response function

Top PDF response function:

PyHRF: A Python Library for the Analysis of fMRI Data Based on Local Estimation of the Hemodynamic Response Function

PyHRF: A Python Library for the Analysis of fMRI Data Based on Local Estimation of the Hemodynamic Response Function

Fig. 1: fMRI BOLD signal [ OLKT90 ]. The BOLD signal measures the local changes in blood oxygenation ocurring during brain activity. fMRI data is acquired by repeated imaging of the brain while the subject or patient executes a task or receives a sensory stimulus during repeated epochs separated by periods of rest. This data is analyzed by correlating the measured time-varying BOLD signal in each image location with a predicted BOLD signal, obtained by convolving the known function representing the stimulus with a Hemodynamic Response Function (HRF) modeling the delay in the vascular response. Locations in the brain where this correlation is statistically significant are considered to exhibit a neuronal response to the task or stimulus, and thus to be involved in its cognitive processing.
En savoir plus

8 En savoir plus

Response function of the large-scale structure of the universe to the small scale inhomogeneities

Response function of the large-scale structure of the universe to the small scale inhomogeneities

the asymptote of the F n kernel function). The independence of q 0 on k is thus in full agreement with PT predictions. 4. Discussion The simulation results give a clear evidence that the mode transfer from small to large scales is suppressed compared to the PT prediction when the mode q enters the nonperturbative regime. However, the origin of the suppression is yet to be understood. In particular it is not clear whether this has its roots in shell crossing or not. For instance, we can find in [32] that vorticity and veloc- ity dispersion generated by shell crossing can alter the evolution of density fluctuations through nonlinear coupling. Especially, the latter is shown to give non-negligible corrections to the density power spectrum even on very large ( ∼ 0 . 1h Mpc − 1 ) scales. This indicates that multistreaming physics, which take place on small scales, are somehow related to the growth of large-scale fluctu- ations, and this is exactly the coupling of large and small scales that we discuss here. Effective Field Theory (EFT) approaches as advocated originally in [33–35] would be a natural framework to invoke for accounting for such multistreaming effects. In these ap- proaches, however, the response function is ultimately encoded in free coefficients for which no theory exists.
En savoir plus

7 En savoir plus

Simulation of a NE213 Gamma Response Function using an Improved Multi-parameter Minimization Procedure

Simulation of a NE213 Gamma Response Function using an Improved Multi-parameter Minimization Procedure

MCNPX2.5e Monte-Carlo code. The MINUIT2 package, developed at C.E.R.N., was used to minimize the χ 2 between measured and calculated pulse height distributions in order to derive the experimental resolution parameters. A C++ code was written to simulate various resolution broadening and background shapes. The results are in good agreement with the experimental response function except in the low energy range (below 100keV) which could be improved by a better description of the detector environment.

5 En savoir plus

Modeling and characterization of an electromagnetic system for the estimation of Frequency Response Function of spindle

Modeling and characterization of an electromagnetic system for the estimation of Frequency Response Function of spindle

a University of Nantes, LS2N (Laboratoire des Sciences du Num´ erique de Nantes, UMR CNRS 6004), Nantes, France Abstract The paper presents an electromagnetic system that has been developed to measure the quasi-static and dynamic behavior of machine-tool spindle, at different spindle speeds. This system consists in four Pulse Width Modulation amplifiers and four electromagnets to produce magnetic forces of ±190N for the static mode and ±80N for the dynamic mode up to 5kHz. In order to measure the Frequency Response Function (FRF) of spindle, the applied force is required, which is a key issue. A dynamic force model is proposed in order to obtain the load from the measured current in the amplifiers. The model depends on the exciting frequency and on the magnetic characteristics of the system. The predicted force at high speed is validated with a specific experiment and the performance limits of the experimental device are investigated. The FRF obtained with the electromagnetic system is compared to a classical tap test measurement.
En savoir plus

16 En savoir plus

Pulvinar modulates contrast response function of neurons in the primary visual cortex

