Iuliacumite: A Novel Chemical Short-Range Order in a Two-Dimensional Wurtzite Single Monolayer InAs1-xSbx Shell on InAs Nanowires.

A chemical short-range order is found in single monolayer InAs1-xSbx shells, which inherit a wurtzite structure from the underlying InAs nanowire, instead of crystallizing in the energetically preferred zincblende structure. The chemical order is characterized by an anticorrelation ordering vector in the ⟨112̅0⟩ direction and arises from strong Sb-Sb repulsive interactions along the atomic chains in the ⟨112̅0⟩ direction.

Composition modulation by twinning in InAsSb nanowires.

We observe a composition modulated axial heterostructure in zincblende (ZB) InAs0.90Sb0.10 nanowires initiated by pseudo-periodic twin boundaries using scanning tunneling microscopy. The twin boundaries exhibit four planes with reduced Sb concentration due to a lower Sb incorporation during lateral overgrowth of a 4H wurtzite as compared to a ZB stacking sequence. We anticipate that this leads to compositional band offsets in addition to known structural band offsets present between 4H and ZB polytypes, changing the band alignment from type II to type I.

[Sleep apnea and cardiovascular disease--results from animal studies]. / Schlaf-Apnoe und Herz-Kreislauf-Erkrankungen: Ergebnisse tierexperimenteller Studien.

Over the last decade the pathophysiology of obstructive sleep apnea (OSA)-related cardiovascular disease has been further elucidated in animal models employing dogs and rats/mice. It was demonstrated that, under the conditions of chronic intermittent hypoxia (CIH), endothelial dysfunction, i. e., a reduction in endothelial-dependent vasorelaxation, occurs. Furthermore, animals were shown to develop arterial hypertension when subjected to CIH for some weeks. Other aspects of the cardiovascular morbidity linked to OSA such as pulmonary hypertension, heart failure and atherosclerosis were also found in these animal models. The common result of these studies is that, apart from sympathetic over-activity, an increased oxidative stress seems to play a key role in the development of OSA-associated cardiovascular disease. It is anticipated that animal studies will continue to enhance our understanding of the pathogenesis of these disorders.

[Obstructive sleep apnoea and metabolic syndrome]. / Obstruktive Schlaf-Apnoe und metabolisches Syndrom.

Metabolic syndrome, i. e., the combined occurrence of obesity, arterial hypertension, insulin resistance and dyslipidaemia (increased triglycerides, reduced HDL cholesterol), is associated with a marked increase in cardiovascular risk. The prevalence of metabolic syndrome in patients with obstructive sleep apnoea (OSA) is very high. Obesity is the main risk factor for OSA and OSA itself is now considered to be the most frequent cause of secondary arterial hypertension. Due to the confounding influence of obesity, the causal connection between OSA and metabolic disturbances is less well established, however, epidemiological data are at least in favour of an independent link between OSA and insulin resistance. It is known that CPAP therapy can ameliorate OSA-associated hypertension. In contrast, the effects of CPAP treatment on insulin resistance and dyslipidaemia have to be further elucidated by large, randomised interventional trials.

Assessing attitudes toward new names for chronic fatigue syndrome.

A questionnaire was distributed at the American Association of Chronic Fatigue Syndrome's biannual convention in Washington in January 2001 as well as through various Internet Web sites and listserves during early February and March of 2001. The sample consisted of 432 respondents. Most respondents (86%) indicated they wanted a name change, although more patients than scientists were in favor of this change. It was also apparent that the patients and physicians were clearly split between adopting a name such as myalgic encephalopathy versus one such as neuro-endocrine immune disorder. Also, among those respondents who selected either of these two choices for a new name, less than 30% of them supported the other name. Although the majority of respondents feel the name should be changed at this time, this survey suggests there are different stakeholders involved in the name-change process, each with strong and sometimes disparate feelings about changing the name.

Self-organized formation of GaSb/GaAs quantum rings.

Ring-shaped GaSb/GaAs quantum dots, grown by molecular beam epitaxy, were studied using cross-sectional scanning tunneling microscopy. These quantum rings have an outer shape of a truncated pyramid with baselengths around 15 nm and heights of about 2 nm but are characterized by a clear central opening extending over about 40% of the outer baselength. They form spontaneously during the growth and subsequent continuous capping of GaSb/GaAs quantum dots due to the large strain and substantial As-for-Sb exchange reactions leading to strong Sb segregation.

Submonolayer quantum dots for high speed surface emitting lasers.

We report on progress in growth and applications of submonolayer (SML) quantum dots (QDs) in high-speed vertical-cavity surface-emitting lasers (VCSELs). SML deposition enables controlled formation of high density QD arrays with good size and shape uniformity. Further increase in excitonic absorption and gain is possible with vertical stacking of SML QDs using ultrathin spacer layers. Vertically correlated, tilted or anticorrelated arrangements of the SML islands are realized and allow QD strain and wavefunction engineering. Respectively, both TE and TM polarizations of the luminescence can be achieved in the edge-emission using the same constituting materials. SML QDs provide ultrahigh modal gain, reduced temperature depletion and gain saturation effects when used in active media in laser diodes. Temperature robustness up to 100 °C for 0.98 µm range vertical-cavity surface-emitting lasers (VCSELs) is realized in the continuous wave regime. An open eye 20 Gb/s operation with bit error rates better than 10-12has been achieved in a temperature range 25-85 °Cwithout current adjustment. Relaxation oscillations up to ∼30 GHz have been realized indicating feasibility of 40 Gb/s signal transmission.

[Pulmonary hypertension and sleep-related breathing disorders]. / Pulmonale Hypertonie und schlafbezogene Atmungsstörungen.

Pulmonary hypertension (PH), i. e. an increase of mean pulmonary artery pressure above 20 mm Hg under resting conditions, can be observed in different forms of sleep-disordered breathing (SDB). In obstructive sleep apnea (OSA) the apnea-associated triggers of hypoxia and intrathoracic pressure swings lead to repetitive rises of pulmonary artery pressure during sleep. In 20 - 30 % of these patients daytime PH occurs. PH in the setting of OSA is usually mild and rarely causes clinically evident cor pulmonale. Effective CPAP therapy has a beneficial influence on pulmonary hemodynamics in OSA. Severe congestive heart failure (i. e. with a LVEF < 40 %) might provoke pulmonary venous hypertension and thereby stimulation of pulmonary stretch and irritant receptors. The ensuing hyperventilation leads to a decrease of pCO (2) levels below the apneic threshold and thus contributes to the emergence of Cheyne Stokes respiration (CSR) in up to one half of the affected patients. Patients suffering from advanced idiopathic pulmonary arterial hypertension (IPAH) might show a similar breathing pattern while asleep. Possible pathogenetic factors of the nocturnal periodic breathing occurring in end-stage IPAH are prolonged circulation times and hypocapnia. In conclusion, SDB might cause PH (OSA-associated PH). On the other hand, PH might lead to the development of SDB (CSR in congestive heart failure, periodic breathing in IPAH).