Making electromagnetic wavelets

Electromagnetic wavelets are constructed using scalar wavelets as superpotentials, together with an appropriate polarization. It is shown that oblate spheroidal antennas, which are ideal for their production and reception, can be made by deforming and merging two branch cuts. This determines a unique field on the interior of the spheroid which gives the boundary conditions for the surface charge-current density necessary to radiate the wavelets. These sources are computed, including the impulse response of the antenna.Comment: 29 pages, 4 figures; minor corrections and addition

Ion-retarding lens improves the abundance sensitivity of tandem mass spectrometers

Ion-retarding lens which increases the abundance sensitivity of tandem magnetic-analyzer mass spectrometers measures isotopes of low abundance in mass positions adjacent to isotopes of high abundance. The lens increases the abundance sensitivity for isotopes lying farther from high abundance isotopes than the energy cutoff of the lens

Economic Impacts of E. Coqui frogs in Hawaii

Eleutherodactylus coqui, a small frog native to Puerto Rico, was introduced to Hawaii in the late 1980s, presumably as a hitchhiker on plant material from the Caribbean or Florida (Kraus et al. 1999). The severity of the frogs' songs on the island of Hawaii has lead to a hypothesis touted both in the scientific community and in the popular media that the presence of the frog on or near a property results in a decline in that property's value. The objective of this study is to explicitly test the extent to which this hypothesis is true, and if it is, what the level of localized damage incurred on a property's value is. The invasion began on either Hawaii or Maui, and has now expanded to Oahu and Kauai. Spread has occurred through the movement of nursery plants and through intentional introduction of the frogs to previously uninfested areas. The coqui frogs have attained some of the highest densities ever observed for terrestrial amphibian populations (up to 133,000 per ha on Hawaii). These extremely dense populations have lead to both economic and ecological concerns, especially on the island of Hawaii. The loud mating song of the male frogs is the most widely cited complaint in Hawaii. The frog's song has been measured to range in the 80-100 decibel level (Beard and Pitt 2005). Given that 45 decibels may be enough to prevent the average person from sleeping , the song of the coqui is considered a form of noise pollution in Hawaii. In this study we focus only on the direct damage costs of the coqui's loud mating songs through a hedonic pricing model. Because this only one component of the economic costs of noise pollution, it should be considered a lower bound estimate of the true cost of their noise and their presence. Since this lower bound is generated through measurable losses in property value, its use in invasive species policy should be welcomingly straightforward compared to survey methods or other efforts to quantify damages from ecosystem change. We find that coqui frogs do impose localized damages to real estate values, but by 800 meters distance from a complaint this damage is declining relative to the effect at 500m. The per-transaction reduction in value when frog complaints have been lodged within 500m appears to be about 0.16%, holding constant district, acreage, financial conditions, zoning, and neighborhood characteristics. This is just over 1/3 of the impact that an increase of 1% in mortgage rates is estimated to have on price.Land Economics/Use,

Low and high intensity velocity selective coherent population trapping in a two-level system

An experimental investigation is made of sub-recoil cooling by velocity selective coherent population trapping in a two-level system in Sr. The experiment is carried out using the narrow linewidth intercombination line at 689 nm. Here, the ratio between the recoil shift and the linewidth is as high as 0.64. We show that, on top of a broader momentum profile, subrecoil features develop, whose amplitude is strongly dependent on the detuning from resonance. We attribute this structure to a velocity selective coherent population trapping mechanism. We also show that the population trapping phenomenon leads to complex momentum profiles in the case of highly saturated transitions, displaying a multitude of subrecoil features at integer multiples of the recoil momentum.Comment: 6 pages and 7 figure

Control of Invasive Species: Lessons from Miconia in Hawaii

Once established, invasive species can rapidly and irreversibly alter ecosystems and degrade the value of ecosystem services. Optimal control of an exotic pest solves for a trajectory of removals that minimizes the present value of removal costs and residual damages from the remaining pest population. The shrubby tree, Miconia calvescens, is used to illustrate dynamic policy options for a forest invader. Potential damages to Hawaii's forest ecosystems are related to decreased aquifer recharge, biodiversity, and other ecosystem values. We find that population reduction is the optimal management policy for the islands of Oahu, Maui, and Hawaii. On the island of Kauai, where tree density is lower and search costs higher, optimal policy calls for deferring removal expenditures until the steady state population is reached.Environmental Economics and Policy,

Global stability analysis of birhythmicity in a self-sustained oscillator

We analyze global stability properties of birhythmicity in a self-sustained system with random excitations. The model is a multi-limit cycles variation of the van der Pol oscillatorintroduced to analyze enzymatic substrate reactions in brain waves. We show that the two frequencies are strongly influenced by the nonlinear coefficients $\alpha$ and $\beta$. With a random excitation, such as a Gaussian white noise, the attractor's global stability is measured by the mean escape time $\tau$ from one limit-cycle. An effective activation energy barrier is obtained by the slope of the linear part of the variation of the escape time $\tau$ versus the inverse noise-intensity 1/D. We find that the trapping barriers of the two frequencies can be very different, thus leaving the system on the same attractor for an overwhelming time. However, we also find that the system is nearly symmetric in a narrow range of the parameters.Comment: 17 pages, 8 figures, to appear on Choas, 201