Historical Forces Research Articles

Numerical modeling and experimental validation of low velocity impact of woven GFRP/CFRP composites

Low-velocity impact of 2D woven glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composite laminates was studied experimentally and numerically. Hybrid laminates containing blocked layers of GFRP/CFRP/GFRP with all plies oriented at 0° were investigated. Relatively high impact energies were used to obtain full perforation of the laminate in a low-velocity impact setup. Numerical simulations were carried out using the in-house transient dynamics finite element code, Sierra/SM, developed at Sandia National Laboratories. A three-dimensional continuum damage model was used to describe the response of a woven composite ply. Two methods for handling delamination were considered and compared: (1) cohesive zone modeling and (2) continuum damage mechanics. The reduced model size achieved by omission of the cohesive zone elements produced acceptable results at reduced computational cost. The comparison between different modeling techniques can be used to inform modeling decisions relevant to low velocity impact scenarios. The modeling was validated by comparing with the experimental results and showed good agreement in terms of predicted damage mechanisms and impactor velocity and force histories.

THE TRAGEDY OF A.S. PUSHKIN “BORIS GODUNOV” AND RUSSIAN LITERATURE OF THE SECOND HALF OF THE XIX CEN

For a long time it was believed that Pushkin in the tragedy “Boris Godunov” made the people the main hero and creative force of history. In reality, there is another hero in it, invisible, who is the supreme arbiter, directs the action in the direction he needs and does it unexpectedly, unpredictably, realizing himself through the unconscious actions and actions of people. The actions of the heroes taking part in this movement do not achieve the results they expected. Pushkin returns to tragedy the truth of the Divine ideal, the Divine will standing above man and humanity, lost during the Renaissance. In Pushkin’s dialogue between a person and the world, a third Person appears, this dialogue invisibly corrects and guides. Thus, Pushkin’s realism began to acquire a sober religious fundamental principle, at the core of which the future Tolstoy, the future Dostoevsky, the future Ostrovsky already lay. The “formula” of this realism did not fit into the “formula” of Western European realism, which placed emphasis on a free, self-sufficient, sovereign person.

Poleward Migration of the Latitude of Maximum Tropical Cyclone Intensity—Forced or Natural?

Abstract Past studies have shown a significant observed poleward trend in the latitude at which tropical cyclones reach their lifetime maximum intensity (LMI), especially in the northwest Pacific basin. Given the brevity of the historical record, it remains difficult to separate the forced trend from internal variability of the climate system. A recently developed tropical cyclone downscaling model is used to downscale the Community Earth System Model, version 2 (CESM2), preindustrial control simulation. It is found that the observed trend in the latitude at which tropical cyclones reach their LMI in the northwest Pacific is very unlikely to be caused by internal variability. The same downscaling model is then used to downscale CESM2 simulations under historical forcing. The resulting trend distribution shows a significant poleward migration of tropical cyclone LMI even after regressing out both natural variability and the part of the forced warming pattern that projects onto natural variability. The results indicate that the observed poleward migration of the latitude at which tropical cyclones reach their LMI in the northwest Pacific basin is likely to be, at least in part, forced. However, the magnitude of the projected poleward trend in climate models can be significantly modulated by the simulated spatial pattern of ocean warming. This highlights how discrepancies between models and observations, with regard to projected changes to the equatorial zonal sea surface temperature gradient under anthropogenic forcing, can lead to large uncertainties in projected changes to the LMI latitude of tropical cyclones. Significance Statement Observations in the northwest Pacific basin show that the latitude at which tropical cyclones are at their most intense has been trending northward in the recent half century. These changes are important since tropical cyclones could bring hazardous weather to coastal areas that are poorly equipped to handle them. Here, we show that natural variations in Earth’s climate are very unlikely to explain the observed poleward trend in the latitude that tropical cyclone reach their maximum intensity. We find that it is much more likely that the observed trend is forced by human-related emissions, though the spatial pattern of warming in response to greenhouse emissions can have significant impacts on the magnitude of the trend.

Addressing Social and Structural Determinants of Health in the Delivery of Reproductive Health Care: ACOG Committee Statement No. 11.

