6,890 research outputs found
Isospin effects on the mass dependence of balance energy
We study the effect of isospin degree of freedom on balance energy throughout
the mass range between 50 and 350 for two sets of isotopic systems with N/Z =
1.16 and 1.33 as well as isobaric systems with N/Z = 1.0 and 1.4. Our findings
indicate that different values of balance energy for two isobaric systems may
be mainly due to the Coulomb repulsion. We also demonstrate clearly the
dominance of Coulomb repulsion over symmetry energy.Comment: 5 pages, 3 figures In this version the discussion is in terms of N/Z
whereas in the journal the whole discussion is in terms of N/A. The
conclusions remain unaffecte
Reconsidering the evidence on returns to T&V extension in Kenya
The authors revisit the widely disseminated results of a study (Bindlish and Evenson 1993, 1997) of the impact of the training and visit (T&V) system of management for public extension services in Kenya. T&V was introduced in Kenya by the World Bank and has since been supported through two successive projects. The impact of the projects continues to be the subject of much debate. The authors'paper suggests the need for greater vigilance in empirical analysis, especially about the quality of data used to support Bank policy and the need to validate potentially influential findings. Using household data from 1990, Bindlish and Evenson found the returns from extension to be very high. But the authors find that the returns estimated by Binslish and Evenson suffer from data errors, and limitations imposed by cross-sectional data. After correcting for several data processing and measurement errors, the authors show the results to be less robust than reported by Bindlish and Evenson and highly sensitive to regional effects. When region-specific effects are included, a positive return to extension cannot be established, using Bindlish and Evenson's data set and cross-sectional model specifications. After testing the robustness of results using a number of tests, the authors could not definitively establish the factors underlying strong regional effects, largely because of the limitations imposed by the cross-sectional framework. Household panel data methods would have allowed greater control for regional effects and would have yielded better insight into the impact of extension. The impact on agricultural productivity in Kenya expected from T&V extension services is not discernible from the available data, and the impact may vary across districts. The hypothesis that T&V had no impact in Kenya between 1982 and 1990 cannot be rejected. The sample data fail to support a positive rate of return on the investment in T&V.Agricultural Knowledge&Information Systems,Statistical&Mathematical Sciences,Environmental Economics&Policies,Labor Policies,Economic Theory&Research,Economic Theory&Research,Health Economics&Finance,Agricultural Knowledge&Information Systems,Environmental Economics&Policies,Statistical&Mathematical Sciences
A Time-Dependent Classical Solution of C=1 String Field Theory and Non-Perturbative Effects
We describe a real-time classical solution of string field theory
written in terms of the phase space density, , of the equivalent
fermion theory. The solution corresponds to tunnelling of a single fermion
above the filled fermi sea and leads to amplitudes that go as \exp(- C/
\gst). We discuss how one can use this technique to describe non-perturbative
effects in the Marinari-Parisi model. We also discuss implications of this type
of solution for the two-dimensional black hole.Comment: 23
Coadjoint orbit action of Virasoro group and two-dimensional quantum gravity dual to SYK/tensor models
The Nambu-Goldstone (NG) bosons of the SYK model are described by a coset
space Diff/, where Diff, or Virasoro group, is the
group of diffeomorphisms of the time coordinate valued on the real line or a
circle. It is known that the coadjoint orbit action of Diff naturally turns out
to be the two-dimensional quantum gravity action of Polyakov without
cosmological constant, in a certain gauge, in an asymptotically flat spacetime.
Motivated by this observation, we explore Polyakov action with cosmological
constant and boundary terms, and study the possibility of such a
two-dimensional quantum gravity model being the AdS dual to the low energy (NG)
sector of the SYK model. We find strong evidences for this duality: (a) the
bulk action admits an exact family of asymptotically AdS spacetimes,
parameterized by Diff/, in addition to a fixed
conformal factor of a simple functional form; (b) the bulk path integral
reduces to a path integral over Diff/ with a
Schwarzian action; (c) the low temperature free energy qualitatively agrees
with that of the SYK model. We show, up to quadratic order, how to couple an
infinite series of bulk scalars to the Polyakov model and show that it
reproduces the coupling of the higher modes of the SYK model with the NG
bosons.Comment: 2+33 pages (including Appendices), 3 figures; v2 has revised
discussion of orbits in Section 2, typos corrected; v3 has a new appendix
analysing the off-shell equations of motion; v4 is published version with
some more typos corrected; v5 corrects some typesetting error
Wave Propagation in Stringy Black Hole
We further study the nonperturbative formulation of two-dimensional black
holes. We find a nonlinear differential equation satisfied by the tachyon in
the black hole background. We show that singularities in the tachyon field
configurations are always associated with divergent semiclassical expansions
and are absent in the exact theory. We also discuss how the Euclidian black
hole emerges from an analytically continued fermion theory that corresponds to
the right side up harmonic oscillator potential.Comment: 23p, TIFR-TH-93/05; (v3) tex error correcte
Non-relativistic Fermions, Coadjoint Orbits of \winf\ and String Field Theory at
We apply the method of coadjoint orbits of \winf-algebra to the problem of
non-relativistic fermions in one dimension. This leads to a geometric
formulation of the quantum theory in terms of the quantum phase space
distribution of the fermi fluid. The action has an infinite series expansion in
the string coupling, which to leading order reduces to the previously discussed
geometric action for the classical fermi fluid based on the group of
area-preserving diffeomorphisms. We briefly discuss the strong coupling limit
of the string theory which, unlike the weak coupling regime, does not seem to
admit of a two dimensional space-time picture. Our methods are equally
applicable to interacting fermions in one dimension.Comment: 22 page
Stringy Quantum Effects in 2-Dimensional Black-Hole
We discuss the classical 2-dim. black-hole in the framework of the
non-perturbative formulation (in terms of non-relativistic fermions) of c=1
string field theory. We identify an off-shell operator whose classical equation
of motion is that of tachyon in the classical graviton-dilaton black-hole
background. The black-hole `singularity' is identified with the fermi surface
in the phase space of a single fermion, and as such is a consequence of the
semi-classical approximation. An exact treatment reveals that stringy quantum
effects wash away the classical singularity.Comment: 17p, TIFR/TH/92-63; (v3) tex error correcte
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