Hartree-Fock ground state of the composite fermion metal

Within the Hartree-Fock approximation the ground state of the composite fermion metal is found. We observe that the single-particle energy spectrum is dominated by the logarithmic interaction exchange term which leads to an infinite jump of the single-particle energy at the Fermi momentum. It is shown that the Hartree-Fock result brings no corrections to the RPA Fermi velocity.Comment: 8 pages (Latex), to appear in Mod.Phys.Lett.

Urban disaster resilience: learning from the 2011 Bangkok flood

Reducing disaster risk, managing rapid urbanisation and tackling poverty is an enormous challenge, particularly in vulnerable neighbourhoods in low and middle-income countries. By 2050, two-thirds of the world’s population will live in towns and cities, with 95 per cent of future urban expansion in the global South. At the same time, disasters are increasing in frequency, severity and intensity. Poorer people in vulnerable neighbourhoods are least equipped to cope with the threat of disaster. When flooding struck Thailand’s capital city Bangkok in 2011, the United Nations estimated that 73 per cent of low-income households were badly affected (UNISDR 2013). With disasters in cities on the rise, current thinking suggests that resilience offers valuable insights for reducing risk. This research seeks to develop and validate a conceptual framework for understanding urban disaster resilience in low-income neighbourhoods. It combines two urban approaches. The first, complex adaptive systems (CAS), views the city as a combination of inter-dependent parts working together at a multitude of scales that shapes its overall behaviour. The second, urban morphology, seeks to understand the creation of urban form by establishing connections between the city’s historical economic, political and social transformations to its modern day form. The conceptual framework was applied to three low-income neighbourhoods in Bangkok affected by the 2011 flood. Through a case study approach, qualitative information was gathered and analysed in order to understand city-scale and neighbourhood level transformations that built patterns of vulnerability and resilience to chronic stresses and acute shocks. This research concludes that combining CAS and morphology provides a valuable conceptual framework for understanding urban disaster resilience. Such a framework places people at the centre while providing a scalar and temporal analysis of co-evolving acute and chronic risks in urban areas. Moreover, the intersections of CAS and urban morphology identify dimensions of resilience, where human systems and the built environment affect each other in a positive or negative ways – before, during and after a disaster. Overall, this research concludes that resilience needs to be built both before and after a disaster to be effective, and that disaster itself is a test of how systems and the built environment have learned from history about how to cope with and adapt to shocks and stresses. To these ends, urban disaster resilience can be defined as the ways in which the built environment, complex adaptive systems and people interact to cope, adapt and transform in order to reduce disaster risk

Exclusion Statistics of Quasiparticles in Condensed States of Composite Fermion Excitations

The exclusion statistics of quasiparticles is found at any level of the hierarchy of condensed states of composite fermion excitations (for which experimental indications have recently been found). The hierarchy of condensed states of excitations in boson Jain states is introduced and the statistics of quasiparticles is found. The quantum Hall states of charged $\alpha$-anyons ($\alpha$ -- the exclusion statistics parameter) can be described as incompressible states of $(\alpha+2p)$-anyons ($2p$ -- an even number).Comment: 4 page

The Composite Fermion Hierarchy: Condensed States of Composite Fermion Excitations?

A composite Fermion hierarchy theory is constructed in a way related to the original Haldane picture by applying the composite Fermion (CF) transformation to quasiparticles of Jain states. It is shown that the Jain theory coincides with the Haldane hierarchy theory for principal CF fillings. Within the Fermi liquid approach for few electron systems on the sphere a simple interpretation of many-quasiparticle spectra is given and provides an explanation of failure of CF hierarchy picture when applied to the hierarchical $4/11$ state.Comment: 6 pages, Revtex, 4 figures in PostScript, submitted to Phys. Rev. Let

Composite Fermions and the Half-Filled State

Under appropriate conditions electron-hole symmetry should apply to a partially filled Landau level of a two-dimensional electron gas. This suggests that the application of Jain’s composite fermion (CF) picture to either electrons or holes should lead to equivalent results. Surprisingly, for a system of Ne electrons on a Haldane sphere, this is not true for three values of the Landau level degeneracy 2S+1. When Ne-1\u3c~S\u3c~Ne, the sum of the electron filling factor ν and the hole filling factor μ, as determined from Jain’s picture, is smaller than unity. Because of this, use of the relation ν=1-μ can lead to “twin” or “alias” states having different values of ν for the same Ne and 2S+1. One example is the “half-filled” state. It is determined by requiring the effective (mean-field) flux 2S* “seen” by one CF to vanish. Different results are obtained when S*e=Se-(Ne-1) and S*h=S-(Nh-1) are set equal to zero. The same problem arises in the CF hierarchy picture when the number of quasielectrons nQE is related to the effective flux 2S* by 2(nQE-1)\u3c~2S*\u3c~2nQE

