Search results for "Arrhenius"

Non-Arrhenius Behavior of Surface Diffusion Near a Phase Transition Boundary

1997

We study the non-Arrhenius behavior of surface diffusion near the second-order phase transition boundary of an adsorbate layer. In contrast to expectations based on macroscopic thermodynamic effects, we show that this behavior can be related to the average microscopic jump rate which in turn is determined by the waiting-time distribution W(t) of single-particle jumps at short times. At long times, W(t) yields a barrier that corresponds to the rate-limiting step in diffusion. The microscopic information in W(t) should be accessible by STM measurements.

Estimation of Nucleation Barriers from Simulations of Crystal Nuclei Surrounded by Fluid in Equilibrium

2016

Nucleation rates for homogeneous nucleation are commonly estimated in terms of an Arrhenius law involving the nucleation barrier, written in terms of a competition of the contribution in surface free energy of the nucleus and the free energy gain proportional to the nucleus volume. For crystal nuclei this “classical nucleation theory” is hampered by the problem that the nucleus in general is non spherical, since the interfacial excess free energy depends on the orientation of the interface relative to the crystal axes. This problem can be avoided by analyzing the equilibrium of a crystal nucleus surrounded by fluid in a small simulation box in thermal equilibrium. Estimating the fluid press…

Mobility determination of lead isotopes in glass for retrospective radon measurements

2008

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of …

Calibration and simulation of ASM2d at different temperatures in a phosphorous removal pilot plant

2006

In this work, an organic and nutrient removal pilot plant was used to study the temperature influence on phosphorus accumulating organisms. Three experiments were carried out at 13, 20 and 24.5 degrees C, achieving a high phosphorus removal percentage in all cases. The ASM2d model was calibrated at 13 and 20 degrees C and the Arrhenius equation constant was obtained for phosphorus removal processes showing that the temperature influences on the biological phosphorus removal subprocesses in a different degree. The 24.5 degrees C experiment was simulated using the model parameters obtained by means of the Arrhenius equation. The simulation results for the three experiments showed good corresp…

Apparent activation energies and apparent frequency factor in polarographic waves of paludrine-Zn(II)

1993

Abstract Arrhenius and Vlcek plots of ac 1 and dp polarograms of paludrine-Zn complexes are tested in order to understand the apparent activation energies and pre-exponential factor, and their dependence on the potential. These empirical treatments are useful for obtaining information about the energetic contributions of the elemental processes associated with the Zn(II) and paludrine ligands in the overall mechanism of reduction of the complex 2:1 on the mercury interface.

Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

1997

The anionic polymerization of methyl methacrylate using tetraphenylphosphonium triphenylmethanide as an initiator proceeds in a living manner even at room temperature. The rate constants of propagation were measured between -20 and +20 °C using a flow tube reactor. At 0 °C the reaction half-lives range from 0.3 to 1 s. The polymerization follows first-order kinetics with respect to monomer conversion (with a short induction period) and shows a linear dependence of the number-average degree of polymerization on conversion with high initiator efficiencies and narrow molecular weight distributions (M w /M n < 1.1). The dependence of the measured rate constants on the active center concentratio…

Synthesis, crystal structures and magnetic properties of M(II)Cu(II) chains (M = Mn and Co) with sterically hindered alkyl-substituted phenyloxamate …

2011

A series of neutral oxamato-bridged heterobimetallic chains of general formula [MCu(L(x)2 (S)2] · p S · q H2O [p = 0-1, q = 0-2.5; L1 = N-2,6-dimethylphenyloxamate, S = DMF with M = Mn (1a) and Co (1b); L2 = N-2,6-diethylphenyloxamate, S = DMF with M = Mn (2a) and Co (2b) or S = DMSO with M = Mn (2c) and Co (2 d); L3 = N-2,6-diisopropylphenyloxamate, S = DMF with M = Mn (3a) and Co (3b) or S = DMSO with M = Mn (3c) and Co (3d)] were prepared by treating the corresponding anionic oxamatocopper(II) complexes [Cu(L(x))(2)]2- (x = 1-3) with M(2+) cations (M = Mn and Co) in DMF or DMSO as the solvent. The single-crystal X-ray structures of 2a and 3a reveal the occurrence of well-isolated, zigzag…

1978

A newly designed automatically controlled stirred reactor suitable for kinetic measurements of reactions with half lives ≥2s has been applied to follow the anionic polymerization of methyl methacrylate in THF with Na+ as a counter ion in the presence of an excess of NaB(C6H5)4. As initiators were used: benzylsodium reacted with α-methylstyrene (I), fluorenylsodium (II), and 9-methylfluorenylsodium (III). With I the initiation is fast as compared with the polymerization reaction which is first order in monomer concentration. Within the range of −50°C to −100°C an almost unperturbed “living” polymerization is observed. The Arrhenius plot of the rate constants results in a straight line with a…

Adaptations to thermal variation in two Mediterranean limpets - cardiac response and haemocyte lysosomal stability

2012

Patella rustica and Patella caerulea are two congeneric limpet species, both occurring along the rocky shores of the Mediterranean but on different tidal heights. P. rustica is dominant in the upper intertidal zone while P. caerulea is more abundant in the lower part of the same zone. Understanding variations in physiological adaptations to thermal stress is vital when investigating intertidal species' distribution. Hence, to investigate the relationship between their physiological thermal tolerance and intertidal zonation, laboratory experiments were designed to test the hypothesis that the lower zoned P. caerulea has reduced upper thermal limits when compared with higher zoned P. rustica,…