Broadband characterisation of in-duct acoustic sources using an equivalent source approach

This paper is concerned with the development of an experimental method capable of independently characterising low Mach number, in-duct fluid machines, such as pumps, fans, etc. The aim is to propose and test a source characterisation method that is suitable for acoustic simulation and the construction Virtual Acoustic Prototypes. Such a requirement demands that the source characterisation be (a) independent, so that components can be virtually (re)combined within different assemblies and (b) valid over a wide frequency range so as to enable the output of a virtual assembly to be auralised. In this regard, standard methods based on sound power are not suitable. An equivalent source approach is proposed, based on a two-stage measurement procedure in which source strengths are obtained by solving an inverse problem. The experimental application of the procedure is illustrated as part of a case study where a high speed compressor unit is independently characterised and the resulting source data used to predict the operational response in a new assembly. Three frequency ranges are identified based on plane wave, modal and statistical behavior within the duct. The same measured data is used within each regime but subject to different processing according to different assumptions. Predictions are shown to be in good agreement with the directly measured response over a broad frequency range (100 Hz–10 kHz)

The Three Dimensional Structure of EUV Accretion Regions in AM Herculis Stars: Modeling of EUV Photometric and Spectroscopic Observations

We have developed a model of the high-energy accretion region for magnetic cataclysmic variables and applied it to {\it Extreme Ultraviolet Explorer} observations of 10 AM Herculis type systems. The major features of the EUV light curves are well described by the model. The light curves exhibit a large variety of features such as eclipses of the accretion region by the secondary star and the accretion stream, and dips caused by material very close to the accretion region. While all the observed features of the light curves are highly dependent on viewing geometry, none of the light curves are consistent with a flat, circular accretion spot whose lightcurve would vary solely from projection effects. The accretion region immediately above the WD surface is a source of EUV radiation caused by either a vertical extent to the accretion spot, or Compton scattering off electrons in the accretion column, or, very likely, both. Our model yields spot sizes averaging 0.06 R$_{WD}$, or $f \sim 1 \times 10^{-3}$ the WD surface area, and average spot heights of 0.023 R$_{WD}$. Spectra extracted during broad dip phases are softer than spectra during the out-of-dip phases. This spectral ratio measurement leads to the conclusion that Compton scattering, some absorption by a warm absorber, geometric effects, an asymmetric temperature structure in the accretion region and an asymmetric density structure of the accretion columnare all important components needed to fully explain the data. Spectra extracted at phases where the accretion spot is hidden behind the limb of the WD, but with the accretion column immediately above the spot still visible, show no evidence of emission features characteristic of a hot plasma.Comment: 30 Pages, 11 Figure

X-Ray Emission and Optical Polarization of V1432 Aquilae: An Asynchronous Polar

A detailed analysis of X-ray data from ROSAT, ASCA, XMM and RXTE for the asynchronous polar V1432 Aql along with Stokes polarimetry data from SAAO, is presented. Power spectra from long-baseline ROSAT data show a spin period of 12150s along with several system related frequency components. However, the second harmonic of the spin period dominates power spectrum in the XMM data. For the optical circular polarization, the dominant period corresponds to half the spin period. The ROSAT data can be explained as due to accretion onto two hot spots that are not anti-podal. The variations seen in the optical polarization and the ASCA and XMM data suggest the presence of at least three accretion foot prints on the white dwarf surface. Two spectral models, a multi-temperature plasma and a photo-ionized plasma model, are used for spectral study. The RXTE PCA data are used to constrain the white dwarf mass to 1.2$\pm$0.1 M_odot using the multi-temperature plasma model. A strong soft X-ray excess (<0.8 keV) in the XMM MOS data is well modeled by a blackbody component having a temperature of 80-90 eV. The plasma emission lines seen at 6.7 and 7.0 keV are well fitted using the multi-temperature plasma model, however an additional Gaussian is needed for the 6.4 keV line. The multi-temperature plasma model requires a homogeneous absorber fully covering the source and a partial absorber covering 65% of the source. The photo-ionized plasma model, with a range of Fe column densities, gives a slightly better overall fit and fits all emission lines. The presence of a strong blackbody component, a spin period of 12150s, modulation of the 6.4 keV line flux with spin period, and a very hard X-ray component suggest that V1432 Aql is a polar with X-ray spectral properties similar to that of a soft intermediate polar.Comment: 46 pages, including 13 figures and 4 tables, To appear in The Astrophysical Journal, 20 May 2005 issue, vol. 625, Added Report-no and Journal-ref, no change in the text of the pape

New Low Accretion-Rate Magnetic Binary Systems and their Significance for the Evolution of Cataclysmic Variables

