Small Shield Research Articles

Geological evolution and construction of a glacierized active intra-oceanic arc volcano: Visokoi Island (South Sandwich Islands)

Visokoi is a small volcanic island in the remote South Sandwich Islands and is unique in being dominated by the basaltic andesite products of highly explosive eruptions. Here, its geology is described in detail for the first time and can be used to characterize the construction of an active glacierized volcano in an intra-oceanic volcanic arc setting. More than 90% of the volcano is submarine and is composed of (1) a ~ 2.5 km-high mound formed of pillow lava and tuff breccia flanked by a low apron of mass flow deposits, together with (2) an overlying unit ~ 200 m thick composed of Surtseyan volcanic products representing a shoaling (and ultimately emergent) volcanic stage. The succeeding island commenced as a small volcanic shield composed of subaerial ‘a ‘ā lavas whose construction terminated in a caldera collapse that repressurized the magma chamber, presaging a major transition to highly explosive pyroclastic eruptions. They were mainly of sub-Plinian and Plinian type and their recognition on the island provides the first viable explanation for the presence of compositionally similar marine tephras sampled by drilling > 500 km from source, previously considered enigmatic. Eruptions probably took place under ice-poor conditions but evidence for quenching of juvenile clasts suggests that the magmas interacted with water high in the conduit sourced from melting of a small ice cap. The major period of high-discharge sub-Plinian and Plinian eruptions appears to have ended and any future events shall probably comprise small-volume eruptions forming Strombolian scoria cones or glaciovolcanic tuff cones.

Geological mapping and characterization of the NW-Phoebe volcano-magmatic center on Venus

Detailed geological mapping (at 1:500,000 scale) of the area located in the eastern part of the BAT region, northwest of Phoebe Regio (∼4°N to 1°S; ∼85° to 78°W) using Magellan SAR images has distinguished 48 volcano-tectonic units and 22 structural units. Stratigraphically, the oldest units are represented by fragments of the tesserae, densely lineated plains and other plains units. Younger units include lobate flow fields oriented in various directions (NE, E, SW) and flows associated with shield clusters.The post-tesserae evolutionary model proposed for this region distinguishes two Stages, early (I) and late (II), and explains the sequence of formation of all the geological features in terms of intraplate magmatism. Stage I consists of multiple corona structures and associated volcanism that are widely dispersed over the study area. Stage II consists of an intermediate-scale volcano with multiple lava flows radiating approximately from its center, and a field of small shield volcanoes near the summit. The units of Stage II appear to be approximately coeval and to define a distinct volcanic event covering an areal extent of ⁓250,000 km2, that we have termed the NW-Phoebe event.

Continuous Slag Discharge Construction Technology for Shield Tunneling in Narrow Space Environment

The shield tunneling method is the main construction method in subway tunnel construction, which has the characteristics of safety, efficiency, mechanization, and high degree of automation. However, the shield tunneling equipment is huge, the supporting facilities are numerous, and the site requirements are high. In response to the problems of slow slag removal speed and low construction efficiency in shield tunneling under the construction conditions of small wellhead shield tunneling sections in urban subways, taking the shield tunneling section of Guangzhou Metro Line 13 Phase II as the background,This article introduces the main components, working principles, installation and transportation processes, fault handling, and benefit analysis of the continuous belt conveyor slag removal system,This article elaborates on the method of using a continuous belt conveyor in the tunnel combined with a vertical lifting system at the wellhead to achieve continuous slag removal during underground shield tunneling construction in a narrow wellhead construction site. This not only improves excavation efficiency but also reduces construction costs, solves construction problems, and provides reference for similar projects in the future.

