Unemployment Dynamics and Cyclical Fluctuations in the Icelandic Labour Market

This paper studies business cycle dynamics in the Icelandic labour market with the focus on two separate but related dimensions. First, which margin for adjustment of labour input, the extensive margin or the intensive margin, accounts for more variation in total working hours? It finds that both margins are important. Variation in employment accounts for 56% of the overall variation in total hours while variation in hours per worker contributes 44% to variation in total hours. Second, which of the two unemployment transition rates, the separation rate or the job-finding rate, drives the observed fluctuations in unemployment, and how do these transition rates move over the business cycle? The results show that fluctuations in the separation rate explain 70% of the total variation in the unemployment rate. Both transition rates are highly cyclical. The procyclical job finding rate moves roughly contemporaneously with the cycle, while the countercyclical separation rate is found to lead the cycle.

The Siciak-Zahariuta extremal function as the envelope of disc functionals

We establish disc formulas for the Siciak-Zahariuta extremal function of an arbitrary open subset of complex affine space, generalizing Lempert's formula for the convex case. This function is also known as the pluricomplex Green function with logarithmic growth or a logarithmic pole at infinity. We extend Lempert's formula for this function from the convex case to the connected case.Comment: Version 3 contains a proof of Lempert's formula for the S-Z function in the convex case, in slightly modified form, for an arbitrary connected open subset of affine space. This was the main problem left unsolved in the earlier versions. The rest of the paper is essentially unchanged from version

Plurisubharmonicity of envelopes of disc functionals on manifolds

We show that a disc functional on a complex manifold has a plurisubharmonic envelope if all its pullbacks by holomorphic submersions from domains of holomorphy in affine space do and it is locally bounded above and upper semicontinuous in a certain weak sense. For naturally defined classes of disc functionals on manifolds, this result reduces a property somewhat stronger than having a plurisubharmonic envelope to the affine case. The proof uses a recent Stein neighbourhood construction of Rosay, who proved the plurisubharmonicity of the Poisson envelope on all manifolds. As a consequence, the Riesz envelope and the Lelong envelope are plurisubharmonic on all manifolds; for the former, we make use of new work of Edigarian. The basic theory of the three main classes of disc functionals is thereby extended to all manifolds.Comment: A few minor changes made 24 January 200

Assessment of the atmospheric impact of volcanic eruptions

The dominant global impact of volcanic activity is likely to be related to the effects of volcanic gases on the Earth's atmosphere. Volcanic gas emissions from individual volcanic arc eruptions are likely to cause increases in the stratospheric optical depth that result in surface landmass temperature decline of 2 to 3 K for less than a decade. Trachytic and intermediate magmas are much more effective in this regard than high-silica magmas, and may also lead to extensive ozone depletion due to effect of halogens and magmatic water. Given the assumed relationship between arc volcanism and subduction rate, and the relatively small variation in global spreading rates in the geologic record, it is unlikely that the rates of arc volcanism have varied greatly during the Cenozoic. Hotspot related basaltic fissure eruptions in the subaerial environment have a higher mass yield of sulfur, but lofting of the valcanic aerosol to levels above the tropopause is required for a climate impact. High-latitude events, such as the Laki 1783 eruption can easily penetrate the tropopause and enter the stratosphere, but formation of a stratospheric volcanic aerosol form low-latitude effusive basaltic eruptions is problematical, due to the elevated low-latitude tropopause. Due to the high sulfur content of hotspot-derived basaltic magmas, their very high mass eruption rates and the episodic behavior, hotspots must be regarded as potentially major modifiers of Earth's climate through the action of their volcanic volatiles on the chemistry and physics of the atmosphere

Planetary Collisions: Electromagnetic Signals

We investigate the electromagnetic signals accompanied with planetary collisions and their event rate, and explore the possibility of directly detecting such events. A typical Earth--Jupiter collision would give rise to a prompt EUV-soft-X-ray flash lasting for hours and a bright IR afterglow lasting for thousands of years. With the current and forthcoming observational technology and facilities, some of these collisional flashes or the post-collision remnants could be discovered.Comment: 4 pages, to appear in Proceedings of 14th Annual October Astrophysics Conference in Maryland, "The Search for Other Worlds". A concise version of ApJ, 596, L95 (2003), astro-ph/030821

Testing gravity in Large Extra Dimensions using Bose-Einstein Condensates

Recent conjectures that there are mesoscopically ``large'' extra dimensions, through which gravity propagates have interesting implications for much of physics. The scenario implies gross departures from Newton's law of gravity at small length scales. Testing departures from Coulomb's law on sub-millimetre scales is hard. It is now possible to routinely create Bose-Einstein condensates with de Broglie wavelengths of order a $\mu m$ and total size of order $10 \mu m$. BEC condensates move coherently under gravitational acceleration, and I propose that the transverse fringe shift due to the acceleration of pair of interfering BECs passing a dense linear mass may be measurable, and provide direct evidence for anomalous gravitational acceleration. Ideally such experiments are best carried out in free fall to maximise the time spent by a BEC in the non-Newtonian regime.Comment: 2 pages, double column, revtex, no figures Int J. Mod Phys D. (Special issue of GRF essays 2002). Int. J. Mod. Phys. D. in pres