Micelle Formation and the Hydrophobic Effect

The tendency of amphiphilic molecules to form micelles in aqueous solution is a consequence of the hydrophobic effect. The fundamental difference between micelle assembly and macroscopic phase separation is the stoichiometric constraint that frustrates the demixing of polar and hydrophobic groups. We present a theory for micelle assembly that combines the account of this constraint with a description of the hydrophobic driving force. The latter arises from the length scale dependence of aqueous solvation. The theoretical predictions for temperature dependence and surfactant chain length dependence of critical micelle concentrations for nonionic surfactants agree favorably with experiment.Comment: Accepted for publication in J. Phys. Chem.

Pursuing unhappiness: city, space, and sentimentalism in post-Cold War American literature

My dissertation examines how contemporary American writers have revived and revised literary sentimentalism to fashion their engagement with publicized scenes of suffering, to critique dominant narratives of national identity, and--in some cases--to offer alternate notions of publicness built on fellow-feeling. I propose that much American literature of the 1990s and early post-millennium--texts often characterized as postmodern--evince a profound, yet veiled investment in sentimentalism's characteristic mode of affective pedagogy. In the texts examined here (including works by Philip Roth, Anna Deavere Smith, John Edgar Wideman, Chang-Rae Lee, Jonathan Safron Foer, John Updike, and Don DeLillo), one encounters a recurrent mode of affective engagement: a suffering figure is spectacularly exposed, sometimes "directly" to the reader but much more often through an intermediary figure whose sympathetic, affective, and/or diagnostic reaction to the suffering pedagogically models ideal affective responses for the reader. One also encounters many of the tropes and topoi characteristic of sentimentalism in the 19th century: a metaphoric linking of domestic, familial spaces for the space of the nation, sustained grief for the lost child, and the possibility of a redemptive community established through fellow feeling. Popular American culture has never set aside its investments in the power of sympathy, the guile of sentiment, and the lure of the endearingly oppressed, but the intertextual recovery of sentimentalism's pedagogical modes, tropes, and topoi by writers renowned for their sophistication, experimentation, and reflexiveness would seem more remarkable. Indeed, this resurrection of an aesthetic mode built on feeling goes directly against the diagnosis of Fredric Jameson, who declared famously that postmodern culture is characterized by a "waning of affect" (10). On the contrary, because many "postmodern" writers in the post Cold War period have made use of the performative power of sympathetic witness and reengaged with the nineteenth-century sentimentalist tradition, I maintain that, if anything, the cultural power of affect has been magnified and inflamed. Thus, this dissertation studies the ways in which many contemporary American writers, writers customarily thought of as literary, academic, and postmodern, have borrowed much from a discourse generally considered popular and debased, have employed sentimentalism's tropes for their power, modified its affective pedagogy for their political purposes, and revised many of its assumptions about the power of sympathetic witnessing. I attempt to elucidate these literary reengagements and give shape to my broader inquiry by situating them in relation to scenes of urban crisis, ruin, and unrest--that is, by reading them in relation to the changes characterizing American cities during the post-Cold War period and in the years immediately preceding it. Following the implementation of neoliberal austerity in the late 1970s, a process of deindustrialization and social stratification that had began in the 1960s rapidly accelerated. During this period, urban life in America was marked by the increasing immiseration of the underclass, the massive influx of new immigrants from Asia and Central America, conflict over scant resources, and an escalation of tensions between the highest and lowest elements in society. Using urban conflict to contextualize these postmodern revisions of sentimentalism is not an arbitrary choice; I follow the lead of the texts themselves. In each chapter, I consider how these authors bring the power of sympathetic witness and the hope of a coherent social body built of fellow-feeling--bring, in short, the power of sentimentalism--to bear on scenes of urban tension, strife, and ruin. The net is cast wide enough to include the relative banality of anti-immigrant chauvinism alongside the spectacular explosion of the 1992 Los Angeles riots as well as the smoldering urban ruin left in the wake of the September 11 terrorist attacks. Though these events and circumstances differ in vast and important ways, each can be thought of as fiery evidence against narratives of America's pastoral unity, coherence, and placid omnipotence. The writers who responded to these sites of turmoil made use of sentimentalism's power and investment in sympathetic projection to engage candidly with the suffering of others, to pedagogically mold the affective responses of their readers, and to suggest the existence of a social body to which both sufferer, witness, and reader belong. However, these texts reveal a persistent ambivalence over sympathy: its nature, its power, and its political provenance. Furthermore, because many of these authors model emotional engagement and witness through the figure of the writer, their scrutiny of the politics of sympathy is inseparable from their performative duplication of it. Thus their ambivalence about the community of fellow feeling goes into the text's performance and reception. Reading these authors for their thematic treatment of America's politics of feeling necessarily leads to reading their modes of sentimental ambivalence performatively. The reading practice governing this study therefore reveals the ways in which these writers entangle the publics they address in powerful sympathetic bonds while nevertheless calling into question what power feeling really has