Design and experiment of high-performance small magnetic shielding box

Investigating the state of cells in zero magnetic or near-zero magnetic environments is an important scientific issue. However, standard cell culture incubators can only provide general conditions such as constant temperature, constant humidity, sterility, and carbon dioxide, and cannot provide zero magnetic or near-zero magnetic environments for cell culture. To address this issue, an optimization method was proposed in this paper based on the combination of the particle swarm optimization algorithm (PSO) and the finite element method (FEM), achieving the optimization design of a magnetic shielding box (MSB) with a small volume, high shielding factor, and low residual field. Firstly, the high-permeability layer and high-conductivity layer were optimized respectively using the PSO and FEM. Then, the effectiveness of this method was analyzed through experiments. The experimental results show that the shielding factors in three directions at the center point of the optimized MSB are 786.8 (east-west), 2182.7 (north-south), and 1389.4 (vertical) respectively at 0.01 Hz. Meanwhile, the maximum residual field in the cubic region with a side length of 10 cm inside the MSB is 11.9 nT. Finally, the MSB designed by this method was placed in a standard cell culture incubator to cultivate cells in a zero-magnetic or near-zero magnetic environment. Then the Cell Counting Kit-8 (CCK8) experiments to evaluate the cytotoxicity of chemotherapy drugs on tumor cells in a weak magnetic environment (WMF). The results show that the lethality of paclitaxel (PTX) to Epidermal carcinoma cell (A431) increases by 25.96 times and the lethality of gemcitabine (GE) to Lung carcinoma cell (NCI-H460) increases by 24.23 times in a WMF. At the same time, the maximum proliferation inhibition rate of 5-fluorouracil (5-FU) on NCI-H460 cells in a WMF environment increased by 15.69%. That is, WMF could significantly improve the therapeutic effect of chemotherapy drugs on tumor cells.

The spatial distribution and evolution of volcanic vents in monogenetic fields in active extensional tectonic setting: Examples from the northern Main Ethiopian Rift (Ethiopia)

Monogenetic volcanic fields are present in different geo-tectonic settings (subduction, divergence and intraplate settings) consisting of tens to hundreds of volcanic constructs (cones, maars, fissures, small shields) that are the physical expression of distributed volcanism.Notably, the spatial distribution of the volcanic constructs in volcanic fields often shows a spatial clustering that is thought to be linked to shallow (i.e., crustal strain, structural inheritance) and deep processes (i.e., magma input, composition and rheology). Noteworthy, the spatial distribution of vents (cones, maars, fissures, small shields) is the final frame of the history of the volcanic field and does not provide information about its time-evolution.Consequently, when a vent spatial clustering is assessed for a particular volcanic field two questions remain unanswered: i) have the vents always been clustered during the life of the volcanic field? ii) If not, when did the clustering of vents begin? To answer these questions, the spatial distributions of vents along with their morphologic classification have been applied to volcanic fields located in an active tectonic and volcanic area. The northern Main Ethiopian Rift, being its geo-tectonic setting and its geologic evolution well known, is the locale where the time evolution of vent spatial clustering can be investigated. Spatial distribution and morphometric analysis of vents have been applied to three well known monogenetic volcanic fields (Debre Zeyt, Wonji and Kone) in the northern Main Ethiopian Rift. Vent clustering initiated when about 60% of the vents formed within each of the above mentioned fields. The Kone volcanic field show vent clustering since the beginning suggesting that, within a specific tectonic setting, vent clustering is favoured by crustal strain partitioning and associated volcanic activity.

The Nieve volcanic cluster: A Pliocene - Pleistocene lava dome cluster in the Michoacán-Guanajuato volcanic field (México)

The Nieve monogenetic volcanic cluster is located in the central–eastern region of the Michoacán–Guanajuato volcanic field, along the Huiramba fault zone, a relay ramp in the Morelia–Acambay fault system produced by oblique north-northwest transtension. This volcanic cluster includes at least 17 middle Pliocene to late Pleistocene lava domes, two small shield volcanoes, and two scoria cones. Between 4 and 3.8 Ma, two effusive eruptions built two small shield volcanoes overlying one another, with a magma volume of 3.93 km3. Between 2.9 Ma and 21.4 ka, 17 lava domes and two scoria cones were emplaced on the flanks of these volcanoes. The entire cluster resulted in a total erupted volume of 17 km3, covering an area of 326 km2 and reaching a thickness of emplaced volcanic material of 1200 m, resulting in a magma eruption rate equivalent to 0.004 km3/ka. All the rocks associated with this cluster are within a relatively restricted range in composition, between 53.9 and 64.2 wt% SiO₂, from andesite enriched in silica to basaltic andesite. The presence of intrusive-rock xenoliths and xenocrysts with dissolution textures reveals that assimilation processes modified the magmas. Based on the regional geological record, we suggest that the establishment of the Nieve volcanic cluster has been controlled by tectonic structures and the basement of the region, which has allowed the chemical evolution of these magma batches that probably had sources in at least two deep reservoirs as reflected by the Nb/Th versus Ta/U ratio.

