Grinnell College

In surface waters, photodegradation is a major abiotic removal pathway of the neurotoxin monomethylmercury (MMHg), acting as a key control on the amounts of MMHg available for biological uptake. Different environmental factors can alter the rate of MMHg photodegradation. However, our understanding of how MMHg photodegradation pathways in complex matrixes along the land-to-ocean aquatic continuum respond to changes in salinity, dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition is incomplete. In a set of laboratory experiments combining several artificial and natural waters, we demonstrate that the interplay of DOC concentration, DOM composition, and salinity affects the photodegradation rate of MMHg. The presence of DOM was found to facilitate MMHg photodegradation, but degradation rates were not altered by varying DOC concentrations over two orders of magnitude. We found DOM composition to have a stronger effect on MMHg photodegradation rates than DOC concentration. However, at high DOC levels, where most UV radiation was lost within the first cm of the reaction vessels, lower MMHg photodegradation rates were observed. When moving from terrestrially influenced waters, characterized by a high degree of humification, towards marine conditions with a protein-rich DOM pool, MMHg photodegradation rates increased. In contrast, salinity had a stabilizing effect on MMHg. Hence, especially in systems with low salt and DOC concentrations, changes in either salinity or DOC concentration can impact the photodegradation rates of MMHg.

The Interactions website (interactions.acm.org) hosts a stable of bloggers who share insights and observations on HCI, often challenging current practices. Each issue we'll publish selected posts from some of the leading and emerging voices in the field.

In cognitive psychology, research on attention is shifting from focusing primarily on how people orient toward stimuli in the environment toward instead examining how people orient internally toward memory representations. With this new shift the question arises: What factors in the environment send attention inward? A recent proposal is that one factor is cue familiarity-detection (Cleary, Irving & Mills, Cognitive Science, 47, e13274, 2023). Within this theoretical framework, we reinterpret a decades-old empirical pattern—a primacy effect in memory for repetitions—in a novel way. The effect is the finding that altered repetitions of an image were remembered as re-occurrences of the first presentation despite having a changed left–right orientation; participants better retained the first orientation while incorrectly remembering changed instantiations as repetitions of the first orientation (DiGirolamo & Hintzman, Psychonomic Bulletin & Review, 4, 121–124, 1997). We argue that this pattern, which has never been fully explained, is an existing empirical test of the newly proposed mechanism of cue familiarity-detection flipping attention inward toward memory. Specifically, an image’s first appearance is novel so draws attention outward toward encoding the stimulus’ attributes like orientation; subsequent mirror-reversed appearances are detected as familiar so flip attention inward toward memory search, which leads to 1) inattentional blindness for the changed orientation due to the familiarity-driven shift of attention inward and 2) memory retrieval of the first instance and its orientation, thereby enhancing memory for the first instance and its previously encoded attributes like orientation.

A major focus in pastoralism studies has been on the socially porous or open-access nature of pastoral tenure systems that allow herd movements to respond to shifting availabilities of water and pasture without social constraints. We address the important question of whether herd movements in socially porous tenure regimes are influenced by the social identities of encampment host and visitor, reflecting other needs of mobile pastoralism requiring social cooperation. We assessed pastoral tenure characteristics and the social identities of encampment hosts and visitors at 1014 mapped encampment points in southeastern Chad. We found that under a socially porous tenure regime, visitation is biased toward co-membership of Arab clans. Informants point to the importance of social connections at encampments that facilitate actions to maintain resource access and reduce security risks. Together, these findings support multi-level institutional hybrid structures often found in customary pastoral organization as an important component in transhumance governance institutions.

Immigration often causes backlash, to the benefit of anti-immigrant parties. Most studies that identify the effect of immigration on native attitudes and behaviors leverage variation in inflows of newcomers who are ethnically distinct from natives. Can we therefore conclude that backlash is the general consequence of exposure to large migration flows? We theorize co-ethnic migrants are not met with backlash and are even welcomed by partisans who are politically aligned with the immigrant group. To test this, we leverage a natural experiment in the exogenous allocation of ethnic Germans arriving from the former USSR to German counties between 1996 and 2006, avoiding bias related to selection effects. Analyses of panel data yield no evidence of increased anxiety over economic issues or crime typically associated with anti-migrant backlash in counties receiving more co-ethnic migrants. Instead, we observe a rise in native empathy for immigrants, conditional on partisanship. Furthermore, we find no anti-migrant electoral backlash. Counties receiving larger inflows saw gains for the CDU party which championed ethnic German migration. This suggests ethnicity and partisanship condition the extent to which local demographic change induces political backlash. Moreover, our case shows that, under certain circumstances, mainstream and pro-immigrant parties can derive significant short-term electoral benefits from immigration.