Searching for Neural Mechanisms of Social Cognition

Social cognition involves the integration and pruning of perceptual information which leads to the formation of an abstract representation, which is also known as the perceptual gist. This study examined 87 differences in visual perception of Mooney face stimuli of differing sizes and the relationship to gist formation in ten individuals with autism compared to neurotypical controls. Parents of both groups completed the Social Responsiveness Scale (SRS-2) to assess social functioning in real-world scenarios

Applicability of dynamic facilitation theory to binary hard disk systems

We numerically investigate the applicability of dynamic facilitation (DF) theory for glass-forming binary hard disk systems where supercompression is controlled by pressure. By using novel efficient algorithms for hard disks, we are able to generate equilibrium supercompressed states in an additive nonequimolar binary mixture, where microcrystallization and size segregation do not emerge at high average packing fractions. Above an onset pressure where collective heterogeneous relaxation sets in, we find that relaxation times are well described by a “parabolic law” with pressure. We identify excitations, or soft spots, that give rise to structural relaxation and find that they are spatially localized, their average concentration decays exponentially with pressure, and their associated energy scale is logarithmic in the excitation size. These observations are consistent with the predictions of DF generalized to systems controlled by pressure rather than temperature

Excitations are localized and relaxation is hierarchical in glass-forming liquids

For several atomistic models of glass formers, at conditions below their glassy dynamics onset temperatures, ${T_\mathrm{o}}$, we use importance sampling of trajectory space to study the structure, statistics and dynamics of excitations responsible for structural relaxation. Excitations are detected in terms of persistent particle displacements of length $a$. At supercooled conditions, for $a$ of the order of or smaller than a particle diameter, we find that excitations are associated with correlated particle motions that are sparse and localized, occupying a volume with an average radius that is temperature independent and no larger than a few particle diameters. We show that the statistics and dynamics of these excitations are facilitated and hierarchical. Excitation energy scales grow logarithmically with $a$. Excitations at one point in space facilitate the birth and death of excitations at neighboring locations, and space-time excitation structures are microcosms of heterogeneous dynamics at larger scales. This nature of dynamics becomes increasingly dominant as temperature $T$ is lowered. We show that slowing of dynamics upon decreasing temperature below $T_\mathrm{o}$ is the result of a decreasing concentration of excitations and concomitant growing hierarchical length scales, and further that the structural relaxation time $\tau$ follows the parabolic law, $\log(\tau / \tau_\mathrm{o}) = J^2(1/T - 1/T_\mathrm{o})^2$, for $T<T_\mathrm{o}$, where $J$, $\tau_\mathrm{o}$ and $T_\mathrm{o}$ can be predicted quantitatively from dynamics at short time scales. Particle motion is facilitated and directional, and we show this becomes more apparent with decreasing $T$. We show that stringlike motion is a natural consequence of facilitated, hierarchical dynamics.Comment: 15 pages, 6 figures, + links to movies; To appear in Phys. Rev.

The C. elegans CHP1 homolog, pbo-1, functions in innate immunity by regulating the pH of the intestinal lumen

This work is licensed under a Creative Commons Attribution 4.0 International License.Caenorhabditis elegans are soil-dwelling nematodes and models for understanding innate immunity and infection. Previously, we developed a novel fluorescent dye (KR35) that accumulates in the intestine of C. elegans and reports a dynamic wave in intestinal pH associated with the defecation motor program. Here, we use KR35 to show that mutations in the Ca2+-binding protein, PBO-1, abrogate the pH wave, causing the anterior intestine to be constantly acidic. Surprisingly, pbo-1 mutants were also more susceptible to infection by several bacterial pathogens. We could suppress pathogen susceptibility in pbo-1 mutants by treating the animals with pH-buffering bicarbonate, suggesting the pathogen susceptibility is a function of the acidity of the intestinal pH. Furthermore, we use KR35 to show that upon infection by pathogens, the intestinal pH becomes neutral in a wild type, but less so in pbo-1 mutants. C. elegans is known to increase production of reactive oxygen species (ROS), such as H2O2, in response to pathogens, which is an important component of pathogen defense. We show that pbo-1 mutants exhibited decreased H2O2 in response to pathogens, which could also be partially restored in pbo-1 animals treated with bicarbonate. Ultimately, our results support a model whereby PBO-1 functions during infection to facilitate pH changes in the intestine that are protective to the host