Mitigation of Roughness-Induced Boundary-Layer Transition on Airfoils Using Shielding Strips

Boundary-layer transition in the wake of a discrete roughness element results in a turbulent wedge that can adversely affect aerodynamic performance. Even when surfaces are designed for laminar flow, roughness that accumulates near the leading edge can cause premature transition and degrade performance. One approach for mitigating such transition is to place small spanwise-oriented shielding strips upstream or downstream of potential roughness elements accumulation sites. Shielding strips have been shown to be effective at eliminating transition in zero-pressure-gradient, flat-plate boundary layers. This work documents the shielding performance near the leading edge of an NACA 63(3)-418 airfoil where the pressure gradient is strongly favorable. Infrared thermography is used to evaluate the laminar or turbulent state of the boundary layer behind multiple roughness elements with and without shielding strips. The performance of various upstream and downstream shielding configurations is evaluated, as well as the performance improvement of combining these two strategies simultaneously. Direct numerical simulations provide validation and additional insight into the mechanisms responsible for the shielding phenomenon.

Analysis of faults and pit chains in Noctis Labyrinthus: Implications for early extension and possible magmatic plumbing

Noctis Labyrinthus has been a region of disputed origin due to its complexity and poor understanding of how various processes and mechanisms may have combined to form it. The surface is an integrated record of intensive tectonic activity expressed by a multiple extended sets of dip-slip faults oriented in different directions, and thought to have acted on this region over its history. These faults are always coalescent to pits and pit chains displaying a complicated geological history in the region. To understand this geological history, we mapped the surface features in Noctis Labyrinthus using the High-Resolution Stereo Camera (HRSC) onboard Mars Express ND2 nadir channel basemaps, and we adapted the Digital Terrain Map (DTM) from the Mission Experiment Gridded Data Record (MEGDR) of Mars Orbiter Laser Altimeter (MOLA) onboard Mars Global Surveyor (MGS) for the topography. We have investigated the spatial distribution and trend of fault systems, the pit chains' morphology, and the correlation between these two types of features. Our results show three fault systems: i) NS and NNE-SSW, ii) EW and ENE-WSW, and iii) NNW-SSE and NW. The analysis of the faults trending, cross-cutting correlation and the superimposition led to identify multiple intersections between these faults that have been alongside with the reactivations of some inherited faults. We interpreted the first system of fault to be related to coeval lateral extension, generated by regional stress tensor, which is probably related to the slight bending of Valles Marineris within two phases of bidirectional extension. The second system of faults has been generated by the radial oblate stress tensor related to the formation of the small shield volcanoes in Syria Planum. However, the third system is likely related to the external driving process, probably in the Tharsis province. We classified pits in four evolutionary stages based on their morphometric attributes. We believe that the formation of the pit chains in Noctis Labyrinthus is related to a surface collapse after a pressure drop related to the magma chamber deflation associated with Syria Planum volcanic province. We propose a deformational model based on early extension and magmatic plumbing as driving processes for the formation of Noctis Labyrinthus.

