Effects of charging and electric field on the properties of silicene and germanene

Using first-principles Density Functional Theory calculations, we showed that electronic and magnetic properties of bare and Ti adatom adsorbed single-layer silicene and germanene, which are charged or exerted by a perpendicular electric field are modified to attain new functionalities. In particular, when exerted by a perpendicular electric field, the symmetry between the planes of buckled atoms is broken to open a gap at the Dirac points. The occupation of 3d-orbitals of adsorbed Ti atom changes with charging or applied electric field to induce significant changes of magnetic moment. We predict that neutral silicene uniformly covered by Ti atoms becomes a half-metal at a specific value of coverage and hence allows the transport of electrons in one spin direction, but blocks the opposite direction. These calculated properties, however exhibit a dependence on the size of the vacuum spacing between periodically repeating silicene and germanene layers, if they are treated using plane wave basis set within periodic boundary condition. We clarified the cause of this spurious dependence and show that it can be eliminated by the use of local orbital basis set.Comment: Accepted for Journal of Physics: Condensed Matte

Effects of antimitotic agents on haploid plant production from unpollinated ovules of sugar beet (beta vulgaris l.)

The effects of antimicrotubule agents on haploid embryo formation from unpollinated ovules of sugar beet (Beta vulgaris L.) were investigated. The antimitotic agent colchicine (at 100 and 150 mg/l) and trifluralin (at 5.0 mg/l) increased the frequency of haploid embryo formation whereas pronamide (at 76.9 and 128.2 mg/l) and trifluralin (at 3.4 mg/l) decreased. Ovules that were non-treated with antimicrotuble agents (i.e., ovules of the control treatment) produced higher percentages of haploid embryos (4.25 %) when compared to the pronamide and trifluralin at 3.4 mg/l concentration. Toxic effects of these agents on embryo formation from ovules were evident. A significant genotypic variation among the lines used was observed. The line M4 produced the highest yield with a mean of 14.71% haploid embryo production while the line M2 producing no embryos at all

An anticipative scheduling approach with controllable processing times

In practice, machine schedules are usually subject to disruptions which have to be repaired by reactive scheduling decisions. The most popular predictive approach in project management and machine scheduling literature is to leave idle times (time buffers) in schedules in coping with disruptions, i.e. the resources will be under-utilized. Therefore, preparing initial schedules by considering possible disruption times along with rescheduling objectives is critical for the performance of rescheduling decisions. In this paper, we show that if the processing times are controllable then an anticipative approach can be used to form an initial schedule so that the limited capacity of the production resources are utilized more effectively. To illustrate the anticipative scheduling idea, we consider a non-identical parallel machining environment, where processing times can be controlled at a certain compression cost. When there is a disruption during the execution of the initial schedule, a match-up time strategy is utilized such that a repaired schedule has to catch-up initial schedule at some point in future. This requires changing machine–job assignments and processing times for the rest of the schedule which implies increased manufacturing costs. We show that making anticipative job sequencing decisions, based on failure and repair time distributions and flexibility of jobs, one can repair schedules by incurring less manufacturing cost. Our computational results show that the match-up time strategy is very sensitive to initial schedule and the proposed anticipative scheduling algorithm can be very helpful to reduce rescheduling costs

Enhanced reduction of graphene oxide by means of charging and electric fields applied to hydroxyl groups

We present a first-principles study of the effects of charging and perpendicular electric fields on hydroxyl groups, both of which mediate the reduction of graphene oxide through the formation of H2O and H 2O2. Starting with an investigation of the interaction between the hydroxyl groups and graphene, we determine the equilibrium binding geometry, binding energy, and the diffusion path with a minimum energy barrier and show that those equilibrium properties are strongly affected by external agents. While co-adsorbed H and O form bound OH, co-adsorbed H and OH in close proximity form H2O with almost no energy barrier. When negatively charged or subjected to a perpendicular electric field, the energy barrier between two OH co-adsorbed in close proximity is weakened or totally suppressed, forming an oxygen atom strongly bound at the bridge site, together with a water molecule. The water molecule by itself is very weakly bound to graphene and is prone to desorb from the surface, leading to the reduction of graphene oxide. It is therefore demonstrated that the reduction of graphene oxide is promoted to a large extent by negative charging or an applied perpendicular electric field, through the formation of weakly bound water molecules from hydroxyl groups. © 2013 IOP Publishing Ltd

Effects of charging and electric field on graphene functionalized with titanium

Titanium atoms are adsorbed to graphene with a significant binding energy and render diverse functionalities to it. Carrying out first-principles calculations, we investigated the effects of charging and static electric field on the physical and chemical properties of graphene covered by Ti adatoms. When uniformly Ti covered graphene is charged positively, its antiferromagnetic ground state changes to ferromagnetic metal and attains a permanent magnetic moment. Static electric field applied perpendicularly causes charge transfer between Ti and graphene, and can induce metal-insulator transition. While each Ti adatom adsorbed to graphene atom can hold four hydrogen molecules with a weak binding, these molecules can be released by charging or applying electric field perpendicularly. Hence, it is demonstrated that charging and applied static electric field induce quasi-continuous and side specific modifications in the charge distribution and potential energy of adatoms absorbed to single-layer nanostructures, resulting in fundamentally crucial effects on their physical and chemical properties. © 2013 IOP Publishing Ltd

