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Register a new userMeasurement of the real dielectric permittivity epsilon_r of glacial ice
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Using data collected by the Askaryan Radio Array (ARA) experiment at the South Pole, we have used long-baseline propagation of radio-frequency signals to extract information on the radio-frequency index-of-refraction in South Polar ice. Owing to the increasing ice density over the upper 150--200 meters, rays are observed along two, nearly parallel paths, one of which is direct and a second which refracts through an inflection point, with differences in both arrival time and arrival angle that can be used to constrain the neutrino properties. We also observe indications, for the first time, of radio-frequency ice birefringence for signals propagating along predominantly horizontal trajectories, corresponding to an asymmetry of order 0.1% between the ordinary and extra-ordinary paths, numerically compatible with previous measurements of birefringent asymmetries for vertically-propagating radio-frequency signals at South Pole. Taken together, these effects offer the possibility of redundantly measuring the range from receiver to a neutrino interaction in Antarctic ice, if receiver antennas are deployed at shallow (25 m<z<100 m) depths. Such range information is essential in determining both the neutrino energy, as well as the incident neutrino direction.
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Ultra high energy neutrinos may be observed in ice by the emission of acoustic signals. The SPATS detector has investigated the possibility of observing GZK-neutrinos in the clear ice near the South Pole at the IceCube detector site. To explore other potential detection sites glacial ice in the Alps and in Antarctica has been surveyed for its acoustical properties. The purpose of the Enceladus Explorer (EnEx), on the other hand, is the search for extraterrestrial life on the Saturn moon Enceladus. Here acoustics is used to maneuver a subsurface probe inside the ice by trilateration of signals. A system of acoustic transducers has been developed to study both applications. In the south polar region of the moon Enceladus there are secluded crevasses. These are filled with liquid water, probably heated by tidal forces due to the short distance to Saturn. We intend to take a sample of water from these crevasses by using a combination of a melt down and steering probe called IceMole (IM). Maneuvering IM requires a good understanding of ice properties such as the speed of sound, the attenuation of acoustic signals in ice, their directional dependencies and their dependence on different frequencies. The technology developed for this positioning system could also contribute to the design of future large scale acoustic neutrino detectors. We present our analysis methods and the findings on attenuation, sound speed, and frequency response obtained at several sites in the Alps and Antarctica.
The IceCube Neutrino Observatory, approximately 1 km^3 in size, is now complete with 86 strings deployed in the Antarctic ice. IceCube detects the Cherenkov radiation emitted by charged particles passing through or created in the ice. To realize the full potential of the detector, the properties of light propagation in the ice in and around the detector must be well understood. This report presents a new method of fitting the model of light propagation in the ice to a data set of in-situ light source events collected with IceCube. The resulting set of derived parameters, namely the measured values of scattering and absorption coefficients vs. depth, is presented and a comparison of IceCube data with simulations based on the new model is shown.
Context: Reliable, directly measured optical properties of astrophysical ice analogs in the infrared (IR) and terahertz (THz) range are missing. These parameters are of great importance to model the dust continuum radiative transfer in dense and cold regions, here thick ice mantles are present, and are necessary for the interpretation of future observations planned in the far-IR region. Aims: Coherent THz radiation allows direct measurement of the complex dielectric function (refractive index) of astrophysically relevant ice species in the THz range. Methods: The time-domain waveforms and the frequency-domain spectra of reference samples of CO ice, deposited at a temperature of 28.5 K and annealed to 33 K at different thicknesses, have been recorded. A new algorithm is developed to reconstruct the real and imaginary parts of the refractive index from the time-domain THz data. Results: The complex refractive index in the wavelength range of 1 mm - 150 ${mu}$m (0.3 - 2.0 THz) has been determined for the studied ice samples, and compared with available data found in the literature. Conclusions: The developed algorithm of reconstructing the real and imaginary parts of the refractive index from the time-domain THz data enables, for the first time, the determination of optical properties of astrophysical ice analogs without using the Kramers-Kronig relations. The obtained data provide a benchmark to interpret the observational data from current ground based facilities as well as future space telescope missions, and have been used to estimate the opacities of the dust grains in presence of CO ice mantles.
The exact suppression of backscattering from rotationally symmetric objects requires dual symmetric materials where ${epsilon_r} = {mu_r}$. This prevents their design at many frequency bands, including the optical one, because magnetic materials are not available. Electromagnetically small non-magnetic spheres of large permittivity offer an alternative. They can be tailored to exhibit balanced electric and magnetic dipole polarizabilities, which result in approximate zero backscattering. In this case, the effect is inherently narrowband. Here, we put forward a different alternative that allows broadband functionality: Electromagnetically large spheres made from low permittivity materials. The effect occurs in a parameter regime that approaches the trivial ${epsilon_r} to {mu_r} =1$ case, where approximate duality is met in a weakly wavelength dependence fashion. Despite the low permittivity, the overall scattering response of the spheres is still significant. Radiation patterns from these spheres are shown to be highly directive across an octave spanning band. The effect is analytically and numerically shown using the Mie coefficients.
This article is concerned with the dynamics of glacial cycles observed in the geological record of the Pleistocene Epoch. It focuses on a conceptual model proposed by Maasch and Saltzman [J. Geophys. Res.,95, D2 (1990), pp. 1955-1963], which is based on physical arguments and emphasizes the role of atmospheric CO2 in the generation and persistence of periodic orbits (limit cycles). The model consists of three ordinary differential equations with four parameters for the anomalies of the total global ice mass, the atmospheric CO2 concentration, and the volume of the North Atlantic Deep Water (NADW). In this article, it is shown that a simplified two-dimensional symmetric version displays many of the essential features of the full model, including equilibrium states, limit cycles, their basic bifurcations, and a Bogdanov-Takens point that serves as an organizing center for the local and global dynamics. Also, symmetry breaking splits the Bogdanov-Takens point into two, with different local dynamics in their neighborhoods.
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