974 research outputs found
High purity nanoparticles exceed stoichiometry limits in rebox chemistry: the nano way to cleaner water
A potentially cheaper and more effective way of cleaning wastewater has been discovered by scientists
at Nazarbayev University and the University of Brighton researching nanotechnology [1]. It is well
established that when particles are reduced to the nanoscale unexpected effects occur. Silver, for example,
interacts with mercury ions in a fixed ratio of atoms (stoichiometry), typically 2:1, which presents a limit
that has never been exceeded. In this project we used an alternative chemical procedure based on modified
quartz sand to immobilise silver nanoparticles (NPs) with control over their size. We found that when the
size of the silver NPs decreased below 35 nm the amount of mercury ions reacting with silver increased
beyond the long-held limit and rose to a maximum of 1:1.2 for 10 nm sized silver
Topological susceptibility from the overlap
The chiral symmetry at finite lattice spacing of Ginsparg-Wilson fermionic
actions constrains the renormalization of the lattice operators; in particular,
the topological susceptibility does not require any renormalization, when using
a fermionic estimator to define the topological charge. Therefore, the overlap
formalism appears as an appealing candidate to study the continuum limit of the
topological susceptibility while keeping the systematic errors under
theoretical control. We present results for the SU(3) pure gauge theory using
the index of the overlap Dirac operator to study the topology of the gauge
configurations. The topological charge is obtained from the zero modes of the
overlap and using a new algorithm for the spectral flow analysis. A detailed
comparison with cooling techniques is presented. Particular care is taken in
assessing the systematic errors. Relatively high statistics (500 to 1000
independent configurations) yield an extrapolated continuum limit with errors
that are comparable with other methods. Our current value from the overlap is
\chi^{1/4} = 188 \pm 12 \pm 5 \MeV.Comment: 18 pages, 7 figure
High purity nanoparticles exceed stoichiometry limits in rebox chemistry: the nano way to cleaner water
A potentially cheaper and more effective way of cleaning wastewater has been discovered by scientists
at Nazarbayev University and the University of Brighton researching nanotechnology [1]. It is well
established that when particles are reduced to the nanoscale unexpected effects occur. Silver, for example,
interacts with mercury ions in a fixed ratio of atoms (stoichiometry), typically 2:1, which presents a limit
that has never been exceeded. In this project we used an alternative chemical procedure based on modified
quartz sand to immobilise silver nanoparticles (NPs) with control over their size. We found that when the
size of the silver NPs decreased below 35 nm the amount of mercury ions reacting with silver increased
beyond the long-held limit and rose to a maximum of 1:1.2 for 10 nm sized silver
Glueballs and k-strings in SU(N) gauge theories : calculations with improved operators
We test a variety of blocking and smearing algorithms for constructing
glueball and string wave-functionals, and find some with much improved overlaps
onto the lightest states. We use these algorithms to obtain improved results on
the tensions of k-strings in SU(4), SU(6), and SU(8) gauge theories. We
emphasise the major systematic errors that still need to be controlled in
calculations of heavier k-strings, and perform calculations in SU(4) on an
anisotropic lattice in a bid to minimise one of these. All these results point
to the k-string tensions lying part-way between the `MQCD' and `Casimir
Scaling' conjectures, with the power in 1/N of the leading correction lying in
[1,2]. We also obtain some evidence for the presence of quasi-stable strings in
calculations that do not use sources, and observe some near-degeneracies
between (excited) strings in different representations. We also calculate the
lightest glueball masses for N=2, ...,8, and extrapolate to N=infinity,
obtaining results compatible with earlier work. We show that the N=infinity
factorisation of the Euclidean correlators that are used in such mass
calculations does not make the masses any less calculable at large N.Comment: 49 pages, 15 figure
Low-Dimensional Long-Range Topological Charge Structure in the QCD Vacuum
While sign-coherent 4-dimensional structures cannot dominate topological
charge fluctuations in the QCD vacuum at all scales due to reflection
positivity, it is possible that enhanced coherence exists over extended
space-time regions of lower dimension. Using the overlap Dirac operator to
calculate topological charge density, we present evidence for such structure in
pure-glue SU(3) lattice gauge theory. It is found that a typical equilibrium
configuration is dominated by two oppositely-charged sign-coherent connected
structures (``sheets'') covering about 80% of space-time. Each sheet is built
from elementary 3-d cubes connected through 2-d faces, and approximates a
low-dimensional curved manifold (or possibly a fractal structure) embedded in
the 4-d space. At the heart of the sheet is a ``skeleton'' formed by about 18%
of the most intense space-time points organized into a global long-range
structure, involving connected parts spreading over maximal possible distances.
