4,758 research outputs found
A contribution to the jet noise installation problem
No full textThe main objective of this thesis is to understand and predict jet noise installation effects for engines mounted below aircraft wings. This is done through a variety of empirical, analytical and computational methods. Aspects of the jet source are examined and a jet source model, suitable for determining installation effects is derived. As part of this research programme a novel and extensive set of model scale jet noise installation effects experiments were undertaken. These results are presented and analyzed in this thesis. A new semi-empirical method, which can readily predict installation effects for heated coaxial jets is presented and validated using experimental data. A new 3D ray theory jet propagation method for sources in a steady inhomogeneous moving medium is presented. This method is benched marked using an analytical solution of the Lilley equation. The 3-D method is further enhanced by combing it with realistic CFD jet velocity profiles, and bench marked using the data from the experimental programm
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
No full textXMM–Newton observations of the supergiant fast X-ray transient IGR J17544?2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272?±?0.0004?d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM–Newton observations (each lasting ?15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544?2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033?erg?s?1 (0.5–10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544?2619 dropped to ?4?×?1032?erg?s?1 (0.5–10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544?2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544?2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the ‘quasi-spherical accretion’ model provides a good description of the behaviour of IGR J17544?2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model
X-ray polarization in relativistic jets
No full textWe investigate the polarization properties of Comptonized X-rays from relativistic jets in active galactic nuclei (AGN) using Monte Carlo simulations. We consider three scenarios commonly proposed for the observed X-ray emission in AGN: Compton scattering of blackbody photons emitted from an accretion disc; scattering of cosmic microwave background (CMB) photons and self-Comptonization of intrinsically polarized synchrotron photons emitted by jet electrons. Our simulations show that for Comptonization of disc and CMB photons, the degree of polarization of the scattered photons increases with the viewing inclination angle with respect to the jet axis. In both cases, the maximum linear polarization is ≈20 per cent. In the case of synchrotron self-Comptonization (SSC), we find that the resulting X-ray polarization depends strongly on the seed synchrotron photon injection site, with typical fractional polarizations P≈ 10–20 per cent when synchrotron emission is localized near the jet base, while P≈ 20–70 per cent for the case of uniform emission throughout the jet. These results indicate that X-ray polarimetry may be capable of providing unique clues to identify the location of particle acceleration sites in relativistic jets. In particular, if synchrotron photons are emitted quasi-uniformly throughout a jet, then the observed degree of X-ray polarization may be sufficiently different for each of the competing X-ray emission mechanisms (synchrotron, SSC or external Comptonization) to determine which is the dominant process. However, X-ray polarimetry alone is unlikely to be able to distinguish between disc and CMB Comptonization
Active X-ray optics for the next generation of X-ray space telescopes
No full textDescribed within is the design, manufacture, metrology and X-ray testing of an active X-ray
prototype intended for the next generation of X-ray telescopes. One of the challenges faced by
the X-ray telescope community is how to combine high resolution and high sensitivity into one
system, as weight limitations place constraints on the optics that can be launched. Therefore the
mandate of the active X-ray prototype is to provide high sensitivity through the ability of the optics
to be nested and to deliver high angular resolution through the active control of the optic’s form.
Piezoelectric unimorph actuators provide the active component: it is intended that they will correct
for figure errors within the optic and therefore increase the angular resolution capability.
The prototype’s design is based upon an ellipsoidal segment which provides point-to-point
focussing of an X-ray source. The prototype itself is composed of an electroformed nickel optic
where the non-reflective surface is populated with 30 piezoelectric actuators and it is the production
of the prototype that is the core of the presented research. Metrology of the actuators’ influence
functions is presented and highlight the prototype’s ability to deform its optic surface by microns.
In addition, the measured influence functions are compared against finite element models and a
distinct similarity between the functions is observed.
The prototype was tested at an X-ray beamline facility in November 2008 and the results
showed the prototype’s ability to correct the optic to achieve an improved angular resolution: from
0.786 arc-minutes to 0.686 arc-minutes in terms of full width half maximum. Finally, difficulties
in the manufacture of the prototype and X-ray testing shall be presented alongside future work in
conclusion to this thesis
Ray P. Holland to Horace Kephart, December 31, 1928
No full textIn a letter to Horace Kephart on December 21, 1928, Ray P. Holland, Editor of “Field & Stream” writes to tell Kephart that his article “Afoot and Awing in the Great Smokies” was chosen as one of the ten best stories of the month by a committee of judges of the Franklin Square Agency.RAY P. HOLLAND
EDITOR
ELTINGE F. WARNER
PUBLISHER
578 Madison Avenue
at fifty-seventh street
New York City
Field & Stream's
CONSERVATION
COUNCIL
D. R. ANTHONY, JR.
Congressman; joint Introducer of the Game Refuge Bill.
HORACE M.ALBRIGHT
Superintendent of Yellowstone National Park.
BROOKE ANDERSON
Member of the Federal
Advisory Board of the
Migratory Bird Treaty
Act.
J. B. HARKIN
Commissioner of the
Canadian National Parks.
GEORGE A. LAWYER
Former Chief United
States Game Warden.
