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A G Green

Publications and source records attributed to A G Green.

At least 19 recordsLinked to original sources
PubMed2006

Current noise in the vicinity of the 2D superconductor-insulator quantum critical point.

Systems near to quantum critical points show universal scaling in response to external probes. We consider whether this scaling is reflected in their out-of-equilibrium fluctuations. We study current noise in the metallic state at the z=1 quantum critical point between a superconductor and an insulator in two dimensions. Using a Boltzmann-Langevin approach within a 1/N expansion, we show that the current noise obeys a universal scaling form S_{j}=TPhi[T/T_{eff}(E)], with T_{eff} proportional, variantsqrt[E]. This treatment recovers Johnson noise in thermal equilibrium and S_{j} proportional, variantsqrt[E] at strong electric fields. The latter differs significantly from both the shot noise in conventional metals (diffusive Fermi liquids) and the free carrier result, due to strong correlations between the critical bosonic excitations. Current-noise measurements could therefore help clarify the physics of the destruction of superconductivity in thin film superconductors.

Journal Article↗
PubMed2005

Nonlinear quantum critical transport and the Schwinger mechanism for a superfluid-mott-insulator transition of bosons.

Scaling arguments imply that quantum-critical points exhibit universal nonlinear responses to external probes. We investigate the origins of such nonlinearities in transport, which is especially problematic since the system is necessarily driven far from equilibrium. We argue that for a wide class of systems the new ingredient that enters is the Schwinger mechanism--the production of carriers from the vacuum by the applied field--which is then balanced against a scattering rate that is itself set by the field. We show by explicit computation how this works for the case of the symmetric superfluid-Mott insulator transition of bosons.

Journal Article↗
PubMed2005

Phase bifurcation and quantum fluctuations in Sr3Ru2O7.

The bilayer ruthenate Sr3Ru2O7 has been cited as a textbook example of itinerant metamagnetic quantum criticality. However, recent studies of the ultrapure system have revealed striking anomalies in magnetism and transport in the vicinity of the quantum critical point. Drawing on fresh experimental data, we show that the complex phase behavior reported here can be fully accommodated within the framework of a simple Landau theory. We discuss the potential physical mechanisms that underpin the phenomenology, and assess the capacity of the ruthenate system to realize quantum tricritial behavior.

Journal Article↗
PubMed2004

Disorder-sensitive phase formation linked to metamagnetic quantum criticality.

Condensed systems of strongly interacting electrons are ideal for the study of quantum complexity. It has become possible to promote the formation of new quantum phases by explicitly tuning systems toward special low-temperature quantum critical points. So far, the clearest examples have been appearances of superconductivity near pressure-tuned antiferromagnetic quantum critical points. We present experimental evidence for the formation of a nonsuperconducting phase in the vicinity of a magnetic field-tuned quantum critical point in ultrapure crystals of the ruthenate metal Sr3Ru2O7, and we discuss the possibility that the observed phase is due to a spin-dependent symmetry-breaking Fermi surface distortion.

Journal Article↗
PubMed2003

Effect of chromatic dispersion on nonlinear phase noise.

We consider the combined effects of amplified spontaneous emission noise, optical Kerr nonlinearity, and chromatic dispersion on phase noise in an optical communication system. The effect of amplified spontaneous emission noise and Kerr nonlinearity were considered previously by Gordon and Mollenauer [Opt. Lett. 15, 1351 (1990)], and the effect of nonlinearity was found to be severe. We investigate the effect of chromatic dispersion on phase noise and show that it can either enhance or suppress the nonlinear noise amplification. For large absolute values of dispersion the nonlinear effect is suppressed, and the phase noise is reduced to its linear value. For a range of negative values of dispersion, however, nonlinear phase noise is enhanced and exhibits a maximum related to the modulation instability found in amplitude fluctuations. Nonlinear phase noise is quenched by these effects even in dispersion-compensated systems; the degree of suppression is sensitively dependent on the dispersion map. We demonstrate these results analytically with a simple linearized model.

Journal Article↗
PubMed2003

Germline hMLH1 promoter mutation in a Newfoundland HNPCC kindred.

Hereditary non-polyposis colon cancer (HNPCC) is an autosomal dominant form of inherited predisposition to colorectal and other malignancies. It is associated with mutations in DNA mismatch-repair genes, especially hMSH2 and hMLH1. Management of HNPCC families is improved if the underlying mutation in each family can be discovered. We describe a Newfoundland kindred, meeting the Amsterdam Criteria for HNPCC, in which a mutation in the promoter region of the hMLH1 gene co-segregates with the disease phenotype. The -42C > T mutation is within a putative Myb proto-oncogene binding site. Using electrophoretic mobility shift assays, we demonstrated that the mutated Myb binding sequence is less effective in binding nuclear proteins than the wild-type promoter sequence. Using in vivo transfection experiments in HeLa cells, we further demonstrated that the mutated promoter has only 37% of the activity of the wild-type promoter in driving the expression of a reporter gene. The average age of onset in six family members affected with colorectal cancer is 62 years, which is substantially later than the typical age of onset in HNPCC families. This is consistent with a substantial decrease, but not total elimination, of mismatch repair function in affected members of this family. This is the first report of a heritable hMLH1 promoter mutation in any HNPCC family.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Schrödinger equation with a spatially and temporally random potential: effects of cross-phase modulation in optical communication.

We model the effects of cross-phase modulation in frequency (or wavelength) division multiplexed optical communications systems, using a Schrödinger equation with a spatially and temporally random potential. Green's functions for the propagation of light in this system are calculated using Feynman path-integral and diagrammatic techniques. This propagation leads to a non-Gaussian joint distribution of the input and output optical fields. We use these results to determine the amplitude and timing jitter of a signal pulse and to estimate the system capacity in analog communication.

