What can we infer about the underlying physics from burst distributions observed in an RMHD simulation ?

We determine that the sizes of bursts in mean-square current density in a reduced magnetohydrodynamic (RMHD)simulation follow power-law probability density function (PDF). The PDFs for burst durations and waiting time between bursts are clearly not exponential and could also be power-law. This suffices to distinguish their behaviour from the original Bak et al. sandpile model which had exponential waiting time PDFs. However, it is not sufficient to distinguish between turbulence, some other SOC-like models, and other red noise sources.Comment: In press, Planetary and Space Science. Proceedings of a session at European Geophysical Society General Assembly, Nice, 200

Reciprocal Recommender System for Learners in Massive Open Online Courses (MOOCs)

Massive open online courses (MOOC) describe platforms where users with completely different backgrounds subscribe to various courses on offer. MOOC forums and discussion boards offer learners a medium to communicate with each other and maximize their learning outcomes. However, oftentimes learners are hesitant to approach each other for different reasons (being shy, don't know the right match, etc.). In this paper, we propose a reciprocal recommender system which matches learners who are mutually interested in, and likely to communicate with each other based on their profile attributes like age, location, gender, qualification, interests, etc. We test our algorithm on data sampled using the publicly available MITx-Harvardx dataset and demonstrate that both attribute importance and reciprocity play an important role in forming the final recommendation list of learners. Our approach provides promising results for such a system to be implemented within an actual MOOC.Comment: 10 pages, accepted as full paper @ ICWL 201

Economies of scale and scope in hospitals: an empirical study of volume spillovers

General hospitals across the world are becoming larger (i.e. admitting more patients each year) and more complex (i.e. offering a wider range of services to patients with more diverse care needs). Prior work suggests that an increase in patient volume in a hospital service is associated with reduced costs per patient in that service. However, it is unclear how volume changes in one service affect the costs of the other services in the same hospital. This paper investigates such volume-cost spillover effects between elective and emergency admissions and across specialties, using condition-level panel data comprising all acute hospital trusts in England over a period of ten years. We provide evidence that increased elective volume at a hospital is associated with an increase in the cost of emergency care (a negative spillover). Furthermore, for emergency admissions, we find evidence that increased emergency activity in one specialty is associated with lower costs of emergency care in other specialties (a positive spillover). By contrast, we find no evidence of spillover effects across specialties for elective admissions. We discuss the implications of these findings for individual hospital growth strategies and for the regional organization of hospital systems

Zero delay synchronization of chaos in coupled map lattices

We show that two coupled map lattices that are mutually coupled to one another with a delay can display zero delay synchronization if they are driven by a third coupled map lattice. We analytically estimate the parametric regimes that lead to synchronization and show that the presence of mutual delays enhances synchronization to some extent. The zero delay or isochronal synchronization is reasonably robust against mismatches in the internal parameters of the coupled map lattices and we analytically estimate the synchronization error bounds.Comment: 9 pages, 9 figures ; To appear in Phys. Rev.

Casorati Determinant Form of Dark Soliton Solutions of the Discrete Nonlinear Schr\"odinger Equation

It is shown that the $N$-dark soliton solutions of the integrable discrete nonlinear Schr\"odinger (IDNLS) equation are given in terms of the Casorati determinant. The conditions for reduction, complex conjugacy and regularity for the Casorati determinant solution are also given explicitly. The relationship between the IDNLS and the relativistic Toda lattice is discussed.Comment: First version was uploaded in 23 Jun 2005. Published in Journal of the Physical Society of Japan in May, 200

Half-metallicity and efficient spin injection in AlN/GaN:Cr (0001) heterostructure

First-principles investigations of the structural, electronic and magnetic properties of Cr-doped AlN/GaN (0001) heterostructures reveal that Cr segregates into the GaN region, that these interfaces retain their important half-metallic character and thus yield efficient (100 %) spin polarized injection from a ferromagnetic GaN:Cr electrode through an AlN tunnel barrier - whose height and width can be controlled by adjusting the Al concentration in the graded bandgap engineered Al(1-x)Ga(x)N (0001) layers.Comment: submitted for publicatio

Magnetic Behavior in RRhX (R = rare earths; X=B, C) Compounds

We report on the magnetic behavior of RRhB (R = La, Ce, Pr, Nd, Gd, Tb and Tm) and RRhC (R = La, Ce, Pr and Gd) compounds crystallizing in the cubic perovskite type structure with space group Pm3m. The heat capacity data on Pauli-paramagnetic LaRhB and LaRhC indicate a high frequency vibrating motion of boron and carbon atoms in the unit cell. Ce is in -like nonmagnetic state in both the compounds. Pr compounds show a dominant crystal field effect with a nonmagnetic singlet ground state in PrRhB and a nonmagnetic quadrupolar doublet in PrRhC. Compounds with other rare earths order ferromagnetically at low temperatures except TmRhB in which the zero field evolution of magnetic interactions is relatively more complicated. The electrical resistivity of GdRhB decreases with increasing temperature in the paramagnetic state in the vicinity of T, which is rarely seen in ferromagnets. The behavior is discussed to be arising due to the short range spin fluctuation and a possible contribution from Fermi surface geometry.Comment: 14 Figs and a text fil

Scaling in long term data sets of geomagnetic indices and solar wind ϵ as seen by WIND spacecraft

We study scaling in fluctuations of the geomagnetic indices (AE, AU, and AL) that provide a measure of magnetospheric activity and of the ε parameter which is a measure of the solar wind driver. Generalized structure function (GSF) analysis shows that fluctuations exhibit self-similar scaling up to about 1 hour for the AU index and about 2 hours for AL, AE and ε when the most extreme fluctuations over 10 standard deviations are excluded. The scaling exponents of the GSF are found to be similar for the three AE indices, and to differ significantly from that of ε. This is corroborated by direct comparison of their rescaled probability density functions