An 80 pc Long Massive Molecular Filament in the Galactic Mid-Plane

The ubiquity of filaments in star forming regions on a range of scales is clear, yet their role in the star formation process remains in question. We suggest that there are distinct classes of filaments which are responsible for their observed diversity in star-forming regions. An example of a massive molecular filament in the Galactic mid-plane formed at the intersection of UV-driven bubbles which displays a coherent velocity structure (< 4 km/s) over 80 pc is presented. We classify such sources as Massive Molecular Filaments (MMFs; M > 10^4 Msun, length > 10 pc, velocity gradient < 5 km/s) and suggest that MMFs are just one of the many different classes of filaments discussed in the literature today. Many MMFs are aligned with the Galactic Plane and may be akin to the dark dust lanes seen in Grand Design Spirals.Comment: To appear in proceedings of the 'Labyrinth of Star Formation' meeting (18-22 June 2012, Chania, Greece), published by Springe

Criticism of "Necessity of simultaneous co-existence of instantaneous and retarded interactions in classical electrodynamics" by Andrew E. Chubykalo and Stoyan J. Vlaev

The demonstration that the electromagnetic fields derived from the Lienard-Wiechert potentials do not satisfy the Maxwell equations is proved to be false. Errors were made in the computation of the derivatives of retarded quantities. The subsequent inference of the necessity of both instantaneous and retarded electromagnetic interactions cannot be made. Different choices of gauge can lead to a variety of forms for the scalar and vector potentials, always with the same retarded fields. Classical electromagnetic theory is complete as usually expressed. One may choose to work in the Lorenz gauge in which all quantities are retarded.Comment: pdf file, 5 pages, submitted to Int. J. Mod. Phy

Toroidal Imploding Detonation Wave Initiator for Pulse Detonation Engines

Imploding toroidal detonation waves were used to initiate detonations in propane–air and ethylene–air mixtures inside of a tube. The imploding wave was generated by an initiator consisting of an array of channels filled with acetylene–oxygen gas and ignited with a single spark. The initiator was designed as a low-drag initiator tube for use with pulse detonation engines. To detonate hydrocarbon–air mixtures, the initiator was overfilled so that some acetylene oxygen spilled into the tube. The overfill amount required to detonate propane air was less than 2% of the volume of the 1-m-long, 76-mm-diam tube. The energy necessary to create an implosion strong enough to detonate propane–air mixtures was estimated to be 13% more than that used by a typical initiator tube, although the initiator was also estimated to use less oxygen. Images and pressure traces show a regular, repeatable imploding wave that generates focal pressures in excess of 6 times the Chapman–Jouguet pressure.Atheoretical analysis of the imploding toroidal wave performed using Whitham’s method was found to agree well with experimental data and showed that, unlike imploding cylindrical and spherical geometries, imploding toroids initially experience a period of diffraction before wave focusing occurs. A nonreacting numerical simulation was used to assist in the interpretation of the experimental data

Prediction of gas leakage of environmental control systems

Mathematical models of leakage configurations and various flow theories are presented with the substantive experimental test data to provide background material for future design and failure analysis. Normal-rate leakage and emergency, high-rate leakage are considered

Data catalog series for space science and applications flight missions. Volume 3A: Descriptions of low- and medium-altitude scientific spacecraft and investigations

Earth orbits spacecraft whose apogees are well below geostationary altitude and whose primary purpose is to conduct investigations in the near-Earth environment are considered

Effect of Deflagration-to-Detonation Transition on Pulse Detonation Engine Impulse

A detonation tube was built to study the deflagration-to-detonation transition (DDT) process and the impulse generated when combustion products exhaust into the atmosphere. The reactants used were stoichiometric ethylene and oxygen mixture with varying amounts of nitrogen present as diluent. The effects of varying the initial pressure from 30 kPa to 100 kPa were studied, as were the effects of varying the diluent concentration from 0% to 73.8% of the total mixture. Measurements were carried out with the tube free of obstacles and with three different obstacle configurations. Each obstacle configuration had a blockage ratio of 0.43. It was found that the inclusion of obstacles dramatically lowered the DDT times and distances as compared to the no obstacle configuration. The obstacles were found to be particularly effective at inducing DDT in mixtures with low pressures and with high amounts of diluent. At the lowest pressures tested (30 kPa), obstacles reduced the DDT time and distance to approximately 12.5% of the no obstacle configuration values. The obstacles also allowed DDT to occur in mixture compositions of up to 60% diluent, while DDT was not achieved with more than 30% diluent in the no obstacle configuration. A ballistic pendulum arrangement was utilized, enabling direct measurement of the impulse by measuring the tube's deflection. Additional means of impulse comparison consisted of integrating the pressure over the front wall of the tube. Impulse measurements were then compared with a theoretical model and were found to fit well cases that did not contain internal obstacles. The inclusion of obstacles allowed DDT to occur in mixtures with high amounts of diluent where DDT was not observed to occur in the cases without obstacles. Roughly 100% more impulse was produced in the obstacle configurations as compared to the no obstacle configuration under these conditions. In instances where DDT occurred in the no obstacle configuration, the use of obstacle configurations lowered the impulse produced by an average of 25%. For cases where no obstacles were used and DDT occurred, the pressure derived impulses (pressure impulse) and impulses determined from the ballistic pendulum (ballistic impulses) are similar. For cases were obstacle configurations were tested, pressure impulses were more than 100% higher on average than ballistic impulses. This difference exists because the pressure model neglects drag due to the obstacle configurations

Planar Detonation Wave Initiation in Large-Aspect-Ratio Channels

In this study, two initiator designs are presented that are able to form planar detonations with low input energy in large-aspect-ratio channels over distances corresponding to only a few channel heights. The initiators use a single spark and an array of small channels to shape the detonation wave. The first design, referred to as the static initiator, is simple to construct as it consists of straight channels which connect at right angles. However, it is only able to create planar waves using mixtures that can reliably detonate in its small-width channels. An improved design, referred to as the dynamic initiator, is capable of detonating insensitive mixtures using an oxyacetylene gas slug injected into the initiator shortly before ignition, but is more complex to construct. The two versions are presented next, including an overview of their design and operation. Design drawings of each initiator are available elsewhere [7]. Finally, photographs and pressure traces of the resulting planar waves generated by each device are shown

Analytical Model for the Impulse of Single-Cycle Pulse Detonation Tube

An analytical model for the impulse of a single-cycle pulse detonation tube has been developed and validated against experimental data. The model is based on the pressure history at the thrust surface of the detonation tube. The pressure history is modeled by a constant pressure portion, followed by a decay due to gas expansion out of the tube. The duration and amplitude of the constant pressure portion is determined by analyzing the gasdynamics of the self-similar flow behind a steadily moving detonation wave within the tube. The gas expansion process is modeled using dimensional analysis and empirical observations. The model predictions are validated against direct experimental measurements in terms of impulse per unit volume, specific impulse, and thrust. Comparisons are given with estimates of the specific impulse based on numerical simulations. Impulse per unit volume and specific impulse calculations are carried out for a wide range of fuel–oxygen–nitrogen mixtures (including aviation fuels) of varying initial pressure, equivalence ratio, and nitrogen dilution. The effect of the initial temperature is also investigated. The trends observed are explained using a simple scaling analysis showing the dependency of the impulse on initial conditions and energy release in the mixture