Circuito cerrado de tv y formación del profesorado

Una de las indiscutibles técnicas modernas, dentro del campo de la formación del profesorado, es la de la utilización del circuito cerrado de TV. Su eficacia está ya fuera del terreno de lo hipotético: el problema radica, más bien, en su incorporación a un sistema de formación eficaz. Antes de entrar en materia, es necesario hacer una aclaración previa. El equipo técnico material del que se compone un circuito cerrado de TV puede variar notablemente en grado de complejidad según los objetivos de utilización del mismo. La determinación de los elementos que le deben integrar en consecuencia de las finalidades que se persigan. Por esta razón, en el presente trabajo prescindimos de descripciones analíticas de circuitos cerrados posibles, por considerarlo un problema secundario. El circuito cerrado de TV para la formación del profesorado puede utilizarse fundamentalmente en dos vertientes: para transmitir información o instruir al profesorado y para la observación de una situación didáctica

2,4-Bis(3-fluoro­phen­yl)-3-aza­bicyclo­[3.3.1]nonan-9-one

The title compound, C20H19F2NO, exhibits a chair–chair conformation, with the aryl groups in the heterocycle in equatorial orientations and oriented at an angle of 33.35 (3)° to one another. A crystallographic mirror plane, passing through the N atom, the C and O atoms of the carbonyl group and the C atom in the 7-position, bis­ects the mol­ecule. The mol­ecular structure is stabilized by one C—H⋯N inter­action and the crystal structure is stabilized by a weak C—H⋯π inter­action

Nitrido-Sodalithe. I Synthese, Struktur und Eigenschaften von Zn7-xH2x[P12N24]Cl2 mit 0 <x< 3

Die Nitrido-Sodalithe Zn7-xH2x[P12N24]Cl2 mit 0 x 3 wurden durch heterogene Druckammonolyse von P3N5 in Gegenwart von ZnCl2 (T = 650°C) dargestellt. Die Verbindungen sind auch zugänglich durch Umsetzung von ZnCl2, (PNCl2)3 und NH4Cl bei 700°C. Die Kristallstrukturen von vier ausgewählten Vertretern der obigen Verbindungsreihe wurden auf der Basis von Röntgen-Pulverdiffraktometerdaten mit Hilfe der Rietveld-Methode verfeinert (I3m, a = 821,61(4) bis 824,21(1) pm, Z = 1). Im Festkörper liegt eine dreidimensionale Gerüststruktur allseitig eckenverknüpfter PN4-Tetraeder vor (PN: 163,6 pm, PNP: 125,6°, Mittelwerte), die dem Sodalith-Typ entspricht. Im Zentrum der -Käfige befinden sich Cl--Ionen, die ihrerseits tetraedrisch durch Zn2+-Ionen umgeben sind. Die Zn2+-Positionen sind statistisch besetzt und gemäß der angegebenen Phasenbreite (0 x 3) kann ein Teil der Zn2+-Ionen durch jeweils zwei H-Atome ersetzt werden, die ihrerseits kovalent an Stickstoffatome des PN-Gerüstes gebunden sind. Im IR-Spektrum der Verbindungen werden charakteristische Schwingungsbanden beobachtet

Understanding Segmental Dynamics in Polymer Electrolytes: A Computer Study

We study the segmental dynamics of poly(ethylene oxide) (PEO) from microscopic simulations in the neat polymer and a polymer electrolyte (PEO/LiBF$_4$) by analyzing the normal modes. We verify the applicability of the Rouse theory, specifically for the polymer electrolyte where dynamic heterogeneities, arising from cation-polymer interactions, alter the mobility non-uniformly along the chains. We find that the Rouse modes for both the systems are orthogonal despite the presence of non-exponential relaxation of the modes and violation of the Gaussian self-similarity of the chains. The slowdown of the segmental dynamics in the polymer electrolyte is rationalised by an order of magnitude increase in the friction coefficient for those monomers which are bound by cations. In general, for the electrolyte the Rouse predictions for the dynamics of segments (both free and/or bound) agree well except for very short times

2,4-Bis(4-bromo­phen­yl)-3-aza­bicyclo­[3.3.1]nonan-9-one

The title compound, C20H19Br2NO, shows a chair–chair conformation for the aza­bicycle with an equatorial disposition of the 4-bromo­phenyl groups [dihedral angle between the aromatic rings = 16.48 (3)°]. In the crystal, a short Br⋯Br contact [3.520 (4) Å] occurs and the structure is further stabilized by N—H⋯O hydrogen bonds and C—H⋯O inter­actions

