2,007 research outputs found
Ion specificity and anomalous electrokinetic effects in hydrophobic nanochannels
We demonstrate with computer simulations that anomalous electrokinetic
effects, such as ion specificity and non-zero zeta potentials for uncharged
surfaces, are generic features of electro-osmotic flow in hydrophobic channels.
This behavior is due to the stronger attraction of larger ions to the
``vapour--liquid-like'' interface induced by a hydrophobic surface. An
analytical model involving a modified Poisson--Boltzmann description for the
ion density distributions is proposed, which allows the anomalous flow profiles
to be predicted quantitatively. This description incorporates as a crucial
component an ion-size-dependent hydrophobic solvation energy. These results
provide an effective framework for predicting specific ion effects, with
important implications for the modeling of biological problems
Exploring the volatile composition of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) with ALMA
Comets formed in the outer and cold parts of the disk which eventually
evolved into our Solar System. Assuming that the comets have undergone no major
processing, studying their composition provides insight in the pristine
composition of the Solar Nebula. We derive production rates for a number of
volatile coma species and explore how molecular line ratios can help constrain
the uncertainties of these rates. We analyse observations obtained with the
Atacama Large Millimetre/Submillimetre Array of the volatile composition of the
comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) at heliocentric
distances of ~1.45 AU and ~0.56 AU, respectively. Assuming a Haser profile with
constant outflow velocity, we model the line intensity of each transition using
a 3D radiative transfer code and derive molecular production rates and parent
scale lengths. We report the first detection of CS in comet ISON obtained with
the ALMA array and derive a parent scale length for CS of ~200 km. Due to the
high spatial resolution of ALMA, resulting in a synthesised beam with a size
slightly smaller than the derived parent scale length, we are able to
tentatively identify CS as a daughter species, i.e., a species produced in the
coma and/or sublimated from icy grains, rather than a parent species. In
addition we report the detection of several CH3OH transitions and confirm the
previously reported detections of HCN, HNC and H2CO as well as dust in the coma
of each comet, and report 3sigma upper limits for HCO+. We derive molecular
production rates relative to water of 0.2% for CS, 0.06-0.1% for HCN,
0.003-0.05% for HNC, 0.1-0.2% for H2CO and 0.5-1.0% for CH3OH, and show that
the modelling uncertainties due to unknown collision rates and kinematic
temperatures are modest and can be mitigated by available observations of
different transitions of HCN.Comment: 10 pages, 4 figures, 2 tables. Accepted for publication in A&
Nanoscale fluid flows in the vicinity of patterned surfaces
Molecular dynamics simulations of dense and rarefied fluids comprising small
chain molecules in chemically patterned nano-channels predict a novel switching
from Poiseuille to plug flow along the channel. We also demonstrate behavior
akin to the lotus effect for a nanodrop on a chemically patterned substrate.
Our results show that one can control and exploit the behavior of fluids at the
nanoscale using chemical patterning.Comment: Phys. Rev. Lett. in pres
Long-lived charged particles and multi-lepton signatures from neutrino mass models
Lepton number violation (LNV) is usually searched for by the LHC
collaborations using the same-sign di-lepton plus jet signature. In this paper
we discuss multi-lepton signals of LNV that can arise with experimentally
interesting rates in certain loop models of neutrino mass generation.
Interestingly, in such models the observed smallness of the active neutrino
masses, together with the high-multiplicity of the final states, leads in large
parts of the viable parameter space of such models to the prediction of
long-lived charged particles, that leave highly ionizing tracks in the
detectors. We focus on one particular 1-loop neutrino mass model in this class
and discuss its LHC phenomenology in some detail.Comment: 14 pages, 9 figure
Two-dimensional conical dispersion in ZrTe5 evidenced by optical spectroscopy
Zirconium pentatelluride was recently reported to be a 3D Dirac semimetal,
with a single conical band, located at the center of the Brillouin zone. The
cone's lack of protection by the lattice symmetry immediately sparked vast
discussions about the size and topological/trivial nature of a possible gap
opening. Here we report on a combined optical and transport study of ZrTe5,
which reveals an alternative view of electronic bands in this material. We
conclude that the dispersion is approximately linear only in the a-c plane,
while remaining relatively flat and parabolic in the third direction (along the
b axis). Therefore, the electronic states in ZrTe5 cannot be described using
the model of 3D Dirac massless electrons, even when staying at energies well
above the band gap 6 meV found in our experiments at low temperatures.Comment: Physical Review Letters 122, 217402 (2019). Corrected acknowledgment
Studies on the internalization mechanisms of cationic cell-penetrating peptides.
