Bottom-up Constraints Research Articles

Shedding black hole light on the emergent string conjecture

Asymptotically massless towers of species are ubiquitous in the string landscape when infinite-distance limits are approached. Due to the remarkable properties of string dualities, they always comprise Kaluza-Klein states or higher-spin excitations of weakly coupled, asymptotically tensionless critical strings. The connection between towers of light species and small black holes warrants seeking a bottom-up rationale for this dichotomoy, dubbed emergent string conjecture. In this paper we move a first step in this direction, exploring bottom-up constraints on towers of light species motivated purely from the consistency of the corresponding thermodynamic picture for small black holes. These constraints shed light on the allowed towers in quantum gravity, and, upon combining them with unitarity and causality constraints from perturbative graviton scattering, they provide evidence for the emergent string scenario with no reference to a specific ultraviolet completion.

Top-down and bottom-up constraints in mechanistic inquiry

Mechanisms play a crucial role in scientific research across various disciplines, and philosophers of science have devoted significant effort into understanding their ontology and epistemology. This paper examines the relationship between mechanisms and phenomena, highlighting the inherent dependence of mechanistic delineation on the characterization of phenomena. By acknowledging that characterizing phenomena is influenced by pragmatic considerations and research interests, the paper argues that mechanistic inquiry is inherently shaped by researchers’ perspectives. This dependence raises concerns about the possibility of a realist view of mechanisms. To address these concerns, the paper explores how top-down constraints, rooted in researchers’ interests and pragmatic concerns, can be balanced by bottom-up constraints derived from empirical considerations. In conclusion, I argue that the interplay between these constraints forms an empirical and realist counterweight to the perspectival nature of top-down constraints.

Feeding guild determines strength of top-down forces in multitrophic system experiencing bottom-up constraints

Nitrogen (N) and water are crucial in crop production but increasingly scarce environmental resources. Reducing their inputs can affect the whole plant-arthropod community including biocontrol agents. In a multitrophic system, we studied the interaction of the bottom-up effects of moderately reduced N concentration and/or water supply as well as the top-down effects of pests of different feeding guilds on plant nutritional quality (N and carbon concentration), direct defense (alkaloids and phenolics), and indirect defense (plant volatile organic compounds); on herbivore performance and host quality (N and carbon) to parasitoids and the latter's performance. Studied organisms were tomato plants, the sap feeders Macrosiphum euphorbiae and Bemisia tabaci, the leaf chewers Tuta absoluta and Spodoptera littoralis, and the parasitic wasps Aphelinus abdominalis and Necremnus tutae. Resource limitation affected plant quality, triggering bottom-up effects on herbivore and parasitoid performance, except for T. absoluta and N. tutae. Feeding guild had a major influence: bottom-up effects were stronger on sap feeders; N effects were stronger on sap feeders while water effects were stronger with leaf chewers (S. littoralis). Top-down effects of leaf chewer herbivory partly attenuated bottom-up effects and partly suppressed plant defenses. Bottom-up effects weakened when cascading up trophic levels. In summary, the interaction between plants, pests, and beneficial insects was modulated by abiotic factors, affecting insect performance. Simultaneous abiotic and biotic impact shaped plant biochemistry depending on the feeding guild: the biotic top-down effect of leaf chewer herbivory attenuated the bottom-up effects of plant nutrition and hence dominated the plant biochemical profile whereas in sap feeder infested leaves, it corresponded to the abiotic impact. This study highlights the plant's finely tuned regulatory system facilitating response prioritization. It offers perspectives on how smart manipulation of plant nutrient solutions might save resources while maintaining efficient biocontrol in crop production.

General prescription for globalU(1)’s in 6D SCFTs

We present a general prescription for determining the global U(1) symmetries of six-dimensional superconformal field theories (6D SCFTs). We use the quiver-like gauge theory description of the tensor branch to identify candidate U(1) symmetries which can act on generalized matter. The condition that these candidate U(1)'s are free of Adler-Bell-Jackiw (ABJ) anomalies provides bottom-up constraints for U(1)'s. This agrees with the answer obtained from symmetry breaking patterns induced by Higgs branch flows. We provide numerous examples illustrating the details of this proposal. In the F-theory realization of these theories, some of these symmetries originate from deformations of non-abelian flavor symmetries localized on a component of the discriminant, while others come from an additional generator of the Mordell-Weil group. We also provide evidence that some of these global U(1)'s do not arise from gauge symmetries, as would happen in taking a decoupling limit of a model coupled to six-dimensional supergravity.

