5,775 research outputs found
Impulse approximation in the n p --> d pi^0 reaction reexamined
The impulse approximation (one-body operator) in the n p --> d pi^0 reaction
is reexamined with emphasis on the issues of reducibility and recoil
corrections. An inconsistency when one pion exchange is included in the
production operator is demonstrated and then resolved via the introduction of
"wave function corrections" which nearly vanish for static nucleon propagators.
Inclusion of the recoil corrections to the nucleon propagators is found to
change the magnitude and sign of the impulse production amplitude, worsening
agreement with the experimental cross section by approximately 30%. A cutoff is
used to account for the phenomenological nature of the external wave functions,
and is found to have a significant impact up to approximately 2.5 GeV.Comment: Published versio
The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective Radius
Based on 58 SLACS strong-lens early-type galaxies with direct total-mass and
stellar-velocity dispersion measurements, we find that inside one effective
radius massive elliptical galaxies with M_eff >= 3x10^10 M_sun are
well-approximated by a power-law ellipsoid with an average logaritmic density
slope of = -dlog(rho_tot)/dlog(r)=2.085^{+0.025}_{-0.018} (random
error on mean) for isotropic orbits with beta_r=0, +-0.1 (syst.) and
sigma_gamma' <= 0.20^{+0.04}_{-0.02} intrinsic scatter (all errors indicate the
68 percent CL). We find no correlation of gamma'_LD with galaxy mass (M_eff),
rescaled radius (i.e. R_einst/R_eff) or redshift, despite intrinsic differences
in density-slope between galaxies. Based on scaling relations, the average
logarithmic density slope can be derived in an alternative manner, fully
independent from dynamics, yielding =1.959 +- 0.077. Agreement
between the two values is reached for =0.45 +- 0.25, consistent with
mild radial anisotropy. This agreement supports the robustness of our results,
despite the increase in mass-to-light ratio with total galaxy mass: M_eff ~
L_{V,eff}^(1.363+-0.056). We conclude that massive early-type galaxies are
structurally close-to homologous with close-to isothermal total density
profiles (<=10 percent intrinsic scatter) and have at most some mild radial
anisotropy. Our results provide new observational limits on galaxy formation
and evolution scenarios, covering four Gyr look-back time.Comment: Accepted for publication by ApJL; 4 pages, 2 figure
The X-shooter Lens Survey - II. Sample presentation and spatially resolved kinematics
We present the X-shooter Lens Survey (XLENS) data. The main goal of XLENS is
to disentangle the stellar and dark matter content of massive early-type
galaxies (ETGs), through combined strong gravitational lensing, dynamics and
spectroscopic stellar population studies. The sample consists of 11 lens
galaxies covering the redshift range from to and having stellar
velocity dispersions between and . All
galaxies have multi-band, high-quality HST imaging. We have obtained long-slit
spectra of the lens galaxies with X-shooter on the VLT. We are able to
disentangle the dark and luminous mass components by combining lensing and
extended kinematics data-sets, and we are also able to precisely constrain
stellar mass-to-light ratios and infer the value of the low-mass cut-off of the
IMF, by adding spectroscopic stellar population information. Our goal is to
correlate these IMF parameters with ETG masses and investigate the relation
between baryonic and non-baryonic matter during the mass assembly and structure
formation processes. In this paper we provide an overview of the survey,
highlighting its scientific motivations, main goals and techniques. We present
the current sample, briefly describing the data reduction and analysis process,
and we present the first results on spatially resolved kinematics.Comment: Accepted for publication in MNRA
Forehead Skin Blood Flow in Normal Neonates during Active and Quiet Sleep, Measured with a Diode Laser Doppler Instrument
Changes in forehead skin blood flow during active and quiet sleep were determined in 16 healthy neonates using a recently developed semi-conductor laser Doppler flow meter without light conducting fibres. Measurements were carried out at a postnatal age varying from 5 hours to 7 days. The two sleep states could be distinguished in 17 recordings. The mean skin blood flow values during active sleep were significantly higher (p<0.01) than those during quiet sleep, the mean increase being 28.1%. The variability of the flow signal, expressed as the coefficient of variation, changed significantly from 23.1% during active sleep to 18.2% during quiet sleep
Effect of the whistle watch device on bronchodilator use in children with asthma
Objective. To determine if the use of the whistle watch (WW), a simple device to monitor peak flow rate, affects the use of bronchodilators at home.Study design. Prospective, randomised, crossover design.Setting. The asthma outpatients' clinic at Coronation Hospital, a tertiary care centre in Johannesburg.Patients and methods. Children between 6 and 18 years of age with moderate or severe asthma for more than a year were enrolled. They were randomised into two groups, with bronchodilator use determined either by the WW or solely by the patient's perceived symptomatology. The patients acted as their own controls, switching over to the other group after 30 days. Eighty patients were enrolled into the study.Results. Forty-three patients completed the study (54%). There were no significant differences between these patients and those who did not complete the study in terms of sex, age and treatment characteristics. There was a significant reduction in the mean monthly number of bronchodilator doses used by the WW group (5.5 doses v. 16.81 doses, paired t-test, t = 3.64, P < 0.001, 95% confidence interval (CI) 6.1 - 16.55). The change in individual participants varied between 13 extra bronchodilator doses and 71 fewer doses per month with the use of the WW device.Conclusion. The WW device is a cheap, easy-to-use and effective tool that reduces the number of bronchodilator doses used by asthmatic children at home
