Transition Zone Research Articles

The influence of roll angles on unsteady aerodynamics in a canard‐configured missile

AbstractDuring the initial stage of vertical launch, a missile may exhibit an uncertain roll angle (φ) and a high angle of attack (α). This study focuses on examining the impact of roll angle variations on the flow field and the unsteady aerodynamics of a canard‐configured missile at α = 75°. Simulations were performed using the validated k‐ω SST turbulence model. The analysis encompasses the temporal development of vortices, the oscillatory characteristics of the lateral force, and the fluctuation of kinetic energy distribution within the framework of proper orthogonal decomposition (POD). The results indicate that the flow field surrounding the canard‐configured missile is characterized by inconsistent shedding cycles of Kármán‐like and canard‐separated vortices. A distinct transition zone is identified between these vortices, where vortex tearing and reconnection phenomena occur. With increasing roll angles from 0° to 45°, there is an observed shift in the dominant frequency of the lateral force from the higher frequency associated with Kármán‐like vortex shedding to the lower frequency of canard vortex shedding. The shedding frequency of Kármán‐like vortices corresponds to the harmonics of the canard vortex shedding frequency, indicative of a higher‐order harmonic resonance. The frequency of the lateral force is observed to decrease with an increase in roll angle, except in configurations lacking distinct canard‐separated vortices, which are characterized by a “+” shape. The POD analysis reveals that the majority of the fluctuation energy is concentrated in the oscillations and shedding of the canard‐separated vortices, leading to pressure fluctuations that are primarily observed on the canard and the downstream region of the canard.

Potassium isotopic evidence for recycling of surface water into the mantle transition zone

Potassium isotopic evidence for recycling of surface water into the mantle transition zone

Amazon Transition - Cerrado: Agricultural Frontier and Sustainability in The State of Mato Grosso, Brazil

Objective: The present study aimed to demonstrate the relevance of agribusiness and highlight sustainable development actions in the Amazon-Cerrado transition zone, in the center-north of the state of Mato Grosso, in line with the Sustainable Development Goals of the United Nations. Theoretical framework: This topic sought to contemplate the aspects of sustainable food production, in a holistic view that minimizes environmental impacts, in order to stimulate sustainable management, efficient use of resources and inputs in the various sustainable economic activities. Method: Theoretical framework on the subject, research based on Web of Science and Google scholar, tabulation of data and elaboration of a table with sustainable initiatives and a map of the location of the Amazon-Cerrado transition zone. Results and conclusion: In parallel to the large-scale agro-export production mode, several initiatives of agroecological production, natural extractivism, integration between forest, crops and livestock were identified in the research using techniques that seek environmental sustainability and sustainable local development in the region of the study. Implications of the research: In line with the environmental theme, the study presents and discusses relevant initiatives in society associating agribusiness and sustainable development. Originality/value: Preparation of an unprecedented map of the municipalities of Mato Grosso that are located in the transition zone of the Amazon - Cerrado biomes and a table with organizations, activities and sustainable actions developed in the transition area and respective associations with the Sustainable Development Goals of the United Nations, with a discussion on proactive activities aimed at developing the region in focus.

In the frontier zone of market transition: Economic possibilities across the market/non-market divide

This paper engages with two important approaches theorising the co-existence and even close entanglement between the market and non-market to rethink the making of actually existing market economies. The first, that is, the diverse/community economies approach, underscores alternative relations and ethics to capitalism but often views community economies as external to market processes. A second approach on market frontiers rejects the idea of the non-market domain as a Utopian space but re-imagines it as a constituent part within capitalism, while powerful actors manage and utilise non-market differences to configure particular regimes of accumulation. However, it says relatively little about how the market/non-market divide is navigated and appropriated to suit the wellbeing of grassroots people and communities. This paper calls for a dialogue between the two approaches and argues that community economies provide important ‘background conditions of possibility’ for ordinary people to advance their needs, interests, and wellbeing by negotiating or traversing the market/non-market divide. Our empirical study investigates recent socioeconomic transformations in two villages, Lolong and Nyiru, located within the Potatso National Park, Yunnan Province, China. In both villages, local people keep alive communal norms of reciprocity and mutual support. The persistence of the non-marketised community economies is partly attributed to a state-capital coalition that outlaws grassroots participation in local tourism economy. Subsequently, villagers devise a number of tactics to penetrate the market realm and meet emerging lifestyle and consumer needs. Three of such tactics are discussed in this study.

