Nonlinear pulse propagation in a quantum dot laser.

We investigate the nonlinear propagation of an ultra-short, 150 fs, optical pulse along the waveguide of a quantum dot (QD) laser operating above threshold. We demonstrate that among the various nonlinear processes experienced by the propagating pulse, four-wave mixing (FWM) between the pulse and the two oscillating counter-propagating cw fields of the laser is the dominant one. FWM has two important consequences. One is the creation of a spectral hole located in the vicinity of the cw oscillating frequency. The width of the spectral hole is determined by an effective carrier and gain relaxation time. The second is a modification of the shape of the trailing edge of the pulse. The wave mixing involves first and second order processes which result in a complicated interaction among several fields inside the cavity, some of which are cw while the others are time varying, all propagating in both directions. The nonlinear pulse propagation is analyzed using two complementary theoretical approaches. One is a semi-analytical model which considers only the wave mixing interaction between six field components, three of which propagate in each direction (two cw fields and four time-varying signals). This model predicts the deformation of the tail of the output signal by a secondary idler wave, produced in a cascaded FWM process, which co-propagates with the original injected pulse. The second approach is a finite-difference time-domain simulation, which considers also additional nonlinear effects, such as gain saturation and self-phase modulation. The theoretical results are confirmed by a series of experiments in which the time dependent amplitude and phase of the pulse after propagation are measured using the cross-frequency-resolved optical gating technique.

To live alone and to be depressed, an alarming combination for the renin-angiotensin-aldosterone-system (RAAS).

INTRODUCTION: The renin-angiotensin-aldosterone-system (RAAS) is one of the most important systems involved in the pathogenesis of cardiovascular diseases. Its role in stress response has been generally neglected, although the progression of cardiovascular disease is considerably increased in the presence of stress and especially in the presence of depression risk. With the present analysis we aimed to evaluate whether the activity of the RAAS correlates with depressive symptomatology and with chronic stress. Moreover, we aimed to analyse whether stress response is altered in the presence of depressed symptomatology. We chose "living alone" to be our paradigm of chronic stress. METHODS AND RESULTS: Aldosterone and renin levels were assessed in 1743 (829 men, 914 women) from the population-based KORA study (Cooperative Health Research in the Region of Augsburg). The relationship between aldosterone, renin levels and the different combinations of living alone and depressive symptomatology was examined in three different multiple linear regression models adjusted for age, sex, creatinine levels, potassium levels, body mass index (BMI) and bio-behavioural factors. Neither "living alone" nor depressive symptomatology alone were associated with an activation of the RAAS, but the combination of living alone and depressive symptomatology yielded a highly significant increase in the aldosterone (p<0.01) and renin level (p=0.03). CONCLUSION: Our findings show that depressive symptomatology is associated with a hyper-responsiveness to chronic stress. Under the condition of chronic stress depressed individuals have an activated RAAS. Activation of the RAAS might explain the known increased risk of negative cardiovascular disease outcomes in this group.

Reboxetine induces similar sleep-EEG changes like SSRI's in patients with depression.

BACKGROUND: Reboxetine is a novel selective noradrenaline reuptake inhibitor. The antidepressive properties of the substance are established. METHODS: The influence of reboxetine on the sleep-EEG of eight patients with depression HAMD (mean +/- SD) 19.7 +/- 1.5 (5 women, 3 men; age range 31 to 75 years) was investigated. Sleep EEG was examined twice. The first examination was performed before starting active medication. The second examination was subsequently performed when patients received 8 to 10 mg reboxetine per day. RESULTS: Conventional sleep-EEG analysis showed a significant increase in intermittent wakefulness and sleep stage 2 and a decrease in sleep efficiency and REM time. Under reboxetine no significant changes were observed in sleep-EEG spectral analysis. CONCLUSION: Our results indicate, that reboxetine induces sleep-EEG changes similar to those after selective serotonin reuptake inhibitors (SSRI's) by increasing intermittent wakefulness and decreasing REM time.

The somatostatin analogue octreotide impairs sleep and decreases EEG sigma power in young male subjects.

The long-acting somatostatin (SRIF) analogue octreotide decreased nonrapid eye movement sleep (NREMS) in the rat. This effect is opposite to the promotion of sleep after growth hormone (GH)-releasing hormone (GHRH) in various species including humans. Therefore, it appears likely that GHRH and SRIF, besides their opposite action on pituitary GH release, interact reciprocally in sleep regulation. In previous studies, SRIF impaired sleep in elderly subjects, although sleep in young men remained unchanged. We hypothesized that octreotide is a useful tool to study the role of SRIF in human sleep regulation. We examined the effect of subcutaneous administration of 0.1 mg octreotide at 2245 on the sleep EEG of seven young male controls (age, mean+/-SD, 22.3+/-3.0 years). In comparison to placebo, octreotide administration prompted decreases of sleep stage 4 during the total night and of rapid eye movement sleep (REMS) density during the first half of the night. Intermittent wakefulness increased during the second half of the night. The spectral analysis of total night NREMS revealed a significant decrease of sigma power. Similar to the effect of the short-acting SRIF in the elderly, the long-acting SRIF analogue octreotide impaired sleep in young healthy subjects. Obviously, the influence of octreotide on sleep is superior to that of short-acting SRIF, which did not affect sleep in young men. We suggest a reciprocal interaction of GHRH and SRIF in sleep regulation.

[A photoelectric investigation of velar height during vowel articulation: first applications of the velograph (author's transl)]. / Photoelektrische Untersuchung zur Velumhöhe bei Vokalen: erste Anwendungen des Velographen.

Some methodological aspects of the main physiological techniques for investigating the velopharyngeal closure mechanism are discussed. A new instrument for optical registration of velar movement is described. The possibilities and limits arising from its mode of operation are discussed. First results corroborate the relation between velar height and tongue height in vowels, which has been established by cineradiographic research. It is argued that the velograph records relative velar height in the speech continuum with reasonable accuracy. Two ways of calibrating the device are proposed so as to allow the measurement of absolute velar elevation (from rest position).