Equivalent Loading Research Articles

Iontophoretic transport kinetics of ketorolac in vitro and in vivo: Demonstrating local enhanced topical drug delivery to muscle

The objective of the study was to investigate the iontophoretic delivery kinetics of ketorolac (KT), a highly potent NSAID and peripherally-acting analgesic that is currently indicated to treat moderate to severe acute pain. It was envisaged that, depending on the amounts delivered, transdermal iontophoretic administration might have two distinct therapeutic applications: (i) more effective and faster local therapy with shorter onset times (e.g. to treat trauma-related pain/inflammation in muscle) or (ii) a non-parenteral, gastrointestinal tract sparing approach for systemic pain relief. The first part of the study investigated the effect of experimental conditions on KT iontophoresis using porcine and human skin in vitro. These results demonstrated that KT electrotransport was linearly dependent on current density – from 0.1875 to 0.5mA/cm2 – (r2>0.99) and drug concentration – from 5 to 20mg/ml (r2>0.99). Iontophoretic permeation of KT from a 2% hydroxymethyl cellulose gel was comparable to that from an aqueous solution with equivalent drug loading (584.59±114.67 and 462.05±66.56μg/cm2, respectively). Cumulative permeation (462.05±66.56 and 416.28±95.71μg/cm2) and steady state flux (106.72±11.70 and 94.28±15.47μg/cm2h), across porcine and human skin, were statistically equivalent confirming the validity of the model. Based on the results in vitro, it was decided to focus on topical rather than systemic applications of KT iontophoresis in vivo. Subsequent experiments, in male Wistar rats, investigated the local enhancement of KT delivery to muscle by iontophoresis. Drug biodistribution was assessed in skin, in the biceps femoris muscle beneath the site of iontophoresis (‘treated muscle’; TM), in the contralateral muscle (‘non-treated muscle’; NTM) and in plasma (P). Passive topical delivery and oral administration served as negative and positive controls, respectively. Iontophoretic administration for 30min was superior to passive topical delivery for 1h and resulted in statistically significant increases in KT levels in the skin (91.04±15.48 vs. 20.16±8.58μg/cm2), in the biceps femoris at the treatment site (TM; 6.74±3.80 vs. <LOQ), in the contralateral site (NTM; 1.26±0.54 vs. <LOQ) and in plasma (P; 8.58±2.37μg/ml vs. <LOD). In addition to increasing bioavailability, iontophoretic administration of KT showed clear selectivity for local delivery to the biceps femoris at the treatment site – the TM:NTM ratio was 5.26±1.45, and the TM:P and NTM:P ratios were 0.75±0.32 and 0.14±0.04, respectively. Furthermore, the post-iontophoretic concentration of KT in the ‘treated’ biceps femoris muscle and the muscle:plasma ratio were also superior to those following oral administration of a 4mg/kg dose (6.74±3.80 vs. 0.62±0.14μg/g and 0.75±0.32 vs. 0.14±0.03, respectively). In conclusion, the results demonstrate that iontophoresis of ketorolac enables local enhanced topical delivery to subjacent muscle; this may have clinical application in the treatment of localised inflammation and pain.

Single modification at position 14 of siRNA strand abolishes its gene‐silencing activity by decreasing both RISC loading and target degradation

Normally siRNA has to be chemically stabilized in therapeutic applications. It is a challenge to obtain optimal stabilizing effects while maintaining full silencing activity due to a lack of understanding of how different chemical modifications would influence the efficacy of siRNA. In the current study, the effect of single 2'-sugar modifications was profiled across the length of the siRNA guide strand. This led to the surprising finding that a single 2'-OMe modification at position 14 of the siRNA guide strand substantially compromised its gene-silencing activity in a manner that was independent of the nucleotide identity at this site or the sequence context around it. We found that modification at position 14 of the siRNA guide strand reduced its RNA-induced silencing complex (RISC) loading tremendously, whereas the loading of the siRNA sense strand was only marginally affected. When comparing the silencing potency of 14th position-modified siRNA (transfected at 16.7 nM) and native control (transfected at 1 nM) at equivalent Ago2 loading levels, the silencing potency of modified siRNA was much lower, even lower than the level of native siRNA transfected at 0.1 nM. These data indicated that modification at position 14 of the siRNA guide strand abolishes its gene-silencing activity by decreasing both RISC loading and target degradation. Using a computational modeling approach, we demonstrated an intimate interaction between the 14th nucleotide of guide strand and the amino acid Q675 in the AGO protein, which is located in a highly conserved loop of PIWI domain. In addition to gaining insights into siRNA-AGO interactions, this study of structure-activity relationship further established a general principle for siRNA modification in siRNA drug development.