Compressive and Tensile Behavior of High-Ductility Alkali-Activated Composites with Polyethylene Terephthalate Powder

Researchers have been engaged in the study of high-ductility concrete (HDC) due to its excellent ductility and cracking control ability. This study combines the concepts of HDC and alkali-activated composites (AAC) to develop high-ductility alkali-activated composites (HDAAC) using polyethylene terephthalate (PET) powder. Experimental investigations were conducted to assess the compressive and tensile properties of HDAAC, focusing on the impact of varying PET powder content (0%, 15%, 30%, and 45%) and fly ash/slag ratios (FA/GGBS, 6:4, 7:3, and 8:2). The results indicated that the compressive strength of HDAAC ranged from approximately 30 MPa to about 100 MPa, with the specimens maintaining good integrity after axial compression failure due to the bridging action of PE fibers. The replacement of quartz powder (QP) with PET powder slightly decreased the compressive strength and elastic modulus of HDAAC, albeit mitigating its brittleness under compression. An increase in GGBS content enhanced the compressive strength and elastic modulus of HDAAC due to the increased formation of the C-A-S-H reaction products, leading to reduced porosity and a denser microstructure. Under axial tension, HDAAC exhibited typical multiple-cracking behavior with significant pseudo-strain hardening. Increases in the PET content and FA/GGBS ratio resulted in finer cracks, indicating excellent crack control and deformation capabilities. The initial cracking strength, tensile strength, and ultimate tensile strain ranged from 3.0 MPa to 4.6 MPa, 4.2 MPa to 8.2 MPa, and 4.1% to 7.2%, respectively. Despite a decrease in the initial cracking strength and tensile strength with higher PET content, the ultimate tensile strain of HDAAC slightly increased. Observations under a scanning electron microscope revealed a distinct interfacial transition zone near the PET powder, leading to poor bonding with the alkali-activated matrix. In contrast, QP dissolved on the surface in highly alkaline environments, forming better interface properties. These variations in interface properties can be used to interpret the variations in the mechanical performance of HDAAC.

Understanding the role of natural pozzolana in regulating the early hydration reaction process and microstructure of Portland cement

The present study examines the regulatory role of natural pozzolana (NP) on the early-age hydration process and microstructural development of Portland cement. Through a series of experiments, including low-field nuclear magnetic resonance (NMR), X-ray diffraction (XRD), thermogravimetric (TG) analysis and scanning electron microscopy (SEM), it was found that NP significantly influences the hydration kinetics and chemical shrinkage of cement paste. The addition of NP was shown to reduce the early-age chemical shrinkage and refine the microstructure by decreasing the quantity of harmful pores and increasing harmless pores, as evidenced by the bimodal distribution observed in pore size distribution (PSD) analysis. XRD and TG results indicate that NP reacts with calcium hydroxide to form additional calcium silicate hydrate (C-S-H) gel, thus improving the interfacial transition zone and resistance to carbonation. SEM micrographs further confirm the improved microstructure with fewer microcracks. The findings suggest that NP can be effectively utilized to optimize the early-age performance of concrete, offering a sustainable approach to improving its durability and long-term structural integrity.

