Small Initial Differences Research Articles

Scaling nonhierarchically: A theory of conflict‐free organizational growth with limited hierarchical growth

AbstractResearch SummaryWe propose a theory that explains variations in the relationship between an organization's size and the extent of its authority hierarchy (as captured in managerial intensity). Conceptualizing authority hierarchy as a means to manage conflicts among subordinates, we formulate a model in which the number of managers required depends on the magnitude of conflicts generated between and within groups of workers. Our analysis shows that scaling non‐hierarchically can be accomplished either by creating low conflict “self‐managing” teams or reducing conflicts between many “self‐contained” teams, but which path is more effective varies by situation. Small initial differences in terms of their emphasis on within vs. between team conflict mitigation can lead to large differences as firms scale over time in the extent of their authority hierarchies.Managerial SummaryManaging without an extensive hierarchy can be attractive for a variety of reasons, but under what conditions is it possible in large scale organizations? We build on the premise that the managerial hierarchy of authority serves to resolve conflicts that employees cannot resolve peer‐to‐peer (i.e., there are limits to scaling groups that manage themselves consensually). We develop a formal theory that predicts that there are three levers that can slow down the growth of managerial hierarchy even as the organization scales: investing in the technology and culture needed to (a) expand managerial capacity particularly toward the apex of the hierarchy (b) create “self‐managed” teams that produce few conflicts in need of managerial resolution and (c) create “self‐contained” teams that generate few conflicts between them that need escalation up the hierarchy for resolution. The third is likely to be the most effective lever as organizations grow.

Race to the canopy: the development of tree size hierarchies following a partial disturbance in a boreal old-growth forest

In boreal old-growth forests, advance regeneration typically attains canopy dominance through growth release events following partial disturbances. We sampled competing Picea mariana (Mill.) and Abies balsamea (L.) in disturbed old-growth stands in Quebec, Canada, to understand the intra- and interspecific size hierarchy development. We reconstructed tree size development and examined the role of initial size difference, time between germination and a disturbance, and the strength of response to the disturbance in determining tree size hierarchies. Trees that regenerated first generally dominated their intraspecific competitors also following a disturbance event. However, prolonged time between germination and disturbance resulted in a less deterministic outcome. Tree size difference prior to disturbance also influenced the development of size hierarchies. In interspecific competition between individuals of the same diameter, A. balsamea had a 61% probability of gaining dominance over P. mariana, the probability being 50% if P. mariana was 5 mm larger than A. balsamea. Dominant trees generally had the strongest response to the disturbance, reinforcing the existing size hierarchies. The largest trees typically gain dominance after a partial disturbance. However, interspecific competition is less predictable than intraspecific competition, small initial size difference, and prolonged time in suppression potentially changing tree size hierarchies.

Optimal Mitigation Policies in a Pandemic: Social Distancing and Working from Home

AbstractWe study an economy’s response to an unexpected epidemic. The spread of the disease can be mitigated by reducing consumption and hours worked in the office. Working from home is subject to learning-by-doing. Private agents’ rational incentives are relatively weak and fatalistic. The planner recognizes infection and congestion externalities and implements front-loaded mitigation. Under our calibration, the planner reduces cumulative fatalities by 48$\%$ compared to 24$\%$ by private agents, although with a sharper drop in consumption. Our model can replicate key industry and/or occupational-level patterns and explain how large variations in outcomes across regions can stem from small initial differences.

