Blocking growth by an electrically active subsurface layer: the effect of Si as an antisurfactant in the growth of GaN.

Combining aberration corrected high resolution transmission electron microscopy and density functional theory calculations we propose an explanation of the antisurfactant effect of Si in GaN growth. We identify the atomic structure of a Si delta-doped layer (commonly called SiN(x) mask) as a SiGaN(3) monolayer that resembles a √3×√3 R30° surface reconstruction containing one Si atom, one Ga atom, and a Ga vacancy (V(Ga)) in its unit cell. Our density functional theory calculations show that GaN growth on top of this SiGaN(3) layer is inhibited by forming an energetically unfavorable electrical dipole moment that increases with layer thickness and that is caused by charge transfer between cation dangling bonds at the surface to V(Ga) bound at subsurface sites.

Pulse oximetry used for documenting oxygen saturation and right-to-left shunting immediately after birth.

The objective of this study was to investigate the clinical applicability of pulse oximetry to measure haemoglobin oxygen saturation and heart rate in the first 20 min of life and to analyse the effect of pre- or post-ductal (hand, respectively, foot) fixation of sensors on oxygen saturation. Measurements were carried out on 53 newborn infants selected at random after delivery by caesarean section. Signal detection occurred significantly faster from the hand (50% after 1.3 min, 90% after 4 min) than from the foot (50% after 3.1 min, 90% after 9 min). Both fixation sites showed equally great sensitivity to motion. The heart rates from pulse oximetry recordings were up to 30% lower than those from ECG recordings. Saturation values from the hand were nearly always higher than those from the foot (median difference in the 5th min was 10%; between the 5th and 10th min it was 7%; no significant difference occurred after the 17th min). We conclude that pulse oximetry can be used for documenting oxygenation and right-to-left shunting in newborn infants during the first minutes of life in spite of limitations due to incomplete pulse wave detection and artifacts.

[Reliability and limitations of pulse oximetry in corrective cyanotic heart surgery]. / Anwendbarketi und Grenzen der Pulsoximetrie bei Korrektur zyanotischer Herzvitien.

The aim of this study was to evaluate the agreement between arterial and pulse oximeter saturation values, especially under hypoxemic conditions, and to test the applicability of the method under routine anesthesia conditions. We studied 13 patients (12 children, 1 adult) with congenital cyanotic heart defects; 12 had a surgical correction during nonpulsatile cardiopulmonary bypass and 1 had a palliative operation. Arterial and pulse oximeter measurements were simultaneously taken and compared during induction of anesthesia, surgery, and in some cases during the postoperative period. Pulse oximeter saturation values were recorded by an Ohmeda Biox 3700 pulse oximeter, and the corresponding arterial saturations determined with a CO Oximeter (OSM2 Hemoximeter, Radiometer). The values lay in the range of 43%-100% arterial oxygen saturation. The results were evaluated while taking into account the steady state and non-steady state situations (i.e., when there were rapidly changing pulse oximetric saturation readings and difficulties in coordinating the comparative arterial measurements time-wise), as well as the equipment's internal characterization of the signal quality (High Quality Signal (HQS)/Low Quality Signal (LQS]. The correlation analysis for all comparative measurements, under both steady state and non-steady state conditions, gave a result of r = 0.927. When the comparison was restricted to the measurements in the steady state conditions, r = 0.935 resulted. The pulse oximetry saturation values had a tendency to lie below the corresponding arterial values. The fact that the pulse oximetry values were designated with HQS or LQS was no indication of a better or worse correlation with the arterial value.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonist discrimination between subtypes of tachykinin receptors in the guinea-pig ileum.

The effects of substance P and eledoisin on spontaneous and electrically-evoked release of [3H]acetylcholine, and on smooth muscle were studied in the guinea-pig myenteric plexus-longitudinal muscle preparation preloaded with [3H]choline. Substance P and eledoisin caused transient increases in spontaneous release of [3H]-acetylcholine and in longitudinal muscle tone. Both tachykinins were equipotent in contracting the muscle, but eledoisin was more potent than substance P in eliciting [3H]acetylcholine release. The release caused by substance P was enhanced in the presence of naloxone and scopolamine which suggests that the release is modulated through opioid and muscarinic receptors. Substance P and eledoisin inhibited the release of [3H]acetylcholine evoked by electrical stimulation at 0.1 Hz. The inhibition was not due to an activation of alpha-adrenoceptors, histamine or opioid receptors. The substance P antagonists (D-Pro2, D-Trp7,9)SP (10 and 30 microM) and (Arg5, D-Trp7,9, Nle11)SP5-11 (1 and 10 microM) competitively antagonized both the contractile effects of substance P and eledoisin, and the inhibition by the tachykinins of the electrically-evoked release of [3H]acetylcholine. The increase in spontaneous [3H]acetylcholine release elicited by substance P and eledoisin was not prevented by the substance P antagonists. The results suggest that the neuronal receptor whose activation causes inhibition of acetylcholine release and the smooth muscle receptor correspond to the SP-P type, whereas the neuronal receptor mediating an increase in spontaneous acetylcholine release is of the SP-E type. The two antagonists, (D-Pro2, D-Trp7,9)SP and (Arg5, D-Trp7,9, Nle11)SP5-11, selectively block only the SP-P receptor.