Evapotranspiration in the Amazon Basin: Couplings, hydrological memory and water feedback

The hydrological cycle of the Amazon Basin is characterized by a multitude of interactions between the atmosphere and surface processes, involving several temporal and spatial scales. Evapotranspiration is a key variable in the water and energy balance, particularly in this watershed that is home to the world largest rainforest. This study analyzed evapotranspiration in the Amazon Basin using the concepts of Coupling (one way relationship between two variables), Memory (temporal permanence of a state or anomaly in the behavior of one variable) and Feedback (two way relationships between two variables), during a 62-year period (12/1959–11/2021). This study found that the seasonality of precipitation, mainly due to the South American Monsoon, determines when evapotranspiration is mainly driven by (or coupled with) net radiation at the surface or soil moisture. Moreover, in the regions where seasonality of precipitation is strong, the previous hydroclimatic conditions due to hydrological memory (reaching just over 90 days in shallow soils) influences the evapotranspiration during the relatively dry season. Regarding water feedback, this study found that the dependence of seasonal precipitation of the Amazon Basin from their hydrobiological processes (fraction of precipitation recycled by Amazonian evapotranspiration) increases with the distance from the Atlantic Ocean, mainly during the non-monsoonal circulation. This process is particularly remarkable in the Amazon-Andes transition zone. However, the spatial pattern and height of water recycled in this watershed is mainly determined by the dominant circulation pattern of atmospheric fluxes in each season.

Моделирование турбулентной естественной конвекции на основе 2-жидкостного подхода

The paper provides mathematical modeling of turbulent natural air convection at a heated vertical plate based on a fairly recently developed two-liquid turbulence model. The considered problem, despite its relative simplicity, contains all the main elements characteristic of the currents near the wall due to buoyancy forces. A significant disadvantage of the RANS turbulence models used to solve such problems is that for their numerical implementation it is necessary to set the laminar-to-turbulent transition point, which must be determined experimentally. Thus, all RANS models are unable to describe a laminar-to-turbulent transition zone. Therefore, the main purpose of the work is to test the ability of the two-liquid turbulence model to describe the transition zone. Well-known publications have shown that the two-liquid model has high accuracy and stability, and is also able to adequately describe anisotropic turbulence. The turbulence model used in this work is supplemented with an additional thermal force, which can be ignored in many flows with forced convection. However, in the natural convection currents, it is this force that contributes to the transition of the flow regime. To validate the model, as well as to verify the computational procedure, the numerical results obtained are compared with the results of the well-known RANS turbulence models (the one-parameter Spalart-Allmaras (SA) model and the Reynolds stress transfer (RSM) model), as well as with the available experimental data. It is shown that the two-liquid model adequately reproduces the laminar-to-turbulent transition zone, and the numerical results obtained are in good agreement with experimental data.

Development of transition schemes and optimization measures between normal slab track and ladder-type sleeper track

Severe vibrations and deterioration of track system are often observed due to the sudden change in support stiffness between normal slab track (NST) and damping track. To improve the dynamic performance of both the train and track system when a train runs on the transition zone between the NST and the damping track, we focused on the ladder-type sleeper track (LS track) and developed several optimized transition schemes. Firstly, a train-LS track coupled dynamics mode is developed, and it was verified using field testing. Afterward, using the dynamic responses of train and track systems in the transition zone between the NST and the resilient-fastener slab track (RFS track) as a reference, the shortcomings of the traditional transition scheme are identified, and the optimal transition scheme is developed by comparison of the proposed multiple schemes. Finally, the device for suppressing track vibration (DSTV) is installed on the longitudinal sleeper to alleviate the vibration of the LS track and improve the overall stability of the vehicle and track system during the transition zone. The results indicate that the optimal transition scheme proposed in this study lead to significant improvements in the dynamic performance of both the vehicle and LS track.

Research on active load reducing optimization strategy for 6061Al low cycle fatigue cropping process based on crack propagation mode transformation