Study on the magnetic shielding properties of nanocrystalline strips under bending stress

The study of the magnetic properties of nanocrystalline materials under stress is of great significance for the construction of small and lightweight magnetic shielding rooms. Therefore, this paper investigates the effect of stress on the magnetic properties of nanocrystalline materials under the action of external bending stress. By comparing the test results of the soft magnetic measuring device with and without bending stress, it is found that the magnetic permeability (μ i) decreases by about 51.41% when the introduced bending stress σ is increased by about 5.96 × 107 pa, whereas the KuFe−Si (induced magnetic anisotropy constant) and Hk (field of magnetic anisotropy) increase by 5.30 × 102 J m–3 and 1.08 × 102 A m−1, respectively. The Jiles-Atherton (J-A) model considering the bending stress and radius of change correlation is established, and the typical parameters of the J-A model are fitted using the Gazelle Optimization Algorithm (GOA), and the RMSE (root mean square error) of all of them are less than 0.056 T. The magnetic domain density increased with the increase of bending stress, which verified the correlation between the J-A model parameters and the bending stress. Our results reveal that the nanocrystalline macroscopic and micromechanical magnetic properties can be effectively combined with the J-A model, which will provide a theoretical basis for the simulation study of the nanocrystalline magnetic shielding device in the actual stress situation.

Prediction method of longitudinal surface settlement caused by double shield tunnelling based on deep learning

The deep learning method faces the challenges of small sample data and high dimensional shield operational parameters in predicting the longitudinal surface settlement caused by shield excavation. In this study, various optimization algorithms were compared, and the slime mould algorithm (SMA) was optimally chosen to optimize the hyperparameters of random forest (RF), and SMA-RF was used for dimensionality reduction and feature contribution analysis. A double-input deep neural network (D-DNN) framework was proposed for the prediction of surface settlement, which considers the influence of twin tunnels and effectively increases the high-fidelity data in the database. The results show that SMA performs best among various optimization algorithms; employing features that have a cumulative contribution value exceeding 90% as input can result in high prediction accuracy; there is significant uncertainty in the feature contribution analysis for small sample data; the reduced shield running parameters show a strong nonlinear relationship with surface settlement; compared with S-DNN, D-DNN takes into account the excavation of twin tunnels and expands the database capacity by more than 1.5 times, with an average increase of 27.85% in the R2 and an average decrease of 53.2% in the MAE.

Mathematical modelling for interaction between soft ground and small curvature shield tunneling considering viscoelastic characteristics influences

The current analytical solutions for predicting the ground settlements induced by small curvature tunneling in soft ground are generally conducted on the assumption of linear elastic foundation and provide little attention on the soil rheology. This paper introduces a mathematical model to estimate the small curvature tunneling induced adjacent ground settlement considering the soil viscoelasticity. By introducing the Boltzmann viscoelastic ground model under the Laplace transform, the time domain parameters converted from Poisson's ratio and shear modulus are derived to further obtain the viscoelastic ground loss solution and the Mindlin solution. Then, the proposed viscoelastic solutions are employed for the ground settlement caused by the over-excavation and imbalanced loads for the small curvature tunnel, which accounts for the soil rheology influence. The accuracy of the mathematical model is then verified by comparisons with in-situ observed data and 3D numerical simulation results, as well as good agreement is obtained. Finally, the parametric analyses are performed to estimate the influence for transverse and longitudinal surface settlements, including tunnel curvature radius, shield cutterhead face radius, over-excavation value, creep time and shear modulus ratio of viscoelastic ground.

Theoretical analysis of stratum horizontal displacements caused by small radius curve shield tunneling

For small radius curve shield tunneling, over excavation is required on the inner side of the curve to corner the shield machine. Currently, there is no corresponding analytical solution for horizontal displacements. In this paper, using the image method and Mindlin solution and considering four factors: additional thrust on the excavation surface, frictional resistance of the shield shell, ground loss, and grouting pressure at the shield tail, a formula for calculating stratum horizontal displacements caused by small radius curve shield tunneling is derived. Based on the 220 kV Rhinoceros Station cable shield tunnel project in Guangzhou, the stratum horizontal displacement law and influencing factors are analyzed. Through comparison and verification with on-site measured data, the results indicate that the theoretical formula derived is reasonable and reliable, providing a new approach for predicting the stratum horizontal displacements induced by curve shield tunneling. The law of stratum horizontal deformation exhibits that the horizontal displacement caused by the over excavation side of the curve moves toward the tunnel side. The outer side of the curve shifts away from the tunnel. The peak appears near the axis of the shield tunnel. The ground loss has the most significant influence on stratum horizontal displacements. Furthermore, on the same tunnel cross-section, the closer the soil is to the tunnel, the greater the horizontal displacement of the soil, and vice versa. The change in shield shell length profoundly affects horizontal displacements. The friction difference coefficient has a significant impact on the stratum horizontal displacement outside the curve.

