138 research outputs found
Periventricular-intraventricular haemorrhage in low-birth-weight infants at Baragwanath Hospital
The prevalence of periventricular-intraventricular haemorrhage (PV-IVH) aInong very-low-birthweight infants at Baragwanath Hospital has not been well docwnented. In this prospective study, a total of 282 live-born infants with birth weights of 1 000 - 1 749 g were studied over a 41/2-month period. Every infant had at least one cranial ultrasound examination at 7 - 10 days of age, while one third of non-ventilated and all ventilated infants had ultrasound examinations on days 3, 7 and 14. Where possible, all infants had a follow-up ultrasound scan at 40 weeks' post-conceptional age. The overall prevalence of PV-IVH was 53% for infants weighing less than 1 500 g at birth and 52% for infants born at less than 35 weeks' gestation, but only 12% had either grade III or grade IV haemorrhages. The prevalence and severity of PV-IVH increased with both decreasing birth weight and decreasing gestational age and was also predicted by the need for active resuscitation at birth, mechanical ventilation and the development of pneumothorax. A total of 93% ofinfants without PV-IVH survived, but survival decreased with increasing grade of PV-IVH. Germinal matrix cysts were noted on follow-up in 55% of surviving infants with grade I PV-IVH. Very-low-birthweight infants at Baragwanath Hospital therefore seem to have a higher prevalence of PV-IVH when compared with reported figures, but this is due mainly to an increase in smaller haemorrhages
The Muonium Atom as a Probe of Physics beyond the Standard Model
The observed interactions between particles are not fully explained in the
successful theoretical description of the standard model to date. Due to the
close confinement of the bound state muonium () can be used as
an ideal probe of quantum electrodynamics and weak interaction and also for a
search for additional interactions between leptons. Of special interest is the
lepton number violating process of sponteanous conversion of muonium to
antimuonium.Comment: 15 pages,6 figure
Jamming at Zero Temperature and Zero Applied Stress: the Epitome of Disorder
We have studied how 2- and 3- dimensional systems made up of particles
interacting with finite range, repulsive potentials jam (i.e., develop a yield
stress in a disordered state) at zero temperature and applied stress. For each
configuration, there is a unique jamming threshold, , at which
particles can no longer avoid each other and the bulk and shear moduli
simultaneously become non-zero. The distribution of values becomes
narrower as the system size increases, so that essentially all configurations
jam at the same in the thermodynamic limit. This packing fraction
corresponds to the previously measured value for random close-packing. In fact,
our results provide a well-defined meaning for "random close-packing" in terms
of the fraction of all phase space with inherent structures that jam. The
jamming threshold, Point J, occurring at zero temperature and applied stress
and at the random close-packing density, has properties reminiscent of an
ordinary critical point. As Point J is approached from higher packing
fractions, power-law scaling is found for many quantities. Moreover, near Point
J, certain quantities no longer self-average, suggesting the existence of a
length scale that diverges at J. However, Point J also differs from an ordinary
critical point: the scaling exponents do not depend on dimension but do depend
on the interparticle potential. Finally, as Point J is approached from high
packing fractions, the density of vibrational states develops a large excess of
low-frequency modes. All of these results suggest that Point J may control
behavior in its vicinity-perhaps even at the glass transition.Comment: 21 pages, 20 figure
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
Aesthetics of protest: An examination of the photojournalistic approach to protest imagery
Images of protests and demonstrations are crucial to both social movements and protesters who wish to communicate their identity and their messages to wider audiences. However, the photographing of such political events by press photographers is a complex process. The current analysis focuses on questions of aesthetics surrounding issues of visuality regarding protests and demonstrations. Based on empirical data from 17 semi-structured in-depth interviews with Greek photojournalists, this paper examines what is photographed during a protest and how this is affected by the photojournalists’ aesthetic criteria. Drawing on scholarly work on photojournalism (Ritchin and Åker) and photography (Sontag), this article discusses that besides the presumption in the principal of recording reality, photojournalists’ practice is also infused with subjective language and influenced by art photographers’ techniques. Thereupon, the main argument of this paper is that the employment of hybridized photographing practices by photojournalists can have an impact upon their visual decisions with regard to what and how is photographed during a protest. The product of such practices is usually high quality, captivating images with apparent affective qualities
Observations of the High Redshift Universe
(Abridged) In these lectures aimed for non-specialists, I review progress in
understanding how galaxies form and evolve. Both the star formation history and
assembly of stellar mass can be empirically traced from redshifts z~6 to the
present, but how the various distant populations inter-relate and how stellar
assembly is regulated by feedback and environmental processes remains unclear.
I also discuss how these studies are being extended to locate and characterize
the earlier sources beyond z~6. Did early star-forming galaxies contribute
significantly to the reionization process and over what period did this occur?
Neither theory nor observations are well-developed in this frontier topic but
the first results presented here provide important guidance on how we will use
more powerful future facilities.Comment: To appear in `First Light in Universe', Saas-Fee Advanced Course 36,
Swiss Soc. Astrophys. Astron. in press. 115 pages, 64 figures (see
http://www.astro.caltech.edu/~rse/saas-fee.pdf for hi-res figs.) For lecture
ppt files see
http://obswww.unige.ch/saas-fee/preannouncement/course_pres/overview_f.htm
Helicity of the W Boson in Lepton+Jets ttbar Events
We examine properties of ttbar candidates events in lepton+jets final states
to establish the helicities of the W bosons in t->W+b decays. Our analysis is
based on a direct calculation of a probability that each event corresponds to a
ttbar final state, as a function of the helicity of the W boson. We use the 125
events/pb sample of data collected by the DO experiment during Run I of the
Fermilab Tevatron collider at sqrt{s}=1.8 TeV, and obtain a longitudinal
helicity fraction of F_0=0.56+/-0.31, which is consistent with the prediction
of F_0=0.70 from the standard model
Hard Single Diffraction in pbarp Collisions at root-s = 630 and 1800 GeV
Using the D0 detector, we have studied events produced in proton-antiproton
collisions that contain large forward regions with very little energy
deposition (``rapidity gaps'') and concurrent jet production at center-of-mass
energies of root-s = 630 and 1800 Gev. The fractions of forward and central jet
events associated with such rapidity gaps are measured and compared to
predictions from Monte Carlo models. For hard diffractive candidate events, we
use the calorimeter to extract the fractional momentum loss of the scattered
protons.Comment: 11 pages 4 figures. submitted to PR
Measurement of the WW production cross section in p anti-p collisions at s**(1/2) = 1.96 TeV
We present a measurement of the W boson pair-production cross section in p
anti-p collisions at a center-of-mass energy of sqrt{s}=1.96 TeV. The data,
collected with the Run II DO detector, correspond to an integrated luminosity
of 224-252 pb^-1 depending on the final state (ee, emu or mumu). We observe 25
candidates with a background expectation of
8.1+/-0.6(stat)+/-0.6(syst)+/-0.5(lum) events. The probability for an upward
fluctuation of the background to produce the observed signal is 2.3x10^-7,
equivalent to 5.2 standard deviations.The measurement yields a cross section of
13.8+4.3/-3.8(stat)+1.2/-0.9(syst)+/-0.9(lum) pb, in agreement with predictions
from the standard model.Comment: submitted to PR
Erratum to Measurement of at 1.96 TeV, published in Phys. Rev. D {71}, 072004 (2005)
A change in estimated integrated luminosity (from 226 pb^{-1}{\sigma (p \bar p \to Z)
\cdot}{(Z \to \tau \tau)}209\pm13(stat.)\pm16(syst.)\pm13(lum) pb
- …