379 research outputs found
Identifying a black hole X-ray transient in M31 with XMM-Newton and Chandra
Stochastic variability in two out of four XMM-Newton observations of XMMU
J004303+4115 along with its power spectra and X-ray luminosities suggest a
low-mass X-ray binary (LMXB) with a black hole primary. However, Chandra
observations resolve the object into two point sources. We use data from 35
Chandra observations to analyse the contributions of each source, and attribute
the variability to CXOM31 J004303.2+411528 (known as r2-3), which varies in
intensity by a factor of ~100 between observations. We assume that the power
density spectra of LMXBs are governed by the luminosity, and that the
transition between types of power density spectra occurs at some critical
luminosity in Eddington units, l_c, that applies to all LMXBs. We use results
from these XMM-Newton observations and past results from the available
literature to estimate this transition luminosity, and find that all results
are consistent with l_c ~0.1 in the 0.3--10 keV band. CXOM31 J004303.2+411528
exhibits a low accretion rate power density spectrum at a 0.3--10 keV
luminosity of (5.3+/-0.6)x10^{37} erg/s. Known stellar mass black holes have
masses of 4--15 M_{\odot}; hence our observations of CXOM31 J004303.2+411528
are consistent with l_c ~0.1 if it has a black hole primary.Comment: Accepted for publication in A&A; 9 pages, 4 figure
Opinion
Organ transplantation has evoked such mixed and even violent reaction that it would seem worthwhile to explore the ethics governing it — and to do this by examining the three major areas of contention: the act itself, the recipient and the donor.IS TRANSPLANTATION ETHICAL?News coverage of transplantation in the popular mass media has been widespread, enthusiastic and, unfortunately, too often sensational and misleading. I t has been misconceived in certain sections of the public both as a panacea and as an unethical and unjustified form of treatment. Neither assertion is accurate.Within our currently limited understanding of immunological attack on an allograft and our inability to prevent such an onslaught, the transplantation of any organ must be accepted as palliative therapy — not a final cure. It achieves palliation which equals, if it does not surpass, some forms of palliation which have been accepted for many years as the only way to deal with malignant diseases. This being established, one cannot accept as unjustifiable or unethical the palliation of symptoms and extension of life itself
Cathodoluminescence-based nanoscopic thermometry in a lanthanide-doped phosphor
Crucial to analyze phenomena as varied as plasmonic hot spots and the spread
of cancer in living tissue, nanoscale thermometry is challenging: probes are
usually larger than the sample under study, and contact techniques may alter
the sample temperature itself. Many photostable nanomaterials whose
luminescence is temperature-dependent, such as lanthanide-doped phosphors, have
been shown to be good non-contact thermometric sensors when optically excited.
Using such nanomaterials, in this work we accomplished the key milestone of
enabling far-field thermometry with a spatial resolution that is not
diffraction-limited at readout.
We explore thermal effects on the cathodoluminescence of lanthanide-doped
NaYF nanoparticles. Whereas cathodoluminescence from such lanthanide-doped
nanomaterials has been previously observed, here we use quantitative features
of such emission for the first time towards an application beyond localization.
We demonstrate a thermometry scheme that is based on cathodoluminescence
lifetime changes as a function of temperature that achieves 30 mK
sensitivity in sub-m nanoparticle patches. The scheme is robust against
spurious effects related to electron beam radiation damage and optical
alignment fluctuations.
We foresee the potential of single nanoparticles, of sheets of nanoparticles,
and also of thin films of lanthanide-doped NaYF to yield temperature
information via cathodoluminescence changes when in the vicinity of a sample of
interest; the phosphor may even protect the sample from direct contact to
damaging electron beam radiation. Cathodoluminescence-based thermometry is thus
a valuable novel tool towards temperature monitoring at the nanoscale, with
broad applications including heat dissipation in miniaturized electronics and
biological diagnostics.Comment: Main text: 30 pages + 4 figures; supplementary information: 22 pages
+ 8 figure
Insight into the Machinery and Applications for Understanding the Pathogen- Vector Interface
The availability of genome sequencing data in combination with knowledge of
expressed genes via transcriptome and proteome data has greatly advanced our
understanding of arthropod vectors of disease. Not only have we gained insight
into vector biology, but also into their respective vector-pathogen
interactions. By combining the strengths of postgenomic databases and reverse
genetic approaches such as RNAi, the numbers of available drug and vaccine
targets, as well as number of transgenes for subsequent transgenic or
paratransgenic approaches, have expanded. These are now paving the way for in-
field control strategies of vectors and their pathogens. Basic scientific
questions, such as understanding the basic components of the vector RNAi
machinery, is vital, as this allows for the transfer of basic RNAi machinery
components into RNAi-deficient vectors, thereby expanding the genetic toolbox
of these RNAi-deficient vectors and pathogens. In this review, we focus on the
current knowledge of arthropod vector RNAi machinery and the impact of RNAi on
understanding vector biology and vector-pathogen interactions for which vector
genomic data is available on VectorBase
Physical changes during Z-track movement in Sco X-1 on the flaring branch
We present results of a detailed study of X-ray flaring in the Z-track source
Sco X-1 in a highly super-Eddington state made using high quality Rossi-XTE
data from the PCA and HEXTE instruments. The emission model successfully used
