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Acceleration
Published in Rob Appleby, Graeme Burt, James Clarke, Hywel Owen, The Science and Technology of Particle Accelerators, 2020
Rob Appleby, Graeme Burt, James Clarke, Hywel Owen
In order to achieve high gradients, the cavities must be specially cleaned to remove any particulates which could lead to field emission or increased surface heating. They must be washed with ultra-pure water (in clean rooms), rinsed using high-pressure water jets and have the walls smoothed using acid. Two methods of surface preparation have been developed for surface preparation of SRF Nb cavities. The first is buffered chemical polishing (BCP). This method uses a mixture of three acids: hydrofluoric acid, nitric acid and phosphoric acid. Nitric acid reacts with Nb to form niobium pentoxide, Nb2O5. Hydrofluoric acid reacts with the pentoxide to form niobium fluoride, NbF5, which is soluble, creating a polished Nb surface. The phosphoric acid serves as a buffer to help keep the reaction rate constant. The other surface preparation method is electro-polishing (EP). Here an acid mixture of mostly sulphuric acid with some hydrofluoric acid is used; the cavity acts as an anode and a cathode electrode is placed inside the cavity, with a potential difference of 10–20 V applied, which activates the polishing process. The enhanced electric field at any protrusion will cause the Nb surface to oxidise there first, thereby smoothing the surface [18].
Modeling Exposure
Published in Samuel C. Morris, Cancer Risk Assessment, 2020
where C is the concentration at the point of interestC0 is the concentration at time zerot is the reaction time between C0 and Ck is a reaction rate constantT is a time constant equal to 1/k, sometimes called the half-life.
The Reactivity Of Copper Sites In The “Blue” Copper Proteins
Published in René Lontie, Copper Proteins and Copper Enzymes, 1984
The cross-reaction rate constant, k12, for an outer-sphere electron-transfer reaction between two species is related to the equilibrium constant of that reaction, K12, and to the self-exchange rates of the two reactants, k11 and k22. This yields the Marcus equation:13
Comparative chemical and biological hydrolytic stability of homologous esters and isosteres
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Hygor M. R. de Souza, Jéssica S. Guedes, Rosana H. C. N. Freitas, Luis G. V. Gelves, Harold H. Fokoue, Carlos Mauricio R. Sant’Anna, Eliezer J. Barreiro, Lidia M. Lima
The enthalpy data for the reactant complexes and the transition states (TS), generated during the base catalysed hydrolysis, were calculated by the semi-empirical PM6-DH2 and were used to compute the activation energy of the base hydrolysis (Table 3 and Figure 7), according to the described methodology. The analysis of the kinetics of the tetrahedral intermediate formation, which is proposed as the rate-determining step of the base-catalysed hydrolysis39, was analysed. According to the Arrhenius kinetic theory, it is expected that a chemical reaction with a higher relative activation energy (Ea) value would present a lower reaction rate constant (k) value and, consequently, a higher t1/2. The relative Ea values calculated with the PM6-DH2 method show that the necessary energy for the reactant complex to reach the TS in the base-catalysed hydrolysis is higher for the n-butyl- (4), followed by the n-propyl- (3), ethyl- (2) and methyl- (1) benzoates (Table 3). These data are in agreement with the experimental t1/2 values determined for compounds 1–4 (Table 2). The longer the alkyl group, the greater the electron density donation towards the carbonyl carbon atom. So, since in the first step of the acyl-oxygen cleavage (BAC2) mechanism a nucleophilic attack of the hydroxide anion on the carbonyl-carbon occurs (with the partial formation of a covalent bond between the carbonyl C atom and the hydroxide O atom formation in the corresponding TS), it is expected that the longer the alkyl group is, the more energetic the TS should be12.
Silymarin loaded floating polymer(s) microspheres: characterization, in-vitro/in-vivo evaluation
Published in Pharmaceutical Development and Technology, 2020
Afaf A. Ramadan, Asmaa M. Elbakry, Hatem A. Sarhan, Salwa H. Ali
The energy of activation (Ea) and the decomposition reaction rate constant at room temperature (K20) was determined. Also, t½ and t90 for each formula estimated. A special computer program was used to determine the kinetic treatment and kinetic parameters of stability for the investigated silymarin microsphere formula. Zero, first, second order kinetics were tried to choose the most suitable order for stability study
Determination of Micropulse Modes with Targeted Damage to the Retinal Pigment Epithelium Using Computer Modeling for the Development of Selective Individual Micropulse Retinal Therapy
Published in Current Eye Research, 2022
Elena V. Ivanova, Pavel L. Volodin, Alexey V. Guskov
To determine the temperature-dependent reaction rate k(T), the Arrhenius equation (Equation 7) was used,35 which describes the dependence of the reaction rate constant k(T) on absolute temperature T in each space point and moment of time