Open Areas Research Articles

Influence of Neltuma flexuosa and rainfall event on the germination of Leptochloa crinita and Pappophorum caespitosum in two different locations along a stress gradient in the central Monte desert

AbstractIn drylands, grass germination occurs after a large rainfall event. However, trees influence the water requirements for germination either by decreasing the rate of evaporation from soil surface or by interception rainfall with their canopy. The aim of this work was to evaluate the role of Neltuma flexuosa tree on the germination of Leptochloa crinita and Pappophorum caespitosum grasses in response to precipitation events of different sizes. The experiment was conducted in two locations within the Monte desert, Argentina: a semi‐arid location with an average annual precipitation of 345 mm and an arid location with an average annual precipitation of 156 mm. Six microsites were established under N. flexuosa canopies and six microsites in open areas at both locations. Within each microsite, 35 seeds of each grass species were exposed to precipitation events of varying sizes. This procedure was repeated 14 times across two growing seasons. Germinated seeds were counted in the laboratory. Generalized linear mixed models were then applied to evaluate the effects of accumulated precipitation and the microsite on the grass germination in both locations. Results showed that N. flexuosa did not influence the germination of either grass species in the arid location. However, in the semi‐arid location, N. flexuosa facilitated the germination of P. caespitosum only. Large precipitation events would act as an environmental signal for these perennial grasses, allowing them to germinate in favorable years regardless of the microsite or the location.

Analysis of train-induced aerodynamic characteristics and pressure-relief measures relating to fully enclosed noise barriers installed on railway bridges

Fully enclosed noise barriers (FENBs) are increasingly being installed on high-speed railway bridges for noise pollution control. However, the aerodynamic effects of high-speed trains passing FENBs have an adverse impact on barrier durability and generate micro-pressure waves. In this paper, a numerical model of a train passing an FENB on a bridge is established. The aerodynamic pressure distribution along the FENB is analyzed for both a single train and two trains passing one another. The propagation characteristics and evolution mechanisms of pressure waves are then investigated. The results show that the pressure is lower at the ends of the FENB and higher in the middle along the direction of train travel. The peak positive and negative pressures at the mid-span are 1.95 and 4.47 times higher than those at the ends, respectively. This distribution is caused by the propagation, superposition, reflection, and attenuation of pressure waves. Compression waves account for 78.9% of the peak positive pressure. An amplification factor must be considered when estimating the impact of two trains passing one another. Analysis of five pressure-relief schemes shows that arranging a single pressure-relief hole at a high-pressure location effectively alleviates the over-pressure in the FENB. The overall pressure-relief effect is an exponential function of the single opening area. Considering a constant opening area, arranging several relief holes at equal spacing optimizes the adverse pressure distribution compared with the single-hole relief scheme. The equivalent forces of the multi-hole scheme are 3.35% and 7.58% lower than in the single-hole scheme.

Plastic litter is a part of the carbon cycle in an urban river: Microplastic and macroplastic accumulate with organic matter in floating debris rafts.

Watershed models of plastic export from rivers to oceans have large uncertainties, and improvements require direct measurements of riverine macroplastic (>5mm) and microplastic (<5mm). Also, plastic represents allochthonous carbon inputs to rivers but is rarely measured as carbon mass. We quantified plastic and organic matter within floating debris rafts and open water in an urban river. Macroplastics only occurred in debris rafts. Microplastics had higher concentrations in debris rafts relative to open water. Across sites, organic matter was positively correlated with microplastics and macroplastics. Last, carbon in plastic was 40% of the carbon mass in coarse particulate organic matter in debris rafts. Floating plastic litter accumulates with particulate organic matter in debris rafts. Plastic is an overlooked and ecological meaningful component of carbon standing stocks in urban rivers. Results will inform improved carbon budget calculation in rivers and watershed models of plastic export. PRACTITIONER POINTS: Plastic particles floating on the surface of an urban river accumulate in debris rafts compared to open water in terms of count and mass. Abundance and composition of plastic particles in debris rafts were distinct from those in open water areas. Plastic litter as units of carbon mass was in the same order of magnitude as carbon mass in course particulate organic matter. Plastic litter moves in similar ways to naturally occurring organic particles and should be measured as a part of the riverine carbon cycle.

