Excitations in time-dependent density-functional theory

An approximate solution to the time-dependent density functional theory (TDDFT) response equations for finite systems is developed, yielding corrections to the single-pole approximation. These explain why allowed Kohn-Sham transition frequencies and oscillator strengths are usually good approximations to the true values, and why sometimes they are not. The approximation yields simple expressions for G\"orling-Levy perturbation theory results, and a method for estimating expectation values of the unknown exchange-correlation kernel.Comment: 4 pages, 1 tabl

Average and worst-case specifications of precipitating auroral electron environment

The precipitation electrons in the auroral environment are highly variable in their energy and intensity in both space and time. As such they are a source of potential hazard to the operation of the Space Shuttle and other large spacecraft operating in polar orbit. In order to assess these hazards both the average and extreme states of the precipitating electrons must be determined. Work aimed at such a specification is presented. First results of a global study of the average characteristics are presented. In this study the high latitude region was divided into spatial elements in magnetic local time and corrected geomagnetic latitude. The average electron spectrum was then determined in each spatial element for seven different levels of activity as measured by K sub p using an extremely large data set of auroral observations. Second a case study of an extreme auroral electron environment is presented, in which the electrons are accelerated through field aligned potential as high as 30,000 volts and in which the spacecraft is seen to charge negatively to a potential approaching .5 kilovolts

Confinement effects in a guided-wave interferometer with millimeter-scale arm separation

Guided-wave atom interferometers measure interference effects using atoms held in a confining potential. In one common implementation, the confinement is primarily two-dimensional, and the atoms move along the nearly free dimension under the influence of an off-resonant standing wave laser beam. In this configuration, residual confinement along the nominally free axis can introduce a phase gradient to the atoms that limits the arm separation of the interferometer. We experimentally investigate this effect in detail, and show that it can be alleviated by having the atoms undergo a more symmetric motion in the guide. This can be achieved by either using additional laser pulses or by allowing the atoms to freely oscillate in the potential. Using these techniques, we demonstrate interferometer measurement times up to 72 ms and arm separations up to 0.42 mm with a well controlled phase, or times of 0.91 s and separations of 1.7 mm with an uncontrolled phase.Comment: 14 pages, 6 figure

Low-magnesium, trans-cleavage activity by type III, tertiary stabilized hammerhead ribozymes with stem 1 discontinuities

BACKGROUND: Low concentrations of free magnesium in the intracellular environment can present critical limitations for hammerhead ribozymes, especially for those that are designed for intermolecular (trans) cleavage of a host or pathogen RNA. Tertiary stabilizing motifs (TSM's) from natural and artificial ribozymes with a "type I" topology have been exploited to stabilize trans-cleaving hammerheads. Ribozymes with "type II" or "type III" topologies might seem incompatible with conversion to trans-cleavage designs, because opening the loop at the end of stem 1 or stem 2 to accommodate substrate binding is expected to disrupt the TSM and eliminate tertiary stabilization. RESULTS: Stem 1, together with single-stranded segments capping or internal to this stem, contains both the substrate-binding and tertiary stabilization functions. This stem was made discontinuous within the sTRSV hammerhead ribozyme, thereby separating the two functions into discrete structural segments. The resulting ribozyme, designated "RzC," cleaved its 13 nucleotide target substrate at MgCl(2 )concentrations as low as 0.2 mM at 25°C and 0.5 mM at 37°C. Under multiple-turnover conditions, nearly thirty turnovers were observed at the highest substrate:RzC ribozyme ratios. Similar stabilization was observed for several derivatives of RzC. Catalytic activity was diminished or eliminated at sub-millimolar MgCl(2 )concentrations for ribozymes with weakened or deleted tertiary interactions. Eadie-Hofstee analysis revealed that the stabilized and non-stabilized ribozymes bind their substrates with equivalent affinities, suggesting that differences in observed activity are not the result of diminished binding. Some of the stabilized and non-stabilized ribozymes appear to fold into a heterogeneous collection of conformers, only a subset of which are catalytically active. CONCLUSION: Hammerhead ribozymes with the "type III" topology can be converted to a tertiary, trans-cleavage design. Separating the stabilization and substrate recognition functions of stem 1 increases cleavage activity at physiological concentrations of divalent magnesium while retaining recognition of exogenous targets. Trans-cleaving ribozymes that exploit the tertiary stabilizing motifs of all natural hammerhead topologies can therefore be used in intracellular applications

R-matrix Floquet theory for laser-assisted electron-atom scattering

A new version of the R-matrix Floquet theory for laser-assisted electron-atom scattering is presented. The theory is non-perturbative and applicable to a non-relativistic many-electron atom or ion in a homogeneous linearly polarized field. It is based on the use of channel functions built from field-dressed target states, which greatly simplifies the general formalism.Comment: 18 pages, LaTeX2e, submitted to J.Phys.

