Search Results (482)

Space conditions offer new insights into fundamental biological and molecular mechanisms. The study aimed to evaluate the enzymatic activity of proteinase K (PK) under extreme conditions relevant to space environments: simulated microgravity, hypergravity, and gamma radiation. PK activity was tested using azocasein (AZO) as a chromogenic substrate, with enzymatic reactions monitored spectrophotometrically at 450 nm. A rotating wall vessel (RWV) simulated microgravity, centrifugation at 1000× g (3303 rpm) generated hypergravity, and gamma radiation exposure used cesium-137 as the ionizing source. PK activity showed no remarkable changes under microgravity after 16 or 48 h; however, higher absorbance values after 96 h indicated enhanced AZO proteolysis compared to 1 g (Earth gravity) controls. In hypergravity, low PK concentrations exhibited slightly increased activity, while higher concentrations led to reduced activity. Meanwhile, gamma radiation caused a dose-dependent decline in PK activity; samples exposed to deep-space equivalent doses showed reduced substrate degradation. PK retained enzymatic activity under all tested conditions, though the type and duration of stress modulated its efficiency. The results suggest that enzyme-based systems may remain functional during space missions and, in some cases, exhibit enhanced activity. Nevertheless, their behavior must be evaluated in a context-dependent manner. These findings may be significant to advance biotechnology, diagnostics, and the development of enzyme systems for space applications. Full article

As a convergent zone of multiple plates, the Caribbean Sea and its adjacent areas have experienced a complex tectonic evolution process and are characterized by prominent microplate development. This region provides a natural laboratory for studying the formation mechanism of continental margins, the evolution process of ocean basins, and the tectonics of microplates. However, the crustal structure and microplate tectonics in this region remain unclear due to limitations of conventional planar gravity inversion methods, which neglect the Earth’s curvature in large-scale areas, as well as the uneven coverage of regional seismic networks. To precisely delineate the crustal structure and microplate boundaries in the Caribbean Sea region, this study employs a nonlinear gravity inversion method based on a spherical coordinate system. By utilizing GOCO06s satellite gravity data, ETOPO1 topographic data, and the CRUST1.0 crustal model, we performed inversion calculations for the Moho depth in the Caribbean Sea and its adjacent regions and systematically analyzed the crustal structure and microplate tectonic characteristics of the region. The results indicate that the gravity inversion method in the spherical coordinate system has good applicability in complex tectonic regions. The inversion results show that the Moho depth in the study area generally presents a spatial distribution pattern of “shallow in the central part and deep in the surrounding areas”. Among them, the Moho depth is the largest (>39 km) at the junction of the Northern Andes and the South American Plate, while it is relatively shallow (<6 km) in regions such as the Cayman Trough, the Colombian Basin, and the Venezuelan Basin. Based on the Moho undulation, gravity anomalies, and topographic features, this study divides the Caribbean Sea and its adjacent areas into 22 microplates and identifies three types of microplates, including oceanic, continental, and accretionary. Among them, there are 10 microplates with oceanic crust, 6 with continental crust, and 5 with accretionary crust, while the Northern Andes Microplate exhibits a mixed type. The crustal structure characteristics revealed in this study support the Pacific origin model of the Caribbean Plate, indicating that most of the plate is a component of the ancient Pacific Plate with standard oceanic crust properties. Locally, the Caribbean Large Igneous Province developed due to hotspot activity, and the subsequent eastward drift and tectonic wedging processes collectively shaped the complex modern microplate tectonic framework of this region. This study not only reveals the variation pattern of crustal thickness in the Caribbean Sea region but also provides new geophysical evidence for understanding the lithospheric structure and microplate evolution mechanism in the area. Full article

