A design study of hydrazine and biowaste resistojets

A generalized modeling program was adapted in BASIC on a personal computer to compare the performance of four types of biowaste resistojets and two types of hydrazine augmenters. Analyzed biowaste design types were: (1) an electrically conductive ceramic heater-exchanger of zirconia; (2) a truss heater of platinum in cross flow; (3) an immersed bicoiled tubular heater-exchanger; and (4) a nonexposed, refractory metal, radiant heater in a central cavity within a heat exchanger case. Concepts 2 and 3 are designed to have an efficient, stainless steel outer pressure case. The hydrazine design types are: (5) an immersed bicoil heater exchanger and (6) a nonexposed radiant heater now with a refractory metal case. The ceramic biowaste resistojet has the highest specific impulse growth potential at 2000 K of 192.5 (CO2) and 269 s (H2O). The bicoil produces the highest augmenter temperature of 1994 K for a 2073 K heater giving 317 s at .73 overall efficiency. Detailed temperature profiles of each of the designs are shown. The scaled layout drawings of each are presented with recommended materials and fabrication methods

Pairing, Ferromagnetism, and Condensation of a normal spin-1 Bose gas

We theoretically study the stability of a normal, spin disordered, homogenous spin-1 Bose gas against ferromagnetism, pairing, and condensation through a Random Phase Approximation which includes exchange (RPA-X). Repulsive spin-independent interactions stabilize the normal state against both ferromagnetism and pairing, and for typical interaction strengths leads to a direct transition from an unordered normal state to a fully ordered single particle condensate. Atoms with much larger spin-dependent interaction may experience a transition to a ferromagnetic normal state or a paired superfluid, but, within the RPA-X, there is no instability towards a normal state with spontaneous nematic order. We analyze the role of the quadratic Zeeman effect and finite system size.Comment: 4 pages, 3 figures, 1 table. Supplementary materials attache

Particle trapping in a stratified flood-dominated estuary

Observations in the Navesink River estuary in northern New Jersey demonstrate that buoyancy augments the particle trapping tendencies of flood-dominated systems because these estuaries heighten tidal period asymmetries in stratification. During the long and slow ebb which typifies flood-dominated systems, a positive feedback between tidal straining and weak vertical mixing stratifies the estuary. In contrast, during flood, turbulence generated by the stronger tidal currents augments overstraining of the density field and the water column becomes well mixed. The tidal period asymmetries in stratification have profound effects on the vertical structure and transport of suspended matter. During ebb, weak vertical mixing allows suspended material to settle downward. In contrast, strong turbulence during flood mixes suspended matter into the water column where it is transported up estuary. Furthermore, observations reveal that resuspension events are marked by multiple turbidity spikes, suggestive of multiple, limited layers of erodible material. The transport of the turbid waters is consistent with horizontal advection modified by horizontal dispersion. Periods of enhanced stratification are also marked by relatively low levels of turbidity during the ebb, consistent with more complete settling of suspended material following times of high river discharge. The interplay between buoyancy and tidal asymmetries are further elucidated with a onedimensional numerical model featuring a turbulent closure scheme and a passively settling tracer. Model results are generally consistent with the field observations, both emphasizing the robust particle trapping tendencies of a stratified flood-dominated estuary. We speculate that enhanced particle trapping following times of high river discharge may have important biological consequences

Embedding generic employability skills in an accounting degree: development and impediments

This paper explores and analyses the views of, and effects on, students of a project that integrated the development of employability skills within the small group classes of two compulsory courses in the first year of an accounting degree at a UK university. The project aimed to build, deliver and evaluate course materials designed to encourage the development of a broad range of employability skills: skills needed for life-long learning and a successful business career. By analysing students' opinions gathered from a series of focus groups spread throughout the year, three prominent skill areas of interest were identified: time management, modelling, and learning to learn. Further analysis highlighted the complex nature of skills development, and brought to light a range of impediments and barriers to both students' development of employability skills and their subject learning. The analysis suggests the need for accounting educators to see skills development as being an essential element of the path to providing a successful accounting education experience

Magnetic tight-binding and the iron-chromium enthalpy anomaly

We describe a self consistent magnetic tight-binding theory based in an expansion of the Hohenberg-Kohn density functional to second order, about a non spin polarised reference density. We show how a first order expansion about a density having a trial input magnetic moment leads to the Stoner--Slater rigid band model. We employ a simple set of tight-binding parameters that accurately describes electronic structure and energetics, and show these to be transferable between first row transition metals and their alloys. We make a number of calculations of the electronic structure of dilute Cr impurities in Fe which we compare with results using the local spin density approximation. The rigid band model provides a powerful means for interpreting complex magnetic configurations in alloys; using this approach we are able to advance a simple and readily understood explanation for the observed anomaly in the enthalpy of mixing.Comment: Submitted to Phys Rev

