Power Utility Maximization in Discrete-Time and Continuous-Time Exponential Levy Models

Consider power utility maximization of terminal wealth in a 1-dimensional continuous-time exponential Levy model with finite time horizon. We discretize the model by restricting portfolio adjustments to an equidistant discrete time grid. Under minimal assumptions we prove convergence of the optimal discrete-time strategies to the continuous-time counterpart. In addition, we provide and compare qualitative properties of the discrete-time and continuous-time optimizers.Comment: 18 pages, to appear in Mathematical Methods of Operations Research. The final publication is available at springerlink.co

The obscured gamma-ray and UHECR universe

Auger results on clustering of > 60 EeV ultra-high energy cosmic ray (UHECR) ions and the interpretation of the gamma-ray spectra of TeV blazars are connected by effects from the extragalactic background light (EBL). The EBL acts as an obscuring medium for gamma rays and a reprocessing medium for UHECR ions and protons, causing the GZK cutoff. The study of the physics underlying the coincidence between the GZK energy and the clustering energy of UHECR ions favors a composition of > 60 EeV UHECRs in CNO group nucleons. This has interesting implications for the sources of UHECRs. We also comment on the Auger analysis.Comment: 11 pages, 10 figures, in the International Conference on Topics in Astroparticle and Underground Physics (TAUP) 2007, Sendai, Japan, September 11-15, 200

CO_2 on Titan

A sharp stratospheric emission feature at 667 cm^(−1) in the Voyager infrared spectra of Titan is associated with the ν_2 Q branch of CO_2. A coupling of photochemical and radiative transfer theory yields an average mole fraction above the 110 mbar level of ƒCO_2 = 1.5 ± ^(1.5)_(0.8) x 10^(-9), with most of the uncertainty being due to imprecise knowledge of the vertical distribution. CO_2 is found to be in a steady state, with its abundance being regulated principally by the ∼72 K cold trap near the tropopause and secondarily by the rate at which water-bearing meteoritic material enters the top of the atmosphere. An influx of water about 0.4 times that at the top of the terrestrial atmosphere is consistent with a combination of the observed CO_2 abundance and a steady state CO mole fraction of 1.1×10^(−4); the theoretical value for CO is close to the value observed by Lutz et al. (1983), although there are large margins for error in both numbers. If steady state conditions for CO prevail, little information is available regarding the evolution of Titan's atmosphere

Multiwavelength Observations of a Flare from Markarian 501

We present multiwavelength observations of the BL Lacertae object Markarian 501 (Mrk 501) in 1997 between April 8 and April 19. Evidence of correlated variability is seen in very high energy (VHE, E > 350 GeV) gamma-ray observations taken with the Whipple Observatory gamma-ray telescope, data from the Oriented Scintillation Spectrometer Experiment of the Compton Gamma-Ray Observatory, and quicklook results from the All-Sky Monitor of the Rossi X-ray Timing Explorer while the Energetic Gamma-Ray Experiment Telescope did not detect Mrk 501. Short term optical correlations are not conclusive but the U-band flux observed with the 1.2m telescope of the Whipple Observatory was 10% higher than in March. The average energy output of Mrk 501 appears to peak in the 2 keV to 100 keV range suggesting an extension of the synchrotron emission to at least 100 keV, the highest observed in a blazar and ~100 times higher than that seen in the other TeV-emitting BL Lac object, Mrk 421. The VHE gamma-ray flux observed during this period is the highest ever detected from this object. The VHE gamma-ray energy output is somewhat lower than the 2-100 keV range but the variability amplitude is larger. The correlations seen here do not require relativistic beaming of the emission unless the VHE spectrum extends to >5 TeV.Comment: 10 pages, 2 figures, accepted for publication in ApJ Letter

Analyzing capacitance-voltage measurements of vertical wrapped-gated nanowires

The capacitance of arrays of vertical wrapped-gate InAs nanowires are analyzed. With the help of a Poisson-Schr"odinger solver, information about the doping density can be obtained directly. Further features in the measured capacitance-voltage characteristics can be attributed to the presence of surface states as well as the coexistence of electrons and holes in the wire. For both scenarios, quantitative estimates are provided. It is furthermore shown that the difference between the actual capacitance and the geometrical limit is quite large, and depends strongly on the nanowire material.Comment: 15 pages, 6 Figures included, to appear in Nanotechnolog

High prevalence of cardiovascular and respiratory abnormalities in advanced, intensively treated (transplanted) myeloma: The case for ‘late effects’ screening and preventive strategies

Objectives: Modern management of myeloma has significantly improved survival, with increasing numbers of patients living beyond a decade. However, little is known about the long-term cardiovascular and respiratory status of intensively treated and multiply relapsed survivors. Methods: We performed detailed cardiovascular and respiratory evaluations in patients with intensively treated, advanced but stable myeloma. All patients had received at least two lines of treatment, including at least one haematopoietic stem cell transplantation procedure, but had stable, controlled disease and were off active treatment at the time of evaluation. Results: Thirty-two patients with a median duration of 6 years (range 2–12) from original diagnosis of myeloma and three lines (range 2–6) of treatment were evaluated. Despite normal physical examination in the majority, there was a high prevalence of sub-clinical cardiac and respiratory dysfunction, reflected by abnormalities of electrocardiography (45%), echocardiography (50%), serum N-terminal pro-B-type natriuretic peptide level (NT-pro-BNP, 50%), and pulmonary function testing (45%). NT-pro-BNP level correlated negatively with quality of life (P = 0.012) and positively with serum ferritin (P = 0.027). Dyspnoea score correlated with BMI (P = 0.001). Risk factors for cardiovascular disease (obesity, hypertension, hyperlipidaemia, and hyperinsulinaemia) were common. Discussion: Even in the absence of overt clinical features, the majority of intensively treated long-term survivors of myeloma have established cardiovascular and/or respiratory dysfunction, above levels expected in the general population of a similar age. Conclusion: This study supports routine screening and lifestyle modification combined with primary and secondary preventive strategies to reduce cardiovascular and respiratory disease and to preserve quality of life in transplanted myeloma patients

Testing Consumer Rationality using Perfect Graphs and Oriented Discs

Given a consumer data-set, the axioms of revealed preference proffer a binary test for rational behaviour. A natural (non-binary) measure of the degree of rationality exhibited by the consumer is the minimum number of data points whose removal induces a rationalisable data-set.We study the computational complexity of the resultant consumer rationality problem in this paper. This problem is, in the worst case, equivalent (in terms of approximation) to the directed feedback vertex set problem. Our main result is to obtain an exact threshold on the number of commodities that separates easy cases and hard cases. Specifically, for two-commodity markets the consumer rationality problem is polynomial time solvable; we prove this via a reduction to the vertex cover problem on perfect graphs. For three-commodity markets, however, the problem is NP-complete; we prove thisusing a reduction from planar 3-SAT that is based upon oriented-disc drawings