2,387 research outputs found
J08069+1527: A newly discovered high amplitude, hybrid subdwarf B pulsator
We present our discovery of a new hybrid pulsating subdwarf B star,
J08069+1527. The effective temperature and surface gravity of 28,500400\,K
and 5.370.04\,dex, respectively, place this object inside the instability
strip and also among other pulsating hot subdwarfs of a hybrid nature, right
next to another fascinating star: Balloon\,090100001. From this proximity, we
anticipated this star could pulsate in both high and low frequency modes.
Indeed, our analysis of photometric data confirmed our prediction. We detected
two peaks in the high frequency region and two other peaks at low frequencies.
In addition, the amplitude of the dominant mode is very high and comparable to
the dominant peaks in other hybrid subdwarf B stars. Since this star is bright,
we performed time-series low resolution spectroscopy. Despite a low
signal-to-noise (S/N) ratio, we were able to detect the main peak from these
data. All our results strongly indicate that J08069+1527 is a high amplitude
pulsating hot subdwarf B star of hybrid nature. By analogy to the other
pulsating sdB star, we judge that the dominant mode we detected here has radial
nature. Future stellar modeling should provide us with quite good constrains as
p- and g-modes presented in this star are driven in different parts of its
interior.Comment: 7 pages, 10 figures, accepted for publication in MNRA
On the mechanical behaviour of a butt jointed thermoplastic composite under bending
In the present work, the mechanical behavior of a recently developed novel butt jointed thermoplastic composite was investigated under bending conditions. The laminated skin and the web were made of carbon fiber (AS4) and polyetherketoneketone (PEKK). The butt joint (filler) was injection molded from 20% short carbon fiber filled with PEKK thermoplastic. The skin and web were co-consolidated together with the butt joint in the form of a hybrid T-shaped structure. A three point bending (3 PB) set-up was used to investigate the mechanical response of the hybrid composite. The crack initiation and propagation mechanisms for the filler and the delamination at the skin-filler interface were captured using a high speed camera. It was found from the experimental observations that the crack initiated in the filler and then propagated towards the skin-filler interface. A numerical model was also developed using the finite element method in ABAQUS including the crack initiation and growth in the filler together with the delamination at the skin-filler interface. For this purpose the virtual crack closure technique (VCCT) was employed for the crack growth in the filler and the traction separation law was applied at the skin-filler interface using a cohesive surface. The residual stresses and deformations coming from the co-consolidation process were predicted by applying a thermal load and taken into account in the quasi-static analysis. A good agreement was found between the predicted and measured
force-displacement curves. The developed numerical model was further employed to address the crack initiation and growth in the filler and delamination at the skin-filler interface using the mix mode effective fracture energies. A linear elastic behavior was found in the structure until the crack initiation in the filler
Ibuprofen Blunts Ventilatory Acclimatization to Sustained Hypoxia in Humans.
Ventilatory acclimatization to hypoxia is a time-dependent increase in ventilation and the hypoxic ventilatory response (HVR) that involves neural plasticity in both carotid body chemoreceptors and brainstem respiratory centers. The mechanisms of such plasticity are not completely understood but recent animal studies show it can be blocked by administering ibuprofen, a nonsteroidal anti-inflammatory drug, during chronic hypoxia. We tested the hypothesis that ibuprofen would also block the increase in HVR with chronic hypoxia in humans in 15 healthy men and women using a double-blind, placebo controlled, cross-over trial. The isocapnic HVR was measured with standard methods in subjects treated with ibuprofen (400 mg every 8 hrs) or placebo for 48 hours at sea level and 48 hours at high altitude (3,800 m). Subjects returned to sea level for at least 30 days prior to repeating the protocol with the opposite treatment. Ibuprofen significantly decreased the HVR after acclimatization to high altitude compared to placebo but it did not affect ventilation or arterial O2 saturation breathing ambient air at high altitude. Hence, compensatory responses prevent hypoventilation with decreased isocapnic ventilatory O2-sensitivity from ibuprofen at this altitude. The effect of ibuprofen to decrease the HVR in humans provides the first experimental evidence that a signaling mechanism described for ventilatory acclimatization to hypoxia in animal models also occurs in people. This establishes a foundation for the future experiments to test the potential role of different mechanisms for neural plasticity and ventilatory acclimatization in humans with chronic hypoxemia from lung disease
Kepler detection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC10001893
KIC10001893 is one out of 19 subdwarf-B (sdB) pulsators observed by the
Kepler spacecraft in its primary mission. In addition to tens of pulsation
frequencies in the g-mode domain, its Fourier spectrum shows three weak peaks
at very low frequencies, which is too low to be explained in terms of g modes.
