7,113 research outputs found
Mesonic correlation functions at finite temperature and density in the Nambu-Jona-Lasinio model with a Polyakov loop
We investigate the properties of scalar and pseudo-scalar mesons at finite
temperature and quark chemical potential in the framework of the
Nambu-Jona-Lasinio (NJL) model coupled to the Polyakov loop (PNJL model) with
the aim of taking into account features of both chiral symmetry breaking and
deconfinement. The mesonic correlators are obtained by solving the
Schwinger-Dyson equation in the RPA approximation with the Hartree (mean field)
quark propagator at finite temperature and density. In the phase of broken
chiral symmetry a narrower width for the sigma meson is obtained with respect
to the NJL case; on the other hand, the pion still behaves as a Goldstone
boson. When chiral symmetry is restored, the pion and sigma spectral functions
tend to merge. The Mott temperature for the pion is also computed.Comment: 24 pages, 9 figures, version to appear in Phys. Rev.
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Grazers and Phytoplankton Growth in the Oceans: an Experimental and Evolutionary Perspective
The taxonomic composition of phytoplankton responsible for primary production on continental shelves has changed episodically through Earth history. Geological correlations suggest that major changes in phytoplankton composition correspond in time to changes in grazing and seawater chemistry. Testing hypotheses that arise from these correlations requires experimentation, and so we carried out a series of experiments in which selected phytoplankton species were grown in treatments that differed with respect to the presence or absence of grazers as well as seawater chemistry. Both protistan (Euplotes sp.) and microarthropod (Acartia tonsa) grazers changed the growth dynamics and biochemical composition of the green alga Tetraselmis suecica, the diatom Thalassiosira weissflogii, and the cyanobacterium Synechococcus sp., increasing the specific growth rate and palatability of the eukaryotic algae, while decreasing or leaving unchanged both parameters in the cyanobacteria. Synechococcus (especially) and Thalassiosira produced toxins effective against the copepod, but ciliate growth was unaffected. Acartia induced a 4-6 fold increase of Si cell quota in the diatom, but Euplotes had no similar effect. The differential growth responses of the eukaryotic algae and cyanobacteria to ciliate grazing may help to explain the apparently coeval radiation of eukaryophagic protists and rise of eukaryotes to ecological prominence as primary producers in Neoproterozoic oceans. The experimental results suggest that phytoplankton responses to the later radiation of microarthropod grazers were clade-specific, and included changes in growth dynamics, toxin synthesis, encystment, and (in diatoms) enhanced Si uptake
Mol-CycleGAN - a generative model for molecular optimization
Designing a molecule with desired properties is one of the biggest challenges
in drug development, as it requires optimization of chemical compound
structures with respect to many complex properties. To augment the compound
design process we introduce Mol-CycleGAN - a CycleGAN-based model that
generates optimized compounds with high structural similarity to the original
ones. Namely, given a molecule our model generates a structurally similar one
with an optimized value of the considered property. We evaluate the performance
of the model on selected optimization objectives related to structural
properties (presence of halogen groups, number of aromatic rings) and to a
physicochemical property (penalized logP). In the task of optimization of
penalized logP of drug-like molecules our model significantly outperforms
previous results
The role of monopoles in a Gluon Plasma
We study the role of magnetic monopoles at high enough temperature ,
when they can be considered heavy, rare objects embedded into matter consisting
mostly of the usual "electric" quasiparticles, quarks and gluons. We review
available lattice results on monopoles at finite temperatures. Then we proceed
to classical and quantum charge-monopole scattering, solving the problem of
gluon-monopole scattering for the first time. We find that, while this process
hardly influences thermodynamic quantities, it does produce a large transport
cross section, significantly exceeding that for pQCD gluon-gluon scattering up
to quite high . Thus, in spite of their relatively small density at high
, monopoles are extremely important for QGP transport properties, keeping
viscosity small enough for hydrodynamics to work at LHC.Comment: 60 pages, 15 Figure
Debye mass and heavy quark potential in a PNJL quark plasma
We calculate the Debye mass for the screening of the heavy quark potential in
a plasma of massless quarks coupled to the temporal gluon background governed
