3,655 research outputs found
PROJECT FOR THE ANALYSIS OF LAND TENURE AND AGRICULTURAL PRODUCTIVITY IN THE REPUBLIC OF MACEDONIA
The paper arises out of the Land Market Project and covers detailed data at the individual farm level and in-depth analyses of legal and historical processes. The agricultural sector in Macedonia is characterized by two very different farm enterprise types: small family farms operating on privately owned land, and large socially owned farms. About 30 percent of the total arable land in Macedonia belongs to socially owned farms. Most of the balance belong to the private farm sector; the cooperative sector occupies a small percentage of the arable land. The Land Markets Project addressed five tasks during the six-month term of the project: (1) assess the appropriateness of legislation, regulations, and institutions affecting land tenure and land use, (2) document and assess the land-related constraints to increased productivity and profitability of private farms, (3) document and assess the land-related constraints to increased productivity and profitability of socially owned farms, (4) propose land policy adjustments that would promote increased productivity and profitability of the agricultural sector, (5) identify financial and technical assistance to support the development of land markets that promote efficient, sustainable, and equitable increases in agricultural incomes. This paper reports the results of the first three tasks and then presents a comparative review of the land tenure and productivity results for both the private and the social sector. This comparison forms a basis for policy dialogue. The paper also includes a comprehensive discussion of the policy recommendations that stem from the Land Markets Project.Land tenure--Macedonia (Republic), Land use, Rural--Economic aspects--Macedonia (Republic), Farms, Size of--Macedonia (Republic), Agriculture--Economic aspects--Macedonia (Republic), Agricultural productivity--Macedonia (Republic), Land markets--Macedonia (Republic), Agrarian structure--Macedonia (Republic), Land Economics/Use, Productivity Analysis,
An almost Poisson structure for the generalized rigid body equations
In this paper we introduce almost Poisson structures on Lie groups which
generalize Poisson structures based on the use of the classical Yang-Baxter identity.
Almost Poisson structures fail to be Poisson structures in the sense that they do
not satisfy the Jacobi identity.In the case of cross products of Lie groups, we show
that an almost Poisson structure can be used to derive a system which is intimately
related to a fundamental Hamiltonian integrable system — the generalized rigid body
equations
Microscopy of a scalable superatom
Strong interactions can amplify quantum effects such that they become
important on macroscopic scales. Controlling these coherently on a single
particle level is essential for the tailored preparation of strongly correlated
quantum systems and opens up new prospects for quantum technologies. Rydberg
atoms offer such strong interactions which lead to extreme nonlinearities in
laser coupled atomic ensembles. As a result, multiple excitation of a
Micrometer sized cloud can be blocked while the light-matter coupling becomes
collectively enhanced. The resulting two-level system, often called
"superatom", is a valuable resource for quantum information, providing a
collective Qubit. Here we report on the preparation of two orders of magnitude
scalable superatoms utilizing the large interaction strength provided by
Rydberg atoms combined with precise control of an ensemble of ultracold atoms
in an optical lattice. The latter is achieved with sub shot noise precision by
local manipulation of a two-dimensional Mott insulator. We microscopically
confirm the superatom picture by in-situ detection of the Rydberg excitations
and observe the characteristic square root scaling of the optical coupling with
the number of atoms. Furthermore, we verify the presence of entanglement in the
prepared states and demonstrate the coherent manipulation of the superatom.
