Hydrogen film cooling of a small hydrogen-oxygen thrust chamber and its effect on erosion rates of various ablative materials

An experimental investigation was conducted to determine what arrangement of film-coolant-injection orifices should be used to decrease the erosion rates of small, high temperature, high pressure ablative thrust chambers without incurring a large penalty in combustion performance. All of the film cooling was supplied through holes in a ring between the outer row of injector elements and the chamber wall. The best arrangement, which had twice the number of holes as there were outer row injection elements, was also the simplest. The performance penalties, presented as a reduction in characteristic exhaust velocity efficiency, were 0.8 and 2.8 percentage points for the 10 and 20 percent cooling flows, respectively, The best film-coolant injector was then used to obtain erosion rates for 19 ablative materials. The throat erosion rate was reduced by a factor of 2.5 with a 10 percent coolant flow. Only the more expensive silica phenolic materials had low enough erosion rates to be considered for use in the nozzle throat. However, some of the cheaper materials might qualify for use in other areas of small nozzles with large throat diameters where the higher erosion rates are more acceptable

Heavy Baryons in a Quark Model

A quark model is applied to the spectrum of baryons containing heavy quarks. The model gives masses for the known heavy baryons that are in agreement with experiment, but for the doubly-charmed baryon Cascade_{cc}, the model prediction is too heavy. Mixing between the Cascade_Q and Cascade_Q^\prime states is examined and is found to be small for the lowest lying states. In contrast with this, mixing between the Cascade_{bc} and Cascade_{bc}^\prime states is found to be large, and the implication of this mixing for properties of these states is briefly discussed. We also examine heavy-quark spin-symmetry multiplets, and find that many states in the model can be placed in such multiplets. We compare our predictions with those of a number of other authors.Comment: Version published in International Journal of Modern Physics

A Fluid Generalization of Membranes

In a certain sense a perfect fluid is a generalization of a point particle. This leads to the question as to what is the corresponding generalization for extended objects. The lagrangian formulation of a perfect fluid is much generalized and this has as a particular example a fluid which is a classical generalization of a membrane, however there is as yet no indication of any relationship between their quantum theories.Comment: To appear in CEJP, updated to coincide with published versio

Monte Carlo simulation of the transmission of measles: Beyond the mass action principle

We present a Monte Carlo simulation of the transmission of measles within a population sample during its growing and equilibrium states by introducing two different vaccination schedules of one and two doses. We study the effects of the contact rate per unit time $\xi$ as well as the initial conditions on the persistence of the disease. We found a weak effect of the initial conditions while the disease persists when $\xi$ lies in the range 1/L-10/L ($L$ being the latent period). Further comparison with existing data, prediction of future epidemics and other estimations of the vaccination efficiency are provided. Finally, we compare our approach to the models using the mass action principle in the first and another epidemic region and found the incidence independent of the number of susceptibles after the epidemic peak while it strongly fluctuates in its growing region. This method can be easily applied to other human, animals and vegetable diseases and includes more complicated parameters.Comment: 15 pages, 4 figures, 1 table, Submitted to Phys.Rev.

The space physics environment data analysis system (SPEDAS)

With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have “crib-sheets,” user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer’s Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its “modes of use” with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.Published versio

Boosting the petrochronology arsenal: REE partitioning between garnet and monazite in Bhutanese pelitic metasediments

Metamorphic studies are increasingly striving to integrate timing information with petrographic analysis and thermobarometry – the developing field of petrochronology. Recent advances in analytical techniques, in particular a variety of in situ methods that can potentially extract the information preserved in disequilibrium features, have reinvigorated metamorphic studies. The strength of petrochronology lies in linking the isotopic age directly to the metamorphic stage, in contrast to earlier studies where accessory phase ages existed in isolation from the thermobaromatric data with which they were tentatively linked. Garnet has proved itself an invaluable tool in metamorphic studies, yielding microstructural, thermobarometric, geochemical and even geochronological information. Although common in amphibolite-facies pelitic metasediments, garnet does not easily yield its chronological data, so the common accessory phase monazite has been used more routinely. Typically, monazite isotopic ages cannot be linked to the development of different metamorphic assemblages because their textural relationships, especially with fabric-forming phases, are commonly obscure. However, their distribution as matrix grains versus inclusions in porphyroblast minerals such as garnet, or in retrograde textures, can yield useful information. In situ investigations of chemical zoning in both monazite and garnet offer the potential to link crystallisation of the two minerals more closely. Since both monazite and garnet incorporate rare earth elements (REE), their equilibrium partitioning behaviour provides not only a useful test of equilibration, but also a way of linking time to temperature. Previously reported garnetmonazite partitioning data record the behaviour expected under granulite-facies (>750°C) conditions. We document REE concentration data from sub-solidus amphibolite-facies (~650-700°C) rocks from the eastern Himalaya (Bhutan), where age and inclusion relationships suggest that garnet and monazite grew simultaneously. The garnet/monazite ratios show steeper heavy REE patterns than those reported from the higher-temperature experimental data. These data suggest either that the partitioning relationships vary with temperature, or that different relationships hold in sub-solidus vs. supra-solidus rocks. Bhutan is an excellent location to test these relationships; abundant pelitic metasediments within a single tectonic unit span metamorphic grades ranging from sub-solidus to supra-solidus. Moreover, these metamorphic rocks (and their counterparts along the strike of the orogen) have been extensively studied in recent years both in terms of their metamorphism and their monazite geochronology, providing an ideal framework for petrochronological research with applications to all major orogens

Direct Urca neutrino rate in colour superconducting quark matter

If deconfined quark matter exists inside compact stars, the primary cooling mechanism is neutrino radiation via the direct Urca processes d->u+e+antinu_e and u+e->d+nu_e. Below a critical temperature, T_c, quark matter forms a colour superconductor, one possible manifestation of which is a condensate of quark Cooper pairs in an electric-charge neutralising background of electrons. We compute the neutrino emission rate from such a phase, including charged pair-breaking and recombination effects, and find that on a material temperature domain below T_c the pairing-induced suppression of the neutrino emission rate is not uniformly exponential. If gapless modes are present in the condensed phase, the emissivity at low temperatures is moderately enhanced above that of completely unpaired matter. The importance of charged current pair-breaking processes for neutrino emission both in the fully gapped and partially gapped regimes is emphasised.Comment: 5 pages, 2 figures; to appear in Phys. Rev. C (Rapid Comm.

Averaging approximation to singularly perturbed nonlinear stochastic wave equations

An averaging method is applied to derive effective approximation to the following singularly perturbed nonlinear stochastic damped wave equation \nu u_{tt}+u_t=\D u+f(u)+\nu^\alpha\dot{W} on an open bounded domain $D\subset\R^n$\,, $1\leq n\leq 3$\,. Here $\nu>0$ is a small parameter characterising the singular perturbation, and $\nu^\alpha$\,, $0\leq \alpha\leq 1/2$\,, parametrises the strength of the noise. Some scaling transformations and the martingale representation theorem yield the following effective approximation for small $\nu$, u_t=\D u+f(u)+\nu^\alpha\dot{W} to an error of \ord{\nu^\alpha}\,.Comment: 16 pages. Submitte