Combined bromine and chlorine release from large explosive volcanic eruptions: A threat to stratospheric ozone?

Large explosive volcanic eruptions inject gases, aerosols, and fine ashes into the stratosphere, potentially influencing climate. Emissions of chlorine (Cl) and bromine (Br) from such large eruptions play an important role for catalytic destruction of ozone in the stratosphere, but hitherto the global effects of simultaneous catastrophic release of volcanic Br and Cl into the stratosphere have not been investigated. The Br release from 14 large explosive eruptions throughout Nicaragua covering an entire subduction zone segment in the past 70 ka was determined with petrologic methods. Melt inclusions in volcanic phenocrysts were analyzed using a new optimized synchrotron–X-ray fluorescence microprobe set-up. Single eruptions produced Br outputs of 4–600 kt, giving an average Br emission of 27 kt per eruption. Using the assumption that 10% of the emitted halogens reach the stratosphere, the average Br and Cl loading to the stratosphere would be 3 ppt and 1500 ppt, respectively, which together would account for 185% of the preindustrial equivalent effective stratospheric Cl loading. We thus conclude that many large tropical volcanic eruptions had and have the potential to substantially deplete ozone on a global scale, eventually forming future ozone holes.

Osteocyte-derived insulin-like growth factor I is essential for determining bone mechanosensitivity

This study sought to determine whether deficient Igf1 expression in osteocytes would affect loading-induced osteogenic response. Tibias of osteocyte Igf1 conditional knockout (KO) mice (generated by cross-breeding Igf1 floxed mice with Dmp1-Cre transgenic mice) and wild-type (WT) littermates were subjected to four-point bending for 2 wk. Microcomputed tomography confirmed that the size of tibias of conditional mutants was smaller. Loading with an equivalent loading strain increased periosteal woven bone and endosteal lamellar bone formation in WT mice but not in conditional KO mice. Consistent with the lack of an osteogenic response, the loading failed to upregulate expression of early mechanoresponsive genes (Igf1, Cox-2, c-fos) or osteogenic genes (Cbfa-1, and osteocalcin) in conditional KO bones. The lack of osteogenic response was not due to reduced osteocyte density or insufficient loading strain. Deficient osteocyte Igf1 expression reduced the loading-induced upregulation of expression of canonical Wnt signaling genes (Wnt10b, Lrp5, Dkk1, sFrp2). The loading also reduced (by 40%) Sost expression in WT mice, but the loading not only did not reduce but upregulated (~1.5-fold) Sost expression in conditional KO mice. Conditional disruption of Igf1 in osteocytes also abolished the loading-induced increase in the bone β-catenin protein level. These findings suggest an impaired response in the loading-induced upregulation of the Wnt signaling in conditional KO mice. In summary, conditional disruption of Igf1 in osteocytes abolished the loading-induced activation of the Wnt signaling and the corresponding osteogenic response. In conclusion, osteocyte-derived IGF-I plays a key determining role in bone mechanosensitivity.

응력 구속조건을 고려한 동하중의 등가정하중으로의 변환

Due to the difficulty in considering dynamic load in the view point of a computer resource and computing time, it is common that external load is assumed as ideal static loads. However, structural analysis under static load cannot guarantee the safety of design of the structures under dynamic loadings. Recently, the systematic method to construct equivalent static load from the given dynamic load has been proposed. Previous study has calculated equivalent static load through the optimization procedure under displacement constraints. However, previously reported works to distribute equivalent static load were based on ad-hoc methods. Improper selection of equivalent static loading positions may results in unreliable prediction of structural design. The present study proposes the selection method of the proper locations of equivalent static loads to dynamically applied loads when we consider transient dynamic structural problems. Moreover, it is appropriate to take into account the stress constraint as well as displacement constraint condition for the safety design. But the previously reported studies of equivalent static load design methods considered only displacement constraint conditions but not stress constraint conditions. In the present study we consider not only displacement constraint but also stress constraint conditions. Through a few numerical examples, the efficiency and reliability of proposed scheme is verified by comparison of the equivalent stress between equivalent static loading and dynamic loading.

