Vacancy-assisted domain-growth in asymmetric binary alloys: a Monte Carlo study

A Monte Carlo simulation study of the vacancy-assisted domain-growth in asymmetric binary alloys is presented. The system is modeled using a three-state ABV Hamiltonian which includes an asymmetry term, not considered in previous works. Our simulated system is a stoichiometric two-dimensional binary alloy with a single vacancy which evolves according to the vacancy-atom exchange mechanism. We obtain that, compared to the symmetric case, the ordering process slows down dramatically. Concerning the asymptotic behavior it is algebraic and characterized by the Allen-Cahn growth exponent x=1/2. The late stages of the evolution are preceded by a transient regime strongly affected by both the temperature and the degree of asymmetry of the alloy. The results are discussed and compared to those obtained for the symmetric case.Comment: 21 pages, 9 figures, accepted for publication in Phys. Rev.

The Lattice and Simplex Structure of States on Pseudo Effect Algebras

We study states, measures, and signed measures on pseudo effect algebras with some kind of the Riesz Decomposition Property, (RDP). We show that the set of all Jordan signed measures is always an Abelian Dedekind complete $\ell$-group. Therefore, the state space of the pseudo effect algebra with (RDP) is either empty or a nonempty Choquet simplex or even a Bauer simplex. This will allow represent states on pseudo effect algebras by standard integrals

Physics of photovoltaic signal modifications in p-n photodiodes

The photovoltaic signal is an important characteristic of photodetectors, including but not limited to those that are based on p-n or p-i-n photodiodes. In an open-circuit configuration, pulsed excitation of the detector with ultrafast (femto or nanosecond) pulses leads to a photovoltaic signal that decays slowly (micro-second time scale). If the physics in the detector is dominated by the recombination of the photo-excited charge carriers, one expects the signal to decay without changing its sign. However, some experiments using short-pulse excitation have found that photovoltaic signals can undergo a sign change as a function of time following excitation, with positive signals immediately following the excitation, turning to negative signals several microseconds later. Here, we study various physical effects (density, temperature, electrostriction, pressure, photostriction, and bandgap renormalization) and determine their effect on photovoltaic signals. If, following ultrafast excitation, the carrier density and temperature are increased, and during relaxation the system reaches a state sufficiently close to the quasi-thermal equilibrium in which the carrier density is still elevated, but smaller than the intrinsic thermal equilibrium density at the elevated temperature, then the signal can become negative. © 2023 Author(s).12 month embargo; first published 03 November 2023This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Understanding the cation-dependent surfactant adsorption on clay minerals in oil recovery

Surfactants have the ability to mobilize residual oil trapped in pore spaces of matrix rocks by lowering the oil-water interfacial tension, resulting in a higher oil recovery. However, the loss of surfactants by adsorption onto the rock surface has become a major concern that reduces the efficiency of the surfactant flooding process. In this study, the adsorption behavior of an anionic surfactant to a clay mineral surface was investigated by quartz crystal microbalance with dissipation monitoring upon variations with different cation conditions. Through recording the change of frequency and dissipation of clay-modified sensors, it allows us to do a real-time quantitative analysis of the surfactant adsorption with nanogram sensitivity. The results revealed that the surfactant adsorption increased in a Ca2+-containing solution with increasing pH from 6 to 11, whereas from a Na+-containing solution, more adsorption occurred at acidic conditions. The adsorbed amount went through a maximum (∼200 mM) as a function of the Ca2+ concentration, and the Voigt model suggested that multilayer adsorption of surfactants could be as many as 4-6 monolayers. Using mixed cation (Ca2+ and Na+) solutions, the amount of adsorbed surfactant decreased linearly with decreasing fraction of CaCl2, but Na+ competed for about ∼30% adsorption sites. The importance of the presence of CaCl2 for the surfactant adsorption was stressed in high-salinity and low-salinity solutions in the presence and absence of Ca2+. Furthermore, increasing the temperature from 23 to 65 °C shows first a small increase of surfactant adsorption followed by a reduction of about 20%. The obtained results contribute to a better understanding of surfactant adsorption on clay surfaces and a guide to optimal flooding conditions with reduced surfactant loss.Green Open Access added to TU Delft Institutional Repository'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.OLD ChemE/Organic Materials and InterfacesMicro and Nano Engineerin

Monte Carlo study of the domain growth in nonstoichiometric two-dimensional binary alloys

