Electro-absorption of silicene and bilayer graphene quantum dots

We study numerically the optical properties of low-buckled silicene and AB-stacked bilayer graphene quantum dots subjected to an external electric field, which is normal to their surface. Within the tight-binding model, the optical absorption is calculated for quantum dots, of triangular and hexagonal shapes, with zigzag and armchair edge terminations. We show that in triangular silicene clusters with zigzag edges a rich and widely tunable infrared absorption peak structure originates from transitions involving zero energy states. The edge of absorption in silicene quantum dots undergoes red shift in the external electric field for triangular clusters, whereas blue shift takes place for hexagonal ones. In small clusters of bilayer graphene with zigzag edges the edge of absorption undergoes blue/red shift for triangular/hexagonal geometry. In armchair clusters of silicene blue shift of the absorption edge takes place for both cluster shapes, while red shift is inherent for both shapes of the bilayer graphene quantum dots.Comment: 7 pages, 7 figure

Magnetic suspension and balance system advanced study

An improved compact design for a superconducting magnetic suspension and balance system for an 8 ft. x 8 ft. transonic wind tunnel is developed. The original design of an MSBS in NASA Cr-3802 utilized 14 external superconductive coils and a superconductive solenoid in the airplane test model suspended in a wind tunnel. The improvements are in the following areas: test model solenoid options, dynamic force limits on the model, magnet cooling options, structure and cryogenic designs, power supply specifications, and cost and performance evaluations. The improvements are: MSBS cost reduction of 28%, weight; reduction of 43%, magnet system ampere-meter reduction of 38%, helium liquifier capacity reduction by 33%, magnet system stored energy reduction by 55%, AC loss to liquid helium reduced by 76%, system power supply reduced by 68%, test coil pole strength increased by 19%, wing magnetization increased by 40%, and control frequency limit increased by 200% from 10 Hz to 30 Hz. The improvements are due to: magnetic holmium coil forms in the test model, better rare earth permanent magnets in the wings, fiberglass-epoxy structure replacing stainless steel, better coil configuration, and new saddle roll coil design

Repulsive force support system feasibility study

A new concept in magnetic levitation and control is introduced for levitation above a plane. A set of five vertical solenoid magnets mounted flush below the plane supports and controls the model in five degrees of freedom. The compact system of levitation coils is contained in a space 2.4 m (96 in) diameter by 1 m (40 in) deep with the top of the levitation system 0.9 m (36 in) below the center line of the suspended model. The levitated model has a permanent magnet core held in position by the five parallel superconductive solenoids symmetrically located in a circle. The control and positioning system continuously corrects for model position in five dimensions using computer current pulses superimposed on the levitation coil base currents. The conceptual designs include: superconductive and Nd-Fe-B permanent magnet model cores and levitation solenoids of either superconductive, cryoresistive, or room temperature windings

Magnetic suspension and balance system study

A compact design for a superconducting magnetic suspension and balance system is developed for a 8 ft. x 8 ft. transonic wind tunnel. The main features of the design are: a compact superconducting solenoid in the suspended airplane model; permanent magnet wings; one common liquid helium dewar for all superconducting coils; efficient new race track coils for roll torques; use of established 11 kA cryostable AC conductor; acceptable AC losses during 10 Hz control even with all steel structure; and a 560 liter/hour helium liquefier. Considerable design simplicity, reduced magnet weights, and reduced heat leak results from using one common dewar which eliminates most heavy steel structure between coils and the suspended model. Operational availability is thought to approach 100% for such magnet systems. The weight and cost of the magnet system is approximately one-third that of previous less compact designs