Bottom-Up and Top-Down Cues in a Comics Reading Task

Readers are increasingly exposed to text that includes both words and images through comics, graphic novels, online materials, and video games. In this study, we use the medium of the 4-panel comic strip to examine how readers make meaning of the word/image composite. We propose a cognitive interactive framework that incorporates both the bottom-up constraints of verbal and visual cues and top-down constraints imposed by global narrative structures to assess the contributions of each in the meaning-making process. Previous research has focused more on the qualitative and sociocultural approaches while this study uses cognitive and quantitative perspectives to explore the meaning making of text that includes both words and images. Results of our analyses show that both bottom-up and top-down constraints make significant and separable contributions to the variance in a comprehension task.

Disturbance-mediated consumer assemblages determine fish community structure and moderate top-down influences through bottom-up constraints.

Disturbance is a strong structuring force that can influence the strength of species interactions at all trophic levels, but controls on the contributions to community structure of top-down and bottom-up processes across such gradients remain poorly understood. Changes in the composition of predator and consumer assemblages, and their associated traits, across gradients of environmental harshness (e.g. flooding), are likely to be a particularly important influence on the strength of top-down control and may drive bottom-up constraints. We examined how consumers with particular traits, and the predators that consumed them, varied across a gradient of stream flooding disturbance and used experiments to assess the predation impact on those contrasting consumer communities (ultimately quantifying how flood disturbance altered the strength of top-down control). Consumer community composition and mobility were strongly related to flood disturbance; the biomass and drift of protected primary consumers (i.e. those with morphological defences) decreased with increasing flood disturbance. Predatory fish species had different disturbance niches, and path analysis identified that both direct flood disturbance effects and indirect bottom-up constraints of flood disturbance on consumers influenced predatory fish composition and biomass. Fish generally fed most effectively on consumer types associated with their particular niche, but all fish were strongly size-selective when feeding on protected consumers. Although protected consumers did not grow large enough to escape predation, an in situ experiment showed protected consumers were at a reduced risk of predation as disturbance increased compared to unprotected consumers. Overall, top-down control declined with flood disturbance, but the effect depended on consumer traits. Predatory fish were only capable of exerting top-down control on protected consumers in benign habitats but impacted unprotected consumers across a larger range of the disturbance gradient. Collectively our findings suggest that a shift towards a more disturbed state will probably result in reduced predator impacts and a weakening of top-down control. Moreover, predicted increases in the frequency and intensity of climatic events causing disturbance, such as flooding, are likely to result in a community shift that disproportionately impacts protected consumers and the predators that utilize them as prey through the subsequent bottom-up constraints.

Phenomenological consequences of the refined swampland conjecture

We discuss phenomenological consequences of the recently-introduced refinements of the de Sitter swampland conjecture. The conjecture constraints the first and the second derivatives of the scalar potential in terms of two $O(1)$ constants $c$ and $c'$, leading to interesting constraints on particle phenomenology, especially inflationary model building. Our work can also be regarded as bottom-up constraints on the values of $c$ and $c'$.

A new version of the CABLE land surface model (Subversion revision r4601) incorporating land use and land cover change, woody vegetation demography, and a novel optimisation-based approach to plant coordination of photosynthesis