Social and structural determinants of health include historical, social, political, and economic forces, many of which are rooted in racism and inequality, that shape the relationship between environmental conditions and individual health. Unmet social needs can increase the risk of many conditions treated by obstetrician-gynecologists (ob-gyns), including, but not limited to, preterm birth, unintended pregnancy, infertility, cervical cancer, breast cancer, and maternal mortality. An individual health care professional's biases (whether overt or unconscious) affect delivery of care and may exacerbate and reinforce health disparities through inequitable treatment. Obstetrician-gynecologists and other health care professionals should seek to understand patients' health care decision making not simply as patients' individual-level behavior, but rather as the result of intersecting sociopolitical conditions, structural inequities, and social needs that create and maintain inequalities in health and health care. Recognizing the importance of social and structural determinants of health can help ob-gyns and other health care professionals to better understand patients, effectively communicate about health-related conditions and behavior, and contribute to improved health outcomes, including patients' experience of care and their trust in the health care system.

Evaluation of a substitute bird for engine fan blade impact tests considering the bird-slicing state

Bird ingestion is one of the major threats to aero engines. To evaluate airworthiness compliance in bird ingestion events, dynamic structural tests are the most straightforward and intuitive method. These tests can be conducted using either real birds or substitute birds, the latter offering enhanced repeatability and more convenient test management. In this study, an equivalent strategy is proposed aimed at developing a suitable substitute bird for impact tests on engine fan blades by evaluating the dynamic bird-slicing responses. Two gelatine recipes are adopted to manufacture the substitute birds and the impact responses are measured with a wedge-Hopkinson bar (WHB) system. It is found that the inertial force is the dominant factor in the impact load, and the gelatin resistance also has a certain influence. Generally, the impact responses of the gelatine birds show a constant distribution of the normalized peak impact force with good dispersion as velocity increases. The momentum transfer (MT) exhibits both a “velocity effect” and a “mass effect”, duplicating the responses observed in real bird tests. Besides, the temporal distribution of the force history for the gelatine birds closely matches that of the real birds. The results indicate that the equivalent strategy effectively evaluates the substitution, and the proposed gelatin recipe can be used for real bird alternatives in engine fan blade tests.

Differing Eco-Phenomenological Discourses in Amitav Ghosh's Ecological Realism and Timothy Morton's Dark Ecology

This paper explores the contrasting yet complementary eco-phenomenological discourses in Amitav Ghosh’s ecological realism and Timothy Morton’s dark ecology. Both thinkers offer crucial insights into the Anthropocene, but they do so from different perspectives. Ghosh, through his historical materialist framework, focuses on the socio-political, historical, and colonial forces driving the current ecological crises. His ecological realism reflects the entanglement of human and non-human histories and advocates for a literary realism that incorporates the agency of nature. Morton, on the other hand, embraces post-humanist philosophies, specifically object-oriented ontology, to develop his concept of "dark ecology"—a framework that highlights the inherent strangeness, ambiguity, and uncanniness of the natural world. Morton introduces the notion of hyperobjects, entities like climate change that are too vast and complex to be fully comprehended by humans. This paper argues that despite their differences, both Ghosh and Morton challenge anthropocentric thinking and offer radical reconfigurations of humanity's relationship with the natural world. By placing their theories in dialogue, this paper underscores the importance of embracing both historical materialist and ontological perspectives to address the ecological challenges of the Anthropocene.

Competing effects of wind and buoyancy forcing on ocean oxygen trends in recent decades

Ocean deoxygenation is becoming a major stressor for marine ecosystems due to anthropogenic climate change. Two major pathways through which climate change affects ocean oxygen are changes in wind fields and changes in air-sea heat and freshwater fluxes. Here, we use a global ocean biogeochemistry model run under historical atmospheric forcing to show that wind stress is the dominant driver of year-to-year oxygen variability in most ocean regions. Only in areas of water mass formation do air-sea heat and freshwater fluxes dominate year-to-year oxygen dynamics. The deoxygenation since the late 1960s has been driven mainly by changes in air-sea heat and freshwater fluxes. Part of this deoxygenation has been mitigated by wind-driven increases in ventilation and interior oxygen supply, mainly in the Southern Ocean. The predicted slowdown in wind stress intensification, combined with continued ocean warming, may therefore greatly accelerate ocean deoxygenation in the coming decades. The fact that the model used here, along with many state-of-the-art forced ocean models, underestimates recent ocean deoxygenation indicates the need to use forcing fields that better represent pre-industrial conditions during their spin-up.

