2,839 research outputs found
Assessing the Effects of Climate Change on Farm Production and Profitability: Dynamic Simulation Approach
In this paper, a dynamic optimization model was developed to simulate how farm-level realized price and profitability respond to yield change which was induced by climate change. Producers' acreage response was included in the dynamic model considering crop rotation effect. In the crop rotation model, a modified Bellman equation was used to dynamically optimize the net present value of farm profit for a five-year interval. This simulation process was repeated through the year 2050. Then yield, price, and acreage response were compiled to generate realized profit. Results generally indicated that reduction in crop yields due to climate change results in reduced farm profitability for most of the states studied. Predicted climate change is more likely to pose a problem for agricultural production and profitability in the southern U.S. states as compared to the northern U.S. states. Our results also suggest that acreage response alone is not sufficient to ameliorate the potential negative effects of global climate change on agricultural production and profitability. The results of this research are expected to provide a foundation for future related research to aid producers' crop rotation decisions in an unstable price environment.Dynamic simulation model, Acreage response, Crop rotation, Expected price, Realized price, Agricultural Finance, Crop Production/Industries, Environmental Economics and Policy, Farm Management, Land Economics/Use, Production Economics, Productivity Analysis, Risk and Uncertainty,
Principal Component Analysis of Crop Yield Response to Climate Change
The objective of this study is to compare the effects of climate change on crop yields across different regions. A Principal Component Regression (PCR) model is developed to estimate the historical relationships between weather and crop yields for corn, soybeans, cotton, and peanuts for several northern and southern U.S. states. Climate change projection data from three climate models are applied to the estimated PCR model to forecast crop yield response. Instead of directly using weather variables as predictor variables, the PCR model uses weather indices transformed from original weather variables by the Principal Component Analysis (PCA) approach. A climate change impact index (CCII) is developed to compare climate change effects across different regions. The key contribution of our study is in identifying a different climate change effects in crop yields in different U.S. states. Specifically, our results indicate that future warmer weather will have a negative impact for southern U.S. counties, while it has insignificant impact for northern U.S. counties in the next four decades.Principal component regression, Crop yield response, Climate change., Crop Production/Industries,
Microscopic calculation of 6Li elastic and transition form factors
Variational Monte Carlo wave functions, obtained from a realistic Hamiltonian
consisting of the Argonne v18 two-nucleon and Urbana-IX three-nucleon
interactions, are used to calculate the 6Li ground-state longitudinal and
transverse form factors as well as transition form factors to the first four
excited states. The charge and current operators include one- and two-body
components, leading terms of which are constructed consistently with the
two-nucleon interaction. The calculated form factors and radiative widths are
in good agreement with available experimental data.Comment: 9 pages, 2 figures, REVTeX, submitted to Physical Review Letters,
with updated introduction and reference
Gravitational lensing of the farthest known supernova SN1997ff
We investigate the effects of gravitational lensing due to intervening
galaxies on the recently discovered Type Ia supernova at z=1.7, SN1997ff, in
the Hubble Deep Field North. We find that it is possible to obtain a wide range
of magnifications by varying the mass and/or the velocity dispersion
normalization of the lensing galaxies. In order to be able to use SN1997ff to
constrain the redshift-distance relation, very detailed modeling of the
galaxies to control the systematic effects from lensing is necessary. Thus we
argue, that based on our current limited knowledge of the lensing galaxies, it
is difficult to use SN1997ff to constrain the values of Omega_M and
Omega_Lambda, or even to place severe limits on grey dust obscuration or
luminosity evolution of Type Ia supernovae.Comment: 5 pages, 4 figures, minor revisions after bug fix, conclusions remain
unchange
Gamma Lines without a Continuum: Thermal Models for the Fermi-LAT 130 GeV Gamma Line
Recent claims of a line in the Fermi-LAT photon spectrum at 130 GeV are
suggestive of dark matter annihilation in the galactic center and other dark
matter-dominated regions. If the Fermi feature is indeed due to dark matter
annihilation, the best-fit line cross-section, together with the lack of any
corresponding excess in continuum photons, poses an interesting puzzle for
models of thermal dark matter: the line cross-section is too large to be
generated radiatively from open Standard Model annihilation modes, and too
small to provide efficient dark matter annihilation in the early universe. We
discuss two mechanisms to solve this puzzle and illustrate each with a simple
reference model in which the dominant dark matter annihilation channel is
photonic final states. The first mechanism we employ is resonant annihilation,
which enhances the annihilation cross-section during freezeout and allows for a
sufficiently large present-day annihilation cross section. Second, we consider
cascade annihilation, with a hierarchy between p-wave and s-wave processes.