Chlorophyll Production in the Amundsen Sea Boosts Heat Flux to Atmosphere and Weakens Heat Flux to Ice Shelves

AbstractThe Amundsen Sea in West Antarctica features rapidly thinning ice shelves, large polynyas, and sizable spring phytoplankton blooms. Although considerable effort has gone into characterizing heat fluxes between the Amundsen Sea, its associated ice shelves, and the overlying atmosphere, the effect of the phytoplankton blooms on the distribution of heat remains poorly understood. In this modeling study, we implement a feedback from biogeochemistry onto physics into MITgcm‐BLING and use it to show that high levels of chlorophyll—concentrated in the Amundsen Sea Polynya and the Pine Island Polynya—have the potential to increase springtime surface warming in polynyas by steepening the attenuation profile of solar radiation with depth. The chlorophyll‐associated warm anomaly (on average between +0.2C and +0.3C) at the surface is quickly dissipated to the atmosphere, by increases in longwave, latent and sensible heat loss from open water areas. Outside of the coastal polynyas, the summertime warm anomaly leads to an average sea ice thinning of 1.7 cm across the region, and stimulates up to 20% additional seasonal melting near the fronts of ice shelves. The accompanying cold anomaly, caused by shading of deeper waters, persists year‐round and affects a decrease in the volume of Circumpolar Deep Water on the continental shelf. This cooling ultimately leads to an average sea ice thickening of 3.5 cm and, together with associated changes to circulation, reduces basal melting of Amundsen Sea ice shelves by approximately 7% relative to the model scenario with no phytoplankton bloom.

Thermal comfort in open spaces in the arid climate of Kuwait: a study of construction training institute students

This article assesses the students’ sensation of thermal comfort in the open areas of the construction training institute in Kuwait, a hyper arid desert. This is carried out using field measurements from the site, and then handing out in-depth questionnaires to 100 students. The questionnaire provides great insight into the students’ perception of thermal comfort, as well as the constituents that impact it. Moreover, the students’ recommendations to improve thermal comfort in open spaces sheds light on the various methods that should be further researched and quantified. These solutions include adding substantial vegetation and trees for shading and redesigning the inadequate existing shading devices on campus. Overall, the findings indicate that the air temperature and humidity are well below the comfort level. These field measurements are sufficiently validated with the questionnaire results that indicate a substantially negative experience. While outdoor thermal comfort is heavily under researched in Kuwait, there are endless opportunitiesfor improvement and development. Consequently, this paper acts as a catalyst for future endeavors, quantitative analysis, and raised awareness

A Survey of Resource Allocation in V2V Communications

In this paper, a comprehensive analysis of resource allocation in vehicle-to-vehicle (V2V) communication systems is presented, which is crucial for enhancing traffic control and improving road safety and driving enjoyment. A variety of resource allocation strategies are classified and examined in this paper, including game theory-based approaches, spectrum allocation, energy allocation, location-based allocation, and machine learning-based procedures. Open research questions and areas that need further study in the field of V2V communication are highlighted for future benefit. This survey helps readers make informed decisions about system design, implementation, and improvement by providing a comprehensive overview of the latest developments in V2V resource allocation. It also indicates areas that need further research and possible directions to enhance the security, flexibility, and scalability of V2V communication networks.

