ASU Scholarship Showcase

The broad recognition specificity exhibited by integrin α_Mβ₂ (Mac-1, CD11b/CD18) has allowed this adhesion receptor to play innumerable roles in leukocyte biology, yet we know little about how and why α_Mβ₂ binds its multiple ligands. Within α_Mβ₂, the α_MI-domain is responsible for integrin’s multiligand binding properties. To identify its recognition motif, we screened peptide libraries spanning sequences of many known protein ligands for α_MI-domain binding and also selected the α_M I-domain recognition sequences by phage display. Analyses of >1400 binding and nonbinding peptides derived from peptide libraries showed that a key feature of the α_MI-domain recognition motif is a small core consisting of basic amino acids flanked by hydrophobic residues. Furthermore, the peptides selected by phage display conformed to a similar pattern. Identification of the recognition motif allowed the construction of an algorithm that reliably predicts the α_MI-domain binding sites in the α_Mβ₂ ligands. The recognition specificity of the α_MI-domain resembles that of some chaperones, which allows it to bind segments exposed in unfolded proteins. The disclosure of the α_Mβ₂ binding preferences allowed the prediction that cationic host defense peptides, which are strikingly enriched in the α_MI-domain recognition motifs, represent a new class of α_Mβ₂ ligands. This prediction has been tested by examining the interaction of α_Mβ₂ with the human cathelicidin peptide LL-37. LL-37 induced a potent α_Mβ₂-dependent cell migratory response and caused activation of α_Mβ₂ on neutrophils. The newly revealed recognition specificity of α_Mβ₂ toward unfolded protein segments and cationic proteins and peptides suggests that α_Mβ₂ may serve as a previously proposed “alarmin” receptor with important roles in innate host defense.

This article advances recent scholarship on energy security by arguing that the concept is best understood as a sociotechnical imaginary, a collective vision for a “good society” realized through technoscientific-oriented policies. Focusing on the 1952 Resources for Freedom report, the authors trace the genealogy of energy security, elucidating how it establishes a morality of efficiency that orients policy action under the guise of security toward the liberalizing of markets in resource states and a robust program of energy research and development in the United States. This evidence challenges the pervasive historical anchoring of the concept in the 1970s and illustrates the importance of the genealogical approach for the emerging literature on energy and sociotechnical imaginaries. Exploring the genealogy of energy security also unpacks key social, political, and economic undercurrents that disrupt the seeming universality of the language of energy, leading the authors to question whether energy security discourse is appropriate for guiding policy action during ongoing global energy transitions.

We derive the null energy condition, understood as a constraint on the Einstein-frame Ricci tensor, from world sheet string theory. For a closed bosonic string propagating in a curved geometry, the spacetime interpretation of the Virasoro constraint condition is precisely the null energy condition, to leading nontrivial order in the α′ expansion. Thus the deepest origin of the null energy condition lies in world sheet diffeomorphism invariance.

In this work, we numerically demonstrate an infrared (IR) frequency-tunable selective thermal emitter made of graphene-covered silicon carbide (SiC) gratings. Rigorous coupled-wave analysis shows temporally-coherent emission peaks associated with magnetic polariton (MP), whose resonance frequency can be dynamically tuned within the phonon absorption band of SiC by varying graphene chemical potential. An analytical inductor–capacitor circuit model is introduced to quantitatively predict the resonance frequency and further elucidate the mechanism for the tunable emission peak. The effects of grating geometric parameters, such as grating height, groove width and grating period, on the selective emission peak are explored. The direction-independent behavior of MP and associated coherent emission are also demonstrated. Moreover, by depositing four layers of graphene sheets onto the SiC gratings, a large tunability of 8.5% in peak frequency can be obtained to yield the coherent emission covering a broad frequency range from 820 to 890 cm^-1. The novel tunable metamaterial could pave the way to a new class of tunable thermal sources in the IR region.

We present stellar evolution models for 0.5 - 1.2 M_⊙ at scaled metallicities of 0.1 - 1.5 Z_⊙ and O/Fe values of 0.44 - 2.28 O/Fe_⊙. The time dependent evolution of habitable zone boundaries are calculated for each stellar evolution track based on stellar mass, effective temperature, and luminosity parameterizations. The rate of change of stellar surface quantities and the surrounding habitable zone position are strong functions of all three quantities explored. The range of orbits that remain continuously habitable, or habitable for at least 2 Gyr, are provided. The results show that the detailed chemical characterization of exoplanet host stars and a consideration of their evolutionary history are necessary to assess the likelihood that a planet found in the instantaneous habitable zone has had sufficient time to develop a biosphere capable of producing detectable biosignatures. This model grid is designed for use by the astrobiology and exoplanet communities to efficiently characterize the time evolution of host stars and their habitable zones for planetary candidates of interest.

The aim of this article was to study sound source localization by cochlear implant (CI) listeners with low-frequency (LF) acoustic hearing in both the operated ear and in the contralateral ear. Eight CI listeners had symmetrical LF acoustic hearing and 4 had asymmetrical LF acoustic hearing. The effects of two variables were assessed: (i) the symmetry of the LF thresholds in the two ears and (ii) the presence/absence of bilateral acoustic amplification. Stimuli consisted of low-pass, high-pass, and wideband noise bursts presented in the frontal horizontal plane. Localization accuracy was 23° of error for the symmetrical listeners and 76° of error for the asymmetrical listeners. The presence of a unilateral CI used in conjunction with bilateral LF acoustic hearing does not impair sound source localization accuracy, but amplification for acoustic hearing can be detrimental to sound source localization accuracy.

We studied young adolescents' seeking out support to understand conflict with their co-resident fathers/stepfathers, and the cognitive and affective implications of such support-seeking, phenomena we call guided cognitive reframing. Our sample included 392 adolescents (M_age = 12.5, 52.3% female) who were either of Mexican or European ancestry and lived with their biological mothers and either a stepfather or a biological father. More frequent reframing was associated with more adaptive cognitive explanations for father/stepfather behavior. Cognitions explained the link between seeking out and feelings about the father/stepfather and self. Feelings about the self were more strongly linked to depressive symptoms than cognitions. We discuss the implications for future research on social support, coping, guided cognitive reframing, and father–child relationships.

Transmission systems are under stress and need to be upgraded. Better utilization of the existing grid provides a fast and cheap alternative to building new transmission. One way to improve the utilization of the transmission network is power flow control via flexible AC transmission system (FACTS) devices. While FACTS devices are used today, the utilization of these devices is limited; traditional dispatch models (e.g., security con-strained economic dispatch) assume a fixed, static transmission grid even though it is rather flexible. The primary barrier is the complexity that is added to the power flow problem. The mathe-matical representation of the DC optimal power flow, with the added modeling of FACTS devices, is a nonlinear program (NLP). This paper presents a method to convert this NLP into a mixed-integer linear program (MILP). The MILP is reformulat-ed as a two-stage linear program, which enforces the same sign for the voltage angle differences for the lines equipped with FACTS. While this approximation does not guarantee optimality, more than 98% of the presented empirical results, based on the IEEE 118 bus and Polish system, achieved global optimality. In the case of suboptimal solutions, the savings were still significant and the solution time was dramatically reduced.