6,242 research outputs found
Isocaling and the Symmetry Energy in the Multifragmentation Regime of Heavy Ion Collisions
The ratio of the symmetry energy coefficient to temperature, , in
Fermi energy heavy ion collisions, has been experimentally extracted as a
function of the fragment atomic number using isoscaling parameters and the
variance of the isotope distributions. The extracted values have been compared
to the results of calculations made with an Antisymmetrized Molecular Dynamics
(AMD) model employing a statistical decay code to account for deexcitation of
excited primary fragments. The experimental values are in good agreement with
the values calculated but are significantly different from those characterizing
the yields of the primary AMD fragments.Comment: 12 pages, 6 figure
The Quantum Nature of a Nuclear Phase Transition
In their ground states, atomic nuclei are quantum Fermi liquids. At finite
temperatures and low densities, these nuclei may undergo a phase change similar
to, but substantially different from, a classical liquid gas phase transition.
As in the classical case, temperature is the control parameter while density
and pressure are the conjugate variables. At variance with the classical case,
in the nucleus the difference between the proton and neutron concentrations
acts as an additional order parameter, for which the symmetry potential is the
conjugate variable. Different ratios of the neutron to proton concentrations
lead to different critical points for the phase transition. This is analogous
to the phase transitions occurring in He-He liquid mixtures. We
present experimental results which reveal the N/Z dependence of the phase
transition and discuss possible implications of these observations in terms of
the Landau Free Energy description of critical phenomena.Comment: 5 pages, 4 figure
Isobaric Yield Ratios and The Symmetry Energy In Fermi Energy Heavy Ion Reactions
The relative isobaric yields of fragments produced in a series of heavy ion
induced multifragmentation reactions have been analyzed in the framework of a
Modified Fisher Model, primarily to determine the ratio of the symmetry energy
coefficient to the temperature, , as a function of fragment mass A. The
extracted values increase from 5 to ~16 as A increases from 9 to 37. These
values have been compared to the results of calculations using the
Antisymmetrized Molecular Dynamics (AMD) model together with the statistical
decay code Gemini. The calculated ratios are in good agreement with those
extracted from the experiment. In contrast, the ratios determined from fitting
the primary fragment distributions from the AMD model calculation are ~ 4 and
show little variation with A. This observation indicates that the value of the
symmetry energy coefficient derived from final fragment observables may be
significantly different than the actual value at the time of fragment
formation. The experimentally observed pairing effect is also studied within
the same simulations. The Coulomb coefficient is also discussed.Comment: 10 pages, 12 figure
A splitting theorem for Kahler manifolds whose Ricci tensors have constant eigenvalues
It is proved that a compact Kahler manifold whose Ricci tensor has two
distinct, constant, non-negative eigenvalues is locally the product of two
Kahler-Einstein manifolds. A stronger result is established for the case of
Kahler surfaces. Irreducible Kahler manifolds with two distinct, constant
eigenvalues of the Ricci tensor are shown to exist in various situations: there
are homogeneous examples of any complex dimension n > 1, if one eigenvalue is
negative and the other positive or zero, and of any complex dimension n > 2, if
the both eigenvalues are negative; there are non-homogeneous examples of
complex dimension 2, if one of the eigenvalues is zero. The problem of
existence of Kahler metrics whose Ricci tensor has two distinct, constant
eigenvalues is related to the celebrated (still open) Goldberg conjecture.
Consequently, the irreducible homogeneous examples with negative eigenvalues
give rise to complete, Einstein, strictly almost Kahler metrics of any even
real dimension greater than 4.Comment: 18 pages; final version; accepted for publication in International
Journal of Mathematic
Experimental evaluation of sub-sampling IQ detection for low-level RF control in particle accelerator systems
The low-level radio frequency (LLRF) control system is one of the fundamental parts of a particle accelerator, ensuring the stability of the electro-magnetic (EM) field inside the resonant cavities. It leverages on the precise measurement of the field by in-phase/quadrature (IQ) detection of an RF probe signal from the cavities, usually performed using analogue downconversion. This approach requires a local oscillator (LO) and is subject to hardware non-idealities like mixer nonlinearity and long-term temperature drifts. In this work, we experimentally evaluate IQ detection by direct sampling for the LLRF system of the Polish free electron laser (PolFEL) now under development at the National Centre for Nuclear Research (NCBJ) in Poland. We study the impact of the sampling scheme and of the clock phase noise for a 1.3-GHz input sub-sampled by a 400-MSa/s analogue-to-digital converter (ADC), estimating amplitude and phase stability below 0.01% and nearly 0.01◦, respectively. The results are in line with state-of-the-art implementations, and demonstrate the feasibility of direct sampling for GHz-range LLRF systems
Critical behavior of the isotope yield distributions in the Multifragmentation Regime of Heavy Ion Reactions
Isotope yields have been analyzed within the framework of a Modified Fisher
Model to study the power law yield distribution of isotopes in the
multifragmentation regime. Using the ratio of the mass dependent symmetry
energy coefficient relative to the temperature, , extracted in
previous work and that of the pairing term, , extracted from this
work, and assuming that both reflect secondary decay processes, the
experimentally observed isotope yields have been corrected for these effects.