Generation and validation of loading profiles for highly accelerated durability tests of ground vehicle components

Accelerated durability tests are designed to quantify the life characteristics of ground vehicle components under normal use conditions by testing at a higher stress level to accelerate the occurrence of failure. Presently, conducting durability tests with a high acceleration factor has become increasingly demanding for the reduction of the time and the cost involved in long period field/durability tests. In previous work, to accelerate the field test, the standard ‘test tailoring approach’ has been modified due to the limitations of testing implementation and required high acceleration factors. In this modified approach, a full period durability loading profile has to be shortened to an equivalent partial period test loading profile, which is repeated in the tests keeping the same amount of damage contents. To apply this new modified approach to industrial durability tests, it needs to be validated. In this work, a computer-aided testing method is developed for the validation of this modified ‘test tailoring approach’. Hence, a new test-piece has been designed by a conjugative approach involving the finite element technique and fatigue analysis for a specific durability life. Afterwards, the loading profiles with various acceleration factors synthesized via the modified approach have been applied on the designed test-piece and the fatigue lives have been simulated to verify the effectiveness of those loading profiles. Simulation results show that, loading profiles with high acceleration factors can be successfully generated with the accuracy above 95%. In addition, synthesized accelerated loading profiles result failure from the identical locations determined using the proposed conjugative approach.

Applicability of Equivalent Constant Amplitude Loading for Assessing the Fatigue Life of Pipelines and Risers and the Influence of Compressive Stress Cycles

Fatigue life assessment of pipelines and risers is a complex process, involving various uncertainties. The selection of an appropriate fatigue model is important for establishing the inspection intervals and maintenance criteria. In offshore structures, the vortex-induced vibration (VIV) could cause severe fatigue damage in risers and pipelines, resulting in leakage or even catastrophic failure. The industry has customarily used simple fatigue models for fatigue life assessment of pipelines and risers (such as the Paris or Walker models); however, these models were developed based on constant amplitude loading scenarios. In contrast, VIV-induced stress-time history has a variable amplitude nature. The use of the simplified approach (which is inherently non conservative), has necessitated the implementation of large safety factors for fatigue design of pipelines and risers. Moreover, most of the experimental investigations conducted to date with the aim of characterizing the fatigue response of pipelines and risers have been done based on incorporation of constant amplitude loading (CAL) scenarios (which is unrealistic), or converting the variable amplitude loading (VAL) scenarios to an equivalent CAL. This study demonstrates that the use of such approaches would not be lead to accurate assessment of the fatigue response of risers subject to VIV-induced VAL. The experimental investigation performed in this study will also clarify the underlying reasons for the use of large safety factors by the industry when assessing the fatigue life of pipelines and risers. In addition, an experimental investigation was also conducted to highlight the influence of the compressive portion of VIV stress-time history on the fatigue life of such components. It is shown that the compressive stress cycles significantly influence the fatigue crack growth response of risers, and their presence should not be ignored.

Using a Two-Stage Hydrogen-Based Membrane Biofilm Reactor (MBfR) to Achieve Complete Perchlorate Reduction in the Presence of Nitrate and Sulfate

