Decay of Magnetic Fields in the Early Universe

We study the evolution of a stochastic helical magnetic field generated in the early Universe after the electroweak phase transition, using standard magnetohydrodynamics (MHD). We find how the coherence length xi, magnetic energy E_M and magnetic helicity H evolve with time. We show that the self-similarity of the magnetic power spectrum alone implies that xi ~ t^{1/2}. This in turn implies that magnetic helicity decays as H ~ t^{-2s}, and that the magnetic energy decays as E_M ~ t^{-0.5-2s}, where s is inversely proportional to the magnetic Reynolds number Re_M. These laws improve on several previous estimates.Comment: 5pp LaTeX + World Sci procs class, 3 eps figs. Talk given at Strong and Electroweak Matter, Oct 2-5 2002, Heidelber

Can the supply of small business loans be increased?

Small and new businesses, widely credited as engines for job growth, have struggled during the recovery. One reason, say some analysts, is that bank lending to small businesses has declined steadily since the start of the recession. If, as many small businesses claim, the supply of credit from banks has contracted, then increasing the supply of small business loans may allow these businesses to grow and create new jobs. Understanding the factors that affect loan supply may help policymakers design policies to increase the supply of small business loans and, therefore, support further job growth. ; Wilkinson and Christensson analyze the potential effectiveness of two strategies that policymakers can use to expand the supply of small business loans: increasing bank capital and reducing problem assets. A review of recent policy initiatives suggests that influencing bank capital may be easier than addressing problem assets. However, reducing problem assets may lead to a larger and more persistent increase in the supply of loans.

Enhancement of Vibronic and Ground-State Vibrational Coherences in 2D Spectra of Photosynthetic Complexes

A vibronic-exciton model is applied to investigate the mechanism of enhancement of coherent oscillations due to mixing of electronic and nuclear degrees of freedom recently proposed as the origin of the long-lived oscillations in 2D spectra of the FMO complex [Christensson et al. J. Phys. Chem. B 116 (2012) 7449]. We reduce the problem to a model BChl dimer to elucidate the role of resonance coupling, site energies, nuclear mode and energy disorder in the enhancement of vibronic-exciton and ground-state vibrational coherences, and to identify regimes where this enhancement is significant. For a heterodimer representing the two coupled BChls 3 and 4 of the FMO complex, the initial amplitude of the vibronic-exciton and vibrational coherences are enhanced by up to 15 and 5 times, respectively, compared to the vibrational coherences in the isolated monomer. This maximum initial amplitude enhancement occurs when there is a resonance between the electronic energy gap and the frequency of the vibrational mode. The bandwidth of this enhancement is about 100 cm-1 for both mechanisms. The excitonic mixing of electronic and vibrational DOF leads to additional dephasing relative to the vibrational coherences. We evaluate the dephasing dynamics by solving the quantum master equation in Markovian approximation and observe a strong dependence of the life-time enhancement on the mode frequency. Long-lived vibronic-exciton coherences are found to be generated only when the frequency of the mode is in the vicinity of the electronic resonance. Although the vibronic-exciton coherences exhibit a larger initial amplitude compared to the ground-state vibrational coherences, we conclude that both type have a similar magnitude at long time for the present model. The ability to distinguish between vibronic-exciton and ground-state vibrational coherences in the general case of molecular aggregate is discussed.Comment: 16 pages, 6 figure

Recommendation to test limonene hydroperoxides 0.3% and linalool hydroperoxides 1.0% in the British Baseline patch test series

