834,872 research outputs found
Letter from X. N. Steeves to Carl Hayden
No full textLetter from X. N. Steeves to Carl T. Hayden describing road conditions around the Grand Canyon National Par
Letter from Carl Hayden to X. N. Steeves
No full textLetter with red pencil corrections from Carl T. Hayden to X. N. Steeves about the construction of an approach road to the canyo
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
Traces and shards of self-injury: Strange accounting with “Author X”
No full textIn this strange account autoethnography, three or four authors explore their lived experiences with self-injury. Strange accounting is both a post-modern style of text, and a method for keeping identities concealed when risks and secrets are in play. Author X, a post-modern place-keeper for an anonymous author who may or may not have contributed to this manuscript, introduces a new dimension and layer of concealment. With Author X in-play and under erasure, the reader will never be sure if there were three or four authors on this manuscript. Through strange accounting, a post-structuralist/postmodernist frame will be applied to understanding the self-injury experience. We frame self-injury as a social practice and, for some, an everyday norm, while remaining acutely aware of the stigma surrounding the topic of self-injury. Each of us, coupled with Author X, provide the others cover to trace stories of self-injury through the literature, our flesh, and our lives
Relations between x-ray timing features and spectral parameters of galactic black hole x-ray binaries
No full textWe present a study of correlations between spectral and timing parameters for a sample of black hole X-ray binary candidates. Data are taken from GX
339-4, H 1743-322, and XTE J1650-500, as the Rossi X-ray Timing Explorer
(RXTE) observed complete outbursts of these sources. In our study we investigate outbursts that happened before the end of 2009 to make use of the high-energy coverage of the HEXTE detector and select observations that
show a certain type of quasi-periodic oscillations (type-C QPOs). The spectral parameters are derived using the empirical convolution model simpl to model the Comptonized component of the emission together with a disc blackbody for the emission of the accretion disc. Additional spectral features, namely a reflection component, a high-energy cut-off, and excess emission at 6.4 keV, are taken into account. Our investigations confirm the known positive
correlation between photon index and centroid frequency of the QPOs and reveal an anti-correlation between the fraction of up-scattered photons and the QPO frequency. We show that both correlations behave as expected in the “sombrero”
geometry. Furthermore, we find that during outburst decay the correlation between photon index and QPO frequency follow a general track, independent of individual outbursts
Giant negative thermal expansion in ultrafine-grained Mn-3(Cu1-xGex)N (x=0.5) bulk
No full textThe advanced negative thermal expansion (NTE) properties of the ultrafine-grained Mn-3(Cu1-xGex)N compound bulk have been reported. The developed preparation route has reduced the fabrication time by more than ten times in contrast to previous studies. As compared with the coarse-grained compound bulk, the NTE start temperature of the ultrafine Mn-3(Cu1-xGex)N (x = 0.5) bulk is reduced to 250 K, and the coefficient of negative thermal expansion (CNTE) reaches -23.7 x 10(-6) K-1, which is remarkably improved. It is found that the nitrogen content in the starting manganese nitride also has significant effects on the NTE start temperature, operating temperature range and CNTE
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
No full textThe existence of black holes of masses similar to 10(2)-10(5)M(circle dot) has important implications for the formation and evolution of star clusters and supermassive black holes. One of the strongest candidates to date is the hyperluminous X-ray source (HLX1), possibly located in the S0- a galaxy ESO 243-49, but the lack of an identifiable optical counterpart had hampered its interpretation. Using the Magellan telescope, we have discovered an unresolved optical source with R = 23.80 +/- 0.25 mag and V = 24.5 +/- 0.3 mag within HLX1's positional error circle. This implies an average X-ray/optical flux ratio similar to 500. Taking the same distance as ESO 243-49, we obtain an intrinsic brightness M-R = -11.0 +/- 0.3 mag, comparable to that of a massive globular cluster. Alternatively, the optical source is consistent with a main-sequence M star in the Galactic halo (for example an M4.4 star at approximate to 2.5 kpc). We also examined the properties of ESO 243-49 by combining Swift/Ultraviolet/Optical Telescope (UVOT) observations with stellar population modelling. We found that the overall emission is dominated by a similar to 5-Gyr-old stellar population, but the UV emission at approximate to 2000 angstrom is mostly due to ongoing star formation at a rate of similar to 0.03M(circle dot) yr(-1). The UV emission is more intense (at least a 9 sigma enhancement above the mean) north-east of the nucleus, in the same quadrant as HLX1. With the combined optical and X-ray measurements, we put constraints on the nature of HLX1. We rule out a foreground star and a background AGN. Two alternative scenarios are still viable. HLX1 could be an accreting intermediate mass black hole in a star cluster, which may itself be the stripped nucleus of a dwarf galaxy that passed through ESO 243-49, an event which might have caused the current episode of star formation. Or, it could be a neutron star in the Galactic halo, accreting from an M4-M5 donor star
High pressure solid state chemistry of C-N-H and Ti-N systems
No full textThis thesis presents the use of molecular precursors for the synthesis of
solid-state materials through the application of extreme conditions. The main
tool for the exploration of these materials was the diamond anvil cell which
generated static pressures of up to 85 GPa. Combined with the use of highpower
lasers, it provides a powerful and efficient technique for high-pressurehigh-
temperature synthesis of solid-state materials. The work presented here is
an investigation into the synthesis and recovery of new materials within two
solid-state systems, C-N-H and Ti-N-O. Crystallographic analysis of these
systems is a challenging process, made more difficult by their relatively light
elemental composition and the use of the diamond anvil cell. In both cases a
systematic experimental and analytical strategy was adopted to enable the
extraction of the best data possible, both qualitatively and statistically.