We evaluated a strategy for achieving complete reduction of perchlorate (ClO(4)(-)) in the presence of much higher concentrations of sulfate (SO(4)(2-)) and nitrate (NO(3)(-)) in a hydrogen-based membrane biofilm reactor (MBfR). Full ClO(4)(-) reduction was achieved by using a two-stage MBfR with controlled NO(3)(-) surface loadings to each stage. With an equivalent NO(3)(-) surface loading larger than 0.65 ± 0.04 g N/m(2)-day, the lead MBfR removed about 87 ± 4% of NO(3)(-) and 30 ± 8% of ClO(4)(-). This decreased the equivalent surface loading of NO(3)(-) to 0.34 ± 0.04-0.53 ± 0.03 g N/m(2)-day for the lag MBfR, in which ClO(4)(-) was reduced to nondetectable. SO(4)(2-) reduction was eliminated without compromising full ClO(4)(-) reduction using a higher flow rate that gave an equivalent NO(3)(-) surface loading of 0.94 ± 0.05 g N/m(2)-day in the lead MBfR and 0.53 ± 0.03 g N/m(2)-day in the lag MBfR. Results from qPCR and pyrosequencing showed that the lead and lag MBfRs had distinctly different microbial communities when SO(4)(2-) reduction took place. Denitrifying bacteria (DB), quantified using the nirS and nirK genes, dominated the biofilm in the lead MBfR, but perchlorate-reducing bacteria (PRB), quantified using the pcrA gene, became more important in the lag MBfR. The facultative anaerobic bacteria Dechloromonas, Rubrivivax, and Enterobacter were dominant genera in the lead MBfR, where their main function was to reduce NO(3)(-). With a small NO(3)(-) surface loading and full ClO(4)(-) reduction, the dominant genera shifted to ClO(4)(-)-reducing bacteria Sphaerotilus, Rhodocyclaceae, and Rhodobacter in the lag MBfR.

Functional Polymer Brushes on Diamond as a Platform for Immobilization and Electrical Wiring of Biomolecules

AbstractFor the biofunctionalization of electronic devices, polymer brushes can provide a route which allows combining the advantages of other commonly used approaches, such as immobilization of functional biomolecules via self assembled monolayers or coated polymer matrices: high stability and loading capacity, efficient electron transport, and excellent biocompatibility. In the work presented here, poly(methacrylic acid) brushes are prepared by self‐initiated photografting and photopolymerization on diamond electrodes. In this straightforward process no prior grafting of initiators is required since the initiation of the polymerization can be conveniently controlled by the hydrogen or oxygen termination of the diamond surface. Boron doped nanocrystalline diamond as an electrode material provides extreme chemical inertness and stability, inherent biocompatibility, and superior electrochemical properties, such as the large accessible potential window and low background currents. As a proof of concept we demonstrate the amperometric detection of glucose by polymer brushes covalently modified with the redox enzyme glucose oxidase and aminomethyl ferrocene as electron mediator. Characterization by X‐ray photoelectron spectroscopy and atomic force microscopy both indicate a high loading of the ferrocene mediator. Consistently, electrochemical cyclic voltammetry shows a multilayer equivalent loading of ferrocene and highly efficient electron transfer throughout the polymer film. Overall, functionalized polymer brushes can provide a promising platform for the immobilization and electrical wiring of biomolecules for bioelectronic and biosensing applications.

Centrifuge modelling of an on-bottom pipeline under equivalent wave and current loading

Pipelines are the main element in transporting hydrocarbons from their extraction sites to on-shore or floating facilities, with preference now given to pipelines laid directly on the seabed due to their fast and economic installation. However, these pipelines are exposed and must be stable under all environmental conditions, and therefore, their design for on-bottom stability is of critical importance. Although accurate prediction of the pipe–soil interaction behaviour under hydrodynamic loads from waves and currents is of major concern, limited physical testing of pipes subjected to these cyclic loading conditions has occurred. Tests have concentrated on simpler load combinations in order to develop pipe–soil friction factors or the key parameters in plasticity models that described pipe–soil behaviour. In this paper, results from geotechnical centrifuge experiments of a model pipe on calcareous sand soil collected from offshore on the North West Shelf of Australia are presented. A sophisticated load control scheme allowed complex paths characteristic of hydrodynamic loads to be applied during the testing. Furthermore, pipe testing could be extended to relatively large horizontal movements of up to 5 pipe diameter. The results of the centrifuge testing programme provide improved understanding of the pipe–soil interaction under complex hydrodynamic load paths. They have also been used to assess a state-of-the-art plasticity model describing pipe–soil interaction on calcareous sands.

