Strain and Electric Field Modulation of the Electronic Structure of Bilayer Graphene

We study how the electronic structure of the bilayer graphene (BLG) is changed by electric field and strain from {\it ab initio} density-functional calculations using the LMTO and the LAPW methods. Both hexagonal and Bernal stacked structures are considered. The BLG is a zero-gap semiconductor like the isolated layer of graphene. We find that while strain alone does not produce a gap in the BLG, an electric field does so in the Bernal structure but not in the hexagonal structure. The topology of the bands leads to Dirac circles with linear dispersion in the case of the hexagonally stacked BLG due to the interpenetration of the Dirac cones, while for the Bernal stacking, the dispersion is quadratic. The size of the Dirac circle increases with the applied electric field, leading to an interesting way of controlling the Fermi surface. The external electric field is screened due to polarization charges between the layers, leading to a reduced size of the band gap and the Dirac circle. The screening is substantial in both cases and diverges for the Bernal structure for small fields as has been noted by earlier authors. As a biproduct of this work, we present the tight-binding parameters for the free-standing single layer graphene as obtained by fitting to the density-functional bands, both with and without the slope constraint for the Dirac cone.Comment: 7 pages, 7 figure

Balancing the Tradeoff between Profit and Fairness in Rideshare Platforms During High-Demand Hours

Rideshare platforms, when assigning requests to drivers, tend to maximize profit for the system and/or minimize waiting time for riders. Such platforms can exacerbate biases that drivers may have over certain types of requests. We consider the case of peak hours when the demand for rides is more than the supply of drivers. Drivers are well aware of their advantage during the peak hours and can choose to be selective about which rides to accept. Moreover, if in such a scenario, the assignment of requests to drivers (by the platform) is made only to maximize profit and/or minimize wait time for riders, requests of a certain type (e.g. from a non-popular pickup location, or to a non-popular drop-off location) might never be assigned to a driver. Such a system can be highly unfair to riders. However, increasing fairness might come at a cost of the overall profit made by the rideshare platform. To balance these conflicting goals, we present a flexible, non-adaptive algorithm, \lpalg, that allows the platform designer to control the profit and fairness of the system via parameters $\alpha$ and $\beta$ respectively. We model the matching problem as an online bipartite matching where the set of drivers is offline and requests arrive online. Upon the arrival of a request, we use \lpalg to assign it to a driver (the driver might then choose to accept or reject it) or reject the request. We formalize the measures of profit and fairness in our setting and show that by using \lpalg, the competitive ratios for profit and fairness measures would be no worse than $\alpha/e$ and $\beta/e$ respectively. Extensive experimental results on both real-world and synthetic datasets confirm the validity of our theoretical lower bounds. Additionally, they show that \lpalg under some choice of $(\alpha, \beta)$ can beat two natural heuristics, Greedy and Uniform, on \emph{both} fairness and profit

Surface excitonic emission and quenching effects in ZnO nanowire/nanowall systems: limiting effects on device potential.

We report ZnO nanowire/nanowall growth using a two-step vapour phase transport method on a-plane sapphire. X-ray diffraction and scanning electron microscopy data establish that the nanostructures are vertically well-aligned with c-axis normal to the substrate, and have a very low rocking curve width. Photoluminescence data at low temperatures demonstrate the exceptionally high optical quality of these structures, with intense emission and narrow bound exciton linewidths. We observe a high energy excitonic emission at low temperatures close to the band-edge which we assign to the surface exciton in ZnO at ~ 3.366 eV, the first time this feature has been reported in ZnO nanorod systems. This assignment is consistent with the large surface to volume ratio of the nanowire systems and indicates that this large ratio has a significant effect on the luminescence even at low temperatures. The band-edge intensity decays rapidly with increasing temperature compared to bulk single crystal material, indicating a strong temperature-activated non-radiative mechanism peculiar to the nanostructures. No evidence is seen of the free exciton emission due to exciton delocalisation in the nanostructures with increased temperature, unlike the behaviour in bulk material. The use of such nanostructures in room temperature optoelectronic devices appears to be dependent on the control or elimination of such surface effects