Two C-N-H systems were investigated: C2N3H and C6N9H3.HCl.
Synchrotron X-ray diffraction and Raman scattering data are reported for the
new dense tetrahedrally bonded phase C2N3H with a defective wurtzite structure.
This is synthesised by laser heating from an organic precursor, dicyandiamide,
C2N4H4 at high-pressure in a diamond anvil cell. This work confirms the
structure deduced in previous work from electron diffraction experiments on
samples recovered to ambient conditions.
The graphitic layered compound C6N9H3.HCl was subjected to pressures
up to 70 GPa in a diamond anvil cell and its structural behaviour was examined
using synchrotron X-ray diffraction. The use of laser heating experiments
revealed the synthesis of a new carbon nitride phase which is recoverable to
ambient conditions.
The second group of systems explored was those based on Ti-O-N.
Amorphous or nano-crystalline precursors were used to attempt the synthesis of
Ti3N4. The high-pressure and temperature behaviour of these materials was
examined using synchrotron X-ray diffraction and Raman spectroscopy, in a
laser-heated diamond anvil cell.
In addition, the high-pressure studies of Ti2.85O4N, a recently discovered
titanium oxynitride phase, are reported here up to 70 GPa. Using synchrotron
angle dispersive techniques two high-pressure phases are observed and an
attempt to elucidate these structures are reported
On the maximal rate of (n+1) x n and (n+2) x n complex orthogonal designs
No full textFor p x n complex orthogonal designs in k variables, where p is the number of channels uses and n is the number of transmit antennas, the maximal rate L of the design is asymptotically half as n increases. But, for such maximal rate codes, the decoding delay p increases exponentially. To control the delay, if we put the restriction that p = n, i.e., consider only the square designs, then, the rate decreases exponentially as n increases. This necessitates the study of the maximal rate of the designs with restrictions of the form p = n+1, p = n+2, p = n+3 etc. In this paper, we study the maximal rate of complex orthogonal designs with the restrictions p = n+1 and p = n+2. We derive upper and lower bounds for the maximal rate for p = n+1 and p = n+2. Also for the case of p = n+1, we show that if the orthogonal design admit only the variables, their negatives and multiples of these by root-1 and zeros as the entries of the matrix (other complex linear combinations are not allowed), then the maximal rate always equals the lower bound
Experimental investigation into the effect of substrate clamping on the piezoelectric behaviour of thick-film PZT elements
No full textThis paper details an experimental investigation of the clamping effect associated with thick-film piezoelectric elements printed on a substrate. The clamping effect reduces the measured piezoelectric coefficient, d33, of the film. This reduction is due to the influence of the d31 component in the film when a deformation of the structure occurs, by either the direct or indirect piezoelectric effect. Theoretical analysis shows a reduction in the measured d33 of 62%, i.e. a standard bulk lead zirconate titanate (PZT)-5H sample with a manufacturer specified d33 of 593pC/N would fall to 227.8pC/N. To confirm this effect, the d33 coefficients of five thin bulk PZT-5H samples of 220µm thickness were measured before and after their attachment to a metallized 96% alumina substrate. The experimental results show a reduction in d33 of 74% from 529pC/N to 139pC/N. The theoretical analysis was then applied to existing University of Southampton thick-film devices. It is estimated that the measured d33 value of 131pC/N of the thick-film devices is the equivalent of an unconstrained d33 of 345pC/N
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