17,458 research outputs found
A critique of monetary protectionism
An argument against attempts to achieve current-account objectives through monetary manipulation of nominal exchange rates, with an explanation of why such tampering--which for various reasons might appear politically attractive--ultimately harms economic welfare.Foreign exchange - Law and legislation ; Monetary policy
Evaluation of flow quality in two large NASA wind tunnels at transonic speeds
Wind tunnel testing of low drag airfoils and basic transition studies at transonic speeds are designed to provide high quality aerodynamic data at high Reynolds numbers. This requires that the flow quality in facilities used for such research be excellent. To obtain a better understanding of the characteristics of facility disturbances and identification of their sources for possible facility modification, detailed flow quality measurements were made in two prospective NASA wind tunnels. Experimental results are presented of an extensive and systematic flow quality study of the settling chamber, test section, and diffuser in the Langley 8 foot transonic pressure tunnel and the Ames 12 foot pressure wind tunnel. Results indicate that the free stream velocity and pressure fluctuation levels in both facilities are low at subsonic speeds and are so high as to make it difficult to conduct meaningful boundary layer control and transition studies at transonic speeds
Convocation
The origins of phenotypic variation within mimetic Heliconius butterflies have long fascinated biologists and naturalists. However, the evolutionary processes that have generated this extraordinary diversity remain puzzling. Here we examine intraspecific variation across Heliconius cydno diversification and compare this variation to that within the closely related H. melpomene and H. timareta radiations. Our data, which consist of both mtDNA and genome scan from nearly 2250 AFLP loci, reveal a complex history of differentiation and admixture at different geographic scales. Both mtDNA and AFLP phylogenies suggest that H. timareta and H. cydno are probably geographic extremes of the same radiation that likely diverged from H. melpomene during the Pliocene-Pleistocene boundary. MtDNA suggest that this radiation originated in Central America or the Northwestern region of South America, with a subsequent colonization of the eastern and western slopes of the Andes. Our genome-scan data indicate significant admixture among sympatric H. cydno/H.timareta and H. melpomene populations across the extensive geographic ranges of the two radiations. Within H. cydno, both mtDNA and AFLP data indicate significant population structure at local scales, with strong genetic differences even among adjacent H. cydno color pattern races. These genetic patterns highlight the importance of past geoclimatic events, intraspecific gene flow, and local population differentiation in the origin and establishment of new adaptive forms
A new super-soft X-ray source in the Small Magellanic Cloud: Discovery of the first Be/white dwarf system in the SMC?
The Small Magellanic Cloud (SMC) hosts a large number of Be/X-ray binaries,
however no Be/white dwarf system is known so far, although population synthesis
calculations predict that they might be more frequent than Be/neutron star
systems. XMMUJ010147.5-715550 was found as a new faint super-soft X-ray source
(SSS) with a likely Be star optical counterpart. We investigate the nature of
this system and search for further high-absorbed candidates in the SMC. We
analysed the XMM-Newton X-ray spectrum and light curve, optical photometry, and
the I-band OGLE III light curve. The X-ray spectrum is well represented by
black-body and white dwarf atmosphere models with highly model-dependent
temperature between 20 and 100 eV. The likely optical counterpart AzV 281
showed low near infrared emission during X-ray activity, followed by a
brightening in the I-band afterwards. We find further candidates for
high-absorbed SSSs with a blue star as counterpart. We discuss
XMMUJ010147.5-715550 as the first candidate for a Be/white dwarf binary system
in the SMC.Comment: 6 pages, 4 figures, accepted by A&
Secondary metabolites of the argan tree (Morocco) may have disease prevention properties
The argan tree (Argania spinosa L. Skeels) is native to Morocco, where after the Holly oak it constitutes the second most common tree in the country. Recent studies suggest that dietary argan oil, an endemic seed oil from argan fruits, may have a relevant role in disease prevention, and its consumption could protect against atherosclerosis and cancer. Unfortunately, in less than a century, more than a third of the forest has disappeared. It is therefore imperative to improve the tree\'s production potential so that it can regain its key position in the agricultural systems of the region. On the basis of ethnobotanical knowledge, researchers are screening metabolites of this rare plant to identify bioactive compounds for the development of new therapeutic agents and food supplements. This includes studies on secondary metabolites with chemopreventive activities. In this review, a complete outline of components (triglycerides, unsaponifiable, phenolic antioxidants and aroma constituents) are described. Finally, a discussion of the biological functions of the polar and non-polar A. spinosa products which have been evaluated using a range of in vitro bioassays are described.African Journal of Biotechnology Vol. 4 (5), pp. 381-388, 200
- …