The mechanical properties of a cell determine many aspects of its behavior, and these mechanics are largely determined by the cytoskeleton. Although the contribution of actin filaments and ...microtubules to the mechanics of cells has been investigated in great detail, relatively little is known about the contribution of the third major cytoskeletal component, intermediate filaments (IFs). To determine the role of vimentin IF (VIF) in modulating intracellular and cortical mechanics, we carried out studies using mouse embryonic fibroblasts (mEFs) derived from wild-type or vimentin−/− mice. The VIFs contribute little to cortical stiffness but are critical for regulating intracellular mechanics. Active microrheology measurements using optical tweezers in living cells reveal that the presence of VIFs doubles the value of the cytoplasmic shear modulus to ∼10 Pa. The higher levels of cytoplasmic stiffness appear to stabilize organelles in the cell, as measured by tracking endogenous vesicle movement. These studies show that VIFs both increase the mechanical integrity of cells and localize intracellular components.
Cells alter their mechanical properties in response to their local microenvironment; this plays a role in determining cell function and can even influence stem cell fate. Here, we identify a robust ...and unified relationship between cell stiffness and cell volume. As a cell spreads on a substrate, its volume decreases, while its stiffness concomitantly increases. We find that both cortical and cytoplasmic cell stiffness scale with volume for numerous perturbations, including varying substrate stiffness, cell spread area, and external osmotic pressure. The reduction of cell volume is a result of water efflux, which leads to a corresponding increase in intracellular molecular crowding. Furthermore, we find that changes in cell volume, and hence stiffness, alter stem-cell differentiation, regardless of the method by which these are induced. These observations reveal a surprising, previously unidentified relationship between cell stiffness and cell volume that strongly influences cell biology.
Molecular motors in cells typically produce highly directed motion; however, the aggregate, incoherent effect of all active processes also creates randomly fluctuating forces, which drive ...diffusive-like, nonthermal motion. Here, we introduce force-spectrum-microscopy (FSM) to directly quantify random forces within the cytoplasm of cells and thereby probe stochastic motor activity. This technique combines measurements of the random motion of probe particles with independent micromechanical measurements of the cytoplasm to quantify the spectrum of force fluctuations. Using FSM, we show that force fluctuations substantially enhance intracellular movement of small and large components. The fluctuations are three times larger in malignant cells than in their benign counterparts. We further demonstrate that vimentin acts globally to anchor organelles against randomly fluctuating forces in the cytoplasm, with no effect on their magnitude. Thus, FSM has broad applications for understanding the cytoplasm and its intracellular processes in relation to cell physiology in healthy and diseased states.
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•Random intracellular motion is driven by active force fluctuations in the cytoplasm•The aggregate random forces enhance motion of small proteins and large organelles•We develop force spectrum microscopy to probe aggregate random cytoplasmic forces•The aggregate random forces are larger in malignant cancer cells than benign cells
A new technique called force spectrum microscopy allows probing random active force fluctuations in the cytoplasm of living cells. These forces drive a diffusive-like mechanism of transport of organelles and proteins in the cytoplasm and are more active in cancer than in normal cells.
Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites ...located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30‐day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30‐day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release.
Earthquake-induced landslides constitute a critical component of seismic hazard in mountainous regions. While many seismic slope stability analysis methods exist with varying degrees of complexity, ...details of interactions between seismic waves and incipient landslides are not well understood and rarely incorporated, in particular for deep-seated slope instabilities. We present a series of 2D distinct-element numerical models aimed at clarifying interactions between earthquakes and large rock slope instabilities. The study has two main goals: 1) to explore the role of amplification in enhancing co-seismic slope deformation — a relationship widely discussed in literature but rarely tested quantitatively; and 2) to compare our numerical results with the well-established Newmark-method, which is commonly used in seismic slope stability analysis. We focus on three amplification phenomena: 1) geometric (topographic) amplification, 2) amplification related to material contrasts, and 3) amplification related to compliant fractures. Slope height, topography, seismic velocity contrasts, and internal strength and damage history were varied systematically in a series of models with a relatively simple, scalable geometry. For each model, we compute the spatial amplification patterns and displacement induced by real earthquake ground motions. We find that material contrasts and internal fracturing create both the largest amplification factors and induced displacements, while the effect of geometry is comparably small. Newmark-type sliding block methods underestimate displacements by not accounting for material contrasts and internal fracturing within the landslide body — both common phenomena in deep-seated slope instabilities. Although larger amplification factors tend to be associated with greater displacements, we did not identify a clear link between ground motion frequency content, spectral amplification, and induced displacement. Nevertheless, observation of amplification patterns can play an important role in seismic slope stability analyses, as: 1) strong amplification (related to material contrasts or compliant fractures) is an indicator of potentially large co-seismic displacements; and 2) amplification patterns can be used to constrain geological and numerical models used for seismic stability analysis. The complexity of wave–slope interactions, as well as the potential to severely underestimate hazard using Newmark-type methods, motivates use of rigorous numerical modeling for quantitative seismic hazard and risk assessment of large landslides.
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•Method to investigate seismic wave amplification+co-seismic displacement of landslides is presented.•Material contrasts and internal fracturing lead to strongest amplification and displacements.•Newmark's analysis underestimates displacements for large deep seated landslides.•Strong amplification indicative of high internal rock mass damage and history of slope deformation.