Chartism’s Critical Carbon Theology: What Fossil Power’s Nineteenth-Century Demonizers Contribute to the Ethics of Energy Justice Today

Recent scholarship on religion and energy highlights the religious attachments some groups of people form with fossil fuels that have served to facilitate their extraction and use in building socially and economically stratified worlds. This scholarship foregrounds the business owners, managers, scientists, inventors, industrial spokespersons, and other panegyrists of the beneficent, civilizing power of coal and oil. However, little research to date has examined the religious attachments formed with fossil fuels by those who mined them, labored with machines powered by them, and lived in places that were diminished to extract, burn, and waste them. This article builds on the work of Andreas Malm and Terra Schwerin Rowe to examine these “critical carbon theologies”. It focuses in particular on the theological themes in popular literature produced by the nineteenth-century British Chartist movement—the first great social movement led by those who experienced in their bodies, communities, and environments the traumas that accompanied the introduction of fossil fuels as a motive power. These Chartist activist-theologians condemned coal power as a demonic force in history and envisioned a way to exorcize an industrializing society of its demons. This article uncovers and evaluates the largely overlooked theological dimensions of this movement and applies them toward a consideration of the ethics of energy transition today.

Inducing post-activation potentiation alters human motor unit behavior of the elbow extensors during unconstrained velocity contractions.

The purpose was to test whether inducing post-activation potentiation (PAP) altered motor unit (MU) activity during dynamic isotonic contractions. From 12 participants (3 females), 39 MUs were recorded from the anconeus (n=31) and lateral triceps brachii (n=8) with fine-wire electrodes during elbow extensions at 50 and 75% of peak power with, and without PAP. To induce PAP participants produced a 2s ramp conditioning contraction (CC) up to maximal isometric elbow extension with a 3s hold. Following the CC (~2s), independent electrical stimulation to the triceps and anconeus showed twitch torques were potentiated by 84 and 66%, respectively, (both p<0.001). Compared to baseline (i.e., without PAP), at both intensities (50 and 75%) PAP increased MU recruitment thresholds (40% and 80%, p<0.001) with lowered mean MU rates (-20 and -26%), and instantaneous rates at recruitment threshold (-26 and -25%) (all p<0.001). Firing rates increased 20% (p<0.001) from 50 to 75% power, but rates during potentiated contractions targeting 75% were lower than baseline at 50% (-10%, p<0.001). Dynamic contractions provide a more functional paradigm to assess MU activity with PAP and showed larger effects across a wider range of contractile intensities compared to previously described isometric tasks. Findings indicate that peripheral feedback from the potentiated muscle is likely not the primary mechanism in modifying MU behaviors as changes occurred at recruitment which is relatively insensitive to afferent feedback. Therefore, MU activity during dynamic contractions is responsive to activation history force potentiation and can make compensatory adjustments to optimize contractile output.

A global poleward shift of atmospheric rivers.

Atmospheric rivers (ARs) are key agents in distributing extratropical precipitation and transporting moisture poleward. Climate models forced by historical anthropogenic forcing suggest an increase in AR activity in the extratropics over the past four decades. However, reanalyses indicate a ~6° to 10° poleward shift of ARs during boreal winter in both hemispheres, featuring a rise along 50°N and 50°S and a decrease along 30°N and 30°S. Our analysis demonstrates that low-frequency sea surface temperature variability in the tropical eastern Pacific exhibits a cooling tendency since 2000 that plays a key role in driving this global AR shift, mostly over extratropical oceans, through a tropical-driven eddy-mean flow feedback. This mechanism also operates on interannual timescales, controlled by the El Niño-Southern Oscillation, and is less pronounced over the Southern Ocean due to weaker eddy activity during austral summer. These highlight the sensitivity of ARs to large-scale circulation changes driven by both internal variability and external forcing in current and upcoming decades.

Ocean Surface Gravity Waves Excited by the 2022 Eruption of Hunga Tonga‐Hunga Ha'apai Volcano

AbstractOn 15 January 2022, a massive underwater eruption occurred at the Hunga Tonga‐Hunga Ha'apai Volcano. The plume reached the mesosphere, and the eruption excited a significant atmospheric Lamb wave, which forced the tsunami. The complicated tsunami waveforms due to ocean‐atmosphere coupling prevented inferring the force history of the excitation. To address this, we analyze ocean surface gravity waves (OSWs) from 15 to 40 mHz, which are decoupled from the Lamb wave due to their slower phase velocities. Modeling these OSWs, we infer that the excitation started at 4:00 UTC with an amplitude of N and lasted for 5 hr, followed by a sub‐event at 8:40 UTC. The observations suggest an initial blowout of seawater above the summit and a subsequent outflow that excited a tsunami below 5 mHz. The 2 hr delayed OSW excitation from 6 to 15 mHz may indicate seawater inflow into the crater.