For a given I = N - Z value, the corrected yields of isotopes relative to the
yield of show a power law distribution, , in the mass range of and the distributions are
almost identical for the different reactions studied. The observed power law
distributions change systematically when I of the isotopes changes and the
extracted value decreases from 3.9 to 1.0 as I increases from -1 to 3.
These observations are well reproduced by a simple de-excitation model, which
the power law distribution of the primary isotopes is determined to
, suggesting that the disassembling system at the
time of the fragment formation is indeed at or very near the critical point.Comment: 5 pages, 5 figure
Experimental reconstruction of primary hot isotopes and characteristic properties of the fragmenting source in the heavy ion reactions near the Fermi energy
The characteristic properties of the hot nuclear matter existing at the time
of fragment formation in the multifragmentation events produced in the reaction
Zn + Sn at 40 MeV/nucleon are studied. A kinematical focusing
method is employed to determine the multiplicities of evaporated light
particles, associated with isotopically identified detected fragments. From
these data the primary isotopic yield distributions are reconstructed using a
Monte Carlo method. The reconstructed yield distributions are in good agreement
with the primary isotope distributions obtained from AMD transport model
simulations. Utilizing the reconstructed yields, power distribution, Landau
free energy, characteristic properties of the emitting source are examined. The
primary mass distributions exhibit a power law distribution with the critical
exponent, , for isotopes, but significantly deviates from
that for the lighter isotopes. Landau free energy plots show no strong
signature of the first order phase transition. Based on the Modified Fisher
Model, the ratios of the Coulomb and symmetry energy coefficients relative to
the temperature, and , are extracted as a function of A.
The extracted values are compared with results of the AMD
simulations using Gogny interactions with different density dependencies of the
symmetry energy term. The calculated values show a close relation
to the symmetry energy at the density at the time of the fragment formation.
From this relation the density of the fragmenting source is determined to be
. Using this density, the symmetry energy
coefficient and the temperature of fragmenting source are determined in a
self-consistent manner as and
MeV
Studies of unicellular micro-organisms Saccharomyces cerevisiae by means of Positron Annihilation Lifetime Spectroscopy
Results of Positron Annihilation Lifetime Spectroscopy (PALS) and microscopic
studies on simple microorganisms: brewing yeasts are presented. Lifetime of
ortho - positronium (o-Ps) were found to change from 2.4 to 2.9 ns (longer
lived component) for lyophilised and aqueous yeasts, respectively. Also
hygroscopicity of yeasts in time was examined, allowing to check how water -
the main component of the cell - affects PALS parameters, thus lifetime of o-Ps
were found to change from 1.2 to 1.4 ns (shorter lived component) for the dried
yeasts. The time sufficient to hydrate the cells was found below 10 hours. In
the presence of liquid water an indication of reorganization of yeast in the
molecular scale was observed.
Microscopic images of the lyophilised, dried and wet yeasts with best
possible resolution were obtained using Inverted Microscopy (IM) and
Environmental Scanning Electron Microscopy (ESEM) methods. As a result visible
changes to the surface of the cell membrane were observed in ESEM images.Comment: Nukleonika (2015
The Isospin Dependence Of The Nuclear Equation Of State Near The Critical Point
We discuss experimental evidence for a nuclear phase transition driven by the
different concentration of neutrons to protons. Different ratios of the neutron
to proton concentrations lead to different critical points for the phase
transition. This is analogous to the phase transitions occurring in 4He-3He
liquid mixtures. We present experimental results which reveal the N/A (or Z/A)
dependence of the phase transition and discuss possible implications of these
observations in terms of the Landau Free Energy description of critical
phenomena.Comment: 14 pages, 18 figure
Harmonic BRST Quantization of Systems with Irreducible Holomorphic Boson and Fermion Constraints
We show that the harmonic Becchi-Rouet-Stora-Tyutin method of quantizing
bosonic systems with second-class constraints or first-class holomorphic
constraints extends to systems having both bosonic and fermionic second-class
or first-class holomorphic constraints. Using a limit argument, we show that
the harmonic BRST modified path integral reproduces the correct Senjanovic
measure.Comment: 11 pages, phyzz
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