Search Results - (Author, Cooperation:Heydt)

1434-6036

Springer Online Journal Archives 1860-2000

Physics

Abstract A statistical model of a driven system is developed. Its microscopic elements are the ion channels through a nerve membrane. Their conductances are stochastically switching under the competing influences of thermal noise and local membrane voltage. A current flow through the membrane induces a coupling between the channels via the electrolytes surrounding the membrane. The long range of the coupling permits a generalized mean field theory for the stationary membrane current as a function of the applied electrode voltage. We derive analytically the macroscopic conductance-voltage-temperature relation for the spatially uniform current state. It shows analogues of first and second order phase transitions. The critical temperature diverges at a finite coupling strength. The theory fits sodium conductance characteristics measured on nerve axon membranes from various species by a variation of only the coupling strength. This supports the hypothesis that this simplest possible model for sodium channels is universal for all species.

Electronic Resource

1434-6036

Springer Online Journal Archives 1860-2000

Physics

Abstract The driven system of conducting channels in a nerve membrane is investigated. A current flow generates a coupling between the channels: the current through a channel is influenced by the presence of other conducting channels via the deformation of the equipotential surfaces within the media adjacent to the membrane. We derive an integral equation for the membrane voltageV(s) (s in the membrane plane) and solve it for different membrane conductance distributionsγ(s) including models for stochastic distributions of conducting channels.V(s) is a nonlinear functional ofγ(s). The system of coupled channels is compared with an Ising model. The system exhibits a multi-channel interaction which can be characterized by two different rangesd int andD 1. For a mean channel distanced 0≫d int interaction effects are negligible, and ford 0≪D 1 all channel-voltages are equal and thus represent a “mean-field” for the channels. Increasing conductivity of the medium decreasesd int and increasesD 1. With experimental data on sodium channels in nerve membranes we find:d int≈d 0, i.e. a 50% decrease of the channel-voltages by the interaction, andD 1≈103⋯104 d 0, which indicates mean-field behaviour of the channels. In a subsequent paper we shall treat the statistics of channels which open and close stochastically under the influence of the local membrane voltage.

Electronic Resource

0009-2940

Chemistry ; Inorganic Chemistry

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Investigations on Diazo Compounds and Azides, XLII. (Diazomethyl)cyclopropenes by Electrophilic Diazoalkane SubstitutionThe (diazomethyl)cyclopropenes 9 and 10 are formed via electrophilic diazoalkane substitution preferably of diazomethylphosphoryl compounds with cyclopropenylium salts. Either the diazomethyl compounds (7a-c) react with the cyclopropenylium salts 6a-e in the presence of triethylamine (method A) or the metallated diazo compounds 8a-d are combined with the cyclopropenylium bromides 6c-e (method B) (details see table 1). The (diazomethyl)cyclopropenes undergo a novel type of isomerization to pyridazines, partly without heating (9d-f → 11b-d), partly by refluxing in toluene (9a,g → 11a,e as well as 10e,f → 12a,b). The bicyclic betaines 15 and 17 are supposed to be intermediates. The diazomethyl compounds 9a and b yield the α,β- unsaturated ketones 20a and b by acid-catalyzed decomposition.

Die (Diazomethyl)cyclopropene 9 und 10 entstehen durch elektrophile Substitution vorzugsweise von Diazomethylphosphorylverbindungen mit Cyclopropenyliumsalzen. Man setzt entweder die Diazomethylverbindungen selbst (7a-c) in Gegenwart von Triethylamin mit den Cyclopropenyliumsalzen 6a-e um (Methode A) oder läßt die metallierten Diazoverbindungen 8a-d mit den Cyclopropenyliumbromiden 6c-e reagieren (Methode B) (Details s. Tab. 1). Die (Diazomethyl)-cyclopropene gehen teils ohne Erwärmen (9d-f → 11b-d), teils beim Erhitzen in Toluol (9a,g → 11a,e sowie 10e,f → 12a,b) eine neuartige Isomerisierung zu Pyridazinen ein; Zwischenstufen sind vermutlich die bicyclischen Betaine 15 und 17. Die Diazomethylverbindungen 9a und b liefern bei der säurekatalysierten Zersetzung die α,β-ungesättigten Ketone 20a und b.

