6,429 research outputs found
Grain Sorghum International Trade: U.S.-Mexico Simulation and Estimation Model
An econometric international supply/demand/trade simulation and forecast sorghum model in a partial equilibrium framework is built in this research paper to quantify the effects of key exogenous variables on the U.S.-Mexico sorghum trade. A forecast baseline is also established by using the validated model and values of exogenous variables provided by FAPRI to project the level of endogenous variables over the period of 2009 to 2017. Impacts of plausible alternative scenarios for key exogenous variables are simulated from 2009 to 2017.Sorghum, International Trade, Simulation, Estimation, International Relations/Trade,
Detecting structural breaks in seasonal time series by regularized optimization
Real-world systems are often complex, dynamic, and nonlinear. Understanding
the dynamics of a system from its observed time series is key to the prediction
and control of the system's behavior. While most existing techniques tacitly
assume some form of stationarity or continuity, abrupt changes, which are often
due to external disturbances or sudden changes in the intrinsic dynamics, are
common in time series. Structural breaks, which are time points at which the
statistical patterns of a time series change, pose considerable challenges to
data analysis. Without identification of such break points, the same dynamic
rule would be applied to the whole period of observation, whereas false
identification of structural breaks may lead to overfitting. In this paper, we
cast the problem of decomposing a time series into its trend and seasonal
components as an optimization problem. This problem is ill-posed due to the
arbitrariness in the number of parameters. To overcome this difficulty, we
propose the addition of a penalty function (i.e., a regularization term) that
accounts for the number of parameters. Our approach simultaneously identifies
seasonality and trend without the need of iterations, and allows the reliable
detection of structural breaks. The method is applied to recorded data on fish
populations and sea surface temperature, where it detects structural breaks
that would have been neglected otherwise. This suggests that our method can
lead to a general approach for the monitoring, prediction, and prevention of
structural changes in real systems.Comment: Safety, Reliability, Risk and Life-Cycle Performance of Structures
and Infrastructures (Edited by George Deodatis, Bruce R. Ellingwood and Dan
M. Frangopol), CRC Press 2014, Pages 3621-362
Life Tables of Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae): with a Mathematical Invalidation for Applying the Jackknife Technique to the Net Reproductive Rate
Life table data for the melon fly, Bactrocera cucurbitae (Coquillett), reared on cucumber (Cucumis sativus L.) were collected under laboratory and simulated field conditions. Means and standard errors of life table parameters were estimated for two replicates using the jackknife technique. At 25ºC, the intrinsic rates of increase (_r_) found for the two replicates were 0.1354 and 0.1002 day-1, and the net reproductive rates (_R_~0~) were 206.3 and 66.0 offspring, respectively. When the cucumbers kept under simulated field conditions were covered with leaves, the _r_ and _R_~0~ for the two replicates were 0.0935 and 0.0909 day-1, 17.5 and 11.4 offspring, respectively. However, when similar cucumbers were left uncovered, the _r_ and _R_~0~ for the two replicates were 0.1043 and 0.0904 day-1, and 27.7 and 10.1 offspring, respectively. Our results revealed that considerable variability between replicates in both laboratory and field conditions is possible; this variability should be taken into consideration in data collection and application of life tables. Mathematical analysis has demonstrated that applying the jackknife technique results in unrealistic pseudo-_R_~0~ and overestimation of its variance. We suggest that the jackknife technique should not be used for the estimation of variability of _R_~0~
Theoretical Study of Corundum as an Ideal Gate Dielectric Material for Graphene Transistors
Using physical insights and advanced first-principles calculations, we
suggest that corundum is an ideal gate dielectric material for graphene
transistors. Clean interface exists between graphene and Al-terminated (or
hydroxylated) Al2O3 and the valence band offsets for these systems are large
enough to create injection barrier. Remarkably, a band gap of {\guillemotright}
180 meV can be induced in graphene layer adsorbed on Al-terminated surface,
which could realize large ON/OFF ratio and high carrier mobility in graphene
transistors without additional band gap engineering and significant reduction
of transport properties. Moreover, the band gaps of graphene/Al2O3 system could
be tuned by an external electric field for practical applications
Probing the Electroweak Phase Transition at the LHC
We study the correlation between the value of the triple Higgs coupling and
the nature of the electroweak phase transition. We use an effective potential
approach, including higher order, non-renormalizable terms coming from
integrating out new physics. We show that if only the dimension six operators
are considered, large positive deviations of the triple Higgs coupling from its
Standard Model (SM) value are predicted in the regions of parameter space
consistent with a strong first order electroweak phase transition (SFOEPT). We
also show that at higher orders sizable and negative deviations of the triple
Higgs coupling may be obtained, and the sign of the corrections tends to be
correlated with the order of the phase transition. We also consider a singlet
extension of the SM, which allows us to establish the connection with the
effective field theory (EFT) approach and analyze the limits of its validity.
Furthermore, we study how to probe the triple Higgs coupling from the double
Higgs production at the LHC. We show that selective cuts in the invariant mass
of the two Higgs bosons should be used, to maximize the sensitivity for values
of the triple Higgs coupling significantly different from the Standard Model
one.Comment: 43 pages, 4 figure
Analytic solution of charge density of single wall carbon nanotube in conditions of field electron emission
We derived the analytic solution of induced electrostatic potential along
single wall carbon nanotubes. Under the hypothesis of constant density of
states in the charge-neutral level, we are able to obtain the linear density of
excess charge in an external field parallel to the tube axis.Comment: 4 pages, 3 figure
Efficient excitation and tuning of toroidal dipoles within individual homogenous nanoparticles
We revisit the fundamental topic of light scattering by single homogenous
nanoparticles from the new perspective of excitation and manipulation of
toroidal dipoles. It is revealed that besides within all-dielectric particles,
toroidal dipoles can also be efficiently excited within homogenous metallic
nanoparticles. Moreover, we show that those toroidal dipoles excited can be
spectrally tuned through adjusting the radial anisotropy parameters of the
materials, which paves the way for further more flexible manipulations of the
toroidal responses within photonic systems. The study into toroidal multipole
excitation and tuning within nanoparticles deepens our understanding of the
seminal problem of light scattering, and may incubate many scattering related
fundamental researches and applications.Comment: Four Figures,Ten Pages and Comments Welcome
Elusive pure anapole excitation in homogenous spherical nanoparticles with radial anisotropy
For homogenous isotropic dielectric nanospheres with incident plane waves,
Cartesian electric and toroidal dipoles can be tunned to cancel each other in
terms of far-field scattering, leading to the effective anopole excitation. At
the same time however, other multipoles such as magnetic dipoles with
comparable scattered power are simultanesouly excited, mixing with the anopole
and leading to a non-negligible total scattering cross section. Here we show
that for homogenous dielectric nanospheres, radial anisotropy can be employed
to significantly suppress the other multipole excitation, which at the same
time does not compromise the property of complete scattering cancallation
between Cartesian electric and toroidal dipoles. This enables an elusive pure
anopole excitation within radially anisotropic dielectric nanospheres, which
may shed new light to many scattering related fundamental researches and
applications.Comment: Invited submission with four figures and ten pages. Comments welcome
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