Pulvinar modulates contrast response function of neurons in the primary visual cortex

Abstract The pulvinar, which is located in the posterior thalamus, establishes reciprocal connections with nearly all of the visual cortical areas and is consequently in a strategic position to influence their stimulus decoding processes. Projections from the pulvinar to the primary visual cortex (V1) are thought to be modulatory, altering the response of neurons without changing their basic receptive field properties. Here, we investigate this issue by studying V1 single unit responses to sine wave gratings during the reversible inactivation of the lateral posterior nucleus (LP) - pulvinar complex in the cat. We also studied the contrast response function of V1 neurons, before and during the inactivation of the LP-pulvinar complex. No change in the preferred orientation or direction selectivity of V1 neurons was observed during pulvinar inactivation. However, for the majority of the cells tested the response amplitude to the optimal stimulus was reduced. The contrast response function of neurons was fitted with the Naka-Rushton function and analysis of the effects of pulvinar deactivation revealed a diverse set of modulations: 35% of cells had a decrease in their peak response, 11% had an increase in their C50, 6% showed modulations of the slope factor and 22% exhibited changes in more than one parameter. Our results suggest that the pulvinar modulates activity of V1 neurons in a contrast dependent manner and provides gain control at lower levels of the visual cortical hierarchy.
En savoir plus

79 En savoir plus

Retrieving the Hemodynamic Response Function in resting state fMRI: Methodology and application

Retrieving the Hemodynamic Response Function in resting state fMRI: Methodology and application

In this paper we present a procedure to retrieve the hemodynamic response function (HRF) from resting state functional magnetic resonance imaging (fMRI) data. The fundamentals of the procedures are further validated by considering simultaneous electroencephalographic (EEG) recordings. The typical HRF shape at rest for a group of healthy subject is presented. Then we present the modifications to the shape of the HRF at rest following two physiological modulations: eyes open versus eyes closed and propofol-induced modulations of consciousness.
En savoir plus

8 En savoir plus

EUAs and CERs : Vector autoregression, impulse response function and cointegration analysis

EUAs and CERs : Vector autoregression, impulse response function and cointegration analysis

Our results show that there is a clear link between EUAs and sCERs prices: not only do they affect each other at statistically significant levels as shown by the vector autoregressive modeling, but also the transmission of shocks from one price series to the other is quite rapid and significant, as shown by impulse response function analysis.

19 En savoir plus

Robust Bayesian estimation of the hemodynamic response function in event-related BOLD fMRI using basic physiological information.

Robust Bayesian estimation of the hemodynamic response function in event-related BOLD fMRI using basic physiological information.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignemen[r]

40 En savoir plus

Estimation of the Hemodynamic Response Function in event-related functional MRI: directed acyclic graphs for a general Bayesian inference framework.

Estimation of the Hemodynamic Response Function in event-related functional MRI: directed acyclic graphs for a general Bayesian inference framework.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignemen[r]

13 En savoir plus

Unsupervised robust nonparametric estimation of the hemodynamic response function for any fMRI experiment.

Unsupervised robust nonparametric estimation of the hemodynamic response function for any fMRI experiment.

a and b: comparison of the HRF estimates computed from one vs four sessions, respectively when the low frequency drift included in the data is modeled with &Û/Ý nuisance variables for ea[r]

