Imaging colloidal gold labels in LVSEM

On biological samples, the topographic imaging capabilities of the new generation of scanning electron microscopes (SEM) (those having both field-emission guns and low aberration lenses) rival those of the replica techniques. In addition, they permit the localization of specific molecules on the sample surface using one of several labeling techniques utilizing heavy metal colloids. Normally, colloidal gold can be detected in the SEM both by the secondary electron signal (shape) and by the backscattered electron signal (BSE, Z-contrast). The new instruments seem to produce their best topographic images using low-beam voltage (1–5 kV) where topographic contrast is higher and the required thickness of the metal coating is less (Haggis and Pawley 1988, Ris and Pawley 1988). Although the detection of backscattered electrons is more difficult at low-beam voltage, we are able to show here that the secondary electron (SE) signal produced with a 2–5-kV beam permits the unambiguous detection of gold particles as small as 5 nm on carbon-coated specimens while a 1-kV beam produces a high-quality topographic image of the same sample.     

The role of endothelium and nitric oxide in rat pial arteriolar dilatory responses to CO2 in vivo

Using a closed cranial window system and intravital microscopy/videometry, we studied the rat pial arteriolar (30-60 microns) responses to CO2 before and following a light/dye (L/D) endothelial injury or topical application of the nitric oxide synthase (NOS) inhibitor, nitro-L-arginine (L-NA) or its inactive form, D-NA. L/D treatment consisted of intravenous injection of sodium fluorescein and the illumination (for 90 s) of arteriolar discrete segments on the cortical surface with light from a mercury lamp. Functional changes in pial arteriolar endothelium were characterized by evaluating responses to topical application of acetylcholine (Ach, 5 x 10(-4) M) and to intravenous (i.v.) oxotremorine (OXO, a stable blood-brain barrier permeant muscarinic agonist, 1 microgram kg-1 min-1). After the L/D injury, dilation to Ach was absent whereas dilations to the NO donor, S-nitrosoacetyl-penicillamine (SNAP, 10(-5) M) and to CO2 (5%) were unchanged (PaCO2 = 70 mm Hg). Loss of Ach response but intact SNAP response confirmed functional endothelial injury and intact smooth-muscle function. The global endothelium-dependent vasodilation induced by i.v. OXO was markedly attenuated when expanding the L/D injury field from 300 microns to 6 mm in diameter. However, the global vasodilation induced by inhalation of CO2 was still unaffected by this increase in the area of light exposure. This provides evidence that the expanded exposure was capable of impairing global vasodilation resulting from endothelium-dependent stimuli but not from inhalation of CO2. The intact CO2 response despite an endothelial dysfunction suggests that the reported NO dependence of hypercapnia-induced cerebral hyperemia in rats cannot be attributed to an endothelial NO source.(ABSTRACT TRUNCATED AT 250 WORDS)     

TAR-RNA binding by HIV-1 Tat protein is selectively inhibited by its L-enantiomer

An oligoribonucleotide, corresponding to the Tat-interactive top half of the HIV-1 TAR RNA stem-loop, was synthesized in both the natural D- and the enantiomeric L-configurations. The affinity of Tat for the two RNAs, assessed by competition binding experiments, was found to be identical and is reduced 10-fold for both, upon replacement of the critical bulge residue U23 with cytidine. It is suggested that this interaction of the flexible Tat protein depends strongly upon the tertiary structure of a binding pocket within TAR, but not upon its handedness, and may be described by a 'hand-in-mitten' model.     

Ein Verfahren zur Identifizierung von Zeichen,deren Wiedergabe stationären statischen Störungen unterworfen ist

Zusammenfassung SeiE={e ₁, ...,e _m } eine Menge zufälliger Ereignissee _i , die mit den WahrscheinlichkeitenP _i auftreten. Auf ein Ereignise _i folgt ein Ereignis aus einer weiteren Ereignismenge mit einer vone _i bedingten Wahrscheinlichkeit. wird ein Zufallsvektor x zugeordnet. Es wird angenommen, daß fürP _i , den Mittelwert und die zentralen Momente zweiter Ordnung bezüglich der bedingten Wahrscheinlichkeit Schätzwerte erhalten werden können. Ferner wird die Hypothese gemacht, daß die bedingte Wahrscheinlichkeit durch eine Dichtefunktionf _i (d _i ) beschrieben werden kann, welche nur von einer positiv definiten quadratischen Formd _i ² (x) abhängt. Dann wird gezeigt, daß für beliebigef _i die quadratische Form durch den Mittelwert und die zentralen Momente zweiter Ordnung bestimmt ist. Weiterhin wird angenommen, daß eine Schätzfunktion für die eindimensionale Dichtefunktionf _i (d) erhalten werden kann. Wird irgendein x vorgelegt, so kann dann nach Wahrscheinlichkeit entschieden werden, welchese _i vor x erfolgt ist.