Relationship between microstructures and resistance in mafic assemblages that deform and transform

Abstract. Syn-kinematic mineral reactions play an important role for the mechanical properties of polymineralic rocks. Mineral reactions (i.e., nucleation of new phases) may lead to grain size reduction, producing fine-grained polymineralic mixtures, which have a strongly reduced viscosity because of the activation of grain-size-sensitive deformation processes. In order to study the effect of deformation–reaction feedback(s) on sample strength, we performed rock deformation experiments on “wet” assemblages of mafic compositions in a Griggs-type solid-medium deformation apparatus. Shear strain was applied at constant strain rate (10−5 s−1) and constant confining pressure (1 GPa) with temperatures ranging from 800 to 900 ∘C. At low shear strain, the assemblages that react faster are significantly weaker than the ones that react more slowly, demonstrating that reaction progress has a first-order control on rock strength. With increasing strain, we document two contrasting microstructural scenarios: (1) the development of a single throughgoing high-strain zone of well-mixed, fine-grained aggregates, associated with a significant weakening after peak stress, and (2) the development of partially connected, nearly monomineralic shear bands without major weakening. The lack of weakening is caused by the absence of interconnected well-mixed aggregates of fine-grained reaction products. The nature of the reaction products, and hence the intensity of the mechanical weakening, is controlled by the microstructures of the reaction products to a large extent, e.g., the amount of amphibole and the phase distribution of reaction products. The samples with the largest amount of amphibole exhibit a larger grain size and show less weakening. In addition to their implications for the deformation of natural shear zones, our findings demonstrate that the feedback between deformation and mineral reactions can lead to large differences in mechanical strength, even at relatively small initial differences in mineral composition.

Benchmarking of codes for plasma burn-through in tokamaks

For the first time, there was an extensive comparison between the plasma burn-through modelling codes presently available—DYON, SCENPLINT, and BKD0. The code benchmarking was carried out over three cases, adding more complexities in the modelling for each step. The first benchmarking was to revisit the mathematical models in the three codes. The simulation results were compared with the simplified settings, where ohmic burn-through of a pure hydrogen plasma was modelled with the ITER-relevant constant parameters. Without any reconciliation work, the three codes already predicted the same threshold prefill gas pressure for the hydrogen burn-through in ITER. However, the three codes produced different time-evolution of plasma parameters. The code developers identified differences in the mathematical models, which resulted in the different time-evolution. This enabled the codes to use the same mathematical models in the second benchmarking, which simulates an ohmic plasma burn-through discharge in a presently operating device. In the second benchmarking, the time-evolution of plasma parameters and impurities was simulated together with time-evolving experimental data from a JET discharge. It was found in this exercise that the time-evolving plasma volume and the electromagnetic modelling of eddy current in the passive structure could significantly change the simulation results, and thus their models need to be improved. For the third benchmarking, stand-alone simulations of the ECH modules in the three codes were compared. The calculated ECH absorption efficiency is identical in DYON and SCENPLINT, while it is about 20% higher in BKD0. Coupling the ECH modules, DYON and SCENPLINT simulated an ECH-assisted plasma burn-through discharge in KSTAR. In the early plasma burn-through phase, similar time-evolution of plasma parameters was reproduced. However, Te evolution starts to deviate from one another at about 100 ms. This is attributed to the sensitivity of ECH power absorption to the small initial difference in Te , which possibly resulted from the different atomic data in the two codes.

Pitch Matching Adapts Even for Bilateral Cochlear Implant Users with Relatively Small Initial Pitch Differences Across the Ears.

There is often a mismatch for bilateral cochlear implant (CI) users between the electrodes in the two ears that receive the same frequency allocation and the electrodes that, when stimulated, yield the same pitch. Studies with CI users who have extreme mismatches between the two ears show that adaptation occurs in terms of pitch matching, reducing the difference between which electrodes receive the same frequency allocation and which ones produce the same pitch. The considerable adaptation that occurs for these extreme cases suggests that adaptation should be sufficient to overcome the relatively minor mismatches seen with typical bilateral CI users. However, even those with many years of bilateral CI use continue to demonstrate a mismatch. This may indicate that adaptation only occurs when there are large mismatches. Alternatively, it may indicate that adaptation occurs regardless of the magnitude of the mismatch, but that adaptation is proportional to the magnitude of the mismatch, and thus never fully counters the original mismatch. To investigate this, six bilateral CI users with initial pitch-matching mismatches of less than 3mm completed a pitch-matching task near the time of activation, 6months after activation, and 1year after activation. Despite relatively small initial mismatches, the results indicated that adaptation still occurred.

