14,579 research outputs found
Economic Convergence and Economic Policies
Many of the crucial debates in development economics are encapsulated in the question of economic convergence. Is there a tendency for the poorer countries to grow more rapidly than the richer countries, and thereby to converge in living standards? Some recent research on endogenous growth has emphasized increasing returns as a possible reason not to expect convergence. Other research has suggested that convergence may be achieved only after poor countries attain a threshold level of income or human capital. This paper presents evidence that a sufficient condition for higher-than-average growth of poorer countries, and therefore convergence, is that poorer countries follow reasonably efficient economic policies, mainly open trade and protection of private property rights.
Natural Resource Abundance and Economic Growth
One of the surprising features of modern economic growth is that economies with abundant natural resources have tended to grow less rapidly than natural-resource-scarce economies. In this paper we show that economies with a high ratio of natural resource exports to GDP in 1971 (the base year) tended to have low growth rates during the subsequent period 1971-89. This negative relationship holds true even after controlling for variables found to be important for economic growth, such as initial per capita income, trade policy, government efficiency, investment rates, and other variables. We explore the possible pathways for this negative relationship by studying the cross-country effects of resource endowments on trade policy, bureaucratic efficiency, and other determinants of growth. We also provide a simple theoretical model of endogenous growth that might help to explain the observed negative relationship.
Extended N=2 Superconformal Structure of Gravity and W-Gravity Coupled to Matter
We show that almost all string theories, including the bosonic string, the
superstring and -string theories, possess a twisted N=2 superconformal
symmetry. This enables us to establish a connection between topological gravity
and the field theoretical description of matter coupled to gravity. We also
show how the \brs operators of the -string can be obtained by hamiltonian
reduction of . The tachyonic and ground ring states of -strings
are described in the light of the N=2 superconformal structure, and the ground
ring generators for the non-critical -string are explicitly constructed.
The relationship to models and quantum integrable systems is also briefly
described.Comment: 48 page
Trends in Regional Inequality in China
Several recent studies have examined the tendency of regions within a nation to exhibit long-term convergence in per capita income levels. Barro and Sala-i-Martin (1991, 1992, 1995) have found a tendency towards convergence among the U.S. states, among Japanese prefectures, and among regions within Western Europe. In this paper we examine the tendency towards convergence among the provinces of China during the period 1952-1993. We find that real income convergence of provinces in China has been a relatively recent phenomenon, emerging strongly only since the reform period began in 1978. During the initial phase of central planning, 1952-1965, there is some evidence for convergence, but it is weak and sensitive to the time period being analyzed. During the cultural revolution, 1965- 1978, there is strong evidence of divergence rather than convergence. We find strong evidence for convergence during the reform period is associated with rural reforms, and is especially strong within the coastal regions where there has been liberalization of international trade and investment flows. However, since 1990 regional incomes have begun to diverge. Such a divergence is entirely explained by the variance between the coastal and interior provinces, rather than increase in variance within each other. Therefore, it seems that China is now on a dual track, with a prosperous and fast growing coastal region and a poor interior growing at a lower rate.