to explain the dipping LMXB, and other classes of LMXB in recent years, was
applied to study the physical evolution along the Z-track which remains a major
problem. This model consists of blackbody emission from the neutron star plus
Comptonized emission from an extended accretion disk corona. As found in
earlier work, major changes take place in the neutron star blackbody emission
with kT increasing in flaring, and the blackbody radius R_BB increasing
substantially to a maximum value of 9.4 +/- 0.6 km, consistent with the radius
of the neutron star, after which R_BB decreases. Thus this result is a
measurement of neutron star radius. The behaviour of Sco X-1 in flaring is
compared with our previous results for the strong flaring that takes place in
the bright dipping, flaring LMXB X 1624-490. Remarkably, during movement along
the Normal Branch towards the apex with the Flaring Branch, the luminosities of
both spectral components decrease, suggesting the possibility that Mdot may
decrease on the Normal Branch, contrary to the widely-held view that Mdot
increases monotonically along the Z-track. During flaring, we detect for the
first time an increase of the Comptonization cut-off energy which may suggest
heating of the ADC plasma by the neutron star flare. The energy of a broad
Gaussian line at 6.4 keV does not change, but the intensity of the line
increases in flaring suggesting either an increase in ADC size in flaring or
the effects of irradiation by the neutron star.Comment: 12 pages including 8 figures, Astronomy and Astrophysics in press;
reference list correcte
Spectral analysis of LMC X-2 with XMM/Newton: unveiling the emission process in the extragalactic Z-source
We present the results of the analysis of an archival observation of LMC X-2
performed with XMM/Newton. The spectra taken by high-precision instruments have
never been analyzed before. We find an X-ray position for the source that is
inconsistent with the one obtained by ROSAT, but in agreement with the Einstein
position and that of the optical counterpart. The correlated spectral and
timing behaviour of the source suggests that the source is probably in the
normal branch of its X-ray color-color diagram. The spectrum of the source can
be fitted with a blackbody with a temperature 1.5 keV plus a disk blackbody at
0.8 keV. Photoelectric absorption from neutral matter has an equivalent
hydrogen column of 4 x 10^{20} cm^{-2}. An emission line, which we identify as
the O VIII Lyman alpha line, is detected, while no feature due to iron is
detected in the spectrum. We argue that the emission of this source can be
straightforwardly interpreted as a sum of the emission from a boundary layer
between the NS and the disc and a blackbody component coming from the disc
itself. Other canonical models that are used to fit Z-sources do not give a
satisfactory fit to the data. The detection of the O VIII emission line (and
the lack of detection of lines in the iron region) can be due to the fact that
the source lies in the Large Magellanic Cloud.Comment: Accepted for publication by Astronomy & Astrophysic
Investigations of a Gandharan stucco head of the Buddha at the Victoria and Albert Museum (IM.3-1931)
This study presents the results of a technical and art historical study of an important Gandharan head from the Victoria and Albert Museum. For several years, the head has played an important role in the history of Gandharan art, because of its high aesthetic qualities. However, the head has received limited scholarly attention since its first display in the 1930s. This study reviewed the head’s physical, curatorial and conservation history and determined its construction using non-invasive and non-contact investigative techniques (technical imaging, FTIR, XRF and FORS). The support consists of several layers of a lime- and gypsum-based plaster (gauging plaster) and only salient elements of the face (e.g. lips, eyes and hairline) and the hair were painted, with a high-quality red ochre and with an unidentified black pigment, respectively. A careful examination of the construction of the head allowed to determine that it probably belonged to an iconic representation of the Buddha, as opposed to a narrative scene
Local sensing of absolute refractive index during protein-binding using microlasers with spectral encoding
Funding: Engineering and Physical Sciences Research Council - EP/P030017/1; Alexander von Humboldt-Stiftung; European Research Council - 640012; Royal Society - DH160102.Multiplexed, specific, and sensitive detection of antigens is critical for the rapid and accurate diagnosis of disease and the informed development of personalized treatment plans. Here, it is shown that polymer microsphere lasers can be used as photonic sensors to monitor and quantify direct surface binding of biomolecules via changes in the refractive index. The unique spectral signature of each individual laser can be used to find their size and effective refractive index which adds a new encoding dimension when compared to conventional fluorescent beads. Antibody-functionalized microlasers selectively detect protein binding, as demonstrated for Immunoglobulin G and C-reactive protein, and have the ability to resolve different stages of the multilayer surface modification. Moreover, by continuously monitoring single lasers, the possibility of real-time monitoring of binding dynamics between antigens in solution phase and the immobilized antibodies is demonstrated. For multiplexed detection, the microlasers are employed in a flow cytometer configuration, with fast spectral detection and identification of microlasers with and without antigen binding. It is envisioned that by combining microlasers with well-established surface modification chemistries and flow geometries, the multiplexing ability of microbead immunoassays can be strongly increased while also opening avenues for single-cell profiling within heterogeneous cell populations.Publisher PDFPeer reviewe
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