Basal Force Research Articles

Simulated Slidequakes: Insights From DEM Simulations Into the High‐Frequency Seismic Signal Generated by Geophysical Granular Flows

AbstractGeophysical granular flows generate seismic signals known as “slidequakes” or “landquakes”, with low‐frequency components whose generation by mean forces is widely used to infer hazard‐relevant flow properties. Many more such properties could be inferred by understanding the fluctuating forces that generate slidequakes' higher frequency components and, to do so, we conducted discrete‐element simulations that examined the fluctuating forces exerted by steady, downslope‐periodic granular flows on fixed, rough bases. Unlike our previous laboratory experiments, our simulations precluded basal slip. We show that, in its absence, simulated basal forces' power spectra have high‐frequency components more accurately predicted using mean shear rates than using depth‐averaged flow velocities, and can have intermediate‐frequency components which we relate to chains of prolonged interparticle contacts. We develop a “minimal model”, which uses a flow's collisional properties to even more accurately predict the high‐frequency components, and empirically parametrize this model in terms of mean flow properties, for practical application. Finally, we demonstrate that the bulk inertial number determines not only the magnitude ratio of rapidly fluctuating and mean forces on a unit basal area, consistent with previous experimental results, but also the relative magnitudes of the high and intermediate‐frequency force components.

Basal Force Fluctuations and Granular Rheology: Linking Macroscopic Descriptions of Granular Flows to Bed Forces With Implications for Monitoring Signals

AbstractGranular flows are ubiquitous in nature with single flows traversing a wide range of dynamic conditions from initiation to deposition. Many of these flows are responsible for significant hazards and can generate remotely detectable seismic signals. These signals provide a potential for real‐time flow measurements from a safe distance. To fully realize the benefit of seismic measurements, basal‐granular forces must be linked to macroscopic internal flow dynamics across a wide range of flow conditions. We utilize discrete element simulations to observe dry and submerged granular flows under plane‐shear and inclined‐flow configurations, relating bulk kinematics to basal‐force distributions. We find that the power and frequency of force fluctuations scale with non‐dimensional shear rate (I). This scaling tracks three pre‐established regimes that are described by μ(I) rheology: (a) an intermittent particle rearrangement regime, where basal forces are dominated by low frequencies; (b) an intermediate regime where basal forces start to increase in frequency while showing correlations in space and (c) a fully collisional regime where the signal is nearly flat up to a cutoff frequency. We further identify a newly defined fourth regime that marks a “phase change” from the intermediate to collisional regime where increases in basal force fluctuations with increasing shear rates stalls as the granular bed dilates, partially destroying the contact network. This effort suggests that basal forces can be used to interpret complex granular processes in geophysical flows.

Solid Concentration as a Main Proxy for Basal Force Fluctuations Generated by Highly Concentrated Sediment Flows

AbstractSediment flows generate ground vibrations by exerting force fluctuations on the riverbed. Linking force fluctuations to properties of highly concentrated sediment flows, however, remains particularly challenging due to complexities arising from grain‐to‐grain interactions. Here, we conduct downscaled flume experiments in which we specifically measure force fluctuations and local seismic vibrations together with flow properties of highly concentrated sediment flows at high spatial and temporal resolution. We observe hysteresis behaviors between force fluctuations amplitude and flow surface elevation and mass that occur during complex changes in internal flow dynamics. By contrast, force fluctuations amplitude exhibits a unique negative relationship with solid concentration. We suggest this is due to the rheology of dense granular flows, where solid concentration is a proxy for particle agitation. We therefore advance that solid concentration should be incorporated in seismic models of such sediment flows as a key parameter describing inter‐particle collisions and impacts to the bed.