Designed Conformation and Fluorescence Properties of Self-Assembled Phenazine-Cored Platinum(II) Metallacycles.

A series of platinum(II) metallacycles were prepared via the coordination-driven self-assembly of a phenazine-cored dipyridyl donor with a 90° Pt(II) acceptor and various dicarboxylate donors in a 1:1:2 ratio. While the metallacycles display similar absorption profiles, they exhibit a trend of blue-shifted fluorescence emission with the decrease in the bite angles between the carboxylate building blocks. Comprehensive spectroscopic and dynamic studies as well as a computational approach were conducted, revealing that the difference in the degree of constraint imposed on the excited-state planarization of the phenazine core within these metallacycles results in their distinct photophysical behaviors. As such, a small initial difference in the dicarboxylate building blocks is amplified into distinct photophysical properties of the metallacycles, which is reminiscent of the efficient functional tuning observed in natural systems. In addition to the pre-assembly approach, the photophysical properties of a metallacycle can also be modulated using a post-assembly modification to the dicarboxylate building block, suggesting another strategy for functional tuning. This research illustrated the potential of coordination-driven self-assembly for the preparation of materials with precisely tailored functionalities at the molecular level.

Transition from Copper to Fiber Broadband: The Role of Connection Speed and Switching Costs

We estimated a mixed logit model using data on the broadband technologies chosen by 94,388 subscribers of a single European broadband operator on a monthly basis between January and December 2014. We found that consumers have similar valuation of DSL connection speeds in the range between 1 and 8 Mbps. Moreover, in January 2014, the valuation of FttH connections with a speed of 100 Mbps was not much higher than of DSL connections with a speed of 1 to 8 Mbps, but it has increased quickly over time. The small initial difference in the valuation of DSL and FttH connections may be because consumers' basic Internet requirements such as browsing, emailing, reading news, shopping, and even watching videos online could be satisfied with a connection speed below 8 Mbps. We also found that consumers face significant switching costs when changing broadband tariff plans, which are substantially higher when switching from DSL to FttH technology. According to counterfactual simulations based on our model, switching costs between technologies are the main factor which slows down consumer transition from DSL to FttH.

Coevolution of parental investment and sexually selected traits drives sex-role divergence.

Sex-role evolution theory attempts to explain the origin and direction of male–female differences. A fundamental question is why anisogamy, the difference in gamete size that defines the sexes, has repeatedly led to large differences in subsequent parental care. Here we construct models to confirm predictions that individuals benefit less from caring when they face stronger sexual selection and/or lower certainty of parentage. However, we overturn the widely cited claim that a negative feedback between the operational sex ratio and the opportunity cost of care selects for egalitarian sex roles. We further argue that our model does not predict any effect of the adult sex ratio (ASR) that is independent of the source of ASR variation. Finally, to increase realism and unify earlier models, we allow for coevolution between parental investment and investment in sexually selected traits. Our model confirms that small initial differences in parental investment tend to increase due to positive evolutionary feedback, formally supporting long-standing, but unsubstantiated, verbal arguments.

Neurociencia y Educación: ¿podemos ir de la investigación básica a su aplicación? Un posible marco de referencia desde la investigación en dislexia

Neuroscience has the potential to transform education because it provides novel methods for understanding human learning and cognitive development. It therefore offers deeper understanding of causal mechanisms in learning and an empirical approach to evaluating the efficacy of different pedagogies. However, this will be a long-term enterprise and there will be few immediate pay-offs. Here I set out one possible framework for linking basic research in neuroscience to pedagogical questions in education. I suggest that the developing field of educational neuroscience must first study how sensory systems build cognitive systems over developmental time. I focus on one cognitive system, language, the efficient functioning of which is critical for reading acquisition. Small initial differences in sensory function, for example auditory function, have the potential to cause large differences in linguistic performance over the learning trajectory. The tools offered by neuroscience can enable better understanding of the causal developmental mechanisms linking audition, phonological development and literacy development, in fine-grained detail. Following this basic research, neuroscience can then inform education and pedagogy by exploring the effects on these neural mechanisms of different learning contexts and pedagogies.