Resonance and surfactant effects on the interaction of a rising bubble and a sedimenting particle in an oscillating fluid

This paper considers the interaction of a rising bubble and a sedimenting fine particle in a liquid with a soluble surfactant subjected to the gravity field, forced flow, and vibrations. The frequency of vibrations is close to the resonance value. The particle motion trajectories are calculated, taking into account its inertia, fluid viscosity, Basset force, buoyancy force, and the mean force acting on the particle due to the inhomogeneity of the pulsating field. The collision efficiency is evaluated, and the cross sections of the sedimenting particles captured by the rising bubble are found. It is demonstrated that even at low vibration intensity but in the presence of a weak surfactant effect, a significant increase in the probability of particle–bubble collision and in the capture cross section can be achieved. The obtained results can be used to intensify the flotation processes by ultrasonic treatment.

The Statue and the Readymade: Thinking is Not Ready-Made

Statues and other monuments that mark the great names of colonization and empire are specifically privatized forms of colonizing memory. To reduce the collective forces of history to a single name is a form of defacement. This essay argues for a mode of history and memory beyond the face and beyond the individual. Debates surrounding the removal or preservation of statues for the sake of history and memory assume a humanized and privatized form of historical time. The destruction of statues is a positive event that opens the possibility of collective time. Rather than preserving history through terms that are readymade, this essay argues for an aesthetics of the ready-made, or the found object that appears alien and out of place.

The influence of the Avar Khanate on the ethno-political situation in South-Eastern Europe

This article provides an in-depth examination of the ethno-political impact of the Avar Khanate in Southeast Europe from the 7th to the 10th centuries. The Avars, through their military prowess and strategic settlement practices, brought about significant changes in the political and cultural landscape of the region. Their influence extended beyond warfare, as they played a crucial role in reshaping the ethnic composition and political equilibrium of Southeast Europe. The article delves into various aspects of Avar life, including their war economy, settlements, and agricultural and craft activities, highlighting how these factors influenced neighboring peoples and cultures. The Avars' interactions with the Byzantine Empire and other neighboring entities are also explored, emphasizing their role in shaping the region's long-term historical trajectory. By analyzing these multifaceted influences, the study provides valuable insights into the ethno-political legacy of the Avar Khanate, offering a nuanced understanding of their lasting impact on the region. The research underscores the importance of the Avars in the broader context of Southeast European history, contributing to a deeper comprehension of the historical forces that have shaped the region's development over the centuries. This comprehensive analysis not only enhances our knowledge of the Avar Khanate but also sheds light on the broader ethno-political processes at play during this critical period in Southeast European history.

Nonstationarity of the Atlantic Meridional Overturning Circulation's Fingerprint on Sea Surface Temperature

AbstractSea surface temperature (SST) has been increasing since industrialization with rising greenhouse gases. However, a warming hole exists in the North Atlantic where SST has cooled by 0.4 K/century during 1900–2017. It has been argued that this cooling is due to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), and subpolar North Atlantic SST has thus been utilized to estimate AMOC variability. We assess the robustness of subpolar North Atlantic SST as a proxy for AMOC strength under historical forcing, abrupt quadrupling of CO2, and a medium future emissions pathway, finding that AMOC's fingerprint on SST depends upon forcing scenarios. AMOC is important in warming hole development during significant warming periods, although SST may introduce uncertainties for AMOC reconstruction in stabilized regimes due to diverse forcing mechanisms and decadal variability. Our results caution against using SST alone as a proxy for AMOC variability—both on paleoclimatic and contemporary time scales.

Unravelling the discursive dynamics of counternarratives in the Dutch energy transition