WM. B. MERSHON
Sportsman — Author —
Conservationist.
E. W. NELSON
Ex-Chief of the U. S.
Biological Survey.
HARRY S. NEW
U. S. Postmaster General;
joint Introducer of the
Game Refuge Bill in the
United States. Senate.
T. GILBERT PEARSON
President of the National
Association of Audubon
Societies.
THEO. ROOSEVELT
First Executive Chairman
of the National Conference on Outdoor Recreation.
December 31, 1928
Mr. Horace Kephart,
Bryson City, N. C.
Dear Mr. Kephart:
I thought you would be interested
in knowing that your story "Afoot and Awing in
the Great Smokies", published in the January
issue, was chosen by a committee of judges of
the Franklin Square Agency, which is owned by
Harper Brothers, as one of the ten best stories
of the month.
With the best of the holiday greetings,
I am
Sincerely yours,
RPHsFTC
Edito
High frequency jet noise installation for an under wing mounted aircraft
No full textThis paper presents a generic 3-dimensional ray-theory based model to predict installation effects on a
distributed jet source for aircraft with under-wing mounted engines. The model extends previous work by
improving the hot jet blockage model from a 2-dimensional empirical model to a fully 3-dimensional semiempirical
model. This new model is based on static rig test experiments described in this paper. Further
improvements are made including variable directivity of the jet source (rather than an omni-directional assumption)
which is important in predicting the correct reflection strengths for sources downstream from the
nozzle. The directivity is determined both from analytic models and empirically using recently acquired data.
The completed enhanced model is then validated using data acquired from a comprehensive novel set of installation
tests carried out at QinetiQ’s Noise Test Facility
The nature of the X-ray transient MAXI J0556−332
No full textPhase-resolved spectroscopy of the newly discovered X-ray transient MAXIJ0556-332 has revealed the presence of narrow emission lines in the Bowen region that most likely arise on the surface of the mass donor star in this low-mass X-ray binary. A period search of the radial velocities of these lines provides two candidate orbital periods (16.43 ± 0.12 and 9.754 ± 0.048h), which differ from any potential X-ray periods reported. Assuming that MAXIJ0556-332 is a relatively high-inclination system that harbours a precessing accretion disc in order to explain its X-ray properties, it is only possible to obtain a consistent set of system parameters for the longer period. These assumptions imply a mass ratio of q≃ 0.45, a radial velocity semi-amplitude of the secondary of K 2≃ 190kms -1 and a compact object mass of the order of the canonical neutron star mass, making a black hole nature for MAXIJ0556-332 unlikely. We also report the presence of strong Niii emission lines in the spectrum, thereby inferring a high N/O abundance. Finally, we note that the strength of all emission lines shows a continuing decay over the ≃1 month of our observations
On the binary nature of the γ-ray sources AGL J2241+4454 (= MWC 656) and HESS J0632+057 (= MWC 148)
No full textWe present optical spectroscopy of MWC 656 and MWC 148, the proposed optical counterparts of the gamma-ray sources AGL J2241+4454 and HESS J0632+0 57, respectively. The main parameters of the Halpha emission line (EW, FWHM and centroid velocity) in these stars are modulated on the proposed orbital periods of 60.37 and 321 days, respectively. These modulations are likely produced by the resonant interaction of the Be discs with compact stars in eccentric orbits. We also present radial velocity curves of the optical stars folded on the above periods and obtain the first orbital elements of the two gamma-ray sources thus confirming their binary nature. Our orbital solution support eccentricities e~0.4 and 0.83+-0.08 for MWC 656 and MWC 148, respectively. Further, our orbital elements imply that the X-ray outbursts in HESS J0632+057/MWC 148 are delayed ~0.3 orbital phases after periastron passage, similarly to the case of LS I +61 303. In addition, the optical photometric light curve maxima in AGL J2241+4454/MWC 656 occur ~0.25 phases passed periastron, similar to what is seen in LS I +61 303. We also find that the orbital eccentricity is correlated with orbital period for the known gamma-ray binaries. This is explained by the fact that small stellar separations are required for the efficient triggering of VHE radiation. Another correlation between the EW of Halpha and orbital period is also observed, similarly to the case of Be/X-ray binaries. These correlations are useful to provide estimates of the key orbital parameters Porb and e from the Halpha line in future Be gamma-ray binary candidates
Mapping of mechanical, thermomechanical and wire-bond strain fields in packaged Si integrated circuits using synchrotron white beam x-ray topography
No full textThermal processing steps used during the production of packaged integrated circuits can lead to severe thermomechanical stresses. In addition, the process of bonding wires to contact pads can also lead to strain field generation. A feasibility study using the application of white beam synchrotron x-ray topography to packaged erasable programmable read-only memory (EPROM) Si integrated circuits (ICs) has been undertaken in order to produce maps of the strain fields induced by such processing steps. This technique provides depth-resolved mapping with spatial resolutions currently in the region of 5-10 μm throughout the entire mapping volume. Furthermore, the use of different experimental geometries allows the user to nondestructively probe the strain fields present at the wafer surface right through to the back side
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