1,094 research outputs found

    Nanofriction mechanisms derived from the dependence of friction on load and sliding velocity from air to UHV on hydrophilic silicon

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    This paper examines friction as a function of the sliding velocity and applied normal load from air to UHV in a scanning force microscope (SFM) experiment in which a sharp silicon tip slides against a flat Si(100) sample. Under ambient conditions, both surfaces are covered by a native oxide, which is hydrophilic. During pump-down in the vacuum chamber housing the SFM, the behavior of friction as a function of the applied normal load and the sliding velocity undergoes a change. By analyzing these changes it is possible to identify three distinct friction regimes with corresponding contact properties: (a) friction dominated by the additional normal forces induced by capillarity due to the presence of thick water films, (b) higher drag force from ordering effects present in thin water layers and (c) low friction due to direct solid-solid contact for the sample with the counterbody. Depending on environmental conditions and the applied normal load, all three mechanisms may be present at one time. Their individual contributions can be identified by investigating the dependence of friction on the applied normal load as well as on the sliding velocity in different pressure regimes, thus providing information about nanoscale friction mechanisms

    Effective action and density functional theory

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    The effective action for the charge density and the photon field is proposed as a generalization of the density functional. A simple definition is given for the density functional, as the functional Legendre transform of the generator functional of connected Green functions for the density and the photon field, offering systematic approximation schemes. The leading order of the perturbation expansion reproduces the Hartree-Fock equation. A renormalization group motivated method is introduced to turn on the Coulomb interaction gradually and to find corrections to the Hartree-Fock and the Kohn-Sham schemes.Comment: New references and a numerical algorithm added, to appear in Phys. Rev. B. 30 pages, no figure

    The Grizzly, October 1, 2015

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    Safety First: New Campus Safety Officer Looks to Connect with Students • Artist Transforms Ursinus Faces into Famous Painting • Design Philly Festival Kicks Off with Pop-up Exhibition • Politics Professor Looks to Expand Research on Africa • U-Imagine Center Promotes Entrepreneurship • UC Students Get Down to the Heart of the Matter • Putting Passion into Practice • Opinions: Is Fun Home Appropriate for CIE?; The Cleaning Staff Should Not be Ignored • In the Swing of Things • Men\u27s and Women\u27s Rugby Teams Prepare for Seasonhttps://digitalcommons.ursinus.edu/grizzlynews/1672/thumbnail.jp

    The Grizzly, November 12, 2015

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    Highlighting a New Trend on Campus • Making Connections: Ursinus Prepares to Break Ground on a Structure Between Pfahler and Thomas • Acclaimed Literary Critic to Give Talk on Campus • Ursinus Brings Top Lawyer Aboard in New Position • International Perspective: How One Student Uses Dance to Connect Ethiopia and Ursinus • Can You Really Netflix and Chill Without Killing Your Grades? • Opinions: Are You a White Feminist?; Bridge of Spies • Defensive Lineman Unleashes Passion for Music • Field Hockey Upsets F&M for Titlehttps://digitalcommons.ursinus.edu/grizzlynews/1677/thumbnail.jp

    Relation of Diabetes to Cognitive Function in Hispanics/Latinos of Diverse Backgrounds in the United States

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    Objectives:To examine the association between diabetes and cognitive function within U.S. Hispanics/Latinos of Central American, Cuban, Dominican, Mexican, Puerto Rican, and South American background. Method: This cross-sectional study included 9,609 men and women (mean age = 56.5 years), who are members of the Hispanic Community Health Study/Study of Latinos. We classified participants as having diabetes, prediabetes, or normal glucose regulation. Participants underwent a neurocognitive battery consisting of tests of verbal fluency, delayed recall, and processing speed. Analyses were stratified by Hispanic/Latino subgroup. Results: From fully adjusted linear regression models, compared with having normal glucose regulation, having diabetes was associated with worse processing speed among Cubans (β = −1.99; 95% CI [confidence interval] = [−3.80, −0.19]) and Mexicans (β = −2.26; 95% CI = [−4.02, −0.51]). Compared with having normal glucose regulation, having prediabetes or diabetes was associated with worse delayed recall only among Mexicans (prediabetes: β = −0.34; 95% CI = [−0.63, −0.05] and diabetes: β = −0.41; 95% CI = [−0.79, −0.04]). No associations with verbal fluency. Discussion: The relationship between diabetes and cognitive function varied across Hispanic/Latino subgroup
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