Reversibility of airway obstruction is considered one of the major criteria in the diagnosis of asthma in children, adolescents and adults [1,2]. Different guidelines for the cut-off value have been proposed for forced expiratory volume in one second (FEV1) and airway resistance (Raw), expressed as either % baseline or as % predicted [3][4][5][6][7][8][9][10].Spirometry is hard to perform in children younger than 6 yrs old. Normal values of Raw [11] and of total respiratory resistance (Rrs) measured with the forced oscillation technique (FOT) [12,13] have been established in children [14][15][16]. Not many data are available on bronchodilation tests in asthmatic children younger than 6 yrs. In some of these studies the impulse oscillation system (IOS) was used [17,18], a FOT involving the application of a rectangular pulse signal, whilst in the FOT a pseudorandom noise signal, containing harmonics up to 24 or 48 Hz, is generally used [13]. Both techniques give similar results (r=0.85) over wide ranges of resistance between 0.1 and 1.5 kPa·L -1 ·s [19]. There are, however, no published data on bronchodilator response in healthy children younger than 6 yrs using oscillator techniques. Yet, as already stated, this research is essential [3] to establish the threshold for a significant response in asthmatic children.The aims of the present study were to establish in children aged from 3-6 yrs: 1) normal reference values for the IOS; 2) the change in Rrs and in respiratory reactance (Xrs) after inhalation of a β 2 -agonist in healthy and in asthmatic children; and 3) to propose threshold values for a significant bronchodilator response.The study protocol was approved by the ethical committee of the university hospital. Materials and methodsThe study population consisted of 281 children with a mean age of 4.5 yrs (range 2.7-6.6), a mean height of 108 cm (range 93-131) and a mean weight of 18 kg (range 12-29); 129 males and 152 females. They were recruited from children attending kindergarten (95% of Belgian children between 3-6 yrs do so). During the first and the third year of kindergarten the children have a medical check-up. A standardized questionnaire on the diagnosis of asthma with a form for informed consent was sent to the parents of 480 of these children invited to the centre in the Leuven region (located in the central, most industrialized part of Belgium). Informed consent was obtained from the parents of 362 children; of these, 81 had to be excluded because of a lack of biometric information (10 children), unavailability at the time of the test (17 children) or failure to perform the test procedure (56 children). Therefore, 281 children, who were examined at the centre between 1 December, 1995 and 20 June, 1996 were included in the study. The relevant items and the scoring system of the standardized questionnaire on the presence of asthma are outlined in table 1. As the questions on wheezing and shortness of breath have proven to be most reproducible [20], these were given the most weight in the interpretat...

We experimentally demonstrate slow-down of light by a factor of three in a 100 microm long semiconductor waveguide at room temperature and at a record-high frequency of 16.7 GHz. It is shown that the group velocity can be controlled all-optically as well as through an applied bias voltage. A semi-analytical model based on the effect of coherent population oscillations and taking into account propagation effects is derived and is shown to well account for the experimental results. It is shown that the carrier lifetime limits the maximum achievable delay. Based on the general model we analyze fundamental limitations in the application of light slowdown due to coherent population oscillations.

Quantum mechanically indistinguishable particles such as photons may show collective behavior. Therefore, an appropriate description of a light field must consider the properties of an assembly of photons instead of independent particles. We have studied multiphoton correlations up to fourth order in the single-mode emission of a semiconductor microcavity in the weak and strong coupling regimes. The counting statistics of single photons were recorded with picosecond time resolution, allowing quantitative measurement of the few-photon bunching inside light pulses. Our results show bunching behavior in the strong coupling case, which vanishes in the weak coupling regime as the cavity starts lasing. In particular, we verify the n factorial prediction for the zero-delay correlation function of n thermal light photons.

Long wavelength lasers and semiconductor optical amplifiers based on InAs quantum wire-/dot-like active regions were developed on InP substrates dedicated to cover the extended telecommunication wavelength range between 1.4 and 1.65 µm. In a brief overview different technological approaches will be discussed, while in the main part the current status and recent results of quantum-dash lasers are reported. This includes topics like dash formation and material growth, device performance of lasers and optical amplifiers, static and dynamic properties and fundamental material and device modelling.

No abstract