Low cycle fatigue cropping technology is a new type of cropping technology with advantages such as no chip waste and low load need. Numerous studies have shown that increasing the fatigue frequency or increasing the displacement load can improve the cropping efficiency, but at the same time, it will reduce the quality of the cross-section and cannot achieve a balance between high efficiency and high quality of cross-section. In response to this issue, this paper found the phenomenon of transition of fracture modes (from fatigue mode to tensile fracture mode) of 6061Al material in LCFC process, and proposed the Active Load Reducing Optimization Strategy for 6061Al in LCFC, which achieves a significant improvement in quality of cross-section with a slight loss of cropping efficiency. Firstly, this paper studied the crack fracture mechanism of 6061Al bar under different displacement loads in the LCFC process. It was found that the transition of crack propagation mode in 6061Al- LCFC process was the main reason for the increase in cross-section roughness. The crack propagation mode changed from fatigue propagation to tensile fracture propagation during the LCFC process, and the roughness of the area significantly increased under the tensile fracture propagation mode. Further research has found that the fundamental reason for the contradiction between the cropping efficiency and section quality of 6061Al is the change in time of crack propagation mode transition and tensile fracture zone area under different displacement loads. Finally, the LCFC process was modeled in a time dimension using acoustic emission(AE) technology, and it was divided into three stages according to the AE signals and the fracture mechanism. As a result, an active load reducing optimization strategy for LCFC process was developed to delay the occurrence of tensile fracture propagation modes. Experiments have shown that compared to the traditional LCFC cropping strategy using constant displacement loads, the active load reducing strategy proposed in this paper can reduce the proportion of tensile fracture area, achieve a significant improvement in quality of cross-section with a slight loss of cropping efficiency, thus achieving a balance between efficiency and section quality to some extent. At the same time, an LCFC process section quality efficiency evaluation index with dual weights of efficiency and section quality has been proposed, which can assist in selecting LCFC active load reducing strategy parameters with consideration of efficiency and section quality weights.

Influence of geometric shape, pore structure and surface modification of recycled fine aggregate on the rheology behaviour and strength development of mortar

The complex physical properties of recycled fine aggregate affect the rheological and mechanical properties of mortar, thereby limiting its application in cement-based materials. This paper evaluated the geometric shape and pore structure of natural fine aggregate (NFA), recycled fine aggregate (RFA), and recycled fine aggregate modified by water glass (MRFA), and studied its water absorption and bulk density. The influence of complex physical properties of RFA before and after modification on the rheological behavior, strength development, and microscopic properties of mortar was analyzed. The rheological tests were carried out on the fresh mortar with 7 mixes, and the compressive strength and flexural strength of hardened mortar after curing for 3, 7 and 28 days were tested. The results shown that the modification of water glass has improved the water absorption and geometric shape of RFA to some extent, resulting in a small increase in the apparent viscosity and yield stress of recycled mortar compared to NFA mortar. When the replacement level of RFA was less than 30 %, the compressive strength of recycled mortar was 13 % higher than that of NFA mortar. As the replacement level increased to 40 %, the incorporation of water glass also helped to improve the mortar strength. The irregular geometric shape and high water absorption of RFA were conducive to achieving dense mechanical bonding and reducing the Ca/Si ratio in the interface transition zone.

Combined onshore and offshore wide-scale seismic data acquisition and imaging for carbon capture and storage exploration in Havnsø, Denmark

Strong global actions for climate change include carbon capture and storage (CCS) as a feasible solution to reach carbon neutrality and raise opportunities for detailed subsurface investigations. An acquisition set-up designed for onshore-offshore zones was maximized for wide-scale high-resolution structural imaging and implemented to cover a domal structure of interest for CCS utilization close to the town of Havnsø (Denmark). The challenges of the combined acquisition and processing of land and marine multisensor data along a 42 km seismic profile are analyzed, the suggested solutions are applied, and the limitations are discussed. On the onshore side, a nodal array and a seismic landstreamer system were simultaneously used, whereas along the transition zone, a marine seismic streamer and ocean-bottom seismometers were added to record the seismic response generated by two seismic vibrator sources. The adopted sensing domains (velocity, acceleration, and pressure) were studied, and different processing steps were evaluated to enable their processing and subsequent data set merging. Results suggest, as the best approach, a separate prestack processing of the different data sets and the computation of new geometries and new surface-consistent residual static correction after their merging. The data acquired in the transition zone illuminate, for the first time, the subsurface geology of the region, delineating an expected domal closure. The final seismic section shows high continuity of the reflections with good resolution along the entire profile, identifying the main reservoir structure and the surrounding areas, which are important to ensure reservoir integrity and safe exploitation over longer time scales. Shallow and deep reflections are consistent with the stratigraphic column from a well log near the profile. The presented study shows a comprehensive workflow for processing such a multisensor data set in onshore and transition zone settings.

