Rear Edge Research Articles

Genetic mechanisms and a stability evaluation of large landslides in Zhangjiawan, Qinghai Province

It is important to study the instability law of typical landslides to understand the evolution of regional landslides and for disaster prevention. This study uses the Zhangjiawan landslide in Xining City, Qinghai Province, as an example. Through field surveys and an analysis of the geological environmental conditions, the formation and evolution mechanisms of the Zhangjiawan landslide are summarized. The stability of the Zhangjiawan landslide was evaluated using limit equilibrium and numerical simulation methods to provide theoretical support for the susceptibility of the Zhangjiawan landslide. The results show that the main reasons for the occurrence of multi-grade landslides are the steep and gentle terrain changes, the poor permeability of the mudstone lithology, the excavation of the front anti-slide section, and rainfall. The whole deformation and failure mechanism of the landslide is the “unloading rebound-tension deformation-creep deformation.” The results of the numerical simulation and the limit equilibrium methods are nearly the same, and the difference in the stability coefficients is small. Under rainstorm conditions, the displacement and the maximum shear strain increments are mainly concentrated on the rear edge of the landslide mass, and the front edge is pushed, which is a typical push-type landslide.

Underwater gas bubbles produced by droplet impact: Mechanism to trigger volumetric oscillations

Oscillating gas bubbles formed when droplets collide with a water surface are studied experimentally. Over a short time interval, before and after the bubble detachment, the bubble surface curvature changes drastically, causing a pulse of Laplace pressure. The leading edge of the pulse occurs before the bubble detachment, and the rear (negative) edge falls on the stage of an already closed bubble, which, like a resonator, is excited into volume oscillations on the natural frequency while simultaneously emitting an acoustic wavepacket. The amplitude and steepness of the pulse are inversely related to the size of the bubble, thereby ensuring that the dynamic parameters of the triggering pulse correspond to the natural frequency of the bubble. The release of pressure during the negative trailing edge of the pulse initiates the beginning of volumetric oscillations from the expansion phase and the acoustic packet from the positive half-wave.

Spatial distribution and failure mechanism of water-induced landslides in the reservoir areas of Southwest China

Water-induced landslides in hydropower reservoirs pose a great threat to both project operation and human life. This paper examines three large reservoirs in Sichuan Province, China. Field surveys, site monitoring data analyses and numerical simulations are used to analyze the spatial distribution and failure mechanisms of water-induced landslides in reservoir areas. First, the general rules of landslide development in the reservoir area are summarized. The first rule is that most of the landslides have rear edge elevations of 100–500 m above the normal water level of the reservoir, with volumes in the range of 10 6 –10 7 m 3 . When the volume exceeds a certain amount, the number of sites at which the landscape can withstand landslides is greatly reduced. Landslide hazards mainly occur in the middle section of the reservoir and less in the annex of the dam site and the latter half of the reservoir area. The second rule is that sedimentary rocks such as sandstone are more prone to landslide hazards than other lithologies. Then, the failure mechanism of changes in the water level that reduces the stability of the slope composed of different geomaterials is analyzed by a proposed slope stability framework that considers displacement and is discussed with the monitoring results. Permeability is an essential parameter for understanding the diametrically opposed deformation behavior of landslides experiencing filling-drawdown cycles during operation. This study seeks to provide inspiration to subsequent researchers, as well as guidance to technicians, on landslide prevention and control in reservoir areas.

The Role of Akt/Rab5A Signalling in Regulating Cell Migration of MDA-MB-231 Breast Cancer Cell Line.