Discoveries of two new white dwarf plus M star binaries with striking optical cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to six the total number of X-ray faint, magnetic accretion binaries that accrete at rates < 10^{-13} Msun/yr, or <1% of the values normally encountered in cataclysmic variables. This fact, coupled with donor stars that underfill their Roche lobes and very cool white dwarfs, brand the binaries as post common-envelope systems whose orbits have not yet decayed to the point of Roche-lobe contact. They are pre-magnetic CVs, or pre-Polars. The systems exhibit spin/orbit synchronism and apparently accrete by efficient capture of the stellar wind from the secondary star, a process that has been dubbed a ``magnetic siphon''. Because of this, period evolution of the binaries will occur solely by gravitational radiation, which is very slow for periods >3 hr. Optical surveys for the cyclotron harmonics appear to be the only means of discovery, so the space density of pre-Polars could rival that of Polars, and the binaries provide an important channel of progenitors (in addition to the asynchronous Intermediate Polars). Both physical and SDSS observational selection effects are identified that may help to explain the clumping of all six systems in a narrow range of magnetic field strength around 60 MG.Comment: 25 pages, 13 figures, Accepted to Ap

Essays in anarchism and religion: Volume 1

Essays in anarchism and religion: Volume

Multi-epoch Doppler tomography and polarimetry of QQ Vul

We present multi-epoch high-resolution spectroscopy and photoelectric polarimetry of the long-period polar (AM Herculis star) QQ Vul. The blue emission lines show several distinct components, the sharpest of which can unequivocally be assigned to the illuminated hemisphere of the secondary star and used to trace its orbital motion. This narrow emission line can be used in combination with Nai-absorption lines from the photosphere of the companion to build a stable long-term ephemeris for the star: inferior conjunction of the companion occurs at HJD = 244 8446.4710(5)+E×0. d 15452011(11). The polarization curves are dissimilar at different epochs, thus supporting the idea of fundamental changes of the accretion geometry, e.g. between one- and two-pole accretion modes. The linear polarization pulses display a random scatter by 0.2 phase units and are not suitable for the determination of the binary period. The polarization data suggest that the magnetic (dipolar) axis has a co-latitude of 23 ◦ , an azimuth of −50 ◦, and an orbital inclination between 50 ◦ and 70 ◦. Doppler images of blue emission and red absorption lines show a clear separatio

Phase-Resolved Infrared H- and K-band Spectroscopy of EF Eridani

We present new phase-resolved H and K-band spectroscopy of the ultra-short period magnetic cataclysmic variable EF Eri in its current, prolonged ``low'' state obtained using NIRI on Gemini-North, and NIRSPEC on Keck II. These new data show that the H-band spectrum of EF Eri appears to be dominated by cyclotron emission during the entire orbital cycle. The {\it K}-band spectrum of EF Eri is likewise dominated by cyclotron emission during most of an orbital period, but near binary phase 0.0, the secondary star spectrum may be visible. We conclude that strong, and highly variable cyclotron emission is responsible for the photometric variation previously reported for EF Eri. The nature of this cyclotron emission is complex: the H-band spectra show that the dominant cyclotron harmonic at phase 0.5 peaks at 1.65 $\mu$m, but at phase 0.0, the harmonic peaks near 1.72 $\mu$m. At phase 0.5, there is another cyclotron feature present that peaks in between the H and K bands (near 1.93 $\mu$m), but at phase 0.0, no such feature is present. These data suggest that cyclotron emission from both poles is occurring.Comment: 23 pages of text, 8 figure

Applications of a hybrid method to a plate with simply supported boundary conditions

* The EN12354 building acoustics prediction standards are based on the statistical energy analysis (SEA) method. In a traditional SEA path analysis, lightweight or heavyweight materials have different principal paths that determine the sound insulation for the specified building acoustics frequency range (50Hz-5000Hz). Different building materials require different applications of the engineering method (EN12354) to determine in-situ sound insulation with flanking. A hybrid method, such as the (finite element method) FEM-SEA hybrid approach, offers an alternative theoretical framework to predict in situ sound insulation with the capacity to combine vastly different methods. In a hybrid model, different power flow contributions (due to the deterministic and direct-field energies) are naturally separated into different matrices. This work investigates the feasibility of using a hybrid model to predict sound insulation. The hybrid method is applied to three different materials. These models are compared against traditional SEA and infinite plate models

The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables

The temperatures of electrons and ions in the post-shock accretion region of a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass flow rates or for sufficiently weak magnetic fields. At lower mass flow rates or in stronger magnetic fields, efficient cyclotron cooling will cool the electrons faster than the electrons can cool the ions and a two-temperature flow will result. Here we investigate the differences in polarized radiation expected from mCV post-shock accretion columns modeled with one- and two-temperature hydrodynamics. In an mCV model with one accretion region, a magnetic field >~30 MG and a specific mass flow rate of ~0.5 g/cm/cm/s, along with a relatively generic geometric orientation of the system, we find that in the ultraviolet either a single linear polarization pulse per binary orbit or two pulses per binary orbit can be expected, depending on the accretion column hydrodynamic structure (one- or two-temperature) modeled. Under conditions where the physical flow is two-temperature, one pulse per orbit is predicted from a single accretion region where a one-temperature model predicts two pulses. The intensity light curves show similar pulse behavior but there is very little difference between the circular polarization predictions of one- and two-temperature models. Such discrepancies indicate that it is important to model some aspect of two-temperature flow in indirect imaging procedures, like Stokes imaging, especially at the edges of extended accretion regions, were the specific mass flow is low, and especially for ultraviolet data.Comment: Accepted for publication in Astrophysics & Space Scienc