Trade studies for nuclear space power systems

As human visions of space applications expand and as we probe further out into the universe, our needs for power will also expand, and missions will evolve which are enabled by nuclear power. A broad spectrum of missions which are enhanced or enabled by nuclear power sources have been defined. These include Earth orbital platforms, deep space platforms, planetary exploration, and terrestrial resource exploration. The recently proposed Space Exploration Initiative (SEI) to the Moon and Mars has more clearly defined these missions and their power requirements. Presented here are results of recent studies of radioisotope and nuclear reactor energy sources, combined with various energy conversion devices for Earth orbital applications, SEI lunar/Mars rovers, surface power, and planetary exploration

An investigation of Fe XV emission lines in solar flare spectra

Previously, large discrepancies have been found between theory and observation for Fe XV emission line ratios in solar flare spectra covering the 224-327 A wavelength range, obtained by the Naval Research Laboratory's S082A instrument on board Skylab. These discrepancies have been attributed to either errors in the adopted atomic data or the presence of additional atomic processes not included in the modelling, such as fluorescence. However our analysis of these plus other S082A flare observations (the latter containing Fe XV transitions between 321-482 A), performed using the most recent Fe XV atomic physics calculations in conjunction with a CHIANTI synthetic flare spectrum, indicate that blending of the lines is primarily responsible for the discrepancies. As a result, most Fe XV lines cannot be employed as electron density diagnostics for solar flares, at least at the spectral resolution of S082A and similar instruments (i.e. ~ 0.1 A). An exception is the intensity ratio I(321.8 A)/I(327.0 A), which appears to provide good estimates of the electron density at this spectral resolution.Comment: 6 pages, 3 figures, Astronomy & Astrophysics, in pres

Effects of Sex and Gender on Adaptation to Space: Musculoskeletal Health

There is considerable variability among individuals in musculoskeletal response to long-duration spaceflight. The specific origin of the individual variability is unknown but is almost certainly influenced by the details of other mission conditions such as individual differences in exercise countermeasures, particularly intensity of exercise, dietary intake, medication use, stress, sleep, psychological profiles, and actual mission task demands. In addition to variations in mission conditions, genetic differences may account for some aspect of individual variability. Generally, this individual variability exceeds the variability between sexes that adds to the complexity of understanding sex differences alone. Research specifically related to sex differences of the musculoskeletal system during unloading is presented and discussed

Three-electron coalescence points in two and three dimensions

The form of the wave function at three-electron coalescence points is examined for several spin states using an alternative method to the usual Fock expansion. We find that, in two- and three-dimensional systems, the non-analytical nature of the wave function is characterized by the appearance of logarithmic terms, reminiscent of those that appear as both electrons approach the nucleus of the helium atom. The explicit form of these singularities is given in terms of the interelectronic distances for a doublet and two quartet states of three electrons in a harmonic well.Comment: 4 pages, 1 figure, accepted for publication as a Communication in the Journal of Chemical Physic

RHESSI and SOHO/CDS Observations of Explosive Chromospheric Evaporation

Simultaneous observations of explosive chromospheric evaporation are presented using data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Coronal Diagnostic Spectrometer (CDS) onboard SOHO. For the first time, co-spatial imaging and spectroscopy have been used to observe explosive evaporation within a hard X-ray emitting region. RHESSI X-ray images and spectra were used to determine the flux of non-thermal electrons accelerated during the impulsive phase of an M2.2 flare. Assuming a thick-target model, the injected electron spectrum was found to have a spectral index of ~7.3, a low energy cut-off of ~20 keV, and a resulting flux of >4x10^10 ergs cm^-2 s^-1. The dynamic response of the atmosphere was determined using CDS spectra, finding a mean upflow velocity of 230+/-38 km s^-1 in Fe XIX (592.23A), and associated downflows of 36+/-16 km s^-1 and 43+/-22 km s^-1 at chromospheric and transition region temperatures, respectively, relative to an averaged quiet-Sun spectra. The errors represent a 1 sigma dispersion. The properties of the accelerated electron spectrum and the corresponding evaporative velocities were found to be consistent with the predictions of theory.Comment: 5 pages, 4 figures, ApJL (In Press

Using variograms to detect and attribute hydrological change

There have been many published studies aiming to identify temporal changes in river flow time series, most of which use monotonic trend tests such as the Mann–Kendall test. Although robust to both the distribution of the data and incomplete records, these tests have important limitations and provide no information as to whether a change in variability mirrors a change in magnitude. This study develops a new method for detecting periods of change in a river flow time series, using temporally shifting variograms (TSVs) based on applying variograms to moving windows in a time series and comparing these to the long-term average variogram, which characterises the temporal dependence structure in the river flow time series. Variogram properties in each moving window can also be related to potential meteorological drivers. The method is applied to 91 UK catchments which were chosen to have minimal anthropogenic influences and good quality data between 1980 and 2012 inclusive. Each of the four variogram parameters (range, sill and two measures of semi-variance) characterise different aspects of the river flow regime, and have a different relationship with the precipitation characteristics. Three variogram parameters (the sill and the two measures of semi-variance) are related to variability (either day-to-day or over the time series) and have the largest correlations with indicators describing the magnitude and variability of precipitation. The fourth (the range) is dependent on the relationship between the river flow on successive days and is most correlated with the length of wet and dry periods. Two prominent periods of change were identified: 1995–2001 and 2004–2012. The first period of change is attributed to an increase in the magnitude of rainfall whilst the second period is attributed to an increase in variability of the rainfall. The study demonstrates that variograms have considerable potential for application in the detection and attribution of temporal variability and change in hydrological systems

Gravitational Interactions in a General Multibrane Model

The gravitational interactions of the four-dimensional effective theory describing a general $N$-brane model in five dimensions without radion stabilization are analyzed. Both uncompactified and orbifolded models are considered. The parameter space is constrained by requiring that there be no ghost modes in the theory, and that the Eddington parameterized post-Newtonian parameter $\gamma$ be consistent with observations. We show that we must reside on the brane on which the warp factor is maximized. The resultant theory contains $N-1$ radion modes in a nonlinear sigma model, with the target space being a subset of hyperbolic space. Imposing observational constraints on the relative strengths of gravitational interactions of dark and visible matter shows that at least 99.8% of the dark matter must live on our brane in this model.Comment: 18 pages, 4 figures. Version 2 (submitted to PRD) adds analysis on orbifold

Co-operative experiments made by the Ohio Agricultural Students' Union in 1896

Caption title.Mode of access: Internet

Validating performance of automotive materials at high strain rate for improved crash design

This paper investigates sources of performance variability in high velocity testing of automotive crash structures. Sources of variability, or so called noise factors, present in a testing environment, arise from uncertainty in structural properties, joints, boundary conditions and measurement system. A box structure, which is representative of a crash component, is designed and fabricated from a high strength Dual Phase sheet steel. Crush tests are conducted at low and high speed. Such tests intend to validate a component model and material strain rate sensitivity data determined from high speed tensile testing. To support experimental investigations, stochastic modeling is used to investigate the effect of noise factors on crash structure performance variability, and to identify suitable performance measures to validate a component model and material strain rate sensitivity data. The results of the project will enable the measurement of more reliable strain rate sensitivity data for improved crashworthiness predictions of automotive structures