171 research outputs found
Splitting Strong and Electromagnetic Interactions in K(L4) Decays
We recently considered decays in the framework of chiral
perturbation theory based on the effective Lagrangian including mesons,
photons, and leptons. There, we published analytic one-loop-level expressions
for form factors and corresponding to the mixed process,
. We propose here a possible splitting
between strong and electromagnetic parts allowing analytic (and numerical)
evaluation of Isospin breaking corrections. The latter are sensitive to the
infrared divergence subtraction scheme and are sizeable near the
production threshold. Our results should be used for the extraction of the
-wave iso-vector phase shift from the outgoing data of the
currently running KTeV experiment at FNAL.Comment: 47 pages, LaTeX, 6 postscript figure
QCD Isospin Breaking in Meson Masses, Decay Constants and Quark Mass Ratios
The procedure to calculate masses and matrix-elements in the presence of
mixing of the basis states is explained in detail. We then apply this procedure
to the two-loop calculation in Chiral Perturbation Theory of pseudoscalar
masses and decay constants including quark mass isospin breaking. These results
are used to update our analysis of done previously and obtain a
value of in addition to values for the low-energy-constants .Comment: 22 pages, uses axodraw.st
- Decays Beyond One Loop
The matrix elements for K\rightarrow \pi \pi \l \nu decays are described by
four form factors and . We complete previous calculations by
evaluating at next-to-leading order in the low-energy expansion. We then
estimate higher order contributions using dispersion relations and determine
the low-energy constants and from data on decays and
on elastic pion scattering. Finally, we present predictions for the slope of
the form factor and for total decay rates.Comment: 31 pages, LaTex, 3 figs. (two figures appended as postscript file),
BUTP-94/4,ROMF2 94/0
Form-Factors and - Scattering
The and form-factors of and the quark condensates are
calculated to in Chiral Perturbation Theory (CHPT). Full
formulas are presented as much as possible. A full refit of most of the CHPT parameters is done with a discussion of all inputs and underlying
assumptions. We discuss the consequences for the vacuum expectation values,
decay constants, pseudoscalar masses and - scattering.Comment: 51 page
The inv dup (15) or idic (15) syndrome (Tetrasomy 15q)
The inv dup(15) or idic(15) syndrome displays distinctive clinical findings represented by early central hypotonia, developmental delay and intellectual disability, epilepsy, and autistic behaviour. Incidence at birth is estimated at 1 in 30,000 with a sex ratio of almost 1:1. Developmental delay and intellectual disability affect all individuals with inv dup(15) and are usually moderate to profound. Expressive language is absent or very poor and often echolalic. Comprehension is very limited and contextual. Intention to communicate is absent or very limited. The distinct behavioral disorder shown by children and adolescents has been widely described as autistic or autistic-like. Epilepsy with a wide variety of seizure types can occur in these individuals, with onset between 6 months and 9 years. Various EEG abnormalities have been described. Muscle hypotonia is observed in almost all individuals, associated, in most of them, with joint hyperextensibility and drooling. Facial dysmorphic features are absent or subtle, and major malformations are rare. Feeding difficulties are reported in the newborn period
The use of two-cistron constructions in improving the expression of a heterologous gene in E. coli.
Many heterologous genes when cloned into bacterial expression vectors are poorly expressed because of an inefficient ribosome binding site (RBS). We have constructed a plasmid which expresses human gamma-interferon (gamma-IF), where the level of expression is limited by the RBS. Expression was increased by placing the gamma-IF sequence immediately downstream of a small translated sequence. The production of gamma-IF was dependent upon the efficiency of translation of this upstream cistron and could be increased to very high levels. The same upstream cistron would greatly improve the expression of gamma-IF in a plasmid where the RBS was very poor due to inhibitory secondary structure at the 5' end of its mRNA. However, it would not improve the efficiency of a poor RBS containing a weak Shine-Dalgarno sequence. The general utility of the two-cistron expression strategy to diagnose a weak RBS is discussed
Heterologous expression in Escherichia coli: effects of alterations in the sequence 5′ to the initiation codon
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