198 research outputs found
Competitive Advantages and Disadvantages in Romania’s Agri-Food Trade -Trends and Challenges
No full textThe paper is part of the studies concerning trade patterns and agri-food foreign trade policies in the EU enlargement context, aiming to assess the competitive trade advantages and disadvantages of the Romania’s agri-food products in the foreign trade relations. The analysis focuses on the challenges of the trade liberalization and its influence on the intensification of the commercial exchanges, the supply diversification and on the trade balance equilibrium, faced by Romania’s agri-food sector over the transition and pre-accession period. The structural reforms of the transition and EU accession preparations induced paramount changes in Romania’s agri-food trade pattern, i.e. a fluctuating evolution of the agri-food foreign trade, either in correlation with the variations in the agricultural supply, the performance deficiencies of the agri-food sector that provoked disequilibria on the export market, or with the effect of political changes upon the trade flows. The recent integration in the Single Market recalls a special attention on the opportunities for the competitive producers to attract benefits offered by the enlarged access possibilities and the openness to third countries. In this context, an in-depth analysis of the bilateral trade relation between Romania and EU has been performed by using an alternative method of the comparative trade advantage index, based on the one developed by Vollrath [1]. The results emphasize the identification of either the competitive agri-food trade potential, or of the sensitive zones that could be affected by the external competition post-accession, as well as the needed improvements in the Romanian agri-food sector’s competitiveness.Agri-food trade, competitiveness, comparative trade advantage index., International Relations/Trade,
Gravity-wave interferometers as probes of a low-energy effective quantum gravity
No full textThe interferometry-based experimental tests of quantum properties of space-time which the author sketched out in a recent short Letter [Nature 398 (1999) 216] are here discussed in self-contained fashion. Besides providing detailed derivations of the results already announced in the previous Letter, some new results are also derived; in particular, the analysis is extended to a larger class of scenarios for space-time fuzziness and an absolute bound on the measurability of the amplitude of a gravity wave is obtained. It is argued that these studies could be helpful for the search of a theory describing a first stage of partial unification of Gravity and Quantum Mechanics.The interferometry-based experimental tests of quantum properties of space-time which the author sketched out in a recent short Letter [Nature 398 (1999) 216] are here discussed in self-contained fashion. Besides providing detailed derivations of the results already announced in the previous Letter, some new results are also derived; in particular, the analysis is extended to a larger class of scenarios for space-time fuzziness and an absolute bound on the measurability of the amplitude of a gravity wave is obtained. It is argued that these studies could be helpful for the search of a theory describing a first stage of partial unification of Gravity and Quantum Mechanics
Degenerate partial differential equations and applications to probability theory and foundations of mathematical finance
No full textIn the first part of our thesis, we prove existence, uniqueness and regularity of solutions for a certain class of degenerate parabolic partial differential equations on the half space which are a generalization of the Heston operator. We use these results to show that the martingale problem associated with the differential operator is well-posed and we build generalized Heston-like processes which match the one-dimensional probability distributions of a certain class of It^o processes. The second part of our thesis is concerned with the study of regularity of solutions to the variational equation associated to the elliptic Heston operator. With the aid of weighted Sobolev spaces, we prove supremum bounds, a Harnack inequality, and H"older continuity near the boundary for solutions to elliptic variational equations defined by the Heston partial differential operator. Finally, we establish stochastic representations of solutions to elliptic and parabolic boundary value problems and obstacle problems associated to the Heston generator. In mathematical finance, solutions to parabolic obstacle problems correspond to value functions for American-style options.Ph. D.Includes bibliographical referencesby Camelia Alexandra Po
Observation of Flat Frequency Bands at Open Edges and Antiphase Boundary Seams in Topological Mechanical Metamaterials
No full textMotivated by the recent theoretical studies on a two-dimensional (2D) chiral Hamiltonian based on the Su-Schrieffer-Heeger chains [L. Zhu, E. Prodan, and K. H. Ahn, Phys. Rev. B 99, 041117(R) (2019)PRBMDO2469-995010.1103/PhysRevB.99.041117], we experimentally and computationally demonstrate that topological flat frequency bands can occur at open edges of 2D planar metamaterials and at antiphase boundary seams of ring-shaped or tubular metamaterials. Specifically, using mechanical systems made of magnetically coupled spinners, we reveal that the presence of the edge or seam bands that are flat in the entire projected reciprocal space follows the predictions based on topological winding numbers. The edge-to-edge distance sensitively controls the flatness of the edge bands and the localization of excitations, consistent with the theoretical analysis. The analog of the fractional charge state is observed. Possible realizations of flat bands in a large class of metamaterials, including photonic crystals and electronic metamaterials, are discussed