Mate-guarding success depends on male investment in a butterfly.

Males of many insects, including butterflies, produce mate-guarding devices, such as mating plugs, to prolong guarding and prevent future female matings in the male's absence. In a few butterflies, large external mate-guarding devices, that is, sphragides, occur. Gór et al. (Behaviour, 160, 2023 and 515-557) found conspicuously large size and morphological variation of mate-guarding devices within a single population of the potentially polyandrous Clouded Apollo (Parnassius mnemosyne, L.) butterfly. They termed the externally visible male-produced devices as Copulatory opening APpendices (CAP) consisting of small devices, termed small CAPs and the much larger shield (i.e. sphragis). Our aim was to reveal CAP replacement dynamics within females during their lifetime and to understand how male investment into small CAPs or shields was (i) related to CAP persistence on the female, that is securing paternity, (ii) associated with female quality, measured as size and (iii) with actual adult sex ratio. We investigated a univoltine Clouded Apollo population to estimate CAP replacement risks, using multistate survival models, in an extensive observational study through 6 years based on mark-recapture. Shields were the most frequent mate-guarding devices and were more persistent than small CAPs, often lasting for life, excluding future matings. Thus, most females bearing a shield were deprived of postcopulatory female choice, and the genetic variance in their offspring could be reduced compared to those bearing small CAPs, thus mating more often. The ratio of shields to all CAPs gradually decreased towards the end of the flight period. Males were more prone to produce a shield when mating females with wider thoraces and when the ratio of males (i.e. competition) was higher in the population. To our best knowledge, this is the first quantitative study to investigate potential factors on which male investment in mate-guarding devices may depend, and how the variation in these devices impacts CAP persistence on females.

Deep and shallow crustal structure control on the late-stage volcanism in Syria Planum (Mars)

Long-lasting widespread volcanism in Mars is testified by the Tharsis volcanic province, one of the largest volcanic provinces with the largest shield volcanoes of the Solar System. However, volcanism on Mars is characterized also by the occurrence of broad volcanic fields, either in the form of small lava shields or monogenic volcanic cones. The region of Syria Planum (SP) is located east of the Tharsis province and between Noctis Labyrinthus to the North and Claritas Fossae to the southwest. It is an example of diffuse volcanism, presenting hundreds of small edifices (namely Syria Colles) which occur on top of a large bulge roughly 300 km × 200 km in size. SP exhibits a complex magmatic and volcano-tectonic evolution spanning from the early-Noachian to the more recent Amazonian. In this work, we investigate the geometry of the plumbing system of the SP volcanic field as well as the geometries of the volcanic constructs (i.e., vent elongation and vent alignment) that may be linked to the structures that fed the magma presenting a possible tectonic and volcanic evolution of the distributed volcanism phase in this area. The spatial distribution of vents and the overall map view shape of the volcanic field were studied in terms of vent clustering and spatial distribution. We show that the widespread and diffuse volcanism in SP presents clear vent clusters that are related to a deep source magma reservoir located at ∼100 km depth. We also show that Syria Colles vent elongations and azimuth distributions suggest that the magma exploited the inherited regional structural framework, coherent with the Syria Colles late-stage Amazonian magmatic event, and highlighting the role of a shallow crustal tectonic framework in shaping the Martian volcanism.

Ferrite Shield to Enhance the Performance of Optically Pumped Magnetometers for Fetal Magnetocardiography.

