Conserving approximations in time-dependent quantum transport: Initial correlations and memory effects

We study time-dependent quantum transport in a correlated model system by means of time-propagation of the Kadanoff-Baym equations for the nonequilibrium many-body Green function. We consider an initially contacted equilibrium system of a correlated central region coupled to tight-binding leads. Subsequently a time-dependent bias is switched on after which we follow in detail the time-evolution of the system. Important features of the Kadanoff-Baym approach are 1) the possibility of studying the ultrafast dynamics of transients and other time-dependent regimes and 2) the inclusion of exchange and correlation effects in a conserving approximation scheme. We find that initial correlation and memory terms due to many-body interactions have a large effect on the transient currents. Furthermore the value of the steady state current is found to be strongly dependent on the approximation used to treat the electronic interactions.Comment: 5 pages, 2 figure

Study of the technique of stellar occultation

The results are reported of a study of the stellar occultation technique for measuring the composition of the atmosphere. The intensity of starlight was monitored during the occultation using the Wisconsin stellar ultraviolet photometers aboard the Orbiting Astronomical Observatory (OAO-A2). A schematic diagram of an occultation is shown where the change in intensity at a given wavelength is illustrated. The vertical projection of the attenuation region is typically 60 km deep for molecular oxygen and 30 km deep for ozone. Intensity profiles obtained during various occultations were analyzed by first determining the tangential columm density of the absorbing gases, and then Abel inverting the column densities to obtain the number density profile. Errors are associated with each step in the inversion scheme and have been considered as an integral part of this study

UEFA-M: Utility-based energy efficient adaptive multimedia mechanism over LTE HetNet small cells

The emerging advances in mobile computing devices enable the adoption of new services like video over LTE (ViLTE), augmented and virtual reality, omnidirectional video, etc. However, these new services cannot be technologically achievable within the current networks without a rethink in the network architecture. A simple increase in system capacity will not be enough without considering the provisioning of Quality of Experience (QoE) as the basis for network control, customer loyalty and retention rate and thus increase in network operators’ revenue. This paper proposes an Utility-based Energy eFficient Adaptive Multimedia Mechanism (UEFA-M) over the LTE HetNet Small Cells environment that combines the use of utility theory and the concept of proactive handover to enable the adaptation of the multimedia stream ahead of the handover process in order to provide a seamless QoE to the mobile user and energy savings for their mobile device. Mathematical models for energy and quality are derived from previous real experimental data and integrated in the adaptation mechanism using the utility theory. The performance of the proposed adaptive multimedia scheme is analyzed and compared against a non-adaptive solution in terms of energy efficiency and Mean Opinion Score (MOS

Ultrafast Magnetization Dynamics in Diluted Magnetic Semiconductors

We present a dynamical model that successfully explains the observed time evolution of the magnetization in diluted magnetic semiconductor quantum wells after weak laser excitation. Based on the pseudo-fermion formalism and a second order many-particle expansion of the exact p-d exchange interaction, our approach goes beyond the usual mean-field approximation. It includes both the sub-picosecond demagnetization dynamics and the slower relaxation processes which restore the initial ferromagnetic order in a nanosecond time scale. In agreement with experimental results, our numerical simulations show that, depending on the value of the initial lattice temperature, a subsequent enhancement of the total magnetization may be observed within a time scale of few hundreds of picoseconds.Comment: Submitted to PR

Crystalline phases in chiral ferromagnets: Destabilization of helical order

In chiral ferromagnets, weak spin-orbit interactions twist the ferromagnetic order into spirals, leading to helical order. We investigate an extended Ginzburg-Landau theory of such systems where the helical order is destabilized in favor of crystalline phases. These crystalline phases are based on periodic arrangements of double-twist cylinders and are strongly reminiscent of blue phases in liquid crystals. We discuss the relevance of such blue phases for the phase diagram of the chiral ferromagnet MnSi.Comment: 6 pages, 5 figures (published version

A Comparative Study of Different Sorbents in the Context of Direct Air Capture (DAC): Evaluation of Key Performance Indicators and Comparisons

Direct air capture can be based on an adsorption system, and the used sorbent (chemisorbents or physisorbents) influences process. In this work, two amine-functionalized sorbents, as chemisorbents, and three different metal organic frameworks, as physisorbents, are considered and compared in terms of some key performance indicators. This was carried out by developing a mathematical model describing the adsorption and desorption stages. An independent analysis was carried out in order to verify data reported in the literature. Results show that the equilibrium loading is a critical parameter for adsorption capacity, energy consumption, and cost. The considered metal organic frameworks are characterized by a lower equilibrium loading (10−4 mol/kg) compared to chemisorbents (10−1 mol/kg). For this reason, physisorbents have higher overall energy consumptions and costs, while capturing a lower amount of carbon dioxide. A reasonable agreement is found on the basis of the operating conditions of the Climeworks company, modelling the use of the same amine cellulose-based sorbent. The same order of magnitude is found for total costs (751 USD/tonneCO2 for our analysis, compared to the value of 600 USD/tonneCO2 proposed by this company)

Comparison of etomidate and propofol as an induction agent to study hemodynamic effects and serum cortisol level following endotracheal intubation in hypertensive patients

Background: The present study aimed to compare hemodynamic parameters (heart rate, blood pressure) and adverse effects (injection pain, myoclonus, postoperative nausea/vomiting) between Etomidate and propofol groups. Methods: Patients were divided into two groups: Etomidate Group E and a Propofol Group P. All hemodynamic data were measured during induction, intubation, and post-intubation up to 15 min. Intravenous cortisol levels were measured at baseline, just after induction and at 24 hours after induction. Results: At 3 min and 5 min SBP was decreased by 22.04% and 18.39% in Group P. At 3 min there was fall in DBP by 20.13% in group P whereas there was an increase in group E by 0.13% which is statistically significant (p<0.001). At 1 min, 3 min and 5 min after intubation, fall in the MAP by 26.07%, 21.08% and 18.60% in group P and 0.77%, 0.42% and 1.30% in group E (p value <0.001). Serum cortisol level immediate after surgery was decrease (54%) in Group E (p value <0.001). In Group P, 40% of the patients and in group E 16.66 % of the patients complained of pain on injection (p value 0.046). Conclusions: The cortisol suppression by Etomidate may be beneficial for intubation stress response. Etomidate is better for its hemodynamic stability over propofol