Book Review of 'Political Attitudes: In Search for Measure' by Camelia Florela Voinea
No full textCamelia Florela Voinea’s new book „Political Attitudes. In Search for Measure”, belongs, as the
author herself says, to a three volume-work which aims at reconfiguring the history of the idea of
„experiment” in psychology, to highlight its relevance for the political thought and, least but not last, to
identify the particular part it played, especially by the end of the 19th century, in the emergence of the new
science of Social Psychology
Doubly-special relativity: Facts, myths and some key open issues
No full textI report, emphasizing some key open issues and some aspects that are particularly relevant for phenomenology, on the status of the development of "doubly-special" relativistic ("DSR") theories with both an observer-independent high-velocity scale and an observer-independent small-length/large-momentum scale, possibly relevant for the Planck-scale/quantum-gravity realm. I also give a true/false characterization of the structure of these theories. In particular, I discuss a DSR scenario without modification of the energy-momentum dispersion relation and without the (-Poincaré Hopf algebra, a scenario with deformed Poincaré symmetries which is not a DSR scenario, some scenarios with both an invariant length scale and an invariant velocity scale which are not DSR scenarios, and a DSR scenario in which it is easy to verify that some observable relativistic (but non-special-relativistic) features are insensitive to possible nonlinear redefinitions of symmetry generators. © 2010 by the author
Topological phonon modes and their role in dynamic instability of microtubules
No full textMicrotubules (MTs) are self-assembled hollow protein tubes playing important functions in live cells. Their building block is a protein called tubulin, which self-assembles in a particulate 2 dimensional lattice. We study the vibrational modes of this lattice and find Dirac points in the phonon spectrum. We discuss a splitting of the Dirac points that leads to phonon bands with nonzero Chern numbers, signaling the existence of topological vibrational modes localized at MTs edges, which we indeed observe after explicit calculations. Since these modes are robust against the large changes occurring at the edges during the dynamic cycle of the MTs, we can build a simple mechanical model to illustrate how they would participate in this phenomenon. © 2009 The American Physical Society
Recommended from our members
Adopting Biophysics Methods in Pursuit of Biogeophysical Research: Advancing the measurement and modeling of electrical signatures of microbe-mineral transformations impacting contaminant transport
No full textThis exploratory project involved laboratory experiments to investigate three hypotheses: (H1) Physics-based modeling of low-frequency dispersions (henceforth referred to as alpha) measured in broadband dielectric spectroscopy (DS) data can quantify pore-scale geometric changes impacting contaminant transport resulting from biomineralization; (H2) Physics-based modeling of high-frequency dispersions (henceforth referred to as beta) measured in broadband dielectric spectroscopy data can quantify rates of mineral growth in/on the cell wall; (H3) Application of this measurement and modeling approach can enhance geophysical interpretation of bioremediation experiments conducted at the RIFLE IFC by providing constraints on bioremediation efficiency (biomass concentration, mineral uptake within the cell wall, biomineralization rate). We tested H1 by performing DS measurements (alpha and beta range) on iron (Fe) particles of dimensions similar to microbial cells, dispersed within agar gels over a range of Fe concentrations. We have tested the ability of the physics-based modeling to predict volume concentrations of the Fe particles by assuming that the Fe particles are polarizable inclusions within an otherwise nonpolarizable medium. We evaluated the smallest volume concentration that can be detected with the DS method. Similar experiments and modeling have been performed on the sulfate-reducing bacteria D. vulgaris. Synchrotron x-ray absorption measurements were conducted to determine the local structure of biominerals coatings on D. vulgaris which were grown in the presence of different Fe concentrations. We imaged the mineral growth on cell wall using SEM. We used dielectric spectroscopy to differentiate between iron sulfide precipitates of biotic and abiotic nature. Biotic measurements were made on D. vulgaris bacteria grown in the presence of different concentrations of iron to form different thicknesses of iron sulfide precipitates around themselves and abiotic measurements were made on different concentrations of pyrrhotite particles suspended in agar. Results show a decrease in dielectric permittivity as a function of frequency for biotic minerals and an opposite trend is observed for abiotic minerals. Our results suggest that dielectric spectroscopy offers a noninvasive and fast approach for distinguishing between abiotic and biotic mineral precipitates
- …