Fetal magnetocardiography (fMCG) has proven to be an important tool for the prenatal monitoring of electrical cardiac activity; however, the high cost of superconducting quantum instrumentation (SQUID) poses a limitation for the dissemination of fMCG as a routine clinical technique. Recently, optically pumped magnetometers (OPMs) operating within person-sized, cylindrical shields have made fMCG more practical, but environmental magnetic interference entering through the shield opening substantially degrades the quality of fMCG signals. The goal of this study was to further attenuate these interferences by placing the OPM array within a small ferrite shield. FMCG recordings were made with and without the ferrite shield in ten subjects inside a person-sized, three-layer mu-metal cylindrical shield. Although the fetal signal was slightly attenuated, the environmental interference was reduced substantially, and maternal interference was also diminished. This increased the signal-to-noise ratio significantly and improved the resolution of the smaller waveform components. The performance improvement was highest in the axial direction and compensated for a major weakness of open-ended, person-sized shields. The ferrite shield is especially beneficial for the deployment of triaxial OPM sensors, which require effective shielding in all directions.

Thermophoretic motion of a charged single colloidal particle.

We calculate the thermophoretic drift of a charged single colloidal particle with hydrodynamically slipping surface immersed in an electrolyte solution in response to a small temperature gradient. Here we rely on a linearized hydrodynamic approach for the fluid flow and the motion of the electrolyte ions while keeping the full nonlinearity of the Poisson-Boltzmann equationof the unperturbed system to account for possible large surface charging. The partial differential equationsare transformed into a coupled set of ordinary differential equationsin linear response. Numerical solutions are elaborated for parameter regimes of small and large Debye shielding and different hydrodynamic boundary conditions encoded in a varying slip length. Our results are in good agreement with predictions from recent theoretical work and successfully describe experimental observations on thermophoresis of DNA. We also compare our numerical results with experimental data on polystyrene beads.

Abundance and movement of fishes among nearshore habitat types in small boreal shield lakes

Abundance and movement of fishes among nearshore habitat types in small boreal shield lakes

Analysis of Excavation Parameters on Face Stability in Small Curvature Shield Tunnels

This study investigates the face stability of small curvature shield tunnels during excavation and its relationship with various excavation parameters. The stability of the excavation face is critical to the safety and efficiency of underground construction projects. Despite the increase in the use of small curvature shield tunnels in urban areas, research works on this type of tunnel are limited and the existing literature focuses only on straight shield tunnels. This study addresses this research gap through numerical simulations, analyzing the effects of different excavation parameters such as jacking force, cutting speed, and soil conditioning on face stability. The results of the study show that the excavation parameters significantly affect face stability. The findings can be used to optimize the performance of small curvature shield tunnels and support their continued development in urban areas.

Influence of Small Radius Curved Shield Tunneling Excavation on Displacement of Surrounding Soil

In contrast to straight tunnels, the mechanisms of displacement of surrounding soil induced by shield excavation of small radius curved tunnels are more complex. Based on field monitoring data of surface settlement and horizontal displacement of a small radius curved shield tunnel in a section of Zhengzhou Metro Line 3, a numerical model using three-dimensional a finite element method is established to evaluate factors of the displacement of surrounding soil. The results verify the validity of numerical simulation by comparison with field monitoring data and the influence of unbalanced additional thrust at tail jacks, curvature radius of a tunnel and tail grouting pressure on surface settlement and horizontal displacement of surrounding soil. Maximum surface settlement and horizontal displacement of surrounding soil at the outer side and inner side of curved tunnel axes are positively related to thrust ratio, while negatively related to curvature radius and grouting pressure. The ultimate objective of this study is to ascertain factors of displacement of surrounding soil induced by small radius shield excavation and provide a theoretical basis and technical support for the design and construction of similar tunnel.

A new and morphologically unusual Cheiroseius mite (Acari: Blattisociidae) found in association with tree sap, with a key to the congeneric species of the Slovak fauna

A new blattisociid mite, Cheiroseius arboricola sp. nov. was described based on females found in tree crevices of old oak (Quercus sp.) heavily soaked with xylem sap in southwestern Slovakia. The new species differs from most other known relatives mainly by the absence of a well-developed poststigmatic projection of the peritreme, the presence of only one pair of preanal setae (JV2) on the relatively small ventrianal shield, and the specific organization of some gnathosomal structures. A dichotomous identification key is presented for the females of thirteen species of Cheiroseius occurring in Slovakia, including the firstly reported species Cheiroseius furcatus Karg and Cheiroseius laelaptoides (Berlese).