The Community Earth System Model (CESM) Large Ensemble Project: A Community Resource for Studying Climate Change in the Presence of Internal Climate Variability

Abstract While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments [e.g., phase 5 of the Coupled Model Intercomparison Project (CMIP5)]. As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. In response, the Community Earth System Model (CESM) community designed the CESM Large Ensemble (CESM-LE) with the explicit goal of enabling assessment of climate change in the presence of internal climate variability. All CESM-LE simulations use a single CMIP5 model (CESM with the Community Atmosphere Model, version 5). The core simulations replay the twenty to twenty-first century (1920–2100) 30 times under historical and representative concentration pathway 8.5 external forcing with small initial condition differences. Two companion 1000+-yr-long preindustrial control simulations (fully coupled, prognostic atmosphere and land only) allow assessment of internal climate variability in the absence of climate change. Comprehensive outputs, including many daily fields, are available as single-variable time series on the Earth System Grid for anyone to use. Early results demonstrate the substantial influence of internal climate variability on twentieth- to twenty-first-century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5. Scientists and stakeholders can use CESM-LE outputs to help interpret the observational record, to understand projection spread and to plan for a range of possible futures influenced by both internal climate variability and forced climate change.

Insect mating signal and mate preference phenotypes covary among host plant genotypes.

Sexual selection acting on small initial differences in mating signals and mate preferences can enhance signal-preference codivergence and reproductive isolation during speciation. However, the origin of initial differences in sexual traits remains unclear. We asked whether biotic environments, a source of variation in sexual traits, may provide a general solution to this problem. Specifically, we asked whether genetic variation in biotic environments provided by host plants can result in signal-preference phenotypic covariance in a host-specific, plant-feeding insect. We used a member of the Enchenopa binotata species complex of treehoppers (Hemiptera: Membracidae) to assess patterns of variation in male mating signals and female mate preferences induced by genetic variation in host plants. We employed a novel implementation of a quantitative genetics method, rearing field-collected treehoppers on a sample of naturally occurring replicated host plant clone lines. We found remarkably high signal-preference covariance among host plant genotypes. Thus, genetic variation in biotic environments influences the sexual phenotypes of organisms living on those environments in a way that promotes assortative mating among environments. This consequence arises from conditions likely to be common in nature (phenotypic plasticity and variation in biotic environments). It therefore offers a general answer to how divergent sexual selection may begin.

Thermomechanically coupled modelling for land-terminating glaciers: a comparison of two-dimensional, first-order and three-dimensional, full-Stokes approaches

AbstractFor many regions, glacier inaccessibility results in sparse geometric datasets for use as model initial conditions (e.g. along the central flowline only). In these cases, two-dimensional (2-D) flowline models are often used to study glacier dynamics. Here we systematically investigate the applicability of a 2-D, first-order Stokes approximation flowline model (FLM), modified by shape factors, for the simulation of land-terminating glaciers by comparing it with a 3-D, ‘full’-Stokes ice-flow model (FSM). Based on steady-state and transient, thermomechanically uncoupled and coupled computational experiments, we explore the sensitivities of the FLM and FSM to ice geometry, temperature and forward model integration time. We find that, compared to the FSM, the FLM generally produces slower horizontal velocities, due to simplifications inherent to the FLM and to the underestimation of the shape factor. For polythermal glaciers, those with temperate ice zones, or when basal sliding is important, we find significant differences between simulation results when using the FLM versus the FSM. Over time, initially small differences between the FLM and FSM become much larger, particularly near cold/temperate ice transition surfaces. Long time integrations further increase small initial differences between the two models. We conclude that the FLM should be applied with caution when modelling glacier changes under a warming climate or over long periods of time.