Quantum Hall Spherical Systems: the Filling Fraction

Within the newly formulated composite fermion hierarchy the filling fraction of a spherical quantum Hall system is obtained when it can be expressed as an odd or even denominator fraction. A plot of $\nu\frac{2S}{N-1}$ as a function of $2S$ for a constant number of particles (up to N=10001) exhibits structure of the fractional quantum Hall effect. It is confirmed that $\nu_e +\nu_h=1$ for all particle-hole conjugate systems, except systems with $N_e =N_h$, and $N_e=N_h \pm 1$.Comment: 3 pages, Revtex, 7 PostScript figures, submitted to Phys. Rev. B Rapid Communicatio

Copper Heat Exchanger for the External Auxiliary Bus-Bars Routing Line in the LHC Insertion Regions

The corrector magnets and the main quadrupoles of the LHC dispersion suppressors are powered by a special superconducting line (called auxiliary bus-bars line N), external to the cold mass and housed in a 50 mm diameter stainless steel tube fixed to the cold mass. As the line is periodically connected to the cold mass, the same gaseous and liquid helium cools both the magnets and the line. The final sub-cooling process (from around 4.5 K down to 1.9 K) consists in the phase transformation from liquid to superfluid helium. Heat is extracted from the line through the magnets via their point of junction. In dispersion suppressor zones, approximately 40 m long, the sub-cooling of the line is slightly delayed with respect to the magnets. This might have an impact on the readiness of the accelerator for operation. In order to accelerate the process, a special heat exchanger has been designed. It is located in the middle of the dispersion suppressor portion of the line. Its main function consists in providing a local point of heat extraction, creating two additional lambda fronts that propagate in opposite directions towards the extremities of the line. Both the numerical model and the sub-cooling analysis are presented in the paper for different configurations of the line. The design, manufacturing and integration aspects of the heat exchanger are described

Role of surface microgeometries on electron escape probability and secondary electron yield of metal surfaces

The influence of microgeometries on the Secondary Electron Yield (SEY) of surfaces is investigated. Laser written structures of different aspect ratio (height to width) on a copper surface tuned the SEY of the surface and reduced its value to less than unity. The aspect ratio of microstructures was methodically controlled by varying the laser parameters. The results obtained corroborate a recent theoretical model of SEY reduction as a function of the aspect ratio of microstructures. Nanostructures - which are formed inside the microstructures during the interaction with the laser beam - provided further reduction in SEY comparable to that obtained in the simulation of structures which were coated with an absorptive layer suppressing secondary electron emission

The continued optical to mid-IR evolution of V838 Monocerotis

The eruptive variable V838 Monocerotis gained notoriety in 2002 when it brightened nine magnitudes in a series of three outbursts and then rapidly evolved into an extremely cool supergiant. We present optical, near-IR, and mid-IR spectroscopic and photometric observations of V838 Monocerotis obtained between 2008 and 2012 at the Apache Point Observatory 3.5m, NASA IRTF 3m, and Gemini South 8m telescopes. We contemporaneously analyze the optical & IR spectroscopic properties of V838 Monocerotis to arrive at a revised spectral type L3 supergiant and effective temperature Teff~2000--2200 K. Because there are no existing optical observational data for L supergiants in the optical, we speculate that V838 Monocerotis may represent the prototype for L supergiants in this wavelength regime. We find a low level of Halpha emission present in the system, consistent with interaction between V838 Monocerotis and its B3V binary; however, we cannot rule out a stellar collision as the genesis event, which could result in the observed Halpha activity. Based upon a two-component blackbody fit to all wavelengths of our data, we conclude that, as of 2009, a shell of ejecta surrounded V838 Monocerotis at a radius of R=263+/-10 AU with a temperature of T=285+/-2 K. This result is consistent with IR interferometric observations from the same era and predictions from the Lynch et al. model of the expanding system, which provides a simple framework for understanding this complicated system.Comment: 6 pages, 2 tables, 6 figures; accepted to A