Flight-test of the glide-slope track and flare-control laws for an automatic landing system for a powered-lift STOL airplane
An automatic landing system was developed for the Augmentor Wing Jet STOL Research Airplane to establish the feasibility and examine the operating characteristics of a powered-lift STOL transport flying a steep, microwave landing system (MLS) glide slope to automatically land on a STOL port. The flight test results address the longitudinal aspects of automatic powered lift STOL airplane operation including glide slope tracking on the backside of the power curve, flare, and touchdown. Three different autoland control laws were evaluated to demonstrate the tradeoff between control complexity and the resulting performance. The flight test and simulation methodology used in developing conventional jet transport systems was applied to the powered-lift STOL airplane. The results obtained suggest that an automatic landing system for a powered-lift STOL airplane operating into an MLS-equipped STOL port is feasible. However, the airplane must be provided with a means of rapidly regulation lift to satisfactorily provide the glide slope tracking and control of touchdown sink rate needed for automatic landings
Imprinted Networks as Chiral Pumps
We investigate the interaction between a chirally imprinted network and a
solvent of chiral molecules. We find, a liquid crystalline polymer network is
preferentially swollen by one component of a racemic solvent. This ability to
separate is linked to the chiral order parameter of the network, and can be
reversibly controlled via temperature or a mechanical deformation. It is
maximal near the point at which the network loses its imprinted structure. One
possible practical application of this effect would be a mechanical device for
sorting mixed chiral molecules.Comment: 4 pages, 5 figure
Finite element solution of low bond number sloshing
The dynamics of liquid propellant in a low Bond number environment which are critical to the design of spacecraft systems with respect to orbital propellant transfer and attitude control system were investigated. Digital computer programs were developed for the determination of liquid free surface equilibrium shape, lateral slosh natural vibration mode shapes, and frequencies for a liquid in a container of arbitrary axisymmetric shape with surface tension forces the same order of magnitude as acceleration forces. A finite volume element representation of the liquid was used for the vibration analysis. The liquid free surface equilibrium shapes were computed for several tanks at various contact angles and ullage volumes. A configuration was selected for vibration analysis and lateral slosh mode shapes and natural frequencies were obtained. Results are documented
A method for determining landing runway length for a STOL aircraft
Based on data obtained from flight tests of the augmentor wing jet STOL research aircraft, a method is proposed for determining the length of the landing runway for powered-lift STOL aircraft. The suggested method determines runway landing length by summing three segments: the touchdown-dispersion distance, the transition distance from touchdown to application of brakes, and the stopping distance after brakes are applied. It is shown how the landing field length can be reduced either through improved autoland system design or by providing the pilot with appropriate information to allow him to identify a "low probability" long or short landing and to execute a go-around. The proposed method appears to determine a safe runway landing length for the STOL application and offers the potential for reducing runway length if great emphasis is placed on a short-runway capability. FAR Parts 25 and 121 appear conservative and suitable for the situation where no great emphasis is placed on reducing the runway length requirement
Smectic-C tilt under shear in Smectic-A elastomers
Stenull and Lubensky [Phys. Rev. E {\bf 76}, 011706 (2007)] have argued that
shear strain and tilt of the director relative to the layer normal are coupled
in smectic elastomers and that the imposition of one necessarily leads to the
development of the other. This means, in particular, that a Smectic-A elastomer
subjected to a simple shear will develop Smectic-C-like tilt of the director.
Recently, Kramer and Finkelmann [arXiv:0708.2024, Phys. Rev. E {\bf 78}, 021704
(2008)] performed shear experiments on Smectic-A elastomers using two different
shear geometries. One of the experiments, which implements simple shear,
produces clear evidence for the development of Smectic-C-like tilt. Here, we
generalize a model for smectic elastomers introduced by Adams and Warner [Phys.
Rev. E {\bf 71}, 021708 (2005)] and use it to study the magnitude of
Smectic-C-like tilt under shear for the two geometries investigated by Kramer
and Finkelmann. Using reasonable estimates of model parameters, we estimate the
tilt angle for both geometries, and we compare our estimates to the
experimental results. The other shear geometry is problematic since it
introduces additional in-plane compressions in a sheet-like sample, thus
inducing instabilities that we discuss.Comment: 8 pages, 5 figure
KUV 01584-0939: A Helium-transferring Cataclysmic Variable with an Orbital Period of 10 Minutes
High speed photometry of KUV 01584-0939 (alias Cet3) shows that is has a
period of 620.26 s. Combined with its hydrogen-deficient spectrum, this implies
that it is an AM CVn star. The optical modulation is probably a superhump, in
which case the orbital period will be slightly shorter than what we have
observed.Comment: Published by PASP. See also the latest Early-Release Research Paper
website of the PAS
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