Dataset for "Volumetric solid concentration as a main proxy for basal force fluctuations generated by highly concentrated sediment flows"

Dataset for "Volumetric solid concentration as a main proxy for basal force fluctuations generated by highly concentrated sediment flows"

Dataset for "Volumetric solid concentration as a main proxy for basal force fluctuations generated by highly concentrated sediment flows"

Dataset for "Volumetric solid concentration as a main proxy for basal force fluctuations generated by highly concentrated sediment flows"

Dataset for "Volumetric solid concentration as a main proxy for basal force fluctuations generated by highly concentrated sediment flows"

Dataset for "Volumetric solid concentration as a main proxy for basal force fluctuations generated by highly concentrated sediment flows"

Analyzing Bulk Flow Characteristics of Debris Flows Using Their High Frequency Seismic Signature

AbstractQuantifying debris‐flow characteristics remains a key challenge in natural hazard research. Recent studies suggest that seismic signals can reveal debris‐flow properties. However, the accuracy and applicability of theoretical models linking bulk flow properties to the seismic signature of a debris flow remain elusive. By extending a previously proposed model of random single‐particle impact forces to multi‐particle force chains acting on the channel bed, we describe the generation of high frequency seismic signals, and thereby estimate the bulk flow dynamics of six debris‐flow events at Illgraben, Switzerland. The theoretically predicted basal force fluctuations agree with in‐situ measurements at a basal force plate and seismic signals recorded adjacent to the channel. According to our model, both random single‐particle impacts and random impacts caused by multi‐particle force chains control basal force fluctuations. The relative contributions of single particles and of multi‐particle force chains may vary significantly for different events and different positions within events. The relative contribution of multi‐particle force chains is expected to be larger in the flow front, where particle concentrations are higher. The ratio between single‐particle and multi‐particle contributions appears to control the non‐linear relation between flow depth and the magnitude of the high frequency seismic signals. Our results suggest that fluctuating basal forces are strongly controlled by particle size and flow depth, and open new perspectives for the understanding of bulk flow characteristics, such as flow depth and weight, and of the high frequency seismic signals generated by debris flows.

Study on the Impact of Hydraulic Fracturing on Surrounding Ancillary Buildings considering SSI

Hydraulic fracturing is a key technology in the development of unconventional oil and gas reservoirs. With the continuous industrialization and large-scale development of shale gas production in China, the workload of hydraulic fracturing is also increasing rapidly, and the induced seismic events are also increasing gradually, resulting in different degrees of damage to the surrounding ancillary buildings. In order to study the impact of hydraulic fracturing on ancillary buildings, the finite element software ABAQUS was used to establish a three-dimensional model of middle and high-rise isolated structures to simulate the earthquake triggered by hydraulic fracturing. Then, considering the SSI (soil-structure interaction) effect of soil-based structure, the nonlinear dynamic response of the structure under the action of ground motion was analyzed. Through the adoption of different types of soil and the foundation depth, the influence of various parameters is discussed. The study found that in the case of not considering SSI, basal shear force, and displacement between floors of the seismic-isolation structure significantly greater than considering SSI, using hard soil layer, base shear displacement is greater than the soft soil layer and interlayer, shows that due to the effect of hydraulic fracturing, making fluid diffusion in soil, the seismic energy dissipation effect. It is also found that the period, base shear, peak displacement, and interlayer displacement of deep foundation pit are increased compared with shallow foundation pit considering SSI effect.

Laboratory Landquakes: Insights From Experiments Into the High‐Frequency Seismic Signal Generated by Geophysical Granular Flows

AbstractGeophysical granular flows exert basal forces that generate seismic signals, which can be used to better monitor and model these severe natural hazards. A number of empirical relations and existing models link these signals' high‐frequency components to a variety of flow properties, many of which are inaccessible by other analyses. However, the range of validity of the empirical relations remains unclear and the models lack validation, owing to the difficulty of adequately controlling and instrumenting field‐scale flows. Here, we present laboratory experiments investigating the normal forces exerted on a basal plate by dense and partially dense flows of spherical glass particles. We measured the power spectra of these forces and inferred predictions for these power spectra from the models for debris flows' seismic signals proposed by Kean et al. (2015, https://doi.org/10.1002/2015GL064811), Lai et al. (2018, https://doi.org/10.1029/2018GL077683), and Farin, Tsai, et al. (2019, https://doi.org/10.1002/esp.4677), using Hertz theory to extend Farin, Tsai, et al. (2019)'s models to higher frequencies. Comparison of our observations to these predictions, and to predictions derived from Bachelet (2018) and Bachelet et al. (2021)'s model for granular flows' seismic signals, shows those of Farin, Tsai, et al. (2019)'s “thin‐flow” model to be the most accurate, so we examine explanations for this accuracy and discuss its implications for geophysical flows' seismic signals. We also consider the normalization, by the mean force exerted by each flow, of the force's mean squared fluctuations, showing that this ratio varies by 4 orders of magnitude over our experiments, but is determined by the bulk inertial number of the flow.

