The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly ...introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects.
2
and
3
. In Sect.
4
, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section
5
discusses physical mechanisms of strain rate effects. Section
6
describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section
7
presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.
Polymer film capacitors are critical components in many high-power electrical systems. Because of the low energy density of conventional polymer dielectrics, these capacitors currently occupy ...significant volume in the entire electrical system. This article reviews recent progress made in the development of polymer dielectrics with high energy storage density, which can potentially lead to significant weight and volume reduction in polymer film capacitors. The increase in energy density is achieved through two approaches, namely (
a
) the development of novel polymers with high electric polarization and optimized dielectric responses and (
b
) the development of nanocomposites containing polymer matrixes with high breakdown strength and inorganic nanofillers with high polarization. Promising progress has been made through both strategies, resulting in a maximum energy density of >30 J cm
3
, which is at least 5 times higher than those of conventional polymer dielectrics. The state-of-the-art manufacturing method for low-cost, high-throughput production of polymer films is also reviewed.
Based on in situ and ground‐based observations, a new type of “polar cap hot patch” has been identified that is different from the classical polar cap enhanced density structure (cold patches). ...Comparing with the classical polar cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the polar cap hot patches are associated with particle precipitations (therefore field‐aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low‐energy particle precipitation and/or ion upflows associated with field‐aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the polar cap region than classical patches. A new type of polar cap patches, “polar cap hot patches,” is identified to differentiate enhanced density structures from classical patches. Hot patches are associated with particle precipitations, ion upflows, field‐aligned currents, and shear flows in the polar cap. Hot patches may lead to slightly stronger ionospheric scintillations of GNSS signals in the polar cap region than classical patches.
Key Points
A new type of polar cap patches, “polar cap hot patches,” is identified to differentiate enhanced density structures from classical patches
Hot patches are associated with particle precipitations, ion upflows, field‐aligned currents, and shear flows in the polar cap
Hot patches may lead to slightly stronger ionospheric scintillations of GNSS signals in the polar cap region than classical patches
Tracking the formation and full evolution of polar cap ionization patches in the polar ionosphere, we directly observe the full Dungey convection cycle for southward interplanetary magnetic field ...(IMF) conditions. This enables us to study how the Dungey cycle influences the patches' evolution. The patches were initially segmented from the dayside storm enhanced density plume at the equatorward edge of the cusp, by the expansion and contraction of the polar cap boundary due to pulsed dayside magnetopause reconnection, as indicated by in situ Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations. Convection led to the patches entering the polar cap and being transported antisunward, while being continuously monitored by the globally distributed arrays of GPS receivers and Super Dual Auroral Radar Network radars. Changes in convection over time resulted in the patches following a range of trajectories, each of which differed somewhat from the classical twin‐cell convection streamlines. Pulsed nightside reconnection, occurring as part of the magnetospheric substorm cycle, modulated the exit of the patches from the polar cap, as confirmed by coordinated observations of the magnetometer at Tromsø and European Incoherent Scatter Tromsø UHF radar. After exiting the polar cap, the patches broke up into a number of plasma blobs and returned sunward in the auroral return flow of the dawn and/or dusk convection cell. The full circulation time was about 3 h.
Key Points
Direct observations of the full Dungey cycle by tracking polar cap patches
Formation and evolution of patches modulated by dayside and nightside reconnections
The full circulation time was about 3 h
We present a detailed experimental procedure for the quantitative determination of mechanical properties and full-field strain measurement of rock material under dynamic loads. Three kinds of testing ...methods, i.e., notched semi-circular bending, Brazilian disc, and uniaxial compression, were conducted using a split Hopkinson pressure bar (SHPB) system. Experimental setup, data acquisition and interpretation were described in detail. The digital image correlation (DIC) technique in conjunction with high-speed (HS) photography was adopted for the measurement of surface deformation characteristics (e.g., strain localization and evolution, and onset of fracture) of rock specimens. To verify the accuracy of this technique, comparative tests were performed in which the strains in the specimens were simultaneously determined using on-specimen strain gauges. Strain gauges were also used to determine the time-to-fracture and crack propagation velocity. Specifically, the scanning electron microscope (SEM) imaging technique was used to investigate the brittle failure micromechanisms of white belt initiated and developed prior to observable cracks in specimens. Experimental results show that dynamic crack initiation toughness, dynamic tensile strength and dynamic uniaxial compressive strength can be well determined, and the HS-DIC technique provides reliable full-field strain fields in the specimens under dynamic loads.
