485 research outputs found
Predicting the steady state thickness of passive films in order to prevent degradations of implant
Some implants have approximately a lifetime of 15 years. The femoral stem,
for example, should be made of 316L/316LN stainless steel. Fretting corrosion,
friction under small displacements, should occur during human gait, due to
repeated loadings and un-loadings, between stainless steel and bone for
instance. Some experimental investigations of fretting corrosion have been
practiced. As well known, metallic alloys and especially stainless steels are
covered with a passive film that prevents from the corrosion and degradation.
This passive layer of few nanometers, at ambient temperature, is the key of our
civilization according to some authors. This work is dedicated to predict the
passive layer thicknesses of stainless steel under fretting corrosion with a
specific emphasis on the role of proteins. The model is based on the Point
Defect Model (micro scale) and an update of the model on the friction process
(micro-macro scale). Genetic algorithm was used for finding solution of the
problem. The major results are, as expected from experimental results, albumin
prevents from degradation at the lowest concentration of chlorides; an
incubation time is necessary for degrading the passive film; under fretting
corrosion and high concentration of chlorides the passive behavior is
annihilated
Diffractive wave guiding of hot electrons by the Au (111) herringbone reconstruction
The surface potential of the herringbone reconstruction on Au(111) is known
to guide surface-state electrons along the potential channels. Surprisingly, we
find by scanning tunneling spectroscopy that hot electrons with kinetic
energies twenty times larger than the potential amplitude (38 meV) are still
guided. The efficiency even increases with kinetic energy, which is reproduced
by a tight binding calculation taking the known reconstruction potential and
strain into account. The guiding is explained by diffraction at the
inhomogeneous electrostatic potential and strain distribution provided by the
reconstruction.Comment: 10 pages, 9 figure
Apparent rippling with honeycomb symmetry and tunable periodicity observed by scanning tunneling microscopy on suspended graphene
Suspended graphene is difficult to image by scanning probe microscopy due to
the inherent van-der-Waals and dielectric forces exerted by the tip which are
not counteracted by a substrate. Here, we report scanning tunneling microscopy
data of suspended monolayer graphene in constant-current mode revealing a
surprising honeycomb structure with amplitude of 50200 pm and lattice
constant of 10-40 nm. The apparent lattice constant is reduced by increasing
the tunneling current , but does not depend systematically on tunneling
voltage or scan speed . The honeycomb lattice of the rippling
is aligned with the atomic structure observed on supported areas, while no
atomic corrugation is found on suspended areas down to the resolution of about
pm. We rule out that the honeycomb structure is induced by the feedback
loop using a changing , that it is a simple enlargement effect of
the atomic resolution as well as models predicting frozen phonons or standing
phonon waves induced by the tunneling current. Albeit we currently do not have
a convincing explanation for the observed effect, we expect that our intriguing
results will inspire further research related to suspended graphene.Comment: 10 pages, 7 figures, modified, more detailed discussion on errors in
vdW parameter
Electrical transport and low-temperature scanning tunneling microscopy of microsoldered graphene
Using the recently developed technique of microsoldering, we perform a
systematic transport study of the influence of PMMA on graphene flakes
revealing a doping effect of up to 3.8x10^12 1/cm^2, but a negligible influence
on mobility and gate voltage induced hysteresis. Moreover, we show that the
microsoldered graphene is free of contamination and exhibits a very similar
intrinsic rippling as has been found for lithographically contacted flakes.
