5,203 research outputs found
Avantage comparatif et performance dans le commerce international des produits différenciés
Ce travail se propose de tester l’hypothèse que les performances nettes réalisées par un pays dans ses échanges extérieurs croisés de produits différenciés sont déterminés 1) par l’avantage comparatif « révélé » défini pour chaque produit, en conformité avec sa base conceptuelle, et 2) par l’effet spécifique propre à l’économie nationale dont l’appropriation au profit de la branche relève des « économies de champs ».Nos résultats empiriques suggèrent que la spécialisation internationale inter-branche tend à se conformer à l’avantage comparatif, malgré une influence certaine exercée par les facteurs spécifiques dans le plus court terme.The paper tests the hypothesis that a country's net performance in its bilateral trade in differentiated products is determined by 1) "revealed" comparative advantage defined for the industry, in accordance with its conceptual basis, and 2) specific factors related to the country, whose benefit to the industry may be viewed as exploitation of economies of scope.Our empirical findings suggest that influence of specific factors could alter somewhat effects of comparative advantage, but the latters still remain dominant in the long run
Super-Alfv\'enic propagation of reconnection signatures and Poynting flux during substorms
The propagation of reconnection signatures and their associated energy are
examined using kinetic particle-in-cell simulations and Cluster satellite
observations. It is found that the quadrupolar out-of-plane magnetic field near
the separatrices is associated with a kinetic Alfv\'en wave. For magnetotail
parameters, the parallel propagation of this wave is super-Alfv\'enic
(V_parallel ~ 1500 - 5500 km/s) and generates substantial Poynting flux (S ~
10^-5 - 10^-4 W/m^2) consistent with Cluster observations of magnetic
reconnection. This Poynting flux substantially exceeds that due to frozen-in
ion bulk outflows and is sufficient to generate white light aurora in the
Earth's ionosphere.Comment: Submitted to PRL on 11/1/2010. Resubmitted on 4/5/201
Tensor Decompositions for Signal Processing Applications From Two-way to Multiway Component Analysis
The widespread use of multi-sensor technology and the emergence of big
datasets has highlighted the limitations of standard flat-view matrix models
and the necessity to move towards more versatile data analysis tools. We show
that higher-order tensors (i.e., multiway arrays) enable such a fundamental
paradigm shift towards models that are essentially polynomial and whose
uniqueness, unlike the matrix methods, is guaranteed under verymild and natural
conditions. Benefiting fromthe power ofmultilinear algebra as theirmathematical
backbone, data analysis techniques using tensor decompositions are shown to
have great flexibility in the choice of constraints that match data properties,
and to find more general latent components in the data than matrix-based
methods. A comprehensive introduction to tensor decompositions is provided from
a signal processing perspective, starting from the algebraic foundations, via
basic Canonical Polyadic and Tucker models, through to advanced cause-effect
and multi-view data analysis schemes. We show that tensor decompositions enable
natural generalizations of some commonly used signal processing paradigms, such
as canonical correlation and subspace techniques, signal separation, linear
regression, feature extraction and classification. We also cover computational
aspects, and point out how ideas from compressed sensing and scientific
computing may be used for addressing the otherwise unmanageable storage and
manipulation problems associated with big datasets. The concepts are supported
by illustrative real world case studies illuminating the benefits of the tensor
framework, as efficient and promising tools for modern signal processing, data
analysis and machine learning applications; these benefits also extend to
vector/matrix data through tensorization. Keywords: ICA, NMF, CPD, Tucker
decomposition, HOSVD, tensor networks, Tensor Train
On the Cause of Supra-Arcade Downflows in Solar Flares
A model of supra-arcade downflows (SADs), dark low density regions also known
as tadpoles that propagate sunward during solar flares, is presented. It is
argued that the regions of low density are flow channels carved by
sunward-directed outflow jets from reconnection. The solar corona is
stratified, so the flare site is populated by a lower density plasma than that
in the underlying arcade. As the jets penetrate the arcade, they carve out
regions of depleted plasma density which appear as SADs. The present
interpretation differs from previous models in that reconnection is localized
in space but not in time. Reconnection is continuous in time to explain why
SADs are not filled in from behind as they would if they were caused by
isolated descending flux tubes or the wakes behind them due to temporally
bursty reconnection. Reconnection is localized in space because outflow jets in
standard two-dimensional reconnection models expand in the normal (inflow)
direction with distance from the reconnection site, which would not produce
thin SADs as seen in observations. On the contrary, outflow jets in spatially
localized three-dimensional reconnection with an out-of-plane (guide) magnetic
field expand primarily in the out-of-plane direction and remain collimated in
the normal direction, which is consistent with observed SADs being thin.