Rab5A and Akt pathways are reported to be responsible for the invasiveness of cancer cells, indicated by the fact that Rab5A activates the downstream Phosphoinositide-3-kinases (PI3K)/Akt signalling pathway, which results in promoting cancer metastasis. However, little attention has been given to the emerging role of Rab5A and Akt signalling pathways in regulating the direction of MDA-MB-231 cell migration. MDA-MB-231 breast cancer cell line was used as a model in this study because it is highly metastatic and motile. Time-lapse microscopy was used to examine the effect of Akt and Rab5A inhibitors on cell migration, proliferation and wound healing. Later, the cells were transfected with GFP-Akt-PH or GFP-Rab5A (used as a biosensor to detect Akt and Rab5A). Therefore, confocal time-lapse images were used to visualize Akt and Rab5A at the front and rear edges of the cells. The recorded data demonstrated that Akt and Rab5A inhibition reduced cell migration, proliferation and wound healing. The results of the current study also demonstrated that Akt localizes at the trailing edge while Rab5A localize more at the leading edge than the trailing edge of cells. This study suggests that Akt and Rab5A inhibition might regulate the direction of breast cancer migration.

Jack pine of all trades: Deciphering intraspecific variability of a key adaptive trait at the rear edge of a widespread fire-embracing North American conifer.

Understanding mechanisms fostering long-term persistence of marginal populations should provide key insights about species resilience facing climate change. Cone serotiny is a key adaptive trait in Pinus banksiana (jack pine), which shows phenotypic variation according to the fire regime. Compared to range-core populations within the fire-prone boreal forest, low and variable serotiny in rear-edge populations suggest local adaptation to uncommon and unpredictable wildfire regime. We assessed environmental/physiological factors that might modulate intraspecific variation in cone serotiny. We experimentally subjected closed cones to incrementing temperatures, then tested seed germination to determine whether and how various ecological factors (cone age, branch height, tree size, tree age) are related to cone dehiscence and seed viability in jack pines from rear-edge and range-core populations in eastern Canada. Cones from rear-edge populations dehisce at a lower opening temperature, which increases with cone age. Cones from range-core stands open at a more constant, yet higher temperature. Cones from rear-edge stands take between 13 and 27 years to reach the level of serotiny achieved at the range core. At the rear edge, seed viability is steady (51%), whereas it decreases from 70% to 30% in 20 years at the range core. We inferred the mechanisms of a bet-hedging strategy in rear-edge populations, which ensures steady recruitment during fire-free intervals and successful postfire regeneration. This capacity to cope with infrequent and unpredictable fire regime should increase the resilience of jack pine populations as global changes alter fire dynamics of the boreal forest.

Acoustic resonance mechanism for axisymmetric screech modes of underexpanded jets impinging on an inclined plate

In this paper, the acoustic resonance mechanism for different axisymmetric screech modes of the underexpanded jets that impinge on an inclined plate is investigated experimentally. The ideally expanded Mach number of jets ( $M_j$ ) ranges from 1.05 to 1.56. The nozzle-to-plate distance at the jet axis and the impingement angle are respectively set as 5.0 $D$ and $30^{\circ }$ , where $D$ is the nozzle exit diameter. The acoustic results show that the $M_j$ range for the A2 screech mode of impinging jets is broader than that of underexpanded free jets, and a new axisymmetric screech mode A3 appears. With the increase of $M_j$ , the effect of the impinging plate on the shock cell structures of jets becomes obvious gradually, and the second suboptimal peaks are evident in the axial wavenumber spectra of mean shock structures. The coherent flow structures at screech frequencies are extracted from time-resolved schlieren images via the spectral proper orthogonal decomposition (SPOD). The axial wavenumber spectra of the selected SPOD modes suggest that the A1, A2 and A3 screech modes are respectively closed by the guided jet modes that are energized by the interactions between the Kelvin–Helmholtz wavepacket and the first three shock wavenumber peaks. The upstream- and downstream-propagating waves that constitute the screech feedback loop are analysed by applying wavenumber filters to the wavenumber spectra of SPOD modes. The frequencies of these three screech modes can be predicted by the phase constraints between the nozzle exit and the rear edge of the third shock cell. For the A3 mode, the inclined plate invades the third shock cell with the increase of $M_j$ , and the phase constraint cannot be satisfied at the lower side of the jets, which leads the A3 mode to fade away. The present results suggest that external boundaries can modulate the frequency and mode of jet screech by changing the axial spacings of shock cells.

