495 research outputs found
Influence of a Point-to-Plane DC Negative Corona Discharge on Gel Surfaces
Point-to-plane corona discharge is widely used for modifying polymer surfaces for biomedical applications and for sterilization and decontamination. This paper focuses on an experimental investigation of the influence of the single-point and multi-point corona discharge electric field on gel surface. Three types of gelatinous agar were used as the gel medium: blood agar, nutrient agar and Endo agar. The gel surface modification was studied for various time periods and discharge currents.
An Unfolded Quantization for Twisted Hopf Algebras
In this talk I discuss a recently developed "Unfolded Quantization
Framework". It allows to introduce a Hamiltonian Second Quantization based on a
Hopf algebra endowed with a coproduct satisfying, for the Hamiltonian, the
physical requirement of being a primitive element. The scheme can be applied to
theories deformed via a Drinfeld twist. I discuss in particular two cases: the
abelian twist deformation of a rotationally invariant nonrelativistic Quantum
Mechanics (the twist induces a standard noncommutativity) and the Jordanian
twist of the harmonic oscillator. In the latter case the twist induces a Snyder
non-commutativity for the space-coordinates, with a pseudo-Hermitian deformed
Hamiltonian. The "Unfolded Quantization Framework" unambiguously fixes the
non-additive effective interactions in the multi-particle sector of the
deformed quantum theory. The statistics of the particles is preserved even in
the presence of a deformation.Comment: 9 pages. Talk given at QTS7 (7th Int. Conf. on Quantum Theory and
Symmetries, Prague, August 2011
An investigation of the circumgalactic medium around z~2.2 AGN with ACA and ALMA
While observations of molecular gas at cosmic noon and beyond have focused on
the gas within galaxies (i.e., the interstellar medium; ISM), it is also
crucial to study the molecular gas reservoirs surrounding each galaxy (i.e., in
the circumgalactic medium; CGM). Recent observations of galaxies and quasars
hosts at high redshift (z>2) have revealed evidence for cold gaseous halos of
scale r_CGM~10kpc, with one discovery of a molecular halo with r_CGM~200kpc and
a molecular gas mass one order of magnitude larger than the ISM of the central
galaxy. As a follow-up, we present deep ACA and ALMA observations of CO(3-2)
from this source and two other quasar host galaxies at z~2.2. While we find
evidence for CO emission on scales of r~10kpc, we do not find evidence for
molecular gas on scales larger than r>20 kpc. Therefore, our deep data do not
confirm the existence of massive molecular halos on scales of ~100 kpc for
these X-ray selected quasars. As an interesting by-product of our deep
observations, we obtain the tentative detection of a negative continuum signal
on scales larger than r>200kpc, which might be tracing the Sunyaev-Zeldovich
effect associated with the halo heated by the active galactic nucleus (AGN). If
confirmed with deeper data, this could be direct evidence of the preventive AGN
feedback process expected by cosmological simulations.Comment: 17 pages, 12 figures. Accepted for publication in MNRA
Cu Nuclear Quadrupole Resonance Study of Site-Disorder and Chemical Pressure Effects on Y(Ba1-xSrx)2Cu4O8
We report a zero-field Cu nuclear quadrupole resonance (NQR) study on the
effects of nonmagnetic Sr substitution for high-Tc superconductors,
Y(Ba1-xSrx)2Cu4O8 (Tc=82-80 K for x=0-0.4), using a spin-echo technique. The
site-disordering and chemical pressure effects associated with doping Sr were
observed in the broadened, shifted Cu NQR spectra. Nevertheless, the site
disorder did not significantly affect the homogeneity of Cu electron spin
dynamics, in contrast to the in-plane impurity. The peak shift of Cu NQR
spectrum due to Sr was different between the chain- and the plane-Cu sites,
more remarkably than those under a hydrostatic physical pressure, suggesting
anisotropic or nonuniform local structural strains. The small decrease of Tc
due to Sr can be traced back to either a cancellation effect on Tc between the
disorder and the pressure, or an anisotropic or nonuniform chemical pressure
effect on Tc.Comment: 4 pages, 5 figure
Formation of helical states in wormlike polymer chains
We propose a potential for wormlike polymer chains which can be used to model
the low-temperature conformational structures. We successfully reproduced helix
ground states up to 6.5 helical loops, using the multicanonical Monte Carlo
simulation method. We demonstrate that the coil-helix transition involves four
distinct phases: coil(gaslike), collapsed globular(liquidlike), and two helical
phases I and II (both solidlike). The helix I phase is characterized by a
helical structure with dangling loose ends, and the helix II phase corresponds
to a near perfect helix ordering in the entire crystallized chain.Comment: 5 pages, 2 figures, Submitted to PR
Krein-Space Formulation of PT-Symmetry, CPT-Inner Products, and Pseudo-Hermiticity
Emphasizing the physical constraints on the formulation of a quantum theory
based on the standard measurement axiom and the Schroedinger equation, we
comment on some conceptual issues arising in the formulation of PT-symmetric
quantum mechanics. In particular, we elaborate on the requirements of the
boundedness of the metric operator and the diagonalizability of the
Hamiltonian. We also provide an accessible account of a Krein-space derivation
of the CPT-inner product that was widely known to mathematicians since 1950's.
