384 research outputs found
Discrete Model of Ideological Struggle Accounting for Migration
A discrete in time model of ideological competition is formulated taking into
account population migration. The model is based on interactions between global
populations of non-believers and followers of different ideologies. The complex
dynamics of the attracting manifolds is investigated.
Conversion from one ideology to another by means of (i) mass media influence
and (ii) interpersonal relations is considered. Moreover a different birth rate
is assumed for different ideologies, the rate being assumed to be positive for
the reference population, made of initially non-believers. Ideological
competition can happen in one or several regions in space. In the latter case,
migration of non-believers and adepts is allowed; this leads to an enrichment
of the ideological dynamics. Finally, the current ideological situation in the
Arab countries and China is commented upon from the point of view of the
presently developed mathematical model. The massive forced conversion by
Ottoman Turks in the Balkans is briefly discussed.Comment: 24 pages, with 5 figures and 52 refs.; prepared for a Special issue
of Advances in Complex System
Incommensurate Charge Density Waves in the adiabatic Hubbard-Holstein model
The adiabatic, Holstein-Hubbard model describes electrons on a chain with
step interacting with themselves (with coupling ) and with a classical
phonon field \f_x (with coupling \l). There is Peierls instability if the
electronic ground state energy F(\f) as a functional of \f_x has a minimum
which corresponds to a periodic function with period , where
is the Fermi momentum. We consider irrational so that
the CDW is {\it incommensurate} with the chain. We prove in a rigorous way in
the spinless case, when \l,U are small and {U\over\l} large, that a)when
the electronic interaction is attractive there is no Peierls instability
b)when the interaction is repulsive there is Peierls instability in the
sense that our convergent expansion for F(\f), truncated at the second order,
has a minimum which corresponds to an analytical and periodic
\f_x. Such a minimum is found solving an infinite set of coupled
self-consistent equations, one for each of the infinite Fourier modes of
\f_x.Comment: 16 pages, 1 picture. To appear Phys. Rev.
Antiferromagnetic 4-d O(4) Model
We study the phase diagram of the four dimensional O(4) model with first
(beta1) and second (beta2) neighbor couplings, specially in the beta2 < 0
region, where we find a line of transitions which seems to be second order. We
also compute the critical exponents on this line at the point beta1 =0 (F4
lattice) by Finite Size Scaling techniques up to a lattice size of 24, being
these exponents different from the Mean Field ones.Comment: 26 pages LaTeX2e, 7 figures. The possibility of logarithmic
corrections has been considered, new figures and tables added. Accepted for
publication in Physical Review
Identification of the factors associated with outcomes in a condition management programme
<p>Background: A requirement of the Government’s Pathways to Work (PtW) agenda was to introduce a Condition Management Programme (CMP). The aim of the present study was to identify the differences between those who engaged and made progress in this telephone-based biopsychosocial intervention, in terms of their health, and those who did not and to determine the client and practitioner characteristics and programme elements associated with success in a programme aimed at improving health.</p>
<p>Methods: Data were obtained from the CMP electronic spreadsheets and clients paper-based case records. CMP
standard practice was that questionnaires were administered during the pre- and post-assessment phases over the
telephone. Each client’s record contains their socio-demographic data, their primary health condition, as well as the pre- and post-intervention scores of the health assessment tool administered. Univariate and multivariate statistical analysis was used to investigate the relationships between the database variables. Clients were included in the study if their records were available for analysis from July 2006 to December 2007.</p>
<p> Results: On average there were 112 referrals per month, totalling 2016 referrals during the evaluation period. The
majority (62.8%) of clients had a mental-health condition. Successful completion of the programme was 28.5% (575
“completers”; 144 “discharges”). Several factors, such as age, health condition, mode of contact, and practitioner
characteristics, were significant determinants of participation and completion of the programme. The results
showed that completion of the CMP was associated with a better mental-health status, by reducing the number of
clients that were either anxious, depressed or both, before undertaking the programme, from 74% to 32.5%.</p>
<p>Conclusions: Our findings showed that an individual's characteristics are associated with success in the
programme, defined as completing the intervention and demonstrating an improved health status. This study
provides some evidence that the systematic evaluation of such programmes and interventions could identify ways
in which they could be improved.</p>
Summing Divergent Perturbative Series in a Strong Coupling Limit. The Gell-Mann - Low Function of the \phi^4 Theory
An algorithm is proposed for determining asymptotics of the sum of a
perturbative series in the strong coupling limit using given values of the
expansion coefficients. Operation of the algorithm is illustrated by test
examples, method for estimating errors is developed, and an optimization
procedure is described. Application of the algorithm to the theory
gives a behavior at large for its Gell-Mann
-- Low function. The fact that the exponent is close to unity can be
interpreted as a manifestation of the logarithmic branching of the type
(with ), which is
confirmed by independent evidence. In any case, the theory is
internally consistent. The procedure of summing perturbartive series with
arbitrary values of expansion parameter is discussed.Comment: 23 pages, PD
Business experience and start-up size: buying more lottery tickets next time around?