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Summary LetE={e ₁, ...,e _m } be a set of random eventse _i occuring with probabilitiesP _i . An evente _i is followed by an event of another set of events with a probability conditional one _i . To is assigned a random vector x. It is assumed that estimates are obtainable forP _i , the mean, and the central second order moments with respect to the conditional probability. Further, the hypothesis is made that the conditional probability can be described by a density functionf _i (d _i ) which depends only on a positive definite quadratic formd _i ² (x). Then it is shown that for arbitraryf _i the quadratic form is determined by the mean and the central second order moments. Let an estimate for the one-dimensional density functionf _i (d) be known. Then, if any x is presented it can be decided in probability whiche _i preceded x.

     

Einfluß des Phosphors auf die Korrosionsgeschwindigkeit weicher,unlegierter Stähle in verdünnter Schwefelsäure

Einfluß von Phosphor auf den zeitlichen Verlauf der Korrosionsgeschwindigkeit am Ruhepotential beim Beizen in verdünnter Schwefelsäure. Unstetigkeit der Stromdichte-Potential-Kurve bei Stählen mit hohen Phosphorgehalten durch Deckschichtbildung. Untersuchungen zum Aufbau und zur chemischen Zusammensetzung der Deckschicht.     

Buried stacked insulator: new SOI-structure formed by ion beam synthesis

The formation of a new SOI-structure is proposed and the first experimental results are presented. Using high dose implantation of nitrogen and oxygen, a buried stacked layer consisting of silicon dioxide (upper part), silicon oxynitride (medium part) and silicon nitride (lower part) was formed in single crystalline silicon.<>     

Origin of nondisjunction in trisomy 8 and trisomy 8 mosaicism

OBJECTIVES: This study explores reactions to low-level chemical challenge, aiming at the development of test procedures for assessing individual sensitivity to smells and chemicals. METHODS: Subjects with symptoms and neuropsychological test results compatible with toxic encephalopathy type 2A (TE-2A) and 2B (TE-2B) and unexposed referents (N=12 in each group) were challenged in an exposure chamber. Toluene exposure was started at 11 mg/m3, and it followed a geometric progression scale with a ratio of 2, until reaching 180 mg/m3. In a counterbalanced design, the subjects were similarly exposed to n-butyl acetate starting at a concentration of 14 mg/m3 and increasing to 228 mg/m3. At each exposure level, smell intensity was measured on a 7-step category scale. Mucous membrane irritation and annoyance reactions were rated on visual analogue scales. RESULTS: Both TE groups showed high sensitivity to the low-level solvent challenge, which provoked immediate annoyance and fatigue reactions. In particular the TE-2B group related smell intensity to various annoyance dimensions during exposure to n-butyl acetate, a pattern not observed during toluene exposure. The reference group clearly separated smell intensity and annoyance reactions in both exposure conditions. CONCLUSIONS: The reaction of the TE cases suggests that chemical sensitivity can be distinguished from normal annoyance reactions by the inability to differentiate between smell intensity and an experience of irritation from mucous membranes in air concentrations well below the trigeminal irritation threshold level. Fatigue coreactivity in challenges to single substances below the neurotoxic level may also be important.     

Clinical relevance of lithium determination in RBC: results of a catamnestic study (author's transl)]

In 34 out-patients Li+- and K+-concentrations were determined in plasma and RBC during 15 months of clinical routine observations. Average frequency of check-ups was 9/patient. Psychopathological state and side effects were documented by the AMP-system. The mean intra-extracellular lithium concentration ratio (LiQ) was 34%. The ratio and the absolute lithium RBC concentration showed a wide intraindividual variability between 5 and 53%. Patients under 50 years old had the same absolute concentration values as the older ones but required a 50% higher average dose. Side effects such as tremor and thirst correlated well the intra-extracellular ratio. No difference was found between unipolar and bipolar depressions. LiQ was slightly reduced and KQ increased in patients with severe relapses or additional psychotropic medication.