2,506 research outputs found
A replica free evaluation of the neuronal population information with mixed continuous and discrete stimuli: from the linear to the asymptotic regime
Recent studies have explored theoretically the ability of populations of
neurons to carry information about a set of stimuli, both in the case of purely
discrete or purely continuous stimuli, and in the case of multidimensional
continuous angular and discrete correlates, in presence of additional quenched
disorder in the distribution. An analytical expression for the mutual
information has been obtained in the limit of large noise by means of the
replica trick. Here we show that the same results can actually be obtained in
most cases without the use of replicas, by means of a much simpler expansion of
the logarithm. Fitting the theoretical model to real neuronal data, we show
that the introduction of correlations in the quenched disorder improves the
fit, suggesting a possible role of signal correlations-actually detected in
real data- in a redundant code. We show that even in the more difficult
analysis of the asymptotic regime, an explicit expression for the mutual
information can be obtained without resorting to the replica trick despite the
presence of quenched disorder, both with a gaussian and with a more realistic
thresholded-gaussian model. When the stimuli are mixed continuous and discrete,
we find that with both models the information seem to grow logarithmically to
infinity with the number of neurons and with the inverse of the noise, even
though the exact general dependence cannot be derived explicitly for the
thresholded gaussian model. In the large noise limit lower values of
information were obtained with the thresholded-gaussian model, for a fixed
value of the noise and of the population size. On the contrary, in the
asymptotic regime, with very low values of the noise, a lower information value
is obtained with the gaussian model.Comment: 34 pages, 5 figure
Replica symmetric evaluation of the information transfer in a two-layer network in presence of continuous+discrete stimuli
In a previous report we have evaluated analytically the mutual information
between the firing rates of N independent units and a set of multi-dimensional
continuous+discrete stimuli, for a finite population size and in the limit of
large noise. Here, we extend the analysis to the case of two interconnected
populations, where input units activate output ones via gaussian weights and a
threshold linear transfer function. We evaluate the information carried by a
population of M output units, again about continuous+discrete correlates. The
mutual information is evaluated solving saddle point equations under the
assumption of replica symmetry, a method which, by taking into account only the
term linear in N of the input information, is equivalent to assuming the noise
to be large. Within this limitation, we analyze the dependence of the
information on the ratio M/N, on the selectivity of the input units and on the
level of the output noise. We show analytically, and confirm numerically, that
in the limit of a linear transfer function and of a small ratio between output
and input noise, the output information approaches asymptotically the
information carried in input. Finally, we show that the information loss in
output does not depend much on the structure of the stimulus, whether purely
continuous, purely discrete or mixed, but only on the position of the threshold
nonlinearity, and on the ratio between input and output noise.Comment: 19 pages, 4 figure
Migration of dendritic cells across blood and lymphatic endothelial barriers.
7openopenDel Prete A; Locati M; Otero K; Riboldi E; Mantovani A; Vecchi A; Sozzani S.DEL PRETE, Annalisa; Locati, M; Otero, K; Riboldi, E; Mantovani, A; Vecchi, A; Sozzani, Silvan
The performance of the LHCf detector for hadronic showers
The Large Hadron Collider forward (LHCf) experiment has been designed to use
the LHC to benchmark the hadronic interaction models used in cosmic-ray
physics. The LHCf experiment measures neutral particles emitted in the very
forward region of LHC collisions. In this paper, the performances of the LHCf
detectors for hadronic showers was studied with MC simulations and beam tests.
The detection efficiency for neutrons is from 60% to 70% above 500 GeV. The
energy resolutions are about 40% and the position resolution is 0.1 to 1.3mm
depend on the incident energy for neutrons. The energy scale determined by the
MC simulations and the validity of the MC simulations were examined using 350
GeV proton beams at the CERN-SPS.Comment: 15pages, 19 figure
Laboratory Tests of Low Density Astrophysical Equations of State
Clustering in low density nuclear matter has been investigated using the
NIMROD multi-detector at Texas A&M University. Thermal coalescence modes were
employed to extract densities, , and temperatures, , for evolving
systems formed in collisions of 47 MeV Ar + Sn,Sn
and Zn + Sn, Sn. The yields of , , He, and
He have been determined at = 0.002 to 0.032 nucleons/fm and
= 5 to 10 MeV. The experimentally derived equilibrium constants for
particle production are compared with those predicted by a number of
astrophysical equations of state. The data provide important new constraints on
the model calculations.Comment: 5 pages, 3 figure
Lactate dehydrogenase in hepatocellular carcinoma: something old, something new
Hepatocellular carcinoma (HCC) is the most common primary liver tumour (80-90%) and represents more than 5.7% of all cancers. Although in recent years the therapeutic options for these patients have increased, clinical results are yet unsatisfactory and the prognosis remains dismal. Clinical or molecular criteria allowing a more accurate selection of patients are in fact largely lacking. Lactic dehydrogenase (LDH) is a glycolytic key enzyme in the conversion of pyruvate to lactate under anaerobic conditions. In preclinical models, upregulation of LDH has been suggested to ensure both an efficient anaerobic/glycolytic metabolism and a reduced dependence on oxygen under hypoxic conditions in tumour cells. Data from several analyses on different tumour types seem to suggest that LDH levels may be a significant prognostic factor. The role of LDH in HCC has been investigated by different authors in heterogeneous populations of patients. It has been tested as a potential biomarker in retrospective, small, and nonfocused studies in patients undergoing surgery, transarterial chemoembolization (TACE), and systemic therapy. In the major part of these studies, high LDH serum levels seem to predict a poorer outcome. We have reviewed literature in this setting trying to resume basis for future studies validating the role of LDH in this diseas
Experimental Determination of In-Medium Cluster Binding Energies and Mott Points in Nuclear Matter
In medium binding energies and Mott points for , , He and
clusters in low density nuclear matter have been determined at specific
combinations of temperature and density in low density nuclear matter produced
in collisions of 47 MeV Ar and Zn projectiles with Sn
and Sn target nuclei. The experimentally derived values of the in
medium modified binding energies are in good agreement with recent theoretical
predictions based upon the implementation of Pauli blocking effects in a
quantum statistical approach.Comment: 5 pages, 3 figure
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