Harmonic mode‐locking (HML) is an important technique enabling the generation of high‐repetition‐rate ultrashort pulses. Using an emerging time‐stretch dispersive Fourier transform technique, the ...experimental observation of the entire buildup process of the passive HML state in an ultrafast fiber laser is reported here. It is unveiled that the whole process of HML buildup successively undergoes seven different ultrafast phases: raised relaxation oscillation, spectral beating behavior, birth of a giant pulse, self‐phase‐modulation‐induced instability, pulse splitting, repulsion and separation of multiple pulses, and a stable HML state. It is observed that the multiple HML pulses originate from a single‐pulse splitting phenomenon and a remarkable breathing behavior occurs at an early stage of the HML buildup process. The numerical results confirm that the effects of dispersive wave, gain depletion and recovery, and acoustic wave play key roles in the earlier, middle, and later stages of this HML buildup process, respectively; as well, the acoustic resonance in the single‐mode fiber stabilizes the final HML state of lasers.
The experimental observation of the entire buildup process of the passive harmonic mode‐locking (HML) state, which undergoes seven different ultrafast phases, is demonstrated. Multiple HML pulses originate from the single‐pulse splitting phenomenon. The acoustic resonance in the single‐mode fiber stabilizes the final HML state of lasers.
Modern geodetic and seismologic observations describe the behavior of fault slip over a vast range of spatial and temporal scales. Slip at sub-seismogenic speeds is evident from top to bottom of ...lithospheric faults and plays an important role throughout the earthquake cycle. Where earthquakes and tremor accompany slow slip, they help illuminate the spatiotemporal evolution of fault slip. Geophysical subsurface imaging and geologic field studies provide information about suitable environments of slow slip. In particular, exhumed fault and shear zones from various depths reveal the importance of multiple deformation processes and fault-zone structures. Most geologic examples feature frictionally weak and velocity-strengthening materials, well-developed mineral fabrics, and abundant veining indicative of near-lithostatic fluid pressure. To produce transient slow slip events and tremor, in addition to the presence of high-pressure fluids a heterogeneous fault-zone structure, composition, and/or metamorphic assemblage may be needed. Laboratory and computational models suggest that velocity-weakening slip patches smaller than a critical dimension needed for earthquake nucleation will also fail in slow slip events. Changes in fluid pressure or slip rate can cause a fault to transition between stable and unstable fault slip behavior. Future interdisciplinary investigations of slow fault slip, directly integrating geophysical, geological and modeling investigations, will further improve our understanding of the dynamics of slow slip and aid in providing more accurate earthquake hazard characterizations.
•Geodetic and seismologic observations show that fault creep and slow slip events can occur at all depths of crustal faults.•Better understanding of slow slip requires integration of geophysical, geological, experimental, and modeling analyses.•There are many successful recipes for making a fault slip slowly.•Changes in fluid pressure or slip rate can cause a fault to transition between stable and unstable fault slip behavior.
•A coupled model for predicting landslide-debris flow hazard chains was proposed.•The coupled model is capable of predicting the hazard chain by the hour.•The input of landslide area influences the ...prediction of debris flow.•The rainfall threshold curve supports landslide prediction in areas lacking data.
Landslides, debris flows, and other destructive natural hazards induced by heavy rainfall in mountainous regions are sometimes not independent but combined to form a disaster chain. Based on the integral link between the triggering of the landslide and the subsequent debris flow, we propose an approach that combines the Transient Rainfall Infiltration and Grid-Based Regional Slope Stability (TRIGRS) model and the Rapid Mass Movements Simulation (RAMMS) model to achieve hourly hazard prediction. The results indicate that the TRIGRS model performed well in predicting the spatial distribution of the shallow landslides, with a success rate of 81.86%. Thus, it is reasonable to use it as the initial input for debris flow simulations. The relationship between the landslide area and the accumulated rainfall obtained using the TRIGRS model is a power-law relationship, which provides a reference for regions that lack rainfall data to predict the material source of a debris flow. The coupled model was found to have a good accuracy of 76.77% in simulating the debris flow. This was close to the debris flow simulation based on the interpreted landslides, and it still produced reasonable results and a more practical value. Furthermore, the proposed coupled model can dynamically predict disasters by the hour based on actual rainfall events. Therefore, the results of this study help provide a more complete hazard prediction picture for rainfall-induced landslide-debris flow hazards in mountainous regions.
