657 research outputs found
Risikoanalyse durch eine wirkungsbezogenen Analytik mit der instrumentellen Hochleistungs-Dünnschichtchromatographie in der Lebensmittelüberwachung
Zusammenfassung.: Als wirkungsbezogene Analytik wird die Kopplung von biochemischen bzw. biologischen Testverfahren an chemisch/physikalische oder chromatographische Verfahren bezeichnet. So lassen sich mittels der Dünnschichtchromatographie die aufgetrennten Komponenten direkt auf dem Chromatogramm physikalisch-chemisch detektieren und quantifizieren. Durch die Kopplung von biochemischen (z.B. enzymatischen Hemmtests) oder biologischen Testverfahren können toxikologisch wirksame Substanzen in situ nachgewiesen werden. Mit diesen biologischen Testsystemen können - direkt auf dem Chromatogramm auf der Dünnschichtplatte - Fungizide, Antibiotika und Lumnineszenz-Hemmstoffen nachgewiesen werden; ein neues molekularbiologisches Testverfahren ermöglicht den qualitativen und quantitativen Nachweis von Hormonen. Mit biochemischen und biologischen Detektionsverfahren können Wirkstoffe in Lebensmittelproben sowie bei der Reinheitskontrolle und in der Metabolismusforschung von Chemikalien nachgewiesen werden. Außerdem können die detektierten Wirkstoffe durch ihre Migrationsstrecke und ihr UV-Spektrum charakterisiert oder auch identifiziert werden. Pflanzliche Lebensmittel wurden mit der wirkungsbezogenen Analytik auf die Gegenwart von Pestiziden hin untersucht. Biochemische und biologische Detektionsverfahren auf dem Dünnschichtchromatogramm sind sehr selektiv und sensitiv und schließen damit die Lücke zwischen biologischen in vitro-Testverfahren und instrumenteller Analytik. Die Detektion von Wirkungsäquivalenten ist als Screening-Verfahren zunächst unabhängig von Referenzsubstanzen. Neben verschiedenen Testverfahren wird ein Konzept zur Risikoanalyse und Risikobewertung vorgestellt, bei dem die wirkungsbezogene Analytik als Bindeglied zwischen Biotests und chemisch/physikalischen Analytik- und Identifizierungsverfahren fungier
Osmotic stress-dependent serine phosphorylation of the histidine kinase homologue DokA
BACKGROUND: Two-component systems consisting of histidine kinases and their corresponding receivers are widespread in bacterial signal transduction. In the past few years, genes coding for homologues of two-component systems were also discovered in eukaryotic organisms. DokA, a homologue of bacterial histidine kinases, is an element of the osmoregulatory pathway in the amoeba Dictyostelium. The work described here addresses the question whether DokA is phosphorylated in vivo in response to osmotic stress. RESULTS: We have endogenously overexpressed individual domains of DokA to investigate post-translational modification of the protein in response to osmotic shock in vivo. Dictyostelium cells were labeled with [(32)P]-orthophosphate, exposed to osmotic stress and DokA fragments were subsequently isolated by immunoprecipitation. Thus, a stress-dependent phosphorylation could be demonstrated, with the site of phosphorylation being located in the kinase domain. We demonstrate biochemically that the phosphorylated amino acid is serine, and by mutational analysis that the phosphorylation reaction is not due to an autophosphorylation of DokA. Furthermore, mutation of the conserved histidine did not affect the osmostress-dependent phosphorylation reaction. CONCLUSIONS: A stimulus-dependent serine phosphorylation of a eukaryotic histidine kinase homologue was demonstrated for the first time in vivo. That implies that DokA, although showing typical structural features of a bacterial two-component system, might be part of a eukaryotic signal transduction pathway that involves serine/threonine kinases
Infinite reduction of couplings in non-renormalizable quantum field theory
I study the problem of renormalizing a non-renormalizable theory with a
reduced, eventually finite, set of independent couplings. The idea is to look
for special relations that express the coefficients of the irrelevant terms as
unique functions of a reduced set of independent couplings lambda, such that
the divergences are removed by means of field redefinitions plus
renormalization constants for the lambda's. I consider non-renormalizable
theories whose renormalizable subsector R is interacting and does not contain
relevant parameters. The "infinite" reduction is determined by i) perturbative
meromorphy around the free-field limit of R, or ii) analyticity around the
interacting fixed point of R. In general, prescriptions i) and ii) mutually
exclude each other. When the reduction is formulated using i), the number of
independent couplings remains finite or slowly grows together with the order of
the expansion. The growth is slow in the sense that a reasonably small set of
parameters is sufficient to make predictions up to very high orders. Instead,
in case ii) the number of couplings generically remains finite. The infinite
reduction is a tool to classify the irrelevant interactions and address the
problem of their physical selection.Comment: 40 pages; v2: more explanatory comments; appeared in JHE
Verifying the Kugo-Ojima Confinement Criterion in Landau Gauge Yang-Mills Theory
Expanding the Landau gauge gluon and ghost two-point functions in a power
series we investigate their infrared behavior. The corresponding powers are
constrained through the ghost Dyson-Schwinger equation by exploiting
multiplicative renormalizability. Without recourse to any specific truncation
we demonstrate that the infrared powers of the gluon and ghost propagators are
uniquely related to each other. Constraints for these powers are derived, and
the resulting infrared enhancement of the ghost propagator signals that the
Kugo-Ojima confinement criterion is fulfilled in Landau gauge Yang-Mills
theory.Comment: 4 pages, no figures; version to be published in Physical Review
Letter
On the infrared freezing of perturbative QCD in the Minkowskian region
The infrared freezing of observables is known to hold at fixed orders of
perturbative QCD if the Minkowskian quantities are defined through the analytic
continuation from the Euclidean region. In a recent paper [1] it is claimed
that infrared freezing can be proved also for Borel resummed all-orders