This study presents a comprehensive analysis of pre- and co-seismic ionospheric disturbances associated with the 2023 Ms6.2 Jishishan earthquake by leveraging the unique observational strengths of BDS, particularly its high-orbit satellites. A multi-parameter space weather index was employed to effectively isolate seismogenic signals from geomagnetic disturbances, confirming that the main shock occurred during geomagnetically quiet conditions. Statistical analysis of 41 historical earthquakes (Mw ≥ 5.5) reveals that 47.2% were associated with detectable Total Electron Content (TEC) anomalies. An inverse correlation between earthquake magnitude and anomaly detectability within a 31-day window suggests prolonged precursor durations for larger events may produce longer-duration precursory signals, which challenge conventional detection methods. The synergistic capabilities of BDS Geostationary Earth Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO) satellites were demonstrated: GEO satellites provide unprecedented temporal stability for continuous TEC monitoring, while IGSO satellites enable high-resolution spatial mapping of Co-seismic Ionospheric Disturbances (CIDs). The detected CIDs propagated at velocities below 1.6 km/s, consistent with acoustic gravity wave (AGW) mechanisms. A case study during a geomagnetically active period further reveals modulated CID propagation characteristics, indicating potential coupling between seismic forcing and space weather. Our findings validate BDS as a powerful and precise tool for ionospheric seismology and provide critical insights into Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) dynamics. Full article

This narrative review of rapid eye movement (REM) focuses on its primary etiology and how it fits into the larger framework of neurophysiology and general physiology. Arterial blood flow in the retina may be sensitive to the full overlying ‘weight’ of its adjacent and contiguous vitreous humor caused by the humoral mass effect in the Earth’s gravitational field. During waking hours of the day, this ‘weight’ is continuously shifted in position due to changing head position and eye movements associated with ordinary environmental observations. This reduces its impact on any one point on the retinal field. However, during sleep, the head may maintain a relatively constant position (often supine), and observational eye movements are minimal, leaving essentially one retinal area exposed at the ‘bottom’ of each eye, relative to gravity. During sleep, REM may provide a mechanism for frequently repositioning the retina with respect to the weight it incurs from its adjacent (overlying) vitreous humor. Our findings were consistent with the intermittent terrestrial nocturnal development of ‘gravitational ischemia’ in the retina, wherein the decreased blood flow is accompanied metabolically by decreased oxygen tension, a critically important metric, with a detrimental influence on nerve-related tissue generally. However, the natural mechanisms for releasing and resolving gravitational ischemia, which likely involve glymphatics and cerebrospinal fluid shifts, as well as REM, may gradually fail in old age. Concurrently associated with old age in some individuals is the deposition of alpha-synuclein and/or tau in the retina, together with similar deposition in the brain, and it is also associated with the development of Parkinson’s disease and/or Alzheimer’s disease, possibly as a maladaptive attempt to release and resolve gravitational ischemia. This suggests that a key metabolic parameter of Parkinson’s disease and Alzheimer’s disease may be a lack of oxygen in some neural tissues. There is some evidence that oxygen therapy (hyperbaric oxygen) may be an effective supplemental treatment. Many of the cardinal features of spaceflight-associated neuro-ocular syndrome (SANS) may potentially be explained as features of gravity opposition physiology, which becomes unopposed by gravity during spaceflight. Gravity opposition physiology may, in fact, create significant challenges for humans involved in long-duration space travel (long-term microgravity). Possible solutions may include the use of artificial gravitational fields in space, such as centrifuges. Full article

Placer deposits constitute important secondary resources for economically valuable minerals, including rare earth elements (REEs) and heavy minerals such as zircon, rutile, and ilmenite. In this study, representative samples from the Hantepe placer deposit (Çanakkale, Türkiye) were processed to investigate the occurrence, distribution, and beneficiation potential of REE-bearing minerals. The ore was subjected to size classification, followed by gravity concentration on a shaking table and subsequent magnetic separation using a low-intensity disc separator. The resulting products were characterized by X-ray diffraction and X-ray fluorescence. The dominant REE-host minerals were identified as titanite, zircon, apatite, monazite and, allanite, accompanied by magnetite, hematite, quartz, and feldspar as gangue constituents. The non-magnetic final concentrate achieved substantial upgrading of critical elements, with Ce increasing from 868 g/t to 5716 g/t, Nd from 308 g/t to 2308 g/t, and Zr from 1435 g/t to 9748 g/t. Additionally, the magnetic concentrate (7.0 wt.%) was strongly enriched in Fe₂O₃ (70.26%) and V (2359 g/t), indicating its potential suitability as an Fe–V source. Overall, the results demonstrate that combined gravity and magnetic separation constitutes an effective beneficiation strategy for critical mineral recovery from placer systems. These findings establish a strong basis for future pilot-scale studies and the techno-economic evaluation of the Hantepe deposit as an emerging source of strategic and industrially relevant heavy minerals. Full article