Morphological and taxonomic studies of Gracilaria and Gracilariopsis species (Gracilariales, Rhodophyta) from South Africa
Southern Africa has an extremely rich and diverse seaweed flora with a wide variety of marine habitats. Increased commercial interest in these seaweed resources has been the stimulus for biodiversity studies. The Gracilariaceae (Rhodophyta) has emerged as one of the families that possess economic potential as a source of agar and as a potential feed for abalone. A lack of knowledge concerning the taxonomic status of many members of this family is a concern. Gross morphological characters have been the main means of identification and incorrect applications have led to a number of misidentifications. Consequently, a comprehensive reappraisal and revision of these species was carried out. The species count for the South African Gracilariaceae is now two Gracilariopsis species, and nine Gracilaria species. Gracilaria crassa has been reduced to a synonym of G. canaliculata. It is believed that G. foliifera was erroneously identified and specimens in South Africa referred to as G. millardetii and G. protea are assigned to G. corticata. South African Gracilariopsis, previously referred to as Gs. lemaneiformis, is confirmed to be conspecific with European Gs. longissima. This species occurs along the west and south coasts of South Africa, co-existing in a few habitats with G. gracilis. The taxonomic identity of G. vieillardii specimens from South Africa and the differentiation of G. canaliculata and G. salicornia has been confirmed based on morphology. Three species of Gracilaria (G. aculeata, G. beckeri and G. capensis) are endemic or near endemic to the South African coast, and a fourth species, G. denticulata is localised in southeast Africa
The Change in Macroalgal Assemblages through the Saldanha Bay/Langebaan Lagoon Ecosystem (South Africa)
Saldanha Bay and Langebaan Lagoon form together one of the few sheltered habitats within the Benguela Marine Province; a wide gradient in environmental factors is found here. The West Coast National Park was established to protect this unique ecosystem, but at the same time an industrially expanding harbour marks this area. In an effort to understand the biological composition of the Saldanha/Langebaan ecosystem, the intertidal macroalgal assemblages were studied in relation to the relatively well-known South African West Coast flora. Three distinct floral entities were identified using various analytical techniques (similarity coefficients, CCA and TWINSPAN): (i) the species poor, though distinct, salt marshes; (ii) the Lagoon sites; and (iii) the Bay and West Coast sites. The transition between the latter two is located at the mouth of the Lagoon. The species richness of the Bay/West Coast entity is larger than in the Lagoon. The change in algal composition can be explained in terms of the environmental variables of which wave exposure is the most significant. Other important environmental parameters are water surface temperature and salinity, which were found to be negatively correlated with wave exposure. Biogeographical affinities of the different algal entities of the Bay/Lagoon system were also determined in relation to the entire South African shoreline. The Bay/West Coast entity supports a typical West Coast flora, with some noticeable effects of uplift of subtidal species into the infralittoral fringe and morphological variation in less exposed areas. The algal flora of the Lagoon is also dominated by West Coast species, but is typified by species characteristic of sheltered habitats, and with a number of species which otherwise only occur on the geographically distant South Coast (east of Cape Agulhas). The algae from the salt marshes occur widely in tropical mangroves and warm temperate salt marshes
Molecular evidence for gender differences in the migratory behaviour of a small seabird
Molecular sexing revealed an unexpectedly strong female bias in the sex ratio of pre-breeding European Storm Petrels (Hydrobates pelagicus), attracted to playback of conspecific calls during their northwards migration past SW Europe. This bias was consistent across seven years, ranging from 80.8% to 89.7% female (mean annual sex ratio ± SD = 85.5% female ±4.1%). The sex ratio did not differ significantly from unity (i.e., 50% female) among (i) Storm Petrel chicks at a breeding colony in NW France, (ii) adults found dead on beaches in Southern Portugal, (iii) breeding birds attending nest burrows in the UK, captured by hand, and (iv) adults captured near a breeding colony in the UK using copies of the same sound recordings as used in Southern Europe, indicating that females are not inherently more strongly attracted to playback calls than males. A morphological discriminant function analysis failed to provide a good separation of the sexes, showing the importance of molecular sexing for this species. We found no sex difference in the seasonal or nocturnal timing of migration past Southern Europe, but there was a significant tendency for birds to be caught in sex-specific aggregations. The preponderance of females captured in Southern Europe suggests that the sexes may differ in migration route or in their colony-prospecting behaviour during migration, at sites far away from their natal colonies. Such differences in migration behaviour between males and females are poorly understood but have implications for the vulnerability of seabirds to pollution and environmental change at sea during the non-breeding season
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