Numerical study on landslide dynamic process and its impact damage prediction to brick-concrete buildings, a case from Fenghuang street landslide in Shaanxi, China

The study of landslide dynamic process and impact damage has important theoretical and practical significance for landslide risk quantitative assessment. Taking Fenghuang Street landslide in Ningqiang County, Shaanxi Province, China as an example, the dynamic process of landslide and its damage to brick-concrete structure buildings are predicted by using discrete element method. Firstly, a three-dimensional numerical landslide model is established by means of the particle flow code system (PFC3D), which is based on landslide investigation, surveying, engineering exploration and geotechnical testing. Secondly, the whole process of landslide deformation, failure, movement and impact damage was simulated, and the velocity, displacement and impact force of the landslide in the motion process were quantitatively studied. Thirdly, the building model (brick-concrete structure) located at the foot of the landslide was constructed by PFC3D and finite element software (Midas/gen), respectively. The characteristics of deformation and displacement of the buildings after the landslide impact are analyzed, and the impact damage of the landslide is predicted. The results show that the rear edge of Fenghuang Street landslide first deforms and fails, and the leading edge is gradually pushed out. After the locking section of the front edge is broken, the landslide begins to slide as a whole, which is a typical push landslide. The main sliding time of the landslide is about 30 s, the maximum average velocity is 3.2 m/s, and the maximum displacement is about 40 m. After the landslide hits the building, the building is displaced in the moving direction of the landslide, and the wall of the building impacted by the landslide is destroyed, resulting in an collapse evident. The relevant research methodologies and findings in this paper can provide a reference for the risk assessment of the same type of landslides, especially the quantitative assessment of the vulnerability for the brick-concrete buildings at risk.

Hypersonic Boundary-Layer Instability Suppression by Transverse Microgrooves with Machining Flaw

Transverse rectangular microgrooves with local machining flaw are investigated using direct numerical simulations from the viewpoint of suppressing the second-mode instability in a Mach 6 hypersonic boundary layer. Two types of machining flaw are modeled for the local deformation of microgrooves, i.e., chamfered and protruded ones. The effect of locally deformed microgrooves on the boundary-layer stability is studied by superposing the second-mode disturbance to the base flow of the boundary layer. The investigated unstable second mode is 400 kHz, and the microgrooves are installed in its synchronous region. The results show that compression and expansion waves are generated on the surface of the deformed microgrooves, and microscale separation bubbles are formed at the rear edge of the deformed microgrooves. With the increase of local deformation height of microgrooves, the suppression effect of the second-mode disturbance gradually increases. As the deformation height reaches 0.09 mm, the amplitude inhibition rate of locally deformed microgrooves on the second-mode disturbance reaches 44.7%, compared to that of the regular one.

Experimental Study of Vertical Tail Model Flow Control Based on Oscillating Jet

In this paper, wind tunnel experiments are conducted to study the control law and mechanism of oscillating jet flow control to improve the aerodynamic characteristics of the vertical tail when a civil aircraft encounters left side gust or significant crosswind during takeoff and landing. We measured the vertical tail scaling model’s aerodynamics, spatial flow field, and surface pressure when the Reynolds number was 2.12 × 105. The maximum momentum coefficient of the oscillating jet actuator reaches 0.332%. In addition, we studied the flow control effect of the three-dimensional vertical tail scaled model in different spanwise positions. The experimental results show that the oscillating jet at the rear edge of the stabilizer can significantly increase the lateral force of the vertical tail, and the increment of the lateral force can reach 36.5% under the worst condition of the negative side slip angle of the vertical tail. We can improve the lateral force coefficient of the vertical tail model by applying flow control alone at different spanwise locations. The wing root’s control effect and the vertical tail’s middle section are better than the wing tip’s. The oscillating jet can effectively restrain the flow separation on the rudder. In addition, the input of a high-energy jet “ejects” the mainstream, which increases the flow velocity at the side of the vertical tail actuator. It increases the circulation of the vertical tail. The oscillating jet flow control technology can effectively improve the vertical tail’s steering efficiency and increase the vertical tail’s lateral force, which is of great significance in improving the safety and economy of civil aircraft.

