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J Vaillant

Publications and source records attributed to J Vaillant.

13 recordsLinked to original sources
PubMed2001

Nonparametric selection method of survival predictors with an application to breast cancer.

Mutual information between a survival variable and covariables provides a new tool for selecting covariables with a high predictive value whenever there is no reasonable parametric model with respect to the observed phenomena. The information rate carried out by covariables can be tested by means of a decomposition similar to the analysis of variance. Moreover, a method based on information conservation can be used for aggregating survival curves corresponding to different modalities of the same selected predictor which increases the prediction efficiency. These results are applied to survival data from 1304 patients with breast cancer followed over a period of ten years.

Breast Neoplasms↗
PubMed2000

Photometric observations of a polychromatic laser guide star.

We report the photometric observation of a polychromatic laser guide star (PLGS) using the AVLIS laser at the Lawrence Livermore National Laboratory (LLNL). The process aims at providing a measurement of the tilt of the incoming wave front at a telescope induced by atmospheric turbulence. It relies on the two-photon coherent excitation of the 4D5/2 energy level of sodium atoms in the mesosphere. We used two laser beams at 589 and 569 nm, with a maximum total average output power of approximately 350 W. For the purpose of photometric calibration, a natural star was observed simultaneously through the same instrument as the PLGS at the focus of the LLNL 50-cm telescope. Photometric measurements of the 330-nm return flux confirm our previous theoretical studies that the PLGS process should allow us at a later stage to correct for the tilt at wavelengths as short as approximately 1 microm at good astronomical sites. They show also that, at saturation of two-photon coherent absorption in the mesosphere, the backscattered flux increases by a factor of approximately 2 when the pulse repetition rate decreases by a factor of 3 at constant average power. This unexpected behavior is briefly discussed.

Journal Article↗
PubMed2000

Multidimensional counting processes and evoked neuronal activity.

It is shown that the joint behaviour of n counting processes can be used for description of neuronal spike generation in a system of n neurons with various synaptic links. This multidimensional process is suggested as a model of neuronal activity evoked by either a homogeneous or an inhomogeneous stimulus during a short time period. Several situations are considered, mainly the joint activity of pairs of neurons. The probability generating functions of the process are obtained for different kinds of intensity functions. The first and second moments of the process are provided as a tool for potential comparison of the model with experimental data.

Evoked Potentials↗
PubMed2000

[Tolerance to valsartan in office practice in 3,197 hypertensive patients (the VALSE study)].

Valsartan, an angiotensin II antagonist with a potent and highly selective effect on AT1 receptors, has been found effective and safe in several randomized, controlled studies versus a placebo, other antihypertensive agents, or other angiotensin II antagonists. An eight-week, open-label, multicenter, prospective, pragmatic, phase IV trial was conducted by office-based cardiologists to evaluate the clinical safety and efficacy of valsartan 80 mg in everyday practice. The efficacy analysis included 3084 patients given valsartan alone for four weeks then, during the next four weeks, either valsartan alone or, if the diastolic blood pressure was still > or = 90 mmHg, valsartan in combination with another antihypertensive agent. The valsartan dosage was 80 mg/day. On day 28, 64% of patients were controlled and 78% were responders. The safety analysis included 3,108 patients. Of the 239 medical adverse events ascribed by the investigators to the study treatment, 72 led to premature study discontinuation. This figure translated into a 2.68% rate among treated patients, which is similar to the 2.3% rate recorded during the placebo-controlled trials performed as part of the valsartan clinical development program. These results confirm the outstanding safety profile of valsartan.

Adolescent↗
PubMed1994

Spontaneous activity of first- and second-order neurons in the frog olfactory system.

The spontaneous activity of first-order neurons (neuroreceptors of the mucosa) and second-order neurons (mitral cells of the bulb) was recorded extracellularly in the frog olfactory system. To assess the influence of peripheral inputs upon mitral cells, the bulb was either normally connected or partially deafferented. Our first set of findings concern the firing behavior. We found that most neurons generated interspike intervals (ISIs) that were stationary in mean and variance, and were not serially correlated at first and second order. Individual spikes in mitral cells and bursts of spikes in neuroreceptors were found to be generated by a Poisson process. Stochastic modeling suggests that the Poissonian behavior depends on the mean value of the membrane potential at the axon hillock. In these models, the mean potential in mitral cells would be far below the firing threshold and in neuroreceptors it would fluctuate at random between two states, one close to resting potential (between bursts) and the other close to the firing threshold with occasional crossings (within bursts). Secondly, partially deafferented mitral cells had significantly higher activity and lower variance than mitral cells receiving normal afferent input. This effect gives evidence that peripheral inputs influence mitral cells at rest not only through direct excitation but also through indirect inhibition exerted by local neurons. Thus, the unstimulated state of the olfactory bulb would not be qualitatively different from its stimulated state in the sense that both states involve the same types of synaptic interactions. Consequently, understanding the synaptic relationships that take place in the bulb network can benefit from studies of its spontaneous activity.