As humanity prepares for prolonged space missions and future extraterrestrial settlements, developing reliable and resilient food-production systems is becoming a critical priority. Space agriculture, the cultivation of plants beyond Earth (particularly on the Moon and Mars), faces a constellation of interdependent environmental, biological, and engineering challenges. These include limited solar radiation, elevated ionizing radiation, large thermal variability, non-Earth atmospheric pressures, reduced gravity, regolith substrates with low nutrient-holding capacity, high-CO₂/low-O₂ atmospheres, pervasive dust, constrained water and nutrient availability, altered plant physiology, and the overarching need for closed-loop, resource-efficient systems. These stressors create an exceptionally challenging environment for plant growth and require tightly engineered agricultural systems. This review examines these constraints by organizing them across environmental differences, resource limitations, biological adaptation, and operational demands, emphasizing their systemic interdependence and the cascading effects that arise when one subsystem changes. By integrating findings from planetary science, plant biology, space systems engineering, biotechnology, robotics, and controlled-environment agriculture (CEA), the review outlines current limitations and highlights emerging strategies such as regolith utilization, advanced hydroponics, crop selection and genetic engineering, and the use of robotics, sensors, and artificial intelligence (AI) for monitoring and automation. Finally, the article underscores the broader relevance of space–agriculture research for terrestrial food security in extreme or resource-limited environments, providing a structured foundation for designing resilient and sustainable agricultural systems for space exploration and beyond. Full article

A series of multi-parameter, multi-layer observations was conducted to study possible electromagnetic precursors associated with the M 6.7 earthquake that struck Iburi, Hokkaido, Japan, at 18:07:59 UT on 5 September 2018. The most significant observation is seismogenic lower-ionospheric perturbations in the propagation anomalies of sub-ionospheric VLF/LF signals recorded in Japan and Russia. Other substantial observations include the GIM-TEC irregularities, the intensification of stratospheric atmospheric gravity waves (AGWs), and the satellite and ground monitoring of air temperature (T), relative humidity (RH), atmospheric chemical potential (ACP), and surface latent heat flux (SLHF). We have found that there were very remarkable VLF/LF anomalies indicative of lower-ionospheric perturbations observed on 4 and 5 September just before the EQ date and even after it from the observations in Japan and Russia. In particular, the anomaly was detected for a particular propagation path from the JJY transmitter (Fukushima) to a VLF station at Wakkanai one day before the EQ, i.e., on 4 September, and is objectively confirmed by machine/deep learning analysis. An anomaly in TEC occurred only on 5 September, but it is unclear whether it is related to a pre-EQ effect or a minor geomagnetic storm. We attempted to determine whether any seismo-related atmospheric gravity wave (AGW) activity occurred in the stratosphere. Although numerous anomalies were detected, they are most likely associated with convective weather phenomena, including a typhoon. Finally, the Earth’s surface parameters based on satellite monitoring seem to indicate some anomalies from 29 August to 3, 4, and 5 September, a few days prior to EQ data, but the ground-based observation close to the EQ epicenter has indicated a clear T/RH and ACP on 2 September with fair weather, but no significant data on subsequent days because of severe meteorological activities. By integrating multi-layer observations, the LAIC (lithosphere–atmosphere–ionosphere coupling) process for the Hokkaido earthquake appears to follow a slow diffusion-type channel, where ionospheric perturbations arise a few days after ground thermal anomalies. This study also provides integrated evidence linking concurrent lower-ionospheric, atmospheric, and surface thermal anomalies, emphasizing the diagnostic value of such multi-parameter observations in understanding EQ-associated precursor signatures. Full article

