8,835 research outputs found
Dimensional Reduction, Hard Thermal Loops and the Renormalization Group
We study the realization of dimensional reduction and the validity of the
hard thermal loop expansion for lambda phi^4 theory at finite temperature,
using an environmentally friendly finite-temperature renormalization group with
a fiducial temperature as flow parameter. The one-loop renormalization group
allows for a consistent description of the system at low and high temperatures,
and in particular of the phase transition. The main results are that
dimensional reduction applies, apart from a range of temperatures around the
phase transition, at high temperatures (compared to the zero temperature mass)
only for sufficiently small coupling constants, while the HTL expansion is
valid below (and rather far from) the phase transition, and, again, at high
temperatures only in the case of sufficiently small coupling constants. We
emphasize that close to the critical temperature, physics is completely
dominated by thermal fluctuations that are not resummed in the hard thermal
loop approach and where universal quantities are independent of the parameters
of the fundamental four-dimensional theory.Comment: 20 pages, 13 eps figures, uses epsfig and pstrick
Chlorinated auxinsâhow does Arabidopsis thaliana deal with them?
Plant hormones have various functions in plants and play crucial roles in all developmental and differentiation stages. Auxins constitute one of the most important groups with the major representative indole-3-acetic acid (IAA). A halogenated derivate of IAA, 4-chloro-indole-3-acetic acid (4-Cl-IAA), has previously been identified in Pisum sativum and other legumes. While the enzymes responsible for the halogenation of compounds in bacteria and fungi are well studied, the metabolic pathways leading to the production of 4-Cl-IAA in plants, especially the halogenating reaction, are still unknown. Therefore, bacterial flavin-dependent tryptophan-halogenase genes were transformed into the model organism Arabidopsis thaliana. The type of chlorinated indole derivatives that could be expected was determined by incubating wild type A. thaliana with different Cl-tryptophan derivatives. We showed that, in addition to chlorinated IAA, chlorinated IAA conjugates were synthesized. Concomitantly, we found that an auxin conjugate synthetase (GH3.3 protein) from A. thaliana was able to convert chlorinated IAAs to amino acid conjugates in vitro. In addition, we showed that the production of halogenated tryptophan (Trp), indole-3-acetonitrile (IAN) and IAA is possible in transgenic A. thaliana in planta with the help of the bacterial halogenating enzymes. Furthermore, it was investigated if there is an effect (i) of exogenously applied Cl-IAA and Cl-Trp and (ii) of endogenously chlorinated substances on the growth phenotype of the plants
Rapid purification of quantum systems by measuring in a feedback-controlled unbiased basis
Rapid-purification by feedback --- specifically, reducing the mean impurity
faster than by measurement alone --- can be achieved by making the eigenbasis
of the density matrix to be unbiased relative to the measurement basis. Here we
further examine the protocol introduced by Combes and Jacobs [Phys.Rev.Lett.
{\bf 96}, 010504 (2006)] involving continuous measurement of the observable
for a -dimensional system. We rigorously re-derive the lower bound
on the achievable speed-up factor, and also an upper bound, namely
, for all feedback protocols that use measurements in unbiased bases.
Finally we extend our results to independent measurements on a register of
qubits, and derive an upper bound on the achievable speed-up factor that
scales linearly with .Comment: v2: published versio
Entanglement in a molecular three-qubit system
We study the entanglement properties of a molecular three-qubit system
described by the Heisenberg spin Hamiltonian with anisotropic exchange
interactions and including an external magnetic field. The system exhibits
first order quantum phase transitions by tuning two parameters, and , of
the Hamiltonian to specific values. The three-qubit chain is open ended so that
there are two types of pairwise entanglement : nearest-neighbour (n.n.) and
next-nearest-neighbour (n.n.n.). We calculate the ground and thermal state
concurrences, quantifying pairwise entanglement, as a function of the
parameters , and the temperature . The entanglement threshold and gap
temperatures are also determined as a function of the anisotropy parameter .
