2,449 research outputs found
What Accounts for the Emergence of Malthusian Fertility in Transition Economies?
The transition to market-oriented economies in Central and Eastern Europe and the former Soviet Union in the 1990s, like the Great Depression in the U.S. and Germany in the 1930s, generated sharp declines in real incomes and a corresponding drop in fertility. This is contrary to the robust negative relationship between income and fertility that has been extensively documented. This paper presents a theoretical model that explains the positive relationship between fertility and income. The model predicts that: i) the perceived level of subsistence consumption fundamentally determines whether fertility and income are positively or negatively related; ii) once incomes decline below a threshold, declining labor income causes fertility to fall; and iii) rising income inequality has a negative impact on fertility rates. Empirical tests using both aggregate and microeconomic data provide strong support for the predictions of the model. Our empirics predict that the perceived subsistence level is a statistically significant determinant of fertility and that the average country in our sample will remain in a Mathusian fertility regime for twenty more years.Fertility; Subsistence Consumption; Transition
Performance evaluation of a six-axis generalized force-reflecting teleoperator
Work in real-time distributed computation and control has culminated in a prototype force-reflecting telemanipulation system having a dissimilar master (cable-driven, force-reflecting hand controller) and a slave (PUMA 560 robot with custom controller), an extremely high sampling rate (1000 Hz), and a low loop computation delay (5 msec). In a series of experiments with this system and five trained test operators covering over 100 hours of teleoperation, performance was measured in a series of generic and application-driven tasks with and without force feedback, and with control shared between teleoperation and local sensor referenced control. Measurements defining task performance included 100-Hz recording of six-axis force/torque information from the slave manipulator wrist, task completion time, and visual observation of predefined task errors. The task consisted of high precision peg-in-hole insertion, electrical connectors, velcro attach-de-attach, and a twist-lock multi-pin connector. Each task was repeated three times under several operating conditions: normal bilateral telemanipulation, forward position control without force feedback, and shared control. In shared control, orientation was locally servo controlled to comply with applied torques, while translation was under operator control. All performance measures improved as capability was added along a spectrum of capabilities ranging from pure position control through force-reflecting teleoperation and shared control. Performance was optimal for the bare-handed operator
Periodic and discrete Zak bases
Weyl's displacement operators for position and momentum commute if the
product of the elementary displacements equals Planck's constant. Then, their
common eigenstates constitute the Zak basis, each state specified by two phase
parameters. Upon enforcing a periodic dependence on the phases, one gets a
one-to-one mapping of the Hilbert space on the line onto the Hilbert space on
the torus. The Fourier coefficients of the periodic Zak bases make up the
discrete Zak bases. The two bases are mutually unbiased. We study these bases
in detail, including a brief discussion of their relation to Aharonov's modular
operators, and mention how they can be used to associate with the single degree
of freedom of the line a pair of genuine qubits.Comment: 15 pages, 3 figures; displayed abstract is shortened, see the paper
for the complete abstrac
An explicit Schr\"odinger picture for Aharonov's Modular Variable concept
We propose to address in a natural manner, the modular variable concept
explicitly in a Schr\"odinger picture. The idea of Modular Variables was
introduced in 1969 by Aharonov, Pendleton and Petersen to explain certain
non-local properties of quantum mechanics. Our approach to this subject is
based on Schwinger's finite quantum kinematics and it's continuous limit.Comment: 16 pages, 9 figure
On quantum mechanics with a magnetic field on R^n and on a torus T^n, and their relation
We show in elementary terms the equivalence in a general gauge of a
U(1)-gauge theory of a scalar charged particle on a torus T^n = R^n/L to the
analogous theory on R^n constrained by quasiperiodicity under translations in
the lattice L. The latter theory provides a global description of the former:
the quasiperiodic wavefunctions defined on R^n play the role of sections of the
associated hermitean line bundle E on T^n, since also E admits a global
description as a quotient. The components of the covariant derivatives
corresponding to a constant (necessarily integral) magnetic field B = dA
generate a Lie algebra g_Q and together with the periodic functions the algebra
of observables O_Q . The non-abelian part of g_Q is a Heisenberg Lie algebra
with the electric charge operator Q as the central generator; the corresponding
Lie group G_Q acts on the Hilbert space as the translation group up to phase
factors. Also the space of sections of E is mapped into itself by g in G_Q . We
identify the socalled magnetic translation group as a subgroup of the
observables' group Y_Q . We determine the unitary irreducible representations
of O_Q, Y_Q corresponding to integer charges and for each of them an associated
orthonormal basis explicitly in configuration space. We also clarify how in the
n = 2m case a holomorphic structure and Theta functions arise on the associated
complex torus. These results apply equally well to the physics of charged
scalar particles on R^n and on T^n in the presence of periodic magnetic field B
and scalar potential. They are also necessary preliminary steps for the
application to these theories of the deformation procedure induced by Drinfel'd
twists.Comment: Latex2e file, 22 pages. Final version appeared in IJT
Symmetry of Quantum Torus with Crossed Product Algebra
In this paper, we study the symmetry of quantum torus with the concept of
crossed product algebra. As a classical counterpart, we consider the orbifold
of classical torus with complex structure and investigate the transformation
property of classical theta function. An invariant function under the group
action is constructed as a variant of the classical theta function. Then our
main issue, the crossed product algebra representation of quantum torus with
complex structure under the symplectic group is analyzed as a quantum version
of orbifolding.
