Jurnal Edukasi
Not a member yet
4879 research outputs found
Sort by
Dynamics of the Heme-binding Bacterial Gas-sensing Dissimilative Nitrate Respiration Regulator (DNR) and Activation Barriers for Ligand Binding and Escape.
No full textInternational audienceDNR (dissimilative nitrate respiration regulator) is a heme-binding transcription factor that is involved in the regulation of denitrification in Pseudomonas aeruginosa. In the ferrous deoxy state, the heme is 6-coordinate; external NO and CO can replace an internal ligand. Using fluorescence anisotropy, we show that high-affinity sequence-specific DNA binding occurs only when the heme is nitrosylated, consistent with the proposed function of DNR as NO sensor and transcriptional activator. This role is moreover supported by the NO "trapping" properties revealed by ultrafast spectroscopy that are similar to those of other heme-based NO sensor proteins. Dissociated CO-heme pairs rebind in an essentially barrierless way. This process competes with migration out of the heme pocket. The latter process is thermally activated (Ea ∼7 kJ/mol). This result is compared with other heme proteins, including the homologous CO sensor/transcription factor CooA, variants of the 5-coordinate mycobacterial sensor DosT and the electron transfer protein cytochrome c. This comparison indicates that thermal activation of ligand escape from the heme pocket is specific for systems where an external ligand replaces an internal one. The origin of this finding and possible implications are discussed
Trois essais en commerce international et les transferts: hétérogénéité entre pays, traitement préférentiel et formation d'habitudes
No full textMy dissertation is a theoretical and empirical study of international transfers and trade between heterogeneous countries. In the first essay, I use the trade war model developed by Kennan and Riezman (1988) with Stone-Geary preferences and show that free trade is the corner solution to the maximization of the global welfare. This maximization problem yields a candidate solution that corresponds to a tariff-subsidy combination where the South (the small country) applies a tariff against its imports, while the North (the large country) subsidies its imports when countries are asymmetric. This candidate solution is of course rejected as it corresponds to a saddle point. These findings shed light on the inefficiency of theunilateral privileged access that ACP countries enjoyed on the European market under the Lomé and the Cotonou agreements, while keeping their tariffs high. In addition, this paper explains the transition from such treaties to WTO-compatible economic partnership agreements.In the second essay, I develop a standard North-South trade agreement model between two heterogeneous countries. I find that the welfare effects of a free trade agreement (FTA) depends on the type of heterogeneity considered. In the presence of sufficient heterogeneity in the supply functions, the country experiencing supply-side constraints (SSCs) – “the small country” – is worse off, while the bigger is better off. In this case, the transfer flows from the large to the small country. However, when countries are sufficiently heterogeneous with respect to either size or demand functions, the small country is better off, while the large country is worse off. Thus, the small country must compensate the large country for the FTA to be incentive-compatible. This model provides an interesting explanation of the FTA between the ACP countries and the EU (Economic Partnership Agreements, EPAs). Indeed, the EPA provides for technical and financial assistance from the EU to the ACP to enable them to overcome the supplyconstraints. Testing this prediction with ACP-EU data, I find that the initiation of the interim EPA has a positive effect on foreign aid allocation decision when supply heterogeneity is taken into account.Finally, using a two-period pure exchange model of free trade, in the third essay, I study the welfare effects of foreign aid in the presence of habit formation. Assuming that the North makes a transfer only in the first period, I show that the terms-of-trade effect of the transfer in the second period operates through the habit parameter; in other words, in the absence of habit formation, the transfer does not distort relative prices and thus, there is no transfer paradox. I prove that its existence crucially depends on the growth of total endowments; actually, the transfer paradox occurs when the world endowment of the North's import (the South's export) good increases sufficiently more that of its export (import) good. Moreover, the model shows that the export-enhancing effect of the transfer is short-lived, since the habit formation effect decreases over time. Testing this claim with aid and trade data between France and 32 ACP countries, I find that only one period lagged transfer affects French exports. The contribution of this essay is to describe the process by which foreign aid benefits the donor countrythrough the formation of habits in the recipient country for the good it exports.Ma thèse est un