Action Potentials↗
PubMed1994

Changes in cervicocephalic kinesthesia after a proprioceptive rehabilitation program in patients with neck pain: a randomized controlled study.

Head repositioning accuracy (HRA) after full range active motion was evaluated in 60 cervicalgic patients. The mean angular error was 7.7 degrees +/- 3.3 (mean +/- SD) and 82% were outside a threshold value of 4.5 degrees. After randomization 30 patients followed a rehabilitation program based on eye-head coupling (RG) and 30 served as a control group (CG). At 10 week follow-up, a greater gain in HRA was observed in the RG (2 degrees +/- 2.7, mean +/- SD) than in the CG (0 +/- 2.6, mean +/- SD) (p = 0.005). Clinical parameters (pain, drug intake, range of motion, and self assessed functional improvement) were also more improved in the RG than in the CG. These data emphasize the role of a neck proprioception alteration in chronic neck pain and suggest that a rehabilitation program based on eye-head coupling should be included in most medical management of cervicalgic patients.

Adult↗
PubMedDate not supplied

Stochastic model of the overdispersion in the place cell discharge.

The spontaneous firing activity of the place cells reflects the position of an experimental animal in its arena. The firing rate is high inside a part of the arena, called the firing field, and low outside. It is generally accepted concept that this is the way in which the hippocampus stores a map of the environment. This well known fact was recently reinvestigated [Fenton, A.A., Muller, R.U., 1998. Proc. Natl. Acad. Sci. USA 95, 3182-3187] and it was found that while the activity was highly reliable in position, it did not retain the same reliability in time. The number of action potentials fired during different passes through the firing field were substantially different (overdispersion). We present a mathematical model based on a doubly stochastic Poisson process which is able to reproduce the experimental findings. Further, it enables us to propose specific statistical inference on the experiments in aim to verify data and model compatibility. The model permits to speculate about the neural mechanisms leading to the overdispersion in the activity of the hippocampal place cells. Namely, the statistical variation of the intensity of firing can be achieved, for example, by introducing a hierarchical structure into the local neural network.

Hippocampus↗
PubMedDate not supplied

[Controlled study of treatment of residual depression by clomipramine versus placebo].

The choice of a new treatment strategy for a patient suffering from residual depression in sometimes difficult; in reality, any change in the prescription involves a risk of losing any benefit, even partial, that has recently been obtained; consequently, can one be sure that a new antidepressant treatment will be beneficial? To attempt to find the answer to this question, the Laboratories Ciba-Geigy have conducted a controlled study versus placebo to evaluate the efficacy of clomipramine in residual depression which has been progressing for more than a year. 207 patients were pre-included in the 7-day wash-out phase and treated with placebo. During this period, a clinical examination and laboratory work-up made it possible to exclude patients with a curable cause of partial resistance to antidepressants (e.g., hypothyroidism) or who were "placebo-responders". After this run-in, 181 patients were included if they complied with the criteria characterizing a major depressive episode in partial remission (according to the DSM III-R), present for at least one year and treated throughout this period with at least two antidepressants at effective dosages. In addition, these patients had to have a score between 15 and 25 on the Montgomery and Asberg Depression Rating Scale (MADRS). The patients included were randomized into two groups, receiving either an clomipramine 75 tablet or a placebo tablet for two weeks; the dosage could be increased to two tablets as at D14 if necessary and maintained for the next six weeks. The only authorized concomitant treatments were tranquillizers (lorazepam or bromazepam) and/or non-barbiturate hypnotics (zopiclone or flunitrazepam).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

[Bovine hypodermyiasis: a quasi sequential procedure for observation of live-stock for surveillance of recrudescence in eradicated zones].

A quasi-sequential sampling plan for observing cattle was undertaken in the framework of Hypoderma bovis epidemiological surveillance. This plan enabled us to test whether or not the prevalence of Hypoderma bovis is within a threshold p0 chosen for an eradication scheme or for qualifying a zone. The sampling cost was reduced but the estimation precision remained acceptable. The sensitivity of monthly controls with respect to the reference period (April, May, June, July) was studied from data observed over 6 consecutive years in Côtes d'Armor, France. The best ratio sensitivity/sampling cost was obtained with a unique counting plan in June where 48% (36 to 60%) of the herds found to be infested during the reference period were detected. The test procedure concerning the prevalence level was then adapted to take into account the sensitivity of the observation method. This is tantamount to reducing the threshold p0.

Animals↗