Princess and the Pea at the nanoscale: Wrinkling and delamination of graphene on nanoparticles

Thin membranes exhibit complex responses to external forces or geometrical constraints. A familiar example is the wrinkling, exhibited by human skin, plant leaves, and fabrics, resulting from the relative ease of bending versus stretching. Here, we study the wrinkling of graphene, the thinnest and stiffest known membrane, deposited on a silica substrate decorated with silica nanoparticles. At small nanoparticle density monolayer graphene adheres to the substrate, detached only in small regions around the nanoparticles. With increasing nanoparticle density, we observe the formation of wrinkles which connect nanoparticles. Above a critical nanoparticle density, the wrinkles form a percolating network through the sample. As the graphene membrane is made thicker, global delamination from the substrate is observed. The observations can be well understood within a continuum elastic model and have important implications for strain-engineering the electronic properties of graphene.Comment: 11 pages, 8 figures. Accepted for publication in Physical Review

XPS and STEM study of the interface formation between ultra-thin Ru and Ir OER catalyst layers and perylene red support whiskers

The interface formation between nano-structured perylene red (PR) whiskers and oxygen evolution reaction (OER) catalysts ruthenium and iridium has been studied systematically by XPS and STEM. The OER catalyst over-layers with thicknesses ranging from ~0.1 to ~50 nm were vapor deposited onto PR ex-situ. STEM images demonstrate that, with increasing thickness, Ru and Ir transform from amorphous clusters to crystalline nanoparticles, which agglomerate with increased over-layer thickness. XPS data show a strong interaction between Ru and PR. Ir also interacts with PR although not to the extent seen for Ru. At low coverages, the entire Ru deposit is in the reacted state while a small portion of the deposited Ir remains metallic. Ru and Ir bonding occur at the PR carbonyl sites as evidenced by the attenuation of carbonyl photoemission and the emergence of new peak assigned to C-O single bond. The curve fitting analysis and the derived stoichiometry indicates the formation of metallo-organic bonds. The co-existence of oxide bonds is also apparent

'Just another vial…': a qualitative study to explore the acceptability and feasibility of routine blood-borne virus testing in an emergency department setting in the UK.

OBJECTIVES: Increased test uptake for HIV and viral hepatitis is fast becoming a health priority at both national and global levels. Late diagnosis of these infections remains a critical public health concern in the UK. Recommendations have been issued to expand blood-borne virus (BBV) testing in alternative settings. Emergency departments (EDs) offer a potentially important point of testing. This paper presents findings from a qualitative study which aimed to explore the acceptability and feasibility of a routine opt-out combined BBV testing intervention implemented at an inner London ED. METHODS: We conducted 22 semistructured interviews with patients and service providers in the ED over a 4-month period during the intervention pilot. A grounded analytical approach was employed to conduct thematic analysis of qualitative study data. RESULTS: Core interrelating thematic areas, identified and analytically developed in relation to test intervention implementation and experience, included the following: the remaking of routine test procedure; notions of responsibility in relation to status knowledge and test engagement; the opportunity and constraints of the ED as a site for testing; and the renegotiation of testing cultures within and beyond the clinic space. CONCLUSION: Study findings demonstrate how relational and spatial dynamics specific to the ED setting shape test meaning and engagement. We found acceptability of the test practice was articulated through narratives of situated responsibility, with the value of the test offset by perceptions of health need and justification of the test expense. Participant accounts indicate that the nontargeted approach of the test affords a productive disruption to 'at-risk' identities, yet they also reveal limits to the test intervention's 'normalising' effect. Evaluation of the intervention must attend to the situated dynamics of the test practice if opportunities of an opt-out BBV test procedure are to be fully realised. Findings also highlight the critical need to further evaluate post-test intervention practices and experiences

‘It Relates to My Everyday Life.’ Critical Pedagogy and Student Explanations of Interest in Sociology Course Topics

We applied critical pedagogy in the college classroom by asking students what topics they would want covered in their Introduction to Sociology courses if they were given the power to decide. Students were also asked to explain why they were interested, and uninterested, in learning about the topics they chose from our questionnaire. Survey data was collected from 191 students at a southeastern community college; the majority were not sociology majors. Overall, students were the most interested in learning about culture, deviance, race, and gender issues. Students were the least interested in learning about topics concerning urbanization and the economy. We found that students are typically interested in topics that are related to general curiosities or are applicable to the students’ personal lives or future careers. However, students were vaguer in their responses regarding why they were uninterested in learning about particular sociological topics; most students claimed that they were simply “just uninterested.” These results support the claim that a student’s desire to learn material is guided by how personally invested he or she is in the topic. By implementing a critical pedagogical teaching approach in the classroom, professors could increase student interest, thus fostering more successful and satisfied students

Optimal Transport, Convection, Magnetic Relaxation and Generalized Boussinesq equations

