64 research outputs found
Planar bubble plumes from an array of nozzles:Measurements and modelling
Bubble curtains are widely used for sound mitigation during offshore pile driving to protect marine life. However, the lack of well validated hydrodynamic models is a major factor in the inability to predict the sound attenuation of a bubble curtain a priori. We present a new dataset resulting from bubble curtain measurements carried out in a 10 m deep and 31 m wide freshwater tank. The data describe the evolution of the void fraction profile and the bubble size distribution along the height of the bubble curtain. On this basis, a new relationship is developed for the dependence of the entrainment parameter of the bubble curtain on the air flowrate. In addition, we have extended a recently developed integral model for round bubble plumes to seamlessly capture the transition from initially individual round plumes to a planar plume after their merger. With additional modifications to the entrainment relation, the effective slip velocity and the initial condition for the bubble size distribution, the new model is found to be in good agreement with the data. In particular, the bubble size distribution sufficiently distant from the source is found to be independent of the gas flowrate, both in the data and in the model.</p
Planar bubble plumes from an array of nozzles: Measurements and modelling
Bubble curtains are widely used for sound mitigation during offshore pile
driving to protect marine life. However, the lack of well validated
hydrodynamic models is a major factor in the inability to predict the sound
attenuation of a bubble curtain a priori. We present a new dataset resulting
from bubble curtain measurements carried out in a 10m deep and 31m wide
freshwater tank. The data describe the evolution of the void fraction profile
and the bubble size distribution along the height of the bubble curtain. On
this basis, a new relationship is developed for the dependence of the
entrainment parameter of the bubble curtain on the air flowrate. In addition,
we have extended a recently developed integral model for round bubble plumes to
seamlessly capture the transition from initially individual round plumes to a
planar plume after their merger. With additional modifications to the
entrainment relation, the effective slip velocity and the initial condition for
the bubble size distribution, the new model is found to be in good agreement
with the data. In particular, the bubble size distribution sufficiently distant
from the source is found to be independent of the gas flowrate, both in the
data and in the model.Comment: 28 pages, 16 figure
Metallicity and Far-Infrared Luminosity of High Redshift Quasars
We present the results of an exploratory study of broad line region (BLR)
metallicity in 34 2.2 < z < 4.6 quasars with far-infrared (FIR) luminosities
(L_FIR) from 10^13.4 to 10^12.1 L_\odot . Quasar samples sorted by L_FIR might
represent an evolutionary sequence if the star formation rates (SFRs) in quasar
hosts generally diminish across quasar lifetimes. We use rest-frame ultraviolet
spectra from the Sloan Digital Sky Survey to construct three composite spectra
sorted by L_FIR, corresponding to average SFRs of 4980, 2130 and 340 M_\odot
yr^-1 after correcting for a nominal quasar FIR contribution. The measured N V
{\lambda} 1240/C IV {\lambda} 1550 and Si IV {\lambda} 1397+O IV] {\lambda}
1402/C IV {\lambda} 1550 emission line ratios indicate super-solar BLR
metallicities in all three composites, with no evidence for a trend with the
star formation rate. The formal derived metallicities, Z ~ 5-9 Z_\odot , are
similar to those derived for the BLRs of other quasars at similar redshifts and
luminosities. These results suggest that the ongoing star formation in the host
is not responsible for the metal enrichment of the BLR gas. Instead, the BLR
gas must have been enriched before the visible quasar phase. These results for
high quasar metallicities, regardless of L_FIR, are consistent with evolution
scenarios wherein visibly bright quasars appear after the main episode(s) of
star formation and metal enrichment in the host galaxies. Finally, young
quasars, those more closely associated with a recent merger or a blowout of gas
and dust, may exhibit tracers of these events, such as redder continuum slopes
and higher incidence of narrow absorption lines. With the caveat of small
sample sizes, we find no relation between L_FIR and the reddening or the
incidence of absorption lines.Comment: 10 pages, 3 figures. Accepted to MNRAS, May 201
Carbohydrate mouth rinse: does it improve endurance exercise performance?
