388 research outputs found
Excitated state properties of 20-chloro-chlorophyll a
The excited-state and lasing properties of 20-chloro-chlorophyll a in ether solution were compared to those of chlorophyll a. Desactivation parameters and cross-sections were obtained from non-linear absorption spectroscopy in combination with a physico-mathematical methods package. The Cl substituent at C-20 (1) increases both intersystem crossing and internal conversion, (2) produces a blue-shift of the S1 absorption spectrum, and (3) leads to pronounced photochemistry
Pressure-induced changes of the vibrational modes of spin-crossover complexes studied by nuclear resonance scattering of synchrotron radiation
Nuclear inelastic scattering (NIS) spectra were recorded for the
spin-crossover complexes STP and ETP (STP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg- ethane)](ClO4)2 and
ETP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg-butane)](ClO4)2) at
30 K and at room temperature and also at ambient pressure and applied pressure
(up to 2.6 GPa). Spin transition from the high-spin (HS) to the low-spin (LS)
state was observed by lowering temperature and also by applying pressure at
room temperature and has been assigned to the hardening of iron-bond stretching
modes due to the smaller volume in the LS isomer
Strong coupling constants of bottom and charmed mesons with scalar, pseudoscalar and axial vector kaons
The strong coupling constants, , ,
, , and
, where , and are scalar, pseudoscalar
and axial vector kaon mesons, respectively are calculated in the framework of
three-point QCD sum rules. In particular, the correlation functions of the
considered vertices when both and mesons are off-shell
are evaluated. In the case of , which is either or
, the mixing between these two states are also taken into account. A
comparison of the obtained result with the existing prediction on
as the only coupling constant among the considered
vertices, previously calculated in the literature, is also made.Comment: 20 Pages, 3 Figures and 8 Table
On insertion-deletion systems over relational words
We introduce a new notion of a relational word as a finite totally ordered
set of positions endowed with three binary relations that describe which
positions are labeled by equal data, by unequal data and those having an
undefined relation between their labels. We define the operations of insertion
and deletion on relational words generalizing corresponding operations on
strings. We prove that the transitive and reflexive closure of these operations
has a decidable membership problem for the case of short insertion-deletion
rules (of size two/three and three/two). At the same time, we show that in the
general case such systems can produce a coding of any recursively enumerable
language leading to undecidabilty of reachability questions.Comment: 24 pages, 8 figure
Two- and three-body color flux tubes in the Chromo Dielectric Model
Using the framework of the Chromo Dielectric Model we perform an analysis of
color electric flux tubes in meson-like and baryon-like quark
configurations. We discuss the Abelian color structure of the model and point
out a symmetry in color space as a remnant of the SU(3) symmetry of QCD. The
generic features of the model are discussed by varying the model parameters. We
fix these parameters by reproducing the string tension MeV/fm and
the transverse width fm of the flux tube obtained in
lattice calculations. We use a bag constant MeV, a glueball
mass MeV and a strong coupling constant . We show that the asymptotic string profile of an infinitely long flux
tube is already reached for separations fm. A connection
to the Dual Color Superconductor is made by extracting a magnetic current from
the model equations and a qualitative agreement between the two descriptions of
confinement is shown. In the study of the system we observe a
-like geometry for the color electric fields and a
\textsf{Y}-like geometry in the scalar fields both in the energy density
distribution and in the corresponding potentials. The resulting total
potential is described neither by the -picture nor by the
\textsf{Y}-picture alone.Comment: 32 pages, 35 eps-figures, revised version, some references + 1
eps-file added, to be published in Phys.Rev.
Short-range correlations in quark matter
We investigate the role of short-range correlations in quark matter within
the framework of the SU(2) NJL model. Employing a next-to-leading order
expansion in 1/N_c for the quark self energy we construct a fully
self-consistent model that is based on the relations between spectral functions
and self energies. In contrast to the usual quasiparticle approximations we
take the collisional broadening of the quark spectral function consequently
into account. Mesons are dynamically generated in the fashion of a random phase
approximation, using full in-medium propagators in the quark loops. The results
are self-consistently fed back into the quark self energy. Calculations have
been performed for finite chemical potentials at zero temperature. The
short-range correlations do not only generate finite widths in the spectral
functions but also have influence on the chiral phase transition.Comment: 40 pages, 23 figures; revised and extended paper, accepted for
publication in Phys. Rev.
QCD sum rule analysis for light vector and axial-vector mesons in vacuum and nuclear matter
Extending previous work we study the constraints of QCD sum rules on mass and
width of light vector and axial-vector mesons in vacuum and in a medium with
finite nuclear density. For the latter case especially the effect of nuclear
pions leading to vector-axial-vector mixing is included in the analysis.Comment: RevTeX, 32 pages, 10 eps figure
Interactions of multi-quark states in the chromodielectric model
We investigate 4-quark () systems as well as multi-quark
states with a large number of quarks and anti-quarks using the chromodielectric
model. In the former type of systems the flux distribution and the
corresponding energy of such systems for planar and non-planar geometries are
studied. From the comparison to the case of two independent -strings
we deduce the interaction potential between two strings. We find an attraction
between strings and a characteristic string flip if there are two degenerate
string combinations between the four particles. The interaction shows no strong
Van-der-Waals forces and the long range behavior of the potential is well
described by a Yukawa potential, which might be confirmed in future lattice
calculations. The multi-quark states develop an inhomogeneous porous structure
even for particle densities large compared to nuclear matter constituent quark
densities. We present first results of the dependence of the system on the
particle density pointing towards a percolation type of transition from a
hadronic matter phase to a quark matter phase. The critical energy density is
found at .Comment: 19 pages, 40 eps-figures, RevTex 4, v2: typos correcte
Low energy onset of nuclear shadowing in photoabsorption
The early onset of nuclear shadowing in photoabsorption at low photon
energies has recently been interpreted as a possible signature of a decrease of
the rho meson mass in nuclei. We show that one can understand this early onset
within simple Glauber theory if one takes the negative real part of the rho N
scattering amplitudes into account, corresponding to a higher effective mass of
the rho meson in nuclear medium.Comment: REVTEX, 9 pages, including 4 eps figure
Nuclear shadowing at low photon energies
We calculate the shadowing effect in nuclear photoabsorption at low photon
energies (1-3 GeV) within a multiple scattering approach. We avoid some of the
high energy approximations that are usually made in simple Glauber theory like
the narrow width and the eikonal approximation. We find that the main
contribution to nuclear shadowing at low energies stems from mesons
with masses well below their pole mass. We also show that the possibility of
scattering in non forward directions allows for a new contribution to shadowing
at low energies: the production of neutral pions as intermediate hadronic
states enhances the shadowing effect in the onset region. For light nuclei and
small photon energies they give rise to about 30% of the total shadowing
effect.Comment: RevTeX, 16 pages including 6 eps figures; new calculation of
effective pion propagator, negligible effect on results; version to be
published in Phys. Rev.
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