32 research outputs found
Observation of Wigner cusps in a metallic carbon nanotube
Previous gate-dependent conductance measurements of metallic carbon nanotubes
have revealed unexplainable conductance suppressions, occurring at two
different gate voltages. These were previously attributed to the
gate-dependency of contact resistance. Our gate-dependent conductivity
measurements on a metallic nanotube with known chirality show that these
bimodal conductance suppressions are the manifestations of Wigner cusps, often
seen in atomic and nuclear physics experiments.Comment: 6 pages, 3 figure
Ring-Exchange Interaction Effects on Magnons in Dirac Magnet CoTiO
In magnetically ordered materials with localized electrons, the fundamental
magnetic interactions are due to exchange of electrons [1-3]. Typically, only
the interaction between pairs of electrons' spins is considered to explain the
nature of the ground state and its excitations, whereas three-, four-, and
six-spin interactions are ignored. When these higher order processes occur in a
loop they are called cyclic or ring exchange. The ring-exchange interaction is
required to explain low temperature behavior in bulk and thin films of solid
He [4-8]. It also plays a crucial role in the quantum magnet LaCuO
[9,10]. Here, we use a combination of time domain THz (TDTS) and magneto-Raman
spectroscopies to measure the low energy magnetic excitations in CoTiO, a
proposed Dirac topological magnon material [11,12] where the origin of the
energy gap in the magnon spectrum at the Brillouin zone center remains unclear.
We measured the magnetic field dependence of the energies of the two lowest
energy magnons and determine that the gap opens due to the ring-exchange
interaction between the six spins in a hexagon. This interaction also explains
the selection rules of the THz magnon absorption. Finally, we clarify that
topological surface magnons are not expected in CoTiO. Our study
demonstrates the power of combining TDTS and Raman spectroscopies with theory
to identify the microscopic origins of the magnetic excitations in quantum
magnets.Comment: 7 pages, 4 figures in main text, 26 pages and 11 figures in
supplemen
Pricing reverse mortgages in Spain
[EN] In Spain, as in other European countries, the continuous ageing of the population creates a need for long-term care services and their financing. However, in Spain the development of this kind of services is still embryonic. The aim of this article is to obtain a calculation method for reverse mortgages in Spain based on the fit and projection of dynamic tables for Spanish mortality, using the Lee and Carter model. Mortality and life expectancy for the next 20 years are predicted using the fitted model, and confidence intervals are obtained from the prediction errors of parameters for the mortality index of the model. The last part of the article illustrates an application of the results to calculate the reverse mortgage model promoted by the Spanish Instituto de Crédito Oficial (Spanish State Financial Agency), for which the authors have developed a computer application.The authors are indebted to Jose Garrido, whose suggestions improved the original
manuscript, and to the anonymous referee for his/her valuable comments. This work was partially
supported by grants from the MEyC (Ministerio de Educacio´n y Ciencia, Spain), projects MTM2010-
14961 and MTM2008-05152.Debón Aucejo, AM.; Montes, F.; Sala, R. (2013). Pricing reverse mortgages in Spain. European Actuarial Journal. 3:23-43. https://doi.org/10.1007/s13385-013-0071-yS23433Blay-Berrueta D (2007) Sistemas de cofinaciaciación de la dependencia: seguro privado frente a hipoteca inversa. Cuadernos de la Fundación, Fundación Mapfre Estudios, Madrid.Booth H (2006) Demographic forecasting: 1980 to 2005 in review. Int J Forecast 22(3):547–582Booth H, Hyndman R, Tickle L, de Jong P (2006) Lee–Carter mortality forecasting: a multi-country comparison of variants and extensions. Demogr Res 15(9):289–310Booth H, Maindonald J, Smith L (2002) Applying Lee–Carter under conditions of variable mortality decline. Popul Stud 56(3):325–336Booth H, Tickle L (2003) The future aged: new projections of Australia’s ederly population. Popul Stud 22(4):38–44Brouhns N, Denuit M, Keilegom IV (2005) Bootstrapping Poisson log-bilinear model for mortality forecasting. 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Parameterizing age patterns of demographic rates with the multiexponential model schedule∗
Incorporating household structure into a discrete event simulation model of tuberculosis and HIV
Human immunodeficiency virus (HIV) increases the risks of developing tuberculosis (TB) disease followinginfection, and speeds up disease progression. This has had a devastating effect on TB epidemics in sub-SaharanAfrica, where incidence rates have more than trebled in the past twenty years. Current control methods for TBdisease have failed to keep pace with this growth in TB, and there is an urgent need to find TB control strategiesthat are effective in high-HIV prevalent settings. This paper describes a discrete-event simulation model ofendemic TB that includes the effects of HIV and of household structure on the transmission dynamics of TB.Incorporating a social structure allows us to compare the effectiveness of contact-tracing interventions withtargeted case-finding at high risk groups. We describe the modeling of the household structure in some detail, asthis has applications to the modeling of other infectious diseases