7,262 research outputs found
A Leslie matrix approach to an age-structured epidemic
We consider a Leslie-type matrix approach to an SIR epidemic in discrete time. We give examples of the population of susceptibles, infectives, and removals for different birth rates and two different infection rates. Finally, when the infection rate depe
Exchange Rates and Local Labor Markets
We document the consequences of real exchange rate movements for the employment, hours, and hourly earnings of workers in manufacturing industries across individual states. Exchange rates have statistically significant wage and employment implications in these local labor markets. The importance and size of these dollar-induced effects vary considerably across industries and are more pronounced in some U.S. regions. In addition to the importance of exchange rate shocks, we confirm prior research results showing that relatively strong local conditions drive up wage in local industries, while anticipated future (positive) local shocks reduce current wages.
The Economic Costs of the Iraq War: An Appraisal Three Years After the Beginning of the Conflict
This paper attempts to provide a more complete reckoning of the costs of the Iraq War, using standard economic and accounting/ budgetary frameworks. As of December 30, 2005, total spending for combat and support operations in Iraq is 500bn. These figures, however, greatly underestimate the War's true costs. We estimate a range of present and future costs, by including expenditures not in the 2 trillion. In either case, the cost is much larger than the administration's original estimate of 60bn. The costs estimated do not include those borne by other countries, either directly (military expenditures) or indirectly (the increased price of oil). Most importantly, we have not included the costs to Iraq, either in terms of destruction of infrastructure or the loss of lives. These would all clearly raise the costs significantly.
Electronic Transport on the Shastry-Sutherland Lattice in Ising-type Rare Earth Tetraborides
In the presence of a magnetic field frustrated spin systems may exhibit
plateaus at fractional values of saturation magnetization. Such plateau states
are stabilized by classical and quantum mechanisms including order-by-disorder,
triplon crystallization, and various competing order effects. In the case of
electrically conducting systems, free electrons represent an incisive probe for
the plateau states. Here we study the electrical transport of Ising-type rare
earth tetraborides B (Er, Tm), a metallic Shastry-Sutherland lattice
showing magnetization plateaus. We find that the longitudinal and transverse
resistivities reflect scattering with both the static and dynamic plateau
structure. We model these results consistently with the expected strong
uniaxial anisotropy in a quantitative level, providing a framework for the
study of plateau states in metallic frustrated systems.Comment: 18 pages, 5 figure
Communication training for aircrews: A review of theoretical and pragmatic aspects of training program design
This study is the final report of a project studying methods of communications training applicable to both civilian and military aviation personnel, including multiperson teams or single pilot fixed wing or rotary wing aircraft. A review is provided of a number of theories proposed as relevant for producing training materials for improved communications. Criteria are given for evaluating the applicability of training programs to the aviation environment, and these criteria are applied to United Airlines' Resources Management Training, as well as to a number of commercially available general purpose training programs. The report considers in detail assertiveness training and grid management training, examining their theoretical background and attempts made to validate their effectiveness. It was found that there are substantive difficulties in assessing the effectiveness of both training programs, as well as problems with the theories underlying them. However, because the aviation environment offers unique advantages for studying the effectiveness of communications training, recommendations are made on the design of appropriate training programs and on procedures that might be used to validate them
Transport Signatures of Fermi Surface Topology Change in BiTeI
We report a quantum magnetotransport signature of a change in Fermi surface
topology in the Rashba semiconductor BiTeI with systematic tuning of the Fermi
level . Beyond the quantum limit, we observe a marked increase/decrease in
electrical resistivity when is above/below the Dirac node that we show
originates from the Fermi surface topology. This effect represents a
measurement of the electron distribution on the low-index () Landau
levels and is uniquely enabled by the finite bulk dispersion along the
-axis and strong Rashba spin-orbit coupling strength of the system. The
Dirac node is independently identified by Shubnikov-de Haas oscillations as a
vanishing Fermi surface cross section at . Additionally we find that the
violation of Kohler's rule allows a distinct insight into the temperature
evolution of the observed quantum magnetoresistance effects.Comment: 12 pages, 4 figure
Extreme Magnetoresistance in Magnetic Rare Earth Monopnictides
The acute sensitivity of the electrical resistance of certain systems to
magnetic fields known as extreme magnetoresistance (XMR) has recently been
explored in a new materials context with topological semimetals. Exemplified by
WTe and rare earth monopnictide La(Sb,Bi), these systems tend to be
non-magnetic, nearly compensated semimetals and represent a platform for large
magnetoresistance driven by intrinsic electronic structure. Here we explore
electronic transport in magnetic members of the latter family of semimetals and
find that XMR is strongly modulated by magnetic order. In particular, CeSb
exhibits XMR in excess of % at fields of 9 T while the
magnetoresistance itself is non-monotonic across the various magnetic phases
and shows a transition from negative magnetoresistance to XMR with field above
magnetic ordering temperature . The magnitude of the XMR is larger than
in other rare earth monopnictides including the non-magnetic members and
follows an non-saturating power law to fields above 30 T. We show that the
overall response can be understood as the modulation of conductivity by the Ce
orbital state and for intermediate temperatures can be characterized by an
effective medium model. Comparison to the orbitally quenched compound GdBi
supports the correlation of XMR with the onset of magnetic ordering and
compensation and highlights the unique combination of orbital inversion and
type-I magnetic ordering in CeSb in determining its large response. These
findings suggest a paradigm for magneto-orbital control of XMR and are relevant
to the understanding of rare earth-based correlated topological materials.Comment: 21 pages, 6 figure
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