Comparison of Coupled and Uncoupled Load Simulations on a Jacket Support Structure

In this article, a comparison of the moments and forces at the joints of a jacket structure is made between fully coupled aero-hydro-elastic simulations in HAWC2 and uncoupled load predictions in the finite element software Abaqus. The jacket sub structure is modelled in moderate deep waters of 50m and designed for the 5MW NREL baseline wind turbine. External conditions are based on wind and wave joint distribution for a site in the North Sea. The turbulent wind field in HAWC2 is generated by random values, defined by the Mann Turbulence model, for each operational mean wind speed. A four-legged jacket structure similar to the Upwind reference jacket is developed in the Abaqus environment, to which is added the transition piece and tower. The aeroelastic loads determined in normal operating conditions of the turbine is integrated and centralized as nodal forces and moments acting at the tower top of the finite element model. Hydrodynamic loads from the incoming waves are computed using the Morison equation and based on a nonlinear irregular wave field. Velocities, accelerations and amplitudes of the wave field as well as tower top forces and moments are used as inputs for the structural analysis in Abaqus. The fully coupled simulation is implemented and performed in HAWC2. In the uncoupled case, the loads (wave loads and tower base loads) are analysed by an implicit structural Finite Element Analysis (Abaqus 6.11-1). A subroutine is used as a preprocessor generating a beam element model and linking the loads to the components as nodal forces. In both simulation cases, the integrated loads acting on the jacket legs are computed as time series and as damage equivalent loading. The analysis and comparison of the fully coupled and decoupled simulation method show that the results vary depending on the structural stiffness and the applied wave loads. Variation in the amplitudes of the moments and forces on the jacket legs up to 25% was observed between the results obtained from coupled and uncoupled simulations.

Single-Event Transient Testing of Low Dropout PNP Series Linear Voltage Regulators

Recommendations are provided for Single Event Transient (SET) testing of low dropout (LDO) PNP series linear voltage regulators. A combination of SPICE circuit simulations and pulsed laser irradiations are used to demonstrate that the equivalent series resistance (ESR), loading conditions and regulator stability are the key elements that govern LDO regulator's SET response. Pulsed laser testing of several light-like candidates shows similar SET trends and dependences. Due to the additional circuits introduced in an LDO design, we reveal the existence of a thermal shutdown mode that can be triggered by a single event that is also load dependent.

Characterization of Piezoresistive-Si-Nanowire-Based Pressure Sensors by Dynamic Cycling Test With Extralarge Compressive Strain

A novel pressure sensor using piezoresistive silicon nanowires (SiNWs) embedded in a suspended multilayered diaphragm is investigated by a probe-based dynamic cycling test combining the standard bulge testing setup. By utilizing the high fracture stress of the SiN <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> film, we explored the behavior of the SiNW under a level of extralarge compressive strain for the first time, including strain levels of more than 2.1% under the static testing and 1.5% under the dynamic testing. Drift of the initial resistances of the SiNW was observed at different time intervals during the dynamic testing under a compressive strain of higher than 1.3%, while the sensitivity of the pressure sensor basically keeps unchanged. However, there was almost no drift or degradation observed in the sensor characteristics when an equivalent point loading within the application working range is applied to the pressure sensor during the dynamic testing.

Influence of Fe2O3 Nanofiller Shape on the Conductivity and Thermal Properties of Solid Polymer Electrolytes: Nanorods versus Nanospheres

The influence of nanofiller shape on the ionic conductivity and thermal properties of solid polymer electrolytes is investigated. Electrolytes of polyethylene oxide (PEO) and LiClO4 filled with 1–20 wt % spherical Fe2O3 nanoparticles and 0.5–10 wt % Fe2O3 nanorods are measured at an ether oxygen to Li ratio of 10:1. Nanorods improve the ionic conductivity to a similar extent as spherical nanoparticles, except at concentrations 10–20 times lower. The maximum conductivity improvement occurs at a spherical metal oxide nanoparticle loading of 10 wt %; however, an equivalent nanorod loading decreases the conductivity below that of the unfilled electrolyte. This result suggests that the long-range morphology of the two nanocomposites differs widely, where high concentrations of nanorods will inhibit instead of enhance Li transport. The shape of the nanofiller also affects the crystallization rate and resulting crystal structure. Differential scanning calorimetry measurements show that samples containing nanorod...