We find that the skeleton is locally 1-dimensional and propose that its
geometrical properties might be relevant for understanding the possible role of
topological charge fluctuations in the physics of chiral symmetry breaking.Comment: 4 pages RevTeX, 4 figures; v2: 6 pages, 5 figures, more explanations
provided, figure and references added, published versio
Quantum Dynamics of a Hydrogen Molecule Confined in a Cylindrical Potential
We study the coupled rotation-vibration levels of a hydrogen molecule in a
confining potential with cylindrical symmetry. We include the coupling between
rotations and translations and show how this interaction is essential to obtain
the correct degeneracies of the energy level scheme. We applied our formalism
to study the dynamics of H molecules inside a "smooth" carbon nanotube as
a function of tube radius. The results are obtained both by numerical solution
of the ()-component radial Schrodinger equation and by developing an
effective Hamiltonian to describe the splitting of a manifold of states of
fixed angular momentum and number of phonons, . For nanotube radius
smaller than \AA, the confining potential has a parabolic shape
and the results can be understood in terms of a simple toy model. For larger
radius, the potential has the "Mexican hat" shape and therefore the H
molecule is off-centered, yielding radial and tangential translational dynamics
in addition to rotational dynamics of H molecule which we also describe
by a simple model. Finally, we make several predictions for the the neutron
scattering observation of various transitions between these levels.Comment: 36 pages, 8 figures, submitted to Phys. Rev. B on 12 December 200
ChPT tests at the NA48 and NA62 experiments at CERN
The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of
rare kaon decays in the Ke4 modes: Ke4(+-) ()
and Ke4(00) () with nearly one percent
background contamination. The detailed study of form factors and branching
rates, based on these data, has been completed recently. The results brings new
inputs to low energy strong interactions description and tests of Chiral
Perturbation Theory (ChPT) and lattice QCD calculations. In particular, new
data support the ChPT prediction for a cusp in the invariant mass
spectrum at the two charged pions threshold for Ke4(00) decay. New final
results from an analysis of about 400 rare
decay candidates collected by the NA48/2 and NA62 experiments at CERN during
low intensity runs with minimum bias trigger configurations are presented. The
results include a model-independent decay rate measurement and fits to ChPT
description.Comment: XIIth International Conference on Heavy Quarks and Leptons 2014,
Mainz, German
Measurement of the branching ratio of the decay
From the 2002 data taking with a neutral kaon beam extracted from the
CERN-SPS, the NA48/1 experiment observed 97 candidates with a background contamination of events.
From this sample, the BR() is measured to be
Recent NA48/2 and NA62 results
The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented
statistics of rare kaon decays in the modes: () and ()
with nearly one percent background contamination. It leads to the improved
measurement of branching fractions and detailed form factor studies. New final
results from the analysis of 381 rare decay
candidates collected by the NA48/2 and NA62 experiments at CERN are presented.
The results include a decay rate measurement and fits to Chiral Perturbation
Theory (ChPT) description.Comment: Prepared for the Proceedings of "Moriond QCD and High Energy
Interactions. March 22-29 2014." conferenc
First Observation and Measurement of the Decay K+- -> pi+- e+ e- gamma
Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e-
gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7
estimated background events. With K+- -> pi+- pi0D as normalisation channel,
the branching ratio is determined in a model-independent way to be Br(K+- ->
pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x
10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass
allow a comparison with predictions of Chiral Perturbation Theory.Comment: 13 pages, 3 figures. Accepted for publication in Phys.Lett.
- …