Abstract. The Community Atmosphere–Biosphere Land Exchange model (CABLE) is a land surface model (LSM) that can be applied stand-alone and provides the land surface–atmosphere exchange within the Australian Community Climate and Earth System Simulator (ACCESS). We describe new developments that extend the applicability of CABLE for regional and global carbon–climate simulations, accounting for vegetation responses to biophysical and anthropogenic forcings. A land use and land cover change module driven by gross land use transitions and wood harvest area was implemented, tailored to the needs of the Coupled Model Intercomparison Project 6 (CMIP6). Novel aspects include the treatment of secondary woody vegetation, which benefits from a tight coupling between the land use module and the Population Orders Physiology (POP) module for woody demography and disturbance-mediated landscape heterogeneity. Land use transitions and harvest associated with secondary forest tiles modify the annually resolved patch age distribution within secondary vegetated tiles, in turn affecting biomass accumulation and turnover rates and hence the magnitude of the secondary forest sink. Additionally, we implemented a novel approach to constrain modelled GPP consistent with the coordination hypothesis and predicted by evolutionary theory, which suggests that electron-transport- and Rubisco-limited rates adjust seasonally and across biomes to be co-limiting. We show that the default prior assumption – common to CABLE and other LSMs – of a fixed ratio of electron transport to carboxylation capacity at standard temperature (Jmax, 0∕Vcmax, 0) is at odds with this hypothesis; we implement an alternative algorithm for dynamic optimisation of this ratio such that coordination is achieved as an outcome of fitness maximisation. The results have significant implications for the magnitude of the simulated CO2 fertilisation effect on photosynthesis in comparison to alternative estimates and observational proxies. These new developments enhance CABLE's capability for use within an Earth system model and in stand-alone applications to attribute trends and variability in the terrestrial carbon cycle to regions, processes and drivers. Model evaluation shows that the new model version satisfies several key observational constraints: (i) trend and interannual variations in the global land carbon sink, including sensitivities of interannual variations to global precipitation and temperature anomalies; (ii) centennial trends in global GPP; (iii) coordination of Rubisco-limited and electron-transport-limited photosynthesis; (iv) spatial distributions of global ET, GPP, biomass and soil carbon; and (v) age-dependent rates of biomass accumulation in boreal, temperate and tropical secondary forests. CABLE simulations agree with recent independent assessments of the global land–atmosphere flux partition that use a combination of atmospheric inversions and bottom-up constraints. In particular, there is agreement that the strong CO2-driven sink in the tropics is largely cancelled by net deforestation and forest degradation emissions, leaving the Northern Hemisphere (NH) extratropics as the dominant contributor to the net land sink.

Abstract TP64: Visual Perception, Cognition, and Non-Contrast CT Aspects

Introduction: As image interpretation is a visual perception task, it is affected by context and task structure. The non-contrast CT Alberta Stroke Program Early CT Score (ASPECTS) is considered an objective radiologic measure of the extent of ischemic change in cases of acute ischemic stroke. We hypothesize that variability in ASPECTS reading is because readers are susceptible to interplay between higher-order, top-down information (clinical background or other imaging) and bottom-up sensory information, and that experts are more resistant to being swayed by these factors than novices. Methods: We tested the effect of three top-down background-information conditions (no information; clinical information with affected side; clinical information plus CT angiography (CTA)) and three environment/task conditions (daylight, core lab, time pressure) on the inter-rater reliability (IRR) of NCCT ASPECTS. Three raters (trainee, fellow, neuro-radiologist) independently scored 150 NCCT scans from acute ischemic stroke patients, with 50 allocated to each environmental task. This was repeated over three sessions, with one for each background-information condition. ASPECTS on CT perfusion Tmax thresholded scans served as ground truth. Results: IRR improved when clinical information and CTA were provided (ICC 0.55 - clinical + CTA, 0.41 - clinical, 0.10 - no information). In some situations (NIHSS <5, onset-to-imaging times >180 min), IRR was greater with clinical information but without CTA. Daylight and time pressure had greater IRR than core lab (ICC 0.59 and 0.7 vs. 0.34, respectively). In general, the trainee assigned lower ASPECTS relative to the fellow and expert. The expert showed greatest concordance with CT perfusion ASPECTS (ICC 0.69), and the trainee the least (ICC 0.47). Conclusion: The cognitive framework that we propose, which includes top-down and bottom-up constraints on visual perception, can explain variability in ASPECTS interpretation on NCCT.

Quantity and quality limit detritivore growth: mechanisms revealed by ecological stoichiometry and co-limitation theory.

Resource quantity and quality are fundamental bottom-up constraints on consumers. Best understood in autotroph-based systems, co-occurrence of these constraints may be common but remains poorly studied in detrital-based systems. Here, we used a laboratory growth experiment to test limitation of the detritivorous caddisfly larvae Pycnopsyche lepida across a concurrent gradient of oak litter quantity (food supply) and quality (phosphorus : carbon [P:C ratios]). Growth increased simultaneously with quantity and quality, indicating co-limitation across the resource gradients. We merged approaches of ecological stoichiometry and co-limitation theory, showing how co-limitation reflected shifts in C and P acquisition throughout homeostatic regulation. Increased growth was best explained by elevated consumption rates and improved P assimilation, which both increased with elevated quantity and quality. Notably, C assimilation efficiencies remained unchanged and achieved maximum 18% at low quantity despite pronounced C limitation. Detrital C recalcitrance and substantive post-assimilatory C losses probably set a minimum quantity threshold to achieve positive C balance. Above this threshold, greater quality enhanced larval growth probably by improving P assimilation toward P-intensive growth. We suggest this interplay of C and P acquisition contributes to detritivore co-limitation, highlighting quantity and quality as potential simultaneous bottom-up controls in detrital-based ecosystems, including under anthropogenic change like nutrient enrichment.

