499 research outputs found
Suitability for Global Maize Production: A Methodology Based on Spatial Analysis
A methodology based on spatial analysis is proposed to investigate suitability of crop, and then applied to analyzing the suitability for global maize production. The suitable and unsuitable maize cultivated regions are given based on the analysis, and maize cultivated regions sensitive to economic incentive is also illustrated and discussed.Crop Production/Industries,
Measuring Hubble's Constant in our Inhomogeneous Universe
Recent observations of Cepheids in the Virgo cluster have bolstered the
evidence that supports a Hubble constant in 70-90 km/s/Mpc range. This
evidence, by and large, probes the expansion of the Universe within 100 Mpc. We
investigate the possibility that the expansion rate within this region is
systematically higher than the true expansion rate due to the presence of a
local, large underdense region or void. We begin by calculating the expected
deviations between the locally measured Hubble constant and the true Hubble
constant for a variety of models. We also discuss the expected correlations
between these deviations and mass fluctuation for the sample volume. We find
that the fluctuations are small for the standard cold dark matter as well as
mixed dark matter models but can be substantial in a number of interesting and
viable nonstandard scenarios. However, deviations in the Hubble flow for a
region of radius 200 Mpc are small for virtually all reasonable models.
Therefore, methods based on supernovae or the Sunyaev-Zel'dovich effect, which
can probe 200 Mpc scales, will be essential in determining the true Hubble
constant. We discuss, in detail, the fluctuations induced in the cosmic
background radiation by voids at the last scattering surface. In addition, we
discuss the dipole and quadrupole fluctuations one would expect if the void
enclosing us is aspherical or if we lie off-center.Comment: 20 pages (58K), 8 Postscript figures (111K compressed); Submitted to
MNRAS. Postscript source available at
http://astro.queensu.ca/~dursi/preprints
Impact of Daily Arctic Sea Ice Variability in CAM3.0 during Fall and Winter
Climate projections suggest that an ice-free summer Arctic Ocean is possible within several decades and with this comes the prospect of increased ship traffic and safety concerns. The daily sea ice concentration tendency in five Coupled Model Intercomparison Project phase 5 (CMIP5) simulations is compared with observations to reveal that many models underestimate this quantity that describes high-frequency ice movements, particularly in the marginal ice zone. To investigate whether high-frequency ice variability impacts the atmosphere, the Community Atmosphere Model, version 3.0 (CAM3.0), is forced by sea ice with and without daily fluctuations. Two 100-member ensemble experiments with daily varying (DAILY) and smoothly varying (SMTH) sea ice are conducted, along with a climatological control, for an anoma- lously low ice period (August 2006–November 2007). Results are presented for three periods: September 2006, October 2006, and December–February (DJF) 2006/07. The atmospheric response differs between DAILY and SMTH. In September, sea ice differences lead to an anomalous high and weaker storm activity over northern Europe. During October, the ice expands equatorward faster in DAILY than SMTH in the Siberian seas and leads to a local response of near-surface cooling. In DJF, there is a 1.5-hPa positive sea level pressure anomaly over North America, leading to anomalous northerly flow and anomalously cool continental U.S. temperatures. While the atmospheric responses are modest, the differences arising from high temporal frequency ice variability cannot be ignored. Increasing the accuracy of coupled model sea ice variations on short time scales is needed to improve short-term coupled model forecasts
Quark Propagation in the Quark-Gluon Plasma
It has recently been suggested that the quark-gluon plasma formed in
heavy-ion collisions behaves as a nearly ideal fluid. That behavior may be
understood if the quark and antiquark mean-free- paths are very small in the
system, leading to a "sticky molasses" description of the plasma, as advocated
by the Stony Brook group. This behavior may be traced to the fact that there
are relatively low-energy resonance states in the plasma leading to
very large scattering lengths for the quarks. These resonances have been found
in lattice simulation of QCD using the maximum entropy method (MEM). We have
used a chiral quark model, which provides a simple representation of effects
due to instanton dynamics, to study the resonances obtained using the MEM
scheme. In the present work we use our model to study the optical potential of
a quark in the quark-gluon plasma and calculate the quark mean-free-path. Our
results represent a specific example of the dynamics of the plasma as described
by the Stony Brook group.Comment: 17 pages, 4 figures, revtex
Probing Quark Distribution Amplitudes Through Generalized Parton Distributions at Large Momentum Transfer
In the large momentum transfer limit, generalized parton distributions can be
calculated through a QCD factorization theorem which involves
perturbatively-calculable hard kernels and light-cone parton distribution
amplitudes of hadrons. We illustrate this through the
distribution for the pion and proton, presenting the hard kernels at leading
order. As a result, experimental data on the generalized parton distributions
in this regime can be used to determine the functional form of the parton
distribution amplitudes which has thus far been quite challenging to obtain.
Our result can also be used as a constraint in phenomenological GPD
parametrizations.Comment: 7 pages, 4 figures; new references and figure added, errors correcte
Lorentz Symmetry and the Internal Structure of the Nucleon
To investigate the internal structure of the nucleon, it is useful to
introduce quantities that do not transform properly under Lorentz symmetry,
such as the four-momentum of the quarks in the nucleon, the amount of the
nucleon spin contributed by quark spin, etc. In this paper, we discuss to what
extent these quantities do provide Lorentz-invariant descriptions of the
nucleon structure.Comment: 6 pages, no figur
Calculation of Screening Masses in a Chiral Quark Model
We consider a simple model for the coordinate-space vacuum polarization
function which is often parametrized in terms of a screening mass. We discuss
the circumstances in which the standard result for the screening mass,
, is obtained. In the model considered here, that result is
obtained when the momenta in the relevant vacuum polarization integral are
small with respect to the first Matsubara frequency.Comment: 6 pages, 2 figure
Counting Rule for Hadronic Light-Cone Wave Functions
We introduce a systematic way to write down the Fock components of a hadronic
light-cone wave function with partons and orbital angular momentum
projection . We show that the wave function amplitude
has a leading behavior
when all parton transverse
momenta are uniformly large, where and are the number of partons
and orbital angular momentum projection, respectively, of an amplitude that
mixes under renormalization. The result can be used as a constraint in modeling
the hadronic light-cone wave functions. We also derive a generalized counting
rule for hard exclusive processes involving parton orbital angular momentum and
hadron helicity flip.Comment: 7 pages, no figur
Mast cell leukemia with prolonged survival on PKC412/midostaurin
Mast cell leukemia (MCL) is a rare and aggressive form of systemic mastocytosis. There are approximately 50 reported cases since 1950s. MCL is refractory to cytoreduction chemotherapy and the average survival is only six months. We report a MCL case in a 71 year-old woman with high tumor load at the initial presentation in 2005, who did not respond to either interleukin-2 or dasatinib therapy. After enrolled in a clinical trial of PKC412 (or Midostaurin) with a daily dose of 100 mg, the patient responded well to PKC412 and became transfusion independent in three months. Since then, her disease had been stably controlled. This is the first report of a high-tumor-load MCL case which achieved prolonged survival (101 months) by PKC 412. The 101-month overall survival is the longest among reported MCL cases in the English literature
Novel Quark Fragmentation Functions and the Nucleon's Transversity Distribution
We define twist-two and twist-three quark fragmentation functions in Quantum
Chromodynamics (QCD) and study their physical implications. Using this
formalism we show how the nucleon's transversity distribution can be measured
in single pion inclusive electroproduction.Comment: 10 pages, uses PHYZZX macro package, 2 PostScript figures (added
using FIGURES). MIT-CTP-215
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