We use a nearest-neighbor antiferromagnetic Ising model with spin-exchange dynamics to study by Monte Carlo simulations the dynamics of ordering in low-temperature quenched nonstoichiometric A xB 1 − x binary alloys. By implementing the conserved spin-exchange dynamics into the Monte Carlo method the system evolves so that the density is preserved while the order parameter is not. The simulations have been carried out on a two-dimensional square lattice and the stoichiometric value of the composition x is x 0 =0.50. By using different values of x ranging from 0.60≤x≤ x 0 =0.50, we study the influence of the off-stoichiometry on the dynamics of ordering. Regarding the behavior of the excess particles all along the ordering process, we obtain two different regimes. (i) At early to intermediate times the density of excess particles at the interfaces rapidly increases, reaching a saturated value. This density of saturation depends on both composition and temperature. As a consequence of this, since the disorder tends to be localized at the interfaces, the local order inside the growing domains is higher than the equilibrium value. (ii) Once saturation is reached, the system evolves so that the density of excess particles at the interfaces remains constant. During this second regime the excess particles are expelled back to the bulk as the total interface length decreases. We use two different measures for the growth: the total interface length and the structure factor. We obtain that during the second regime scaling holds and the domain-growth process can be characterized, independently on x, by a unique length which evolves according to l(t)∼ t n being n ∼ (0.50–0.40). Although the growth process tends to be slower as x increases, we find that the domain-wall motion follows the main assumptions underlying the Allen-Cahn theory. This is indicative that the coupling between diffusive excess particles and curvature-driven interface motion does not modify the essential time dependence but varies (slows down) the growth rate of the growth law, i.e., l(t)= k 1 / 2 xt , with k x decreasing with x. We suggest that the logarithmic growth experimentally observed in some nonstoichiometric binary materials has to do with the existence of specific interactions (not present in our case) between diffusive particles and domain walls. These interactions are of crucial importance in determining the essential time dependence of the growth law

Рандомизированное исследование по оценке безопасности и эффективности двух дозировок ленватиниба - 18 и 24 мг - у пациентов с радиойодрефрактерным дифференцированным раком щитовидной железы

Введение. Ленватиниб является мультикиназным ингибитором, одобренным для лечения радиойодрефрактерного дифференцированного рака щитовидной железы (РЙР-ДРЩЖ) в стартовой дозе 24 мг/день. Данное двойное слепое исследование было проведено с целью определения, будет ли использование ленватиниба в стартовой дозе 18 мг/день наряду со снижением токсичности обеспечивать такую же эффективность, как и его применение в дозе 24 мг/день. Методы. Пациенты с РЙР-ДРЩЖ были рандомизированы в 2 группы в соответствии с дозировкой ленватиниба: 24 и 18 мг/день. Первичной конечной точкой эффективности была частота объективного ответа через 24 нед (ЧОО24 нед). Границей эквивалентности было принято значение 0,4. Первичной конечной точкой безопасности была частота тяжелых (III степени тяжести и выше) нежелательных явлений, возникших после начала лечения (НЯП), по состоянию на 24-ю неделю. Опухоли оценивались с помощью Критериев оценки ответа солидных опухолей, версия 1.1 (Response Evaluation Criteria In Solid Tumors version 1.1, RECIST 1.1). Нежелательные явления, возникшие после начала лечения, тщательно мониторировались и регистрировались. Результаты. Частота объективного ответа через 24 нед в группе применения ленватиниба в дозе 24 мг/сут составила 57,3 % (95 % доверительный интервал (ДИ) 46,1–68,5), в группе применения ленватиниба в дозе 18 мг/сут – 40,3 % (95 % ДИ 29,3–51,2); отношение шансов (18/24 мг) 0,50 (95 % ДИ 0,26–0,96). К 24-й неделе серьезные НЯП, возникшие после начала лечения, были зафиксированы у 61,3 % пациентов в группе применения ленватиниба в дозе 24 мг/сут и у 57,1 % в группе применения ленватиниба в дозе 18 мг/сут. Разница составила –4,2 % (95 % ДИ 19,8–11,4). Заключение. Использование стартовой дозы ленватиниба 18 мг/сут не продемонстрировало эквивалентной эффективности по сравнению с использованием стартовой дозы 24 мг/сут, что подтверждено показателями ЧОО24 нед у пациентов с РЙР-ДРЩЖ. Была выявлена клинически значимая разница в ЧОО24 нед. Профили безопасности 2 дозировок ленватиниба были сопоставимыми, клинически значимых различий не наблюдалось. Полученные результаты подтверждают оправданность утвержденной стартовой дозы ленватиниба 24 мг/сут у пациентов с РЙР-ДРЩЖ и дальнейшей ее корректировки по мере необходимости.N