Comparing finite element and constitutive modelling techniques for predicting rutting of asphalt pavements

This paper focuses on a comprehensive evaluation of the effects of different finite element (FE) modelling techniques and material constitutive models on predicting rutting in asphalt pavements under repeated loading conditions. Different simplified 2D and more realistic 3D loading techniques are simulated and compared for predicting asphalt rutting. This study also evaluates and compares the rutting performance predictions using different material constitutive behaviours such as viscoelastic–viscoplastic, elasto-viscoplastic and coupled viscoelastic, viscoplastic and viscodamage behaviours. The simulations show that the assumption of the equivalency between a pulse loading and an equivalent loading, which are commonly used as simplified loading assumptions for predicting rutting, is reasonable for viscoelastic–viscoplastic and elasto-viscoplastic constitutive behaviours. However, these loading assumptions and material constitutive models overestimate rutting as damage grows. Results show that the 2D plane strain FE simulations significantly overestimate rutting as compared with the rutting performance predictions from more realistic 3D FE simulations.

Metal microfibers entrapped catalysts as effective ambient temperature CO oxidation catalysts

CO oxidation reaction on a highly active Pt–CeO2/SiO2 catalyst was found to be diffusion controlled at ambient conditions (T<50°C; 50–90% RH); therefore, the use of smaller catalyst particles was imperative for optimum Pt utilization. Packed beds (PBs) of smaller particles (dia.<500μm) cause problems such as flow maldistribution and channeled flow due to cluster formation. Also these PBs are susceptible to changes in orientations and vibrations resulting in catalyst bypass and reduced activity. Nickel metal microfibrous entrapped Pt–CeO2/SiO2 catalysts (MFECs) were developed to circumvent these problems with the PBs. These MFECs outperformed the conventional catalyst PB with equivalent catalyst loading over a wide range of CO concentrations (100–10,000ppm) and exhibited greater stability. The entrapment of catalyst particles has a significant impact on the heat and mass transport properties of the reactor. Therefore, the effects of transport properties on activity were investigated experimentally using diluted PBs and by reactor simulation using a transient, non-isothermal model to understand the activity improvement by MFECs. Experimental and simulation results showed that while the thermal properties significantly affect the activity, the axial mass dispersion had negligible impact on the activity. MFECs have greater thermal conductivity due to the presence of Ni fibers and the inert thermal mass of the Ni fibers was minimal (33% of the catalyst PB). MFECs have a uniform and more open (void: 0.5–0.8) structure and the entrapment of particles minimizes cluster formation. Due to these better heat and mass transport properties, MFECs outperformed PBs. Also, these MFECs are flexible and pleatable which makes them a potential candidate for CO removal applications.

Development of salt minibasins initiated by sedimentary topographic relief

Can sedimentary topographic relief (here termed uneven sedimentation) explain the enigmatic early initiation of salt minibasins at rifted continental margins when the sediment fill is less dense than the underlying salt? Using isostatic balancing arguments for compacting sediments, we first demonstrate that minibasin-scale thickness variations in a weak sedimentary overburden can cause lateral pressure differences large enough to initiate salt minibasins. These contribute toward the minibasin attaining the Rayleigh–Taylor threshold, the point at which sediments sink into an underlying salt layer. Secondly, using two-dimensional plane-strain finite element models, we show that uneven sediment loading on a viscous salt channel can initiate salt minibasins even when sediments have finite strength. Uneven sedimentation (sedimentary topographic relief) is idealized in the models as uniform aggradation of compacting sediment with a superimposed smooth sinusoidal topographic perturbation, wavelength λ, maximum height hl.Our main goal is to estimate the minimum duration that uneven sedimentation must persist, tP, such that the strength of the sediments is overcome and the minibasin continues to develop and mature (a successful minibasin) when uneven sedimentation is replaced by uniform aggradation. We investigate models with widths, W, equal to λ (confined salt models), and greater than λ (unconfined salt models). Our results suggest that for models that develop successful minibasins there is an optimal value of λ, λOPT, for which tRT, the time to attain the theoretical Rayleigh–Taylor threshold based on isostasy arguments, and tP are the smallest. This wavelength selection exists when the sediments have moderate (e.g., shale) to high (e.g., carbonates) density but is not prominent for low density sediments. For confined salt models at λOPT, tP varies from 8.0 to 2.25Ma for low to high density sediments, respectively, when hl ranges from 40 to 80m. In unconfined models, where salt can be expelled over larger distances than λ, tP ranges from 7 to 1.5Ma. For a given sediment density and compaction model, there is a lower limit of λ below which uneven sedimentation alone does not initiate minibasins. However, successful minibasins develop over a wider range of λ in unconfined models and when W≫λ, uneven sedimentation in one location can indirectly lead to the development of outboard basins.Uneven sediment may alternatively be deposited on a uniformly thick, compacting pre-kinematic sediment layer. Under these circumstances tP is further reduced to 9.0–0.5Ma depending on the density of the sediments. Weak in-plane contraction can further reduce tP to 3.5–0.375Ma even for low density sediments. Under optimal conditions a period of uneven sedimentation of this type in an otherwise uniformly aggrading sequence need only have a topographic amplitude of 40–80m and persist for 0.05–2Ma in order to seed the development of a successful minibasin. Our idealized uneven sedimentation model is interpreted as a proxy for channel–levee systems, turbidite lobe complexes, and/or lateral sediment density variations that cause equivalent sediment loading, and which occur both in the down-dip and along-strike directions of a rifted margin.