Organic carbon cycling in the sediments of Prydz Bay, Eastern Antarctica: Implications for a high carbon sequestration potential

Understanding the dynamics of sedimentary organic carbon (SOC) in the productive continental marginal sea surrounding Antarctica is crucial for elucidating the effect of this sea on the global carbon cycle. We analyzed 31 surface sediment samples and eight sediment cores collected from Prydz Bay (PB) and the adjacent basin area. The element and stable isotope compositions, grain size compositions, and biogenic silica and lithogenic minerals of these samples were used to evaluate the spatial variations in the sources, transport mechanisms, and preservation patterns of SOC, with a particular focus on the efficiency of the biological carbon pump (BCP). Our findings reveal that the SOC originated from mixed marine/terrestrial sources. The δ13C values were higher in the Prydz Bay Gyre (PBG) region than in the open sea area. Biogenic matter-rich debris, associated with fine-grained particles (silt and clay), was concentrated in the PBG, while abiotic ice-rafted debris and coarse-grained particles were preferentially deposited in the bank and ice shelf front regions. Lithogenic matter predominated in the basin sediments. The annual accumulation rate of SOC in PB ranged from 1.6 to 6.2 g·m−2·yr−1 (mean 4.2 ± 1.9 g·m−2·yr−1), and the rates were higher in the PBG than in the ice shelf front region. Estimates based on our tentative box model suggest that the efficiency of the BCP, which refers to the proportion of surface-produced organic carbon successfully transferred to deep waters, is approximately 5.7 % in PB, surpassing the global average (∼0.8 %) and the efficiencies reported for other polar environments. Furthermore, our calculations indicate that the SOC preservation efficiency (the ratio of preserved to initially deposited organic carbon in sediments) in PB is approximately 79 % ± 20 %, underscoring the significant carbon sequestration potential within PB. The results of this study have important implications for the effects of sediment dynamics on the carbon cycle in the sea surrounding Antarctica.

Experimental study on the propagation mechanism of acetylene-air detonation waves in a unilaterally intermittently constrained channel

This study experimentally explores the propagation mechanisms of acetylene/air detonation waves within a channel intermittently constrained on one side, utilizing soot foil and high-speed schlieren photography to capture the cellular structure and shock-flame evolution. The experiments revealed that the detonation waves traverse the semi-enclosed channel with various discrete wall configurations on the side in three distinct propagation modes: (I) periodic detonation failure and re-initiation; (II) single extinction and re-initiation; (III) non-extinction. Mode I occurs exclusively when the open area ratio exceeds 0.85, while detonation tends to favour Mode II when the gaps between discrete walls exceed three times the cell size; otherwise, it tends towards Modes III. The re-initiation mechanism of detonation involves curvature shocks inducing local explosions of reactive mixtures through multiple Mach reflections off the discrete walls. The self-sustained propagation mechanism of the detonation wave is maintained by the interaction of strong transverse shocks reflected from discrete walls with the inherent transverse waves within the detonation structure, sustaining the instability of the cellular detonation.

Numerical design of a flow restrictor for tanked liquid nitrogen undergoing reduced-gravity flights

NASA and the United States are designing multiple reduced-gravity cryogenic payloads to study various two-phase flow phenomena that will be ground-tested and subsequently flight-tested onboard parabolic flights. The setup will undergo 25+ parabolas per flight, during which liquid nitrogen will be cyclically or continuously demanded from a supply Dewar. The minimum gravity level during a parabolic maneuver is 0 ± 0.05 g, which can last around 20 seconds, and the maximum expected gravity is 2 g, which lasts for 40-50 seconds. This Computational Fluid Dynamics (CFD) study focuses on the design and optimization of a bi-directional perforated plate and a ring baffle to help ensure single-phase liquid nitrogen outflow during all flight phases, regardless of supply tank liquid level or gravity level. CFD analyses carried out using ANSYS FLUENT indicate that a double perforated plate with an open area percent equal or less than 0.63% can achieve high values of expulsion efficiency. Structural analyses performed using the ANSYS Static Structural solver determined the minimum plate thickness needed to withstand gravitational and hydrodynamic forces experienced during the flight.

