Excitations in the dilute A_L lattice model: E_6, E_7 and E_8 mass spectra

On the basis of features observed in the exact perturbation approach solution for the eigenspectrum of the dilute A_3 model, we propose expressions for excitations in the dilute A_4 and A_6 models. Principally, we require that these expressions satisfy the appropriate inversion relations. We demonstrate that they give the expected E_7 and E_6 mass spectra, and universal amplitudes, and agree with numerical expressions for the eigenvalues.Comment: 16 pages, Latex, Elsevier style file

Advanced microwave radiometer antenna system study

The practicability of a multi-frequency antenna for spaceborne microwave radiometers was considered in detail. The program consisted of a comparative study of various antenna systems, both mechanically and electronically scanned, in relation to specified design goals and desired system performance. The study involved several distinct tasks: definition of candidate antennas that are lightweight and that, at the specified frequencies of 5, 10, 18, 22, and 36 GHz, can provide conical scanning, dual linear polarization, and simultaneous multiple frequency operation; examination of various feed systems and phase-shifting techniques; detailed analysis of several key performance parameters such as beam efficiency, sidelobe level, and antenna beam footprint size; and conception of an antenna/feed system that could meet the design goals. Candidate antennas examined include phased arrays, lenses, and optical reflector systems. Mechanical, electrical, and performance characteristics of the various systems were tabulated for ease of comparison

Participation And performance In 8.02x Electricity And Magnetism: The First Physics MOOC From MITx

Massive Open Online Courses are an exciting new avenue for instruction and research, yet they are full of unknowns. In the Spring of 2013, MITx released its first introductory physics MOOC through the edX platform, generating a total enrollment of 43,000 students from around the world. We describe the population of participants in terms of their age, gender, level of education, and country of origin, highlighting both the diversity of 8.02x enrollees as well as gender gap and retention. Using three midterm exams and the final as waypoints, we highlight performance by different demographic subpopulations and their retention rates. Our work is generally aimed at making a bridge between available MOOC data and topics associated with the Physics Education Research community.Comment: 4 pages, 5 figures, Accepted for publication in the Physics Education Research Conference Proceedings, Portland OR 201

The dilute A4_4 model, the E7_7 mass spectrum and the tricritical Ising model

The exact perturbation approach is used to derive the (seven) elementary correlation lengths and related mass gaps of the two-dimensional dilute A$_4$ lattice model in regime 2- from the Bethe ansatz solution. This model provides a realisation of the integrable $\phi(1,2)$ perturbation of the c=7/10 conformal field theory, which is known to describe the off-critical thermal behaviour of the tricritical Ising model. The E$_7$ masses predicted from purely elastic scattering theory follow in the approach to criticality. Universal amplitudes for the tricritical Ising model are calculated.Comment: 24 pages, LaTeX, submitted to Journal of Mathematical Physics. One paragraph added and some minor typos correcte

Electronic effects in high-energy radiation damage in iron

Electronic effects are believed to be important in high--energy radiation damage processes where high electronic temperature is expected, yet their effects are not currently understood. Here, we perform molecular dynamics simulations of high-energy collision cascades in $\alpha$-iron using the coupled two-temperature molecular dynamics (2T-MD) model that incorporates both effects of electronic stopping and electron-ion interaction. We subsequently compare it with the model employing the electronic stopping only, and find several interesting novel insights. The 2T-MD results in both decreased damage production in the thermal spike and faster relaxation of the damage at short times. Notably, the 2T-MD model gives a similar amount of the final damage at longer times, which we interpret to be the result of two competing effects: smaller amount of short-time damage and shorter time available for damage recovery.Comment: 8 pages, 6 figure

Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas

Three-body recombination, an important collisional process in plasmas, increases dramatically at low electron temperatures, with an accepted scaling of T_e^-9/2. We measure three-body recombination in an ultracold neutral xenon plasma by detecting recombination-created Rydberg atoms using a microwave-ionization technique. With the accepted theory (expected to be applicable for weakly-coupled plasmas) and our measured rates we extract the plasma temperatures, which are in reasonable agreement with previous measurements early in the plasma lifetime. The resulting electron temperatures indicate that the plasma continues to cool to temperatures below 1 K.Comment: 5 pages, 3 figure