447 research outputs found
Is gastro-oesophageal reflux a factor in exercise-induced asthma?
AbstractExercise-induced bronchoconstriction (EIB) occurs in the majority of patients with asthma. The relationship between asthma and gastro-oesophageal reflux (GER) is well defined, and the reports of exertional gastro-oesophageal acid reflux in healthy subjects, prompted us to study the relationship between EIB and GER.Following an overnight fast and medication withholding, 15 asthmatics and 15 normal subjects were placed on continuous monitoring of oesophageal pH and ECG. After baseline monitoring of oesophageal pH, at rest, for 30 min, spirometry was performed. Thereafter, the subjects underwent rigorous treadmill exercise for 8 min followed by spirometry, 10 min after running.Twelve out of 15 asthmatics and none in the control group demonstrated significant fall in FEV1 in response to exercise. However, only six out of 15 normal subjects and three in the asthmatic group had evidence of GER during or following exercise.We concluded that there is no significant correlation between EIB and GER in patients with asthma
New limits on di-nucleons decay into invisible channels
Data of the radiochemical experiment [E.L.Fireman, 1978] with 1.7 t of
KC_2H_3O_2, accumulated deep underground during ~1 yr, were reanalyzed to set
limits on di-nucleons (nn and np) decays into invisible channels
(disappearance, decay into neutrinos, etc.). The obtained lifetime bounds
tau_np > 2.1 10^25 yr and tau_nn > 4.2 10^25 yr (at 90% C.L.) are better (or
competitive) than those established in the recent experiments.Comment: 3 pages, accepted in JETP Letter
1ES 1927+654: Persistent and rapid X-ray variability in an AGN with low intrinsic neutral X-ray absorption and narrow optical emission lines
We present X-ray and optical observations of the X-ray bright AGN 1ES
1927+654. The X-ray observations obtained with ROSAT and Chandra reveal
persistent, rapid and large scale variations, as well as steep 0.1-2.4 keV
(Gamma = 2.6 +/- 0.3) and 0.3-7.0 keV (Gamma = 2.7 +/- 0.2) spectra. The
measured intrinsic neutral X-ray column density is approximately 7e20cm^-2. The
X-ray timing properties indicate that the strong variations originate from a
region, a few hundred light seconds from the central black hole, typical for
type 1 AGN. High quality optical spectroscopy reveals a typical Seyfert 2
spectrum with some host galaxy contamination and no evidence of Fe II
multiplets or broad hydrogen Balmer wings. The intrinsic optical extinction
derived from the BLR and NLR are A_V >= 3.7 and A_V=1.7, respectively. The
X-ray observations give an A_V value of less than 0.58, in contrast to the
optical extinction values. We discuss several ideas to explain this apparent
difference in classification including partial covering, an underluminous BLR
or a high dust to gas ratio.Comment: 8 pages including 10 figures. Accepted for publication in Astronomy
and Astrophysic
The Active Quiescence of HR Del (Nova Del 1967)
This new UV study of the ex-nova HR Del is based on all of the data obtained
with the IUE satellite, and includes the important series of spectra taken in
1988 and 1992 that have not been analyzed so far. After the correction for the
reddening (EB-V)=0.16), adopting a distance d =850 pc, we have derived a mean
UV luminosity close to Luv ~ 56 Lsun, the highest value among classical novae
in "quiescence". Also the "average" optical absolute magnitude Mv=+2.30 is
indicative of a bright object. The UV continuum luminosity, the HeII 1640 A
emission line luminosity, and the optical absolute magnitude all give a mass
accretion rate Mdot very close to 1.4*10**(-7) Msun/yr, if one assumes that the
luminosity of the old nova is due to a non-irradiated accretion disk. The
continuum distribution is well fitted with either a black body of 33,900 K, or
a power-law F(lambda) ~ lambda**(-2.20). We show that the "quiescent" optical
magnitude at mv ~ 12 comes from the hot component and not from the companion
star. Since most IUE observations correspond to the "quiescent" magnitude at mv
~ 12, the same as in the pre-eruption stage, we infer that the pre-nova, for at
least 70 years prior to eruption, was also very bright at near the same Luv,
Mv, Mdot and T values as derived in the present study for the ex-nova. The wind
components in the P Cyg profiles of the CIV 1550 A and NV 1240 A resonance
lines are strong and variable on short timescales, with vedge up to -5000 km/s,
a remarkably high value. The phenomenology in the short-time variations of the
wind indicates the presence of an inhomogeneous outflow. We discuss the nature
of the strong UV continuum and wind features and the implications of the
presence of a "bright" state a long time before and after outburst on our
present knowledge of the pre-nova and post-nova behavior.Comment: 15 pages, 10 figures, accepted for Astronomy and Astrophysic
Soft X-ray spectral variations of the narrow line Seyfert l galaxy Markarian 766
The X-ray variability of the narrow-line Seyfert 1 galaxy Markarian 766 is studied using nine ROSAT PSPC data sets. The spectrum is well described by a power law combined with a blackbody (kT ∼ 70 eV) soft excess. Examination of flux ratio changes and variability amplitude in three X-ray bands shows that the power-law component varies continuously on time-scales of ∼ 5000 s and is steeper when it is brighter. In contrast, variability of the soft excess is not detected. Spectral modelling of 31 spectra from different observations and at a range of count rates is also consistent with a picture in which the power law is steeper when it is brighter, and in which the soft-excess component does not vary. The power-law variability can be explained if the power law is produced by variable thermal or non-thermal Comptonization of soft photons. This behaviour is similar to that of Galactic black hole candidates in the low state. The X-ray and multiwavelength properties of Markarian 766 are shown to be very similar to those of other narrow-line Seyfert 1s. This may mean that the rapid X-ray variability seen in other narrow-line Seyfert 1s may also not originate in their strong soft-excess components