Dispersion management dual-pass self-phase modulation-enabled spectral selection

Self-phase modulation-enabled spectral selection (SESS) technology can generate wavelength-tunable femtosecond pulses, and it is expected to replace traditional complex optical parametric oscillators, and thus has attracted much attention. However, the positive dispersion in the fiber leads the modulation depth of the spectral lobes to decrease, while optical wave breaking hinders the spectral broadening. In order to solve the two problems, we propose a dual-pass SESS technology based on dispersion management which optimizes the shape of the front edge and rear edge of the pulse prior to the second pass by introducing negative dispersion, and compresses the pulse width for increasing the peak power of the pulse. The resulting spectrum features broader spectrum with a deeper modulation depth. By numerical simulation, we find that adjusting the value of the second-order dispersion compensated after the single pass, a broader spectral lobe can be obtained than both the single-pass case and the double-pass case without dispersion compensation. To verify our numerical simulation, we conduct experiments by using a 2-cm-long LMA-8 fiber for spectral broadening and several chirped mirrors to provide negative dispersion, which controls the nonlinear evolution of the pulse in the second pass of the LMA-8 fiber. We study the spectral output corresponding to different amounts of dispersion compensation and find that an optimal dispersion value is required to produce a clear and broader spectral lobe. We also investigate the effect of input pulse energy on spectral broadening under the same dispersion compensation conditions. With 15-nJ input pulse energy and –420 fs<sup>2</sup> dispersion compensation, the resulting SESS source delivers 6 nJ, 113-fs pulses with the peak wavelength at 920 nm.

Hedging at the rear edge: Intraspecific trait variability drives the trajectory of marginal populations in a widespread boreal tree species

Abstract Rear‐edge populations at the warm margin of species distribution are small, isolated and face environmental conditions at the limit of species bioclimatic envelope. Intraspecific phenotypic variation contributing to the persistence of peripheral populations is expected to become increasingly important under future climate conditions to avoid local extirpation where range shifts lag behind climate change velocity. We investigated the putative role of intraspecific phenotypic variation for the maintenance of rear‐edge populations of fire‐prone jack pine (Pinus banksiana), an obligate pyriscent boreal species. We assessed whether variation in cone serotiny is associated with the population trajectory of marginal stands located south of the boreal biome, in the temperate forest where natural wildfires are infrequent and unpredictable. To this end, we estimated stand‐scale serotiny, minimal age and tree size structure in 26 jack pine stands from the rear edge (n = 17 sites) and the core (n = 9 sites) of the species' range in eastern Canada. On average, rear‐edge jack pine populations are less serotinous albeit more variably compared with range‐core populations where serotiny is more uniformly high. Rear‐edge stands are generally older and display reverse J‐shape tree size structure indicative of a multi‐aged demographic equilibrium, whereas range‐core stands are younger and show a unimodal stand structure depicting a single ageing cohort generally lacking interfire recruitment. Eco‐evolutionary dynamics shifts from a dependency on wildfires in range‐core populations to stands that can regenerate and persist without recurrent fires at the rear edge, where stand‐scale serotiny reaches values below 85%. Synthesis. Unlike range‐core populations, rear‐edge jack pine populations can locally rely on a dual life‐history strategy to ensure both steady recruitment during fire‐free intervals and successful postfire regeneration. This capacity to cope with infrequent and unpredictable fire regime should increase the resilience and resistance of jack pine populations as global changes alter fire dynamics of the boreal forest. More generally, unique intraspecific phenotypic variation in rear‐edge populations contributes to long‐term species persistence in marginal environmental conditions that might scale up with global changes. The conservation of rear‐edge populations and their genetic legacy appears crucial for the resilience of species.

Eukaryotic CRFK Cells Motion Characterized with Atomic Force Microscopy.

We performed a time-lapse imaging with atomic force microscopy (AFM) of the motion of eukaryotic CRFK (Crandell-Rees Feline Kidney) cells adhered onto a glass surface and anchored to other cells in culture medium at 37 °C. The main finding is a gradient in the spring constant of the actomyosin cortex along the cells axis. The rigidity increases at the rear of the cells during motion. This observation as well as a dramatic decrease of the volume suggests that cells may organize a dissymmetry in the skeleton network to expulse water and drive actively the rear edge.

