156 research outputs found
Inhomogeneous phase of a Gluon Plasma at finite temperature and density
By considering the non-perturbative effects associated with the fundamental
modular region, a new phase of a Gluon Plasma at finite density is proposed. It
corresponds to the transition from glueballs to non-perturbative gluons which
condense at a non vanishing momentum. In this respect the proposed phase is
analogous to the color superconducting LOFF phase for fermionic systems.Comment: 5 pages, 2 figure
Controlling chaos in diluted networks with continuous neurons
Diluted neural networks with continuous neurons and nonmonotonic transfer
function are studied, with both fixed and dynamic synapses. A noisy stimulus
with periodic variance results in a mechanism for controlling chaos in neural
systems with fixed synapses: a proper amount of external perturbation forces
the system to behave periodically with the same period as the stimulus.Comment: 11 pages, 8 figure
Mental flexibility in Parkinson's disease with central fatigue: Data from the frontal assessment battery
Background and aims
Central fatigue is defined as a reduced energy level or an
increased perception of effort, often associated to a failure in
initiating and maintaining tasks that require self-motivation. It is
common in Parkinson's disease population and it has been
hypothesized to be related to a dysfunction in the striato-talamo-
prefrontal loop. The aim of the present study was to explore the
association between fatigue and executive functions as index of
integrity of the striato-thalamo-prefrontal loop.
Methods
Twenty-nine non-demented PD patients without fatigue - PDnF,
28 non-demented PD patients with fatigue - PDF and 26 age and sex-
matched controls underwent an evaluation with the Frontal
Assessment Battery (FAB), MMSE, PSQI, BDI, STAI Y1-2, PDQ-39.
Differences between groups in FAB scores (total and subitems) were
analyzed by means of Kruskal-Wallis test. Moreover, a correlation
between fatigue and FAB was also analyzed.
Results
Overall parkinsonian population displayed worse performance
than controls in frontal scores especially inhibitory control (p =
0.008) and sensitivity to interference (p = 0.014). PDF displayed
significantly worse than PDnF in verbal fluency (p = 0.05). Fatigue
severity inversely correlated with executive performance (p b 0.001).
Conclusions
Phonemic fluency tasks are thought to reflect the simultaneous
engagement of several executive functions such as attention,
working memory, retrieval, information processing. The association
of central fatigue with a deficit in mental flexibility, could support
the hypothesis that central fatigue is a reliable index of the
impairment of higher executive functions needed in order to
effectively assess costs and benefits related to adaptive decision-
making behavior
Cerebellum in timing control: Evidence from contingent negative variation after cerebellar tDCS
Background and aims
Timing control is defined as the ability to quantify time. The temporal estimation of supra-seconds range is generally seen as a conscious cognitive process, while the sub-seconds range is a more automatic cognitive process. It is accepted that cerebellum contributes to temporal processing, but its function is still debated. The aim of this research was to better explore the role of cerebellum in timing control. We transitorily inhibited cerebellar activity and studied the effects on CNV components in healthy subjects.
Methods
Sixteen healthy subjects underwent a S1-S2 duration discrimination motor task, prior and after cathodal and sham cerebellar tDCS, in two separate sessions. In S1-S2 task they had to judge whether the duration of a probe interval trial was shorter (Short-ISI-trial:800 ms), longer (long-ISI-trail:1600 ms), or equal to the Target interval of 1200 ms. For each interval trial for both tDCS sessions, we measured: total and W2-CNV areas, the RTs of correct responses and the absolute number of errors prior and after tDCS.
Results
After cathodal tDCS a significant reduction in total-CNV and W2-CNV amplitudes selectively emerged for Short (p < 0.001; p = 0.003 respectively) and Target-ISI-trial (total-CNV: p < 0.001; W2-CNV:p = 0.003); similarly, a significant higher number of errors emerged for Short (p = 0.004) and Target-ISI-trial (p = 0.07) alone. No differences were detected for Longer-ISI-trials and after sham stimulation.