The perplexity of double peaks in Pb(II) detections has been a threat to the reliability of Pb(II) electroanalysis results for a long term. For the complexity of electrode interfaces, rare studies ...were taken on mechanisms of Pb(II) double peaks through interfacial kinetics. In this work, analyses on experimental signals and interfacial simulations were working together to reveal that the generation of Pb(II) double peaks in Pb(II)-Cu(II) systems is the deposition of Pb(II) on Cu deposits occurring in parallel. By applying anode stripping voltammetry and cyclic voltammetry, a parallel deposition reaction was found to influence the shape of Pb(II) peaks, and the existence of the second peak was controlled through the adjustment of experimental conditions. A kinetic model was built to reveal the interference of electroanalysis signals caused by a parallel deposition reaction and simulations based on the model were combined with experiments to illustrate that double peaks of Pb(II) were caused by the parallel deposition on Cu(II) deposits. This work proposes another insight of Pb(II) double peaks from macroscale kinetics and pays more attention on the dynamic procedure of electroanalysis interfaces, which makes the study on environmental electroanalysis interface phenomena more clear and is enlightening to develop efficient electrical methods for pollutant monitoring.
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•Double peaks of Pb(II) in Pb(II)-Cu(II) systems were verified to a parallel deposition reaction.•Voltammetry signals were analyzed to study bimodal interferences.•A novel kinetic model described parallel Faraday reactions was built.•Numerical simulations were combined with experiments to investigate transient phenomena.
Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) ...transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure–lithology–pressure–temperature–time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at ∼800 °C and ∼600 °C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration.
•Mechanical strength of mantle wedge and slab crust switch during subduction infancy.•Rheological switches control slab penetration and metamorphic sole formation.•Explains dynamics of metamorphic sole accretion beneath ophiolites worldwide.•Documents transient accretion processes across the subduction plate interface.
Using electrical impedance tomography (EIT) to drive a pressure mapping device shows great potential, due to the customisability of the sensing domain and the non-invasive nature of the boundary ...electrodes. A pressure mapping system has been developed in this work that uses a carbon black silicone rubber (CBSR) nanoparticle sensing domain, giving the sensing domain a comparable softness to human skin tissue. To take this technology into a commercial application the performance of such an EIT-based sensor must be quantifiable and repeatable. In this work a series of experiments were repeated for various load locations, strains, and carbon black percentages. Capturing this data gave insight into the how the sensing domain performs over time and captured the transient events limiting the sensor. Metrics were determined to quantify the sensor’s spatial resolution. Load localisation could be determined with error values as low as 0.67 mm. A series of randomised test loads gave similar spatial performance results to the more structured experiments. A quasi-static conductance-force model of the material was developed with an accuracy of ± 0.78 N. One important metric is temporal resolution, as it is the least quantified performance metric in literature, however can be the most important for some applications. For the sensor domains tested, average settling times of between 19.0 – 44.5 s and 22.5 – 36.0 s were determined for 8 and 9 wt% CBSR samples. This sensor platform shows promise for future soft surface pressure mapping applications. Further use of the developed performance metrics will allow for a variety of sensor applications to be validated.
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•EIT is a method for detecting resistive transients in 2D in piezoresistive elastomers•A quasi-static 1D stress to resistance model can be applied to map a 2D surface•Performance metrics have been developed for validation of 2D EIT sensor materials•The inhomogeneous piezoresistive EIT-based pressure sensor can map and estimate force
Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals. We evaluate the mechanisms of ...planetesimal evaporation in the early solar system and the conditions that controlled attendant isotope fractionations.
Energy balance at the surface of a body accreted within ~1 Myr of CAI formation and heated from within by 26Al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order <1 m that would be subject to foundering. Bodies that are massive enough to form magma oceans by radioisotope decay (≥0.1% M⊕) can retain hot rock vapor even in the absence of ambient nebular gas. We find that a steady-state rock vapor forms within minutes to hours and results from a balance between rates of magma evaporation and atmospheric escape. Vapor pressure buildup adjacent to the surfaces of the evaporating magmas would have inevitably led to an approach to equilibrium isotope partitioning between the vapor phase and the silicate melt. Numerical simulations of this near-equilibrium evaporation process for a body with a radius of ~700 km yield a steady-state far-field vapor pressure of 10−8 bar and a vapor pressure at the surface of 10−4 bar, corresponding to 95% saturation. Approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation due to the formation of steady-state rock vapor atmospheres and/or the presence of protostellar gas.