Orthometric heights are practically determined from levelling and gravity measurements by applying orthometric corrections to levelled height differences. Currently, Helmert’s definition of orthometric heights is mostly used, with the mean gravity computed only approximately from observed surface gravity by applying the Poincaré–Prey gravity reduction. In this study, we apply the state-of-the-art method for the orthometric height determination and demonstrate its practical applicability. The method utilizes advanced numerical procedures to account for the topographic relief and mass density variations, while adopting the Earth’s spherical approximation. The non-topographic contribution of masses inside the geoid is evaluated by solving geodetic boundary-values problems. We apply this method for the first time to practically determine the orthometric heights of levelling benchmarks from levelling and gravity measurements and digital terrain and rock density models. The results obtained after the readjustment of newly determined orthometric heights at the levelling network covering Hong Kong territories are compared with Helmert’s orthometric heights. This comparison revealed that errors in Helmert’s orthometric heights vary between −3.13 and 0.95 cm. Such errors are very significant when compared to accurate values of the cumulative orthometric correction between −1.88 and 0.84 cm. Moreover, large errors (up to 1 cm) already occur at levelling benchmarks at very low elevations (<100 m). These findings demonstrate that the accurate determination of orthometric heights is crucial, even for regions with moderately elevated topography. Full article

This paper presents a mathematical model that describes the propagation of internal inertia–gravity waves in a stratified atmosphere under the approximations of an incompressible fluid and a traditional β-plane. It demonstrates that, in the incompressible fluid approximation, the temperature field is inconsistent with the heat conduction equation. The system of equations that describes internal inertia–gravity waves is considered in the general case, taking into account the buoyancy force, and reduced to a single equation. The solution is sought in the form of traveling plane waves. A dispersion relation has been obtained in the form of a cubic equation that represents a hypersurface in wave number space, without the assumption of small vertical wavelength. Cross-sections of this surface are plotted, and an extremum study is performed. This shows that a new frequency region appears in the low-frequency spectrum $0<\omega <f_{0z}$ that was not present in the f-plane approximation. Here, $f_{0z}=2{\omega }_0\cdot \sin \phi$ is the Coriolis parameter, and $\phi$ is the latitude. Furthermore, these waves only propagate in the negative direction of the x-axis, i.e., in the opposite direction of the Earth’s rotation. It is also shown that there is a region with a minimum frequency in the “high-frequency” spectrum determined by buoyancy $\omega <f_{0z}$, and that waves propagate in the negative direction as well. Thus, the dispersion surface is shown to have two extremum points. The first is a minimum in the “high-frequency” spectrum ${\omega }_1\approx 0.826f_{0z}$ and the second is a maximum in the “low-frequency” spectrum ${\omega }_2\approx 0.564f_{0z}$. Full article

To facilitate easy accessibility to the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) results for the geoscientific community, multiple institutions have successively developed mass anomaly grid products including mass concentration (mascon) grids; these were provided at the Gravity Information Service (GravIS) portal. However, an assessment of their consistency for studying large-scale mass redistribution and transport in Earth’s system is still not available. Here, we compare three major mascon solutions separately from the Center for Space Research (CSR), the Jet Propulsion Laboratory (JPL), the Goddard Space Flight Center (GSFC) and GravIS products based on the Combination Service for Time-variable Gravity fields (COST-G) by analyzing the Antarctic Ice Sheet (AIS) mass changes in four aspects. Our results demonstrate that: (1) the four datasets exhibit strong consistency on the entire AIS mass change time series, with the largest difference occurring in the Antarctic Peninsula; (2) mass trend estimates show better agreement over longer periods and larger regions, but differences with a percentage of 20–40 exist during the late stage of GRACE and the whole GRACE-FO timespan; (3) notable discrepancies arise in the annual statistics of the Eastern AIS in 2016, leading to inconsistency on the sign of annual AIS mass change; (4) good agreement can be seen among these interannual mass variations over the AIS and its three subregions during 2003–2023, excluding the period from mid-2016 to mid-2018. These findings may provide key insights into improving algorithms for mascon solutions and grid products towards refining their applications in ice mass balance studies. Full article

