156 research outputs found
Molecular Functionalization of Carbon Nanotubes and Use as Substrates for Neuronal Growth
A cell and substrate system and nerve regeneration implant are disclosed including a carbon nanotube and a neuron growing on the carbon nanotube. Both unfunctionalized carbon nanotubes and carbon nanotubes functionalized with a neuronal growth promoting agent may be utilized in the invention. A method is also disclosed for promoting neuronal growth
First observations of the X-ray transient EXO 2030+375 with IBIS/ISGRI
We present a first INTEGRAL observation of the 42s transient X-ray pulsar EXO
2030+375 with IBIS/ISGRI. The source was detected during Cyg X-1 observations
in December 2002. We analyzed observations during the outburst period from 9 to
21 December 2002 with a total exposure time of ~770 kiloseconds. EXO 2030+375
was almost always detected during single ~30 minute exposures in the 18-45
energy bands. The source light curve shows the characteristic outburst shape
observed in this source.Comment: 4 pages, 3 figures (1 in CMYK color), accepted by Astronomy and
Astrophysics, INTEGRAL special issue, 200
Serum butyrylcholinesterase in type 2 diabetes mellitus: a biochemical and bioinformatics approach
BACKGROUND: Butyrylcholinesterase is an enzyme that may serve as a marker of metabolic syndrome. We (a) measured its level in persons with diabetes mellitus, (b) constructed a family tree of the enzyme using nucleotide sequences downloaded from NCBI. Butyrylcholinesterase was estimated colorimetrically using a commercially available kit (Randox Lab, UK). Phylogenetic trees were constructed by distance method (Fitch and Margoliash method) and by maximum parsimony method. RESULTS: There was a negative correlation between serum total cholesterol and butyrylcholinesterase (-0.407; p < 0.05) and between serum LDL cholesterol and butyrylcholinesterase (-0.435; p < 0.05). There was no statistically significant correlation among the other biochemical parameters. In the evolutionary tree construction both methods gave similar trees, except for an inversion in the position of Sus scrofa (M62778) and Oryctolagus cuniculus (M62779) between Fitch and Margoliash, and maximum parsimony methods. CONCLUSION: The level of butyrylcholinesterase enzyme was inversely related to serum cholesterol; dendrogram showed that the structures from evolutionarily close species were placed near each other
Estimating Be Star Disk Radii using H-alpha Emission Equivalent Widths
We present numerical models of the circumstellar disks of Be stars, and we
describe the resulting synthetic H-alpha emission lines and maps of the
wavelength-integrated emission flux projected onto the sky. We demonstrate that
there are monotonic relationships between the emission line equivalent width
and the ratio of the angular half-width at half maximum of the projected disk
major axis to the radius of the star. These relationships depend mainly upon
the temperatures of the disk and star, the inclination of the disk normal to
the line of sight, and the adopted outer boundary for the disk radius. We show
that the predicted H-alpha disk radii are consistent with those observed
directly through long baseline interferometry of nearby Be stars (especially
once allowance is made for disk truncation in binaries and for dilution of the
observed H-alpha equivalent width by continuum disk flux in the V-band).Comment: 12 pages, 2 figures, ApJL in pres
4U2206+54 - an Unusual High Mass X-ray Binary with a 9.6 Day Orbital Period but No Strong Pulsations
Rossi X-ray Timing Explorer All-Sky Monitor observations of the X-ray source
4U2206+54, previously proposed to be a Be star system, show the X-ray flux to
be modulated with a period of approximately 9.6 days. If the modulation is due
to orbital variability then this would be one of the shortest orbital periods
known for a Be star X-ray source. However, the X-ray luminosity is relatively
modest whereas a high luminosity would be predicted if the system contains a
neutron star accreting from the denser inner regions of a Be star envelope.
