Modelling crystal aggregation and deposition\ud in the catheterised lower urinary tract

Urethral catheters often become encrusted with crystals of magnesium struvite and calcium phosphate. The encrustation can block the catheter, which can cause urine retention in the bladder and reflux into the kidneys. We develop a mathematical model to investigate crystal deposition on the catheter surface, modelling the bladder as a reservoir of fluid and the urethral catheter as a rigid channel. At a constant rate, fluid containing crystal particles of unit size enters the reservoir, and flows from the reservoir through the channel and out of the system. The crystal particles aggregate, which we model using Becker–Döring coagulation theory, and are advected through the channel, where they continue to aggregate and are deposited on the channel’s walls. Inhibitor particles also enter the reservoir, and can bind to the crystals, preventing further aggregation and deposition. The crystal concentrations are spatially homogeneous in the reservoir, whereas the channel concentrations vary spatially as a result of advection, diffusion and deposition. We investigate the effect of inhibitor particles on the amount of deposition. For all parameter values, we find that crystals deposit along the full length of the channel, with maximum deposition close to the channel’s entrance

MULTIPAC, a multiple pool processor and computer for a spacecraft central data system, phase 2 Final report

MULTIPAC, multiple pool processor and computer for deep space probe central data syste

Reverse rotations in the circularly-driven motion of a rigid body

We study the dynamical response of a circularly-driven rigid body, focusing on the description of intrinsic rotational behavior (reverse rotations). The model system we address is integrable but nontrivial, allowing for qualitative and quantitative analysis. A scale free expression defining the separation between possible spinning regimes is obtained.Comment: This work is accepted for publication as a Rapid Communication in Physical Review

Tide and Tidal Current Prediction by High Speed Digital Computer

The Tide and Tidal Current Tables of the U. S. Coast and Geodetic Survey for 1966 have been computed and edited by a digital computer, the IBM 7094. Prediction by this method is found to be more economical and expedient than by the tide prediction machine in use since 1910. The shift to digital predictions has been gradual. The first program was prepared in 1956 to predict hourly tide heights only, for use in storm surge research. The greatest advantage to digital prediction at that time was the elimination of the hour or more required to set up a new problem on the tide predicting machine, when highly accurate predictions were needed for many short periods. Later, as more efficient computers became available, this program was expanded to include the computation of highs and lows, editing the data in a form suitable for publication and the complete prediction and editing of the tidal current tables. The existing program, to a large degree, reproduced the same calculations formerly made on the analogue tide predicting machine, and with comparable accuracy. The greater versatility of this system invites experimentation, not feasible with the analogue computer. Thus, it is expected that in the long run the switch to digital calculations will lead to an increase in the accuracy of the predictions for stations having complex tide problems. The program grew through the years, and is not the most efficient that could be prepared today. Nevertheless, it appears doubtful that the improved efficiency would justify a complete revision. This report gives a general description of the program, the input data specifications and samples of the results

The Solar Energetic Particle Event of 6 May 1998

The abundances of elements from helium to iron have been measured in more than a dozen moderate to large solar energetic particle (SEP) events using the Solar Isotope Spectrometer (SIS) on-board the Advanced Composition Explorer (ACE). Time variations within some of these events and from event to event have been reported previously. This paper presents an analysis of the event of 6 May 1998, for which relatively time-independent abundance ratios are found. This event has been considered to be an example of an impulsive event, a gradual event, and as a hybrid of the two. Difficulties with classifying this event are discussed

Observations of Anomalous Cosmic Rays at 1 AU

Anomalous cosmic rays (ACRs) provide a sensitive probe of the access of energetic particles to the inner heliosphere, varying in intensity by more than two orders of magnitude during the course of the solar cycle. New data which are becoming available from the Advanced Composition Explorer (ACE) can provide a detailed record of ACR intensity and spectral changes on short (~ 1 day) time scales during the approach to solar maximum, which will help address issues of ACR modulation and transport. The elemental and isotopic composition of ACRs provides important information on the source or sources of these particles, while their ionic charge state composition and its energy dependence serves as a diagnostic of their acceleration time scale. We review measurements of the ACR elemental, isotopic, and charge state composition and spectra as determined at 1 AU by SAMPEX, ACE, Wind, and other spacecraft. These results are important input to models of the acceleration, modulation, and transport of ACRs

A novel technique to infer ionic charge states of solar energetic particles

In some large solar energetic particle (SEP) events, the intensities of higher energy SEPs decay more rapidly than at lower energies. This energy dependence varies with particle species, as would be expected if the decay timescale depended on a rigidity-dependent diffusion mean free path. By comparing the decay timescales of carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron, mean charge states are inferred for these (and other) elements in three SEP events between 1997 and 2002 at energies between 10 and 200 MeV nucleon−1. In a fourth event, upper limits for the charge states are inferred. The charge states of many different particle species are all consistent with a single source temperature; in two events in 1997 and 2002, the best-fit temperature is much higher than that of the corona, which could imply a contribution from solar flare material. However, comparison with lower energy iron charge states for the 1997 event implies that the observed high-energy charge state could also be understood as the result of stripping during shock acceleration in the corona

Solar Coronal Abundances of Rare Elements Based on Solar Energetic Particles

Although solar energetic particle (SEP) abundances vary from event to event, it has been shown that by accounting for these variations it is possible to use SEP data to obtain reliable estimates of elemental abundances for the solar corona. We analyze ~20 to 65 MeV/nucleon measurements from the Solar Isotope Spectrometer on ACE in large SEP events observed from November 1997 to January 2001 to obtain new values of the average SEP composition of rare species, P, Cl, K, Ti, Mn, Cr, Co, Cu, and Zn, which have had limited statistical accuracy in SEPs in the past. The measured SEP abundances are compared with other sources of solar-system composition data