796 research outputs found
Nanofriction mechanisms derived from the dependence of friction on load and sliding velocity from air to UHV on hydrophilic silicon
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
Impact of DOTA Conjugation on Pharmacokinetics and Immunoreactivity of [177Lu]Lu-1C1m-Fc, an Anti TEM-1 Fusion Protein Antibody in a TEM-1 Positive Tumor Mouse Model.
1C1m-Fc, an anti-tumor endothelial marker 1 (TEM-1) scFv-Fc fusion protein antibody, was previously successfully radiolabeled with <sup>177</sup> Lu. TEM-1 specific tumor uptake was observed together with a non-saturation dependent liver uptake that could be related to the number of dodecane tetraacetic acid (DOTA) chelator per 1C1m-Fc. The objective of this study was to verify this hypothesis and to find the best DOTA per 1C1m-Fc ratio for theranostic applications. 1C1m-Fc was conjugated with six concentrations of DOTA. High-pressure liquid chromatography, mass spectrometry, immunoreactivity assessment, and biodistribution studies in mice bearing TEM-1 positive tumors were performed. A multi-compartment pharmacokinetic model was used to fit the data and a global pharmacokinetic model was developed to illustrate the effect of liver capture and immunoreactivity loss. Organ absorbed doses in mice were calculated from biodistribution results. A loss of immunoreactivity was observed with the highest DOTA per 1C1m-Fc ratio. Except for the spleen and bone, an increase of DOTA per 1C1m-Fc ratio resulted in an increase of liver uptake and absorbed dose and a decrease of uptake in tumor and other tissues. Pharmacokinetic models correlated these results. The number of DOTA per antibody played a determining role in tumor targeting. One DOTA per 1C1m-Fc gave the best pharmacokinetic behavior for a future translation of [ <sup>177</sup> Lu]Lu-1C1m-Fc in patients
Predicting local and non-local effects of resources on animal space use using a mechanistic step selection model
1. Predicting space use patterns of animals from their interactions with the
environment is fundamental for understanding the effect of habitat changes on
ecosystem functioning. Recent attempts to address this problem have sought to
unify resource selection analysis, where animal space use is derived from
available habitat quality, and mechanistic movement models, where detailed
movement processes of an animal are used to predict its emergent utilization
distribution. Such models bias the animal's movement towards patches that are
easily available and resource-rich, and the result is a predicted probability
density at a given position being a function of the habitat quality at that
position. However, in reality, the probability that an animal will use a patch
of the terrain tends to be a function of the resource quality in both that
patch and the surrounding habitat. 2. We propose a mechanistic model where this
non-local effect of resources naturally emerges from the local movement
processes, by taking into account the relative utility of both the habitat
where the animal currently resides and that of where it is moving. We give
statistical techniques to parametrize the model from location data and
demonstrate application of these techniques to GPS data of caribou in
Newfoundland. 3. Steady-state animal probability distributions arising from the
model have complex patterns that cannot be expressed simply as a function of
the local quality of the habitat. In particular, large areas of good habitat
are used more intensively than smaller patches of equal quality habitat,
whereas isolated patches are used less frequently. 4. Whilst we focus on
habitats in this study, our modelling framework can be readily used with any
environmental covariates and therefore represents a unification of mechanistic
modelling and step selection approaches to understanding animal space use
A lattice calculation of vector meson couplings to the vector and tensor currents using chirally improved fermions
We present a quenched lattice calculation of , the coupling of
vector mesons to the tensor current normalized by the vector meson decay
constant. The chirally improved lattice Dirac operator, which allows us to
reach small quark masses, is used. We put emphasis on analyzing the quark mass
dependence of and find only a rather weak dependence. Our
results at the and masses agree well with QCD sum rule
calculations and those from previous lattice studies.Comment: 6 pages, 3 figures, one sentence remove
Refining human palaeodietary reconstruction using amino acid delta N-15 values of plants, animals and humans.