A temporally periodic model is presented to describe the vertical profile of internal gravity waves in the F region of the Earth’s ionosphere where the waves are subject to a magnetic force due to the high concentration of ions. The configuration studied is representative of the situation where the geomagnetic field is approximately constant and is so strong that the angular gyrofrequency of the ions is very large compared with the ion-neutral collision frequency, which is in turn larger than the angular frequency of the gravity waves. We examine the situation where the gravity wave amplitude is small enough that the equations for the neutral fluid flow can be linearized. This allows for the description of wave propagation in terms of a system of coupled equations that include the effects of ion drag on waves for any orientation of the magnetic field. It is assumed that the background neutral fluid flow is nonzero and horizontal, but there is no vertical shear, and that the wave amplitude depends on altitude only, and an exact analytical solution is readily found. This dynamical model captures some essential features of ionospheric gravity waves that are consistent with observational measurements. In particular, the ion drag acts to damp the waves in the direction of vertical propagation and increase their vertical wavelength relative to the corresponding wavelength in the neutral atmosphere. The vertical damping rate and the vertical wavelength both depend on the dip angle of the magnetic field. When the magnetic field acts in the direction of the gravity lines of constant phase, there is no damping, and the vertical wavelength is the same as that of the corresponding waves in the neutral atmosphere. The dip angles that produce stronger damping also result in waves with greater wavelengths. Full article

The origin of humans on Earth is closely linked to understanding how ancient populations dispersed into adjacent territories. Traditionally, studies have identified landscape and climatic changes as the primary factors in this dispersal. However, we propose that regional tectonic and geodynamic factors also played a significant role in shaping these movements. To analyze this phenomenon, we employed several primary methods, including radiometric dating, magnetostratigraphy, paleomagnetic correlation, isotope–oxygen analysis, tectonothermal studies, gravity mapping, paleobiogeographic assessment, lithofacies analysis, and event and cyclic stratigraphy. Our research indicates that the Akchagylian hydrospheric maximum, which reached up to +200 m, significantly limited the early dispersal of hominins from Africa to Eurasia. The migration corridor was shaped by tectonic activity between the Dead Sea Transform and the boundary of the Mesozoic Terrane Belt carbonate platform. We argue that, during the early stages of hominin evolution in East Africa, the Levantine Corridor (LC) had not yet developed into an optimal route for dispersal, either tectonically or paleogeographically. Suitable habitats for early hominins emerged only after the regression at the end of the Middle Gelasian, around two million years ago, when sea level fell by approximately 200 m, leading to the dissection of the coastal high plateau of the Eastern Mediterranean. We therefore suggest that the LC became established only after the termination of the Akchagylian transgression and the subsequent landscape reconfiguration of the Eastern Mediterranean. Our integrated analysis, combining paleomagnetic, structural, tectonic, and event stratigraphy data, indicates that the age of the renowned ‘Ubeidiya site in northern Israel is several thousand years older than previously thought. This paleogeographic impact had not been considered in earlier studies. Considering the diverse and complex factors that governed hominin dispersal from Africa into Eurasia within this multifaceted region, we propose that the scope of research should be broadened. Our detailed study of the Carmel area, located northeast of the Levantine Corridor and influenced by it during the Pleistocene, indicates that this region was inundated during the early phases of hominin migration out of Eastern Africa. Besides this, we have conducted an integrated geological–geophysical landscape analysis of the central part of the Israeli coastal plain. Full article

