987 research outputs found
Oxygen enhanced atomic chain formation
We report experimental evidence for atomic chain formation during stretching
of atomic-sized contacts for gold and silver, that is strongly enhanced due to
oxygen incorporation. While gold has been known for its tendency to form atomic
chains, for silver this is only observed in the presence of oxygen. With oxygen
the silver chains are as long as those for gold, but the conductance drops with
chain length to about 0.1 conductance quantum. A relation is suggested with
previous work on surface reconstructions for silver (110) surfaces after
chemisorption of oxygen.Comment: 4 pages, 4 figure
Vibrationally Induced Two-Level Systems in Single-Molecule Junctions
Single-molecule junctions are found to show anomalous spikes in dI/dV
spectra. The position in energy of the spikes are related to local vibration
mode energies. A model of vibrationally induced two-level systems reproduces
the data very well. This mechanism is expected to be quite general for
single-molecule junctions. It acts as an intrinsic amplification mechanism for
local vibration mode features and may be exploited as a new spectroscopic tool.Comment: 4 pages, 4 figure
Electrostatic potential between charged particles at an oil-water interface
Electrostatic interactions between point charges embedded into interfaces
separating dielectric media are omnipresent in soft matter systems and often
control their stability. Such interactions are typically complicated and do not
resemble their bulk counterparts. For instance, the electrostatic potential of
a point charge at an air-water interface falls off as , where is
the distance from the charge, exhibiting a dipolar behaviour. This behaviour is
often assumed to be generic, and is widely referred to when interpreting
experimental results. Here we explicitly calculate the in-plane potential of a
point charge at an interface between two electrolyte solutions with different
dielectric permittivities and Debye screening lengths. We show that the
asymptotic behaviour of this potential is neither a dipole, which characterises
the potential at air-water interfaces, nor a screened monopole, which describes
the bulk behaviour in a single electrolyte solution. By considering the same
problem in arbitrary dimensions, we find that the physics behind this
difference can be traced to the asymmetric propagation of the interaction in
the two media. Our results are relevant, for instance, to understand the
physics of charged colloidal particles trapped at oil-water interfaces.Comment: 11 pages, 7 figure
Emulsification in binary liquids containing colloidal particles: a structure-factor analysis
We present a quantitative confocal-microscopy study of the transient and
final microstructure of particle-stabilised emulsions formed via demixing in a
binary liquid. To this end, we have developed an image-analysis method that
relies on structure factors obtained from discrete Fourier transforms of
individual frames in confocal image sequences. Radially averaging the squared
modulus of these Fourier transforms before peak fitting allows extraction of
dominant length scales over the entire temperature range of the quench. Our
procedure even yields information just after droplet nucleation, when the
(fluorescence) contrast between the two separating phases is scarcely
discernable in the images. We find that our emulsions are stabilised on
experimental time scales by interfacial particles and that they are likely to
have bimodal droplet-size distributions. We attribute the latter to coalescence
together with creaming being the main coarsening mechanism during the late
stages of emulsification and we support this claim with (direct)
confocal-microscopy observations. In addition, our results imply that the
observed droplets emerge from particle-promoted nucleation, possibly followed
by a free-growth regime. Finally, we argue that creaming strongly affects
droplet growth during the early stages of emulsification. Future investigations
could clarify the link between quench conditions and resulting microstructure,
paving the way for tailor-made particle-stabilised emulsions from binary
liquids.Comment: http://iopscience.iop.org/0953-8984/22/45/455102
Image effects in transport at metal-molecule interfaces
We present a method for incorporating image-charge effects into the
description of charge transport through molecular devices. A simple model
allows us to calculate the adjustment of the transport levels, due to the
polarization of the electrodes as charge is added to and removed from the
molecule. For this, we use the charge distributions of the molecule between two
metal electrodes in several charge states, rather than in gas phase, as
obtained from a density-functional theory-based transport code. This enables us
to efficiently model level shifts and gap renormalization caused by
image-charge effects, which are essential for understanding molecular transport
experiments. We apply the method to benzene di-amine molecules and compare our
results with the standard approach based on gas phase charges. Finally, we give
a detailed account of the application of our approach to porphyrin-derivative
devices recently studied experimentally by Perrin et al. [Nat. Nanotechnol. 8,
282 (2013)], which demonstrates the importance of accounting for image-charge
effects when modeling transport through molecular junctions
Impulsive correction to the elastic moduli obtained using the stress-fluctuation formalism in systems with truncated pair potential
The truncation of a pair potential at a distance r_cut is well-known to imply
in general an impulsive correction to the pressure and other moments of the
first derivatives of the potential. That depending on r_cut the truncation may
also be of relevance to higher derivatives is shown theoretically for the Born
contributions to the elastic moduli obtained using the stress-fluctuation
formalism in d dimensions. Focusing on isotropic liquids for which the shear
modulus G must vanish by construction, the predicted corrections are tested
numerically for binary mixtures and polydisperse Lennard-Jones beads in,
respectively, d=3 and d=2 dimensions
Exploratory assessment of left ventricular strain-volume loops in severe aortic valve diseases.
