3,916 research outputs found
Diversity and function of phage encoded depolymerases
Bacteriophages of the Podoviridae family often exhibit so-called depolymerases as structural components of the virion. These enzymes appear as tail spike proteins (TSPs). After specific binding to capsular polysaccharides (CPS), exopolysaccharides (EPS) or lipopolysaccharide (LPS) of the host bacteria, polysaccharide-repeating units are specifically cleaved. Finally, the phage reaches the last barrier, the cell wall, injects its DNA, and infects the cell. Recently, similar enzymes from bacteriophages of the Ackermannviridae, Myoviridae, and Siphoviridae families were also described. In this mini-review the diversity and function of phage encoded CPS-, EPS-, and LPSdegrading depolymerases is summarized. The function of the enzymes is described in terms of substrate specificity and applications in biotechnology
On the holomorphic factorization for superconformal fields
For a generic value of the central charge, we prove the holomorphic
factorization of partition functions for free superconformal fields which are
defined on a compact Riemann surface without boundary. The partition functions
are viewed as functionals of the Beltrami coefficients and their fermionic
partners which variables parametrize superconformal classes of metrics.Comment: 5 pages, LATEX, MPI-Ph/92-7
An example of resonance saturation at one loop
We argue that the large-Nc expansion of QCD can be used to treat a Lagrangian
of resonances in a perturbative way. As an illustration of this we compute the
L_10 coupling of the Chiral Lagrangian by integrating out resonance fields at
one loop. Given a Lagrangian and a renormalization scheme, this is how in
principle one can answer in a concrete and unambiguous manner questions such as
at what scale resonance saturation takes place.Comment: 9 pages, 5 figures. Enlarged discussion, results unchanged. To be
published in Phys. Rev.
Decay of pseudoscalars into lepton pairs and large-Nc QCD
The counterterm combination that describes the decay of pseudoscalar mesons
into charged lepton pairs at lowest order in chiral perturbation theory is
considered within the framework of QCD in the limit of a large number of
colours Nc. When further restricted to the lowest meson dominance approximation
to large-Nc QCD, our results agree well with the available experimental data.Comment: 5 pages, 2 figure
Patterns of Spontaneous Chiral Symmetry Breaking in the Large-Nc Limit of QCD-Like Theories
It is shown that in vector-like gauge theories, such as QCD, and in the limit
of a large number of colours Nc, the ordering pattern of narrow vector and
axial-vector states at low energies is correlated with the size of the possible
local order parameters of chiral symmetry breaking. This has implications on
the underlying dynamics of spontaneous chiral symmetry breaking in QCD, and
also on possible values of the parameter S for oblique electroweak corrections,
the analogue of the QCD low energy constant L10.Comment: 12 pages, 2 figures, plain Late
Geometric approach to condensates in holographic QCD
An SU(Nf)xSU(Nf) Yang-Mills theory on an extra-dimensional interval is
considered, with appropriate symmetry-breaking boundary conditions on the IR
brane. UV-brane to UV-brane correlators at high energies are compared with the
OPE of two-point functions of QCD quark currents. Condensates correspond to
departure from AdS of the (different) metrics felt by vector and axial
combinations, away from the UV brane. Their effect on hadronic observables is
studied: the extracted condensates agree with the signs and orders of magnitude
expected from QCD.Comment: References added: published version plus misprints correction
pi-N charge exchange and pi(+)-pi(0) scattering at low energies
pi-N and pi-pi interactions near threshold are uniquely sensitive to the
chiral symmetry breaking part of the strong interaction. The pi-N sigma-term
value with its implications for nucleon quark structure and the recent
controversy concerning the size of the scalar quark condensate have renewed the
experimental interest in these two fundamental systems. We report new
differential cross sections for the reaction at 27.5 MeV
pion incident kinetic energy, measured between and
. Our results are in excellent agreement with the existing
comprehensive pi-N phase shift analysis. We also report on a Chew-Low analysis
of exclusive data at 260 MeV pion incident energy.Comment: Talk given by D. Pocanic at QULEN97, Osaka, 20-23 May 1997; 4 pages,
2 PostScript figures, writen in LaTeX 2e, uses packages "epsfig" and
"espcrc1
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