Hypertrophic (HCM) and dilated (DCM) cardiomyopathies are inherited diseases with a high incidence of death due to electric abnormalities or outflow tract obstruction. In many of the families ...afflicted with either disease, causative mutations have been identified in various sarcomeric proteins. In this review, we focus on mutations in the cardiac muscle molecular motor, myosin, and its associated light chains. Despite the >300 identified mutations, there is still no clear understanding of how these mutations within the same myosin molecule can lead to the dramatically different clinical phenotypes associated with HCM and DCM. Localizing mutations within myosin's molecular structure provides insight into the potential consequence of these perturbations to key functional domains of the motor. Review of biochemical and biophysical data that characterize the functional capacities of these mutant myosins suggests that mutant myosins with enhanced contractility lead to HCM, whereas those displaying reduced contractility lead to DCM. With gain and loss of function potentially being the primary consequence of a specific mutation, how these functional changes trigger the hypertrophic response and lead to the distinct HCM and DCM phenotypes will be the future investigative challenge.
The dynamic properties of freestanding rock landforms are a function of fundamental material and mechanical parameters, facilitating noninvasive vibration‐based structural assessment. ...Characterization of resonant frequencies, mode shapes, and damping ratios, however, can be challenging at culturally sensitive geologic features, such as rock arches, where physical access is limited. Using sparse ambient vibration measurements, we describe three resonant modes between 1 and 40 Hz for 17 natural arches in Utah spanning a range of lengths from 3–88 m. Modal polarization data are evaluated to combine field observations with 3‐D numerical models. We find outcrop‐scale elastic moduli vary from 0.8 to 8.0 GPa, correlated with diagenetic processes and identify low damping at all sites. Correlation of dense‐array measurements from one arch validates predictions of simple bending modes and fixed boundary conditions. Our results establish use of sparse ambient resonance measurements for structural assessment and monitoring of arches and similar freestanding geologic features worldwide.
Plain Language Summary
Natural rock arches vibrate under ambient conditions with a unique set of frequencies controlled by geometry, host material, and interactions with nearby bedrock. Recent rockfall events at well‐known arches in Utah have highlighted the need to develop noninvasive assessment methods to better understand how these sensitive landforms evolve. To reduce site impacts, we employed limited instrumentation to measure ambient vibrations of 17 arches across Utah for identification of resonant frequencies. We combine direct observations with predictive numerical models to visualize resonant mode shapes and describe the controlling material properties and structural boundaries. In defining the first three modes of each site, we are able to characterize dynamic properties at arches encompassing several geologic formations and a range of length scales. These results establish a versatile method for structural evaluations of arches and other significant freestanding geologic features.
Key Points
Single‐station ambient vibration data and numerical modeling describe the dynamic response of natural arches with limited site access
Dense seismic array directly resolves resonant mode shapes, validating predictions of simple bending modes and fixed boundary conditions
Sandstone arches in Utah resonate between 1 and 40 Hz, exhibit low damping, and have stiffness that vary with diagenetic conditions
Seismic data analysis is a powerful tool for remote characterization of rock slope failures. Here we develop quantitative estimates of fundamental rockslide properties (e.g., volume) based solely on ...data from an existing regional seismic network. We assembled a data set of twenty known rockslides in the central Alps (with volumes between 1,000 and 2,000,000 m3) and analyzed their corresponding seismograms. Common signal characteristics include emergent onsets, slowly decaying tails, and a triangular spectrogram shape. The main component of seismic energy is contained in frequencies below ∼3–4 Hz, while higher‐frequency signals may be caused by block impacts. Location estimates were generated using automatic arrival time picks and resulted in a mean location error of 10.9 km. A linear relationship for the detection limit of a rockslide as a function of volume was identified for our seismic station network. To estimate rockslide volume, runout distance, drop height, potential energy, and Fahrböschung (angle of reach), we extracted five simple metrics from each seismogram: signal duration, peak value of the ground velocity envelope, velocity envelope area, risetime, and average ground velocity. Using multivariate linear regression, the combination of duration, peak envelope velocity, and envelope area best estimated event parameters, with r2 values ranging between 0.8 and 0.88. Three new rockslides were then used to validate our method, and volume, runout, drop height, and potential energy were estimated within the correct order of magnitude. When provided with a suitable data set of rockslide events, our method can be easily adapted to other regions and seismic networks.
Key Points
Rockslide seismic signals have a common characteristic signature
Seismic metrics can be used to estimate rockslide parameters
Parameter estimation works for unknown rockslide events in the same region
PurposeFixing problems in an organization often involves developing managers in order to increase leader effectiveness. This paper aims to discuss the aforementioned ...issue.Design/methodology/approachData collection includes multiple surveys and small group interviews. Analysis uses rigorous coding methods to construct a model of critical organizational values and behaviors essential for leadership effectiveness. The authors bring “theory to practice” by applying complexity leadership concepts in the authors’ intervention strategy.FindingsFindings are categorized into three parts: identifying critical culture value gaps, applying complexity concepts to a scenario-based training intervention, and identifying intervention outcomes. Outcomes include transformed work environment led by leaders who respect others, share decision-making and enable employees to be interdependent.Research limitations/implicationsThis explanatory case study contributes to research by applying complexity leadership theory to create a practical consulting intervention.Practical implicationsThis work provides a template and process for managers using complexity leadership to inform their client interventions.Originality/valueThis case study identifies value shortfalls in a manufacturing plant, documents a scenario-based training intervention which develops managers to build organizational trust. Results include reducing turnover, improving job satisfaction and increasing production.
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