This paper explores the determinants of start-up size by focusing on a cohort of 6247 businesses that started trading in 2004, using a unique dataset on customer records at Barclays Bank. Quantile regressions show that prior business experience is significantly related with start-up size, as are a number of other variables such as age, education and bank account activity. Quantile treatment effects (QTE) estimates show similar results, with the effect of business experience on (log) start-up size being roughly constant across the quantiles. Prior personal business experience leads to an increase in expected start-up size of about 50%. Instrumental variable QTE estimates are even higher, although there are concerns about the validity of the instrument
Divergent Perturbation Series
Various perturbation series are factorially divergent. The behavior of their
high-order terms can be found by Lipatov's method, according to which they are
determined by the saddle-point configurations (instantons) of appropriate
functional integrals. When the Lipatov asymptotics is known and several lowest
order terms of the perturbation series are found by direct calculation of
diagrams, one can gain insight into the behavior of the remaining terms of the
series. Summing it, one can solve (in a certain approximation) various
strong-coupling problems. This approach is demonstrated by determining the
Gell-Mann - Low functions in \phi^4 theory, QED, and QCD for arbitrary coupling
constants. An overview of the mathematical theory of divergent series is
presented, and interpretation of perturbation series is discussed. Explicit
derivations of the Lipatov asymptotic forms are presented for some basic
problems in theoretical physics. A solution is proposed to the problem of
renormalon contributions, which hampered progress in this field in the late
1970s. Practical schemes for summation of perturbation series are described for
a coupling constant of order unity and in the strong-coupling limit. An
interpretation of the Borel integral is given for 'non-Borel-summable' series.
High-order corrections to the Lipatov asymptotics are discussed.Comment: Review article, 45 pages, PD
Summary of cerebrospinal fluid routine parameters in neurodegenerative diseases
In neurodegenerative diseases, cerebrospinal fluid analysis (CSF) is predominantly performed to exclude inflammatory diseases and to perform a risk assessment in dementive disorders by measurement of tau proteins and amyloid beta peptides. However, large scale data on basic findings of CSF routine parameters are generally lacking. The objective of the study was to define a normal reference spectrum of routine CSF parameters in neurodegenerative diseases. Routine CSF parameters (white cell count, lactate and albumin concentrations, CSF/serum quotients of albumin (Qalb), IgG, IgA, IgM, and oligoclonal IgG bands (OCB)) were retrospectively analyzed in an academic research setting. A total of 765 patients (Alzheimer’s disease (AD), Parkinson’s disease (PD), Parkinson’s disease dementia (PDD), vascular dementia (VD), frontotemporal lobar degeneration (FTLD), progressive supranuclear palsy (PSP), multisystem atrophy (MSA), motor neuron diseases (MND), spinocerebellar ataxia (SCA), Huntington’s disease (HD)) and non-demented control groups including a group of patients with muscular disorders (MD). The main outcome measures included statistical analyses of routine CSF parameters. Mildly elevated Qalb were found in a small percentage of nearly all subgroups and in a higher proportion of patients with PSP, MSA, VD, PDD, and MND. With the exception of 1 MND patient, no intrathecal Ig synthesis was observed. Isolated OCBs in CSF were sometimes found in patients with neurodegenerative diseases without elevated cell counts; lactate levels were always normal. A slightly elevated Qalb was observed in a subgroup of patients with neurodegenerative diseases and does not exclude the diagnosis. Extensive elevation of routine parameters is not characteristic and should encourage a re-evaluation of the clinical diagnosis
Aspects of noncommutative descriptions of planar systems in high magnetic fields
We study some aspects of recent proposals to use the noncommutative
Chern-Simons theory as an effective description of some planar condensed matter
models in strong magnetic fields, such as the Quantum Hall Effect. We present
an alternative justification for such a description, which may be extended to
other planar systems where a uniform magnetic field is present
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