Objectives The purpose of this study was to examine left ventricular (LV) strain (ԑ)-volume loops to provide novel insight into the haemodynamic cardiac consequences of aortic valve stenosis (AS) and aortic valve regurgitation (AR). Methods 27 participants were retrospectively recruited: AR (n = 7), AS (n = 10) and controls (n = 10). Standard transthoracic echocardiography was utilised to obtain apical 4 chamber images to construct ԑ-volume relationships were assessed by: Early systolic ԑ (ԑ_ES), slope of ԑ-volume relation during systole (Sslope), End-systolic peak ԑ (peak ԑ), Diastolic uncoupling (systolic ԑ-diastolic ԑ at same volume) during early diastole (UNCOUP_ED) and late diastole (UNCOUP_LD). ROC-curves were used to determine the ability to detect impaired LV function. Results Whilst LV ejection fraction was comparable between groups, longitudinal peak ԑ was similarly reduced compared to controls. In contrast, ԑ_ES and Sslope were lower in both pathologies compared to controls (P  0.05) to distinguish AS vs Controls, AR vs Controls and AS vs AR, respectively. Conclusions Temporal changes in ԑ-volume characteristics provide novel insight into the haemodynamic cardiac impact of AS and AR. Contrary to traditional measures (i.e. ejection fraction, peak ԑ), these novel measures successfully distinguish between the haemodynamic cardiac impact of AS and AR. This article is protected by copyright. All rights reserved
Effects of acute exercise on cutaneous thermal sensation
The aim of this study was to assess the effect of exercise intensity on thermal sensory function of active and inactive limbs. In a randomised and counterbalanced manner 13 healthy young male participants (25±6 yr, 1.8±0.1 m, 77±6 kg) conducted; 1) 30 minutes low (50% heart rate maximum, HRmax; LOW) intensity, 2) 30 minutes high (80% HRmax; HIGH) intensity cycling exercise and 3) 30 minutes seated rest (CONTROL). Before, immediately and 1-hour after each intervention thermal sensory function of the non-dominant dorsal forearm and posterior calf were examined by increasing local skin temperature (1°C/s) to assess perceptual heat sensitivity and pain thresholds. Relative to pre-exercise, forearm heat sensitivity thresholds were increased immediately and 1-hr after HIGH but there were no changes after LOW exercise or during CONTROL (main effect of trial; P=0.017). Relative to pre-exercise, calf heat sensitivity thresholds were not changed after LOW or HIGH exercise or during CONTROL (main effect of trial; P=0.629). There were no changes in calf (main effect of trial; P=0.528) or forearm (main effect of trial; P=0.088) heat pain thresholds after exercise in either LOW or HIGH or CONTROL. These results suggest that cutaneous thermal sensitivity function of an inactive limb is only reduced after higher intensity exercise but is not changed in a previously active limb after exercise. Exercise does not affect heat pain sensitivity in either active or inactive limbs
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
- …