Single-cell mass cytometry of TCR signaling: amplification of small initial differences results in low ERK activation in NOD mice.

Signaling from the T-cell receptor (TCR) conditions T-cell differentiation and activation, requiring exquisite sensitivity and discrimination. Using mass cytometry, a high-dimensional technique that can probe multiple signaling nodes at the single-cell level, we interrogate TCR signaling dynamics in control C57BL/6 and autoimmunity-prone nonobese diabetic (NOD) mice, which show ineffective ERK activation after TCR triggering. By quantitating signals at multiple steps along the signaling cascade and parsing the phosphorylation level of each node as a function of its predecessors, we show that a small impairment in initial pCD3ζ activation resonates farther down the signaling cascade and results in larger defects in activation of the ERK1/2-S6 and IκBα modules. This nonlinear property of TCR signaling networks, which magnifies small initial differences during signal propagation, also applies in cells from B6 mice activated at different levels of intensity. Impairment in pCD3ζ and pSLP76 is not a feedback consequence of a primary deficiency in ERK activation because no proximal signaling defect was observed in Erk2 KO T cells. These defects, which were manifest at all stages of T-cell differentiation from early thymic pre-T cells to memory T cells, may condition the imbalanced immunoregulation and tolerance in NOD T cells. More generally, this amplification of small initial differences in signal intensity may explain how T cells discriminate between closely related ligands and adopt strongly delineated cell fates.

Diagnosing Snowband Predictability Using a Multimodel Ensemble System

Abstract The forecast uncertainty of mesoscale snowband formation and evolution is compared using predictions from a 16-member multimodel ensemble at 12-km grid spacing for the 25 December 2002, 12 February 2006, and 14 February 2007 northeast U.S. snowstorms. Using these predictions, the case-to-case variability in the predictability of band formation and evolution is demonstrated. Feature-based uncertainty information is also presented as an example of what may be operationally feasible from postprocessing information from future short-range ensemble forecast systems. Additionally, the initial condition sensitivity of band location in each case is explored by contrasting the forecast evolutions of initial condition members with large differences in snowband positions. Considerable uncertainty in the occurrence, and especially timing and location, of band formation and subsequent evolution was found, even at forecast projections <24 h. The ensemble provided quantitative mesoscale band uncertainty information, and differentiated between high-predictability (14 February 2007) and low-predictability (12 February 2006) cases. Among the three cases, large (small) initial differences in the upper-level PV distribution and surface mean sea level pressure of the incipient cyclone were associated with large (small) differences in forecast snowband locations, suggesting that case-to-case differences in predictability may be related to the quality of the initial conditions. The complexity of the initial flow may also be a discriminator. Error growth was evident in each case, consistent with previous mesoscale predictability research, but predictability differences were not correlated to the degree of convection. Discussion of these results and future extensions of the work are presented.

High predictability of spring phytoplankton biomass in mesocosms at the species, functional group and community level

Summary1. Models aim to predict phytoplankton dynamics based on observed initial conditions and a set of equations and parameters. However, our knowledge about initial conditions in nature is never perfect. Thus, if phytoplankton dynamics are sensitive to small variations in initial conditions, they are difficult to predict.2. We used time‐series data from indoor mesocosm experiments with natural phyto‐ and zooplankton communities to quantify the extent to which small initial differences in the species, functional group and community biomass in parallel treatments were amplified or buffered over time. We compared the differences in dynamics between replicates and among all mesocosms of 1 year.3. Temperature‐sensitive grazing during the exponential growth phase of phytoplankton caused divergence. In contrast, negative density dependence caused convergence.4. Mean differences in biomass between replicates were similar for all hierarchical levels. This indicates that differences in their initial conditions were amplified to the same extent. Even though large differences in biomass occasionally occurred between replicates for a short time, dynamics returned to the same path at all hierarchical levels. This suggests that internal feedback mechanisms make the spring development of phytoplankton highly predictable.