It is well known that carbohydrate (CHO) supplementation can improve performance in endurance exercises through several mechanisms such as maintenance of glycemia and sparing endogenous glycogen as well as the possibility of a central nervous-system action. Some studies have emerged in recent years in order to test the hypothesis of ergogenic action via central nervous system. Recent studies have demonstrated that CHO mouth rinse can lead to improved performance of cyclists, and this may be associated with the activation of brain areas linked to motivation and reward. These findings have already been replicated in other endurance modalities, such as running. This alternative seems to be an attractive nutritional tool to improve endurance exercise performance
Characterisation of Herschel-selected strong lens candidates through HST and sub-mm/mm observations
We have carried out HST snapshot observations at 1.1 m of 281 candidate
strongly lensed galaxies identified in the wide-area extragalactic surveys
conducted with the Herschel space observatory. Our candidates comprise systems
with flux densities at m mJy. We model and subtract
the surface brightness distribution for 130 systems, where we identify a
candidate for the foreground lens candidate. After combining visual inspection,
archival high-resolution observations, and lens subtraction, we divide the
systems into different classes according to their lensing likelihood. We
confirm 65 systems to be lensed. Of these, 30 are new discoveries. We
successfully perform lens modelling and source reconstruction on 23 systems,
where the foreground lenses are isolated galaxies and the background sources
are detected in the HST images. All the systems are successfully modelled as a
singular isothermal ellipsoid. The Einstein radii of the lenses and the
magnifications of the background sources are consistent with previous studies.
However, the background source circularised radii (between 0.34 kpc and 1.30
kpc) are 3 times smaller than the ones measured in the sub-mm/mm for a
similarly selected and partially overlapping sample. We compare our lenses with
those in the SLACS survey, confirming that our lens-independent selection is
more effective at picking up fainter and diffuse galaxies and group lenses.
This sample represents the first step towards characterising the near-IR
properties and stellar masses of the gravitationally lensed dusty star-forming
galaxies.Comment: 57 pages, 18 figures, 11 tables. Accepted for publication in MNRA
Characterisation of analogue Monolithic Active Pixel Sensor test structures implemented in a 65 nm CMOS imaging process
Analogue test structures were fabricated using the Tower Partners
Semiconductor Co. CMOS 65 nm ISC process. The purpose was to characterise and
qualify this process and to optimise the sensor for the next generation of
Monolithic Active Pixels Sensors for high-energy physics. The technology was
explored in several variants which differed by: doping levels, pixel geometries
and pixel pitches (10-25 m). These variants have been tested following
exposure to varying levels of irradiation up to 3 MGy and 1 MeV
n cm. Here the results from prototypes that feature direct
analogue output of a 44 pixel matrix are reported, allowing the
systematic and detailed study of charge collection properties. Measurements
were taken both using Fe X-ray sources and in beam tests using minimum
ionizing particles. The results not only demonstrate the feasibility of using
this technology for particle detection but also serve as a reference for future
applications and optimisations
NIKA2, a dual-band millimetre camera on the IRAM 30 m telescope to map the cold universe
A consortium led by Institut NĂ©el (Grenoble) has just finished installing a new powerful millimetre camera NIKA2 on the IRAM 30 m telescope. It has an instantaneous field-of-view of 6.5 arcminutes at both 1.2 and 2.0 mm with polarimetric capabilities at 1.2 mm. NIKA2 provides a near diffraction-limited angular resolution (resp. 12 and 18 arcseconds). The 3 detector arrays are made of more than 1000 KIDs each. KIDs are new superconducting devices emerging as an alternative to bolometers. The commissionning is ongoing in 2016 with a likely opening to the IRAM community in early 2017. NIKA2 is a very promising multi-purpose instrument which will enable many scientific discoveries in the coming decade
Road traffic noise and children's inattention
BACKGROUND: An increasing number of children are exposed to road
traffic noise levels that may lead to adverse effects on health
and daily functioning. Childhood is a period of intense growth
and brain maturation, and children may therefore be especially
vulnerable to road traffic noise. The objective of the present
study was to examine whether road traffic noise was associated
with reported inattention symptoms in children, and whether this
association was mediated by sleep duration. METHODS: This study
was based on the Norwegian Mother and Child Cohort Study
conducted by the Norwegian Institute of Public Health. Parental
reports of children's inattention at age 8 were linked to
modelled levels of residential road traffic noise. We
investigated the association between inattention and noise
exposure during pregnancy (n = 1934), noise exposure averaged
over 5 years (age 3 to 8 years; n = 1384) and noise exposure at
age 8 years (n = 1384), using fractional logit response models.
The participants were children from Oslo, Norway. RESULTS: An
association with inattention at age 8 years was found for road
traffic noise exposure at age 8 years (coef = .0083, CI =
[.0012, .0154]; 1.2% point increase in inattention score per 10
dB increase in noise level), road traffic noise exposure average
for the last 5 years (coef = .0090, CI = [.0016, .0164]; 1.3%
point increase/10 dB), and for pregnancy road traffic noise
exposure for boys (coef = .0091, CI = [.0010, .0171]), but not
girls (coef = -.0021, CI = [-.0094, .0053]). Criteria for doing
mediation analyses were not fulfilled. CONCLUSION: Results
indicate that road traffic noise has a negative impact on
children's inattention. We found no mediation by sleep duration
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