Bi-Directional Energy Cascades and the Origin of Kinetic Alfv\'enic and Whistler Turbulence in the Solar Wind

The observed sub-proton scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quite-time suggest them as possible source of free energy to drive the turbulence. Using particle-in-cell simulations, we explore how free energy in energetic electrons, released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfv\'enic and whistler waves are excited that evolve through inverse and forward magnetic energy cascades.Comment: 12 pages, 5 figures, Submitted to Physical Review Letter

Studies of fullerenes and carbon nanotubes by an extended bond order potential

We present a novel approach to combine bond order potentials with long-range nonbond interactions. This extended bond order potential consistently takes into account bond terms and nonbond terms. It not only captures the advantages of the bond order potentials (i.e. simulating bond forming and breaking), but also systematically includes the nonbond contributions to energy and forces in studying the structure and dynamics of covalently bonded systems such as graphite, diamond, nanotubes, fullerenes and hydrocarbons, in their crystal and melt forms. Using this modified bond order potential, we studied the structure and thermal properties (including thermal conductivity) of C60 crystal, and the elastic properties and plastic deformation processes of the single-walled and double-walled nanotubes. This extended bond order potential enables us to simulate large deformations of a nanotube under tensile and compressive loads. The basic formulation in this paper is transferable to other bond order potentials and traditional valence force fields

Decoupling Liability: Optimal Incentives for Care and Litigation

A "decoupled" liability system is one in which the award to the plaintiff differs from the payment by the defendant. The optimal system of decoupling makes the defendant's payment as high as possible. Such a policy allows the award to the plaintiff to be lowered, thereby reducing the plaintiff's incentive to sue -- and hence litigation costs -- without sacrificing the defendant's incentive to exercise care. The optimal award to the plaintiff may be less than or greater than the optimal payment by the defendant. The possibility of an out-of-court settlement does not qualitatively affect these results. If the settlement can be monitored, it may be desirable to decouple it as well.

Factors Influencing the Achievement in Mathematics of Malay Secondary School Students

The present situation of many secondary school students having difficulty in learning mathematics needs to be thoroughly investigated. Various factors need to be studied in order to determine why these students failed to perform satisfactorily in mathematics. For this research, a group of three hundred secondary school students were studied in order to determine the influence of students' internal characteristics on achievements in mathematics. This research focused on the following seven internal characteristics: Attitudes towards mathematics, mathematics anxiety, motivation to study mathematics, personality and behavioural characteristics, cognitive readiness, learning strategies, and learning styles.For learning styles, Kolb's Learning Style Inventory (1985) was used. Cognitive readiness test consisted of questions involving abstract reasoning, logical thinking, and numerical computation. For the other variables. the tests consisted of questionnaires using likert scale from one to five. Mathematics achievements were determined by the scores that the students got for mathematics in the Trial SPM Examination, 1999. The research findings showed that mathematics achievements were significantly and positively correlated with attitudes towards mathematics. motivation to study mathematics, and personality and behavioural characteristics. Mathematics anxiety, on the other hand, had negative influence on achievements in mathematics. The result suggested that efforts must be made to reduce the level of mathematics anxiety in order to raise the students' performance in mathematics. Mathematics achievements were found to correl ate strongly with abstract reasoning, logical thinking, and numerical computational abilities. As for learning strategies, higher achievers were found to be more oriented towards meaningful learning, as opposed to rote memorising. The findings for learning styles indicated that higher achievers were more oriented towards abstract conceptualisation and active experimentation modes of learning. Convergence was found to be the dominant learning style of students who were excellent in mathematics.In the inter-groups comparison analyses, the findings showed that weak students did not have positive attitudes and strong motivation to succeed in learning mathematics. Their levels of mathematics anxiety were relatively high, and their personality and behavioural characteristics1 were relatively unfavourable. Weak students also had a relatively lower level of ability in abstract reasoning, logical thinking, and numerical computation. Weak students were more oriented towards rote memorising and concrete experiencing mode of learning

Thermal conductivity of carbon nanotubes

As the sizes of electronic and mechanical devices are decreased to the micron and nanometre level, it becomes particularly important to predict the thermal transport properties of the components. Using molecular level theories, such predictions are particularly important for modelling nano-electronic devices where scaling laws may change substantially but it is most difficult to accurately measure the properties. Hence, using the empirical bond order dependent force field, we have studied here the thermal conductivity of nanotubes' dependence on structure, defects and vacancies. The anisotropic character of the thermal conductivity of the graphite crystal is naturally reflected in the carbon nanotubes. We found that the carbon nanotubes have very high thermal conductivity comparable to diamond crystal and in-plane graphite sheet. In addition, nanotube bundles show very similar properties as graphite crystal in which dramatic difference in thermal conductivities along different crystal axis

Streda-like formula in spin Hall effect

A generalized Streda formula is derived for the spin transport in spin-orbit coupled systems. As compared with the original Streda formula for charge transport, there is an extra contribution of the spin Hall conductance whenever the spin is not conserved. For recently studied systems with quantum spin Hall effect in which the z-component spin is conserved, this extra contribution vanishes and the quantized value of spin Hall conductivity can be reproduced in the present approach. However, as spin is not conserved in general, this extra contribution can not be neglected, and the quantization is not exact.Comment: 4 pages, no figur

QM(DFT) and MD studies on formation mechanisms of C_(60) fullerenes

One of the most puzzling aspects of fullerenes is how such complicated symmetric molecules are formed from a gas of atomic carbons, namely, the atomistic or chemical mechanisms. Are the atoms added one by one or as molecules (C2, C3)? Is there a critical nucleus beyond which formation proceeds at gas kinetic rates? What determines the balance between forming buckyballs, buckytubes, graphite and soot? The answer to these questions is extremely important in manipulating the systems to achieve particular products. A difficulty in current experiments is that the products can only be detected on time scales of microseconds long after many of the important formation steps have been completed. Consequently, it is necessary to use simulations, quantum mechanics and molecular dynamics, to determine these initial states. Experiments serve to provide the boundary conditions that severely limit the possibilities. Using quantum mechanical methods (density functional theory (DFT)) we derived a force field (MSXX FF) to describe one-dimensional (rings) and two-dimensional (fullerene) carbon molecules. Combining DFT with the MSXX FF, we calculated the energetics for the ring fusion spiral zipper (RFSZ) mechanism for formation of C60 fullerenes. Our results shows that the RFSZ mechanism is consistent with the quantum mechanics (with a slight modification for some of the intermediates)

Nonlinear Development of Streaming Instabilities In Strongly Magnetized Plasmas

The nonlinear development of streaming instabilities in the current layers formed during magnetic reconnection with a guide field is explored. Theory and 3-D particle-in-cell simulations reveal two distinct phases. First, the parallel Buneman instability grows and traps low velocity electrons. The remaining electrons then drive two forms of turbulence: the parallel electron-electron two-stream instability and the nearly-perpendicular lower hybrid instability. The high velocity electrons resonate with the turbulence and transfer momentum to the ions and low velocity electrons.Comment: Accepted by PR