Combined Scattering, Interferometric, and Fluorescence Oblique Illumination for Live Cell Nanoscale Imaging

To determine the molecular and/or mechanical basis of cell migration using live cell imaging tools, it is necessary to correlate multiple 3D spatiotemporal events simultaneously. Fluorescence nanoscopy and label-free nanoscale imaging can complement each other by providing both molecular specificity and structural dynamics of sub-cellular structures. A combined imaging system would permit obtaining quantitative 3D spatial temporal details of individual cellular components. In this paper, we empirically determined optimal azimuthal scanning angles of rotating beams to achieve simultaneous and label-free nanoscale and fluorescence imaging. Label-free nanoscale imaging here refers to interferometric, bright-field (BF) and dark-field (DF) rotating coherence scattering (ROCS) microscopy, while fluorescence refers to high-inclined laminated oblique (HiLO) and total internal reflection fluorescence (TIRF) imaging. The combined capabilities of interferometric, scattering, and fluorescence imaging enable (1) the identification of molecular targets (substrate or organelle), (2) quantification of 3D cell morphodynamics, and (3) tracking of intracellular organelles in 3D. This combined imaging tool was then used to characterize migrating platelets and endothelial cells, both critical to the process of infection and wound healing. The combined imaging results of more than ∼1000 platelets suggest that serum albumin (bovine) is necessary for platelets to migrate and scavenge fibrin/fibrinogen. Furthermore, we identified new asynchronous membrane fluctuations between the leading and rear edges of a migrating platelet. We further demonstrated that interferometric imaging permits the quantification of mitochondrial dynamics on human lung microvascular endothelial cells. Our data suggests that axial displacement of mitochondria is minimal when it is closer to the nucleus or the leading edge of a cell membrane. Taken together, this combined nanoscopy platform helps to quantify multiple spatial temporal events of a migrating cell that will undoubtedly open ways to new quantitative correlative nanoscale live cell imaging.

Weak genetic differentiation but strong climate-induced selective pressure toward the rear edge of mountain pine in north-eastern Spain

Local differentiation at distribution limits may influence species' adaptive capacity to environmental changes. However, drivers, such gene flow and local selection, are still poorly understood. We focus on the role played by range limits in mountain forests to test the hypothesis that relict tree populations are subjected to genetic differentiation and local adaptation. Two alpine treelines of mountain pine (Pinus uncinata Ram. ex DC) were investigated in the Spanish Pyrenees. Further, an isolated relict population forming the species' southernmost distribution limit in north-eastern Spain was also investigated. Using genotyping by sequencing, a genetic matrix conformed by single nucleotide polymorphisms (SNPs) was obtained. This matrix was used to perform genotype-environment and genotype-phenotype associations, as well as to model risk of non-adaptedness. Increasing climate seasonality appears as an essential element in the interpretation of SNPs subjected to selective pressures. Genetic differentiations were overall weak. The differences in leaf mass area and radial growth rate, as well as the identification of several SNPs subjected to selective pressures, exceeded neutral predictions of differentiation among populations. Despite genetic drift might prevail in the isolated population, the Fst values (0.060 and 0.066) showed a moderate genetic drift and Nm values (3.939 and 3.555) indicate the presence of gene flow between the relict population and both treelines. Nonetheless, the SNPs subjected to selection pressures provide evidences of possible selection in treeline ecotones. Persistence in range boundaries seems to involve several selective pressures in species' traits, which were significantly related to enhanced drought seasonality at the limit of P. uncinata distribution range. We conclude that gene flow is unlikely to constrain adaptation in the P. uncinata rear edge, although this species shows vulnerability to future climate change scenarios involving warmer and drier conditions.

