Quantitative Nanofriction Characterization of Corrugated Surfaces by Atomic Force Microscopy

Atomic Force Microscopy (AFM) is a suitable tool to perform tribological characterization of materials down to the nanometer scale. An important aspect in nanofriction measurements of corrugated samples is the local tilt of the surface, which affects the lateral force maps acquired with the AFM. This is one of the most important problems of state-of-the-art nanotribology, making difficult a reliable and quantitative characterization of real corrugated surfaces. A correction of topographic spurious contributions to lateral force maps is thus needed for corrugated samples. In this paper we present a general approach to the topographic correction of AFM lateral force maps and we apply it in the case of multi-asperity adhesive contact. We describe a complete protocol for the quantitative characterization of the frictional properties of corrugated systems in the presence of surface adhesion using the AFM.Comment: 33 pages, 9 figures, RevTex 4, submitted to Journal of Applied Physic

Serving the Underserved Amid COVID-19: The Case of a Virtual, Culturally Responsive Summer Engineering Camp

The societal disruptions due to the novel coronavirus (COVID-19) pandemic are well noted, especially in the context of science, technology, engineering, and mathematics (STEM) education. Absent a concerted effort to sustain hands-on learning opportunities in STEM amid the crisis, the consequences of COVID-19 may exacerbate existing inequities and racial disparities among youth of color further stratifying the STEM fields. In the current study, we applied a mixed-method descriptive case study design, using online learning theory and culturally responsive pedagogy as our conceptual framework, to describe how participants experienced this camp, held online due to disruptions of COVID-19, in the southeastern region of the USA. We also share findings from the implementation of a justice bots project, which enabled participants to connect social justice and engineering. Participants included middle school youth, undergraduate engineering students, and in-service math and science teachers. Data sources entailed focus groups, pre-post surveys, observations, and artifacts. Our results indicated that participants experienced gains in their communication skills, positive changes in attitudes toward STEM for middle school youth, established meaningful connections, and enhanced their technical knowledge. Middle school youth reported enjoying the online summer camp environment, though they had experienced more than a year of education online. Undergraduate engineering students asserted that it was challenging to communicate coding and other technical knowledge virtually but having to do so strengthened their capacity to teach others while honing their own competencies. Lastly, in-service math and science teachers reported a better understanding of the connection between engineering and social justice based on their experiences in the camp. We conclude this article with implications for engineering education

Universality of the critical conductance distribution in various dimensions

We study numerically the metal - insulator transition in the Anderson model on various lattices with dimension $2 < d \le 4$ (bifractals and Euclidian lattices). The critical exponent $\nu$ and the critical conductance distribution are calculated. We confirm that $\nu$ depends only on the {\it spectral} dimension. The other parameters - critical disorder, critical conductance distribution and conductance cummulants - depend also on lattice topology. Thus only qualitative comparison with theoretical formulae for dimension dependence of the cummulants is possible

Measuring the Stellar Masses of z~7 Galaxies with Spitzer Ultrafaint Survey Program (SURFS UP)

We present Spitzer/IRAC observations of nine $z'$-band dropouts highly magnified (2<mu<12) by the Bullet Cluster. We combine archival imaging with our Exploratory program (SURFS UP), which results in a total integration time of ~30 hr per IRAC band. We detect (>3sigma) in both IRAC bands the brightest of these high-redshift galaxies, with [3.6]=23.80+-0.28 mag, [4.5]=23.78+-0.25 mag, and (H-[3.6])=1.17+-0.32 mag. The remaining eight galaxies are undetected to [3.6]~26.4 mag and [4.5]~26.0 mag with stellar masses of ~5x10^7 M_sol. The detected galaxy has an estimated magnification of mu=12+-4, which implies this galaxy has an ultraviolet luminosity of L_1500~0.3 L*_{z=7} --- the lowest luminosity individual source detected in IRAC at z>7. By modeling the broadband photometry, we estimate the galaxy has an intrinsic star-formation rate of SFR~1.3 M_sol/yr and stellar mass of M~2x10^9 M_sol, which gives a specific star-formation rate of sSFR~0.7 Gyr^-1. If this galaxy had sustained this star-formation rate since z~20, it could have formed the observed stellar mass (to within a factor of ~2), we also discuss alternate star-formation histories and argue the exponentially-increasing model is unlikely. Finally, based on the intrinsic star-formation rate, we estimate this galaxy has a likely [C II] flux of = 10^{-17} erg/s/cm2.Comment: Accepted to ApJL. 6 pages, 3 figures, 2 table

The Politics of Commerce : The Congress of Chambers of Commerce of the Empire, 1886-1914

Peer reviewedPublisher PD