Forecast of emergency situations with the spillage of liquid rocket fuel components in the territory for the disposal of chemically hazardous substances

Introduction. Liquid fuel includes two main components – fuel and oxidizer. Common liquid rocket fuels components are highly toxic compounds – heptyl (asymmetric dimethylhydrazine) and amyl (nitrogen tetraoxide). The calculation of emergency scenarios with the spill of liquid rocket fuel components on the terrain is intended for operational forecasting of the scale of pollution, optimization of work in the zone of chemical contamination and the development of a system for providing medical care to the population in case of an extreme situation. Material and methods. The article presents scenarios of emergency situations with the spill of liquid rocket fuel components on the territory of chemically hazardous facilities and during transportation. Results. The calculation of the distribution of approximate concentrations at spills in an open area of nitrogen tetroxide (NT) and asymmetric dimethylhydrazine (UDMH) is investigated. The received scenarios of emergency situations indicate the possibility of distribution of toxic concentrations: at the level of CL50 within 1 km at the UDMH spill from 0.5 to 10 tons, NT – from 0.1 to 5 tons; at the level of 1/10 CL50 – threshold toxodose (concentration) at a distance of 0.5–0.7 km at the UDMH spill 0.5–1.0 t, and NT – up to 1 t. Limitations. When studying emergency scenarios with the spillage of liquid rocket fuel components in the territory, an assessment was made of the distribution of approximate concentrations of components according to the regulatory document on the methodology for predicting the extent of contamination of highly toxic substances in accidents (destruction) at chemically hazardous facilities and transportation. Conclusion. As a result of the study, it was revealed that the population living within a radius of more than 2 km from the accident site may suffer from the spread of liquid rocket fuel components, which depends on the volume of the spill, the type of emergency hazardous chemicals and the wind direction in the chemical damage zone.

Establishment of a postoperative bowel adhesion model in Rats

Postoperative adhesive bowel obstruction is a frequent cause of hospital admission in a surgical department. Emergency surgery is needed in a majority of patients with bowel ischemia or peritonitis; most adhesive bowel obstruction can be managed non-operatively. Many studies have investigated benefits of using oral water-soluble contrast to manage adhesive bowel obstruction. Treatment recommendations are still controversial. Intestinal adhesions commonly occur in patients after abdominal surgery, often between intestines, between intestines and the abdominal wall, or within the peritoneum. Adhesions can lead to symptoms such as abdominal pain, constipation, and bloating, and may result in serious complications such as intestinal obstruction, bowel necrosis, acute peritonitis, and sepsis, which can be life-threatening. Therefore, reducing the occurrence of intestinal adhesions is crucial for abdominal surgery. To minimize adhesions, endoscopic techniques can be employed to reduce the abdominal opening area and thus decrease the probability of adhesion formation. However, this approach requires specialized equipment and surgical skills, making it somewhat challenging. Alternatively, anti-adhesion products can be used to lower the risk of adhesion formation. In this study, a murine cecal abrasion adhesion model was established and will be simulated common adhesion scenarios observed in patients after abdominal surgery. The efficacy of anti-adhesion gel materials will be then evaluated to assess their anti-adhesion properties. The record of gross adhesion severity assessment was performed. The adhesion status between the cecum and abdominal wall was observed on postoperative days 3 and 14. The results was shown that three days post-surgery operation, the group exhibited more severe adhesions upon gross examination. By day 14 post-surgery operation (at animal sacrifice), the histopathological analysis revealed that the group exhibited thicker fibrous tissue thickness, increased neovascularization, and higher collagen accumulation in the peritoneum. Therefore, based on the results of this experiment, a postoperative bowel adhesion rat is reliable and can be safely used to test the efficacy of novel anti-adhesive formulations to prevent intra-abdominal adhesions by using this model.

Revitalisasi Taman Balai Desa Bicak, Kecamatan Trowulan, Kabupaten Mojokerto

. KKN is one of the community service activities carried out by students from universities. KKN-T Bela Negara of National Development University “Veteran” East Java was conducted in Bicak Village, Trowulan, Mojokerto. The work program carried out by the KKN-T Bela Negara Group 04 Wave 2 was the revitalization of the Bicak Village Hall park. The park is an open area that has several types of plants, trees, shrubs, bushes and grasses. The condition of the garden at Bicak Village Hall is poorly maintained, some plants are dead and overgrown with grass. This revitalization activity is carried out with several methods from direct observation and survey. As for some of the activities carried out in revitalizing the park, such as community service cleaning the park area and Bicak Village Hall, arranging rocks in the area to the right and left of the park, and planting several ornamental plants. Group 04 Wave 2 KKN-T Bela Negara revitalized the Bicak Village Hall park which aims to increase the SDGs score of the Environmentally Concerned Village, improve the function of the park and increase the aesthetic value of the Village Hall.