25 En savoir plus

The partition function of the two-matrix model as an isomonodromic tau-function

The partition function of the two-matrix model as an isomonodromic tau-function

was used to model two-dimensional quantum gravity 14 and was investigated from a more math- ematical point of view in Refs. 25 , 17 , 4 , 5 , 7 , 12 , and 8 ; the partition function of the model Z N 共V 1 ,V 2 兲 = 冕冕 d ␮ 共M 1 , M 2 兲 共1.2兲 has important properties in the large N limit for the enumeration of discrete maps on surfaces 15 of arbitrary genus and it is also known to be a ␶ function for the 2-Toda hierarchy. In the case of the Witten conjecture, proved by Kontsevich 23 with the use of matrix integrals not too dissimilar from the above one, the enumerative properties of the ␶ function imply some nonlinear 共hierarchy of兲 partial differential equations 共PDEs兲 关the Korteweg-de Vries 共KdV兲 hierarchy for the mentioned example兴. On a similar level, one expects some hierarchy of PDEs for the case of the two-matrix model and possibly some Painlevé property 共namely, the absence of movable essential singulari- ties兲. The Painlevé property is characteristic of ␶ functions for isomonodromic families of ordinary differential equations 共ODEs兲 that depend on parameters; hence, a way of establishing such prop- erty for the partition function Z N is that of identifying it with an instance of isomonodromic ␶
En savoir plus

18 En savoir plus

"Response to Nuñez"

"Response to Nuñez"

Full text at www.sciencemag.org/cgi/content/full/321/5894/1295c RESPONSE TO COMMENT ON “Fire-Derived Charcoal Causes Loss of Forest Humus” David A. Wardle, Marie-Charlotte Nilsson, Olle Zackrisson We find the suggestion that substantial charcoal loss occurred in the humus-charcoal mixtures implausible and dis- cuss why complexing of soluble carbon released from the mixtures by underlying mineral soil should be minor. This exchange highlights our limited knowledge about charcoal effects on native soil carbon, indicating that strong advocacy for charcoal addition to offset CO 2 emissions remains premature.
En savoir plus

5 En savoir plus

Function failure annotation

Function failure annotation

syntax that will probably the more commonly used interfaces, if not the only ones that survive the scrutiny of the standardisation process. 3.1. Function declaration attributes The different versions of myabs can basically be seen as mechanical rewriting of the same code. This may be due to the simplicity of the base function in question, or it could be a general property of the error convention using errno and the floating exception flags. In fact, a first inspection of a concrete implementation of the C library (musl libc) has shown that the error handling is concentrated in some easily identifiable error paths, and that an annotation of these can be done mostly automatically.
En savoir plus

13 En savoir plus

The aggregate matching function

The aggregate matching function

Using the aggregate matching function, we build a simple model of the labor market.. which focuses on the flows in Sections 2 and 3.[r]

78 En savoir plus

The photon wave function

The photon wave function

e pl E and B have a physical reality, because they are changed by this phase shift. Second, the two circular polarization plane waves solutions require two different identifications of the components of their wave function ψ (one with E and one with B as the real part of ψ Finally, the w ve function ψ ). a   E i B does not have e right properties under spac if the real components are considered as physical electroma- gnetic fields. Indeed, electric fields change sign, whereas magnetic fields do not, and the Hamiltonian in Equation (4) commutes with the parity operator.
En savoir plus

12 En savoir plus

Platelet function in aging

Platelet function in aging

Aging is associated with an increased incidence of cardiovascular disease and thrombosis. Platelets play a major role in maintaining hemostasis and in thrombus formation, making them a key player in thrombotic disorders. Whereas it is well-known that platelet aggregability is increased in vascular diseases, the contribution of age-related changes in platelet biology to cardiovascular risk is not well-understood. Several lines of evidence support that platelets from older subjects differ in their function and structure, making platelets more prone to activation and less sensitive to inhibition. These age-related changes could lead to platelet hyperactivity and to the development of a prothrombotic state in advanced age. This review will focus on platelet biochemical modifications during aging and on the mechanisms by which these alterations could lead to thrombotic disease.
En savoir plus

8 En savoir plus

Disorders of mitochondrial function

Disorders of mitochondrial function

Waterham HR, Koster J, van Roermund CW, et al. A lethal defect of mitochon- drial and peroxisomal fission. N Engl J Med 2007; 356:1736–1741. This article opens a new field of human pathology, demonstrating that mutation in the DLP1 gene, which encodes a dynamin-like protein implicated in mitochondrial and peroxisomal fission, causes morphologically striking defects in both organelles and severe clinical symptoms of systemic lactic acidosis, increased plasma very long chain fatty acids, microcephaly and cerebral gyration defect. Respiratory chain function was normal in patient homogenates, suggesting that mitochondrial position is an important determinant of function.
En savoir plus