A great deal of data has been amassed suggesting that
cationic peptides are able to translocate into eucaryotic
cells in a temperature-independent manner. Although
such peptides are widely used to promote the intracellular delivery of bioactive molecules, the mechanism by
which this cell-penetrating activity occurs still remains
unclear. Here, we present an in vitro study of the cellular uptake of peptides, originally deriving from protegrin (the SynB peptide vectors), that have also been
shown to enhance the transport of drugs across the
blood-brain barrier. In parallel, we have examined the
internalization process of two lipid-interacting peptides, SynB5 and pAntp-(43â58), the latter corresponding to the translocating segment of the Antennapedia
homeodomain. We report a quantitative study of the
time- and dose-dependence of internalization and demonstrate that these peptides accumulate inside vesicular structures. Furthermore, we have examined the role
of endocytotic pathways in this process using a variety
of metabolic and endocytosis inhibitors. We show that
the internalization of these peptides is a temperatureand energy-dependent process and that endosomal
transport is a key component of the mechanism. Altogether, our results suggest that SynB and pAntp-(43â58)
peptides penetrate into cells by an adsorptive-mediated
endocytosis process rather than temperature-independent translocation
Low Friction Flows of Liquids at Nanopatterned Interfaces
With the recent important development of microfluidic systems,
miniaturization of flow devices has become a real challenge. Microchannels,
however, are characterized by a large surface to volume ratio, so that surface
properties strongly affect flow resistance in submicrometric devices. We
present here results showing that the concerted effect of wetting . properties
and surface roughness may considerably reduce friction of the fluid past the
boundaries. The slippage of the fluid at the channel boundaries is shown to be
drastically increased by using surfaces that are patterned at the nanometer
scale. This effect occurs in the regime where the surface pattern is partially
dewetted, in the spirit of the 'superhydrophobic' effects that have been
recently discovered at the macroscopic scales. Our results show for the first
time that, in contrast to the common belief, surface friction may be reduced by
surface roughness. They also open the possibility of a controlled realization
of the 'nanobubbles' that have long been suspected to play a role in
interfacial slippag
Disruption of Candida albicans IFF4 gene involves modifications of the cell electrical surface properties.
During the past two decades, the prevalence of candidiasis has increased markedly and Candida albicans has now become one of the most important causes of nosocomial infections, especially after colonization of inert surfaces such as catheters or prostheses. In a previous report, we demonstrated the overexpression of 35 unidentified genes in response to adherence of C. albicans germ tubes to plastic. Therefore, a bioinformatic analysis was performed searching for genes encoding surface proteins potentially involved in adherence. Nineteen genes were thus selected, and one of them, CaIFF4, was further investigated. The deduced protein of this CaIFF4 gene revealed a glycosylphosphatidylinositol (GPI)-anchored site as well as the presence of a N-terminal signal peptide. Disruption of both alleles of CaIFF4 gene from C. albicans parent strain BWP17 was performed by PCR method. Then investigations of properties of null mutant for CaIFF4 gene showed a decrease of adherence of germ tubes to plastic in comparison to the parent strain BWP17. Besides, electrophoretic mobilities of germ tubes of CaIFF4 null mutant and of parental strain BWP17 were measured. Data were then analysed with soft particles analysis theory. Results point out a less important electrophoretic mobility of germ tubes of CaIFF4 null mutant in comparison to germ tubes of BWP17 parental strain
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