Decarbonization of the energy system to combat climate change poses a significant challenge for the Netherlands, often attributed to carbon lock-in: a persistent dependence on fossil fuels shaped by historical forces. Carbon lock-in also occurs at the discursive level, which is why research on sustainability transitions increasingly explores discourses as a crucial element for change. Our research contributes to this knowledge by exploring how counternarratives shape the discursive dynamics surrounding the fossil fuel industry's role in the Dutch energy system. Using an interpretive approach, we examine how the role of Shell, as the ‘epitome’ of the Dutch fossil fuel industry, is framed by both Shell itself and three discursive agents opposing fossil fuel-based pathways. To this end, we reconstruct the counternarratives by Friends of the Earth NL, Follow This, Code Rood and Shell around how they envision the role of Shell in the Dutch energy system, with the goal to identify how discursive agents position their narratives vis-à-vis each other and if coalitions are formed. Our findings reveal that discursive agents deploy a variety of strategic practices to increase the successful reproduction of their narratives: first, Code Rood strategically adopts a radical narrative that stimulates imagination, polarizing the discursive struggle surrounding Shell's role in the energy system. Second, Follow This strategically adopts a marginal narrative, designed to persuade incumbents of alternative interpretations, especially to rethink the profitability of fossil fuels. Third, Friends of the Earth NL and Follow This enhance their discursive agency through coalition building. Since unlocking institutionalized discourses becomes more important, further research should shed light on discursive dynamics within the institutionalized discourse. By offering insights into the pivotal role(s) of counternarratives in instigating discursive change, this study contributes to the growing body of knowledge crucial for accelerating the shift toward a decarbonized energy system.

Shear behavior of reinforced concrete walls under variable axial tension‐compression and cyclic lateral loads

AbstractUnder a strong earthquake, the axial force of shear walls in tall buildings may vary from compression to tension, but few studies have been conducted on this. Three low‐aspect‐ratio reinforced concrete (RC) wall specimens subjected to coupled variable axial tension‐compression and lateral load were tested in this study, to investigate the effect of the fluctuating range of axial force and loading histories on the shear behavior of RC walls. The test results indicated that shear‐compression failure occurred under the compressive‐shear loading for all test wall specimens, and no obvious post‐peak strength degradation in tension‐shear loading. The hysteretic curves of test wall specimens were strongly affected by the loading histories; the shear strength and deformation capacity were mainly affected by the fluctuation of axial forces, especially for tension‐shear strength. The equation of ACI 318‐19 and JGJ 3‐2010 conservatively predicted the shear strength of RC walls under the variable axial force, while the equation of ASCE/SEI 43‐05 accurately predicted the shear strength with the mean values of the VTest/VASCE of 0.97 and 0.94 for compression‐shear and tension‐shear strength, respectively. Comparison with an RC wall under constant axial tension revealed that the failure modes of RC walls were strongly dependent on the initial cracking patterns. Finally, a finite element (FE) model was developed, and parametric analyses were carried out to further estimate the effect of variable axial force on the cyclic shear behavior of RC walls.

The Great Force of History

The Great Force of History

Impact response of fractionally damped rectangular plates made of viscoelastic composite materials

The paper aims to find dynamic response of fractionally damped rectangular viscoelastic plates under low-velocity impact of a mass. The general fractional (Rubbery, Transition and Glassy) RTG model for the plate material was considered. First, the governing equation of the plate is derived and solved. Next, using the modified Hertz contact law, the governing integral equation of the problem in terms of indentation is derived and solved. Finally, relation between indentation and impact force is discretized and using the Mittag-Leffler function, history of impact force is obtained. The work is validated by comparison of the results with some particular cases and available experimental data.

The Elusive Borders of Regional Feeling: Re-Imagining the Federalist Map in Early West Germany

While a rich body of work on nations and national borderlands has demonstrated how the ideal of the nation state resulted in ever greater (and often violent) demands for geographic fixity, this article shows how territorial visions of regional communities permitted a tremendous level of flexibility and were able to hold highly divergent geographic imaginings in suspension. The article seeks to demonstrate this by looking at a unique moment in post-war West German history when spatial planers, parliamentary committees, regionalists and an army of experts sought to determine the boundaries of regional belonging in preparation for a planned redrawing of the West German federal map. Many believed that a viable federalist democracy required stronger federal states rooted in a sense of regional community. The states created by the Allies were initially seen as temporary, and Article 29 of the new constitution required that states be redrawn by considering boundaries of regional belonging. The intense efforts of experts, politicians, and regionalists, however, ultimately failed and revealed widely diverging ideas about which territories corresponded to a common sense of regional community. Conflicting historic state borders, the historic force of physical geographies, confession, orientation to urban centres, a profusion of dialect borders, and regional cultural practices all shaped geographic visions of region, but simultaneously underpinned widely-variant cognitive maps. While the failure to redraw the West German map resulted in this episode of history largely being forgotten, I argue that it speaks volumes about how forms of community beyond and beneath the nation state have been imagined in territorial space.