Experimental assessment of the effective friction at the base of granular chute flows on a smooth incline.

We report on direct measurements of the basal force components for granular material flowing down a smooth incline. We investigate granular flows for a large range of inclination angles from θ=13.4^{∘} to 83.6° and various gate openings of the chute. We find that the effective basal friction coefficient μ_{B}, obtained from the ratio of the longitudinal force to the normal one, exhibits a systematic increase with increasing slope angle and a significant weakening with increasing particle holdup H (the depth-integrated particle volume fraction). At low angles, the basal friction is slightly less than or equal to tanθ.The deviation from tanθcan be interpreted as a contribution from the sidewall to the overall friction. At larger angles, the basal friction μ_{B} saturates at an asymptotic value that is dependent on the gate opening of the chute. Importantly, our data confirm the outcomes of recent discrete numerical simulations. First, for steady and fully developed flows as well as for moderately accelerated ones, the variation of the basal friction can be captured through a unique dimensionless number, the Froude number Fr, defined as Fr=U[over ¯]/(gHcosθ)^{1/2}, where U[over ¯] is the mean flow velocity. Second, the mean velocity scales with the particle holdup H with a power exponent close to 1/4, contrasting with the Bagnold scaling (U[over ¯]∼H^{3/2}).

No impact of sex and age on beta-adrenoceptor-mediated inotropy in human right atrial trabeculae.

There is an increasing awareness of the impact of age and sex on cardiovascular diseases (CVDs). Differences in physiology are suspected. Beta-adrenoceptors (beta-ARs) are an important drug target in CVD and potential differences might have significant impact on the treatment of many patients. To investigate whether age and sex affects beta-AR function, we analysed a large data set on beta-AR-induced inotropy in human atrial trabeculae. We performed multivariable analysis of individual atrial contractility data from trabeculae obtained during heart surgery of patients in sinus rhythm (535 trabeculae from 165 patients). Noradrenaline or adrenaline were used in the presence of the beta2 -selective antagonist (ICI 118551, 50nmol/L) or the beta1 -selective antagonist (CGP 20712A, 300nmol/L) to stimulate beta1 -AR or beta2 -AR respectively. Agonist concentration required to achieve half-maximum inotropic effects (EC50 ) was taken as a measure of beta-AR sensitivity. Impact of clinical variables was modelled using multivariable mixed model regression. As previously reported, chronic treatment with beta-blockers sensitized beta-AR. However, there was no significant interaction between basal force, maximum force and beta-AR sensitivity when age and sex were modelled continuously. In addition, there was no statistically significant effect of body mass index or diabetes on atrial contractility. Our large, multivariable analysis shows that neither age nor sex affects beta-AR-mediated inotropy or catecholamine sensitivity in human atrial trabeculae. These findings may have important clinical implications because beta-ARs, as a common drug target in CVD and heart failure, do not behave differently in women and men across age decades.

Measuring Basal Force Fluctuations of Debris Flows Using Seismic Recordings and Empirical Green's Functions

AbstractWe present a novel method for measuring the fluctuating basal normal and shear stresses of debris flows by using along‐channel seismic recordings. Our method couples a simple parameterization of a debris flow as a seismic source with direct measurements of seismic path effects using empirical Green's functions generated with a force hammer. We test this method using two large‐scale (8 and 10 m3) experimental flows at the U.S. Geological Survey debris‐flow flume that were recorded by dozens of three‐component seismic sensors. The seismically derived basal stress fluctuations compare well in amplitude and timing to independent force plate measurements within the valid frequency range (15–50 Hz). We show that although the high‐frequency seismic signals provide band‐limited forcing information, there are systematic relations between the fluctuating stresses and independently measured flow properties, especially mean basal shear stress and flow thickness. However, none of the relationships are simple, and since the flow properties also correlate with one another, we cannot isolate a single factor that relates in a simple way to the fluctuating forces. Nevertheless, our observations, most notably the gradually declining ratio of fluctuating to mean basal stresses during flow passage and the distinctive behavior of the coarse, unsaturated flow front, imply that flow style may be a primary control on the conversion of translational to vibrational kinetic energy. This conversion ultimately controls the radiation of high‐frequency seismic waves. Thus, flow style may provide the key to revealing the nature of the relationship between fluctuating forces and other flow properties.

