150,292 research outputs found
Teacher Education Interventions on Teacher TPACK: A Meta Analysis Study
No full textThe coding manual, coding results, and meta-analysis data for the review article
Appendix B Metadata for the search paper code table(Teacher Education Interventions on Teacher TPACK: A Meta Analysis)
No full textThe coding manual, coding results, and meta-analysis data for the review article
Teacher Education Interventions on Teacher TPACK: A Meta Analysis Study
No full textThe coding manual, coding results, and meta-analysis data for the review article
Appendix C Metadata for the database search keywords (Teacher Education Interventions on Teacher TPACK-A meta-analysis)
No full textSearch keywords from four databases: Web of Science, Google Scholar, ProQuest and Scopus
Appendix A Metadata for the selected articles (Teacher Education Interventions on Teacher TPACK)
No full textThe key metadata information for the 59 selected articles for the systematic review
Reflexiones en tomo a la NEP y la estrategia de industrialización acelerada en la URSS, 1921-1929
No full textEditada en la Fundación SEPILa década de los años veinte del siglo XX estuvo caracterizada en la URSS
por dos cambios de rumbo muy significativos: el abandono del «Comunismo
de Guerra» y su sustitución por la «Nueva Política Económica» (NEP) en
1921, y la adopción de una estrategia de industrialización acelerada, cristalizada
en el Primer Plan Quinquenal (PPQ) de la economía, en 1929. En
los últimos años, diversos especialistas han argumentado, en contra de la opinión
tradicional, que la industrialización acelerada no tenía por qué haber
implicado un abandono de la NEP, la supresión del mercado y la consiguiente
colectivización de la agricultura, sino que hubiera podido mantenerse en el
marco de la vigencia de la Ley del Valor. El presente trabajo trata de mostrar,
desde una perspectiva teórica, y con ayuda del modelo más representativo
de la filosofía del PPQ, que dicha interpretación no es correcta.The Soviet Union experienced two very pronounced changes of direction
in 1921 and 1929. At the beginning of the decade, the strategy of «War Communism
» was abandoned, substituted by the completely different «New Economic
Policy» (NEP); and changed again, at the end of those years, towards
a strategy of forced industrialization based on the collectivisation of the agricultural
sector. In recent years, some specialists have argued that this second change was unnecessary: i.e., rapid industrialization could have been achieved
wíthin the framework of NEP and the Law of Value. The purpose of this
paper is to argüe, froin a theoretical point of view, and with the help of the
model that best summarizes the strategy of rapid industríalization, that this
new interpretation cannot be sustained, and that those authors that defended
the incompatibiHty of NEP and rapid industrialization were correct.Publicad
Catalyst-Site-Controlled Coordination Polymerization of Polar Vinyl Monomers to Highly Syndiotactic Polymers
No full textAbstract: This contribution reports a combined synthetic, kinetic, mechanistic, and theoretical/computational
study of the recently discovered catalyst-site-controlled coordination polymerization of polar vinyl monomers
[such as methyl methacrylate (MMA) and N,N-dimethylacrylamide (DMAA)] into highly syndiotactic polymers.
Among the 12 Cs-ligated ansa-cyclopentadienyl (Cp)-R2E(C,Si)-fluorenyl (Flu) group 4 metallocene catalyst
systems examinedswhich varied in metal center, anion structure, bridging atom and substituents, and
ligand substitution patternscationic ansa-metallocene ester enolate catalyst 6+[B(C6F5)4]-, derived from
the activation of the precatalyst [Ph2C(Cp)(2,7-tBu2-Flu)]Zr[OC(OiPr)dCMe2]2 with [Ph3C][B(C6F5)4], stood
out as the best catalyst in all aspects of the MMA polymerization at room temperature, including the highest
activity (1554 h-1 TOF), efficiency (98% I*), syndiotacticity (94% rr), and control (predicted number-average
molecular weight and 1.14 molecular weight distribution). Kinetic and mechanistic results are consistent
with a catalyst-site-controlled, monometallic coordination-addition mechanism, involving fast intramolecular
addition within the catalyst-monomer complex leading to the resting eight-membered ester enolate chelate,
followed by the rate-limiting ring-opening of the chelate to regenerate the active species. This work has
also uncovered several unique features of this polymerization system that are in marked contrast to the
propylene polymerization by analogous Cs-ligated cationic alkyl catalysts: a constant syndiotacticity of PMMA
produced over a wide polymerization temperature range (i.e., from 0 C, 94% rr to 25 C, 94% rr to 50 C,
93% rr); insensitivity of its high activity, degree of control, and stereoselectivity to solvent polarity and structure
of weakly coordinating anions; and deviation from a pure site-control mechanism at high [MMA]/[catalyst]
ratios. Computational results provide theoretical support for the proposed monomer-assisted, catalyst-site
epimerization, after an enantiofacial mistake, to a thermodynamically more stable resting state, which
accounts for the observed higher than expected [mr] contents based on a pure site-controlled mechanism.
DFT calculations rationalize why the Ph2C< bridged catalyst 6 exhibits higher stereoselectivity than other
catalysts with the Me2C< or Me2Si< bridge: the bridge rigidity pushes the η3-bound Flu ligand closer to the
growing chain and the monomer, thereby increasing ΔEstereo between the competing transition states for
the addition of a monomer molecule to the opposite (correct and wrong) enantiofaces of the enolate growing
chain. The relative polymerization activity of this catalyst series is shown to correlate with the relative
energetics of the back-biting of the penultimate unit and ion-pair formation
Syndioselective MMA Polymerization by Group 4 Constrained Geometry Catalysts: A Combined Experimental and Theoretical Study
No full textThis contribution reports a combined experimental (with kinetics and tangible effects on
syndioselectivity) and theoretical (with density functional theory) study of (CGC)M catalysts [M ) Ti, Zr; CGC
) Me2Si(η5-Me4C5)(tBuN)], addressing a need for a fundamental understanding of the stereoselectivity observed
for such catalysts in polymerization of methyl methacrylate (MMA) and an explanation for the chain-end control
nature of the syndioselective MMA polymerization by the chiral (CGC)Ti catalyst. The living/controlled MMA
polymerization by (CGC)TiMe+MeB(C6F5)3
- (1) follows the zero-order kinetics in [MMA], implying a faster
ring-opening process of the cyclic chelate relative to MMA addition within the catalyst-monomer complex in a
unimetallic propagation cycle. The syndioselectivity of 1 is insensitive to monomer and catalyst concentrations
as well as to ion-pairing strength varied with counterion structure and solvent polarity. Comparative studies using
identical (CGC)M bis(isopropyl ester enolate) structures show that the (CGC)Ti system exhibits noticeably higher
syndioselectivity than the isostructural Zr system at ambient temperature. Density functional calculations rationalize
the higher syndioselectivity observed for the (CGC)Ti catalyst and lend a theoretical support for the mechanism
of MMA- or counterion-assisted catalyst site epimerization after a stereomistake, which accounts for the formation
of the predominately isolated m stereoerrors
- …