Two-dimensional proof-of-principle simulations of reconnection with an
out-of-plane (guide) magnetic field confirm the creation of SAD-like depletion
regions and the necessity of density stratification. Three-dimensional
simulations confirm that localized reconnection remains collimated.Comment: 16 pages, 5 figures, accepted to Astrophysical Journal Letters in
August, 2013. This version is the accepted versio
Evaluator services for optimised service placement in distributed heterogeneous cloud infrastructures
Optimal placement of demanding real-time interactive applications in a distributed heterogeneous cloud very quickly results in a complex tradeoff between the application constraints and resource capabilities. This requires very detailed information of the various requirements and capabilities of the applications and available resources. In this paper, we present a mathematical model for the service optimization problem and study the concept of evaluator services as a flexible and efficient solution for this complex problem. An evaluator service is a service probe that is deployed in particular runtime environments to assess the feasibility and cost-effectiveness of deploying a specific application in such environment. We discuss how this concept can be incorporated in a general framework such as the FUSION architecture and discuss the key benefits and tradeoffs for doing evaluator-based optimal service placement in widely distributed heterogeneous cloud environments
Detection of lithium in nearby young late-M dwarfs
Late M-type dwarfs in the solar neighborhood include a mixture of very
low-mass stars and brown dwarfs which is difficult to disentangle due to the
lack of constraints on their age such as trigonometric parallax, lithium
detection and space velocity.
We search for young brown dwarf candidates among a sample of 28 nearby late-M
dwarfs with spectral types between M5.0 and M9.0, and we also search for debris
disks around three of them.
Based on theoretical models, we used the color , the -band absolute
magnitude and the detection of the Li I 6708 doublet line as a strong
constraint to estimate masses and ages of our targets. For the search of debris
disks, we observed three targets at submillimeter wavelength of 850 m.
We report here the first clear detections of lithium absorption in four
targets and a marginal detection in one target. Our mass estimates indicate
that two of them are young brown dwarfs, two are young brown dwarf candidates
and one is a young very low-mass star. The closest young field brown dwarf in
our sample at only 15 pc is an excellent benchmark for further studying
physical properties of brown dwarfs in the range 100150 Myr. We did not
detect any debris disks around three late-M dwarfs, and we estimated upper
limits to the dust mass of debris disks around them.Comment: 10 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Those wonderful elastic waves
We consider in a simple and general way elastic waves in isotropic and
anisotropic media, their polarization, speeds, reflection from interfaces with
mode conversion, and surface waves. Reflection of quasi transverse waves in
anisotropic media from a free surface is shown to be characterized by three
critical angles.Comment: 11 Figures 26 page
IASB & FASB Convergence Project: Revenue Recognition
Accounting revenue recognition practices have a pervasive, profound impact on the financial statements of a business entity. As such, soon after committing to a plan for convergence of two major sets of accounting standards with the Norwalk Agreement of 2002, the Financial Accounting Standards Board (FASB) of the United States and the International Accounting Standards Board (IASB) undertook a project to converge their standards of revenue recognition. Through an analysis of historical practices of the two boards and progress to date on the convergence of revenue recognition standards, this paper presents further recommendation for improvement of the convergence effort. Acknowledging the progress to date, we recommend further international and industry collaboration measures to ensure that the resulting standard provides the most useful information possible to financial statement users. Progress to date along with our recommendation assure that the resulting worldwide standard of revenue recognition provides specific principle based guidance that promotes international consistency while providing the flexibility for national and industry specific application
Biological activities of in vitro liverwort Marchantia polymorpha L. extracts
To overcome the problems in liverwort collecting such as small size and easily mixed with other species in the wild, we have successfully cultivated Marchantia polymorpha L. under in vitro conditions in the previous study. The aim of this study is to evaluate the biological activities of this in vitro biomass as a confirmation of the sufficient protocol in cultivation this species. Cultured biomass was dried at a temperature of 45-50 oC to constant weight and ground into a fine powder. The coarse powder was extracted with organic solvents of increasing polarization including n-hexane, chloroform, ethyl acetate, and ethanol using the maceration technique. Four extracts were investigated antioxidant (iron reduction power, DPPH), antibacterial (agar diffusion), tyrosinase inhibitory activity, anti-proliferation on MCF-7 cells. Additionally, the presence of natural metabolite groups of the extracts was detected by using specific reagents. For antioxidant activity, ethyl acetate fraction extract had the highest iron reducing power and DPPH free radical scavenging ability with IC50 = 439.31 µg ml-1. All three n-hexane, chloroform, and ethyl acetate extracts possessed resistance to the bacterial strain tested. At a concentration of 2 mg ml-1, n-hexane and chloroform extracts had the highest percentage of tyrosinase inhibition (69.54 and 69.10%, respectively). The n-hexane extract is a potent extract that inhibits the proliferation of MCF-7 cells with the lowest IC50 of 38.15 µg ml-1. A preliminary chemical composition survey showed that the cultured biomass liverwort contains many bioactive compounds, particularly the compounds of range of non- and less-polarized fractions
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