Unraveling Functional Diversity Patterns in Hyporheic Zones: A Trait-Based Approach Applied to Copepods from the Rio Gamberale Creek

Despite the recognized ecological significance of hyporheic zones, biological investigations into their ecology, especially concerning functional diversity, remain limited. This is particularly true for copepod assemblages, abundant in the transitional zone between groundwater and surface waters, requiring more thorough exploration. To bridge this knowledge gap, our study extensively monitored a hyporheic zone within a mountain creek and examined nine functional traits across twelve copepod species found in this environment. Through the application of RLQ and fourth-corner analysis, as well as functional diversity indices including functional richness, evenness, divergence, and dispersion, we aimed to establish links between functional traits and environmental factors. Our findings revealed relationships between environmental features—specifically electrical conductivity, pH, and ammonium concentration—and the trait composition of copepod assemblages, which were influenced by species abundances. Considering the intimate connection between functional traits and ecosystem services, assessing functional diversity within hyporheic zones offers valuable insights into its functionality in terms of services rendered. This study emphasizes the importance of understanding and managing functional diversity in hyporheic zone dynamics to ensure the health and stability of ecotones and, by extension, riverine and groundwater ecosystems.

Thermomechanical fatigue behavior of CF/PEKK composite under low and ultrasonic frequencies

This study aimed to extract the thermomechanical fatigue behavior of a CF/PEKK composite under low and ultrasonic frequency fatigue tests (LFFTs and UFFTs) in the presence of the self-heating effect. Preliminary increasing amplitude tests (IATs) were performed to obtain the minimum load level at which the self-heating is observable. Extracting the fatigue strength from T-σ curves for three mean stress levels resulted in constructing S-N curves for the LFFT regime at different load levels using a shift procedure. However, combining LFFT and UFFT results via S-N curve was impractical, while joining such results through the heat dissipation rate (q̇) was feasible for various constant amplitude tests and IATs. The derived σ-q̇ curves from combining LFFT and UFFT results and comparing the fracture mechanisms of CF/PEKK composite using fractography would make a step for bridging the transition zone between LFFTs and UFFTs and making the results transferable. The microscopy images obtained from fractography also confirmed the similarities of fatigue fracture mechanisms between LFFTs and UFFTs.

Mesoscopic simulation of uniaxial compression fracture of concrete via the nonlocal macro–meso-scale consistent damage model

To capture the uniaxial compression fracture of concrete composite is still a great challenging problem. To this end, the newly proposed nonlocal macro–meso-scale consistent damage (NMMD) model is extended to simulate uniaxial compression fracture of concrete composites. In the NMMD model, a mesoscopic structure composed of material point pairs is attached to each material point. A decomposition scheme suitable for masonry-like materials is adopted to decompose the elongation quantity of point pairs. The topologic damage is defined as the weighted summation of mesoscopic damage in neighboring material point pairs driven by the decomposed elongation quantity. The physically-based energetic degradation function is employed to bridge the geometric discontinuity in solids and the energy dissipation, and thus the topologic damage is integrated into the framework of continuum damage mechanics. The Monte-Carlo method and two-phase random field model are employed to generate stochastic circular and irregular aggregates representing the meso structure of concrete, respectively. The interface transition zone is prescribed by reducing the critical value of interface point pairs. Numerical results indicate that both the crack patterns and stress–strain curves of the uniaxial compression experiments on concrete panels can be well captured by the proposed NMMD model without mesh size sensitivity. The influence of horizontal constraints on the top and bottom surfaces is investigated and shown to have an effect on the crack patterns, strength and deformation capability of the specimen. The necessity of decomposition is also illustrated.

