391 research outputs found
Time-resolved X-Shooter spectra and RXTE light curves of the ultra-compact X-ray binary candidate 4U 0614+091
In this paper we present X-Shooter time resolved spectroscopy and RXTE PCA
light curves of the ultra-compact X-ray binary candidate 4U 0614+091. The
X-Shooter data are compared to the GMOS data analyzed previously by Nelemans et
al. (2004). We confirm the presence of C III and O II emission features at ~
4650 {\AA} and ~ 5000 {\AA}. The emission lines do not show evident Doppler
shifts that could be attributed to the motion of the donor star/hot spot around
the center of mass of the binary. We note a weak periodic signal in the
red-wing/blue-wing flux ratio of the emission feature at ~ 4650 {\AA}. The
signal occurs at P = 30.23 +/- 0.03 min in the X-Shooter and at P = 30.468 +/-
0.006 min in the GMOS spectra when the source was in the low/hard state. Due to
aliasing effects the period in the GMOS and X-Shooter data could well be the
same. We deem it likely that the orbital period is thus close to 30 min,
however, as several photometric periods have been reported for this source in
the literature already, further confirmation of the 30 min period is warranted.
We compare the surface area of the donor star and the disc of 4U 0614+091 with
the surface area of the donor star and the disc in typical hydrogen-rich
low-mass X-ray binaries and the class of AM Canum Venaticorum stars and argue
that the optical emission in 4U 0614+091 is likely dominated by the disc
emission. Additionally, we search for periodic signals in all the publicly
available RXTE PCA light curves of 4U 0614+091 which could be associated with
the orbital period of this source. A modulation at the orbital period with an
amplitude of ~ 10% such as those that have been found in other ultra-compact
X-ray binaries (4U 0513-40, 4U 1820-30) is not present in 4U 0614+091.Comment: Accepted for publication in MNRAS, 11 pages, 7 figure
Atomic Spectral Features During Thermonuclear Flashes on Neutron Stars
The gravitational redshift measured by Cottam, Paerels and Mendez for the
neutron star (NS) in the low-mass X-ray binary EXO 0748-676 depends on the
identification of an absorption line during a type I burst as the H
line from hydrogenic Fe. We show that Fe is present above the photosphere as
long as during the burst. In
this limit, the total Fe column is for incident material of solar abundances and only depends on the
nuclear physics of the proton spallation. The Fe destruction creates many heavy
elements with which may imprint photo-ionization edges on the NS spectra
during a radius expansion event or in a burst cooling tail. Detecting these
features in concert with those from Fe would confirm a redshift measurement. We
also begin to address the radiative transfer problem, and find that a
concentrated Fe layer with and column (depending on the line depth) above the hotter
continuum photosphere is required to create the H line of the observed
strength. This estimate must be refined by considerations of non-LTE effects as
well as resonant line transport. Until these are carried out, we cannot say
whether the Fe column from accretion and spallation is in conflict with the
observations. We also show that hydrogenic Fe might remain in the photosphere
due to radiative levitation from the high burst flux.Comment: Substantially revised version, to appear in Ap J Letter
The characterisation of the microstructure and mechanical properties of diamond - like carbon (DLC) for endoprosthesis
The paper presents the results of research of DLC coating of a - C:H type obtained by using a technique of physical vapor deposition (PVD) on the surface of CoCrMo alloy, commonly used for the elements of the endoprosthesis. The surface has been observed using a scanning electron microscope (SEM). Analysis of the chemical composition and distribution of the different elements were performed using glow discharge optical emission spectrometry analysis (GDOES). It has been shown that the DLC elements are characterized by high hardness and good adhesion to the substrate
The characterisation of pure titanium for biomedical applications
The paper presents results of research on the use of pure titanium medical implants, dental and orthopedics â as pins hip replacements. The properties of metal biomaterials, including their hardness, determine the usefulness of the material and are one of the criteria for its use. They depend on their chemical composition and structure. Studies included the observation of the microstructure and mechanical properties of pure titanium. The observations surface were carried out using a scanning electron microscope SEM. The optical profiler was used to depict the geometric structure of the surface, and to carry out the nanoindentation tests a nano hardness tester was used
