3,588 research outputs found
Simplex solid states of SU(N) quantum antiferromagnets
I define a set of wavefunctions for SU(N) lattice antiferromagnets, analogous
to the valence bond solid states of Affleck, Kennedy, Lieb, and Tasaki (AKLT),
in which the singlets are extended over N-site simplices. As with the valence
bond solids, the new simplex solid (SS) states are extinguished by certain
local projection operators, allowing us to construct Hamiltonians with local
interactions which render the SS states exact ground states. Using a coherent
state representation, we show that the quantum correlations in each SS state
are calculable as the finite temperature correlations of an associated
classical model, with N-spin interactions, on the same lattice. In three and
higher dimensions, the SS states can spontaneously break SU(N) and exhibit
N-sublattice long-ranged order, as a function of a discrete parameter which
fixes the local representation of SU(N). I analyze this transition using a
classical mean field approach. For N>2 the ordered state is selected via an
"order by disorder" mechanism. As in the AKLT case, the bulk representations
fractionalize at an edge, and the ground state entropy is proportional to the
volume of the boundary.Comment: 14 pages, 8 figures, minor typos correcte
Evaluation of Three Rapid Tests for Diagnosis of P. Falciparum and P. Vivax Malaria in Colombia.
The diagnostic capacity of three malaria rapid diagnostic tests (RDTs), NOW-Malaria-ICT, OptiMAL-IT, and Paracheck-Pf, was evaluated against expert microscopy in Colombia. We tested 896 patients, of whom microscopy confirmed 139 P. falciparum, 279 P. vivax, and 13 mixed P.f/P.v infections and 465 negatives. Paracheck-Pf and NOW-malaria-ICT were more accurate in detecting P. falciparum (sensitivities 90.8% and 90.1%, respectively) in comparison with Optimal-IT (83.6%). NOW showed an acceptable Pf detection rate at low densities (< 500/microL), but resulted in a higher proportion of false positives. For P. vivax diagnosis, Optimal-IT had a higher sensitivity than NOW (91.0% and 81.4%, respectively). The choice between the two Pf/Pv detecting RDTs balances P. falciparum and P. vivax detection rates. Considering some degree of P. falciparum overtreatment and failure to detect all P. vivax cases as more acceptable than missing some cases of P. falciparum, we recommend careful implementation of NOW-malaria-ICT in areas where microscopy is lacking. The price is however still a constraint
Exact dimer ground states for a continuous family of quantum spin chains
Using the matrix product formalism, we define a multi-parameter family of
spin models on one dimensional chains, with nearest and next-nearest neighbor
anti-ferromagnetic interaction for which exact analytical expressions can be
found for its doubly degenerate ground states. The family of Hamiltonians which
we define, depend on 5 continuous parameters and the Majumdar-Ghosh model is a
particular point in this parameter space. Like the Majumdar-Ghosh model, the
doubly degenerate ground states of our models have a very simple structure,
they are the product of entangled states on adjacent sites. In each of these
states there is a non-zero staggered magnetization, which vanishes when we take
their translation-invariant combination as the new ground states. At the
Majumdar-Ghosh point, these entangled states become the spin-singlets
pertaining to this model. We will also calculate in closed form the two point
correlation functions, both for finite size of the chain and in the
thermodynamic limit.Comment: 11 page
Characterization of hemodialysis membranes by inverse size exclusion chromatography
Inverse size exclusion chromatography (i-SEC) was used to characterize three different cellulosic hollow fiber hemodialysis membranes, i.e. low-flux cuprophan and hemophan and high-flux RC-HP400A. With the i-SEC technique the pore size distribution and porosity of a membrane can be determined and adsorption phenomena can be studied. The membranes showed clear differences in pore size and porosity, the high-flux RC-HP400A membrane has a larger pore size as well as a higher porosity. For all the membranes it was found that the elution curves were best described by a homoporous pore volume distribution. It appeared that the bound or non-freezing water in the membranes was at least partly accessible to solutes. The test molecules creatinine and vitamin B 12 both adsorbed to the cellulosic membranes. The adsorption behavior of creatinine was strongly dependent on the NaCl concentration present. The observations could be explained by assuming that cuprophan and RC-HP400A are negatively charged whereas hemophan is positively charged due to the modification with N,N-diethylaminoethyl ether. The net charge of the hemophan is smaller
Automated Dynamic Error Analysis Methods for Optimization of Computer Arithmetic Systems
Computer arithmetic is one of the more important topics within computer science and engineering. The earliest implementations of computer systems were designed to perform arithmetic operations and cost if not all digital systems will be required to perform some sort of arithmetic as part of their normal operations. This reliance on the arithmetic operations of computers means the accurate representation of real numbers within digital systems is vital, and an understanding of how these systems are implemented and their possible drawbacks is essential in order to design and implement modern high performance systems. At present the most widely implemented system for computer arithmetic is the IEEE754 Floating Point system, while this system is deemed to the be the best available implementation it has several features that can result in serious errors of computation if not implemented correctly. Lack of understanding of these errors and their effects has led to real world disasters in the past on several occasions. Systems for the detection of these errors are highly important and fast, efficient and easy to use implementations of these detection systems is a high priority. Detection of floating point rounding errors normally requires run-time analysis in order to be effective. Several systems have been proposed for the analysis of floating point arithmetic including Interval Arithmetic, Affine Arithmetic and Monte Carlo Arithmetic. While these systems have been well studied using theoretical and software based approaches, implementation of systems that can be applied to real world situations has been limited due to issues with implementation, performance and scalability. The majority of implementations have been software based and have not taken advantage of the performance gains associated with hardware accelerated computer arithmetic systems. This is especially problematic when it is considered that systems requiring high accuracy will often require high performance. The aim of this thesis and associated research is to increase understanding of error and error analysis methods through the development of easy to use and easy to understand implementations of these techniques
Mechanics of cooling liquids by forced evaporation in bubbles
Injecting a non-dissolvable gas into a saturated liquid results in
sub-cooling of the liquid due to forced evaporation into the bubble. Previous
studies assumed the rate of evaporation of liquid into the bubble to be
independent of the degree of sub-cooling. In our study we quantify the bubble
growth by direct observation using high speed imaging and prove that this
hypothesis is not true. A phenomenological model of the bubble growth as a
function of the degree of sub-cooling is developed and we find excellent
agreement between the measurements and theory. This bubble cooling process is
employed in cooling a liquid. By identification of all heat flows, we can well
describe the cool down curve using bubble cooling. Bubble cooling provides an
alternative cooling method for liquids without the use of complicated cooling
techniques
Current ethical issues in synthetic biology: Where should we go from here?
Synthetic Biology (SynBio) is an emerging scientific field which has quickly established momentum
and visibility. Although no single definition of SynBio prevails, the field broadly encompasses the
application of engineering principles to biology; re-designing biological materials and using them as
new substrates to create products and entities not otherwise found in nature. This paper first
reviews SynBio, highlighting the novel aspects of this technology. It then synthesises ethical issues
highlighted in the literature to date and makes some initial claims that research on the ethical
aspects of SynBio should: avoid creating a new sub-type of bioethics, concentrate on novel concepts
and problems and be situated within a context of cooperative inter-disciplinary investigation.
Keywords: Synthetic biology, ethical issues, regulation, creating life.This article was written by Dr Ainsley Newson during the time of her employment with the University of Bristol, UK (2006-2012). Self-archived in the Sydney eScholarship Repository with permission of Bristol University, Sept 2014
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