12 En savoir plus

Structure and function of epipelagic mesozooplankton and their response to dust deposition events during the spring PEACETIME cruise in the Mediterranean Sea

Structure and function of epipelagic mesozooplankton and their response to dust deposition events during the spring PEACETIME cruise in the Mediterranean Sea

Correspondence: François Carlotti (francois.carlotti@mio.osupytheas.fr) Received: 8 April 2020 – Discussion started: 4 May 2020 Revised: 21 August 2020 – Accepted: 31 August 2020 – Published: 12 November 2020 Abstract. The PEACETIME cruise (May–June 2017) was a basin-scale survey covering the Provencal, Algerian, Tyrrhe- nian, and Ionian basins during the post-spring bloom period and was dedicated to tracking the impact of Saharan dust deposition events on the Mediterranean Sea pelagic ecosys- tem. Two such events occurred during this period, and the cruise strategy allowed for the study of the initial phase of the ecosystem response to one dust event in the Algerian Basin (during 5 d at the so-called “FAST long-duration station”) as well as the study of a latter response to another dust event in the Tyrrhenian Basin (by sampling from 5 to 12 d after the de- position). This paper documents the structural and functional patterns of the zooplankton component during this survey, including their responses to these two dust events. The meso- zooplankton were sampled at 12 stations using nets with two different mesh sizes (100 and 200 µm) that were mounted on a Bongo frame for vertical hauls within the depth layer from 0 to 300 m.
En savoir plus

26 En savoir plus

CD40 signalling in platelet function

CD40 signalling in platelet function

31 Atherothrombotic diseases are the leading cause of mortality, and account for more than 25% of deaths worldwide. 244 Development of a clot, following atherosclerotic plaque rupture or erosion, in the coronary or cerebral circulation (causing acute myocardial infarction or ischemic stroke, respectively) is now the single most common cause of morbidity and mortality globally, and involves both aggravated platelet and coagulation cascade activation. Although the endothelium actively secretes a range of molecules that inhibit platelet activation (PGI 2 , NO, NTPDase-1) and thrombin generation (thrombomodulin), plaque rupture in combination with a severe pre-existing arterial stenosis (abnormal narrowing of blood vessel) leads to an exaggerated platelet aggregation response. 245, 246 Exposure of the sub-endothelial matrix as well as the highly thrombogenic necrotic core to the circulation, following plaque rupture, leads to platelet adhesion and activation onto the components of the sub-endothelial matrix (vWF and collagen), and the subsequent recruitment and activation of circulating platelets by secreted secondary mediators (ADP and TxA 2 ). In addition, at the surface of the growing thrombus, blood flow is accelerated, thereby subjecting platelets and immobilized ligands, such as vWF, to extensional drag forces. 247 Thus platelet recruitment onto the thrombus surface becomes extensively dependent on vWF and platelet GPIbα interactions, which is then followed by the stable platelet-platelet aggregates mediated by the α IIb β 3 integrin interactions with its ligands, such as vWF, fibrinogen, fibrin, and/or fibronectin, and P-selectin interactions with its cognate ligands on platelets (see section 1.4.4). 87
En savoir plus

244 En savoir plus

Capacity of a noisy function

Capacity of a noisy function

While the definition of F does not relate to f , the capacity of F depends upon the desired function f . According to the function f to be ”extracted” from F , the capacity will be more or less. The limit case is when H(f (X) |F (X)) is minimum (i.e., 0) which corresponds to the availability of perfect decoding : f (X) is a deterministic function of F (X). This is possible if F is itself deterministic, thus either perfect or ”totally” noisy.

6 En savoir plus

Show all 3761 documents...