quantities in perturbative QCD. In the present paper we obtain the Minkowskian
quantities by the analytic continuation of the all-orders Euclidean amplitudes
expressed in terms of the inverse Mellin transform of the corresponding Borel
functions [2]. Our result shows that if the principle of analytic continuation
is preserved in Borel-type resummations, the Minkowskian quantities exhibit a
divergent increase in the infrared regime, which contradicts the claim made in
[1]. We discuss the arguments given in [1] and show that the special
redefinition of Borel summation at low energies adopted there does not
reproduce the lowest order result obtained by analytic continuation.Comment: 19 pages, 1 figur
An Algebraic Criterion for the Ultraviolet Finiteness of Quantum Field Theories
An algebraic criterion for the vanishing of the beta function for
renormalizable quantum field theories is presented. Use is made of the descent
equations following from the Wess-Zumino consistency condition. In some cases,
these equations relate the fully quantized action to a local gauge invariant
polynomial. The vanishing of the anomalous dimension of this polynomial enables
us to establish a nonrenormalization theorem for the beta function ,
stating that if the one-loop order contribution vanishes, then will
vanish to all orders of perturbation theory. As a by-product, the special case
in which is only of one-loop order, without further corrections, is
also covered. The examples of the N=2,4 supersymmetric Yang-Mills theories are
worked out in detail.Comment: 1+32 pages, LaTeX2e, typos correcte
The anomalous threshold, confinement, and an essential singularity in the heavy-light form factor
The analytic behavior of the heavy-light meson form factor is investigated
using several relativistic examples including unconfined, weakly confined, and
strongly confined mesons. It is observed that confinement erases the anomalous
threshold singularity and also induces an essential singularity at the normal
annihilation threshold. In the weak confinement limit, the "would be" anomalous
threshold contribution is identical to that of the real singularity on its
space-like side.Comment: Latex 2.09 with epsf.sty. 24 pages of text and 8 postscript figures.
Postscript version of complete paper will also be available soon at
http://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-983 or at
ftp://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-98
Glueballs in a Hamiltonian Light-Front Approach to Pure-Glue QCD
We calculate a renormalized Hamiltonian for pure-glue QCD and diagonalize it.
The renormalization procedure is designed to produce a Hamiltonian that will
yield physical states that rapidly converge in an expansion in free-particle
Fock-space sectors. To make this possible, we use light-front field theory to
isolate vacuum effects, and we place a smooth cutoff on the Hamiltonian to
force its free-state matrix elements to quickly decrease as the difference of
the free masses of the states increases. The cutoff violates a number of
physical principles of light-front pure-glue QCD, including Lorentz covariance
and gauge covariance. This means that the operators in the Hamiltonian are not
required to respect these physical principles. However, by requiring the
Hamiltonian to produce cutoff-independent physical quantities and by requiring
it to respect the unviolated physical principles of pure-glue QCD, we are able
to derive recursion relations that define the Hamiltonian to all orders in
perturbation theory in terms of the running coupling. We approximate all
physical states as two-gluon states, and use our recursion relations to
calculate to second order the part of the Hamiltonian that is required to
compute the spectrum. We diagonalize the Hamiltonian using basis-function
expansions for the gluons' color, spin, and momentum degrees of freedom. We
examine the sensitivity of our results to the cutoff and use them to analyze
the nonperturbative scale dependence of the coupling. We investigate the effect
of the dynamical rotational symmetry of light-front field theory on the
rotational degeneracies of the spectrum and compare the spectrum to recent
lattice results. Finally, we examine our wave functions and analyze the various
sources of error in our calculation.Comment: 75 pages, 17 figures, 1 tabl
Reduction of Couplings in Quantum Field Theories with applications in Finite Theories and the MSSM
We apply the method of reduction of couplings in a Finite Unified Theory and
in the MSSM. The method consists on searching for renormalization group
invariant relations among couplings of a renormalizable theory holding to all
orders in perturbation theory. It has a remarkable predictive power since, at
the unification scale, it leads to relations between gauge and Yukawa couplings
in the dimensionless sectors and relations involving the trilinear terms and
the Yukawa couplings, as well as a sum rule among the scalar masses and the
unified gaugino mass in the soft breaking sector. In both the MSSM and the FUT
model we predict the masses of the top and bottom quarks and the light Higgs in
remarkable agreement with the experiment. Furthermore we also predict the
masses of the other Higgses, as well as the supersymmetric spectrum, both being
in very confortable agreement with the LHC bounds on Higgs and supersymmetric
particles.Comment: 18 pages, 4 figures. To appear in the proceedings of LT-10, Varna.
Based on invited talks given at: LT-10, Varna; PACT-2013, Madrid; SQS'2013,
Dubna; CORFU 2013, Corfu, and in several invited seminar
Stringent constraints on the scalar K pi form factor from analyticity, unitarity and low-energy theorems
We investigate the scalar K pi form factor at low energies by the method of
unitarity bounds adapted so as to include information on the phase and modulus
along the elastic region of the unitarity cut. Using at input the values of the
form factor at t=0 and the Callan-Treiman point, we obtain stringent
constraints on the slope and curvature parameters of the Taylor expansion at
the origin. Also, we predict a quite narrow range for the higher order ChPT
corrections at the second Callan-Treiman point.Comment: 5 pages latex, uses EPJ style files, 3 figures, replaced with version
accepted by EPJ
- …