1,782 research outputs found
Maize in China: Production Systems, Constraints, and Research Priorities
Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,
Using Economics to Explain Spatial Diversity in a Wheat Crop: Examples from Australia and China
Spatial diversity indicators may serve an important function for policymakers as they seek to manage crop genetic diversity and potential externalities associated with diffusion of some types of genetically improved crops. This paper adapts spatial diversity indices employed by ecologists in the study of species diversity to area distributions of modern wheat varieties in contrasting production systems of Australia and China. The variation in three interrelated concepts of diversity "richness, abundance, and evenness" is explained by factors related to the demand and supply of varieties, agroecology, and policies using the econometric method of Zellner's seemingly unrelated regression (SUR). Results suggest that in addition to expected yield and profitability, other variety characteristics are important in explaining variation in the spatial distribution of modern wheat varieties. Environmental factors and policy variables related to the supply of varieties, international research spillins, and market liberalization are also determinants of the diversity in these systems. Explanatory factors affect richness, abundance and evenness in the distribution of modern wheat varieties in different ways. Comparing results between a small, commercial wheat-producing shire in Australia and a large, heterogeneous area in seven provinces of China illustrates the importance of scale and the nature of the farming system. Further research might include: (1) refinement of methods used to construct spatial diversity indices by incorporating geographically-referenced information; (2) more explicit treatment of the relationship between scale of measurement and diversity indices; (3) refinements in the specification of policy variables, and (4) application of similar methods in zones where traditional varieties are grown.Crop Production/Industries,
Exact analytical solutions to the master equation of quantum Brownian motion for a general environment
We revisit the model of a quantum Brownian oscillator linearly coupled to an
environment of quantum oscillators at finite temperature. By introducing a
compact and particularly well-suited formulation, we give a rather quick and
direct derivation of the master equation and its solutions for general spectral
functions and arbitrary temperatures. The flexibility of our approach allows
for an immediate generalization to cases with an external force and with an
arbitrary number of Brownian oscillators. More importantly, we point out an
important mathematical subtlety concerning boundary-value problems for
integro-differential equations which led to incorrect master equation
coefficients and impacts on the description of nonlocal dissipation effects in
all earlier derivations. Furthermore, we provide explicit, exact analytical
results for the master equation coefficients and its solutions in a wide
variety of cases, including ohmic, sub-ohmic and supra-ohmic environments with
a finite cut-off.Comment: 37 pages (26 + appendices), 14 figures; this paper is an evolution of
arXiv:0705.2766v1, but contains far more general and significant results; v2
minor changes, double column, improved Appendix
Spin swap gate in the presence of qubit inhomogeneity in a double quantum dot
We study theoretically the effects of qubit inhomogeneity on the quantum
logic gate of qubit swap, which is an integral part of the operations of a
quantum computer. Our focus here is to construct a robust pulse sequence for
swap operation in the simultaneous presence of Zeeman inhomogeneity for quantum
dot trapped electron spins and the finite-time ramp-up of exchange coupling in
a double dot. We first present a geometric explanation of spin swap operation,
mapping the two-qubit operation onto a single-qubit rotation. We then show that
in this geometric picture a square-pulse-sequence can be easily designed to
perform swap in the presence of Zeeman inhomogeneity. Finally, we investigate
how finite ramp-up times for the exchange coupling negatively affect the
performance of the swap gate sequence, and show how to correct the problems
numerically.Comment: published versio
Relations between entanglement, Bell-inequality violation and teleportation fidelity for the two-qubit X states
Based on the assumption that the receiver Bob can apply any unitary
transformation, Horodecki {\it et al.} [Phys. Lett. A {\bf 222}, 21 (1996)]
proved that any mixed two spin-1/2 state which violates the Bell-CHSH
inequality is useful for teleportation. Here, we further show that any X state
which violates the Bell-CHSH inequality can also be used for nonclassical
teleportation even if Bob can only perform the identity or the Pauli rotation
operations. Moreover, we showed that the maximal difference between the two
average fidelities achievable via Bob's arbitrary transformations and via the
sole identity or the Pauli rotation is 1/9.Comment: 5 pages, to be published in "Quantum Information Processing
Local channels preserving maximal entanglement or Schmidt number
Maximal entanglement and Schmidt number play an important role in various