P5992Why aortic valve disease may persist after surgery? A joint basic science - Clinical effort

Abstract Background Diseases of the aortic valve are a common reason for heart surgery. Aortic stenosis (AS) is associated with pressure and aortic regurgitation (AR) with a volume overload of the left ventricle (LV). Over time both pathologies lead to systolic and diastolic heart failure, while progressive downregulation of β-adrenoceptors occurs. While LV re-remodeling occurs in the majority of patients after aortic valve surgery, LV dysfunction persists in one fourth of such patients and leads to a terminal heart failure. We aimed to investigate whether differential remodeling in the protein kinase A (PKA) dependent inotropic response in myocytes and myocardial tissue obtained from patients undergoing aortic valve surgery is associated with the LV re-remodeling after surgery. Methods Preoperatively, pro BNP levels were measured and left ventricular strain analysis via echocardiography was performed. Interventricular septal biopsy was obtained intraoperatively in 10 patients who underwent aortic valve surgery. In-vitro contractility was analyzed in myocardial tissue paced with 4 Hz at 37 °C. Freshly isolated cells were transduced with an adenovirus expressing a cytosolic Förster resonance energy transfer (FRET) based cAMP biosensor (Epac1-camps). After 48 hours of culture, Föster-resonance energy transfer (FRET) was used for the first time to measure cAMP in 60 isolated human ventricular myocytes. Isoprenaline (10 nM – 10 μM) was used for β-adrenoceptor activation and forskolin (10 μmol) to activate adenylyl cyclase directly. Results We found a significantly downregulated β-adrenergic sensitivity in cardiomyocytes of patients with aortic valve disease, although contractile response to forskolin was maintained. Furthermore, we found a clear association between reduced sensitivity to isoprenaline (i.e., high EC50 values) and low maximum effect size to isoprenaline in myocardial tissue of patients with aortic valve disease, pointing out relevant β-adrenoceptor dysfunction. There were no significant differences in basal myocardial force between tissue samples of patients with AR and AS. Conclusion Collectively, our data show a profound remodelling in the cAMP/PKA pathway in patients with aortic valve disease. These disturbances may have an impact on the postoperative ventricular function and possibly on the long-term LV re-remodelling after aortic valve surgery.

Which phosphodiesterase can decrease cardiac effects of 5-HT4 receptor activation in transgenic mice?

Serotonin (5-hydroxy-tryptamine, 5-HT) exerted concentration-dependent positive inotropic effects or positive chronotropic effects in transgenic (TG) mice which overexpress the human 5-HT4a receptor in the heart but not in littermate wild-type (WT) mice. These positive inotropic effects and positive chronotropic effects are thought to be mediated by cyclic adenosine 3',5'-monophosphate (cAMP) in TG cardiomyocytes. To determine whether these effects are antagonized by endogenous phosphodiesterases (PDEs), the inotropic and chronotropic effects of 5-HT were tested in the additional presence of the PDE inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA) (1μM, a PDE2 inhibitor) or cilostamide (1μM, a PDE3 inhibitor), rolipram (0.1μM and 1μM, a PDE4 inhibitor), and their combinations. For comparison, 3-isobutyl-1-methylxanthine (IBMX), an unspecific PDE inhibitor, was investigated. The use of 10μM IBMX, the combination of rolipram (1μM) and EHNA (1μM), and the combination of rolipram (0.1μM) and cilostamide (1μM) each increased the potency of 5-HT to elevate the force of contraction in TG mice, but not the potency of 5-HT to increase the beating rate in TG mice. This indicates that PDE4 and PDE2 regulate the inotropic but not the chronotropic effects of 5-HT in TG mice. In contrast, cilostamide (1μM) alone, EHNA (1μM) alone, or in combination decreased the potency of 5-HT to increase force of contraction in TG mice. In summary, our present data suggest that the positive chronotropic effect of 5-HT in TG mice does not involve PDE activities, whereas the positive inotropic effect of 5-HT and the basal force in TG mice are diminished by endogenous activity of PDE4. Phosphorylation of PDE4, when PDE2 or PDE3 is inhibited, might enhance the activity of PDE4.

