571 research outputs found
Adoption, Management, and Impact of Hybrid Maize Seed in India
This paper presents results of a 1995 survey of 864 maize-growing households in six states that account for more than 70% of India's maize area: Andhra Pradesh, Bihar, Karnataka, Madhya Pradesh, Rajasthan, and Uttar Pradesh. The current adoption of improved open-pollinated maize varieties (OPVs) and hybrids is quantified, the relationship between adoption of improved germplasm and use of improved crop management practices is examined, the economic impacts of adoption are estimated, farmers' seed procurement and management practices are described, and implications for maize research and development policy are discussed. On the whole, the survey results confirm that India's national maize seed industry is expanding rapidly. Since seed policy reforms were introduced in the late 1980s, the area planted to improved OPVs and hybrids has grown rapidly, and adoption of improved germplasm has fueled important changes in farmers' crop management practices. However, special policy measures may be needed to ensure that the benefits of improved germplasm are widely shared, such as the introduction of targeted input subsidies designed to reduce the cost of adopting improved seed and complementary inputs, government investment in irrigation infrastructure to reduce production risk in drought-prone environments, and market development initiatives to provide small-scale producers with access to stable and reliable outlets where they can sell surplus grain.Crop Production/Industries,
High-Order Variational Calculation for the Frequency of Time-Periodic Solutions
We develop a convergent variational perturbation theory for the frequency of
time-periodic solutions of nonlinear dynamical systems. The power of the theory
is illustrated by applying it to the Duffing oscillator.Comment: Author Information under http://www.physik.fu-berlin.de/~pelster/,
http://www.physik.fu-berlin.de/~kleinert/ and
http://www.informatik.uni-stuttgart.de/ipvr/bv/personen/schanz.htm
Microlenses array made with AZ4562 photoresist for stereoscopic acquisition
In this paper is presented a fabrication process for obtaining refractive microlenses arrays with high reproducibility
and low cost. This process was specifically optimized for the AZ4562 photoresist. Functional prototypes of
microlenses arrays with dimensions in the range of 30 m, 4.9 mm and 5 m for width, length and thickness,
respectively, were fabricated and tested. The pre-thermal reflow spacing between adjacent isosceles trapezoids is
1.35-5.43 m, from bottom to top, respectively. This separation allows the photoresist to reflow and join the adjacent
microlens creating a consistent and homogeneous array.This work and Rui Pedro Rocha are fully supported by the Portuguese Foundation for Science and Technology under the project FCT/PTDC/EEA-ELC/109936/2009 and the financial grant SFRH/BD/33733/2009, respectively. The authors would also like to acknowledge Dr.-Ing Christian Koch from MicroChemicals GmbH for the technical support
Affine and toric hyperplane arrangements
We extend the Billera-Ehrenborg-Readdy map between the intersection lattice
and face lattice of a central hyperplane arrangement to affine and toric
hyperplane arrangements. For arrangements on the torus, we also generalize
Zaslavsky's fundamental results on the number of regions.Comment: 32 pages, 4 figure
X-ray and Radio Monitoring of GX 339-4 and Cyg X-1
Previous work by Motch et al. (1985) suggested that in the low/hard state of
GX339-4, the soft X-ray power-law extrapolated backward in energy agrees with
the IR flux level. Corbel and Fender (2002) later showed that the typical hard
state radio power-law extrapolated forward in energy meets the backward
extrapolated X-ray power-law at an IR spectral break, which was explicitly
observed twice in GX339-4. This has been cited as further evidence that jet
synchrotron radiation might make a significant contribution to the observed
X-rays in the hard state. We explore this hypothesis with a series of
simultaneous radio/X-ray hard state observations of GX339-4. We fit these
spectra with a simple, but remarkably successful, doubly broken power-law model
that indeed requires a spectral break in the IR. For most of these
observations, the break position as a function of X-ray flux agrees with the
jet model predictions. We then examine the radio flux/X-ray flux correlation in
Cyg X-1 through the use of 15 GHz radio data, obtained with the Ryle radio
telescope, and Rossi X-ray Timing Explorer data, from the All Sky Monitor and
pointed observations. We find evidence of `parallel tracks' in the radio/X-ray
correlation which are associated with `failed transitions' to, or the beginning
of a transition to, the soft state. We also find that for Cyg X-1 the radio
flux is more fundamentally correlated with the hard, rather than the soft,
X-ray flux.Comment: To Appear in the Proceedings of "From X-ray Binaries to Quasars:
Black Hole Accretion on All Mass Scales" (Amsterdam, July 2004). Eds. T
Maccarone, R. Fender, L. H
Special section on advances in reachability analysis and decision procedures: contributions to abstraction-based system verification