Both mechanisms require mass near-degeneracies and predict states with masses
closely related to the dark matter mass; resonant freezeout in addition
requires new charged particles at the TeV scale.Comment: 17 pages, 8 figure
Viable tax constitutions
Taxation is only sustainable if the general public complies with it. This observation is uncontroversial with tax practitioners but has been ignored by the public finance tradition, which has interpreted tax constitutions as binding contracts by which the power to tax is irretrievably conferred by individuals to government, which can then levy any tax it chooses. However, in the absence of an outside party enforcing contracts between members of a group, no arrangement within groups can be considered to be a binding contract, and therefore the power of tax must be sanctioned by individuals on an ongoing basis. In this paper we offer, for the first time, a theoretical analysis of this fundamental compliance problem associated with taxation, obtaining predictions that in some cases point to a re-interptretation of the theoretical constructions of the public finance tradition while in others call them into question
Tax evasion and exchange equity: a reference-dependent approach
The standard portfolio model of tax evasion with a public good produces the perverse conclusion that when taxpayers perceive the public good to be under-/overprovided, an increase in the tax rate increases/decreases evasion. The author treats taxpayers as thinking in terms of gains and losses relative to an endogenous reference level, which reflects perceived exchange equity between the value of taxes paid and the value of public goods supplied. With these alternative behavioral assumptions, the author overturns the aforementioned result in a direction consistent with the empirical evidence. The author also finds a role for relative income in determining individual responses to a change in the marginal rate of tax
Validation of a Multivariate Serum Profile for Epithelial Ovarian Cancer Using a Prospective Multi-Site Collection
In previous studies we described the use of a retrospective collection of ovarian cancer and benign disease samples, in combination with a large set of multiplexed immunoassays and a multivariate pattern recognition algorithm, to develop an 11-biomarker classification profile that is predictive for the presence of epithelial ovarian cancer. In this study, customized, Luminex-based multiplexed immunoassay kits were GMP-manufactured and the classification profile was refined from 11 to 8 biomarkers (CA-125, epidermal growth factor receptor, CA 19-9, C-reactive protein, tenascin C, apolipoprotein AI, apolipoprotein CIII, and myoglobin). The customized kits and the 8-biomarker profile were then validated in a double-blinded manner using prospective samples collected from women scheduled for surgery, with a gynecologic oncologist, for suspicion of having ovarian cancer. The performance observed in model development held in validation, demonstrating 81.1% sensitivity (95% CI 72.6 – 87.9%) for invasive epithelial ovarian cancer and 85.4% specificity (95% CI 81.1 – 88.9%) for benign ovarian conditions. The specificity for normal healthy women was 95.6% (95% CI 83.6 – 99.2%). These results have encouraged us to undertake a second validation study arm, currently in progress, to examine the performance of the 8-biomarker profile on the population of women not under the surgical care of a gynecologic oncologist
First Observation of the Rare Decay Mode K-long -> e+ e-
In an experiment designed to search for and study very rare two-body decay
modes of the K-long, we have observed four examples of the decay K-long -> e+
e-, where the expected background is 0.17+-0.10 events. This observation
translates into a branching fraction of 8.7^{+5.7}_{-4.1} X 10^{-12},
consistent with recent theoretical predictions. This result represents by far
the smallest branching fraction yet measured in particle physics.Comment: 9 pages, 3 figure
- …