The Preliminary Study About the Involvement of Relaxine in Adverse Effect of Polychlorinated Biphenyls on Bovine Myometrial Contractions

Polychlorinated biphenyls (PCBs) are a group of synthetic xenobiotics, which were used in lots of industrial applications. Two individual congers (PCB 153 and PCB 77) belong to the most prominent environmental contaminations among PCBs, but they have opposite type of configuration and therefore they can exert a different way of action. Since PCBs increased the force of myometrial contractions, in this work, their effect on myometrial sensitivity on inhibitor of myometrial contractions (relaxine, RLX) was studied. Bovine myometrial cells and strips, and luteal cell at 4-8 month of pregnancy, were obtained accidentally in commercial abattoir. They were treated by PCB 153 and PCB 77 and mRNA expression of RLX receptor in myometrial cells and contractions of myometrial strips as well as the secretion of progesterone (P4) and oxytocin (OT) from luteal cells, were measured under their effect. Both studied congeners decreased (P<0.05) the mRNA expression of RLX receptor in myometrium. Admittedly, both PCB 77 and 153 increased (P<0.05) the basal force of contractions, while RLX showed any effect on myometrial contractions. Studied PCBs increased also (P<0.05) secretion of P4 and OT from luteal cells. It is suggested that PCBs can decreased the sensitivity of myometrium on RLX but their direct effect on RLX function have to be further investigated.

Equivalent static wind loads analysis of tall television towers considering terrain factors of hilltops based on force measurement experiment

Wind field in mountainous regions demonstrates unique distribution characteristic as compared with the wind field of the flat area, wind load and wind effect are the key considerations in structural design of television towers situated in mountainous regions. The television tower to be constructed is located at the top of Xiushan Mountain in Nanjing, China. In order to investigate the impact of terrain factors of hilltops on wind loads, firstly a wind tunnel test was performed for the mountainous area within 800m from the television tower. Then the tower basal forces such as bending moments and shear strength were obtained based on high frequency force balance (HFFB) test. Based on the experiments, the improved method for determining the load combinations was applied to extract the response distribution patterns of foundation internal force and peak acceleration of the tower top, then the equivalent static wind loads were computed under different wind angles, load conditions and equivalent goals. The impact of terrain factors, damping ratio and equivalent goals on the wind load distribution of a television tower was discussed. Finally the equivalent static wind loads of the television tower under the 5 most adverse wind angles and 5 most adverse load conditions were computed. The experimental method, computations and research findings provide important references for the anti-wind design of high-rise structure built on hilltops.

New arylsparteine derivatives as positive inotropic drugs

Positive inotropic agents are fundamental in the treatment of heart failure; however, their arrhythmogenic liability and the increased myocardial oxygen demand strongly limit their therapeutic utility. Pursuing our study on cardiovascular activities of lupin alkaloid derivatives, several 2-(4-substituted-phenyl)-2-dehydrosparteines and 2-(4-substituted-phenyl)sparteines were prepared and tested for inotropic and chronotropic activities on isolated guinea pig atria. Four compounds (6b, 6e, 7b, and 7f) exhibited significant inotropism that, at the higher concentrations, was followed by negative inotropism or toxicity. Compound 7e (2-(4-tolyl)sparteine) exhibited a steep dose-depending inotropic activity up to the highest concentration tested (300 µM) with an Emax of 116.5 ± 3.4% of basal force, proving less potent but much more active in comparison to the highest concentrations tested of digoxin and milrinone having Emax of 87.5 ± 3.1% and 52.2 ± 1.1%, respectively. Finally, docking studies suggested that the relevant sparteine derivatives could target the sigma-1 receptor, whose involvement in cardiac activity is well documented.