Journal Article↗
PubMed2001

Construct design for efficient, effective and high-throughput gene silencing in plants.

Post-transcriptional silencing of plant genes using anti-sense or co-suppression constructs usually results in only a modest proportion of silenced individuals. Recent work has demonstrated the potential for constructs encoding self-complementary 'hairpin' RNA (hpRNA) to efficiently silence genes. In this study we examine design rules for efficient gene silencing, in terms of both the proportion of independent transgenic plants showing silencing, and the degree of silencing. Using hpRNA constructs containing sense/anti-sense arms ranging from 98 to 853 nt gave efficient silencing in a wide range of plant species, and inclusion of an intron in these constructs had a consistently enhancing effect. Intron-containing constructs (ihpRNA) generally gave 90-100% of independent transgenic plants showing silencing. The degree of silencing with these constructs was much greater than that obtained using either co-suppression or anti-sense constructs. We have made a generic vector, pHANNIBAL, that allows a simple, single PCR product from a gene of interest to be easily converted into a highly effective ihpRNA silencing construct. We have also created a high-throughput vector, pHELLSGATE, that should facilitate the cloning of gene libraries or large numbers of defined genes, such as those in EST collections, using an in vitro recombinase system. This system may facilitate the large-scale determination and discovery of plant gene functions in the same way as RNAi is being used to examine gene function in Caenorhabditis elegans.

Arabidopsis↗
PubMed2000

Feeling-of-knowing judgments and strategy selection in spelling.

Metacognitive processes, such as monitoring one's knowledge and selecting appropriate strategies, may be important in skilled spelling. We hypothesized that skilled spellers have knowledge of which words they know how to spell and also that the accuracy with which people monitor their knowledge should be related to the spelling strategies they select. College students provided Feeling-of-Knowing ratings about the spellings of words and also spelled the same words and indicated whether they sounded out or remembered the spellings. Feeling-of-Knowing ratings were moderately correlated with Spelling Accuracy and were more strongly predictive of Spelling Accuracy when Feeling-of-Knowing ratings and spellings were done as part of the same task rather than as separate tasks. Analyses indicate that those who were better at monitoring their knowledge of spelling also chose more congruent spelling strategies. The results suggest that skilled spellers can monitor which words they know how to spell, but this ability to monitor is far from perfect and varies considerably. Further, the results suggest that ability to monitor spelling knowledge is related to strategy selection in spelling.

Achievement↗
PubMed2000

High-oleic acid Australian Brassica napus and B. juncea varieties produced by co-suppression of endogenous Delta12-desaturases.

Genetic engineering methods have been used successfully to modify the fatty acid profile of elite Australian germplasm of Brassica napus and B. juncea. Co-suppression plasmids carrying oleate desaturase genes from each species have been constructed and transferred into Australian elite breeding lines of B. napus and B. juncea using Agrobacterium tumifaciens plant-transformation techniques. Modifications to existing Brassica transformation protocols and the use of an intron-interrupted hygromycin-resistance gene as the selectable marker have resulted in improved transformation efficiencies. Silencing of the endogenous oleate desaturase genes has resulted in substantial increases in oleic acid levels, up to 89% in B. napus and 73% in B. juncea.

2S Albumins, Plant↗
PubMed1999

Regrets.

A year or so ago I was invited by an Italian dentist to spend a day with him in his practice and to attend a two-day seminar, which he was presenting. The location, in the mountains near to Lake Como and the Swiss border, was enough to persuade me to accept. However I was to find out that the professional aspects of the trip were not only most invigorating but that they would also cause me to look back with concern to my own career. Had I done as well for my patients, my family and myself as I could have done?

Efficiency, Organizational↗
PubMed1995

Canadian immigration policy: the effectiveness of the point system and other instruments.

"This paper examines the effects of changes in Canadian immigration policy on the occupational composition of immigration. We focus on 1967 changes that created a regulatory system, including the point system, that still forms the framework of Canadian immigration policy. We find that the point system provides some control over occupational composition but that its effectiveness in fine tuning is limited by the large number of other characteristics it seeks to control. We also find that entry class and source country composition of inflow have impacts that have swamped the effects of the point system in the last two decades." (SUMMARY IN FRE)

Americas↗
PubMed1994

Insurance--a dental viewpoint. Part IV: Professional risks indemnity.

Over the last decade professional practice has changed in many ways, not least in the willingness of patients to seek damages. The treasurer of the Medical Defence Union, in his report on the year 1989, stated that claims paid out on behalf of doctors in Britain doubled in frequency and the average amount awarded also doubled between 1985 and 1988, subscription rates increased fourfold. By contrast, 40 years ago life membership of a 'defence organisation' was available for less that an annual subscription today.

Humans↗
PubMed1994

Law and ethics.

Explore the source record for details and available documents.

Ethics↗
PubMed1994

Insurance--a dental viewpoint. Part II: Sickness and accident.

It is a very fortunate dentist indeed who survives an average 40-year working life without suffering illness or an accident. This will normally keep the dentist away from work and the ability to earn for a period of time. In the worst cases the disability may prevent a return to normal work with disastrous effects upon career earnings. Insurance against loss of earnings has therefore a very high priority.

Dentists↗
PubMed1994

Insurance--a dental viewpoint. Part I: An introduction.

Current changes in the market are likely to alter our perception of insurance companies and brokers. Brokers will soon be required to disclose the amounts of commission earned and this may drive individuals back into the arms of the salesmen from individual companies. This series of articles sets out to show the options that are available to the dentist and to show how to use the range of expert advice available.

Dentists↗