We model the Si and Mg isotopic composition of bulk Earth as a consequence of accretion of planetesimals that evaporated subject to the conditions described above. The results show that the best fit to bulk Earth is for a carbonaceous chondrite-like source material with about 12% loss of Mg and 15% loss of Si resulting from near-equilibrium evaporation into the solar protostellar disk of H2 on timescales of 104 to 105 years.
•Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments attributed to evaporation of molten planetesimals.•We evaluate the mechanisms of planetesimal evaporation and the conditions that controled attendant isotope fractionations.•A steady-state rock vapor forms within minutes to hours from a balance between rates of magma evaporation and atmospheric escape.•Approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation.•The best fit to bulk Earth is for a carbonaceous chondrite-like source material with about 12% loss of Mg and 15% loss of Si.
Studies of the lunar atmosphere have shown it to be a stable, low-density surface boundary exosphere for the last 3 billion years. However, substantial volcanic activity on the Moon prior to 3 Ga may ...have released sufficient volatiles to form a transient, more prominent atmosphere. Here, we calculate the volume of mare basalt emplaced as a function of time, then estimate the corresponding production of volatiles released during the mare basalt-forming eruptions. Results indicate that during peak mare emplacement and volatile release ∼3.5 Ga, the maximum atmospheric pressure at the lunar surface could have reached ∼1 kPa, or ∼1.5 times higher than Mars' current atmospheric surface pressure. This lunar atmosphere may have taken ∼70 million years to fully dissipate. Most of the volatiles released by mare basalts would have been lost to space, but some may have been sequestered in permanently shadowed regions on the lunar surface. If only 0.1% of the mare water vented during these eruptions remains in the polar regions of the Moon, volcanically-derived volatiles could account for all hydrogen deposits – suspected to be water – currently observed in the Moon's permanently shadowed regions. Future missions to such locations may encounter evidence of not only asteroidal, cometary, and solar wind-derived volatiles, but also volatiles vented from the interior of the Moon.
•Peak lunar volcanic activity 3.5 Ga released ∼1019 g of volatiles around the Moon.•Erupted volatiles formed a lunar atmosphere 1.5× thicker than is currently on Mars.•Lunar polar H/H2O may have originated as volatiles released in peak mare eruptions.
Although equilibrium has long been considered the attractor state for landscapes, the time required to reach equilibrium or even the possibility of reaching equilibrium is still debated. Using ...10Be-based catchment-averaged denudation rates, topographic analysis, and analysis of the basin topology and geometry, including its area-channel length scaling relationship, we show that an ancient postorogenic dome on the North American Craton, the Ozark dome, is not in a state of equilibrium. The persistent state of disequilibrium on the Ozark dome is characterized by nonuniform erosion rates that vary by a factor of three, asymmetric drainage divides, and evidence for drainage rearrangement via stream capture. We find that planform geometric disequilibrium of river basins and drainage area exchange between adjoining basins can hold river networks in a disequilibrium state for potentially hundreds of million years and that, when sustained over time, erosion rate differences associated with drainage area exchange can lead to transient events such as stream capture and production of relief in the form of elevated, low-relief surfaces. Our results suggest that landscapes with slowly moving drainage divides might not reach equilibrium, and that river basin dynamics may contribute to setting the large-scale morphology of old cratonic landscapes.
•The Paleozoic-aged Ozark dome is in a persistent state of geometric disequilibrium.•10Be erosion rates are nonuniform and vary by up to a factor of three.•Differences in erosion rates result in capture and elevated, low-relief surfaces.•Landscapes with slowly moving drainage divides might never reach equilibrium.•Basin dynamics may influence the large-scale morphology of cratonic landscapes.
THE ACTIVE ASTEROIDS Jewitt, David
The Astronomical journal,
03/2012, Letnik:
143, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass-losing asteroids (also called "main-belt ...comets") can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider 11 dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses, and thermal fracture, in addition to the sublimation of ice. In two objects (133P and 238P) the repetitive nature of the observed activity leaves ice sublimation as the only reasonable explanation, while in a third ((596) Scheda), a recent impact is the cause. Another impact may account for activity in P/2010 A2, but this tiny object can also be explained as having shed mass after reaching rotational instability. Mass loss from (3200) Phaethon is probably due to cracking or dehydration at extreme (~1000 K) perihelion temperatures, perhaps aided by radiation pressure sweeping. For the other bodies, the mass-loss mechanisms remain unidentified, pending the acquisition of more and better data. While the active asteroid sample size remains small, the evidence for an astonishing diversity of mass-loss processes in these bodies is clear.
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