Search results for "ESA"

A Contradiction between Pulsed and Steady-State Studies in the Recombination Kinetics of Close Frenkel Defects in KBr and KCl Crystals

1994

Theoretical study of the kinetics of the correlated annealing of pairs of close (geminate) F-H centers in KCl and KBr crystals controlled by their diffusion and elastic attraction shows that the multi-step (kink) decay in defect concentrations observed more than once in thermostimulated experiments takes place only for very close F-H center pairs which are no further than fourth nearest neighbors. On the other hand, it is demonstrated (both theoretically and experimentally) that such F-H center pairs should be destroyed by the tunneling recombination already at time ≤10 -4 s, i.e. much before beginning of the thermostimulated experiments. Possible explanations of this contradiction are sugg…

Contribution to modeling the viscosity Arrhenius-type equation for some solvents by statistical correlations analysis

2014

Abstract Estimation and knowledge of transport properties of fluids are essential for heat and mass flow. Viscosity is one of the important properties which are affected by temperature and pressure. In the present work, based on the use of econometric and statistical techniques for parametric and non-parametric regression analysis and statistical correlation tests, we propose an equation modeling the relationship between the two parameters of viscosity Arrhenius-type equation, such as the Arrhenius energy ( E a ) or the pre-exponential factor ( A s ). In addition, we introduce a third interesting parameter called Arrhenius temperature ( T A ), to enrich the discussion. Empirical validation …

Cationic Mn12 Single-Molecule Magnets and Their Polyoxometalate Hybrid Salts

2003

A carboxy-substituted alkylammonium salt, namely, (4-carboxybenzyl)tributylammonium hexafluorophosphate, ZHPF(6), was prepared and used as incoming carboxylate ligand in a ligand-exchange reaction with [Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4)] (1) to afford a new Mn(12) single-molecule magnet (SMM), [Mn(12)O(12)(Z)(16)(H(2)O)(4)][PF(6)](16) (2), bearing 16 cationic units appended in the periphery. This compound behaves as a single-molecule magnet, exhibiting an out-of-phase ac magnetic susceptibility chi' '(M) signal that shows a single maximum in the 3.1-5.4 K temperature range. The frequency dependence of the maximum follows an Arrhenius law, with an effective energy barrier for reorientati…

1986

The kinetics of polyamidation was investigated for the reaction of diphenyl terephthalate as activated diester with trimethylhexamethylenediamine (1 : 1 mixture of 2,2,4- and 2,4,4-trimethyl isomers) in dimethyl sulfoxide. The good solubility of the resulting polyamide (Trogamid®(poly(iminoterephthaloylimino-x,y,z-trimethylhexamethylene))) assured a reaction in which all reactants, especially the polyamide, were soluble. The conversion was followed by analysis of the phenol set free and by measuring the number-average degree of polymerization Pn of the polyamide. The reaction obeyed an overall second order with the principle of equal reactivity of functional groups fulfilled for Pn ≿ 16. De…

Kinetischer nachweis zweier arten von ionenpaaren bei der anionischen polymerisation von styrol in tetrahydropyran

1967

Die durch Na-Naphthalin angeregte Polymerisation des Styrols in THP wurde im Temperaturbereich von -40 bis +50°C kinctisch verfolgt. Die Geschwindigkeitskonstante kw(±) der uber das lonenpaar erfolgenden Polymerisation wurde gemessen, indem die elektrolytische Dissoziation durch Zusatz von Tetraphenylbornatrium unterdruckt wurde. Oberhalb von 20°C ergibt sich bei Auftragung nach ARRHENIUS eine Gerade, aus welcher Aktivierungsenergie Ec und Frequenzfaktor Ac des Kontaktionenpaares zu berechnen sind. Diese Parameter stimmen in guter Naherung mit den E- und A- Werten uberein, die in sehr schwach polaren Losungsmitteln fur die anionische Polymerisation erhalten werden. Unterhalb von +20°C weich…

Characterization of water mobility in dry and wetted roasted coffee using low-field proton nuclear magnetic resonance

2007

Abstract Roasted and ground coffee was studied by low-field 1 H nuclear magnetic resonance at various water contents and temperatures. The spin–spin relaxation times ( T 2 ) were measured with single pulse free induction decay (FID) and Carr–Purcell–Meiboom–Gill (CPMG) sequences. Four relaxing components were distinguished: the solid population was observed with FID sequence at T 2s ∼9 μs; the other three populations, measured with the CPMG sequence, corresponded to an apolar phase, the coffee oil, and two polar phases. The two polar populations, observed at T 2m ∼6 ms and ∼27 ms (for coffee with 50% water content at 90 °C) were attributed to water in cell wall polymers and in water filling…

MBE growth and properties of low-density InAs/GaAs quantum dot structures.

2011

We present the results of a comprehensive study carried out on morphological, structural and optical properties of InAs/GaAs quantum dot structures grown by Molecular Beam Epitaxy. InAs quantum dots were deposited at low growth rate and high growth temperature and were capped with InGaAs upper confining layers. Owing to these particular design and growth parameters, quantum dot densities are in the order of 4-5x109 cm-2 with emission wavelengths ranging from 1.20 to 1.33 µm at 10 K, features that make these structures interesting for single-photon operation at telecom wavelength. High resolution structural techniques show that In content and composition profiles in the structures depend on …

1981

The anionic polymerization of tert-butyl methacrylate (TBMA) in tetrahydrofuran, using Na+ and Cs+ as counterions proceeds without side reactions even at room temperature. The resulting molecular weight distributions are nearly monodisperse (Mw/Mn ⩽ 1,01). The rate constants for the propagation of ion pairs were measured in the range from + 15 to −100°C. The Arrhenius plots are linear, but different for the two counterions, resulting in the following numerical values for the frequency exponent A and the activation energy Ea: A = 8,5 and Ea = 7,2 kcal/mol = 30 kJ/mol for Na+; A = 9,5 and Ea = 5,6 kcal/mol = 23 kJ/mol for Cs+. The difference between the counterions, which is in contrast to th…

1986

The aminolysis of diphenyl terephthalate by means of hexylamine was studied in dimethyl sulfoxide as a model reaction for polyamidation. The kinetic analysis showed that the two ester groups of the diphenyl ester do not react independently. Furthermore, the reaction of the first ester group was of mixed second and third order, while the reaction of the second ester group contained only a second order term. The rate constants found were used to determine the Arrhenius activation parameters.

La factoría de la Empresa Nacional Elcano en Manises : una valoración patrimonial

2010

La factoría de la Empresa Nacional Elcano de Manises (Valencia) fue construida entre 1946 y 1953 dentro de los planes estatales de reconstrucción industrial de la postguerra. Sus arquitecturas plantean una dualidad entre la modernidad y racionalidad de los espacios productivos y la tradición historicista de los edificios representativos, directamente relacionada con los programas ideológicos del Régimen. De su valoración a partir de los criterios establecidos por el Ministerio de Cultura para el Plan Nacional de Patrimonio Industrial, se desprende el extraordinario valor de la factoría como conjunto, el cual se sitúa por encima de la ya alta calidad de sus edificios a nivel individual, por …