We show how this derivation is linked with the pseudo-Hermitian formulation of
PT-symmetric quantum mechanics.Comment: published version, 17 page
Testing earthquake links in Mexico from 1978 to the 2017 M = 8.1 Chiapas and M = 7.1 Puebla Shocks
The M = 8.1 Chiapas and the M = 7.1 Puebla earthquakes occurred in the bending part of the
subducting Cocos plate 11 days and ~600 km apart, a range that puts them well outside the typical
aftershock zone. We find this to be a relatively common occurrence in Mexico, with 14% of M > 7.0
earthquakes since 1900 striking more than 300 km apart and within a 2 week interval, not different from a
randomized catalog. We calculate the triggering potential caused by crustal stress redistribution from large
subduction earthquakes over the last 40 years. There is no evidence that static stress transfer or dynamic
triggering from the 8 September Chiapas earthquake promoted the 19 September earthquake. Both recent
earthquakes were promoted by past thrust events instead, including delayed afterslip from the 2012 M = 7.5
Oaxaca earthquake. A repeated pattern of shallow thrust events promoting deep intraslab earthquakes is
observed over the past 40 years
Non-perturbative flow equations from continuous unitary transformations
We use a novel parameterization of the flowing Hamiltonian to show that the
flow equations based on continuous unitary transformations, as proposed by
Wegner, can be implemented through a nonlinear partial differential equation
involving one flow parameter and two system specific auxiliary variables. The
implementation is non-perturbative as the partial differential equation
involves a systematic expansion in fluctuations, controlled by the size of the
system, rather than the coupling constant. The method is applied to the Lipkin
model to construct a mapping which maps the non-interacting spectrum onto the
interacting spectrum to a very high accuracy. This function is universal in the
sense that the full spectrum for any (large) number of particles can be
obtained from it. In a similar way expectation values for a large class of
operators can be obtained, which also makes it possible to probe the stucture
of the eigenstates.Comment: 24 pages, 13 figure
Supplement 1) Peer-reviewed paper
Abstract The FAO publication, Livestock's Long Shadow, indicated that livestock is responsible for 18% of the world's greenhouse gas production thereby creating the perception that livestock is a major cause of global warming. Methane (CH 4 ) makes up 16% of total world gas emissions and is the second most important greenhouse gas (GHG) after carbon dioxide (CO 2 ). Ruminants are important to mankind since most of the world's vegetation biomass is rich in fibre and only ruminants can convert this vegetation into high quality protein sources for human consumption. In spite of this important role of livestock, it is singled out as producing large quantities of GHG that contribute to climate change, since enteric fermentation is responsible for 28% of global CH 4 emissions. However, the net effect from livestock is only a 4.5% contribution to GHG. The livestock industry should be aware of the effect of livestock on climate change and therefore it is important that mechanisms are put in place to mitigate this effect. The improvement of production efficiency through increased production per constant unit, crossbreeding and genetic improvement may be a cost effective and permanent way of reducing the carbon footprint of beef cattle. _______________________________________________________________________________
Assessment of the repeatability of pubic and ischial measurements
Forensic anthropologists frequently use measurements of the human skeleton to
determine sex and ancestry. Since the establishment of the Daubert criteria of
admissibility of scientific evidence to court, methodologies used by anthropologists came
under severe scrutiny. It is therefore important to ensure that the osteometric standards
that are used in skeletal analyses are clearly explained, repeatable and reliable. Adams
and Byrd (2002) found that measurements of the pelvis that originated from a point inside
the acetabulum could not be repeated accurately. The purpose of this paper was to use
three different sets of pubic and ischial measurements to establish whether they can be
repeated with high precision between four different observers, and also by the observers
themselves. Generally, high levels of repeatability were obtained, with intra-class
correlations (ICC) above 0.8. Pubic and ischial measurements using a point in the
acetabulum as origin performed the worst (ICC values of 0.82 and 0.79 respectively for
inter-observer repeatability), whereas other methods performed better with ICC values
above 0.9. It is advised that pubic and ischial measurements should be taken using the
origin of the iliac blade as landmark.The research of M Steyn and EN L’Abbé is funded by the National Research Foundation
of South Africa (NRF).http://www.elsevier.com/locate/forsciin
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