ensemble d’essais à la fois théoriques et empiriques sur les transferts internationaux et le commerce entre pays hétérogènes. Dans le premier essai, j’utilise le modèle de guerre tarifaire développé par Kennan and Riezman (1988) et montre qu’avec des fonctions d’utilité Stone-Geary, la maximisation du bien-être global conduit à une solution en coin qui correspond au libre-échange. La résolution de ce problème suggère également une autre solution qui, lorsque les pays sont asymétriques, est tel que le Sud applique un tarif alors que le Nord subventionne ses importations. Cette solution est toutefois rejetée puisqu’elle correspond, non pas à un maximum, mais plutôt à un point de selle. Les résultats de cette recherche mettent en lumière l’inefficacité des accords de Lomé et de Cotonou conclus entre les pays ACP et l’Union européenne qui accordent un accès préférentiel aux exportations des pays ACP sur le marché européen et qui, par ailleurs, permettent aux ACPs de maintenir leurs tarifs. Cette étude permet ainsi de comprendre la transition qui s’opère dans les traités ACP-UE d’un système de tarifs préférentiels vers des accords de partenariat économique, lesquels sont compatibles avec les règles de l’OMC. Dans le deuxième essai, je développe un modèle d’accord commercial entre deux pays hétérogènes (le Nord et le Sud) afin d’étudier l’effet d'un accord de libre-échange (ALE) sur le bien-être. Ces effets dépendent du type d’hétérogénéité considéré. Lorsque les fonctions d’offre sont suffisamment, le pays qui a des contraintes de capacité d’offre (CCO) – « le petit pays » – subit une perte de bien-être, contrairement à son partenaire dont le bien-être s’accroît. Dans ce cas précis, le petit pays ne ratifiera l’ALE que s’il reçoit un transfert compensatoire de son partenaire. Cependant, en présence d’une forte asymétrie de taille ou de suffisamment d’hétérogénéité dans les fonctions de demande, c’est le petit pays qui bénéfice de l’ALE, tandis que le grand pays subit une baisse de bien-être. Ainsi, le petit pays doit compenser le grand pays pour l’inciter à conclure l’ALE. Ce modèle permet de comprendre pourquoi les Accords de partenariat économique (APE) entre les pays ACP et l’UE prévoient une assistance technique et financière de l’UE aux ACP qui ont des CCOs. Par ailleurs, le test empirique avec les données ACP-UE montre que l’initiation des APEs intérimaires a un effet positif sur l’aide étrangère allouée par les pays de l’UE aux ACP lorsque l’hétérogénéité de l’offre est prise en compte dans le modèle. Enfin, dans le troisième essai, j’utilise un modèle d’échange pur à deux périodes, afin d’étudier les effets de l’aide internationale sur le bien-être en présence de formation d’habitudes. En supposant que le Nord effectue le transfert en période 1, je montre que l'effet de ce dernier sur les termes de l’échange en période 2 opère à travers le paramètre mesurant les habitudes. Ainsi, en l’absence de formation d’habitudes, le transfert n’entraîne pas de distorsion des prix relatifs et donc, il n’y a pas de paradoxe des transferts. L’existence de ce dernier dépend essentiellement de la croissance des dotations totales des deux biens; en effet, le paradoxe des transferts se produit lorsque la dotation totale du bien importé par le Nord (exporté par le Sud) augmente suffisamment plus que la dotation du bien qu’il exporte (importe). En outre, le modèle montre que l’impact du transfert sur les exportations est de courte durée, puisque l’effet d’habitudes diminue au fil du temps. Le test empirique réalisé à partir des données de l’aide internationale et des exportations françaises vers 32 pays ACP corrobore cette prédiction, puisque le transfert stimule les exportations françaises vers ces pays avec un retard d’une période. La contribution de cet article est de décrire le processus par lequel l’aide étrangère bénéficie aux pays donateurs à travers la formation des habitudes dans les pays récipiendaires de l’aide
Comparative study of the effects of electron irradiation and natural disorder in single crystals of SrFe 2 (As 1−x P x ) 2 superconductor (x = 0.35)
No full textInternational audienceThe London penetration depth λ(T) was measured in single crystals of a SrFe 2 (As 1−x P x) 2 (x = 0.35) iron-based superconductor. The influence of disorder on the transition temperature T c and on λ(T) was investigated. The effects of scattering controlled by the annealing of as-grown crystals was compared with the effects of artificial disorder introduced by 2.5 MeV electron irradiation. The low-temperature behavior of λ(T) can be described by a power-law function λ(T) = AT n , with the exponent n close to one in pristine annealed samples, as expected for a superconducting gap with line nodes. Upon electron irradiation with a dose of 1.2 × 10 19 e/cm 2 , the exponent n increases rapidly, exceeding a dirty limit value of n = 2, implying that the nodes in the superconducting gap are accidental and can be lifted by the disorder. The variation of the exponent n with T c is much stronger in the irradiated crystals compared to the crystals in which disorder was controlled by the annealing of the growth defects. We discuss the results in terms of different influence of different types of disorder on intraband and interband scattering