Finally, we demonstrate a current induced closing of the previously found
phonon gap appearing in scanning tunneling spectroscopy experiments, strongly
non-linear features at higher bias probably caused by vibrations of the flake
and a B-field induced double peak attributed to the 0.Landau level of graphene.Comment: 8 pages, 3 figure
An Exploratory Investigation of Comparisons of Student Evaluations of Learning Pre and Post COVID-19 at Private and Public Universities
Although universities attempted to provide as little disruption to student learning as possible, problems arose with their responses to the COVID-19 pandemic. The current literature is rich with studies reporting experiences with the transition to the virtual learning of the pandemic era. In pursuit of the most effective learning and instructional modes to transition to in times of crisis, university administrators and faculty members need to know more regarding what worked and did not work in the initial response to the COVID- 19 crisis. Questions remain. Given the pre-COVID-19 dominance of face-to-face instruction did student opinion of online learning change based on their experiences with the mandated transitions to virtual learning? Are the perceptions different for students at private versus public and small versus large institutions? This paper reports the results of an exploratory study of these bifurcations based on an online survey of student opinion conducted in Spring 2021. The findings provide some insight to student perceptions of the efficacy of the changed learning environment experienced by the subject populations
Fretting corrosion damage of total hip prosthesis: Friction coefficient and damage rate constant approach
International audienceThis paper analyzes friction coefficient evolution between materials related to total hip prosthesis. Fretting corrosion tests were conducted with stainless steel and poly(methyl methacrylate) interacting surfaces. In the course of fretting corrosion tests, the Coulomb friction coefficient is determined as a function of the number of cycles. It was found that the friction coefficient growth rate can be expressed as a power-law function. The influences of ionic strength, applied potential, pH, and albumin content on fretting corrosion were then investigated on the basis of the evolution of the friction coefficient. Finally, we identify the damage rate constant as being relevant for linking the mechanical and chemical parameters in the evolution of damage
Apparent rippling with honeycomb symmetry and tunable periodicity observed by scanning tunneling microscopy on suspended graphene
Suspended graphene is difficult to image by scanning probe microscopy due to the inherent van der Waals and dielectric forces exerted by the tip, which are not counteracted by a substrate. Here, we report scanning tunneling microscopy data of suspended monolayer graphene in constant-current mode, revealing a surprising honeycomb structure with amplitude of 50-200 pm and lattice constant of 10-40 nm. The apparent lattice constant is reduced by increasing the tunneling current I, but does not depend systematically on tunneling voltage V or scan speed v(scan). The honeycomb lattice of the rippling is aligned with the atomic structure observed on supported areas, while no atomic corrugation is found on suspended areas down to the resolution of about 3-4 pm. We rule out that the honeycomb structure is induced by the feedback loop using a changing vscan, that it is a simple enlargement effect of the atomic lattice, as well as models predicting frozen phonons or standing phonon waves induced by the tunneling current. Although we currently do not have a convincing explanation for the observed effect, we expect that our intriguing results will inspire further research related to suspended graphene
Dark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy
The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most
attractive targets for indirect searches of dark matter. In this work, we
reconstruct the dark matter annihilation (J-factor) and decay profiles for the
newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis
of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS), we
find Reticulum II's J-factor to be among the largest of any Milky Way dSph. We
have checked the robustness of this result against several ingredients of the
analysis. Unless it suffers from tidal disruption or significant inflation of
its velocity dispersion from binary stars, Reticulum II may provide a unique
window on dark matter particle properties.Comment: 5 pages, 4 figures. Match the ApJL accepted versio
Dark matter annihilation and decay in dwarf spheroidal galaxies: The classical and ultrafaint dSphs
Dwarf spheroidal (dSph) galaxies are prime targets for present and future
gamma-ray telescopes hunting for indirect signals of particle dark matter. The
interpretation of the data requires careful assessment of their dark matter
content in order to derive robust constraints on candidate relic particles.
Here, we use an optimised spherical Jeans analysis to reconstruct the
`astrophysical factor' for both annihilating and decaying dark matter in 21
known dSphs. Improvements with respect to previous works are: (i) the use of
more flexible luminosity and anisotropy profiles to minimise biases, (ii) the
use of weak priors tailored on extensive sets of contamination-free mock data
to improve the confidence intervals, (iii) systematic cross-checks of binned
and unbinned analyses on mock and real data, and (iv) the use of mock data
including stellar contamination to test the impact on reconstructed signals.
Our analysis provides updated values for the dark matter content of 8
`classical' and 13 `ultrafaint' dSphs, with the quoted uncertainties directly
linked to the sample size; the more flexible parametrisation we use results in
changes compared to previous calculations. This translates into our ranking of
potentially-brightest and most robust targets---viz., Ursa Minor, Draco,
Sculptor---, and of the more promising, but uncertain targets---viz., Ursa
Major 2, Coma---for annihilating dark matter. Our analysis of Segue 1 is
extremely sensitive to whether we include or exclude a few marginal member
stars, making this target one of the most uncertain. Our analysis illustrates
challenges that will need to be addressed when inferring the dark matter
content of new `ultrafaint' satellites that are beginning to be discovered in
southern sky surveys.Comment: 19 pages, 14 figures, submitted to MNRAS. Supplementary material
available on reques
Leading issues in business research methods volume 2
In selecting the current papers, the editors have sought to cover a representative set of papers from both quantitative and qualitative strands. Papers that set out what research methods were adopted, their epistemological and philosophical positions, considerations of alternative research methods (interviews, surveys, the Web, focus groupsâŠ) and epistemological positions (positivism, interpretivism, constructivismâŠ), why these might not have been chosen and what contributions were made to the field have generally been selected for the current volume. It is the editorsâ view that established and early career researchers as well as students learning to do research will benefit from the selection
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