42 research outputs found
On random flights with non-uniformly distributed directions
This paper deals with a new class of random flights defined in the real space characterized
by non-uniform probability distributions on the multidimensional sphere. These
random motions differ from similar models appeared in literature which take
directions according to the uniform law. The family of angular probability
distributions introduced in this paper depends on a parameter which
gives the level of drift of the motion. Furthermore, we assume that the number
of changes of direction performed by the random flight is fixed. The time
lengths between two consecutive changes of orientation have joint probability
distribution given by a Dirichlet density function.
The analysis of is not an easy task, because it
involves the calculation of integrals which are not always solvable. Therefore,
we analyze the random flight obtained as
projection onto the lower spaces of the original random
motion in . Then we get the probability distribution of
Although, in its general framework, the analysis of is very complicated, for some values of , we can provide
some results on the process. Indeed, for , we obtain the characteristic
function of the random flight moving in . Furthermore, by
inverting the characteristic function, we are able to give the analytic form
(up to some constants) of the probability distribution of Comment: 28 pages, 3 figure
Vibrations and fractional vibrations of rods, plates and Fresnel pseudo-processes
Different initial and boundary value problems for the equation of vibrations
of rods (also called Fresnel equation) are solved by exploiting the connection
with Brownian motion and the heat equation. The analysis of the fractional
version (of order ) of the Fresnel equation is also performed and, in
detail, some specific cases, like , 1/3, 2/3, are analyzed. By means
of the fundamental solution of the Fresnel equation, a pseudo-process ,
with real sign-varying density is constructed and some of its properties
examined. The equation of vibrations of plates is considered and the case of
circular vibrating disks is investigated by applying the methods of
planar orthogonally reflecting Brownian motion within . The composition of
F with reflecting Brownian motion yields the law of biquadratic heat
equation while the composition of with the first passage time of
produces a genuine probability law strictly connected with the Cauchy process.Comment: 33 pages,8 figure
A Markovian event-based framework for stochastic spiking neural networks
In spiking neural networks, the information is conveyed by the spike times,
that depend on the intrinsic dynamics of each neuron, the input they receive
and on the connections between neurons. In this article we study the Markovian
nature of the sequence of spike times in stochastic neural networks, and in
particular the ability to deduce from a spike train the next spike time, and
therefore produce a description of the network activity only based on the spike
times regardless of the membrane potential process.
To study this question in a rigorous manner, we introduce and study an
event-based description of networks of noisy integrate-and-fire neurons, i.e.
that is based on the computation of the spike times. We show that the firing
times of the neurons in the networks constitute a Markov chain, whose
transition probability is related to the probability distribution of the
interspike interval of the neurons in the network. In the cases where the
Markovian model can be developed, the transition probability is explicitly
derived in such classical cases of neural networks as the linear
integrate-and-fire neuron models with excitatory and inhibitory interactions,
for different types of synapses, possibly featuring noisy synaptic integration,
transmission delays and absolute and relative refractory period. This covers
most of the cases that have been investigated in the event-based description of
spiking deterministic neural networks
Prise en charge des dyades mère traumatisée-bébé: une contrainte à la pensée et à la pratique
The views and experiences of suicidal children and young people of mental health support services: A meta-ethnography.
Background: Suicide is amongst the leading causes of death in young people globally and a health priority worldwide. For children and young people (CYP) attempting or considering suicide there is no agreed treatment model. Development of treatment models should be informed by the views and experiences of CYP using services. Methods: Meta-ethnography was used to systematically identify and synthesise studies reporting the views of CYP who used mental health services following suicidal behaviour. Relevant studies were quality appraised. First order (participants) and second order (original author) data were translated to identify common and disconfirming themes and concepts. Translated findings were synthesised and led to a new hypothesis supported by additional ‘linguistic analysis’ of texts to construct a novel third order line-of-argument. Results: Four studies conducted since 2006 in three countries involving 44 young people aged 11-24 years were synthesised. Translation revealed that suicidal CYP do not know where or how to access help, they cannot access help directly and when seen by mental health practitioners they do not feel listened to. Line-of-argument synthesis identified a silence around suicidality within the conversations CYP have with mental health practitioners and within academic research reporting. Use of the term ‘self-harm’ to encompass suicidal behaviours potentially contributes to this silence by avoiding the word ‘suicide’. Conclusions: CYP who are suicidal need to have easy access to mental health services. When using services, they want to feel listened to and have suicidal feelings acknowledged. This involves professionals referring explicitly to suicide not just self-harm
Rôle de l’impulsivité dans la relation entre surpoids et TDAH chez l’enfant : étude exploratoire des caractéristiques cliniques, neuropsychologiques et neurobiochimiques
Étude qualitative de l'expérience des parents après la tentative de suicide de leur adolescent
International audienceIntroduction: Suicidal attempts are frequent during adolescence and concern the whole family, particularly parents whose role is crucial in provision of therapeutic support. Yet very few studies have been performed bearing on their lived experience. In this study, we will analyze the experience of parents after the suicidal attempt of their adolescent. Participants & methods: Qualitative study based on semi-structured interviews of 13 parents of teenagers followed in child and adolescent psychiatry for suicidal behavior. Interview included 5 to 6 open and conversational questions. We analyzed interviews, after transcription, using the Interpretative Phenomenological Analysis approach. Results: The parents’ wellness and behavior are directly affected by their child's mental status. When they are informed of the suicidal attempt, they feel very deep sadness, in a form of initial distress which is part of the grieving process regarding their image of idealized parents. They feel anger against the teenager, their anger is also directed against family members and close friends as well as against caregivers. Given the uncertainty, they doubt their own educative and empathetic competences, and lack confidence in their capacity for providing help. They express their need for help and support with regard to understanding their child's suicidal attempt, with regard to the emotional turmoil they experience and in reinforcing their competencies as carers. Conclusion: It appears that parents are extremely touched by their teenager suicidal attempt. They need a personal follow up, including familial medical care but also a personal space of support. Parents group, as well as psycho educative intervention, are also welcomed to give efficient method to lift their child