Thorium has emerged as a promising alternative to uranium in nuclear energy systems due to its higher natural abundance, favorable conversion to fissile ²³³U, and reduced generation of long-lived transuranic waste. This review provides a comprehensive overview of advanced techniques for thorium recovery from primary ores and secondary resources. The main mineralogical carriers—including monazite, thorianite, thorite, and cheralite as well as industrial by-products such as rare-earth processing tailings—are critically examined with respect to their occurrence and processing potential. Physical enrichment methods (gravity, magnetic, and electrostatic separation) and hydrometallurgical approaches (acidic and alkaline leaching) are analyzed in detail, highlighting their efficiencies, limitations, and environmental implications. Particular emphasis is placed on modern separation strategies such as solvent extraction with organophosphorus reagents, diglycolamides, and ionic liquids, as well as extraction chromatography, nanocomposite sorbents, ion-imprinted polymers, and electrosorption on carbon-based electrodes. These techniques demonstrate significant progress in enhancing selectivity, reducing reagent consumption, and enabling recovery from low-grade and secondary feedstocks. Environmental and radiological aspects, including waste minimization, immobilization, and regulatory frameworks, are discussed as integral components of sustainable thorium management. Finally, perspectives on hybrid technologies, digital process optimization, and economic feasibility are outlined, underscoring the need for interdisciplinary approaches that combine chemistry, materials science, and environmental engineering. Collectively, the analysis highlights the transition from conventional practices to integrated, scalable, and environmentally responsible technologies for thorium recovery. Full article

In order to enhance the separation efficiency of fine-grained Bayan Obo Niobium Ore, a novel gravity separation equipment named Slime Vibrating Table (SVT) was developed. The SVT employs an electromagnetic drive to generate a reciprocating motion for the table, with a lower stroke and higher frequency than a conventional Slime Shaking Table (SST). Key parameters of SVT, including table slope, wash-water flow rate, vibration voltage, and vibration frequency, were tested for a niobium ore assaying 0.19% Nb₂O₅ with a particle size below 74 um by 68.78%. Under the optimized condition, SVT was able to obtain a primary concentrate assaying 1.31% Nb₂O₅ with a recovery of 52.64%, which was 0.22% and 26.59% higher than that of SST, respectively. Size-by-size analysis indicated that the enhanced separation performance of SVT was mainly attributed to its superior recovery of Nb₂O₅ in the −38 μm fraction. The SVT introduced in this study shows great potential for efficient recovery of fine-grained strategic metals, including rare earths, tantalum, tungsten, tin, and antimony, etc. Full article

This study investigates the use of preliminary thermochemical activation in a NaHCO₃ solution under elevated pressure and temperature to modify the chemically stable and hard-to-process phase composition of various mineral raw materials and improve the recovery of valuable components. The method was tested on various types of mineral raw materials, including slag from the reductive smelting of red mud from alumina production prior to acid leaching, ash before chemical beneficiation, gibbsite–kaolinite bauxite prior to gravity separation, and nephelines, for which the sintering process was replaced with chemical beneficiation. The slag from the reductive smelting of red mud was also tested before acid leaching. The activation of slag enhanced tricalcium silicate formation lead to leaching recoveries of ~96% for rare earth elements, ~92% for TiO₂, ~98% for CaO and Al₂O₃, and 50% for Fe₂O₃, compared to much lower values without activation. With ash, activation eliminated the sillimanite and hedenbergite phases, increased mullite and free silica, and formed calcite, resulting in a 15–20% higher silica recovery. With gibbsite–kaolinite bauxite, activation altered kaolinite, siderite, quartz, and hematite contents; eliminated calcium silicate; and improved the silicon modulus of the sand fraction by 35.9% during gravity beneficiation. For nepheline ore, activation promoted the formation of albite and hydrosodalite, eliminated corundum and andradite, and increased silica recovery from 33.58% to 59.6%. These results demonstrate that thermochemical activation effectively transforms mineral structures and significantly improves the efficiency of subsequent beneficiation processes. Full article