2,952 research outputs found
Guesstimation
Macroeconomic model builders attempting to construct forecasting models frequently face constraints of data scarcity in terms of short time series of data, and also of parameter non-constancy and underspecification. Hence, a realistic alternative is often to guess rather than to estimate parameters of such models. This paper concentrates on repetitive guessing (drawing) parameters from iteratively changing distributions, with the straightforward objective function being that of minimisation of squares of ex-post prediction errors, weighted by penalty weights and subject to a learning process. The numerical Monte Carlo examples are those of a regression problem and a dynamic disequilibrium model.estimation; short data series; macromodels; computations; methodology
Ex-ante dynamics of real effects of monetary policy: Theory and evidence for Poland and Russia, 2001-2003
The paper proposes a new indicator of expected real effects of a policy aimed at controlling inflation. The indicator, called real effect of inflation targeting (REIT), involves the comparison of expected and output-neutral inflation. It is shown that it can be derived from a simple two-dimensional vector autoregressive model of inflation and output gap. The microdynamics of such model are explained in terms of the foundations of Taylor-type staggered wage contracts. It is assumed that the monetary authority has some discretion regarding the timing of monetary actions. Here REIT can be used to set the optimal times for such actions, if the control of output is regarded as a secondary policy target. A simulation experiment illustrates the rationale of such a device for timing monetary measures. The REIT has been used by the Polish Monetary Policy Council since 2001 in it's inflation targeting and is thought to have contributed to a substantial decline in Polish inflation in 2003 and to an increase in output growth in 2004. A similar indicator computed for Russia as a means of monitoring monetary policy rather than as an active tool confirms that active expansionary policy in 2002 and 2003 might have contributed to Russian economic growth in 2004 and 2005, whereas similar policy measures for 2004 are likely to prove ineffective.
libcloudph++ 0.2: single-moment bulk, double-moment bulk, and particle-based warm-rain microphysics library in C++
This paper introduces a library of algorithms for representing cloud
microphysics in numerical models. The library is written in C++, hence the name
libcloudph++. In the current release, the library covers three warm-rain
schemes: the single- and double-moment bulk schemes, and the particle-based
scheme with Monte-Carlo coalescence. The three schemes are intended for
modelling frameworks of different dimensionality and complexity ranging from
parcel models to multi-dimensional cloud-resolving (e.g. large-eddy)
simulations. A two-dimensional prescribed-flow framework is used in example
simulations presented in the paper with the aim of highlighting the library
features. The libcloudph++ and all its mandatory dependencies are free and
open-source software. The Boost.units library is used for zero-overhead
dimensional analysis of the code at compile time. The particle-based scheme is
implemented using the Thrust library that allows to leverage the power of
graphics processing units (GPU), retaining the possibility to compile the
unchanged code for execution on single or multiple standard processors (CPUs).
The paper includes complete description of the programming interface (API) of
the library and a performance analysis including comparison of GPU and CPU
setups.Comment: The library description has been updated to the new library API (i.e.
v0.1 -> v0.2 update). The key difference is that the model state variables
are now mixing ratios as opposed to densities. The particle-based scheme was
supplemented with the "particle recycling" process. Numerous editorial
corrections were mad
John Wheeler, relativity, and quantum information
In spring 1952, as John Wheeler neared the end of design work for the first thermonuclear explosion, he plotted a radical change of research direction: from particles and atomic nuclei to general relativity
Single-freeze-out model for ultra relativistic heavy-ion collisions at TeV and the LHC proton puzzle
The single-freeze-out model with parametrized hypersurface and flow geometry
is employed to analyze the transverse-momentum spectra of hadrons produced in
the Pb+Pb collisions at the collision energy of { TeV}
at the CERN Large Hadron Collider (LHC). With the notable exception for protons
and antiprotons, we find a very good agreement between the model results and
the data for the measured hadron species. The additional analysis of the HBT
radii of pions helps us to select, from several different types of freeze-out
studied in this work, the most realistic form of the freeze-out hypersurface.
We find that discrepancy ratio between the model and experiment for the
proton/antiproton spectra depends on , dropping from 2 in the soft region
to 1 around GeV.Comment: 9 pages, 10 figure
A ring of BEC pools as a trap for persistent flow
Mott insulator - superfluid transition in a periodic lattice of Josephson
junctions can be driven by tunneling rate increase. Resulting winding numbers
of the condensate wavefunction decrease with increasing quench time in
accord with the Kibble-Zurek mechanism (KZM). However, in very slow quenches
Bose-Hubbard dynamics rearranges wavefunction phase so that its random walk
cools, decreases and eventually the wavefunction becomes too cold
to overcome potential barriers separating different . Thus, in contrast with
KZM, in very slow quenches is set by random walk with "critical"
step size, independently of .Comment: Decompressed version to appear in Phys. Rev.
Analyse praxeÌologique et approche systeÌmique
Cette preÌsentation introduit aux concepts fondamentaux de lâanalyse praxeÌologique et aÌ la relation de celle-ci avec lâapproche systeÌmique. Les sujets suivants seront abordeÌs : lâefficaciteÌ et lâefficience de lâaction, le travail, lâaction humaine et son design, lâexplication teÌleÌologique, les composants de lâaction humaine ( reÌalisateur, buts, criteÌres dâeÌvaluation, outils, ressources, circonstances, temps, meÌthodes), lâefficaciteÌ meÌthodologique, le contexte axiologique de lâaction humaine ou les rapports entre praxeÌologie et eÌthique.This presentation introduces the fundamental concepts of praxiological analysis and its relation to systems approach. The following topics are discussed in this paper: effectiveness and efficiency of action, work, human action and their design, teleological explanation, components of human action (realisers, purposes, evaluation criteria, tools, resources, circumstances, time, methods), methodological efficacy, axiological context of human action or praxiology and ethics
Quench from Mott Insulator to Superfluid
We study a linear ramp of the nearest-neighbor tunneling rate in the
Bose-Hubbard model driving the system from the Mott insulator state into the
superfluid phase. We employ the truncated Wigner approximation to simulate
linear quenches of a uniform system in 1,2, and 3 dimensions, and in a harmonic
trap in 3 dimensions. In all these setups the excitation energy decays like one
over third root of the quench time. The -1/3 scaling arises from an
impulse-adiabatic approximation - a variant of the Kibble-Zurek mechanism -
describing a crossover from non-adiabatic to adiabatic evolution when the
system begins to keep pace with the increasing tunneling rate.Comment: 10 pages, 13 figures; version published in Phys. Rev.
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