Integrated aircraft and passenger recovery with cruise time controllability

Disruptions in airline operations can result in infeasibilities in aircraft and passenger schedules. Airlines typically recover aircraft schedules and disruptions in passenger itineraries sequentially. However, passengers are severely affected by disruptions and recovery decisions. In this paper, we present a mathematical formulation for the integrated aircraft and passenger recovery problem that considers aircraft and passenger related costs simultaneously. Using the superimposition of aircraft and passenger itinerary networks, passengers are explicitly modeled in order to use realistic passenger related costs. In addition to the common routing recovery actions, we integrate several passenger recovery actions and cruise speed control in our solution approach. Cruise speed control is a very beneficial action for mitigating delays. On the other hand, it adds complexity to the problem due to the nonlinearity in fuel cost function. The problem is formulated as a mixed integer nonlinear programming (MINLP) model. We show that the problem can be reformulated as conic quadratic mixed integer programming (CQMIP) problem which can be solved with commercial optimization software such as IBM ILOG CPLEX. Our computational experiments have shown that we could handle several simultaneous disruptions optimally on a four-hub network of a major U.S. airline within less than a minute on the average. We conclude that proposed approach is able to find optimal tradeoff between operating and passenger-related costs in real time. © 2013, Springer Science+Business Media New York

Effects of charging and electric field on graphene oxide

We present a first-principles study of various effects of charging and electric field on the oxidation/deoxidation of graphene oxide consisting of only epoxy groups. We first determined the proper basis set, which hinders the spurious spilling of electrons of graphene oxide when negatively charged or exerted by perpendicular electric field, and treated with periodic boundary conditions. We then showed that the electric field perpendicularly applied to graphene surface provide side-specific functionalization. We found that the bonds between oxygen and graphene are weakened under applied electric field. For specific values of excess charge or electric field, an oxygen atom that is normally adsorbed to the bridge site in equilibrium moves to the top site. By directly charging and/or by applying electric field, one can monitor this migration as well as desorption of the oxygen adatom. In spite of the negative formation energy, an energy barrier prevents individually adsorbed oxygen atoms from forming oxygen molecules. This energy barrier is dramatically weakened upon negative charging or exertion of an electric field. Our results explain why the reduction of graphene oxide can be facilitated by these external effects. © 2013 American Chemical Society

An integrated approach for airline scheduling, aircraft fleeting and routing with cruise speed control

To place an emphasis on profound relations among airline schedule planning problems and to mitigate the effect of unexpected delays, we integrate schedule design, fleet assignment and aircraft routing problems within a daily planning horizon while passengers' connection service levels are ensured via chance constraints. We propose a nonlinear mixed integer programming model due to the nonlinear fuel consumption and CO2 emission cost terms in the objective function, which is handled by second order conic reformulation. The key contribution of this study is to take into account the cruise time control for the first time in an integrated model of these three stages of airline operations. Changing cruise times of flights in an integrated model enables to construct a schedule to increase utilization of fuel efficient aircraft and even to decrease total number of aircraft needed while satisfying the same service level and maintenance requirements for aircraft fleeting and routing. There is a critical tradeoff between the number of aircraft needed to fulfill the required flights and overall operational expenses. We also propose two heuristic methods to solve larger size problems. Finally, computational results using real data obtained from a major U.S. carrier are presented to demonstrate potential profitability in applying the proposed solution methods. © 2016 Elsevier Ltd

Flight network-based approach for integrated airline recovery with cruise speed control

Airline schedules are generally tight and fragile to disruptions. Disruptions can have severe effects on existing aircraft routings, crew pairings, and passenger itineraries that lead to high delay and recovery costs. A recovery approach should integrate the recovery decisions for all entities (aircraft, crew, passengers) in the system as recovery decisions about an entity directly affect the others' schedules. Because of the size of airline flight networks and the requirement for quick recovery decisions, the integrated airline recovery problem is highly complex. In the past decade, an increasing effort has been made to integrate passenger and crew related recovery decisions with aircraft recovery decisions both in practice and in the literature. In this paper, we develop a new flight network based representation for the integrated airline recovery problem. Our approach is based on the flowof each aircraft, crewmember, and passenger through the flight network of the airline. The proposed network structure allows common recovery decisions such as departure delays, aircraft/crew rerouting, passenger reaccommodation, ticket cancellations, and flight cancellations. Furthermore, we can implement aircraft cruise speed (flight time) decisions on the flight network. For the integrated airline recovery problem defined over this network, we propose a conic quadratic mixed integer programming formulation that can be solved in reasonable CPU times for practical size instances. Moreover, we place a special emphasis on passenger recovery. In addition to aggregation and approximation methods, our model allows explicit modeling of passengers and evaluating a more realistic measure of passenger delay costs. Finally, we propose methods based on the proposed network representation to control the problem size and to deal with large airline networks. © 2017 INFORMS