The Nature of the Emission Components in the Quasar/NLS1 PG1211+143
We present the study of the emission properties of the quasar PG1211+143,
which belongs to the class of Narrow Line Seyfert 1 galaxies. On the basis of
observational data analyzed by us and collected from the literature, we study
the temporal and spectral variability of the source in the optical/UV/X-ray
bands and we propose a model that explains the spectrum emitted in this broad
energy range. In this model, the intrinsic emission originating in the warm
skin of the accretion disk is responsible for the spectral component that is
dominant in the softest X-ray range. The shape of reflected spectrum as well as
Fe K line detected in hard X-rays require the reflecting medium to be mildly
ionized (xi~500). We identify this reflector with the warm skin of the disk and
we show that the heating of the skin is consistent with the classical alpha
P_{tot} prescription, while alpha P_{gas} option is at least two orders of
magnitude too low to provide the required heating. We find that the mass of the
central black hole is relatively small (M_BH~10^7- 10^8 Msun, which is
consistent with the Broad Line Region mapping results and characteristic for
NLS1 class.Comment: 22 pages, 10 figures, accepted to Ap
Dystrophin deficiency affects human astrocyte properties andresponse to damage
In addition to progressive muscular degeneration due to dystrophin mutations, 1/3 of Duchenne muscular dystrophy (DMD) patients present cognitive deficits. However, there is currently an incomplete understanding about the function of the multiple dystrophin isoforms in human brains. Here, we tested the hypothesis that dystrophin deficiency affects glial function in DMD and could therefore contribute to neural impairment. We investigated human dystrophin isoform expression with development and differentiation and response to damage in human astrocytes from control and induced pluripotent stem cells from DMD patients. In control cells, short dystrophin isoforms were up-regulated with development and their expression levels changed differently upon neuronal and astrocytic differentiation, as well as in 2-dimensional versus 3-dimensional astrocyte cultures. All DMD-astrocytes tested displayed altered morphology, proliferative activity and AQP4 expression. Furthermore, they did not show any morphological change in response to inflammatory stimuli and their number was significantly lower as compared to stimulated healthy astrocytes. Finally, DMD-astrocytes appeared to be more sensitive than controls to oxidative damage as shown by their increased cell death. Behavioral and metabolic defects in DMD-astrocytes were consistent with gene pathway dysregulation shared by lines with different mutations as demonstrated by bulk RNA-seq analysis. Together, our DMD model provides evidence for altered astrocyte function in DMD suggesting that defective astrocyte responses may contribute to neural impairment and might provide additional potential therapeutic targets
Lifetime measurement of the metastable 3d 2D5/2 state in the 40Ca+ ion using the shelving technique on a few-ion string
We present a measurement of the lifetime of the metastable 3d 2D5/2 state in
the 40Ca+ ion, using the so-called shelving technique on a string of five
Doppler laser-cooled ions in a linear Paul trap. A detailed account of the data
analysis is given, and systematic effects due to unwanted excitation processes
and collisions with background gas atoms are discussed and estimated. From a
total of 6805 shelving events, we obtain a lifetime
tau=1149+/-14(stat.)+/-4(sys.)ms, a result which is in agreement with the most
recent measurements.Comment: 10 pages, 7 figures. Submitted for publicatio
An optimized TOPS+ comparison method for enhanced TOPS models
This article has been made available through the Brunel Open Access Publishing Fund.Background
Although methods based on highly abstract descriptions of protein structures, such as VAST and TOPS, can perform very fast protein structure comparison, the results can lack a high degree of biological significance. Previously we have discussed the basic mechanisms of our novel method for structure comparison based on our TOPS+ model (Topological descriptions of Protein Structures Enhanced with Ligand Information). In this paper we show how these results can be significantly improved using parameter optimization, and we call the resulting optimised TOPS+ method as advanced TOPS+ comparison method i.e. advTOPS+.