Cyberbullying entails multiple, problematic consequences for its victims. However, little is known about the factors that influence the dispersion of these damaging messages. Drawing on theories of social interaction, we argue that perpetrators disseminate messages containing sexist and racist slurs that reinforce stereotypical, social norms to enhance their online visibility. We collected cross-sectional and longitudinal samples of tweets (N = 539,558 and 248,497, respectively) that included either gender or Asian slurs. We find that tweets containing gender or Asian slurs that were more negative in sentiment had a significantly higher number of retweets than more positive tweets, thereby heightening a user’s online presence and the reach of their content. Two historical events unfolded during our study—the onset of COVID-19 and the murder of George Floyd by a police officer. Tweet negativity increased following both events. Our findings demonstrate the capacity of aggressive tweets to generate wide-ranging networks, a process which is exacerbated further by public crises. Results suggest that the practice of sending such messages is strategic. Perpetrators likely engage in cyberbullying, consciously or not, to increase their online attention. Moreover, this strategy appears to be successful.

Introduction Intrapleural injections of cholera toxin B conjugated to saporin (CTB-SAP) result in selective respiratory (e.g., phrenic) motor neuron death and mimics aspects of motor neuron disease [(e.g., amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA)], such as breathing deficits. This rodent model allows us to study the impact motor neuron death has on the output of surviving phrenic motor neurons as well as the compensatory mechanisms that are recruited. Microglial density in the phrenic motor nucleus as well as cervical gene expression of markers associated with inflammation (e.g., tumor necrosis factor α; TNF-α) are increased following CTB-SAP-induced phrenic motor neuron death, and ketoprofen (nonsteroidal anti-inflammatory drug) delivery attenuated phrenic long-term facilitation (pLTF) in 7 day (d) CTB-SAP rats but enhanced pLTF in 28d CTB-SAP rats. Methods Here, we worked to determine the impact of TNF-α in the phrenic motor nucleus by: 1) quantifying TNFR1 (a high affinity transmembrane receptor for TNF-α) expression; 2) investigating astrocytes (glial cells known to release TNF-α) by performing a morphological analysis in the phrenic motor nucleus; and 3) determining whether acute TNFR1 inhibition differentially affects phrenic plasticity over the course of CTB-SAP-induced motor neuron loss by delivering an inhibitor for TNF-α receptor 1 (sTNFR1i) in 7d and 28d male CTB-SAP and control rats. Results Results revealed that TNFR1 expression was increased on phrenic motor neurons of 28d CTB-SAP rats (p < 0.05), and that astrocytes were increased and exhibited reactive morphology (consistent with an activated phenotype; p < 0.05) in the phrenic motor nucleus of CTB-SAP rats. Additionally, we found that pLTF was attenuated in 7d CTB-SAP rats but enhanced in 28d CTB-SAP rats (p < 0.05) following intrathecal sTNFR1i delivery. Conclusion This work suggests that we could harness TNFR1 as a potential therapeutic agent in CTB-SAP rats and patients with respiratory motor neuron disease by increasing compensatory plasticity in surviving neurons to improve phrenic motor neuron function and breathing as well as quality of life. Future studies will focus on microglial and astrocytic cytokine release, the role they play in the differential mechanisms of pLTF utilized by 7d and 28d CTB-SAP rats, and potential therapies that target them.

A nonlocal model for dynamic brittle damage is introduced consisting of two phases, one elastic and the other inelastic. Evolution from the elastic to the inelastic phase depends on material strength. Existence and uniqueness of the displacement-failure set pair follow from an initial value problem describing the evolution. The displacement-failure pair satisfies energy balance. The length of nonlocality $\epsilon$ is taken to be small relative to the domain in $\mathbb{R}^{d}$, d=2,3. The strain is formulated as a difference quotient of the displacement in the nonlocal model. The two point force is expressed in terms of a weighted difference quotient and delivers an evolution on a subset of $\mathbb{R}^{d}\times \mathbb{R}^{d}$. This evolution provides an energy balance between external energy, elastic energy, and damage energy including fracture energy. For any prescribed loading the deformation energy resulting in material failure over a region R is uniformly bounded as $\epsilon \rightarrow 0$. For fixed $\epsilon$, the failure energy is discovered to be is nonzero for $d-1$ dimensional regions R associated with flat crack surfaces. Calculation shows, this failure energy is the Griffith fracture energy given by the energy release rate multiplied by area for d=3 (or length for d=2). The nonlocal field theory is shown to recover a solution of Naiver’s equation outside a propagating flat traction free crack in the limit of vanishing spatial nonlocality. The theory and simulations presented here corroborate the recent experimental findings of (Rozen-Levy et al. in Phys. Rev. Lett. 125(17):175501, 2020) that cracks follow the location of maximum energy dissipation inside the intact material. Simulations show fracture evolution through the generation of a traction free internal boundary seen as a wake left behind a moving strain concentration.

