20,331 research outputs found
Biogeography and Long-Run Economic Development
The transition from a hunter-gather economy to agricultural production, which made possible the endogenous technological progress that ultimately led to the industrial revolution, is one of the most important events in the thousands of years of humankindâs economic development. In this paper we present theory and evidence showing that exogenous geography and initial condition biogeography exerted decisive influence on the location and timing of transitions to sedentary agriculture, to complex social organization and, eventually, to modern industrial production. Evidence from a large cross-section of countries indicates that the effects of geographic and biogeographic endowments on contemporary levels of economic development are remarkably strong.Geography biogeography and growth; Economic development; Agricultural revolution; Institutions and growth; Plants animals and growth
Vortex glass transitions in disordered three-dimensional XY models: Simulations for several different sets of parameters
The anisotropic frustrated 3D XY model with strong disorder in the coupling
constants is studied as a model of a disordered superconductor in an applied
magnetic field. Simulations with the exchange Monte Carlo method are performed
for frustrations f=1/5 and f=1/4, corresponding to two different values of the
magnetic field along the z direction. The anisotropy is also varied. The
determination of the helicity modulus from twist histograms is discussed in
some detail and the helicity modulus is used in finite size scaling analyses of
the vortex glass transition. The general picture is that the behavior in [Phys.
Rev. Lett. 91, 077002 (2003)] is confirmed. For strong (e.g. isotropic)
coupling in the z direction the helicity modulus fails to scale and it is
argued that this is due to a too small effective randomness of such systems for
the accessible system sizes
Discreteness-Induced Slow Relaxation in Reversible Catalytic Reaction Networks
Slowing down of the relaxation of the fluctuations around equilibrium is
investigated both by stochastic simulations and by analysis of Master equation
of reversible reaction networks consisting of resources and the corresponding
products that work as catalysts. As the number of molecules is decreased,
the relaxation time to equilibrium is prolonged due to the deficiency of
catalysts, as demonstrated by the amplification compared to that by the
continuum limit. This amplification ratio of the relaxation time is represented
by a scaling function as , and it becomes prominent as
becomes less than a critical value , where is the inverse
temperature and is the energy gap between a product and a resource
Bethe--Salpeter equation in QCD
We extend to regular QCD the derivation of a confining
Bethe--Salpeter equation previously given for the simplest model of scalar QCD
in which quarks are treated as spinless particles. We start from the same
assumptions on the Wilson loop integral already adopted in the derivation of a
semirelativistic heavy quark potential. We show that, by standard
approximations, an effective meson squared mass operator can be obtained from
our BS kernel and that, from this, by expansion the
corresponding Wilson loop potential can be reobtained, spin--dependent and
velocity--dependent terms included. We also show that, on the contrary,
neglecting spin--dependent terms, relativistic flux tube model is reproduced.Comment: 23 pages, revte
Reach the person behind the dementia: physical therapists' reflections and strategies when composing physical training
Dementia is a disease characterized by cognitive impairment and physical decline that worsens over time. Exercise is one lifestyle factor that has been identified as a potential means of reducing or delaying progression of the symptoms of dementia, maximizing function and independence. The purpose of this study was to explore physical therapists' (PTs) experiences and reflections on facilitating high-intensity functional exercise with older people living with dementia, in residential care home settings. The study used a qualitative design based on interviews, individually or in small groups, with seven PTs engaged as leaders in the training of older people with dementia. The interviews were analyzed with a modified Grounded Theory method with focus on constant comparisons. To increase trustworthiness the study used triangulation within investigators and member checking. The core category "Discover and act in the moment-learn over time" reflects how the PTs continuously developed their own learning in an iterative process. They built on previous knowledge to communicate with residents and staff and to tailor the high intensity training in relation to each individual at that time point. The category "Be on your toes" highlights how the PTs searched for sufficient information about each individual, before and during training, by eliciting the person's current status from staff and by interpreting the person's body language. The category "Build a bond with a palette of strategies" describes the importance of confirmation to build up trust and the use of group members and the room to create an interplay between exercise and social interaction. These findings highlight the continuous iterative process of building on existing knowledge, sharing and reflecting, being alert to any alterations needed for individuals that day, communication skills (both with residents and staff) and building a relationship and trust with residents in the effective delivery of high intensity functional exercise to older people living with dementia in care settings
Kink-Antikink Unbinding Transition in the Two Dimensional Fully Frustrated XY Model
We carry out the first numerical simulations to directly confirm the
existence of a kink-antikink unbinding transition, T_w, along Ising-like domain
walls in the two dimensional fully frustrated XY model. We comment on the
possible implications of kink-antikink unbinding for the bulk phase transitions
of the model.Comment: 8 pages, 10 figures - expanded version of original submission as
accepted by Phys. Rev. B. Some correction to the analysis lead to an increase
in the value of the kink unbinding transition temperatur
Constraint-preserving boundary conditions in the 3+1 first-order approach
A set of energy-momentum constraint-preserving boundary conditions is
proposed for the first-order Z4 case. The stability of a simple numerical
implementation is tested in the linear regime (robust stability test), both
with the standard corner and vertex treatment and with a modified
finite-differences stencil for boundary points which avoids corners and
vertices even in cartesian-like grids. Moreover, the proposed boundary
conditions are tested in a strong field scenario, the Gowdy waves metric,
showing the expected rate of convergence. The accumulated amount of
energy-momentum constraint violations is similar or even smaller than the one
generated by either periodic or reflection conditions, which are exact in the
Gowdy waves case. As a side theoretical result, a new symmetrizer is explicitly
given, which extends the parametric domain of symmetric hyperbolicity for the
Z4 formalism. The application of these results to first-order BSSN-like
formalisms is also considered.Comment: Revised version, with conclusive numerical evidence. 23 pages, 12
figure
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
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