Double Beta Decay: Historical Review of 75 Years of Research
Main achievements during 75 years of research on double beta decay have been
reviewed. The existing experimental data have been presented and the
capabilities of the next-generation detectors have been demonstrated.Comment: 25 pages, typos adde
New constraints on protostellar jet collimation from high-density gas UV tracers
The analysis of high-resolution profiles of the semiforbidden UV lines of C III](1908) and Si III](1892) in the spectra of T Tauri stars (TTSs) shows the following : (1) There is C III](1908) and Si III](1892) emission at velocities that are similar to those observed in the optical forbidden lines formed in the TTSs jets. The luminosity of the UV lines is comparable to that of the optical lines. (2) The comparison between the optical and UV light curves indicates that the C III](1908) and Si III](1892) emission of RY Tau is not associated with accretion shocks, but it is produced farther than 2 R-* from the star. (3) The profiles of the UV semiforbidden lines are significantly broader than those of the optical forbidden lines. These profiles cannot be produced in a narrow collimated beam, and they are most likely produced in a bow-shaped shock wave formed at the base of the optical jet, where the hot gas emits in a broad range of projected radial velocities. (4) The atmosphere of RU Lup contributes significantly to the Si III](1892) emission. (5) A puzzling narrow feature is observed close to the C III](1908) line. The feature is blueshifted by -260 km s(-1), which corresponds to the wind terminal velocity measured in the P Cygni profile of the Mg II (UV1) lines. Moreover, constraints are derived on the characteristics of the C III](1908) and Si III](1892) emitting region in RY Tau. It is shown that 4.7 less than or equal to log T-e less than or equal to 5.0 and 10(9) cm(-3) less than or equal to N-e less than or equal to 10(11) cm(-3) provided that the emission is produced in a collisional plasma and that the 1665 Angstrom feature observed in low-dispersion International Ultraviolet Explorer (IUE) spectra is confirmed to be O III](1665) emission produced in the wind. These very high densities are difficult to generate in the shocks produced by the magnetic pinching of centrifugally driven magnetized disk winds. The data also suggest that the shocked layer has a radius of some few stellar radii and it is closer than similar to 38 R-* to the star
Early bronchopulmonary involvement in Crohn disease: a case report
BACKGROUND: Bronchopulmonary manifestations of Crohn disease have been rarely described in children, including both subclinical pulmonary involvement and severe lung disease. CASE PRESENTATION: A 6.5-year-old girl is described with early recurrent bronchopulmonary symptoms both at presentation and in the quiescent phase of Crohn disease. Pulmonary function tests (lung volumes and flows, bronchial reactivity and carbon monoxide diffusing capacity) were normal. Bronchoalveolar cytology showed increased (30%) lymphocyte counts and bronchial biopsy revealed thickening of basal membrane and active chronic inflammation. CONCLUSIONS: Clinical and histological findings in our young patient suggest involvement of both distal and central airways in an early phase of lung disease. The pathogenesis of Crohn disease-associated lung disorders is discussed with reference to the available literature. A low threshold for pulmonary evaluation seems to be advisable in all children with CD
Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo
The observed hard X-ray (HXR) flux spectrum from solar flares
is a combination of primary bremsstrahlung photons with a
spectrally modified component from photospheric Compton backscatter of downward
primary emission. The latter can be significant, distorting or hiding the true
features of the primary spectrum which are key diagnostics for acceleration and
propagation of high energy electrons and of their energy budget. For the first
time in solar physics, we use a Green's function approach to the backscatter
spectral deconvolution problem, constructing a Green's matrix including
photoelectric absorption. This approach allows spectrum-independent extraction
of the primary spectrum for several HXR flares observed by the {\it Ramaty High
Energy Solar Spectroscopic Imager} (RHESSI). We show that the observed and
primary spectra differ very substantially for flares with hard spectra close to
the disk centre. We show in particular that the energy dependent photon
spectral index is very different
for and for and that inferred mean source
electron spectra differ greatly. Even for a forward fitting of a
parametric to the data, a clear low-energy cutoff required to fit
essentially disappears when the fit is to - i.e.
when albedo correction is included. The self-consistent correction for
backscattered photons is thus shown to be crucial in determining the energy
spectra of flare accelerated electrons, and hence their total number and
energy.Comment: 8 pages, 8 figures, Accepted to Astronomy and Astrophysic
Room-Temperature Ionic Liquids for Electrochemical Capacitors
A document discusses room-temperature ionic liquids (RTILs) used as electrolytes in carbon-nanotube-based, electrochemical, double-layer capacitors. Unlike the previous electrolyte (EtNB4 in acetonitrile), the RTIL used here does not produce cyanide upon thermal decomposition and does not have a moisture sensitivity
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