Salt geometry influence on present-day stress orientations in the Nile Delta: Insights from numerical modeling

The offshore Nile Delta displays sharply contrasting orientations of the maximum horizontal stress, SH, in regions above Messinian evaporites (suprasalt) and regions below Messinian evaporites (subsalt). Published stress orientation data predominantly show margin-normal suprasalt SH orientations but a margin-parallel subsalt SH orientation. While these data sets provide the first major evidence that evaporite sequences can act as mechanical detachment horizons, the cause for the stress orientation contrast remains unclear. In this study, 3D finite element analysis is used to investigate the causes for stress re-orientation based on two different hypotheses. The modeling study evaluates the influence of different likely salt geometries and whether stress reorientations are the result of basal drag forces induced by gravitational gliding or whether they represent localized variations due to mechanical property contrasts. The modeling results show that when salt is present as a continuous layer, gravitational gliding occurs and basal drag forces induced in the suprasalt layers result in the margin-normal principal stress becoming the maximum horizontal stress. With the margin-normal stress increase being confined to the suprasalt layers, the salt acts as a mechanical detachment horizon, resulting in different SH orientations in the suprasalt compared to the subsalt layers. When salt is present as isolated bodies localized stress variations occur due to the mechanical property contrasts imposed by the salt, also resulting in different SH orientations in the suprasalt compared to the subsalt layers. The modeling results provide additional quantitative evidence to confirm the role of evaporite sequences as mechanical detachment horizons.

Cholesterol-induced lipophobic interaction between transmembrane helices using ensemble and single-molecule fluorescence resonance energy transfer.

The solvent environment regulates the conformational dynamics and functions of solvated proteins. In cell membranes, cholesterol, a major eukaryotic lipid, can markedly modulate protein dynamics. To investigate the nonspecific effects of cholesterol on the dynamics and stability of helical membrane proteins, we monitored association-dissociation dynamics on the antiparallel dimer formation of two simple transmembrane helices (AALALAA)3 with single-molecule fluorescence resonance energy transfer (FRET) using Cy3B- and Cy5-labeled helices in lipid vesicles (time resolution of 17 ms). The incorporation of 30 mol % cholesterol into phosphatidylcholine bilayers significantly stabilized the helix dimer with average lifetimes of 450-170 ms in 20-35 °C. Ensemble FRET measurements performed at 15-55 °C confirmed the cholesterol-induced stabilization of the dimer (at 25 °C, ΔΔG(a) = -9 kJ mol(-1) and ΔΔHa = -60 kJ mol(-1)), most of which originated from "lipophobic" interactions by reducing helix-lipid contacts and the lateral pressure in the hydrocarbon core region. The temperature dependence of the dissociation process (activation energy of 48 kJ) was explained by the Kramers-type frictional barrier in membranes without assuming an enthalpically unfavorable transition state. In addition to these observations, cholesterol-induced tilting of the helices, a positive ΔC(p(a)), and slower dimer formation compared with the random collision rate were consistent with a hypothetical model in which cholesterol stabilizes the helix dimer into an hourglass shape to relieve the lateral pressure. Thus, the liposomal single-molecule approach highlighted the significance of the cholesterol-induced basal force for interhelical interactions, which will aid discussions of complex protein-membrane systems.

Mapping the dynamics of force transduction at cell-cell junctions of epithelial clusters.

Force transduction at cell–cell adhesions regulates tissue development, maintenance and adaptation. We developed computational and experimental approaches to quantify, with both sub-cellular and multi-cellular resolution, the dynamics of force transmission in cell clusters. Applying this technology to spontaneously-forming adherent epithelial cell clusters, we found that basal force fluctuations were coupled to E-cadherin localization at the level of individual cell–cell junctions. At the multi-cellular scale, cell–cell force exchange depended on the cell position within a cluster, and was adaptive to reconfigurations due to cell divisions or positional rearrangements. Importantly, force transmission through a cell required coordinated modulation of cell-matrix adhesion and actomyosin contractility in the cell and its neighbors. These data provide insights into mechanisms that could control mechanical stress homeostasis in dynamic epithelial tissues, and highlight our methods as a resource for the study of mechanotransduction in cell–cell adhesions [corrected].