Characterizations of GEM detector prototype

At NISER-IoP detector laboratory an initiative is taken to build and test Gas Electron Multiplier (GEM) detectors for ALICE experiment. The optimisation of the gas flow rate and the long-term stability test of the GEM detector are performed. The method and test results are presented.Comment: 3 Pages, 4 figure

Power quality improvement in 3-ϕ power system using shunt active filter with synchronous detection method

Active filters with synchronous detection methodologies are vividly employed in distribution system to make sure that the harmonics generated by non-linear loads is reduced and results in less voltage distortion and leads to lesser power superiority problems. The three physical characteristics that mostly underline the power quality and a power quality issues are Voltage, Current and Frequency. Harmonics is defined as a disturbance demonstrated in current or voltage or frequency waveforms which result in devastation, or failure of final equipment. The greater switching frequency as well as the non-linearity in the characteristics of the power electronics equipment is mostly creditworthy for the power quality issue. So significance is being given to the procurement of Active Power Filters to equate these problems to improvise power quality and of all these, shunt active power filter is used to take care of harmonics of voltage and load currents and for reactive power compensating. The shunt active power filters have been built up on the basis of on control strategies like compensation scheme (p-q control) and instantaneous active and reactive current control scheme (Id-Iq control). Taking into consideration its superior quality, an analysis on the Id-Iq control scheme based shunt active filter presented in this project. The compensation is given by the usage of PI based controllers. A theory based study on both the compensation schemes is carried out in the project and then Id-Iq control scheme is implemented in simulation using MATLAB/SIMULINK® work and its harmonic compensation results are analysed. Then synchronous detection scheme algorithms are worked out for unbalanced three phase systems and simulation is done

Tensile and Wear Behavior of Calotropis Gigentea Fruit Fiber Reinforced Polyester Composites

AbstractAn experimental study has been carried out to investigate the tensile and wear characterization of polymer composites made by reinforcing Calotropis Gigentea fruit fiber as a new natural fiber into a polyester resin. The Calotropis Gigentea fibres extracted by manual processes have been used to fabricate the composites. The composites are fabricated up to a maximum volume fraction of fibre of 0.35. The tensile strength increased with increase in fiber content. Further, the wear behavior of the Calotropis Gigentea fruit fiber composite were studied with increase in fiber content

Vascularised fibular graft in the management of non-union of fracture shaft of radius: a less ventured entity

Introduction: Non-union of the radius and ulna is a major complication of forearm fractures, accounting upto 10% of all forearm fractures. Multiple modalities are available for the treatment of non-union. Vascular grafts are a less sought-after surgical choice owing to the need of expertise and skills of surgeons. We discuss a case of gap non-union of fracture shaft radius treated with vascular fibula graft. Case Report: We describe a case of 45yr old lady with closed fracture of both bones of left forearm. She underwent open reduction and internal fixation with 3.5 small DCP (6 hole) two days following trauma. On subsequent follow up in 6 months the radius fracture showed signs of infected non-union with osteolysis at screw sites while the ulnar side showed signs of satisfactory union. The patient underwent debridement with implant removal and osteosynthesis with vascularised fibula for gap non-union as second stage. 3 and 6 months follow up showed improvement in DASH score as well as VAS score and fair return of regular activity. Conclusion: In management of gap non-union of Shaft radius with gap (>6cm) vascularised fibular graft provides excellent functional outcome with far less donor site complications

Models and techniques for hotel revenue management using a rolling horizon.

This paper studies decision rules for accepting reservations for stays in a hotel based on deterministic and stochastic mathematical programming techniques. Booking control strategies are constructed that include ideas for nesting, booking limits and bid prices. We allow for multiple day stays. Instead of optimizing a decision period consisting of a fixed set of target booking days, we simultaneously optimize the complete range of target booking dates that are open for booking at the moment of optimization. This yields a rolling horizon of overlapping decision periods, which will conveniently capture the effects of overlapping stays