217 research outputs found
Low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) carriage in women from former Yugoslavia living in Switzerland
It is erroneous to draw too many conclusions about global university rankings. Making a university’s reputation rest on the subjective judgement of senior academics and over-reliance on interpreting and utilising secondary data from bibliometrics and peer assessments have created an enmeshed culture of performativity and over-emphasis on productivity. This trend has exacerbated unhealthy competition and mistrust within the academic community and also discord outside its walls. Surely if universities are to provide service and thrive with the advancement of knowledge as a primary objective, it is important to address the methods, concepts, and representation necessary to move from an emphasis on quality assurance to an emphasis on quality enhancement.This overview offers an analysis of the practice of international ranking. US News and World Report Best Global Universities Rankings, the Times Supplement World University Rankings, and the Shanghai Jiao Tong University Academic Ranking of World Universities are analysed. While the presence of Nobel laureates in the hard sciences has been seized upon for a number of years as quantifiable evidence of producing world-class university education, Nobel laureates in peace and literature have been absent from such rankings. Moreover, rankings have been based on employment rather than university affiliation. Previously unused secondary data from institutions where Nobel peace and literature laureates completed their terminal degrees are presented. The purpose has been to determine whether including peace and literature laureates might modify rankings. A caveat: since the presence of awarded Nobel laureates affiliated at various institutions results in the institutions receiving additional ranking credit in the hard sciences of physics, chemistry, medicine, and economic sciences, this additional credit is not recognised in the approach used in this study. Among other things, this study suggests that if educational history were used in assembling the rankings as opposed to one’s university affiliation, conclusions might be very different
Stability of an oscillating tip in Non-Contact Atomic Force Microscopy: theoretical and numerical investigations
This paper is a theoretical and a numerical investigation of the stability of
a tip-cantilever system used in Non-Contact Atomic Force Microscopy (NC-AFM)
when it oscillates close to a surface. No additional dissipative force is
considered. The theoretical approach is based on a variationnal method
exploiting a coarse grained operation that gives the temporal dependence of the
nonlinear coupled equations of motion in amplitude and phase of the oscillator.
Stability criterions for the resonance peak are deduced and predict a stable
behavior of the oscillator in the vicinity of the resonance. The numerical
approach is based on results obtained with a virtual NC-AFM developped in our
group. The effect of the size of the stable domain in phase is investigated.
These results are in particularly good agreement with the theoretical
predictions. Also they show the influence of the phase shifter in the feedback
loop and the way it can affect the damping signal
The Role of Nonlinear Dynamics in Quantitative Atomic Force Microscopy
Various methods of force measurement with the Atomic Force Microscope (AFM)
are compared for their ability to accurately determine the tip-surface force
from analysis of the nonlinear cantilever motion. It is explained how
intermodulation, or the frequency mixing of multiple drive tones by the
nonlinear tip-surface force, can be used to concentrate the nonlinear motion in
a narrow band of frequency near the cantilevers fundamental resonance, where
accuracy and sensitivity of force measurement are greatest. Two different
methods for reconstructing tip-surface forces from intermodulation spectra are
explained. The reconstruction of both conservative and dissipative tip-surface
interactions from intermodulation spectra are demonstrated on simulated data.Comment: 25 pages (preprint, double space) 7 figure
Distance dependence of force and dissipation in non-contact atomic force microscopy on Cu(100) and Al(111)
The dynamic characteristics of a tip oscillating in the nc-AFM mode in close
vicinity to a Cu(100)-surface are investigated by means of phase variation
experiments in the constant amplitude mode. The change of the quality factor
upon approaching the surface deduced from both frequency shift and excitation
versus phase curves yield to consistent values. The optimum phase is found to
be independent of distance. The dependence of the quality factor on distance is
related to 'true' damping, because artefacts related to phase misadjustment can
be excluded. The experimental results, as well as on-resonance measurements at
different bias voltages on an Al(111) surface, are compared to Joule
dissipation and to a model of dissipation in which long-range forces lead to
viscoelastic deformations
Probing the shape of atoms in real space
The structure of single atoms in real space is investigated by scanning
tunneling microscopy. Very high resolution is possible by a dramatic reduction
of the tip-sample distance. The instabilities which are normally encountered
when using small tip-sample distances are avoided by oscillating the tip of the
scanning tunneling microscope vertically with respect to the sample. The
surface atoms of Si(111)-(7 x 7) with their well-known electronic configuration
are used to image individual samarium, cobalt, iron and silicon atoms. The
resulting images resemble the charge density corresponding to 4f, 3d and 3p
atomic orbitals.Comment: Submitted to Phys. Rev. B, 17 pages, 7 figure
Interaction imaging with amplitude-dependence force spectroscopy
Knowledge of surface forces is the key to understanding a large number of
processes in fields ranging from physics to material science and biology. The
most common method to study surfaces is dynamic atomic force microscopy (AFM).