Across two studies, we examined intergroup relations between Black-White multiracial and Black monoracial people in the U.S. Study 1 showed that Black-White multiracial participants reported more solidarity with Black than White people, but less solidarity with Black people than Black participants reported. Likewise, their race-relevant political attitudes were somewhat more aligned with Black than White participants, but not completely aligned with Black participants. Reflecting this pattern, Black participants perceived that Black-White multiracial people feel more solidarity with Black than White people, but less solidarity with Black people than they themselves feel. Solidarity perceptions were consequential. Both Study 1 (correlational) and Study 2 (experimental) showed that Black participants’ perceptions of Black-White multiracial people’s solidarity with Black people were related to their inclusion of multiracial people. Furthermore, contingent on high levels of solidarity with Black people, multiracial people’s relationships with White people were less consequential for Black participants’ inclusion of them.

The hybrid particle-based computational platform that couples peridynamics with the discrete element method (PeriDEM) is used to model vehicle mobility over roadbeds. We consider wheels rolling over gravel beds, where gravel is allowed to deform and fracture. The motion of particles are not constrained to translation and rotation as in DEM and grains can deform elastically or inelastically. This allows for more modes of inter-particle interaction. The effects of gravel shape and topology on the vehicle mobility are examined using the higher fidelity modeling. Here we study how these aspects affect vehicle range, average vehicle velocity, traction as measured by wheel slip, as well as the overall energy needed to travel a prescribed distance. When intraparticle fracture can occur, computations identify conditions on gravel particle topology that enhance vehicle mobility. In other computer simulations it is found that the driving torque is monotonically increasing with slip and capture trends seen in experiment Smith (Journal of Terramechanics, 2014). Graphical abstract

Premise The selection of Arabidopsis as a model organism played a pivotal role in advancing genomic science. The competing frameworks to select an agricultural‐ or ecological‐based model species were rejected, in favor of building knowledge in a species that would facilitate genome‐enabled research. Methods Here, we examine the ability of models based on Arabidopsis gene expression data to predict tissue identity in other flowering plants. Comparing different machine learning algorithms, models trained and tested on Arabidopsis data achieved near perfect precision and recall values, whereas when tissue identity is predicted across the flowering plants using models trained on Arabidopsis data, precision values range from 0.69 to 0.74 and recall from 0.54 to 0.64. Results The identity of belowground tissue can be predicted more accurately than other tissue types, and the ability to predict tissue identity is not correlated with phylogenetic distance from Arabidopsis. k‐nearest neighbors is the most successful algorithm, suggesting that gene expression signatures, rather than marker genes, are more valuable to create models for tissue and cell type prediction in plants. Discussion Our data‐driven results highlight that the assertion that knowledge from Arabidopsis is translatable to other plants is not always true. Considering the current landscape of abundant sequencing data, we should reevaluate the scientific emphasis on Arabidopsis and prioritize plant diversity.

Objective We use a survey experiment to study what explains white “not in my backyard” opposition (NIMBYism) to dense and affordable housing—racial threat, material self‐interest, or both. Methods In a survey experiment on white U.S. respondents, we vary the presence of a racial prime about black and Latinx community organizations and the proximity of the housing development to the subject's home. We then measure levels of support for a proposed hypothetical housing development, willingness to take political action in support of or opposition to the development, and support for a number of housing‐related and redistributive policies. Results We find that a racial threat, a material self‐interest threat, and a combined racial and material self‐interest threat decrease support for a proposed housing development. These effects are moderated by racial resentment, ideology, and partisanship such that the effects of the treatments are primarily driven by Republicans, conservatives, and the highly racially resentful. These groups are more threatened than others by either Latinx and black people moving in, the development being in their own neighborhood, or both. Conclusion These findings indicate that racial and material perceived threats play important and interlocking roles in white Americans’ resistance to multifamily housing being built. In a context where local political institutions empower an unrepresentative group of disproportionately white, economically privileged neighbors to mount opposition to dense housing, it is important to understand how white opposition to new dense housing is shaped by racial and financial concerns.