Climate aridity and habitat drive geographical variation in morphology and thermo-hydroregulation strategies of a widespread lizard species

Abstract Thermo-hydroregulation strategies involve concurrent changes in functional traits related to energy, water balance and thermoregulation and play a key role in determining life-history traits and population demography of terrestrial ectotherms. Local thermal and hydric conditions should be important drivers of the geographical variation of thermo-hydroregulation strategies, but we lack studies that examine these changes across climatic gradients in different habitat types. Here, we investigated intraspecific variation of morphology and thermo-hydroregulation traits in the widespread European common lizard (Zootoca vivipara louislantzi) across a multidimensional environmental gradient involving independent variation in air temperature and rainfall and differences in habitat features (access to free-standing water and forest cover). We sampled adult males for morphology, resting metabolic rate, total and cutaneous evaporative water loss and thermal preferences in 15 populations from the rear to the leading edge of the distribution across an elevational gradient ranging from sea level to 1750 m. Besides a decrease in adult body size with increasing environmental temperatures, we found little effect of thermal conditions on thermo-hydroregulation strategies. In particular, relict lowland populations from the warm rear edge showed no specific ecophysiological adaptations. Instead, body mass, body condition and resting metabolic rate were positively associated with a rainfall gradient, while forest cover and water access in the habitat throughout the season also influenced cutaneous evaporative water loss. Our study emphasizes the importance of rainfall and habitat features rather than thermal conditions for geographical variation in lizard morphology and physiology.

Migration‐based simulations for Canadian trees show limited tracking of suitable climate under climate change

AbstractAimSpecies distribution models typically project climatically suitable habitat for trees in eastern North America to shift hundreds of kilometres this century. We simulated potential migration, accounting for various traits that affect species' ability to track climatically suitable habitat.LocationEastern Canada, covering ~3.7 million km2.MethodsWe simulated migration‐constrained range shifts through 2100 using a hybrid approach combining projections of climatically suitable habitat based on two Representative Concentration Pathways (RCP4.5, RCP8.5) for three time periods and two species distribution modelling approaches with process‐based models parameterized using data related to dispersal ability and generation time. We developed a unique “migration kernel” that uses seed dispersal traits and observed migration velocities to obtain kernel shape and dispersal probabilities for each tree species. We then calculated lags between the migration‐constrained range limits obtained through simulations and limits of climatically suitable habitat.ResultsAll species demonstrated northward range shifts at the leading edge of their simulated distribution through 2100, but the magnitude and rate of that shift varied by species and time period. Climatically suitable habitat limits were found to be north of simulated distribution limits across both RCPs, with lags increasing through time. On average, simulated distribution that remained within climatically suitable habitat declined more under RCP8.5 than RCP4.5, with large areas of the rear edge of the simulated distribution becoming partially or completely climatically unsuitable for many species.Main conclusionsClimatically suitable habitat limits projected for 2100 far exceeded migration‐constrained range limits for all 10 tree species, particularly for temperate species. This study underlines the limited extent to which tree species will track climate change via natural migration. Integrating observed migration velocities, seed dispersal and generation time with SDM outputs allows for more realistic evaluations of tree migration ability under climate change and may help orient forest conservation and restoration efforts.

Методика расчетных исследований усиления предварительно напряженной базальтокомпозитной арматурой стен камер шлюзов с учетом фактических данных об их эксплуатационном состоянии

Introduction. Calculation studies have shown that due to the long-term operation of hydraulic structures of the sluice, opening of horizontal and vertical construction joints, as well as corrosion of reinforcement at the rear edge of the reinforced concrete wall of the sluice in the areas of horizontal construction joints, the bearing capacity of the structure as a whole is reduced. In this regard, it is necessary to strengthen the structure, the methodology of which is given in this study. Materials and methods. The analysis of scientific and technical documentation has been made, instrumental examination of the state of structures has been carried out, a spatial mathematical model has been developed on the basis of the finite-element method. Multivariant calculated researches of the actual stressed-strained state (SSS) of structures have been made. Calculation studies of the SSS structures were performed taking into account the reinforcement of prestressed basalt composite reinforcement (BCR). Results. Visual and instrumental inspection showed a presence of cracking on the front face of the reinforced concrete wall of the sluice chamber. Modeling of the actual state of SSS structures is performed, according to the results of calculations, a scheme for strengthening structures of prestressed BCR is proposed and justified. Conclusions. As a result of the calculated studies of the deflected stresses, the occurrence of cracks and opening of horizontal and vertical construction joints in the reinforced concrete structure of the sluice chamber wall was confirmed. At the same time, taking into account corrosion of reinforcement at the rear edge of the sluice’s reinforced concrete wall in the areas of horizontal construction joints, stresses in it reach the design resistance of the reinforcement of class A-II. In order to ensure further safe operation of the structures, the scheme of strengthening the structures with prestressed BCR has been proposed and substantiated.