An established method of estimating the trophic level of an organism is through stable isotope analysis of
its tissues and those of its diet. This method has been used in archaeology to reconstruct past human diet
from the stable nitrogen isotope (d15N) values of human and herbivore bone collagen. However, this
approach, using the 15N-enrichment of human bone collagen d15N values over associated herbivore bone
collagen d15N values to predict the relative importance of animal protein, relies on the assumptions that:
(i) the d15N values of plants consumed by humans and herbivores are identical, and (ii) the 15Nenrichment
between diet and consumer is consistent. Bone collagen amino acid d15N values have the
potential to tackle these uncertainties, as they constrain the factors influencing bone collagen d15N
values. In this study, the d15N values of glutamic acid and phenylalanine in human and herbivore bone
collagen isolates from Neolithic sites in Germany, Greece and Turkey were determined by gas
chromatography-combustion-isotope ratio mass spectrometry. The fraction of animal protein in total
dietary protein consumed by the humans was estimated by: (i) comparing bulk human and herbivore
collagen d15N values, (ii) comparing bulk human and herbivore collagen and ancient charred cereal grain
d15N values, (iii) comparing human bone collagen d15NGlutamic acid and d15NPhenylalanine values, and (iv)
comparing d15NGlutamic acid values of human and herbivore bone collagen and estimated d15NGlutamic acid
values of ancient charred cereal grains. Where determined cereal grain d15N values are higher than
estimated herbivore forage values, estimates of animal protein consumption are significantly lower,
emphasising the importance of the plant nitrogen contribution to human bone collagen. This study also
highlights the need for further investigation into: (i) the D15NConsumer-Diet values of glutamic acid and
phenylalanine in terrestrial ecosystems, and (ii) D15NGlutamic acid-Phenylalanine values of common plant foods
in order to improve the accuracy and more widespread applicability of amino acid-based methods for
palaeodietary reconstruction
Constraining warm dark matter with cosmic shear power spectra
We investigate potential constraints from cosmic shear on the dark matter
particle mass, assuming all dark matter is made up of light thermal relic
particles. Given the theoretical uncertainties involved in making cosmological
predictions in such warm dark matter scenarios we use analytical fits to linear
warm dark matter power spectra and compare (i) the halo model using a mass
function evaluated from these linear power spectra and (ii) an analytical fit
to the non-linear evolution of the linear power spectra. We optimistically
ignore the competing effect of baryons for this work. We find approach (ii) to
be conservative compared to approach (i). We evaluate cosmological constraints
using these methods, marginalising over four other cosmological parameters.
Using the more conservative method we find that a Euclid-like weak lensing
survey together with constraints from the Planck cosmic microwave background
mission primary anisotropies could achieve a lower limit on the particle mass
of 2.5 keV.Comment: 26 pages, 9 figures, minor changes to match the version accepted for
publication in JCA
Topological and geometrical restrictions, free-boundary problems and self-gravitating fluids
Let (P1) be certain elliptic free-boundary problem on a Riemannian manifold
(M,g). In this paper we study the restrictions on the topology and geometry of
the fibres (the level sets) of the solutions f to (P1). We give a technique
based on certain remarkable property of the fibres (the analytic representation
property) for going from the initial PDE to a global analytical
characterization of the fibres (the equilibrium partition condition). We study
this analytical characterization and obtain several topological and geometrical
properties that the fibres of the solutions must possess, depending on the
topology of M and the metric tensor g. We apply these results to the classical
problem in physics of classifying the equilibrium shapes of both Newtonian and
relativistic static self-gravitating fluids. We also suggest a relationship
with the isometries of a Riemannian manifold.Comment: 36 pages. In this new version the analytic representation hypothesis
is proved. Please address all correspondence to D. Peralta-Sala
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201
Planck scale effects in neutrino physics
We study the phenomenology and cosmology of the Majoron (flavon) models of
three active and one inert neutrino paying special attention to the possible
(almost) conserved generalization of the Zeldovich-Konopinski-Mahmoud lepton
charge. Using Planck scale physics effects which provide the breaking of the
lepton charge, we show how in this picture one can incorporate the solutions to
some of the central issues in neutrino physics such as the solar and
atmospheric neutrino puzzles, dark matter and a 17 keV neutrino. These
gravitational effects induce tiny Majorana mass terms for neutrinos and
considerable masses for flavons. The cosmological demand for the sufficiently
fast decay of flavons implies a lower limit on the electron neutrino mass in
the range of 0.1-1 eV.Comment: 24 pages, 1 figure (not included but available upon request), LaTex,
IC/92/196, SISSA-140/92/EP, LMU-09/9
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