Development of an IoT-Based Device for Data Collection on Sheep and Goat Herding in Silvopastoral Systems.

To evaluate the ecosystem services of silvopastoral systems through grazing activities, an advanced Internet of Things (IoT) framework is introduced for capturing extensive data on the spatial dynamics of sheep and goat grazing. The methodology employed an innovative IoT system, integrating a Global Navigation Satellite System (GNSS) tracker and environmental sensors mounted on the animals to accurately monitor the extent, intensity, and frequency of grazing. The experimental results demonstrated the high performance and robustness of the IoT system, with minimal data loss and significant battery efficiency, validating its suitability for long-term field evaluations. Long Range (LoRa) technology ensured consistent communication over long distances, covering the entire grazing zone and a range of 6 km in open areas. The superior battery performance, enhanced by a solar panel, allowed uninterrupted operation for up to 37 days with 5-min interval acquisitions. The GNSS module provided high-resolution data on movement patterns, with an accuracy of up to 10 m after firmware adjustments. The two-part division of the device ensured it did not rotate on the animals' necks. The system demonstrated adaptability and resilience in various terrains and animal conditions, confirming the viability of IoT-based systems for pasture monitoring and highlighting their potential to improve silvopastoral management, promoting sustainable practices and conservation strategies. This work uniquely focuses on documenting the shepherd's role in the ecosystem, providing a low-cost solution that distinguishes itself from commercial alternatives aimed primarily at real-time flock tracking.

Large-deformation finite-element modelling of face instability during tunnelling in clayey soils: Incorporating dynamic excavation process

Earth pressure balance (EPB) shield tunnelling plays a crucial role in urban infrastructure development but faces challenges due to potential face instability. Previous studies often overlook the impact of dynamic excavation processes on face stability, particularly in clayey soils. This study proposes a three-dimensional coupled Eulerian-Lagrangian (CEL) large-deformation approach to explore the failure process of tunnel face in clayey soils during both EPB shutdown and excavation conditions by incorporating the influence of dynamic excavation process. The findings reveal that the face stability during dynamic excavation conditions is consistently lower than that during EPB shutdown, indicating that neglecting dynamic excavation effects could overestimate face stability, potentially compromising construction safety. Moreover, when considering the dynamic excavation process, the opening ratio ξ (the ratio between the cross-section area of cutterhead opening to the total area of tunnel face) is a critical factor affecting face stability. As expected, the face is more stable for a small opening ratio (e.g., ξ = 15 %) while face stability is reduced for a large opening ratio (e.g., ξ = 30 % and 50 %). This is because for large opening ratio, the soil disturbance caused by the cutterhead excavation process exceeds the supportive effect that the cutterhead panels can provide to the face. Finally, the obtained numerical results were used to calculate support pressure in a real tunnel project considering the dynamic excavation process, which matches well with the measured data in the project, validating the effectiveness and superiority of the current CEL approach in modelling face instability and estimating face support pressure. This study offers a significant advancement over the traditional methods for the design of support pressure in clayey soils, providing new insight into the dynamic cutterhead-soil interaction and valuable guidance for reducing the risk of face collapse.