Finally, we investigate the breakdown of the superatom picture when two Rydberg
excitations are present in the system, which leads to dephasing and a loss of
coherence.Comment: 7 pages, 5 figure
Discrete rigid body dynamics and optimal control
We analyze an alternative formulation of the rigid body equations, their relationship with the discrete rigid body equations of Moser-Veselov (1991) and their formulation as an optimal control problem. In addition we discuss a general class of discrete optimal control problems
AGRARIAN REFORM IN UZBEKISTAN AND OTHER CENTRAL ASIAN COUNTRIES
The five Central Asian countries that gained their independence at the breakup of the Soviet Union in 1991 have followed different paths of transition to a market economy in the agricultural sector. Kyrgyzstan has been the most aggressive in restructuring agricultural enterprises, privatizing land, and promoting individual farming. Kazakstan and Turkmenistan have had similar legal and policy reforms, but implementation has lagged. Tajikistan's efforts at reform have been hampered by civil strife and continued weakness of government. Uzbekistan, in contrast to the others, has attempted to control its progress towards market-oriented agriculture very closely, with the result that the agrarian sector looks on the surface very similar today to what it looked like in 1991. After a brief discussion of the similarities and differences among the Central Asian countries, this essay explores the results of Uzbekistan's choice to proceed "step by step," as the government says, by examining the country's characteristics of agrarian structure, agricultural production, and policy concerns.Land reform -- Uzbekistan, Land reform -- Asia, Central, Agriculture and state -- Uzbekistan, Agriculture -- Economic aspects -- Uzbekistan, Agrarian structure (Post-reform) -- Uzbekistan, Privatization -- Uzbekistan, Agricultural and Food Policy,
Designing Frustrated Quantum Magnets with Laser-Dressed Rydberg Atoms
We show how a broad class of lattice spin-1/2 models with angular- and
distance-dependent couplings can be realized with cold alkali atoms stored in
optical or magnetic trap arrays. The effective spin-1/2 is represented by a
pair of atomic ground states, and spin-spin interactions are obtained by
admixing van der Waals interactions between fine-structure split Rydberg states
with laser light. The strengths of the diagonal spin interactions as well as
the "flip-flop", and "flip-flip" and "flop-flop" interactions can be tuned by
exploiting quantum interference, thus realizing different spin symmetries. The
resulting energy scales of interactions compare well with typical temperatures
and decoherence time-scales, making the exploration of exotic forms of quantum
magnetism, including emergent gauge theories and compass models, accessible
within state-of-the-art experiments.Comment: 11 pages, 7 figure
Coherent light scattering from a two-dimensional Mott insulator
We experimentally demonstrate coherent light scattering from an atomic Mott
insulator in a two-dimensional lattice. The far-field diffraction pattern of
small clouds of a few hundred atoms was imaged while simultaneously laser
cooling the atoms with the probe beams. We describe the position of the
diffraction peaks and the scaling of the peak parameters by a simple analytic
model. In contrast to Bragg scattering, scattering from a single plane yields
diffraction peaks for any incidence angle. We demonstrate the feasibility of
detecting spin correlations via light scattering by artificially creating a
one-dimensional antiferromagnetic order as a density wave and observing the
appearance of additional diffraction peaks.Comment: 4 pages, 4 figure
Spatially Resolved Detection of a Spin-Entanglement Wave in a Bose-Hubbard Chain
Entanglement is an essential property of quantum many-body systems. However,
its local detection is challenging and was so far limited to spin degrees of
freedom in ion chains. Here we measure entanglement between the spins of atoms
located on two lattice sites in a one-dimensional Bose-Hubbard chain which
features both local spin- and particle-number fluctuations. Starting with an
initially localized spin impurity, we observe an outwards propagating
entanglement wave and show quantitatively how entanglement in the spin sector
rapidly decreases with increasing particle-number fluctuations in the chain.Comment: 6 pages, 4 figure
Exciton photon strong-coupling regime for a single quantum dot in a microcavity
We report on the observation of the strong coupling regime between a single
GaAs quantum dot and a microdisk optical mode. Photoluminescence is performed
at various temperatures to tune the quantum dot exciton with respect to the
optical mode. At resonance, we observe an anticrossing, signature of the strong
coupling regime with a well resolved doublet. The Vacuum Rabi splitting amounts
to 400 μeV and is twice as large as the individual linewidths.Comment: submitted on November 7th 200
A variational problem on Stiefel manifolds
In their paper on discrete analogues of some classical systems such as the
rigid body and the geodesic flow on an ellipsoid, Moser and Veselov introduced
their analysis in the general context of flows on Stiefel manifolds. We
consider here a general class of continuous time, quadratic cost, optimal
control problems on Stiefel manifolds, which in the extreme dimensions again
yield these classical physical geodesic flows. We have already shown that this
optimal control setting gives a new symmetric representation of the rigid body
flow and in this paper we extend this representation to the geodesic flow on
the ellipsoid and the more general Stiefel manifold case. The metric we choose
on the Stiefel manifolds is the same as that used in the symmetric
representation of the rigid body flow and that used by Moser and Veselov. In
the extreme cases of the ellipsoid and the rigid body, the geodesic flows are
known to be integrable. We obtain the extremal flows using both variational and
optimal control approaches and elucidate the structure of the flows on general
Stiefel manifolds.Comment: 30 page
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