3 Tab.

Electronic Resource

book

2006

Soziale Situation ; Bildungspolitik ; Förderungsmaßnahme ; Interkultureller Faktor ; Wirtschaftslage ; Arbeitsmarktchance ; Berufliche Integration ; Krankenschwester ; Kontaktstudium ; Hochschule ; Weiterbildung ; Konferenzschrift ; Zuwanderung ; Hochschulabsolvent ; Arzt ; Flüchtling ; Hoch Qualifizierter ; Migrant ; Australien ; Großbritannien ; Niederlande

German

Online

2008

Bildungserfolg ; Grundbildung ; Kompetenz ; Empirische Untersuchung ; Forschung ; Forschungsdesign ; Methode ; Vergleich ; Bildungsbeteiligung ; Soziale Ungleichheit ; Einstellung (Psy) ; Bildungsangebot ; Bildungsertrag ; Schulform ; Ganztagsschule ; Schüler ; Interesse ; Lesekompetenz ; Mathematikunterricht ; Mathematische Kompetenz ; Naturwissenschaftlicher Unterricht ; Bundesland ; Migrationshintergrund ; PISA (Programme for International Student Assessment) ; Deutschland

German

Literaturangaben S. 23

book

2001

Demokratische Bildung ; Staatsbürgerliche Erziehung ; Begriff ; Europäische Erziehung ; Europäische Identität ; Definition ; Europa

English

article

2001

Gymnasiale Oberstufe ; Leistungsbeurteilung ; Selbstständiges Lernen ; Lernkonzept ; Fragend-entwickelnder Unterricht ; Lerntheoretische Didaktik ; Unterrichtsmethode ; Unterrichtsmodell ; Seminar ; Kurs

Pädagogisches Handeln, Bd. 5 (2001) H. 2, S. 7-30, 1434-2111

German

Literaturangaben

book

2004

Grundschule ; Schüler ; Unterricht ; Mehrfachbehinderung

English

CD-ROM 1

article

2008

Lernfeld ; Steuerungs- und Regelungstechnik ; Berufsschule ; Ausstattung

Berufsbildung : Zeitschrift für Theorie, Praxis, Dialog, Bd. 62 (2008) H. 113/114, S. 36-37, 0005-9536

German

2018-07-03

The American Association for Cancer Research (AACR)

1078-0432

1557-3265

Medicine

2013-02-22

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Aging/genetics/pathology/*physiology ; Animals ; Apoptosis ; DNA Damage ; Fibrosis/genetics/pathology ; Gene Deletion ; *Gene Expression Regulation ; Gene Knockout Techniques ; Genetic Therapy ; Heart/*physiology ; Mice ; Mice, Inbred C57BL ; MicroRNAs/*genetics/metabolism ; Myocardial Infarction/genetics/pathology/therapy ; Myocardium/cytology/*metabolism/pathology ; Myocytes, Cardiac/cytology/metabolism/pathology ; Substrate Specificity ; Telomere/genetics/metabolism

