151 research outputs found
Pyrenosetin D, a new pentacyclic decalinoyltetramic acid derivative from the algicolous fungus Pyrenochaetopsis sp. FVE-087
The fungal genus Pyrenochaetopsis is commonly found in soil, terrestrial, and marine environments, however, has received little attention as a source of bioactive secondary metabolites so far. In a recent work, we reported the isolation and characterization of three new anticancer decalinoyltetramic acid derivatives, pyrenosetins A–C, from the Baltic Fucus vesiculosus-derived endophytic fungus Pyrenochaetopsis sp. FVE-001. Herein we report a new pentacyclic decalinoylspirotetramic acid derivative, pyrenosetin D (1), along with two known decalin derivatives wakodecalines A (2) and B (3) from another endophytic strain Pyrenochaetopsis FVE-087 isolated from the same seaweed and showed anticancer activity in initial screenings. The chemical structures of the purified compounds were elucidated by comprehensive analysis of HR-ESIMS, FT-IR, [α]D, 1D and 2D NMR data coupled with DFT calculations of NMR parameters and optical rotation. Compounds 1–3 were evaluated for their anticancer and toxic potentials against the human malignant melanoma cell line (A-375) and the non-cancerous keratinocyte cell line (HaCaT). Pyrenosetin D (1) showed toxicity towards both A-375 and HaCaT cells with IC50 values of 77.5 and 39.3 µM, respectively, while 2 and 3 were inactive. This is the third chemical study performed on the fungal genus Pyrenochaetopsis and the first report of a pentacyclic decalin ring system from the fungal genus Pyrenochaetopsis
Semiclassical analysis of the quantum interference corrections to the conductance of mesoscopic systems
The Kubo formula for the conductance of a mesoscopic system is analyzed
semiclassically, yielding simple expressions for both weak localization and
universal conductance fluctuations. In contrast to earlier work which dealt
with times shorter than , here longer times are taken to
give the dominant contributions. For such long times, many distinct classical
orbits may obey essentially the same initial and final conditions on positions
and momenta, and the interference between pairs of such orbits is analyzed.
Application to a chain of classically ergodic scatterers connected in
series gives the following results: for the
weak localization correction to the zero--temperature dimensionless
conductance, and for the variance of its
fluctuations. These results interpolate between the well known ones of random
scattering matrices for , and those of the one--dimensional diffusive wire
for .Comment: 53 pages, using RevTeX, plus 3 postscript figures mailed separately.
A short version of this work is available as cond-mat/950207
What is the meaning of the statistical hadronization model?
The statistical model of hadronization succeeds in reproducing particle
abundances and transverse momentum spectra in high energy collisions of
elementary particles as well as of heavy ions. Despite its apparent success,
the interpretation of these results is controversial and the validity of the
approach very often questioned. In this paper, we would like to summarize the
whole issue by first outlining a basic formulation of the model and then
comment on the main criticisms and different kinds of interpretations, with
special emphasis on the so-called "phase space dominance". While the ultimate
answer to the question why the statistical model works should certainly be
pursued, we stress that it is a priority to confirm or disprove the fundamental
scheme of the statistical model by performing some detailed tests on the rates
of exclusive channels at lower energy.Comment: 14 pages, to be published in the Proceedings of the International
workshop "Focus on multiplicity", Bari (Italy) June 17-19 200
Cold and Ultracold Rydberg Atoms in Strong Magnetic Fields
Cold Rydberg atoms exposed to strong magnetic fields possess unique
properties which open the pathway for an intriguing many-body dynamics taking
place in Rydberg gases consisting of either matter or anti-matter systems. We
review both the foundations and recent developments of the field in the cold
and ultracold regime where trapping and cooling of Rydberg atoms have become
possible. Exotic states of moving Rydberg atoms such as giant dipole states are
discussed in detail, including their formation mechanisms in a strongly
magnetized cold plasma. Inhomogeneous field configurations influence the
electronic structure of Rydberg atoms, and we describe the utility of
corresponding effects for achieving tightly trapped ultracold Rydberg atoms. We
review recent work on large, extended cold Rydberg gases in magnetic fields and
their formation in strongly magnetized ultracold plasmas through collisional
recombination. Implications of these results for current antihydrogen
production experiments are pointed out, and techniques for trapping and cooling
of such atoms are investigated.Comment: 46 pages, 38 figures, to appear in Physics Report
Experimental study of the quantum driven pendulum and its classical analogue in atoms optics
We present experimental results for the dynamics of cold atoms in a far detuned amplitude-modulated optical standing wave. Phase-space resonances constitute distinct peaks in the atomic momentum distribution containing up to 65% of all atoms resulting from a mixed quantum chaotic phase space. We characterize the atomic behavior in classical and quantum regimes and we present the applicable quantum and classical theory, which we have developed and refined. We show experimental proof that the size and the position of the resonances in phase space can be controlled by varying several parameters, such as the modulation frequency, the scaled well depth, the modulation amplitude, and the scaled Planck's constant of the system. We have found a surprising stability against amplitude noise. We present methods to accurately control the momentum of an ensemble of atoms using these phase-space resonances which could be used for efficient phase-space state preparation
Equation of State, Radial Flow and Freeze-out in High Energy Heavy Ion Collisions
We have shown that recent experimental data on radial flow, both from AGS and
SPS energies, are in agreement with the Equation of State (EOS) including the
QCD phase transition. New hydro-kinetic model (HKM) is developed, which
incorporates hydrodynamical treatment of expansion and proper kinetics of the
freeze-out. We show that the freeze-out surfaces for different secondaries and
different collisions are very different, and they are not at all isotherms (as
was assumed in most previous hydro works). Comparison of HKM results with
cascade-based event generator RQMD is also made in some details: we found that
both EOS and flow are in rather good agreement, while the space-time picture is
still somewhat different
Statistical hadronization with exclusive channels in e+e- annihilation
We perform a systematic analysis of exclusive hadronic channels in e+e-
collisions at centre-of-mass energies between 2.1 and 2.6 GeV within the
statistical hadronization model. Because of the low multiplicities involved,
calculations have been carried out in the full microcanonical ensemble,
including conservation of energy-momentum, angular momentum, parity, isospin,
and all relevant charges. We show that the data is in an overall good agreement
with the model for an energy density of about 0.5 GeV/fm^3 and an extra
strangeness suppression parameter gamma_S ~ 0.7, essentially the same values
found with fits to inclusive multiplicities at higher energy.Comment: 27 pages, 12 figure
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