The results obtained are of relevance in understanding the entanglement
features of the recently engineered molecular --
complex which serves as a three-qubit system at sufficiently low temperatures.Comment: 9 pages, 13 figures, revtex
Sustainable development as a framework for ethics and skills in higher education computing courses
The impact of sustainable development on the curriculum remains variable, and in some disciplines the inclusion is considered by some to be inappropriate or not relevant. This paper considers the ways in which sustainable development can be embedded within the curriculum, with the dual aims of showing how it can be made both relevant to students within the context of their discipline, and how sustainable development can provide a framework for developing an appreciation of the legal, social, ethical and professional (LSEP) aspects of the discipline and to develop awareness of sustainability values in students, i.e. the meaning and aspects of sustainable development. The paper focusses on a case study in embedding sustainable development within Computer Science degree programmes, where the LSEP requirements are recognised by accrediting bodies and by many employers as essential characteristics and skills in graduates. The paper will describe how sustainable development provides an overarching framework within which to explore these issues. Moreover, the paper will include some examples of how this is successful in engaging students who may otherwise struggle to appreciate the LSEP topics. The success will be demonstrated through some objective data showing the impact of this approach to students understanding and acknowledgment of sustainability and how this may be applied to other disciplines and national contexts
Short gamma-ray bursts within 200 Mpc
We present a systematic search for short-duration gamma-ray bursts (GRBs) in the local Universe based on 14âyr of observations with the Neil Gehrels Swift Observatory. We cross-correlate the GRB positions with the GLADE catalogue of nearby galaxies, and find no event at a distance âČ100 Mpc and four plausible candidates in the range 100âMpc âČ DââČ 200âMpc. Although affected by low statistics, this number is higher than the one expected for chance alignments to random galaxies, and possibly suggests a physical association between these bursts and nearby galaxies. By assuming a local origin, we use these events to constrain the range of properties for X-ray counterparts of neutron star mergers. Optical upper limits place tight constraints on the onset of a blue kilonova, and imply either low masses (â âČ10â3Mââ ) of lanthanide-poor ejecta or unfavorable orientations (Ξ_(obs) âł 30 deg). Finally, we derive that the all-sky rate of detectable short GRBs within 200 Mpc is 1.3^(+1.7)_(â0.8) yrâ»Âč (68 perâcent confidence interval), and discuss the implications for the GRB outflow structure. If these candidates are instead of cosmological origin, we set a upper limit of âČ2.0 yrâ»Âč (90 perâcent confidence interval) to the rate of nearby events detectable with operating gamma-ray observatories, such as Swift and Fermi
Fine Structure of the 1s3p ^3P_J Level in Atomic ^4He: Theory and Experiment
We report on a theoretical calculation and a new experimental determination
of the 1s3p ^3P_J fine structure intervals in atomic ^4He. The values from the
theoretical calculation of 8113.730(6) MHz and 658.801(6) MHz for the nu_{01}
and nu_{12} intervals, respectively, disagree significantly with previous
experimental results. However, the new laser spectroscopic measurement reported
here yields values of 8113.714(28) MHz and 658.810(18) MHz for these intervals.
These results show an excellent agreement with the theoretical values and
resolve the apparent discrepancy between theory and experiment.Comment: 9 pages, 3 figure
Overcoming synecdoche: why practice development and quality improvement approaches should be better integrated
Commentary on: Lavery, G. (2016) Quality improvement â rival or ally of practice development? International Practice Development Journal. Vol. 6. No. 1. Article 1
A Semantic-Based Method for Extracting Concept Definitions from Scientific Publications: Evaluation in the Autism Phenotype Domain
Background: A variety of informatics approaches have been developed that use information retrieval, NLP and text-mining techniques to identify biomedical concepts and relations within scientific publications or their sentences. These approaches have not typically addressed the challenge of extracting more complex knowledge such as biomedical definitions. In our efforts to facilitate knowledge acquisition of rule-based definitions of autism phenotypes, we have developed a novel semantic-based text-mining approach that can automatically identify such definitions within text.
Results: Using an existing knowledge base of 156 autism phenotype definitions and an annotated corpus of 26 source articles containing such definitions, we evaluated and compared the average rank of correctly identified rule definition or corresponding rule template using both our semantic-based approach and a standard term-based approach. We examined three separate scenarios: (1) the snippet of text contained a definition already in the knowledge base; (2) the snippet contained an alternative definition for a concept in the knowledge base; and (3) the snippet contained a definition not in the knowledge base. Our semantic-based approach had a higher average rank than the term-based approach for each of the three scenarios (scenario 1: 3.8 vs. 5.0; scenario 2: 2.8 vs. 4.9; and scenario 3: 4.5 vs. 6.2), with each comparison significant at the p-value of 0.05 using the Wilcoxon signed-rank test.
Conclusions: Our work shows that leveraging existing domain knowledge in the information extraction of biomedical definitions significantly improves the correct identification of such knowledge within sentences. Our method can thus help researchers rapidly acquire knowledge about biomedical definitions that are specified and evolving within an ever-growing corpus of scientific publications
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