Nucleon-Nucleon Interactions on the Lattice

We consider the nucleon-nucleon potential in quenched and partially-quenched QCD. The leading one-meson exchange contribution to the potential is found to fall off exponentially at long-distances, in contrast with the Yukawa-type behaviour found in QCD. This unphysical component of the two-nucleon potential has important implications for the extraction of nuclear properties from lattice simulations.Comment: 6 pages LaTeX, 2 eps fig

Chiral Perturbation Theory and Weak Matrix Elements

I describe recent developments in quenched chiral perturbation theory (QChPT) and the status of weak matrix elements involving light quarks. I illustrate how, with improved statistical errors, and with calculations of the masses of baryons containing non-degenerate quarks, there is now a clear need for extrapolations of higher order than linear in the quark mass. I describe how QChPT makes predictions for the functional forms to use in such extrapolations, and emphasize the distinction between contributions coming from chiral loops which are similar to those present in unquenched theories, and those from $\eta'$ loops which are pure quenched artifacts. I describe a fit to the baryon masses using the predictions of QChPT. I give a status report on the numerical evidence for $\eta'$ loops, concluding that they are likely present, and are characterized by a coupling $\delta=0.1-0.2$. I use the difference between chiral loops in QCD and quenched QCD to estimate the quenching errors in a variety of quantities. I then turn to results for matrix elements, largely from quenched simulations. Results for quenched decay constants cannot yet be reliably extrapolated to the continuum limit. By contrast, new results for $B_K$ suggest a continuum, ``quenched'' value of $B_K(NDR, 2 GeV) = 0.5977 \pm 0.0064 \pm 0.0166$, based on a quadratic extrapolation in $a$. The theoretical basis for using a quadratic extrapolation has been confirmed. For the first time there is significant evidence that unquenching changes $B_K$, and my estimate for the value in QCD is $B_K(NDR, 2 GeV) = 0.66 \pm 0.02 \pm 0.11$. Here the second error is a conservative estimate of the systematic error due to uncertainties in the effect of quenching. A less conservative viewpoint reduces $0.11$ to $0.03$.Comment: 16 pages, 11 figures, Latex using espcrc2.sty and psfig. Talk presented at LATTICE96(phenomenology

A primary care Symptoms Clinic for patients with medically unexplained symptoms : pilot randomised trial

Peer reviewedPublisher PD

Tax Policy and Tax Research in Canada

In a survey of tax reform in recent years, Richard Bird and Michael Smart explore the relationship between tax policy and tax research. They conclude that there have been important examples of apparent influences of research on policy. For instance, they are encouraged that the downward pressure on personal and corporate taxes has certainly been supported, if not initiated, by the increasing evidence of distortions caused by high marginal tax rates. In their view, the adoption of the GST can be explained by the acceptance of the federal government of the economic argument that Canada had to switch to a value-added tax to reduce economic distortions. On the other hand, they are disappointed that the equally convincing economic studies of the damage done by poorly-designed excise, property and payroll taxes do not seem to have had any effect. Consequently, they believe that political economy factors were probably the more dominant explanation of the tax reforms than the simple acceptance of advice from economists. Their conclusion is that if economists want to have a greater influence on policy, they need to pay more attention to the issues that motivate policymakers, including, most notably, distributional issues, and they need to write in a way, and in a forum, that will most likely come to the notice of the policy-makers.Canada, Taxation, Income Tax, Value-Added Tax, Value Added Tax, VAT

Emerging technologies for learning (volume 1)

Collection of 5 articles on emerging technologies and trend

Pd deposition on TiO2(110) and nanoparticle encapsulation

The effect of sputtering, annealing and oxidation on the surface properties of TiO2(110), and on the same surfaces with nanoparticles present, has been investigated. Sputtering the crystal clean gives a much reduced surface with Ti2+ as the dominant species. This,surface is mainly Ti3+,4+ after annealing in vacuum. Oxidation reduces the surface Ti3+ considerably. When Pd nanoparticles are annealed on any of the investigated titania surfaces the particles become encapsulated by a film of titanium oxide. This is particularly noticeable in ISS (ion scattering spectroscopy) where the Pd:Ti ratio drops by a factor of 300 after annealing to 750 K, indicating complete coverage of the Pd nanoparticles by the oxide film. This happens most easily for the nanoparticles deposited on the reduced surfaces (beginning at ~673K) but also occurs for the very oxidized surface at~773K. Thus reduced Ti from the subsurface region can migrate onto the Pd surface to form the sub-oxide, the sub-oxide being a thin TiO-like layer

Is the up-quark massless?

We report on determinations of the low-energy constants alpha5 and alpha8 in the effective chiral Lagrangian at O(p^4), using lattice simulations with N_f=2 flavours of dynamical quarks. Precise knowledge of these constants is required to test the hypothesis whether or not the up-quark is massless. Our results are obtained by studying the quark mass dependence of suitably defined ratios of pseudoscalar meson masses and matrix elements. Although comparisons with an earlier study in the quenched approximation reveal small qualitative differences in the quark mass behaviour, numerical estimates for alpha5 and alpha8 show only a weak dependence on the number of dynamical quark flavours. Our results disfavour the possibility of a massless up-quark, provided that the quark mass dependence in the physical three-flavour case is not fundamentally different from the two-flavour case studied here.Comment: references added, typos correcte