Although a 392s pulse period was previously reported from EXOSAT observations,
a reexamination of the EXOSAT light curves does not show this or any other
periodicity. An analysis of archival RXTE Proportional Counter Array
observations also fails to show any X-ray pulsations. We consider possible
models that may explain the properties of this source including a neutron star
with accretion halted at the magnetosphere and an accreting white dwarf.Comment: Accepted for publication in the Astrophysical Journa
Crustal Heating and Quiescent Emission from Transiently Accreting Neutron Stars
Nuclear reactions occurring deep in the crust of a transiently accreting
neutron star efficiently maintain the core at a temperature >5e7 K. When
accretion halts, the envelope relaxes to a thermal equilibrium set by the flux
from the hot core, as if the neutron star were newly born. For the
time-averaged accretion rates typical of low-mass X-ray transients, standard
neutrino cooling is unimportant and the core thermally re-radiates the
deposited heat. The resulting luminosity has the same magnitude as that
observed from several transient neutron stars in quiescence. Confirmation of
this mechanism would strongly constrain rapid neutrino cooling mechanisms for
neutron stars. Thermal emission had previously been dismissed as a predominant
source of quiescent emission since blackbody spectral fits implied an emitting
area much smaller than a neutron star's surface. However, as with thermal
emission from radio pulsars, fits with realistic emergent spectra will imply a
substantially larger emitting area. Other emission mechanisms, such as
accretion or a pulsar shock, can also operate in quiescence and generate
intensity and spectral variations over short timescales. Indeed, quiescent
accretion may produce gravitationally redshifted metal photoionization edges in
the quiescent spectra (detectable with AXAF and XMM). We discuss past
observations of Aql~X-1 and note that the low luminosity X-ray sources in
globular clusters and the Be star/X-ray transients are excellent candidates for
future study.Comment: 5 pages, 2 ps figures, uses AASTEX macros. To appear in ApJ letters,
10 September 1998. Revised to conform with journal; minor numerical
correction
Quasi-periodic flares in EXO 2030+375 observed with INTEGRAL
Context: Episodic flaring activity is a common feature of X-ray pulsars in
HMXBs. In some Be/X-ray binaries flares were observed in quiescence or prior to
outbursts. EXO 2030+375 is a Be/X-ray binary showing "normal" outbursts almost
every ~46 days, near periastron passage of the orbital revolution. Some of
these outbursts were occasionally monitored with the INTEGRAL observatory.
Aims: The INTEGRAL data revealed strong quasi-periodic flaring activity during
the rising part of one of the system's outburst. Such activity has previously
been observed in EXO 2030+375 only once, in 1985 with EXOSAT. (Some indications
of single flares have also been observed with other satellites.) Methods: We
present the analysis of the flaring behavior of the source based on INTEGRAL
data and compare it with the flares observed in EXO 2030+375 in 1985. Results:
Based on the observational properties of the flares, we argue that the
instability at the inner edge of the accretion disk is the most probable cause
of the flaring activity.Comment: Accepted for publication in A&A Lette
Optical pulsations in the cataclysmic binary 3A 0729+103
Fast photometric observations of the newly discovered cataclysmic variable 3A 0729+103 are reported. Regular optical pulsations, with an average semiamplitude of ~0.15 mag in B-band and having a period in agreement with that reported by McHardy et al. (1982) are clearly detected in the light curve of the star. The optical pulse has a sinusoidal shape. Flares with a maximum amplitude of ~0.43 mag have also been observed. There is also suggestion of flickering on time scales of ≧10s. It is suggested that 3A 0729+103 is similar in characteristics to H 2252-035 class of cataclysmic binaries containing rapidly rotating white dwarfs. Interpretation of the period of optical pulse as the beat period leads to prediction of X-ray pulse period to be about 847s for prograde rotation and 991s for retrograde rotation of the white dwarf compared to the reported ~900-1000s period. Alternative interpretation of the observed optical pulse being due to directly beamed radiation from the vicinity of the pole of the white dwarf is also considered
Photometric Observations of Three High Mass X-Ray Binaries and a Search for Variations Induced by Orbital Motion
We searched for long period variation in V-band, Ic-band and RXTE X-ray light
curves of the High Mass X-ray Binaries (HMXBs) LS 1698 / RX J1037.5-5647, HD
110432 / 1H 1249-637 and HD 161103 / RX J1744.7-2713 in an attempt to discover
orbitally induced variation. Data were obtained primarily from the ASAS
database and were supplemented by shorter term observations made with the 24-
and 40-inch ANU telescopes and one of the robotic PROMPT telescopes. Fourier
periodograms suggested the existence of long period variation in the V-band
light curves of all three HMXBs, however folding the data at those periods did
not reveal convincing periodic variation. At this point we cannot rule out the
existence of long term V-band variation for these three sources and hints of
longer term variation may be seen in the higher precision PROMPT data. Long
term V-band observations, on the order of several years, taken at a frequency
of at least once per week and with a precision of 0.01 mag, therefore still
have a chance of revealing long term variation in these three HMXBs.Comment: Accepted, RAA, May, 201
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