An evaluation of the spatial resolution of soil moisture information

Rainfall-amount patterns in the central regions of the U.S. were assessed. The spatial scales of surface features and their corresponding microwave responses in the mid western U.S. were investigated. The usefulness for U.S. government agencies of soil moisture information at scales of 10 km and 1 km. was ascertained. From an investigation of 494 storms, it was found that the rainfall resulting from the passage of most types of storms produces patterns which can be resolved on a 10 km scale. The land features causing the greatest problem in the sensing of soil moisture over large agricultural areas with a radiometer are bodies of water. Over the mid-western portions of the U.S., water occupies less than 2% of the total area, the consequently, the water bodies will not have a significant impact on the mapping of soil moisture. Over most of the areas, measurements at a 10-km resolution would adequately define the distribution of soil moisture. Crop yield models and hydrological models would give improved results if soil moisture information at scales of 10 km was available

Improvement of Energy Efficiency for Wastewater Treatment

Wastewater treatment requires the elimination of pathogens and reduction of organic matter in the treated sludge to acceptable levels. One process used to achieve this is Autothermal Thermophylic Aerobic Digestion (ATAD), which relies on promoting non-pathogenic thermophilic bacteria to digest organic matter and kill pathogens through metabolic heat generation. This process requires continuous aeration that may be energy consuming, and the final aim of the study is to identify how the process design can minimize the energy input per mass of treated sludge. Appropriate modeling of the reactor process is an essential ingredient, so we explore properties of an existing model and propose a simplified alternative model

Ejaculate allocation by male sand martins, Riparia riparia

Males of many species allocate sperm to ejaculates strategically in response to variation in the risk and intensity of sperm competition. The notable exception is passerine birds, in which evidence for strategic allocation is absent. Here we report the results of a study testing for strategic ejaculate allocation in a passerine bird, the sand martin (Riparia riparia). Natural ejaculates were collected from males copulating with a model female. Ejaculates transferred in the presence of a rival male contained significantly more sperm than ejaculates transferred in the absence of a rival male. There was no evidence that this difference was due to the confounding effects of the year of ejaculate collection, the identity of the model female, the colony, the stage of season or the period of the day in which ejaculates were collected. A more detailed examination of the ejaculate patterns of individual males, achieved by the DNA profiling of ejaculates, provided additional evidence for strategic allocation of sperm

InAs nanowire transistors with multiple, independent wrap-gate segments

We report a method for making horizontal wrap-gate nanowire transistors with up to four independently controllable wrap-gated segments. While the step up to two independent wrap-gates requires a major change in fabrication methodology, a key advantage to this new approach, and the horizontal orientation more generally, is that achieving more than two wrap-gate segments then requires no extra fabrication steps. This is in contrast to the vertical orientation, where a significant subset of the fabrication steps needs to be repeated for each additional gate. We show that cross-talk between adjacent wrap-gate segments is negligible despite separations less than 200 nm. We also demonstrate the ability to make multiple wrap-gate transistors on a single nanowire using the exact same process. The excellent scalability potential of horizontal wrap-gate nanowire transistors makes them highly favourable for the development of advanced nanowire devices and possible integration with vertical wrap-gate nanowire transistors in 3D nanowire network architectures.Comment: 18 pages, 5 figures, In press for Nano Letters (DOI below

Enhanced mapping of artificially modified ground in urban areas : using borehole, map and remotely sensed data

The report described here is focused on how using boreholes and attributes from boreholes increased and enhanced the mapping of Artificially Modified Ground, and helped measure landscape evolution change in the urban environment. These attributes from boreholes include the presence of AMG in a borehole, the thickness of AMG recorded, the start height of a borehole and the location of boreholes (and other boreholes in close proximity) with modern topological features and geological maps