11,199 research outputs found
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 -collisionality regime
and need to be modified in the -regime. The correction due to
finite collisionality is also discussed and is found to scale as
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 âsectionalâ guiding layer devices are demonstrated using protein adsorption from solution
Identifying the Prevalence of the âDark Triadâ 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 lawyersâ personalities as narcissistic, psychopathic and high in Machiavellian attitudes. Together, these three traits form the âDark Triadâ of personality. 53 law students from 3 law schools in Ontario completed a survey measuring their levels on the âDark Triadâ. Results show that the law students from the present sample do not display any âDark Triadâ trait significantly greater than the general population. It found that male law students were not significantly âdarkerâ 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
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
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
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