Probabilistic model for 3D interactive segmentation

Fully-automated segmentation algorithms offer fast, objective, and reproducible results for large data collections. However, these techniques cannot handle tasks that require contextual knowledge not readily available in the images alone. Thus, the supervision of an expert is necessary.We present a generative model for image segmentation, based on a Bayesian inference. Not only does our approach support an intuitive and convenient user interaction subject to the bottom-up constraints introduced by the image intensities, it also circumvents the main limitations of a human observer—3D visualization and modality fusion. The user “dialogue” with the segmentation algorithm via several mouse clicks in regions of disagreement, is formulated as a continuous probability map, that represents the user’s certainty to whether the current segmentation should be modified. Considering this probability map as the voxel-vise Bernoulli priors on the image labels allows spatial encoding of the user-provided input. The method is exemplified for the segmentation of cerebral hemorrhages (CH) in human brain CT scans; ventricles in degenerative mice brain MRIs, and tumors in multi-modal human brain MRIs and is shown to outperform three interactive, state-of-the-art segmentation methods in terms of accuracy, efficiency and user-workload.

Institutionalized computer workaround practices in a Mediterranean country: an examination of two organizations

Information systems research often treats computer workarounds tangentially and as temporary phenomena. This exploratory research embraces anomalous system use in general and computer workarounds in particular by suggesting why the latter can be institutionalized and how they may be manifested in practice. Anomalous use is defined as sociomaterial actions around an IT artifact not consistent with its design or related official rules that nevertheless constitute system enactment in practice. The persistence of computer workarounds might be explained by the tension between top-down pressures from the external environment and bottom-up constraints from day-to-day operational work. These insights are drawn from an up-close study of workarounds in two cases from the Mediterranean region. The workaround practices involve decoupling and loose coupling, effectively creating ‘equilibrium’ between the aforementioned top-down and bottom-up influences. This may be attributed to parity between the influence exercised by external regulatory/accrediting bodies and the constraints of day-to-day work within the focal organization (i.e., work ethos, material constraints, and discretion to decouple). Our results show why some computer workarounds exhibit institutionalized behavior and their antecedent conditions. We also suggest that constituent workaround practices may exist as twin but distinctive behavioral patterns – non-compliance (or partial compliance) with an official rule and partially (or fully) working around designed systems.

The face and person perception: Insights from social cognition

Social-cognitive investigations of face perception have tended to be motivated by different goals than cognitive and neuropsychological studies-namely, to understand the dynamics of social categorization rather than identity recognition-and the result has been a lack of cross-pollination of insights and ideas between the disciplines. We review the evidence from social cognition, with an eye to discussing how this work aligns with the Bruce and Young (1986) model of face recognition. Acknowledging the invaluable impact the model has exerted on our understanding of face recognition, we suggest that considering the bottom-up constraints of visual processing and the top-down influences of semantic knowledge will contribute to a more comprehensive understanding of face perception.

Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis

Abstract Hunt, G. L., Coyle, K. O., Eisner, L. B., Farley, E. V., Heintz, R. A., Mueter, F., Napp, J. M., Overland, J. E., Ressler, P. H., Salo, S., and Stabeno, P. J. 2011. Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis. – ICES Journal of Marine Science, 68: 1230–1243. Walleye pollock (Theragra chalcogramma) is an important component of the eastern Bering Sea ecosystem and subject to major fisheries. The Oscillating Control Hypothesis (OCH) predicted that recruitment of pollock year classes should be greatest in years with early ice retreat and late blooms in warm water, because more energy would flow into the pelagic (vs. benthic) community. The OCH further predicted that, with pollock population growth, there should be a shift from bottom-up to top-down regulation. New data support the predictions that in those years with early ice retreat, more primary production accrues to the pelagic compartment and that large numbers of age-0 pollock survive to summer. However, in these years, production of large crustacean zooplankton is reduced, depriving age-0 pollock of lipid-rich prey in summer and autumn. Consequently, age-0 pollock energy reserves (depot lipids) are low and predation on them is increased as fish switch to age-0 pollock from zooplankton. The result is weak recruitment of age-1 recruits the following year. A revised OCH indicates bottom-up constraints on pollock recruitment in very warm periods. Prolonged warm periods with decreased ice cover will likely cause diminished pollock recruitment and catches relative to recent values.

