy requires attracting a sufficient level of investment on mutually beneficial terms.
 The article assesses the investment attractiveness level on the example of one of the business entities using various methods, compares the results obtained, and forms scenarios for ensuring investment attractiveness. Depending on the level of investment attractiveness of the enterprise and the corresponding type of investment potential, as well as the investment attractiveness of the industry, it is proposed to use one of the basic scenarios for ensuring investment attractiveness and the formation and realization of investment potential, which involve the implementation of one or another strategy

Bird strike tests, analyses, and design optimisation of a tilt-rotor aircraft composite inlet

Collisions of aircraft with foreign objects are very common phenomena, so they must be anticipated, and their consequences must be individually checked. Since these incidents can result in severe engine damage and the engine is the aircraft's only thrust-providing system, the effect of bird strikes on engine air intakes and similar systems must be investigated and mitigated with special attention. Principally for tilt-rotor convertible aircraft, this effect is crucial in terms of operational safety, flight mechanics and overall aircraft control. The objective of this work is to demonstrate the durability of the composite air intake for a new tilt-rotor aircraft, which is experimentally verified on components of basic geometric shapes such as plate and cylindrical section. Based on computer-supported simulations, which are correlated with the basic tests, the consequences of the impact on the real air-duct were analysed and potentially dangerous regions were found. Sizing and optimisation was carried out and a design improvement proposal was developed.

Modern aspects of the labor market functioning in Ukraine: problems and solutions

The article analyzes the main trends and problems of the labor market in the conditions of transformational processes taking place in the country's economy. In particular, attention is focused on the high level of unemployment, the uneven distribution of the labor force between regions, the outflow of qualified personnel abroad, and the imbalance between demand and supply in the labor market. The authors examine the impact of global crisis phenomena, such as the Covid-19 pandemic and war, on structural changes in employment and wages. The work identifies key problems that limit the effective functioning of the labor market, including low wages, insufficient adaptation of the education system to the needs of the market. Special attention was paid to the problem of increasing the level of employment of IDPs, encouraging IDPs to open their businesses or self-employment based on microcredit, grants, training in entrepreneurial skills and consulting, an analysis of key factors affecting the employment of IDPs was carried out, as well as state support programs that stimulate the relocation of enterprises from dangerous regions to safer ones, will allow saving jobs and avoiding the reduction of production capacities. The authors offer several ways to solve the outlined problems, including raising the level of social standards, stimulating small and medium-sized businesses, introducing effective state employment programs, etc. The need for retraining, training in new professions and adaptation to market requirements is indicated. The article examines the role of international cooperation in solving migration problems. The authors also drew attention in the article to the fact that employers are forced to offer comprehensive packages that satisfy both financial and non-financial needs. Although salary remains an important factor in today's conditions, candidates are increasingly paying attention to other aspects: opportunities for training, career growth, vacations, work environment, corporate culture. The authors proposed several strategic steps that can help stabilize and develop the labor market. Thus, the article highlights a comprehensive approach to the analysis of modern challenges in the labor market of Ukraine and offers recommendations for its stabilization and further development.

Spain on fire: A novel wildfire risk assessment model based on image satellite processing and atmospheric information

Each year, wildfires destroy larger areas of Spain, threatening numerous ecosystems. Humans cause 90% of them (negligence or provoked) and the behaviour of individuals is unpredictable. However, atmospheric and environmental variables affect the spread of wildfires, and they can be analysed by using deep learning. In order to mitigate the damage of these events, we proposed the novel Wildfire Assessment Model (WAM). Our aim is to anticipate the economic and ecological impact of a wildfire, assisting managers in resource allocation and decision-making for dangerous regions in Spain, Castilla y León and Andalucía. The WAM uses a residual-style convolutional network architecture to perform regression over atmospheric variables and the greenness index, computing necessary resources, the control and extinction time, and the expected burnt surface area. It is first pre-trained with self-supervision over 100,000 examples of unlabelled data with a masked patch prediction objective and fine-tuned using a very small dataset, composed of 445 samples. The pretraining allows the model to understand situations, outclassing baselines with a 1,4%, 3,7% and 9% improvement estimating human, heavy and aerial resources; 21% and 10,2% in expected extinction and control time; and 18,8% in expected burnt area. Using the WAM we provide an example assessment map of Castilla y León, visualizing the expected resources over an entire region.

