Modeling and analysis of adipocytes dynamic with a differentiation process

We propose in this article a model describing the dynamic of a system of adipocytes, structured by their sizes. This model takes into account the differentiation of a population of mesenchymal cells into preadipocytes and of preadipocytes into adipocytes; the differentiation rates depend on the mean adipocyte radius. The considered equations are therefore ordinary differential equations, coupled with an advection equation, the growth rate of which depends on food availability and on the total surface of adipocytes. Since this velocity is discontinuous, we need to introduce a convenient notion of solutions coming from Filippov theory. We are consequently able to determine the stationary solutions of the system, to prove the existence and uniqueness of solutions and to describe the asymptotic behavior of solutions in some simple cases. Finally, the parameters of the model are fitted thanks to some experimental data and numerical simulations are displayed; a spatial extension of the model is studied numerically

Normalized GNSS Interference Pattern Technique

It is well known that water level and snow height can be monitored with the ground reflectometry GNSS-R approach [1, 2]. In this approach the antenna situated on a mast, receives a direct GNSS signal coming from the satellite and a nadir signal reflected by the observed surface. Assuming that the antenna position is known we can compute the position of the surface of reflection. For water level monitoring and snow determination, this approach provides precise localization and dating of the measures that allows to process spatio-temporal comparison of water level and snow cover, respectively. These parameters are very important for flood monitoring, avalanche prevention, as well as for hydroelectic companies. Furthermore the approach is noninvasive and can be easily implemented on a portable instrument and embedded in a vehicle with a mast. The Interference Pattern Technique considers the behavior of the SNR of the received GNSS signal as a function of the satellite elevation [1]. The received signal is indeed the integration by the antenna of the direct and nadir reflected GNSS signals. Due to their different phase variations, the SNR oscillates at a rate proportional to the height between the antenna and the surface of specular reflection. Unfortunately the measurement is typically very long because it needs to process the SNR for high satellite elevation variations. We indeed need to observe a sufficient number of SNR oscillations to estimate the frequency and derive the surface height. In order to reduce the estimation time to a fraction of one period of the SNR variation, we propose to normalize the measures. The normalization consists in varying the antenna height of a value dh in order to read the minimum and maximum value of SNR for a given satellite elevation, and then in processing with these values the SNR measured for different satellite elevations. We show in this paper that the normalization allows to compute the cosine of the phase delay between the direct and reflected signals and to estimate the signal frequency on a fraction of a period. We also derive the minimum antenna variation range dh as a function of the satellite elevation. We deduce from this function the minimum time of observation as a function of the satellite elevation rate. We derive the exact evolution of the SNR as a function of the signals parameters (Doppler frequency, code delay, CN0) of the visible satellites [3]. The proposed method is assessed on real and synthetic signals

A Postnatal Critical Period for Orientation Plasticity in the Cat Visual Cortex

Orientation selectivity of primary visual cortical neurons is an important requisite for shape perception. Although numerous studies have been previously devoted to a question of how orientation selectivity is established and elaborated in early life, how the susceptibility of orientation plasticity to visual experience changes in time remains unclear. In the present study, we showed a postnatal sensitive period profile for the modifiability of orientation selectivity in the visual cortex of kittens reared with head-mounted goggles for stable single-orientation exposure. When goggle rearing (GR) started at P16-P30, 2 weeks of GR induced a marked over-representation of the exposed orientation, and 2 more weeks of GR consolidated the altered orientation maps. GR that started later than P50, in turn, induced the under-representation of the exposed orientation. Orientation plasticity in the most sensitive period was markedly suppressed by cortical infusion of NMDAR antagonist. The present study reveals that the plasticity and consolidation of orientation selectivity in an early life are dynamically regulated in an experience-dependent manner

ネコ初期視覚野における視体験効果の可視化

九州工業大学博士学位論文 学位記番号:生工博乙第4号 学位授与年月日:平成20年9月30

Parsimony, exhaustivity and balanced detection in neocortex

International audienceThe layout of sensory brain areas is thought to subtend perception. The principles shapingthese architectures and their role in information processing are still poorly understood.Weinvestigate mathematically and computationally the representation of orientation and spatialfrequency in cat primary visual cortex. We prove that two natural principles, local exhaustivityand parsimony of representation, would constrain the orientation and spatial frequencymaps to display a very specific pinwheel-dipole singularity. This is particularly interestingsince recent experimental evidences show a dipolar structures of the spatial frequency mapco-localized with pinwheels in cat. These structures have important properties on informationprocessing capabilities. In particular, we show using a computational model of visualinformation processing that this architecture allows a trade-off in the local detection of orientationand spatial frequency, but this property occurs for spatial frequency selectivitysharper than reported in the literature. We validated this sharpening on high-resolution opticalimaging experimental data. These results shed new light on the principles at play in theemergence of functional architecture of cortical maps, as well as their potential role in processinginformation

Pinwheel-dipole configuration in cat early visual cortex.

International audienceIn the early visual cortex, information is processed within functional maps whose layouts are thought to underlie visual perception. However, the precise organization of these functional maps as well as their interrelationships remain unsettled. Here, we show that spatial frequency representation in cat early visual cortex exhibits singularities around which the map organizes like an electric dipole potential. These singularities are precisely co-located with singularities of the orientation map: the pinwheel centers. To show this, we used high resolution intrinsic optical imaging in cat areas 17 and 18. First, we show that a majority of pinwheel centers exhibit in their neighborhood both semi-global maximum and minimum in the spatial frequency map (i.e. extreme values of the spatial frequency in a hypercolumn). This contradicts pioneering studies suggesting that pinwheel centers are placed at the locus of a single spatial frequency extremum. Based on an analogy with electromagnetism, we proposed a mathematical model for a dipolar structure, accurately fitting optical imaging data. We conclude that a majority of orientation pinwheel centers form spatial frequency dipoles in cat early visual cortex. Given the functional specificities of neurons at singularities in the visual cortex, it is argued that the dipolar organization of spatial frequency around pinwheel centers could be fundamental for visual processing

Robustness of the balanced detection for dipolar architectures <i>γ</i>_<i>α</i>.

<p>Top: fitted architectures for <i>α</i> = 0.5, 1, 1.5 visually look very different. Bottom: SF tuning corresponding to balanced detection as a function of <i>α</i>, computed with the same procedure as in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004623#pcbi.1004623.g005" target="_blank">Fig 5</a>. The gray band corresponds to the SF tuning width on the whole map <math><msubsup><mi>w</mi><mrow><mi>e</mi><mi>x</mi><mi>p</mi></mrow><mrow><mi>a</mi><mi>l</mi><mi>l</mi></mrow></msubsup></math> and the pink band to our estimate in the vicinity of PCs <math><msubsup><mi>w</mi><mrow><mi>e</mi><mi>x</mi><mi>p</mi></mrow><mrow><mi>P</mi><mi>C</mi><mn>17</mn></mrow></msubsup></math> (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004623#pcbi.1004623.g006" target="_blank">Fig 6</a>). Blue circles and error bars correspond to the mean and standard deviation of the SF FWHH at the tradeoff for different values of the parameter <i>α</i>.</p

Parameter space coverage near PCs for dipolar and orthogonal architectures.

<p>Pairs of preferred OR and SF (white pixels) represented (A) in the dipole model and (B) in the putative orthogonal architecture. Corresponding SF maps displayed on top.</p