127 research outputs found
Cognitive development following ART: effect of choice of comparison group, confounding and mediating factors
BACKGROUND: Epidemiological studies have examined the health of children born after assisted reproductive technology (ART), with contradictory results. In this article, we address the question 'Do singletons born after ART have a poorer cognitive developmental outcome at 3 years of age?' We assess the implications of using different comparison groups, and discuss appropriate analytical approaches for the control of confounding and mediating variables. METHODS: Data were drawn from the Millennium Cohort Study. Interviews captured sociodemographic, behavioural and pregnancy information. Developmental assessments conducted at age three included the British Ability Scales II Naming Vocabulary (BAS-NV) instrument. We compared ART infants (born after IVF or ICSI) to four comparison groups: a 'matched' group; a 'subfertile' group (time to conception >12 months); a 'fertile' group (time to conception <12 months); and an 'any spontaneous conceptions' group. Linear regression provided estimates of the difference in mean BAS-NV scores in the ART and comparison groups; both unadjusted estimates and those adjusted for confounding and mediating factors are presented. RESULTS: In the unadjusted analyses, ART children gained significantly better BAS-NV test results than did the comparison group children. When converted to an estimate of developmental age gap, ART children were 2.5, 2.7, 3.6 and 4.5 months ahead of the 'matched', 'subfertile', 'fertile' and 'spontaneous conception' children, respectively. After adjusting for confounding and mediating factors, the differences were reduced, and were not statistically significant. CONCLUSIONS: ART is not associated with poorer cognitive development at 3 years. We have highlighted methodological considerations for researchers planning to study the effect of infertility and ART on childhood outcomes
MHV Rules for Higgs Plus Multi-Gluon Amplitudes
We use tree-level perturbation theory to show how non-supersymmetric one-loop
scattering amplitudes for a Higgs boson plus an arbitrary number of partons can
be constructed, in the limit of a heavy top quark, from a generalization of the
scalar graph approach of Cachazo, Svrcek and Witten. The Higgs boson couples to
gluons through a top quark loop which generates, for large top mass, a
dimension-5 operator H tr G^2. This effective interaction leads to amplitudes
which cannot be described by the standard MHV rules; for example, amplitudes
where all of the gluons have positive helicity. We split the effective
interaction into the sum of two terms, one holomorphic (selfdual) and one
anti-holomorphic (anti-selfdual). The holomorphic interactions give a new set
of MHV vertices -- identical in form to those of pure gauge theory, except for
momentum conservation -- that can be combined with pure gauge theory MHV
vertices to produce a tower of amplitudes with more than two negative
helicities. Similarly, the anti-holomorphic interactions give anti-MHV vertices
that can be combined with pure gauge theory anti-MHV vertices to produce a
tower of amplitudes with more than two positive helicities. A Higgs boson
amplitude is the sum of one MHV-tower amplitude and one anti-MHV-tower
amplitude. We present all MHV-tower amplitudes with up to four
negative-helicity gluons and any number of positive-helicity gluons (NNMHV).
These rules reproduce all of the available analytic formulae for Higgs +
n-gluon scattering (n<=5) at tree level, in some cases yielding considerably
shorter expressions.Comment: 34 pages, 8 figures; v2, references correcte
'Education, education, education' : legal, moral and clinical
This article brings together Professor Donald Nicolson's intellectual interest in professional legal ethics and his long-standing involvement with law clinics both as an advisor at the University of Cape Town and Director of the University of Bristol Law Clinic and the University of Strathclyde Law Clinic. In this article he looks at how legal education may help start this process of character development, arguing that the best means is through student involvement in voluntary law clinics. And here he builds upon his recent article which argues for voluntary, community service oriented law clinics over those which emphasise the education of students
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Biogeochemical silica mass balances in Lake Michigan and Lake Superior
Silica budgets for Lake Michigan and Lake Superior differ in several respects. Mass balance calculations for both lakes agree with previous studies in that permanent burial of biogenic silica in sediments may be only about 5% of the biogenic silica produced by diatoms. Because dissolution rates are large, good estimates of permanent burial of diatoms can not be obtained indirectly from the internal cycle of silica (silica uptake by diatoms and subsequent dissolution) but must be obtained from the sediment stratigraphy. The annual net production of biogenic silica in Lake Michigan requires 71% of the winter maximum silica reservoir which must be maintained primarily by internal cycling in this large lake whereas the comparable silica demand in Lake Superior is only 8.3%. The greater silica demand in Lake Michigan is the result of phosphorus enrichment which has increased diatom production. It is hypothesized that steady-state silica dynamics in Lake Michigan were disrupted by increased diatom production between 1955 and 1970 and that a new steady state based on silica-limited diatom production developed after 1970. Mass balance calculations for Lake Michigan show in contrast with previous work that the hypothesized water column silica depletion of 3.0 g · m −3 could have occurred even though 90% or more of the biogenic silica production is recycled.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42471/1/10533_2004_Article_BF02187199.pd
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