Dimensional fundamental constants and their application in astronomy

A discussion is given of the role of dimensional fundamental constants in gravitational and particle physics. It is concluded that such constants can most usefully be interpreted as representing asymptotic states. This interpretation is in agreement with the widespread use of dimensional analysis in astronomy, and implies that angular momentum can be expected to vary like the mass squared in the astronomical limit of large masses.     

An Update on Ultra-Heavy Elements in Solar Energetic Particles above 10 MeV/Nucleon

Measurements below several MeV/nucleon from Wind/LEMT and ACE/ULEIS show that elements heavier than Zn (Z=30) can be enhanced by factors of ∼100 to 1000, depending on species, in ³He-rich solar energetic particle (SEP) events. Using the Solar Isotope Spectrometer (SIS) on ACE we find that even large SEP (LSEP) shock-accelerated events at energies from ∼10 to >100 MeV/nucleon are often very iron rich and might contain admixtures of flare seed material. Studies of ultra-heavy (UH) SEPs (with Z>30) above 10 MeV/nucleon can be used to test models of acceleration and abundance enhancements in both LSEP and ³He-rich events. We find that the long-term average composition for elements from Z=30 to 40 is similar to standard solar system values, but there is considerable event-to-event variability. Although most of the UH fluence arrives during LSEP events, UH abundances are relatively more enhanced in ³He-rich events, with the (34<Z<40)/O ratio on average more than 50 times higher in ³He-rich events than in LSEP events. At energies >10 MeV/nucleon, the most extreme event in terms of UH composition detected so far took place on 23 July 2004 and had a (34<Z<40)/O enhancement of ∼250–300 times the standard solar value.     

一种应用在航天探测器上的二氧化碳两相回路热控系统冷凝器的设计优化

阿尔法磁谱仪中的轨迹探测器是探测空间反物质的核心探测器,它工作于由超流液氦冷却的超导磁体的中心,其正常运作需要体积小、散热及温控能力强的热控系统的支持,以应对国际空间站上复杂的太空热流环境及真空、微重力等因素.介绍了利用SINDA/FLUINT模拟方法,对轨迹探测器的热控系统冷凝器进行设计优化.     

The role of ultraviolet imaging in studies of resolved and unresolved young stellar populations. M31 and M33

We discuss the relevance of UV data in the detection and characterization of hot massive stars and young stellar populations in galaxies. We show results from recent extensive surveys in M31 and M33 with Hubble Space Telescope (HST) multi-wavelength data including UV filters, which imaged several regions at a linear resolution (projected) of less than half a pc in these galaxies, and from GALEX far-UV and near-UV wide-field, low-resolution imaging of the entire galaxies. Both datasets allow us to study the hierarchical structure of star formation: the youngest stellar groups are the most compact, and are often arranged within broader, sparser structures. The derived recent star-formation rates are rather similar for the two galaxies, when scaled for the respective areas. We show how uncertainties in metallicity and type of selective extinction for the internal reddening may affect the results, and how an appropriate complement of UV filters could reduce such uncertainties, and significantly alleviate some parameter degeneracies.     

The AWIATOR airborne LIDAR turbulence sensor

The development and first flight tests are described of a short pulse direct measuring UV LIDAR for the measurement of gusts, turbulence and potentially wake vortices. The results of these stage 1 tests confirm that relative wind velocities can be measured with a standard deviation of below 10 m/s even at high altitudes with no appreciable aerosol concentrations. Operating the system under various flight conditions including rain, dense clouds, and clear air up to 24,000 ft was highly successful. Means to push the standard deviation below 1.6 m/s, foremost by increasing the laser output power and the efficiency of the light collecting system, are identified and quantified. Questions of instrument stability are addressed.     

Local orbital debris flux study in the geostationary ring

A local orbital debris flux analysis is performed in the geostationary (GEO) ring to investigate how frequently near-miss events occur for each longitude slot in the GEO ring. The current resident space object (RSO) environment at GEO is evaluated, and publicly-available two-line element (TLE) data are utilized in tandem with a geostationary torus configuration to simulate near-miss events incurred by the trackable RSO population at GEO. Methodology for determining near-miss events with this formulation is introduced, and the results of the analysis for a one-year time frame are provided to illustrate the need for active GEO remediation.     

3D radar wavefield tomography of comet interiors

Answering fundamental questions about the origin and evolution of small planetary bodies hinges on our ability to image their surface and interior structure in detail and at high resolution. The interior structure is not easily accessible without systematic imaging using, e.g., radar transmission and reflection data from multiple viewpoints, as in medical tomography. Radar tomography can be performed using methodology adapted from terrestrial exploration seismology. Our feasibility study primarily focuses on full wavefield methods that facilitate high quality imaging of small body interiors. We consider the case of a monostatic system (co-located transmitters and receivers) operated in various frequency bands between 5 and 15?MHz, from a spacecraft in slow polar orbit around a spinning comet nucleus. Using realistic numerical experiments, we demonstrate that wavefield techniques can generate high resolution tomograms of comets nuclei with arbitrary shape and complex interior properties.     

The LES model's role in jet noise

Problem definition, near wall modeling and other factors, including grid structure along with its implications on filter definition, are suggested to be of potentially greater importance for practical jet simulations than the LES (large eddy simulation) model. This latter element in itself can be theoretically questionable. When moving to realistic engine conditions, it is noted that disentangling numerical influences from the LES model's appear difficult and negates the model value with its omission potentially being beneficial. Evidence cited suggests that if using an LES model for jets, choosing the numerically best conditioned or the one the code has or, for a dissipative solver, even LES model omission seems sensible. This view point precludes combustion modeling. Tensors of additional derivatives, used in non-linear LES models, when expanded, can yield potentially several hundred interesting derivatives. It is suggested that the MILES (monotone-integrated LES) and LES communities should move towards seeing where modified equation derivatives connect with derivatives that appear in more state of the art non-linear LES models. Then the best features could be combined to form mixed MILES–LES models or even mixed MILES–LES–RANS models. Combustion modeling also presents hybridization potential but in a different context. Most MILES-modified equation analysis focus on the spatial discretization and not the temporal. However, with some codes the spatial discretization terms are deliberately constructed to cancel temporal truncation error terms. Hence, the two things work in harmony and the temporal discretization can make a strong impact on resolved scales.     

The STEREO IMPACT Boom

An essential component of the STEREO IMPACT investigation is its nearly 6 m long boom that provides several of the instruments with a sufficiently clean magnetic environment and minimally restricted fields of view, while having the required rigidity to ensure the spacecraft pointing accuracy for the STEREO imaging investigations. Details of the customized telescoping IMPACT Boom design, construction and testing are described in this review. The successful completion and verification of the IMPACT Booms represents a demonstration of the use of Stacers as motive forces for rigid boom deployment.