Adaptive strategies for managing uncertainty may explain personality‐related differences in behavioural plasticity

There is growing evidence that individuals within populations show consistent differences in their behaviour across contexts (personality), and that personality is associated with the extent to which individuals adjust their behaviour as function of changing conditions (behavioural plasticity). We propose an evolutionary explanation for a link between personality and plasticity based upon how individuals manage uncertainty. Individuals can employ three categories of tactics to manage uncertainty. They can 1) gather information (sample) to reduce uncertainty, 2) show strategic (state‐dependent) preferences for options that differ in their associated variances in rewards (i.e. variance‐sensitivity), or 3) invest in insurance to mitigate the consequences of uncertainty. We explicitly outline how individual differences in the use of any of these tactics can generate personality‐related differences in behavioural plasticity. For example, sampling effort is likely to co‐vary with individual activity and exploration behaviours, while simultaneously creating population variation in reactions to changes in environmental conditions. Individual differences in the use of insurance may be associated with differences in risk‐taking behaviours, such as boldness in the face of predation, thereby influencing the degree of adaptive plasticity across individuals. Population variation in responsiveness to environmental changes may also reflect individual differences in variance‐sensitivity, because stochastic change in the environment increases variances in rewards, which may both attract and benefit variance‐prone individuals, but not variance‐averse individuals. We review the existing evidence that individual variation in strategies for managing uncertainty exist, and describe how positive‐feedbacks between sampling, variance‐sensitivity and insurance can maintain and exaggerate even small initial differences between individuals in the relative use of these tactics. Given the pervasiveness of the problem of uncertainty, alternative strategies for managing uncertainty may provide a powerful explanation for consistent differences in behaviour and behavioural plasticity for a wide range of traits.

Self‐Assembly of M24L48 Polyhedra Based on Empirical Prediction

Critical structural switch: A small initial difference in the angle within bidentate ligands (see scheme) is amplified into an incommensurable difference in the resultant structures (M12L24 or M24L48). This molecular-level emergent behavior was predicted from the empirical threshold of the ligand bend angle, determined by a ligand mixing experiment, for the critical M12L24/M24L48 switchover.

Annual Research Review: Developmental considerations of gene by environment interactions

Biological development is driven by a complex dance between nurture and nature, determined not only by the specific features of the interacting genetic and environmental influences but also by the timing of their rendezvous. The initiation of large-scale longitudinal studies, ever-expanding knowledge of genetics, and increasing availability of neuroimaging data to provide endophenotypic bridges between molecules and behavior are beginning to provide some insight into interactions of developmental stage, genes, and the environment, although daunting challenges remain. Prominent amongst these challenges are difficulties in identifying and quantifying relevant environmental factors, discerning the relative contributions to multiply determined outcomes, and the likelihood that brain development is a non-linear dynamic process in which small initial differences may yield large later effects. Age-sensitive mechanisms include developmental changes in gene expression, epigenetic modifications, synaptic arborization/pruning, and maturational improvements in our capacity to seek out environments of our choosing. Greater understanding of how genetic and environmental factors interact differently across ages is an important step toward elucidating the mechanisms by which phenotypes are created - and how they may differ in health and disease. This knowledge may also provide clues to guide the type and timing of interventions to maximize outcomes.

Car Ownership and the Labor Markets of Ethnic Minorites

We show how small initial wealth differences between low skilled black and white workers can generate large differences in their labor-market outcomes. This even occurs in the absence of a taste for discrimination against blacks or exogenous differences in the distance to jobs. Because of the initial wealth difference, blacks cannot afford cars while whites can. Car ownership allows whites to reach more jobs per unit of time and this gives them a better bargaining position. As a result, in equilibrium, blacks end up with both higher unemployment rates and lower wages than whites. Furthermore, it takes more time for blacks to reach their jobs even though they travel less miles. Those predictions are consistent with the data. Better access to capital markets or better public transportation will reduce the differences in labor market outcomes.