Incoherent charge transport through molecular wires: interplay of Coulomb interaction and wire population

The influence of Coulomb interaction on the electron transport through molecular wires is studied in the regime of incoherent tunneling. In the limit of strong Coulomb repulsion, the current for spinless electrons is determined. It is shown that the voltage profile along the wire crucially influences the dependence of the current on the wire length. Upon inclusion of the spin degree of freedom one finds a blocking effect which depends both on the interaction strength and on the population of the wire. For finite Coulomb interaction, the temperature dependence of the blocking is studied and it is shown that several regimes with different blocking strength may exist.Comment: 18 pages, 8 figures, elsart.cls v2.18 include

Environmental impacts of first generation biofuels: how to assess and deal with impacts on natural resources and climate? Overview of assessment and monitoring tools for biofuels’ production environmental impacts

Face aux enjeux du changement climatique, l’Union Européenne s’est fixé des objectifs d’incorporation d’agrocarburants dans le secteur des transports. Suite à la flambée, en 2008, des cours des produits agricoles, de sévères critiques sur les impacts environnementaux ont été portées contre, les agrocarburants de première génération. Contre toute attente, un cadre réglementaire environnemental existe dans la législation de quasiment tous les pays : conventions internationales pour la protection des forêts et des écosystèmes vulnérables, loi sur les études d’impact environnemental, plans locaux de gestion des ressources naturelles. La limite est donc moins dans l’existence des dispositifs que des faibles capacités institutionnelles et financières pour les faire fonctionner : intégration des préoccupations environnementales dans les politiques sectorielles, moyens disponibles pour assurer un cadre durable de gestion des ressources naturelles et la mise en place de services publics assurant cette fonction de gouvernance environnementale. Ce cadre réglementaire traditionnel est complété par des outils d’analyse propre aux enjeux climatiques : analyse de cycle de vie, bilan carbone. Ces outils relativement récents nécessitent d’être consolidés et harmonisés pour servir de référence. Néanmoins, ils permettent, dès à présent, de cerner l’enjeu majeur de durabilité des agrocarburants et de guider les politiques en la matière : éviter le changement d’usage des sols pour la culture de matières premières. La prise en compte des enjeux de durabilité se traduit également par l’élaboration de référentiels de bonnes pratiques et systèmes de certification pour la production d’agrocarburants. La mise en place de tels référentiels a lieu sur une base concertée et nécessite donc un dialogue à l’échelle internationale, comme dans le cas de la Roundtable on Sustainable Palm Oil, entre les parties prenantes des filières : communautés rurales, agriculteurs, entreprises de plantations et agro-industrielles, traders. La principale difficulté consiste à traduire des référentiels de principe en critères réalistes et applicables, ce qui nécessite du temps et des concessions. En parallèle de ces initiatives, la plupart des pays européens ont, dès à présent, mis en place des systèmes de suivi pour évaluer l’impact climatique des agrocarburants importés et utilisés dans le cadre de leur consommation nationale, à l’image du RTFO en Grande Bretagne. La durabilité des agrocarburants constitue un prisme pour questionner la durabilité des modèles actuels de consommations énergétiques et alimentaires. Ainsi, contrairement aux idées reçues, les initiatives pour instaurer des systèmes de suivi et de contrôle se sont particulièrement développées ces cinq dernières années

Magnetic-field effects on transport in carbon nanotube junctions

Here we address a theoretical study on the behaviour of electronic states of heterojunctions and quantum dots based on carbon nanotubes under magnetic fields. Emphasis is put on the analysis of the local density of states, the conductance, and on the characteristic curves of current versus voltage. The heterostructures are modeled by joining zigzag tubes through single pentagon-heptagon pair defects, and described within a simple tight binding calculation. The conductance is calculated using the Landauer formula in the Green functions formalism. The used theoretical approach incorporates the atomic details of the topological defects by performing an energy relaxation via Monte Carlo calculation. The effect of a magnetic field on the conductance gap of the system is investigated and compared to those of isolated constituent tubes. It is found that the conductance gap of the studied CNHs exhibits oscillations as a function of the magnetic flux. However, unlike the pristine tubes case, they are not Aharonov-Bohm periodic oscillations

Bone marrow-derived cells are implicated as a source of lymphatic endothelial progenitors in human breast cancer.

Bone marrow-derived endothelial progenitor cells (EPCs) infiltrate into sites of neovascularization in adult tissues and mature into functional blood endothelial cells (BECs) during a process called vasculogenesis. Human marrow-derived EPCs have recently been reported to display a mixed myeloid and lymphatic endothelial cell (LEC) phenotype during inflammation-induced angiogenesis; however, their role in cancer remains poorly understood. We report the in vitro differentiation of human cord blood CD133(+)CD34(+) progenitors into podoplanin(+) cells expressing both myeloid markers (CD11b, CD14) and the canonical LEC markers vascular endothelium growth factor receptor 3 (VEGFR-3), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), and prospero homeobox 1 (PROX-1). These podoplanin(+) cells displayed sprouting behavior comparable to that of LECs in vitro and a dual hemangiogenic and lymphangiogenic activity in vivo in an endothelial cell sprouting assay and corneal vascularization assay, respectively. Furthermore, these cells expressed vascular endothelium growth factor (VEGF) family members A, -C, and -D. Thus, bone-marrow derived EPCs stimulate hemangiogenesis and lymphangiogenesis through their ability to differentiate into LECs and to produce angiogenic factors. Importantly, plasma from patients with breast cancer induced differentiation of CD34(+) cord blood progenitors into hemangiogenic and lymphangiogenic CD11b(+) myeloid cells, whereas plasma from healthy women did not have this effect. Consistent with these findings, circulating CD11b(+) cells from breast cancer patients, but not from healthy women, displayed a similar dual angiogenic activity. Taken together, our results show that marrow-derived EPCs become hemangiogenic and lymphangiogenic upon exposure to cancer plasma. These newly identified functions of bone-marrow derived EPCs are expected to influence the diagnosis and treatment of breast cancer

