8,097 research outputs found
Numerical analysis of a relaxed variational model of hysteresis in two-phase solids
This paper presents the numerical analysis for a variational formulation of rate-independent phase transformations in elastic solids due to Mielke et al. The new model itself suggests an implicit time-discretization which is combined with the finite element method in space. A priori error estimates are established for the quasioptimal spatial approximation of the stress field within one time-step. A posteriori error estimates motivate an adaptive mesh-refining algorithm for efficient discretization. The proposed scheme enables numerical simulations which show that the model allows for hysteresis
Majorisation with applications to the calculus of variations
This paper explores some connections between rank one convexity,
multiplicative quasiconvexity and Schur convexity. Theorem 5.1 gives simple
necessary and sufficient conditions for an isotropic objective function to be
rank one convex on the set of matrices with positive determinant. Theorem 6.2
describes a class of possible non-polyconvex but multiplicative quasiconvex
isotropic functions. This class is not contained in a well known theorem of
Ball (6.3 in this paper) which gives sufficient conditions for an isotropic and
objective function to be polyconvex. We show here that there is a new way to
prove directly the quasiconvexity (in the multiplicative form). Relevance of
Schur convexity for the description of rank one convex hulls is explained.Comment: 13 page
Can one control systematic errors of QCD sum rule predictions for bound states?
We study the possibility to control systematic errors of the ground-state
parameters obtained by Shifman-Vainshtein-Zakharov (SVZ) sum rules, making use
of the harmonic-oscillator potential model as an example. In this case, one
knows the exact solution for the polarization operator, which allows one to
obtain both the OPE to any order and the parameters (masses and decay
constants) of the bound states. We determine the parameters of the ground state
making use of the standard procedures of the method of QCD sum rules, and
compare the obtained results with the known exact values. We show that in the
situation when the continuum contribution to the polarization operator is not
known and is modelled by an effective continuum, the method of sum rules does
not allow to control the systematic errors of the extracted ground-state
parameters.Comment: RevTex, 7 pages, figure 4 modified, version to be published in Phys.
Lett.
ShopSmart 4 Health - protocol of a skills-based randomised controlled trial promoting fruit and vegetable consumption among socioeconomically disadvantaged women
BackgroundThere is a need for evidence on the most effective and cost-effective approaches for promoting healthy eating among groups that do not meet dietary recommendations for good health, such as those with low incomes or experiencing socioeconomic disadvantage. This paper describes the ShopSmart 4 Health study, a randomised controlled trial conducted by Deakin University, Coles Supermarkets and the Heart Foundation, to investigate the effectiveness and cost-effectiveness of a skill-building intervention for promoting increased purchasing and consumption of fruits and vegetables amongst women of low socioeconomic position (SEP).Methods/designShopSmart 4 Health employed a randomised controlled trial design. Women aged 18–60 years, holding a Coles store loyalty card, who shopped at Coles stores within socioeconomically disadvantaged neighbourhoods and met low-income eligibility criteria were invited to participate. Consenting women completed a baseline survey assessing food shopping and eating habits and food-related behaviours and attitudes. On receipt of their completed survey, women were randomised to either a skill-building intervention or a wait-list control condition. Intervention effects will be evaluated via self-completion surveys and using supermarket transaction sales data, collected at pre- and post-intervention and 6-month follow-up. An economic evaluation from a societal perspective using a cost-consequences approach will compare the costs and outcomes between intervention and control groups. Process evaluation will be undertaken to identify perceived value and effects of intervention components.DiscussionThis study will provide data to address the currently limited evidence base regarding the effectiveness and cost-effectiveness of skill-building intervention strategies aimed at increasing fruit and vegetable consumption among socioeconomically disadvantaged women, a target group at high risk of poor diets.<br /
Critical Analysis of Theoretical Estimates for to Light Meson Form Factors and the Data
We point out that current estimates of form factors fail to explain the
non-leptonic decays and that the combination of data
on the semi-leptonic decays and on the non-leptonic
decays (in particular recent po\-la\-ri\-za\-tion
data) severely constrain the form (normalization and dependence) of the
heavy-to-light meson form factors, if we assume the factorization hypothesis
for the latter. From a simultaneous fit to \bpsi and \dk data we find that
strict heavy quark limit scaling laws do not hold when going from to
and must have large corrections that make softer the dependence on the masses.
We find that should increase slower with \qq than .