Passive Drag Reduction of the Square Back Truck Body

Drag is one of the most significant factors that increase fuel consumption, followed by operating cost of the vehicle. Square-back road vehicles like trucks and buses are common and popular means of transport across the globe. In this background, it is of great research value to reduce the drag on vehicles, improve their fuel efficiency and reduce their operational cost. In this work, a simplified model of a truck was considered, and its drag was reduced by modifying its geometry using passive drag reduction devices. The passive devices used in this study were backward-facing step, fins, splitter plates/tabs, dimple, vents, and channels. These devices, of different sizes and configurations, were numerically studied using CFD software Star CCM+ at a Reynolds number of 2.4127×10^6. Drag reduction up to 9.9% was achieved, when backward-facing step was placed at the bottom rear edge of the truck. Further, multiple circular channels used on the truck’s sides reduced the drag up to 6.5%, while multiple rectangular channels on the sides of the truck achieved 5.1% drag reduction. The maximum drag reduction of the fins was found to be 4.6%. In spite of these, no significant drag reduction was observed when using splitter plates/tabs, dimple and vents.

Control of the noise production in a supersonic jet impinging an inclined plate using grooved surface

This paper presents an experimental investigation on free jet and jets impinging on smooth and grooved surfaces. Acoustic studies are performed using free-field microphones, while two dimensional (2D)-particle imaging velocimetry (PIV) is utilized to investigate the velocity fields. The effects of nozzle-plate spacing distance, nozzle pressure ratio (NPR) and plate inclination are also investigated. The results demonstrate that a high-speed jet impinging on a grooved plate generates lesser acoustic radiation on an inclined plate surface when compared to a smooth plate with 2.16 < NPR < 3.1 in the range of L/d = 3 ∼ 5. Reduction of the amplitude of discrete tones is an important factor in its noise reduction. To present a detailed explanation of this phenomenon, this paper further coupled the acoustic discrete tones and mean fluctuating flow velocities. Results showed that screech tone is mainly caused by the interaction between the rear edge of the fourth shock cells and the large vortical structures in the mixing layer, and the shear layer of the wall-jet has a certain shielding effect on the near-wall acoustic power, and the acoustic power decreases at high-speed impinging jets.

Evaluation of multi-bit domain wall motion by low current density to obtain ultrafast data rate in a compensated ferrimagnetic wire

Architectures based on multi-bit magnetic domain walls (DWs) take advantage of the fast speed, high density, nonvolatility, and flexible design of DWs to process and store data bits. However, controlling multi-bit DWs driven by electric current at an ideal position remains a significant challenge for developing integrated spintronic applications with high reliability and low power consumption. We exhibit the possibility of driving fast and stable multi-bit DWs at low current density without an in-plane external magnetic field in Fe-rich GdFeCo magnetic wires. When an in-plane magnetic field is applied in the wire direction, the front edge accelerates, although the rear edge decelerates, and the recorded data are destroyed. Hence, this method is not practical. Here, the DW speed of the multi-bit DWs is 1500 m/s under a low current density of 29 × 1010 (A/m2). A straight DW shape is required to accurately read the bits of information by the tunneling magnetoresistance head in real DW memory devices. Moreover, we demonstrate that the DW position is related to the DW shape after injecting a pulse current into the magnetic wire. A straight DW shape is exhibited for 3 ns pulse duration width, while the DW shape became rounded for 30 and 50 ns pulse duration widths. Our finding provides a practical concept for multiple-bit-per-cell memory and presents a viable platform for DW memory applications.