Stellarator bootstrap current and plasma flow velocity at low collisionality

The bootstrap current and flow velocity of a low-collisionality stellarator plasma are calculated. As far as possible, the analysis is carried out in a uniform way across all low-collisionality regimes in general stellarator geometry, assuming only that the confinement is good enough that the plasma is approximately in local thermodynamic equilibrium. It is found that conventional expressions for the ion flow speed and bootstrap current in the low-collisionality limit are accurate only in the $1/\nu$-collisionality regime and need to be modified in the $\sqrt{\nu}$-regime. The correction due to finite collisionality is also discussed and is found to scale as $\nu^{2/5}$

Surveying the solar system by measuring angles and times: from the solar density to the gravitational constant

A surprisingly large amount of information on our solar system can be gained from simple measurements of the apparent angular diameters of the sun and the moon. This information includes the average density of the sun, the distance between earth and moon, the radius of the moon, and the gravitational constant. In this note it is described how these and other quantities can be obtained by simple earthbound measurements of angles and times only, without using any explicit information on distances between celestial bodies. The pedagogical and historical aspects of these results are also discussed briefly.Comment: 12 pges, one figur

ST Quartz Acoustic Wave Sensors with Sectional Guiding Layers

We report the effect of removing a section of guiding layer from the propagation paths of ST-quartz Love wave sensors; this offers the ease of fabrication of a polymer guiding layer whilst retaining the native surface of the quartz which may then be used for the attachment of a sensitizing layer. Data is presented for rigid and viscous loading, which indicates a small reduction in mass sensitivity compared to a Love wave device. Biosensing capabilities of these discontinuous ‘sectional’ guiding layer devices are demonstrated using protein adsorption from solution

A simple derivation of Kepler's laws without solving differential equations

Proceeding like Newton with a discrete time approach of motion and a geometrical representation of velocity and acceleration, we obtain Kepler's laws without solving differential equations. The difficult part of Newton's work, when it calls for non trivial properties of ellipses, is avoided by the introduction of polar coordinates. Then a simple reconsideration of Newton's figure naturally leads to en explicit expression of the velocity and to the equation of the trajectory. This derivation, which can be fully apprehended by beginners at university (or even before) can be considered as a first application of mechanical concepts to a physical problem of great historical and pedagogical interest

Identifying the Prevalence of the “Dark Triad” Personality Traits in Law Students: Eradicating an Unwarranted Stereotype

The personalities of lawyers are often categorized to be immoral, at least more so than those of other professionals. An abundance of literature parallels this generalization and depicts lawyers’ personalities as narcissistic, psychopathic and high in Machiavellian attitudes. Together, these three traits form the “Dark Triad” of personality. 53 law students from 3 law schools in Ontario completed a survey measuring their levels on the “Dark Triad”. Results show that the law students from the present sample do not display any “Dark Triad” trait significantly greater than the general population. It found that male law students were not significantly “darker” than female law students. 1st year law students were found to score significantly higher on the narcissism trait than both second and third-year students. There were no other significant differences between the students in different years of schooling. Those entering criminal law scored significantly higher on Machiavellianism than those entering tax law. No other fields of law differed significantly on any trait. These findings suggest that law students are not deserving of the pejorative stereotype assigned to them. It suggests that male law students are no more responsible for the stereotype than females. The present research implies that law school may actually reduce the narcissism trait suggested to be present in law students. Lastly, those aspiring to enter criminal law may be more responsible for the stereotype whereas those aspiring to enter tax law experience the most apparent wrongful stereotyping

The importance of the classical channel in the impurity transport of optimized stellarators

In toroidal magnetic confinement devices, such as tokamaks and stellarators, neoclassical transport is usually an order of magnitude larger than its classical counterpart. However, when a high-collisionality species is present in a stellarator optimized for low Pfirsch-Schl\"uter current, its classical transport can be comparable to the neoclassical transport. In this letter, we compare neoclassical and classical fluxes and transport coefficients calculated for Wendelstein 7-X (W7-X) and Large Helical Device (LHD) cases. In W7-X, we find that the classical transport of a collisional impurity is comparable to the neoclassical transport for all radii, while it is negligible in the LHD cases, except in the vicinity of radii where the neoclassical transport changes sign. In the LHD case, electrostatic potential variations on the flux-surface significantly enhance the neoclassical impurity transport, while the classical transport is largely insensitive to this effect in the cases studied.Comment: 10 pages, 2 figure

Scattering of charge carriers by point defects in bilayer graphene

Theory of scattering of massive chiral fermions in bilayer graphene by radial symmetric potential is developed. It is shown that in the case when the electron wavelength is much larger than the radius of the potential the scattering cross-section is proportional to the electron wavelength. This leads to the mobility independent on the electron concentration. In contrast with the case of single-layer, neutral and charged defects are, in general, equally relevant for the resistivity of the bilayer graphene.Comment: final versio

Influence of branch points in the complex plane on the transmission through double quantum dots

We consider single-channel transmission through a double quantum dot system consisting of two single dots that are connected by a wire and coupled each to one lead. The system is described in the framework of the S-matrix theory by using the effective Hamiltonian of the open quantum system. It consists of the Hamiltonian of the closed system (without attached leads) and a term that accounts for the coupling of the states via the continuum of propagating modes in the leads. This model allows to study the physical meaning of branch points in the complex plane. They are points of coalesced eigenvalues and separate the two scenarios with avoided level crossings and without any crossings in the complex plane. They influence strongly the features of transmission through double quantum dots.Comment: 30 pages, 14 figure

Spectrum of an open disordered quasi-two-dimensional electron system: strong orbital effect of the weak in-plane magnetic field

The effect of an in-plane magnetic field upon open quasi-two-dimensional electron and hole systems is investigated in terms of the carrier ground-state spectrum. The magnetic field, classified as weak from the viewpoint of correlation between size parameters of classical electron motion and the gate potential spatial profile is shown to efficiently cut off extended modes from the spectrum and to change singularly the mode density of states (MDOS). The reduction in the number of current-carrying modes, right up to zero in magnetic fields of moderate strength, can be viewed as the cause of magnetic-field-driven metal-to-insulator transition widely observed in two-dimensional systems. Both the mode number reduction and the MDOS singularity appear to be most pronounced in the mode states dephasing associated with their scattering by quenched-disorder potential. This sort of dephasing is proven to dominate the dephasing which involves solely the magnetic field whatever level of the disorder.Comment: RevTeX-4 class, 12 pages, 5 eps figure