A comparative study of the nonuniqueness problem of the potential equation

The nonuniqueness problem occurring at transonic speeds with the conservative potential equation is investigated numerically. The study indicates that the problem is not an inviscid phenomenon, but results from approximate treatment of shock waves inherent in the conservative potential model. A new bound on the limit of validity of the conservative potential model is proposed

Why Do Firms Engage in Selective Hedging?

Surveys of corporate risk management document that selective hedging, where managers incorporate their market views into firms’ hedging programs, is widespread in the U.S. and other countries. Stulz (1996) argues that selective hedging could enhance the value of firms that possess an information advantage relative to the market and have the financial strength to withstand the additional risk from market timing. We study the practice of selective hedging in a 10-year sample of North American gold mining firms and find that selective hedging is most prevalent among firms that are least likely to meet these valuemaximizing criteria -- (a) smaller firms, i.e., firms that are least likely to have private information about future gold prices; and (b) firms that are closest to financial distress. The latter finding provides support for the alternative possibility suggested by Stulz that selective hedging may also be driven by asset substitution motives. We detect weak relationships between selective hedging and some corporate governance measures, especially board size, but find no evidence of a link between selective hedging and managerial compensation.Corporate risk management, selective hedging, speculation, financial distress, corporate governance, managerial compensation

On The Reduced Canonical Quantization Of The Induced 2D-Gravity

The quantization of the induced 2d-gravity on a compact spatial section is carried out in three different ways. In the three approaches the supermomentum constraint is solved at the classical level but they differ in the way the hamiltonian constraint is imposed. We compare these approaches establishing an isomorphism between the resulting Hilbert spaces.Comment: 17 pages, plain LaTeX. FTUV/93-15, IFIC/93-10, Imperial-TP/93-94/1

Rubiaceae family: Flora Argentina, history and evolution

The Rubiaceae family in Argentina is represented by 41 genera and 146 species, of which 9 spp., 2 subspp., and 1 variety are endemic. The highest concentration and endemism are found in the NE ofthe country, in savannas, rainforests, riverside forests, followed by the NW of Argentina, from sea level to 1000-4000 m in the Andes. They also inhabit the heterogeneous landscape of the Center Region of the country, and few species grow in the Patagonian zone. This work is the contribution to the integral study of the Flora of our country. The beginning of knowledge of Argentina’s vegetation dates back to the mid 19th century, with foreign naturalists attracted by the virgin vegetation of the country. The Academy of Science and the first Institute of Botany were founded in Córdoba, where the herbarium and methodical study of native plants began. The first floristic works were carried out, which were enriched in the 20th century, with the improvement of instruments, development of new methods, which changed the analysis and interpretation of data. Fast means of transportation and communication facilitated the exchange of ideas and the increase in botanical expeditions. Despite the advances in the local botany, a comprehensive work on the country’s flora was still missing. It began with species checklists, regional catalogues and flora from various provinces. At the Instituto Botánica Darwinion (IBODA), the project “Flora Argentina” began methodically with the hand-picking of species bibliography, collection and identification activities. Professor Nélida Bacigalupo began to work there in 1949. She worked for more than 60 years and her publications about Rubiaceae taxa were the first in the country. When we met her, we had the privilege of valuing her predisposition and her wisdom as “Teacher”, which led to the transfer of her knowledge to three generations, for which we express our appreciation and gratitude

REAM intensity modulator-enabled 10Gb/s colorless upstream transmission of real-time optical OFDM signals in a single-fiber-based bidirectional PON architecture

Reflective electro-absorption modulation-intensity modulators (REAM-IMs) are utilized, for the first time, to experimentally demonstrate colorless ONUs in single-fiber-based, bidirectional, intensity-modulation and direct-detection (IMDD), optical OFDM PONs (OOFDM-PONs) incorporating 25km SSMFs and OLT-side-seeded CW optical signals. The colorlessness of the REAM-IMs is characterized, based on which optimum REAM-IM operating conditions are identified. In the aforementioned PON architecture, 10Gb/s colorless upstream transmissions of end-to-end realtime OOFDM signals are successfully achieved for various wavelengths within the entire C-band. Over such a wavelength window, corresponding minimum received optical powers at the FEC limit vary in a range as small as <0.5dB. In addition, experimental measurements also indicate that Rayleigh backscattering imposes a 2.8dB optical power penalty on the 10Gb/s over 25km upstream OOFDM signal transmission. Furthermore, making use of on-line adaptive bit and power loading, a linear trade-off between aggregated signal line rate and optical power budget is observed, which shows that, for the present PON system, a 10% reduction in signal line rate can improve the optical power budget by 2.6dB. © 2012 Optical Society of America

Transcription in vitro of ø29 DNA and EcoRI fragments by Bacillus subtilis RNA polymerase

EcoRI fragments A, B and C produced from linear φ29 DNA, but not D or E fragments, are transcribed by purified Bacillus subtilis RNA polymerase. The transcription of fragments A and C is initiated preferentially with GTP and to a lesser extent with ATP; the reverse happens in the case of fragment B. The dinucleotides GpU and GpA respectively, compete specifically with the incorporation of [γ-32P]GTP directed by fragments A and C. The RNA synthesized in vitro by purified B. subtilis RNA polymerase is highly asymmetric. Most of the RNA synthesis directed by fragments A and C is early RNA. However, most of the RNA produced by fragment B is anti-late-RNA. Addition of crude extracts inhibit the transcription of fragment B but not that of fragments A and C.Comisión Asesora para el Desarrollo de la Investigación Científica y Técnica y Dirección General de SanidadPeer reviewe

Black hole radiance, short distances, and TeV gravity

Using a derivation of black hole radiance in terms of two-point functions one can provide a quantitative estimate of the contribution of short distances to the spectrum. Thermality is preserved for black holes with $\kappa l_P <<1$. However, deviations from the Planckian spectrum can be found for mini black holes in TeV gravity scenarios, even before reaching the Planck phase.Comment: LaTeX, 4 pages, 1 figure. Misprints correcte