Gapless Hamiltonians for the toric code using the projected entangled pair state formalism.

We study Hamiltonians which have Kitaev's toric code as a ground state, and show how to construct a Hamiltonian which shares the ground space of the toric code, but which has gapless excitations with a continuous spectrum in the thermodynamic limit. Our construction is based on the framework of projected entangled pair states, and can be applied to a large class of two-dimensional systems to obtain gapless "uncle Hamiltonians."

Influence exerted on drug prescribing by patients' attitudes and expectations and by doctors' perception of such expectations: a cohort and nested case-control study.

Rationale, Aims And Objectives: Although demand for medication is regarded as one of the most important factors in pharmaceutical expenditure, little is known about patients' influence on drug prescribing. This study assesses the influence exerted on drug prescribing by patients' attitudes and expectations, and by doctors' perception of such expectations.

Method: We conducted a population-based cohort study covering 937 subjects attending a health centre in the northwest of Spain.

Determination of fungicide residues in white grapes for winemaking by gas chromatography with mass spectrometric detection and assessment of matrix effects.

A new analytical method, based on organic solvent extraction with dichloromethane-acetone (75 + 25, v/v) followed by gas chromatography with mass spectrometric detection, is presented for the determination of residues of 10 fungicides in white grapes for vinification. Some of them (cyprodinil, fludioxonil, and pyrimethanil) have been used for only 2-3 years and, therefore, no methods are available in the scientific literature for such a screening. Quality parameters yielded good precision (relative standard deviation of <10%) and detection limits (ranging between 1 and 18 microg/kg) that are lower than the maximum residue limits (MRLs) set by the 76/895/European Economic Community (EEC) and 90/642/EEC Directives.