Magnetic suspension and balance system advanced study, 1989 design

The objectives are to experimentally confirm several advanced design concepts on the Magnetic Suspension and Balance Systems (MSBS). The advanced design concepts were identified as potential improvements by Madison Magnetics, Inc. (MMI) during 1984 and 1985 studies of an MSBS utilizing 14 external superconductive coils and a superconductive solenoid in an airplane test model suspended in a wind tunnel. This study confirmed several advanced design concepts on magnetic suspension and balance systems. The 1989 MSBS redesign is based on the results of these experiments. Savings of up to 30 percent in supporting magnet ampere meters and 50 percent in energy stored over the 1985 design were achieved

Do grain reserves necessarily contribute to prices stability and food security in Sudan? An assessment

AbstractMost governments in Africa implement policies aiming to stabilize the prices of staple foods, which often include building up grain reserves, besides other trade measures insulating their domestic market from the world market. The mechanism should ideally work as follows, grains should be bought and stored from areas, during the surplus seasons (after harvest) so as to assure fair prices to producers and should be distributed during deficit seasons, in deficit areas besides in cases of emergencies. However, ideal approaches are not necessarily followed in many developing countries due to different constraints and situations. The Strategic Reserve Corporation (SRC) is an institution that is established ten years ago to play such a role in Sudan. This paper tries to assess the performance of the SRC against the overall goals and to study the related obstacles if any. We use a sample of 112 respondents from the SRC staff, related and grain farmers as our data source. Results of the research revealed numerous financial and administrative constraints that obstruct SRC from playing the intended role, which need to be considered so as to contribute to price stability and food security in Sudan

On the comparative performance of socially responsible and Islamic mutual funds

This is the first study to provide comprehensive analyses of the relative performance of both socially responsible investment (SRI) and Islamic mutual funds. The analysis proceeds in two stages. In the first, the performance of the two categories of funds is measured using partial frontier methods. In the second stage, we use quantile regression techniques. By combining two variants of the Free Disposal Hull (FDH) methods (order-m and order-α) in the first stage of analysis and quantile regression in the second stage, we provide detailed analyses of the impact of different covariates across methods and across different quantiles. In spite of the differences in the screening criteria and portfolio management of both types of funds, variation in the performance is only found for some of the quantiles of the conditional distribution of mutual fund performance. We established that for the most inefficient funds the superior performance of SRI funds is significant. In contrast, for the best mutual funds this evidence vanished and even Islamic funds perform better than SRI. These results show the benefits of performing the analysis using quantile regression

Is ethical money sensitive to past returns? The case of portfolio constraints and persistence in Islamic funds.

In this paper, we analyze the performance persistence and survivorship bias of Islamic funds. The remarkable growth of these types of ethical funds raises the question of how non-financial attributes, including beliefs and value systems, influence performance and its persistence. A procedure commonly used in prior literature to assess persistence is the measuring of the performance of investment strategies based on past performance. In this context, we propose a refined version of this methodology that controls the cross-sectional significance of the performance of these strategies. This procedure correctly identifies whether abnormal performance is due to a dynamic investment strategy based on past performance, or whether it is obtained by investing in a particular set of mutual funds. The significance of the persistence varies depending on the time horizon (yearly/half-yearly), survivorship, or the tail of the distribution. In particular, we find that persistence only exists for the best funds, whereas for the worst funds, the results are not significant

Am I prepared for Calculus? An action-research study of female students emerging from patriarchy

In this action-research study, the inquiry phase aims to examine the extent to which self-evaluations of Math prerequisite competency relate to the past and current Math performance of STEM female students from a society emerging from strict patriarchy. Its ancillary aim is to determine whether attitudes toward Math and its instruction and assessment are related to past and current performance. Undergraduate Engineering and Computer Science students were surveyed at the start of a Calculus course. As per earlier courses, Calculus was taught through an inquiry-based learning model. Findings illustrated that Math prerequisite competency was underestimated relative to past performance but accurate relative to current performance. Positive attitudes towards Math were correlated with past but not current performance. Students’ preferences for modes of instruction and assessment suggested areas of improvement. During the pragmatic phase of the study, these findings informed instructional changes to enhance Math learning in Engineering and Computer Science