2,4-Bis(3-methoxy­phen­yl)-3-aza­bicyclo­[3.3.1]nonan-9-one

In the crystal structure, the title compound, C22H25NO3, exists in a twin-chair conformation with equatorial orientations of the meta-methoxy­phenyl groups on both sides of the secondary amino group. The title compound is a positional isomer of 2,4-bis­(2-methoxy­phen­yl)-3-aza­bicyclo­[3.3.1]nonan-9-one and 2,4-bis­(4-methoxy­phen­yl)-3-aza­bicyclo­[3.3.1]nonan-9-one, which both also exhibit twin-chair conformations with equatorial dispositions of the anisyl rings on both sides of the secondary amino group. In the title compound, the meta-methoxy­phenyl rings are orientated at an angle of 25.02 (3)° with respect to each other, whereas in the ortho and para isomers, the anisyl rings are orientated at dihedral angles of 33.86 (3) and 37.43 (4)°, respectively. The crystal packing is dominated by van der Waals inter­actions and by an inter­molecular N—H⋯O hydrogen bond, whereas in the ortho isomer, an inter­molecular N—H⋯π inter­action (H⋯Cg = 2.75 Å) is found

2,4-Bis(4-chloro­phen­yl)-1-methyl-3-aza­bicyclo­[3.3.1]nonan-9-one

The title compound, C21H21Cl2NO, exists in a twin-chair conformation with an equatorial orientation of the 4-chloro­phenyl groups on both sides of the secondary amino group; the dihedral angle between the 4-chloro­phenyl rings is 36.58 (2)°. The crystal packing is stabilized by an inter­molecular N—H⋯O hydrogen bond and a weak Cl⋯Cl [3.4331 (9) Å] inter­action

Stochastic lattice models for the dynamics of linear polymers

Linear polymers are represented as chains of hopping reptons and their motion is described as a stochastic process on a lattice. This admittedly crude approximation still catches essential physics of polymer motion, i.e. the universal properties as function of polymer length. More than the static properties, the dynamics depends on the rules of motion. Small changes in the hopping probabilities can result in different universal behavior. In particular the cross-over between Rouse dynamics and reptation is controlled by the types and strength of the hoppings that are allowed. The properties are analyzed using a calculational scheme based on an analogy with one-dimensional spin systems. It leads to accurate data for intermediately long polymers. These are extrapolated to arbitrarily long polymers, by means of finite-size-scaling analysis. Exponents and cross-over functions for the renewal time and the diffusion coefficient are discussed for various types of motion.Comment: 60 pages, 19 figure

2,4-Bis(2-eth­oxy­phen­yl)-7-methyl-3-aza­bicyclo­[3.3.1]nonan-9-one

The crystal structure of the title compound, C25H31NO3, exists in a twin-chair conformation with an equatorial orientation of the ortho-eth­oxy­phenyl groups. According to Cremer and Pople [Cremer & Pople (1975 ▶), J. Am. Chem. Soc. 97, 1354–1358], both the piperidone and cyclo­hexa­none rings are significantly puckered with total puckering amplitutdes Q T of 0.5889 (18) and 0.554 (2) Å, respectively. The ortho-eth­oxy­phenyl groups are located on either side of the secondary amino group and make a dihedral angle of 12.41 (4)° with respect to each other. The methyl group on the cyclo­hexa­none part occupies an exocyclic equatorial disposition. The crystal packing is stabilized by weak van der Waals inter­actions

Evidence of Final-State Suppression of High-p_T Hadrons in Au + Au Collisions Using d + Au Measurements at RHIC

Transverse momentum spectra of charged hadrons with ${p_{T} <}$ 6 GeV/c have been measured near mid-rapidity (0.2 $< \eta <$ 1.4) by the PHOBOS experiment at RHIC in Au + Au and d + Au collisions at ${\sqrt{s_{_{NN}}} = \rm {200 GeV}}$. The spectra for different collision centralities are compared to ${p + \bar{p}}$ collisions at the same energy. The resulting nuclear modification factor for central Au + Au collisions shows evidence of strong suppression of charged hadrons in the high-$p_{T}$ region (${>2}$ GeV/c). In contrast, the d + Au nuclear modification factor exhibits no suppression of the high-$p_{T}$ yields. These measurements suggest a large energy loss of the high-$p_{T}$ particles in the highly interacting medium created in the central Au + Au collisions. The lack of suppression in d + Au collisions suggests that it is unlikely that initial state effects can explain the suppression in the central Au + Au collisions.Comment: 3 pages, 4 figures, International Europhysics Conference on High Energy Physics EPS (July 17th-23rd 2003) in Aachen, German