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

Formation spectra of light kaonic nuclei by in-flight (Kˉ,N{\bar K},N) reactions with chiral unitary amplitude

We study theoretically the in-flight ($K^-,N$) reactions for the formation of light kaonic nuclear systems to get deeper physical insights on the expected spectra, and to investigate the experimental feasibility of the reaction at new facilities like J-PARC. We show the expected spectra for the formation of the $K^-pp, K^-pn$, $K^-nn$ and $K^-$-$^{11}$B systems which are accessible by the ($K^-,N$) experiments. By considering the conversion part of the Green's function, we can show the missing mass spectra of the ($K^-,N$) reactions coincidence with the particle emissions due to ${\bar K}$ absorption in ${\bar K}N\to \pi Y$ processes. To calculate the cross sections, we use the so-called $T\rho$ approximation to evaluate the optical potential. As for the amplitude $T$, we adopt the chiral unitary amplitude of ${\bar K}N$ channel in vacuum for simplicity, and we also check the medium effects by applying the chiral amplitude at finite density. The effects of the p-wave optical potential of $\Sigma$(1385) channel and the contribution from ${\bar K^0}$ mixing in $^3$He($K^-,n$) reaction are also evaluated numerically. To understand the meanings of the spectrum shape, we also study the behavior of the poles of kaon Green's function in nuclear matter. We conclude that $^3$He($K^-,n$) and $^3$He($K^-,p$) reactions coincident with the $\pi\Sigma$ emission due to ${\bar K}$ absorption may show the certain structure in the bound region spectra indicating the existence of the unstable kaonic nuclear bound states. As for the $^{12}$C($K^-,p$) spectra with the $\pi\Sigma$ emission, we may also observe the structure in the bound region, however, we need to evaluate the medium effects carefully for larger nuclei.Comment: 14 pages, 12 figure

Terminal velocity and drag reduction measurements on superhydrophobic spheres

Super water-repellent surfaces occur naturally on plants and aquatic insects and are created in the laboratory by combining micro- or nanoscale surface topographic features with hydrophobic surface chemistry. When such types of water-repellent surfaces are submerged they can retain a film of air (a plastron). In this work, we report measurements of the terminal velocity of solid acrylic spheres with various surface treatments settling under the action of gravity in water. We observed increases in terminal velocity corresponding to drag reduction of between 5% and 15% for superhydrophobic surfaces that carry plastrons

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

Presenting Computer Science Concepts to High School Students

Computer science at high school often focusses on programming, but a broader view of other areas of computer science has key benefits for both writing programs that are more efficient and making more theoretical concepts more accessible to those who do not find programming intrinsically interesting. With the introduction of computer science at high schools, a lack of coherent resources for teachers and students prompted the development of the NZ Computer Science Field Guide, an open-source, on-line textbook. This paper describes the design of the Field Guide, which has fourteen chapters about various topics of computer science. The design includes written text, videos, classroom activities and interactive applications. The need for a broad view of computer science is discussed, and programming exercises to go with the topics are suggested

Comment on "On Mach's critique of Newton and Copernicus"

Hartman and Nissim-Sabat have argued that Mach's idea of the relativity of rotational motion suffers from internal inconsistencies and leads to a contradiction that there cannot be a stationary bucket in a rotating universe. They also claimed that non-inertial electromagnetic and stellar aberration observations can distinguish between a rotating and a stationary universe, whereas according to Mach there cannot be any observable way to distinguish these two cases. We contest these objections.Comment: Six pages, to appear in AJ

Adoption of Computer Science in NZ schools

In 2011, Programming and Computer Science standards were made available as part of NCEA in New Zealand high schools. Because little guidance and professional development was available initially, teachers have found it challenging to present the content effectively to their students. In response to this, several resources and professional development opportunities have been made available, including the widely used Computer Science Field Guide for Computer Science, and several programming resources specific to the new standards. In this paper we outline the deployment of the new standards and supporting material, and look at the uptake of the new standards over the first three years that they were phased in. This reveals increasing participation at schools, and higher enrolments at university as a flow-on effect. The introduction of Computer Science has also helped to address perception and stereotypes about the industry, with high achievement by female students, although participation rates are not ideal

Detection of Multi-drug Resistant \u3cem\u3eEscherichia coli\u3c/em\u3e in the Urban Waterways of Milwaukee, WI

Urban waterways represent a natural reservoir of antibiotic resistance which may provide a source of transferable genetic elements to human commensal bacteria and pathogens. The objective of this study was to evaluate antibiotic resistance of Escherichia coli isolated from the urban waterways of Milwaukee, WI compared to those from Milwaukee sewage and a clinical setting in Milwaukee. Antibiotics covering 10 different families were utilized to determine the phenotypic antibiotic resistance for all 259 E. coli isolates. All obtained isolates were determined to be multi-drug resistant. The E. coli isolates were also screened for the presence of the genetic determinants of resistance including ermB (macrolide resistance), tet(M) (tetracycline resistance), and β-lactamases (blaOXA, blaSHV, and blaPSE). E. coli from urban waterways showed a greater incidence of antibiotic resistance to 8 of 17 antibiotics tested compared to human derived sources. These E. coli isolates also demonstrated a greater incidence of resistance to higher numbers of antibiotics compared to the human derived isolates. The urban waterways demonstrated a greater abundance of isolates with co-occurrence of antibiotic resistance than human derived sources. When screened for five different antibiotic resistance genes conferring macrolide, tetracycline, and β-lactam resistance, clinical E. coli isolates were more likely to harbor ermB and blaOXA than isolates from urban waterway. These results indicate that Milwaukee’s urban waterways may select or allow for a greater incidence of multiple antibiotic resistance organisms and likely harbor a different antibiotic resistance gene pool than clinical sources. The implications of this study are significant to understanding the presence of resistance in urban freshwater environments by supporting the idea that sediment from urban waterways serves as a reservoir of antibiotic resistance

S-matrix poles and the second virial coefficient

For cutoff potentials, a condition which is not a limitation for the calculation of physical systems, the S-matrix is meromorphic. We can express it in terms of its poles, and then calculate the quantum mechanical second virial coefficient of a neutral gas. Here, we take another look at this approach, and discuss the feasibility, attraction and problems of the method. Among concerns are the rate of convergence of the 'pole' expansion and the physical significance of the 'higher' poles.Comment: 20 pages, 8 tables, submitted to J. Mol. Phy