► A detailed experimental procedure is presented for determining dynamic mechanical properties. ► The DIC technique in conjunction with high-speed camera provides full-field strain fields. ► Dynamic mechanical properties of the Fangshan marble increase with increasing strain rate. ► Failure mechanisms of strain rate are mostly induced by fracture mode transitions in the marble.
Two types of poleward moving plasma concentration enhancements (PMPCEs) were observed during a sequence of pulsed reconnection events, both in the morning convection cell: Type L (low density) was ...associated with a cusp flow channel and seems likely to have been produced by ionization associated with particle precipitation, while Type H (high density) appeared to originate from the segmentation of the tongue of ionization by the processes which produced the Type L events. As a result, the Type L and Type H PMPCEs were interspersed, producing a complex density structure which underlines the importance of cusp flow channels as a mechanism for segmenting and structuring electron density in the cusp and shows the necessity of differentiating between at least two classes of electron density patches.
Key Points
First observed TOI patches in the morning cell
Differentiating between at least two classes of electron density patches
TOI patches segmented by flow channels with precipitation electrons
Zirconium phosphate (ZrP) has recently been demonstrated as an excellent sorbent for heavy metals due to its high selectivity, high thermal stability, and absolute insolubility in water. However, it ...cannot be readily adopted in fixed beds or any other flowthrough system due to the excessive pressure drop and poor mechanical strength resulting from its fine submicrometer particle sizes. In the present study a hybrid sorbent, i.e., polymer-supported ZrP, was prepared by dispersing ZrP within a strongly acidic cation exchanger D-001 and used for enhanced lead removal from contaminated waters. D-001 was selected as a host material for sorbent preparation mainly because of the Donnan membrane effect resulting from the nondiffusible negatively charged sulfonic acid group on the exchanger surface, which would enhance permeation of the targeted metal ions. The hybrid sorbent (hereafter denoted ZrP-001) was characterized using a nitrogen adsorption technique, scanning electron microscope (SEM), and X-ray diffraction (XRD). Lead sorption onto ZrP-001 was found to be pH dependent due to the ion-exchange mechanism, and its sorption kinetics onto ZrP-001 followed the pseudo-first-order model. Compared to D-001, ZrP-001 exhibited more favorable lead sorption particularly in terms of high selectivity, as indicated by its substantially larger distribution coefficients when other competing cations Na
+, Ca
2+, and Mg
2+ coexisted at a high level in solution. Fixed-bed column runs showed that lead sorption on ZrP-001 resulted in a conspicuous decrease of this toxic metal from 40 mg/L to below 0.05 mg/L. By comparison with D-001 and ZrP-CP (ZrP dispersion within a neutrally charged polymer CP), enhanced removal efficiency of ZrP-001 resulted from the Donnan membrane effect of the host material D-001. Moreover, its feasible regeneration by diluted acid solution and negligible ZrP loss during operation also helps ZrP-001 to be a potential candidate for lead removal from water. Thus, all the results suggested that ZrP-001 offers excellent potential for lead removal from contaminated water.
A new hybrid sorbent ZrP-D001 based on the Donnan membrane effect was prepared for enhanced lead removal from contaminated water.
In nature, complex terpene natural products are formed by the so-called tail-to-head terpene (THT) cyclization. The cationic reaction cascade is promoted efficiently in complex enzyme pockets, in ...which cationic intermediates and transition states are stabilized. In solution, the reaction is hard to control and man-made catalysts able to perform selective THT cyclizations are lacking. We herein report the first example of a successful THT cyclization inside a supramolecular structure. The basic mode of operation in cyclase enzymes was mimicked successfully and a catalytic non-stop THT was achieved with geranyl acetate as the substrate. The results presented have implications for the postulated reaction mechanism in cyclase enzymes. Evidence indicates that the direct isomerization of a geranyl cation to the cisoid isomer, which so far was considered unlikely, is feasible.
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