20,102 research outputs found
On model selection criteria for climate change impact studies
Climate change impact studies inform policymakers on the estimated damages of
future climate change on economic, health and other outcomes. In most studies,
an annual outcome variable is observed, e.g. annual mortality rate, along with
higher-frequency regressors, e.g. daily temperature and precipitation.
Practitioners use summaries of the higher-frequency regressors in fixed effects
panel models. The choice over summary statistics amounts to model selection.
Some practitioners use Monte Carlo cross-validation (MCCV) to justify a
particular specification. However, conventional implementation of MCCV with
fixed testing-to-full sample ratios tends to select over-fit models. This paper
presents conditions under which MCCV, and also information criteria, can
deliver consistent model selection. Previous work has established that the
Bayesian information criterion (BIC) can be inconsistent for non-nested
selection. We illustrate that the BIC can also be inconsistent in our
framework, when all candidate models are misspecified. Our results have
practical implications for empirical conventions in climate change impact
studies. Specifically, they highlight the importance of a priori information
provided by the scientific literature to guide the models considered for
selection. We emphasize caution in interpreting model selection results in
settings where the scientific literature does not specify the relationship
between the outcome and the weather variables.Comment: Additional simulation results available from authors by reques
Berry's phase with quantized field driving: effects of inter-subsystem coupling
The effect of inter-subsystem couplings on the Berry phase of a composite
system as well as that of its subsystem is investigated in this paper. We
analyze two coupled spin- particles with one driven by a quantized
field as an example, the pure state geometric phase of the composite system as
well as the mixed state geometric phase for the subsystem is calculated and
discussed.Comment: 4 pages, 1 figur
Effect of inter-subsystem couplings on the evolution of composite systems
The effect of inter-subsystem coupling on the adiabaticity of composite
systems and that of its subsystems is investigated. Similar to the adiabatic
evolution defined for pure states, non-transitional evolution for mixed states
is introduced; conditions for the non-transitional evolution are derived and
discussed. An example that describes two coupled qubits is presented to detail
the general presentation. The effects due to non-adiabatic evolution on the
geometric phase are also presented and discussed.Comment: 5 pages, 1 figur
Enhancement of Transition Temperature in FexSe0.5Te0.5 Film via Iron Vacancies
The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8<x<1) on
superconductivity and electronic properties have been studied. A significant
enhancement of the superconducting transition temperature (TC) up to 21K was
observed in the most Fe deficient film (x=0.8). Based on the observed and
simulated structural variation results, there is a high possibility that Fe
vacancies can be formed in the FexSe0.5Te0.5 films. The enhancement of TC shows
a strong relationship with the lattice strain effect induced by Fe vacancies.
Importantly, the presence of Fe vacancies alters the charge carrier population
by introducing electron charge carriers, with the Fe deficient film showing
more metallic behavior than the defect-free film. Our study provides a means to
enhance the superconductivity and tune the charge carriers via Fe vacancy, with
no reliance on chemical doping.Comment: 15 pages, 4 figure
Long valley relaxation time of free carriers in monolayer WSe<font size=-1><sub>2</sub></font>
published_or_final_versio
Do strange stars exist in the Universe?
Definitely, an affirmative answer to this question would have implications of
fundamental importance for astrophysics (a new class of compact stars), and for
the physics of strong interactions (deconfined phase of quark matter, and
strange matter hypothesis). In the present work, we use observational data for
the newly discovered millisecond X-ray pulsar SAX J1808.4-3658 and for the
atoll source 4U 1728-34 to constrain the radius of the underlying compact
stars. Comparing the mass-radius relation of these two compact stars with
theoretical models for both neutron stars and strange stars, we argue that a
strange star model is more consistent with SAX J1808.4-3658 and 4U 1728-34, and
suggest that they are likely strange star candidates.Comment: In memory of Bhaskar Datta. -- Invited talk at the Pacific Rim
Conference on Stellar Astrophysics (Hong Kong, aug. 1999
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