We establish a connection between Optimal Transport Theory and classical Convection Theory for geophysical flows. Our starting point is the model designed few years ago by Angenent, Haker and Tannenbaum to solve some Optimal Transport problems. This model can be seen as a generalization of the Darcy-Boussinesq equations, which is a degenerate version of the Navier-Stokes-Boussinesq (NSB) equations. In a unified framework, we relate different variants of the NSB equations (in particular what we call the generalized Hydrostatic-Boussinesq equations) to various models involving Optimal Transport (and the related Monge-Ampere equation. This includes the 2D semi-geostrophic equations and some fully non-linear versions of the so-called high-field limit of the Vlasov-Poisson system and of the Keller-Segel for Chemotaxis. Finally, we show how a ``stringy'' generalization of the AHT model can be related to the magnetic relaxation model studied by Arnold and Moffatt to obtain stationary solutions of the Euler equations with prescribed topology

Constraining Lyman-alpha spatial offsets at 3<z<5.53<z<5.5 from VANDELS slit spectroscopy

We constrain the distribution of spatially offset Lyman-alpha emission (Ly$\alpha$) relative to rest-frame ultraviolet emission in $\sim300$ high redshift ($3<z<5.5$) Lyman-break galaxies (LBGs) exhibiting Ly$\alpha$ emission from VANDELS, a VLT/VIMOS slit-spectroscopic survey of the CANDELS Ultra Deep Survey and Chandra Deep Field South fields (${\simeq0.2}~\mathrm{deg}^2$ total). Because slit spectroscopy compresses two-dimensional spatial information into one spatial dimension, we use Bayesian inference to recover the underlying Ly$\alpha$ spatial offset distribution. We model the distribution using a 2D circular Gaussian, defined by a single parameter $\sigma_{r,\mathrm{Ly}\alpha}$, the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample ($3<z<5.5$), we find $\sigma_{r,\mathrm{Ly}\alpha}=1.70^{+0.09}_{-0.08}$ kpc ($68\%$ conf.), corresponding to $\sim0.25$ arcsec at $\langle z\rangle=4.5$. We also find that $\sigma_{r,\mathrm{Ly}\alpha}$ decreases significantly with redshift. Because Ly$\alpha$ spatial offsets can cause slit-losses, the decrease in $\sigma_{r,\mathrm{Ly}\alpha}$ with redshift can partially explain the increase in the fraction of Ly$\alpha$ emitters observed in the literature over this same interval, although uncertainties are still too large to reach a strong conclusion. If $\sigma_{r,\mathrm{Ly}\alpha}$ continues to decrease into the reionization epoch, then the decrease in Ly$\alpha$ transmission from galaxies observed during this epoch might require an even higher neutral hydrogen fraction than what is currently inferred. Conversely, if spatial offsets increase with the increasing opacity of the IGM, slit losses may explain some of the drop in Ly$\alpha$ transmission observed at $z>6$. Spatially resolved observations of Ly$\alpha$ and UV continuum at $6<z<8$ are needed to settle the issue.Comment: Submitted to MNRA

Beyond the New Jim Crow: Public Support for Removing and Regulating Collateral Consequences

In The New Jim Crow, Michelle Alexander drew national attention to the extensive imposition of collateral consequences on those convicted of a crime and to their racially disparate effects. Based on a 2017 national-level YouGov survey, supplemented by a second 2019 YouGov survey, the current study finds that the public is split on allowing ex-offenders to sit on juries, but supportive of removing barriers to voting and employment. The respondents also favored providing defendants with a list of restrictions linked to conviction as well as having lawmakers review and eliminate collateral consequences found to have no purpose and to not reduce crime

Effect of impurities on pentacene island nucleation

Pentacenequinone (PnQ) impurities have been introduced into a pentacene source material in a controlled manner to quantify the relative effects of the impurity content on grain boundary structure and thin film nucleation. Atomic force microscopy (AFM) has been employed to directly characterize films grown using 0.0-7.5% PnQ by weight in the source material. Analysis of the distribution of capture zones areas of submonolayer islands as a function of impurity content shows that for large PnQ content the critical nucleus size for forming a Pn island is smaller than for low PnQ content. This result indicates a favorable energy for formation of Pn-PnQ complexes, which in turn suggests that the primary effect of PnQ on Pn mobility may arise from homogeneous distribution of PnQ defects.Comment: 16 Pages, 5 figures, 1 Tabl

Warped Phenomenology

We explore the phenomenology associated with the recently proposed localized gravity model of Randall and Sundrum where gravity propagates in a 5-dimensional non-factorizable geometry and generates the 4-dimensional weak-Planck scale hierarchy by an exponential function of the compactification radius, called a warp factor. The Kaluza-Klein tower of gravitons which emerge in this scenario have strikingly different properties than in the factorizable case with large extra dimensions. We derive the form of the graviton tower interactions with the Standard Model fields and examine their direct production in Drell-Yan and dijet events at the Tevatron and LHC as well as the KK spectrum line-shape at high-energy linear \epem colliders. In the case where the first KK excitation is observed, we outline the procedure to uniquely determine the parameters of this scenario. We also investigate the effect of KK tower exchanges in contact interaction searches. We find that present experiments can place meaningful constraints on the parameters of this model.Comment: 14 pages, LaTex, 3 fig