quantum information tasks. In this paper, it is shown that a local channel
preserves maximal entanglement state(MES) or preserves pure states with Schmidt
number ( is a fixed integer) if and only if it is a local unitary
operation.Comment: 10 page
Decoherence Strength of Multiple Non-Markovian Environments
It is known that one can characterize the decoherence strength of a Markovian
environment by the product of its temperature and induced damping, and order
the decoherence strength of multiple environments by this quantity. We show
that for non-Markovian environments in the weak coupling regime there also
exists a natural (albeit partial) ordering of environment-induced
irreversibility within a perturbative treatment. This measure can be applied to
both low-temperature and non-equilibrium environments.Comment: 6 pages, 1 figure, v3 included figure, appendix, and clarification of
result
Gate errors in solid state quantum computer architectures
We theoretically consider possible errors in solid state quantum computation
due to the interplay of the complex solid state environment and gate
imperfections. In particular, we study two examples of gate operations in the
opposite ends of the gate speed spectrum, an adiabatic gate operation in
electron-spin-based quantum dot quantum computation and a sudden gate operation
in Cooper pair box superconducting quantum computation. We evaluate
quantitatively the non-adiabatic operation of a two-qubit gate in a
two-electron double quantum dot. We also analyze the non-sudden pulse gate in a
Cooper-pair-box-based quantum computer model. In both cases our numerical
results show strong influences of the higher excited states of the system on
the gate operation, clearly demonstrating the importance of a detailed
understanding of the relevant Hilbert space structure on the quantum computer
operations.Comment: 6 pages, 2 figure
Decoherence by a nonlinear environment: canonical vs. microcanonical case
We compare decoherence induced in a simple quantum system (qubit) for two
different initial states of the environment: canonical (fixed temperature) and
microcanonical (fixed energy), for the general case of a fully interacting
oscillator environment. We find that even a relatively compact oscillator bath
(with the effective number of degrees of freedom of order 10), initially in a
microcanonical state, will typically cause decoherence almost indistinguishable
from that by a macroscopic, thermal environment, except possibly at
singularities of the environment's specific heat (critical points). In the
latter case, the precise magnitude of the difference between the canonical and
microcanonical results depends on the critical behavior of the dissipative
coefficient, characterizing the interaction of the qubit with the environment.Comment: 18 pages, revtex, 2 figures; minor textual changes, corrected typo in
eq. (53) (v2); textual changes, mostly in the introduction (v3
Identification of differentially expressed genes induced by Bamboo mosaic virus infection in Nicotiana benthamiana by cDNA-amplified fragment length polymorphism
Background: The genes of plants can be up- or down-regulated during viral infection to influence the replication of viruses. Identification of these differentially expressed genes could shed light on the defense systems employed by plants and the mechanisms involved in the adaption of viruses to plant cells. Differential gene expression in Nicotiana benthamiana plants in response to infection with Bamboo mosaic virus (BaMV) was revealed using cDNA-amplified fragment length polymorphism (AFLP). Results: Following inoculation with BaMV, N. benthamiana displayed differential gene expression in response to the infection. Isolation, cloning, and sequencing analysis using cDNA-AFLP furnished 90 cDNA fragments with eight pairs of selective primers. Fifteen randomly selected genes were used for a combined virus-induced gene silencing (VIGS) knockdown experiment, using BaMV infection to investigate the roles played by these genes during viral infection, specifically addressing the means by which these genes influence the accumulation of BaMV protein. Nine of the 15 genes showed either a positive or a negative influence on the accumulation of BaMV protein. Six knockdown plants showed an increase in the accumulation of BaMV, suggesting that they played a role in the resistance to viral infection, while three plants showed a reduction in coat protein, indicating a positive influence on the accumulation of BaMV in plants. An interesting observation was that eight of the nine plants showing an increase in BaMV coat protein were associated with cell rescue, defense, death, aging, signal transduction, and energy production. Conclusions: This study reports an efficient and straightforward method for the identification of host genes involved in viral infection. We succeeded in establishing a cDNA-AFLP system to help track changes in gene expression patterns in N. benthamiana plants when infected with BaMV. The combination of both DNA-AFLP and VIGS methodologies made it possible to screen a large number of genes and identify those associated with infections of plant viruses. In this report, 9 of the 15 analyzed genes exhibited either a positive or a negative influence on the accumulation of BaMV in N. benthamiana plants
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