The dynamic implications of energy-intensive capital accumulation
No full textWe study the implications of assuming diff erent energy intensities for physical capital accumulation and fi nal good production in an overlapping generations (OLG) resource economy. Diff ering from the standard OLG literature, but consistently with the empirical evidence, physical capital accumulation is assumed to be relatively more energy-intensive than consumption. Focusing on exhaustible resources, we fi nd that OLG equilibria can exhibit a "non-classical behaviour": our model can generate complex dynamics where extraction may increase during some periods and decrease afterwards. As a consequence, in contrast to the classical response predicted by the standard approach, resource prices may not increase monotonically. This result points out the importance of the assumptions about energy intensity considered in the literature
Quasiparticle Self-Consistent GW Method for the Spectral Properties of Complex Materials
No full textInternational audienceThe GW approximation to the formally exact many-body perturbation theory has been applied successfully to materials for several decades. Since the practical calculations are extremely cumbersome, the GW self-energy is most commonly evaluated using a first-order perturbative approach: This is the so-called G 0 W 0 scheme. However, the G 0 W 0 approximation depends heavily on the mean-field theory that is employed as a basis for the perturbation theory. Recently, a procedure to reach a kind of self-consistency within the GW framework has been proposed. The quasiparticle self-consistent GW (QSGW) approximation retains some positive aspects of a self-consistent approach, but circumvents the intricacies of the complete GW theory, which is inconveniently based on a non-Hermitian and dynamical self-energy. This new scheme allows one to surmount most of the flaws of the usual G 0 W 0 at a moderate calculation cost and at a reasonable implementation burden. In particular, the issues of small band gap semiconductors, of large band gap insulators, and of some transition metal oxides are then cured. The QSGW method broadens the range of materials for which the spectral properties can be predicted with confidence
Vibrational Signatures of S-Nitroso Glutathione as Gaseous, Protonated Species
No full textInternational audienceThe gas-phase ions of protonated L-glutathione as native species, [GSH+H]+, and S-nitroso derivative, [GSNO+H]+, have been generated by electrospray ionization and probed via infrared multiple photon dissociation (IRMPD) action spectroscopy. Insight into the conformational landscape is gained from the interpretation of the IR spectra aided by high-level theoretical calculations, which enables a structural assignment disclosing both the site of protonation and the intramolecular hydrogen bond network. Calculations yield the low-energy structures of [GSNO+H]+. A admixture of the four most stable ones (SN1, AN1, SN2 and AN2) is apt to account for the experimental IRMPD spectra obtained in both the 1000-2000 cm-1 and the 3100-3700 cm-1 spectral ranges. The most stable form of [GSNO+H]+, SN1, protonated at the amino group, presents a syn conformation at the S-N (partial) double bond and all peptidic carbonyls involved in (strong) C=O...H-N hydrogen bonds, so allowing the closure of a C5 (β-strand), two C7 (γ-turn) and one C9 membered rings. An appreciable barrier to rotation of 43 kJ mol-1 about the S-N bond is found to separate SN1 from the analogous anti isomer AN1, which lies only 0.70 kJ mol-1 higher in free energy. Conformers obtained for [GSH+H]+ are very similar to the [GSNO+H]+ counterparts, indicating that the S-nitrosation motif does not affect significantly the geometry of the peptide. The observed ν(NO) signatures at 1622 and 1690 cm−1, merged with other absorptions, are revealed by their sensitivity to 15NO isotope labeling, and by comparison with the IRMPD spectrum of native [GSH+H]+, providing a diagnostic probe for the S-nitrosation feature in natural peptides
Search for standard model production of four top quarks in the lepton + jets channel in pp collisions at sqrt(s) = 8 TeV
No full textSubmitted to JHEP . See paper for full list of authorsA search is presented for standard model (SM) production of four top quarks (t t-bar t t-bar) in pp collisions in the lepton + jets channel. The data correspond to an integrated luminosity of 19.6 inverse femtobarns recorded at a centre-of-mass energy of 8 TeV with the CMS detector at the CERN LHC. The expected cross section for SM four top quark production is approximately 1 fb. A combination of kinematic reconstruction and multivariate techniques is used to distinguish between the small signal and large background. The data are consistent with expectations of the SM, and an upper limit of 32 fb is set at a 95% confidence level on the cross section for producing four top quarks in the SM, where a limit of 32 +/- 17 fb is expected