On the Energy of Dynamic Fractures

Abstract The validity of the constant propagation fracture energy postulation for dynamic fracture is discussed. As shown from existing direct and indirect experimental results, this assumption may not represent the physical reality. For spontaneous fractures, the fracture energy was shown to increase linearly with the crack length, and for dynamic fractures driven by known amplitude impulsive loading (generated by planar impact), the fracture energy was not a constant either. Despite of its phenomenogical origin, the Broberg’s theory developed for self-similar crack growth works well for both spontaneous fractures and dynamic fractures produced by well defined dynamic loading. In this theory, the fracture energy is not a constant. Furthermore, with given far-field loading or equivalent far-field loading, the crack speed is uniquely determined by a strength-like material parameter. This parameter is related to the cohesive strength as proposed by H. J. Gao for hyperelastic materials in the crack-tip process zone. It is proposed in this work that the strength-like parameter (or equivalently the constant fracture speed) is a better material parameter to describe the dynamic fracture propagation process for most dynamic fractures.

On the Energy of Dynamic Fractures

Abstract The validity of the constant propagation fracture energy postulation for dynamic fracture is discussed. As shown from existing direct and indirect experimental results, this assumption may not represent the physical reality. For spontaneous fractures, the fracture energy was shown to increase linearly with the crack length, and for dynamic fractures driven by known amplitude impulsive loading (generated by planar impact), the fracture energy was not a constant either. Despite of its phenomenogical origin, the Broberg's theory developed for self-similar crack growth works well for both spontaneous fractures and dynamic fractures produced by well defined dynamic loading. In this theory, the fracture energy is not a constant. Furthermore, with given far-field loading or equivalent far-field loading, the crack speed is uniquely determined by a strength-like material parameter. This parameter is related to the cohesive strength as proposed by H. J. Gao for hyperelastic materials in the crack-tip process zone. It is proposed in this work that the strength-like parameter (or equivalently the constant fracture speed) is a better material parameter to describe the dynamic fracture propagation process for most dynamic fractures.

On the Energy of Dynamic Fractures

Abstract The validity of the constant propagation fracture energy postulation for dynamic fracture is discussed. As shown from existing direct and indirect experimental results, this assumption may not represent the physical reality. For spontaneous fractures, the fracture energy was shown to increase linearly with the crack length, and for dynamic fractures driven by known amplitude impulsive loading (generated by planar impact), the fracture energy was not a constant either. Despite of its phenomenogical origin, the Broberg’s theory developed for self-similar crack growth works well for both spontaneous fractures and dynamic fractures produced by well defined dynamic loading. In this theory, the fracture energy is not a constant. Furthermore, with given far-field loading or equivalent far-field loading, the crack speed is uniquely determined by a strength-like material parameter. This parameter is related to the cohesive strength as proposed by H. J. Gao for hyperelastic materials in the crack-tip process zone. It is proposed in this work that the strength-like parameter (or equivalently the constant fracture speed) is a better material parameter to describe the dynamic fracture propagation process for most dynamic fractures.