Study on the influence of fractal dimension and size effect of coarse aggregate on the frost resistance of hydraulic concrete

In cold regions, hydraulic concrete structures are exposed to harsh environmental conditions that greatly impact their durability and safety. The role of aggregates in influencing concrete performance is paramount. This study aims to investigate how the fractal distribution and size of aggregates affect the frost resistance of hydraulic concrete, with air void characteristics, mass loss rate, Elastic Modulus of dynamic, and strength serving as primary references. Two experiment series, fractal distribution influence and aggregate size influence of concrete frost resistance, were conducted to analyze the frost resistance of hydraulic concrete with different aggregates. Based on the fractal theory, four grading fractal distributions were utilized to fractalize aggregate gradation, aiming to investigate the influence of aggregate fractal dimension on the frost resistance of hydraulic concrete. Simultaneously, concrete specimens of fully graded aggregate and wet-screened aggregate were also constructed to simultaneous freeze-thaw cycle tests, the impact of aggregate size on concrete's frost resistance performance was also studied by analyzing the air void structure in the frost-resistant concrete specimens. Results indicate that the specimens exhibit varying frost resistance performance under different aggregate gradation fractals, ranking from strongest to weakest as follows: D=2.5, D=2.3, D=2.1, D=2.7, which is attributed to the differences of air void spacing factors. Increasing aggregate size leads to greater internal structural heterogeneity in concrete, resulting in an increase in defects and weak points. This causes microcracks to develop more rapidly in the transition zone of fully graded concrete during freeze-thaw cycles, leading to more severe damage. The findings of this study can serve as a fundamental scientific basis for the designing and constructing of hydraulic concrete structures in cold areas.

Regulating sulfur migration and transformation in low water-binder ratio cementitious system incorporating phosphogypsum aggregate: Environmentally friendly clean materials

The paper aims to clarify the regulation mechanism of sulfur migration and transformation in a low water-binder ratio system incorporating phosphogypsum aggregate (LWC-PG). Firstly, the combination of S-containing adhesive material and phosphate gypsum aggregate can reduce the migration of sulfate ions (SO42−) in the phosphate gypsum aggregate. The reaction mechanism and macro and micro properties of LWC-PG are characterized by universal testing machine, low field nuclear magnetic field, isothermal calorimeter, XRD diffractometer, scanning electron microscope and nano-indentation. The results show that the calcium sulfoaluminate cementitious system (CSA) is compatible with PG. The results show that CSA is compatible with PG, and the 28d strength of 80 % phosphogypsum is 83.4 MPa, which can maintain the required strength for high-performance concrete. Secondly, the sulfides in PG react with C4A6S in CSA, resulting in the formation of ettringite that coats the surface of the C–S–H gel, thereby retarding the hydration rate of the slurry. However, due to the presence of phosphate gypsum aggregate, the reaction continues, enhancing the hydration of sulfate cement. Moreover, the interfacial transition zone between the PG and matrix exhibits a strong bond and shows no significant signs of deterioration. Lastly, when using 80 % phosphogypsum aggregate instead of natural sand and gravel to produce 100 m3 of concrete, 42 t of phosphogypsum aggregate can be used, which reduces the consumption of natural sand and gravel by 61.4 t, decreases energy consumption by 3070 MJ, reduces CO2 emissions by 178.06 kg, SO2 emissions by 0.37 kg, NOX emissions by 0.25 kg, and dust emissions by 0.087 kg. Life cycle evaluation demonstrates that the production of LWC-PG is associated with low carbon emissions and environmental friendliness, which significantly reduces environmental burden. This is of significant research importance for solid waste management and energy-saving and carbon reduction efforts.