Spin Josephson effect in ferromagnet/ferromagnet tunnel junctions

We consider the tunnel spin current between two ferromagnetic metals from a perspective similar to the one used in superconductor/superconductor tunnel junctions. We use fundamental arguments to derive a Josephson-like spin tunnel current $I_J^{\rm spin}\propto\sin(\theta_1-\theta_2)$. Here the phases are associated with the planar contribution to the magnetization, $\sim e^{i\theta}$. The crucial step in our analysis is the fact that the $z$-component of the spin is canonically conjugate to the phase of the planar contribution: $[\theta,S^z]=i$. This is analogous to the commutation relation $[\phi,N]=i$ in superconductors, where $\phi$ is the phase associated to the superconducting order parameter and $N$ is the Cooper pair number operator. We briefly discuss the experimental consequences of our theoretical analysis.Comment: LaTex, seven pages, no figures; version to appear in Europhys. Lett.; in order to make room for a more extended microscopic analysis, the phenomenological discussion contained in v2 was remove

The Fish Crow (\u3ci\u3eCorvus ossifragus\u3c/i\u3e) Reaches Nebraska

The Fish Crow (Corvus ossifragus) was formerly endemic to the southeastern United States where it inhabited coastal areas along the Atlantic and Gulf Coasts (McGowan 2001). Since the early 1900s, the species has steadily expanded north and west along major river systems (McGowan 2001). Fish Crow range expansion has followed a logical pattern, expanding along major rivers in regions close to established populations, in adjacent states to the south and east of Nebraska. The species was first recorded in Missouri in 1964 (Robbins and Easterla 1992). In 1984, Fish Crow was first reported in Kansas and by 1991 was found breeding in that state (Thomson and Ely 1992). Iowa\u27s first record was in 1991 (Kent and Dinsmore 1996). There are no records from adjacent states to the north and west of Nebraska (Tallman et al. 2002, Andrews and Righter 1992, Scott 1993, Wyoming Game and Fish Department 1997). The Fish Crow has long been considered an inevitable addition to Nebraska\u27s avifauna. During the summer of 2009, we observed an adult Fish Crow on multiple occasions on the lower Platte River (LPR) near its confluence with the Missouri River. Documentation was provided to the Nebraska Ornithologists\u27 Union Records Committee (NOURC) and this observation was subsequently accepted as the first documented record for the species in Nebraska (Mark Brogie, NOURC Chairperson, personal communication). Here, we describe our observations and comment on the future occurrence of the species in Nebraska

Spin Susceptibility of an Ultra-Low Density Two Dimensional Electron System

We determine the spin susceptibility in a two dimensional electron system in GaAs/AlGaAs over a wide range of low densities from 2$\times10^{9}$cm$^{-2}$ to 4$\times10^{10}$cm$^{-2}$. Our data can be fitted to an equation that describes the density dependence as well as the polarization dependence of the spin susceptibility. It can account for the anomalous g-factors reported recently in GaAs electron and hole systems. The paramagnetic spin susceptibility increases with decreasing density as expected from theoretical calculations.Comment: 5 pages, 2 eps figures, to appear in PR

Landau-Zener-Stueckelberg effect in a model of interacting tunneling systems

The Landau-Zener-Stueckelberg (LZS) effect in a model system of interacting tunneling particles is studied numerically and analytically. Each of N tunneling particles interacts with each of the others with the same coupling J. This problem maps onto that of the LZS effect for a large spin S=N/2. The mean-field limit N=>\infty corresponds to the classical limit S=>\infty for the effective spin. It is shown that the ferromagnetic coupling J>0 tends to suppress the LZS transitions. For N=>\infty there is a critical value of J above which the staying probability P does not go to zero in the slow sweep limit, unlike the standard LZS effect. In the same limit for J>0 LZS transitions are boosted and P=0 for a set of finite values of the sweep rate. Various limiting cases such as strong and weak interaction, slow and fast sweep are considered analytically. It is shown that the mean-field approach works well for arbitrary N if the interaction J is weak.Comment: 13 PR pages, 15 Fig

Russell Lecture: Dark Star Formation and Cooling Instability

Optically thin cooling gas at most temperatures above 30K will make condensations by pressure pushing material into cool dense regions. This works without gravity. Cooling condensations will flatten and become planar/similarity solutions. Most star formation may start from cooling condensations - with gravity only important in the later stages. The idea that some of the dark matter could be pristine white dwarfs that condensed slowly on to planetary sized seeds without firing nuclear reactions is found lacking. However, recent observations indicate fifty times more halo white dwarfs than have been previously acknowledged; enough to make the halo fraction observed as MACHOS. A cosmological census shows that only 1% of the mass of the Universe is of known constitution.Comment: 32 Pages, Latex (uses aastex & natbib), 5 eps figures, submitted to ApJ April 200