We propose a simple parametrization of these corrections based on a quark
model or on an extension of the \hhs laws to the \hl case, complemented with an
approximately constant . We analyze in the light of these data and
theoretical input various theoretical approaches (lattice calculations, QCD sum
rules, quark models) and point out the origin of the difficulties encountered
by most of these schemes. In particular we check the compatibility of several
quark models with the heavy quark scaling relations.Comment: 48 pages, DAPNIA/SPP/94-24, LPTHE-Orsay 94/1
O(N) models within the local potential approximation
Using Wegner-Houghton equation, within the Local Potential Approximation, we
study critical properties of O(N) vector models. Fixed Points, together with
their critical exponents and eigenoperators, are obtained for a large set of
values of N, including N=0 and N\to\infty. Polchinski equation is also treated.
The peculiarities of the large N limit, where a line of Fixed Points at d=2+2/n
is present, are studied in detail. A derivation of the equation is presented
together with its projection to zero modes.Comment: 27 pages, LaTeX with psfig, 7 PostScript figures. One reference
corrected and one added with respect to the journal versio
Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit of QCD
We argue that the Large Energy Effective Theory (LEET), originally proposed
by Dugan and Grinstein, is applicable to exclusive semileptonic, radiative and
rare heavy-to-light transitions in the region where the energy release E is
large compared to the strong interaction scale and to the mass of the final
hadron, i.e. for q^2 not close to the zero-recoil point. We derive the
Effective Lagrangian from the QCD one, and show that in the limit of heavy mass
M for the initial hadron and large energy E for the final one, the heavy and
light quark fields behave as two-component spinors. Neglecting QCD
short-distance corrections, this implies that there are only three form factors
describing all the pseudoscalar to pseudoscalar or vector weak current matrix
elements. We argue that the dependence of these form factors with respect to M
and E should be factorizable, the M-dependence (sqrt(M)) being derived from the
usual heavy quark expansion while the E-dependence is controlled by the
behaviour of the light-cone distribution amplitude near the end-point u=1. The
usual expectation of the (1-u) behaviour leads to a 1/E^2 scaling law, that is
a dipole form in q^2. We also show explicitly that in the appropriate limit,
the Light-Cone Sum Rule method satisfies our general relations as well as the
scaling laws in M and E of the form factors, and obtain very compact and simple
expressions for the latter. Finally we note that this formalism gives
theoretical support to the quark model-inspired methods existing in the
literature.Comment: Latex2e, 25 pages, no figure. Slight changes in the title and the
phrasing. Misprint in Eq. (25) corrected. To appear in Phys. Rev.
Recent progress in hadronic tau decays
The determination of alpha_s from hadronic tau decays is impeded by the fact
that two choices for the renormalisation group resummation, namely fixed-order
(FOPT) and contour-improved perturbation theory (CIPT), yield systematically
differing results. On the basis of a model for higher-order terms in the
perturbative series, which incorporates well-known structure from renormalons,
it is found that FOPT smoothly approaches the Borel sum for the tau hadronic
width, while CIPT is unable to account for the resummed series. An example for
the behaviour of QCD spectral function moments, displaying a similar behaviour,
is presented as well.Comment: 6 pages, 3 figures. Talk presented at 11th International Workshop on
Tau Lepton Physics, Manchester, UK, 13-17 September 201
Constraints on the IR behaviour of gluon and ghost propagator from Ward-Slavnov-Taylor identities
We consider the constraints of the Slavnov-Taylor identity of the IR
behaviour of gluon and ghost propagators and their compatibility with solutions
of the ghost Dyson-Schwinger equation and with the lattice picture.Comment: 5 pages, 2 figure
Heavy Quarks from QCD Spectral Sum Rules
This is a short review of the present status of the dynamics of the heavy
quarks extracted from QCD spectral sum rules. We discuss the determination of
the ``perturbative" quark mass, the decay constants of the and mesons,
the form factors of the semileptonic and radiative decays of the mesons,
the slope of the Isgur--Wise function and the emerged value of . We
mention shortly some properties of the hybrid and mesons.Comment: CERN-TH 7277/94, Updated version. Latex file (run twice). Talk given
at the {\it XXIXth Rencontre de Moriond on `` QCD and High Energy Hadronic
Interactions"}, M\'eribel, Haute-Savoie, 19--26th March 1994 and at the {\it
Rencontre entre experimentateurs et theoriciens sur ``la violation de CP"},
Orsay, 6--7th May 199
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