by the Polyakov loop potential within the PNJL model in RPA approximation. We
give a physical motivation for a recent phenomenological fit of lattice data by
applying the calculated Debye mass with its suppression in the confined phase
due to the Polyakov-loop to a description of the temperature dependence of the
singlet free energy for QCD with a heavy quark pair at infinite separation. We
compare the result to lattice data.Comment: 6 pages, 1 figure, contribution to Proceedings of the 6th
International Conference on "Critical Point and Onset of Deconfinement", to
appear in Phys. At. Nucl., vol. 7
Divergence of the single-copy DNA sequences of the Western Grebe (Aechmophorus occidentalis) and Clark’s Grebe (A. clarkii), as indicated by DNA-DNA hybridization
Single-copy nuclear DNA sequences of individuals of Aechmophorus occidentalis and A. ciarkii were compared by DNA-DNA hybridization. In each of three experimental sets the average thermal stability of homoduplex and within-species DNA-DNA hybrids did not differ, but the between-species DNA-DNA hybrids dissociated at an average temperature 0.57°C below the median melting temperature of homoduplex and within-species hybrids. The difference was highly significant in all three sets. The median DNA sequence distance between A. occidentalis and A. clarkii is comparable to such distances between other closely related congeneric species
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The coupling impedance of the RHIC injection kicker system
In this paper, results from impedance measurements on the RHIC injection kickers are reported. The kicker is configured as a {open_quotes}C{close_quotes} cross section magnet with interleaved ferrite and high-permittivity dielectric sections to achieve a travelling wave structure. The impedance was measured using the wire method in which a resistive match provides a smooth transition from the network analyzer to the reference line in the set-up. Accurate results are obtained by interpreting the forward scattering coefficient via the log-formula. The four kickers with their ceramic beam tubes contribute a Z/n = 0.22 {Omega}/ring in the interesting frequency range from 0.1 to 1 GHz, and less above. At frequencies above {approximately}100 MHZ, the impedance is ferrite dominated and not affected by the kicker terminations. Below 100 MHz, the Blumlein pulser with the {approximately}75 m feeding cables is visible in the impedance but makes no significant contribution to the results. The measurements show that the kicker coupling impedance is tolerable without the need for impedance reducing measures
The Coupling Impedance of the RHIC Injection Kicker System
In this paper, results from impedance measurements on the RHIC injection kickers are reported. The kicker is configured as a {open_quotes}C{close_quotes} cross section magnet with interleaved ferrite and high-permittivity dielectric sections to achieve a travelling wave structure. The impedance was measured using the wire method in which a resistive match provides a smooth transition from the network analyzer to the reference line in the set-up. Accurate results are obtained by interpreting the forward scattering coefficient via the log-formula. The four kickers with their ceramic beam tubes contribute a Z/n = 0.22 {Omega}/ring in the interesting frequency range from 0.1 to 1 GHz, and less above. At frequencies above {approximately}100 MHZ, the impedance is ferrite dominated and not affected by the kicker terminations. Below 100 MHz, the Blumlein pulser with the {approximately}75 m feeding cables is visible in the impedance but makes no significant contribution to the results. The measurements show that the kicker coupling impedance is tolerable without the need for impedance reducing measures
Equivalent Circuit Analysis of the RHIC Injection Kicker
The RHIC injection kicker is built as a traveling wave structure in order to assure the required 95 nsec risetime in the deflection strength. The kicker is constructed from 14 cells, each 7.5 cm long, with alternating ferrite and high-permittivity dielectric sections. The cell structure permits an analysis of the electrical properties of the kicker using lumped L, C, and R circuit elements. Their values are obtained directly from impedance measurements of the full-length kicker, the inductance and shunt capacitance values by measuring the input impedance at 1 MHz with the output shorted and open, respectively. A lossy series resonance circuit in each cell is found to reproduce the measured input impedance of the terminated kicker up to {approximately}100 MHz. The validity of the equivalent circuit was confirmed by comparing the measured output current pulse shape time with that computed by the P-Spice program
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