Conclusions
These data indicate that cerebellar inhibition selectively altered the ability to make time estimations for second and sub-second intervals. We speculate that cerebellum regulates the attentional mechanisms of automatic timing control by making predictions of interval timing
Self-consistent evaluation of quark masses in three flavor crystalline color superconductivity
We present a self-consistent evaluation of the constituent quark masses in
the three flavor Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phases of QCD,
employing an improved Nambu-Jona Lasinio model. This result allows to determine
the window for values of the baryonic chemical potential where the LOFF state
is energetically favored.Comment: 17 pages, 5 figures, JHEP3 style. A second treatment of the
ultraviolet cutoff added. Three figures adapted to the new cutoff. Two
references added. Version accepted for publication on JHE
R-mode oscillations and rocket effect in rotating superfluid neutron stars. I. Formalism
We derive the hydrodynamical equations of r-mode oscillations in neutron
stars in presence of a novel damping mechanism related to particle number
changing processes. The change in the number densities of the various species
leads to new dissipative terms in the equations which are responsible of the
{\it rocket effect}. We employ a two-fluid model, with one fluid consisting of
the charged components, while the second fluid consists of superfluid neutrons.
We consider two different kind of r-mode oscillations, one associated with
comoving displacements, and the second one associated with countermoving, out
of phase, displacements.Comment: 10 page
The rigidity of crystalline color superconducting quark matter
We calculate the shear modulus of crystalline color superconducting quark
matter, showing that this phase of dense, but not asymptotically dense,
three-flavor quark matter responds to shear stress like a very rigid solid. To
evaluate the shear modulus, we derive the low energy effective Lagrangian that
describes the phonons that originate from the spontaneous breaking of
translation invariance by the spatial modulation of the gap parameter .
These massless bosons describe space- and time-dependent fluctuations of the
crystal structure and are analogous to the phonons in ordinary crystals. The
coefficients of the spatial derivative terms of the phonon effective Lagrangian
are related to the elastic moduli of the crystal; the coefficients that encode
the linear response of the crystal to a shearing stress define the shear
modulus. We analyze the two particular crystal structures which are
energetically favored over a wide range of densities, in each case evaluating
the phonon effective action and the shear modulus up to order in a
Ginzburg-Landau expansion, finding shear moduli which are 20 to 1000 times
larger than those of neutron star crusts. The crystalline color superconducting
phase has long been known to be a superfluid -- by picking a phase its order
parameter breaks the quark-number symmetry spontaneously. Our results
demonstrate that this superfluid phase of matter is at the same time a rigid
solid. We close with a rough estimate of the pinning force on the rotational
vortices which would be formed embedded within this rigid superfluid upon
rotation. Our results raise the possibility that (some) pulsar glitches could
originate within a quark matter core deep within a neutron star.Comment: 38 pages, 5 figures. v3. Two new paragraphs in Section V
(Conclusion); some additional small changes. A paragraph discussing
supercurrents added in Section I (Introduction). Version to appear in Phys.
Rev.
Q\bar{Q} modes in the Quark-Gluon Plasma
We study the evolution of heavy quarkonium states with temperature in a
Quark-Gluon Plasma by evaluating an in-medium Q\bar{Q} T-matrix within a
reduced Bethe-Salpeter equation in S- and P-wave channels. The interaction
kernel is extracted from finite-temperature QCD lattice calculations of the
singlet free energy of a Q\bar{Q} pair. Quarkonium bound states are found to
gradually move across the Q\bar{Q} threshold after which they rapidly dissolve
in the hot system. We calculate Euclidean-time correlation functions and
compare to results from lattice QCD. We also study finite-width effects in the
heavy-quark propagators.Comment: 3 pages, 6 figures, to appear in the proceedings of the IV
International Conference on Quarks and Nuclear Physics (QNP06), Madrid,
Spain, June 5-10, 200
Diluted neural networks with adapting and correlated synapses
We consider the dynamics of diluted neural networks with clipped and adapting
synapses. Unlike previous studies, the learning rate is kept constant as the
connectivity tends to infinity: the synapses evolve on a time scale
intermediate between the quenched and annealing limits and all orders of
synaptic correlations must be taken into account. The dynamics is solved by
mean-field theory, the order parameter for synapses being a function. We
describe the effects, in the double dynamics, due to synaptic correlations.Comment: 6 pages, 3 figures. Accepted for publication in PR
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