Dynamic AFM has been enormously successful in imaging surface topography, even
to atomic resolution, but the force between the AFM tip and the surface remains
unknown during imaging. Here, we present a new approach that combines high
accuracy force measurements and high resolution scanning. The method, called
amplitude-dependence force spectroscopy (ADFS) is based on the
amplitude-dependence of the cantilever's response near resonance and allows for
separate determination of both conservative and dissipative tip-surface
interactions. We use ADFS to quantitatively study and map the nano-mechanical
interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is
compatible with commercial atomic force microscopes and we anticipate its
wide-spread use in taking AFM toward quantitative microscopy
Deep-sea fragmentation style of Havre revealed by dendrogrammatic analyses of particle morphometry
In 2012, the eruption of deep-sea volcano Havre produced an abundance of fine ash at a depth of ~ 1000 m below sea level. In this study the 2D shapes of Havre ash grains retrieved from the seafloor were compared quantitatively with those of particles generated in a suite of different fragmentation experiments, which used remelted rhyolitic rock and pumice from the eruption site. A new statistical data analysis technique, denoted as Dendrogrammatic Analysis of Particle Morphology (DAPM) is introduced. It is designed to compare large numbers of morphometric data sets containing shape information for a set of ash particles to group them by morphological similarities and to visualize these clusters in a dendrogram. Further steps involve t tests and equivalence tests and reveal morphometric differences as well as matching features. The DAPM suggests that the majority of Havre ash was thermohydraulically produced by induced fuel coolant-interaction. A subset of ash particles features an elongated tube morphology. Their morphometry matches that of particles that were experimentally produced by a combination of shearing and quenching, and we infer that the natural particles were formed by synextrusive ash-venting.This study was supported by MARSDEN grant U001616; Havre samples were obtained with NSF funding EAR1447559. T.D. is supported by the Icelandic Research Fund (Rannís) Grant Nr. 206527-051. R.J.C. was funded by Australian Research Council grants DP110102196 and DE150101190, and by US National Science Foundation grant OCE1357443.Peer Reviewe
Premelting of Thin Wires
Recent work has raised considerable interest on the nature of thin metallic
wires. We have investigated the melting behavior of thin cylindrical Pb wires
with the axis along a (110) direction, using molecular dynamics and a
well-tested many-body potential. We find that---in analogy with cluster
melting---the melting temperature of a wire with radius is lower
than that of a bulk solid, , by . Surface melting
effects, with formation of a thin skin of highly diffusive atoms at the wire
surface, is observed. The diffusivity is lower where the wire surface has a
flat, local (111) orientation, and higher at (110) and (100) rounded areas. The
possible relevance to recent results on non-rupturing thin necks between an STM
tip and a warm surface is addressed.Comment: 10 pages, 4 postscript figures are appended, RevTeX, SISSA Ref.
131/94/CM/S
An all silicon quantum computer
A solid-state implementation of a quantum computer composed entirely of
silicon is proposed. Qubits are Si-29 nuclear spins arranged as chains in a
Si-28 (spin-0) matrix with Larmor frequencies separated by a large magnetic
field gradient. No impurity dopants or electrical contacts are needed.
Initialization is accomplished by optical pumping, algorithmic cooling, and
pseudo-pure state techniques. Magnetic resonance force microscopy is used for
readout. This proposal takes advantage of many of the successful aspects of
solution NMR quantum computation, including ensemble measurement, RF control,
and long decoherence times, but it allows for more qubits and improved
initialization.Comment: ReVTeX 4, 5 pages, 2 figure
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