The Agro-Pastoral Transitional Zone in Northern China: Continuously Intensifying Land Use Competition Leading to Imbalanced Spatial Matching of Ecological Elements

The agro-pastoral transitional zone (APTZ) in northern China is a typical ecologically vulnerable zone and a comprehensive geographical transitional zone. Its land use pattern has significant type diversity and spatial interlocking, which is always related to the play of ecological barrier functions and the sustainability of social-ecological systems. Accurately grasping the spatial competition relationship and comprehensive geographical effects of land types of APTZ in northern China is a key proposition for achieving coordinated and sustainable development between humans and land. To explore the spatial competition mechanism and comprehensive geographical effects of land use in the research area, this study focuses on revealing the evolutionary characteristics of land use patterns based on the center of gravity migration model. Based on the process of land use center of gravity migration, the spatial competition relationship of land types is explored to reveal the evolutionary trend and basic characteristics of land use in the APTZ. The results show the following: (1) Cultivated land and meadow are the main land types of the APTZ in northern China, accounting for up to 70% of the total regional area. The spatial competition between the two land types is the main contradiction in regional land use competition. (2) Drifting of the center of gravity of cultivated land towards the northwest direction is an important land use migration feature of the APTZ in northern China. Between 1980 and 2020, the center of gravity of cultivated land shifted by about 2 km to the northwest, and the center of gravity of grassland shifted by 8–10 km to the southwest. (3) The center of gravity of arable land and grassland in the entire region is constantly approaching, which has decreased from 70.95 km in 1980 to 61.38 km in 2020. The intensification of their interweaving has led to more intense land use competition. Grasping the basic characteristics and driving mechanisms of land type competition is an important means to achieve sustainable spatial governance. (4) The scale differentiation and regional differentiation characteristics of gradient effects are significant, and it is essential to prevent the risk of mismatch between land use and natural endowments in the northeast and north China sections. The research has surpassed the traditional method of analyzing land use competition, and by introducing a centroid model to analyze the spatial mechanism of land use competition, it has expanded the methodology for expanding research in the field of land science and provided basic references for regional sustainable development.

Variability of soil organic carbon and nutrient content across land uses and agriculturally induced land use changes in the forest-savanna transition zone of Cameroon

Data expressing the effects of land use change on soil attributes is still very scarce in Cameroon as in most of Africa. In this regard, this study aimed to assess soil organic carbon (OC), nitrogen (N), phosphorus (P), and potassium (K) content across land uses and agricultural-induced land use changes in the forest-savanna transition zone of Cameroon. Nine land uses were identified in the study area showing five directions of land use changes namely the change from the native forest to cocoa agroforestry, native savannah to cocoa agroforestry, native savannah to cropland, savannah fallow to cropland, and transition zone fallow to cropland. The soil was sampled at 0–10 cm (upper layer) and 10–30 cm (lower layer) depths in three replicates for each land use and analyzed for physicochemical properties. There were significant differences across the land uses for OC (p < 0.02), N (p < 0.01), C/N (p < 0.01), pH (p < 0.02), soil organic carbon stocks (SOCS) (p < 0.01), and soil nitrogen stocks (SNS) (p < 0.01), with a relatively higher magnitude in the upper soil layer. Higher magnitudes of OC (26.1 to 22.5 g kg−1), N (2.5 to 1.6 g kg−1), SOCS (32.1 to 27.8 Mg ha−1), and SNS (2.9 to1.9 Mg ha−1) were observed in native lands and cocoa agroforestry with the highest in the native forest and the forest-based cocoa agroforestry. Meanwhile, the effect of land use change on soil properties was mainly significant in the change from native savannah to croplands at p < 0.05 for OC, N, SOCS, and SNS, and p < 0.02 for P. Therefore, agroforestry is an alternative to enhance the ecological resilience of lands affected by land use changes.

Border Externalization and the Geography of Negative Views Toward Transit Migrants in Honduras

Transit migration through Honduras has grown at a time of increasing US border externalization, which raises barriers to mobility through Central America. This research note presents a descriptive analysis of how Hondurans view transit migrants traveling across the country. Honduras is a major migrant-sending country, one that has become an important transit country for migrants of different backgrounds. This article will present results from an original survey of Hondurans asking respondents of their opinions of transit migrants from Haiti, Nicaragua, Cuba, and other regions. We find that negative attitudes toward transit migrants tend to be concentrated in the exit regions near the border with Guatemala. We argue that border externalization generates bottlenecks to mobility that can prolong exposure to transit migrants. We propose recommendations for future research to better understand how border externalization may lead countries to become new transit zones and how attitudes toward transit migrants vary regionally.