Mobile sediments in a karst aquifer

In karst aquifers, mobile sediments may play a fundamental role in determining water quality by concentrating and transporting contaminants. This study investigates spatial characteristics of sediment in a karst aquifer, examines temporal characteristics of sediment discharging from a karst spring, and describes a new method for tracing sediment in karst terrane. Sediment samples were collected from different compartments of a karst aquifer (the Edwards Aquifer, Central Texas) and analyzed for mineralogy, grainsize distribution, organic carbon content, and specific surface area. Suspended sediment samples discharging from a karst spring in response to two storms were analyzed for mineralogy and grainsize distribution. To test the hypothesis that allochthonous sediment can move through karst systems, a sediment tracer--montmorillonite clay homoionized to the lanthanide form--was developed. Statistical analysis of sediment characteristics separated the sampling sites into three groups: 1) streambeds, sinkholes, and small springs; 2) wells; and 3) caves. Characteristics of sediments from Barton Springs (the main spring in the region) showed a mixture of the characteristics of these three groups. The mineralogic signature of sediments discharging from Barton Springs in response to storms was initially allochthonous and then became more autochthonous. Temporal changes in aqueous chemistry of Barton Springs varied in response to rainfall, seasonal changes in aquifer level, and draining of the pool over the spring. The results indicate that some sediments, containing calcite and a high organic carbon content, are allochthonous, and others, containing dolomite and a low organic carbon content, are autochthonous. Sediments issuing from Barton Springs contain a mix of both allochthonous and autochthonous sediments. Based on geochemical characteristics, allochthonous sediments have a greater potential to sorb and transport contaminants than do autochthonous sediments. Development and testing of the sediment tracer verified that allochthonous sediments can be transported through karst. Sediments, particularly allochthonous sediments, can play a crucial role in contaminant transport in karst; the volume of these sediments will increase with increasing urbanization. Because those sediment characteristics which determine contaminant transport potential vary both spatially and temporally, determination of sediment volume and type is critical to evaluating its impact on water quality.Geological Science

Failure of Effective Potential Approach: Nucleus-Electron Entanglement in the He-Ion

Entanglement may be considered a resource for quantum-information processing, as the origin of robust and universal equilibrium behaviour, but also as a limit to the validity of an effective potential approach, in which the influence of certain interacting subsystems is treated as a potential. Here we show that a closed three particle (two protons, one electron) model of a He-ion featuring realistic size, interactions and energy scales of electron and nucleus, respectively, exhibits different types of dynamics depending on the initial state: For some cases the traditional approach, in which the nucleus only appears as the center of a Coulomb potential, is valid, in others this approach fails due to entanglement arising on a short time-scale. Eventually the system can even show signatures of thermodynamical behaviour, i.e. the electron may relax to a maximum local entropy state which is, to some extent, independent of the details of the initial state.Comment: Submitted to Europhysics Letter

The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MEGaSaURA) I: The Sample and the Spectra

We introduce Project MEGaSaURA: The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises medium-resolution, rest-frame ultraviolet spectroscopy of N=15 bright gravitationally lensed galaxies at redshifts of 1.68$<$z$<$3.6, obtained with the MagE spectrograph on the Magellan telescopes. The spectra cover the observed-frame wavelength range $3200 < \lambda_o < 8280$ \AA ; the average spectral resolving power is R=3300. The median spectrum has a signal-to-noise ratio of $SNR=21$ per resolution element at 5000 \AA . As such, the MEGaSaURA spectra have superior signal-to-noise-ratio and wavelength coverage compared to what COS/HST provides for starburst galaxies in the local universe. This paper describes the sample, the observations, and the data reduction. We compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum. We provide the MEGaSaURA spectra to the astronomical community through a data release.Comment: Resubmitted to AAS Journals. Data release will accompany journal publication. v2 addresses minor comments from refere

THz absorption spectrum of the CO2–H2O complex: Observation and assignment of intermolecular van der Waals vibrations

Terahertz absorption spectra have been recorded for the weakly bound CO2-H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems' flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point energy of 273 ± 15 cm(-1) from the class of intermolecular van der Waals vibrations is proposed and the combination with high-level quantum chemical calculations provides a value of 726 ± 15 cm(-1) for the dissociation energy D0

Ignorance based inference of optimality in thermodynamic processes

We derive ignorance based prior distribution to quantify incomplete information and show its use to estimate the optimal work characteristics of a heat engine.Comment: Latex, 10 pages, 3 figure

On the Stability and the Approximation of Branching Distribution Flows, with Applications to Nonlinear Multiple Target Filtering

We analyse the exponential stability properties of a class of measure-valued equations arising in nonlinear multi-target filtering problems. We also prove the uniform convergence properties w.r.t. the time parameter of a rather general class of stochastic filtering algorithms, including sequential Monte Carlo type models and mean eld particle interpretation models. We illustrate these results in the context of the Bernoulli and the Probability Hypothesis Density filter, yielding what seems to be the first results of this kind in this subject

Strong Purcell effect observed in single thick shell CdSe/CdS nanocrystals coupled to localized surface plasmons

High quality factor dielectric cavities designed to a nanoscale accuracy are mostly used to increase the spontaneous emission rate of a single emitter. Here we show that the coupling, at room temperature, between thick shell CdSe/CdS nanocrystals and random metallic films offers a very promising alternative approach. Optical modes confined at the nanoscale induce strong Purcell factors reaching values as high as 60. Moreover the quantum emission properties can be tailored: strong antibunching or radiative biexcitonic cascades can be obtained with high photon collection efficiency and extremely reduced blinking.Comment: 16 pages, 7 figure