2,163 research outputs found
NEMA, a functional–structural model of nitrogen economy within wheat culms after flowering. II. Evaluation and sensitivity analysis
Background and Aims Simulating nitrogen economy in crop plants requires formalizing the interactions between soil nitrogen availability, root nitrogen acquisition, distribution between vegetative organs and remobilization towards grains. This study evaluates and analyses the functional–structural and mechanistic model of nitrogen economy, NEMA (Nitrogen Economy Model within plant Architecture), developed for winter wheat (Triticum aestivum) after flowering.Methods NEMA was calibrated for field plants under three nitrogen fertilization treatments at flowering. Model behaviour was investigated and sensitivity to parameter values was analysed. Key Results Nitrogen content of all photosynthetic organs and in particular nitrogen vertical distribution along the stem and remobilization patterns in response to fertilization were simulated accurately by the model, from Rubisco turnover modulated by light intercepted by the organ and a mobile nitrogen pool. This pool proved to be a reliable indicator of plant nitrogen status, allowing efficient regulation of nitrogen acquisition by roots, remobilization from vegetative organs and accumulation in grains in response to nitrogen treatments. In our simulations, root capacity to import carbon, rather than carbon availability, limited nitrogen acquisition and ultimately nitrogen accumulation in grains, while Rubisco turnover intensity mostly affected dry matter accumulation in grains. Conclusions NEMA enabled interpretation of several key patterns usually observed in field conditions and the identification of plausible processes limiting for grain yield, protein content and root nitrogen acquisition that could be targets for plant breeding; however, further understanding requires more mechanistic formalization of carbon metabolism. Its strong physiological basis and its realistic behaviour support its use to gain insights into nitrogen economy after flowering
Alternative Solution of Strong CP
In this talk I begin with some general discussion of the history of CP
violation, then move on to aspects of a spontaneous CP violation model
including the production of new particles at LHC, implications for B decay,
generalized Cabibbo mixing and a reevaluation of kaon CP violation. Finally
there is a summary.Comment: 4 pages Latex. Talk at Fifth IFT Workshop: Axions. March 199
Stability Boundaries for Offshore Wind Park Distributed Voltage Control
In order to identify mechanisms causing slow reactive power oscillations observed in an existing offshore wind power plant, and be able to avoid similar events in the future, voltage control is studied in this paper for a plant with a static synchronous compensator, type-4 wind turbines and a park pilot control. Using data from the actual wind power plant, all stabilizing subsystem voltage proportional-integral controller parameters are first characterized based on their Hurwitz signature. Inner loop current control is then designed using Internal Mode Control principles, and guidelines for feed forward filter design are given to obtain required disturbance rejection properties. The paper contributes by providing analytical relations between power plant control, droop, sampling time, electrical parameters and voltage control characteristics, and by assessing frequencies and damping of reactive power modes over a realistic envelope of electrical impedances and control parameters
Comments on MHV Tree Amplitudes for Conformal Supergravitons from Topological B-Model
We use the twistor-string theory on the B-model of CP^{3|4} to compute the
maximally helicity violating(MHV) tree amplitudes for conformal supergravitons.
The correlator of a bilinear in the affine Kac-Moody current(Sugawara
stress-energy tensor) can generate these amplitudes. We compare with previous
results from open string version of twistor-string theory. We also compute the
MHV tree amplitudes for both gravitons and gluons from the correlators between
stress-energy tensor and current.Comment: 27p
Photoresponsive and Ultraviolet to Visible-Light Range Photocatalytic Properties of ZnO:Sb Nanowires
100學年度研究獎補助論文[[abstract]]Zinc oxide (ZnO) doped antimony (Sb) nanowires have been synthesized for improving ultraviolet sensing and photocatalytic properties. Upon illumination by UV light (365nm , 2.33mWcm−2 ), the photoelectric current of the ZnO:Sb nanowires exhibited a rapid photoresponse as compared to that of the ZnO nanowires. A highest ratio of photocurrent to dark current of around 48.8-fold was achieved in the as-synthesized ZnO:Sb nanowires. A UV-visible spectrophotometer was used to investigate the absorbance spectrum of the ZnO:Sb nanowires, which exhibited a high absorbance ratio with redshift effect in contrast to that of the ZnO nanowires. Visible-light photocatalysis and UV photoresponsive properties of the ZnO:Sb nanowires are superior to those of the ZnO nanowires.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]電子
Magnetic-field dependence of electron spin relaxation in n-type semiconductors
We present a theoretical investigation of the magnetic field dependence of
the longitudinal () and transverse () spin relaxation times of
conduction band electrons in n-type III-V semiconductors. In particular, we
find that the interplay between the Dyakonov-Perel process and an additional
spin relaxation channel, which originates from the electron wave vector
dependence of the electron -factor, yields a maximal at a finite
magnetic field. We compare our results with existing experimental data on
n-type GaAs and make specific additional predictions for the magnetic field
dependence of electron spin lifetimes.Comment: accepted for publication in PRB, minor changes to previous manuscrip
When do colliding bubbles produce an expanding universe?
It is intriguing to consider the possibility that the Big Bang of the
standard (3+1) dimensional cosmology originated from the collision of two
branes within a higher dimensional spacetime, leading to the production of a
large amount of entropy. In this paper we study, subject to certain
well-defined assumptions, under what conditions such a collision leads to an
expanding universe. We assume the absence of novel physics, so that ordinary
(4+1) -dimensional Einstein gravity remains a valid approximation. It is
necessary that the fifth dimension not become degenerate at the moment of
collision. First the case of a symmetric collision of infinitely thin branes
having a hyperbolic or flat spatial geometry is considered. We find that a
symmetric collision results in a collapsing universe on the final brane unless
the pre-existing expansion rate in the bulk just prior to the collision is
sufficiently large in comparison to the momentum transfer in the fifth
dimension. Such prior expansion may either result from negative spatial
curvature or from a positive five-dimensional cosmological constant. The
relevance of these findings to the Colliding Bubble Braneworld Universe
scenario is discussed. Finally, results from a numerical study of colliding
thick-wall branes is presented, which confirm the results of the thin-wall
approximation.Comment: 24 pages, 13 figures. Minor changes and references include
Setting the scale for the Luescher-Weisz action
We study the quark-antiquark potential of quenched SU(3) lattice gauge theory
with the Luescher-Weisz action. After blocking the gauge fields with the
recently proposed hypercubic transformation we compute the Sommer parameter,
extract the lattice spacing a and set the scale at 6 different values of the
gauge coupling in a range from a = 0.084 fm to 0.136 fm.Comment: Remarks and references added, to appear in Phys. Rev.
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