Sistema Presupuestario Público Argentino: El Presupuesto de Santa Fe

El sistema presupuestario público se inscribe como uno de los pilares del proceso de las finanzas públicas. Se ocupa de organizar la gestión pública y vincular las responsabilidades del Estado en el cumplimiento de sus funciones y en la realización de los planes y programas proyectados. El presupuesto público es el límite de gastos que una entidad puede realizar durante un año, de acuerdo a los ingresos que espera recibir, y debe ser la expresión financiera de los programas y proyectos que ejecutará para alcanzar los objetivos del plan de gobierno. Permite estimar los recursos que se obtendrán y distribuirlos de acuerdo a las prioridades de gobierno, entre las distintas instituciones. En consecuencia, es el principal instrumento de política pública, a través del cual se concretan los objetivos de gobierno y se identifican a las entidades responsables, siendo asimismo un mecanismo redistributivo de la riqueza. El resultado esperado de este proceso es un presupuesto público idóneo como instrumento de gestión y de información de las políticas públicas previstas para el corto y mediano plazo y el grado de efectividad y eficiencia en su cumplimiento. Considerando el carácter federal de nuestro país, las políticas fiscales vinculadas con las jurisdicciones provinciales y municipales, y sus implicancias financieras, deben estar articuladas razonable y adecuadamente con sus propias realidades económicas y sociales, de modo de obtener un panorama multidimensional de la situación de los gobiernos sub-nacionales en el marco de las políticas públicas nacionales, definidas en el presupuesto nacional. Los presupuestos tienen impactos muy concretos en la vida de las personas y el ejercicio efectivo de sus derechos. Los más directos se vinculan con la forma en que se gastan los recursos públicos y las prioridades a las que se asignan los fondos. Pero también existen efectos indirectos como los impactos que un presupuesto tiene en cuestiones como el empleo o la inflación.Fil: Ameriso, Claudia C. Universidad Nacional de Rosario; Argentin

Detection of Posner's clusters during calcium phosphate nucleation: a molecular dynamics study

Hydroxyapatite (HA), the main mineral phase of mammalian tooth enamel and bone, originates in body fluids from amorphous calcium phosphate (ACP). ACP presents short-range order in the form of small domains with size of 0.9 nm and chemical formula Ca9(PO4)6, known as Posner's clusters. In this study, the aggregation and clustering of calcium and phosphate ions in water has been investigated by means of shell-model molecular dynamics simulations. Calcium phosphate aggregates form in solution with compositions and Ca coordination that are similar to those found in Posner's cluster, but the stoichiometry of these species is dependent on the ionic composition of the solution: calcium-deficient clusters in solutions with low Ca : P ratio; cluster containing protonated phosphate groups in neutral solutions; sodium ions partially substituting calcium in solutions containing a mixture of sodium and calcium ions. These Posner-like clusters can be connected by phosphate groups, which act as a bridge between their central calcium ions. The simulations of the aggregation in solution of calcium phosphate clusters are an unbiased and unequivocal validation of Posner's model, and reveal for the first time the structure and composition of the species that form during the early stages of ACP nucleation at a scale still inaccessible to experiment

Quantum Interference Effects in Electronic Transport through Nanotube Contacts

Quantum interference has dramatic effects on electronic transport through nanotube contacts. In optimal configuration the intertube conductance can approach that of a perfect nanotube ($4e^2/h$). The maximum conductance increases rapidly with the contact length up to 10 nm, beyond which it exhibits long wavelength oscillations. This is attributed to the resonant cavity-like interference phenomena in the contact region. For two concentric nanotubes symmetry breaking reduces the maximum intertube conductance from $4e^2/h$ to $2e^2/h$. The phenomena discussed here can serve as a foundation for building nanotube electronic circuits and high speed nanoscale electromechanical devices

Physico-chemical and thermochemical studies of the hydrolytic conversion of amorphous tricalcium phosphate into apatite

The conversion of amorphous tricalcium phosphate with different hydration ratio into apatite in water at 25 °C has been studied by microcalorimetry and several physical–chemical methods. The hydrolytic transformation was dominated by two strong exothermic events. A fast, relatively weak, wetting process and a very slow but strong heat release assigned to a slow internal rehydration and the crystallization of the amorphous phase into an apatite. The exothermic phenomenon related to the rehydration exceeded the crystalline transformation enthalpy. Rehydration occurred before the conversion of the amorphous phase into apatite and determined the advancement of the hydrolytic reaction. The apatitic phases formed evolved slightly with time after their formation. The crystallinity increased whereas the amount of HPO4 2− ion decreased. These data allow a better understanding of the behavior of biomaterials involving amorphous phases such as hydroxyapatite plasma-sprayed coating

Electron Wave Function in Armchair Graphene Nanoribbons

By using analytical solution of a tight-binding model for armchair nanoribbons, it is confirmed that the solution represents the standing wave formed by intervalley scattering and that pseudospin is invariant under the scattering. The phase space of armchair nanoribbon which includes a single Dirac singularity is specified. By examining the effects of boundary perturbations on the wave function, we suggest that the existance of a strong boundary potential is inconsistent with the observation in a recent scanning tunneling microscopy. Some of the possible electron-density superstructure patterns near a step armchair edge located on top of graphite are presented. It is demonstrated that a selection rule for the G band in Raman spectroscopy can be most easily reproduced with the analytical solution.Comment: 7 pages, 4 figure