Awareness and Filling-in of the Human Blind Spot: Linking Psychophysics with Retinal Topography

To link psychophysical thresholds for blind spot awareness and filling-in with early neural components that underpin these perceptions. Blind spot dimensions were quantified, after which an intrinsic stimulus (i.e., a rectangular bar of varying length centered within the blind spot) was used to determine blind spot awareness and filling-in for five subjects. Histologic examination of six human retinas at 20-μm intervals from the temporal and nasal neural rims of the optic nerve head out to 1040 μm allowed the quantification of outer nuclear layer thickness, a direct correlate of photoreceptor density. Blind spot awareness was reported for bar extensions beyond 0.4° to 0.8° from the edge of the blind spot. Partial and total blind spot filling-in were reported between 1.1° and 1.3° and beyond 1.5°, respectively. Histologic measures of ONL thickness were correlated with previously published data of photoreceptor spatial density to determine the percentage of photoreceptor density required to trigger a 75% probability response. Blind spot awareness was achieved by stimulating 43% to 70% of the maximum photoreceptor density. Partial and total filling-in of the blind spot required between 78% and 83% and more than 85% photoreceptor spatial densities, respectively. A novel intrinsic stimulus has been used to concurrently investigate blind spot awareness and blind spot filling-in. Retinal neural correlates of each visual experience have been quantified. Future computational models will have to integrate bottom-up constraints with long-range cortical receptive field activity and higher order cognitive factors.

From perceptual rags to metaphoric riches—Bodily, social, and cultural constraints on sociocognitive metaphors: Comment on Landau, Meier, and Keefer (2010).

What leads people to describe some of their interpersonal relationships as "close" and "warm" and others as "distant" and "cold"? Landau, Meier, and Keefer (2010) proposed that conceptual metaphors facilitate social cognition by allowing people to use knowledge from a relatively concrete (source) domain (e.g., physical distance) in understanding a different, usually more abstract (target) concept (e.g., love). We concur that such a notion of metaphors can greatly enrich the field of social cognition. At the same time, we believe it is important to devote greater theoretical attention to the nature of metaphorical representations in social cognition. We believe that Landau et al. place too much emphasis on sociocognitive metaphors as top-down knowledge structures and pay too little attention to the constraints that shape metaphors from the bottom up. In the present contribution, we highlight important bottom-up constraints, imposed through bodily constraints and social scaffolds. Sociocognitive metaphors do not exist just for mental representation but for action as well. We discuss the relevance of grounding sociocognitive metaphors for broader motivational purposes.

Integrating neuroscience, psychology, and evolutionary biology through a teleological conception of function

The idea of integrating evolutionary biology and psychology has great promise, but one that will be compromised if psychological functions are conceived too abstractly and neuroscience is not allowed to play a contructive role. We argue that the proper integration of neuroscience, psychology, and evolutionary biology requires a telelogical as opposed to a merely componential analysis of function. A teleological analysis is required in neuroscience itself; we point to traditional and curent research methods in neuroscience, which make critical use of distinctly teleological functional considerations in brain cartography. Only by invoking teleological criteria can researchers distinguish the fruitful ways of identifying brain components from the myriad of possible ways. One likely reason for reluctance to turn to neuroscience is fear of reduction, but we argue that, in the context of a teleological perspective on function, this concern is misplaced. Adducing such theoretical considerations as top-down and bottom-up constraints on neuroscientific and psychological models, as well as existing cases of productive, multidisciplinary cooperation, we argue that integration of neuroscience into psychology and evolutionary biology is likely to be mutually beneficial. We also show how it can be accommodated methodologically within the framework of an interfield theory.

Constraints on computational models of auditory scene analysis, as derived from human perception.

Auditory scene analysis (ASA) groups the sensory evidence derived from a mixture of sound sources and derives separate descriptions of the individual sources. There are two possible ways of doing this:(a) using knowledge of the properties of certain classes of sounds, such as speech, in a top-down fashion;(b) using, in a bottom-up manner, those properties in the input (such as harmonic relations) that are typically found when two or more sound sources (e.g., voice and footsteps) affect the input at the same time. Some properties of the ASA done by humans are discussed and proposed as specifications for a computational model: the adding up of evidence, the coherence of the ASA system, the combining of top-down and bottom-up constraints, as illustrated in the duplex perception of speech, and the propagation of influences across the auditory field.