We perform this analysis with Manin's so-called model II quantum theta
function approach. The symplectic group Sp(2n,Z) satisfies the consistency
condition of crossed product algebra representation. However, only a subgroup
of Sp(2n,Z) satisfies the consistency condition for orbifolding of quantum
torus.Comment: LaTeX 17pages, changes in section 3 on crossed product algebr
Influence of 16S rRNA Hypervariable Region on Estimates of Bacterial Diversity and Community Composition in Seawater and Marine Sediment
To assess the influence of 16S ribosomal RNA (rRNA) tag choice on estimates of microbial diversity and/or community composition in seawater and marine sediment, we examined bacterial diversity and community composition from a site in the Central North Atlantic and a site in the Equatorial Pacific. For each site, we analyzed samples from four zones in the water column, a seafloor sediment sample, and two subseafloor sediment horizons (with stratigraphic ages of 1.5 and 5.5 million years old). We amplified both the V4 and V6 hypervariable regions of the 16S rRNA gene and clustered the sequences into operational taxonomic units (OTUs) of 97% similarity to analyze for diversity and community composition. OTU richness is much higher with the V6 tag than with the V4 tag, and subsequently OTU-level community composition is quite different between the two tags. Vertical patterns of relative diversity are broadly the same for both tags, with maximum taxonomic richness in seafloor sediment and lowest richness in subseafloor sediment at both geographic locations. Genetic dissimilarity between sample locations is also broadly the same for both tags. Community composition is very similar for both tags at the class level, but very different at the level of 97% similar OTUs. Class-level diversity and community composition of water-column samples are very similar at each water depth between the Atlantic and Pacific. However, sediment communities differ greatly from the Atlantic site to the Pacific site. Finally, for relative patterns of diversity and class-level community composition, deep sequencing and shallow sequencing provide similar results
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A Layered-Manufacturing Process For the Fabrication of Glass-Fiber-Reinforced Composites
In this paper, we present a rapid manufacturing process for the layered fabrication of
polymer-based composite parts using short discontinuous fibers as reinforcements. In the recent
past, numerous research efforts, similar to ours, have been made to produce fiber-reinforced
plastic parts via layered manufacturing methods. However, most of these attempts have not
resulted in the development of an effective commercially-viable manufacturing process. Our
proposed fabrication process on the other hand has been experimentally verified to yield
composite parts comparable in quality to pure polymer parts manufactured on a commercial
stereolithography system.Mechanical Engineerin
Algebraic Geometry Approach to the Bethe Equation for Hofstadter Type Models
We study the diagonalization problem of certain Hofstadter-type models
through the algebraic Bethe ansatz equation by the algebraic geometry method.
When the spectral variables lie on a rational curve, we obtain the complete and
explicit solutions for models with the rational magnetic flux, and discuss the
Bethe equation of their thermodynamic flux limit. The algebraic geometry
properties of the Bethe equation on high genus algebraic curves are
investigated in cooperationComment: 28 pages, Latex ; Some improvement of presentations, Revised version
with minor changes for journal publicatio
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