Indicators of woody plants and soil in the urbanised environment of the Southern Urals (green zone of Ufa, Russia)

ABSTRACT The study investigates biometric indicators of assimilation and reproductive organs of coniferous and deciduous trees in urban environments: leaf area, inflorescence flower count, stipule length of Tilia cordata Mill. and needle length and weight of Scots pine (Pinus sylvestris L.). Samples of wood, needles, leaves and soil from the planting sites were analysed for 17 chemical elements, including Hazard Class I elements (Arsenic, Lead, Cadmium, Mercury, Selenium) and Hazard Class II elements (Chromium, Cobalt, Nickel, Copper, Molybdenum, Antimony). Tree plantations decreased airborne dust by 30–40% compared to open areas. Concentrations of PM2.5 and PM10 particles showed a direct correlation with busy roads (p < 0.05). In instances of environmental degradation, healthy trees exhibited in needle an increase in biomass and a reduction in weight and length. Consequently, forestry measurements and the impact of the urban environment require specific and individual monitoring of trees, rather than a general assessment of plantations.

Microbial and hydrothermal dolomite formation in Early Cretaceous lacustrine sediments in Yin'e Basin: Insights from petrology and geochemistry

Dolomite is widely present in geological history, but its origin has always been a prominent problem that troubles sedimentologists. For lacustrine dolomite, current research has not yet provided a reliable explanation for its complex genesis mechanism. The Early Cretaceous lakes in Northwest China host various morphological dolomites, providing valuable materials for exploring the origin of dolomites. According to their petrological and mineralogical characteristics, it can be divided into thick laminated dolomite, thin laminated dolomite, dolomitic mudstone, and vein dolomite. The ratios of trace elements and rare earth elements show that these dolomites precipitated in a brackish–suboxic environment. The high δ13C values (>8 ‰VPDB) of thick laminated dolomite and some thin laminated dolomite suggest the involvement of methane-producing microorganisms in the precipitation of dolomite, and the appearance of microscale/nanoscale spherical dolomite aggregates and the dispersed organic matter around dolomite particles jointly confirm that microbial-mediated biological activity promotes dolomite precipitation. The dolomite stoichiometry (mole % MgCO3) confirms that thick laminated dolomite was deposited in a restricted shallow water environment, while dolomitic mudstone is mainly deposited in relatively open water areas. The thin laminated dolomite in the shale laminae represents short-term or seasonal climatic and environmental fluctuations. In addition, some carbonate minerals of dolomitic mudstone in shallow water environment recrystallized by post-depositional hydrothermal effect, resulting in δ18O value decreased (<−10 ‰VPDB). The vein dolomite is characterized by high rare earth content and low δ13C and δ18O values, and its Sr isotope (0.712894 ± 0.000374) values reflect that the hydrothermal fluid may have been formed by the mixing of infiltrating lake water and crustal magmatic water. According to the characteristics of fluid inclusions, it is inferred that the hydrothermal fluid has the characteristics of low temperature (108.3 °C–159.8 °C), medium salinity (3.5 wt%–14.3 wt% NaCl) and high density (0.95–1.00 g/cm3). The microbial mediation and tectonic hydrothermal fluids play an important role in the formation of the Early Cretaceous lacustrine dolomite.

Bubble sizes inferred from their gas composition in a temperate freshwater fish pond

ABSTRACT Rising bubbles play a fundamental role in emitting greenhouse gases from shallow waters. Their size is crucial for bubble dissolution, gas exchange with the surrounding water, and the release of gases into the atmosphere. However, little is known about bubble sizes in shallow waters. To address this, we investigated bubble diameters in a 1.2 m deep fish pond, employing 2 methods: first, we measured the bubble size distributions by optical bubble sensors; second, we used an existing single bubble dissolution model to determine diameters representative for the respective bubble size distributions at the water surface based on measured bubble oxygen contents and dissolved oxygen concentrations. Results from optical bubble sensors were relatively similar at all sites; however, subsequent analysis revealed problems, particularly in detecting small bubbles under turbid, shallow water conditions. Model-derived bubble diameters ranged from 0.5 to 10.5 mm, varied spatially within the pond, and displayed diurnal fluctuations. With increasing bubble flux, bubble diameters increased; bubbles at feeding sites were larger than in the open water area. A detailed sensitivity analysis revealed that, depending on the bubble size distribution, the uncertainty of the model increases with increasing water depth. For a typical bubble diameter of 5 mm, the simple method can provide robust estimates of representative bubble size in waters shallower than 50 m.

