Roton Interactions In Superfluid Helium

Based on a hard-sphere model for superfluid helium we derive a microscopic theory for quasiparticle interactions in this liquid. A satisfactory upper bound for the roton-roton collision frequency is obtained from this model. This theory also leads to an attractive coupling of two rotons with opposite momenta but the coupling strength is an order of magnitude larger than the phenomenological estimates based on experiments. However, as our analysis reveals, this large coupling strength is compatible with other physical considerations presented in this paper and does not contradict experimental data. © 1976 The American Physical Society.1451932194

Non-Hausdorff Symmetries of C*-algebras

Symmetry groups or groupoids of C*-algebras associated to non-Hausdorff spaces are often non-Hausdorff as well. We describe such symmetries using crossed modules of groupoids. We define actions of crossed modules on C*-algebras and crossed products for such actions, and justify these definitions with some basic general results and examples.Comment: very minor changes. To appear in Math. An

Equivariant comparison of quantum homogeneous spaces

We prove the deformation invariance of the quantum homogeneous spaces of the q-deformation of simply connected simple compact Lie groups over the Poisson-Lie quantum subgroups, in the equivariant KK-theory with respect to the translation action by maximal tori. This extends a result of Neshveyev-Tuset to the equivariant setting. As applications, we prove the ring isomorphism of the K-group of Gq with respect to the coproduct of C(Gq), and an analogue of the Borsuk-Ulam theorem for quantum spheres.Comment: 21 page

Toward Green Mobility: The Evolution of Transport

We envisage a transport system producing zero emissions and sparing the surface landscape, while people, on average, range hundreds of kilometers daily. We believe this prospect of "green mobility" is consistent with historical evolution. We lay out the general principles, extracted from widespread observations of human behavior over long periods of time, and use them to explain past transport systems and project the next 50-100 years. We discuss in detail railroads, cars, aeroplanes, and magnetically levitated trains (maglevs)

Management of fiscal and monetary policies interdependence in South African economy : A Bayesian VAR approach

Abstract: Purpose of the study: This study revisits the management and interaction aspects between fiscal and monetary policies in South Africa using a Bayesian vector autoregressive model (BVA). Design/methodology/approach: Monthly data on the inflation rate, interest rate, money supply, tax revenue, government spending and government debt for the period 2009 - 2019 were sourced from the South African Reserve Bank. Findings: The impulse response analysis shows that positive shocks to money supply prompt monetary authority to raise the economy's interest rate, which increases the bank rate. Inflation does not respond to shock to government spending and could drive inflation in the South African economy from the supply side rather than the demand side. Tax revenue and money supply shocks are significant sources of variation in inflation. These variables account for 7 and 18 percent variation in government spending. Recommendations/value: The study concludes that monetary authority must employ supply-side measures to manage the price level

Quantum teardrops

Algebras of functions on quantum weighted projective spaces are introduced, and the structure of quantum weighted projective lines or quantum teardrops are described in detail. In particular the presentation of the coordinate algebra of the quantum teardrop in terms of generators and relations and classification of irreducible *-representations are derived. The algebras are then analysed from the point of view of Hopf-Galois theory or the theory of quantum principal bundles. Fredholm modules and associated traces are constructed. C*-algebras of continuous functions on quantum weighted projective lines are described and their K-groups computed.Comment: 18 page

Eutrofiering in Nederland.

Een derde onderzoek is uitgevoerd naar de eutrofieringstoestand in de (semi-) stagnante zoete oppervlaktewateren in ons land. Van 121 plassen en meren werden min of meer volledige gegevens ontvangen betreffende de fysische, chemische en biologische kenmerke

Aspects of the FM Kondo Model: From Unbiased MC Simulations to Back-of-an-Envelope Explanations

Effective models are derived from the ferromagnetic Kondo lattice model with classical corespins, which greatly reduce the numerical effort. Results for these models are presented. They indicate that double exchange gives the correct order of magnitude and the correct doping dependence of the Curie temperature. Furthermore, we find that the jump in the particle density previously interpreted as phase separation is rather explained by ferromagnetic polarons.Comment: Proceedings of Wandlitz Days of Magnetism 200