Background: There is a significant rate of sensitisation worldwide to the oxidised fragrance terpenes limonene and linalool. Patch testing to oxidised terpenes is not routinely carried out; the ideal patch test concentration is unknown.Objectives: To determine the best test concentrations for limonene and linalool hydroperoxides, added to the British baseline patch test series, to optimise detection of true allergy and minimise irritant reactions.Methods: During 2013-2014, 4563 consecutive patients in 12 UK centres were tested to hydroperoxides of limonene in petrolatum (pet.) 0.3%, 0.2% and 0.1%, and hydroperoxides of linalool 1.0%, 0.5% and 0.25% pet. Irritant (IR) reactions were recorded separately from doubtful (?+) reactions. Concomitant reactions to other fragrance markers and clinical relevance were documented.Results: Limonene hydroperoxide 0.3% gave positive reactions in 241 (5.3%) patients, irritant reactions in 93 (2.0%) and doubtful reactions in 110 (2.4%). Linalool hydroperoxide 1.0% gave positive reactions in 352 (7.7%), irritant reactions in 178 (3.9%), and doubtful reactions in 132 (2.9%). 119 patients with crescendo reactions to 0.3% limonene would have been missed if only tested with 0.1%. 131 patients with crescendo reactions to 1.0% linalool would have been missed if only tested with 0.25%. In almost two-thirds of patients with positive patch tests to limonene and linalool the reaction was clinically relevant. The majority of patients did not react to any fragrance marker in the baseline series.Conclusions: We recommend that limonene hydroperoxides be tested at 0.3% and linalool hydroperoxides at 1.0% in the British baseline patch test series.</p

What can financial stability reports tell us about macroprudential supervision?

Many countries have suggested macroprudential supervision as a means for earlier identification and better control of the risks that might lead to a financial crisis. Since macroprudential supervision would focus on the financial system in its entirety and on major risks that could threaten financial stability, it shares many of the same goals as the financial stability reports written by most central banks. This article examines the financial stability reports of five central banks to assess how effective they were in identifying the problems that led to the recent financial crisis and what implications they might have for macroprudential supervision. ; The financial stability reports in these five countries were generally successful in foreseeing the risks that contributed to the crisis, but the reports underestimated the severity of the crisis and did not fully anticipate the timing and pattern of important events. While the stress tests in these reports provided insights into the resiliency and capital needs of the banks in these countries, the stresses and scenarios tested often differed from what actually occurred and some of the reports did not consider them to be likely events. One other major challenge for the central banks was in taking the concerns expressed in financial stability reports and linking them to effective and timely supervisory policy. Overall, the reports were a worthwhile exercise in identifying and monitoring key financial trends and emerging risks, but they also indicate the significant challenges macroprudential supervision will have in anticipating and addressing financial market disruptions.

Financial stability reports: how useful during a financial crisis?

Many of the origins of the recent financial crisis were in the United States, beginning with subprime mortgages and mortgage securities. As the crisis spread globally, few market participants or regulatory authorities saw it coming and all underestimated its severity. ; In the United States, the crisis has sparked many proposals to address its perceived causes and prevent a recurrence. One approach already used in many other countries is publishing financial stability reports. These reports review the condition of the financial system, identify and assess risks to the system, and suggest market or policy changes to address significant risk concerns. They are usually prepared by the country’s central bank and appear on a regular basis. ; Wilkinson, Spong, and Christensson analyze the financial stability reports prepared by four European countries that were affected by the financial crisis the United Kingdom, Sweden, the Netherlands, and Spain. They find that these four reports were generally successful in identifying the risks that played important roles in the crisis although they underestimated the severity of this crisis. While it is not clear that the reports helped to reduce the damages, it would be a mistake to dismiss them as a useful tool. Overall, publishing financial stability reports appears to be a worthwhile exercise that encourages central banks and international authorities to identify and monitor important financial trends and emerging risks and to develop a better understanding of the underlying structure of domestic and global financial markets.

Metastability of persistent currents in trapped gases of atoms

We examine the conditions that give rise to metastable, persistent currents in a trapped Bose-Einstein condensate. A necessary condition for the stability of persistent currents is that the trapping potential is not a monotonically increasing function of the distance from the trap center. Persistent currents also require that the interatomic interactions are sufficiently strong and repulsive. Finally, any off-center vortex state is shown to be unstable, while a driven gas shows hysteresis.Comment: 7 pages, RevTex, 5 figure