The most convincing explanation is that we are seeing the orbital modulation of
three Earth-size planets (or planetary remnants) in very tight orbits, which
are illuminated by the strong stellar radiation. The orbital periods are
P1=5.273, P2=7.807, and P3=19.48 hours, and the period ratios P2/P1=1.481 and
P3/P2=2.495 are very close to the 3:2 and 5:2 resonances, respectively. One of
the main pulsation modes of the star at 210.68 {\mu}Hz corresponds to the third
harmonic of the orbital frequency of the inner planet, suggesting that we see,
for the first time in an sdB star, g-mode pulsations tidally excited by a
planetary companion. The extreme planetary system that emerges from the Kepler
data is very similar to the recent discovery of two Earth-size planets orbiting
the sdB pulsator KIC05807616 (Charpinet et al. 2011a).Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
On the Invariant Theory of Weingarten Surfaces in Euclidean Space
We prove that any strongly regular Weingarten surface in Euclidean space
carries locally geometric principal parameters. The basic theorem states that
any strongly regular Weingarten surface is determined up to a motion by its
structural functions and the normal curvature function satisfying a geometric
differential equation. We apply these results to the special Weingarten
surfaces: minimal surfaces, surfaces of constant mean curvature and surfaces of
constant Gauss curvature.Comment: 16 page
The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign
We present the results of a multisite photometric campaign on the pulsating
sdB star Balloon 090100001. The star is one of the two known hybrid hot
subdwarfs with both long- and short-period oscillations. The campaign involved
eight telescopes with three obtaining UBVR data, four B-band data, and one
Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal
resolution of 0.36microHz with a detection threshold of about 0.2mmag in
B-filter data.
Balloon 090100001 has the richest pulsation spectrum of any known pulsating
subdwarf B star and our analysis detected 114 frequencies including 97
independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz
region is most likely radial while the remaining ones in this region form two
nearly symmetric multiplets: a triplet and quintuplet, attributed to
rotationally split \ell=1 and 2 modes, respectively. We find clear increases of
splitting in both multiplets between the 2004 and 2005 observing campaigns,
amounting to 15% on average. The observed splittings imply that the rotational
rate in Bal09 depends on stellar latitude and is the fastest on the equator. We
use a small grid of models to constrain the main mode (f_1), which most likely
represents the radial fundamental pulsation. The groups of p-mode frequencies
appear to lie in the vicinity of consecutive radial overtones, up to the third
one. Despite the large number of g-mode frequencies observed, we failed to
identify them, most likely because of the disruption of asymptotic behaviour by
mode trapping. The observed frequencies were not, however, fully exploited in
terms of seismic analysis which should be done in the future with a larger grid
of reliable evolutionary models of hot subdwarfs.Comment: accepted for publication in MNRA
Enzymatic degradation behavior and cytocompatibility of silk fibroin–starch–chitosan conjugate membranes
The objective of this study was to investigate the influence of silk fibroin and oxidized starch conjugation on
the enzymatic degradation behavior and the cytocompatability of chitosan based biomaterials. The tensile
stress of conjugate membranes, which was at 50 Megapascal (MPa) for the lowest fibroin and starch composition
(10 weight percent (wt.%)), was decreased significantly with the increased content of fibroin and
starch. The weight loss of conjugates in α-amylase was more notable when the starch concentration was
the highest at 30 wt.%. The conjugates were resistant to the degradation by protease and lysozyme except
for the conjugates with the lowest starch concentration. After 10 days of cell culture, the proliferation of
osteoblast-like cells (SaOS-2) was stimulated significantly by higher fibroin compositions and the DNA synthesis
on the conjugate with the highest fibroin (30 wt.%) was about two times more compared to the native
chitosan. The light microscopy and the image analysis results showed that the cell area and the lengths were
decreased significantly with higher fibroin/chitosan ratio. The study proved that the conjugation of fibroin
and starch with the chitosan based biomaterials by the use of non-toxic reductive alkylation crosslinking significantly
improved the cytocompatibility and modulated the biodegradation, respectively.E.T. Baran thanks the Portuguese Foundation for Science and Technology for providing him a PostDoc scholarship (SFRH/BPD/30768/2006). This work was partially supported by the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758)
Conjugation of fibroin and starch to chitosan for increasing cell proliferation capacity
[Excerpt] In this study, chitosan conjugates with starch and fibroin were produced for increasing degradability in the presence of physiological enzymes and cell proliferation capacities of biomaterials. The degradation profile was monitored over prolonged time periods and characterization of chemical changes during degradation periods were investigated by spectroscopic methods. Various ratios of starch, fibroin and chitosan (%, (weight/weight)) were prepared. The in vitro cell culture studies were conducted to evaluate biocompatibility and proliferation capacities of conjugate materials. [...]info:eu-repo/semantics/publishedVersio
All-trans retinoic acid release from biodegradable polyester microcapsules
[Excerpt] Tissue engineering strategies frequently include a scaffold, living cells and bioactive substances to promote cell growth and guide cell differentiation. The encapsulation in carriers enables protects
the bioactivity of those substances upon implantation, avoids being transported by the body fluids and also allows controlling the release rate. Encapsulation materials are preferably biodegradable
polymers. In this work, all-trans retinoic acid (atRA) was used as a model bioactive agent; since it was shown that atRA enhances the expression of osteocalcin, a specific osteogenic marker. [...]info:eu-repo/semantics/publishedVersio
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