Watershed Delineation from DEM by Model Builder in ArcGIS

The water level fluctuates continuously at local, continental, and global levels. Consequently, remote sensing offers extensive data for assessing the location, extent, and variability of change, including the causes and changes that occur and the reactions and repercussions of change. Considering the significance of the water level, this research focuses on describing the methodology and process to determine the water level in the Al-Zab River. This study offers a straightforward and cost-effective approach and procedure for precisely delineating flood danger regions in the Al-Zab River basin utilizing a geographic information system and the existing database. The proposed strategy for regionally dispersing flood risks combines the size of prior flood events and the geographical distribution of their causes. This approach allows for the calculation of a weighted score for each participant's causative component. The regional distribution of the flood hazard intensity level is obtained by categorizing the spatial patterns of the flood hazard index. The 30-m digital elevation model with a high resolution was utilized to evaluate the water level in this river. Furthermore, this work is considered the first step towards enhancing information management in the studied area. This study mainly aims to explain how to outline and define watersheds using ArcGIS for flood mapping. Doi: 10.28991/CEJ-2023-09-11-011 Full Text: PDF

Meeting Users’ Information Needs Online during the Russian-Ukrainian War

abstract: This article explores users’ level of satisfaction with the information in the online space of a university library during the pandemic and the russian-Ukrainian war. The authors analyzed the services and activities that the library provided online and examined whether they satisfied users’ information needs. Using a questionnaire, the study surveyed students and faculty members of the Kyiv National University of Culture and Arts in 2023. The study revealed that users rely on online library services for many different information needs. The authors do not rule out that their results were influenced by current conditions in Ukraine, such as intensive military operations lasting more than a year, forced relocation of students and teachers to less dangerous regions, concern for the safety of educational and informational activities during constant rocket attacks, power outages, and unstable Internet connection. This article will be useful to those interested in meeting library users’ information needs during a pandemic, war, or other instability. Respondents’ suggestions for service improvement, conclusions, and recommendations will help university libraries to organize their activities more effectively to maximize users’ satisfaction in the online space.

AutoBar: Automatic Barrier Coverage Formation for Danger Keep Out Applications in Smart City.

Barrier coverage is a fundamental application in wireless sensor networks, which are widely used for smart cities. In applications, the sensors form a barrier for the intruders and protect an area through intrusion detection. In this paper, we study a new branch of barrier coverage, namely warning barrier coverage (WBC). Different from the classic barrier coverage, WBC has the inverse protect direction, which moves the sensors surrounding a dangerous region and protects any unexpected visitors by warning them away from the dangers. WBC holds a promising prospect in many danger keep out applications for smart cities. For example, a WBC can enclose the debris area in the sea and alarm any approaching ships in order to avoid their damaging propellers. One special feature of WBC is that the target region is usually dangerous and its boundary is previously unknown. Hence, the scattered mobile nodes need to detect the boundary and form the barrier coverage themselves. It is challenging to form these distributed sensor nodes into a barrier because a node can sense only the local information and there is no global information of the unknown region or other nodes. To this end, in response to the newly proposed issue of the formation of barrier cover, we propose a novel solution AutoBar for mobile sensor nodes to automatically form a WBC for smart cities. Notably, this is the first work to trigger the coverage problem of the alarm barrier, wherein the regional information is not pre-known. To pursue the high coverage quality, we theoretically derive the optimal distribution pattern of sensor nodes using convex theory. Based on the analysis, we design a fully distributed algorithm that enables nodes to collaboratively move toward the optimal distribution pattern. In addition, AutoBar is able to reorganize the barrier even if any node is broken. To validate the feasibility of AutoBar, we develop the prototype of the specialized mobile node, which consists of two kinds of sensors: one for boundary detection and another for visitor detection. Based on the prototype, we conduct extensive real trace-driven simulations in various smart city scenarios. Performance results demonstrate that AutoBar outperforms the existing barrier coverage strategies in terms of coverage quality, formation duration, and communication overhead.