Composition and diversity of ground beetles within wooded pastures and alternative land-use systems in Swiss Jura mountains

AbstractWooded pastures combine trees and pastures in a land-use system resulting from traditional silvopastoral practices. With their sparse tree cover, wooded pastures represent an ecotone between open area pastures and forests with potentially high species diversity, although this is poorly tested for animal groups especially insects. In this study, we aimed to characterise and compare species communities in terms of species composition and diversity indices, biomass and ecological traits of ground beetles in wooded pastures, forests and non-wooded pastures. Pitfall traps were set up in 29 study sites located in the Swiss Jura mountains. Ground beetle communities in wooded pastures largely encompass those in open pastures and forests, although some species are found only in forests or open areas. Wooded pastures and open pastures have an equivalent species diversity level, which is significantly higher than the one in forests. Ground beetle diversity is positively correlated with the surfaces of Biodiversity Promotion Areas within a 100 m radius. Areas with high tree cover (70–100%) favour brachypterous and hygrophilic species, whereas areas with reduced tree cover (0–20%) favour xerophilic and winged species. Ground beetles’ size and biomass increase with tree cover. Wooded pastures are an important ecotone, ensuring a gradual change of land-use systems between open areas and forests, where a wide range of species from both land-use systems are found. These semi-natural systems are important for the conservation of ground beetles.

Does double pre-notches have a greater impact than single pre-notch on the mechanical and fracture behavior of rock? Insights from three-point bending tests using the numerical approach of grain-based model

The mechanical performance of rock masses is significantly impacted by the existence of cracks. Distribution of the cracks may result in different mechanical or fracture behaviors of rock. To gain a preliminary understanding of such problems, a series of numerical tests of three-point bending (TPB) are designed and carried out with the consideration of single pre-notch and double pre-notches. The numerical method of grain-based model (GBM) approach is employed in this paper, with a validation implemented by comparing the results with previous experiments to demonstrate the reliability of this model. Afterward, a comprehensive investigation, including the mechanical behavior, strength characteristics, crack evolution and progressive failure mechanism of the above mentioned TPB tests are conducted. The conclusions are as follows: (1) During TPB tests, as the offset distance increases, the fracture mode of the single pre-notched specimens gradually transitions from Mode I to Mode II, with the peak fracture toughness occurring at a mixed Mode I-II fracture condition (2p/s = 0.4). Moreover, the failure angle, notch open degree and expansion area all tend to rise regardless of specimens of single or double pre-notches. (2) A thorough exploration of crack evolution shows that the specimens primarily fracture during the crack propagation and failure stages. Shear failure predominates among these stages, with microcracks mostly occurring inside the rock mineral grains. (3) When offset distance increases to a certain degree (2p/s = 0.8), the fracture of specimen ceases to be governed by the pre-notch; instead, it occurs directly from the middle of the beam specimen. This phenomenon can be attributed to the reduction of stress concentration at the notch tip, as inferred from analysis of the contact force chain. (4) In double pre-notched specimen, microcracks initiate at both pre-notches, but the final failure results from crack propagation at one notch tip. Compared to single pre-notched specimen, the presence of double pre-notches exhibits superior fracture resistance performance.

Potential of the Indonesian Navy in Protecting Maritime Border Areas: Measurement through Mahan's Theory

Indonesia as an archipelagic country has open sea areas and the existence of the Indonesian Archipelagic Sea Lane (ALKI) which can create vulnerabilities to various possible maritime threats. The country of Indonesia, most of which is territorial waters, requires a strong Navy to maintain security and the country's territorial boundaries. The aim of this research is to see the potential of the Indonesian National Army Navy through Mahan's Theory. This research uses a qualitative method with a descriptive approach. The data collection technique in this research was carried out through searching secondary data obtained from books, articles, news, comments and government publications. The results of this research indicate that there must be an increase in the Indonesian Navy and modernization of Alusista must also be carried out.