Results
We have developed a TOPS+ string model as an improvement to the TOPS [1-3] graph model by considering loops as secondary structure elements (SSEs) in addition to helices and strands, representing ligands as first class objects, and describing interactions between SSEs, and SSEs and ligands, by incoming and outgoing arcs, annotating SSEs with the interaction direction and type. Benchmarking results of an all-against-all pairwise comparison using a large dataset of 2,620 non-redundant structures from the PDB40 dataset [4] demonstrate the biological significance, in terms of SCOP classification at the superfamily level, of our TOPS+ comparison method.
Conclusions
Our advanced TOPS+ comparison shows better performance on the PDB40 dataset [4] compared to our basic TOPS+ method, giving 90 percent accuracy for SCOP alpha+beta; a 6 percent increase in accuracy compared to the TOPS and basic TOPS+ methods. It also outperforms the TOPS, basic TOPS+ and SSAP comparison methods on the Chew-Kedem dataset [5], achieving 98 percent accuracy. Software Availability: The TOPS+ comparison server is available at http://balabio.dcs.gla.ac.uk/mallika/WebTOPS/.This article is available through the Brunel Open Access Publishing Fun
Sub-dekahertz ultraviolet spectroscopy of 199Hg+
Using a laser that is frequency-locked to a Fabry-Perot etalon of high
finesse and stability, we probe the 5d10 6s 2S_1/2 (F=0) - 5d9 6s 2D_5/2 (F=2)
Delta-m_F = 0 electric-quadrupole transition of a single laser-cooled 199Hg+
ion stored in a cryogenic radio-frequency ion trap. We observe
Fourier-transform limited linewidths as narrow as 6.7 Hz at 282 nm (1.06 X
10^15 Hz), yielding a line Q = 1.6 X 10^14. We perform a preliminary
measurement of the 5d9 6s2 2D_5/2 electric-quadrupole shift due to interaction
with the static fields of the trap, and discuss the implications for future
trapped-ion optical frequency standards.Comment: 4 pages, 4 figures, submitted for publicatio
A Remarkable Three Hour Thermonuclear Burst From 4U 1820-30
We present a detailed observational and theoretical study of a ~3 hr long
X-ray burst (the ``super burst'') observed by the Rossi X-ray Timing Explorer
(RXTE) from the low mass X-ray binary (LMXB) 4U 1820-30. This is the longest
X-ray burst ever observed from this source, and perhaps one of the longest ever
observed in great detail from any source. We show that the super burst is
thermonuclear in origin. The level of the accretion driven flux as well as the
total energy release of ~1.5 x 10^{42} ergs indicate that helium could not be
the energy source for the super burst. We outline the physics relevant to
carbon production and burning on helium accreting neutron stars and present
calculations of the thermal evolution and stability of a carbon layer and show
that this process is the most likely explanation for the super burst. We show
that for large columns of accreted carbon fuel, a substantial fraction of the
energy released in the carbon burning layer is radiated away as neutrinos, and
the heat that is conducted from the burning layer in large part flows inward,
only to be released on timescales longer than the observed burst. Thus the
energy released possibly exceeds that observed in X-rays by more than a factor
of ten. Spectral analysis during the super burst reveals the presence of a
broad emission line between 5.8 - 6.4 keV and an edge at 8 - 9 keV likely due
to reflection of the burst flux from the inner accretion disk in 4U 1820-30. We
believe this is the first time such a signature has been unambiguously detected
in the spectrum of an X-ray burst.Comment: AASTEX, 44 pages, 14 figures. Accepted for publication in the
Astrophysical Journa
- âŠ