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The optical near-field response of a three dimensional subwavelength aperture-semiconductor system is analyzed within a finite difference time domain scheme for Maxwell's and excitonic material equations. The analysis includes the field modification due to the high refractive index environment and the excitonic response to a near-field distribution. The resonant optical response is illustrated for anisotropic dipole transitions in quantum wells and the enhancement of the quadrupole transition in materials with dipole forbidden interband transitions. © 2000 American Institute of Physics.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract An artificial osmotic cell has been constructed using reverse osmosis membranes. The cell consisted of a thin film of an osmotic solution (thickness: 100 to 200 μm) containing a non-permeating solute and was bounded between the membrane and the front plate of a pressure transducer which continuously recorded cell turgor. The membrane was supported by metal grids to withstand positive and negative pressures (P). At maximum, negative pressures of up to –0.7 MPa (absolute) could be created within the film on short-term and pressures of up to –0.3 MPa could be maintained without cavitation for several hours. As with living plant cells, the application of osmotic solutions of a non-permeating solute resulted in monophasic relaxations of turgor pressure from which the hydraulic conductivity of the membrane (Lp) and the elastic modulus of the cell (ɛ) could be estimated. The application of solutions with permeating solutes resulted in biphasic pressure relaxation curves (as for living cells) from which the permeability (Ps) and reflection (σs) coefficients could be evaluated for the given membrane. Lp, Ps, and σs were independent of P and did not change upon transition from the positive to the negative range of pressure. It is concluded that the artificial cell could be used to simulate certain transport properties of living cells and to study phenomena of negative pressure as they occur in the xylem and, perhaps, also in living cells of higher plants.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

We studied the relation between anatomical structure and functional properties of cells in area V2 of the macaque. Visual function was assessed in the alert animal during fixation of gaze. Recording sites were reconstructed with respect to cortical lamination and the cytochrome oxidase pattern. We measured orientation and direction selectivity, end-stopping, sensitivity to binocular disparity and ocular dominance, and determined more complex functions like sensitivity to anomalous contours and lines defined by coherent motion. Orientation selectivity was found in all parts of area V2, with high frequencies in the pale and thick stripes of the cytochrome oxidase pattern, and with lower frequency in the thin stripes. Representations of anomalous contours were found in the pale and thick stripes with similar frequencies, but generally not in the thin stripes, which have been thought to process colour. Lines defined by coherent motion were most frequently represented in the thick stripes; they were less frequent in the pale stripes, and (as with anomalous contours) were not found in the thin stripes. Sensitivity to binocular disparity was found in all types of stripes, but more frequently in the thick stripes, where the exclusively binocular neurons were also concentrated. By contrast, no segregation was found for direction selectivity and end-stopping. All neuronal properties were distributed evenly across cortical laminae. We conclude that mechanisms for figure–ground segregation involve the pale and the thick stripes of the cytochrome oxidase pattern, perhaps with greater emphasis on 'shape from motion’and 'stereoscopic depth’in the thick stripes, while more elementary neuronal properties are distributed almost evenly across the stripe pattern.

Electronic Resource

0146-5945

Political Science

1551-2916

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

The crystallographic texture and thermal conductivity of zirconia coatings deposited by electron beam evaporation on a variety of substrates have been measured. It was found that the thermal conductivity of coatings deposited at the same temperature was independent of whether they were deposited on polycrystalline alumina, single-crystal sapphire, single-crystal zirconia, or fused silica. The room-temperature thermal conductivity of the coatings deposited at 700°C was 0.32 W/(m·K), increasing to 1.36 W/(m·K) for coatings deposited at 1150°C. Similarly, the crystallographic texture was also independent of the substrate and had a (111) fiber texture at 700° and 900°C, switching to a (200) fiber texture by 1050°C. The exception was the coating deposited at 1150°C on (111) single-crystal zirconia which was epitaxial and exhibited a thermal conductivity of 2.46 W/(m·K). It is concluded that the properties of zirconia thermal barrier coatings are determined by the growth conditions rather than those associated with nucleation on the underlying substrate.

Electronic Resource

1468-5922

Blackwell Publishing Journal Backfiles 1879-2005

Psychology

Electronic Resource

1468-5922

Blackwell Publishing Journal Backfiles 1879-2005

Psychology

Electronic Resource

1468-5922

Blackwell Publishing Journal Backfiles 1879-2005

Psychology

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Johnny Morton stood in the trapezoid silhouette of the New York Public Library. Four marble statues of literary figures guarded the entryway under an awning propped up by gleaming black columns. Clarke, Wells, Verne, Bulgakov, all gazing westward across the plaza and beyond. Above this was the ...

Electronic Resource