Reachability analysis asks whether a system can evolve from legitimate initial states to unsafe states. It is thus a fundamental tool in the validation of computational systems - be they software, hardware, or a combination thereof. We recall a standard approach for reachability analysis, which captures the system in a transition system, forms another transition system as an over-approximation, and performs an incremental fixed-point computation on that over-approximation to determine whether unsafe states can be reached. We show this method to be sound for proving the absence of errors, and discuss its limitations for proving the presence of errors, as well as some means of addressing this limitation. We then sketch how program annotations for data integrity constraints and interface specifications - as in Bertrand Meyers paradigm of Design by Contract - can facilitate the validation of modular programs, e.g., by obtaining more precise verification conditions for software verification supported by automated theorem proving. Then we recap how the decision problem of satisfiability for formulae of logics with theories - e.g., bit-vector arithmetic - can be used to construct an over-approximating transition system for a program. Programs with data types comprised of bit-vectors of finite width require bespoke decision procedures for satisfiability. Finite-width data types challenge the reduction of that decision problem to one that off-the-shelf tools can solve effectively, e.g., SAT solvers for propositional logic. In that context, we recall the Tseitin encoding which converts formulae from that logic into conjunctive normal form - the standard format for most SAT solvers - with only linear blow-up in the size of the formula, but linear increase in the number of variables. Finally, we discuss the contributions that the three papers in this special section make in the areas that we sketched above. © Springer-Verlag 2009
Theory of a Scanning Tunneling Microscope with a Two-Protrusion Tip
We consider a scanning tunneling microscope (STM) such that tunneling occurs
through two atomically sharp protrusions on its tip. When the two protrusions
are separated by at least several atomic spacings, the differential conductance
of this STM depends on the electronic transport in the sample between the
protrusions. Furthermore two-protrusion tips commonly occur during STM tip
preparation. We explore possible applications to probing dynamical impurity
potentials on a metallic surface and local transport in an anisotropic
superconductor.Comment: revtex, 11 pages, 6 figures upon reques
Angular dependence of domain wall resistivity in SrRuO films
is a 4d itinerant ferromagnet (T 150 K) with
stripe domain structure. Using high-quality thin films of SrRuO we study
the resistivity induced by its very narrow ( nm) Bloch domain walls,
(DWR), at temperatures between 2 K and T as a function of the
angle, , between the electric current and the ferromagnetic domains
walls. We find that which provides the first experimental
indication that the angular dependence of spin accumulation contribution to DWR
is . We expect magnetic multilayers to exhibit a similar
behavior.Comment: 5 pages, 5 figure
Modeling Amyloid Beta Peptide Insertion into Lipid Bilayers
Inspired by recent suggestions that the Alzheimer's amyloid beta peptide (A
beta) can insert into cell membranes and form harmful ion channels, we model
insertion of the 40 and 42 residue forms of the peptide into cell membranes
using a Monte Carlo code which is specific at the amino acid level. We examine
insertion of the regular A-beta peptide as well as mutants causing familial
Alzheimer's disease, and find that all but one of the mutants change the
insertion behavior by causing the peptide to spend more simulation steps in
only one leaflet of the bilayer. We also find that A-beta 42, because of the
extra hydrophobic residues relative to A-beta 40, is more likely to adopt this
conformation than A-beta 40 in both wild-type and mutant forms. We argue
qualitatively why these effects happen. Here, we present our results and
develop the hypothesis that this partial insertion increases the probability of
harmful channel formation. This hypothesis can partly explain why these
mutations are neurotoxic simply due to peptide insertion behavior. We further
apply this model to various artificial A-beta mutants which have been examined
experimentally, and offer testable experimental predictions contrasting the
roles of aggregation and insertion with regard to toxicity of A-beta mutants.
These can be used through further experiments to test our hypothesis.Comment: 14 pages; 8 figures; 2nd revisio
Estimating the feasibility of transition paths in extended finite state machines
There has been significant interest in automating testing on the basis of an extended finite state machine (EFSM) model of the required behaviour of the implementation under test (IUT). Many test criteria require that certain parts of the EFSM are executed. For example, we may want to execute every transition of the EFSM. In order to find a test suite (set of input sequences) that achieves this we might first derive a set of paths through the EFSM that satisfy the criterion using, for example, algorithms from graph theory. We then attempt to produce input sequences that trigger these paths. Unfortunately, however, the EFSM might have infeasible paths and the problem of determining whether a path is feasible is generally undecidable. This paper describes an approach in which a fitness function is used to estimate how easy it is to find an input sequence to trigger a given path through an EFSM. Such a fitness function could be used in a search-based approach in which we search for a path with good fitness that achieves a test objective, such as executing a particular transition, and then search for an input sequence that triggers the path. If this second search fails then we search for another path with good fitness and repeat the process. We give a computationally inexpensive approach (fitness function) that estimates the feasibility of a path. In order to evaluate this fitness function we compared the fitness of a path with the ease with which an input sequence can be produced using search to trigger the path and we used random sampling in order to estimate this. The empirical evidence suggests that a reasonably good correlation (0.72 and 0.62) exists between the fitness of a path, produced using the proposed fitness function, and an estimate of the ease with which we can randomly generate an input sequence to trigger the path
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